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