TNF and major depressive disorder: Although it is difficult to find a consensus in the many different cytokines that have been reported to be altered in MDD patients in various studies, the levels in both blood and cerebrospinal fluid (CSF) of TNFα, IL-6 and IL-1β have very often been found to be significantly elevated in individuals with MDD compared to healthy controls (Maes et al., 1997; Levine et al., 1999; Tuglu et al., 2003; O’Brien et al., 2004; Howren et al., 2009; Lindqvist et al., 2009; Dowlati et al., 2010; Hiles et al., 2012; Haapakoski et al., 2015; Kohler et al., 2017).