TLR4 and Alzheimer disease: Because soluble Aβ42 is thought to be neurotoxic and levels of soluble Aβ42 in the brains of 9-month-old TLR4M Tg mice increased compared to those in TLR4W Tg mice, we evaluated the effects of the TLR4 mutation on spatial learning and memory by the Morris water maze in the AD mouse model at 9 months of age.