TNF and Parkinson disease: We also checked the enrichment of two pro-inflammatory cytokines with elevated expression in the brains of PD patients, including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) to find that IL-6 are also marginally enriched in the DA microbes (p-value = 9.7e−3; combined score = 4.42).