It recognizes a protein of 65-76kDa, which is identified antichymotrypsin (AACT). AACT is a plasma protease inhibitor synthesized in the liver as a single glycopeptide chain. In human, the normal serum level of AACT is about one-tenth that of 伪 1-antitrypsin (AAT), with which it shares nucleic acid and protein sequence homology. Both are major acute phase reactants; their concentrations in plasma increase in response to trauma, surgery and infection. Elevated levels of AACT are widely, but not universally, reported in the cerebrospinal fluid and plasma of AD patients. Prostate-specific antigen (PSA) and its SDS-stable complex with AACT are in widespread use as markers for the diagnosis of prostate cancer. AACT deficiency may also be a possible cause of chronic liver disease. AACT antibody reacts with histiocytes and histiocytic neoplasms. It is widely used to identify histiocytes and tumors derived from them. Acinar tumors of the pancreas and salivary gland may also exhibit AACT positivity.