iPSC-based macrophage models reveal interferon-dependent control of RSV permissiveness and syncytia formation.

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory illness worldwide and affects mainly infants, immunocompromised individuals, and older adults. Understanding how immune cells contribute to RSV pathogenesis is crucial for developing interventions. However, the lack of model systems that accurately mimic in vivo immune responses has hampered progress in this field. Here, we present iPSC-derived macrophages (iMacs) as a promising model for the analysis of tissue-resident macrophage responses during RSV infection. Using monocyte-derived macrophages as a comparison, we show that iMacs are less susceptible to RSV infection. RNA-Seq of iMacs and monocyte-derived macrophages revealed fundamental differences in the baseline expression of immune-related genes between the cell types. Differences in permissiveness were attributed to interferon (IFN) signaling, as a deficiency in IFNAR signaling increased iMac susceptibility to RSV infection, accompanied by increased syncytia formation. These findings present iMacs as a promising research model system for primary macrophages and identify the IFN signaling cascade as a crucial aspect of antiviral responses during RSV infection.IMPORTANCERespiratory syncytial virus (RSV) infections remain a global health burden, with persistent gaps in understanding immune responses that may contribute to disease severity. Early innate immune responses by tissue-resident macrophages are a crucial factor in restricting RSV spread, yet limitations in accessible models have hindered progress in understanding their contribution to protective and harmful immune responses. This study presents iPSC-derived macrophages (iMacs) as a reliable and accessible tool that more accurately replicates the tissue-resident macrophage state compared to monocyte-derived alternatives. Our findings demonstrate the crucial role of effective interferon signaling in limiting susceptibility to RSV infection and the formation of RSV-induced syncytia. Disruptions in interferon signaling increased susceptibility, viral replication, and syncytia formation, revealing key host factors involved in RSV-induced cytopathology. The presented iMac model, therefore, provides deeper insights into protective immune responses, guiding improved therapies and model systems for respiratory virus research.