TLR9 and Parkinson disease: Since the neurotoxin 1-methyl-4-phenylpyridinium (MPP+) causes oxidative stress and mitochondrial dysfunction and thus injures dopaminergic neurons, leading to PD pathophysiology [14–16], we applied MPP+ to BV-2 cells to induce PD-like pathophysiology in the in vitro model and detected the changes in TLR2/TLR4/TLR9 expression and inflammatory reaction.