Interleukin-17 receptor deficiency results in impaired synovial expression of interleukin-1 and matrix metalloproteinases 3, 9, and 13 and prevents cartilage destruction during chronic reactivated streptococcal cell wall-induced arthritis

A critical role of Cyr61 in interleukin-17-dependent proliferation of fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

Fibroblast-like synoviocytes (FLS) are a major component of the hyperplastic synovial pannus that aggressively invades cartilage and bone during the course of rheumatoid arthritis (RA). Cyr61 (CCN1) is a product of a growth factor-inducible immediate early gene and is involved in cell adhesion, proliferation, and differentiation. However, the role that Cyr61 plays in FLS proliferation has remained undetermined. The aim of this study was to identify the role of Cyr61 in regulating the proliferation of FLS derived from patients with RA.

METHODS

Expression of Cyr61 in synovial tissue (ST) and in FLS was determined simultaneously using immunohistochemistry, real-time polymerase chain reaction, and Western blotting. Cyr61 levels in synovial fluid (SF) were determined by enzyme-linked immunosorbent assay. FLS proliferation stimulated by SF, Cyr61, and interleukin-17 (IL-17) was measured by thymidine incorporation. Activation of signal transduction pathways was determined by Western blotting and confocal microscopy.

RESULTS

Cyr61 was overexpressed in ST, FLS, and SF samples from RA patients as compared with samples from normal controls. Elevated levels of Cyr61 in RA SF promoted the proliferation of FLS, an effect that was abrogated by a neutralizing monoclonal antibody against human Cyr61. Furthermore, in samples from RA patients, Cyr61 was found to protect FLS from apoptosis and to sustain the expression of Bcl-2 in FLS. Most importantly, the expression of Cyr61 in FLS was regulated by IL-17 mainly via the p38 MAPK and NF-kappaB signaling pathways. Knockdown of expression of the Cyr61 gene inhibited IL-17-stimulated FLS proliferation.

CONCLUSION

Our findings indicate that Cyr61 plays a critical role in IL-17-mediated proliferation of FLS in RA and likely contributes to hyperplasia of synovial lining cells and eventually to joint destruction in patients with RA.

Transfer of tolerance to collagen type V suppresses T-helper-cell-17 lymphocyte-mediated acute lung transplant rejection

BACKGROUND

Rat lung allograft rejection is mediated by collagen type V (col(V)) specific T-helper-cell 17 (Th17) cells. Adoptive transfer of these cells is sufficient to induce rejection pathology in isografts, whereas tolerance to col(V) suppresses allograft rejection. Therefore, we tested whether regulatory T cells from tolerant rats could suppress the Th17-mediated rejection in the syngeneic model of lung transplantation.

METHODS

Rats were subjected to syngeneic left lung transplantation, and acute rejection was induced by adoptive transfer of lymph node cells from col(V)-immunized rats. Tolerance was induced by intravenous injection of col(V), and spleen lymphocytes were used for adoptive transfer. CD4+ T cells were depleted using magnetic beads. Lung isografts were analyzed using micro-positron emission tomography imaging and histochemistry. The transvivo delayed type hypersensitivity assay was used to analyze the Th17 response.

RESULTS

Adoptive cotransfer of col(V)-specific effector cells with cells from col(V)-tolerized rats suppressed severe vasculitis and bronchiolitis with parenchymal inflammation, and the expression of interleukin (IL)-17 transcripts in mediastinal lymph nodes induced by effector cells alone. Analysis by transvivo delayed type hypersensitivity showed that the reactivity to col(V) was dependent on the presence of tumor necrosis factor-alpha and IL-17 but not interferon-gamma. Depletion of CD4+ T cells from the suppressor cell population abrogated the col(V)-specific protection.

CONCLUSION

Th17-mediated acute rejection after lung transplantation is ameliorated by CD4+ col(V)-specific regulatory T cells. The mechanism for this Th17 suppression is consistent with tolerance induction to col(V). The goal of transplantation treatment, therefore, should target Th17 development and not suppression of T-cell activation by suppressing IL-2.

IFN-gamma regulates the requirement for IL-17 in proteoglycan-induced arthritis

The contribution of the proinflammatory cytokines IFN-gamma and IL-17 to the pathogenesis of experimental arthritis is controversial. In proteoglycan (PG)-induced arthritis (PGIA), severe arthritis is dependent on the production of IFN-gamma, whereas IL-17 is dispensable. In collagen-induced arthritis and Ag-induced arthritis, although high levels of IFN-gamma are secreted, disease is exacerbated in IFN-gamma or IFN-gamma receptor-deficient mice due to the ability of IFN-gamma to suppress IL-17 expression. In the current study, we investigated the effect of IFN-gamma on the IL-17 response and its consequences in PGIA. In PG-immunized IFN-gamma(-/-) mice, despite reduction in arthritis, the PG-specific CD4(+) T cell IL-17 response was significantly increased. Elevated IL-17 contributed to development of arthritis, as disease in IFN-gamma/IL-17(-/-) was significantly reduced in comparison with either IFN-gamma(-/-) or IL-17(-/-) mice. A contribution of IFN-gamma and IL-17 to the development of arthritis was also identified in T-bet(-/-) mice. PG-specific CD4(+) T cells from T-bet(-/-) mice produced reduced IFN-gamma and elevated concentrations of IL-17. Both IFN-gamma and IL-17 contribute to arthritis, as T-bet(-/-) mice lacking IL-17 (T-bet/IL-17(-/-)) were resistant, whereas wild-type, T-bet(-/-), and IL-17(-/-) mice were susceptible to PGIA. T cell proliferation and autoantibody production did not correlate with development of disease; however, expression of cytokines and chemokines in joint tissues demonstrate that IFN-gamma and IL-17 cooperatively contribute to inflammation. These results demonstrate that both IFN-gamma and IL-17 have the potential to induce PGIA, but it is the strength of the IFN-gamma response that regulates the contribution of each of these Th effector cytokines to disease.

RANKL inhibition by osteoprotegerin prevents bone loss without affecting local or systemic inflammation parameters in two rat arthritis models: comparison with anti-TNFalpha or anti-IL-1 therapies

INTRODUCTION

Rat adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) feature bone loss and systemic increases in TNFalpha, IL-1beta, and receptor activator of NF-kappaB ligand (RANKL). Anti-IL-1 or anti-TNFalpha therapies consistently reduce inflammation in these models, but systemic bone loss often persists. RANKL inhibition consistently prevents bone loss in both models without reducing joint inflammation. Effects of these therapies on systemic markers of bone turnover and inflammation have not been directly compared.

METHODS

Lewis rats with established AIA or CIA were treated for 10 days (from day 4 post onset) with either PBS (Veh), TNFalpha inhibitor (pegsunercept), IL-1 inhibitor (anakinra), or RANKL inhibitor (osteoprotegerin (OPG)-Fc). Local inflammation was evaluated by monitoring hind paw swelling. Bone mineral density (BMD) of paws and lumbar vertebrae was assessed by dual X-ray absorptiometry. Markers and mediators of bone resorption (RANKL, tartrate-resistant acid phosphatase 5b (TRACP 5B)) and inflammation (prostaglandin E2 (PGE2), acute-phase protein alpha-1-acid glycoprotein (alpha1AGP), multiple cytokines) were measured in serum (day 14 post onset).

