Age-dependent expression and antiviral activity of interferon epsilon in respiratory epithelium

Respiratory syncytial virus (RSV) disease burden is greatest between 6 weeks and 6 months of life, with young age the most common risk factor among hospitalized children. A robust innate immune response in the airway epithelium is crucial for mitigating RSV-associated disease, but early-life immune responses to infection remain largely unexplored. RNA-seq analysis of RSV-infected primary nasal epithelial cell cultures from healthy infants at birth and 1 year revealed diminished expression of interferon epsilon (IFNE), a poorly characterized type I IFN, in newborns vs 1 year. We hypothesized, therefore, that IFNE plays an important role during infant RSV infection. We found that IFNE is basally expressed in airway epithelial cell lines. Recombinant human IFNε (rhIFNε) induced an antiviral state against an RSV clinical isolate and related Sendai virus, but not SARS-CoV-2 under the conditions tested. The antiviral potency of rhIFNε was diminished relative to rhIFN beta (rhIFNβ1) or rhIFN lambda-1 (rhIFNλ1), as evidenced by IC₅₀ data. Importantly, rhIFNε induced similar ISGs as rhIFNβ1 but demonstrated a transient temporal expression profile that differed from both rhIFNβ1 and rhIFNλ1. These results suggest that lower IFNε expression at birth may contribute to increased susceptibility to severe RSV-associated disease, offering insights into potential interventions.

Respiratory syncytial virus (RSV) is a major pediatric respiratory pathogen. Despite advances in vaccine development and monoclonal antibody prophylaxis, the immune factors driving RSV-associated disease remain unclear. Notably, severe disease is not limited to recognized high-risk groups; most affected children share only young age as a risk factor. To better understand virus-host interactions in early life, we previously derived primary airway epithelial cell cultures from the same healthy newborns at birth and at 1 year, infected them with a clinical RSV isolate, and performed total RNA sequencing. In this study, we present evidence that the transcriptional expression of interferon epsilon (IFNE), a relatively understudied type I interferon, varies with chronological age, coinciding with the period of the greatest burden of severe RSV-associated disease. We also show that recombinant human IFNε exhibits antiviral activity against RSV in airway epithelial cells, although with reduced potency compared to other type I and III interferons. These results expand our understanding of interferon responses during early-life RSV infection and suggest that reduced IFNε expression in newborns may partly explain their increased vulnerability to severe disease.