The role of virus-specific immunoglobulin E in airway hyperresponsiveness

Respiratory Syncytial Virus-Specific Antibodies and Atopic Diseases in Children: A 10-Year Follow-Up

Background: Respiratory syncytial virus (RSV) stimulates the production of specific immunoglobulin (Ig) E and IgG4 antibodies as a hallmark of the Th2 immune response. In this paper, we evaluated the occurrence of atopic diseases in 10-year-old children who were positive for RSV-specific IgG antibodies during infancy. Methods: The prospective follow-up of 72 children included a physical examination, an International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire and the determination of RSV-specific antibodies and total and allergen-specific IgE. Results: Children with asthma had their first wheezing episode at a younger age (χ2 8.097, df = 1, p = 0.004). RSV-specific IgG4 levels at year one were positively correlated with atopic dermatitis (AD) (tau_b = 0.211, p = 0.049) and current AD (tau_b = 0.269, p = 0.012); and RSV-specific IgE levels were positively correlated with allergic rhinitis (AR) (tau_b = 0.290, p = 0.012) and current AR (tau_b = 0.260, p = 0.025). Positive RSV-specific IgE at the age of one increased the chances of asthma occurrence by 5.94 (OR = 5.94, 95% CI = 1.05–33.64; p = 0.044) and the chances of AR by more than 15 times (OR = 15.03, 95% CI = 2.08–108.72; p = 0.007). A positive family history of atopy increased the chances of asthma occurrence by 5.49 times (OR = 5.49, 95% CI = 1.01–30.07; p = 0.049), and a longer duration of exclusive breastfeeding lowered that chance (OR = 0.63, 95% CI = 0.45–0.89; p = 0.008). Prenatal smoking increased the chances of AR occurrence by 7.63 times (OR = 7.63, 95% CI = 1.59–36.53; p = 0.011). Conclusion: RSV-specific IgE and RSV-specific IgG4 antibodies could be risk markers for the development of atopic diseases in children.

Exploring Key Genes and Mechanisms in Respiratory Syncytial Virus-Infected BALB/c Mice via Multi-Organ Expression Profiles

Respiratory syncytial virus (RSV) a leading cause of pediatric and adult morbidity and mortality worldwide. It can cause complications in multiple organs, thus increasing hospital stays and costs. However, RSV-based studies have primarily focused on effects in the lungs and blood, thereby potentially neglecting critical genes and pathways. Hence, studying RSV infection via a novel multi-organ approach is important. In this study, lung, intestine, brain, and spleen tissues from six BALB/c mice (6–8 weeks old; three in control group and three in RSV-infected group) were subjected to RNA sequencing. Differentially expressed genes (DEGs) in each organ were obtained and functional enrichment analysis was performed. We first used CIBERSORT to evaluate the immune-infiltration landscape. Subsequently, common DEGs (co-DEGs) among the four organs were analyzed to identify key genes and pathways. After quantitative reverse transcription-polymerase chain reaction, western blotting, and external validation analysis of key hub genes, their correlation with immune cells and potential functions were explored. We found that the host response to RSV infection varied among the four organs regarding gene expression profiles and immune cell infiltration. Analysis of the 16 co-DEGs indicated enrichment in the platelet and neutrophil degranulation pathways. Importantly, the key gene hemopexin (Hpx) was strongly correlated with the immune cell fraction in the lungs and may participate in the regulation of platelet activation and immune response.

A Pilot Study for IgE as a Prognostic Biomarker in COVID-19

Background

Laboratory biomarkers to estimate the severity of COVID‐19 are crucial during the pandemic, since resource allocation must be carefully planned.

Aim

In the present study, we aim to evaluate the effects of basal serum total immunoglobulin E (IgE) levels and changes in inflammatory parameters on the clinical progression of patients hospitalized with COVID‐19.

Methods

Patients hospitalized with confirmed COVID‐19 were included in the study. Laboratory data and total IgE levels were measured upon admission. Lymphocyte, eosinophil, ferritin, d‐dimer and CRP parameters were recorded on the baseline and on the 3^rd and 14^th days of hospitalization.

Results

The study enrolled 202 patients, of which 102(50.5%) were males. The average age was 50.17 ± 19.68. Of the COVID‐19 patients, 41 (20.3%) showed clinical progression. Serum total IgE concentrations were markedly higher (172.90 [0‐2124] vs 38.70 [0‐912], p<0.001) and serum eosinophil levels were significantly lower (0.015 [0‐1.200] vs 0.040 [0‐1.360], p=0.002) in clinically worsened COVID‐19 patients when compared to stable patients. The optimal cut‐off for predicting clinical worsening was 105.2 ng/L; with 61% sensitivity, 82% specificity, 46.3% positive predictive value and 89.2% negative predictive value (area under the curve=0.729). Multivariable analysis to define risk factors for disease progression identified higher total IgE and CRP levels as independent predictors.

