The development and in vivo function of T helper 9 cells

Transcriptional regulation of CD4+ TH cells that mediate tissue inflammation

Acquired and genetic immunodeficiencies have revealed an indispensable role for CD4⁺ T cells in the induction of protective host immune responses against a myriad of microbial pathogens. Influenced by the cytokines present in the microenvironment, activated CD4⁺ T cells may differentiate into several highly-specialized helper subsets defined by the production of distinct signature cytokines tailored to combat diverse classes of pathogens. The process of specification and differentiation is controlled by networks of core, master, and accessory transcription factors, which ensure that CD4⁺ T helper (T_H ) cell responses mounted against an invading microbe are of the correct specificity and type. However, aberrant activation or inactivation of transcription factors can result in sustained and elevated expression of immune-related genes, leading to chronic activation of CD4⁺ T_H  cells and organ-specific autoimmunity. In this review, we provide an overview of the molecular basis of CD4⁺ T_H  cell differentiation and examine how combinatorial expression of transcription factors, which promotes genetic plasticity of CD4⁺ T_H  cells, can contribute to immunological dysfunction of CD4⁺ T_H responses. We also discuss recent studies which highlight the potential of exploiting the genetic plasticity of CD4⁺ T_H  cells in the treatment of autoimmune and other immune-mediated disorders.

B lymphocyte-induced maturation protein 1 controls TH9 cell development, IL-9 production, and allergic inflammation

BACKGROUND

The transcriptional repressor B lymphocyte-induced maturation protein 1 (Blimp-1) has a key role in terminal differentiation in various T-cell subtypes. However, whether Blimp-1 regulates T_H9 differentiation and its role in allergic inflammation are unknown.

OBJECTIVE

We aimed to investigate the role of Blimp-1 in T_H9 differentiation and in the pathogenesis of allergic airway inflammation.

METHODS

In vitro T_H9 differentiation, flow cytometry, ELISA, and real-time PCR were used to investigate the effects of Blimp-1 on T_H9 polarization. T cell-specific Blimp-1-deficient mice, a model of allergic airway inflammation, and T-cell adoptive transfer to recombination-activating gene 1 (Rag-1)^-/- mice were used to address the role of Blimp-1 in the pathogenesis of allergic inflammation.

RESULTS

We found that Blimp-1 regulates T_H9 differentiation because deleting Blimp-1 increased IL-9 production in CD4⁺ T cells in vitro. In addition, we showed that in T cell-specific Blimp-1-deficient mice, deletion of Blimp-1 in T cells worsened airway disease, and this worsening was inhibited by IL-9 neutralization. In asthmatic patients CD4⁺ T cells in response to TGF-β plus IL-4 increased IL-9 expression and downregulated Blimp-1 expression compared with expression in healthy control subjects. Blimp-1 overexpression in human T_H9 cells inhibited IL-9 expression.

CONCLUSION

Blimp-1 is a pivotal negative regulator of T_H9 differentiation and controls allergic inflammation.

Th1/Th17 polarization persists following whole-cell pertussis vaccination despite repeated acellular boosters

In the mid-1990s, whole-cell pertussis (wP) vaccines were associated with local and systemic adverse events that prompted their replacement with acellular pertussis (aP) vaccines in many high-income countries. In the past decade, rates of pertussis disease have increased in children receiving only aP vaccines. We compared the immune responses to aP boosters in individuals who received their initial doses with either wP or aP vaccines using activation-induced marker (AIM) assays. Specifically, we examined pertussis-specific memory CD4+ T cell responses ex vivo, highlighting a type 2/Th2 versus type 1/Th1 and Th17 differential polarization as a function of childhood vaccination. Remarkably, after a contemporary aP booster, cells from donors originally primed with aP were (a) associated with increased IL-4, IL-5, IL-13, IL-9, and TGF-β and decreased IFN-γ and IL-17 production, (b) defective in their ex vivo capacity to expand memory cells, and (c) less capable of proliferating in vitro. These differences appeared to be T cell specific, since equivalent increases of antibody titers and plasmablasts after aP boost were seen in both groups. In conclusion, our data suggest that there are long-lasting effects and differences in polarization and proliferation of T cell responses in adults originally vaccinated with aP compared with those that initially received wP, despite repeated acellular boosters.

IL-9 receptor signaling in memory B cells regulates humoral recall responses

Memory B cells (B_mem cells) are the basis of long-lasting humoral immunity. They respond to re-encountered antigens by rapidly producing specific antibodies and forming germinal centers (GCs), a recall response that has been known for decades but remains poorly understood. We found that the receptor for the cytokine IL-9 (IL-9R) was induced selectively on B_mem cells after primary immunization and that IL-9R-deficient mice exhibited a normal primary antibody response but impaired recall antibody responses, with attenuated population expansion and plasma-cell differentiation of B_mem cells. In contrast, there was augmented GC formation, possibly due to defective downregulation of the ligand for the co-stimulatory receptor ICOS on B_mem cells. A fraction of B_mem cells produced IL-9. These findings indicate that IL-9R signaling in B_mem cells regulates humoral recall responses.

Human TH9 differentiation is dependent on signal transducer and activator of transcription (STAT) 3 to restrain STAT1-mediated inhibition

BACKGROUND

Patients with loss-of-function (LOF) signal transducer and activator of transcription 3 (STAT3) mutations have dermatitis, enhanced IgE production despite a relative lack of immediate hypersensitivity, recurrent infection, and an increased rate of lymphoma in addition to a number of skeletal and connective tissue abnormalities. Patients with STAT1 gain-of-function (GOF) mutations also have susceptibility to candidiasis and sinopulmonary infection, as well as autoimmunity and squamous cell carcinoma, in addition to even more broad phenotypes.

OBJECTIVE

Because of the link between T_H9 cells and allergic inflammation, autoimmunity, and antitumor surveillance and because evidence shows a role for either STAT3 or STAT1 in T_H9 differentiation conflicts, we sought to determine the status on this lineage of STAT1 GOF and STAT3 LOF mutations in human subjects.

METHODS

We detected IL-9 levels and T_H9 differentiation in patients with STAT3 LOF and STAT1 GOF mutations, together with T_H9 transcript factors, and partially rescued their deficiency in vitro by adding cytokines they lacked or transfecting key molecules.

RESULTS

We found that PBMCs or sorted naive CD4⁺ T cells from patients with STAT3 LOF and STAT1 GOF mutations had impaired T_H9 generation/differentiation. STAT3 inhibition in normal T_H9 cultures diminished early IL-21 induction and late IL-9 production, whereas exogenous IL-21 enhanced T_H9 differentiation, even with STAT3 inhibition, by restoring suppressor of cytokine signaling 3 expression and thus inhibiting excessive phosphorylated signal transducer and activator of transcription (p-STAT) 1 activation. Furthermore, exogenous expression of suppressor of cytokine signaling 3 or either T-bet or STAT1 RNA interference in STAT3 LOF cells partially rescued IL-9 differentiation.

