Respiratory syncytial virus infection induces expression of the anti-apoptosis gene IEX-1L in human respiratory epithelial cells

By means of differential display reverse-transcriptase polymerase chain reaction, increased expression of the mRNA encoding the anti-apoptosis gene IEX-IL was found in respiratory epithelial cells infected with respiratory syncytial virus (RSV). IEX-IL mRNA expression increased 5-7-fold in RSV-infected cells at 72 h after infection but remained unchanged in cells exposed to irradiated, replication-incompetent RSV, Because IEX-IL is reported to protect cells from apoptosis induced by tumor necrosis factor (TNF)-alpha, the effect of TNF-alpha on epithelial cell apoptosis in the context of RSV infection was determined. Epithelial cells were exposed to vehicle, RSV, or irradiated RSV for 72 h, and then TNF-alpha was added to appropriate cultures, Cytochemical staining of cellular DNA with 4,6-diamidino-2-phenylindole demonstrated TNF-alpha-induced apoptosis in 23.4% of control cells but only 5% of RSV-infected cells. These data show that RSV infection protects epithelial cells from TNF-alpha-induced apoptosis and that this effect is temporally associated with IEX-IL gene expression.