Another animal study demonstrated that transplanting the gut microbiota from normal mice into PD mice alleviated BBB damage, inhibited neuroinflammation in the SN, and suppressed the TLR4/MyD88/NF-κB signaling pathway and downstream proinflammatory products in both the SN and colon, thereby alleviating PD symptoms in mice [96]. This evidence concerns the gene TLR4 and Parkinson disease.