Analysis of the mechanism of platelet adhesion enhancement by VWF in platelet-reduced blood under flow conditions. (A) Erythrocyte fraction (< 3000 platelets/μL) suspended in HEPES-Tyrode/2% BSA (hematocrit, 35%-40%) containing 4 RCo U/mL VWF was perfused on the collagen-coated glass plate for 2 minutes (VWF-pretreatment) and then immediately changed to flow platelet-reduced blood on the same glass plate for 2 minutes at a shear rate of 1600 s^–1; the platelet adhesion was measured as indicated in “Materials and methods.” The 0 and 4 indicate the addition of 0 and 4 VWF:RCo U/mL purified VWF in the platelet-reduced blood. Data are each a mean ± SEM (n = 3). (B) Platelet-reduced blood (4-5 × 10⁴ platelets/μL) prepared with PPACK-treated whole blood containing 2 RCo U/mL VWF/FVIII complex was perfused with anti-GPIb (NNKY5-5), anti-α₂β₁ (Gi9), or anti-α_IIbβ₃ (P2) monoclonal antibodies at the concentrations 20 μg/mL for 2 minutes at a shear rate of 1600 s^–1. Platelet adhesions of platelet-reduced blood with no additions 0 (n = 11), 2 (n = 6) VWF:RCo U/mL VWF/FVIII complex, NNKY5-5 (n = 3), P2 (n = 3), and Gi9 (n = 3). Data are each a mean ± SEM.