Influence of respiratory syncytial virus infection on cytokine and inflammatory responses in allergic mice

The effect of Ma-Xin-Gan-Shi decoction on asthma exacerbated by respiratory syncytial virus through regulating TRPV1 channel

ETHNOPHARMACOLOGICAL RELEVANCE

The incidence and mortality of bronchial asthma are increasing, and respiratory syncytial virus (RSV) is widely regarded as the common cause of clinical exacerbation of asthma. Ma-Xing-Gan-Shi decoction (MXGSD), a classic traditional Chinese medicine prescription, is well-known for treating respiratory diseases, while the mechanism of effecting on RSV-exacerbated asthma remains to be explored.

AIM OF THE STUDY

In this study, we investigated the mechanism by which MXGSD exerts a protective effect on asthma exacerbated by RSV in vivo and in vitro.

MATERIALS AND METHODS

MXGSD is composed of four Chinese medicine, including Ephedra intermedia Schrenk & C.A.Mey. (herbaceous stem, 27g), Prunus armeniaca L. (dry seed, 27g), Glycyrrhiza uralensis Fisch. (radix and rhizome, 18g), and Gypsum fibrosum (main component: CaSO4·2H2O, 54g). In the present study, the exacerbated asthmatic mice model with the treatment of OVA plus RSV was replicated, and accompanied by the TMT proteomic analysis and further experimental investigations. Then, the protective effect of MXGSD (13.2, 6.6, 3.3 g/kg/d, 7d) on the mice treated by OVA plus RSV, and the mechanism of regulating TRPV1 was explored. In addition, the intracellular Ca2+ concentration of 16HBE cells pretreated with MXGSD medicated serum was also tested after stimulation with the TRPV1 agonist capsaicin.

RESULTS

The results suggested that MXGSD could reduce the levels of inflammation cells, airway hyperresponsiveness, and pathological damage of lung tissue. TMT quantitative proteomics analysis and further experimental exploration revealed that MXGSD could reduce the levels of IL-4, IL-13, PGE2, and SP in BAL and down-regulate the expression of TRPV1 mRNA and protein in lung tissue. Furthermore, 16HBE cells stimulated by capsaicin showed an increased intracellular Ca2+ concentration, while the pretreatment of MXGSD medicated serum could reduce it.

CONCLUSION

MSGSD showed a protective effect on RSV-exacerbated asthma, which may be related to its regulation of TRPV1 expression and reduction of Th2 cytokines and neurogenic inflammatory mediators. It may provide an objective basis and reference for the clinical application of MXGSD.

A Systematic Review and Meta-analysis of Animal Studies Investigating the Relationship Between Serum Antibody, T Lymphocytes, and Respiratory Syncytial Virus Disease

BACKGROUND

Respiratory syncytial virus (RSV) infections occur in human populations around the globe, causing disease of variable severity, disproportionately affecting infants and older adults (>65 years of age). Immune responses can be protective but also contribute to disease. Experimental studies in animals enable detailed investigation of immune responses, provide insights into clinical questions, and accelerate the development of passive and active vaccination. We aimed to review the role of antibody and T-cell responses in relation to RSV disease severity in animals.

METHODS

Systematic review and meta-analysis of animal studies examining the association between T-cell responses/phenotype or antibody titers and severity of RSV disease. The PubMed, Zoological Record, and Embase databases were screened from January 1980 to May 2018 to identify animal studies of RSV infection that assessed serum antibody titer or T lymphocytes with disease severity as an outcome. Sixty-three studies were included in the final review.

RESULTS

RSV-specific antibody appears to protect from disease in mice, but such an effect was less evident in bovine RSV. Strong T-cell, Th1, Th2, Th17, CD4/CD8 responses, and weak Treg responses accompany severe disease in mice.

CONCLUSIONS

Murine studies suggest that measures of T-lymphocyte activity (particularly CD4 and CD8 T cells) may be predictive biomarkers of severity. Further inquiry is merited to validate these results and assess relevance as biomarkers for human disease.

Respiratory Syncytial Virus Infection Reduces Kynurenic Acid Production and Reverses Th17/Treg Balance by Modulating Indoleamine 2,3-Dioxygenase (IDO) Molecules in Plasmacytoid Dendritic Cells

Background

Respiratory syncytial virus (RSV) infection causes a world-wide medical and economic burden. This study analyzed the effects of RSV infection on plasmacytoid dendritic cells (pDCs) and evaluated the immunopathogenesis of RSV infection by measuring relative numbers of FoxP3+ Treg cells and Th17 cells.

Material/Methods

pDCs were isolated from human blood samples, purified using magnetic microbeads, and treated with RSV, IFN-γ, or vehicle. These cells were mixed with purified CD4+ T cells to yield preparations of pDCs+T cells+vehicle, pDCs+T cells+RSV, and pDCs+T cells+IFN-γ. Preparations of pDCs+T cells+RSV were also incubated with an inducer or an inhibitor of indoleamine 2,3-dioxygenase (IDO). Kynurenic acid concentration was measured by high-pressure liquid chromatography (HPLC). The differentiation of Foxp3+ Treg and Th17 cells from CD4+ T cells was determined by flow cytometry.

