STAT1 and infection: IFN-α-induced phospho-STAT1 expression were largely reduced in NDV-infected A549 cells (designated IFNα+/infection+) at 2 hpi and were undetectable after 4 hpi (Fig 2A); while the STAT1 in uninfected cells was phosphorylated (designated IFNα+/infection-) after stimulation with IFN-α.