CCL2 and obesity due to melanocortin 4 receptor deficiency: During obesity, the energy excess leads to adipose expansion generating hypertrophic adipocytes that produce a wide variety of proinflammatory molecules, such as monocyte chemoattractant protein-1 (MCP-1), TNF-α, IL-1β, and IL-6 that activate and attract the immune system cells (McArdle et al., 2013).