Demonstration of the presence of TAFI in rabbit plasma. (A) The concentration-dependent potentiation of lysis time by the carboxypeptidase inhibitor from the potato (PTI). Lysis times were determined using a turbidometric assay as indicated in Materials and Methods. The inset represents a Western blot of purified human TAFI, human plasma, and rabbit plasma in lanes A, B, and C, respectively. (B) The concentration-dependent potentiation of lysis time by the factor Xa inhibitor, TAP. Clots were formed as indicated in Materials and Methods, but with 294 pmol/L tPA. The effect of various concentrations of TAP (0 to 10 μmol/L) on lysis time was determined for clots produced in the absence (○) or presence (•) of 5 μg/mL PTI. Indicated values are the average from 2 experiments, in which the range did not exceed 5% of the mean. These data indicate that rabbit plasma contains TAFI, which, when activated by thrombin, is able to prolong lysis time and is inhibited by the carboxypeptidase inhibitor PTI.