Induction of Neonatal Tolerance to Oxidized Lipoprotein Reduces Atherosclerosis In ApoE Knockout Mice

Atherosclerosis and autoimmunity: a growing relationship

Atherosclerosis is regarded as one of the leading causes of mortality and morbidity in the world. Nowadays, it seems that atherosclerosis cannot be defined merely through the Framingham traditional risk factors and that autoimmunity settings exert a remarkable role in its mechanobiology. Individuals with autoimmune disorders show enhanced occurrence of cardiovascular complications and subclinical atherosclerosis. The mechanisms underlying the atherosclerosis in disorders like rheumatoid arthritis, systemic lupus erythematosus, antiphospholipid syndrome, systemic sclerosis and Sjögren's syndrome, seem to be the classical risk factors. However, chronic inflammatory processes and abnormal immune function may also be involved in atherosclerosis development. Autoantigens, autoantibodies, infectious agents and pro-inflammatory mediators exert a role in that process. Being armed with the mechanisms underlying autoimmunity in the etiopathogenesis of atherosclerosis in rheumatic autoimmune disorders and the shared etiologic pathway may result in substantial developing therapeutics for these patients.

Immune-mediated mechanisms of atherosclerosis and implications for the clinic

INTRODUCTION

A large body of evidence supports the inflammatory hypothesis of atherosclerosis, and both innate and adaptive immune responses play important roles in all disease stages. Areas covered: Here, we review our understanding of the role of the immune response in atherosclerosis, focusing on the pathways currently amenable to therapeutic modulation. We also discuss the advantages or undesirable effects that may be foreseen from targeting the immune response in patients at high cardiovascular risk, suggesting new avenues for research. Expert commentary: There is an extraordinary opportunity to directly test the inflammatory hypothesis of atherosclerosis in the clinic using currently available therapeutics. However, a more balanced interpretation of the experimental and translational data is needed, which may help address and identify in more detail the appropriate settings where an immune pathway can be targeted with minimal risk.

Atheroprotective immunity and cardiovascular disease: therapeutic opportunities and challenges

Emerging knowledge of the role of atheroprotective immune responses in modulating inflammation and tissue repair in atherosclerotic lesions has provided promising opportunities to develop novel therapies directly targeting the disease process in the artery wall. Regulatory T (Treg) cells have a protective role through release of anti-inflammatory cytokines and suppression of autoreactive effector T cells. Studies in experimental animals have shown that blocking the generation or action of Treg cells is associated with more aggressive development of atherosclerosis. Conversely, cell transfer and other approaches to expand Treg cell populations in vivo result in reduced atherosclerosis. There have been relatively few clinical studies of Treg cells and cardiovascular disease, but the available evidence also supports a protective function. These observations have raised hope that it may be possible to develop therapies that act by enforcing the suppressive activities of Treg cells in atherosclerotic lesions. One approach to achieve this goal has been through development of vaccines that stimulate immunological tolerance for plaque antigens. Several pilot vaccines based on LDL-derived antigens have demonstrated promising results in preclinical testing. If such therapies can be shown to be effective also in clinical trials, this could have an important impact on cardiovascular prevention and treatment. Here, we review the current knowledge of the mode of action of atheroprotective immunity and of the ways to stimulate such pathways in experimental settings. The challenges in translating this knowledge into the clinical setting are also discussed within the perspective of the experience of introducing immune-based therapies for other chronic noninfectious diseases.

Attenuation of early atherosclerotic lesions by immunotolerance with β2 glycoprotein I and the immunomodulatory effectors interleukin 2 and 10 in a murine model

OBJECTIVE

This study assessed the effect of cellular and humoral autoimmune response inhibition after immunization with β2-glycoprotein I (β2-GPI) and the effect of immunomodulation with interleukin (IL)-2 and IL-10 in the development of early atherosclerotic vascular lesion in a murine model. Atherosclerosis is increasingly considered a chronic inflammatory disease with pathogenic autoimmune processes. Regulatory T cells, and their cytokines, have been implicated in the inhibition of the development of atherosclerotic lesions and involved in the immunologic tolerance induction.