Results

pDCs were successfully isolated and purified using the magnetic microbeads. Compared with preparations of pDCs+T cells+vehicle, RSV infection (pDCs+T cells+RSV) significantly reduced and IFN-γ treatment (pDC+T cells+IFN-γ) increased kynurenic acid concentrations and the proportions of Foxp3⁺ Tregs (p<0.05 each). Conversely, RSV infection increased and IFN-γ treatment decreased the proportions of Th17 cells (p<0.05 each). RSV infection reduced kynurenic acid concentrations and inhibited the transformation from Th17 to Foxp3⁺ Tregs by modulating IDO molecules.

Conclusions

RSV infection reduced the production of kynurenic acid and inhibited transformation from Th17 to Foxp3⁺ Tregs (Th17/Treg balance) by modulating IDO molecules in pDCs.

MicroRNA-21 drives severe, steroid-insensitive experimental asthma by amplifying phosphoinositide 3-kinase-mediated suppression of histone deacetylase 2

BACKGROUND

Severe steroid-insensitive asthma is a substantial clinical problem. Effective treatments are urgently required, however, their development is hampered by a lack of understanding of the mechanisms of disease pathogenesis. Steroid-insensitive asthma is associated with respiratory tract infections and noneosinophilic endotypes, including neutrophilic forms of disease. However, steroid-insensitive patients with eosinophil-enriched inflammation have also been described. The mechanisms that underpin infection-induced, severe steroid-insensitive asthma can be elucidated by using mouse models of disease.

OBJECTIVE

We sought to develop representative mouse models of severe, steroid-insensitive asthma and to use them to identify pathogenic mechanisms and investigate new treatment approaches.

METHODS

Novel mouse models of Chlamydia, Haemophilus influenzae, influenza, and respiratory syncytial virus respiratory tract infections and ovalbumin-induced, severe, steroid-insensitive allergic airway disease (SSIAAD) in BALB/c mice were developed and interrogated.

RESULTS

Infection induced increases in the levels of microRNA (miRNA)-21 (miR-21) expression in the lung during SSIAAD, whereas expression of the miR-21 target phosphatase and tensin homolog was reduced. This was associated with an increase in levels of phosphorylated Akt, an indicator of phosphoinositide 3-kinase (PI3K) activity, and decreased nuclear histone deacetylase (HDAC)2 levels. Treatment with an miR-21-specific antagomir (Ant-21) increased phosphatase and tensin homolog levels. Treatment with Ant-21, or the pan-PI3K inhibitor LY294002, reduced PI3K activity and restored HDAC2 levels. This led to suppression of airway hyperresponsiveness and restored steroid sensitivity to allergic airway disease. These observations were replicated with SSIAAD associated with 4 different pathogens.

CONCLUSION

We identify a previously unrecognized role for an miR-21/PI3K/HDAC2 axis in SSIAAD. Our data highlight miR-21 as a novel therapeutic target for the treatment of this form of asthma.

Neonatal respiratory syncytial virus infection has an effect on lung inflammation and the CD4(+) CD25(+) T cell subpopulation during ovalbumin sensitization in adult mice

In BALB/c adult mice, respiratory syncytial virus (RSV) infection enhances the degree of lung inflammation before and/or after ovalbumin (OVA) respiratory sensitization. However, it is unclear whether RSV infection in newborn mice has an effect on the immune response to OVA respiratory sensitization in adult mice. The aim of this study was to determine if RSV neonatal infection alters T CD4(+) population and lung inflammation during OVA respiratory sensitization in adult mice. BALB/c mice were infected with RSV on the fourth day of life and challenged by OVA 4 weeks later. We found that in adult mice, RSV neonatal infection prior to OVA sensitization reduces the CD4(+) CD25(+) and CD4(+) CD25(+) forkhead protein 3 (FoxP3)(+) cell populations in the lungs and bronchoalveolar lavage. Furthermore, it also attenuates the inflammatory infiltrate and cytokine/chemokine expression levels in the mouse airways. In conclusion, the magnitude of the immune response to a non-viral respiratory perturbation in adult mice is not enhanced by a neonatal RSV infection.

A Cross-Study Biomarker Signature of Human Bronchial Epithelial Cells Infected with Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in children, elderly, and immunocompromised individuals. Despite of advances in diagnosis and treatment, biomarkers of RSV infection are still unclear. To understand the host response and propose signatures of RSV infection, previous studies evaluated the transcriptional profile of the human bronchial epithelial cell line—BEAS-2B—infected with different strains of this virus. However, the evolution of statistical methods and functional analysis together with the large amount of expression data provide opportunities to uncover novel biomarkers of inflammation and infections. In view of those facts publicly available microarray datasets from RSV-infected BEAS-2B cells were analyzed with linear model-based statistics and the platform for functional analysis InnateDB. The results from those analyses argue for the reevaluation of previously reported transcription patterns and biological pathways in BEAS-2B cell lines infected with RSV. Importantly, this study revealed a biosignature constituted by genes such as ABCC4, ARMC8, BCLAF1, EZH1, FAM118A, FAM208B, FUS, HSPH1, KAZN, MAP3K2, N6AMT1, PRMT2, S100PBP, SERPINA1, TLK2, ZNF322, and ZNF337 which should be considered in the development of new molecular diagnosis tools.

