High Quality Content by WIKIPEDIA articles! 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 not on red blood cells, though they are found on platelets). 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.