SerpinA1, also known as Alpha-1 Antitrypsin （AAT）, is a prototype member of the Serpin superfamily, which are serine protease inhibitors. This inhibitor specifically targets the protease neutrophil elastase. Primarily produced in the liver, Alpha-1 Antitrypsin functions as an antiprotease, with its main role being the inactivation of neutrophil elastase to prevent tissue damage. SerpinA1 （Alpha-1 Antitrypsin）, an acute phase protein and a classical inhibitor of neutrophil elastase, is localized within lipid rafts in primary human monocytes in vitro. Its association with monocytes is modulated by cholesterol levels; it is inhibited by cholesterol-depleting agents such as nystatin, filipin, methyl-beta-cyclodextrin （MbetaCD）, and oxidized low-density lipoprotein （oxLDL）, and conversely, enhanced by the presence of free cholesterol.