Differential cytopathogenesis of respiratory syncytial virus prototypic and clinical isolates in primary pediatric bronchial epithelial cells

All Eyes on the Prefusion-Stabilized F Construct, but Are We Missing the Potential of Alternative Targets for Respiratory Syncytial Virus Vaccine Design?

Respiratory Syncytial Virus (RSV) poses a significant global health concern as a major cause of lower respiratory tract infections (LRTIs). Over the last few years, substantial efforts have been directed towards developing vaccines and therapeutics to combat RSV, leading to a diverse landscape of vaccine candidates. Notably, two vaccines targeting the elderly and the first maternal vaccine have recently been approved. The majority of the vaccines and vaccine candidates rely solely on a prefusion-stabilized conformation known for its highly neutralizing epitopes. Although, so far, this antigen design appears to be successful for the elderly, our current understanding remains incomplete, requiring further improvement and refinement in this field. Pediatric vaccines still have a long journey ahead, and we must ensure that vaccines currently entering the market do not lose efficacy due to the emergence of mutations in RSV's circulating strains. This review will provide an overview of the current status of vaccine designs and what to focus on in the future. Further research into antigen design is essential, including the exploration of the potential of alternative RSV proteins to address these challenges and pave the way for the development of novel and effective vaccines, especially in the pediatric population.

Identification of potential immune/diagnosis related gene-immunocyte subtype networks in extracellular immune response to respiratory syncytial virus infection

INTRODUCTION

Respiratory syncytial virus (RSV) is one of the important pathogenic agents of pediatric respiratory tract infection. Weighted gene co-expression network analysis (WGCNA) is used to study autoimmune diseases, which can find potential hub genes. The diagnostic model based on hub genes and machine learning makes it possible to diagnose the extracellular immune response to RSV infection early.

OBJECTIVE

The aim of the present study was to identify potential immune, diagnose and treatment related genes expressed in RSV-infected cells.

METHODS

Firstly, gene expression data were downloaded from the Gene Expression Omnibus (GEO) to identify differentially expressed genes (DEGs). Secondly, WGCNA was performed based on DEGs to obtain hub genes related to immunity score. Thirdly, protein-protein interaction (PPI) and the immune infiltration analysis of hub immune related genes were performed. Finally, diagnostic and immune related genes were identified by machine learning, followed by functional analysis.

RESULTS

Totally, 2063 DEGs were identified in the extracellular immune response to RSV infection. Among which, 10 key immune and diagnosis related genes were identified, including ITGA2B, GP9, ITGB3, SELP, PPBP, MPL, CXCL8, NFE2, PTGS1 and LY6G6F. Several immune/diagnosis related gene-immunocyte subtype networks were identified, such as CXCL8-Type 17 T helper cell, LY6G6F-CD56 bright natural killer cell, PPBP-activated CD4 T cell/T follicular helper cell, NFE2/PTGS1/SELP-activated dendritic cell, GP9/ITGA2B/MPL-activated CD8 T cell. ITGB3, MPL and PTGS1 could be considered as therapeutic targets. Some significantly enriched signaling pathways were identified, including hematopoietic cell lineage (involving GP9 and ITGA2B), cytokine-cytokine receptor interaction (involving MPL), chemokine signaling pathway (involving PPBP) and arachidonic acid metabolism (involving PTGS1).

CONCLUSIONS

The 10-immune related gene signature may be used as potential diagnostic markers for the extracellular immune response to RSV infection, which may provide a new field in searching for diagnostic and therapeutic molecules in the extracellular immune response to RSV infection.

Effect of Vibrating Mesh Nebulizer Aerosol Technology on the In Vitro Activity of Ribavirin Against Respiratory Syncytial Virus

BACKGROUND

Ribavirin is an antiviral drug that for many years has been administered to the lungs by aerosolization. Despite advancements in oral delivery routes, there has been a renewed interested in delivering ribavirin via the pulmonary system in select patients and the severely ill. The vibrating mesh nebulizer was previously demonstrated to be an effective alternative to the small-particle aerosol generator in particle size, chemical makeup, and concentrations of the ribavirin before and after nebulization. However, the antiviral activity of ribavirin has never been examined. We sought to study ribavirin's activity before and after nebulization via vibrating mesh nebulizer.

METHODS

We grew and infected human epithelial type 2 cells and primary airway epithelial cells with respiratory syncytial virus (RSV). We then compared the antiviral effect of non-nebulized (control) and aerosolized ribavirin to untreated controls. We used traditional plaque assay and real-time polymerase chain reaction to determine the quantity of virus.

RESULTS

Both non-nebulized (control) and nebulized ribavirin reduced the size of RSV plaques compared to untreated controls. Additionally, the non-nebulized and nebulized ribavirin equally inhibited RSV replication. There were no statistically significant differences between the non-nebulized and nebulized ribavirin across all time points.

CONCLUSIONS

The vibrating mesh nebulizer did not affect the antiviral properties of nebulized ribavirin when compared to non-nebulized drug. Our findings add supporting evidence for the use of the vibrating mesh nebulizer in the administration of inhaled ribavirin.

Short-chain fatty acid acetate triggers antiviral response mediated by RIG-I in cells from infants with respiratory syncytial virus bronchiolitis

Background

Gut microbiota-derived short-chain fatty-acid (SFCA) acetate protects mice against RSV A2 strain infection by increasing interferon-β production and expression of interferon-stimulated genes (ISGs). However, the role of SFCA in RSV infection using strains isolated from patients is unknown.

Methods

We first used RSV clinical strains isolated from infants hospitalized with RSV bronchiolitis to investigate the effects of in vitro SCFA-acetate treatment of human pulmonary epithelial cells. We next examined whether SCFA-acetate treatment is beneficial in a mouse model of RSV infection using clinical isolates. We sought to investigate the relationship of gut microbiota and fecal acetate with disease severity among infants hospitalized with RSV bronchiolitis, and whether treating their respiratory epithelial cells with SCFA-acetate ex-vivo impacts viral load and ISG expression. We further treated epithelial cells from SARS-CoV-2 infected patients with SCFA-acetate.

Findings

In vitro pre-treatment of A549 cells with SCFA-acetate reduced RSV infection with clinical isolates and increased the expression of RIG-I and ISG15. Animals treated with SCFA-acetate intranasally recovered significantly faster, with reduction in the RSV clinical isolates viral load, and increased lung expression of IFNB1 and the RIG-I. Experiments in RIG-I knockout A549 cells demonstrated that the protection relies on RIG-I presence. Gut microbial profile was associated with bronchiolitis severity and with acetate in stool. Increased SCFA-acetate levels were associated with increasing oxygen saturation at admission, and shorter duration of fever. Ex-vivo treatment of patients’ respiratory cells with SCFA-acetate reduced RSV load and increased expression of ISGs OAS1 and ISG15, and virus recognition receptors MAVS and RIG-I, but not IFNB1. These SCFA-acetate effects were not found on cells from SARS-CoV-2 infected patients.

Interpretation

SCFA-acetate reduces the severity of RSV infection and RSV viral load through modulation of RIG-I expression.

Funding

FAPERGS (FAPERGS/MS/CNPq/SESRS no. 03/2017 - PPSUS 17/2551-0001380-8 and COVID-19 20/2551-0000258-6); CNPq 312504/2017-9; CAPES) - Finance Code 001.

Direct Lysis RT-qPCR of SARS-CoV-2 in Cell Culture Supernatant Allows for Fast and Accurate Quantification

Studying the entire virus replication cycle of SARS-CoV-2 is essential to identify the host factors involved and treatments to combat infection. Quantification of released virions often requires lengthy procedures, whereas quantification of viral RNA in supernatant is faster and applicable to clinical isolates. Viral RNA purification is expensive in terms of time and resources, and is often unsuitable for high-throughput screening. Direct lysis protocols were explored for patient swab samples, but the lack of virus inactivation, cost, sensitivity, and accuracy is hampering their application and usefulness for in vitro studies. Here, we show a highly sensitive, accurate, fast, and cheap direct lysis RT-qPCR method for quantification of SARS-CoV-2 in culture supernatant. This method inactivates the virus and permits detection limits of 0.043 TCID50 virus and <1.89 copy RNA template per reaction. Comparing direct lysis with RNA extraction, a mean difference of +0.69 ± 0.56 cycles was observed. Application of the method to established qPCR methods for RSV (-ve RNA), IAV (segmented -ve RNA), and BHV (dsDNA) showed wider applicability to other enveloped viruses, whereby IAV showed poorer sensitivity. This shows that accurate quantification of SARS-CoV-2 and other enveloped viruses can be achieved using direct lysis protocols, facilitating a wide range of high- and low-throughput applications.

