Recognizes a single protein of 33-34kDa, identified as the prostate specific antigen (PSA). This MAb is highly specific to PSA and stains prostatic secretory and ductal epithelium in both normal and neoplastic tissues. PSA is a chymotrypsin-like serine protease (kallikrein family) exclusively produced by the prostate epithelium, and abundant in seminal fluid. PSA can be detected in the sera of patients with prostatic carcinoma. It is predominantly complexed to a liver-derived serine protease inhibitor, alpha-1-antichymotrypsin (ACT). A higher proportion of serum PSA is complexed to ACT in prostate cancer than in benign prostate hyperplasia. This MAb makes an excellent pair with MAb A67-B/E3 for PSA tests.