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

Tyrosine kinase 2 promotes sepsis-associated lethality by facilitating production of interleukin-27

The aim of this study was to test the hypothesis that gene expression and release of IL-27 may be modulated by Tyk2. Macrophages derived from the peritoneum or bone marrow of C57BL/10SnJ (WT) mice produced abundant amounts of IL-27(p28) following TLR4 activation by LPS. In contrast, production of IL-27(p28), but not EBI3, was reduced by ∼50% in TLR4-activated macrophages derived from mice with genetic deficiency of Tyk2 compared with WT macrophages. Frequencies of IL-27(p28)+F4/80+CD11b+ cells were lower in TLR4-activated macrophages derived from Tyk2-/- mice. Mechanistically, Tyk2-/- resulted in disruption of a type I IFN-dependent mechanism for production of IL-27(p28), which was induced by type I IFNs, and release of IL-27 was defective in macrophages from IFN-β-/- and IFNAR1-/- mice. In contrast, Tyk2 was not required to mediate the effects of IL-27 on target gene expression in CD4(+) T cells. In vivo, we observed that Tyk2-/- mice have improved survival following endotoxic shock or polymicrobial sepsis induced by CLP. Plasma levels of IL-27(p28) during endotoxic shock or polymicrobial sepsis were markedly reduced in Tyk2-/- mice compared with WT mice. Disruption of IL-27 signaling using IL-27RA-/- mice was protective against sepsis-associated mortality. These data suggest that Tyk2 may mediate adverse outcomes of SIRS by promoting the production of IL-27. In conclusion, this report identifies Tyk2 as a prerequisite factor in the molecular networks that are involved in generation of IL-27.

IL-27 in human secondary lymphoid organs attracts myeloid dendritic cells and impairs HLA class I-restricted antigen presentation

Different cytokines play crucial roles in inflammation and in polarizing immune responses, including IL-27 that exerts pro- and anti-inflammatory functions. Although the activity of IL-27 is well characterized in murine immune cells, only limited information is available regarding the natural cellular sources of IL-27 in humans and its effects on human immune cells. Dendritic cells (DCs) are the most potent professional APCs that in the immature state are positioned throughout peripheral tissues by acting as sentinels, sensing the presence of Ags. Activated DCs migrate into the lymph nodes and direct Ag-specific T cell responses, thus acting as key players in both adaptive and innate immunity. In this study we asked whether IL-27 is produced by human secondary lymphoid organs and what is its functional role on human DCs. To our knowledge, we provide the first evidence that 1) in lymph nodes, macrophages are the major source for IL-27; 2) immature and mature human DCs express functional IL-27R; 3) IL-27 exerts immunosuppressive activity by crippling the Ag processing machinery in immature DCs under steady-state conditions and after pulsing with a viral Ag; and 4) IL-27 is chemotactic for human DCs. Our findings highlight novel mechanisms underlying the immunosuppressive activity of IL-27, suggesting that this cytokine may function as a homeostatic cytokine in secondary lymphoid organs by limiting duration and/or intensity of ongoing adaptive immune responses. The results presented in this study pave the way to future studies aimed at investigating whether dysregulation of IL-27 expression and function may be involved in pathogenesis of autoimmune disease and cancer.

IL-27 improves migrational and antiviral potential of CB dendritic cells

Interleukin (IL)-27 is known to be increased considerably in cord blood (CB) dendritic cells (DCs) after TLR ligation. Previously, we demonstrated that also basal IL-27 levels are higher in CB DCs. Here, we examined effects of IL-27 on monocyte derived dendritic cells (moDCs) to approach its particular role in the specialized immune system of the human neonate. Exogenous IL-27 promotes IL-27 transcription in CB and adult blood (AB) moDCs. IL-27 acts on CB moDCs primarily by significantly augmenting IL-27 protein, secondarily by increasing transcription of CXCL10 among other chemokines, chemokine receptor CCR1, interferon stimulated genes, transcription factor IRF8 and genes involved in antigen presentation. Furthermore, CB moDCs respond to IL-27 with augmented IL-8 and Tumor necrosis factor (TNF)-α. The results suggest that IL-27 enhances migrational and antiviral properties of CB dendritic cells.

High level of IL-27 positively correlated with Th17 cells may indicate liver injury in patients infected with HBV

BACKGROUND

Interleukin-6/IL-12 family cytokines play a key role in inflammatory diseases via their effects on the differentiation or regulation of T helper cells.

AIMS

The aim of this study was to determine the role of interleukin-27 (IL-27) and its association with helper T cells in hepatitis B virus (HBV)-infected patients.

METHODS

Samples were assessed from 51 HBV-infected patients [28 chronic hepatitis B (CHB) subjects and 23 acute-on-chronic liver failure (ACLF) subjects] and 18 normal controls (NC). Serum IL-27 levels were examined by enzyme-linked immunosorbent assay. Circulating helper T cells were determined using flow cytometry and associations between IL-27 expression and helper T cells were analysed.

RESULTS

Serum IL-27 levels rose in HBV-infected patients (502.88 ± 23.35 pg/ml) compared to (NC, 277.14 ± 23.96 pg/ml, P < 0.0001). Furthermore, it significantly increased in patients with ACLF (587.90 ± 33.08 pg/ml) when compared with CHB (433.04 ± 26.57 pg/ml, P = 0.001). However, no statistically significant differences were observed between IL-27 and the presence of HBeAg. High levels of IL-27 then positively correlated with Tbil levels (r = 0.401, P = 0.004), but negatively associated with prothrombin time activity levels (r = -0.496, P < 0.001), and a slightly negative correlation trend with HBV-DNA loads (r = -0.228, P = 0.107) existed in these HBV-infected subjects. Additionally, frequency of circulating interleukin-17-producing CD4(+) T cells (Th17 cells) increased in HBV-infected patients (ACLF, mean, 5.39%; CHB, median, 3.12%) as compared to NC subjects (median, 2.22%, P < 0.0001). Moreover, correlation analysis showed that serum IL-27 level was positively associated with circulating Th17 cells (r = 0.342, P = 0.036).

CONCLUSION

These results provided evidence that IL-27 was positively correlated with Th17 cells commitment, and may exerted a proinflammatory effect in the development of liver injury in HBV-infected patients.

The transcription factor IRF8 activates integrin-mediated TGF-β signaling and promotes neuroinflammation

Recent epidemiological studies have identified interferon regulatory factor 8 (IRF8) as a susceptibility factor for multiple sclerosis (MS). However, how IRF8 influences the neuroinflammatory disease has remained unknown. By studying the role of IRF8 in experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, we found that Irf8(-/-) mice are resistant to EAE. Furthermore, expression of IRF8 in antigen-presenting cells (APCs, such as macrophages, dendritic cells, and microglia), but not in T cells, facilitated disease onset and progression through multiple pathways. IRF8 enhanced αvβ8 integrin expression in APCs and activated TGF-β signaling leading to T helper 17 (Th17) cell differentiation. IRF8 induced a cytokine milieu that favored growth and maintenance of Th1 and Th17 cells, by stimulating interleukin-12 (IL-12) and IL-23 production, but inhibiting IL-27 during EAE. Finally, IRF8 activated microglia and exacerbated neuroinflammation. Together, this work provides mechanistic bases by which IRF8 contributes to the pathogenesis of MS.