RESULTS

Arthritis progression significantly increased paw swelling and ankle and vertebral BMD loss. Anti-TNFalpha reduced paw swelling in both models, and reduced ankle BMD loss in AIA rats. Anti-IL-1 decreased paw swelling in CIA rats, and reduced ankle BMD loss in both models. Anti-TNFalpha and anti-IL-1 failed to prevent vertebral BMD loss in either model. OPG-Fc reduced BMD loss in ankles and vertebrae in both models, but had no effect on paw swelling. Serum RANKL was elevated in AIA-Veh and CIA-Veh rats. While antiTNFalpha and anti-IL-1 partially normalized serum RANKL without any changes in serum TRACP 5B, OPG-Fc treatment reduced serum TRACP 5B by over 90% in both CIA and AIA rats. CIA-Veh and AIA-Veh rats had increased serum alpha1AGP, IL-1beta, IL-8 and chemokine (C-C motif) ligand 2 (CCL2), and AIA-Veh rats also had significantly greater serum PGE2, TNFalpha and IL-17. Anti-TNFalpha reduced systemic alpha1AGP, CCL2 and PGE2 in AIA rats, while anti-IL-1 decreased systemic alpha1AGP, IL-8 and PGE2. In contrast, RANKL inhibition by OPG-Fc did not lessen systemic cytokine levels in either model.

CONCLUSIONS

Anti-TNFalpha or anti-IL-1 therapy inhibited parameters of local and systemic inflammation, and partially reduced local but not systemic bone loss in AIA and CIA rats. RANKL inhibition prevented local and systemic bone loss without significantly inhibiting local or systemic inflammatory parameters.

Translational mini-review series on Th17 cells: are T helper 17 cells really pathogenic in autoimmunity?

In this review the authors discuss the evidence for T helper type 17 (Th17) cells as pathogenic T cells in autoimmunity. Studies with cytokine-deficient mice or blocking of interleukin (IL)-17, IL-21 and IL-22 have resulted in a conflicting data set. Although in the experimental autoimmune encephalomyelitis model the role of Th17 cells remains a point of debate, this IL-17-producing T cell in experimental arthritis is clearly contributing to inflammation and destruction.

Regulation of gastric B cell recruitment is dependent on IL-17 receptor A signaling in a model of chronic bacterial infection

Th17-driven immune responses contribute to the pathogenesis of many chronic inflammatory diseases. In this study, we investigated the role of IL-17 signaling in chronic gastric inflammation induced by Helicobacter pylori, a Gram-negative bacterium that persistently colonizes the human stomach. Wild-type C57BL/6 mice and mice lacking IL-17RA (IL-17RA(-/-)) were orogastrically infected with H. pylori. Differences in bacterial colonization density and gastric inflammation were not apparent at 1 mo postinfection, but by 3 mo postinfection, H. pylori colonization density was higher and mononuclear gastric inflammation more severe in infected IL-17RA(-/-) mice than in infected wild-type mice. A striking feature was a marked increase in gastric B cells, plasma cells, and lymphoid follicles, along with enhanced H. pylori-specific serum Ab responses, in infected IL-17RA(-/-) mice. Fewer gastric neutrophils and lower levels of neutrophil-recruiting chemokines were detected in infected IL-17RA(-/-) mice than in infected wild-type mice. Gastric IL-17a and IL-21 transcript levels were significantly higher in infected IL-17RA(-/-) mice than in infected wild-type mice or uninfected mice, which suggested that a negative feedback loop was impaired in the IL-17RA(-/-) mice. These results underscore an important role of IL-17RA signaling in regulating B cell recruitment. In contrast to many chronic inflammatory diseases in which IL-17RA signaling promotes an inflammatory response, IL-17RA signaling down-regulates the chronic mononuclear inflammation elicited by H. pylori infection.

The inhibitory Fc gamma IIb receptor dampens TLR4-mediated immune responses and is selectively up-regulated on dendritic cells from rheumatoid arthritis patients with quiescent disease

Rheumatoid arthritis (RA) is a common autoimmune disease leading to profound disability and premature death. Although a role for FcgammaRs and TLRs is accepted, their precise involvement remains to be elucidated. FcgammaRIIb is an inhibitory FcR important in the maintenance of tolerance. We hypothesized that the inhibitory FcgammaRIIb inhibits TLR responses on monocyte-derived dendritic cells (DC) and serves as a counterregulatory mechanism to dampen inflammation, and we surmised that this mechanism might be defective in RA. The expression of the inhibitory FcgammaRIIb was found to be significantly higher on DCs from RA patients having low RA disease activity in the absence of treatment with antirheumatic drugs. The expression of activating FcgammaRs was similarly distributed among all RA patients and healthy controls. Intriguingly, only DCs with a high expression of FcgammaRIIb were able to inhibit TLR4-mediated secretion of proinflammatory cytokines when stimulated with immune complexes. In addition, when these DCs were coincubated with the combination of a TLR4 agonist and immune complexes, a markedly inhibited T cell proliferation was apparent, regulatory T cell development was promoted, and T cells were primed to produce high levels of IL-13 compared with stimulation of the DCs with the TLR4 agonist alone. Blocking FcgammaRIIb with specific Abs fully abrogated these effects demonstrating the full dependence on the inhibitory FcgammaRIIb in the induction of these phenomena. This TLR4-FcgammaRIIb interaction was shown to dependent on the PI3K and Akt pathway.

The role of T helper type 17 cells in inflammatory arthritis

While T cells have been implicated in the pathogenesis of inflammatory arthritis for more than three decades, the focus on the T helper type 17 (Th17) subset of CD4 T cells and their secreted cytokines, such as interleukin (IL)-17, is much more recent. Proinflammatory actions of IL-17 were first identified in the 1990s, but the delineation of a distinct Th17 subset in late 2005 has sparked great interest in the role of these cells in a broad range of immune-mediated diseases. This review summarizes current understanding of the role of Th17 cells and their products in both animal models of inflammatory arthritis and human immune-driven arthritides.

Attenuated atherosclerosis upon IL-17R signaling disruption in LDLr deficient mice

Atherosclerosis is an inflammatory disease characterized by the influx of macrophages and T cells and IL-17 may connect innate and adaptive immune responses involved in atherogenesis. We investigated the role of IL-17 receptor signaling in atherosclerosis and transplanted LDLr deficient recipient mice with IL-17R deficient bone marrow. Induction of atherosclerosis by Western-type diet induced a 46% reduction in lesion size in the aortic root and the plaque composition revealed no significant changes in collagen content and neutrophil counts, but a reduction in mast cell number and an increase in macrophage number. In addition, we observed a decrease in anti-oxLDL antibodies of the IgG class upon IL-17R BMT, while introduction of IL-17R deficient bone marrow resulted in a reduced IL-6 production and an increased IL-10 production. In conclusion, signaling via the IL-17 receptor in bone marrow derived cells enhances the process of atherosclerosis.

Human rheumatoid arthritis tissue production of IL-17A drives matrix and cartilage degradation: synergy with tumour necrosis factor-alpha, Oncostatin M and response to biologic therapies

INTRODUCTION

The aim of this study was to examine IL-17A in patients, following anti-TNF-alpha therapy and the effect of IL-17A on matrix turnover and cartilage degradation.

