Effect of fXI on thrombin generation in fXI-deficient plasma. Thrombin generation in plasma is shown as areas under the curve for panels A and B or thrombin generation over time for panels C through E. Coagulation was initiated with (A) TF and Ca²⁺ in the presence (□) or absence (■) of fXI; (B) TF (0.23 pM) and Ca²⁺ (□) or Ca²⁺ alone (■) at various fXI concentrations; (C) Ca²⁺ and 1.6 pM (1 and 2) or 0.23 pM (3 and 4) TF in the presence (1 and 3) or absence (2 and 4) of fXI; (D) Ca²⁺ and 30 pM (1 and 2) or 6 pM (3 and 4) fXa, in the presence (1 and 3) or absence (2 and 4) of fXI; and (E) 5 nM α-thrombin in the presence (1) or absence (2) of fXI. Error bars for panels A and B represent one SD.