International Immunology

International Immunology 2005 17(1):1-14; doi:10.1093/intimm/dxh186

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© 2005 The Japanese Society for Immunology

REVIEW ARTICLE

Toll-like receptors in innate immunity

Kiyoshi Takeda¹ and Shizuo Akira^2,3

¹ Department of Molecular Genetics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, ² Department of Host Defense, Research Institute for Microbial Diseases, Osaka University and ³ ERATO, Japan Science and Technology Agency, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan

Corresponding author: S. Akira; E-mail: sakira{at}biken.osaka-u.ac.jp

	Abstract

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Functional characterization of Toll-like receptors (TLRs) has established that innate immunity is a skillful system that detects invasion of microbial pathogens. Recognition of microbial components by TLRs initiates signal transduction pathways, which triggers expression of genes. These gene products control innate immune responses and further instruct development of antigen-specific acquired immunity. TLR signaling pathways are finely regulated by TIR domain-containing adaptors, such as MyD88, TIRAP/Mal, TRIF and TRAM. Differential utilization of these TIR domain-containing adaptors provides specificity of individual TLR-mediated signaling pathways. Several mechanisms have been elucidated that negatively control TLR signaling pathways, and thereby prevent overactivation of innate immunity leading to fatal immune disorders. The involvement of TLR-mediated pathways in autoimmune and inflammatory diseases has been proposed. Thus, TLR-mediated activation of innate immunity controls not only host defense against pathogens but also immune disorders.

Keywords: adaptor, innate immunity, signal transduction, TIR domain, Toll-like receptor

	Introduction

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Host defense against invading microbial pathogens is elicited by the immune system, which consists of two components: innate immunity and acquired immunity. Both components of immunity recognize invading microorganisms as non-self, which triggers immune responses to eliminate them. To date, both components have been characterized independently, and the main research interest in the immunology field has been confined to acquired immunity. In acquired immunity, B and T lymphocytes utilize antigen receptors such as immunoglobulins and T cell receptors to recognize non-self. The mechanisms by which these antigen receptors recognize foreign antigens have been intensively analyzed, and the major mechanisms, such as diversity, clonality and memory, have been well characterized. However, these receptors are present only in vertebrates, and accordingly we do not fully understand the mechanism for non-self recognition in less evolved organisms. In addition, the innate immune system in mammals has not been well studied. As a result, although mammalian innate immune cells such as macrophages and dendritic cells are known to be activated by microbial components (non-self) such as lipopolysaccharide (LPS) from Gram-negative bacteria, a receptor responsible for the recognition remained unknown.

At the end of the 20th century, Toll was shown to be an essential receptor for host defense against fungal infection in Drosophila, which only has innate immunity (1). One year later, a mammalian homolog of the Toll receptor (now termed TLR4) was shown to induce expression of genes involved in inflammatory responses (2). In addition, a point mutation in the Tlr4 gene has been identified in a mouse strain that is unresponsive to LPS (3). These studies have made innate immunity a very attractive subject of research, and in recent years there has been rapid progress in our understanding that the innate immune system possesses a skillful system that senses invasion of microbial pathogens by Toll-like receptors (TLRs). Furthermore, activation of innate immunity is a critical step to the development of antigen-specific acquired immunity. In this review, we will describe the mechanisms by which innate immunity is activated through TLRs.

	Identification of the TLR family

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
After the characterization of the first mammalian TLR, TLR4, several proteins that are structurally related to TLR4 were identified and named Toll-like receptors (4). Mammalian TLRs comprise a large family consisting of at least 11 members. TLR1–9 are conserved between the human and mouse. However, although TLR10 is presumably functional in the human, the C-terminal half of the mouse Tlr10 gene is substituted to an unrelated and non-productive sequence, indicating that mouse TLR10 is non-functional (our unpublished observation). Similarly, mouse TLR11 is functional, but there is a stop codon in the human TLR11 gene, which results in a lack of production of human TLR11 (5).

The cytoplasmic portion of TLRs shows high similarity to that of the IL-1 receptor family, and is termed a Toll/IL-1 receptor (TIR) domain. Despite this similarity, the extracellular portions of both types of receptors are structurally unrelated. The IL-1 receptors possess an immunoglobulin-like domain, whereas TLRs bear leucine-rich repeats (LRRs) in the extracellular domain. Functionally, a critical role of TLR4 in the recognition of the microbial component LPS was initially characterized (3). Subsequently, it has been rapidly established that individual TLRs play important roles in recognizing specific microbial components derived from pathogens including bacteria, fungi, protozoa and viruses (Fig. 1).

View larger version (37K): [in this window] [in a new window]   Fig. 1. TLRs and their ligands. TLR2 is essential in the recognition of microbial lipopeptides. TLR1 and TLR6 cooperate with TLR2 to discriminate subtle differences between triacyl and diacyl lipopeptides, respectively. TLR4 is the receptor for LPS. TLR9 is essential in CpG DNA recognition. TLR3 is implicated in the recognition of viral dsRNA, whereas TLR7 and TLR8 are implicated in viral-derived ssRNA recognition. TLR5 recognizes flagellin. Thus, the TLR family members recognize specific patterns of microbial components.

 

	TLR1, TLR2 and TLR6

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
TLR2 recognizes a variety of microbial components. These include lipoproteins/lipopeptides from various pathogens, peptidoglycan and lipoteichoic acid from Gram-positive bacteria, lipoarabinomannan from mycobacteria, glycosylphosphatidylinositol anchors from Trypanosoma cruzi, a phenol-soluble modulin from Staphylococcus epidermis, zymosan from fungi and glycolipids from Treponema maltophilum (6). In addition, TLR2 reportedly recognizes LPS preparations from non-enterobacteria such as Leptospira interrogans, Porphyromonas gingivalis and Helicobacter pyroli (7–9). These LPS structurally differ from the typical LPS of Gram-negative bacteria recognized by TLR4 in the number of acyl chains in the lipid A component, which presumably confers differential recognition (10). However, a recent report indicates that LPS preparation from P. gingivalis contaminates lipoproteins that activate TLR2, and LPS from P. gingivalis only poorly activates TLR4 (11). Therefore, more careful analysis will be required to conclude that some LPS are recognized by TLR2, but not TLR4.

There are two aspects proposed for mechanisms that could explain why TLR2 recognizes a wide spectrum of microbial components. The first explanation is that TLR2 forms heterophilic dimers with other TLRs such as TLR1 and TLR6, both of which are structurally related to TLR2. Macrophages from TLR6-deficient mice did not show any production of inflammatory cytokines in response to mycoplasma-derived diacyl lipopeptides. However, these cells showed normal production of inflammatory cytokines in response to triacyl lipopeptides derived from Gram-negative bacteria (12). In contrast, macrophages from TLR1-deficient mice showed a normal response to mycoplasma-derived diacyl lipopeptides, but an impaired response to triacyl lipopeptides (13). Thus, TLR1 and TLR6 functionally associate with TLR2 and discriminate between diacyl or triacyl lipopeptides. Moreover, the involvement of TLR1 in the recognition of the outer surface lipoprotein of Borrelia burgdorferi has also been shown (14). The second explanation involves recognition of fungal-derived components by TLR2 (15). In this model, TLR2 has been shown to functionally collaborate with distinct types of receptors such as dectin-1, a lectin family receptor for the fungal cell wall component ß-glucan. Thus, TLR2 recognizes a wide range of microbial products through functional cooperation with several proteins that are either structurally related or unrelated.

	TLR3

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Expression of human TLR3 in the double-stranded RNA (dsRNA)-non-responsive cell line 293 confers enhanced activation of NF-B in response to dsRNA. In addition, TLR3-deficient mice are impaired in their response to dsRNA (16). dsRNA is produced by most viruses during their replication and induces the synthesis of type I interferons (IFN-/ß), which exert anti-viral and immunostimulatory activities. Thus, TLR3 is implicated in the recognition of dsRNA and viruses. However, TLR3-independent mechanisms of dsRNA recognition exist, as discussed below.

	TLR4

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
As described above, TLR4 is an essential receptor for LPS recognition (3,17). In addition, TLR4 is implicated in the recognition of taxol, a diterpene purified from the bark of the western yew (Taxus brevifolia) (18,19). Furthermore, TLR4 has been shown to be involved in the recognition of endogenous ligands, such as heat shock proteins (HSP60 and HSP70), the extra domain A of fibronectins, oligosaccharides of hyaluronic acid, heparan sulfate and fibrinogen. However, all of these endogenous ligands require very high concentrations to activate TLR4. In addition, it has been shown that contamination of LPS in the HSP70 preparation confers ability to activate TLR4 (20). LPS is a very potent immuno-activator, and accordingly, TLR4 can be activated by a very small amount of LPS, contaminating these endogenous ligand preparations. Therefore, more careful experiments will be required before we can conclude that TLR4 recognizes these endogenous ligands.

	TLR5

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Enforced expression of human TLR5 in CHO cells confers response to flagellin, a monomeric constituent of bacterial flagella (21). TLR5 has further been shown to recognize an evolutionarily conserved domain of flagellin through close physical interaction between TLR5 and flagellin (22). TLR5 is expressed on the basolateral, but not the apical side of intestinal epithelial cells (23). TLR5 expression is also observed in the intestinal endothelial cells of the subepithelial compartment (24). In addition, flagellin activates lung epithelial cells to induce inflammatory cytokine production (25). These findings indicate the important role of TLR5 in microbial recognition at the mucosal surface. A common stop codon polymorphism in the ligand-binding domain of TLR5 has been shown to be associated with susceptibility to pneumonia caused by the flagellated bacterium Legionella pneumophila (25).

	TLR7 and TLR8

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
TLR7 and TLR8 are structurally highly conserved proteins, and recognize the same ligand in some cases. Analysis of TLR7-deficient mice revealed that murine TLR7 recognizes synthetic compounds, imidazoquinolines, which are clinically used for treatment of genital warts associated with viral infection (26). Human TLR7 and TLR8, but not murine TLR8, recognizes imidazoquinoline compounds (27). Murine TLR7 has also been shown to recognize another synthetic compound, loxoribine, which has anti-viral and anti-tumor activities (28,29). Both imidazoquinoline and loxoribine are structurally related to guanosine nucleoside. Therefore, TLR7 and human TLR8 were predicted to recognize a nucleic acid-like structure of the virus. This prediction has recently been shown to be true from the finding that TLR7 and human TLR8 recognize guanosine- or uridine-rich single-stranded RNA (ssRNA) from viruses such as human immunodeficiency virus, vesicular stomatitis virus and influenza virus (30–32). ssRNA is abundant in the host, but usually the host-derived ssRNA is not detected by TLR7 or TLR8. This might be due to the fact that TLR7 and TLR8 are expressed in the endosome, and host-derived ssRNA is not delivered to the endosome.

	TLR9

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Analysis of TLR9-deficient mice revealed that TLR9 is a receptor for CpG DNA (33). Bacterial DNA contains unmethylated CpG motifs, which confer its immunostimulatory activity. In vertebrates, the frequency of CpG motifs is severely reduced and the cysteine residues of CpG motifs are highly methylated, leading to abrogation of the immunostimulatory activity. There are at least two types of CpG DNA, termed A/D-type CpG DNA and B/K-type CpG DNA. B/K-type CpG DNA is conventional, which was identified first, and is a potent inducer of inflammatory cytokines such as IL-12 and TNF-. A/D-type CpG DNA is structurally different from conventional CpG DNA and has a greater ability to induce IFN- production from plasmacytoid dendritic cells (PDC), but less ability to induce IL-12 (34,35). TLR9 has been shown to be essential for the recognition of both types of CpG DNA (36). The fact that TLR9 recognition of A/D-type CpG DNA leads to induction of an anti-viral cytokine IFN- in PDC indicates that TLR9 is involved in viral recognition. Indeed, in addition to bacterial CpG DNA, TLR9 has been shown to recognize viral-derived CpG DNA in PDC (37,38). Furthermore, TLR9-mutant mice have been shown to be susceptible to mouse cytomegalovirus (MCMV) infection (39). TLR9-dependent recognition of MCMV in PDC or other types of DC elicits an anti-MCMV response through activation of NK cells (40). In addition to bacterial and viral CpG DNA, TLR9 is presumably involved in pathogenesis of autoimmune disorders. Sequential engagement of IgG2a–chromatin complex by the B cell receptor and TLR9 mediates effective production of rheumatoid factor by auto-reactive B cells (41). In this model, the IgG2a is bound and internalized by the B cell receptor, and the chromatin, including hypomethylated CpG motifs, is then able to engage TLR9, thereby inducing rheumatoid factor (42). Similarly, internalization by the Fc receptor and subsequent exposure of the chromatin to TLR9 mediates PDC induction of IFN- by immune complexes containing IgG and chromatin, which are implicated in the pathogenesis of systemic lupus erythematosus (SLE) (43). Thus, TLR9 appears to be involved in the pathogenesis of several autoimmune diseases through recognition of the chromatin structure. Chloroquine is clinically used for treatment of rheumatoid arthritis and SLE, but its mechanisms are unknown. Since chloroquine also blocks TLR9-dependent signaling through inhibition of the pH-dependent maturation of endosomes by acting as a basic substance to neutralize acidification in the vesicle (44), it may act as an anti-inflammatory agent by inhibiting TLR9-dependent immune responses.

