IL6 and Parkinson disease: Elevated levels of IL-6 have been found in the serum, cerebrospinal fluid, and SNc of patients with PD already at Braak stages 1 and 2 (51, 52), and higher IL-6 levels have been correlated with a worse PD prognosis (53, 54), suggesting that IL-6/IL-6R signaling can be an important therapeutic target.