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Our recent non-biased proteomic screening study revealed elevated SerpinA1 i.e. alpha-1-antitrypsin ( AAT) levels in induced sputum of smokers with Chronic obstructive pulmonary disease ( COPD). This study was designed to further investigate the role of AAT in smokers and subjects with COPD. The expression/distribution of AAT was studied by immunohistochemistry/digital image morphometry in the lung, by Western blot in the lung and sputum, and by ELISA in the plasma at baseline (n = 349) and after a 2-year follow-up (n = 58). AAT was localized mainly in airway and alveolar epithelium and endothelium, especially in smokers and in those with COPD. AAT was elevated in smokers and in subjects with COPD in the lung endothelial cells. Total lung AAT immunoreactivity was elevated in subjects with moderate COPD compared with smokers and with non-smokers. AAT showed elevated tendency in sputum of smokers with COPD compared with 'healthy' smokers. Plasma AAT levels were elevated in smokers with/without COPD compared with non-smokers. In the follow-up, plasma AAT concentrations decreased significantly after quitting smoking. Chronic smoking/ COPD leads to AAT elevation especially in the endothelium of the lung periphery; these changes reflect only modestly to the AAT in sputum, while plasma AAT significantly reflects smoking-related systemic manifestations, and decreases after smoking cessation. [ABSTRACT FROM AUTHOR]