CCL2 and obesity due to melanocortin 4 receptor deficiency: They become the main source of proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 [13,14,15,16], and the chemokine monocyte chemoattractant protein-1 (MCP-1) that is elevated in both the adipose tissue [13,14,17] and plasma [17] of mice with diet-induced obesity.