Structure and function of interleukin-17 family cytokines

The recently identified interleukin-17 (IL-17) cytokines family, which comprises six members in mammals (IL-17A-F), plays essential roles in the host immunity against infectious diseases and chronic inflammatory diseases. The three-dimensional structures containing IL-17A or IL-17F have become available and revealed the unique structural features of IL-17s as well as their receptors. Molecular modeling in this review shows that IL-17s may adopt a "cysteine knot" fold commonly seen in nerve growth factor (NGF) and other neurotrophins. Further modeling analysis unmasks a signature interaction feature of the IL-17F/IL-17RA complex, where a small loop of IL-17RA slots into the deep groove of the interface of IL-17F homodimer. This is quite different from the interaction between the best known four-helix cytokines and their cognate receptors. On the other hand, structure of IL-17A and its monoclonal antibody (CAT-2200) shows that, albeit that the antigenic epitope of IL-17A resides outside of the IL-17A homodimer interface, its physical proximity to the receptor binding groove may explain that antibody blockage would be achieved by interfering with the ligand-receptor interaction. This review is to summarize the advance in understanding the structure and function of IL-17 family cytokines, focusing mainly on IL-17A, IL-17F and IL-17E, in the hope of gaining better knowledge of immunotherapeutic strategies against various inflammatory diseases.

IL-17A- versus IL-17F-induced intracellular signal transduction pathways and modulation by IL-17RA and IL-17RC RNA interference in rheumatoid synoviocytes

OBJECTIVE

The aim of this study was to compare the effects of interleukin (IL)-17A and IL-17F on gene expression and signalling in human rheumatoid arthritis (RA) synoviocytes.

METHODS

IL-17A- and IL-17F-induced mRNA expression was analysed using Affymetrix microarrays. IL-6 and IL-8 secretion was evaluated by ELISA. Inhibition of two receptors (IL-17RA and IL-17RC) was achieved by small interfering RNA (saran). The effects on mitogen-activated protein kinase (MAPK), activator protein 1 (AP-1) and nuclear factor κB (NF-κB) expression and activation were evaluated by western blotting, qRT-PCR and DNA binding assay.

RESULTS

IL-17A and IL-17F induced a molecular pattern characterised by 27 inflammation-related genes for IL-17F and 165 for IL-17A. Virtually all IL-17A and IL-17F inducible genes were dependent on NF-κB activation, whereas a small number were modulated by p38. IL-17A induced activation of all three MAPKs (ERK, p38 and JNK) and downstream transcription factors AP-1 and p65 NF-κB. IL-17F was less potent but induced activation of p50 NF-κB. IL-17A was more potent at inducing IL-6 secretion than IL-17F, which was inactive alone. IL-17A and, to a lesser extent, IL-17F induced TRAF6 but not MyD88. Inhibition of either IL-17RA or IL-17RC expression via siRNA led to near complete abrogation of IL-6 expression mediated by IL-17A and the combination of IL-17F and tumour necrosis factor α.

CONCLUSION

Like IL-17A, IL-17F regulates proinflammatory gene expression by a very similar but not identical signalling pathway involving IL-17RA and IL-17RC.

What's new in asthma pathophysiology and immunopathology?

Research on asthma pathophysiology over the past decade has expanded the complex repertoire involved in the pathophysiology of asthma to include inflammatory, immune and structural cells, as well as a wide range of mediators. Studies have identified a role for connective and other mesenchymal tissues involved in airway remodeling. Recent findings have implicated the innate immune response in asthma and have revealed interesting patterns of interaction between the innate and adaptive immune response and the associated complex chronic inflammatory reaction. New immune cell populations have also been added to this repertoire, including Tregs, natural killer T cells and Th17 cells. The role of the eosinophil, a prominent pathological feature in most asthma phenotypes, has also been expanding to include roles such as tissue modifiers and immune regulators via a number of fascinating and hitherto unexplored mechanistic pathways. In addition, new and significant roles have been proposed for airway smooth muscle cells, fibroblasts, epithelial and endothelial cells. Tissue remodeling is now considered an integral element of asthma pathophysiology. Finally, an intricate network of mediators, released from both immune and inflammatory cells, including thymus stromal lymphopoietin and matrix metalloproteinases, have added to the complex milieu of asthma immunity and inflammation. These findings have implications for therapy and the search for novel strategies towards better disease management. Sadly, and perhaps due to the complex nature of asthma, advances in therapeutic discoveries and developments have been limited. Thus, understanding the precise roles played by the numerous dramatis personae in this odyssey, both individually and collectively within the context of asthma pathophysiology, continues to pose new challenges. It is clear that the next stage in this saga is to embark on studies that transcend reductionist approaches to involve system analysis of the complex and multiple variables involved in asthma, including the need to narrow down the phenotypes of this condition based on careful analysis of the organs (lung and airways), cells, mediators and other factors involved in bronchial asthma.

