Thymic self-reactivity selects natural interleukin 17-producing T cells that can regulate peripheral inflammation

Immunological perspectives on atherosclerotic plaque formation and progression

Atherosclerosis serves as the primary catalyst for numerous cardiovascular diseases. Growing evidence suggests that the immune response is involved in every stage of atherosclerotic plaque evolution. Rapid, but not specific, innate immune arms, including neutrophils, monocytes/macrophages, dendritic cells (DCs) and other innate immune cells, as well as pattern-recognition receptors and various inflammatory mediators, contribute to atherogenesis. The specific adaptive immune response, governed by T cells and B cells, antibodies, and immunomodulatory cytokines potently regulates disease activity and progression. In the inflammatory microenvironment, the heterogeneity of leukocyte subpopulations plays a very important regulatory role in plaque evolution. With advances in experimental techniques, the fine mechanisms of immune system involvement in atherosclerotic plaque evolution are becoming known. In this review, we examine the critical immune responses involved in atherosclerotic plaque evolution, in particular, looking at atherosclerosis from the perspective of evolutionary immunobiology. A comprehensive understanding of the interplay between plaque evolution and plaque immunity provides clues for strategically combating atherosclerosis.

S1PR1 mediates Th17 cell migration from the thymus to the skin in health and disease

Th17 cells play crucial roles in host defense and the pathogenesis of autoimmune diseases in the skin. While their differentiation mechanisms have been extensively studied, the origin of skin Th17 cells remains unclear. In this study, we analyzed single-cell RNA-sequencing data and identify the presence of Th17 cells in the human thymus. Thymic Th17 cells were characterized by high expression levels of Sphingosine-1-Phosphate Receptor 1 (S1PR1), a receptor crucial for T cell egress from lymphoid tissues. In mice, Th17 cell-specific knockout of S1pr1 resulted in the accumulation of Th17 cells in the thymus and a corresponding decrease in their numbers in the skin. Th17 cells that accumulated in the thymus exhibited a lower IL-17A production capacity compared to those in the skin, indicating that the local environment in the skin is important for maintaining the Th17 cell phenotype. Additionally, using a murine psoriasis model, we demonstrated that Th17 cell-specific knockout of S1pr1 reduced their migration to the inflamed skin, thereby ameliorating disease progression. Collectively, our data suggest that S1PR1 mediates Th17 cell migration from the thymus to the skin, thereby modulating their functional engagement in both homeostatic and inflammatory conditions.

The role of γδT lymphocytes in atherosclerosis

Atherosclerosis poses a significant threat to human health, impacting overall well-being and imposing substantial financial burdens. Current treatment strategies mainly focus on managing low-density lipids (LDL) and optimizing liver functions. However, it's crucial to recognize that Atherosclerosis involves more than just lipid accumulation; it entails a complex interplay of immune responses. Research highlights the pivotal role of lipid-laden macrophages in the formation of atherosclerotic plaques. These macrophages attract lymphocytes like CD4 and CD8 to the inflamed site, potentially intensifying the inflammatory response. γδ T lymphocytes, with their diverse functions in innate and adaptive immune responses, pathogen defense, antigen presentation, and inflammation regulation, have been implicated in the early stages of Atherosclerosis. However, our understanding of the roles of γδ T cells in Atherosclerosis remains limited. This mini-review aims to shed light on the characteristics and functions of γδ T cells in Atherosclerosis. By gaining insights into the roles of γδ T cells, we may uncover a promising strategy to mitigate plaque buildup and dampen the inflammatory response, thereby opening new avenues for effectively managing this condition.

The role of immune cells in different stages of atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of immune cells in the intima of arteries. Experimental and clinical evidence shows that both innate and adaptive immunity orchestrate the progression of atherosclerosis. The heterogeneous nature of immune cells within atherosclerosis lesions is important. Studies utilizing high-dimensional mass spectrometry and single-cell RNA sequencing of leukocytes from atherosclerotic lesions show the diversity and adaptability of these immune cell subtypes. Their migration, compositional changes, phenotypic alterations, and adaptive responses are key features throughout atherosclerosis progression. Understanding how these immune cells and their subtypes affect atherogenesis would help to develop novel therapeutic approaches that control atherosclerosis progression. Precise targeting of specific immune system components involved in atherosclerosis, rather than broad suppression of the immune system with anti-inflammatory agents, can more accurately regulate the progress of atherosclerosis with fewer side effects. In this review, we cover the most recent advances in the field of atherosclerosis to understand the role of various immune cells on its development. We focus on the complex network of immune cells and the interaction between the innate immune system and adaptive immune system.

D-galacto-D-mannan-mediated Dectin-2 activation orchestrates potent cellular and humoral immunity as a viral vaccine adjuvant

Introduction

Conventional foot-and-mouth disease (FMD) vaccines have been developed to enhance their effectiveness; however, several drawbacks remain, such as slow induction of antibody titers, short-lived immune response, and local side effects at the vaccination site. Therefore, we created a novel FMD vaccine that simultaneously induces cellular and humoral immune responses using the Dectin-2 agonist, D-galacto-D-mannan, as an adjuvant.

Methods

We evaluated the innate and adaptive (cellular and humoral) immune responses elicited by the novel FMD vaccine and elucidated the signaling pathway involved both in vitro and in vivo using mice and pigs, as well as immune cells derived from these animals.

Results

D-galacto-D-mannan elicited early, mid-, and long-term immunity via simultaneous induction of cellular and humoral immune responses by promoting the expression of immunoregulatory molecules. D-galacto-D-mannan also enhanced the immune response and coordinated vaccine-mediated immune response by suppressing genes associated with excessive inflammatory responses, such as nuclear factor kappa B, via Sirtuin 1 expression.

Conclusion

Our findings elucidated the immunological mechanisms induced by D-galacto-D-mannan, suggesting a background for the robust cellular and humoral immune responses induced by FMD vaccines containing D-galacto-D-mannan. Our study will help to facilitate the improvement of conventional FMD vaccines and the design of next-generation FMD vaccines.

Targeting interleukin-17 in radiation-induced toxicity and cancer progression

Recent strategies to combine chemoradiation with immunotherapy to treat locally advanced lung cancer have improved five-year survival outcomes. However, collateral toxicity to healthy lungs, esophagus, cardiac, and vascular tissue continues to limit the effectiveness of curative-intent thoracic radiation (tRT). It is necessary to gain a deeper comprehension of the fundamental mechanisms underlying inflammation-mediated radiation-induced damage to normal cells. Several cells have been linked in published studies to the release of cytokines and chemokines after radiation therapy. Several inflammatory mediators, such as IL-1, IL-6, TNF-α, and TGF-β, also cause the production of Interleukin-17 (IL-17), a cytokine that is essential for maintaining immunological homeostasis and plays a role in the toxicity caused by radiation therapy. However, currently, the role of IL-17 in RT-induced toxicity in conjunction with cancer progression remains poorly understood. This review provides an overview of the most recent data from the literature implicating IL-17 in radiation-mediated tissue injuries and the efficacy of tRT in lung cancer, as well as its potential as a therapeutic target for interventions to reduce the side effects of tRT with curative intent and to boost an anti-tumor immune response to improve treatment outcomes. IL-17 may also act as a biomarker for predicting the effectiveness of a given treatment as well as the toxicity caused by tRT.

Caecum OX40+CD4 T-cell subset associates with mucosal damage and key markers of disease in treated HIV-infection

BACKGROUND

Blood OX40-expressing CD4 T-cells from antiretroviral (ART)-treated people living with HIV (PWH) were found to be enriched for clonally-expanded HIV sequences, hence contributing to the HIV reservoir. OX40-OX40L is also a checkpoint regulator of inflammation in multiple diseases. We explored gut mucosal OX40+CD4+ T-cells and their potential significance in HIV disease.