Cytokine regulation of immune tolerance

The immune system provides defenses against invading pathogens while maintaining immune tolerance to self-antigens. This immune homeostasis is harmonized by the direct interactions between immune cells and the cytokine environment in which immune cells develop and function. Herein, we discuss three non-redundant paradigms by which cytokines maintain or break immune tolerance. We firstly describe how anti-inflammatory cytokines exert direct inhibitory effects on immune cells to enforce immune tolerance, followed by discussing other cytokines that maintain immune tolerance through inducing CD4(+)Foxp3(+) regulatory T cells (Tregs), which negatively control immune cells. Interleukin (IL)-2 is the most potent cytokine in promoting the development and survival of Tregs, thereby mediating immune tolerance. IL-35 is mainly produced by Tregs, but its biology function remains to be defined. Finally, we discuss the actions of proinflammatory cytokines that breach immune tolerance and induce autoimmunity, which include IL-7, IL-12, IL-21, and IL-23. Recent genetic studies have revealed the role of these cytokines (or their cognate receptors) in susceptibility to autoimmune diseases. Taken together, we highlight in this review the cytokine regulation of immune tolerance, which will help in further understanding of human diseases that are caused by dysregulated immune system.

A requirement of dendritic cell-derived interleukin-27 for the tumor infiltration of regulatory T cells

Tregs (Foxp3⁺CD4⁺) are enriched in tumors to foster a tolerant microenvironment that inhibits antitumor immune response. IL-27 is reported to regulate the development and function of Tregs in vitro and in vivo; however, the effects of endogenous IL-27 on Tregs in the tumor microenvironment remain elusive. We demonstrated that in the absence of DC-derived IL-27, Tregs were decreased significantly in transplanted B16 melanoma, transplanted EL-4 lymphoma, and MCA-induced fibrosarcoma by using IL-27p28 conditional KO mice. Further studies revealed that IL-27 promoted the expression of CCL22, which is established to mediate the recruitment of peripheral Tregs into tumors. Tumor-associated DCs were identified as the major source of CCL22 in tumor sites, and IL-27 could induce CCL22 expression in an IL-27R-dependent manner. Intratumoral reconstitution of rmCCL22 or rmIL-27, but not rmIL-27p28, significantly restored the tumor infiltration of Tregs in IL-27p28 KO mice. Correlated with a decreased number of Tregs, tumor-infiltrating CD4 T cells were found to produce much more IFN-γ in IL-27p28 KO mice, which highlighted the physiological importance of Tregs in suppressing an antitumor immune response. Overall, our results identified a novel mechanism of action of IL-27 on Tregs in the context of cancers.

Oral delivery of IL-27 recombinant bacteria attenuates immune colitis in mice

BACKGROUND & AIMS

Treatment of inflammatory bowel disease would benefit from specific targeting of therapeutics to the intestine. We developed a strategy for localized delivery of the immunosuppressive cytokine interleukin (IL)-27, which is synthesized actively in situ by the food-grade bacterium Lactococcus lactis (LL-IL-27), and tested its ability to reduce colitis in mice.

METHODS

The 2 genes encoding mouse IL-27 were synthesized with optimal codon use for L lactis and joined with a linker; a signal sequence was added to allow for product secretion. The construct was introduced into L lactis. Colitis was induced via transfer of CD4(+)CD45RB(hi) T cells into Rag(-/-) mice to induce colitis; 7.5 weeks later, LL-IL-27 was administered to mice via gavage. Intestinal tissues were collected and analyzed.

RESULTS

LL-IL-27 administration protected mice from T-cell transfer-induced enterocolitis and death. LL-IL-27 reduced disease activity scores, pathology features of large and small bowel, and levels of inflammatory cytokines in colonic tissue. LL-IL-27 also reduced the numbers of CD4(+) and IL-17(+) T cells in gut-associated lymphoid tissue. The effects of LL-IL-27 required production of IL-10 by the transferred T cells. LL-IL-27 was more effective than either LL-IL-10 or systemic administration of recombinant IL-27 in reducing colitis in mice. LL-IL-27 also reduced colitis in mice after administration of dextran sodium sulfate.

CONCLUSIONS

LL-IL-27 reduces colitis in mice by increasing the production of IL-10. Mucosal delivery of LL-IL-27 could be a more effective and safer therapy for inflammatory bowel disease.

The good and the bad of neuroinflammation in multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory, demyelinating, neurodegenerative disorder of the central nervous system (CNS). It is widely considered a T-cell mediated autoimmune disease that develops in genetically susceptible individuals, possibly under the influence of certain environmental trigger factors. The invasion of autoreactive CD4+ T-cells into the CNS is thought to be a central step that initiates the disease. Several other cell types, including CD8+ T-cells, B-cells and phagocytes appear to be involved in causing inflammation and eventually neurodegeneration. But inflammation is not entirely deleterious in MS. Evidence has accumulated in the recent years that show the importance of regulatory immune mechanisms which restrain tissue damage and initiate regeneration. More insight into the beneficial aspects of neuroinflammation might allow us to develop new treatment strategies for this enigmatic disease.

Helper T cell plasticity: impact of extrinsic and intrinsic signals on transcriptomes and epigenomes

CD4(+) helper T cells are crucial for autoimmune and infectious diseases; however, the recognition of the many, diverse fates available continues unabated. Precisely what controls specification of helper T cells and preserves phenotypic commitment is currently intensively investigated. In this review, we will discuss the major factors that impact helper T cell fate choice, ranging from cytokines and the microbiome to metabolic control and epigenetic regulation. We will also discuss the technological advances along with the attendant challenges presented by "big data," which allow the understanding of these processes on comprehensive scales.

Th17 cells in immunity and autoimmunity

Th17 and IL-17 play important roles in the clearance of extracellular bacterial and fungal infections. However, strong evidence also implicates the Th17 lineage in several autoimmune disorders including multiple sclerosis, psoriasis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, and asthma. The Th17 subset has also been connected with type I diabetes, although whether it plays a role in the pathogenicity of or protection from the disease remains a controversial issue. In this review we have provided a comprehensive overview of Th17 pathogenicity and function, including novel evidence for a protective role of Th17 cells in conjunction with the microbiota gut flora in T1D onset and progression.

