Multiple case-control studies of major depressive disorder (MDD) have reported increased peripheral blood concentrations of CRP (Cohen’s d ∼0.50) and proinflammatory cytokines such as interleukin 6 (d ∼0.50) and tumor necrosis factor (d ∼0.40) in MDD 2, 3. This evidence concerns the gene IL6 and major depressive disorder.