Anticoagulant properties of anti-A2 mAbs. (A) Residual fVIII activity was measured by 1-stage coagulation assay following incubation of normal human plasma with varying concentrations of mAbs for 2 hours at 37°C. Data represent sample means and sample standard deviations. The curves represent least-squares fits to the data. The inhibitor titer in Bethesda units per milliter was obtained by determining the dilution of mAb producing 50% inhibition and converted to Bethesda units per milligram using the mAb concentration. (B) BDD human fVIII (50 nM) was incubated with the indicated concentrations of anti-A2 mAbs for 30 minutes and then thrombin for 60 seconds, followed by sample dilution into fIXa/PCPS phospholipid vesicles, addition of fX, and measurement of fXa as described in “Intrinsic fXase assay.” Results are presented as the percentage of fXa formed in the absence of mAb.