A quantitative ELISA for the measurement of complexes of prostate-specific antigen with protein C inhibitor when using a purified standard

Abstract

The serine protease inhibitor protein C inhibitor is present in semen at a relatively high concentration and forms in vivo complexes with two plasminogen activators also present in semen, urokinase-type and tissue-type plasminogen activators. Therefore, the fact that prostate-specific antigen (PSA), a major prostate enzyme, complexes and inactivates protein C inhibitor (PCI) in semen could have implications in human reproduction. The present study was undertaken to develop an enzyme-linked immunosorbent assay (ELISA) for complexes of PSA with PCI (PSA:PCI) with purified PSA:PCI complexes as a standard. Seminal plasma was utilized as the starting material for purification of complexes by affinity chromatography on heparin-Sepharose and gel filtration. The final preparation contained equimolar concentrations of PSA and PCI and was used for calibration of an ELISA for PSA:PCI complexes involving polyclonal anti-PSA and horseradish peroxidase-labeled anti-PCI antibodies. The ELISA had a detection limit of about 0.2 ng/ml of complex and was specific for PSA:PCI complexes because no color was developed at PSA or PCI concentrations up to 100 microgram/ml. Normal plasma or plasma from patients with prostate carcinoma who had high PSA levels had no detectable PSA:PCI complexes. Seminal plasma from voluntary donors collected in the absence of inhibitors and incubated at room temperature for at least 3 hours had PSA:PCI complex levels ranging from 30 to 46 micrograms/ml, accounting for up to 34% of the total PCI in seminal plasma.(ABSTRACT TRUNCATED AT 250 WORDS)