CCL5 and major depressive disorder: In the serum and cerebrospinal fluid of MDD patients, elevated concentrations of chemokines such as interleukin-8 (IL-8/CXCL8), monocyte chemoattractant protein-4 (MCP-4), and normal T cells expressed and secreted (RANTES/CCL5) are detected [6, 25, 26].