Sputum Interleukin 5 in eosinophilic and non-eosinophilic severe asthma

Background: Interleukin 5, an archetypal type 2 cytokine, is fundamental to eosinophilic airways disease, considered to signal the bone marrow to promote eosinophil progenitor maturation and increase levels of eosinophils in the circulation. Aim: To investigate the relationship between airway IL-5 concentrations and inflammatory phenotypes of severe asthma. Methods: Healthy volunteers and biologic naive severe asthma patients were clinically characterised and had blood and induced sputum samples collected. Sputum was analysed for differential cell count and supernatant (PBS processed) proteins, measured by single plex ELISA. Eosinophilic asthma was defined as sputum eosinophils >2%. Between group comparisons were assessed by Kruskal Wallis and relationships between variables by spearman rank correlations. Results: 17 healthy controls, 53 non-eosinophilic and 26 eosinophilic patients with severe asthma participated in the study. In severe asthma, there were modest correlations between sputum IL-5 and sputum eosinophils (r = 0.519, p Discussion: Despite high levels of steroid treatment, there is persistent IL-5 generation within the airways of severe asthma.