Autoantibodies to OxLDL fail to alter the clearance of injected OxLDL in apolipoprotein E-deficient mice

Lipoproteins as targets and markers of lipoxidation

Lipoproteins are essential systemic lipid transport particles, composed of apolipoproteins embedded in a phospholipid and cholesterol monolayer surrounding a cargo of diverse lipid species. Many of the lipids present are susceptible to oxidative damage by lipid peroxidation, giving rise to the formation of reactive lipid peroxidation products (rLPPs). In view of the close proximity of the protein and lipid moieties within lipoproteins, the probability of adduct formation between rLPPs and amino acid residues of the proteins, a process called lipoxidation, is high. There has been interest for many years in the biological effects of such modifications, but the field has been limited to some extent by the availability of methods to determine the sites and exact nature of such modification. More recently, the availability of a wide range of antibodies to lipoxidation products, as well as advances in analytical techniques such as liquid chromatography tandem mass spectrometry (LC-MSMS), have increased our knowledge substantially. While most work has focused on LDL, oxidation of which has long been associated with pro-inflammatory responses and atherosclerosis, some studies on HDL, VLDL and Lipoprotein(a) have also been reported. As the broader topic of LDL oxidation has been reviewed previously, this review focuses on lipoxidative modifications of lipoproteins, from the historical background through to recent advances in the field. We consider the main methods of analysis for detecting rLPP adducts on apolipoproteins, including their advantages and disadvantages, as well as the biological effects of lipoxidized lipoproteins and their potential roles in diseases.

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Lipoproteins can be modified by reactive Lipid Peroxidation Products (rLPPs).

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Lipoprotein lipoxidation is known to occur in several inflammatory diseases.

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Biochemical, immunochemical and mass spectrometry methods can detect rLPP adducts.

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Due to higher information output, MS can facilitate localization of modifications.

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Antibodies against some rLPPs have been used to identify lipoxidation in vivo.

Adaptive (T and B cells) immunity and control by dendritic cells in atherosclerosis

Chronic inflammation in response to lipoprotein accumulation in the arterial wall is central in the development of atherosclerosis. Both innate and adaptive immunity are involved in this process. Adaptive immune responses develop against an array of potential antigens presented to effector T lymphocytes by antigen-presenting cells, especially dendritic cells. Functional analysis of the role of different T-cell subsets identified the Th1 responses as proatherogenic, whereas regulatory T-cell responses exert antiatherogenic activities. The effect of Th2 and Th17 responses is still debated. Atherosclerosis is also associated with B-cell activation. Recent evidence established that conventional B-2 cells promote atherosclerosis. In contrast, innate B-1 B cells offer protection through secretion of natural IgM antibodies. This review discusses the recent development in our understanding of the role of T- and B-cell subsets in atherosclerosis and addresses the role of dendritic cell subpopulations in the control of adaptive immunity.

Protective autoantibodies in the rheumatic diseases: lessons for therapy

The adaptive immune system augments host defenses against diverse infectious threats, yet also carries intertwined risks for the development of autoimmune disease. The immune system incorporates homeostatic pathways for essential housekeeping functions that involve recognition of oxidation-modified endogenous molecules. Now, the properties of a physiological class of natural autoantibodies, which seem to modulate the severity or even prevent the onset of autoimmune disease, are beginning to be defined. Whereas disease-associated IgG autoantibodies to nuclear antigens and citrulline-modified self-proteins have been shown to activate innate pattern recognition receptors leading to increased cell death and tissue injury, a class of IgM autoantibodies to oxidation-associated neo-antigens can oppose these pathogenic effects. These naturally arising regulatory IgM autoantibodies enhance the capacity for the phagocytic clearance of host cells affected by programmed death pathways. These antibodies can also suppress key signalling pathways in the innate immune system involved in the control and resolution of inflammatory responses to Toll-like receptor agonists and disease-associated IgG autoantibodies.

