Double-stranded RNA exacerbates pulmonary allergic reaction through TLR3: implication of airway epithelium and dendritic cells

Virological Profile of Asthma Exacerbation in Children: A Hospital-Based Retrospective Study

Introduction Viruses are the most common triggering factors for asthma exacerbation during the autumn and winter seasons. Viruses, such as influenza A and rhinovirus, play a major role in the occurrence of severe exacerbation of asthma. This association between viral infection and asthma exacerbation in children is a result of the antiviral response of the immune system and various anti-inflammatory phenomena. In this work, we aimed to identify the virological profile of asthma exacerbation in children and analyze the correlation between viral infection type and the severity of exacerbation. Materials and methods This retrospective study was conducted from January 2016 to January 2024. The study included children hospitalized for asthma exacerbation associated with signs of viral-like respiratory infection with positive virological testing by multiplex real-time polymerase chain reaction or rapid test in the case of influenza A or respiratory syncytial virus (RSV). Data analysis was performed with Microsoft Excel and SPSS software using a previously established data collection sheet Results Thirty cases were collected for the study period. The mean age of the patients was 4 years and 8 months, with a male-to-female ratio of 3.3. Eighteen patients were known to have asthma, of which nine had uncontrolled asthma, and exacerbation was inaugural in 12 patients. Viral shedding was found in 14 patients. A viral agent was found in all patients, with coinfection of two or more viruses in three patients. The viruses found were influenza A (18 cases), coupled rhinovirus/enterovirus (eight cases), RSV (eight cases), human metapneumovirus (three patients), and parainfluenza type IV in only one inaugural patient. Asthma exacerbation was severe in 20 patients, moderate in eight patients, and two patients had severe acute asthma requiring intensive care management. We noted a higher frequency of severe exacerbation among those with an influenza A viral infection. All patients with RSV infection exhibited moderate exacerbation. No other significant correlation between asthma severity and other types of viruses was found. Conclusions Our results demonstrate the major role played by viruses in triggering asthma exacerbation, primarily influenza virus, followed by enterovirus, rhinovirus, RSV, and metapneumovirus. Larger-scale studies should be carried out to establish a more complete virological profile and further investigate the viral factor in the management of asthma in children.

Is There a Role for Immunoregulatory and Antiviral Oligonucleotides Acting in the Extracellular Space? A Review and Hypothesis

Here, we link approved and emerging nucleic acid-based therapies with the expanding universe of small non-coding RNAs (sncRNAs) and the innate immune responses that sense oligonucleotides taken up into endosomes. The Toll-like receptors (TLRs) 3, 7, 8, and 9 are located in endosomes and can detect nucleic acids taken up through endocytic routes. These receptors are key triggers in the defense against viruses and/or bacterial infections, yet they also constitute an Achilles heel towards the discrimination between self- and pathogenic nucleic acids. The compartmentalization of nucleic acids and the activity of nucleases are key components in avoiding autoimmune reactions against nucleic acids, but we still lack knowledge on the plethora of nucleic acids that might be released into the extracellular space upon infections, inflammation, and other stress responses involving increased cell death. We review recent findings that a set of single-stranded oligonucleotides (length of 25-40 nucleotides (nt)) can temporarily block ligands destined for endosomes expressing TLRs in human monocyte-derived dendritic cells. We discuss knowledge gaps and highlight the existence of a pool of RNA with an approximate length of 30-40 nt that may still have unappreciated regulatory functions in physiology and in the defense against viruses as gatekeepers of endosomal uptake through certain routes.

The Role of Airway Epithelial Cell Alarmins in Asthma

The airway epithelium is the first line of defense for the lungs, detecting inhaled environmental threats through pattern recognition receptors expressed transmembrane or intracellularly. Activation of pattern recognition receptors triggers the release of alarmin cytokines IL-25, IL-33, and TSLP. These alarmins are important mediators of inflammation, with receptors widely expressed in structural cells as well as innate and adaptive immune cells. Many of the key effector cells in the allergic cascade also produce alarmins, thereby contributing to the airways disease by driving downstream type 2 inflammatory processes. Randomized controlled clinical trials have demonstrated benefit when blockade of TSLP and IL-33 were added to standard of care medications, suggesting these are important new targets for treatment of asthma. With genome-wide association studies demonstrating associations between single-nucleotide polymorphisms of the TSLP and IL-33 gene and risk of asthma, it will be important to understand which subsets of asthma patients will benefit most from anti-alarmin therapy.

Development of a safe and effective novel synthetic mucosal adjuvant SF-10 derived from physiological metabolic pathways and function of human pulmonary surfactant

A safe and effective mucosal adjuvant is required for vaccination against influenza A virus (IAV) infection. Previously, we described that intranasally administration of surfacten®, a medicine derived from bovine pulmonary surfactant (PS), with IAV vaccine can induce IAV-specific IgA in the respiratory tract mucosa and IgG in serum. PS is secreted by alveolar type II cells and Clara cells and serves to reduce lung surface tension. PS finished its rules is incorporated by antigen presenting cells (APCs), such as alveolar macrophages and dendritic cells, and alveolar type II cells and rapidly metabolized. We focused on the metabolic pathways and rapid metabolic turnover of PS and developed a PS-based mucosal adjuvant. First, we determined the essential components of PS adjuvanticity and found that the complex of three PS lipids and surfactant protein-C can enhance to deliver the vaccine antigen and activate APCs. Later, we improved the safety, efficacy and ease of manufacture and finally succeeded in developing SF-10. The use of SF-10 with influenza split vaccine (HAv) (HAv-SF-10) enhances HAv incorporation into APCs both in vitro and in vivo, and intranasal instillation of HAv-SF-10 induced systemic and mucosal HAv-specific immunities in not only mice but also cynomolgus monkeys. The report that PS has physiological effects on the gastrointestinal mucosa prompted us develop a new SF-10-based vaccine that can be administered orally. In this review, We summarize our work on the development of clinically effective PS-based nasal and oral mucosal adjuvants for influenza vaccine.

Differential maturation trajectories of innate antiviral immunity in health and atopy

BACKGROUND

The maturation of innate immune responses in health and atopy is still incompletely understood.

METHODS

We aimed to evaluate age-related trajectories of the TLR3 and TLR7/8 pathways from birth to adulthood and whether these differ between healthy and atopic individuals. Peripheral blood mononuclear cells (PBMCs) were isolated from 39 otherwise healthy, atopic and 39 non-atopic subjects, aged 0-45 years. Selected cytokines involved in antiviral responses were measured by Luminex in culture supernatants of poly(I:C)- and R848-stimulated PBMCs. The non-parametric correlation between age and cytokine expression and differences in developmental trajectories between healthy and atopic subjects were estimated. Patterns of cytokine development were identified with principal component analysis.

RESULTS

Normal innate immune maturation entails significant and progressive age-related changes in the production of IL-1β, TNF-α, MIP-1β, MCP-3, IP-10, IL-10, IL-12p70, and IFN-γ upon TLR3 and/or TLR7/8 stimulation. Individual cytokines made small contributions to the observed variability; chemokines MCP-3 and IP-10 were key contributors. The development of these pathways deviated in atopic subjects with significant differences observed in the trajectories of IL-1β, MIP-1β, and IL-10 syntheses.

CONCLUSION

TLR3 and TLR7/8 pathways mature during childhood, while atopy is associated with an abnormal maturation pattern. Suboptimal responses in Th1, inflammatory cytokine, and chemokine production may be implicated in poor antiviral immunity in atopics. Moreover, the deficient maturation of IL-10 synthesis may be implicated in the breaking of tolerance, characterizing the onset of atopic disease.

TLR3-Activated Monocyte-Derived Dendritic Cells Trigger Progression from Acute Viral Infection to Chronic Disease in the Lung

Acute infection is implicated as a trigger for chronic inflammatory disease, but the full basis for this switch is uncertain. In this study, we examine this issue using a mouse model of chronic lung disease that develops after respiratory infection with a natural pathogen (Sendai virus). We investigate this model using a combination of TLR3-deficient mice and adoptive transfer of immune cells into these mice versus the comparable responses in wild-type mice. We found that acute and transient expression of TLR3 on monocyte-derived dendritic cells (moDCs) was selectively required to induce long-term expression of IL-33 and consequent type 2 immune-driven lung disease. Unexpectedly, moDC participation was not based on canonical TLR3 signaling and relied instead on a trophic effect to expand the alveolar epithelial type 2 cell population beyond repair of tissue injury and thereby provide an enriched and persistent cell source of IL-33 required for progression to a disease phenotype that includes lung inflammation, hyperreactivity, excess mucus production, and remodeling. The findings thereby provide a framework wherein viral infection activates TLR3 in moDCs as a front-line immune cell niche upstream of lung epithelial cells to drive the type 2 immune response, leading to chronic inflammatory diseases of the lung (such as asthma and chronic obstructive pulmonary disease in humans) and perhaps progressive and long-term postviral disease in general.

