HLA-A

HLA-A are a group of human leukocyte antigens (HLA) that are encoded by the HLA-A locus on human chromosome 6p. The HLA genes constitute a large subset of the Major histocompatibility complex (MHC) of humans. HLA-A is a component of certain MHC class I cell surface receptor isoforms that resides on the surface of all nucleated cells and platelets. The receptor is a heterodimer, and is composed of a heavy, alpha (α) chain and smaller beta (β) chain. The alpha chain is encoded by a variant HLA-A gene, and the beta chain (β₂-microglobulin) is composed by the invariant Beta-2 microglobulin gene.

MHC Class I molecules are part of a process that presents polypeptides from host of foreign derivation to the immune system. Under normal conditions, if a peptide of foreign, pathogenic, source is detected, it alerts the immune system that the cell may be infected with a virus, and, thus, target the cell for destruction.

For humans, as in most mammalian populations, MHC Class I molecules are extremely variable in their primary structure, and HLA-A is ranked among the genes in humans with the fastest-evolving coding sequence. After typing millions of individuals, hundreds of variant alleles and isoforms have been identified. This level of variation on MHC Class I is the primary cause of transplant rejection, as random transplantation between donor and host is unlikely to result in a matching of HLA-A, B or C antigens.

Further information: History and naming of human leukocyte antigens