CD8A and Parkinson disease: The total number of CD8 cells in the SN was significantly higher in PSP compared with PD brains [mean ± standard deviation (SD) in PSP = 203 ± 107, in PD = 20 ± 24; P < 0.001] and CO brains (mean ± SD = 8.81 ± 7.61; P < 0.001; Fig. 1A).