IL17A and Parkinson disease: Moreover, it has also been observed decreased plasma concentrations of several cytokines in PD; e.g., IL-6, IL-1β, IL-10, TNF-α, IFN-γ, and IL-17 (Hasegawa et al., 2000; Rocha et al., 2018), indicating rather an impaired cytokine production in advanced PD.