EXTENDED REPORT High avidity anti-b2-glycoprotein I antibodies in patients with antiphospholipid syndrome

Objective: To evaluate avidity of IgG anti-b2-glycoprotein I antibodies (anti-b2-GPI) in patients with antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) in relation to thrombosis, and to demonstrate a possible affinity maturation of IgG anti-b2-GPI during the disease course. Methods: 64 sera from 32 patients (18 with primary or secondary APS, 14 with SLE without APS) and their respective IgG fractions or affinity purified anti-b2-GPI were studied by anticardiolipin (aCL) and anti-b2GPI enzyme linked immunosorbent assay and by chaotropic assay. Results: Six, 12, and 14 patients had high, low, and heterogeneous avidity IgG anti-b2-GPI, respectively. In 12 patients an increase in antibody avidity was observed over a period of between four and 12 years. More patients with APS were in the high avidity than in the low avidity anti-b2-GPI group, while the opposite was observed for SLE alone (both p,0.05). The most common clinical feature among patients with high avidity anti-b2-GPI was thrombosis, mainly venous thrombosis (p,0.05 and p,0.02, respectively, v the low avidity anti-b2-GPI group). Conclusions: Patients with APS with or without SLE may have anti-b2-GPI of high, low, or heterogeneous avidity. High avidity anti-b2-GPI appear to be associated with thrombosis and APS, while in pure SLE low avidity anti-b2-GPI may prevail. Monitoring of avidity may help elucidate the role of anti-b2-GPI affinity maturation in the pathogenesis of APS.