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Oropharyngeal candidiasis (OPC) is the most common human fungal infection, arising typically from T cell immune impairments. IL-17 and IL-22 contribute individually to OPC responses, but here we demonstrate that the combined actions of both cytokines are essential for resistance to OPC. Mice lacking IL-17RA and IL-22RA1 exhibited high fungal loads in esophagus- and intestinal tract, severe weight loss, and symptoms of colitis. Ultimately, mice succumbed to infection. Dual loss of IL-17RA and IL-22RA impaired expression of small proline rich proteins (SPRRs), a class of antimicrobial effectors not previously linked to fungal immunity. Sprr2a1 exhibited direct candidacidal activity in vitro, and Sprr1-3a-/- mice were susceptible to OPC. Thus, cooperative actions of Type 17 cytokines mediate oral mucosal anti-Candida defenses and reveal a role for SPRRs., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Aggor et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The IL-23/IL-17 axis plays causative roles in the development and progression of systemic lupus erythematosus (SLE). However, it remains unclear if the IL-17RA + and IL-23R + T helper (Th) cells populations are associated with the serum IL-17 and IL-23 levels, or with the immunological parameters and disease activities in SLE patients. Herein, we examined the proportion of IL-17RA + and IL-23R + Th cells and serum levels of IL-17 and IL-23 in established SLE patients (n = 50) compared with healthy controls (n = 50). The associations of these interleukins and their receptors with immunological parameters [anti-nuclear antibody (ANA), anti-dsDNA antibody, and C-reactive protein (CRP)] and SLE disease activity (SLEDAI-2K scores) in SLE patients were assessed. CD3 + CD4 + Th cells of SLE patients demonstrated significantly elevated IL-17RA + ( p = 1.12 x 10 -4 ) or IL-23R + ( p  = 1.98 x 10 -29 ) populations compared with the healthy controls. Serum IL-17 levels were significantly lower in SLE patients compared with the healthy controls ( p = 8.32 x 10 -5 ), while no significant difference was observed for the IL-23 serum levels between both groups. IL-23R + Th cells population was significantly associated with higher SLEDAI-2K scores ( p  = 0.017). In multivariate analysis, the proportion of IL-23R + Th cells remained significantly associated with higher SLEDAI-2K scores independent of prednisolone intake ( p = 0.027). No associations were observed between the interleukin parameters (i.e., IL-17, IL-23, IL-17RA + Th cells, and IL-23R + Th cells) with ANA, anti-dsDNA, and CRP status, suggesting that the IL-17/IL-23 axis acts independently of these immunological parameters. In conclusion, our results support that therapeutic inhibition of the IL-23/IL-17 axis receptors on Th cells, particularly IL-23R, is potentially relevant in SLE patients., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Izati, Mohd Shukri, Wan Ghazali, Che Hussin and Wong.)

Candida albicans, a ubiquitous commensal fungus that colonizes human mucosal tissues and skin, can become pathogenic, clinically manifesting most commonly as oropharyngeal candidiasis and vulvovaginal candidiasis (VVC). Studies in mice and humans convincingly show that T-helper 17 (Th17)/interleukin 17 (IL-17)-driven immunity is essential to control oral and dermal candidiasis. However, the role of the IL-17 pathway during VVC remains controversial, with conflicting reports from human data and mouse models. Like others, we observed induction of a strong IL-17-related gene signature in the vagina during estrogen-dependent murine VVC. As estrogen increases susceptibility to vaginal colonization and resulting immunopathology, we asked whether estrogen use in the standard VVC model masks a role for the Th17/IL-17 axis. We demonstrate that mice lacking IL-17RA, Act1, or interleukin 22 showed no evidence for altered VVC susceptibility or immunopathology, regardless of estrogen administration. Hence, these data support the emerging consensus that Th17/IL-17 axis signaling is dispensable for the immunopathogenesis of VVC., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Johne's disease (JD) is a chronic inflammatory gastrointestinal disease of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Control of JD is difficult largely due to insensitive diagnostic tools, a long subclinical stage of infection, and lack of effective vaccines. Correlates of protection are lacking in model systems of JD and the sources of inflammation due to JD are not well characterized. Commonly studied immune responses, such as the Th1/Th2 paradigm, do not adequately explain host responses to MAP. A potential role for non-classical immune responses to MAP, such as that mediated by Th17 cells, has been suggested. Indeed, MAP antigens induce mRNAs encoding the cytokines IL-23 and IL-17a in bovine peripheral blood mononuclear cells (PBMCs). IL-23 and IL-17a production have both been associated with Th17-like immune responses. Th17 cells are also defined by surface expression of the IL-23 receptor (IL-23R). To determine the relative prevalence of potential Th17 cells in PBMCs from MAP test positive and MAP test negative cows, PBMCs were isolated and analyzed by immunostaining and flow cytometry. Fresh PBMCs from MAP test positive cows (n = 12) contained a significantly higher proportion of IL-23R positive cells in populations of CD4+, CD8+, and Yδ + T cells than in cells from MAP test negative cows (n = 12; p < 0.05). Treatment with MAP antigens increased the percentage of all T cell subsets with surface expression of IL-23R when compared to untreated (n = 12; p < 0.05) cells. ELISA results for IL-17a secretion revealed a higher concentration of IL-17a secreted from PBMCs treated with MAP antigen (n = 20) than from PBMCs not treated with MAP antigens (n = 20) (p < 0.001), regardless of the JD test status of source cows. Also, we observed a moderate negative correlation between JD diagnostic scores for JD + cows and plasma IL-17a concentration (n = 42; r = -0.437; p-value < 0.004). Plasma with low and mid JD- scores (n = 31; n = 9; 0.1 ≤ X < 0.3) had significantly more IL-17a when compared to plasma with high JD- scores (n = 10; 0.3 ≤ X < 0.46; p-values < 0.05). Similarly, plasma with low JD + score values (0.55 ≤ X < 1.0; n = 9) had significantly more IL-17a when compared to plasma with high JD + score values (X ≥ 2.0; n = 21; p < 0.05). Overall, plasma from JD + cows (0.55 < X ≤ 2.86; n = 41) had significantly less IL-17a than plasma from JD- cows (0 < X ≤ 0.46; n = 70). Our data suggests that Th17-like cells may indeed play a role in early immune responses to MAP infection and development or control of JD., (Copyright © 2019 Elsevier B.V. All rights reserved.)