Natural IgM in immune equilibrium and harnessing their therapeutic potential

Natural IgM Abs are the constitutively secreted products of B1 cells (CD5(+) in mice and CD20(+)CD27(+)CD43(+)CD70(-) in humans) that have important and diverse roles in health and disease. Whereas the role of natural IgM as the first line of defense for protection against invading microbes has been extensively investigated, more recent reports have highlighted their potential roles in the maintenance of tissue homeostasis via clearance of apoptotic and altered cells through complement-dependent mechanisms, inhibition of inflammation, removal of misfolded proteins, and regulation of pathogenic autoreactive IgG Abs and autoantibody-producing B cells. These observations have provided the theoretical underpinnings for efforts that currently seek to harness the untapped therapeutic potential of natural IgM either by boosting in vivo natural IgM production or via therapeutic infusions of monoclonal and polyclonal IgM preparations.

Regulation of dendritic cells and macrophages by an anti-apoptotic cell natural antibody that suppresses TLR responses and inhibits inflammatory arthritis

Although natural Abs (NAbs) are present from birth, little is known about what drives their selection and whether they have housekeeping functions. The prototypic T15-NAb, first identified because of its protective role in infection, is representative of a special type of NAb response that specifically recognizes and forms complexes with apoptotic cells and which promotes cell-corpse engulfment by phagocytes. We now show that this T15-NAb IgM-mediated clearance process is dependent on the recruitment of C1q and mannose-binding lectin, which have known immune modulatory activities that also provide "eat me" signals for enhancing phagocytosis. Further investigation revealed that the addition of T15-NAb significantly suppressed in vitro LPS-induced TNF-alpha and IL-6 secretion by the macrophage-like cell line, RAW264.7, as well as TLR3-, TLR4-, TLR7-, and TLR9-induced maturation and secretion of a range of proinflammatory cytokines and chemokines by bone marrow-derived conventional dendritic cells. Significantly, high doses of this B-1 cell produced NAb also suppressed in vivo TLR-induced proinflammatory responses. Although infusions of apoptotic cells also suppressed such in vivo inflammatory responses and this effect was associated with the induction of high levels of IgM antiapoptotic cell Abs, apoptotic cell treatment was not effective at suppressing such TLR responses in B cell-deficient mice. Moreover, infusions of T15-NAb also efficiently inhibited both collagen-induced arthritis and anti-collagen II Ab-mediated arthritis. These studies identify and characterize a previously unknown regulatory circuit by which a NAb product of innate-like B cells aids homeostasis by control of fundamental inflammatory pathways.

RAGE mediates oxidized LDL-induced pro-inflammatory effects and atherosclerosis in non-diabetic LDL receptor-deficient mice

AIMS

Receptor for advanced glycation end products (RAGE) plays a pivotal role in the genesis of diabetic vascular diseases. To further explore the mechanisms underlying atherosclerosis under non-diabetic conditions, we examined the effect of RAGE deficiency on atherosclerosis in hyperlipidaemic mice.

METHODS AND RESULTS

RAGE-/- mice were crossed with low-density lipoprotein receptor-deficient (LDLr-/-) mice to generate the double knockout (DKO) mice. After feeding with high-fat diet for 12 weeks, aortic atherosclerotic lesions were analysed histologically in these mice. Although there were no differences in serum levels of glucose and known RAGE ligands between DKO and LDLr-/- mice, DKO mice exhibited a significant decrease in the size and macrophage content in atherosclerotic lesions compared with LDLr-/- mice. Expression of intracellular adhesion molecule-1 and vascular cell adhesion molecule-1 in the aorta was lower in DKO mice than in LDLr-/- mice. Fluorescence-based assays revealed that oxidative stress in the vessel wall was attenuated in DKO mice than in LDLr-/- mice. Cell culture experiments revealed that RAGE mediated oxidative LDL-induced activation of p42/44 mitogen-activated protein kinases and oxidative stress in macrophages.

CONCLUSION

Oxidative LDL may be a ligand of RAGE in the hyperlipidaemic state. RAGE inactivation inhibits the atherosclerosis through reducing oxLDL-induced pro-inflammatory responses and oxidative stress in hyperlipidaemia.

The role of oxidized phospholipids in mediating lipoprotein(a) atherogenicity

PURPOSE OF REVIEW

To review emerging data on the relationship between lipoprotein(a) and oxidized phospholipids.