Oral Escherichia coli colonization factor antigen I fimbriae ameliorate arthritis via IL-35, not IL-27

A Salmonella therapeutic expressing enterotoxigenic Escherichia coli colonization factor Ag I (CFA/I) fimbriae protects against collagen-induced arthritis (CIA) by eliciting two regulatory T cell (Treg) subsets: TGF-β-producing Foxp3(-)CD39(+)CD4(+) T cells and IL-10-producing Foxp3(+)CD39(+)CD4(+) T cells. However, it is unclear whether CFA/I fimbriae alone are protective and whether other regulatory cytokines are involved, especially in the context for the EBI3-sharing cytokines, Treg-derived IL-35 and APC-derived IL-27, both capable of suppressing Th17 cells and regulating autoimmune diseases. Subsequent evaluation revealed that a single oral dose of purified, soluble CFA/I fimbriae protected against CIA as effectively as did Salmonella-CFA/I and found that Foxp3(+)CD39(+)CD4(+) T cells were the source of secreted IL-35, whereas IL-27 production by CD11c(+) cells was inhibited. Inquiring into their relevance, CFA/I fimbriae-treated IL-27R-deficient (WSX-1(-/-)) mice were equally protected against CIA as were wild-type mice, suggesting a limited role for IL-27. In contrast, CFA/I fimbriae-mediated protection was abated in EBI3(-/-) mice, accompanied by the loss of TGF-β- and IL-10-producing Tregs. Adoptive transfer of C57BL/6 CD39(+)CD4(+) T cells to EBI3(-/-) mice with concurrent CFA/I plus IL-35 treatment effectively stimulated Tregs suppressing proinflammatory collagen II-specific Th cells. In contrast, recipients cotransferred with C57BL/6 and EBI3(-/-) CD39(+)CD4(+) T cells and treated with CFA/I plus IL-35 were not protected, implicating the importance of endogenous IL-35 for conferring CFA/I-mediated protection. Thus, CFA/I fimbriae stimulate IL-35 required for the coinduction of TGF-β and IL-10.

Evaluating the potential of IL-27 as a novel therapeutic agent in HIV-1 infection

Interleukin 27 (IL-27) is an immunomodulatory cytokine with important roles in both the innate and adaptive immune systems. In the last five years, the addition of exogenous IL-27 to primary cell cultures has been demonstrated to decrease HIV-1 replication in a number of cell types including peripheral blood mononuclear cells (PBMCs), CD4+ T cells, macrophages and dendritic cells. These in vitro findings suggest that IL-27 may have therapeutic value in the setting of HIV-1 infection. In this review, we describe the current knowledge of the biology of IL-27, its effects primarily on HIV-1 replication but also in other viral infections and explore its potential role as a therapeutic cytokine for the treatment of patients with HIV-1 infection.

IL-25 prevents T cell-mediated neurotoxicity by decreasing LFA-1 expression

Autoimmune diseases such as multiple sclerosis (MS) are thought to develop due to a dysregulation in the normal T(H)1-T(H)17/T(H)2 immune system balance, where pro-inflammatory responses with a T(H)1/T(H)17 prevalence develop. Some therapeutic treatments in MS promote a shift toward a TH2-prevalent environment and this has been shown to be protective. However, not all patients respond to current immunomodulatory treatments in MS so that new immunomodulatory drugs that can promote a shift of the immune system into an anti-inflammatory T(H)2 status are needed. IL-25 is a cytokine of the IL-17 family with powerful anti-inflammatory properties. This study demonstrates that IL-25 exerts neuroprotective functions by reducing T cell-mediated killing of human fetal neurons. The mechanism of action of this IL-25-mediated neuroprotective effect appears to be linked to reduction in the expression of the adhesion molecule LFA-1, which is relevant in stabilizing the immune synapse during cytotoxicity.

In vivo action of IL-27: reciprocal regulation of Th17 and Treg cells in collagen-induced arthritis

Interleukin (IL)-27 is a novel cytokine of the IL-6/IL-12 family that has been reported to be involved in the pathogenesis of autoimmune diseases and has a pivotal role as both a pro- and anti-inflammatory cytokine. We investigated the in vivo effects of IL-27 on arthritis severity in a murine collagen-induced arthritis (CIA) model and its mechanism of action regarding control of regulatory T (Tregs) and IL-17-producing T helper 17 (Th17) cells. IL-27-Fc-treated CIA mice showed a lower severity of arthritis. IL-17 expression in the spleens was significantly decreased in IL-27-Fc-treated CIA mice compared with that in the CIA model. The Th17 population was decreased in the spleens of IL-27-Fc-treated CIA mice, whereas the CD4⁺CD25⁺Foxp3⁺ Treg population increased. In vitro studies revealed that IL-27 inhibited IL-17 production in murine CD4⁺ T cells, and the effect was associated with retinoic acid-related orphan receptor γT and signal transducer and activator of transcription 3 inhibition. In contrast, fluorescein isothiocyanate-labeled forkhead box P3 (Foxp3) and IL-10 were profoundly augmented by IL-27 treatment. Regarding the suppressive capacity of Treg cells, the proportions of CTLA-4⁺ (cytotoxic T-lymphocyte antigen 4), PD-1⁺ (programmed cell death protein 1) and GITR⁺ (glucocorticoid-induced tumor necrosis factor receptor) Tregs increased in the spleens of IL-27-Fc-treated CIA mice. Furthermore, in vitro differentiated Treg cells with IL-27 exerted a more suppressive capacity on T-cell proliferation. We found that IL-27 acts as a reciprocal regulator of the Th17 and Treg populations in CD4⁺ cells isolated from healthy human peripheral blood mononuclear cells (PBMCs), as well as from humans with rheumatoid arthritis (RA) PBMCs. Our study suggests that IL-27 has the potential to ameliorate overwhelming inflammation in patients with RA through a reciprocal regulation of Th17 and Treg cells.

Alteration of intestinal microbiota in mice orally administered with salmon cartilage proteoglycan, a prophylactic agent

Proteoglycan (PG) extracted from salmon nasal cartilage has potential to be a prophylactic agent. Daily oral administration of the PG attenuates systemic inflammatory response in the experimental mouse models. In this study, we applied the culture-independent approach to investigate an alteration of intestinal microbiota composition in PG-administered mice. The results indicated that the population level of bacilli increased in the small and large intestine upon PG administration. On the other hand, the population level of clostridia decreased in the large intestine. The proportion of bacteria that are able to ferment saccharides and produce short-chain fatty acids increased in the small intestine and decreased in the large intestine. Importantly, population level of probiotic lactobacilli and bacteria exhibiting the immunomodulatory effect increased in the PG-administered mice. In addition, several disease-associated bacteria decreased upon PG administration. These results provided an understanding of the specific role of PG involved in host immune modulation and supported our hypothesis that daily oral administration of PG improves the overall balance in composition of the intestinal microbial community.

