Function of the respiratory syncytial virus small hydrophobic protein

Human metapneumovirus SH protein promotes JAK1 degradation to impair host IL-6 signaling

Human metapneumovirus (HMPV) is a leading cause of respiratory infections in children, older adults, and those with underlying conditions 1,2,3,4. HMPV must evade immune defenses to replicate successfully; however, the viral proteins used to accomplish this are poorly characterized. The HMPV small hydrophobic (SH) protein has been reported to inhibit signaling through type I and type II interferon (IFN) receptors in vitro, in part by preventing STAT1 phosphorylation5. HMPV infection also inhibits IL-6 signaling. However, the mechanisms by which SH inhibits signaling, and its involvement in IL-6 signaling inhibition are unknown. Here, we used transfection of SH expression plasmids and SH-deleted virus (ΔSH) to show that SH is the viral factor responsible for inhibition of IL-6 signaling during HMPV infection. Transfection of SH-expression vectors or infection with wildtype, but not ΔSH virus, blocked IL-6 mediated STAT3 activation. Further, JAK1 protein (but not RNA) was significantly reduced in cells infected with wildtype but not ΔSH virus. The SH-mediated reduction of JAK1 was partially restored by addition of proteasome inhibitors, suggesting proteasomal degradation of JAK1. Confocal microscopy indicated that infection relocalized JAK1 to viral replication factories. Co-immunoprecipitation showed that SH interacts with JAK1 and ubiquitin, further linking SH to proteasomal degradation machinery. These data indicate that SH inhibits IL-6 and IFN signaling in infected cells in part by promoting proteasomal degradation of JAK1 and that SH is necessary for IL-6 and IFN signaling inhibition in infection. These findings enhance our understanding of the immune evasion mechanisms of an important respiratory pathogen.

Isolation, genome analysis and comparison of a novel parainfluenza virus 5 from a Siberian tiger (Panthera tigris)

Paramyxoviruses are important pathogens affecting various animals, including mammals and humans. Parainfluenza virus 5 (PIV5)-a member of the family Paramyxoviridae-is a major threat to the health of mammals and humans. However, studies on terrestrial wild animals infected with PIV5 are scanty. In this study, we utilized reverse transcription PCR to detect PIV5 infection in the visceral organ tissues of a Siberian tiger (Panthera tigris ssp. altaica) with vomiting, diarrhea, and dyspnea before its death. A novel PIV5 (named SR strain) with a slowly progressive cytopathic effect was isolated in Vero cells and validated using a transmission electron microscope. Full-length sequencing and analysis revealed that the whole genome of the PIV5 SR strain contained 15,246 nucleotides (nt) and seven non-overlapping genes (3'-N-V/P-M-F-SH-HN-L-5') encoding eight proteins. Phylogenetic analysis of three PIV5 strains identified in the same zoo confirmed that PIV5 strains SR and ZJQ-221 shared the closest genetic relationship as they were clustered in the same branch, while the recently found Siberian tiger strain SZ2 kept a certain distance and formed a relatively unique branch. Furthermore, mutations of nt and amino acids (aa) between strains ZJQ-221, SR, and SZ2 were identified. In summary, we report the identification and genomic characterization of a novel PIV5 strain SR isolated in a Siberian tiger, which may help future research on interspecific transmission mechanisms.

The implication of infection with respiratory syncytial virus in pediatric recurrent wheezing and asthma: knowledge expanded post-COVID-19 era

BACKGROUND

Respiratory syncytial virus (RSV) infection has been identified to serve as the primary cause of acute lower respiratory infectious diseases in children under the age of one and a significant risk factor for the emergence and development of pediatric recurrent wheezing and asthma, though the exact mechanism is still unknown.

METHODS AND RESULTS

In this study, we discuss the key routes that lead to recurrent wheezing and bronchial asthma following RSV infection. It is interesting to note that following the coronavirus disease 2019 (COVID-19) epidemic, the prevalence of RSV changes significantly. This presents us with a rare opportunity to better understand the associated mechanism for RSV infection, its effects on the respiratory system, and the immunological response to RSV following the COVID-19 epidemic. To better understand the associated mechanisms in the occurrence and progression of pediatric asthma, we thoroughly described how the RSV infection directly destroys the physical barrier of airway epithelial tissue, promotes inflammatory responses, enhances airway hyper-responsiveness, and ultimately causes the airway remodeling. More critically, extensive discussion was also conducted regarding the potential impact of RSV infection on host pulmonary immune response.

CONCLUSION

In conclusion, this study offers a comprehensive perspective to better understand how the RSV infection interacts in the control of the host's pulmonary immune system, causing recurrent wheezing and the development of asthma, and it sheds fresh light on potential avenues for pharmaceutical therapy in the future.

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.

Pathogenicity and virulence of human respiratory syncytial virus: Multifunctional nonstructural proteins NS1 and NS2

Human respiratory syncytial virus (hRSV) is a major cause of acute lower respiratory tract infections in children under the age of two as well as in the elderly and immunocompromised worldwide. Despite its discovery over 60 years ago and the global impact on human health, limited specific and effective prophylactic or therapeutic options have been available for hRSV infections. Part of the lack of treatment options is attributed to the legacy of vaccine failure in the 1960s using a formalin-inactivated RSV (FI-RSV), which led to enhancement of disease post exposure to hRSV infection and hampered subsequent development of vaccine candidates. Recent FDA approval of a vaccine for older adults and impending approval for a maternal vaccine are major advancements but leaves children between 6 months and 5 years of age unprotected. Part of this limitation can be attributed to a lack of complete understanding of the factors that contribute to hRSV pathogenesis. The nonstructural proteins NS1 and NS2 are multifunctional virulence factors that are unique to hRSV and that play critical roles during hRSV infection, including antagonizing interferon (IFN) signalling to modulate host responses to hRSV infection. However, the molecular mechanisms by which the nonstructural proteins mediate their IFN inhibitory functions have not been completely defined. Current progress on the characterization of NS1 and NS2 during infection provides deeper insight into their roles. Furthermore, reverse genetics systems for hRSV provide a viable strategy to generate attenuated viruses by introduction of select mutations while maintaining immunogenicity required to elicit a long-term protective response. Here we will review the current state of knowledge of the nonstructural proteins, their contributions to RSV pathogenesis, and their potential as targets for therapeutic development.

Modulation of endoplasmic reticulum stress response pathways by respiratory viruses

Acute respiratory infections (ARIs) are amongst the leading causes of death and disability, and the greatest burden of disease impacts children, pregnant women, and the elderly. Respiratory viruses account for the majority of ARIs. The unfolded protein response (UPR) is a host homeostatic defence mechanism primarily activated in response to aberrant endoplasmic reticulum (ER) resident protein accumulation in cell stresses including viral infection. The UPR has been implicated in the pathogenesis of several respiratory diseases, as the respiratory system is particularly vulnerable to chronic and acute activation of the ER stress response pathway. Many respiratory viruses therefore employ strategies to modulate the UPR during infection, with varying effects on the host and the pathogens. Here, we review the specific means by which respiratory viruses affect the host UPR, particularly in association with the high production of viral glycoproteins, and the impact of UPR activation and subversion on viral replication and disease pathogenesis. We further review the activation of UPR in common co-morbidities of ARIs and discuss the therapeutic potential of modulating the UPR in virally induced respiratory diseases.

Respiratory syncytial virus infection and novel interventions

The large global burden of respiratory syncytial virus (RSV) respiratory tract infections in young children and older adults has gained increased recognition in recent years. Recent discoveries regarding the neutralization-specific viral epitopes of the pre-fusion RSV glycoprotein have led to a shift from empirical to structure-based design of RSV therapeutics, and controlled human infection model studies have provided early-stage proof of concept for novel RSV monoclonal antibodies, vaccines and antiviral drugs. The world's first vaccines and first monoclonal antibody to prevent RSV among older adults and all infants, respectively, have recently been approved. Large-scale introduction of RSV prophylactics emphasizes the need for active surveillance to understand the global impact of these interventions over time and to timely identify viral mutants that are able to escape novel prophylactics. In this Review, we provide an overview of RSV interventions in clinical development, highlighting global disease burden, seasonality, pathogenesis, and host and viral factors related to RSV immunity.

