IRF3 and infection: Consistent with data for FluΔNS1 (Fig 2A and 2C), which displayed no dependency on PKR for IFN production, infection of PKR-null MEFs with another RIG-I agonist and strong inducer of IRF3 phosphorylation, Sendai virus (SeV), did not result in a significant defect in IRF3 activation (Fig 4).