Other studies showed that the levels of proinflammatory cytokines in the peripheral nervous system and CNS tissue of patients with depression were higher as compared to those in healthy subjects [32], and the brain tissue obtained from the victims of depressive suicide exhibited elevated expression levels of interleukin-1beta (IL-1β), IL-6, and tumor necrosis factor (TNF) [33, 34]. Here, IL6 is linked to major depressive disorder.