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International Immunology 2007 19(8):913-921; doi:10.1093/intimm/dxm049
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© The Japanese Society for Immunology. 2007. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Selective suppression of Th2-mediated airway eosinophil infiltration by low-molecular weight CCR3 antagonists

Akio Mori1, Koji Ogawa1,2, Koichiro Someya3, Yuichi Kunori3, Daisuke Nagakubo4, Osamu Yoshie4, Fujiko Kitamura5, Takachika Hiroi5 and Osamu Kaminuma1,2,5

1 Clinical Research Center for Allergy and Rheumatology, National Sagamihara Hospital, 18-1 Sakuradai, Sagamihara, Kanagawa 228-8522, Japan
2 Discovery Research Laboratory, Tanabe Seiyaku Co., Ltd, Toda, Saitama 335-8505, Japan
3 Pharmaceutical Discovery Research Laboratories, Institute for Biomedical Research, Teijin Pharma Ltd, Hino, Tokyo 191-8512, Japan
4 Department of Microbiology, Kinki University School of Medicine, Osaka-Sayama, Osaka 589-8511, Japan
5 Department of Allergy and Immunology, Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113-8613, Japan

Correspondence to: A. Mori; E-mail: mori-kkr{at}umin.ac.jp


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Supplementary data
 References
 
The effects of selective CC chemokine receptor (CCR)-3 antagonists on antigen-induced leukocyte accumulation in the lungs of mice adoptively transferred with in vitro-differentiated Th1 and Th2 were investigated. Inhalation of antigen by mice injected with Th1 and Th2 initiated the migration of T cells themselves into the lungs. Subsequently, neutrophils massively accumulated in Th1-transferred mice, whereas eosinophil infiltration was specifically induced by Th2. CCR3 antagonists, SB-297006 and/or SB-328437, suppressed antigen-induced accumulation of Th2 as well as eosinophils in the lungs, whereas they failed to affect Th1-mediated airway inflammation. Not only Th2 and eosinophil infiltration but also cellular mobilization in Th1-transferred mice was attenuated by an anti-CC chemokine ligand-11 antibody. CCR3 antagonists reduced chemokine production in the lungs of mice transferred with Th2 but not Th1, suggesting that down-regulation of chemokine synthesis is involved in the selective inhibition of Th2-mediated eosinophil infiltration by CCR3 antagonists.

Keywords: asthma, chemokine, mouse, T cell


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Supplementary data
 References
 
The crucial contribution of Th2 to the development of allergic eosinophilic inflammation has been established (1). Accumulating evidence suggests that CC chemokine receptor (CCR)-3 plays a critical role in the accumulation of eosinophils as well as T cells during allergic inflammation (2–4). Enhanced expression of CCR3 and its ligands has been recognized in bronchial asthma (5). Gene disruption and/or blockade of CCR3 as well as its ligand, CC chemokine ligand (CCL)-11, resulted in a reduction of eosinophilic infiltration in animal models of asthma (6–9).

However, the contribution of CCR3 to allergic diseases remains controversial in view of the apparently contradictory findings that substantial eosinophilic inflammation still occurs in animal models of asthma under disruption or neutralization of CCR3 as well as CCL11 (6–10). Furthermore, Yang et al. (11) found no difference in the recruitment of eosinophils between CCL11-intact and -deficient mice, using several models of inflammation. Humbles et al. (9) demonstrated up-regulation of antigen-induced bronchial hyperresponsiveness (BHR) in CCR3-knockout mice. Above all, the lack of a selective antagonist against CCR3 that is available for in vivo administration has confounded accurate assessment of the clinical efficacy of CCR3 blockers to treat allergic disorders. A number of CCR3 antagonists have been investigated (2), though most of them are peptides/proteins. Recently, the potent, selective, low-molecular weight CCR3 antagonists, SB-297006 and SB-328437, were identified (12). These compounds inhibit CCL11-induced Ca2+ mobilization and eosinophil chemotaxis in vitro. The selectivity of these compounds was confirmed using panels of chemokines and other seven-transmembrane receptors (12).

