TLR4 and Parkinson disease: Increasing evidence indicates that α-syn interacts with both TLR2 and TLR4 to mediate immune activation allowing α-syn aggregation and chronic inflammation [61], thus leading to progressive damage to neuronal cells; furthermore, chronic activation of gut and enteric cell TLRs secondary to microbial dysbiosis may further contribute to impaired immunity and disease progression in PD patients [62].