Clinical studies have found that levels of inflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), are abnormally elevated in the peripheral blood and cerebrospinal fluid of patients with depression, and that inflammatory cytokines in patients with depression can return to normal levels after administration of antidepressants [9,10,11]. Here, TNF is linked to major depressive disorder.