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

Exposure to ambient ozone (O-3) is associated with increased exacerbations of asthma. We sought to determine whether mast-cell degranulation is induce d by in vivo exposure to O-3 in mice and whether mast cells play an essenti al role in the development of pulmonary pathophysiological alterations indu ced by O-3 For this we exposed mast cell-deficient WBB6F(1)-kis(W)/kit(W-v) (kit(W)/kit(W-v)) mice and the congenic normal WBB6F(1) (+/+) mice to air or to 1 or 3 parts/million O-3 for 4 h and studied them at different interv als from 4 to 72 h later. We found evidence of O-3-induced cutaneous, as we ll as bronchial, mast cell degranulation. Polymorphonuclear cell influx int o the pulmonary parenchyma was observed after exposure to 1 part/million O- 3 only in mice that possessed mast cells. Airway hyperresponsiveness to int ravenous methacholine measured in vivo under pentobarbital anesthesia was o bserved in both kif(W)/kit(W-v) and +/+ mice after exposure to O-3. Thus, a lthough mast cells are activated in vivo by O-3 and participate in O-3-indu ced polymorphonuclear cell infiltration into the pulmonary parenchyma, they do not participate detectably in the development of O-3-induced airway hyp erresponsiveness in mice.