Von Willebrand factor: another janus-faced hemostasis protein.

von Willebrand factor (VWF) is a multimeric plasma protein that mediates platelet adhesion and aggregation at sites of vascular injury and also acts as a protective carrier of factor VIII. Although the acquired or inherited deficiency of VWF is associated with a bleeding tendency, there is increasing evidence that VWF also plays a pivotal role in thrombosis. The presence in plasma of unusually large VWF multimers, due to the congenital or acquired deficiency of the VWF-cleaving metalloproteinase ADAMTS13, has been implicated in the pathogenesis of thrombotic thrombocytopenic purpura. In addition, high plasma levels of VWF have been associated with an increased risk of atherothrombosis. The current article reviews the literature and provides evidence for the two-faced character that VWF therefore represents.