Involvement of CD100, a lymphocyte semaphorin, in the activation of the human immune system via CD72: implications for the regulation of immune and inflammatory responses

CD100/Sema4D belongs to the semaphorin family, factors known to act as repulsive cues for axons during neuronal development. Mouse CD100 plays a crucial role in both humoral and cellular immunity through ligation of the lymphocyte receptor, CD72. It remains controversial, however, whether human CD100 can function through human CD72 in a manner similar to mouse CD100. To determine the function of human CD100, we generated a recombinant soluble human CD100 protein comprised of the extracellular region of human CD100 fused to the human IgG1 Fc region (hCD100–Fc). hCD100–Fc specifically binds to cells expressing human CD72. As observed previously in the mouse, hCD100–Fc induces the tyrosine dephosphorylation of human CD72, leading to the dissociation of SHP‐1 from the CD72 cytoplasmic tail. Consistent with findings for mouse CD100, hCD100–Fc exerts a co‐stimulatory effect on B cells and dendritic cells that are stimulated with anti‐CD40 mAb. Furthermore, both hCD100–Fc and anti‐human CD72 agonistic mAb induce the production of the pro‐inflammatory cytokines tumor necrosis factor‐α, IL‐6 and IL‐8, even in the absence of anti‐CD40 mAb. Collectively, our findings not only demonstrate that human CD100, interacting with human CD72, can function as a ligand in a manner similar to mouse CD100, but also suggest the involvement of human CD100 in inflammatory responses.