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

• Published in: The Journal of clinical investigation 1999-01, Vol.103 (1), p.117-128
• Main Authors: Hörkkö, S, Bird, D A, Miller, E, Itabe, H, Leitinger, N, Subbanagounder, G, Berliner, J A, Friedman, P, Dennis, E A, Curtiss, L K, Palinski, W, Witztum, J L
• Format: Article
• Language: English
• Subjects: Animals; Antibodies, Monoclonal - immunology; Antibodies, Monoclonal - metabolism; Apolipoproteins E - deficiency; Apolipoproteins E - genetics; Autoantibodies - immunology; Autoantibodies - metabolism; Copper - pharmacology; Emulsions - metabolism; Epitopes - immunology; Immunoglobulin Fab Fragments - immunology; Immunoglobulin Fab Fragments - metabolism; Lipid Peroxides - immunology; Lipoproteins, LDL - immunology; Lipoproteins, LDL - metabolism; Liposomes - immunology; Liposomes - metabolism; Macrophages, Peritoneal - metabolism; Mice; Phospholipids - immunology; Protein Binding
• ISSN: 0021-9738
• DOI: 10.1172/jci4533

We recently cloned monoclonal IgM autoantibodies which bind to epitopes of oxidized low-density lipoprotein (OxLDL) from apoE-deficient mice (EO- autoantibodies). We now demonstrate that those EO- autoantibodies that were originally selected for binding to copper-oxidized low-density lipoproteins (CuOx-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 (OxPAPC) and to the specific oxidized phospholipid, 1-palmitoyl-2-(5-oxovaleroyl)-phosphatidyl-choline (POVPC), whereas oxidation of fatty acids (linoleic or arachidonic acid) or cholesteryl esters (cholesteryl-oleate or cholesteryl-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 macrophages. F(ab')2 fragments of EO6 were equally effective as the intact EO6 in preventing the binding of CuOx-LDL by macrophages. The molar ratios of IgM to LDL needed to maximally inhibit the binding varied from approximately 8 to 25 with different CuOx-LDL preparations. Finally, a POVPC-bovine serum albumin (BSA) adduct also inhibited CuOx-LDL uptake by macrophages. These data suggest that oxidized phospholipid epitopes, present either as lipids or as lipid-protein adducts, represent one class of ligands involved in the recognition of OxLDL by macrophages, and that apoE-deficient mice have IgM autoantibodies that can bind to these neoepitopes and inhibit OxLDL uptake.