Structural basis for IFN antagonism by human respiratory syncytial virus nonstructural protein 2

Development of innate and adaptive immunity to RSV in young children

Infection of the respiratory tract with respiratory syncytial virus (RSV) is common and occurs repeatedly throughout life with most severe disease occurring at the extremes of age: in young infants and the elderly. Effective anti-viral therapeutics are not available and therefore prevention has been the primary strategy for reducing the disease burden. Our current understanding of respiratory mucosal cell biology and the immune response within the respiratory tract is inadequate to prevent infection caused by a pathogen like RSV that does not disseminate outside of this environment. Gaps in our understanding of the activation of innate and adaptive immunity in response to RSV and the role of age upon infection also limit improvements in the design of therapeutics and vaccines for young infants. However, advancements in structural biology have improved our ability to characterize antibodies against viral proteins and in 2023 the first vaccines for those over 60 years and pregnant women became available, potentially reducing the burden of disease. This review will examine our current understanding of the critical facets of anti-RSV immune responses in infants and young children as well as highlight areas where more research is needed.

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.

The matrix protein of respiratory syncytial virus suppresses interferon signaling via RACK1 association

IMPORTANCE

Respiratory syncytial virus (RSV) matrix (M) protein is indispensable for virion assembly and release. It is localized to the nucleus during early infection to perturb host transcription. However, the function of RSV M protein in other cellular activities remains poorly understood. In this study, several interferon response-associated host factors, including RACK1, were identified by proteomic analysis as RSV M interactors. Knockdown of RACK1 attenuates RSV-restricted IFN signaling leading to enhanced host defense against RSV infection, unraveling a role of M protein in antagonizing IFN response via association with RACK1. Our study uncovers a previously unrecognized mechanism of immune evasion by RSV M protein and identifies RACK1 as a novel host factor recruited by RSV, highlighting RACK1 as a potential new target for RSV therapeutics development.

Exploring the Immune Response against RSV and SARS-CoV-2 Infection in Children

Viral respiratory tract infections are a significant public health concern, particularly in children. RSV is a prominent cause of lower respiratory tract infections among infants, whereas SARS-CoV-2 has caused a global pandemic with lower overall severity in children than in adults. In this review, we aimed to compare the innate and adaptive immune responses induced by RSV and SARS-CoV-2 to better understand differences in the pathogenesis of infection. Some studies have demonstrated that children present a more robust immune response against SARS-CoV-2 than adults; however, this response is dissimilar to that of RSV. Each virus has a distinctive mechanism to escape the immune response. Understanding the mechanisms underlying these differences is crucial for developing effective treatments and improving the management of pediatric respiratory infections.

Interferons-Implications in the Immune Response to Respiratory Viruses

Interferons (IFN) are an assemblage of signaling proteins made and released by various host cells in response to stimuli, including viruses. Respiratory syncytial virus (RSV), influenza virus, and SARS-CoV-2 are major causes of respiratory disease that induce or antagonize IFN responses depending on various factors. In this review, the role and function of type I, II, and III IFN responses to respiratory virus infections are considered. In addition, the role of the viral proteins in modifying anti-viral immunity is noted, as are the specific IFN responses that underly the correlates of immunity and protection from disease.

Innate Immune Evasion by Human Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory infection in young children. Nearly all individuals become infected in their early childhood, and reinfections with RSV are common throughout life. Primary infection with RSV is usually involved in the symptom of bronchiolitis and pneumonia in the lower respiratory tract, which accounts for over 3 million hospitalizations and approximately 66,000 deaths annually worldwide. Despite the widespread prevalence and high morbidity and lethality rates of diseases caused by RSV infection, there is currently no licensed RSV vaccine. During RSV infection, innate immunity plays the first line of defense to suppress RSV infection and replication. However, RSV has evolved multiple mechanisms to evade the host’s innate immune responses to gain a window of opportunity for efficient viral replication. This review discusses the comprehensive interaction between RSV infection and the host antiviral innate immunity and updates recent findings on how RSV modulates the host innate immune response for survival, which may provide novel insights to find potent drug targets and vaccines against RSV.

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.

Mechanisms of Viral Degradation of Cellular Signal Transducer and Activator of Transcription 2

Virus infection of eukaryotes triggers cellular innate immune response, a major arm of which is the type I interferon (IFN) family of cytokines. Binding of IFN to cell surface receptors triggers a signaling cascade in which the signal transducer and activator of transcription 2 (STAT2) plays a key role, ultimately leading to an antiviral state of the cell. In retaliation, many viruses counteract the immune response, often by the destruction and/or inactivation of STAT2, promoted by specific viral proteins that do not possess protease activities of their own. This review offers a summary of viral mechanisms of STAT2 subversion with emphasis on degradation. Some viruses also destroy STAT1, another major member of the STAT family, but most viruses are selective in targeting either STAT2 or STAT1. Interestingly, degradation of STAT2 by a few viruses requires the presence of both STAT proteins. Available evidence suggests a mechanism in which multiple sites and domains of STAT2 are required for engagement and degradation by a multi-subunit degradative complex, comprising viral and cellular proteins, including the ubiquitin–proteasomal system. However, the exact molecular nature of this complex and the alternative degradation mechanisms remain largely unknown, as critically presented here with prospective directions of future study.

Domain-specific biochemical and serological characterization of SARS-CoV-2 nucleocapsid protein

Nucleocapsid proteins are essential for SARS-CoV-2 life cycle. Here, we describe protocols to gather domain-specific insights about essential properties of nucleocapsids. These assays include dynamic light scattering to characterize oligomerization, fluorescence polarization to quantify RNA binding, hydrogen-deuterium exchange mass spectrometry to map RNA binding regions, negative-stain electron microscopy to visualize oligomeric species, interferon reporter assay to evaluate interferon signaling modulation, and a serology assay to reveal insights for improved sensitivity and specificity. These assays are broadly applicable to RNA-encapsidated nucleocapsids. For complete details on the use and execution of this protocol, please refer to Wu et al. (2021).

Respiratory syncytial virus: from pathogenesis to potential therapeutic strategies

Respiratory syncytial virus (RSV) is one of the most important viral pathogens causing respiratory tract infection in infants, the elderly and people with poor immune function, which causes a huge disease burden worldwide every year. It has been more than 60 years since RSV was discovered, and the palivizumab monoclonal antibody, the only approved specific treatment, is limited to use for passive immunoprophylaxis in high-risk infants; no other intervention has been approved to date. However, in the past decade, substantial progress has been made in characterizing the structure and function of RSV components, their interactions with host surface molecules, and the host innate and adaptive immune response to infection. In addition, basic and important findings have also piqued widespread interest among researchers and pharmaceutical companies searching for effective interventions for RSV infection. A large number of promising monoclonal antibodies and inhibitors have been screened, and new vaccine candidates have been designed for clinical evaluation. In this review, we first briefly introduce the structural composition, host cell surface receptors and life cycle of RSV virions. Then, we discuss the latest findings related to the pathogenesis of RSV. We also focus on the latest clinical progress in the prevention and treatment of RSV infection through the development of monoclonal antibodies, vaccines and small-molecule inhibitors. Finally, we look forward to the prospects and challenges of future RSV research and clinical intervention.