beta-amyloid immunoreactivity in astrocytes in Alzheimer's disease brain biopsies: An electron microscope study

The deposition of amyloid beta (A beta) protein plays a central role in the neuropathology of Alzheimer's disease (AD) and it constitutes the core of classical senile plaques. However, little is known about its intracellular distribution. An immunogold electron microscope study was therefore carried out on biopsies of brain tissue from patients with AD using a monoclonal a ntibody raised against residues 8 to 17 of the A beta protein. Specific A b eta immunogold labeling was observed over extracellular amyloid fibrils ass ociated with senile plaques. In addition, widespread intracellular A beta i mmunolabeling was observed adjacent to granular structures (30-40 nm in dia meter) within membrane-bound processes, Pretreatment of some sections with amylase or omission of lead citrate staining from others strongly suggests that the electron-dense granular structures associated with A beta immunore activity are glycogen. Some of the A beta-immunolabeled processes contained gliofilaments and immunolabeling of alternate sections for glial fibrillar y acidic protein confirmed that the A beta-immunolabeled processes were ast rocytic. A beta immunolabeling was not observed over neuronal or microglial processes, Whether the presence of A beta protein in astrocytes is the res ult of synthetic or degradation processes requires further investigation. ( C) 1999 Academic Press.