Morphogenesis of amyloid plaques in mice with Creutzfeldt-Jakob disease.

Amyloid plaques were experimentally produced in the brains of mice inoculated with human Creutzfeldt-Jakob disease (CJD) brain homogenate. Light-microscopically, these plaques were mostly round and oval and were surrounded by macrophages and astrocytes. Ultramicroscopically, amyloid plaques were present in the cytoplasm of macrophages or were surrounded by these cells. The macrophages had numerous Golgi apparatuses, endoplasmic reticula (ER), ribosomes, polysomes, and lysosomes with inoculated materials or degenerating products. The bundles of amyloid fibrils were intermingled with the cytoplasm of macrophages, and sometimes limiting membranes were absent. Some bundles of amyloid fibrils projected from the Golgi apparatuses or rough ER and were partly exposed to the extracellular spaces, but there were no amyloid fibrils in the lysosomes. These findings confirmed that amyloid fibrils in the brains of CJD-infected mice were produced by macrophages.