Mounting evidence suggests that the levels of some pro-inflammatory cytokines [e.g., interleukin (IL)-1β, IL-6, IL-18, and tumor necrosis factor (TNF)-α] are increased in depressive disorder, whereas some anti-inflammatory cytokines [e.g., IL-10 and transforming growth factor (TGF)- β1] are decreased (73, 74). Here, IL18 is linked to depressive disorder.