Enhancement of the TFPI-mediated inhibition of thrombin generation by WT protein S and protein S/Gas6 chimeras I to III. Thrombin generation was measured in protein S–depleted plasma supplemented with 50 μM phospholipids and 1 pM TF, in the presence or absence of 1 nM TFPI, and in the presence or absence of titrated (0-100 nM) WT protein S (A), chimera I (B), chimera II (C), or chimera III (D). Representative experiments are shown (n = 3). (E) Peak thrombin was plotted against protein S concentrations. The peak height in the presence of TFPI alone represents 100%. Results are expressed as mean ± SD (n = 3). PS, protein S.