TNF and Parkinson disease: Nonetheless, active microglia cause a deleterious cycle in PD and other neurodegenerative disorders by producing pro-inflammatory cytokines and other factors, such as IL-1α, IL-1β, IL-6, IL-10, TNF-α, reactive oxygen species (ROS) and nitric oxide (NO), all of which can provoke apoptosis and cell death (Nagatsu and Sawada, 2005).