FIG. 3.
Entry and syncytium formation of IBV are blocked by furin inhibitor. (a) Pretreatment with furin inhibitor did not affect attachment but blocked IBV entry. The gRNA level in virus-infected cells was investigated with a quantitative real-time RT-PCR. The values are shown as relative amounts against 0 μM of furin inhibitor treatment. ND, not done. The error bars indicate standard deviations of the means. (b) The number of infected cells was reduced by pretreatment with furin inhibitor, while posttreatment blocked giant syncytium formation. Syncytium formation was observed by IF staining with the S2 Ab at 16 h postinfection. Giant syncytia caused by primary infection are indicated by arrows. (c) Inhibitory effects of pretreatment with furin inhibitor were caused by less primary infection, while those of posttreatment were due to blocking of cell-to-cell spread and secondary infection. The effects of furin inhibitor treatments on rIBV-Luc infection were investigated. Luciferase activity in virus-infected cells was measured at 7, 10, 13, and 16 h postinfection. The error bars indicate standard deviations of the means.