METHODS

IL-17A expression was examined by ELISA and immunohistology in the rheumatoid arthritis (RA) joints. RA whole synovial tissue explant (RA ST), primary synovial fibroblasts (RASFC), human cartilage and chondrocyte cultures were stimulated with IL-17A +/- TNF-alpha and Oncostatin M (OSM). Matrix metalloproteinase (MMP) and tissue inhibitor (TIMP-1) were assessed by ELISA and zymography. Cartilage proteoglycan release was assessed histologically by Safranin-O staining. Clinical parameters, IL-17A, MMP/TIMP were assessed in patients pre/post biologic therapy.

RESULTS

IL-17A levels were higher in RA vs osteoarthritis (OA)/normal joints (P < 0.05). IL-17A up-regulated MMP-1, -2, -9, and -13 in RA ST, RASFC, cartilage and chondrocyte cultures (P < 0.05). In combination with TNF-alpha and OSM, IL-17A shifted the MMP:TIMP-1 ratio in favor of matrix degradation (all P < 0.05). Cartilage proteoglycan depletion in response to IL-17A was mild; however, in combination with TNF-alpha or OSM showed almost complete proteoglycan depletion. Serum IL-17A was detected in 28% of patients commencing biologic therapy. IL-17A negative patients demonstrated reductions post therapy in serum MMP1/TIMP4, MMP3/TIMP1 and MMP3/TIMP4 ratios and an increase in CS846 (all P < 0.05). No significant changes were observed in IL-17A positive patients.

CONCLUSIONS

IL-17A is produced locally in the inflamed RA joint. IL-17A promotes matrix turnover and cartilage destruction, especially in the presence of other cytokines, mimicking the joint environment. IL-17A levels are modulated in vivo, following anti-TNF therapy, and may reflect changes in matrix turnover.

Interleukin-17 regulates chemokine and gelatinase B expression in fibroblasts to recruit both neutrophils and monocytes

Interleukin 17 (IL-17) is a proinflammatory cytokine, produced only by activated lymphocytes, but with a broad cellular host range. The effects of IL-17 on fibroblasts were investigated by analysis of the induction of chemokine and matrix metalloprotease (MMP) mRNA levels by RT-PCR. IL-17 stimulated CC chemokine (monocyte chemotactic protein-1; MCP-1/JE) and CXC (KC, MIP-2) chemokine and TIMP-1 mRNA expression in fibroblastoid L929 cells. In normal mouse embryonic fibroblasts (MEF) this induction profile by IL-17 was extended with the mRNAs encoding the chemokine granulocyte chemotactic protein-2 (GCP-2) and the proteases MMP-3, MMP-9 and MMP-13. The MMP-9 and GCP-2 induction by IL-17 in MEF, and the absence of induction in L929 cells, were corroborated by gelatin zymography and ELISA, respectively. The induction of MCP-1/CCL2 by IL-17 was confirmed in human diploid fibroblasts. We conclude that IL-17 regulates differentially chemokine and MMP expression by normal and transformed fibroblasts and is indirectly capable of attracting both monocytes and neutrophils to the inflammatory focus.

IL-17 and IFN-gamma mediate the elicitation of contact hypersensitivity responses by different mechanisms and both are required for optimal responses

Hapten-induced contact hypersensitivity (CHS) in the skin is a delayed type cellular immune response that can be mediated by CD8(+) T cells that produce IFN-gamma or IL-17. However, mechanisms for these cytokines in the elicitation of CHS remain to be fully elucidated. In this study, we show that adoptive transfer of CHS with hapten-primed wild-type (WT) CD8(+) T cells is reduced in IFN-gammaR(-/-) or IL-17R(-/-) mice compared with WT controls. The infiltration of granulocytes and macrophages in the hapten challenged skin of IL-17R(-/-) recipients is significantly reduced whereas it is less affected in IFN-gammaR(-/-) recipients although CD8(+) T cell infiltration is inhibited in both recipients. In contrast, the activity of reactive oxidative species is significantly inhibited in IFN-gammaR(-/-) but is less affected in IL-17R(-/-) recipients. Further analysis reveals that the expression of chemokines and cytokines is differentially regulated in the hapten-challenged skin of IFN-gammaR(-/-) or IL-17R(-/-) recipients compared with WT controls. Interestingly, injection of rIL-17 in the skin induces inflammation with a high level of leukocyte infiltration whereas injection of IFN-gamma induces inflammation with a high level of reactive oxidative species. Moreover, neutralization of IL-17 in IFN-gammaR(-/-) or IFN-gamma in IL-17R(-/-) mice further suppresses the adoptive transfer of CHS by hapten-primed WT CD8(+) T cells. The study demonstrates that IFN-gamma and IL-17 mediate the elicitation of CHS by different mechanisms and that both cytokines are required for optimal responses. This outcome improves understanding of pathogenesis and provides new insights into therapeutic strategies for CHS.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

A mutation in the Nlrp3 gene causing inflammasome hyperactivation potentiates Th17 cell-dominant immune responses

Missense mutations of the gene encoding NLRP3 are associated with autoinflammatory disorders characterized with excessive production of interleukin-1beta (IL-1beta). Here we analyzed the immune responses of gene-targeted mice carrying a mutation in the Nlrp3 gene equivalent to the human mutation associated with Muckle-Wells Syndrome. We found that antigen-presenting cells (APCs) from such mice produced massive amounts of IL-1beta upon stimulation with microbial stimuli in the absence of ATP. This was likely due to a diminished inflammasome activation threshold that allowed a response to the small amount of agonist. Moreover, the Nlrp3 gene-targeted mice exhibited skin inflammation characterized by neutrophil infiltration and a Th17 cytokine-dominant response, which originated from hematopoietic cells. The inflammation of Nlrp3 gene-targeted mice resulted from excess IL-1beta production from APCs, which augmented Th17 cell differentiation. These results demonstrate that the NLRP3 mutation leads to inflammasome hyperactivation and consequently Th17 cell-dominant immunopathology in autoinflammation.

Breaking old paradigms: Th17 cells in autoimmune arthritis

Aberrant helper T cell activation has been implicated in the pathogenesis of an array of autoimmune diseases. In this review, we summarize evidence that suggests the involvement of a novel T cell subset, the Th17 lineage, in rheumatoid arthritis. In particular, we focus on the role of Th17 cells in inducing and perpetuating the chronic inflammation, cartilage damage, and bone erosion that are hallmark phases of joint destruction and consider current and emerging therapies that seek to disrupt the inflammatory Th17 network and shift the immune system back towards homeostasis.

Accelerated pathological and clinical nephritis in systemic lupus erythematosus-prone New Zealand Mixed 2328 mice doubly deficient in TNF receptor 1 and TNF receptor 2 via a Th17-associated pathway

TNF-alpha has both proinflammatory and immunoregulatory functions. Whereas a protective role for TNF administration in systemic lupus erythematosus (SLE)-prone (New Zealand Black x New Zealand White)F(1) mice has been established, it remains uncertain whether this effect segregates at the individual TNFR. We generated SLE-prone New Zealand Mixed 2328 mice genetically deficient in TNFR1, in TNFR2, or in both receptors. Doubly-deficient mice developed accelerated pathological and clinical nephritis with elevated levels of circulating IgG anti-dsDNA autoantibodies and increased numbers of CD4(+) T lymphocytes, especially activated memory (CD44(high)CD62L(low)) CD4(+) T cells. We show that these cells expressed a Th17 gene profile, were positive for IL-17 intracellular staining by FACS, and produced exogenous IL-17 in culture. In contrast, immunological, pathological, and clinical profiles of mice deficient in either TNFR alone did not differ from those in each other or from those in wild-type controls. Thus, total ablation of TNF-alpha-mediated signaling was highly deleterious to the host in the New Zealand Mixed 2328 SLE model. These observations may have profound ramifications for the use of TNF and TNFR antagonists in human SLE and related autoimmune disorders, as well as demonstrate, for the first time, the association of the Th17 pathway with an animal model of SLE.