Conclusions

Our single‐center pilot study determined that total IgE levels may be a negative prognostic factor for clinical progression in patients hospitalized due to COVID‐19 infection. Future studies are required to determine the impact of individuals' underlying immune predispositions on outcomes of COVID‐19 infections.

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Immunoglobulin E-Dependent Activation of Immune Cells in Rhinovirus-Induced Asthma Exacerbation

Acute exacerbation is the major cause of asthma morbidity, mortality, and health-care costs. Respiratory viral infections, particularly rhinovirus (RV) infections, are associated with the majority of asthma exacerbations. The risk for bronchoconstriction with RV is associated with allergic sensitization and type 2 airway inflammation. The efficacy of the humanized anti-IgE monoclonal antibody omalizumab in treating asthma and reducing the frequency and severity of RV-induced asthma exacerbation is well-known. Despite these clinical data, mechanistic details of omalizumab's effects on RV-induced asthma exacerbation have not been well-defined for years due to the lack of appropriate animal models. In this Perspective, we discuss potential IgE-dependent roles of mast cells and dendritic cells in asthma exacerbations.

Anti-IgE monoclonal antibodies as potential treatment in COVID-19

Coronavirus disease 2019 (COVID-19) is associated with irreversible effects on vital organs, especially the respiratory and cardiac systems. While the immune system plays a key role in the survival of patients to viral infections, in COVID-19, there is a hyperinflammatory immune response evoked by all the immune cells, such as neutrophils, monocytes, and includes release of various cytokines, resulting in an exaggerated immune response, named cytokine storm. This severe, dysregulated immune response causes multi-organ damage, which eventually leads to high mortality. One of the most important components of hypersensitivity is immunoglobulin E (IgE), which plays a major role in susceptibility to respiratory infections and can lead to the activation of mast cells. There is also a negative association between IgE and IFN-α, which can reduce Toll-like receptor (TLR) nine receptor expression and TLR-7 signaling to disrupt IFN production. Moreover, anti-IgE drugs such as omalizumab reduces the severity and duration of COVID-19. In addition to its anti-IgE effect, omalizumab inhibits inflammatory cells such as neutrophils. Hence, blockade of IgE may have clinical utility as an immunotherapy for COVID-19.

Herpes simplex virus 1 proteins can induce skin inflammation in an atopic dermatitis-like mouse model

Herpes simplex virus type 1 (HSV-1) can induce in certain individuals with atopic dermatitis (AD) severe cutaneous infections that can spread throughout the entire body, a condition named as AD complicated by eczema herpeticum (ADEH). It has been recently found that ADEH patients can produce specific IgE against HSV-1 proteins, which may contribute to lower protection against HSV-1. However, little is known about the capacity of these HSV-1 proteins to produce an inflammatory response at the skin level. In this study, using a mouse model of AD-like dermatitis, three HSV-1 proteins (glycoprotein D -gD-, glycoprotein B -gB- and VP22) were applied on tape-stripped back skin mice in three exposures periods. Ovalbumin (OVA) and 0.9% NaCl were used as positive and negative controls, respectively. Skin samples were obtained for analysis of specific cell components of skin infiltration. The results showed that the viral protein gD induced a statistically significant increase in the number of dermal infiltrating CD3+, CD4+ cells and mast cells compared with the negative control group. gD was also able to induce epidermal thickening and epidermal infiltration of T cells closely related to the one produced in mice sensitized with OVA. However, VP22 and gB contributed to a lesser extent to skin inflammation. These results showed that proteins from HSV-1, especially gD, can have per se an important T cell and mast cell-driven inflammatory potential at the skin level.

Viruses and asthma: the role of common respiratory viruses in asthma and its potential meaning for SARS-CoV-2

Viral infections and atopic diseases are closely related and contribute to each other. The physiological deficiencies and immune mechanisms that underlie atopic diseases can result in a suboptimal defense against multiple viruses, and promote a suitable environment for their proliferation and dissemination. Viral infections, on the other hand, can induce per se several immunological mechanisms involved in allergic inflammation capable to promote the initiation or exacerbation of atopic diseases such as atopic asthma. In a world that is affected more and more by factors that significantly impact the prevalence of atopic diseases, coronavirus disease 2019 (COVID-19) induced by the novel coronavirus severe acute respiratory syndrome (SARS-CoV-2) is having an unprecedented impact with still unpredictable consequences. Therefore, it is of crucial importance to revise the available scientific literature regarding the association between common respiratory viruses and asthma, as well as the newly emerging data about the molecular mechanisms of SARS-CoV-2 infection and its possible relation with asthma, to better understand the interrelation between common viruses and asthma and its potential meaning on the current global pandemic of COVID-19.

