Inflammasome activation is required for human rhinovirus-induced airway inflammation in naive and allergen-sensitized mice

Inflammasome signalling pathway in the regulation of inflammation - its involvement in the development and exacerbation of asthma and chronic obstructive pulmonary disease

Inflammasomes are multiprotein oligomers, whose main function is the recruitment and activation of caspase-1, which cleaves the precursor forms of interleukin (IL)-1β and IL-18, generating biologically active cytokines. Activation of inflammasome is an essential component of the innate immune response, and according to recent reports it is involved in epithelial homeostasis and type 2 T helper cell (Th2) differentiation. In recent years, the contribution of inflammasome dependent signalling pathways to the development of inflammatory diseases became a topic of multiple research studies. Asthma and chronic obstructive pulmonary disease (COPD) are the most prevalent obstructive lung diseases. Recent studies have focused on inflammatory aspects of asthma and COPD development, demonstrating the key role of inflammasome-dependent processes. Factors responsible for activation of inflammasome complex are similar in both asthma and COPD and include bacteria, viruses, cigarette smoke, and particulate matter. Some recent studies have revealed that NLRP3 inflammasome plays a crucial role, particularly in the development of acute exacerbations of COPD (AECOPD). Activation of NLRP3 inflammasome has been linked with neutrophilic severe steroid-resistant asthma. Although most of the studies on inflammasomes in asthma and COPD focused on the NLRP3 inflammasome, there are scarce scientific reports linking other inflammasomes such as AIM2 and NLRP1 with obstructive lung diseases. In this mini review we focus on the role of molecular pathways associated with inflammasome in the most prevalent lung diseases such as asthma and COPD. Furthermore, we will try to answer the question of whether inhibition of inflammasome can occur as a modern therapy in these diseases.

Breaking Bad: Inflammasome Activation by Respiratory Viruses

The nucleotide-binding domain leucine-rich repeat-containing receptor (NLR) family is a group of intracellular sensors activated in response to harmful stimuli, such as invading pathogens. Some NLR family members form large multiprotein complexes known as inflammasomes, acting as a platform for activating the caspase-1-induced canonical inflammatory pathway. The canonical inflammasome pathway triggers the secretion of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 by the rapid rupture of the plasma cell membrane, subsequently causing an inflammatory cell death program known as pyroptosis, thereby halting viral replication and removing infected cells. Recent studies have highlighted the importance of inflammasome activation in the response against respiratory viral infections, such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While inflammasome activity can contribute to the resolution of respiratory virus infections, dysregulated inflammasome activity can also exacerbate immunopathology, leading to tissue damage and hyperinflammation. In this review, we summarize how different respiratory viruses trigger inflammasome pathways and what harmful effects the inflammasome exerts along with its antiviral immune response during viral infection in the lungs. By understanding the crosstalk between invading pathogens and inflammasome regulation, new therapeutic strategies can be exploited to improve the outcomes of respiratory viral infections.

Programmed Cell Death in Asthma: Apoptosis, Autophagy, Pyroptosis, Ferroptosis, and Necroptosis

Bronchial asthma is a complex heterogeneous airway disease, which has emerged as a global health issue. A comprehensive understanding of the different molecular mechanisms of bronchial asthma may be an efficient means to improve its clinical efficacy in the future. Increasing research evidence indicates that some types of programmed cell death (PCD), including apoptosis, autophagy, pyroptosis, ferroptosis, and necroptosis, contributed to asthma pathogenesis, and may become new targets for future asthma treatment. This review briefly discusses the molecular mechanism and signaling pathway of these forms of PCD focuses on summarizing their roles in the pathogenesis and treatment strategies of asthma and offers some efficient means to improve clinical efficacy of therapeutics for asthma in the near future.

Rhinovirus-induced epithelial RIG-I inflammasome suppresses antiviral immunity and promotes inflammation in asthma and COVID-19

Rhinoviruses and allergens, such as house dust mite are major agents responsible for asthma exacerbations. The influence of pre-existing airway inflammation on the infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is largely unknown. We analyse mechanisms of response to viral infection in experimental in vivo rhinovirus infection in healthy controls and patients with asthma, and in in vitro experiments with house dust mite, rhinovirus and SARS-CoV-2 in human primary airway epithelium. Here, we show that rhinovirus infection in patients with asthma leads to an excessive RIG-I inflammasome activation, which diminishes its accessibility for type I/III interferon responses, leading to their early functional impairment, delayed resolution, prolonged viral clearance and unresolved inflammation in vitro and in vivo. Pre-exposure to house dust mite augments this phenomenon by inflammasome priming and auxiliary inhibition of early type I/III interferon responses. Prior infection with rhinovirus followed by SARS-CoV-2 infection augments RIG-I inflammasome activation and epithelial inflammation. Timely inhibition of the epithelial RIG-I inflammasome may lead to more efficient viral clearance and lower the burden of rhinovirus and SARS-CoV-2 infections.

