TNF and depressive disorder: Production of proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β by peripheral immune cells and central nervous system (CNS)-resident microglia has been proposed as a biochemical link between pain and depression (Fasick et al., 2015, Fiore and Austin, 2016, Laumet et al., 2017, Walker et al., 2014, Zhou et al., 2015).