Interleukin 27 limits autoimmune encephalomyelitis by suppressing the development of interleukin 17-producing T cells

IL-6 promotes NK cell production of IL-17 during toxoplasmosis

Previous studies have implicated T cell production of IL-17 in resistance to Toxoplasma gondii as well as the development of immune-mediated pathology during this infection. Analysis of C57BL/6 and C57BL/6 RAG(-/-) mice challenged with T. gondii-identified NK cells as a major innate source of IL-17. The ability of soluble Toxoplasma Ag to stimulate NK cells to produce IL-17 was dependent on the presence of accessory cells and the production of IL-6, IL-23, and TGF-beta. In contrast, these events were inhibited by IL-2, IL-15, and IL-27. Given that IL-6 was one of the most potent enhancers of NK cell production of IL-17, further studies revealed that only a subset of NK cells expressed both chains of the IL-6R, IL-6 upregulated expression of the Th17-associated transcription factor RORgammat, and that IL-6(-/-) mice challenged with T. gondii had a major defect in NK cell production of IL-17. Together, these data indicate that many of the same cytokines that regulate Th17 cells are part of a conserved pathway that also control innate production of IL-17 and identify a major role for IL-6 in the regulation of NK cell responses.

Exacerbation of delayed-type hypersensitivity responses in EBV-induced gene-3 (EBI-3)-deficient mice

Epstein-Barr virus-induced gene-3 (EBI-3) associates with p28 to form interleukin-27 (IL-27) or with IL-12p35 to form IL-35. Both IL-27 and IL-35 have immunosuppressive functions and especially IL-35 has been implicated in the suppressive function of regulatory T cells (Treg). To address the role of EBI-3 in immune regulation, delayed-type hypersensitivity (DTH) responses were examined in EBI-3-deficient (EBI-3(-/-)) mice. EBI-3(-/-) mice developed deteriorated DTH responses as shown by the enhanced footpad swelling and augmented infiltration of inflammatory cells into the antigen-challenged footpads as compared with wild-type (WT) mice. While EBI-3-deficiency showed little effects on antigen-specific IFN-gamma production of lymph node cells, IL-17 production was drastically augmented in EBI-3(-/-) cells as compared with in WT cells. In addition, reduced IL-10 production was also evident in EBI-3(-/-) CD4(+) T cells. Interestingly, the development and suppressive function of Treg to inhibit effector T cell proliferation was not affected by EBI-3-deficiency. These data clearly demonstrated the immunosuppressive function of EBI-3 and provided complementary evidence that EBI-3 and EBI-3-containing cytokines might be taken into consideration as potential targets for some immune-related diseases.

Pharmacologic inhibition of MEK-ERK signaling enhances Th17 differentiation

The cytokines and transcription factors that promote Th17 cell development have been extensively studied. However, the signaling pathways that antagonize Th17 differentiation remain poorly characterized. In this study, we report that pharmacologic inhibition of MEK-ERK signaling enhances the in vitro differentiation of Th17 cells and increases their gene expression of il-17a, il-17f, il-21, il-22, and il-23r. IL-2, which suppresses Th17 differentiation via STAT5 activation, also acts through ERK signaling to inhibit Th17 generation. In turn, ERK signaling is found to potentiate the production of IL-2 and activate STAT5, suggesting the existence of an autoregulatory loop to constrain Th17 development. Finally, compared with the transfer of untreated Th17 cells, the transfer of ERK-inhibited Th17 cells leads to accelerated onset and exacerbated colitis in immunodeficient mice. Our data indicate that MEK-ERK signaling negatively regulates Th17 differentiation in a Th cell-intrinsic manner.

T-cell based immunotherapy in experimental autoimmune encephalomyelitis and multiple sclerosis

One of the reasons multiple sclerosis (MS) has been considered a T-cell mediated autoimmune disease is that a similar experimental disease can be induced in certain rodents and primates by immunization with myelin antigens, leading to T-cell-mediated inflammatory demyelination in the CNS. In addition, most if not all pharmacological treatments available for MS are biologically active on T cells. In this article we review the principles of T-cell-based immunotherapies and the specific actions of current and novel treatments on T-cell functions, when these are known. For both licensed and innovative agents, we also discuss biological actions on other immune cell types. Finally, we offer a brief perspective on expected changes in the use of MS immunotherapies in the near future.

IRF4 and its regulators: evolving insights into the pathogenesis of inflammatory arthritis?

Accumulating evidence from murine and human studies supports a key role for interleukin-17 (IL-17) and IL-21 in the pathogenesis of inflammatory arthritis. The pathways and molecular mechanisms that underlie the production of IL-17 and IL-21 are being rapidly elucidated. This review focuses on interferon regulatory factor 4 (IRF4), a member of the IRF family of transcription factors, which has emerged as a crucial controller of both IL-17 and IL-21 production. We first outline the complex role of IRF4 in the function of CD4(+) T cells and then discuss recent studies from our laboratory that have revealed a surprising role for components of Rho GTPase-mediated pathways in controlling the activity of IRF4. A better understanding of these novel pathways will hopefully provide new insights into mechanisms responsible for the development of inflammatory arthritis and potentially guide the design of novel therapeutic approaches.

