TNF and major depressive disorder: Researchers have observed high levels of pro-inflammatory cytokines including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) in the blood of patients suffering from depression and anxiety (Tang et al., 2018; Petralia et al., 2020; Primo de Carvalho Alves and Sica da Rocha, 2020).