METHODS

Biopsies of caecum and terminal-ileum of ART-treated PWH (n = 32) were obtained and mucosal damage and HIV reservoir were assessed. Mucosal OX40+ and Ki67+ CD4 T-cell subsets, as well as several tissue T-cell subsets modulating mucosal integrity and homeostasis (Th17, Th22, Treg, Tc17, Tc22, IL17+TCRγδ, IL22+TCRγδ) were quantified. Inflammatory-related markers, T-cell activation and thymic output were also determined in blood samples. Correlations were explored using Spearman rank test and corrected for multiple comparisons by Benjamini-Hochberg.

RESULTS

Compared to healthy controls, a high frequency of mucosal, mainly caecum, CD4 T-cells were OX40+ in PWH. Such frequency strongly correlated with nadir CD4 (r = -0.836; p < 0.0001), CD4/CD8 ratio (r = -0.630; p = 0.002), caecum mucosal damage (r = 0.606; p = 0.008), caecum Th22 (r = -0.635; p = 0.002), caecum Th17 (r = 0.474; p = 0.03) and thymic output (r = -0.686; p < 0.001). It also correlated with Neutrophil-to-Lymphocyte Ratio and blood CD4 T-cell activation and tended to with mucosal HIV reservoir.

CONCLUSION

High frequencies of caecum OX40+CD4 T-cells are found in people with HIV (PWH) and successful viral control. Interestingly, this cellular subset reflects key markers of disease and peripheral T-cell activation, as well as HIV-driven mucosal damage. OX40+CD4 T-cells deserve further investigation since they could expand because of T-cell homeostatic proliferation and relate to the Th22/Th17 gut mucosal ratio.

The role of IL-23/IL-17 axis in ischemic stroke from the perspective of gut-brain axis

Bidirectional communication between central nervous system (CNS) and intestine is mediated by nerve, endocrine, immune and other pathways in gut-brain axis. Many diseases of CNS disturb the homeostasis of intestine and gut microbiota. Similarly, the dysbiosis of intestinal and gut microbiota also promotes the progression and deterioration of CNS diseases. IL-23/IL-17 axis is an important inflammatory axis which is widely involved in CNS diseases such as experimental autoimmune encephalomyelitis (EAE), multiple sclerosis (MS), and ischemic stroke (IS). Attributing to the long anatomically distances between ischemic brain and gut, previous studies on IL-23/IL-17 axis in IS are rarely focused on intestinal tissues. However, recent studies have found that IL-17⁺T cells in CNS mainly originate from intestine. The activation and migration of IL-17⁺T cells to CNS is likely to be affected by the altered intestinal homeostasis. These studies promoted the attention of IL-23/IL-17 axis and gut-brain axis. IS is difficult to treat because of its extremely complex pathological mechanism. This review mainly discusses the relationship between IL-23/IL-17 axis and IS from the perspective of gut-brain axis. By analyzing the immune pathways in gut-brain axis, the activation of IL-23/IL-17 axis, the roles of IL-23/IL-17 axis in gut, CNS and other systems after stoke, this review is expected to provide new enlightenments for the treatment strategies of IS.

The star target in SLE: IL-17

PURPOSE

The purpose of this review is to discuss the significance of IL-17 in SLE and the potential of IL-17-targeted therapy.

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disease that can affect many organs and tissues throughout the body. It is characterized by overactive B and T cells and loss of immune tolerance to autoantigens. Interleukin-17 (IL-17) is a cytokine that promotes inflammation and has been implicated in the pathogenesis of several autoimmune diseases as well as inflammatory diseases. In in vitro cellular experiments in lupus susceptible mice or SLE patients, there is substantial evidence that IL-17 is a highly promising therapeutic target.

METHODS

We searched papers from PubMed database using the search terms, such as interleukin-17, systemic lupus erythematosus, treatment targets, T cells, lupus nephritis, and other relevant terms.

RESULTS

We discuss in this paper the molecular mechanisms of IL-17 expression, Th17 cell proliferation, and the relationship between IL-17 and Th17. The significance of IL-17 in SLE and the potential of IL-17-targeted therapy are further discussed in detail.

CONCLUSION

IL-17 has a very high potential for the development as a star target in SLE.

IL-17 and IL-17-producing cells in protection versus pathology

IL-17 cytokine family members have diverse biological functions, promoting protective immunity against many pathogens but also driving inflammatory pathology during infection and autoimmunity. IL-17A and IL-17F are produced by CD4⁺ and CD8⁺ T cells, γδ T cells, and various innate immune cell populations in response to IL-1β and IL-23, and they mediate protective immunity against fungi and bacteria by promoting neutrophil recruitment, antimicrobial peptide production and enhanced barrier function. IL-17-driven inflammation is normally controlled by regulatory T cells and the anti-inflammatory cytokines IL-10, TGFβ and IL-35. However, if dysregulated, IL-17 responses can promote immunopathology in the context of infection or autoimmunity. Moreover, IL-17 has been implicated in the pathogenesis of many other disorders with an inflammatory basis, including cardiovascular and neurological diseases. Consequently, the IL-17 pathway is now a key drug target in many autoimmune and chronic inflammatory disorders; therapeutic monoclonal antibodies targeting IL-17A, both IL-17A and IL-17F, the IL-17 receptor, or IL-23 are highly effective in some of these diseases. However, new approaches are needed to specifically regulate IL-17-mediated immunopathology in chronic inflammation and autoimmunity without compromising protective immunity to infection.

A gut-oral microbiome-driven axis controls oropharyngeal candidiasis through retinoic acid

A side effect of antibiotics is outgrowth of the opportunistic fungus Candida albicans in the oropharynx (oropharyngeal candidiasis, OPC). IL-17 signaling is vital for immunity to OPC, but how the microbiome impacts antifungal immunity is not well understood. Mice in standard specific pathogen-free (SPF) conditions are resistant to OPC, whereas we show that germ-free (GF) or antibiotic-treated mice are susceptible. Oral type 17 cells and IL-17-dependent responses were impaired in antibiotic-treated and GF mice. Susceptibility could be rescued in GF mice by mono-colonization with segmented filamentous bacterium (SFB), an intestine-specific constituent of the microbiota. SFB protection was accompanied by restoration of oral IL-17+CD4+ T cells and gene signatures characteristic of IL-17 signaling. Additionally, RNA-Seq revealed induction of genes in the retinoic acid (RA) and RA receptor-α (RARα) pathway. Administration of RA rescued immunity to OPC in microbiome-depleted or GF mice, while RAR inhibition caused susceptibility in immunocompetent animals. Surprisingly, immunity to OPC was independent of serum amyloids. Moreover, RAR inhibition did not alter oral type 17 cytokine levels. Thus, mono-colonization with a component of the intestinal microflora confers protection against OPC by type 17 and RA/RARα, which act in parallel to promote antifungal immunity. In principle, manipulation of the microbiome could be harnessed to maintain antifungal immunity.

