Binding of radioiodinated human von Willebrand factor to Bernard-Soulier, thrombasthenic and von Willebrand's disease platelets

The ristocetin-induced binding of purified human ¹²⁵I-von Willebrand factor (vWF) polymers to formalinized and fresh washed giant platelets from three Bernard-Soulier syndrome (BSS) patients (two different families) was 0%, 1–2% and 7–18%, respectively, compared to normal platelets prepared at the same time, under the same conditions, and adjusted to the same final platelet counts. This abnormal ¹²⁵I-vWF binding was associated with absent BSS platelet agglutination in response to ristocetin and human vWF, and to bovine vWF alone (without ristocetin). Thus, it is defective attachment of exogenous vWF which prevents vWF-mediated agglutination of BSS platelets, rather than defective platelet-to-platelet contact subsequent to vWF-BSS platelet binding. In contrast to BSS platelets, there was normal to increased ristocetin-induced binding of ¹²⁵I-vWF to platelets prepared from two clinically normal heterozygous parents of BSS patients, two patients with thrombasthenia, and two individuals with von Willebrand's disease.