TNF and major depressive disorder: The pattern recognition receptor toll-like receptors (TLRs), especially TLR4, are critical to initiate the inflammatory response for microglia to promote the occurrence of depression (46, 47) and characterized by increased proinflammatory cytokines TNF-α, IL-1β, IL-6, and IL-12 through the Myd88-dependent pathway (48, 49).