TNF and Parkinson disease: For two decades, PD researchers have known about the presence of elevated levels of cytokines[including TNF (tumour necrosis factor), IL (interleukin)-1β, IL-2, IL-4 and IL-6] inpost-mortem SN of PD patients (Mogi et al., 1994a, 1994b; Hunot and Hirsch, 2003).