TNF-α and Macrophages Are Critical for Respiratory Syncytial Virus-Induced Exacerbations in a Mouse Model of Allergic Airways Disease

Viral respiratory infections trigger severe exacerbations of asthma, worsen disease symptoms, and impair lung function. To investigate the mechanisms underlying viral exacerbation, we established a mouse model of respiratory syncytial virus (RSV)-induced exacerbation after allergen sensitization and challenge. RSV infection of OVA-sensitized/challenged BALB/c mice resulted in significantly increased airway hyperresponsiveness (AHR) and macrophage and neutrophil lung infiltration. Exacerbation was accompanied by increased levels of inflammatory cytokines (including TNF-α, MCP-1, and keratinocyte-derived protein chemokine [KC]) compared with uninfected OVA-treated mice or OVA-treated mice exposed to UV-inactivated RSV. Dexamethasone treatment completely inhibited all features of allergic disease, including AHR and eosinophil infiltration, in uninfected OVA-sensitized/challenged mice. Conversely, dexamethasone treatment following RSV-induced exacerbation only partially suppressed AHR and failed to dampen macrophage and neutrophil infiltration or inflammatory cytokine production (TNF-α, MCP-1, and KC). This mimics clinical observations in patients with exacerbations, which is associated with increased neutrophils and often poorly responds to corticosteroid therapy. Interestingly, we also observed increased TNF-α levels in sputum samples from patients with neutrophilic asthma. Although RSV-induced exacerbation was resistant to steroid treatment, inhibition of TNF-α and MCP-1 function or depletion of macrophages suppressed features of disease, including AHR and macrophage and neutrophil infiltration. Our findings highlight critical roles for macrophages and inflammatory cytokines (including TNF-α and MCP-1) in viral-induced exacerbation of asthma and suggest examination of these pathways as novel therapeutic approaches for disease management.

Mouse models of acute exacerbations of allergic asthma

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

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

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

Differences in respiratory syncytial virus and influenza infection in a house-dust-mite-induced asthma mouse model: consequences for steroid sensitivity

A significant number of clinical asthma exacerbations are triggered by viral infection. We aimed to characterize the effect of virus infection in an HDM (house dust mite) mouse model of asthma and assess the effect of oral corticosteroids. HDM alone significantly increased eosinophils, lymphocytes, neutrophils, macrophages and a number of cytokines in BAL (bronchoalveolar lavage), all of which were sensitive to treatment with prednisolone (with the exception of neutrophils). Virus infection also induced cell infiltration and cytokines. RSV (respiratory syncytial virus) infection in HDM-treated animals further increased all cell types in BAL (except eosinophils, which declined), but induced no further increase in HDM-elicited cytokines. However, while HDM-elicited TNF-α (tumour necrosis factor-α), IFN-γ (interferon-γ), IL (interleukin)-2, IL-5 and IL-10 were sensitive to prednisolone treatment, concomitant infection with RSV blocked the sensitivity towards steroid. In contrast, influenza infection in HDM- challenged animals resulted in increased BAL lymphocytes, neutrophils, IFN-γ, IL-1β, IL-4, IL-5, IL-10 and IL-12, but all were attenuated by prednisolone treatment. HDM also increased eNO (exhaled NO), which was further increased by concomitant virus infection. This increase was only partially attenuated by prednisolone. RSV infection alone increased BAL mucin. However, BAL mucin was increased in HDM animals with virus infection. Chronic HDM challenge in mice elicits a broad inflammatory response that shares many characteristics with clinical asthma. Concomitant influenza or RSV infection elicits differing inflammatory profiles that differ in their sensitivity towards steroids. This model may be suitable for the assessment of novel pharmacological interventions for asthmatic exacerbation.

Elevated macrophage inflammatory protein 1α and interleukin-17 production in an experimental asthma model infected with respiratory syncytial virus

BACKGROUND

Respiratory syncytial virus (RSV) infection is associated with both the development and exacerbation of bronchial asthma. We examined eosinophil infiltration and the cytokine profiles of both airway and peripheral blood in antigen-sensitized mice infected with RSV to investigate the pathogenesis of exacerbations of asthma due to RSV infection.

METHODS

Ovalbumin (OVA)-sensitized mice were challenged by OVA inhalation 3 times and then infected with RSV [10(5) TCID50 (50% of tissue culture infectious dose)/25 g body weight] or mock infection immediately after the last challenge. Animals from each group, namely, the control (PBS instead of OVA inhalation plus mock infection), RSV (PBS plus RSV), OVA (OVA plus mock) and OVA/RSV (OVA plus RSV) were analyzed. Analysis included evaluation of airway responsiveness to methacholine, pathological findings in the airway by hematoxylin and eosin (HE) and Luna staining, bronchoalveolar fluid (BALF) and peripheral leukocytes counts, and concentrations of multiple cytokines/chemokines in both BALF and serum.

RESULTS

Airway responsiveness was significantly enhanced in the OVA and OVA/RSV groups compared with the control group. Levels of tissue and BALF eosinophils were higher in the OVA and OVA/RSV groups than in the RSV or control group. Significantly higher levels of macrophage inflammatory protein (MIP)-1α in BALF were observed in the OVA/RSV group compared with the 3 other groups. Production of serum IL-17 was also significantly elevated in the OVA/RSV group compared with the control or OVA group.

CONCLUSIONS

These findings suggest that MIP-1α and IL-17 may play important roles in acute exacerbation of asthma induced by RSV in an animal model.

