To characterise the source of lung IL-18 in this study and investigate its possible dysregulation in COPD, we carried out a detailed mapping of the IL-18 localization by immunohistochemistry using tissue sections from COPD patients of different disease severity (n = 31), never-smokers (n = 8) and smokers with normal lung function (n = 7). This evidence concerns the gene IL18 and chronic obstructive pulmonary disease.