title: Role of TNF-α in virus-induced airway hyperresponsiveness and neuronal M₂ muscarinic receptor dysfunction.
abstract: OBJECTIVE
  Infections with respiratory viruses induce exacerbations of asthma, increase acetylcholine release and potentiate vagally mediated bronchoconstriction by blocking inhibitory M₂ muscarinic receptors on parasympathetic neurons. Here we test whether virus-induced M₂ receptor dysfunction and airway hyperresponsiveness are tumour necrosis factor-alpha (TNF-α) dependent.
  
  
  METHODS
  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. M₂ receptor function was assessed by the potentiation by gallamine (an M₂ 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-α concentration in supernatant was measured before supernatant was applied to human neuroblastoma cells. M₂ receptor expression in these neuroblastoma cells was measured by qRT-PCR.
  
  
  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 M₂ receptor dysfunction. Etanercept prevented virus-induced airway hyperresponsiveness and M₂ 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-α release from isolated epithelial cells, sufficient to decrease M₂ receptors in neuroblastoma cells. This ability of supernatants from infected epithelial cells to inhibit M₂ receptor expression was blocked by etanercept.
  
  
  CONCLUSIONS
  TNF-α is a key mediator of virus-induced M₂ muscarinic receptor dysfunction and airway hyperresponsiveness.
authors: Department of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, USA.
authors: Zhenying
authors: Z
authors: Nie
authors: Gregory D
authors: GD
authors: Scott
authors: Patrick D
authors: PD
authors: Weis
authors: Asako
authors: A
authors: Itakura
authors: Allison D
authors: AD
authors: Fryer
authors: David B
authors: DB
authors: Jacoby
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D016535:Bronchial Hyperreactivity / Q000235:genetics / Q000378:metabolism* / Q000821:virology*; D018893:Bronchoalveolar Lavage / Q000379:methods; D016084:Bronchoconstriction / Q000187:drug effects; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004558:Electric Stimulation / Q000379:methods; D004847:Epithelial Cells / Q000378:metabolism; D000068800:Etanercept; D005260:Female; D005703:Gallamine Triethiodide / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007249:Inflammation / Q000378:metabolism; D008168:Lung / Q000378:metabolism / Q000821:virology; D016676:Macrophages, Alveolar / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism; D043585:Receptor, Muscarinic M2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics* / Q000378:metabolism*; D014630:Vagus Nerve / Q000187:drug effects / Q000378:metabolism*; D014780:Viruses / Q000472:pathogenicity
chemical_list: D007074:Immunoglobulin G; D043585:Receptor, Muscarinic M2; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D000109:Acetylcholine; D000068800:Etanercept; D005703:Gallamine Triethiodide