Mature Th17 Cells Research Articles

Pro- or anti-inflammatory properties of cytokines in COVID-19: which offer better protection against disease?

Pro- or anti-inflammatory properties of cytokines in COVID-19: which offer better protection against disease I read the article by Al-Mquter et al. that compared circulating levels of 3 cytokines(IL-6, IL-25 and IL-35) amongst healthy controls(HC) and patients with COVID-19. They reported a significant increase in the serum concentration of these cytokines in patients versus HC(1). Their results confirmed again that assessment of cytokine profiles could be used as COVID-19 markers and may also provide practical implications for disease treatment. Nonetheless, understanding the role of cytokines in COVID-19 is complicated because of the complex nature of cytokine networks and the pathogenesis of COVID-19(2). IL-6 is one of the first cytokines produced during COVID-19 and increasing evidence suggests that its alteration may be associated with disease outcome. IL-6 is a pleotropic cytokine and has both pro- and anti- inflammatory effects. Therefore, it appears to operate in protective or pathological immunity to COVID-19. IL-6 can promote immune processes associated with resistance to different pathogens including COVID-19. It contributes to host defense via different pathways, including the stimulation of acute phase responses and hematopoiesis. Nonetheless, dysregulated and persistent synthesis of IL-6 can be resulted to the onset and development of pathological conditions. These different effector functions may be associated with different concentration of IL-6 that may result from different signaling pathwaysIL-6 signaling includes at least three distinct pathways: cis-signalling; trans-signalling and trans-presentation. It seems that IL-6 trans-signalling and trans-presentation are probably responsible for severe progressive COVID-19. These signaling pathways can trigger diffuse inflammation at various levels. Conversely, IL-6 cis-signalling mediates negative feedback mechanisms on proinflammatory cytokines, including suppression of their production, stimulation of their decoy receptors, and inhibition the maturation of Th17 cells. Circulatory IL-6 in COVID-19 patients reaches the peak level at advanced stages around two weeks of disease. Elevated IL-6 (e.g., > 100-120 pg/mL) levels in critical COVID-19 may reflect augmented IL-6 cis-signalling in an attempt to exert homeostatic functions, although there is no general consensus on this issue(3).

Expressed Sequence Tags-1-Targeted MiRNA-326 in Gastric Cancer Induces Local Immune Inflammatory Microenvironment by Inducing T Helper Cell 17 Cell Differentiation

This study intends to assess miRNA-326’s effect on the immune-inflammatory microenvironment and its mechanism in gastric cancer (GC). GC adjacent tissues and tumor tissues were collected to analyze inflammatory factors by immunohistochemistry and ELISA, Est-1 and miRNA-326 level by Western blot or PCR, Th17 cells by flow cytometry. CD4+ T cells were transfected with Est-1 inhibitor, Est-1 mimics, or miR-326 mimics followed by measurement of Th17 differentiation-related genes via gene chips and inflammatory factor release. Inflammatory factors in serum of GC patients were significantly increased and miR-326 was upregulated with decreased Est-1 and unbalanced Th17/Treg cell ratio. miR-326 targeted Est-1 to inhibit its expression. After transfection with Est-1 inhibitor, Th17 differentiation-related genes were upregulated. After transfection with miR-326 mimics, Est-1 level was reduced and inflammation was enhanced with maturation of Th17 cells. In conclusion, miRNA-326 induces Th17 cell differentiation by targeting Est-1, thereby promoting the release of inflammatory factors and inducing immune inflammatory microenvironment.

Loss of miR-673-5p expression in the cornea promotes rat corneal allograft rejection by promoting Th17 cell differentiation mediated by JAK2/STAT3.