	TLR11

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
The most recently identified TLR11 has been shown to be expressed in bladder epithelial cells and mediate resistance to infection by uropathogenic bacteria in mouse (5). TLR11-deficient mice are highly susceptible to uropathogenic bacterial infection. Although the ligand has not yet been identified, these findings indicate that mouse TLR11 mediates anti-uropathogenic bacterial response. As described above, there is no functional TLR11 protein in the human (5). These findings may indicate that the human TLR11 protein was futile in the human environment and became lost through evolution.

	Subcellular localization of TLRs

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Individual TLRs are differentially distributed within the cell. TLR1, TLR2 and TLR4 are expressed on the cell surface, as demonstrated by positive staining of the cell surface by specific antibodies. In contrast, TLR3, TLR7, TLR8 and TLR9 have been shown to be expressed in intracellular compartments such as endosomes (29,45–47). TLR3-, TLR7- or TLR9-mediated recognition of their ligands has been shown to require endosomal maturation (30–32,44,46,48). The TLR9 ligand CpG DNA is first non-specifically captured into endosomes, where TLR9 is recruited from the endoplasmic reticulum upon non-specific uptake of CpG DNA (44,47,49). Thus, it can be hypothesized that in the case of bacterial infection, macrophages and dendritic cells engulf bacteria by phagocytosis. CpG DNA is then exposed after degradation of bacteria in phagosomes/lysosomes or endosomes/lysosomes, where TLR9 is recruited or expressed. In the case of viral infection, viruses invade cells by receptor-mediated endocytosis, and the viral contents are exposed to the cytoplasm by fusion of the viral membrane and the endosomal membrane. Occasionally, the viral particles are degraded in the endosomal compartment, which results in exposure of TLR ligands such as dsRNA, ssRNA and CpG DNA. Even TLR2, which is expressed on the cell surface, is recruited to the phagosomal compartment of macrophages after exposure to zymosan (50). Thus, phagosomal/lysosomal or endosomal/lysosomal compartments may be the main sites for TLR recognition of microbial components.

	TLR-independent recognition of micro-organisms

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
TLR-independent recognition of viruses and dsRNA
Although TLR3 is involved in the recognition of viral-derived dsRNA, the impairment observed in TLR3-deficient mice is only partial (16,51). In addition, introduction of dsRNA into the cytoplasm of dendritic cells leads to the induction of type I IFNs via a mechanism partially dependent on dsRNA-dependent protein kinase (PKR), but independent of TLR3 (52). These findings indicate that molecules responsible for TLR3-independent recognition of dsRNA and viruses do exist. Although PKR is implicated in dsRNA recognition, it is still controversial whether PKR plays a critical role in dsRNA-induced type I IFN expression (53). Recently, a key molecule was identified, which mediates the TLR3-independent dsRNA recognition (Fig. 2). Retinoic acid-inducible gene I (RIG-I), which encodes a DExD/H box RNA helicase containing a caspase recruitment domain, was identified from the screening of a cDNA library that augments dsRNA-dependent activation of the IRF-3-dependent promoter. Studies with ectopic expression and RNA interference (RNAi)-mediated knockdown of RIG-I clearly demonstrated that RIG-I is critical in dsRNA- and viral infection-induced type I IFN expression (54). It is interesting to analyze the correlation between TLR3 and RIG-I in the recognition of dsRNA and viruses.

View larger version (27K): [in this window] [in a new window]   Fig. 2. TLR-dependent and -independent recognition of microbial components. TLR2 has previously been shown to mediate peptidoglycan (PGN) recognition. However, NOD1 and NOD2 have recently been shown to recognize motifs found in the layer of PGN. It is possible that TLR2 recognizes lipoprotein contamination in the PGN layer. Viral recognition is also mediated by TLR-dependent and -independent mechanisms. TLR3-mediated recognition of viruses or dsRNA results in TRIF-dependent activation of IRF-3 and NF-B. However, viruses or dsRNA are recognized in a TLR3-independent manner, since the impairment of the responsiveness to viruses or dsRNA in TLR3-deficient mice is only partial. RIG-I is identified as a molecule that is responsible for viral recognition and that mediates activation of IRF-3.

 
NOD1 and NOD2
TLRs are membrane-bound molecules that recognize microbial components on the surface or within extracellular compartments of cells. Accordingly, intracellular recognition of bacteria appears to involve a TLR-independent system. Recent accumulating evidence indicates that the nucleotide-binding oligomerization domain (NOD) family of proteins plays an important role in the recognition of intracellular bacteria (Fig. 2). Peptidoglycan (PGN) has previously been shown to be recognized by TLR2 (55). However, PGN is a thick rigid layer that is composed of an overlapping lattice of two sugars that are crosslinked by amino acid bridges, and the exact structure of PGN that is recognized by TLR2 remains unclear. NOD1 was originally identified as a molecule that is structurally related to the apoptosis regulator, Apaf-1. It contains a caspase-recruitment domain (CARD), a NOD domain and a C-terminal LRR domain. Recent studies have demonstrated that overexpression of NOD1 enables 293 cells to respond to preparations of PGN (56,57). Characterization of the PGN motif detected by NOD1 revealed that -D-glutamyl-meso diaminopimelic acid (iE-DAP) is the minimal structure required for NOD1 detection. NOD2 was identified as a molecule that shows structural similarity to NOD1, but which possesses two CARD domains in its N-terminal region. Similar to NOD1, expression of NOD2 confers responsiveness to PGN in 293 cells. Biochemical analyses identified the essential structure recognized by NOD2 as muramyl dipeptide MurNAc-L-Ala-D-isoGln (MDP) derived from PGN (58,59). Thus, NOD1 and NOD2 recognize different structures within PGN. MDP is found in almost all bacteria, whereas iE-DAP is restricted to Gram-negative bacteria. Therefore, NOD1 may play an important role in sensing Gram-negative bacterial infection inside cells. Although TLR2 has been reported to recognize PGN, it is possible that TLR2 recognizes lipoprotein/lipopeptide contaminants that are trapped within the layers of the PGN mesh.

Mutations in the NOD2 gene have been shown to be associated with Crohn's disease, an inflammatory bowel disease of unknown etiology (60,61). These mutations are found in the LRR domain of NOD2, and result in defective NF-B activation. However, the mechanisms by which NOD2 mutations result in an increased susceptibility to Crohn's disease are unclear. One of the answers to this question has recently been demonstrated. In the absence of NOD2 or the presence of a Crohn's disease-like Nod2 mutation, TLR2-mediated activation of NF-B, especially the cRel subunit, has been shown to be enhanced, which explains enhanced NF-B activity and Th1 responses in Crohn's disease patients (62). NOD2 mutations are also associated with Blau syndrome, a disease characterized by granulomatous arthritis, uveitis and skin rash (63). The NOD2 mutations in Blau syndrome patients are located in the NOD domain, leading to an increase in NF-B activity. Thus, NOD2 is associated with certain human diseases.

Recognition of PGN motifs by NOD1 and NOD2 results in their oligomerization, which induces the recruitment of Rip2/RICK, a serine/threonine kinase (64). Rip2/RICK has a CARD domain in its C-terminal portion and an N-terminal catalytic domain that shares sequence similarity with Rip, a factor essential for NF-B activation through the TNF receptor. NODs and Rip2/RICK interact via their respective CARD domains, and induce recruitment of the IKK complex to the central region of Rip2/RICK. This in turn leads to activation of NF-B. Rip2/RICK-deficient mice have been shown to be highly sensitive to infection with the intracellular pathogen Listeria monocytogenes (65). Introduction of NOD1 or NOD2 into Rip2/RICK-deficient embryonic fibroblast cells does not induce NF-B activation (66). Thus, Rip2/RICK is essential for NOD1- and NOD2-mediated responses, although its involvement in the recognition of PGN motifs needs to be more precisely analyzed in Rip2/RICK-deficient mice.

	Phagocytosis and TLRs

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Phagocytosis is an important step for host defense against microbial pathogens, since it triggers both degradation of pathogens and subsequent presentation of pathogen-derived peptide antigen. TLR recognition of pathogens leads to expression of genes such as inflammatory cytokines and co-stimulatory molecules. Phagocytosis-mediated antigen presentation together with TLR-dependent gene expression of inflammatory cytokines and co-stimulatory molecules, instruct development of antigen-specific acquired immunity (Fig. 3). Therefore, it is of interest to characterize the relationship between phagocytosis and TLRs. In the absence of TLR2/TLR4 or MyD88, a common adaptor in TLR signaling, phagocytosis of bacteria including Escherichia coli, Salmonella typhimurium and Staphylococcus aureus has been shown to be impaired due to impaired phagosome maturation (67). Further studies indicate that TLR-mediated MyD88-dependent activation of p38 is required for phagosome maturation (67,68). Thus, TLRs are linked to phagocytosis of bacteria.

View larger version (31K): [in this window] [in a new window]   Fig. 3. Innate and adaptive immunity. Innate immune cells, such as dendritic cells and macrophages, engulf pathogens by phagocytosis, and present pathogen-derived peptide antigens to naïve T cells. In addition, TLRs recognize pathogen-derived components and induce expression of genes, such as co-stimulatory molecules and inflammatory cytokines. Phagocytosis-mediated antigen presentation, together with TLR-mediated expression of co-stimulatory molecules and inflammatory cytokines, instruct development of antigen-specific adaptive immunity, especially Th1 cells.

 

	TLR signaling pathways

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Stimulation of TLRs by microbial components triggers expression of several genes that are involved in immune responses. The molecular mechanisms by which TLRs induce gene expression are now rapidly being elucidated through analyses of TLR-mediated signaling pathways (69). Microbial recognition of TLRs facilitates dimerization of TLRs. TLR2 is shown to form a heterophilic dimer with TLR1 or TLR6, but in other cases TLRs are believed to form homodimers (70). Dimerization of TLRs triggers activation of signaling pathways, which originate from a cytoplasmic TIR domain. In the signaling pathways downstream of the TIR domain, a TIR domain-containing adaptor, MyD88, was first shown to be essential for induction of inflammatory cytokines such as TNF- and IL-12 through all TLRs (21,26,71–74). However, activation of specific TLRs leads to slightly different patterns of gene expression profiles. For example, activation of TLR3 and TLR4 signaling pathways results in induction of type I interferons (IFNs), but activation of TLR2- and TLR5-mediated pathways does not (75–77). TLR7, TLR8 and TLR9 signaling pathways also lead to induction of type I IFNs through mechanisms distinct from TLR3/4-mediated induction (36,78). Thus, individual TLR signaling pathways are divergent, although MyD88 is common to all TLRs. It has also become clear that there are MyD88-dependent and MyD88-independent pathways (Fig. 4).

View larger version (39K): [in this window] [in a new window]   Fig. 4. TLR signaling pathway. TLR signaling pathways originate from the cytoplasmic TIR domain. A TIR domain-containing adaptor, MyD88, associates with the cytoplasmic TIR domain of TLRs, and recruits IRAK to the receptor upon ligand binding. IRAK then activates TRAF6, leading to the activation of the IB kinase (IKK) complex consisting of IKK, IKKß and NEMO/IKK. The IKK complex phosphorylates IB, resulting in nuclear translocation of NF-B which induces expression of inflammatory cytokines. TIRAP, a second TIR domain-containing adaptor, is involved in the MyD88-dependent signaling pathway via TLR2 and TLR4. In TLR3- and TLR4-mediated signaling pathways, activation of IRF-3 and induction of IFN-ß are observed in a MyD88-independent manner. A third TIR domain-containing adaptor, TRIF, is essential for the MyD88-independent pathway. Non-typical IKKs, IKKi/IKK and TBK1, mediate activation of IRF-3 downstream of TRIF. A fourth TIR domain-containing adaptor, TRAM, is specific to the TLR4-mediated MyD88-independent/TRIF-dependent pathway.

 

	MyD88-dependent pathway

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
A MyD88-dependent pathway is analogous to signaling pathways through the IL-1 receptors. MyD88, harboring a C-terminal TIR domain and an N-terminal death domain, associates with the TIR domain of TLRs. Upon stimulation, MyD88 recruits IRAK-4 to TLRs through interaction of the death domains of both molecules, and facilitates IRAK-4-mediated phosphorylation of IRAK-1. Activated IRAK-1 then associates with TRAF6, leading to the activation of two distinct signaling pathways. One pathway leads to activation of AP-1 transcription factors through activation of MAP kinases. Another pathway activates the TAK1/TAB complex, which enhances activity of the IB kinase (IKK) complex. Once activated, the IKK complex induces phosphorylation and subsequent degradation of IB, which leads to nuclear translocation of transcription factor NF-B.

As its name suggests, in the MyD88-dependent pathway, MyD88 plays a crucial role. MyD88-deficient mice do not show production of inflammatory cytokines such as TNF- and IL-12p40 in response to all TLR ligands (21,26,71–74). Thus, MyD88 is essential for inflammatory cytokine production through all TLRs.

