The failure of STAT6-deficient mice to develop airway eosinophilia and airway hyperresponsiveness is overcome by interleukin-5

Human germline gain-of-function in STAT6: from severe allergic disease to lymphoma and beyond

Signal transducer and activator of transcription (STAT)-6 is a transcription factor central to pro-allergic immune responses, although the function of human STAT6 at the whole-organism level has long remained unknown. Germline heterozygous gain-of-function (GOF) rare variants in STAT6 have been recently recognized to cause a broad and severe clinical phenotype of early-onset, multi-system allergic disease. Here, we provide an overview of the clinical presentation of STAT6-GOF disease, discussing how dysregulation of the STAT6 pathway causes severe allergic disease, and identifying possible targeted treatment approaches. Finally, we explore the mechanistic overlap between STAT6-GOF disease and other monogenic atopic disorders, and how this group of inborn errors of immunity (IEIs) powerfully inform our fundamental understanding of common human allergic disease.

Evidence that oncostatin M synergizes with IL-4 signaling to induce TSLP expression in chronic rhinosinusitis with nasal polyps

BACKGROUND

Oncostatin M (OSM) may promote type 2 inflammation in chronic rhinosinusitis with nasal polyps (CRSwNP) by inducing thymic stromal lymphopoietin (TSLP).

OBJECTIVE

We sought to study the impact of OSM on TSLP synthesis and release from nasal epithelial cells (NECs).

METHODS

OSM receptors, IL-4 receptors (IL-4R), and TSLP were evaluated in mucosal tissue and primary NECs from patients with CRSwNP by quantitative PCR and immunofluorescence. Air-liquid interface-cultured NECs were stimulated with cytokines, including OSM, and quantitative PCR, ELISA, Western blot, and flow cytometry were used to assess the expression of OSM receptors, IL-4R, and TSLP.

RESULTS

Increased levels of OSM receptor β chain (OSMRβ), IL-4Rα, and TSLP were observed in nasal polyp tissues and primary epithelial cells from nasal polyps of patients with CRSwNP compared with control tissues or cells from control subjects. The level of expression of OSMRβ in tissue was correlated with levels of both IL-4Rα and TSLP. OSM stimulation of NECs increased the expression of OSMRβ and IL-4Rα. Stimulation with IL-4 plus OSM augmented the production of TSLP; the response was suppressed by a signal transducer and activator of transcription 6 inhibitor. Stimulation of NECs with IL-4 plus OSM increased the expression of proprotein convertase subtilisin/kexin 3, an enzyme that truncates and activates TSLP.

CONCLUSIONS

OSM increases the expression of IL-4Rα and synergizes with IL-4 to induce the synthesis and release of TSLP in NECs. Because the combination of IL-4 and OSM also augmented the expression of proprotein convertase subtilisin/kexin 3, these results suggest that OSM can induce both synthesis and posttranslational processing/activation of TSLP, promoting type 2 inflammation.

The STAT6 inhibitor AS1517499 reduces the risk of asthma in mice with 2,4-dinitrochlorobenzene-induced atopic dermatitis by blocking the STAT6 signaling pathway

BACKGROUND

Epidemiological studies have revealed a link between atopic dermatitis (AD) and asthma. AS1517499, a selective signal transducer and activation of transcription 6 (STAT6) inhibitor, has been shown to effectively block this connection. In this study, we further explored the underlying mechanism by constructing an AD mouse model.

METHODS

Female BALB/c mice were randomly divided into four groups (n = 10/group). The AD mouse model was established by 2,4-dinitrochlorobenzene induction with repeated ovalbumin challenge. AS1517499 and corn oil were used as treatment interventions. The features of airway inflammation, remodeling, and hyperactivity were analyzed.

RESULTS

Active use of AS1517499 in AD mice effectively reduced Th2-related cytokine levels, alleviated airway eosinophil and lymphocyte infiltration, and regulated GATA3/Foxp3 levels and subepithelial collagen deposition. These changes might be due to specific blockade of the STAT6 signaling pathway.

CONCLUSION

AS1517499 could partially block the association between AD and asthma by specifically inhibiting the STAT6 signaling pathway.

Immunoengineering approaches for cytokine therapy

Since the discovery of cytokines, much effort has been put forth to achieve therapeutic translation for treatment of various diseases, including cancer and autoimmune diseases. Despite these efforts, very few cytokines have cleared regulatory approval, and those that were approved are not commonly used due to their challenging toxicity profile and/or limited therapeutic efficacy. The main limitation in translation has been that wild-type cytokines have unfavorable pharmacokinetic and pharmacodynamic profiles, either eliciting unwanted systemic side effects or insufficient residence in secondary lymphoid organs. In this review, we address protein-engineering approaches that have been applied to both proinflammatory and anti-inflammatory cytokines to enhance their therapeutic indices, and we highlight diseases in which administration of engineered cytokines is especially relevant.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

Dupilumab: Basic aspects and applications to allergic diseases

Interleukin (IL)-4 and IL-13, signature type 2 cytokines, exert their actions by binding to two types of receptors sharing the IL-4R α chain (IL-4Rα). Since IL-4 and IL-13 play important and redundant roles in the pathogenesis of allergic diseases, blocking both the IL-4 and IL-13 signals would be a powerful and effective strategy for treating allergic diseases. Dupilumab (Dupixent®) is a fully human monoclonal antibody recognizing IL-4Rα and blocking both the IL-4 and IL-13 signals. Dupilumab was first prescribed for atopic dermatitis (AD) patients and has been widely approved for adult patients with moderate to severe AD since 2018. Dupilumab has since been used for asthma, receiving approval for uncontrolled asthma in 2019. A phase 3 study using dupilumab for chronic rhinosinusitis with nasal polyps (CRSwNP) has been just completed, with positive results. Several clinical trials of dupilumab for other diseases in which type 2 inflammation is dominant are now underway. It is hoped that dupilumab will open the door to a new era for treating allergic patients with AD, asthma, and CRSwNP, and for more patients with type 2 inflammations.

Luteolin Attenuates Allergic Nasal Inflammation via Inhibition of Interleukin-4 in an Allergic Rhinitis Mouse Model and Peripheral Blood From Human Subjects With Allergic Rhinitis

Objectives: Luteolin is the active component of Perilla frutescens, an herb for the treatment of allergy in Asia. In this study, we aimed to investigate the effects and mechanisms of luteolin treatment.

Methods: BALB/c mice sensitized with house dust mite (HDM) to induce allergic rhinitis (AR), and treated with dexamethasone or luteolin. In addition, mononuclear cells from peripheral blood (PBMC) of AR patients were co-cultured with dexamethasone or luteolin, and were re-stimulated with HDM.

