We then analyzed immune checkpoint markers known to regulate immune responses in the context of inflammation and cancer31 and found a significant difference in PD-1 as well as CTLA4, GITR, GZMA, Ki-67, LAG3 and TIM3 in T cells housed in the colon of individuals living with PD, as compared to NHC (Fig. 6E). Here, TNFRSF18 is linked to Parkinson disease.