Regulatory B Cell–Specific Interleukin-10 Is Dispensable for Atherosclerosis Development in Mice

Targeting gut microbiota to regulate the adaptive immune response in atherosclerosis

Atherosclerosis, the leading cause of death worldwide, is a chronic inflammatory disease leading to the accumulation of lipid-rich plaques in the intima of large and medium-sized arteries. Accumulating evidence indicates the important regulatory role of the adaptive immune system in atherosclerosis during all stages of the disease. The gut microbiome has also become a key regulator of atherosclerosis and immunomodulation. Whilst existing research extensively explores the impact of the microbiome on the innate immune system, only a handful of studies have explored the regulatory capacity of the microbiome on the adaptive immune system to modulate atherogenesis. Building on these concepts and the pitfalls on the gut microbiota and adaptive immune response interaction, this review explores potential strategies to therapeutically target the microbiome, including the use of prebiotics and vaccinations, which could influence the adaptive immune response and consequently plaque composition and development.

Causal Relationships between Lymphocyte Subsets and Risk of Coronary Artery Disease: A Two-Sample Mendelian Randomization Study

Background

Currently, the causal relationship between lymphocyte subsets and coronary artery disease (CAD) remains unclear. Therefore, we utilized Mendelian randomization (MR) to assess the association between lymphocyte subsets and CAD.

Methods

We performed a two-sample MR analysis using publicly available genome-wide association studies (GWAS) datasets. The primary method of analysis to comprehensively evaluate causal effects was the inverse variance-weighted (IVW) method. The four additional MR approaches were MR-Egger, weighted median, simple mode, and weighted mode. Sensitivity analysis incorporated Cochran's Q and MR-Egger intercept tests to identify residual heterogeneity and potential horizontal pleiotropy, respectively. The MR-PRESSO distortion test was applied to identify potential pleiotropic outliers. Leave-one-out analysis confirmed that no single single-nucleotide polymorphism (SNP) significantly affected the MR estimate. We conducted reverse MR analysis to investigate the impact of variables correlated with outcomes in forward MR analysis.

Results

The IVW method revealed a significant positive association between B cell count and CAD (odds ratio (OR) = 1.08 (95% CI: 1.04, 1.11), p = 2.67 × 10-5). A similar association was observed between B cell count and myocardial infarction (MI) (OR = 1.07 (95% CI: 1.03, 1.11), p = 5.69 × 10-4). Sensitivity analyses detected no outliers, heterogeneity, or pleiotropy. The reverse MR analysis was conducted to investigate the impact of CAD and MI on B cell count, and the IVW results showed no statistical significance.

Conclusions

Our study suggests that a higher absolute B cell count is linked to an increased risk of CAD and MI.

Identification of macrophage differentiation related genes and subtypes linking atherosclerosis plaque processing and metabolic syndrome via integrated bulk and single-cell sequence analysis

Metabolic syndrome(MS) is a separate risk factor for the advancement of atherosclerosis(AS) plaque but mechanism behind this remains unclear. There may be a significant role for the immune system in this process. This study aims to identify potential diagnostic genes in MS patients at a higher risk of developing and progressing to AS. Datasets were retrevied from gene expression omnibus(GEO) database and differentially expressed genes were identified. Hub genes, immune cell dysregulation and AS subtypes were identified using a conbination of muliple bioinformatic analysis, machine learning and consensus clustering. Diagnostic value of hub genes was estimated using a nomogram and ROC analysis. Finally, enrichment analysis, competing endogenous RNA(ceRNA) network, single-cell RNA(scRNA) sequencing analysis and drug-protein interaction prediction was constructed to identify the functional roles, potential regulators and distribution for hub genes. Four hub genes and two macrophage-related subtypes were identified. Their strong diagnostic value was validated and functional process were identified. ScRNA analysis identified the macrophage differentiation regulation function of F13A1. CeRNA network and drug-protein binding modes revealed the potential therapeutic method. Four immune-correlated hub genes(F13A1, MMRN1, SLCO2A1 and ZNF521) were identified with their diagnostic value being assesed, which F13A1 was found strong correlated with macrophage differentiation and could be potential diagnostic and therapeutic marker for AS progression in MS patients.

Adaptive immunity and atherosclerosis: aging at its crossroads

Adaptive immunity plays a profound role in atherosclerosis pathogenesis by regulating antigen-specific responses, inflammatory signaling and antibody production. However, as we age, our immune system undergoes a gradual functional decline, a phenomenon termed "immunosenescence". This decline is characterized by a reduction in proliferative naïve B- and T cells, decreased B- and T cell receptor repertoire and a pro-inflammatory senescence associated secretory profile. Furthermore, aging affects germinal center responses and deteriorates secondary lymphoid organ function and structure, leading to impaired T-B cell dynamics and increased autoantibody production. In this review, we will dissect the impact of aging on adaptive immunity and the role played by age-associated B- and T cells in atherosclerosis pathogenesis, emphasizing the need for interventions that target age-related immune dysfunction to reduce cardiovascular disease risk.

Atherosclerosis antigens as targets for immunotherapy

Atherosclerosis is a chronic inflammatory disease of the arteries that can lead to thrombosis, infarction and stroke, underlying the first cause of mortality worldwide. Adaptive immunity plays critical roles in atherosclerosis, and numerous studies have ascribed both atheroprotective and atherogenic functions to specific subsets of T and B cells. However, less is known on how antigen specificity determines the protective or adverse outcome of such adaptive responses. Understanding antigen triggers in atherosclerosis is crucial to delve deeper into mechanisms of disease initiation and progression and to implement specific immunotherapeutic approaches, including vaccination strategies. Here we review the role of adaptive immunity in atherosclerosis and the insights that single-cell technology has provided into the function of distinct immune cell subsets. We outline the most relevant atherosclerosis antigens and antibodies reported to date and examine their immunotherapeutic potential. Finally, we review the most promising vaccination-based clinical trials targeting the adaptive immune system.

Insights into the roles of IL-10-producing regulatory B cells in cardiovascular disorders: recent advances and future perspectives

Interleukin-10-producing regulatory B (B10) cells mediate the immunomodulatory functions of biosystems by secreting anti-inflammatory factors, thus playing vital roles in cardiovascular diseases such as viral myocarditis, myocardial infarction, and ischemia-reperfusion injury. However, several challenges hinder B10 cells from regulating the immunoreactivity of organisms in specific cardiovascular diseases, such as atherosclerotic disease. Regarding the regulatory mechanisms of B10 cells, the interplay between B10 cells and the cardiovascular and immune systems is complex and requires clarification. In this study, we summarize the roles of B10 cells in bacterial and aseptic heart injuries, address their regulatory functions in different stages of cardiovascular disorders, and discuss their challenges and opportunities in addressing cardiovascular diseases from bench to bedside.

