Mucosal immune responses predict clinical outcomes during influenza infection independently of age and viral load (HUM8P.346)

Children are an at-risk population for developing complications following influenza infection, but immunological correlates of disease severity are not understood. We hypothesized that innate cellular immune responses at the site of infection would correlate with disease outcome. To test this hypothesis, we established an observational cohort study with longitudinal sampling of peripheral and mucosal sites in 84 naturally influenza-infected individuals, including infants. Cellular responses, viral loads, and cytokines were quantified from nasal lavages and blood, and correlated to clinical severity. We found that while viral loads in children and adults were similar, innate responses in the airways were stronger in children and varied considerably between plasma and site of infection. Adjusting for age and viral load, an innate immune profile characterized by increased nasal lavage MCP-3, IFNα2 and plasma IL-10 levels at enrollment predicted progression to severe disease. Increased plasma IL-10, MCP-3, and IL-6 levels predicted hospitalization. This inflammatory cytokine production correlated significantly with monocyte localization from the blood to the site of infection, with conventional monocytes positively correlating with inflammation. Increased frequencies of CD14lo monocytes were in the airways of participants with lower inflammatory cytokine levels. An innate profile was identified that correlated with disease progression independent of viral dynamics and age.