Nie_2011_Br.J.Pharmacol_164_444

BACKGROUND AND PURPOSE: Infections with respiratory viruses induce exacerbations of asthma, increase acetylcholine release and potentiate vagally mediated bronchoconstriction by blocking inhibitory M(2) muscarinic receptors on parasympathetic neurons. Here we test whether virus-induced M(2) receptor dysfunction and airway hyperresponsiveness are tumour necrosis factor-alpha (TNF-alpha) dependent. EXPERIMENTAL APPROACH: Guinea pigs were pretreated with etanercept or phosphate-buffered saline 24 h before intranasal infection with parainfluenza. Four days later, pulmonary inflation pressure, heart rate and blood pressure were measured. M(2) receptor function was assessed by the potentiation by gallamine (an M(2) receptor antagonist) of bronchoconstriction caused by electrical stimulation of the vagus nerves and measured as increased pulmonary inflation pressure. Human airway epithelial cells were infected with influenza and TNF-alpha concentration in supernatant was measured before supernatant was applied to human neuroblastoma cells. M(2) receptor expression in these neuroblastoma cells was measured by qRT-PCR. KEY
RESULTS: Influenza-infected animals were hyperresponsive to vagal stimulation but not to intravenous ACh. Gallamine did not potentiate vagally induced bronchoconstriction in virus-infected animals, indicating M(2) receptor dysfunction. Etanercept prevented virus-induced airway hyperresponsiveness and M(2) receptor dysfunction, without changing lung viral titres. Etanercept caused a non-significant decrease in total cells, macrophages and neutrophils in bronchoalveolar lavage. Influenza infection significantly increased TNF-alpha release from isolated epithelial cells, sufficient to decrease M(2) receptors in neuroblastoma cells. This ability of supernatants from infected epithelial cells to inhibit M(2) receptor expression was blocked by etanercept. CONCLUSIONS AND IMPLICATIONS: TNF-alpha is a key mediator of virus-induced M(2) muscarinic receptor dysfunction and airway hyperresponsiveness.