Monoclonal autoantibodies specific for oxidized phospholipids or oxidized phospholipid-protein adducts inhibit macrophage uptake of oxidized low-density lipoproteins

We recently cloned monoclonal IgM autoantibodies which bind to epitopes of oxidized low-density lipoprotein (OxLDL) from apoE-deficient mice (EO- auto antibodies). We now demonstrate that those EO- autoantibodies that were ori ginally selected for binding to copper-oxidized low-density Lipoproteins (C uOx-LDL), also bound both to the oxidized protein and to the oxidized Lipid moieties of CuOx-LDL. The same EO- autoantibodies showed specific binding to products of oxidized 1-palmitoyl-2-arachidonoyl-phosphatidylcholine (OxP APC) and to the specific oxidized phospholipid, 1-palmitoyl-2-(5-oxovaleroy l)-phosphatidyl-choline (POVPC), whereas oxidation of fatty acids (linoleic or arachidonic acid) or cholesteryl eaters (cholesteryl-oleate or choleste ryl-linoleate) did not yield any binding activity. Those EO- autoantibodies that bound to oxidized phospholipids (e.g., EO6) inhibited the binding and degradation of CuOx-LDL by mouse peritoneal macrophages up to 91%, whereas other IgM EO- autoantibodies, selected for binding to malondialdehyde (MDA )-LDL, had no influence on binding of either CuOx-LDL or MDA-LDL by macroph ages. F(ab')(2) fragments of EO6 were equally effective as the intact EO6 i n preventing the binding of CuOx-LDL by macrophages. The molar ratios of Ig M to LDL needed to maximally inhibit the binding varied from similar to 8 t o 25 with different CuOx-LDL preparations. Finally, a POVPC-bovine serum al bumin (BSA) adduct also inhibited CuOx-LDL uptake by macrophages. These dat a suggest that oxidized phospholipid epitopes, present either as lipids or as lipid-protein adducts, represent one class of ligands involved in the re cognition of OxLDL by macrophages, and that apoE-deficient mice have IgM au toantibodies that can bind to these neoepitopes and inhibit OxLDL uptake.