α1‐Antitrypsin is a glycoprotein consisting of a polypeptide chain to which 3 oligosaccharide chains are bonded (54000 daltons). It is synthesized in hepatocytes. α1‐Antitrypsin is quantitatively the most important proteinase inhibitor (Pi) in serum and plasma. It specifically inactivates serine proteases (e.g. trypsin, chymotrypsin, collagenase, leukocyte elastase, plasmin and thrombin), with which it reversibly forms an enzyme‐inhibitor complex. α1‐Antitrypsin constitutes the major fraction of the electrophoretic α1‐globulin fraction. Because it is a small molecule, α1‐antitrypsin diffuses rapidly into other body fluids including bronchial secretions.
α1‐Antitrypsin is an important, positive acute phase reactant found in elevated concentrations in inflammatory processes (e.g. infectious and rheumatoid diseases), tissue necrosis, malignancy and traumas. Inflammation of the liver parenchymal cells is often accompanied by elevated α1‐antitrypsin levels, although levels of other acute phase reactants are not affected.
Acute hereditary α1‐antitrypsin deficiency is suspected in cases of neonatal hepatitis accompanied by progressive liver cirrhosis in early childhood. It is also suspected when severe pulmonary emphysema occurs in adults due to the prevalence of leukocyte elastase, which can lead to unrestrained proteolytic degradation of the pulmonary parenchymal cells.