Neonatal macrophages express elevated levels of interleukin-27 that oppose immune responses

Microbial infections are a major cause of infant mortality worldwide because of impaired immune defences in this population. The nature of this work was to further understand the mechanistic limitations of the neonatal and infant immune response. Interleukin-27 (IL-27) is a heterodimeric cytokine of the IL-12 family that is produced primarily by antigen-presenting cells and is immunosuppressive toward a variety of immune cell types. We show that IL-27 gene expression is elevated in cord blood-derived macrophages relative to macrophages originating from healthy adults. We also evaluated the duration over which elevated IL-27 gene expression may impact immune responses in mice. Age-dependent analysis of IL-27 gene expression indicated that levels of IL-27 remained significantly elevated throughout infancy and then declined in adult mice. Flow cytometric analysis of intracellular cytokine-stained splenocytes further confirmed these results. Interleukin-27 may be induced during pregnancy to contribute to the immunosuppressive environment at the fetal-maternal interface because we demonstrate dose-responsive gene expression to progesterone in macrophages. Neutralization of IL-27 in neonatal macrophages improved the ability of these cells to limit bacterial replication. Moreover, neutralization of IL-27 during incubation with the Mycobacterium bovis bacillus Calmette-Guérin vaccine augmented the level of interferon-γ elicited from allogeneic CD4+ T lymphocytes. This suggests that blocking IL-27 during vaccination and infection may improve immune responses in newborn and infant populations. Furthermore, mice will be a suitable model system to further address these possibilities.

IL-27p28 inhibits central nervous system autoimmunity by concurrently antagonizing Th1 and Th17 responses

Central nervous system (CNS) autoimmunity such as uveitis and multiple sclerosis is accompanied by Th1 and Th17 responses. In their corresponding animal models, experimental autoimmune uveitis (EAU) and experimental autoimmune encephalomyelitis (EAE), both responses are induced and can drive disease independently. Because immune responses have inherent plasticity, therapeutic targeting of only one pathway could promote the other, without reducing pathology. IL-27p28 antagonizes gp130, required for signaling by IL-27 and IL-6, which respectively promote Th1 and Th17 responses. We therefore examined its ability to protect the CNS by concurrently targeting both effector responses. Overexpression of IL-27p28 in vivo ameliorated EAU as well as EAE pathology and reduced tissue infiltration by Th1 and Th17 cells in a disease prevention, as well as in a disease reversal protocol. Mechanistic studies revealed inhibition of Th1 and Th17 commitment in vitro and decreased lineage stability of pre-formed effectors in vivo, with reduction in expression of gp130-dependent transcription factors and cytokines. Importantly, IL-27p28 inhibited polarization of human T cells to the Th1 and Th17 effector pathways. The ability of IL-27p28 to inhibit generation as well as function of pathogenic Th1 and Th17 effector cells has therapeutic implications for controlling immunologically complex autoimmune diseases.

Epstein Barr virus-induced 3 (EBI3) together with IL-12 negatively regulates T helper 17-mediated immunity to Listeria monocytogenes infection

Although the protective functions by T helper 17 (Th17) cytokines against extracellular bacterial and fungal infection have been well documented, their importance against intracellular bacterial infection remains unclear. Here, we investigated the contribution of Th17 responses to host defense against intracellular bacteria Listeria monocytogenes and found that Th17 cell generation was suppressed in this model. Unexpectedly, mice lacking both p35 and EBI3 cleared L. monocytogenes as efficiently as wild-type mice, whereas p35-deficient mice failed to do so. Furthermore, both innate cells and pathogen-specific T cells from double-deficient mice produced significantly higher IL-17 and IL-22 compared to wild-type mice. The bacterial burden in the liver of double-deficient mice treated with anti-IL-17 was significantly increased compared to those receiving a control Ab. Transfer of Th17 cells specific for listeriolysin O as well as administration of IL-17 and IL-22 significantly suppressed bacterial growth in p35-deficient mice, indicating the critical contribution of Th17 responses to host defense against the intracellular pathogen in the absence of IL-12 and proper Th1 responses. Our findings unveil a novel immune evasion mechanism whereby the intracellular bacteria exploit IL-27EBI3 to suppress Th17-mediated protective immunity.

IL-27 acts on DCs to suppress the T cell response and autoimmunity by inducing expression of the immunoregulatory molecule CD39

Dendritic cells (DCs) control the balance between effector T cells and regulatory T cells in vivo. Hence, the study of DCs might identify mechanisms of disease pathogenesis and guide new therapeutic approaches for disorders mediated by the immune system. We found that interleukin 27 (IL-27) signaling in mouse DCs limited the generation of effector cells of the TH1 and TH17 subsets of helper T cells and the development of experimental autoimmune encephalomyelitis (EAE). The effects of IL-27 were mediated at least in part through induction of the immunoregulatory molecule CD39 in DCs. IL-27-induced CD39 decreased the extracellular concentration of ATP and downregulated nucleotide-dependent activation of the NLRP3 inflammasome. Finally, therapeutic vaccination with IL-27-conditioned DCs suppressed established relapsing-remitting EAE. Thus, IL-27 signaling in DCs limited pathogenic T cell responses and the development of autoimmunity.

Immune privilege as an intrinsic CNS property: astrocytes protect the CNS against T-cell-mediated neuroinflammation

Astrocytes have many functions in the central nervous system (CNS). They support differentiation and homeostasis of neurons and influence synaptic activity. They are responsible for formation of the blood-brain barrier (BBB) and make up the glia limitans. Here, we review their contribution to neuroimmune interactions and in particular to those induced by the invasion of activated T cells. We discuss the mechanisms by which astrocytes regulate pro- and anti-inflammatory aspects of T-cell responses within the CNS. Depending on the microenvironment, they may become potent antigen-presenting cells for T cells and they may contribute to inflammatory processes. They are also able to abrogate or reprogram T-cell responses by inducing apoptosis or secreting inhibitory mediators. We consider apparently contradictory functions of astrocytes in health and disease, particularly in their interaction with lymphocytes, which may either aggravate or suppress neuroinflammation.

Modulation of inflammation by interleukin-27

A growing body of evidence suggests an essential role of the heterodimeric cytokine, IL-27, for regulating immunity. IL-27 is composed of two subunits (p28 and EBI3) and is classified as a member of the IL-12 family of cytokines. APCs have been recognized as a major cellular source of IL-27 following activation with microbial products or IFNs (types I and II). In this review, we describe the current knowledge of the implications of IL-27 during the pathogenesis of infectious and autoimmune diseases. Experimental studies have used genetically targeted IL-27RA-/- mice, EBI3-/- mice, and p28-/- mice or involved study designs with administration of bioengineered IL-27/IL-27RA homologs. Whereas many reports have described that IL-27 suppresses inflammation, we also review the current literature, suggesting promotion of inflammation by IL-27 in some settings. Recent advances have also been made in understanding the cross-talk of cleavage products of the complement system with IL-27-mediated immune responses. Additional data on IL-27 have been obtained recently by observational studies in human patients with acute and chronic inflammatory diseases. Collectively, the findings from the past decade identify IL-27 as a critical immunoregulatory cytokine, especially for T cells, whereas some controversy is fueled by results challenging the view of IL-27 as a classical silencer of inflammation.

