Activin A and TGF-β promote T(H)9 cell-mediated pulmonary allergic pathology

IL-33 induced airways inflammation is partially dependent on IL-9

Asthma is an inflammatory disease of the airways and numerous cytokines contribute to this pathogenesis. It is shown that challenge of airways with IL-33 induces asthma-like pathological changes in mice, but the possible downstream cytokines in this process remain to be characterised. To explore this, we compared changes in the airways of wildtype (WT) and IL-9 deficient mice challenged with IL-33. In line with previous report, per-nasal challenge of WT mice with IL-33 significantly increased the responsiveness of the airways along with infiltration of inflammatory cells, goblet cell hyperplasia, collagen deposition and smooth muscle hypertrophy, and the expression of cytokines compared with control group. Surprisingly, all of these pathological changes were significantly attenuated in IL-9 deficient mice following identical IL-33 challenge. These data suggest that IL-9 is one downstream cytokine relevant to the effects of IL-33 in asthmatic airways and consequently a potential therapeutic target for the treatment of asthma.

BATF3 is sufficient for the induction of Il9 expression and can compensate for BATF during Th9 cell differentiation

Th9 cells preferentially produce IL-9 and participate in allergic responses and asthma. Differentiation of Th9 cells is induced by IL-4 and TGF-β, and then the cells are amplified by OX40 signals. The transcription factors PU.1, IRF4, and BATF are required for Th9 differentiation. BATF3 is an AP-1 family transcription factor that is highly homologous to BATF; however, its role in Th9 cells is poorly defined. Here, we show that OX40 signaling induced the expression of Batf3 and that its overexpression in the presence or absence of OX40 signaling increased the expression of IL-9 in Th9 cells. BATF3 physically interacted with IRF4 and was bound to the Il9 locus. A transient reporter assay revealed that the BATF3–IRF4 complex induced Il9 promoter activity. BATF3 rescued Il9 expression and restored the capacity to induce the airway inflammation in Batf KO Th9 cells. Thus, BATF3 itself is sufficient for the induction of Th9 cell differentiation and can substitute for BATF during Th9 cell differentiation.

A protein that regulates gene expression in immune cells may contribute to airway inflammation in asthma and allergies. A subset of immune cells known as Th9 cells plays a prominent role in these respiratory disorders, and researchers led by Gap Ryol Lee at Sogang University in Seoul, South Korea, set out to characterize signaling mechanisms that promote Th9 production. They focused specifically on a protein called BATF3, which regulates genes responsible for maturation of a variety of other immune cell types, but whose role with regard to Th9 is poorly understood. They determined that BATF3 has a potent effect in terms of inducing Th9 cell activity, and can even take the place of another known Th9-inducing protein. These findings could assist in the development of treatments that keep airway-constricting inflammation in check.

T-Cell Differentiation to T Helper 9 Phenotype is Elevated by Extremely Low-Frequency Electromagnetic Fields Via Induction of IL-2 Signaling

Owing to the development of information technology and the electronics industry, and the increase in the use of electronic products, an increasing number of people are exposed to electromagnetic fields (EMFs) in daily life. There has been concern about the effects of EMFs on the human body. Th9 cells, which are characterized by the generation of interleukin-(IL-9), are a recently defined subset of T helper (Th) cells. In this study, we investigated the effect of extremely low-frequency (60 Hz) EMFs, such as those generated by household power sources, at 0.8 mT intensity on CD4⁺ T cells. The exposure of CD4⁺ T cells to such EMFs under Th9-polarizing conditions increased IL-9 secretion and gene expression of transcription factors that are important for Th9 development. The expression of GATA3 increased in the early stage, and the phosphorylation of STAT5 and STAT6, which regulate the expression of GATA3, increased. In addition, EMFs increased the expression of IL-2 by the T cells. In conclusion, the differentiation of CD4⁺ T cells to the Th9 phenotype was increased by exposure to extremely low-frequency EMFs, and this appeared to be dependent on the IL-2 signaling pathway. Furthermore, co-cultures of EMF-exposed Th9 cells and mast cells showed an increased expression of mast cell proteases, FcεR1α, and mast cell-derived inflammatory cytokines compared with co-cultures of non-EMF-exposed Th9 cells and mast cells. Our results suggest that EMFs enhance the differentiation of CD4⁺ T cells to the Th9 phenotype, resulting in mast cell activation and inflammation. Bioelectromagnetics. 2019;40:588-601. © 2019 Bioelectromagnetics Society.

Targeting NLRP3 Inflammasome Activation in Severe Asthma

Severe asthma (SA) is a chronic lung disease characterized by recurring symptoms of reversible airflow obstruction, airway hyper-responsiveness (AHR), and inflammation that is resistant to currently employed treatments. The nucleotide-binding oligomerization domain-like Receptor Family Pyrin Domain Containing 3 (NLRP3) inflammasome is an intracellular sensor that detects microbial motifs and endogenous danger signals and represents a key component of innate immune responses in the airways. Assembly of the NLRP3 inflammasome leads to caspase 1-dependent release of the pro-inflammatory cytokines IL-1β and IL-18 as well as pyroptosis. Accumulating evidence proposes that NLRP3 activation is critically involved in asthma pathogenesis. In fact, although NLRP3 facilitates the clearance of pathogens in the airways, persistent NLRP3 activation by inhaled irritants and/or innocuous environmental allergens can lead to overt pulmonary inflammation and exacerbation of asthma manifestations. Notably, administration of NLRP3 inhibitors in asthma models restrains AHR and pulmonary inflammation. Here, we provide an overview of the pathophysiology of SA, present molecular mechanisms underlying aberrant inflammatory responses in the airways, summarize recent studies pertinent to the biology and functions of NLRP3, and discuss the role of NLRP3 in the pathogenesis of asthma. Finally, we contemplate the potential of targeting NLRP3 as a novel therapeutic approach for the management of SA.

Interleukin-9 blockage reduces early hepatic granuloma formation and fibrosis during Schistosoma japonicum infection in mice

Hepatic fibrosis induced by schistosomes is regulated by a complex network of cytokines. T helper type 9 (Th9) cells are a new type of effector T helper cells, which mainly secrete the specific cytokine interleukin-9 (IL-9). Interleukin-9 has been shown to contribute to liver fibrosis in patients with chronic hepatitis B and in a mouse model due to carbon tetrachloride. However, the role of IL-9 in schistosomiasis fibrosis remains unknown. In this study, we investigated the roles of IL-9 in schistosomiasis through in vivo and in vitro studies. The in vivo studies found that neutralization of IL-9 reduced liver granulomatous inflammation and collagen deposition around parasite eggs. The in vitro studies found that the treatment of primary hepatic stellate cells with IL-9 induced a significant increase of collagen and α-smooth-muscle actin. Moreover, we also described the dynamics and relevance of IL-9 and IL-4 in mice infected with Schistosoma japonicum. We found that IL-9 might appear more quickly and at higher levels than IL-4. Hence, our findings indicated that IL-9 might play a role in regulating hepatic fibrosis in early-stage schistosomiasis and become a promising approach for regulating hepatic fibrosis caused by S. japonicum.

