IL-13 induces airways hyperreactivity independently of the IL-4R alpha chain in the allergic lung

Post-viral lung diseases: the microbiota as a key player

Viral infections of the respiratory tract can lead to chronic lung injury through immunopathological mechanisms that remain unclear. Communities of commensal bacteria colonising the respiratory tract, known as the respiratory tract microbiota, are altered in viral infections, which can contribute to inflammation, lung epithelial damage and subsequent development of lung disease. Emerging evidence on post-viral lung injury suggests an interplay between viral infections, immune responses and airway microbiota composition in the development of viral-induced lung diseases. In this review, we present the clinical characteristics of post-viral lung injury, along with the underlying immunopathological mechanisms and host-bacteria interactions, with a focus on influenza virus, respiratory syncytial virus and coronaviruses. Additionally, considering the important role of the airway microbiota in viral-induced pulmonary sequelae, we suggest key areas for future research on respiratory microbiota involvement in the development of post-viral lung diseases.

Geniposidic acid inhibits OVA-induced asthma by suppressing allergic airway inflammation and regulating gut microbiota

Asthma is a serious chronic inflammatory disease of the respiratory system. In this study, we aimed to explore the role of geniposidic acid (GPA) in ovalbumin (OVA)-induced asthma in mice and to clarify its underlying mechanism. The mice were divided into control group, OVA group, OVA+GPA (12.5, 25, 50 mg/kg) groups. Inflammatory mediators were measured by ELISA. Gut microbiota was detected by 16S RNA sequencing. The results demonstrated that GPA attenuated OVA-induced lung injury, inflammatory cell infiltration, and mucus hypersecretion. OVA-induced IL-4, IL-5, IL-13, and IgE production was also inhibited by GPA. IFN-γ production was increased by GPA. Furthermore, GPA inhibited OVA-induced NF-κB activation and increased Nrf2 expression. In addition, GPA alleviated the dysbiosis of gut microbiota induced by OVA. After GPA treatment, the diversity and abundance of intestinal microbiota in asthma mice increased. At the phylum level, GPA significantly reduced the relative abundance of Ligilactobacillus, Lachnospiraceae, Helicobacter, and Bacteroidales and significantly increased the relative abundance of Muribaculaceae and Muribaculum. In conclusion, GPA protect mice against OVA-induced asthma through suppressing inflammation and regulating gut microbiota.

The bioflavonoid hispidulin effectively attenuates T helper type 2-driven allergic lung inflammation in the ovalbumin-induced allergic asthma mouse model

BACKGROUND

Allergic asthma affects nearly 300 million people worldwide and causes ahigh burden of disability and death. Effective treatments rely heavily on corticosteroids, which are associated with various complications. So, the alternative treatment is of significance. Hispidulin is a bioflavonoid found in herbs that were used in traditional medicine to treat inflammatory diseases, including asthma. This study aims to investigate the efficacy of hispidulin compound in the treatment of allergic lung inflammation using the mouse model of allergic asthma.

METHODS

BALB/c mice were sensitized and challenged with chicken egg ovalbumin. Cells and cytokines from bronchoalveolar lavage (BAL) fluid were examined. Lung tissues were collected for histologic study. Mouse splenic CD4+ cells were cultured to observe the effect of hispidulin on T-helper 2 (Th2) cell differentiation in vitro.

RESULTS

Hispidulin treatment could alleviate allergic airway inflammation as evidenced by a significant reduction in the inflammatory cell count and Th2 cytokines interleukin (IL)-4, IL-5, IL-13 in BAL fluid. Histologic examination of lung tissues revealed lower inflammatory cell infiltration to the bronchi and less airway goblet cell hyperplasia in the treatment group compared to the control group. At the cellular level, hispidulin (25, 50, and 100 μM) was found to directly suppress the differentiation and proliferation of Th2 cells and to suppress the production of Th2 cytokines, such as IL-4, IL-5, and IL-13, in vitro.

CONCLUSIONS

Hispidulin treatment was shown to effectively decrease type 2 lung inflammation in an ovalbumin-induced allergic asthma mouse model by directly suppressing Th2 cell differentiation and functions.

7-Amino acid peptide (7P) decreased airway inflammation and hyperresponsiveness in a murine model of asthma

A 7-amino acid peptide (7P), (Gly-Gln-Thr-Tyr-Thr-Ser-Gly) is one of the synthesized mimic polypeptides, which is the second envelope protein at hypervariable region 1 of chronic hepatitis C virus (HCV HVR1). It contributed to the anti-inflammatory reaction and inhibited lung Th9 responses in asthma through binding to CD81. In this study, we examined the effects of 7P on bronchoconstriction, acute inflammation of the airways, and lung Th2-type responses during allergic lung inflammation. Our results determined that 7P decreased bronchoconstriction and inhibited both acute inflammatory cytokines (TNFα, IL-1β, and IL-6) and Th2 cell cytokine responses (IL-5, IL-4, and IL-13) during allergic lung inflammation. 7P directly inhibited lung Th2 cell differentiation (7P: 5.1% vs. vehicle:12.2% and control 7P:12.2%) and suppressed airway inflammatory cytokine signal transduction to decrease Th2 cell response. Overall, 7P significantly decreased airway hyperresponsiveness (AHR), airway inflammation, and Th2 responses, which may serve as a novel therapeutic candidate during allergic lung inflammation.

Identification and biochemical characterization of Asp t 36, a new fungal allergen from Aspergillus terreus

Aspergillus terreus is an allergenic fungus, in addition to causing infections in both humans and plants. However, the allergens in this fungus are still unknown, limiting the development of diagnostic and therapeutic strategies. We used a proteomic approach to search for allergens, identifying 16 allergens based on two-dimensional immunoblotting with A. terreus susceptible patient sera. We further characterized triose-phosphate isomerase (Asp t 36), one of the dominant IgE (IgE)-reactive proteins. The gene was cloned and expressed in Escherichia coli. Phylogenetic analysis showed Asp t 36 to be highly conserved with close similarity to the triose-phosphate isomerase protein sequence from Dermatophagoides farinae, an allergenic dust mite. We identified four immunodominant epitopes using synthetic peptides, and mapped them on a homology-based model of the tertiary structure of Asp t 36. Among these, two were found to create a continuous surface patch on the 3D structure, rendering it an IgE-binding hotspot. Biophysical analysis indicated that Asp t 36 shows similar secondary structure content and temperature sensitivity with other reported triose-phosphate isomerase allergens. In vivo studies using a murine model displayed that the recombinant Asp t 36 was able to stimulate airway inflammation, as demonstrated by an influx of eosinophils, goblet cell hyperplasia, elevated serum Igs, and induction of Th2 cytokines. Collectively, our results reveal the immunogenic property of Asp t 36, a major allergen from A. terreus, and define a new fungal allergen more broadly. This allergen could serve as a potent candidate for investigating component resolved diagnosis and immunotherapy.

A key role for IL-13 signaling via the type 2 IL-4 receptor in experimental atopic dermatitis

IL-13 and IL-4 are potent mediators of type 2-associated inflammation such as those found in atopic dermatitis (AD). IL-4 shares overlapping biological functions with IL-13, a finding that is mainly explained by their ability to signal via the type 2 IL-4 receptor (R), which is composed of IL-4Rα in association with IL-13Rα1. Nonetheless, the role of the type 2 IL-4R in AD remains to be clearly defined. Induction of two distinct models of experimental AD in Il13ra1 ^-/- mice, which lack the type 2 IL-4R, revealed that dermatitis, including ear and epidermal thickening, was dependent on type 2 IL-4R signaling. Expression of TNF-α was dependent on the type 2 IL-4R, whereas induction of IL-4, IgE, CCL24, and skin eosinophilia was dependent on the type 1 IL-4R. Neutralization of IL-4, IL-13, and TNF-α as well as studies in bone marrow-chimeric mice revealed that dermatitis, TNF-α, CXCL1, and CCL11 expression were exclusively mediated by IL-13 signaling via the type 2 IL-4R expressed by nonhematopoietic cells. Conversely, induction of IL-4, CCL24, and eosinophilia was dependent on IL-4 signaling via the type 1 IL-4R expressed by hematopoietic cells. Last, we pharmacologically targeted IL-13Rα1 and established a proof of concept for therapeutic targeting of this pathway in AD. Our data provide mechanistic insight into the differential roles of IL-4, IL-13, and their receptor components in allergic skin and highlight type 2 IL-4R as a potential therapeutic target in AD and other allergic diseases such as asthma and eosinophilic esophagitis.

