CD4 and Parkinson disease: PD patients exhibited a significantly lower percentage of total CD4 cells than control subjects (13.76 ± 7.05 and 17.27 ± 7.96, respectively, P = 0.0002, as determined from size dot plots; 33.58 ± 9.73 and 40.59 ± 9.50, respectively, P = 0.0001, as determined from size/dispersion dot plots).