Immunological basis for the development of tissue inflammation and organ-specific autoimmunity in animal models of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis (MS) that has shaped our understanding of autoimmune tissue inflammation in the central nervous system (CNS). Major therapeutic approaches to MS have been first validated in EAE. Nevertheless, EAE in all its modifications is not able to recapitulate the full range of clinical and histopathogenic aspects of MS. Furthermore, autoimmune reactions in EAE-prone rodent strains and MS patients may differ in terms of the relative involvement of various subsets of immune cells. However, the role of specific molecules that play a role in skewing the immune response towards pathogenic autoreactivity is very similar in mice and humans. Thus, in this chapter, we will focus on the identification of a novel subset of inflammatory T cells, called Th17 cells, in EAE and their interplay with other immune cells including protective regulatory T cells (T-regs). It is likely that the discovery of Th17 cells and their relationship with T-regs will change our understanding of organ-specific autoimmune diseases in the years to come.

Negative regulation of autoimmune demyelination by the inhibitory receptor CLM-1

Multiple sclerosis and its preclinical model, experimental autoimmune encephalomyelitis, are marked by perivascular inflammation and demyelination. Myeloid cells, derived from circulating progenitors, are a prominent component of the inflammatory infiltrate and are believed to directly contribute to demyelination and axonal damage. How the cytotoxic activity of these myeloid cells is regulated is poorly understood. We identify CMRF-35-like molecule-1 (CLM-1) as a negative regulator of autoimmune demyelination. CLM-1 is expressed on inflammatory myeloid cells present in demyelinating areas of the spinal cord after immunization of mice with MOG35-55 (myelin oligodendrocyte glycoprotein) peptide. Absence of CLM-1 resulted in significantly increased nitric oxide and proinflammatory cytokine production, along with increased demyelination and worsened clinical scores, whereas T cell responses in the periphery or in the spinal cord remained unaffected. This study thus identifies CLM-1 as a negative regulator of myeloid effector cells in autoimmune demyelination.

Potential role of Th17 cells in the pathogenesis of inflammatory bowel disease

The etiopathology of inflammatory bowel disease (IBD) remains elusive. Accumulating evidence suggests that the abnormality of innate and adaptive immunity responses plays an important role in intestinal inflammation. IBD including Crohn’s disease (CD) and ulcerative colitis (UC) is a chronic inflammatory disease of the gastrointestinal tract, which is implicated in an inappropriate and overactive mucosal immune response to luminal flora. Traditionally, CD is regarded as a Th1-mediated inflammatory disorder while UC is regarded as a Th2-like disease. Recently, Th17 cells were identified as a new subset of T helper cells unrelated to Th1 or Th2 cells, and several cytokines [e.g. interleukin (IL)-21, IL-23] are involved in regulating their activation and differentiation. They not only play an important role in host defense against extracellular pathogens, but are also associated with the development of autoimmunity and inflammatory response such as IBD. The identification of Th17 cells helps us to explain some of the anomalies seen in the Th1/Th2 axis and has broadened our understanding of the immunopathological effects of Th17 cells in the development of IBD.

Immunomodulatory Activity of IL-27 in Human Periapical Lesions

IL-27, a cytokine with pro-inflammatory and anti-inflammatory properties, is a new member of the IL-6/IL-12 family, whose function in periapical lesions is unknown. We hypothesized that the production of IL-27 and its effect depend upon the type of immune/inflammatory response and clinical presentation of periapical lesions. We tested this hypothesis by studying the expression and function of IL-27 in human periapical lesions, both in situ and in culture. Immunohistochemistry demonstrated the strongest expression of IL-27 by endothelial cells and mononuclear phagocytes. Its production by periapical lesion mononuclear cells (PL-MNC), especially in symptomatic lesions, was significantly higher compared with that in peripheral blood MNC and correlated with the frequency of CD14+ and CD3+ cells. Exogenous IL-27 stimulated Th1 and down-regulated Th17 cytokine production by PL-MNC from symptomatic lesions, but down-regulated Th1 and Th2 responses in asymptomatic lesions. These findings suggest that IL-27 is an immunomodulatory cytokine in periapical lesions, with complex biological effects.

Intestinal effector T cells in health and disease

Crohn's disease and ulcerative colitis are the two major forms of chronic relapsing inflammatory disorders of the human intestines collectively referred to as inflammatory bowel disease (IBD). Though a complex set of autoinflammatory disorders that can be precipitated by diverse genetic and environmental factors, a feature that appears common to IBD pathogenesis is a dysregulated effector T cell response to the commensal microbiota. Due to the heightened effector T cell activity in IBD, developmental and functional pathways that give rise to these cells are potential targets for therapeutic intervention. In this review, we highlight recent advances in our understanding of effector T cell biology in the context of intestinal immune regulation and speculate on their potential clinical significance.

Differential effect of IL-27 on developing versus committed Th17 cells

IL-27 counters the effect of TGF-beta+IL-6 on naive CD4(+) T cells, resulting in near complete inhibition of de novo Th17 development. In contrast, little is known about the effect of IL-27 on already differentiated Th17 cells. A better understanding of how IL-27 regulates these cells is needed to evaluate the therapeutic potential of IL-27 in Th17 cells-associated diseases. In this study, we show that IL-27 had surprisingly little effect on committed Th17 cells, despite its expression of a functional IL-27R. Contrary to de novo differentiation of Th17 cells, IL-27 did not suppress expression of retinoid-related orphan receptor (ROR)gammat or RORalpha in committed Th17 cells. Consistent with this finding, the frequency of committed Th17 cells and their cytokine secretion remained unaffected by IL-27. Both memory Th17 cells (CD4(+)CD25(-)CD62L(low)) that developed in vivo and encephalitogenic Th17 cells infiltrating the CNS of mice developing experimental autoimmune encephalomyelitis produced similar amounts of IL-17A when reactivated with IL-23 in the absence and presence of exogenous IL-27. Finally, IL-27 failed to suppress encephalitogenicity of Th17 cells in an adoptive transfer of experimental autoimmune encephalomyelitis. Analysis ex vivo of transferred Th17 cells in the spleen and CNS of recipient mice showed that cells retained similar phenotype irrespective of whether cells were treated or not with IL-27. Our data demonstrate that in contrast to inhibition of de novo differentiation of Th17 cells, IL-27 has little or no effect on committed Th17 cells. These findings indicate that therapeutic applications of IL-27 might have a limited efficacy in inflammatory conditions where aggressive Th17 responses have already developed.