BackgroundCluster of differentiation 4 positive (CD4+) T cells play an important role in corneal graft rejection, especially the dynamic balance between regulatory T cells and helper T cells. This study aims to explore the upstream and downstream regulatory mechanisms of Th17 cell differentiation-mediated corneal allograft rejection.MethodsBy establishing rat corneal allograft transplantation model, transcriptome analysis was carried out to screen the differentially expressed genes related to T helper 17 (Th17) cell differentiation, and then cell experiments were used to verify the effect of miR-673-5p/Janus Kinase 2 (JAK2) signal on naïve CD4+ T cell differentiation and the proliferation, migration, and tube formation ability of human umbilical vein endothelial cells (HUVECs). Finally, the role of miR-673-5p/JAK2 signal in corneal allograft rejection was verified by animal model in vivo.ResultsThe results showed that JAK2/STAT3 signaling activation-mediated Th17 cell differentiation was significantly up-regulated during corneal allograft rejection, and miR-673-5p expression was down-regulated after corneal allograft rejection. Low expression of miR-673-5p promoted Th17 cell differentiation by up-regulating JAK2, and then promoted placental growth factor (PLGF)mediated corneal neovascularization (CNV).ConclusionsThe results of this study suggested that low expression of miR-673-5p is a promoter of corneal allograft rejection. Overexpression of miR-673-5p can improve the survival rate of corneal allografts by inhibiting the differentiation and maturation of Th17 cells mediated by JAK2/STAT3 signaling.

Preconceptional immunization with an allergen inhibits offspring thymic Th17 cells maturation without influence on Th1 and Th2 cells.

The mechanisms through which maternal immunization can modulate offspring thymic maturation of lymphocytes are not fully understood. Here, we aimed to evaluate whether maternal OVA-immunization can inhibit the maturation of Th17 cells on offspring thymus. C57BL/6 females were immunized with OVA in Alum or Alum alone and mated with normal WT males. Offspring thymus was evaluated at three or 20 days of age. The demonstration that maternal OVA-immunization can inhibit offspring allergy development validated our experimental protocol. First, we observed that maternal OVA-immunization can inhibit the expression of R or γT and IL-17 molecules on immature T cells (CD4+CD8+) and TCD4 cells (CD4+CD8-) without interference on TCD8 cells (CD4-CD8+) on three-day-old offspring. A very similar effect could be observed on 20-day-old offspring. Additionally, a Th2 skewed profile could be found on the spleen of immunized pups from OVA-immunized mothers, but no influence was detected on offspring thymic Th1/Th2 profiles. Together, these data demonstrate that maternal immunization with an allergen can modulate offspring thymic maturation of Th17 cells without influencing Th1/Th2 patterns.

Kunxian Capsule for Rheumatoid Arthritis: Inhibition of Inflammatory Network and Reducing Adverse Reactions Through Drug Matching.

Tripterygium wilfordii Hook.f and Tripterygium hypoglaucum (H.Lév.) Hutch is effective herbs to prevent aggravation of Rheumatoid arthritis (RA). However, both of them show severe side effects in the reproductive system and other systems. Kunxian Capsule (KX), a Traditional Chinese Medicine (TCM) patent prescription, comprised of 4 herbs, including H.Lév. Hutch, is reported to be an available prescription in treating RA with fewer side effects as compares to Tripterygium tablets. To reveal the pharmacological mechanism of KX in RA treatment and side effect alleviation, we collected related information of KX from open-access databases and performed various analyses. 1354 targets were identified in KX. These targets were enriched in the calcium signaling pathway, cAMP signaling pathway, cGMP-PKG signaling pathway and PI3K-AKT signaling pathway, forming biological functions, such as cofactor binding, coenzyme binding, etc. These pathways or functions mostly affect cell cycle, differentiation, and maturation of Th17 cells, macrophage, and synovial fibroblast. These targets also act on the IL-17 signaling pathway, Th17 cell differentiation signaling pathway and TNF signaling pathway, which is related to inflammation response inhibition. Next, a disease network was constructed, which indicated IMPDH2, MTHFD1 are the key genes answering for the side effects of H.Lév. Hutch. The side effect–related genes lead to the negative regulation of nucleic acid, which could be restored by the rest 3 herbs through some positive amino acid metabolism. In conclusion, KX is a relatively safe alternative approach in RA intervention.

