Depression is accompanied by a chronic, low-grade inflammatory state; the dysregulation of the innate and adaptive immune system; enhanced production of various cytokines, such as interleukin (IL)-1, IL-2, IL-6, IL-10, IL-12, IL-13, and IL-1β and tumor necrosis factor (TNF)-α; and decreased concentrations of interferon (INF)-γ [139,140,141,142,143]. This evidence concerns the gene IL6 and major depressive disorder.