Induction of oral tolerance to oxidized low-density lipoprotein ameliorates atherosclerosis

Thymus in Cardiometabolic Impairments and Atherosclerosis: Not a Silent Player?

The thymus represents a primary organ of the immune system, harboring the generation and maturation of T lymphocytes. Starting from childhood, the thymus undergoes involution, being replaced with adipose tissue, and by an advanced age nearly all the thymus parenchyma is represented by adipocytes. This decline of thymic function is associated with compromised maturation and selection of T lymphocytes, which may directly impact the development of inflammation and induce various autoinflammatory disorders, including atherosclerosis. For a long time, thymus health in adults has been ignored. The process of adipogenesis in thymus and impact of thymic fat on cardiometabolism remains a mysterious process, with many issues being still unresolved. Meanwhile, thymus functional activity has a potential to be regulated, since islets of thymopoeisis remain in adults even at an advanced age. The present review describes the intricate process of thymic adipose involution, focusing on the issues of the thymus' role in the development of atherosclerosis and metabolic health, tightly interconnected with the state of vessels. We also review the recent information on the key molecular pathways and biologically active substances that may be targeted to manipulate both thymic function and atherosclerosis.

T-cell Cholesterol Accumulation, Aging, and Atherosclerosis

PURPOSE OF REVIEW

The majority of leukocytes in advanced human atherosclerotic plaques are T-cells. T-cell subsets exert pro- or anti-atherogenic effects largely via the cytokines they secrete. Tregulatory cells (Tregs) are anti-inflammatory, but may lose these properties during atherosclerosis, proposed to be downstream of cholesterol accumulation. Aged T-cells also accumulate cholesterol. The effects of T-cell cholesterol accumulation on T-cell fate and atherosclerosis are not uniform.

RECENT FINDINGS

T-cell cholesterol accumulation enhances differentiation into pro-atherogenic cytotoxic T-cells and boosts their killing capacity, depending on the localization and extent of cholesterol accumulation. Excessive cholesterol accumulation induces T-cell exhaustion or T-cell apoptosis, the latter decreasing atherosclerosis but impairing T-cell functionality in terms of killing capacity and proliferation. This may explain the compromised T-cell functionality in aged T-cells and T-cells from CVD patients. The extent of T-cell cholesterol accumulation and its cellular localization determine T-cell fate and downstream effects on atherosclerosis and T-cell functionality.

Two decades of vaccine development against atherosclerosis

Atherosclerosis is an immune-mediated chronic inflammatory disease that leads to the development of fatty plaques in the arterial walls, ultimately increasing the risk of thrombosis, stroke, and myocardial infarction. The immune response in this complex disease is both atheroprotective and pro-atherogenic, involving both innate and adaptive immunity. Current treatments include the adjustment of lifestyle factors, cholesterol-lowering drugs such as statins, and immunotherapy, whereas vaccine development has received comparatively little attention. In this review, we discuss the potential of antigen-specific vaccination as a preventative approach based on more than 20 years of research and innovation. Vaccination targets include proteins that are more abundant in atherosclerotic patients, such as oxidized low-density lipoprotein (LDL), apolipoprotein B-100, proprotein convertase subtilisin/kexin type-9 serine protease (PCSK9), cholesteryl ester transfer protein (CETP), and heat shock proteins HSP60 and HSP65. Immunization with such proteins or their peptide epitopes has been shown to induce T-cell activation, produce antigen-specific antibodies, reduce the size of atherosclerotic lesions, and/or reduce serum cholesterol levels. Vaccination against atherosclerosis therefore offers a new strategy to address the burden on healthcare systems caused by cardiovascular disease, the leading cause of death worldwide.

Evolving concepts in the pathophysiology of atherosclerosis: from endothelial dysfunction to thrombus formation through multiple shades of inflammation

Atherosclerosis is the anatomo-pathological substrate of most cardio, cerebro and vascular diseases such as acute and chronic coronary syndromes, stroke and peripheral artery diseases. The pathophysiology of atherosclerotic plaque and its complications are under continuous investigation. In the last 2 decades our understanding on the formation, progression and complication of the atherosclerotic lesion has greatly improved and the role of immunity and inflammation is now well documented and accepted. The conventional risk factors modulate endothelial function determining the switch to a proatherosclerotic phenotype. From this point, lipid accumulation with an imbalance from cholesterol influx and efflux, foam cells formation, T-cell activation, cytokines release and matrix-degrading enzymes production occur. Lesions with high inflammatory rate become vulnerable and prone to rupture. Once complicated, the intraplaque thrombogenic material, such as the tissue factor, is exposed to the flowing blood, thus inducing coagulation cascade activation, platelets aggregation and finally intravascular thrombus formation that leads to clinical manifestations of this disease. Nonconventional risk factors, such as gut microbiome, are emerging novel markers of atherosclerosis. Several data indicate that gut microbiota may play a causative role in formation, progression and complication of atherosclerotic lesions. The gut dysbiosis-related inflammation and gut microbiota-derived metabolites have been proposed as the main working hypothesis in contributing to disease formation and progression. The current evidence suggest that the conventional and nonconventional risk factors may modulate the degree of inflammation of the atherosclerotic lesion, thus influencing its final fate. Based on this hypothesis, targeting inflammation seems to be a promising approach to further improve our management of atherosclerotic-related diseases.

The Role of Monoclonal Antibodies in the Treatment of Atherosclerosis

Atherosclerosis is an inflammatory disease that involves antibody immune responses. Progression of hyperlipidemia can lead to atherosclerosis and subsequently cardiovascular diseases with high mortality. Additional lipid-lowering therapies other than statins are currently being studied, such as monoclonal antibodies. In this contemporary review, we examine the various monoclonal antibody therapies targeted toward atherosclerotic disease.

Crosstalk between dendritic cells and T lymphocytes during atherogenesis: Focus on antigen presentation and break of tolerance

Atherosclerosis is a chronic disease resulting from an impaired lipid and immune homeostasis, where the interaction between innate and adaptive immune cells leads to the promotion of atherosclerosis-associated immune-inflammatory response. Emerging evidence has suggested that this response presents similarities to the reactivity of effector immune cells toward self-epitopes, often as a consequence of a break of tolerance. In this context, dendritic cells, a heterogeneous population of antigen presenting cells, play a key role in instructing effector T cells to react against foreign antigens and T regulatory cells to maintain tolerance against self-antigens and/or to patrol for self-reactive effector T cells. Alterations in this delicate balance appears to contribute to atherogenesis. The aim of this review is to discuss different DC subsets, and their role in atherosclerosis as well as in T cell polarization. Moreover, we will discuss how loss of T cell tolerogenic phenotype participates to the immune-inflammatory response associated to atherosclerosis and how a better understanding of these mechanisms might result in designing immunomodulatory therapies targeting DC-T cell crosstalk for the treatment of atherosclerosis-related inflammation.

Tc17 CD8+ T cells accumulate in murine atherosclerotic lesions, but do not contribute to early atherosclerosis development

AIMS

CD8+ T cells can differentiate into subpopulations that are characterized by a specific cytokine profile, such as the Tc17 population that produces interleukin-17. The role of this CD8+ T-cell subset in atherosclerosis remains elusive. In this study, we therefore investigated the contribution of Tc17 cells to the development of atherosclerosis.

METHODS AND RESULTS

Flow cytometry analysis of atherosclerotic lesions from apolipoprotein E-deficient mice revealed a pronounced increase in RORγt+CD8+ T cells compared to the spleen, indicating a lesion-specific increase in Tc17 cells. To study whether and how the Tc17 subset affects atherosclerosis, we performed an adoptive transfer of Tc17 cells or undifferentiated Tc0 cells into CD8-/- low-density lipoprotein receptor-deficient mice fed a Western-type diet. Using flow cytometry, we showed that Tc17 cells retained a high level of interleukin-17A production in vivo. Moreover, Tc17 cells produced lower levels of interferon-γ than their Tc0 counterparts. Analysis of the aortic root revealed that the transfer of Tc17 cells did not increase atherosclerotic lesion size, in contrast to Tc0-treated mice.

