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 x 10(5)/ml) to 6.3 +/- 1.2 x 10(5)/ml (P < 0.01) at 24 h and to 5.7 +/- 0.9 x 10(5)/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.