IFNG and chronic obstructive pulmonary disease: NK cells exhibit hyperresponsiveness in COPD, as evidenced by the findings that CD16+ NK cells kill autologous lung CD326+ epithelial cells and that NK cells from CS-exposed mice produce higher levels of IFN-γ upon stimulation with cytokines or TLR ligands (poly(I:C), ssRNA40, or ODN1826) (34, 134, 135).