IRF3 and infection: Phosphorylation of IRF3 and of the NF-κB repressor IκBα in response to SeV Cantell HD occurred rapidly and was sustained even in type I IFN receptor KO cells (Ifnar1−/−) (Fig. 1B and C), while no phosphorylation of IRF3 or IκBα was observed for up to ten hours post-infection with SeV Cantell LD despite equivalent or higher expression of the viral protein Np (Fig. 1D).