FIG 3.

A B-allele reassortant is not deficient in controlling the host IFN response in mammalian cell culture. (A, B) Ability of viruses to replicate despite established antiviral conditions. A549 cells were pretreated with various concentrations of human recombinant IFN-β for 24 h prior to infection with the indicated PR8 viruses at an MOI of 0.01. (A) Virus in the supernatant was titrated by plaque assay at 24 to 48 h p.i. Data are the mean titers from 24-h and 48-h multicycle infections. (B) Cell lysates were prepared at 48 h p.i., subjected to SDS-PAGE, and immunoblotted for cellular IFN-inducible Mx-1, viral NP, and tubulin. (C to E) Induction of host cell type I IFN response during infection with reassortant viruses. (C) Human lung A549 cells were infected for 24 h at various multiplicities, and active type I IFN in the supernatant was quantified using the HEK-Blue reporter cell line. (D, E) Results of assay performed as described in the legend to panel C but at an MOI of 3.