Generation of pathogenic T(H)17 cells in the absence of TGF-β signalling

TGF-β in Th17 cell development: the truth is out there

As Th17 cell developmental requirements continue to be studied, Gutcher et al. (2011) demonstrate in this issue of Immunity that autocrine TGF-β cytokine promotes Th17 cell development and maintenance.

Role of IL-1 beta in the development of human T(H)17 cells: lesson from NLPR3 mutated patients

BACKGROUND

T helper 17 cells (T(H)-17) represent a lineage of effector T cells critical in host defence and autoimmunity. In both mouse and human IL-1β has been indicated as a key cytokine for the commitment to T(H)-17 cells. Cryopyrin-associated periodic syndromes (CAPS) are a group of inflammatory diseases associated with mutations of the NLRP3 gene encoding the inflammasome component cryopyrin. In this work we asked whether the deregulated secretion of IL-1β secondary to mutations characterizing these patients could affect the IL-23/IL-17 axis.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 11 CAPS, 26 systemic onset juvenile idiopathic arthritis (SoJIA) patients and 20 healthy controls were analyzed. Serum levels of IL-17 and IL-6 serum were assessed by ELISA assay. Frequency of T(H)17 cells was quantified upon staphylococcus enterotoxin B (SEB) stimulation. Secretion of IL-1β, IL-23 and IL-6 by monocyte derived dendritic cells (MoDCs), were quantified by ELISA assay. A total of 8 CAPS and 11 SoJIA patients were also analysed before and after treatment with IL-1β blockade. Untreated CAPS patients showed significantly increased IL-17 serum levels as well as a higher frequency of T(H)17 compared to control subjects. On the contrary, SoJIA patients displayed a frequency of T(H)17 similar to normal donors, but were found to have significantly increased serum level of IL-6 when compared to CAPS patients or healthy donors. Remarkably, decreased IL-17 serum levels and T(H)17 frequency were observed in CAPS patients following in vivo IL-1β blockade. On the same line, MoDCs from CAPS patients exhibited enhanced secretion of IL-1β and IL-23 upon TLRs stimulation, with a reduction after anti-IL-1 treatment.

CONCLUSION/SIGNIFICANCE

These findings further support the central role of IL-1β in the differentiation of T(H)17 in human inflammatory conditions.

Genomic views of STAT function in CD4+ T helper cell differentiation

Signal transducer and activator of transcription (STAT) proteins are well known for their essential roles in transmitting cytokine-mediated signals and specifying T helper (T(H)) cell differentiation. Recent technological advances have revealed that STAT proteins have broad and complex roles in gene regulation and epigenetic control, including important roles as functional repressors. However, the challenge of how to link signal transduction, nucleosome biology and gene regulation remains. The relevance of tackling this problem is highlighted by genome-wide association studies that link cytokine signalling and STATs to various autoimmune or immune deficiency disorders. Defining exactly how extrinsic signals control the specification and plasticity of T(H) cells will provide important insights and perhaps therapeutic opportunities in these diseases.

How do immune cells overcome the blood-brain barrier in multiple sclerosis?

The presence of the blood-brain barrier (BBB) restricts the movement of soluble mediators and leukocytes from the periphery to the central nervous system (CNS). Leukocyte entry into the CNS is nonetheless an early event in multiple sclerosis (MS), an inflammatory disorder of the CNS. Whether BBB dysfunction precedes immune cell infiltration or is the consequence of perivascular leukocyte accumulation remains enigmatic, but leukocyte migration modifies BBB permeability. Immune cells of MS subjects express inflammatory cytokines, reactive oxygen species (ROS) and enzymes that can facilitate their migration to the CNS by influencing BBB function, either directly or indirectly. In this review, we describe how immune cells from the peripheral blood overcome the BBB and promote CNS inflammation in MS through BBB disruption.

