Th9 cells: differentiation and disease

Immunological Processes Driving IgE Sensitisation and Disease Development in Males and Females

IgE sensitisation has increased significantly over the last decades and is a crucial factor in the development of allergic diseases. IgE antibodies are produced by B cells through the process of antigen presentation by dendritic cells, subsequent differentiation of CD4⁺ Th2 cells, and class switching in B cells. However, many of the factors regulating these processes remain unclear. These processes affect males and females differently, resulting in a significantly higher prevalence of IgE sensitisation in males compared to females from an early age. Before the onset of puberty, this increased prevalence of IgE sensitisation is also associated with a higher prevalence of clinical symptoms in males; however, after puberty, females experience a surge in the incidence of allergic symptoms. This is particularly apparent in allergic asthma, but also in other allergic diseases such as food and contact allergies. This has been partly attributed to the pro- versus anti-allergic effects of female versus male sex hormones; however, it remains unclear how the expression of sex hormones translates IgE sensitisation into clinical symptoms. In this review, we describe the recent epidemiological findings on IgE sensitisation in male and females and discuss recent mechanistic studies casting further light on how the expression of sex hormones may influence the innate and adaptive immune system at mucosal surfaces and how sex hormones may be involved in translating IgE sensitisation into clinical manifestations.

Cholesterol negatively regulates IL-9-producing CD8+ T cell differentiation and antitumor activity

CD8⁺ T cells can be polarized into IL-9-secreting (Tc9) cells. We previously showed that adoptive therapy using tumor-specific Tc9 cells generated stronger antitumor responses in mouse melanoma than classical Tc1 cells. To understand why Tc9 cells exert stronger antitumor responses, we used gene profiling to compare Tc9 and Tc1 cells. Tc9 cells expressed different levels of cholesterol synthesis and efflux genes and possessed significantly lower cholesterol content than Tc1 cells. Unique to Tc9, but not other CD8⁺ or CD4⁺ T cell subsets, manipulating cholesterol content in polarizing Tc9 cells significantly affected IL-9 expression and Tc9 differentiation and antitumor response in vivo. Mechanistic studies showed that IL-9 was indispensable for Tc9 cell persistence and antitumor effects, and cholesterol or its derivatives inhibited IL-9 expression by activating liver X receptors (LXRs), leading to LXR Sumoylation and reduced p65 binding to Il9 promoter. Our study identifies cholesterol as a critical regulator of Tc9 cell differentiation and function.

Th9 Cells: Probable players in ulcerative colitis pathogenesis

T lymphocytes represent an important part of adaptive immune system undertaking different functions to regulate immune responses. CD4+ T cells are the most important activator cells in inflammatory conditions. Depending on the type of induced cells and inflamed sites, expression and activity of different subtypes of helper T cells are changed. Recent studies have confirmed the existence of a new subset of helper T lymphocytes called Th9. Naive T cells can differentiate into Th9 subtypes if they are exposed simultaneously by interleukin (IL) 4 and transforming growth factor β and also secondary activation of a complicated network of transcription factors such as interferon regulatory factor 4 (IRF4) and Smads which are essential for adequate induction of this phenotype. Th9 cells specifically produce interleukin 9 and their probable roles in promoting intestinal inflammation are being investigated in human subjects and experimental models of ulcerative colitis (UC). Recently, infiltration of Th9 cells, overexpression of IL-9, and certain genes associated with Th9 differentiation have been demonstrated in inflammatory microenvironment of UC. Intestinal oversecretion of IL-9 protein is likely to break down epithelial barriers and compromise tolerance to certain commensal microorganisms which leads to inflammation. Th9 pathogenicity has not yet been adequately explored in UC and they are far from being considered as inflammatory cells in this milieu, therefore precise understanding the role of these newly identified cells in particular their potential role in gut pathogenesis may enable us to develop novel therapeutic approaches for inflammatory bowel disease. So, this article tries to discuss the latest knowledge on the above-mentioned field.

The tolerogenic role of IFN-γ

Due to its extremely pleiotropic nature, the complex effects of IFN-γ exerted both on immune and non-immune cell types still remain only partially understood. The longstanding view of IFN-γ as being a predominantly inflammatory cytokine is constantly challenged by increasing demonstrations of its direct or indirect regulatory roles. Interferon-γ can exert tolerogenic effects on both innate and adaptive immune cell types, promoting tolerance of various antigen-presenting cells, and augmenting function and differentiation of regulatory T cells, respectively. Its capacity to induce IDO-competence is not limited to immune cells but extends to other cell types such as mesenchymal stem cells, epithelial cells, and tumors. The pro-inflammatory role of IFN-γ in tumor immune surveillance can backfire by directly inducing inhibitory molecule expression, such as PDL-1, on tumor cells. With increasing knowledge regarding the role of different helper T cell subsets in certain autoimmune diseases, the once contradictory observations of disease attenuation by IFN-γ can now be explained by its opposing interplay with other effector cytokines, particularly IL-17. The paradoxically immunosuppressive role of IFN-γ is also becoming evident in the transplantation setting, and graft-versus-host-disease. In the present review, we will discuss the latest findings that help to elucidate this dual role of IFN-γ at a cellular level, and in various pathophysiological states.

IL-9: Function, Sources, and Detection

IL-9 is a pleiotropic cytokine produced in different amounts by a wide variety of cells including mast cells, NKT cells, Th2, Th17, Treg, ILC2, and Th9 cells. Th9 cells are considered to be the main CD4+ T cells that produce IL-9. IL-9 exerts its effects on multiple types of cells and different tissues. To date, its main role has been found in the immune responses against parasites and pathogenesis of allergic diseases such as asthma and bronchial hyperreactivity. Additionally, it induces the proliferation of hematologic neoplasias, including Hodgkin's lymphoma in humans. However, IL-9 also has antitumor properties in solid tumors such as melanoma. The objective of this review is to describe IL-9, its function, sources, and methods of detection.