Respiratory syncytial virus reverses airway hyperresponsiveness to methacholine in ovalbumin-sensitized mice

Each year, approximately 20% of asthmatics in the United States experience acute symptom exacerbations, which commonly result from pulmonary viral infections. The majority of asthma exacerbations in very young children follow infection with respiratory syncytial virus (RSV). However, pathogenic mechanisms underlying induction of asthma exacerbations by RSV are not well understood. We therefore investigated the effect of post-sensitization RSV infection on lung function in ovalbumin (OVA)-sensitized BALB/c mice as a model of RSV asthma exacerbations. OVA sensitization of uninfected female BALB/c mice increased bronchoalveolar lavage fluid (BALF) eosinophil levels and induced airway hyperresponsiveness to the muscarinic agonist methacholine, as measured by the forced-oscillation technique. In contrast, intranasal infection with replication-competent RSV strain A2 for 2–8 days reduced BALF eosinophil counts and reversed airway hyperresponsiveness in a pertussis toxin-sensitive manner. BALF levels of the chemokine keratinocyte cytokine (KC; a murine homolog of interleukin-8) were elevated in OVA-sensitized, RSV-infected mice and reversal of methacholine hyperresponsiveness in these animals was rapidly inhibited by KC neutralization. Hyporesponsiveness could be induced in OVA-sensitized, uninfected mice by recombinant KC or the Gαi agonist melittin. These data suggest that respiratory syncytial virus induces KC-mediated activation of Gαi, resulting in cross-inhibition of Gαq-mediated M₃-muscarinic receptor signaling and reversal of airway hyperresponsiveness. As in unsensitized mice, KC therefore appears to play a significant role in induction of airway dysfunction by respiratory syncytial virus. Hence, interleukin-8 may be a promising therapeutic target to normalize lung function in both asthmatics and non-asthmatics with bronchiolitis. However, the OVA-sensitized, RSV-infected mouse may not be an appropriate model for investigating the pathogenesis of viral asthma exacerbations.

The Role of RSV Infection in Asthma Initiation and Progression: Findings in a Mouse Model

Respiratory syncytial virus (RSV) is a common cause of severe lower respiratory tract diseases (bronchiolitis and pneumonia) during infancy and early childhood. There is increasing evidence which indicates that severe pulmonary disease caused by RSV infection in infancy is associated with recurrent wheezing and development of asthma later in childhood. However, the underlying mechanisms linking RSV infection to persistent airway hyperresponsiveness and dysfunction are not fully defined. To study these processes in ways which are not available in humans, animal models have been established and have provided valuable insight into the pathophysiology of RSV-induced disease. In this paper, we discuss experimental models of RSV infection in mice and highlight a new investigative approach in which mice are initially infected as neonates and then reinfected later in life. The findings shed light on the mechanisms underlying the association between early severe RSV infection and development of asthma later in childhood.

Pulmonary infection of mice with human metapneumovirus induces local cytotoxic T-cell and immunoregulatory cytokine responses similar to those seen with human respiratory syncytial virus

Human metapneumovirus (hMPV) is a major cause of upper and lower respiratory-tract infection in infants, the elderly and immunocompromised individuals. Virus-directed cellular immunity elicited by hMPV infection is poorly understood, in contrast to the phylogenetically and clinically related pathogen human respiratory syncytial virus (hRSV). In a murine model of acute lower respiratory-tract infection with hMPV, we demonstrate the accumulation of gamma interferon (IFN-gamma)-producing CD8+ T cells in the airways and lungs at day 7 post-infection (p.i.), associated with cytotoxic T lymphocytes (CTLs) directed to an epitope of the M2-1 protein. This CTL immunity was accompanied by increased pulmonary expression of Th1 cytokines IFN-gamma and interleukin (IL)-12 and antiviral cytokines (IFN-beta), as well as chemokines Mip-1alpha, Mip-1beta, Mig, IP-10 and CX3CL1. There was also a moderate increase in Th2-type cytokines IL-4 and IL-10 compared with uninfected mice. At 21 days p.i., a strong CTL response could be recalled from the spleen. A similar pattern of CTL induction to the homologous M2-1 CTL epitope of hRSV, and of cytokine/chemokine induction, was observed following infection with hRSV, highlighting similarities in the cellular immune response to the two related pathogens.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

Asthma is a common and debilitating disease that has substantially increased in prevalence in Western Societies in the last 2 decades. Respiratory tract infections by respiratory syncytial virus (RSV) and rhinovirus (RV) are widely implicated as common causes of the induction and exacerbation of asthma. These infections in early life are associated with the induction of wheeze that may progress to the development of asthma. Infections may also promote airway inflammation and enhance T helper type 2 lymphocyte (Th2 cell) responses that result in exacerbations of established asthma. The mechanisms of how RSV and RV induce and exacerbate asthma are currently being elucidated by clinical studies, in vitro work with human cells and animal models of disease. This research has led to many potential therapeutic strategies and, although none are yet part of clinical practise, they show much promise for the prevention and treatment of viral disease and subsequent asthma.

TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells

Thymic stromal lymphopoietin (TSLP) is elevated in asthma and triggers dendritic cell-mediated activation of Th2 inflammatory responses. Although TSLP has been shown to be produced mainly by airway epithelial cells, the regulation of epithelial TSLP expression has not been extensively studied. We investigated the expression of TSLP in cytokine- or TLR ligand-treated normal human bronchial epithelial cells (NHBE). The mRNA for TSLP was significantly up-regulated by stimulation with IL-4 (5.5-fold) and IL-13 (5.3-fold), weakly up-regulated by TNF-alpha, TGF-beta, and IFN-beta, and not affected by IFN-gamma in NHBE. TSLP mRNA was only significantly up-regulated by the TLR3 ligand (dsRNA) among the TLR ligands tested (66.8-fold). TSLP was also induced by in vitro infection with rhinovirus. TSLP protein was detected after stimulation with dsRNA (120 +/- 23 pg/ml). The combination of TNF-alpha and IL-4 produced detectable levels of TSLP protein (40 +/- 13 pg/ml). In addition, TSLP was synergistically enhanced by a combination of IL-4 and dsRNA (mRNA; 207-fold, protein; 325 +/- 75 pg/ml). The induction of TSLP by dsRNA was dependent upon NF-kappaB and IFN regulatory factor 3 (IRF-3) signaling via TLR3 as indicated by a study with small interfering RNA. The potent topical glucocorticoid fluticasone propionate significantly suppressed dsRNA-dependent TSLP production in NHBE. These results suggest that the expression of TSLP is induced in airway epithelial cells by stimulation with the TLR3 ligand and Th2 cytokines and that this response is suppressed by glucocorticoid treatment. This implies that respiratory viral infection and the recruitment of Th2 cytokine producing cells may amplify Th2 inflammation via the induction of TSLP in the asthmatic airway.

IL-13 regulates cilia loss and foxj1 expression in human airway epithelium

Mucociliary clearance is essential to the defense mechanisms of the respiratory system. Loss of normal mucociliary clearance contributes to the pathogenesis of genetic and acquired lung diseases. Treatment of cultured differentiated human airway epithelial tissue with IL-13 resulted in a loss of ciliated epithelial cells and an increase in mucus-secreting cells. The loss of ciliated cells was characterized by mislocation of basal bodies and loss of ezrin from the apical cell compartment. In addition to the loss of ciliated cells and increase in mucous cells after IL-13 treatment, cells with characteristics of both ciliated and mucous cells were observed in the airway epithelium. In association with the decrease in ciliated cells after IL-13 treatment, there was noted a decrease in foxj1 expression in the airway epithelium, characterized by a decrease in the number of foxj1-expressing cells. Within the foxj1 promoter, a STAT-binding element was identified and inhibition of foxj1 expression by STAT-6 and IL-13 was demonstrated. These findings suggest molecular and cellular mechanisms for cilia loss in pulmonary disease. Inhibition of foxj1 expression results in loss of apical localization of ezrin and basal bodies with subsequent loss of axonemal structures. These findings have important implications for the pathogenesis and treatment of airway diseases.

Respiratory syncytial virus differentially activates murine myeloid and plasmacytoid dendritic cells

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis in young children. Upon infection both T helper 1 (Th1) and Th2 cytokines are produced. Because RSV-induced Th2 responses have been associated with severe immunopathology and aggravation of allergic reactions, the regulation of the immune response following RSV infection is crucial. In this study we examined the influence of RSV on the activation and function of murine bone marrow-derived dendritic cells (DCs). RSV induced the expression of maturation markers on myeloid DCs (mDCs) in vitro. The mDCs stimulated with RSV and ovalbumin (OVA) enhanced proliferation of OVA-specific T cells, which produced both Th1 and Th2 cytokines. In contrast to mDCs, RSV did not induce the expression of maturation markers on plasmacytoid DCs (pDCs), not did it enhance the proliferation of OVA-specific T cells that were cocultured with pDCs. However, RSV stimulated the production of interferon-alpha (IFN-alpha) by pDCs. Our findings indicate a clear difference in the functional activation of DC subsets. RSV-stimulated mDCs may have immunostimulatory effects on both Th1 and Th2 responses, while RSV-stimulated pDCs have direct antiviral activity through the release of IFN-alpha.

Respiratory viral infections drive chemokine expression and exacerbate the asthmatic response

A number of investigations have linked respiratory vial infections and the intensity and subsequent exacerbation of asthma through host response mechanisms. For example, it is likely that the immune-inflammatory response to respiratory syncytial virus can cause a predisposition toward an intense inflammatory reaction associated with asthma, and adenovirus might cause exacerbation of the immune response associated with chronic obstructive pulmonary disease. In each of these situations, the host's immune response plays a critical mechanistic role through the production of certain cytokines and chemokines. Specific aspects of these augmented immune responses are determined by the biology of the virus, the genetic variability of the host, and the cytokine-chemokine phenotype of the involved tissue. For instance, the type 1/type 2 cytokine ratio in the airways during infection with rhinovirus determines how long the viral infection endures. By this same theory, it has been demonstrated that chemokine levels produced during respiratory syncytial virus infection determine host responses to later immune stimuli in the lung, with the potential to augment the asthmatic response. Further research in this area will clarify cytokines, chemokines, or cell targets, which will provide the basis for next-generation therapies.

Alternaria aerosol during a bovine respiratory syncytial virus infection alters the severity of subsequent re-infection and enhances IgE production

BACKGROUND

Previous studies with cattle and rodent models have shown that bovine and human RSV infections influence the immune response to inhaled allergen. In the present study, we extended these observations to examine the effect of fungal allergen Alternaria alternata aerosol exposure (prior to and during BRSV infection) on the immune response and clinical outcome of a secondary BRSV infection.