Proinflammatory cytokines in the pathogenesis of inflammatory bowel diseases

The cytokine responses characterizing the inflammatory bowel diseases are the key pathophysiologic elements that govern the initiation, evolution, and, ultimately, the resolution of these forms of inflammation. Studies during the last 2 decades now provide a detailed (but not yet complete) picture of the nature of these responses. The first tier of cytokine responses are governed by the T-cell differentiation patterns dominating the disease. In Crohn's disease, the major cytokines arise from T-helper cell (Th) 1 and Th17 CD4(+) T-cell differentiation and consist of interferon-γ and interleukin (IL)-17/IL-22 generated by these types of differentiation. The relative importance of these cytokines to Crohn's inflammation is still unclear, although evidence is mounting that interferon-γ is primus inter pare (first among equals). In contrast, in ulcerative colitis, a Th2-like differentiation process is paramount, which results in expansion of natural killer T cells producing IL-13 (and perhaps IL-5). These disease-specific cytokine patterns give rise to a second tier of cytokines that span the Th1/Th17-Th2 divide and act as upstream facilitators and downstream mediators of inflammation. These cytokines include the well-known tumor necrosis factor-α, IL-1β, IL-6 triumphirate, as well as a more recently studied cytokine known as TL1A (tumor necrosis factor-like ligand). In this review, we will explore this cytokine landscape with the view of providing an understanding of how recent and future anticytokine therapies actually function.

RORγt drives production of the cytokine GM-CSF in helper T cells, which is essential for the effector phase of autoimmune neuroinflammation

Although the role of the T(H)1 and T(H)17 subsets of helper T cells as disease mediators in autoimmune neuroinflammation remains a subject of some debate, none of their signature cytokines are essential for disease development. Here we report that interleukin 23 (IL-23) and the transcription factor RORγt drove expression of the cytokine GM-CSF in helper T cells, whereas IL-12, interferon-γ (IFN-γ) and IL-27 acted as negative regulators. Autoreactive helper T cells specifically lacking GM-CSF failed to initiate neuroinflammation despite expression of IL-17A or IFN-γ, whereas GM-CSF secretion by Ifng(-/-)Il17a(-/-) helper T cells was sufficient to induce experimental autoimmune encephalomyelitis (EAE). During the disease effector phase, GM-CSF sustained neuroinflammation via myeloid cells that infiltrated the central nervous system. Thus, in contrast to all other known helper T cell-derived cytokines, GM-CSF serves a nonredundant function in the initiation of autoimmune inflammation regardless of helper T cell polarization.

The encephalitogenicity of T(H)17 cells is dependent on IL-1- and IL-23-induced production of the cytokine GM-CSF

Interleukin 17 (IL-17)-producing helper T cells (T(H)17 cells) require exposure to IL-23 to become encephalitogenic, but the mechanism by which IL-23 promotes their pathogenicity is not known. Here we found that IL-23 induced production of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) in T(H)17 cells and that GM-CSF had an essential role in their encephalitogenicity. Our findings identify a chief mechanism that underlies the important role of IL-23 in autoimmune diseases. IL-23 induced a positive feedback loop whereby GM-CSF secreted by T(H)17 cells stimulated the production of IL-23 by antigen-presenting cells. Such cross-regulation of IL-23 and GM-CSF explains the similar pattern of resistance to autoimmunity when either of the two cytokines is absent and identifies T(H)17 cells as a crucial source of GM-CSF in autoimmune inflammation.

Mechanisms controlling Th17 cytokine expression and host defense

Th17 cells contribute to mucosal immunity by stimulating epithelial cells to induce antimicrobial peptides, granulopoiesis, neutrophil recruitment, and tissue repair. Recent studies have identified important roles for commensal microbiota and Ahr ligands in stabilizing Th17 gene expression in vivo, linking environmental cues to CD4 T cell polarization. Epigenetic changes that occur during the transition from naïve to effector Th17 cells increase the accessibility of il17a, il17f, and il22 loci to transcription factors. In addition, Th17 cells maintain the potential for expressing T-bet, Foxp3, or GATA-binding protein-3, explaining their plastic nature under various cytokine microenvironments. Although CD4 T cells are major sources of IL-17 and IL-22, innate cell populations, including γδ T cells, NK cells, and lymphoid tissue-inducer cells, are early sources of these cytokines during IL-23-driven responses. Epithelial cells and fibroblasts are important cellular targets for IL-17 in vivo; however, recent data suggest that macrophages and B cells are also stimulated directly by IL-17. Thus, Th17 cells interact with multiple populations to facilitate protection against intracellular and extracellular pathogens.

