Effect of murine recombinant interleukin‐5 on bronchial reactivity in guinea‐pigs

We have reported that an intratracheal injection of murine recombinant interleukin-5 (mrIL-5, 15 micrograms/0.25 ml/animal) induces the increased number of inflammatory leucocytes and epithelial cells in bronchoalveolar lavage fluid (BALF) 24 hr after administration of mrIL-5 in guinea-pigs [1]. In this paper, we have examined the effects of mrIL-5 on bronchial reactivity in guinea-pigs. An intratracheal injection of mrIL-5 (15 micrograms/0.25 ml/animal) induced airway hyperresponsiveness to acetylcholine (ACh) which was accompanied with eosinophilia and neutrophilia in blood at 24 hr in guinea-pigs. Bovine serum albumin (BSA, 15 micrograms/0.25 ml/animal) used as a reference material did not cause airway hyperresponsiveness, blood eosinophilia and neutrophilia. Prednisolone (20 mg/kg, i.p.) inhibited mrIL-5-induced airway hyperresponsiveness, eosinophilia and neutrophilia. Ketotifen (2 mg/kg, i.p.) also reduced this airway hyperresponsiveness and neutrophilia but not eosinophilia. In contrast, the injection of 2% disodium cromoglycate (DSCG) into the trachea showed the tendency of inhibitory effects against mrIL-5-induced airway hyperresponsiveness, eosinophilia and neutrophilia. The present data indicate that mrIL-5 induces airway hyperresponsiveness, blood eosinophilia and neutrophilia in guinea-pigs and that prednisolone and ketotifen inhibit mrIL-5-induced airway hyperresponsiveness accompanied with reduction of the increased number of leucocytes, suggesting that eosinophils and neutrophilia in blood may be important for the onset of bronchial hyperresponsiveness caused by mrIL-5 in guinea-pigs.