PB or CSF of PD patients: CD4 to CD8 ratio changes (He et al., 2022; Fu et al., 2023); decreased number (Baek et al., 2016); CD8+ T cell terminal effector phenotype (Marsh et al., 2016), with high expression of TNFα (Wang P. et al., 2021; Heming et al., 2022) and show immunosenescence (Hisanaga et al., 2001; Chen et al., 2021). Brain tissue of PD patients: significant infiltration in the SN (Williams-Gray et al., 2018; Kouli et al., 2021; Jiang et al., 2023). Mice model of PD: present in the PD brains (Brochard et al., 2009; Galiano-Landeira et al., 2020). This evidence concerns the gene CD4 and Parkinson disease.