A database search for molecules that are structurally related to MyD88 led to identification of the second TIR domain-containing molecule TIRAP (TIR domain-containing adaptor protein)/Mal (MyD88-adaptor-like) (79,80). Similar to MyD88-deficient macrophages, TIRAP/Mal-deficient macrophages show impaired inflammatory cytokine production in response to TLR4 and TLR2 ligands (81,82). However, TIRAP/Mal-deficient mice are not impaired in their response to TLR3, TLR5, TLR7 and TLR9 ligands, Thus, TIRAP/Mal has been shown to be essential for the MyD88-dependent signaling pathway via TLR2 and TLR4.

	MyD88-independent/TRIF-dependent pathway

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
In MyD88-deficient macrophages, TLR4 ligand-induced production of inflammatory cytokines is not observed; however, activation of NF-B is observed with delayed kinetics (72). This indicates that although TLR4-mediated production of inflammatory cytokines completely depends on the MyD88-dependent pathway, a MyD88-independent component exists in TLR4 signaling. Subsequent studies have demonstrated that TLR4 stimulation leads to activation of the transcription factor IRF-3, as well as the late phase of NF-B activation in a MyD88-independent manner (83). TLR4-induced activation of IRF-3 leads to production of IFN-ß. IFN-ß in turn activates Stat1 and induces several IFN-inducible genes (75–77). Viral infection or dsRNA was found to activate IRF-3 (84). Accordingly, the TLR3-mediated pathway also activates IRF-3 and thereby induces IFN-ß in a MyD88-independent manner. Hence, TLR3 and TLR4 utilize the MyD88-independent component to induce IFN-ß.

Characterization of MyD88 and TIRAP/Mal prompted us to hypothesize that TIR domain-containing molecules regulate the MyD88-independent pathway, and also facilitated the search for such molecules. A database search led to identification of a third TIR domain-containing adaptor, TIR domain-containing adaptor inducing IFN-ß (TRIF) (85). This molecule was identified as a TLR3-associated molecule by two-hybrid screening and was named TIR domain-containing adaptor molecule (TICAM-1) (86). The physiological role of TRIF/TICAM-1 was then demonstrated by generation of TRIF-mutant mice. TRIF-deficient mice generated by gene targeting showed no activation of IRF-3 and had impaired expression of IFN-ß- and IFN-inducible genes in response to TLR3 and TLR4 ligands (52). Another mouse strain mutated in the Trif gene generated by random germline mutagenesis also revealed that they were defective in TLR3- and TLR4-mediated induction of IFN-ß- and IFN-inducible genes (87). Thus, TRIF has been demonstrated to be essential for TLR3- and TLR4-mediated MyD88-independent pathways.

Database searches further led to identification of a fourth TIR domain-containing adaptor, TRIF-related adaptor molecules (TRAM)/TICAM-2 (88–91). Studies with TRAM-deficient mice and RNAi-mediated knockdown of TRAM expression showed that TRAM is involved in TLR4-mediated, but not TLR3-mediated, activation of IRF-3 and induction of IFN-ß- and IFN-inducible genes (88–90). Thus, TRAM is essential for the TLR4-mediated MyD88-independent/TRIF-dependent pathway.

In TRIF- and TRAM-deficient mice, inflammatory cytokine production induced by TLR2, TLR7 and TLR9 ligands was observed, as well as TLR4 ligand-induced phosphorylation of IRAK-1 (52,89). These findings indicate that the MyD88-dependent pathway is not impaired in these mice. However, TLR4 ligand-induced inflammatory cytokine production was not observed in TRIF- and TRAM-deficient mice. Therefore, activation of both the MyD88-dependent and MyD88-independent/TRIF-dependent components is required for the TLR4-induced inflammatory cytokine production, but the mechanisms are unknown.

Key molecules that mediate IRF-3 activation have been revealed to be non-canonical IKKs, TBK1 and IKKi/IKK (92). Introduction of TBK1 or IKKi/IKK, but not IKKß, resulted in phosphorylation and nuclear translocation of IRF-3. RNAi-mediated inhibition of TBK1 or IKKi/IKK expression led to impaired induction of IFN-ß in response to viruses and dsRNA (92,93). Embryonic fibroblast cells obtained from TBK1-deficient mice showed impaired activation of IRF-3 and expression of IFN-ß and IFN-inducible genes in response to TLR3 and TLR4 ligands (94–96). In contrast, embryonic fibroblast cells from IKKi/IKK-deficient mice were not defective in their response to TLR3 and TLR4 ligands (95). However, TLR3-mediated activation of IRF-3 and expression of IFN-ß and IFN-inducible genes were almost completely abolished in embryonic fibroblast cells lacking both TBK1 and IKKi/IKK. Thus, TBK1 and IKKi/IKK are critical regulators of IRF-3 activation in the MyD88-independent pathway.

The mechanisms by which the TRIF-dependent pathway leads to activation of NF-B and IRF-3 are now under investigation. The TIR domain of TRIF is located in the middle portion of this molecule, flanked by the N-terminal and C-terminal portions. Both N-terminal and C-terminal portions of TRIF mediate activation of the NF-B-dependent promoter, whereas only the N-terminal portion is involved in IFN-ß promoter activation (85). Accordingly, the N-terminal portion of TRIF was shown to associate with IKKi/IKK and TBK1, which mediate IRF-3-dependent IFN-ß induction (93,97). The N-terminal portion of TRIF was also shown to associate with TRAF6 (97,98). Since TRAF6 is critically involved in TLR-mediated NF-B activation (99), TRAF6 may regulate NF-B activation derived from the N-terminal portion of TRIF. The C-terminal portion of TRIF was shown to associate with RIP1 (100). Embryonic fibroblast cells from RIP1-deficient mice showed impaired NF-B activation in response to the TLR3 ligand. Thus, RIP1 is shown to be responsible for NF-B activation that originates from the C-terminal portion of TRIF.

	Negative regulation of TLR signaling

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Stimulation of TLRs by microbial components triggers the induction of inflammatory cytokines such as TNF-, IL-6 and IL-12. When all these cytokines are produced in excess, they induce serious systemic disorders with a high mortality rate in the host. It is therefore not surprising that organisms have evolved mechanisms for modulating their TLR-mediated responses.

Exposure to microbial components such as LPS results in a severely reduced response to a subsequent challenge by LPS. This phenomenon was first described over 50 years ago and is now called endotoxin (or LPS) tolerance, but the precise mechanisms remain unclear (101). The mechanisms are now being analyzed in the context of TLR signaling, and several models are proposed. LPS stimulation of macrophages results in reduced surface expression of the LPS receptor complex composed of TLR4 and MD-2, a co-factor that facilitates LPS binding (102,103). TLR2, TLR7 and TLR4 ligands induce reduced expression of IRAK-1 (104–106). Several other mechanisms are also shown to be involved in LPS tolerance (107).

In addition, molecules that negatively regulate TLR signaling have been identified. IRAK-M, a member of the IRAK family of serine/threonine kinases, is induced by TLR stimulation in monocyte/macrophages, and lacks kinase activity (108). IRAK-M-deficient mice show increased production of inflammatory cytokines in response to TLR ligands and defective induction of LPS tolerance (109). Inhibitory activity of IRAK-M seems to be elicited by IRAK-M prevention of IRAK-1/IRAK-4 dissociation from MyD88, thereby preventing formation of the IRAK-1–TRAF6 complex.

An alternatively spliced variant of MyD88 that lacks the intermediary domain of MyD88 (MyD88s) is induced in monocytes upon LPS stimulation. Overexpression of MyD88s results in impaired LPS-induced NF-B activation through inhibition of IRAK-4-mediated IRAK-1 phosphorylation (110).

SOCS1 is a member of the SOCS family of proteins that are induced by cytokines and that negatively regulate cytokine signaling pathways (111). In addition to cytokines, TLR ligands such as LPS and CpG DNA induced expression of SOCS1 in macrophages (112,113). SOCS1-deficient mice were hypersensitive to LPS-induced endotoxin shock and showed defective induction of LPS tolerance (114,115). Ectopic expression of SOCS1 resulted in impaired LPS-induced NF-B activation in macrophages. These findings indicate that SOCS1 directly down-modulates TLR signaling pathways, although the precise mechanism by which SOCS1 inhibits TLR signaling remains unclear.

Membrane-bound proteins harboring the TIR domain, such as SIGIRR (single immunoglobulin IL-1 receptor-related molecule) and T1/ST2, have also been shown to be involved in negative regulation of TLR signaling. In both SIGIRR- and T1/ST2-deficient mice, the LPS-induced inflammatory response was enhanced (116,117).

Ubiquitination-mediated degradation of TLRs is also proposed as a mechanism to inhibit activation of the signaling pathway. A RING finger protein, Triad3A, is shown to act as an E3 ubiquitin ligase and enhance ubiquitination and proteolytic degradation of TLR4 and TLR9 (118). Thus, several molecules are postulated to modulate TLR signaling pathways (Fig. 5). Combination of these negative regulators may finely coordinate the TLR signaling pathway to limit exaggerated innate responses causing harmful disorders.

View larger version (38K): [in this window] [in a new window]   Fig. 5. Negative regulation of TLR signaling pathways. TLR signaling pathways are negatively regulated by several molecules. IRAK-M inhibits dissociation of IRAK-1/IRAK-4 complex from the receptor. MyD88s blocks association of IRAK-4 with MyD88. SOCS1 is likely to associate with IRAK-1 and inhibits its activity. TRIAD3A induces ubiquitination-mediated degradation of TLR4 and TLR9. TIR domain-containing receptors SIGIRR and T1/ST2 are also shown to negatively modulate TLR signaling.

 

	Involvement of TLRs and immune disorders

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
Several lines of evidence indicate that TLRs are implicated in inflammatory and immune disorders. For example, constitutive activation of innate immune cells caused by defective IL-10 signaling results in development of chronic enterocolitis (119). Introduction of TLR4 deficiency into these mutant mice results in improvement of intestinal inflammation, indicating that TLR-mediated microbial recognition in the intestine triggers development of chronic enterocolitis (120). The MyD88-dependent pathway is seemingly involved in allograft rejection (121). Development of atherosclerosis observed in apolipoprotein E-deficient mice is rescued by introduction of MyD88 deficiency, indicating that the TLR-mediated pathway is responsible for the development of atherosclerosis (122,123). Involvement of the TLR9–MyD88-dependent pathway in the induction of auto-antibodies in SLE and rheumatoid arthritis was also demonstrated, as described above. In addition to these immune-related disorders, TLR recognition of commensal bacteria has been shown to play a crucial role in the maintenance of intestinal epithelial homeostasis (124). Thus, TLR-mediated pathways are probably involved in many aspects of immune responses, even in the absence of infection.

	Phylogenetic divergence in the role of Toll

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
It is well established that mammalian TLRs recognize specific molecular patterns found in microbial components, possibly through a close physical interaction. The Toll receptor in Drosophila melanogaster plays an essential role in the host defense against infection by fungi and Gram-positive bacteria. In Drosophila, fungal and Gram-positive bacterial infection triggers activation of the Toll-mediated pathway. Toll signaling induces the activation of the Pelle serine/threonine kinase via the adaptor DmMyD88 and degradation of the ankyrin-repeat protein Cactus, and causes activation of the Rel-type transcription factors Dorsal and DIF. Thus, the Drosophila Toll signaling pathway is very similar to that of mammalian TLR, especially the participation of the adaptor MyD88, the serine/threonine kinase IRAK, the ankyrin-repeat protein IB and the Rel-type transcription factor NF-B (125,126). However, there are some functional differences between the mammalian TLR system and the Drosophila Toll system (Fig. 6). First, unlike the mammalian TLR-mediated pathway, the Drosophila Toll pathway does not seem to utilize homologs of the mammalian IKKß and IKK/NEMO proteins. These molecules have been shown to be involved in the IMD pathway that senses Gram-negative bacterial infection (125,126). In addition, Drosophila Toll is activated by an endogenous ligand, Spätzle (127). Spätzle is initially produced as a pro-Spätzle, and is cleaved into the active signaling form by an as yet unidentified serine protease in response to invasion by fungi or Gram-positive bacteria. This indicates that Toll is not directly involved in the pattern recognition of micro-organisms. In the case of fungal infections, a serine protease that is encoded by the Persephone gene has been shown to activate Toll (128). The Persephone gene product possesses no obvious pattern recognition motif. Thus, the molecule that is responsible for the recognition of fungi remains unclear. In the case of Gram-positive bacterial infections, Gram-negative binding protein (GNBP) and PGRP-SA, a member of the peptidoglycan recognition protein (PGRP) family, play an essential role in the activation of Toll. This is demonstrated by the finding that mutant flies lacking GNBP or PGRP-SA are defective in the activation of the Toll-mediated pathway in response to Gram-positive bacterial infection (129,130). Subsequently, PGRP-SA has been shown to be responsible for the recognition of Gram-positive lysine-type peptidoglycan, demonstrating that PGRP-SA is a pattern recognition molecule in Drosophila (131). In addition, another member of the PGRP family, PGRP-LC, has been shown to play an essential role in the host defense against Gram-negative bacterial infection through the recognition of Gram-negative diaminopimelic acid-type peptidoglycan (132–134). In sharp contrast, mammalian PGRP-S has been shown to play only a minor role in the recognition of pathogens (135). Thus, although the signaling molecules associated with Drosophila Toll and mammalian TLR are shared, the actual pattern recognition of pathogens is mediated by quite different mechanisms. In particular, it is of note that only one Toll is actually involved in the Drosophila immune response (126). The complete lack of immune functions in other members (18-Wheeler/Toll-2 to Toll-9) of the Drosophila Toll family strongly suggests that the ancestral function of the Toll family is not to mediate immune response. In contrast, all members of the mammalian TLR family are specialized for functioning in immune responses, indicating that they have arisen from a common ancestor possessing immune recognition function. Thus, the systems by which pathogens are recognized in vertebrates and insects seem to have evolved separately.

