IL17A and chronic obstructive pulmonary disease: Compared to patients with stable COPD, AECOPD exhibits greater levels of IL-2, IFN-γ, IL-4, IL-10, IL-17, and IgE, and they have lower Th1/Th2 and Il-17/IgE ratios probably due to increased production of Th2 cells [53, 54].