Respiratory syncytial virus entry mechanism in host cells: A general overview

Respiratory syncytial virus (RSV) is a virus that causes acute respiratory infections in neonates and older adults. To infect host cells, the attachment glycoprotein (G) interacts with a cell surface receptor. This interaction determines the specific cell types that are susceptible to infection. RSV possesses a type I fusion protein F. Type I fusion proteins are metastable when rearrangement of the prefusion F occurs; the fusion peptide is exposed transforming the protein into postfusion form. The transition between the prefusion form and its postfusion form facilitates the viral envelope and the host cell membrane to fuse, enabling the virus to enter the host cell. Understanding the entry mechanism employed by RSV is crucial for developing effective antiviral therapies. In this review, we will discuss the various types of viral fusion proteins and explore the potential entry mechanisms utilized by RSV. A deeper understanding of these mechanisms will provide valuable insights for the development of novel approaches to treat RSV infections.

Cryo-EM structure of the nucleocapsid-like assembly of respiratory syncytial virus

Respiratory syncytial virus (RSV) is a nonsegmented, negative strand RNA virus that has caused severe lower respiratory tract infections of high mortality rates in infants and the elderly, yet no effective vaccine or antiviral therapy is available. The RSV genome encodes the nucleoprotein (N) that forms helical assembly to encapsulate and protect the RNA genome from degradation, and to serve as a template for transcription and replication. Previous crystal structure revealed a decameric ring architecture of N in complex with the cellular RNA (N-RNA) of 70 nucleotides (70-nt), whereas cryo-ET reconstruction revealed a low-resolution left-handed filament, in which the crystal monomer structure was docked with the helical symmetry applied to simulate a nucleocapsid-like assembly of RSV. However, the molecular details of RSV nucleocapsid assembly remain unknown, which continue to limit our complete understanding of the critical interactions involved in the nucleocapsid and antiviral development that may target this essential process during the viral life cycle. Here we resolve the near-atomic cryo-EM structure of RSV N-RNA that represents roughly one turn of the helical assembly that unveils critical interaction interfaces of RSV nucleocapsid and may facilitate development of RSV antiviral therapy.

Genome-wide study of globally distributed respiratory syncytial virus (RSV) strains implicates diversification utilizing phylodynamics and mutational analysis

Respiratory syncytial virus (RSV) is a common respiratory pathogen that causes mild cold-like symptoms and severe lower respiratory tract infections, causing hospitalizations in children, the elderly and immunocompromised individuals. Due to genetic variability, this virus causes life-threatening pneumonia and bronchiolitis in young infants. Thus, we examined 3600 whole genome sequences submitted to GISAID by 31 December 2022 to examine the genetic variability of RSV. While RSVA and RSVB coexist throughout RSV seasons, RSVA is more prevalent, fatal, and epidemic-prone in several countries, including the United States, the United Kingdom, Australia, and China. Additionally, the virus's attachment glycoprotein and fusion protein were highly mutated, with RSVA having higher Shannon entropy than RSVB. The genetic makeup of these viruses contributes significantly to their prevalence and epidemic potential. Several strain-specific SNPs co-occurred with specific haplotypes of RSVA and RSVB, followed by different haplotypes of the viruses. RSVA and RSVB have the highest linkage probability at loci T12844A/T3483C and G13959T/C2198T, respectively. The results indicate that specific haplotypes and SNPs may significantly affect their spread. Overall, this analysis presents a promising strategy for tracking the evolving epidemic situation and genetic variants of RSV, which could aid in developing effective control, prophylactic, and treatment strategies.

Advanced fluorescence microscopy in respiratory virus cell biology

Respiratory viruses are a major public health burden across all age groups around the globe, and are associated with high morbidity and mortality rates. They can be transmitted by multiple routes, including physical contact or droplets and aerosols, resulting in efficient spreading within the human population. Investigations of the cell biology of virus replication are thus of utmost importance to gain a better understanding of virus-induced pathogenicity and the development of antiviral countermeasures. Light and fluorescence microscopy techniques have revolutionized investigations of the cell biology of virus infection by allowing the study of the localization and dynamics of viral or cellular components directly in infected cells. Advanced microscopy including high- and super-resolution microscopy techniques available today can visualize biological processes at the single-virus and even single-molecule level, thus opening a unique view on virus infection. We will highlight how fluorescence microscopy has supported investigations on virus cell biology by focusing on three major respiratory viruses: respiratory syncytial virus (RSV), Influenza A virus (IAV) and SARS-CoV-2. We will review our current knowledge of virus replication and highlight how fluorescence microscopy has helped to improve our state of understanding. We will start by introducing major imaging and labeling modalities and conclude the chapter with a perspective discussion on remaining challenges and potential opportunities.

The RSV F p27 peptide: current knowledge, important questions

Respiratory syncytial virus (RSV) remains a leading cause of hospitalizations and death for young children and adults over 65. The worldwide impact of RSV has prioritized the search for an RSV vaccine, with most targeting the critical fusion (F) protein. However, questions remain about the mechanism of RSV entry and RSV F triggering and fusion promotion. This review highlights these questions, specifically those surrounding a cleaved 27 amino acids long peptide within F, p27.

Respiratory Syncytial Virus: A Comprehensive Review of Transmission, Pathophysiology, and Manifestation

With an increasing global incidence in children younger than the age of five, respiratory syncytial virus (RSV) is one of the most common viral respiratory infections worldwide. Despite the increasing number of cases among infants and young children, RSV can infect any age group; however, some individuals are more high risk than others. Premature infants, young children, elderly, and immunocompromised individuals are the most likely to suffer a more severe presentation of RSV in comparison to healthy adults. RSV is transmitted through respiratory droplets via direct contact with an infected individual or with contaminated surfaces. The viral genome of RSV consists of 11 proteins. Out of these 11, two proteins allow for the attachment of the virus to the respiratory epithelial cells and fusion with host cells. Upon fusion, the viral material transfers to the host cell, where viral replication occurs. It is important to acknowledge that an individual is considered infectious and can transmit the virus even before the symptomatic presentation of RSV begins. As long as the individual is shedding the virus, he or she is considered infectious. The length of viral shedding also differs depending on the severity of the infection, who is infected, and the underlying immune status of an individual. Currently, there is no definitive treatment for RSV; however, supportive therapy is considered the mainstay treatment. Some pharmaceutical treatments such as ribavirin have been FDA-approved; however, the administration is typically limited to children and infants. Palivizumab is also administered as an immune prophylaxis; however, both therapies are constantly at the end of a cost-effective debate due to their extensively expensive nature and questionable adverse effect profiles. Supportive therapy includes hydration, supplemental oxygen, and mechanical ventilation in hospitalized cases; however, most RSV cases can be treated as outpatient cases. Prevention techniques such as hand washing and maintaining social distancing are imperative to minimize the transmission of the virus as much as remotely possible.

Nationwide and long-term molecular epidemiologic studies of mumps viruses that circulated in Japan between 1986 and 2017

In Japan, major mumps outbreaks still occur every 4–5 years because of low mumps vaccine coverage (30–40%) owing to the voluntary immunization program. Herein, to prepare for a regular immunization program, we aimed to reveal the nationwide and long-term molecular epidemiological trends of the mumps virus (MuV) in Japan. Additionally, we performed whole-genome sequencing (WGS) using next-generation sequencing to assess results from conventional genotyping using MuV sequences of the small-hydrophobic (SH) gene. We analyzed 1,064 SH gene sequences from mumps clinical samples and MuV isolates collected from 25 prefectures from 1986 to 2017. The results showed that six genotypes, namely B (110), F (1), G (900), H (3), J (41), and L (9) were identified, and the dominant genotypes changed every decade in Japan since the 1980s. Genotype G has been exclusively circulating since the early 2000s. Seven clades were identified for genotype G using SH sequence-based classification. To verify the results, we performed WGS on 77 representative isolates of genotype G using NGS and phylogenetically analyzed them. Five clades were identified with high bootstrap values and designated as Japanese clade (JPC)-1, -2, -3, -4, -5. JPC-1 and -3 accounted for over 80% of the total genotype G isolates (68.3 and 13.8%, respectively). Of these, JPC-2 and -5, were newly identified clades in Japan through this study. This is the first report describing the nationwide and long-term molecular epidemiology of MuV in Japan. The results provide information about Japanese domestic genotypes, which is essential for evaluating the mumps elimination progress in Japan after the forthcoming introduction of the mumps vaccine into Japan’s regular immunization program. Furthermore, the study shows that WGS analysis using NGS is more accurate than results obtained from conventional SH sequence-based classification and is a powerful tool for accurate molecular epidemiology studies.

