Astrocytosis and amyloid deposition in scrapie-infected hamsters

In scrapie infection, prion protein (PrP^Sc) is localized in areas where there is neurodegeneration and astrocytosis. It is thought that PrP^Sc is toxic to neurons and trophic for astrocytes. In our study, paraffin sections from scrapie infected (263K and 139H) and control hamsters were examined with histological and immunocytochemical staining. We found that PrP^Sc was present in the ependymal cells of both 263K- and 139H-infected hamsters. In 139H-infected hamsters, PrP^Sc was found in the cytoplasm of neurons in cerebral cortex and in hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. In contrast, neuronal cytoplasm and nuclei, were positive for PrP^Sc in most areas such as cortex, hippocampus, and thalamus in 263K-infected hamsters. Many aggregations of PrP^Sc could be seen in the cortex, hippocampus, substantia nigra and around the Pia mater, corpus callosum, fimbria, ventricles, and blood vessels in sections from 139H- and/or 263K-positive animals. Furthermore, PrP^Sc was also co-localized with glial fibrillary acidic protein (GFAP) in many reactive astrocytes (approximately 90%) in certain areas such as the hippocampus in 263K-infected hamsters, but not 139H-infected hamsters. The patterns of astrocytosis and PrP^Sc formation were different between 139H- and 263K-infected hamsters, which may be used for a diagnosis purpose. Our results suggest a hypothesis that multiple cell-types are capable of PrP^Sc production. Our results also confirm that reactive astrocytes can produce and/or accumulate PrP^Sc during some scrapie strain infections. The findings suggest a `snowball effect', that is: astrocytosis might play an important role in amyloidosis, while amyloidosis may induce further astrocytosis at least in 263K-infected hamsters.     

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     

Changes in the distribution of anionic sites in brain micro-blood vessels with and without amyloid deposits in scrapie-infected mice

Summary Cationic colloidal gold (CCG) and scrapie-infected mouse brain samples embedded in Lowicryl K4M were used for ultrastructural localization of negatively charged microdomains (anionic sites) in the cerebral microvasculature. The distribution of anionic sites on both fronts (luminal and abluminal) of endothelial cells and in the basement membrane (BM) in 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 (especially capillaries), however, located inside the plaque areas and surrounded directly by amyloid fibers contained attenuated endothelium, the luminal surface of which showed a segmental lack or diminution of anionic sites. In these vessels the BM was frequently infiltrated and replaced by the amyloid fibers. In some vessels located mainly in the areas of the neuropil vacuolization deposits of homogenous material causing the thickening of the BM were noted. These changes were accompanied by irregular labeling of the BM with gold particles. At the sites of bifurcation of some MBVs, predominantly in the area of the venular estuary at the mouth of capillary (at capillary-venular connections), a discontinuity in the distribution of anionic sites was noted. The observed disturbances in the distribution of anionic sites can be associated with a previously noted increased permeability of some MBVs in the brains of scrapie-infected mice.Supported in part by a grant from NINCDS No. 17271-08     

Genetic control of antibody production to myelin basic protein in mice

Experimental allergic encephalomyelitis (EAE) is a disease produced by inoculation of myelin basic protein (BP) into susceptible animals. Data in this report link the production of anti-BP antibody to the murine H-2 histocompatibility background. H-2k and H-2a animals produce high levels of anti-BP antibodies as measuring during both primary and secondary immune responses. Strains with H-2b,d,p,q,s haplotypes are poor responders after primary immunization; however some H-2s and H-2d animals showed an increase in antibody after boosting. The use of M. tuberculosis instead of M. butyricum resulted in greater antibody production in H-2d strains. The response observed in 4 congenic pairs of mice support the association between antibody formation and the H-2 complex. Experiments with recombination inbred strains indicate that responsible genes reside in the I-A region of the H-2 complex.     