In order to delineate the role of CCR3 in the development of allergic inflammation in more detail, an antigen-induced murine airway inflammation model, separately initiated by Th1 and Th2, was employed in this study, with monitoring of the migration of inflammatory cells including antigen-specific T cells. The contribution of CCR3 and its ligands to Th1- and Th2-mediated cellular mobilization in the lungs and BHR was examined using these selective low-molecular weight antagonists and blocking antibodies.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Supplementary data
 References
 
In vitro polarization of T cells
Ovalbumin (OVA)-specific naive CD4+ T cells were isolated from the spleen of mice expressing the transgene for DO11.10 TCR{alpha}ß by a combination of negative and positive selection using a CD4+ T cell isolation kit and CD62L microbeads, respectively, with a magnetic cell sorting system (Miltenyi, Bergisch Gladbach, Germany). Cells were cultured in AIM-V medium (Invitrogen, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum (FBS) in the presence of 100 µg ml–1 OVA, 10 U ml–1 recombinant IL-2 (BD Biosciences, San Jose, CA, USA) and X-ray-irradiated splenocytes of BALB/c mice. For Th1 phenotype development, 10 U ml–1 recombinant murine IL-12 (PeproTech, Rocky Hill, NJ, USA) and 1 µg ml–1 neutralizing anti-IL-4 mAb (BD Biosciences) were added and for Th2 phenotype development, 10 U ml–1 recombinant murine IL-4 (PeproTech) and 1 µg ml–1 anti-IL-12 mAb (BD Biosciences) were used. Seven to ten days after stimulation, cells were harvested, purified by centrifugation over Ficoll-Paque (GE Healthcare Bio-Sciences, Uppsala, Sweden) and then used as Th1 and Th2. To determine the integrity of polarization, cells were activated by plate-bound anti-CD3 mAb (145-2C11; BD Biosciences) for 24 h at 37°C in a 5% CO2-humidified incubator. For antibody immobilization, wells of culture plates were pre-incubated with 10 µg ml–1 anti-CD3 mAb in 0.05 M carbonate–bicarbonate buffer (pH 9.6) at 4°C overnight. The resulting culture supernatants were collected and subjected to measurement of cytokine and chemokine levels by ELISA.

CCR expression in T cells
Naive and differentiated T cells were re-suspended (106 ml–1) in AIM-V medium containing 10% FBS and either left unstimulated or stimulated with plate-bound anti-CD3 mAb. After 8 h, cells were harvested and total RNA was then extracted and reverse transcribed using oligo(dT)12–18 primer and ReverTra ACE® (Toyobo, Osaka, Japan). Quantitative real-time reverse transcription (RT)–PCR was performed using Assay-on-DemandTM Gene Expression products (TaqMan® MGB probes) with an ABI prism 7900 sequence detection system (Applied Biosystems, Foster City, CA, USA). Transcripts of CCR3, CCR4, CCR5, CCR8 and CXC chemokine receptor (CXCR)-3 were normalized to 18S rRNA abundance. In some experiments, the expression of CCR3 on the surface of Th2 was determined by flow cytometry upon staining with an anti-CCR3 antibody (R&D systems) or isotype-matched control antibody.

Chemotaxis assay
Chemotaxis of Th2 was measured using 24 transwells with polycarbonate membranes (3 µm; Corning Incorporated, Corning, NY, USA). Chemokines were diluted in 0.6 ml chemotaxis buffer (RPMI 1640 medium containing 0.5% BSA) and added to the lower chemotaxis chamber. Th2 (106) were re-suspended in 0.1 ml chemotaxis buffer and added to the top chamber insert. Chemotaxis plates were then incubated for 2 h. After incubation, the cells from the bottom well were collected and counted by flow cytometry.