TLR2-hif1α-mediated glycolysis contributes to pyroptosis and oxidative stress in allergic airway inflammation

As a pattern recognition receptor which activates innate immune system, toll-like receptor 2 (TLR2) has been reportedly mediates allergic airway inflammation (AAI), yet the underlying mechanism remains elusive. Here, in a murine AAI model, TLR2^-/- mice showed decreased airway inflammation, pyroptosis and oxidative stress. RNA-sequencing revealed that allergen-induced hif1 signaling pathway and glycolysis were significantly downregulated when TLR2 was deficient, which were confirmed by lung protein immunoblots. Glycolysis inhibitor 2-Deoxy-d-glucose (2-DG) inhibited allergen-induced airway inflammation, pyroptosis, oxidative stress and glycolysis in wild type (WT) mice, while hif1α stabilizer ethyl 3,4-dihydroxybenzoate (EDHB) restored theses allergen-induced changes in TLR2^-/- mice, indicating TLR2-hif1α-mediated glycolysis contributes to pyroptosis and oxidative stress in AAI. Moreover, upon allergen challenge, lung macrophages were highly activated in WT mice but were less activated in TLR2^-/- mice, 2-DG replicated while EDHB reversed such effect of TLR2 deficiency on lung macrophages. Likewise, both in vivo and ex vivo WT alveolar macrophages (AMs) exhibited higher TLR2/hif1α expression, glycolysis and polarization activation in response to ovalbumin (OVA), which were all inhibited in TLR2^-/- AMs, suggesting AMs activation and metabolic switch are dependent on TLR2. Finally, depletion of resident AMs in TLR2^-/- mice abolished while transfer of TLR2^-/- resident AMs to WT mice replicated the protective effect of TLR2 deficiency on AAI when administered before allergen challenge. Collectively, we suggested that loss of TLR2-hif1α-mediated glycolysis in resident AMs ameliorates allergic airway inflammation that inhibits pyroptosis and oxidative stress, therefore the TLR2-hif1α-glycolysis axis in resident AMs may be a novel therapeutic target for AAI.

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.

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.

Relaxin Affects Airway Remodeling Genes Expression through Various Signal Pathways Connected with Transcription Factors

Fibrosis is one of the parameters of lung tissue remodeling in asthma. Relaxin has emerged as a natural suppressor of fibrosis, showing efficacy in the prevention of a multiple models of fibrosis. Therefore, the aim of this study was to analyze the aptitudes of relaxin, in the context of its immunomodulatory properties, in the development of airway remodeling. WI-38 and HFL1 fibroblasts, as well as epithelial cells (NHBE), were incubated with relaxin. Additionally, remodeling conditions were induced with two serotypes of rhinovirus (HRV). The expression of the genes contributing to airway remodeling were determined. Moreover, NF-κB, c-Myc, and STAT3 were knocked down to analyze the pathways involved in airway remodeling. Relaxin decreased the mRNA expression of collagen I and TGF-β and increased the expression of MMP-9 (p < 0.05). Relaxin also decreased HRV-induced expression of collagen I and α-SMA (p < 0.05). Moreover, all the analyzed transcription factors—NF-κB, c-Myc, and STAT3—have shown its influence on the pathways connected with relaxin action. Though relaxin requires further study, our results suggest that this natural compound offers great potential for inhibition of the development, or even reversing, of factors related to airway remodeling. The presented contribution of the investigated transcription factors in this process additionally increases its potential possibilities through a variety of its activity pathways.

Gelsolin Attenuates Neonatal Hyperoxia-Induced Inflammatory Responses to Rhinovirus Infection and Preserves Alveolarization

Prematurity and bronchopulmonary dysplasia (BPD) increase the risk of asthma later in life. Supplemental oxygen therapy is a risk factor for chronic respiratory symptoms in infants with BPD. Hyperoxia induces cell injury and release of damage-associated molecular patterns (DAMPs). Cytoskeletal filamentous actin (F-actin) is a DAMP which binds Clec9a, a C-type lectin selectively expressed on CD103+ dendritic cells (DCs). Co-stimulation of Clec9a and TLR3 induces maximal proinflammatory responses. We have shown that neonatal hyperoxia (a model of BPD) increases lung IL-12+Clec9a+CD103+ DCs, pro-inflammatory responses and airway hyperreactivity following rhinovirus (RV) infection. CD103+ DCs and Clec9a are required for these responses. Hyperoxia increases F-actin levels in bronchoalveolar lavage fluid (BALF). We hypothesized that the F-actin severing protein gelsolin attenuates neonatal hyperoxia-induced Clec9a+CD103+ DC-dependent pro-inflammatory responses to RV and preserves alveolarization. We exposed neonatal mice to hyperoxia and treated them with gelsolin intranasally. Subsequently we inoculated the mice with RV intranasally. Alternatively, we inoculated normoxic neonatal mice with BALF from hyperoxia-exposed mice (hyperoxic BALF), RV and gelsolin. We analyzed lung gene expression two days after RV infection. For in vitro studies, lung CD11c+ cells were isolated from C57BL/6J or Clec9a^gfp-/- mice and incubated with hyperoxic BALF and RV. Cells were analyzed by flow cytometry. In neonatal mice, gelsolin blocked hyperoxia-induced Il12p40, TNF-α and IFN-γ mRNA and protein expression in response to RV infection. Similar effects were observed when gelsolin was co-administered with hyperoxic BALF and RV. Gelsolin decreased F-actin levels in hyperoxic BALF in vitro and inhibited hyperoxia-induced D103lo DC expansion and inflammation in vivo. Gelsolin also attenuated hyperoxia-induced hypoalveolarization. Further, incubation of lung CD11c+ cells from WT and Clec9a^gfp-/- mice with hyperoxic BALF and RV, showed Clec9a is required for maximal hyperoxic BALF and RV induced IL-12 expression in CD103+ DCs. Finally, in tracheal aspirates from mechanically ventilated human preterm infants the F-actin to gelsolin ratio positively correlates with FiO2, and gelsolin levels decrease during the first two weeks of mechanical ventilation. Collectively, our findings demonstrate a promising role for gelsolin, administered by inhalation into the airway to treat RV-induced exacerbations of BPD and prevent chronic lung disease.

