Background-T cells play an important role during the immune response that accompanies atherosclerosis. To date, the role for interleukin (IL)-17A in atherogenesis is not well defined. Here, we tested the hypothesis that atherosclerosisprone conditions induce the differentiation of IL-17A-producing T cells, which in turn promote atherosclerosis. Methods and Results-IL-17A was found to be elevated in the plasma and tissues of apolipoprotein E-deficient (Apoe A therosclerosis is the leading cause of cardiovascular disease worldwide. Defined as chronic inflammation of the artery wall, its progression from fatty streaks to more complex lesions and plaque rupture involves a complicated interplay between many different cell types and cytokine networks. Both innate and adaptive immune responses have been shown to regulate local and systemic inflammation during atherogenesis. 1,2 T cells are found within the adventitia of normal/noninflamed vessels as a result of a constitutive T-cell homing into the aorta. 3 Atherosclerosis-prone conditions accelerate T-cell recruitment into the aorta of apolipoprotein E-deficient (Apoe Ϫ/Ϫ ) mice in both the early and advanced stages of atherosclerosis. 3 The majority of aortic T cells are T-cell receptor ␣␤ ϩ CD4 ϩ cells, with few CD8 ϩ and ␥␦ ϩ T cells present. 1,4 Of the CD4 ϩ T cells, T helper 1 (Th1) cells predominate over T helper 2 (Th2) cells during early lesion formation and respond with an elevated production of interferon (IFN)-␥ and interleukin (IL)-6. In the later stages of the disease, a switch to a Th2 response and IL-4 production is evident in the atherosclerotic lesions of Apoe Ϫ/Ϫ mice. 5 Clinical Perspective on p 1755IL-17A is a member of the IL-17 family, which includes IL-17A, IL-17B, IL-17C, IL-17D, IL-17E, and IL-17F. 6 Many lymphocyte subsets secrete IL-17A in response to cytokine or monoclonal antibody stimulation, including CD4 ϩ ␣␤ ϩ (Th17 cells) CD8 ϩ , CD4 Ϫ CD8 Ϫ ␣␤ low , natural killer T cells, and ␥␦ ϩ T cells. 7 The expression of IL-17A is low under normal/noninflamed conditions, in which ␥␦ ϩ T cells are the largest IL-17A-producing T-cell subset. 6 In several murine models of autoimmune diseases, including multiple sclerosis, inflammatory bowel disease, and arthritis, serum IL-17A levels are elevated, and the T helper 17 (Th17) cell population is expanded and plays a highly pathogenic role. 8 Conversely, IL-17A is a protective cytokine in host responses against extracellular pathogens through the induction of proinflammatory cytokines such as IL-6, tumor

Rationale Foxp3+ T regulatory cells (Tregs) are key players in maintaining immune homeostasis. Evidence suggests that Tregs respond to environmental cues to permit or suppress inflammation. In atherosclerosis, Th1-driven inflammation affects Treg homeostasis, but the mechanisms governing this phenomenon are unclear. Objective Here, we address whether atherosclerosis impacts Treg plasticity and functionality in Apoe−/− mice, and what effect Treg plasticity might have on the pathology of atherosclerosis. Methods and Results We demonstrate that atherosclerosis promotes Treg plasticity, resulting in the reduction of CXCR3+ Tregs, and the accumulation of an intermediate Th1-like IFNγ+CCR5+ Treg subset (Th1/Tregs) within the aorta. Importantly, Th1/Tregs arise in atherosclerosis from bona fide Tregs, rather than T effector cells. We show that Th1/Tregs recovered from atherosclerotic mice are dysfunctional in suppression assays. Using an adoptive transfer system and plasticity-prone Mir146a−/− Tregs, we demonstrate that elevated IFNγ+ Mir146a−/− Th1/Tregs are unable to adequately reduce atherosclerosis, arterial Th1, or macrophage content within Apoe−/− mice, in comparison to Mir146a+/+ Tregs. Lastly, via single cell RNA-sequencing and RT-PCR we show that Th1/Tregs possess a unique transcriptional phenotype characterized by co-expression of Treg and Th1 lineage genes, and a down-regulation of Treg-related genes, including Ikzf2, Ikzf4, Tigit, Lilrb4, and Il10. Additionally, an ingenuity pathway analysis further implicates IFNγ, IFNα, IL-2, IL-7, CTLA4, T cell receptor, and Csnk2b-related pathways in regulating Treg plasticity. Conclusions Atherosclerosis drives Treg plasticity, resulting in the accumulation of dysfunctional IFNγ+ Th1/Tregs that may permit further arterial inflammation and atherogenesis.

