The major histocompatibility complex and its relationship to allergic disease.

Two tests, the mixed leukocyte culture (MLC) and cell-mediated lympholysis (CML) tests, have been used as in vitro models of the in vivo allograft reaction. These tests have been applied to histocompatibility testing for transplantation as well as to assay of immune function. They involve the use of peripheral blood lymphocytes as "responding" cells in mixed leukocyte culture or as "stimulating" cells in the generation of a proliferative or a cytotoxic response. The proliferative events in MLC are primarily in response to LD antigens of the major histocompatibility complex; the cytotoxic cells use as their targets the SD antigens of that complex. A new method for defining the LD antigens, the primed LD typing (PLT) test, is based on in vitro sensitization of lymphocytes to certain LD antigens of the major histocompatibility complex and their subsequent restimulation with test cells.