Altered Differentiation and Inflammation Profiles Contribute to Enhanced Innate Responses in Severe COPD Epithelium to Rhinovirus Infection

Background

Respiratory viral infections are closely associated with COPD exacerbations, hospitalisations, and significant morbidity and mortality. The consequences of the persisting inflammation and differentiation status in virus associated severe disease is not fully understood. The aim of this study was to evaluate barrier function, cellular architecture, the inflammatory response in severe COPD bronchial epithelium to human rhinovirus (HRV) induced pathological changes and innate immune responses.

Methods

Well-differentiated primary bronchial epithelial cells (WD-PBECs) derived from severe COPD patients and age-matched healthy controls were cultured in the air-liquid interface (ALI) model. The differentiation phenotype, epithelial barrier integrity, pathological response and cytokine secreting profile of these cultures before and after HRV infection were investigated.

Results

WD-PBECs derived from severe COPD patients showed aberrant epithelium differentiation with a decreased proportion of ciliated cells but increased numbers of club cells and goblet cells compared with healthy controls. Tight junction integrity was compromised in both cultures following HRV infection, with heightened disruptions in COPD cultures. HRV induced increased epithelial cell sloughing, apoptosis and mucus hypersecretion in COPD cultures compared with healthy controls. A Th1/Th2 imbalance and a strong interferon and pro-inflammatory cytokine response was also observed in COPD cultures, characterized by increased levels of IFNγ, IFNβ, IP-10, IL-10 and decreased TSLP and IL-13 cytokine levels prior to HRV infection. Significantly enhanced basolateral secretion of eotaxin 3, IL-6, IL-8, GM-CSF were also observed in both mock and HRV infected COPD cultures compared with corresponding healthy controls. In response to HRV infection, all cultures displayed elevated levels of IFNλ1 (IL-29), IP-10 and TNFα compared with mock infected cultures. Interestingly, HRV infection dramatically reduced IFNλ levels in COPD cultures compared with healthy subjects.

Conclusion

An altered differentiation phenotype and cytokine response as seen in severe COPD WD-PBECs may contribute to increased disease susceptibility and an enhanced inflammatory response to HRV infection.

Neutrophil Extracellular Traps Do Not Induce Injury and Inflammation in Well-Differentiated RSV-Infected Airway Epithelium

Respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) causes a major burden of disease. The host response in RSV-LRTI is characterized by airway epithelial injury, inflammation and neutrophil influx, with the formation of neutrophil extracellular traps (NETs). However, the precise role of NETs in the pathophysiology of RSV-LRTI remains to be elucidated. Here, we used well-differentiated human airway epithelial cultures (HAE) of a pediatric and adult donor to study whether NETs cause airway epithelial injury and inflammation in the setting of RSV infection. The exposure of uninfected and RSV-infected HAE cultures to NETs, as produced by stimulation of neutrophils by a low dose of phorbol 12-myristate 13-acetate (PMA), did not induce or aggravate cell injury or inflammation. RSV infection of HAE cultures caused release of pro-inflammatory cytokines such as IL-6 and RANTES in both adult and pediatric cultures, but the differential gene expression for regulated cell death differed between culture donors. In this in vitro airway epithelial model, NETs in the setting of RSV infection did not cause or aggravate epithelial injury or inflammation.

Clinical and biological consequences of respiratory syncytial virus genetic diversity

Respiratory syncytial virus (RSV) is one of the most common etiological agents of global acute respiratory tract infections with a disproportionate burden among infants, individuals over the age of 65, and immunocompromised populations. The two major subtypes of RSV (A and B) co-circulate with a predominance of either group during different epidemic seasons, with frequently emerging genotypes due to RSV's high genetic variability. Global surveillance systems have improved our understanding of seasonality, disease burden, and genomic evolution of RSV through genotyping by sequencing of attachment (G) glycoprotein. However, the integration of these systems into international infrastructures is in its infancy, resulting in a relatively low number (~2200) of publicly available RSV genomes. These limitations in surveillance hinder our ability to contextualize RSV evolution past current canonical attachment glycoprotein (G)-oriented understanding, thus resulting in gaps in understanding of how genetic diversity can play a role in clinical outcome, therapeutic efficacy, and the host immune response. Furthermore, utilizing emerging RSV genotype information from surveillance and testing the impact of viral evolution using molecular techniques allows us to establish causation between the clinical and biological consequences of arising genotypes, which subsequently aids in informed vaccine design and future vaccination strategy. In this review, we aim to discuss the findings from current molecular surveillance efforts and the gaps in knowledge surrounding the consequence of RSV genetic diversity on disease severity, therapeutic efficacy, and RSV-host interactions.

An endogenously activated antiviral state restricts SARS-CoV-2 infection in differentiated primary airway epithelial cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the coronavirus disease-19 (COVID-19) pandemic, was identified in late 2019 and caused >5 million deaths by February 2022. To date, targeted antiviral interventions against COVID-19 are limited. The spectrum of SARS-CoV-2 infection ranges from asymptomatic to fatal disease. However, the reasons for varying outcomes to SARS-CoV-2 infection are yet to be elucidated. Here we show that an endogenously activated interferon lambda (IFNλ1) pathway leads to resistance against SARS-CoV-2 infection. Using a well-differentiated primary nasal epithelial cell (WD-PNEC) culture model derived from multiple adult donors, we discovered that susceptibility to SARS-CoV-2 infection, but not respiratory syncytial virus (RSV) infection, varied. One of four donors was resistant to SARS-CoV-2 infection. High baseline IFNλ1 expression levels and associated interferon stimulated genes correlated with resistance to SARS-CoV-2 infection. Inhibition of the JAK/STAT pathway in WD-PNECs with high endogenous IFNλ1 secretion resulted in higher SARS-CoV-2 titres. Conversely, prophylactic IFNλ treatment of WD-PNECs susceptible to infection resulted in reduced viral titres. An endogenously activated IFNλ response, possibly due to genetic differences, may be one explanation for the differences in susceptibility to SARS-CoV-2 infection in humans. Importantly, our work supports the continued exploration of IFNλ as a potential pharmaceutical against SARS-CoV-2 infection.

Immune Response to Viruses

Viruses are essentially, obligate intracellular parasites. They require a host to replicate their genetic material, spread to other cells, and eventually to other hosts. For humans, most viral infections are not considered lethal, regardless if at the cellular level, the virus can obliterate individual cells. Constant genomic mutations, (which can alter the antigenic content of viruses such as influenza or coronaviruses), zoonosis or immunosuppression/immunocompromisation, is when viruses achieve higher host mortality. Frequent examples of the severe consequenses of viral infection can be seen in children and the elderly. In most instances, the immune system will take a multifaceted approach in defending the host against viruses. Depending on the virus, the individual, and the point of entry, the immune system will initiate a robust response which involves multiple components. In this chapter, we expand on the total immune system, breaking it down to the two principal types: Innate and Adaptive Immunity, their different roles in viral recognition and clearance. Finally, how different viruses activate and evade different arms of the immune system.

In Vitro Modelling of Respiratory Virus Infections in Human Airway Epithelial Cells - A Systematic Review

Respiratory tract infections (RTI) are a major cause of morbidity and mortality in humans. A large number of RTIs is caused by viruses, often resulting in more severe disease in infants, elderly and the immunocompromised. Upon viral infection, most individuals experience common cold-like symptoms associated with an upper RTI. However, in some cases a severe and sometimes life-threatening lower RTI may develop. Reproducible and scalable in vitro culture models that accurately reflect the human respiratory tract are needed to study interactions between respiratory viruses and the host, and to test novel therapeutic interventions. Multiple in vitro respiratory cell culture systems have been described, but the majority of these are based on immortalized cell lines. Although useful for studying certain aspects of viral infections, such monomorphic, unicellular systems fall short in creating an understanding of the processes that occur at an integrated tissue level. Novel in vitro models involving primary human airway epithelial cells and, more recently, human airway organoids, are now in use. In this review, we describe the evolution of in vitro cell culture systems and their characteristics in the context of viral RTIs, starting from advances after immortalized cell cultures to more recently developed organoid systems. Furthermore, we describe how these models are used in studying virus-host interactions, e.g. tropism and receptor studies as well as interactions with the innate immune system. Finally, we provide an outlook for future developments in this field, including co-factors that mimic the microenvironment in the respiratory tract.

Human Respiratory Syncytial Virus Subgroup A and B Infections in Nasal, Bronchial, Small-Airway, and Organoid-Derived Respiratory Cultures

Human respiratory syncytial virus (HRSV) is the major cause of bronchiolitis and pneumonia in young infants and causes almost 200,000 deaths per year. Currently, there is no vaccine or treatment available, only a prophylactic monoclonal antibody (palivizumab).

