Th17 Cell Effector Function Research Articles

CRACR2A-Mediated TCR Signaling Promotes Local Effector Th1 and Th17 Responses

Ca2+ release-activated Ca2+ channel regulator 2A (CRACR2A) is expressed abundantly in T cells and acts as a signal transmitter between TCR stimulation and activation of the Ca2+/NFAT and JNK/AP1 pathways. CRACR2A has been linked to human diseases in numerous genome-wide association studies and was shown to be one of the most sensitive targets of the widely used statin drugs. However, the physiological role of CRACR2A in T cell functions remains unknown. In this study, using transgenic mice for tissue-specific deletion, we show that CRACR2A promotes Th1 responses and effector function of Th17 cells. CRACR2A was abundantly expressed in Th1 and Th17 cells. In vitro, deficiency of CRACR2A decreased Th1 differentiation under nonpolarizing conditions, whereas the presence of polarizing cytokines compensated this defect. Transcript analysis showed that weakened TCR signaling by deficiency of CRACR2A failed to promote Th1 transcriptional program. In vivo, conditional deletion of CRACR2A in T cells alleviated Th1 responses to acute lymphocytic choriomeningitis virus infection and imparted resistance to experimental autoimmune encephalomyelitis. Analysis of CNS from experimental autoimmune encephalomyelitis-induced mice showed impaired effector functions of both Th1 and Th17 cell types, which correlated with decreased pathogenicity. Collectively, our findings demonstrate the requirement of CRACR2A-mediated TCR signaling in Th1 responses as well as pathogenic conversion of Th17 cells, which occurs at the site of inflammation.

Retraction Note: DDX5 and its associated lncRNA Rmrp modulate TH17 cell effector functions.

Change History: This Article has been retracted; see accompanying Retraction. Corrected online 20 January: In this Article, author Frank Rigo was incorrectly listed with a middle initial; this has been corrected in the online versions of the paper.

Egr2 is required for the activation of the TH17 pathogenetic program

Abstract CD4+ TH17 lineage are a heterogenous population of CD4+ effector cells; some of which have been guardians of tissue homeostasis while others have been linked to tissue inflammation and autoimmunity. TH17 cells can alter their differentiation program ultimately giving rise to either protective non-pathogenic or pro-inflammatory pathogenic cells. Molecular switches that control the development of “pathogenic” versus “non-pathogenic” TH17 cells remain largely unknown. In this study, we identified the transcription factor Egr2 as a critical regulator of the TH17 pathogenic program. We found Egr2 was transiently expressed in the early-intermediate stage (24–48 hours) of TH17 differentiation. When ectopically expressed under TH17-polarizing conditions, Egr2 significantly enhanced the expression of TH17 signature genes in a RORγt-dependent manner. Although Egr2 was dispensable for TH17 lineage commitment, its expression was required for the generation of pathogenetic TH17 cells. Mice with T cell-specific deletion of Egr2 were less susceptible to experimental autoimmune encephalomyelitis (EAE) than WT mice. Myelin-specific Egr2-deficeint TH17 cells failed to induce a chronic inflammatory response in the CNS. Transcriptional analysis revealed that Egr2 promoted the pathogenicity of TH17 cells by regulating the expression of pathogenicity-associated genes. Interestingly, Egr2 was not required for the effector function of protective gut-resident TH17 cells in response to Citrobacter rodentium challenge. These findings indicate that Egr2 represents an attractive candidate for the therapeutic targeting of pathogenic TH17 cells while preserving tissue-protective functions of TH17 cells at barrier sites.

S-nitrosoglutathione reductase (GSNOR) inhibitor as an immune modulator in experimental autoimmune encephalomyelitis.

