Smoking attenuates the age‐related decrease in IgE levels and maintains eosinophilic inflammation

Summary Background Epidemiological studies have shown that smoking increases the propensity for atopy and asthma. However, the effects of smoking on atopy and eosinophilic inflammation in asthmatics, including the elderly, remain unknown. Objective To determine the effects of smoking on serum immunoglobulin E ( IgE ) levels and eosinophilic inflammation in asthmatics of all ages. Methods The associations of serum IgE levels, blood eosinophil counts and fractional exhaled nitric oxide ( FeNO ) levels with smoking and age in steroid‐naive asthmatics were cross‐sectionally assessed ( n  = 307). Levels of sputum eosinophil and thymic stromal lymphopoietin ( TSLP ) that promotes Th2 inflammation were also analysed. Current smokers were excluded when analysing contributing factors of FeNO . Results Levels of serum IgE , blood eosinophil and FeNO decreased with increasing age in never‐smokers, whereas decrease in serum IgE levels with increasing age was not observed in current smokers. In addition, current smoking was associated with higher blood eosinophil counts. In atopic asthmatics, age‐related declines in serum IgE levels were less steep in ex‐smokers than in never‐smokers, and atopic ex‐smokers with asthma showed higher blood eosinophil counts and higher FeNO irrespective of age. Lastly, sputum TSLP levels were associated with sputum eosinophil proportions and pack‐years. Current and ex‐smokers had higher TSLP levels than never‐smokers. Conclusions and Clinical Relevance In steroid‐naive asthmatics, smoking may attenuate the age‐related decrease in IgE levels and maintain eosinophilic inflammation, in which TSLP may be involved.