Aortic intimal monocyte recruitment in the normo and hypercholesterolemic baboon (Papio cynocephalus). An ultrastructural study: implications in atherogenesis.

The ultrastructural features of peripheral blood monocyte margination, migration, and aortic intimal accumulation have been described in the normo- and mildly hypercholesterolemic baboon. Intimal monocyte-macrophage recruitment over fatty streaks and fibro-fatty plaques was enhanced by dietary cholesterol-fat supplementation, resulting in an 8-fold increase in monocyte-macrophages and macrophage-derived foam cells in the subendothelial space. Margination or attachment observed over both plaques and normal areas was not associated with morphologic evidence of endothelial injury. Migration through continuous aortic endothelium was principally between endothelial cells via junctions. Transitional sequences from the typical morphology of the blood monocyte to the lipid-containing macrophage or foam cell were discerned. The intimal accumulation of monocytes and macrophages reinforces our view of atherosclerosis as an inflammatory process, in which monocyte attachment is likely to reflect changes in the endothelial surface-membrane complex and surface charge, while migration to and accumulation in the SES may result from one or more chemoattractants originating in the intima or media.