Influenza infected macrophages release vRNA that shape the local host response

Airway epithelial cells and macrophages represent the cellular targets of infection by influenza A virus (IAV). Epithelial cells are highly susceptible to IAV infection and support viral growth by enabling the generation and release of new viral particles (productive replication). In contrast, even though macrophages are also susceptible to the initial infection, they inhibit the release of infectious viral particles (abortive infection), thereby forming a dead-end for influenza virus infection. Despite the lack of infectious virions released from infected airway macrophages, we detected newly synthesised viral RNA for multiple gene segments and NP protein in the supernatant of infected airway macrophages. We show that viral RNA released from infected macrophages is packaged into vRNP complexes and these vRNPs elicited potent inflammatory responses rather than antiviral responses when exposed to uninfected human monocytes. Virus-depleted supernatant from infected airway macrophages specifically induced CXCL13, IL-32, CCL4 and CXCL10 and is at least partially sensed through the RIG-I/MDA5 pathway. While airway macrophages represent a dead-end for IAV infection (abortive replication), we show that infected airway macrophages release vRNPs which shape the immune response of bystander cells.