Characterization of host genetic expression patterns in HIV-infected individuals with divergent disease progression

The course of HIV-1 infection shows a variety of clinical phenotypes with an important involvement of host factors. We compare host gene expression patterns in CD3+ T cells from two of these phenotypes: long-term non-progressor patients (LTNP) and matched control patients with standard HIV disease progression. Array analysis revealed over-expression of 322 genes in progressors and 136 in LTNP. Up-regulated genes in progressors were mainly implicated in the regulation of DNA replication, cell cycle and DNA damage stimulus and mostly localized into cellular organelles. In contrast, most up-regulated genes in LTNP were located at the plasmatic membrane and involved in cytokine-cytokine receptor interaction, negative control of apoptosis or regulation of actin cytoskeleton. Regarding gene interactions, a higher number of viral genes interacting with cellular factors were seen in progressors. Our study offers new comparative insights related to disease status and can distinguish differentiated patterns of gene expression among clinical phenotypes.

Human RORγt+ TH17 cells preferentially differentiate from naive FOXP3+Treg in the presence of lineage-specific polarizing factors

RORγt(+) T(H)17 cells are a proinflammatory CD4(+) T-cell population associated with autoimmune tissue injury. In mice, priming of T(H)17 requires TGF-β, which alone directs the priming of FOXP3(+) regulatory T cells (Treg), in association with inflammatory cytokines. Priming of human T(H)17 cells from conventional naive CD4(+) T cells under similar conditions, however, has proved difficult to achieve. Here, we report that differentiation of human T(H)17 cells preferentially occurs from FOXP3(+) naive Treg (NTreg) in the presence of IL-2 and IL-1β and is increased by IL-23 and TGF-β. IL-1β-mediated differentiation correlated with IL-1RI expression in stimulated NTreg and was accompanied by induction of RORγt along with down-regulation of FOXP3. IL-17-secreting cells in NTreg cultures cosecreted TNF-α and IL-2 and contained distinct subpopulations cosecreting or not cosecreting IFN-γ and other T(H)17-associated cytokines. Polarized NTreg contained significant subpopulations of CCR6-expressing cells that were highly enriched in IL-17-secreting cells. Finally, analysis of CCR6 expression with respect to that of IL-1RI identified distinct IL-17-secreting subpopulations that had maintained or lost their suppressive functions. Together our results support the concept that priming of human T(H)17 from naive CD4(+) T cells preferentially takes place from FOXP3(+) Treg precursors in the presence of lineage-specific polarizing factors.

γδ T cells protect against lung fibrosis via IL-22

Inflammation-induced pulmonary fibrosis (PF) leads to irreversible loss of lung function and is a predictor of mortality in numerous lung diseases. Why some subjects with lung inflammation but not others develop PF is unclear. In a mouse model of hypersensitivity pneumonitis that progresses to lung fibrosis upon repeated exposure to the ubiquitous microorganism Bacillus subtilis, γδ T cells expand in the lung and inhibit collagen deposition. We show that a subset of these γδ cells represents the predominant source of the Th17 cytokine IL-22 in this model. Preventing expression of IL-22, either by mutating the aryl hydrocarbon receptor (AhR) or inhibiting AhR signaling, accelerated lung fibrosis. Direct blockade of IL-22 also enhanced collagen deposition in the lung, whereas administration of recombinant IL-22 inhibited lung fibrosis. Moreover, the presence of protective γδ T cells and IL-22 diminished recruitment of CD4(+) T cells to lung. These data reveal a protective pathway that involves the inhibition of αβ T cells by regulatory IL-22-secreting γδ T cells.

