IL6 and Parkinson disease: A systematic review and meta-analysis demonstrated significantly increased levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and C-reactive protein (CRP) in both the blood and cerebral spinal fluid (CSF), as well as increased levels of interleukin-4 (IL-4), interferon-γ (IFN-γ), soluble tumor necrosis factor receptor 1 (STNFR1), and fractalkine only in blood samples of PD patients [168].