CONCLUSION

Collectively, these results suggest that human T_H9 differentiation depends on normal p-STAT3 and IL-21 production to suppress p-STAT1 activation and T-bet transcription.

Th9 Cells Represent a Unique Subset of CD4+ T Cells Endowed with the Ability to Eradicate Advanced Tumors

The antitumor effector T helper 1 (Th1) and Th17 cells represent two T cell paradigms: short-lived cytolytic Th1 cells and "stem cell-like" memory Th17 cells. We report that Th9 cells represent a third paradigm-they are less-exhausted, fully cytolytic, and hyperproliferative. Only tumor-specific Th9 cells completely eradicated advanced tumors, maintained a mature effector cell signature with cytolytic activity as strong as Th1 cells, and persisted as long as Th17 cells in vivo. Th9 cells displayed a unique Pu.1-Traf6-NF-κB activation-driven hyperproliferative feature, suggesting a persistence mechanism rather than an antiapoptotic strategy. Th9 antitumor efficacy depended on interleukin-9 and upregulated expression of Eomes and Traf6. Thus, tumor-specific Th9 cells are a more effective CD4+ T cell subset for adoptive cancer therapy.

ZIKV Infection Induces an Inflammatory Response but Fails to Activate Types I, II, and III IFN Response in Human PBMC

The recent epidemic in the Americas caused by Zika virus (ZIKV), Asian lineage, spurred the research towards a better understanding of how ZIKV infection affects the host immune response. The aim of this study was to evaluate the effects of Asian and East African ZIKV strain infection on the induction of IFN and proinflammatory and Th2 cytokines in human PBMC. We reported a slight modulation of type II IFN in PBMC exposed to Asian strain, but not to African strain, and a complete lack of type I and III IFN induction by both strains, suggesting the ability of ZIKV to evade the IFN system not only inhibiting the antiviral IFN response but also IFN production. Moreover, we highlighted a polyfunctional immune activation only in PBMC exposed to Asian strain, due to the induction of an inflammatory profile (IL-6, IL-8) and of a Th9 (IL-9) response. Overall, our data show a different ability of the ZIKV Asian strain, with respect to the African strain, to activate host immune response that may have pathogenetic implications for virus spread in vivo, including mother-to-child transmission and induction of severe fetal complications, as birth defects and neurological disorders.

Prospective Analysis of Adoptive TIL Therapy in Patients with Metastatic Melanoma: Response, Impact of Anti-CTLA4, and Biomarkers to Predict Clinical Outcome

Purpose: Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TIL) has consistently demonstrated clinical efficacy in metastatic melanoma. Recent widespread use of checkpoint blockade has shifted the treatment landscape, raising questions regarding impact of these therapies on response to TIL and appropriate immunotherapy sequence.Patients and Methods: Seventy-four metastatic melanoma patients were treated with autologous TIL and evaluated for clinical response according to irRC, overall survival, and progression-free survival. Immunologic factors associated with response were also evaluated.Results: Best overall response for the entire cohort was 42%; 47% in 43 checkpoint-naïve patients, 38% when patients were exposed to anti-CTLA4 alone (21 patients) and 33% if also exposed to anti-PD1 (9 patients) prior to TIL ACT. Median overall survival was 17.3 months; 24.6 months in CTLA4-naïve patients and 8.6 months in patients with prior CTLA4 blockade. The latter patients were infused with fewer TIL and experienced a shorter duration of response. Infusion of higher numbers of TIL with CD8 predominance and expression of BTLA correlated with improved response in anti-CTLA4 naïve patients, but not in anti-CTLA4 refractory patients. Baseline serum levels of IL9 predicted response to TIL ACT, while TIL persistence, tumor recognition, and mutation burden did not correlate with outcome.Conclusions: This study demonstrates the deleterious effects of prior exposure to anti-CTLA4 on TIL ACT response and shows that baseline IL9 levels can potentially serve as a predictive tool to select the appropriate sequence of immunotherapies. Clin Cancer Res; 24(18); 4416-28. ©2018 AACR.

Intraperitoneal administration of the anti-IL-23 antibody prevents the establishment of intestinal nematodes in mice

Previous studies have established that an increased Th-9 response creates a hostile environment for nematode parasites. Given that IL-23, a cytokine required for maintenance of the IL-17-secreting phenotype, has inhibitory effects on IL-9 production, we hypothesized that reducing circulating IL-23 by treatment with anti-IL-23 antibodies would reduce the establishment and development of parasitic intestinal nematodes. In this study, we show that animals treated with anti-IL-23 monoclonal antibodies showed a drastic reduction in the number of mouse pinworms (Aspiculuris tetraptera) recovered from the intestine (p < 0.001) at 23 days post-infection compared to the untreated animals. The cytokine levels in Peyer's patches (PP) in treated and infected animals increase the expression of interleukins such as IL-25, IL-21, and IL-9, augmenting mucus production in the crypts, and boosting chemokines, such as OX40 and CCL20 in the mucosa. Our results suggest that the Th17/Th2 regulatory mechanism provoked by the administration of the anti-IL-23 antibody prevents the implantation of the intestinal nematode in mice. The diminished inflammatory IL-17 levels alter the Th9 environment perhaps as a consequence of IL-17 inhibiting IL-9 expression. These Th9 conditions may explain the successful treatment against Inflammatory Bowel Disease (IBD) both with antibodies against IL-23 or through parasitization with nematodes.

The role of the common gamma-chain family cytokines in γδ T cell-based anti-cancer immunotherapy

Cytokines of the common gamma-chain receptor family, comprising interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are vital with respect to organizing and sustaining healthy immune cell functions. Supporting the anti-cancer immune response, these cytokines inspire great interest for their use as vaccine adjuvants and cancer immunotherapies. It is against this background that gamma delta (γδ) T cells, as special-force soldiers and natural contributors of the tumor immunosurveillance, also received a lot of attention the last decade. As γδ T cell-based cancer trials are coming of age, this present review focusses on the effects of the different cytokines of the common gamma-chain receptor family on γδ T cells with respect to boosting γδ T cells as a therapeutic target in cancer immunotherapy. This review also gathers data that IL-15 in particular exhibits key features for augmenting the anti-tumor activity of effector killer γδ T cells whilst overcoming the myriad of immune escape mechanisms used by cancer cells.

Transcriptional Control of Th9 Cells: Role of Foxo1 in Interleukin-9 Induction

Interleukin (IL) 9-producing helper T (Th) 9 cells play a major role in contributing immunity against extracellular pathogens. In addition, the role of Th9 cells was demonstrated in the pathogenesis of allergic, skin, and intestinal inflammation. The functions of Th9 cells were further extended in antitumor immune response, as Th9 cells were suggested to be potent antitumor Th cells. Given the pleotropic functions of IL-9 in various pathophysiological conditions, it is essential to understand the differentiation and stability of Th9 cells and other IL-9-producing T cells. In addition to Th9 cells, Th2 and Th17 cells as well as induced Foxp3+ regulatory T cells (iTregs) cells also produce IL-9, but how IL-9 production is regulated in these cell types is not yet clearly defined. Although Th2, Th9 and Th17 cells as well as iTregs develop in the presence of distinct differentiating factors, yet they all express IL-9 together with their own lineage specific cytokines. Here, in this review, we summarize the current understanding of signaling pathways that lead to the promotion of differentiation of Th9 cells and IL-9 induction in Th2 and Th17 cells, as well as in iTregs. We further discuss the transcriptional regulation of Th9 cells in context of Foxo1, as an essential transcription factor required for the development and functions of Th9 and other IL-9-producing T cells.

