Oligoclonal T cell expansions in atherosclerotic lesions of apolipoprotein E-deficient mice

Targeting pro-inflammatory T cells as a novel therapeutic approach to potentially resolve atherosclerosis in humans

Atherosclerosis (AS), a leading cause of cardio-cerebrovascular disease worldwide, is driven by the accumulation of lipid contents and chronic inflammation. Traditional strategies primarily focus on lipid reduction to control AS progression, leaving residual inflammatory risks for major adverse cardiovascular events (MACEs). While anti-inflammatory therapies targeting innate immunity have reduced MACEs, many patients continue to face significant risks. Another key component in AS progression is adaptive immunity, but its potential role in preventing AS remains unclear. To investigate this, we conducted a retrospective cohort study on tumor patients with AS plaques. We found that anti-programmed cell death protein 1 (PD-1) monoclonal antibody (mAb) significantly reduces AS plaque size. With multi-omics single-cell analyses, we comprehensively characterized AS plaque-specific PD-1+ T cells, which are activated and pro-inflammatory. We demonstrated that anti-PD-1 mAb, when captured by myeloid-expressed Fc gamma receptors (FcγRs), interacts with PD-1 expressed on T cells. This interaction turns the anti-PD-1 mAb into a substitute PD-1 ligand, suppressing T-cell functions in the PD-1 ligands-deficient context of AS plaques. Further, we conducted a prospective cohort study on tumor patients treated with anti-PD-1 mAb with or without Fc-binding capability. Our analysis shows that anti-PD-1 mAb with Fc-binding capability effectively reduces AS plaque size, while anti-PD-1 mAb without Fc-binding capability does not. Our work suggests that T cell-targeting immunotherapy can be an effective strategy to resolve AS in humans.

Inflammation in HIV and Its Impact on Atherosclerotic Cardiovascular Disease

People living with HIV have a 1.5- to 2-fold increased risk of developing cardiovascular disease. Despite treatment with highly effective antiretroviral therapy, people living with HIV have chronic inflammation that makes them susceptible to multiple comorbidities. Several factors, including the HIV reservoir, coinfections, clonal hematopoiesis of indeterminate potential (CHIP), microbial translocation, and antiretroviral therapy, may contribute to the chronic state of inflammation. Within the innate immune system, macrophages harbor latent HIV and are among the prominent immune cells present in atheroma during the progression of atherosclerosis. They secrete inflammatory cytokines such as IL (interleukin)-6 and tumor necrosis-α that stimulate the expression of adhesion molecules on the endothelium. This leads to the recruitment of other immune cells, including cluster of differentiation (CD)8+ and CD4+ T cells, also present in early and late atheroma. As such, cells of the innate and adaptive immune systems contribute to both systemic inflammation and vascular inflammation. On a molecular level, HIV-1 primes the NLRP3 (NLR family pyrin domain containing 3) inflammasome, leading to an increased expression of IL-1β, which is important for cardiovascular outcomes. Moreover, activation of TLRs (toll-like receptors) by HIV, gut microbes, and substance abuse further activates the NLRP3 inflammasome pathway. Finally, HIV proteins such as Nef (negative regulatory factor) can inhibit cholesterol efflux in monocytes and macrophages through direct action on the cholesterol transporter ABCA1 (ATP-binding cassette transporter A1), which promotes the formation of foam cells and the progression of atherosclerotic plaque. Here, we summarize the stages of atherosclerosis in the context of HIV, highlighting the effects of HIV, coinfections, and antiretroviral therapy on cells of the innate and adaptive immune system and describe current and future interventions to reduce residual inflammation and improve cardiovascular outcomes among people living with HIV.

Itaconate suppresses atherosclerosis by activating a Nrf2-dependent antiinflammatory response in macrophages in mice

Itaconate has emerged as a critical immunoregulatory metabolite. Here, we examined the therapeutic potential of itaconate in atherosclerosis. We found that both itaconate and the enzyme that synthesizes it, aconitate decarboxylase 1 (Acod1, also known as immune-responsive gene 1 [IRG1]), are upregulated during atherogenesis in mice. Deletion of Acod1 in myeloid cells exacerbated inflammation and atherosclerosis in vivo and resulted in an elevated frequency of a specific subset of M1-polarized proinflammatory macrophages in the atherosclerotic aorta. Importantly, Acod1 levels were inversely correlated with clinical occlusion in atherosclerotic human aorta specimens. Treating mice with the itaconate derivative 4-octyl itaconate attenuated inflammation and atherosclerosis induced by high cholesterol. Mechanistically, we found that the antioxidant transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), was required for itaconate to suppress macrophage activation induced by oxidized lipids in vitro and to decrease atherosclerotic lesion areas in vivo. Overall, our work shows that itaconate suppresses atherogenesis by inducing Nrf2-dependent inhibition of proinflammatory responses in macrophages. Activation of the itaconate pathway may represent an important approach to treat atherosclerosis.

Application and challenges of TCR and BCR sequencing to investigate T- and B-cell clonality in elastase-induced experimental murine abdominal aortic aneurysm

Background

An abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease. Although its pathogenesis is still poorly understood, recent evidence suggests that AAA displays autoimmune disease characteristics. Particularly, T cells responding to AAA-related antigens in the aortic wall may contribute to an initial immune response. Single-cell RNA (scRNA) T cell receptor (TCR) and B cell receptor (BCR) sequencing is a powerful tool for investigating clonality. However, difficulties such as limited numbers of isolated cells must be considered during implementation and data analysis, making biological interpretation challenging. Here, we perform a representative single-cell immune repertoire analysis in experimental murine AAA and show a reliable bioinformatic processing pipeline highlighting opportunities and limitations of this approach.

Methods

We performed scRNA TCR and BCR sequencing of isolated lymphocytes from the infrarenal aorta of male C57BL/6J mice 3, 7, 14, and 28 days after AAA induction via elastase perfusion of the aorta. Sham-operated mice at days 3 and 28 and non-operated mice served as controls.

Results

Comparison of complementarity-determining region (CDR3) length distribution of 179 B cells and 796 T cells revealed neither differences between AAA and control nor between the disease stages. We found no clonal expansion of B cells in AAA. For T cells, we identified several clones in 11 of 16 AAA samples and one of eight control samples. Immune receptor repertoire comparison indicated that only a few clones were shared between the individual AAA samples. The most frequently used V-genes in the TCR beta chain in AAA were TRBV3, TRBV19, and the splicing variant TRBV12-2 + TRBV13-2.

