As shown in Figures 2(b), 2(d), 2(f), and 2(h), there were no significant differences in the frequencies of CD107a+ NK cells and CD107a+ NKT-like cells stimulated by K562 cells between patients and controls, while the frequencies of IFN-γ-secreting NK cells and NKT-like cells stimulated by PMA and ionomycin were significantly less in COPD patients than in controls (P = 0.001, P = 0.037, Figures 2(a), 2(c), 2(e), and 2(g)). Here, IFNG is linked to chronic obstructive pulmonary disease.