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

Epidemiology and Immunopathogenesis of Virus Associated Asthma Exacerbations

Asthma is a common airway disease, affecting millions of people worldwide. Although most asthma patients experience mild symptoms, it is characterized by variable airflow limitation, which can occasionally become life threatening in the case of a severe exacerbation. The commonest triggers of asthma exacerbations in both children and adults are viral infections. In this review article, we will try to investigate the most common viruses triggering asthma exacerbations and their role in asthma immunopathogenesis, since viral infections in young adults are thought to trigger the development of asthma either right away after the infection or at a later stage of their life. The commonest viral pathogens associated with asthma include the respiratory syncytial virus, rhinoviruses, influenza and parainfluenza virus, metapneumovirus and coronaviruses. All these viruses exploit different molecular pathways to infiltrate the host. Asthmatics are more prone to severe viral infections due to their unique inflammatory response, which is mostly characterized by T2 cytokines. Unlike the normal T1 high response to viral infection, asthmatics with T2 high inflammation are less potent in containing a viral infection. Inhaled and/or systematic corticosteroids and bronchodilators remain the cornerstone of asthma exacerbation treatment, and although many targeted therapies which block molecules that viruses use to infect the host have been used in a laboratory level, none has been yet approved for clinical use. Nevertheless, further understanding of the unique pathway that each virus follows to infect an individual may be crucial in the development of targeted therapies for the commonest viral pathogens to effectively prevent asthma exacerbations. Finally, biologic therapies resulted in a complete change of scenery in the treatment of severe asthma, especially with a T2 high phenotype. All available data suggest that monoclonal antibodies are safe and able to drastically reduce the rate of viral asthma exacerbations.

Airway epithelial development and function: A key player in asthma pathogenesis?

Though asthma is a common and relatively easy to diagnose disease, attempts at primary or secondary prevention, and cure, have been disappointing. The widespread use of inhaled steroids has dramatically improved asthma control but has offered nothing in terms of altering long-term outcomes or reversing airway remodeling and impairment in lung function. The inability to cure asthma is unsurprising given our limited understanding of the factors that contribute to disease initiation and persistence. New data have focused on the airway epithelium as a potentially key factor orchestrating the different stages of asthma. In this review we summarize for the clinician the current evidence on the central role of the airway epithelium in asthma pathogenesis and the factors that may alter epithelial integrity and functionality.

C57Bl/6N mice have an attenuated lung inflammatory response to dsRNA compared to C57Bl/6J and BALB/c mice

BACKGROUND

Lower respiratory infections caused by ssRNA viruses are a major health burden globally. Translational mouse models are a valuable tool for medical research, including research on respiratory viral infections. In in vivo mouse models, synthetic dsRNA can be used as a surrogate for ssRNA virus replication. However, studies investigating how genetic background of mice impacts the murine lung inflammatory response to dsRNA is lacking. Hence, we have compared lung immunological responses of BALB/c, C57Bl/6N and C57Bl/6J mice to synthetic dsRNA.

METHODS

dsRNA was administered intranasally to BALB/c, C57Bl/6N and C57Bl/6J mice once/day for three consecutive days. Lactate dehydrogenase (LDH) activity, inflammatory cells, and total protein concentration were analyzed in bronchoalveolar lavage fluid (BALF). Pattern recognition receptors levels (TLR3, MDA5 and RIG-I) were measured in lung homogenates using RT-qPCR and western blot. Gene expression of IFN-β, TNF-α, IL-1β and CXCL1 was assessed in lung homogenates by RT-qPCR. ELISA was used to analyze protein concentrations of CXCL1 and IL-1β in BALF and lung homogenates.

RESULTS

BALB/c and C57Bl/6J mice showed infiltration of neutrophils to the lung, and an increase in total protein concentration and LDH activity in response to dsRNA administration. Only modest increases in these parameters were observed for C57Bl/6N mice. Similarly, dsRNA administration evoked an upregulation of MDA5 and RIG-I gene and protein expression in BALB/c and C57Bl/6J, but not C57Bl/6N, mice. Further, dsRNA provoked an increase in gene expression of TNF-α in BALB/c and C57Bl/6J mice, IL-1β only in C57Bl/6N mice and CXCL1 exclusively in BALB/c mice. BALF levels of CXCL1 and IL-1β were increased in BALB/c and C57Bl/6J mice in response to dsRNA, whereas the response of C57Bl/6N was blunt. Overall, inter-strain comparisons of the lung reactivity to dsRNA revealed that BALB/c, followed by C57Bl/6J, had the most pronounced respiratory inflammatory responses, while the responses of C57Bl/6N mice were attenuated.