Lung innervation in the eye of a cytokine storm: neuroimmune interactions and COVID-19

COVID-19 is an infectious disease caused by the coronavirus SARS-CoV-2, which was first reported in Wuhan, China, in December 2019 and has caused a global pandemic. Acute respiratory distress syndrome (ARDS) is a common feature of severe forms of COVID-19 and can lead to respiratory failure, especially in older individuals. The increasing recognition of the neurotropic potential of SARS-CoV-2 has sparked interest in the role of the nervous system in respiratory failure in people with COVID-19. However, the neuroimmune interactions in the lung in the context of ARDS are poorly understood. In this Perspectives article, we propose the concept of the neuroimmune unit as a critical determinant of lung function in the context of COVID-19, inflammatory conditions and ageing, focusing particularly on the involvement of the vagus nerve. We discuss approaches such as neurostimulation and pharmacological neuromodulation to reduce tissue inflammation with the aim of preventing respiratory failure.

Acute respiratory distress syndrome is a common occurrence in COVID-19, an infectious disease caused by the coronavirus SARS-CoV-2. In this article, the authors consider how lung innervation might crosstalk with the immune system to modulate lung function and influence outcomes in COVID-19.

CEACAM3 decreases asthma exacerbations and modulates respiratory syncytial virus latent infection in children

BACKGROUND

Respiratory syncytial virus (RSV) is associated with childhood asthma. Nevertheless, not all children exposed to RSV develop asthma symptoms, possibly because genes modulate the effects of RSV on asthma exacerbations.

OBJECTIVE

The purpose of this study was to identify genes that modulate the effect of RSV latent infection on asthma exacerbations.

METHODS

We performed a meta-analysis to investigate differentially expressed genes (DEGs) of RSV infection from Gene Expression Omnibus datasets. Expression quantitative trait loci (eQTL) methods were applied to select single nucleotide polymorphisms (SNPs) that were associated with DEGs. Gene-based analysis was used to identify SNPs that were significantly associated with asthma exacerbations in the Taiwanese Consortium of Childhood Asthma Study (TCCAS), and validation was attempted in an independent cohort, the Childhood Asthma Management Program (CAMP). Gene-RSV interaction analyses were performed to investigate the association between the interaction of SNPs and RSV latent infection on asthma exacerbations.

RESULTS

A total of 352 significant DEGs were found by meta-analysis of RSV-related genes. We used 38 123 SNPs related to DEGs to investigate the genetic main effects on asthma exacerbations. We found that eight RSV-related genes (GADD45A, GYPB, MS4A3, NFE2, RNASE3, EPB41L3, CEACAM6 and CEACAM3) were significantly associated with asthma exacerbations in TCCAS and also validated in CAMP. In TCCAS, rs7251960 (CEACAM3) significantly modulated the effect of RSV latent infection on asthma exacerbations (false-discovery rate <0.05). The rs7251960 variant was associated with CEACAM3 mRNA expression in lung tissue (p for trend=1.2×10^-7). CEACAM3 mRNA was reduced in nasal mucosa from subjects with asthma exacerbations in two independent datasets.

CONCLUSIONS

rs7251960 is an eQTL for CEACAM3, and CEACAM3 mRNA expression is reduced in subjects experiencing asthma exacerbations. CEACAM3 may be a modulator of RSV latent infection on asthma exacerbations.

Protective and pathogenic roles for mast cells during viral infections

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At the host-environment interfaces such as skin or mucosae mast cells act as immune sentinels for variety of pathogens including viruses.

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Mast cells initiate cellular immune responses at the infection site by recruitment of various subsets of T cells.

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Systemic activation of mast cells is associated with vascular pathologies during viral infections.

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Targeting of mast cell specific products has a promising therapeutic potential in treating virus induced immune pathologies.

Mast cells (MCs) are long-lived immune cells. They are armed with preformed mediators within granules that can be instantaneously released in response to an invading pathogen, including certain viruses. At the skin and mucosae, they initiate innate immune responses and promote the development of adaptive immune responses, through cellular recruitment or antigen presentation. However, systemic MC activation may promote immune pathologies through their vasoactive proteases and biogenic amines. Recently, MC products were identified to contribute to pathologies associated with viral hemorrhagic fever, such vascular leakage and thrombocytopenia. Similar associations of MCs with disease severity have been noted for certain respiratory viral pathogens. Here we discuss the specific MC responses to viruses and their influences on functional immune outcomes during infection.

Total and specific immunoglobulin E in induced sputum in allergic and non-allergic asthma

Background

Most patients with nonallergic asthma have normal serum immunoglobulin E (IgE) levels. Recent reports suggest that total and aeroallergen-specific IgE levels in induced sputum may be higher in nonallergic asthmatics than in healthy controls. Our objective is to compare total and dust-mite specific (Der p 1) IgE levels in induced sputum in allergic and nonallergic asthmatics and healthy controls.

