CCL2 and major depressive disorder: Elevated levels of white blood cells (WBC) [8], C-reactive protein [9], and both peripheral and central inflammatory cytokines, such as IL-6 [10, 11], the proinflammatory protein tumor necrosis factor-α (TNFα) [12, 13], and monocyte chemoattractant protein (MCP)-1/CCL2 [14] have been identified in patients with depression, suggesting a potential link between inflammation and depressive symptomatology.