Foam cells of the rabbit atherosclerotic plaque arrested in metaphase by colchicine show a macrophage phenotype.

Proliferative activity of smooth muscle cells and foam cells characterizes experimental atherosclerotic plaques as they first appear. Immunohistochemical and ultrastructural methods were applied to cells arrested in metaphase by colchicine and the phenotype of cells in mitosis was detected. Most of the metaphase arrested FC found in aortic plaques of cholesterol fed New Zealand rabbits were positive to the anti-macrophage monoclonal antibody and negative to the anti-smooth muscle actin monoclonal antibody. Moreover, most of the metaphase blocked FC had the ultrastructural features of macrophages. These preliminary results further strengthen previous observations on rabbit plaques that the FC pool is mainly constituted by macrophages and show, for the first time, that the dimension of this pool depends not only on migration of circulating monocytes but also on the in situ proliferation of macrophages.