Cell transfer and challenge procedures
Before transfer, polarized Th1 and Th2 were stained with a fluorescein-based dye, 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (Molecular Probes, Eugene, OR, USA), as described previously (13). Twenty-four hours after cell transfer, mice were challenged with aerosolized 10% OVA dissolved in 0.9% saline. In some experiments, the same challenge was performed 1 week after the first challenge. For blocking studies, SB-297006 [(S)-ethyl-2-benzoylamino-3-(4-nitrophenyl)propionate] or SB-328437 [(S)-methyl-2-napthoylamino-3-(4-nitrophenyl)propionate], synthesized in the Discovery Research Laboratory of Tanabe Seiyaku Co., Ltd (Osaka, Japan), suspended in PBS containing 0.1% Tween 80, was administered subcutaneously. The dose of the compounds was determined as 100 mg kg–1, since both agents displayed a slight sedative effect in mice that received more than this dose (data not shown). A rabbit anti-CCL7 or anti-CCL11 antibody (PeproTech) dissolved in PBS was administered intravenously 30 min before OVA challenge. The vehicle alone did not affect any parameter examined (data not shown). Cellular infiltration in the lungs was examined by bronchoalveolar lavage (BAL) as described previously (13, 14). BHR was assessed as the degree of bronchoconstriction following infusion of 300 µg kg–1 acetylcholine, at which the maximum difference in respiratory overflow volume between specific antigen- and BSA-challenged animals was obtained, according to the method described previously (14). We have demonstrated that the cellular profile in BAL fluid well reflects the pathological features and resultant BHR developed in the lungs of Th2-transferred mice (13, 14).

Cytokine ELISA
Purified rat anti-mouse IL-5 mAb (TRFK-5; BD Biosciences) and anti-mouse CCL7 antibody (R&D Systems) were used as the capture antibodies and biotinylated rat anti-mouse IL-5 mAb (TRFK4; BD Biosciences) and goat anti-mouse CCL7 antibody (R&D Systems) as the detection antibodies for ELISA. IL-4 and IFN-{gamma} were assayed using Duo Set® (Genzyme, Cambridge, MA, USA), CCL2 using OptEIATM mouse MCP-1 set (BD Biosciences) and CCL11 using a Quantikine® M mouse eotaxin immunoassay kit (R&D Systems), according to the manufacturer's instructions.

Statistics
Statistical analysis was performed using one-way analysis of variance with Bonferroni's method. P < 0.05 was considered to indicate statistical significance.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Supplementary data
 References
 
Characterization of in vitro-differentiated T cells
The first experiment was carried out to verify successful polarization of DO11.10 T cells after stimulation culture under the respective conditions for Th1 and Th2. As shown in Table 1, the Th1 condition facilitated the preferential production of IFN-{gamma} but minimal IL-4 and IL-5 upon stimulation with a relevant antigen, whereas the Th2 condition resulted in a reciprocal pattern. These findings suggest that single stimulation culture under the appropriate condition is sufficient for Th1–Th2 differentiation from naive T cells.


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  		Table 1. Cytokine production by DO11.10 T cells in vitro

 
We further examined whether naive and differentiated T cells produce chemokines. A CC chemokine, CCL7, was released in the culture supernatant of antigen-stimulated naive DO11.10 T cells and its production was enhanced after Th1–Th2 differentiation. The amount of CCL7 produced by Th2 was three times higher than that by Th1. The other CC chemokines, CCL2 and CCL11, were not detectable in any condition examined (Table 1).

It has been documented that CCR3 is preferentially expressed in Th2 of human origin (7, 15, 16), though its expression pattern in murine Th has not been fully characterized. Therefore, the expression of CCR3 and other Th1/Th2-specific chemokine receptors in DO11.10 T cells was next determined by a quantitative real-time RT–PCR. As shown in Fig. 1(A), CCR3 was significantly expressed in naive T cells and was slightly up-regulated by stimulation through TCR. Both basal and inducible expression levels of CCR3 were minimally affected by Th1 and Th2 differentiation. On the other hand, the expression of CCR4 in Th2 was much higher than that in Th1 and naive T cells, while CCR8 was specifically induced in Th2 upon stimulation. In contrast, CCR5 and CXCR3 were highly up-regulated following stimulation in Th1, but not in naive or Th2 (Fig. 1A). Flow cytometric analysis further revealed that CCR3 was weakly but definitely expressed on the surface of Th1 and Th2 (Fig. 1B).