T helper 17 (T H 17) cells and interleukin-17A (IL-17A) produced by them are critical in autoinflammatory diseases, such as psoriasis. IL-17A has been shown to signal through IL-17 receptor A/IL-17 receptor C (IL-17RA/IL-17RC) complex to drive inflammatory responses. However, in a psoriasis model, we found that Il17rc deficiency did not completely ameliorate the disease, suggesting another receptor. In search for another IL-17A-interacting receptor, we found that IL-17RD directly bound IL-17A but not IL-17F or IL-17A/F heterodimer and formed a heterodimer with IL-17RA. IL-17A-, but not IL-17F- or IL-17A/F-, mediated gene expression was defective in Il17rd -deficient keratinocytes. Il17rd deficiency in nonhemopoietic cells attenuated imiquimod-induced psoriasis-like skin inflammation. Although IL-17RC and IL-17RD differentially activated IL-17A-dependent signaling and gene expression, their compound mutation led to complete deficits in keratinocytes. IL-23 was found induced by IL-17A in keratinocytes, dependent on both IL-17RC and IL-17RD, suggesting feed-forward regulation of IL-23/IL-17 axis in psoriasis. Together, IL-17RD constitutes a second functional receptor for IL-17A and, together with IL-17RC, mediates the proinflammatory gene expression downstream of IL-17A., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Interleukin-17 (IL-17) is a pro-inflammatory cytokine and is involved in the development of many diseases. Recent studies have revealed that IL-17-producing γδ T cells (γδ17 cells) in addition to IL-17-producing CD4 + T cells [T helper type 17 (Th17) cells] are often the main producers of IL-17 in mouse models of inflammatory diseases. γδ T cells are functionally committed during intra-thymic differentiation. γδ thymocytes capable of producing IL-17, which express the transcription factor retinoic-acid-receptor-related orphan receptor γt and the signature cytokine receptor IL-23R, leave the thymus, and produce IL-17 rapidly by the stimulation with IL-1β and IL-23 in the periphery. Therefore, γδ17 cells play important roles in the early phase of host defence against pathogens and in inflammatory diseases. γδ T cells that can produce IL-17 are also increased in the skin of patients with psoriasis and in peripheral blood of patients with ankylosing sclerosis. Indeed, the therapy targeting IL-17 has been approved or is in clinical trials, and proved to be very efficient to treat psoriasis, psoriatic arthritis and ankylosing sclerosis. In this review, we discuss recent knowledge about the pathophysiological function of γδ17 cells in infection and inflammatory diseases and therapeutic advances targeting IL-17., (© 2018 The Authors. Immunology Published by John Wiley & Sons Ltd.)

Background: Ankylosing spondylitis (AS) results from the combined effects of susceptibility genes and environmental factors. Polymorphisms in genes regulating inflammation may explain part of the heritability of AS., Methods: Using a candidate gene approach in this case-control study, 51 mainly functional single nucleotide polymorphisms (SNPs) in genes regulating inflammation were assessed in 709 patients with AS and 795 controls. Data on the patients with AS were obtained from the DANBIO registry where patients from all of Denmark are monitored in routine care during treatment with conventional and biologic disease modifying anti-rheumatic drugs (bDMARDs). The results were analyzed using logistic regression (adjusted for age and sex)., Results: Nine polymorphisms were associated with risk of AS (p < 0.05). The polymorphisms were in genes regulating a: the TNF-α pathway (TNF -308 G > A (rs1800629), and - 238 G > A (rs361525); TNFRSF1A -609 G > T (rs4149570), and PTPN22 1858 G > A (rs2476601)), b: the IL23/IL17 pathway (IL23R G > A (rs11209026), and IL18-137 G > C (rs187238)), or c: the NFkB pathway (TLR1 743 T > C (rs4833095), TLR4 T > C (rs1554973), and LY96-1625 C > G (rs11465996)). After Bonferroni correction the homozygous variant genotype of TLR1 743 T > C (rs4833095) (odds ratios (OR): 2.59, 95% confidence interval (CI): 1.48-4.51, p = 0.04), and TNFRSF1A -609 G > T (rs4149570) (OR: 1.79, 95% CI: 1.31-2.41, p = 0.01) were associated with increased risk of AS and the combined homozygous and heterozygous variant genotypes of TNF -308 G > A (rs1800629) (OR: 0.56, 95% CI: 0.44-0.72, p = 0.0002) were associated with reduced risk of AS., Conclusion: We replicated associations between AS and the polymorphisms in TNF (rs1800629), TNFRSF1A (rs4149570), and IL23R (rs11209026). Furthermore, we identified novel risk loci in TNF (rs361525), IL18 (rs187238), TLR1 (rs4833095), TLR4 (rs1554973), and LY96 (rs11465996) that need validation in independent cohorts. The results suggest that genetically determined high activity of the TNF-α, IL23/IL17, and NFkB pathways increase risk of AS.

Background: Interleukin (IL)-25 is a member of the IL-17 family, which can promote and augment T-helper (Th) type 2 responses. The expression of IL-25 and its cognate receptor, IL-25 receptor (IL-25R), is upregulated and correlated with disease activity in Th2-associated diseases., Objectives: To examine the expression and function of IL-25 in cutaneous T-cell lymphoma (CTCL)., Methods: Expression and location of IL-25 in lesional skin was investigated with immunohistochemistry. The effect of various cytokines on IL-25 production from normal human epidermal keratinocytes was assessed by quantitative reverse-transcription real-time polymerase chain reaction. Serum IL-25 levels were measured by enzyme-linked immunosorbent assay. The direct effect of IL-25 on tumour cells was also examined using CTCL cell lines and peripheral blood mononuclear cells in patients with Sézary syndrome., Results: IL-25 expression was increased in epidermal keratinocytes in lesional skin of CTCL. Th2 cytokines, IL-4 and IL-13, and periostin induced IL-25 expression by normal human epidermal keratinocytes. Serum IL-25 levels were increased in patients with advanced CTCL and correlated with serum lactate dehydrogenase levels. MyLa cells expressed IL-25R and its expression was augmented by stimulation with IL-25. IL-25 enhanced IL-13 production from MyLa cells via phosphorylation of signal transducer and activator of transcription 6. Peripheral blood mononuclear cells from one patient with Sézary syndrome expressed IL-25R and showed increase of IL-13 production by IL-25., Conclusions: Th2 cytokines highly expressed in CTCL lesional skin induce IL-25 production by epidermal keratinocytes, which may, in turn, lead to formation of a Th2-dominant microenvironment through the direct induction of IL-13 by tumour cells., (© 2017 British Association of Dermatologists.)

