CCL2 and obesity due to melanocortin 4 receptor deficiency: In fact, increased circulating levels of pro-inflammatory mediators such as C-reactive protein (CRP) [9], tumor necrosis factor α (TNFα) [10], monocyte chemoattractant protein-1 (MCP-1) [11] and interleukin-6 (IL-6) [12] have been observed in obesity-associated IR.