Prothrombin F1 and F2 alleviate histone-induced systemic coagulation activation in vivo. C57BL/6 male mice were anesthetized and infused with different doses of histones through tail veins. One hour after infusion, blood were taken for platelet count, prothrombin time (PT) and concentrations of TAT complexes, fibrinogen, and D-dimer; DIC scores were also calculated (A). (B) Lung sections from histone-infused mice and saline controls were immunohistochemically stained with anti-fibrin antibody, and typical images are presented. Arrows indicate thrombi. Scale bar, 50 μm. (C) Platelet counts (left), TAT (middle), and fibrinogen (right) levels following prothrombin F1 + F2 infusion ± histones. *P < .05  compared to F1/F2 alone; ^#P < .05 when compared to histones alone (ANOVA).