Psoriasis is a chronic autoinflammatory skin disease. Although interleukin-17, derived from lymphocytes, has been shown to be critical in psoriasis, the initiation and maintenance of chronic skin inflammation has not been well understood. IL-25 (also called IL-17E), another IL-17 family cytokine, is well known to regulate allergic responses and type 2 immunity. Here we have shown that IL-25, also highly expressed in the lesional skin of psoriasis patients, was regulated by IL-17 in murine skin of a imiquimod (IMQ)-induced psoriasis model. IL-25 injection induced skin inflammation, whereas germline or keratinocyte-specific deletion of IL-25 caused resistance to IMQ-induced psoriasis. Via IL-17RB expression in keratinocytes, IL-25 stimulated the proliferation of keratinocytes and induced the production of inflammatory cytokines and chemokines, via activation of the STAT3 transcription factor. Thus, our data demonstrate that an IL-17-induced autoregulatory circuit in keratinocytes is mediated by IL-25 and suggest that this circuit could be targeted in the treatment of psoriasis patients., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Retinoic acid receptor-related-orphan-receptor-C (RORγt) is the key transcription factor that is driving the differentiation of IL-17 producing T-helper 17 (Th17) cells that are implicated in the pathology of various autoimmune and inflammatory diseases. Based on the importance of RORγt in promoting Th17-driven pathology, there is considerable interest to develop low-molecular-weight compounds with the aim of inhibiting the transcriptional activity of this nuclear hormone receptor. In this article, we describe the in vitro and in vivo pharmacology of a potent and selective small-molecular-weight RORγt inverse agonist. The compound binds to the ligand binding domain (LBD) of RORγt leading to displacement of a co-activator peptide. We show for the first time that a RORγt inverse agonist down-regulates permissive histone H3 acetylation and methylation at the IL17A and IL23R promoter regions, thereby providing insight into the transcriptional inhibition of RORγt-dependent genes. Consistent with this, the compound effectively reduced IL-17A production by polarized human T-cells and γδT-cells and attenuated transcription of RORγt target genes. The inhibitor showed good in vivo efficacy in an antigen-induced arthritis model in rats and reduced the frequencies of IL-17A producing cells in ex vivo recall assays. In summary, we demonstrate that inhibiting RORγt by a low-molecular-weight inhibitor results in efficient and selective blockade of the pro-inflammatory Th17/IL-17A pathway making it an attractive target for Th17-mediated disorders.

Donor T-cell-derived interleukin-17A (IL-17A) can mediate late immunopathology in graft-versus-host disease (GVHD), however protective roles remain unclear. Using multiple cytokine and cytokine receptor subunit knockout mice, we demonstrate that stem cell transplant recipients lacking the ability to generate or signal IL-17 develop intestinal hyper-acute GVHD. This protective effect is restricted to the molecular interaction of IL-17A and/or IL-17F with the IL-17 receptor A/C (IL-17RA/C). The protection from GVHD afforded by IL-17A required secretion from, and signaling in, both hematopoietic and nonhematopoietic host tissue. Given the intestinal-specificity of the disease in these animals, we cohoused wild-type (WT) with IL-17RA and IL-17RC-deficient mice, which dramatically enhanced the susceptibility of WT mice to acute GVHD. Furthermore, the gut microbiome of WT mice shifted toward that of the IL-17RA/C mice during cohousing prior to transplant, confirming that an IL-17-sensitive gut microbiota controls susceptibility to acute GVHD. Finally, induced IL-17A depletion peritransplant also enhanced acute GVHD, consistent with an additional protective role for this cytokine independent of effects on dysbiosis., (© 2017 by The American Society of Hematology.)

IL-17A has been strongly associated with epidermal hyperplasia in many cutaneous disorders. However, because IL-17A is mainly produced by αβ and γδT cells in response to IL-23, the role of T cells and IL-23 has overshadowed any IL-17A-independent actions. In this article, we report that IL-17A gene transfer induces epidermal hyperplasia in Il23r -/- Rag1 -/- - and Tcrδ-deficient mice, which can be prevented by neutrophil depletion. Moreover, adoptive transfer of CD11b + Gr-1 hi cells, after IL-17A gene transfer, was sufficient to phenocopy the disease. We further show that the IL-17A-induced pathology was prevented in transgenic mice with impaired neutrophil extracellular trap formation and/or neutrophils with conditional deletion of the master regulator of selective autophagy, Wdfy3. Our data demonstrate a novel T cell-independent mechanism that is associated with neutrophil extracellular trap formation and selective autophagy in IL-17A-mediated epidermal hyperplasia., (Copyright © 2016 by The American Association of Immunologists, Inc.)

Background: Women have an increased prevalence of severe asthma compared with men. IL-17A is associated with severe asthma and requires IL-23 receptor (IL-23R) signaling, which is negatively regulated by let-7f microRNA., Objective: We sought to Determine the mechanism by which 17β-estradiol (E2) and progesterone (P4) increase IL-17A production., Methods: IL-17A production was determined by using flow cytometry in TH17 cells from women (n = 14) and men (n = 15) with severe asthma. Cytokine levels were measured by using ELISA, and IL-23R and let-7f expression was measured by using quantitative PCR in TH17-differentiated cells from healthy women (n = 13) and men (n = 14). In sham-operated or ovariectomized female mice, 17β-E2, P4, 17β-E2+P4, or vehicle pellets were administered for 3 weeks before ex vivo TH17 cell differentiation. Airway neutrophil infiltration and CXCL1 (KC) expression were also determined in ovalbumin (OVA)-challenged wild-type female recipient mice with an adoptive transfer of OVA-specific TH17 cells from female and male mice., Results: In patients with severe asthma and healthy control subjects, IL-17A production was increased in TH17 cells from women compared with men. IL-23R expression was increased and let-7f expression was decreased in TH17-differentiated cells from women compared with men. In ovariectomized mice IL-17A and IL-23R expression was increased and Let-7f expression was decreased in TH17 cells from mice administered 17β-E2+P4 compared with those administered vehicle. Furthermore, transfer of female OVA-specific TH17 cells increased acute neutrophil infiltration in the lungs of OVA-challenged recipient mice compared with transfer of male OVA-specific TH17 cells., Conclusions: 17β-E2+P4 increased IL-17A production from TH17 cells, providing a potential mechanism for the increased prevalence of severe asthma in women compared with men., (Copyright © 2015 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