Clinical predictive value of naïve and memory T cells in advanced NSCLC

Currently, there is no sensitive prognostic biomarker to screen out benefit patients from the non-benefit population in advanced non-small cell lung cancer patients (aNSCLCs). The 435 aNSCLCs and 278 normal controls (NCs) were recruited. The percentages and absolute counts (AC) of circulating naïve and memory T lymphocytes of CD4+ and CD8+ T cells (Tn/Tm) were measured by flow cytometry. The percentage of CD4+ naïve T (Tn), CD8+ Tn, CD8+ T memory stem cell (Tscm), and CD8+ terminal effector T cell decreased obviously. Still, all AC of Tn/Tm of aNSCLCs was significantly lower compared to NCs. Higher AC and percentage of CD4+ Tn, CD8+ Tn, and CD4+ Tscm showed markedly longer median PFS in aNSCLCs. Statistics demonstrated the AC of CD4+ Tn (≥ 3.7 cells/μL) was an independent protective factor for PFS. The analysis of the prognosis of immunotherapy showed the higher AC and percentage of CD4+ Tn and CD4+ Tscm and higher AC of CD8+ Tscm had significantly longer median PFS and the AC of CD4+ Tn (≥ 5.5 cells/μL) was an independent protective factor for PFS. Moreover, higher AC and percentages of Tn/Tm suggested higher disease control rate and lower progressive disease rate. The AC of Tn/Tm showed more regular patterns of impairment and was more relative with the disease progression than percentages in aNSCLCs. AC had a better predictive value than percentages in Tn/Tm for PFS. Notably, the AC of CD4+ Tn was a potential prognostic biomarker for the PFS and efficacy of immunotherapy.

Interleukin-17 Links Inflammatory Cross-Talks Between Comorbid Psoriasis and Atherosclerosis

Psoriasis is a chronic, systemic, immune-mediated inflammatory disorder that is associated with a significantly increased risk of cardiovascular disease (CVD). Studies have shown that psoriasis often coexists with atherosclerosis, a chronic inflammatory disease of large and medium-sized arteries, which is a major cause of CVD. Although the molecular mechanisms underlying this comorbidity are not fully understood, clinical studies have shown that when interleukin (IL)-17A inhibitors effectively improve psoriatic lesions, atherosclerotic symptoms are also ameliorated in patients with both psoriasis and atherosclerosis. Also, IL-17A levels are highly expressed in the psoriatic lesions and atherosclerotic plaques. These clinical observations implicit that IL-17A could be a crucial link for psoriasis and atherosclerosis and IL-17A-induced inflammatory responses are the major contribution to the pathogenesis of comorbid psoriasis and atherosclerosis. In this review, the current literature related to epidemiology, genetic predisposition, and inflammatory mechanisms of comorbidity of psoriasis and atherosclerosis is summarized. We focus on the immunopathological effects of IL-17A in both diseases. The goal of this review is to provide the theoretical base for future preventing or treating psoriasis patients with atherosclerosis comorbidity. The current evidence support the notion that treatments targeting IL-17 seem to be hold some promise to reduce cardiovascular risk in patients with psoriasis.

Functionally specialized human CD4+ T-cell subsets express physicochemically distinct TCRs

The organizational integrity of the adaptive immune system is determined by functionally discrete subsets of CD4⁺ T cells, but it has remained unclear to what extent lineage choice is influenced by clonotypically expressed T-cell receptors (TCRs). To address this issue, we used a high-throughput approach to profile the αβ TCR repertoires of human naive and effector/memory CD4⁺ T-cell subsets, irrespective of antigen specificity. Highly conserved physicochemical and recombinatorial features were encoded on a subset-specific basis in the effector/memory compartment. Clonal tracking further identified forbidden and permitted transition pathways, mapping effector/memory subsets related by interconversion or ontogeny. Public sequences were largely confined to particular effector/memory subsets, including regulatory T cells (Tregs), which also displayed hardwired repertoire features in the naive compartment. Accordingly, these cumulative repertoire portraits establish a link between clonotype fate decisions in the complex world of CD4⁺ T cells and the intrinsic properties of somatically rearranged TCRs.

Th17/Treg Imbalance and Atherosclerosis

Atherosclerosis is nowadays recognized as a chronic inflammatory disease of large arteries. In recent years, cellular and molecular biology studies on atherosclerosis confirmed that the occurrence and development are related to inflammation and autoimmunity. A variety of immune cells, cytokines, and transcription factors are involved in this process. Current studies found that T helper cell 17, regulatory T cells, and their cytokines play an important role in the development of atherosclerosis and vulnerable plaque rupture. Here, we provide a review of the up-to-date applications of T helper cell 17, regulatory T cells, cytokines, and their balance in the prognosis and therapy of atherosclerosis.

The Role of Gamma-Delta T Cells in Diseases of the Central Nervous System

Gamma-delta (γδ) T cells are a subset of T cells that promote the inflammatory responses of lymphoid and myeloid lineages, and are especially vital to the initial inflammatory and immune responses. Given the capability to connect crux inflammations of adaptive and innate immunity, γδ T cells are responsive to multiple molecular cues and can acquire the capacity to induce various cytokines, such as GM-CSF, IL-4, IL-17, IL-21, IL-22, and IFN-γ. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, particularly in the context of the central nervous system (CNS) diseases. CNS disease, usually leading to irreversible cognitive and physical disability, is becoming a worldwide public health problem. Here, we offer a review of the neuro-inflammatory and immune functions of γδ T cells, intending to understand their roles in CNS diseases, which may be crucial for the development of novel clinical applications.

Recognition of Candida albicans and Role of Innate Type 17 Immunity in Oral Candidiasis

Candida albicans is an opportunistic pathogenic fungus considered to be a common member of the human microflora. Similar to some other opportunistic microbes, C. albicans can invade and benefit from its host when the immune status of that host is weakened. Most often this happens to immunocompromised individuals, leading to the infection of oral and vaginal mucosae or the systemic spread of the pathogen throughout the entire body. Oropharyngeal candidiasis (OPC) occurs in up to 90 percent of patients with acquired immunodeficiency syndrome (AIDS), making it the most frequent opportunistic infection for this group. Upon first signs of fungal invasion, a range of host signaling activates in order to eliminate the threat. Epithelial and myeloid type cells detect C. albicans mainly through receptor tyrosine kinases and pattern-recognition receptors. This review provides an overview of downstream signaling resulting in an adequate immune response through the activation of various transcription factors. The study discusses recent advances in research of the interleukin-17 (IL-17) producing innate cells, including natural T helper 17 (nTh17) cells, γδ T cells, invariant natural killer T (iNKT) cells and type 3 innate lymphoid cells (ILC3) that are involved in response to oral C. albicans infections.

Could cross-reactivity rescue Foxp3+ regulatory T cell precursors from thymic deletion?

Thymocytes that bind with high affinity to peptides displayed by MHC class II (pMHC-II) are deleted while low-affinity binders differentiate into naive CD4+ T cells. However, Foxp3+ regulatory T cells (Tregs) seem to defy this binary choice as their precursors require high-affinity interaction with pMHC-II for maturation in the thymus. Here, we rely on the antigen-specific interpretive framework, SPIRAL (Specific ImmunoRegulatory Algorithm), to propose that Tregs escape thymic deletion by forming dyads with IL-2-producing T cells via antigen cross-reactivity. This interpretation reconciles contradictions related to Treg ontogeny in the thymus and their role in modulating antigen-specific immune responses.

Does hereditary angioedema make COVID-19 worse?