Interleukin-1 drives pathogenic Th17 cells during spontaneous arthritis in interleukin-1 receptor antagonist-deficient mice

OBJECTIVE

Interleukin-1 receptor antagonist-deficient (IL-1Ra-/-) mice spontaneously develop an inflammatory and destructive arthritis due to unopposed excess IL-1 signaling. In this study, the role of Th17 cells and the effect of neutralization of IL-17, IL-1, and tumor necrosis factor alpha (TNFalpha) were investigated in this IL-1-driven murine arthritis model.

METHODS

T cells isolated from IL-1Ra-/- and wild-type (WT) mice were stained for IL-17 and interferon-gamma, with results assessed by fluorescence-activated cell sorting analysis. To investigate the contribution of IL-1 and IL-17 in further progression of arthritis in this model, mice were treated with neutralizing antibodies after the onset of arthritis.

RESULTS

Compared with WT mice, IL-1Ra-/- mice had similar levels of Th1 cells but clearly enhanced levels of Th17 cells; this increase in the number of Th17 cells was evident even before the onset of arthritis, in young, nonarthritic IL-1Ra-/- mice. The percentage of Th17 cells increased even more after the onset of arthritis and, similar to the serum levels and local messenger RNA levels of IL-17, the percentage of IL-17+ Th17 cells clearly correlated with the severity of arthritis. Anti-IL-17 treatment prevented any further increase in inflammation and bone erosion, whereas blocking of TNFalpha after the onset of arthritis had no effect. In contrast, neutralization of IL-1 resulted in a complete suppression of arthritis. Interestingly, this anti-IL-1 treatment also significantly reduced the percentage of IL-17+ Th17 cells in the draining lymph nodes of these arthritic mice.

CONCLUSION

Increased levels of Th17 cells can be detected in IL-1Ra-/- mice even preceding the onset of arthritis. In addition, the results of cytokine-blocking studies demonstrated that IL-17 contributes to the inflammation and bone erosion in this model, which suggests that IL-1 is the driving force behind the IL-17-producing Th17 cells.

IL-17 expression by breast-cancer-associated macrophages: IL-17 promotes invasiveness of breast cancer cell lines

Introduction

IL-17 plays an important role in autoimmunity, promoting autoimmunity, inflammation and invasion in multiple sclerosis, rheumatoid arthritis and type I diabetes. The role of IL-17 in cancer is unclear, however, as there are few studies examining IL-17 protein expression in cancer. We therefore examined IL-17 protein expression in human breast cancer and modelled its potential biological significance in vitro.

Methods

Immunohistochemistry was used to determine IL-17 expression in breast cancers. Matrigel invasion assays were employed to examine the effect of IL-17 on cancer cell invasion by a panel of breast cancer cell lines. The role of matrix metalloproteinases (MMPs) was investigated with selective antagonists and immunoassays for MMP-2, MMP-3, MMP-9 and tissue inhibitor of MMP.

Results

IL-17-expressing cells with macrophage morphology were identified in the peritumoural area of a proportion of patients (8/19 patients). Macrophages were confirmed by CD68 staining on serial sections. With the exception of occasional lymphocytes, one patient with rare multinucleate giant cells and one patient with occasional expression of IL-17 in tumour cells, no other IL-17-positive cells were detected. Addition of IL-17 to cell lines in vitro stimulated marked invasion of Matrigel. In contrast, IL-17 did not promote the invasion of MCF7 or T47D cell lines. Invasion was initially thought to be dependent on MMPs, as evidenced by the broad-spectrum MMP inhibitor GM6001 and selective antagonists of MMP-2/MMP-9 and MMP-3. Measurement of MMP-2, MMP-3 and MMP-9, and tissue inhibitor of MMP 1 secretion, failed to reveal any changes in expression following IL-17 exposure. In contrast, TNF promoted secretion of MMPs but IL-17 did not augment TNF, indicating that IL-17 acts via an independent mechanism.

Conclusions

The present study is the first to describe in situ expression of IL-17 protein in human breast tumours and to propose a direct association between IL-17 and breast cancer invasion. The precise effectors of IL-17-dependent invasion remain to be characterised but could include a range of proteases such as a disintegrin and metalloproteinase protein or astacins. Nevertheless, this work identifies a novel potential mechanism for breast cancer invasion and tumour progression, the prognostic implication of which is currently under investigation.

The roles of the classical and alternative nuclear factor-kappaB pathways: potential implications for autoimmunity and rheumatoid arthritis

Nuclear factor-κB (NF-κB) is an inducible transcription factor controlled by two principal signaling cascades, each activated by a set of signal ligands: the classical/canonical NF-κB activation pathway and the alternative/noncanonical pathway. The former pathway proceeds via phosphorylation and degradation of inhibitor of NF-κB (IκB) and leads most commonly to activation of the heterodimer RelA/NF-κB1(p50). The latter pathway proceeds via phosphorylation and proteolytic processing of NF-κB2 (p100) and leads to activation, most commonly, of the heterodimer RelB/NF-κB2 (p52). Both pathways play critical roles at multiple levels of the immune system in both health and disease, including the autoimmune inflammatory response. These roles include cell cycle progression, cell survival, adhesion, and inhibition of apoptosis. NF-κB is constitutively activated in many autoimmune diseases, including diabetes type 1, systemic lupus erythematosus, and rheumatoid arthritis (RA). In this review we survey recent developments in the involvement of the classical and alternative pathways of NF-κB activation in autoimmunity, focusing particularly on RA. We discuss the involvement of NF-κB in self-reactive T and B lymphocyte development, survival and proliferation, and the maintenance of chronic inflammation due to cytokines such as tumor necrosis factor-α, IL-1, IL-6, and IL-8. We discuss the roles played by IL-17 and T-helper-17 cells in the inflammatory process; in the activation, maturation, and proliferation of RA fibroblast-like synovial cells; and differentiation and activation of osteoclast bone-resorbing activity. The prospects of therapeutic intervention to block activation of the NF-κB signaling pathways in RA are also discussed.

