Function and polymorphism of human leukocyte antigen-A,B,C molecules.

Human class I major histocompatibility complex, human leukocyte antigen (HLA)-A,B,C molecules are peptide-binding proteins that present degraded fragments of antigens to cytotoxic T lymphocytes. HLA-A,B,C loci are highly polymorphic and their products are strong alloantigens. Comparison of the primary structure of 39 HLA-A,B,C molecules shows that variation is found at many positions in the extracellular domains (alpha 1, alpha 2, and alpha 3). Positions with high variability are concentrated in and around the peptide-binding groove formed by the alpha 1- and alpha 2-domains and defined by crystallographic analysis of HLA-A2. It is likely that the polymorphic differences serve to alter both the peptide-binding specificity and the interaction with T cell receptors. This in turn may result in differences in immune responsiveness, susceptibility, and resistance to disease, and in alloantigenicity.