The use of alpha-smooth muscle actin as a marker of smooth muscle cells in atherosclerosis is complicated by the fact that ∼40% of these cells are also positive for CD68 positive in human coronary atherosclerotic plaques.46,47 Yet, smooth muscle cells present in the cap, producing collagen and contributing to plaque stability have, in contrast to the smooth muscle cells closer to the media, been shown to strongly express alpha-actin. This evidence concerns the gene CD68 and atherosclerosis.