IFN-beta inhibits human Th17 cell differentiation

IFN-beta-1a has been used over the past 15 years as a primary therapy for relapsing-remitting multiple sclerosis (MS). However, the immunomodulatory mechanisms that provide a therapeutic effect against this CNS inflammatory disease are not yet completely elucidated. The effect of IFN-beta-1a on Th17 cells, which play a critical role in the development of the autoimmune response, has not been extensively studied in humans. We have investigated the effect of IFN-beta-1a on dendritic cells (DCs) and naive CD4(+)CD45RA(+) T cells derived from untreated MS patients and healthy controls in the context of Th17 cell differentiation. We report that IFN-beta-1a treatment down-regulated the expression of IL-1beta and IL-23p19 in DCs, whereas it induced the gene expression of IL-12p35 and IL-27p28. We propose that IFN-beta-1a-mediated up-regulation of the suppressor of cytokine signaling 3 expression, induced via STAT3 phosphorylation, mediates IL-1beta and IL-23 down-regulation, while IFN-beta-1a-induced STAT1 phosphorylation induces IL-27p28 expression. CD4(+)CD45RA(+) naive T cells cocultured with supernatants from IFN-beta-1a-treated DCs exhibited decreased gene expression of the Th17 cell markers retinoic acid-related orphan nuclear hormone receptor c (RORc), IL-17A, and IL-23R. A direct IFN-beta-1a treatment of CD45RA(+) T cells cultured in Th17-polarizing conditions also down-regulated RORc, IL-17A, and IL-23R, but up-regulated IL-10 gene expression. Studies of the mechanisms involved in the Th17 cell differentiation suggest that IFN-beta-1a inhibits IL-17 and induces IL-10 secretion via activated STAT1 and STAT3, respectively. IFN-beta's suppression of Th17 cell differentiation may represent its most relevant mechanism of selective suppression of the autoimmune response in MS.

Role of interleukin-12 family cytokines in the cellular response to mycobacterial disease

Interleukin (IL)-12 is a multifunctional cytokine acting as a key regulator of cell-mediated immune responses through the differentiation of naïve CD4+ T cells into type 1 helper T cells (Th1) producing interferon-gamma. As our knowledge of IL-12 family members is rapidly growing, it will be important to specify their involvement in the regulation of mycobacterial infection. This article is a review of the current knowledge regarding the functions of the IL-12 family cytokines in the immune host defense system against mycobacteria. Specifically, this review aims to describe recent scientific evidence concerning the protective role of some members of the IL-12 family cytokines for the control of mycobacterial infection, as well as to summarize knowledge of the potential use of the IL-12 family members as potent adjuvants in the prevention and treatment of mycobacterial infectious diseases. In addition, recent data supporting the importance of the IL-12 family members in mycobacterial diseases in relation to Th17 function are discussed. This examination will help to improve our understanding of the immune response to mycobacterial infection and also improve vaccine design and immunotherapeutic intervention against tuberculosis.

IL-27 regulates IL-10 and IL-17 from CD4+ cells in nonhealing Leishmania major infection

Control of infection caused by Leishmania major requires the development of IFN-gamma+CD4+ lymphocytes for the induction of microbicidal activity in host macrophages. We recently reported on the inability of conventionally resistant C57BL/6 mice to successfully resolve infection by an isolate of L. major, despite a strong IFN-gamma response by the host. Susceptibility was caused by Ag-specific IL-10 from CD4+ cells that were also producing IFN-gamma. In the present studies, we have explored the role for IL-27 in the regulation of IL-10 from Th1 cells in leishmaniasis. Cytokine analysis of CD4+ cells in the lesions and draining lymph nodes of infected IL-27R-deficient (WSX-1(-/-)) mice revealed diminished IL-10 from IFN-gamma+ CD4+ cells, which was accompanied by a reduction in total IFN-gamma+CD4+ cells and an increase in IL-4. Despite the inhibition of IL-10 from CD4+ cells, no significant change in parasite numbers was observed, due both to the shift in the Th1/Th2 balance and to residual levels of IL-10. Strikingly, infected WSX-1(-/-) mice developed more severe lesions that were associated with the appearance of IL-17+ CD4+ cells, demonstrating a function for IL-27 in blocking the development of inappropriate Th17 cells during L. major infection. The results demonstrate the pleiotropic effects that IL-27 has on L. major-driven Th1, Th2, and Th17 development, and reinforce its function as a key regulatory cytokine that controls the balance between immunity and pathology.

