Effect of ristocetin on aggregation of HWP after adding porcine and human vWF–A1-domain transfected COS-7 cells. HWP were prepared as described in Materials and Methods. The extent of aggregation is represented by the percentage of the maximal light transmission 10 minutes following addition of porcine (P) and human (H) vWF–A1-domain expressing COS-7 cells at low ratios (1:1,200 cells/platelets). Incubation of HWP with ristocetin (R) (0.32 mg/mL) alone or in combination with empty vector–transfected COS-7 cells (E) excluded significant human vWF contamination in platelet preparations. Specificity for A1-domain–GPIb interaction was further proven by incubating platelets with 6D1, a specific antibody known to block GPIb-mediated aggregation by vWF.