Activin-A in the regulation of immunity in health and disease

The TGF-β superfamily of cytokines plays pivotal roles in the regulation of immune responses protecting against or contributing to diseases, such as, allergy, autoimmunity and cancer. Activin-A, a member of the TGF-β superfamily, was initially identified as an inducer of follicle-stimulating hormone secretion. Extensive research over the past decades illuminated fundamental roles for activin-A in essential biologic processes, including embryonic development, stem cell maintenance and differentiation, haematopoiesis, cell proliferation and tissue fibrosis. Activin-A signals through two type I and two type II receptors which, upon ligand binding, activate their kinase activity, phosphorylate the SMAD2 and 3 intracellular signaling mediators that form a complex with SMAD4, translocate to the nucleus and activate or silence gene expression. Most immune cell types, including macrophages, dendritic cells (DCs), T and B lymphocytes and natural killer cells have the capacity to produce and respond to activin-A, although not in a similar manner. In innate immune cells, including macrophages, DCs and neutrophils, activin-A exerts a broad range of pro- or anti-inflammatory functions depending on the cell maturation and activation status and the spatiotemporal context. Activin-A also controls the differentiation and effector functions of Th cell subsets, including Th9 cells, T_FH cells, Tr1 Treg cells and Foxp3⁺ Treg cells. Moreover, activin-A affects B cell responses, enhancing mucosal IgA secretion and inhibiting pathogenic autoantibody production. Interestingly, an array of preclinical and clinical studies has highlighted crucial functions of activin-A in the initiation, propagation and resolution of human diseases, including autoimmune diseases, such as, systemic lupus erythematosus, rheumatoid arthritis and pulmonary alveolar proteinosis, in allergic disorders, including allergic asthma and atopic dermatitis, in cancer and in microbial infections. Here, we provide an overview of the biology of activin-A and its signaling pathways, summarize recent studies pertinent to the role of activin-A in the modulation of inflammation and immunity, and discuss the potential of targeting activin-A as a novel therapeutic approach for the control of inflammatory diseases.

IL-9-producing CD8+ T cells represent a distinctive subset with different transcriptional characteristics from conventional CD8+ T cells, and partially infiltrate breast tumors

Accumulating evidence suggests that IL-9 and IL-9-producing cells exert various roles in antitumor immunity. Our study examined the IL-9 production in CD8⁺ T cells from breast cancer patients as compared to healthy controls. IL-9 secretion was undetectable in CD8⁺ T cells ex vivo, but could be readily detected following anti-TCR or PMA + ionomycin stimulation, and was higher in breast cancer patients than in healthy controls. The capacity to express IL-9 was not universal to all CD8⁺ T cells, but was favored in IL-9R^high CD8⁺ T cells, which were also present in breast cancer patients at significantly higher frequency than in healthy controls. Interestingly, exogenous IL-9 could significantly increase the expression of both IL-9 and IL-9R in IL-9R^high, but not IL-9R^low, CD8⁺ T cells. IL-9R^high CD8⁺ T cells ex vivo presented lower expression of KLRG-1, PD-1, and Tim-3 than IL-9R^low CD8⁺ T cells. Additionally, IL-9R^high CD8⁺ T cells following anti-TCR and PMA + ionomycin stimulation presented higher IL-2 and IL-17 expression, and lower IFN-γ expression, than IL-9R^low CD8⁺ T cells. IL-9-expressing CD8⁺ T cells could be found in some, but not all, resected breast tumors. IL-9R expression, on the other hand, was readily present in CD8⁺ T cells, but with high variability from patient to patient. Patients with high intratumoral IL-9 expression also tended to present high IL-9R expression. Together, these data demonstrate that a transcriptionally distinctive IL-9-producing CD8⁺ T cell subset was elevated in breast cancer patients and could be found inside the tumor, with higher capacity to produce IL-2 and IL-17 and lower expression of inhibitory receptors.

Genetic evidence for the role of transforming growth factor-β in atopic phenotypes

New evidence in humans and mice supports a role for transforming growth factor-β (TGF-β) in the initiation and effector phases of allergic disease, as well as in consequent tissue dysfunction. This pleiotropic cytokine can affect T cell activation and differentiation and B cell immunoglobulin class switching following initial encounter with an allergen. TGF-β can also act on mast cells during an acute allergic episode to modulate the strength of the response, in addition to driving tissue remodeling following damage caused by an allergic attack. Accordingly, genetic disorders leading to altered TGF-β signaling can result in increased rates of allergic disease.

Th 9 cells in Behçet disease: Possible involvement of IL-9 in pulmonary manifestations

Behçet disease (BD) is a multisystemic disease some of whose manifestations are characterized by pulmonary involvements. The purpose of the study was to evaluate the level of T-helper type 9 (Th9) cells and the cytokine interleukin (IL)-9 in peripheral blood and in bronchoalveolar lavage (BAL) of patients with Behçet's disease (BD) affected by pulmonary manifestations. Nevertheless, until recently there have been no studies on its role in BD. The Th9 (CD4⁺IL-9⁺T) cell, transcription factor PU.1 and IL-9 mRNA levels, as well as serum and BAL IL-9 concentration, were measured in BD patients and healthy controls. The Th9 cell percentage and absolute number, PU.1 and IL-9 expression levels of BD patients were all increased significantly compared with the control group. Absolute number of Th9 cells was particularly increased in patients with active BD compared to inactive BD patients. The levels of IL-9 associated to Th9 expression depended on BD severity. These parameters were markedly expressed in the BAL of BD patients with pulmonary manifestations. IL-17 and the epithelial inflammatory cytokine TSLP were significantly correlated to IL-9 levels. This cytokine trio decreased in inactive BD patients after corticosteroïd treatment. In addition, IL-9 levels were correlated to CD4⁺ IL-9⁺ cells in BAL and in PBMCs. LPS stimulated PBMCs and macrophages induced increased secretion of IL-9 and the encoding transcription factors PU.1 and IRF4. In conclusion, the expansion of the Th9 cell subset, up-regulation of the PU.1 transcription factor and increased secretion of the IL-9 cytokine may contribute to the pathogenesis of BD, which may be supported by the increased release of IL-17 and TSLP. We provide evidence that Th9 T cells are increased in BD patients with pulmonary manifestations. This suggests an important role of IL-9 in the pathogenesis of BD particularly in patients suffering from lung involvement.

