TNF and depressive symptom measurement: For instance, under stress conditions, there is evidence that dysfunction of inflammatory markers such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-10, transforming growth factor (TGF)-β in microglia (the major resident immune cells in the brain) of patients with depression participates in worsening PD symptoms [53, 59, 146].