CONCLUSION

These findings demonstrate a lesion-localized increase in Tc17 cells in an atherosclerotic mouse model. Tc17 cells appeared to be non-atherogenic, in contrast to their Tc0 counterpart.

Recent Advances on the Role and Therapeutic Potential of Regulatory T Cells in Atherosclerosis

Atherosclerotic diseases, including ischemic heart disease and stroke, are a main cause of mortality worldwide. Chronic vascular inflammation via immune dysregulation is critically involved in the pathogenesis of atherosclerosis. Accumulating evidence suggests that regulatory T cells (Tregs), responsible for maintaining immunological tolerance and suppressing excessive immune responses, play an important role in preventing the development and progression of atherosclerosis through the regulation of pathogenic immunoinflammatory responses. Several strategies to prevent and treat atherosclerosis through the promotion of regulatory immune responses have been developed, and could be clinically applied for the treatment of atherosclerotic cardiovascular disease. In this review, we summarize recent advances in our understanding of the protective role of Tregs in atherosclerosis and discuss attractive approaches to treat atherosclerotic disease by augmenting regulatory immune responses.

Effects of fatty acids on T cell function: role in atherosclerosis

T cells are among the most common cell types present in atherosclerotic plaques and are increasingly being recognized as a central mediator in atherosclerosis development and progression. At the same time, triglycerides and fatty acids have re-emerged as crucial risk factors for atherosclerosis. Triglycerides and fatty acids are important components of the milieu to which the T cell is exposed from the circulation to the plaque, and increasing evidence shows that fatty acids influence T cell function. In this Review, we discuss the effects of fatty acids on four components of the T cell response - metabolism, activation, proliferation and polarization - and the influence of these changes on the pathogenesis of atherosclerosis. We also discuss how quiescent T cells can undergo a type of metabolic reprogramming induced by exposure to fatty acids in the circulation that influences the subsequent functions of T cells after activation, such as in atherosclerotic plaques.

Promoting athero-protective immunity by vaccination with low density lipoprotein-derived antigens

Immune responses activated by LDL particles that have been trapped and oxidized in the arterial wall play an important role in atherosclerosis. Some of these immune responses are protective by facilitating the removal of pro-inflammatory and toxic lipid species formed as result of LDL oxidation. However, should these protective immune responses be insufficient, other more potent pro-inflammatory immune responses instead contributing to disease progression will gradually become dominant. The importance of the balance between protective and pathogenic immunity is particularly apparent when it comes to the adaptive immune system where pro-inflammatory T helper 1 (Th1) type T cells aggravate atherosclerosis, while regulatory T cells (Tregs) have an opposing role. As oxidized LDL is a key autoantigen in atherosclerosis, it has become an interesting possibility that immune-modulatory therapy that favors the activity of apolipoprotein B peptide-specific Tregs could be developed into a novel treatment strategy for prevention/stabilization of atherosclerosis and ischemic cardiovascular events. Indeed, several such oxidized LDL tolerance vaccines have shown promising results in animal models of atherosclerosis. This review will discuss the experimental background for development of atherosclerosis vaccines based on LDL-derived antigens as well as the challenges involved in translating these findings into clinical application.

Atherosclerosis: immunopathogenesis and strategies for immunotherapy

Atherosclerosis, a chronic inflammatory condition in which atheroma accumulates within the intima of the arterial wall, is a life-threatening manifestation of cardiovascular disease, due to atheroma rupture, chronic luminal narrowing and thrombosis. Current knowledge of the role of a protective immune response in atherosclerotic lesions has provided promising opportunities to develop new immunotherapeutic strategies. In particular, Tregs exert an atheroprotective role by releasing anti-inflammatory cytokines (IL-10/TGF-β) and suppressing autoreactive T lymphocytes. In vivo animal experiments have shown that this can be achieved by developing vaccines that stimulate immunological tolerance to atheroma antigens. Here, we present an overview of the current knowledge of the proatherogenic immune response, and we discuss the strategies currently used as immunoregulatory therapy.

Anti-inflammatory and Immunomodulatory Therapies in Atherosclerosis

Hypercholesterolemia is a major risk factor in atherosclerosis development and lipid-lowering drugs (i.e., statins) remain the treatment of choice. Despite effective reduction of LDL cholesterol in patients, a residual cardiovascular risk persists in some individuals, highlighting the need for further therapeutic intervention. Recently, the CANTOS trial paved the way toward the development of specific therapies targeting inflammation, a key feature in atherosclerosis progression. The pre-existence of multiple drugs modulating both innate and adaptive immune responses has significantly accelerated the number of translational studies applying these drugs to atherosclerosis. Additional preclinical research has led to the discovery of new therapeutic targets, offering promising perspectives for the treatment and prevention of atherosclerosis. Currently, both drugs with selective targeting and broad unspecific anti-inflammatory effects have been tested. In this chapter, we aim to give an overview of current advances in immunomodulatory treatment approaches for atherosclerotic cardiovascular diseases.

Immune responses against oxidized LDL as possible targets for prevention of atherosclerosis in systemic lupus erythematosus

Patients suffering from systemic lupus erythematosus (SLE) are at increased risk of developing cardiovascular disease (CVD) and traditional therapies including statins provide insufficient protection. Impaired removal of apoptotic material is a common pathogenic mechanism in both SLE and atherosclerosis and is considered to be a key factor in the development of autoimmunity. Since oxidized LDL and apoptotic material bind to the same receptors, we aimed to investigate if targeting the oxidized LDL autoimmunity can affect atherosclerosis in SLE. To investigate the possible role of oxidized LDL autoimmunity in the accelerated atherosclerosis associated with SLE we used a hypercholesterolemic SLE mouse model (B6.lpr.ApoE^-/- mice). Promoting LDL tolerance through mucosal immunization with an apolipoprotein B-100 peptide p45 (amino acids 661-680) and cholera toxin B-subunit fusion protein increased regulatory T cells and B cells in mesenteric lymph nodes and reduced plaque development in the aorta by 33%. Treatment with the oxidized LDL-specific antibody Orticumab reduced aortic atherosclerosis by 43%, subvalvular plaque area by 50% and the macrophage content by 31%. The present study provides support for oxLDL as a possible target for prevention of cardiovascular complications in SLE.

Regulatory T Cell-Enhancing Therapies to Treat Atherosclerosis

Experimental studies have provided strong evidence that chronic inflammation triggered by the sub-endothelial accumulation of cholesterol-rich lipoproteins in arteries is essential in the initiation and progression of atherosclerosis. Recent clinical trials highlighting the efficacy of anti-inflammatory therapies in coronary patients have confirmed that this is also true in humans Monocytes/macrophages are central cells in the atherosclerotic process, but adaptive immunity, through B and T lymphocytes, as well as dendritic cells, also modulates the progression of the disease. Analysis of the role of different T cell subpopulations in murine models of atherosclerosis identified effector Th1 cells as proatherogenic, whereas regulatory T cells (Tregs) have been shown to protect against atherosclerosis. For these reasons, better understanding of how Tregs influence the atherosclerotic process is believed to provide novel Treg-targeted therapies to combat atherosclerosis. This review article summarizes current knowledge about the role of Tregs in atherosclerosis and discusses ways to enhance their function as novel immunomodulatory therapeutic approaches against cardiovascular disease.

