IL17A and chronic obstructive pulmonary disease: Thus, the increased expression of the Th17-related cytokines and the potential role of IL-17 and IL-17 producing cells in driving the small airway inflammation in smokers has been suggested before [20–22] and an increased number of IL-17 producing cells in bronchial tissue from COPD patients compared with non-smokers has been reported [21, 23–25].