IgG Autoantibodies against β₂-Glycoprotein I Complexed with a Lipid Ligand Derived from Oxidized Low-Density Lipoprotein are Associated with Arterial Thrombosis in Antiphospholipid Syndrome

We recently reported [J. Lipid Res. 42 (2001), 697; 43 (2002), 1486; 44 (2003), 716] that β₂-glycoprotein I (β₂GPI) forms complexes with oxidized LDL (oxLDL) and autoantibodies against these complexes are present in patients with SLE and antiphospholipid syndrome (APS). The relationship of β₂GPI/oxLDL complexes and IgG autoantibodies against β₂GPI complexed with oxLig-1 I (an oxLDL-derived defived ligand) with clinical manifestations of APS was studied in 150 APS and SLE patients. The β₂GPI/oxLDL levels of APS patients were similar to those of SLE patients without APS, but they were significantly higher than healthy individuals. There was no difference in the complex levels among the patients with arterial, venous thrombosis, or pregnancy morbidity. IgG anti-β₂GPI/oxLig-1 levels of APS were significantly higher than those of SLE without APS and healthy individuals. Further, antibody levels of APS patients with arterial thrombosis were significantly higher than those patients with venous thrombosis and pregnancy morbidity. Thus, oxidation of LDL leads the complex formation with β ₂GPI in SLE and APS patients. In contrast, anti-β ₂GPI/oxLig-1 autoantibodies were generated only in APS and were strongly associated with arterial thrombosis. These results suggest that autoantibodies against β₂GPI/oxLDL complexes are etiologically important in the development of atherosclerosis in APS.