Coupled with the observation that MHCII expression in PD brain correlates with deposition of α-synuclein28 and is increased relative to control brains6, the current evidence suggests the possibility that immune cells phagocytose and present α-synuclein-derived peptides or antigens from α-synuclein-burdened, degenerating neurons to CD4 + T cells in PD. This evidence concerns the gene CD4 and Parkinson disease.