Mast cell activation is not required for induction of airway hyperresponsiveness by ozone in mice

Exposure to ambient ozone(O₃) is associated withincreased exacerbations of asthma. We sought to determine whether mastcell degranulation is induced by in vivo exposure toO₃ in mice and whether mast cellsplay an essential role in the development of pulmonarypathophysiological alterations induced byO₃. For this we exposed mastcell-deficientWBB6F₁-kit^W/kit^W-v(kit^W/kit^W-v)mice and the congenic normalWBB6F₁ (+/+) mice to air or to 1 or 3 parts/million O₃ for 4 h andstudied them at different intervals from 4 to 72 h later. We foundevidence of O₃-induced cutaneous,as well as bronchial, mast cell degranulation. Polymorphonuclear cellinflux into the pulmonary parenchyma was observed after exposure to 1 part/milllion O₃ only in mice thatpossessed mast cells. Airway hyperresponsiveness to intravenousmethacholine measured in vivo under pentobarbital anesthesia wasobserved in bothkit^W/kit^W-vand +/+ mice after exposure to O₃.Thus, although mast cells are activated in vivo byO₃ and participate inO₃-induced polymorphonuclear cellinfiltration into the pulmonary parenchyma, they do not participate detectably in the development ofO₃-induced airwayhyperresponsiveness in mice.