TH9 cell differentiation, transcriptional control and function in inflammation, autoimmune diseases and cancer

Naïve CD4⁺T cells differentiate into various T cell subsets depending on the specific cytokine environment. T_H9 cells are less well-characterized than other T cell subsets, and factors that control their development and function have only recently been identified. It is now clear that T_H9 cells play critical roles in immune-mediated diseases, including allergic airway, autoimmune and inflammatory bowel diseases, and cancer. Thus, the promotion or suppression of T_H9 cell differentiation, transcriptional control and function may provide novel treatments for clinical inflammation, autoimmune diseases and tumors.

Flow Cytometric Assessment of STAT Molecules in Th9 Cells

IL-9-producing Th9 cells are a novel subset of T helper cells that develop independently of other T helper subsets. Th9 cells have been implicated in the pathogenesis of allergic asthma and autoimmunity, while also serving as critical effector T cells in mediating antitumor immune responses. Concomitant presence of TGF-β and IL-4 lead to the differentiation of naïve CD4⁺ T cells towards the Th9 phenotype. In addition, several cytokines, including IL-1β, IL-2, IL-25, and IL-33, further amplify Th9 responses. Negative regulators of Th9 cells include other cytokines such as IFN-γ, IL-23, and IL-27. Here, we describe a detailed protocol for the analysis of STAT molecules involved in the differentiation of Th9 cells and Th9 inhibition by IL-27.

Investigating the roles of regulatory T cells, mast cells and interleukin-9 in the control of skin inflammation by vitamin D

Topical application of biologically active vitamin D [1,25-dihydroxyvitamin D (1,25(OH)₂D)], or low-calcemic analogues, curb skin inflammation through mechanisms that involve migratory dendritic cells (DCs) and regulatory T (T_Reg) cells. 1,25(OH)₂D also promotes immunoregulation by mast cells, and inhibits the development of T helper type-9 (Th9) cells that secrete interleukin-9 (IL-9). Here, we investigated the ability of topical 1,25(OH)₂D to suppress contact dermatitis through an IL-9-dependent process, examining mast cells and IL-9-secreting T cells. Contact dermatitis was modelled in adult BALB/c female mice by initiating a "biphasic ear swelling response" following a single application of 2,4-dinitrofluorobenzene (DNFB). Topical 1,25(OH)₂D (125 ng) applied to ear pinnae prior to (but not after) DNFB sensitisation suppressed the efferent phase of the ear swelling response. This dose of 1,25(OH)₂D did not cause hypercalcemia. At the peak of the efferent ear swelling response, proportions of T_Reg (CD3 + Foxp3+) cells and numbers of mast cells were increased in ear skin of 1,25(OH)₂D-treated mice. Topical 1,25(OH)₂D increased the proportion of Foxp3 + IL-9 + T_Reg cells and the capacity of T_Reg cells to secrete IL-9 ex vivo. However, the proportion of the IL-9 + cells of the total T_Reg cell population was small (< 1%), and the amount of IL-9 secreted by T_Reg cells from mice treated with IL-9 was low (< 50 pg/ml). Furthermore, injection of anti-IL-9 neutralising antibody (100 µg, intraperitoneally) prior to sensitisation did not significantly reverse the suppressive effects of 1,25(OH)₂D. In conclusion, topically applied 1,25(OH)₂D suppressed the efferent phase of a biphasic cutaneous ear swelling response through mechanism(s) that may be dependent on mast cells and T_Reg cells; however, the role of IL-9 in mediating these responses is uncertain. More studies are needed to further characterise the mechanisms by which topical 1,25(OH)₂D modulates cell-mediated immune responses central to its suppressive effects upon contact dermatitis.

Specifically differentiated T cell subset promotes tumor immunity over fatal immunity

Allogeneic immune cells, particularly T cells in donor grafts, recognize and eliminate leukemic cells via graft-versus-leukemia (GVL) reactivity, and transfer of these cells is often used for high-risk hematological malignancies, including acute myeloid leukemia. Unfortunately, these cells also attack host normal tissues through the often fatal graft-versus-host disease (GVHD). Full separation of GVL activity from GVHD has yet to be achieved. Here, we show that, in mice and humans, a population of interleukin-9 (IL-9)-producing T cells activated via the ST2-IL-33 pathway (T9IL-33 cells) increases GVL while decreasing GVHD through two opposing mechanisms: protection from fatal immunity by amphiregulin expression and augmentation of antileukemic activity compared with T9, T1, and unmanipulated T cells through CD8α expression. Thus, adoptive transfer of allogeneic T9IL-33 cells offers an attractive approach for separating GVL activity from GVHD.

Leprosy As a Complex Infection: Breakdown of the Th1 and Th2 Immune Paradigm in the Immunopathogenesis of the Disease

Leprosy is a chronic infectious disease whose evolution involves complex immune mechanisms of the host that influence the clinical presentation of the disease. For many years, the main interpretation of the host defense response was based on characterization of the established immune paradigm between T helper (Th) 1 and Th2 lymphocytes. However, with advances in the knowledge of immunology, new approaches have emerged along with the development of new immunological pathways that have changed the interpretation of the long-established paradigm of the polar forms of the disease, especially with the identification of new subtypes of T lymphocytes such as Th9, Th17, Th22, and Tregs. Thus, this review discusses the role of these new subtypes of T helper lymphocytes and how the development of the immune response of these cells modifies the pattern of the Th1/Th2 response in the immunopathogenesis of leprosy.

Immune checkpoint inhibition: prospects for prevention and therapy of hepatocellular carcinoma

The global prevalence of liver cancer is rapidly rising, mostly as a result of the amplified incidence rates of viral hepatitis, alcohol abuse and obesity in recent decades. Treatment options for liver cancer are remarkably limited with sorafenib being the gold standard for advanced, unresectable hepatocellular carcinoma but offering extremely limited improvement of survival time. The immune system is now recognised as a key regulator of cancer development through its ability to protect against infection and chronic inflammation, which promote cancer development, and eliminate tumour cells when present. However, the tolerogenic nature of the liver means that the immune response to infection, chronic inflammation and tumour cells within the hepatic environment is usually ineffective. Here we review the roles that immune cells and cytokines have in the development of the most common primary liver cancer, hepatocellular carcinoma (HCC). We then examine how the immune system may be subverted throughout the stages of HCC development, particularly with respect to immune inhibitory molecules, also known as immune checkpoints, such as programmed cell death protein-1, programmed cell death 1 ligand 1 and cytotoxic T lymphocyte antigen 4, which have become therapeutic targets. Finally, we assess preclinical and clinical studies where immune checkpoint inhibitors have been used to modify disease during the carcinogenic process. In conclusion, inhibitory molecule-based immunotherapy for HCC is in its infancy and further detailed research in relevant in vivo models is required before its full potential can be realised.