Induction of specific T helper-9 cells to inhibit glioma cell growth

The effects of Staphylococcal enterotoxin B (SEB) on regulation of immune response have been recognized; whether SEB can enhance the effects of immunotherapy on glioma remains to be investigated. This study tests a hypothesis that administration with SEB enhances the effects of specific immunotherapy on glioma growth in mice. In this study, a glioma-bearing mouse model was developed by adoptive transfer with GL261 cells (a mouse glioma cell line). The mice were treated with the GL261 cell extracts (used as an Ag) with or without administration of SEB. We observed that treating glioma-bearing mice with the glioma Ag and SEB induced glioma-specific Th9 cells in both glioma tissue and the spleen. Treating CD4⁺ CD25⁻ T cells with SEB increased p300 phosphorylation, histone H3K4 acetylation at the interleukin (IL)-9 promoter locus, and increased the IL-9 transcriptional factor binding to the IL-9 promoter. Treating CD4⁺ CD25⁻ T cells with both SEB and glioma Ag induced glioma-specific Th9 cells. The glioma-specific Th9 cells induced glioma cell apoptosis in the culture. Treating the glioma-bearing mice with SEB and glioma Ag significantly inhibited the glioma growth. In conclusion, SEB plus glioma Ag immunotherapy inhibits the experimental glioma growth, which may be a novel therapeutic remedy for the treatment of glioma.

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.

Synovial IL-9 facilitates neutrophil survival, function and differentiation of Th17 cells in rheumatoid arthritis

Background

Role of Th9 cells and interleukin-9 (IL-9) in human autoimmune diseases such as psoriasis and ulcerative colitis has been explored only very recently. However, their involvement in human rheumatoid arthritis (RA) is not conclusive. Pathogenesis of RA is complex and involves various T cell subsets and neutrophils. Here, we aimed at understanding the impact of IL-9 on infiltrating immune cells and their eventual role in synovial inflammation in RA.

Methods

In vitro stimulation of T cells was performed by engagement of anti-CD3 and anti-CD28 monoclonal antibodies. Flow cytometry was employed for measuring intracellular cytokine, RORγt in T cells, evaluating apoptosis of neutrophils. ELISA was used for measuring soluble cytokine, Western blot analysis and confocal microscopy were used for STAT3 phosphorylation and nuclear translocation.

Results

We demonstrated synovial enrichment of Th9 cells and their positive correlation with disease activity (DAS28-ESR) in RA. Synovial IL-9 prolonged the survival of neutrophils, increased their matrix metalloprotienase-9 production and facilitated Th17 cell differentiation evidenced by induction of transcription factor RORγt and STAT3 phosphorylation. IL-9 also augmented the function of IFN-γ + and TNF-α + synovial T cells.

Conclusions

We provide evidences for critical role of IL-9 in disease pathogenesis and propose that targeting IL-9 may be an effective strategy to ameliorate synovial inflammation in RA. Inhibiting IL-9 may have wider impact on the production of pathogenic cytokines involved in autoimmune diseases including RA and may offer better control over the disease.

Electronic supplementary material

The online version of this article (10.1186/s13075-017-1505-8) contains supplementary material, which is available to authorized users.

Guidance of super-enhancers in regulation of IL-9 induction and airway inflammation

Xiao et al. demonstrate that formation of super-enhancers at Il9 locus is critical for robust IL-9 expression and Th9 cell induction, and assembly of Il9 super-enhancers is driven by OX40-mediated chromatin acetylation.

Th9 cells are prominently featured in allergic lung inflammation, but the mechanism that regulates IL-9 induction in T helper cells remains poorly defined. Here we demonstrate that formation of super-enhancers (SEs) is critical in robust induction of IL-9 and that assembly of the Il9 SEs in Th cells requires OX40-triggered chromatin acetylation. Mechanistically, we found that OX40 costimulation induces RelB expression, which recruits the histone acetyltransferase p300 to the Il9 locus to catalyze H3K27 acetylation. This allows binding of the SE factor Brd4 to organize assembly of the SE complex, which in turn drives robust IL-9 expression and Th9 cell induction. Thus, Th9 cells are strongly induced upon OX40 stimulation, and disruption of SEs abolished Th9 cell induction in vitro and inhibited Th9 cell–mediated allergic airway inflammation in vivo. Together, our data suggest that formation of SEs is essential in IL-9 expression and Th9 cell induction. These findings may have important clinical implications.

VEGF-C mediated enhancement of lymphatic drainage reduces intestinal inflammation by regulating IL-9/IL-17 balance and improving gut microbiota in experimental chronic colitis

BACKGROUND

Inflammation-associated lymphangiogenesis (IAL) induced by vascular endothelial growth factor (VEGF)-C/VEGF receptor-3 (VEGFR-3) pathway plays a crucial role in chronic intestinal inflammation. This study aimed to investigate the effects of VEGF-C mediated enhancement of lymphatic drainage on the intestinal inflammation in experimental chronic colitis (CC) and the potential mechanism was explored.

METHODS

Mouse CC model was established by three cycles of 2% DSS administration for 5 days following water administration for 5 days. CC mice were injected via the tail vein with AD-VEGF-C-EGFP (VEGF-C+DSS group) or AD-EGFP (AD-EGFP group) at the end of each cycle and animals in control group were given access to drinking water only. Disease activity index (DAI), lymphatic vessel density (LVD), colonic cytokines, Th9 cells (CD3⁺ cells) and CD68⁺ macrophage infiltration, and lymph flow were detected. Fresh feces were collected and processed for DNA extraction and MiSeq Illumina sequencing of V4 region of bacterial 16S rRNA gene. Alpha- and beta diversities and compositional differences at phylum and genus levels were determined in intestinal microbiota.

RESULTS

AD-VEGF-C treatment significantly reduced colon inflammation, elevated the increase in lymph drainage, decreased CD68⁺ macrophages and CD3⁺ T cells (Th9 cells), reduced IL-9, and increased IL-17 in colon mucosa when compared with DSS mice. In addition, VEGF-C treated mice showed significantly increased the abundance of Bacterioidate and decreased Firmicutes at phylum level in fecal samples.