Pulmonary delivery of ORMDL3 short hairpin RNA - a potential tool to regulate allergen-induced airway inflammation

Aim/Purpose: Exposure to various allergens has been shown to increase expression of ORMDL3 in the lung in models of allergic asthma. Studies using genetically modified (transgenic or knock out) mice have revealed some of the functions of ORMDL3 in asthma pathogenesis, although amid debate. The goal of this study was to use targeted post-transcriptional downregulation of ORMDL3 in allergen-challenged wild-type (WT) mice by RNA interference to further elucidate the functional role of ORMDL3 in asthma pathogenesis and evaluate a potential therapeutic option.Methods: Allergen (ovalbumin [OVA])-challenged WT mice were administered intranasally (i.n) with a single dose of five short hairpin RNA (shRNA) constructs with different target sequence for murine ORMDL3 cloned in a lentiviral vector or with the empty vector (control). Mice were evaluated for allergen-induced airway hyperresponsiveness (AHR) and various features of airway inflammation after 72 hours.Results: I.n administration of a single dose of ORMDL3 shRNAs to OVA-challenged mice resulted in reduction of ORMDL3 gene expression in the lungs associated with a significant reduction in AHR to inhaled methacholine and in the number of inflammatory cells recruited in the airways, specifically eosinophils, as well as in airway mucus secretion compared to OVA-challenged mice that received the empty vector. Administration of ORMDL3 shRNAs also significantly inhibited levels of IL-13, eotaxin-2 and sphingosine in the lungs. Additionally, ORMDL3 shRNAs significantly inhibited the allergen-mediated increase in monohexyl ceramides C22:0 and C24:0.Conclusions: Post-transcriptional down regulation of ORMDL3 in allergic lungs using i.n-delivered ORMDL3 shRNA (akin to inhaled therapy) attenuates development of key features of airway allergic disease, confirming the involvement of ORMDL3 in allergic asthma pathogenesis and serving as a model for a potential therapeutic strategy.

Single and Synergistic Effects of Type 2 Cytokines on Eosinophils and Asthma Hallmarks

The type 2 cytokines IL-5, IL-13, and IL-4 play an important role in the induction and progression of asthma. According to the Global Initiative for Asthma guidelines, blood eosinophil numbers are one marker that helps to guide treatment decisions in patients suffering from severe forms of asthma. Effects of type 2 cytokines were analyzed, alone or in combination, on eosinophils in blood and other compartments and on the development of asthma symptoms. C57BL/6 mice received a single intranasal application of equimolar amounts of IL-5, IL-13, and IL-4, alone or in combination. Numbers, activation state, and migratory behavior of eosinophils in bone marrow (BM), blood, lung, and bronchoalveolar lavage as well as airway hyperresponsiveness and goblet cell metaplasia were evaluated. Only IL-13 was associated with airway eosinophilia, development of airway hyperresponsiveness, and goblet cell metaplasia, without any synergistic effects. IL-5 increased the number of eosinophils in BM and lung tissue but failed to affect structural changes. IL-4 had similar, but weaker, effects to IL-13. Cytokine combinations synergistically affected eosinophils but failed to enhance IL-13-driven effects on lung function or goblet cell metaplasia. IL-5 and IL-13 markedly increased eosinophil numbers locally in lung and airways and distally in blood and BM, whereas IL-5 and IL-4 only increased eosinophils in lung and BM. IL-13 together with IL-4 failed to demonstrate any synergistic effect. These insights into single and combined effects of type 2 cytokines on disease-driving mechanisms could improve understanding of the impact and effectiveness of new therapies in asthma.

Ozone Inhalation Attenuated the Effects of Budesonide on Aspergillus fumigatus-Induced Airway Inflammation and Hyperreactivity in Mice

Inhaled glucocorticoids form the mainstay of asthma treatment because of their anti-inflammatory effects in the lung. Exposure to the air pollutant ozone (O₃) exacerbates chronic airways disease. We and others showed that presence of the epithelial-derived surfactant protein-D (SP-D) is important in immunoprotection against inflammatory changes including those induced by O₃ inhalation in the airways. SP-D synthesis requires glucocorticoids. We hypothesized here that O₃ exposure impairs glucocorticoid responsiveness (including SP-D production) in allergic airway inflammation. The effects of O₃ inhalation and glucocorticoid treatment were studied in a mouse model of allergic asthma induced by sensitization and challenge with Aspergillus fumigatus (Af) in vivo. The role of O₃ and glucocorticoids in regulation of SP-D expression was investigated in A549 and primary human type II alveolar epithelial cells in vitro. Budesonide inhibited airway hyperreactivity, eosinophil counts in the lung and bronchoalveolar lavage (BAL) and CCL11, IL-13, and IL-23p19 release in the BAL of mice sensitized and challenged with Af (p < 0.05). The inhibitory effects of budesonide were attenuated on inflammatory changes and were completely abolished on airway hyperreactivity after O₃ exposure of mice sensitized and challenged with Af. O₃ stimulated release of pro-neutrophilic mediators including CCL20 and IL-6 into the airways and impaired the inhibitory effects of budesonide on CCL11, IL-13 and IL-23. O₃ also prevented budesonide-induced release of the immunoprotective lung collectin SP-D into the airways of allergen-challenged mice. O₃ had a bi-phasic direct effect with early (<12 h) inhibition and late (>48 h) activation of SP-D mRNA (sftpd) in vitro. Dexamethasone and budesonide induced sftpd transcription and translation in human type II alveolar epithelial cells in a glucocorticoid receptor and STAT3 (an IL-6 responsive transcription factor) dependent manner. Our study indicates that O₃ exposure counteracts the effects of budesonide on airway inflammation, airway hyperreactivity, and SP-D production. We speculate that impairment of SP-D expression may contribute to the acute O₃-induced airway inflammation. Asthmatics exposed to high ambient O₃ levels may become less responsive to glucocorticoid treatment during acute exacerbations.

FABP4 regulates eosinophil recruitment and activation in allergic airway inflammation

Fatty acid binding protein 4 (FABP4), a member of a family of lipid-binding proteins, is known to play a role in inflammation by virtue of its ability to regulate intracellular events such as lipid fluxes and signaling. Studies have indicated a proinflammatory role for FABP4 in allergic asthma although its expression and function in eosinophils, the predominant inflammatory cells recruited to allergic airways, were not investigated. We examined expression of FABP4 in murine eosinophils and its role in regulating cell recruitment in vitro as well as in cockroach antigen (CRA)-induced allergic airway inflammation. CRA exposure led to airway recruitment of FABP4-expressing inflammatory cells, specifically eosinophils, in wild-type (WT) mice. FABP4 expression in eosinophils was induced by TNF-α as well as IL-4 and IL-13. FABP4-deficient eosinophils exhibited markedly decreased cell spreading/formation of leading edges on vascular cell adhesion molecule-1 and significantly decreased adhesion to intercellular adhesion molecule-1 associated with reduced β2-integrin expression relative to WT cells. Furthermore, FABP4-deficient eosinophils exhibited decreased migration, F-actin polymerization, calcium flux, and ERK(1/2) phosphorylation in response to eotaxin-1. In vivo, CRA-challenged FABP4-deficient mice exhibited attenuated eosinophilia and significantly reduced airway inflammation (improved airway reactivity, lower IL-5, IL-13, TNF-α, and cysteinyl leukotriene C4 levels, decreased airway structural changes) compared with WT mice. In conclusion, expression of FABP4 in eosinophils is induced during conditions of inflammation and plays a proinflammatory role in the development of allergic asthma by promoting eosinophil adhesion and migration and contributing to the development of various aspects of airway inflammation.

Modelling the asthma phenotype: impact of cigarette smoke exposure

Background

Asthmatics that are exposed to inhaled pollutants such as cigarette smoke (CS) have increased symptom severity. Approximately 25% of adult asthmatics are thought to be active smokers and many sufferers, especially in the third world, are exposed to high levels of inhaled pollutants. The mechanism by which CS or other airborne pollutants alter the disease phenotype and the effectiveness of treatment in asthma is not known. The aim of this study was to determine the impact of CS exposure on the phenotype and treatment sensitivity of rodent models of allergic asthma.

