Remarkably, studies identifying Th17 by means of intracellular IL-17 staining reported increased Th17 in PD patients, with the only exception of Cen et al. (98) who found no differences between patients and HS, while studies identifying Th17 cells by means of surface markers found similar or even reduced Th17 in patients in comparison to HS. This evidence concerns the gene IL17A and Parkinson disease.