Conclusion

We found no clonal expansion of B cells but evidence for clonal expansion of T cells in elastase-induced AAA in mice. Our findings imply that a more precise characterization of TCR and BCR distribution requires a more extensive number of lymphocytes to prevent undersampling and potentially detect rare clones. Thus, further experiments are necessary to confirm our findings. In summary, this paper examines TCR and BCR sequencing results, identifies limitations and pitfalls, and offers guidance for future studies.

T Cells in Atherosclerosis: Key Players in the Pathogenesis of Vascular Disease

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of lipid-rich plaques within arterial walls. T cells play a pivotal role in the pathogenesis of atherosclerosis in which they help orchestrate immune responses and contribute to plaque development and instability. Here, we discuss the recognition of atherosclerosis-related antigens that may trigger T cell activation together with additional signaling from co-stimulatory molecules and lesional cytokines. Although few studies have indicated candidates for the antigen specificity of T cells in atherosclerosis, further research is needed. Furthermore, we describe the pro-atherogenic and atheroprotective roles of diverse subsets of T cells such as CD4+ helper, CD8+ cytotoxic, invariant natural killer, and γδ T cells. To classify and quantify T cell subsets in atherosclerosis, we summarize current methods to analyze cellular heterogeneity including single cell RNA sequencing and T cell receptor (TCR) sequencing. Further insights into T cell biology will help shed light on the immunopathology of atherosclerosis, inform potential therapeutic interventions, and pave the way for precision medicine approaches in combating cardiovascular disease.

The emerging role of Th1 cells in atherosclerosis and its implications for therapy

Atherosclerosis is a chronic progressive inflammatory disease of the large and medium-sized artery walls. The molecular mechanisms regulating the onset and progression of atherosclerosis remain unclear. T cells, one of the most common immune cell types in atherosclerotic plaques, are increasingly recognized as a key mediator in the pathogenesis of atherosclerosis. Th1 cells are a subset of CD4⁺ T helper cells of the adaptive immune system, characterized by the expression of the transcription factor T-bet and secretion of cytokines such as IFN-γ. Converging evidence shows that Th1 cells play a key role in the onset and progression of atherosclerosis. Besides, Th1 is the central mediator to orchestrate the adaptive immune system. In this review, we aim to summarize the complex role of Th1 cells in atherosclerosis and propose novel preventative and therapeutic approaches targeting Th1 cell-associated specific cytokines and receptors to prevent atherogenesis.

Antibodies in action: the role of humoral immunity in the fight against atherosclerosis

The sequestering of oxidation-modified low-density lipoprotein by macrophages results in the accumulation of fatty deposits within the walls of arteries. Necrosis of these cells causes a release of intercellular epitopes and the activation of the adaptive immune system, which we predict leads to robust autoantibody production. T cells produce cytokines that act in the plaque environment and further stimulate B cell antibody production. B cells in atherosclerosis meanwhile have a mixed role based on subclass. The current model is that B-1 cells produce protective IgM antibodies in response to oxidation-specific epitopes that work to control plaque formation, while follicular B-2 cells produce class-switched antibodies (IgG, IgA, and IgE) which exacerbate the disease. Over the course of this review, we discuss further the validation of these protective antibodies while evaluating the current dogma regarding class-switched antibodies in atherosclerosis. There are several contradictory findings regarding the involvement of class-switched antibodies in the disease. We hypothesize that this is due to antigen-specificity, and not simply isotype, being important, and that a closer evaluation of these antibodies' targets should be conducted. We propose that specific antibodies may have therapeutical potential in preventing and controlling plaque development within a clinical setting.

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.

Circulating Autoantibodies Recognizing Immunodominant Epitopes From Human Apolipoprotein B Associate With Cardiometabolic Risk Factors, but Not With Atherosclerotic Disease

Rationale

Atherosclerosis is a chronic inflammatory disease of large arteries that involves an autoimmune response with autoreactive T cells and auto-antibodies recognizing Apolipoprotein B (ApoB), the core protein of low-density lipoprotein (LDL). Here, we aimed to establish a clinical association between circulating human ApoB auto-antibodies with atherosclerosis and its clinical risk factors using a novel assay to detect auto-antibodies against a pool of highly immunogenic ApoB-peptides.

Methods and Results

To detect polyclonal IgM- and IgG-antibodies recognizing ApoB, we developed a chemiluminescent sandwich ELISA with 30 ApoB peptides selected by an in silico assay for a high binding affinity to MHC-II, which cover more than 80% of known MHC-II variants in a Caucasian population. This pre-selection of immunogenic self-peptides accounted for the high variability of human MHC-II, which is fundamental to allow T cell dependent generation of IgG antibodies. We quantified levels of ApoB-autoantibodies in a clinical cohort of 307 patients that underwent coronary angiography. Plasma anti-ApoB IgG and IgM concentrations showed no differences across healthy individuals (n = 67), patients with coronary artery disease (n = 179), and patients with an acute coronary syndrome (n = 61). However, plasma levels of anti-ApoB IgG, which are considered pro-inflammatory, were significantly increased in patients with obesity (p = 0.044) and arterial hypertension (p < 0.0001). In addition, patients diagnosed with the metabolic syndrome showed significantly elevated Anti-ApoB IgG (p = 0.002). Even when normalized for total plasma IgG, anti-ApoB IgG remained highly upregulated in hypertensive patients (p < 0.0001). We observed no association with triglycerides, total cholesterol, VLDL, or LDL plasma levels. However, total and normalized anti-ApoB IgG levels negatively correlated with HDL. In contrast, total and normalized anti-ApoB IgM, that have been suggested as anti-inflammatory, were significantly lower in diabetic patients (p = 0.012) and in patients with the metabolic syndrome (p = 0.005).

Conclusion

Using a novel ELISA method to detect auto-antibodies against ApoB in humans, we show that anti-ApoB IgG associate with cardiovascular risk factors but not with the clinical appearance of atherosclerosis, suggesting that humoral immune responses against ApoB are shaped by cardiovascular risk factors but not disease status itself. This novel tool will be helpful to develop immune-based risk stratification for clinical atherosclerosis in the future.