Childhood asthma heterogeneity at the era of precision medicine: Modulating the immune response or the microbiota for the management of asthma attack

Exacerbations are a main characteristic of asthma. In childhood, the risk is increasing with severity. Exacerbations are a strong phenotypic marker, particularly of severe and therapy-resistant asthma. These early-life events may influence the evolution and be involved in lung function decline. In children, asthma attacks are facilitated by exposure to allergens and pollutants, but are mainly triggered by microbial agents. Multiple studies have assessed immune responses to viruses, and to a lesser extend bacteria, during asthma exacerbation. Research has identified impairment of innate immune responses in children, related to altered pathogen recognition, interferon release, or anti-viral response. Influence of this host-microbiota dialog on the adaptive immune response may be crucial, leading to the development of biased T helper (Th)2 inflammation. These dynamic interactions may impact the presentations of asthma attacks, and have long-term consequences. The aim of this review is to synthesize studies exploring immune mechanisms impairment against viruses and bacteria promoting asthma attacks in children. The potential influence of the nature of infectious agents and/or preexisting microbiota on the development of exacerbation is also addressed. We then discuss our understanding of how these diverse host-microbiota interactions in children may account for the heterogeneity of endotypes and clinical presentations. Finally, improving the knowledge of the pathophysiological processes induced by infections has led to offer new opportunities for the development of preventive or curative therapeutics for acute asthma. A better definition of asthma endotypes associated with precision medicine might lead to substantial progress in the management of severe childhood asthma.

The IL-17 receptor IL-17RE mediates polyIC-induced exacerbation of experimental allergic asthma

BACKGROUND

The interleukin 17 receptor E (IL-17RE) is specific for the epithelial cytokine interleukin-17C (IL-17C). Asthma exacerbations are frequently caused by viral infections. Polyinosinic:polycytidylic acid (pIC) mimics viral infections through binding to pattern recognition receptors (e.g. TLR-3). We and others have shown that pIC induces the expression of IL-17C in airway epithelial cells. Using different mouse models, we aimed to investigate the function of IL-17RE in the development of experimental allergic asthma and acute exacerbation thereof.

METHODS

Wild-type (WT) and IL-17RE deficient (Il-17re-/-) mice were sensitized and challenged with OVA to induce allergic airway inflammation. pIC or PBS were applied intranasally when allergic airway inflammation had been established. Pulmonary expression of inflammatory mediators, numbers of inflammatory cells, and airway hyperresponsiveness (AHR) were analyzed.

RESULTS

Ablation of IL-17RE did not affect the development of OVA-induced allergic airway inflammation and AHR. pIC induced inflammation independent of IL-17RE in the absence of allergic airway inflammation. Treatment of mice with pIC exacerbated pulmonary inflammation in sensitized and OVA-challenged mice in an IL-17RE-dependent manner. The pIC-induced expression of cytokines (e.g. keratinocyte-derived chemokine (KC), granulocyte-colony stimulating factor (G-CSF)) and recruitment of neutrophils were decreased in Il-17re-/- mice. pIC-exacerbated AHR was partially decreased in Il-17re-/- mice.

CONCLUSIONS

Our results indicate that IL-17RE mediates virus-triggered exacerbations but does not have a function in the development of allergic lung disease.

Peroxisome Proliferator-Activated Receptors as a Therapeutic Target in Asthma

The complexity of the pathogenetic mechanisms of the development of chronic inflammation in asthma determines its heterogeneity and insufficient treatment effectiveness. Nuclear transcription factors, which include peroxisome proliferator-activated receptors, that is, PPARs, play an important role in the regulation of initiation and resolution of the inflammatory process. The ability of PPARs to modulate not only lipid homeostasis but also the activity of the inflammatory response makes them an important pathogenetic target in asthma therapy. At present, special attention is focused on natural (polyunsaturated fatty acids (PUFAs), endocannabinoids, and eicosanoids) and synthetic (fibrates, thiazolidinediones) PPAR ligands and the study of signaling mechanisms involved in the implementation of their anti-inflammatory effects in asthma. This review summarizes current views on the structure and function of PPARs, as well as their participation in the pathogenesis of chronic inflammation in asthma. The potential use of PPAR ligands as therapeutic agents for treating asthma is under discussion.

Distinct roles for MDA5 and TLR3 in the acute response to inhaled double-stranded RNA

The airway epithelial barrier is critical for preventing pathogen invasion and translocation of inhaled particles into the lung. Epithelial cells also serve an important sentinel role after infection and release various pro-inflammatory mediators that recruit and activate immune cells. Airway epithelial barrier disruption has been implicated in a growing number of respiratory diseases including viral infections. It is thought that when a pathogen breaks the barrier and gains access to the host tissue, pro-inflammatory mediators increase, which further disrupts the barrier and initiates a vicious cycle of leak. However, it is difficult to study airway barrier integrity in vivo, and little is known about relationship between epithelial barrier function and airway inflammation. Current assays of pulmonary barrier integrity quantify the leak of macromolecules from the vasculature into the airspaces (or “inside/out” leak). However, it is also important to measure the ease with which inhaled particles, allergens, or pathogens can enter the subepithelial tissues (or “outside/in” leak). We challenged mice with inhaled double stranded RNA (dsRNA) and explored the relationship between inside/out and outside/in barrier function and airway inflammation. Using wild-type and gene-targeted mice, we studied the roles of the dsRNA sensors Toll Like Receptor 3 (TLR3) and Melanoma Differentiation-Associated protein 5 (MDA5). Here we report that after acute challenge with inhaled dsRNA, airway barrier dysfunction occurs in a TLR3-dependent manner, whereas leukocyte accumulation is largely MDA5-dependent. We conclude that airway barrier dysfunction and inflammation are regulated by different mechanisms at early time points after exposure to inhaled dsRNA.

Influenza in Asthmatics: For Better or for Worse?

Asthma and influenza are two pathologic conditions of the respiratory tract that affect millions worldwide. Influenza virus of the 2009 pandemic was highly transmissible and caused severe respiratory disease in young and middle-aged individuals. Asthma was discovered to be an underlying co-morbidity that led to hospitalizations during this influenza pandemic albeit with less severe outcomes. However, animal studies that investigated the relationship between allergic inflammation and pandemic (p)H1N1 infection, showed that while characteristics of allergic airways disease were exacerbated by this virus, governing immune responses that cause exacerbations may actually protect the host from severe outcomes associated with influenza. To better understand the relationship between asthma and severe influenza during the last pandemic, we conducted a systematic literature review of reports on hospitalized patients with asthma as a co-morbid condition during the pH1N1 season. Herein, we report that numerous other underlying conditions, such as cardiovascular, neurologic, and metabolic diseases may have been underplayed as major drivers of severe influenza during the 2009 pandemic. This review synopses, (1) asthma and influenza independently, (2) epidemiologic data surrounding asthma during the 2009 influenza pandemic, and (3) recent advances in our understanding of allergic host–pathogen interactions in the context of allergic airways disease and influenza in mouse models. Our goal is to showcase possible immunological benefits of allergic airways inflammation as countermeasures for influenza virus infections as a learning tool to discover novel pathways that can enhance our ability to hinder influenza virus replication and host pathology induced thereof.

Dual Role of Toll-like Receptors in Human and Experimental Asthma Models

Asthma is a chronic airway inflammatory disease that is influenced by the interplay between genetic factors and exposure to environmental allergens, microbes, or microbial products where toll-like receptors (TLRs) play a pivotal role. TLRs recognize a wide range of microbial or endogenous molecules as well as airborne environmental allergens and act as adjuvants that influence positively or negatively allergic sensitization. TLRs are qualitatively and differentially expressed on hematopoietic and non-hematopoietic stromal or structural airway cells that when activated by TLRs agonists exert an immune-modulatory role in asthma development. Therefore, understanding mechanisms and pathways by which TLRs orchestrate asthma outcomes may offer new strategies to control the disease. Here, we aim to review and critically discuss the role of TLRs in human asthma and murine models of allergic airway inflammation, highlighting the complexity of TLRs function in development, exacerbation, or control of airway allergic inflammation.