METHODS

Eight-week-old male C57BL6 LDL-receptor deficient (LDLR(-/-)) mice were fed a cholesterol-rich (2.8%), high-saturated-fat (82%) diet for a week and divided in five groups. The groups received the following intravenous immunizations: group I (control group): one dose of 5 μg β2-GPI; group II: 5 μg β2-GPI I and 1 μg IL-2; group III: 5 μg β2-GPI and 0.75 μg of IL-10; and group IV: 5 μg β2-GPI, 1 μg IL-2, and 0.75 μg IL-10. The aortas of the mice were assessed 8 weeks after inoculation to determine the aortic lesion size and composition in all groups.

RESULTS

β2-GPI immunization attenuated the early atherosclerotic lesions development compared with the control group (P = .001). Macroscopic and histologic aortic atherosclerotic lesions were significantly decreased in the IL-2 and IL-10-treated groups in β2-GPI-tolerant mice compared with the β2-GPI-tolerant group without cytokine injection (P = .001). The association of both cytokines did not provoke a major inhibition in the atherosclerosis development when compared with groups injected with the two cytokines separately.

CONCLUSIONS

The immunotolerance induction against β2-GPI attenuates the development of atherosclerosis lesions in an animal model, enhanced by downregulation of the cellular and humoral autoimmune response provoked by IL-2 and IL-10.

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.

Linking immunity to atherosclerosis: implications for vascular pharmacology--a tribute to Göran K. Hansson

For the past decade, we have deepened our understanding of the pathogenesis of atherosclerosis, a chronic arterial disease that causes cardiac and cerebral infarction and peripheral vascular disorders. Because of this extended understanding, more effective strategies for prevention and treatment of this disease are emerging. One of the fundamental mechanisms that lead to progress or regression in atherosclerosis, thus influencing its life-threatening complications, occurs through functional changes in vascular immunity and inflammation. This review briefly summarizes the discoveries in basic and translational sciences in this area and recent advances in clinical medicine against atherosclerotic vascular diseases.

The potential role of preventing atherosclerosis by induction of neonatal tolerance to VLDL

Induction of immune tolerance to ox-LDL could reduce atherosclerosis by modulation immune response. We suppose that very low density lipoprotein (VLDL) may have a similar role to ox-LDL in autoimmune response of atherosclerosis. In this study, neonatal rats were injected with ox-LDL, VLDL, or equal-volume saline, respectively. Vaccination with ox-LDL reduced the level of specific antibody, T cells proliferation response, and the level of endothelins. The method also had a tendency of reducing blood lipids. Vaccination with VLDL obviously reduced the level of specific antibody and T cells proliferation. Though there was also a tendency of reducing blood lipids and endothelins, the effect was less prominent than that with ox-LDL. We conclude that, although the effect was less obvious, vaccination with VLDL to induce neonatal tolerance had an effect on modulating immune response, protecting endothelial cells, and reducing blood lipids.

Cellular immunity, low-density lipoprotein and atherosclerosis: break of tolerance in the artery wall

Atherosclerosis is a chronic inflammatory disease. Atherosclerotic plaques contain abundant immune cells that can dictate and effect inflammatory responses. Among them, T cells are present during all stages of the disease suggesting that they are essential in the initiation as well as the progression of plaque. Experimental as well as clinical research has demonstrated different T cell subsets, i.e. CD4+ Th1, Th2, Th17, and Treg as well as CD8+ and NKT cells in the plaque. Moreover, candidate antigens inducing T cell responses have been identified. Knowledge about the pathological role of these cells in atherogenesis may lead to development of new therapies. This review provides an overview of the research field of cellular immunity in atherosclerosis. It emphasises the events and findings involving antigen specific T cells, in particular low-density lipoprotein-specific T cells.

