It is possible that the differences in smoking status and inhaled steroid therapy affect the upward shift of Sirt1 expression through IL-6 expression in patients with severe COPD, because of the relatively lower expression of IL-6 mRNA in ex-smokers and ICS treated patients with severe COPD (Figs. 4a and 5a). Here, SIRT1 is linked to chronic obstructive pulmonary disease.