Abeta42 gene vaccination reduces brain amyloid plaque burden in transgenic mice

OBJECTIVE: To demonstrate that in APPswe/PS1DeltaE9 transgenic mice, gene gun mediated Abeta42 gene vaccination elicits a high titer of anti-Abeta42 antibodies causal of a significant reduction of Abeta42 deposition in brain. METHODS: Gene gun immunization is conducted with transgenic mice using the Abeta42 gene in a bacterial plasmid with the pSP72-E3L-Abeta42 construct. Enzyme-linked immunoabsorbent assays (ELISA) and Western blots are used to monitor anti-Abeta42 antibody levels in serum and Abeta42 levels in brain tissues. Enzyme-linked immunospot (ELISPOT) assays are used for detection of peripheral blood T cells to release gamma-interferon. Immunofluorescence detection of Abeta42 plaques and quantification of amyloid burden of brain tissue were measured and sections were analyzed with Image J (NIH) software. RESULTS: Gene gun vaccination with the Abeta42 gene resulted in high titers of anti-Abeta42 antibody production of the Th2-type. Levels of Abeta42 in treated transgenic mouse brain were reduced by 60-77.5%. The Mann-Whitney U-test P=0.0286. INTERPRETATION: We have developed a gene gun mediated Abeta42 gene vaccination method that is efficient to break host Abeta42 tolerance without using adjuvant and induces a Th2 immune response. Abeta42 gene vaccination significantly reduces the Abeta42 burden of the brain in treated APPswe/PS1DeltaE9 transgenic mice with no overlap between treated and control mice.     

Peripheral treatment with enoxaparin exacerbates amyloid plaque pathology in Tg2576 mice

Alzheimer's disease (AD) is a complex, progressive neurological disorder characterized by the formation of extracellular amyloid plaques composed of β‐amyloid protein (Aβ), the key component in pathogenesis of AD. Peripheral administration of enoxaparin (ENO) reportedly reduces the level of Aβ and the amyloid plaques in the cortex of amyloid precursor protein (APP) transgenic mice. However, the exact mechanism of these effects is unclear. Our previous studies indicated that ENO can inhibit APP processing to Aβ in primary cortical cells from Tg2576 mice by downregulating BACE1 levels. This study examines whether ENO‐induced reduction of amyloid load is due to the decreased APP processing to Aβ in Tg2576 mice. Surprisingly, our results indicated that ENO significantly increases the Aβ42/Aβ40 ratio in cortex and enhances the amyloid plaque load in both cortex and hippocampus, although overall APP processing was not influenced by ENO. Moreover, ENO stimulated the aggregation of both Aβ40 and Aβ42 in vitro. Although ENO has been reported to improve cognition in vivo and has potential as a therapeutic agent for AD, the results from our study suggest that ENO can exacerbate the amyloid pathology, and the strategy of using ENO for the treatment of AD may require further assessment. © 2016 Wiley Periodicals, Inc.     

Increased blood-brain barrier permeability in scrapie-infected mice

The present investigation was designed to study the ultrastructural integrity of the blood-brain barrier (BBB) in the cerebral microvasculature of scrapie-infected mice showing clinical illness. Cerebral microvessels from either IM, VM, or C57BL/6J mice, terminally affected with various strains of scrapie agent showed a focal leakage of horseradish peroxidase (HRP) in all agent-strain and mouse-strain combinations. This leakage was most pronounced in and near the primary site of agent inoculation, but was also observed in microvessels scattered throughout the brain. Cytochemical studies also revealed a redistribution of plasmalemma-bound alkaline phosphatase in the endothelial cells. In control mice, the enzymatic activity was mainly concentrated in the luminal plasmalemma, while in the scrapie-infected mice the activity also appeared in the abluminal side in the majority of microvessels. Our observations are evidence that the BBB of the mouse is altered in some way by the scrapie agent. Such an alteration may have important implications for human disease, since the scrapie agent is related to the group of "slow" viral infections, including kuru and Creutzfeldt-Jakob disease. Scrapie may also serve as an important model for the study of senile dementia of the Alzheimer type (SDAT).     

Manipulation of PrPres production in scrapie-infected neuroblastoma cells

In the present study the accumulation of protease resistant prion protein (PrPres) in scrapie-infected neuroblastoma cells (ScN2a cells) was shown to be dependent on culture conditions. The highest levels of PrPres were found in slow growing cells. Further increases in PrPres accumulation were observed in ScN2a cells treated with retinoic acid, a compound that is associated with neuronal differentiation. The effects of retinoic acid were dose-dependent with a maximal effect at 200 ng/ml. A similar increase in PrPres was observed in another prion-infected cell line, scrapie-mouse brain (SMB) cells, treated with retinoic acid while retinoic acid increased the amount of PrPC in non-infected cells. Other drugs reported to cause neuronal differentiation, such as phorbol esters, did not increase the PrPres content of ScN2a cells. The survival of retinoic acid-treated ScN2a cells co-cultured with microglia was significantly reduced when compared to untreated ScN2a cells and an inverse correlation was demonstrated between the PrPres content of cells and their survival when co-cultured with microglia. The production of interleukin-6 by microglia cultured with retinoic acid-treated ScN2a cells was significantly higher than that of microglia cultured with untreated ScN2a cells.     

