TNF and Parkinson disease: During PD pathology, over-produced or misfolded α-synuclein is secreted in many regions of the brain by neurons which activates microglia, leading to pro-inflammatory responses with elevated levels of cytokines including IL-1β, IL-6, and TNF-α, the production of free radicals, and contributions to neuron toxicity [87], which subsequently drives the PD progression.