Several lines of evidence have demonstrated the involvement of IL-1β in MDD (44): (1) epidemiological data showed that levels of IL-1β in peripheral circulation and cerebrospinal fluid (CSF) of patients with MDD were increased; (2) antidepressants treatment could change the levels of IL-1β; (3) IL-1β administration could induce depression-like behaviors in rats. This evidence concerns the gene IL1B and major depressive disorder.