We previously reported that S-nitrosoglutathione (GSNO), an endogenous nitric oxide carrier, attenuated TH17-mediated immune responses in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Cellular GSNO homeostasis is regulated via its synthesis by reaction between nitric oxide and glutathione and its enzymatic catabolism by GSNO reductase (GSNOR). In this study, we evaluated potential of reversible inhibitor of GSNOR (N6022) in comparison with exogenous GSNO in immunopathogenesis of EAE. Daily treatment of EAE mice with N6022 or exogenous GSNO significantly attenuated the clinical disease of EAE, but N6022 treatment showed greater efficacy than GSNO. Both N6022 and exogenous GSNO treatments increased the spleen levels of GSNO, as documented by increased protein-associated S-nitrosothiols, and inhibited polarization and CNS effector function of proinflammatory TH17 cells while inducing the polarization and CNS effector function of anti-inflammatory CD4+ CD25+ FOXP3- regulatory T (Treg) cells. Moreover, N6022 further attenuated TH1 while inducing TH2 and CD4+ CD25+ FOXP3+ Treg in their polarization and CNS effector functions. Similar to GSNO, the N6022 treatment protected against the EAE disease induced demyelination. However, neither exogenous GSNO nor N6022 treatment did not cause significant systemic lymphopenic effect as compared to FTY720. Taken together, these data document that optimization of cellular GSNO homeostasis by GSNOR inhibitor (N6022) in NO metabolizing cells attenuates EAE disease via selective inhibition of pro-inflammatory subsets of CD4+ cells (TH1/TH17) while upregulating anti-inflammatory subsets of CD4+ cells (TH2/Treg) without causing lymphopenic effects and thus offers a potential treatment option for MS/EAE.

Update on regulation and effector functions of Th17 cells.

T-helper cells that produce IL-17 are recognized as a significant subset within cell-mediated adaptive immunity. These cells are implicated in both the pathology of inflammatory disorders as well as the clearance of extracellular infections and the maintenance of the microbiota. However, the dynamic nature of this cell type has created controversy in understanding Th17 induction as well as Th17 phenotyping, since these cells may switch from Th17 to Treg or Th17 to Th1 cytokine profiles under certain conditions. This review highlights recent advances in Th17 cells in understanding their role in commensal regulation, sex difference in immune outcomes and the immunology of pregnancy, as well as inventive experimental models that have allowed for an increased understanding of Th17 regulation and induction.

Notch regulates Th17 differentiation and controls trafficking of IL-17 and metabolic regulators within Th17 cells in a context-dependent manner.

Th17 cells play critical roles in host defense and autoimmunity. Emerging data support a role for Notch signaling in Th17 cell differentiation but whether it is a positive or negative regulator remains unclear. We report here that T cell-specific deletion of Notch receptors enhances Th17 cell differentiation in the gut, with a corresponding increase in IL-17 secretion. An increase in Th17 cell frequency was similarly observed following immunization of T cell specific Notch mutant mice with OVA/CFA. However, in this setting, Th17 cytokine secretion was impaired, and increased intracellular retention of IL-17 was observed. Intracellular IL-17 co-localized with the CD71 iron transporter in the draining lymph node of both control and Notch-deficient Th17 cells. Immunization induced CD71 surface expression in control, but not in Notch-deficient Th17 cells, revealing defective CD71 intracellular transport in absence of Notch signaling. Moreover, Notch receptor deficient Th17 cells had impaired mTORC2 activity. These data reveal a context-dependent impact of Notch on vesicular transport during high metabolic demand suggesting a role for Notch signaling in the bridging of T cell metabolic demands and effector functions. Collectively, our findings indicate a prominent regulatory role for Notch signaling in the fine-tuning of Th17 cell differentiation and effector function.

CD39 mediated regulation of Th17-cell effector function is impaired in juvenile autoimmune liver disease