[Immune regulation by IL-27 for therapeutic usage]

Cytokine-mediated immunity plays a crucial role in the pathogenesis of various diseases including autoimmunity. Recently, IL-27 was identified, which along with IL-12, 23 and 35 belongs to the IL-12 cytokine family. These family members play roles in regulation of Th cell differentiation. IL-27 is unique in that while it induces Th1 differentiation, the same cytokine suppresses immune responses. In the absence of IL-27-mediated immunosuppression, hyper-production of various pro-inflammatory cytokines concomitant with severe inflammation in affected organs was observed in IL-27 receptor alpha chain (WSX-1)-deficient mice infected with Trypanosoma cruzi. Experimental allergic or inflammatory responses were also enhanced in WSX-1-deficient mice. The immunosuppressive effects of IL-27 depend on inhibition of the development of Th 17 cells (a newly identified inflammatory T helper population), and induction of IL-10 production. Moreover, administration of IL-27 or augmentation of IL-27 signaling suppresses some diseases of autoimmune or allergic origin, including encephalitis, arthritis, and systemic lupus erythematosus, demonstrating its potential in therapy of diseases mediated by inflammatory cytokines.

Th17 cells at the crossroads of innate and adaptive immunity against infectious diseases at the mucosa

T helper type 17 (Th17) cells are a distinct lineage of T cells that produce the effector molecules IL-17, IL-17F, IL-21, and IL-22. Although the role of Th17 cells in autoimmunity is well documented, there is growing evidence that the Th17 lineage and other interleukin (IL)-17-producing cells are critical for host defense against bacterial, fungal, and viral infections at mucosal surfaces. Here we summarize recent progress in our understanding of the function of IL-17-producing cells as a bridge between innate and adaptive immunity against infectious diseases at the mucosa.

Production of both IL-27 and IFN-gamma after the treatment with a ligand for invariant NK T cells is responsible for the suppression of Th2 response and allergic inflammation in a mouse experimental asthma model

Using an allergen-induced airway inflammation model, we show that an injection of alpha-galactosylceramide (alpha-GalCer), a ligand for invariant NK T (iNKT) cells, induced IL-27 and that this process is essential for the attenuation of the Th2 response. After the systemic administration of alpha-GalCer into the mice primed with OVA in alum, Th2 cytokine production of OVA-primed CD4(+) T cells in their lymph nodes, IgG1 and IgE Ab formation, and infiltration of eosinophils in bronchoalveolar lavage after the OVA challenge were suppressed. Systemic administration of rIFN-gamma into OVA-primed mice could not reproduce these effects of alpha-GalCer. IL-27p28 was detected both in the culture supernatant of alpha-GalCer-stimulated spleen cells and in the serum of the alpha-GalCer-treated mice, but not in the iNKT cell-deficient mice. Splenic iNKT cells produced IL-27p28 in the culture supernatant upon stimulation with PMA plus ionomycin, although the transcript of IL-27p28 in the iNKT cells was constitutively expressed regardless of the stimulation. By contrast, the transcript of IL-27EBI3 was induced in the iNKT cells upon stimulation with PMA plus ionomycin in vitro and with alpha-GalCer treatment in vivo, suggesting that IL-27 (p28/EBI3) could be produced by iNKT cells in an activation-dependent manner. Although repeated injections of rIL-27 did not substitute for the effects of a single injection of alpha-GalCer, administration of rIL-27 along with rIFN-gamma reproduced in vivo effects of the alpha-GalCer injection. These data indicate that production of both IL-27 and IFN-gamma by the alpha-GalCer treatment is responsible for suppression of the Th2 response and allergic inflammation.

IL-27 is a key regulator of IL-10 and IL-17 production by human CD4+ T cells

Although the physiologic pathways that control regulatory T cells (Foxp3-expressing regulatory T cells, IL-10-secreting Tr1 cells) and Th17 cells in rodents have been defined, the factors that control these differentiation pathways in humans are not well understood. In this study, we show that IL-27 promotes the differentiation of IL-10-secreting Tr1 cells while inhibiting Th17 generation and molecules associated with Th17 function. Furthermore, IL-27 inhibits IL-17-polarizing cytokines on dendritic cells, which in turn decrease IL-17 secretion from T cells. Our results demonstrate that IL-27 plays a key role in human T cells by promoting IL-10-secreting Tr1 cells and inhibiting Th17 cells and thus provides a dual regulatory mechanism to control autoimmunity and tissue inflammation.

Tolerogenic signals delivered by dendritic cells to T cells through a galectin-1-driven immunoregulatory circuit involving interleukin 27 and interleukin 10

Despite their central function in orchestrating immunity, dendritic cells (DCs) can respond to inhibitory signals by becoming tolerogenic. Here we show that galectin-1, an endogenous glycan-binding protein, can endow DCs with tolerogenic potential. After exposure to galectin-1, DCs acquired an interleukin 27 (IL-27)-dependent regulatory function, promoted IL-10-mediated T cell tolerance and suppressed autoimmune neuroinflammation. Consistent with its regulatory function, galectin-1 had its highest expression on DCs exposed to tolerogenic stimuli and was most abundant from the peak through the resolution of autoimmune pathology. DCs lacking galectin-1 had greater immunogenic potential and an impaired ability to halt inflammatory disease. Our findings identify a tolerogenic circuit linking galectin-1 signaling, IL-27-producing DCs and IL-10-secreting T cells, which has broad therapeutic implications in immunopathology.

Periplocoside A prevents experimental autoimmune encephalomyelitis by suppressing IL-17 production and inhibits differentiation of Th17 cells

AIM

The aim of this study was to determine the therapeutic effect of Periplocoside A (PSA), a natural product isolated from the traditional Chinese herbal medicine Periploca sepium Bge, in MOG(35-55) (myelin oligodendrocyte glycoprotein 35-55)-induced experimental autoimmune encephalomyelitis (EAE).

METHODS

Female C57BL/6 mice immunized with MOG(35-55) were treated with (50 mg/kg or 25 mg/kg) or without PSA following immunization and continuously throughout the study. The degree of CNS inflammation was evaluated by H&E staining. Anti-MOG-specific recall responses were analyzed by [3H]-Thymidine incorporation, ELISA, and RT-PCR. The proportion of IL-17-producing T cells was measured by flow cytometry.

