Acquired thrombotic thrombocytopenic purpura(TTP), characterized by widespread thrombus formation in the microcirculation, is a ponderous complication of antiphospholipid syndrome. Recently, von Willebrand factor-cleaving protease(VWF-CPase) activity has been reported as a possible determinant for the occurrence of TTP. To clarify the role of VWF-CPase in the thrombus formation associated with antiphospholipid syndrome, we investigated plasma VWF-CPase activity in patients of collagen diseases with lupus anticoagulant(LA).
Decreased plasma VWF-CPase activity less than 50% of the normal activity was observed in 25.7%(n＝18) in 70 patients with collagen diseases and 7(10%) cases of them showed more lower VWF-CPase activity less than 25%. The IgG fractions obtained from 2 patients with the low VWF-CPase activity strongly inhibited the proteolytic reaction of normal VWF-CPase. There was no significant relationship between LA and plasma VWF-CPase activity. Thrombotic episodes, especially arterial thrombosis, were more frequently observed in LA-positive patients with low VWF-CPase activity. These results suggest that decreased activity of VWF-CPase, partly due to IgG type inhibitor to the enzyme activity may be an additional risk factor for arterial thrombosis in collagen disease patients with antiphospholipid antibodies.

*1Department of Clinical Laboratory, St. Marianna University School of Medicine Hospital, Kawasaki 216-8511

【Key Words】Von Willebrand factor cleaving protease: VWF-CPase, antiphospholipid antibodies: APA, Thrombotic thrombocytopenic purpura: TTP