PATHOPHYSIOLOGY OF ANTIPROTHROMBIN AUTOANTIBODIES

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Antiphospholipid antibodies (Apl) are immunoglobulins associated with a variety of clinical phenomena, including arterial and venous thrombosis. The term "antiphospholipid syndrome" (APS) is used to link these clinical manifestations to the persistence of Apl. Autoantibody against prothrombin is one of the most common and potent aPLs associated with vascular diseaeses. It has been shown that phosphatidylserine dependent antiprothrombin antibodies (Aps/PT) is a specific marker of APS and highly correlate with the presence of lupus anticoagulant. I raised mouse monoclonal Aps/PT (231D), which had high binding to phosphatidylserine-prothrombin complex but little binding to immobilized prothrombin directly on irradiated ELISA plates. This property was similar to autoimmune Aps/PT found in patients with APS. Normal plasma mixed with 231D had prolonged clotting time in a dose dependent fashion, and the excess of phospholipid reduced the prolongation of clotting time, thus 231D had a strong LA activity. In this study, I established a semiquantitative LA assay using 23ID as a standard. I showed that our semi-quantitative LA assay is simple and useful for the diagnosis of LA with very high sensitivity, thus this method is practical for the first screening for APS.In addition, I investigated the epitope of aPS/PT on prothrombin molecule. I digested andpurified prothrombin fragments (F1 and F1+2) and studies the binding between phosphatidylserine-fragments complex and aPS/PT. No binding of aPS/PT was found and the epitope may be on prethrombin side or comformational. In the next experiments, I shall prepare recombinant prothrombin and its mutant to investigate the importance of structure of prothrombin molecule.