Immunolocalization of the amyloid precursor protein within the senile plaque.

The isolation and sequencing of three transcripts for the precursor of the cerebral amyloid of Alzheimer disease have greatly facilitated understanding the relationship of the amyloid precursor protein (APP) to its 42 amino acid residue fragment (beta-protein or A4) which composes amyloid fibrils. In this study, we have used the 695 amino acid residue sequence described by Kang and co-workers to prepare antisera to synthetic peptides corresponding to various regions of APP in order to identify localized concentrations of this protein in cerebral cortex in cases of Alzheimer disease. We found that antisera to APP regions outside those of the amyloidogenic beta protein recognize diffuse non-congophilic plaques. While these antisera did not recognize the congophilic senile plaque core, they did recognize a halo surrounding them. Interestingly, cell processes were often identified in this halo region. In contrast, those antisera raised to sequences contained within beta-protein recognized both congophilic amyloid cores as well as non-congophilic diffuse plaques. Our findings suggest that accumulation of APP precedes development of and probably defines the senile plaque and the site of APP processing.