Immune Checkpoint Therapies and Atherosclerosis: Mechanisms and Clinical Implications: JACC State-of-the-Art Review

Immune checkpoint inhibitor therapy has revolutionized the treatment of advanced malignancies in recent years. Numerous reports have detailed the myriad of possible adverse inflammatory effects of immune checkpoint therapies, including within the cardiovascular system. However, these reports have been largely limited to myocarditis. The critical role of inflammation and adaptive immunity in atherosclerosis has been well characterized in preclinical studies, and several emerging clinical studies indicate a potential role of immune checkpoint targeting therapies in the development and exacerbation of atherosclerosis. In this review, we provide an overview of the role of T-cell immunity in atherogenesis and describe the molecular effects and clinical associations of both approved and investigational immune checkpoint therapy on atherosclerosis. We also highlight the role of cholesterol metabolism in oncogenesis and discuss the implications of these associations on future treatment and monitoring of atherosclerotic cardiovascular disease in the oncologic population receiving immune checkpoint therapy.

Salt-Sensitivity of Blood Pressure and Insulin Resistance

Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular morbidity and mortality that is seen in both hypertensive and normotensive populations. Insulin resistance (IR) strongly correlates with SSBP and affects nearly 50% of salt sensitive people. While the precise mechanism by which IR and SSBP relate remains elusive, several common pathways are involved in the genesis of both processes, including vascular dysfunction and immune activation. Vascular dysfunction associated with insulin resistance is characterized by loss of nitric oxide (NO)-mediated vasodilation and heightened endothelin-1 induced vasoconstriction, as well as capillary rarefaction. It manifests with increased blood pressure (BP) in salt sensitive murine models. Another common denominator in the pathogenesis of insulin resistance, hypertension, and salt sensitivity (SS) is immune activation involving pro-inflammatory cytokines like tumor necrosis factor (TNF)-α, IL-1β, and IL-6. In the last decade, a new understanding of interstitial sodium storage in tissues such as skin and muscle has revolutionized traditional concepts of body sodium handling and pathogenesis of SS. We have shown that interstitial Na⁺ can trigger a T cell mediated inflammatory response through formation of isolevuglandin protein adducts in antigen presenting cells (APCs), and that this response is implicated in salt sensitive hypertension. The peroxisome proliferator-activated receptor γ (PPARγ) is a transcription factor that modulates both insulin sensitivity and BP. PPARγ agonists increase insulin sensitivity and ameliorate salt sensitivity, whereas deficiency of PPARγ results in severe insulin resistance and hypertension. These findings suggest that PPARγ plays a role in the common pathogenesis of insulin sensitivity and salt sensitivity, perhaps via effects on the immune system and vascular function. The goal of this review is to discuss those mechanisms that may play a role in both SSBP and in insulin resistance.

Anti-inflammatory Strategies in Atherosclerosis

Atherosclerotic vascular disease and its related complications are the major cause of mortality in Western societies. Atherosclerosis is a chronic inflammatory disease of the arterial wall triggered by traditional and nontraditional risk factors and mediated by inflammatory and immune responses. Recent clinical trials provided compelling evidence corroborating that atherosclerosis is an inflammatory disease and demonstrated efficacy of anti-inflammatory interventions in reducing cardiovascular events and mortality. Traditional risk factors drive vascular inflammation, further justifying the instrumental role of intensified risk factor management in attenuating and preventing atherosclerotic disease and complications. Promising therapeutic approaches specifically related to inhibition of inflammation span traditional anti-inflammatory drugs, specific immunomodulation, and development of vaccination against atherosclerotic disease. Here, we review the inflammatory component in atherogenesis, the available evidence from clinical trials evaluating efficacy of therapeutic anti-inflammatory interventions in patients with high cardiovascular risk, and discuss potential future targets for anti-inflammatory or immune modulatory treatment in atherosclerotic cardiovascular disease.

Modulating Autoimmunity against LDL: Development of a Vaccine against Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall that leads to the build-up of occluding atherosclerotic plaques. Its clinical sequelae, myocardial infarction and stroke, represent the most frequent causes of death worldwide. Atherosclerosis is a multifactorial pathology that involves traditional risk factors and chronic low-grade inflammation in the atherosclerotic plaque and systemically. This process is accompanied by a strong autoimmune response that involves autoreactive T cells in lymph nodes and atherosclerotic plaques, as well as autoantibodies that recognize low-density lipoprotein (LDL) and its main protein component apolipoprotein B (ApoB). In the past 60 years, numerous preclinical observations have suggested that immunomodulatory vaccination with LDL, ApoB, or its peptides has the potential to specifically dampen autoimmunity, enhance tolerance to atherosclerosis-specific antigens, and protect from experimental atherosclerosis in mouse models. Here, we summarize and discuss mechanisms, challenges, and therapeutic opportunities of immunomodulatory vaccination and other strategies to enhance protective immunity in atherosclerosis.

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.

Humoral immunity in atherosclerosis and myocardial infarction: from B cells to antibodies

Immune mechanisms are critically involved in the pathogenesis of atherosclerosis and its clinical manifestations. Associations of specific antibody levels and defined B cell subsets with cardiovascular disease activity in humans as well as mounting evidence from preclinical models demonstrate a role of B cells and humoral immunity in atherosclerotic cardiovascular disease. These include all aspects of B cell immunity, the generation of antigen-specific antibodies, antigen presentation and co-stimulation of T cells, as well as production of cytokines. Through their impact on adaptive and innate immune responses and the regulation of many other immune cells, B cells mediate both protective and detrimental effects in cardiovascular disease. Several antigens derived from (oxidised) lipoproteins, the vascular wall and classical autoantigens have been identified. The unique antibody responses they trigger and their relationship with atherosclerotic cardiovascular disease are reviewed. In particular, we focus on the different effector functions of specific IgM, IgG, and IgE antibodies and the cellular responses they trigger and highlight potential strategies to target B cell functions for therapy.

