Airway Eosinophilia in Severe Asthma is Associated with Smoking History

Introduction: The underlying mechanisms driving eosinophilic inflammation in severe asthma are not fully understood. Experimental studies have suggested cigarette smoke as a potential driver of eosinophilic inflammation through a non-TH2-mediated innate immune response. Objective: To examine the association between eosinophilic airway inflammation and smoking history in a real-life cohort of patients with severe asthma. Methods: The SATS study examined a cohort consisting of all patients managed for severe asthma (according to ERS/ATS guidelines) across four hospitals in Denmark over a 12-month period. Patients were divided into groups based on smoking history (≥10 cigarette pack years) and airway eosinophilia (≥3% eosinophils in induced sputum). Results: A total of 117 patients were enrolled in the study. 59% were female and 52% atopic. Mean(±SD) age 46.75±14.5 (min-max 20-80), mean age at onset 28.1±20.1 (min-max 0-78). Of the 117 patients included, 94 produced a viable sputum sample. Twenty-two of the 94 (23.4%) had a history of smoking (≥10 pack years). Smoking history and airway eosinophilia were found significantly associated (eosinophilia was found in 54.5% of the (ex)smokers vs. 27.8% in non-smokers; p = 0.02). In a linear regression model including age, age at onset, atopy and smoking history, smoking history independently predicted airway eosinophilia (p=0.03). There was no association between blood eosinophilia and smoking. Conclusion: In this severe asthma cohort with predominantly late-onset asthma, airway eosinophilia was significantly associated with a smoking history of ≥10 pack years. Further research is needed to explore underlying mechanisms driving eosinophilic airway inflammation in severe asthma.