M2 tumor-associated macrophages produce interleukin-17 to suppress oxaliplatin-induced apoptosis in hepatocellular carcinoma

M2 macrophages are a major component of the tumor microenvironment and are important promoters of tumor occurrence and progression. In this study, we detected large numbers of M2 macrophages in hepatocellular carcinoma tissues using immunohistochemistry and immunofluorescence. Moreover, upon oxaliplatin treatment, the M2 macrophages overexpressed interleukin-17, an important inflammatory cytokine, and thus inhibited oxaliplatin-induced apoptosis. By knocking down the interleukin-17 receptor and lysosome-associated membrane protein 2A (a key protein in chaperone-mediated autophagy) in hepatocellular carcinoma cells, we found that interleukin-17 stimulated chaperone-mediated autophagy, which further suppressed apoptosis upon oxaliplatin treatment. Chaperone-mediated autophagy induced tolerance to oxaliplatin treatment by reducing cyclin D1 expression; thus, cyclin D1 overexpression stimulated oxaliplatin-induced apoptosis. In addition, cyclin D1 expression was inhibited by interleukin-17, but increased when the interleukin-17 receptor was knocked down. Thus M2 macrophages in the hepatocellular carcinoma microenvironment generate large amounts of interleukin-17, which suppress oxaliplatin-induced tumor cell apoptosis by activating chaperone-mediated autophagy and in turn reducing cyclin D1 expression. These findings may facilitate the development of novel therapeutic strategies for chemorefractory liver cancer.

Microbiota-activated CD103+ DCs stemming from microbiota adaptation specifically drive γδT17 proliferation and activation

BACKGROUND

IL-17-producing γδT cells (γδT17) promote autoinflammatory diseases and cancers. Yet, γδT17 peripheral regulation has not been thoroughly explored especially in the context of microbiota-host interaction. The potent antigen-presenting CD103⁺ dendritic cell (DC) is a key immune player in close contact with both γδT17 cells and microbiota. This study presents a novel cellular network among microbiota, CD103⁺ DCs, and γδT17 cells.

METHODS

Immunophenotyping of IL-17r^-/- mice and IL-17r^-/- IRF8^-/- mice were performed by ex vivo immunostaining and flow cytometric analysis. We observed striking microbiome differences in the oral cavity and gut of IL-17r^-/- mice by sequencing 16S rRNA gene (v1-v3 region) and analyzed using QIIME 1.9.0 software platform. Principal coordinate analysis of unweighted UniFrac distance matrix showed differential clustering for WT and IL-17r^-/- mice.

RESULTS

We found drastic homeostatic expansion of γδT17 in all major tissues, most prominently in cervical lymph nodes (cLNs) with monoclonal expansion of Vγ6 γδT17 in IL-17r^-/- mice. Ki-67 staining and in vitro CFSE assays showed cellular proliferation due to cell-to-cell contact stimulation with microbiota-activated CD103⁺ DCs. A newly developed double knockout mice model for IL-17r and CD103⁺ DCs (IL-17r^-/-IRF8^-/-) showed a specific reduction in Vγ6 γδT17. Vγ6 γδT17 expansion is inhibited in germ-free mice and antibiotic-treated specific pathogen-free (SPF) mice. Microbiota transfer using cohousing of IL-17r^-/- mice with wildtype mice induces γδT17 expansion in the wildtype mice with increased activated CD103⁺ DCs in cLNs. However, microbiota transfer using fecal transplant through oral gavage to bypass the oral cavity showed no difference in colon or systemic γδT17 expansion.

CONCLUSIONS

These findings reveal for the first time that γδT17 cells are regulated by microbiota dysbiosis through cell-to-cell contact with activated CD103⁺ DCs leading to drastic systemic, monoclonal expansion. Microbiota dysbiosis, as indicated by drastic bacterial population changes at the phylum and genus levels especially in the oral cavity, was discovered in mice lacking IL-17r. This network could be very important in regulating both microbiota and immune players. This critical regulatory pathway for γδT17 could play a major role in IL-17-driven inflammatory diseases and needs further investigation to determine specific targets for future therapeutic intervention.

Blocking IL-17A Alleviates Diabetic Retinopathy in Rodents

BACKGROUND/AIMS

Interleukin (IL)-17A, a proinflammatory cytokine, has been implicated in several autoimmune diseases. However, it is unclear whether IL-17A is involved in diabetic retinopathy (DR), one of the most serious complications of autoimmune diabetes. This study aimed to demonstrate that IL-17A exacerbates DR by affecting retinal Müller cell function.

METHODS

High glucose (HG)-treated rat Müller cell line (rMC-1) was exposed to IL-17A, anti-IL-17A-neutralizing monoclonal antibody (mAb) or/and anti-IL-17 receptor (R)A-neutralizing mAb for 24 h. For in vivo study, DR was induced by intraperitoneal injections of streptozotocin (STZ). DR model mice were treated with anti-IL-17A mAb or anti-IL-17RA mAb in the vitreous cavity. Mice that were prepared for retinal angiography were sacrificed two weeks after intravitreal injection, while the rest were sacrificed two days after intravitreal injection.

RESULTS

IL-17A production and IL-17RA expression were increased in both HG-treated rMC-1 and DR retina. HG induced rMC-1 activation and dysfunction, as determined by the increased GFAP, VEGF and glutamate levels as well as the downregulated GS and EAAT1 expression. IL-17A exacerbated the HG-induced rMC-1 functional disorders, whereas either anti-IL-17A mAb or anti-IL-17RA mAb alleviated the HG-induced rMC-1 disorders. Intravitreal injections with anti-IL-17A mAb or anti-IL-17RA mAb in DR model mice reduced Müller cell dysfunction, vascular leukostasis, vascular leakage, tight junction protein downregulation and ganglion cell apoptosis in the retina.

CONCLUSIONS

IL-17A aggravates DR-like pathology at least partly by impairing retinal Müller cell function. Blocking IL-17A is a potential therapeutic strategy for DR.

The Impact of MicroRNA-223-3p on IL-17 Receptor D Expression in Synovial Cells

OBJECTIVE

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease affecting joints. Elevated plasma levels of microRNA-223-3p (miR-223-3p) in patients with RA are implicated in the pathogenesis of the disease. This study aimed to analyze the functional role of miR-223-3p in the pathogenesis of RA by overexpressing miR-223-3p in synovial cell lines.

METHODS

Arthritis was induced in the RA model of SKG mice by injection of ß-glucan. The histopathologic features of joints were examined using hematoxylin and eosin and immunohistochemical staining. Plasma levels of miRNA were determined by panel real-time PCR analysis. Target genes of the differentially expressed miRNAs in SKG mice were analyzed using miRNA target prediction algorithms. The dual-luciferase reporter system was used to evaluate the relationship between miR-223-3p and IL-17 receptor D (IL-17RD). The activity of miR-223-3p was analyzed by transfection of plasmid vectors overexpressing miR-223-3p into IL-17RD-expressing NIH3T3 and MH7A cell lines. Il6 and Il17rd mRNA expression was analyzed by quantitative real-time PCR. IL-17RD protein expression was analyzed by western blot analysis.

RESULTS

We identified 17 upregulated miRNAs (fold change > 2.0) in plasma of SKG mice injected with ß-glucan relative to untreated SKG mice. Il17rd was identified as the candidate target gene of miR-223-3p using five miRNA target prediction algorithms. The transfection of plasmid vectors overexpressing miR-223-3p into NIH3T3 and MH7A cells resulted in the downregulation of Il17rd expression and upregulation of Il6 expression. Expression of miR-223-3p and Il6 mRNA in MH7A cells was upregulated; however, that of Il17rd mRNA was downregulated following TNF-α stimulation. IL-17RD expression in synovial tissues from SKG mice and RA patients was inversely correlated with the severity of arthritis.

CONCLUSION

This study is the first to demonstrate that miR-223-3p downregulates IL-17RD in both mouse and human cells; miR-223-3p may contribute to the pathogenesis of RA by downregulating the expression of IL-17RD and upregulating that of IL-6 in synovial cells.

Molecular characterization and evolution analysis of five interleukin-17 receptor genes in large yellow croaker Larimichthys crocea

Interleukin-17s (IL-17s) play critical roles in inflammatory response and host defense against extracellular pathogens. IL-17s induce the immune response signaling through the specific IL-17 receptors (IL-17Rs) that consist of five members (IL-17RA to E). In the present work, we have identified the five IL-17R orthologs (LycIL-17Rs) from large yellow croaker Larimichthys crocea. The deduced protein of each LycIL-17R exhibits a typical IL-17R domain architecture, including a signal peptide, the extracellular FNIII domain (IL-17RA/RB/RD) or IL-17_R_N domain (IL-17RC/RE), a transmembrane domain, and a SEFIR domain in cytoplasmic region. In particular, the extracellular regions of teleost IL-17RB are much shorter than those in mammals and lack an FNIII domain (FN2). Phylogenetic tree shows that IL-17Rs are classified into two main groups: IL-17RA/RB/RD group and IL-17RC/RE group, which is distinct from previous proposal that grouped IL-17RB into IL-17RC/RE. The surrounding genes of IL-17Rs are conservatively aligned in genomes between teleosts and mammals. The five LycIL-17Rs were constitutively expressed in all tissues examined, but with different expression patterns. Aeromonas hydrophila infection significantly upregulated LycIL-17RA, RC, RD and RE in both mucosal tissue (gills) and systemic immune tissues (head kidney and spleen), while the increase of LycIL-17RB expression could be detected in gills, indicating that LycIL-17Rs may be involved in host defense against bacterial infection. Thus, these results suggest that teleost IL-17Rs may function in mediating immune response as their mammalian orthologs. To our knowledge, this is the first report of molecular characterization of the five IL-17Rs (IL-17RA/RB/RD and IL-17RC/RE) in teleost fish.

