Serum levels of proinflammatory cytokines, including interleukin (IL)-1, IL-6, IL-8, IL-12, interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α), are increased in patients with depression15,16, and serum levels of IL-4, TNF-α, IL-1β, and IL-6 are higher in patients with bipolar disorder than in healthy controls17,18. Here, IL6 is linked to bipolar disorder.