A prostate-specific antigen, distinct from acid phosphatase, was identified by immunologic procedures in prostate tissues (normal, benign hypertrophic, and cancerous) and seminal plasma, as well as in sera of patients with prostatic cancer and of nude mice bearing human prostatic tumor. This antigen was shown by immunoperoxidase staining to be confined to epithelial cells comprising the prostatic ductal elements. Prostate antigen was purified from prostatic tissue and seminal plasma, and it was shown to have a molecular weight of 33,000-34,000 with no subunit component. The isoelectric point of purified antigen was around 6.9, though several unpurified isomers with different isoelectric points also were observed. Serum-borne prostate antigen showed a molecular weight of 90,000-100,000 but it exhibited a molecular weight of 36,000 in the presence of sodium dodecyl sulfate. A sandwich-type, peroxidase-linked immunosorbent assay capable of detecting 0.1 ng of the antigen per milliliter of blood was developed. With this technique, serum level of the antigen was found to increase in patients with prostatic cancer as compared with normal males. The prostate-specific antigen can be a useful marker for detection of prostatic cancer.

A reverse enzyme-linked immunosorbent assay (ELISA) modified from a prostate antigen (PA) assay previously reported has been developed to measure circulating PA-binding globulin (PABG). Serum specimens taken from normal males, normal females, male patients with nonprostatic cancers, patients with benign prostatic hypertrophy, and patients with various stages of prostate cancer were analyzed for PABG. Results revealed that only patients with an advanced stage of prostatic cancer exhibited an elevated level of PABG. PABG was then isolated from prostatic cancer patients' serum by PA affinity chromatography. Upon immunodiffusion and immunoelectrophoresis, this PABG preparation reacted with purified PA, anti-PA xenoantibodies and anti-human IgG. By the immunoperoxidase technique, PABG stained positively in prostatic ductal epithelial cells and negatively in all other tissues examined. An additional PABG preparation, which reacted with anti-PA and anti-human IgG and not with purified PA, was also isolated by an anti-PA affinity chromatography. These PABG preparations were separately subjected to high-performance liquid chromatography for further purification. Three major protein peaks at Mr of greater than 240K, 150K, and 34K were obtained. These results demonstrated that circulating IgG antibody reactive with PA was present in patients with metastatic cancer of the prostate, and this in part was in complexed form with PA and was specifically reactive with ductal epithelial elements of the prostate.