A Single Nucleotide Polymorphism in the Il17ra Promoter Is Associated with Functional Severity of Ankylosing Spondylitis

The aim of this study was to identify new genetic variants associated with the severity of ankylosing spondylitis (AS). We sequenced the exome of eight patients diagnosed with AS, selected on the basis of the severity of their clinical parameters. We identified 27 variants in exons and regulatory regions. The contribution of candidate variants found to AS severity was validated by genotyping two Spanish cohorts consisting of 180 cases/300 controls and 419 cases/656 controls. Relationships of SNPs and clinical variables with the Bath Ankylosing Spondylitis Disease Activity and Functional Indices BASDAI and BASFI were analyzed. BASFI was standardized by adjusting for the duration of the disease since the appearance of the first symptoms. Refining the analysis of SNPs in the two cohorts, we found that the rs4819554 minor allele G in the promoter of the IL17RA gene was associated with AS (p<0.005). This variant was also associated with the BASFI score. Classifying AS patients by the severity of their functional status with respect to BASFI/disease duration of the 60th, 65th, 70th and 75th percentiles, we found the association increased from p60 to p75 (cohort 1: p<0.05 to p<0.01; cohort 2: p<0.01 to p<0.005). Our findings indicate a genetic role for the IL17/ILRA axis in the development of severe forms of AS.

Common variants in IL-17A/IL-17RA axis contribute to predisposition to and progression of congestive heart failure

Heart failure is characterized by immune activation leading to production and release of proinflammatory cytokines. Interleukin 17A (IL-17A) is a proinflammatory cytokine and multiple lines of evidence from animal and human studies suggest crucial roles of IL-17A in heart failure. Therefore, we investigated whether common polymorphisms of genes IL17A and IL17RA (coding interleukin 17 receptor A) contribute to genetic predisposition to heart failure and adverse clinical outcomes associated with it.A total of 1713 adult patients with congestive heart failure and 1713 age- and sex-matched controls were genotyped for promoter single nucleotide polymorphisms (SNPs), rs2275913 and rs8193037 in IL17A and rs4819554 in IL17RA, to assess the relationship between individual SNPs and the risk of congestive heart failure. Results showed that rs8193037 in IL17A was associated with the risk of congestive heart failure (odds ratio [OR] = 0.76; 95% confidence interval [CI] 0.63-0.90, adjusted P = 0.002) after adjustment for multiple cardiovascular risk factors including age, sex, smoking status, diabetes, hypertension, and dyslipidemia. This association was evident in both ischemic and nonischemic heart failure (P = 0.005 and P = 0.05, respectively). Furthermore, prospective follow-up of 12.7 months for the occurrence of adverse clinical outcomes showed that rs4819554 in IL17RA was significantly associated with cardiovascular mortality (hazard ratio [HR] = 1.28; 95% CI = 1.02-1.59, adjusted P = 0.03) after adjustments for multiple cardiovascular risk factors and New York Heart Association functional class.This study demonstrated associations of rs8193037 in the promoter of IL17A with the risk of congestive heart failure, and of rs4819554 in the promoter of IL17RA with the risk of cardiovascular mortality in patients with congestive heart failure. These data lend further support to the notion that immune activation and genetic polymorphisms contribute to heart failure pathogenesis and progression.

Card9- and MyD88-Mediated Gamma Interferon and Nitric Oxide Production Is Essential for Resistance to Subcutaneous Coccidioides posadasii Infection

Coccidioidomycosis is a potentially life-threatening respiratory disease which is endemic to the southwestern United States and arid regions of Central and South America. It is responsible for approximately 150,000 infections annually in the United States alone. Almost every human organ has been reported to harbor parasitic cells of Coccidioides spp. in collective cases of the disseminated form of this mycosis. Current understanding of the mechanisms of protective immunity against lung infection has been largely derived from murine models of pulmonary coccidioidomycosis. However, little is known about the nature of the host response to Coccidioides in extrapulmonary tissue. Primary subcutaneous coccidioidal infection is rare but has been reported to result in disseminated disease. Here, we show that activation of MyD88 and Card9 signal pathways are required for resistance to Coccidioides infection following subcutaneous challenge of C57BL/6 mice, which correlates with earlier findings of the protective response to pulmonary infection. MyD88(-/-) andCard9(-/-) mice recruited reduced numbers of T cells, B cells, and neutrophils to the Coccidioides-infected hypodermis com pared to wild-type mice; however, neutrophils were dispensable for resistance to skin infection. Further studies have shown that gamma interferon (IFN-γ) production and activation of Th1 cells characterize resistance to subcutaneous infection. Furthermore, activation of a phagosomal enzyme, inducible nitric oxide synthase, which is necessary for NO production, is a requisite for fungal clearance in the hypodermis. Collectively, our data demonstrate that MyD88- and Card9-mediated IFN-γ and nitric oxide production is essential for protection against subcutaneous Coccidioides infection.

Role of IL-17 Variants in Preeclampsia in Chinese Han Women

Previous studies have suggested an important role for IL-17, mainly secreted by Th17 cells, in the development of systemic inflammation in preeclampsia (PE). This study therefore investigated the association between genetic variants in IL-17A, IL-17F, and IL-17RA and susceptibility to PE in Chinese Han women. We recruited 1,031 PE patients and 1,298 controls of later pregnant women, and used TaqMan allelic discrimination real-time PCR to genotype the polymorphisms of IL17A rs2275913, IL-17F rs763780, and IL-17RA rs4819554. No significant differences in genotypic or allelic frequencies were found at all three polymorphic sites between PE patients and controls (rs2275913: genotype χ2 = 0.218, p = 0.897 and allele χ2 = 0.157, p = 0.692, OR = 1.024, 95%CI 0.911-1.152; rs763780: genotype χ2 = 1.948, p = 0.377 and allele χ2 = 1.242, p = 0.265, OR = 0.897, 95%CI 0.741-1.086; rs4819554: genotype χ2 = 0.633, p = 0.729 and allele χ2 = 0.115, p = 0.735, OR = 1.020, 95%CI 0.908-1.146). There were also no significant differences in genetic distributions between mild/severe PE or early/late-onset PE and control subgroups. Our data indicate that the genetic variants of rs2275913 in IL-17A, rs763780 in IL-17F, and rs4819554 in IL-17RA may not play a role in the pathogenesis of PE in Chinese Han women. However, these findings should be confirmed in other ethnic populations.

Human mast cells are major IL-22 producers in patients with psoriasis and atopic dermatitis

BACKGROUND

Psoriasis is a systemic inflammatory disease in which IL-17 and IL-22 levels are markedly increased in the skin and blood. The prevalent concept, using skin cells that are isolated from psoriatic plaques and examined after cell expansion and in vitro stimulation, is that IL-17 and IL-22 production essentially results from T cells and the rare type 3 innate lymphoid cells.

OBJECTIVE

We sought to examine the cellular source of IL-17A and IL-22 at the protein and transcriptional single-cell level immediately after ex vivo skin cell isolation from psoriatic plaques.

METHODS

Skin biopsy specimens were collected from patients with psoriasis, as well as from patients with atopic dermatitis. Cell suspensions were prepared by combining mild enzymatic digestion and mechanical dissociation and analyzed for cytokine expression without prior in vitro culture and stimulation. Expression of IL-17 and IL-22 was quantified at the protein and mRNA single-cell level by using flow cytometry.

RESULTS

IL-22 is predominantly expressed by CD3(-)c-Kit(+) cells relative to CD3(+) T cells in lesional skin of patients with psoriasis and patients with atopic dermatitis. Strikingly, we identified c-Kit(+)FcεRI(+) mast cells as major IL-22 producers. The proportion of mast cells that produce IL-22 ranges from 20% to 80% in patients with psoriasis or those with atopic dermatitis. Skin mast cells express IL-22 and IL-17 mRNA. Conversely, IL-17-producing T cells outnumber IL-17-producing mast cells, which also express IL-17 receptor.

CONCLUSION

Human skin mast cells are previously unrecognized IL-22 producers. We further established that skin mast cells express IL-17. Thus mast cells might play an important role in the physiopathology of chronic inflammatory skin disorders.

Unexpected Role for Adaptive αβTh17 Cells in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating disorder characterized by increased alveolar permeability with no effective treatment beyond supportive care. Current mechanisms underlying ARDS focus on alveolar endothelial and epithelial injury caused by products of innate immune cells and platelets. However, the role of adaptive immune cells in ARDS remains largely unknown. In this study, we report that expansion of Ag-specific αβTh17 cells contributes to ARDS by local secretion of IL-17A, which in turn directly increases alveolar epithelial permeability. Mice with a highly restrictive defect in Ag-specific αβTh17 cells were protected from experimental ARDS induced by a single dose of endotracheal LPS. Loss of IL-17 receptor C or Ab blockade of IL-17A was similarly protective, further suggesting that IL-17A released by these cells was responsible for this effect. LPS induced a rapid and specific clonal expansion of αβTh17 cells in the lung, as determined by deep sequencing of the hypervariable CD3RβVJ region of the TCR. Our findings could be relevant to ARDS in humans, because we found significant elevation of IL-17A in bronchoalveolar lavage fluid from patients with ARDS, and rIL-17A directly increased permeability across cultured human alveolar epithelial monolayers. These results reveal a previously unexpected role for adaptive immune responses that increase alveolar permeability in ARDS and suggest that αβTh17 cells and IL-17A could be novel therapeutic targets for this currently untreatable disease.

