Chemokines Control Monocyte Homeostasis Under Steady State and in Hypercholesterolemia

Monocytes and macrophages are abundantly present in both human atherosclerotic plaques and lesions obtained from animal models. Direct evidence for the importance of monocytes in atherogenesis could be demonstrated in a study where their depletion reduced the plaque formation in rabbits. Three principal monocyte subsets (named classical, intermediate, and nonclassical) have been described in mice and man. In humans, monocytes can be differentiated based on the expression of CD14 and CD16. Classical monocytes are defined as CD14CD16, intermediate monocytes as CD14CD16, whereas nonclassical monocytes are CD14CD16. In mice, CD115 monocyte subsets are mainly discriminated based on the expression of lymphocyte antigen 6C (Ly6C) but also CD43. Monocytes being Ly6CCD43 are CX 3 CR1CCR2 and thought to correspond to human classical monocytes. In contrast, murine Ly6CCD43 monocytes being CX 3 CR1CCR2 are phenotypic equivalents of human nonclassical monocytes. Of note, although yet unconfirmed, a recent study provides evidence for classical monocytes to be of dominant importance in atherogenesis and progression as compared with their nonclassical counterparts in mice.