Phosphorylcholine-Primed Dendritic Cells Aggravate the Development of Atherosclerosis in ApoE-/- Mice

Background: Atherosclerosis is an inflammatory disease involving activation of adaptive and innate immune responses to antigens, including oxidized low-density lipoprotein (oxLDL) and phosphorylcholine (PC). Dendritic cells (DCs), which are antigen-presenting cells that activate T cells, are present in atherosclerotic lesions and are activated in immune organs. However, the mechanism by which PC promotes atherosclerosis is unclear.

Methods and Results: To evaluate whether PC promotes atherosclerosis via DCs, 2×10⁵ DCs activated by PC-keyhole limpet hemocyanin (DCs+PC-KLH) were injected into ApoE^−/− mice and the features of the plaques and the effects of the DCs on cellular and humoral immunity against PC-KLH were determined. Mice injected with DCs+PC-KLH had significantly larger atherosclerotic lesions than controls, with increased inflammation in the lesions and plaque instability. Furthermore, DCs+PC-KLH were characterized using flow cytometry after coculture of bone marrow-derived DCs and naïve T cells. DCs+PC-KLH showed an inflammatory phenotype, with increased CD86, CD40, and major histocompatibility complex Class II molecules (MHC-II), which promoted PC-specific T helper (Th) 1 and Th17 cell differentiation in vivo and in vitro. Moreover, 2 weeks after the administration of DCs+PC-KLH to mice, these mice produced PC- and oxLDL-specific IgG2a, compared with no production in the controls.

Conclusions: These findings suggest that DCs presenting PC promote specific immunity to PC, increase lesion inflammation, and accelerate atherosclerosis, which may explain how PC promotes atherosclerosis.

Vaccination in Atherosclerosis

Atherosclerosis is the major underlying pathology of cardiovascular diseases that together are the leading cause of death worldwide. The formation of atherosclerotic plaques is driven by chronic vascular inflammation. Although several risk factors have been identified and significant progress in disease prevention and treatment has been made, no therapeutic agents targeting inflammation are clinically available. Recent clinical trials established the potential of anti-inflammatory therapies as a treatment of atherosclerosis. However, adverse impacts on host defense have raised safety concerns about these therapies. Scientific evidence during the past 40 years implicated an adaptive immune response against plaque-associated autoantigens in atherogenesis. Preclinical data have underscored the protective potential of immunization against such targets precisely and without the impairment of host defense. In this review, we discuss the current vaccination strategies against atherosclerosis, supposed mechanisms of action, therapeutic potential, and the challenges that must be overcome in translating this idea into clinical practice.

Modulation of immune responses using adjuvants to facilitate therapeutic vaccination

Therapeutic vaccination offers great promise as an intervention for a diversity of infectious and non-infectious conditions. Given that most chronic health conditions are thought to have an immune component, vaccination can at least in principle be proposed as a therapeutic strategy. Understanding the nature of protective immunity is of vital importance, and the progress made in recent years in defining the nature of pathological and protective immunity for a range of diseases has provided an impetus to devise strategies to promote such responses in a targeted manner. However, in many cases, limited progress has been made in clinical adoption of such approaches. This in part results from a lack of safe and effective vaccine adjuvants that can be used to promote protective immunity and/or reduce deleterious immune responses. Although somewhat simplistic, it is possible to divide therapeutic vaccine approaches into those targeting conditions where antibody responses can mediate protection and those where the principal focus is the promotion of effector and memory cellular immunity or the reduction of damaging cellular immune responses as in the case of autoimmune diseases. Clearly, in all cases of antigen-specific immunotherapy, the identification of protective antigens is a vital first step. There are many challenges to developing therapeutic vaccines beyond those associated with prophylactic diseases including the ongoing immune responses in patients, patient heterogeneity, and diversity in the type and stage of disease. If reproducible biomarkers can be defined, these could allow earlier diagnosis and intervention and likely increase therapeutic vaccine efficacy. Current immunomodulatory approaches related to adoptive cell transfers or passive antibody therapy are showing great promise, but these are outside the scope of this review which will focus on the potential for adjuvanted therapeutic active vaccination strategies.

Tolerogenic vaccines for the treatment of cardiovascular diseases

Atherosclerosis is the main pathology behind most cardiovascular diseases. It is a chronic inflammatory disease characterized by the formation of lipid-rich plaques in arteries. Atherosclerotic plaques are initiated by the deposition of cholesterol-rich LDL particles in the arterial walls leading to the activation of innate and adaptive immune responses. Current treatments focus on the reduction of LDL blood levels using statins, however the critical components of inflammation and autoimmunity have been mostly ignored as therapeutic targets. The restoration of immune tolerance towards atherosclerosis-relevant antigens can arrest lesion development as shown in pre-clinical models. In this review, we evaluate the clinical development of similar strategies for the treatment of inflammatory and autoimmune diseases like rheumatoid arthritis, type 1 diabetes or multiple sclerosis and analyse the potential of tolerogenic vaccines for atherosclerosis and the challenges that need to be overcome to bring this therapy to patients.

The severity of internal carotid artery stenosis is associated with the circulating Th17 level

Aim

Immune and inflammatory reactions contribute to the progression of atherosclerosis. The walls of the different arteries and segments of the arteries have heterogeneous haemodynamic and histological features. We aimed to explore the relationship between the circulating T-cell subsets and the abundance of carotid atherosclerosis in different segments of carotid arteries.

Methods

70 patients underwent ultrasound duplex scanning to determine the degree of stenosis of the common carotid artery (CCA), the CCA bifurcation or the internal carotid artery (ICA). The blood frequencies of T-, B-, NK-cells, regulatory T cells (Treg), activated T-helpers (Th), IL10-producing Th, Th1 and Th17, as well as blood levels of hsCRP, sCD25, IL10 and IL17a were assessed.

Results

The frequencies of Th17 were increased in patients with ICA stenosis >35% and >50% vs. patients with ICA stenosis <35%. Th17 blood level ≥0.55 % of lymphocytes was associated with more severe stenosis of ICA (OR 4.3 (1.0–17.6), p < 0.05 for ICA stenosis of 35–50% and 6.8 (1.3–35.0), p < 0.05 for ICA stenosis >50%). BMI positively correlated with the CCA bifurcation stenosis degree (r = 0.33, p < 0.05).

Conclusion

The severity of ICA stenosis can be associated with the circulating Th17 level.

Regulatory T Cells License Macrophage Pro-Resolving Functions During Atherosclerosis Regression

RATIONALE

Regression of atherosclerosis is an important clinical goal; however, the pathways that mediate the resolution of atherosclerotic inflammation and reversal of plaques are poorly understood. Regulatory T cells (Tregs) have been shown to be atheroprotective, yet the numbers of these immunosuppressive cells decrease with disease progression, and whether they contribute to atherosclerosis regression is not known.

OBJECTIVE

We investigated the roles of Tregs in the resolution of atherosclerotic inflammation, tissue remodeling, and plaque contraction during atherosclerosis regression.

METHODS AND RESULTS

Using multiple independent mouse models of atherosclerosis regression, we demonstrate that an increase in plaque Tregs is a common signature of regressing plaques. Single-cell RNA-sequencing of plaque immune cells revealed that unlike Tregs from progressing plaques that expressed markers of natural Tregs derived from the thymus, Tregs in regressing plaques lacked Nrp1 expression, suggesting that they are induced in the periphery during lipid-lowering therapy. To test whether Tregs are required for resolution of atherosclerotic inflammation and plaque regression, Tregs were depleted using CD25 monoclonal antibody in atherosclerotic mice during apolipoprotein B antisense oligonucleotide-mediated lipid lowering. Morphometric analyses revealed that Treg depletion blocked plaque remodeling and contraction, and impaired hallmarks of inflammation resolution, including dampening of the T helper 1 response, alternative activation of macrophages, efferocytosis, and upregulation of specialized proresolving lipid mediators.

