We report here the microglial (macrophage) and astrocytic reaction in several models of transmissible spongiform encephalopathies (TSEs) or prion diseases. With the low power electron microscopy it was readily apparent that myelinated vacuoles were surrounded by cells and their processes. The latter belonged either to hyperplastic reactive astrocytes or to macrophages. Typically reactive astrocytes exhibited cytoplasm filled with innumerable glial filaments and, occasionally, other organelles (like cilia) and abundant tortuous intercellular junctions of adhesive plaque junction type. Desmosome-like junctions connecting astrocytic elements were also seen. As described earlier, astrocytic processes were occasionally interdigitated with oligodendroglial cells and their processes. Two types of macrophages were readily described. The majority of them exhibited electron-dense cytoplasm and numerous ?empty? vacuoles (digestive chambers) containing cellular debris. Occasional vacuoles were surrounded by a thin collar reminiscent of ?lyre-like inclusions? of the second type of macrophages. The latter were rare and characterized by numerous ?lyre-like? inclusions. Several mylinated fibres were clearly engulfed by the cytoplasm of a macrophage containing unusual annulate lamellae.
Classical and ultrastructural neuropathology of prion diseases are generally well described. Here we report that alterations of myelinated fibres in hamsters infected either with polioencephalopathic strains of scrapie or panencephalopathic strains of CJD (Echigo-1) are virtually identical and differ only quantitatively. In contrast, mice infected with the panencephalopathic Fujisaki strain of CJD exhibited much more elaborate changes of myelinated fibres.
Prion diseases are a group of etiologically heterogenous diseases. In addition to familial cases linked to mutations of PRNP open reading frame they include also cases of unknown etiology. One of the susceptibility factors to sporadic as well as iatrogenic prion diseases are PRNP polymorphisms. In the present study, we analyzed sequences of the PRNP gene codon 219 of 16 Polish CJD cases and we found heterozygous GAG to GAT changes on the sense strand and only wild type sequence on an antisense strand. The RFLP technique was used to verify this divergence and only wild type sequences were revealed.
We report here on the exuberant glial reaction in the optic nerves affected by prion diseases. Optic nerves from CJD- and GSS-, and scrapie-infected mice and hamsters showed severe pathology. These lesions were qualitatively indistinguishable from each other but were more intense in the Fujisaki model than in the hamsters inoculated with Echigo-1. Exuberant cellular reaction comprised of macrophages containing numerous mitochondria, abundant rough endoplasmic reticulum, and secondary lysosomes filled with digested myelin debris, electron-dense material and occasionally, entire myelin-bound vacuoles were readily observed in both models. Macrophages actively digesting myelin fragments and containing lyre-like bodies and paracrystalline inclusions were frequently noted. Some macrophages extended long filopodia to form labyrinth-like structures, and within a few macrophages, concentric arrays of cisterns and channels sequestrated part of the cytoplasm. An analogous network of narrow cisterns was seen to surround whole segments of the myelinated fibers.
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