The Relationship of the Major Murine Histocompatibility Region Associated IA Antigens to Mitogen Responses l

The mouse and other mammals have a large number of histocompatibility (H) gene loci (perhaps several hundred) controlling cell-membrane alloantigens. Only one locus, however, is a strong H locus and is termed the major histocompatibility complex (MHC). A difference between donor and recipient at the MHC will prevent the growth of nearly all tumor allotransplants and result in rapid rejection of skin allografts. The murine MHC, (H-2), is located in the ZXth linkage group of the 17th chromosome and is composed of five regions denoted as K, I, S, G, D [l]. The H-2 gene complex has served as a model for MHC of other mammals and the similarity of H-2 and the HL-A gene complex of man is striking. In addition to the classical H-2 histocompatibility antigens of the K and D regions, the Z region, originally defined by immune response (Zr-I) genes [2], contains genes coding for a system of lymphocyte alloantigens. These antigens have been designated Ia (I region associated) [3] and to date 21 specificities have been identified (for review, Ref. [4]). The Ia antigens have a restricted distribution with expression on the majority of B lymphocytes and a subpopulation of T lymphocytes [5-l I].