IL-36γ signaling controls the induced regulatory T cell-Th9 cell balance via NFκB activation and STAT transcription factors

Regulatory and effector T helper (Th) cells are abundant at mucosal surfaces, especially in the intestine, where they control the critical balance between tolerance and inflammation. However, the key factors that reciprocally dictate differentiation along these specific lineages remain incompletely understood. Here we report that the interleukin-1 (IL-1) family member IL-36γ signals through IL-36 receptor, myeloid differentiation primary response gene 88, and nuclear factor-κBp50 in CD4⁺ T cells to potently inhibit Foxp3-expressing induced regulatory T cell (T_reg) development, while concomitantly promoting the differentiation of Th9 cells via a IL-2-STAT5- (signal transducer and activator of transcription factor 5) and IL-4-STAT6-dependent pathway. Consistent with these findings, mice deficient in IL-36γ were protected from Th cell-driven intestinal inflammation and exhibited increased colonic T_reg cells and diminished Th9 cells. Our findings thus reveal a fundamental contribution for the IL-36/IL-36R axis in regulating the T_reg-Th9 cell balance with broad implications for Th cell-mediated disorders, such as inflammatory bowel diseases and particularly ulcerative colitis.

Heterogeneity of Human CD4(+) T Cells Against Microbes

CD4(+) T helper (Th) cells play a central role in the adaptive immune response by providing help to B cells and cytotoxic T cells and by releasing different types of cytokines in tissues to mediate protection against a wide range of pathogenic microorganisms. These functions are performed by different types of Th cells endowed with distinct migratory capacities and effector functions. Here we discuss how studies of the human T cell response to microbes have advanced our understanding of Th cell functional heterogeneity, in particular with the discovery of a distinct Th1 subset involved in the response to Mycobacteria and the characterization of two types of Th17 cells specific for extracellular bacteria or fungi. We also review new approaches to dissect at the clonal level the human CD4(+) T cell response induced by pathogens or vaccines that have revealed an unexpected degree of intraclonal diversification and propose a progressive and selective model of CD4(+) T cell differentiation.

Blockade of αEβ7 integrin suppresses accumulation of CD8+ and Th9 lymphocytes from patients with IBD in the inflamed gut in vivo

OBJECTIVE

Therapeutically targeting lymphocyte adhesion is of increasing relevance in IBD. Yet, central aspects of the action of antiadhesion compounds are incompletely understood. We investigated the role of αEβ7 and α4β7 integrins and their blockade by vedolizumab and etrolizumab for trafficking of IBD T lymphocytes in an in vivo model of homing to and retention in the inflamed gut.

DESIGN

We explored integrin expression in patients with IBD by flow cytometry and immunohistochemistry, while regulation of integrins was studied in T cell cultures. The functional relevance of integrins was assessed by adhesion assays and a recently established humanised mouse model in dextran sodium sulfate-treated immunodeficient mice.

RESULTS

High expression of αEβ7 was noted on CD8⁺ and CD4⁺ Th9 cells, while α4β7 was expressed on CD8⁺, Th2 and Th17 cells. T cell receptor stimulation and transforming growth factor β were key inducers of αEβ7 on human T cells, while butyric acid suppressed αEβ7. In comparison to α4β7 blockade via vedolizumab, blockade of β7 via etrolizumab surrogate antibody superiorly reduced colonic numbers of CD8⁺ and Th9 cells in vivo after 3 hours, while no difference was noted after 0.5 hours. AEβ7 expression was higher on CD8⁺ T cells from patients with IBD under vedolizumab therapy.

CONCLUSIONS

AEβ7 is of key relevance for gut trafficking of IBD CD8⁺ T cells and CD4⁺ Th9 cells in vivo and mainly retention might account for this effect. These findings indicate that blockade of αEβ7 in addition to α4β7 may be particularly effective in intestinal disorders with expansion of CD8⁺ and Th9 cells such as IBD.

Unlike Th1/Th17 cells, Th2/Th9 cells selectively migrate to the limbus/conjunctiva and initiate an eosinophilic infiltration process

In this study we compared polarized mouse T-helper (Th) lymphocytes of four populations, sensitized against an ocular antigen, for their patterns of migration and induction of inflammatory processes in recipient mouse eyes expressing the target antigen. Th1, Th2, Th9 and Th17 cells transgenically expressing T-cell receptor (TCR) specific against hen egg lysozyme (HEL) were adoptively transferred to recipient mice expressing HEL in their eyes. Recipient eyes collected 4 or 7 days post injection were analyzed for histopathological changes. Th1 and Th17 cells induced moderate to severe intraocular inflammation in the recipient mouse eyes, but essentially did not migrate into the conjunctiva. In contrast, Th2 and Th9 cells invaded minimally the intraocular space of recipient eyes, but accumulated in the limbus and migrated into the conjunctiva of the recipient mice and initiated allergy-like inflammatory responses, as indicated by remarkable eosinophil involvement. These data thus shed new light on the differences between the migration patterns and ocular pathogenic processes mediated by Th1/Th17 and by Th2/Th9 populations.

The γ c family of cytokines: fine-tuning signals from IL-2 and IL-21 in the regulation of the immune response

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on the sharing of a receptor component, the common cytokine receptor γ chain, γ _c, which is encoded by the gene mutated in humans with X-linked severe combined immunodeficiency (XSCID). Together, these cytokines play critical roles in lymphoid development, differentiation, growth, and survival as well as mediating effector function. Here, we provide an overview of the main actions of members of this cytokine family but then primarily focus on IL-2 and IL-21, discussing their dynamic interplay and contributions to a fine-tuned immune response. Moreover, we discuss the therapeutic utility of modulating their actions, particularly for autoimmunity and cancer.

The Immunogenicity of Branded and Biosimilar Infliximab in Rheumatoid Arthritis According to Th9-Related Responses

Our objective was to evaluate the immunogenicity of branded and biosimilar infliximab by detecting changes in T-helper-9 (Th9) percentages induced by an in vitro stimulation test.

METHODS

Peripheral blood mononuclear cells collected from 55 consecutive rheumatoid arthritis (RA) outpatients (15 drug free, 20 successfully treated with branded infliximab, 20 branded infliximab inadequate responders) and 10 healthy controls were cultured, with or without 50 μg/mL of infliximab originator (Remicade^®) or 50 μg/mL of infliximab biosimilar (Remsima^®) for 18 h. Th9 lymphocytes were identified by means of flow cytometry as PU.1 and IRF4-expressing, IL-9-secreting CD4⁺ T cells. Furthermore, the markers CCR7 and CD45RA were used to distinguish naïve from memory IL-9 producer cells.