METHODS

Calves were either Alternaria (Alt)/mock Alt (mAlt) and BRSV/mBRSV exposed. Exposures began on day -6 and continued every other day until day 6 post infection. A second set of aerosols/infection began on day 103 and continued as before. Clinical outcome during infections was measured in each group. IgG1, IgA, and IgE responses to Alternaria were measured in serum or bronchiolar alveolar lavage fluid (BALF). Cytokine responses, including IL-4, were also measured.

RESULTS

Alternaria did not influence primary infection; however, the Alt/BRSV group had less disease than mAlt/BRSV group (median clinical score 8 vs 476.5; p<or=0.01) after secondary infection. Exposure to Alternaria facilitated IgE antibody production in BRSV infected calves. IgE responses to Alternaria were higher in Alt/BRSV than Alt/mBRSV animals on day 10 (mean baseline fold increase 1.97 vs 1.06; p=0.013) and 109 (1.40 vs 0.810; p=0.008). Comparatively, Alt/BRSV calves had less Alternaria specific IgG1 than Alt/mBRSV calves on days 0, 107, 109, 113, 115, and 120 (p<or=0.05) with more lung eosinophils and IL-4 secreting PBMCs.

CONCLUSION

Alternaria aerosols during primary and secondary BRSV infections decreased disease in secondary infections; however, BRSV infection enhanced Th2 responses against inhaled Alternaria.

Immune mechanisms of pathogenetic synergy in concurrent bovine pulmonary infection with Haemophilus somnus and bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) and Haemophilus somnus are two bovine respiratory pathogens that cause disease singly or as part of a polymicrobial infection. BRSV infection is often associated with a predisposition towards production of a T helper type 2 (Th2) response and IgE production. In contrast, an IgG2 response to H. somnus has been shown to be most important for recovery. An experiment was performed to evaluate the hypothesis that infection with H. somnus on day 6 of experimental BRSV infection would result in disease enhancement and potentially an altered immune response when compared with single infection. Three groups of calves were either dually infected or singly infected with H. somnus or BRSV. Serum and bronchoalveolar lavage fluid (BALF) pathogen specific IgG1, IgG2, IgE, and IgA responses were evaluated by ELISA. TaqMan RT-PCR was used to examine cytokine gene expression by PBMC and BAL cells. Clinical signs were evaluated for 28 days after BRSV infection, followed by necropsy and histological examination of the lungs. In dually infected calves, disease was significantly more severe, H. somnus was isolated from the lungs at necropsy, and high IgE and IgG responses were detected to H. somnus antigens. Cytokine profiles on day 27 were elevated in dually infected calves, but did not reflect a skewed profile. These results contrasted with singly infected calves that were essentially normal by day 10 of infection and lacked both lung pathology and the presence of H. somnus in the lung at necropsy. The increase in IgE antibodies specific for antigens of H. somnus presents a possible mechanism for pathogenesis of the disease enhancement.

Relationship between atopic status and nasal interleukin 10 and 11 levels in infants with respiratory syncytial virus bronchiolitis

BACKGROUND

Interleukin 10 (IL-10) and IL-11 are known to have anti-inflammatory activities, and they have been implicated in the pathogenesis of respiratory syncytial virus (RSV) infection.

OBJECTIVES

To determine IL-10, IL-11, and myeloperoxidase levels in nasal secretions of infants with acute RSV bronchiolitis and to investigate whether there are any differences in these levels in patients with vs without atopy.

METHODS

We measured IL-10, IL-11, and myeloperoxidase levels in nasal secretions of 44 infants (20 were atopic) with acute RSV bronchiolitis. The nasal secretion samples were obtained from patients at hospital admission and were stored immediately at -70 degrees C until analysis. Atopy was defined as having at least 1 positive skin prick test reaction to common allergens, a history of atopic dermatitis, or a high serum IgE level compared with age-matched controls.

RESULTS

Levels of IL-10, IL-11, and myeloperoxidase increased significantly in samples from infants with acute RSV bronchiolitis. Levels of IL-10 and IL-11 were significantly lower in patients with vs without atopy (P < .05). Myeloperoxidase levels showed no significant difference in patients with vs without atopy (P = .18). Patients with severe symptoms tended to have lower IL-10 levels (P = .09), but no relationship was shown between symptom severity and IL-11 levels. Nasal myeloperoxidase levels were significantly higher in patients with severe symptoms (P < .05).

CONCLUSIONS

Production of IL-10 and IL-11 was significantly lower in patients with vs without atopy during acute RSV bronchiolitis. The airway inflammation induced by RSV infection may be different in patients with vs without atopy, and this is associated with lower induction of these immunoregulatory cytokines in children with atopy.