IL-17 is a pro-inflammatory mediator that is believed to play a critical role in regulating tissue inflammation during asthma, COPD, as well as other inflammatory disorders. The level of expression of IL-17 has been shown to be upregulated in lung bronchial tissue of asthmatic patients. Several reports have provided further evidence that this cytokine could play a key role in enhancing the migration of inflammatory as well as structural cells of the bronchial lung tissue during asthma and COPD. B cell infiltration to sites of inflammation during inflammatory disorders such as bowel disease, asthma and COPD has been reported. Accordingly, in this study we hypothesized that IL-17 may exert a chemotactic effect on primary B cells during asthma. We observed that B cells from asthmatic patients expressed significantly higher levels of IL-17RA and IL-17RC, compared to those of healthy subjects. Using an in-vitro migration assay, B cells were shown to migrate towards both IL-17A and IL-17F. Interestingly, blocking IL-17A and IL-17F signaling using either anti-IL-17R antibodies or MAP kinase inhibitors prevented in vitro migration of B cell towards IL-17. These observations indicate a direct chemotactic effect of IL-17 cytokines on primary peripheral blood B cells with higher effect being on asthmatic B cells. These findings revealed a key role for IL-17 in enhancing the migration of B cells to the lung tissue during asthma or COPD.

The dysregulation of inflammatory cytokines can cause a variety of diseases, such as autoimmunity and cancer. Since their identification in 2005, Th17 cells and its signature cytokine IL-17, have been implicated in the pathogenesis of autoimmune diseases such as psoriasis and rheumatoid arthritis (RA), and inflammatory associated cancers such as colorectal carcinoma (CRC). Recently, IL-22 a Th17 related cytokine has been shown to be pathogenic in psoriasis and RA. In this review, we will summarize the biological functions of IL-17 and IL-22, their role in autoimmune diseases and briefly review results from clinical trials targeting IL-17 or its receptor for the treatment of autoimmune diseases. Next, we will discuss pre-clinical and clinical data supporting the rationale of targeting other cytokines implicated in the Th17/IL-17 pathway, such as IL-22 and IL-23. Finally, we discuss the role of IL-17, and in particularly IL-22 in tumour immunity and possible therapeutic interventions.

Psoriasis is a common and chronic inflammatory skin disease in which T cells play a key role. Effective treatment heals the skin without scarring, but typically psoriasis recurs in previously affected areas. A pathogenic memory within the skin has been proposed, but the nature of such site-specific disease memory is unknown. Tissue-resident memory T (TRM) cells have been ascribed a role in immunity after resolved viral skin infections. Because of their localization in the epidermal compartment of the skin, TRM may contribute to tissue pathology during psoriasis. In this study, we investigated whether resolved psoriasis lesions contain TRM cells with the ability to maintain and potentially drive recurrent disease. Three common and effective therapies, narrowband-UVB treatment and long-term biologic treatment systemically inhibiting TNF-α or IL-12/23 signaling were studied. Epidermal T cells were highly activated in psoriasis and a high proportion of CD8 T cells expressed TRM markers. In resolved psoriasis, a population of cutaneous lymphocyte-associated Ag, CCR6, CD103, and IL-23R expressing epidermal CD8 T cells was highly enriched. Epidermal CD8 T cells expressing the TRM marker CD103 responded to ex vivo stimulation with IL-17A production and epidermal CD4 T cells responded with IL-22 production after as long as 6 y of TNF-α inhibition. Our data suggest that epidermal TRM cells are retained in resolved psoriasis and that these cells are capable of producing cytokines with a critical role in psoriasis pathogenesis. We provide a potential mechanism for a site-specific T cell-driven disease memory in psoriasis.

Objective: IL-22 is elevated in patients with inflammatory arthritis and correlates with disease activity. IL-22 deficient mice have reduced incidence of arthritis. Recombinant IL-22 restrains progression of arthritis via increase in IL-10 responses when administered prior to onset of arthritis. These findings imply a possible dual role of IL-22 in inflammatory arthritis depending on the phase of arthritis. Experiments outlined here were designed to elucidate the contribution of endogenous IL-22 before and after the onset of arthritis., Methods: Collagen induced arthritis (CIA) was induced in DBA1 or IFN-γ deficient mice following immunization with collagen and complete Freund's adjuvant. Anti-IL-22 antibody or isotype control were administered prior to or after onset of arthritis and disease progression assessed by clinical scoring and histopathology. IL-22, IL-17 and IFN-γ responses were measured by ELISA and flowcytometry. Anti-collagen antibody responses were analyzed by ELISA. Expression of IL-22R1 in CD4+ cells was elucidated by flowcytometry and real time PCR., Results: Collagen specific IL-22 responses were expanded during arthritis and IL-22 producing cells were discrete from IL-17 or IFN-γ producing cells. Neutralization of IL-22 after onset of arthritis resulted in significant increase in Th1 responses and significantly reduced severity of arthritis. CD4+ cells from arthritic mice showed increased surface expression of IL-22R1. In vitro, CD4+T cells cultured with antigen presenting cells in the presence or absence of IL-22 suppressed or induced IFN-γ, respectively. The protective effect of anti-IL-22 was reversed in IFN-γ deficient mice. Moreover, administration of anti-IL-22 prior to onset of arthritis augmented arthritis severity., Conclusion: We show for the first time that IL-22 plays a dual role: protective prior to the onset of arthritis and pathogenic after onset of arthritis. The pathogenic effect of IL-22 is dependent on suppression of IFN-γ responses. IL-17 responses remained unchanged with the administration of anti-IL22 antibody. IL-22R1 is upregulated on CD4+T cells during arthritis and regulates IFN-γ in T cells.

Acne vulgaris is the most common skin disorder affecting millions of people worldwide and inflammation resulting from the immune response targeting Propionibacterium acnes has a significant role in its pathogenesis. In this study, we have demonstrated that P. acnes is a potent inducer of T helper 17 (Th17) and Th1, but not Th2 responses in human peripheral blood mononuclear cells (PBMCs). P. acnes stimulated expression of key Th17-related genes, including IL-17A, RORα, RORc, IL-17RA, and IL-17RC, and triggered IL-17 secretion from CD4(+), but not from CD8(+) T cells. Supernatants from P. acnes-stimulated PBMCs were sufficient to promote the differentiation of naive CD4(+)CD45RA T cells into Th17 cells. Furthermore, we found that the combination of IL-1β, IL-6, and transforming growth factor-β-neutralizing antibodies completely inhibited P. acnes-induced IL-17 production. Importantly, we showed that IL-17-expressing cells were present in skin biopsies from acne patients but not from normal donors. Finally, vitamin A (all-trans retinoic acid) and vitamin D (1,25-dihydroxyvitamin D3) inhibited P. acnes-induced Th17 differentiation. Together, our data demonstrate that IL-17 is induced by P. acnes and expressed in acne lesions and that both vitamin A and D could be effective tools to modulate Th17-mediated diseases such as acne.

