THE RELATIONSHIP BETWEEN PREEXISTING SUBENDOTHELIAL SMOOTH-MUSCLE CELL ACCUMULATIONS AND FOAM CELL LESIONS IN CHOLESTEROL-FED RABBITS

We investigated whether pre-existing subendothelial smooth muscle cell (SMC) accumulations in cholesterol-fed rabbits are transformed into f oam cell plaques. Twenty-four rabbits received a standard diet supplem ented with 2% cholesterol for 4 or 8 weeks. Six rabbits received a sup plement of 0.3% cholesterol for 35 weeks. The aorta and other systemic and pulmonary vessels were studied by immunohistochemistry for smooth muscle cells SMC (alpha-SMC actin), macrophages (RAM11), cell replica tion (proliferating cell nuclear antigen) and endothelial cells (von W illebrand factor; vWF). Initially the foam cell plaques were composed exclusively of foam cells of macrophage origin (MFC). In more advanced lesions SMC and collagen fibres were also present, leading to a fibro us transformation of the plaque. Cell replication was mainly located i n the MFC. The endothelial cells covering the plaques showed an increa sed immunoreactivity for vWF which was also deposited in the interstit ium between the FC. Pre-existing subendothelial SMC did not transform into FC. The newly formed FC plaques remained clearly separated from t he pre-existing subendothelial SMC. The development of the plaques can be attributed not only to monocyte recruitment but also to macrophage multiplication.