CX3CL1 and Parkinson disease: In addition, IL-8 and CX3CL1 levels in the plasma were also higher in the participants with PD (IL-8: 4.4 ± 10.9 vs. 1.4 ± 0.7 pg/mL, p < 0.001; CX3CL1: 4768.9 ± 2570.7 vs. 3913.2 ± 1571.6 pg/mL, p = 0.006; Fig. 1b, c).