CD4 and Parkinson disease: Other studies also reported that the naïve CD4 T cells and gamma delta T cells were decreased in PD compared with those in HC (Saunders et al., 2012; Zhou et al., 2020), while NK cells and neutrophils were increased in PD (Niwa et al., 2012; Saunders et al., 2012; Cen et al., 2017), which were all observed in this study.