Methods

Models of allergic asthma were configured that mimicked aspects of the asthma phenotype and the effect of CS exposure investigated. In some experiments, treatment with gold standard asthma therapies was investigated and end-points such as airway cellular burden, late asthmatic response (LAR) and airway hyper-Reactivity (AHR) assessed.

Results

CS co-exposure caused an increase in the LAR but interestingly attenuated the AHR. The effectiveness of LABA, LAMA and glucocorticoid treatment on LAR appeared to be retained in the CS-exposed model system. The eosinophilia or lymphocyte burden was not altered by CS co-exposure, nor did CS appear to alter the effectiveness of glucocorticoid treatment. Steroids, however failed to reduce the neutrophilic inflammation in sensitized mice exposed to CS.

Conclusions

These model data have certain parallels with clinical findings in asthmatics, where CS exposure did not impact the anti-inflammatory efficacy of steroids but attenuated AHR and enhanced symptoms such as the bronchospasm associated with the LAR. These model systems may be utilised to investigate how CS and other airborne pollutants impact the asthma phenotype; providing the opportunity to identify novel targets.

Regulatory effects of IL-15 on allergen-induced airway obstruction

BACKGROUND

Airway obstruction is a physiologic feature of asthma, and IL-15 might have an important role in asthma pathogenesis.

OBJECTIVE

We tested the hypothesis that regulation of IL-15 is critical for preservation of allergen-induced airway hyperresponsiveness (AHR), airway resistance, and compliance in response to methacholine.

METHODS

Airway inflammation, AHR, resistance, and compliance were assessed in Il15 gene-deficient mice and IL-15-overexpressing mice in an allergen-induced murine model of asthma. We assessed eosinophil numbers by using anti-major basic protein immunostaining, goblet cell hyperplasia by using periodic acid-Schiff staining, and cytokine and chemokine levels by performing quantitative PCR and ELISA.

RESULTS

We made a novel observation that IL-15 deficiency promotes baseline airway resistance in naive mice. Moreover, rIL-15 delivery to the lung downregulates expression of proinflammatory cytokines and improves allergen-induced AHR, airway resistance, and compliance. These observations were further validated in doxycycline-inducible CC10-IL-15 bitransgenic mice. Doxycycline-exposed, Aspergillus species extract-challenged CC10-IL-15 bitransgenic mice exhibited significantly reduced levels of proinflammatory cytokines (IL-4, IL-5, and IL-13) and decreased goblet cell hyperplasia. Airway obstruction, including AHR and airway resistance, was diminished in allergen-challenged doxycycline-exposed compared with non-doxycycline-exposed CC10-IL-15 bitransgenic mice. Mechanistically, we observed that IL-15-mediated protection of airway obstruction is associated with induced IFN-γ- and IL-10-producing regulatory CD4+CD25+ forkhead box p3 (Foxp3)+ T cells. Additionally, we found that a human IL-15 agonist (ALT-803) improved airway resistance and compliance in an experimental asthma model.

CONCLUSION

We report our novel finding that IL-15 has a potent inhibitory effect on the airway obstruction that occurs in response to environmental allergens.

Combination Therapy with Budesonide and Salmeterol in Experimental Allergic Inflammation

The aim of this study was to determinate bronchodilator, antitussive, and ciliomodulatory activity of inhaled combination therapy with budesonide and salmeterol, and to correlate the results with the anti-inflammatory effect. The experiments were performed using two models of allergic inflammation (21 and 28 days long sensitization with ovalbumine) in guinea pigs. The animals were treated daily by aerosols of budesonide (1 mM), salmeterol (0.17 mM), and a half-dose combination of the two drugs. Antitussive and bronchodilator activities were evaluated in vivo. The ciliary beat frequency (CBF) was assessed in vitro in tracheal brushed samples, and inflammatory cytokines (IL-4, IL-5, IL-13, GM-CSF, and TNF-α) were determined in bronchoalveolar lavage fluid (BALF). We found that the combination therapy significantly decreased the number of cough efforts, airway reactivity, and the level of inflammatory cytokines in both models of allergic asthma. Three weeks long sensitization led to an increase in CBF and all three therapeutic approaches have shown a ciliostimulatory effect in order: salmeterol < budesonid < combination therapy. Four weeks long ovalbumine sensitization, on the other hand, decreased the CBF, increased IL-5, and decreased IL-13. In this case, only the combination therapy was able to stimulate the CBF. We conclude that a half-dose combination therapy of budesonide and salmeterol shows comparable antitussive, bronchodilator, and the anti-inflammatory effect to a full dose therapy with budesonide alone, but had a more pronounced stimulatory effect on the CBF.

IL-13 regulates IL-17C expression by suppressing NF-κB-mediated transcriptional activation in airway epithelial cells

The cytokine interleukin (IL)-17C is highly expressed in epithelial tissues and involved in innate immune responses; however, the regulation of IL-17C expression in the airways remains poorly understood. Here, we show that IL-1β strongly induces both IL-17C mRNA and protein expression in primary normal human bronchial epithelial cells. Conversely, IL-13 significantly reduced the IL-1β-induced IL-17C expression. Attenuation of the nuclear factor (NF)-κB-signaling pathway using an NF-κB-subunit p65-specific small-interfering RNA (siRNA), reduced IL-1β-induced IL-17C expression, demonstrating the importance of NF-κB signaling in IL-17C regulation. The inhibitory effects of IL-13 on IL-17C expression were abolished when the Janus kinase (JAK)/signal transducer and activator of transcription 6 (STAT6)-signaling pathway was impaired, using either the JAK inhibitor ruxolitinib or a STAT6-specific siRNA. Western blot analysis demonstrated that IL-1β promoted both IκB-α phosphorylation and degradation, and p65 nuclear translocation. Although IL-13 induced STAT6 phosphorylation and nuclear translocation, it did not affect the activation of the IL-1β-mediated NF-κB-pathway. Using chromatin immunoprecipitation, we confirmed that IL-1β enhanced p65 binding to regions within the IL-17C promoter that flank putative NF-κB-binding sites (-130/-120 and -157/-147). Interestingly, IL-13 treatment reduced the IL-1β-mediated p65 binding to these regions. These findings demonstrate that NF-κB-mediated transcriptional mechanisms are critically involved in the IL-1β-mediated IL-17C induction, and that IL-13 negatively regulates this induction by suppressing NF-κB-based transcriptional activation.

Sensing and responding to allergic response cytokines through a genetically encoded circuit

While constantly rising, the prevalence of allergies is globally one of the highest among chronic diseases. Current treatments of allergic diseases include the application of anti-histamines, immunotherapy, steroids, and anti-immunoglobulin E (IgE) antibodies. Here we report mammalian cells engineered with a synthetic signaling cascade able to monitor extracellular pathophysiological levels of interleukin 4 and interleukin 13, two main cytokines orchestrating allergic inflammation. Upon activation of transgenic cells by these cytokines, designed ankyrin repeat protein (DARPin) E2_79, a non-immunogenic protein binding human IgE, is secreted in a precisely controlled and reversible manner. Using human whole blood cell culturing, we demonstrate that the mammalian dual T helper 2 cytokine sensor produces sufficient levels of DARPin E2_79 to dampen histamine release in allergic subjects exposed to allergens. Hence, therapeutic gene networks monitoring disease-associated cytokines coupled with in situ production, secretion and systemic delivery of immunomodulatory biologics may foster advances in the treatment of allergies.

The standard treatment for an allergic response is anti-histamines, steroids and anti-IgE antibodies. Here the authors present a genetic circuit that senses IL-4 and IL-13 and responses with DARPin production to bind IgE.

IL-17RB+ granulocytes are associated with airflow obstruction in asthma

BACKGROUND

Interleukin (IL)-25 (IL-17E) is a proinflammatory cytokine that plays an important role in the T-helper type 2 cell pathway. The effects of IL-25 are mediated by its specific receptor, IL-17RB. Previous studies have defined an IL-17RB⁺ granulocyte population known as type 2 myeloid (T2M) cells that express T-helper type 2 cell cytokines. The correlation of IL-17RB⁺ granulocytes, T2M cells, and asthma parameters is unknown.

OBJECTIVE

To investigate the relation of IL-17RB⁺ granulocytes (and its subset, T2M cells) in patients with asthma with clinical parameters including spirometric values and the Asthma Control Test (ACT).

