To determine whether pre-treatment of cells with IFN-β would override the inhibitory effects of NS1-wt, we treated A549s cells with increasing doses of IFN-β 16 h prior to infection with the rIAVs (i.e., to eliminate the inhibitory effects of NS1 by generating IFN-inducible antiviral responses that would precede infection). Here, IFNA1 is linked to infection.