CONCLUSIONS

We report clear differences of the lung innate inflammatory response to dsRNA between BALB/c, C57Bl/6J and C57Bl/6N mice. Of particular note, the highlighted differences in the inflammatory response of C57Bl/6J and C57Bl/6N substrains underscore the value of strain selection in mouse models of respiratory viral infections.

Altered RNA Editing in Atopic Dermatitis Highlights the Role of Double-Stranded RNA for Immune Surveillance

Atopic dermatitis (AD) is associated with dysregulated type 1 IFN‒mediated responses, in parallel with the dominant type 2 inflammation. However, the pathophysiology of this dysregulation is largely unknown. Adenosine-to-inosine RNA editing plays a critical role in immune regulation by preventing double-stranded RNA recognition by MDA5 and IFN activation. We studied global adenosine-to-inosine editing in AD to elucidate the role played by altered editing in the pathophysiology of this disease. Analysis of three RNA-sequencing datasets of AD skin samples revealed reduced levels of adenosine-to-inosine RNA editing in AD. This reduction was seen globally throughout Alu repeats as well as in coding genes and in specific pre-mRNA loci expected to create long double-stranded RNA, the main substrate of MDA5 leading to type I IFN activation. Consistently, IFN signature genes were upregulated. In contrast, global editing was not altered in systemic lupus erythematosus and systemic sclerosis, despite IFN activation. Our results indicate that altered editing leading to impairment of the innate immune response may be involved in the pathogenesis of AD. Possibly, it may be relevant for additional autoimmune and inflammatory diseases.

TSLP regulates mitochondrial ROS-induced mitophagy via histone modification in human monocytes

Background

Thymic stromal lymphopoietin (TSLP) is a Th2-like cytokine involved in asthma pathogenesis. Excessive reactive oxygen species (ROS) production can lead to airway inflammation, hyperresponsiveness and remodeling. Mitophagy, followed by ROS production, is the selective degradation of mitochondria by autophagy and often occurs in defective mitochondria. In the present study, we aimed to examine the effects of TSLP on ROS production and mitophagy in human monocytes and to investigate the underlying mechanisms, including epigenetic regulation.

Results

TSLP induced ROS generation, and the effects were reversed by the antioxidant N-acetylcysteine (NAC) in THP-1 cells. Transmission electron microscopy images showed donut-shaped mitochondria that lost the cristae ultrastructure after TSLP stimulation. A decrease in mitochondrial membrane potential, decreased MTCO2 expression, and increased mitochondrial DNA release after TSLP stimulation were found. TSLP enhanced mitochondrial complex I and complex II/III activity and increased mitochondrial copy numbers and the expression of the complex II SHDA gene. TSLP-induced SHDA expression was inhibited by the histone acetyltransferase inhibitor anacardic acid (AA) and the histone methyltransferase inhibitor methylthioadenosine (MTA), and chromatin immunoprecipitation assays revealed that TSLP enhanced H3 acetylation, H4 acetylation, and H3K4 and H3K36 trimethylation in the SHDA promoter. Confocal laser microscopy showed that TSLP treatment increased the signals of the mitophagy-related proteins PINK1, LC3, phospho-parkin and phospho-ubiquitin, and pretreatment with AA and MTA reduced TSLP-induced PINK1 and LC3 accumulation in mitochondria. Western blot analysis showed that TSLP significantly increased phosphor-AMPK signal intensity, and the effects were inhibited by the antioxidant NAC. The increased signal intensities of the mitophagy-related proteins PINK1, Parkin and LC3 I/II were decreased by dorsomorphin, an AMPK inhibitor. TSLP decreased M1-related cytokine CXCL-10 production and increased M2-related cytokine CCL-1 and CCL-22 production, which was suppressed by the mitophagy inhibitor Mdivi-1 and PINK1 gene knockdown.

Conclusions

Epithelial-derived TSLP regulates ROS production and mitophagy through AMPK activation and histone modification and alters M1/M2 chemokine expression in human monocytes.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00767-w.

Viral Infection and Airway Epithelial Immunity in Asthma

Viral respiratory tract infections are associated with asthma development and exacerbation in children and adults. In the course of immune responses to viruses, airway epithelial cells are the initial platform of innate immunity against viral invasion. Patients with severe asthma are more vulnerable than those with mild to moderate asthma to viral infections. Furthermore, in most cases, asthmatic patients tend to produce lower levels of antiviral cytokines than healthy subjects, such as interferons produced from immune effector cells and airway epithelial cells. The epithelial inflammasome appears to contribute to asthma exacerbation through overactivation, leading to self-damage, despite its naturally protective role against infectious pathogens. Given the mixed and complex immune responses in viral-infection-induced asthma exacerbation, this review examines the diverse roles of airway epithelial immunity and related potential therapeutic targets and discusses the mechanisms underlying the heterogeneous manifestations of asthma exacerbations.

