CXCL8 and major depressive disorder: A meta-analysis on major depression concluded that two pro-inflammatory cytokines, interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-α), were consistently elevated in depression, while other cytokines IL-1β, IL-4, IL-2, IL-8, IL-10, and interferon-γ were not consistently elevated in depressed patients [3].