[Role of Th17 cells in rheumatoid arthritis]

Th17 cells are the newly described subset of the CD4(+) T lymphocytes. Activated Th17 cells are characterized by their ability to produce IL-17A and other pro-inflammatory cytokines. IL-17A regulates immune function through its cell-surface receptor expressed on epithelial-and endothelial cells, fibroblasts and leukocytes by promoting neutrophil recruitment and releasing further pro-inflammatory mediators. Failures of the susceptible balance of the immunoregulation may lead to unchecked immune response and autoimmune diseases. The central role of Th17 cells and cytokines produced by Th17 cells were confirmed in a wide variety of human autoimmune diseases, including rheumatoid arthritis. Recently Th17 cells and its cytokines come into the focus of immunological research as potential therapeutic targets.

Differential response to treatment of relapsing–remitting multiple sclerosis with IFN-β: is there a dichotomy into T-helper-1 and -17 driven disease?

Evaluation of: Axtell RC, de Jong BA, Boniface K et al.: T helper type 1 and type 17 cells determine efficacy of interferon-β in multiple sclerosis and experimental encephalomyelitis. Nat. Med. 16, 406–412 (2010). This study aimed to assess the mechanism of action of IFN-β in the treatment of relapsing–remitting multiple sclerosis (MS). It shows that IFN-β leads to amelioration of experimental autoimmune encephalomyelitis, the animal model of MS, if disease is induced with T-helper (Th)1 cells. In this case, response to therapy requires the presence of IFN-γ, and IL-10-secreting cells are induced. By contrast, in experimental autoimmune encephalomyelitis induced with Th17 cells, treatment with IFN-β leads to an aggravation of the condition. Patients with relapsing–remitting MS were subsequently stratified into responder (n = 12) and nonresponders (n = 14) to IFN-β treatment. In nonresponder patients, high pretreatment levels of IL-17F and endogenous IFN-β were present. These findings lead to the conclusion that there might be a dichotomy of disease biology of relapsing–remitting MS: MS patients with a Th1-biased disease respond to IFN-β, while patients with a Th17-biased disease do not. The study contains a number of interesting observations; however, further studies with larger numbers of patients are necessary to evaluate and possibly confirm the findings.

Interleukin-17A during local and systemic Staphylococcus aureus-induced arthritis in mice

Staphylococcus aureus is one of the dominant pathogens that induce septic arthritis in immunocompromised hosts, e.g., patients suffering from rheumatoid arthritis treated with immunosuppressive drugs. S. aureus-induced arthritis leads to severe joint destruction and high mortality despite antibiotic treatment. Recently, interleukin-17A (IL-17A) has been discovered to be an important mediator of aseptic arthritis both in mice and humans, but its function in S. aureus-induced arthritis is largely unknown. Here, we investigated the role of IL-17A in host defense against arthritis following systemic and local S. aureus infection in vivo. IL-17A knockout mice and wild-type mice were inoculated systemically (intravenously) or locally (intra-articularly) with S. aureus. During systemic infection, IL-17A knockout mice lost significantly more weight than the wild-type mice did, but no differences were found in the mortality rate. The absence of IL-17A had no impact on clinical arthritis development but led to increased histopathological erosivity late during systemic S. aureus infection. Bacterial clearance in kidneys was increased in IL-17A knockout mice compared to the level in wild-type mice only 1 day after bacterial inoculation. During systemic S. aureus infection, serum IL-17F protein levels and mRNA levels in the lymph nodes were elevated in the IL-17A knockout mice compared to the level in wild-type mice. In contrast to systemic infection, the IL-17A knockout mice had increased synovitis and erosions and locally decreased clearance of bacteria 3 days after local bacterial inoculation. On the basis of these findings, we suggest that IL-17A is more important in local host defense than in systemic host defense against S. aureus-induced arthritis.