In vivo equilibrium of proinflammatory IL-17+ and regulatory IL-10+ Foxp3+ RORgamma t+ T cells

The nuclear hormone receptor retinoic acid receptor–related orphan receptor γt (RORγt) is required for the generation of T helper 17 cells expressing the proinflammatory cytokine interleukin (IL)-17. In vivo, however, less than half of RORγt⁺ T cells express IL-17. We report here that RORγt⁺ Tαβ cells include Foxp3⁺ cells that coexist with IL-17–producing RORγt⁺ Tαβ cells in all tissues examined. The Foxp3⁺ RORγt⁺ Tαβ express IL-10 and CCL20, and function as regulatory T cells. Furthermore, the ratio of Foxp3⁺ to IL-17–producing RORγt⁺ Tαβ cells remains remarkably constant in mice enduring infection and inflammation. This equilibrium is tuned in favor of IL-10 production by Foxp3 and CCL20, and in favor of IL-17 production by IL-6 and IL-23. In the lung and skin, the largest population of RORγt⁺ T cells express the γδ T cell receptor and produce the highest levels of IL-17 independently of IL-6. Thus, potentially antagonistic proinflammatory IL-17–producing and regulatory Foxp3⁺ RORγt⁺ T cells coexist and are tightly controlled, suggesting that a perturbed equilibrium in RORγt⁺ T cells might lead to decreased immunoreactivity or, in contrast, to pathological inflammation.

Lymphocyte-derived cytokines in inflammatory arthritis

Inflammatory bone loss is observed in a number of disorders including rheumatoid arthritis (RA), osteoporosis and periodontal disease. Lymphocytes are key components in the onset and exacerbation of autoimmune diseases and the cytokines produced by these cells have a powerful impact on disease progression. Many cytokines implicated in inflammation impact upon osteoclast (OCL) differentiation and function either directly or indirectly by modulating the relative expression of RANKL and OPG. This review highlights the contribution of lymphocyte-derived cytokines to the bone loss observed in RA and other autoimmune disorders. A greater understanding of the cytokines involved in these disorders will ultimately lead to the identification of novel therapeutic strategies for the prevention of bone loss in these diseases.

Structure-function relationships in the IL-17 receptor: implications for signal transduction and therapy

IL-17 is the defining cytokine of a newly-described "Th17" population that plays critical roles in mediating inflammation and autoimmunity. The IL-17/IL-17 receptor superfamily is the most recent class of cytokines and receptors to be described, and until recently very little was known about its function or molecular biology. However, in the last year important new insights into the composition and dynamics of the receptor complex and mechanisms of downstream signal transduction have been made, which will be reviewed here.

IL-17B and IL-17C are associated with TNF-alpha production and contribute to the exacerbation of inflammatory arthritis

IL-17A is a T cell-derived proinflammatory cytokine that contributes to the pathogenesis of rheumatoid arthritis. Recently, six related molecules have been identified to form the IL-17 family, as follows: IL-17A, IL-17B, IL-17C, IL-17D, IL-17E, and IL-17F. Whereas IL-17A and IL-17F up-regulate IL-6 in synovial fibroblasts, IL-17B and IL-17C are reported to stimulate the release of TNF-alpha and IL-1beta from the monocytic cell line, THP-1 cell. However, their detailed function remains to be elucidated. We report in this study the effects of IL-17 family on the collagen-induced arthritis (CIA) progression by T cell gene transfer and bone marrow chimeric mice. The mRNA expressions of IL-17 family (IL-17A, IL-17B, IL-17C, and IL-17F) and their receptor (IL-17R and IL-17Rh1) genes in the arthritic paws of CIA mice were elevated compared with controls. Although IL-17A and IL-17F were expressed in CD4(+) T cells, IL-17B and IL-17C were expressed in the cartilage and in various cell populations in the CIA arthritic paws, respectively. In vitro, IL-17A, IL-17B, IL-17C, and IL-17F induced TNF-alpha production in mouse peritoneal exudate cells. In vivo, adoptive transfer of IL-17B- and IL-17C-transduced CD4(+) T cells evidently exacerbated arthritis. Bone marrow chimeric mice of IL-17B and IL-17C exhibited elevated serum TNF-alpha concentration and the high arthritis score upon CIA induction. Moreover, neutralization of IL-17B significantly suppressed the progression of arthritis and bone destruction in CIA mice. Therefore, not only IL-17A, but also IL-17B and IL-17C play an important role in the pathogenesis of inflammatory arthritis.

Interleukin-17 gene expression in patients with rheumatoid arthritis

Interleukin-17 is a proinflammatory cytokine. Recent animal studies have shown that IL-17 plays a role in the initiation and progression of arthritis. However, whether IL-17 has a prominent role in human rheumatoid arthritis (RA) or not remains unclear. Here we investigated the role of IL-17 in patients with RA. cDNA was prepared from knee joint synovial tissues of RA (n = 11) and osteoarthritic (OA, n = 10) patients and PBMC of RA (n = 52) and healthy subjects (n = 34). IL-17 gene expression level was measured by real-time PCR, and was compared with various clinical parameters. IL-17 gene expression in synovial tissues of RA was similar to that in OA. IL-17 gene expression level in PBMC of RA patients was significantly higher than in the control. The response (changes in DAS) to two-week treatment with anti-TNF-alpha blockers (infliximab or etanercept) did not correlate with changes in IL-17 gene expression levels. The IL-17/TNF-alpha gene expression ratio at baseline (before treatment) tended to be lower in responders to the treatment. Expression of IL-17 gene in PBMC may be associated with the inflammatory process of RA. IL-17/TNF-alpha expression ratio is a potentially suitable marker of response to anti-TNF-alpha therapy.

Anti-IL-17A autovaccination prevents clinical and histological manifestations of experimental autoimmune encephalomyelitis

Excessive or inappropriate production of IL-17A has been reported in diseases such as rheumatoid arthritis, asthma, and multiple sclerosis. The potential clinical relevance of these correlations was suggested by the protective effects of anti-IL-17A monoclonal antibodies in various mouse disease models. However, the chronic nature of the corresponding human afflictions raises great challenges for Ab-based therapies. An alternative to passive Ab therapy is autovaccination. Covalent association of self-cytokines with foreign proteins has been reported to induce the production of antibodies capable of neutralizing the biological activity of the target cytokine. We recently reported that cross-linking of IL-17A to ovalbumin produced highly immunogenic complexes that induced long-lasting IL-17A-neutralizing antibodies. Vaccinated SJL mice were completely protected against experimental autoimmune encephalomyelitis (EAE) induced by proteolipid protein peptide (PLP 139-151), and a monoclonal anti-IL-17A Ab (MM17F3), derived from C57Bl/6 mice vaccinated against IL-17A-OVA, also prevented disease development. Here we report that this Ab also protects C57Bl/6 mice from myelin oligdendrocyte glycoprotein (MOG)-induced EAE. Histological analysis of brain sections of C57Bl/6 mice treated with MM17F3 showed a complete absence of inflammatory infiltrates and evidence for a marked inhibition of chemokine and cytokine messages in the spinal cord. These results further extend the analytical and therapeutic potential of the autovaccine procedure.

Act1 modulates autoimmunity through its dual functions in CD40L/BAFF and IL-17 signaling

Coordinated regulation of T and B cell-mediated immune responses plays a critical role in the control and modulation of autoimmune diseases. This review is focused on the adapter molecule Act1 and its regulation of autoimmunity through its impact on both T and B cell-mediated immune responses. Whereas Act1 molecule is an important negative regulator for B cell-mediated humoral immune responses through its function in CD40L and BAFF signaling, recent studies have shown that Act1 is also a key positive signaling component for IL-17 signaling pathway, critical for T(H)17-mediated autoimmune and inflammatory responses. The dual functions of Act1 are evident in Act1-deficient mice that displayed B cell-mediated autoimmune phenotypes (including dramatic increase in peripheral B cells, lymphadenopathy and splenomegaly, hypergammaglobulinemia and Sjogren's disease in association with Lupus Nephritis), but showed resistance to T(H)17-dependent EAE and colitis. Such seemingly opposite functions of Act1 in CD40-BAFFR and IL-17R signaling are orchestrated by different domains in Act1. Whereas Act1 interacts with the IL-17R through the C-terminal SEFIR domain, Act1 is recruited to CD40 and BAFFR indirectly, which is mediated by TRAF3 through the TRAF binding site in Act1. Such delicate regulatory mechanisms may provide a common vehicle to promote balance between host defense to pathogens and tolerance to self.

