Furthermore, increased levels of different genes and proteins related to innate immunity, such as interleukins 1β (IL-1β) and 6 (IL-6), tumor necrosis factor (TNF) and toll-like receptors 3 (TLR3) and 4 (TLR4), have been observed in the brain of patients with MDD [54,55]. This evidence concerns the gene TLR3 and major depressive disorder.