Results: Luteolin-treated mice had decreased allergic symptoms, and serum HDM-specific IgE when compared to the untreated group. Flow cytometric analyses of splenocytes and nasal lymphoid tissues from AR mice found that luteolin decreased CD4+ IL-4-secreting T cells when compared to those from vehicle treated AR mice. Histopathology sections showed reduced infiltration of eosinophils and decreased mucus secretion of mouse nasal epithelium. In the in vitro study, the results showed that luteolin reduced the percentage of CD4+ IL-4-secreting splenocytes expression was through reducing expression of pSTAT6 and GATA3. PBMCs from AR patients pretreated with luteolin could decrease percentage of CD4+ IL-4-secreting cells.

Conclusion: Our study identified that luteolin attenuates allergic nasal inflammation via inhibition of IL-4 production, which supports the potential pharmaceutical application of luteolin treatment for AR.

The Ethanol Extract of Holotrichia diomphalia Larvae, Containing Fatty acids and Amino acids, Exerts Anti-Asthmatic Effects through Inhibition of the GATA-3/Th2 Signaling Pathway in Asthmatic Mice

Holotrichia diomphalia larvae (HD), a natural product from an insect resource, possesses many pharmacological properties, including anticoagulant, antitumor, anti-inflammatory, and analgesic activity. The major bioactive ingredients include oleic acid, palmitic acid, palmitoleic acid, linoleic acid, proline, and glutamic acid. Although HD is associated with immunoregulatory activities in allergic diseases, the therapeutic mechanisms of the action of HD in allergic diseases have not been investigated. The aim of this study was to evaluate the anti-asthmatic potential of HD in an ovalbumin (OVA)-induced mouse model of allergic asthma. Moreover, the anti-inflammatory potential of HD was examined to identify a plausible mechanism of action of HD in vitro. HD strongly reduced goblet cell hyperplasia, eosinophil infiltration, and reactive oxygen species (ROS), which reduced airway hyperresponsiveness (AHR), inflammation, and the expression of Th2 cytokines (IL-5 and IL-13) in bronchoalveolar lavage fluid (BALF). The expression of IL-5, IL-4, eotaxin-2, lysyl oxidase-like 2 (loxl2), and GATA-binding protein 3 (GATA-3) was attenuated in the lungs. In an in vitro assay, HD exerted immunomodulatory effects through the suppression of Th2 cytokines (IL-5, IL-13), IL-17, and tumor necrosis factor (TNF)-α production through downregulation of GATA-3 expression in EL-4 T cells. These findings suggest that the anti-asthmatic activity of HD may occur through the suppression of Th2 cytokines and total Immunoglobulin E (IgE) production by inhibition of the GATA-3 transcription pathway. Our results suggest that HD may be a potential alternative therapy, or a novel therapeutic traditional medicine, for the treatment of allergic asthma.

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.

Role of Transcription Factors in Pulmonary Artery Smooth Muscle Cells: An Important Link to Hypoxic Pulmonary Hypertension

Hypoxia, namely a lack of oxygen in the blood, induces pulmonary vasoconstriction and vasoremodeling, which serve as essential pathologic factors leading to pulmonary hypertension (PH). The underlying molecular mechanisms are uncertain; however, pulmonary artery smooth muscle cells (PASMCs) play an essential role in hypoxia-induced pulmonary vasoconstriction, vasoremodeling, and PH. Hypoxia causes oxidative damage to DNAs, proteins, and lipids. This damage (oxidative stress) modulates the activity of ion channels and elevates the intracellular calcium concentration ([Ca²⁺]_i, Ca²⁺ signaling) of PASMCs. The oxidative stress and increased Ca²⁺ signaling mutually interact with each other, and synergistically results in a variety of cellular responses. These responses include functional and structural abnormalities of mitochondria, sarcoplasmic reticulum, and nucleus; cell contraction, proliferation, migration, and apoptosis, as well as generation of vasoactive substances, inflammatory molecules, and growth factors that mediate the development of PH. A number of studies reveal that various transcription factors (TFs) play important roles in hypoxia-induced oxidative stress, disrupted PAMSC Ca²⁺ signaling and the development and progress of PH. It is believed that in the pathogenesis of PH, hypoxia facilitates these roles by mediating the expression of multiple genes. Therefore, the identification of specific genes and their transcription factors implicated in PH is necessary for the complete understanding of the underlying molecular mechanisms. Moreover, this identification may aid in the development of novel and effective therapeutic strategies for PH.

STAT6 and PARP Family Members in the Development of T Cell-dependent Allergic Inflammation

Allergic inflammation requires the orchestration of altered gene expression in the target tissue and in the infiltrating immune cells. The transcription factor STAT6 is critical in activating cytokine gene expression and cytokine signaling both in the immune cells and in target tissue cells including airway epithelia, keratinocytes and esophageal epithelial cells. STAT6 is activated by the cytokines IL-4 and IL-13 to mediate the pathogenesis of allergic disorders such as asthma, atopic dermatitis, food allergy and eosinophilic esophagitis (EoE). In this review, we summarize the role of STAT6 in allergic diseases, its interaction with the co-factor PARP14 and the molecular mechanisms by which STAT6 and PARP14 regulate gene transcription.

Eosinophilic myositis as first manifestation in a patient with type 2 myotonic dystrophy CCTG expansion mutation and rheumatoid arthritis

Eosinophilic myositis is characterized by eosinophilic infiltration of skeletal muscles. In the absence of an identifiable causative factor or source (including parasitic infection, intake of drugs or L-tryptophan, certain systemic disorders as well as malignant diseases), the diagnosis of idiopathic eosinophilic myositis is usually retained. However, some muscular dystrophies have been recently identified in this subset of eosinophilic myositis. Here, we report a patient with an 8 kb CCTG expansion in intron 1 of the CNBP gene, a mutation characteristic of myotonic dystrophy type 2 (DM2), whose first manifestation was "idiopathic" eosinophilic myositis. This report suggests that in "idiopathic" eosinophilic myositis, clinicians should consider muscular dystrophies, including DM2.

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.

Association of the STAT-6 rs324011 (C2892T) variant but not rs324015 (G2964A), with atopic asthma in a Saudi Arabian population

BACKGROUND

The signal transducer and activator of transcription 6 (STAT6) transduces signals in response to IL-4 and IL-13 cytokine stimulations, resulting in many cell-specific responses. Some common STAT6 SNPs were associated with asthma predisposition and/or IgE levels, although discrepancies have also been reported.

OBJECTIVE

To determine whether STAT6 rs324011 and rs324015 polymorphisms are associated with atopic asthma in Saudi Arabian patients.

METHODS

A total of 536 Saudi individuals aged 11-70years old (230 atopic asthmatics, 306 healthy subjects) were recruited. DNA was purified from peripheral blood and genotyping for rs324011 and rs324015 polymorphisms was performed by PCR amplification, followed by cycle sequencing of the purified PCR fragments using BigDye chain terminator and capillary electrophoresis.