Staphylococcus aureus causes most infections of human skin and soft tissue and is a major infectious cause of mortality. Host defense mechanisms against S. aureus are incompletely understood. Interleukin 19 (IL-19), IL-20 and IL-24 signal through type I and type II IL-20 receptors and are associated with inflammatory skin diseases such as psoriasis and atopic dermatitis. We found here that those cytokines promoted cutaneous infection with S. aureus in mice by downregulating IL-1β- and IL-17A-dependent pathways. We noted similar effects of those cytokines in human keratinocytes after exposure to S. aureus, and antibody blockade of the IL-20 receptor improved outcomes in infected mice. Our findings identify an immunosuppressive role for IL-19, IL-20 and IL-24 during infection that could be therapeutically targeted to alter susceptibility to infection.

We have previously reported that, depending on their activation status, mouse γδ T cells can either enhance or inhibit the activity of IL-17(+) autoreactive T cells in experimental autoimmune uveitis. In this study, we showed that γδ T cells in naive C57BL/6 (B6) mouse do not express the IL-23R, whereas in immunized mice, it is expressed on >50% of γδ T cells. In vitro studies showed that IL-23R expression on γδ T cells is modulated by their state of activation, as weakly activated γδ T cells expressed the IL-23R, but highly activated γδ T cells did not. Functional studies showed that IL-23R(+) γδ T cells had the strongest suppressive effect on IL-17(+) autoreactive T cells, and that this effect was inhibited when the IL-23R was blocked by anti-IL-23R Ab or in the presence of excessive amounts of exogenous IL-23. We conclude that the balance between the enhancing and inhibitory effects of γδ T cells is regulated by their level of IL-23R expression. The expression of variable IL-23R levels allows γδ T cells to have different regulatory effects on adaptive immune responses, conceivably as a result of αβ and γδ T cells competing for IL-23.

TH17 cells (interleukin-17 (IL-17)-producing helper T cells) are highly proinflammatory cells that are critical for clearing extracellular pathogens and for inducing multiple autoimmune diseases. IL-23 has a critical role in stabilizing and reinforcing the TH17 phenotype by increasing expression of IL-23 receptor (IL-23R) and endowing TH17 cells with pathogenic effector functions. However, the precise molecular mechanism by which IL-23 sustains the TH17 response and induces pathogenic effector functions has not been elucidated. Here we used transcriptional profiling of developing TH17 cells to construct a model of their signalling network and nominate major nodes that regulate TH17 development. We identified serum glucocorticoid kinase 1 (SGK1), a serine/threonine kinase, as an essential node downstream of IL-23 signalling. SGK1 is critical for regulating IL-23R expression and stabilizing the TH17 cell phenotype by deactivation of mouse Foxo1, a direct repressor of IL-23R expression. SGK1 has been shown to govern Na(+) transport and salt (NaCl) homeostasis in other cells. We show here that a modest increase in salt concentration induces SGK1 expression, promotes IL-23R expression and enhances TH17 cell differentiation in vitro and in vivo, accelerating the development of autoimmunity. Loss of SGK1 abrogated Na(+)-mediated TH17 differentiation in an IL-23-dependent manner. These data demonstrate that SGK1 has a critical role in the induction of pathogenic TH17 cells and provide a molecular insight into a mechanism by which an environmental factor such as a high salt diet triggers TH17 development and promotes tissue inflammation.

Although the causes of inflammatory arthritis elude us, aberrant cytokine expression has been linked to joint pathology. Consequently, several approaches in the clinic and/or in clinical trials are targeting cytokines, e.g. tumor necrosis factor (TNF), Interleukin 23 (IL-23) and Interleukin 17 (IL-17), with the goal of antagonizing their respective biologic activity through therapeutic neutralizing antibodies. Such, cytokine signaling-dependent molecular networks orchestrate synovial inflammation on multiple levels including differentiation of myeloid cells to osteoclasts, the central cellular players in arthritis-associated pathologic bone resorption. Hence, understanding of the cellular and molecular mechanisms elicited by synovial cytokine networks that dictate recruitment, differentiation and activation of osteoclast precursors and osteoclasts, respectively, is central to shaping novel therapeutic options for inflammatory arthritis patients. In this article we are discussing the complex signaling interactions involved in the regulation of inflammatory arthritis and it's associated bone loss with a focus on Interleukin 27 (IL-27). The present review will discuss the primary bone-degrading cell, the osteoclast, and on how IL-27, directly or indirectly, modulates osteoclast activity in autoimmune-driven inflammatory joint diseases., (Published by Elsevier Ltd.)

Inflammation has a central role in cancer progression. Metastatic tumors arise at sites of chronic inflammation, and tumors or tumor-infiltrating immune cells produce inflammatory mediators. By contrast, natural killer (NK) cells and cytotoxic T cells (CTLs) help eliminate premalignant lesions and limit the rate of tumor metastasis. Interleukin (IL)-27 is an IL-12 family cytokine chiefly produced by antigen-presenting cells (APCs) such as dendritic cells (DCs) and macrophages, and alone or in combination with other cytokines, IL-27 boosts antitumor immunity by contributing to the development of NK cells and CTLs - a central immnunomodulatory effect - and by exerting potent antiangiogenic and antimetastatic activities, a local antitumor effect. In this review, we argue that by virtue of its rate-limiting functions in innate and adaptive immune responses, modulating IL-27 holds considerable promise for future cancer immunotherapy., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Interleukin (IL)-33, a member of the IL-1 cytokine family, is an important modulator of the immune system associated with several immune-mediated disorders. High levels of IL-33 are expressed by the central nervous system (CNS) suggesting a potential role of IL-33 in autoimmune CNS diseases. We have investigated the expression and function of IL-33 in the development of experimental autoimmune encephalomyelitis (EAE) in mice. We report here that IL-33 and its receptor ST2 (IL-33Rα) are highly expressed in spinal cord tissue, and ST2 expression is markedly increased in the spinal cords of mice with EAE. Furthermore, ST2-deficient (ST2(-/-) ) mice developed exacerbated EAE compared with wild-type (WT) mice while WT, but not ST2(-/-) EAE mice treated with IL-33 developed significantly attenuated disease. IL-33-treated mice had reduced levels of IL-17 and IFN-γ but produced increased amounts of IL-5 and IL-13. Lymph node and splenic macrophages of IL-33-treated mice showed polarization toward an alternatively activated macrophage (M2) phenotype with significantly increased frequency of MR(+) PD-L2(+) cells. Importantly, adoptive transfer of these IL-33-treated macrophages attenuated EAE development. Our data therefore demonstrate that IL-33 plays a therapeutic role in autoimmune CNS disease by switching a predominantly pathogenic Th17/Th1 response to Th2 activity, and by polarization of anti-inflammatory M2 macrophages., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The role of interleukin (IL)-17 in cellular communication in inflammation has been well described, and a positive correlation between the severity of periodontitis and the level of IL-17 was reported. Although epithelial cells are a major target of IL-17, little is known about the effect of IL-17 on the production of chemokines by human gingival epithelial cells (HGECs). We evaluated the effects of IL-17 on the expression of CXCL8 and CCL2 by HGECs using quantitative real-time PCR and ELISA. In addition, the role of the nuclear factor (NF)-κB signalling pathway in the IL-17-mediated expression of chemokines was assessed using a specific inhibitor. Stimulation with IL-17 up-regulated the expression of CXCL8 mRNA but not of CCL2 mRNA in HGECs, whereas tumour necrosis factor-α (TNF-α) elevated the expression of mRNA for both chemokines. Stimulation with IL-17 up-regulated the secretion of CXCL8 protein, but not the secretion of CCL2 protein. The effect of IL-17 on CXCL8 production was suppressed using an anti-IL-17R Ig, suggesting a role for a specific receptor-ligand interaction. Inhibition of the NF-κB signalling pathway demonstrated that NF-κB activation is required for the CXCL8 expression in HGECs. In conclusion, IL-17 is involved in the regulation of the innate immune response in HGECs by inducing CXCL8 production., (© 2011 Eur J Oral Sci.)