Histone H3K27me3 demethylases regulate human Th17 cell development and effector functions by impacting on metabolism

T helper (Th) cells are CD4+ effector T cells that play a critical role in immunity by shaping the inflammatory cytokine environment in a variety of physiological and pathological situations. Using a combined chemico-genetic approach, we identify histone H3K27 demethylases KDM6A and KDM6B as central regulators of human Th subsets. The prototypic KDM6 inhibitor GSK-J4 increases genome-wide levels of the repressive H3K27me3 chromatin mark and leads to suppression of the key transcription factor RORγt during Th17 differentiation. In mature Th17 cells, GSK-J4 induces an altered transcriptional program with a profound metabolic reprogramming and concomitant suppression of IL-17 cytokine levels and reduced proliferation. Single-cell analysis reveals a specific shift from highly inflammatory cell subsets toward a resting state upon demethylase inhibition. The root cause of the observed antiinflammatory phenotype in stimulated Th17 cells is reduced expression of key metabolic transcription factors, such as PPRC1. Overall, this leads to reduced mitochondrial biogenesis, resulting in a metabolic switch with concomitant antiinflammatory effects. These data are consistent with an effect of GSK-J4 on Th17 T cell differentiation pathways directly related to proliferation and include regulation of effector cytokine profiles. This suggests that inhibiting KDM6 demethylases may be an effective, even in the short term, therapeutic target for autoimmune diseases, including ankylosing spondylitis.

Activated CLL B Cells Variably Modulate microRNA-155 Levels in Naïve CD4+ T Cells, and the Direction and Magnitude of microRNA-155 Change Correlates with Th17 Levels and Clinical Course

T-helper 17 (Th17) cells constitute a subset of T cells that characteristically secrete IL-17. In addition to their normal adaptive immune functions, Th17 cells also play roles in supporting dysfunctional immune responses found in autoimmunity and cancer. Several studies suggest that Th17 cells play a protective role in chronic lymphocytic leukemia (CLL). For example, CLL patients exhibit varied levels of circulating Th17 cells, and elevated levels positively correlate with better clinical outcome regardless of IGHV-mutation status. To understand this relationship and elucidate the cellular and molecular mechanisms of Th17 generation in CLL, in particular the role of microRNAs known to affect Th17 development, we investigated cross-talk between naïve CD4+ T cells and CLL B cells. Moreover, since intraclonal leukemic B-cell subpopulations differing in time since cell birth/division can exhibit different functional effects on antigen presentation, we explored the effect of B-cell activation on this T - leukemic B-cell dialogue and how it affects the generation of Th17 cells.To determine potential candidates differentially expressed in CLL, we conducted genome-wide single-cell expression analysis comparing fluorescence activated cell sorting (FACS)-purified mature Th17 cells (CD3+/CD4+/CD45+/CD161+/CCR6+/ CCR4+/CXCR3-) from CLL patients and healthy donors. Selected candidate genes met the criteria of >7-fold increase in expression in CLL, adjusted p-value <1.5 x 10-6, and link to lymphocyte biology. Among selected candidates, microRNA-155 (miR-155), a critical regulator of Th17 differentiation, was found. Follow-up real time, quantitative PCR (RT-qPCR) analyses indicated a significant increase (P < 0.01) in miR-155 expression in CLL Th17 cells as compared to Th17 cells from healthy controls. Since there was no difference in expression between naïve T cells (CD3+/CD4+/CD62L+/CD45RO-) cells, this suggested a CLL-unique mechanism of miR-155 modulation.To determine whether CLL cells directly influence miR-155 levels in naïve CD4+ T cells, co-culture experiments using autologous leukemic or healthy B cells were carried out. FACS-purified peripheral blood naïve CD4+ T cells and B cells from CLL patients and from age-matched healthy controls were co-cultured for 3 days, and expression of T-cell miR-155 was determined by RT-qPCR. In the presence of unstimulated CLL or healthy B cells, miR-155 expression in naïve T cells remained unchanged across all co-cultures. However, upon activation, healthy and leukemic B cells exerted differential effects on miR-155 expression in autologous naïve T cells. In the presence of autologous healthy B cells pre-activated with CpG-ODN2006 and IL-15, miR-155 expression in healthy naïve T cells was significantly increased (P = 0.0313) across all samples. Conversely, CLL naïve T cells co-cultured with autologous, pre-activated leukemic B cells showed heterogeneous modulation of miR-155. Of interest, the magnitude and direction of miR-155 changes in the autologous CLL co-cultures positively correlated not only with circulating Th17 levels (P = 0.019), as determined by flow cytometry, but also with patient time to first treatment (P = 0.0003). Moreover, when samples were divided into 2 groups based on an increase or decrease in miR-155 levels after exposure to activated compared to resting CLL B cells, a significant difference was seen with median survival of 237 months and 67 months, respectively (P = 0.005). Consistent with previous observations from our lab, this correlation was independent of various prognostic markers, including IGHV-mutation status.Our results suggest the existence of a miR-155 modulatory mechanism mediated by CLL B cells that differs based on leukemic B-cell activation state and the degree of change occurring when naïve T cells are exposed to resting vs. activated B cells. Moreover, this variable effect in CLL patients differs from that in normal individuals, and the effect influences number of Th17 cells and patient outcome. Studies are underway to determine the effects that leukemic B cells, unstimulated or CpG-ODN2006 + IL-15 stimulated, have on autologous naïve T-cell maturation into Th17 cells, and the extent that this process depends on the variable miR-155 modulatory capacity of leukemic B cells. DisclosuresChiorazzi:Janssen, Inc: Consultancy; AR Pharma: Equity Ownership.