The coronavirus disease 2019 (COVID-19) pandemic has spread rapidly worldwide. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, enters host cells via angiotensin-converting enzyme 2 (ACE2) and depletes ACE2, which is necessary for bradykinin metabolism. The depletion of ACE2 results in the accumulation of des-Arg (9)-bradykinin and possible bradykinin, both of which bind to bradykinin receptors and induce vasodilation, lung injury, and inflammation. It is well known that an overactivated contact system and excessive production of bradykinin comprise the key mechanisms that drive the pathogenesis of hereditary angioedema (HAE). It is reasonable to speculate that COVID-19 may increase disease activity in patients with HAE and vice versa. In this review, we explore the potential interactions between COVID-19 and HAE in terms of the contact system, the complement system, cytokine release, increased T helper 17 cells, and hematologic abnormalities. We conclude with the hypothesis that comorbidity with HAE might favor COVID-19 progression and may worsen its outcomes, while COVID-19 might in turn aggravate pre-existing HAE and prompt the onset of HAE in asymptomatic carriers of HAE-related mutations. Based on the pathophysiologic links, we suggest that long-term prophylaxis should be considered in patients with HAE at risk of SARS-CoV-2 infection, especially the prophylactic use of C1 inhibitor and lanadelumab and that HAE patients must have medications for acute attacks of angioedema. Additionally, therapeutic strategies employed in HAE should be considered for the treatment of COVID-19, and clinical trials should be performed.

Control of Persistent Salmonella Infection Relies on Constant Thymic Output Despite Increased Peripheral Antigen-Specific T Cell Immunity

Recent thymic emigrants are the youngest subset of peripheral T cells and their involvement in combating persistent bacterial infections has not been explored. Here, we hypothesized that CD4⁺ recent thymic emigrants are essential immune mediators during persistent Salmonella infection. To test this, we thymectomized adult mice either prior to, or during, persistent Salmonella infection. We found that thymic output is crucial in the formation of protective immune responses during the early formation of a Salmonella infection but is dispensable once persistent Salmonella infection is established. Further, we show that thymectomized mice demonstrate increased infection-associated mortality and bacterial burdens. Unexpectedly, numbers of Salmonella-specific CD4⁺ T cells were significantly increased in thymectomized mice compared to sham control mice. Lastly, we found that T cells from thymectomized mice may be impaired in producing the effector cytokine IL-17 at early time points of infection, compared to thymically intact mice. Together, these results imply a unique role for thymic output in the formation of immune responses against a persistent, enteric pathogen.

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.

Oral epithelial IL-22/STAT3 signaling licenses IL-17-mediated immunity to oral mucosal candidiasis

Oropharyngeal candidiasis (OPC; thrush) is an opportunistic infection caused by the commensal fungus Candida albicans Interleukin-17 (IL-17) and IL-22 are cytokines produced by type 17 lymphocytes. Both cytokines mediate antifungal immunity yet activate quite distinct downstream signaling pathways. While much is now understood about how IL-17 promotes immunity in OPC, the activities of IL-22 are far less well delineated. We show that, despite having similar requirements for induction from type 17 cells, IL-22 and IL-17 function nonredundantly during OPC. We find that the IL-22 and IL-17 receptors are required in anatomically distinct locations within the oral mucosa; loss of IL-22RA1 or signal transducer and activator of transcription 3 (STAT3) in the oral basal epithelial layer (BEL) causes susceptibility to OPC, whereas IL-17RA is needed in the suprabasal epithelial layer (SEL). Transcriptional profiling of the tongue linked IL-22/STAT3 not only to oral epithelial cell proliferation and survival but also, unexpectedly, to driving an IL-17-specific gene signature. We show that IL-22 mediates regenerative signals on the BEL that replenish the IL-17RA-expressing SEL, thereby restoring the ability of the oral epithelium to respond to IL-17 and thus to mediate antifungal events. Consequently, IL-22 signaling in BEL "licenses" IL-17 signaling in the oral mucosa, revealing spatially distinct yet cooperative activities of IL-22 and IL-17 in oral candidiasis.

Evidence for a pathogenic role of extrafollicular, IL-10-producing CCR6+B helper T cells in systemic lupus erythematosus

Interleukin 10 (IL-10) is an antiinflammatory cytokine, but also promotes B cell responses and plays a pathogenic role in systemic lupus erythematosus (SLE). CD4⁺CCR6⁺IL-7R⁺T cells from human tonsils produced IL-10 following stimulation by naïve B cells, which promoted B cell immunoglobulin G (IgG) production. These tonsillar CCR6⁺B helper T cells were phenotypically distinct from follicular helper T (T_FH) cells and lacked BCL6 expression. In peripheral blood, a CCR6⁺T cell population with similar characteristics was identified, which lacked Th17- and T_FH-associated gene signatures and differentiation-associated surface markers. CD4⁺CCR6⁺T cells expressing IL-10, but not IL-17, were also detectable in the spleens of cytokine reporter mice. They provided help for IgG production in vivo, and expanded systemically in pristane-induced lupus-like disease. In SLE patients, CD4⁺CCR6⁺IL-7R⁺T cells were associated with the presence of pathogenic anti-dsDNA (double-stranded DNA) antibodies, and provided spontaneous help for autoantibody production ex vivo. Strikingly, IL-10-producing CCR6⁺T cells were highly abundant in lymph nodes of SLE patients, and colocalized with B cells at the margins of follicles. In conclusion, we identified a previously uncharacterized population of extrafollicular B helper T cells, which produced IL-10 and could play a prominent pathogenic role in SLE.

Interleukin-17: Potential Target for Chronic Wounds

Chronic wounds exhibit persistent inflammation with markedly delayed healing. The significant burden of chronic wounds, which are often resistant to standard therapy, prompts further research on novel therapies. Since the interleukin-17 family has been implicated as a group of proinflammatory cytokines in immune-mediated diseases in the gut and connective tissue, as well as inflammatory skin conditions, we consider here if it may contribute to the pathogenesis of chronic wounds. In this review, we discuss the interleukin-17 family's signaling pathways and role in tissue repair. A PubMed review of the English literature on interleukin-17, wound healing, chronic wounds, and inflammatory skin conditions was conducted. Interleukin-17 family signaling is reviewed in the context of tissue repair, and preclinical and clinical studies examining its role in the skin and other organ systems are critically reviewed. The published work supports a pathologic role for interleukin-17 family members in chronic wounds, though this needs to be more conclusively proven. Clinical studies using monoclonal interleukin-17 antibodies to improve healing of chronic skin wounds have not yet been performed, and only a few studies have examined interleukin-17 family expression in chronic skin wounds. Furthermore, different interleukin-17 family members could be playing selective roles in the repair process. These studies suggest a therapeutic role for targeting interleukin-17A to promote wound healing; therefore, interleukin-17A may be a target worthy of pursuing in the near future.

Interleukin-17: Functional and Structural Features, Application as a Therapeutic Target

Cytokines of the IL-17 family play a key role in the host organism defense against bacterial and fungal infections. At the same time, upregulated synthesis of IL-17 cytokines is associated with immunoinflammatory and autoimmune diseases such as psoriasis, rheumatoid arthritis, systemic lupus erythematosus, and others. The members of this family are important therapeutic targets in the treatment of various human chronic inflammatory disorders. Elucidation of signaling pathways involving IL-17 family proteins and analysis of the structure of cytokine complexes with specific antibodies, inhibitors, and receptors are essential for the development of new drugs for the therapy of immunoinflammatory rheumatic diseases.

