Rhinovirus-induced macrophage cytokine expression does not require endocytosis or replication

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.

Broad Impact of Exchange Protein Directly Activated by cAMP 2 (EPAC2) on Respiratory Viral Infections

The recently discovered exchange protein directly activated by cAMP (EPAC), compared with protein kinase A (PKA), is a fairly new family of cAMP effectors. Soon after the discovery, EPAC has shown its significance in many diseases including its emerging role in infectious diseases. In a recent study, we demonstrated that EPAC, but not PKA, is a promising therapeutic target to regulate respiratory syncytial virus (RSV) replication and its associated inflammation. In mammals, there are two isoforms of EPAC-EPAC1 and EPAC2. Unlike other viruses, including Middle East respiratory syndrome coronavirus (MERS-CoV) and Ebola virus, which use EPAC1 to regulate viral replication, RSV uses EPAC2 to control its replication and associated cytokine/chemokine responses. To determine whether EPAC2 protein has a broad impact on other respiratory viral infections, we used an EPAC2-specific inhibitor, MAY0132, to examine the functions of EPAC2 in human metapneumovirus (HMPV) and adenovirus (AdV) infections. HMPV is a negative-sense single-stranded RNA virus belonging to the family Pneumoviridae, which also includes RSV, while AdV is a double-stranded DNA virus. Treatment with an EPAC1-specific inhibitor was also included to investigate the impact of EPAC1 on these two viruses. We found that the replication of HMPV, AdV, and RSV and the viral-induced immune mediators are significantly impaired by MAY0132, while an EPAC1-specific inhibitor, CE3F4, does not impact or slightly impacts, demonstrating that EPAC2 could serve as a novel common therapeutic target to control these viruses, all of which do not have effective treatment and prevention strategies.

Genetic determinants of host immunity against human rhinovirus infections

Human rhinoviruses (RV) are a frequent cause of respiratory tract infections with substantial morbidity and mortality in some patients. Nevertheless, the genetic basis of susceptibility to RV in humans has been relatively understudied. Experimental infections of mice and in vitro infections of human cells have indicated that various pathogen recognition receptors (TLRs, RIG-I, and MDA5) regulate innate immune responses to RV. However, deficiency of MDA5 is the only one among these so far uncovered that confers RV susceptibility in humans. Other work has shown increased RV susceptibility in patients with a polymorphism in CDHR3 that encodes the cellular receptor for RV-C entry. Here, we provide a comprehensive review of the genetic determinants of human RV susceptibility in the context of what is known about RV biology.

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

Activation of the inflammasome is a key function of the innate immune response that regulates inflammation in response to microbial substances. Inflammasome activation by human rhinovirus (RV), a major cause of asthma exacerbations, has not been well studied. We examined whether RV induces inflammasome activation in vivo, molecular mechanisms underlying RV-stimulated inflammasome priming and activation, and the contribution of inflammasome activation to RV-induced airway inflammation and exacerbation. RV infection triggered lung mRNA and protein expression of pro-IL-1β and NLRP3, indicative of inflammasome priming, as well as cleavage of caspase-1 and pro-IL-1β, completing inflammasome activation. Immunofluorescence staining showed IL-1β in lung macrophages. Depletion with clodronate liposomes and adoptive transfer experiments showed macrophages to be required and sufficient for RV-induced inflammasome activation. TLR2 was required for RV-induced inflammasome priming in vivo. UV irradiation blocked inflammasome activation and RV genome was sufficient for inflammasome activation in primed cells. Naive and house dust mite-treated NLRP3-/- and IL-1β-/- mice, as well as IL-1 receptor antagonist-treated mice, showed attenuated airway inflammation and responsiveness following RV infection. We conclude that RV-induced inflammasome activation is required for maximal airway inflammation and hyperresponsiveness in naive and allergic mice. The inflammasome represents a molecular target for RV-induced asthma exacerbations.

