When studying the effect of CD8+ and CD4+ T cell involvement in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models of PD, a notable decrease in dopaminergic cell death was observed in Cd4−/− mice compared to WT littermates and Cd8a−/− mice [310]. The gene discussed is CD4; the disease is Parkinson disease.