Effect of VWFpp on SIPAct and SIPA. (A) Different concentrations of VWFpp were added to citrated whole blood before the application of shear in a cone-plate viscometer at a shear rate of 3500 s−1 for 3 minutes. Annexin V–PE binding to platelets was used to quantify platelet activation. VWFpp partially inhibits platelet activation (*P < .05 with respect to run without VWFpp). (B) VWFpp (10 μg/mL) was incubated with each of the anti-VWFpp mAbs before the addition of whole blood and application of shear under the conditions described in panel A. 239.3 fully restored platelet-activation levels by countering/blocking the effect of VWFpp (*P < .05). (C) Platelets (107/mL) in plasma were sheared in a viscometer at 9600 s−1 in the presence or absence of anti-D′D3 mAbs. MAb DD3.1, but not other anti-D′D3 mAbs, inhibited platelet activation by approximately 75%. *P < .05 with respect to all other treatments. (D) Approximately 108/mL platelets diluted in plasma were incubated with 100 μg/mL of anti-D′D3 mAb (DD3.1), 20 μg/mL of anti–VWF-A1 domain mAb (AVW-3), or 100 μg/mL of VWFpp for 10 minutes before shear application at 9600 s−1. All reagents reduced platelet aggregation. Data are representative of 3 independent experiments.
