Specifically, levels of TNF in thehealthy adult brain are generally very low and produced primarily by neurons (Breder et al., 1993); however, in the area of maximal destruction where thevulnerable melanized DA-producing neurons reside in the ventral midbrain, the levels of TNF,IL-1β and IFNγ (interferon γ) are significantly increased in PD patientscompared with normal controls (Hirsch et al., 1998). Here, IFNG is linked to Parkinson disease.