TNF and major depressive disorder: Several meta-analyses demonstrate that depression is associated with increased levels of peripheral inflammatory markers, such as CRP (an acute phase reactant produced by the liver in response to innate immune cytokines, notably interleukin (IL)-6 and tumor necrosis factor (TNF) (Felger et al., 2020)) and cytokines within blood (important regulators of acute and chronic inflammation) (Goldsmith et al., 2016; Howren et al., 2009; Mac Giollabhui et al., 2021).