Immunotherapy with tolerogenic apolipoprotein B-100-loaded dendritic cells attenuates atherosclerosis in hypercholesterolemic mice

BACKGROUND

Atherosclerosis is a chronic inflammatory disease characterized by a massive intimal accumulation of low-density lipoprotein that triggers chronic vascular inflammation with an autoimmune response to low-density lipoprotein components.

METHODS AND RESULTS

To dampen the inflammatory component of atherosclerosis, we injected hypercholesterolemic huB100(tg) × Ldlr(-/-) mice (mice transgenic for human apolipoprotein B100 [ApoB100] and deficient for the low-density lipoprotein receptor) intravenously with dendritic cells (DCs) that had been pulsed with the low-density lipoprotein protein ApoB100 in combination with the immunosuppressive cytokine interleukin-10. DCs treated with ApoB100 and interleukin-10 reduced proliferation of effector T cells, inhibited production of interferon-γ, and increased de novo generation of regulatory T cells in vitro. Spleen cells from mice treated with DCs plus ApoB100 plus interleukin-10 showed diminished proliferative responses to ApoB100 and significantly dampened T-helper 1 and 2 immunity to ApoB100. Spleen CD4(+) T cells from these mice suppressed activation of ApoB100-reactive T cells in a manner characteristic of regulatory T cells, and mRNA analysis of lymphoid organs showed induction of transcripts characteristic of these cells. Treatment of huB100(tg) × Ldlr(-/-) mice with ApoB100-pulsed tolerogenic DCs led to a significant (70%) reduction of atherosclerotic lesions in the aorta, with decreased CD4(+) T-cell infiltration and signs of reduced systemic inflammation.

CONCLUSIONS

Tolerogenic DCs pulsed with ApoB100 reduced the autoimmune response against low-density lipoprotein and may represent a novel possibility for treatment or prevention of atherosclerosis.

Inhibition of T cell response to native low-density lipoprotein reduces atherosclerosis

Immune responses to oxidized low-density lipoprotein (oxLDL) are proposed to be important in atherosclerosis. To identify the mechanisms of recognition that govern T cell responses to LDL particles, we generated T cell hybridomas from human ApoB100 transgenic (huB100(tg)) mice that were immunized with human oxLDL. Surprisingly, none of the hybridomas responded to oxidized LDL, only to native LDL and the purified LDL apolipoprotein ApoB100. However, sera from immunized mice contained IgG antibodies to oxLDL, suggesting that T cell responses to native ApoB100 help B cells making antibodies to oxLDL. ApoB100 responding CD4(+) T cell hybridomas were MHC class II-restricted and expressed a single T cell receptor (TCR) variable (V) beta chain, TRBV31, with different Valpha chains. Immunization of huB100(tg)xLdlr(-/-) mice with a TRBV31-derived peptide induced anti-TRBV31 antibodies that blocked T cell recognition of ApoB100. This treatment significantly reduced atherosclerosis by 65%, with a concomitant reduction of macrophage infiltration and MHC class II expression in lesions. In conclusion, CD4(+) T cells recognize epitopes on native ApoB100 protein, this response is associated with a limited set of clonotypic TCRs, and blocking TCR-dependent antigen recognition by these T cells protects against atherosclerosis.

Inhibition of foam cell formation using a soluble CD68-Fc fusion protein

The appearance of lipid-rich foam cells is a major feature of vulnerable atherosclerotic plaque formation. The transformation of macrophages into foam cells results from excessive uptake of cholesterol-rich particles by scavenger receptors such as CD68. We cloned a CD68-Fc immunoadhesin, a fusion protein consisting of the extracellular domain of the human CD68 and a human Fc domain, and investigated the function in vitro. Specific binding of CD68-Fc to OxLDL with an affinity of 10 nmol/L was determined by surface plasmon resonance and increased binding to lipid-rich human and ApoE(-/-) mice plaque tissue. This was confirmed both by immunohistochemical staining of CD68-Fc-treated paraffin sections from human plaques and by ELISA-based quantification of CD68-Fc binding to human atherosclerotic plaque extracts. In an in vitro model of macrophage/foam cell formation, CD68-Fc reduced foam cell formation significantly. This was caused both by interference of CD68-Fc with OxLDL uptake into macrophages and platelets and by the inhibition of platelet/OxLDL phagocytosis. Finally, expression of metalloproteinases by macrophages/foam cells was inhibited by CD68-Fc. In conclusion, CD68-Fc seems to be a promising new tool for preventing macrophage/foam cell formation. Thus, CD68-Fc might offer a novel therapeutic strategy for patients with acute coronary syndrome by modulating the generation of vulnerable plaques.