Coinfection with Leishmania major and Staphylococcus aureus enhances the pathologic responses to both microbes through a pathway involving IL-17A

Cutaneous leishmaniasis (CL) is a parasitic disease causing chronic, ulcerating skin lesions. Most humans infected with the causative Leishmania protozoa are asymptomatic. Leishmania spp. are usually introduced by sand flies into the dermis of mammalian hosts in the presence of bacteria from either the host skin, sand fly gut or both. We hypothesized that bacteria at the dermal inoculation site of Leishmania major will influence the severity of infection that ensues. A C57BL/6 mouse ear model of single or coinfection with Leishmania major, Staphylococcus aureus, or both showed that single pathogen infections caused localized lesions that peaked after 2–3 days for S. aureus and 3 weeks for L. major infection, but that coinfection produced lesions that were two-fold larger than single infection throughout 4 weeks after coinfection. Coinfection increased S. aureus burdens over 7 days, whereas L. major burdens (3, 7, 28 days) were the same in singly and coinfected ears. Inflammatory lesions throughout the first 4 weeks of coinfection had more neutrophils than did singly infected lesions, and the recruited neutrophils from early (day 1) lesions had similar phagocytic and NADPH oxidase capacities. However, most neutrophils were apoptotic, and transcription of immunomodulatory genes that promote efferocytosis was not upregulated, suggesting that the increased numbers of neutrophils may, in part, reflect defective clearance and resolution of the inflammatory response. In addition, the presence of more IL-17A-producing γδ and non-γδ T cells in early lesions (1–7 days), and L. major antigen-responsive Th17 cells after 28 days of coinfection, with a corresponding increase in IL-1β, may recruit more naïve neutrophils into the inflammatory site. Neutralization studies suggest that IL-17A contributed to an enhanced inflammatory response, whereas IL-1β has an important role in controlling bacterial replication. Taken together, these data suggest that coinfection of L. major infection with S. aureus exacerbates disease, both by promoting more inflammation and neutrophil recruitment and by increasing neutrophil apoptosis and delaying resolution of the inflammatory response. These data illustrate the profound impact that coinfecting microorganisms can exert on inflammatory lesion pathology and host adaptive immune responses.

Cutaneous leishmaniasis (CL) is a vector-borne ulcerating skin disease affecting several million people worldwide. The causative Leishmania spp. protozoa are transmitted by infected phlebotomine sand flies. During a sand fly bite, bacteria can be coincidentally inoculated into the dermis with the parasite. Staphylococcus aureus is the most common bacterium in CL skin lesions. Symptomatic CL is characterized by papulonodular skin lesions that ulcerate and resolve with scarring, although most cutaneous Leishmania infections are asymptomatic. We sought to explore factors that determine whether infection with a cutaneous Leishmania species would result in symptomatic CL rather than asymptomatic infection. We hypothesized that local bacteria promote the development of symptomatic CL lesions during infection with Leishmania major. We discovered that cutaneous lesions were significantly larger in mice inoculated simultaneously with S. aureus and L. major than in mice infected with either organism alone. Coinfection led to increased S. aureus growth in skin lesions, whereas L. major parasite numbers were unchanged by coinfection. The size of the exacerbated lesion correlated with early increased numbers of neutrophils and elevated levels of proinflammatory cytokines IL-1β and IL-17A during the first 7 days, and with sustained increases in IL-17A through 28 days of coinfection. Neutralizing antibody experiments suggested IL-17A was partially responsible for lesion exacerbation during coinfection, whereas IL-1β was important for both control of early lesion exacerbation and promotion of IL-17A production. These data suggest that treatment of symptomatic CL targeting the parasite, local commensal bacteria, and host proinflammatory IL-17A immune responses might improve the outcome of CL.

Invariant NKT Cells and Control of the Thymus Medulla

Most αβ T cells that form in the thymus are generated during mainstream conventional thymocyte development and involve the generation and selection of a diverse αβ TCR repertoire that recognizes self-peptide/MHC complexes. Additionally, the thymus also supports the production of T cell subsets that express αβ TCRs but display unique developmental and functional features distinct from conventional αβ T cells. These include multiple lineages of CD1d-restricted invariant NKT (iNKT) cells that express an invariant αβ TCR, branch off from mainstream thymocytes at the CD4⁺CD8⁺ stage, and are potent producers of polarizing cytokines. Importantly, and despite their differences, iNKT cells and conventional αβ T cells share common requirements for thymic epithelial microenvironments during their development. Moreover, emerging evidence suggests that constitutive cytokine production by iNKT cells influences both conventional thymocyte development and the intrathymic formation of additional innate CD8⁺ αβ T cells with memory-like properties. In this article, we review evidence for an intrathymic innate lymphocyte network in which iNKT cells play key roles in multiple aspects of thymus function.

Gastric Cancer Stem Cells Effect on Th17/Treg Balance; A Bench to Beside Perspective

Gastric cancer stem cells (GCSCs), a small population among tumor cells, are responsible for tumor initiation, development, metastasis, and recurrence. They play a crucial role in immune evasion, immunomodulation, and impairment of effector immunity and believed to be emerged to change the balance of the immune system, importantly CD4⁺ T cells in the chronic inflamed tumor site. However, different subtypes of innate and adaptive immune cells are involved in the formation of the immune system in the tumor microenvironment, we would look at T cells in this study. Tumor microenvironment induces differentiation of CD4⁺ T cells into different subsets of T cells, mainly suppressive regulatory T cells (Treg), and T helper 17 (Th17) cells, although their exact role in tumor immunity is still under debate depending on tumor types and stages. Counterbalance between Th17 and Treg cells in the gastrointestinal system result in the homeostasis and normal function of the immune system, particularly mucosal immunity. Recent data demonstrated a high infiltration of Th17 and Treg cells into the gastric tumor site and proved that tumor microenvironment might disturb the balance between Th17 and Treg. It is possible to assume an association between activation of CSCs which contribute to metastasis in late stages, and the imbalanced Th17/Treg cells observed in advanced gastric cancer patients. This review intends to clarify the importance of gastric tumor microenvironment specifically CSCs in relation to Th17/Tregs balance firstly and to highlight the relevance of imbalanced Th17/Treg subsets in determining the stages and behavior of the tumor secondly. Finally, the present study suggests a clinical approach looking at the plasticity of T cells with a focus on Th17 as a promising dedicated arm in cancer immunotherapy.

The Interleukin-17 Family of Cytokines in Breast Cancer

Breast cancer (BC) is the most common cancer in women worldwide and remains a major cause of mortality with an expected 137,000 death this year in Europe. Standard management of metastatic BC comprises hormonotherapy, chemotherapy, and targeted therapies. Cyclin dependent kinase (CDK) and mammalian target of rapamycin (mTOR) inhibitors have recently proved their efficiency in hormonal receptor expressing BC. Checkpoint proteins inhibition is being evaluated in phase 3 studies. Since inflammation is constantly present in cancers, research teams have focused their attention on the interleukin-17 (IL-17) family of proinflammatory cytokines. Preclinical experiments have reported both pro and antitumor effects depending on the conditions. In the present article, we review the accumulating evidences about the roles of IL-17 in BC and discuss whether this family of cytokines could be a new target in anticancer treatments.

The complex alteration in the network of IL-17-type cytokines in patients with hereditary angioedema

Hereditary angioedema (HAE) is a rare autosomic-dominant disorder characterized by a deficiency of C1 esterase inhibitor which causes episodic swellings of subcutaneous tissues, bowel walls and upper airways that are disabling and potentially life-threatening. We evaluated n = 17 patients with confirmed HAE diagnosis during attack and remission state and n = 19 healthy subjects. The samples were tested for a panel of IL (Interleukin)-17-type cytokines (IL-1β, IL-6, IL-10, granulocyte-macrophage colony stimulating factor (GM-CSF), IL-17, IL-21, IL-22, IL-23) and transforming growth factor-beta (TGF-β) subtypes. Data indicate that there are variations of cytokine levels in HAE subjects comparing the condition during the crisis respect to the value in the remission phase, in particular type 17 signature cytokines are increased, whereas IL-23 is unmodified and TGF-β3 is significantly reduced. When comparing healthy and HAE subjects in the remission state, we found a significant difference for IL-17, GM-CSF, IL-21, TGF-β1 and TGF-β2 cytokines. These results confirm and extend our previous findings indicating that in HAE there is operating an inflammatory activation process, which involves also T helper 17 (Th17) cytokines and TGF-β isoforms, associated with localized angioedema attacks and characterized by elevated bradykinin levels.

