However, there remains the discrepancy that an increased level of oxidative stress is suggested in the HBECs from COPD patients and NAC treatment decreased the IL-33 expression from the basal levels only in COPD patients, but there is no increase in the expression of IL-33 in the HBECs from COPD patients compared to healthy subjects. This evidence concerns the gene IL33 and chronic obstructive pulmonary disease.