Figure 2: Main metabolic pathways in M1 and M2 macrophages. Left: classically activated macrophages (M1) induce an aerobic glycolytic program that results in lactate production. The pentose phosphate pathway (PPP) provides ROS for killing response. L-arginine is a substrate for iNOS which produces NO, the major effector molecule in M1 macrophage-mediated cytotoxicity. M1 macrophages display iron retention characterized by high ferritin and low ferroportin. Right: alternatively activated macrophages (M2) trigger a metabolic program including β- oxidation, Krebs cycle and oxidative phosphorylation. Arginase 1 (Arg-1) produces polyamines and L-ornithine responsible for tissue repair. Iron release (low ferritin and high ferroportin) favors tissue repair and cell proliferation.