Plasmin-mediated inactivation of FXIII-A2* does not occur during normal clot formation, but does occur during fibrinolysis and thrombolytic conditions. (A-B) Clot formation in normal plasma with tPA (200 pM) and, in some cases, TXA (7.5 mM). Western blots against (A) FXIII-A and (B) fibrin(ogen) (n = 3). (C-E) TEG analyses of clot formation and cross-linking of exogenous (purified) fibrin in plasma. Schematics on the left show timelines of the procedures and characteristic shear elastic moduli (G, dashed lines), with shaded areas indicating time periods analyzed with TEG. Charts on the right show measured moduli of fibrin clots, a direct indicator of FXIII-A2* activity and fibrin structure. Control samples contain exogenous FXIIIa or T101. (C) Moduli of clots from plasminogen-deficient, normal, and α2-antiplasmin–deficient plasma formed in the presence of tPA (200 pM). (D) Moduli of exogenous fibrin (indicator of residual FXIIIa activity), added following clot lysis. Exogenous fibrinogen (1.4 mg/mL) and TXA were added 1 or 3 hours after clot lysis by tPA (800 nM). (E) Moduli of exogenous fibrin that was added during clot formation under thrombolytic conditions. TXA and then fibrinogen were added 4 minutes after clotting was initiated in the presence of tPA (50 nM or for α2-antiplasmin–deficient plasma, 5 nM). Samples contain combinations of Innovin (I), tPA (T), and TXA (X). **P < .01, ***P < .001. n = 3 for all experiments. TF, tissue factor.