Segmented Filamentous Bacteria - Metabolism Meets Immunity.

Segmented filamentous bacteria (SFB) are a group of host-adapted, commensal organisms that attach to the ileal epithelium of vertebrate and invertebrate hosts. A genetic relative of the genus Clostridium, these morphologically unique bacteria display a replication and differentiation lifecycle initiated by epithelial tissue binding and filamentation. SFB intimately bind to the surface of absorptive intestinal epithelium without inducing an inflammatory response. Rather, their presence impacts the generation of innate and differentiation of acquired immunity, which impact the clearance of extracellular bacterial or fungal pathogens in the gastrointestinal and respiratory tracts. SFB have recently garnered attention due to their role in promoting adaptive and innate immunity in mice and rats through the differentiation and maturation of Th17 cells in the intestinal tract and production of immunoglobulin A (IgA). SFB are the first commensal bacteria identified that impact the maturation and development of Th17 cells in mice. Recently, microbiome studies have revealed the presence of Candidatus Arthromitus (occasionally designated as Candidatus Savagella), a proposed candidate species of SFB, in higher proportions in higher-performing flocks as compared to matched lower-performing flocks, suggesting that SFB may serve to establish a healthy gut and protect commercial turkeys from pathogens resulting in morbidity and decreased performance. In this review we seek to describe the life cycle, host specificity, and genetic capabilities of SFB, such as bacterial metabolism, and how these factors influence the host immunity and microbiome. Although the role of SFB to induce antigen-specific Th17 cells in poultry is unknown, they may play an important role in modulating the immune response in the intestinal tract to promote resistance against some infectious diseases and promote food-safety. This review demonstrates the importance of studying and further characterizing commensal, host-specific bacteria in food-producing animals and their importance to animal health.

Protein Kinase CK2 Controls the Fate between Th17 Cell and Regulatory T Cell Differentiation.

CK2 is a highly conserved and pleiotropic serine/threonine kinase that promotes many prosurvival and proinflammatory signaling pathways, including PI3K/Akt/mTOR and JAK/STAT. These pathways are essential for CD4+ T cell activation and polarization, but little is known about how CK2 functions in T cells. In this article, we demonstrate that CK2 expression and kinase activity are induced upon CD4+ T cell activation. Targeting the catalytic activity of CK2 using the next-generation small molecule inhibitor CX-4945 in vitro significantly and specifically inhibited mouse and human Th17 cell differentiation while promoting the generation of Foxp3+ regulatory T cells (Tregs). These findings were associated with suppression of PI3K/Akt/mTOR activation and STAT3 phosphorylation upon CX-4945 treatment. Furthermore, we demonstrate that CX-4945 treatment inhibits the maturation of Th17 cells into inflammatory IFN-γ-coproducing effector cells. The Th17/Treg axis and maturation of Th17 cells are major contributing factors to the pathogenesis of many autoimmune disorders, including multiple sclerosis. Using a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis, we demonstrate that in vivo administration of CX-4945 targets Akt/mTOR signaling in CD4+ T cells and the Th17/Treg axis throughout disease. Importantly, CX-4945 treatment after disease initiation significantly reduced disease severity, which was associated with a significant decrease in the frequency of pathogenic IFN-γ+ and GM-CSF+ Th17 cells in the CNS. Our data implicate CK2 as a regulator of the Th17/Treg axis and Th17 cell maturation and suggest that CK2 could be targeted for the treatment of Th17 cell-driven autoimmune disorders.