View larger version (38K): [in this window] [in a new window]   Fig. 6. Toll pathway in Drosophila and TLR pathway in mammals. In Drosophila, fungal and Gram-positive bacterial infections are sensed by pattern recognition proteins. GNBP1 and PGRP-SA are responsible for the recognition of Gram-positive bacteria. Recognition of micro-organisms is followed by activation of proteolytic cascades, leading to the cleavage of Spätzle. Spätzle activates Toll, which leads to degradation of Cactus and nuclear translocation of the Rel-type transcription factor DIF. In the case of Gram-negative bacterial infection, the IMD pathway is activated in Drosophila. In mammals, microbial infections are sensed by TLRs, which leads to activation of the Rel-type transcription factor NF-B.

 

	Future prospects

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 
We now know that innate immunity plays an important role in the initiation of an immune response that follows the activation of antigen-specific acquired immunity. Although signaling pathways via TLRs are now being unveiled, there still remain several unanswered questions. For example, activation of TLR7, TLR8 and TLR9 leads to induction of IFN-/ß in a MyD88-dependent manner in PDC. It is possible that there might be a unique pathway downstream of MyD88 that specifies the signaling cascade of these TLRs. The mechanism for regulation of TLR-mediated gene induction is also of interest. A TLR-inducible nuclear factor, IB, has been shown to regulate a subset of TLR-inducible genes (136). In this model, IB, which is immediately induced by TLR stimulation, mediates induction of a certain group of TLR-inducible genes such as IL-6, IL-12p40 and GM-CSF in macrophages. It is of interest to analyze whether this two-step TLR-mediated gene induction model can be applied to other subsets of genes that are induced by TLRs. A complete understanding of the mechanisms of innate immunity will be helpful for the future development of innovative therapies for manipulation of infectious diseases, cancer and allergies.

	Acknowledgements

 
We thank M. Hashimoto and M. Kurata for secretarial assistance. This work was supported by grants from the Special Coordination Funds of the Ministry of Education, Culture, Sports, Science and Technology, the Uehara Memorial Foundation and the Naito Foundation.

	Abbreviations

 

CARD	caspase-recruitment domain
dsRNA	double-stranded RNA
HSP	heat shock proteins
iE-DAP	-D-glutamyl-meso diaminopimelic acid
IKK	IB kinase
LRRs	leucine-rich repeats
Mal	MyD88-adaptor-like
MCMV	mouse cytomegalovirus
MDP	MurNAc-L-Ala-D-isoGln
NOD	nucleotide-binding oligomerization domain
PDC	plasmacytoid dendritic cells
PGN	peptidoglycan
PGRP	peptidoglycan recognition protein
PKR	dsRNA-dependent protein kinase
RNAi	RNA interference
SIGIRR	single immunoglobulin IL-1 receptor-related molecule
ssRNA	single-stranded RNA
TICAM	TIR domain-containing adaptor molecule
TIR	Toll/IL-1 receptor
TIRAP	TIR domain-containing adaptor protein
TLRs	Toll-like receptors
TRIF	TIR domain-containing adaptor inducing IFN-ß

	References

Top Abstract Introduction Identification of the TLR... TLR1, TLR2 and TLR6 TLR3 TLR4 TLR5 TLR7 and TLR8 TLR9 TLR11 Subcellular localization of TLRs TLR-independent recognition of... Phagocytosis and TLRs TLR signaling pathways MyD88-dependent pathway MyD88-independent/TRIF-dependent... Negative regulation of TLR... Involvement of TLRs and... Phylogenetic divergence in the... Future prospects References

 

