Plasma IL-1β concentrations were also elevated after psychosocial stressors in humans, but this change was fairly transient (Steptoe et al., 2007; Yamakawa et al., 2009), again supporting the view that this cytokine in the blood might play a less prominent role in depression, although these data may not speak to the central involvement of IL-1β in mediating this disorder. This evidence concerns the gene IL1B and major depressive disorder.