Interferon-β deficiency at asthma exacerbation promotes MLKL mediated necroptosis

Defective production of antiviral interferon (IFN)-β is thought to contribute to rhinovirus-induced asthma exacerbations. These exacerbations are associated with elevated lung levels of lactate dehydrogenase (LDH), indicating occurrence of cell necrosis. We thus hypothesized that reduced lung IFN-β could contribute to necrotic cell death in a model of asthma exacerbations. Wild-type and IFN-β^−/− mice were given saline or house dust mite (HDM) intranasally for 3 weeks to induce inflammation. Double-stranded RNA (dsRNA) was then given for additional 3 days to induce exacerbation. HDM induced an eosinophilic inflammation, which was not associated with increased expression of cleaved caspase-3, cleaved PARP or elevated bronchoalveolar lavage fluid (BALF) LDH levels in wild-type. However, exacerbation evoked by HDM + dsRNA challenges increased BALF levels of LDH, apoptotic markers and the necroptotic markers receptor-interacting protein (RIP)-3 and phosphorylation of mixed linage kinase domain-like protein (pMLKL), compared to HDM + saline. Absence of IFN-β at exacerbation further increased BALF LDH and protein expression of pMLKL compared to wild-type. We demonstrate that cell death markers are increased at viral stimulus-induced exacerbation in mouse lungs, and that absence of IFN-β augments markers of necroptotic cell death at exacerbation. Our data thus suggest a novel role of deficient IFN-β production at viral-induced exacerbation.

The TLR4-TRIF pathway can protect against the development of experimental allergic asthma

The Toll-like receptor (TLR) adaptor proteins myeloid differentiating factor 88 (MyD88) and Toll, interleukin-1 receptor and resistance protein (TIR) domain-containing adaptor inducing interferon-β (TRIF) comprise the two principal limbs of the TLR signalling network. We studied the role of these adaptors in the TLR4-dependent inhibition of allergic airway disease and induction of CD4⁺ ICOS⁺ T cells by nasal application of Protollin™, a mucosal adjuvant composed of TLR2 and TLR4 agonists. Wild-type (WT), Trif^-/- or Myd88^-/- mice were sensitized to birch pollen extract (BPEx), then received intranasal Protollin followed by consecutive BPEx challenges. Protollin's protection against allergic airway disease was TRIF-dependent and MyD88-independent. TRIF deficiency diminished the CD4⁺ ICOS⁺ T-cell subsets in the lymph nodes draining the nasal mucosa, as well as their recruitment to the lungs. Overall, TRIF deficiency reduced the proportion of cervical lymph node and lung CD4⁺ ICOS⁺ Foxp3^- cells, in particular. Adoptive transfer of cervical lymph node cells supported a role for Protollin-induced CD4⁺ ICOS⁺ cells in the TRIF-dependent inhibition of airway hyper-responsiveness. Hence, our data demonstrate that stimulation of the TLR4-TRIF pathway can protect against the development of allergic airway disease and that a TRIF-dependent adjuvant effect on CD4⁺ ICOS⁺ T-cell responses may be a contributing mechanism.

Regulation of airway inflammation and remodeling in asthmatic mice by TLR3/TRIF signal pathway

This paper aims to investigate the effect of Toll-like receptors 3 (TLR3)/TIR-domain-containing adapter-inducing interferon-β (TRIF) signal pathway on the airway inflammation and remodeling in asthmatic mice. C57BL/6 and TLR3^-/- mice were randomly divided into three groups (10 mice per group), including Control group (mice inhaled phosphate buffer saline (PBS)), Asthma group (mice inhaled ovalbumin (OVA)) and polyriboinosinic-ribocytidylic acid (poly (I: C)) group (asthmatic mice were injected intraperitoneally with TLR3 agonist poly (I: C)). Hematoxylin-eosin (HE) staining, Wright-Giemsa staining, Enzyme-linked immunosorbent assay (ELISA), Immunohistochemistry, Hydroxyproline assay, quantitative real time polymerase chain reaction (qRT-PCR) and Western blot were used to assess for the indices of airway inflammation and remodeling. In terms of WT mice, all asthma groups with or without the addition of poly (I: C) showed exaggerated inflammation and remodeling in the airways as compared to Control group, which were more seriously in poly (I: C) group than Asthma group. Furthermore, we observed the significant inhibition of airway inflammation and remodeling in the TLR3^-/- mice in both Asthma no matter with or without addition of poly (I: C) than the WT mice. TLR3 knockout could obviously relieve the airway inflammation and remodeling in asthma through inhibiting TLR3/TRIF signaling pathway.

Versican Deficiency Significantly Reduces Lung Inflammatory Response Induced by Polyinosine-Polycytidylic Acid Stimulation

Viral infection is an exacerbating factor contributing to chronic airway diseases, such as asthma, via mechanisms that are still unclear. Polyinosine-polycytidylic acid (poly(I:C)), a Toll-like receptor 3 (TLR3) agonist used as a mimetic to study viral infection, has been shown to elicit inflammatory responses in lungs and to exacerbate pulmonary allergic reactions in animal models. Previously, we have shown that poly(I:C) stimulates lung fibroblasts to accumulate an extracellular matrix (ECM), enriched in hyaluronan (HA) and its binding partner versican, which promotes monocyte adhesion. In the current study, we aimed to determine the in vivo role of versican in mediating inflammatory responses in poly(I:C)-induced lung inflammation using a tamoxifen-inducible versican-deficient mouse model (Vcan^-/- mice). In C57Bl/6 mice, poly(I:C) instillation significantly increased accumulation of versican and HA, especially in the perivascular and peribronchial regions, which were enriched in infiltrating leukocytes. In contrast, versican-deficient (Vcan^-/-) lungs did not exhibit increases in versican or HA in these regions and had strikingly reduced numbers of leukocytes in the bronchoalveolar lavage fluid and lower expression of inflammatory chemokines and cytokines. Poly(I:C) stimulation of lung fibroblasts isolated from control mice generated HA-enriched cable structures in the ECM, providing a substrate for monocytic cells in vitro, whereas lung fibroblasts from Vcan^-/- mice did not. Moreover, increases in proinflammatory cytokine expression were also greatly attenuated in the Vcan^-/- lung fibroblasts. These findings provide strong evidence that versican is a critical inflammatory mediator during poly(I:C)-induced acute lung injury and, in association with HA, generates an ECM that promotes leukocyte infiltration and adhesion.

Critical role of Toll-like receptors in pathophysiology of allergic asthma

Allergic asthma is an airway disease, characterized by reversible bronchoconstriction, chronic inflammation of the airway, and thickness of smooth muscle in the respiratory tract. Asthma is orchestrated by an excessive Th2-adaptive immune response, in which innate immunity plays a key role. Recently TLRs have received more and more attention as they are central to orchestrate the innate immune responses. TLRs are localized as integral membrane or intracellular glycoproteins with those on the cell surface sensing microbial antigens and the ones, localized in intracellular vesicles, sensing microbial nucleic acid species. Having recognized microbial antigens, TLRs conduct the immune response towards a pro- or anti-allergy response. As a double-edged sword, they could initiate either harmful or helpful responses by the immune system in case of allergic asthma. In the current review, we will describe the role of TLRs and their signaling pathways in allergic asthma.

The genetic and epigenetic landscapes of the epithelium in asthma

Asthma is a global health problem with increasing prevalence. The airway epithelium is the initial barrier against inhaled noxious agents or aeroallergens. In asthma, the airway epithelium suffers from structural and functional abnormalities and as such, is more susceptible to normally innocuous environmental stimuli. The epithelial structural and functional impairments are now recognised as a significant contributing factor to asthma pathogenesis. Both genetic and environmental risk factors play important roles in the development of asthma with an increasing number of genes associated with asthma susceptibility being expressed in airway epithelium. Epigenetic factors that regulate airway epithelial structure and function are also an attractive area for assessment of susceptibility to asthma. In this review we provide a comprehensive discussion on genetic factors; from using linkage designs and candidate gene association studies to genome-wide association studies and whole genome sequencing, and epigenetic factors; DNA methylation, histone modifications, and non-coding RNAs (especially microRNAs), in airway epithelial cells that are functionally associated with asthma pathogenesis. Our aims were to introduce potential predictors or therapeutic targets for asthma in airway epithelium. Overall, we found very small overlap in asthma susceptibility genes identified with different technologies. Some potential biomarkers are IRAKM, PCDH1, ORMDL3/GSDMB, IL-33, CDHR3 and CST1 in airway epithelial cells. Recent studies on epigenetic regulatory factors have further provided novel insights to the field, particularly their effect on regulation of some of the asthma susceptibility genes (e.g. methylation of ADAM33). Among the epigenetic regulatory mechanisms, microRNA networks have been shown to regulate a major portion of post-transcriptional gene regulation. Particularly, miR-19a may have some therapeutic potential.

Increased expression of upstream TH2-cytokines in a mouse model of viral-induced asthma exacerbation

Background

Exacerbations of asthma caused by respiratory viral infections are serious conditions in need of novel treatment. To this end animal models of asthma exacerbations are warranted. We have shown that dsRNA challenges or rhinoviral infection produce exacerbation effects in mice with ovalbumin (OVA)-induced allergic asthma. However, house dust mite (HDM) is a more human asthma-relevant allergen than OVA. We thus hypothesised that dsRNA challenges in mice with HDM-induced experimental asthma would produce important translational features of asthma exacerbations.

