Williams et al. (2021) reported that α-syn-responsive T cells in the SN are primarily composed of IFN-γ-producing CD4+ T cells, as the neurodegenerative effects of α-syn are diminished following the knockout or pharmacological depletion of CD4+ T cells, but not CD8+ T cells, in PD mice. The gene discussed is IFNG; the disease is Parkinson disease.