Background & aimsT-helper-type 17 (Th17) cells are involved in autoimmune tissue damage. CD39 is an ectonucleotidase that catalyzes extracellular ATP/ADP hydrolysis, culminating in the generation of immunosuppressive adenosine. Functional CD39 expression confers immunosuppressive properties upon immune cells. As the proportion of CD39 lymphocytes is decreased in juvenile autoimmune liver disease (AILD), we have explored whether decreased CD39 expression is present on Th17 cells and whether this phenomenon is associated with heightened effector function and inflammation. MethodsThirty-eight patients with juvenile AILD (22 autoimmune hepatitis and 16 autoimmune sclerosing cholangitis), 8 disease controls (DC) and 16 healthy subjects (HS) were studied. Peripheral blood cell phenotype was determined by flow cytometry; ability to suppress by inhibition of cell proliferation/effector cytokine production; ectoenzymatic activity by thin layer chromatography; expression of adenosine receptor, adenosine deaminase (ADA) and phosphodiesterases (PDE) by quantitative real-time PCR or by Western Blot. ResultsCD39+ Th17 (Th17CD39+) cells from HS appear activated and contain high frequencies of lymphocytes producing regulatory cytokines. In AILD, however, Th17CD39+ cells are markedly diminished and fail to generate AMP/adenosine, thereby limiting control of both target cell proliferation and IL-17 production. When compared to HS, Th17 cells from AILD patients also show lower A2A adenosine receptor expression while displaying similar levels of PDE4A, PDE4B and ADA. Only rare Th17CD39+ cells are observed by liver immunohistochemistry. ConclusionsTh17CD39+ cells in juvenile AILD are both quantitatively decreased and qualitatively deficient. Low levels CD39 and A2A expression may contribute to the perpetuation of Th17 cell effector properties and unfettered inflammation in this disease.

BACE1: a novel player in the pathogenesis of Th17 cells in EAE

Abstract Th17 cells are implicated in autoimmune disease, including attack of the central nervous system (CNS) in multiple sclerosis. β-site APP-cleaving enzyme 1 (BACE1) is a membrane protease expressed in neurons and astrocytes. BACE1 is most well known for its role in promoting neurodegeneration in Alzheimer’s disease by cleaving amyloid precursor protein, although it also plays a role in central nervous system myelination. BACE1 has also been reported to contribute to lesion severity following brain injury, as has IL-17, although these two molecules have not previously been linked. We observed that BACE1 is upregulated in experimental autoimmune encephalomyelitis (EAE) lesions, a mouse model of multiple sclerosis, suggesting a role in autoimmune CNS damage. Surprisingly, we discovered that Bace1-deficient MOG-reactive T cells were defective in IL-17A production. In vitro differentiated Th17 cells were similarly defective in IL-17A. Conversely, overexpression of Bace1 increased IL-17A production. Transfer experiments demonstrated that BACE1 deficiency in T cells impairs their pathogenic function and confers resistance in EAE. Although the impact on IL-17A production was dramatic, there was only a mild defect in expression of RORγt, IL-23R and other prototypic Th17-associated molecules such as IL-17F. This was confirmed by RNA-Seq, which revealed other potential Bace1 targets outside the classic Th17 armory. Therefore, we propose that Bace1 is a novel modulator of the effector function of Th17 cells, particularly IL-17A production.

DDX5 and its associated lncRNA Rmrp modulate TH17 cell effector functions.

Th17 lymphocytes protect mucosal barriers from infections, but also contribute to multiple chronic inflammatory diseases. Their differentiation is controlled by RORγt, a ligand-regulated nuclear receptor. We identified the DEAD-box RNA helicase DDX5 as a RORγt partner that coordinates transcription of selective Th17 genes and is required for Th17-mediated inflammatory pathologies. Surprisingly, the ability of DDX5 to interact with RORγt and co-activate its targets depends on its intrinsic RNA helicase activity and binding of a conserved nuclear long noncoding RNA (lncRNA), Rmrp, which is mutated in Cartilage-Hair Hypoplasia (CHH) patients. A targeted Rmrp mutation in mice, corresponding to one in CHH patients, abrogated the lncRNA’s chromatin recruitment, ability to potentiate DDX5-RORγt interaction and RORγt target gene transcription. Elucidation of the link between Rmrp and the DDX5-RORγt complex reveals a role for RNA helicases and lncRNAs in tissue-specific transcriptional regulation and promises new opportunities for therapeutic intervention in Th17-dependent diseases.