CONCLUSION

VEGF-C improves intestinal inflammation by enhancing lymphatic drainage, reducing intestinal Th9 cells, regulating intestinal IL-9/IL-17 balance and increasing intestinal Bacterioidate abundance in CC mice.

Preferential susceptibility of Th9 and Th2 CD4+ T cells to X4-tropic HIV-1 infection

OBJECTIVE

The functional polarization of CD4 T cells determines their antimicrobial effector profile, but may also impact the susceptibility to infection with HIV-1. Here, we analyzed the susceptibility of CD4 T cells with different functional polarization to infection with X4 and R5-tropic HIV-1.

METHODS

CD4 T cells with a Th1, Th2, Th17, and Th9 polarization were subjected to in-vitro infection assays with X4, R5, or vesicular stomatitis virus-G protein-pseudotyped HIV-1. In addition, we sorted differentially polarized CD4 T-cell subsets from individuals treated with antiretroviral therapy and analyzed the tropism of viral env sequences.

RESULTS

Th9-polarized CD4 T cells and, to a lesser extent, Th2-polarized CD4 T cells expressed higher surface levels of CXCR4, and are more permissive to X4-tropic infection in vitro. In contrast, Th1 and Th17 CD4 T cells exhibited stronger surface expression of CCR5, and were more susceptible to infection with R5-tropic viruses. Correspondingly, the distribution of X4-tropic viral sequences in antiretroviral therapy-treated HIV-1-infected patients was biased toward Th9/Th2 cells, whereas R5-tropic sequences were more frequently observed in Th17 cells.

CONCLUSION

CD4 T-cell polarization is associated with a distinct susceptibility to X4 and R5-tropic HIV-1 infection.

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.

Increased levels of the T-helper 22-associated cytokine (interleukin-22) and transcription factor (aryl hydrocarbon receptor) in patients with periodontitis are associated with osteoclast resorptive activity and severity of the disease

BACKGROUND AND OBJECTIVE

Two new T-helper (Th) phenotypes have been recently described and named Th9 and Th22 lymphocytes; however, their role in the pathogenesis of periodontitis remains unclear. This study was aimed to assess whether Th9 and Th22 lymphocytes, through interleukin (IL)-9 and IL-22 production, respectively, are associated with the severity of periodontitis and bone resorption.

MATERIAL AND METHODS

Gingival crevicular fluid samples and biopsies were obtained from patients with moderate-to-advanced chronic periodontitis and gingivitis, and healthy controls. The levels for the Th9 and Th22-associated cytokines and master-switch transcription factors Spi-B and aryl hydrocarbon receptor (AhR) were quantified by enzyme-linked immunosorbent assay, real-time reverse-transcription quantitative polymerase chain reaction and flow cytometry. In addition, the osteoclast activity in response to tissue homogenates from periodontitis and healthy samples was analyzed quantifying the number of TRAP-positive cells and areas of bone resorption pits produced, in the presence or absence of recombinant human IL-22 and anti-IL-22 neutralization antibody.

RESULTS

Higher levels of IL-22 and AhR were detected in patients with periodontitis compared with gingivitis and healthy individuals. In addition, higher levels of IL-9 and Spi-B were detected in gingivitis patients compared with periodontitis and healthy individuals. In patients with periodontitis, a significant positive correlation was detected between secreted levels of IL-22 and clinical attachment level of the sampled periodontal pockets. When osteoclasts were exposed to tissue homogenates obtained from patients with periodontitis, higher levels of resorptive activity were observed as compared with the same cells exposed to tissue homogenates obtained from healthy individuals, and this increment was dependent on the presence and neutralization of IL-22.

CONCLUSION

Increased levels of IL-22 produced by Th22 lymphocytes are associated with the pathogenesis of periodontitis, in particular, with osteoclast resorptive activity and severity of disease.

HDAC4 is expressed on multiple T cell lineages but dispensable for their development and function

Histone deacetylation, reciprocally mediated by histone deacetylases (HDAC) and acetyltransferases, represents one major form of post-translational modification. Previous research indicates that HDACs play an essential regulatory role in the development of various immune cells. However, the specific function of individual HDACs remains largely unexplored. HDAC4, a member of class II HDACs, profoundly investigated in the nervous system, while the expression profile and function of HDAC4 in T cells are barely known. For the first time, we report here that HDAC4 is expressed in the multiple T cell lineages. Using T-cell-specific HDAC4-deficient mice, we discovered that lack of HDAC4 did not alter the frequencies of conventional T cells, invariant NKT (iNKT) cells or regulatory T cells within both the thymus and secondary lymphoid organs. Moreover, conventional T cells and iNKT cells from wild-type and HDAC4-deficient mice displayed no significant difference in cytokine production. In conclusion, our results imply that under steady stage, HDAC4 is not required for the development and function of multiple T cell lineages, including conventional T cells and iNKT cells.

MicroRNA mediated regulation of immunity against gram-negative bacteria

Evidence over the last couple decades has comprehensively established that short, highly conserved, non-coding RNA species called microRNA (miRNA) exhibit the ability to regulate expression and function of host genes at the messenger RNA (mRNA) level. MicroRNAs play key regulatory roles in immune cell development, differentiation, and protective function. Intrinsic host immune response to invading pathogens rely on intricate orchestrated events in the development of innate and adaptive arms of immunity. We discuss the involvement of miRNAs in regulating these processes against gram negative pathogens in this review.

Building conventions for unconventional lymphocytes

Falling between the classical characteristics of innate immune cells and adaptive T and B cells are a group of lymphocytes termed "unconventional." These cells express antigen-specific T or B cell receptors, but behave with innate characteristics. Well-known members of this group include the gamma-delta T cell and the Natural Killer T cell. Recent literature has greatly expanded scientific knowledge of unconventional lymphocytes, but key questions remain unresolved in the field, including why these cells have been maintained concurrently with conventional innate and adaptive immune cells. Here, we summarize current literature that suggests what their unique purposes may be, including specialized functions with the microbiota and in early development. From the consensus literature, we discuss where we see unconventional lymphocytes fit into the logical organization of the complete immune system.