Human respiratory syncytial virus (HRSV) is the leading cause of bronchiolitis in infants. Two subgroups of HRSV (A and B) routinely cocirculate. Most research has been performed with HRSV-A strains because these are easier to culture than HRSV-B strains. In this study, we aimed to compare the replicative fitness and HRSV-induced innate cytokine responses of HRSV-A and HRSV-B strains in disease-relevant cell culture models. We used two recombinant (r) clinical isolate-based HRSV strains (A11 and B05) and one recombinant laboratory-adapted HRSV strain (A2) to infect commercially available nasal, bronchial, and small-airway cultures. Epithelial cells from all anatomical locations were susceptible to HRSV infection despite the induction of a dominant type III interferon response. Subgroup A viruses disseminated and replicated faster than the subgroup B virus. Additionally, we studied HRSV infection and innate responses in airway organoids (AOs) cultured at air-liquid interface (ALI). Results were similar to the commercially obtained bronchial cells. In summary, we show that HRSV replicates well in cells from both the upper and the lower airways, with a slight replicative advantage for subgroup A viruses. Lastly, we showed that AOs cultured at ALI are a valuable model for studying HRSV ex vivo and that they can be used in the future to study factors that influence HRSV disease severity.

IMPORTANCE Human respiratory syncytial virus (HRSV) is the major cause of bronchiolitis and pneumonia in young infants and causes almost 200,000 deaths per year. Currently, there is no vaccine or treatment available, only a prophylactic monoclonal antibody (palivizumab). An important question in HRSV pathogenesis research is why only a fraction (1 to 3%) of infants develop severe disease. Model systems comprising disease-relevant HRSV isolates and accurate and reproducible cell culture models are indispensable to study infection, replication, and innate immune responses. Here, we used differentiated AOs cultured at ALI to model the human airways. Subgroup A viruses replicated better than subgroup B viruses, which we speculate fits with epidemiological findings that subgroup A viruses cause more severe disease in infants. By using AOs cultured at ALI, we present a highly relevant, robust, and reproducible model that allows for future studies into what drives severe HRSV disease.

Recombinant subtype A and B human respiratory syncytial virus clinical isolates co-infect the respiratory tract of cotton rats

Human respiratory syncytial virus (HRSV) is an important respiratory pathogen causing a spectrum of illness, from common cold-like symptoms, to bronchiolitis and pneumonia requiring hospitalization in infants, the immunocompromised and the elderly. HRSV exists as two antigenic subtypes, A and B, which typically cycle biannually in separate seasons. There are many unresolved questions in HRSV biology regarding the interactions and interplay of the two subtypes. Therefore, we generated a reverse genetics system for a subtype A HRSV from the 2011 season (A11) to complement our existing subtype B reverse genetics system. We obtained the sequence (HRSVA11) directly from an unpassaged clinical sample and generated the recombinant (r) HRSVA11. A version of the virus expressing enhanced green fluorescent protein (EGFP) from an additional transcription unit in the fifth (5) position of the genome, rHRSVA11EGFP(5), was also generated. rHRSVA11 and rHRSVA11EGFP(5) grew comparably in cell culture. To facilitate animal co-infection studies, we derivatized our subtype B clinical isolate using reverse genetics toexpress the red fluorescent protein (dTom)-expressing rHRSVB05dTom(5). These viruses were then used to study simultaneous in vivo co-infection of the respiratory tract. Following intranasal infection, both rHRSVA11EGFP(5) and rHRSVB05dTom(5) infected cotton rats targeting the same cell populations and demonstrating that co-infection occurs in vivo. The implications of this finding on viral evolution are important since it shows that inter-subtype cooperativity and/or competition is feasible in vivo during the natural course of the infection.

Antibody and Local Cytokine Response to Respiratory Syncytial Virus Infection in Community-Dwelling Older Adults

Respiratory syncytial virus (RSV) can cause severe morbidity and mortality in certain risk groups, especially infants and older adults. Currently no (prophylactic) treatment is available, except for a partially effective yet highly expensive monoclonal antibody. RSV therefore remains a major public health concern. To allow targeted development of novel vaccines and therapeutics, it is of great importance to understand the immunological mechanisms that underlie (protection from) severe disease in specific risk populations. Since most RSV-related studies focus on infants, there are only very limited data available concerning the response to RSV in the elderly population. Therefore, in this study, RSV-induced antibody responses and local cytokine secretion were assessed in community-dwelling older adults. These data provide novel insights that will benefit ongoing efforts to design safe and effective prevention and treatment strategies for RSV in an understudied risk group.

Respiratory syncytial virus (RSV) is increasingly recognized for causing severe morbidity and mortality in older adults, but there are few studies on the RSV-induced immune response in this population. Information on the immunological processes at play during RSV infection in specific risk groups is essential for the rational and targeted design of novel vaccines and therapeutics. Here, we assessed the antibody and local cytokine response to RSV infection in community-dwelling older adults (≥60 years of age). During three winters, serum and nasopharyngeal swab samples were collected from study participants during acute respiratory infection and recovery. RSV IgG enzyme-linked immunosorbent assays (ELISA) and virus neutralization assays were performed on serum samples from RSV-infected individuals (n = 41) and controls (n = 563 and n = 197, respectively). Nasal RSV IgA and cytokine concentrations were determined using multiplex immunoassays in a subset of participants. An in vitro model of differentiated primary bronchial epithelial cells was used to assess RSV-induced cytokine responses over time. A statistically significant increase in serum neutralization titers and IgG concentrations was observed in RSV-infected participants compared to controls. During acute RSV infection, a statistically significant local upregulation of beta interferon (IFN-β), IFN-λ1, IFN-γ, interleukin 1β (IL-1β), tumor necrosis factor alpha (TNF-α), IL-6, IL-10, CXCL8, and CXCL10 was found. IFN-β, IFN-λ1, CXCL8, and CXCL10 were also upregulated in the epithelial model upon RSV infection. In conclusion, this study provides novel insights into the basic immune response to RSV infection in an important and understudied risk population, providing leads for future studies that are essential for the prevention and treatment of severe RSV disease in older adults.

IMPORTANCE Respiratory syncytial virus (RSV) can cause severe morbidity and mortality in certain risk groups, especially infants and older adults. Currently no (prophylactic) treatment is available, except for a partially effective yet highly expensive monoclonal antibody. RSV therefore remains a major public health concern. To allow targeted development of novel vaccines and therapeutics, it is of great importance to understand the immunological mechanisms that underlie (protection from) severe disease in specific risk populations. Since most RSV-related studies focus on infants, there are only very limited data available concerning the response to RSV in the elderly population. Therefore, in this study, RSV-induced antibody responses and local cytokine secretion were assessed in community-dwelling older adults. These data provide novel insights that will benefit ongoing efforts to design safe and effective prevention and treatment strategies for RSV in an understudied risk group.

In vivo comparison of a laboratory-adapted and clinical-isolate-based recombinant human respiratory syncytial virus

Human respiratory syncytial virus (HRSV) is the leading cause of severe respiratory tract disease in infants. Most HRSV infections remain restricted to the upper respiratory tract (URT), but in a small percentage of patients the infection spreads to the lower respiratory tract, resulting in bronchiolitis or pneumonia. We have a limited understanding of HRSV pathogenesis and what factors determine disease severity, partly due to the widespread use of tissue-culture-adapted viruses. Here, we studied early viral dissemination and tropism of HRSV in cotton rats, BALB/cJ mice and C57BL/6 mice. We used a novel recombinant (r) strain based on a subgroup A clinical isolate (A11) expressing EGFP [rHRSV^A11EGFP(5)]. A recombinant laboratory-adapted HRSV strain [rHRSV^A2EGFP(5)] was used as a direct comparison. Our results show that rHRSV^A11EGFP(5) replicated to higher viral titres than laboratory-adapted rHRSV^A2EGFP(5) in the URT of cotton rats and mice. HRSV-infected cells were detected as early as 2 days post-inoculation in both species in the nasal septa and lungs. Infection was predominantly present in ciliated epithelial cells in cotton rats and in the olfactory mucosa of mice. In our opinion, this study highlights that the choice of virus strain is important when studying HRSV pathogenesis in vivo and demonstrates that A11 is a representative clinical-based virus. Additionally, we show critical differences in tropism and inflammation when comparing HRSV infection of cotton rats and mice.