Targeting gut microbiota and immune crosstalk: potential mechanisms of natural products in the treatment of atherosclerosis

Atherosclerosis (AS) is a chronic inflammatory reaction that primarily affects large and medium-sized arteries. It is a major cause of cardiovascular disease and peripheral arterial occlusive disease. The pathogenesis of AS involves specific structural and functional alterations in various populations of vascular cells at different stages of the disease. The immune response is involved throughout the entire developmental stage of AS, and targeting immune cells presents a promising avenue for its treatment. Over the past 2 decades, studies have shown that gut microbiota (GM) and its metabolites, such as trimethylamine-N-oxide, have a significant impact on the progression of AS. Interestingly, it has also been reported that there are complex mechanisms of action between GM and their metabolites, immune responses, and natural products that can have an impact on AS. GM and its metabolites regulate the functional expression of immune cells and have potential impacts on AS. Natural products have a wide range of health properties, and researchers are increasingly focusing on their role in AS. Now, there is compelling evidence that natural products provide an alternative approach to improving immune function in the AS microenvironment by modulating the GM. Natural product metabolites such as resveratrol, berberine, curcumin, and quercetin may improve the intestinal microenvironment by modulating the relative abundance of GM, which in turn influences the accumulation of GM metabolites. Natural products can delay the progression of AS by regulating the metabolism of GM, inhibiting the migration of monocytes and macrophages, promoting the polarization of the M2 phenotype of macrophages, down-regulating the level of inflammatory factors, regulating the balance of Treg/Th17, and inhibiting the formation of foam cells. Based on the above, we describe recent advances in the use of natural products that target GM and immune cells crosstalk to treat AS, which may bring some insights to guide the treatment of AS.

Circulating Regulatory B-Lymphocytes in Patients with Acute Myocardial Infarction: A Pilot Study

Background: Inflammation plays on important role in plaque instability and acute coronary syndromes. The anti-inflammatory effects of B-regulatory lymphocytes (B-regs) in atherosclerosis was tested mainly in animal models with inconclusive results. Herein, we studied for the first time, levels of circulating B-regs in patients with acute myocardial infarction (MI). Methods: We examined circulating levels of B-regs by flow cytometry in 29 patients with recent ST-segment elevation MI and 18 patients with stable angina pectoris (SAP) and coronary artery disease. We re-assessed B-reg levels on average 4 months later. Results: The mean level of CD20+ cells was similar in patients with MI and patients with SAP (p = 0.60). The levels of CD24hiCD38hi cells among CD20+ cells were 5.7 ± 4% and 11.6 ± 6% in patients with MI and SAP, respectively, (p < 0.001). The level of CD24hiCD38hi B-regs remained related to acute MI after correcting for age, gender, and risk factors. Circulating levels of CD24hiCD38hi B-regs in patients with MI did not change significantly at follow-up in a small patient groups (p = 0.408). Conclusions: Circulating B-regs are reduced in patients with MI compared to patients with SAP. This finding may shed further light on the inflammatory pathophysiologic factors related to plaque rupture.

Deleting interleukin-10 from myeloid cells exacerbates atherosclerosis in Apoe-/- mice

Atherosclerosis is initiated by subendothelial retention of lipoproteins and cholesterol, which triggers a non-resolving inflammatory process that over time leads to plaque progression in the artery wall. Myeloid cells and in particular macrophages are the primary drivers of the inflammatory response and plaque formation. Several immune cells including macrophages, T cells and B cells secrete the anti-inflammatory cytokine IL-10, known to be essential for the atherosclerosis protection. The cellular source of IL-10 in natural atherosclerosis progression is unknown. This study aimed to determine the main IL10-producing cell type in atherosclerosis. To do so, we crossed VertX mice, in which IRES-green fluorescent protein (eGFP) was placed downstream of exon 5 of the Il10 gene, with atherosclerosis-prone Apoe-/- mice. We found that myeloid cells express high levels of IL-10 in VertX Apoe-/- mice in both chow and western-diet fed mice. By single cell RNA sequencing and flow cytometry analysis, we identified resident and inflammatory macrophages in atherosclerotic plaques as the main IL-10 producers. To address whether IL-10 secreted by myeloid cells is essential for the protection, we utilized LyzMCre+Il10fl/fl mice crossed into the Apoe-/- background and confirmed that macrophages were unable to secrete IL-10. Chow and western diet-fed LyzMCre+Il10fl/fl Apoe-/- mice developed significantly larger atherosclerotic plaques as measured by en face morphometry than LyzMCre-Il10 fl/flApoe-/-. Flow cytometry and cytokine measurements suggest that the depletion of IL-10 in myeloid cells increases Th17 cells with elevated CCL2, and TNFα in blood plasma. We conclude that macrophage-derived IL-10 is critical for limiting atherosclerosis in mice.

Immuno-cardio-oncology: Killing two birds with one stone?

Inflammation and a dysregulated immune system are common denominators of cancer and cardiovascular disease (CVD). Immuno-cardio-oncology addresses the interconnected immunological aspect in both cancer and CVD and the integration of immunotherapies and anti-inflammatory therapies in both distinct disease entities. Building on prominent examples of convergent inflammation (IL-1ß biology) and immune disbalance (CD20 cells) in cancer and CVD/heart failure, the review tackles both the roadblocks and opportunities of repurposed use of IL-1ß drugs and anti-CD20 antibodies in both fields, and discusses the use of advanced therapies e.g. chimeric antigen receptor (CAR) T cells, that can address the raising burden of both cancer and CVD. Finally, it is discussed how inspired by precision medicine in oncology, the use of biomarker-driven patient stratification is needed to better guide anti-inflammatory/immunomodulatory therapeutic interventions in cardiology.

The Spectrum of B Cell Functions in Atherosclerotic Cardiovascular Disease

B cells are a core element of the pathophysiology of atherosclerotic cardiovascular disease (ASCVD). Multiple experimental and epidemiological studies have revealed both protective and deleterious functions of B cells in atherosclerotic plaque formation. The spearhead property of B cells that influences the development of atherosclerosis is their unique ability to produce and secrete high amounts of antigen-specific antibodies that can act at distant sites. Exposure to an atherogenic milieu impacts B cell homeostasis, cell differentiation and antibody production. However, it is not clear whether B cell responses in atherosclerosis are instructed by atherosclerosis-specific antigens (ASA). Dissecting the full spectrum of the B cell properties in atherosclerosis will pave the way for designing innovative therapies against the devastating consequences of ASCVD.