RECENT FINDINGS

We have recently proposed that a unique physiological role of lipoprotein(a) may be to bind and transport proinflammatory oxidized phospholipids and that this interaction may mediate a common biological influence on cardiovascular disease. In a large series of clinical studies performed to date, a very strong correlation was found between plasma levels of lipoprotein(a) and the content of oxidized phospholipids on apolipoprotein B-100 particles (OxPL/apoB), measured by monoclonal antibody E06, which binds the phosphocholine head group of oxidized phospholipids but not native phospholipids. The correlation of OxPL/apoB to lipoprotein(a) is very strong in individuals with small apolipoprotein(a) isoforms (r = approximately 0.95) and modest in individuals with large isoforms (r = approximately 0.60). In-vitro studies have demonstrated that the vast majority of oxidized phospholipids detected by E06 are bound to lipoprotein(a) in human plasma. A similarly strong association with oxidized phospholipids was also documented in transgenic mice overexpressing lipoprotein(a), even in mice not fed atherogenic diets or with overt atherosclerosis.

SUMMARY

A better understanding of the ability of human lipoprotein(a) to bind oxidized phospholipids may allow clinically important insights into the role of oxidized phospholipids and lipoprotein(a) in human atherogenesis and cardiovascular disease and may provide novel diagnostic tools and therapeutic interventions aimed at measuring and treating elevated levels of OxPL/apoB and lipoprotein(a).

A novel function of lipoprotein [a] as a preferential carrier of oxidized phospholipids in human plasma

Oxidized phospholipids (OxPLs) on apolipoprotein B-100 (apoB-100) particles are strongly associated with lipoprotein [a] (Lp[a]). In this study, we evaluated whether Lp[a] is preferentially the carrier of OxPL in human plasma. The content of OxPL on apoB-100 particles was measured with monoclonal antibody E06, which recognizes the phosphocholine (PC) headgroup of oxidized but not native phospholipids. To assess whether OxPLs were preferentially bound by Lp[a] as opposed to other lipoproteins, immunoprecipitation and ultracentrifugation experiments, in vitro transfer studies, and chemiluminescent ELISAs were performed. Immunoprecipitation of Lp[a] from human plasma with an apolipoprotein [a] (apo[a])-specific antibody demonstrated that more than 85% of E06 reactivity (i.e., OxPL) coimmunoprecipitated with Lp[a]. Ultracentrifugation experiments showed that nearly all OxPLs were found in fractions containing apo[a], as opposed to other apolipoproteins. In vitro transfer studies showed that oxidized LDL preferentially donates OxPLs to Lp[a], as opposed to LDL, in a time- and temperature-dependent manner, even in aqueous buffer. Approximately 50% of E06 immunoreactivity could be extracted from isolated Lp[a] following exposure of plasma to various lipid solvents. These data demonstrate that Lp[a] is the preferential carrier of PC-containing OxPL in human plasma. This unique property of Lp[a] suggests novel insights into its physiological function and mechanisms of atherogenicity.

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.

A neutralizing antibody against receptor for advanced glycation end products (RAGE) reduces atherosclerosis in uremic mice

Chronic renal failure markedly accelerates atherogenesis in apolipoprotein E-deficient (apoE(-/-)) mice. To study the putative role of receptor for advanced glycation end products (RAGE) in development of uremic atherosclerosis, apoE(-/-) mice received intraperitoneal injections thrice weekly of a neutralizing murine RAGE-antibody (RAGE-ab) (n=21) or an isotype-matched control antibody (placebo-ab) (n=23). Treatment was started 4 weeks after surgical 5/6 nephrectomy in 16 weeks old mice and continued for 12 weeks. The RAGE-ab did not affect blood pressure, plasma cholesterol or measures of uremia. However, the aortic plaque area fraction was reduced by 59% in RAGE-ab compared with placebo-ab-treated mice (0.016 +/- 0.002 versus 0.039 +/- 0.005, P<0.001). In plasma, the RAGE-ab reduced concentrations of oxidized phospholipid neo-epitopes in plasma as detected by the specific monoclonal antibody EO6 (P<0.05) and titers of IgG antibodies against oxidized low-density lipoprotein (P<0.001). In the aorta of treated mice, the RAGE-ab did not affect the mRNA expression of eight selected genes associated with inflammation. The results suggest that blockade of RAGE reduces the proatherogenic effects of uremia, possibly through a systemic decrease in oxidative stress.

