T helper type 2 cytokine receptors and associated transcription factors GATA-3, c-MAF, and signal transducer and activator of transcription factor-6 in induced sputum of atopic asthmatic patients

Regulation of Eosinophilia in Asthma-New Therapeutic Approaches for Asthma Treatment

Asthma is a complex and chronic inflammatory disease of the airways, characterized by variable and recurring symptoms, reversible airflow obstruction, bronchospasm, and airway eosinophilia. As the pathophysiology of asthma is becoming clearer, the identification of new valuable drug targets is emerging. IL-5 is one of these such targets because it is the major cytokine supporting eosinophilia and is responsible for terminal differentiation of human eosinophils, regulating eosinophil proliferation, differentiation, maturation, migration, and prevention of cellular apoptosis. Blockade of the IL-5 pathway has been shown to be efficacious for the treatment of eosinophilic asthma. However, several other inflammatory pathways have been shown to support eosinophilia, including IL-13, the alarmin cytokines TSLP and IL-33, and the IL-3/5/GM-CSF axis. These and other alternate pathways leading to airway eosinophilia will be described, and the efficacy of therapeutics that have been developed to block these pathways will be evaluated.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

GATA-3-specific DNAzyme - A novel approach for stratified asthma therapy

It is now well established that type-2 immune mechanisms drive the inflammation in about 50% of asthma patients. The major cellular and molecular players regulating this important network have been identified. In terms of therapeutic intervention, cytokine and cytokine-receptor pathways have been given major attention, since these molecules are relatively easily accessible for a blockade through monoclonal antibodies, and a number of positive clinical results support this concept. However, targeting events controlling the type-2 immunity network upstream of selective cytokine pathways would be equally attractive. Type-2 immunity is regulated through a delicate interplay of several transcription factors (including GATA-3, STAT-6, NFAT, IRF4, c-maf), with GATA-3 as master regulator in this regard. Since transcription factors are intracellularly located they cannot be directly targeted by monoclonal antibodies. For intracellular targets, antisense technologies such as antisense DNA and siRNA have been shown to be a promising approach, and have recently made major advances toward clinical application. Here, we summarize the development of a GATA-3-specific DNAzyme-a molecule class that combines the superior specificity of antisense molecules with an inherent RNA-cleaving enzymatic activity-for the treatment of type-2-driven asthma from preclinical development toward a proof-of-concept clinical study.

Allergen-Specific CD4(+) T Cells in Human Asthma

In allergic asthma, aeroallergen exposure of sensitized individuals mobilizes robust innate and adaptive airway immune responses, stimulating eosinophilic airway inflammation and the activation and infiltration of allergen-specific CD4(+) T cells into the airways. Allergen-specific CD4(+) T cells are thought to be central players in the asthmatic response as they specifically recognize the allergen and initiate and orchestrate the asthmatic inflammatory response. In this article, we briefly review the role of allergen-specific CD4(+) T cells in the pathogenesis of human allergic airway inflammation in allergic individuals, discuss the use of allergen-major histocompatibility complex class II tetramers to characterize allergen-specific CD4(+) T cells, and highlight current gaps in knowledge and directions for future research pertaining to the role of allergen-specific CD4(+) T cells in human asthma.

Wheezing and itching: The requirement for STAT proteins in allergic inflammation

The development of allergic inflammation requires the orchestration of gene expression from the inflamed tissue and from the infiltrating immune cells. Since many of the cytokines that promote allergic inflammation signal through hematopoietin family receptors, the Signal Transducer and Activator of Transcription (STAT) family have obligate roles in pro-allergic cytokine-induced gene regulation in multiple cell types. In this review, we summarize work defining the contribution of each of the STAT family members to the development of allergic inflammation, using data from mouse models of allergic inflammation, studies on patient samples and correlations with single nucleotide polymorphisms in STAT genes.

Targeting interleukin-4 in asthma: lost in translation?

