Intracellular neurofibrillary tangle-like aggregations. A constantly present amyloid alteration in the aging choroid plexus.

Intracellular neurofibrillary tangles is one of the most characteristic findings in Alzheimer's disease and senile dementia of Alzheimer type. In the present paper the authors show that intracellular accumulation of paired helical filaments is also a constant finding in the epithelial cells of the choroid plexus of aging persons. Like the neurofibrillary tangles, the fibrils of the choroid plexus show staining properties typical of amyloid. The nature of the fibrils could not be clarified by electron microscopy or by immunohistochemistry with the use of antisera to gamma-trace or to amyloid fibril proteins of AA and prealbumin type. Amyloid protein AP, found in all amyloid substances except for neurofibrillary tangles and amyloid of senile plaques in the brain, was not demonstrated in the inclusions of the choroid plexus.