Phosphatase wild-type p53-induced phosphatase 1 controls the development of TH9 cells and allergic airway inflammation

BACKGROUND

Allergic asthma is one of the most common diseases worldwide, resulting in a burden of diseases. No available therapeutic regimens can cure asthma thus far.

OBJECTIVE

We sought to identify new molecular targets for T_H9 cell-mediated allergic airway inflammation.

METHODS

Wild-type p53-induced phosphatase 1 (Wip1) gene knockout mice, Wip1 inhibitor-treated mice, and ovalbumin-induced allergic airway inflammation mouse models were used to characterize the roles of Wip1 in allergic airway inflammation. The induction of T_H cell subsets in vitro, real-time PCR, immunoblots, luciferase assays, and chromatin immunoprecipitation assays were used to determine the regulatory pathways of Wip1 in T_H9 differentiation.

RESULTS

Here we demonstrate that Wip1-deficient mice are less prone to allergic airway inflammation, as indicated by the decreased pathologic alterations in lungs. Short-term treatment with a Wip1-specific inhibitor significantly ameliorates allergic inflammation progression. Intriguingly, Wip1 selectively impaired T_H9 but not T_H1, T_H2, and T_H17 cell differentiation. Biochemical assays show that Wip1 deficiency increases c-Jun/c-Fos activity in a c-Jun N-terminal kinase-dependent manner and that c-Jun/c-Fos directly binds to Il9 promoter and inhibits Il9 transcription.

CONCLUSION

Wip1 controls T_H9 cell development through regulating c-Jun/c-Fos activity on the Il9 promoter and is important for the pathogenesis of allergic airway inflammation. These findings shed light on the previously unrecognized roles of Wip1 in T_H9 cell differentiation. The inhibitory effects of a Wip1 inhibitor on the pathogenesis of allergic airway inflammation can have important implications for clinical application of Wip1 inhibitors in allergy therapies.

Dynamics of Th9 cells and their potential role in immunopathogenesis of murine schistosomiasis

Background

Th1, Th2, Th17, Treg and Tfh cells play important roles in schistosomiasis. Th9 cells secrete IL-9 as a signature cytokine and contribute to several classes of inflammatory disease. However, the effects of Th9 cells in schistosomiasis are unknown. We aimed to explore the dynamic changes and potential roles of Th9 cells in the pathogenesis of hepatic egg granulomatous inflammation in mice infected with Schistosoma japonicum.

Methods

Twenty mice with S. japonicum infection and five normal controls (NC) were used as models. The average areas of egg granulomas were estimated by hematoxylin-eosin (H & E) staining. Hepatic IL-9 and transcription factor PU.1 levels were detected by immunohistochemistry. Flow cytometry techniques were used to analyze the proportions of Th9 cells. With the help of ELISA, serum levels of IL-9 were examined.

Results

The egg granulomas began to form from four weeks after infection and continued to develop. In parallel with the development of egg granulomas, the hepatic levels of IL-9 and PU.1 increased very slowly during the first four weeks post-infection and increased rapidly thereafter. Moreover, the proportions of splenic Th9 cells and levels of serum IL-9 had similar developmental trends with the egg granulomas.

Conclusion

The proliferation of Th9 cells and levels of IL-9 were significantly higher in S. japonicum-infected mice compared to NC. In addition, dynamic changes of Th9 and IL-9 were synchronous with the developmental trend of hepatic egg granulomatous inflammation, suggesting that Th9 cells might be a new subset in the pathogenesis of schistosomiasis.

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.

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.

Interleukin-9 and T helper type 9 cells in rheumatic diseases

Interleukin (IL)-9 is a 28-30 kDa monomeric glycosylated polypeptide belonging to the IL-7/IL-9 family of proteins that bind to a composite receptor consisting of the private receptor IL-9R and the IL-2 receptor, gamma (IL-2RG), a common gamma subunit shared by the receptors of many different cytokines. The IL-9R is expressed widely and IL-9 impacts a number of effector cells, such as effector T cells, B cells, innate lymphoid cells, mast cells, polymorphonuclear cells, epithelial cells and smooth muscle cells, playing an important role in regulating inflammatory immunity. The critical role of IL-9 in promoting cellular and humoral immune responses makes it an important focus of potential therapeutic interventions. Recently, a defined subset of T helper type cells, Th9 cells, has been identified by the potent production of IL-9. The involvement of the Th9 cell subset has been described in many types of inflammatory diseases, namely atopic diseases, helminth infections, experimental autoimmune encephalomyelitis and ulcerative colitis. In this review, we summarize the IL-9 biological activities, highlighting roles for IL-9 and Th9 cells in rheumatoid and psoriatic arthritis, systemic vasculitis, systemic lupus erythematosus and systemic sclerosis.

Overexpression and varied clinical significance of Th9 versus Th17 cells in distinct subtypes of oral lichen planus

OBJECTIVE

Oral lichen planus (OLP) presents with large numbers of T lymphocytes accumulating beneath the epithelium of the oral mucosa; however, its aetiology remains obscure. A potential role for an emerging novel T cell subset, Th9, in OLP has recently been suggested but remains to be clarified. The current aim was to investigate the expression and potential clinical significance of Th9 cells in distinct subtypes of OLP.

MATERIALS AND METHODS

Peripheral blood samples were collected from 41 OLP patients and 18 healthy controls (HCs). Flow cytometric analysis was used to detect the CD4+ T helper subset Th9 (IL-9⁺IL-17^-CD4⁺ Th cells) and Th17 (IL-9^-IL-17⁺CD4⁺ Th cells) expression levels.

RESULTS

Flow cytometry results showed significantly elevated levels of Th9 cells in reticular and erosive OLP compared to HCs. Th9 expression in erosive OLP was less than in reticular OLP, indicating that Th9 but not Th17 cells may play a predominant role in reticular disease. However, in erosive OLP patients, we found much higher levels of Th17 cells compared to reticular OLP patients and HCs, indicating that Th17 dominates in erosive OLP. Statistical analysis showed positive correlations of Th9 cells and Th17 cells in patients with reticular or erosive OLP but none in HCs.

