CCL2 and major depressive disorder: In patients with MDD, the level of inflammatory mediators including cytokines, chemokines and other various inflammatory mediators, increases in the peripheral and central nervous system A meta-analysis showed that peripheral levels of interleukin-6 (IL-6), tumour necrosis factor (TNF)-alpha, IL-10, the soluble IL-2 receptor, C-C motif chemokine ligand 2 (CCL2), IL-13, IL-18, IL-12, the IL-1 receptor antagonist (IL-1RA), and the soluble TNF receptor 2 were elevated in patients with MDD compared to those in healthy controls, whereas interferon-gamma levels were lower in MDD patients (48).