von Willebrand factor in the pathophysiology of thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a disorder of systemic platelet aggregation. Evidence has accumulated that the aggregating agonist in TTP of all types is likely to be von Willebrand factor, especially unusually large von Willebrand factor multimers derived from endothelial cells. Recent evidence indicates that a metalloproteinase involved in von Willebrand factor breakdown is not present in adequate amounts in children with chronic relapsing TTP. Chronic relapsing TTP is, therefore, likely to be a congenital deficiency of von Willebrand factor metalloproteinase. In adults with single episode or intermittent types of TTP, the von Willebrand factor metalloproteinase is inhibited by autoantibodies that are present either transiently or intermittently in patient blood. Single episode and intermittent types of TTP in adults are, therefore, autoimmune processes of a short-term and recurrent nature, respectively.