CONCLUSIONS

Our data establish essential roles for Tregs in resolving atherosclerotic cardiovascular disease and provide mechanistic insight into the pathways governing plaque remodeling and regression of disease.

Vaccination Strategies and Immune Modulation of Atherosclerosis

Adaptive as well as innate immune responses contribute to the development of atherosclerosis. Studies performed in experimental animals have revealed that some of these immune responses are protective while others contribute to the progression of disease. These observations suggest that it may be possible to develop novel therapies for cardiovascular disease by selectively modulating such atheroprotective and proatherogenic immunity. Recent advances in cancer treatment using immune check inhibitors and CAR (chimeric antigen receptor) T-cell therapy serve as excellent examples of the possibilities of targeting the immune system to combat disease. LDL (low-density lipoprotein) that has accumulated in the artery wall is a key autoantigen in atherosclerosis, and activation of antigen-specific T helper 1–type T cells is thought to fuel plaque inflammation. Studies aiming to prove this concept by immunizing experimental animals with oxidized LDL particles unexpectedly resulted in activation of atheroprotective immunity involving regulatory T cells. This prompted several research groups to try to develop vaccines against atherosclerosis. In this review, we will discuss the experimental and clinical data supporting the possibility of developing immune-based therapies for lowering cardiovascular risk. We will also summarize ongoing clinical studies and discuss the challenges associated with developing an effective and safe atherosclerosis vaccine.

Getting to the Heart of the Matter: The Role of Regulatory T-Cells (Tregs) in Cardiovascular Disease (CVD) and Atherosclerosis

Cardiovascular diseases (CVD) are the leading cause of mortality worldwide. Atherosclerosis is directly associated with CVD and is characterized by slow progressing inflammation which results in the deposition and accumulation of lipids beneath the endothelial layer in conductance and resistance arteries. Both chronic inflammation and disease progression have been associated with several risk factors, including but not limited to smoking, obesity, diabetes, genetic predisposition, hyperlipidemia, and hypertension. Currently, despite increasing incidence and significant expense on the healthcare system in both western and developing countries, there is no curative therapy for atherosclerosis. Instead patients rely on surgical intervention to avoid or revert vessel occlusion, and pharmacological management of the aforementioned risk factors. However, neither of these approaches completely resolve the underlying inflammatory environment which perpetuates the disease, nor do they result in plaque regression. As such, immunomodulation could provide a novel therapeutic option for atherosclerosis; shifting the balance from proatherogenic to athero-protective. Indeed, regulatory T-cells (Tregs), which constitute 5-10% of all CD4⁺ T lymphocytes in the peripheral blood, have been shown to be athero-protective and could function as new targets in both CVD and atherosclerosis. This review aims to give a comprehensive overview about the roles of Tregs in CVD, focusing on atherosclerosis.

Mucosal Administration of E-selectin Limits Disability in Models of Multiple Sclerosis

E-selectin plays an important role in mediating the rolling of leukocytes along and thus, the subsequent extravasation across activated endothelial cells comprising the microvasculature of the blood brain barrier (BBB). In multiple sclerosis (MS) and other inflammatory disorders of the central nervous system (CNS), the microvasculature is altered and immune cells infiltrate the brain and spinal cord contributing to damage, demyelination and ultimately disability. While mucosal administration is typically used to affect lymphocyte hyporesponsiveness or tolerance to suspect autoantigens, intranasal administration to E-selectin has previously been shown to protect against CNS inflammatory insults. We characterized the potential for mucosal administration of E-selectin to modulate CNS autoimmunity in the experimental autoimmune encephalomyelitis (EAE) model of MS. Intranasally administered E-selectin reduced swelling by as much as 50% in delayed-type hypersensitivity reactions compared to ovalbumin-tolerized controls. Intranasal E-selectin delivery prior to disease induction with myelin oligodendrocyte glycoprotein (MOG)_35-55 reduced disease severity and total disease burden by more than 50% compared to PBS-tolerized animals; this protection was not associated with differences in the magnitude of the autoimmune response. Examination after the onset of disease showed that protection was associated with significant reductions in inflammatory infiltrates throughout the spinal cord. Tolerization to E-selectin did not influence encephalitogenic characteristics of autoreactive T cells such as IFN-gamma or IL-17 production. Clinical disease was also significantly reduced when E-selectin was first delivered after the onset of clinical symptoms. Splenic and lymph node (LN) populations from E-selectin-tolerized animals showed E-selectin-specific T cell responses and production of the immunomodulatory cytokine IL-10. Transfer of enriched CD4+ T cells from E-selectin tolerized mice limited disability in the passive SJL model of relapsing remitting MS. These results suggest a role for influencing E-selectin specific responses to limit neuroinflammation that warrants further exploration and characterization to better understand its potential to mitigate neurodegeneration in disorders such as MS.

Anionic 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) liposomes induce antigen-specific regulatory T cells and prevent atherosclerosis in mice

Atherosclerosis is the predominant underlying pathology of many types of cardiovascular disease and is one of the leading causes of death worldwide. It is characterized by the retention of oxidized low-density lipoprotein (ox-LDL) in lipid-rich macrophages (foam cells) in the intima of arteries. Autoantigens derived from oxLDL can be used to vaccinate against atherosclerosis. However, a major challenge is the induction of antigen-specific Tregs in a safe and effective way. Here we report that liposomes containing the anionic phospholipid 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) induce Tregs that are specific for the liposomes' cargo. Mechanistically, we show a crucial role for the protein corona that forms on the liposomes in the circulation, as uptake of DSPG-liposomes by antigen-presenting cells is mediated via complement component 1q (C1q) and scavenger receptors (SRs). Vaccination of atherosclerotic mice on a western-type diet with DSPG-liposomes encapsulating an LDL-derived peptide antigen significantly reduced plaque formation by 50% and stabilized the plaques, and reduced serum cholesterol concentrations. These results indicate that DSPG-liposomes have potential as a delivery system in vaccination against atherosclerosis.

Regulatory T cells as a new therapeutic target for atherosclerosis

Atherosclerosis is an autoimmune disease caused by self- and non-self-antigens contributing to excessive activation of T and B cell immune responses. These responses further aggravate vascular infiammation and promote progression of atherosclerosis and vulnerability to plaques via releasing pro-infiammatory cytokines. Regulatory T cells (Tregs) as the major immunoregulatory cells, in particular, induce and maintain immune homeostasis and tolerance by suppressing the immune responses of various cells such as T and B cells, natural killer (NK) cells, monocytes, and dendritic cells (DCs), as well as by secreting inhibitory cytokines interleukin (IL)-10, IL-35 and transcription growth factor β (TGF-β) in both physiological and pathological states. Numerous evidence demonstrates that reduced numbers and dysfunction of Treg may be involveved in atherosclerosis pathogenesis. Increasing or restoring the numbers and improving the immunosuppressive capacity of Tregs may serve as a fundamental immunotherapy to treat atherosclerotic cardiovascular diseases. In this article, we briefiy present current knowledge of Treg subsets, summarize the relationship between Tregs and atherosclerosis development, and discuss the possibilities of regulating Tregs for prevention of atherosclerosis pathogenesis and enhancement of plaque stability. Although the exact molecular mechanisms of Treg-mediated protection against atherosclerosis remain to be elucidated, the strategies for targeting the regulation of Tregs may provide specific and significant approaches for the prevention and treatment of atherosclerotic cardiovascular diseases.