Th17 cells: effector T cells with inflammatory properties

Upon activation, naïve CD4(+) T cells differentiate into effector T cells with specific effector functions and cytokine profiles. The Th1/Th2 paradigm has recently been reevaluated to include a third population of T helper cells, producing IL-17 and designated Th17. The differentiation of Th17 cells requires the coordinate and specific action of the proinflammatory cytokine IL-6 and the immunosuppressive cytokine TGF-beta. In addition, the IL-12 family member IL-23 is involved in the maintenance of these cells. Analogous to other T helper cell subsets, Th17 commitment is initiated by sequential involvement of STAT molecules, i.e. STAT3 downstream of cytokine receptors, and specific transcription factors, i.e. ROR-gammat. Recent data also support the existence of a complex network of cytokines regulating Th17 cells. Clearly, the specific effector functions of Th17 cells expand beyond previously described effects of Th1 and Th2 immunity, with specific roles in host defense against certain pathogens and in organ-specific autoimmunity. The potential dynamics of Th17 cell populations and their interplay with other inflammatory cells in the induction of tissue inflammation in host defense and organ-specific autoimmunity are discussed.

The dynamics of effector T cells and Foxp3+ regulatory T cells in the promotion and regulation of autoimmune encephalomyelitis

The Th1/Th2 paradigm of T helper cell subsets had to be revised when IL-17 producing T cells (Th17) were identified as a distinct T helper cell lineage. Th17 cells are very efficient inducers of tissue inflammation and crucial initiators of organ-specific autoimmunity. Whereas Th17 cells promote autoimmune tissue inflammation, Foxp3+ regulatory T cells (T-reg) are necessary and sufficient to prevent autoimmunity throughout the life span of an individual. Here, we review recent findings of how responses of effector T cells and T-reg cells with a defined antigen-specificity develop in autoimmune encephalomyelitis. Moreover, Th17 cells and Foxp3+ T-reg seem to be dichotomously related in that TGF-beta induces Foxp3 in naïve T cells, but TGF-beta and IL-6 together drive the generation of Th17 cells. Thus, we give an overview of how Th17 cells, induced Foxp3+ T-reg, as well as how naturally occurring T-reg cells might cooperate to promote and regulate autoimmune inflammation of the central nervous system (CNS). The monitoring of the population dynamics of these T cell subsets in reporter mice in vivo will enable us to revisit the pathogenic concept of autoimmune inflammation in the CNS and design rational and phase-specific therapeutic interventions.

TH17 cells in the big picture of immunology

The pathogenesis of chronic inflammatory diseases is assumed to depend on activated T cells interacting with resident tissue cells or migratory inflammatory cells. The discovery of new T-cell subsets such as the IL-17-producing T(H)17 and T-regulatory cells innovated our understanding of T-cell biology. Studies on new subsets confirm the important role of T cells in the instruction of tissue cells and also demonstrate the important role of feedback regulation for the polarization toward distinct T-cell subsets. The understanding of IL-17 and T(H)17 differentiation pathways has also changed the perspective of immunologists regarding the basis of chronic tissue inflammation, particularly where T(H)1 cells were considered as driving force of the pathology. This review summarizes the recent developments on T(H) cell subsets and integrates these findings into existing concepts of immunopathologic mechanisms.

Genetic regulation of T regulatory, CD4, and CD8 cell numbers by the arthritis severity loci Cia5a, Cia5d, and the MHC/Cia1 in the rat

T cells have a central role in the pathogenesis of autoimmune arthritis, and several abnormalities in T cell homeostasis have been described in rheumatoid arthritis (RA). We hypothesized that T cell phenotypes, including frequencies of different subsets of T regulatory (Treg) cells and in vitro functional responses could be genetically determined. Furthermore, we considered that the genetic contribution would be accounted for by one of the arthritis regulatory quantitative trait loci (QTL), thus providing novel clues to gene mode of action. T cells were isolated from thymus, peripheral blood, and spleen from DA (arthritis-susceptible) and ACI and F344 (arthritis-resistant) strains and from F344.DA(Cia1), DA.F344(Cia5a), and DA.F344(Cia5d) rats congenic for arthritis QTL. T cell subpopulations differed significantly between DA, F344, and ACI. DA rats had an increased frequency of CD4(+) cells, and a reduction in CD8(+) and CD4(+)CD45RC(|o) Treg cells, compared with F344. The differences in CD4/CD8 and CD4(+)CD45RC(|o) Treg cells were accounted for by Cia5a. DA rats also had a reduced frequency of CD8(+)CD45RC(|o) CD25(+) Treg cells compared with F344, and that difference was explained by Cia5d. DA rats also had a significantly lower frequency of CD4(+)CD25(+) and CD8(+)CD25(+) thymocytes, and of peripheral blood CD8(+)CD45RC(|o) Treg cells, compared with F344 rats, and that difference was accounted for by the MHC. This is the first identification of arthritis severity QTL regulating numbers of CD4(+)CD45RC(|o) (Cia5a) and CD8(+)CD45RC(|o) CD25(+) (Cia5d) Treg cells. The MHC effect on CD8(+) Treg cells and CD25(+) thymocytes raises a novel potential explanation for its association with arthritis.

Interleukins 1beta and 6 but not transforming growth factor-beta are essential for the differentiation of interleukin 17-producing human T helper cells

Interleukin 17 (IL-17)-producing CD4(+) helper T cells (T(H)-17 cells) have been linked to host defense and autoimmune diseases. In mice, the differentiation of T(H)-17 cells requires transforming growth factor-beta and IL-6 and the transcription factor RORgammat. We report here that for human naive CD4(+) T cells, RORgammat expression and T(H)-17 polarization were induced by IL-1beta and enhanced by IL-6 but were suppressed by transforming growth factor-beta and IL-12. Monocytes and conventional dendritic cells, but not monocyte-derived dendritic cells activated by microbial stimuli, efficiently induced T(H)-17 priming, and this function correlated with antigen-presenting cell production of IL-1beta and IL-6 but not IL-12. Our results identify cytokines, antigen-presenting cells and microbial products that promote the polarization of human T(H)-17 cells and emphasize an important difference in the requirements for the differentiation of T(H)-17 cells in humans and mice.