Epithelial cell dysfunction, a major driver of asthma development

Airway epithelial barrier dysfunction is frequently observed in asthma and may have important implications. The physical barrier function of the airway epithelium is tightly interwoven with its immunomodulatory actions, while abnormal epithelial repair responses may contribute to remodelling of the airway wall. We propose that abnormalities in the airway epithelial barrier play a crucial role in the sensitization to allergens and pathogenesis of asthma. Many of the identified susceptibility genes for asthma are expressed in the airway epithelium, supporting the notion that events at the airway epithelial surface are critical for the development of the disease. However, the exact mechanisms by which the expression of epithelial susceptibility genes translates into a functionally altered response to environmental risk factors of asthma are still unknown. Interactions between genetic factors and epigenetic regulatory mechanisms may be crucial for asthma susceptibility. Understanding these mechanisms may lead to identification of novel targets for asthma intervention by targeting the airway epithelium. Moreover, exciting new insights have come from recent studies using single‐cell RNA sequencing (scRNA‐Seq) to study the airway epithelium in asthma. This review focuses on the role of airway epithelial barrier function in the susceptibility to develop asthma and novel insights in the modulation of epithelial cell dysfunction in asthma.

Sensing and signaling of immunogenic extracellular RNAs restrain group 2 innate lymphoid cell-driven acute lung inflammation and airway hyperresponsiveness

Repeated exposures to environmental allergens in susceptible individuals drive the development of type 2 inflammatory conditions such as asthma, which have been traditionally considered to be mainly mediated by Th2 cells. However, emerging evidence suggest that a new innate cell type, group 2 innate lymphoid cells (ILC2), plays a central role in initiating and amplifying a type 2 response, even in the absence of adaptive immunity. At present, the regulatory mechanisms for controlling ILC2 activation remain poorly understood. Here we report that respiratory delivery of immunogenic extracellular RNA (exRNAs) derived from RNA- and DNA-virus infected cells, was able to activate a protective response against acute type 2 lung immunopathology and airway hyperresponsiveness (AHR) induced by IL-33 and a fungal allergen, A. flavus, in mice. Mechanistically, we found that the innate immune responses triggered by exRNAs had a potent suppressive effect in vivo on the proliferation and function of ILC2 without the involvement of adaptive immunity. We further provided the loss-of-function genetic evidence that the TLR3- and MAVS-mediated signaling axis is essential for the inhibitory effects of exRNAs in mouse lungs. Thus, our results indicate that the host detection of extracellular immunostimulatory RNAs generated during respiratory viral infections have an important function in the regulation of ILC2-driven acute lung inflammation.

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.

A Perspective on RNAi-Based Biopesticides

Sustainable agriculture relies on practices and technologies that combine effectiveness with a minimal environmental footprint. RNA interference (RNAi), a eukaryotic process in which transcript expression is reduced in a sequence-specific manner, can be co-opted for the control of plant pests and pathogens in a topical application system. Double-stranded RNA (dsRNA), the key trigger molecule of RNAi, has been shown to provide protection without the need for integration of dsRNA-expressing constructs as transgenes. Consequently, development of RNA-based biopesticides is gaining momentum as a narrow-spectrum alternative to chemical-based control measures, with pests and pathogens targeted with accuracy and specificity. Limitations for a commercially viable product to overcome include stable delivery of the topically applied dsRNA and extension of the duration of protection. In addition to the research focus on delivery of dsRNA, development of regulatory frameworks, risk identification, and establishing avoidance and mitigation strategies is key to widespread deployment of topical RNAi technologies. Once in place, these measures will provide the crop protection industry with the certainty necessary to expend resources on the development of innovative dsRNA-based products. Readily evident risks to human health appear minimal, with multiple barriers to uptake and a long history of consumption of dsRNA from plant material. Unintended impacts to the environment are expected to be most apparent in species closely related to the target. Holistic design practices, which incorporate bioinformatics-based dsRNA selection along with experimental testing, represent important techniques for elimination of adverse impacts.

