A–D , Levels of Aβ in plasma ( A , B ) or CSF ( C , D ) in PDAPP mice expressing one of the human apolipoprotein E alleles (E2, E3, or E4) at 3 or 18 months. B , C , ***p < 0.001 versus all groups at 18 months of age, **p < 0.01 versus E2 at 3 months of age, *p < 0.01 versus E4 at 3 months of age, ANOVA, Tukey–Kramer post test, ***p < 0.001, **p < 0.01 t test.