Resistance of differentiated human airway epithelium to infection by rhinovirus

Rhinoviruses, allergic inflammation, and asthma

Viral infections affect wheezing and asthma in children and adults of all ages. In infancy, wheezing illnesses are usually viral in origin, and children with more severe wheezing episodes are more likely to develop recurrent episodes of asthma and to develop asthma later in childhood. Children who develop allergen-specific immunoglobulin E (allergic sensitization) and those who wheeze with human rhinoviruses (HRV) are at especially high risk for asthma. In older children and adults, HRV infections generally cause relatively mild respiratory illnesses and yet contribute to acute and potentially severe exacerbations in patients with asthma. These findings underline the importance of understanding the synergistic nature of allergic sensitization and infections with HRV in infants relative to the onset of asthma and in children and adults with respect to exacerbations of asthma. This review discusses clinical and experimental evidence of virus-allergen interactions and evaluates theories which relate immunologic responses to respiratory viruses and allergens to the pathogenesis and disease activity of asthma. Greater understanding of the relationship between viral respiratory infections, allergic inflammation, and asthma is likely to suggest new strategies for the prevention and treatment of asthma.

Rhinovirus-associated wheeze during infancy and asthma development

Rhinovirus is commonly associated with bronchiolitis - only second to RSV during the first year life. The prevalence of HRV-bronchiolitis may be very high in predisposed infants. HRV diagnosis is almost exclusively based on PCR, which detects respiratory infections with or without symptoms. Two immunologic factors, interferon responses and atopy, have been associated with susceptibility to HRV-bronchiolitis in multiple studies. The current data supports the hypothesis that susceptibility to HRV-bronchiolitis is likely to be an early manifestation of biased immune responses, which are linked to both decreased viral defence and atopic airway inflammation. Prospective studies have consistently shown that early wheezing associated with HRV infection is closely associated with recurrent wheezing and the development of asthma in children. Collectively, these studies suggest that HRV infection in wheezing children could serve as a clinically useful marker for early identification of asthma prone children. The findings to date provide the rationale for future studies to incorporate rhinovirus illnesses into asthma risk indices.

Randomized trial of omalizumab (anti-IgE) for asthma in inner-city children

BACKGROUND

Research has underscored the effects of exposure and sensitization to allergens on the severity of asthma in inner-city children. It has also revealed the limitations of environmental remediation and guidelines-based therapy in achieving greater disease control.

METHODS

We enrolled inner-city children, adolescents, and young adults with persistent asthma in a randomized, double-blind, placebo-controlled, parallel-group trial at multiple centers to assess the effectiveness of omalizumab, as compared with placebo, when added to guidelines-based therapy. The trial was conducted for 60 weeks, and the primary outcome was symptoms of asthma.

RESULTS

Among 419 participants who underwent randomization (at which point 73% had moderate or severe disease), omalizumab as compared with placebo significantly reduced the number of days with asthma symptoms, from 1.96 to 1.48 days per 2-week interval, a 24.5% decrease (P<0.001). Similarly, omalizumab significantly reduced the proportion of participants who had one or more exacerbations from 48.8 to 30.3% (P<0.001). Improvements occurred with omalizumab despite reductions in the use of inhaled glucocorticoids and long-acting beta-agonists.

CONCLUSIONS

When added to a regimen of guidelines-based therapy for inner-city children, adolescents, and young adults, omalizumab further improved asthma control, nearly eliminated seasonal peaks in exacerbations, and reduced the need for other medications to control asthma. (Funded by the National Institute of Allergy and Infectious Diseases and Novartis; ClinicalTrials.gov number, NCT00377572.).

Virus/allergen interactions and exacerbations of asthma

Clinical research findings indicate that there are synergistic interactions between allergy and viral infection that cause increased severity of asthma exacerbations. This article summarizes the current literature linking these 2 risk factors for asthma exacerbation, and reviews experimental data suggesting potential mechanisms for interactions between viral infection and allergy that cause asthma exacerbations. In addition, the authors discuss clinical evidence that treatment of allergic inflammation could help to reduce the frequency and severity of virus-induced exacerbations of asthma.

The human rhinovirus: human-pathological impact, mechanisms of antirhinoviral agents, and strategies for their discovery

As the major etiological agent of the common cold, human rhinoviruses (HRV) cause millions of lost working and school days annually. Moreover, clinical studies proved an association between harmless upper respiratory tract infections and more severe diseases e.g. sinusitis, asthma, and chronic obstructive pulmonary disease. Both the medicinal and socio-economic impact of HRV infections and the lack of antiviral drugs substantiate the need for intensive antiviral research. A common structural feature of the approximately 100 HRV serotypes is the icosahedrally shaped capsid formed by 60 identical copies of viral capsid proteins VP1-4. The capsid protects the single-stranded, positive sense RNA genome of about 7,400 bases in length. Both structural as well as nonstructural proteins produced during the viral life cycle have been identified as potential targets for blocking viral replication at the step of attachment, entry, uncoating, RNA and protein synthesis by synthetic or natural compounds. Moreover, interferon and phytoceuticals were shown to protect host cells. Most of the known inhibitors of HRV replication were discovered as a result of empirical or semi-empirical screening in cell culture. Structure-activity relationship studies are used for hit optimization and lead structure discovery. The increasing structural insight and molecular understanding of viral proteins on the one hand and the advent of innovative computer-assisted technologies on the other hand have facilitated a rationalized access for the discovery of small chemical entities with antirhinoviral (anti-HRV) activity. This review will (i) summarize existing structural knowledge about HRV, (ii) focus on mechanisms of anti-HRV agents from synthetic and natural origin, and (iii) demonstrate strategies for efficient lead structure discovery.