Immune Sensing of Aeroallergen-Associated Double-Stranded RNA Triggers an IFN Response and Modulates Type 2 Lung Inflammation

The innate immune sensing of allergens or allergen-associated components regulate the development of type 2 inflammatory responses. However, the underlying molecular basis by which allergens or allergen-associated components are detected by innate immune receptors remains elusive. In this study, we report that the most common aeroallergen, house dust mite (HDM), harbors a dsRNA species (HDM-dsRNA) that can activate TLR3-mediated IFN responses and counteract the development of an uncontrolled type 2 immune response. We demonstrate that the mouse strains defective in the dsRNA-sensing pathways show aggravated type 2 inflammation defined by severe eosinophilia, elevated level of type 2 cytokines, and mucus overproduction in a model of allergic lung inflammation. The inability to sense HDM-dsRNA resulted in significant increases in airway hyperreactivity. We further show that the administration of the purified HDM-dsRNA at a low dose is sufficient to induce an immune response to prevent the onset of a severe type 2 lung inflammation. Collectively, these results unveil a new role for the HDM-dsRNA/TLR3-signaling axis in the modulation of a type 2 lung inflammation in mice.

Innate immunity in allergy

Innate immune system quickly responds to invasion of microbes and foreign substances through the extracellular and intracellular sensing receptors, which recognize distinctive molecular and structural patterns. The recognition of innate immune receptors leads to the induction of inflammatory and adaptive immune responses by activating downstream signaling pathways. Allergy is an immune-related disease and results from a hypersensitive immune response to harmless substances in the environment. However, less is known about the activation of innate immunity during exposure to allergens. New insights into the innate immune system by sensors and their signaling cascades provide us with more important clues and a framework for understanding allergy disorders. In this review, we will focus on recent advances in the innate immune sensing system.

Dual mechanism of action of T2 inhibitor therapies in virally induced exacerbations of asthma: evidence for a beneficial counter-regulation

Biological agents such as omalizumab and monoclonal antibodies (mAbs) that inhibit type 2 (T2) immunity significantly reduce exacerbations, which are mainly due to viral infections, when added to inhaled corticosteroids in patients with severe asthma. The mechanisms for the therapeutic benefit of T2 inhibitors in reducing virally induced exacerbations, however, remain to be fully elucidated. Pre-clinical and clinical evidence supports the existence of a close counter-regulation of the high-affinity IgE receptor and interferon (IFN) pathways, and a potential dual mechanism of action and therapeutic benefit for omalizumab and other T2 inhibitors that inhibit IgE activity, which may enhance the prevention and treatment of virally induced asthma exacerbations. Similar evidence regarding some novel T2 inhibitor therapies, including mAbs and small-molecule inhibitors, suggests that such a dual mechanism of action with enhancement of IFN production working through non-IgE pathways might also exist. The specific mechanisms for this dual effect could be related to the close counter-regulation between T2 and T1 immune pathways, and potential key underlying mechanisms are discussed. Further basic research and better understanding of these underlying counter-regulatory mechanisms could provide novel therapeutic targets for the prevention and treatment of virally induced asthma exacerbations, as well as T2- and non-T2-driven asthma. Future clinical research should examine the effects of T2 inhibitors on IFN responses and other T1 immune pathways, in addition to any effects on the frequency and severity of viral and other infections and related exacerbations in patients with asthma as a priority.

Rhinovirus and Asthma Exacerbations

Rhinovirus (RV) is ubiquitous and typically causes only minor upper respiratory symptoms. However, especially in children and adolescent asthmatics, RV is responsible for most exacerbations. This ability of RV to drive exacerbations typically requires the concomitant presence of exposure to a bystander allergen. Susceptibility to RV-mediated exacerbations is also related to the genetic background of the host, which contributes to greater infectivity, more severe infections, altered immune responses, and to greater inflammation and loss of asthma control. Given these responses, there are several treatments available or being developed that should improve the control of exacerbations related to RV infection.

In vivo experimental models of infection and disease

Human and animal models continue to play a crucial role in research to understand host immunity to rhinovirus (RV) and identify disease mechanisms. Human models have provided direct evidence that RV infection is capable of exacerbating chronic respiratory diseases and identified immunological processes that correlate with clinical disease outcomes. Mice are the most commonly used nonhuman experimental RV infection model. Although semipermissive, under defined experimental conditions sufficient replication occurs to induce host immune responses that recapitulate immunity and disease during human infection. The capacity to use genetically modified mouse strains and drug interventions has shown the mouse model to be an invaluable research tool defining causal relationships between host immunity and disease and supporting development of new treatments. Used in combination the insights achieved from human and animal experimental infection models provide complementary insights into RV biology and yield novel therapeutic options to reduce the burden of RV-induced disease.

