Anti-ACP4 antibodies are used in the immunodetection of the protein acid phosphatase 4. In humans, the canonical protein has a reported length of 426 amino acid residues and a mass of 46.1 kDa. Its subcellular localization is in the membrane. Alternative splicing is reported to yield 3 different isoforms for this protein. It is notably expressed in the testis. A member of a the Histidine acid phosphatase protein family, ACP4 is believed to dephosphorylate receptor tyrosine-protein kinase ERBB4 and inhibits its ligand-induced proteolytic cleavage. Post-translational modifications have been described, including glycosylation. Synonyms for this target antigen include testicular acid phosphatase and acid phosphatase, testicular.