Therapeutic strategies targeting inflammation and immunity in atherosclerosis: how to proceed?

Atherosclerosis is a chronic inflammatory disease of the arterial wall, characterized by the formation of plaques containing lipid, connective tissue and immune cells in the intima of large and medium-sized arteries. Over the past three decades, a substantial reduction in cardiovascular mortality has been achieved largely through LDL-cholesterol-lowering regimes and therapies targeting other traditional risk factors for cardiovascular disease, such as hypertension, smoking, diabetes mellitus and obesity. However, the overall benefits of targeting these risk factors have stagnated, and a huge global burden of cardiovascular disease remains. The indispensable role of immunological components in the establishment and chronicity of atherosclerosis has come to the forefront as a clinical target, with proof-of-principle studies demonstrating the benefit and challenges of targeting inflammation and the immune system in cardiovascular disease. In this Review, we provide an overview of the role of the immune system in atherosclerosis by discussing findings from preclinical research and clinical trials. We also identify important challenges that need to be addressed to advance the field and for successful clinical translation, including patient selection, identification of responders and non-responders to immunotherapies, implementation of patient immunophenotyping and potential surrogate end points for vascular inflammation. Finally, we provide strategic guidance for the translation of novel targets of immunotherapy into improvements in patient outcomes.

In this Review, the authors provide an overview of the immune cells involved in atherosclerosis, discuss preclinical research and published and ongoing clinical trials assessing the therapeutic potential of targeting the immune system in atherosclerosis, highlight emerging therapeutic targets from preclinical studies and identify challenges for successful clinical translation.

Inflammation is an important component of the pathophysiology of cardiovascular disease; an imbalance between pro-inflammatory and anti-inflammatory processes drives chronic inflammation and the formation of atherosclerotic plaques in the vessel wall.

Clinical trials assessing canakinumab and colchicine therapies in atherosclerotic cardiovascular disease have provided proof-of-principle of the benefits associated with therapeutic targeting of the immune system in atherosclerosis.

The immunosuppressive adverse effects associated with the systemic use of anti-inflammatory drugs can be minimized through targeted delivery of anti-inflammatory drugs to the atherosclerotic plaque, defining the window of opportunity for treatment and identifying more specific targets for cardiovascular inflammation.

Implementing immunophenotyping in clinical trials in patients with atherosclerotic cardiovascular disease will allow the identification of immune signatures and the selection of patients with the highest probability of deriving benefit from a specific therapy.

Clinical stratification via novel risk factors and discovery of new surrogate markers of vascular inflammation are crucial for identifying new immunotherapeutic targets and their successful translation into the clinic.

Stimulation of the PD-1 Pathway Decreases Atherosclerotic Lesion Development in Ldlr Deficient Mice

Aim: Signaling through the coinhibitory programmed death (PD)-1/PD-L1 pathway regulates T cell responses and can inhibit ongoing immune responses. Inflammation is a key process in the development of atherosclerosis, the underlying cause for the majority of cardiovascular diseases. Dampening the excessive immune response that occurs during atherosclerosis progression by promoting PD-1/PD-L1 signaling may have a high therapeutic potential to limit disease burden. In this study we therefore aimed to assess whether an agonistic PD-1 antibody can diminish atherosclerosis development.

Methods and Results: Ldlr^−/− mice were fed a western-type diet (WTD) while receiving 100 μg of an agonistic PD-1 antibody or control vehicle twice a week. Stimulation of the PD-1 pathway delayed the WTD-induced monocyte increase in the circulation up to 3 weeks and reduced T cell activation and proliferation. CD4⁺ T cell numbers in the atherosclerotic plaque were reduced upon PD-1 treatment. More specifically, we observed a 23% decrease in atherogenic IFNγ-producing splenic CD4⁺ T cells and a 20% decrease in cytotoxic CD8⁺ T cells, whereas atheroprotective IL-10 producing CD4⁺ T cells were increased with 47%. Furthermore, we found an increase in regulatory B cells, B1 cells and associated atheroprotective circulating oxLDL-specific IgM levels in agonistic PD-1-treated mice. This dampened immune activation following agonistic PD-1 treatment resulted in reduced atherosclerosis development (p < 0.05).

Conclusions: Our data show that stimulation of the coinhibitory PD-1 pathway inhibits atherosclerosis development by modulation of T- and B cell responses. These data support stimulation of coinhibitory pathways as a potential therapeutic strategy to combat atherosclerosis.

B Lymphocyte-Deficiency in Mice Causes Vascular Dysfunction by Inducing Neutrophilia

B lymphocytes have been implicated in the development of insulin resistance, atherosclerosis and certain types of hypertension. In contrast to these studies, which were performed under pathological conditions, the present study provides evidence for the protective effect of B lymphocytes in maintaining vascular homeostasis under physiological conditions. In young mice not exposed to any known risk factors, the lack of B cells led to massive endothelial dysfunction. The vascular dysfunction in B cell-deficient mice was associated with an increased number of neutrophils in the circulating blood. Neutrophil depletion in B cell-deficient mice resulted in the complete normalization of vascular function, indicating a causal role of neutrophilia. Moreover, vascular function in B cell-deficient mice could be restored by adoptive transfer of naive B-1 cells isolated from wild-type mice. Interestingly, B-1 cell transfer also reduced the number of neutrophils in the recipient mice, further supporting the involvement of neutrophils in the vascular pathology caused by B cell-deficiency. In conclusion, we report in the present study the hitherto undescribed role of B lymphocytes in regulating vascular function. B cell dysregulation may represent a crucial mechanism in vascular pathology.

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.

The Emerging Role of B Lymphocytes in Cardiovascular Disease

B cells are traditionally known for their ability to produce antibodies in the context of adaptive immune responses. However, over the last decade B cells have been increasingly recognized as modulators of both adaptive and innate immune responses, as well as players in an important role in the pathogenesis of a variety of human diseases. Here, after briefly summarizing our current understanding of B cell biology, we present a systematic review of the literature from both animal models and human studies that highlight the important role that B lymphocytes play in cardiac and vascular disease. While many aspects of B cell biology in the vasculature and, to an even greater extent, in the heart remain unclear, B cells are emerging as key regulators of cardiovascular adaptation to injury.