Functions of Viroporins in the Viral Life Cycle and Their Regulation of Host Cell Responses

Viroporins are virally encoded transmembrane proteins that are essential for viral pathogenicity and can participate in various stages of the viral life cycle, thereby promoting viral proliferation. Viroporins have multifaceted effects on host cell biological functions, including altering cell membrane permeability, triggering inflammasome formation, inducing apoptosis and autophagy, and evading immune responses, thereby ensuring that the virus completes its life cycle. Viroporins are also virulence factors, and their complete or partial deletion often reduces virion release and reduces viral pathogenicity, highlighting the important role of these proteins in the viral life cycle. Thus, viroporins represent a common drug-protein target for inhibiting drugs and the development of antiviral therapies. This article reviews current studies on the functions of viroporins in the viral life cycle and their regulation of host cell responses, with the aim of improving the understanding of this growing family of viral proteins.

How RSV Proteins Join Forces to Overcome the Host Innate Immune Response

Respiratory syncytial virus (RSV) is the leading cause of severe acute lower respiratory tract infections in infants worldwide. Although several pattern recognition receptors (PRRs) can sense RSV-derived pathogen-associated molecular patterns (PAMPs), infection with RSV is typically associated with low to undetectable levels of type I interferons (IFNs). Multiple RSV proteins can hinder the host’s innate immune response. The main players are NS1 and NS2 which suppress type I IFN production and signalling in multiple ways. The recruitment of innate immune cells and the production of several cytokines are reduced by RSV G. Next, RSV N can sequester immunostimulatory proteins to inclusion bodies (IBs). N might also facilitate the assembly of a multiprotein complex that is responsible for the negative regulation of innate immune pathways. Furthermore, RSV M modulates the host’s innate immune response. The nuclear accumulation of RSV M has been linked to an impaired host gene transcription, in particular for nuclear-encoded mitochondrial proteins. In addition, RSV M might also directly target mitochondrial proteins which results in a reduced mitochondrion-mediated innate immune recognition of RSV. Lastly, RSV SH might prolong the viral replication in infected cells and influence cytokine production.

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 overview on the RSV-mediated mechanisms in the onset of non-allergic asthma

Respiratory syncytial virus (RSV) infection is recognized as an important risk factor for wheezing and asthma, since it commonly affects babies during lung development. While the role of RSV in the onset of atopic asthma is widely recognized, its impact on the onset of non-atopic asthma, mediated via other and independent causal pathways, has long been also suspected, but the association is less clear. Following RSV infection, the release of local pro-inflammatory molecules, the dysfunction of neural pathways, and the compromised epithelial integrity can become chronic and influence airway development, leading to bronchial hyperreactivity and asthma, regardless of atopic status. After a brief review of the RSV structure and its interaction with the immune system and neuronal pathways, this review summarizes the current evidence about the RSV-mediated pathogenic pathways in predisposing and inducing airway dysfunction and non-allergic asthma development.

Role of ARP2/3 Complex-Driven Actin Polymerization in RSV Infection

Respiratory syncytial virus (RSV) is the leading viral agent causing bronchiolitis and pneumonia in children under five years old worldwide. The RSV infection cycle starts with macropinocytosis-based entry into the host airway epithelial cell membrane, followed by virus transcription, replication, assembly, budding, and spread. It is not surprising that the host actin cytoskeleton contributes to different stages of the RSV replication cycle. RSV modulates actin-related protein 2/3 (ARP2/3) complex-driven actin polymerization for a robust filopodia induction on the infected lung epithelial A549 cells, which contributes to the virus’s budding, and cell-to-cell spread. Thus, a comprehensive understanding of RSV-induced cytoskeletal modulation and its role in lung pathobiology may identify novel intervention strategies. This review will focus on the role of the ARP2/3 complex in RSV’s pathogenesis and possible therapeutic targets to the ARP2/3 complex for RSV.

The contribution of bovines to human health against viral infections

In the last 40 years, novel viruses have evolved at a much faster pace than other pathogens. Viral diseases pose a significant threat to public health around the world. Bovines have a longstanding history of significant contributions to human nutrition, agricultural, industrial purposes, medical research, drug and vaccine development, and livelihood. The life cycle, genomic structures, viral proteins, and pathophysiology of bovine viruses studied in vitro paved the way for understanding the human counterparts. Calf model has been used for testing vaccines against RSV, papillomavirus vaccines and anti-HCV agents were principally developed after using the BPV and BVDV model, respectively. Some bovine viruses-based vaccines (BPIV-3 and bovine rotaviruses) were successfully developed, clinically tried, and commercially produced. Cows, immunized with HIV envelope glycoprotein, produced effective broadly neutralizing antibodies in their serum and colostrum against HIV. Here, we have summarized a few examples of human viral infections for which the use of bovines has contributed to the acquisition of new knowledge to improve human health against viral infections covering the convergence between some human and bovine viruses and using bovines as disease models. Additionally, the production of vaccines and drugs, bovine-based products were covered, and the precautions in dealing with bovines and bovine-based materials.

Respiratory syntycial virus: Current treatment strategies and vaccine approaches

Respiratory Syncytial Virus is a yearly respiratory virus that causes significant frequencies of morbidities, particularly in the young and elderly populations. However, preventive vaccines and/or treatment therapies are generally lacking, although much attention is now being placed on this virus. Moreover, there are now multiple strategies currently being explored in a race to the first licensed vaccine. While vaccines are being developed, multiple treatment strategies are being explored to attenuate the severity of infection and thus reduce hospitalization rates in vulnerable populations. This review outlines current strategies to prevent or treat this virus in the hopes of reducing significant human morbidity and mortality that occurs yearly with this seasonal virus.

Humoral and Mucosal Antibody Response to RSV Structural Proteins in RSV-Infected Adult Hematopoietic Cell Transplant (HCT) Recipients

Respiratory syncytial virus (RSV) is an important cause of lower respiratory tract infection in infants, the elderly, and immunocompromised patients. RSV antibodies play a role in preventing reinfection and in clearance of RSV, but data regarding the levels of viral protein-specific antibodies elicited and their contribution to patient recovery from RSV-induced disease are limited. We prospectively enrolled a cohort of RSV-infected adult hematopoietic cell transplant (HCT) recipients (n = 40). Serum and nasal-wash samples were obtained at enrollment (acute samples) and convalescence (convalescent samples). We measured (1) humoral IgG and mucosal IgA binding antibody levels to multiple RSV proteins (F, G, N, P, and M2-1) by Western blot (WB); (2) neutralizing antibody (Nt Ab) titers by microneutralization assay; and (3) palivizumab-like antibody (PLA) concentrations by an ELISA-based competitive binding assay developed in the lab. Finally, we tested for correlations between protein-specific antibody levels and duration of viral shedding (normal: cleared in <14 days and delayed: cleared ≥14 days), as well as RSV/A and RSV/B subtypes. Convalescent sera from HCT recipients had significantly higher levels of anti-RSV antibodies to all 5 RSV structural proteins assayed (G, F, N, P, M2-1), higher Nt Abs to both RSV subtypes, and higher serum PLAs than at enrollment. Significantly higher levels of mucosal antibodies to 3 RSV structural proteins (G, N, and M2-1) were observed in the convalescent nasal wash versus acute nasal wash. Normal viral clearance group had significantly higher levels of serum IgG antibodies to F, N, and P viral proteins, higher Nt Ab to both RSV subtypes, and higher PLA, as well as higher levels of mucosal IgA antibodies to G and M2-1 viral proteins, and higher Nt Ab to both RSV subtypes compared to delayed viral clearance group. Normal RSV clearance was associated with higher IgG serum antibody levels to F and P viral proteins, and PLAs in convalescent serum (p < 0.05). Finally, overall antibody levels in RSV/A- and/B-infected HCT recipients were not significantly different. In summary, specific humoral and mucosal RSV antibodies are associated with viral clearance in HCT recipients naturally infected with RSV. In contrast to the humoral response, the F surface glycoprotein was not a major target of mucosal immunity. Our findings have implications for antigen selection in the development of RSV vaccines.

