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.