Immunization with oligomeric or fibrillar Aβ at 12–16 months decreases astrocyte activation relative to untreated or adjuvant treated age matched controls. A. GFAP reactivity (red) around fibrillar plaques (thioflavine, green) at 16 months in Tg2576 mice either untreated (Control), or immunized at 12–16 months of age with adjuvant only (CFA), oligo Aβ or fAβ. Scale bar = 50 microns. B. Image analysis of GFAP immunoreactivity in cortex of animals immunized at 12–16 months. Mean of each animal is the average of 2–4 sections (total 4–8 images per section) in which most to all of the area of study was analyzed. Bars represent group mean ± SD of n mice per group: untreated = 4, CFA n = 4, oligo Aβ n = 7, fAβ n = 5. *p < 0.03, **p < 0.01 by ANOVA.