Ultrastructural neuropathology of chronic wasting disease in captive mule deer

Summary Chronic wasting disease (CWD), a progressive and uniformly fatal neurological disorder, is characterized neuropathologically by intraneuronal vacuolation, spongiform change of the neuropil and astrocytic hyperplasia and hypertrophy. Ultrastructural neuropathological findings consist of (1) extensive vacuolation in neuronal processes, within myelin sheaths, formed by splitting at the major dense lines or within axons; (2) dystrophic neurites (dendrites, axonal preterminals and myelinated axons containing degenerating mitochondria and pleomorphic, electron-dense inclusion bodies); (3) prominent astrocytic gliosis; (4) amyloid plaques; and (5) giant neuronal autophagic vacuoles. Other findings include activated macrophages and occasional spheroidal structures containing densely packed fibrillar material of unknown origin, abundant structures suggestive of degenerating microtubules entrapped in filamentous masses, vacuoles and myelin figures. Similar findings have been previously observed in scrapie-infected hamsters and Creutzfeldt-Jakob disease (CJD)-infected mice, bovine spongiform encephalopathy, and CJD indicating that CWD in captive mule deer belongs to the subacute spongiform encephalopathies (transmissible brain amyloidoses).     

Fibrils in brains of Rocky Mountain elk with chronic wasting disease contain scrapie amyloid

Summary Chronic wasting disease (CWD), a progressive, fatal neurological disorder of captive mule deer and Rocky Mountain elk, is characterized neuropathologically by spongiform change in the neuropil, intraneuronal vacuolation and astrocytic hypertrophy and hyperplasia. Recently, scrapie amyloid-immunoreactive plaques have been demontrated in brain tissues of CWD-affected captive mule deer, Rocky Mountain elk and hybrids of captive mule deer and white-tailed deer. We now report on the presence of abnormal fibrils isolated from brain tissues of Rocky Mountain elk using negative-stain electron microscopy. These fibrils resemble those found in scrapie-infected hamster brain. Furthermore, protein bands with relative molecular masses of 26 to 30 kilodaltons were shown to be immunoreactive to antibodies raised against scrapie amyloid by Western immunoblotting. Immuno-dot blot showed similar reactivity. Our data support the clinical and pathological diagnosis of the disease and provide further evidence that CWD belongs to the subacute spongiform encephalopathies.Supported by the Sonderforschungsbereich 194, Deutsche Forschungsgemeinschaft (to D.C.G.)     

Lectin histochemistry of scrapie amyloid plaques

Summary Peroxidase-labeled lectins were used for detection of specific monosaccharide residues in amyloid plaques in brains of scrapie-infected mice. The lectins tested recognize the following residues: -d-galactosyl (Ricinus communis agglutinin 120, RCA-1), -d-galactosyl and -d-galactopyranoside (Bandeirea simplicifolia aggl., BSA), -d-mannosyl and -d-glucosyl (Concanavalin A, Con A), N-acetylglucosaminyl and sialyl (Wheat germ aggl., WGA), sialoglycoconjugates (Limulus polyphemus aggl., LPA), -l-fucosyl (Ulex europeus aggl., UEA-1 and Tetragonolobus aggl., TPA), N-acetyl-d-galactosaminyl (Helix pomatia aggl., HPA). The most intense staining reaction in amyloid plaques was observed with BSA and WGA; it was less intense with RCA-1, Con A, and HPA. This indicates that the plaque material contains glycoproteins with abundance of accessible residues of - and -galactose, N-acetyl-d-glucosamine and N-actyl-d-galactosamine, and some types of sialoglycoconjugates recognized by WGA. Such residues, like -l-flucosyl recognized by UEA-1 and TPA, were almost undectectable in the examined plaques.There were also some differences in the staining intensity between small and large plaques (WGA and HPA) and between central and peripheral areas of the plaques.In the wall of micro-blood vessels relatively strong staining reaction was observed with RCA and BSA and less intense with WGA and Con A.Support in part by grant no. 5PO1 AG 04220-03 from the National Institute of Aging, NIH     