Th 17 cells interplay with Foxp3+ Tregs in regulation of inflammation and autoimmunity

T helper 17 cells (Th17) are a new CD4+ T helper subset that has been implicated in inflammatory and autoimmune diseases. Th17, along with CD4(+)CD25(high) Foxp3(+) regulatory T cells (Tregs) and other new T helper subsets, have expanded the Th1-Th2 paradigm. Although this new eight-subset paradigm significantly improved our understanding on the differentiation and regulation of CD4+ T helper subsets, many questions remain to be answered. Here we will briefly review the following issues: a) Old Th1-Th2 paradigm versus new multi-subset paradigm; b) Structural features of IL-17 family cytokines; c) Th17 cells; d) Effects of IL-17 on various cell types and tissues; e) IL-17 receptor and signaling pathways; f) Th17-mediated inflammations; and g) Protective mechanisms of IL-17 in infections. Lastly, we will examine the interactions of Th17 and Treg in autoimmune diseases and inflammation: Th17 cells interplay with Tregs. Regulation of autoimmunity and inflammation lies in the interplays of the different T helper subsets, therefore, better understanding of these subsets' interactions would greatly improve our approaches in developing therapy to combat inflammatory and autoimmune diseases.

IL-17 signaling in host defense and inflammatory diseases

Interleukin (IL)-17, the signature cytokine secreted by T helper (Th) 17 cells, plays important roles in host defense against extracellular bacterial infection and fungal infection and contributes to the pathogenesis of various autoimmune inflammatory diseases. Here we review the recent advances in IL-17-mediated functions with emphasis on the studies of IL-17-mediated signal transduction, providing perspective on potential drug targets for the treatment of autoimmune inflammatory diseases.

Hypothyroidism in Noninterferon Treated-HCV Infected Individuals Is Associated with Abnormalities in the Regulation of Th17 Cells

HCV-Ag-specific TH17 cells secrete IL17, a cytokine involved in autoimmune diseases and regulated by IL10 and TGF-b. 5–12% of patients with chronic HCV infection have hypothyroidism. We evaluated the role of these cytokines in this patients by determining serum concentration of TsH, T3, free T4, IL2, IL10, IL12, IL17, TGF-b, anti-TG, TPO, CCP, GBM, and cardiolipin antibodies in 87 chronically noninterferon treated HCV-infected patients. 20 patients (group A) had elevated TsH values (>5 μUI/ml) whereas the remaining 67 (group B) had normal values. The percentage of anti-TPO, TG, GBM, and cardiolipin antibodies in group A patients (33%, 41%, 5% and 5%, resp.) as well as IL17, IL2 and TGF-b concentrations (25 ± 23 pg/ml, 643 ± 572 pg/ml, and 618 ± 221 pg/ml, resp.) were significantly higher than group B. Abnormal Th17 regulation mediated by IL-2 and low TGF-b concentrations is associated with hypothyroidism in chronically-infected HCV patients.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Role of IL-23 and Th17 Cells in Airway Inflammation in Asthma

Asthma is characterized by chronic airway inflammation with intense eosinophil and lymphocyte infiltration, mucus hyperproduction, and airway hyperresponsiveness. Accumulating evidence indicates that antigen-specific Th2 cells and their cytokines such as IL-4, IL-5, and IL-13 orchestrate these pathognomonic features of asthma. In addition, we and others have recently shown that IL-17-producing CD4⁺ T cells (Th17 cells) and IL-23, an IL-12-related cytokine that is essential for survival and functional maturation of Th17 cells, are involved in antigen-induced airway inflammation. In this review, our current understanding of the roles of IL-23 and Th17 cells in the pathogenesis of allergic airway inflammation will be summarized.

The IL-17 family cytokines in immunity and disease

INTRODUCTION

Accumulating evidence suggests that the interleukin (IL)-17 cytokines are major players in the immune response to foreign pathogens. In addition, the pathogeneses of a number of inflammatory diseases have been linked to uncontrolled expression of these cytokine pathways.

DISCUSSION

Genetic and biochemical analyses have elucidated the cellular and molecular events triggered by these proteins during an inflammatory response. While significant efforts have been placed on understanding the functions of IL-17A, IL-17F, and IL-17E, the significance of the other family members, IL-17B-D, in inflammation remains to be determined.