1. Lemaitre, B., Nicolas, E., Michaut, L., Reichhart, J.-M. and Hoffmann, J. A. 1996. The dorsoventral regulatory gene cassette spätzle/Toll/cactus controls the potent antifungal response in Drosophila adults. Cell 86:973.[CrossRef][Web of Science][Medline]
2. Medzhitov, R., Preston-Hurlburt, P. and Janeway, C. A. Jr. 1997. A human homologue of the Drosophila Toll protein signals activation of adaptive immunity. Nature 388:394.[CrossRef][Web of Science][Medline]
3. Poltorak, A. et al. 1998. Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutation in Tlr4 gene. Science 282:2085.[Abstract/Free Full Text]
4. Rock, F. L., Hardiman, G., Timans, J. C., Kastelein, R. A. and Bazan, J. F. 1998. A family of human receptors structurally related to Drosophila Toll. Proc. Natl Acad. Sci. USA 95:588.[Abstract/Free Full Text]
5. Zhang, D., Zhang, G., Hayden, M. S., Greenblatt, M. B., Bussey, C., Flavell, R. A. and Ghosh, S. 2004. A toll-like receptor that prevents infection by uropathogenic bacteria. Science 303:1522.[Abstract/Free Full Text]
6. Takeda, K., Kaisho, T. and Akira, S. 2003. Toll-like receptors. Annu. Rev. Immunol. 21:335.[CrossRef][Web of Science][Medline]
7. Hirschfeld, M. et al. 2001. Signaling by Toll-like receptor 2 and 4 agonists results in differential gene expression in murine macrophages. Infect. Immun. 69:1477.[Abstract/Free Full Text]
8. Werts, C. et al. 2001. Leptospiral lipopolysaccharide activates cells through a TLR2-dependent mechanism. Nat. Immunol. 2:346.[CrossRef][Web of Science][Medline]
9. Smith, M. F. Jr., Mitchell, A., Li, G., Ding, S., Fitzmaurice, A. M., Ryan, K., Crowe, S. and Goldberg, J. B. 2003. Toll-like receptor (TLR) 2 and TLR5, but not TLR4, are required for Helicobacter pylori-induced NF-B activation and chemokine expression by epithelial cells. J. Biol. Chem. 278:32552.[Abstract/Free Full Text]
10. Netea, M. G., van Deuren, M., Kullberg, B. J., Cavaillon, J. M. and Van der Maer, W. M. 2002. Does the shape of lipid A determine the interaction of LPS with Toll-like receptors? Trends Immunol. 23:135.[CrossRef][Web of Science][Medline]
11. Hashimoto, M., Asai, Y. and Ogawa, T. 2004. Separation and structural analysis of lipoprotein in a lipopolysaccharide preparation from Porphyromonas gingivalis. Int. Immunol. 16:1431.[Abstract/Free Full Text]
12. Takeuchi, O., Kawai, T., Muhlradt, P. F., Radolf, J. D., Zychlinsky, A., Takeda, K. and Akira, S. 2001. Discrimination of bacterial lipoproteins by Toll-like receptor 6. Int. Immunol. 13:933.[Abstract/Free Full Text]
13. Takeuchi, O., Horiuchi, T., Hoshino, K., Takeda, K., Dong, Z., Modlin, R. L. and Akira, S. 2002. Role of TLR1 in mediating immune response to microbial lipoproteins. J. Immunol. 169:10.[Abstract/Free Full Text]
14. Alexopoulou, L. et al. 2002. Hyporesponsiveness to vaccination with Borrelia burgdorferi OspA in humans and in TLR1- and TLR2-deficient mice. Nat. Medicine 8:878.[Web of Science][Medline]
15. Gantner, B. N., Simmons, R. M., Canavera, S. J., Akira, S. and Underhill, D. M. 2003. Collaborative induction of inflammatory responses by dectin-1 and Toll-like receptor 2. J. Exp. Med. 197:1107.[Abstract/Free Full Text]
16. Alexopoulou, L., Holt, A. C., Medzhitov, R. and Flavell, R. A. 2001. Recognition of double-stranded RNA and activation of NF-B by Toll-like receptor 3. Nature 413:732.[CrossRef][Medline]
17. Hoshino, K., Takeuchi, O., Kawai, T., Sanjo, H., Ogawa, T., Takeda, Y., Takeda, K. and Akira, S. 1999. Cutting Edge: Toll-like receptor 4 (TLR4)-deficient mice are hyporesponsive to lipopolysaccharide: evidence for TLR4 as the Lps hene product. J. Immunol. 162:749.
18. Byrd-Leifer, C. A., Block, E. F., Takeda, K., Akira, S. and Ding, A. 2001. The role of MyD88 and TLR4 in the LPS-mimetic activity of Taxol. Eur. J. Immunol. 31:2448.[CrossRef][Web of Science][Medline]
19. Kawasaki, K., Akashi, S., Shimazu, R., Yoshida, T., Miyake, K. and Nishijima, M. 2000. Mouse Toll-like receptor 4-MD-2 complex mediates lipopolysaccharide-mimetic signal transduction by Taxol. J. Biol. Chem. 275:2251.[Abstract/Free Full Text]
20. Gao, B. and Tsan, M. F. 2003. Endotoxin contamination in recombinant human heat shock protein 70 (Hsp70) preparation is responsible for the induction of tumor necrosis factor release by murine macrophages. J. Biol. Chem. 278:174.[Abstract/Free Full Text]
21. Hayashi, F. et al. 2001. The innate immune response to bacterial flagellin is mediated by Toll-like receptor-5. Nature 410:1099.[CrossRef][Medline]
22. Smith, K. D., Andersen-Nissen, E., Hayashi, F., Strobe, K., Bergman, M. A., Barrett, S. L., Cookson, B. T. and Aderem, A. 2003. Toll-like receptor 5 recognizes a conserved site on flagellin required for protofilament formation and bacterial motility. Nat. Immunol. 4:1247.[CrossRef][Web of Science][Medline]
23. Gewirtz, A. T., Navas, T. A., Lyons, S., Godowski, P. J. and Madara, J. L. 2001. Cutting edge: Bacterial flagellin activates basolaterally expressed TLR5 to induce epithelial proinflammatory gene expression. J. Immunol. 167:1882.[Abstract/Free Full Text]
24. Maaser, C., Heidemann, J., von Eiff, C., Lugering, A., Spahn, T. W., Binion, D. G., Domschke, W., Lugering, N. and Kucharzik, T. 2004. Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin. J. Immunol. 172:5056.[Abstract/Free Full Text]
25. Hawn, T. R. et al. 2003. A common dominant TLR5 stop codon polymorphism abolishes flagellin signaling and is associated with susceptibility to legionnaires' disease. J. Exp. Med. 198:1563.[Abstract/Free Full Text]
26. Hemmi, H. et al. 2002. Small antiviral compounds activate immune cells via TLR7 MyD88-dependent signalling pathway. Nat. Immunol. 3:196.[CrossRef][Web of Science][Medline]
27. Jurk, M., Heil, F., Vollmer, J., Schetter, C., Krieg, A. M., Wagner, H., Lipford, G. and Bauer, S. 2002. Human TLR7 or TLR8 independently confer responsiveness to the antiviral compound R-848. Nat. Immunol. 3:499.[CrossRef][Web of Science][Medline]
28. Lee, J., Chuang, T. H., Redecke, V., She, L., Pitha, P. M., Carson, D. A., Raz, E. and Cottam, H. B. 2003. Molecular basis for the immunostimulatory activity of guanine nucleoside analogs: activation of Toll-like receptor 7. Proc. Natl Acad. Sci. USA 100:6646.[Abstract/Free Full Text]
29. Heil, F. et al. 2003. The Toll-like receptor 7 (TLR7)-specific stimulus loxoribine uncovers a strong relationship within the TLR7, 8 and 9 subfamily. Eur. J. Immunol. 33:2987.[CrossRef][Web of Science][Medline]
30. Heil, F. et al. 2004. Species-specific recognition of single-stranded RNA via Toll-like receptor 7 and 8. Science 303:1526.[Abstract/Free Full Text]
31. Diebold, S. S., Kaisho, T., Hemmi, H., Akira, S. and Reis E Sousa, C. 2004. Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA. Science 303:1529.[Abstract/Free Full Text]
32. Lund, J. M., Alexopoulou, L., Sato, A., Karow, M., Adams, N. C., Gale, N. W., Iwasaki, A. and Flavell, R. A. 2004. Recognition of single-stranded RNA viruses by Toll-like receptor 7. Proc. Natl Acad. Sci. USA 101:5598.[Abstract/Free Full Text]
33. Hemmi, H. et al. 2000. A Toll-like receptor recognizes bacterial DNA. Nature 408:740.[CrossRef][Medline]
34. Krug, A. et al. 2001. Identification of CpG oligonucleotide sequences with high induction of IFN-/ß in plasmacytoid dendritic cells. Eur. J. Immunol. 31:2154.[CrossRef][Web of Science][Medline]
35. Verthelyi, D., Ishii, K. J., Gursel, M., Takeshita, F. and Klinman, D. M. 2001. Human peripheral blood cells differentially recognize and respond to two distinct CpG motifs. J. Immunol. 166:2372.[Abstract/Free Full Text]
36. Hemmi, H., Kaisho, T., Takeda, K. and Akira, S. 2003. The roles of Toll-like receptor 9, MyD88 and DNA-PKcs in the effects of two distinct CpG DNAs on dendritic cell subsets. J. Immunol. 170:3059.[Abstract/Free Full Text]
37. Lund, J., Sato, A., Akira, S., Medzhitov, R. and Iwasaki, A. 2003. Toll-like receptor 9-mediated recognition of Herpes simplex virus-2 by plasmacytoid dendritic cells. J. Exp. Med. 198:513.[Abstract/Free Full Text]
38. Krug, A., Luker, G. D., Barchet, W., Leib, D. A., Akira, S. and Colonna, M. 2004. Herpes simplex virus type 1 activates murine natural interferon-producing cells through toll-like receptor 9. Blood 103:1433.[Abstract/Free Full Text]
39. Tabeta, K. et al. 2004. Toll-like receptors 9 and 3 as essential components of innate immune defense against mouse cytomegalovirus infection. Proc. Natl Acad. Sci. USA 101:3516.[Abstract/Free Full Text]
40. Krug, A. et al. 2004. TLR9-dependent recognition of MCMV by IPC and DC generates coordinated cytokine responses that activate antiviral NK cell function. Immunity 21:107.[CrossRef][Web of Science][Medline]
41. Leadbetter, E. A., Rifkin, I. R., Hohlbaum, A. M., Beaudette, B. C., Shlomchik, M. J. and Marshak-Rothstein, A. 2002. Chromatin–IgG complexes activate B cells by dual engagement of IgM and Toll-like receptors. Nature 416:603.[CrossRef][Medline]
42. Viglianti, G. A., Lau, C. M., Hanley, T. M., Miko, B. A., Shlomchik, M. J. and Marshak-Rothstein, A. 2003. Activation of autoreactive B cells by CpG dsDNA. Immunity 19:837.[CrossRef][Web of Science][Medline]
43. Boule, M. W., Broughton, C., Mackay, F., Akira, S., Marshak-Rothstein, A. and Rifkin, I. R. 2004. Toll-like receptor 9-dependent and -independent dendritic cell activation by chromatin-immunoglobulin G complexes. J. Exp. Med. 199:1631.[Abstract/Free Full Text]
44. Hacker, H. et al. 1998. CpG-DNA-specific activation of antigen-presenting cells requires stress kinase activity and is preceded by non-specific endocytosis and endosomal maturation. EMBO J. 17:6230.[CrossRef][Web of Science][Medline]
45. Matsumoto, M., Funami, K., Tanabe, M., Oshiumi, H., Shingai, M., Seto, Y., Yamamoto, A. and Seya, T. 2003. Subcellular localization of Toll-like receptor 3 in human dendritic cells. J. Immunol. 171:3154.[Abstract/Free Full Text]
46. Ahmad-Nejad, P., Hacker, H., Rutz, M., Bauer, S., Vabulas, R. M. and Wagner, H. 2002. Bacterial CpG-DNA and lipopolysaccharides activate Toll-like receptors at distinct cellular compartments. Eur. J. Immunol. 32:1958.[CrossRef][Web of Science][Medline]
47. Latz, E. et al. 2004. TLR9 signals after translocating from the ER to CpG DNA in the lysosome. Nat. Immunol. 5:190.[CrossRef][Web of Science][Medline]
48. Funami, K., Matsumoto, M., Oshiumi, H., Akazawa, T., Yamamoto, A. and Seya, T. 2004. The cytoplasmic ‘linker region’ in Toll-like receptor 3 controls receptor localization and signaling. Int. Immunol. 16:1143.[Abstract/Free Full Text]
49. Leifer, C. A., Kennedy, M. N., Mazzoni, A., Lee, C., Kruhlak, M. J. and Segal, D. M. 2004. TLR9 is localized in the endoplasmic reticulum prior to stimulation. J. Immunol. 173:1179.[Abstract/Free Full Text]
50. Underhill, D. M., Ozinsky, A., Hajjar, A. M., Stevens, A., Wilson, C. B., Bassetti, M. and Aderem, A. 1999. The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens. Nature 401:811.[CrossRef][Medline]
51. Yamamoto, M. et al. 2003. Role of adaptor TRIF in the MyD88-independent Toll-like receptor signaling pathway. Science 301:640.[Abstract/Free Full Text]
52. Diebold, S. S. et al. 2003. Viral infection switches non-plasmacytoid dendritic cells into high interferon producers. Nature 424:324.[CrossRef][Medline]
53. Smith, E. J., Marie, I., Prakash, A., Garcia-Sastre, A. and Levy, D. E. 2001. IRF3 and IRF7 phosphorylation in virus-infected cells does not require double-stranded RNA-dependent protein kinase R or IB kinase but is blocked by vaccinia virus E3L protein. J. Biol. Chem. 276:8951.[Abstract/Free Full Text]
54. Yoneyama, M. et al. 2004. The RNA helicase RIG-I has an essential function in double-stranded RNA-induced innate antiviral responses. Nat. Immunol. 5:730.[CrossRef][Web of Science][Medline]
55. Takeuchi, O., Hoshino, K., Kawai, T., Sanjo, H., Takada, H., Ogawa, T., Takeda, K. and Akira, S. 1999. Differential roles of TLR2 and TLR4 in recognition of Gram-negative and Gram-positive bacterial cell wall components. Immunity 11:443.[CrossRef][Web of Science][Medline]
56. Girardin, S. E. et al. 2003. Nod1 detects a unique muropeptide from Gram-negative bacterial peptidoglycan. Science 300:1584.[Abstract/Free Full Text]
57. Chamaillard, M. et al. 2003. An essential role for NOD1 in host recognition of bacterial peptidoglycan containing diaminopimelic acid. Nat. Immunol. 4:702.[CrossRef][Web of Science][Medline]
58. Girardin, S. E., Boneca, I. G., Viala, J., Chamaillard, M., Labigne, A., Thomas, G., Philpott, D. J. and Sansonetti, P. J. 2003. Nod2 is a general sensor of peptidoglycan through muramyl dipeptide (MDP) detection. J. Biol. Chem. 278:8869.[Abstract/Free Full Text]
59. Inohara, N. et al. 2003. Host recognition of bacterial muramyl dipeptide mediated through NOD2: implications for Crohn's disease. J. Biol. Chem. 278:5509.[Abstract/Free Full Text]
60. Ogura, Y. et al. 2001. A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease. Nature 411:603.[CrossRef][Medline]
61. Hugot, J. P. et al. 2001. Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease. Nature 411:599.[CrossRef][Medline]
62. Watanabe, T., Kitani, A., Murray, P. J. and Strober, W. 2004. NOD2 is a negative regulator of Toll-like receptor 2-mediated T helper type 1 responses. Nat. Immunol. 5:800.[CrossRef][Web of Science][Medline]
63. Miceli-Richard, C. et al. 2001. CARD15 mutations in Blau syndrome. Nat. Genet. 29:19.[CrossRef][Web of Science][Medline]
64. Inohara, N. and Nunez, G. 2003. NODs: intracellular proteins involved in inflammation and apoptosis. Nat. Rev. Immunol. 3:371.[CrossRef][Web of Science][Medline]
65. Chin, A. I., Dempsey, P. W., Bruhn, K., Miller, J. F., Xu, Y. and Cheng, G. 2002. Involvement of receptor-interacting protein 2 in innate and adaptive immune responses. Nature 416:190.[CrossRef][Medline]
66. Kobayashi, K., Inohara, N., Hernandez, L. D., Galan, J. E., Nunez, G., Janeway, C. A., Medzhitov, R. and Flavell, R. A. 2002. RICK/Rip2/CARDIAK mediates signalling for receptors of the innate and adaptive immune systems. Nature 416:194.[CrossRef][Medline]
67. Blander, J. M. and Medzhitov, R. 2004. Regulation of phagosome maturation by signals from toll-like receptors. Science 304:1014.[Abstract/Free Full Text]
68. Doyle, S. E. et al. 2004. Toll-like receptors induce a phagocytic gene program through p38. J. Exp. Med. 199:81.[Abstract/Free Full Text]
69. Akira, S. and Takeda, K. 2004. Toll-like receptor signalling. Nat. Rev. Immunol. 4:499.[CrossRef][Web of Science][Medline]