The Secretome Profiling of a Pediatric Airway Epithelium Infected with hRSV Identified Aberrant Apical/Basolateral Trafficking and Novel Immune Modulating (CXCL6, CXCL16, CSF3) and Antiviral (CEACAM1) Proteins

The respiratory epithelium comprises polarized cells at the interface between the environment and airway tissues. Polarized apical and basolateral protein secretions are a feature of airway epithelium homeostasis. Human respiratory syncytial virus (hRSV) is a major human pathogen that primarily targets the respiratory epithelium. However, the consequences of hRSV infection on epithelium secretome polarity and content remain poorly understood. To investigate the hRSV-associated apical and basolateral secretomes, a proteomics approach was combined with an ex vivo pediatric human airway epithelial (HAE) model of hRSV infection (data are available via ProteomeXchange and can be accessed at https://www.ebi.ac.uk/pride/ with identifier PXD013661). Following infection, a skewing of apical/basolateral abundance ratios was identified for several individual proteins. Novel modulators of neutrophil and lymphocyte activation (CXCL6, CSF3, SECTM1 or CXCL16), and antiviral proteins (BST2 or CEACAM1) were detected in infected, but not in uninfected cultures. Importantly, CXCL6, CXCL16, CSF3 were also detected in nasopharyngeal aspirates (NPA) from hRSV-infected infants but not healthy controls. Furthermore, the antiviral activity of CEACAM1 against RSV was confirmed in vitro using BEAS-2B cells. hRSV infection disrupted the polarity of the pediatric respiratory epithelial secretome and was associated with immune modulating proteins (CXCL6, CXCL16, CSF3) never linked with this virus before. In addition, the antiviral activity of CEACAM1 against hRSV had also never been previously characterized. This study, therefore, provides novel insights into RSV pathogenesis and endogenous antiviral responses in pediatric airway epithelium.

Comparative primary paediatric nasal epithelial cell culture differentiation and RSV-induced cytopathogenesis following culture in two commercial media

The culture of differentiated human airway epithelial cells allows the study of pathogen-host interactions and innate immune responses in a physiologically relevant in vitro model. As the use of primary cell culture has gained popularity the availability of the reagents needed to generate these cultures has increased. In this study we assessed two different media, Promocell and PneumaCult, during the differentiation and maintenance of well-differentiated primary nasal epithelial cell cultures (WD-PNECs). We compared and contrasted the consequences of these media on WD-PNEC morphological and physiological characteristics and their responses to respiratory syncytial virus (RSV) infection. We found that cultures generated using PneumaCult resulted in greater total numbers of smaller, tightly packed, pseudostratified cells. However, cultures from both media resulted in similar proportions of ciliated and goblet cells. There were no differences in RSV growth kinetics, although more ciliated cells were infected in the PneumaCult cultures. There was also significantly more IL-29/IFNλ1 secreted from PneumaCult compared to Promocell cultures following infection. In conclusion, the type of medium used for the differentiation of primary human airway epithelial cells may impact experimental results.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

MEK inhibition drives anti-viral defence in RV but not RSV challenged human airway epithelial cells through AKT/p70S6K/4E-BP1 signalling

BACKGROUND

The airway epithelium is a major target tissue in respiratory infections, and its antiviral response is mainly orchestrated by the interferon regulatory factor-3 (IRF3), which subsequently induces type I (β) and III (λ) interferon (IFN) signalling. Dual specificity mitogen-activated protein kinase kinase (MEK) pathway contributes to epithelial defence, but its role in the regulation of IFN response in human primary airway epithelial cells (AECs) is not fully understood. Here, we studied the impact of a small-molecule inhibitor (MEKi) on the IFN response following challenge with two major respiratory viruses rhinovirus (RV2) and respiratory syncytial virus (RSVA2) and a TLR3 agonist, poly(I:C).

METHODS

The impact of MEKi on viral load and IFN response was evaluated in primary AECs with or without a neutralising antibody against IFN-β. Quantification of viral load was determined by live virus assay and absolute quantification using qRT-PCR. Secretion of cytokines was determined by AlphaLISA/ELISA and expression of interferon-stimulated genes (ISGs) was examined by qRT-PCR and immunoblotting. A poly(I:C) model was also used to further understand the molecular mechanism by which MEK controls IFN response. AlphaLISA, siRNA-interference, immunoblotting, and confocal microscopy was used to investigate the effect of MEKi on IRF3 activation and signalling. The impact of MEKi on ERK and AKT signalling was evaluated by immunoblotting and AlphaLISA.

RESULTS

Here, we report that pharmacological inhibition of MEK pathway augments IRF3-driven type I and III IFN response in primary human AECs. MEKi induced activation of PI3K-AKT pathway, which was associated with phosphorylation/inactivation of the translational repressor 4E-BP1 and activation of the protein synthesis regulator p70 S6 kinase, two critical translational effectors. Elevated IFN-β response due to MEKi was also attributed to decreased STAT3 activation, which consequently dampened expression of the transcriptional repressor of IFNB1 gene, PRDI-BF1. Augmented IFN response translated into inhibition of rhinovirus 2 replication in primary AECs but not respiratory syncytial virus A2.

CONCLUSIONS

Our findings unveil MEK as a key molecular mechanism by which rhinovirus dampens the epithelial cell's antiviral response. Our study provides a better understanding of the role of signalling pathways in shaping the antiviral response and suggests the use of MEK inhibitors in anti-viral therapy against RV.

A Contemporary View of Respiratory Syncytial Virus (RSV) Biology and Strain-Specific Differences

Respiratory syncytial virus (RSV) is a human respiratory pathogen which remains a leading viral cause of hospitalizations and mortality among infants in their first year of life. Here, we review the biology of RSV, the primary laboratory isolates or strains which have been used to best characterize the virus since its discovery in 1956, and discuss the implications for genetic and functional variations between the established laboratory strains and the recently identified clinical isolates.

A quantitative assessment of dynamical differences of RSV infections in vitro and in vivo

Experimental results in vitro and in animal models are used to guide researchers in testing vaccines or treatment in humans. However, viral kinetics are different in vitro, in animals, and in humans, so it is sometimes difficult to translate results from one system to another. In this study, we use a mathematical model to fit experimental data from multiple cycle respiratory syncytial virus (RSV) infections in vitro, in african green monkey (AGM), and in humans in order to quantitatively compare viral kinetics in the different systems. We find that there are differences in viral clearance rate, productively infectious cell lifespan, and eclipse phase duration between in vitro and in vivo systems and among different in vivo systems. We show that these differences in viral kinetics lead to different estimates of drug effectiveness of fusion inhibitors in vitro and in AGM than in humans.

An in vitro transepithelial migration assay to evaluate the role of neutrophils in Respiratory Syncytial Virus (RSV) induced epithelial damage

Large numbers of neutrophils migrate into the lungs of children with severe Respiratory Syncytial Virus (RSV) disease. It is unclear how these cells contribute to viral clearance and recovery from infection or whether they contribute to disease pathology. We have developed a novel in vitro model to study neutrophil migration through airway epithelial cells (AECs), the main cellular target of RSV infection. Our model reproduces a physiologically relevant cell polarity and directionality of neutrophil migration. Using this model, we found that RSV infected AECs induced rapid neutrophil transepithelial migration. We also detected increased AEC damage associated with RSV infection, with a further increase in epithelial cells shedding from the Transwell membrane following neutrophil migration. This was not observed in the mock infected controls. Neutrophils that migrated through the RSV infected AECs showed increased cell surface expression of CD11B and MPO compared to neutrophils that had not migrated. In conclusion, our in vitro co-culture assay can be used to identify critical mechanisms that mediate epithelial cell damage and promote inflammation in children with severe RSV disease.

A comparison of RSV and influenza in vitro kinetic parameters reveals differences in infecting time

Influenza and respiratory syncytial virus (RSV) cause acute infections of the respiratory tract. Since the viruses both cause illnesses with similar symptoms, researchers often try to apply knowledge gleaned from study of one virus to the other virus. This can be an effective and efficient strategy for understanding viral dynamics or developing treatment strategies, but only if we have a full understanding of the similarities and differences between the two viruses. This study used mathematical modeling to quantitatively compare the viral kinetics of in vitro RSV and influenza virus infections. Specifically, we determined the viral kinetics parameters for RSV A2 and three strains of influenza virus, A/WSN/33 (H1N1), A/Puerto Rico/8/1934 (H1N1), and pandemic H1N1 influenza virus. We found that RSV viral titer increases at a slower rate and reaches its peak value later than influenza virus. Our analysis indicated that the slower increase of RSV viral titer is caused by slower spreading of the virus from one cell to another. These results provide estimates of dynamical differences between influenza virus and RSV and help provide insight into the virus-host interactions that cause observed differences in the time courses of the two illnesses in patients.

Conditional reprogramming of pediatric airway epithelial cells: A new human model to investigate early-life respiratory disorders

BACKGROUND

Airway epithelial cells (AEC) are quite difficult to access in newborns and infants. It is critically important to develop robust life-extended models to conduct translational studies in this age group. We propose the use of a recently described cell culture technology (conditionally reprogrammed cells-CRC) to generate continuous primary cell cultures from nasal and bronchial AEC of young children.

