Studies on the pathophysiology and treatment of von willebrand''s disease. IV. Mechanism of increased ristocetin-induced platelet aggregation in von willebrand''s disease

The binding of factor VIII to platelets in the presence of ristocetin was investigated in four patients with von Willebrand's disease that showed an increased ristocetin-induced platelet aggregation (RIPA). The binding of plasma factor VIII-related antigen (VIIIR:Ag) from these patients to normal washed or formalin-fixed platelets was decreased in three patients and was normal in one patient. Washed platelets prepared from these patients, however, showed an increased binding affinity for normal VIIIR:Ag. It was suggested that the increased RIPA was brought about by an increased ristocetin-induced binding affinity of patients' platelets for factor VIII.