RESULTS

By the contrast of alleles tests, no significant differences between asthma and healthy groups were detected for both variants (rs324011: X(2)=0.25, Pearson's P-value=0.617; rs324015: X(2)=0.068, Pearson's P=0.814).When testing for genotypes, rs324011 homozygous T/T genotype was significantly associated with asthma, when the Recessive model is considered (T/T vs. C/C+C/T) (adjusted, OR=2.49, 95% CI=1.18-5.25, Pearson's P=0.014(∗), Yates' P=0.022(∗)). In contrast, rs324015 variant was not significantly associated with asthma.

CONCLUSIONS

Rs324011 homozygous T/T genotype was significantly associated with asthma risk whereas rs324015 genotypes were not in the Saudi population.

STAT6 siRNA matrix-loaded gelatin nanocarriers: formulation, characterization, and ex vivo proof of concept using adenocarcinoma cells

The clinical utility of siRNA therapy has been hampered due to poor cell penetration, nonspecific effects, rapid degradation, and short half-life. We herewith proposed the formulation development of STAT6 siRNA (S6S) nanotherapeutic agent by encapsulating them within gelatin nanocarriers (GNC). The prepared nanoformulation was characterized for size, charge, loading efficiency, release kinetics, stability, cytotoxicity, and gene silencing assay. The stability of S6S-GNC was also assessed under conditions of varying pH, serum level, and using electrophoretic assays. In vitro cytotoxicity performance was evaluated in human adenocarcinoma A549 cells following MTT assay. The developed formulation resulted in an average particle size, surface charge, and encapsulation efficiency as 70 ± 6.5 nm, +10 ± 1.5 mV, and 85 ± 4.0%, respectively. S6S-GNC showed an insignificant (P < 0.05) change in the size and charge in the presence of buffer solutions (pH 6.4 to 8.4) and FBS (10% v/v). A549 cells were treated with native S6S, S6S-lipofectamine, placebo-GNC, and S6S-GNC using untreated cells as a control. It was observed that cell viability was decreased significantly with S6S-GNC by 55 ± 4.1% (P < 0.001) compared to native S6S (2.0 ± 0.55%) and S6S-lipofectamine complex (40 ± 3.1%). This investigation infers that gelatin polymer-based nanocarriers are a robust, stable, and biocompatible strategy for the delivery of siRNA.

STAT6 controls the number of regulatory T cells in vivo, thereby regulating allergic lung inflammation

STAT6 plays a central role in IL-4-mediated allergic responses. Several studies indicate that regulatory T cells (Tregs) can be modulated by IL-4 in vitro. We previously showed that STAT6(-/-) mice are highly resistant to allergic lung inflammation even when wild-type Th2 effectors were provided and that they have increased numbers of Tregs. However, the role of STAT6 in modulating Tregs in vivo during allergic lung inflammation has not been thoroughly investigated. To examine Treg and STAT6 interaction during allergic inflammation, STAT6(-/-), STAT6xRAG2(-/-), and RAG2(-/-) mice were subjected to OVA sensitization and challenge following adoptive transfer of OVA-specific, wild-type Th2 effectors with or without prior Treg depletion/inactivation, using anti-CD25 (PC61). As expected, STAT6(-/-) mice were highly resistant to airway inflammation and remodeling. In contrast, allergic lung inflammation was partially restored in STAT6(-/-) mice treated with PC61 to levels observed in STAT6xRAG2(-/-) mice. In some cases, STAT6xRAG2(-/-) mice were also given natural Tregs along with Th2 effectors. Adoptive transfer of natural Tregs caused a substantial reduction in bronchoalveolar lavage eosinophil composition and suppressed airway remodeling and T cell migration into the lung in STAT6xRAG2(-/-) mice to levels comparable to those in STAT6(-/-) mice. These results demonstrate the STAT6-dependent suppression of Tregs in vivo to promote allergic airway inflammation.

Signal transducer and activator of transcription 6 directly regulates human ORMDL3 expression

Orosomucoid-like 3 (ORMDL3) has been associated with asthma and a series of autoimmune disorders, and is involved in endoplasmic reticulum-mediated inflammatory responses. However, its clinical significance and the molecular mechanism underlying its expression are still largely unclear. To elucidate the mechanisms of human ORMDL3 transcriptional regulation, we cloned a 1.5 kb genomic DNA fragment containing the putative promoter region and evaluated its transcriptional activity in a luciferase reporter system by deletion analysis. We identified a 68 bp region that functions as a minimal promoter. Bioinformatics analysis predicted that the -64 to -56 bp region contained a signal transducer and activator of transcription 6 (STAT6) binding site. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated that STAT6 bound to its binding site within the ORMDL3 promoter. STAT6 over-expression or knockdown trans-activated or trans-inhibited, respectively, the ORMDL3 promoter containing the STAT6-binding motif. Treatment with interleukins 4 or 13 increased ORMDL3 promoter activity as well as endogenous ORMDL3 expression. Immunoprecipitation and ChIP/Re-ChIP assays revealed that STAT6 and p300 exist in the same protein complex that binds to the ORMDL3 promoter. Our study confirmed that STAT6 plays important roles in regulating the expression of human ORMDL3 by directly binding to the promoter region, which may shed light on a possible role in various human diseases.

Role of transcription factors in the pathogenesis of asthma and COPD

Inflammation is a central feature of asthma and chronic obstructive pulmonary disease (COPD). Despite recent advances in the knowledge of the pathogenesis of asthma and COPD, much more research on the molecular mechanisms of asthma and COPD are needed to aid the logical development of new therapies for these common and important diseases, particularly in COPD where no effective treatments currently exist. In the future the role of the activation/repression of different transcription factors and the genetic regulation of their expression in asthma and COPD may be an increasingly important aspect of research, as this may be one of the critical mechanisms regulating the expression of different clinical phenotypes and their responsiveness to therapy, particularly to anti-inflammatory drugs.

STAT6 promotes bi-directional modulation of PKM2 in liver and adipose inflammatory cells in rosiglitazone-treated mice

STAT6 interacts with PPARγ to elicit macrophage polarization towards an anti-inflammatory, insulin-sensitizing phenotype. Mice deficient in STAT6 display liver lipid accumulation (hepatosteatosis). Rosiglitazone (RSG), a PPARγ agonist, ameliorates hepatosteatosis and enhances insulin sensitivity. To elucidate the role of STAT6 in PPARγ action on hepatosteatosis we compared liver proteomes of RSG-treated wild type and STAT6-deficient mice and we identified pyruvate kinase M2 (PKM2), a glycolysis and proliferation-regulating enzyme that displayed STAT6-dependent expression. RSG induced PKM2 within inflammatory cells in liver but suppressed its expression in adipose tissue. RSG diminished hepatosteatosis and oxidative stress, enhanced fat accumulation and improved insulin sensitivity in STAT6-deficient mice. Our data reveal a complex interaction between STAT6 and PPARγ in the regulation of liver and adipose tissue lipid depot distribution and design STAT6 as a novel link between inflammatory cell metabolism and adipocyte and hepatocyte function.