Atheroregressive Potential of the Treatment with a Chimeric Monoclonal Antibody against Sulfated Glycosaminoglycans on Pre-existing Lesions in Apolipoprotein E-Deficient Mice

The retention of lipoprotein particles in the intima, in particular to glycosaminoglycan side chains of proteoglycans, is a critical step in atherosclerosis initiation. Administration of chP3R99, a chimeric mouse/human monoclonal antibody inducing an anti-idiotypic network response against glycosaminoglycans was previously shown to prevent atherosclerotic lesion progression, yet its effect in the late-stage progression of lesions remains unknown. This study investigated the effect of chP3R99 at a late stage of disease development in apolipoprotein E-deficient mice and the vascular mechanisms involved. Male apolipoprotein E-deficient mice were fed a high-fat high-cholesterol diet from 4 to 19 weeks old, at which time mice were fed normal chow and 5 doses of chP3R99 (50 μg) or isotype-matched IgG (hR3) were administered subcutaneously weekly for the first 3 administrations, then at weeks 24 and 26 before sacrifice (week 28). Lesions progression was reduced by 88% in treated mice with no change in total plasma cholesterol levels, yet with increased sera reactivity to chP3R99 idiotype and heparin, suggesting the induction of an anti-idiotype antibody cascade against glycosaminoglycans, which was likely related with the atheroprotective effect. chP3R99 treatment initiated regression in a significant number of mice. Circulating levels of interleukin-6 were reduced along with a striking diminution of inflammatory cell accumulation in the vessel wall, and of VCAM-1 labeling in vivo. The ratio of IL-10/iNOS gene expression in aortas increased in chP3R99-treated mice. In conclusion, our results show that treatment with chP3R99 reduces vascular inflammatory burden and halts lesion progression with potential for regression in the late phase of the disease in atherosclerotic mice, and support the therapeutic intervention against glycosaminoglycans as a novel strategy to reverse atherosclerosis.

Amygdalin ameliorates the progression of atherosclerosis in LDL receptor‑deficient mice

Previous studies have demonstrated that regulatory T cells (Tregs) are pivotal in the regulation of T cell-mediated immune responses in atherosclerosis, a chronic autoimmune-like disease. In the authors' previous studies, it was demonstrated that amygdalin ameliorated atherosclerosis by the regulation of Tregs in apolipoprotein E-deficient (ApoE^−/−) mice. Therefore, the aim of the present study was to investigate the therapeutic effect of amygdalin on low-density lipoprotein (LDL) receptor deficient (LDLR^−/−) mice, and to examine its immune regulatory function by the stimulation of Tregs. To establish an atherosclerosis mouse model, the LDLR^−/− mice were fed a high fat and high cholesterol diet then the total plasma cholesterol, triglyceride, LDL and chemokines levels were measured by an ELISA. Following sacrificing the mice, the upper sections of the aorta were stained by hematoxylin and eosin, and Oil red O to assess the plaque area. Then western blotting and reverse transcription polymerase chain reactions were performed to analysis the expression levels of cluster of differentiation 68, monocyte chemoattractant protein-1, matrix metalloproteinase (MMP)-2, MMP-9 and forkhead box P3 (Foxp3). To further confirm the activation of FOXP3 by amygdalin, lentiviruses carrying Foxp3 shRNA were injected into the mice, and the serum cytokines levels were measured by ELISA. Following feeding of the mice with a high-fat/high-cholesterol diet, the LDLR^−/− mice demonstrated comparatively higher levels of triglyceride, total cholesterol and LDL, compared with levels in the amygdalin-treated mice. By comparing the vessel area, lumen area, plaque area, and percentage aortic plaque coverage, the effects of amygdalin on pre-existing lesions were assessed. In addition, the levels of CD68, monocyte chemoattractant protein-1, MMP-2 and MMP-9 were analyzed, and analysis of the expression of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α indicated that the mice treated with amygdalin had decreased expression of pro-inflammatory cytokines. The mRNA and protein levels of Foxp3 were also quantified, and the mice treated with amygdalin demonstrated an increased number of Tregs. The knockdown of Foxp3mRNA resulted in the increased secretion of IL-1β, IL-6 and TNF-α. Therefore, the data indicated that amygdalin regulated the formation of atherosclerosis and stabilized the plaque by suppressing inflammatory responses and promoting the immune-modulation function of Tregs. Taken together, the results demonstrated the therapeutic effect of amygdalin on atherosclerosis.

Immune regulation by oral tolerance induces alternate activation of macrophages and reduces markers of plaque destabilization in Apobtm2Sgy/Ldlrtm1Her/J mice

Atherosclerosis is the leading cause for cardiovascular mortality. We determined the effect of multi-antigenic construct expressing three peptides AHC (ApoB100, HSP60 and outer membrane protein of chlamydia pneumonia) in stabilizing advanced atherosclerosis in Apob^tm2Sgy/Ldlr^tm1Her/J mice. Atherosclerosis was induced by feeding high fat diet (HFD) to mice for 10 weeks, followed by five oral dosing with purified AHC or ovalbumin on alternate days and continued on HFD for another 10 weeks. Tolerance was associated with significantly higher numbers of regulatory T cells both in aortic sinus and spleen with higher mRNA expression of CTLA4 (3 fold), Foxp3 (1.4 folds) and TGF-β (1.62) in aorta. Tregs cells were found to induce alternate activation of macrophages to M2 phenotype, with a reduction in plaque inflammation. AHC treatment showed evidence of plaque stabilization as observed by reduction in plaque necrosis in aortic sinus (35.8%) and in brachiocephalic artery (26%), with reduced expression of Tissue factor and MMP9. Macrophage apoptosis was reduced and collagen content was enhanced by treatment. Our results suggest that tolerance to atherogenic peptides increases regulatory T cells which activate M2 macrophages, prevent T cell proliferation and reduce plaque destabilization and inflammatory markers thus providing evidences for plaque stabilization in mice with advanced atherosclerosis.

Immune checkpoint proteins: exploring their therapeutic potential to regulate atherosclerosis

The immune system provides a large variety of immune checkpoint proteins, which involve both costimulatory and inhibitory proteins. Costimulatory proteins can promote cell survival, cell cycle progression and differentiation to effector and memory cells, whereas inhibitory proteins terminate these processes to halt ongoing inflammation. Immune checkpoint proteins play a pivotal role in atherosclerosis by regulating the activation and proliferation of various immune and non-immune cells, such as T-cells, macrophages and platelets. Upon activation within the atherosclerotic lesions or in secondary lymphoid organs, these cells produce large amounts of pro-atherogenic cytokines that contribute to the growth and destabilization of lesions, which can result in rupture of the lesion causing acute coronary syndromes, such as a myocardial infarction. Given the presence and regulatory capacity of immune checkpoint proteins in the circulation and atherosclerotic lesions of cardiovascular patients, modulation of these proteins by, for example, the use of monoclonal antibodies, offers unique opportunities to regulate pro-inflammatory immune responses in atherosclerosis. In this review, we highlight the latest advances on the role of immune checkpoint proteins, such as OX40-OX40L, CTLA-4 and TIM proteins, in atherosclerosis and discuss their therapeutic potential as promising immunotherapies to treat or prevent cardiovascular disease.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

The immunology of atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, both in the general population and among patients with chronic kidney disease (CKD). In most cases, the underlying cause of the cardiovascular event is atherosclerosis - a chronic inflammatory disease. CKD accelerates atherosclerosis via augmentation of inflammation, perturbation of lipid metabolism, and other mechanisms. In the artery wall, subendothelial retention of plasma lipoproteins triggers monocyte-derived macrophages and T helper type 1 (T_H1) cells to form atherosclerotic plaques. Inflammation is initiated by innate immune reactions to modified lipoproteins and is perpetuated by T_H1 cells that react to autoantigens from the apolipoprotein B100 protein of LDL. Other T cells are also active in atherosclerotic lesions; regulatory T cells inhibit pathological inflammation, whereas T_H17 cells can promote plaque fibrosis. The slow build-up of atherosclerotic plaques is asymptomatic, but plaque rupture or endothelial erosion can induce thrombus formation, leading to myocardial infarction or ischaemic stroke. Targeting risk factors for atherosclerosis has reduced mortality, but a need exists for novel therapies to stabilize plaques and to treat arterial inflammation. Patients with CKD would likely benefit from such preventive measures.