Background: IL-25 is thought to participate in allergic inflammation by propagating T(h)2-type responses., Objective: To address the hypothesis that allergen provocation increases expression of IL-25 and its receptor IL-25R in the asthmatic bronchial mucosa and skin dermis of atopic subjects., Methods: Sequential single and double immunostaining was used to evaluate the numbers and phenotypes of IL-25 and IL-25R immunoreactive cells in bronchial biopsies from mild atopic subjects with asthma (n = 10) before and 24 hours after allergen inhalation challenge and skin biopsies from atopic subjects (n = 10) up to 72 hours after allergen subepidermal injection., Results: IL-25 immunoreactivity was expressed by a majority of epidermal cells in both organs at baseline and was not further augmented by challenge. IL-25R immunoreactive cells were rare in the epidermis before or after challenge. Allergen challenge was associated with significantly (P < .01) increased expression of IL-25 and IL-25R immunoreactivity in the submucosa of both organs. IL-25 immunoreactivity colocalized with eosinophils, mast cells, and endothelial cells, whereas IL-25R immunoreactivity colocalized with eosinophils, mast cells, endothelial cells, and T lymphocytes. In both organs, correlations were observed between increases in IL-25 expression and the magnitudes of the late-phase allergen-induced clinical responses., Conclusion: Allergen provocation induces functionally relevant, increased expression of IL-25 and its receptor in the asthmatic bronchial mucosa and dermis of sensitized atopic subjects. In addition to T cells, eosinophils, mast cells, and endothelial cells are potential sources and targets of IL-25 in the course of allergic inflammation., (Copyright © 2011 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Neuronal or photoreceptor deficit observed in uveitis and multiple sclerosis derives in part from inability to control inflammatory responses in neuroretina or brain. Recently, IL-27 was found to play a role in suppressing experimental autoimmune uveitis and experimental autoimmune encephalomyelitis, two animal models that share essential pathological features of human uveitis and multiple sclerosis, respectively. However, the mechanism by which interleukin-27 (IL-27) inhibits central nervous system (CNS) inflammation is not clear. In this study we have investigated mechanisms that mitigate or curtail intraocular inflammation (uveitis) and examined whether inhibitory effects of IL-27 are mediated locally by neuroretinal cells or by regulatory T cells. We show here that microglia cells in the neuroretina constitutively secrete IL-27 and its expression is up-regulated during uveitis. We further show that photoreceptors constitutively express IL-27 receptor and respond to IL-27 signalling by producing anti-inflammatory molecules, IL-10 and suppressor of cytokine signalling 1 (SOCS1) through signal transducer and activator of transcription 1 (STAT1) -dependent mechanisms. Moreover, STAT1-deficient mice produced reduced amounts of IL-27, IL-10 and SOCS1 and developed more severe uveitis. Surprisingly, IL-10-producing regulatory T cells had marginal roles in suppressing uveitis. These results suggest that suppression of intraocular inflammation might be mediated through endogenous production of IL-27 and IL-10 by retinal cells, whereas SOCS proteins induced by IL-27 during uveitis may function to protect the neuroretinal cells from the toxic effects of pro-inflammatory cytokines. Targeted delivery of IL-27 into immune privileged tissues of the CNS may therefore be beneficial in the treatment of CNS inflammatory diseases, such as uveitis and multiple sclerosis., (© 2011 The Authors. Immunology © 2011 Blackwell Publishing Ltd.)

Churg-Strauss syndrome (CSS) is characterized by systemic vasculitis and blood and tissue eosinophilia. Blood eosinophilia correlates with disease activity, and activated T cells from CSS patients are predominantly T helper 2 (Th2). Interleukin (IL)-25 has been shown to link innate and adaptive immunity by enhancing Th2 cytokine production. We sought to determine the involvement of IL-25 and its receptor IL-17RB in the pathogenesis of CSS. We found increased levels of IL-25 in the serum of active CSS patients (952 ± 697 vs 75 ± 49 pg/mL in inactive patients and 47 ± 6 pg/mL in healthy donors). IL-25 was correlated with disease activity and eosinophil level. Eosinophils were the main source of IL-25, whereas activated CD4(+) memory T cells were the IL-17RB-expressing cells in CSS. IL-25 enhanced the production of IL-4, IL-5, and IL-13 by activated peripheral blood mononuclear cells. IL-25 and IL-17RB were observed within the vasculitic lesions of patients with CSS, and IL-17RB colocalized with T cells. Increased expression of IL-17RB, tumor necrosis factor receptor-associated factor 6, and JunB in vasculitic lesions of CSS underscored the IL-25-mediated activation, whereas up-regulation of GATA3 and IL-10 supported Th2 differentiation. Our findings suggest that eosinophils, through the production of IL-25, exert a critical role in promoting Th2 responses in target tissues of CSS.

