However, long-term over-activation of microglia in the PD brain significantly up-regulates the expression of a large group of pro-inflammatory cytokines including TNF-α, IL-1β, interleukin-6 (IL-6) and IFN-γ, which contribute to the acceleration of nigral DA neuron degeneration [36, 37]. This evidence concerns the gene IL6 and Parkinson disease.