IRF3 and infection: To analyze at the single-cell level how infected cells induce an antiviral state in bystander cells, we performed infections at an MOI of 0.1, fixed the cells at 24 h postinfection, and immunostained them for active IRF3 (as evidence of the detection of viral RNA by cell), phosphorylated STAT1 (p-STAT1) (used as an indicator of the antiviral state), and viral proteins.