Humoral responses to oxidized low-density lipoprotein and related bacterial antigens after pneumococcal vaccine

Antibodies to oxidized low-density lipoprotein (oxLDL) may modulate the development of atherosclerosis. Antibodies to oxLDL may also react with cell wall polysaccharides (CWPS) of Streptococcus pneumoniae because both antigens share a common phosphorylcholine moiety. In hypercholesteremic mice, immunization with pneumococcal organisms elicited antibodies to oxLDL and protection against atherosclerosis. In humans, we determined whether the widely used adult pneumococcal polysaccharide vaccine augmented antibodies to oxLDL, CWPS, and phosphorylcholine, providing the potential to retard atherogenesis. Before and 4 weeks after pneumococcal vaccination of 23 healthy adults (11 smokers and 12 matched nonsmokers), we characterized IgG, IgM, and IgA to pneumococcal capsular polysaccharides, CWPS, and phosphorylcholine, IgG and IgM to oxLDL, and fasting serum lipids. The pneumococcal vaccine elicited significant increases in each antibody class to surface capsular polysaccharides. In contrast, only IgG to CWPS increased modestly and only among smokers. Moreover, antibodies to neither phosphorylcholine nor oxLDL increased consistently in either group. The pneumococcal polysaccharide vaccine effectively elicits antibodies to the bacterial capsule. The vaccine had no effect on serum lipids. The vaccine did not augment antibodies to CWPS, to its component phosphorylcholine, or to oxLDL, which are antibodies that have been proposed to modify the uptake of oxLDL by macrophages and the pathogenesis of atherosclerosis.

Phosphorylcholine-Targeting Immunization Reduces Atherosclerosis

OBJECTIVES

The present study evaluated the effect of phosphorylcholine (PC) immunization on the extent of experimental atherosclerosis.

BACKGROUND

Immunization against oxidized lipoprotein (oxLDL) or Streptococcus pneumoconiae reduces atherosclerosis. Phosphorylcholine is the main epitope recognized by both antipneumococcus and anti-oxLDL antibodies. Therefore we reasoned that PC-specific antibodies might play an important role in atherogenesis.

METHODS

Apolipoprotein E knockout mice were immunized with PC every second week over 4 months. At the end of the study, serum antibodies directed to either PC or oxLDL were measured. Splenic and peritoneal B cells were analyzed by flow cytometry. Aortic root atherosclerotic lesions were quantified by morphometry and phenotyped by immunohistochemistry. Immune and control sera were also tested for their effect on foam cell formation in macrophage culture in the presence of oxLDL.

RESULTS

The PC-immunized mice showed 3-fold increase in titers of anti-PC and -oxLDL antibodies compared with control mice (p < 0.01). The PC-immunized mice also showed a significant increase in the number of splenic mature B cells. The extent of atherosclerotic aorta root lesions was reduced by >40% in the PC-immunized mice (p < 0.01). Immunohistochemistry showed reduced expression of major histocompatibility complex class II antigens (p < 0.05) and the presence of B-cell clusters in plaques of PC-immunized mice. Finally, PC-immune serum was able to reduce macrophage-derived foam cell formation in the presence of oxLDL in vitro.

CONCLUSIONS

Phosphorylcholine immunization drives a specific humoral immune response that reduces foam cell formation in vitro and is atheroprotective in vivo.

Anti-oxidized low-density lipoprotein antibodies in myeloperoxidase-positive vasculitis patients preferentially recognize hypochlorite-modified low density lipoproteins

