Interleukin-10 signaling in regulatory T cells is required for suppression of Th17 cell-mediated inflammation

The microbiome in infectious disease and inflammation

The mammalian alimentary tract harbors hundreds of species of commensal microorganisms (microbiota) that intimately interact with the host and provide it with genetic, metabolic, and immunological attributes. Recent reports have indicated that the microbiota composition and its collective genomes (microbiome) are major factors in predetermining the type and robustness of mucosal immune responses. In this review, we discuss the recent advances in our understanding of host-microbiota interactions and their effect on the health and disease susceptibility of the host.

Animal models of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory condition that is medicated by genetic, immune, and environmental factors. At least 66 different kinds of animal models have been established to study IBD, which are classified primarily into chemically induced, cell-transfer, congenial mutant, and genetically engineered models. These IBD models have provided significant contributions to not only dissect the mechanism but also develop novel therapeutic strategies for IBD. In addition, recent advances on genetically engineered techniques such as cell-specific and inducible knockout as well as knockin mouse systems have brought novel concepts on IBD pathogenesis to the fore. Further, mouse models, which lack some IBD susceptibility genes, have suggested more complicated mechanism of IBD than previously predicted. This chapter summarizes the distinct feature of each murine IBD model and discusses the previous and current lessons from the IBD models.

The battle against immunopathology: infectious tolerance mediated by regulatory T cells

Infectious tolerance is a process whereby one regulatory lymphoid population confers suppressive capacity on another. Diverse immune responses are induced following infection or inflammatory insult that can protect the host, or potentially cause damage if not properly controlled. Thus, the process of infectious tolerance may be critical in vivo for exerting effective immune control and maintaining immune homeostasis by generating specialized regulatory sub-populations with distinct mechanistic capabilities. Foxp3(+) regulatory T cells (T(regs)) are a central mediator of infectious tolerance through their ability to convert conventional T cells into induced regulatory T cells (iT(regs)) directly by secretion of the suppressive cytokines TGF-β, IL-10, or IL-35, or indirectly via dendritic cells. In this review, we will discuss the mechanisms and cell populations that mediate and contribute to infectious tolerance, with a focus on the intestinal environment, where tolerance induction to foreign material is critical.

Regulatory role of antigen-induced interleukin-10, produced by CD4(+) T cells, in airway neutrophilia in a murine model for asthma

It has been suggested that interleukin (IL)-10 exerts immunosuppressive effects on allergic inflammation, including asthma, mainly through inhibition of Th2 cell-mediated eosinophilic airway inflammation. In a model of experimental asthma utilizing multiple intratracheal antigen challenges in sensitized mice, IL-10 production as well as eosinophilia and neutrophilia in the lung were induced by the multiple challenges. In this study, we set out to reveal the cellular source of endogenously produced IL-10, and the roles of IL-10 in airway leukocyte inflammation using an anti-IL-10 receptor monoclonal antibody. Balb/c mice were sensitized i.p. with ovalbumin+Al(OH)(3), and then challenged by intratracheal administration of ovalbumin 4 times. Flow cytometric analyses revealed that the cellular source of IL-10 was CD4(+) T cells lacking the transcription factor, forkhead box P3. Treatment with anti-IL-10 receptor monoclonal antibody prior to the 4th challenge significantly augmented airway neutrophilia as well as the production of IL-1β, and CXC chemokines, keratinocyte-derived chemokine (KC) and macrophage inflammatory protein (MIP)-2, but not airway eosinophilia, Th2 cytokine (IL-4 and IL-5) production, or a late-phase increase in specific airway resistance. Approximately 40% of IL-10 receptor(+) cells expressed the macrophage marker F4/80, whereas only 3-4% of the IL-10 receptor(+) cells were granulocyte differentiation antigen (Gr)-1(high) cells (neutrophils). In conclusion, multiple airway antigen challenges induced the proliferation of IL-10-expressing CD4(+) T cells in regulating airway neutrophilia. Systemic blockade of IL-10 function coincided with increases in IL-1β and CXC chemokines. Thus, IL-1β and CXC chemokines may be targets for development of novel pharmacotherapy for neutrophilic asthma.

Induction of Treg cells in the mouse colonic mucosa: a central mechanism to maintain host-microbiota homeostasis

CD4+ regulatory T (Treg) cells expressing the transcription factor forkhead box P3 (Foxp3) play a critical role in maintaining immunological homeostasis. Treg cells are highly abundant in the mouse intestinal lamina propria, particularly in the colon. Recent studies using germ-free and gnotobiotic mice have revealed that specific components of the intestinal microbiota influence the number and function of Treg cells. Substantial changes in the composition of microbiota have been associated with inflammatory bowel disease. In this review, we will discuss recent findings that associate intestinal microbiota in mice with Treg responses and with the maintenance of intestinal immune homeostasis.

