• PD patients demonstrate lower absolute counts but not frequency of Th17 cells and Tregs• PHA stimulation caused greater increase in IFN-γ and TNF-α in PD patients than HS, however no difference in IL-17A was observed and IL-10 was increased in HS but not in PD patients relative to non-stimulated cells• Co-culture of Teff and Treg cells caused ~80% reduction of IFN-γ and TNF-α in HS but only ~20% in PD patients. This evidence concerns the gene IFNG and Parkinson disease.