TNF and major depressive disorder: In the pathogenesis of depression, immune responses to stressful stimuli within the central nervous system (CNS) are marked by the rapid activation of microglial cells and astrocytes, leading to the release of pro-inflammatory cytokines such as interleukin-1β (IL-1β), tumor necrosis factor (TNF)-α, and prostaglandin E2 (PGE2) [9].