There was higher expression of IFN-β, IFIT1, IFIT3, ISG15, and IRF7 mRNA in A549 XRN1 KO cells after 8 h of infection with various virus strains, including WSN (H1N1), PR8 (H1N1), CA04 (H1N1), and HK4801 (H3N2). This evidence concerns the gene ISG15 and infection.