Antibody levels in cerebrospinal fluid (CSF). (A) Anti-Aβ42 and (B) anti-Aβ40 antibody levels were significantly lower at week 16 post-immunization in aged (n = 9) than in juvenile non-human primates (n = 8). Bars represent median and interquartile range. (C) Scatterplot displaying the difference (ΔAβ42) between CSF Aβ42 levels at week 16 and baseline . A significant positive correlation was seen for the aged (P < 0.05) but not the juvenile cohort.