The first discovery that interleukin-4 (IL-4) is crucial in the development of allergic airway inflammation originates from the early 1990s. Whereas initial studies in experimental animal models provided the community with the optimistic view that targeting IL-4 would be the ultimate solution for treating asthma, the translation of these findings to the clinic has not been evident and has not yet fulfilled the expectations. Many technical challenges have been encountered in the attempts to modulate IL-4 expression or activity and in transferring knowledge of preclinical studies to clinical trials. Moreover, biological redundancies between IL-4 and IL-13 have compelled a simultaneous blockade of both cytokines. A number of phase I/II studies are now providing us with clinical evidence that targeting IL-4/IL-13 may provide some clinical benefit. However, the initial view that asthma is a purely Th2-mediated disease had to be revised. Currently, different asthma phenotypes have been described, implying that blocking specifically Th2 cytokines, such as IL-4, IL-5, and IL-13, should be targeted to only a specific subset of patients. Taking this into consideration, IL-4 (together with IL-13) deserves attention as subject of further investigations to treat asthma. In this review, we will address the role of IL-4 in asthma, describe IL-4 signaling, and give an overview of preclinical and clinical studies targeting the IL-4 Receptor pathway.

Th2 cells as targets for therapeutic intervention in allergic bronchial asthma

Th2 cells play a central role in the pathogenesis of allergic bronchial asthma, since each of their characteristic cytokines such as IL-4, IL-5, IL-9 and IL-13 contributes to hallmarks of this disease, including airway eosinophilia, increased mucus production, production of allergen-specific IgE and development of airway hyper-responsiveness. Therefore, these cells are predisposed as target cells for therapeutic intervention. Experimental approaches targeted Th2-type effector cytokines, Th2-cell recruitment and Th2-cell development. Another strategy uses the immunomodulatory potential of tolerance-inducing cytokines such as IL-10 or of cytokines such as IL-12, IL-18 and IFN-gamma that are able to induce a counterbalancing Th1 immune response.

New drugs targeting Th2 lymphocytes in asthma

Asthma represents a profound worldwide public health problem. The most effective anti-asthmatic drugs currently available include inhaled beta2-agonists and glucocorticoids and control asthma in about 90-95% of patients. The current asthma therapies are not cures and symptoms return soon after treatment is stopped even after long term therapy. Although glucocorticoids are highly effective in controlling the inflammatory process in asthma, they appear to have little effect on the lower airway remodelling processes that appear to play a role in the pathophysiology of asthma at currently prescribed doses. The development of novel drugs may allow resolution of these changes. In addition, severe glucocorticoid-dependent and resistant asthma presents a great clinical burden and reducing the side-effects of glucocorticoids using novel steroid-sparing agents is needed. Furthermore, the mechanisms involved in the persistence of inflammation are poorly understood and the reasons why some patients have severe life threatening asthma and others have very mild disease are still unknown. Drug development for asthma has been directed at improving currently available drugs and findings new compounds that usually target the Th2-driven airway inflammatory response. Considering the apparently central role of T lymphocytes in the pathogenesis of asthma, drugs targeting disease-inducing Th2 cells are promising therapeutic strategies. However, although animal models of asthma suggest that this is feasible, the translation of these types of studies for the treatment of human asthma remains poor due to the limitations of the models currently used. The myriad of new compounds that are in development directed to modulate Th2 cells recruitment and/or activation will clarify in the near future the relative importance of these cells and their mediators in the complex interactions with the other pro-inflammatory/anti-inflammatory cells and mediators responsible of the different asthmatic phenotypes. Some of these new Th2-oriented strategies may in the future not only control symptoms and modify the natural course of asthma, but also potentially prevent or cure the disease.

An insight into molecular mechanisms of human T helper cell differentiation

Selective activation of T helper (Th) cell subsets plays an important role in immune response to pathogens as well as in the pathogenesis of human allergy and inflammatory diseases. Th1 cells along with the recently discovered Th17 cells play a role in the pathogenesis of autoimmune diseases. Th2 cytokines lead to series of inflammatory processes characteristic for asthma and other atopic diseases. To understand the pathogenesis of immune-mediated diseases it is crucial to dissect pathways and regulatory networks leading to the development of distinct Th subsets. Such knowledge may lead to better strategies for developing diagnostics and therapies for these diseases. The differentiation of Th1, Th2, and Th17 effector cells is driven by signals originating from T cell and costimulatory receptors as well as cytokines in the surroundings of activated naive T helper cells. There are several proteins involved in the regulation of this differentiation process. Most of the data on T helper cell differentiation have been acquired using mouse. In this review, we have summarized what is known about human T helper differentiation. In addition, selected differences between human and mouse will be discussed.

