IL6 and major depressive disorder: Recent meta-analyses from human studies support this hypothesis by identifying that the levels of peripheral inflammatory markers, such as C-reactive protein (CRP), interleukin-1 (IL-1), IL-2, IL-6, interferon-γ (IFN-γ), and tumor necrosis factor-α, were elevated in MDD patients compared to healthy controls (HCs) [4,5,6].