FIG. 6.

IFN-γ preincubation is essential and sufficient to block VACV growth in mouse fibroblasts. Comparison of VACV WR replication in BALB/c MEF (infected at 0.05 PFU/cell) under various conditions of IFN treatment. Cells were incubated with 500 IU/ml IFN-α (top left panel) or 500 U/ml IFN-γ (top right panel) for 48 h prior to VACV infection, and IFN exposure was maintained thereafter (top panels). Bottom left panel, IFN-γ treatment was started at the time point of VACV infection and maintained. Bottom right panel, cells were incubated with 500 U/ml IFN-γ for 48 h prior to VACV infection before IFN-containing medium was removed and cells were washed and incubated in the absence of IFN.