CD74，also known as the MHC class II associated invariant chain (Ii)，is a type II transmembrane protein which binds to the peptide binding groove of newly synthesized MHC class II alpha/beta heterodimers and prevents their premature association with endogenous polypeptides. CD74 is produced in molar excess over MHC class II and some of this is expressed by an unknown pathway on the cell surface independent of，or in association with，MHC class II molecules. The half life of CD74 on the cell surface is only 3 to 4 min after which it is internalized. It has been proposed that cell surface CD74 binds The protein encoded by this gene associates with class II major histocompatibility complex (MHC) and is an important chaperone that regulates antigen presentation for immune response. It also serves as cell surface receptor for the cytokine macrophage migration inhibitory factor (MIF) which，when bound to the encoded protein，initiates survival pathways and cell proliferation. This protein also interacts with