The molecular mechanisms of Foxp3 gene regulation

Induction of Foxp3 gene expression and acquisition of regulatory T cell fate is, understandably, a highly controlled process and one which many investigators want to illuminate. In studying the regulation of Foxp3 gene expression, several conserved non-coding regions have been identified and the role of various transcription factors at these sites has been explored. What emerges is that many factors, some positive, some negative, interact to collectively drive Foxp3 gene expression and then maintain its expression in Foxp3(+) regulatory T cells. TCR signaling is imperative for Foxp3 gene expression and TGF-β is a key cytokine for initiating Foxp3 gene expression in naïve T cells. But other signaling pathways are also known to play a role in properly orchestrating Foxp3 gene expression and regulatory T cell expansion. Here we review the recent progress in understanding the complex molecular events that drive Foxp3 gene expression and allow functional regulatory T cells to develop.

T-regulatory cells in primary immune deficiencies

PURPOSE OF REVIEW

To summarize studies on the development and function of T-regulatory (TR) cells in primary immune deficiencies (PIDs).

RECENT FINDINGS

PIDs are associated with high rates of autoimmunity. TR cells, which are critical to the control of autoimmunity, appear involved in the pathogenesis of PID-related autoimmunity. A number of PIDs, including Omenn's syndrome and Wiskott-Aldrich syndrome, have been associated with impaired production and/or function of thymus-derived (natural) TR cells. Recently defined primary immunodeficiencies, including Stim1 deficiency, IL-10 receptor deficiency, and xIAP deficiency, have been associated with defects in TR cells. De-novo generated TR cells from peripheral CD4 conventional T cells is impaired in the hyper IgE syndrome.

SUMMARY

Gene defects underlying PIDs may also compromise the TR cell, leading to breakdown of peripheral tolerance.

Gut-tropic T cells that express integrin α4β7 and CCR9 are required for induction of oral immune tolerance in mice

BACKGROUND & AIMS

Induction of oral immune tolerance (OT) blocks proinflammatory responses to orally administered antigens and might be used to treat autoimmune conditions. We investigated whether gut-tropic T cells that express the integrin α4β7 and the chemokine receptor CCR9 are required for OT.

METHODS

Skin delayed-type hypersensitivity and experimental autoimmune encephalomyelitis were used to monitor OT in mice. To assess the role of receptors that mediate localization of lymphocytes to the gut (gut-homing receptors) in induction of OT, we studied CCR9(-/-) and β7(-/-) mice and also blocked the α4β7 ligand MAdCAM-1 in wild-type mice. We used DEREG and Scurfy mice to assess the role of Foxp3(+) regulatory T cells (Treg) and IL-10(-/-) and IL-10Rβ(-/-) mice to examine the role of interleukin (IL)-10 in induction of OT.

RESULTS

OT could not be induced in CCR9(-/-) or β7(-/-) mice, or when MAdCAM-1 was blocked in wild-type mice, indicating that gut-homing receptors are required for oral tolerization. Consistent with the role of all-trans retinoic acid in inducing gut-homing T cells, OT could not be induced in mice depleted of vitamin A. OT was rescued in CCR9(-/-) mice following adoptive transfer of wild-type T cells, but not CCR9(-/-) or β7(-/-) T cells. Gut-homing T cells are therefore necessary and sufficient to induce OT. Wild-type Treg and IL-10 were required to restore OT to CCR9(-/-) mice, indicating that homing and functional differentiation of IL-10-producing Treg in the gut is required for OT. Conversely, transfer of CCR9(-/-) or β7(-/-) T cells to wild-type mice partially inhibited OT.

CONCLUSIONS

Expression of CCR9 and α4β7 on T cells and their subsequent localization to the gut is required for induction of OT in mice. Therapies designed to block gut-homing receptors might, under some conditions, interfere with normal tolerogenic mechanisms in the intestinal mucosa.

Microbiota in autoimmunity and tolerance

The composition of a host's intestinal microbiota directs the type of mucosal and systemic immune responses by affecting the proportion and number of functionally distinct T cell subsets. In particular, the microbiota composition affects the differentiation of intestinal Th17 cells and Foxp3(+) regulatory T cells, both of which play critical roles in maintaining mucosal barrier functions and in controlling immunological homeostasis. In this review, we discuss the recent advances in our understanding of how the intestinal microbiota affects T cell differentiation and host susceptibility to autoimmune disease.

