Regulatory T Cells and Tolerogenic Dendritic Cells as Critical Immune Modulators in Atherogenesis

Advances in immunotherapy modalities for atherosclerosis

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. Atherosclerosis is the pathological basis of atherosclerotic cardiovascular disease (ASCVD). Atherosclerosis is now understood to be a long-term immune-mediated inflammatory condition brought on by a complicated chain of factors, including endothelial dysfunction, lipid deposits in the artery wall, and monocyte-derived macrophage infiltration, in which both innate immunity and adaptive immunity play an indispensable role. Recent studies have shown that atherosclerosis can be alleviated by inducing a protective immune response through certain auto-antigens or exogenous antigens. Some clinical trials have also demonstrated that atherosclerotic is associated with the presence of immune cells and immune factors in the body. Therefore, immunotherapy is expected to be a new preventive and curative measure for atherosclerosis. In this review, we provide a summary overview of recent progress in the research of immune mechanisms of atherosclerosis and targeted therapeutic pathways.

A bibliometric analysis of T cell and atherosclerosis

Atherosclerosis (AS) is widespread and develops into circulatory system problems. T cells play an essential regulatory role in AS occurrence and development. So far, there is no bibliometric research on T cells and AS. To learn more about T cell and AS development, 4,381 records were retrieved from Web of Science™ Core Collection. Then, these records were scientometrically analyzed using CiteSpace and VOSviewer in terms of spatiotemporal distribution, author distribution, subject categories, topic distribution, references, and keywords. Our analysis provides basic information on research in the field, demonstrates that the field has stabilized over the past decade, and identifies potential partners for interested researchers. Current research hotspots in this field mainly include the inflammatory mechanism, immune mechanism, related diseases, and related cytokines of AS. B cell, mortality, inhibition, and monocyte represent the frontiers of research in this field, undergoing an explosive phase. We hope that this work will provide new ideas for advancing the scientific research and clinical application of T cell and AS.

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.

Immunobiology of Atherosclerosis: A Complex Net of Interactions

Cardiovascular disease is the leading cause of mortality worldwide, and atherosclerosis the principal factor underlying cardiovascular events. Atherosclerosis is a chronic inflammatory disease characterized by endothelial dysfunction, intimal lipid deposition, smooth muscle cell proliferation, cell apoptosis and necrosis, and local and systemic inflammation, involving key contributions to from innate and adaptive immunity. The balance between proatherogenic inflammatory and atheroprotective anti-inflammatory responses is modulated by a complex network of interactions among vascular components and immune cells, including monocytes, macrophages, dendritic cells, and T, B, and foam cells; these interactions modulate the further progression and stability of the atherosclerotic lesion. In this review, we take a global perspective on existing knowledge about the pathogenesis of immune responses in the atherosclerotic microenvironment and the interplay between the major innate and adaptive immune factors in atherosclerosis. Studies such as this are the basis for the development of new therapies against atherosclerosis.

CTLA-4 Protects against Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice

Vascular inflammation via T-cell-mediated immune responses has been shown to be critically involved in the pathogenesis of abdominal aortic aneurysm (AAA). T-cell coinhibitory molecule cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4) is known to act as a potent negative regulator of immune responses. However, the role of this molecule in the development of AAA remains completely unknown. We determined the effects of CTLA-4 overexpression on experimental AAA. We continuously infused CTLA-4 transgenic (CTLA-4-Tg)/apolipoprotein E–deficient (Apoe^−/−) mice or control Apoe^−/− mice fed a high-cholesterol diet with angiotensin II by implanting osmotic mini-pumps and evaluated the development of AAA. Ninety percent of angiotensin II-infused mice developed AAA, with 50% mortality because of aneurysm rupture. Overexpression of CTLA-4 significantly reduced the incidence (66%), mortality (26%), and diameter of AAA. These protective effects were associated with a decreased number of effector CD4⁺ T cells and the downregulated expression of costimulatory molecules CD80 and CD86, ligands for CTLA-4, on CD11c⁺ dendritic cells in lymphoid tissues. CTLA-4-Tg/Apoe^−/− mice had reduced accumulation of macrophages and CD4⁺ T cells, leading to attenuated aortic inflammation, preserved vessel integrity, and decreased susceptibility to AAA and aortic rupture. Our findings suggest T-cell coinhibitory molecule CTLA-4 as a novel therapeutic target for AAA.

