Respiratory syncytial virus (RSV) is an important etiological agent of respiratory infection in children for which no specific treatment option is available. The RSV virion contains two surface glycoproteins (F and G) that are vital for the initial phases of infection, making them critical targets for RSV therapeutics. Recent studies have identified the broad-spectrum antiviral properties of silver nanoparticles (AgNPs) against respiratory pathogens, such as adenovirus, parainfluenza, and influenza. AgNPs achieve this by attaching to viral glycoproteins, blocking entry into the host cell. The objective of this study was to evaluate the antiviral and immunomodulatory effects of AgNPs in RSV infection. Herein we demonstrate AgNP-mediated reduction in RSV replication, both in epithelial cell lines and in experimentally infected BALB/c mice. Marked reduction in pro-inflammatory cytokines (i.e., IL-1α, IL-6, TNF-α) and pro-inflammatory chemokines (i.e., CCL2, CCL3, CCL5) was also observed. Conversely, CXCL1, G-CSF, and GM-CSF were increased in RSV-infected mice treated with AgNPs, consistent with an increase of neutrophil recruitment and activation in the lung tissue. Following experimental antibody-dependent depletion of neutrophils, the antiviral effect of AgNPs in mice treated was ablated. To our knowledge, this is the first in vivo report demonstrating antiviral activity of AgNPs during RSV infection.

We have recently shown that endogenous hydrogen sulfide (H₂S), an important cellular gaseous mediator, exerts an antiviral and anti-inflammatory activity in vitro and in vivo, and that exogenous H₂S delivered via the synthetic H₂S-releasing compound GYY4137 also has similar properties. In this study, we sought to extend our findings to a novel class of H₂S donors, thiol-activated gem-dithiol-based (TAGDDs). In an in vitro model of human respiratory syncytial virus (RSV) infection, TAGDD-1 treatment significantly reduced viral replication, even when added up to six hours after infection. Using a mouse model of RSV infection, intranasal delivery of TAGDD-1 to infected mice significantly reduced viral replication and lung inflammation, markedly improving clinical disease parameters and pulmonary dysfunction, compared to vehicle treated controls. Overall our results indicate that this novel synthetic class of H₂S-releasing compounds exerts antiviral and anti-inflammatory activity in the context of RSV infection and represents a potential novel pharmacological approach to ameliorate viral-induced lung disease.

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis in infants and young children. Although some clinical studies have speculated that tumor necrosis factor (TNF)-α is a major contributor of RSV-mediated airway disease, experimental evidence remains unclear or conflicting. TNF-α initiates inflammation and cell death through two distinct receptors: TNF-receptor (TNFR)1 and TNFR2. Here we delineate the function of TNF-α by short-lasting blockade of either receptor in an experimental BALB/c mouse model of RSV infection. We demonstrate that antibody-mediated blockade of TNFR1, but not TNFR2, results in significantly improved clinical disease and bronchoconstriction as well as significant reductions of several inflammatory cytokines and chemokines, including IL-1α, IL-1β, IL-6, Ccl3, Ccl4, and Ccl5. Additionally, TNFR1 blockade was found to significantly reduce neutrophil number and activation status, consistent with the concomitant reduction of pro-neutrophilic chemokines Cxcl1 and Cxcl2. Similar protective activity was also observed when a single-dose of TNFR1 blockade was administered to mice following RSV inoculation, although this treatment resulted in improved alveolar macrophage survival rather than reduced neutrophil activation. Importantly, short-lasting blockade of TNFR1 did not affect RSV peak replication in the lung. This study suggests a potential therapeutic approach for RSV bronchiolitis based on selective blockade of TNFR1.

