Defective ¹²⁵I-Factor VIII Binding to Platelets in Patients with Bernard-Soulier Syndrome and Von Willebrand’s Disease

Binding of human factor VIII to normal, Bernard-Soulier and von Willebrand platelets were studied. Purified factor VIII was labeled with ¹²⁵iodine(¹²⁵I-VIII) by using Bolton-Hunter reagent. Platelets suspended in 10mM Tris, 0.15M NaCl were incubated for 3 min at 22° with I-VIII (1,250 ng/ml) in the presence of ristocetin. Platelets were then separated from suspending medium by centrifugation for 1 min at 7,000xg through silicon oil. The binding of ^l25I-VIII was determined from the radioactivity of the pellets. Amount of ¹²⁵I-VIII bound to normal platelets was only 20.3ng/10⁸plts in the absence of ristocetin. The addition of ristocetin to platelet suspension(5xl0⁸plts/ml) in the cone, of 0.4, 0.8, 1.2 and 1.6mg/ml Increased ¹²⁵I-VIII binding to 70, 85.6, 90.3 and 94.7 ng/ 10pits. The binding of ¹²⁵I-VIII was found to be time-dependent, reaching plateau in 3min(1.2mg rlstocetln/ml). ¹²⁵I-VIII binding to platelets from a patint with Bernard-Soulier Syndrome was found to be only minimum even 3 mln after addition of 1.2mg/ml ris-tocetin(24.9ng/10⁸plcs), and those from 4 cases with von Willebrand’s disease were decreased (50. 5±9. 6). These results not only indicate defective interaction of Bernard-Soulier platelets with factor VIII but also suggest that besides depletion of factor VIII in plasma, platelets were impaired In the interaction with factor VIII in vW disease. This defect in platelets itself may involve the bleeding of this disease.