Interleukin-13-induced activation of signal transducer and activator of transcription 6 is mediated by an activation of Janus kinase 1 in cultured human bronchial smooth muscle cells

BACKGROUND

The current study was carried out to identify the JAK molecule(s) that is involved in the IL-13-induced activation of STAT6 in cultured human bronchial smooth muscle cells (hBSMCs).

METHODS

Cultured hBSMCs were stimulated with IL-13 in the absence and presence of JAK inhibitor-I (a nonspecific JAKs inhibitor), tyrphostin-AG490 (a specific JAK2 inhibitor), WHI-P131 (a specific JAK3 inhibitor), or tyrphostin-AG9 (a specific Tyk2 inhibitor), and levels of phosphorylated STAT6 were measured by immunoblot analyses.

RESULTS

The IL-13-induced phosphorylation of STAT6 was abolished by JAK inhibitor-I, whereas the other inhibitors had no significant effect.

CONCLUSION

These findings indicate that the STAT6 phosphorylation/activation induced by IL-13 is mediated by an activation of JAK1 in cultured hBSMCs.

STAT6 expression in T cells, alveolar macrophages and bronchial biopsies of normal and asthmatic subjects

Background

Asthma is characterised by increased numbers of Th2-like cells in the airways and IgE secretion. Generation of Th2 cells requires interleukin (IL)-4 and IL-13 acting through their specific receptors and activating the transcription factor, signal transducer and activator of transcription 6 (STAT6). STAT6 knockout mice fail to produce IgE, airway hyperresponsiveness and bronchoalveolar lavage eosinophilia after allergen sensitisation, suggesting a critical role for STAT6 in allergic responses.

Methods

We have investigated the expression of STAT6 in peripheral blood T-lymphocytes, alveolar macrophages and bronchial biopsies from 17 normal subjects and 18 mild-moderate steroid-naïve stable asthmatic patients.

Results

STAT6 expression was variable and was detected in T-lymphocytes, macrophages and bronchial epithelial cells from all subjects with no difference between normal and stable asthmatic subjects.

Conclusions

STAT6 expression in different cells suggests that it may be important in regulating the expression of not only Th2-like cytokines in T cells of man, but may also regulate STAT-inducible genes in alveolar macrophages and airway epithelial cells.

Signal transducer and activation of transcription 6 (STAT6) regulates T helper type 1 (Th1) and Th17 nephritogenic immunity in experimental crescentic glomerulonephritis

Experimental crescentic glomerulonephritis is driven by systemic cellular immune responses. A pathogenic role for T helper type 1 (Th1) and Th17 cells is well established. T-bet, a key transcription factor required for Th1 lineage commitment, and retinoic acid-related orphan receptor-γt (Rorγt), a key Th17 transcription factor, are required for full expression of disease. Similarly, several Th1- and Th17-associated cytokines have been implicated in disease augmentation. The role of Th2 cells in the disease is less clear, although Th2-associated cytokines, interleukin (IL)-4 and IL-10, are protective. We sought to determine the role of signal transducer and activation of transcription 6 (STAT6), a key regulator of Th2 responses, in experimental crescentic glomerulonephritis. Compared to wild-type mice, histological and functional renal injury was enhanced significantly in STAT6(-/-) mice 21 days after administration of sheep anti-mouse glomerular basement membrane globulin. Consistent with the enhanced renal injury, both Th1 and Th17 nephritogenic immune responses were increased in STAT6(-/-) mice. Conversely, production of IL-5, a key Th2-associated cytokine, was decreased significantly in STAT6(-/-) mice. Early in the disease process systemic mRNA expression of T-bet and Rorγ was increased in STAT6(-/-) mice. We conclude that STAT6 is required for attenuation of Th1 and Th17 nephritogenic immune responses and protection from crescentic glomerulonephritis.

An alternate STAT6-independent pathway promotes eosinophil influx into blood during allergic airway inflammation

Background

Enhanced eosinophil responses have critical roles in the development of allergic diseases. IL-5 regulates the maturation, migration and survival of eosinophils, and IL-5 and eotaxins mediate the trafficking and activation of eosinophils in inflamed tissues. CD4⁺ Th2 cells are the main producers of IL-5 and other cells such as NK also release this cytokine. Although multiple signalling pathways may be involved, STAT6 critically regulates the differentiation and cytokine production of Th2 cells and the expression of eotaxins. Nevertheless, the mechanisms that mediate different parts of the eosinophilic inflammatory process in different tissues in allergic airway diseases remain unclear. Furthermore, the mechanisms at play may vary depending on the context of inflammation and microenvironment of the involved tissues.

Methodology/Principal Findings

We employed a model of allergic airway disease in wild type and STAT6-deficient mice to explore the roles of STAT6 and IL-5 in the development of eosinophilic inflammation in this context. Quantitative PCR and ELISA were used to examine IL-5, eotaxins levels in serum and lungs. Eosinophils in lung, peripheral blood and bone marrow were characterized by morphological properties. CD4⁺ T cell and NK cells were identified by flow cytometry. Antibodies were used to deplete CD4⁺ and NK cells. We showed that STAT6 is indispensible for eosinophilic lung inflammation and the induction of eotaxin-1 and -2 during allergic airway inflammation. In the absence of these chemokines eosinophils are not attracted into lung and accumulate in peripheral blood. We also demonstrate the existence of an alternate STAT6-independent pathway of IL-5 production by CD4⁺ and NK cells that mediates the development of eosinophils in bone marrow and their subsequent movement into the circulation.

Conclusions

These results suggest that different points of eosinophilic inflammatory processes in allergic airway disease may be differentially regulated by the activation of STAT6-dependent and -independent pathways.

Antigen challenge influences various transcription factors of rat bronchus: protein/DNA array study

Although the transcription factors are required for expression of the proinflammatory cytokines and immune proteins which are involved in airway hyperresponsiveness and inflammation of bronchial asthma, the antigen-induced alterations of the transcription factors in bronchi have not yet been revealed. Therefore, in order to profile the alteration pattern of the transcription factors after antigen challenge in bronchi, we used protein/DNA arrays. Rats were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen. Half, 1, 2 and 4 h after the last antigen challenge, protein/DNA array was performed with nuclear extract of bronchial tissue. Twenty-one the transcription factors exhibited an activation after the last antigen challenge in rat bronchial tissue. Among them, upstream transcription factor-1 (USF-1) and CAAT box general (CBF) were markedly activated after the last antigen challenge. Conversely, 4 transcription factors were inactivated after the last challenge. In development of bronchial asthma, some of the transcription factors may have an ability to modulate the transcription of inflammatory proteins such as cytokines, inflammatory enzymes, etc. Furthermore, the transcription factors, such as USF-1 and CBF, which have not been taken notice so far are also presumed to play an important role in the development of bronchial asthma.