Uncoating of human rhinoviruses

Human rhinoviruses (HRVs) are a major cause of the common cold. The more than one hundred serotypes, divided into species HRV-A and HRV-B, either bind intercellular adhesion molecule 1 (major group viruses) or members of the low-density lipoprotein receptor (minor group viruses) for cell entry. Some major group HRVs can also access the host cell via heparan sulphate proteoglycans. The cell attachment protein(s) of the recently discovered phylogenetic clade HRV-C is unknown. The respective receptors direct virus uptake via clathrin-dependent or independent endocytosis or via macropinocytosis. Triggered by ICAM-1 and/or the low pH environment in endosomes the virions undergo conformational alterations giving rise to hydrophobic subviral particles. These are handed over from the receptors to the endosomal membrane. According to the current view, the RNA genome is released through an opening at one of the fivefold axes of the icosahedral capsid and crosses the membrane through a pore presumably formed by viral proteins. Alternatively, the membrane may be ruptured allowing subviral particles and RNA to enter the cytosol. Whether a channel is formed or the membrane is disrupted most probably depends on the respective HRV receptor.

[Adult asthma exacerbations in questions]

In this article a French working party critically review the international literature to revise the definition, pathophysiology, treatment and cost of exacerbations of adult asthma. The various guidelines do not always provide a consistent definition of exacerbations of asthma. An exacerbation can be defined as deterioration of clinical and/or functional parameters lasting more than 24 hours, without return to baseline, requiring a change of treatment. No single clinical or functional criterion can be used as an early marker of an exacerbation. Innate and acquired immune mechanisms, modified by contact with infectious, irritant or allergenic agents, participate in the pathogenesis of exacerbations, which are accompanied by bronchial inflammation. In 2010, mortality is related to progression of exacerbations, often occurring before the patient seeks medical attention. The objective of treatment is to control asthma and prevent exacerbations. However, many factors can trigger exacerbations and often cannot be controlled. The efficacy of inhaled corticosteroids has been demonstrated on reduction of the number of exacerbations and the number of asthma-related deaths. This treatment is cost-effective, especially in terms of reduction of exacerbations.

Role of viral respiratory infections in asthma and asthma exacerbations

Viral respiratory tract infections are common and usually selflimited illnesses. For patients at risk of asthma, or with existing asthma, viral respiratory tract infections can have a profound effect on the expression of disease or loss of control. New evidence has shown that wheezing episodes early in life due to human rhinoviruses are a major risk factor for the later diagnosis of asthma at age 6 years. For those with existing asthma, exacerbations are a major cause of morbidity, can need acute care, and can, albeit rarely, result in death. Viral respiratory tract infections, predominantly those caused by human rhinoviruses, are associated with asthma exacerbations. There is also evidence that deficiencies in antiviral activity and the integrity of the airway epithelial barrier could make individuals with asthma more likely to have severe viral respiratory infections of the lower airway, and thus increase the risk of exacerbation. In view of the effect of respiratory viruses on many aspects of asthma, efforts to understand the mechanisms and risk factors by which these airway infections cause changes in airway pathophysiology are a first step towards improved treatment.

The ABCs of rhinoviruses, wheezing, and asthma

Human rhinoviruses (HRVs) were discovered as common cold pathogens over 50 years ago. Recent advances in molecular viral diagnostics have led to an appreciation of their role in more-significant respiratory illnesses, including bronchiolitis in infancy, childhood pneumonia, and acute exacerbations of chronic respiratory diseases such as asthma, chronic obstructive lung disease, and cystic fibrosis. Until a few years ago, only two groups of HRVs (A and B) had been recognized. However, full and partial sequencing of HRVs led to the discovery of a third species of HRV (HRV-C) that has distinct structural and biologic features. Risk factors and pathogenic mechanisms for more-severe HRV infections are being defined, and yet fundamental questions persist about mechanisms relating this common pathogen to allergic diseases and asthma. The close relationship between HRV infections and asthma suggests that antiviral treatments could have a major impact on the morbidity associated with this chronic respiratory disease.

The efficacy of Echinacea in a 3-D tissue model of human airway epithelium

We evaluated the antirhinovirus efficacy of a standardized preparation of Echinacea purpurea (Echinaforce) in a 3-dimensional organotypic model of normal human airway epithelium (EpiAirway tissue). Individual replicate tissue samples, maintained as inserts in culture for 3 days or 3 weeks, were infected with rhinovirus type 1A (RV1A), Echinacea alone, a combination of the two, or medium only. None of the treatments affected the histological appearance or integrity of the tissues, all of which maintained a high level of cell viability and preservation of cilia. RV infection resulted in increased mucopolysaccharide inclusions in the goblet cells, but this feature was reversed by Echinacea treatment. This result was confirmed by measurements of mucin secretion, which was stimulated by RV but reversed by Echinacea, suggesting that mucus production during colds could be ameliorated by Echinacea. We did not find evidence of virus replication, although the RV-infected tissues secreted substantial amounts of the pro-inflammatory cytokines IL-6 and IL-8 (CXCL8), and this response was reversed by Echinacea treatment. These results confirmed previous findings derived from studies of bronchial and lung epithelial cell lines, namely, that RV infection results in a substantial inflammatory response in the absence of virus replication.

