Indeed, converging lines of evidence from post-mortem clinical observations [89–91] and α-syn-based animal models of PD [90, 92, 93] reported the presence of infiltrating peripheral adaptive immune cells, specifically CD3+, CD4 + and CD8 + T cells, in PD-diseased brains and in close proximity to microglia and astrocytes, suggesting their potential role in activating brain-resident immune cells and to promoting inflammation and neurodegeneration [90, 91]. The gene discussed is CD4; the disease is Parkinson disease.