Higher inflammatory eosinophil levels in eosinophilic bronchitis compared to mild allergic asthma

<bold>Rationale:</bold> Patients with chronic cough often can have eosinophilic bronchitis (EB) with asthma or non-asthmatic eosinophilic bronchitis, despite similar eosinophil levels to patients with allergic asthma (AA) without chronic cough. We investigated if the frequency of eosinophil subtypes in blood and sputum is different in AA compared to EB. <bold>Methods:</bold> Patients with EB (chronic cough, FEV1≥70% predicted, sputum eosinophils>2%) and patients with mild AA (FEV1≥70% predicted, methacholine PC20≤16mg/mL and skin-prick positive) provided blood and sputum that were stained for eosinophils (CD45+CD16-CD15+) expressing resident (rEOS:CD62L+CD123-) and inflammatory (iEOS:CD62L-CD123+) and activation marker CD69 and expressed as % of total eosinophils. <bold>Results:</bold> Blood (250μl and 300μl) and sputum (3.8% and 3.2%) eosinophils in AA and EB, respectively, were similar. EB had a significantly higher frequency of iEOS and CD123+ eosinophils in blood and sputum, and higher levels of CD69+ eosinophils in sputum. <bold>Conclusion:</bold> A higher frequency of iEOS in both circulation and airways together with elevated levels of the activation marker CD69 in sputum eosinophils of EB compared to AA demonstrates a higher overall level of activated eosinophils. It is unclear whether eosinophils contribute to the pathophysiology of EB, but ongoing clinical trials with anti-IL-5 therapy will determine their relationship to cough.