A biological role for the major histocompatibility antigens.

A central function of the major histo-compatibility (H) antigens may be to signal changes in self to the immune system. Virus-induced modification of strong transplantation antigens apparently results in recognition by thymus-derived lymphocytes (T cells), with subsequent clonal expansion and immune elimination of cells bearing non-self determinants. The extreme genetic polymorphism found in the major H antigen systems of higher vertebrates may reflect evolutionary pressure exerted by this immunological surveillance mechanism.