High IFN-γ and low SLPI mark severe asthma in mice and humans

Severe asthma (SA) is a challenge to control, as patients are not responsive to high doses of systemic corticosteroids (CS). In contrast, mild-moderate asthma (MMA) is responsive to low doses of inhaled CS, indicating that Th2 cells, which are dominant in MMA, do not solely orchestrate SA development. Here, we analyzed broncholalveolar lavage cells isolated from MMA and SA patients and determined that IFN-γ (Th1) immune responses are exacerbated in the airways of individuals with SA, with reduced Th2 and IL-17 responses. We developed a protocol that recapitulates the complex immune response of human SA, including the poor response to CS, in a murine model. Compared with WT animals, Ifng-/- mice subjected to this SA model failed to mount airway hyperresponsiveness (AHR) without appreciable effect on airway inflammation. Conversely, AHR was not reduced in Il17ra-/- mice, although airway inflammation was lower. Computer-assisted pathway analysis tools linked IFN-γ to secretory leukocyte protease inhibitor (SLPI), which is expressed by airway epithelial cells, and IFN-γ inversely correlated with SLPI expression in SA patients and the mouse model. In mice subjected to our SA model, forced SLPI expression decreased AHR in the absence of CS, and it was further reduced when SLPI was combined with CS. Our study identifies a distinct immune response in SA characterized by a dysregulated IFN-γ/SLPI axis that affects lung function.

Increased chemokine receptor IL-17RA expression is associated with poor survival in gastric cancer patients

BACKGROUND

Previous researchers have identified that the chemokine interleukin-17 (IL-17) was associated with survival time of patients with gastric cancer, but the roles of its receptors (IL-17R) in gastric cancer remain unknown. Our studies were designed to clarify the function of IL-17RA and to explore their potential role in gastric cancer.

MATERIALS AND METHODS

The expression of IL-17RA was determined in primary gastric cancer tissues (n=101) using Real-time RT-PCR, immunohistochemistry, and western blotting. To investigate the functional significance of IL-17RA expression, IL-17RA expression and clinical parameters, multivariate survival was analyzed in patients with gastric cancer.

RESULTS

IL-17RA was overexpression in gastric cancer tissues compared with adjacent normal tissues (P<0.05). The elevated expression level of IL-17RA was observed correlated significantly with tumor progression (P=0.003), Lymphatic invasion (P=0.019), lymphoid nodal status (P=0.001), distant metastasis (P<0.001) of gastric cancer patients, TNM stage (P=0.0013) and was one of the independent prognostic factors for patient's overall survival.

CONCLUSIONS

These results demonstrated that the expression of IL-17RA plays an important role in gastric cancer progression, migration and prognosis of gastric cancer. The IL-17-IL-17RA signaling mechanism may be a potential novel target.

Identification of a 6-cytokine prognostic signature in patients with primary glioblastoma harboring M2 microglia/macrophage phenotype relevance

BACKGROUND

Glioblastomas (GBM) are comprised of a heterogeneous population of tumor cells, immune cells, and extracellular matrix. Interactions among these different cell types and pro-/anti-inflammatory cytokines may promote tumor development and progression.

AIMS

The objective of this study was to develop a cytokine-related gene signature to improve outcome prediction for patients with primary GBM.

METHODS

Here, we used Cox regression and risk-score analysis to develop a cytokine-related gene signature in primary GBMs from the whole transcriptome sequencing profile of the Chinese Glioma Genome Atlas (CGGA) database (n=105). We also examined differences in immune cell phenotype and immune factor expression between the high-risk and low-risk groups.

RESULTS

Cytokine-related genes were ranked based on their ability to predict survival in the CGGA database. The six genes showing the strongest predictive value were CXCL10, IL17R, CCR2, IL17B, IL10RB, and CCL2. Patients with a high-risk score had poor overall survival and progression-free survival. Additionally, the high-risk group was characterized by increased mRNA expression of M2 microglia/macrophage markers and elevated levels of IL10 and TGFβ1.

CONCLUSION

The six cytokine-related gene signature is sufficient to predict survival and to identify a subgroup of primary GBM exhibiting the M2 cell phenotype.

Age-related increase in IL-17 activates pro-inflammatory signaling in prostate cells

BACKGROUND

A close relationship between aging, inflammation, and prostate cancer is widely accepted. Aging is accompanied by a progressive increase in pro-inflammatory cytokines, including interleukin 17 (IL-17), a key pro-inflammatory cytokine that becomes dysregulated with age. However, the contribution of IL-17 to age-related prostate tumorigenesis remains unclear. The aim of this study was to investigate the role of age-related IL-17 dysregulation in prostate tumorigenesis.

METHODS

Serum and splenic T-lymphocytes from young GPAT-1 knock-out aging-mimic T cell mice as well as young and aged wild-type mice were collected. shRNA was used to knock down the IL-17 receptor in LNCaP prostate cancer cells and RWPE-1 non-transformed prostate epithelial cells, which were then exposed to the mouse sera or conditioned media from stimulated T-lymphocytes. NF-κB activation, NF-κB target gene expression, and cell proliferation were all measured in these cells by luciferase assay, qPCR, Western blot analysis, and MTT assay, respectively.

RESULTS

T-lymphocyte-secreted IL-17 from aging-mimic mice induced NF-κB activity and target gene expression in LNCaP and RWPE-1 cells. It also promoted proliferation of these cells.

CONCLUSION

Aging-mimic T cell mice produce increased levels of IL-17, which stimulates the pro-inflammatory NF-κB pathway in prostate epithelial cells. NF-κB increases inflammation, carcinogenesis and metastatic potential in the prostate. These findings provide evidence that the dysregulation of cytokine production seen in aged T cells may directly contribute to the increased risk for prostate cancer in the elderly.

The elevated expression of Th17-related cytokines and receptors is associated with skin lesion severity in early systemic sclerosis

OBJECTIVE

The objective was to survey the expression and localization of Th17-related cytokines and their correlation with skin lesion severity in early systemic sclerosis (SSc).

METHODS

The mRNA expression was detected by real-time quantitative polymerase chain reaction (RT-qPCR) from 21 SSc patients and 12 healthy controls (HC). The protein expression was examined by immunohistochemistry (IHC) and Western blotting.

RESULTS

The RT-qPCR analysis showed a significantly higher expression of IL-17A, IL-21, IL-22, IL-26, IL-17RA, IL-21R, and IL-22R1 mRNA; consistently, the IHC analysis showed an over-expression of IL-17RA, IL-21R and IL-22R1 and the Western blotting analysis showed an over-expression of IL-17A, IL-21, IL-21R and IL-22R1 in early SSc skin lesions. The mRNA levels of IL-21 were higher in diffuse cutaneous than limited cutaneous SSc lesions. The mRNA expression of IL-26, IL-22, IL-22R1, mRNA and protein expression of IL-17A, IL-21, IL-21R were positively correlated with the modified Rodnan skin score of SSc. In addition, the mRNA levels of ICAM-1 were positively correlated with IL-17A/IL-17RA, and VEGFA and IL-4 were both positively correlated with IL-21/IL-21R, while TGF-β were moderately negatively correlated with IL-22/IL-22R1.

CONCLUSIONS

Th17 cytokines contribute to progression in early SSc skin lesions. IL-21/IL-21R could act as potential biomarkers presenting early SSc skin lesions severity.

Cytokine-regulated neutrophil recruitment is required for brain but not spinal cord inflammation during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease in which inflammatory lesions lead to tissue injury in the brain and/or spinal cord. The specific sites of tissue injury are strong determinants of clinical outcome in MS, but the pathways that determine whether damage occurs in the brain or spinal cord are not understood. Previous studies in mouse models of MS demonstrated that IFN-γ and IL-17 regulate lesion localization within the brain; however, the mechanisms by which these cytokines mediate their effects have not been identified. In the present study, we show that IL-17 promoted, but IFN-γ inhibited, ELR(+) chemokine-mediated neutrophil recruitment to the brain, and that neutrophil infiltration was required for parenchymal tissue damage in the brain. In contrast, IFN-γ promoted ELR(+) chemokine expression and neutrophil recruitment to the spinal cord. Surprisingly, tissue injury in the spinal cord did not exhibit the same dependence on neutrophil recruitment that was observed for the brain. Our results demonstrate that the brain and spinal cord exhibit distinct sensitivities to cellular mediators of tissue damage, and that IL-17 and IFN-γ differentially regulate recruitment of these mediators to each microenvironment. These findings suggest an approach toward tailoring therapies for patients with distinct patterns of neuroinflammation.