Nucleic Acid Sensing in Allergic Disorders

Recent advances indicate that there is crosstalk between allergic disorders and nucleic acid sensing. Triggers that activate inflammatory mechanisms via nucleic acid sensors affect both allergic phenotypes and anti-viral responses, depending on the timing and the order of exposure. Viral respiratory infections, such as those caused by the rhinovirus, influenza, and respiratory syncytial virus, are the most frequent cause of significant asthma exacerbations through effects mediated predominantly by TLR3. However, agonists of other nucleic acid sensors, such as TLR7/8 and TLR9 agonists, may inhibit allergic inflammation and reduce clinical manifestations of disease. The allergic state can predispose the immune system to both exaggerated responses to viral infections or protection from anti-viral inflammatory responses. T_H2 cytokines appear to alter the epithelium, leading to defective viral clearance or exaggerated responses to viral infections. However, a T_H2 skewed allergic response may be protective against a T_H1-dependent inflammatory anti-viral response. This review briefly introduces the receptors involved in nucleic acid sensing, addresses mechanisms by which nucleic acid sensing and allergic responses can counteract one another, and discusses the strategies in experimental settings, both in animal and human studies, to harness the nucleic acid sensing machinery for the intervention of allergic disorders.

IL-1β mediates lung neutrophilia and IL-33 expression in a mouse model of viral-induced asthma exacerbation

BACKGROUND

Viral-induced asthma exacerbations, which exhibit both Th1-type neutrophilia and Th2-type inflammation, associate with secretion of Interleukin (IL)-1β. IL-1β induces neutrophilic inflammation. It may also increase Th2-type cytokine expression. We hypothesised that IL-1β is causally involved in both Th1 and Th2 features of asthma exacerbations. This hypothesis is tested in our mouse model of viral stimulus-induced asthma exacerbation.

METHOD

Wild-type (WT) and IL-1β deficient (IL-1β^-/-) mice received house dust mite (HDM) or saline intranasally during three weeks followed by intranasal dsRNA (PolyI:C molecule known for its rhinovirus infection mimic) for three consecutive days to provoke exacerbation. Bronchoalveolar lavage fluid was analysed for inflammatory cells and total protein. Lung tissues were stained for neutrophilic inflammation and IL-33. Tissue homogenates were analysed for mRNA expression of Muc5ac, CXCL1/KC, TNF-α, CCL5, IL-25, TSLP, IL-33, IL-1β, CCL11 and CCL2 using RT-qPCR.

RESULTS

Expression of IL-1β, neutrophil chemoattractants, CXCL1 and CCL5, the Th2-upstream cytokine IL-33, and Muc5ac were induced at exacerbation in WT mice and were significantly inhibited in IL-1β^-/- mice at exacerbation. Effects of HDM alone were not reduced in IL-1β-deficient mice.

CONCLUSION

Without being involved in the baseline HDM-induced allergic asthma, IL-1β signalling was required to induce neutrophil chemotactic factors, IL-33, and Muc5ac expression at viral stimulus-induced exacerbation. We suggest that IL-1β has a role both in neutrophilic and Th2 inflammation at viral-induced asthma exacerbations.

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.

Release of Type 2 Cytokines by Epithelial Cells of Nasal Polyps

Background. T2 inflammation of chronic rhinosinusitis with nasal polyps (CRSwNP) may be influenced by epithelial cytokines release (TSLP, IL-25, and IL-33). We investigated the release of TSLP, IL-25, and IL-33 by epithelial CRSwNP cells compared to epithelial sinus mucosa cells of patients with chronic rhinosinusitis without nasal polyps (CRSsNP). Methods. IL-25, IL-33, and TSLP were measured by ELISA in the supernatant of cell cultures derived by CRSwNP (9 patients, 6 atopic) and CRSsNP (7 patients, 2 atopic) in baseline condition and following stimulation with Dermatophagoides pteronyssinus (DP), Aspergillus fumigatus (AF), and poly(I:C). Results. CRSwNP epithelial cells released increased levels of IL-25 (from 0.12 ± 0.06 pg/ml to 0.27 ± 0.1 pg/ml, p < 0.01) and TSLP (from 0.77 ± 0.5 pg/ml to 2.53 ± 1.17 pg/ml, p < 0.001) following poly(I:C) stimulation, while CRSsNP epithelial cells released increased levels of IL-25 and IL-33 following AF and DP stimulation, respectively (IL-25: from 0.18 ± 0.07 pg/ml to 0.51 ± 0.1 pg/ml, p < 0.001; IL-33: from 2.57 ± 1.3 pg/ml to 5.7 ± 3.1 pg/ml, p < 0.001). Conclusions. CRSwNP epithelial cells release TSLP and IL-25 when stimulated by poly(I:C) but not by DP or AF, suggesting that viral infection may contribute to maintain and amplify the T2 immune response seen in CRSwNP.

