DR alpha chain precursor, DRB1, DRB4, HLA class II histocompatibility antigen, HLA class II histocompatibility antigen DR alpha chain, HLA DR1B, HLA DR3B, HLA DRA, HLA DRA1, HLA DRB3, HLA DRB4, HLA DRB5, HLADR4B, HLADRA1, HLADRB, Major histocompatibility complex class II DR alpha, Major histocompatibility complex class II DR beta 1, Major histocompatibility complex class II DR beta 3, Major histocompatibility complex class II DR beta 4, Major histocompatibility complex class II DR beta 5, MGC117330, MHC cell surface glycoprotein, MHC class II antigen DRA, MHC II, DRA_HUMAN.
Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route, where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules, and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments, exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides, autophagosomes constitutively fuse with MHC class II loading compartments.