Structure of the unique SEFIR domain from human interleukin 17 receptor A reveals a composite ligand-binding site containing a conserved α-helix for Act1 binding and IL-17 signaling

Interleukin 17 (IL-17) cytokines play a crucial role in mediating inflammatory and autoimmune diseases. A unique intracellular signaling domain termed SEFIR is found within all IL-17 receptors (IL-17Rs) as well as the key adaptor protein Act1. SEFIR-mediated protein-protein interaction is a crucial step in IL-17 cytokine signaling. Here, the 2.3 Å resolution crystal structure of the SEFIR domain of IL-17RA, the most commonly shared receptor for IL-17 cytokine signaling, is reported. The structure includes the complete SEFIR domain and an additional α-helical C-terminal extension, which pack tightly together to form a compact unit. Structural comparison between the SEFIR domains of IL-17RA and IL-17RB reveals substantial differences in protein topology and folding. The uniquely long insertion between strand βC and helix αC in IL-17RA SEFIR is mostly well ordered, displaying a helix (αCC'ins) and a flexible loop (CC'). The DD' loop in the IL-17RA SEFIR structure is much shorter; it rotates nearly 90° with respect to the counterpart in the IL-17RB SEFIR structure and shifts about 12 Å to accommodate the αCC'ins helix without forming any knots. Helix αC was identified as critical for its interaction with Act1 and IL-17-stimulated gene expression. The data suggest that the heterotypic SEFIR-SEFIR association via helix αC is a conserved and signature mechanism specific for IL-17 signaling. The structure also suggests that the downstream motif of IL-17RA SEFIR together with helix αC could provide a composite ligand-binding surface for recruiting Act1 during IL-17 signaling.

Characterization and mucosal responses of interleukin 17 family ligand and receptor genes in channel catfish Ictalurus punctatus

Interleukin (IL) 17 family cytokines are important mediators of mucosal immune responses, tightly regulated by signals from the complex milieu of pathogenic and commensal microbes, epithelial cells and innate and adaptive leukocytes found at tissue barriers. In mammals, IL17 ligand expression has been linked not only to protective immunity but also excessive tissue inflammation and damage in the gut and lungs. To better understand the scope and action of the IL17 family in channel catfish Ictalurus punctatus, we identified and characterized seven IL17 ligands and four IL17 receptor (IL17R) homologues from transcriptomic and genomic databases. To gain insight into the mucosal actions of the IL17A/Fs-associated pathway in inflammatory processes, the expression profiles of three IL17A/Fs and their putative receptors IL17RA and IL17RC in mucosal tissues of catfish following experimental challenge with Edwardsiella ictaluri and Flavobacterium columnare were investigated. Bacterial challenge induced higher expression of the catfish IL17A/Fs as early at 4 h post-infection, particularly in gill tissue. In contrast, in the catfish intestine, where IL17 function is best understood in mouse models, IL17A/F expression showed minimal early responses to E. ictaluri infection. Instead, a significant up-regulation of IL17 ligands and receptors was observed in the intestine at 7 d, highlighting species and tissue-specific regulation of the IL17 family.

Interleukin-17 retinotoxicity is prevented by gene transfer of a soluble interleukin-17 receptor acting as a cytokine blocker: implications for age-related macular degeneration

Age-related macular degeneration (AMD) is a common yet complex retinal degeneration that causes irreversible central blindness in the elderly. Pathology is widely believed to follow loss of retinal pigment epithelium (RPE) and photoreceptor degeneration. Here we report aberrant expression of interleukin-17A (IL17A) and the receptor IL17RC in the macula of AMD patients. In vitro, IL17A induces RPE cell death characterized by the accumulation of cytoplasmic lipids and autophagosomes with subsequent activation of pro-apoptotic Caspase-3 and Caspase-9. This pathology is reduced by siRNA knockdown of IL17RC. IL17-dependent retinal degeneration in a mouse model of focal retinal degeneration can be prevented by gene therapy with adeno-associated virus vector encoding soluble IL17 receptor. This intervention rescues RPE and photoreceptors in a MAPK-dependent process. The IL17 pathway plays a key role in RPE and photoreceptor degeneration and could hold therapeutic potential in AMD.

IL-17 regulates systemic fungal immunity by controlling the functional competence of NK cells

Interleukin 17 (IL-17)-mediated immunity plays a key role in protection from fungal infections in mice and man. Here, we confirmed that mice deficient in the IL-17 receptor or lacking the ability to secrete IL-17 are highly susceptible to systemic candidiasis, but we found that temporary blockade of the IL-17 pathway during infection in wild-type mice did not impact fungal control. Rather, mice lacking IL-17 receptor signaling had a cell-intrinsic impairment in the development of functional NK cells, which accounted for the susceptibility of these mice to systemic fungal infection. NK cells promoted antifungal immunity by secreting GM-CSF, necessary for the fungicidal activity of neutrophils. These data reveal that NK cells are crucial for antifungal defense and indicate a role for IL-17 family cytokines in NK cell development. The IL-17-NK cell axis may impact immunity against not only fungi but also bacteria, viruses, and tumors.

Interleukin 17 receptor A modulates monocyte subsets and macrophage generation in vivo

Interleukin (IL)-17A signaling via Interleukin 17 receptor A (Il17ra) contributes to the inflammatory host response by inducing recruitment of innate immune cells, but also plays a role in homeostatic neutrophilic granulocyte regulation. Monocytes, the other main innate immune cell, have a longer life span and can pursue multiple differentiation pathways towards tissue macrophages. Monocytes are divided into two subpopulations by expression of the Ly6C/Gr1 surface marker in mice. We here investigated the role of Il17ra in monocyte homeostasis and macrophage generation. In Il17ra^-/- and in mixed bone marrow chimeric wt/Il17ra^-/- mice, the concentrations of circulating Il17ra^-/-Gr1^low monocytes were significantly decreased compared to wt cells. Pulmonary, splenic and resident peritoneal Il17ra^-/- macrophages were significantly fewer than of wt origin. Bone marrow progenitor and monocyte numbers were equal, but the proportion of Il17ra^-/-Gr1^low monocytes was already decreased at bone marrow level. After monocyte depletion, initial Gr1^high and Gr1^low monocyte regeneration of Il17ra^-/- and wt cells was very similar. However, Il17ra^-/-Gr1^low counts were not sustained. After labeling with either fluorescent beads or BrdU, Il17ra^-/-Gr1^high monocyte transition to Gr1^low cells was not detectable unlike wt cells. Monocyte recruitment in acute peritonitis, which is known to be largely due to Gr1^high cell migration, was unaffected in an identical environment. Unilateral ureteral obstruction induces a less acute inflammatory and fibrotic kidney injury. Compared to wt cells in the same environment, Il17ra^-/- macrophage accumulation in the kidney was decreased. In the absence of Il17ra on all myeloid cells, renal fibrosis was significantly attenuated. Our data show that Il17ra modulates Gr1^low monocyte counts and suggest defective Gr1^high to Gr1^low monocyte transition as an underlying mechanism. Lack of Il17ra altered homeostatic tissue macrophage formation and diminished renal inflammation and fibrosis. Il17ra appears to be a novel modulator of monocyte phenotype and possible therapeutic target in renal fibrosis.

An ACT1 mutation selectively abolishes interleukin-17 responses in humans with chronic mucocutaneous candidiasis

Patients with inborn errors of interleukin-17F (IL-17F) or IL-17RA display chronic mucocutaneous candidiasis (CMC). We report a biallelic missense mutation (T536I) in the adaptor molecule ACT1 in two siblings with CMC. The mutation, located in the SEFIR domain, abolished the homotypic interaction of ACT1 with IL-17 receptors, with no effect on homodimerization. The patients' fibroblasts failed to respond to IL-17A and IL-17F, and their T cells to IL-17E. By contrast, healthy individuals homozygous for the common variant D10N, located in the ACT1 tumor necrosis factor receptor-associated factor-interacting domain and previously associated with psoriasis, had impaired, but not abolished, responses to IL-17 cytokines. SEFIR-independent interactions of ACT1 with other proteins, such as CD40, heat shock protein 70 (HSP70) and HSP90, were not affected by the T536I mutation. Overall, human IL-17A and IL-17F depend on ACT1 to mediate protective mucocutaneous immunity. Moreover, other ACT1-dependent IL-17 cytokines seem to be largely redundant in host defense.

In vivo delivery of adenoviral vector containing interleukin-17 receptor a reduces cardiac remodeling and improves myocardial function in viral myocarditis leading to dilated cardiomyopathy

Th17 cells have been implicated in the pathogenesis of myocarditis. Interleukin (IL)-17A produced by Th17 cells is dispensable for viral myocarditis but essential for the progression to dilated cardiomyopathy (DCM). This study investigated whether the adenoviral transfer of the IL-17 receptor A reduces myocardial remodeling and dysfunction in viral myocarditis leading to DCM. In a mouse model of Coxsackievirus B3 (CVB3)-induced chronic myocarditis, the delivery of the adenovirus-containing IL-17 receptor A (Ad-IL17RA:Fc) reduced IL-17A production and decreased the number of Th17 cells in the spleen and heart, leading to the down-regulation of systemic TNF-α and IL-6 production. Cardiac function improved significantly in the Ad-IL17R:Fc- compared with the Ad-null-treated mice 3 months after the first CVB3 infection. Ad-IL17R:Fc reduced the left ventricle dilation and decreased the mortality in viral myocarditis, leading to DCM (56% in the Ad-IL17R:Fc versus 76% in the Ad-null group). The protective effects of Ad-IL17R-Fc on remodeling correlated with the attenuation of myocardial collagen deposition and the reduction of fibroblasts in CVB3-infected hearts, which was accompanied by the down-regulation of A distintegrin and metalloprotease with thrombospondin type 1 motifs (ADAMTS-1), Matrix metalloproteinase-2(MMP-2), and collagen subtypes I and III in the heart. Moreover, in cultured cardiac fibroblasts, IL-17A induced the expression of ADAMTS-1, MMP-2, and collagen subtypes I and III and increased the proliferation of fibroblasts. We determined that the delivery of IL-17-RA:Fc reduces cardiac remodeling, improves function, and decreases mortality in viral myocarditis leading to DCM, possibly by suppressing fibrosis. Therefore, the adenoviral transfer of the IL-17 receptor A may represent an alternative therapy for chronic viral myocarditis and its progression to DCM.

