Current understanding of the complexity of the HLA antigen system.

The beneficial effect of HLA matching in allotransplantation and the associations of HLA antigens with a variety of diseases are probably manifestations of a more basic function of self-discrimination and immune regulation served by the HLA complex. Despite these important conceptual advances, the specific HLA determinants and the exact mechanisms which favor allograft survival are still undetermined, as are the mechanisms of disease susceptibility conferred by the HLA complex. The currently recognized HLA loci may be only the top of a larger iceberg, and it is likely that additional important loci and functions will be defined in time to come.