Abstract 5464: CD40 Targeted Imaging of Atherosclerotic Plaque Lesions in ApoE−/− Mice
Active inflammation has been identified as major criteria for vulnerable atherosclerotic plaques. So far, they are not detectable by conventional diagnostic methods, such as coronary angiography. Therefore, we wanted to investigate whether molecules expressed in inflammatory, unstable plaques, such as CD40 receptor, can be used for molecular imaging and identification of such lesions. Monoclonal antibodies against CD40 were either coupled to cross-linked dextran-coated iron particles (CLIO) for MR imaging, or to the dye Cy5′5 for near-infrared fluorescence (NIRF) imaging. A matched IgG2A isotype antibody was used as negative control. ApoE−/− mice were fed for 4 month with high cholesterol diet and used as a model of atherosclerosis. Histological specimens of aortic tissues showed abundant expression of CD40 in atherosclerotic lesions of these animals. For NIRF imaging, either 25μg or 500μg Cy5′5-CD40 or Cy5′5-IgG2A were injected into the tail vein, and the aorta was imaged 6 and 24 hours after injection. For MR-imaging CLIO-CD40 (25μg/ml protein) or CLIO-IgG2A were injected and MR images were acquired 2 and 6 hours after injection using a 7 T scanner (Bruker). To prove the specificity of this approach NIRF imaging was also performed in double knockout Apo−/− CD40−/− mice High antibody concentrations (500μg Cy5′5-antiCD40) induced high fluorescence in the aortic wall and no difference to Cy5′5-control IgG2A at 6 and at 24 hours was detectable. Low concentrations (25μg) resulted in accumulation of fluorescence in Sudan-positive areas (r2=0.62) whereas low background fluorescence was detected after injection of Cy5′5-IgG2A (p < 0,05, n = 4) and in double knockout Apo−/− CD40−/− mice in the aortic arch. Fluorescence increased slightly after 24 hours compared to 6 hours after injection. Injection of CLIO-anti-CD40 induced a stable signal in the aortic arch in T2 weighted images of ApoE−/− mice compared to control CLIO-IgG2A. Detection of CD40 in atherosclerotic plaques with different imaging modalities is feasible. The approach might serve as a tool for detection of lesions with high inflammatory activity.