Transcriptomic Analysis Reveals Priming of The Host Antiviral Interferon Signaling Pathway by Bronchobini® Resulting in Balanced Immune Response to Rhinovirus Infection in Mouse Lung Tissue Slices

Rhinovirus (RV) is the predominant virus causing respiratory tract infections. Bronchobini^® is a low dose multi component, multi target preparation used to treat inflammatory respiratory diseases such as the common cold, described to ease severity of symptoms such as cough and viscous mucus production. The aim of the study was to assess the efficacy of Bronchobini^® in RV infection and to elucidate its mode of action. Therefore, Bronchobini^®’s ingredients (BRO) were assessed in an ex vivo model of RV infection using mouse precision-cut lung slices, an organotypic tissue capable to reflect the host immune response to RV infection. Cytokine profiles were assessed using enzyme-linked immunosorbent assay (ELISA) and mesoscale discovery (MSD). Gene expression analysis was performed using Affymetrix microarrays and ingenuity pathway analysis. BRO treatment resulted in the significant suppression of RV-induced antiviral and pro-inflammatory cytokine release. Transcriptome analysis revealed a multifactorial mode of action of BRO, with a strong inhibition of the RV-induced pro-inflammatory and antiviral host response mediated by nuclear factor kappa B (NFkB) and interferon signaling pathways. Interestingly, this was due to priming of these pathways in the absence of virus. Overall, BRO exerted its beneficial anti-inflammatory effect by priming the antiviral host response resulting in a reduced inflammatory response to RV infection, thereby balancing an otherwise excessive inflammatory response.

Myristoylated rhinovirus VP4 protein activates TLR2-dependent proinflammatory gene expression

Asthma exacerbations are often caused by rhinovirus (RV). We and others have shown that Toll-like receptor 2 (TLR2), a membrane surface receptor that recognizes bacterial lipopeptides and lipoteichoic acid, is required and sufficient for RV-induced proinflammatory responses in vitro and in vivo. We hypothesized that viral protein-4 (VP4), an internal capsid protein that is myristoylated upon viral replication and externalized upon viral binding, is a ligand for TLR2. Recombinant VP4 and myristoylated VP4 (MyrVP4) were purified by Ni-affinity chromatography. MyrVP4 was also purified from RV-A1B-infected HeLa cells by urea solubilization and anti-VP4 affinity chromatography. Finally, synthetic MyrVP4 was produced by chemical peptide synthesis. MyrVP4-TLR2 interactions were assessed by confocal fluorescence microscopy, fluorescence resonance energy transfer (FRET), and monitoring VP4-induced cytokine mRNA expression in the presence of anti-TLR2 and anti-VP4. MyrVP4 and TLR2 colocalized in TLR2-expressing HEK-293 cells, mouse bone marrow-derived macrophages, human bronchoalveolar macrophages, and human airway epithelial cells. Colocalization was absent in TLR2-null HEK-293 cells and blocked by anti-TLR2 and anti-VP4. Cy3-labeled MyrVP4 and Cy5-labeled anti-TLR2 showed an average fractional FRET efficiency of 0.24 ± 0.05, and Cy5-labeled anti-TLR2 increased and unlabeled MyrVP4 decreased FRET efficiency. MyrVP4-induced chemokine mRNA expression was higher than that elicited by VP4 alone and was attenuated by anti-TLR2 and anti-VP4. Cytokine expression was similarly increased by MyrVP4 purified from RV-infected HeLa cells and synthetic MyrVP4. We conclude that, during RV infection, MyrVP4 and TLR2 interact to generate a proinflammatory response.

Rhinovirus infection induces distinct transcriptome profiles in polarized human macrophages

Infections with rhinovirus (RV) cause asthma exacerbations. Recent studies suggest that macrophages play a role in asthmatic airway inflammation and the innate immune response to RV infection. Macrophages exhibit phenotypes based on surface markers and gene expression. We hypothesized that macrophage polarization state alters gene expression in response to RV infection. Cells were derived from human peripheral blood derived monocytes. M1 and M2 polarization was carried out by using IFN-γ and IL-4, respectively, and RNA was extracted for Affymetrix Human Gene ST2.1 exon arrays. Selected genes were validated by quantitative (q)PCR. Treatment of nonactivated (M0) macrophages with IFN-γ and IL-4 induced the expression of 252 and 153 distinct genes, respectively, including previously-identified M1 and M2 markers. RV infection of M0 macrophages induced upregulation of 232 genes; pathway analysis showed significant overrepresentation of genes involved in IFN-α/β signaling and cytokine signaling in the immune system. RV infection induced differential expression of 195 distinct genes in M1-like macrophages but only seven distinct genes in M2-like-polarized cells. In a secondary analysis, comparison between M0-, RV-infected, and M1-like-polarized, RV-infected macrophages revealed differential expression of 227 genes including those associated with asthma and its exacerbation. qPCR demonstrated increased expression of CCL8, CXCL10, TNFSF10, TNFSF18, IL6, NOD2, and GSDMD and reduced expression of VNN1, AGO1, and AGO2. Together, these data show that, in contrast to M2-like-polarized macrophages, gene expression of M1-like macrophages is highly regulated by RV.