The Changing Landscape of Naive T Cell Receptor Repertoire With Human Aging

Human aging is associated with a profound loss of thymus productivity, yet naïve T lymphocytes still maintain their numbers by division in the periphery for many years. The extent of such proliferation may depend on the cytokine environment, including IL-7 and T-cell receptor (TCR) “tonic” signaling mediated by self pMHCs recognition. Additionally, intrinsic properties of distinct subpopulations of naïve T cells could influence the overall dynamics of aging-related changes within the naïve T cell compartment. Here, we investigated the differences in the architecture of TCR beta repertoires for naïve CD4, naïve CD8, naïve CD4⁺CD25⁻CD31⁺ (enriched with recent thymic emigrants, RTE), and mature naïve CD4⁺CD25⁻CD31⁻ peripheral blood subsets between young and middle-age/old healthy individuals. In addition to observing the accumulation of clonal expansions (as was shown previously), we reveal several notable changes in the characteristics of T cell repertoire. We observed significant decrease of CDR3 length, NDN insert, and number of non-template added N nucleotides within TCR beta CDR3 with aging, together with a prominent change of physicochemical properties of the central part of CDR3 loop. These changes were similar across CD4, CD8, RTE-enriched, and mature CD4 subsets of naïve T cells, with minimal or no difference observed between the latter two subsets for individuals of the same age group. We also observed an increase in “publicity” (fraction of shared clonotypes) of CD4, but not CD8 naïve T cell repertoires. We propose several explanations for these phenomena built upon previous studies of naïve T-cell homeostasis, and call for further studies of the mechanisms causing the observed changes and of consequences of these changes in respect of the possible holes formed in the landscape of naïve T cell TCR repertoire.

Mucocutaneous IL-17 immunity in mice and humans: host defense vs. excessive inflammation

Interleukin (IL)-17A is a pro-inflammatory cytokine in mice and humans. It is recognized as a key factor for the protection of mice against various pathogens, but it also underlies pathogenic inflammatory responses in numerous mouse models. The inborn errors of IL-17A- and IL-17F-mediated immunity identified in humans in the last decade have revealed that IL-17A and IL-17F are key players in mucocutaneous immunity to Candida albicans, and, to a lesser extent, Staphylococcus aureus. By contrast, there is currently no genetic evidence for a causal link between excess of IL-17 and autoimmunity, autoinflammation, or allergy in humans. We discuss here the physiological and pathological roles of mouse and human IL-17A and IL-17F in host defense and excessive inflammation. We highlight recent advances in our understanding of the consequences of deficient or excessive IL-17 immunity at various mucocutaneous sites, including the oral cavity, skin, intestine, lungs, and vagina.

Interleukin 17 Family Cytokines: Signaling Mechanisms, Biological Activities, and Therapeutic Implications

The cytokines of the interleukin 17 (IL-17) family play a central role in the control of infections, especially extracellular fungi. Conversely, if unrestrained, these inflammatory cytokines contribute to the pathology of numerous autoimmune and chronic inflammatory conditions. Recent advances have led to the approval of IL-17A-blocking biologics for the treatment of moderate to severe plaque psoriasis, but much remains to be understood about the biological functions, regulation, and signaling pathways downstream of these factors. In this review, we outline the current knowledge of signal transduction and known physiological activities of IL-17 family cytokines. We will highlight in particular the current understanding of these cytokines in the context of skin manifestations of disease.

STAT-3-independent production of IL-17 by mouse innate-like αβ T cells controls ocular infection

St. Leger et al. identify and examine innate-like αβ T cells that circumvent canonical STAT-3 phosphorylation to produce protective IL-17. These cells can exist in the ocular mucosa and protect the ocular surface from pathogenic Staphylococcus aureus infection.

Appropriate regulation of IL-17 production in the host can mean the difference between effective control of pathogens and uncontrolled inflammation that causes tissue damage. Investigation of conventional CD4⁺ T cells (Th17 cells) has yielded invaluable insights into IL-17 function and its regulation. More recently, we and others reported production of IL-17 from innate αβ+ T cell populations, which was shown to occur primarily via IL-23R signaling through the transcription factor STAT-3. In our current study, we identify promyelocytic leukemia zinc finger (PLZF)–expressing iNKT, CD4⁻/CD8⁺, and CD4⁻/CD8⁻ (DN) αβ+T cells, which produce IL-17 in response to TCR and IL-1 receptor ligation independently of STAT-3 signaling. Notably, this noncanonical pathway of IL-17 production may be important in mucosal defense and is by itself sufficient to control pathogenic Staphylococcus aureus infection at the ocular surface.

Oral epithelial cells orchestrate innate type 17 responses to Candida albicans through the virulence factor candidalysin

Candida albicans is a dimorphic commensal fungus that causes severe oral infections in immunodeficient patients. Invasion of C. albicans hyphae into oral epithelium is an essential virulence trait. Interleukin-17 (IL-17) signaling is required for both innate and adaptive immunity to C. albicans During the innate response, IL-17 is produced by γδ T cells and a poorly understood population of innate-acting CD4+ αβ T cell receptor (TCRαβ)+ cells, but only the TCRαβ+ cells expand during acute infection. Confirming the innate nature of these cells, the TCR was not detectably activated during the primary response, as evidenced by Nur77eGFP mice that report antigen-specific signaling through the TCR. Rather, the expansion of innate TCRαβ+ cells was driven by both intrinsic and extrinsic IL-1R signaling. Unexpectedly, there was no requirement for CCR6/CCL20-dependent recruitment or prototypical fungal pattern recognition receptors. However, C. albicans mutants that cannot switch from yeast to hyphae showed impaired TCRαβ+ cell proliferation and Il17a expression. This prompted us to assess the role of candidalysin, a hyphal-associated peptide that damages oral epithelial cells and triggers production of inflammatory cytokines including IL-1. Candidalysin-deficient strains failed to up-regulate Il17a or drive the proliferation of innate TCRαβ+ cells. Moreover, candidalysin signaled synergistically with IL-17, which further augmented the expression of IL-1α/β and other cytokines. Thus, IL-17 and C. albicans, via secreted candidalysin, amplify inflammation in a self-reinforcing feed-forward loop. These findings challenge the paradigm that hyphal formation per se is required for the oral innate response and demonstrate that establishment of IL-1- and IL-17-dependent innate immunity is induced by tissue-damaging hyphae.

The Th17 Lineage: From Barrier Surfaces Homeostasis to Autoimmunity, Cancer, and HIV-1 Pathogenesis

The T helper 17 (Th17) cells represent a subset of CD4+ T-cells with unique effector functions, developmental plasticity, and stem-cell features. Th17 cells bridge innate and adaptive immunity against fungal and bacterial infections at skin and mucosal barrier surfaces. Although Th17 cells have been extensively studied in the context of autoimmunity, their role in various other pathologies is underexplored and remains an area of open investigation. This review summarizes the history of Th17 cell discovery and the current knowledge relative to the beneficial role of Th17 cells in maintaining mucosal immunity homeostasis. We further discuss the concept of Th17 pathogenicity in the context of autoimmunity, cancer, and HIV infection, and we review the most recent discoveries on molecular mechanisms regulating HIV replication/persistence in pathogenic Th17 cells. Finally, we stress the need for novel fundamental research discovery-based Th17-specific therapeutic interventions to treat pathogenic conditions associated with Th17 abnormalities, including HIV infection.