Method

Mouse airways were challenged locally with HDM or saline three times a week for three weeks to establish experimental asthma. Then daily local dsRNA challenges were given for three consecutive days to induce exacerbation. Bronchoalveolar lavage fluid (BALF) was analysed for inflammatory cells, total protein, the necrosis marker LDH and the alarmin ATP. Lung homogenates were analysed for mRNA expression (RT-qPCR) of TNF-α, CCL2, CCL5, IL-1β, IL-33, thymic stromal lymphopoietin (TSLP), and IL-25 as well as pattern recognition receptors (PRRs) RIG-I, MDA5 and TLR3. Lung tissue IL-33 was analysed with ELISA and PRRs were quantified by western blot. Immunohistochemistry indicated lung distribution of IL-33.

Results

HDM challenge alone caused sustained increase in BALF total protein, eosinophils, lymphocytes and neutrophils, and transient increase in lung tissue expression of TSLP, IL-33 and TNF-α. dsRNA-induced exacerbation markedly and dose-dependently exaggerated these effects. Further, BALF levels of LDH and ATP, and lung tissue expression of CCL2, CCL5, IL-1β, IL-25 and PRRs were increased exclusively at the exacerbations. Lung protein levels of IL-33 were transiently increased by HDM and further increased at exacerbation.

Conclusion

We demonstrate several novel aspects of HDM-induced experimental asthma and added exacerbation effects of dsRNA. General inflammatory parameters in BALF such as exuded proteins, mixed granulocytes, LDH and ATP were increased at the present exacerbations as they are in human asthma exacerbations. We suggest that this model of asthma exacerbation involving dsRNA challenges given to mice with established HDM-induced asthma has translational value and suggest that it may be particularly suited for in vivo studies involving pharmacological effects on exacerbation-induced expression of major upstream TH₂-cytokines; IL-33, TSLP and IL-25, as well as PRRs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0808-x) contains supplementary material, which is available to authorized users.

Double-stranded RNA evokes exacerbation in a mouse model of corticosteroid refractory asthma

RNA viruses are a major cause of respiratory infections and are known to exacerbate asthma and other respiratory diseases. Our aim was to test the ability of poly(I:C) (polyinosinic:polycytidylic acid), a viral surrogate, to elicit exacerbation in a model of severe asthma driven by HDM (house dust mite) in FCA (Freund's complete adjuvant). Poly(I:C) was administered intranasally around the HDM challenge in FCA-HDM-sensitized animals. Changes in AHR (airway hyperresponsiveness), BALF (bronchoalveolar lavage fluid) inflammatory infiltrate, HDM-specific immunoglobulins and cytokine/chemokine release were evaluated at different points after the challenge. The effect of oral dexamethasone was also assessed. Exacerbation was achieved when poly(I:C) was administered 24 h before the HDM challenge and was characterized by enhanced AHR and an increase in the numbers of neutrophils, macrophages and lymphocytes in the BALF. Th1, Th2 and Th17 cytokines were also elevated at different time points after the challenge. Peribronchial and alveolar inflammation in lung tissue were also augmented. AHR and inflammatory infiltration showed reduced sensitivity to dexamethasone treatment. We have set up a model that mimics key aspects of viral exacerbation in a corticosteroid-refractory asthmatic phenotype which could be used to evaluate new therapies for this condition.

Early childhood wheezers: identifying asthma in later life

Wheeze in young children is common, and asthma is the most common noncommunicable disease in children. Prevalence studies of recurrent asthma-like symptoms in children under the age of 5 years have reported that one third of children in the US and Europe are affected, and rates and severity appear to be higher in developing countries. Over the last few decades, significant research efforts have focused on identification of risk factors and predictors of wheeze and on tools to identify which children who wheeze will progress to develop asthma. We reviewed the phenotypes of childhood wheezing, genetic risk factors, environmental factors, testing/predictive indices, and primary prevention. While it is generally agreed that a complex interaction of environmental exposure and genetic susceptibility contributes to the development of asthma, limitations in predictive tools and tests restrict our ability to provide families with guidance as to whether their child with wheeze will ultimately develop asthma. Additional research is needed to clarify childhood wheeze phenotypes, to develop tools to determine which children will develop asthma, and to determine how and when to intervene. If these areas can be addressed, it would help reduce this large burden on children, families, and society.

Impact of genetic polymorphisms on paediatric atopic dermatitis

In order to investigate whether polymorphisms of genes encoding some factors of innate and adaptive immunity play a role in the development of, or protection against atopic dermatitis (AD) and condition its severity, we genotyped 33 candidate genes and 47 single nucleotide polymorphisms (SNPs) using Custom TaqMan Array Microfluidic Cards and an ABI 7900HT analyser (Applied Biosystems, Foster City, CA, USA). The study involved 104 children with AD (29 with mild-to-moderate and 75 with severe disease; 42 girls; mean age ± SD, 5.8 ± 3.3 years) and 119 healthy controls (49 girls; mean age, 4.8 ± 3.0 years). IL10-rs1800872T, TG and MBL2-rs500737AG were all significantly more frequent among the children with AD ( P = 0.015, P = 0.004 and P = 0.030), whereas IL10-rs1800896C and TC were more frequent in those without AD ( P = 0.028 and P = 0.032). The VEGFA-rs2146326A and CTLA4-rs3087243AG SNPs were significantly more frequent in the children with mild/moderate AD than in those with severe AD ( P = 0.048 and P = 0.036). IL10-rs1800872T and TG were significantly more frequent in the children with AD and other allergic diseases than in the controls ( P = 0.014 and P = 0.007), whereas IL10-rs1800896TC and C were more frequent in the controls than in the children with AD and other allergic diseases ( P = 0.0055 and P = 0.0034). These findings show that some of the polymorphisms involved in the immune response are also involved in some aspects of the development and course of AD and, although not conclusive, support the immunological hypothesis of the origin of the inflammatory lesions.

Directional secretory response of double stranded RNA-induced thymic stromal lymphopoetin (TSLP) and CCL11/eotaxin-1 in human asthmatic airways

BACKGROUND

Thymic stromal lymphoproetin (TSLP) is a cytokine secreted by the airway epithelium in response to respiratory viruses and it is known to promote allergic Th2 responses in asthma. This study investigated whether virally-induced secretion of TSLP is directional in nature (apical vs. basolateral) and/or if there are TSLP-mediated effects occurring at both sides of the bronchial epithelial barrier in the asthmatic state.

METHODS

Primary human bronchial epithelial cells (HBEC) from control (n = 3) and asthmatic (n = 3) donors were differentiated into polarized respiratory tract epithelium under air-liquid interface (ALI) conditions and treated apically with dsRNA (viral surrogate) or TSLP. Sub-epithelial effects of TSLP were examined in human airway smooth muscle cells (HASMC) from normal (n = 3) and asthmatic (n = 3) donors. Clinical experiments examined nasal airway secretions obtained from asthmatic children during naturally occurring rhinovirus-induced exacerbations (n = 20) vs. non-asthmatic uninfected controls (n = 20). Protein levels of TSLP, CCL11/eotaxin-1, CCL17/TARC, CCL22/MDC, TNF-α and CXCL8 were determined with a multiplex magnetic bead assay.

RESULTS

Our data demonstrate that: 1) Asthmatic HBEC exhibit an exaggerated apical, but not basal, secretion of TSLP after dsRNA exposure; 2) TSLP exposure induces unidirectional (apical) secretion of CCL11/eotaxin-1 in asthmatic HBEC and enhanced CCL11/eotaxin-1 secretion in asthmatic HASMC; 3) Rhinovirus-induced asthma exacerbations in children are associated with in vivo airway secretion of TSLP and CCL11/eotaxin-1.

CONCLUSIONS

There are virally-induced TSLP-driven secretory immune responses at both sides of the bronchial epithelial barrier characterized by enhanced CCL11/eotaxin-1 secretion in asthmatic airways. These results suggest a new model of TSLP-mediated eosinophilic responses in the asthmatic airway during viral-induced exacerbations.

Polymorphisms of endotoxin pathway and endotoxin exposure: in vitro IgE synthesis and replication in a birth cohort

BACKGROUND

Genetic variants in endotoxin signaling pathway are important in modulating the effect of environmental endotoxin on asthma and atopic phenotypes. Our objective was to determine the single nucleotide polymorphisms (SNPs) in the endotoxin signaling pathway that may influence in vitro IgE synthesis and to investigate the relationship between these variants and endotoxin exposure in relation to the development of asthma and atopy in a birth cohort.

METHODS

Peripheral blood mononuclear cells from 45 children with asthma were stimulated with 2 and 200 ng/ml lipopolysaccharide in vitro and IgE was measured in the culture supernatants. Children were genotyped for 121 SNPs from 30 genes in the endotoxin signaling pathway. Variants with a dose-response IgE production in relation to lipopolysaccharide (LPS) were selected for replication in a population-based birth cohort, in which we investigated the interaction between these SNPs and endotoxin exposure in relation to airway hyper-responsiveness, wheeze, and atopic sensitization.

