Clinical studies have discovered the presence of various inflammatory mediators such as IL-1β, IL-6, tumor necrosis factor α (TNF-α), Toll-like receptor 3 (TLR3), and Toll-like receptor 4 (TLR4) in brains of patients with MDD patients who committed suicide, and the levels of these inflammatory factors were significantly higher than those of normal individuals (25). Here, TNF is linked to major depressive disorder.