Th9 Cells in Allergic Disease

PURPOSES OF REVIEW

Th9 cells are recognized as a novel subset of effector T helper cells that preferentially produce IL-9. Here, we provide a current update on the reports related to the function of Th9 cells in allergic inflammatory diseases.

RECENT FINDINGS

The effector Th9 cells differentiating from naïve T helper cells have recently been identified. Because of accumulating findings of Th9 cells in many inflammatory diseases, including allergic diseases, diverse functions of Th9 cells in regulating immune responses have been suggested. Related reports indicate multiple sources of IL-9 besides Th9 cells and their association with the pathogenesis of allergic rhinitis, asthma, atopic dermatitis, contact dermatitis, and food allergy. More recently, elements of the epigenetic landscape involving in the regulation of IL-9 by Th9 cells have been identified to be the potential target for allergic inflammation. This review provides the most recent information about Th9 cells and their contribution in airway allergic disease, skin, and food allergy.

IL-4 together with IL-1β induces antitumor Th9 cell differentiation in the absence of TGF-β signaling

IL-9-producing CD4⁺ (Th9) cells are a subset of CD4⁺ T-helper cells that are endowed with powerful antitumor capacity. Both IL-4 and TGF-β have been reported to be indispensable for Th9 cell-priming and differentiation. Here we show, by contrast, that Th9 cell development can occur in the absence of TGF-β signaling. When TGF-β was replaced by IL-1β, the combination of IL-1β and IL-4 efficiently promoted IL-9-producing T cells (Th9^IL-4+IL-1β). Th9^{IL-4+ IL-1β} cells are phenotypically distinct T cells compared to classic Th9 cells (Th9^IL-4+TGF-β) and other Th cells, and are enriched for IL-1 and NF-κB gene signatures. Inhibition of NF-κB but not TGF-β-signaling negates IL-9 production by Th9^IL-4+IL-1β cells. Furthermore, when compared with classic Th9^IL-4+TGF-β cells, Th9^IL-4+IL-1β cells are less exhausted, exhibit cytotoxic T effector gene signature and tumor killing function, and exert a superior antitumor response in a mouse melanoma model. Our study thus describes an alternative pathway for Th9 cell differentiation and provides a potential avenue for antitumor therapies.

CD4⁺ helper T cells producing IL-9 (Th9) have been implicated in anti-tumor immunity, with Th9 differentiation inducible in vitro via IL-4 and TGFβ treatment. Here the authors show that replacing TGFβ with IL-1β induces a distinct IL-9⁺ CD4⁺ population that have strong cytotoxic and anti-tumor activity in preclinical mouse models.

[New protagonists in asthma pathophysiology]

Asthma is often associated with a Th2-type immune response with well-known cellular and molecular actors such as eosinophils, Th2 lymphocytes and associated cytokines such as interleukin-5 or IL-4. Nevertheless, some of the asthmatic patients show clinical manifestations and characteristics that do not correspond to the current pattern of the pathophysiology of asthma. Thus, recently new cellular and molecular actors in the development of asthma have been demonstrated in animal models and in humans. Among these are components of the innate immune system such as type 2 innate lymphoid cells or adaptive immune system such as Th9 lymphocytes. At the cellular level, the role of small G proteins in asthma is also highlighted as well as the role of major cytokines like IL-17 or those derived from the epithelium. A better knowledge of the physiopathology of asthma and the taking into account of these new actors allows the identification of new therapeutic targets for different endotypes of patients.

Novel cutaneous mediators of chemical allergy

Chemical allergy can manifest into allergic contact dermatitis and asthma and the importance of skin sensitization in both of these diseases is increasingly being recognized. Given the unique characteristics of chemical allergy, coupled with the distinct immunological microenvironment of the skin research is still unraveling the mechanisms through which sensitization and elicitation occur. This review first describes the features of chemical sensitization and the known steps that must occur to develop a chemical allergy. Next, the unique immunological properties of the skin - which may influence chemical sensitization - are highlighted. Additionally, mediators involved with the development of allergy are reviewed, starting with early ones - including the properties of haptens, skin integrity, the microbiome, the inflammasome, and toll-like receptors (TLR). Novel cellular mediators of chemical sensitization are highlighted, including innate lymphoid cells, mast cells, T-helper (T_H) cell subsets, and skin intrinsic populations including γδ T-cells and resident memory T-cells. Finally, this review discusses two epigenetic mechanisms that can influence chemical sensitization, microRNAs and DNA methylation. Overall, this review highlights recent research investigating novel mediators of chemical allergy that are present in the skin. It also emphasizes the need to further explore these mediators to gain a better understanding of what makes a chemical an allergen, and how best to prevent the development of chemical-induced allergic diseases.

Stimulation of histamine H4 receptors increases the production of IL-9 in Th9 polarized cells

BACKGROUND AND PURPOSE

Th9 cells represent a recently defined subset of CD4⁺ T-helper cells, characterized by a high production of IL-9. They are found at increased frequency in lesions of atopic dermatitis, where IL-9 is also elevated. As histamine is up-regulated in lesions of inflammatory skin diseases, we investigated the expression profile of histamine receptors and their functional role on Th9 cells.

EXPERIMENTAL APPROACH

Naïve CD4⁺ T-cells were purified from human peripheral blood mononuclear cells, using magnetic beads and further differentiated into Th9 cells. During differentiation, cells were additionally stimulated with histamine receptor agonists or left untreated. Histamine receptor expression as well as IL-9 production was measured.

KEY RESULTS

As proof of a successful differentiation, IL-9 production was measured at mRNA and protein level. Expression of mRNA for histamine H₁ , H₂ and H₄ receptors were up-regulated in differentiated Th9 cells compared to Th0 cells, while no mRNA for the H₃ receptor was detectable. Stimulation of Th9 cells with histamine significantly up-regulated expression of mRNA and protein for IL-9 . Experiments with specific histamine receptor agonists and antagonists revealed that this up-regulation was mediated by H₄ receptors.

CONCLUSIONS AND IMPLICATIONS

In summary, our study demonstrates a functional role for histamine H₄ receptors on Th9 cells, which might amplify the pro-inflammatory potency of these cells. Together with earlier studies on Th2 and Th17 cells, this study underlines the promising approach for the use of H₄ receptor antagonists in inflammatory and allergic diseases such as atopic dermatitis.

