TNF and major depressive disorder: Among the few studies that have examined brain cytokine variations associated with depressive illnesses, several pro-inflammatory cytokines, including IL-1 and a precursor of the soluble form of TNF-α, TNF trans-membrane, were reported to be up-regulated in post-mortem PFC of patients with major depression (Dean et al., 2010; Shelton et al., 2011).