Vaccination against T-cell epitopes of native ApoB100 reduces vascular inflammation and disease in a humanized mouse model of atherosclerosis

BACKGROUND AND OBJECTIVES

The T-cell response to low-density lipoprotein (LDL) in the vessel wall plays a critical role in atherosclerotic plaque formation and stability. In this study, we used a new translational approach to investigate epitopes from human apolipoprotein B100 (ApoB100), the protein component of LDL, which triggers T-cell activation. We also evaluated the potential of two selected native ApoB100 epitopes to modulate atherosclerosis in human ApoB100-transgenic Ldlr^-/- (HuBL) mice.

METHODS AND RESULTS

HuBL mice were immunized with human atherosclerotic plaque homogenate to boost cellular autoimmune response to tissue-derived ApoB100 epitopes. In vitro challenge of splenocytes from immunized mice with a library of overlapping native peptides covering human ApoB100 revealed several sequences eliciting T-cell proliferation. Of these sequences, peptide (P) 265 and P295 were predicted to bind several human leucocyte antigen (HLA) haplotypes and induced high levels of interferon (IFN)-γ. Vaccination of HuBL mice with these peptides mounted a strong adaptive immune response to native ApoB100, including high levels of epitope-specific plasma IgGs. Interestingly, P265 and P295 vaccines significantly decreased plaque size, reduced macrophage infiltration and increased IgG1 deposition in the plaques. Purified IgGs from vaccinated mice displayed anti-inflammatory properties against macrophages in vitro, reducing their response to LPS in a dose-dependent manner.

CONCLUSION

We identified two specific epitopes from human native ApoB100 that trigger T-cell activation and protect HuBL mice against atherosclerosis when used in a vaccine. Our data suggest that vaccination-induced protective mechanisms may be mediated at least in part through specific antibody responses to LDL that inhibit macrophage activation.

Oral administration of recombinant Mycobacterium smegmatis expressing a tripeptide construct derived from endogenous and microbial antigens prevents atherosclerosis in ApoE(-/-) mice

INTRODUCTION

Immunotherapy by inducing oral tolerance to atherogenic self-antigens is gaining importance as an alternative treatment modality for atherosclerosis. The use of live bacterial vectors to express the recombinant antigen in vivo will obviate the need for large-scale purification of recombinant protein and may also augment the efficacy of oral tolerance induction.

AIM

The objective of the study was to explore the use of recombinant Mycobacterium smegmatis as a live vector for oral delivery of antigens to induce immune tolerance.

METHOD AND RESULTS

We developed a M. smegmatis vector to secrete a recombinant tripeptide construct (AHC; peptides from Apolipoprotein B, Heat-shock protein 60 and Chlamydia pneumoniae outer membrane protein) expressed in a dendroaspin protein scaffold in pJH154 background. Immune response and oral tolerance to the cloned peptides were studied in C57/BL6 mice. The efficacy of this live vaccine to control atherosclerosis was studied in ApoE(-/-) knockout mice in C57/BL6 background. Oral administration of M. smegmatis secreting the cloned AHC antigen was found to induce tolerance to cloned protein and reduce the development of atherosclerosis by 24.0% compared to control. Protection against atherosclerosis was associated with increase in expression of regulatory T cell-associated markers including CTLA4 (1.8-fold), Foxp3 (2.6-fold), TGF-β (2.8-fold), IL10 (2.9-fold), and reduction in lipids, macrophage infiltration, and expression of inflammatory mediators in aorta.

CONCLUSIONS

Our results suggest that M. smegmatis can be developed as an oral carrier of recombinant proteins to treat inflammatory autoimmune diseases.

Adaptive Response of T and B Cells in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is initiated by the retention and accumulation of cholesterol-containing lipoproteins, particularly low-density lipoprotein, in the artery wall. In the arterial intima, lipoprotein components that are generated through oxidative, lipolytic, and proteolytic activities lead to the formation of several danger-associated molecular patterns, which can activate innate immune cells as well as vascular cells. Moreover, self- and non-self-antigens, such as apolipoprotein B-100 and heat shock proteins, can contribute to vascular inflammation by triggering the response of T and B cells locally. This process can influence the initiation, progression, and stability of plaques. Substantial clinical and experimental data support that the modulation of adaptive immune system may be used for treating and preventing atherosclerosis. This may lead to the development of more selective and less harmful interventions, while keeping host defense mechanisms against infections and tumors intact. Approaches such as vaccination might become a realistic option for cardiovascular disease, especially if they can elicit regulatory T and B cells and the secretion of atheroprotective antibodies. Nevertheless, difficulties in translating certain experimental data into new clinical therapies remain a challenge. In this review, we discuss important studies on the function of T- and B-cell immunity in atherosclerosis and their manipulation to develop novel therapeutic strategies against cardiovascular disease.

Chlamydomonas reinhardtii chloroplasts express an orally immunogenic protein targeting the p210 epitope implicated in atherosclerosis immunotherapies

An algae-based vaccine model against atherosclerosis was developed with positive findings in terms of antigen yield and immunogenicity in mouse. Several immunotherapies against atherosclerosis have been evaluated at the preclinical level thus far, with some of them currently under evaluation in clinical trials. In particular, the p210 epitope from ApoB100 is known to elicit atheroprotective responses. Considering that Chlamydomonas reinhardtii is an attractive host for the production and delivery of subunit vaccines, in this study a chimeric protein consisting of the B subunit of the cholera toxin and the p210 epitope from ApoB100 (CTB:p210) has been expressed in C. reinhardtii chloroplast as an attempt to establish an oral vaccine candidate against atherosclerosis. The Chlamydomonas-made CTB:p210 protein was successfully expressed at levels of up to 60 µg per g of fresh weight biomass. The antigenic activity of the CTB and the p210 moiety was preserved in the CTB:p210 chimera. Moreover the algae-made CTB:p210 showed an immunogenic activity, when orally administered to BALB/c mice, as evidenced the presence of anti-p210 serum antibodies in mice treated with the algae-derived CTB:p210. The antibody response lasts for at least 80 days after the last boost. This experimental model is proposed as a convenient tool in the development of low cost atherosclerosis vaccines of easy compliance and friendly delivery. Further studies will determine the therapeutic potential of this algae-made vaccine in atherosclerosis animal models.

2015 Russell Ross Memorial Lecture in Vascular Biology: Protective Autoimmunity in Atherosclerosis

Atherosclerosis is an inflammatory disease of the arterial wall. It is accompanied by an autoimmune response against apolipoprotein B-100, the core protein of low-density lipoprotein, which manifests as CD4 T cell and antibody responses. To assess the role of the autoimmune response in atherosclerosis, the nature of the CD4 T cell response against apolipoprotein B-100 was studied with and without vaccination with major histocompatibility complex-II-restricted apolipoprotein B-100 peptides. The immunologic basis of autoimmunity in atherosclerosis is discussed in the framework of theories of adaptive immunity. Older vaccination approaches are also discussed. Vaccinating Apoe(-/-) mice with major histocompatibility complex-II-restricted apolipoprotein B-100 peptides reduces atheroma burden in the aorta by ≈40%. The protective mechanism likely includes secretion of interleukin-10. Protective autoimmunity limits atherosclerosis in mice and suggests potential for developing preventative and therapeutic vaccines for humans.

