TNF and Parkinson disease: As the main immune cells in the central nervous system (CNS), microglia are activated and produce a large amount of pro-inflammatory cytokines including interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α, which impact neuronal function and increase cell death in PD (Kannarkat et al., 2013; Moehle and West, 2015).