Precocious Interleukin 21 Expression in Naive Mice Identifies a Natural Helper Cell Population in Autoimmune Disease

Interleukin 21 (IL-21) plays key roles in humoral immunity and autoimmune diseases. It is known to function in mature CD4+ T follicular B cell helper (TFH) cells, but its potential involvement in early T cell ontogeny is unclear. Here, we find that a significant population of newly activated thymic and peripheral CD4+ T cells functionally expresses IL-21 soon after birth. This naturally occurring population, termed natural (n)TH21 cells, exhibits considerable similarity to mature TFH cells. nTH21 cells originating and activated in the thymus are strictly dependent on autoimmune regulator (AIRE) and express high levels of NUR77, consistent with a bias toward self-reactivity. Their activation/expansion in the periphery requires gut microbiota and is held in check by FoxP3+ TREG cells. nTH21 cells are the major thymic and peripheral populations of IL-21+ cells to expand in an IL-21-dependent humoral autoimmune disease. These studies link IL-21 to T cell ontogeny, self-reactivity, and humoral autoimmunity.

Regulatory T CD4 + CD25+ lymphocytes increase in symptomatic carotid artery stenosis

BACKGROUND

Atherosclerosis is a multifactorial disease characterized by an immune-inflammatory remodeling of the arterial wall. Treg and Th17 subpopulations are detectable inside atherosclerotic plaque; however, their behavior in symptomatic carotid artery stenosis (CAS) is not fully elucidated. The aim of this study was to evaluate Th17 and Treg subsets and their ratio in patients affected by symptomatic and asymptomatic CAS.

METHODS

14 patients with symptomatic CAS (CAS-S group), 41 patients with asymptomatic CAS (CAS-A group), 32 subjects with traditional cardiovascular risk factors (RF group), and 10 healthy subjects (HS group) were enrolled. Th17 and Treg frequency was determined by flow cytometry and by histology and immunohistochemistry. Interleukin (IL)-10, IL-17, and metalloproteinase (MMP)-12 levels were measured by ELISA.

RESULTS

Th17 were significantly increased in CAS-A versus RF and versus HS. Tregs were significantly increased in CAS-S versus CAS-A. Tregs/Th17 ratio was significantly reduced in CAS-A versus RF and versus HS, whereas it was significantly increased in CAS-S versus CAS-A.

CONCLUSIONS

The results of this study suggest that Th17 are related to the late stages of CAS but not to plaque instability. Moreover, Treg expansion seems to represent a specific cellular pattern displayed by patients with symptomatic CAS and associated with brain injury. KEY MESSAGES Tregs expansion seems to represent a specific cellular pattern displayed by patients with symptomatic CAS and associated with CD4+ effector depletion and brain ischemic injury. Th17 lymphocytes are related to the late stages of CAS but not to plaque instability.

Th17 Responses to Collagen Type V, kα1-Tubulin, and Vimentin Are Present Early in Human Development and Persist Throughout Life

T helper 17 (Th17)-dependent autoimmune responses can develop after heart or lung transplantation and are associated with fibro-obliterative forms of chronic rejection; however, the specific self-antigens involved are typically different from those associated with autoimmune disease. To investigate the basis of these responses, we investigated whether removal of regulatory T cells or blockade of function reveals a similar autoantigen bias. We found that Th17 cells specific for collagen type V (Col V), kα1-tubulin, and vimentin were present in healthy adult peripheral blood mononuclear cells, cord blood, and fetal thymus. Using synthetic peptides and recombinant fragments of the Col V triple helical region (α1[V]), we compared Th17 cells from healthy donors with Th17 cells from Col V-reactive heart and lung patients. Although the latter responded well to α1(V) fragments and peptides in an HLA-DR-restricted fashion, Th17 cells from healthy persons responded in an HLA-DR-restricted fashion to fragments but not to peptides. Col V, kα1-tubulin, and vimentin are preferred targets of a highly conserved, hitherto unknown, preexisting Th17 response that is MHC class II restricted. These data suggest that autoimmunity after heart and lung transplantation may result from dysregulation of an intrinsic mechanism controlling airway and vascular homeostasis.

The Role of IL-17 and Related Cytokines in Inflammatory Autoimmune Diseases

Interleukin-17 (IL-17) induces the production of granulocyte colony-stimulating factor (G-CSF) and chemokines such as CXCL1 and CXCL2 and is a cytokine that acts as an inflammation mediator. During infection, IL-17 is needed to eliminate extracellular bacteria and fungi, by inducing antimicrobial peptides such as defensin. This cytokine also plays an important role in chronic inflammation that occurs during the pathogenesis of autoimmune diseases and allergies such as human rheumatoid arthritis (RA) for which a mouse model of collagen-induced arthritis (CIA) is available. In autoimmune diseases such as RA and multiple sclerosis (MS), IL-17 is produced by helper T (Th) cells that are stimulated by IL-1β and IL-6 derived from phagocytes such as macrophages and from tissue cells. IL-17 contributes to various lesions that are produced by Th17 cells, one subset of helper T cells, and by γδ T cells and innate lymphoid cells. It strongly contributes to autoimmune diseases that are accompanied by chronic inflammation. Thus, a functional understanding of Th17 cells is extremely important. In this review, we highlight the roles of cytokines that promote the development and maintenance of pathogenic Th17 cells in autoimmune diseases.

CD31, a Valuable Marker to Identify Early and Late Stages of T Cell Differentiation in the Human Thymus

Although CD31 expression on human thymocytes has been reported, a detailed analysis of CD31 expression at various stages of T cell development in the human thymus is missing. In this study, we provide a global picture of the evolution of CD31 expression from the CD34⁺ hematopoietic precursor to the CD45RA⁺ mature CD4⁺ and CD8⁺ single-positive (SP) T cells. Using nine-color flow cytometry, we show that CD31 is highly expressed on CD34⁺ progenitors and stays high until the early double-positive stage (CD3^-CD4⁺CD8α⁺β^-). After β-selection, CD31 expression levels become low to undetectable. CD31 expression then increases and peaks on CD3^highCD4⁺CD8⁺ double-positive thymocytes. However, following positive selection, CD31 expression differs dramatically between CD4⁺ and CD8⁺ lineages: homogeneously high on CD8 SP but lower or negative on CD4 SP cells, including a subset of CD45RA⁺CD31^- mature CD4⁺ thymocytes. CD31 expression on TCRγδ thymocytes is very similar to that of CD4 SP cells. Remarkably, there is a substantial subset of semimature (CD45RA^-) CD4 SP thymocytes that lack CD31 expression. Moreover, FOXP3⁺ and ICOS⁺ cells are overrepresented in this CD31^- subpopulation. Despite this CD31^-CD45RA^- subpopulation, most egress-capable mature CD45RA⁺ CD4 SP thymocytes express CD31. The variations in CD31 expression appear to coincide with three major selection processes occurring during thymopoiesis: β-selection, positive selection, and negative selection. Considering the ability of CD31 to modulate the TCR's activation threshold via the recruitment of tyrosine phosphatases, our results suggest a significant role for CD31 during T cell development.

Th17 Cells Require You to Chew before You Swallow

How immunity is regulated at distinct epithelial tissues that vary in microbial occupancy and environmental and tissue specific cues isn't clear. Dutzan et al. (2017) report that mechanical-derived signals, not those from micro-organisms, are key to maintaining interleukin-17-expressing T helper (Th17) cells at the oral epithelia.