Comparison of spongiform lesions in experimental scrapie and rabies in skunks

Summary Striped skunks were inoculated intracerebrally with the scrapie agent (suspension of brain from a naturally infected Suffolk sheep) or intramuscularly with street rabies virus (suspension of salivary glands from naturally infected skunks). Those given the scrapie agent developed clinical signs of weakness, posterior ataxia, and emaciation after incubation periods of 8 to 23 months. Those inoculated with rabies virus developed clinical signs of rabies (aggressive behavior, hyperexcitability, ataxia and paralysis) after incubation periods of 20 to 62 days. The gross lesions in the brains of the skunks given the scrapie agent consisted of marked atrophy of the thalamus and moderate atrophy of the cerebrum. No gross lesions occurred in the rabid skunks. Histologically, the type of spongiform lesion in rabies was the same as that in scrapie. However, spongiform change of rabies infected brains was less extensive (only rarely affected the basal ganglia, hippocampus or hypothalamus) than that of brains infected with the scrapie agent and was characterized by fewer numbers of small vacuoles (as a proportion of total number of vacuoles) than occurred in scrapie spongiform change.     

Deposition patterns of disease-associated prion protein in captive mule deer brains with chronic wasting disease

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) in captive and free-ranging cervids in the USA; its origin is obscure. Archival formalin-fixed and paraffin-embedded specimens of 16 captive mule deer brains with CWD were analyzed using immunocytochemistry for the disease-associated prion protein (PrP). The most prominent pattern of PrP deposition were plaque-like structures, a substantial proportion of which were florid plaques surrounded by a rim of spongiform vacuoles. The percentage of florid plaques was highly variable according to region, ranging from 0% to 52.7%. The highest percentage was observed in the medulla and basal ganglia, the lowest in the cerebral cortex. Only three brains contained no florid plaques. There were also punctate synaptic-type and perivascular deposits, particularly in areas of severe spongiform change, and subpial and subependymal plaque-like deposits, whereas cerebellar involvement was mild. Thus, CWD brain pathology prominently features florid PrP plaques, as does variant Creutzfeldt-Jakob disease (vCJD), but differs in other characteristics from vCJD.     

Distributions of amyloid plaques in four regions of the brains of mice infected with scrapie by intracerebral and intraperitoneal routes of injection

Summary VM mice were inoculated by intracerebral and intraperitoneal routes with brain homogenates containing the 87V strain of scrapie. The distribution and numbers of plaques were found for the parietal cortex, cingulate cortex, corpus callosum and hippocampus/dentate in coronal sections cut at the level of the thalamus and stained with Masson's trichrome. For the intracerebrally injected animals, the greatest numbers were seen on the side of the brain that had been injected. In the four regions, they were most numerous in the corpus callosum and least numerous in the parietal cotex and hippocampus/dentate. Following an intraperitoneal injection, plaques were absent from the corpus callosum and, in the remaining three regions, they were less numerous than in intracerebrally injected animals, although their relative numbers were similar. The distribution of the plaques was suggestive of an inital passive spread of inoculum following intracerebral injection and a tendency for plaques to be associated with myelinated axon tracts.     

Relationship of microglia and scrapie amyloid-immunoreactive plaques in kuru,Creutzfeldt-Jakob disease and Gerstmann-Sträußler syndrome

Kuru, Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler syndrome (GSS) are transmissible dementias affecting humans characterized neuropathologically by intraneuronal vacuolation, spongiform change, astrocytic hypertrophy and hyperplasia and the variable presence of amyloid plaques. It has been suggested that microglia are amyloid-forming cells, which play an essential role in amyloid plaque formation. To study the relationship between microglia and amyloid plaques in kuru, CJD and GSS, cerebellar tissues were examined by the double-immunostaining technique using anti-ferritin antibodies as the microglial marker and anti-scrapie amyloid antibody as plaque marker. Ferritin-immunoreactive microglia were observed interdigitating with and among unicentric, multicentric and diffuse types of scrapie amyloid-immunoreactive plaques and were found to a lesser extent in the neuropil. In kuru and CJD, scrapie amyloid-immunoreactive plaques were predominantly unicentric and were observed in the granular layer. In kuru, 53% of the amyloid plaques were associated with microglia, whereas only 30% of plaques in CJD were. In contrast, scrapie-amyloid-immunoreactive plaques in GSS were of the multicentric type, predominantly observed in the molecular layer, and 90% of these plaques were associated with microglia. Our data indicate that microglia are frequently associated with scrapie amyloid-immunoreactive plaques in GSS, less commonly in kuru and to a much lesser extent in CJD, suggesting that microglia may play a variable but important role in the formation of plaques in the transmissible spongiform encephalopathies.D.C. Guiroy is supported by the Sonderforschungsbereich 194 from the Deutsche Forschungsgemeinschaft; P.P. Liberski is a recipient of a grant from the Kosciuszko Foundation while in USA and the intramural grant from the Medical Academy Lodz, while in Poland     