Rhinovirus and childhood asthma: an update

Asthma is recognized as a complex disease resulting from interactions between multiple genetic and environmental factors. Accumulating evidence suggests that respiratory viral infections in early life constitute a major environmental risk factor for the development of childhood asthma. Respiratory viral infections have also been recognized as the most common cause of asthma exacerbation. The advent of molecular diagnostics to detect respiratory viruses has provided new insights into the role of human rhinovirus (HRV) infections in the pathogenesis of asthma. However, it is still unclear whether HRV infections cause asthma or if wheezing with HRV infection is simply a predictor of childhood asthma. Recent clinical and experimental studies have identified plausible pathways by which HRV infection could cause asthma, particularly in a susceptible host, and exacerbate disease. Airway epithelial cells, the primary site of infection and replication of HRV, play a key role in these processes. Details regarding the role of genetic factors, including ORMDL3, are beginning to emerge. This review discusses recent clinical and experimental evidence for the role of HRV infection in the development and exacerbation of childhood asthma and the potential underlying mechanisms that have been proposed.

Polymorphisms in Toll-like receptor 3 are associated with asthma-related phenotypes in the Chinese Han patients

Toll-like receptor (TLR) 3 mediates antivirus immunity and is involved in asthma exacerbation and development. However, the genetic association between TLR3 and asthma remains unclear. This study aimed to evaluate the effects of polymorphisms within TLR3 on asthma risk and asthma-related phenotypes in the Chinese Han population. A total number of 462 unrelated adult patients with asthma and 398 healthy volunteers were enrolled in this study. The genotypes of tagging single nucleotide polymorphisms (SNPs) in TLR3 gene were determined using multiplex SNaPshot SNP genotyping assays. Case-control and case-only studies were used to assess any links with asthma and asthma-related phenotypes. The results showed that the genetic variants in TLR3 were associated with asthma-related phenotypes, including eosinophil counts, serum immunoglobulin E levels and lung function. However, there was no obvious association between the TLR3 SNPs and asthma susceptibility or asthma severity. TLR3 polymorphisms may play a considerable role in the pathogenesis of asthma. It will help in better understanding the pathogenesis of asthma and development of more effective strategies for the prevention, prediction and treatment of asthma.

Multiple Functions of the New Cytokine-Based Antimicrobial Peptide Thymic Stromal Lymphopoietin (TSLP)

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine, hitherto mostly known to be involved in inflammatory responses and immunoregulation. The human tslp gene gives rise to two transcription and translation variants: a long form (lfTSLP) that is induced by inflammation, and a short, constitutively-expressed form (sfTSLP), that appears to be downregulated by inflammation. The TSLP forms can be produced by a number of cell types, including epithelial and dendritic cells (DCs). lfTSLP can activate mast cells, DCs, and T cells through binding to the lfTSLP receptor (TSLPR) and has a pro-inflammatory function. In contrast, sfTSLP inhibits cytokine secretion of DCs, but the receptor mediating this effect is unknown. Our recent studies have demonstrated that both forms of TSLP display potent antimicrobial activity, exceeding that of many other known antimicrobial peptides (AMPs), with sfTSLP having the strongest effect. The AMP activity is primarily mediated by the C-terminal region of the protein and is localized within a 34-mer peptide (MKK34) that spans the C-terminal α-helical region in TSLP. Fluorescent studies of peptide-treated bacteria, electron microscopy, and liposome leakage models showed that MKK34 exerted membrane-disrupting effects comparable to those of LL-37. Expression of TSLP in skin, oral mucosa, salivary glands, and intestine is part of the defense barrier that aids in the control of both commensal and pathogenic microbes.

Advances in the treatment of virus-induced asthma

Viral exacerbations continue to represent the major burden in terms of morbidity, mortality and health care costs associated with asthma. Those at greatest risk for acute asthma are those with more severe airways disease and poor asthma control. It is this group with established asthma in whom acute exacerbations triggered by virus infections remain a serious cause of increased morbidity. A range of novel therapies are emerging to treat asthma and in particular target this group with poor disease control, and in most cases their efficacy is now being judged by their ability to reduce the frequency of acute exacerbations. Critical for the development of new treatment approaches is an improved understanding of virus-host interaction in the context of the asthmatic airway. This requires research into the virology of the disease in physiological models in conjunction with detailed phenotypic characterisation of asthma patients to identify targets amenable to therapeutic intervention.

