Monoclonal Autoantibody Against a Cryptic Epitope on Tissue-Adherent Low-Density Lipoprotein for Molecular Imaging in Atherosclerosis

Background: Antibody-based constructs for molecular imaging and therapeutic delivery provide promising opportunities for the diagnosis and treatment of atherosclerosis. Objectives: The authors aimed to generate and characterize immunoglobulin (Ig)G monoclonal autoantibodies in atherosclerosis for targeting of novel molecular determinants. Methods: The authors created hybridomas from an unimmunized low-density lipoprotein (LDL) receptor-deficient (Ldlr^−/−) mouse and selected an IgG2b isotype autoantibody, LO9, for further characterization. Results: LO9 reacted well with native LDL bound to immobilized matrix components and less well to oxidized LDL. LO9 binding to immobilized native LDL was not neutralized by fluid-phase native LDL, indicating an adhesion-dependent epitope. The authors localized the epitope to a 20 amino-acid peptide sequence (P5) in the globular amino-terminus of apolipoprotein B. LO9 reacted with antigen in mouse atherosclerosis and in both human stable and ruptured coronary atherosclerosis. Furthermore, in vivo near-infrared fluorescence molecular tomographic imaging, and ex vivo confocal microscopy showed that intravenously injected LO9 localized beneath endothelium of the aortic arch in Ldlr^−/− mice, in the vicinity of macrophages. Conclusions: The authors believe LO9 is the first example of an IgG autoantibody that reacts with a native LDL epitope revealed by adherence to tissue matrix. Antibodies against adherent native LDL have potential as molecular targeting agents for imaging of and therapeutic delivery to atherosclerosis.