Real-time analysis of mural thrombus formation in various platelet aggregation disorders: Distinct shear-dependent roles of platelet receptors and adhesive proteins under flow

We evaluated real-time processes of platelet thrombus formation on a collag en surface in a flow chamber with whole blood from patients with various pl atelet aggregation disorders, such as Bernard-Soulier syndrome (BSS), Glanz mann's thrombasthenia (GTA), type 3 von Willebrand disease (vWD), and conge nital afibrinogenemia (Af), who lack platelet glycoprotein (GP) Ib-IX compl ex, GP IIb-IIIa, von Willebrand factor (VWF), and fibrinogen, respectively. Blood from GTA patients showed impaired thrombus growth but significant in itial platelet-surface interaction under all shear conditions tested (50 to 1,500 s(-1)). By contrast, blood from patients with BSS or type 3 vWD show ed no platelet-surface interaction under high shear (greater than or equal to 1,210 s(-1)) but normal thrombus formation under low shear (less than or equal to 340 s(-1)). When shear rate was increased stepwise to 1,500 s(-1) during perfusion, the thrombus growth observed in type 3 vWD or BSS under low shear was arrested, whereas that in control blood was sharply accelerat ed as a function of shear rate. Overall thrombus formation in Af appeared i ndistinguishable from that of a control under shear rates between 50 and 1, 500 s(-1). However, Af thrombi formed under such conditions collapsed immed iately when shear rate was further increased to 4,500 s(-1), whereas thromb i of type 3 vWD or BSS formed under low shear were stable even when shear r ate was elevated to 9,000 s(-1) during perfusion. These findings suggest th at distinct molecular mechanisms underlie the pathologic bleeding in these diseases and point to the distinct roles of two major adhesive proteins, VW F and fibrinogen. In mural thrombus formation under flow conditions, vWF, p erhaps mainly through its interaction with GP Ib-IX, acts as an "initiator and promoter," whereas fibrinogen, via its binding to GP IIb-IIIa, acts as a "stabilizer" against heightened shear forces that could lead to peeling o ff of platelets from the surface. (C) 1999 by The American Society of Hemat ology.