CD4 and Parkinson disease: In a study of postmortem human PD specimens and a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, CD4+ and CD8 + T cell infiltration was observed, and MPTP-induced nigrostriatal dopaminergic cell death was attenuated by the removal of CD4+ T cells [6].