IL33 and chronic obstructive pulmonary disease: IL-33 serum concentrations were significantly elevated in COPD subjects (32.86±1.74 pg/ml) compared with healthy non-smokers (22.12±1.45 pg/ml; p < 0.001) and smokers without COPD (24.45±1.33 pg/ml; p < 0.01) (Fig. 2a).