CD4 and Parkinson disease: Indeed, studies of the SNc from patients with PD and of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice show an infiltration of CD4+ lymphocytes10, whereas other studies of the SNc from PD patients and of individuals intoxicated with MPTP have reported gliosis11,12.