THE PRESENCE AND RELEASE OF ALPHA-2-ANTIPLASMIN FROM HUMAN-PLATELETS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 58  (6) , 1069-1074
Abstract
An antigen immunochemically indistinguishable from plasma .alpha.2-antiplasmin, the primary plasmin inhibitor, was detected in human platelets. By radioimmunoassay, 33-114 ng .alpha.2-antiplasmin antigen was quantitated in the detergent-soluble extract of 109 washed human platelets from 10 normal donors with a mean level of 62 .+-. 24 ng/109 platelets. Plasma .alpha.2-antiplasmin, either in the platelet suspending medium or on the surface of the platelets, could account for < 8% of the antigen present in the platelet extracts. When stimulated with thrombin, the platelets released .alpha.2-antiplasmin antigen without cell lysis, and > 85% of the .alpha.2-antiplasmin antigen was released at a high thrombin dose. At a lower dose of thrombin, .alpha.2-antiplasmin and platelet factor 4 were partially released without concomitant secretion of serotonin. No .alpha.2-antiplasmin antigen was detected in extracts of red blood cells, polymorphonuclear leukocytes and adherent and nonadherent mononuclear cells. The platelet is the only peripheral blood cell containing significant amounts of .alpha.2-antiplasmin.