RESULTS

Under unstimulated conditions, the drug-free RA patients had the highest percentages of Th9 lymphocytes. Following stimulation with branded infliximab, the percentages of PU.1 and IRF4-expressing Th9 cells, CCR7⁺, CD45RA^- (central memory) and CCR7^-, CD45RA^- (effector memory) cells significantly increased in the group of inadequate responders, but no significant variation was observed after exposure to the biosimilar of infliximab.

CONCLUSIONS

Th9 cells seem to be involved in the immune response to the epitopes of branded, but not biosimilar, infliximab, and this may depend on the recall and stimulation of both central and effector memory cells.

Foxo1 and Foxp1 play opposing roles in regulating the differentiation and antitumor activity of TH9 cells programmed by IL-7

Tumor-specific CD4⁺ T helper 9 (T_H9) cells, so-called because of their production of the cytokine interleukin-9 (IL-9), are a powerful effector T cell subset for cancer immunotherapy. We found that pretreatment of naïve CD4⁺ T cells with IL-7 further enhanced their differentiation into T_H9 cells and augmented their antitumor activity. IL-7 markedly increased the abundance of the histone acetyltransferase p300 by activating the STAT5 and PI3K-AKT-mTOR signaling pathways and promoting the acetylation of histones at the Il9 promoter. As a result, the transcriptional regulator Foxo1 was dephosphorylated and translocated to the nucleus, bound to the Il9 promoter, and induced the production of IL-9 protein. In contrast, Foxp1, which bound to the Il9 promoter in naïve CD4⁺ T cells and inhibited Il9 expression, was outcompeted for binding to the Il9 promoter by Foxo1 and translocated to the cytoplasm. Furthermore, forced expression of Foxo1 or a deficiency in Foxp1 in CD4⁺ T cells markedly increased the production of IL-9, whereas a deficiency in Foxo1 inhibited the ability of IL-7 to enhance the differentiation and antitumor activity of T_H9 cells. Thus, we identified the roles of Foxo1 as a positive regulator and Foxp1 as a negative regulator of T_H9 cell differentiation and antitumor activity, which may provide potential targets for cancer immunotherapy.

Transcription factor Foxo1 is essential for IL-9 induction in T helper cells

Interleukin 9 (IL-9)-producing helper T (Th9) cells have a crucial function in allergic inflammation, autoimmunity, immunity to extracellular pathogens and anti-tumor immune responses. In addition to Th9, Th2, Th17 and Foxp3⁺ regulatory T (Treg) cells produce IL-9. A transcription factor that is critical for IL-9 induction in Th2, Th9 and Th17 cells has not been identified. Here we show that the forkhead family transcription factor Foxo1 is required for IL-9 induction in Th9 and Th17 cells. We further show that inhibition of AKT enhances IL-9 induction in Th9 cells while it reciprocally regulates IL-9 and IL-17 in Th17 cells via Foxo1. Mechanistically, Foxo1 binds and transactivates IL-9 and IRF4 promoters in Th9, Th17 and iTreg cells. Furthermore, loss of Foxo1 attenuates IL-9 in mouse and human Th9 and Th17 cells, and ameliorates allergic inflammation in asthma. Our findings thus identify that Foxo1 is essential for IL-9 induction in Th9 and Th17 cells.The transcription factor Foxo1 can control regulatory T cell and Th1 function. Here the authors show that Foxo1 is also critical for IL-9 production by Th9 cells and other IL-9-producing cells.

Neutralization of interleukin-9 ameliorates symptoms of allergic rhinitis by reducing Th2, Th9, and Th17 responses and increasing the Treg response in a murine model

A novel independent Th-cell subset, characterized by high expression of interleukin (IL)-9, has been recognized as the "Th9" subset. Although Th9 cells are important in many diseases, their contribution to allergic rhinitis (AR) remains unclear. We therefore first determined whether Th9 cells were present in a mouse model of AR. We then investigated the their involvement in the distribution of CD4+ T-cell subsets and the symptoms of AR by treating mice with anti-IL-9 antibodies (Abs). Anti-IL-9 Abs were administered intranasally during rechallenge of ovalbumin (OVA)-induced AR in BALB/c mice. We measured nasal rubbing motion, sneezing and eosinophils, as well as the Th1 (Th1 cell percentage, Ifn-γ mRNA/protein, T-bet mRNA), Th2 (Th2 cell percentage, Il-4 mRNA/protein, Gata3 mRNA), Th9 (Th9 cell percentages Il-9 mRNA/protein, PU.1 and Irf4 mRNA), Th17 (Th17 cell percentage, Il-17 mRNA/protein, Rorγt mRNA), and Treg (Treg cell percentage, Foxp3 mRNA) responses in the nasal mucosa. Treatment with anti-IL-9 Abs markedly reduced nasal rubbing, sneezing, eosinophil infiltration, and Th2, Th9, and Th17 responses, and increased the Treg response. Our findings emphasize the importance of IL-9/Th9 in the pathogenesis of AR, and suggest that anti-IL-9 Ab treatment may be an effective therapeutic strategy for AR.

The Multifaceted Role of T-Helper Responses in Host Defense against Aspergillus fumigatus

The ubiquitous opportunistic fungal pathogen Aspergillus fumigatus rarely causes infections in immunocompetent individuals. A healthy functional innate immune system plays a crucial role in preventing Aspergillus-infection. This pivotal role for the innate immune system makes it a main research focus in studying the pathogenesis of aspergillosis. Although sometimes overshadowed by the innate immune response, the adaptive immune response, and in particular T-helper responses, also represents a key player in host defense against Aspergillus. Virtually all T-helper subsets have been described to play a role during aspergillosis, with the Th1 response being crucial for fungal clearance. However; morbidity and mortality of aspergillosis can also be partly attributed to detrimental immune responses resulting from adaptive immune activation. Th2 responses benefit fungal persistence; and are the foundation of allergic forms of aspergillosis. The Th17 response has two sides; although crucial for granulocyte recruitment, it can be involved in detrimental immunopathology. Regulatory T-cells, the endogenous regulators of inflammatory responses, play a key role in controlling detrimental inflammatory responses during aspergillosis. The current knowledge of the adaptive immune response against A. fumigatus is summarized in this review. A better understanding on how T-helper responses facilitate clearance of Aspergillus-infection and control inflammation can be the fundamental basis for understanding the pathogenesis of aspergillosis and for the development of novel host-directed therapies.

Serum Interleukin 9 Levels Predict Disease Severity and the Clinical Efficacy of Infliximab in Patients with Crohn's Disease

BACKGROUND

Interleukin (IL)-9 drives gut inflammation, but its role in Crohn's disease (CD) is unclear. We aimed to analyze correlations between serum IL-9 levels and disease severity and to evaluate their predictive value in relation to the clinical efficacy of infliximab (IFX) in patients with CD.

METHODS

Between January 2013 and December 2015, 100 consecutive patients with active CD and 50 age- and sex-matched control individuals were recruited from a tertiary center. Their serum IL-9 levels were measured using an enzyme-linked immunosorbent assay. Correlations between the serum IL-9 levels and disease severity were examined. The serum IL-9 level was explored as a predictor of clinical remission and mucosal healing at week 30 in 50 patients for whom IFX therapy was administered.