Association of ORMDL3 with rhinovirus-induced endoplasmic reticulum stress and type I Interferon responses in human leucocytes

BACKGROUND

Children with risk alleles at the 17q21 genetic locus who wheeze during rhinovirus illnesses have a greatly increased likelihood of developing childhood asthma. In mice, overexpression of the 17q21 gene ORMDL3 leads to airway remodelling and hyperresponsiveness. However, the mechanisms by which ORMDL3 predisposes to asthma are unclear. Previous studies have suggested that ORMDL3 induces endoplasmic reticulum (ER) stress and production of the type I interferon (IFN)-regulated chemokine CXCL10.

OBJECTIVE

The purpose of this study was to determine the relationship between ORMDL3 and rhinovirus-induced ER stress and type I IFN in human leucocytes.

METHODS

ER stress was monitored by measuring HSPA5, CHOP and spliced XBP1 gene expression, and type I IFN by measuring IFNB1 (IFN-β) and CXCL10 expression in human cell lines and primary leucocytes following treatment with rhinovirus. Requirements for cell contact and specific cell type in ORMDL3 induction were examined by transwell assay and depletion experiments, respectively. Finally, the effects of 17q21 genotype on the expression of ORMDL3, IFNB1 and ER stress genes were assessed.

RESULTS

THP-1 monocytes overexpressing ORMDL3 responded to rhinovirus with increased IFNB1 and HSPA5. Rhinovirus-induced ORMDL3 expression in primary leucocytes required cell-cell contact, and induction was suppressed by plasmacytoid dendritic cell depletion. The degree of rhinovirus-induced ORMDL3, HSPA5 and IFNB1 expression varied by leucocyte type and 17q21 genotype, with the highest expression of these genes in the asthma-associated genotype.

CONCLUSIONS AND CLINICAL RELEVANCE

Multiple lines of evidence support an association between higher ORMDL3 and increased rhinovirus-induced HSPA5 and type I IFN gene expression. These associations with ORMDL3 are cell type specific, with the most significant 17q21 genotype effects on ORMDL3 expression and HSPA5 induction evident in B cells. Together, these findings have implications for how the interaction of increased ORMDL3 and rhinovirus may predispose to asthma.

Impairing the function of MLCK, myosin Va or myosin Vb disrupts Rhinovirus B14 replication

Together, the three human rhinovirus (RV) species are the most frequent cause of the common cold. Because of their high similarity with other viral species of the genus Enterovirus, within the large family Picornaviridae, studies on RV infectious activities often offer a less pathogenic model for more aggressive enteroviruses, e.g. poliovirus or EV71. Picornaviruses enter via receptor mediated endocytosis and replicate in the cytosol. Most of them depend on functional F-actin, Rab proteins, and probably motor proteins. To assess the latter, we evaluated the role of myosin light chain kinase (MLCK) and two myosin V isoforms (Va and Vb) in RV-B14 infection. We report that ML-9, a very specific MLCK inhibitor, dramatically reduced RV-B14 entry. We also demonstrate that RV-B14 infection in cells expressing dominant-negative forms of myosin Va and Vb was impaired after virus entry. Using immunofluorescent localization and immunoprecipitation, we show that myosin Va co-localized with RV-B14 exclusively after viral entry (15 min post infection) and that myosin Vb was present in the clusters of newly synthesized RNA in infected cells. These clusters, observed at 180 min post infection, are reminiscent of replication sites. Taken together, these results identify myosin light chain kinase, myosin Va and myosin Vb as new players in RV-B14 infection that participate directly or indirectly in different stages of the viral cycle.

Critical Role of Plasmacytoid Dendritic Cells in Regulating Gene Expression and Innate Immune Responses to Human Rhinovirus-16

