Th17 cells: interactions with predisposing factors in the immunopathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory state of the GI tract of unknown etiology. Classically, tissue injury in IBD is thought to be primarily mediated by Th1 cells in Crohn's disease or Th2 cells in ulcerative colitis. The discoveries of new subsets of T-helper cells, especially Th17 cells, have revolutionized our understanding of the disease immunopathology. Th17 cells seem to affect both innate and adaptive immune responses by the release of regulatory cytokines. Understanding the role of Th17 cells in IBD pathogenesis and targeting their regulatory cytokines may provide potential therapeutic approaches for the treatment of IBD in the future.     

The Th17 Cell Population and the Immune Homeostasis of the Gastrointestinal Tract

Th17 cells are a recently discovered subset of CD4⁺ T lymphocytes filling a hole in the repertoire of effector T cells. Th17 cells produce multiple cytokines, with pivotal impact on immune homeostasis, inflammation, and influencing a wide range of intestinal cell targets. The current issue of the International Reviews of Immunology is entirely dedicated to the various roles of Th17 T cells in the immune homeostasis and inflammation occurring in the gut. In addition to describing diverse Th17-mediated molecular pathways, a specific focus is being given to Th17 cell plasticity. This enables the Th17 cells to shift towards a Th1 profile, or to express IL-22, a protective cytokine in experimental colitis. Participation of microbiota-specific Th17 cells to normal immune homeostasis, and their role in the pathogenesis of inflammatory bowel disease (IBD), or of gluten specific-Th17 cells in celiac disease, are also being discussed. Neutralizing antibodies against IL-17A and IL-17F have commenced clinical testing in IBD. In conclusion, Th17 cells emerge as a key immune cell population and further elucidation of their roles and functional plasticity are warranted to support the discovery of novel therapies against IBD and other intestinal disorders.     

Th17细胞与Treg细胞比例失衡在慢性炎症性疾病中研究进展

慢性炎症性疾病涉及许多疾病的发展过程,如变应性鼻炎、支气管哮喘、类风湿性关节炎（rheumatoid arthritis,R A）、炎症性肠病（inflammator y bowel disease,IBD）等。研究发现,Th17和Treg细胞通过其自身及产生的相应细胞因子,在慢性炎症性疾病发生发展过程中起着重要作用,而Th17和调节性T细胞（T Regulator Cell,Treg细胞）的分化共用了TGF-β这个细胞因子,提示他们在分化过程中有某种关联。本文旨在阐述Th17细胞与Treg细胞比例失衡在相关慢性炎症性疾病的发生发展中所起的关键作用。     

Th17及Th17型细胞因子与炎症性肠病

Th17细胞已被划分为一个不同于Th1、Th2和Treg的新的T细胞亚群,以分泌IL-17为主要特征。Th17在防御胞外细菌感染、介导慢性炎症和自身免疫性疾病的发病机制中发挥重要作用。炎症性肠病属于自身免疫性疾病的一种,免疫调节紊乱是其发病的关键因素。免疫学和基因学的发现表明Th17及Th17效应因子在炎症性肠病发病机理中起重要作用。对Th17的进一步深入研究可以加深我们对相关疾病发病机制的认识并指导临床治疗。     

Th17细胞在慢性阻塞性肺疾病肺部炎症中的作用

由于长期吸烟的刺激,活化的辅助性T细胞17（Th17）能浸润到肺组织并参与肺泡壁的破坏及肺气肿的形成.Th17细胞在IL-23的作用下,分泌IL-17、IL-21、IL-22等多种细胞因子,其中IL-17可以促进气道中性粒细胞的募集和激活,IL-21在维持、增强Th17细胞的数量及功能的同时,能增加CD8＋细胞的数量及其细胞毒活性,在吸烟诱导的慢性阻塞性疾病（COPD）肺部连续炎症中发挥持续放大效应.在不同的炎症环境中,Th17细胞及其分泌的细胞因子与Th1细胞、调节性T细胞（Treg）以及多种参与固有免疫应答的细胞间相互作用和调节,共同参与COPD的发病,并构成了固有免疫与适应性免疫之间的桥梁.     