Mechanisms of amyloid plaque pathogenesis

The first ultrastructural investigations of Alzheimer’s disease noted the prominence of degenerating mitochondria in the dystrophic neurites of amyloid plaques, and speculated that this degeneration might be a major contributor to plaque pathogenesis. However, the fate of these organelles has received scant consideration in the intervening decades. A number of hypotheses for the formation and progression of amyloid plaques have since been suggested, including glial secretion of amyloid, somal and synaptic secretion of amyloid-beta protein from neurons, and endosomal–lysosomal aggregation of amyloid-beta protein in the cell bodies of neurons, but none of these hypotheses fully account for the focal accumulation of amyloid in plaques. In addition to Alzheimer’s disease, amyloid plaques occur in a variety of conditions, and these conditions are all accompanied by dystrophic neurites characteristic of disrupted axonal transport. The disruption of axonal transport results in the autophagocytosis of mitochondria without normal lysosomal degradation, and recent evidence from aging, traumatic injury, Alzheimer’s disease and transgenic mice models of Alzheimer’s disease, suggests that the degeneration of these autophagosomes may lead to amyloid production within dystrophic neurites. The theory of amyloid plaque pathogenesis has thus come full circle, back to the intuitions of the very first researchers in the field.     

Simvastatin treatment prolongs the survival of scrapie-infected mice

Statins, drugs that decrease cholesterol biosynthesis, are known to reduce the formation of the disease-associated isoform of the prion protein (PrP) in neuroblastoma cells in vitro. In this study, we report the effects of simvastatin, a clinically approved statin that penetrates the brain, on mice infected with the ME7 strain of scrapie. The decline in motor functions associated with scrapie infection was delayed in mice receiving (1 mg/kg) simvastatin, a dosage used to treat hypercholesterolemia in humans. Simvastatin treatment also significantly prolonged the survival times of infected mice (193 vs. 183 days). These results indicate that low-dosage simvastatin treatment affects the progression of experimental scrapie, and supports the concept that statin treatment may influence the prion pathogenesis.     

Dendritic and synaptic alterations of hippocampal pyramidal neurones in scrapie-infected mice

Neurone damage and eventual loss may underlie the clinical signs of disease in the transmissible spongiform encephalopathies (TSEs). Although neurone death appears to be through apoptosis, the trigger for this form of cell death in the TSEs is not known. Using two different murine scrapie models, hippocampal pyramidal cells were studied through microinjection of fluorescent dye, and synaptic integrity, using p38-immunoreactivity (p38-IR), both visualized using confocal laser scanning microscopy. Intradendritic distensions and dendritic spine loss were found to co-localize to areas of vacuolar and prion protein pathology in the hippocampus of mice infected with ME7 or 87 V scrapie. A significant reduction in p38-IR was found concomitantly in the hippocampus in ME7 scrapie mice. These results indicate that both pre- and post-synaptic sites are altered by scrapie infection; this would disrupt neuronal circuitry and may initiate apoptotic cell death, giving rise to the neurological disturbances manifested in clinical TSE cases.     

Increased expression and localization of cyclooxygenase-2 in astrocytes of scrapie-infected mice

A number of aspects of the pathogenesis of scrapie, the archetype disease of the transmissible spongiform encephalopathies (prion disorders), remain to be elucidated. There is increasing evidence that there are cerebral based inflammatory processes that may contribute to the pathogenesis and to the progression of a number of neurodegenerative disorders, including prion diseases. In peripheral tissues, a key element that controls the generation of proinflammatory mediators is the highly inducible protein cyclooxygenase-2 (COX-2). In this study, in order to examine the possible association of COX-2 with the pathogenesis of scrapie, we analyzed the expression level and the cellular localization of COX-2 in the brains of control and scrapie-infected mice. The COX-2 mRNA and protein levels were increased significantly compared to the control group of mice. By immunohistological analysis, intense immunoreactivity of COX-2 was localized primarily in reactive astrocytes, with virtually no staining in sections from control mice. The staining for COX-2 was co-localized with the pathological form of the prion protein (PrP(Sc)) and with nuclear factor-kappa B (NF-kappaB). These results suggest that the upregulation of COX-2 expression in astrocytes may be related to the accumulation of PrP(Sc), and that COX-2 may then lead to the progression of scrapie, possibly by propagation of a cerebral inflammatory response.     

Serotonin concentrations in brain and blood of scrapie-infected and normal hamsters and mice

Whole brains and bloods of scrapie-infected and control mice and hamsters were assayed for serotonin content. Late clinical scrapie-infected mice showed a 20% reduction in whole-brain serotonin concentrations but no change in blood concentrations relative to controls. Late clinical scrapie-infected hamsters showed no change in whole-brain serotonin concentrations but a 2.5-fold decrease in blood concentrations relative to controls.     