Elucidation of the Host Bronchial Lymph Node miRNA Transcriptome Response to Bovine Respiratory Syncytial Virus

Bovine respiratory disease (BRD) causes substantial morbidity and mortality, affecting cattle of all ages. One of the main causes of BRD is an initial inflammatory response to bovine respiratory syncytial virus (BRSV). MicroRNAs are novel and emerging non-coding small RNAs that regulate many biological processes and are implicated in various inflammatory diseases. The objective of the present study was to elucidate the changes in the bovine bronchial lymph node miRNA transcriptome in response to BRSV following an experimental viral challenge. Holstein-Friesian calves were either administered a challenge dose of BRSV (103.5 TCID50/ml × 15 ml) (n = 12) or were mock inoculated with sterile phosphate buffered saline (n = 6). Daily scoring of clinical signs was performed and calves were euthanized at day 7 post-challenge. Bronchial lymph nodes were collected for subsequent RNA extraction and sequencing (75 bp). Read counts for known miRNAs were generated using the miRDeep2 package using the UMD3.1 reference genome and the bovine mature miRNA sequences from the miRBase database (release 22). EdgeR was used for differential expression analysis and Targetscan was used to identify target genes for the differentially expressed (DE) miRNAs. Target genes were examined for enriched pathways and gene ontologies using Ingenuity Pathway Analysis (Qiagen). Multi-dimensional scaling (MDS) based on miRNA gene expression changes, revealed a clearly defined separation between the BRSV challenged and control calves, although the clinical manifestation of disease was only mild. One hundred and nineteen DE miRNAs (P < 0.05, FDR < 0.1, fold change > 1.5) were detected between the BRSV challenged and control calves. The DE miRNAs were predicted to target 465 genes which were previously found to be DE in bronchial lymph node tissue, between these BRSV challenged and control calves. Of the DE predicted target genes, 455 had fold changes that were inverse to the corresponding DE miRNAs. There were eight enriched pathways among the DE predicted target genes with inverse fold changes to their corresponding DE miRNA including: granulocyte and agranulocyte adhesion and diapedesis, interferon signalling and role of pathogen recognition receptors in recognition of bacteria and viruses. Functions predicted to be increased included: T cell response, apoptosis of leukocytes, immune response of cells and stimulation of cells. Pathogen recognition and proliferation of cytotoxic T cells are vital for the recognition of the virus and its subsequent elimination.

Mucosal Delivery of Recombinant Vesicular Stomatitis Virus Vectors Expressing Envelope Proteins of Respiratory Syncytial Virus Induces Protective Immunity in Cotton Rats

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract (LRT) infections, with increased severity in high-risk human populations, such as infants, the immunocompromised, and the elderly. Although the virus was identified more than 60 years ago, there is still no licensed vaccine available. Over the years, several vaccine delivery strategies have been evaluated. In this study, we developed two recombinant vesicular stomatitis virus (rVSV) vector-based vaccine candidates expressing the RSV-G (attachment) protein (rVSV-G) or F (fusion) protein (rVSV-F). All vectors were evaluated in the cotton rat animal model for their in vivo immunogenicity and protective efficacy against an RSV-A2 virus challenge. Intranasal (i.n.) delivery of rVSV-G and rVSV-F together completely protected the lower respiratory tract (lungs) at doses as low as 10³ PFU. In contrast, doses greater than 10⁶ PFU were required to protect the upper respiratory tract (URT) completely. Reimmunization of RSV-immune cotton rats was most effective with rVSV-F. In immunized animals, overall antibody responses were sufficient for protection, whereas CD4 and CD8 T cells were not necessary. A prime-boost immunization regimen increased both protection and neutralizing antibody titers. Overall, mucosally delivered rVSV-vector-based RSV vaccine candidates induce protective immunity and therefore represent a promising immunization regimen against RSV infection.IMPORTANCE Even after decades of intensive research efforts, a safe and efficacious RSV vaccine remains elusive. Expression of heterologous antigens from rVSV vectors has demonstrated several practical and safety advantages over other virus vector systems and live attenuated vaccines. In this study, we developed safe and efficacious vaccine candidates by expressing the two major immunogenic RSV surface proteins in rVSV vectors and delivering them mucosally in a prime-boost regimen. The main immune parameter responsible for protection was the antibody response. These vaccine candidates induced complete protection of both the upper and lower respiratory tracts.

Revisiting respiratory syncytial virus's interaction with host immunity, towards novel therapeutics

Every year there are > 33 million cases of Respiratory Syncytial Virus (RSV)-related respiratory infection in children under the age of five, making RSV the leading cause of lower respiratory tract infection (LRTI) in infants. RSV is a global infection, but 99% of related mortality is in low/middle-income countries. Unbelievably, 62 years after its identification, there remains no effective treatment nor vaccine for this deadly virus, leaving infants, elderly and immunocompromised patients at high risk. The success of all pathogens depends on their ability to evade and modulate the host immune response. RSV has a complex and intricate relationship with our immune systems, but a clearer understanding of these interactions is essential in the development of effective medicines. Therefore, in a bid to update and focus our research community's understanding of RSV's interaction with immune defences, this review aims to discuss how our current knowledgebase could be used to combat this global viral threat.

The emerging role of microRNAs in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection

The novel coronavirus disease 2019 (COVID-19) pandemic has imposed significant public health problems for the human populations worldwide after the 1918 influenza A virus (IVA) (H1N1) pandemic. Although numerous efforts have been made to unravel the mechanisms underlying the coronavirus, a notable gap remains in our perception of the COVID-19 pathogenesis. The innate and adaptive immune systems have a pivotal role in the fate of viral infections, such as COVID-19 pandemic. MicroRNAs (miRNAs) are known as short noncoding RNA molecules and appear as indispensable governors of almost any cellular means. Several lines of evidence demonstrate that miRNAs participate in essential mechanisms of cell biology, regulation of the immune system, and the onset and progression of numerous types of disorders. The immune responses to viral respiratory infections (VRIs), including influenza virus (IV), respiratory syncytial virus (RSV), and rhinovirus (RV), are correlated with the ectopic expression of miRNAs. Alterations of the miRNA expression in epithelial cells may contribute to the pathogenesis of chronic and acute airway infections. Hence, analyzing the role of these types of nucleotides in antiviral immune responses and the characterization of miRNA target genes might contribute to understanding the mechanisms of the interplay between the host and viruses, and in the future, potentially result in discovering therapeutic strategies for the prevention and treatment of acute COVID-19 infection. In this article, we present a general review of current studies concerning the function of miRNAs in different VRIs, particularly in coronavirus infection, and address all available therapeutic prospects to mitigate the burden of viral infections.

