MHC Molecule Definition

Any of various polymorphic transmembrane proteins that are coded for by the genes of the major histocompatibility complex and that function in the immune system to present foreign antigens to T cells. Class I MHC molecules are found in most nucleated cells and present antigens originating intracellularly, such as virus fragments, to cytotoxic T lymphocytes. Class II MHC molecules are found in dendritic cells, macrophages, and other antigen-presenting cells and present antigens from extracellular pathogens, such as bacteria and parasites, to helper T cells.