Gut microbiota, probiotics and inflammatory bowel disease

The colonization of humans with commensals is critical for our well-being. This tightly regulated symbiotic relationship depends on the flora and an intact mucosal immune system. A disturbance of either compound can cause intestinal inflammation. This review summarizes extrinsic and intrinsic factors contributing to intestinal dysbiosis and inflammatory bowel disease.

Digoxin and its derivatives suppress TH17 cell differentiation by antagonizing RORγt activity

CD4(+) T helper lymphocytes that express interleukin-17 (T(H)17 cells) have critical roles in mouse models of autoimmunity, and there is mounting evidence that they also influence inflammatory processes in humans. Genome-wide association studies in humans have linked genes involved in T(H)17 cell differentiation and function with susceptibility to Crohn's disease, rheumatoid arthritis and psoriasis. Thus, the pathway towards differentiation of T(H)17 cells and, perhaps, of related innate lymphoid cells with similar effector functions, is an attractive target for therapeutic applications. Mouse and human T(H)17 cells are distinguished by expression of the retinoic acid receptor-related orphan nuclear receptor RORγt, which is required for induction of IL-17 transcription and for the manifestation of T(H)17-dependent autoimmune disease in mice. By performing a chemical screen with an insect cell-based reporter system, we identified the cardiac glycoside digoxin as a specific inhibitor of RORγt transcriptional activity. Digoxin inhibited murine T(H)17 cell differentiation without affecting differentiation of other T cell lineages and was effective in delaying the onset and reducing the severity of autoimmune disease in mice. At high concentrations, digoxin is toxic for human cells, but non-toxic synthetic derivatives 20,22-dihydrodigoxin-21,23-diol and digoxin-21-salicylidene specifically inhibited induction of IL-17 in human CD4(+) T cells. Using these small-molecule compounds, we demonstrate that RORγt is important for the maintenance of IL-17 expression in mouse and human effector T cells. These data indicate that derivatives of digoxin can be used as chemical templates for the development of RORγt-targeted therapeutic agents that attenuate inflammatory lymphocyte function and autoimmune disease.

The yin and yang of signaling in Tregs and TH17 cells

Substantial advances in our understanding of the developmental and functional relationship between regulatory T cells (T(regs)) and T helper 17 (T(H)17) cells and their potential clinical applications have been made. In response to these breakthroughs, the second international conference entitled "China Tregs/Th17 2010 Shanghai Conference," held in Shanghai, China, was dedicated to this topic. Various types of T(regs) and T(H)17 cells, as well as their relevant cytokines, were discussed. Here, we summarize some of the findings shared at the conference, specifically focusing on the biology of T(H)17 cells, including interleukin-17 (IL-17)-producing innate cells, T(regs), and the factors that control the critical balance between T(regs) and cells of the T(H)17 lineage.

Marked induction of c-Maf protein during Th17 cell differentiation and its implication in memory Th cell development

Until recently, effector T helper (Th) cells have been classified into two subsets, Th1 and Th2 cells. Since the discovery of Th17 cells, which produce IL-17, much attention has been given to Th17 cells, mainly because they have been implicated in the pathogenesis of various inflammatory diseases. We have performed transcriptome analysis combined with factor analysis and revealed that the expression level of c-Maf, which is considered to be important for Th2 differentiation, increases significantly during the course of Th17 differentiation. The IL-23 receptor (IL-23R), which is important for Th17 cells, is among putative transcriptional targets of c-Maf. Interestingly, the analysis of c-Maf transgenic Th cells revealed that the overexpression of c-Maf did not lead to the acceleration of the early stage of Th17 differentiation but rather to the expansion of memory phenotype cells, particularly with Th1 and Th17 traits. Consistently, mouse wild-type memory Th cells expressed higher mRNA levels of c-Maf, IL-23R, IL-17, and IFN-γ than control cells; in contrast, Maf(-/-) memory Th cells expressed lower mRNA levels of those molecules. Thus, we propose that c-Maf is important for the development of memory Th cells, particularly memory Th17 cells and Th1 cells.