Vitamin A and immune regulation: role of retinoic acid in gut-associated dendritic cell education, immune protection and tolerance

The vitamin A (VA) metabolite all-trans retinoic acid (RA) plays a key role in mucosal immune responses. RA is produced by gut-associated dendritic cells (DC) and is required for generating gut-tropic lymphocytes and IgA-antibody-secreting cells (IgA-ASC). Moreover, RA modulates Foxp3(+) regulatory T cell (T(REG)) and Th17 effector T cell differentiation. Thus, although RA could be used as an effective "mucosal adjuvant" in vaccines, it also appears to be required for establishing intestinal immune tolerance. Here we discuss the roles proposed for RA in shaping intestinal immune responses and tolerance at the gut mucosal interface. We also focus on recent data exploring the mechanisms by which gut-associated DC acquire RA-producing capacity.

Th17 response and inflammatory autoimmune diseases

The proinflammatory activity of T helper 17 (Th17) cells can be beneficial to the host during infection. However, uncontrolled or inappropriate Th17 activation has been linked to several autoimmune and autoinflammatory pathologies. Indeed, preclinical and clinical data show that Th17 cells are associated with several autoimmune diseases such as arthritis, multiple sclerosis, psoriasis, and lupus. Furthermore, targeting the interleukin-17 (IL-17) pathway has attenuated disease severity in preclinical models of autoimmune diseases. Interestingly, a recent report brings to light a potential role for Th17 cells in the autoinflammatory disorder adult-onset Still's disease (AOSD). Whether Th17 cells are the cause or are directly involved in AOSD remains to be shown. In this paper, we discuss the biology of Th17 cells, their role in autoimmune disease development, and in AOSD in particular, as well as the growing interest of the pharmaceutical industry in their use as therapeutic targets.

Role of interleukin-10 in breast cancer

Cytokines are low molecular weight regulatory proteins or glycoprotein that modulates the intensity and duration of immune response by stimulating or inhibiting the activation, proliferation, and/or differentiation of target cells. Different cytokines are known to have diverse role in breast cancer initiation and progression. Interleukin-10 (IL-10), a pleiotropic anti-inflammatory cytokine, induces immunosuppression and assists in escape from tumor immune surveillance. Like several other cytokines, IL-10 also can exert dual proliferative and inhibitory effect on breast tumor cells indicating a complex role of IL-10 in breast cancer initiation and progression. In this review, we tried to put together a comprehensive current view on significance of IL-10 in promotion, inhibition, and importance as prognosticator in breast cancer based on in vitro, in vivo, and clinical evidences. For literature collection, we conducted PubMed search with keywords "IL-10" and "breast cancer".

Molecular mechanisms underlying the regulation and functional plasticity of FOXP3(+) regulatory T cells

CD4(+) CD25(+) regulatory T (Treg) cells engage in the maintenance of immunological self-tolerance and homeostasis by limiting aberrant or excessive inflammation. The transcription factor forkhead box P3 (FOXP3) is critical for the development and function of Treg cells. The differentiation of the Treg cell lineage is not terminal, as developmental and functional plasticity occur through the sensing of inflammatory signals in the periphery. Here, we review the recent progress in our understanding of the molecular mechanisms underlying the regulation and functional plasticity of CD4(+) CD25(+) FOXP3(+) Treg cells, through the perturbation of FOXP3 and its complex at a transcriptional, translational and post-translational level.

Two modes of immune suppression by Foxp3(+) regulatory T cells under inflammatory or non-inflammatory conditions

Foxp3-expressing regulatory T cells (Tregs) play a crucial role in maintaining immune tolerance and homeostasis. One of the key issues for understanding Treg immunobiology is to determine how they suppress excessive or aberrant immune responses. Although a number of molecules have been reported to contribute to Treg suppressive function, the importance and precise role of each molecule is not clear. In this review, we propose and discuss that two modes of suppression can be distinguished. In the physiological and steady state, activation of naïve T cells can be suppressed by natural Tregs via deprivation of activation signals including CD28 signal and IL-2 from antigen-reactive T cells, keeping the latter in a naïve state in lymphoid tissues. These deprivation mechanisms are transiently abrogated in inflammatory conditions, allowing T cells to respond to antigen. In contrast, in highly inflammatory environments, for example, in microbial infection, activated Tregs acquire the capacity to kill or inactivate effector T cells and antigen-presenting cells, for example, via granzyme/perforin formation and IL-10 secretion, thereby actively damping excessive immune responses. Understanding these processes will help effectively controlling physiological and pathological immune responses via Tregs.