CONCLUSION

This review will focus on the cellular sources, target cell/receptors that are utilized by these cytokines to control pathogenesis, and the therapeutic potential of targeting these pathways to treat inflammatory disorders.

Epithelium: the interplay between innate and Th2 immunity

Mucosal epithelium functions not only as a physical barrier, but also as a regulator of innate and adaptive immune responses against foreign substances and microorganisms. In particular, epithelial cells have been directly implicated in Th2 responses, serving as a critical interface between innate immune responses and Th2 immunity. Emerging studies have revealed the cellular and molecular mechanisms by which the epithelium modulates Th2 responses through the production of a group of epithelial-derived Th2-driving cytokines, including interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin. These epithelial-derived Th2-driving cytokines execute a regulatory function of the epithelium on mucosal immunity by promoting Th2 responses and maintaining the balance of host immune homeostasis and defense against various pathogens. Dysregulation of these Th2-driving cytokines can lead to detrimental Th2-dependent inflammatory responses, often manifested in various forms of allergic and inflammatory diseases.

Structural basis of receptor sharing by interleukin 17 cytokines

T helper type 17 (T_H-17) cells, together with their effector cytokines including interleukin 17 (IL-17) family members, are emerging as key mediators of chronic inflammatory and autoimmune disorders. Here we present the crystal structure of a 1:2 complex of IL-17RA bound to IL-17F. The manner of complex formation is unique for cytokines, and involves two fibronectin-type domains of IL-17RA engaging IL-17 within a groove between the IL-17 homodimer interface in a knob-and-hole fashion. The first receptor-binding event to the IL-17 cytokines modulates the affinity and specificity of the second receptor-binding event, thereby promoting heterodimeric versus homodimeric complex formation. IL-17RA utilizes a common recognition strategy to bind to several IL-17 family members, allowing it to potentially act as a shared receptor within multiple different signaling complexes.

Structure and signalling in the IL-17 receptor family

Interleukin-17A (IL-17A), the hallmark cytokine of the newly defined T helper 17 (T(H)17) cell subset, has important roles in protecting the host against extracellular pathogens, but also promotes inflammatory pathology in autoimmune disease. IL-17A and its receptor (IL-17RA) are the founding members of a newly described family of cytokines and receptors that have unique structural features which distinguish them from other cytokine families. Research defining the signal transduction pathways induced by IL-17R family cytokines has lagged behind that of other cytokine families, but studies in the past 2 years have begun to delineate unusual functional motifs and new proximal signalling mediators used by the IL-17R family to mediate downstream events.

The biological and clinical importance of the 'new generation' cytokines in rheumatic diseases

A better understanding of cytokine biology over the last two decades has allowed the successful development of cytokine inhibitors against tumour necrosis factor and interleukin (IL)-1 and IL-6. The introduction of these therapies should be considered a breakthrough in the management of several rheumatic diseases. However, many patients will exhibit no or only partial response to these therapies, thus emphasising the importance of exploring other therapeutic strategies. In this article, we review the most recent information on novel cytokines that are often members of previously described cytokine families such as the IL-1 superfamily (IL-18 and IL-33), the IL-12 superfamily (IL-27 and IL-35), the IL-2 superfamily (IL-15 and IL-21), and IL-17. Several data derived from experimental models and clinical samples indicate that some of these cytokines contribute to the pathophysiology of arthritis and other inflammatory diseases. Targeting of some of these cytokines has already been tested in clinical trials with interesting results.

Novel therapeutic targets along the Th17 pathway

The recent discovery of IL-17-producing CD4(+) Th subset significantly revised the Th1/Th2 dichotomy model proposed by Mosmann and Coffman almost two decades ago. Th17 cells are involved in the pathogenesis of many human autoimmune diseases. Th17 cells, their developmental pathways and their effector functions, therefore, provide novel therapeutic targets.