Figure 1
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  		Fig. 1. Expression of chemokine receptors in T cells. (A) Naive or Th1- and Th2-differentiated DO11.10 T cells (106) were either left unstimulated or stimulated with plate-bound anti-CD3 mAb. After 8 h, mRNA was extracted and the expression of CCR3, CCR4, CCR5, CCR8 and CXCR3 was measured by quantitative real-time RT–PCR method. Results are shown as mean ± SEM of triplicate cultures normalized to 18S rRNA abundance. (B) Polarized Th1 and Th2 were stained with rat anti-mouse CCR3 antibody or isotype-matched control antibody. After additional staining with PE-conjugated anti-rat IgG antibody, the expression of CCR3 was detected by flow cytometry.

 
Effects of CCR3 antagonists on chemotaxis of Th2 in vitro
The CCR3 antagonist, SB-328437, has been reported to block human eosinophil chemotaxis evoked by CCL11, CCL13 and CCL24 with similar potencies (IC50 values of 32, 25 and 55 nM, respectively) (12). However, the effect of a CCR3 antagonist on chemotaxis of murine cells has not been evaluated well. In order to elucidate whether CCR3 antagonists interfere with the murine CCR3/CCR3 ligand-mediated response, the effects of structurally related agents, SB-297006 and SB-328437, on CCL11-induced chemotaxis of Th2 were examined. On average, ~10% of Th2 migrated in response to CCL11, though no significant chemotactic response was observed in naive or Th1 (data not shown). SB-297006 and SB-328437 suppressed CCL11-induced Th2 chemotaxis, with IC50 values of 2.5 and 10 µM, respectively (Fig. 2). The inhibitory effects of these compounds on CCL11-induced Th2 chemotaxis were selective, as they failed to affect CCL17-induced migration of Th2 even at 10 µM (Fig. 2).


Figure 2
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  		Fig. 2. Effects of CCR3 antagonists on chemotactic activity of Th2. Chemotaxis of Th2 was induced by 100 nM CCL11 or CCL17 in the presence of SB-297006 or SB-328437. Data are expressed as mean ± SEM of quadruplicate cultures. *P < 0.05, compared with ligand alone-stimulated control.

 
Effects of CCR3 antagonists on Th1- and Th2-mediated cellular mobilization in lung
The role of CCR3 in T cell-mediated leukocyte accumulation was examined in vivo using its selective antagonists. In mice that underwent transfer of Th1- and Th2-polarized DO11.10 T cells, migration of antigen-specific T cells themselves in the lungs was detectable upon inhalation challenge with OVA (Fig. 3). Subsequently, massive accumulation of neutrophils occurred in Th1-transferred mice, whereas eosinophil infiltration was specifically induced by Th2, consistent with previous findings (17–20). The migration of neutrophils and eosinophils was dependent on infused T cells and their specific antigen, since they failed to infiltrate the lungs of BSA-challenged mice. In addition, OVA challenge to unprimed mice, even when it was performed twice with 1-week interval, did not affect any parameter examined. SB-297006 and SB-328437 suppressed antigen-induced accumulation of eosinophils as well as antigen-specific T cells in Th2-transferred mice (Fig. 3A). In contrast, infiltration of T cells and neutrophils in Th1-transferred mice was not affected by these agents.


Figure 3
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  		Fig. 3. Effects of CCR3 antagonists and anti-chemokine antibodies on antigen-induced cellular infiltration in lungs of Th1- and Th2-transferred mice. Differentiated Th1 and Th2 (3 x 107) were stained with 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (CFSE) and transferred to normal mice by intravenous injection. After 24 h, these mice were challenged with inhaled 10% OVA or BSA for 60 min. BAL was performed 48 h after challenge and the numbers of neutrophils and eosinophils in BAL fluid were counted in Th1- and Th2-transferred mice, respectively. The number of CFSE-positive cells was also determined by flow cytometry. CCR3 antagonists (100 mg kg–1) were administered subcutaneously (A) and neutralizing antibodies (20 mg kg–1) were administered intravenously (B) 30 min before OVA challenge. *P < 0.05, **P < 0.01, compared with OVA-challenged control animals (n = 4–12).