Ultrastructural studies of glycoconjugates in brain micro-blood vessels and amyloid plaques of scrapie-infected mice

Summary Lectin or glycoprotein-gold complexes and samples of scrapie-infected mouse brain embedded in Lowicryl K4M were used for ultrastructural localization of glycoconjugates. The lectins tested recognize the following residues: -D-galactosyl [RCA,Ricinus communis agglutinin (aggl.) 120], N-acetyl and N-glycolyl neuraminic acid (LFA,Limax flavus aggl.), N-acetyl-D-glucosaminyl and sialyl (WGA, Wheat germ aggl.), N-acetyl-D-galactosaminyl (HPA,Helix pomatia aggl., and DBA,Dolichosbiflorus aggl.), -D-mannosyl/-D-glucosyl (Con A, Concanavalin A), -D-galactosyl and -D-galactopyranoside (BSA,Bandeirea simplicifolia aggl., izolectin B₄). Labeling of the majority of micro-blood vessels (MBVs) located outside the plaque area and in the remaining cerebral cortex was similar to that which has been previously observed in non-infected animals. Some MBVs, however, located inside the plaque area and surrounded directly by amyloid fibers showed attenuation of the endothelium, the surface of which was scarcely and irregularly decorated with RCA, LFA, WGA and Con A. These abnormalities in the composition of glycoconjugates can be associated with previously noted increased permeability of some MBVs in the brains of scrapie-infected mice. Some vessels in the plaque area were encapsulated by perivascular deposits of homogenous or flocculogranular material containing several glycoconjugates. A very intimate structural relation between reactive (microglial-like) cells and amyloid fibers suggests the participation of these cells in elaboration of plaque material. Labeling of the cell surface and adjacent amyloid fibers with the same lectins (RCA, WGA, DBA, Con A) suggests the possibility that the glycosylation of these fibers occurs extracellularly. Only WGA and DBA were occasionally labeling some Golgi elements of the reactive cells.Supported in part by a grant from NINCDS No. 17271-06     

Low amyloid (Aβ) plaque load and relative predominance of diffuse plaques distinguish argyrophilic grain disease from Alzheimer's disease

Argyrophilic grain disease constitutes one cause of late-onset dementia. Its classification among dementia disorders is still unclear because most of the reported argyrophilic grain disease cases are associated with neurofibrillary lesions (e.g. neurofibrillary tangles) which are also typical of Alzheimer's disease. In the present study we determine whether argyrophilic grain disease is associated with the senile plaques of Alzheimer's disease. The distribution and density of senile plaques was systematically investigated in 11 demented argyrophilic grain disease cases using Abeta immunohistochemistry and stereological techniques, and the results were compared with 11 Alzheimer's disease cases. All subjects with argyrophilic grain disease exhibited neurofibrillary changes corresponding to Braak stages I-III. Three of the 11 argyrophilic grain disease cases (27%) were completely devoid of Abeta deposits. In argyrophilic grain disease cases with senile plaques, the average total plaque-load was significantly lower (1%) than in Alzheimer's disease (3.1%) (P<0. 005). The regional distribution of the senile plaques and the proportion of diffuse vs. primitive or mature plaques in argyrophilic grain disease resembled values of senile plaques reported in non-demented elderly subjects, and was significantly different from Alzheimer's disease. Similarly the immunocytochemical profile of the Abeta deposition in argyrophilic grain disease resembled that of non-demented elderly subjects rather than that of subjects with Alzheimer's disease. As all argyrophilic grain disease cases under investigation were demented, including those devoid of senile plaques, the present study further supports the thesis that dementia in argyrophilic grain disease correlates more with the density and distribution of argyrophilic grains than with associated lesions of the Alzheimer-type.     

Further observation of Japanese Creutzfeldt-Jacob disease with widespread amyloid plaques

Summary An autopsy case of Creutzfeld-Jacob disease with widespread amyloid plaques is reported. A 45-year-old Japanese man, whose father had died of a similar disease, had a 5-year illness characterized by progressive cerebellar signs. Mental changes and brain-stem signs developed in the late stage. Myoclonus frequently occurred. Akinetic mutism ensued. The autopsy revealed spongiform encephalopathy with widespread amyloid plaques and extensive degeneration of the white matter. This disease, Western Gerstmann-Sträussler-Scheinker disease and panencephalopathic type of Creutzfeld-Jacob disease are discussed.     

