Allergen-induced late airways reaction in the pig : influence of endogenous and exogenous glucocorticoids

Abstract

A novel model for studies of the allergen-induced late reaction in the lower airways was developed in the pig. The influence on late bronchial obstruction and granulocyte function of endogenous cortisol levels and treatment with the glucocorticoid budesonide (BUD) was evaluated. In anaesthetized and mechanically ventilated pigs actively-sensitized to Ascaris suum allergen,challenge in the lower airways caused an acute increase in total lung resistance lasting approximately 1 h. A late bronchial obstruction starting 3.5-4 h after allergen challenge was seen in pigs treated with the cortisol-synthesis inhibitor metyrapone, but not in pigs with high cortisol levels obtained in response to stress due to anaesthesia and surgical manipulation.

Bloodflow in the bronchial circulation was measured, and both acute and late decrease in bronchialvascular resistance was seen, the latter even if late bronchial obstruction was absent. An increase of the urinary metabolites of the mast cell-derived mediators histamine and leukotriene (LT) C 4(i.e. methylhistamine and LTE4, respectively) was detected during the acute reaction and this increase correlated with the magnitude of the acute bronchial obstruction. No late increase in urinary methylhistamine was seen, but late increases in LTE4 were seen in some of the pigs with late airways reactions.

Eosinophil peroxidase (EPO) was purified from Ascaris suum-infested pigs and was used to raise polyclonal antibodies recognizing porcine eosinophils by immunostaining techniques. Neutrophils in lung tissue were detected by antibodies raised against porcine myeloperoxidase (MPO). Released EPO and MPO were detected in bronchoalveolar lavage (BAL) fluid by newly developed immunoassays. A blood eosinophilia starting 4 h after allergen challenge was seenand at 8 h eosinophils were increased in lung parenchyma, around bronchioles and in BAL fluid. An increase in the activation marker EPO was also detected in BAL fluid at 8 h.Neutrophil infiltration around bronchioles was not increased after allergen challenge, even though higher numbers of neutrophils were found in BAL fluid. The levels of MPO in BALfluid were increased in some animals only.

High doses of BUD (50 µg kg-l, i.v.) given 3 h and 0.5 h before allergen challenge inhibited the late bronchial obstruction, cysteinyl LT release, blood eosinophilia, and eosinophil infiltration and activation, and reduced the number of neutrophils in BAL fluid. BUD in clinically relevant, lower doses given as an aerosol (10 µg kg-l) or in equivalent doses as an i.v.infusion (5 µg kg-l ), 1 h before allergen challenge had similar effects on granulocyte infiltration and activation. However, the aerosol treatment inhibited the late bronchial obstruction and LTrelease, whereas the systemic treatment did not. In conclusion, the actively-sensitized pig seems to be a relevant model for studies of the allergen-induced late bronchial obstruction and activation of the eosinophil and neutrophil granulocyte. This model shows that the effect of BUD on late bronchial obstruction is locally mediated and that the late obstruction does not seem to be caused by granulocyte infiltration.