IL6 and depressive disorder: Meta-analyses of cross-sectional studies confirm that serum concentrations of pro-inflammatory cytokines [e.g., interleukin 6 (IL-6)] and acute phase proteins [e.g., C-reactive protein (CRP)] are elevated in acutely unwell patients with depression in comparison with controls (Dowlati et al., 2010, Goldsmith et al., 2016, Haapakoski et al., 2015, Howren et al., 2009).