RESULTS

Twenty-one SNPs in nine genes (CD14, TLR4, IRF3, TRAF-6, TIRAP, TRIF, IKK-1, ST-2, SOCS1) were found to modulate the effect of endotoxin on in vitro IgE synthesis, with six displaying high linkage disequilibrium. Of the remaining 15 SNPs, for seven we found significant relationships between genotype and endotoxin exposure in the genetic association study in relation to symptomatic airway hyper-responsiveness (CD14-rs2915863 and rs2569191, TRIF-rs4807000), current wheeze (ST-2-rs17639215, IKK-1-rs2230804, and TRIF-rs4807000), and atopy (CD14-rs2915863 and rs2569192, TRAF-6-rs5030411, and IKK-1-rs2230804).

CONCLUSIONS

Variants in the endotoxin signaling pathway are important determinants of asthma and atopy. The genotype effect is a function of the environmental endotoxin exposure.

TRIF Deficiency does not Affect Severity of Ovalbumin-induced Airway Inflammation in Mice

Allergic asthma is a chronic pulmonary inflammatory disease characterized by reversible airway obstruction, hyperresponsiveness and eosinophils infiltration. Toll-like receptors (TLRs) signaling are closely associated with asthma and have emerged as a novel therapeutic target in allergic disease. The functions of TLR3 and TLR4 in allergic airway inflammation have been studied; however, the precise role of TIR-domain-containing adapter-inducing interferon-β (TRIF), the adaptor molecule for both TLR3 and TLR4, is not yet fully understood. To investigate this, we developed a mouse model of OVA-induced allergic airway inflammation and compared the severity of allergic airway inflammation in WT and TRIF^-/- mice. Histopathological assessment revealed that the severity of inflammation in airway inflammation in TRIF-deficient mice was comparable to that in WT mice. The total number of cells recovered from bronchoalveolar lavage fluid did not differ between WT and TRIF-deficient mice. Moreover, TRIF deficiency did not affect Th1 and Th2 cytokine production in lung tissue nor the level of serum OVA-specific IgE, IgG₁ and IgG_2c. These findings suggest that TRIF-mediated signaling may not be critical for the development of allergic airway inflammation.

Genetic polymorphisms and risk of recurrent wheezing in pediatric age

Background

Wheezing during early life is a very common disorder, but the reasons underlying the different wheezing phenotypes are still unclear. The aims of this study were to analyse the potential correlations between the risk of developing recurrent wheezing and the presence of specific polymorphisms of some genes regulating immune system function, and to study the relative importance of the associations of different viruses and genetic polymorphisms in causing recurrent episodes.

Methods

The study involved 119 otherwise healthy infants admitted to hospital for a first episode of wheezing (74 of whom subsequently experienced recurrent episodes) and 119 age- and sex-matched subjects without any history of respiratory problem randomly selected from those attending our outpatient clinic during the study period. All of the study subjects were followed up for two years, and 47 single nucleotide polymorphisms (SNPs) in 33 candidate genes were genotyped on whole blood using an ABI PRISM 7900 HT Fast Real-time instrument.

Results

IL8-rs4073AT, VEGFA-rs833058CT, MBL2-rs1800450CT and IKBKB-rs3747811AT were associated with a significantly increased risk of developing wheezing (p = 0.02, p = 0.03, p = 0.05 and p = 0.0018), whereas CTLA4-rs3087243AG and NFKBIB-rs3136641TT were associated with a significantly reduced risk (p = 0.05 and p = 0.04). IL8-rs4073AT, VEGFA-rs2146323AA and NFKBIA-rs2233419AG were associated with a significantly increased risk of developing recurrent wheezing (p = 0.04, p = 0.04 and p = 0.03), whereas TLR3-rs3775291TC was associated with a significantly reduced risk (p = 0.03). Interestingly, the study of gene-environment interactions showed that rhinovirus was significantly associated with recurrent wheezing in the presence of IL4Ra-rs1801275GG and G (odds ratio [OR] 6.03, 95% confidence interval [CI]: 1.21-30.10, p = 0.03) and MAP3K1-rs702689AA (OR 4.09, 95% CI: 1.14-14.61, p = 0.03).

Conclusions

This study shows a clear relationship between the risk of wheezing and polymorphisms of some genes involved in the immune response. Although further studies are needed to confirm the results, these findings may be useful for the early identification of children at the highest risk of developing recurrent episodes and possibly subsequent asthma.

Respiratory viral infection, epithelial cytokines, and innate lymphoid cells in asthma exacerbations

Exacerbations of asthma are most commonly triggered by viral infections, which amplify allergic inflammation. Cytokines released by virus-infected AECs may be important in driving this response. This review focuses on accumulating evidence in support of a role for epithelial cytokines, including IL-33, IL-25, and TSLP, as well as their targets, type 2 innate lymphoid cells (ILC2s), in the pathogenesis of virus-induced asthma exacerbations. Production and release of these cytokines lead to recruitment and activation of ILC2s, which secrete mediators, including IL-5 and IL-13, which augment allergic inflammation. However, little information is currently available about the induction of these responses by the respiratory viruses that are strongly associated with exacerbations of asthma, such as rhinoviruses. Further human studies, as well as improved animal experimental models, are needed to investigate appropriately the pathogenetic mechanisms in virus-induced exacerbations of asthma, including the role of ILCs.

Functional effects of Toll-like receptor (TLR)3, 7, 9, RIG-I and MDA-5 stimulation in nasal epithelial cells

BACKGROUND

The human nasal epithelium is an important physical barrier, and a part of the innate immune defense that protect against pathogens. The epithelial cells recognize microbial components by pattern-recognition receptors (PRRs), and thereby trigger an immune response. Even though TLR3, TLR7, TLR9, RIG-I and MDA-5 are all known to respond to viral stimulation, their potential role in chronic airway inflammation triggered by local cytokine release remains to be established.

METHODS

mRNA and corresponding protein expression of TLR3, TLR7, TLR9, RIG-I and MDA-5 were analyzed in nasal biopsies and various upper airway epithelial cell lines using real-time reverse transcription PCR, immunohistochemistry and flow cytometry. Ligand induced, cytokine release, was evaluated with ELISA.

RESULTS

Nasal biopsies were found to express TLR3, TLR7, TLR9, RIG-I and MDA-5, with the most abundant expression in the surface epithelium. These receptors were verified in primary human nasal epithelial cell (HNEC) as well as in the airway epithelial cell lines Detroit-562 and FaDu. Poly(I:C) (TLR3) and R-837 (TLR7) stimulation increased secretion of IL-6 and GM-CSF from the nasal mucosa and the epithelial cell lines. CpG (TLR9) stimulation caused release of IL-8 in the nasal mucosa and in FaDu. Poly(I:C)/LyoVec (RIG-I/MDA-5) stimulation activated the secretion of IFN-β in the nasal mucosa. A corresponding release was also detected from HNEC and Detroit-562.

CONCLUSION

The nasal epithelium has the ability to recognize viral intrusion through TLR and RLR receptors, and the subsequent response might have a role in exacerbation of inflammatory diseases like allergic rhinitis and chronic rhinosinusitis.

Inhaled dsRNA and rhinovirus evoke neutrophilic exacerbation and lung expression of thymic stromal lymphopoietin in allergic mice with established experimental asthma

Background

Rhinovirus infection or dsRNA stimulation increased thymic stromal lymphopoietin (TSLP), an upstream pro-allergic cytokine, in asthmatic bronchial epithelial cells. We hypothesized that dsRNA challenges superimposed on established experimental allergic asthma constitute a useful exacerbation model. We further hypothesized that TSLP is induced at dsRNA- and rhinoviral infection-induced exacerbations.

Methods

Allergic mice were challenged with OVA followed by three daily intranasal challenges with dsRNA or saline. Bronchoalveolar lavage fluid (BALF) was analysed for total protein, lactate dehydrogenase (LDH), CXCL1/KC, CCL2/MCP-1 and differential cell counts. Lung tissue histology, neutrophils and TSLP, TNF-α, IFN-β and IFN-λ mRNA were examined. Alternatively, allergen-challenged mice received intranasal rhinovirus-(RV)-1B followed by lung TSLP immunostaining.

Results

In mice with allergic airway inflammation, dsRNA challenges caused a significant exacerbation increasing lung tissue inflammation score and tissue neutrophilia. Bronchoalveolar lavage fluid neutrophils, total protein, LDH, CXCL1/KC and CCL2/MCP-1 were also increased (P < 0.01), and so were lung tissue expressions of TNF-α, IFN-λ and TSLP (P < 0.01), but IFN-β was not increased. TSLP, IFN-λ and LDH were not increased by allergen or dsRNA challenges alone, but increased exclusively at exacerbations. RV1B infection-induced exacerbation also increased lung tissue TSLP (P < 0.05).

