Summary
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, α2-macroglobulin contributed 56%, α1-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.