LINKED ARTICLES

This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Butyrate Attenuates Lung Inflammation by Negatively Modulating Th9 Cells

Th9 cells orchestrate allergic lung inflammation by promoting recruitment and activation of eosinophils and mast cells, and by stimulating epithelial mucus production, which is known to be mainly dependent on IL-9. These cells share developmental pathways with induced regulatory T cells that may determine the generation of one over the other subset. In fact, the FOXP3 transcription factor has been shown to bind il9 locus and repress IL-9 production. The microbiota-derived short-chain fatty acids (SCFAs) butyrate and propionate have been described as FOXP3 inducers and are known to have anti-inflammatory properties. While SCFAs attenuate lung inflammation by inducing regulatory T cells and suppressing Th2 responses, their effects on Th9 cells have not been addressed yet. Therefore, we hypothesized that SCFAs would have a protective role in lung inflammation by negatively modulating differentiation and function of Th9 cells. Our results demonstrated that butyrate is more effective than propionate in promoting FOXP3 expression and IL-9 repression. In addition, propionate was found to negatively impact in vitro differentiation of IL-13-expressing T cells. Butyrate treatment attenuated lung inflammation and mucus production in OVA-challenged mice, which presented lower frequency of lung-infiltrated Th9 cells and eosinophils. Both Th9 cell adoptive transfer and IL-9 treatment restored lung inflammation in butyrate-treated OVA-challenged mice, indicating that the anti-inflammatory effects of butyrate may rely on suppressing Th9-mediated immune responses.

Features and roles of T helper 9 cells and interleukin 9 in immunological diseases

T helper 9 (T_H9) cells are considered as newly classified helper T cells that have an important role in the regulation of immune responses. Since these cells preferentially produce IL-9, these cells are termed T_H9 cells. Recently, the role of T_H9 and its signature cytokine (IL-9) has been investigated in a wide range of diseases, including autoimmunity, allergy, infections, cancer and immunodeficiency. Herein, we review the most recent data concerning T_H9 cells and IL-9 as well as their roles in disease. These insights suggest that T_H9 cells are a future target for therapeutic intervention.

TGFβ Superfamily Members as Regulators of B Cell Development and Function-Implications for Autoimmunity

The TGFβ superfamily is composed of more than 33 growth and differentiation factors, including TGFβ1, β2, β3, BMPs, GDFs, nodal-related proteins, and activins. These members usually exert pleiotropic actions on several tissues and control multiple cellular processes, such as cell growth, cell survival, cell migration, cell fate specification, and differentiation, both during embryonic development and postnatal life. Although the effects of these factors on immune responses were elucidated long ago, most studies have been focused on the actions of TGFβs on T cells, as major regulators of adaptive immunity. In this review, we discuss new findings about the involvement of TGFβ superfamily members in the control of B cell development and function. Moreover, the potential contribution of TGFβ signaling to control B cell-mediated autoimmune diseases and its utility in the design of new therapies are also discussed.

The Key Role of TNF-TNFR2 Interactions in the Modulation of Allergic Inflammation: A Review

Tumor necrosis factor-alpha (TNF) is a pleiotropic cytokine, which is thought to play a major role in the pathogenesis of inflammatory diseases, including allergy. TNF is produced at the early stage of allergen sensitization, and then continues to promote the inflammation cascade in the effector phase of allergic reactions. Consequently, anti-TNF treatment has been proposed as a potential therapeutic option. However, recent studies reveal anti-intuitive effects of TNF in the activation and proliferative expansion of immunosuppressive Tregs, tolerogenic DCs and MDSCs. This immunosuppressive effect of TNF is mediated by TNFR2, which is preferentially expressed by immunosuppressive cells. These findings redefine the role of TNF in allergic reaction, and suggest that targeting TNF-TNFR2 interaction itself may represent a novel strategy in the treatment of allergy.

Deficient Follistatin-like 3 Secretion by Asthmatic Airway Epithelium Impairs Fibroblast Regulation and Fibroblast-to-Myofibroblast Transition

Bronchial epithelial cells (BECs) from healthy children inhibit human lung fibroblast (HLF) expression of collagen and fibroblast-to-myofibroblast transition (FMT), whereas asthmatic BECs do so less effectively, suggesting that diminished epithelial-derived regulatory factors contribute to airway remodeling. Preliminary data demonstrated that secretion of the activin A inhibitor follistatin-like 3 (FSTL3) by healthy BECs was greater than that by asthmatic BECs. We sought to determine the relative secretion of FSTL3 and activin A by asthmatic and healthy BECs, and whether FSTL3 inhibits FMT. To quantify the abundance of the total proteome FSTL3 and activin A in supernatants of differentiated BEC cultures from healthy children and children with asthma, we performed mass spectrometry and ELISA. HLFs were cocultured with primary BECs and then HLF expression of collagen I and α-smooth muscle actin (α-SMA) was quantified by qPCR, and FMT was quantified by flow cytometry. Loss-of-function studies were conducted using lentivirus-delivered shRNA. Using mass spectrometry and ELISA results from larger cohorts, we found that FSTL3 concentrations were greater in media conditioned by healthy BECs compared with asthmatic BECs (4,012 vs. 2,553 pg/ml; P = 0.002), and in media conditioned by asthmatic BECs from children with normal lung function relative to those with airflow obstruction (FEV1/FVC ratio < 0.8; n = 9; 3,026 vs. 1,922 pg/ml; P = 0.04). shRNA depletion of FSTL3 in BECs (n = 8) increased HLF collagen I expression by 92% (P = 0.001) and α-SMA expression by 88% (P = 0.02), and increased FMT by flow cytometry in cocultured HLFs, whereas shRNA depletion of activin A (n = 6) resulted in decreased α-SMA (22%; P = 0.01) expression and decreased FMT. Together, these results indicate that deficient FSTL3 expression by asthmatic BECs impairs epithelial regulation of HLFs and FMT.

Epigenetic regulation of T-helper cell differentiation, memory, and plasticity in allergic asthma

An estimated 300 million people currently suffer from asthma, which causes approximately 250 000 deaths a year. Allergen-specific T-helper (Th) cells produce cytokines that induce many of the hallmark features of asthma including airways hyperreactivity, eosinophilic and neutrophilic inflammation, mucus hypersecretion, and airway remodeling. Cytokine-producing Th subsets including Th1 (IFN-γ), Th2 (IL-4, IL-5, IL-13), Th9 (IL-9), Th17 (IL-17), Th22 (IL-22), and T regulatory (IL-10) cells have all been suggested to play a role in the development of asthma. Th differentiation involves genetic regulation of gene expression through the concerted action of cytokines, transcription factors, and epigenetic regulators. We describe how Th differentiation and plasticity is regulated by epigenetic histone and DNA modifications, with a focus on the regulation of histone methylation by members of the polycomb and trithorax complexes. In addition, we outline environmental influences that could influence epigenetic regulation of Th cells and discuss the potential to regulate Th plasticity and function through drugs targeting the epigenetic machinery. It is also becoming apparent that epigenetic regulation of allergen-specific memory Th cells may be important in the development and persistence of chronic allergies. Finally, we describe how epigenetic modifiers regulate cytokine memory in Th cells and describe recently identified hybrid, plastic, and pathogenic memory Th subsets the context of allergic asthma.