Expression of the interleukin 17 in cortical tubers of the tuberous sclerosis complex

The role of interleukin 17 (IL-17) to epilepsy-associated cortical tubers of tuberous sclerosis complex (TSC) is unknown. We investigated the expression patterns of the IL-17 and IL-17 receptor (IL-17R) in cortical tubers of TSC compared with normal control cortex (CTX). We found that IL-17 and IL-17R were clearly upregulated in cortical tubers at the protein levels. Immunostaining indicated that IL-17 was specifically distributed in the innate immunity cells (DNs, GCs, astrocytes, and microglia) and adaptive immunity cells (T-lymphocytes) as well as the endothelial cells of blood vessels. The overexpression and distribution patterns of IL-17 may be involved in the epileptogenicity of cortical tubers in TSC.

Interleukin 17 receptor gene polymorphism in periimplantitis and chronic periodontitis

Gene polymorphism of cytokines influencing their function has been known as a contributing factor in the pathogenesis of inflammatory diseases of the tooth and implant supporting tissues. The aim of this study was to investigate the association of IL-17R gene polymorphism (rs879576) with chronic periodontitis and periimplantitis in an Iranian population. 73 patients with chronic periodontitis, 37 patients with periimplantitis and 83 periodontally healthy patients were enrolled in this study. 5cc blood was obtained from each subject's arm vein and transferred to tubes containing EDTA. Genomic DNA was extracted using Miller's Salting Out technique. The DNA was transferred into 96 division plates, transported to Kbioscience Institute in United Kingdom and analyzed using the Kbioscience Competitive Allele Specific PCR (KASP) technique. Chi-square and Kruskal Wallis tests were used to analyze differences in the expression of genotypes and frequency of alleles in disease and control groups (P-Value less than 0.05 was considered statistically significant). There were no significant differences between periodontitis, periimplantitis with AA, GG, GA genotype of IL-17R gene (P=0.8239). Also comparison of frequency of alleles in SNP rs879576 of IL-17R gene between the chronic periodontitis group and periimplantitis group did not revealed statistically significant differences (P=0.8239). The enigma of IL-17 and its polymorphism-role in periodontitis and periimplantitis is yet to be investigated more carefully throughout further research but this article demonstrates that polymorphism of IL-17R plays no significant role in incidence of chronic periodontitis and Periimplantitis.

IL-22 modulates IL-17A production and controls inflammation and tissue damage in experimental dengue infection

Dengue virus (DENV), a mosquito-borne flavivirus, is a public health problem in many tropical countries. IL-22 and IL-17A are key cytokines in several infectious and inflammatory diseases. We have assessed the contribution of IL-22 and IL-17A in the pathogenesis of experimental dengue infection using a mouse-adapted DENV serotype 2 strain (P23085) that causes a disease that resembles severe dengue in humans. We show that IL-22 and IL-17A are produced upon DENV-2 infection in immune-competent mice. Infected IL-22(-/-) mice had increased lethality, neutrophil accumulation and pro-inflammatory cytokines in tissues, notably IL-17A. Viral load was increased in spleen and liver of infected IL-22(-/-) mice. There was also more severe liver injury, as seen by increased transaminases levels and tissue histopathology. γδ T cells and NK cells are sources of IL-17A and IL-22, respectively, in liver and spleen. We also show that DENV-infected HepG2 cells treated with rhIL-22 had reduced cell death and decreased IL-6 production. IL-17RA(-/-) mice were protected upon infection and IL-17A-neutralizing-Ab-treatment partially reversed the phenotype observed in IL-22(-/-) -infected mice. We suggest that disrupting the balance between IL-22 and IL-17A levels may represent an important strategy to reduce inflammation and tissue injury associated with severe dengue infection.

An alternative pathway of imiquimod-induced psoriasis-like skin inflammation in the absence of interleukin-17 receptor a signaling

Topical application of imiquimod (IMQ) on the skin of mice induces inflammation with common features found in psoriatic skin. Recently, it was postulated that IL-17 has an important role both in psoriasis and in the IMQ model. To further investigate the impact of IL-17RA signaling in psoriasis, we generated IL-17 receptor A (IL-17RA)-deficient mice (IL-17RA(del)) and challenged these mice with IMQ. Interestingly, the disease was only partially reduced and delayed but not abolished when compared with controls. In the absence of IL-17RA, we found persisting signs of inflammation such as neutrophil and macrophage infiltration within the skin. Surprisingly, already in the naive state, the skin of IL-17RA(del) mice contained significantly elevated numbers of Th17- and IL-17-producing γδ T cells, assuming that IL-17RA signaling regulates the population size of Th17 and γδ T cells. Upon IMQ treatment of IL-17RA(del) mice, these cells secreted elevated amounts of tumor necrosis factor-α, IL-6, and IL-22, accompanied by increased levels of the chemokine CXCL2, suggesting an alternative pathway of neutrophil and macrophage skin infiltration. Hence, our findings have major implications in the potential long-term treatment of psoriasis by IL-17-targeting drugs.

Inflammatory mediators alter interleukin-17 receptor, interleukin-12 and -23 expression in human osteoarthritic and rheumatoid arthritis synovial fibroblasts: immunomodulation by vasoactive intestinal Peptide

AIMS

To assess the contribution of fibroblast-like synoviocytes (FLS) to the inflammatory joint microenvironment under different pathogenic stimuli and their potential to respond to interleukin (IL)-17 and to determine whether the neuroimmunomodulatory vasoactive intestinal peptide (VIP) is able to modulate IL-17 receptor (IL-17R) and related cytokines.

METHODS

The effect of proinflammatory cytokines [tumor necrosis factor α (TNFα) and IL-17] and Toll-like receptor (TLR) ligands [poly(I:C) and lipopolysaccharide (LPS)] on IL-17R expression and IL-12 and IL-23 production was studied in osteoarthritis (OA)- and rheumatoid arthritis (RA)-FLS, involved in Th1/Th17 differentiation. The effect of VIP was also determined. IL-17RA, IL-17RC, IL-12p35 and IL-23p19 expression was measured by real-time polymerase chain reaction. IL-12 and IL-23 protein levels were measured by ELISA in supernatant cultures.

RESULTS

TNFα, LPS and poly(I:C) induced an increase in IL-17RA in RA-FLS, whereas TNFα, TNFα plus IL-17 and poly(I:C) enhanced IL-17RC transcripts in FLS. VIP diminished the upregulated expression of IL-17RA in RA-FLS following TNFα and poly(I:C). TNFα, LPS and poly(I:C) increased IL-12 and IL-23 levels in cells derived from patients presenting both pathologies. However, IL-17A DECREASED IL-12 AND AUGMENTED IL-23. VIP DECREASED IL-12P35 MRNA UPREGULATION BY POLY(I:C) AND IL-23P19 TRANSCRIPTS IN LPS-TREATED FLS.

CONCLUSIONS

Inflammatory cytokines and TLR ligands modulate IL-17R, IL-12 and IL-23 possibly favoring the cross talk between FLS and Th1/Th17 cells. The ability of VIP to counteract the enhancing effect of proinflammatory molecules on IL-17R and the IL-12 family of cytokines corroborates and amplifies the beneficial effect of this endogenous neuroimmunopeptide in rheumatic diseases.

Gene polymorphisms of interleukin-17 and interleukin-17 receptor are associated with end-stage kidney disease

BACKGROUND

Inflammation could be a causal factor in progression of chronic kidney disease. To date, there is convincing experimental and clinical evidence to support the notion that interleukin (IL)-17-producing T cells contribute to kidney injury in renal diseases. However, the genetic relationship between end-stage renal disease (ESRD) and the T-helper 17 pathway has never been studied. In this study, we hypothesized that polymorphisms of IL-17 or their receptors may be associated with ESRD.

METHODS

A total of 290 nondiabetic ESRD patients and 289 normal controls were included. We analyzed 13 single nucleotide polymorphisms located within the four genes of IL17A, IL17E, IL17RA and IL17RB.

RESULTS

The ESRD patients had a significantly higher allele frequency compared to control subjects for the IL17E rs10137082*C and IL17RA rs4819554*A alleles. Genotyping analysis demonstrated that 2 SNPs among 13 were significantly associated with ESRD after adjusting for age and sex, which were shown by IL17E rs10137082 (odds ratio (OR) 1.48 in codominant 1, OR 1.54 in dominant, OR 1.47 in log-additive) and IL17RA rs4819554 (OR 1.46 in codominant 1, OR 1.79 in codominant 2, OR 1.54 in dominant, OR 1.39 in log-additive).

CONCLUSIONS

Two polymorphisms within the IL17E and IL17RA genes are associated with ESRD independent of age and sex. This is the first finding to suggest that genetic variations of IL17 genes affect the risk of development of ESRD.

Interleukin-25 promotes basic fibroblast growth factor expression by human endothelial cells through interaction with IL-17RB, but not IL-17RA

BACKGROUND

Unlike other IL-17 family members, the Th2-derived cytokine IL-25 (IL-17E) induces (promotes) Th2 responses. One or both of the two receptors for IL-25 (IL-17RA, IL-17RB) is expressed on inflammatory cells and tissue structural cells, suggesting that in addition to promoting Th2-type inflammation IL-25 may also act on structural cells at sites of Th2-type inflammation such as in the asthmatic bronchial mucosa to promote remodelling changes.