The IL-18 antagonist IL-18-binding protein is produced in the human ovarian cancer microenvironment

PURPOSE

Interleukin (IL)-18 is an immune-enhancing cytokine, which induces IFN-γ production, T-helper 1 responses, and antitumor effects. In turn, IFN-γ stimulates IL-18-binding protein production, which blocks IL-18 activity. In view of the potential use of IL-18 in epithelial ovarian cancer (EOC) immunotherapy, here, we studied IL-18BP expression and its regulation by cytokines in EOC cells in vitro and in vivo.

EXPERIMENTAL DESIGN

Expression and production of IL-18BP in EOC cell lines, primary ovarian carcinomas, and the corresponding normal tissues, patients' serum, and ascites were investigated by immunochemistry, ELISA, screening of gene expression profiles, and reverse-transcription PCR.

RESULTS

Analysis of gene expression profiles revealed that IL18BP mRNA is increased in EOC tumors compared with normal ovary cells. Release of IL-18BP was detectable in EOC sera and to a greater extent in the ascites, indicating production at the tumor site. Indeed, immunochemical analyses on cells isolated from the ascites and on tumor sections indicated that IL-18BP is expressed in both tumor cells and tumor-associated leukocytes, which displayed a CD3-CD20-NKp46-CD13+CD14low phenotype. EOC cell lines do not constitutively express IL-18BP. However, its release is inducible both by IFN-γ stimulation in vitro and by xenotransplantation of EOC cells in immune-deficient mice, suggesting a role for the microenvironment. In vitro experiments and immunochemistry indicated that IL-27 is also involved in IL-18BP upregulation in EOC cell lines and primary cells through STAT1 activation. Together, these data indicate that IL-18BP, which is produced in EOC in response to microenvironmental factors, may inhibit endogenous or exogenous IL-18 activity.

Overexpression of Epstein-Barr virus-induced gene 3 protein (EBI3) in MRL/lpr mice suppresses their lupus nephritis by activating regulatory T cells

To identify the effect of an imbalance of Th1/Th2 cytokines on the development of autoimmune glomerulonephritis (lupus nephritis), we studied the modification of pathological changes in diffuse proliferative glomerulonephritis (DPGN) and membranous glomerulonephritis (MGN) in MRL/lpr mice, which are animal models of systemic lupus erythematosus (SLE). Transgenic MRL/lpr mice (Tg) that overexpressed Epstein--Barr virus-induced gene 3 (EBI3) showed almost normal renal function, which was demonstrated by healing of glomerulonephritis upon renal histology, as compared to the wild-type MRL/lpr (Wt) mice. The levels of anti-dsDNA antibodies and IgE decreased in the Tg mice compared to Wt mice. Quantitative real-time PCR indicated an increase in the mRNA levels of FoxP3, and a decrease in that of IFNγ in the splenocytes of Tg mice as compared to Wt mice. In addition, flow cytometric analysis showed an increase in CD4(+)CD25(+)FoxP3(+)-T cells in the former, as compared to the latter. Our findings suggest that EBI3-overexpression in MRL/lpr mice induces generation of regulatory T cells, which causes suppression of autoimmune and inflammatory reactions by affecting the Th1/Th2 cytokine balance.

Cytokine mediated tissue fibrosis

Acute inflammation is a recognised part of normal wound healing. However, when inflammation fails to resolve and a chronic inflammatory response is established this process can become dysregulated resulting in pathological wound repair, accumulation of permanent fibrotic scar tissue at the site of injury and the failure to return the tissue to normal function. Fibrosis can affect any organ including the lung, skin, heart, kidney and liver and it is estimated that 45% of deaths in the western world can now be attributed to diseases where fibrosis plays a major aetiological role. In this review we examine the evidence that cytokines play a vital role in the acute and chronic inflammatory responses that drive fibrosis in injured tissues. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

IL-27 paves different roads to Tr1

Tr1 cells are non-Foxp3-expressing regulatory CD4(+) T cells that execute suppressor functions by secreting the anti-inflammatory cytokine IL-10. Differentiation of this T-cell subset is facilitated by the heterodimeric cytokine IL-27, which can activate transcription factors such as c-Maf and Ahr to positively regulate the differentiation of Tr1 cells and their IL-10 production. In this issue of the European Journal of Immunology, an alternate transcriptional network regulated by IL-27 to induce IL-10 production in Tr1 cells is reported by Iwasaki et al. [Eur. J. Immunol. 2013. 43: 1063-1073]. This study shows that IL-27 initiates tandem activation of the transcription factors STAT3 and Egr-2 to induce il10 in Tr1 cells in a Blimp1-dependent fashion. These findings indicate a c-Maf/Ahr independent mechanism that activates IL-10 production by Tr1 cells and suggest that Il10 induction may depend on both the cytokine environment and the molecular context. Thus, Tr1 cells may be another example of the remarkable plasticity of CD4(+) T cells and indeed may not constitute a separate lineage of CD4(+) T cells but rather represent a developmental endpoint of several T helper cell differentiation pathways.

The suppressive effect of IL-27 on encephalitogenic Th17 cells induced by multiwalled carbon nanotubes reduces the severity of experimental autoimmune encephalomyelitis

BACKGROUND

Both Th1 and Th17 cells specific for neuroantigen are described as encephalitogenic in the experimental autoimmune encephalomyelitis (EAE) model.

AIM

The proposal of this study was to investigate how carbon nanotubes internalized by antigen-presenting cells (APCs) affect the development of encephalitogenic CD4(+) T cells.

METHODS

Therefore, we stimulated encephalitogenic T cells in the presence or not of multiwalled carbon nanotube (MWCNT). After the incubation, we analyzed the expression profile of the encephalitogenic T cells and their capacity to induce EAE.

RESULTS

Encephalitogenic CD4(+) T cells cultured with APCs that were previously incubated with MWCNTs do not express IL-17. The adoptive transfer of these cells causes less severe EAE than the transfer of both Th1 and Th17 cells that are not incubated with MWCNTs. These results suggest that the increased IL-27 level produced by the APCs incubated with the carbon nanotubes inhibits the development of Th17 cells. This observation is confirmed by the concomitant reduction in the level of RORγt, which is a transcription factor essential for the development of Th17 cells. Moreover, the incubation of encephalitogenic T cells devoid of Th17 cells with neutralizing anti-IL-27 antibodies restored the production of IL-17.

CONCLUSION

This finding confirms the suppressive effect of IL-27 on encephalitogenic Th17 cells. The results presented suggest that the stimulation of APCs with carbon nanoparticles prior to neuroantigen presentation affects the development of the Th17 subset of encephalitogenic CD4(+) T lymphocytes and results in less severe EAE.