MCPIP1/Regnase-1 Restricts IL-17A- and IL-17C-Dependent Skin Inflammation

The IL-17 family cytokines IL-17A and IL-17C drive the pathogenesis of psoriatic skin inflammation, and anti-IL-17A Abs were recently approved to treat human psoriasis. Little is known about mechanisms that restrain IL-17 cytokine-mediated signaling, particularly IL-17C. In this article, we show that the endoribonuclease MCP-1-induced protein 1 (MCPIP1; also known as regnase-1) is markedly upregulated in human psoriatic skin lesions. Similarly, MCPIP1 was overexpressed in the imiquimod (IMQ)-driven mouse model of cutaneous inflammation. Mice with an MCPIP1 deficiency (Zc3h12a^+/-) displayed no baseline skin inflammation, but they showed exacerbated pathology following IMQ treatment. Pathology in Zc3h12a^+/- mice was associated with elevated expression of IL-17A- and IL-17C-dependent genes, as well as with increased accumulation of neutrophils in skin. However, IL-17A and IL-17C expression was unaltered, suggesting that the increased inflammation in Zc3h12a^+/- mice was due to enhanced downstream IL-17R signaling. Radiation chimeras demonstrated that MCPIP1 in nonhematopoietic cells is responsible for controlling skin pathology. Moreover, Zc3h12a^+/-Il17ra^-/- mice given IMQ showed almost no disease. To identify which IL-17RA ligand was essential, Zc3h12a^+/-Il17a^-/- and Zc3h12a^+/-Il17c^-/- mice were given IMQ; these mice had reduced but not fully abrogated pathology, indicating that MCPIP1 inhibits IL-17A and IL-17C signaling. Confirming this hypothesis, Zc3h12a^-/- keratinocytes showed increased responsiveness to IL-17A and IL-17C stimulation. Thus, MCPIP1 is a potent negative regulator of psoriatic skin inflammation through IL-17A and IL-17C. Moreover, to our knowledge, MCPIP1 is the first described negative regulator of IL-17C signaling.

Germ-free and Antibiotic-treated Mice are Highly Susceptible to Epithelial Injury in DSS Colitis

BACKGROUND AND AIMS

Intestinal microbiota is required to maintain immune homeostasis and intestinal barrier function. At the same time, intraluminal bacteria are considered to be involved in inflammatory bowel disease and are required for colitis induction in animal models, with the possible exception of dextran sulphate sodium [DSS] colitis. This study was carried out to ascertain the mechanism underlying the induction of colitis by DSS in the absence of bacteria.

METHODS

Conventional and germ-free [GF] Naval Medical Research Institute [NMRI] mice were used, plus conventional mice treated with an antibiotic cocktail to deplete the intestinal microbiota ['pseudo-GF' or PGF mice]. The differential response to DSS was assessed.

RESULTS

Conventional mice developed DSS-induced colitis normally, whereas GF mice showed only minimal inflammation [no colonic thickening, lower myeloperoxidase activity, IL-6, IL-17, TNF-α, and IFN-γ secretion by splenocytes and mesenteric cell cultures, etc.]. However, these mice suffered enhanced haemorrhage, epithelial injury and mortality as a consequence of a weakened intestinal barrier, as shown by lower occludin, claudin 4, TFF3, MUC3, and IL-22. In contrast, PGF mice had a relatively normal, albeit attenuated, inflammatory response, but were less prone to haemorrhage and epithelial injury than GF mice. This was correlated with an increased expression of IL-10 and Foxp3 and preservation barrier-related markers.

CONCLUSIONS

We conclude that enteric bacteria are essential for the development of normal DSS-induced colitis. The absence of microbiota reduces DSS colonic inflammation dramatically but it also impairs barrier function, whereas subtotal microbiota depletion has intermediate effects at both levels.

Interleukin-23 Secreted by Activated Macrophages Drives γδT Cell Production of Interleukin-17 to Aggravate Secondary Injury After Intracerebral Hemorrhage

BACKGROUND

Neuroinflammation plays a key role in intracerebral hemorrhage (ICH)-induced secondary brain injury, but the specific roles of peripheral inflammatory cells such as macrophages and lymphocytes remain unknown. The purpose of this study was to explore the roles of macrophages, T lymphocytes, and the cytokines they secrete as potential targets for treating secondary brain injury after ICH.

METHODS AND RESULTS

Our results showed that peripheral macrophages and T lymphocytes successively infiltrated the brain, with macrophage counts peaking 1 day after ICH and T-lymphocyte counts peaking after 4 days. These peaks in cellular infiltration corresponded to increases in interleukin (IL)-23 and IL-17 expression, respectively. We found that hemoglobin from the hematoma activated IL-23 secretion by infiltrating macrophages by inducing the formation of toll-like receptor (TLR) 2/4 heterodimer. This increased IL-23 expression stimulated γδT-cell production of IL-17, which increased brain edema and neurologic deficits in the model mice as a proinflammatory factor. Finally, we found that sparstolonin B (SsnB) could ameliorate brain edema and neurologic deficits in ICH model mice via inhibition of TLR2/TLR4 heterodimer formation, and notably, SsnB interacted with myeloid differentiation factor 88 Arg196.

CONCLUSIONS

Together, our results reveal the importance of the IL-23/IL-17 inflammatory axis in secondary brain injury after ICH and thus provide a new therapeutic target for ICH treatment.

Apoptosis in response to microbial infection induces autoreactive TH17 cells

Microbial infections often precede the onset of autoimmunity. How infections trigger autoimmunity remains poorly understood. We investigated the possibility that infection might create conditions that allow the stimulatory presentation of self peptides themselves and that this might suffice to elicit autoreactive T cell responses that lead to autoimmunity. Self-reactive CD4(+) T cells are major drivers of autoimmune disease, but their activation is normally prevented through regulatory mechanisms that limit the immunostimulatory presentation of self antigens. Here we found that the apoptosis of infected host cells enabled the presentation of self antigens by major histocompatibility complex class II molecules in an inflammatory context. This was sufficient for the generation of an autoreactive TH17 subset of helper T cells, prominently associated with autoimmune disease. Once induced, the self-reactive TH17 cells promoted auto-inflammation and autoantibody generation. Our findings have implications for how infections precipitate autoimmunity.

Potassium supplementation inhibits IL-17A production induced by salt loading in human T lymphocytes via p38/MAPK-SGK1 pathway

High salt intake contributes to the development of autoimmune/inflammatory diseases, while potassium supplementation antagonizes the effects. Interleukin (IL)-17A are tightly related with autoimmune/inflammatory diseases. Thus, we explored the effects and underlying molecular mechanism of high salt and potassium supplementation on IL-17A production in T lymphocytes. Forty-nine healthy participants received a low-salt, high-salt, followed by a high-salt diet plus potassium supplement for 7 days, respectively. Human T lymphocyte Jurkat cells were treated with different concentrations of NaCl and KCl. In the participants, IL-17A levels in plasma and in peripheral blood mononuclear cells (PBMC) were significantly increased after a high-salt diet, which was dramatically reversed when potassium was supplemented. In Jurkat cells, the addition of 40 mM NaCl markedly enhanced IL-17A production and the expression of phosphorylated p38/mitogen-activated protein kinase (MAPK) and its downstream target, serum/glucocorticoid-regulated kinase (SGK)1, whereas combined treatment with additional 2 mM KCl significantly decreased them. Respective inhibition of p38/MAPK and SGK1 suppressed IL-17A expression induced by NaCl, and KCl inhibited IL-17A production induced by specific activator of p38/MAPK. We conclude potassium supplementation has a blocking effect on IL-17A production in T lymphocytes induced by salt loading. This protective effect is mediated through the direct suppression of p38/MAPK-SGK1 pathway.