Dysregulated airway epithelial antiviral immunity in Down Syndrome impairs type III IFN response and amplifies airway inflammation during RSV infection.

Trisomy 21 (TS21), also known as Down syndrome (DS), increases pediatric mortality risk from respiratory syncytial virus (RSV) by nine-fold, yet its underlying immunological basis remains unclear. Here, we investigated RSV-induced immunological responses in TS21 airway epithelial cells (AECs), the primary site of respiratory virus entry and host defense. TS21 AECs exhibit hyperactive interferon (IFN) signaling and reduced RSV infectivity, but they also show impaired type-III IFN responses during viral infection. Furthermore, TS21 AECs demonstrate heightened production of proinflammatory mediators CXCL5 and CXCL10 both before and after RSV exposure. Infants with DS suffering from severe viral bronchiolitis demonstrate dysregulated airway immune responses in vivo, characterized by diminished type-III IFN levels and increased CXCL5/CXCL10 secretion. Our results indicate that RSV severity in DS is not due to impaired viral control but to dysregulated airway proinflammatory responses, offering new therapeutic opportunities to mitigate the severity of RSV infection in children with DS.