Regulatory T cells inhibit acute IFN-γ synthesis without blocking T-helper cell type 1 (Th1) differentiation via a compartmentalized requirement for IL-10

CD4(+)CD25(+)Forkhead box P3 (Foxp3)(+) regulatory T cells (Tregs) control immune responses to self and foreign antigens in secondary lymphoid organs and at tissue sites of inflammation. Tregs can modify the function of many immune cells and have been proposed to block early proliferation, differentiation, and effector function. Acute ablation of Tregs has revealed rapid cytokine production immediately after Treg removal, suggesting that Tregs may regulate effector function acutely rather than regulating the programming for immune function. We developed in vitro and in vivo models that enabled the direct test of Treg regulation of T-helper cell type 1 (Th1) differentiation. CD28 signaling is known to abrogate Treg suppression of IL-2 secretion and proliferation, but our studies show that Treg suppression of IFN-γ during Th1 priming proceeds despite enhanced CD28 signaling. Importantly, during Th1 differentiation, Tregs inhibited early IFN-γ transcription without disrupting expression of Th1-specific T-box transcription factor (Tbet) and Th1 programming. Acute shutoff of effector cytokine production by Tregs was selective for IFN-γ but not TNF-α and was independent of TGF-β and Epstein-Barr virus-induced gene 3. In vivo, Tregs potently controlled CD4 IFN-γ and CD4 effector cell expansion in the lymph node (four- to fivefold reduction) but not Th1 programming, independent of IL-10. Tregs additionally reduced CD4 IFN-γ in the inflamed dermis (twofold reduction) dependent on their production of IL-10. We propose a model for Treg inhibition of effector function based on acute cytokine regulation. Interestingly, Tregs used different regulatory mechanisms to regulate IFN-γ (IL-10-dependent or -independent) subject to the target T-cell stage of activation and its tissue location.

The role of tumour necrosis factor-α and tumour necrosis factor receptor signalling in inflammation-associated systemic genotoxicity

Chronic inflammatory diseases are characterised by systemically elevated levels of tumour necrosis factor (TNF)-α, a proinflammatory cytokine with pleiotropic downstream effects. We have previously demonstrated increased genotoxicity in peripheral leukocytes and various tissues in models of intestinal inflammation. In the present study, we asked whether TNF-α is sufficient to induce DNA damage systemically, as observed in intestinal inflammation, and whether tumour necrosis factor receptor (TNFR) signalling would be necessary for the resultant genotoxicity. In the wild-type mice, 500 ng per mouse of TNF-α was sufficient to induce DNA damage to multiple cell types and organs 1-h post-administration. Primary splenic T cells manifested TNF-α-induced DNA damage in the absence of other cell types. Furthermore, TNFR1(-/-)TNFR2(-/-) mice demonstrated decreased systemic DNA damage in a model of intestinal inflammation and after TNF-α injection versus wild-type mice, indicating the necessity of TNFR signalling. Nuclear factor (NF)-κB inhibitors were also able to decrease damage induced by TNF-α injection in wild-type mice. When TNF-α administration was combined with interleukin (IL)-1β, another proinflammatory cytokine, DNA damage persisted for up to 24 h. When combined with IL-10, an anti-inflammatory cytokine, decreased genotoxicity was observed in vivo and in vitro. TNF-α/TNFR-mediated signalling is therefore sufficient and plays a large role in mediating DNA damage to various cell types, subject to modulation by other cytokines and their mediators.

Role of microbiota in postnatal maturation of intestinal T-cell responses

PURPOSE OF REVIEW

Taking advantage of their rapid growth and capacity for continuous genetic adaptation, prokaryotes have colonized all possible ecological environments on earth, including the body surfaces of eukaryotes and their gastrointestinal tract. The mammalian gut contains a complex community of 10 bacteria with a meta-genome containing 1500-fold more genes than the human genome. The forces that control the relationships between eukaryotic hosts and their intestinal bacterial symbionts have, thus, become a major focus of interest.

RECENT FINDINGS

Recent data have highlighted how the dialogue between mammalian hosts and their microbiota stimulates the postnatal maturation of an efficient intestinal barrier that promotes niche colonization by symbiotic bacteria and opposes colonization by pathogens. Herein, we review microbiota-induced T-cell responses and discuss how individual bacteria may shape the balance between regulatory and inflammatory responses. We will also show how host factors might influence the outcome of gut immune responses and affect the structure of the microbiota.