Though human rhinoviruses (HRVs) are usually innocuous viruses, they can trigger serious consequences in certain individuals, especially in the setting of impaired interferon (IFN) synthesis. Plasmacytoid dendritic cells (pDCs) are key IFN producing cells, though we know little about the role of pDC in HRV-induced immune responses. Herein, we used gene expression microarrays to examine HRV-activated peripheral blood mononuclear cells (PBMCs) from healthy people, in combination with pDC depletion, to assess whether observed gene expression patterns were pDC dependent. As expected, pDC depletion led to a major reduction in IFN-α release. This was associated with profound differences in gene expression between intact PBMC and pDC-depleted PBMC, and major changes in upstream regulators: 70–80% of the HRV activated genes appeared to be pDC dependent. Real-time PCR confirmed key changes in gene expression, in which the following selected genes were shown to be highly pDC dependent: the transcription factor IRF7, both IL-27 chains (IL-27p28 and EBI3), the alpha chain of the IL-15 receptor (IL-15RA) and the IFN-related gene IFI27. HRV-induced IL-6, IFN-γ, and IL-27 protein synthesis were also highly pDC dependent. Supplementing pDC-depleted cultures with recombinant IL-15, IFN-γ, IL-27, or IL-6 was able to restore the IFN-α response, thereby compensating for the absence of pDC. Though pDC comprise only a minority population of migratory leukocytes, our findings highlight the profound extent to which these cells contribute to the immune response to HRV.

Human Airway Epithelial Cells Direct Significant Rhinovirus Replication in Monocytic Cells by Enhancing ICAM1 Expression

Human rhinovirus (RV) is the major cause of common cold, and it also plays a significant role in asthma and asthma exacerbation. The airway epithelium is the primary site of RV infection and production. In contrast, monocytic cells (e.g., monocytes and macrophages) are believed to be nonpermissive for RV replication. Instead, RV has been shown to modulate inflammatory gene expressions in these cells via a replication-independent mechanism. In the study presented here, replication of RV16 (a major-group RV) was found to be significantly enhanced in monocytes when it was cocultivated with airway epithelial cells. This effect appeared to be mediated by secretory components from epithelial cells, which stimulated RV16 replication and significantly elevated the expression of a number of proinflammatory cytokines. The lack of such an effect on RV1A, a minor-group RV that enters the cell by a different receptor, suggests that intercellular adhesion molecule 1 (ICAM1), the receptor for major-group RVs, may be involved. Indeed, conditioned media from epithelial cells significantly increased ICAM1 expression in monocytes. Consistently, ICAM1 overexpression and ICAM1 knockdown enhanced and blocked RV production, respectively, confirming the role of ICAM1 in this process. Thus, this is the first report demonstrating that airway epithelial cells direct significant RV16 replication in monocytic cells via an ICAM1-dependent mechanism. This finding will open a new avenue for the study of RV infection in airway disease and its exacerbation.

Rhinoviruses and Their Receptors: Implications for Allergic Disease

Human rhinoviruses (RVs) are picornaviruses that can cause a variety of illnesses including the common cold, lower respiratory tract illnesses such as bronchitis and pneumonia, and exacerbations of asthma. RVs are classified into three species, RV-A, B, and C, which include over 160 types. They utilize three major types of cellular membrane glycoproteins to gain entry into the host cell: intercellular adhesion molecule 1 (ICAM-1) (the majority of RV-A and all RV-B), low-density lipoprotein receptor (LDLR) family members (12 RV-A types), and cadherin-related family member 3 (CDHR3) (RV-C). CDHR3 is a member of cadherin superfamily of transmembrane proteins with yet unknown biological function, and there is relatively little information available about the mechanisms of RV-C interaction with CDHR3. A coding single nucleotide polymorphism (rs6967330) in CDHR3 could promote RV-C infections and illnesses in infancy, which could in turn adversely affect the developing lung to increase the risk of asthma. Further studies are needed to determine how RV infections contribute to pathogenesis of asthma and to develop the optimal treatment approach to control asthma exacerbations.

Toll-like receptor 2-expressing macrophages are required and sufficient for rhinovirus-induced airway inflammation

BACKGROUND

We have shown that rhinovirus, a cause of asthma exacerbation, colocalizes with CD68⁺ and CD11b⁺ airway macrophages after experimental infection in human subjects. We have also shown that rhinovirus-induced cytokine expression is abolished in Toll-like receptor (TLR2)^-/- bone marrow-derived macrophages.

OBJECTIVE

We hypothesize that TLR2⁺ macrophages are required and sufficient for rhinovirus-induced airway inflammation in vivo.

METHODS

Naive and ovalbumin (OVA)-sensitized and challenged C57BL/6 wild-type and TLR2^-/- mice were infected with RV1B, followed by IgG or anti-TLR2, to determine the requirement and sufficiency of TLR2 for rhinovirus-induced airway responses. Bone marrow chimera experiments using OVA-treated C57BL/6 and TLR2^-/- mice were also performed. Finally, naive TLR2^-/- mice underwent intranasal transfer of bone marrow-derived wild-type macrophages.

