Granulocyte function in the airways of allergen-challenged pigs: effects of inhaled and systemic budesonide.

BACKGROUND: Late airways obstruction and eosinophil infiltration after allergen challenge are often seen in human asthma and animal models of allergy. This inflammatory reaction, which may be a link between acute and chronic asthma, is blocked by glucocorticoid pretreatment. However, the role of eosinophils in late airways obstruction and the primary site of action of glucocorticoids, i.e. locally or systemically, have not been fully determined.

OBJECTIVES: This study was initiated to find out the role of eosinophils and neutrophils in allergen-induced late airways obstruction in the pig. The effect of pretreatment with budesonide (BUD) given locally or systemically on cellular responses seen within 8 h after allergen challenge was also studied.

METHODS: Twenty-five minipigs were actively sensitized with Ascaris suum antigen and challenged under anaesthesia with antigen in the lower airways. Pigs were given BUD as an aerosol (10 micrograms/kg) or an intravenous infusion (5 micrograms/kg) 1 h before allergen challenge. In one group, high doses of BUD (50 micrograms/kg) were infused twice with a 3-h interval before allergen challenge. As a positive control, one group was given the BUD vehicle as an infusion and as a negative control, one group not treated with BUD was given the irrelevant antigen ovalbumin. Eosinophils and neutrophils in lung tissue specimens were detected and levels of eosinophil peroxidase (EPO) and myeloperoxidase (MPO) in bronchoalveolar lavage (BAL) fluid were measured using specific antibodies against porcine EPO and MPO.

RESULTS: The number of eosinophils in lung tissue and BAL fluid and the level of EPO in BAL fluid were significantly increased 8 h after A. suum challenge in pigs not treated with BUD. With regard to possible recruitment and activation of neutrophils the only significant finding was an increase in the number of cells in BAL fluid. The eosinophil numbers and the level of EPO in BAL fluid were shown to be decreased by all BUD treatments in all the compartments studied compared to the positive control. However, the number of eosinophils in lung tissue and EPO levels in BAL fluid did not correlate with the magnitude of the late airways obstruction.

CONCLUSION: Although eosinophils are present in the bronchial wall and lumen and are apparently activated, a causative relationship between this granulocyte and the late bronchial obstruction could not be established in this model.