Modulation of innate and adaptive immune responses by tofacitinib (CP-690,550)

Inhibitors of the JAK family of nonreceptor tyrosine kinases have demonstrated clinical efficacy in rheumatoid arthritis and other inflammatory disorders; however, the precise mechanisms by which JAK inhibition improves inflammatory immune responses remain unclear. In this study, we examined the mode of action of tofacitinib (CP-690,550) on JAK/STAT signaling pathways involved in adaptive and innate immune responses. To determine the extent of inhibition of specific JAK/STAT-dependent pathways, we analyzed cytokine stimulation of mouse and human T cells in vitro. We also investigated the consequences of CP-690,550 treatment on Th cell differentiation of naive murine CD4(+) T cells. CP-690,550 inhibited IL-4-dependent Th2 cell differentiation and interestingly also interfered with Th17 cell differentiation. Expression of IL-23 receptor and the Th17 cytokines IL-17A, IL-17F, and IL-22 were blocked when naive Th cells were stimulated with IL-6 and IL-23. In contrast, IL-17A production was enhanced when Th17 cells were differentiated in the presence of TGF-β. Moreover, CP-690,550 also prevented the activation of STAT1, induction of T-bet, and subsequent generation of Th1 cells. In a model of established arthritis, CP-690,550 rapidly improved disease by inhibiting the production of inflammatory mediators and suppressing STAT1-dependent genes in joint tissue. Furthermore, efficacy in this disease model correlated with the inhibition of both JAK1 and JAK3 signaling pathways. CP-690,550 also modulated innate responses to LPS in vivo through a mechanism likely involving the inhibition of STAT1 signaling. Thus, CP-690,550 may improve autoimmune diseases and prevent transplant rejection by suppressing the differentiation of pathogenic Th1 and Th17 cells as well as innate immune cell signaling.

Regulating Il9 transcription in T helper cells

T helper (Th) cells are crucial for the development of immunity to infections and inflammatory disease. The acquisition of specific cytokine-secreting profiles, primed by the cytokine microenvironment, is required for effector function of Th cells. The most recent addition to the growing list of effector subsets are Th9 cells that secrete IL-9. In this review, we propose a model for the transcriptional regulation of the Il9 gene in IL-9-expressing T cells and the relatedness of this subset to other Th phenotypes. We suggest that transcription factors restricted to certain Th subsets and common among several subsets might play a role in the plasticity of Th9 cells.

Mouse and human intestinal immunity: same ballpark, different players; different rules, same score

The study of animal immune physiology and animal models of human disease have accelerated many aspects of translational research by allowing direct, definitive investigations. In particular, the use of mice has allowed genetic manipulation, adoptive transfer, immunization, and focused cell and tissue sampling, which would obviously be unthinkable for studies in humans. However, the disease relevance of some animal models may be uncertain and difficulties in interpretation may occur as a consequence of immunological differences between the two species. In this review, we will consider general differences in the structure and development of human and mouse mucosal lymphoid microenvironments and then discuss species differences in mucosal B- and T-cell biology that relate to the current concepts of intestinal immune function.

Opposing regulation of the locus encoding IL-17 through direct, reciprocal actions of STAT3 and STAT5

Interleukin 2 (IL-2), a cytokine linked to human autoimmune disease, limits IL-17 production. Here we found that deletion of the gene encoding the transcription factor STAT3 in T cells abrogated IL-17 production and attenuated autoimmunity associated with IL-2 deficiency. Whereas STAT3 induced IL-17 and the transcription factor RORγt and inhibited the transcription factor Foxp3, IL-2 inhibited IL-17 independently of Foxp3 and RORγt. STAT3 and STAT5 bound to multiple common sites across the locus encoding IL-17. The induction of STAT5 binding by IL-2 was associated with less binding of STAT3 at these sites and the inhibition of associated active epigenetic marks. 'Titration' of the relative activation of STAT3 and STAT5 modulated the specification of cells to the IL-17-producing helper T cell (T(H)17 cell) subset. Thus, the balance rather than the absolute magnitude of these signals determined the propensity of cells to make a key inflammatory cytokine.