METHODS

We collected nasal and/or bronchial AEC from a total of 23 subjects of different ages including newborns/infants/toddlers (0-2 years; N = 9), school-age children (4-11 years; N = 6), and a group of adolescent/adult donors (N = 8). For CRC generation, we used conditioned medium from mitotically inactivated 3T3 fibroblasts and Rho-associated kinase (ROCK) inhibitor (Y-27632). Antiviral immune responses were studied using 25 key antiviral genes and protein production of type III epithelial interferon (IFN λ1) after double-stranded (ds) RNA exposure.

RESULTS

CRC derived from primary AEC of neonates/infants and young children exhibited: (i) augmented proliferative capacity and life extension, (ii) preserved airway epithelial phenotype after multiple passages, (iii) robust immune responses characterized by the expression of innate antiviral genes and parallel nasal/bronchial production of IFN λ1 after exposure to dsRNA, and (iv) induction of airway epithelial inflammatory and remodeling responses to dsRNA (eg, CXCL8 and MMP9).

CONCLUSION

Conditional reprogramming of AEC from young children is a feasible and powerful translational approach to investigate early-life airway epithelial immune responses in humans.

Distinct patterns of innate immune activation by clinical isolates of respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major respiratory pathogen of infants and young children. Multiple strains of both subgroup A and B viruses circulate during each seasonal epidemic. Genetic heterogeneity among RSV genomes, in large part due to the error prone RNA-dependent, RNA polymerase, could mediate variations in pathogenicity. We evaluated clinical strains of RSV for their ability to induce the innate immune response. Subgroup B viruses were used to infect human pulmonary epithelial cells (A549) and primary monocyte-derived human macrophages (MDM) from a variety of donors. Secretions of IL-6 and CCL5 (RANTES) from infected cells were measured following infection. Host and viral transcriptome expression were assessed using RNA-SEQ technology and the genomic sequences of several clinical isolates were determined. There were dramatic differences in the induction of IL-6 and CCL5 in both A549 cells and MDM infected with a variety of clinical isolates of RSV. Transcriptome analyses revealed that the pattern of innate immune activation in MDM was virus-specific and host-specific. Specifically, viruses that induced high levels of secreted IL-6 and CCL5 tended to induce cellular innate immune pathways whereas viruses that induced relatively low level of IL-6 or CCL5 did not induce or suppressed innate immune gene expression. Activation of the host innate immune response mapped to variations in the RSV G gene and the M2-1 gene. Viral transcriptome data indicated that there was a gradient of transcription across the RSV genome though in some strains, RSV G was the expressed in the highest amounts at late times post-infection. Clinical strains of RSV differ in cytokine/chemokine induction and in induction and suppression of host genes expression suggesting that these viruses may have inherent differences in virulence potential. Identification of the genetic elements responsible for these differences may lead to novel approaches to antiviral agents and vaccines.

Broad-Spectrum Inhibition of Respiratory Virus Infection by MicroRNA Mimics Targeting p38 MAPK Signaling

The majority of antiviral therapeutics target conserved viral proteins, however, this approach confers selective pressure on the virus and increases the probability of antiviral drug resistance. An alternative therapeutic strategy is to target the host-encoded factors that are required for virus infection, thus minimizing the opportunity for viral mutations that escape drug activity. MicroRNAs (miRNAs) are small noncoding RNAs that play diverse roles in normal and disease biology, and they generally operate through the post-transcriptional regulation of mRNA targets. We have previously identified cellular miRNAs that have antiviral activity against a broad range of herpesvirus infections, and here we extend the antiviral profile of a number of these miRNAs against influenza and respiratory syncytial virus. From these screening experiments, we identified broad-spectrum antiviral miRNAs that caused >75% viral suppression in all strains tested, and we examined their mechanism of action using reverse-phase protein array analysis. Targets of lead candidates, miR-124, miR-24, and miR-744, were identified within the p38 mitogen-activated protein kinase (MAPK) signaling pathway, and this work identified MAPK-activated protein kinase 2 as a broad-spectrum antiviral target required for both influenza and respiratory syncytial virus (RSV) infection.

Human Metapneumovirus Impairs Apoptosis of Nasal Epithelial Cells in Asthma via HSP70

Asthmatics are highly susceptible to respiratory viral infections, possibly due to impaired innate immunity. However, the exact mechanisms of susceptibility are likely to differ amongst viruses. Therefore, we infected primary nasal epithelial cells (NECs) from adults with mild-to-moderate asthma, with respiratory syncytial virus (RSV) or human metapneumovirus (hMPV) in vitro and investigated the antiviral response. NECs from these asthmatics supported elevated hMPV but not RSV infection, compared to non-asthmatic controls. This correlated with reduced apoptosis and reduced activation of caspase-9 and caspase-3/7 in response to hMPV, but not RSV. The expression of heat shock protein 70 (HSP70), a known inhibitor of caspase activation and subsequent apoptosis, was amplified in response to hMPV infection. Chemical inhibition of HSP70 function restored caspase activation and reduced hMPV infection in NECs from asthmatic subjects. There was no impairment in the production of IFN by NECs from asthmatics in response to either hMPV or RSV, demonstrating that increased infection of asthmatic airway cells by hMPV is IFN-independent. This study demonstrates, for the first time, a mechanism for elevated hMPV infection in airway epithelial cells from adult asthmatics and identifies HSP70 as a potential target for antiviral and asthma therapies.

Ferrets as a Novel Animal Model for Studying Human Respiratory Syncytial Virus Infections in Immunocompetent and Immunocompromised Hosts

Human respiratory syncytial virus (HRSV) is an important cause of severe respiratory tract disease in immunocompromised patients. Animal models are indispensable for evaluating novel intervention strategies in this complex patient population. To complement existing models in rodents and non-human primates, we have evaluated the potential benefits of an HRSV infection model in ferrets (Mustela putorius furo). Nine- to 12-month-old HRSV-seronegative immunocompetent or immunocompromised ferrets were infected with a low-passage wild-type strain of HRSV subgroup A (10⁵ TCID₅₀) administered by intra-tracheal or intra-nasal inoculation. Immune suppression was achieved by bi-daily oral administration of tacrolimus, mycophenolate mofetil, and prednisolone. Throat and nose swabs were collected daily and animals were euthanized four, seven, or 21 days post-infection (DPI). Virus loads were determined by quantitative virus culture and qPCR. We observed efficient HRSV replication in both the upper and lower respiratory tract. In immunocompromised ferrets, virus loads reached higher levels and showed delayed clearance as compared to those in immunocompetent animals. Histopathological evaluation of animals euthanized 4 DPI demonstrated that the virus replicated in the respiratory epithelial cells of the trachea, bronchi, and bronchioles. These animal models can contribute to an assessment of the efficacy and safety of novel HRSV intervention strategies.

Generation and Characterization of ALX-0171, a Potent Novel Therapeutic Nanobody for the Treatment of Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is an important causative agent of lower respiratory tract infections in infants and elderly individuals. Its fusion (F) protein is critical for virus infection. It is targeted by several investigational antivirals and by palivizumab, a humanized monoclonal antibody used prophylactically in infants considered at high risk of severe RSV disease. ALX-0171 is a trimeric Nanobody that binds the antigenic site II of RSV F protein with subnanomolar affinity. ALX-0171 demonstrated in vitro neutralization superior to that of palivizumab against prototypic RSV subtype A and B strains. Moreover, ALX-0171 completely blocked replication to below the limit of detection for 87% of the viruses tested, whereas palivizumab did so for 18% of the viruses tested at a fixed concentration. Importantly, ALX-0171 was highly effective in reducing both nasal and lung RSV titers when delivered prophylactically or therapeutically directly to the lungs of cotton rats. ALX-0171 represents a potent novel antiviral compound with significant potential to treat RSV-mediated disease.