Translational Mini‐Review Series on Th17 Cells: Function and regulation of human T helper 17 cells in health and disease

T helper (Th) cell have a central role in modulating immune responses. While Th1 and Th2 cells have long been known to regulate cellular and humoral immunity, Th17 cells have been identified only recently as a Th lineage that regulates inflammation via production of distinct cytokines such as interleukin (IL)-17. There is growing evidence that Th17 cells are pathological in many human diseases, leading to intense interest in defining their origins, functions and developing strategies to block their pathological effects. The cytokines that regulate Th17 differentiation have been the focus of much debate, due primarily to inconsistent findings from studies in humans. Evidence from human disease suggests that their in vivo development is driven by specialized antigen-presenting cells. Knowledge of how Th17 cells interact with other immune cells is limited, but recent data suggest that Th17 cells may not be subject to strict cellular regulation by T regulatory cells. Notably, Th17 cells and T regulatory cells appear to share common developmental pathways and both cell types retain significant plasticity. Herein, we will discuss the molecular and cellular regulation of Th17 cells with an emphasis on studies in humans.     

Molecular Mechanisms and Cell Targets of Th17 Cells in the Gastrointestinal Tract: An Innate Sense of Adaptivity

T-helper (TH) 17 activation is crucial for protective immune responses against bacteria and fungi at mucosal surfaces, but it can also be implicated in the pathogenesis of several autoimmune and chronic inflammatory diseases, such as inflammatory bowel diseases (IBD). Although rapid progress was made elucidating induction and functional heterogeneity of Th17 responses, the underlying molecular effects of Th17 response including the most relevant different cell targets of Th17 cytokines remain poorly understood. Cytokines produced by Th17 cells have broad effects on both hematopoietic and nonhematopoietic cells and can act in synergy with various inflammatory factors. In this review, we will focus on the effects of Th17-derived cytokines in the gastrointestinal tract and discuss how Th17 responses can affect both innate and adaptive immunity and may contribute to the pathogenesis of inflammatory GI processes.     

Th17 Cytokines in Inflammatory Bowel Diseases: Discerning the Good from the Bad

T helper (Th) 17 cells are a branch of the CD4+ T cell compartment involved in host protection against bacterial and fungal infections as well as in orchestration of chronic inflammation and autoimmunity in many organs. Th17 cells produce interleukin (IL)-17A and variable amounts of IL-17F, IL-21, IL-22 and IL-26, under the regulation of retinoic-acid-related orphan receptors (ROR)-γt and ROR-α. Accumulating evidence supports the involvement of Th17 cells in the tissue-damaging immune response occurring in patients with Crohn's disease and patients with ulcerative colitis, the two major forms of inflammatory bowel disease (IBD) in human beings. However in the gut, Th17 cells can also have tissue-protective effects, mostly depending on their ability to enhance epithelial barrier function and counter-regulatory mechanisms. In this article, we summarize the available data on the dual role of Th17 cells in gut homeostasis and inflammation and discuss whether and how Th17 cytokine blockers can enter into the therapeutic armamentarium of IBD.     

Interleukin-23 and T helper 17-type responses in intestinal inflammation: from cytokines to T-cell plasticity

Interleukin-23 (IL-23) plays an essential role in driving intestinal pathology in experimental models of both T-cell-dependent and innate colitis. Furthermore, genome-wide association studies have identified several single-nucleotide polymorphisms in the IL-23 receptor (IL-23R) gene that are associated with either susceptibility or resistance to inflammatory bowel disease in humans. Although initially found to support the expansion and maintenance of CD4(+) T helper 17 (Th17) cells, IL-23 is now recognized as having multiple effects on the immune response, including restraining Foxp3(+) regulatory T-cell activity and inducing the expression of Th17-type cytokines from non-T-cell sources. Here we focus on Th17 cells and their associated cytokines IL-17A, IL-17F, IL-21 and IL-22. We review studies performed in mouse models of colitis where these effector cytokines have been shown to have either a pathogenic or a tissue-protective function. We also discuss the heterogeneity found within the Th17 population and the phenomenon of plasticity of Th17 cells, in particular the ability of these lymphocytes to extinguish IL-17 expression and turn on interferon-γ production to become Th1-like 'ex-Th17' cells. Interleukin-23 has been identified as a key driver in this process, and this may be an additional mechanism by which IL-23 promotes pathology in the intestinal tract. These 'ex-Th17' cells may contribute to disease pathogenesis through their secretion of pro-inflammatory mediators.     