Methods

Total and Der p 1-specific IgE were measured in induced sputum (ImmunoCAP immunoassay) from 56 age- and sex-matched asthmatics (21 allergic, 35 nonallergic) and 9 healthy controls. Allergic asthma was defined as asthma with a positive prick test and/or clinically-significant Der p 1-specific serum IgE levels.

Results

Patients with allergic asthma presented significantly higher total and Der p 1-specific serum IgE levels. There were no significant between-group differences in total sputum IgE. However, Der p 1-specific sputum IgE levels were significantly higher (p = 0.000) in the allergic asthmatics, but without differences between the controls and nonallergic asthmatics. Serum and sputum IgE levels were significantly correlated, both for total IgE (rho = 0.498; p = 0.000) and Der p 1-specific IgE (rho, 0.621; p = 0001).

Conclusions

Total IgE levels measured in serum and induced sputum are significantly correlated. No significant differences were found between the differents groups in total sputum IgE. Nevertheless, the levels of Der p 1-specific sputum IgE levels were significantly higher in the allergic asthmatics, but without differences between the controls and nonallergic asthmatics. Probably due to the lack of sensitivity of the test used, but with the growing evidence for local allergic reactions better methods are need to explore its presence. The Clinical Trials Identifier for this project is NCT03640936.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Inhibition of CD23-mediated IgE transcytosis suppresses the initiation and development of allergic airway inflammation

The epithelial lining of the airway tract and allergen-specific IgE are considered essential controllers of inflammatory responses to allergens. The human low affinity IgE receptor, CD23 (FcɛRII), is capable of transporting IgE or IgE-allergen complexes across the polarized human airway epithelial cell (AEC) monolayer in vitro. However, it remains unknown whether the CD23-dependent IgE transfer pathway in AECs initiates and facilitates allergic inflammation in vivo, and whether inhibition of this pathway attenuates allergic inflammation. To this end, we show that in wild-type (WT) mice, epithelial CD23 transcytosed both IgE and ovalbumin (OVA)-IgE complexes across the airway epithelial barrier, whereas neither type of transcytosis was observed in CD23 knockout (KO) mice. In chimeric mice, OVA sensitization and aerosol challenge of WT/WT (bone-marrow transfer from the WT to WT) or CD23KO/WT (CD23KO to WT) chimeric mice, which express CD23 on radioresistant airway structural cells (mainly epithelial cells) resulted in airway eosinophilia, including collagen deposition and a significant increase in goblet cells, and increased airway hyperreactivity. In contrast, the absence of CD23 expression on airway structural or epithelial cells, but not on hematopoietic cells, in WT/CD23KO (the WT to CD23KO) chimeric mice significantly reduced OVA-driven allergic airway inflammation. In addition, inhalation of the CD23-blocking B3B4 antibody in sensitized WT mice before or during airway challenge suppressed the salient features of asthma, including bronchial hyperreactivity. Taken together, these results identify a previously unproven mechanism in which epithelial CD23 plays a central role in the development of allergic inflammation. Further, our study suggests that functional inhibition of CD23 in the airway is a potential therapeutic approach to inhibit the development of asthma.

Respiratory syncytial virus--a comprehensive review

Respiratory syncytial virus (RSV) is amongst the most important pathogenic infections of childhood and is associated with significant morbidity and mortality. Although there have been extensive studies of epidemiology, clinical manifestations, diagnostic techniques, animal models and the immunobiology of infection, there is not yet a convincing and safe vaccine available. The major histopathologic characteristics of RSV infection are acute bronchiolitis, mucosal and submucosal edema, and luminal occlusion by cellular debris of sloughed epithelial cells mixed with macrophages, strands of fibrin, and some mucin. There is a single RSV serotype with two major antigenic subgroups, A and B. Strains of both subtypes often co-circulate, but usually one subtype predominates. In temperate climates, RSV infections reflect a distinct seasonality with onset in late fall or early winter. It is believed that most children will experience at least one RSV infection by the age of 2 years. There are several key animal models of RSV. These include a model in mice and, more importantly, a bovine model; the latter reflects distinct similarity to the human disease. Importantly, the prevalence of asthma is significantly higher amongst children who are hospitalized with RSV in infancy or early childhood. However, there have been only limited investigations of candidate genes that have the potential to explain this increase in susceptibility. An atopic predisposition appears to predispose to subsequent development of asthma and it is likely that subsequent development of asthma is secondary to the pathogenic inflammatory response involving cytokines, chemokines and their cognate receptors. Numerous approaches to the development of RSV vaccines are being evaluated, as are the use of newer antiviral agents to mitigate disease. There is also significant attention being placed on the potential impact of co-infection and defining the natural history of RSV. Clearly, more research is required to define the relationships between RSV bronchiolitis, other viral induced inflammatory responses, and asthma.

