Effect of soluble VWF on hPF4 and KKO binding to endothelium. Expression of (A) hPF4 and (B) KKO on VWF strings in the microfluidic chamber after elutriation with low (10 µg/mL) or high (20 µg/mL) concentrations of plasma VWF or BSA. Heparin (4 U/mL) was also studied as a positive control. Means ± 1 SEM are shown for N ≥ 4 separate channels in the case of control and N ≥ 5 for all experimental additions. P values were determined using a 1-way ANOVA to compare residual relative binding in the absence vs the presence of added protein or heparin.