The critical role of epithelial-derived Act1 in IL-17- and IL-25-mediated pulmonary inflammation

IL-25 initiates, promotes, and augments Th2 immune responses. In this study, we report that Act1, a key component in IL-17-mediated signaling, is an essential signaling molecule for IL-25 signaling. Although Act1-deficient mice showed reduced expression of KC (CXCL1) and neutrophil recruitment to the airway compared with wild-type mice in response to IL-17 stimulation, Act1 deficiency abolished IL-25-induced expression of IL-4, IL-5, IL-13, eotaxin-1 (CCL11), and pulmonary eosinophilia. Using a mouse model of allergic pulmonary inflammation, we observed diminished Th2 responses and lung inflammation in Act1-deficient mice compared with wild-type mice. Importantly, Act1 deficiency in epithelial cells reduced the phenotype of allergic pulmonary inflammation due to loss of IL-17-induced neutrophilia and IL-25-induced eosinophilia, respectively. These results demonstrate the essential role of epithelial-derived Act1 in allergic pulmonary inflammation through the distinct impact of the IL-17R-Act1 and IL-25R-Act1 axes. Such findings are crucial for the understanding of pathobiology of atopic diseases, including allergic asthma, which identifies Act1 as a potential therapeutic target.

Interleukin-17A inhibits adipocyte differentiation in human mesenchymal stem cells and regulates pro-inflammatory responses in adipocytes

The immune system is closely linked to human metabolic diseases. Serum levels of IL-6 increase with obesity and insulin resistance. Not only does IL-6 decrease the insulin sensitivity of human cells such as adipocytes, but it also regulates the lineage commitment of naïve T cells into interleukin (IL)-17A-producing CD4(+) T (Th17) cells. Although IL-17A exerts a variety of effects on somatic tissues, its functional role in human adipocytes has not been identified. In this work, we show that IL-17A inhibits adipocyte differentiation in human bone marrow mesenchymal stem cells (hBM-MSCs), while promoting lipolysis of differentiated adipocytes. We find that IL-17A increases both mRNA and protein secretion of IL-6 and IL-8 during adipocyte differentiation in hBM-MSCs. IL-17A up-regulates cyclooxygenase (COX)-2 gene expression and thereby increases the level of prostaglandin (PG) E(2) in differentiated adipocyes. The suppression of anti-adipogenic PGE(2) by COX inhibitors such as aspirin and NS-398 partially blocked the effect of IL-17A on adipocyte differentiation in hBM-MSCs. Therefore, IL-17A exhibits its inhibitory effect in part via the COX-2 induction in differentiated adipocytes. In addition, treatment with anti-IL-17A antibody neutralizes IL-17A-mediated effects on adipocyte differentiation and function. These results suggest that IL-17A plays a regulatory role in both the metabolic and inflammatory processes of human adipocytes, similar to other pro-inflammatory cytokines such as IL-1, IFNgamma, and TNFalpha.

Differential roles of interleukin-17A and -17F in host defense against mucoepithelial bacterial infection and allergic responses

Interleukin-17A (IL-17A) is a cytokine produced by T helper 17 (Th17) cells and plays important roles in the development of inflammatory diseases. Although IL-17F is highly homologous to IL-17A and binds the same receptor, the functional roles of this molecule remain largely unknown. Here, we demonstrated with Il17a(-/-), Il17f(-/-), and Il17a(-/-)Il17f(-/-) mice that IL-17F played only marginal roles, if at all, in the development of delayed-type and contact hypersensitivities, autoimmune encephalomyelitis, collagen-induced arthritis, and arthritis in Il1rn(-/-) mice. In contrast, both IL-17F and IL-17A were involved in host defense against mucoepithelial infection by Staphylococcus aureus and Citrobacter rodentium. IL-17A was produced mainly in T cells, whereas IL-17F was produced in T cells, innate immune cells, and epithelial cells. Although only IL-17A efficiently induced cytokines in macrophages, both cytokines activated epithelial innate immune responses. These observations indicate that IL-17A and IL-17F have overlapping yet distinct roles in host immune and defense mechanisms.