 
Next, the effects of CCR3 antagonists were compared with those of specific antibodies against CCR3-related chemokines. Antigen-induced migration of T cells as well as eosinophils in Th2-transferred mice was suppressed by treatment with antibodies against CCL7 and CCL11 (Fig. 3B). An anti-CCL11 antibody also inhibited the migration of Th1 and, less potently, neutrophils in Th1-transferred mice. Non-specific control antibody failed to affect cellular infiltration in Th1- and Th2-transferred mice (Fig. 3B). These findings clearly suggest that a CCL11–CCR3 interaction is required for the accumulation of antigen-induced Th2 and eosinophils in the lungs.

Effects of CCR3 antagonists on Th1- and Th2-mediated cytokine production in lung
Recent investigations demonstrated that neutralization of chemokines potentially affects the synthesis of cytokines and chemokines themselves in vivo (21). Therefore, the effects of CCR3 antagonists on cytokine production in the lungs were next determined. The concentrations of Th2 cytokines, IL-4 and IL-5, a Th1 cytokine, IFN-{gamma}, and CC chemokines, CCL2, CCL7 and CCL11, in the BAL fluid of Th1- and Th2-transferred mice were measured by ELISA. As shown in Fig. 4, IFN-{gamma} was specifically produced in the lungs of Th1-transferred mice upon challenge with a relevant antigen. On the other hand, IL-4 and IL-5 were preferentially produced by Th2, while CCL2, CCL7 and CCL11 were produced in both Th1- and Th2-transferred mice. Th2-mediated IL-4 and IL-5 production in vivo was minimally attenuated, if at all, by treatment with SB-297006 and SB-328437 (Fig. 4), even though they suppressed the migration of antigen-specific Th2 (Fig. 3). The CCR3 antagonists did not affect any cytokine production in the lungs of Th1-transferred mice (Fig. 4).


Figure 4
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  		Fig. 4. Effects of CCR3 antagonists on antigen-induced cytokine production in lungs of Th1- and Th2-transferred mice. Differentiated Th1 and Th2 (3 x 107) were transferred to normal mice by intravenous injection. After 24 h, these mice were challenged with inhaled 10% OVA or BSA for 60 min. BAL was performed 24 h after challenge, and the concentrations of IL-4, IL-5, IFN-{gamma}, CCL2, CCL7 and CCL11 in BAL fluid were measured by ELISA. CCR3 antagonists (100 mg kg–1) were administered subcutaneously 30 min before OVA challenge. *P < 0.05, **P < 0.01, compared with OVA-challenged control animals (n = 4–6).

 
In contrast, blocking of CCR3 by its antagonists effectively attenuated the production of CCL2, CCL7 and CCL11 only in the lungs of Th2-transferred mice (Fig. 4), suggesting that a reduction of chemokine production participates in the selective suppression of Th2-mediated cellular mobilization by CCR3 antagonists.

Effects of CCR antagonist on Th2-mediated BHR
Our present findings suggest that CCR3 blockers will be effective to treat allergic diseases associated with eosinophilic inflammation. However, the role of CCR3 in the change of airway function due to eosinophilic inflammation is controversial. Therefore, our next investigation was performed to evaluate the effect of a CCR3 antagonist on antigen-induced BHR in T cell-transferred mice. Single administration of OVA failed to produce significant BHR in mice transferred with Th1- and Th2-differentiated DO11.10 T cells (data not shown). However, bronchial responsiveness to acetylcholine was clearly up-regulated in Th2-transferred mice upon second antigen challenge 1 week after the first challenge (Fig. 5B). Accordingly, a 4-fold larger number of eosinophils accumulated in the lungs (Fig. 5A), compared with that after a single challenge (Fig. 3). As shown in our previous investigations (14), BHR peaked at 96 h after the second challenge and was not observed in Th1- or naive T cell-transferred mice (data not shown).