Trained immunity in type 2 immune responses

Immunological memory of innate immune cells, also termed "trained immunity", allows for cross-protection against distinct pathogens, but may also drive chronic inflammation. Recent studies have shown that memory responses associated with type 2 immunity do not solely rely on adaptive immune cells, such as T- and B cells, but also involve the innate immune system and epithelial cells. Memory responses have been described for monocytes, macrophages and airway epithelial cells of asthmatic patients as well as for macrophages and group 2 innate lymphoid cells (ILC2) from allergen-sensitized or helminth-infected mice. The metabolic and epigenetic mechanisms that mediate allergen- or helminth-induced reprogramming of innate immune cells are only beginning to be uncovered. Trained immunity has been implicated in helminth-driven immune regulation and allergen-specific immunotherapy, suggesting its exploitation in future therapies. Here, we discuss recent advances and key remaining questions regarding the mechanisms and functions of trained type 2 immunity in infection and inflammation.

ESR2 regulates PINK1-mediated mitophagy via transcriptional repression of microRNA-423 expression to promote asthma development

Asthma represents an inflammatory airway disease related to the induction of airway eosinophilia, mucus overproduction, and bronchial hyperresponsiveness. This study explored the effects of microRNA-423 (miR-423) on mitophagy and inflammation in asthmatic mice challenged with house dust mites (HDMs) and rhinovirus (RV). By searching for differentially expressed miRNAs in the GSE25230 microarray, miR-423 was identified as our target. Moreover, miR-423 was expressed at low levels in the lung tissues from patients with asthma, and agomiR-423 significantly inhibited RV-induced inflammatory injury and activation of inflammasome signaling in mouse lung tissues. Additionally, miR-423 downregulated the expression of IL-1β/NLRP3/Caspase-1 inflammasome signaling by targeting phosphatase and tensin homolog-induced putative kinase 1 (PINK1). Furthermore, luciferase reporter experiments and ChIP-qPCR assays revealed that estrogen receptor 2 (ESR2) transcriptionally repressed miR-423 expression by coordinating with H3K9me2 modification of the miR-423 promoter histone. Overall, ESR2 synergized with the H3K9me2 modification of the miR-423 promoter histone to transcriptionally repress miR-423 expression and increase PINK1 expression in lung tissues, resulting in asthma exacerbation.

Epithelial Aryl Hydrocarbon Receptor Protects From Mucus Production by Inhibiting ROS-Triggered NLRP3 Inflammasome in Asthma

Background

Despite long-standing recognition in the significance of mucus overproduction in asthma, its etiology remains poorly understood. Muc5ac is a secretory mucin that has been associated with reduced pulmonary function and asthma exacerbations.

Objectives

We sought to investigate the immunological pathway that controls Muc5ac expression and allergic airway inflammation in asthma.

Methods

Cockroach allergen-induced Muc5ac expression and aryl hydrocarbon receptor (AhR) signaling activation was examined in the human bronchial epithelial cells (HBECs) and mouse model of asthma. AhR regulation of Muc5ac expression, mitochondrial ROS (Mito-ROS) generation, and NLRP3 inflammasome was determined by AhR knockdown, the antagonist CH223191, and AhR-/- mice. The role of NLRP3 inflammasome in Muc5ac expression and airway inflammation was also investigated.

Results

Cockroach allergen induced Muc5ac overexpression in HBECs and airways of asthma mouse model. Increased expression of AhR and its downstream genes CYP1A1 and CYP1B1 was also observed. Mice with AhR deletion showed increased allergic airway inflammation and MUC5AC expression. Moreover, cockroach allergen induced epithelial NLRP3 inflammasome activation (e.g., NLRP3, Caspase-1, and IL-1β), which was enhanced by AhR knockdown or the antagonist CH223191. Furthermore, AhR deletion in HBECs led to enhanced ROS generation, particularly Mito-ROS, and inhibition of ROS or Mito-ROS subsequently suppressed the inflammasome activation. Importantly, inhibition of the inflammasome with MCC950, a NLRP3-specifc inhibitor, attenuated allergic airway inflammation and Muc5ac expression. IL-1β generated by the activated inflammasomes mediated cockroach allergen-induced Muc5ac expression in HBECs.

