Figure 1. Heterogeneity of Mononuclear Phagocytes in the Atheroma.
In early atherosclerotic plaques (shown on the left-hand side of the diagram), proinflammatory leukocytes, characterized by high levels of Ly6c and the chemokine receptor CCR2, preferentially adhere to the activated endothelial monolayer overlying the early plaque. The adherent leukocytes enter the intima by diapedesis. Accumulation of mononuclear phagocytes in the early atherosclerotic plaque occurs primarily by recruitment from blood. In the advancing atheroma (right-hand portion of the diagram), monocyte macrophage replication occurs in response to hematopoietic growth factors, some of which may arise from a specialized set of B lymphocytes known as immune response activator B cells (34). The mitotic figures indicate cellular replication. Mononuclear phagocytes resident in the intima ultimately will accumulate cholesteryl ester, forming foam cells, the hallmark of the atherosclerotic lesion. CCR = CC chemokine receptor.