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

Interleukin-17A (IL-17A) and IL-17F are 2 of several cytokines produced by T helper 17 cells (Th17), which are able to indirectly induce the recruitment of neutrophils. Recently, human Th17 cells have been phenotypically characterized and shown to express discrete chemokine receptors, including CCR2 and CCR6. Herein, we show that highly purified neutrophils cultured with interferon-gamma plus lipopolysaccharide produce the CCL2 and CCL20 chemokines, the known ligands of CCR2 and CCR6, respectively. Accordingly, supernatants from activated neutrophils induced chemotaxis of Th17 cells, which was greatly suppressed by anti-CCL20 and anti-CCL2 antibodies. We also discovered that activated Th17 cells could directly chemoattract neutrophils via the release of biologically active CXCL8. Consistent with this reciprocal recruitment, neutrophils and Th17 cells were found in gut tissue from Crohn disease and synovial fluid from rheumatoid arthritis patients. Finally, we report that, although human Th17 cells can directly interact with freshly isolated or preactivated neutrophils via granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interferon-gamma release, these latter cells cannot be activated by IL-17A and IL-17F, because of their lack of IL-17RC expression. Collectively, our results reveal a novel chemokine-dependent reciprocal cross-talk between neutrophils and Th17 cells, which may represent a useful target for the treatment of chronic inflammatory diseases.

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.

Cytokines orchestrate the tumor-promoting interplay between malignant cells and the immune system. In many experimental and human cancers, the cytokine TNF-alpha is an important component of this interplay, but its effects are pleiotropic and therefore remain to be completely defined. Using a mouse model of ovarian cancer in which either TNF receptor 1 (TNFR1) signaling was manipulated in different leukocyte populations or TNF-alpha was neutralized by antibody treatment, we found that this inflammatory cytokine maintained TNFR1-dependent IL-17 production by CD4+ cells and that this led to myeloid cell recruitment into the tumor microenvironment and enhanced tumor growth. Consistent with this, in patients with advanced cancer, treatment with the TNF-alpha-specific antibody infliximab substantially reduced plasma IL-17 levels. Furthermore, expression of IL-1R and IL-23R was downregulated in CD4+CD25- cells isolated from ascites of ovarian cancer patients treated with infliximab. We have also shown that genes ascribed to the Th17 pathway map closely with the TNF-alpha signaling pathway in ovarian cancer biopsy samples, showing particularly high levels of expression of genes encoding IL-23, components of the NF-kappaB system, TGF-beta1, and proteins involved in neutrophil activation. We conclude that chronic production of TNF-alpha in the tumor microenvironment increases myeloid cell recruitment in an IL-17-dependent manner that contributes to the tumor-promoting action of this proinflammatory cytokine.

Th17 cells, CD4(+) T cells that secrete interleukin-17 (IL-17), are pathogenic in autoimmune diseases and their development and expansion is driven by the cytokines IL-6, TGF-beta, IL-21, IL-1, and IL-23. However, there are also innate sources of IL-17. Here, we show that gammadelta T cells express IL-23R and the transcription factor RORgammat and produce IL-17, IL-21, and IL-22 in response to IL-1beta and IL-23, without T cell receptor engagement. IL-17-producing gammadelta T cells were found at high frequency in the brain of mice with experimental autoimmune encephalomyelitis (EAE). gammadelta T cells activated by IL-1beta and IL-23 promoted IL-17 production by CD4(+) T cells and increased susceptibility to EAE, suggesting that gammadelta T cells act in an amplification loop for IL-17 production by Th17 cells. Our findings demonstrate that gammadelta T cells activated by IL-1beta and IL-23 are an important source of innate IL-17 and IL-21 and provide an alternative mechanism whereby IL-1 and IL-23 may mediate autoimmune inflammation.

IL-23, an IL-12 family member, has been implicated in the development of Th17 cells and the progression of autoimmune diseases. However, due to the lack of availability of sensitive Ab reagents specific for the IL-23 receptor (IL-23R), it has been difficult to characterize the cell types that express the IL-23R and are responsive to IL-23 in vivo. To address the role of IL-23 in vivo, we have generated a novel "knock-in" mouse in which we have replaced the intracellular domain of the IL-23R with the GFP. We show that in addition to Th17 cells, a subset of myeloid cells express IL-23R and respond to IL-23 by producing IL-17 and IL-22. Our studies further demonstrate that IL-23R expression is crucial for generation of encephalitogenic Th17 cells, but its expression on the innate immune system is dispensible in the development of experimental autoimmune encephalomyelitis.

Background: IL-17-producing T(H) (T(H)17) cells are key mediators of chronic inflammation in mice. Recent studies have implicated T(H)17-mediated inflammation in the pathogenesis of human autoimmune diseases; however, the involvement of T(H)17 cells in allergic disorders remains largely elusive., Objective: To investigate T(H)17-mediated inflammation in human beings with allergic contact dermatitis; in particular, the innate response of keratinocytes to contact allergen, the induction of allergen-specific T(H)17 cells, and the presence of T(H)17-related effector cells in inflamed skin., Methods: Human keratinocytes were stimulated with nickel in vitro followed by measurements of IL-23 and IL-12 production by quantitative PCR and ELISA. Allergen-specific memory T cells from the blood of individuals with nickel allergy and healthy controls were identified and characterized by using a short-term ex vivo assay. Nickel patch test lesions and normal skin were analyzed for the expression of T(H)17-related cells and molecules by using immunohistochemistry., Results: Keratinocytes were found to produce IL-23, but no detectable IL-12, in a response to nickel stimulation. Memory T cells isolated from peripheral blood of individuals with nickel allergy, but not healthy controls, contained T(H)17 and T(H)1 cells proliferating in response to nickel-pulsed DCs. Inflamed skin of nickel-challenged allergic individuals contained infiltrating neutrophils and cells expressing IL-17, IL-22, CCR6, and IL-22R., Conclusion: Our results demonstrate the involvement of T(H)17-mediated immunopathology in human allergic contact dermatitis, including both innate and adaptive immune responses to contact allergens.

Interleukin (IL)-27, a heterodimer composed of Epstein-Barr virus-induced gene 3 (EBI3) and p28, is an early product of activated dendritic cells (DC). Binding of IL-27 to the WSX-1 receptor initiates Th1 (Thelper 1) responses in naïve T cells. In order to assess the Th1 responses in human neonates with high susceptibility to infectious diseases, expression of EBI3-, p28- and WSX-1-mRNA in response to Toll-like receptor ligands was compared in neonate and adult monocyte-derived (m)DC. Only the combined addition of ligands induced expression of IL-27p28 mRNA. Surprisingly, neonatal mDC produced significantly more IL-27p28 mRNA than that obtained from adults. Furthermore, there was enhanced expression of EBI3 mRNA in cord blood as compared with adult blood. In addition, the secretion of WSX-1 mRNA in neonatal mDC and T cells was also significantly increased. Taken together, these findings indicate that the restricted Th1 responses in human newborns owing to deficient IL-12 production may be compensated for, in part, by enhanced IL-27 secretion.