Conclusions

These results reveal a previously unidentified functional axis of AhR-ROS-NLRP3 inflammasome in regulating Muc5ac expression and airway inflammation.

Deficient inflammasome activation permits an exaggerated asthma phenotype in rhinovirus C-infected immature mice

Compared to other RV species, RV-C has been associated with more severe respiratory illness and is more likely to occur in children with a history of asthma or who develop asthma. We therefore inoculated 6-day-old mice with sham, RV-A1B, or RV-C15. Inflammasome priming and activation were assessed, and selected mice treated with recombinant IL-1β. Compared to RV-A1B infection, RV-C15 infection induced an exaggerated asthma phenotype, with increased mRNA expression of Il5, Il13, Il25, Il33, Muc5ac, Muc5b, and Clca1; increased lung lineage-negative CD25+CD127+ST2+ ILC2s; increased mucous metaplasia; and increased airway responsiveness. Lung vRNA, induction of pro-inflammatory type 1 cytokines, and inflammasome priming (pro-IL-1β and NLRP3) were not different between the two viruses. However, inflammasome activation (mature IL-1β and caspase-1 p12) was reduced in RV-C15-infected mice compared to RV-A1B-infected mice. A similar deficiency was found in cultured macrophages. Finally, IL-1β treatment decreased RV-C-induced type 2 cytokine and mucus-related gene expression, ILC2s, mucous metaplasia, and airway responsiveness but not lung vRNA level. We conclude that RV-C induces an enhanced asthma phenotype in immature mice. Compared to RV-A, RV-C-induced macrophage inflammasome activation and IL-1β are deficient, permitting exaggerated type 2 inflammation and mucous metaplasia.

Mechanism of Rhinovirus Immunity and Asthma

The majority of asthma exacerbations in children are caused by Rhinovirus (RV), a positive sense single stranded RNA virus of the Picornavirus family. The host has developed virus defense mechanisms that are mediated by the upregulation of interferon-activated signaling. However, the virus evades the immune system by inducing immunosuppressive cytokines and surface molecules like programmed cell death protein 1 (PD-1) and its ligand (PD-L1) on immunocompetent cells. Initially, RV infects epithelial cells, which constitute a physiologic mucosal barrier. Upon virus entrance, the host cell immediately recognizes viral components like dsRNA, ssRNA, viral glycoproteins or CpG-DNA by host pattern recognition receptors (PRRs). Activation of toll like receptors (TLR) 3, 7 and 8 within the endosome and through MDA-5 and RIG-I in the cytosol leads to the production of interferon (IFN) type I and other antiviral agents. Every cell type expresses IFNAR1/IFNAR2 receptors thus allowing a generalized antiviral activity of IFN type I resulting in the inhibition of viral replication in infected cells and preventing viral spread to non-infected cells. Among immune evasion mechanisms of the virus, there is downregulation of IFN type I and its receptor as well as induction of the immunosuppressive cytokine TGF-β. TGF-β promotes viral replication and is associated with induction of the immunosuppression signature markers LAP3, IDO and PD-L1. This article reviews the recent advances on the regulation of interferon type I expression in association with RV infection in asthmatics and the immunosuppression induced by the virus.

Long-lived macrophage reprogramming drives spike protein-mediated inflammasome activation in COVID-19

Innate immunity triggers responsible for viral control or hyperinflammation in COVID-19 are largely unknown. Here we show that the SARS-CoV-2 spike protein (S-protein) primes inflammasome formation and release of mature interleukin-1β (IL-1β) in macrophages derived from COVID-19 patients but not in macrophages from healthy SARS-CoV-2 naïve individuals. Furthermore, longitudinal analyses reveal robust S-protein-driven inflammasome activation in macrophages isolated from convalescent COVID-19 patients, which correlates with distinct epigenetic and gene expression signatures suggesting innate immune memory after recovery from COVID-19. Importantly, we show that S-protein-driven IL-1β secretion from patient-derived macrophages requires non-specific monocyte pre-activation in vivo to trigger NLRP3-inflammasome signaling. Our findings reveal that SARS-CoV-2 infection causes profound and long-lived reprogramming of macrophages resulting in augmented immunogenicity of the SARS-CoV-2 S-protein, a major vaccine antigen and potent driver of adaptive and innate immune signaling.

Loss of regulatory capacity in Treg cells following rhinovirus infection

BACKGROUND

Respiratory infections with rhinoviruses (RV) are strongly associated with development and exacerbations of asthma, and they pose an additional health risk for subjects with allergy.

OBJECTIVE

How RV infections and chronic allergic diseases are linked and what role RV plays in the breaking of tolerance in regulatory T (Treg) cells is unknown. Therefore, this study aims to investigate the effects of RV on Treg cells.