Intracellular RNA recognition pathway activates strong anti-viral response in human mast cells

Mast cells have been implicated in the first line of defence against parasites and bacteria, but less is known about their role in anti-viral responses. Allergic diseases often exacerbate during viral infection, suggesting an increased activation of mast cells in the process. In this study we investigated human mast cell response to double-stranded RNA and viral infection. Cultured human mast cells were incubated with poly(I:C), a synthetic RNA analogue and live Sendai virus as a model of RNA parainfluenza virus infection, and analysed for their anti-viral response. Mast cells responded to intracellular poly(I:C) by inducing type 1 and type 3 interferons and TNF-α. In contrast, extracellular Toll-like receptor 3 (TLR)-3-activating poly(I:C) failed to induce such response. Infection of mast cells with live Sendai virus induced an anti-viral response similar to that of intracellular poly(I:C). Type 1, but not type 3 interferons, up-regulated the expression of melanoma differentiation-associated gene 5 (MDA-5) and retinoic acid-inducible gene-1 (RIG-1), and TLR-3, demonstrating that human mast cells do not express functional receptors for type 3 interferons. Furthermore, virus infection induced the anti-viral proteins MxA and IFIT3 in human mast cells. In conclusion, our results support the notion that mast cells can recognize an invading virus through intracellular virus sensors and produce high amounts of type 1 and type 3 interferons and the anti-viral proteins human myxovirus resistance gene A (MxA) and interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) in response to the virus infection.

Need for a safe vaccine against respiratory syncytial virus infection

Human respiratory syncytial virus (HRSV) is a major cause of severe respiratory tract illnesses in infants and young children worldwide. Despite its importance as a respiratory pathogen, there is currently no licensed vaccine for HRSV. Following failure of the initial trial of formalin-inactivated virus particle vaccine, continuous efforts have been made for the development of safe and efficacious vaccines against HRSV. However, several obstacles persist that delay the development of HRSV vaccine, such as the immature immune system of newborn infants and the possible Th2-biased immune responses leading to subsequent vaccine-enhanced diseases. Many HRSV vaccine strategies are currently being developed and evaluated, including live-attenuated viruses, subunit-based, and vector-based candidates. In this review, the current HRSV vaccines are overviewed and the safety issues regarding asthma and vaccine-induced pathology are discussed.

The microbiology of asthma

Asthma remains an important human disease that is responsible for substantial worldwide morbidity and mortality. The causes of asthma are multifactorial and include a complex mix of environmental, immunological and host genetic factors. In addition, epidemiological studies show strong associations between asthma and infection with respiratory pathogens, including common respiratory viruses such as rhinoviruses, human respiratory syncytial virus, adenoviruses, coronaviruses and influenza viruses, as well as bacteria (including atypical bacteria) and fungi. In this Review, we describe the many roles of microorganisms in the risk of developing asthma and in the pathogenesis of and protection against the disease, and we discuss the mechanisms by which infections affect the severity and prevalence of asthma.

The prevalence and identity of Chlamydia-specific IgE in children with asthma and other chronic respiratory symptoms

Background

Recent studies have confirmed the presence of viable Chlamydia in the bronchoalveolar lavage (BAL) fluid of pediatric patients with airway hyperresponsiveness. While specific IgG and IgM responses to C. pneumoniae are well described, the response and potential contribution of Ag-specific IgE are not known. The current study sought to determine if infection with Chlamydia triggers the production of pathogen-specific IgE in children with chronic respiratory diseases which might contribute to inflammation and pathology.

Methods

We obtained BAL fluid and serum from pediatric respiratory disease patients who were generally unresponsive to corticosteroid treatment as well as sera from age-matched control patients who saw their doctor for wellness checkups. Chlamydia-specific IgE was isolated from BAL and serum samples and their specificity determined by Western blot techniques. The presence of Chlamydia was confirmed by species-specific PCR and BAL culture assays.

Results

Chlamydial DNA was detected in the BAL fluid of 134/197 (68%) patients. Total IgE increased with age until 15 years old and then decreased. Chlamydia-specific IgE was detected in the serum and/or BAL of 107/197 (54%) patients suffering from chronic respiratory disease, but in none of the 35 healthy control sera (p < 0.0001). Of the 74 BAL culture-positive patients, 68 (91.9%, p = 0.0001) tested positive for Chlamydia-specific IgE. Asthmatic patients had significantly higher IgE levels compared to non-asthmatics (p = 0.0001). Patients who were positive for Chlamydia DNA or culture had significantly higher levels of serum IgE compared to negative patients (p = 0.0071 and p = 0.0001 respectively). Only 6 chlamydial antigens induced Chlamydia-specific IgE and patients with C. pneumoniae-specific IgE had significantly greater levels of total IgE compared to C. pneumoniae-specific IgE negative ones (p = 0.0001).

Conclusions

IgE antibodies play a central role in allergic inflammation; therefore production of Chlamydia-specific IgE may prove significant in the exacerbation of chronic, allergic airway diseases, thus highlighting a direct role for Chlamydia in asthma pathogenesis.