Ibrutinib Can Modulate the T Cell Response in Chronic Lymphocytic Leukemia By Reducing PD1/PDL1 Interactions

INTRODUCTION: The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib is a covalent inhibitor of BTK, a member of the B-cell receptor (BCR) signaling pathway and induces objective clinical responses in the majority of CLL patients (Byrd et al., NEJM 2013). Interestingly this drug also inhibits L2-inducible T cell kinase (ITK), an essential enzyme for the development and effector function of Th2 and Th17 cells, and has been shown to shift the balance towards a Th1 response. The purpose of the study was to determine how ibrutinib influences the Th1/Th17/T regulatory cell response, expression of immune checkpoint blockade molecules on T cells and the functional pathogen-specific T cell recovery.METHODS: Here we present data from a clinical trial of ibrutinib versus ibrutinib + rituximab in previously treated patients (NCT02007044). Peripheral blood and serum were collected at baseline, 3 months and 6 months during therapy. Multicolor flow cytometry was used to characterize B cell subsets, T-cell subsets, expression of PD-1, PD-L1 and CTLA-4 and T-cell effector function. For statistical analysis of pre-treatment to on-treatment measurements the paired Student t-test was used.RESULTS: Here we report on the phenotypic and functional recovery of immune subsets in 41 CLL patients treated with ibrutinib (n=17) or ibrutinib + rituximab (n=25). Both PD-1 and PD-L1 were expressed at high levels on CLL cells. Interestingly, by 3 and 6 months, there was a significant decrease in PD-1 expression from a pre-treatment median of 15% to 4% (at 3 months) and 3% (at 6 months; P<0.0001). Similarly, PD-L1 levels decreased from 5% to 3% and 2% respectively (P=0.004) (Fig. 1). We next sought to determine the functional impact of ibrutinib therapy on T cell subsets and function. After an initial reduction from a pretreatment level of4800/µL to 3000/µL at 3 months (P=0.003), CD3+ T cells increased to 4000 (µL) by 6 months; P=0.03. This was associated with a significant down-regulation of PD-1 expression on T cells from 28% pre-treatment to 24% and 21% at 3 and 6 months respectively (Fig.2 ) (P<0.0001). A significant reduction in the frequencies of regulatory T cells (Teg) (8% vs. 7% vs 6% respectively; P=0.004) was also documented. Ibrutinib has been reported to skew the T cell response toward a Th1 profile. We stimulated PBMC with PMA/Inomycin and performed intracellular staining for IFN-γ, IL-2, TNF-α and IL-17. Following ibrutinib therapy, there was a significant improvement in the CD8+ IFN-γ (P=0.04) and TNF-α response (P=0.01), and a reduction in the CD4+IL-17 response. To understand the functional relevance of these results, we are currently analyzing the CD8+ T cell response to stimulation with CEF (epitopes derived from CMV, EBV and Influenza) as a surrogate for pathogen-specific T cell recovery.CONCLUSION:Based on these data we propose that ibrutinib therapy can modulate the T cell response through multiple mechanisms which include (i) direct inhibition of ITK and skewing of the T cell response toward a Th1 profile; (ii) reduction in PD1/PDL1 expression on B and T cells and (iii). suppression of Tregs. It is unclear how ibrutinib influences the PD1/PDL1 interaction and whether this is a direct effect of the drug on essential components of B and T cell-receptor signaling or whether it is an indirect effect related to a reduction in the leukemia burden. Mechanistic studies to understand how ibrutinib modulates the PD1/PL1 axis are currently underway. [Display omitted] [Display omitted] DisclosuresBurger:Pharmacyclics LLC, an AbbVie Company: Research Funding. Wierda:Glaxo-Smith-Kline Inc.: Research Funding; Celgene Corp.: Consultancy. Rezvani:Pharmacyclics: Research Funding.

Immunology: A bacterial nudge to T-cell function.

The epithelial cells that line the intestine have been found to sense tight attachment of bacteria, and to respond by producing proteins that shape the effector functions of the immune system's TH17 cells.

Disparate Effects of Mesenchymal Stem Cells in Experimental Autoimmune Encephalomyelitis and Cuprizone-Induced Demyelination.

