EFFECT OF INHALED INTERLEUKIN-5 ON AIRWAY HYPERREACTIVITY AND EOSINOPHILIA IN ASTHMATICS

In order to investigate the role of interleukin-5 (IL-5) in airway hyp erreactivity and eosinophilia, we observed the effect of inhaled recom binant human IL-5 on airway responsiveness to methacholine and cell po pulations in induced sputum in eight patients with allergic bronchial asthma using a placebo-controlled study design. Our results demonstrat ed that the inhalation of IL-S did not alter lung function in allergic asthmatics. In the control experiments receiving either vehicle or 0. 4 ng of endotoxin, methacholine PC20 values did not change nor did the numbers of eosinophils or eosinophil cationic protein (ECP) sputum va lues change from baseline. In contrast, after IL-5 inhalation, methach oline PC20 fell from baseline (0.90 +/- 166 mg/ml) to 0.32 +/- 1.63 mg /ml (p < 0.01) at 24 h, and to 0.55 +/- 1.49 mg/ml (p < 0.05) at 48 h. Accompanying this increased airway sensitivity was a significant eosi nophilia and elevated concentrations of ECP in induced sputum. Our dat a provided direct evidence that IL-5 increases airway responsiveness a nd infiltration of activated eosinophils into the airway in patients w ith allergic bronchial asthma. It also could be concluded that the obs erved airway hyperreactivity and eosinophilia were not endotoxin relat ed.