Genetic regulation of T regulatory, CD4, and CD8 cell numbers by the arthritis severity loci Cia5a, Cia5d, and the MHC/Cia1 in the rat

T cells have a central role in the pathogenesis of autoimmune arthritis, and several abnormalities in T cell homeostasis have been described in rheumatoid arthritis (RA). We hypothesized that T cell phenotypes, including frequencies of different subsets of T regulatory (Treg) cells and in vitro functional responses could be genetically determined. Furthermore, we considered that the genetic contribution would be accounted for by one of the arthritis regulatory quantitative trait loci (QTL), thus providing novel clues to gene mode of action. T cells were isolated from thymus, peripheral blood, and spleen from DA (arthritis-susceptible) and ACI and F344 (arthritis-resistant) strains and from F344.DA(Cia1), DA.F344(Cia5a), and DA.F344(Cia5d) rats congenic for arthritis QTL. T cell subpopulations differed significantly between DA, F344, and ACI. DA rats had an increased frequency of CD4(+) cells, and a reduction in CD8(+) and CD4(+)CD45RC(|o) Treg cells, compared with F344. The differences in CD4/CD8 and CD4(+)CD45RC(|o) Treg cells were accounted for by Cia5a. DA rats also had a reduced frequency of CD8(+)CD45RC(|o) CD25(+) Treg cells compared with F344, and that difference was explained by Cia5d. DA rats also had a significantly lower frequency of CD4(+)CD25(+) and CD8(+)CD25(+) thymocytes, and of peripheral blood CD8(+)CD45RC(|o) Treg cells, compared with F344 rats, and that difference was accounted for by the MHC. This is the first identification of arthritis severity QTL regulating numbers of CD4(+)CD45RC(|o) (Cia5a) and CD8(+)CD45RC(|o) CD25(+) (Cia5d) Treg cells. The MHC effect on CD8(+) Treg cells and CD25(+) thymocytes raises a novel potential explanation for its association with arthritis.

Interferon-gamma regulates susceptibility to collagen-induced arthritis through suppression of interleukin-17

OBJECTIVE

The enhanced expression of experimental arthritis in the absence of interferon-gamma (IFNgamma) suggests that IFNgamma suppresses arthritis. Interleukin-17 (IL-17) is a pivotal T cell cytokine in arthritis, and in vitro studies have indicated that IFNgamma suppresses IL-17 production. We undertook this study to test the hypothesis that resistance to collagen-induced arthritis (CIA) in C57BL/6 (B6) mice is regulated by IFNgamma-mediated suppression of IL-17.

METHODS

Wild-type (WT) B6 mice, IFNgamma-knockout (KO) B6 mice, and DBA/1 mice were immunized with type II collagen (CII) in Freund's complete adjuvant (CFA). Lymphocytes from immunized mice were analyzed for cytokine production ex vivo by intracellular staining or restimulation with CII and enzyme-linked immunosorbent assays. In vivo blockade of IL-17 was achieved with an anti-IL-17 monoclonal antibody (mAb).

RESULTS

CII restimulation of T cells from CII/CFA-immunized mice resulted in an approximately 5-fold increase in IL-17 production in IFNgamma-KO B6 mice compared with WT B6 mice. Neutralization of IFNgamma increased IL-17 production in WT B6 mice, and neutralization of IL-4 had a synergistic effect. Interestingly, the prototypical CIA-susceptible strain DBA/1 also demonstrated a high IL-17 and a low IFNgamma cytokine profile compared with WT B6 mice. Administration of the anti-IL-17 mAb attenuated arthritis in DBA/1 mice and almost completely prevented expression of arthritis in IFNgamma-KO B6 mice.

CONCLUSION

These results indicate that sensitivity of IFNgamma-deficient B6 mice to CIA is associated with high IL-17 production and that this cytokine is required for expression of arthritis in this strain.

Potential new targets in arthritis therapy: interleukin (IL)-17 and its relation to tumour necrosis factor and IL-1 in experimental arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterised by chronic joint inflammation and destruction. Interleukin (IL)-17 is a T cell cytokine expressed in the synovium and synovial fluid of patients with RA. IL-17 is a potent inducer of various cytokines such as tumour necrosis factor (TNF) and IL-1. IL-17 has been shown to have additive or even synergistic effects with TNF and IL-1 during the induction of cytokine expression and joint damage in vitro and in vivo. TNFalpha and IL-1 are considered powerful targets in the treatment of RA because of their leading role in driving the enhanced production of cytokines, chemokines, and degradative enzymes. Besides anti-TNF and anti-IL-1 therapies, whose clinical efficacy is now established, new targets have been proposed for RA which is not responding to conventional treatments. This paper discusses the role of IL-17 in experimental arthritis and its interrelationship with TNF and IL-1, currently the most targeted cytokines in the treatment of RA. IL-17 is involved in both initiation and progression of murine experimental arthritis. Studies have shown that IL-17 not only synergises with TNF, but also enhances inflammation and destruction independent of IL-1 and TNF. On the basis of these studies, the authors propose IL-17 as an interesting additional target in the treatment of RA.

The adaptor Act1 is required for interleukin 17-dependent signaling associated with autoimmune and inflammatory disease

T helper cells that produce interleukin 17 (IL-17) are associated with inflammation and the control of certain bacteria. We report here the essential involvement of the adaptor protein Act1 in IL-17 receptor (IL-17R) signaling and IL-17-dependent immune responses. After stimulation with IL-17, recruitment of Act1 to IL-17R required the IL-17R conserved cytoplasmic 'SEFIR' domain, followed by recruitment of the kinase TAK1 and E3 ubiquitin ligase TRAF6, which mediate 'downstream' activation of transcription factor NF-kappaB. IL-17-induced expression of inflammation-related genes was abolished in Act1-deficient primary astroglial and gut epithelial cells. This reduction was associated with much less inflammatory disease in vivo in both autoimmune encephalomyelitis and dextran sodium sulfate-induced colitis. Our data show that Act1 is essential in IL-17-dependent signaling in autoimmune and inflammatory disease.

Prostaglandin E2 exacerbates collagen-induced arthritis in mice through the inflammatory interleukin-23/interleukin-17 axis

OBJECTIVE

Recently, Th17 cells, a new subset of CD4+ T cells, emerged as major players in inflammation/autoimmunity. Maintenance of the Th17 phenotype requires interleukin-23 (IL-23), whereas the Th1-promoting cytokine IL-12p70 exerts a negative effect on Th17 cell differentiation. The lipid mediator prostaglandin E(2) (PGE(2)) acts primarily as a proinflammatory agent in autoimmune conditions, through mechanisms that remain to be elucidated. The aim of this study was to investigate whether PGE(2) released in inflammatory foci activates resident dendritic cells (DCs) to express IL-23 (at the expense of IL-12) and IL-6, resulting in a shift toward Th17 cell responses.

METHODS

The effect of PGE(2) on IL-23 production by DCs and subsequent induction of T cell-derived IL-17 was assessed in vitro and in vivo. The effect of the stable PGE analog misoprostol was evaluated in a murine model of rheumatoid arthritis, in conjunction with IL-23 and IL-17 expression in affected joints and draining lymph nodes.

RESULTS

In vivo administration of PGE(2) induced IL-23-dependent IL-17 production. Administration of misoprostol exacerbated collagen-induced arthritis (CIA). CIA exacerbation was associated with increased levels of IL-23p19/p40 messenger RNA and reduced expression of IL-12p35, and with increased levels of the proinflammatory cytokines IL-17, IL-1beta, IL-6, and tumor necrosis factor in the affected joint. Following ex vivo restimulation, draining lymph node cells from misoprostol-treated mice secreted higher levels of IL-17 and lower levels of interferon-gamma.

CONCLUSION

Our results indicate that PGE(2) enhances DC-derived IL-6 production and induces a shift in the IL-23/IL-12 balance in favor of IL-23, resulting in increased IL-17 production, presumably through the amplification of self-reactive Th17 cells.