Activin A regulates activation of mouse neutrophils by Smad3 signalling

Activin A, a member of the transforming growth factor beta superfamily, acts as a pro-inflammatory factor in acute phase response, and influences the pathological progress of neutrophil-mediated disease. However, whether activin A can exert an effect on the activities of neutrophils remains unclear. In this study, we found that the release of activin A was enhanced from neutrophils of mouse when stimulated with lipopolysaccharide. Furthermore, neutrophils were not only the source of activin A but also the target cells in response to activin A, in which canonical activin signalling components existed, and levels of ACTRIIA, SMAD3 and p-SMAD3 proteins were elevated in activin A-treated neutrophils. Next, the role of activin A was determined in regulation of neutrophils activities. Our data revealed that activin A induced O₂⁻ release and reactive oxygen species production, promoted IL-6 release, and enhanced phagocytosis, but failed to attract neutrophils migrating across the trans-well membrane. Moreover, we found that effect of activin A on IL-6 release from the peritoneal neutrophils of mouse was significantly attenuated by in vivo Smad3 knockdown. In summary, these data demonstrate that activin A can exert an effect on neutrophils activation in an autocrine/paracrine manner through Smad3 signalling, suggesting that activin A is an important regulator of neutrophils.

CD96 expression determines the inflammatory potential of IL-9-producing Th9 cells

T helper type (Th) 9 cells demonstrate both pro- and antiinflammatory properties, pointing to a functional heterogeneity not examined so far. Applying single cell gene expression analysis of alloreactive Th9 cells, we revealed the existence of two major subsets, CD96^high and CD96^low Th9 cells, with strongly opposing inflammatory and, especially, colitis-inducing potential. Mechanistically, we found that CD96 controls cytokine and colitis-inducing potential of Th9 cells, providing strong evidence for an inhibitory role of CD96 in controlling CD4⁺ T-cell effector functions. Thus, interfering with CD96-mediated immune inhibition would be a promising approach in preventing Th9-mediated diseases, such as ulcerative colitis, or reinforcement of Th9-mediated immune control of tumors and infections.

Recent findings demonstrated proinflammatory functions of interleukin (IL)-9–producing T helper type (Th) 9 cells in the pathogenesis of intestinal bowel diseases (IBDs). However, also antiinflammatory properties have been ascribed to Th9 cells, pointing to a functional heterogeneity. To dissect the specific expression pattern and, especially, diversity of murine antigen-specific Th9 cells, we applied single cell transcription profiling. Th9 cells displayed reduced expression of typical activation markers, such as Cd40 ligand and Cd96, whereas expression of Cd25 and Cd83 was increased compared with other Th subsets. Importantly, we identified two subsets of Th9 cells differing above all in their CD96 expression. The heterogeneous CD96 expression was specific for Th9 cells and not observed for other Th subtypes, such as Th1 cells. Lower CD96 expression was also observed in human IL-9⁺ compared with IFN-γ⁺ T cells. Although Il9 was highly transcribed by all Th9 cells, IL-9 mRNA and protein expression was increased in CD96^low cells. Transfer of CD96^low Th9 cells into recombination activating gene 1-deficient (Rag1^−/−) mice caused severe weight loss, intestinal and colonic inflammation, and destruction of allogeneic skin grafts and thus showed high inflammatory potential. This was associated with their expansion and tissue accumulation. Contrastingly, CD96^high Th9 cells did not cause colitis and showed reduced expansion and migratory potential. Blockade of CD96 completely restored the expansion and inflammatory properties of CD96^high Th9 cells. Collectively, our data suggest an inhibitory role for the cosignaling receptor CD96 in Th9 cells, raising new opportunities in the treatment of IL-9–associated inflammations such as IBD.

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.

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.

mTORC2 controls Th9 polarization and allergic airway inflammation

BACKGROUND

T helper type 9 (Th9) cells, a subpopulation of CD4⁺ T cells, play a critical role in the pathogenesis of allergic airway inflammation. However, it remains unknown whether mTORC2 regulates Th9 differentiation or function during allergic inflammation.

METHODS

T-cell-specific Rictor-deficient mice, a mouse model of allergic airway inflammation induced by ovalbumin (OVA) sensitization and a mouse model of adoptive transfer of induced Th9 cells, were used to address the roles of mTORC2 in the pathogenesis of allergic airway inflammation. The in vitro Th9 induction, multiple colors flow cytometry, real-time PCR, and Western blots were used to investigate the molecular effects of mTORC2 in Th9 induction.

RESULTS

The differentiation of naïve CD4⁺ T cells into Th9 cells was significantly diminished in the absence of Rictor, the core component of mTORC2. Using a mouse model of allergic airway inflammation induced by OVA sensitization, T-cell-specific Rictor-deficient mice show much less severe allergic airway inflammation characterized by decreased pathological alterations and fibrosis of the lungs, which was accompanied with reduced Th9 differentiation and infiltration. Importantly, the isolated Rictor-deficient Th9 cells mediate less severe allergic pathogenesis upon adoptive transfer. Rictor deficiency impairs Th9 cell differentiation by reducing IRF4 expression rather than affecting Foxo1/Foxo3a transcriptional activity, which is likely due to decreased Akt and/or STAT6 activation.

CONCLUSIONS

These findings uncover a novel role of mTORC2 in Th9 cell differentiation and may have important implications for therapeutic intervention of allergic diseases.

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.

IL-9 and Th9 cells in health and diseases-From tolerance to immunopathology

CD4+ T cells have the capacity to differentiate into various T helper (Th) cell subsets after activation, and by acquiring distinct cytokine profiles and effector functions, they regulate the nature as well as the outcomes of immune responses. Th9 cells are a relatively new member in the Th cell family. The signature cytokine for Th9 cells is IL-9, a cytokine in the IL-2Rγc-chain family. Over the past few years, there has been an explosion of knowledge on the roles of Th9 cells in immunity and immunopathology, but the exact mechanisms in the control of Th9 cells remain poorly defined. This apparent paradox presents both challenges and opportunities. Here we review recent advances in our understanding of the fundamental biology of IL-9 and Th9 cells, highlighting the challenges and unanswered questions in the field. We also discuss potential opportunities in targeting Th9 cells for therapeutic purposes in the clinic.

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.

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.