CONCLUSIONS

Th9 and Th17 cells may take the predominant roles in reticular and erosive OLP respectively, and their numbers were positively correlated in reticular and erosive OLP patients. Elevated circulating Th9 cells may help maintain immune balance in OLP immunopathogenesis, which requires further investigation.

Epigenetics and allergy: from basic mechanisms to clinical applications

Allergic diseases are on the rise in the Western world and well-known allergy-protecting and -driving factors such as microbial and dietary exposure, pollution and smoking mediate their influence through alterations of the epigenetic landscape. Here, we review key facts on the involvement of epigenetic modifications in allergic diseases and summarize and critically evaluate the lessons learned from epigenome-wide association studies. We show the potential of epigenetic changes for various clinical applications: as diagnostic tools, to assess tolerance following immunotherapy or possibly predict the success of therapy at an early time point. Furthermore, new technological advances such as epigenome editing and DNAzymes will allow targeted alterations of the epigenome in the future and provide novel therapeutic tools.

Epigenetic Alterations in Cellular Immunity: New Insights into Autoimmune Diseases

Epigenetic modification is an additional regulator in immune responses as the genome-wide profiling somehow fails to explain the sophisticated mechanisms in autoimmune diseases. The effect of epigenetic modifications on adaptive immunity derives from their regulations to induce a permissive or negative gene expression. Epigenetic events, such as DNA methylation, histone modifications and microRNAs (miRNAs) are often found in T cell activation, differentiation and commitment which are the major parts in cellular immunity. Recognizing the complexity of interactions between epigenetic mechanisms and immune disturbance in autoimmune diseases is essential for the exploration of efficient therapeutic targets. In this review, we summarize a list of studies that indicate the significance of dysregulated epigenetic modifications in autoimmune diseases while focusing on T cell immunity.

Differential human Th22-lymphocyte response triggered by Aggregatibacter actinomycetemcomitans serotypes

OBJECTIVE

In Aggregatibacter actinomycetemcomitans, different serotypes have been described based on lipopolysaccharide (LPS) antigenicity. When T lymphocytes were stimulated with these serotypes, different patterns of T-helper (Th)1 and Th17-type of immune responses were reported. Recently, two new Th phenotypes have been described and named Th9 and Th22 lymphocytes; however, their role in the pathogenesis of periodontitis remains unclear. This study aimed to investigate the potential Th9 and/or Th22 lymphocyte responses when stimulated with autologous dendritic cells infected with different A. actinomycetemcomitans serotypes.

METHODS

Monocyte-derived dendritic cells and naïve CD4⁺ T lymphocytes were obtained from healthy donors and stimulated with different serotypes of A. actinomycetemcomitans at a multiplicity of infection MOI=10² or their purified LPS (10-50ng/ml). The levels for the Th9 and Th22-associated cytokines, as well as the transcription factor master-switch genes implied in their differentiation Spi-B and AhR, were quantified by qPCR and ELISA.

RESULTS

When stimulated with the serotype b of A. actinomycetemcomitans, higher levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α were detected in dendritic cells, as well as higher levels of IL-22 and AhR were detected in T lymphocytes, when compared with stimulation with the other serotypes.

CONCLUSIONS

The serotype b of A. actinomycetemcomitans has a higher capacity of trigger Th22-type of immune response in both dendritic cells and T lymphocytes. These data allow us to suggest that, when the serotype b of A. actinomycetemcomitans is a significant part of the subgingival biofilm, the Th22 polarization might be triggered within the periodontal lesion.

A mast cell-ILC2-Th9 pathway promotes lung inflammation in cystic fibrosis

T helper 9 (Th9) cells contribute to lung inflammation and allergy as sources of interleukin-9 (IL-9). However, the mechanisms by which IL-9/Th9 mediate immunopathology in the lung are unknown. Here we report an IL-9-driven positive feedback loop that reinforces allergic inflammation. We show that IL-9 increases IL-2 production by mast cells, which leads to expansion of CD25⁺ type 2 innate lymphoid cells (ILC2) and subsequent activation of Th9 cells. Blocking IL-9 or inhibiting CD117 (c-Kit) signalling counteracts the pathogenic effect of the described IL-9-mast cell-IL-2 signalling axis. Overproduction of IL-9 is observed in expectorates from cystic fibrosis (CF) patients, and a sex-specific variant of IL-9 is predictive of allergic reactions in female patients. Our results suggest that blocking IL-9 may be a therapeutic strategy to ameliorate inflammation associated with microbial colonization in the lung, and offers a plausible explanation for gender differences in clinical outcomes of patients with CF.

In patients with cystic fibrosis, IL-9 signalling is increased. The authors describe an inflammatory loop in which IL-9 produced by Th9 cells drives mast cells to produce IL-2, resulting in ILC2 cell activation, and show inhibition of this loop with blocking antibodies to IL-9 in a mouse model of pulmonary infection.

Prediction and Validation of Transcription Factors Binding Sites in the Il9 Locus

Over the past decade, multiple effector T cell subsets have been identified with varying differentiation conditions in the milieu as well as a broad diversity of cytokine expression. Interleukin-9 (IL-9) secreting T helper 9 (Th9) cells are the newest member of this family. T helper cell differentiation including Th9 cells appears to be an epigenetic phenomenon requiring the coordination of a large variety of transcription factors to reshape the chromatin landscape and generate various T helper phenotypes. This chapter details methods for both predicting and validating potential transcription factor binding sites as well as their downstream epigenetic effect using a variety of in silico and in vitro methods in both primary Th9 cells and IL-9-producing T cell lines.