Mesenchymal stem cells (MSCs) are pleiotropic cells with potential therapeutic benefits for a wide range of diseases. Because of their immunomodulatory properties they have been utilized to treat autoimmune diseases such as multiple sclerosis (MS), which is characterized by demyelination. The microenvironment surrounding MSCs is thought to affect their differentiation and phenotype, which could in turn affect the efficacy. We thus sought to dissect the potential for differential impact of MSCs on central nervous system (CNS) disease in T cell mediated and non-T cell mediated settings using the MOG35–55 experimental autoimmune encephalomyelitis (EAE) and cuprizone-mediated demyelination models, respectively. As the pathogeneses of MS and EAE are thought to be mediated by IFNγ-producing (TH1) and IL-17A-producing (TH17) effector CD4+ T cells, we investigated the effect of MSCs on the development of these two key pathogenic cell groups. Although MSCs suppressed the activation and effector function of TH17 cells, they did not affect TH1 activation, but enhanced TH1 effector function and ultimately produced no effect on EAE. In the non- T cell mediated cuprizone model of demyelination, MSC administration had a positive effect, with an overall increase in myelin abundance in the brain of MSC-treated mice compared to controls. These results highlight the potential variability of MSCs as a biologic therapeutic tool in the treatment of autoimmune disease and the need for further investigation into the multifaceted functions of MSCs in diverse microenvironments and the mechanisms behind the diversity.

IL-7/IL-7 Receptor Signaling Differentially Affects Effector CD4+ T Cell Subsets Involved in Experimental Autoimmune Encephalomyelitis.

IL-17-producing CD4(+) T (Th17) cells, along with IFN-γ-expressing Th1 cells, represent two major pathogenic T cell subsets in experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). The cytokines and transcription factors involved in the development and effector functions of Th1 and Th17 cells have been largely characterized. Among them, IL-23 is essential for the generation of stable and encephalitogenic Th17 cells and for the development of EAE. The IL-7/IL-7R signaling axis participates in cell survival, and perturbation of this pathway has been associated with enhanced susceptibility to MS. A link between IL-23-driven pathogenic T cells and IL-7/IL-7R signaling has previously been proposed, but has not been formally addressed. In the current study, we showed that Th17 cells from mice with EAE express high levels of IL-7Rα compared with Th1 cells. Using mice that constitutively express IL-7Rα on T cells, we determined that sustained IL-7R expression in IL-23R-deficient mice could not drive pathogenic T cells and the development of EAE. IL-7 inhibited the differentiation of Th17 cells, but promoted IFN-γ and GM-CSF secretion in vitro. In vivo IL-7/anti-IL-7 mAb complexes selectively expanded and enhanced the proliferation of CXCR3-expressing Th1 cells, but did not impact Th17 cells and EAE development in wild-type and IL-23R-deficient mice. Importantly, high IL-7 expression was detected in the CNS during EAE and could drive the plasticity of Th17 cells to IFN-γ-producing T cells. Together, these data address the contribution of IL-23/IL-23R and IL-7/IL-7R signaling in Th17 and Th1 cell dynamics during CNS autoimmunity.

RORgT modulates key features in adult thymopoiesis (HEM2P.235)

Abstract Recent studies have elucidated the molecular mechanism of RORgT transcriptional network controlling Th17 cell lineage fate and effector function. RORgT was initially identified as a transcription factor required for thymopoiesis by maintaining survival of CD4+CD8+ (DP) thymocytes. There are increasing efforts to target RORgT for the treatment of autoimmune disorders, but it remains unclear how inhibition of RORgT in adult animals may impact thymic T cell development. Here, we show that RORgT is required to maintain adult thymopoiesis using both ERT2-CRE-mediated conditional genetic ablation and pharmacological inhibition with a selective small-molecule antagonist. RNA-SEQ analysis demonstrated that RORgT regulates thymocyte migration, positive selection, proliferation, inflammation and DNA synthesis involved in thymopoiesis beyond DP cell survival. RORgT also directly engages multiple target DNA in close proximity to key transcription factors such as T cell factor-1, Ikaros family zink finger protein 1 and others required for thymocyte development. Our work illustrates a new perspective in thymic development by showing that RORgT modulates adult thymopoiesis via cooperation with other major transcription factors.

