Distinguished effects of antiphospholipid antibodies and anti-oxidized LDL antibodies on oxidized LDL uptake by macrophages

Several interpretations have been made regarding the specificity of antiphospholipid antibodies and antibodies against oxidized low-density lipoprotein (oxLDL), but these are still controversial. In the present study, we delineated specificity of these two types of antibodies and analyzed their regulatory effect on oxLDL and/or β²-glycoprotein I (β²GPI) binding to macrophages. Scavenger receptor-mediated binding of oxLDL (or its β²GPI complexes) to macrophages was observed and the binding was partly prevented by β²GPI. The IgG monoclonal anti-β²GPI antibody (WB-CAL-1), which was derived from NZW X BXSB F1 mouse (a model of antiphospholipid syndrome), significantly increased the oxLDL/β²GPI binding to macrophages. In contrast, IgM anti-oxLDL natural antibody, EO6 (derived from apoe^-/- mouse), prevented the binding. Different antigenic specificity of these antibodies to oxLDL and its β²GPI complexes was also confirmed in TLC-ligand blot and ELISA. Thus, IgG anti-β²GPI autoantibodies contribute to lipid metabolism (housekeeping of oxLDL by macrophages) whereas IgM natural anti-oxLDL antibodies may protect against atherogenesis. In addition, in vitro data suggest that relatively high dose of intravenous immunoglobulin preparations (mainly contain IgG anti-oxLDL antibodies) might also prevent atherogenesis by inhibiting the oxLDL binding to macrophages.