The roles of immune cells in atherosclerotic calcification

Atherosclerosis is the leading cause of acute cardiovascular events, and vascular calcification is an important pathological phenomenon in atherosclerosis. Recently, many studies have shown that immune cells are closely associated with the development of atherosclerosis and calcification, but there are many conflicting viewpoints because of immune system complications, such as the pro-atherosclerotic and atheroprotective effects of regulatory B cells (Bregs), T helper type 2 (Th2) cells and T helper type 17 (Th17) cells. In this review, we summarize the studies on the roles of immune cells, especially lymphocytes and macrophages, in atherosclerotic calcification. Furthermore, we prepared graphs showing the relationship between T cells, B cells and macrophages and atherosclerotic calcification. Finally, we highlight some potential issues that are closely associated with the function of immune cells in atherosclerotic calcification. Based on current research results, this review summarizes the relationship between immune cells and atherosclerotic calcification, and it will be beneficial to understand the relationship of immune cells and atherosclerotic calcification.

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.

B Cells in Atherosclerosis: Mechanisms and Potential Clinical Applications

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B cells regulate atherosclerotic plaque formation through production of antibodies and cytokines, and effects are subset specific (B1 and B2).

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Putative human atheroprotective B1 cells function similarly to murine B1 in their spontaneous IgM antibody production. However, marker strategies in identifying human and murine B1 are different.

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IgM antibody to oxidation specific epitopes produced by B1 cells associate with human coronary artery disease.

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Neoantigen immunization may be a promising strategy for atherosclerosis vaccine development, but further study to determine relevant antigens still need to be done.

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B-cell–targeted therapies, used in treating autoimmune diseases as well as lymphoid cancers, might have potential applications in treating cardiovascular diseases. Short- and long-term cardiovascular effects of these agents need to be assessed.

Because atherosclerotic cardiovascular disease is a leading cause of death worldwide, understanding inflammatory processes underpinning its pathology is critical. B cells have been implicated as a key immune cell type in regulating atherosclerosis. B-cell effects, mediated by antibodies and cytokines, are subset specific. In this review, we focus on elaborating mechanisms underlying subtype-specific roles of B cells in atherosclerosis and discuss available human data implicating B cells in atherosclerosis. We further discuss potential B cell–linked therapeutic approaches, including immunization and B cell–targeted biologics. Given recent evidence strongly supporting a role for B cells in human atherosclerosis and the expansion of immunomodulatory agents that affect B-cell biology in clinical use and clinical trials for other disorders, it is important that the cardiovascular field be cognizant of potential beneficial or untoward effects of modulating B-cell activity on atherosclerosis.

Act Locally, Act Globally-Microbiota, Barriers, and Cytokines in Atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease that is characterized by the formation and progressive growth of atherosclerotic plaques in the wall of arteries. Atherosclerosis is a major predisposing factor for stroke and heart attack. Various immune-mediated mechanisms are implicated in the disease initiation and progression. Cytokines are key mediators of the crosstalk between innate and adaptive immune cells as well as non-hematopoietic cells in the aortic wall and are emerging players in the regulation of atherosclerosis. Progression of atherosclerosis is always associated with increased local and systemic levels of pro-inflammatory cytokines. The role of cytokines within atherosclerotic plaque has been extensively investigated; however, the cell-specific role of cytokine signaling, particularly the role of cytokines in the regulation of barrier tissues tightly associated with microbiota in the context of cardiovascular diseases has only recently come to light. Here, we summarize the knowledge about the function of cytokines at mucosal barriers and the interplay between cytokines, barriers, and microbiota and discuss their known and potential implications for atherosclerosis development.

Functional Role of B Cells in Atherosclerosis

Atherosclerosis is a lipid-driven inflammatory disease of blood vessels, and both innate and adaptive immune responses are involved in its development. The impact of B cells on atherosclerosis has been demonstrated in numerous studies and B cells have been found in close proximity to atherosclerotic plaques in humans and mice. B cells exert both atheroprotective and pro-atherogenic functions, which have been associated with their B cell subset attribution. While B1 cells and marginal zone B cells are considered to protect against atherosclerosis, follicular B cells and innate response activator B cells have been shown to promote atherosclerosis. In this review, we shed light on the role of B cells from a different, functional perspective and focus on the three major B cell functions: antibody production, antigen presentation/T cell interaction, and the release of cytokines. All of these functions have the potential to affect atherosclerosis by multiple ways and are dependent on the cellular milieu and the activation status of the B cell. Moreover, we discuss B cell receptor signaling and the mechanism of B cell activation under atherosclerosis-prone conditions. By summarizing current knowledge of B cells in and beyond atherosclerosis, we are pointing out open questions and enabling new perspectives.

An overview of the innate and adaptive immune system in atherosclerosis

Cardiovascular disease is the leading cause of death globally. Coronary artery disease (CAD) is a chronic inflammatory disease usually caused by atherosclerosis, in which the coronary arteries become narrowed by atheromatous plaque. Plaques in atherosclerosis are formed through the accumulation of lipids and various immune cells. Both adaptive and innate immune systems are involved in the pathogenesis of atherosclerosis and facilitate plaque formation and disease progression. Almost all immune system cells, including neutrophils, B cells, T cells monocytes, macrophages, foam cells, and dendritic cells (DCs), play a vital role in atherosclerotic plaque. Atherogenesis, the normal function of the endothelium, is initially disrupted and, then, cells of the immune system are recruited to the endothelium following increased expression of cell adhesion molecules. Accumulation of immune cells and lipids leads to the formation of a necrotic nucleus. As the disease progresses, smooth muscle cells form fibrous layers, whose rupture results in exposing the necrotic nucleus and thrombosis. Accordingly, the present review was conducted to determine the role of different cells in innate and adaptive immune systems in inhibition and progression of atherosclerosis.

Low-dose oral cyclophosphamide therapy reduces atherosclerosis progression by decreasing inflammatory cells in a murine model of atherosclerosis

Background

Atherosclerosis is a chronic inflammatory disease responsible for most cases of heart disease and stroke in Western countries. The cytotoxic drug cyclophosphamide (CPA) can modulate immune functions, and it has therefore been used to treat patients with autoimmune diseases. Extension of survival of patients with severe atherosclerosis has been reported after CPA treatment, but the underlying mechanism is still poorly understood.

Methods and results

We have investigated the effects of CPA in a murine model of atherosclerosis. Continuous oral administration of low-dose CPA (20 mg/kg/day) prevented atherosclerosis in apolipoprotein E-deficient (apoE^-/-) mice fed with a high fat diet. After 12 weeks, CPA treatment delayed progression of atherosclerosis in the mice (9.92% vs 3.32%, P < 0.05, n = 7) and reduced the macrophage content of plaques (1.228 vs 0.2975 mm², P < 0.001). Flow cytometry (FACS) showed that, in peripheral blood and spleen cells, the numbers of B cells and inflammatory T cells (Th1 cells) decreased, and inflammatory monocytes also decreased. However, there were no differences in the bone marrow cells between the two groups. The mRNA levels in the aorta showed significantly decreased inflammatory cytokine (interleukin-6) (P < 0.05), and tended to increase anti-inflammatory cytokine (argininase-1), but no significant differences between the two groups. High dose CPA has cardiotoxicity, but the dose used in this study did not show significant cardiotoxicity.

