IL6 and Parkinson disease: Alterations in cytokine levels have been observed in PD brains, with elevated immunoreactivity of interleukin-1β (IL-1β), interleukin-2 (IL-2), interleukin-6 (IL-6), tumour necrosis factor (TNF), and transforming growth factor-β1 (TGF-β1) detected specifically in the striatal dopaminergic regions of PD brains (Mogi et al., 1994a, b).