Many patients surviving vasculitis are prone to accelerated atherosclerosis and often have enhanced levels of antibodies to oxidized low-density lipoprotein (oxLDL). To measure anti-oxLDL antibodies, oxidation of LDL is achieved with copper (Cu) or malondialdehyde (MDA). Because, in vivo, LDL may be oxidized with myeloperoxidase (MPO) or its product hypochlorite, we measured anti-hypochlorite LDL antibodies in patients with vasculitis, haemodialysis patients and healthy controls. A newly developed enzyme-linked immunosorbent assay (ELISA) was used to detect antibodies to oxLDL as modified by hypochlorite. Results are compared with data obtained by standard LDL oxidation using MDA-LDL or Cu-LDL as substrate. Results were compared between anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) patients (n = 93), haemodialysis (HD) patients (n = 59) and healthy controls (HC; n = 43). Furthermore, patients with MPO-ANCA-associated vasculitis (n = 47) were compared with patients with proteinase 3 (PR3)-ANCA associated vasculitis (n = 46). Optimal cut-off points were determined by receiver operator characteristic (ROC) curve analysis. Anti-oxLDL antibodies are enhanced in AAV patients (MDA-LDL and hypochlorite-LDL) and in HD patients (hypochlorite-LDL), when compared to HC. Furthermore, patients with MPO-ANCA-associated vasculitis had higher levels of antibodies to hypochlorite-LDL than patients with PR3-ANCA-associated vasculitis. Our newly developed assay, in which hypochlorite-LDL is used as substrate, seems a more sensitive assay than traditional assays to measure oxLDL antibodies. Furthermore, our results suggest that enhanced MPO-mediated LDL oxidation occurs in patients with MPO-ANCA.

Paraoxonase-2 Deficiency Aggravates Atherosclerosis in Mice Despite Lower Apolipoprotein-B-containing Lipoproteins

Paraoxonases (PONs) are a family of proteins that may play a significant role in providing relief from both toxic environmental chemicals as well as physiological oxidative stress. Although the physiological roles of the PON family of proteins, PON1, PON2, and PON3, remain unknown, epidemiological, biochemical, and mouse genetic studies of PON1 suggest an anti-atherogenic function for paraoxonases. To determine whether PON2 plays a role in the development of atherosclerosis in vivo, we generated PON2-deficient mice. When challenged with a high fat, high cholesterol diet for 15 weeks, serum levels of high density lipoprotein cholesterol, triglycerides, and glucose were not significantly different between wild-type and PON2-deficient mice. In contrast, serum levels of very low density lipoprotein (VLDL)/low density lipoprotein (LDL) cholesterol were significantly lower (-32%) in PON2-deficient mice compared with wild-type mice. However, despite lower levels of VLDL/LDL cholesterol, mice deficient in PON2 developed significantly larger (2.7-fold) atherosclerotic lesions compared with their wild-type counterparts. Enhanced inflammatory properties of LDL, attenuated anti-atherogenic capacity of high density lipoprotein, and a heightened state of oxidative stress coupled with an exacerbated inflammatory response from PON2-deficient macrophages appear to be the main mechanisms behind the larger atherosclerotic lesions in PON2-deficient mice. These results demonstrate that PON2 plays a protective role in atherosclerosis.

Immunization using an Apo B-100 related epitope reduces atherosclerosis and plaque inflammation in hypercholesterolemic apo E (−/−) mice

Immune system modulates atherosclerosis and immunization using homologous LDL reduces atherosclerosis in hyperlipidemic animals. The nature of athero-protective antigenic epitopes in LDL remains unclear. We have recently identified nearly a 100 antigenic epitopes in human apo B-100 and in this study we evaluated the effects of immunization with two such epitopes on atherosclerosis in hypercholesterolemic apo E (-/-) mice. Male apo E (-/-) mice were immunized at 6-7 weeks of age with two different apo B-100 related peptide sequences using alum as adjuvant and mice immunized with alum alone served as controls. Peptide-2 immunization reduced aortic atherosclerosis by 40% and plaque inflammation by 80% compared to controls without a reduction in circulating cholesterol levels whereas Peptide-1 immunization had no effect. Peptide-2 immunization also reduced the progression of aortic lesions when mice were immunized at 16 weeks of age, suggesting the possibility of immuno-modulation in treating established atherosclerosis. The athero-protective effect of Peptide-2 immunization was absent in splenectomized mice but could be conveyed to non-immunized mice via adoptive transfer of splenocytes from peptide-2 immunized mice. In conclusion, immunization with a specific apo B-100 related peptide sequence reduces aortic atherosclerosis and plaque inflammation. Such acquired immunity and athero-protective effect appears to be mediated by splenocytes. These data demonstrate the feasibility of peptide based immunomodulating therapy for atherosclerosis.

Humoral Immune Response Against Defined Oxidized Low-Density Lipoprotein Antigens Reflects Structure and Disease Activity of Carotid Plaques

Background— Immune responses against oxidized low-density lipoprotein (LDL) play an important role in atherosclerosis. The aim of this study was to investigate if humoral immune response against specific oxidized LDL antigens, such as aldehyde-modified peptide sequences of apolipoprotein B-100, reflects disease activity and structure of atherosclerotic plaques.

