APOE4 is involved in lipid transport and is consideredan important risk factor for AD (Figure 2) as it has a scarce ability to bind Aβ,so its expression contributes to Aβ accumulation and aggregationwithin neurons.41 A mouse model humanizedfor the APOE3 or the APOE4 alleles infected with HSV-1 showed thatmice with APOE4 have a higher virus load in the brain compared tothose with APOE3.71 Another study usingtransgenic mice with APOE knockouts for APOE3, or APOE4 alleles infectedwith HSV-1, found that in the CNS, APOE knockout mice had a lowerHSV-1 level then APOE3 and APOE4 mice. This evidence concerns the gene APOE and Alzheimer disease.