In patients with COPD, the proportions of Th17/Th1 cells, identified as CD4+IFN-γ+IL-17+, among CD4 cells (median 0.203%) in the peripheral blood were significantly higher compared with never-smokers (median 0.075%, p < 0.001) and smokers (median 0.107%, p < 0.001) (Fig. 1c and Fig. 3a). Here, IFNG is linked to chronic obstructive pulmonary disease.