The results showed that CD8<sup>+</sup> T cells were significantly reduced in the PD group compared with healthy controls (p < 0.001), and CXCR3 expression was significantly increased on peripheral blood CD4<sup>+</sup> effector T cells and CD8<sup>+</sup> T cells of PD patients (p < 0.001). This evidence concerns the gene CD4 and Parkinson disease.