HLA-DM and the MHC class II antigen presentation pathway

The MHC class II antigen processing pathway provides a mechanism to selecti vely present peptides generated in the endosomal compartments of antigen pr esenting cells to CD4(+) T cells. Transport of newly synthesized class II m olecules to the endosomal pathway requires the function of an accessory pro tein, invariant chain, which contains a region that interacts directly with the class II peptide binding site. Release of invariant chain and peptide loading by class II molecules are facilitated by a second accessory protein , HLA-DM. This MHC-encoded membrane protein catalyzes peptide exchange reac tions, influencing the repertoire of peptides that are available for recogn ition by T cells.