Assay of functional activity of alpha 1-antichymotrypsin in plasma

We introduce a novel assay for measuring active alpha 1-antichymotrypsin (alpha 1X) in human plasma. The assay works on the principle that cathepsin G, immobilized in microtiter plates, preferentially binds alpha 1X, which then can be specifically quantified immunologically. alpha 1X activity can be detected even after 50,000-fold dilution of normal plasma. A linear range was defined for reproducible quantification. There was no interference by alpha 1-proteinase inhibitor or alpha 2-macroglobulin. The assay is designed to detect conditions having decreased alpha 1X activity to further elucidate the biological function of this prominent acute-phase protein.