Different molecular forms of uncomplexed prostate specific antigen (PSA) show similar immunoreactivities

PSA exists in multiple molecular forms in serum, with the majority complexe d to proteinase inhibitors such as alpha(1)-antichymotrypsin and alpha(2)-m acroglobulin. The uncomplexed, or "free" forms of PSA represent a very hete rogenous distribution of molecular isoforms. It has been suggested that the se variations in uncomplexed PSA may cause differences in their immunologic characteristics which may lead to analytical differences between various P SA assays. We report that various isoforms of uncomplexed PSA purified from seminal fluid as previously described show no differences in relative immu noreactivity and demonstrate equimolar behavior as measured by the TOSOH AI A(R)-600 assay, which is a PSA assay based upon monoclonal PSA and monoclon al detecting antibodies (mono-mono). Furthermore, we show that carbohydrate side-chain modification does not change the equimolar immunoreactivity of these isoforms.