T-helper type 2-dependent early recruitment of antigen non-specific CD4+ T cells in experimental asthma

BACKGROUND

Following antigen challenge, adoptively transferred antigen-specific CD4(+) T cells induce allergic airway inflammation, comprised primarily of an increase in lymphocytes and eosinophils.

OBJECTIVE

Our goal was to better understand the contribution of the GATA-3 transcription factor to the ability of adoptively transferred T cells to induce airway inflammation in the Brown Norway rat model of adoptively transferred asthma.

METHODS

We transduced antigen-stimulated CD4+ T cells with recombinant retroviruses encoding enhanced green fluorescent protein (EGFP) only or EGFP and the GATA-3 transcription factor. Each population of transduced cells was adoptively transferred to naïve recipients that were then challenged with antigen. Airway inflammatory responses were then quantified.

RESULTS

Our data indicate that T cells transduced with retroviruses encoding GATA-3 expressed high levels of GATA-3 protein as well as T-helper type 2 cytokines. Following adoptive transfer and airway antigen challenge, these gene-modified T cells induced robust inflammatory responses in the lungs and draining lymph nodes. Increased numbers of total inflammatory cells and eosinophils were recovered in the bronchoalveolar lavage fluid (BALF). In addition, the number of antigen non-specific CD4+ T cells recovered in the BALF as well as the lung and draining lymph nodes was enhanced in recipients of GATA-3 overexpressing T cells following antigen challenge. Nevertheless, the transduced CD4+ T cells comprised only a small percentage of the population of CD4+ T cells infiltrating the lung and were not detectable at all in the draining lymph nodes.

CONCLUSION

These data provide evidence that GATA-3 plays a significant role in the ability of antigen-specific T cells to amplify allergic inflammatory responses in vivo by promoting the recruitment of endogenous antigen non-specific T cells to the lung.

Interleukin-4 induction of the CC chemokine TARC (CCL17) in murine macrophages is mediated by multiple STAT6 sites in the TARC gene promoter

Background

Macrophages (Mθ) play a central role in the innate immune response and in the pathology of chronic inflammatory diseases. Macrophages treated with Th2-type cytokines such as Interleukin-4 (IL-4) and Interleukin-13 (IL-13) exhibit an altered phenotype and such alternatively activated macrophages are important in the pathology of diseases characterised by allergic inflammation including asthma and atopic dermatitis. The CC chemokine Thymus and Activation-Regulated Chemokine (TARC/CCL17) and its murine homologue (mTARC/ABCD-2) bind to the chemokine receptor CCR4, and direct T-cell and macrophage recruitment into areas of allergic inflammation. Delineating the molecular mechanisms responsible for the IL-4 induction of TARC expression will be important for a better understanding of the role of Th2 cytokines in allergic disease.

Results

We demonstrate that mTARC mRNA and protein are potently induced by the Th2 cytokine, Interleukin-4 (IL-4), and inhibited by Interferon-γ (IFN-γ) in primary macrophages (Mθ). IL-4 induction of mTARC occurs in the presence of PI3 kinase pathway and translation inhibitors, but not in the absence of STAT6 transcription factor, suggesting a direct-acting STAT6-mediated pathway of mTARC transcriptional activation. We have functionally characterised eleven putative STAT6 sites identified in the mTARC proximal promoter and determined that five of these contribute to the IL-4 induction of mTARC. By in vitro binding assays and transient transfection of isolated sites into the RAW 264.7 Mθ cell-line, we demonstrate that these sites have widely different capacities for binding and activation by STAT6. Site-directed mutagenesis of these sites within the context of the mTARC proximal promoter revealed that the two most proximal sites, conserved between the human and mouse genes, are important mediators of the IL-4 response.

