Abstract-An inactivated form of ␣ 1 -antitrypsin (AT) and LDL coelutes in gel permeation chromatography. To characterize and to quantify the amount of this fraction of AT, a monoclonal antibody was established against chloramine T-oxidized AT and named OxAT-4. OxAT-4 recognized the oxidatively modified AT, including hexylaldehyde-or 4-hydroxy-2-nonenal-modified AT, but neither normal active AT nor trypsin/AT complex. Comigration of apoB and oxidized AT was demonstrated by Western blotting analysis of AT-LDL by means of anti-apoB monoclonal antibody and OxAT-4. A complex of oxidized AT and LDL (AT-LDL) was isolated from human plasma LDL by affinity column with an OxAT-4 antibody-coated carrier. AT-LDL was degraded 4 times more effectively by mouse peritoneal macrophages, but this was not mediated by scavenger receptor class A type I. Localization of AT-LDL was detected in human atherosclerotic lesions of the coronary artery, but distribution of it was not completely identical to that of macrophages. In situ hybridization revealed AT expression by macrophages, which were present in intimal layers of the coronary artery. From these findings, we concluded that AT is produced and oxidized by macrophages, then attached to LDL in the intimal layer of the arterial wall. Although AT-LDL that escapes into the blood stream can be cleared by hepatocytes, the remaining AT-LDL may be taken up by macrophages and contribute to the lipid accumulation in arterial wall cells as the early stage of atherogenesis. Key Words:erine proteinase activity is regulated by a group of inhibitors of the serine proteinases (also called serpin). ␣ 1 -Antitrypsin (AT) is one of the serpin family proteins. It is produced mainly in the liver, and partly by macrophages stimulated by interleukin-6 or lipopolysaccharide. 1-5 At inflammatory sites, AT protects the tissue against damage caused by proteinases derived from white blood cells; in the lung, AT is produced by monocytes, which are stimulated by endotoxin, interleukin-1, and tumor necrosis factor-␣ and protect the alveolar microstructure against excess activity of proteinases. 6,7 After formation of complexes of AT with serine proteinase, AT is cleaved at the site of the serpin reactive loop and changed into the inactive form. 8,9 The resulting 4-kDa carboxy-terminal fragment of 36 residues (C-36) still binds the complex noncovalently, but under denaturing conditions in vitro, the C-36 fragment dissociates from the complex. 10,11 Recent studies have elucidated the biological activities of the C-36 fragment: upregulation of expression of the LDL receptor in HepG2 cells [12][13][14] and induction of cytokine production and CD36 expression in monocytes. 15 Furthermore, it is involved in neutrophil recruitment. 16,17 Thus, not only AT itself but also the byproducts of its enzymatic inhibition possess biological activities at the locus of inflammation.Oxidized AT is another modified form of ␣ 1 -AT, which is found in inflammatory exudates at levels of Ϸ5% to 10% of total AT 18,19 and inflammatory sy...