Regulation of the expression of Th17 cells and regulatory T cells by IL-27 in patients with unexplained early recurrent miscarriage

In normal pregnancy, tolerance of the maternal immune system with regard to the genetically incompatible fetus depends on the interactions of an array of cytokines secreted by maternal and fetal cells at the site of implantation. Earlier research indicating that altered immunity exists in unexplained recurrent miscarriage (RM) has been dominated by the Th1/Th2 hypothesis. Recently, the Th1/Th2 paradigm has been expanded into the Th1/Th2/Th17 and regulatory T cells paradigm. We recently demonstrated a prevalence of Th17 cells, an inverse relationship between Th17 cells and regulatory T cells and deregulation of Th17 cells by regulatory T cells in early pregnancy in unexplained RM patients. In this study, we investigated the expression of IL-27 and the role of the cytokine IL-27 in the regulation of Th17/Treg expression. Quantitative real-time RT-PCR and Western blot analyses were performed to evaluate IL-27 expression in deciduas from unexplained RM patients, spontaneous miscarriage (SM) patients and healthy women following elective abortion in the early stages of normal pregnancy (control). Regulation of IL-17, TGF-β and IL-10 expression in CD4(+) T cells in unexplained RM patients by IL-27 was assessed using enzyme-linked immunosorbent assay (ELISA). Expression of IL-27 was lower in deciduas of patients with unexplained RM compared with SM and control subjects. IL-27 inhibited IL-17 expression and enhanced IL-10 expression in a dose-dependent manner. IL-27 had no effect on TGF-β expression. IL-27 regulates the expression of IL-17 and IL-10, which are predominantly secreted by Th17 cells and regulatory T cells in unexplained RM patients.

Leishmania-infected MHC class IIhigh dendritic cells polarize CD4+ T cells toward a nonprotective T-bet+ IFN-γ+ IL-10+ phenotype

A differential behavior among infected and bystander dendritic cells (DCs) has been explored in different infection models. We have analyzed both populations sorted on contact with visceral Leishmania infantum on a susceptible mice model evaluating the subsequent repercussions on adaptive immune response. Our results demonstrate a clear dichotomy between the immunomodulatory abilities of bystander and infected DCs. The bystander population presents increased levels of IL-12p40 and costimulatory molecules being capable to induce CD4(+) T cell activation with immune protective capabilities. In contrast, infected DCs, which express lower costimulatory molecules and higher levels of IL-10, promote the development of Leishmania Ag-specific, nonprotective T-bet(+)IFN-γ(+)IL-10(+) CD4(+) T cells with an effector phenotype. This specific polarization was found to be dependent on IL-12p70. Splenic infected DCs recovered from chronic infected animals are similarly capable to polarize ex vivo syngeneic naive CD4(+) T cells toward a T-bet(+)IFN-γ(+)IL-10(+) phenotype. Further analysis revealed that only MHC class II(high)-infected DCs were responsible for this polarization. The adoptive transfer of such polarized CD4(+) T cells facilitates visceral leishmaniasis in BALB/c mice in a clear contrast with their counterpart generated with bystander DCs that significantly potentiate protection. Further, we demonstrated that CD4(+) T cells primed by infected DCs in an IL-10 free system, thus deprived of T-bet(+)IFN-γ(+)IL-10(+) population, restore the immune response and reduce parasite load, supporting a deleterious role of IFN-γ(+)IL-10(+) T cells in the maintenance of infection. Overall, our results highlight novel subversion mechanisms by which nonprotective T-bet(+)IFN-γ(+)IL-10(+) T cells are associated with chronicity and prolonged parasite persistence.

Interleukin 27 inhibits atherosclerosis via immunoregulation of macrophages in mice

Chronic inflammation in arterial wall that is driven by immune cells and cytokines plays pivotal roles in the development of atherosclerosis. Interleukin 27 (IL-27) is a member of the IL-12 family of cytokines that consists of IL-27p28 and Epstein-Barr virus induced gene 3 (EBI3) and has anti-inflammatory properties that regulate T cell polarization and cytokine production. IL-27-deficient (Ldlr-/-Ebi3-/-) and IL-27 receptor-deficient (Ldlr-/-WSX-1-/-) Ldlr-/- mice were generated and fed with a high-cholesterol diet to induce atherosclerosis. Roles of bone marrow-derived cells in vivo and macrophages in vitro were studied using bone marrow reconstitution by transplantation and cultured peritoneal macrophages, respectively. We demonstrate that mice lacking IL-27 or IL-27 receptor are more susceptible to atherosclerosis compared with wild type due to enhanced accumulation and activation of macrophages in arterial walls. The number of circulating proinflammatory Ly6C(hi) monocytes showed no significant difference between wild-type mice and mice lacking IL-27 or IL-27 receptor. Administration of IL-27 suppressed the development of atherosclerosis in vivo and macrophage activation in vitro that was indicated by increased uptake of modified low-density lipoprotein and augmented production of proinflammatory cytokines. These findings define a novel inhibitory role for IL-27 in atherosclerosis that regulates macrophage activation in mice.

IL-27 suppresses the production of IL-22 in human CD4(+) T cells by inducing the expression of SOCS1

IL-27, a member of IL-6/IL-12 cytokine family, plays pro- and anti-inflammatory functions in immune responses. It can promote inflammation by inducing Th1 differentiation and exert the inhibitory effects on Th2 and Th17 mediated immune responses. Moreover, IL-27 suppresses CD28-mediated IL-2 production from mouse naive CD4(+) T cells. In the present study, we demonstrate that IL-27 inhibits the production of IL-22 and induces the expression of IFN-γ in CD4(+) T cells from human umbilical cord blood mononuclear cells (CBMCs) stimulated with anti-CD3 and anti-CD28 in dose-dependent manner. In addition, the suppression of IL-22 is not dependent on the production of IFN-γ and IL-10. Importantly, IL-27 promotes the expression of SOCS1, which could be inhibited by a Jak2/STAT inhibitor, AG490. Importantly, the expression of IL-22 could not be inhibited under the circumstances with the lower expression of SOCS1. Moreover, IL-27 inhibits the production of IL-22 in CD4(+)CD45RA(+) and CD4(+)CD45RO(+) T cells from PBMCs. These data identify that IL-27 may suppress the production of IL-22 by inducing the expression of SOCS1 in human CD4(+) T cells. Furthermore, it demonstrates that IL-27 may be a therapeutic approach in the treatment of IL-22-mediated diseases.

