CST3 and chronic obstructive pulmonary disease: An unexpected result from our study was that, among the COPD patients and AR subjects, plasma cathepsin S and cathepsin S/cystatin C ratios were inversely correlated with the extent of airflow obstruction and emphysema severity, as assessed by LAA on CT scans, even after normalizing for various confounding factors including age, gender, BMI, renal function, smoking history, the presence of hypertension, and treatment with ICS.