F. Espana et al., A QUANTITATIVE ELISA FOR THE MEASUREMENT OF COMPLEXES OF PROSTATE-SPECIFIC ANTIGEN WITH PROTEIN-C INHIBITOR WHEN USING A PURIFIED STANDARD, The Journal of laboratory and clinical medicine, 122(6), 1993, pp. 711-719
The serine protease inhibitor protein C inhibitor is present in semen
at a relatively high concentration and forms in vivo complexes with tw
o plasminogen activators also present in semen, urokinase-type and tis
sue-type plasminogen activators. Therefore, the fact that prostate-spe
cific antigen (PSA), a major prostate enzyme, complexes and inactivate
s protein C inhibitor (PCI) in semen could have implications in human
reproduction. The present study was undertaken to develop an enzyme-li
nked immunosorbent assay (ELISA) for complexes of PSA with PCI (PSA:PC
I) with purified PSA:PCI complexes as a standard. Seminal plasma was u
tilized as the starting material for purification of complexes by affi
nity chromatography on heparin-Sepharose and gel filtration. The final
preparation contained equimolor concentrations of PSA and PCI and was
used for calibration of an ELISA for PSA:PCI complexes involving poly
clonal anti-PSA and horseradish peroxidase-labeled anti-PCI antibodies
. The ELISA had a detection limit of about 0.2 ng/ml of complex and wa
s specific for PSA:PCI complexes because no color was developed at PSA
or PCI concentrations up to 100 mug/ml. Normal plasma or plasma from
patients with prostate carcinoma who had high PSA levels had no detect
able 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 mug/ml
, accounting for up to 34% of the total PCI in seminal plasma. When se
men was collected in the presence of 1,10 phenanthroliniumchloride, to
block PSA activity, the mean level of PSA: PCI complex was 11 +/- 6 m
ug/ml and the amount of PCI complexed to PSA was 6% +/- 2% of the tota
l semen PCI level. The assay therefore makes it possible to carry out
further studies on the interaction of PSA and PCI in vivo and in vitro
.