Neutrophil extracellular traps cause airway obstruction during respiratory syncytial virus disease

Abstract

Human respiratory syncytial virus (RSV) is the most important cause of severe lower respiratory tract disease (LRTD) in young children worldwide. Extensive neutrophil accumulation in the lungs and occlusion of small airways by DNA-rich mucus plugs are characteristic features of severe RSV-LRTD. Activated neutrophils can release neutrophil extracellular traps (NETs), extracellular networks of DNA covered with antimicrobial proteins, as part of the first-line defence against pathogens. NETs can trap and eliminate microbes; however, abundant NET formation may also contribute to airway occlusion. In this study, we investigated whether NETs are induced by RSV and explored their potential anti-viral effect in vitro. Second, we studied NET formation in vivo during severe RSV-LRTD in infants and bovine RSV-LRTD in calves, by examining bronchoalveolar lavage fluid and lung tissue sections, respectively. NETs were visualized in lung cytology and tissue samples by DNA and immunostaining, using antibodies against citrullinated histone H3, elastase and myeloperoxidase. RSV was able to induce NET formation by human neutrophils in vitro. Furthermore, NETs were able to capture RSV, thereby precluding binding of viral particles to target cells and preventing infection. Evidence for the formation of NETs in the airways and lungs was confirmed in children with severe RSV-LRTD. Detailed histopathological examination of calves with RSV-LRTD showed extensive NET formation in dense plugs occluding the airways, either with or without captured viral antigen. Together, these results suggest that, although NETs trap viral particles, their exaggerated formation during severe RSV-LRTD contributes to airway obstruction.

Broadly Reactive Anti-Respiratory Syncytial Virus G Antibodies from Exposed Individuals Effectively Inhibit Infection of Primary Airway Epithelial Cells

“…Other membranes were embedded in paraffin, and 5-m-thick sections were cut. Immunohistochemical staining of CX3CR1 on HAE cell cultures was performed as described before (38) with an anti-CX3CR1 antibody (eBioscience; kind gift of C. Verseijden, Tytgat Institute, Amsterdam, The Netherlands).…”

Viral–bacterial interactions in the respiratory tract

“…Infection of neutrophils with RSV or influenza was found to enhance NET formation (Cortjens et al, 2016;Narasaraju et al, 2011). But whereas superinfection of influenza-infected mice with S. pneumoniae has been shown to further increase the formation of NETs, these did not confer protection against bacteria, due to partial degradation and loss of antibacterial activity (Narayana Moorthy et al, 2013).…”

Respiratory Syncytial Virus: Infection, Detection, and New Options for Prevention and Treatment

“…Although traditionally identified as antibacterial in nature, NETs occur when stimulated neutrophils eject their genomic DNA along with antimicrobial proteins like neutrophil elastase and myeloperoxidase (167). These NETs serve to sequester and inactivate pathogens, including RSV (168,169). Intact RSV particles and purified RSV-F fusion protein induce NETs in a TLR4-, p38 mitogen-activated protein (MAP) kinase-, and extracellular signal-regulated kinase 1 and 2 (ERK1/2) MAP kinase-dependent manner in vitro (168,169).…”

“…These NETs serve to sequester and inactivate pathogens, including RSV (168,169). Intact RSV particles and purified RSV-F fusion protein induce NETs in a TLR4-, p38 mitogen-activated protein (MAP) kinase-, and extracellular signal-regulated kinase 1 and 2 (ERK1/2) MAP kinase-dependent manner in vitro (168,169). NETs were later observed in vivo using bronchoalveolar lavage samples from children with RSV LRT infection and histological sections of lower airway obstructions in calves infected with bovine RSV (168).…”

“…Intact RSV particles and purified RSV-F fusion protein induce NETs in a TLR4-, p38 mitogen-activated protein (MAP) kinase-, and extracellular signal-regulated kinase 1 and 2 (ERK1/2) MAP kinase-dependent manner in vitro (168,169). NETs were later observed in vivo using bronchoalveolar lavage samples from children with RSV LRT infection and histological sections of lower airway obstructions in calves infected with bovine RSV (168). Despite the ability of NETs to bind viral particles, less than half of the lower airway obstructions observed in infected calves contained viral antigens (168).…”