Loss of pulmonary tissue protection and neutrophil microbicidal defects promote severe <i>Aspergillus fumigatus</i> infection during influenza A virus infection

Invasive pulmonary aspergillosis (IPA) is a severe fungal disease caused by <i>Aspergillus fumigatus</i> (<i>Af</i>) that may spread hematogenously to extrapulmonary organs. IPA is typically associated with a broad spectrum of immunocompromised conditions and constitutes a high mortality rate. While the association of influenza as a risk for secondary bacterial infections is well appreciated, emerging evidence indicates that influenza-hospitalized patients demonstrate increased susceptibility to severe aspergillosis infection. In this study, we developed a murine Influenza A Virus (IAV)-<i>Af</i> co-infection model and investigated the role of IAV host response in promoting invasive <i>Af</i> infection. Our data show that IAV temporarily suppresses neutrophil recruitment in the early phase of <i>Af</i> co-infection (24 hours), followed by a subsequent increase in neutrophil levels (48 hours). RNA sequencing analysis of neutrophils from IAV-<i>Af</i> co-infected lungs (48 hours) reveals enrichment of pathways regulating inflammatory responses and phagocytosis. Despite higher inflammatory response and phagocytosis, the host response from IAV-<i>Af</i> co-infected lungs had suppressive effects on neutrophil conidial killing, correlating with lung fungal load and invasion. However, the increased fungal invasion observed at 24 hours post co-infection, despite similar fungal loads in both groups (<i>Af</i> vs. IAV-<i>Af</i>), suggests that IAV-induced pathologic lung inflammation and vascular damage likely promote <i>Af</i> invasiveness during the initial phase of co-infection, and subsequently, the defects in neutrophil fungicidal response and exacerbated lung damage lead to sustained and fatal IPA pathogenesis in the later phase of co-infection.