Transplant tolerance modifying antibody to CD200 receptor, but not CD200, alters cytokine production profile from stimulated macrophages.

Increased C57BL/6 allograft survival following donor-specific dendritic cell (DC) portal vein (pv) pre-transplant immunization of C3H mice is associated with increased expression of the molecule CD200 on DC, delivery of suppressive signals by CD200(r+) macrophages, and polarization in cytokine production towards type-2 cytokines. Infusion of anti-mouse CD200 monoclonal antibody abolishes these effects. We have used whole Ig, and F(ab')(2) fragments, of anti-CD200 and anti-CD200(r) mAb to explore the relative signaling role of CD200(+) versus CD200(r+) cells in suppression of type-1 cytokine production in mixed leukocyte cultures (MLC), and enhanced graft survival in vivo. Simple neutralization of CD200 [even by F(ab')(2) antibody] reversed CD200-mediated suppression. However, only whole anti-CD200(r) antibody was effective in stimulating suppression from CD200(r+) cells. Suppression of cytokine induction following cross-linking of CD200(r+) cells in vitro was attenuated by anti-IL-6 mAb. Our data are consistent with the hypothesis that CD200(r) itself delivers the crucial intracellular signal leading to immunosuppression, a feature likely of importance in autoimmunity and transplantation.