Conclusions

The results demonstrate that oral treatment with CPA inhibits initiation and progression of atherosclerosis in the apoE^-/- mouse model through immunomodulatory effects on lymphoid and inflammatory cells.

Low frequency of IL-10+ B cells in patients with atherosclerosis is related with inflammatory condition

Background and aims

B cells involvement in animal models of atherosclerosis has been unequivocally established. However, the role of these cells in patients with atherosclerosis is almost unknown. Besides the production of antibodies, B cells can also exhibit regulatory functions mainly through IL-10. Here, we characterized human B cell subsets, their production of IL-10 in patients with atherosclerosis and their potential association with inflammation.

Methods

Patients with confirmed atherosclerotic events and controls with low cardiovascular risk were included. B cells subsets were determined in mononuclear cells (PBMC) using flow cytometry. PBMC were cultured ex vivo (5 h) and in vitro (48 h) to determine IL-10⁺ B cells and in some cases TNF-α⁺ and IFN-γ⁺ CD4⁺ T cells. The inflammatory state of the participants was determined through high sensitivity C reactive protein levels.

Results

Increase in percentage and number of plasmablasts was observed in patients with atherosclerosis compared with controls. A decreased frequency of IL-10⁺ B cells was observed in patients, both in ex vivo and in vitro cultures. This decrease was detected in transitional, memory, and plasmablast subsets. Interestingly, the reduction of IL-10⁺ B cells negatively and significantly correlated with the inflammatory condition of the studied subjects and associated with an increased frequency of TNF-α⁺ and IFN-γ⁺ CD4⁺ T cells. The blockade of IL-10R did not show further effect in T cells activation.

Conclusions

There is an association between the inflammatory state and a reduction of IL-10⁺ B cells that could contribute to the development of atherosclerosis.

B- and T-lymphocyte attenuator stimulation protects against atherosclerosis by regulating follicular B cells

AIMS

The immune system is strongly involved in atherosclerosis and immune regulation generally leads to attenuated atherosclerosis. B- and T-lymphocyte attenuator (BTLA) is a novel co-receptor that negatively regulates the activation of B and T cells; however, there have been no reports of BTLA and its function in atherosclerosis or cardiovascular disease (CVD). We aimed to assess the dominant BTLA expressing leucocyte in CVD patients and to investigate whether BTLA has a functional role in experimental atherosclerosis.

METHODS AND RESULTS

We show that BTLA is primarily expressed on B cells in CVD patients and follicular B2 cells in low-density lipoprotein receptor-deficient (Ldlr-/-) mice. We treated Ldlr-/- mice that were fed a western-type diet (WTD) with phosphate-buffered saline, an isotype antibody, or an agonistic BTLA antibody (3C10) for 6 weeks. We report here that the agonistic BTLA antibody significantly attenuated atherosclerosis. This was associated with a strong reduction in follicular B2 cells, while regulatory B and T cells were increased. The BTLA antibody showed similar immunomodulating effects in a progression study in which Ldlr-/- mice were fed a WTD for 10 weeks before receiving antibody treatment. Most importantly, BTLA stimulation enhanced collagen content, a feature of stable lesions, in pre-existing lesions.

CONCLUSION

Stimulation of the BTLA pathway in Ldlr-/- mice reduces initial lesion development and increases collagen content of established lesions, presumably by shifting the balance between atherogenic follicular B cells and atheroprotective B cells and directing CD4+ T cells towards regulatory T cells. We provide the first evidence that BTLA is a very promising target for the treatment of 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.

Impact of B-Cell–Targeted Therapies on Cardiovascular Disease

Atherosclerosis is a lipid-driven chronic inflammatory disease that is modulated by many immune cell subsets, including B cells. Therefore, targeting the inflammatory component of cardiovascular disease represents a promising therapeutic strategy. In the past years, immunotherapy has revolutionized the treatment of autoimmunity and cancer. Many of these clinically used strategies target B cells. Given the multifaceted role of B cells in atherogenesis, it is conceivable that B-cell–directed therapies can modulate disease development. Here, we review clinically available B-cell–targeted therapies and the possible benefits or detrimental effects on cardiovascular disease.

[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.

B Cell-Activating Factor Neutralization Aggravates Atherosclerosis

BACKGROUND

Atherosclerotic cardiovascular disease (heart attacks and strokes) is the major cause of death globally and is caused by the buildup of a plaque in the arterial wall. Genomic data showed that the B cell-activating factor (BAFF) receptor pathway, which is specifically essential for the survival of conventional B lymphocytes (B-2 cells), is a key driver of coronary heart disease. Deletion or antibody-mediated blockade of BAFF receptor ablates B-2 cells and decreases experimental atherosclerosis. Anti-BAFF immunotherapy is approved for treatment of autoimmune systemic lupus erythematosus, and can therefore be expected to limit their associated cardiovascular risk. However, direct effects of anti-BAFF immunotherapy on atherosclerosis remain unknown.

METHODS

To investigate the effect of BAFF neutralization in atherosclerosis, the authors treated Apoe^-/- and Ldlr^-/- mice with a well-characterized blocking anti-BAFF antibody. Moreover, to investigate the mechanism by which BAFF impacts atherosclerosis, the authors studied atherosclerosis-prone mice that lack the alternative receptor for BAFF: transmembrane activator and calcium modulator and cyclophilin ligand interactor.

RESULTS

The authors demonstrate here that anti-BAFF antibody treatment increased atherosclerosis in mice, despite efficient depletion of mature B-2 cells, suggesting a unique mechanism of action. Indeed, myeloid cell-specific deletion of transmembrane activator and calcium modulator and cyclophilin ligand interactor also results in increased atherosclerosis, while B cell-specific transmembrane activator and calcium modulator and cyclophilin ligand interactor deletion had no effect. Mechanistically, BAFF-transmembrane activator and calcium modulator and cyclophilin ligand interactor signaling represses macrophage IRF7-dependent (but not NF-κB-dependent) Toll-like receptor 9 responses including proatherogenic CXCL10 production.

CONCLUSIONS

These data identify a novel B cell-independent anti-inflammatory role for BAFF in atherosclerosis and may have important clinical implications.

Bidirectional effects of IL-10+ regulatory B cells in Ldlr-/- mice

BACKGROUND AND AIMS

Limiting the pro-inflammatory immune response is critical for the treatment of atherosclerosis. Regulatory B cells (Bregs) can modulate the immune response through interleukin-10 (IL-10). Current data regarding Bregs and atherosclerosis is scarce and conflicting.