RESULTS

Oral administration of PSA significantly reduced the incidence and severity of EAE, which closely paralleled the inhibition of MOG(35-55)-specific IL-17 production. Importantly, PSA inhibited the transcription of IL-17 mRNA and RORgammat. Further studies examining intracellular staining and adoptive transfer EAE validated the direct suppressive effect of PSA on Th17 cells. In vitro studies also showed that PSA significantly inhibited the differentiation of Th17 cells from murine purified CD4+ T cells in a dose-dependent manner.

CONCLUSION

PSA ameliorated EAE by suppressing IL-17 production and inhibited the differentiation of Th17 cells in vitro. Our results provide new insight into the potential mechanisms underlying the immunosuppressive and anti-inflammatory effects of PSA.

IL-27 regulates homeostasis of the intestinal CD4+ effector T cell pool and limits intestinal inflammation in a murine model of colitis

IL-27 limits CD4(+) T(H)17 cell development in vitro and during inflammatory responses in the CNS. However, whether IL-27-IL-27R interactions regulate the homeostasis or function of CD4(+) T cell populations in the intestine is unknown. To test this, we examined CD4(+) T cell populations in the intestine of wild-type and IL-27R(-/-) mice. Naive IL-27R(-/-) mice exhibited a selective decrease in the frequency of IFN-gamma producing CD4(+) T(H)1 cells and an increase in the frequency of T(H)17 cells in gut-associated lymphoid tissues. Associated with elevated expression of IL-17A, IL-27R(-/-) mice exhibited earlier onset and significantly increased severity of clinical disease compared with wild-type controls in a murine model of intestinal inflammation. Rag(-/-)/IL-27R(-/-) mice were also more susceptible than Rag(-/-) mice to development of dextran sodium sulfate-induced intestinal inflammation, indicating an additional role for IL-27-IL-27R in the regulation of innate immune cell function. Consistent with this, IL-27 inhibited proinflammatory cytokine production by activated neutrophils. Collectively, these data identify a role for IL-27-IL-27R interaction in controlling the homeostasis of the intestinal T cell pool and in limiting intestinal inflammation through regulation of innate and adaptive immune cell function.

Epstein-barr virus-induced gene-3 is expressed in human atheroma plaques

Atherosclerosis is characterized by a complex immune response in the vessel wall, involving both inflammation and autoimmune processes. Epstein-Barr virus-induced gene 3 (Ebi3) is a member of the interleukin (IL)-12 heterodimeric cytokine family, which has important immunomodulatory functions. To date, little is known about the role of Ebi3 in vascular disease. We examined the expression of Ebi3 in human atheromatous lesions and analyzed its transcriptional regulation in vascular cells. The in situ expression of Ebi3 in human endarterectomy specimens was analyzed by immunohistochemistry. In these lesions, smooth muscle cells expressed Ebi3 as well as the IL-27alpha/p28 and IL-12alpha/p35 subunits. Primary aortic smooth muscle cells up-regulated Ebi3 in response to proinflammatory stimuli like tumor necrosis factor-alpha and interferon-gamma. Interestingly, pretreatment of these cells with the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone strongly reduced Ebi3 induction. Chromatin immunoprecipitation experiments revealed that this inhibition is due to interference with p65/RelA recruitment to the Ebi3 promoter. Our data support a possible role of Ebi3 in atherogenesis either as homodimer or as IL-27/IL-35 heterodimer, and suggest that Ebi3 could be an interesting target for therapeutic manipulation in atherosclerosis.

The role of retinoic acid-related orphan receptor variant 2 and IL-17 in the development and function of human CD4+ T cells

Th17 cells are defined by their capacity to produce IL-17, and are important mediators of inflammation and autoimmunity. Human Th17 cells express high levels of the retinoic acid-related orphan receptor variant 2 (RORC2), but it is currently unclear whether expression of this transcription factor alone is sufficient to recapitulate all the known properties of Th17 cells. We used lentivirus-mediated transduction to investigate the role of RORC2 in defining aspects of the human Th17 cell lineage. Expression of RORC2 induced production of IL-17A, IL-22, IL-6 and TNF-alpha, a Th17-cell-associated chemokine receptor profile and upregulation of CD161. RORC2-transduced T cells were hypo-responsive to TCR-mediated stimulation, a property shared with ex vivo Th17 cells and overcome by addition of exogenous IL-2 or IL-15. Co-culture experiments revealed that RORC2-expressing cells were partially resistant to Treg cells since production of IL-17 and proliferation were not suppressed. Evidence that IL-17 stimulates CD4(+) T cells to produce IL-2 and proliferate suggested that the resistance of Th17 cells to Treg-mediated suppression may be partly attributed to IL-17 itself. These findings demonstrate that expression of RORC2 in T cells has functional consequences beyond altering cytokine production and provides insight into the factors regulating the development of human Th17 cells.

Homeostatic (IL-7) and effector (IL-17) cytokines as distinct but complementary target for an optimal therapeutic strategy in inflammatory bowel disease

PURPOSE OF REVIEW

This review focuses on CD4+ T cells involved in the mediation of inflammatory tissue damage in murine models of inflammatory bowel diseases (IBDs). In particular, we describe the distinct roles of the homeostatic cytokine IL-7, which is essential to the maintenance of colitogenic memory CD4+ cells, and the newly discovered effector cytokine IL-17. We also discuss the close correlation between colitogenic Th17-type CD4+ T cells and inducible CD4+CD25+Foxp3+ regulatory T cells.