Activin-A co-opts IRF4 and AhR signaling to induce human regulatory T cells that restrain asthmatic responses

Type 1 regulatory T (Tr1) cells play a pivotal role in restraining human T-cell responses toward environmental allergens and protecting against allergic diseases. Still, the precise molecular cues that underlie their transcriptional and functional specification remain elusive. Here, we show that the cytokine activin-A instructs the generation of CD4⁺ T cells that express the Tr1-cell-associated molecules IL-10, inducible T-Cell costimulator (ICOS), lymphocyte activation gene 3 protein (LAG-3), and CD49b, and exert strongly suppressive functions toward allergic responses induced by naive and in vivo-primed human T helper 2 cells. Moreover, mechanistic studies reveal that activin-A signaling induces the activation of the transcription factor interferon regulatory factor (IRF4), which, along with the environmental sensor aryl hydrocarbon receptor, forms a multipartite transcriptional complex that binds in IL-10 and ICOS promoter elements and controls gene expression in human CD4⁺ T cells. In fact, IRF4 silencing abrogates activin-A-driven IL10 and ICOS up-regulation and impairs the suppressive functions of human activin-A-induced Tr1-like (act-A-iTr1) cells. Importantly, using a humanized mouse model of allergic asthma, we demonstrate that adoptive transfer of human act-A-iTr1 cells, both in preventive and therapeutic protocols, confers significant protection against cardinal asthma manifestations, including pulmonary inflammation. Overall, our findings uncover an activin-A-induced IRF4-aryl hydrocarbon receptor (AhR)-dependent transcriptional network, which generates suppressive human Tr1 cells that may be harnessed for the control of allergic diseases.

T regulatory cell mediated immunotherapy for solid organ transplantation: A clinical perspective

T regulatory cells (Tregs) play a vital role in suppressing heightened immune responses, and thereby promote a state of immunological tolerance. Tregs modulate both innate and adaptive immunity, which make them a potential candidate for cell-based immunotherapy to suppress uncontrolled activation of graft specific inflammatory cells and their toxic mediators. These grafts specific inflammatory cells (T effector cells) and other inflammatory mediators (Immunoglobulins, active complement mediators) are mainly responsible for graft vascular deterioration followed by acute/chronic rejection. Treg mediated immunotherapy is under investigation to induce allospecific tolerance in various ongoing clinical trials in organ transplant recipients. Treg immunotherapy is showing promising results but the key issues regarding Treg immunotherapy are not yet fully resolved including their mechanism of action, and specific Treg cell phenotype responsible for a state of tolerance. This review highlights the involvement of various subsets of Tregs during immune suppression, novelty of Tregs functions, effects on angiogenesis, emerging technologies for effective Treg expansion, plasticity and safety associated with clinical applications. Altogether this information will assist in designing single/combined Treg mediated therapies for successful clinical trials in solid organ transplantations.

Th9 Cells: New Member of T Helper Cell Family

T Helper cells (CD4+ T cells) constitute one of the key arms of adaptive immune responses. Differentiation of naïve CD4+ T cells into multiple subsets ensure a proper protection against multitude of pathogens in immunosufficient individual. After differentiation, T helper cells secrete specific cytokines that are critical to provide immunity against various pathogens. The recently discovered Th9 cells secrete the pleiotropic cytokine, IL-9. Although IL-9 was cloned more than 25 years ago and characterized as a Th2 cell-specific cytokine, not many studies were carried out to define the function of IL-9. This cytokine has been demonstrated to act on multiple cell types as a growth factor. After the discovery of Th9 cells as an abundant source of IL-9, renewed focus has been generated. In this chapter, I discuss the biology and development of IL-9-secreting Th9 cells. Furthermore, I highlight the role of Th9 cells and IL-9 in health and diseases.

Role of Regulatory Cells in Oral Tolerance

The immune system is continuously exposed to great amounts of different antigens from both food and intestinal microbes. Immune tolerance to these antigens is very important for intestinal and systemic immune homeostasis. Oral tolerance is a specific type of peripheral tolerance induced by exposure to antigen via the oral route. Investigations on the role of intestinal immune system in preventing hypersensitivity reactions to innocuous dietary and microbial antigens have been intensively performed during the last 2 decades. In this review article, we discuss how food allergens are recognized by the intestinal immune system and draw attention to the role of regulatory T (Treg) and B (Breg) cells in the establishment of oral tolerance and tolerogenic features of intestinal dendritic cells. We also emphasize the potential role of tonsils in oral tolerance induction because of their anatomical location, cellular composition, and possible usage to develop novel ways of specific immunotherapy for the treatment of allergic diseases.

Anti-Interleukin-9 Antibody Increases the Effect of Allergen-Specific Immunotherapy in Murine Allergic Rhinitis

Purpose

Interleukin (IL)-9 induces allergic responses; however, the roles of anti-IL-9 antibody in the induction of tolerance remain unclear. This study investigated the effects of anti-IL-9 antibody on oral tolerance (OT) in a mouse model of allergic rhinitis (AR).

Methods

BALB/c mice were divided into 4 groups: the control, AR, OT, and OT with anti-IL-9 antibody (OT+IL9AB) groups. Ovalbumin (OVA) was used for sensitization and challenge. Mice in the OT and OT+IL9AB groups were fed OVA for immunotherapy. During immunotherapy, OT+IL9AB mice were injected with anti-IL-9 antibody. Allergic symptoms, tissue eosinophil counts, and serum OVA-specific immunoglobulin E (IgE) were measured. The mRNA expressions of cytokines and transcription factors of T cells of nasal mucosa were determined by real-time polymerase chain reaction (PCR). The protein levels of GATA3, ROR-γt, and Foxp3 in nasal mucosa were determined by Western blot. CD4⁺CD25⁺Foxp3⁺ T cells in the spleen were analyzed by flow cytometry.

Results

Administration of anti-IL-9 antibody decreased allergic symptoms, OVA-specific IgE levels, and eosinophil counts. In addition, it inhibited T-helper (Th) 2 responses, but had no effect on Th1 responses. Protein levels of ROR-γt and mRNA levels of PU.1 and ROR-γt were reduced by anti-IL-9 antibody. Anti-IL-9 antibody increased Foxp3 and IL-10 mRNA expression, Foxp3 protein, and induction of CD4⁺CD25⁺Foxp3⁺ T cells.

Conclusions

Anti-IL-9 antibody decreased allergic inflammation through suppression of Th2 and Th17 cells. Anti-IL-9 antibody enhanced the tolerogenic effects of regulatory T cells. These results suggest that anti-IL-9 antibody might represent a potential therapeutic agent for allergen immunotherapy in patients with uncontrolled allergic airway disease.

