IRF3 and infection: This inhibition of IRF3 activation by ActD was observed even when the multiplicity of infection was considerably increased; while ∼50 PFU/cell PR8-ΔNS1 induced substantial levels of phospho-IRF3 in untreated and CHX-treated A549 cells, negligible IRF3 activation was detectable in ActD-treated infected cells (Fig. 3E).