SUMMARY

Deciphering host-microbiota reciprocal influence may not only help in understanding the recent outburst of intestinal inflammatory diseases but also point to strategies able to maintain or restore intestinal homeostasis.

Highlights of 10 years of immunology in Nature Reviews Immunology

As Nature Reviews Immunology reaches its 10(th) anniversary, the authors of one of the top-cited articles from each year take a trip down memory lane. We've asked them to look back on the state of research at the time their Review was published, to consider why the article has had the impact it has and to discuss the future directions of their field. This Viewpoint article provides an interesting snapshot of some of the fundamental advances in immunology over the past 10 years. Highlights include our improved understanding of Toll-like receptor signalling, and of immune regulation mediated by regulatory T cells, indoleamine 2,3-dioxygenase, myeloid-derived suppressor cells and interleukin-10. The complexities in the development and heterogeneity of macrophages, dendritic cells and T helper cells continue to engage immunologists, as do the immune processes involved in diseases such as atherosclerosis. We look forward to what the next 10 years of immunology research may bring.

The many faces of Th17 cells

Th17 cells have been shown to be strong inducers of tissue inflammation and autoimmune diseases. However, not all Th17 cells are pathogenic and increasing data suggest that Th17 cells may come in different flavors. Thus, Th17 cells cannot be described using a narrow schematic, but instead Th17 cells comprise a wide spectrum with a range of effector phenotypes. Here, we review the key factors that generate such diversity, as well as the cytokines and transcription factors that are differentially expressed in pathogenic and nonpathogenic Th17 cells. This new knowledge can be used to identify molecules that make Th17 cells pathogenic and determine how these cells could be targeted to suppress autoimmune diseases.

Interpreting mixed signals: the cell's cytokine conundrum

Cytokines are essential for the activation, differentiation and control of the immune system. Many cytokines, alone or in combination with other cytokines, have multiple functions and can often act on many different cell types with distinct developmental or functional consequences. Despite the myriad of cytokines and cytokine receptors, there are relatively few signaling molecules that transduce these diverse cytokine signals. In this review, we will discuss the potential mechanisms used by cytokines to mediate distinct cellular outcomes from a small number of signaling molecules. Understanding this paradigm in cytokine signaling can aid in the development of potential therapeutic approaches involving cytokine targeting or use.

Distinct regulatory CD4+T cell subsets; differences between naïve and antigen specific T regulatory cells

Effector T cells have functional subpopulations with distinct cytokine, cytokine receptor, chemokine receptor and transcription factors. We review how activation of antigen specific Treg induces expression of cytokines, cytokine receptors and chemokine receptors depending upon the effector lineage they are activated by. Activated Treg express receptors that are directly related to the effector T cell lineage. Other classes of Treg are induced in the periphery from effector lineage CD4(+)CD25(-)FOXP3(-)CD127(high)T cells, either by IL-10 or TGF-β or by association with activated CD4(+)CD25(+)FOXP3(+)Treg. Thus Treg are produced and adapt to the specific immune inflammatory environment they are activated within. Activated Treg produce different molecules to mediate suppression, which are tailored to the immune response they are activated by and control.

TGF-β in transplantation tolerance

TGF-β is a cytokine required for the induction and maintenance of transplantation tolerance in animal models. TGF-β mediates anti-inflammatory effects by acting on many immune cell-types. Central for transplantation tolerance is the role for TGF-β in the induction of Foxp3 and regulatory capacity in CD4(+) T cells. Recently, however, the general anti-inflammatory role of TGF-β in CD4(+) T cell polarization was questioned by the discovery that, in the presence of inflammatory cytokines such as IL-6 or IL-1, TGF-β drives the differentiation of Th17 cells associated with transplant rejection. A better understanding of the factors determining TGF-β production and activation, Foxp3 induction and Treg stability is vital for the development of tolerogenic strategies in transplantation.

Contribution of cytokines to pathology and protection in virus infection

Acute and chronic viral infections greatly contribute to global health burden. While concerted action of multiple elements of the immune system help the host cope with most viruses, some infections lead to host damage or death. Cytokines are central drivers and controllers of both immune-mediated virus elimination and of immunopathology. Here, we review recent progress in understanding the protective and damaging roles in viral infections of cytokines and chemokines associated with innate, regulatory, and Th1, Th2 and Th17 responses.

At 17, in-10's passion need not inflame

In this issue of Immunity, Chaudhry et al. (2011) and Huber et al. (2011) report that control of Th17 cell responses during colonic inflammation requires direct signaling by IL-10 in regulatory T cells and Th17 cells.