IL6 and infection: As an independent metric for corroborating virus replication, we measured levels of the inflammatory cytokines IL-6 and IFNβ in lungs during infection, which mirrored viral loads, with IFITM3 KO passage 10 inducing a statistically significant increase in both IL-6 (Fig. 4d) and IFNβ (Fig. 4e) compared to infection with parent virus.