TNF and major depressive disorder: Recently, results from a number of studies have demonstrated that activation of pro-inflammatory factors, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-a (TNF-α) may act as a significant factors in the neuronal damage associated with major depressive disorder (MDD) (Maes et al., 2012; Rawdin et al., 2013).