OBJECTIVE

Our previous studies showed elevated expression of IL-25 and IL-17RB immunoreactivity in asthmatic airways with co-localization of the latter to endothelial cells. We therefore hypothesized that IL-25 acts on endothelial cells through this receptor to induce production of the key angiogenic and remodelling cytokine basic fibroblast growth factor (bFGF).

METHODS

Polymerase chain reaction (PCR) immunocytochemistry/immunohistochemistry and ELISA were employed to detect expression of IL-17RB, IL-17RA and bFGF by human vascular endothelial cells (HUVEC) and immunoreactivity for IL-25 and bFGF in asthmatic bronchial biopsies. Receptor-blocking antibodies, PCR and an in vitro angiogenesis assay were used to investigate whether IL-25 acts on IL-17RB or IL-17RA to induce bFGF expression and angiogenesis. PCR was also employed to investigate the signalling pathways involved in IL-25-mediated bFGF expression.

RESULTS

HUVEC constitutively expressed IL-17RB, IL-17RA and bFGF. Production of the latter was further increased by IL-25, but attenuated after blockade of the IL-17RB, but not the IL-17RA receptor. Neutralization of endogenous VEGF and bFGF completely abrogated IL-25-induced angiogenesis which was also inhibited by blocking IL-17RB, but not IL-17RA. The PI3K-specific inhibitor LY294002 also completely attenuated IL-25-induced bFGF expression. Immunoreactivity for IL-25 and bFGF was elevated in the asthmatic bronchial mucosa and the expression of each correlated with the other.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data support the hypothesis that IL-25 contributes to elevated bFGF in asthmatic airways by acting on the endothelial cell IL-17RB receptor through PI3K-signalling pathways. Targeting the pathways might benefit therapy of airways remodelling.

Transcriptional regulation of IL-17A and other inflammatory markers during the development of soybean meal-induced enteropathy in the distal intestine of Atlantic salmon (Salmo salar L.)

Progression of soybean meal (SBM)-induced enteropathy in Atlantic salmon (Salmo salar L.) distal intestine (DI) was studied to investigate pathophysiological mechanisms and immune responses. Seawater-adapted salmon were fed an extracted SBM-containing diet (200 g kg(-1)) from day 1-21 and compared with fish fed a fishmeal-based diet (day 0). Histological evaluation of the DI revealed signs of inflammation from day 5, which progressively increased in severity and affected more fish with increasing SBM exposure time. The expression profiles of 16 genes were analyzed by quantitative PCR. The pro-inflammatory cytokines interleukin 17A (IL-17A), IL-1β, interferon α (IFNα) and IFNγ, as well as IL-17A receptor, T-cell receptor γ (TCRγ), cluster of differentiation 4α (CD4α), CD8β, transforming growth factor β (TGFβ), trypsin, protease-activated receptor 2 (PAR2) and myeloid differentiation primary response gene 88 (MyD88) were significantly up-regulated during early and/or late inflammation stages, whereas interferon-γ-inducible lysosomal thiol reductase (GILT) was downregulated. Up-regulation of TCRγ from day seven suggests proliferation of intraepithelial γδ T cells. IL-17A, up-regulated by 218-fold during early inflammation, indicates involvement of T helper 17 cells in the pathogenesis of the SBM-induced inflammatory response.

Interleukin-17 signaling in inflammatory, Kupffer cells, and hepatic stellate cells exacerbates liver fibrosis in mice

BACKGROUND & AIMS

Interleukin (IL)-17 signaling has been implicated in lung and skin fibrosis. We examined the role of IL-17 signaling in the pathogenesis of liver fibrosis in mice.

METHODS

Using cholestatic and hepatotoxic models of liver injury, we compared the development of liver fibrosis in wild-type mice with that of IL-17RA(-/-) mice and of bone marrow chimeric mice devoid of IL-17 signaling in immune and Kupffer cells (IL-17RA(-/-) to wild-type and IL-17A(-/-) to wild-type mice) or liver resident cells (wild-type to IL-17RA(-/-) mice).

RESULTS

In response to liver injury, levels of Il-17A and its receptor increased. IL-17A increased appeared to promote fibrosis by activating inflammatory and liver resident cells. IL-17 signaling facilitated production of IL-6, IL-1, and tumor necrosis factor-α by inflammatory cells and increased the expression of transforming growth factor-1, a fibrogenic cytokine. IL-17 directly induced production of collagen type I in hepatic stellate cells by activating the signal transducer and activator of transcription 3 (Stat3) signaling pathway. Mice devoid of Stat3 signaling in hepatic stellate cells (GFAPStat3(-/-) mice) were less susceptible to fibrosis. Furthermore, deletion of IL-23 from immune cells attenuated liver fibrosis, whereas deletion of IL-22 exacerbated fibrosis. Administration of IL-22 and IL-17E (IL-25, a negative regulator of IL-23) protected mice from bile duct ligation-induced liver fibrosis.

CONCLUSIONS

IL-17 induces liver fibrosis through multiple mechanisms in mice. Reagents that block these pathways might be developed as therapeutics for patients with cirrhosis.

IL-17-induced Act1-mediated signaling is critical for cuprizone-induced demyelination

Cuprizone inhibits mitochondrial function and induces demyelination in the corpus callosum, which resembles pattern III lesions in multiple sclerosis patients. However, the molecular and cellular mechanism by which cuprizone induces demyelination remains unclear. Interleukin-17 (IL-17) secreted by T helper 17 cells and γδT cells are essential in the development of experimental autoimmune encephalomyelitis. In this study, we examined the importance of IL-17 signaling in cuprizone-induced demyelination. We found that mice deficient in IL-17A, IL-17 receptor C (IL-17RC), and adaptor protein Act1 (of IL-17R) all had reduced demyelination accompanied by lessened microglial and polydendrocyte cellular reactivity compared with that in wild-type mice in response to cuprizone feeding, demonstrating the essential role of IL-17-induced Act1-mediated signaling in cuprizone-induced demyelination. Importantly, specific deletion of Act1 in astrocytes reduced the severity of tissue injury in this model, indicating the critical role of CNS resident cells in the pathogenesis of cuprizone-induced demyelination. In cuprizone-fed mice, IL-17 was produced by CNS CD3(+) T cells, suggesting a source of IL-17 in CNS upon cuprizone treatment.

Development and function of invariant natural killer T cells producing T(h)2- and T(h)17-cytokines

Four distinct subsets of invariant natural killer T (NKT) cells are shown to differentiate in the thymus, then migrate to peripheral tissues where they retain their phenotypic and functional characteristics.

There is heterogeneity in invariant natural killer T (iNKT) cells based on the expression of CD4 and the IL-17 receptor B (IL-17RB), a receptor for IL-25 which is a key factor in T_H2 immunity. However, the development pathway and precise function of these iNKT cell subtypes remain unknown. IL-17RB⁺iNKT cells are present in the thymic CD44^+/− NK1.1⁻ population and develop normally even in the absence of IL-15, which is required for maturation and homeostasis of IL-17RB⁻iNKT cells producing IFN-γ. These results suggest that iNKT cells contain at least two subtypes, IL-17RB⁺ and IL-17RB⁻ subsets. The IL-17RB⁺iNKT subtypes can be further divided into two subtypes on the basis of CD4 expression both in the thymus and in the periphery. CD4⁺ IL-17RB⁺iNKT cells produce T_H2 (IL-13), T_H9 (IL-9 and IL-10), and T_H17 (IL-17A and IL-22) cytokines in response to IL-25 in an E4BP4-dependent fashion, whereas CD4⁻ IL-17RB⁺iNKT cells are a retinoic acid receptor-related orphan receptor (ROR)γt⁺ subset producing T_H17 cytokines upon stimulation with IL-23 in an E4BP4-independent fashion. These IL-17RB⁺iNKT cell subtypes are abundantly present in the lung in the steady state and mediate the pathogenesis in virus-induced airway hyperreactivity (AHR). In this study we demonstrated that the IL-17RB⁺iNKT cell subsets develop distinct from classical iNKT cell developmental stages in the thymus and play important roles in the pathogenesis of airway diseases.

T cells are a diverse group of immune cells involved in cell-mediated acquired immunity. One subset of T cells is the innate-like invariant natural killer T (iNKT) cells that recognize glycolipid ligands on target cells instead of peptides. We know that functionally distinct subtypes of iNKT cells are involved in specific pathologies, yet their development, phenotypes, and functions are not well understood. Here, we determine the relationship between various mouse iNKT cell subsets, identify reliable molecular markers for these subsets, and show that these contribute to their functional differences. We identify four iNKT cell subsets that we show arise via different developmental pathways and exhibit different cytokine profiles. Importantly, we show that these subsets can be isolated from the thymus (the organ of all T cells), as well as from peripheral tissues such as spleen, liver, lung, and lymph nodes. Contrary to the general understanding that iNKT cells mature after their exit from the thymus and their migration into peripheral tissues, we conclude that distinct phenotypic and functional iNKT cell subsets can be distinguished in the thymus by virtue of the presence or absence of the cytokine receptor IL-17RB and another cell surface molecule called CD4, and these subsets then migrate to peripheral tissues where they retain their phenotypic and functional characteristics. Regarding functional significance, we show that those iNKT cell subsets that lead to airway hyper-responsiveness to respiratory viruses are different to those that lead to allergen-induced airway hyperreactivity, which will enable researchers to focus on specific subsets as potential targets for therapeutic intervention.