RECENT FINDINGS

IBDs are characterized by wasting and chronic intestinal inflammation induced by many different cytokine-mediated pathways. It is clearly recognized that medical and surgical interventions do not cure Crohn's disease because relapse is the rule after remission. Until a few years ago, IBD was classified into Th1-dependent, that is, Crohn's disease, and Th2-dependent, that is, ulcerative colitis, phenotypes. However, in recent years, it has been shown that new T-cell subclasses, that is, Th17 and regulatory T cells (T(R)), exist independently of Th1 and Th2 and that they play a central role in modulating IBD.

SUMMARY

The persistence of IL-7-dependent colitogenic memory CD4+ T cells is critical to the maintenance of experimental colitis. On the other hand, though Th1 and Th2 colitogenic memory CD4+ cells exist, in recent years the central role of IL-17-producing Th17-type cells in IBD has attracted renewed interest. The development of molecularly targeted therapies aimed at a variety of different Th-dependent pathogenic mechanisms may represent a novel approach to IBD therapy.

Expression of WSX1 in tumors sensitizes IL-27 signaling-independent natural killer cell surveillance

It is well known that the interleukin (IL)-27 receptor WSX1 is expressed in immune cells and induces an IL-27-dependent immune response. Opposing this conventional dogma, this study reveals a much higher level of WSX1 expression in multiple types of epithelial tumor cells when compared with normal epithelial cells. Expression of exogenous WSX1 in epithelial tumor cells suppresses tumorigenicity in vitro and inhibits tumor growth in vivo. Different from the role of WSX1 in immune cells, the antitumor activity of WSX1 in epithelial tumor cells is independent of IL-27 signaling but is mainly dependent on natural killer (NK) cell surveillance. Deficiency of either the IL-27 subunit EBV-induced gene 3 or the IL-27 receptor WSX1 in the host animals had no effect on tumor growth inhibition induced by WSX1 expression in tumor cells. Expression of WSX1 in epithelial tumor cells enhances NK cell cytolytic activity against tumor cells, whereas the absence of functional NK cells impairs the WSX1-mediated inhibition of epithelial tumor growth. The underlying mechanism by which WSX1 expression in tumor cells enhances NK cytolytic activity is dependent on up-regulation of NKG2D ligand expression. Our results reveal an IL-27-independent function of WSX1: sensitizing NK cell-mediated antitumor surveillance via a NKG2D-dependent mechanism.

TGF-beta promotes Th17 cell development through inhibition of SOCS3

TGF-beta, together with IL-6 and IL-21, promotes Th17 cell development. IL-6 and IL-21 induce activation of STAT3, which is crucial for Th17 cell differentiation, as well as the expression of suppressor of cytokine signaling (SOCS)3, a major negative feedback regulator of STAT3-activating cytokines that negatively regulates Th17 cells. However, it is still largely unclear how TGF-beta regulates Th17 cell development and which TGF-beta signaling pathway is involved in Th17 cell development. In this report, we demonstrate that TGF-beta inhibits IL-6- and IL-21-induced SOCS3 expression, thus enhancing as well as prolonging STAT3 activation in naive CD4(+)CD25(-) T cells. TGF-beta inhibits IL-6-induced SOCS3 promoter activity in T cells. Also, SOCS3 small interfering RNA knockdown partially compensates for the action of TGF-beta on Th17 cell development. In mice with a dominant-negative form of TGF-beta receptor II and impaired TGF-beta signaling, IL-6-induced CD4(+) T cell expression of SOCS3 is higher whereas STAT3 activation is lower compared with wild-type B6 CD4(+) T cells. The addition of a TGF-beta receptor I kinase inhibitor that blocks Smad-dependent TGF-beta signaling greatly, but not completely, abrogates the effect of TGF-beta on Th17 cell differentiation. Our data indicate that inhibition of SOCS3 and, thus, enhancement of STAT3 activation is at least one of the mechanisms of TGF-beta promotion of Th17 cell development.

T(H)17 versus Treg cells in renal transplant candidates: effect of a previous transplant

INTRODUCTION

The T(H)1 and T(H)2 cells were described several years ago. However, this dichotomy has been disrupted by the description of other CD4(+) T cell subsets: the proinflammatory interleukin (IL)-17-producing T cells (T(H)17) and regulatory T cells (Tregs). The latter group inhibits the immune responses driven by T(H)1, T(H)2, and T(H)17 cells. IL-6 is involved in T(H)17 development, down-regulating Treg differentiation. Our hypothesis suggested that an imbalance between T(H)17 and Tregs enhances immune responses among renal transplant patients.

MATERIALS AND METHODS

We studied 26 end-stage renal disease (ESRD) subjects and 10 patients awaiting a second renal transplant after previous graft dysfunction. We assessed the number of CD4(+)CD25(+)Foxp3(+) cells and serum levels of IL-17, the prototypic interleukin of T(H)17 cells.

RESULTS

We observed a lower number of CD4(+)CD25(+)Foxp3(+) T cells among patients with previous graft dysfunction than those with ESRD (median 3.37 vs 8.63 cells/mm(3), P = .008). In contrast, IL-17 serum levels were augmented in graft dysfunction (median 4.45 pg/mL) compared with ESRD patients (1.39 pg/mL, P = .036), suggesting a proinflammatory state in patients awaiting a second renal transplant.

