SulCOS1 cells were transfected with efficient small interfering RNA (siRNA) against AIF (AIF1) or inefficient siRNA (AIF2 and GFP1) as a control. Mock means transfection without siRNA into infected cells. A, AIF and GAPDH were immunoblotted at 48 h posttransfection. B–D, After transfection with siRNA for 48 h, the cells were infected with the virus as described in the Material and Methods section. B, Fluorescent staining of AIF, NP, and nuclei at 7 h postinfection as described in the legend of Figure 2. C, Inhibitory effect of AIF1 on progeny virus production at 24 h postinfection. The progeny virus titers (± standard deviation) in supernatants are expressed as a relative percentage of those of mock treatment and are average values of three experiments. Student's t-test was used for statistical analysis compared to mock treatment in (C). **, p<0.01. D, Inhibitory effect of AIF1 on virus-induced apoptosis at 24 h postinfection. The results shown in (D) are representative data of two repeated experiments.