METHODS

Peripheral blood from subjects with asthma and healthy controls was collected and analyzed by flow cytometry. Granulocytes were gated for IL-17RB⁺, T2M (CD11b⁺CD16⁺CD177⁺IL-17RB⁺), and eosinophil (CD16^-) populations. Spirometry testing was performed on subjects with asthma. ACT scores and medical histories were collected by questionnaire and chart review. Correlations of IL-17RB⁺ cells and T2M cells with spirometry and ACT score were analyzed.

RESULTS

Percentages of IL-17RB⁺ granulocytes and T2M cells were larger in subjects with asthma than in controls. Furthermore, percentages of the 2 cell populations were negatively correlated with degree of airway obstruction as measured by the ratio of percentage-predicted forced expiratory volume in 1 second to force vital capacity (r = -0.17, P = .043 for IL-17RB⁺ granulocytes; r = -0.32, P = .03 for T2M cells). There was no correlation with ACT score. The percentage of eosinophils was increased in subjects with asthma. However, IL-17RB⁺ eosinophil percentages were similar between subjects with asthma and controls and did not correlate with any clinical parameter.

CONCLUSION

IL-17RB⁺ granulocytes and T2M cells from peripheral blood were increased in subjects with asthma, and the 2 cell types correlated with degree of airflow obstruction.

Lebrikizumab for the treatment of asthma

INTRODUCTION

In asthma, most commonly, 'conventional' anti-inflammatory medications represented by inhaled corticosteroids and leukotriene inhibitors are effective. In some patients however additional inhibition of the airways inflammation is necessary. Such compounds might be molecules inhibiting specifically certain inflammation pathways and lebrikizumab an anti IL-13 molecule might represent a relevant example as a potential asthma therapy.

AREAS COVERED

Discussion of the rationale for the use of lebrikizumab in asthma. Analysis of the related preclinical and clinical data on lebrikizumab in asthma.

EXPERT OPINION

Lebrikizumab demonstrated efficacy in an asthma subset characterized by high serum periostin levels and by heavy eosinophilic inflammation. Phase III data are necessary in order to better position this therapy in asthma including as a potential personalized approach.

Interleukin-13 Receptor α1-Dependent Responses in the Intestine Are Critical to Parasite Clearance

Nematode infection upregulates interleukin-4 (IL-4) and IL-13 and induces STAT6-dependent changes in gut function that promote worm clearance. IL-4 and IL-13 activate the type 2 IL-4 receptor (IL-4R), which contains the IL-13Rα1 and IL-4Rα chains. We used mice deficient in IL-13Rα1 (IL-13Rα1(-/-)) to examine the contribution of IL-13 acting at the type 2 IL-4R to immune and functional responses to primary (Hb1) and secondary (Hb2) infections with the gastrointestinal nematode parasite Heligmosomoides bakeri There were differences between strains in the IL-4 and IL-13 expression responses to Hb1 but not Hb2 infection. Following Hb2 infection, deficient mice had impaired worm expulsion and higher worm fecundity despite normal production of Th2-derived cytokines. The upregulation of IL-25 and IL-13Rα2 in Hb1- and Hb2-infected wild-type (WT) mice was absent in IL-13Rα1(-/-)mice. Goblet cell numbers and resistin-like molecule beta (RELM-β) expression were attenuated significantly in IL-13Rα1(-/-)mice following Hb2 infections. IL-13Rα1 contributes to the development of alternatively activated macrophages, but the type 1 IL-4R is also important. Hb1 infection had no effects on smooth muscle function or epithelial permeability in either strain, while the enhanced mucosal permeability and changes in smooth muscle function and morphology observed in response to Hb2 infection in WT mice were absent in IL-13Rα1(-/-)mice. Notably, the contribution of claudin-2, which has been linked to IL-13, does not mediate the increased mucosal permeability following Hb2 infection. These results show that activation of IL-13Rα1 is critical for key aspects of the immune and functional responses to Hb2 infection that facilitate expulsion.

Targeting the JAK-STAT pathway in the treatment of 'Th2-high' severe asthma

Severe asthma is a heterogeneous disease characterized by reversible airway obstruction, chronic inflammation and airway remodeling. Phenotyping and/or endotyping can lead to a more personalized treatment strategy, improving the efficacy of novel drugs. Atopic asthma is associated with high levels of Th2 cells, implicated in a number of inflammatory responses. Differentiation of these cells from naive T cells occurs primarily via the JAK-STAT signaling pathway. Targeting this pathway through inhibition of activating cytokines (IL-4 and IL-13) and their receptors, the JAKs or the STATs, has been shown to have a therapeutic effect on asthma pathology. There are a number of novel drugs currently in development, which target various pathway components; these include both biologics and small molecules at various stages of development.

CCL7 and IRF-7 Mediate Hallmark Inflammatory and IFN Responses following Rhinovirus 1B Infection

Rhinovirus (RV) infections are common and have the potential to exacerbate asthma. We have determined the lung transcriptome in RV strain 1B-infected naive BALB/c mice (nonallergic) and identified CCL7 and IFN regulatory factor (IRF)-7 among the most upregulated mRNA transcripts in the lung. To investigate their roles we employed anti-CCL7 Abs and an IRF-7-targeting small interfering RNA in vivo. Neutralizing CCL7 or inhibiting IRF-7 limited neutrophil and macrophage influx and IFN responses in nonallergic mice. Neutralizing CCL7 also reduced activation of NF-κB p65 and p50 subunits, as well as airway hyperreactivity (AHR) in nonallergic mice. However, neither NF-κB subunit activation nor AHR was abolished with infection of allergic mice after neutralizing CCL7, despite a reduction in the number of neutrophils, macrophages, and eosinophils. IRF-7 small interfering RNA primarily suppressed IFN-α and IFN-β levels during infection of allergic mice. Our data highlight a pivotal role of CCL7 and IRF-7 in RV-induced inflammation and IFN responses and link NF-κB signaling to the development of AHR.

Pro-inflammatory role of natural killer cells in the development of allergic airway disease

BACKGROUND

Natural Killer (NK) cells have been implicated in the development of allergic airway inflammation. However, the in vivo role of NK cells has not been firmly established due to the lack of animal models with selective deficiencies in NK cells.

OBJECTIVE

To determine the specific contribution of NK cells in a murine model of allergic airway disease (AAD).

METHODS

The role of NK cells in AAD was studied using NK-deficient (NKD) mice, perforin(-/-) mice, and mice depleted of Ly49A/D/G(+) NK cell subsets in an ovalbumin-induced model of allergic airway disease (OVA-AAD).

RESULTS

Induction of OVA-AAD in C57BL/6 wild-type (WT) mice resulted in the expansion of airway NK cells and the development of pronounced airway eosinophilia. In the absence of NK cells or specific subsets of NK cells, either in NKD mice, or after the depletion of Ly49A/D/G(+) NK cells, the development of OVA-AAD was significantly impaired as seen by decreased airway inflammation and eosinophilia, decreased secretion of the Th2 cytokines IL-4, IL-5 and IL-13 and diminished OVA-specific antibody production. Furthermore, while OVA-exposure induced a dramatic expansion of dendritic cells (DCs) in WT mice, their induction was significantly attenuated in NKD mice. Development of OVA-AAD in perforin(-/-) mice suggested that the proinflammatory role of NK cells is not dependent on perforin-mediated cytotoxicity. Lastly, induction of allergic disease by OVA-specific CD4 T cells from WT but not NK-depleted or NKD mice in RAG(-/-) recipients, demonstrates that NK cells are essential for T cell priming.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data demonstrate that conventional NK cells play an important and distinct role in the development of AAD. The presence of activated NK cells has been noted in patients with asthma. Understanding the mechanisms by which NK cells regulate allergic disease is therefore an important component of treatment approaches.

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

Inhibiting AKT phosphorylation employing non-cytotoxic anthraquinones ameliorates TH2 mediated allergic airways disease and rhinovirus exacerbation

BACKGROUND

Severe asthma is associated with T helper (TH) 2 and 17 cell activation, airway neutrophilia and phosphoinositide-3-kinase (PI3K) activation. Asthma exacerbations are commonly caused by rhinovirus (RV) and also associated with PI3K-driven inflammation. Anthraquinone derivatives have been shown to reduce PI3K-mediated AKT phosphorylation in-vitro.

