IL6 and major depressive disorder: At the same time, proinflammatory cytokines and acute-phase proteins are found significantly higher in plasma or cerebrospinal fluid (CSF) concentrations among patients with major depressive disorder (MDD), with a fairly unanimous consensus of increases in several interleukins (IL) such as IL-1β, IL-6, tumor necrosis factor-alfa (TNFα), and C-reactive protein (CRP) compared to healthy controls [39, 40].