TNF and major depressive disorder: Clinical investigations reported the activation of macrophages and lymphocyte subtypes, such as M1, M2, T help (h)1 and Th17 cells, and their excessively secreted pro-inflammatory cytokines, such as interleukin (IL)-1, IL-6, interferon (IFN)-γ and tumor necrosis factor (TNF)-α, in patients with major depression [3].