Inflammatory and autoimmune reactions in atherosclerosis and vaccine design informatics

Atherosclerosis is the leading pathological contributor to cardiovascular morbidity and mortality worldwide. As its complex pathogenesis has been gradually unwoven, the regime of treatments and therapies has increased with still much ground to cover. Active research in the past decade has attempted to develop antiatherosclerosis vaccines with some positive results. Nevertheless, it remains to develop a vaccine against atherosclerosis with high affinity, specificity, efficiency, and minimal undesirable pathology. In this review, we explore vaccine development against atherosclerosis by interpolating a number of novel findings in the fields of vascular biology, immunology, and bioinformatics. With recent technological breakthroughs, vaccine development affords precision in specifying the nature of the desired immune response—useful when addressing a disease as complex as atherosclerosis with a manifold of inflammatory and autoimmune components. Moreover, our exploration of available bioinformatic tools for epitope-based vaccine design provides a method to avoid expenditure of excess time or resources.

Immunomodulation of vascular diseases: atherosclerosis and autoimmunity

The autoimmune disease atherosclerosis contributes to several vascular complications. Besides vascular cells, inflammatory cells occur prominently in atherosclerotic lesions; lymphocytes play a detrimental role in the initiation and progression of this common vascular disease. Recent discoveries have led to the identification of several important lymphocyte types within the atherosclerotic lesions. However, peripheral lymphocytes and those in the lymphoid organs both figure critically in the regulation of atherosclerotic lesion growth. Although the concept of atherosclerosis as an autoimmune disease is well known, the ways in which autoantigens and autoantibodies contribute to atherogenesis in human or even in animal models remains largely unknown. For example, autoantigen immunisation can either promote or attenuate atherogenesis in animals, depending on the antigen types and the routes and carriers of immunisation. This article summarises recent findings regarding lesion inflammatory cell types, autoantigens and autoantibody isotypes that can affect the initiation and progression of atherosclerosis from both human and animal studies.

Vaccination, atherosclerosis and systemic lupus erythematosus

Atherosclerosis is an inflammatory disease, leading to the formation of pro-inflammatory and pro-oxidative lipids that generate an immune response. Several antigens have been shown to activate the immune response and affect the development of atherogenesis. Systemic lupus erythematosus is an autoimmune and inflammatory disease strongly associated with premature development of atherosclerotic plaques. Modulation of the immune system could represent a useful approach to prevent and/or treat atherosclerosis. A vaccination-based approach might be a useful, effective tool in the modern arsenal of cardiovascular therapies and could be used on a large scale at a low cost. In non-systemic lupus erythematosus populations, vaccines against oxidized low-density lipoprotein, beta-2-glycoprotein I, heat shock proteins, lipoproteins, cholesterol, molecules involved in cholesterol metabolism, and other molecules (CD99, vascular endothelial growth factor-receptor, and interleukin-2) have been tested, with promising results. However, there are no studies of vaccination against atherosclerosis in systemic lupus erythematosus.

Autoimmunity in atherosclerosis: a protective response losing control?

