human leukocyte antigen (HLA) class I

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Cell surface receptors composed of an alpha chain and a non-covalently associated protein called beta-2 microglobubin that are expressed on all nucleated cells in the body and used to identify non-self protein antigens derived from the cell cytoplasm. Receptors are encoded by the Major Histocompatibility Complex (MHC) genes located on chromosome 6. There are three genes encoding functional receptors called HLA-A, -B and Cw. If the cell is infected by a virus, the cell displays viral peptides (or antigen) in combination with HLA class I molecules. The presence of the foreign peptide antigen binding to the HLA class I molecule activates CD8+ CTLs (cytotoxic T lymphocytes) specific for that antigen. Certain alleles of HLA class I receptors also interact with Natural Killer cells expressing killer-cell immunoglobulin-like receptors (KIRs) and play a role in detection of cancererous or virus-infected cells.

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