IL-23/IL-17轴在银屑病免疫发病机制中的作用

银屑病是一种以T淋巴细胞异常活化和浸润为主要特征的慢性炎性反应皮肤病。Th17细胞及IL-23/IL-17轴在银屑病的发病机制中可能处于关键地位,并成为新的治疗靶标。IL-23诱导Th17细胞分化增殖,分化成熟的Th17可以分泌IL-17、IL-21、IL-22等多种细胞因子,Th17类细胞因子在银屑病等多种自身免疫疾病和炎性疾病中起重要作用。     

Th17细胞及白细胞介素17A在慢性气道炎症性疾病中的作用

长期以来,人们对于T淋巴细胞的研究集中在辅助性T细胞1型、2型(Th1、Th2)、调节性T细胞(Treg)以及细胞毒性T细胞(Tc)等亚群上。传统理论认为,Th1细胞介导细胞免疫,在抗胞内菌感染的过程中发挥作用;而Th2细胞介导体液免疫,与过敏性疾病以及抗寄生虫感染的过程紧密相关。Th1/Th2失衡被认为是许多疾病产生和发展的重要因素。     

The cytokine milieu in the interplay of pathogenic Th1/Th17 cells and regulatory T cells in autoimmune disease

The propagation and regulation of an immune response is driven by a network of effector and regulatory T (Treg) cells. The interplay of effector T and Treg cells determines the direction of the immune response towards inflammation or its resolution in an autoimmune disease setting. In autoimmune diseases, this interplay shifts the balance in favor of the development of autoreactive effector T cells, resulting in inflammatory pathology. The objective of an effective therapeutic approach for autoimmune disease is to restore this balance. In this review, we describe the characteristics and development of pathogenic T helper 1 (Th1) and Th17 cells and the beneficial Treg cells in autoimmune diseases and the crucial roles of the cytokine milieu in influencing the balance of these T-cell subsets. Given the importance of cytokines, we discuss current immunotherapeutic strategies using cytokine or cytokine receptor antibodies for the treatment of autoimmune diseases.     

Serotonin decreases the production of Th1/Th17 cytokines and elevates the frequency of regulatory CD4+ T‐cell subsets in multiple sclerosis patients

Excessive levels of proinflammatory cytokines in the CNS are associated with reduced serotonin (5‐HT) synthesis, a neurotransmitter with diverse immune effects. In this study, we evaluated the ability of exogenous 5‐HT to modulate the T‐cell behavior of patients with MS, a demyelinating autoimmune disease mediated by Th1 and Th17 cytokines. Here, 5‐HT attenuated, in vitro, T‐cell proliferation and Th1 and Th17 cytokines production in cell cultures from MS patients. Additionally, 5‐HT reduced IFN‐γ and IL‐17 release by CD8⁺ T cells. By contrast, 5‐HT increased IL‐10 production by CD4⁺ T cells from MS patients. A more accurate analysis of these IL‐10‐secreting CD4⁺ T cells revealed that 5‐HT favors the expansion of FoxP3⁺CD39⁺ regulatory T cells (Tregs) and type 1 regulatory T cells. Notably, this neurotransmitter also elevated the frequency of Treg17 cells, a novel regulatory T‐cell subset. The effect of 5‐HT in upregulating CD39⁺ Treg and Treg17 cells was inversely correlated with the number of active brain lesions. Finally, in addition to directly reducing cytokine production by purified Th1 and Th17 cells, 5‐HT enhanced in vitro Treg function. In summary, our data suggest that serotonin may play a protective role in the pathogenesis of MS.     

