Nucleotide-mediated inhibition of alveolar fluid clearance in BALB/c mice after respiratory syncytial virus infection

Abstract

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in infants and children worldwide. Intranasal infection of BALB/c mice with RSV strain A2, but not ultraviolet-inactivated RSV, for 2 or 4 days reduced basal alveolar fluid clearance (AFC), a seminal function of bronchoalveolar epithelium, and caused loss of AFC sensitivity to amiloride inhibition. Reduced AFC was temporally associated with increased lung water content but was not a consequence of increased epithelial permeability or cell death. Reduced AFC was also not due to decreased transcription of epithelial Na+channel subunit genes in lung tissue. RSV-mediated inhibition of AFC 2 days after infection was rapidly prevented by addition to the instillate of P2Y receptor antagonists (suramin and XAMR-0721) or enzymes that degrade UTP, but not those that degrade ATP. After UTP degradation, AFC returned to control levels but was no longer sensitive to amiloride. UTP at nanomolar concentrations recapitulated the AFC inhibitory effect of RSV in normal mice and mice infected with RSV for 6 days, indicating that normalization of AFC at this time point is a consequence of cessation of UTP release, rather than P2Y receptor desensitization. We conclude that RSV infection of the bronchoalveolar epithelium results in reduced AFC as a consequence of autocrine feedback inhibition mediated by UTP. These studies are the first to demonstrate AFC inhibition by an important pulmonary viral pathogen. Reduced AFC may result in formation of an increased volume of fluid mucus, airway congestion, and rhinorrhea, all features of severe RSV disease.