Conclusions

dsRNA-induced exacerbation in mice with experimental asthma involved general inflammation, cytokines and interferons, in agreement with previous observations in exacerbating human asthma. Additionally, both dsRNA and RV1B infection increased lung TSLP exclusively at exacerbations. Our data suggest that dsRNA challenges superimposed on allergic inflammation are suited for pharmacological studies of asthma exacerbations including the regulation of lung tissue TSLP, TNF-α, IFN-β and IFN-λ.

Asthma exacerbations: predisposing factors and prediction rules

PURPOSE OF REVIEW

Asthma is a multifaceted disease that is associated with decreased lung function, multiple symptoms, varying levels of asthma control, and risk of acute exacerbations. The ability to predict the risk of developing acute exacerbations may improve the management of asthmatics and facilitate identification of these patients for interventional studies.

RECENT FINDINGS

Factors that are associated with different manifestations of asthma differ. Biomarkers that are correlated with airways hyper-responsiveness do not necessarily correlate with risk of future exacerbations. Genetic factors that segregate with exacerbation risk are beginning to emerge. Outcome measures that demonstrate predictive validity have been developed and may facilitate patient management and provide novel clinically meaningful endpoints in clinical trials.

SUMMARY

This review will emphasize underlying factors associated with asthma exacerbations and clinical prediction rules that correlate with the risk of developing severe exacerbations of asthma.

Receptor Interacting Protein 2 (RIP2) Is Dispensable for OVA-Induced Airway Inflammation in Mice

Purpose

Asthma is a pulmonary chronic inflammatory disease characterized by airway obstruction and hyperresponsiveness. Pattern recognition receptors are known to play a key role in the development of allergic diseases as well as host defenses against microbial infection. Receptor interacting protein 2 (RIP2), a serine/threonine kinase, is an adaptor molecule of NOD1 and NOD2, and genetic variation in this receptor is known to be associated with the severity of allergic asthma in children. In this study, we examined the role of RIP2 in the development of allergic airway inflammation in a mouse model.

Methods

Airway inflammation was induced in mice through intranasal administration of ovalbumin (OVA) after 2 intraperitoneal immunizations with OVA. Lung inflammation and mucus hypersecretion were examined histologically and total cell infiltration in bronchoalveolar (BAL) fluids was determined. Levels of the Th2-related cytokines, IL-5 and IL-13, in lung extracts were measured by ELISA. Serum antigen-specific IgE and IgG1 levels were also assessed.

Results

OVA-induced lung inflammation and mucus hypersecretion were not different between WT and RIP2-deficient mice. The IL-5 and IL-13 levels in the bronchoalveolar (BAL) fluids were also not impaired in RIP2-deficient mice compared to WT mice. Moreover, RIP2 deficiency did not affect serum OVA-specific IgG1 and IgE levels.

Conclusions

Our results suggest that RIP2 is not associated with the development of allergic airway inflammation.

Viral infections in asthma and COPD

Airway viral infections are associated with the pathogenesis of asthma and COPD. It has been argued that respiratory syncytial virus (RSV) infection in infancy is a probable causal factor in the development of pediatric asthma. RSV infections tend to induce Th2-biased immune responses in the host airways. RSV infection, atopy, and low pulmonary function in neonates may work synergistically toward the development of pediatric asthma. Human rhinovirus (HRV) is a representative virus associated with the exacerbation of asthma in both children and adults. Viral infections trigger innate immune responses including granulocytic inflammation and worsen the underlying inflammation due to asthma and COPD. The innate immune responses involve type-I and -III interferon (IFN) production, which plays an important role in anti-viral responses, and the airway epithelia of asthmatics reportedly exhibit defects in the virus-induced IFN responses, which renders these individuals more susceptible to viral infection. A similarly impaired IFN response is seen in COPD, and several investigators propose that latent adenoviral infection may be involved in COPD development. Persistent RSV infections were detected in a sub-population of patients with COPD and were associated with the accelerated decline of lung function. The virus-induced upregulation of co-inhibitory molecules in the airway epithelium partly accounts for the persistent infections. Experimental animal models for virus-asthma/COPD interactions have shed light on the underlying immune mechanisms and are expected to help develop novel approaches to treat respiratory diseases.

Toll-like receptor (TLR) 7 decreases and TLR9 increases the airway responses in mice with established allergic inflammation

Toll-like receptor (TLR) 7 and TLR9 recognise microbial products of viral descent. Since viruses are a common trigger of asthma exacerbations these TLRs have emerged as interesting therapeutic targets. Even though their effects on allergic inflammation have been evaluated in several models their effects on established allergic airway inflammation remains to be described. Therefore, mice with an on-going ovalbumin (OVA)-induced allergic airway inflammation were given R848 or CpG (TLR7 and TLR9 agonists, respectively) intranasally during four consecutive days. At day five, the R848 treatment had reduced OVA-induced airway hyperresponsiveness (measured as the increased resistance to methacholine), counteracted the accompanying influx of eosinophils and macrophages, and decreased the OVA-enhanced release of interleukin (IL)-5 and leukotriene (LT) B4 in bronchoalveolar lavage fluid. CpG, which by itself caused airway hyperresponsiveness, did not influence the OVA-induced airway hyperresponsiveness, and release of IL-5 and LTB4, but decreased the OVA-induced influx of cells in bronchoalveolar lavage fluid, and increased the amount of pro-inflammatory mediators like IL-12, CXCL1 and CXCL9. To conclude, TLR7 dampens the allergic airway reactivity and local inflammation, whereas TLR9 that causes airway hyperresponsiveness and increased cellular response per se, do generally not interfere with the effects induced by allergic inflammation.

Effects of Rhinovirus Infection on Nasopharyngeal Bacterial Colonization in Infants With Wild or Variant Types of Mannose-Binding Lectin and Toll-Like Receptors 3 and 4

BACKGROUND

Development of respiratory tract infections is determined by interactions between viruses, bacteria, and the host innate immune response. We investigated the impact of natural rhinovirus infection on nasopharyngeal bacterial colonization in infants with or without gene polymorphisms of mannose-binding lectin (MBL) and Toll-like receptors (TLRs) 3 and 4.

METHODS

Rhinoviruses were detected by reverse transcription-polymerase chain reaction and bacteria by culture of nasopharyngeal specimens from 2- to 3-month-old infants. Gene polymorphisms in MBL at codons 52, 54, and 57, TLR3 Leu412Phe, and TLR4 Asp299Gly were detected by pyrosequencing.

RESULTS

Of 337 infants, 61 were positive for rhinovirus and 187 were colonized by Streptococcus pneumoniae, Moraxella catarrhalis, Haemophilus influenzae, or Staphylococcus aureus. Gene polymorphisms of MBL were detected in 32%, TLR3 in 51%, and TLR4 in 18% of subjects. Presence of rhinovirus was associated with increased colonization by S pneumoniae in children with MBL polymorphisms (8 of 20 [40%] with rhinovirus, vs 9 of 87 [10%] without rhinovirus; P = .003), but not in those with wild-type MBL. In logistic regression analyses, S pneumoniae colonization associated with MBL variant (P = .035) and with the interaction between rhinovirus and MBL variant (P = .004), and M catarrhalis colonization associated with the detection of rhinovirus (P = .033).

CONCLUSIONS

The association between rhinovirus infection and nasopharyngeal pneumococcal colonization in early infancy is linked to genetic variations of MBL.

Analysis of global gene expression changes in human bronchial epithelial cells exposed to spores of the allergenic fungus, Alternaria alternata

Exposure and sensitivity to ubiquitous airborne fungi such as Alternaria alternata have long been implicated in the development, onset, and exacerbation of chronic allergic airway disorders. This present study is the first to investigate global changes in host gene expression during the interaction of cultured human bronchial epithelial cells and live Alternaria spores. In in vitro experiments human bronchial epithelial cells (BEAS-2B) were exposed to spores or media alone for 24 h. RNA was collected from three biological replicates per treatment and was used to assess changes in gene expression patterns using Affymetrix Human Genome U133 Plus 2.0 Arrays. In cells treated with Alternaria spores compared to controls, 613 probe sets representing 460 individual genes were found differentially expressed (p ≤ 0.05). In this set of 460 statistically significant, differentially expressed genes, 397 genes were found to be up-regulated and 63 were down-regulated. Of these 397 up-regulated genes, 156 genes were found to be up-regulated ≥2 fold. Interestingly, none of the 63 down-regulated genes were found differentially expressed at ≤−2 fold. Differentially expressed genes were identified following statistical analysis and subsequently used for pathway and network evaluation. Interestingly, many cytokine and chemokine immune response genes were up-regulated with a particular emphasis on interferon-inducible genes. Genes involved in cell death, retinoic acid signaling, and TLR3 response pathways were also significantly up-regulated. Many of the differentially up-regulated genes have been shown in other systems to be associated with innate immunity, inflammation and/or allergic airway diseases. This study now provides substantial information for further investigating specific genes and innate immune system pathways activated by Alternaria in the context of allergic airway diseases.