METHODS

In this study, we investigated the frequency of IL-10⁺ B cells during the development of atherosclerosis in low-density lipoprotein receptor-deficient (Ldlr^-/-) mice and studied the effect of adoptive transfer of IL-10⁺ B cells on atherosclerosis.

RESULTS

We found a very strong inverse correlation between atherosclerosis severity and the frequency of IL-10⁺ B cells. This effect was cholesterol-independent and observed in spleen, draining lymph nodes and peritoneal cavity. To directly assess the effects of IL-10⁺ B cells on atherosclerosis, we expanded IL-10⁺ B cells ex vivo with anti-CD40 and selected pure and viable IL-10-secreting B cells and IL-10^- B cells and adoptively transferred them to Ldlr^-/- mice, respectively. While IL-10^- B cells were strongly atherogenic compared to control-treated mice, IL-10⁺ B cells did not affect lesion size. Adoptive transfer of IL-10⁺ B cells strongly reduced circulating leukocyte numbers and inflammatory monocytes. In addition, they decreased CD4⁺ T cell activation and increased IL-10⁺ CD4⁺ T cell numbers. Interestingly, both IL-10⁺ and IL-10^- B cells exacerbated serum cholesterol levels and resulted in fatty livers, which potentially masked the beneficial effects of IL-10⁺ B cells on atherosclerosis.

CONCLUSIONS

These findings underscore the strong immune-regulating function of IL-10⁺ B cells and provide additional incentives to explore effective strategies that expand IL-10⁺ B cells in atherosclerosis.

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.

Interleukin-10 production and T cell-suppressive capacity in B cell subsets from atherosclerotic apoE -/- mice

The evidence regarding the role of regulatory B cells (Breg) in atherosclerosis are scarce, and there are contradictory data about their atheroprotective properties. Due to the demonstrated protective function of Breg in different inflammatory diseases mainly through interleukin-10 (IL-10) production, the knowledge of their participation in atherosclerosis immunopathology would be very valuable. To further study which B cell subsets participate in IL-10 production and their regulatory role, splenocytes from apolipoprotein-E-deficient mice were evaluated by ex vivo and in vitro cultures. Atherosclerotic mice had increased frequency of IL-10⁺ B cells, which presented high CD1d, CD19, and IgM, but variable CD5, CD21, and CD23 expression. IL-10⁺ B cells were not enriched in B cell subsets previously reported as Breg. Increased frequency of IL-10⁺ B cells with transitional 1-like (T1-like) and follicular (FO) and reduced CD5⁺ and marginal zone (MZ) phenotypes were observed ex vivo. Increased frequency of IL-10⁺ B cells with T1-like and MZ, and decreased IL-10⁺ FO and T2 phenotypes were also observed in vitro. To determine regulatory capacity of B cells in the atherosclerotic model, each subset were co-cultured with CD4⁺CD25^- T cells. CD5⁺, FO, MZ, and T1-like cells from atherosclerotic mice exhibited regulation in an IL-10-dependent manner. However, only FO cells decreased both frequency of interferon gamma (IFN-γ)⁺ and tumor necrosis factor alpha (TNF-α)⁺ and proliferation of T cells. Finally, splenocytes showed increased frequency of IFN-γ⁺ and TNF-α⁺ cells only when FO-depleted B cells were evaluated. These results suggest that mainly FO B cells can modulate in some level the inflammatory responses observed in atherosclerosis.

Anti-TIM-1 Monoclonal Antibody (RMT1-10) Attenuates Atherosclerosis By Expanding IgM-producing B1a Cells

Background

Peritoneal B1a cells attenuate atherosclerosis by secreting natural polyclonal immunoglobulin M (IgM). Regulatory B cells expressing T‐cell immunoglobulin mucin domain‐1 (TIM‐1) expanded through TIM‐1 ligation by anti‐TIM‐1 monoclonal antibody (RMT1‐10) induces immune tolerance.

Methods and Results

We examined the capacity of RMT1‐10 to expand peritoneal B1a cells to prevent atherosclerosis development and retard progression of established atherosclerosis. RMT1‐10 treatment selectively doubled peritoneal B1a cells, tripled TIM‐1⁺ B1a cells and increased TIM‐1⁺IgM⁺interleukin (IL)‐10⁺ by 3‐fold and TIM‐1⁺IgM⁺IL‐10⁻ B1a cells by 2.5‐fold. Similar expansion of B1a B cells was observed in spleens. These effects reduced atherosclerotic lesion size, increased plasma IgM and lesion IgM deposits, and decreased oxidatively modified low‐density lipoproteins in lesions. Lesion CD4⁺ and CD8⁺ T cells, macrophages and monocyte chemoattractant protein‐1, vascular cell adhesion molecule‐1, expression of proinflammatory cytokines monocyte chemoattractant protein‐1, vascular cell adhesion molecule‐1, IL1β, apoptotic cell numbers and necrotic cores were also reduced. RMT1‐10 treatment failed to expand peritoneal B1a cells and reduce atherosclerosis after splenectomy that reduces B1a cells, indicating that these effects are B1a cell‐dependent. Apolipoprotein E‐KO mice fed a high‐fat diet for 6 weeks before treatment with RMT1‐10 also increased TIM‐1⁺IgM⁺IL‐10⁺ and TIM‐1⁺IgM⁺IL‐10⁻ B1a cells and IgM levels and attenuated progression of established atherosclerosis.

Conclusions

RMT1‐10 treatment attenuates atherosclerosis development and progression by selectively expanding IgM producing atheroprotective B1a cells. Antibody‐based in vivo expansion of B1a cells could be an attractive approach for treating atherosclerosis.

Follicular B Cells Promote Atherosclerosis via T Cell–Mediated Differentiation Into Plasma Cells and Secreting Pathogenic Immunoglobulin G

Objective—

B cells promote or protect development of atherosclerosis. In this study, we examined the role of MHCII (major histocompatibility II), CD40 (cluster of differentiation 40), and Blimp-1 (B-lymphocyte–induced maturation protein) expression by follicular B (FO B) cells in development of atherosclerosis together with the effects of IgG purified from atherosclerotic mice.

