Consequently Th1 cells, which do not differ between PD patients and healthy subjects in terms of absolute count, are increased with respect to other subsets, leading to a putative Th1 bias, also confirmed by a preferential differentiation of naïve CD4+ T cells of PD patients toward the Th1 lineage and by increased production of IFN-γ and TNF-α (but not of other cytokines, including IL-17) (30). This evidence concerns the gene IFNG and Parkinson disease.