Ultraviolet B Exposure Inhibits Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice by Expanding CD4+Foxp3+ Regulatory T Cells

Background

Pathogenic immune responses are known to play an important role in abdominal aortic aneurysm (AAA) development. Ultraviolet B (UVB) irradiation has been demonstrated to have therapeutic potential not only for cutaneous diseases but also for systemic inflammatory diseases in mice by suppressing immunoinflammatory responses. We investigated the effect of UVB irradiation on experimental AAA.

Methods and Results

We used an angiotensin II–induced AAA model in apolipoprotein E–deficient mice fed a high‐cholesterol diet. Mice aged 10 weeks were irradiated with 5 kJ/m²UVB once weekly for 6 weeks (UVB‐irradiated, n=38; nonirradiated, n=42) and were euthanized for evaluation of AAA formation at 16 weeks. Overall, 93% of angiotensin II–infused mice developed AAA, with 60% mortality possibly because of aneurysm rupture. UVB irradiation significantly decreased the incidence (66%) and mortality (29%) of AAA (P=0.004 and P=0.006, respectively). UVB‐irradiated mice had significantly smaller diameter AAA (P=0.008) and fewer inflammatory cells in the aortic aneurysm tissue than nonirradiated mice, along with systemic expansion of CD4⁺Foxp3⁺ regulatory T cells and decreased effector CD4⁺CD44^highCD62L^low T cells in para‐aortic lymph nodes. Genetic depletion of regulatory T cells abrogated these beneficial effects of UVB treatment, demonstrating a critical role of regulatory T cells.

Conclusions

Our data suggest that UVB‐dependent expansion of regulatory T cells has beneficial effects on experimental AAA and may provide a novel strategy for the treatment of AAA.

UVB Exposure Prevents Atherosclerosis by Regulating Immunoinflammatory Responses

OBJECTIVE

UVB irradiation is an established treatment for immunoinflammatory cutaneous disorders and has been shown to suppress cutaneous and systemic inflammatory diseases through modulation of the adaptive immune response. However, it remains unknown whether UVB irradiation prevents an immunoinflammatory disease of arteries such as atherosclerosis.

APPROACH AND RESULTS

Here, we show that UVB exposure inhibits the development and progression of atherosclerosis in atherosclerosis-prone mice by expanding and enhancing the functional capacity of CD4⁺ forkhead box P3⁺ regulatory T cells and regulating proatherogenic T-cell responses. Experimental studies in Langerhans cell-depleted mice revealed that epidermal Langerhans cells play a critical role in UVB-dependent induction of CD4⁺ forkhead box P3⁺ regulatory T cells, suppression of proatherogenic T-cell responses, and prevention of atherosclerotic plaque development.

CONCLUSIONS

Our findings suggest the skin immune system as a novel therapeutic target for atherosclerosis and provide a novel strategy for the treatment and prevention of atherosclerosis.

Overexpression of Cytotoxic T-Lymphocyte-Associated Antigen-4 Prevents Atherosclerosis in Mice

OBJECTIVE

Although T-cell-mediated chronic inflammation contributes to atherosclerosis development, the role of a negative regulatory molecule cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) in atherosclerosis is poorly understood. We investigated the effects of CTLA-4 overexpression on atherosclerosis in apolipoprotein E-deficient (Apoe(-/-)) mice.

APPROACH AND RESULTS

We generated CTLA-4 transgenic (CTLA-4-Tg)/Apoe(-/-) mice that display constitutive cell surface and intracellular expression of CTLA-4 in T cells and assessed atherosclerosis at age 16 weeks. CTLA-4 overexpression significantly reduced atherosclerotic lesion formation and intraplaque accumulation of macrophage and CD4(+) T cells in the aortic root compared with controls. CTLA-4-Tg/Apoe(-/-) mice showed decreased numbers of effector CD4(+) T cells and decreased expression of costimulatory molecules CD80 and CD86, ligands for CTLA-4, and a costimulatory molecule CD28, on CD11c(+) dendritic cells compared with controls. Consistent with in vivo findings, in vitro experiments revealed that CD4(+) T cells from CTLA-4-Tg/Apoe(-/-) mice showed decreased proliferative capacity and proinflammatory cytokine production, downregulated CD80 expression on CD11c(+) dendritic cells, and suppressed the proliferation of other T cells by limiting the costimulatory pathway. Moreover, CD11c(+) dendritic cells from CTLA-4-Tg/Apoe(-/-) mice showed reduced proliferative activity of T cells in vitro, suggesting the suppression of dendritic cell maturation in vivo.

CONCLUSIONS

CTLA-4 regulates atherosclerosis by suppressing proatherogenic immune responses and could be an attractive therapeutic target for atherosclerosis.