This study showed that, despite limited replication in AMs, swIAV inhibited PRRSV replication in porcine AMs, likely through IFNβ modulation, with variations based on AMs origin. Co-culture with respiratory epithelial cells significantly enhanced swIAV-induced PRRSV inhibition, indicating a synergistic antiviral response. These findings revealed a plausible role of animal sanitary status on swIAV-PRRSV interactions, justifying further research into viral dynamics and respiratory immunity. The long lifespan and susceptibility of AMs to infections call for more studies on long-term effects in the swine respiratory disease complex.

Alveolar macrophages (AMs) are important for defending the lungs against respiratory infections, such as influenza. In pigs, the interaction between AMs and swine influenza A virus (swIAV) requires further investigation, particularly due to its association with other pathogens within the porcine respiratory disease complex (PRDC). Among these pathogens, porcine reproductive and respiratory syndrome virus (PRRSV) infects and depletes AMs, whereas swIAV primarily targets epithelial cells in the respiratory tract. In this study, we explored the effects of swIAV on AMs, as well as the impact of swIAV/PRRSV co-infection on AMs and within a porcine epithelial cell line/ AMs co-culture system using AMs from swine with different health statuses.