RESULTS

The serum IL-9 levels were significantly higher in the patients with active CD (22.0 pg/mL) than in the control individuals (6.3 pg/mL) (P < 0.001); they differed according to disease severity (moderate-to-severe CD: 29.1 pg/mL versus mild CD: 12.9 pg/mL) (P < 0.001), and they correlated well with the clinical activity of CD. IFX lowered the serum IL-9 level in patients who achieved efficacy at week 30. The areas under the curves for the IL-9 levels at weeks 14 and 30 that could predict clinical remission and mucosal healing at week 30 were 0.803 and 0.752 and 0.746 and 0.781, respectively.

CONCLUSIONS

Serum IL-9 levels correlate with disease severity and the clinical efficacy of IFX in patients with CD, and IL-9 may be a promising novel biomarker for CD monitoring.

S100A4 contributes to colitis development by increasing the adherence of Citrobacter rodentium in intestinal epithelial cells

S100A4 has been implicated in cancer and several inflammatory diseases, but its role in inflammatory bowel disease has not been well investigated. Here, upon infection with Citrobacter rodentium, a model for enteropathogenic Escherichia coli infection in humans, induced the infiltration of a large number of S100A4⁺ cells into the colon in wild type (WT) mice. Deficiency of S100A4 reduced weight loss, bacterial colonization and colonic pathology. Furthermore, the expression of inflammatory cytokines and the recruitment of macrophages and neutrophils also decreased significantly in S100A4 knock out (S100A4 ^-/-) mice. In vitro, soluble S100A4 directly up-regulated expression of integrin β-1 in intestinal epithelial cells and significantly increased the adherence of C. rodentium to intestinal epithelial cells. Additionally, the effects of S100A4 on the adherence of C. rodentium to epithelial cells could be abolished by a receptor for advanced glycation end products (RAGE)-specific inhibitor (FPS-ZM1). Therefore, these data indicate a novel mechanism for S100A4 that promotes colitis development by enhancing host adhesion and colonization of Citrobacter rodentium through the S100A4-mediated host inflammatory responses.

Integrated STAT3 and Ikaros Zinc Finger Transcription Factor Activities Regulate Bcl-6 Expression in CD4+ Th Cells

B cell lymphoma-6 (Bcl-6) is a transcriptional repressor that is required for the differentiation of T follicular helper (T_FH) cell populations. Currently, the molecular mechanisms underlying the transcriptional regulation of Bcl-6 expression are unclear. In this study, we have identified the Ikaros zinc finger transcription factors Aiolos and Ikaros as novel regulators of Bcl-6. We found that increased expression of Bcl-6 in CD4⁺ Th cell populations correlated with enhanced enrichment of Aiolos and Ikaros at the Bcl6 promoter. Furthermore, overexpression of Aiolos or Ikaros, but not the related family member Eos, was sufficient to induce Bcl6 promoter activity. Intriguingly, STAT3, a known Bcl-6 transcriptional regulator, physically interacted with Aiolos to form a transcription factor complex capable of inducing the expression of Bcl6 and the T_FH-associated cytokine receptor Il6ra Importantly, in vivo studies revealed that the expression of Aiolos was elevated in Ag-specific T_FH cells compared with that observed in non-T_FH effector Th cells generated in response to influenza infection. Collectively, these data describe a novel regulatory mechanism through which STAT3 and the Ikaros zinc finger transcription factors Aiolos and Ikaros cooperate to regulate Bcl-6 expression.

Interleukin-9 over-expression and T helper 9 polarization in systemic sclerosis patients

T helper 9 (Th9) cells and interleukin (IL)-9 are involved in the pathogenesis of several autoimmune diseases. The exact role of IL-9 and Th9 cells in patients with systemic sclerosis (SSc) have not yet been studied adequately. IL-9, IL-9R, transcription factor PU.1 (PU.1), IL-4, thymic stromal lymphopoietin (TSLP) and transforming growth factor (TGF)-β expression were assessed in skin and kidney biopsies of SSc patients and healthy controls (HC) by immunohistochemistry (IHC). The cellular source of IL-9 was also analysed by confocal microscopy analysis. Peripheral IL-9-producing cells were also studied by flow cytometry. The functional relevance of IL-9 increased expression in SSc was also investigated. Our results demonstrated a strong expression of IL-9, IL-9R, IL-4, TSLP and TGF-β in skin tissues of patients with both limited and diffuse SSc. IL-9 expression was observed mainly in the context of skin infiltrating mononuclear cells and keratinizing squamous epithelium. IL-9 over-expression was also observed in renal biopsies of patients with SSc. IL-9 producing cells in the skin were identified as Th9 cells. Similarly, Th9 cells were expanded and were the major source of IL-9 among SSc peripheral blood mononuclear cells (PBMC), their percentage being correlated directly with the modified Rodnan skin score. Infiltrating mononuclear cells, mast cells and neutrophils expressed IL-9R. In in-vitro studies stimulation with rIL-9 significantly induced NET (neutrophil extracellular traps) release by dying cells (NETosis) in neutrophils, expansion of mast cells and increase of anti-systemic scleroderma 70 (Scl70) production by B cells. Our findings suggest that Th9 cells and IL-9 could be implicated in the pathogenesis of SSc.

Role of interleukin-1-family cytokines on effector CD4 T cell differentiation

The ability of CD4 T cells to differentiate into various effector or regulatory T cell subsets explains the successful adaptation of immune responses to different types of infectious pathogens. Immune responses in the context of cancer are also shaped by CD4 T cells, which can directly affect cancer prognosis in patients. While the proinflammatory mediator interleukin (IL)-1β was initially shown to enhance Th2 cell responses, recent findings support a predominant role of two other members of the IL-1 family, IL-18 and IL-33, on the production of Th1 and Th2-derived cytokines. In addition, IL-1β was found to profoundly affect the biology of two recently identified CD4 T cell subsets, Th17 and Th9 cells. IL-1β is critical for Th17 cell differentiation and it enhances the production of IL-9 and IL-21 by Th9 cells, thus increasing their anticancer properties. We will here review the mechanisms accounting for the ability of IL-1 cytokines to affect the differentiation of CD4 effector T cells with a focus on Th17 and Th9 cells. The physiopathological relevance of IL-1-driven effects on CD4 T cells will also be discussed.

Toll like Receptor 2 engagement on CD4+ T cells promotes TH9 differentiation and function

We have recently demonstrated that mycobacterial ligands engage Toll like receptor 2 (TLR2) on CD4⁺ T cells and up-regulate T-cell receptor (TCR) triggered Th1 responses in vitro and in vivo. To better understand the role of T-cell expressed TLR2 on CD4⁺ T-cell differentiation and function, we conducted a gene expression analysis of murine naïve CD4⁺ T-cells stimulated in the presence or absence of TLR2 co-stimulation. Unexpectedly, naïve CD4⁺ T-cells co-stimulated via TLR2 showed a significant up-regulation of Il9 mRNA compared to cells co-stimulated via CD28. Under TH9 differentiation, we observed up-regulation of TH9 differentiation, evidenced by increases in both percent of IL-9 secreting cells and IL-9 in culture supernatants in the presence of TLR2 agonist both in polyclonal and Ag85B cognate peptide specific stimulations. Under non-polarizing conditions, TLR2 engagement on CD4⁺ T-cells had minimal effect on IL-9 secretion and TH9 differentiation, likely due to a prominent effect of TLR2 signaling on IFN-γ secretion and TH1 differentiation. We also report that, TLR2 signaling in CD4⁺ T cells increased expression of transcription factors BATF and PU.1, known to positively regulate TH9 differentiation. These results reveal a novel role of T-cell expressed TLR2 in enhancing the differentiation and function of TH9 T cells.