Conclusion

The induction of mTARC by IL-4 results from cooperative interactions between STAT6 sites within the mTARC gene promoter. Significantly, we have shown that transfer of the nine most proximal mTARC STAT6 sites in their endogenous conformation confers potent (up to 130-fold) IL-4 inducibility on heterologous promoters. These promoter elements constitute important and sensitive IL-4-responsive transcriptional units that could be used to drive transgene expression in sites of Th2 inflammation in vivo.

DNA binding activity of transcription factors in bronchial cells of horses with recurrent airway obstruction

Horses with recurrent airway obstruction (RAO) present many similarities with human asthmatics including airway inflammation, hyperresponsiveness, reversible obstruction, and increased NF-kappaB expression. Studies in experimental asthma models have shown that transcriptions factors such as activator protein-1 (AP-1), GATA-3, cyclic AMP response element binding protein (CREB) and CAAT/enhancer binding protein (C/EBP) may also play an important role in airway inflammation. The purpose of this study was to measure DNA binding activity of these transcription factors in the airways of horses with RAO and to compare it to pulmonary function and bronchoalveolar lavage fluid (BALF) cytology. Seven horses with RAO and six control animals were studied during a moldy hay challenge and after 2 months at pasture. Pulmonary function, BALF cytology and transcription factors' activities in bronchial brushings were measured during hay and pasture exposures. During moldy hay challenge, RAO-affected horses developed severe airway obstruction and inflammation and a significantly higher airway AP-1 binding activity than in controls. After 2 months on pasture, pulmonary function and airway AP-1 binding activity were not different between RAO and control horses. The DNA binding activity of CREB in airways of RAO-affected horses increased significantly after 2 months at pasture and became higher than in controls. A significant positive correlation was detected between AP-1 binding activity and indicators of airway obstruction and inflammation. Airway GATA-3, CEBP and CREB binding activities were negatively correlated with indices of airway obstruction. However, contrarily to CREB binding activity, GATA-3 and CEBP binding activities were not different between RAO and control horses and were unaffected by changes in environment. These data support the view that AP-1 and CREB play a role in modulating airway inflammation in horses with RAO.

Regulation of GATA-3, c-maf and T-bet mRNA expression in bronchoalveolar lavage cells and bronchial biopsies after segmental allergen challenge

BACKGROUND

GATA-3 (GATA binding protein 3) and the proto-oncogene c-maf are Th2-regulating transcription factors that control the expression of interleukin (IL)-4 and IL-5, while T-bet (T-box expressed in T cells) is a Th1-specific transcription factor that controls the expression of interferon (IFN-gamma). Allergen provocation in asthmatics induces a Th2-dominated cytokine profile, but so far it is unknown whether the skewed cytokine expression is reflected by the expression of the respective transcriptional regulators.

OBJECTIVE

The aim of this study was to determine the regulation of Th1- and Th2-specific transcription factors and cytokines in 10 atopic subjects with mild asthma and 5 nonatopic healthy controls at baseline and after segmental sham and allergen challenge.

METHODS

The mRNA expression of GATA-3, c-maf and T-bet was determined by real-time polymerase chain reaction in bronchoalveolar lavage (BAL) cells and bronchial biopsies. The percentage of IL-4+, IL-5+ and IFN-gamma+ BAL T cells was determined by flow cytometry, and BAL levels of these cytokines were measured by ELISA.

RESULTS

In BAL cells of asthmatics, the mRNA expression of all transcription factors was increased after allergen challenge. In bronchial biopsies, the basal expression of GATA-3 was increased in asthmatics compared to healthy controls but decreased after allergen challenge. Compared to sham challenge, the percentage of IL-5+/CD4+ BAL T cells was increased after allergen challenge in asthmatics while the percentage of IFN-gamma+/CD4+ and IFN-gamma+/CD8+ T cells was decreased. Expression of c-maf mRNA in BAL cells correlated with IL-4+/CD4+ BAL cells and BAL IL-5 levels.

CONCLUSIONS

Segmental allergen challenge in asthmatics leads to increased GATA-3, c-maf and T-bet expression in BAL cells but not in bronchial biopsies.