Intradermal exposure of BALB/c strain mice to peanut protein elicits a type 2 cytokine response

There is a growing need for the development of methods to characterize the allergenic properties of novel proteins, particularly those expressed by transgenic crop plants. Hence, there is considerable interest in the development of suitable animal models for this purpose. The production of specific IgE antibody has been reported following sensitization with food allergen via oral or systemic (intraperitoneal) routes of exposure. We have characterized cytokine profiles induced by intradermal treatment of BALB/c strain mice with a purified peanut allergen, Arachis hypogea lectin. Mice were exposed to peanut lectin by intradermal administration and the cytokine responses in the lymph node draining the site of exposure analyzed at the secreted protein level by enyzme-linked immunosorbent assay (ELISA) and cytokine mRNA level by ribonuclease protection assay (RPA). Exposure to peanut lectin, under conditions that induced robust IgE antibody titers, was found to be associated with a T helper 2 (Th2)-type cytokine expression profile at both the mRNA and secreted protein levels. Culture of naïve lymph node cells with peanut lectin failed to stimulate marked proliferation or cytokine production, confirming this protein is not mitogenic for mouse lymphocytes. Furthermore, the expression of Th2 cytokines was associated with the effector/memory CD62L- cell population. Similar treatment with a non-allergenic protein, potato acid phosphatase, failed to induce Th2 cytokine expression. These data demonstrate that exposure of mice to peanut allergen results in the selective stimulation of a Th2-type response.

Nasal mucosa in natural colds: effects of allergic rhinitis and susceptibility to recurrent sinusitis

The mechanisms of virus-induced airway hyperresponsiveness in asthma and allergy and the failure of host defence in patients suffering from secondary airway infections are still largely unknown. The aim of this study was to examine whether the presence of allergic rhinitis or susceptibility to recurrent sinusitis affects the structural and cellular changes in nasal mucosa during natural colds and convalescence. We compared the mucosal changes in biopsy samples during acute natural colds (days 2-4 of illness) and convalescence (3 weeks later) in patients with allergic rhinitis (n = 9), patients with susceptibility to sinusitis (n = 19) and healthy controls (n = 20). We saw similarly increased numbers of mucosal T and B lymphocytes and mast cells and increased vascular density during the acute colds compared to convalescence in all the three groups. The allergic subjects had elevated levels of eosinophils in the acute phase (P = 0.03), and the allergic and sinusitis-prone subjects had elevated levels of epithelial T cells (P = 0.04) and low levels of mast cells (P = 0.005) in convalescence compared to the control group. The sinusitis-prone subjects lacked intraepithelial cytotoxic cells in convalescence. In the allergic subjects, the reticular basement membrane was thicker in the acute phase compared to the convalescence (P = 0.05). These results suggest that various cells of the airways, including inflammatory and structural cells, are involved during viral respiratory infections in subjects with allergic rhinitis. The small numbers of mast cells and cytotoxic lymphocytes in the sinusitis-prone subjects may be related to their susceptibility to bacterial complications.

Soluble CD14 as a predictor of subsequent development of recurrent wheezing in hospitalized young children with respiratory syncytial virus-induced bronchiolitis

BACKGROUND

Respiratory syncytial virus (RSV) infection in infancy that causes severe bronchiolitis had been implicated as potentially responsible for the subsequent development of asthma. The CD14 receptor responds to the microbial burden in the environment and modulates the development of the allergic phenotype.

OBJECTIVE

To investigate the relationship between the serum level of soluble CD14 (sCD14) in children hospitalized because of RSV-induced bronchiolitis and the subsequent development of recurrent wheezing.

METHODS

Serum levels of sCD14 were measured in 21 children younger than 14 months who were hospitalized because of RSV-induced bronchiolitis. The diagnosis of significant wheezing was evaluated by recurrent episodes of coughing, wheezing, and respiratory distress, which were relieved by inhalation of beta-agonists and corticosteroids.

RESULTS

Of the 21 children, 19 were followed up for 12 months. The mean sCD14 serum level of 14,521 +/- 1,773 pg/mL in the group of 6 children who did not exhibit recurrent wheezing was significantly higher than the level of 11,243 +/- 3,264 pg/mL in the group of 13 children who exhibited significant recurrent wheezing (P < .05). The subsequent development of recurrent wheezing was not influenced by positive family history of asthma, number of siblings, sex, or breast-feeding.

CONCLUSION

A follow-up period of 12 months in this small pilot group showed that high serum levels of sCD14 modulate the influence of RSV on subsequent recurrent episodes of wheezing.

Respiratory syncytial virus, pneumonia virus of mice, and influenza A virus differently affect respiratory allergy in mice

BACKGROUND

Respiratory viral infections in early childhood may interact with the immune system and modify allergen sensitization and/or allergic manifestations. In mice, respiratory syncytial virus (RSV) infection during allergic provocation aggravates the allergic T helper (Th) 2 immune response, characterized by the production of IL-4, IL-5, and IL-13, and inflammatory infiltrates. However, it is unclear whether the RSV-enhanced respiratory allergic response is a result of non-specific virus-induced damage of the lung, or virus-specific immune responses.

OBJECTIVE

In the present study we investigated whether RSV, pneumonia virus of mice (PVM) and influenza A virus similarly affect the allergic response.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin (OVA), and inoculated with virus during the challenge period. Pulmonary inflammation, lung cytokine mRNA responses, and IgE production in serum were assessed after the last OVA-challenge.

RESULTS

Like RSV, PVM enhanced the OVA-induced pulmonary IL-4, IL-5, and IL-13 mRNA expression, which was associated with enhanced perivascular inflammation. In addition, PVM increased the influx of eosinophils in lung tissue. In contrast, influenza virus decreased the Th2 cytokine mRNA expression in the lungs. However, like PVM, influenza virus enhanced the pulmonary eosinophilic infiltration in OVA-allergic mice.

