Fig. (1) Schematic representation of macrophage polarization. Circulating blood monocytes are cells with high plasticity that under influence of certain inflammatory mediators can originate different macrophage populations. First monocytes have to leave the blood compartment and then enter the tissues. Within the tissue, monocytes will be exposed to different mediators present in the microenvironment. In this way, the generation of a particular tissue macrophage population will highly be dependent on the factors present in the tissue milieu. When monocytes are exposed to pro-inflammatory cytokines such as TNF-α or IFN-γ, or LPS the generation of classically activated macrophages (M1) will take place. These macrophage populations are characterized by high production of pro-inflammatory cytokines such as TNF-α, IL-6, IL-12, IL-15 and IL-23. Inversely, when monocytes are exposed to IL-4, IL-13 or IL-10, the generation of alternatively activated macrophages (M2) will take place, which are characterized by low production of pro-inflammatory cytokines and high production of anti-inflammatory mediators such as IL-10, IL1ra and TGF-β.