The aim of this study was to evaluate kallikreins and its substrate, CCN, in COPD patients. Kallikreins are a subgroup of serine proteases, enzymes which are able to cleave peptide bonds in proteins. Kallicrein profile is unkonwn in COPD. The investigators will assess Kallikrein 1 to 15 and CCN 1 to 6 in sputum of patients. Three groups of patients will be included: Healthy smoker subjects, stable COPD patients and COPD patients with acute exacerbation. Kallicrein levels in sputum will be compared in these groups.