TLR4 and Parkinson disease: Enteric neurons are the main cell population expressing α-synuclein in the gut, and given the proximity of the ENS to the gut lumen coupled with the critical role of TLR2 and TLR4 signalling in enteric innervation and function discussed above, further studies are required to investigate the contribution of TLR2 and TLR4 to  ENS changes and α-synuclein pathology in the context of PD.