QUANTITATIVE IMMUNOASSAY FOR COMPLEXES OF PROSTATE-SPECIFIC ANTIGEN WITH ALPHA(2)-MACROGLOBULIN

We have developed two ELISAs for quantifying complexes of prostate-spe cific antigen (PSA) with alpha(2)-macroglobulin (alpha(2)M), using par tially purified PSA:alpha(2) complex as the calibrator, One ELISA was designed to evaluate PSA:alpha(2)M complex in fluids containing a huge excess of PSA over the amount of complex (semen-derived fluids), the other for use in fluids containing an excess of alpha(2)M over PSA (bl ood plasma). The range of the assays was 2-1000 mu g/L for PSA complex ed to alpha(2)M; the detection limit was 3 mu g/L. Intra- and interass ay CVs were 7-13% and 11-17%, respectively, at complexed PSA concentra tions of 6-500 mu g/L. Seminal fluid from healthy men (n = 60) contain ed 5.2 +/- 2.6 mg/L PSA complexed with alpha(2)M. Prostatic and semina l vesicle fluids contained 6.5 +/- 2.9 and 0.3 +/- 0.2 mg/L PSA comple xed to alpha(2)M, respectively. When purified PSA was incubated with c itrated plasma, between 45% and 65% of the added PSA was recovered as free PSA, whereas similar to 25% formed complexes with alpha(2)M, 10% complexedwith alpha(1)-antichymotrypsin, and only 0.1-6% was complexed with protein C inhibitor. Of 30 patients with prostate disease, 20 sh owed detectable plasma PSA:alpha(2)M complexes; however, the potential diagnostic significance of this complex requires further investigatio n.