Aβ immunotherapy increased neurogenesis and dendritic arborization of newly born neurons in 11–12-month-old APP/PS1 mice. Aβ immunotherapy significantly increased numbers of mature BrdU+/NeuN+; this increase was accompanied by a trend for higher numbers of immature PSA-NCAM+ neurons (APP/PS1+ct ab: 306 ± 31 vs APP/PS1+α-Aβ: 452 ± 42 BrdU+/NeuN+ cells; p < 0.05; and APP/PS1+ct ab: 219 ± 79 vs APP/PS1+α-Aβ: 842 ± 275 PSA-NCAM+ cells; p = 0.06). A, B, Representative low-magnification images of PSA-NCAM+ neurons in the dentate gyrus of control-treated (A) and Aβ immunotherapy-treated (B) mice. Aβ immunotherapy significantly increased the number of dendrites of PSA-NCAM+ neurons in APP/PS1 mice and the length of dendrites of PSA-NCAM+ neurons in APP/PS1 mice (number of dendrites per cell: APP/PS1+ct ab: 2.45 ± 0.3 vs APP/PS1+α-Aβ: 4 ± 0.4; p < 0.01; and length of dendrites: APP/PS1+ct ab: 54.4 ± 7 vs APP/PS1+α-Aβ: 85.5 ± 10 μm; p < 0.01). C, D, High-magnification confocal details, including corresponding computer renderings resulting from quantitative NeuronJ analyses of the cells shown in the yellow squares in A and B, respectively, taken from comparable regions within the dentate gyrus. Scale bars: A, 60 μm; C, 20 μm. N = 40 cells were analyzed per group. Unpaired t test.