Previous work in the neurotoxin 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models of Parkinson’s disease have provided important evidence of immune activation,42 and pointed to the role of CD4 T cells in mediating aspects of the inflammation and neurodegeneration in those models.4 The gene discussed is CD4; the disease is Parkinson disease.