METHODS

Treg cells were isolated from subjects with asthma and controls after experimental infection with the RV-A16 (RV16) and analyzed with next-generation sequencing. Additionally, suppression assays, quantitative PCR assays, and protein quantifications were performed with Treg cells after in vitro RV16 infection.

RESULTS

RV16 induced a strong antiviral response in Treg cells from subjects with asthma and controls, including the upregulation of IFI44L, MX1, ISG15, IRF7, and STAT1. In subjects with asthma, the inflammatory response was exaggerated and showed a dysregulated immune response compared with that in the controls. Furthermore, subjects with asthma failed to upregulate several immunosuppressive molecules such as CTLA4 and CD69, and they upregulated the inflammasome-related genes PYCARD and AIM2. Additionally, RV16 reduced the suppressive capacity of Treg cells from healthy subjects and subjects with asthma in vitro and increased T_H2 cell-type cytokine production.

CONCLUSIONS

Treg cells from healthy subjects and subjects with asthma displayed an antiviral response after RV infection and showed reduced suppressive capacity. These data suggest that Treg cell function might be altered or impaired during RV infections, which might play an important role in the association between RV and the development of asthma and asthma exacerbations.

Rhinovirus C Infection Induces Type 2 Innate Lymphoid Cell Expansion and Eosinophilic Airway Inflammation

Rhinovirus C (RV-C) infection is associated with severe asthma exacerbations. Since type 2 inflammation is an important disease mechanism in asthma, we hypothesized that RV-C infection, in contrast to RV-A, preferentially stimulates type 2 inflammation, leading to exacerbated eosinophilic inflammation. To test this, we developed a mouse model of RV-C15 airways disease. RV-C15 was generated from the full-length cDNA clone and grown in HeLa-E8 cells expressing human CDHR3. BALB/c mice were inoculated intranasally with 5 x 106 ePFU RV-C15, RV-A1B or sham. Mice inoculated with RV-C15 showed lung viral titers of 1 x 105 TCID50 units 24 h after infection, with levels declining thereafter. IFN-α, β, γ and λ2 mRNAs peaked 24-72 hrs post-infection. Immunofluorescence verified colocalization of RV-C15, CDHR3 and acetyl-α-tubulin in mouse ciliated airway epithelial cells. Compared to RV-A1B, mice infected with RV-C15 demonstrated higher bronchoalveolar eosinophils, mRNA expression of IL-5, IL-13, IL-25, Muc5ac and Gob5/Clca, protein production of IL-5, IL-13, IL-25, IL-33 and TSLP, and expansion of type 2 innate lymphoid cells. Analogous results were found in mice treated with house dust mite before infection, including increased airway responsiveness. In contrast to Rorafl/fl littermates, RV-C-infected Rorafl/flIl7rcre mice deficient in ILC2s failed to show eosinophilic inflammation or mRNA expression of IL-13, Muc5ac and Muc5b. We conclude that, compared to RV-A1B, RV-C15 infection induces ILC2-dependent type 2 airway inflammation, providing insight into the mechanism of RV-C-induced asthma exacerbations.

Role of ILC2 in Viral-Induced Lung Pathogenesis

Innate lymphoid type-2 cells (ILC2) are a population of innate cells of lymphoid origin that are known to drive strong Type 2 immunity. ILC2 play a key role in lung homeostasis, repair/remodeling of lung structures following injury, and initiation of inflammation as well as more complex roles during the immune response, including the transition from innate to adaptive immunity. Remarkably, dysregulation of this single population has been linked with chronic lung pathologies, including asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrotic diseases (IPF). Furthermore, ILC2 have been shown to increase following early-life respiratory viral infections, such as respiratory syncytial virus (RSV) and rhinovirus (RV), that may lead to long-term alterations of the lung environment. The detrimental roles of increased ILC2 following these infections may include pathogenic chronic inflammation and/or alterations of the structural, repair, and even developmental processes of the lung. Respiratory viral infections in older adults and patients with established chronic pulmonary diseases often lead to exacerbated responses, likely due to previous exposures that leave the lung in a dysregulated functional and structural state. This review will focus on the role of ILC2 during respiratory viral exposures and their effects on the induction and regulation of lung pathogenesis. We aim to provide insight into ILC2-driven mechanisms that may enhance lung-associated diseases throughout life. Understanding these mechanisms will help identify better treatment options to limit not only viral infection severity but also protect against the development and/or exacerbation of other lung pathologies linked to severe respiratory viral infections.

Immunological Roles of NLR in Allergic Diseases and Its Underlying Mechanisms

Our understanding on the immunological roles of pathogen recognition in innate immunity has vastly increased over the past 20 years. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLR) are cytosolic pattern recognition receptors (PRR) that are responsible for sensing microbial motifs and endogenous damage signals in mammalian cytosol for immune surveillance and host defense. The accumulating discoveries on these NLR sensors in allergic diseases suggest that the pathogenesis of allergic diseases may not be confined to the adaptive immune response. Therapy targeting NLR in murine models also shields light on its potential in the treatment of allergies in man. In this review, we herein summarize the recent understanding of the role of NLR sensors and their molecular mechanisms involved in allergic inflammation, including atopic dermatitis and allergic asthma.

