In patients with major depressive disorder, the blood levels of pro-inflammatory cytokines (IL-2, IL-12, and TNF-α) and monocyte chemoattractant protein-1 (MCP-1) are relatively higher, while, the blood levels of anti-inflammatory cytokines like IL-4 and TGF-β are relatively lower 59. This evidence concerns the gene CCL2 and major depressive disorder.