Human monocytic cells direct the robust release of CXCL10 by bronchial epithelial cells during rhinovirus infection

BACKGROUND

Human rhinovirus (HRV) infections are a major cause of exacerbations in chronic respiratory conditions such as asthma and chronic obstructive pulmonary disease, but HRV-induced immune responses of the lower airway are poorly understood. Earlier work examining cytokine release following HRV infection has focused on epithelial cells because they serve as the principal site of viral replication, and internalization and replication of viral RNA appear necessary for epithelial cell mediator release. However, during HRV infection, only a small proportion of epithelial cells become infected. As HRV-induced cytokine levels in vivo are markedly elevated, this observation suggests that other mechanisms independent of direct viral infection may induce epithelial cell cytokine release.

OBJECTIVE

Our aim was to test for the importance of interactions between human bronchial epithelial cells (HBECs) and monocytic cells in the control of mediator release during HRV exposure.

METHODS

In vitro models of HRV serotype-16 (HRV16) infection of primary HBECs and human monocytic cells, in mono or co-culture, were used. We assessed HRV16-induced CXCL10 and CCL2 protein release via ELISA.

RESULTS

Co-culture of human monocytic and bronchial epithelial cells promoted a synergistic augmentation of CXCL10 and CCL2 protein release following HRV16 challenge. Transfer of conditioned media from HRV16-treated monocytic cells to epithelial cultures induced a robust release of CXCL10 by the epithelial cells. This effect was greatly attenuated by type I IFN receptor blocking antibodies, and could be recapitulated by IFN-alpha addition.

CONCLUSIONS

Our data indicate that epithelial CXCL10 release during HRV infection is augmented by a monocytic cell-dependent mechanism involving type I IFN(s). Our findings support a key role for monocytic cells in the amplification of epithelial cell chemokine production during HRV infection, and help to explain how an inflammatory milieu is created in the lower airways even in the absence of extensive viral replication and epithelial infection.

All-trans retinoic acid mediates DUOX2 expression and function in respiratory tract epithelium

DUOX1 and DUOX2 are members of the NADPH oxidase family that are specifically regulated to produce hydrogen peroxide in epithelia of the thyroid, gastrointestinal tract, and respiratory tract. The determinants of DUOX1 or DUOX2 expression in various tissues have not been established. Using respiratory tract epithelial cells as a model, we investigated changes in DUOX mRNA and protein expression during the first 10 days of differentiation. By comparing a respiratory tract cell line, HBE1, with primary tracheobronchial epithelial (TBE) cells, we determined that DUOX2 was significantly expressed only in cell conditions that included all-trans retinoic acid (ATRA). In HBE1 cells, DUOX2 mRNA increased 6-fold after ATRA treatment. Similarly, ATRA induced a 19-fold increase in DUOX2 mRNA expression in primary TBE cells with parallel increases in DUOX protein and DUOX-mediated H(2)O(2) production as well. In addition, DUOX2 induction by rhinovirus required the presence of ATRA. ATRA had no effect on DUOX1 expression for all the conditions studied. Our data indicate that for respiratory epithelial cells, ATRA is important in the regulation of DUOX2 expression, function, and rhinovirus-mediated DUOX2 inducibility.

Cigarette smoke decreases innate responses of epithelial cells to rhinovirus infection

Exposure to cigarette smoke is associated with a significant increase in the risk for respiratory viral infections. The airway epithelium is the primary target for both cigarette smoke and respiratory viral infection. We investigated the effects of cigarette smoke on the response of airway epithelial cells to rhinovirus infection. We found that pre-exposure of BEAS-2B cells or primary normal human bronchial epithelial cells (NHBEs) to cigarette smoke extract (CSE) reduced the induction of mRNA of the chemokines CXCL10 and CCL5 by either the viral mimic polyinosine-polycytidylic acid (Poly I:C) or human rhinovirus 16 (HRV-16) infection. The HRV-16-induced release of CXCL10 and CCL5 was also significantly suppressed by CSE. Activation of the IFN mediator STAT-1 and the activation of JNK by poly I:C and HRV-16 were partially suppressed by pre-exposure to CSE. In contrast, the poly I:C-induced and HRV-16-induced phosphorylation of ERK1/2 was unaffected by CSE. HRV-16-stimulated IFN-β mRNA was also significantly reduced by CSE. Because suppression of the IFN response to viral infection was associated with increased viral production, we assessed HRV-16 RNA concentrations. Exposure to CSE resulted in an increase in HRV-16 RNA at 48 hours after the infection of BEAS-2B cells. These data demonstrate that exposure to CSE alters the response of airway epithelial cells to HRV infection, leading to decreased activation of the IFN-STAT-1 and SAP-JNK pathways, the suppression of CXCL10 and CCL5 production, and increased viral RNA. A diminished, early epithelial-initiated antiviral response to rhinovirus infection could contribute to the increased susceptibility of subjects to prolonged respiratory viral infections after exposure to cigarette smoke.

Controller medications and their effects on asthma exacerbations temporally associated with upper respiratory infections

BACKGROUND

Exacerbations are a major risk and a cause of asthma morbidity and healthcare utilization. Viral-induced upper respiratory tract infections are the most frequent trigger of asthma-related exacerbations. Studies have traditionally assessed exacerbations without documentation regarding exacerbation etiology. Therefore, it remains unknown whether asthma medications can alter exacerbation susceptibility based on a specific etiology.

OBJECTIVE

To examine whether treatment with inhaled corticosteroids plus long-acting beta(2)-agonists reduced the number of exacerbations associated with upper respiratory tract infections versus inhaled corticosteroids alone.

METHODS

Two large datasets comparing treatment with fluticasone propionate and fluticasone propionate plus salmeterol were analyzed, including the number of clinically reported upper respiratory tract infections, asthma-related exacerbations, and the presence of an exacerbation and concurrent report of an upper respiratory tract infection.

