To observe the effects of an IFN-induced antiviral state on influenza virus infection, human lung epithelial A549 cells untreated or pretreated with 1,000 U/ml alpha interferon (IFN-α) for 16 h were infected with A/Udorn/72 (H3N2) (Udorn) virus at a multiplicity of infection (MOI) of 5. This evidence concerns the gene IFNA1 and infection.