OBJECTIVE

To determine the anti-inflammatory potential of anthraquinones in-vivo.

METHODS

BALB/c mice were sensitized and challenged with crude house dust mite extract to induce allergic airways disease and treated with mitoxantrone and a novel non-cytotoxic anthraquinone derivative. Allergic mice were also infected with RV1B to induce an exacerbation.

RESULTS

Anthraquinone treatment reduced AKT phosphorylation, hypoxia-inducible factor-1α and vascular endothelial growth factor expression, and ameliorated allergen- and RV-induced airways hyprereactivity, neutrophilic and eosinophilic inflammation, cytokine/chemokine expression, mucus hypersecretion, and expression of TH2 proteins in the airways. Anthraquinones also boosted type 1 interferon responses and limited RV replication in the lung.

CONCLUSION

Non-cytotoxic anthraquinone derivatives may be of therapeutic benefit for the treatment of severe and RV-induced asthma by blocking pro-inflammatory pathways regulated by PI3K/AKT.

Ablation of Arg1 in hematopoietic cells improves respiratory function of lung parenchyma, but not that of larger airways or inflammation in asthmatic mice

Asthma is a chronic inflammatory disease of the small airways, with airway hyperresponsiveness (AHR) and inflammation as hallmarks. Recent studies suggest a role for arginase in asthma pathogenesis, possibly because arginine is the substrate for both arginase and NO synthase and because NO modulates bronchial tone and inflammation. Our objective was to investigate the importance of increased pulmonary arginase 1 expression on methacholine-induced AHR and lung inflammation in a mouse model of allergic asthma. Arginase 1 expression in the lung was ablated by crossing Arg1(fl/fl) with Tie2Cre(tg/-) mice. Mice were sensitized and then challenged with ovalbumin. Lung function was measured with the Flexivent. Adaptive changes in gene expression, chemokine and cytokine secretion, and lung histology were quantified with quantitative PCR, ELISA, and immunohistochemistry. Arg1 deficiency did not affect the allergic response in lungs and large-airway resistance, but it improved peripheral lung function (tissue elastance and resistance) and attenuated adaptive increases in mRNA expression of arginine-catabolizing enzymes Arg2 and Nos2, arginine transporters Slc7a1 and Slc7a7, chemokines Ccl2 and Ccl11, cytokines Tnfa and Ifng, mucus-associated epithelial markers Clca3 and Muc5ac, and lung content of IL-13 and CCL11. However, expression of Il4, Il5, Il10, and Il13 mRNA; lung content of IL-4, IL-5, IL-10, TNF-α, and IFN-γ protein; and lung pathology were not affected. Correlation analysis showed that Arg1 ablation disturbed the coordinated pulmonary response to ovalbumin challenges, suggesting arginine (metabolite) dependence of this response. Arg1 ablation in the lung improved peripheral lung function and affected arginine metabolism but had little effect on airway inflammation.

Allergic conjunctivitis renders CD4(+) T cells resistant to t regulatory cells and exacerbates corneal allograft rejection

Allergic diseases rob corneal allografts of immune privilege and increase immune rejection. Corneal allograft rejection in BALB/c allergic hosts was analyzed using a short ragweed (SWR) pollen model of allergic conjunctivitis. Allergic conjunctivitis did not induce exaggerated T-cell responses to donor C57BL/6 (B6) alloantigens or stimulate cytotoxic T lymphocyte (CTL) responses. Allergic conjunctivitis did affect T regulatory cells (Tregs) that support graft survival. Exogenous IL-4, but not IL-5 or IL-13, prevented Treg suppression of CD4(+) effector T cells isolated from naïve mice. However, mice with allergic conjunctivitis developed Tregs that suppressed CD4(+) effector T-cell proliferation. In addition, IL-4 did not inhibit Treg suppression of IL-4Rα(-/-) CD4(+) T-cell responses, suggesting that IL-4 rendered effector T cells resistant to Tregs. SRW-sensitized IL-4Rα(-/-) mice displayed the same 50% graft survival as nonallergic WT mice, that was significantly less than the 100% rejection that occurred in allergic WT hosts, supporting the role of IL-4 in the abrogation of immune privilege. Moreover, exacerbation of corneal allograft rejection in allergic mice was reversed by administering anti-IL-4 antibody. Thus, allergy-induced exacerbation of corneal graft rejection is due to the production of IL-4, which renders effector T cells resistant to Treg suppression of alloimmune responses.

Anti-STAT6 CTL activity in Stat6 (-/-) mice: A cautionary tale

The generation of germline gene mutations in mice has been an invaluable tool for experimental biology. However, studying immune responses that develop in the absence of a specific protein that could alter thymic selection complicates experimental interpretations. We observed that CD8⁺ T cells from Stat6^−/− mice displayed “autoreactivity” to STAT6-expressing cells, associated with specific STAT6 peptides binding to MHC class I molecules. These results suggest caution in interpreting experiments where STAT6-expressing cells are transferred into Stat6^−/− mice, or where adoptive transfer of Stat6^−/− lymphocytes is performed. Our results further highlight additional considerations when studying immune responses involving cell transfer into gene-deficient mice.

The E3 ubiquitin ligase midline 1 promotes allergen and rhinovirus-induced asthma by inhibiting protein phosphatase 2A activity

Allergic airway inflammation is associated with activation of innate immune pathways by allergens. Acute exacerbations of asthma are commonly associated with rhinovirus infection. Here we show that, after exposure to house dust mite (HDM) or rhinovirus infection, the E3 ubiquitin ligase midline 1 (MID1) is upregulated in mouse bronchial epithelium. HDM regulates MID1 expression in a Toll-like receptor 4 (TLR4)- and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-dependent manner. MID1 decreases protein phosphatase 2A (PP2A) activity through association with its catalytic subunit PP2Ac. siRNA-mediated knockdown of MID1 or pharmacological activation of PP2A using a nonphosphorylatable FTY720 analog in mice exposed to HDM reduces airway hyperreactivity and inflammation, including the expression of interleukin-25 (IL-25), IL-33 and CCL20, IL-5 and IL-13 release, nuclear factor (NF)κB activity, p38 mitogen-activated protein kinase (MAPK) phosphorylation, accumulation of eosinophils, T lymphocytes and myeloid dendritic cells, and the number of mucus-producing cells. MID1 inhibition also limited rhinovirus-induced exacerbation of allergic airway disease. We found that MID1 was upregulated in primary human bronchial epithelial cells upon HDM or rhinovirus exposure, and this correlated with TRAIL and CCL20 expression. Together, these findings identify a key role of MID1 in allergic airway inflammation and links innate immune pathway activation to the development and exacerbation of asthma.

Cross-roads in the lung: immune cells and tissue interactions as determinants of allergic asthma

Allergic asthma is a chronic disease of the lung characterized by underlying Th2- and IgE-mediated inflammation, structural alterations of the bronchial wall, and airway hyperresponsiveness. Initial allergic sensitization and later development of chronic disease are determined by close interactions between lung structural cells and the resident and migratory immune cells in the lung. Epithelial cells play a crucial role in allergic sensitization by directly influencing dendritic cells induction of tolerant or effector T cells and production of type 2 cytokines by innate immune cells. During chronic disease, the bronchial epithelium, stroma, and smooth muscle become structurally and functionally altered, contributing to the perpetuation of tissue remodeling. Thus, targeting tissue-driven pathology in addition to inflammation may increase the effectiveness of asthma treatment.

Th2 cytokine antagonists: potential treatments for severe asthma

INTRODUCTION

Asthma is a major disease burden worldwide. Treatment with steroids and long acting β-agonists effectively manage symptoms in many patients but do not treat the underlying cause of disease and have serious side effects when used long term and in children. Therapies targeting the underlying causes of asthma are urgently needed. T helper type 2 (Th2) cells and the cytokines they release are clinically linked to the presentation of all forms of asthma. They are the primary drivers of mild to moderate and allergic asthma. They also play a pathogenetic role in exacerbations and more severe asthma though other factors are also involved. Much effort using animal models and human studies has been dedicated to the identification of the pathogenetic roles of these cells and cytokines and whether inhibition of their activity has therapeutic benefit in asthma.

AREAS COVERED

We discuss the current status of Th2 cytokine antagonists for the treatment of asthma. We also discuss the potential for targeting Th2-inducing cytokines, Th2 cell receptors and signaling as well as the use of Th2 cell antagonists, small interfering oligonucleotides, microRNAs, and combination therapies.