RESULTS

Both treatment groups had similar incidences of upper respiratory tract infections. Of those reporting an upper respiratory tract infection, statistically significantly fewer reported an asthma-related exacerbation comparing fluticasone propionate plus salmeterol with fluticasone propionate (p=0.0057).

DISCUSSION

This retrospective analysis suggests that therapy with fluticasone propionate plus salmeterol provides protection against asthma exacerbations temporally associated with upper respiratory tract infections. This retrospective analysis supports the hypothesis that specific therapeutic approaches to mitigate virus-associated exacerbations may benefit asthma care. Well-controlled prospective studies are warranted.

Interleukin-13-induced mucous metaplasia increases susceptibility of human airway epithelium to rhinovirus infection

Infection of airway epithelium by rhinovirus is the most common cause of asthma exacerbations. Even in mild asthma, airway epithelium exhibits mucous metaplasia, which increases with increasing severity of the disease. We previously showed that squamous cultures of human airway epithelium manifest rhinoviral infection at levels many times higher than in well-differentiated cultures of a mucociliary phenotype. Here we tested the hypothesis that mucous metaplasia is also associated with increased levels of rhinoviral infection. Mucous metaplasia was induced with IL-13, which doubled the numbers of goblet cells. In both control (mucociliary) and IL-13- treated (mucous metaplastic) cultures, goblet cells were preferentially infected by rhinovirus. IL-13 doubled the numbers of infected cells by increasing the numbers of infected goblet cells. Furthermore, IL-13 increased both the maturity of goblet cells and the probability that a goblet cell would be infected. The infection of cells other than goblet cells was unaltered by IL-13. Treatment with IL-13 did not alter the levels of rhinovirus receptor ICAM-1, nor did the proliferative effects of IL-13 enhance infection, because rhinovirus did not colocalize with dividing cells. However, the induction of mucous metaplasia caused changes in the apical membrane structure, notably a marked decrease in overall ciliation, and an increase in the overall flatness of the apical surface. We conclude that mucous metaplasia in asthma increases the susceptibility of airway epithelium to infection by rhinovirus because of changes in the overall architecture of the apical surface.

Rhinovirus-induced modulation of gene expression in bronchial epithelial cells from subjects with asthma

Rhinovirus (RV) infections trigger asthma exacerbations. Genome-wide expression analysis of RV1A-infected primary bronchial epithelial cells from normal and asthmatic donors was performed to determine whether asthma is associated with a unique pattern of RV-induced gene expression. Virus replication rates were similar in cells from normal and asthmatic donors. Overall, RV downregulated 975 and upregulated 69 genes. Comparisons of transcriptional profiles generated from microarrays and confirmed by quantitative reverse transcription PCR and cluster analysis showed some up- and downregulated genes in asthma cells involved in immune responses (IL1B, IL1F9, IL24, and IFI44) and airway remodeling (LOXL2, MMP10, FN1). Notably, most of the asthma-related differences in RV-infected cells were also present in the cells before infection. These findings suggest that differences in RV-induced gene expression profiles of cells from normal and mild asthmatic subjects could affect the acute inflammatory response to RV, and subsequent airway repair and remodeling.

Rhinovirus and the initiation of asthma

PURPOSE OF REVIEW

Virus-induced wheezing in infancy is a risk factor for asthma, and recent studies have highlighted the role of rhinoviruses in causing acute illnesses and as a possible contributing factor to chronic asthma.

RECENT FINDINGS

Human rhinoviruses (HRVs) have long been known as the most common cause of common cold in infants and children. Recent developments in molecular diagnostics have led to the discovery of new viruses and have also provided data to implicate HRV as an important cause of lower respiratory infections and acute virus-induced wheezing in preschool children. In addition, HRV-induced wheezing episodes appear to identify children who are at increased risk for the subsequent development of childhood asthma.

SUMMARY

Collectively, these findings raise the possibility that lower respiratory infections with pathogens such as HRV and respiratory syncytial virus could participate in the causation of asthma, especially in children with suboptimal antiviral defenses. A variety of experimental models and clinical studies have been used to identify possible mechanisms related to the infection and the ensuing host response that could disturb normal lung and immunologic development to promote asthma. Defining these relationships could lead to new therapeutic and preventive approaches to common forms of childhood asthma.

Localization of type I interferon receptor limits interferon-induced TLR3 in epithelial cells

Previous studies have shown that influenza infections increase Toll-like receptor 3 (TLR3) expression and that type I interferons (IFNs) may play a role in this response. This study aimed to expand on the role of type I IFNs in the influenza-induced upregulation of TLR3 and determine whether and how the localization of the IFN-alpha/beta receptor (IFNAR) in respiratory epithelial cells could modify IFN-induced responses. Using differentiated primary human airway epithelial cells this study demonstrates that soluble mediators secreted in response to influenza infection upregulate TLR3 expression in naive cells. This response was associated with an upregulation of type I IFNs and stimulation with type I, but not type II, IFNs enhanced TLR3 expression. Interestingly, although influenza infection results in IFN-beta release both toward the apical and basolateral sides of the epithelium, TLR3 expression is only enhanced in cells stimulated with IFN-beta from the basolateral side. Immunohistochemical analysis demonstrates that IFNAR expression is limited to the basolateral side of differentiated human airway epithelial cells. However, non- or poorly differentiated epithelial cells express IFNAR more toward the apical side. These data demonstrate that restricted expression of the IFNAR in the differentiated airway epithelium presents a potential mechanism of regulating type I IFN-induced TLR3 expression.

In vitro susceptibility to rhinovirus infection is greater for bronchial than for nasal airway epithelial cells in human subjects

BACKGROUND

Human rhinoviruses (HRVs) characteristically cause upper respiratory tract infection, but they also infect the lower airways, causing acute bronchitis and exacerbating asthma.

