IL6 and Parkinson disease: According to a review conducted in 2019, higher serum interleukin-6 (IL-6), interleukin-1 receptor antagonist (IL-1-Ra), soluble interleukin-2 receptor (sIL-2R), and vascular cell adhesion molecule-1 (VCAM-1) were found to be associated with higher fatigue levels among patients with PD.