In an experimental model of Parkinson's disease that utilized injection of the dopaminergic specific neurotoxin MPTP the number of activated microglial cells in the substantia nigra pars compacta of IL-18 KO mice was reduced compared to wild-type [117], indicating the possibility that IL-18 may participate in microglial activation and dopaminergic neurodegeneration. The gene discussed is IL18; the disease is Parkinson disease.