VWF and thrombotic thrombocytopenic purpura: Currently, the prevailing opinion is that the cause of TTP is multifactorial, including extensive injury of the vascular endothelium, reduced prostacyclin concentration in blood, and the formation of von Willebrand factor (VWF) multimers due to impaired cleavage of ultra-large von Willebrand factor (UL-VWF), in addition to the damaging effects of autoantibodies and oxidants that promote platelet activation.