70. Saitoh, S. et al. 2004. Lipid A antagonist, lipid IVa, is distinct from lipid A in interaction with Toll-like receptor 4 (TLR4)-MD-2 and ligand-induced TLR4 oligomerization. Int. Immunol. 16:961.[Abstract/Free Full Text]
71. Takeuchi, O., Takeda, K., Hoshino, K., Adachi, O., Ogawa, T. and Akira, S. 2000. Cellular responses to bacterial cell wall components are mediated through MyD88-dependent signaling cascades. Int. Immunol. 12:113.[Abstract/Free Full Text]
72. Kawai, T., Adachi, O., Ogawa, T., Takeda, K. and Akira, S. 1999. Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity 11:115.[CrossRef][Web of Science][Medline]
73. Schnare, M., Holt, A. C., Takeda, K., Akira, S. and Medzhitov, R. 2000. Recognition of CpG DNA is mediated by signaling pathways dependent on the adaptor protein MyD88. Curr. Biol. 10:1139.[CrossRef][Web of Science][Medline]
74. Hacker, H., Vabulas, R. M., Takeuchi, O., Hoshino, K., Akira, S. and Wagner, H. 2000. Immune cell activation by bacterial CpG-DNA through myeloid differentiation marker 88 and tumor necrosis factor receptor-associated factor (TRAF)6. J. Exp. Med. 192:595.[Abstract/Free Full Text]
75. Toshchakov, V. et al. 2002. TLR4, but not TLR2, mediates IFN-ß-induced STAT1/ß-dependent gene expression in macrophages. Nat. Immunol. 3:392.[CrossRef][Web of Science][Medline]
76. Hoshino, K., Kaisho, T., Iwabe, T., Takeuchi, O. and Akira, S. 2002. Differential involvement of IFN-ß in Toll-like receptor-stimulated dendritic cell activation. Int. Immunol. 14:1225.[Abstract/Free Full Text]
77. Doyle, S. E. et al. 2002. IRF3 mediates a TLR3/TLR4-specific antiviral gene program. Immunity 17:251.[CrossRef][Web of Science][Medline]
78. Ito, T. et al. 2002. Interferon- and interleukin-12 are induced differentially by Toll-like receptor 7 ligands in human blood dendritic cell subsets. J. Exp. Med. 195:1507.[Abstract/Free Full Text]
79. Horng, T., Barton, G. M. and Medzhitov, R. 2001. TIRAP: an adapter molecule in the Toll signaling pathway. Nat. Immunol. 2:835.[CrossRef][Web of Science][Medline]
80. Fitzgerald, K. A. et al. 2001. Mal (MyD88-adaptor-like) is required for Toll-like receptor-4 signal transduction. Nature 413:78.[CrossRef][Medline]
81. Horng, T., Barton, G. M., Flavell, R. A. and Medzhitov, R. The adaptor molecule TIRAP provides signaling specificity for Toll-like receptors. Nature 420:329.
82. Yamamoto, M. et al. 2002. Essential role of TIRAP/Mal for activation of the signaling cascade shared by TLR2 and TLR4. Nature 420:324.[CrossRef][Medline]
83. Kawai, T., Takeuchi, O., Fujita, T., Inoue, J., Mühlradt, P. F., Sato, S., Hoshino, K. and Akira, S. 2001. Lipopolysaccharide stimulates the MyD88-independent pathway and results in activation of IRF-3 and the expression of a subset of LPS-inducible genes. J. Immunol. 167:5887.[Abstract/Free Full Text]
84. Yoneyama, M., Suhara, W., Fukuhara, Y., Fukuda, M., Nishida, E. and Fujita, T. 1998. Direct triggering of the type I interferon system by virus infection: activation of a transcription factor complex containing IRF-3 and CBP/p300. EMBO J. 17:1087.[CrossRef][Web of Science][Medline]
85. Yamamoto, M., Sato, S., Mori, K., Takeuchi, O., Hoshino, K., Takeda, K. and Akira, S. 2002. A novel TIR domain-containing adaptor that preferentially activates the interferon-ß promoter. J. Immunol. 169:6668.[Abstract/Free Full Text]
86. Oshiumi, H., Matsumoto, M., Funami, K., Akazawa, T. and Seya, T. 2003. TICAM-1, an adaptor molecule that participates in Toll-like receptor 3-mediated interferon-ß induction. Nat. Immunol. 4:161.[CrossRef][Web of Science][Medline]
87. Hoebe, K. et al. 2003. Identification of Lps2 as a key transducer of MyD88-independent TIR signalling. Nature 424:743.[CrossRef][Medline]
88. Fitzgerald, K. A. et al. 2003. LPS–TLR4 signaling to IRF-3/7 and NF-B involves the Toll adapters TRAM and TRIF. J. Exp. Med. 198:1043.[Abstract/Free Full Text]
89. Yamamoto, M. et al. 2003. TRAM is specifically involved in the TLR4-mediated MyD88-independent signaling pathway. Nat. Immunol. 4:1144.[CrossRef][Web of Science][Medline]
90. Oshiumi, H., Sasai, M., Shida, K., Fujita, T., Matsumoto, M. and Seya, T. 2003. TIR-containing adapter molecule (TICAM)-2, a bridging adapter recruiting to Toll-like receptor 4 TICAM-1 that induces interferon-ß. J. Biol. Chem. 278:49751.[Abstract/Free Full Text]
91. Bin, L. H., Xu, L. G. and Shu, H. B. 2003. TIRP, a novel Toll/interleukin-1 receptor (TIR) domain-containing adapter protein involved in TIR signaling. J. Biol. Chem. 278:24526.[Abstract/Free Full Text]
92. Sharma, S., ten Oever, B. R., Grandvaux, N., Zhou, G. P., Lin, R. and Hiscott, J. 2003. Triggering the interferon antiviral response through an IKK-related pathway. Science 300:1148.[Abstract/Free Full Text]
93. Fitzgerald, K. A. et al. 2003. IKK and TBK1 are essential components of the IRF3 signaling pathway. Nat. Immunol. 4:491.[CrossRef][Web of Science][Medline]
94. McWhirter, S. M., Fitzgerald, K. A., Rosains, J., Rowe, D. C., Golenbock, D. T. and Maniatis, T. 2004. IFN-regulatory factor 3-dependent gene expression is defective in Tbk1-deficient mouse embryonic fibroblasts. Proc. Natl Acad. Sci. USA 101:233.[Abstract/Free Full Text]
95. Hemmi, H. et al. 2004. The roles of two IB kinase-related kinases in lipopolysaccharide and double stranded RNA signaling and viral infection. J. Exp. Med. 199:1641.[Abstract/Free Full Text]
96. Perry, A. K., Chow, E. K., Goodnough, J. B., Yeh, W. C. and Cheng, G. 2004. Differential requirement for TANK-binding kinase-1 in type I interferon responses to Toll-like receptor activation and viral infection. J. Exp. Med. 199:1651.[Abstract/Free Full Text]
97. Sato, S., Sugiyama, M., Yamamoto, M., Watanabe, Y., Kawai, T., Takeda, K. and Akira, S. 2003. Toll/IL-1 receptor domain-containing adaptor inducing IFN-ß (TRIF) associates with TNF receptor-associated factor 6 and TANK-binding kinase 1 and activates two distinct transcription factors, NF-B and IFN-regulatory factor-3, in the Toll-like receptor signaling. J. Immunol. 171:4304.[Abstract/Free Full Text]
98. Jiang, Z., Mak, T. W., Sen, G. and Li, X. 2004. Toll-like receptor 3-mediated activation of NF-B and IRF3 diverges at Toll-IL-1 receptor domain-containing adapter inducing IFN-ß. Proc. Natl Acad. Sci. USA 101:3533.[Abstract/Free Full Text]
99. Gohda, J., Matsumura, T. and Inoue, J. 2004. Cutting edge: TNFR-associated factor 6 is essential for MyD88-dependent pathway but not Toll/IL-1 receptor domain-containing adaptor-inducing IFN-ß-dependent pathway in TLR signaling. J. Immunol. 173:2913.[Abstract/Free Full Text]
100. Meylan, E., Burns, K., Hofmann, K., Blancheteau, V., Martinon, F., Kelliher, M. and Tschopp, J. 2004. RIP1 is an essential mediator of Toll-like receptor 3-induced NF-B activation. Nat. Immunol. 5:503.[CrossRef][Web of Science][Medline]
101. Beeson, P. B. 1947. Tolerance to bacterial pyrogens. I. Factors influencing its development. J. Exp. Med. 86:29.[Abstract]
102. Nomura, F. et al. 2000. Endotoxin tolerance in mouse peritoneal macrophages correlates with downregulation of surface Toll-like receptor 4 expression. J. Immunol. 164:3476.[Abstract/Free Full Text]
103. Akashi, S., Shimazu, R., Ogata, H., Nagai, Y., Takeda, K., Kimoto, M. and Miyake, K. 2000. Cutting edge: Cell surface expression and lipopolysaccharide signaling via the Toll-like receptor 4-MD-2 complex on mouse peritoneal macrophages. J. Immunol. 164:3471.[Abstract/Free Full Text]
104. Li, L., Cousart, S., Hu, J. and McCall, C. E. 2000. Characterization of interleukin-1 receptor-associated kinase in normal and endotoxin-tolerant cells. J. Biol. Chem. 275:23340.[Abstract/Free Full Text]
105. Sato, S., Takeuchi, O., Fujita, T., Tomizawa, H., Takeda, K. and Akira, S. 2002. A variety of microbial components induce tolerance to lipopolysaccharide by differentially affecting MyD88-dependent and -independent pathways. Int. Immunol. 14:783.[Abstract/Free Full Text]
106. Siedlar, M., Frankenberger, M., Benkhart, E., Espevik, T., Quirling, M., Brand, K., Zembala, M. and Ziegler-Heitbrock, L. 2004. Tolerance induced by the lipopeptide Pam3Cys is due to ablation of IL-1R-associated kinase-1. J. Immunol. 173:2736.[Abstract/Free Full Text]
107. Fan, H. and Cook, J. A. 2004. Molecular mechanisms of endotoxin tolerance. J. Endotoxin Res. 10:71.[CrossRef][Medline]
108. Wesche, H., Gao, X., Li, X., Kirschning, C. J., Stark, G. R. and Cao, Z. 1999. IRAK-M is a novel member of the Pelle/interleukin-1 receptor-associated kinase (IRAK) family. J. Biol. Chem. 274:19403.[Abstract/Free Full Text]
109. Kobayashi, K., Hernandez, L. D., Galan, J. E., Janeway, C. A. Jr, Medzhitov, R. and Flavell, R. A. IRAK-M is a negative regulator of Toll-like receptor signaling. Cell 110:191.
110. Burns, K., Janssens, S., Brissoni, B., Olivos, N., Beyaert, R. and Tschopp, J. 2003. Inhibition of interleukin 1 receptor/Toll-like receptor signaling through the alternatively spliced, short form of MyD88 is due to its failure to recruit IRAK-4. J. Exp. Med. 197:263.[Abstract/Free Full Text]
111. Yasukawa, H., Sasaki, A. and Yoshimura, A. 2000. Negative regulation of cytokine signaling pathways. Annu. Rev. Immunol. 18:143.[CrossRef][Web of Science][Medline]
112. Stoiber, D., Kovarik, P., Cohney, S., Johnston, J. A., Steinlein, P. and Decker, T. 1999. Lipopolysaccharide induces in macrophages the synthesis of the suppressor of cytokine signaling 3 and suppresses signal transduction in response to the activating factor IFN-. J. Immunol. 163:2640.[Abstract/Free Full Text]
113. Dalpke, A. H., Opper, S., Zimmermann, S. and Heeg, K. 2001. Suppressors of cytokine signaling (SOCS)-1 and SOCS-3 are induced by CpG-DNA and modulate cytokine responses in APCs. J. Immunol. 166:7082.[Abstract/Free Full Text]
114. Kinjyo, I. et al. 2002. SOCS1/JAB is a negative regulator of LPS-induced macrophage activation. Immunity 17:583.[CrossRef][Web of Science][Medline]
115. Nakagawa, R. et al. 2002. SOCS-1 participates in negative regulation of LPS responses. Immunity 17:677.[CrossRef][Web of Science][Medline]
116. Brint, E. K., Xu, D., Liu, H., Dunne, A., McKenzie, A. N., O'Neill, L. A. and Liew, F. Y. 2004. ST2 is an inhibitor of interleukin 1 receptor and Toll-like receptor 4 signaling and maintains endotoxin tolerance. Nat Immunol. 5:373.[CrossRef][Web of Science][Medline]
117. Wald, D. et al. 2003. SIGIRR, a negative regulator of Toll-like receptor-interleukin 1 receptor signaling. Nat. Immunol. 4:920.[CrossRef][Web of Science][Medline]
118. Chuang, T. H. and Ulevitch, R. J. 2004. Triad3A, an E3 ubiquitin-protein ligase regulating Toll-like receptors. Nat. Immunol. 5:495.[CrossRef][Web of Science][Medline]
119. Takeda, K., Clausen, B., Kaisho, T., Tsujimura, T., Terada, N., Förster, I. and Akira, S. 1999. Enhanced Th1 activity and development of chronic enterocolitis in mice devoid of Stat3 in macrophages and neutrophils. Immunity 10:39.[CrossRef][Web of Science][Medline]
120. Kobayashi, M., Kweon, M., Kuwata, H., Kiyono, H., Takeda, K. and Akira, S. 2003. Toll-like receptor-dependent IL-12p40 production causes chronic enterocolitis in myeloid cell-specific Stat3-deficient mice. J. Clin. Invest. 111:1297.[CrossRef][Web of Science][Medline]
121. Goldstein, D. R., Tesar, B. M., Akira, S. and Lakkis, F. G. 2003. Critical role of the Toll-like receptor signal adaptor protein MyD88 in acute allograft rejection. J. Clin. Invest. 111:1571.[CrossRef][Web of Science][Medline]
122. Bjorkbacka, H. et al. 2004. Reduced atherosclerosis in MyD88-null mice links elevated serum cholesterol levels to activation of innate immunity signaling pathways. Nat. Med. 10:416.[CrossRef][Web of Science][Medline]
123. Michelsen, K. S. et al. 2004. Lack of Toll-like receptor 4 or myeloid differentiation factor 88 reduces atherosclerosis and alters plaque phenotype in mice deficient in apolipoprotein E. Proc. Natl Acad. Sci. USA 101:10679.[Abstract/Free Full Text]
124. Rakoff-Nahoum, S., Paglino, J., Eslami-Varzaneh, F., Edberg, S. and Medzhitov, R. 2004. Recognition of commensal microflora by Toll-like receptors is required for intestinal homeostasis. Cell 118:229.[CrossRef][Web of Science][Medline]
125. Hoffmann, J. A. and Reichhart, J. M. 2001. Drosophila innate immunity: an evolutionary perspective. Nat. Immunol. 3:121.
126. Hoffmann, J. A. 2003. The innate immune response in Drosophila. Nature 426:33.[CrossRef][Web of Science][Medline]
127. Weber, A. N. et al. Binding of the Drosophila cytokine Spätzle to Toll is direct and establishes signaling. Nat. Immunol. 4:794.
128. Ligoxygakis, P., Pelte, N., Hoffmann, J. A. and Reichhart, J. M. 2002. Activation of Drosophila Toll during fungal infection by a blood serine protease. Science 297:114.[Abstract/Free Full Text]
129. Michel, T., Reichhart, J. M., Hoffmann, J. A. and Royet, J. 2001. Drosophila Toll is activated by Gram-positive bacteria through a circulating peptidoglycan recognition protein. Nature 414:756.[CrossRef][Web of Science][Medline]
130. Gobert, V., Gottar, M., Matskevich, A. A., Rutschmann, S., Royet, J., Belvin, M., Hoffmann, J. A. and Ferrandon, D. 2003. Dual activation of the Drosophila Toll pathway by two pattern recognition receptors. Science 302:2126.[Abstract/Free Full Text]
131. Leulier, F., Parquet, C., Pili-Floury, S., Ryu, J. H., Caroff, M., Lee, W. J., Mengin-Lecreulx, D. and Lemaitre, B. 2003. The Drosophila immune system detects bacteria through specific peptidoglycan recognition. Nat. Immunol. 4:478.[CrossRef][Web of Science][Medline]
132. Choe, K. M., Werner, T., Stoven, S., Hultmark, D. and Anderson, K. V. 2002. Requirement of a peptidoglycan recognition protein (PGRP) in Relish activation and antibacterial immune resonses in Drosophila. Science 296:359.[Abstract/Free Full Text]
133. Gottar, M., Gobert, V., Michel, T., Belvin, M., Duyk, G., Hoffmann, J. A., Ferrandon, D. and Royet, J. 2002. The Drosophila immune response against Gram-negative bacteria is mediated by a peptidoglycan recognition protein. Nature 416:640.[CrossRef][Medline]
134. Ramet, M., Manfruelli, P., Pearson, A., Mathey-Prevota, B. and Ezekowitz, A. B. 2002. Functional genomic analysis of phagocytosis and identification of a Drosophila receptor for E. coli. Nature 416:644.
135. Dziarski, R., Platt, K. A., Gelius, E., Steiner, H. and Gupta, D. 2003. Defect in neutrophil killing and increased susceptibility to infection with nonpathogenic gram-positive bacteria in peptidoglycan recognition protein-S (PGRP-S)-deficient mice. Blood 102:689.[Abstract/Free Full Text]
136. Yamamoto, M. et al. 2004. Regulation of Toll/IL-1-receptor-mediated gene expression by the inducible nuclear protein IB. Nature 430:218.[CrossRef][Medline]