Regulatory T cells in atherosclerosis: critical immune regulatory function and therapeutic potential

Atherosclerosis is a chronic inflammatory disease that is mediated by innate and adaptive immune responses. The disease is characterized by sub-endothelial accumulation and modification of lipids in the artery wall triggering an inflammatory reaction which promotes lesion progression and eventual plaque rupture, thrombus formation, and the respective clinical sequelae such as myocardial infarction or stroke. During the past decade, T-cell-mediated immune responses, especially control of pro-inflammatory signals by regulatory T cells (Tregs), have increasingly attracted the interest of experimental and clinical researchers. By suppression of T cell proliferation and secretion of anti-inflammatory cytokines, such as interleukin-10 (IL-10) and transforming growth factor-β, Tregs exert their atheroprotective properties. Atherosclerosis-prone, hyperlipidemic mice harbor systemically less Tregs compared to wild-type mice, suggesting an imbalance of immune cells which affects local and systemic inflammatory and potentially metabolic processes leading to atherogenesis. Restoring or increasing Treg frequency and enhancing their suppressive capacity by various modulations may pose a promising approach for treating inflammatory conditions such as cardiovascular diseases. In this review, we briefly summarize the immunological basics of atherosclerosis and introduce the role and contribution of different subsets of T cells. We then discuss experimental data and current knowledge pertaining to Tregs in atherosclerosis and perspectives on manipulating the adaptive immune system to alleviate atherosclerosis and cardiovascular disease.

Tolerization against atherosclerosis using heat shock protein 60

Atherosclerosis is a chronic inflammatory disease of the artery wall, and both innate and adaptive immunity play important roles in the pathogenesis of this disease. In several experimental and human experiments of early atherosclerotic lesions, it has been shown that the first pathogenic event in atherogenesis is intimal infiltration of T cells at predilection sites. These T cells react to heat shock protein 60 (HSP60), which is a ubiquitous self-antigen expressed on the surface of endothelial cells (ECs) together with adhesion molecules in response to classical risk factors for atherosclerosis. When HSP60 is expressed on the EC surface, it can act as a "danger-signal" for both cellular and humoral immune reactions. Acquired by infection or vaccination, beneficial protective immunity to microbial HSP60 and bona fide autoimmunity to biochemically altered autologous HSP60 is present in all humans. Thus, the development of atherosclerosis during aging is paid by the price for lifelong protective preexisting anti-HSP60 immunity by harmful (auto)immune cross-reactive attack on arterial ECs maltreated by atherosclerosis risk factors. This is supported by experiments, which shows that bacterial HSP60 immunization can lead and accelerate experimental atherosclerosis. This review article presents accumulating proof that supports the idea that tolerization with antigenic HSP60 protein or its peptides may arrest or even prevent atherosclerosis by increased production of regulatory T cells and/or anti-inflammatory cytokines. Recent data indicates that HSP60, or more likely some of its derivative peptides, has immunoregulatory functions. Therefore, these peptides may have important potential for being used as diagnostic agents or therapeutic targets.

Association of Soluble Fibrinogen-like Protein 2 with the Severity of Coronary Artery Disease

Objective The purpose of this study was to investigate the relationship between circulating soluble fibrinogen-like protein 2 (sFGL2) concentrations and the severity of coronary artery disease (CAD) in patients who underwent first-time angiography for suspected CAD. Methods Serum sFGL2 concentrations were measured in 102 consecutive patients by an enzyme-linked immunosorbent assay (ELISA). The number of circulating CD4(+)CD25(+)CD127(low) T regulatory cells (Tregs) was determined by flow cytometry and effecter cytokines, including transforming growth factor-β1 and interleukin-10 (IL-10), were also evaluated by an ELISA. Associations between sFGL2 and Tregs with angiographic indexes of the severity of CAD (i.e., number of diseased vessels and the modified Gensini score) were estimated. Results The sFGL2 levels in patients with angiographically confirmed CAD were significantly lower than those in patients with normal coronary arteries (26.95±8.53 vs. 9.88±5.46 ng/mL, p<0.001). Significant correlations were observed between the serum sFGL2 level and number of diseased vessels (r=-0.860, p<0.001) and modified Gensini score (r=-0.833, p<0.001). Using a multivariate analysis, the serum sFGL2 level was independently associated with the presence and severity of CAD. Conclusion The serum sFGL2 levels are significantly lower in the presence of CAD and correlate with the severity of the disease. Further clinical studies are needed to confirm the use of sFGL2 as a biomarker for the detection and extent of CAD.

Mucosal Administration of Collagen V Ameliorates the Atherosclerotic Plaque Burden by Inducing Interleukin 35-dependent Tolerance

We have shown previously that collagen V (col(V)) autoimmunity is a consistent feature of atherosclerosis in human coronary artery disease and in the Apoe(-/-) mouse model. We have also shown sensitization of Apoe(-/-) mice with col(V) to markedly increase the atherosclerotic burden, providing evidence of a causative role for col(V) autoimmunity in atherosclerotic pathogenesis. Here we sought to determine whether induction of immune tolerance to col(V) might ameliorate atherosclerosis, providing further evidence for a causal role for col(V) autoimmunity in atherogenesis and providing insights into the potential for immunomodulatory therapeutic interventions. Mucosal inoculation successfully induced immune tolerance to col(V) with an accompanying reduction in plaque burden in Ldlr(-/-) mice on a high-cholesterol diet. The results therefore demonstrate that inoculation with col(V) can successfully ameliorate the atherosclerotic burden, suggesting novel approaches for therapeutic interventions. Surprisingly, tolerance and reduced atherosclerotic burden were both dependent on the recently described IL-35 and not on IL-10, the immunosuppressive cytokine usually studied in the context of induced tolerance and amelioration of atherosclerotic symptoms. In addition to the above, using recombinant protein fragments, we were able to localize two epitopes of the α1(V) chain involved in col(V) autoimmunity in atherosclerotic Ldlr(-/-) mice, suggesting future courses of experimentation for the characterization of such epitopes.

Intranasal immunization with heat shock protein 60 induces CD4(+) CD25(+) GARP(+) and type 1 regulatory T cells and inhibits early atherosclerosis

Atherosclerosis is an autoimmune inflammatory disease involving both innate and adaptive immune mechanisms. Immune tolerance induction may have therapeutic potential for the suppression of atherosclerosis. Current interest is directed towards mucosal tolerance induction, especially nasal tolerance. Previous studies have shown that heat shock protein 60 (HSP60) is recognized as an important autoantigen in atherosclerosis, and nasal or oral HSP60 can induce tolerance and ameliorate atherosclerosis by inducing several subsets of regulatory T cells (Tregs ) such as latency-associated peptide (LAP)(+) and forkhead box transcription factor 3 (FoxP3)(+) Tregs. However, little is known regarding the detailed mechanisms of nasal tolerance. Here, we again investigated the impact of nasal HSP60 on atherosclerosis and the mechanisms underlying the anti-atherosclerosis responses. We found that nasal HSP60 caused a significant 33·6% reduction in plaque size at the aortic root in the early stages of atherosclerosis (P < 0·001). Notably, a significant increase in activated CD4(+) CD25(+) glycoprotein A repetitions predominant (GARP)(+) Tregs, type 1 Tregs (Tr1 cells), and CD4(+) CD25(+) FoxP3(+) Tregs, as well as a marked decrease in the numbers of type 1 and 17 T helper cells was detected in the spleens and cervical lymph nodes of HSP60-treated mice. Moreover, nasal HSP60 increases the production of transforming growth factor (TGF)-β and interleukin (IL)-10 and decreases the secretion of IFN-γ and IL-17. Interestingly, the atheroprotective role of nasal HSP60 treatment was abrogated partly by the neutralization of IL-10. Our findings show that nasal administration of HSP60 can attenuate atherosclerotic formation by inducing GARP(+) Tregs, Tr1 cells and FoxP3(+) Tregs, and that these Tregs maintain immune homeostasis by secreting IL-10 and TGF-β.