Neuronal and glial beta-secretase (BACE) protein expression in transgenic Tg2576 mice with amyloid plaque pathology

We measured tissue distribution and expression pattern of the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE) in the brains of transgenic Tg2576 mice that show amyloid pathology. BACE protein was expressed at high levels in brain; at lower levels in heart and liver; and at very low levels in pancreas, kidney, and thymus and was almost absent in spleen and lung when assayed by Western blot analysis. We observed strictly neuronal expression of BACE protein in the brains of nontransgenic control mice, with the most robust immunocytochemical labeling present in the cerebral cortex, hippocampal formation, thalamus, and cholinergic basal forebrain nuclei. BACE protein levels did not differ significantly between control and transgenic mice or as a result of aging. However, in the aged, 17-month-old Tg2576 mice there was robust amyloid plaque formation, and BACE protein was also present in reactive astrocytes present near amyloid plaques, as shown by double immunofluorescent labeling and confocal laser scanning microscopy. The lack of astrocytic BACE immunoreactivity in young transgenic Tg2576 mice suggests that it is not the APP overexpression but rather the amyloid plaque formation that stimulates astrocytic BACE expression in Tg2576 mice. Our data also suggest that the neuronal overexpression of APP does not induce the overexpression of its metabolizing enzyme in neurons. Alternatively, the age-dependent accumulation of amyloid plaques in the Tg2576 mice does not require increased neuronal expression of BACE. Our data support the hypothesis that neurons are the primary source of beta-amyloid peptides in brain and that astrocytic beta-amyloid generation may contribute to amyloid plaque formation at later stages or under conditions when astrocytes are activated.     

Immunocytochemical evaluation of blood-brain barrier to endogenous albumin in scrapie-infected mice

A quantitative immunocytochemical procedure was used for evaluation of the blood-brain barrier (BBB) to endogenous albumin in plaque-forming (PF) and non-plaque-forming (NPF) groups of scrapie-infected mice at the clinical stage of disease. Ultrathin sections of brain samples (cerebral cortex, hippocampus and cerebellum) embedded in resin (Lowicryl K4M) were exposed to anti-mouse albumin antiserum followed by protein A-gold. Using morphometry, the density of immunosignals (gold particles per μm²) was recorded over four compartments: vascular lumen, endothelium, subendothelial space, and brain parenchyma (neuropil). Morphometric and statistical analyses did not reveal significant differences in the barrier function of the microvasculature of the cerebral cortex and hippocampus in either group of mice, although a slight increase in the number of leaking vessels in the PF group was noted. In contrast, in the cerebellum, the permeability of the microvessels to albumin was significantly higher in the PF than in the NPF mouse group, and this was paralleled by the infiltration of the walls of numerous vascular profiles with amyloid deposits (amyloid angiopathy). These data also indicate the existence of distinct regional differences in BBB function in the brain of scrapie-infected mice. The vascular amyloid deposits and the amyloid plaques present in the cerebral cortex of PF mice were labeled with numerous immunosignals suggesting the affinity of extravasated albumin to these deposits. In conclusion, no convincing evidence was obtained indicating that impairment of the BBB, manifested by increased permeability of vascular segments, is directly related to the deposition of amyloid in the vascular wall and in plaques. Segmental impairment of the barrier function seems to be rather the result of disturbed structural integrity of the components of the vascular wall. Received: 8 May 1996 / Revised: 26 August 1996, 13 October 1996 / Accepted: 15 October 1996     

The expression of RANTES and chemokine receptors in the brains of scrapie-infected mice

While chemokines play an important role in host defense, it has become abundantly clear that their expression is not solely restricted to immune cells. In this study, to investigate the role of chemokines in pathogenic mechanism of neurodegeneration in prion diseases, we determined the cerebral expression of RANTES, a major chemoattractant of monocytes and activated lymphocytes, and its receptors CCR1, CCR3 and CCR5 in ME7 scrapie-infected mice. The mRNA of RANTES gene was upregulated in the brains of scrapie-infected mice. Intense immunoreactivity of RANTES was observed only in glial fibrillary acidic protein (GFAP)-positive astrocytes of the hippocampus of the infected mice. In addition, the levels of mRNA expression of CCR1, CCR3, and CCR5 were increased in hippocampus of scrapie-infected brains compared to the values in controls. Immunostaining of CCR1, CCR3, and CCR5 was observed in reactive astrocytes of the hippocampal region of scrapie-infected brains. In addition, immunoreactivity of CCR5 was also observed in microglia of scrapie-infected brains. These results suggest that RANTES and its receptors may participate in amplifying proinflammatory responses and, thereby, exacerbate the neurodegeneration of prion diseases.     

