A plethora of immune cytokines have been found to be implicated in the pathophysiology of depression, including interleukins (IL)-1β, IL-2, IL-4, IL-6, IL-8, IL-10 interferon gamma (IFN-γ), C-reactive protein (CRP), tumor necrosis factor α (TNFα) and the chemokine monocyte chemoattractant protein-1 (MCP-1) [56,57]. This evidence concerns the gene CCL2 and major depressive disorder.