OBJECTIVE

Our purpose was to study ex vivo the differences in the response to HRV infection of nasal and bronchial epithelial cultures from the same healthy and asthmatic individuals using conditions favoring development of fully differentiated, pseudostratified mucociliary epithelium.

METHODS

Cells from the inferior turbinates and bronchial tree of 5 healthy and 6 asthmatic individuals were cultured at an air-liquid interface. Cultures were infected with HRV-16, and after 48 hours, the degree of infection was measured.

RESULTS

Baseline median transepithelial resistance was lower in human bronchial epithelial (HBE) cell cultures than in human nasal epithelial (HNE) cell cultures (195 Omega.cm2 [95% CI, 164-252] vs 366 Omega.cm2 [95% CI, 234-408], respectively; P < .01). Virus replicated more easily in HBE cells than in HNE cells based on virus shedding in apical wash (log tissue culture infective dose of 50%/0.1 mL = 2.0 [95% CI, 1.0-2.5] vs 0.5 [95% CI, 0.5-1.5], P < .01) and on a 20- to 30-fold greater viral load and number of infected cells in HBE cell cultures than in HNE cell cultures. The increases in expression of RANTES and double-stranded RNA-dependent protein kinase were greater in HBE cell cultures than in HNE cell cultures, as were the concentrations of IL-8, IL-1alpha, RANTES, and IP-10 in basolateral medium. However, no significant differences between asthmatic and healthy subjects (including IFN-beta1 expression) were found.

CONCLUSIONS

Differentiated nasal epithelial cells might have mechanisms of increased resistance to rhinovirus infection compared with bronchial epithelial cells. We could not confirm previous reports of increased susceptibility to HRV infection in epithelial cells from asthmatic subjects.

Respiratory virus induction of alpha-, beta- and lambda-interferons in bronchial epithelial cells and peripheral blood mononuclear cells

BACKGROUND

Respiratory viruses, predominantly rhinoviruses are the major cause of asthma exacerbations. Impaired production of interferon-beta in rhinovirus infected bronchial epithelial cells (BECs) and of the newly discovered interferon-lambdas in both BECs and bronchoalveolar lavage cells, is implicated in asthma exacerbation pathogenesis. Thus replacement of deficient interferon is a candidate new therapy for asthma exacerbations. Rhinoviruses and other respiratory viruses infect both BECs and macrophages, but their relative capacities for alpha-, beta- and lambda-interferon production are unknown.

METHODS

To provide guidance regarding which interferon type is the best candidate for development for treatment/prevention of asthma exacerbations we investigated respiratory virus induction of alpha-, beta- and lambda-interferons in BECs and peripheral blood mononuclear cells (PBMCs) by reverse transferase-polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Rhinovirus infection of BEAS-2B BECs induced interferon-alpha mRNA expression transiently at 8 h and interferon-beta later at 24 h while induction of interferon-lambda was strongly induced at both time points. At 24 h, interferon-alpha protein was not detected, interferon-beta was weakly induced while interferon-lambda was strongly induced. Similar patterns of mRNA induction were observed in primary BECs, in response to both rhinovirus and influenza A virus infection, though protein levels were below assay detection limits. In PBMCs interferon-alpha, interferon-beta and interferon-lambda mRNAs were all strongly induced by rhinovirus at both 8 and 24 h and proteins were induced: interferon-alpha>-beta>-lambda. Thus respiratory viruses induced expression of alpha-, beta- and lambda-interferons in BECs and PBMCs. In PBMCs interferon-alpha>-beta>-lambda while in BECs, interferon-lambda>-beta>-alpha.

CONCLUSIONS

We conclude that interferon-lambdas are likely the principal interferons produced during innate responses to respiratory viruses in BECs and interferon-alphas in PBMCs, while interferon-beta is produced by both cell types.

[Infections and asthma]

Asthma is a chronic inflammatory disorder of the airways. Allergen-induced airway inflammation plays a central role in the pathogenesis of the disease whereas infections are known to be important triggers of acute exacerbations. Chronic or latent infections may also influence and enhance the local inflammation. The aim of this review is to give an overview of the different pathogens and to present the current understanding of the role of respiratory viruses and atypical bacteria in the pathogenesis of the disease.

Innate immune response to viral infection of the lungs

Viral respiratory tract infections are the most common infectious illnesses, though they are usually self-limiting and confined to the respiratory tract. The rapid identification of viruses and their effective elimination with minimal local and systemic inflammation is a testament to the efficiency of the innate immune response within the airways and lungs. A failure of this response appears to occur in those with asthma and chronic obstructive pulmonary disease, where viral infection is an important trigger for acute exacerbations. The innate immune response to viruses requires their early detection through pathogen recognition receptors and the recruitment of the efficient antiviral response that is centred around the release of type 1 interferons. The airway epithelium provides both a barrier and an early detector for viruses, and interacts closely with cells of the innate immune response, especially macrophages and dendritic cells, to eliminate infection and trigger a specific adaptive immune response.

Early identification of atopy in the prediction of persistent asthma in children

The long-term solution to the asthma epidemic is thought to be prevention, and not treatment of established disease. Atopic asthma arises from gene-environment interactions, which mainly take place during a short period in prenatal and postnatal development. These interactions are not completely understood, and hence primary prevention remains an elusive goal. We argue that primary-care physicians, paediatricians, and specialists lack knowledge of the role of atopy in early life in the development of persistent asthma in children. In this review, we discuss how early identification of children at high risk is feasible on the basis of available technology and important for potential benefits to the children. Identification of an asthmatic child's atopic status in early life has practical clinical and prognostic implications, and sets the basis for future preventative strategies.

