Increasing sputum basophils is a marker for eosinophil-dominant airway inflammation in adult asthma

Background: We previously reported the numbers of sputum basophils are positively correlated with the numbers of sputum eosinophils in asthmatic patients. However, it remains unknown whether increasing airway basophils indicate a specific inflammatory phenotype or not. Objectives: The aim of this study is to clarify the specific phenotype increasing sputum basophils. Methods: We analyzed induced sputum samples from adult asthmatic patients who were treated with ICS more than 2 months. Sputum basophils were examined by flow cytometry and sputum eosinophils and neutrophils were examined under microscopy. The airway inflammation was divided into 4 subtypes, which are paucicellular type (neutrophils 60%, eosinophils 2%) and mixed cellular type (neutrophils >60%, eosinophils>2%). Chronic sinusitis was evaluated by CT scan and scored by the Lund-Mackay system. Results: Sixty-eight samples were examined. Sputum basophils were increased in eosinophilic type. On the other hand, the numbers of sputum basophils were not increased in mixed cellular type as well as paucicellular type and neutrophilic type. CT scan to evaluate chronic sinusitis revealed a positive correlation between the numbers of sputum basophils and ethmoid scores. Conclusion: Increasing sputum basophils were observed in eosinophil-dominant inflammtion but not in mixed cellular inflammation. Airway basophils may be a useful biomarker to select appropriate therapies in biologics era.