细胞因子在炎症性肠病中作用机制的研究进展

炎症性肠病(IBD),包括克罗恩病和溃疡性结肠炎两种类型.它是在多种致病因素共同作用下由肠道免疫调节紊乱引发的炎症性疾病.近年来的研究发现,多种免疫细胞和细胞因子参与了两型IBD的发生和发展,其中ICE、辅助T细胞Th1/Th2在两型IBD中的功能和角色受到重视.对细胞因子在炎症性肠病中作用机制的深入研究为IBD的治疗提供了新的线索.     

Elevated levels of Th17 cells and Th17-related cytokines are associated with disease activity in patients with inflammatory bowel disease

Objective

Interleukin-17(IL-17)-producing T helper(Th)17 cells are considered as a new subset of cells critical to the development of inflammatory bowel disease (IBD). We aimed to investigate the distribution of Th17 cells, the expressions of Th17-related cytokines (IL-17, IL-21 and IL-22) and their association with disease activity in IBD patients.

Methods

We collected intestinal tissue biopsies from 40 patients with active ulcerative colitis (UC), 20 patients with active Crohn’s disease (CD) and 20 healthy controls. The distribution of Th17 cells and expressions of Th17-related cytokines in colonic tissues were evaluated by a standard immunohistochemical procedure. Serum IL-17, IL-21 and IL-22 levels were determined by ELISA. Pearson’s and Spearman’s correlation analyses were performed to analyze the correlation between the number of Th17 cells, the expressions of Th17-related cytokines and disease activity index, endoscopic and histological grading, and CRP and PLT levels, respectively.

Results

Compared with healthy controls, the number of Th17 cells and the expressions of IL-17, IL-21 and IL-22 were significantly increased in active IBD patients (P < 0.05). In addition, Pearson’s and Spearman’s correlation analyses showed that the number of Th17 cells and the expressions of Th17-related cytokines were correlated with disease activity index, endoscopic and histological grading, CRP and PLT levels (P < 0.05).

Conclusions

Th17 cells and Th17-related cytokines (IL-17, IL-21 and IL-22) were increased in the intestinal mucosa in active IBD patients and may play an important role in disease activity and mucosal damage.     

Immunoregulation of Inflammatory and Inhibitory Cytokines by Vitamin D3 in Patients with Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a group of idiopathic, chronic and relapsing inflammatory conditions of the gastrointestinal tract, caused by an aberrant and exaggerated immunological response in the gut. Supplementation of vitamin D3 in patients with IBD exerts both direct and indirect regulatory roles on the naïve T cells, thereby maintaining a balance between inflammatory and inhibitory cytokines. The direct actions of vitamin D3 on naïve T cells result in the proliferation of more regulatory T cells and inhibitory cytokines such as IL‐4, IL‐10 and IL‐5. The binding of vitamin D to dendritic cells (DCs) through vitamin D receptors inhibits the action of IL‐12 on DCs, resulting in the downregulation of Th1 and Th17. On the other hand, this interaction favours Th2 and Treg upregulation and facilitates the maintenance of immune homoeostasis between inflammatory and inhibitory cytokines which is essentially significant in the management of patients with IBD. The aim of this review was to explore the current and mounting scientific evidence on the roles of vitamin D3 in immunoregulation of inflammatory and inhibitory cytokines in patients with IBDs. An extensive literature search was conducted using keywords such as Vitamin D3*, IBD*, inflammatory cytokines*, inhibitory cytokines*, naïve‐T‐cells* and antigen presenting cells* through PubMed, SCOPUS and MEDLINE search engines. The results of the accumulated bodies of research that have been conducted demonstrate that vitamin D3 plays a major role not only in the immunoregulation of cytokines involved in the pathogenesis of IBDs but also in many other inflammatory disorders.