Respiratory Syncytial Virus Sequesters NF-κB Subunit p65 to Cytoplasmic Inclusion Bodies To Inhibit Innate Immune Signaling

Viruses routinely employ strategies to prevent the activation of innate immune signaling in infected cells. Respiratory syncytial virus (RSV) is no exception, as it encodes two accessory proteins (NS1 and NS2) which are well established to block interferon signaling. However, RSV-encoded mechanisms for inhibiting NF-κB signaling are less well characterized. In this study, we identified RSV-mediated antagonism of this pathway, independent of the NS1 and NS2 proteins and indeed distinct from other known viral mechanisms of NF-κB inhibition. In both human and bovine RSV-infected cells, we demonstrated that the p65 subunit of NF-κB is rerouted to perinuclear puncta in the cytoplasm, which are synonymous with viral inclusion bodies (IBs), the site for viral RNA replication. Captured p65 was unable to translocate to the nucleus or transactivate a NF-κB reporter following tumor necrosis factor alpha (TNF-α) stimulation, confirming the immune-antagonistic nature of this sequestration. Subsequently, we used correlative light electron microscopy (CLEM) to colocalize the RSV N protein and p65 within bovine RSV (bRSV) IBs, which are granular, membraneless regions of cytoplasm with liquid organelle-like properties. Additional characterization of bRSV IBs indicated that although they are likely formed by liquid-liquid phase separation (LLPS), they have a differential sensitivity to hypotonic shock proportional to their size. Together, these data identify a novel mechanism for viral antagonism of innate immune signaling which relies on sequestration of the NF-κB subunit p65 to a biomolecular condensate-a mechanism conserved across the Orthopneumovirus genus and not host-cell specific. More generally, they provide additional evidence that RNA virus IBs are important immunomodulatory complexes within infected cells.IMPORTANCE Many viruses replicate almost entirely in the cytoplasm of infected cells; however, how these pathogens are able to compartmentalize their life cycle to provide favorable conditions for replication and to avoid the litany of antiviral detection mechanisms in the cytoplasm remains relatively uncharacterized. In this manuscript, we show that bovine respiratory syncytial virus (bRSV), which infects cattle, does this by generating inclusion bodies in the cytoplasm of infected cells. We confirm that both bRSV and human RSV viral RNA replication takes place in these inclusion bodies, likely meaning these organelles are a functionally conserved feature of this group of viruses (the orthopneumoviruses). Importantly, we also showed that these organelles are able to capture important innate immune transcription factors (in this case NF-KB), blocking the normal signaling processes that tell the nucleus the cell is infected, which may help us to understand how these viruses cause disease.

GBP5 Is an Interferon-Induced Inhibitor of Respiratory Syncytial Virus

Guanylate binding protein 5 (GBP5) belongs to the GTPase subfamily, which is mainly induced by interferon gamma (IFN-γ) and is involved in many important cellular processes, including inflammasome activation and innate immunity against a wide variety of microbial pathogens. However, it is unknown whether GBP5 inhibits respiratory syncytial virus (RSV) infection. In this study, we identified GBP5 as an effector of the anti-RSV activity of IFN-γ and found that in children, the weaker immune response, especially the weaker IFN-γ response and the decreased GBP5 expression, leads to RSV susceptibility. Furthermore, we revealed that GBP5 reduced the cell-associated levels of the RSV small hydrophobic (SH) protein, which was identified as a viroporin. In contrast, overexpression of the SH protein rescued RSV replication in the presence of GBP5. The GBP5-induced decrease in intracellular SH protein levels is because GBP5 promotes the release of the SH protein into the cell culture. Moreover, the GBP5 C583A mutants with changes at the C terminus or the GBP5 ΔC mutant lacking the C-terminal region, which impairs GBP5 localization in the Golgi, could not inhibit RSV infection, whereas the GTPase-defective GBP5 maintained RSV inhibition, suggesting that Golgi localization but not the GTPase activity of GBP5 is required for RSV inhibition. Interestingly, we found that RSV infection or RSV G protein downregulates GBP5 expression by upregulating DZIP3, an E3 ligase, which induces GBP5 degradation through the K48 ubiquitination and proteasomal pathways. Thus, this study reveals a complicated interplay between host restrictive factor GBP5 and RSV infection and provides important information for understanding the pathogenesis of RSV.IMPORTANCE RSV is a highly contagious virus that causes multiple infections in infants within their first year of life. It can also easily cause infection in elderly or immunocompromised individuals, suggesting that individual differences in immunity play an important role in RSV infection. Therefore, exploring the pathogenic mechanisms of RSV and identifying essential genes which inhibit RSV infection are necessary to develop an effective strategy to control RSV infection. Here, we report that the IFN-inducible gene GBP5 potently inhibits RSV replication by reducing the cell-associated levels of the RSV small hydrophobic (SH) protein, which is a viroporin. In contrast, the RSV G protein was shown to upregulate the expression of the DZIP3 protein, an E3 ligase that degrades GBP5 through the proteasomal pathway. Our study provides important information for the understanding of the pathogenic mechanisms of RSV and host immunity as well as the complicated interplay between the virus and host.

Summer Outbreak of Severe RSV-B Disease, Minnesota, 2017 Associated with Emergence of a Genetically Distinct Viral Lineage

BACKGROUND

Respiratory syncytial virus (RSV) typically causes winter outbreaks in temperate climates. During summer 2017, the Minnesota Department of Health received a report of increased cases of severe RSV-B infection.

METHODS

We compared characteristics of summer 2017 cases with those of 2014-2018 summers. To understand the genetic relatedness among viruses, we performed high-throughput sequencing of RSV from patients with a spectrum of illness from sites in Minnesota and Wisconsin.

RESULTS

From May to September 2017, 58 RSV cases (43 RSV-B) were reported compared to 20-29 cases (3-7 RSV-B) during these months in other years. Median age and frequency of comorbidities were similar, but 55% (24/43) were admitted to the ICU in 2017 compared to 12% in preceding 3 years (odds ratio, 4.84, P < .01). Sequencing was performed on 137 specimens from March 2016 to March 2018. Outbreak cases formed a unique clade sharing a single conserved nonsynonymous change in the SH gene. We observed increased cases during the following winter season, when the new lineage was the predominant strain.

CONCLUSIONS

We identified an outbreak of severe RSV-B disease associated with a new genetic lineage among urban Minnesota children during a time of expected low RSV circulation.

Innate Immune Components that Regulate the Pathogenesis and Resolution of hRSV and hMPV Infections

The human respiratory syncytial virus (hRSV) and human Metapneumovirus (hMPV) are two of the leading etiological agents of acute lower respiratory tract infections, which constitute the main cause of mortality in infants. However, there are currently approved vaccines for neither hRSV nor hMPV. Moreover, despite the similarity between the pathology caused by both viruses, the immune response elicited by the host is different in each case. In this review, we discuss how dendritic cells, alveolar macrophages, neutrophils, eosinophils, natural killer cells, innate lymphoid cells, and the complement system regulate both pathogenesis and the resolution of hRSV and hMPV infections. The roles that these cells play during infections by either of these viruses will help us to better understand the illnesses they cause. We also discuss several controversial findings, relative to some of these innate immune components. To better understand the inflammation in the lungs, the role of the respiratory epithelium in the recruitment of innate immune cells is briefly discussed. Finally, we review the main prophylactic strategies and current vaccine candidates against both hRSV and hMPV.

Evaluation of the protective potential of antibody and T cell responses elicited by a novel preventative vaccine towards respiratory syncytial virus small hydrophobic protein

The small hydrophobic (SH) glycoprotein of human respiratory syncytial virus (RSV) is a transmembrane protein that is poorly accessible by antibodies on the virion but has an ectodomain (SHe) that is accessible and expressed on infected cells. The SHe from RSV strain A has been formulated in DPX, a unique delivery platform containing an adjuvant, and is being evaluated as an RSV vaccine candidate. The proposed mechanism of protection is the immune-mediated clearance of infected cells rather than neutralization of the virion. Our phase I clinical trial data clearly showed that vaccination resulted in robust antibody responses, but it was unclear if these immune responses have any correlation to immune responses to natural infection with RSV. Therefore, we embarked on this study to examine these immune responses in older adults with confirmed RSV infection. We compared vaccine-induced (DPX-RSV(A)) immune responses from participants in a Phase 1 clinical trial to paired acute and convalescent titers from older adults with symptomatic laboratory-confirmed RSV infection. Serum samples were tested for anti-SHe IgG titers and the isotypes determined. T cell responses were evaluated by IFN-γ ELISPOT. Anti-SHe titers were detected in 8 of 42 (19%) in the acute phase and 16 of 42 (38%) of convalescent serum samples. IgG1, IgG3, and IgA were the prevalent isotypes generated by both vaccination and infection. Antigen-specific T cell responses were detected in 9 of 16 (56%) of vaccinated participants. Depletion of CD4⁺ but not CD8⁺ T cells abrogated the IFN-γ ELISPOT response supporting the involvement of CD4⁺ T cells in the immune response to vaccination. The data showed that an immune response like that induced by DPX-RSV(A) could be seen in a subset of participants with confirmed RSV infection. These findings show that older adults with clinically significant infection as well as vaccinated adults generate a humoral response to SHe. The induction of both SHe-specific antibody and cellular responses support further clinical development of the DPX-RSV(A) vaccine.