Figure 5
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  		Fig. 5. Effects of SB-297006 and anti-CCL11 antibody on antigen-induced BHR in Th2-transferred mice. Differentiated Th2 (3 x 107) were transferred to normal mice by intravenous injection. On days 1 and 7, these mice were challenged with inhaled 10% OVA or BSA for 60 min. Assessment of bronchoconstriction induced by the infusion of acetylcholine (300 µg kg–1), and BAL were performed 96 h after the second challenge. SB-297006 (100 mg kg–1) and an anti-CCL11 antibody (20 mg kg–1) were administered subcutaneously and intravenously, respectively, 30 min before each OVA challenge. *P < 0.05, compared with OVA-challenged control animals (n = 4–12).

 
The effects of CCR3 antagonists and an anti-CCL11 antibody were examined in this experimental system. As shown in Fig. 5, antigen-induced accumulation of eosinophils in the lungs as well as BHR was significantly suppressed by an anti-CCL11 antibody. Although the effect of SB-297006 was not statistically significant in the present experiments, this compound may be weakly inhibitory to both reactions. SB-328437 failed to affect antigen-induced lung eosinophilia and BHR, according to the relative low potency of this compound to suppress CCL11-induced Th2 chemotaxis in vitro (Fig. 2).


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Supplementary data
 References
 
The contribution of CCR3 to the development of allergic eosinophilic inflammation has been investigated in vivo using gene-disrupted animals and/or neutralizing antibodies against CCR3 and CCR3 ligands, especially CCL11 (6–9, 22). Nevertheless, the potential of CCR3 antagonists to treat allergic disorders associated with eosinophilic inflammation remains unclear. We here evaluated the effects of CCR3 antagonists on allergic airway inflammation models separately induced by antigen-specific Th1 and Th2. CCR3 specifically participated in antigen-induced migration of Th2 and eosinophils in the lungs. Further, suppression of chemokine synthesis was suggested to be involved in the mechanism by which a CCR3 antagonist attenuated Th2-mediated eosinophil accumulation in the lungs.

A number of investigations have demonstrated that Th1 and Th2 express distinct sets of chemokine receptors: Th1 preferentially express CCR5 and CXCR3, while CCR3, CCR4 and CCR8 are dominantly expressed on Th2 (2, 3, 7, 15, 16), even though several reports conflict with this statement (23–26). Our present findings generally agree with these investigations, whereas the expression of CCR3 in murine Th was not strongly affected by their polarization status and stimulation (Fig. 1). The present results are supported by Bonecchi et al. (15) who reported that the difference between the expression of CCR3 in Th1 and Th2 was much smaller than that of CCR4, CCR5 and CXCR3. Lloyd et al. (7) found differential expression of CCR3 after three-round stimulation culture under a Th1–Th2 differentiation condition, whereas we confirmed that CCR3 expression on Th2 was not up-regulated even after two additional round stimulation culture (Supplementary Fig. 1, available at International Immunology Online). Therefore, further investigation will be required to clarify the relationship between the polarization status and CCR3 expression property of T cells.

Nevertheless, a functional difference in CCR3 expressed on Th1 and Th2 was observed in the present study (Fig. 3), even though CCL11 as well as CCL7 was equivalently produced in vivo (Fig. 4). The reason for the discrepancy between the expression and function of CCR3 in Th1–Th2 is not clear, but it is potentially due to a difference in signaling cascades through this receptor. CCR3 is a seven-transmembrane domain G protein-coupled receptor, and the interaction of CCR3 with its ligands evokes Ca2+ influx (27, 28). It has been reported that the Ca2+ mobilization pattern is different in Th1 and Th2, even though it is in the case that T cells are stimulated through TCR but not through CCR3 (29, 30). Therefore, signaling events through CCR3 in Th1–Th2 remain to be further analyzed. Our present data that CCR3 antagonists specifically suppressed Th2-mediated airway eosinophilic infiltration not only indicate the clinical efficacy of CCR3 antagonists against allergic disorders but also suggest that they do not exhibit undesirable side effects, at least due to the suppression of Th1-mediated host defense activity against numerous infectious pathogens.

