Respiratory syncytial virus infection of human respiratory epithelial cells enhances inducible nitric oxide synthase gene expression

The induction kinetics of the mRNA of interferon regulatory factor 1 (IRF-1 ), inducible nitric oxide synthase (iNOS), and proinflammatory cytokines in respiratory syncytial virus (RSV)-infected infected human type 2 alveolar epithelial cells (A549 cells) were analyzed semiquantitatively by RT-PCR, R SV enhanced IRF-1 and iNOS mRNA expression as early as 4 h after RSV infect ion and this enhancement lasted several hours, No IFN-gamma, gene expressio n was observed during the whole course of the infection, Expression of IFN- gamma, IL-1 beta, and TNF-alpha genes was observed slightly at 4 h and beca me marked 7 h after infection, Addition of neutralizing antibodies to these cytokines to the culture had no effect on the induction of iNOS mRNA. The iNOS transcriptional activity in RSV-infected cells was significantly enhan ced by an exogenous cytokine mixture (IL-1 beta, TNF-alpha, and IFN-gamma), An apparent nitric oxide (NO) production was identified only when cytokine s were added together with RSV infection. A significant increase of iNOS ge ne expression was observed in nasopharyngeal exudate cells obtained from in fants during the acute phase of RSV bronchiolitis. These observations sugge st that RSV infection of human respiratory epithelial cells induces the iNO S gene both in vitro and in vivo; this induction may occur rather promptly and involves transcriptional activator IRF-1 induced by the RSV infection i tself, The iNOS gene, which is initially induced by RSV infection, may be f urther enhanced in a paracrine fashion by proinflammatory cytokines release d by infection-activated inflammatory cells.