Aβ40 is a major form of β-amyloid in nonhuman primates

Because aged nonhuman primates show β-amyloid (Aβ) deposition in senile plaques and blood vessels similar to that seen in human aging and AD, we used C-terminal specific antibodies to Aβ40 and Aβ42 to investigate Aβ peptide length in the brains of 11 aged rhesus monkeys and a 59-year-old chimpanzee. In contrast to AD, where the earliest and most prominent form of Aβ in senile plaques is Aβ42, in the monkey, Aβ40-positive plaques predominated. The ratio of Aβ4): Aβ42-positive plaques averaged 2.08 in the monkey, as compared to a mean ratio of 0.37 in 68 human AD subjects (p < 0.001). Aβ40 was also more prominent in the chimpanzee than in humans. Possible explanations for these findings include species differences in the cleavage of Aβ from the amyloid precursor protein or in the activity of a putative carboxy peptidase forming Aβ40 from Aβ42 in situ.