Regulatory T cells more effectively suppress Th1-induced airway inflammation compared with Th2

Asthma is a syndrome with different inflammatory phenotypes. Animal models have shown that, after sensitization and allergen challenge, Th2 and Th1 cells contribute to the development of allergic airway disease. We have previously demonstrated that naturally occurring regulatory T cells (nTregs) can only marginally suppress Th2-induced airway inflammation and airway hyperresponsiveness. In this study, we investigated nTreg-mediated suppression of Th2-induced and Th1-induced acute allergic airway disease. We demonstrate in vivo that nTregs exert their suppressive potency via cAMP transfer on Th2- and Th1-induced airway disease. A comparison of both phenotypes revealed that, despite similar cAMP transfers, Th1-driven airway hyperresponsiveness and inflammation are more susceptible to nTreg-dependent suppression, suggesting that potential nTreg-based therapeutic strategies might be more effective in patients with predominantly neutrophilic airway inflammation based on deregulated Th1 response.

STAT6 expression in multiple cell types mediates the cooperative development of allergic airway disease

Th2 cells induce asthma through the secretion of cytokines. Two such cytokines, IL-4 and IL-13, are critical mediators of many features of this disease. They both share a common receptor subunit, IL-4Rα, and signal through the STAT6 pathway. STAT6(-/-) mice have impaired Th2 differentiation and reduced airway response to allergen. Transferred Th2 cells were not able to elicit eosinophilia in response to OVA in STAT6(-/-) mice. To clarify the role of STAT6 in allergic airway inflammation, we generated mouse bone marrow (BM) chimeras. We observed little to no eosinophilia in OVA-treated STAT6(-/-) mice even when STAT6(+/+) BM or Th2 cells were provided. However, when Th2 cells were transferred to STAT6×Rag2(-/-) mice, we observed an eosinophilic response to OVA. Nevertheless, the expression of STAT6 on either BM-derived cells or lung resident cells enhanced the severity of OVA-induced eosinophilia. Moreover, when both the BM donor and recipient lacked lymphocytes, transferred Th2 cells were sufficient to induce the level of eosinophilia comparable with that of wild-type (WT) mice. The expression of STAT6 in BM-derived cells was more critical for the enhanced eosinophilic response. Furthermore, we found a significantly higher number of CD4(+)CD25(+)Foxp3(+) T cells (regulatory T cells [Tregs]) in PBS- and OVA-treated STAT6(-/-) mouse lungs compared with that in WT animals suggesting that STAT6 limits both naturally occurring and Ag-induced Tregs. Tregs obtained from either WT or STAT6(-/-) mice were equally efficient in suppressing CD4(+) T cell proliferation in vitro. Taken together, our studies demonstrate multiple STAT6-dependent and -independent features of allergic inflammation, which may impact treatments targeting STAT6.

Retrovirus-mediated delivery of an IL-4 receptor antagonist inhibits allergic responses in a murine model of asthma

This work reports the investigation of the effect of airway IL-4RA gene transfer by a recombinant retroviral vector on airway inflammation and airway responsiveness in asthmatic mice. The retrovirus-mediated delivery of IL-4RA to the airways of mice inhibited elevations of airway responsiveness and the development of allergic inflammation in asthmatic mice, and regulated the Th1/Th2 balance in OVA-sensitized and -challenged mouse models. This suggests that gene therapy is a therapeutic option for treating and controlling chronic airway inflammation and asthma symptoms.

Toxoplasma rhoptry protein 16 (ROP16) subverts host function by direct tyrosine phosphorylation of STAT6

The obligate intracellular parasite, Toxoplasma gondii, modulates host immunity in a variety of highly specific ways. Previous work revealed a polymorphic, injected parasite factor, ROP16, to be a key virulence determinant and regulator of host cell transcription. These properties were shown to be partially mediated by dysregulation of the host transcription factors STAT3 and STAT6, but the molecular mechanisms underlying this phenotype were unclear. Here, we use a Type I Toxoplasma strain deficient in ROP16 to show that ROP16 induces not only sustained activation but also an extremely rapid (within 1 min) initial activation of STAT6. Using recombinant wild-type and kinase-deficient ROP16, we demonstrate in vitro that ROP16 has intrinsic tyrosine kinase activity and is capable of directly phosphorylating the key tyrosine residue for STAT6 activation, Tyr(641). Furthermore, ROP16 co-immunoprecipitates with STAT6 from infected cells. Taken together, these data strongly suggest that STAT6 is a direct substrate for ROP16 in vivo.

Importance of cytokines in murine allergic airway disease and human asthma

Asthma is a common, disabling inflammatory respiratory disease that has increased in frequency and severity in developed nations. We review studies of murine allergic airway disease (MAAD) and human asthma that evaluate the importance of Th2 cytokines, Th2 response-promoting cytokines, IL-17, and proinflammatory and anti-inflammatory cytokines in MAAD and human asthma. We discuss murine studies that directly stimulate airways with specific cytokines or delete, inactivate, neutralize, or block specific cytokines or their receptors, as well as controversial issues including the roles of IL-5, IL-17, and IL-13Ralpha2 in MAAD and IL-4Ralpha expression by specific cell types. Studies of human asthmatic cytokine gene and protein expression, linkage of cytokine polymorphisms to asthma, cytokine responses to allergen stimulation, and clinical responses to cytokine antagonists are discussed as well. Results of these analyses establish the importance of specific cytokines in MAAD and human asthma and have therapeutic implications.

Ablation of tumor progression locus 2 promotes a type 2 Th cell response in Ovalbumin-immunized mice

The protein kinase encoded by the Tpl2 proto-oncogene regulates ERK activation and cytokine gene expression in macrophages in response to LPS and TNF-alpha. In this study we show that OVA-immunized Tpl2(-/-) mice express high levels of IgE and develop more severe bronchoalveolar eosinophilic inflammation than Tpl2(+/+) controls, when challenged with OVA intranasally. Bronchoalveolar exudates and supernatants of OVA-stimulated splenocytes from immunized Tpl2(-/-) mice express elevated levels of IL-4 and IL-5, suggesting that Tpl2 ablation promotes the Th2 polarization of the T cell response. Anti-CD3 stimulation of CD4(+) T cells of wild-type and Tpl2 knockout mice revealed that Tpl2 ablation gives rise to a cell autonomous T cell defect that is primarily responsible for the Th2 polarization of the T cell response to Ag. This observation was further supported by experiments addressing the expression of Th1 and Th2 cytokines in OVA-stimulated mixed cultures of CD4(+) T cells from Tpl2(+/+)/OT2 or Tpl2(-/-)/OT2 mice and dendritic cells from Tpl2(+/+) or Tpl2(-/-) mice. Further studies revealed that Th1 cells express significantly higher levels of Tpl2 than Th2 cells. As a result, Tpl2(-/-) Th1 cells exhibit a stronger defect in ERK activation by anti-CD3 than Th2 cells and express low levels of T-bet. Given that the development of Th1 and Th2 cells depends on positive feedback signals from the T cells, themselves, the functional defect of the Tpl2(-/-) Th1 cells provides a mechanistic explanation for the T cell autonomous Th2 polarization in Tpl2(-/-) mice.

