Use of expectorated sputum to assess airway inflammation of smoking and its cessation

: To investigate the usefulness of expectorated sputum in the assessment of airway inflammation by smoking. I examined cytokine expression in the sputum of healthy smokers and non-smokers, and compared them before, and at 8,12 and 16 weeks after, cessation of smoking. Four cytokines, interleukin (IL) 8, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and IL-10, were assessed by immunohistochemistry. In smokers, the percentage of bronchial epithelial (BE) cells and macrophages with high intracellular contents of the pro-inflammatory cytokines IL-8, IFN-gamma and TNF-alpha, were significantly increased in comparison with non-smokers. In contrast, expression of IL-10 was significantly decreased in smokers. After smoking cessation, expression of IL-8 was significantly decreased by the 16th week, that of IFN-gamma was significantly decreased by the 12th to the 16th week, but that of TNF-alpha was unchanged even at 16 weeks post-cessation, and that of IL-10 was significantly increased at that time. Cytokine expression in BE cells was similar to that in macrophages. From the data, we concluded that expectorated sputum is useful for assessing airway inflammation due to smoking and for following the series of changes that follow smoking cessation.