Atherosclerosis is a chronic inflammatory disease characterized by accumulation of oxidized lipoproteins, increased cell death and hypertrophic degeneration of the arterial intima. The disease process is associated with local formation of modified self antigens that are targeted by both innate and adaptive immune responses. Although it remains to be firmly established it is likely that these autoimmune responses initially have a beneficial effect facilitating the removal of potentially harmful rest products from oxidized LDL and dying cells. However, studies performed on hypercholesterolaemic mice deficient in different components of the immune system uniformly suggest that the net effect of immune activation is pro-atherogenic and that atherosclerosis, at least to some extent, should be regarded as an autoimmune disease. These observations point to the possibility of developing new treatments for atherosclerosis based on modulation of immune responses against plaque antigens, an approach presently tested clinically for several other chronic inflammatory diseases with autoimmune components. Pilot studies in animals have provided promising results for both parental and oral vaccines based on oxidized LDL antigens. The time when this concept is ready for clinical testing is rapidly approaching but it will be important not to underestimate the difficulties that will be encountered in transferring the promising results from experimental animals into humans.

Inflammation and atherosclerosis

Atherosclerosis, the cause of myocardial infarction, stroke, and ischemic gangrene, is an inflammatory disease. The atherosclerotic process is initiated when cholesterol-containing low-density lipoproteins accumulate in the intima and activate the endothelium. Leukocyte adhesion molecules and chemokines promote recruitment of monocytes and T cells. Monocytes differentiate into macrophages and upregulate pattern recognition receptors, including scavenger receptors and toll-like receptors. Scavenger receptors mediate lipoprotein internalization, which leads to foam-cell formation. Toll-like receptors transmit activating signals that lead to the release of cytokines, proteases, and vasoactive molecules. T cells in lesions recognize local antigens and mount T helper-1 responses with secretion of pro-inflammatory cytokines that contribute to local inflammation and growth of the plaque. Intensified inflammatory activation may lead to local proteolysis, plaque rupture, and thrombus formation, which causes ischemia and infarction. Inflammatory markers are already used to monitor the disease process and anti-inflammatory therapy may be useful to control disease activity.

Immunomodulation of the inflammatory response in atherosclerosis

PURPOSE OF REVIEW

Cardiovascular disease, as manifested in the formation of atherosclerotic lesions, can be described as a chronic inflammatory autoimmune-like disease that proceeds in the context of enhanced plasma lipid levels. Modulation of the immune response may therefore form a valuable therapy in addition to standardized cholesterol and blood pressure-lowering therapies. The purpose of this review is to describe a number of recent approaches to immunomodulate atherosclerosis: immunization against mediators involved in atherosclerosis, such as cytokines and modified low-density lipoprotein; intervention in cytokine pathways; intervention in co-stimulatory pathways; activation of regulatory T cells; and modulation of natural killer T cells.

RECENT FINDINGS

The most recent findings point to an important role for regulatory T cells in atherosclerotic lesion formation. The function of the regulatory T cells is modulated by chemokines and by co-stimulatory pathways, whereas the function of these cells can be strongly upregulated by anti-CD3 treatment and tolerance induction.

SUMMARY

In the near future the first exponents of this approach, such as immunization and enhancement of the function of regulatory T cells, may enter the first phase of clinical trials, and may ultimately add to the current therapies in 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.

The proatherogenic role of T cells requires cell division and is dependent on the stage of the disease

OBJECTIVE

The mechanism by which T cells exert a proatherogenic potential is unclear. In order to determine whether this potential requires their replication, we crossed atherosclerosis-prone apolipoprotein E knockout mice (ApoE degrees) with transgenic mice in which exclusive and conditional ablation of dividing T cells relies on their specific expression of the herpes simplex type 1 thymidine kinase (TK) suicide gene.

METHODS AND RESULTS

We first showed that conalbumin-immunized ApoE degrees TK mice mounted a significant immune response to the antigen that was fully and specifically blocked by an in vivo ganciclovir (GCV) treatment. Next, ApoE degrees TK mice and ApoE degrees mice were treated or not with GCV either during the first 4 weeks (GCV 1 to 4w), the last 4 weeks (GCV 5 to 8w), or during 8 weeks (GCV 1 to 8w). Strikingly, ApoE degrees TK mice displayed a dramatic decrease in lesion development in the GCV 1 to 8w and GCV 5 to 8w groups, whereas the GCV had no effect when administered during the first 4 weeks. In protected mice, the inflammatory parameters in lesions, the percentage of CD69+ CD3+ splenocytes, and the circulating natural killer T cells were reduced.

