CD74 molecule, major histocompatibility complex, class II invariant chain; Plays a critical role in MHC class II antigen processing by stabilizing peptide-free class II alpha/beta heterodimers in a complex soon after their synthesis and directing transport of the complex from the endoplasmic reticulum to compartments where peptide loading of class II takes place. Serves as cell surface receptor for the cytokine MIF (296 aa)