Table 3.

Effects of different TLRs on Parkinson’s disease.

TLR	Effects on Parkinson’s Disease (PD)	Reference
TLR2	Upregulated in PD patients, especially in the substantia nigra and in late stages in the striatum.	[45]
	α-Synuclein activates microglia via TLR2.	[48]
	Activation of microglial TLR2 reduces neuronal viability.
TLR4	Activation of TLR4 can be neurotoxic or neuroprotective, depending on context.	[47]
	It is shown to help clear α-synuclein aggregates in PD.	[47]
	In oxidative stress-induced PD models, TLR4 activation is associated with cell death.	[56]
TLR9	Overexpressed in PD models in regions such as the substantia nigra and the putamen.	[58]
	Its activation leads to an enhancement of oxidative stress for neuronal cells, which exacerbates cell death in PD.	[59]
	Activation of microglia TLR9 reduces neuronal viability.	[59,61]