TLR4 and Alzheimer disease: In this context, some genetic variants of TLR4 have been linked to AD and the increased expression of TLR2 has been identified in AD models (Balistreri et al., 2009; Letiembre et al., 2009), whereas the enhanced transcription of TLR2 and TLR4 have been detected in α-synuclein and MPTP mouse models of PD (Panaro et al., 2008; Letiembre et al., 2009), indicating that immune regulation is harmfully altered in AD and PD.