ROLE OF AIRWAY EOSINOPHILS IN THE DEVELOPMENT OF ALLERGEN-INDUCED AIRWAY HYPERRESPONSIVENESS IN DOGS

role of the eosinophil in the development of allergen-induced airway h yperresponsiveness is uncertain. We examined whether the development o f airway hyperresponsiveness in 17 dogs after inhalation of Ascaris su um allergen (10(-6) to 10(-2) weight/volume [w/v]) was associated with increases in the number and level of activation of eosinophils before and after allergen inhalation. Airway responsiveness to inhaled acety lcholine was measured before and 24 h after Ascaris inhalation. Eosino phil number was assessed by bronchoalveolar lavage performed 1 wk befo re allergen inhalation and 15 min after the 24 h acetylcholine challen ge. Dogs that developed Ascaris-induced airway hyperresponsiveness (n = 8) had a signficantly greater number of bronchoalveolar lavage eosin ophils before allergen inhalation (mean +/- SEM: 4.6 +/- 1.94 x 10(4) cells/ml) than dogs that did not become hyperresponsive (n = 9) (1.2 /- 0.81 x 10(4) cells/ml) (p = 0.03). Ascaris-induced airway hyperresp onsiveness, measured 24 h after allergen inhalation, was not associate d with increases in eosinophil number after allergen challenge. These results suggest that the presence of airway eosinophils before allerge n inhalation is necessary for the development of allergen-induced airw ay hyperresponsiveness.