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.

miR-34c inhibits PDGF-BB-induced HAVSMCs phenotypic transformation and proliferation via PDGFR-β/SIRT1 pathway

The purpose of this study was to explore the effect of miR-34c on PDGF-BB-induced HAVSMCs phenotypic transformation and proliferation via PDGFR-β/SIRT1 pathway, so as to find a new method for early diagnosis and treatment of cardiovascular disease. HA-VSMCs were treated with platelet-derived growth factor-BB (PDGF-BB) at 0 h, 12 h, 24 h, 48 h or 36 h to explore the optimal time for phenotypic transformation of VSMCs. And then, PDGF-BB-induced HA-VSMCs were transfected with miR-34c mimics/mimics NC and pcDNA3.1-PDGFR-β/pcDNA3.1-NC to observe cell biological behaviour. CCK8 was used to detect cell proliferation activity. Transwell chamber assay was used to detect cell invasion. Early apoptosis was analyzed by flow cytometry. The expression of α-SMA and Smemb was detected by immunofluorescence staining. The expressions of PDGFR-β, IRF9, Acetyl-NF-κB/p65, Acetyl-p53 and CyclinD1 were analyzed by Western blot analysis. The expression of miR-34a, miR-34b and miR-34c was detected by RT-PCR, and the targeting relationship between miR-34c and PDGFR-β was detected by luciferase reporting assay. The results indicated the proliferation and migration of PDGF-BB-induced HA-VSMCs significantly increased, and apoptosis significantly decreased. Besides, α-SMA decreased significantly, while Smemb increased significantly. Furthermore, expressions of PDGFR-β, IRF9, Acetyl-NF-κB/p65, Acetyl-p53 and CyclinD1 increased significantly, and SIRT1 decreased significantly. Experimental results showed that, miR-34c mimics significantly inhibited cell proliferation and migration, and promoted cell apoptosis, and miR-34c inhibitor had the opposite effects. MiR-34c mimics significantly increased α-SMA expression and decreased Smemb expression, while the opposite effects were reflected after transfection with miR-34c inhibitor. Moreover, miR-34c mimics significantly decreased the expressions of PDGFR-β, IRF9, Acetyl-NF-κB/p65, Acetyl-p53 and CyclinD1, and significantly increased the expression of SIRT1, while miR-34c inhibitor had the opposite effects. Luciferase assay confirmed that PDGFR-β was a potential target of miR-34c. Subsequently, PDGF-BB-induced HA-VSMCs were co-transfected with miR-34c mimics and pcDNA3.1-PDGFR-β. The results indicated that PDGFR-β reversed the biological function of miR-34c mimic. The results revealed the potential application value of miR-34c as a marker molecule of phenotypic transformation, providing a potential target for improving phenotypic transformation.

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.

ApoB-Specific CD4+ T Cells in Mouse and Human Atherosclerosis

Atherosclerosis is a chronic inflammatory condition of the arterial wall that leads to the formation of vessel-occluding plaques within the subintimal space of middle-sized and larger arteries. While traditionally understood as a myeloid-driven lipid-storage disease, growing evidence suggests that the accumulation of low-density lipoprotein cholesterol (LDL-C) ignites an autoimmune response with CD4⁺ T-helper (T_H) cells that recognize self-peptides from Apolipoprotein B (ApoB), the core protein of LDL-C. These autoreactive CD4⁺ T cells home to the atherosclerotic plaque, clonally expand, instruct other cells in the plaque, and induce clinical plaque instability. Recent developments in detecting antigen-specific cells at the single cell level have demonstrated that ApoB-reactive CD4⁺ T cells exist in humans and mice. Their phenotypes and functions deviate from classical immunological concepts of distinct and terminally differentiated T_H immunity. Instead, ApoB-specific CD4⁺ T cells have a highly plastic phenotype, can acquire several, partially opposing and mixed transcriptional programs simultaneously, and transit from one T_H subset into another over time. In this review, we highlight adaptive immune mechanisms in atherosclerosis with a focus on CD4⁺ T cells, introduce novel technologies to detect ApoB-specific CD4⁺ T cells at the single cell level, and discuss the potential impact of ApoB-driven autoimmunity in atherosclerosis.

CD8+ T Cells in Atherosclerosis

Atherosclerotic lesions are populated by cells of the innate and adaptive immune system, including CD8⁺ T cells. The CD8⁺ T cell infiltrate has recently been characterized in mouse and human atherosclerosis and revealed activated, cytotoxic, and possibly dysfunctional and exhausted cell phenotypes. In mouse models of atherosclerosis, antibody-mediated depletion of CD8⁺ T cells ameliorates atherosclerosis. CD8⁺ T cells control monopoiesis and macrophage accumulation in early atherosclerosis. In addition, CD8⁺ T cells exert cytotoxic functions in atherosclerotic plaques and contribute to macrophage cell death and necrotic core formation. CD8⁺ T cell activation may be antigen-specific, and epitopes of atherosclerosis-relevant antigens may be targets of CD8⁺ T cells and their cytotoxic activity. CD8⁺ T cell functions are tightly controlled by costimulatory and coinhibitory immune checkpoints. Subsets of regulatory CD25⁺CD8⁺ T cells with immunosuppressive functions can inhibit atherosclerosis. Importantly, local cytotoxic CD8⁺ T cell responses may trigger endothelial damage and plaque erosion in acute coronary syndromes. Understanding the complex role of CD8⁺ T cells in atherosclerosis may pave the way for defining novel treatment approaches in atherosclerosis. In this review article, we discuss these aspects, highlighting the emerging and critical role of CD8⁺ T cells in atherosclerosis.

Heterogeneity of T Cells in Atherosclerosis Defined by Single-Cell RNA-Sequencing and Cytometry by Time of Flight

The infiltration and accumulation of pro- and anti-inflammatory leukocytes within the intimal layer of the arterial wall is a hallmark of developing and progressing atherosclerosis. While traditionally perceived as macrophage- and foam cell-dominated disease, it is now established that atherosclerosis is a partial autoimmune disease that involves the recognition of peptides from ApoB (apolipoprotein B), the core protein of LDL (low-density lipoprotein) cholesterol particles, by CD4⁺ T-helper cells and autoantibodies against LDL and ApoB. Autoimmunity in the atherosclerotic plaque has long been understood as a pathogenic T-helper type-1 driven response with proinflammatory cytokine secretion. Recent developments in high-parametric cell immunophenotyping by mass cytometry, single-cell RNA-sequencing, and in tools exploring antigen-specificity have established the existence of several unforeseen layers of T-cell diversity with mixed T_H1 and T regulatory cells transcriptional programs and unpredicted fates. These findings suggest that pathogenic ApoB-reactive T cells evolve from atheroprotective and immunosuppressive CD4⁺ T regulatory cells that lose their protective properties over time. Here, we discuss T-cell heterogeneity in atherosclerosis with a focus on plasticity, antigen-specificity, exhaustion, maturation, tissue residency, and its potential use in clinical prediction.