Nasal interferon responses to community rhinovirus infections are similar in controls and children with asthma

BACKGROUND

Rhinovirus (RV) is the main cause of asthma exacerbations in children. Some studies reported that persons with asthma have attenuated interferon (IFN) responses to experimental RV infection compared with healthy individuals. However, responses to community-acquired RV infections in controls and children with asthma have not been compared.

OBJECTIVE

To evaluate nasal cytokine responses after natural RV infections in people with asthma and healthy children.

METHODS

We compared nasal cytokine expression among controls and children with asthma during healthy, virus-negative surveillance weeks and self-reported RV-positive sick weeks. A total of 14 controls and 21 patients with asthma were studied. Asthma disease severity was based on symptoms and medication use. Viral genome was detected by multiplex polymerase chain reaction. Nasal cytokine protein levels were determined by multiplex assays.

RESULTS

Two out of 47 surveillance weeks tested positive for RV, illustrating an asymptomatic infection rate of 5%. A total of 38 of 47 sick weeks (81%) tested positive for the respiratory virus. Of these, 33 (87%) were positive for RV. During well weeks, nasal interleukin 8 (IL-8), IL-12, and IL-1β levels were higher in children with asthma than controls. Compared with healthy virus-negative surveillance weeks, IL-8, IL-13, and interferon beta increased during colds only in patients with asthma. In both controls and children with asthma, the nasal levels of interferon gamma, interferon lambda-1, IL-1β, IL-8, and IL-10 increased during RV-positive sick weeks. During RV infection, IL-8, IL-1β, and tumor necrosis factor-α levels were strongly correlated.

CONCLUSION

In both controls and patients with asthma, natural RV infection results in robust type II and III IFN responses.

Inhibition of uric acid or IL-1β ameliorates respiratory syncytial virus immunopathology and development of asthma

BACKGROUND

Respiratory syncytial virus (RSV) affects most infants early in life and is associated with increased asthma risk. The specific mechanism remains unknown.

OBJECTIVE

To investigate the role of uric acid (UA) and IL-1β in RSV immunopathology and asthma predisposition.

METHODS

Tracheal aspirates from human infants with and without RSV were collected and analyzed for pro-IL-1β mRNA and protein to establish a correlation in human disease. Neonatal mouse models of RSV were employed, wherein mice infected at 6-7 days of life were analyzed at 8 days postinfection, 5 weeks postinfection, or after a chronic cockroach allergen asthma model. A xanthine oxidase inhibitor or IL-1 receptor antagonist was administered during RSV infection.

RESULTS

Human tracheal aspirates from RSV-infected infants showed elevated pro-IL-1β mRNA and protein. Inhibition of UA or IL-1β during neonatal murine RSV infection decreased mucus production, reduced cellular infiltrates to the lung (especially ILC2s), and decreased type 2 immune responses. Inhibition of either UA or IL-1β during RSV infection led to chronic reductions in pulmonary immune cell composition and reduced type 2 immune responses and reduced similar responses after challenge with cockroach antigen.

CONCLUSIONS

Inhibiting UA and IL-1β during RSV infection ameliorates RSV immunopathology, reduces the consequences of allergen-induced asthma, and presents new therapeutic targets to reduce early-life viral-induced asthma development.

IL-1β prevents ILC2 expansion, type 2 cytokine secretion, and mucus metaplasia in response to early-life rhinovirus infection in mice

BACKGROUND

Early-life wheezing-associated respiratory infection with human rhinovirus (RV) is associated with asthma development. RV infection of 6-day-old immature mice causes mucous metaplasia and airway hyperresponsiveness which is associated with the expansion of IL-13-producing type 2 innate lymphoid cells (ILC2s) and dependent on IL-25 and IL-33. We examined regulation of this asthma-like phenotype by IL-1β.

METHODS

Six-day-old wild-type or NRLP3-/- mice were inoculated with sham or RV-A1B. Selected mice were treated with IL-1 receptor antagonist (IL-1RA), anti-IL-1β, or recombinant IL-1β.

RESULTS

Rhinovirus infection induced Il25, Il33, Il4, Il5, Il13, muc5ac, and gob5 mRNA expression, ILC2 expansion, mucus metaplasia, and airway hyperresponsiveness. RV also induced lung mRNA and protein expression of pro-IL-1β and NLRP3 as well as cleavage of caspase-1 and pro-IL-1β, indicating inflammasome priming and activation. Lung macrophages were a major source of IL-1β. Inhibition of IL-1β signaling with IL-1RA, anti-IL-1β, or NLRP3 KO increased RV-induced type 2 cytokine immune responses, ILC2 number, and mucus metaplasia, while decreasing IL-17 mRNA expression. Treatment with IL-1β had the opposite effect, decreasing IL-25, IL-33, and mucous metaplasia while increasing IL-17 expression. IL-1β and IL-17 each suppressed Il25, Il33, and muc5ac mRNA expression in cultured airway epithelial cells. Finally, RV-infected 6-day-old mice showed reduced IL-1β mRNA and protein expression compared to mature mice.

