ABSTRACT
Class I molecules are composed of 2 noncovalently bound polypeptides, a p chain (p2 microglobulin) which does not vary and an a chain which is highly polymorphic and may be from several different loci. The classical class I (a chain) loci are HLA-A, -B, -C. Nonclassical class I (a chain) loci include HLA-E, -F, -G, -H. The distribution and functions of the nonclassical HLA class I genes are not well understood. HLA-A, -B and -C molecules are present on the surface of all nucleated cells and are recognized by cytotoxic T lympho cytes (CTL). Class I molecules present intracellular (endogenous) proteins that have been processed into peptides of 7-9 amino acids.