Cutting edge: Limiting MHC class II expression to dendritic cells alters the ability to develop Th2- dependent allergic airway inflammation

In allergic airway inflammation, dendritic cells (DCs) are required for Th2 generation, recruitment, and activation in the respiratory tract. DCs have been shown to be necessary and sufficient for the induction of Th1 immune responses. In Th2 immunity and allergic airway inflammation, the ability of a DC to function as the sole APC has not been tested. We show that CD11c/A(beta)(b) mice with MHC class II expression restricted to CD11c-expressing DCs develop airway neutrophilia rather than allergic airway inflammation. Although CD11c/A(beta)(b) mice are capable of Th2 recruitment and activation in the lung, Th2 priming in CD11c/A(beta)(b) mice results in IFN-gamma production. Effective Th2 generation and allergic airway inflammation was achieved in CD11c/A(beta)(b) mice after treatment with anti-IFN-gamma. These studies show that DCs alone cannot drive the development of Th2 cells but require an additional MHC class II signal to stimulate effective Th2 immunity.

Small interfering RNA against transcription factor STAT6 inhibits allergic airway inflammation and hyperreactivity in mice

In the context of allergic immune responses, activation of STAT6 is pivotal for Th2-mediated IgE production and development of airway inflammation and hyperreactivity. We analyzed whether gene silencing of STAT6 expression by RNA interference was able to suppress allergen-induced immune and airway responses. Knockdown effectiveness of three different STAT6 siRNA molecules was analyzed in murine and human cell cultures. The most potent siRNA was used for further testing in a murine model of allergen-induced airway inflammation and airway hyperreactivity (AHR). BALB/c mice were sensitized with OVA/alum twice i.p. (days 1 and 14), and challenged via the airways with allergen (days 28-30). Intranasal application of STAT6 siRNA before and during airway allergen challenges reduced levels of infiltrating cells, especially of eosinophils, in the bronchoalveolar lavage fluid, compared with GFP siRNA-treated sensitized and challenged controls. Allergen-induced alterations in lung tissues (goblet cell hyperplasia, peribronchial inflammation with eosinophils and CD4 T cells) were significantly reduced after STAT6 siRNA treatment. Associated with decreased inflammation was a significant inhibition of the development of allergen-induced in vivo AHR after STAT6 siRNA treatment, compared with GFP siRNA-treated sensitized and challenged controls. Importantly, mRNA and protein expression levels of IL-4 and IL-13 in lung tissues of STAT6-siRNA treated mice were significantly diminished compared with sensitized and challenged controls. These data show that targeting the key transcription factor STAT6 by siRNA effectively blocks the development of cardinal features of allergic airway disease, like allergen-induced airway inflammation and AHR. It may thus be considered as putative approach for treatment of allergic airway diseases such as asthma.

Immune and genetic aspects of asthma, allergy and parasitic worm infections: evolutionary links

There are important parallels in the immunobiology of allergy and asthma, and of the human host's response to parasitic worms. Th-2 immune actions with 'weep and sweep' mucosal biology are common to both - pathological in the first and protective in the second. Common up-regulating genetic variants of Th-2 immunity, notably in IL13 and STAT6, predict increased risk of asthma and allergy, but diminished intensity of infection by Ascaris and Schistosoma. Endemic exposures of humans to parasitic worms may have been one evolutionary force selecting for genetic variants that promote asthma and allergy.

A novel STAT6 inhibitor AS1517499 ameliorates antigen-induced bronchial hypercontractility in mice

Interleukin-13 (IL-13) is one of the central mediators for development of airway hyperresponsiveness in asthma. The signal transducer and activation of transcription 6 (STAT6) is one of the major signal transducers activated by IL-13, and a possible involvement of IL-13/STAT6 pathway in the augmented bronchial smooth muscle (BSM) contraction has been suggested. In the present study, the effect of a novel STAT6 inhibitor, AS1517499, on the development of antigen-induced BSM hyperresponsiveness was investigated. In cultured human BSM cells, IL-13 (100 ng/ml) caused a phosphorylation of STAT6 and an up-regulation of RhoA, a monomeric GTPase responsible for Ca2+ sensitization of smooth muscle contraction: both events were inhibited by co-incubation with AS1517499 (100 nM). In BALB/c mice that were actively sensitized and repeatedly challenged with ovalbumin antigen, an increased IL-13 level in bronchoalveolar lavage fluids and a phosphorylation of STAT6 in bronchial tissues were observed after the last antigen challenge. These mice had an augmented BSM contractility to acetylcholine together with an up-regulation of RhoA in bronchial tissues. Intraperitoneal injections of AS1517499 (10 mg/kg) 1 hour before each ovalbumin exposure inhibited both the antigen-induced up-regulation of RhoA and BSM hyperresponsiveness, almost completely. A partial but significant inhibition of antigen-induced production of IL-13 was also found. These findings suggest that the inhibitory effects of STAT6 inhibitory agents, such as AS1517499, both on RhoA and IL-13 up-regulations might be useful for asthma treatment.

IFN-gamma, IL-4 and IL-13 modulate responsiveness of human airway smooth muscle cells to IL-13

Background

IL-13 is a critical mediator of allergic asthma and associated airway hyperresponsiveness. IL-13 acts through a receptor complex comprised of IL-13Rα1 and IL-4Rα subunits with subsequent activation of signal transducer and activator of transcription 6 (STAT6). The IL-13Rα2 receptor may act as a decoy receptor. In human airway smooth muscle (HASM) cells, IL-13 enhances cellular proliferation, calcium responses to agonists and induces eotaxin production. We investigated the effects of pre-treatment with IL-4, IL-13 and IFN-γ on the responses of HASM cells to IL-13.

Methods

Cultured HASM were examined for expression of IL-13 receptor subunits using polymerase chain reaction, immunofluorescence microscopy and flow cytometry. Effects of cytokine pre-treatment on IL-13-induced cell responses were assessed by looking at STAT6 phosphorylation using Western blot, eotaxin secretion and calcium responses to histamine.