[Effect of IL-17 on the expression of monocyte chemoattractant protein-1 in the cardiac myocytes]

AIM

To investigate the effect of interleukin-17 (IL-17) on the expression of monocyte chemoattractant protein-1(MCP-1) in the primary cultured cardiac myocytes.

METHODS

The cardiac myocytes were isolated from neonatal mice by different adhesion method. The expressions of IL-17R and MCP-1 in the cardiac myocytes were evaluated by reverse transcription-polymerase chain reaction (RT-PCR). And the concentration of MCP-1 in the culture supernatant of the cardiac myocytes was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

There was the expression of IL-17R in the cardiac myocytes. After stimulated by IL-17, the expressions of MCP-1 in the cardiac myocytes were significantly increased in dose-dependent manner compared with that of culture medium control (P<0.05). The amount of MCP-1 mRNA in the cardiac myocytes was the highest at 4 h after stimulated by IL-17. And then the amount of MCP-1 mRNA in the cardiac myocytes began to descend. The concentrations of MCP-1 in the culture supernatant of the cardiac myocytes increased in time-dependent manner and had significant differences with the control group (P<0.05).

CONCLUSION

The cardiac myocytes could express IL-17R. IL-17 could up-regulate the expression of MCP-1 in the cardiac myocytes, which was associated with the dose and stimulation time of IL-17.

[Effects of interleukin-17 on murine pulmonary fibroblast proliferation, transformation and collagen synthesis]

OBJECTIVE

To investigate the effects of interleukin-17 (IL-17) on the proliferation, transformation and collagen synthesis of the lung fibroblasts in mice with bleomycin-induced pulmonary fibrosis.

METHODS

In a mouse model of pulmonary fibrosis established by intratracheal administration of 5 mg/kg bleomycin, the dynamic expressions of IL-17/IL-17 receptor (IL-17R) mRNAs were detected by RT-PCR. At 14 days following bleomycin administration, the pulmonary fibroblasts were isolated, cultured and identified. MTT assay was used to assess the proliferation of the pulmonary fibroblasts in response to IL-17 treatment at different concentrations, and RT-PCR and Western blotting were employed to examine the mRNA and protein expressions of α-smooth muscle actin (α-SMA) and types I and III collagen.

RESULTS

IL-17/IL-17R mRNA levels were increased obviously in the pulmonary fibroblasts of rats with pulmonary fibrosis, and the highest expressions occurred at 14 days following bleomycin administration. Exogenous IL-17, at the optimal concentration of 50 ng/ml, significantly promoted the proliferation of the pulmonary fibroblasts in primary culture and obviously increased α-SMA expression and types I and III collagen synthesis in the fibroblasts.

CONCLUSION

IL-17 can promote the proliferation, transformation, and collagen synthesis of the pulmonary fibroblasts from rats with bleomycin-induced pulmonary fibrosis.

MicroRNAs and other mechanisms regulate interleukin-17 cytokines and receptors

Interleukin-17 cytokines are a family of pro-inflammatory cytokines. Our current studies found: i) IL-17 cytokines are not ubiquitously expressed, but several receptors and TRAF3IP2 are ubiquitously expressed in tissues with a few exceptions; ii) heart and vascular tissue are in the second tier of readiness to respond to IL-17 cytokine stimulation; iii) alternative transcription starting sites and alternative spliced isoforms are found in IL-17 cytokine and receptor transcripts; iv) higher hypomethylation status is associated with higher expressions of IL-17 receptors; v) the binding sites of several RNA binding proteins are found in the 3'UTRs of the mRNAs of IL-17 cytokines and receptors; and vi) numerous microRNA binding sites are statistically equivalent to that of experimentally verified microRNAs-mRNA interactions in the 3'UTRs of IL-17 cytokine and receptor mRNAs. These results suggest that mechanisms including alternative promoters, alternative splicing, RNA binding proteins, and microRNAs regulate the structures and expressions of IL-17 cytokines and receptors. These results provide an insight into the roles of IL-17 in mediating inflammation and immunity.

Genomics of fish IL-17 ligand and receptors: a review

Interleukin-17 (IL-17) is a cytokine family composed of six ligands (A-F). Especially, the IL-17A and IL-17F are best characterized cytokines of IL-17 family cytokine. These are produced by Th17 cells and induce the expression of many mediators of inflammation properties. In addition, the five member of IL-17 receptor family (RA-RE) have been identified in mammals. Although the research on fish IL-17 is a little to date, this review discusses some of the recent advances in research on IL-17 ligand and receptor genes in fish. IL-17 family member was chosen from the fish genome database, and its structure and phylogeny is analyzed in detail. Moreover, invertebrate IL-17 genes are also discussed, and the isolation and current status of fish IL-17 receptor genes are summarized. Comparative genomic analysis of the IL-17 family among mammals, teleost and invertebrates provided new insights. Novel IL-17 ligand (IL-17N) was identified from teleost, moreover it was suggested that IL-17N may be a teleost specific ligand by synteny and phylogenetic analysis. On the other hand, IL-17 receptors are well conserved between mammal and teleost, the five member of IL-17 receptor family: IL-17RA-RE were found on the teleost genome. In addition, the IL-17RA gene was duplicated in tandem on the stickleback and medaka genome. Knowledge about the IL-17 ligand/receptor in fish is very limited. Therefore this review will hopefully encourage future studies of IL-17 in fish.

Dynamic evolution of CIKS (TRAF3IP2/Act1) in metazoans

CIKS (TRAF3IP2/Act1) is important for inflammatory responses and autoimmunity control through its dual functions in CD40L/BAFF and IL17 signaling in mammalians. In this study, we performed comparative and evolutionary analyses of CIKSs from metazoans. Although nematode (Caenorabditis elegans) and sea urchin (Strongylocentrotus purpuratus) have IL17 and IL17 receptors, we found no CIKS in their genomes. The ancient CIKS-like (CIKSL) genes from the invertebrates lottia (Lottia gigantea) and amphioxus (Branchiostoma floridae) have an additional DEATH domain compared with other CIKSLs/CIKSs. Our data suggest that the ancient CIKSL evolved into early chordate CIKS possibly through gene tandem duplication and gene fission. Based on phylogenetic and synteny analyses, vertebrate CIKS genes are divided into two groups, one of which is orthologous to human CIKS and the other is paralogous. Expression analysis indicated that cephalochordata amphioxus IL17 together with CIKS might play an ancient and conserved role in host defense against bacterial infections. During the evolutionary process, the CIKS genes have obtained more and more functions through cooperation with other genes.

Interleukin-17A stimulates cardiac fibroblast proliferation and migration via negative regulation of the dual-specificity phosphatase MKP-1/DUSP-1

The dual-specificity mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) inactivates MAP kinases by dephosphorylation. Here we show that the proinflammatory cytokine interleukin (IL)-17A induces adult mouse primary cardiac fibroblast (CF) proliferation and migration via IL-17 receptor A//IL-17 receptor C-dependent MKP-1 suppression, and activation of p38 MAPK and ERK1/2. IL-17A mediated p38 MAPK and ERK1/2 activation is inhibited by MKP-1 overexpression, but prolonged by MKP-1 knockdown. IL-17A induced miR-101 expression via PI3K/Akt, and miR-101 inhibitor reversed MKP-1 down regulation. Importantly, MKP-1 knockdown, pharmacological inhibition of p38 MAPK and ERK1/2, or overexpression of dominant negative MEK1, each markedly attenuated IL-17A-mediated CF proliferation and migration. Similarly, IL-17F and IL-17A/F heterodimer that also signal via IL-17RA/IL-17RC, stimulated CF proliferation and migration. These results indicate that IL-17A stimulates CF proliferation and migration via Akt/miR-101/MKP-1-dependent p38 MAPK and ERK1/2 activation. These studies support a potential role for IL-17 in cardiac fibrosis and adverse myocardial remodeling.

IL-17RE is the functional receptor for IL-17C and mediates mucosal immunity to infection with intestinal pathogens

Interleukin 17 receptor E (IL-17RE) is an orphan receptor of the IL-17 receptor family. Here we show that IL-17RE is a receptor specific to IL-17C and has an essential role in host mucosal defense against infection. IL-17C activated downstream signaling through IL-17RE-IL-17RA complex for the induction of genes encoding antibacterial peptides as well as proinflammatory molecules. IL-17C was upregulated in colon epithelial cells during infection with Citrobacter rodentium and acted in synergy with IL-22 to induce the expression of antibacterial peptides in colon epithelial cells. Loss of IL-17C-mediated signaling in IL-17RE-deficient mice led to lower expression of genes encoding antibacterial molecules, greater bacterial burden and early mortality during infection. Together our data identify IL-17RE as a receptor of IL-17C that regulates early innate immunity to intestinal pathogens.

[Eukaryotic expression of human IL17-RD-ECD and generation of its monoclonal antibody]

IL-17 Receptor D (IL-17 RD) is a cytokine receptor that mediates IL-17 signaling and plays an important role in responding to the invasion of extracellular pathogens and many inflammatory and autoimmune diseases such as rheumatoid arthritis. In this study we report the generation of a mouse monoclonal antibody against human IL-17 RD. The recombinant human IL-17RD extracellular domain (hIL-17RD-ECD) was produced in the baculovirus expression system and purified from culture medium of sf9 insect cells. The purified protein was used as a T-dependent antigen to immune Balb/C mice. B cells from the spleen of immunized mice were fused with murine cell SP2/0. Hybridoma cell lines were screened for the production of the monoclonal antibody against hIL-17-RD-ECD using ELISA. A hybridoma cell line 1F8 was found to have a high production of the antibody, which was further confirmed for the specificity by both western blot and ELISA analyses. The monoclonal antibody obtained from hybridoma 1F8 was characterized to be IgG1+Kappa subclass. This study provided a base for the further therapeutic application of the antibody on the autoimmune disease including rheumatoid arthritis.

