Apolipoprotein E-immunoreactivity in aged rhesus monkey cortex: colocalization with amyloid plaques.

In the present study, we examined the relationship between ApoE and amyloid containing profiles within the cerebral cortex of young, middle aged, and aged Rhesus monkeys. Polymerase chain reaction analysis revealed a pattern consistent with the ApoE e4 phenotype in the rhesus monkey similar to that reported in humans. We found numerous ApoE immunoreactive plaques within the temporal neocortex and amygdala, whereas the hippocampus contained only a few such plaques. Although virtually all ApoE-immunoreactive plaques coexpressed beta-amyloid, most plaques were beta A4 positive/ApoE immunonegative within the aged monkey cortex. Moreover, we observed a close correspondence between ApoE and thioflavin-positive (i.e., amyloid) plaques suggesting that ApoE may play a critical role in the conversion of beta A4 to its beta-pleated form. Because ApoE, beta A4 and amyloid are expressed in plaques within the aged Rhesus macaque cortex, this species may provide an in vivo model for investigations aimed at clarifying the interactions between these proteins in normal and pathologic aging.