GPIbα is not required for aggregation induced by 4N1-1.

(A) Untreated or fixed human platelets were pretreated for 10 minutes with 10 μg/mL of an anti-GPIbα antibody (6D1) before stimulation with 25 μM 4N1-1 or 10 μg/mL vWF activated with 1 mg/mL ristocetin. After full aggregation, platelets were fixed and the number of single platelets was determined. Results were expressed as a percentage of nonstimulated platelets and are representative of experiments using 2 different donors. (B) Platelets from patients with BSS were stimulated with 25 μM 4N1-1, 1 μg/mL convulxin, or 10 μg/mL vWF activated with 1 mg/mL ristocetin. Aggregation was monitored by light transmission. Arrow indicates addition of agonist. Results are representative of one experiment using platelets from 3 different patients with BSS.