EXPERT OPINION

Th2 antagonists may be most effective in particular asthma subtypes/endotypes where specific cytokines are known to be active through the analysis of biomarkers. Targeting common receptors and pathways used by these cytokines may have additional benefit. Animal models have been valuable in identifying therapeutic targets in asthma, however the results from such studies need to be carefully interpreted and applied to appropriately stratified patient cohorts in well-designed clinical studies and trials.

The role of the T follicular helper cells in allergic disease

T follicular helper (Tfh) cells were discovered just over a decade ago as germinal centre T cells that help B cells make antibodies. Included in this role is affinity maturation and isotype switching. It is here that their functions become less clear. Tfh cells principally produce IL-21 which inhibits class switching to IgE. Recent studies have questioned whether the germinal centre is the main site of IgE class switching or IgE affinity maturation. In this review, I will examine the evidence that these cells are responsible for regulating IgE class switching and the relationship between Tfh cells and T helper 2 (Th2) effector cells.

OX40 ligand and programmed cell death 1 ligand 2 expression on inflammatory dendritic cells regulates CD4 T cell cytokine production in the lung during viral disease

CD4 Th differentiation is influenced by costimulatory molecules expressed on conventional dendritic cells (DCs) in regional lymph nodes and results in specific patterns of cytokine production. However, the function of costimulatory molecules on inflammatory (CD11b(+)) DCs in the lung during recall responses is not fully understood, but it is important for development of novel interventions to limit immunopathological responses to infection. Using a mouse model in which vaccination with vaccinia virus vectors expressing the respiratory syncytial virus (RSV) fusion protein (rVVF) or attachment protein (rVVG) leads to type 1- or type 2-biased cytokine responses, respectively, upon RSV challenge, we found expression of CD40 and OX40 ligand (OX40L) on lung inflammatory DCs was higher in rVVF-primed mice than in rVVG-primed mice early after RSV challenge, whereas the reverse was observed later in the response. Conversely, programmed cell death 1 ligand 2 (PD-L2) was higher in rVVG-primed mice throughout. Inflammatory DCs isolated at the resolution of inflammation revealed that OX40L on type 1-biased DCs promoted IL-5, whereas OX40L on type 2-biased DCs enhanced IFN-γ production by Ag-reactive Th cells. In contrast, PD-L2 promoted IFN-γ production, irrespective of conditions, suppressing IL-5 only if expressed on type 1-biased DCs. Thus, OX40L and PD-L2 expressed on DCs differentially regulate cytokine production during recall responses in the lung. Manipulation of these costimulatory pathways may provide a novel approach to controlling pulmonary inflammatory responses.

Regulation of eosinophil trafficking by SWAP-70 and its role in allergic airway inflammation

Eosinophils are the predominant inflammatory cells recruited to allergic airways. In this article, we show that human and murine eosinophils express SWAP-70, an intracellular RAC-binding signaling protein, and examine its role in mediating eosinophil trafficking and pulmonary recruitment in a murine model of allergic airway inflammation. Compared with wild-type eosinophils, SWAP-70-deficient (Swap-70(-/-)) eosinophils revealed altered adhesive interactions within inflamed postcapillary venules under conditions of blood flow by intravital microscopy, exhibiting enhanced slow rolling but decreased firm adhesion. In static adhesion assays, Swap-70(-/-) eosinophils adhered poorly to VCAM-1 and ICAM-1 and exhibited inefficient leading edge and uropod formation. Adherent Swap-70(-/-) eosinophils failed to translocate RAC1 to leading edges and displayed aberrant cell surface localization/distribution of α4 and Mac-1. Chemokine-induced migration of Swap-70(-/-) eosinophils was significantly decreased, correlating with reduced intracellular calcium levels, defective actin polymerization/depolymerization, and altered cytoskeletal rearrangement. In vivo, recruitment of eosinophils to the lungs of allergen-challenged Swap-70(-/-) mice, compared with wild-type mice, was significantly reduced, along with considerable attenuation of airway inflammation, indicated by diminished IL-5, IL-13, and TNF-α levels; reduced mucus secretion; and improved airway function. These findings suggest that regulation of eosinophil trafficking and migration by SWAP-70 is important for the development of eosinophilic inflammation after allergen exposure.

Cytokine/anti-cytokine therapy - novel treatments for asthma?

Asthma is a chronic inflammatory disease of the airways and there are no preventions or cures. Inflammatory cells through the secretion of cytokines and pro-inflammatory molecules are thought to play a critical role in pathogenesis. Type 2 CD4(+) lymphocytes (Th2 cells) and their cytokines predominate in mild to moderate allergic asthma, whereas severe steroid-resistant asthma has more of a mixed Th2/Th1 phenotype with a Th17 component. Other immune cells, particularly neutrophils, macrophages and dendritic cells, as well structural cells such as epithelial and airway smooth muscle cells also produce disease-associated cytokines in asthma. Increased levels of these immune cells and cytokines have been identified in clinical samples and their potential role in disease demonstrated in studies using mouse models of asthma. Clinical trials with inhibitors of cytokines such as interleukin (IL)-4, -5 and tumour necrosis factor-α have had success in some studies but not others. This may reflect the design of the clinical trials, including treatments regimes and the patient population included in these studies. IL-13, -9 and granulocyte-macrophage colony-stimulating factor are currently being evaluated in clinical trials or preclinically and the outcome of these studies is eagerly awaited. Roles for IL-25, -33, thymic stromal lymphopoietin, interferon-γ, IL-17 and -27 in the regulation of asthma are just emerging, identifying new ways to treat inflammation. Careful interpretation of results from mouse studies will inform the development and application of therapeutic approaches for asthma. The most effective approaches may be combination therapies that suppress multiple cytokines and a range of redundant and disconnected pathways that separately contribute to asthma pathogenesis. Astute application of these approaches may eventually lead to the development of effective asthma therapeutics. Here we review the current state of knowledge in the field.

CD38 identifies a hypo-proliferative IL-13-secreting CD4+ T-cell subset that does not fit into existing naive and memory phenotype paradigms

CD38 is commonly regarded as an activation marker for human T cells. Herein, we show that CD38 expression identifies a hypo-proliferative CD4(+) T-cell subset that, following TCR stimulation, retains expression of naive cell surface markers including CD45RA, CD62L and CCR7. Hypo-proliferation was mediated by reduced CD25 up-regulation upon TCR stimulation compared to CD4(+) CD38(-) cells and lack of responsiveness to exogenous IL-2. Instead, CD4(+) CD38(+) T cells expressed CD127, and hypo-proliferation was reversed by addition of IL-7, further associated with increased STAT5 phosphorylation. This phenotype was exacerbated by addition of an agonistic CD38-binding antibody, suggesting that signaling through CD38 promotes this cell profile. Activated CD4(+) CD38(+) cells had a bias towards IL-13 secretion, but not other Th2 cytokines such as IL-4 or IL-5. In comparison, the CD4(+) CD38(-) cells had a clear bias towards secretion of Th1-associated cytokines IFN-γ and TNF. The existence of such CD4(+) CD38(+) T cells may play an important role in pathologies such as asthma, which are associated with IL-13, but not IL-4 and IL-5. Coupled with responsiveness to IL-7 but not IL-2, and the involvement of CD38 ligation, our results highlight a unique T-cell subpopulation that does not fit into existing naive and memory cell paradigms.

Interleukin-19: multiple roles in immune regulation and disease

First reported in 1999, IL-19 remains a mystery in many ways. Despite appearing in many genome scans and candidate gene studies, and having been searched for specifically as part of the IL-10 family, its function is still to be defined. Nonetheless, a pattern of Th2 promotion is coalescing from this nebulous body of work, supported by increasing evidence for a role in asthma. Similarly, a clear but less intuitive role as a subtle immunomodulator is emerging in psoriasis and chronic inflammatory disorders in general. Indeed, several human diseases and their animal models have highlighted a role for IL-19. Key questions remain, relating to the nature of its receptor, its function (if any) on leukocytes and how its effects are distinguished by the cell from those of IL-20 and IL-24. In this review, I shall attempt to bring together a summary of the known work - disparate as it may be - as well as presenting a picture of these two important clinical disorders and the potential involvement of this somewhat enigmatic cytokine.

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.