Th17 inflammation in the lungs is sustained by multiple exposures to house dust and is dependent on TLR4 and conventional dendritic cells

Abstract Microbial products can prime antigen-specific T helper 17 cell responses to inhaled allergens. However, once established, it is unclear how pathogenic lung Th17 responses are sustained. To study this, we sensitized mice to inhaled ovalbumin (OVA)together with various environmental adjuvants, including house dust extract(HDE). Animals were then chronically challenged with OVA alone, or OVA plus the adjuvant previously used during sensitization. Challenge with OVA plus HDE elicited greater airway neutrophilia, lymphocytosis and IL-17A than did challenge with OVA alone. HDE exposure with OVA also promoted greater expansion of adoptively transferred, OVA-specific, IL-17A-fate mapping Th17 cells. These effects were independent of enzymatic activity in HDE, but required TLR4 in recipient mice. Analysis of Tlr4 bone marrow chimeric mice and conditional TLR4 knockout mice indicated that Th17 proliferation is sustained by HDE via TLR4 signaling predominantly in hematopoietic cells, including CD11c+ cells, rather than in airway epithelial cells. IL-23 contributes to the maintenance of these lung Th17 cells. Use of genetically modified mice lacking distinct lung myeloid cell subsets, and co-culture of various lung antigen-presenting cell types with mature Th17 cells, revealed that conventional dendritic cells (either CD103+ or CD11b+), rather than lung macrophages or B cells, support the revival of Th17 clonal expansion and activation. Thus, maintenance of Th17-dependent inflammation in the lung requires persistent innate immune responses, TLR4, and the presence of conventional dendritic cells.

Atopic diseases and inflammation of the brain in the pathogenesis of autism spectrum disorders.

Autism spectrum disorders (ASDs) affect as many as 1 in 45 children and are characterized by deficits in sociability and communication, as well as stereotypic movements. Many children also show severe anxiety. The lack of distinct pathogenesis and reliable biomarkers hampers the development of effective treatments. As a result, most children with ASD are prescribed psychopharmacologic agents that do not address the core symptoms of ASD. Autoantibodies against brain epitopes in mothers of children with ASD and many such children strongly correlate with allergic symptoms and indicate an aberrant immune response, as well as disruption of the blood–brain barrier (BBB). Recent epidemiological studies have shown a strong statistical correlation between risk for ASD and either maternal or infantile atopic diseases, such as asthma, eczema, food allergies and food intolerance, all of which involve activation of mast cells (MCs). These unique tissue immune cells are located perivascularly in all tissues, including the thalamus and hypothalamus, which regulate emotions. MC-derived inflammatory and vasoactive mediators increase BBB permeability. Expression of the inflammatory molecules interleukin (IL-1β), IL-6, 1 L-17 and tumor necrosis factor (TNF) is increased in the brain, cerebrospinal fluid and serum of some patients with ASD, while NF-kB is activated in brain samples and stimulated peripheral blood immune cells of other patients; however, these molecules are not specific. Instead the peptide neurotensin is uniquely elevated in the serum of children with ASD, as is corticotropin-releasing hormone, secreted from the hypothalamus under stress. Both peptides trigger MC to release IL-6 and TNF, which in turn, stimulate microglia proliferation and activation, leading to disruption of neuronal connectivity. MC-derived IL-6 and TGFβ induce maturation of Th17 cells and MCs also secrete IL-17, which is increased in ASD. Serum IL-6 and TNF may define an ASD subgroup that benefits most from treatment with the natural flavonoid luteolin. Atopic diseases may create a phenotype susceptible to ASD and formulations targeting focal inflammation of the brain could have great promise in the treatment of ASD.

SP0054 The Many Faces of Mesenchymal Stem Cell Immunomodulation

Mesenchymal stem cells (MSC) initially isolated in bone marrow have been since identified in other tissues including adipose, synovium, periosteum, perichondrium, dental pulp and tonsil. These cells are characterized by...

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.