Results

IL-13Rα1, IL-4Rα and IL-13Rα2 subunits were expressed on HASM cells. IL-13 induced phosphorylation of STAT6 which reached a maximum by 30 minutes. Pre-treatment with IL-4, IL-13 and, to a lesser degree, IFN-γ reduced peak STAT6 phosphorylation in response to IL-13. IL-13, but not IFN-γ, pre-treatment abrogated IL-13-induced eotaxin secretion. Pre-treatment with IL-4 or IL-13 abrogated IL-13-induced augmentation of the calcium transient evoked by histamine. Cytokine pre-treatment did not affect expression of IL-13Rα1 and IL-4Rα but increased expression of IL-13Rα2. An anti-IL-13Rα2 neutralizing antibody did not prevent the cytokine pre-treatment effects on STAT6 phosphorylation. Cytokine pre-treatment increased SOCS-1, but not SOCS-3, mRNA expression which was not associated with significant increases in protein expression.

Conclusion

Pre-treatment with IL-4 and IL-13, but not IFN-γ, induced desensitization of the HASM cells to IL-13 as measured by eotaxin secretion and calcium transients to histamine. The mechanism of IL-4 and IL-13 induced desensitization does not appear to involve either downregulation of receptor expression or induction of the IL-13Rα2 or the SOCS proteins.

Growth factors temporally associate with airway responsiveness and inflammation in allergen-exposed mice

BACKGROUND

To clarify whether growth factors play critical roles in the development of airway hyperresponsiveness (AHR) and airway inflammation in the early stages of asthma, the relationship between growth factors and AHR and airway inflammation were analyzed in a mouse model of asthma.

METHODS

Following ovalbumin (OVA) sensitization and challenge, airway function, inflammation, cytokine and growth factor levels were monitored.

RESULTS

AHR to inhaled methacholine increased at 6 h, peaked at 48 h, and remained elevated for 14 days. IL-4 and IL-5 levels in bronchoalveolar lavage (BAL) fluid were increased at 6 h, peaked at 24 h, but returned to baseline quickly. IL-13 levels increased up to 14 days, peaking at 48 h. Increases in BAL fluid transforming growth factor-beta(1) and platelet-derived growth factor were observed at 12 h, and remained elevated at 14 days. Nerve growth factor levels were increased at 24-28 days. BAL fluid hepatocyte growth factor (HGF) was detected at 12 h, peaked at 24 h, and returned to baseline by 72 h. c-Met/HGF receptor was detected in the airways at 6 h, before HGF in the BAL, and continued to be observed 96 h after the last OVA challenge.

CONCLUSIONS

These data identify a temporal association between growth factor production and Th2 cytokine production and the kinetics of AHR. Growth factors may play important roles in the development of allergic airway inflammation and AHR even in the early stages of asthma, before remodeling is initiated.

Role of the phosphoinositide 3-kinase p110delta in generation of type 2 cytokine responses and allergic airway inflammation

Phosphoinositide 3-kinases (PI3K) regulate immune activation via their roles in signal transduction of multiple classes of receptors. Here, we examined the effect of genetic inactivation of the hemopoietic cell-restricted PI3K isoform p110delta on systemic cytokine and chemokine responses and allergic airway inflammation. We found that type 2 cytokine responses (IL-4, IL-5 and IL-13) are significantly decreased in p110delta mutants, whereas type 1 cytokine responses (IFN-gamma and CXCL10) were robust. Elevated IFN-gamma production during the primary response to ovalbumin (OVA) was associated with reduced production of the regulatory cytokine IL-10. IFN-gamma and IL-10 production normalized after secondary OVA immunization; however, type 2 cytokine production was persistently reduced. Type 2 cytokine-dependent airway inflammation elicited by intranasal challenge with OVA was dramatically reduced, with reduced levels of eosinophil recruitment and mucus production observed in the lungs. Induction of respiratory hyper-responsiveness to inhaled methacholine, a hallmark of asthma, was markedly attenuated in p110delta-inactivated mice. Adoptive transfer of OVA-primed splenocytes from normal but not p110delta-inactivated mice could induce airway eosinophilia in naive, airway-challenged recipient mice. These data demonstrate a novel functional role for p110delta signaling in induction of type 2 responses in vivo and may offer a new therapeutic target for Th2-mediated airway disease.

Signal transducer and activator of transcription signals in allergic disease

Signal transducer and activator of transcription (STAT) proteins are a group of transcription factors that transmit signals from the extracellular milieu of cells to the nucleus. They are crucial for the signaling of many cytokines that are mediators of allergic inflammation and impact various cell types critical to allergy including epithelial cells, mast cells, lymphocytes, dendritic cells, and eosinophils. Dysregulation of STAT signaling has been implicated in allergic disease, highlighting the importance of these ubiquitous molecules in allergic inflammation and the potential of these pathways as a target for therapeutic intervention. This review will summarize the current understanding of the roles of STAT signaling in allergic disease and the potential of targeting STATs for the treatment of allergic disorders, emphasizing recent observations.

A latex-induced allergic airway inflammation model in mice

Latex allergy is important due to serious health impacts and widespread use of its products. Latex allergic reactions can be induced in skin and mucosal surfaces including the respiratory tract. The development of murine models of allergic airway inflammation has provided a framework to dissect out the cellular and molecular mechanisms of allergic respiratory inflammation. In this study we have developed a new mouse model of latex allergic airway inflammation using aerosol inhalation. The allergic inflammatory responses were characterized in this model. Mice were injected intraperitoneally with 0, 10, 50, or 200 microg of latex extract and their serum anti-latex IgE titers were determined. In the second stage, a standard protocol of inhalation was designed and three doses of latex extract solutions including 1%, 0.1%, and 0.01% were used to induce allergic airway inflammation. Bronchoalveolar lavage cytokines (IL-5 and IL-13) and serum anti-latex IgE and IgG(1) titers were determined by ELISA. Eosinophil levels in lung, peripheral blood, bronchoalveolar lavage and bone marrow were also evaluated. Histological analysis of lung tissue was also performed after latex inhalation. The aerosol inhalation of 1% latex allergens solution and presensitization with 50 mug of latex in this study resulted in the development of allergic airway inflammation characterized by elevated allergen specific IgE and IgG(1), peripheral blood, bronchoalveolar lavage and bone marrow eosinophilia. Histological analysis of the lung revealed an inflammatory response characterized by eosinophil accumulation. Elevated levels of Th2 cytokines IL-5 and IL-13 also were shown in bronchoalveolar lavage samples. These studies demonstrate that sensitization and subsequent aerosol inhalational challenge of latex allergen extract promotes allergic airway inflammation characterized by elevated IL-5 and IL-13 and eosinophils.

