INCREASED LEVELS OF BETA(2) GLYCOPROTEIN-I ANTIGEN AND BETA(2) GLYCOPROTEIN-I BINDING-ANTIBODIES ARE ASSOCIATED WITH A HISTORY OF THROMBOEMBOLIC COMPLICATIONS IN PATIENTS WITH SLE AND PRIMARY ANTIPHOSPHOLIPID SYNDROME

beta(2) Glycoprotein-I (beta(2)GPI), a plasma component with in vitro anticoagulant properties, has been identified as a cofactor for the bi nding of some antiphospholipid antibodies (aPAs). In order to determin e whether beta(2)GPI changes were associated with the thromboembolic c omplications of aPAs, we measured beta(2)GPI antigen (beta(2)GPI:Ag), beta(2)GPI aPA cofactor activity (beta(2)GPI:Cof) and antibodies to be ta(2)GPI (alpha beta(2)GPI) in 44 systemic lupus erythematosus (SLE) p atients, of whom 19 had evidence of aPAs (SLE-aPA+) and 17 patients wi th primary antiphospholipid syndrome (PaPS). beta(2)GPI:Ag levels were significantly increased in SLE-aPA+ patients and PaPS patients compar ed with SLE-aPA- patients and normal healthy controls. The ratio of be ta(2)GPI:Cof/Ag was significantly reduced in SLE-aPA+ patients compare d with SLE-aPA- patients, indicating functional modification of beta(2 )GPI in SLE-aPA+ patients. Eighty per cent of patients with anticardio lipin (aCL) IgG also had alpha beta(2)GPI, and 13% patients with no de tectable aCL IgG had alpha beta(2)GPI. Increased beta(2)GPI:Ag and alp ha beta(2)GPI were associated with a clinical history of thrombosis or recurrent fetal loss. The results of these investigations suggest tha t beta(2)GPI may play a role in the pathogenic mechanism of thrombosis associated with aPAs.