Deficiency of β-arrestin1 ameliorates collagen-induced arthritis with impaired TH17 cell differentiation

Rheumatoid arthritis (RA) is an inflammatory disease in which interleukin 17 (IL-17)-producing T helper 17 (T(H)17) cells have been critically involved. We show that in patients with RA, the expression of a multifunctional regulator β-arrestin1 was significantly up-regulated in peripheral and synovial CD4(+) T cells, which correlated well with active phases of RA. In collagen-induced arthritis, deficiency of β-arrestin1 ameliorated disease with decreased T(H)17 cell differentiation, proinflammatory cytokine production, synovitis, and cartilage and bone destruction. Further mechanistic study reveals that β-arrestin1 promoted signal transducer and activator of transcription 3 (STAT3) activation required for T(H)17 cell differentiation through scaffolding the interaction of Janus kinase 1 and STAT3. These findings indicate a critical role for β-arrestin1 in the pathogenesis of collagen-induced arthritis and T(H)17 cell differentiation and suggest β-arrestin1 as a potential diagnostic biomarker and therapeutic target for RA.

Inborn errors of human IL-17 immunity underlie chronic mucocutaneous candidiasis

PURPOSE OF REVIEW

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent symptomatic infection of the nails, skin and mucosae mostly by Candida albicans. CMC is common in patients with profound primary T-cell immunodeficiency, who often display multiple infectious and autoimmune diseases. Patients with syndromic CMC, including autosomal dominant hyper IgE syndrome (AD-HIES) and autosomal recessive autoimmune polyendocrinopathy syndrome type I (APS-I), display fewer other infections. Patients with isolated CMC (CMCD) rarely display any other severe disease. We review here recent progress in the genetic dissection of these three types of inherited CMC.

RECENT FINDINGS

Low IL-17 T-cell proportions were reported in patients with AD-HIES bearing heterozygous STAT3 mutations, prone to CMC and staphylococcal diseases, and in a kindred with autosomal recessive CARD9 deficiency, prone to CMC and other fungal infections. High levels of neutralizing autoantibodies against IL-17 cytokines were documented in patients with APS-I presenting with CMC as their only infectious disease. The first three genetic causes of CMCD were then reported: autosomal recessive IL-17RA and autosomal dominant IL-17F deficiencies and autosomal dominant STAT1 gain-of-function, impairing IL-17-producing T-cell development.

SUMMARY

Inborn errors of human IL-17 immunity underlie CMC. Impaired IL-17 immunity may therefore account for CMC in other settings, including patients with acquired immunodeficiency.

Role of Th17 cells in the pathogenesis of CNS inflammatory demyelination

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). The etiology of MS is not well understood, but it is believed that myelin-specific CD4(+) T cells play a central role in initiating and orchestrating CNS inflammation. In this scenario, CD4(+) T cells, activated in the periphery, infiltrate the CNS, where, by secreting cytokines and chemokines, they start an inflammatory cascade. Given the central role of CD4(+) T cells in CNS autoimmunity, they have been studied extensively, principally by using experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the late 1980s, CD4(+) T cells, based on their cytokine production, were divided into two helper lineages, Th1 and Th2 cells. It was postulated that Th1 cells, which produce IFN-γ, mediate inflammation of the CNS in MS/EAE, while Th2 cells, which produce IL-4, have a beneficial effect in disease, because of their antagonistic effect on Th1 cells. The Th1/Th2 paradigm remained the prevailing view of MS/EAE pathogenesis until 2005, when a new lineage, Th17, was discovered. In a relatively short period of time it became apparent that Th17 cells, named after their hallmark cytokine, IL-17A, play a crucial role in many inflammatory diseases, including EAE, and likely in MS as well. The Th17 paradigm developed rapidly, initiating the debate of whether Th1 cells contribute to EAE/MS pathogenesis at all, or if they might even have a protective role due to their antagonistic effects on Th17 cells. Numerous findings support the view that Th17 cells play an essential role in autoimmune CNS inflammation, perhaps mainly in the initial phases of disease. Th1 cells likely contribute to pathogenesis, with their role possibly more pronounced later in disease. Hence, the current view on the role of Th cells in MS/EAE pathogenesis can be called the Th17/Th1 paradigm. It is certain that Th17 cells will continue to be the focus of intense investigation aimed at elucidating the pathogenesis of CNS autoimmunity.

IL-17 mediates immunopathology in the absence of IL-10 following Leishmania major infection

Leishmaniasis, resulting from infection with the protozoan parasite Leishmania, consists of a wide spectrum of clinical manifestations, from healing cutaneous lesions to fatal visceral infections. A particularly severe form of cutaneous leishmaniasis, termed mucosal leishmaniasis, exhibits decreased IL-10 levels and an exaggerated inflammatory response that perpetuates the disease. Using a mouse model of leishmaniasis, we investigated what cytokines contribute to increased pathology when IL-10-mediated regulation is absent. Leishmania major infected C57BL/6 mice lacking IL-10 regulation developed larger lesions than controls, but fewer parasites. Both IFN-γ and IL-17 levels were substantially elevated in mice lacking the capacity to respond to IL-10. IFN-γ promoted an increased infiltration of monocytes, while IL-17 contributed to an increase in neutrophils. Surprisingly, however, we found that IFN-γ did not contribute to increased pathology, but instead regulated the IL-17 response. Thus, blocking IFN-γ led to a significant increase in IL-17, neutrophils and disease. Similarly, the production of IL-17 by cells from leishmaniasis patients was also regulated by IL-10 and IFN-γ. Additional studies found that the IL-1 receptor was required for both the IL-17 response and increased pathology. Therefore, we propose that regulating IL-17, possibly by downregulating IL-1β, may be a useful approach for controlling immunopathology in leishmaniasis.

Leishmaniasis is a tropical disease transmitted by sand flies that causes visceral and cutaneous lesions. In humans, the most severe form of cutaneous leishmaniasis is the mucosal form, causing disfiguring lesions in the nasal and oral mucosa. Why these patients develop severe disease is not clear. It is known, however, that the severe disease is not due to an overwhelming number of parasites, but rather appears to be due to an uncontrolled inflammatory response that includes elevated production of IFN-γ and IL-17. Here, we used a murine model of leishmaniasis to identify the factors involved in this pathology, and found that mice infected with Leishmania major developed severe lesions in the absence of IL-10 or IL-10 signaling, and similar to patients, contained high levels of IFN-γ and IL-17. While both of these cytokines have the potential to induce pathology, we found that IL-17 was responsible for the severe pathology seen in the absence of IL-10 regulation, and furthermore that IL-17 levels were higher and pathology greater in the absence of IFN-γ. Thus, our study suggests that IL-17, but not the IFN-γ, is a strong candidate to be targeted in strategies to control the severe immunopathology observed in mucosal leishmaniasis patients.

Interleukin-27 signaling promotes immunity against endogenously arising murine tumors

Interleukin-27 (IL-27) is a pleiotropic cytokine but its immunosuppressive effects predominate during many in vivo immunological challenges. Despite this, evidence from tumor cell line transfer models suggested that IL-27 could promote immune responses in the tumor context. However, the role of IL-27 in immunity against tumors that develop in situ and in tumor immunosurveillance remain undefined. In this study, we demonstrate that tumor development and growth are accelerated in IL-27 receptor α (Il27ra)-deficient mice. Enhanced tumor growth in both carcinogen-induced fibrosarcoma and oncogene-driven mammary carcinoma was associated with decreased interferon-γ production by CD4 and CD8 T cells and increased numbers of regulatory T-cells (T_reg). This is the first study to show that IL-27 promotes protective immune responses against endogenous tumors, which is critical as the basis for future development of an IL-27 based therapeutic agent.

