However, another recent study by Sommer et al. showed increases in Th17 cells in PD relative to controls and follow up studies using these Th17 cells expressing IL-17A from PD patients had direct toxic effects on iPSC-derived neurons expressing IL-17R, suggesting Th17 cells may be regulators of dopaminergic neuronal survival in an experimental model of PD [162]. Here, IL17A is linked to Parkinson disease.