[Binding of factor VIII/Willebrand to Bernard-Soulier and thrombasthenic platelets (author's transl)].

We have studied the binding of Factor VIII/Willebrand factor (FVIII/WF) to the platelets of ten normal donors, five patients with Bernard-Soulier syndrome (BSS), three clinically normal patients heterozygous for BSS (BSS hetero), and three with Glanzmann's thrombasthenia (GT). The amount of 125I-FVIII/WF bound to the platelets was measured in the presence or absence of ristocetin, the results expressed as percentage of total radioactivity added. The time course of 125I-FVIII/WF showed that maximum binding to the platelets was observed at 30 min, and then a plateau was reached. The binding was ristocetin-dependent and was relative to the concentration of ristocetin added. At a final concentration of 0.5 mg/ml of ristocetin, specific binding to the normal platelets was 30.9 +/- 2.5 %; at 1.0 mg/Ml, specific binding was 34.7 +/- 3.2% in the normal donors. In the five BSS patients lacking platelet membrane Glycoprotein 1 (GPI), reduced binding of 125I-FVII/WF was observed. At a final concentration of 1 mg/ml of ristocetin, the mean value of the binding was 13.7 % (11.5 % -14.8 %); at a final concentration of 0.5 mg/ml of ristocetin, the mean value decreased to 5.6 % (2.9 %-7.2 %). In the three BSS hetero patients, binding was near normal, although there were reduced amounts of platelet membrane GPI. Binding was slightly decreased in the three thrombasthenic patients lacking GP IIb/IIIa.