IL-17A and IL-17F do not contribute vitally to autoimmune neuro-inflammation in mice

The clear association of Th17 cells with autoimmune pathogenicity implicates Th17 cytokines as critical mediators of chronic autoimmune diseases such as EAE. To study the impact of IL-17A on CNS inflammation, we generated transgenic mice in which high levels of expression of IL-17A could be initiated after Cre-mediated recombination. Although ubiquitous overexpression of IL-17A led to skin inflammation and granulocytosis, T cell-specific IL-17A overexpression did not have a perceptible impact on the development and health of the mice. In the context of EAE, neither the T cell-driven overexpression of IL-17A nor its complete loss had a major impact on the development of clinical disease. Since IL-17F may be able to compensate for the loss of IL-17A, we also generated IL-17F-deficient mice. This strain was fully susceptible to EAE and displayed unaltered emergence and expansion of autoreactive T cells during disease. To eliminate potential compensatory effects of either cytokine, we treated IL-17F-deficient mice with antagonistic monoclonal antibodies specific for IL-17A and found again only a minimal beneficial impact on disease development. We conclude therefore that both IL-17A and IL-17F, while prominently expressed by an encephalitogenic T cell population, may only marginally contribute to the development of autoimmune CNS disease.

Th17 cytokines and their emerging roles in inflammation and autoimmunity

T-helper 17 (Th17) cells are a new lineage of CD4(+) T cells that are characterized by their production of interleukin-17A (IL-17A). Recent studies show that these cells can also express IL-17F, IL-22, and IL-21. IL-17A and IL-17F can form a heterodimeric cytokine, which mediates biological activities, at least in part, through shared receptors with IL-17A and IL-17F homodimers. The cytokines made by Th17 cells represent three distinct gene families, highlighting the unique biology of these cells. Accumulating data support a role for Th17 cells and these cytokines in inflammatory processes and in animal models of autoimmunity or inflammation. Emerging data in clinical trials support our understanding of the importance of Th17 cells in inflammatory disease. Future clinical studies will allow us to evaluate the role of each cytokine independently in contributing to human diseases with immune-mediated pathologies and to design optimal cytokine-targeted therapies for these diseases.

Expression of interleukin-17RC protein in normal human tissues

Background

Interleukin-17 (IL-17) cytokines and receptors play an important role in many autoimmune and inflammatory diseases. IL-17 receptors IL-17RA and IL-17RC have been found to form a heterodimer for mediating the signals of IL-17A and IL-17F cytokines. While the function and signaling pathway of IL-17RA has been revealed, IL-17RC has not been well characterized. The function and signaling pathway of IL-17RC remain largely unknown. The purpose of the present study was to systematically examine IL-17RC protein expression in 53 human tissues.

Results

IL-17RC expression in 51 normal human tissues and two benign tumors (i.e., lymphangioma and parathyroid adenoma) on the tissue microarrays was determined by immunohistochemical staining, using two polyclonal antibodies against IL-17RC. IL-17RC protein was expressed in many cell types including the myocardial cells, vascular and lymphatic endothelial cells, glandular cells (of the adrenal, parathyroid, pituitary, thyroid, pancreas, parotid salivary, and subepidermal glands), epithelial cells (of the esophagus, stomach, intestine, anus, renal tubule, breast, cervix, Fallopian tube, epididymis, seminal vesicle, prostate, gallbladder, bronchus, lung, and skin), oocytes in the ovary, Sertoli cells in the testis, motor neurons in the spinal cord, autonomic ganglia and nerves in the intestine, skeletal muscle cells, adipocytes, articular chondrocytes, and synovial cells. High levels of IL-17RC protein expression were observed in most vascular and lymphatic endothelium and squamous epithelium. The epithelium of the breast, cervix, Fallopian tube, kidney, bladder and bronchus also expressed high levels of IL-17RC, so did the glandular cells in the adrenal cortex, parotid salivary and subepidermal glands. In contrast, IL-17RC protein was not detectable in the smooth muscle cells, fibroblasts, antral mucosa of the stomach, mucosa of the colon, endometrium of the uterus, neurons of the brain, hepatocytes, or lymphocytes. Nevertheless, IL-17RC protein was expressed in the vascular endothelium within the tissues where the IL-17RC-negative cells resided.

Conclusion

IL-17RC protein is expressed in most human tissues, the function of which warrants further investigation.