Anti-proteoglycan 4 antibodies are used for the immunodetection of the protein encoded by the PRG4 gene. In humans, the canonical protein has a reported length of 1404 amino acid residues and a mass of 151.1 kDa. It is known to be a secreted protein. Alternative splicing is reported to yield 6 different isoforms for this protein. It is reported to be highly expressed in synovial tissue, cartilage and liver and weakly in the heart and lung. It is reported to play a role in boundary lubrication within articulating joints. Post-translational modifications have been described, including O-glycosylation, N-glycosylation and protein cleavage. Other names for this target antigen include HAPO, JCAP, MSF, SZP, articular superficial zone protein, hemangiopoietin, lubricin, and CACP. Gene orthologs have been identified in the mouse, rat, bovine, frog, chimpanzee and chicken species. A number of proteoglycan 4 antibodies have been mentioned in research publications and have associated citations. These antibodies are most commonly used in Western Blot experiments, among other applications.