CD4 signaling and Pneumocystis clearance: a critical role of IL-21R and STAT3 for effector function (MPF2P.745)

Abstract Pneumocystis jirovecii is an opportunist infection that is a significant cause of disease in immunocompromised patients. Patients whose blood CD4 counts drop below 200 cell/μl due to HIV infection or immunosuppressive therapies are at high risk of developing Pneumocystis jirovecii pneumonia (PJP). However, the exact role of CD4 cells and the specific effector subtype that is required for clearance has yet to be determined. We investigated this question with several cytokine and STAT knock out mice using both in vivo infection as well as the assessment of effector CD4+ T-cell function by adoptive transfer into Pneumocystis infected Rag1-/- mice. We observe that classical Th1, Th2, Th17, and Tfh cell effector functions are dispensable for organism clearance. However we found an essential role for both IL21 receptor signaling on CD4 cells as well as CD4+ T-cell intrinsic STAT3 activation are required for clearance. These data are consistent with the recent identification of human IL21R deficiency and susceptibility to PJP. We are currently examining potential novel downstream mechanisms that may mediate immunity against Pneumocystis pneumonia in this context.

Halofuginone-Induced Amino Acid Starvation Regulates Stat3-Dependent Th17 Effector Function and Reduces Established Autoimmune Inflammation

The IL-23 pathway is genetically linked to autoimmune disease in humans and is required for pathogenic Th17 cell function in mice. However, because IL-23R-expressing mature Th17 cells are rare and poorly defined in mice at steady-state, little is known about IL-23 signaling. In this study, we show that the endogenous CCR6(+) memory T cell compartment present in peripheral lymphoid organs of unmanipulated mice expresses Il23r ex vivo, displays marked proinflammatory responses to IL-23 stimulation in vitro, and is capable of transferring experimental autoimmune encephalomyelitis. The prolyl-tRNA synthetase inhibitor halofuginone blocks IL-23-induced Stat3 phosphorylation and IL-23-dependent proinflammatory cytokine expression in endogenous CCR6(+) Th17 cells via activation of the amino acid starvation response (AAR) pathway. In vivo, halofuginone shows therapeutic efficacy in experimental autoimmune encephalomyelitis, reducing both established disease progression and local Th17 cell effector function within the CNS. Mechanistically, AAR activation impairs Stat3 responses downstream of multiple cytokine receptors via selective, posttranscriptional suppression of Stat3 protein levels. Thus, our study reveals latent pathogenic functions of endogenous Th17 cells that are regulated by both IL-23 and AAR pathways and identifies a novel regulatory pathway targeting Stat3 that may underlie selective immune regulation by the AAR.

T cell-specific BLIMP-1 deficiency exacerbates experimental autoimmune encephalomyelitis in nonobese diabetic mice by increasing Th1 and Th17 cells

Recently, we demonstrated that B lymphocyte-induced maturation protein 1 (BLIMP-1) has a role in regulating the differentiation and effector function of Th1 and Th17 cells. As these cells play critical roles in the induction and pathogenesis of experimental autoimmune encephalomyelitis (EAE), we investigated the potential role of T cell BLIMP-1 in modulating MOG35-55-induced EAE. We established T cell-specific BLIMP-1 conditional knockout (CKO) NOD mice to dissect the role of BLIMP-1 in EAE using loss-of-function model. Our results indicate that EAE severity is dramatically exacerbated in CKO mice. The numbers of CNS-infiltrating Th1, Th17, IFN-γ(+)IL-17A(+), and IL-21(+)IL-17A(+) CD4(+) T cells are remarkably increased in brain and spinal cord of CKO mice. Moreover, the ratio of Tregs/effectors and IL-10 production of Tregs are significantly downregulated in CNS of CKO mice. We conclude that BLIMP-1 suppresses autoimmune encephalomyelitis via downregulating Th1 and Th17 cells and impairing Treg cells.

