BMP4 and atherosclerosis: The BMP4- and monocyte/macrophage-positive areas were largely colocalized in the atherosclerotic plaque of aortic roots, as shown in Figure 4A. Lesional monocytes and macrophages are the main cell types involved in the progression of atherosclerotic plaques, because the phagocytic activity of macrophages in the plaque contributes to the development of atherosclerosis and plaque instability.