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.

Regulating Inflammatory Immune Response to Atherogenic Antigens Prevents Development and Progression of Atherosclerosis in New Zealand White Rabbits

BACKGROUND

Inflammatory immune response to atherogenic self-antigens plays an important role in the development of atherosclerosis. We evaluated the role of oral tolerance to three peptides in controlling atherosclerosis in New Zealand white rabbits.

METHODS

Peptides derived from apolipoprotein B (ApoB), heat shock protein 60, and outer membrane protein from Chlamydia pneumoniae were expressed as part of the dendroaspin protein scaffold (AHC). Groups of 3-month-old rabbits were dosed orally with purified AHC protein either before the onset of disease or 2 months after inducing atherosclerosis; they were euthanized at the age of 7 months to study disease development and progression.

RESULTS

Oral treatment with AHC resulted in a marked increase in regulatory T cells in the lymphoid organs and reduced the development and progression of atherosclerosis by 48.6% and 28.4%, respectively (P < 0.05). Oral tolerance decreased plaque inflammation, enhanced expression of anti-inflammatory and regulatory markers in the aorta, and attenuated the adaptive immune response to self-antigens. AHC treatment in rabbits with established disease significantly decreased vascular cell adhesion molecule 1 (VCAM-1) (6.2 fold) and monocyte chemoattractant protein-1(MCP-1) (3 fold) expression and reduced the infiltration of macrophages into the aorta. Collagen content and the smooth muscle cell-to-macrophage ratio were higher in treated animals, whereas markers of plaque vulnerability, including matrix metalloproteinase expression, were reduced.

CONCLUSIONS

Our results suggest that oral tolerance to multiantigenic AHC molecule restores the immune balance and induces markers of plaque stability in rabbits.

Atherosclerosis and the role of immune cells

Atherosclerosis is a chronic inflammatory disease arising from lipids, specifically low-density lipoproteins, and leukocytes. Following the activation of endothelium with the expression of adhesion molecules and monocytes, inflammatory cytokines from macrophages, and plasmacytoid dendritic cells, high levels of interferon (IFN)-α and β are generated upon the activation of toll-like receptor-9, and T-cells, especially the ones with Th1 profile, produce pro-inflammatory mediators such as IFN-γ and upregulate macrophages to adhere to the endothelium and migrate into the intima. This review presents an exhaustive account for the role of immune cells in the atherosclerosis.

Antisense oligonucleotides, microRNAs, and antibodies

The specificity of Watson-Crick base pairing and the development of several chemical modifications to oligonucleotides have enabled the development of novel drug classes for the treatment of different human diseases. This review focuses on promising results of recent preclinical or clinical studies on targeting HDL metabolism and function by antisense oligonucleotides and miRNA-based therapies. Although many hurdles regarding basic mechanism of action, delivery, specificity, and toxicity need to be overcome, promising results from recent clinical trials and recent approval of these types of therapy to treat dyslipidemia suggest that the treatment of HDL dysfunction will benefit from these unique clinical opportunities. Moreover, an overview of monoclonal antibodies (mAbs) developed for the treatment of dyslipidemia and cardiovascular disease and currently being tested in clinical studies is provided. Initial studies have shown that these compounds are generally safe and well tolerated, but ongoing large clinical studies will assess their long-term safety and efficacy.

Modulation of autoimmunity and atherosclerosis - common targets and promising translational approaches against disease

Atherosclerosis is a chronic inflammatory disease of the arterial wall that is influenced by several risk factors, including hyperlipidemia and hypertension. Autoimmune diseases substantially increase the risk for cardiovascular disease (CVD). Although atherosclerotic CVD, such as myocardial and stroke, is much more prevalent than classical autoimmune conditions such as rheumatoid arthritis, psoriasis, and systemic lupus erythematosus, these types of pathology have many similarities, raising the possibility that therapies against autoimmune disease can have beneficial effects on CVD. Substantial clinical and experimental data support the potential for immunomodulatory approaches to combating both autoimmune and cardiovascular diseases, including classical immunosuppressants, anticytokine therapy, the targeting of T and B cells and their responses, and vaccination. In this review, we discuss experimental and clinical studies that have used immunomodulatory approaches to mitigate autoimmune reactions and examine their potential to prevent and treat atherosclerotic CVD.

Vaccination to modulate atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the artery wall. Adaptive immunity plays a key role in the pathogenesis of atherosclerosis. Recently, modulation of the immune response against atherosclerotic plaque antigen(s) has attracted attention as a potentially preventive and therapeutic approach. Here, we review a series of studies on immunization with various antigens targeting treatment and prevention of atherosclerosis. Atherosclerosis-related antigens include oxidized low-density lipoprotein (LDL), apolipoprotein B-100 (ApoB-100) and heat shock protein (HSP) 60/65. Accumulating evidence supports the idea that immunization with these antigenic proteins or peptides may reduce atherosclerosis. In this review, we discuss the current status of immunization studies and possible associated mechanisms of atheroprotection.

Anti-inflammatory therapies for atherosclerosis

The view of atherosclerosis as an inflammatory disease has emerged from observations of immune activation and inflammatory signalling in human atherosclerotic lesions, from the definition of inflammatory biomarkers as independent risk factors for cardiovascular events, and from evidence of low-density lipoprotein-induced immune activation. Studies in animal models of hyperlipidaemia have also supported the beneficial effects of countering inflammation to delay atherosclerosis progression. Specific inflammatory pathways with relevance to human diseases have been identified, and inhibitors of these pathways are either already in use for the treatment of other diseases, or are under development and evaluation. These include 'classic' drugs (such as allopurinol, colchicine, and methotrexate), biologic therapies (for example tumour necrosis factor inhibitors and IL-1 neutralization), as well as targeting of lipid mediators (such as phospholipase inhibitors and antileukotrienes) or intracellular pathways (inhibition of NADPH oxidase, p38 mitogen-activated protein kinase, or phosphodiesterase). The evidence supporting the use of anti-inflammatory therapies for atherosclerosis is mainly based on either observational or small interventional studies evaluating surrogate markers of disease activity. Nevertheless, these data are crucial to understand the role of inflammation in atherosclerosis, and to design randomized controlled studies to evaluate the effect of specific anti-inflammatory strategies on cardiovascular outcomes.

Treating atherosclerosis with regulatory T cells

Regulatory T cells (Tregs) play an important role in the regulation of T-cell-mediated immune responses through suppression of T-cell proliferation and secretion of inhibitory cytokines, such as interleukin-10 and transforming growth factor-β. Impaired Treg numbers and function have been associated with numerous diseases, and an imbalance between proinflammatory/proatherogenic cells and Tregs promotes atherosclerotic disease. Restoration of this balance by inducing Tregs has great therapeutic potential to prevent cardiovascular disease. In addition to suppressing differentiation and function of effector T cells, Tregs have been shown to induce anti-inflammatory macrophages, inhibit foam cell formation and to influence cholesterol metabolism. Furthermore, Tregs suppress immune responses of endothelial cells and innate lymphoid cells. In this review, we focus on the recent knowledge on Treg subsets, their activity and function in atherosclerosis, and discuss promising strategies to use Tregs as a therapeutic tool to prevent cardiovascular disease.