IL-9 Production by Nonconventional T helper Cells

IL-9 is a pro-inflammatory cytokine implicated in certain immune-mediated diseases where chronic or acute inflammation of the mucosa plays an important role. Although initially described as being produced by what was then thought to be Th2 cells, it was later described that specialized lymphocyte populations are involved in IL-9 production. In addition to the classical Th9 effector (subset of CD4+ T cells), IL-9 is also produced by nonconventional lymphocytes, namely invariant natural killer T (iNKT) cells and innate lymphoid cells (ILCs). The identification of IL-9-producing cells by flow cytometry and cytokine measurements are pivotal for assigning and defining functional cellular phenotypes. In this chapter we provide methods for the in vitro polarization of IL-9-producing nonconventional lymphocytes and the best conditions for the detection of IL-9 production by intracellular staining.

A Method to In Vitro Differentiate Th9 Cells from Mouse Naïve CD4+ T Cells

CD4+ T helper cells with the ability to produce effector cytokines provide host protection by regulating immune responses against pathogens. In contrast, these cells are responsible for the development of various inflammatory disease if not regulated properly. Previous studies using naïve CD4+ T cell activation in vitro have shown the requirement of various cytokine combinations in addition to TCR activation to differentiate naïve CD4+ T cells into various effector T helper lineages. The recently discovered CD4+ T helper subset is IL-9-producing Th9 cells. Since Th9 cell differentiation in vitro is essential in understanding the molecular mechanism in regulating Th9 cell development, it is critical to develop a basic protocol in polarizing naïve CD4+ T cells to Th9 cells in vitro. Here we describe a simple method for Th9 cell culture conditions in vitro that can be used for other molecular analyses.

An Overview of the Innate and Adaptive Immune System in Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs) are thought to develop as a result of complex interactions between host genetics, the immune system and the environment including the gut microbiome. Although an improved knowledge of the immunopathogenesis of IBDs has led to great advances in therapy such as the highly effective anti-tumor necrosis factor class of medications, a significant proportion of patients with Crohn's disease and ulcerative colitis do not respond to anti-tumor necrosis factor antibodies. Further understanding of the different immune pathways involved in the genesis of chronic intestinal inflammation is required to help find effective treatments for IBDs. In this review, the role of the mucosal innate and adaptive immune system in IBD is summarized, highlighting new areas of discovery which may hold the key to identifying novel predictive or prognostic biomarkers and new avenues of therapeutic discovery.

Pro-Tumor and Anti-Tumor Functions of IL-17 and of TH17 Cells in Tumor Microenvironment

The current review reveals the seven subclasses of CD4+ T helper cells, i.e. Th1, Th2, Th9, Th17, Th22, regulatory T cells and Tfh, the cytokines produced by them and their role in tumor microenvironment. Main attention was paid to IL-17 and Th17 cells. IL-17-producing cells were described, among which were Treg17 cells and Tc17 cells. The transcription factors, engaged in the activation of Th17 cell differentiation were reviewed. It was shown that Th17 cells might possess regulatory functions in tumor microenvironments that directs toward immunosuppression. The reciprocity between Treg and Th17 cells is realized when the production of a large amount of TGF-β in tumors causes Treg cell differentiation, and the addition of IL-6 shifts the differentiation of naïve T cells to Th17 cells. The main pro-tumor role of IL-17 is the promotion of tumor angiogenesis through stimulation of fibroblasts and endothelial cells. The antitumor functions of IL-17 are associated with enhancement of cytotoxic activity of tumor specific CTL cells and with angiogenesis that provide channels through which immune cells might invade tumor and promote antitumor immunity.

The effects of vitamin B on the immune/cytokine network and their involvement in depression

Increasing evidence indicates that there are various interactions between the nervous system and the immune system, and that the immune system plays an important role in the pathogenesis of depression. Pro-inflammatory cytokines (such as IL-1, IL-6, TNF-α) have been implicated in the neurobiological manifestations of depression. The immune/cytokine network has a powerful influence on the brain. In addition, deficiency in B vitamins has been linked to depression. Hence, greater knowledge of how immune cells change in the presence of vitamin B derivatives could improve understanding of how immune changes may correlate with depression, all of which are discussed herein.

Th9 cells in inflammatory bowel diseases

Inflammatory bowel diseases are chronic, relapsing, immunologically mediated disorders of the gastrointestinal tract. Emerging evidence suggests a critical functional role of transcription factors and T cell-related cytokines in ulcerative colitis and Crohn's disease. Gut-residing T cells from patients with inflammatory bowel disease produce high amounts of IL-9. Experimental models of colitis highlighted that IL-9-producing T cells critically interfered with an intact barrier function of the intestinal epithelium by impacting cellular proliferation and tight junction molecules. The blockade of IL-9 was suited to significantly ameliorate the disease activity and severity in experimental models of inflammatory bowel disease thereby suggesting that targeting IL-9 might function as a novel targeted approach for therapy.

Increased circulating IL-9-producing CD8+ T cells are associated with eosinophilia and high FeNO in allergic asthmatics

Allergic asthma is a chronic airway disorder mediated by Th2 cells. It has been shown that IL-9-producing CD8⁺ cytotoxic T (Tc9) cells promote the subsequent onset of allergic airway inflammation in mice mediated by abnormal Th2 immunity. Whether Tc9 cells are associated with the immunopathogenesis of asthmatic patients remains unknown. In the present study, peripheral blood mononuclear cells (PBMCs) were separated by Ficoll-Hypaque gradient centrifugation from all subjects. The frequency of Tc9 cells was measured by flow cytometry. Serum IL-9 levels were assessed by enzyme-linked immunosorbent assay (ELISA). mRNA expression levels of IL-9, STAT6, and IRF4 in PBMCs from healthy controls and asthmatic patients were detected by reverse transcription-quantitative polymerase chain reaction. The results showed that the numbers of Tc9 cells in allergic asthmatics were significantly increased, compared with healthy controls (P<0.0001). Notably, IL-9 protein and mRNA levels were increased in allergic asthmatics and STAT6 and IRF4 mRNA levels were elevated, as compared with healthy controls. In addition, circulating numbers of Tc9 cells were positively correlated with blood eosinophil counts and fractioned exhaled nitric oxide (FeNO) levels in asthmatic patients. Moreover, the number of Tc9 cells and serum IL-9 levels in asthmatic patients were significantly decreased after treatment with glucocorticoids (P<0.05). These findings suggest that increased circulating Tc9 cells are associated with eosinophilia and high FeNO of allergic asthma, and that abnormal Tc9 immunity may contribute to the pathogenesis of allergic asthmatics.