Neutralization of CCL11, which utilizes CCR3, resulted in the attenuation of not only Th2-mediated cellular mobilization but also Th1 migration and subsequent infiltration of neutrophils, whereas an antibody against CCL7, another ligand for CCR3, specifically suppressed the accumulation of Th2 and eosinophils. The reason why antibodies against two CCR3 ligands showed different effects on Th1-mediated airway inflammation is not clear. However, it has been suggested that CCR5 as well as CCR2 acts as a receptor for CCL11 (31, 32), while CCL7 associates with CCR1 and CCR2 (4). Like CXCR3, CCR5 was preferentially expressed on Th1 (2; Fig. 1), suggesting that the engagement of CCR5 with CCL11 potentially participates in the migration of Th1. As no chemokine that interacts with CCR5 alone has been identified, further examination using CCR5 antagonists as well as CCR5-deficient animals is required to elucidate the functional role of CCR5 in Th1-mediated allergic inflammation.

Two structurally related CCR3 antagonists exhibited their specific activity against murine Th2 in vitro. Thus, SB-297006 and SB-328437 suppressed Th2 chemotaxis induced by CCL11 but not CCL17 (Fig. 2). However, the effective dose range of these compounds (IC50 = 2.5 and 10 µM) was much higher than that investigated by White et al. (12) employing human eosinophils (IC50 = 3.3 nM for SB-328437). The relative weakness of CCR3 antagonists to suppress chemotaxis of murine cells, compared with that of human cells, may have been due to species specificity of the compounds. In fact, White et al. (12) reported that the effects of CCR3 antagonists on CCL11/CCR3 binding of murine and guinea pig origin were much weaker than that of human origin. Our present findings are consistent with their report, and further indicate that SB-297006 and SB-328437 selectively interfere with CCL11-mediated migration of murine Th2.

CCR3 antagonists failed to affect IL-4 and IL-5 production in the lungs (Fig. 4), even though they suppressed the migration of antigen-specific Th2 cells (Figs 2 and 3). In addition, we have demonstrated that the production of cytokines in the lungs of T cell-transferred mice preceded the accumulation of T cells (13, 17), suggesting that a small number of antigen-specific T cells that were infused and spontaneously distributed in the lungs before antigen challenge were the predominant source of Th1–Th2 cytokines. In contrast, blocking of CCR3 by its antagonists effectively attenuated the production of CCR3-related and -unrelated chemokines only in the lungs of Th2-transferred mice (Fig. 4), suggesting that a reduction in chemokine production participates in the selective suppression of Th2-mediated cellular mobilization by CCR3 antagonists. T cells employed for adoptive transfer have the capacity to produce CCL7 but not CCL2 and CCL11 in vitro (Table 1). Therefore, antigen-specific T cells existing in the lungs are unlikely to produce most of the chemokines detected. The exact sources of those chemokines were not identified in the present study; however, mRNA and protein expression of CCR3-ligands has been detected in many different cell types at sites of inflammation (2, 33, 34). Resident cells such as epithelial cells, fibroblasts and endothelial cells have been shown to produce significant levels of such chemokines upon activation (34–37). Although infused T cells could produce CCL7 in vitro (Table 1), it has been shown that this chemokine is predominantly released by airway epithelial cells in vivo, which also express CCR3 (33, 38). In addition, the existence of a regulatory cascade by which chemokines induce the synthesis of chemokines themselves has been suggested. Thus, an anti-CCL17 mAb inhibited the expression of CCL11 mRNA in the lungs of a murine model of asthma (21). Taking these findings together, CCR3-active chemokines, including CCL7, initially released by infused T cells upon antigen challenge may evoke explosive production of a variety of chemokines by airway epithelial cells and other cell types. CCR3 antagonists potentially inhibited the engagement of CCR3 ligands to their receptors on chemokine-releasing cells including airway epithelial cells, and subsequently, massive chemokine synthesis by those cells might be attenuated.