Human Respiratory Syncytial Virus: Role of Innate Immunity in Clearance and Disease Progression

Human respiratory syncytial virus (HRSV) infections have worldwide records. The virus is responsible for bronchiolitis, pneumonia, and asthma in humans of different age groups. Premature infants, young children, and immunocompromised individuals are prone to severe HRSV infection that may lead to death. Based on worldwide estimations, millions of cases were reported in both developed and developing countries. In fact, HRSV symptoms develop mainly as a result of host immune response. Due to inability to establish long lasting adaptive immunity, HRSV infection is recurrent and hence impairs vaccine development. Once HRSV attached to the airway epithelia, interaction with the host innate immune components starts. HRSV interaction with pulmonary innate defenses is crucial in determining the disease outcome. Infection of alveolar epithelial cells triggers a cascade of events that lead to recruitment and activation of leukocyte populations. HRSV clearance is mediated by a number of innate leukocytes, including macrophages, natural killer cells, eosinophils, dendritic cells, and neutrophils. Regulation of these cells is mediated by cytokines, chemokines, and other immune mediators. Although the innate immune system helps to clear HRSV infection, it participates in disease progression such as bronchiolitis and asthma. Resolving the mechanisms by which HRSV induces pathogenesis, different possible interactions between the virus and immune components, and immune cells interplay are essential for developing new effective vaccines. Therefore, the current review focuses on how the pulmonary innate defenses mediate HRSV clearance and to what extent they participate in disease progression. In addition, immune responses associated with HRSV vaccines will be discussed.

Induction and Antagonism of Antiviral Responses in Respiratory Syncytial Virus-Infected Pediatric Airway Epithelium

Airway epithelium is the primary target of many respiratory viruses. However, virus induction and antagonism of host responses by human airway epithelium remains poorly understood. To address this, we developed a model of respiratory syncytial virus (RSV) infection based on well-differentiated pediatric primary bronchial epithelial cell cultures (WD-PBECs) that mimics hallmarks of RSV disease in infants. RSV is the most important respiratory viral pathogen in young infants worldwide. We found that RSV induces a potent antiviral state in WD-PBECs that was mediated in part by secreted factors, including interferon lambda 1 (IFN-λ1)/interleukin-29 (IL-29). In contrast, type I IFNs were not detected following RSV infection of WD-PBECs. IFN responses in RSV-infected WD-PBECs reflected those in lower airway samples from RSV-hospitalized infants. In view of the prominence of IL-29, we determined whether recombinant IL-29 treatment of WD-PBECs before or after infection abrogated RSV replication. Interestingly, IL-29 demonstrated prophylactic, but not therapeutic, potential against RSV. The absence of therapeutic potential reflected effective RSV antagonism of IFN-mediated antiviral responses in infected cells. Our data are consistent with RSV nonstructural proteins 1 and/or 2 perturbing the Jak-STAT signaling pathway, with concomitant reduced expression of antiviral effector molecules, such as MxA/B. Antagonism of Jak-STAT signaling was restricted to RSV-infected cells in WD-PBEC cultures. Importantly, our study provides the rationale to further explore IL-29 as a novel RSV prophylactic.

IMPORTANCE

Most respiratory viruses target airway epithelium for infection and replication, which is central to causing disease. However, for most human viruses we have a poor understanding of their interactions with human airway epithelium. Respiratory syncytial virus (RSV) is the most important viral pathogen of young infants. To help understand RSV interactions with pediatric airway epithelium, we previously developed three-dimensional primary cell cultures from infant bronchial epithelium that reproduce several hallmarks of RSV infection in infants, indicating that they represent authentic surrogates of RSV infection in infants. We found that RSV induced a potent antiviral state in these cultures and that a type III interferon, interleukin IL-29 (IL-29), was involved. Indeed, our data suggest that IL-29 has potential to prevent RSV disease. However, we also demonstrated that RSV efficiently circumvents this antiviral immune response and identified mechanisms by which this may occur. Our study provides new insights into RSV interaction with pediatric airway epithelium.

Activation of the Mitochondrial Apoptotic Signaling Platform during Rubella Virus Infection

Mitochondria- as well as p53-based signaling pathways are central for the execution of the intrinsic apoptotic cascade. Their contribution to rubella virus (RV)-induced apoptosis was addressed through time-specific evaluation of characteristic parameters such as permeabilization of the mitochondrial membrane and subsequent release of the pro-apoptotic proteins apoptosis-inducing factor (AIF) and cytochrome c from mitochondria. Additionally, expression and localization pattern of p53 and selected members of the multifunctional and stress-inducible cyclophilin family were examined. The application of pifithrin μ as an inhibitor of p53 shuttling to mitochondria reduced RV-induced cell death to an extent similar to that of the broad spectrum caspase inhibitor z-VAD-fmk (benzyloxycarbonyl-V-A-D-(OMe)-fmk). However, RV progeny generation was not altered. This indicates that, despite an increased survival rate of its cellular host, induction of apoptosis neither supports nor restricts RV replication. Moreover, some of the examined apoptotic markers were affected in a strain-specific manner and differed between the cell culture-adapted strains: Therien and the HPV77 vaccine on the one hand, and a clinical isolate on the other. In summary, the results presented indicate that the transcription-independent mitochondrial p53 program contributes to RV-induced apoptosis.

Viral Specific Factors Contribute to Clinical Respiratory Syncytial Virus Disease Severity Differences in Infants

Background

There is a wide range of severity of respiratory syncytial viral (RSV) disease in previously healthy infants. Host factors have been well demonstrated to contribute to disease severity differences. However the possibility of disease severity differences being produced by factors intrinsic to the virus itself has rarely been studied.

Methods

Low-passage isolates of RSV collected prospectively from infants with different degrees of RSV disease severity were evaluated in vitro, holding host factors constant, so as to assess whether isolates induced phenotypically different cytokine/chemokine concentrations in a human lung epithelial cell line. Sixty-seven RSV isolates from previously healthy infants (38 hospitalized for acute RSV infection (severe disease) and 29 never requiring hospitalization (mild disease)) were inoculated into A549, lung epithelial cells at precisely controlled, low multiplicity of infection to mimic natural infection. Cultures were evaluated at 48 hours, 60 hours, and 72 hours to evaluate area under the curve (AUC) cytokine/chemokine induction.

Results

Cells infected with isolates from severely ill infants produced higher mean concentrations of all cytokine/chemokines tested (IL-1α, IL-6, IL-8 and RANTES) at all-time points tested. RSV isolates collected from infants with severe disease induced significantly higher AUCIL-8 and AUCRANTES secretion in infected cultures than mild disease isolates (p=0.028 and p=0.019 respectively). IL-8 and RANTES concentrations were 4 times higher at 48 hours for these severely ill infant isolates. Additionally, 38 isolates were evaluated at all-time points for quantity of virus. RSV concentration significantly correlated with both IL-8 and RANTES at all-time points. Neither cytokine/chemokine concentrations nor RSV concentrations were associated with RSV subgroup.

Discussion

Infants’ RSV disease severity differences may be due in part to intrinsic viral strain-specific characteristics.

CX3CR1 is an important surface molecule for respiratory syncytial virus infection in human airway epithelial cells

Respiratory syncytial virus (RSV) is a major cause of severe pneumonia and bronchiolitis in infants and young children, and causes disease throughout life. Understanding the biology of infection, including virus binding to the cell surface, should help develop antiviral drugs or vaccines. The RSV F and G glycoproteins bind cell surface heparin sulfate proteoglycans (HSPGs) through heparin-binding domains. The G protein also has a CX3C chemokine motif which binds to the fractalkine receptor CX3CR1. G protein binding to CX3CR1 is not important for infection of immortalized cell lines, but reportedly is so for primary human airway epithelial cells (HAECs), the primary site for human infection. We studied the role of CX3CR1 in RSV infection with CX3CR1-transfected cell lines and HAECs with variable percentages of CX3CR1-expressing cells, and the effect of anti-CX3CR1 antibodies or a mutation in the RSV CX3C motif. Immortalized cells lacking HSPGs had low RSV binding and infection, which was increased markedly by CX3CR1 transfection. CX3CR1 was expressed primarily on ciliated cells, and ∼50 % of RSV-infected cells in HAECs were CX3CR1+. HAECs with more CX3CR1-expressing cells had a proportional increase in RSV infection. Blocking G binding to CX3CR1 with anti-CX3CR1 antibody or a mutation in the CX3C motif significantly decreased RSV infection in HAECs. The kinetics of cytokine production suggested that the RSV/CX3CR1 interaction induced RANTES (regulated on activation normal T-cell expressed and secreted protein), IL-8 and fractalkine production, whilst it downregulated IL-15, IL1-RA and monocyte chemotactic protein-1. Thus, the RSV G protein/CX3CR1 interaction is likely important in infection and infection-induced responses of the airway epithelium, the primary site of human infection.

