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Effect of inhaled interleukin-5 on eosinophil progenitors in the bronchi and bone marrow of asthmatic and non-asthmatic volunteers

Authors


Correspondence:
Prof. A. B. Kay, Leukocyte Biology Section, NHLI Division, Imperial College London, South Kensington Campus London SW7 2AZ, UK.
E-mail: a.b.kay@imperial.ac.uk

Summary

Background Asthma is characterized by increases in mature eosinophils and their progenitors within the bronchus and bone marrow. IL-5 plays a key role in eosinophil development in the bone marrow and at the site of allergic inflammation. We therefore studied the effects of nebulized IL-5 on eosinophils, their progenitors and in situ haemopoiesis within the airway and bone marrow.

Methods Nine atopic asthmatics and 10 non-atopic non-asthmatic control volunteers inhaled 10 μg of IL-5 or placebo via a nebulizer in a double-blind, randomized, cross-over study. Bronchoscopy, bone marrow aspiration and peripheral blood sampling were performed 24 h after nebulization. Four weeks later, volunteers inhaled the alternative solution and underwent a repeat bronchoscopy and bone marrow aspiration.

Results Inhalation of IL-5 significantly decreased CD34+/IL-5Rα mRNA+ cells within the bronchial mucosa and the percentage of CD34+ cells that were CCR3+ within the bone marrow of atopic asthmatic, but not control, volunteers. Inhalation of IL-5 also induced a significant increase in bronchial mucosal eosinophils in the non-atopic non-asthmatic control volunteers, but not in the asthmatics. IL-5 had no effect on spirometry or airways hyper-reactivity in either group.

Conclusions Inhaled IL-5 modulated eosinophil progenitor numbers in both the airways and bone marrow of asthmatics and induced local eosinophilia in non-asthmatics.

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