For instance, (1) liver fibrosis depends on recruitment of monocytes into the liver and precisely the chemokine receptor CCR2 and its ligand CCL2 participate in regulating monocyte subset infiltration [28,29]; (2) CCL2 induces human hepatoma cell migration and invasion [30]; (3) Obesity activates hepatocyte expression of CCL2 leading to hepatic recruitment of CCR2(+) myeloid cells that promote hepatosteatosis. The gene discussed is CCL2; the disease is obesity due to melanocortin 4 receptor deficiency.