ORIGINAL ARTICLESSole existence of antithrombin antibody in patients with systemic lupus erythematosus showing tendency of its antigenic determinants directing against exosite II (antithrombin/heparin binding site) of thrombinMatsuda, Juzoa,b; Matsuyama, Atsushia; Atsumi, Genb; Ohkura, NaokibAuthor Information aDepartment of Medicine, Teikyo University School of Medicine, Tokyo, Japan bDepartment of Clinical Molecular Biology, Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan Received 30 March, 2007 Revised 25 September, 2007 Accepted 26 September, 2007 Correspondence to Juzo Matsuda, MD, Department of Medicine, Teikyo University School of Medicine, 11-1 Kaga 2-Chome, Itabashi-Ku, Tokyo 173-8605, Japan Tel: +81 3964 4146; fax:+81 5375 1308; e-mail: email@example.com Blood Coagulation & Fibrinolysis: January 2008 - Volume 19 - Issue 1 - p 66-69 doi: 10.1097/MBC.0b013e3282f2b5a9 Buy Metrics Abstract We conducted an investigation to determine the antigenic determinants of antithrombin antibody (aThr), which has recently been recognized as a new antiphospholipid antibody mostly co-existing with antiprothrombin antibody, employing patients with systemic lupus erythematosus and antiphospholipid syndrome. Using an enzyme-linked immunosorbent assay we found aThr in 34 of 83 patients (40.9%), and 27 of these 34 patients (79.4%) with aThr were all negative for other antiphospholipid antibodies. An optical density value of six of 30 patients (20.0%) with aThr showed more than a 40% reduction of reactivity to thrombin with the addition of antithrombin in a dose-dependent manner. The inhibition percentage of aThr to thrombin was prominently increased to 11 of 30 (37%) along with its inhibition rate (100% at the highest) by the co-existence of heparin. Seven out of 30 patients with aThr (23.3%) showed a reduction of the optical density value with the addition of hirudin. Our findings suggest that aThr exists solely in patients with systemic lupus erythematosus without other antiphospholipid antibodies, and the antigenic determinants of aThr are directed to exosite I (hirudin binding site) and exosite II (antithrombin/heparin binding site) on the thrombin surface, with exosite II predominance. Accordingly, aThr could be an isolated and additional new marker of thrombosis/hemostasis. Since our patients who were positive only for aThr do not have a past history of antiphospholipid-associated complications at this stage, however, further long-term follow-up and additional studies in these clinical settings are needed to verify our hypothesis in the future. © 2008 Lippincott Williams & Wilkins, Inc.