CONCLUSION

Macrophage IL-1β limits type 2 inflammation and mucous metaplasia following RV infection by suppressing epithelial cell innate cytokine expression. Reduced IL-1β production in immature animals provides a mechanism permitting asthma development after early-life viral infection.

Emerging therapeutic targets and preclinical models for severe asthma

INTRODUCTION

Asthma is a heterogeneous disease with complex multifactorial causes. It is possible to subclassify asthma into different phenotypes that have distinct immunological features. Eosinophilic asthma is a well-known phenotype of severe asthma; however, a large body of clinical and experimental evidence strongly associates persistent airway inflammation, including the accumulation of neutrophils in the bronchial mucosa, and resistance to corticosteroid therapy and non-Type-2 immune responses with severe asthma. Importantly, mainstay therapies are often ineffective in severe asthma and effective alternatives are urgently needed.

AREAS COVERED

Here, we discussed recently developed mouse models of severe asthma that recapitulates key features of the disease in humans. We also provide findings from clinically relevant experimental models that have identified potential therapeutic targets for severe asthma. The most relevant publications on the topic of interest were selected from PubMed.

EXPERT COMMENTARY

Increasing the understanding of disease-causing mechanisms in severe asthma may lead to the identification of novel therapeutic targets and the development of more effective therapies. Intense research interest into investigating the pathophysiological mechanisms of severe asthma has driven the development and interrogation of a myriad of mouse models that aim to replicate hallmark features of severe asthma in humans.

Rhinovirus and Innate Immune Function of Airway Epithelium

Airway epithelial cells, which lines the respiratory mucosa is in direct contact with the environment. Airway epithelial cells are the primary target for rhinovirus and other inhaled pathogens. In response to rhinovirus infection, airway epithelial cells mount both pro-inflammatory responses and antiviral innate immune responses to clear the virus efficiently. Some of the antiviral responses include the expression of IFNs, endoplasmic reticulum stress induced unfolded protein response and autophagy. Airway epithelial cells also recruits other innate immune cells to establish antiviral state and resolve the inflammation in the lungs. In patients with chronic lung disease, these responses may be either defective or induced in excess leading to deficient clearing of virus and sustained inflammation. In this review, we will discuss the mechanisms underlying antiviral innate immunity and the dysregulation of some of these mechanisms in patients with chronic lung diseases.

EphA2 phosphorylates NLRP3 and inhibits inflammasomes in airway epithelial cells

Inflammasomes are intracellular complexes that form in the cytosol of inflammatory cells. NLRP3 is one of the sensor proteins in the complex that can recognize a wide variety of stimuli ranging from microbial components to environmental particulates. Here, we report that in mouse airway epithelial cells (AECs), inflammasome activation is inhibited by EphA2, a member of the transmembrane tyrosine kinase receptor family, via tyrosine phosphorylation of NLRP3 in a model of reovirus infection. We find that EphA2 depletion markedly enhances interleukin-1β (IL-1β) and interleukin-18 (IL-18) production in response to the virus. EphA2^-/- mice show stronger inflammatory infiltration and enhanced inflammasome activation upon viral infection, and aggravated asthma symptoms upon ovalbumin (ova) induction. Mechanistically, EphA2 binds to NLRP3 and induces its phosphorylation at Tyr132, thereby interfering with ASC speck formation and blocking the activation of the NLRP3-inflammasome. These data demonstrate that reovirus employs EphA2 to suppress inflammasome activation in AECs and that EphA2 deficiency causes a pathological exacerbation of asthma in an ova-induced asthma model.

Rhinovirus Infection Is Associated With Airway Epithelial Cell Necrosis and Inflammation via Interleukin-1 in Young Children With Cystic Fibrosis