Increased activity of Th-17 and Th-9 lymphocytes and a skewing of the post-thymic differentiation pathway are seen in Alzheimer's disease

Inflammatory mediators are responsible for the neuroinflammation observed in Alzheimer's disease (AD), a phenomenon that might be the culprit of disease or, possibly, a reaction to pathology. To better investigate inflammation in AD we performed an extensive immunophenotypic and functional analysis of amyloid-beta (Aβ) stimulated T lymphocytes in patients with a diagnosis of AD comparing data to those obtained in individuals with mild cognitive impairment (MCI) or aged-matched healthy individuals (HC). Results showed that IL-21- and IL-9-producing Aβ stimulated CD4(+) T cells, as well as IL-23- and IL-6-producing monocytes and CD4(+) T cells expressing the RORγ and NFATc1 transcriptional factors (TF), were significantly increased, whereas IL-10-producing monocytes were decreased in AD. Notably, GATA-3 TF-expressing CD4(+) T lymphocytes were significantly increased in MCI alone. Analysis of the post-thymic differentiation pathway indicated that Aβ specific naïve and central memory CD4(+) T lymphocytes were diminished whereas effector memory and terminally differentiated CD4(+) T lymphocytes were increased in AD and MCI compared to HC. Data herein indicate that cytokines (IL-21, IL-6, IL-23) and TF (RORγ) involved in the differentiation of Th-17 cells), as well as cytokines (IL-21, IL-22) generated by such cells, and IL-9, produced by Th-9 cells, are significantly increased in AD. This is accompanied by a shift of post-thymic differentiation pathways favoring the accumulation of differentiated, effector T lymphocytes. These data shed light on the nature of AD-associated neuroinflammation. A better understanding of the complexity of this phenomenon could facilitate the search for novel therapeutic strategies.

The pro- and anti-inflammatory properties of the cytokine interleukin-6

Interleukin-6 is a cytokine not only involved in inflammation and infection responses but also in the regulation of metabolic, regenerative, and neural processes. In classic signaling, interleukin-6 stimulates target cells via a membrane bound interleukin-6 receptor, which upon ligand binding associates with the signaling receptor protein gp130. Gp130 dimerizes, leading to the activation of Janus kinases and subsequent phosphorylation of tyrosine residues within the cytoplasmic portion of gp130. This leads to the engagement of phosphatase Src homology domains containing tyrosin phosphatase-2 (SHP-2) and activation of the ras/raf/Mitogen-activated protein (MAP) kinase (MAPK) pathway. In addition, signal transducer and activator of transcription factors are recruited, which are phosphorylated, and consequently dimerize whereupon they translocate into the nucleus and activate target genes. Interestingly, only few cells express membrane bound interleukin-6 receptor whereas all cells display gp130 on the cell surface. While cells, which only express gp130, are not responsive to interleukin-6 alone, they can respond to a complex of interleukin-6 bound to a naturally occurring soluble form of the interleukin-6 receptor. Therefore, the generation of soluble form of the interleukin-6 receptor dramatically enlarges the spectrum of interleukin-6 target cells. This process has been named trans-signaling. Here, we review the involvement of both signaling modes in the biology of interleukin-6. It turns out that regenerative or anti-inflammatory activities of interleukin-6 are mediated by classic signaling whereas pro-inflammatory responses of interleukin-6 are rather mediated by trans-signaling. This is important since therapeutic blockade of interleukin-6 by the neutralizing anti-interleukin-6 receptor monoclonal antibody tocilizumab has recently been approved for the treatment of inflammatory diseases. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Role of Th17 cells and IL-17 in lung transplant rejection

In the past decade, advances in immunology have led to the recognition that T cell differentiation is not simply Th1 or Th2 but involves differentiation to other subsets, such as T regulatory cells, T follicular helper cells, and Th17 cells. Th17 cells, characterized by production of IL-17, IL-22, and IL-21, have been implicated in the pathogenesis of autoimmune diseases, like rheumatoid arthritis and multiple sclerosis, but also play an important role in host defense and mucosal immunity. IL-17, with its pleiotropic effects on stromal cells, as well as hematopoietic cells, has long been recognized as a possible mediator of rejection after lung transplantation. Recent data have implicated IL-17 and Th17 cells in the development of autoimmunity and chronic rejection after lung transplantation in both animal models and humans. In this review, we will discuss the current data on Th17 and the prospects for the future for lung transplantation.

