Avidity of anti-β2-glycoprotein I and thrombosis or pregnancy loss in patients with antiphospholipid syndrome

We aimed to evaluate avidity of anti-beta(2)-glycoprotein I antibodies (anti-beta(2)-GPIs) in patients with anti phospholipid syndrome (APS) at the time of acute thrombotic events or pregnancy loss as compared with clinical eventfree periods. To do so, 69 sera samples from 16 patients (6 with primary APS and 10 with APS secondary to systemic lupus erythematosus) were selected on the basis of anti-beta(2)-GPI positivity. Avidity of IgG anti-beta(2)-GPIs was determined by chaotropic enzyme-linked immunosorbent assay (ELISA), using increased NaCl concentration during antibody binding. High, heterogeneous, and low-avidity anti-beta(2)-GPIs were measured in APS patients, with no clear pattern regarding the time of thrombotic events or pregnancy failure. In general, anti-beta(2)-GPI avidity did not change substantially during disease course. We concluded that avidity of anti-beta(2)-GPIs appears to be a rather stable parameter in an individual APS patient. Considering the previously shown association of high-avidity anti-beta(2)-GPIs with venous thrombosis, avidity of anti-beta(2)-GPIs may be a better predictor of predisposition to thrombosis and unsuccessful pregnancy than levels of anti phospholipid antibodies, which may fluctuate over time owing to several factors.