The Metalloprotease ADAM12 Regulates the Effector Function of Human Th17 Cells

A key modulator of immune homeostasis, TGFβ has an important role in the differentiation of regulatory T cells (Tregs) and IL-17-secreting T cells (Th17). How TGFβ regulates these functionally opposing T cell subsets is not well understood. We determined that an ADAM family metalloprotease called ADAM12 is specifically and highly expressed in both Tregs and CCR6+ Th17 cells. ADAM12 is induced in vitro upon differentiation of naïve T cells to Th17 cells or IL-17-secreting Tregs. Remarkably, silencing ADAM12 expression in CCR6+ memory T cells enhances the production of Th17 cytokines, similar to suppressing TGFβ signaling. Further, ADAM12 knockdown in naïve human T cells polarized towards Th17/Treg cells, or ectopically expressing RORC, greatly enhances IL-17-secreting cell differentiation, more potently then inhibiting TGFβ signals. Together, our findings reveal a novel regulatory role for ADAM12 in Th17 cell differentiation or function and may have implications in regulating their aberrant responses during immune pathologies.

MicroRNA-155 Confers Encephalogenic Potential to Th17 Cells by Promoting Effector Gene Expression

Th17 cells are central to the pathogenesis of autoimmune disease, and recently specific noncoding microRNAs have been shown to regulate their development. However, it remains unclear whether microRNAs are also involved in modulating Th17 cell effector functions. Consequently, we examined the role of miR-155 in differentiated Th17 cells during their induction of experimental autoimmune encephalomyelitis. Using adoptive transfer experiments, we found that highly purified, myelin oligodendrocyte glycoprotein Ag-specific Th17 cells lacking miR-155 were defective in their capacity to cause experimental autoimmune encephalomyelitis. Gene expression profiling of purified miR-155(-/-)IL-17F(+) Th17 cells identified a subset of effector genes that are dependent on miR-155 for their proper expression through a mechanism involving repression of the transcription factor Ets1. Among the genes reduced in the absence of miR-155 was IL-23R, resulting in miR-155(-/-) Th17 cells being hyporesponsive to IL-23. Taken together, our study demonstrates a critical role for miR-155 in Th17 cells as they unleash autoimmune inflammation and finds that this occurs through a signaling network involving miR-155, Ets1, and the clinically relevant IL-23-IL-23R pathway.

Combinatorial Control of Th17 and Th1 Cell Functions by Genetic Variations in Genes Associated With the Interleukin‐23 Signaling Pathway in Spondyloarthritis

Recent genome-wide association studies have revealed numerous genetic associations between specific single-nucleotide polymorphisms (SNPs) and immune-mediated inflammatory diseases. The current challenge is to identify associations of the genetic variants with effector mechanisms implicated in pathogenesis. This study was undertaken to investigate the link between genetic variation at loci associated with spondyloarthritis (SpA) and the effector function of CD4+ T lymphocyte subsets involved in chronic inflammatory disease. Expression of Th17 and Th1 cytokines and transcription factors was measured in CD4+ T cells isolated from patients with SpA. Correlation analyses were performed to assess potential associations of these expression levels with the patient's genotype at loci genetically linked to SpA. The effector functions of Th17 and Th1 cells in patients with SpA were found to be under combinatorial control by multiple SNPs at genes associated with the interleukin-23 (IL-23)/Th17 pathway. Patients with SpA carrying risk-associated alleles of genes in the IL-23/Th17 pathway expressed the highest levels of genes involved in the differentiation and function of Th17 and Th1 cells, whereas the presence of protective alleles was associated with low-level expression of these genes. In contrast, variation at loci that were genetically linked to SpA, but not associated with the IL-23 pathway, did not affect the expression of Th17- and Th1-specific genes, suggesting that these SNPs may contribute to the pathogenesis of SpA through distinct cellular mechanisms. These results show that genetic variations at genes associated with the IL-23 signaling pathway may influence the effector functions of Th17 and Th1 cells in patients with SpA. These findings provide a framework to delineate the mechanisms by which genetic variants contribute to pathology.