A monoclonal antibody against oxidized lipoprotein recognizes foam cells in atherosclerotic lesions. Complex formation of oxidized phosphatidylcholines and polypeptides.

In this study we have used homogenates of human atheromatous plaque as immunogen to establish a murine monoclonal antibody which recognizes oxidized low density lipoprotein (LDL). This monoclonal antibody, FOH1a/DLH3, reacted with oxidized LDL, but enzyme-linked immunosorbent assay showed that it had no reaction with native, acetylated, or malonaldehyde-treated LDL. The antibody cross-reacted with oxidized high density lipoprotein, suggesting that specific sequences of the apolipoprotein B are not essential for antigen recognition by the antibody. Immunohistochemical analysis of thin paraffin sections from human coronary arteries showed that foam cells derived from macrophages in atherosclerotic lesions were heavily stained by this antibody. Several other structures in the lesions, including swollen collagen fibers, cellular debris in necrotic cores, and endothelial cells, were moderately stained. The epitope of this antibody was characterized by a model antigen-generating system using ferrous ion-induced peroxidation of lipids. When the total lipid fraction extracted from LDL was treated with the ferrous ion-induced peroxidation system, the reaction mixture was recognized by the antibody. Antigenic product(s) was produced only when phosphatidylcholine (PC) was treated with the ferrous ion-induced peroxidation, other lipids failed to react to the antibody. To investigate the possible formation of a complex of antigenic product with a polypeptide, a synthetic peptide and a rabbit antiserum against the peptide were used. Reaction mixture of ferrous ion-induced peroxidation of PC in the presence of the peptide was added to a microtiter well precoated with the monoclonal antibody FOH1a/DLH3. After washing, the peptide remaining in the well was detected with rabbit antiserum against the peptide, whereas no reactivity was observed when peptide alone was added to the well. Binding of the antigenic complex to the precoated monoclonal antibody was competed by oxidized PC produced in the absence of any polypeptide. We conclude that oxidized phospholipid product(s) is the epitope of the monoclonal antibody and that the oxidized phospholipid forms complexes with polypeptides. The antigenic materials are detected in foam cells in atherosclerotic lesions.