Lectin histochemistry of plaques and tangles in Alzheimer's disease

Summary Biotinyl derivatives of several lectins and avidin-horseradish peroxidase were used to study the localization of glycoconjugates in amyloid plaques and in neuritic tangles in brains of patients with Alzheimer's disease (AD), Downs syndrome (DS) and Gerstmann-Sträussler syndrome (GSS). The lectins tested recognize the following residues: -d-galactosyl [Ricinus communis agglutinin 120, (RCA-1) and peanut agglutinin, (PNA)]; -d-galactosyl [Griffonia simplicifolia agglutinin (GSA)]; -d-mannosyl>-d-glucosyl [concanavalin A (Con A) andLens culinaris agglutinin (LcH)];N-acetyl- andN-glycolylneuraminic acid [Limax flavus agglutinin (LFA) andLimulus polyphemus agglutinin (LPA)];N-acetyl-glucosaminyl and sialyl [wheat germ agglutinin (WGA)];N-acetyl-d-galactosaminyl [Helix pomatia agglutinin (HPA) andDolichos biflorus agglutinin (DBA)] and -l-fucosyl [Ulex europeus agglutinin (UEA-1)]. The majority of lectins listed above bind preferentially to the peripheral area of AD plaques, whereas in plaques of DS they are mainly bound to central amyloid core. In neurofibrillary tangles of AD brains only residues recognized by WGA and HPA or DBA were found, whereas in DS brains, in addition to above mentioned, -d-galactose (RCA-1) and sialic acid (LFA) were also present. In brain microblood vessels the strongest reaction in endothelia appeared with UEA-1 and RCA-1, indicating the abundance of -l-fucosyl and -d-galactosyl residues. In AD brains deposits of amyloid were noted in the wall of some blood vessels, where monosaccharide residues recognized by RCA-1, GSA, UEA and WGA but not by Con A and LFA were present. However, our studies of some organs (liver, kidney, heart and testes) of patients with generalized amyloidosis revealed a lack of these sugar residues. It indicates, that the composition of amyloid present in brains of AD is different to that in other organs in generalized amyloidosis.Supported in part by grant no. AG 04220-03 from the National Institute of Aging, NIH     

Ubiquitin-reactive axons have a widespread distribution and are unrelated to prion protein plaques in Creutzfeldt-Jakob disease

The amyloid plaques of Alzheimer disease (AD) are surrounded by dystrophic axons that contain ubiquitinated dense bodies. To investigate whether deposits of other types of amyloid cause axonal degeneration we studied 5 cases of Creutzfeldt-Jakob disease (CJD) with immunocytochemical methods using ubiquitin and prion protein (PrP) antisera. One of these cases contained PrP plaques in the cerebellum. In all cases dystrophic axons, which contain ubiquitinated dense bodies, were observed in neocortical and cerebellar grey matter, in absence of PrP-reactive amyloid deposits. Only a minority of PrP plaques present in the cerebellum was associated with ubiquitin positive neurites. The results indicate that, unlike in AD, the occurrence of ubiquitinated dystrophic axons is independent from amyloid deposition in CJD and is likely to be a primary phenomenon.     

An electron microscopic study of inclusion bodies in synaptic terminals of scrapie-infected animals

Summary Inclusion bodies consisting of vesicles of about 25 nm diameter and occurring in the synaptic terminals of scrapie-infected animals have been described by a number of people. In the present study these inclusion bodies were looked for in the neocortex, hippocampus and corpus callosum in a variety of strains of mice (C3H, LM, RIII, IM, VL) infected with different strains of scrapie agent (22C, 79A, ME7, 87V) after intracerebral inoculation. In plaque-bearing models of scrapie, terminals containing synaptic inclusion bodies were frequently found surrounding the amyloid plaque cores in the neocortex but not in the corpus callosum. In non-plaque-bearing models, terminals containing synaptic inclusion bodies were found in the neuropil of the neocortex and hippocampus. For all models, these bodies were either presynaptic or postsynaptic but were not, as a rule, found on both sides of the same synapse. Fibrillary material was frequently seen in the postsynaptic terminals containing the inclusion bodies in both the plaque- and non-plaque-bearing models. On one occasion fibrillary material was seen, together with the inclusion bodies, in a neuron cell body. Inclusion bodies were also seen in the neocortex of hamsters infected with the 263K strain of scrapie agent and a Cheviot sheep infected with the ME7 strain of agent. The inclusion bodies and the fibrillary material were thought to be derived from the breakdown of neurotubules.     