CONCLUSIONS

The present study, therefore, shows that the proatherogenic potential of T cells is crucial in the progression of fatty streaks to mature plaques and requires cell division.

Cytokines and cardiovascular disease

The role of cytokines in the pathogenesis of cardiovascular disease is increasingly evident since the identification of immune/inflammatory mechanisms in atherosclerosis and heart failure. In this review, we describe how innate and adaptive immune cascades trigger the release of cytokines and chemokines, resulting in the initiation and progression of atherosclerosis. We discuss how cytokines have direct and indirect effects on myocardial function. These include myocardial depressant effects of nitric oxide (NO) synthase-generated NO, as well as the biochemical effects of cytokine-stimulated arachidonic acid metabolites on cardiomyocytes. Cytokine influences on myocardial function are time-, concentration-, and subtype-specific. We provide a comprehensive review of these cytokine-mediated immune and inflammatory cascades implicated in the most common forms of cardiovascular disease.

Atherosclerosis and the immune system

The immune system is involved at all stages of the atherosclerotic disease process. Innate immunity, represented by macrophages and other cells, is directly activated by microbial components and possibly also by autologous lipids and proteins. It elicits inflammatory activity, which is a key component of the atherosclerotic lesion. Adaptive immunity is initiated by recognition of disease-related antigens, which include oxidatively modified lipoproteins, heat shock proteins and microbial macromolecules. In the artery wall, adaptive immune recognition mainly leads to Thl effector responses, which are characterized by secretion of proinflammatory cytokines and by activation of macrophages and vascular cells. Therefore, both the innate and adaptive arms of the immune system lead to inflammation in the developing atherosclerotic lesion. Interestingly, several effector pathways of cellular as well as humoral immunity tend to counteract proatherogenic, proinflammatory immunity. The notion that immunity plays an important role in the development of atherosclerosis has focused attention on a number of potential novel targets for intervention based on modulation of such immune responses.

Atherosclerotic plaque formation and risk factors

Atherosclerosis (AT) is a progressive disease characterized by the accumulation of lipids, fibrous materials, and mineral in the arteries. Although many generalized or systemic risk factors predispose to its development, AT affect various regions of the circulation preferentially and yields distinct clinical manifestations depending on the particular circulatory bed affected. The progression of AT is currently believed to involve the interaction of endothelium, monocytes, and leukocytes, as well as the influences of cytokines, oxidized lipoproteins, hypertension, tobacco use, dyslipidemia, homocystinemia, and genetic determinants.

Innate and adaptive immunity in the pathogenesis of atherosclerosis

This review considers critically the evidence for the involvement of mediators of innate and acquired immunity in various stages of atherosclerosis. Rapidly mobilized arms of innate immunity, including phagocytic leukocytes, complement, and proinflammatory cytokines, contribute to atherogenesis. In addition, adaptive immunity, with its T cells, antibodies, and immunoregulatory cytokines, powerfully modulates disease activity and progression. Atherogenesis involves cross talk between and shared pathways involved in adaptive and innate immunity. Immune processes can influence the balance between cell proliferation and death, between synthetic and degradative processes, and between pro- and antithrombotic processes. Various established and emerging risk factors for atherosclerosis modulate aspects of immune responses, including lipoproteins and their modified products, vasoactive peptides, and infectious agents. As we fill in the molecular details, new potential targets for therapies will doubtless emerge.

Role of oxidized low-density lipoprotein in renal disease

Accelerated atherosclerosis is often observed in patients with chronic renal failure. In the present review we summarize and discuss the recent literature on the pathogenic role of low-density lipoproteins modified by oxidative processes in atherosclerosis and the possible role in renal diseases. Pathogenetically, the oxidation of low-density lipoproteins is considered to be a key event in the development of atherosclerosis, in part by causing enhanced uptake of lipids by macrophages. In addition, oxidation of low-density lipoproteins exerts cytotoxic, proinflammatory and immunogenic properties, all of which could potentially contribute to the development and progression of atherosclerosis.