Inhaled birch pollen extract induces airway hyperresponsiveness via oxidative stress but independently of pollen-intrinsic NADPH oxidase activity, or the TLR4-TRIF pathway

Oxidative stress in allergic asthma may result from oxidase activity or proinflammatory molecules in pollens. Signaling via TLR4 and its adaptor Toll-IL-1R domain-containing adapter inducing IFN-β (TRIF) has been implicated in reactive oxygen species-mediated acute lung injury and in Th2 immune responses. We investigated the contributions of oxidative stress and TLR4/TRIF signaling to experimental asthma induced by birch pollen exposure exclusively via the airways. Mice were exposed to native or heat-inactivated white birch pollen extract (BPEx) intratracheally and injected with the antioxidants, N-acetyl-L-cysteine or dimethylthiourea, prior to sensitization, challenge, or all allergen exposures, to assess the role of oxidative stress and pollen-intrinsic NADPH oxidase activity in allergic sensitization, inflammation, and airway hyperresponsiveness (AHR). Additionally, TLR4 signaling was antagonized concomitantly with allergen exposure, or the development of allergic airway disease was evaluated in TLR4 or TRIF knockout mice. N-acetyl-L-cysteine inhibited BPEx-induced eosinophilic airway inflammation and AHR except when given exclusively during sensitization, whereas dimethylthiourea was inhibitory even when administered with the sensitization alone. Heat inactivation of BPEx had no effect on the development of allergic airway disease. Oxidative stress-mediated AHR was also TLR4 and TRIF independent; however, TLR4 deficiency decreased, whereas TRIF deficiency increased BPEx-induced airway inflammation. In conclusion, oxidative stress plays a significant role in allergic sensitization to pollen via the airway mucosa, but the pollen-intrinsic NADPH oxidase activity and TLR4 or TRIF signaling are unnecessary for the induction of allergic airway disease and AHR. Pollen extract does, however, activate TLR4, thereby enhancing airway inflammation, which is restrained by the TRIF-dependent pathway.

Double-stranded RNA attenuates the barrier function of human pulmonary artery endothelial cells

Circulating RNA may result from excessive cell damage or acute viral infection and can interact with vascular endothelial cells. Despite the obvious clinical implications associated with the presence of circulating RNA, its pathological effects on endothelial cells and the governing molecular mechanisms are still not fully elucidated. We analyzed the effects of double stranded RNA on primary human pulmonary artery endothelial cells (hPAECs). The effect of natural and synthetic double-stranded RNA (dsRNA) on hPAECs was investigated using trans-endothelial electric resistance, molecule trafficking, calcium (Ca²⁺) homeostasis, gene expression and proliferation studies. Furthermore, the morphology and mechanical changes of the cells caused by synthetic dsRNA was followed by in-situ atomic force microscopy, by vascular-endothelial cadherin and F-actin staining. Our results indicated that exposure of hPAECs to synthetic dsRNA led to functional deficits. This was reflected by morphological and mechanical changes and an increase in the permeability of the endothelial monolayer. hPAECs treated with synthetic dsRNA accumulated in the G1 phase of the cell cycle. Additionally, the proliferation rate of the cells in the presence of synthetic dsRNA was significantly decreased. Furthermore, we found that natural and synthetic dsRNA modulated Ca²⁺ signaling in hPAECs by inhibiting the sarco-endoplasmic Ca²⁺-ATPase (SERCA) which is involved in the regulation of the intracellular Ca²⁺ homeostasis and thus cell growth. Even upon synthetic dsRNA stimulation silencing of SERCA3 preserved the endothelial monolayer integrity. Our data identify novel mechanisms by which dsRNA can disrupt endothelial barrier function and these may be relevant in inflammatory processes.

Activation of basophils by the double-stranded RNA poly(A:U) exacerbates allergic inflammation

BACKGROUND

It is commonly acknowledged that asthma is exacerbated by viral infections. On the other hand, basophil infiltration of lung tissues has been evidenced postmortem in cases of fatal disease, raising the question of a possible link between these two observations.

OBJECTIVES

Herein, we addressed the relationship between asthma exacerbation by viral infection and basophil activation and expansion by investigating how stimulation with the dsRNA polyadenylic/polyuridylic acid [poly(A:U)] affected basophil activities and recruitment in an allergic airway inflammation model.

METHODS

The effect of dsRNA on basophils was assessed by measuring the cytokine levels produced upon stimulation. We used an OVA-induced experimental model of allergic asthma. Airway hyperreactivity, recruitment of infiltrating cells, and cytokine production were determined in the lung of mice having received poly(A:U), as compared with untreated controls. The exacerbating effect of basophils was assessed both by adoptive transfer of poly(A:U)-treated basophils and by their in vivo depletion with Ba103 antibody.

RESULTS

We found that in vitro treatment with poly(A:U) increased basophil functions by inducing TH 2-type cytokine and histamine production, whereas in vivo treatment increased peripheral basophil recruitment. Furthermore, we provide the first demonstration for increased infiltration of basophils in the lung of mice suffering from airway inflammation. In this model, disease symptoms were clearly exacerbated upon adoptive transfer of basophils exposed to poly(A:U), relative to their unstimulated counterpart. Conversely, in vivo basophil depletion alleviated disease syndromes, thus validating the transfer data.

CONCLUSIONS

Our findings provide the first evidence for airway inflammation exacerbation by basophils following dsRNA stimulation.

Basic research on virus-induced asthma exacerbation: inhibition of inflammatory chemokine expression by fluticasone propionate

BACKGROUND

Viral infection can exacerbate asthma by inducing the accumulation of inflammatory cells in the airway. We have previously reported that double-stranded RNA (dsRNA), a viral product and ligand of the Toll-like receptor-3 (TLR3), activates the transcription factors NF-κB and IRF-3 and upregulates the expression of inflammatory chemokines in airway epithelial cells. Here, we examined the effects of the glucocorticoid fluticasone propionate (FP) on the expression of the inflammatory chemokines CCL5, CXCL8 and CXCL10.

METHODS

The airway epithelial cell line BEAS-2B was used for this study. Expression of CCL5, CXCL8 and CXCL10 mRNA and protein was quantified by real-time PCR and ELISA assay, respectively. To examine the association of FP with the physiology of chemokine production, we included several methods. Nuclear translocation of transcription factors was determined by performing Western blot analysis. Histone deacetylase (HDAC) activity in nuclear extracts was measured using a colorimetric assay. Stability of the chemokine mRNAs was examined in cells incubated with actinomycin D. The activities of the CCL5 promoter and the transcription factors NF-κB and IRF-3 were assessed using luciferase reporter assays.

RESULTS

Treatment of BEAS-2B cells with FP significantly and dose-dependently (10(-9) to 10(-6)M) inhibited dsRNA-induced expression of CCL5, CXCL8 and CXCL10 protein and mRNA, but did not affect mRNA stability. FP also significantly inhibited dsRNA-stimulated CCL5 promoter activity. However, FP had no effect on the activity of HDAC or the nuclear translocation of NF-κB and IRF-3.

CONCLUSIONS

FP inhibits the dsRNA-stimulated expression of inflammatory chemokines in airway epithelial cells. FP may act by inhibiting chemokine transcription through an as yet unidentified mechanism.

Alternaria inhibits double-stranded RNA-induced cytokine production through Toll-like receptor 3

BACKGROUND

Fungi may be involved in asthma and chronic rhinosinusitis (CRS). Peripheral blood mononuclear cells from CRS patients produce interleukin (IL)-5, IL-13 and interferon (IFN)-γ in the presence of Alternaria. In addition, Alternaria produces potent Th2-like adjuvant effects in the airway. Therefore, we hypothesized that Alternaria may inhibit Th1-type defense mechanisms against virus infection.

METHODS

Dendritic cells (DCs) were generated from mouse bone marrow. The functional responses were assessed by expression of cell surface molecules by FACS (MHC class II, CD40, CD80, CD86 and OX40L). Production of IL-6, chemokine CXCL10 (IP-10), chemokine CXCL11 (I-TAC) and IFN-β was measured by ELISA. Toll-like receptor 3 (TLR3) mRNA and protein expression was detected by quantitative real-time PCR and Western blot.

RESULTS

Alternaria and polyinosinic-polycytidylic acid (poly I:C) enhanced cell surface expression of MHC class II, CD40, CD80, CD86 and OX40L, and IL-6 production in a concentration-dependent manner. However, Alternaria significantly inhibited production of IP-10, I-TAC and IFN-β, induced by viral double-stranded RNA (dsRNA) mimic poly I:C. TLR3 mRNA expression and protein production by poly I:C were significantly inhibited by Alternaria. These reactions are likely caused by heat-stable factor(s) in Alternaria extract with >100 kDa molecular mass.

