In keeping with the view that stressful events might influence cytokine levels and thus promote depression, a meta-analysis revealed that psychosocial stressors increased plasma concentrations of pro-inflammatory cytokines, especially that of IL-6 (Steptoe et al., 2007), and this outcome was greater among individuals with a history of childhood maltreatment (Carpenter et al., 2010), a condition that also favors the development of depression. This evidence concerns the gene IL6 and major depressive disorder.