Nevertheless, the contribution of CCR3 to chemokine production in the lungs of Th1-transferred mice was negligible (Fig. 4). In the case of Th1-mediated responses, the interaction of a Th1-specific chemokine and its receptor other than CCR3 or IFN-{gamma} by itself might play a major role in the synthesis of a variety of chemokines in vivo. Further studies will be required to elucidate additional details of the mechanism by which CCR3 antagonists suppressed chemokine production specifically in Th2-transferred mice.

The development of BHR in Th2-transferred mice was weakly and significantly suppressed by SB-297006 and anti-CCL11 antibody, respectively (Fig. 5), though the inhibitory potency of CCR3 antagonists and anti-CCL11 antibody was lower than that observed in Fig. 3. It could be explained, at least in part, by the relative severity of the inflammatory response that occurred upon repeated antigen provocation. On the other hand, the lower potency of CCR3 antagonists, compared with that of an antibody against CCL11, may be due to a difference in the stability of chemical compounds and antibody in mice. We have found that the blood concentration of SB-297006 was already below its in vitro effective dose range 24 h after the administration (data not shown), whereas Ig is one of the most stable proteins in serum and injected anti-CCL11 antibody probably neutralized CCL11 for several days or weeks.

Several contradictory findings have been reported regarding the role of CCR3 in BHR. Ma et al. (10) demonstrated that antigen-induced BHR in epicutaneously immunized mice was abolished by gene disruption of CCR3, though Humbles et al. (9) from the same group observed enhancement of BHR in CCR3–/– mice sensitized by intra-peritoneal antigen injection. The reason for the discrepancy was explained by the contribution of mast cells; thus, antigen-induced mast cell mobilization into the airway epithelium was increased in intra-peritoneally sensitized CCR3–/– mice (9), but not in epicutaneously immunized CCR3–/– mice (10). The contribution of mast cells in our experimental system employed in this study seems to be low, since there is no process to synthesize antigen-specific IgE. In this condition, we have demonstrated that the intensity of BHR was significantly correlated with the number of eosinophils accumulated in the lungs (14). Further examination will be required to elucidate the effects of CCR3 antagonists on mast cell-dependent responses; however, the present study suggests that these agents are potentially effective against antigen-induced BHR, at least that mediated by Th2. As the most recent report suggested that CCR3 is involved in dysfunction of the M2 muscarinic receptor in a guinea pig asthma model (39), the relationship between cellular and neuronal inflammation, both in which CCR3 is implicated, should be next investigated.

In conclusion, we demonstrated that CCR3 selectively participates in the induction of Th2-mediated infiltration of eosinophils as well as T cells themselves in the lungs. CCL11 contributes to airway inflammation initiated by both Th1 and Th2. Specific CCR3 antagonists, that attenuate the migration of Th2 and eosinophils, can potentially be used to treat allergic diseases.


   Supplementary data
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary data
References
 
Supplementary Figure 1 is available at International Immunology Online.


   Acknowledgements
 
We would like to thank D. Loh and T. Saito for kindly providing DO11.10 mice. This work was supported in part by Health and Labor Sciences Research Grants for Research on Allergic Diseases and Immunology (A.M.), the Program for Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation (NIBIO) (A.M.), and the Charitable Trust Clinical Pathology Research Foundation of Japan (A.M.).


   Abbreviations
 
BAL, bronchoalveolar lavage
BHR, bronchial hyperresponsiveness
CCL, CC chemokine ligand
CCR, CC chemokine receptor
CXCR, CXC chemokine receptor
FBS, fetal bovine serum
OVA, ovalbumin
RT, reverse transcription

   Notes
 
Transmitting editor: M. Miyasaka

Received 10 January 2007, accepted 29 March 2007.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary data
 References
 

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