Respiratory syncytial virus deficient in soluble G protein induced an increased proinflammatory response in human lung epithelial cells.

Respiratory syncytial virus (RSV) is worldwide the single most important respiratory pathogen in infancy and early childhood. The G glycoprotein of RSV, named attachment protein, is produced by RSV-infected lung epithelial cells in both a membrane-anchored (mG protein) and a soluble form (sG protein) that is secreted by the epithelial cell. Currently, the biological role of the sG protein in primary RSV infection is still elusive. Therefore, we analyzed the inflammatory response of human lung epithelial cells (A549) infected either with wild-type RSV (RSV-WT) or a spontaneous mutant thereof deficient in the production of secreted G protein (RSV-DeltasG). Our data reveal that RSV-DeltasG, in comparison to RSV-WT, induced an increased cell surface expression of ICAM-1 on A549 cells and an enhanced release of the chemokines IL-8 and RANTES after 20 h postinfection. The increased protein expression pattern correlated with an enhanced mRNA level encoding for ICAM-1, IL-8, and RANTES, respectively. Furthermore, epithelial cells infected with RSV-DeltasG showed a more increased binding activity of the transcription factor NF-kappaB when compared to RSV-WT. In contrast, the mutant RSV-DeltasG replicated less efficiently in A549 cells than RSV-WT. Our data suggest that RSV, in the course of an ongoing infection, reduces by the production of sG protein the detrimental inflammatory response evolved by the infected resident lung epithelial cell and thereby supports its own replication.