Independent and interdependent immunoregulatory effects of IL-27, IFN-β, and IL-10 in the suppression of human Th17 cells and murine experimental autoimmune encephalomyelitis

IFN-β, IL-27, and IL-10 have been shown to exert a range of similar immunoregulatory effects in murine and human experimental systems, particularly in Th1- and Th17-mediated models of autoimmune inflammatory disease. In this study we sought to translate some of our previous findings in murine systems to human in vitro models and delineate the interdependence of these different cytokines in their immunoregulatory effects. We demonstrate that human IL-27 upregulates IL-10 in T cell-activated PBMC cultures and that IFN-β drives IL-27 production in activated monocytes. IFN-β-driven IL-27 is responsible for the upregulation of IL-10, but not IL-17 suppression, by IFN-β in human PBMCs. Surprisingly, IL-10 is not required for the suppression of IL-17 by either IL-27 or IFN-β in this model or in de novo differentiating Th17 cells, nor is IL-27 signaling required for the suppression of experimental autoimmune encephalomyelitis (EAE) by IFN-β in vivo. Furthermore, and even more surprisingly, IL-10 is not required for the suppression of Th17-biased EAE by IL-27, in sharp contrast to Th1-biased EAE. In conclusion, IFN-β and IL-27 both induce human IL-10, both suppress human Th17 responses, and both suppress murine EAE. However, IL-27 signaling is not required for the therapeutic effect of IFN-β in EAE. Suppression of Th17-biased EAE by IL-27 is IL-10-independent, in contrast to its mechanism of action in Th1-biased EAE. Taken together, these findings delineate a complex set of interdependent and independent immunoregulatory mechanisms of IFN-β, IL-27, and IL-10 in human experimental models and in murine Th1- and Th17-driven autoimmunity.

Th17 cell development: from the cradle to the grave

T cells surviving the clonal selection process emigrate from the thymus to the periphery as immature naive T cells. In the periphery, upon activation under specific cytokine milieus, naive T cells adopt specific effector phenotypes, e.g. T-helper 1 (Th1), Th2, or Th17, and acquire diverse functions to control a myriad of pathogens, tissue injuries, and other immunological insults. Interleukin-23 (IL-23) is one of the key cytokines that shapes the development and function of Th17 cells with characteristic expression of retinoic acid receptor-related orphan receptor γ-t (RORγt), IL-17, IL-22, and granulocyte macrophage colony-stimulating factor (GM-CSF). More recently, emerging data suggest that IL-23 also promotes development of 'natural Th17' (nTh17) cells that arise from the thymus, analogous to natural regulatory T cells (nTreg). We are just beginning to understand the unique thymic developmental path of nTh17 cells, which are distinct from antigen-experienced memory Th17 cells. In this review, we explore the differentiation and function of inducible, natural, and memory Th17 subsets, which encompass a broad range of immune functions while maintaining tissue hemostasis, and highlight the participation of IL-23 during the life cycle of Th17 cells.

Interleukin-27 suppresses osteoclastogenesis via induction of interferon-γ

Interleukin (IL)-27 is a heterodimeric cytokine that is known to have both stimulatory and inhibitory functions during immune responses. We investigated the effects of IL-27 on arthritis and bone erosion in the murine collagen-induced arthritis (CIA) model. We demonstrate that the inhibitory effect of IL-27 on osteoclastogenesis is associated with interferon-γ (IFN-γ) production by using an IFN-γ knockout mouse model. The IL-27-Fc was injected into both CIA and IFN-γ-deficient mice. The effects of IL-27-Fc on osteoclast differentiation were evaluated both in vitro and in vivo. The IL-27-Fc-injected mice showed significantly lower arthritis indices and fewer tartrate-resistant acid-phosphatase-positive osteoclasts in their joint tissues than untreated mice. Interleukin-27 inhibited osteoclastogenesis from bone marrow-derived mononuclear cells in vitro, which was counteracted by the addition of anti-IFN-γ antibody. The IL-27-Fc did not affect arthritis in IFN-γ knockout mice. Interleukin-27 also suppressed osteoclast differentiation in human and intriguingly, it could promote the expression of IFN-γ on priming osteoclasts. These results imply that IL-27 suppressed the generation of CIA and osteoclastogenesis, which were mediated by the induction of IFN-γ.

Egr-2 transcription factor is required for Blimp-1-mediated IL-10 production in IL-27-stimulated CD4+ T cells

Interleukin-27 (IL-27) suppresses immune responses through inhibition of the development of IL-17 producing Th17 cells and induction of IL-10 production. We previously showed that forced expression of early growth response gene 2 (Egr-2), a transcription factor required for T-cell anergy induction, induces IL-10 and lymphocyte activation gene 3 expression and confers regulatory activity on CD4(+) T cells in vivo. Here, we evaluated the role of Egr-2 in IL-27-induced IL-10 production. Among various IL-10-inducing factors, only IL-27 induced high levels of Egr-2 and lymphocyte activation gene 3 expression. Intriguingly, IL-27 failed to induce IL-10 in Egr-2-deficient T cells. IL-27-mediated induction of Prdm1 that codes B lymphocyte induced maturation protein-1, a transcriptional regulator important for IL-10 production in CD4(+) T cells, was also impaired in the absence of Egr-2. Although IL-27-mediated IL-10 induction was dependent on both STAT1 and STAT3, only STAT3 was required for IL-27-mediated Egr-2 induction. These results suggest that IL-27 signal transduction through Egr-2 and B lymphocyte induced maturation protein-1 plays an important role in IL-10 production. Furthermore, Egr-2-deficient CD4(+) T cells showed dysregulated production of IFN-γ and IL-17 in response to IL-27 stimulation. Therefore, Egr-2 may play key roles in controlling the balance between regulatory and effector cytokines.

Interleukin-27: balancing protective and pathological immunity

It has been more than 15 years since the identification of individual interleukin-27 (IL-27) and IL-27 receptor components. The last decade has seen the description of the signaling pathways engaged by IL-27, and an appreciation has emerged that this cytokine can modulate the intensity and duration of many classes of T cell responses. Here we provide an overview of the immunobiology of IL-27 and review advances in understanding the functions of individual IL-27 and IL-27 receptor subunits and the role of IL-27 in dictating the balance between protective and pathological immunity. Additionally, this cytokine has been proposed as a therapy to modify inflammatory conditions or to promote antitumor responses, and situations where experimental and clinical data sets implicate IL-27 in the outcome of disease are highlighted.