Fate mapping of IL-17-producing T cells in inflammatory responses

We describe a reporter mouse strain designed to fate-map cells that have activated IL-17A. Here we show that T_H17 cells show distinct plasticity in different inflammatory settings. Chronic inflammatory conditions in EAE caused a switch to alternative cytokines in T_H17 cells, whereas acute cutaneous infection with Candida albicans, did not result in deviation of T_H17 to alternative cytokine production, although IL-17A production was shut off in the course of the infection. During development of EAE, IFN-γ and other pro-inflammatory cytokines in the spinal cord were produced almost exclusively by ‘ex-T_H17’ cells whose conversion was driven by IL-23. Thus, this model allows relating the actual functional fate of effector T cells to T_H17 developmental origin irrespective of IL-17 expression.

Th17 cells expressing KIR3DL2+ and responsive to HLA-B27 homodimers are increased in ankylosing spondylitis

CD4 Th cells producing the proinflammatory cytokine IL-17 (Th17) have been implicated in a number of inflammatory arthritides including the spondyloarthritides. Th17 development is promoted by IL-23. Ankylosing spondylitis, the most common spondyloarthritis (SpA), is genetically associated with both HLA-B27 (B27) and IL-23R polymorphisms; however, the link remains unexplained. We have previously shown that B27 can form H chain dimers (termed B27(2)), which, unlike classical HLA-B27, bind the killer-cell Ig-like receptor KIR3DL2. In this article, we show that B27(2)-expressing APCs stimulate the survival, proliferation, and IL-17 production of KIR3DL2(+) CD4 T cells. KIR3DL2(+) CD4 T cells are expanded and enriched for IL-17 production in the blood and synovial fluid of patients with SpA. Despite KIR3DL2(+) cells comprising a mean of just 15% of CD4 T in the peripheral blood of SpA patients, this subset accounted for 70% of the observed increase in Th17 numbers in SpA patients compared with control subjects. TCR-stimulated peripheral blood KIR3DL2(+) CD4 T cell lines from SpA patients secreted 4-fold more IL-17 than KIR3DL2(+) lines from controls or KIR3DL2(-) CD4 T cells. Strikingly, KIR3DL2(+) CD4 T cells account for the majority of peripheral blood CD4 T cell IL-23R expression and produce more IL-17 in the presence of IL-23. Our findings link HLA-B27 with IL-17 production and suggest new therapeutic strategies in ankylosing spondylitis/SpA.

Dectin-1 diversifies Aspergillus fumigatus-specific T cell responses by inhibiting T helper type 1 CD4 T cell differentiation

By modifying dendritic cell cytokine production, Dectin-1 suppresses Th1 differentiation in mice infected with the fungal pathogen Aspergillus fumigatus.

Pulmonary infection of mice with Aspergillus fumigatus induces concurrent T helper type 1 (Th1) and Th17 responses that depend on Toll-like receptor/MyD88 and Dectin-1, respectively. However, the mechanisms balancing Th1 and Th17 CD4 T cell populations during infection remain incompletely defined. In this study, we show that Dectin-1 deficiency disproportionally increases Th1 responses and decreases Th17 differentiation after A. fumigatus infection. Dectin-1 signaling in A. fumigatus–infected wild-type mice reduces IFN-γ and IL-12p40 expression in the lung, thereby decreasing T-bet expression in responding CD4 T cells and enhancing Th17 responses. Absence of IFN-γ or IL-12p35 in infected mice or T-bet in responding CD4 T cells enhances Th17 differentiation, independent of Dectin-1 expression, in A. fumigatus–infected mice. Transient deletion of monocyte-derived dendritic cells also reduces Th1 and boosts Th17 differentiation of A. fumigatus–specific CD4 T cells. Our findings indicate that Dectin-1–mediated signals alter CD4 T cell responses to fungal infection by decreasing the production of IL-12 and IFN-γ in innate cells, thereby decreasing T-bet expression in A. fumigatus–specific CD4 T cells and enabling Th17 differentiation.

Interleukin 1 receptor antagonist mediates the beneficial effects of systemic interferon beta in mice: implications for rheumatoid arthritis

OBJECTIVES

Interferon beta (IFNβ) therapy is effective in multiple sclerosis and murine models of arthritis. Surprisingly, systemic IFNβ treatment induces only minimal improvement in rheumatoid arthritis (RA). To explain this paradox, the authors evaluated the mechanism of IFNβ benefit in passive K/BxN arthritis and the effect of IFNβ treatment on RA synovium.

