Electron microscopy of amyloid fibrils and microvessels.

Senile plaques and microvessels in the cortices of brains with Alzheimer's disease were examined using serial sections under light and electron microscopes. In addition, observations were carried out by using an immunostaining method. The results obtained were as follows: (1) Every senile, plaque contains some amyloid fibrils, and many senile plaques have degenerated capillaries with amyloid fibrils. (2) Amyloid fibrils without senile plaques continue directly to the capillaries. (3) A considerable number of preamyloids are observed surrounding the capillaries when a methenamine silver stain is used. (4) Alpha 1-antichymotrypsin is found in amyloid fibrils, endothelial cells, and vascular feet or astrocytic processes. Our findings strongly suggest that amyloid fibrils forming senile plaques have a close relationship to the capillaries. Moreover, a protease inhibitor, such as alpha 1-antichymotrypsin, could possibly play an important role in producing the amyloid fibrils.