Resolution of inflammation by interleukin-9-producing type 2 innate lymphoid cells

Inflammatory diseases such as arthritis are chronic conditions that fail to resolve spontaneously. While the cytokine and cellular pathways triggering arthritis are well defined, those responsible for the resolution of inflammation are incompletely characterized. Here we identified interleukin (IL)-9-producing type 2 innate lymphoid cells (ILC2s) as the mediators of a molecular and cellular pathway that orchestrates the resolution of chronic inflammation. In mice, the absence of IL-9 impaired ILC2 proliferation and activation of regulatory T (T_reg) cells, and resulted in chronic arthritis with excessive cartilage destruction and bone loss. In contrast, treatment with IL-9 promoted ILC2-dependent T_reg activation and effectively induced resolution of inflammation and protection of bone. Patients with rheumatoid arthritis in remission exhibited high numbers of IL-9⁺ ILC2s in joints and the circulation. Hence, fostering IL-9-mediated ILC2 activation may offer a novel therapeutic approach inducing resolution of inflammation rather than suppression of inflammatory responses.

Interleukin-9 Overexpression and Th9 Polarization Characterize the Inflamed Gut, the Synovial Tissue, and the Peripheral Blood of Patients With Psoriatic Arthritis

OBJECTIVE

To investigate the expression and tissue distribution of Th9-related cytokines in patients with psoriatic arthritis (PsA).

METHODS

Quantitative gene expression analysis of Th1, Th17, and Th9 cytokines was performed in intestinal biopsy samples obtained from patients with PsA, HLA-B27-positive patients with ankylosing spondylitis (AS), patients with Crohn's disease (CD), and healthy controls. Expression and tissue distribution of interleukin-23 (IL-23), IL-17, IL-22, IL-9, and IL-9 receptor (IL-9R) were evaluated by immunohistochemistry and confocal microscopy. Flow cytometry was used to study the frequency of Th9 cells among peripheral blood, lamina propria, and synovial fluid mononuclear cells. The functional relevance of IL-9R expression on epithelial cells was assessed in functional in vitro studies. Th9 cells in synovial tissue from patients with PsA were also studied.

RESULTS

Subclinical gut inflammation in PsA patients was characterized by a clear Th17 and Th22, but not Th1, polarized immune response. Unlike AS and CD, a strong and significant up-regulation of IL-9 was observed in PsA gut, especially among infiltrating mononuclear cells, high endothelial venules, and Paneth cells. IL-9-positive mononuclear cells were demonstrated to be in large part Th9 cells. IL-9 overexpression was accompanied by significant Paneth cell hyperplasia. Paneth cells strongly overexpressed IL-9R, and stimulation of epithelial cells, isolated from PsA patients, with IL-9 resulted in overexpression of α-defensin 5 and IL-23p19. Peripheral and synovial expansion of α4β7+ Th9 cells was also observed in patients with PsA. Increased expression of IL-9 and IL-9R was also found in synovial tissue.

CONCLUSION

Strong IL-9/Th9 polarization seems to be the predominant immunologic signature in patients in PsA.

Pro-inflammatory and anti-inflammatory T cells in giant cell arteritis

Giant cell arteritis is an autoimmune disease defined by explicit tissue tropism to the walls of medium and large arteries. Pathognomic inflammatory lesions are granulomatous in nature, emphasizing the functional role of CD4T cells and macrophages. Evidence for a pathogenic role of antibodies and immune complexes is missing. Analysis of T cell populations in giant cell arteritis, both in the tissue lesions and in the circulation, has supported a model of broad, polyclonal T cell activation, involving an array of functional T cell lineages. The signature of T cell cytokines produced by vasculitic lesions is typically multifunctional, including IL-2, IFN-γ, IL-17, IL-21, and GM-CSF, supportive for a general defect in T cell regulation. Recent data describing the lack of a lymph node-based population of anti-inflammatory T cells in giant cell arteritis patients offers a fresh look at the immunopathology of this vasculitis. Due to defective CD8+NOX2+ regulatory T cells, giant cell arteritis patients appear unable to curtail clonal expansion within the CD4T cell compartment, resulting in widespread CD4T cell hyperimmunity. Why unopposed expansion of committed CD4 effector T cells would lead to invasion of the walls of medium and large arteries needs to be explored in further investigations.

Osteoblasts support megakaryopoiesis through production of interleukin-9

Osteoblast-produced IL-9 supports megakaryopoiesis and platelet formation. IL-9 is a promising therapeutic agent for treatment of thrombocytopenia.

Systemic interleukin-9 in inflammatory bowel disease: Association with mucosal healing in ulcerative colitis

AIM

To evaluate circulating IL9 in inflammatory bowel disease and disease-associated anemia/cachexia and assess its potential as a mucosal healing marker.

METHODS

Serum IL9 as well as other cytokines (IL1β, IL6, IL13, IFNγ, TNFα, and VEGF-A) were determined in 293 individuals: 97 patients with Crohn’s disease (CD) and 74 with ulcerative colitis (UC) and in 122 apparently healthy controls. The clinical activity of CD and UC was expressed in terms of the Crohn’s Disease Activity Index (CDAI) and the Mayo Scoring System (MDAI), respectively, and the severity of bowel inflammation in UC patients was assessed using Mayo endoscopic score. Cytokine concentrations were measured by a flow cytometry-based method using Luminex xMAP^® technology. High-sensitive C-reactive protein concentrations (hsCRP) were determined in CD and UC patients using the enhanced immunoturbidimetric method.

RESULTS

Systemic IL9 was significantly lower in healthy individuals [9 pg/mL (95%CI: 8.2-10)] than in patients with inflammatory bowel disease (IBD): both inactive [14.3 pg/mL (11.9-19.9)] and active [27.6 pg/mL (24.5-32), P < 0.0001]. Cytokine concentrations were significantly higher in active CD [27.4 pg/mL (23.4-32.2)] and in active UC [32.7 pg/mL (27-38.9)] compared to inactive diseases [15.9 pg/mL (10.8-23.4) in CD and 19.4 pg/mL (13.9-27.1) in UC, P = 0.001]. IL9 correlated weakly with CDAI (ρ = 0.32, P = 0.003) and MDAI (ρ = 0.35, P = 0.002) and strongly with endoscopic inflammation in UC (ρ = 0.74, P < 0.0001). As a negative marker of mucosal healing (MH), IL9 had an accuracy superior to hsCRP and IL6 [97% (P < 0.0001), 67% (P = 0.071), and 55% (P = 0.525), respectively]. IL9 was significantly higher in cachectic IBD patients [30.25 pg/mL (24.4-37.5) vs 21.88 pg/mL (18-26.5), P = 0.026] and negatively correlated with hemoglobin concentrations (ρ = -0.27, P < 0.001). Multiple regression showed IL1β and IL13 to be the independent predictors of circulating IL9 in healthy individuals, IFNγ or IL6 in active and inactive UC, respectively, and IL13 and VEGF-A in both active and inactive CD.