Impact of Respiratory Syncytial Virus Infection on Host Functions: Implications for Antiviral Strategies

Respiratory syncytial virus (RSV) is one of the leading causes of viral respiratory tract infection in infants, the elderly, and the immunocompromised worldwide, causing more deaths each year than influenza. Years of research into RSV since its discovery over 60 yr ago have elucidated detailed mechanisms of the host-pathogen interface. RSV infection elicits widespread transcriptomic and proteomic changes, which both mediate the host innate and adaptive immune responses to infection, and reflect RSV's ability to circumvent the host stress responses, including stress granule formation, endoplasmic reticulum stress, oxidative stress, and programmed cell death. The combination of these events can severely impact on human lungs, resulting in airway remodeling and pathophysiology. The RSV membrane envelope glycoproteins (fusion F and attachment G), matrix (M) and nonstructural (NS) 1 and 2 proteins play key roles in modulating host cell functions to promote the infectious cycle. This review presents a comprehensive overview of how RSV impacts the host response to infection and how detailed knowledge of the mechanisms thereof can inform the development of new approaches to develop RSV vaccines and therapeutics.

MicroRNAs in Asthma and Respiratory Infections: Identifying Common Pathways

MicroRNAs (miRs) are single-stranded RNAs of 18-25 nucleotides. These molecules regulate gene expression at the post-transcriptional level; several of these are differentially expressed in asthma as well as in viral acute respiratory infections (ARIs), the main triggers of acute asthma exacerbations. In recent years, miRs have been studied in order to discover drug targets as well as biomarkers for diagnosis, disease severity and prognosis. We describe recent findings on miR expression and function in asthma and their role in the regulation of viral ARIs, according to cell tissue specificity and asthma severity. By combining the above information, we identify miRs that may be important in virus-induced asthma exacerbations. This is the first attempt to link miR profiles of asthmatic patients and ARI-induced miRs, addressing the question of whether there might be a specific miR deficit in asthmatic subjects that make them more susceptible and/or reactive to infection.

Molecular epidemiology of human respiratory syncytial virus and human metapneumovirus in hospitalized children with acute respiratory infections in Croatia, 2014-2017

Acute respiratory infection (ARI) is the most common infection in children under 5 years of age and it is frequently caused by two pneumoviruses, human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV). Epidemic seasons of these viruses overlap and disease manifestations are highly similar, including severe lower ARI such as bronchiolitis or pneumonia. Reinfections with pneumoviruses are frequent and limited prevention treatment is available. Genetic diversity of HRSV and HMPV strains circulating in Croatia was monitored during four consecutive years (2014-2017). Co-circulation of multiple lineages was observed for both viruses. Within HRSV group A, ON1 strains gained strong predominance during the 4-year period, while previously dominant genotype NA1 was detected only sporadically. Similarly, newly occurring HMPV genotype A2c gained predominance over genotype A2b during this period, resulting in all infection in 2017 being caused by A2c. Along with phylogenetic analysis based on the commonly used fragments for detection and genotyping of these viruses, full length G and SH genes were also analysed. Evolutionary dynamics showed that inferred substitution rates of HRSV and HMPV are between 2.51 × 10^-3 and 3.61 × 10^-3 substitutions/site/year. This study established presence of recently described HMPV strains containing large duplications in the G gene in Croatia. Viruses with either of the two duplications belong to a subcluster A2c, which has completely replaced all other group A subclusters in 2017.

Host Components Contributing to Respiratory Syncytial Virus Pathogenesis

Respiratory syncytial virus (RSV) is the most prevalent viral etiological agent of acute respiratory tract infection. Although RSV affects people of all ages, the disease is more severe in infants and causes significant morbidity and hospitalization in young children and in the elderly. Host factors, including an immature immune system in infants, low lymphocyte levels in patients under 5 years old, and low levels of RSV-specific neutralizing antibodies in the blood of adults over 65 years of age, can explain the high susceptibility to RSV infection in these populations. Other host factors that correlate with severe RSV disease include high concentrations of proinflammatory cytokines such as interleukins (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and thymic stromal lymphopoitein (TSLP), which are produced in the respiratory tract of RSV-infected individuals, accompanied by a strong neutrophil response. In addition, data from studies of RSV infections in humans and in animal models revealed that this virus suppresses adaptive immune responses that could eliminate it from the respiratory tract. Here, we examine host factors that contribute to RSV pathogenesis based on an exhaustive review of in vitro infection in humans and in animal models to provide insights into the design of vaccines and therapeutic tools that could prevent diseases caused by RSV.

Phylogenetic evidence of a novel lineage of canine pneumovirus and a naturally recombinant strain isolated from dogs with respiratory illness in Thailand

BACKGROUND

Canine pneumovirus (CPV) is a pathogen that causes respiratory disease in dogs, and recent outbreaks in shelters in America and Europe have been reported. However, based on published data and documents, the identification of CPV and its variant in clinically symptomatic individual dogs in Thailand through Asia is limited. Therefore, the aims of this study were to determine the emergence of CPV and to consequently establish the genetic characterization and phylogenetic analysis of the CPV strains from 209 dogs showing respiratory distress in Thailand.

RESULTS

This study identified and described the full-length CPV genome from three strains, designated herein as CPV_CP13 TH/2015, CPV_CP82 TH/2016 and CPV_SR1 TH/2016, that were isolated from six dogs out of 209 dogs (2.9%) with respiratory illness in Thailand. Phylogenetic analysis suggested that these three Thai CPV strains (CPV TH strains) belong to the CPV subgroup A and form a novel lineage; proposed as the Asian prototype. Specific mutations in the deduced amino acids of these CPV TH strains were found in the G/glycoprotein sequence, suggesting potential substitution sites for subtype classification. Results of intragenic recombination analysis revealed that CPV_CP82 TH/2016 is a recombinant strain, where the recombination event occurred in the L gene with the Italian prototype CPV Bari/100-12 as the putative major parent. Selective pressure analysis demonstrated that the majority of the nucleotides in the G/glycoprotein were under purifying selection with evidence of positive selection sites.

CONCLUSIONS

This collective information on the CPV TH strains is the first evidence of CPV emergence with genetic characterization in Thailand and as first report in Asia, where homologous recombination acts as a potential force driving the genetic diversity and shaping the evolution of canine pneumovirus.

Respiratory syncytial virus (RSV): a scourge from infancy to old age

Respiratory syncytial virus (RSV) is the most common single cause of respiratory hospitalisation of infants and is the second largest cause of lower respiratory infection mortality worldwide. In adults, RSV is an under-recognised cause of deterioration in health, particularly in frail elderly persons. Infection rates typically rise in late autumn and early winter causing bronchiolitis in infants, common colds in adults and insidious respiratory illness in the elderly. Virus detection methods optimised for use in children have low detection rate in adults, highlighting the need for better diagnostic tests. There are many vaccines under development, mostly based on the surface glycoprotein F which exists in two conformations (prefusion and postfusion). Much of the neutralising antibody appears to be to the prefusion form. Vaccines being developed include live attenuated, subunit, particle based and live vectored agents. Different vaccine strategies may be appropriate for different target populations: at-risk infants, school-age children, adult caregivers and the elderly. Antiviral drugs are in clinical trial and may find a place in disease management. RSV disease is one of the major remaining common tractable challenges in infectious diseases and the era of vaccines and antivirals for RSV is on the near horizon.

Importance of Virus Characteristics in Respiratory Syncytial Virus-Induced Disease

Severe lower respiratory tract infection in infants and young children is most frequently caused by respiratory syncytial virus (RSV). RSV infects the smallest airways, making breathing difficult and in some infants requiring medical support. Severity is affected by viral dose, infant age, virus genotype, and effectiveness of the innate/adaptive immune responses. Severe disease correlates with later wheezing and asthma in some children. The adaptive immune response is protective but wanes after each infection, likely due to the ability of the RSV NS1/NS2 proteins to inhibit the innate immune response. Several vaccine approaches and candidates are currently in clinical trials.

