Alteration of airway neuropeptide expression and development of airway hyperresponsiveness following respiratory syncytial virus infection.

The mechanisms by which respiratory syncytial virus (RSV) infection causes airway hyperresponsiveness (AHR) are not fully established. We hypothesized that RSV infection may alter the expression of airway sensory neuropeptides, thereby contributing to the development of altered airway function. BALB/c mice were infected with RSV followed by assessment of airway function, inflammation, and sensory neuropeptide expression. After RSV infection, mice developed significant airway inflammation associated with increased airway resistance to inhaled methacholine and increased tracheal smooth muscle responsiveness to electrical field stimulation. In these animals, substance P expression was markedly increased, whereas calcitonin gene-related peptide (CGRP) expression was decreased in airway tissue. Prophylactic treatment with Sendide, a highly selective antagonist of the neurokinin-1 receptor, or CGRP, but not the CGRP antagonist CGRP(8-37), inhibited the development of airway inflammation and AHR in RSV-infected animals. Therapeutic treatment with CGRP, but not CGRP(8-37) or Sendide, abolished AHR in RSV-infected animals despite increased substance P levels and previously established airway inflammation. These data suggest that RSV-induced airway dysfunction is, at least in part, due to an imbalance in sensory neuropeptide expression in the airways. Restoration of this balance may be beneficial for the treatment of RSV-mediated airway dysfunction.