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				D. A. Pippig, J. C. Hellmuth, S. Cui, A. Kirchhofer, K. Lammens, A. Lammens, A. Schmidt, S. Rothenfusser, and K.-P. Hopfner The regulatory domain of the RIG-I family ATPase LGP2 senses double-stranded RNA Nucleic Acids Res., April 1, 2009; 37(6): 2014 - 2025. [Abstract] [Full Text] [PDF]

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				Q. Chen, S. Gupta, and A. B. Pernis Regulation of TLR4-mediated signaling by IBP/Def6, a novel activator of Rho GTPases J. Leukoc. Biol., March 1, 2009; 85(3): 539 - 543. [Abstract] [Full Text] [PDF]

				Y. TAMAKI, Y. TAKAKUBO, K. GOTO, T. HIRAYAMA, K. SASAKI, Y. T. KONTTINEN, S. B. GOODMAN, and M. TAKAGI Increased Expression of Toll-like Receptors in Aseptic Loose Periprosthetic Tissues and Septic Synovial Membranes Around Total Hip Implants J Rheumatol, March 1, 2009; 36(3): 598 - 608. [Abstract] [Full Text] [PDF]

				C. KOHCHI, H. INAGAWA, T. NISHIZAWA, and G.-I. SOMA ROS and Innate Immunity Anticancer Res, March 1, 2009; 29(3): 817 - 821. [Abstract] [Full Text] [PDF]

				V. Cerovic, C. D. Jenkins, A. G. C. Barnes, S. W. F. Milling, G. G. MacPherson, and L. S. Klavinskis Hyporesponsiveness of Intestinal Dendritic Cells to TLR Stimulation Is Limited to TLR4 J. Immunol., February 15, 2009; 182(4): 2405 - 2415. [Abstract] [Full Text] [PDF]

				B. M. Elzinga, C. Twomey, J. C. Powell, F. Harte, and J. V. McCarthy Interleukin-1 Receptor Type 1 Is a Substrate for {gamma}-Secretase-dependent Regulated Intramembrane Proteolysis J. Biol. Chem., January 16, 2009; 284(3): 1394 - 1409. [Abstract] [Full Text] [PDF]

				S. C. Ha, D. Kim, H.-Y. Hwang, A. Rich, Y.-G. Kim, and K. K. Kim The crystal structure of the second Z-DNA binding domain of human DAI (ZBP1) in complex with Z-DNA reveals an unusual binding mode to Z-DNA PNAS, December 30, 2008; 105(52): 20671 - 20676. [Abstract] [Full Text] [PDF]

				C. M. Kane, E. Jung, and E. J. Pearce Schistosoma mansoni Egg Antigen-Mediated Modulation of Toll-Like Receptor (TLR)-Induced Activation Occurs Independently of TLR2, TLR4, and MyD88 Infect. Immun., December 1, 2008; 76(12): 5754 - 5759. [Abstract] [Full Text] [PDF]

				A. R. Ashtekar, P. Zhang, J. Katz, C. C. S. Deivanayagam, P. Rallabhandi, S. N. Vogel, and S. M. Michalek TLR4-mediated activation of dendritic cells by the heat shock protein DnaK from Francisella tularensis J. Leukoc. Biol., December 1, 2008; 84(6): 1434 - 1446. [Abstract] [Full Text] [PDF]

				A. Lundberg, L. A. Wikberg, J. Ilonen, O. Vaarala, and M. F. Bottcher Lipopolysaccharide-Induced Immune Responses in Relation to the TLR4(Asp299Gly) Gene Polymorphism Clin. Vaccine Immunol., December 1, 2008; 15(12): 1878 - 1883. [Abstract] [Full Text] [PDF]

				T. A. Zola, E. S. Lysenko, and J. N. Weiser Mucosal Clearance of Capsule-Expressing Bacteria Requires Both TLR and Nucleotide-Binding Oligomerization Domain 1 Signaling J. Immunol., December 1, 2008; 181(11): 7909 - 7916. [Abstract] [Full Text] [PDF]

				S Moller-Larsen, M Nyegaard, A Haagerup, J Vestbo, T A Kruse, and A D Borglum Association analysis identifies TLR7 and TLR8 as novel risk genes in asthma and related disorders Thorax, December 1, 2008; 63(12): 1064 - 1069. [Abstract] [Full Text] [PDF]

				R. Dai, R. A. Phillips, Y. Zhang, D. Khan, O. Crasta, and S. A. Ahmed Suppression of LPS-induced Interferon-{gamma} and nitric oxide in splenic lymphocytes by select estrogen-regulated microRNAs: a novel mechanism of immune modulation Blood, December 1, 2008; 112(12): 4591 - 4597. [Abstract] [Full Text] [PDF]

				H. Wang, C. A. Garcia, K. Rehani, C. Cekic, P. Alard, D. F. Kinane, T. Mitchell, and M. Martin IFN-{beta} Production by TLR4-Stimulated Innate Immune Cells Is Negatively Regulated by GSK3-{beta} J. Immunol., November 15, 2008; 181(10): 6797 - 6802. [Abstract] [Full Text] [PDF]

				S. Chen, R. Sorrentino, K. Shimada, Y. Bulut, T. M. Doherty, T. R. Crother, and M. Arditi Chlamydia pneumoniae-Induced Foam Cell Formation Requires MyD88-Dependent and -Independent Signaling and Is Reciprocally Modulated by Liver X Receptor Activation J. Immunol., November 15, 2008; 181(10): 7186 - 7193. [Abstract] [Full Text] [PDF]

				V. Balloy, J.-M. Sallenave, Y. Wu, L. Touqui, J.-P. Latge, M. Si-Tahar, and M. Chignard Aspergillus fumigatus-induced Interleukin-8 Synthesis by Respiratory Epithelial Cells Is Controlled by the Phosphatidylinositol 3-Kinase, p38 MAPK, and ERK1/2 Pathways and Not by the Toll-like Receptor-MyD88 Pathway J. Biol. Chem., November 7, 2008; 283(45): 30513 - 30521. [Abstract] [Full Text] [PDF]

				R. Shechter, A. Ronen, A. Rolls, A. London, S. Bakalash, M. J. Young, and M. Schwartz Toll-like receptor 4 restricts retinal progenitor cell proliferation J. Cell Biol., November 3, 2008; 183(3): 393 - 400. [Abstract] [Full Text] [PDF]

				D. S. Spinner, I. S. Cho, S. Y. Park, J. I. Kim, H. C. Meeker, X. Ye, G. LaFauci, D. J. Kerr, M. J. Flory, B. S. Kim, et al. Accelerated Prion Disease Pathogenesis in Toll-Like Receptor 4 Signaling-Mutant Mice J. Virol., November 1, 2008; 82(21): 10701 - 10708. [Abstract] [Full Text] [PDF]

				C. C. Toledo, T. J. Rogers, M. Svensson, R. Tati, H. Fischer, C. Svanborg, and D. Karpman Shiga Toxin-Mediated Disease in MyD88-Deficient Mice Infected with Escherichia coli O157:H7 Am. J. Pathol., November 1, 2008; 173(5): 1428 - 1439. [Abstract] [Full Text] [PDF]

				L. C. Parker, E. C. Prestwich, J. R. Ward, E. Smythe, A. Berry, M. Triantafilou, K. Triantafilou, and I. Sabroe A Phosphatidylserine Species Inhibits a Range of TLR- but Not IL-1{beta}-Induced Inflammatory Responses by Disruption of Membrane Microdomains J. Immunol., October 15, 2008; 181(8): 5606 - 5617. [Abstract] [Full Text] [PDF]

				P. A. Taylor, M. J. Ehrhardt, C. J. Lees, A. Panoskaltsis-Mortari, A. M. Krieg, A. H. Sharpe, W. J. Murphy, J. S. Serody, H. Hemmi, S. Akira, et al. TLR agonists regulate alloresponses and uncover a critical role for donor APCs in allogeneic bone marrow rejection Blood, October 15, 2008; 112(8): 3508 - 3516. [Abstract] [Full Text] [PDF]

				J. Fischer, C. Suire, and H. Hale-Donze Toll-Like Receptor 2 Recognition of the Microsporidia Encephalitozoon spp. Induces Nuclear Translocation of NF-{kappa}B and Subsequent Inflammatory Responses Infect. Immun., October 1, 2008; 76(10): 4737 - 4744. [Abstract] [Full Text] [PDF]

				F. Al-Salleeh and T. M. Petro Promoter Analysis Reveals Critical Roles for SMAD-3 and ATF-2 in Expression of IL-23 p19 in Macrophages J. Immunol., October 1, 2008; 181(7): 4523 - 4533. [Abstract] [Full Text] [PDF]

				I-T. Lee, S.-W. Wang, C.-W. Lee, C.-C. Chang, C.-C. Lin, S.-F. Luo, and C.-M. Yang Lipoteichoic Acid Induces HO-1 Expression via the TLR2/MyD88/c-Src/NADPH Oxidase Pathway and Nrf2 in Human Tracheal Smooth Muscle Cells J. Immunol., October 1, 2008; 181(7): 5098 - 5110. [Abstract] [Full Text] [PDF]

				K. N. Khan, M. Kitajima, T. Imamura, K. Hiraki, A. Fujishita, I. Sekine, T. Ishimaru, and H. Masuzaki Toll-like receptor 4-mediated growth of endometriosis by human heat-shock protein 70 Hum. Reprod., October 1, 2008; 23(10): 2210 - 2219. [Abstract] [Full Text] [PDF]

				P I Sidiropoulos, G Goulielmos, G K Voloudakis, E Petraki, and D T Boumpas Inflammasomes and rheumatic diseases: evolving concepts Ann Rheum Dis, October 1, 2008; 67(10): 1382 - 1389. [Abstract] [Full Text] [PDF]

				A. M. Keestra and J. P. M. van Putten Unique Properties of the Chicken TLR4/MD-2 Complex: Selective Lipopolysaccharide Activation of the MyD88-Dependent Pathway J. Immunol., September 15, 2008; 181(6): 4354 - 4362. [Abstract] [Full Text] [PDF]

				T. Kubota, M. Matsuoka, T.-H. Chang, P. Tailor, T. Sasaki, M. Tashiro, A. Kato, and K. Ozato Virus Infection Triggers SUMOylation of IRF3 and IRF7, Leading to the Negative Regulation of Type I Interferon Gene Expression J. Biol. Chem., September 12, 2008; 283(37): 25660 - 25670. [Abstract] [Full Text] [PDF]

				N. Anderson and J. Borlak Molecular Mechanisms and Therapeutic Targets in Steatosis and Steatohepatitis Pharmacol. Rev., September 1, 2008; 60(3): 311 - 357. [Abstract] [Full Text] [PDF]

				S. F. Martin, J. C. Dudda, E. Bachtanian, A. Lembo, S. Liller, C. Durr, M. M. Heimesaat, S. Bereswill, G. Fejer, R. Vassileva, et al. Toll-like receptor and IL-12 signaling control susceptibility to contact hypersensitivity J. Exp. Med., September 1, 2008; 205(9): 2151 - 2162. [Abstract] [Full Text] [PDF]

				H. Wu, H. Wang, W. Xiong, S. Chen, H. Tang, and D. Han Expression Patterns and Functions of Toll-Like Receptors in Mouse Sertoli Cells Endocrinology, September 1, 2008; 149(9): 4402 - 4412. [Abstract] [Full Text] [PDF]

				A. O. Weinzierl, G. Szalay, H. Wolburg, M. Sauter, H.-G. Rammensee, R. Kandolf, S. Stevanovic, and K. Klingel Effective Chemokine Secretion by Dendritic Cells and Expansion of Cross-Presenting CD4-/CD8+ Dendritic Cells Define a Protective Phenotype in the Mouse Model of Coxsackievirus Myocarditis J. Virol., August 15, 2008; 82(16): 8149 - 8160. [Abstract] [Full Text] [PDF]

				H. Shen, B. M. Tesar, W. E. Walker, and D. R. Goldstein Dual Signaling of MyD88 and TRIF Is Critical for Maximal TLR4-Induced Dendritic Cell Maturation J. Immunol., August 1, 2008; 181(3): 1849 - 1858. [Abstract] [Full Text] [PDF]

				H. G. Kim, J. Y. Kim, M. G. Gim, J. M. Lee, and D. K. Chung Mechanical stress induces tumor necrosis factor-{alpha} production through Ca2+ release-dependent TLR2 signaling Am J Physiol Cell Physiol, August 1, 2008; 295(2): C432 - C439. [Abstract] [Full Text] [PDF]

				G. W. Moran, F. C. Leslie, S. E. Levison, and J. T. McLaughlin Review: Enteroendocrine cells: Neglected players in gastrointestinal disorders? Therapeutic Advances in Gastroenterology, July 1, 2008; 1(1): 51 - 60. [Abstract] [PDF]