Aims/hypothesis Chronic inflammation in type 2 diabetes is proposed to affect islets as well as insulin target organs. However, the nature of islet inflammation and its effects on islet function in type 2 diabetes remain unclear. Moreover, the immune cell profiles of human islets in healthy and type 2 diabetic conditions are undefined. We aimed to investigate the correlation between proinflammatory cytokine expression, islet leucocyte composition and insulin secretion in type 2 diabetic human islets. Methods Human islets from organ donors with or without type 2 diabetes were studied. First and second phases of glucose-stimulated insulin secretion were determined by perifusion. The expression of inflammatory markers was obtained by quantitative PCR. Immune cells within human islets were analysed by FACS. Results Type 2 diabetic islets, especially those without first-phase insulin secretion, displayed higher CCL2 and TNFa expression than healthy islets. CD45+ leucocytes were elevated in type 2 diabetic islets, to a greater extent in moderately functional type 2 diabetic islets compared with poorly functional ones, and corresponded with elevated ALOX12 but not with CCL2 or TNFa expression. T and B lymphocytes and CD11c+ cells were detectable within both non-diabetic and type 2 diabetic islet leucocytes. Importantly, the proportion of B cells was significantly elevated within type 2 diabetic islets. Conclusions/interpretation Elevated total islet leucocyte content and proinflammatory mediators correlated with islet dysfunction, suggesting that heterogeneous insulitis occurs during the development of islet dysfunction in type 2 diabetes. In addition, the altered B cell content highlights a potential role for the adaptive immune response in islet dysfunction.

Rationale Atherosclerosis is a disease of large and medium sized arteries that is characterized by chronic vascular inflammation. While the role of Th1, Th2 and T-regulatory subsets in atherogenesis is established, the involvement of IL-17A-producing cells remains unclear. Objective To investigate the role of the IL-17A/IL-17RA axis in atherosclerosis. Methods and Results We bred Apolipoprotein-E-deficient (Apoe−/−) mice with IL-17A-deficient and IL-17 receptor A-deficient mice to generate Il17a−/−Apoe−/− and Il17ra−/−Apoe−/− mice. Western diet fed Il17a−/−Apoe−/− and Il17ra−/−Apoe−/− mice had smaller atherosclerotic plaques in the aortic arch and aortic roots, but showed little difference in plaque burden in the thoracoabdominal aorta compared with Apoe−/− controls. Flow cytometric analysis of Il17a−/−Apoe−/− and Il17ra−/−Apoe−/− aortas revealed that deficiency of IL-17A/IL-17RA preferentially reduced aortic arch, but not thoracoabdominal aortic T cell, neutrophil and macrophage content in comparison to Apoe−/− aortic segments. In contrast to ubiquitous IL-17RA expression throughout the aorta, IL-17A was preferentially expressed within the aortic arch of WD fed Apoe−/− mice. Deficiency of IL-17A or IL-17RA reduced aortic arch, but not thoracoabdominal aortic TNFα and CXCL2 expression. Aortic vascular IL-17RA supports monocyte adherence to explanted aortas in ex vivo adhesion assays. Short–term homing experiments revealed that the recruitment of adoptively transferred monocytes and neutrophils to the aortas of Il17ra−/−Apoe−/− mice is impaired compared with Apoe−/− recipients. Conclusions The IL-17A/IL-17RA axis increases aortic arch inflammation during atherogenesis through the induction of aortic chemokines, and the acceleration of neutrophil and monocyte recruitment to this site.

Atherosclerosis continues to be the leading cause of cardiovascular disease. Development of atherosclerosis depends on chronic inflammation in the aorta and multiple immune cells are involved in this process. Importantly, resident macrophages and dendritic cells (DCs) are present within the healthy aorta, but the functions of these cells remain poorly characterized. Local inflammation within the aortic wall promotes the recruitment of monocytes and DC precursors to the aorta and micro-environmental factors direct the differentiation of these emigrated cells into multiple subsets of macrophages and DCs. Recent data suggest that several populations of macrophages and DCs can co-exist within the aorta. Although the functions of M1, M2, Mox, and M4 macrophages are well characterized in vitro, there is a limited set of data on the role of these populations in atherogenesis in vivo. Recent studies on the origin and the potential role of aortic DCs provide novel insights into the biology of aortic DC subsets and prospective mechanisms of the immune response in atherosclerosis. This review integrates the results of experiments analyzing heterogeneity of DCs and macrophage subsets in healthy and diseased vessels and briefly discusses the known and potential functions of these cells in atherogenesis.