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Oxidant tone regulates IL-8 production in epithelium infected with respiratory syncytial virus
J G Mastronarde1, M M Monick, G W Hunninghake
1Division of Pulmonary, Critical Care and Occupational Medicine, University of Iowa College of Medicine, Iowa City, USA.
Abstract:
Respiratory syncytial virus (RSV) is an important respiratory pathogen that preferentially infects epithelial cells in the airway, and causes a local inflammatory response. Although it has been previously demonstrated that RSV-infected airway epithelial produce cytokines, including interleukin-8 (IL-8), which contributes to the inflammatory response, the regulation of this effect of RSV is unknown. To further characterize the mechanisms by which RSV infection triggers release of IL-8, we first exposed cultured A549 cells to RSV, and measured IL-8 release via enzyme-linked immunosorbent assays (ELISA), and IL-8 messenger RNA (mRNA) induction via Northern blot analysis. We observed a dose- and time-dependent release of IL-8 in response to RSV. The optimal dose of RSV was 10(4) TCID50/ml, and maximal release of IL-8 was measured at 72 to 96 h after infection. RSV induced a biphasic (early and late) increase in IL-8 mRNA. The early phase was independent of viral infection, whereas the more pronounced late phase required the presence of live virus and infection of the epithelium. Partial (< 50%) cytopathic effects were noted at 48 h and progressed to 75% at 96 h. The monolayer was still intact at 96 h. Inhibitors of nitric oxide, including NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (L-NAME), and aminoguanidine had no effect on IL-8 release or IL-8 mRNA induction. We did, however, demonstrate a dose-dependent decrease in IL-8 release and IL-8 mRNA induction in RSV-infected epithelial treated with the antioxidants dimethyl sulfoxide (DMSO) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Peak effects were noted at a concentration of 2% DMSO and 50 microM DMPO. The antioxidants did not inhibit viral replication or infection. This data suggest that RSV-induced IL-8 production in airway epithelium is mediated via changes in oxidant tone. The data also suggest a potential therapeutic role for antioxidants in RSV infections.