THE ROLE OF PLATELET VON-WILLEBRAND-FACTOR IN PLATELET-ADHESION AND THROMBUS FORMATION - A STUDY OF 34 PATIENTS WITH VARIOUS SUBTYPES OF TYPE-I VON-WILLEBRAND DISEASE

In order to investigate the respective role of plasma and platelet von Willebrand factor (vWF) in mediating platelet adhesion and thrombus f ormation, we performed ex vivo perfusion studies with native blood fro m patients with various subtypes of type I von Willebrand disease (vWD ). We studied 34 patients with type I vWD (19 'platelet normal', five 'platelet low', two 'platelet discordant', eight 'Vicenza'). Parallel studies were carried out on nine patients with severe vWD (type III). At high shear rate (2600 s(-1)) we found that the defect in platelet-v essel wall interactions in patients having a normal platelet VWF conte nt ('platelet normal' and 'Vicenza') involved thrombus formation, wher eas platelet adhesion was normal. At this high shear rate, platelet ad hesion and thrombus volume were significantly decreased in patients wi th subtypes 'platelet low' and 'platelet discordant', i.e. when platel et vWF is either low or dysfunctional. These results indicate that pla telet vWF may substitute for plasma vWF to promote platelet adhesion, emphasizing the important role of platelet vWF. They also confirm the role of VWF in thrombus formation at high shear rate because an abnorm al thrombus volume was observed in all patients, even when platelet ad hesion was normal.