NTHi-IAV coinfection of macrophages alters infection outcomes and inflammatory responses

Nontypeable Haemophilus influenzae (NTHi) chronically colonises the airway of individuals with chronic respiratory disease, with persistence suggested to be facilitated by invasion of airway macrophages. Previous data supports an interaction between NTHi colonisation and the risk of viruses exacerbating underlying respiratory diseases. As exacerbations are the main cause of morbidity and mortality of respiratory diseases, the drivers of this increased risk need to be identified. The aim of this work was to investigate whether prior NTHi infection compromises the ability of macrophages to respond to a subsequent viral challenge. A monocyte-derived macrophage (MDM)-NTHi intracellular persistence model was adapted to include coinfection with the influenza A virus (IAV). Compared to pathogen-alone controls, NTHi presence significantly increased by 190% (p<0.05), whereas the percentage of IAV-infected MDM significantly decreased (23.9% to 6.8%, p<0.01) during co-infection. This decreased viral infection was associated with NTHi-mediated transcriptomic upregulation of MDM antiviral responses (FDR p<0.05) and IFN-β release (p<0.05) prior to IAV challenge. Coinfected MDM released higher levels of inflammatory mediators (TNF-α, IL-1β, IL-6, IL-8, IL-15, IL-23 and IL-36β, all p<0.05) compared to IAV infection alone. This work demonstrates that although prior NTHi infection primed MDM to better respond to IAV infection, coinfection resulted in increased NTHi load and MDM pro-inflammatory responses. Considering the interactions of colonising airway bacteria and viral infections on host immune responses may better inform on treatment strategies to reduce exacerbations.