Mouse models of acute exacerbations of allergic asthma

Most of the healthcare costs associated with asthma relate to emergency department visits and hospitalizations because of acute exacerbations of underlying chronic disease. Development of appropriate animal models of acute exacerbations of asthma is a necessary prerequisite for understanding pathophysiological mechanisms and assessing potential novel therapeutic approaches. Most such models have been developed using mice. Relatively few mouse models attempt to simulate the acute-on-chronic disease that characterizes human asthma exacerbations. Instead, many reported models involve relatively short-term challenge with an antigen to which animals are sensitized, followed closely by an unrelated triggering agent, so are better described as models of potentiation of acute allergic inflammation. Triggers for experimental models of asthma exacerbations include (i) challenge with high levels of the sensitizing allergen (ii) infection by viruses or fungi, or challenge with components of these microorganisms (iii) exposure to environmental pollutants. In this review, we examine the strengths and weaknesses of published mouse models, their application for investigation of novel treatments and potential future developments.

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.

Rhinovirus-Induced Airway Disease: A Model to Understand the Antiviral and Th2 Epithelial Immune Dysregulation in Childhood Asthma

Rhinovirus (RV) infections account for most asthma exacerbations among children and adults, yet the fundamental mechanism responsible for why asthmatics are more susceptible to RV than otherwise healthy individuals remains largely unknown. Nonetheless, the use of models to understand the mechanisms of RV-induced airway disease in asthma has dramatically expanded our knowledge about the cellular and molecular pathogenesis of the disease. For instance, ground-breaking studies have recently established that the susceptibility to RV in asthmatic subjects is associated with a dysfunctional airway epithelial inflammatory response generated after innate recognition of viral-related molecules, such as double-stranded RNA. This review summarizes the novel cardinal features of the asthmatic condition identified in the past few years through translational and experimental RV-based approaches. Specifically, we discuss the evidence demonstrating the presence of an abnormal innate antiviral immunity (airway epithelial secretion of types I and III interferons), exaggerated production of the master Th2 molecule thymic stromal lymphopoietin, and altered antimicrobial host defense in the airways of asthmatic individuals with acute RV infection.

Synergistic Proinflammatory Responses by IL-17A and Toll-Like Receptor 3 in Human Airway Epithelial Cells

Viral respiratory infections activate the innate immune response in the airway epithelium through Toll-like receptors (TLRs) and induce airway inflammation, which causes acute exacerbation of asthma. Although increases in IL-17A expression were observed in the airway of severe asthma patients, the interaction between IL-17A and TLR activation in airway epithelium remains poorly understood. In this study, we demonstrated that IL-17A and polyI:C, the ligand of TLR3, synergistically induced the expression of proinflammatory cytokines and chemokines (G-CSF, IL-8, CXCL1, CXCL5, IL-1F9), but not type I interferon (IFN-α1, -β) in primary culture of normal human bronchial epithelial cells. Synergistic induction after co-stimulation with IL-17A and polyI:C was observed from 2 to 24 hours after stimulation. Treatment with cycloheximide or actinomycin D had no effect, suggesting that the synergistic induction occurred without de novo protein synthesis or mRNA stabilization. Inhibition of the TLR3, TLR/TIR-domain-containing adaptor-inducing interferon β (TRIF), NF-κB, and IRF3 pathways decreased the polyI:C- and IL-17A/polyI:C-induced G-CSF and IL-8 mRNA expression. Comparing the levels of mRNA induction between co-treatment with IL-17A/polyI:C and treatment with polyI:C alone, blocking the of NF-κB pathway significantly attenuated the observed synergism. In western blotting analysis, activation of both NF-κB and IRF3 was observed in treatment with polyI:C and co-treatment with IL-17A/polyI:C; moreover, co-treatment with IL-17A/polyI:C augmented IκB-α phosphorylation as compared to polyI:C treatment alone. Collectively, these findings indicate that IL-17A and TLR3 activation cooperate to induce proinflammatory responses in the airway epithelium via TLR3/TRIF-mediated NF-κB/IRF3 activation, and that enhanced activation of the NF-κB pathway plays an essential role in synergistic induction after co-treatment with IL-17A and polyI:C in vitro.

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.

Hyporeactivity of Alveolar Macrophages and Higher Respiratory Cell Permissivity Characterize DBA/2J Mice Infected by Influenza A Virus

Influenza A virus remains a major public health problem. Mouse models have been widely used to study influenza infection in mammals. DBA/2J and C57BL/6J represent extremes in terms of susceptibility to influenza A infection among inbred laboratory mouse strains. Several studies focused specifically on the factors responsible for the susceptibility of DBA/2J or the resistance of C57BL/6J and resulted in impressive lists of candidate genes or factors over- or underexpressed in one of the strains. We adopted a different phenotypical approach to identify the critical steps of the infection process accounting for the differences between DBA/2J and C57BL/6J strains. We concluded that both a dysfunction of alveolar macrophages and an increased permissivity of respiratory cells rendered DBA/2J more susceptible to influenza infection.