Anisakis pegreffii-induced airway hyperresponsiveness is mediated by gamma interferon in the absence of interleukin-4 receptor alpha responsiveness

Infection with the fish parasite Anisakis following exposure to contaminated fish can lead to allergic reactions in humans. The present study examined the immunological mechanisms underlying the development of allergic airway inflammation in mice after different routes of sensitization to Anisakis. Wild-type and interleukin-4 receptor alpha (IL-4Ralpha)-deficient BALB/c mice were sensitized intraperitoneally with live or heat-killed Anisakis larvae or by intranasal administration of an Anisakis extract and were subsequently challenged intranasally with an Anisakis extract. Both routes of sensitization induced IL-4Ralpha-dependent allergic airway responses, whereas allergen-specific antibody responses developed only when mice were sensitized intraperitoneally. Intranasal sensitization induced airway hyperresponsiveness (AHR) in wild-type mice only, showing that AHR was IL-4/IL-13 dependent. Unexpectedly, infection with Anisakis larvae induced AHR in both wild-type and IL-4Ralpha-deficient mice. IL-4Ralpha-independent AHR was mediated by gamma interferon (IFN-gamma), as evidenced by the fact that in vivo neutralization of IFN-gamma abrogated AHR. Together, these results demonstrate that both infection with larvae and inhalational exposure to Anisakis proteins are potent routes of allergic sensitization to Anisakis, explaining food- and work-related allergies in humans. Importantly for diagnosis, allergic airway inflammation can be independent of detectable Anisakis-specific antibodies. Moreover, depending on the route of sensitization, AHR can be induced either by IL-4/IL-13 or by IFN-gamma.

Chlamydial respiratory infection during allergen sensitization drives neutrophilic allergic airways disease

Neutrophilic asthma is a prevalent, yet recently described phenotype of asthma. It is characterized by neutrophilic rather than eosinophilic airway inflammation and airways hyperresponsiveness (AHR) and may have an infectious origin. Chlamydial respiratory infections are associated with asthma, but how these Th1-inducing bacteria influence Th2-mediated asthma remains unknown. The effects of chlamydial infection on the development of asthma were investigated using a BALB/c mouse model of OVA-induced allergic airways disease (AAD). The effects of current and resolved Chlamydia muridarum infection during OVA sensitization on AAD were assessed and compared with uninfected and nonsensitized controls. Current, but not resolved, infection attenuated hallmark features of AAD: pulmonary eosinophil influx, T cell production of IL-5, mucus-secreting cell hyperplasia, and AHR. Current infection also induced robust OVA-driven neutrophilic inflammation and IFN-gamma release from T cells. The phenotype of suppressed but persistent Th2 responses in association with enhanced neutrophilia is reminiscent of neutrophilic asthma. This phenotype was also characterized by increased pulmonary IL-12 and IL-17 expression and activation of APCs, as well as by reduced thymus- and activation-regulated chemokine. Inhibition of pulmonary neutrophil influx during infection blocked OVA-induced neutrophilic inflammation and T cell IFN-gamma production and reversed the suppressive effects on mucus-secreting cell hyperplasia and AHR during AAD. These changes correlated with decreased IL-12 and IL-17 expression, increased thymus- and activation-regulated chemokine and altered APC activation. Blocking IFN-gamma and IL-17 during OVA challenge had no effect. Thus, active chlamydial respiratory infection during sensitization enhances subsequent neutrophilic inflammation and Th1/Th17 responses during allergen exposure and may have a role in the pathogenesis of neutrophilic asthma.

Interferon-gamma and pulmonary macrophages contribute to the mechanisms underlying prolonged airway hyperresponsiveness

BACKGROUND

Airway hyperresponsiveness (AHR) in asthmatics includes a variable component that persists following an allergen challenge. This may be dissociated from inflammatory cell recruitment, implying a role for resident pulmonary cells in regulating the response.

OBJECTIVE

Using improved methods of assessing AHR in a mouse model of allergic airway disease, to investigate the basis of the development of prolonged AHR.

METHOD

BALB/c mice were systemically sensitized and then challenged with aerosolized ovalbumin (OVA). Airway and tissue responsiveness were measured at baseline and at 1 day, and 1, 2 and 3 weeks after the last OVA challenge. Inflammatory cell numbers in BALF and levels of mRNA for eotaxin-1 and -2, IFN-gamma, IL-5 and -13 in the lung were measured at each time-point. In further experiments, the roles of IFN-gamma and of CCR3(+) and CD4(+) cells in the development of prolonged AHR were assessed by blockade or depletion with monoclonal antibodies. The role of pulmonary macrophages was assessed by selective chemical depletion of these cells.

RESULTS

Airway responsiveness was increased above baseline at 1 day after the last OVA challenge, and this was sustained for 1 week. In contrast, tissue-specific responsiveness was only significantly increased above baseline at 1 day. Development of prolonged AHR was inhibited by neutralization of IFN-gamma or by depletion of pulmonary macrophages, but not by depletion of either CD4(+) T cells or CCR3(+) eosinophils.

CONCLUSION

An interaction between IFN-gamma and pulmonary macrophages contributed to the prolongation of airway hyperresponsiveness. In contrast, T cells and eosinophils did not contribute to prolongation of AHR. These findings emphasize the importance of the innate host response in the development of manifestations of asthma, as well as its potential relevance as a target for therapeutic intervention.

Antigen-induced increases in pulmonary mast cell progenitor numbers depend on IL-9 and CD1d-restricted NKT cells

Pulmonary mast cell progenitor (MCp) numbers increase dramatically in sensitized and aerosolized Ag-challenged mice. This increase depends on CD4(+) T cells, as no MCp increase occurs in the lungs of sensitized wild-type (WT) mice after mAb depletion of CD4(+) but not CD8(+) cells before aerosol Ag challenge. Neither the genetic absence of IL-4, IL-4Ralpha chain, STAT-6, IFN-gamma, or IL-12p40 nor mAb blockade of IFN-gamma, IL-3, IL-4, IL-5, IL-6, IL-10, IL-13, IL-17A, IL-12p40, or IL-12p40Rbeta1 before Ag challenge in WT mice reduces the pulmonary MCp increase. However, sensitized and Ag-challenged IL-9-deficient mice and sensitized WT mice given mAb to IL-9 just before Ag challenge show significant reductions in elicited lung MCp/10(6) mononuclear cells of 47 and 66%, respectively. CD1d-deficient mice and WT mice receiving anti-CD1d before Ag challenge also show significant reductions of 65 and 59%, respectively, in elicited lung MCp/10(6) mononuclear cells, revealing an additional requirement for MCp recruitment. However, in Jalpha18-deficient mice, which lack only type 1 or invariant NKT cells, the increase in the numbers of lung MCp with Ag challenge was intact, indicating that their recruitment must be mediated by type 2 NKT cells. Furthermore, anti-CD1d treatment of IL-9-deficient mice or anti-IL-9 treatment of CD1d-deficient mice does not further reduce the significant partial impairment of MCp recruitment occurring with a single deficiency. These findings implicate type 2 NKT cells and IL-9 as central regulators that function in the same pathway mediating the Ag-induced increase in numbers of pulmonary MCp.

Allergic sensitization is enhanced in early life through toll-like receptor 7 activation

BACKGROUND

Prospective cohort studies suggest that children hospitalized in early life with severe infections are significantly more likely to develop recurrent wheezing and asthma.

OBJECTIVE

Using an inhalational mouse model of allergic airways inflammation, we sought to determine the effect of viral and bacterial-associated molecular patterns on the magnitude of the allergic inflammatory response and whether this effect was age dependent.

METHODS

BALB/c mice were sensitized by intranasal administration of endotoxin(low) ovalbumin (OVA) in the absence or presence of viral single-stranded (ss)RNA, lipoteichoic acid or flagellin as neonates (within the first 24 h of life) or as weanlings (4 weeks of age). Mice were challenged four times with OVA at 6 weeks of age and end-points (bronchoalveolar lavage cytology, histology, antigen-specific T and B cell responses) determined at 7 weeks of age.