Mast cells in lung inflammation

Mast cells play an important role in the lung in both health and disease. Their primary role is to initiate an appropriate program of inflammation and repair in response to tissue damage initiated by a variety of diverse stimuli. They are important for host immunity against bacterial infection and potentially in the host immune response to non small cell lung cancer. In situations of ongoing tissue damage, the sustained release of numerous pro-inflammatory mediators, proteases and cytokines, contributes to the pathophysiology of lung diseases such as asthma and interstitial lung disease. A key goal is the development of treatments which attenuate adverse mast cell function when administered chronically to humans in vivo. Such therapies may offer a novel approach to the treatment of many life-threatening diseases.

The use of a neonatal mouse model to study respiratory syncytial virus infections

Respiratory syncytial virus (RSV) infection is the most significant cause of viral death in infants worldwide. The significant morbidity and mortality associated with this disease underscores the urgent need for the development of an RSV vaccine. The development of an RSV vaccine has been hampered by our limited understanding of the human host immune system, which plays a significant role in RSV pathogenesis, susceptibility and vaccine efficacy. As a result, animal models have been developed to better understand the mechanisms by which RSV causes disease. Within the past few years, a revolutionary variation on these animal models has emerged--age at time of initial infection--and early studies in neonatal mice (aged <7 days at time of initial infection) indicate the validity of this model to understand RSV infection in infants. This article reviews available information on current murine and emerging neonatal mouse RSV models.

Pediatric asthma: a different disease

Asthma currently affects the lives of more than 30 million Americans from infancy to the elderly. In many ways, pediatric asthma differs from adult asthma, including childhood-onset adult asthma. Despite many advances in our understanding of the disease, the natural history of asthma is not well defined, especially in different subsets of patients. For many with allergic asthma the disease has its origins in early childhood, associated with early sensitization to aeroallergens and exposure to repeated viral infections. These early life exposures, coupled with genetically determined susceptibility, have a major impact on the natural history of the disease. A number of risk factors during the critical early stages in the initiation of asthma have been associated with subsequent outcomes. In addition, protective factors linked to early life experiences have also been delineated which may impact the development of atopy and asthma and reduce the prevalence of these diseases. Cumulatively, the data highlight the critical nature of this early period in which immune/inflammatory responses in the lung are initiated and serve to maintain the disease in subsequent years.

Mast cell degranulation is induced by A549 airway epithelial cell infected with respiratory syncytial virus

Respiratory syncytial virus (RSV), a major causative agent of respiratory tract infections, influences allergic diseases. Mast cells, important effector cells in allergic disease, also express chemokine (C-X(3)-C motif) receptor 1 (CX(3)CR1). The RSV attachment glycoprotein (G protein) is structurally similar to CX(3)C ligand 1 (CX(3)CL1), the CX(3)CR1 ligand, suggesting that RSV directly interacts with and affects mast cell function, including degranulation. In this paper, the effect of RSV infection on mast cell function was studied using the human mast cell line (HMC-1). The results showed that RSV infection and replication was inefficient in HMC-1 cells than in human epithelial A549 cells. Additionally, HMC-1 degranulation occurred only in coculture with RSV-infected A549 cells, with up-regulation of TNFalpha secretion. However, direct RSV inoculation and incubation with RSV-infected A549 cell culture medium failed to induce HMC-1 degranulation, suggesting that virus-infected cells are critical for degranulation during RSV infection; however, degranulation does not occur by direct RSV infection into mast cells.

Virus-specific IgE enhances airway responsiveness on reinfection with respiratory syncytial virus in newborn mice

BACKGROUND

Respiratory syncytial virus (RSV)-specific IgE is a component of the host response to RSV infection, but its role in the subsequent enhancement of altered airway responsiveness is unknown.

OBJECTIVE

To define the role of RSV-specific IgE in the enhancement of airway responsiveness on reinfection of newborn mice.

METHODS

Mice were infected as newborns with RSV and were reinfected 5 weeks later. The role of IgE was determined by documenting RSV-specific IgE response after neonatal infection, and by assessing airway responsiveness on reinfection.

RESULTS

After neonatal infection, wild-type (WT) mice developed an RSV-specific IgE response. On reinfection, these mice developed enhanced airway hyperresponsiveness (AHR), airway eosinophilia, and mucus hyperproduction, and their T-cell cytokine response was skewed toward a T(H)2 phenotype. None of these altered responses developed on reinfection of IL-4(-/-)/IL-13(-/-) mice, and no RSV-specific IgE could be detected after neonatal infection of these mice. Fc epsilon RI(-/-) mice did not develop the enhanced AHR on reinfection, and airway eosinophilia and mucus production were significantly attenuated. These responses could be restored in deficient mice reconstituted with WT mast cells. In RSV-infected newborn WT mice, administration of anti-IgE prevented the enhancement of AHR and attenuated eosinophilia and mucus hyperproduction on reinfection, an effect that was associated with diminished T(H)2 cytokine production and increased IFN-gamma production.

