Jiang S, et al. - In patients with stable chronic obstructive pulmonary disease (COPD), the serum levels of interleukin (IL)-17, IL-10, and IL-35, as well as correlations between their expression levels and clinical factors of patients were determined. Upregulation of serum level of IL-17, and a positive correlation of increased IL-17 expression with the Global Initiative for Chronic Obstructive Lung Disease (GOLD) grading, modified Medical Research Council (mMRC) score, and long clinical history, was observed. Increased IL-17 expression was negatively correlated with the pulmonary function of patients. Downregulation of serum levels of IL-10 and IL-35 was reported. A negative correlation of decreased IL-10 and IL-35 levels with the smoking status, GOLD grading, mMRC score, and long clinical history, but positive correlation with the pulmonary function of patients, was also observed. Overall, serum levels of IL-17, IL-10, and IL-35 can serve as indicators to estimate the progression of COPD.