Approach and Results—

Using mixed chimeric Ldlr −/− mice whose B cells are deficient in MHCII or CD40, we demonstrate that these molecules are critical for the proatherogenic actions of FO B cells. During development of atherosclerosis, these deficiencies affected T–B cell interactions, germinal center B cells, plasma cells, and IgG. As FO B cells differentiating into plasma cells require Blimp-1, we also assessed its role in the development of atherosclerosis. Blimp-1-deficient B cells greatly attenuated atherosclerosis and immunoglobulin—including IgG production, preventing IgG accumulation in atherosclerotic lesions; Blimp-1 deletion also attenuated lesion proinflammatory cytokines, apoptotic cell numbers, and necrotic core. To determine the importance of IgG for atherosclerosis, we purified IgG from atherosclerotic mice. Their transfer but not IgG from nonatherosclerotic mice into Ldlr −/− mice whose B cells are Blimp-1-deficient increased atherosclerosis; transfer was associated with IgG accumulating in atherosclerotic lesions, increased lesion inflammatory cytokines, apoptotic cell numbers, and necrotic core size.

Conclusions—

The mechanism by which FO B cells promote atherosclerosis is highly dependent on their expression of MHCII, CD40, and Blimp-1. FO B cell differentiation into IgG-producing plasma cells also is critical for their proatherogenic actions. Targeting B–T cell interactions and pathogenic IgG may provide novel therapeutic strategies to prevent atherosclerosis and its adverse cardiovascular complications.

Plan B (-cell) in atherosclerosis

Atherosclerosis is a leading cause of death worldwide. It is a complex chronic inflammatory disease involving interactions between vascular, circulating and immune cells. B cells play an important role in chronic inflammation producing antibodies and regulating T and natural killer (NKT) cell activation. The role of B cells in atherosclerosis is complex, with atherogenic and protective roles assigned for distinct B cell subsets. Drugs that deplete B cells or modulate their functions are now used in the treatment of various autoimmune diseases in humans. Here, we briefly review the roles of B cell subsets in atherogenesis, and emphasize the potential impact of B cell targeted therapies on the cardiovascular risk of treated patients. Developing more B cell subset-specific therapies would lead to more effective treatments with enhanced safety profile.

Angiotensin II synergizes with BAFF to promote atheroprotective regulatory B cells

Angiotensin II (AngII) promotes hypertension, atherogenesis, vascular aneurysm and impairs post-ischemic cardiac remodeling through concerted roles on vascular cells, monocytes and T lymphocytes. However, the role of AngII in B lymphocyte responses is largely unexplored. Here, we show that chronic B cell depletion (Baffr deficiency) significantly reduces atherosclerosis in Apoe^−/− mice infused with AngII. While adoptive transfer of B cells in Apoe^−/−/Baffr^−/− mice reversed atheroprotection in the absence of AngII, infusion of AngII in B cell replenished Apoe^−/−/Baffr^−/− mice unexpectedly prevented the progression of atherosclerosis. Atheroprotection observed in these mice was associated with a significant increase in regulatory CD1d^hiCD5⁺ B cells, which produced high levels of interleukin (IL)-10 (B10 cells). Replenishment of Apoe^−/−/Baffr^−/− mice with Il10^−/− B cells reversed AngII-induced B cell-dependent atheroprotection, thus highlighting a protective role of IL-10⁺ regulatory B cells in this setting. Transfer of AngII type 1A receptor deficient (Agtr1a^−/−) B cells into Apoe^−/−/Baffr^−/− mice substantially reduced the production of IL-10 by B cells and prevented the AngII-dependent atheroprotective B cell phenotype. Consistent with the in vivo data, AngII synergized with BAFF to induce IL-10 production by B cells in vitro via AngII type 1A receptor. Our data demonstrate a previously unknown synergy between AngII and BAFF in inducing IL-10 production by B cells, resulting in atheroprotection.

Angiotensin II synergizes with BAFF to promote atheroprotective regulatory B cells

Angiotensin II (AngII) promotes hypertension, atherogenesis, vascular aneurysm and impairs post-ischemic cardiac remodeling through concerted roles on vascular cells, monocytes and T lymphocytes. However, the role of AngII in B lymphocyte responses is largely unexplored. Here, we show that chronic B cell depletion (Baffr deficiency) significantly reduces atherosclerosis in Apoe ^-/- mice infused with AngII. While adoptive transfer of B cells in Apoe ^-/- /Baffr ^-/- mice reversed atheroprotection in the absence of AngII, infusion of AngII in B cell replenished Apoe ^-/- /Baffr ^-/- mice unexpectedly prevented the progression of atherosclerosis. Atheroprotection observed in these mice was associated with a significant increase in regulatory CD1d^hiCD5⁺ B cells, which produced high levels of interleukin (IL)-10 (B10 cells). Replenishment of Apoe ^-/- /Baffr ^-/- mice with Il10 ^-/- B cells reversed AngII-induced B cell-dependent atheroprotection, thus highlighting a protective role of IL-10⁺ regulatory B cells in this setting. Transfer of AngII type 1A receptor deficient (Agtr1a ^-/-) B cells into Apoe ^-/- /Baffr ^-/- mice substantially reduced the production of IL-10 by B cells and prevented the AngII-dependent atheroprotective B cell phenotype. Consistent with the in vivo data, AngII synergized with BAFF to induce IL-10 production by B cells in vitro via AngII type 1A receptor. Our data demonstrate a previously unknown synergy between AngII and BAFF in inducing IL-10 production by B cells, resulting in atheroprotection.

B cells and atherosclerosis

B cells have emerged as important immune cells in cardiovascular disease. Initial studies have suggested that B cells protect against atherosclerosis development. However, subsequent studies demonstrating aggravation of atherosclerosis by B-2 cells have shed light on the subset-dependent effects of B cells. Here, we review the literature that has led to our current understanding of B cell regulation of atherosclerosis, touching on the importance of subsets, local regulation, human translation, and therapeutic potential.

Atheroprotective vaccination with MHC-II-restricted ApoB peptides induces peritoneal IL-10-producing CD4 T cells

