siFXIIIB delays crosslinking of α2-antiplasmin, leading to clots that are more susceptible to lysis ex vivo. (A-B) Representative TEG curve tracings using blood from mice treated with siLuc (A, lavender) or with siFXIIIB (B, green). In each case, recombinant tissue factor was added to stimulate clotting and 4 nM of tPA was added to enhance lysis. (C-E) TEG curves were quantified for (C) maximum clot stiffness, (D) percent of clot lysed after 30 minutes, and (E) time until complete clot lysis; n = 3 mice per treatment group. (F-G) Western blot against FXIII-A and TEG curve tracing of plasma from untreated (Unt) mice (lavender), mice pretreated with siFXIIIB (green), and mice pretreated with siFXIIIB and given an IV dose of mFXIII (yellow). (H-I) Representative western blots against (H) fibrin(ogen) and (I) α2-antiplasmin comparing the HMW species in plasma clotted for 1 hour from untreated mice or those treated with siFXIIIB 2 weeks previously. Clots were formed and lysed in plasma samples with platelets (PRP) or without platelets (PPP) 1 hour after adding CaCl₂ to plasma. Non-recalcified plasma was used as a control for unactivated (UA) FXIII, and plasma with an inhibitor of FXIII-A* was added in vitro as a control (T101, 0.8 mM). (J-K) Crosslinking of fibrin and α2-antiplasmin was assessed over time by western blot of PPP clots from untreated mice (lavender) or siFXIIIB pretreated mice (green) and quantified using densitometry. Graphs show the percentage of fibrin or α2-antiplasmin found in the HMW range (100-200 kDa) compared with the total amount of fibrin or α2-antiplasmin. For all graphs, values represent mean ± SEM. **P < .01, and ns indicates not significant.