Comparison of Palivizumab-Like Antibody Binding to Different Conformations of the RSV F Protein in RSV-Infected Adult Hematopoietic Cell Transplant Recipients

Background

Most respiratory syncytial virus (RSV) vaccine candidates include fusion (F) protein in different conformations. Antigenic site II found in the different F conformations is the target of palivizumab, the only US Food and Drug Administration approved monoclonal antibody (mAb). Serum palivizumab-like antibody (PLA) is a potential serologic correlate of immunity. Our objective was to determine if different conformations of F protein in a palivizumab competitive antibody (PCA) assay affect the PLA concentrations.

Methods

Four PCA assays were standardized using mAbs. Each contained prefusion, postfusion, or intermediate F forms. PLA concentrations were measured in acute and convalescent sera from 22 RSV/A and 18 RSV/B-infected adult hematopoietic cell transplant (HCT) recipients. PLA concentrations were calculated using a 4-parameter logistic regression model and analyzed for statistical significance.

Results

PCA assays revealed significantly greater PLA concentrations in convalescent sera; comparable increases in PLA concentration in RSV/A and RSV/B-infected HCT recipients; and significantly reduced PLA concentrations in HCT recipients who shed RSV ≥14 days. A significant positive correlation was observed between PCA assays and RSV neutralizing antibody titers.

Conclusions

F protein conformation does not appear to have a measurable impact on PCA assays for measuring PLA induced by RSV/A or RSV/B infection.

Characterization of the role of N-glycosylation sites in the respiratory syncytial virus fusion protein in virus replication, syncytium formation and antigenicity

Respiratory syncytial virus (RSV) is a leading cause of infant hospitalization worldwide each year and there is presently no licensed vaccine to prevent severe RSV infections. Two major RSV glycoproteins, attachment (G) and fusion (F) protein, regulate viral replication and both proteins contain potential glycosylation sites which are highly variable for the G protein and conserved for the F protein among virus isolates. The RSV F sequence possesses five N-glycosylation sites located in the F2 subunit (N27 and N70), the p27 peptide (N116 and N126) and the F1 subunit (N500). The importance of RSV F N-glycosylation in virus replication and immunogenicity is not yet fully understood, and a better understanding may provide new insights for vaccine development. By using a BAC-based reverse genetics system, recombinant viruses expressing F proteins with loss of N-glycosylation sites were made. Mutant viruses with single N-glycosylation sites removed could be recovered, while this was not possible with the mutant with all N-glycosylation sites removed. Although the individual RSV F N-glycosylation sites were shown not to be essential for viral replication, they do contribute to the efficiency of in vitro and in vivo viral infection. To evaluate the role of N-glycosylation sites on RSV F antigenicity, serum antibody titers were determined after infection of BALB/c mice with RSV expressing the glycomutant F proteins. Infection with recombinant virus lacking the N-glycosylation site at position N116 (RSV F N116Q) resulted in significant higher neutralizing antibody titers compared to RSV F WT infection, which is surprising since this N-glycan is present in the p27 peptide which is assumed to be absent from the mature F protein in virions. Thus, single or combined RSV F glycomutations which affect virus replication and fusogenicity, and which may induce enhanced antibody responses upon immunization could have the potential to improve the efficacy of RSV LAV approaches.

Respiratory syncytial virus entry and how to block it

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract disease in young children and elderly people. Although the virus was isolated in 1955, an effective RSV vaccine has not been developed, and the only licensed intervention is passive immunoprophylaxis of high-risk infants with a humanized monoclonal antibody. During the past 5 years, however, there has been substantial progress in our understanding of the structure and function of the RSV glycoproteins and their interactions with host cell factors that mediate entry. This period has coincided with renewed interest in developing effective interventions, including the isolation of potent monoclonal antibodies and small molecules and the design of novel vaccine candidates. In this Review, we summarize the recent findings that have begun to elucidate RSV entry mechanisms, describe progress on the development of new interventions and conclude with a perspective on gaps in our knowledge that require further investigation.

The Impact of RSV-Associated Respiratory Disease on Children in Asia

Acute respiratory tract infections (ARTIs) are leading contributors to the global infectious disease burden, which is estimated to be 112,900,000 disability adjusted life years. Viruses contribute to the etiology of ARTIs in a big way compared with other microorganisms. Since the discovery of respiratory syncytial virus (RSV) 61 years ago, the virus has been recognized as a major cause of ARTI and hospitalization in children. The morbidity and mortality attributable to RSV infection appear to be higher in infants < 3 months and in those with known risk factors such as prematurity, chronic lung, and congenital heart diseases. Crowded living conditions, exposure to tobacco smoke, and industrial or other types of air pollution also increase the risk of RSV-associated ARTI. Many epidemiological studies have been conducted in developed countries to understand the seasonal patterns and risk factors associated with RSV infections. Dearth of information on RSV-associated morbidity and mortality in Asian and developing countries indicates the need for regional reviews to evaluate RSV-associated disease burden in these countries. Epidemiological studies including surveillance is the key to track the disease burden including risk factors, seasonality, morbidity, and mortality associated with RSV infection in these countries. These data will contribute to improve the clinical diagnosis and plan preventive strategies in resource-limited developing countries.

microRNAs in viral acute respiratory infections: immune regulation, biomarkers, therapy, and vaccines

MicroRNAs (miRNAs) are single-stranded RNAs of 17-24 nt. These molecules regulate gene expression at the post-transcriptional level and are differentially expressed in viral acute respiratory infections (ARIs), which are responsible for high morbidity and mortality around the world. In recent years, miRNAs have been studied in order to discover anti-viral ARI drug targets as well as biomarkers for diagnosis, severity, and prognosis. This review presents an analysis of the regulatory response to viral ARIs of miRNAs, including their participation in the innate immune response, their utility as biomarkers, and their potential for future therapies and vaccine development.

Human Metapneumovirus: Mechanisms and Molecular Targets Used by the Virus to Avoid the Immune System

Human metapneumovirus (hMPV) is a respiratory virus, first reported the year 2001. Since then, it has been described as one of the main etiological agents that causes acute lower respiratory tract infections (ALRTIs), which is characterized by symptoms such as bronchiolitis, wheezing and coughing. Susceptible population to hMPV-infection includes newborn, children, elderly and immunocompromised individuals. This viral agent is a negative-sense, single-stranded RNA enveloped virus, that belongs to the Pneumoviridae family and Metapneumovirus genus. Early reports—previous to 2001—state several cases of respiratory illness without clear identification of the responsible pathogen, which could be related to hMPV. Despite the similarities of hMPV with several other viruses, such as the human respiratory syncytial virus or influenza virus, mechanisms used by hMPV to avoid the host immune system are still unclear. In fact, evidence indicates that hMPV induces a poor innate immune response, thereby affecting the adaptive immunity. Among these mechanisms, is the promotion of an anergic state in T cells, instead of an effective polarization or activation, which could be induced by low levels of cytokine secretion. Further, the evidences support the notion that hMPV interferes with several pattern recognition receptors (PRRs) and cell signaling pathways triggered by interferon-associated genes. However, these mechanisms reported in hMPV are not like the ones reported for hRSV, as the latter has two non-structural proteins that are able to inhibit these pathways. Several reports suggest that viral glycoproteins, such as G and SH, could play immune-modulator roles during infection. In this work, we discuss the state of the art regarding the mechanisms that underlie the poor immunity elicited by hMPV. Importantly, these mechanisms will be compared with those elicited by other common respiratory viruses.

Active prophylaxis for respiratory syncytial virus: current knowledge and future perspectives

Respiratory syncytial virus (RSV) is the most common respiratory pathogen in infants and young children but represents also an important cause of morbidity in adults, particularly in the elderly and immunocompromised persons. Despite its global impact on human health, no effective treatment is available except for supportive care and no safe vaccine has been licensed yet. Vaccine development has been hindered by several factors including vaccine enhanced disease associated with formalin-inactivated RSV vaccine, ethical concerns and lack of consensus concerning the most appropriate target antigen. In this review, we analyze history of RSV vaccine and current approaches for preventing RSV including live-attenuated, vector-based, subunit, nucleic acid-based, particle-based vaccines and we debate about concerns on target population, correlates of protection and obstacles that are slowing the progress toward a successful RSV vaccination strategy.

