International Immunology Advance Access originally published online on August 19, 2005
International Immunology 2005 17(10):1277-1282; doi:10.1093/intimm/dxh307
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Requirement for CD100–CD72 interactions in fine-tuning of B-cell antigen receptor signaling and homeostatic maintenance of the B-cell compartment
1 Department of Molecular Immunology, Research Institute for Microbial Diseases and CREST Program of JST, 2 Department of Otolaryngology and Sensory Organ Surgery (E8) and 3 Laboratory of Immune Regulation, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
4 Division of Immunology and Rheumatology, Lab Surge Building, P-306 Stanford University School of Medicine, Stanford, CA 94305, USA
Correspondence to: H. Kikutani; E-mail: kikutani{at}ragtime.biken.osaka-u.ac.jp
Co-receptors on the B-cell surface regulate B-cell antigen receptor (BCR) signaling; however, it remains unclear how BCR signals are coordinated to maintain immune homeostasis. CD72, a negative regulator of B-cell responses, has immunoreceptor tyrosine-based inhibitory motifs within its cytoplasmic region, and the tyrosine phosphatase SHP-1 binds these sites. The natural ligand of CD72, CD100/Sema4D, belongs to the semaphorin family and induces the dissociation of SHP-1 from CD72, thereby switching off the negative signals of CD72. In the absence of CD100, BCR signals are significantly suppressed due to the constitutive association of SHP-1 with CD72, resulting in B-cell hyporesponsiveness. Here we show that CD100 regulates the sensitivity of the BCR by preventing the association of the CD72 with BCR, and this interaction is required for proper B-cell homeostasis. Consequently, as CD100-deficient mice age, they accumulate marginal zone B cells and develop high auto-antibody levels and autoimmunity. Collectively, our findings indicate that the strength of BCR signals is strictly tuned by the interaction of CD100 with CD72, and this interaction is essential for maintaining immunological homeostasis as well as generating a proper immune response.
Keywords: autoimmunity, CD72, CD100, co-receptor, semaphorin
* These authors contributed equally to this study.
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