Membrane-bound eotaxin-3 mediates eosinophil transepithelial migration in IL-4-stimulated epithelial cells

Epithelial cells play an important role in orchestrating mucosal immune responses. In allergic-type inflammation, epithelial cells control the recruitment of eosinophils into the mucosa. Th2-type cytokine-driven release of eosinophil-active chemokines from epithelial cells directs eosinophil migration into the mucosal epithelium. CCR3, the main eosinophil chemokine receptor, regulates this process; however, the respective contribution of individual CCR3 ligands in eosinophil transepithelial migration is less well understood. Using an in vitro transepithelial chemotaxis system, we found that eotaxin-3 produced by IL-4-stimulated airway epithelial cells and CCR3 on eosinophils exclusively mediate eosinophil transepithelial migration. Eotaxin-3 protein levels were also increased in the nasal mucosal epithelium recovered from allergic patients as compared to non-allergic patients. Surprisingly, eotaxin-3 in IL-4-stimulated airway epithelial cells was predominantly cell surface bound, and the cell surface form was critical for eosinophil transepithelial migration. Eotaxin-3 cell surface association was partially glycosaminoglycan (GAG) dependent, but was completely protein dependent, suggesting that eotaxin-3 associates with both GAG and cell surface proteins. We thus provide evidence that cell surface-associated eotaxin-3 is the critical IL-4-dependent chemotactic signal mediating eosinophil transepithelial migration in the setting of allergic inflammation.

Inhibition of phosphodiesterase activity, airway inflammation and hyperresponsiveness by PDE4 inhibitor and glucocorticoid in a murine model of allergic asthma

Phosphodiesterase 4 (PDE4) isozyme plays important roles in inflammatory and immunomodulatory cells. In this study, piclamilast, a selective PDE4 inhibitor, was used to investigate the role of PDE4 in respiratory function and inflammation in a murine asthma model. Sensitized mice were challenged with aerosolized ovalbumin for 7 days, piclamilast (1, 3 and 10 mg/kg) and dexamethasone (2 mg/kg) were orally administered once daily during the period of challenge. Twenty-four hours after the last challenge, airway hyperresponsiveness to methacholine was determined by whole-body plethysmography, airway inflammation and mucus secretion by histomorphometry, pulmonary cAMP-PDE activity by HPLC, cytokine levels in bronchoalveolar lavage fluid and their mRNA expression in lung by ELISA and RT-PCR, respectively. In control mice, significant induction of cAMP-PDE activity was parallel to the increases of hyperresponsiveness, inflammatory cells, cytokine levels, mRNA expression as well as goblet cell hyperplasia. However, piclamilast dose-dependently and significantly improved airway resistance and dynamic compliance, and the maximal effect was similar to that of dexamethasone. Piclamilast treatment dose-dependently and significantly prevented the increase in inflammatory cell number and goblet cell hyperplasia, as well as production of cytokines, including eotaxin, TNFalpha and IL-4. Piclamilast exerted a weaker inhibitory effect than dexamethasone on eosinophils and neutrophils, had no effect on lymphocyte accumulation. Moreover, piclamilast inhibited up-regulation of cAMP-PDE activity and cytokine mRNA expression; the maximal inhibition of cAMP-PDE was greater than that exerted by dexamethasone, and was similar to dexamethasone on cytokine mRNA expression. This study suggests that inhibition of PDE4 by piclamilast robustly improves the pulmonary function, airway inflammation and goblet cell hyperplasia in murine allergenic asthma.

Transgenic mice expressing the T cell antigen receptor specific for an immunodominant epitope of a major allergen of house dust mite develop an asthmatic phenotype on exposure of the airways to allergen

BACKGROUND

Current studies on mechanisms underlying allergen-induced pulmonary inflammation and asthma are hampered by the lack of appropriate physiological in vivo models that reflect the natural route of allergen exposure and sensitization.

OBJECTIVE

To generate and phenotype a transgenic mouse strain expressing the T cell receptor (TCR) specific for an immunodominant domain of the major inhalant allergen Dermatophagoides pteronyssinus species of house dust mite (Der p 1), for the development of an in vivo model of allergic asthma.

METHODS

Der p 1 transgenic mice were generated using TCR-alphabeta derived from a CD4+ T cell hybridoma reactive with Der p 1 residues p 110-131. The frequency and functional activity of peripheral T cells were determined and parameters of airway inflammation assessed following allergen challenge of the airways with Der p 1.

RESULTS

CD4+ T cells are functionally active, exhibiting dose-dependent proliferation and IL-4 production on primary stimulation with Der p 1 or Der p 1, p 110-131 in vitro, independent of in vivo antigen priming. On sensitization of the airways with allergen, in the absence of systemic priming or the application of adjuvants, the TCR transgenic mice develop airway inflammation characterized by a marked lymphocytic and eosinophilic infiltrate with goblet cell hyperplasia and enhanced mucin production.

CONCLUSION

The Der p 1 TCR transgenic mice provide a model for investigating the pathophysiological mechanisms of pulmonary inflammation following sensitization by exposure of the airways to allergen and for investigating the mode of action and efficacy of novel immunotherapeutics.

Interleukins and STAT signaling

Metazoan cells secrete small proteins termed cytokines that execute a variety of biological functions essential for the survival of organisms. Binding of cytokines that belong to the hematopoietin- or interferon-family, to their cognate receptors on the surface of target cells, induces receptor aggregation, which in turn sequentially triggers tyrosine-phosphorylation-dependent activation of receptor-associated Janus-family tyrosine kinases (JAKs), receptors, and signal transducers and activators of transcription (STATs). Phosphorylated STATs form dimers that migrate to the nucleus, bind to cognate enhancer elements and activate transcription of target genes. Each cytokine activates a specific set of genes to execute its biological functions with a certain degree of redundancy. Cytokine signals are, in general, transient in nature. Therefore, under normal physiological conditions, initiation and attenuation of cytokine signals are tightly controlled via multiple cellular and molecular mechanisms. Aberrant activation of cytokine signaling pathways is, however, found under a variety of patho-physiological conditions including cancer and immune diseases.

Absence of leukotriene B4 receptor 1 confers resistance to airway hyperresponsiveness and Th2-type immune responses

Bronchial asthma is an increasingly common disorder that remains poorly understood and difficult to manage. The disease is characterized by airway hyperresponsiveness, chronic inflammation, and mucus overproduction. Based on the finding that leukotriene B4 receptor 1 (BLT1) is expressed highly in Th2 lymphocytes, we analyzed the roles of BLT1 using an OVA-induced bronchial asthma model. BLT1-null mice did not develop airway hyperresponsiveness, eosinophilic inflammation, and hyperplasia of goblet cells. Attenuated symptoms were accompanied by reduced IgE production, and accumulation of IL-5 and IL-13 in bronchoalveolar lavage fluid, suggesting attenuated Th2-type immune response in BLT1-null mice. Peribronchial lymph node cells of sensitized BLT1-null mice showed much attenuated proliferation and production of Th2 cytokines upon re-stimulation with Ag in vitro. Thus, LTB4-BLT1 axis is required for the development of Th2-type immune response, and blockade of LTB4 functions through BLT1 would be novel and useful in the effort to ameliorate bronchial asthma and related Th2-biased immune disorders.