Although immunization with major histocompatibility complex (MHC) class II-restricted apolipoprotein B (ApoB) peptides has been shown to be atheroprotective, the mechanism is unclear. Here, we investigated CD4⁺ T cell populations in immunized atherosclerotic mice. Peptides (16-mers) from mouse ApoB, the core protein of low-density lipoprotein (LDL), were screened for binding to I-A^b by computer prediction and confirmed by radiolabeled peptide competition. Three new peptides, P101 (FGKQGFFPDSVNKALY, 5.5 nM IC₅₀), P102 (TLYALSHAVNSYFDVD, 6.8 nM), and P103 (LYYKEDKTSLSASAAS, 95 nM), were tested in an atherosclerosis model (Apoe^-/- mice on Western diet). Immunization with each of the three peptides (1 time in complete Freund's adjuvant subcuntaneously and 4 time in incomplete Freund's adjuvant intraperitoneally) but not with adjuvant alone showed significantly reduced atherosclerotic plaques in the aortic root by serial sections and in the whole aorta by en face staining. There were no differences in body weight, LDL cholesterol, or triglycerides. Peritoneal leukocytes from ApoB peptide-immunized mice, but not control mice, secreted significant amounts of IL-10 (150 pg/ml). Flow cytometry showed that peptide immunization induced IL-10 in 10% of peritoneal CD4⁺ T cells, some of which also expressed chemokine (C-C motif) receptor 5 (CCR5). Vaccination with ApoB peptides expanded peritoneal FoxP3⁺ regulatory CD4⁺ T cells and more than tripled the number of CCR5⁺FoxP3⁺ cells. Similar trends were also seen in the draining mediastinal lymph nodes but not in the nondraining inguinal lymph nodes. We conclude that vaccination with MHC class II-restricted autologous ApoB peptides induces regulatory T cells (Tregs) and IL-10, suggesting a plausible mechanism for atheroprotection.NEW & NOTEWORTHY Vaccination against apolipoprotein B (ApoB), the protein of LDL, attracts attention as a novel approach to prevent atherosclerosis. We discovered major histocompatibility complex class II-restricted ApoB peptides, which reduce atherosclerosis and induce IL-10-producing CD4⁺ T cells and chemokine (C-C motif) receptor 5 expression on regulatory T cells, suggesting that immunization with ApoB peptides inhibits atherosclerosis by inducing anti-inflammatory cytokines.

Toll-Like Receptor (TLR)4 and MyD88 are Essential for Atheroprotection by Peritoneal B1a B Cells

BACKGROUND

We previously identified peritoneal B1a cells that secrete natural IgM as a key atheroprotective B cell subset. However, the molecules that activate atheroprotective B1a cells are unknown. Here, we investigated whether Toll-like receptors (TLRs) TLR2, TLR4, and TLR9 expressed by B1a cells are required for IgM-mediated atheroprotection.

METHODS AND RESULTS

We adoptively transferred B1a cells from wild-type mice or from mice deficient in TLR2, TLR4, TLR9, or myeloid differentiation primary response 88 (MyD88) into ApoE-/- mice depleted of peritoneal B1a cells by splenectomy and fed a high-fat diet for 8 weeks. Elevations in plasma total, anti-oxLDL (oxidized low-density lipoprotein), anti-leukocyte, anti-CD3, anti-CD8, and anti-CD4 IgMs in atherosclerotic mice required B1a cells expressing TLR4 and MyD88, indicating a critical role for TLR4-MyD88 signaling for IgM secretion. Suppression of atherosclerosis was also critically dependent on B1a cells expressing TLR4-MyD88. Atherosclerosis suppression was associated not only with reductions in lesion apoptotic cells, necrotic cores, and oxLDL, but also with reduced lesion CD4+ and CD8+ T cells. Transforming growth factor beta 1 (TGF-β1) expression, including macrophages expressing TGF-β1, was increased, consistent with increased IgM-mediated phagocytosis of apoptotic cells by macrophages. Reductions in lesion inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin (IL) 1β, and IL-18 were consistent with augmented TGF-β1 expression.

CONCLUSIONS

TLR4-MyD88 expression on B1a cells is critical for their IgM-dependent atheroprotection that not only reduced lesion apoptotic cells and necrotic cores, but also decreased CD4 and CD8 T-cell infiltrates and augmented TGF-β1 expression accompanied by reduced lesion inflammatory cytokines TNF-α, IL-1β, and IL-18.

Novel B-cell subsets in atherosclerosis

PURPOSE OF REVIEW

The number of deaths associated with cardiovascular disease remains high, despite great advances in treating the associated high levels of cholesterol. The main underlying pathology of cardiovascular disease is atherosclerosis, which is recognized as a chronic autoimmune-like inflammatory disease. Hence, there is a pressing need to shed light on the immune pathways associated with atherosclerosis. B cells have long been thought to have a general protective effect in atherosclerosis. However, findings in the last decade have challenged this paradigm, showing that it is crucial to differentiate between the various B-cell subsets when assessing their role/effect on atherosclerosis.

RECENT FINDINGS

It has become increasingly recognized lately that B cells can have significant effects on the immune system independent of antibody production. The understanding that B cells form a major source of cytokines and can directly influence T-cell responses via surface markers, have led to the identification of novel B-cell subsets. These subsets are important modulators of autoimmune disorders but have not yet been fully investigated in atherosclerosis.

SUMMARY

Here we review the current known roles of B-cell subsets and the putative effects of recently identified B cells on atherosclerosis.

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.

Artery Tertiary Lymphoid Organs Control Multilayered Territorialized Atherosclerosis B-Cell Responses in Aged ApoE-/- Mice

Supplemental Digital Content is available in the text.

Objective—

Explore aorta B-cell immunity in aged apolipoprotein E-deficient (ApoE^−/−) mice.

Approach and Results—

Transcript maps, fluorescence-activated cell sorting, immunofluorescence analyses, cell transfers, and Ig-ELISPOT (enzyme-linked immunospot) assays showed multilayered atherosclerosis B-cell responses in artery tertiary lymphoid organs (ATLOs). Aging-associated aorta B-cell–related transcriptomes were identified, and transcript atlases revealed highly territorialized B-cell responses in ATLOs versus atherosclerotic lesions: ATLOs showed upregulation of bona fide B-cell genes, including Cd19, Ms4a1 (Cd20), Cd79a/b, and Ighm although intima plaques preferentially expressed molecules involved in non–B effector responses toward B-cell–derived mediators, that is, Fcgr3 (Cd16), Fcer1g (Cd23), and the C1q family. ATLOs promoted B-cell recruitment. ATLO B-2 B cells included naive, transitional, follicular, germinal center, switched IgG1⁺, IgA⁺, and IgE⁺ memory cells, plasmablasts, and long-lived plasma cells. ATLOs recruited large numbers of B-1 cells whose subtypes were skewed toward interleukin-10⁺ B-1b cells versus interleukin-10⁻ B-1a cells. ATLO B-1 cells and plasma cells constitutively produced IgM and IgG and a fraction of plasma cells expressed interleukin-10. Moreover, ApoE^−/− mice showed increased germinal center B cells in renal lymph nodes, IgM-producing plasma cells in the bone marrow, and higher IgM and anti–MDA-LDL (malondialdehyde-modified low-density lipoprotein) IgG serum titers.

Conclusions—

ATLOs orchestrate dichotomic, territorialized, and multilayered B-cell responses in the diseased aorta; germinal center reactions indicate generation of autoimmune B cells within the diseased arterial wall during aging.