CD4 and Parkinson disease: • Post-mortem tissue of PD patients and MPTP-mouse model demonstrates infiltration of CD8+ and CD4+ T cells in PD• MHCI expression was observed on dopamine neurons of the SN in PD post-mortem samples• MPTP-induced neurodegeneration decreased in the absence of T cells and cell death was attenuated by a lack of CD4+ T cells not CD8+ T cell