IL-9-producing cells in the development of IgE-mediated food allergy

Food allergy is a harmful immune reaction driven by uncontrolled type 2 immune responses. Considerable evidence demonstrates the key roles of mast cells, IgE, and TH2 cytokines in mediating food allergy. However, this evidence provides limited insight into why only some, rather than all, food allergic individuals are prone to develop life-threatening anaphylaxis. Clinical observations suggest that patients sensitized to food through the skin early in life may later develop severe food allergies. Aberrant epidermal thymic stromal lymphopoietin and interleukin (IL) 33 production and genetic predisposition can initiate an allergic immune response mediated by dendritic cells and CD4+TH2 cells in inflamed skin. After allergic sensitization, intestinal IL-25 and food ingestion enhance concerted interactions between type 2 innate lymphoid cells (ILC2s) and CD4+TH2 cells, which perpetuate allergic reactions from the skin to the gut. IL-4 and cross-linking of antigen/IgE/FcεR complexes induce emigrated mast cell progenitors to develop into the multi-functional IL-9-producing mucosal mast cells, which produce prodigious amounts of IL-9 and mast cell mediators to drive intestinal mastocytosis in an autocrine loop. ILC2s and TH9 cells may also serve as alternative cellular sources of IL-9 to augment the amplification of intestinal mastocytosis, which is the key cellular checkpoint in developing systemic anaphylaxis. These findings provide a plausible view of how food allergy develops and progresses in a stepwise manner and that atopic signals, dietary allergen ingestion, and inflammatory cues are fundamental in promoting life-threatening anaphylaxis. This information will aid in improving diagnosis and developing more effective therapies for food allergy-triggered anaphylaxis.

Allergic Inflammation and Atopic Disease: Role of Th9 Cells

IL-9-producing T helper cells (Th9) have recently emerged as an important T cell subset contributing to the pathogenicity of allergic diseases. Here, we describe the role of Th9 cells in allergic inflammation and provide detailed protocols to characterize IL-9-producing T cells and analyze OVA-specific IL-9 production in allergic lung diseases using a mouse model of OVA-induced chronic allergic lung inflammation.

Th9 and other IL-9-producing cells in allergic asthma

Allergic asthma is a worldwide increasing chronic disease of the airways which affects more than 300 million people. It is associated with increased IgE, mast cell activation, airway hyperresponsiveness (AHR), mucus overproduction and remodeling of the airways. Previously, this pathological trait has been associated with T helper type 2 (Th2) cells. Recently, different CD4⁺ T cell subsets (Th17, Th9) as well as cells of innate immunity, like mast cells and innate lymphoid cells type 2 (ILC2s), which are all capable of producing the rediscovered cytokine IL-9, are known to contribute to this disease. Regarding Th9 cells, it is known that naïve T cells develop into IL-9-producing cells in the presence of interleukin-4 (IL-4) and transforming growth factor beta (TGFβ). Downstream of IL-4, several transcription factors like signal transducer and activator of transcription 6 (STAT6), interferon regulatory factor 4 (IRF4), GATA binding protein 3 (GATA3), basic leucine zipper transcription factor, ATF-like (BATF) and nuclear factor of activated T cells (NFAT) are activated. Additionally, the transcription factor PU.1, which is downstream of TGFβ signaling, also seems to be crucial in the development of Th9 cells. IL-9 is a pleiotropic cytokine that influences various distinct functions of different target cells such as T cells, B cells, mast cells and airway epithelial cells by activating STAT1, STAT3 and STAT5. Because of its pleiotropic functions, IL-9 has been demonstrated to be involved in several diseases, such as cancer, autoimmunity and other pathogen-mediated immune-regulated diseases. In this review, we focus on the role of Th9 and IL-9-producing cells in allergic asthma.

Activin A and follistatin in patients with asthma. Does severity make the difference?

BACKGROUND AND OBJECTIVE

Activin A is a pleiotropic cytokine holding a fundamental role in inflammation and tissue remodelling. Follistatin can modulate the bioactivity of activin. We aimed to measure activin A and follistatin in sputum supernatants and bronchoalveolar lavage (BAL) of asthmatic patients and to determine the possible associations with severity as well as with inflammatory and remodelling indices.

METHODS

A total of 58 asthmatic patients (33 with severe refractory asthma (SRA)) and 10 healthy controls underwent sputum induction for % cells, activin A, follistatin, eosinophilic cationic protein (ECP), transforming growth factor beta 1 (TGF-β1), IL-13 and IL-8 measurements. In 22 asthmatic patients, BAL and bronchial biopsies were also performed for the assessment of the above-mentioned variables, measurement of remodelling indices and immunostaining for different activin A receptors.

RESULTS

Sputum activin A (pg/mL) was higher in patients with SRA (median (interquartile ranges): 76 (33-185)) compared to mild-to-moderate asthma (44 (18-84); P = 0.005), whereas follistatin did not differ between the two groups. BAL activin A (pg/mL) was higher in patients with SRA compared to those with mild-to-moderate disease. A significant association was observed between activin A and TGF-β1, eosinophils in sputum and/or in BAL, while reticular basement membrane (RBM) thickness was significantly associated with BAL activin levels only. No difference in immunostaining for activin receptor type IB was observed between patients with SRA and those with mild-to-moderate asthma.

CONCLUSION

Sputum and BAL levels of activin A are higher in SRA. The association of activin A with TGF-β1, eosinophils and RBM thickness may indicate a role of this cytokine in the inflammatory and remodelling process in SRA.

Allergen-Induced IL-6 Regulates IL-9/IL-17A Balance in CD4+ T Cells in Allergic Airway Inflammation

IL-9-secreting Th9 cells have been considered to play a pivotal role in the pathogenesis of atopic diseases. To what extent IL-9-producing cells are induced or regulated by sensitization with naturally occurring allergens is not yet clear. Naturally occurring allergens are capable of inducing IL-6 production in dendritic cells (DCs). Whether allergen-induced IL-6 supports a Th9 subtype by increasing IL-9 production, as observed in in vitro studies, or rather favors Th17 differentiation is not finally resolved. Therefore, in the present study we have investigated the impact of IL-6 on the Th9/Th17 balance depending on the predominant cytokine milieu and, additionally, in vivo using a DC-driven murine asthma model. In vitro, IL-6 increases Th9 cells under strong IL-4 and TGF-β activation, whereas under moderate IL-4 and TGF-β activation the presence of IL-6 shifts naive CD4(+) cells to Th17 cells. To induce allergic airway inflammation, OVA-pulsed DCs from IL-6-deficient or wild-type donors were adoptively transferred into BALB/c mice. Recipients receiving IL-6-producing wild-type DCs showed a significant decrease of Th9- and IL-4-producing Th2 cells but an increase of Th17 cells in lung tissue in comparison with recipients sensitized with IL-6-deficient DCs. Our data suggest that the IL-6-mediated reduction of Th2-related IL-4 leads to a decline of the Th9 immune response and allows Th17 differentiation.