Basal cells of differentiated bronchial epithelium are more susceptible to rhinovirus infection

We used an in vitro model of differentiated tracheobronchial epithelium to analyze the susceptibility of different cell types to infection with rhinoviruses (RVs). Primary cells from control subjects were cultured in an air-liquid interface to form differentiated epithelia. Suprabasal and basal fractions were separated after trypsin digestion, and cell suspensions were infected with serotypes RV16 and RV1A. These cell fractions were analyzed for expression of viral capsid protein VP2 (flow cytometry), viral replication (real-time PCR), cytokeratin-14, and intercellular adhesion molecule-1 (ICAM-1). Compared with suprabasal fraction, basal cells had increased percentages of cells staining positive for VP2 (RV1A: 37.8% versus 9.1%, P < 0.01; RV16: 12.0 versus 3.0%, P < 0.05). The average number of viral RNA copies per cell was also higher in basal cells (2.2- and 2.4-fold increase in RV1A- and RV16-infected cells, respectively) compared with suprabasal cells. Furthermore, ICAM-1 was expressed by 33.3% of basal cells, compared with 8.1% of suprabasal cells (P < 0.05). Finally, in culture models of epithelial injury (detached suprabasal cells or scratched surface), there was significantly greater replication of RV1A compared with intact cell layer. These findings demonstrate that basal cells are more susceptible to RV infection than suprabasal cells. For major group RV, this may be in part due to increased expression of ICAM-1; however, minor group RV also replicated more effectively in basal cells. These results suggest the possibility that epithelial cell differentiation is associated with the maturation of antiviral defense mechanisms.

The cigarette smoke component acrolein inhibits expression of the innate immune components IL-8 and human beta-defensin 2 by sinonasal epithelial cells

BACKGROUND

Tobacco use is associated with poorer outcomes of medical and surgical therapy for chronic rhinosinusitis (CRS), although the underlying mechanism is unknown. Acrolein (AC) is a major component of cigarette smoke that has been shown to suppress innate immune gene expression by human bronchial epithelial cells and murine macrophages. In this study, we explore whether exposure of human sinonasal epithelial cells (HSNECs) to AC similarly reduces their innate immune gene expression.

METHODS

Primary HSNECs from CRS patients were grown in culture, either differentiated or submerged. HSNECs were treated for 30 minutes with 0-50 microM of AC and were subsequently analyzed by real-time polymerase chain reaction and ELISA to determine IL-8 and human beta-defensin (HBD) 2 expression. Total glutathione was measured to see the oxidative stress within the treatment range.

RESULTS

In primary HSNEC, IL-8 mRNA levels decreased dose dependently in the range of 10-50 microM of AC with an eightfold decrease at 50 microM. In addition, a 125-fold decrease at 50 microM for IL-8 protein was observed. HBD-2 mRNA decreased twofold and HBD-2 protein decreased fourfold at 50 microM of AC in primary HSNEC. However, differentiated HSNEC showed a marginal decrease in a dose-dependent manner for both IL-8 and HBD-2 within the range of 10-50 microM of AC. There was no oxidative stress observed over this range of AC concentration.

CONCLUSION

The tobacco smoke component AC has the capacity to suppress the inflammatory and innate immune function of sinonasal epithelial cells. Whether this effect contributes to the negative clinical impact of smoking on CRS outcomes merits additional investigation.

Cooperative effects of rhinovirus and TNF-{alpha} on airway epithelial cell chemokine expression

Rhinovirus (RV) infections trigger exacerbations of airways disease, but underlying mechanisms remain unknown. We hypothesized that RV and cytokines present in inflamed airways combine to induce augmented airway epithelial cell chemokine expression, promoting further inflammation. To test this hypothesis in a cellular system, we examined the combined effects of RV39 and TNF-alpha, a cytokine increased in asthma and chronic obstructive pulmonary disease, on airway epithelial cell proinflammatory gene expression. Costimulation of 16HBE14o- human bronchial epithelial cells and primary mucociliary-differentiated tracheal epithelial cells with RV and TNF-alpha induced synergistic increases in IL-8 and epithelial neutrophil attractant-78 production. Similar synergism was observed for IL-8 promoter activity, demonstrating that the effect is transcriptionally mediated. Whereas increases in ICAM-1 expression and viral load were noted 16-24 h after costimulation, cooperative effects between RV39 and TNF-alpha were evident 4 h after stimulation and maintained despite incubation with blocking antibody to ICAM-1 given 2 h postinfection or UV irradiation of virus, implying that effects were not solely due to changes in ICAM-1 expression. Furthermore, RV39 infection induced phosphorylation of ERK and transactivation of the IL-8 promoter AP-1 site, which functions as a basal level enhancer, leading to enhanced TNF-alpha responses. We conclude that RV infection and TNF-alpha stimulation induce cooperative increases in epithelial cell chemokine expression, providing a cellular mechanism for RV-induced exacerbations of airways disease.

Expression of Toll-like receptors in cultured nasal epithelial cells

CONCLUSIONS

Nasal epithelial cells are constitutively equipped with all Toll-like receptors (TLRs) which are essential for innate immunity. Both mRNA and protein levels of TLR3 expression increased in more differentiated nasal epithelial cells. Considering that the ligand for TLR3 is viral dsRNA, this result is in good accordance with previous reports demonstrating that more differentiated airway epithelial cells have increased resistance to rhinovirus infection.

