| Respiratory syncytial virus (RSV) is a major cause of infectious bronchiolitis and is responsible for significant morbidity and mortality. While those at highest risk of infection include infants, the elderly and immunocompromised adults, no one generates long-term, protective immunity to RSV. Links have been established between severe RSV infection in infancy and subsequent development of asthma and between RSV disease and exacerbation of asthma in all age groups.;Chemokines and cytokines are induced by RSV from infected respiratory epithelia. Using the alveolar epithelial cell line A549 as a model, we have shown that RSV infection leads to the induction of protein and mRNA expression of the chemokines interleukin (IL)-8, monocyte chemoattractant protein (MCP)-1, and regulated upon activation, normal T cell expressed and secreted (RANTES) as well as the cytokine IL-15. The primary objectives of this work were to identify genes activated in A549 cells by RSV and investigate the mechanism of their induction. Ribonuclease protection assay (RPA) showed increased levels of a variety of mRNA including IL-1alpha, IL-6, IL-8, IL-15, lymphotoxin (LT)-beta, MCP-1 and RANTES. Similar mRNA profiles were induced by the proinflammatory cytokine, tumor necrosis factor (TNF) alpha. However, the kinetics of induction by the cytokine were different from those of RSV, which were lower in magnitude and delayed. Addition of two inhibitors, dexamethasone (DEX), a synthetic glucocorticoid, and N-acetyl-L-cysteine (NAC), an antioxidant precursor to glutathione, demonstrated discriminating effects on gene induction. NAC consistently inhibited RSV inductions of mRNAs while not inhibiting or even enhancing TNFalpha induction. In contrast, DEX inhibited predominantly TNFalpha induction.;Analysis of transcription factor binding activity showed that both agonists enhanced NF-kappaB translocation with RSV preferentially augmenting RelA. NAC and DEX did not decrease binding of RelA or NF-kappaB1 induced by TNFalpha. Inhibition of RSV induced binding of RelA was predominant over NF-kappaB1 by both DEX and NAC. While the mechanisms of induction of genes by RSV and TNFalpha each utilize enhancement of NF-kappaB binding, the proteins involved in the complexes differ indicating that different mechanisms are used by the agonists. These mechanisms lead to specific induction of chemokines and cytokines by RSV in contrast with TNFalpha. |