CONCLUSION

These findings suggest that the fungus Alternaria may inhibit production of IFN-β and other cytokines by DCs by suppressing TLR3 expression. These results indicate that Alternaria may inhibit host innate immunity against virus infection.

Toll-like receptor 7 stimulates production of specialized pro-resolving lipid mediators and promotes resolution of airway inflammation

Although specialized pro-resolving mediators (SPMs) biosynthesized from polyunsaturated fatty acids are critical for the resolution of acute inflammation, the molecules and pathways that induce their production remain elusive. Here, we show that TLR7, a receptor recognizing viral ssRNA and damaged self-RNA, mobilizes the docosahexaenoic acid (DHA)-derived biosynthetic pathways that lead to the generation of D-series SPMs. In mouse macrophages and human monocytes, TLR7 activation triggered production of DHA-derived monohydroxy metabolome markers and generation of protectin D1 (PD1) and resolvin D1 (RvD1). In mouse allergic airway inflammation, TLR7 activation enhanced production of DHA-derived SPMs including PD1 and accelerated the catabasis of Th2-mediated inflammation. D-series SPMs were critical for TLR7-mediated resolution of airway inflammation as this effect was lost in Alox15^−/− mice, while resolution was enhanced after local administration of PD1 or RvD1. Together, our findings reveal a new previously unsuspected role of TLR7 in the generation of D-series SPMs and the resolution of allergic airway inflammation. They also identify TLR stimulation as a new approach to drive SPMs and resolution of inflammatory diseases.

Toll-like receptor expression and induction of type I and type III interferons in primary airway epithelial cells

Interferons (IFNs) are a critical component of the first line of antiviral defense. The activation of Toll-like receptors (TLRs) expressed by dendritic cells triggers different signaling cascades that result in the production of large amounts of IFNs. However, the functional consequences of TLR activation and differential IFN production in specific cell populations other than antigen-presenting cells have not yet been fully elucidated. In this study, we investigated TLR expression and polarization in airway epithelial cells (AECs) and the consequences of TLR agonist stimulation for the production of type I (IFN-α/β) and type III (IFN-λ) IFNs. Our results show that the pattern of expression and polarization of all TLRs in primary AEC cultures mirrors that of the human airways ex vivo and is receptor specific. The antiviral TLRs (TLR3, TLR7, and TLR9) are mostly expressed on the apical cell surfaces of epithelial cells in the human trachea and in primary polarized AECs. Type III IFN is the predominant IFN produced by the airway epithelium, and TLR3 is the only TLR that mediates IFN production by AECs, while all TLR agonists tested are capable of inducing AEC activation and interleukin-8 production. In response to influenza virus infection, AECs can produce IFN-λ in an IFNAR- and STAT1-independent manner. Our results emphasize the importance of using primary well-differentiated AECs to study TLR and antiviral responses and provide further insight into the regulation of IFN production during the antiviral response of the lung epithelium.

Association study of matrix metalloproteinase-12 gene polymorphisms and asthma in a Japanese population

BACKGROUND

Matrix metalloproteinase 12 gene (MMP12) has been shown to be associated with asthma in a Caucasian population. In this study, we investigate whether single-nucleotide polymorphisms (SNPs) of MMP12 are associated with a risk for asthma in a Japanese population.

METHODS

We tested for an association between SNPs in MMP12 and asthma, including its severity, in a Japanese population (630 pediatric and 417 adult patients with atopic asthma and 336 children and 632 adults as controls). The rs652438 A and G variants (N357S) were generated by site-directed mutagenesis and an assay with artificial peptide substrates was used to compare two types of MMP12 activity. The effect of MMP12 inhibition with MMP12-specific small interfering RNA (siRNA) on chemokine secretion from airway epithelial cells was also tested in vitro.

RESULTS

N357S showed a p value <0.05 for childhood and combined (adult plus childhood) asthma in the dominant model [odds ratio (OR) 1.60, 95% confidence interval (CI) 1.00-2.56, p = 0.047; OR 1.40, 95% CI 1.04-1.89, p = 0.028, respectively]. This risk variant is associated with asthma severity in adult patients. In the functional assay, the minor-allele enzyme showed significantly lower activity than the major-allele enzyme. MMP12-specific siRNA suppressed IP-10 secretion from airway epithelial cells upon stimulation with IFN-β.

CONCLUSIONS

Our results suggest that MMP12 confers susceptibility to asthma and is associated with asthma severity in a Japanese population. MMP12 may be associated with asthma through inappropriate attraction of leukocytes to the inflamed tissue.

Toll-like receptor 3 L412F polymorphisms in infants with bronchiolitis and postbronchiolitis wheezing

BACKGROUND

Innate immunity receptors play a critical role in host defense. In addition, the expression of Toll-like receptors (TLRs) has been connected to allergy and asthma.

AIMS

: To evaluate the association between the TLR3 L412F polymorphism and viral findings, clinical characteristics and subsequent wheezing in young infants with bronchiolitis.

METHODS

In all, 129 full-term infants hospitalized for bronchiolitis at age <6 months have been followed-up until the mean age of 1.5 years. Genotyping of the TLR3 L412F gene mutation was made by pyrosequencing.

RESULTS

TLR3 L412F gene polymorphism including the minor allele T was overrepresented (52%) in infants hospitalized with bronchiolitis. The presence of the major allele C as homozygous was associated with repeated postbronchiolitis wheezing (7.06, 95% confidence interval 2.30-21.66).

CONCLUSION

Preliminary evidence was found that TLR3 L412F gene polymorphism may be associated with bronchiolitis leading to hospitalization and postbronchiolitis wheezing.

Scavenger receptors in human airway epithelial cells: role in response to double-stranded RNA

Scavenger receptors and Toll-like receptors (TLRs) cooperate in response to danger signals to adjust the host immune response. The TLR3 agonist double stranded (ds)RNA is an efficient activator of innate signalling in bronchial epithelial cells. In this study, we aimed at defining the role played by scavenger receptors expressed by bronchial epithelial cells in the control of the innate response to dsRNA both in vitro and in vivo. Expression of several scavenger receptor involved in pathogen recognition was first evaluated in human bronchial epithelial cells in steady-state and inflammatory conditions. Their implication in the uptake of dsRNA and the subsequent cell activation was evaluated in vitro by competition with ligand of scavenger receptors including maleylated ovalbumin and by RNA silencing. The capacity of maleylated ovalbumin to modulate lung inflammation induced by dsRNA was also investigated in mice. Exposure to tumor necrosis factor-α increased expression of the scavenger receptors LOX-1 and CXCL16 and the capacity to internalize maleylated ovalbumin, whereas activation by TLR ligands did not. In contrast, the expression of SR-B1 was not modulated in these conditions. Interestingly, supplementation with maleylated ovalbumin limited dsRNA uptake and inhibited subsequent activation of bronchial epithelial cells. RNA silencing of LOX-1 and SR-B1 strongly blocked the dsRNA-induced cytokine production. Finally, administration of maleylated ovalbumin in mice inhibited the dsRNA-induced infiltration and activation of inflammatory cells in bronchoalveolar spaces and lung draining lymph nodes. Together, our data characterize the function of SR-B1 and LOX-1 in bronchial epithelial cells and their implication in dsRNA-induced responses, a finding that might be relevant during respiratory viral infections.

Single-stranded DNA oligonucleotides inhibit TLR3-mediated responses in human monocyte-derived dendritic cells and in vivo in cynomolgus macaques

TLR3 is a key receptor for recognition of double-stranded RNA and initiation of immune responses against viral infections. However, hyperactive responses can have adverse effects, such as virus-induced asthma. Strategies to prevent TLR3-mediated pathology are therefore desired. We investigated the effect of single-stranded DNA oligonucleotides (ssDNA-ODNs) on TLR3 activation. Human monocyte-derived dendritic cells up-regulate maturation markers and secrete proinflammatory cytokines on treatment with the synthetic TLR3 ligand polyinosine-polycytidylic acid (poly I:C). These events were inhibited in cultures with ssDNA-ODNs. Poly I:C activation of nonhematopoietic cells was also inhibited by ssDNA-ODNs. The uptake of poly I:C into cells was reduced in the presence of ssDNA-ODNs, preventing TLR3 engagement from occurring. To confirm this inhibition in vivo, we administered ssDNA-ODNs and poly I:C, alone or in combination, via the intranasal route in cynomolgus macaques. Proinflammatory cytokines were detected in nasal secretions in the poly I:C group, while the levels were reduced in the groups receiving ssDNA-ODNs or both substances. Our results demonstrate that TLR3-triggered immune activation can be modulated by ssDNA-ODNs and provide evidence of dampening proinflammatory cytokine release in the airways of cynomolgus macaques. These findings may open novel perspectives for clinical strategies to prevent or treat inflammatory conditions exacerbated by TLR3 signaling.