Methods and Results— Plaques were obtained from 114 symptomatic subjects referred to carotid endarterectomy and characterized immunohistochemically and histologically. Plasma levels of IgG and IgM against aldehyde-modified apolipoprotein B-100 amino acid sequences 661 to 680, 3136 to 3155 (peptide 210), and 3661 to 3680 (peptide 240) were determined by enzyme-linked immunosorbent assay. High levels of IgG against peptide 210 were associated with increased plaque content of lipids ( r =0.24, P <0.05) and hemorrhage ( r =0.27, P =0.005), with decreased content of fibrous tissue ( r =−0.25, P =0.01), but also with lower total plaque volume ( r =−0.21, P <0.05). In contrast, high levels of IgM against peptide 240 were associated with plaques with more fibrous tissue ( r =0.35, P <0.001), less lipids ( r =−0.34, P <0.001), and less macrophages ( r =−0.24, P <0.05). IgM against peptide 210 were found to be associated with plaque fibrous tissue ( r =0.20, P <0.05), less lipids ( r =−0.21, P <0.05), and less macrophages ( r =−0.27, P =0.01).

Conclusion— These findings support the notion that immune responses against oxidized LDL epitopes are involved in atherosclerosis and that the level of circulating antibodies against these structures may reflect disease activity in the arterial wall.

The role of natural antibodies in atherogenesis

Atherosclerosis is now widely recognized as a chronic inflammatory disease that involves innate and adaptive immune responses. Both cellular and humoral components of the immune system have been implicated in atherogenesis. Natural antibodies can be considered humoral factors of innate immunity, and their functional role in health and disease has been reexamined in recent years. Natural antibodies exhibit a remarkably conserved repertoire that includes a broad specificity for self-antigens. For this reason, they are believed to be a product of natural selection and have been suggested to play an important role in "housekeeping" functions. Recent evidence has revealed that oxidation-specific epitopes are important and maybe immunodominant targets of natural antibodies, suggesting an important function for these antibodies in the host response to consequences of oxidative stress, for example, to the oxidative events that occur when cells undergo apoptosis. This review will focus on these recent findings and discuss the emerging evidence for an important role of natural antibodies in atherogenesis.

Natural antibodies and the autoimmunity of atherosclerosis

In recent years, the subject of natural antibodies has been revisited and the immunobiological roles of these humoral factors are being better defined. These antibodies are secreted by distinct sets of innate-like B cells, B-1 cells and marginal zone B cells, which arise early in development to become the sources of "natural immune memory". Due to their interactions with a variety of self-determinants, natural antibodies have previously been postulated to play roles in the maintenance of host homeostasis. A central paradigm has recently been developed from the demonstration that oxidation derived epitopes on apoptotic cells and oxidized low-density lipoproteins are recognized by the phosphorylcholine-specific germline encoded B-1 cell natural antibody, T15, which has provided important insights into possible "house-keeping" functions under both normal and pathological conditions. In this review, the potential functions of natural antibodies in the pathogenesis and progression of the chronic inflammatory condition of atherosclerosis are discussed, as well as their capacities for apoptotic cell binding and clearance. These interactions of natural antibodies and oxidation-epitopes from phospholipids appear to provide a dynamic immunobiological connection linking host responses in infection, autoimmunity and atherosclerosis.

Immunomodulation of atherosclerosis: implications for vaccine development

A number of studies have shown activation of the immune system throughout various stages of atherosclerosis. Recent observations have suggested that activation of immune responses may promote atherosclerosis on one hand by inducing and perpetuating arterial inflammation, whereas on the other hand, selective activation of certain immune functions may inhibit atherosclerosis and arterial inflammation. These observations suggest the possibility that selective suppression of proatherogenic immune responses or selective activation of antiatherogenic immune responses may provide new approaches for atherosclerosis prevention and treatment. Several antigens activating immune responses affecting development of atherosclerosis have been identified. These immune responses may be modulated by presenting the antigens together with different types of adjuvants as well as through the route of administration. In this review, we summarize recent experimental studies using immunomodulatory approaches for treatment of atherosclerosis.