Poly(inosinic-cytidylic) acid-triggered exacerbation of experimental asthma depends on IL-17A produced by NK cells

Viral infection of the respiratory tract represents the major cause of acute asthma exacerbations. dsRNA is produced as an intermediate during replication of respiratory viruses and triggers immune responses via TLR3. This study aimed at clarifying the mechanisms underlying TLR3 triggered exacerbation of experimental allergic asthma. The TLR3 ligand poly(inosinic-cytidylic) acid was applied intranasally to mice with already established experimental allergic asthma. Airway inflammation, cytokine expression, mucus production, and airway reactivity was assessed in wild-type, IL-17A, or IL-23p19-deficient, and in NK cell-depleted mice. Local application of poly(inosinic-cytidylic) acid exacerbated experimental allergic asthma in mice as characterized by enhanced release of proinflammatory cytokines, aggravated airway inflammation, and increased mucus production together with pronounced airway hyperresponsiveness. This was further associated with augmented production of IL-17 by Th17 cells and NK cells. Whereas experimental exacerbation could be induced in IL-23p19-deficient mice lacking mature, proinflammatory Th17 cells, this was not possible in mice lacking IL-17A or in NK cell-depleted animals. These experiments indicate a central role for IL-17 derived from NK cells but not from Th17 cells in the pathogenesis of virus-triggered exacerbation of experimental asthma.

MicroRNA-26a/-26b-COX-2-MIP-2 Loop Regulates Allergic Inflammation and Allergic Inflammation-promoted Enhanced Tumorigenic and Metastatic Potential of Cancer Cells

Cyclooxgenase-2 (COX-2) knock-out mouse experiments showed that COX-2 was necessary for in vivo allergic inflammation, such as passive cutaneous anaphylaxis, passive systemic anaphylaxis, and triphasic cutaneous allergic reaction. TargetScan analysis predicted COX-2 as a target of miR-26a and miR-26b. miR-26a/-26b decreased luciferase activity associated with COX-2-3'-UTR. miR-26a/-26b exerted negative effects on the features of in vitro and in vivo allergic inflammation by targeting COX-2. ChIP assays showed the binding of HDAC3 and SNAIL, but not COX-2, to the promoter sequences of miR-26a and miR-26b. Cytokine array analysis showed that the induction of chemokines, such as MIP-2, in the mouse passive systemic anaphylaxis model occurred in a COX-2-dependent manner. ChIP assays showed the binding of HDAC3 and COX-2 to the promoter sequences of MIP-2. In vitro and in vivo allergic inflammation was accompanied by the increased expression of MIP-2. miR-26a/-26b negatively regulated the expression of MIP-2. Allergic inflammation enhanced the tumorigenic and metastatic potential of cancer cells and induced positive feedback involving cancer cells and stromal cells, such as mast cells, macrophages, and endothelial cells. miR-26a mimic and miR-26b mimic negatively regulated the positive feedback between cancer cells and stromal cells and the positive feedback among stromal cells. miR-26a/-26b negatively regulated the enhanced tumorigenic potential by allergic inflammation. COX-2 was necessary for the enhanced metastatic potential of cancer cells by allergic inflammation. Taken together, our results indicate that the miR26a/-26b-COX-2-MIP-2 loop regulates allergic inflammation and the feedback relationship between allergic inflammation and the enhanced tumorigenic and metastatic potential.

Translational value of animal models of asthma: Challenges and promises

Asthma is a heterogeneous disease in which various environmental stimuli as well as different genes, cell types, cytokines and mediators are implicated. This chronic inflammatory disorder of the airways is estimated to affect as many as 300 million people worldwide. Animal models of asthma, despite their limitations, have contributed greatly to our understanding of disease pathology and the identification of key processes, cells and mediators in asthma. However, it is less likely to develop an animal model of asthma that takes into account all aspects of human disease. The focus in current asthma research is increasingly on severe asthma because this group of patients is not well treated today. Recent advances in studies of asthma exacerbation are thus considered. We therefore need to develop translational model systems for pharmacological evaluation and molecular target discovery of severe asthma and asthma exacerbations. In this review we attempted to discuss the different animal models of asthma, with special emphasis on ovalbumin and house dust mite models, their merits and their limitations.

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.

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.