				G. Fedele, M. Nasso, F. Spensieri, R. Palazzo, L. Frasca, M. Watanabe, and C. M. Ausiello Lipopolysaccharides from Bordetella pertussis and Bordetella parapertussis Differently Modulate Human Dendritic Cell Functions Resulting in Divergent Prevalence of Th17-Polarized Responses J. Immunol., July 1, 2008; 181(1): 208 - 216. [Abstract] [Full Text] [PDF]

				X. Dai, K. Sayama, M. Tohyama, Y. Shirakata, L. Yang, S. Hirakawa, S. Tokumaru, and K. Hashimoto The NF-{kappa}B, p38 MAPK and STAT1 pathways differentially regulate the dsRNA-mediated innate immune responses of epidermal keratinocytes Int. Immunol., July 1, 2008; 20(7): 901 - 909. [Abstract] [Full Text] [PDF]

				O. S. Shin, R. R. Isberg, S. Akira, S. Uematsu, A. K. Behera, and L. T. Hu Distinct Roles for MyD88 and Toll-Like Receptors 2, 5, and 9 in Phagocytosis of Borrelia burgdorferi and Cytokine Induction Infect. Immun., June 1, 2008; 76(6): 2341 - 2351. [Abstract] [Full Text] [PDF]

				T. G. Loof, O. Goldmann, and E. Medina Immune Recognition of Streptococcus pyogenes by Dendritic Cells Infect. Immun., June 1, 2008; 76(6): 2785 - 2792. [Abstract] [Full Text] [PDF]

				M.-L. Baron, D. Gauchat, R. La Motte-Mohs, N. Kettaf, A. Abdallah, T. Michiels, J.-C. Zuniga-Pflucker, and R.-P. Sekaly TLR Ligand-Induced Type I IFNs Affect Thymopoiesis J. Immunol., June 1, 2008; 180(11): 7134 - 7146. [Abstract] [Full Text] [PDF]

				M. A. Christman II, D. J. Goetz, E. Dickerson, K. D. McCall, C. J. Lewis, F. Benencia, M. J. Silver, L. D. Kohn, and R. Malgor Wnt5a is expressed in murine and human atherosclerotic lesions Am J Physiol Heart Circ Physiol, June 1, 2008; 294(6): H2864 - H2870. [Abstract] [Full Text] [PDF]

				S. Alper, R. Laws, B. Lackford, W. A. Boyd, P. Dunlap, J. H. Freedman, and D. A. Schwartz Identification of innate immunity genes and pathways using a comparative genomics approach PNAS, May 13, 2008; 105(19): 7016 - 7021. [Abstract] [Full Text] [PDF]

				M. Peiser, J. Koeck, C. J. Kirschning, B. Wittig, and R. Wanner Human Langerhans cells selectively activated via Toll-like receptor 2 agonists acquire migratory and CD4+T cell stimulatory capacity J. Leukoc. Biol., May 1, 2008; 83(5): 1118 - 1127. [Abstract] [Full Text] [PDF]

				L. M. Gargano, J. M. Moser, and S. H. Speck Role for MyD88 Signaling in Murine Gammaherpesvirus 68 Latency J. Virol., April 15, 2008; 82(8): 3853 - 3863. [Abstract] [Full Text] [PDF]

				M. M. Weck, S. Appel, D. Werth, C. Sinzger, A. Bringmann, F. Grunebach, and P. Brossart hDectin-1 is involved in uptake and cross-presentation of cellular antigens Blood, April 15, 2008; 111(8): 4264 - 4272. [Abstract] [Full Text] [PDF]

				D. Escors, L. Lopes, R. Lin, J. Hiscott, S. Akira, R. J. Davis, and M. K. Collins Targeting dendritic cell signaling to regulate the response to immunization Blood, March 15, 2008; 111(6): 3050 - 3061. [Abstract] [Full Text] [PDF]

				S. S. Yoon and J. J. Mekalanos Decreased Potency of the Vibrio cholerae Sheathed Flagellum To Trigger Host Innate Immunity Infect. Immun., March 1, 2008; 76(3): 1282 - 1288. [Abstract] [Full Text] [PDF]

				P. F.-Y. Cheung, C.-K. Wong, W.-K. Ip, and C. W.-K. Lam FAK-mediated activation of ERK for eosinophil migration: a novel mechanism for infection-induced allergic inflammation Int. Immunol., March 1, 2008; 20(3): 353 - 363. [Abstract] [Full Text] [PDF]

				N. Semaan, G. Alsaleh, J.-E. Gottenberg, D. Wachsmann, and J. Sibilia Etk/BMX, a Btk Family Tyrosine Kinase, and Mal Contribute to the Cross-Talk between MyD88 and FAK Pathways J. Immunol., March 1, 2008; 180(5): 3485 - 3491. [Abstract] [Full Text] [PDF]

				S. Hapfelmeier, A. J. Muller, B. Stecher, P. Kaiser, M. Barthel, K. Endt, M. Eberhard, R. Robbiani, C. A. Jacobi, M. Heikenwalder, et al. Microbe sampling by mucosal dendritic cells is a discrete, MyD88-independent stepin {Delta}invG S. Typhimurium colitis J. Exp. Med., February 18, 2008; 205(2): 437 - 450. [Abstract] [Full Text] [PDF]

				S. Thakran, H. Li, C. L. Lavine, M. A. Miller, J. E. Bina, X. R. Bina, and F. Re Identification of Francisella tularensis Lipoproteins That Stimulate the Toll-like Receptor (TLR) 2/TLR1 Heterodimer J. Biol. Chem., February 15, 2008; 283(7): 3751 - 3760. [Abstract] [Full Text] [PDF]

				T. Andoh, H. Kishi, K. Motoki, K. Nakanishi, Y. Kuraishi, and A. Muraguchi Protective Effect of IL-18 on Kainate- and IL-1{beta}-Induced Cerebellar Ataxia in Mice J. Immunol., February 15, 2008; 180(4): 2322 - 2328. [Abstract] [Full Text] [PDF]

				P. Mendez-Samperio, A. Trejo, and A. Perez Mycobacterium bovis Bacillus Calmette-Guerin Induces CCL5 Secretion via the Toll-Like Receptor 2-NF-{kappa}B and -Jun N-Terminal Kinase Signaling Pathways Clin. Vaccine Immunol., February 1, 2008; 15(2): 277 - 283. [Abstract] [Full Text] [PDF]

				B. Petersen, K. D. Bloch, F. Ichinose, H.-S. Shin, M. Shigematsu, A. Bagchi, W. M. Zapol, and J. Hellman Activation of Toll-like receptor 2 impairs hypoxic pulmonary vasoconstriction in mice Am J Physiol Lung Cell Mol Physiol, February 1, 2008; 294(2): L300 - L308. [Abstract] [Full Text] [PDF]

				D. Torres, C. Paget, J. Fontaine, T. Mallevaey, T. Matsuoka, T. Maruyama, S. Narumiya, M. Capron, P. Gosset, C. Faveeuw, et al. Prostaglandin D2 Inhibits the Production of IFN-{gamma} by Invariant NK T Cells: Consequences in the Control of B16 Melanoma J. Immunol., January 15, 2008; 180(2): 783 - 792. [Abstract] [Full Text] [PDF]

				J. N. Leonard, R. Ghirlando, J. Askins, J. K. Bell, D. H. Margulies, D. R. Davies, and D. M. Segal The TLR3 signaling complex forms by cooperative receptor dimerization PNAS, January 8, 2008; 105(1): 258 - 263. [Abstract] [Full Text] [PDF]

				J.-Y. Kim, E. Omori, K. Matsumoto, G. Nunez, and J. Ninomiya-Tsuji TAK1 Is a Central Mediator of NOD2 Signaling in Epidermal Cells J. Biol. Chem., January 4, 2008; 283(1): 137 - 144. [Abstract] [Full Text] [PDF]

				M. Iyori, H. Kataoka, H. M. Shamsul, K. Kiura, M. Yasuda, T. Nakata, A. Hasebe, and K.-i. Shibata Resveratrol Modulates Phagocytosis of Bacteria through an NF-{kappa}B-Dependent Gene Program Antimicrob. Agents Chemother., January 1, 2008; 52(1): 121 - 127. [Abstract] [Full Text] [PDF]

				N. Fitzner, S. Clauberg, F. Essmann, J. Liebmann, and V. Kolb-Bachofen Human Skin Endothelial Cells Can Express All 10 TLR Genes and Respond to Respective Ligands Clin. Vaccine Immunol., January 1, 2008; 15(1): 138 - 146. [Abstract] [Full Text] [PDF]

				W.-J. Won, M. F. Bachmann, and J. F. Kearney CD36 Is Differentially Expressed on B Cell Subsets during Development and in Responses to Antigen J. Immunol., January 1, 2008; 180(1): 230 - 237. [Abstract] [Full Text] [PDF]

				M. Cho, K. Ishida, J. Chen, J. Ohkawa, W. Chen, S. Namiki, A. Kotaki, N. Arai, K.-i. Arai, and Y. Kamogawa-Schifter SAGE library screening reveals ILT7 as a specific plasmacytoid dendritic cell marker that regulates type I IFN production Int. Immunol., January 1, 2008; 20(1): 155 - 164. [Abstract] [Full Text] [PDF]

				T. Y. Cannon, D. Guttridge, J. Dahlman, J. R. George, V. Lai, C. Shores, P. Buzkova, and M. E. Couch The Effect of Altered Toll-like Receptor 4 Signaling on Cancer Cachexia Arch Otolaryngol Head Neck Surg, December 1, 2007; 133(12): 1263 - 1269. [Abstract] [Full Text] [PDF]

				S. Sivori, M. Falco, S. Carlomagno, E. Romeo, L. Moretta, and A. Moretta Heterogeneity of TLR3 mRNA transcripts and responsiveness to poly (I:C) in human NK cells derived from different donors Int. Immunol., December 1, 2007; 19(12): 1341 - 1348. [Abstract] [Full Text] [PDF]

				J. Klesney-Tait and M. Colonna Uncovering the TREM-1-TLR connection Am J Physiol Lung Cell Mol Physiol, December 1, 2007; 293(6): L1374 - L1376. [Full Text] [PDF]

				L. Macedo, G. Pinhal-Enfield, V. Alshits, G. Elson, B. N. Cronstein, and S. J. Leibovich Wound Healing Is Impaired in MyD88-Deficient Mice: A Role for MyD88 in the Regulation of Wound Healing by Adenosine A2A Receptors Am. J. Pathol., December 1, 2007; 171(6): 1774 - 1788. [Abstract] [Full Text] [PDF]

				M. T. A. Nguyen, S. Favelyukis, A.-K. Nguyen, D. Reichart, P. A. Scott, A. Jenn, R. Liu-Bryan, C. K. Glass, J. G. Neels, and J. M. Olefsky A Subpopulation of Macrophages Infiltrates Hypertrophic Adipose Tissue and Is Activated by Free Fatty Acids via Toll-like Receptors 2 and 4 and JNK-dependent Pathways J. Biol. Chem., November 30, 2007; 282(48): 35279 - 35292. [Abstract] [Full Text] [PDF]

				N. Funderburg, M. M. Lederman, Z. Feng, M. G. Drage, J. Jadlowsky, C. V. Harding, A. Weinberg, and S. F. Sieg Human -defensin-3 activates professional antigen-presenting cells via Toll-like receptors 1 and 2 PNAS, November 20, 2007; 104(47): 18631 - 18635. [Abstract] [Full Text] [PDF]

				J. P. McAleer, D. J. Zammit, L. Lefrancois, R. J. Rossi, and A. T. Vella The Lipopolysaccharide Adjuvant Effect on T Cells Relies on Nonoverlapping Contributions from the MyD88 Pathway and CD11c+ Cells J. Immunol., November 15, 2007; 179(10): 6524 - 6535. [Abstract] [Full Text] [PDF]

				K. L. Hokeness-Antonelli, M. J. Crane, A. M. Dragoi, W.-M. Chu, and T. P. Salazar-Mather IFN-{alpha}beta-Mediated Inflammatory Responses and Antiviral Defense in Liver Is TLR9-Independent but MyD88-Dependent during Murine Cytomegalovirus Infection J. Immunol., November 1, 2007; 179(9): 6176 - 6183. [Abstract] [Full Text] [PDF]

				A. M. Lundberg, S. K. Drexler, C. Monaco, L. M. Williams, S. M. Sacre, M. Feldmann, and B. M. Foxwell Key differences in TLR3/poly I:C signaling and cytokine induction by human primary cells: a phenomenon absent from murine cell systems Blood, November 1, 2007; 110(9): 3245 - 3252. [Abstract] [Full Text] [PDF]

				X.-N. Kong, H.-X. Yan, L. Chen, L.-W. Dong, W. Yang, Q. Liu, L.-X. Yu, D.-D. Huang, S.-Q. Liu, H. Liu, et al. LPS-induced down-regulation of signal regulatory protein {alpha} contributes to innate immune activation in macrophages J. Exp. Med., October 29, 2007; 204(11): 2719 - 2731. [Abstract] [Full Text] [PDF]

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