The measurement of human plasma antiplasmin activity by radial diffusion assay

An assay of human antiplasmins has been developed utilizing radial diffusion of plasma from wells cut in plasmin-enriched, fibrinogen-agarose plates. After diffusion the fibrinogen is clotted. Zones of fibrin protected from background fibrinolysis develop as the result of plasma antiplasmin activity. A pooled plasma standard was taken to contain 100% antiplasmin activity. Antiplasmin activity of 52 normal subjects varied from 64 to 132%. Washed platelets contained 1-5% antiplasmin activity. Using antisera to precipitate individual inhibitors, physical methods of separation, and electrophoresis of plasma in agarose, several different proteins were found to have antiplasmin activity in this assay. Thus, alpha2-macroglobulin contributed 56%, alpha1-antitrypsin 20%, antithrombin III 2%, and other proteins 22% of the total antiplasmin activity. 1 ml of whole plasma neutralized 7.0 CTA units of plasmin.