Effect of Inhaled Interleukin-5 on Number and Activity of Eosinophils in Circulation from Asthmatics

The aim of the present study was to examine the effects of interleukin-5 (IL-5) inhalation on changes in the activity and number of circulating eosinophils, as well as concentrations of serum total IgE, in allergic asthmatics. A randomized double-blind, placebo-controlled study design was employed in which each subject acted as his or her own control. Eight nonsmoking patients with allergic asthma were administered recombinant human IL-5 by nebulization. Total white blood cell counts and differentials, as well as concentrations of ECP and total IgE in serum, were determined before and at 2, 24, and 48 h after inhalation. Our results demonstrated that eosinophil numbers increased from baseline (3.6 ± 1.1 × 105/ml) to 6.3 ± 1.2 × 105/ml (P< 0.01) at 24 h and to 5.7 ± 0.9 × 105/ml (P< 0.01) at 48 h after IL-5 inhalation in asthmatics. Accompanying this significantly increased blood eosinophilia were significantly elevated serum ECP levels. Compared with baseline (6.3 ± 1.1 ng/ml), ECP levels increased with time following IL-5 inhalation, reaching 17.6 ± 2.8 ng/ml (P< 0.01) at 24 h and remaining elevated at 48 h (18.1 ± 2.9 ng/ml,P< 0.01). IL-5 inhalation had no significant effect on levels of serum total IgE, however. These findings provide direct evidence that nebulized IL-5 not only induces a significant blood eosinophilia but also results in the activation of circulating eosinophils. Our data further support the importance of IL-5 in the pathogenesis of bronchial asthma in humans.