New anti-inflammatory therapies and targets for asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are diseases of the airways with an underlying inflammatory component. The prevalence and healthcare burden of asthma and COPD is still rising and is predicted to continue to rise in the foreseeable future. Beta-agonists and corticosteroids form the basis of the therapies available to treat asthma. However, the treatments available for COPD, corticosteroids and anticholinergics, reduce the number and severity of exacerbations, but have a limited effect on slowing the progression of the disease. The inflammatory processes underlying the pathology of asthma have received a great deal of attention and more recently, those underlying COPD have begun to be elucidated. This has resulted in the identification of new targets that will allow the development of novel approaches by the pharmaceutical industry, which will be able to focus its efforts in an attempt to provide new and improved therapies to treat these debilitating diseases. The resultant therapies should impinge on the underlying development of these diseases rather than providing symptomatic relief or palliative treatment alone. This review will outline new targets and novel approaches currently under investigation, which may provide opportunities for novel anti-inflammatory therapeutic interventions that slow or halt disease progression in asthma and COPD.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

A stage-specific functional role of the leucine zipper transcription factor c-Maf in lung Th2 cell differentiation

The transcription factor c-Maf controls IL-4 gene expression in CD4(+) T cells, and its expression is up-regulated in human asthmatic airways after allergen challenge. In the present study, we addressed the role of c-Maf in asthma by studying transgenic (Tg) mice overexpressing c-Maf in CD4(+) T cells under the control of the CD2 promoter. As shown, lung CD4(+) T cells of c-maf-Tg mice produced more IL-5 at the early stage (day 2) of culture in the presence of IL-4 than wild-type control cells. Consistently, c-maf-Tg mice spontaneously showed increased IL-5 expression and eosinophils in the bronchial alveolar lavage fluid (BALF) and activated IL-5 signal transduction via Raf-1 and Ras in lung eosinophils. Finally, IL-13 was suppressed in the BALF of c-maf-Tg mice and in supernatants of Tg lung CD4(+) T cells cultured in the presence of IL-2. Consistently, retroviral overexpression of c-Maf suppressed IL-13 production in developing lung Th2 cells. In summary, c-Maf induces IL-5 production in lung CD4(+) T cells at an early stage, but along with IL-2 suppresses IL-13 production in differentiating lung Th2 cells, thereby explaining the finding that overexpression of c-Maf does not cause airway hyperresponsiveness, a hallmark feature of asthma.

Differential expression of mRNA for Th1 and Th2 cytokine-associated transcription factors and suppressors of cytokine signalling in peripheral blood mononuclear cells of patients with atopic dermatitis

Atopic dermatitis is characterized by Th2-dominant immunity. Recently many intracellular molecules have been reported to regulate cytokine expression and T cell differentiation. GATA-3 and T-box expressed in T cells (T-bet) are transcription factors that play a critical role in the development of Th2 and Th1 immunity, respectively. Suppressor of cytokine signalling (SOCS)-3 and SOCS-5, are negative regulators of the cytokine signalling induced by IL-12 and IL-4, respectively. Txk is a transcription factor that activates IFN-gamma gene directly. The present study was designed to identify intracellular molecules that are responsible for the pathogenesis and the imbalance of cytokines in atopic dermatitis. Semi-quantitative RT-PCR revealed that in peripheral blood mononuclear cells without any stimulation the levels of mRNA for GATA-3 and SOCS-3 were elevated, the levels of mRNA for Txk were depressed and the levels of mRNA for T-bet and SOCS-5 were comparable in patients with atopic dermatitis as compared with healthy controls. In addition, successful therapy normalized levels of mRNA for GATA-3 and Txk, although those for the others including IL-4, IL-5, IL-10, IL-13 and IFN-gamma did not change. Levels of Txk mRNA correlated with those of IFN-gamma, while the mRNA levels of the other regulators did not correlate with those of any of the cytokines. These results suggest GATA-3 and Txk might be involved in skin lesions, while SOCS-3 might be associated with an imbalance of cytokines that is difficult to normalize in atopic dermatitis.