ISOLATION AND CHARACTERIZATION OF AN ANTI-FACTOR VIII ANTIBODY FROM A PATIENT WITH ACQUIRED HEMOPHILIA
Abstract number: P-S-141
Bukys1 M.A., Simioni2 P., Smith1 K.M., Spiezia2 L., Kalafatis1 M.
11Chemistry, Cleveland State University, Cleveland, United States 22Medical and Surgical Sciences, University of Padua, Padua, Italy
How-to-cite Bukys MA, Simioni P, Smith KM, Spiezia L, Kalafatis M. ISOLATION AND CHARACTERIZATION OF AN ANTI-FACTOR VIII ANTIBODY FROM A PATIENT WITH ACQUIRED HEMOPHILIA. J Thromb Haemost 2007; 5 Supplement 2: P-S-141
Introduction: Patients with hemophilia A develop inhibitory antibodies to factor VIII (fVIII) that result in an hemorrhagic syndrome. However, in some cases individuals spontaneously develop autoantibodies to fVIII resulting in acquired hemophilia A.
Methods: A 78-year-old woman was admitted to the Internal Medicine Department of the University-Hospital of Padua for severe anaemia and syncope. She developed an acute hemorrhagic syndrome characterized by extended subcutaneous intramuscular haematomas on both legs. The patient's family history was negative for hemorrhagic manifestations. Preliminary laboratory analyses revealed a significant prolongation of the aPTT to 60 sec and a mild prolongation of the PT to 15 sec. Mixing experiments with normal plasma failed to correct the patient's aPTT. Plasma fVIII levels were ~6%. Assay for fVIII inhibitor revealed a level of 6 Bethesda Units (BU).
Results: The total immunoglobulin fraction was isolated from the patient's plasma and found to induce a prolongation of the clotting time in an aPTT assay. The immunoglobulin fraction was also found to inhibit intrinsic tenase activity in an assay using purified reagents and a chromogenic substrate that detects factor X (fX) activation. Immunoprecipitation experiments with the total immunoglobulins fraction purified from the patient's plasma revealed that the antibody recognizes epitopes on the light chain of the cofactor. Immunobloting experiments performed with the same material demonstrated that the antibody recognizes fVIII heavy and light chains. Following activation by thrombin it was found that the antibody recognizes the Mr 73,000 light chain and the A2 domain of the cofactor.
Conclusions: These data demonstrate that the immunoglobulin fraction isolated from the patient's plasma has more than one epitope on the cofactor. We have thus identified an anti-fVIII acquired autoantibody with low titer which is not related to the presence of antiphospholipid antibodies and is responsible for a severe hemorrhagic syndrome.
To cite this abstract use the following format:
Journal of Thrombosis and Haemostasis 2007; Volume 5, Supplement 2: abstract number
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