TNF and Parkinson disease: Interestingly, an early increase in many proinflammatory cytokines including TNF-α, IFN-γ, IL-6 and IL-1β, has been observed in the gastro-intestinal tract of PD patients (Devos et al., 2013), which has led to the suggestion that gut inflammation may contribute to and even represent an early event in PD pathogenesis (Chen et al., 2019).