Activated microglia subsequently secrete a wide range of inflammatory mediators, such as TNFα, IL-6, nitric oxide synthase 2 (NOS2), COX2, and ROS, leading to cell proliferation, followed by slow degeneration, and finally the death of dopaminergic neurons.28 Furthermore, clinical studies in PD patients examined the CSF and peripheral blood, showing elevated serum IL-1, IL-6, and TGF-β in CSF.29 Recently, mitochondrial dysfunction has been proven to induce neuroinflammation.18 Here, NOS2 is linked to Parkinson disease.