The potential for novel anti-inflammatory therapies for coronary artery disease

Although drugs that lead to cholesterol and lipid lowering have proved to have significant effects in lowering cardiovascular morbidity and mortality, coronary artery disease remains a principal cause of death worldwide. There is a clear need to discover further therapeutic approaches to control this disease adequately. This review focuses on the mechanisms that have been implicated in the recruitment, activation and differentiation of inflammatory monocytes/macrophages in nascent vascular lesions into lipid-laden foam cells. These mechanisms might provide attractive targets for novel therapies for coronary artery disease.

Immunomodulation for treatment and prevention of atherosclerosis

In recent years, it has become clear that the immune system has a major role in atherosclerosis development and progression. More specifically, atherosclerosis fulfills all four criteria to define a condition as being an autoimmune in nature. This association also suggests that modification of the immune response in atherosclerosis could affect this process. In this review, we summarize different aspects of immunomodulation in atherosclerosis. These include immunosuppression, active immunization, induction of tolerance, administration of intravenous immunoglobulin, gene therapy, cytokine network manipulation and statins.

Immune mechanisms in atherosclerosis

Atherosclerosis is an inflammatory disease. Its lesions are filled with immune cells that can orchestrate and effect inflammatory responses. In fact, the first lesions of atherosclerosis consist of macrophages and T cells. Unstable plaques are particularly rich in activated immune cells, suggesting that they may initiate plaque activation. We have seen a rapid increase in the understanding of the mechanisms that govern the recruitment, differentiation, and activation of immune cells in atherosclerosis. Experimental research has identified several candidate antigens, and there are encouraging data suggesting that immune modulation as well as immunization can reduce the progression of the disease. This review provides an overview of our current understanding of the role of immune mechanisms in atherosclerosis.

Effect of immune deficiency on lipoproteins and atherosclerosis in male apolipoprotein E-deficient mice

To determine whether T cells and B cells influence lipid metabolism and atherosclerosis, we crossed apolipoprotein E-deficient (apoE degrees ) mice with recombination activating gene 2-deficient (RAG2 degrees ) mice. Total plasma cholesterol levels were approximately 20% higher in male apoE degrees mice compared with the apoE degrees RAG2 degrees mice at 8 weeks of age, and plasma triglyceride levels were 2.5-fold higher in the apoE degrees mice even when plasma cholesterol levels were similar. Male mice with plasma cholesterol levels between 400 and 600 mg/dL at 8 weeks of age were euthanized at 27 and 40 weeks of age. The aortic root lesion area in the apoE degrees RAG2 degrees mice, compared with that in the immune-competent apoE degrees mice, was 81% and 57% smaller at 27 and 40 weeks of age, respectively. In contrast, there was no difference in the size of the brachiocephalic trunk lesions. Similar results were obtained with mice euthanized at 40 weeks of age that had 8-week cholesterol levels between 300 and 399 mg/dL. In apoE degrees RAG2 degrees mice, aortic root atherosclerosis was more profoundly suppressed at lower cholesterol levels. Thus, T and B cells and their products differentially influence the development of atherosclerosis at different sites. We also demonstrate a profound effect of the immune system on plasma lipid homeostasis.

Mouse models of atherosclerosis

Atherosclerosis bears many features of a chronic inflammation that affects the intima of large and medium-sized arteries. In recent years apolipoprotein E-deficient and LDL receptor-deficient mice have been used to examine the effects of various gene products on the development of atherosclerosis. In the present review the effects of genetics, apolipoprotein E, inflammatory gene modifiers, lipoprotein modifications, lipoprotein receptors, vessel wall expression of lipoprotein-metabolizing enzymes, and the atheroprotective role of HDL on atherosclerosis in these mice are discussed. The importance of examining lesions that are more advanced than fatty streaks and careful histologic and immunologic examination of lesion composition is emphasized.