Mycobacterium vaccae Nebulization Can Protect against Asthma in Balb/c Mice by Regulating Th9 Expression

Asthma is a heterogeneous disease characterized by chronic airway inflammation. CD4(+) T-helper 9 (Th9) cells are closely linked to asthma, helping to regulate inflammation and immunity. Epidemiological studies showed that mycobacteria infections are negatively associated with asthma. Our previous research showed that inactivated Mycobacterium phlei nebulization alleviated the airway hyperresponsiveness and inflammation of asthma. However, the relationship between Th9 cells and mycobacteria remains unknown. Here, we evaluated the relationship between Mycobacterium vaccae nebulization and Th9 cells in asthmatic mice. Eighteen Balb/c mice were randomized into 3 groups of 6 mice each (normal control group, asthma control group, and nebulization asthma group [Neb. group]). The Neb. group was nebulized with M. vaccae one month before establishment of the asthmatic model with ovalbumin (OVA) sensitization, and the normal and asthma control groups were nebulized with phosphate-buffered saline. The hyperresponsiveness of the mouse airways was assessed using a non-invasive lung function machine. Lung airway inflammation was evaluated by hematoxylin and eosin and periodic acid-Schiff staining. Cytokine interlukin-9 (IL-9) concentration and OVA-specific IgE in the bronchoalveolar lavage fluid were measured by enzyme-linked immunosorbent assays. The percentages of γδTCR+ CD3+, IL-9+CD3+, IL-10+CD3+ lymphocytes, and IL9+γδT and IL-10+γδT cells were detected by flow cytometry. The airway inflammation and concentration of IL-9 and OVA-specific IgE were significantly reduced in the Neb. group compared to the asthma control group. The Neb. group had lower airway hyperresponsiveness, percentages of γδTCR+CD3+ and IL-9+CD3+ lymphocytes, and IL9+γδT cells, and higher percentages of IL-10+CD3+ lymphocytes and IL-10+γδT cells compared to the asthma control group. Thus, mouse bronchial asthma could be prevented by M. vaccae nebulization. The mechanism could involve M. vaccae-mediated effects on induction of IL-9 secretion and suppression of IL-10 secretion from γδT cells. γδT cells showed prominent IL-10 expression, indicating that they possibly belong to the Th9 family.

Activin A programs the differentiation of human TFH cells

Follicular helper T (T_FH) cells are CD4⁺ T cells specialized in helping B cells and are associated both with protective antibody responses and autoimmune diseases. The promise of targeting T_FH cells therapeutically has been limited by fragmentary understanding of extrinsic signals regulating human T_FH cell differentiation. A screen of a human protein library identified activin A as new regulator of T_FH cell differentiation. Activin A orchestrated expression of multiple T_FH-associated genes, independently or in concert with additional signals. T_FH programming by activin A was antagonized by the cytokine IL-2. Activin A’s capacity to drive T_FH cell differentiation in vitro was conserved for non-human primates but not mice. Finally, activin A-induced T_FH programming was dependent on SMAD2 and SMAD3 signaling and blocked by pharmacological inhibitors.

Cylindromatosis (Cyld) gene mutation in T cells promotes the development of an IL-9-dependent allergic phenotype in experimental asthma

Cylindromatosis (CYLD) is a ubiquitously expressed deubiquitinating enzyme which removes activating ubiquitin residues from important signaling molecules of the NF-κB pathway. In CYLD^ex7/8 transgenic mice, a naturally occurring short isoform (sCYLD) is overexpressed in the absence of full length CYLD, leading to excessive NF-κB activity. Herein, we investigated the impact of the CYLD^ex7/8 mutation selectively in T cells on the development of experimental allergic airway disease induced by sensitization and challenge with ovalbumin. Compared with their wildtype littermates, mice bearing the T cell-specific mutation (CD4⁺CYLD^ex7/8) display stronger eosinophilia and mucus production in the lungs and higher IgE serum levels. The reason for these observations is excessive production of T cell-derived IL-9, a cytokine to whom allergy-promoting properties were ascribed. Consequently, blockade of IL-9 in CD4⁺CYLD^ex7/8 mice alleviates the development of disease symptoms. Thus, by polarization of the T cell cytokine response, sCYLD can favor the development of allergic airway disease.

The immunoregulatory and fibrotic roles of activin A in allergic asthma

Activin A, a member of the TGF-β superfamily of cytokines, was originally identified as an inducer of follicle stimulating hormone release, but has since been ascribed roles in normal physiological processes, as an immunoregulatory cytokine and as a driver of fibrosis. In the last 10–15 years, it has also become abundantly clear that activin A plays an important role in the regulation of asthmatic inflammation and airway remodelling. This review provides a brief introduction to the activin A/TGF-β superfamily, focussing on the regulation of receptors and signalling pathways. We examine the contradictory evidence for generalized pro- vs. anti-inflammatory effects of activin A in inflammation, before appraising its role in asthmatic inflammation and airway remodelling specifically by evaluating data from both murine models and clinical studies. We identify key issues to be addressed, paving the way for safe exploitation of modulation of activin A function for treatment of allergic asthma and other inflammatory lung diseases.

Initial immunological changes as predictors for house dust mite immunotherapy response

BACKGROUND

Although specific immunotherapy is the only aetiological treatment for allergic disorders, the underlying mechanisms are not fully understood. Specific immunotherapy induces changes in lymphocyte Th subsets from Th2 to Th1/Treg. Whether differences in immunological patterns underlie patient response to immunotherapy has not yet been established.

OBJECTIVES

We studied the immunological changes occurring during a 1-year period of Dermatophagoides pteronyssinus (DP) immunotherapy and their relation with clinical outcome.

METHODS

We included 34 patients with DP allergy who received subcutaneous specific immunotherapy (SCIT) for 1 year. Following treatment, patients were classified as responders or non-responders. Fourteen allergic subjects who did not receive SCIT were included as controls. Peripheral blood was obtained at 0, 1, 3, 6 and 12 months and cultured with nDer p 1. Phenotypic changes, cytokine production and basophil response were analysed by flow cytometry; transcription factors were measured by mRNA quantification. Serum immunoglobulin levels were also measured.

RESULTS

After 1 year of SCIT, 82% of cases showed improved symptoms (responders). Although increases in sIgG4 were observed, BAT reactivity was not modified in these patients. Increases in T-BET/FOXP3 as well as nDer p 1-specific Th1/Treg frequencies were also observed, along with a decrease in Th2, Th9 and Th17. These changes corresponded to changes in cytokine levels.

CONCLUSION

Patients who respond well to DP-SCIT show immunological differences compared to non-responders. In responders, basal differences include a lower frequency of Th1 and higher frequencies of Th2, Th9 and Th17 cells. After 1 year of treatment, an increased production of sIgG4 was observed in responders, along with a change in Th2 response towards Th1/Treg.