TGF-β-induced phosphorylation of Akt and Foxo transcription factors negatively regulates induced regulatory T cell differentiation

Transforming growth factor-β (TGF-β) is a pivotal cytokine in the differentiation of regulatory T cells, and Foxo transcription factors positively regulate this process. On the other hand, the function of Foxo transcription factors is negatively regulated by PI3K/Akt signaling, which is activated by TGF-β in many types of cells; yet the role of TGF-β in Akt activity and its downstream substrates in CD4⁺ T cells, including Foxo transcription factors, remains to be determined. Herein, we demonstrate that TGF-β selectively induces Akt phosphorylation at Ser473 but not at Thr308 in a class I_A PI3K-dependent manner in CD4⁺ T cells, resulting in the phosphorylation and inhibition of Foxo transcription factors and negatively regulating the differentiation of induced regulatory T cells (iTregs). These observations reveal a novel negative regulatory mechanism involving Akt and Foxo transcription factors induced by TGF-β in the iTreg differentiation process.

Alkaline Cytosolic pH and High Sodium Hydrogen Exchanger 1 (NHE1) Activity in Th9 Cells

CD4⁺ T helper 9 (Th9) cells are a newly discovered Th cell subset that produce the pleiotropic cytokine IL-9. Th9 cells can protect against tumors and provide resistance against helminth infections. Given their pivotal role in the adaptive immune system, understanding Th9 cell development and the regulation of IL-9 production could open novel immunotherapeutic opportunities. The Na⁺/H⁺ exchanger 1 (NHE1; gene name Slc9α1)) is critically important for regulating intracellular pH (pH_i), cell volume, migration, and cell survival. The pH_i influences cytokine secretion, activities of membrane-associated enzymes, ion transport, and other effector signaling molecules such as ATP and Ca²⁺ levels. However, whether NHE1 regulates Th9 cell development or IL-9 secretion has not yet been defined. The present study explored the role of NHE1 in Th9 cell development and function. Th cell subsets were characterized by flow cytometry and pH_i was measured using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-acetoxymethyl ester (BCECF-AM) dye. NHE1 functional activity was estimated from the rate of realkalinization following an ammonium pulse. Surprisingly, in Th9 cells pH_i and NHE1 activity were significantly higher than in all other Th cell subsets (Th1/Th2/Th17 and induced regulatory T cells (iTregs)). NHE1 transcript levels and protein abundance were significantly higher in Th9 cells than in other Th cell subsets. Inhibition of NHE1 by siRNA-NHE1 or with cariporide in Th9 cells down-regulated IL-9 and ATP production. NHE1 activity, Th9 cell development, and IL-9 production were further blunted by pharmacological inhibition of protein kinase Akt1/Akt2. Our findings reveal that Akt1/Akt2 control of NHE1 could be an important physiological regulator of Th9 cell differentiation, IL-9 secretion, and ATP production.

Thymic and Postthymic Regulation of Naïve CD4(+) T-Cell Lineage Fates in Humans and Mice Models

Our understanding of how thymocytes differentiate into many subtypes has been increased progressively in its complexity. At early life, the thymus provides a suitable microenvironment with specific combination of stromal cells, growth factors, cytokines, and chemokines to induce the bone marrow lymphoid progenitor T-cell precursors into single-positive CD4⁺ and CD8⁺ T effectors and CD4⁺CD25⁺ T-regulatory cells (Tregs). At postthymic compartments, the CD4⁺ T-cells acquire distinct phenotypes which include the classical T-helper 1 (Th1), T-helper 2 (Th2), T-helper 9 (Th9), T-helper 17 (Th17), follicular helper T-cell (Tfh), and induced T-regulatory cells (iTregs), such as the regulatory type 1 cells (Tr1) and transforming growth factor-β- (TGF-β-) producing CD4⁺ T-cells (Th3). Tregs represent only a small fraction, 5–10% in mice and 1-2% in humans, of the overall CD4⁺ T-cells in lymphoid tissues but are essential for immunoregulatory circuits mediating the inhibition and expansion of all lineages of T-cells. In this paper, we first provide an overview of the major cell-intrinsic developmental programs that regulate T-cell lineage fates in thymus and periphery. Next, we introduce the SV40 immortomouse as a relevant mice model for implementation of new approaches to investigate thymus organogenesis, CD4 and CD8 development, and thymus cells tumorogenesis.

Synergistically increased ILC2 and Th9 cells in lung tissue jointly promote the pathological process of asthma in mice

In recent years, T helper (Th) 9 cells have been demonstrated to be key mediators in immune responses in asthmatic lungs, and innate lymphoid cells 2 (ILC2s) have been described as a novel type of innate immunocyte with the ability to enhance immunoglobulin E (IgE) production. However, the interaction between ILC2s and Th9 cells in the pulmonary system of a mouse model of asthma remains to be elucidated. In the present study, the response state of lung tissue with regards to Th9 and ILC2s in a mouse model of asthma was investigated by detecting Th9‑ and ILC2‑associated cytokine receptors. The present study also investigated the association between the expression levels of the cytokine receptors in lung tissue samples and the IgE levels in sera samples from mouse models of asthma. Results from the present study demonstrated that the frequency of ILC2s and Th9 cells was significantly increased in the lung tissue samples, indicating that a Th2-type immune response had occurred. In addition, high mRNA expression levels of RAR‑related orphan receptor α, interleukin 1 receptor‑like 1, transcription factor PU.1 and interleukin (IL)‑9 were observed. Furthermore, IL‑5Rα, IL‑13Rα2 and high‑affinity IgE receptor were increased in mouse models of asthma, and a positive association was observed between the expression levels of ILC2‑ or Th9‑associated receptors in tissue samples and IgE levels in the sera. This indicated that ILC2s and Th9 were in a state of polarization and may promote each other in the lung tissue of mouse models of asthma, and that the lung tissue was responding to the two types of cells via increased expression of receptors.

