Given that the chemokine MCP-1 disrupts the integrity of the blood–brain barrier (BBB) (Yao and Tsirka, 2014), the chemokine MCP-1 may also act in obesity as a signal to recruit bone marrow-derived monocytes/macrophages into the hypothalamus. The gene discussed is CCL2; the disease is obesity due to melanocortin 4 receptor deficiency.