CONCLUSION

The systemic IL9 level is higher in IBD and corresponds with endoscopic inflammation, suggesting its possible application as a negative marker of mucosal healing in UC.

Intestinal dysbiosis and innate immune responses in axial spondyloarthritis

PURPOSE OF REVIEW

Inflammatory innate and adaptive immune cell responses to commensal bacteria underlie the pathogenesis of human chronic inflammatory diseases. Intestinal dysbiosis has been described in patients with spondyloarthritis (SpA) and seems to be correlated with histologic and immunologic alterations. Purpose of this review is to discuss the relationship occurring between intestinal dysbiosis and innate immune responses in patients with axial SpA.

RECENT FINDINGS

Intestinal dysbiosis and differential activation of intestinal immune responses in patients with SpA have been demonstrated. Furthermore, innate cells that appear to be involved in the pathogenesis of SpA may control intestinal homeostasis through induction of apoptotic cell death and deletion of activated commensal bacteria-specific T cells.

SUMMARY

Although the evidence shows that dysbiosis occurs in SpA, it is not clear the role of dysbiosis in regulating innate immune responses in SpA. Relationships between cause and effect remain to be answered.

VIDEO ABSTRACT

http://links.lww.com/COR/A34.

Microbiota in T-cell homeostasis and inflammatory diseases

The etiology of disease pathogenesis can be largely explained by genetic variations and several types of environmental factors. In genetically disease-susceptible individuals, subsequent environmental triggers may induce disease development. The human body is colonized by complex commensal microbes that have co-evolved with the host immune system. With the adaptation to modern lifestyles, its composition has changed depending on host genetics, changes in diet, overuse of antibiotics against infection and elimination of natural enemies through the strengthening of sanitation. In particular, commensal microbiota is necessary in the development, induction and function of T cells to maintain host immune homeostasis. Alterations in the compositional diversity and abundance levels of microbiota, known as dysbiosis, can trigger several types of autoimmune and inflammatory diseases through the imbalance of T-cell subpopulations, such as Th1, Th2, Th17 and Treg cells. Recently, emerging evidence has identified that dysbiosis is involved in the progression of rheumatoid arthritis, type 1 and 2 diabetic mellitus, and asthma, together with dysregulated T-cell subpopulations. In this review, we will focus on understanding the complicated microbiota-T-cell axis between homeostatic and pathogenic conditions and elucidate important insights for the development of novel targets for disease therapy.

Characteristics of IL-9 induced by Schistosoma japonicum infection in C57BL/6 mouse liver

Liver granulomatous inflammation and fibrosis were the primary pathological changes observed during Schistosoma japonicum (S. japonicum) infection. In the present study, the characteristics of IL-9 were investigated in the liver of S. japonicum infection C57BL/6 mice. Immunofluorescence, qRT-PCR, and ELISA results demonstrated that the expression of IL-9 significantly increased after infection (P < 0.01). FACS results indicated that the peak of IL-9⁺ Th9 cells in the liver mononuclear cells appeared at the early phase of infection (week 5), except that Th9 cells, CD8⁺ Tc cells, NKT and γδT cells could secrete IL-9 in this model. Although IL-9 neutralization has a limited effect on liver granulomatous inflammation, it could decrease the level of fibrosis-associated factor, PC-III, in the serum of infected mice (P < 0.05). Taken together, our results indicated that IL-9 was an important type of cytokine involved in the progression of S. japonicum infection-induced hepatic damage.

Reciprocal regulation of the Il9 locus by counteracting activities of transcription factors IRF1 and IRF4

The T helper 9 (Th9) cell transcriptional network is formed by an equilibrium of signals induced by cytokines and antigen presentation. Here we show that, within this network, two interferon regulatory factors (IRF), IRF1 and IRF4, display opposing effects on Th9 differentiation. IRF4 dose-dependently promotes, whereas IRF1 inhibits, IL-9 production. Likewise, IRF1 inhibits IL-9 production by human Th9 cells. IRF1 counteracts IRF4-driven Il9 promoter activity, and IRF1 and IRF4 have opposing function on activating histone modifications, thus modulating RNA polymerase II recruitment. IRF1 occupancy correlates with decreased IRF4 abundance, suggesting an IRF1-IRF4-binding competition at the Il9 locus. Furthermore, IRF1 shapes Th9 cells with an interferon/Th1 gene signature. Consistently, IRF1 restricts the IL-9-dependent pathogenicity of Th9 cells in a mouse model of allergic asthma. Thus our study reveals that the molecular ratio between IRF4 and IRF1 balances Th9 fate, thus providing new possibilities for manipulation of Th9 differentiation.

IFN-γ signalling inhibits production of IL-9, the defining cytokine of the Th9 cell subset. Here the authors show that IFN-γ does this by driving IRF1 to compete with IRF4 for Il9 promoter binding and skewing these cells towards a Th1 phenotype, an effect that reduces asthmatic inflammation in mice.

Retroviral Transduction and Reporter Assay: Transcription Factor Cooperation in Th9 Cell Development

Naïve CD4+ T cells differentiate into different T helper subsets in response to specific cytokine environment and transcription factors. Th9 cells are induced in response to signals from cytokines, TGF-β and IL-4. Transcription factors that are downstream of these cytokines converge to drive the development of Th9 cells. Retroviral transduction allows the genetic modification in T cells thereby helping us to better understand the molecular mechanisms that control their development as well as function. In this chapter, an optimized protocol for retroviral transduction of murine Th9 cells as well as transient transfection of Th9 cells with luciferase reporter constructs is described.

Determining the Frequencies of Th9 Cells from Whole Blood

Th9 cells are a subset of CD4+ T cells producing the cytokine, IL-9. Th9 cells are increasingly recognized as being important player in allergy, autoimmunity, and antitumor responses. The polarization and expansion of Th9 cells requires the cytokines IL-4, TGF-β. In this chapter, we described the protocol for measuring Th9 frequencies using whole blood.

Metabolic Instruction of Immunity

Choices have consequences. Immune cells survey and migrate throughout the body and sometimes take residence in niche environments with distinct communities of cells, extracellular matrix, and nutrients that may differ from those in which they matured. Imbedded in immune cell physiology are metabolic pathways and metabolites that not only provide energy and substrates for growth and survival, but also instruct effector functions, differentiation, and gene expression. This review of immunometabolism will reference the most recent literature to cover the choices that environments impose on the metabolism and function of immune cells and highlight their consequences during homeostasis and disease.