Main features of human T helper 17 cells

In addition to T helper type 1 (Th1) and Th2 cells, Th17 cells are a third arm of effector CD4(+) T cells. Human Th17 cells express RORC and CD161 and originate from RORC-expressing CD161(+) precursors, which migrate to lymphoid tissue and differentiate into mature Th17 cells in response to interleukin (IL)-1β and IL-23. Human Th17 cells are rare in inflammed tissues for two reasons: (1) Th17 cells do not produce IL-2 and, therefore, do not proliferate in response to TCR signaling, mainly because of RORC-dependent IL-4I1-mediated mechanisms that interfere with IL-2 gene activation; and (2) Th17 cell shift to a Th1 phenotype in the presence of IL-12; such Th17-derived Th1 cells are considered to be nonclassical Th1 cells and can be distinguished from classical Th1 cells. The possible role of Th17 cells in human tumors is still unclear and even controversial.

Nuclear Receptor NR4A2 Orchestrates Th17 Cell-Mediated Autoimmune Inflammation via IL-21 Signalling

IL-17-producing CD4+ T helper 17 (Th17) cells are pathogenic in a range of human autoimmune diseases and corresponding animal models. We now demonstrate that such T cells infiltrating the target organ during the induction of experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune uveoretinitis (EAU) specifically express NR4A2. Further, we reveal a critical involvement of NR4A2 in Th17 cell functions and Th17 cell-driven autoimmune diseases. When NR4A2 expression was blocked with siRNA, full Th17 differentiation was prevented in vitro: although cells expressed the master Th17 regulator, RORγt, they expressed reduced levels of IL-23R and were unable to produce IL-17 and IL-21. Notably, Th17 differentiation in the absence of NR4A2 was restored by exogenous IL-21, indicating that NR4A2 controls full maturation of Th17 cells via autocrine IL-21 signalling. Preventing NR4A2 expression in vivo by systemic treatment with NR4A2-specific siRNA also reduced Th17 effector responses and furthermore protected mice from EAE induction. In addition, the lack of disease was associated with a reduction in autocrine IL-21 production and IL-23R expression. Similar modulation of NR4A2 expression was also effective as an intervention, reversing established autoimmune responses and ameliorating clinical disease symptoms. Thus, NR4A2 appears to control Th17 differentiation and so plays an essential role in the development of Th17-mediated autoimmune disease. As NR4A2 is also upregulated during human autoimmune disease, targeting NR4A2 may provide a new therapeutic approach in treating autoimmune disease.

Mesenchymal stem cells repress Th17 molecular program through the PD-1 pathway

MSC display potent suppressive properties initially described a decade ago. Since then, MSC suppressive activities on T-cell effector pathways have been highly investigated. MSC modulate CD4 cell differentiation through different mechanisms depending on culture conditions and display disparate activities on T cells according to their differentiation status. A significant amount of evidence for MSC effects on Th17 cells revealed that MSC could be suppressive under diverse circumstances but also enhance Th17 cell activity under other conditions. In the present study, we investigated the suppressive effects of MSC on Th1 and Th17 subsets of T cells using T cells undergoing Th1 and Th17 polarization or, on mature Th1 and Th17 cells. We showed that MSC inhibited the proliferation of mature Th1 cells and T cells during their differentiation toward Th1 cells. This suppressive effect was maintained in a transwell culture insert, where MSC were plated in the insert, demonstrating the major role played by soluble factors. Using the transwell barrier, we observed that MSC decrease the number of T cells undergoing Th17 differentiation whereas they did not affect IL-17 production by mature Th17, demonstrating the need for cell contact for suppressing Th17 cell function. We observed a high level of PD-L1 expression on MSC co-cultured with differentiating or polarized Th1 and Th17 cells. Importantly, using neutralizing antibodies specific for PD-L1 and PD-1, we showed that the mechanisms by which MSC mediate Th17 cell repolarization depend on PD-L1 expression on MSC. Taken together, our results demonstrated a cell-to-cell contact depend mechanism in the selective immunosuppression of MSC on mature Th17 cells through up-regulation of PD-L1.

