EPCR levels modulate the hemostatic effect of rFVIIa in hemophilia. Wild-type, Tie2-EPCR, and EPCR-deficient mice were administered intravenously with saline or FVIII mAb (1 mg/kg) to induce hemophilia. Two hours after administering the antibody, the hemophilia-induced mice were injected with saline (0), 0.25, 1.0, or 4.0 mg/kg rFVIIa via the tail vein. Five minutes following rFVIIa administration, the bleeding was initiated by the saphenous vein incision and average time to achieve hemostasis and blood loss were determined. At the end of the experimental period, blood from a group of mice receiving saline or FVIII mAb but not treated with rFVIIa was obtained by cardiac puncture to isolate plasma to measure FVIII clotting activity. (A) FVIII clotting activity levels; (B) average time to achieve hemostasis; (C) blood loss (n = 9-12 mice/group). (D) Protein C levels in plasma of wild-type mice and Tie2-EPCR mice administered with varying concentrations of rFVIIa. Plasmas were obtained from mice groups (B) following the completion of bleeding analysis. *P < .05; **P < .01; ***P < .001. When performing the statistical comparison between rFVIIa effectiveness in restoring hemostasis in Ab-induced hemophilic wild-type and Tie2-EPCR mice, each dose of rFVIIa was individually compared between wild-type and Tie2-EPCR mice. Note: The data shown for Con and Ab-induced hemophilia with 0, 0.25, and 1.0 mg/kg of rFVIIa in wild-type mice (B-C) were essentially the same as shown in Figure 2A-B, respectively, except for minor differences in the number of animals in some groups.