The aorta can act as a site of naïve CD4+ T-cell priming

AIMS

Aortic adaptive immunity plays a role in atherosclerosis; however, the precise mechanisms leading to T-cell activation in the arterial wall remain poorly understood.

METHODS AND RESULTS

Here, we have identified naïve T cells in the aorta of wild-type and T-cell receptor transgenic mice and we demonstrate that naïve T cells can be primed directly in the vessel wall with both kinetics and frequency of T-cell activation found to be similar to splenic and lymphoid T cells. Aortic homing of naïve T cells is regulated at least in part by the P-selectin glycosylated ligand-1 receptor. In experimental atherosclerosis the aorta supports CD4+ T-cell activation selectively driving Th1 polarization. By contrast, secondary lymphoid organs display Treg expansion.

CONCLUSION

Our results demonstrate that the aorta can support T-cell priming and that naïve T cells traffic between the circulation and vessel wall. These data underpin the paradigm that local priming of T cells specific for plaque antigens contributes to atherosclerosis progression.

T cell subsets and functions in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall and the primary underlying cause of cardiovascular disease. Data from in vivo imaging, cell-lineage tracing and knockout studies in mice, as well as clinical interventional studies and advanced mRNA sequencing techniques, have drawn attention to the role of T cells as critical drivers and modifiers of the pathogenesis of atherosclerosis. CD4+ T cells are commonly found in atherosclerotic plaques. A large body of evidence indicates that T helper 1 (TH1) cells have pro-atherogenic roles and regulatory T (Treg) cells have anti-atherogenic roles. However, Treg cells can become pro-atherogenic. The roles in atherosclerosis of other TH cell subsets such as TH2, TH9, TH17, TH22, follicular helper T cells and CD28null T cells, as well as other T cell subsets including CD8+ T cells and γδ T cells, are less well understood. Moreover, some T cells seem to have both pro-atherogenic and anti-atherogenic functions. In this Review, we summarize the knowledge on T cell subsets, their functions in atherosclerosis and the process of T cell homing to atherosclerotic plaques. Much of our understanding of the roles of T cells in atherosclerosis is based on findings from experimental models. Translating these findings into human disease is challenging but much needed. T cells and their specific cytokines are attractive targets for developing new preventive and therapeutic approaches including potential T cell-related therapies for atherosclerosis.

An Updated Review of Pro- and Anti-Inflammatory Properties of Plasma Lysophosphatidylcholines in the Vascular System

Lysophosphatidylcholines are a group of bioactive lipids heavily investigated in the context of inflammation and atherosclerosis development. While present in plasma during physiological conditions, their concentration can drastically increase in certain inflammatory states. Lysophosphatidylcholines are widely regarded as potent pro-inflammatory and deleterious mediators, but an increasing number of more recent studies show multiple beneficial properties under various pathological conditions. Many of the discrepancies in the published studies are due to the investigation of different species or mixtures of lysophatidylcholines and the use of supra-physiological concentrations in the absence of serum or other carrier proteins. Furthermore, interpretation of the results is complicated by the rapid metabolism of lysophosphatidylcholine (LPC) in cells and tissues to pro-inflammatory lysophosphatidic acid. Interestingly, most of the recent studies, in contrast to older studies, found lower LPC plasma levels associated with unfavorable disease outcomes. Being the most abundant lysophospholipid in plasma, it is of utmost importance to understand its physiological functions and shed light on the discordant literature connected to its research. LPCs should be recognized as important homeostatic mediators involved in all stages of vascular inflammation. In this review, we want to point out potential pro- and anti-inflammatory activities of lysophospholipids in the vascular system and highlight recent discoveries about the effect of lysophosphatidylcholines on immune cells at the endothelial vascular interface. We will also look at their potential clinical application as biomarkers.

Atherosclerosis: Beyond the lipid storage hypothesis. The role of autoimmunity

Atherosclerosis has long been considered as a lipid storage disease. Recent data suggest that autoimmune mechanisms seem to be involved in the pathophysiology of atherosclerosis. The presence of activated endothelial vascular cells, neutrophils, macrophages, T and to a lesser extent B cells in atherosclerotic plaques, together with the proinflammatory cytokine burden suggest mobilization of both innate and adaptive immune pathways in atherosclerosis pathobiology. The development of antibodies to oxidized low-density lipoprotein (ox-LDL), the experimental induction of atherosclerosis either via the transfer of T cells or immunization with autoantigens such as β2 glycoprotein Ι (β2-GPI) and heat shock proteins (HSP) further support the autoimmune nature of atherosclerosis. However, classical immunosuppressive and immune-modulatory drugs, successfully used in the therapy of autoimmune rheumatic diseases have shown limited benefits so far in the treatment of atherosclerosis.

SULT2B1b inhibits reverse cholesterol transport and promotes cholesterol accumulation and inflammation in lymphocytes from AMI patients with low LDL-C levels

The current main treatment for coronary artery disease (CAD) is to reduce low-density lipoprotein cholesterol (LDL-C) by statins, which could decrease the incidence of major adverse cardiovascular events (MACEs) by 30%. However, many residual risks still remain. To clarify the mechanism involved, we studied patients with acute myocardial infarction (AMI) with low LDL-C levels. Lymphocytes were isolated, and it was found that despite no difference in plasma LDL-C level, the lymphocyte cholesterol content was higher in AMI patient than those in non-CAD patients; thus, the decrease in intracellular cholesterol content was inconsistent with that in the plasma. Additionally, [3H]-cholesterol efflux rates were lower and mRNA levels of the inflammatory factors tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) higher in AMI lymphocytes. It was found that sulphotransferase 2B1b (SULT2B1b) expression was higher in AMI lymphocytes. Further research using Jurkat T lymphocytes confirmed that SULT2B1b knockdown increased cholesterol efflux capacity and decreased mRNA levels of TNF-α and IFN-γ by increasing liver X receptor (LXR)-β levels. Furthermore, the degree of CpG island methylation in the SULT2B1b promoter was reduced in cells from AMI patients. In conclusion, SULT2B1b up-regulation due to hypomethylation of its promoter promotes cholesterol accumulation and inflammation by inhibiting LXR-β in lymphocytes of AMI patients with low LDL-C levels. Therefore, reducing intracellular cholesterol is also important as plasma cholesterol levels. Therapeutic approaches to decrease SULT2B1b expression might be potentially beneficial for CAD prevention by decreasing intracellular cholesterol.

