IL6 and major depressive disorder: Major psychiatric disorders such as depression, psychosis and anxiety are associated with low-grade systemic inflammation, as reflected by elevated concentrations of pro-inflammatory cytokines, e.g. interleukin-6, and acute phase proteins, e.g. C-reactive protein (CRP), in peripheral blood during acute illness (Dickerson et al., 2016; Goldsmith et al., 2016; Howren et al., 2009; Maes, 1999; Upthegrove et al., 2014; Vogelzangs et al., 2013).