CX3CR1 Is Expressed in Differentiated Human Ciliated Airway Cells and Co-Localizes with Respiratory Syncytial Virus on Cilia in a G Protein-Dependent Manner

Respiratory syncytial virus (RSV) is the principal cause of bronchiolitis in infants and a significant healthcare problem. The RSV Glycoprotein (G) mediates attachment of the virus to the cell membrane, which facilitates interaction of the RSV Fusion (F) protein with nucleolin, thereby triggering fusion of the viral and cellular membranes. However, a host protein ligand for G has not yet been identified. Here we show that CX3CR1 is expressed in the motile cilia of differentiated human airway epithelial (HAE) cells, and that CX3CR1 co-localizes with RSV particles. Upon infection, the distribution of CX3CR1 in these cells is significantly altered. Complete or partial deletion of RSV G results in viruses binding at least 72-fold less efficiently to cells, and reduces virus replication. Moreover, an antibody targeting an epitope near the G protein’s CX3CR1-binding motif significantly inhibits binding of the virus to airway cells. Given previously published evidence of the interaction of G with CX3CR1 in human lymphocytes, these findings suggest a role for G in the interaction of RSV with ciliated lung cells. This interpretation is consistent with past studies showing a protective benefit in immunizing against G in animal models of RSV infection, and would support targeting the CX3CR1-G protein interaction for prophylaxis or therapy. CX3CR1 expression in lung epithelial cells may also have implications for other respiratory diseases such as asthma.

Human parainfluenza virus type 3 (HPIV3) induces production of IFNγ and RANTES in human nasal epithelial cells (HNECs)

Background

Human parainfluenza virus type 3 (HPIV3), while infecting lower airway epithelial cells induces pneumonia and bronchiolitis in infants and children, and may lead to asthma exacerbations in children and adults. Respiratory viruses invading the airway epithelium activate innate immune response and induce inflammatory cytokine release contributing to the pathophysiology of upper and lower airway disorders. However, the effects of HPIV3 infection on nasal epithelial cells have not been well defined.

The aim of this study was to evaluate the effect of the HPIV3 infection on cultured human nasal epithelial cells (HNECs) and the release of interferon gamma and other cytokines.

Methods

RPMI 2650, a human nasal epithelial cell line was cultured into confluence and was infected with HPIV3 (MOI of 0.1, 0.01 and 0.001). The protein release into supernatants and mRNA expression of selected cytokines were assessed 24, 48 and 72 h after infection. Cytokine concentrations in supernatants were measured by ELISA and expression of cytokine mRNA in RPMI 2650 cells confirmed by real time RT-PCR analysis.

Results

HNECs infection with HPIV3 did not induce cytotoxicity for at least 48 hours, but significantly increased IFN-γ protein concentration in the cell supernatants at 24 h and 48 h post infection (by 387% and 485% respectively as compared to mock infected cells). At 24 h a significant increase in expression of mRNA for IFNγ was observed. RANTES protein concentration and mRNA expression were significantly increased at 72 h after infection (mean protein concentration: 3.5 ± 1.4 pg/mL for 0.001 MOI, 10.8 ± 4.6 pg/mL for 0.01 MOI and 61.5 ± 18.4 pg/mL for 0.1 MOI as compared to 2.4 ± 1.3 pg/mL for uninfected cells). No measurable concentrations of TNF-α, IL-10, TSLP, IL-8, GM-CSF or eotaxin, were detected in virus infected cells supernatants.

Conclusions

HPIV3 effectively infects upper airway epithelial cells and the infection is associated with induction of IFN-γ and generation of RANTES.

Respiratory syncytial virus (RSV) and its propensity for causing bronchiolitis

Infants and young children with acute onset of wheezing and reduced respiratory airflows are often diagnosed with obstruction and inflammation of the small bronchiolar airways, ie bronchiolitis. The most common aetological agents causing bronchiolitis in young children are the respiratory viruses, and of the commonly encountered respiratory viruses, respiratory syncytial virus (RSV) has a propensity for causing bronchiolitis. Indeed, RSV bronchiolitis remains the major reason why previously healthy infants are admitted to hospital. Why RSV infection is such a predominant cause of bronchiolitis is the subject of this review. By reviewing the available histopathology of RSV bronchiolitis, both in humans and relevant animal models, we identify hallmark features of RSV infection of the distal airways and focus attention on the consequences of columnar cell cytopathology occurring in the bronchioles, which directly impacts the development of bronchiolar obstruction, inflammation and disease. Copyright © 2014 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Proteomic analysis of mitochondria in respiratory epithelial cells infected with human respiratory syncytial virus and functional implications for virus and cell biology

OBJECTIVES

The aim of this study was to quantitatively characterise the mitochondrial proteome of airway epithelial cells infected with human respiratory syncytial virus (HRSV), a major cause of paediatric illness.

METHODS

Quantitative proteomics, underpinned by stable isotope labelling with amino acids in cell culture, coupled to LC-MS/MS, was applied to mitochondrial fractions prepared from HRSV-infected and mock-infected cells 12 and 24 h post-infection. Datasets were analysed using ingenuity pathway analysis, and the results were validated and characterised using bioimaging, targeted inhibition and gene depletion.

KEY FINDINGS

The data quantitatively indicated that antiviral signalling proteins converged on mitochondria during HRSV infection. The mitochondrial receptor protein Tom70 was found to act in an antiviral manner, while its chaperone, Hsp90, was confirmed to be a positive viral factor. Proteins associated with different organelles were also co-enriched in the mitochondrial fractions from HRSV-infected cells, suggesting that alterations in organelle dynamics and membrane associations occur during virus infection.

CONCLUSIONS

Protein and pathway-specific alterations occur to the mitochondrial proteome in a spatial and temporal manner during HRSV infection, suggesting that this organelle may have altered functions. These could be targeted as part of potential therapeutic strategies to disrupt virus biology.

Immunity to RSV in Early-Life

Respiratory Syncytial Virus (RSV) is the commonest cause of severe respiratory infection in infants, leading to over 3 million hospitalizations and around 66,000 deaths worldwide each year. RSV bronchiolitis predominantly strikes apparently healthy infants, with age as the principal risk factor for severe disease. The differences in the immune response to RSV in the very young are likely to be key to determining the clinical outcome of this common infection. Remarkable age-related differences in innate cytokine responses follow recognition of RSV by numerous pattern recognition receptors, and the importance of this early response is supported by polymorphisms in many early innate genes, which associate with bronchiolitis. In the absence of strong, Th1 polarizing signals, infants develop T cell responses that can be biased away from protective Th1 and cytotoxic T cell immunity toward dysregulated, Th2 and Th17 polarization. This may contribute not only to the initial inflammation in bronchiolitis, but also to the long-term increased risk of developing wheeze and asthma later in life. An early-life vaccine for RSV will need to overcome the difficulties of generating a protective response in infants, and the proven risks associated with generating an inappropriate response. Infantile T follicular helper and B cell responses are immature, but maternal antibodies can afford some protection. Thus, maternal vaccination is a promising alternative approach. However, even in adults adaptive immunity following natural infection is poorly protective, allowing re-infection even with the same strain of RSV. This gives us few clues as to how effective vaccination could be achieved. Challenges remain in understanding how respiratory immunity matures with age, and the external factors influencing its development. Determining why some infants develop bronchiolitis should lead to new therapies to lessen the clinical impact of RSV and aid the rational design of protective vaccines.

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.

Rapid spread of the novel respiratory syncytial virus A ON1 genotype, central Italy, 2011 to 2013

Respiratory infections positive for human respiratory syncytial virus (RSV) subtype A were characterised in children admitted to hospitals in Rome and Ancona (Italy) over the last three epidemic seasons. Different strains of the novel RSV-A genotype ON1, first identified in Ontario (Canada) in December 2010, were detected for the first time in Italy in the following 2011/12 epidemic season. They bear an insertion of 24 amino acids in the G glycoprotein as well as amino acid changes likely to change antigenicity. By early 2013, ON1 strains had spread so efficiently that they had nearly replaced other RSV-A strains. Notably, the RSV peak in the 2012/13 epidemic season occurred earlier and, compared with the previous two seasons, influenza-like illnesses diagnoses were more frequent in younger children; bronchiolitis cases had a less severe clinical course. Nonetheless, the ON1-associated intensive care unit admission rate was similar, if not greater, than that attributable to other RSV-A strains. Improving RSV surveillance would allow timely understanding of the epidemiological and clinicopathological features of the novel RSV-A genotype.

The impact of viral genotype on pathogenesis and disease severity: respiratory syncytial virus and human rhinoviruses

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection (LRI) and viral death in infants. RSV disease in infants is characterized by epithelial desquamation, neutrophilic bronchiolitis and pneumonia and obstructive pulmonary mucus. Human rhinoviruses (HRVs) are by far the most common cause of symptomatic upper respiratory tract infection (URI) in people and are more recently appreciated as a significant cause of LRI. RSV and HRV are also implicated in asthma pathogenesis. Within both RSV and HRV, viral genetic differences play a role in disease severity and/or prevalence in patient populations, and viral genetic differences affect pathogenesis. Here, we review data on how viral genetic differences impact disease using RSV and HRV as examples, including effects on the host immune response. Virus genotype–phenotype relationships can be exploited in the laboratory to gain insight into mechanisms by which respiratory viruses modulate host immune responses and cause disease.

