The Major Histocompatibility Complex
The major histocompatibility complex (MHC) is a large group of closely-linked, highly polymorphic genes. The proteins encoded by these genes are crucial for the generation and execution of immune responses. MHC gene products are necessary for T cell antigen recognition, for collaboration of T cells with accessory cells and B cells in the induction of humoral immune responses, and for cellular immunity against infected cells, or foreign or allogeneic cells (graft rejection). A similar gene complex exists in all vertebrate species yet examined, indicating its conservation over a long period of evolutionary time.