METHODS

Interleukin 10 (IL-10) null, IL-1 receptor antagonist (IL-1Ra) null, IL-1Ra transgenic and wild-type mice were administered K/BxN serum and in some cases treated with IFNβ or normal saline. Clinical response and histological scores were assessed. Gene expression was measured by quantitative PCR. Serum IL-1Ra and IL-6 were measured by ELISA. Paired synovial biopsy specimens from RA patients pre-IFNβ and post-IFNβ treatment (purified natural fibroblast IFNβ (Frone) subcutaneously three times weekly 6 million IU, 12 million IU or 18 million IU) were immunostained for IL-1Ra and IL-10.

RESULTS

Il1rn transgenic mice had an attenuated course of arthritis, whereas Il1rn(-/-) and Il10(-/-) mice had more severe serum transfer arthritis than wild-type mice. Daily IFNβ treatment significantly decreased arthritis severity in Il10(-/-) but not Il1rn(-/-) mice. IFNβ treatment did not reduce the histological scores in Il1rn(-/-) mice or gene expression of articular cytokines and chemokines. Paired synovial biopsy specimens from RA patients treated with IFNβ demonstrated a trend towards increased IL-1Ra and reduced IL-10 expression on day 85 levels compared with pretreatment specimens.

CONCLUSIONS

The anti-inflammatory effects of IFNβ in passive K/BxN arthritis are dependent on IL-1Ra, but not IL-10. Systemic IFNβ treatment in RA increases synovial IL-1Ra production, but also decreases IL-10 production.

T helper cell differentiation more than just cytokines

CD4(+) T helper (T(H)) cells play a critical role in orchestrating a pleiotropy of immune activities against a large variety of pathogens. It is generally thought that this is achieved through the acquisition of highly specialized functions after activation followed by the differentiation into various functional subsets. The differentiation process of naive precursor T(H) cells into defined effector subsets is controlled by cells of the innate immune system and their complex array of effector molecules such as secreted cytokines and membrane bound costimulatory molecules. These provide a unique quantitative or qualitative signal initiating T(H) development, which is subsequently reinforced via T cell-mediated feedback signals and selective survival and proliferative cues, ultimately resulting in the predominance of a particular T cell subset. In recent years, the number of defined T(H)cell subsets has expanded and the once rigid division of labor among them has been blurred with reports of plasticity among the subsets. In this chapter, we summarize and speculate on the current knowledge of the differentiation requirements of T(H) cell lineages, with particular focus on the T(H)17 subset.

The control of adaptive immune responses by the innate immune system

The mammalian immune system comprises an adaptive and an innate component. The innate immune system employs a limited number of germ-line-encoded pattern-recognition receptors (PRRs) that recognize invariant pathogen-associated molecular patterns (PAMPs). In contrast, the adaptive immune system depends on the generation of a diverse repertoire of antigen receptors on T and B lymphocytes and subsequent activation and clonal expansion of cells carrying the appropriate antigen-specific receptors. Induction of adaptive immunity not only depends on direct antigen recognition by the antigen receptors but also relies on essential signals that are delivered by the innate immune system. In recent years, we have witnessed the discovery of a still expanding array of different PRR systems that govern the generation of adaptive immunity. Here, we review our current understanding of innate control of adaptive immunity. In particular, we discuss how PRRs initiate adaptive immune responses in general, discuss specific mechanisms that shape the ensuing T and B cell responses, and highlight open questions that are still awaiting answers.

T-bet represses T(H)17 differentiation by preventing Runx1-mediated activation of the gene encoding RORγt

Overactive T_H17 responses are tightly linked to the development of autoimmunity, yet the factors that negatively regulate differentiation of this lineage remain unknown. Here, we report that T-bet suppresses the development of the T_H17 cell lineage by inhibiting the transcription of Rorc. T-bet interacts with the transcription factor Runx1 and this interaction blocks Runx1-mediated transactivation of Rorc. T-bet residue Tyr³⁰⁴ is required for T-bet-Runx1 complex formation, for blocking Runx1 activity and for inhibiting the T_H17 differentiation program. These data reinforce the concept of master regulators that shape immune responses by simultaneously activating one genetic program while silencing the activity of competing regulators in a common progenitor cell.