CONCLUSION

The emerging alloresponse from a previous transplant favors the generation of T(H)17 instead of Treg cells. The enhanced activity of T(H)17 cells in retransplanted patients may down-regulate Treg cells, producing a proinflammatory environment that favors rejection of the next transplant.

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.

IL-27 blocks RORc expression to inhibit lineage commitment of Th17 cells

IL-27 is secreted by APCs in response to inflammatory stimuli and exerts a proinflammatory Th1-enhancing activity but also has significant anti-inflammatory functions. We examined the molecular mechanism by which IL-27 regulates TGFbeta plus IL-6- or IL-23-dependent Th17 development in the mouse and human systems. IL-27 inhibited the production of IL-17A and IL-17F in naive T cells by suppressing, in a STAT1-dependent manner, the expression of the Th17-specific transcription factor RORgamma t. The in vivo significance of the role of IL-27 was addressed in delayed-type hypersensitivity response and experimental autoimmune encephalomyelitis (EAE). By generating mice deficient for the p28 subunit of IL-27, we showed that IL-27 regulated the severity of delayed-type hypersensitivity response and EAE through its effects on Th17 cells. Furthermore, up-regulation of IL-10 in the CNS, which usually occurs late after EAE onset and plays a role in the resolution of the disease, was notably absent in IL-27p28(-/-) mice. These results show that IL-27 acts as a negative regulator of the developing IL-17A response in vivo, suggesting a potential therapeutic role for IL-27 in autoimmune diseases.

IL-23 drives pathogenic IL-17-producing CD8+ T cells

IL-17-producing CD8(+) T cells (Tc17) appear to play a role in a range of conditions, such as autoimmunity and cancer. Thus far, Tc17 cells have been only marginally studied, resulting in a paucity of data on their biology and function. We demonstrate that Tc17 and Th17 cells share similar developmental characteristics, including the previously unknown promoting effect of IL-21 on Tc17 cell differentiation and IL-23-dependent expression of IL-22. Both STAT1 and STAT4 are required for optimal development of Tc17 cells and maximal secretion of cytokines. Tc17 cells are cytotoxic, and they can be either pathogenic or nonpathogenic upon adoptive transfer in the model of autoimmune diabetes. Tc17 cells treated with TGF-beta1 plus IL-6 are not diabetogenic, whereas IL-23-treated cells potently induce the disease. IL-17A and IL-17F are necessary but not sufficient for diabetes induction by Tc17 cells. Tc17 cells treated with TGF-beta1 plus IL-6 or IL-23 likely differ in pathogenicity due to their disparate capacity to attract other immune cells and initiate inflammation.

Plasticity of CD4+ T cell lineage differentiation

The differentiation of naive CD4(+) T cells into lineages with distinct effector functions has been considered to be an irreversible event. T helper type 1 (Th1) cells stably express IFN-gamma, whereas Th2 cells express IL-4. The discovery and investigation of two other CD4(+) T cell subsets, induced regulatory T (iTreg) cells and Th17 cells, has led to a rethinking of the notion that helper T cell subsets represent irreversibly differentiated endpoints. Accumulating evidence suggests that CD4(+) T cells, particularly iTreg and Th17 cells, are more plastic than previously appreciated. It appears that expression of Foxp3 by iTreg cells or IL-17 by Th17 cells may not be stable and that there is a great degree of flexibility in their differentiation options. Here, we will discuss recent findings that demonstrate the plasticity of CD4(+) T cell differentiation and the biological implications of this flexibility.

IL-27 is expressed in chronic human eczematous skin lesions and stimulates human keratinocytes

BACKGROUND

IL-27 is produced by antigen-presenting cells early during immune responses. IL-27 has been described to support T-cell polarization along the T(H)1 lineage but also to exert important anti-inflammatory responses in later phases of inflammation in murine models.

OBJECTIVE

It was the aim of this study to analyze the potential role of IL-27 in epidermal inflammatory skin responses in human subjects.

METHODS

Surface receptor expression and apoptosis of human primary keratinocytes were analyzed by means of flow cytometry. Supernatants of stimulated keratinocytes were either analyzed by means of ELISA or submitted to chemotaxis assays. RT-PCR from lesional skin and phospho-specific Western blotting were performed.

RESULTS

Both subunits of IL-27 were expressed in chronic lesional allergic eczematous skin, whereas the IL-27 subunit EBV-induced gene 3 was not detectable in the acute phase of eczema. Human primary keratinocytes responded to IL-27. Stimulation of keratinocytes with IL-27 resulted in activation of the signal transducer and activator of transcription 1 and 3 pathways. Major effects found for IL-27 include CXCL10 production and MHC class I upregulation. Importantly, we could demonstrate that IL-27 acts as a priming signal on keratinocytes able to amplify chemokine production and surface molecule expression when used before a second signal, such as TNF-alpha. The effects of IL-27 could not be mimicked by IL-6, IL-12, or IL-23.

CONCLUSION

These results support the notion that IL-27 might act in an inflammatory, disease-maintaining manner in the epidermal compartment of patients with eczema.

Autoimmune T cell responses in the central nervous system

Autoreactive T cell responses have a crucial role in central nervous system (CNS) diseases such as multiple sclerosis. Recent data indicate that CNS autoimmunity can be mediated by two distinct lineages of CD4+ T cells that are defined by the production of either interferon-gamma or interleukin-17. The activity of these CD4+ T cell subsets within the CNS influences the pathology and clinical course of disease. New animal models show that myelin-specific CD8+ T cells can also mediate CNS autoimmunity. This Review focuses on recent progress in delineating the pathogenic mechanisms, regulation and interplay between these different T cell subsets in CNS autoimmunity.

