Isotypes of anti-β₂-glycoprotein I antibodies: Association with thrombosis in patients with systemic lupus erythematosus

Objective. To evaluate the association between isotypes of anti-β₂-glycoprotein I antibodies (anti-β₂-GPI) and thrombosis and to identify antiphospholipid antibodies (aPL) that are most associated with thrombosis in patients with systemic lupus erythematosus (SLE). Methods. IgG anticardiolipin antibody (aCL) and isotypes of anti-β₂-GPI were measured by ELISA, and clinical evidence of thrombosis was analyzed in 270 patients with SLE. Results. IgG, IgM, and IgA anti-β₂-GPI were positive in 38.1, 13.7, and 34.8% of patients, respectively. Patients with a history of thrombosis were significantly more likely to have lupus anticoagulant (LAC), IgG aCL, and the 3 anti-β₂-GPI isotypes. Arterial thrombosis was associated with the presence of IgG aCL and the 3 anti-β₂-GPI isotypes, whereas venous thrombosis was associated with LAC, IgG aCL, and IgA anti-β₂-GPI. In stepwise multivariate logistic regression analysis, the variable that was associated with thrombosis was IgA anti-β₂-GPI. The occurrence of arterial thrombosis was associated with IgG aCL and that of venous thrombosis was related to IgA anti-β₂-GPI in stepwise multivariate analysis. The IgG, IgM, and IgA anti-β₂-GPI titers were closely correlated with IgG aCL titers. The IgA anti-β₂-GPI titers were also significantly correlated with those of IgG and IgM anti-β₂-GPI. Conclusion. The results suggest that anti-β₂-GPI isotypes are related to the occurrence of thrombosis, and measurements of IgA anti-β₂-GPI may be useful for predicting thrombotic episodes in patients with SLE.