Th17 cells require IL-6 and TGFbeta for lineage commitment and IL-23 for maintenance. Unexpectedly, naive IL-6(-/-) splenocytes stimulated with anti-CD3 and IL-23 produced normal amounts of IL-17 during the first 24 h of culture. These rapid IL-6-independent IL-17 producers were identified as predominantly DX5(+) TCRbeta(+) NKT cells, and a comparable response could be found using the invariant NKT-specific ligand alpha-galactosylceramide. Human NKT cells also produced IL-17. NKT cells constitutively expressed IL-23R and RORgammat. Ligation of either TCR or IL-23R triggered IL-17 production and both together had a synergistic effect, suggesting independent but convergent pathways. IL-17 production was not restricted to a particular subset of NKT cells but they were NK1.1 negative. Importantly, in vivo administration of alpha-galactosylceramide triggered a rapid IL-17 response in the spleen. These data suggest an important biological role for innate IL-17 production by NKT cells that is rapid and precedes the adaptive IL-17 response.

IL-17 and its receptor are founding members of a novel family of inflammatory cytokines. IL-17 plays a pathogenic role in rheumatoid arthritis (RA)-associated bone destruction. However, IL-17 is also an important regulator of host defense through granulopoiesis and neutrophil trafficking. Therefore, the role of IL-17 in pathogen-initiated bone loss was not obvious. The most common form of infection-induced bone destruction occurs in periodontal disease (PD). In addition to causing significant morbidity, PD is a risk factor for atherosclerotic heart disease and chronic obstructive pulmonary disease (COPD). Similar to RA, bone destruction in PD is caused by the immune response. However, neutrophils provide critical antimicrobial defense against periodontal organisms. Since IL-17 is bone destructive in RA but a key regulator of neutrophils, we examined its role in inflammatory bone loss induced by the oral pathogen Porphyromonas gingivalis in IL-17RA-deficient mice. These mice showed enhanced periodontal bone destruction, suggesting a bone-protective role for IL-17, reminiscent of a neutrophil deficiency. Although IL-17RA-deficient neutrophils functioned normally ex vivo, IL-17RA knock-out (IL-17RA(KO)) mice exhibited reduced serum chemokine levels and concomitantly reduced neutrophil migration to bone. Consistently, CXCR2(KO) mice were highly susceptible to alveolar bone loss; interestingly, these mice also suggested a role for chemokines in maintaining normal bone homeostasis. These results indicate a nonredundant role for IL-17 in mediating host defense via neutrophil mobilization.

Background: IL-17E is a new TH2 cytokine that promotes airway eosinophilia in mice. IL-17E proinflammatory activity has been proposed to involve induction of cytokine and chemokine production. Recruitment of inflammatory cells may be mediated by tissue-resident cells., Objective: This study aimed to evaluate whether fibroblasts represent a target of IL-17E for the production of eosinophil active mediators in the lung., Methods: Expression of IL-17B receptor (IL-17BR), a receptor for IL-17E, was evaluated by immunofluorescent staining, Western blot, and real-time PCR in human primary lung fibroblasts. Mediator production was analyzed by using real-time PCR and ELISA after stimulation of fibroblasts with IL-17E alone or in combination with TNF-alpha and TGF-beta1. Expression of IL-17E and of eosinophil major basic protein was evaluated by immunohistochemistry in bronchial biopsies from subjects with asthma., Results: Human primary lung fibroblasts constitutively expressed IL-17BR. IL-17BR mRNA levels were increased in cells stimulated with TNF-alpha and decreased with TGF-beta1. IL-17E slightly upregulated CC chemokine ligand (CCL)-5, CCL-11, GM-CSF, and CXC chemokine ligand (CXCL)-8 mRNA in fibroblasts. Moreover, IL-17E and TNF-alpha synergistically induced GM-CSF and CXCL-8 mRNA. IL-17E also potentiated the upregulation of CXCL-8 transcripts observed with TGF-beta1. In contrast, TGF-beta1 decreased IL-17E-induced CCL-11 mRNA. The capacity of IL-17E to enhance GM-CSF and CXCL-8 responses to TNF-alpha was accompanied by production and secretion of both proteins by lung fibroblasts. Finally, IL-17E was detected in asthma in eosinophil-infiltrated bronchial submucosa., Conclusion: IL-17E may contribute to the induction and maintenance of eosinophilic inflammation in the airways by acting on lung fibroblasts. This study supports a role for IL-17E in asthma pathophysiology.

The proinflammatory cytokine IL-17A, mainly produced by specialized T cells, plays an important homeostatic role in regulating neutrophil production and blood neutrophil counts. This review will assemble and discuss the evidence for this function of IL-17A-producing cells, which are collectively called neutrophil-regulatory T cells or Tn cells. IL-17A-producing lymphocytes are most abundant in the mesenteric lymph node, where they account for 0.15% of all lymphocytes. About 60% of the Tn cells are gammadelta T cells, about 25% NKTlike cells, and less than 15% are CD4 T cells. These latter cells are also known as T-17 or ThIL-17 cells, a subset of Tn cells that also plays an important role in autoimmune diseases. IL-17A produced by Tn cells regulates the production of G-CSF, which in turn promotes the proliferation of promyelocytes and maturation of neutrophils. This homeostatic mechanism plays an important role in normal physiology and in host defense against bacterial infections. This review is aimed at highlighting the important role of IL-17A-producing T cells at the interface between the adaptive and innate immune system.

IL-17A was cloned more than 10 years ago and six IL-17 family members (IL-17A-F) have subsequently been described. IL-17A is largely produced by activated memory T lymphocytes but stimulates innate immunity and host defense. IL-17A and IL-17F both mobilize neutrophils partly through granulopoeisis and CXC chemokine induction, as well as increased survival locally. IL-17A and IL-17F production by T lymphocytes is regulated by IL-23 independent of T cell receptor activation. Increasing evidence shows that IL-17 family members play an active role in inflammatory diseases, autoimmune diseases, and cancer. This places IL-17 family members and their receptors as potential targets for future pharmacotherapy.