The participation of plasma thromboplastin antecedent (Factor XI) in contact-activated fibrinolysis.

Abstract

SummaryExposure of human plasma to foreign surfaces, under certain conditions, may lead to the development of fibrinolytic activity. To assess the role of plasma thromboplastin antecedent (PTA, Factor XI) in contact-mediated activation of plasminogen, kaolin-induced plasmin generation was examined in 11 severely PTA-deficient plasmas. PTA-deficient plasmas generated significantly less plasmin activity, as measured upon a substrate of H-D-Valyl-L-leucyl-L-lysine-P-nitroanilide, than normal plasmas. Impaired plasmin generation was not due to the presence of excessive inhibitors, nor due to a deficiency of plasminogen, Hageman factor, prekallikrein, or high-molecular-weight kininogen. Reconstitution of PTA-deficient plasmas with purified PTA completely corrected impaired contact-activated plasmin generation. These results suggest a requirement of PTA in the contact-activated generation of plasmin in human plasma, and support a hypothesis that PTA functions not only as a blood-clotting factor, but also as a c...