TNF and major depressive disorder: Several studies have shown that a rapid increase in inflammatory factors in the peripheral serum and brain tissue in mice is one of the most important features of LPS intraperitoneal injection, an index used to model the increase in inflammatory factors in depressed patients, and the mRNA and protein expression levels of TNF-α, IL-6, and IL-1β were significantly increased in the cortices of suicidal patients with depression [43,44,45].