Studies have shown that microglia are activated regionally in the SN of PD patients and animal models (16,18,19,118), and that the levels of a number of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-2 and IL-6, are also upregulated in PD (119–122), indicating the involvement of the inflammatory response in PD pathogenesis. Here, IL2 is linked to Parkinson disease.