The IL-17 cytokine family

IL-17A and its receptor are the founding members of a recently described cytokine family, with unique sequences and functions in the immune system and elsewhere. Consisting of six ligands (IL-17A-F) and five receptors (IL-17RA-IL-17RE) in mammals, these molecules have distinct primary amino acid structures with only minimal homology to other cytokine families. By far the best studied of these cytokines to date are IL-17A and its receptor, IL-17RA. IL-17A is produced primarily by T cells, and is the hallmark cytokine of a newly defined T helper cell subset that appears to be involved in generation of autoimmunity. Despite its production by the adaptive immune system, IL-17A exhibits proinflammatory activities similar to innate immune cytokines such as IL-1beta and TNF-alpha and appears to play important and nonredundant roles in regulating granulocytes in vivo. As a result, IL-17A also plays key roles in host defense. In contrast to the restricted expression of IL-17A, the IL-17RA receptor is ubiquitously expressed, and thus most cells are potential physiological targets of IL-17A. This chapter describes the major molecular properties, biological activities, and known signaling pathways of the IL-17 family, with an emphasis on IL-17A and IL-17RA.

IL-23 stimulates epidermal hyperplasia via TNF and IL-20R2-dependent mechanisms with implications for psoriasis pathogenesis

Aberrant cytokine expression has been proposed as an underlying cause of psoriasis, although it is unclear which cytokines play critical roles. Interleukin (IL)-23 is expressed in human psoriasis and may be a master regulator cytokine. Direct intradermal administration of IL-23 in mouse skin, but not IL-12, initiates a tumor necrosis factor-dependent, but IL-17A-independent, cascade of events resulting in erythema, mixed dermal infiltrate, and epidermal hyperplasia associated with parakeratosis. IL-23 induced IL-19 and IL-24 expression in mouse skin, and both genes were also elevated in human psoriasis. IL-23-dependent epidermal hyperplasia was observed in IL-19-/- and IL-24-/- mice, but was inhibited in IL-20R2-/- mice. These data implicate IL-23 in the pathogenesis of psoriasis and support IL-20R2 as a novel therapeutic target.

A crucial role for interleukin (IL)-1 in the induction of IL-17-producing T cells that mediate autoimmune encephalomyelitis

It was recently demonstrated that interleukin (IL)-23–driven IL-17–producing (ThIL-17) T cells mediate inflammatory pathology in certain autoimmune diseases. We show that the induction of antigen-specific ThIL-17 cells, but not T helper (Th)1 or Th2 cells, by immunization with antigens and adjuvants is abrogated in IL-1 receptor type I–deficient (IL-1RI^−/−) mice. Furthermore, the incidence of experimental autoimmune encephalomyelitis (EAE) was significantly lower in IL-1RI^−/− compared with wild-type mice, and this correlated with a failure to induce autoantigen-specific ThIL-17 cells, whereas induction of Th1 and Th2 responses was not substantially different. However, EAE was induced in IL-1RI^−/− mice by adoptive transfer of autoantigen-specific cells from wild-type mice with EAE. IL-23 alone did not induce IL-17 production by T cells from IL-1RI^−/− mice, and IL-23–induced IL-17 production was substantially enhanced by IL-1α or IL-1β, even in the absence of T cell receptor stimulation. We demonstrate essential roles for phosphatidylinositol 3-kinase, nuclear factor κB, and novel protein kinase C isoforms in IL-1– and IL-23–mediated IL-17 production. Tumor necrosis factor α also synergized with IL-23 to enhance IL-17 production, and this was IL-1 dependent. Our findings demonstrate that IL-1 functions upstream of IL-17 to promote pathogenic ThIL-17 cells in EAE.

Interleukin-17 acts independently of TNF-alpha under arthritic conditions

The proinflammatory T cell cytokine IL-17 is a potent inducer of other cytokines such as IL-1 and TNF-alpha. The contribution of TNF in IL-17-induced joint inflammation is unclear. In this work we demonstrate using TNF-alpha-deficient mice that TNF-alpha is required in IL-17-induced joint pathology under naive conditions in vivo. However, overexpression of IL-17 aggravated K/BxN serum transfer arthritis to a similar degree in TNF-alpha-deficient mice and their wild-type counterparts, indicating that the TNF dependency of IL-17-induced pathology is lost under arthritic conditions. Also, during the course of the streptococcal cell wall-induced arthritis model, IL-17 was able to enhance inflammation and cartilage damage in the absence of TNF. Additional blocking of IL-1 during IL-17-enhanced streptococcal cell wall-induced arthritis did not reduce joint pathology in TNF-deficient mice, indicating that IL-1 is not responsible for this loss of TNF dependency. These data provide further understanding of the cytokine interplay during inflammation and demonstrate that, despite a strong TNF dependency under naive conditions, IL-17 acts independently of TNF under arthritic conditions.

Cutting Edge: Interleukin 17 Signals through a Heteromeric Receptor Complex

IL-17 is an inflammatory cytokine produced primarily by a unique lineage of CD4 T cells that plays critical roles in the pathogenesis of multiple autoimmune diseases. IL-17RA is a ubiquitously expressed receptor that is essential for IL-17 biologic activity. Despite widespread receptor expression, the activity of IL-17 is most classically defined by its ability to induce the expression of inflammatory cytokines, chemokines, and other mediators by stromal cells. The lack of IL-17 responsiveness in mouse stromal cells genetically deficient in IL-17RA is poorly complemented by human IL-17RA, suggesting the presence of an obligate ancillary component whose activity is species specific. This component is IL-17RC, a distinct member of the IL-17R family. Thus, the biologic activity of IL-17 is dependent on a complex composed of IL-17RA and IL-17RC, suggesting a new paradigm for understanding the interactions between the expanded family of IL-17 ligands and their receptors.

Identification of IRF-8 and IRF-1 target genes in activated macrophages

Interferon regulatory factor 1 (IRF-1) and IRF-8, also known as interferon consensus sequence binding protein (ICSBP), are important regulators of macrophage differentiation and function. These factors exert their activities through the formation of heterocomplexes. As such, they are coactivators of various interferon-inducible genes in macrophages. To gain better insights into the involvement of these two transcription factors in the onset of the innate immune response and to identify their regulatory network in activated macrophages, DNA microarray was employed. Changes in the expression profile were analyzed in peritoneal macrophages from wild type mice and compared to IRF-1 and IRF-8 null mice, before and following 4 h exposure to IFN-gamma and LPS. The expression pattern of 265 genes was significantly changed (up/down) in peritoneal macrophages extracted from wild type mice following treatment with IFN-gamma and LPS, while no changes in the expression levels of these genes were observed in samples of the same cell-type from both IRF-1 and IRF-8 null mice. Among these putative target genes, numerous genes are involved in macrophage activity during inflammation. The expression profile of 10 of them was further examined by quantitative RT-PCR. In addition, the promoter regions of three of the identified genes were analyzed by reporter gene assay for the ability to respond to IRF-1 and IRF-8. Together, our results suggest that both IRF-1 and IRF-8 are involved in the transcriptional regulation of these genes. We therefore suggest a broader role for IRF-1 and IRF-8 in macrophages differentiation and maturation, being important inflammatory mediators.