In fact, the Toll-like receptor has been reviewed earlier as a mediator of the microbiome–gut–brain axis and innate immune system in Parkinson’s disease patients (79), and this section focuses on the role of Toll-like receptor 2 and Toll-like receptor 4 in overall intestinal physiology and the possible role of local effects on early Parkinson’s disease pathogenesis and enteric nervous system function. Here, TLR4 is linked to Parkinson disease.