RESULTS

Inhalational sensitization (<24 h or 4 weeks of age) and challenge with OVA induced a mild allergic inflammatory response in the airways as indicated by increased numbers of eosinophils and mucus cells, elevated serum OVA-specific IgG1, and production of T helper 2 (Th2) cytokines. Mice sensitized to endotoxin(low) OVA at birth in the presence of ssRNA or lipoteichoic acid, but not flagellin, showed an increase in the numbers of airway and tissue eosinophils, mucus producing cells and antigen-specific production of IL-13 as compared with mice exposed only to endotoxin(low) OVA. By contrast, all three TLR ligands failed to increase the magnitude of OVA-induced allergic inflammation in mice sensitized as weanlings.

CONCLUSIONS

Recognition of distinct microbial-associated patterns in early life may preferentially promote the de novo differentiation of bystander, antigen-specific CD4(+) T cells toward a Th2 phenotype, and promote an asthma-like phenotype upon cognate antigen exposure in later life.

Emerging role of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) as a key regulator of inflammatory responses

1. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumour cells while leaving most non-transformed cells unharmed. Binding of TRAIL to its death receptors (DR4 and DR5) activates the extrinsic apoptotic pathway by recruiting procaspase 8 into the death-inducing silencing complex. Cleavage of the BH-3 only peptide Bid by caspase 8 links the apoptotic TRAIL signal to the mitochondrial pathway and the subsequent release of cytochrome c. 2. In addition, TRAIL binds to neutralizing decoy receptors (DcR1 and DcR2). Signalling through DcR2, DR4 and DR5 can activate pro-inflammatory intracellular molecules such as mitogen-activated protein kinase, protein kinase B and nuclear factor-kappaB. 3. Recent studies have identified an important role for TRAIL in regulating immune responses to viruses, self-antigen and allergens. Increased concentrations of TRAIL are found in virus infections of the lung and TRAIL affects the antiviral response and resolution of infection. In addition, TRAIL is upregulated in the airways of asthmatics and inhibition results in reduced inflammation, T helper 2 cytokine and CCL20 release, as well as abolishing the development of airway hyperreactivity in experimental models. 4. Characterization of the specific receptor systems activated and the pro-inflammatory factors regulated by TRAIL in vivo may lead to the development of novel therapeutic strategies for diseases as diverse as infection, autoimmunity and asthma.

Pathogenesis of steroid-resistant airway hyperresponsiveness: interaction between IFN-gamma and TLR4/MyD88 pathways

Chronic inflammation and airway hyperresponsiveness (AHR) in asthmatics are usually managed effectively by treatment with glucocorticoids. However, a subset of patients remains refractory to therapy. The underlying mechanisms are largely unknown, although recruitment of neutrophils (rather than eosinophils) is strongly correlated, suggesting a role for nonallergic host defense responses. Increased levels of IFN-gamma and endotoxins are also related to severe asthma and because these activate host defense pathways, we investigated a possible common etiologic link to steroid-resistant disease. To be able to unravel the complexity of asthmatic inflammation, we used two model systems which permitted dissection of the relevant molecular pathways. In the first of these, we transferred transgenic OVA(323-339) peptide-specific IFN-gamma-producing Th1 cells into mice. These animals were subsequently challenge via the airways with OVA(323-339) peptide and/or LPS. Challenge with both components, but not with either one individually, induced AHR. Importantly, AHR was resistant to treatment with dexamethasone. Development of AHR was dependent on IFN-gamma, inhibited by depletion of pulmonary macrophages (but not neutrophils) and abrogated in TLR4- or MyD88-deficient mice. In contrast, in the second model in which we transferred OVA(323-339) peptide-activated Th2 cells, eosinophilic inflammation and AHR were induced, and both were suppressed by steroid treatment. We conclude that cooperative signaling between IFN-gamma and TLR4/MyD88 constitutes a previously unrecognized pathway that regulates macrophage-dependent steroid-resistant AHR.

Transplacental passage of interleukins 4 and 13?

The mechanisms by which prenatal events affect development of adult disease are incompletely characterized. Based on findings in a murine model of maternal transmission of asthma risk, we sought to test the role of the pro-asthmatic cytokines interleukin IL-4 and -13. To assess transplacental passage of functional cytokines, we assayed phosphorylation of STAT-6, a marker of IL-4 and -13 signaling via heterodimeric receptor complexes which require an IL-4 receptor alpha subunit. IL-4 receptor alpha−/− females were mated to wild-type males, and pregnant females were injected with supraphysiologic doses of IL-4 or 13. One hour after injection, the receptor heterozygotic embryos were harvested and tissue nuclear proteins extracts assayed for phosphorylation of STAT-6 by Western blot. While direct injection of embryos produced a robust positive control, no phosphorylation was seen after maternal injection with either IL-4 or -13, indicating that neither crossed the placenta in detectable amounts. The data demonstrate a useful approach to assay for transplacental passage of functional maternal molecules, and indicate that molecules other than IL-4 and IL-13 may mediate transplacental effects in maternal transmission of asthma risk.

Interferon-lambda1 (interleukin-29) preferentially down-regulates interleukin-13 over other T helper type 2 cytokine responses in vitro

Interferon (IFN)-lambda1 [interleukin (IL)-29] is a member of the interferon lambda family (also known as type III interferons), whose members are distantly related to both the type I interferons and members of the IL-10 family. While IFN-lambda1 has significant antiviral activity, it is also becoming apparent that it has important immunoregulatory properties, especially with regard to the T helper type 2 (Th2) response. Previously, we have shown that IFN-lambda1 is capable of down-regulating IL-13 production in an IFN-gamma-independent manner and that this is mediated in part via monocyte-derived dendritic cells. Here, we have extended our knowledge of IFN-lambda1 regulation of the human in vitro Th2 response by examining the regulation of three major Th2 cytokines, IL-4, IL-5 and IL-13, by IFN-lambda1. Our results reveal that IFN-lambda1 preferentially inhibits IL-13 production, compared with IL-4 or IL-5. Levels of IL-13 mRNA, the amount of secreted IL-13 protein and numbers of IL-13-positive CD3(+) CD4(+) cells were all significantly diminished by IFN-lambda1. IFN-lambda1 significantly decreased some aspects of IL-4 and IL-5 production, but its effects were not as consistent as those seen on IL-13. IFN-lambda1 was also effective at decreasing IL-13 secretion under conditions designed to support the generation of Th2 cells. Irrespective of whether Concanavalin-A or T-cell-stimulatory microbeads were used, IFN-lambda1 markedly diminished IL-13 secretion in cultures where IL-4 had been added. Thus, IFN-lambda1 appears to be an inhibitor of human Th2 responses whose action is primarily directed towards IL-13 but which may also affect Th2 responses generally and does not invoke a complementary elevation of IFN-gamma secretion.

Interleukin-4-promoted T helper 2 responses enhance Nippostrongylus brasiliensis-induced pulmonary pathology

The role of CD4(+) T-cell interleukin-4 (IL-4) receptor alpha (IL-4Ralpha) expression in T helper 2 (TH2) immune responses has not been defined. To examine this role, we infected CD4(+) T-cell IL-4Ralpha knockout (KO) mice with the parasitic nematode Nippostrongylus brasiliensis, which induces strong host TH2 responses. Although N. brasiliensis expulsion was not affected in CD4(+) T-cell IL-4Ralpha KO mice, the associated lung pathology was reduced. Infected CD4(+) T-cell IL-4Ralpha KO mice showed abrogation of airway mucus production. Furthermore, CD4(+) T-cell IL-4Ralpha KO mouse lungs contained reduced numbers of lymphocytes and eosinophils. Restimulation of pulmonary region-associated T-cell populations showed that TH2 cytokine responses were disrupted. Secretion of IL-4, but not secretion of IL-13 or IL-5, from mediastinal lymph node CD4(+) T cells was reduced in infected CD4(+) T-cell IL-4Ralpha KO mice. Restimulation of tissue-derived CD4(+) T cells resulted in equivalent levels of IL-4 and IL-13 on day 7 postinfection (p.i.) in control and CD4(+) T-cell IL-4Ralpha KO mice. By day 10 p.i. the TH2 cytokine levels had significantly declined in CD4(+) T-cell IL-4Ralpha KO mice. Restimulation with N. brasiliensis antigen of total lung cell populations and populations with CD4(+) T cells depleted showed that CD4(+) T cells were a key TH2 cytokine source. These data demonstrated that CD4(+) T-cell IL-4 responsiveness facilitates eosinophil and lymphocyte recruitment, lymphocyte localization, and TH2 cytokine production in the allergic pathology associated with N. brasiliensis infections.