The expression of interleukin (IL)-17 and IL-17 receptor and MMP-9 in human pituitary adenomas

The IL-17 plays a crucial role in the invasion of tumors. However, the effects of IL-17 on the invasion of human pituitary adenomas are still unknown. The current study is designed to investigate the possible involvement of IL-17 in the invasion of adenomas. By collecting invasive and non-invasive pituitary adenomas, the mRNA and protein levels of IL-17, IL-17R and MMP-9 are investigated. The results obtained from IHC showed that the strong positive rate and the total positive rate of IL-17, IL-17R and MMP-9 expression cells in the non-invasive group were 17.1 and 51.43%, 14.3 and 54.3%, 17.1 and 57.1%, respectively. In contrast, the strong positive rate and the total positive rate of the invasive group were significantly higher than that of the non-invasive group, which were 37.5 and 82.5%, 52.5 and 87.5%, 67.5 and 92.5%, respectively. Meanwhile, the serum IL-17 level in the invasive pituitary adenomas patients was significantly higher than in the non-invasive groups (P < 0.05). Furthermore, the mRNA levels of IL-17, IL-17R and MMP-9 were also higher in the invasive group than in the non-invasive group with statistical differences (P < 0.05), and where the expression levels of IL-17 and IL-17R had positive correlation with that of MMP-9 in the invasive group. These results suggested that IL-17 may promote the invasion of pituitary adenomas.

Lentivirus mediated IL-17R blockade improves diastolic cardiac function in spontaneously hypertensive rats

BACKGROUND

Hypertension causes cardiac fibrosis characterized by low-grade inflammation. We hypothesized that proinflammatory cytokine, interleukin-17 (IL-17) is important in hypertensive cardiac fibrosis. The pre-ligand assembly domain (PLAD) of IL-17 receptor A (IL-17RA) mediates receptor-chain associations essential for signaling. This study was designed to explore the role of IL-17 RA PLAD in hypertension-induced cardiac fibrosis.

METHODS

Eight-week-old male spontaneously hypertensive rats (SHRs) were divided into 2 groups, depending on receiving IL-17RA PLAD-Ig or green fluorescent protein (GFP) lentivirus. Age-matched Wistar Kyoto rats served as controls. Cardiac function was determined by echocardiography. Cardiac hypertrophy and fibrosis were histopathologically examined. Matrix metalloproteinase (MMP) and tissue inhibitors of metalloproteinase (TIMP) expression were quantified by immunoblotting. Collagen content was quantified.

RESULTS

Both cardiac systolic and diastolic function and myocardial fibrosis in SHRs was improved significantly by the IL-17RA PLAD. Expression of MMP-2 and MMP-9, TIMP-1 and -2, type I and type III collagen were statistically decreased by IL-17RA PLAD-Ig treatment. Collagen quantitation, as well as collagen concentration and collagen cross-linking, were reduced by IL-17/IL-17R signal blockade.

CONCLUSIONS

IL-17/IL-17RA signaling plays an important role in myocardial collagen metabolism in hypertension-induced diastolic dysfunction.

Chronic mucocutaneous candidiasis in humans with inborn errors of interleukin-17 immunity

Chronic mucocutaneous candidiasis disease (CMCD) is characterized by recurrent or persistent infections of the skin, nails, and oral and genital mucosae caused by Candida albicans and, to a lesser extent, Staphylococcus aureus, in patients with no other infectious or autoimmune manifestations. We report two genetic etiologies of CMCD: autosomal recessive deficiency in the cytokine receptor, interleukin-17 receptor A (IL-17RA), and autosomal dominant deficiency of the cytokine interleukin-17F (IL-17F). IL-17RA deficiency is complete, abolishing cellular responses to IL-17A and IL-17F homo- and heterodimers. By contrast, IL-17F deficiency is partial, with mutant IL-17F-containing homo- and heterodimers displaying impaired, but not abolished, activity. These experiments of nature indicate that human IL-17A and IL-17F are essential for mucocutaneous immunity against C. albicans, but otherwise largely redundant.

Upregulation of IL17RB during natural allergen exposure in patients with seasonal allergic rhinitis

BACKGROUND

Seasonal allergic rhinitis (SAR) to Japanese cedar (Cryptomeria japonica; JC) is an IgE-mediated type I allergy affecting the nasal mucosa. However, the molecular mechanisms that underlie SAR are only partially understood. The aim of the study was to identify novel genes related to SAR during natural exposure to pollens, by using microarray analysis.

METHODS

Subjects were 32 SAR patients and 25 controls. Total RNA was extracted from CD4(+) T cells isolated from peripheral blood mononuclear cells and subjected to microarray analysis with Illumina Human Ref8 BeadChip arrays. The Mann-Whitney test was performed to identify genes whose expression was altered during allergen exposure. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed on samples collected from SAR patients and controls to verify the microarray results.

RESULTS

Microarray analysis showed that the expression of 3 genes was significantly altered during allergen exposure. Among these 3 genes, the expression of interleukin 17 receptor beta (IL17RB) was confirmed to be upregulated in SAR patients compared to that of the IL17RB gene in healthy, non-allergic controls. The average fold change of IL17RB expression in the real-time RT-PCR experiment was 3.9 (P = 0.003).

CONCLUSIONS

The present study identified upregulation of IL17RB during natural allergen exposure in patients with SAR, which may further elucidate the molecular mechanisms underlying SAR.

IL-22 defines a novel immune pathway of antifungal resistance

The role of IL-17 and Th17 cells in immunity vs. pathology associated with the human commensal Candida albicans remains controversial. Both positive and negative effects on immune resistance have been attributed to IL-17/Th17 in experimental candidiasis. In this study, we provide evidence that IL-22, which is also produced by Th17 cells, has a critical, first-line defense in candidiasis by controlling the growth of infecting yeasts as well as by contributing to the host's epithelial integrity in the absence of acquired Th1-type immunity. The two pathways are reciprocally regulated, and IL-22 is upregulated under Th1 deficiency conditions and vice versa. Whereas both IL-17A and F are dispensable for antifungal resistance, IL-22 mediates protection in IL-17RA-deficient mice, in which IL-17A contributes to disease susceptibility. Thus, our findings suggest that protective immunity to candidiasis is made up of a staged response involving an early, IL-22-dominated response followed by Th1/Treg reactivity that will prevent fungal dissemination and supply memory.

Critical role of Th17 responses in a murine model of Neisseria gonorrhoeae genital infection

Host immune responses, including the characteristic influx of neutrophils, against Neisseria gonorrhoeae are poorly understood; adaptive immunity is minimal and non-protective. We hypothesize that N. gonorrhoeae selectively elicits Th17-dependent responses, which trigger innate defense mechanisms, including neutrophils and antimicrobial proteins, that it can resist. We found that N. gonorrhoeae induced the production of interleukin-17 (IL-17) in mouse T-cells and Th17-inducing cytokines in mouse and human APCs in vitro. IL-17 was induced in the iliac lymph nodes in vivo in a female mouse model of genital tract gonococcal infection. Antibody blockade of IL-17 or deletion of the major IL-17 receptor (IL-17R) in IL-17RA(KO) mice led to prolonged infection and diminished neutrophil influx. Genital tract tissue from IL-17RA(KO) mice showed reduced production of neutrophil-attractant chemokines in response to culture with N. gonorrhoeae. These results imply a crucial role for IL-17 and Th17 cells in the immune response to N. gonorrhoeae.

IL-17 promotes tumor development through the induction of tumor promoting microenvironments at tumor sites and myeloid-derived suppressor cells

The role of immune responses in tumor development is a central issue for tumor biology and immunology. IL-17 is an important cytokine for inflammatory and autoimmune diseases. Although IL-17-producing cells are detected in cancer patients and tumor-bearing mice, the role of IL-17 in tumor development is controversial, and mechanisms remain to be fully elucidated. In the current study, we found that the development of tumors was inhibited in IL-17R-deficient mice. A defect in IFN-gammaR increased tumor growth, whereas tumor growth was inhibited in mice that were deficient in both IL-17R and IFN-gammaR compared with wild-type animals. Further experiments showed that neutralization of IL-17 by Abs inhibited tumor growth in wild-type mice, whereas systemic administration of IL-17 promoted tumor growth. The IL-17R deficiency increased CD8 T cell infiltration, whereas it reduced the infiltration of myeloid-derived suppressor cells (MDSCs) in tumors. In contrast, administration of IL-17 inhibited CD8 T cell infiltration and increased MDSCs in tumors. Further analysis indicated that IL-17 was required for the development and tumor-promoting activity of MDSCs in tumor-bearing mice. These data demonstrate that IL-17-mediated responses promote tumor development through the induction of tumor-promoting microenvironments at tumor sites. IL-17-mediated regulation of MDSCs is a primary mechanism for its tumor-promoting effects. The study provides novel insights into the role of IL-17 in tumor development and has major implications for targeting IL-17 in treatment of tumors.