CD8A and Parkinson disease: Although many immune cell subsets are dysregulated in PD, the key role of CD4+ T cells in the pathogenesis of the disease is supported by their presence, together with CD8+ T cells, in the brain in both postmortem human PD specimens and in the MPTP mouse model of PD, and evidence obtained in the animal model indicate that CD4+ T cells are determinants of T cell-mediated dopaminergic cell death11.