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.

Immunity and Inflammation in Atherosclerosis

There is now overwhelming experimental and clinical evidence that atherosclerosis is a chronic inflammatory disease. Lessons from genome-wide association studies, advanced in vivo imaging techniques, transgenic lineage tracing mice, and clinical interventional studies have shown that both innate and adaptive immune mechanisms can accelerate or curb atherosclerosis. Here, we summarize and discuss the pathogenesis of atherosclerosis with a focus on adaptive immunity. We discuss some limitations of animal models and the need for models that are tailored to better translate to human atherosclerosis and ultimately progress in prevention and treatment.

[Immunity and inflammation in atherosclerosis]

There is now overwhelming experimental and clinical evidence that arteriosclerosis is a chronic inflammatory disease. Lessons learned from genome-wide association studies, advanced in vivo imaging techniques, transgenic lineage tracing mice models and clinical interventional studies have shown that both innate and adaptive immune mechanisms can accelerate or curb arteriosclerosis. This article summarizes and discusses the pathogenesis of arteriosclerosis with a focus on the role of the adaptive immune system. Some limitations of animal models are discussed and the need for models that are tailored to better translate to human atherosclerosis and ultimately progress in prevention and treatment are emphasized.

Follicular regulatory T cell in atherosclerosis

Atherosclerosis is a chronic inflammatory disease involving the infiltration of immune cells, such as monocytes/macrophages, neutrophils, T cells, and B cells, into the inner layer of vessel walls. T and B cell functions in the process of atherogenesis, as well as their mutual regulation, have been investigated but several aspects remain to be clarified. In the present review, we give a brief overview of the functions of follicular regulatory T cell (Tfr) on follicular T (Tfh) and B cell regulation related to atherosclerosis pathogenesis, including their influence on lymphangiogenesis and lipoprotein metabolism. We will also discuss their potential therapeutics properties in the resolution of established atherosclerotic lesions.

Dendritic cells in atherosclerosis: Functions in immune regulation and beyond

Chronic inflammation drives the development of atherosclerosis. Dendritic cells (DCs) are known as central mediators of adaptive immune responses and the development of immunological memory and tolerance. DCs are present in non-diseased arteries, and accumulate within atherosclerotic lesions where they can be localised in close vicinity to T cells. Recent work has revealed important functions of DCs in regulating immune mechanisms in atherogenesis, and vaccination strategies using DCs have been explored for treatment of disease. However, in line with a phenotypical and functional overlap with plaque macrophages vascular DCs were also identified to engulf lipids, thus contributing to lipid burden in the vessel wall and initiation of lesion growth. Furthermore, a function of DCs in regulating cholesterol homeostasis has been revealed. Finally, phenotypically distinct plasmacytoid dendritic cells (pDCs) have been identified within atherosclerotic lesions. This review will dissect the multifaceted contribution of DCs and pDCs to the initiation and progression of atherosclerosis and the experimental approaches utilising DCs in therapeutic vaccination strategies.

Cytokine-induced autophagy promotes long-term VCAM-1 but not ICAM-1 expression by degrading late-phase IκBα

Pro-inflammatory cytokines are known to induce endothelial cell autophagy, but the role of autophagy in regulating the expression of pro-inflammatory molecules has not been characterized. We hypothesized that autophagy facilitates expression of endothelial adhesion molecules. TNFα and IL-1β induced autophagy markers in human umbilical vein endothelial cells and inhibition of autophagy by 3-methyladenine (3-MA) blocked adhesion of Jurkat lymphocytes. Interestingly, 3-MA suppressed VCAM-1 but not ICAM-1 expression at 24 hours but not 6 hours. 3-MA suppressed VCAM-1 transcription and decreased nuclear NF-κB p65 level at 6 hours but not at 2 hours. Cytokines induced a biphasic degradation of IκBα and 3-MA selectively blocked the late-phase IκBα degradation. Our results suggest that cytokine-induced autophagy contributes to late-phase IκBα degradation, facilitates NF-κB nuclear translocation and VCAM-1 transcription for long-term VCAM-1 expression. With a cytokines array assay, we found that 3-MA also inhibited IP-10 expression. These findings provide new information about the role of endothelial autophagy in persistent expression of VCAM-1 and IP-10 which enhance lymphocyte recruitment and adhesion to endothelium.

New Insights into the Role of Inflammation in the Pathogenesis of Atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of lipids, smooth muscle cell proliferation, cell apoptosis, necrosis, fibrosis, and local inflammation. Immune and inflammatory responses have significant effects on every phase of atherosclerosis, and increasing evidence shows that immunity plays a more important role in atherosclerosis by tightly regulating its progression. Therefore, understanding the relationship between immune responses and the atherosclerotic microenvironment is extremely important. This article reviews existing knowledge regarding the pathogenesis of immune responses in the atherosclerotic microenvironment, and the immune mechanisms involved in atherosclerosis formation and activation.

Deletion of Batf3-dependent antigen-presenting cells does not affect atherosclerotic lesion formation in mice

Atherosclerosis is the main underlying cause for cardiovascular events such as myocardial infarction and stroke and its development might be influenced by immune cells. Dendritic cells (DCs) bridge innate and adaptive immune responses by presenting antigens to T cells and releasing a variety of cytokines. Several subsets of DCs can be discriminated that engage specific transcriptional pathways for their development. Basic leucine zipper transcription factor ATF-like 3 (Batf3) is required for the development of classical CD8α+ and CD103+ DCs. By crossing mice deficient in Batf3 with atherosclerosis-prone low density lipoprotein receptor (Ldlr-/-)-deficient mice we here aimed to further address the contribution of Batf3-dependent CD8α+ and CD103+ antigen-presenting cells to atherosclerosis. We demonstrate that deficiency in Batf3 entailed mild effects on the immune response in the spleen but did not alter atherosclerotic lesion formation in the aorta or aortic root, nor affected plaque phenotype in low density lipoprotein receptor-deficient mice fed a high fat diet. We thus provide evidence that Batf3-dependent antigen-presenting cells do not have a prominent role in atherosclerosis.

