FIG. 10.

(A and B) Confluent VeroE6 and Calu-3 cells were left untreated (lanes 0 and 1) or pretreated with increasing concentrations of IFN-α (lanes 2 to 9, 3, 10, 30, 100, 300, 1,000, 3,000, and 10,000 U/ml) for 24 h. Cells were left uninfected (U) or were infected with VSV for 1 h (MOI, ∼1), after which all cells were washed and further incubated for 17 h, when supernatants were titrated by limiting dilution (A) and cell extracts were analyzed by immunoblotting (B). (C to E) Confluent VeroE6 and Calu-3 cells were pretreated with increasing concentrations of IFN-α as described above, infected with WT SARS-CoV (W) or m1 (m) for 1 h (MOI, ∼1) or left uninfected (U), washed, and further incubated for 17 h, when supernatants were titrated by limiting dilution (C and D) and cell extracts were analyzed by immunoblotting (E). (F) Confluent VeroE6 and Calu-3 cells were infected with WT SARS-CoV and m1 (MOI, ∼1) for 12 h, and titers were determined by limiting dilution. (G) Confluent VeroE6 and Calu-3 cells were infected with WT SARS-CoV and m1 at a low MOI of ∼4 × 10⁻⁵, and supernatants were harvested at the indicated times (hpi) and titrated by limiting dilution. Each data point represents the average titer of 9 samples for VeroE6 cells with titers of at least 7 × 10⁵ PFU/ml at 48 hpi or the average titer of 12 samples for Calu-3 cells (for Calu-3 cells, two WT SARS-CoV samples and six SARS-CoV m1 samples had undetectable levels of virus, i.e., <4.4 PFU/ml).