CONCLUSION

Respiratory syncytial virus-specific IgE enhances the development of T(H)2-biased airway responsiveness on reinfection of mice initially infected as newborns.

Human mast cell activation with virus-associated stimuli leads to the selective chemotaxis of natural killer cells by a CXCL8-dependent mechanism

Human mast cells are found in skin and mucosal surfaces and next to blood vessels. They play a sentinel cell role in immunity, recognizing invading pathogens and producing proinflammatory mediators. Mast cells can recruit granulocytes, and monocytes in allergic disease and bacterial infection, but their ability to recruit antiviral effector cells such as natural killer (NK) cells and T cells has not been fully elucidated. To investigate the role of human mast cells in response to virus-associated stimuli, human cord blood-derived mast cells (CBMCs) were stimulated with polyinosinic.polycytidylic acid, a double-stranded RNA analog, or infected with the double-stranded RNA virus, reovirus serotype 3 Dearing for 24 hours. CBMCs responded to stimulation with polyinosinic.polycytidylic acid by producing a distinct chemokine profile, including CCL4, CXCL8, and CXCL10. CBMCs produced significant amounts of CXCL8 in response to low levels of reovirus infection, while both skin- and lung-derived fibroblasts were unresponsive unless higher doses of reovirus were used. Supernatants from CBMCs infected with reovirus induced substantial NK cell chemotaxis that was highly dependent on CXCL8 and CXCR1. These results suggest a novel role for mast cells in the recruitment of human NK cells to sites of early viral infection via CXCL8.

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.

IFN-gamma production during initial infection determines the outcome of reinfection with respiratory syncytial virus

RATIONALE

Severe respiratory syncytial virus (RSV) bronchiolitis has been associated with deficient IFN-gamma production in humans, but the role of this cytokine in determining the outcome of reinfection is unknown.

OBJECTIVES

To define the role of IFN-gamma in the development of RSV-mediated airway hyperresponsiveness (AHR) and lung histopathology in mice.

METHODS

Wild-type (WT) and IFN-gamma knockout mice were infected with RSV in the newborn or weaning stages and reinfected 5 weeks later. Airway responses were assessed on Day 6 after the primary or secondary infection.

MEASUREMENTS AND MAIN RESULTS

Both WT and IFN-gamma knockout mice developed similar levels of AHR and airway inflammation after primary infection. After reinfection, IFN-gamma knockout mice, but not WT mice, developed AHR, airway eosinophilia, and mucus hyperproduction. Intranasal administration of IFN-gamma during primary infection but not during reinfection prevented the development of these altered airway responses on reinfection in IFN-gamma knockout mice. Adoptive transfer of WT T cells into IFN-gamma knockout mice before primary infection restored IFN-gamma production in the lungs and prevented the development of altered airway responses on reinfection. Treatment of mice with IFN-gamma during primary neonatal infection prevented the enhancement of AHR and the development of airway eosinophilia and mucus hyperproduction on reinfection.

CONCLUSIONS

IFN-gamma production during primary RSV infection is critical to the development of protection against AHR and lung histopathology on reinfection. Provision of IFN-gamma during primary infection in infancy may be a potential therapeutic approach to alter the course of RSV-mediated long-term sequelae.

Induction of high-affinity IgE receptor on lung dendritic cells during viral infection leads to mucous cell metaplasia

Respiratory viral infections are associated with an increased risk of asthma, but how acute Th1 antiviral immune responses lead to chronic inflammatory Th2 disease remains undefined. We define a novel pathway that links transient viral infection to chronic lung disease with dendritic cell (DC) expression of the high-affinity IgE receptor (FcepsilonRIalpha). In a mouse model of virus-induced chronic lung disease, in which Sendai virus triggered a switch to persistent mucous cell metaplasia and airway hyperreactivity after clearance of replicating virus, we found that FceRIa(-/-) mice no longer developed mucous cell metaplasia. Viral infection induced IgE-independent, type I IFN receptor-dependent expression of FcepsilonRIalpha on mouse lung DCs. Cross-linking DC FcepsilonRIalpha resulted in the production of the T cell chemoattractant CCL28. FceRIa(-/-) mice had decreased CCL28 and recruitment of IL-13-producing CD4(+) T cells to the lung after viral infection. Transfer of wild-type DCs to FceRIa(-/-) mice restored these events, whereas blockade of CCL28 inhibited mucous cell metaplasia. Therefore, lung DC expression of FcepsilonRIalpha is part of the antiviral response that recruits CD4(+) T cells and drives mucous cell metaplasia, thus linking antiviral responses to allergic/asthmatic Th2 responses.