Serum Interleukin (IL)-9 and IL-10, but not T-Helper 9 (Th9) Cells, are Associated With Survival of Patients With Acute-on-Chronic Hepatitis B Liver Failure

CD4 T helper (Th) cells are reported to be essential for initiating and maintaining an effective immune response to hepatitis B virus (HBV) infection. Th9 cells are a new subset of CD4 Th cells that produce interleukin (IL)-9 and IL-10. The present study aimed to investigate the percentage of Th9 cells relative to the number of CD4 cells in peripheral blood. We also measured serum IL-9 and IL-10 levels in different stages of HBV infection and their relationship with progress and prognosis of liver disease. Whole blood samples from 111 patients with HBV infection, including 39 chronic hepatitis B (CHB), 25 HBV-liver cirrhosis (HBV-LC), 21 acute-on-chronic liver failure (ACLF) patients, and 26 healthy controls were collected. The percentage of Th9 cells and serum IL-9 and IL-10 levels were determined. There was no significant difference in the percentage of Th9 cells and serum IL-9 and IL-10 levels among different groups, nor were these related to hepatitis B e antigen status, complications of cirrhosis, inflammation index, or prognosis indexes. There was no change in the percentage of Th9 cells before and after antiviral treatment in CHB patients. There was no correlation of Th9 cells with survival of ACLF patients. However, IL-9 and IL-10 levels were significantly higher in the nonsurvived ACLF patients compared to survived ACLF patients. Furthermore, baseline IL-9 level predicted the prognosis of ACLF patients with 87.5% sensitivity and 61.5% specificity.Thus, our data indicate that Th9 cells were unlikely involved in the pathogenesis of HBV infection, but elevation in IL-9 and IL-10 may signal poor prognosis for ACLF.

IL-9 signaling as key driver of chronic inflammation in mucosal immunity

Recent studies have highlighted a crucial regulatory role of the cytokine IL-9 in driving immune responses in chronic inflammatory and autoimmune diseases at mucosal surfaces. IL-9 activates various types of immune and non-immune cells carrying the membrane bound IL-9R. IL-9 signaling plays a pivotal role in controlling the differentiation and activation of these cells by inducing the Jak/STAT pathway. In particular, IL-9 induces activation of T helper cells and affects the function of various tissue resident cells such as mast cells and epithelial cells in the mucosa. Importantly, recent findings suggest that blockade of IL-9 signaling is effective in treating experimental models of autoimmune and chronic inflammatory diseases such as inflammatory bowel diseases, allergic disorders such as food allergy and asthma. Thus, blockade of IL-9 and IL-9R signaling emerges as potentially novel approach for therapy of inflammatory diseases in the mucosal immune system.

E3 ubiquitin ligases as novel targets for inflammatory diseases

Ubiquitination is one of the post translational modifications which decide the fate of various proteins in the cells, by either directing them towards proteasomal degradation or participation in several cell signalling pathways. Recently, the role of ubiquitination has been unravelled in pathogenesis and progression of various diseases, where inflammation is critical, like obesity, insulin resistance, atherosclerosis, angiotensin-II induced cardiac inflammation and asthma. E3 ligases are known to be instrumental in regulation of the inflammatory cascade. This review focuses on the role of different E3 ligases in the development of inflammatory diseases and thus may help us to target these E3 ligases in future drug discovery to prevent inflammation.

IL-10- and TGFβ-mediated Th9 Responses in a Human Helminth Infection

Background

Th9 cells are a subset of CD4⁺ T cells that express the protoypical cytokine, IL-9. Th9 cells are known to effect protective immunity in animal models of intestinal helminth infections. However, the role of Th9 cells in human intestinal helminth infections has never been examined.

Methodology

To examine the role of Th9 cells in Strongyloidis stercoralis (Ss), a common intestinal helminth infection, we compared the frequency of Th9 expressing IL-9 either singly (mono-functional) or co-expressing IL-4 or IL-10 (dual-functional) in Ss-infected individuals (INF) to frequencies in uninfected (UN) individuals.

Principal Findings

INF individuals exhibited a significant increase in the spontaneously expressed and/or antigen specific frequencies of both mono- and dual-functional Th9 cells as well as Th2 cells expressing IL-9 compared to UN. The differences in Th9 induction between INF and UN individuals was predominantly antigen-specific as the differences were no longer seen following control antigen or mitogen stimulation. In addition, the increased frequency of Th9 cells in response to parasite antigens was dependent on IL-10 and TGFx since neutralization of either of these cytokines resulted in diminished Th9 frequencies. Finally, following successful treatment of Ss infection, the frequencies of antigen-specific Th9 cells diminished in INF individuals, suggesting a role for the Th9 response in active Ss infection. Moreover, IL-9 levels in whole blood culture supernatants following Ss antigen stimulation were higher in INF compared to UN individuals.

Conclusion

Thus, Ss infection is characterized by an IL-10- and TGFβ dependent expansion of Th9 cells, an expansion found to reversible by anti-helmintic treatment.

Strongyloides stercoralis is a common intestinal parasite affecting about 50–100 million people worldwide. It is characterized by a complex lifecycle involving both free- living and parasitic stages and the clinical manifestations range from asymptomatic infection to multi-organ failure. It has the propensity to cause disseminated disease and death in immunocompromised individuals. Therefore, an in depth understanding of the immune responses to this helminth parasite is warranted. However, what we know about the immunity to this infection is mostly derived from animal studies. Th9 cells are a subset of CD4+ T cells producing the cytokine—IL-9. Since Th9 cells are increasingly recognized as being important in immunity to intestinal infection with helminths, we examined the induction and regulation Th9 cell responses to Ss infection utilizing infected and uninfected individuals from an endemic area in India. We show that Ss infection is characterized by profound alterations in the Th9 compartment and that this response is mainly regulated by the cytokines—IL-10 and TGFβ. In addition, we also demonstrate that active infection is a pre-requisite for this regulation and anti-Ss treatment can dampen enhanced Th9 responses.