TNF and major depressive disorder: A meta-analysis study by Köhler et al. indicated that pro-inflammatory factors such as interleukin-6(IL-6), tumor necrosis factor-α(TNF-α), interleukin-13(IL-13), interleukin-12(IL-12), etc., are significantly elevated in major depressive disorder (MDD) patients, which associates inflammation with depression [24].