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(Circulation Research. 2007;100:884.)
© 2007 American Heart Association, Inc.

Cellular Biology

Monocyte/Macrophage Suppression in CD11b Diphtheria Toxin Receptor Transgenic Mice Differentially Affects Atherogenesis and Established Plaques

Victoria Stoneman, Denise Braganza, Nichola Figg, John Mercer, Richard Lang, Martin Goddard, Martin Bennett

From the Division of Cardiovascular Medicine (V.S., D.B., N.F., J.M., M.B.), University of Cambridge, UK; Divisions of Developmental Biology and Ophthalmology (R.L.), Children’s Hospital Research Foundation, Children’s Hospital Medical Center, Department of Ophthalmology, University of Cincinnati, Ohio; and Department of Pathology (M.G.), Papworth Hospital, Cambridge, UK.

Correspondence to Martin Bennett, Division of Cardiovascular Medicine, University of Cambridge, PO Box 110, Addenbrooke’s Hospital, Cambridge CB2 2QQ, UK. E-mail mrb{at}mole.bio.cam.ac.uk

Although monocytes/macrophages are considered important in atherogenesis, their role in established plaques is unclear. For example, macrophage content is associated with plaque instability, but their loss through cell death is observed at sites of plaque rupture. To examine the role of monocytes/macrophages in atherosclerosis, we developed CD11b–diphtheria toxin (DT) receptor (DTR) transgenic mice, whereby administration of DT selectively kills monocytes/macrophages. DT treatment reduced peripheral blood monocytes and tissue macrophages and inhibited macrophage function in CD11b-DTR mice and apolipoprotein E–null (apoE^–/–) mice transplanted with CD11b-DTR bone marrow. In atherogenesis experiments, DT markedly reduced plaque development and altered plaque composition, reducing collagen content and necrotic core formation. In mice with established plaques, acute DT treatment induced macrophage apoptosis and reduced macrophage content but did not induce plaque inflammation, thrombosis, or rupture. Furthermore, despite a 50% reduction in monocytes, chronic DT treatment of these mice did not alter plaque extent or composition, most likely because of ongoing recruitment/proliferation of monocytes with recovery of macrophage content. We conclude that monocytes/macrophages are critical to atherogenesis, but established plaques are more resistant to reductions in monocytes.

Key Words: apoptosis • atherosclerosis • macrophages

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