CCL2 and obesity due to melanocortin 4 receptor deficiency: Although it was demonstrated that MCP-1/CCR2 signaling is important for obesity-induced insulin resistance and that the use of a CCR2 antagonist can ameliorate this condition without affecting macrophage infiltration into adipose tissue, it is difficult to state if IR is induced by MCP-1 per se or if it depends on recruited macrophages that release other cytokines (Kanda et al., 2006; Panee, 2012).