Respiratory syncytial virus (RSV) infection in mouse and human lung is associated with pathogenic inflammation and oxidative injury. RSV impairs antioxidant responses by increasing the degradation of transcription factor NF-E2-related factor 2 (NRF2), which controls the expression of several antioxidant enzymes (AOEs). In addition to its protective effects, type I IFNs have been increasingly recognized as important mediators of host pathogenic responses during acute respiratory viral infections. We used a mouse model of RSV infection to investigate the effect of lack of type I interferon (IFN) receptor on viral-mediated clinical disease, airway inflammation, NRF2 expression, and antioxidant defenses. In the absence of type I IFN signaling, RSV-infected mice showed significantly less body weight loss and airway obstruction, as well as a significant reduction in cytokine and chemokine secretion and airway inflammation. Lack of type I IFN receptor was associated with greatly reduced virus-induced promyelocytic leukemia lung protein expression, which we showed to be necessary for virus-induced NRF2 degradation in a cell model of infection, resulting in restoration of NRF2 levels, AOE expression, and airway antioxidant capacity. Our data support the concept that modulation of type I IFN production and/or signaling could represent an important therapeutic strategy to ameliorate severity of RSV-induced lung disease.

Severe respiratory syncytial virus (RSV) infections in early life have been linked to the development of chronic airway disease. RSV triggers the production of reactive oxygen species (ROS), which contributes to inflammation and enhanced clinical disease. NF-E2-related factor 2 (Nrf2) is an important redox-responsive protein that helps to protect cells and whole organisms from oxidative stress and injury. The role of Nrf2 in the context of viral-mediated chronic lung injury is not known. Herein, we show that RSV experimental infection of adult Nrf2-deficient BALB/c mice (Nrf2^−/−; Nrf2 KO) is characterized by enhanced disease, increased inflammatory cell recruitment to the bronchoalveolar compartment and a more robust upregulation of innate and inflammatory genes and proteins, compared to wild-type Nrf2^+/+ competent mice (WT). These events that occur at very early time points lead to increased peak RSV replication in Nrf2 KO compared to WT mice (day 5). To evaluate longitudinal changes in the lung architecture, mice were scanned weekly via high-resolution micro-computed tomography (micro-CT) imaging up to 28 days after initial viral inoculation. Based on micro-CT qualitative 2D imaging and quantitative reconstructed histogram-based analysis of lung volume and density, we found that RSV-infected Nrf2 KO mice developed significantly greater and prolonged fibrosis compared to WT mice. The results of this study underscore the critical role of Nrf2-mediated protection from oxidative injury, not only in the acute pathogenesis of RSV infection but also in the long-term consequences of chronic airway injury.

Respiratory syncytial virus (RSV) is the leading cause of respiratory infections in children. Extracellular vesicles (EVs), released by airway epithelial cells, contain proteins and different families of non-coding RNAs (EV cargo) that can modulate the responses of target cells to viral infection. Nasal mucosa is a primary site of viral entry and the source of EVs present in the upper airway secretions. In this study we characterized proteins, including inflammatory mediators and cytokines, and the piwi-interacting RNA (piRNAs) cargo of EVs isolated from pediatric human nose organoids (HNO) and nasopharyngeal secretions (NPS) positive for RSV. Using Proximity Extension Assay (PEA) and Luminex multi-target arrays, we found significant enrichment in several chemokines and other mediators/biomarkers, including CCL2, CCL20, CXCL5, CX3CL1, CXCL6, MMP-1, MMP-10, uPA, Flt3L, ARNT and CD40 in EVs secreted by RSV-infected HNO compared to control mock HNO. Analysis of NPS samples from RSV infected children revealed that CCL3, CCL20, CXCL8, uPA, VEGFA, were concentrated in the NPS-EV fraction. LC-MS/MS and Gene Ontology indicated that RSV positive NPS-EVs originate from different cellular sources, with the most abundant proteins from neutrophils and epithelial cells. A total of 490 piRNAs were detected by NGS sequencing of small RNA libraries obtained from NPS-EVs, which has not been reported prior to this study. Identification of inflammatory mediators and small non-coding RNAs which are compartmentalized in EVs contributes to understanding mechanisms of virus-mediated pathogenesis in RSV infections.