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During the progression of atherosclerosis, autoantibodies are induced to epitopes of oxidized low-density lipoprotein (oxLDL) and active immunization of hypercholesterolemic mice with oxLDL ameliorates atherogenesis. We unexpectedly found that many autoantibodies to oxLDL derived from 'naive' atherosclerotic mice share complete genetic and structural identity with antibodies from the classic anti-phosphorylcholine B-cell clone, T15, which protect against common infectious pathogens, including pneumococci. To investigate whether in vivo exposure to pneumococci can affect atherogenesis, we immunized Ldlr(-/-) mice with Streptococcus pneumoniae. This induced high circulating levels of oxLDL-specific IgM and a persistent expansion of oxLDL-specific T15 IgM-secreting B cells primarily in the spleen, which were cross-reactive with pneumococcal determinants. Pneumococcal immunization decreased the extent of atherosclerosis, and plasma from these mice had an enhanced capacity to block the binding of oxLDL to macrophages. These studies show molecular mimicry between epitopes of oxLDL and S. pneumoniae and indicate that these immune responses can have beneficial effects.

C-reactive protein (CRP) is an acute-phase protein that binds specifically to phosphorylcholine (PC) as a component of microbial capsular polysaccharide and participates in the innate immune response against microorganisms. CRP elevation also is a major risk factor for cardiovascular disease. We previously demonstrated that EO6, an antioxidized LDL autoantibody, was a T15 clono-specific anti-PC antibody and specifically binds to PC on oxidized phosphatidylcholine (PtC) but not on native PtC. Similarly, EO6 binds apoptotic cells but not viable cells. In addition, such oxidized phospholipids are recognized by macrophage scavenger receptors, implying that these innate immune responses participate in the clearance because of their proinflammatory properties. We now report that CRP binds to oxidized LDL (OxLDL) and oxidized PtC (OxPtC), but does not bind to native, nonoxidized LDL nor to nonoxidized PtC, and its binding is mediated through the recognition of a PC moiety. Reciprocally, CRP binds to PC, which can be competed for by OxLDL and OxPtC but not by native LDL, nonoxidized PtC, or by oxidized phospholipids without the PC headgroup. CRP also binds to apoptotic cells, and this binding is competed for by OxLDL, OxPtC, and PC. These data suggest that CRP binds OxLDL and apoptotic cells by recognition of a PC moiety that becomes accessible as a result of oxidation of PtC molecule. We propose that, analogous to EO6 and scavenger receptors, CRP is a part of the innate immune response to oxidized PC-bearing phospholipids within OxLDL and on the plasma membranes of apoptotic cells.atherosclerosis ͉ innate immunity ͉ scavenger receptors ͉ autoantibody EO6

Apoptosis is recognized as important for normal cellular homeostasis in multicellular organisms. Although there have been great advances in our knowledge of the molecular events regulating apoptosis, much less is known about the receptors on phagocytes responsible for apoptotic cell recognition and phagocytosis or the ligands on apoptotic cells mediating such recognition. The observations that apoptotic cells are under increased oxidative stress and that oxidized low-density lipoprotein (OxLDL) competes with apoptotic cells for macrophage binding suggested the hypothesis that both OxLDL and apoptotic cells share oxidatively modified moieties on their surfaces that serve as ligands for macrophage recognition. To test this hypothesis, we used murine monoclonal autoantibodies that bind to oxidation-specific epitopes on OxLDL. In particular, antibodies EO6 and EO3 recognize oxidized phospholipids, including 1-palmitoyl 2-(5-oxovaleroyl) phosphatidylcholine (POVPC), and antibodies EO12 and EO14 recognize malondialdehydelysine, as in malondialdehyde-LDL. Using FACS analysis, we demonstrated that each of these EO antibodies bound to apoptotic cells but not to normal cells, whereas control IgM antibodies did not. Confocal microscopy demonstrated cell-surface expression of the oxidation-specific epitopes on apoptotic cells. Furthermore, each of these antibodies inhibited the phagocytosis of apoptotic cells by elicited peritoneal macrophages, as did OxLDL. In addition, an adduct of POVPC with BSA also effectively prevented phagocytosis. These data demonstrate that apoptotic cells express oxidation-specific epitopes-including oxidized phospholipids-on their cell surface, and that these serve as ligands for recognition and phagocytosis by elicited macrophages.