Systemic inflammation is markedly evident in a number of human and mouse models of obesity, as determined by increased plasma levels of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1). Here, CCL2 is linked to obesity due to melanocortin 4 receptor deficiency.