OBJECTIVE

Nasal epithelial cells use innate immune responses to combat inspired potential pathogens. TLRs are receptors that recognize pathogen-associated molecular patterns of microbes. Therefore, we investigated the expression of TLRs in cultured nasal epithelial cells obtained from nasal polyps.

MATERIALS AND METHODS

Submerged single layer (SSL) and air-liquid interface (ALI) nasal epithelial cell cultures with or without 10(-7) M retinoid acid (+/- RA) were created.

RESULTS

ALI + RA culture developed ciliary differentiation as observed by light and scanning electron microscopic examination in 3 weeks. It had higher interleukin (IL)-8 basal secretion (21.9 vs 0.82-1.45 ng/ml) and transepithelial potential (-20.4 mV). TLR1-10 mRNA expression in cultured nasal epithelial cells was determined by RT-PCR. Only TLR3 mRNA significantly increased at day 20 vs day 1 (n=5, p=0.02) in ALI + RA cell culture. Higher TLR3 protein was also expressed at day 20 in ALI + RA cell culture but not in SSL culture by western blotting.

Differentiated structure and function of primary cultures of monkey oviductal epithelium

We have established well-differentiated, polarized cultures of monkey oviductal epithelium. Oviductal epithelial cells were isolated by protease digestion and plated on collagen-coated, porous cell culture inserts. About 5 d after plating, cells developed detectable transepithelial electrical resistance of up to 2000 Omega.cm(2) (an index of tight junction formation) and transepithelial voltages of up to 20 mV (an index of vectorial transepithelial ion transport). Measurements of short-circuit current in Ussing chambers indicated that active secretion of Cl was the major transepithelial active ion transport process, and that this was stimulated by elevation of either cAMP or Ca(i). Furthermore, estimates of the volume of mucosal liquid were consistent with Cl secretion mediating fluid secretion. Various microscopical methods showed that the cultures were densely ciliated and contained mature secretory cells. Transport across the oviductal epithelium determines the composition of the oviductal fluid, and the study of the relevant transport processes will be greatly enhanced by well-differentiated cultures of oviductal epithelium of the kind established here.

Asthma exacerbations . 3: Pathogenesis

Asthma exacerbations are an exaggerated lower airway response to an environmental exposure. Respiratory virus infection is the most common environmental exposure to cause a severe asthma exacerbation. Airway inflammation is a key part of the lower airway response in asthma exacerbation, and occurs together with airflow obstruction and increased airway responsiveness. The patterns of airway inflammation differ according to the trigger factor responsible for the exacerbation. The reasons for the exaggerated response of asthmatic airways are not completely understood, but recent studies have identified a deficient epithelial type 1 interferon response as an important susceptibility mechanism for viral infection.

IL-17A promotes the growth of airway epithelial cells through ERK-dependent signaling pathway

The effects of IL-17A on mucin production and growth of airway epithelial cells were examined. Histological and immunohistochemical analyses revealed that IL-17A increased the mucin production and number of tracheal epithelial cells in air-liquid interface cultures. The biological property of IL-17A to stimulate the mucin production by tracheal epithelial cells was determined using an ELISA. The mitogenic effect of IL-17A on tracheal epithelial cells was confirmed with Calcein-AM assay. The growth-stimulatory effect of IL-17A was dose-dependent and mediated via the ERK MAP kinase pathway. Inhibitors of MEK abrogated the mitogenic effect of IL-17A, whereas an inhibitor of p38 or JNK displayed no significant inhibitory effect. Moreover, relatively lower doses of IL-13 also significantly increased the growth of tracheal epithelial cells through a distinct signaling pathway from that of IL-17A. These findings provide the first evidence that IL-17A stimulates the growth of airway epithelial cells through the ERK MAP kinase pathway.

H. influenzae potentiates airway epithelial cell responses to rhinovirus by increasing ICAM-1 and TLR3 expression

Rhinovirus (RV) is an important trigger of chronic obstructive pulmonary disease (COPD) exacerbations. In addition, respiratory viruses are more likely to be isolated in patients with a history of frequent exacerbations, suggesting that these patients are more susceptible to viral infection. To examine potential mechanisms for cooperative effects between bacterial and viral infection in COPD, we studied the responses of cultured human airway epithelial cells to nontypeable Hemophilus influenzae and RV. In both 16HBE14o- and primary mucociliary-differentiated cells, preincubation with H. influenzae enhanced RV serotype 39-induced protein expression of interleukin (IL)-8, epithelial-derived neutrophil attractant-78, and growth-related oncogene-alpha. H. influenzae infection also increased the binding of RV39 to cultured cells, as well as expression of intercellular adhesion molecule (ICAM)-1 and Toll-like receptor (TLR)-3, receptors for RV and dsRNA, respectively. Neutralizing antibody against tumor necrosis factor-alpha inhibited IL-8 expression induced by H. influenzae and RV39. Finally, siRNA against TLR3 attenuated RV-induced IL-8 expression. We conclude that H. influenzae infection increases airway epithelial cell ICAM-1 and TLR3 expression, leading to enhanced binding of RV and a potentiation of RV-induced chemokine release. These data provide a cellular mechanism by which H. influenzae infection may increase the susceptibility of COPD patients to RV-induced exacerbations.

