Cluster of Differentiation 74 (CD74) is also known as HLA class II histocompatibility antigen gamma chain (HLADG), DHLAG, Ia-GAMMA, invariant chain (Abbreviated Ii). CD74 / HLADG is a polypeptide involved in the formation and transport of MHC class II protein. The cell surface form of the invariant chain is known as CD74. CD74 is upregulated in several cancers and is also expressed by non-immune cells during inflammation. CD74 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 the endosomal / lysosomal system where the antigen processing and binding of antigenic peptides to MHC class II takes place. CD74 / DHLAG also serves as cell surface receptor for the cytokine MIF.