Major histocompatibility antigens
(Science: immunology) a set of plasmalemmal glycoprotein antigens involved in rapid (e.g. 7 days in the mouse) graft rejection and other immune phenomena. The minor histocompatibility antigens are involved in much slower rejection phenomena. The major antigens show remarkable polymorphism and occur as class i and class ii types in mammals, birds may have a class iii molecule as well.