For instance, age-associated shifts in the microbial profile and immune system (“inflamm-aging”) are linked to age-related diseases [189, 190], and a recent study demonstrated that intranasal LPS infusion causes an increased inflammatory response and greater PD pathology in aged mice compared to young mice [191], although the expression or priming of TLR4 was not studied. Here, TLR4 is linked to Parkinson disease.