Oxidized Low-Density Lipoprotein/β₂-Glycoprotein I Complexes and Autoantibodies to oxLig-1/β₂-Glycoprotein I in Patients with Systemic Lupns Erythematosus and Antiphospholipid Syndrome

Oxidized low-density lipoprotein (oxLDL) interacts with β ₂-glycoprotein I (β₂-GPI) via oxLDL-derived specific ligands (oxLig-1) forming complexes. The prevalence and significance of oxLDL/β₂-GPI complexes and antibodies to oxLig-1/β ₂-GPI were evaluated in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The oxLDL/β₂-GPI complex was 69% positive (above mean + 3 SD of control subjects) in 97 consecutive patients with SLE, 62% in 40 patients with SLE with secondary APS, and 60% in 50 control patients with SLE without APS. IgG anti-oxLig-1/β ₂-GPI antibody was positive in 31 (32%) of 97 consecutive patients with SLE, in 26 (65%) of 40 patients with SLE with secondary APS, and in 6 (19%) of 32 control patients with SLE. Anti-oxLig-1/β₂-GPI antibodies were 93.7% specific with a positive predictive value of 90.0% for APS, better than anticardiolipin antibodies (80.0% specific, 71.4% predictive value). These results confirm that oxLDL/β₂-GPI complexes are common in SLE and suggest a possible immunogenic role in APS. In contrast, IgG anti-oxLig-1/β2-GPI antibodies not only are associated with but also are clinically useful risk factors for APS.