Antibodies to β₂-glycoprotein I and clinical manifestations in patients with systemic lupus erythematosus

Objective. To investigate whether anticardiolipin antibodies (aCL) in patients with systemic lupus erythematosus (SLE) bind to β₂-glycoprotein I (β₂GPI), and to search for a relationship between the presence of IgG and/or IgM anti-β₂GPI antibody and clinical manifestations in SLE patients. Methods. IgG and IgM anti-β₂GPI in 308 Japanese SLE patients were measured using phospholipid-independent enzyme immunoassays. Relationships to clinical histories and to various laboratory data were examined. Results. The values of anti-β₂GPI and aCL, as measured by conventional enzyme immunoassay, showed a strong correlation, but the anti-β₂GPI assay was more useful in distinguishing β₂GPI-dependent aCL from β₂GPI-independent aCL. The presence of IgG anti-β₂GPI was associated with an increased frequency of a history of thrombosis. Comparisons of various laboratory data suggested that the titer of anti-β₂GPI may fluctuate with disease activity. Conclusion. The results suggest that pathogenic aCL is directed against structurally altered β₂GPI and that enzyme immunoassay for anti-β₂GPI may prove useful in evaluating the risk of thrombosis and monitoring the clinical course in patients with SLE.