It is though that TLR4, a pattern recognition receptor, plays a crucial role in mediating the disease process because an elevation of TLR4 in colonic tissues and TLR4-downstream inflammatory mediators [e.g., nuclear factor-κB (NF-κB) and TNF-α] has been observed in PD patients and mouse models of PD. Here, TLR4 is linked to Parkinson disease.