S110 Neutrophil extracellular traps drive severity of virus-induced exacerbations in COPD

<h3>Introduction</h3> Neutrophils are recognised to be an immunological driver in chronic obstructive pulmonary disease (COPD) and can release neutrophil extracellular traps (NETs), which may have protective and detrimental roles. We hypothesised that NET formation drives immunopathology and severity during viral exacerbations of COPD. <h3>Methods</h3> Nine COPD patients, 10 healthy smokers and 11 healthy non-smokers were experimentally challenged with rhinovirus (RV)-A16. Markers of NET formation including nucleosome components histone (H)3.1, H3 citrullinated at arginine 8 (H3R8Cit), and DNA-elastase complexes were quantified in sputum, before and during infection over a period of 42 days. In subsequent studies, C57BL/6 mice were treated with intranasal elastase to recapitulate features of COPD, followed by intraperitoneal administration of a NET inhibitor (NETi) GW311616A prior to infection with RV-A1. Inflammatory cytokines and lung function were measured at 24 and 96 hours post-infection. <h3>Results</h3> H3.1 was induced by rhinovirus infection in COPD and, to a lesser extent, in healthy smokers on day 9 post-infection (figure 1A). H3R8Cit and DNA-elastase complexes were only induced in COPD at day 9 post-infection (figure 1B&amp;C). Concentrations of H3.1 and H3R8Cit correlated positively with sputum virus loads, cellular responses (sputum neutrophils) and virus-induced pro-inflammatory responses including TNF-α, IL-6, CXCL10/IP-10, IL-1β and MUC5AC (figure 1D&amp;E). Both markers also correlated positively with clinical exacerbation severity (lower respiratory tract symptoms), with non-significant trends towards positive correlation with decline in peak expiratory flow rate (PEFR) during exacerbation. Concentration of DNA-elastase complexes correlated positively with sputum virus loads, cellular responses, neutrophil elastase and the proinflammatory cytokines IL-1β and CXCL10/IP-10 (figure 1F). In the animal model of elastase-induced COPD, administration of NETi prior to viral infection reduced concentrations of H3R8Cit at day one post-infection (p&lt;0.05). NETi treatment also attenuated RV-induction of pro-inflammatory responses (IL-6 (P&lt;0.01), TNF-α, IP-10 and RANTES concentrations, P&lt;0.05), MUC5AC (<i>P</i>=0.11) and improved lung function measured by whole body plethysmography (P&lt;0.001), indicating that NETs are a mechanistic driver of immunopathology during exacerbations. <h3>Conclusion</h3> NETs drive immunopathology and severity during viral exacerbations of COPD. Targeting of NETs in COPD exacerbations could represent a future effective intervention to improve clinical outcomes.