EXTENDING THE B7 (CD80) GENE FAMILY

B7-1 and B7-2 are members of the immunoglobulin superfamily (IgSF) and important regulators of T cell-mediated immune responses. Despite sha ring only limited sequence identity, B7-1 and B7-2 bind common recepto rs, CD28 and CTLA-4, on T cells and have similar functional properties . We have found that the extracellular V(ariable)-like domains of B7-1 and B7-2 share significant sequence similarities with 3 major histoco mpatibility complex (MHC)-encoded members of the IgSF: butyrophilin, m yelin/oligodendrocyte glycoprotein, and the chicken MHC molecule, B-G. This raises the question whether there is an evolutionary link betwee n the MHC, which encodes molecules regulating the antigen specificity of T lymphocyte responses, and B7 molecules, which co-stimulate these responses in antigen-nonspecific fashion.