CONCLUSION

The Paramyxoviruses RSV and PVM both are able to enhance the allergic Th2 cytokine response and perivascular inflammation in BALB/c mice, while the Orthomyxovirus influenza A is not.

Is there a causative role for tetanus toxoid vaccination in the development of allergy-like symptoms and in the increasing prevalence of atopic diseases?

Allergic diseases are a worldwide health problem. They mainly affect people living in developed countries where an increasing prevalence of allergy symptoms has been recorded in the last 20-30 years. The cause of this increase is still disputed, and, among others, the "hygiene hypothesis" supported the concept that relevant changes in lifestyle could have a relationship with the phenomenon. More recently the recorded parallel increase in autoimmune diseases has suggested to consider the "hygiene hypothesis" as a cause of a more general disregulation of the immune system leading to both allergy and to autoimmunity. Here are reported a series of observations, evidence, and data from the literature leading to a different hypothesis. The key points are: (1) the presence of two subsets of patients having allergy symptoms based on an IgE-mediated mechanism or not; (2) the positive results obtained with the autologous serum skin test in either cutaneous or respiratory affected subjects, mainly in children and adult females; (3) the presence of IgG autoantibodies against the alpha-chain of the high affinity IgE receptor (FcepsilonRIalpha) in non-IgE-mediated urticaria and even in respiratory subjects; (4) the cross-reactivity between epitopes of the tetanus toxoid molecule and the FcepsilonRIalpha detected by means of an alpha-chain affinity purified IgG fraction; (5) the positive skin reactivity obtained using IgG anti-tetanus toxoid preparations in allergic and non-allergic volunteers. The presence of IgG autoantibodies actively generated by the population-based vaccination with tetanus toxoid could induce both mediator release from activated mast cell and Th2 cytokine production early in life. There are epidemiological evidences that tetanus toxoid vaccination could be linked with an increased tendency to have allergy symptoms. The different epidemiological distribution of non-IgE-mediated symptoms, mainly affecting young infants would be in agreement with the present hypothesis. The prevalent mother-to-child relationship in terms of risk for allergy symptoms could be explained with the trans-placenta transfer of IgG. A similar transfer could also take place through the mother milk during breast feeding. It may thus be hypothesized that the increased prevalence of allergic diseases could be caused by the generalized tetanus toxoid immunization procedure, progressively extended to most of the countries worldwide in the last 30-40 years. Both the induction of non-IgE-mediated symptoms caused by the mast cell activation via the anti-FcepsilonRIalpha IgG and the long lasting Th2 inflammation of affected tissues would be the inducing mechanisms. This hypothesis would re-configure part of the allergic diseases as a Th2 phenotypic expression of an autoimmune disease.

The complex relationship between respiratory syncytial virus and allergy in lung disease

Epidemiologic studies suggest a strong link between severe respiratory syncytial virus (RSV)-induced bronchiolitis in infancy and allergic disease; however, the mechanisms determining this relationship are currently unknown. In this review article, we summarize data from human clinical studies that explore the association between RSV infection and allergy, some that suggest that RSV bronchiolitis requiring hospitalization leads to an increased incidence of the allergic phenotype and others that suggest that pre-existing allergy is a risk factor for severe RSV bronchiolitis. We also review the published murine models that combine RSV infection and allergic sensitization that attempt to explain the complex relationship between these two factors in regard to lung immunopathology and physiologic dysfunction.

Respiratory syncytial virus enhances respiratory allergy in mice despite the inhibitory effect of virus-induced interferon-gamma

In mice, respiratory syncytial virus (RSV) infection during allergic provocation aggravates the allergic Th2 immune response, characterised by production of interleukin (IL)-4, IL-5, and IL-13, and eosinophilic inflammation. This enhancement of the Th2 response occurs simultaneously with a strong RSV-induced Th1 cytokine response (IL-12 and IFN-gamma). The present study investigated whether IFN-gamma and IL-12 are critically involved in this RSV-enhanced OVA allergy. Therefore, IFN-gammaR- and IL-12-deficient mice (both on a 129/Sv/Ev background) were sensitised and challenged with ovalbumin (OVA) and infected with RSV during the OVA challenge period. Neither gene deletion affected the development of ovalbumin-induced allergic inflammation in mice. However, when OVA-allergic IFN-gammaR deficient mice were infected with RSV, an increased pulmonary eosinophilic infiltrate and increased IL-4 and IL-13 mRNA expression in lung tissue were observed compared with identically treated wild-type mice. In contrast, deficiency of IL-12 did not aggravate the Th2 immune and inflammatory response in OVA/RSV-treated mice, compared with wild-type. In conclusion, the virus-induced IFN-gamma response diminishes the Th2 inflammatory response during OVA allergy but fails to prevent totally the enhancement of the OVA allergy by RSV. In contrast, IL-12 is not involved in inhibiting nor increasing the RSV-enhanced allergy in 129/Sv/Ev mice.

The quest for an efficacious antiviral for respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalized and the elderly. To date, ribavirin (Virazole) remains the only therapeutic agent approved for the treatment of RSV. The prophylactic administration of palivizumab is problematic and costly. The quest for an efficacious RSV antiviral has produced a greater understanding of the viral fusion process, a new hypothesis for the mechanism of action of ribavirin, and a promising antisense strategy combining the 2'-5' oligoadenylate antisense (2-5A-antisense) approach and RSV genomics.