MHC Class I

MHC Class I

MHC class I molecules are one of two primary classes of major histocompatibility complex (MHC) molecules (the other one being MHC class II) and are found on every nucleated cell of the body (and thus are scarce on red blood cells and platelets: the presence of MHC class I antigen on these anucleated cells is presumed to be owed to their genetically active nucleated cell-line precursors). Their function is to display fragments of proteins from within the cell to T cells; healthy cells will be ignored, while cells containing foreign proteins will be attacked by the immune system. Because MHC class I molecules present peptides derived from cytosolic proteins, the pathway of MHC class I presentation is often called the cytosolic or endogenous pathway.