RESULTS

RV1B infection of naive wild-type mice induced an influx of airway neutrophils and CD11b⁺ exudative macrophages, which was reduced in TLR2^-/- mice. After allergen exposure, rhinovirus-induced neutrophilic and eosinophilic airway inflammation and hyperresponsiveness were reduced in TLR2^-/- and anti-TLR2-treated mice. Transfer of TLR2^-/- bone marrow into wild-type, OVA-treated C57BL/6 mice blocked rhinovirus-induced airway responses, whereas transfer of wild-type marrow to TLR2^-/- mice restored them. Finally, transfer of wild-type macrophages to naive TLR2^-/- mice was sufficient for neutrophilic inflammation after rhinovirus infection, whereas macrophages treated with IL-4 (to induce M2 polarization) were sufficient for eosinophilic inflammation, mucous metaplasia, and airways hyperresponsiveness.

CONCLUSIONS

TLR2 is required for early inflammatory responses induced by rhinovirus, and TLR2⁺ macrophages are sufficient to confer airway inflammation to TLR2^-/- mice, with the pattern of inflammation depending on the macrophage activation state.

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.

Recent advances from studies on the role of structural proteins in enterovirus infection

Enteroviruses are a large group of small nonenveloped viruses that cause common and debilitating illnesses affecting humans and animals worldwide. The capsid composed by viral structural proteins packs the RNA genome. It is becoming apparent that structural proteins of enteroviruses play versatile roles in the virus–host interaction in the viral life cycle, more than just a shell. Furthermore, structural proteins to some extent may be associated with viral virulence and pathogenesis. Better understanding the roles of structural proteins in enterovirus infection may lead to the development of potential antiviral strategies. Here, we discuss recent advances from studies on the role of structural proteins in enterovirus infection and antiviral therapeutics targeted structural proteins.

Viral infections and asthma: an inflammatory interface?

Asthma is a chronic inflammatory disease of the airways in which the majority of patients respond to treatment with corticosteroids and β₂-adrenoceptor agonists. Acute exacerbations of asthma substantially contribute to disease morbidity, mortality and healthcare costs, and are not restricted to patients who are not compliant with their treatment regimens. Given that respiratory viral infections are the principal cause of asthma exacerbations, this review article will explore the relationship between viral infections and asthma, and will put forward hypotheses as to why virus-induced exacerbations occur. Potential mechanisms that may explain why current therapeutics do not fully inhibit virus-induced exacerbations, for example, β₂-adrenergic desensitisation and corticosteroid insensitivity, are explored, as well as which aspects of virus-induced inflammation are likely to be attenuated by current therapy.

Asthma is associated with multiple alterations in anti-viral innate signalling pathways

BACKGROUND

Human rhinovirus (HRV) infection is a major trigger for asthma exacerbations. Anti-viral immunity appears to be abnormal in asthma, with immune dysfunction reported in both airway structural cells and migratory, bone marrow derived cells. Though decreased capacity to produce anti-viral interferons (IFNs) has been reported in asthma, a detailed analysis of the molecular events involved has not been undertaken.

OBJECTIVE

To compare the molecular pathway controlling type I IFN synthesis in HRV-stimulated peripheral blood mononuclear cells (PBMC) from asthmatic and healthy subjects.

METHODS

PBMC from 22 allergic asthmatics and 20 healthy donors were cultured with HRV for 24 hours. Multiple components of the Toll-like receptor (TLR), IFN regulatory and NFκβ pathways were compared at the mRNA and protein level.

RESULTS

Multiple deficiencies in the innate immune response to HRV were identified in asthma, with significantly lower expression of IFNα, IFNβ and interferon stimulated genes than in healthy subjects. This was accompanied by reduced expression of intra-cellular signalling molecules including interferon regulatory factors (IRF1, IRF7), NF-κB family members (p50, p52, p65 and IκKα) and STAT1, and by reduced responsiveness to TLR7/TLR8 activation. These observations could not be attributed to alterations in the numbers of dendritic cell (DC) subsets in asthma or baseline expression of the viral RNA sensing receptors TLR7/TLR8. In healthy subjects, blocking the activity of type-I IFN or depleting plasmacytoid DC recapitulated many of the abnormalities observed in asthma.

CONCLUSIONS

Multiple abnormalities in innate anti-viral signalling pathways were identified in asthma, with deficiencies in both IFN-dependent and IFN-independent molecules identified.