Oxidation-specific epitopes are important targets of innate immunity.
During the oxidation of LDL, a central pathophysiological component of atherogenesis, a wide variety of chemical and physical changes occur leading to the generation of oxidation-specific neoepitopes. These epitopes are not only immunogenic, leading to adaptive humoral responses, but are also a prominent target of multiple arcs of innate immunity. The pattern recognition receptors (PRRs) of innate immunity are germ line encoded, conserved by natural selection, and bind to pathogen-associated molecular patterns (PAMPs) common on multiple structures. However, it is not intuitive as to why they should recognize oxidation-specific neoepitopes. Yet it is clear that multiple macrophage scavenger receptors, which are classic PRRs, recognize oxidation-specific epitopes, such as those found on oxidized LDL (OxLDL). Other innate proteins, such as C-reactive protein, also bind to OxLDL. Natural antibodies (NAbs), the humoral arc of innate immunity, provide a nonredundant role in the first line of defence against pathogens, but are also believed to provide important homeostatic house-keeping functions against self-antigens. Our work demonstrates that oxidation-specific epitopes, as found on OxLDL, are a major target of NAbs. In this review, we will discuss the specific example of the prototypic NAb T15/E06, which is increased in atherosclerotic mice and mediates atheroprotection, and discuss the potential role of NAbs in atherogenesis, and in inflammation in general. We also review data that oxidation-specific epitopes are generated whenever cells undergo programmed cell death, forming a common set of PAMPs recognized by oxidation-specific PRRs on macrophages, NAbs and innate proteins. We present the hypothesis that oxidation-specific epitopes on apoptotic cells exerted evolutionary pressure for the conservation of these PRRs and also serve to maintain the expansion of a substantial proportion of NAbs directed to these stress-induced self-antigens.
Chou
M-Y
MY
Department of Medicine, University of California at San Diego, La Jolla, CA, USA.
Hartvigsen
K
K
Hansen
L F
LF
Fogelstrand
L
L
Shaw
P X
PX
Boullier
A
A
Binder
C J
CJ
Witztum
J L
JL
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D050197:Atherosclerosis / Q000276:immunology* / Q000503:physiopathology; D001402:B-Lymphocytes / Q000276:immunology; D000939:Epitopes / Q000096:biosynthesis / Q000276:immunology*; D007113:Immunity, Innate / Q000276:immunology*; D007075:Immunoglobulin M / Q000276:immunology; D008077:Lipoproteins, LDL; D051379:Mice; D011817:Rabbits; D051192:Receptors, Pattern Recognition
D000939:Epitopes; D007075:Immunoglobulin M; D008077:Lipoproteins, LDL; D051192:Receptors, Pattern Recognition; C099252:oxidized low density lipoprotein