Mast cells--key effector cells in immune responses

Mast cells are best known for their potent effector functions in allergic disorders. In recent years, however, mast cells have been identified to be involved in a surprisingly complex range of immune functions that go far beyond allergies and include the development of autoimmune disorders and peripheral tolerance, and the initiation and maintenance of adaptive and innate host responses. Here, we review the key signals and effector mechanisms that have lately been identified for mast cell functions in these immune responses.

Omalizumab decreases nonspecific airway hyperresponsiveness in vitro

BACKGROUND

In asthmatic patients, both symptoms and hyperresponsiveness are related to immunoglobulin E (IgE) concentration in serum. The anti-IgE monoclonal antibody omalizumab improved the control of asthma, but its effect on airway hyperresponsiveness is controversial. Passive sensitization reproduced in vitro a bronchial hyperresponsiveness, an increase in IgE bearing cells, and a mast cell degranulation. This study was designed to examine the effect of omalizumab on passive sensitization-induced hyperresponsiveness, alterations in IgE positive inflammatory cells and mast cell degranulation within the bronchial wall.

METHODS

Proximal (3-5 mm diameter) and distal (0.5-1.5 mm diameter) human bronchi dissected out from 10 lung specimens were incubated in normal or asthmatic serum containing various concentrations of omalizumab. Contractile responses to histamine or Dermatophagoides pteronyssinus (D. pter) were recorded using an organ bath system and expressed as percentage of maximal contractile response to acetylcholine (ACh). Immunohistochemistry was performed using monoclonal antibodies directed against IgE or tryptase. Mast cells were classified as fully granulated (type I), partly (type II) or largely degranulated (type III).

RESULTS

The specific bronchial hyperresponsiveness to D. pter and the nonspecific bronchial hyperresponsiveness to histamine following passive sensitization were significantly inhibited by omalizumab in both distal and proximal airways. Passive sensitization-induced increase in IgE positive cells was also abolished by omalizumab in a concentration dependent manner. Mast cell degranulation which was inhibited by omalizumab was positively correlated with the contractile response to D. pter.

CONCLUSIONS

Omalizumab blocks specific and nonspecific bronchial hyperresponsiveness. Anti-IgE also decreases IgE bearing cell number and mast cell degranulation.

Allergic rhinitis and its impact on otorhinolaryngology

Allergic rhinitis (AR) is a disease with growing impact on everyday medical practice, as its prevalence has steadily increased during the last decades. Immunoglobulin-E (IgE)-mediated airway inflammation may manifest itself as AR, asthma or both. Allergic inflammation in upper and lower airways is now considered as one airway disease, with manifestation of symptoms in upper, lower or global airway. This insight into allergic inflammation of the whole respiratory tract has consequences for the diagnostic and therapeutic approach of affected patients, as highlighted in the ARIA document. In contrast to asthma, the link between AR and associated conditions in the upper airways like rhinosinusitis, nasal polyps, recurrent viral infections, adenoid hypertrophy, tubal dysfunction, otitis media with effusion and laryngitis remains less explored. It is however of utmost importance to consider the aetiological role of IgE-mediated inflammation of the nasal mucosa in several diseases of the upper respiratory tract, as they represent a large body of patient population seen by the general practitioner as well as the paediatrician, allergologist and otorhinolaryngologist. We here aim at reviewing the current literature on the relationship between AR and conditions in upper airways frequently encountered in everyday clinical practice, and highlight the need for further studies exploring the role of allergic inflammation in the development of these diseases.

Virus-induced airway dysfunction: pathogenesis and biomechanisms

BACKGROUND

Viral respiratory tract infections cause significant morbidity and mortality. Respiratory viruses are suspected to play a role in the inception of asthma early in life. Respiratory syncytial virus (RSV) is the most common cause of infant bronchiolitis, which is associated with the development of childhood wheezing and asthma. However, it is not clear whether this association is "causal" or "circumstantial."

METHODS

Animal models have been pivotal in studying the pathophysiology of viral respiratory infections. Various approaches to assessing airway inflammation and function have been used to define the mechanisms of virus-induced airway dysfunction and to address clinically relevant questions regarding the role of RSV in wheezing and asthma after bronchiolitis.

RESULTS

Viral lower respiratory tract infections alter airway function in humans and animals. The extent and duration of the alterations may depend on the virus itself, host factors and environmental factors. Animal studies demonstrated that viral infection induces airway hyperresponsiveness and enhances this alteration in the allergen-sensitized and exposed host. This altered airway function is mediated by immune and neurogenic inflammatory mechanisms. Recent studies in mice show that neonatal RSV infection sensitizes the newborn to develop an asthma-like phenotype on reinfection, providing further opportunities to investigate the role of RSV in postbronchiolitis wheezing and asthma in this animal model.

CONCLUSIONS

Further studies are needed to fully establish the mechanisms underlying the pathophysiology of viral respiratory tract infections and to clarify their role in the inception and/or progression of chronic airway diseases such as asthma. The results of ongoing therapeutic studies promise to minimize the impact of such viral infections.