Adhesion of human platelets to purified solid-phase von Willebrand factor: studies of normal and Bernard-Soulier platelets.

ABSTRACT

Human Factor VIII associated von Willebrand factor (VIIIvWF) binds to human platelets in vitro only in the presence of a mediator such as ristocetin, thrombin or ADP. Studies reported here were designed to determine if human platelets will adhere to solid-phase VIIIvWF. Human VIIIvWF was purified from a phosphate precipitate of A1(OH)3 absorbed plasma using 4% agarose and DEAE cellulose. Purified VIIIvWF (90 units of VIIIvWF activity/mg) was coated on dialysis membranes using ultrafiltration (final concentration of 0.4 units/cm2). Membranes (0.5 cm2) were held stationary in human citrated PRP suspension or washed platelet suspensions and stirred continuously for 5 minutes at 37 degrees C. The membranes were then rinsed in phosphate buffered saline, fixed, stained, and examined by light and scanning electron microscopy. Abundant normal platelets adhered to VIIIvWF-coated membranes, while minimal adhesion was seen on uncoated membranes and membranes coated with albumin. Adhesion occurred without ristocetin, thrombin, ADP or other agonist and in the presence of Ca+2/Mg+2 ions. Preincubation of the VIIIvWF coated membranes with monospecific rabbit anti-VIIIvWF inhibited the adhesion reaction. However, preincubation of VIIIvWF coated membranes with naturally occurring human anti-FVIIIc antibodies failed to interfere with platelet adhesion. Platelets from a patient with Bernard-Soulier Syndrome (BSS) which did not bind human VIIIvWF in the presence of ristocetin or aggregate with bovine cryoprecipitate also did not adhere to VIIIvWF-coated membranes.