The relationship of rhinovirus-associated asthma hospitalizations with inhaled corticosteroids and smoking

BackgroundAlthough rhinovirus (RV) respiratory infections trigger asthma exacerbations, the etiologic association between this virus and severe exacerbations, as well as the clinical characteristics of adults at risk for RV-associated asthma that necessitates hospitalization, have not been established

MethodsDuring 1999–2003, we conducted a cohort study of 101 adults prospectively enrolled at hospital admission for an asthma exacerbation. Patient characteristics and frequencies of RV in nasal specimens were analyzed, by reverse-transcription polymerase chain reaction (RT-PCR), at asthma-related hospital admission and at a 3-month convalescent follow-up visit

ResultsRV was detected by RT-PCR in 21% of hospitalized patients over a 4-year period and in 1.3% of patients who returned for a 3-month follow-up visit. RV detection was strongly associated with hospitalization for asthma (adjusted odds ratio [OR], 15.1 [95% confidence interval {CI}, 1.88–121.4]). After adjustment for baseline asthma severity, RV-positive patients were more likely than RV-negative patients to be current smokers and nonusers of inhaled corticosteroids (ICSs) (adjusted OR, 11.18 [95% CI, 2.37–52.81]; P=.002)

ConclusionsRV respiratory infection is an etiologic agent in severe asthma exacerbations necessitating hospitalization in adults. Compared with hospitalized patients with asthma who were RV negative, RV-positive patients were significantly more likely to be smokers and nonusers of ICSs

Rhinovirus infection induces cytotoxicity and delays wound healing in bronchial epithelial cells

BACKGROUND

Human rhinoviruses (RV), the most common triggers of acute asthma exacerbations, are considered not cytotoxic to the bronchial epithelium. Recent observations, however, have questioned this knowledge. The aim of this study was to evaluate the ability of RV to induce epithelial cytotoxicity and affect epithelial repair in-vitro.

METHODS

Monolayers of BEAS-2B bronchial epithelial cells, seeded at different densities were exposed to RV serotypes 1b, 5, 7, 9, 14, 16. Cytotoxicity was assessed chromatometrically. Epithelial monolayers were mechanically wounded, exposed or not to RV and the repopulation of the damaged area was assessed by image analysis. Finally epithelial cell proliferation was assessed by quantitation of proliferating cell nuclear antigen (PCNA) by flow cytometry.

RESULTS

RV1b, RV5, RV7, RV14 and RV16 were able to induce considerable epithelial cytotoxicity, more pronounced in less dense cultures, in a cell-density and dose-dependent manner. RV9 was not cytotoxic. Furthermore, RV infection diminished the self-repair capacity of bronchial epithelial cells and reduced cell proliferation.

CONCLUSION

RV-induced epithelial cytotoxicity may become considerable in already compromised epithelium, such as in the case of asthma. The RV-induced impairment on epithelial proliferation and self-repair capacity may contribute to the development of airway remodeling.

Rhinovirus induces airway epithelial gene expression through double-stranded RNA and IFN-dependent pathways

Rhinovirus (RV) infection is the major cause of common colds and of asthma exacerbations. Because the epithelial cell layer is the primary target of RV infection, we hypothesize that RV-induced airway disease is associated with the perturbation of airway epithelial gene expression. In this study, well differentiated primary human airway epithelial cells were infected with either RV16 (major group) or RV1B (minor group). Transcriptional gene profiles from RV-infected and mock-infected control cells were analyzed by Affymetrix Genechip, and changes of the gene expression were confirmed by real-time RT-PCR analysis. At 24 h after infection, 48 genes induced by both viruses were identified. Most of these genes are related to the IFN pathway, and have been documented to have antiviral functions. Indeed, a significant stimulation of IFN-beta secretion was detected after RV16 infection. Neutralizing antibody specific to IFN-beta and a specific inhibitor of the Janus kinase pathway both significantly blocked the induction of RV-inducible genes. Further studies demonstrated that 2-aminopurine, a specific inhibitor double-stranded RNA-dependent protein kinase, could block both IFN-beta production and RV-induced gene expression. Thus, IFN-beta-dependent pathway is a part of the double-stranded RNA-initiated pathway that is responsible for RV-induced gene expression. Consistent with its indispensable role in the induction of antiviral genes, deactivation of this signaling pathway significantly enhanced viral production. Because increase of viral yield is associated with the severity of RV-induced airway illness, the discovery of an epithelial antiviral signaling pathway in this study will contribute to our understanding of the pathogenesis of RV-induced colds and asthma exacerbations.

Differential regulation of dual NADPH oxidases/peroxidases, Duox1 and Duox2, by Th1 and Th2 cytokines in respiratory tract epithelium

Partially reduced metabolites of molecular oxygen, superoxide (O2-) and hydrogen peroxide (H2O2), are detected in respiratory tract lining fluid, and it is assumed that these are key components of innate immunity. Whether these reactive oxygen species (ROS) are produced specifically by the respiratory epithelium in response to infection, or are a non-specific by-product of oxidant-producing inflammatory cells is not well characterized. Increasing evidence supports the hypothesis that the dual function NAD(P)H oxidases/peroxidases, Duox1 and Duox2, are important sources of regulated H2O2 production in respiratory tract epithelium. However, no studies to date have characterized the regulation of Duox gene expression. Accordingly, we examined Duox1 and Duox2 mRNA expression by real-time PCR in primary respiratory tract epithelial cultures after treatment with multiple cytokines. Herein, we determined that Duox1 expression was increased several-fold by treatment with the Th2 cytokines IL-4 and IL-13, whereas Duox2 expression was highly induced following treatment with the Th1 cytokine IFN-gamma. Duox2 expression was also elevated by polyinosine-polycytidylic acid (poly(I:C)) and rhinovirus infection. Diphenyleneiodonium (DPI)-inhibitable apical H2O2 production was similarly increased by the addition of Th1 or Th2 cytokines. These results demonstrate for the first time the regulation of Duox expression by immunomodulatory Th1 and Th2 cytokines, and suggest a mechanism by which ROS production can be regulated in the respiratory tract as part of the host defense response.