Atopic Neutrophils Prevent Postviral Airway Disease

Respiratory syncytial virus (RSV) infection in infancy is associated with increased risk of asthma, except in those with allergic disease at the time of infection. Using house dust mite allergen, we examined the effect of pre-existing atopy on postviral airway disease using Sendai virus in mice, which models RSV infection in humans. Sendai virus drives postviral airway disease in nonatopic mice; however, pre-existing atopy protected against the development of airway disease. This protection depended upon neutrophils, as depletion of neutrophils at the time of infection restored the susceptibility of atopic mice to postviral airway disease. Associated with development of atopy was an increase in polymorphonuclear neutrophil–dendritic cell hybrid cells that develop in Th2 conditions and demonstrated increased viral uptake. Systemic inhibition of IL-4 reversed atopic protection against postviral airway disease, suggesting that increased virus uptake by neutrophils was IL-4 dependent. Finally, human neutrophils from atopic donors were able to reduce RSV infection of human airway epithelial cells in vitro, suggesting these findings could apply to the human. Collectively our data support the idea that pre-existing atopy derives a protective neutrophil response via potential interaction with IL-4, preventing development of postviral airway disease.