TLR4 and Parkinson disease: Interestingly, Toll-like receptor 4 (TLR4)-mediated inflammatory signaling could be responsible for the increased gut permeability, since a higher number of TLR4 and CD3+ T cells, as well as a lower number of tight junction-related proteins, have been found in mucosal biopsies of people with PD with respect to healthy controls [24].