FXIa promotes clot formation in circulating whole bovine blood and TG after intravenous injection in mice. (A) Images of blood clots formed in circulating whole bovine blood spiked with (from left to right) 0, 10, 50, 100, 200, and 500 pM human FXIa. Shown representative of 2 repeats. (B) The weight of thrombi (from panel A) increased in an FXIa concentration-dependent manner, whereas the concentration of platelets in the remaining liquid blood (after 30 min of circulation) decreased (raw data are provided in supplemental Table 1). Shown representative of 2 repeats. (C) Schematic depiction of the approach used to characterize the effect of FXIa on TG by calculating ΔTPH between ex vivo TG experiments with and without the anti-FXI antibody (αFXI-2). (D) TG assay-based pharmacokinetics of intravenously administered human FXIa in mice. Blood from ∼2 to 5 mice was collected at the indicated time points and tested using the TG assay, as indicated in panel C. Mean ± S.D is shown. TPH, thrombin peak height; ΔTPH, change in TPH; i.v., intravenously.