alpha-1-antitrypsin (alpha-1-AT) which exists in a number of genetic variants. MM variant is the most common. Alpha-1-AT is synthesized in the liver and it acts as an inhibitor of proteases such as trypsin, elastase, chymotrypsin, collagenase, leucocytic proteases, plasmin, and thrombin, which may be released during inflammatory reactions in the lung. In the absence of alpha-1-AT, these enzymes are not inhibited and they may digest pulmonary parenchyma. Alpha-1-AT deficiency is associated with chronic obstructive lung disease (emphysema) and less frequently with hepatic cirrhosis in infants and respiratory distress of the newborn. Increase in alpha-1-AT occurs as an acute phase response to tissue necrosis and inflammation. Serum level of alpha-1-AT is elevated in rheumatoid arthritis, bacterial infections, vasculitis, and carcinomatosis.