Relative respiratory syncytial virus cytopathogenesis in upper and lower respiratory tract epithelium

RATIONALE

Respiratory syncytial virus (RSV) is a major pathogen that primarily infects airway epithelium. Most infants suffer mild upper respiratory tract (URT) symptoms, whereas approximately one-third progress to lower respiratory tract (LRT) involvement. Despite the ubiquity of URT infection, little is known about the relative cytopathogenesis of RSV infection in infant URT and LRT.

OBJECTIVES

This study aimed to compare RSV cytopathogenesis in nasal- and bronchial-derived epithelium from the same individuals using novel models derived from well-differentiated primary pediatric nasal (WD-PNECs) and bronchial epithelial cells (WD-PBECs).

METHODS

WD-PNECs and WD-PBECs were generated from nasal and bronchial brushes, respectively, and mock-infected or infected with RSV BT2a. RSV tropism, infectivity, cytopathology, growth kinetics, cell sloughing, apoptosis, and cytokine and chemokine responses were determined.

MEASUREMENTS AND MAIN RESULTS

RSV infection in both cultures was restricted to apical ciliated cells and occasional nonciliated cells but not goblet cells. It did not cause gross cytopathology. Infection resulted in apical release of progeny virus, increased apical cell sloughing, apoptosis, and occasional syncytia. RSV growth kinetics and peak titers were higher in WD-PBECs, coincident with higher ciliated cell contents, cell sloughing, and slightly compromised tight junctions. However, proinflammatory chemokine responses were similar for both cultures. Also, lambda IFNs, especially IL-29, were induced by RSV infection.

CONCLUSIONS

RSV induced remarkably similar, albeit quantitatively lower, cytopathogenesis and proinflammatory responses in WD-PNECs compared with WD-PBECs that reproduce many hallmarks of RSV pathogenesis in infants. WD-PNECs may provide an authentic surrogate model with which to study RSV cytopathogenesis in infant airway epithelium.

Pathogen recognition receptor crosstalk in respiratory syncytial virus sensing: a host and cell type perspective

Human respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infection in young children, immunocompromised adults, and the elderly. The innate immune response plays a pivotal role in host defense against RSV, but whether severe outcomes following RSV infection result from excessive or poor innate immune recognition remains unclear. Recent research suggests a situation in which crosstalk between families of pattern recognition receptors (PRRs) occurs in a cell type-dependent manner. The current challenge to empower novel therapeutic approaches and vaccine development is to confirm the role of the individual receptors in RSV pathogenesis in humans.

Respiratory syncytial virus vaccine development

The importance of RSV as a respiratory pathogen in young children made it a priority for vaccine development shortly after it was discovered. Unfortunately, after over 50 years of vaccine development no vaccine has yet been licensed and it is not certain which if any vaccines being developed will be successful. The first candidate vaccine, a formalin inactivated RSV vaccine (FI-RSV), was tested in children in the 1960s and predisposed young recipients to more serious disease with later natural infection. The ongoing challenges in developing RSV vaccines are balanced by advances in our understanding of the virus, the host immune response to vaccines and infection, and pathogenesis of disease. It seems likely that with efficient and appropriately focused effort a safe and effective vaccine is within reach. There are at least 4 different target populations for an RSV vaccine, i.e. the RSV naïve young infant, the RSV naïve infant >4-6 months of age, pregnant women, and elderly adults. Each target population has different issues related to vaccine development. Numerous vaccines from live attenuated RSV to virus like particle vaccines have been developed and evaluated in animals. Very few vaccines have been studied in humans and studies in humans are needed to determine which vaccines are worth moving toward licensure. Some changes in the approach may improve the efficiency of evaluating candidate vaccines. The complexity of the challenges for developing RSV vaccines suggests that collaboration among academic, government, and funding institutions and industry is needed to most efficiently achieve an RSV vaccine.

Mechanisms of respiratory syncytial virus modulation of airway immune responses

Respiratory syncytial virus (RSV) most often causes severe respiratory disease in the very young and the elderly. Acute disease can also cause exacerbations of asthma in any age group. Recent findings provide insight into how the innate and adaptive immune systems respond to RSV infection and provide preliminary evidence that these effects vary significantly by RSV strain and host. Components of cell signaling pathways that induce inflammatory cytokine expression during the innate immune response and alter epithelial cell polarity through activating transcription factors, namely NF-κB, are now more clearly understood. New studies also reveal how RSV infection skews T helper (Th) cell differentiation away from the cell-mediated Th1 subset and towards the Th2 subset. There are also new data supporting preferential Th17 differentiation during RSV infection. In addition, effective immune system regulation of IL-10 expression and T regulatory cell (Treg) airway accumulation are essential for effective RSV clearance.

Respiratory syncytial virus interaction with human airway epithelium

Although respiratory syncytial virus (RSV) is a major human respiratory pathogen, our knowledge of how it causes disease in humans is limited. Airway epithelial cells are the primary targets of RSV infection in vivo, so the generation and exploitation of RSV infection models based on morphologically and physiologically authentic well-differentiated primary human airway epithelial cells cultured at an air-liquid interface (WD-PAECs) provide timely developments that will help to bridge this gap. Here we review the interaction of RSV with WD-PAEC cultures, the authenticity of the RSV-WD-PAEC models relative to RSV infection of human airway epithelium in vivo, and future directions for their exploitation in our quest to understand RSV pathogenesis in humans.

Development of asthma is determined by the age-dependent host response to respiratory virus infection: therapeutic implications

Lower respiratory tract virus infections are the major cause of asthma exacerbations. Severity of infection and age at initial encounter with virus appear to be major determinants of the risk for allergic asthma later in life. In animal models, reinfection of mice initially infected as neonates leads to markedly enhanced alterations in airway function and inflammation, unlike reinfection of older mice. Both innate and adaptive immune responses contribute to this susceptibility with lung dendritic cells showing marked differences in phenotype and function in young compared to older mice, and these differences are further enhanced following virus infection. These findings have implications for therapeutic targeting, for example, of RSV G and F surface proteins at different stages of the response to infection.

Induction of IL-6 and CCL5 (RANTES) in human respiratory epithelial (A549) cells by clinical isolates of respiratory syncytial virus is strain specific

BACKGROUND

Respiratory syncytial virus (RSV) is the major respiratory pathogen of infants and young children. During each seasonal epidemic, multiple strains of both subgroup A and B viruses circulate in the community. Like other RNA viruses, RSV genome replication is prone to errors that results in a heterogeneous population of viral strains some of which may possess differences in virulence. We sought to determine whether clinical isolates of RSV differ in their capacity to induce inflammatory cytokines IL-6 and CCL5 (previously known as RANTES [regulated upon activation, normal T-cell expressed and secreted protein]), which are known to be induced in vitro and in vivo in response to RSV, during infection of A549 cells.

RESULTS

Screening of subgroup A and B isolates revealed heterogeneity among strains to induce IL-6 and CCL5. We chose two subgroup B strains, New Haven (NH)1067 and NH1125, for further analysis because of their marked differences in cytokine inducing properties and because subgroup B strains, in general, are less genetically heterogeneous as compared to subgroup A strains. At 12 and 24 hours post infection RSV strains, NH1067 and NH1125 differed in their capacity to induce IL-6 by an order of magnitude or more. The concentrations of IL-6 and CCL5 were dependent on the dose of infectious virus and the concentration of these cytokines induced by NH1125 was greater than that of those induced by NH1067 when the multiplicity of infection of NH1067 used was as much as 10-fold higher than that of NH1125. The induction of IL-6 was dependent on viable virus as infection with UV-inactivated virus did not induce IL-6. The difference in IL-6 induction most likely could not be explained by differences in viral replication kinetics. The intracellular level of RSV RNA, as determined by quantitative RT-PCR, was indistinguishable between the 2 strains though the titer of progeny virus produced by NH1125 was greater than that produced by NH1067 at 16, 24 and 36 hours but essentially equal at 48 and 72 hours. Full genome sequencing of the 2 strains revealed 193 polymorphisms and 4 insertions in NH1067 when compared to NH1125 (2 single base insertions in non-coding regions and 2 duplications of 3 and 60 bases in the RSV G gene). Of the polymorphisms, 147 occurred in coding regions and only 30 resulted in amino acid changes in 7 of the RSV genes.

CONCLUSIONS

These data suggest that RSV strains may not be homogeneous with regard to pathogenesis or virulence. Identification of the genetic polymorphisms associated with variations in cytokine induction may lead to insights into RSV disease and to the development of effective antiviral agents and vaccines.