The IL-23/Th17 axis in the immunopathogenesis of psoriasis

Abnormal production of inflammatory mediators is believed to play an important role in the pathogenesis of psoriasis. Emerging data, both in mice and in humans, put the spotlight on a new subset of T helper (Th) cells, in part characterized by their production of IL-17 and accordingly named Th17 cells. Here, we review the development, characterization, and function of human Th17 cells as well as the crucial role of IL-23 in the context of Th17-cell-dependent chronic inflammation in psoriasis. We further discuss recent clinical trials targeting the IL-23/Th17 axis in psoriasis.

TLR2 deficiency leads to increased Th17 infiltrates in experimental brain abscesses

TLR2 plays a pivotal role in recognizing Staphylococcus aureus, a common etiologic agent of CNS parenchymal infections, such as brain abscess. We previously reported that brain abscesses of TLR2 knockout (KO) mice exhibited elevated IL-17 levels, suggesting the presence of an alternative pathway available to respond to S. aureus infection that may involve Th17 cells. Both CD4(+) and CD8(+) T cell infiltrates were elevated in brain abscesses of TLR2 KO mice at days 3, 7, and 14 postinfection compared with wild-type animals. Intracellular cytokine staining revealed a significant increase in the frequency of IL-17-producing Th17 cells in TLR2 KO mice with relatively few IFN-gamma-positive cells. gammadelta T cells were also a source of IL-17 in brain abscesses. Microglia, astrocytes, and macrophages were shown to express both IL-17RA and IL-17RC. Despite receptor expression, IL-17 was relatively ineffective at eliciting glial activation, whereas the cytokine augmented the ability of TNF-alpha to induce CXCL2 and CCL2 expression by macrophages. Based on the ability of IL-17 to elicit the release of chemokines and other proinflammatory mediators, we propose that the exaggerated IL-17 response that occurs in TLR2 KO mice functions in a compensatory manner to control brain abscess pathogenesis, with cells other than glia as targets for IL-17 action. This is supported by our findings in which innate immune infiltrates were not significantly different between TLR2 KO and wild-type mice in conjunction with the lack of prolonged alterations in the synthesis of other proinflammatory molecules during the course of infection.

Th17 cells in rheumatoid arthritis and systemic lupus erythematosus

Recent work has implicated a novel Th effector cell subset, the Th17 cell subset, in the development of both rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) because of the ability of Th17 cells to produce cytokines like IL-17 and IL-21 that can drive both inflammatory and humoral responses. In this review, we will discuss recent studies that have begun elucidating the factors that regulate the development of Th17 cells and provide a brief overview of the role of Th17 cells in RA and SLE.

Barrier immunity and IL-17

CD4+ T(H)17 cells display a featured role in barrier immunity. This effector population of T cells is important for clearance of microorganisms but can also promote autoimmunity at barrier sites. Recent work has indicated that these effector cells share a pathway with CD4+ regulatory T cells (T(R) cells) that also have a critical function in barrier protection and immune regulation. The development and function of T(H)17 cells, and their relationship with T(R) cells are discussed.

Therapeutic potential of IL-27 in multiple sclerosis?

BACKGROUND

Multiple sclerosis (MS) is a debilitating neurological disease, characterized by inflammatory demyelination and axonal degeneration in the CNS. Currently approved therapies are partially effective, however safer and more effective treatments are needed.

OBJECTIVE/METHODS

To assess the therapeutic potential of the heterodimeric cytokine, IL-27 in MS, based on the current literature.

RESULTS/CONCLUSIONS

IL-27 exerts profound anti-inflammatory effects in several infectious and experimental autoimmune models. In particular, suppressive effects on helper T cells, which are implicated in the pathogenesis of MS, suggest that IL-27 may be therapeutically relevant in MS. However, while exciting discoveries have been made, further work is required particularly in human health and disease, to understand the diverse roles of IL-27 and its therapeutic potential.

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.

IL-31-IL-31R interactions limit the magnitude of Th2 cytokine-dependent immunity and inflammation following intestinal helminth infection

IL-31 is a recently identified cytokine made predominantly by CD4(+) Th2 cells and its receptor, IL-31R, is expressed by a number of cell types including monocytes, epithelial cells, and T cells. Originally identified as a potential mediator of inflammation in the skin, we recently reported a novel function for endogenous IL-31R interactions in limiting type 2 inflammation in the lung. However, whether IL-31-IL-31R interactions regulate immunity or inflammation at other mucosal sites, such as the gut, is unknown. In this study, we report a regulatory role for IL-31-IL-31R interactions in the intestine following infection with the gastrointestinal helminth Trichuris muris, immunity to which is critically dependent on CD4(+) Th2 cells that produce IL-4 and IL-13. IL-31Ralpha was constitutively expressed in the colon and exposure to Trichuris induced the expression of IL-31 in CD4(+) T cells. In response to Trichuris infection, IL-31Ralpha(-/-) mice exhibited increased Th2 cytokine responses in the mesenteric lymph nodes and elevated serum IgE and IgG1 levels compared with wild type mice. IL-31Ralpha(-/-) mice also displayed enhanced goblet cell hyperplasia and a marked increase in secretion of goblet cell-derived resistin-like molecule beta into the intestinal lumen. Consistent with their exacerbated type 2 inflammatory responses, IL-31Ralpha(-/-) mice exhibited accelerated expulsion of Trichuris with significantly decreased worm burdens compared with their wild type counterparts early following infection. Collectively, these data provide the first evidence of a function for IL-31-IL-31R interactions in limiting the magnitude of type 2 inflammatory responses within the intestine.