Role of Small Hydrophobic Protein of J Paramyxovirus in Virulence

J paramyxovirus (JPV) was first isolated from moribund mice with hemorrhagic lung lesions in Australia in 1972. It is a paramyxovirus classified under the newly proposed genus Jeilongvirus JPV has a genome of 18,954 nucleotides, consisting of eight genes in the order 3'-N-P/V/C-M-F-SH-TM-G-L-5'. JPV causes little cytopathic effect (CPE) in tissue culture cells but severe disease in mice. The small hydrophobic (SH) protein is an integral membrane protein encoded by many paramyxoviruses, such as mumps virus (MuV) and respiratory syncytial virus (RSV). However, the function of SH has not been defined in a suitable animal model. In this work, the functions of SH of JPV, MuV, and RSV have been examined by generating recombinant JPV lacking the SH protein (rJPV-ΔSH) or replacing SH of JPV with MuV SH (rJPV-MuVSH) or RSV SH (rJPV-RSVSH). rJPV-ΔSH, rJPV-MuVSH, and rJPV-RSVSH were viable and had no growth defect in tissue culture cells. However, more tumor necrosis factor alpha (TNF-α) was produced during rJPV-ΔSH infection, confirming the role of SH in inhibiting TNF-α production. rJPV-ΔSH induced more apoptosis in tissue culture cells than rJPV, rJPV-MuVSH, and rJPV-RSVSH, suggesting that SH plays a role in blocking apoptosis. Furthermore, rJPV-ΔSH was attenuated in mice compared to rJPV, rJPV-MuVSH, and rJPV-RSVSH, indicating that the SH protein plays an essential role in virulence. The results indicate that the functions of MuV SH and RSV SH are similar to that of JPV SH even though they have no sequence homology.IMPORTANCE Paramyxoviruses are associated with many devastating diseases in animals and humans. J paramyxovirus (JPV) was isolated from moribund mice in Australia in 1972. Newly isolated viruses, such as Beilong virus (BeiPV) and Tailam virus (TlmPV), have genome structures similar to that of JPV. A new paramyxovirus genus, Jeilongvirus, which contains JPV, BeiPV, and TlmPV, has been proposed. Small hydrophobic (SH) protein is present in many paramyxoviruses. Our present study investigates the role of SH protein of JPV in pathogenesis in its natural host. Understanding the pathogenic mechanism of Jeilongvirus is important to control and prevent potential diseases that may emerge from this group of viruses.

Patterns of antibody response during natural hRSV infection: insights for the development of new antibody-based therapies

INTRODUCTION

The human respiratory syncytial virus (hRSV) is the main cause of acute lower respiratory tract infection in susceptible population worldwide, such as young children and the elderly. Although hRSV is a major public health burden, there are no licensed vaccines and the only available therapy is palivizumab. During life, reinfections with hRSV are common, suggesting that the virus can impair the development of an efficient host immune response. This feature has hindered the development of efficient therapies.

AREAS COVERED

This article focuses on research about the natural development of antibodies in humans after the exposure to hRSV. The difficulties of developing anti-hRSV therapies based on monoclonal antibodies have been recently associated to the relationship between the disease outcome and the pattern of antibody response.

EXPERT OPINION

Development of monoclonal antibodies is a potentially successful approach to prevent the population from suffering severe respiratory diseases caused by hRSV infection, for which there are no available vaccines. Although the use of palivizumab is safe, its effectiveness is controversial. Recent data have prompted research to develop therapies targeting alternative viral antigens, rather than focusing only on the F protein, as well as the development of antibodies with a cell-mediated function.

Suppression of NF-κB Activity: A Viral Immune Evasion Mechanism

Nuclear factor-κB (NF-κB) is an important transcription factor that induces the expression of antiviral genes and viral genes. NF-κB activation needs the activation of NF-κB upstream molecules, which include receptors, adaptor proteins, NF-κB (IκB) kinases (IKKs), IκBα, and NF-κB dimer p50/p65. To survive, viruses have evolved the capacity to utilize various strategies that inhibit NF-κB activity, including targeting receptors, adaptor proteins, IKKs, IκBα, and p50/p65. To inhibit NF-κB activation, viruses encode several specific NF-κB inhibitors, including NS3/4, 3C and 3C-like proteases, viral deubiquitinating enzymes (DUBs), phosphodegron-like (PDL) motifs, viral protein phosphatase (PPase)-binding proteins, and small hydrophobic (SH) proteins. Finally, we briefly describe the immune evasion mechanism of human immunodeficiency virus 1 (HIV-1) by inhibiting NF-κB activity in productive and latent infections. This paper reviews a viral mechanism of immune evasion that involves the suppression of NF-κB activation to provide new insights into and references for the control and prevention of viral diseases.

Variability analysis and inter-genotype comparison of human respiratory syncytial virus small hydrophobic gene

Background

Small hydrophobic (SH) gene is one of the mostly diverse genomic regions of human respiratory syncytial virus (HRSV). Its coding region constitutes less than 50% of the complete gene length, enabling SH gene to be highly variable and the SH protein highly conserved. In standard HRSV molecular epidemiology studies, solely sequences of the second hypervariable region of the glycoprotein gene (HVR2) are analyzed. To what extent do the strains identical in HVR2 differ elsewhere in genomes is rarely investigated. Our goal was to investigate whether diversity and inter-genotype differences observed for HVR2 are also present in the SH gene.

Methods

We sequenced 198 clinical samples collected within a limited area and time frame. In this HRSV collection, rapid and significant changes in HVR2 occurred.

Results

Over 20% of strains from this pool (containing HRSV genotypes NA1, ON1, GA5, BA9 and BA10) would be incorrectly assumed to be identical to another strain if only the HVR2 region was analysed. The majority of differences found in SH gene were located in the 5′ untranslated region (UTR). Seven indels were detected, one was genotype GA5 specific. An in-frame deletion of 9 nucleotides (coding for amino acids 49–51) was observed in one of group A strains. Fifteen different SH protein sequences were detected; 68% of strains possessed the consensus sequence and most of others differed from the consensus in only one amino acid (only 4 strains differed in 2 amino acids). The majority of differing amino acids in group A viruses had the same identity as the corresponding amino acids in group B strains. When analysis was restricted to strains with identical HVR2 nucleotide sequences and differing SH protein sequences, 75% of differences observed in the SH ectodomain were located within region coding for amino acids 49–51.

Conclusions

Basing HRSV molecular epidemiology studies solely on HVR2 largely underestimates the complexity of circulating virus populations. In strain identification, broadening of the genomic target sequence to SH gene would provide a more comprehensive insight into viral pool versatility and its evolutionary processes.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1020-9) contains supplementary material, which is available to authorized users.

A Respiratory Syncytial Virus Vaccine Based on the Small Hydrophobic Protein Ectodomain Presented With a Novel Lipid-Based Formulation Is Highly Immunogenic and Safe in Adults: A First-in-Humans Study

Background

Respiratory syncytial virus infection can cause lower respiratory tract infection in older adults comparable to influenza, but no vaccines are available.

Methods

This was a randomized, observer-blinded, first-in-humans study of a novel synthetic RSV antigen based on the ectodomain of the small hydrophobic glycoprotein (SHe) of RSV subgroup A, formulated with either the lipid and oil-based vaccine platform DepoVax (DPX-RSV[A]) or alum (RSV[A]-Alum), in healthy, 50-64-year-old individuals. Two dose levels (10 or 25 µg) of SHe with each formulation were compared to placebo. A booster dose was administered on day 56.

Results

There was no indication that the vaccine was unsafe. Mild pain, drowsiness, and muscles aches were the most common solicited adverse events (AEs), and the frequencies of the AEs did not increase after dose 2. Robust anti-SHe-specific immune responses were demonstrated in the DPX-RSV(A) 10-μg and 25-μg groups (geometric mean titer, approximately 10-fold and 100-fold greater than that of placebo at days 56 and 236, respectively), and responses were sustained in the DPX-RSV(A) 25-μg group at day 421. Responses to the RSV(A)-Alum vaccines were very low.

Conclusions

A novel antigen from the SH protein of RSV, formulated in a lipid and oil-based vaccine platform, was highly immunogenic, with sustained antigen-specific antibody responses, and had an acceptable safety profile.