Fibrillar prion peptide (106-126) and scrapie prion protein hamper phagocytosis in microglia

The inflammatory response in prion diseases is dominated by microglial activation. As macrophages of the central nervous system, the phagocytic capacity of microglia is well recognized, and it is possible that microglia are involved in the removal and processing of amyloid fibrils, thus preventing their harmful effect. We have analyzed the effects of a synthetic peptide of the human prion protein, PrP(106-126), which can form fibrils, and the pathogenic form of prion protein, PrPsc, on phagocytosis in microglia isolated from neonatal rat brain cultures. To some extent, fibrillar PrP(106-126) is internalized and processed. However, both synthetic prion peptide PrP(106-126) in a fibrillar form and pathogenic prion protein PrPsc severely hamper the phagocytic activity as measured by the uptake of beads by microglia. At a concentration that does not induce microglial death, PrP(106-126) reduced the number of beads internalized and altered their cytoplasmic distribution. This effect was not due to decreased binding of beads to the cell surface, nor restricted to specific classes of receptors. Although the PrP(106-126) did not prevent F-actin and Rac1 accumulation at sites of particle engulfment, it appeared to interfere with a later step of the internalization process.     

Morphogenesis of amyloid plaques in 87V murine scrapie†

Amyloid plaques of scrapie–infected mouse brains are composed of fibrillar forms of a host coded, cell surface sialoglycoprotein called PrP (prion protein). Serial ultrastructural immunogold staining was performed on plaques identified by light microscopic immunocytochemistry of brains of VM mice infected with the 8 7V strain of scrapie. Classical plaques, of a kuru–type morphology, were composed of a central core of bundles of amyloid fibrils. Amyloid fibrils of classical plaques were immunoreactive for PrP. In addition, PrP was also found at the plaque periphery, in the absence of fibrils, at the plasmalemma of cell processes and in the associated extracellular spaces. Frequent microglial cells and occasional astrocytes contained PrP within lysosomes. Other plaques with few or no recognizable amyloid fibrils were frequent and were termed primitive plaques. PrP could be demonstrated in a non–fibrillar form at the plasmalemma and in the extracellular spaces between neurites of such plaques. Many primitive plaques showed little or no sub–cellular pathology associated with the PrP accumulation. PrP was closely associated with the plasma–lemma of occasional dendrites passing towards the centre of primitive plaques. These results suggest that plaques are formed around one or more PrP releasing dendrites. PrP accumulates in the extracellular spaces adjacent to such processes prior to its spontaneous aggregation into fibrils. Lysosomal accumulation of PrP in microglia and astrocytes located at the periphery of plaques suggest that these cells are involved in the phagocytosis of excess or abnormal PrP.     

Amyloid in central nervous system disease

A review is presented of diseases of the central nervous system associated with amyloid deposition. The name amyloid is given to substances with particular physical characteristics which are independent of the chemical constitution of the proteins in the substance. Ideally, a classification of amyloid diseases should be based on the chemical composition of the amyloid deposits; this has only been partially realized. The best documented group of diseases with amyloid deposition in the central nervous system is the group of ‘cerebral β amyloid diseases’, characterized by the deposition of β-protein. This group includes: Alzheimer's disease, sporadic cerebral amyloid angiopathy, Down's syndrome, Parkinson-dementia of Guam, hereditary cerebral hemorrhage with amyloidosis-Dutch type and age-related asymptomatic amyloid angiopathy.     