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.

ATVB Distinguished Scientist Award: How Costimulatory and Coinhibitory Pathways Shape Atherosclerosis

OBJECTIVE

Immune cells play a critical role in atherosclerosis. Costimulatory and coinhibitory molecules of the tumor necrosis factor receptor and CD28 immunoglobulin superfamilies not only shape T-cell and B-cell responses but also have a major effect on antigen-presenting cells and nonimmune cells.

APPROACH AND RESULTS

Pharmacological inhibition or activation of costimulatory and coinhibitory molecules and genetic deletion demonstrated their involvement in atherosclerosis. This review highlights recent advances in understanding how costimulatory and coinhibitory pathways shape the immune response in atherosclerosis.

CONCLUSIONS

Insights gained from costimulatory and coinhibitory molecule function in atherosclerosis may inform future therapeutic approaches.

Protein arginine methyltransferase 1 (PRMT1) represses MHC II transcription in macrophages by methylating CIITA

Efficient presentation of alien antigens triggers activation of T lymphocytes and robust host defense against invading pathogens. This pathophysiological process relies on the expression of major histocompatibility complex (MHC) molecules in antigen presenting cells such as macrophages. Aberrant MHC II transactivation plays a crucial role in the pathogenesis of atherosclerosis. Class II transactivator (CIITA) mediates MHC II induction by interferon gamma (IFN-γ). CIITA activity can be fine-tuned at the post-translational level, but the mechanisms are not fully appreciated. We investigated the role of protein arginine methyltransferase 1 (PRMT1) in this process. We report here that CIITA interacted with PRMT1. IFN-γ treatment down-regulated PRMT1 expression and attenuated PRMT1 binding on the MHC II promoter. Over-expression of PRMT1 repressed MHC II promoter activity while PRMT1 depletion enhanced MHC II transactivation. Mechanistically, PRMT1 methylated CIITA and promoted CIITA degradation. Therefore, our data reveal a previously unrecognized role for PRMT1 in suppressing CIITA-mediated MHC II transactivation.

Heterogeneity of B Cell Functions in Stroke-Related Risk, Prevention, Injury, and Repair

It is well established that post-stroke inflammation contributes to neurovascular injury, blood-brain barrier disruption, and poor functional recovery in both animal and clinical studies. However, recent studies also suggest that several leukocyte subsets, activated during the post-stroke immune response, can exhibit both pro-injury and pro-recovery phenotypes. In accordance with these findings, B lymphocytes, or B cells, play a heterogeneous role in the adaptive immune response to stroke. This review highlights what is currently understood about the various roles of B cells, with an emphasis on stroke risk factors, as well as post-stroke injury and repair. This includes an overview of B cell functions, such as antibody production, cytokine secretion, and contribution to the immune response as antigen presenting cells. Next, evidence for B cell-mediated mechanisms in stroke-related risk factors, including hypertension, diabetes, and atherosclerosis, is outlined, followed by studies that focus on B cells during endogenous protection from stroke. Subsequently, animal studies that investigate the role of B cells in post-stroke injury and repair are summarized, and the final section describes current B cell-related clinical trials for stroke, as well as other central nervous system diseases. This review reveals the complex role of B cells in stroke, with a focus on areas for potential clinical intervention for a disease that affects millions of people globally each year.

Atherosclerosis: the interplay between lipids and immune cells

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of mortality worldwide. The underlying cause of the majority of cardiovascular disease is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. However, today's picture of the pathogenesis of atherosclerosis is much more complex, with a key role for immune cells and inflammation in conjunction with hyperlipidemia, especially elevated (modified) LDL levels. Knowledge on immune cells and immune responses in atherosclerosis has progressed tremendously over the past decades, and the same is true for the role of lipid metabolism and the different lipid components. However, it is largely unknown how lipids and the immune system interact. In this review, we will describe the effect of lipids on immune cell development and function, and the effects of immune cells on lipid metabolism.

RECENT FINDINGS

Recently, novel data have emerged that show that immune cells are affected, and behave differently in a hyperlipidemic environment. Moreover, immune cells have reported to be able to affect lipid metabolism.

SUMMARY

In this review, we will summarize the latest findings on the interactions between lipids and the immune system, and we will discuss the potential consequences of these novel insights for future therapies for atherosclerosis.

Immune-inflammatory responses in atherosclerosis: Role of an adaptive immunity mainly driven by T and B cells

Adaptive immune response plays an important role in atherogenesis. In atherosclerosis, the proinflammatory immune response driven by Th1 is predominant but the anti-inflammatory response mediated mainly by regulatory T cells is also present. The role of Th2 and Th17 cells in atherogenesis is still debated. In the plaque, other T helper cells can be observed such as Th9 and Th22 but is little is known about their impact in atherosclerosis. Heterogeneity of CD4(+) T cell subsets presented in the plaque may suggest for plasticity of T cell that can switch the phenotype dependening on the local microenvironment and activating/blocking stimuli. Effector T cells are able to recognize self-antigens released by necrotic and apoptotic vascular cells and induce a humoral immune reaction. Tth cells resided in the germinal centers help B cells to switch the antibody class to the production of high-affinity antibodies. Humoral immunity is mediated by B cells that release antigen-specific antibodies. A variety of B cell subsets were found in human and murine atherosclerotic plaques. In mice, B1 cells could spontaneously produce atheroprotective natural IgM antibodies. Conventional B2 lymphocytes secrete either proatherogenic IgG, IgA, and IgE or atheroprotective IgG and IgM antibodies reactive with oxidation-specific epitopes on atherosclerosis-associated antigens. A small population of innate response activator (IRA) B cells, which is phenotypically intermediate between B1 and B2 cells, produces IgM but possesses proatherosclerotic properties. Finally, there is a minor subset of splenic regulatory B cells (Bregs) that protect against atherosclerotic inflammation through support of generation of Tregs and production of anti-inflammatory cytokines IL-10 and TGF-β and proapoptotic molecules.

Expansion of CD8(+) T cells lacking the IL-6 receptor α chain in patients with coronary artery diseases (CAD)

BACKGROUND AND AIMS

The pathogenesis of coronary artery disease (CAD) is closely associated with chronic inflammatory processes. CD8(+) T cells are a key participant in the pathogenesis of atherosclerosis, the major cause of CAD; however, it remains unclear which CD8(+) T-cell subset is responsible. We investigated the immunological features of CD8(+) T cells expressing low and high levels of the IL-6 receptor α chain (IL-6Rα), a cytokine known to play a key role in cardiovascular diseases.