Introduction: The responses of cystic fibrosis (CF) airway epithelial cells (AEC) to rhinovirus (RV) infection are likely to contribute to early pathobiology of lung disease with increased neutrophilic inflammation and lower apoptosis reported. Necrosis of AEC resulting in airway inflammation driven by IL-1 signaling is a characteristic finding in CF detectable in airways of young children. Being the most common early-life infection, RV-induced epithelial necrosis may contribute to early neutrophilic inflammation in CF via IL-1 signaling. As little is known about IL-1 and biology of CF lung disease, this study assessed cellular and pro-inflammatory responses of CF and non-CF AEC following RV infection, with the hypothesis that RV infection drives epithelial necrosis and IL-1 driven inflammation. Methods:Primary AEC obtained from children with (n = 6) and without CF (n = 6) were infected with RV (MOI 3) for 24 h and viable, necrotic and apoptotic events quantified via flow cytometry using a seven-step gating strategy (% total events). IL-1α, IL-1β, IL-1Ra, IL-8, CXCL10, CCL5, IFN-β, IL-28A, IL-28B, and IL-29 were also measured in cell culture supernatants (pg/mL). Results:RV infection reduced viable events in non-CF AEC (p < 0.05), increased necrotic events in non-CF and CF AEC (p < 0.05) and increased apoptotic events in non-CF AEC (p < 0.05). Infection induced IL-1α and IL-1β production in both phenotypes (p < 0.05) but only correlated with necrosis (IL-1α: r = 0.80; IL-1β: r = 0.77; p < 0.0001) in CF AEC. RV infection also increased IL-1Ra in non-CF and CF AEC (p < 0.05), although significantly more in non-CF AEC (p < 0.05). Finally, infection stimulated IL-8 production in non-CF and CF AEC (p < 0.05) and correlated with IL-1α (r = 0.63 & r = 0.74 respectively; p < 0.0001). Conclusions:This study found RV infection drives necrotic cell death in CF AEC. Furthermore, RV induced IL-1 strongly correlated with necrotic cell death in these cells. As IL-1R signaling drives airway neutrophilia and mucin production, these observations suggest RV infection early in life may exacerbate inflammation and mucin accumulation driving early CF lung disease. Since IL-1R can be targeted therapeutically with IL-1Ra, these data suggest a new anti-inflammatory therapeutic approach targeting downstream effects of IL-1R signaling to mitigate viral-induced, muco-inflammatory triggers of early lung disease.

Ameliorative effect of selective NLRP3 inflammasome inhibitor MCC950 in an ovalbumin-induced allergic rhinitis murine model

Allergic rhinitis (AR) is a complex IgE-mediated nasal allergic and inflammatory disease. Nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) is essential in the process of allergic and inflammatory responses. MCC950 is a selective NLRP3 inhibitor. However, its role and mechanism in AR remains undetermined. The present study aimed to explore the effect and mechanism of MCC950 on an ovalbumin (OVA) induced mouse model of AR. The AR BALB/c mice were constructed using OVA and administrated intranasally with MCC950. Concentrations of OVA-specific IgE, histamines and leukotrienes C4 (LTC4) in serum, and OVA-specific IgE, ECP, IFN-γ, IL-4, IL-5, IL-13, IL-1β and IL-18 in nasal lavage fluid (NLF) were assayed by enzyme-linked immunosorbent assay (ELISA). Inflammatory cells were counted in NLF. HE and PAS staing were used for evaluating eosinophils and goblet cells. Immunohistochemistry (IHC) staining were employed to evaluate immunolabeling of NLRP3, Caspase-1, ASC, IL-1β and IL-18 in nasal mucosas of mice. Real-time PCR was conducted to assay NLRP3, Caspase-1, ASC, IL-1β and IL-18 mRNA levels. In vitro studies, western blotting, real-time PCR and ELISA were performed to evaluate the effects and mechanisms of OVA and NLRP3 inhibitor MCC950 on spleen mononuclear cells. We found significant downregulation of sneezing, nasal rubbing, inflammatory cytokines, inflammatory cells and NLRP3, Caspase-1, ASC, IL-1β and IL-18 expression in MCC950 treated mice compared with untreated AR mice. In spleen mononuclear cells culture and stimulation experiment, NLRP3, Caspase-1, ASC, IL-1β and IL-18 levels were upregulated by OVA but inhibited by MCC950. In conclusion, MCC950 could effectively exert its ameliorative effect in murine AR by inhibiting NLRP3 and leads to reduction of Caspase-1, ASC, IL-1β and IL-18, resulting in the attenuation of the allergic and inflammatory responses.

Targeting NLRP3 Inflammasome Activation in Severe Asthma

Severe asthma (SA) is a chronic lung disease characterized by recurring symptoms of reversible airflow obstruction, airway hyper-responsiveness (AHR), and inflammation that is resistant to currently employed treatments. The nucleotide-binding oligomerization domain-like Receptor Family Pyrin Domain Containing 3 (NLRP3) inflammasome is an intracellular sensor that detects microbial motifs and endogenous danger signals and represents a key component of innate immune responses in the airways. Assembly of the NLRP3 inflammasome leads to caspase 1-dependent release of the pro-inflammatory cytokines IL-1β and IL-18 as well as pyroptosis. Accumulating evidence proposes that NLRP3 activation is critically involved in asthma pathogenesis. In fact, although NLRP3 facilitates the clearance of pathogens in the airways, persistent NLRP3 activation by inhaled irritants and/or innocuous environmental allergens can lead to overt pulmonary inflammation and exacerbation of asthma manifestations. Notably, administration of NLRP3 inhibitors in asthma models restrains AHR and pulmonary inflammation. Here, we provide an overview of the pathophysiology of SA, present molecular mechanisms underlying aberrant inflammatory responses in the airways, summarize recent studies pertinent to the biology and functions of NLRP3, and discuss the role of NLRP3 in the pathogenesis of asthma. Finally, we contemplate the potential of targeting NLRP3 as a novel therapeutic approach for the management of SA.