FOXP3 and RORγt: transcriptional regulation of Treg and Th17

FOXP3(+)CD4(+)CD25(+) Regulatory T (Treg) cells and IL-17 producing helper T cells (Th17) are critical subsets of T cells which play essential roles in immune homeostasis. The Forkhead family transcription factor FOXP3 is predominantly expressed in Treg cells, where the FOXP3 ensemble is essential for Treg cell development and function. As FOXP3 is to Treg cells, the orphan retinoic acid nuclear receptor (ROR) family transcription factor RORγt is essential for Th17 development and function. In this review, we summarize recent progress of our understanding towards the molecular mechanisms underlying the differentiation and function of FOXP3(+) Treg cells and RORγt expressing Th17 cells. These may provide new insights into therapeutic intervention and targeting of human immune-deficient diseases.

Integral role of integrins in Th17 development

A lineage of CD4+ T cells known as Th17 cells, which are derived by exposure of naive CD4+ T cells to IL-6 and TGF-β, have been implicated in several autoimmune diseases. In this issue of the JCI, studies by Acharya et al. and Melton et al. show that TGF-β is activated at the DC/CD4+ T cell synapse by αv integrins and that this activation is required for Th17 differentiation and autoimmunity in the central nervous system. Thus, these studies offer a potential therapeutic target in fighting autoimmune diseases.

Signal transduction pathways and transcriptional regulation in Th17 cell differentiation

Over the last decade, our understanding of helper/effector T cell differentiation has changed dramatically. The discovery of interleukin (IL-)17-producing T cells (Th17) and other subsets has changed our view of T cell-mediated immunity. Characterization of the signaling pathways involved in the Th17 commitment has provided exciting new insights into the differentiation of CD4+ T cells. Importantly, the emerging data on conversion among polarized T helper cells have raised the question how we should view such concepts as T cell lineage commitment, terminal differentiation and plasticity. In this review, we will discuss the current understanding of the signaling pathways, molecular interactions, and transcriptional and epigenetic events that contribute to Th17 differentiation and acquisition of effector functions.

IL-17A is increased in the serum and in spinal cord CD8 and mast cells of ALS patients

The contribution of inflammation to neurodegenerative diseases is increasingly recognized, but the role of inflammation in sporadic amyotrophic lateral sclerosis (sALS) is not well understood and no animal model is available. We used enzyme-linked immunosorbent assays (ELISAs) to measure the cytokine interleukin-17A (IL-17A) in the serum of ALS patients (n = 32; 28 sporadic ALS (sALS) and 4 familial ALS (fALS)) and control subjects (n = 14; 10 healthy subjects and 4 with autoimmune disorders). IL-17A serum concentrations were 5767 ± 2700 pg/ml (mean ± SEM) in sALS patients and 937 ± 927 pg/ml in fALS patients in comparison to 7 ± 2 pg/ml in control subjects without autoimmune disorders (p = 0.008 ALS patients vs. control subjects by Mann-Whitney test). Sixty-four percent of patients and no control subjects had IL-17A serum concentrations > 50 pg/ml (p = 0.003 ALS patients vs. healthy subjects by Fisher's exact test). The spinal cords of sALS (n = 8), but not control subjects (n = 4), were infiltrated by interleukin-1β- (IL-1β-), and tumor necrosis factor-α-positive macrophages (co-localizing with neurons), IL-17A-positive CD8 cells, and IL-17A-positive mast cells. Mononuclear cells treated with aggregated forms of wild type superoxide dismutase-1 (SOD-1) showed induction of the cytokines IL-1β, interleukin-6 (IL-6), and interleukin-23 (IL-23) that may be responsible for induction of IL-17A. In a microarray analysis of 28,869 genes, stimulation of peripheral blood mononuclear cells by mutant superoxide dismutase-1 induced four-fold higher transcripts of interleukin-1α (IL-1α), IL-6, CCL20, matrix metallopeptidase 1, and tissue factor pathway inhibitor 2 in mononuclear cells of patients as compared to controls, whereas the anti-inflammatory cytokine interleukin-10 (IL-10) was increased in mononuclear cells of control subjects. Aggregated wild type SOD-1 in sALS neurons could induce in mononuclear cells the cytokines inducing chronic inflammation in sALS spinal cord, in particular IL-6 and IL-17A, damaging neurons. Immune modulation of chronic inflammation may be a new approach to sALS.