We next examined the association between the percentage of IL-4-expressing Th2 cells, and demographic characteristics and key features of COPD including age, sex, tobacco exposure (pack-years, ex-versus current smokers), respiratory symptoms (dyspnea, chronic bronchitis), severity of airway obstruction (FEV1 and FEV1/FVC) and hyperinflation (residual volume, total lung capacity), CT-scan emphysema score, systemic eosinophils count, history of exacerbation and use of inhaled corticosteroids. This evidence concerns the gene IL4 and chronic obstructive pulmonary disease.