Anti-CD74 molecule antibodies are used in the immunodetection of the protein encoded by the CD74 gene. In humans, the canonical protein has a reported length of 296 amino acid residues and a mass of 33.5 kDa. Its subcellular localization is in the ER, golgi, lysosomes, cell membrane, and is also secreted. It is notably expressed in urine. It is known to play an important 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. Post-translational modifications have been described, including O-glycosylation. Other names for this target antigen include DHLAG, HLADG, II, Ia-GAMMA, p33, and CLIP.