Mesenchymal Stem Cells Repress Th17 Molecular Program through the PD-1 Pathway

MSC display potent suppressive properties initially described a decade ago. More recently, MSC suppressive activities on T-cell effector pathways have been investigated. MSC modulate CD4 differentiation through different mechanisms depending on culture conditions and display disparate activities on T cells according to their differentiation status. A significant amount of evidence for MSC effects on Th17 cells revealed that MSC could be suppressive under diverse circumstances but also enhance Th17 cell activity under other conditions. In the present study, we investigated the suppressive effects of MSC on Th1 and Th17 subsets of T cells using T cells undergoing Th1 and Th17 polarization or mature Th1 and Th17 cells. MSC inhibited the proliferation of T cells during their differentiation toward Th1 cells and mature Th1 cells. This suppressive effect was maintained in a transwell cell culture insert demonstrating the major role played by soluble factors. Using the transwell cell separation barrier, we observed that MSC decrease the number of T cells undergoing Th17 differentiation whereas they did not affect IL-17 production by mature Th17, demonstrating the need for cell contact for suppressing Th17 cell function. Moreover, we reported that PD-L1 is highly expressed on MSC co-cultured with differentiating or polarized Th1 and Th17 cells. Using neutralizing antibodies specific for PD-L1 and PD-1 we showed that the mechanisms by which MSC mediate Th17 cell repolarization depend on PD-L1 expression on MSC. Taken together our results demonstrated a cell-to-cell contact depend mechanism in the selective immunosuppression of MSC on mature Th17 cells through up-regulation of PD-L1.

Prostaglandin E2 Suppresses Antifungal Immunity by Inhibiting Interferon Regulatory Factor 4 Function and Interleukin-17 Expression in T Cells

T helper 17 (Th17) cells play an important role in mucosal host defense through production of the signature cytokines IL-17 and IL-22. Prostaglandin E2 (PGE2) has been shown to enhance IL-17 production by mature Th17 cells. However, when present during Th17 cell differentiation, we found that PGE2 inhibited the transcription factor IRF4 and suppressed production of IL-17 but not IL-22. We show that IRF4 was required for IL-17 expression but inhibited IL-22 expression, highlighting the potential for discordant regulation of these two cytokines in Th17 cells. The pathogenic fungus Cryptococcus neoformans produces PGE2, and we found that it uses PGE2- and IRF4-dependent mechanisms to specifically inhibit induction of IL-17 during Th17 cell differentiation. Blockade of host PGE2 during infection led to increased IL-17 production from CD4(+) T cells and increased survival of mice. These findings suggest that host- or pathogen-derived PGE2 can act directly on Th17 cells during differentiation to inhibit IL-17-dependent antimicrobial responses.

Ursolic Acid Suppresses Interleukin-17 (IL-17) Production by Selectively Antagonizing the Function of RORγt Protein

Th17 cells have recently emerged as a major player in inflammatory and autoimmune diseases via the production of pro-inflammatory cytokines IL-17, IL-17F, and IL-22. The differentiation of Th17 cells and the associated cytokine production is directly controlled by RORγt. Here we show that ursolic acid (UA), a small molecule present in herbal medicine, selectively and effectively inhibits the function of RORγt, resulting in greatly decreased IL-17 expression in both developing and differentiated Th17 cells. In addition, treatment with UA ameliorated experimental autoimmune encephalomyelitis. The results thus suggest UA as a valuable drug candidate or leading compound for developing treatments of Th17-mediated inflammatory diseases and cancer.

IL-23-Mediated Epidermal Hyperplasia Is Dependent on IL-6

Psoriasis is a chronic inflammatory skin disease primarily driven by Th17 cells. IL-23 facilitates the differentiation and induces complete maturation of Th17 cells. Lesional psoriatic skin has increased levels of IL-23 and recent studies show that intradermal injections of IL-23 induce a psoriasis-like skin phenotype in mice. We have now characterized the IL-23-induced skin inflammation in mice at the molecular level and found a significant correlation with the gene expression profile from lesional psoriatic skin. As observed in psoriasis, the pathogenesis of the IL-23-induced skin inflammation in mice is driven by Th17 cells. We demonstrate a dramatic upregulation of IL-6 mRNA and protein after intradermal injections of IL-23 in mice. Using IL-6(-/-) mice we show that IL-6 is essential for development of the IL-23-elicited responses. Despite producing high levels of IL-22, IL-6(-/-) mice were unable to express the high-affinity IL-22 receptor chain and produced minimal IL-17A in response to intradermal injections of IL-23. In conclusion, we provide evidence for the critical role played by IL-6 in IL-23-induced skin inflammation and show that IL-6 is required for expression of IL-22R1A.