Tubulovesicular particles occur early in the incubation period of murine scrapie

Tubulovesicular bodies are structures, apparently specific to the transmissible spongiform encephalopathies, which are of unknown composition and significance. Prion protein (PrP) is absent from tubulovesicular bodies when tissues are examined by immunogold electron microscopy. In the F1 cross of C57 and VM mice (CVF1) infected with ME7 scrapie there is a marked degeneration of hippocampal CA1 neurons. In this model the earliest changes seen, at about 100 days post inoculation (dpi) are a degeneration of axon terminals and synaptic loss. Terminal disease is around 250 dpi. In blind coded trials we counted the number of tubulovesicular particles and estimated their density in 56–76 electron micrographs taken from the stratum radiatum of each of one or two CVF1 ME7-infected mice at 84, 100, 126, 154 and 181 dpi and from four normal brain inoculated control mice. Tubulovesicular particles were present from 98 dpi and the density of particles increased with increasing incubation period. The very early occurrence of tubulovesicular particles, before the presence of significant pathology, argues that tubulovesicular particles are a part of the primary disease and are not epiphenomena. Received: 28 June 1999 / Revised: 30 August 1999 / Accepted: 6 September 1999     

A presenilin 1 mutation (L420R) in a family with early onset Alzheimer disease,seizures and cotton wool plaques,but not spastic paraparesis

Over 100 mutations in the presenilin‐1 gene (PSEN1) have been shown to result in familial early onset Alzheimer disease (EOAD), but only a relatively few give rise to plaques with an appearance like cotton wool (CWP) and/or spastic paraparesis (SP). A family with EOAD, seizures and CWP was investigated by neuropathological study and DNA sequencing of the PSEN1 gene. Aβ was identified in leptomeningeal vessels and in cerebral plaques. A single point mutation, p.L420R (g.1508T > G) that gives rise to a missense mutation in the eighth transmembrane (TM8) domain of PS1 was identified in two affected members of the family. p.L420R (g.1508T > G) is the mutation responsible for EOAD, seizures and CWP without SP in this family.     

Diffuse Lewy body disease: light and electron microscopic immunocytochemistry of senile plaques

Summary The nature of senile plaques (SP) in 27 cases of diffuse Lewy body disease (LBD) was investigated using immunocytochemistry and antibodies to beta amyloid protein synthetic peptides (BetaSP), ubiquitin (UBQ), paired helical filaments (PHF; Ab39) and a 68-kDa protein in Alzheimer brains (Alz50). Lewy bodies were present in widespread areas of the neocortex of all cases and were more easily detected with ubiquitin immunocytochemistry than with conventional stains. All cases had neocortical SP, but only six cases had neocortical neurofibrillary tangles (NFT). SP were very numerous in most cases and were usually pale, diffuse or very primitive plaques with thioflavin S fluorescent microscopy. SP in diffuse LBD were immunostained with BetaSP. Several cases had extensive amyloid angiopathy that was also immunoreactive with BetaSP. SP in diffuse LBD were characterized by amyloid deposits with few or no neuritic elements that could be detected with thioflavin S, Bielschowsky's stain or double staining with BetaSP and Bodian's silver stain. They differed from plaques in Alzheimer's disease by lack of PHF-type neurites that could be stained with Ab39. In diffuse LBD, SP contained PHF-type neurites only in areas coexistent with NFT. Some SP had round, granular neurites that were immunoreactive with UBQ, but weakly argyrophilic with Bodian's stain and nonfluorescent with thioflavin S. Diffuse LBD lacked significant neuritic change in the neuropil that could be detected with UBQ, Ab39 and Alz50. The latter finding is a characteristic feature that distinguishes Alzheimer's disease from diffuse LBD.Supported by grant NIA AG06803     

Electron microsocopy of brain amyloid plaques from a patient with new variant Creutzfeldt-Jakob disease

Cerebral cortex biopsy from a patient with new variant Creutzfeldt-Jakob disease (nvCJD) has been examined at the electron microscope level. Spongiform changes corresponded mostly to distended neurites scattered in the neuropil or surrounding amyloid plaques. These latter exhibited heterogeneous submicroscopic morphology including variable amount of loosely interwoven amyloid fibrils admixed in a cellular-rich environment constituted essentially by abnormal neuronal processes. By immunoelectron microscopy, fibrils and some membrane structures reacted with anti-prion protein (PrP) antibodies. One striking aspect was the presence of many small dystrophic neurites without paired helical filaments. Moreover, amyloid fibrils showed unexpected intimate association with abnormal membranes, suggesting a relationship between PrP fibrillogenesis and membrane alteration. These ultrastructural findings provide an additional criterion to distinguish nvCJD- from sporadic CJD-type plaques and reinforce the hypothesis that nvCJD brain is infected by a distinctive strain of the transmissible agent encephalopathy. Received: 7 June 1999 / Accepted: 21 September 1999