METHODS

The expression of IL-6Rα on CD8(+) T cells and its association with plasma levels of soluble components of the IL-6/IL-6Rs as well as with clinical parameters were analyzed using FACS analysis and ELISA of CAD patients and age-matched healthy controls (HCs). Immunological characteristics of CD8(+) T cells expressing low and high levels of IL-6Rα (CD8(+)IL-6Rα(low or high)) were examined by in vitro culture and intracellular FACS analysis.

RESULTS

CAD patients had higher frequencies of circulating CD8(+)IL-6Rα(low) effector memory (EM) T cells compared with HCs (median frequency; 74.59% vs. 60.09%, p = 0.0158). Expanded CD8(+)IL-6Rα(low) T cells positively correlated with the frequency of senescent, cytotoxic CD8(+)CD57(+) T cells (r = 0.6655, p < 0.0001) and plasma IL-6 level (r = 0.3995, p = 0.0432) in CAD patients. Loss of IL-6Rα expression on CD8(+) T cells was induced by the combination of IL-6 and IL-15 with accompanying TCR-independent proliferation (p = 0.0101). Moreover, these CD8(+)IL-6Rα(low) T cells had features of type 1 cytotoxic CD8(+) T cells.

CONCLUSIONS

Our findings suggest the possible involvement of expanded CD8(+)IL-6Rα(low) EM T cells in CAD through their pro-inflammatory and highly cytotoxic capacities.

Beyond vascular inflammation--recent advances in understanding atherosclerosis

Atherosclerosis is the most life-threatening pathology worldwide. Its major clinical complications, stroke, myocardial infarction, and heart failure, are on the rise in many regions of the world--despite considerable progress in understanding cause, progression, and consequences of atherosclerosis. Originally perceived as a lipid-storage disease of the arterial wall (Die cellularpathologie in ihrer begründung auf physiologische und pathologische gewebelehre. August Hirschwald Verlag Berlin, [1871]), atherosclerosis was recognized as a chronic inflammatory disease in 1986 (New Engl J Med 314:488-500, 1986). The presence of lymphocytes in atherosclerotic lesions suggested autoimmune processes in the vessel wall (Clin Exp Immunol 64:261-268, 1986). Since the advent of suitable mouse models of atherosclerosis (Science 258:468-471, 1992; Cell 71:343-353, 1992; J Clin Invest 92:883-893, 1993) and the development of flow cytometry to define the cellular infiltrate in atherosclerotic lesions (J Exp Med 203:1273-1282, 2006), the origin, lineage, phenotype, and function of distinct inflammatory cells that trigger or inhibit the inflammatory response in the atherosclerotic plaque have been studied. Multiphoton microscopy recently enabled direct visualization of antigen-specific interactions between T cells and antigen-presenting cells in the vessel wall (J Clin Invest 122:3114-3126, 2012). Vascular immunology is now emerging as a new field, providing evidence for protective as well as damaging autoimmune responses (Int Immunol 25:615-622, 2013). Manipulating inflammation and autoimmunity both hold promise for new therapeutic strategies in cardiovascular disease. Ongoing work (J Clin Invest 123:27-36, 2013; Front Immunol 2013; Semin Immunol 31:95-101, 2009) suggests that it may be possible to develop antigen-specific immunomodulatory prevention and therapy-a vaccine against atherosclerosis.

The intravenous injection of oxidized LDL- or Apolipoprotein B100--Coupled splenocytes promotes Th1 polarization in wildtype and Apolipoprotein E--Deficient mice

BACKGROUND

Th1 responses in atherosclerosis are mainly associated with the aggravation of atherosclerotic plaques, whereas Th2 responses lead to a less pronounced disease in mouse models. The fixation of antigens on cells by means of ethylene carbodiimide (ECDI), and subsequent injection of these antigen-coupled splenocytes (Ag-SP) to induce tolerance against the attached antigens, has been successfully used to treat murine type 1 diabetes or encephalomyelitis in. We analyzed this approach in a mouse model for atherosclerosis.

METHODS AND RESULTS

OTII-transgenic mice that were treated with a single dose of 5 × 10(7) OVA-coupled splenocytes (OVA-SP), had decreased splenocyte proliferation, and lower IFNγ production in vitro upon antigen recall. However, in vivo CD4 cell activation was increased. To try lipoprotein-derived, "atherosclerosis-associated" antigens, we first tested human oxidized LDL. In wild type mice, an increase of IFNγ production upon in vitro recall was detected in the oxLDL-SP group. In Apolipoprotein E - deficient (ApoE-/-) mice that received oxLDL-SP every 5 weeks for 20 weeks, we did not find any difference of atherosclerotic plaque burden, but again increased IFNγ production. To overcome xenogenous limitations, we then examined the effects of mouse Apolipoprotein B100 peptides P3 and P6. ApoB100-SP treatment again promoted a more IFNγ pronounced response upon in vitro recall. Flow cytometry analysis of cytokine secreting spleen cells revealed CD4 positive T cells to be mainly the source for IFNγ. In ApoE-/- mice that were administered ApoB100-SP during 20 weeks, the atherosclerotic plaque burden in aortic roots as well as total aorta was unchanged compared to PBS treated controls. Splenocyte proliferation upon antigen recall was not significantly altered in ApoB100-SP treated ApoE-/- mice.

CONCLUSION

Although we did not observe a relevant anti-atherosclerotic benefit, the treatment with antigen-coupled splenocytes in its present form already impacts the immune responses and deserves further exploration.

Immunoactivation at the crossroads of human disease

It is becoming increasingly clear that immunoactivation, which evolved as a system of host defense against pathogens, can become dysregulated and promote the pathogenesis of diverse diseases with both known and unknown etiologies (eg, acquired immune deficiency syndrome, age-related macular degeneration, cancer, as well as aging). Immunoactivation seems to be a "common denominator" or general mechanism of pathogenesis and may explain the association and similarities in pathology among otherwise unrelated human diseases. Identification of general mechanisms of immunoactivation may lead to the development of new therapeutic strategies applicable to many diseases even before detailed knowledge of specific etiology and pathogenesis may be available.

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.