Binding of anti–GP Ib monoclonal antibodies to CHO cells.

(A) Representative sets of flow cytometry data using an FITC-labeled secondary antibody measuring the binding of anti–GP Ibα monoclonal antibodies WM23, AK2, and AP1 to CHO βIX cells or CHO βIX cells expressing wild-type GP Ibα or canine–human GP Ibα chimeras. (B) Epitopes of anti–GP Ibα monoclonal antibodies based on the flow cytometry data represented in panel A. (C) The effect of antibodies (10 μg/mL final concentration) on specific binding of¹²⁵I-labeled vWf (1 μg/mL final concentration) to washed human platelets (5 × 10⁷/mL final concentration) in the presence of 1 mg/mL ristocetin [R] or 2.5 μg/mL botrocetin [B]: AN51, 6D1, AK2, HPL7, AP1, TM60, MB45, LJIB10 (this study); C-34, VM16d, SZ2,12 Hip126 (this study). Inhibition of ristocetin-dependent vWf binding was tested by platelet aggregation in citrated platelet-rich plasma.