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). This evidence concerns the gene CRP and major depressive disorder.