Ultrastructural observations of spinal cord lesions and blood-brain barrier changes in scrapie-infected mice

Summary Spinal cord samples from IM or VM mice injected intracerebrally with the 87V scrapie agent were examined ultrastructurally at the clinical stage of disease for changes in blood vessel permeability and for pathological alterations. In several animals, (3 of 16), massive changes were noted in the cervical spinal cords in the subependymal area of the cortical gray matter immediately surrounding the central canal including ependymal cell changes, the presence of amyloid plaque in close association with microglial cells, extensive neuropil vacuolation, the appearance of reactive astrocytes, degenerating neurites and vacuolated neurons. In those regions showing structural damage, localized increased permeability to horseradish peroxidase across the blood-brain barrier was noticed along with the appearance of numerous vesiculo-canalicular profiles in micro-blood vessel endothelial cells with extravasation of the tracer to the neuropil. Some damaged neurons appeared flooded with this tracer. These changes were not observed in either the thoracic or lumbar spinal cord regions. The occurrence of pathological changes in the spinal cords of a small percentage of intracerebrally injected mice was probably due to a high concentration of the scrapie agent which localized in the cervical spinal cord, presumably after entering the spinal fluid via the lateral ventricle at the time of injection.Supported in part by a grant from the NINCDS No. 18079     

Viral-induced inflammation is accompanied by beta-amyloid plaque reduction in brains of amyloid precursor protein transgenic Tg2576 mice

Amyloid plaques, one of the neuropathological hallmarks of Alzheimer's disease, and their main constituent, the amyloid beta-peptide (Abeta), are triggers of the activation of innate inflammatory mechanisms involving the activation of microglia. To dissect the effects of a non-Abeta-specific microglial activation on the Abeta metabolism, we employed a viral infection-based model. Transgenic mice expressing a mutated form of the human amyloid precursor protein (Tg2576) were used. In preceding experiments, 2-week-old transgenic mice and non-transgenic littermates were infected intracerebrally with the neurotropic Borna disease virus and investigated at 2, 4 and 14 weeks post-infection. The Borna disease virus-inoculated mice showed a persisting, subclinical infection of cortical and limbic brain areas characterized by slight T-cell infiltrates, expression of cytokines and a massive microglial activation in the hippocampus and neocortex. Viral-induced effects reached their peak at 4 weeks post-infection. In 14-month-old Tg2576 mice, characterized by the deposition of diffuse and dense-core amyloid plaques in cortical brain regions, Borna disease virus-induced microglial activation in the vicinity of Abeta deposits was used to investigate the influence of a local inflammatory response on these deposits. At 4 weeks post-infection, histometric analyses employing Abeta immunohistochemistry revealed a decrease of the cortical and hippocampal Abeta-immunopositive area. This overall decrease was accompanied by a decrease of parenchymal thioflavin-S-positive amyloid deposits and an increase of such deposits in the walls of cerebral vessels, which indicates that the elicitation of a non-Abeta-specific microglial activation may contribute to a reduction of Abeta in the brain parenchyma.     

Delayed amyloid plaque deposition and behavioral deficits in outcrossed AβPP/PS1 mice

Alzheimer's disease (AD) is a progressive neurodegenerative dementia characterized by amyloid plaque accumulation, synapse/dendrite loss, and cognitive impairment. Transgenic mice expressing mutant forms of amyloid‐β precursor protein (AβPP) and presenilin‐1 (PS1) recapitulate several aspects of this disease and provide a useful model system for studying elements of AD progression. AβPP/PS1 mice have been previously shown to exhibit behavioral deficits and amyloid plaque deposition between 4–9 months of age. We crossed AβPP/PS1 animals with mice of a mixed genetic background (C57BL/6 × 129/SvJ) and investigated the development of AD‐like features in the resulting outcrossed mice. The onset of memory‐based behavioral impairment is delayed considerably in outcrossed AβPP/PS1 mice relative to inbred mice on a C57BL/6 background. While inbred AβPP/PS1 mice develop deficits in radial‐arm water maze performance and novel object recognition as early as 8 months, outcrossed AβPP/PS1 mice do not display defects until 18 months. Within the forebrain, we find that inbred AβPP/PS1 mice have significantly higher amyloid plaque burden at 12 months than outcrossed AβPP/PS1 mice of the same age. Surprisingly, inbred AβPP/PS1 mice at 8 months have low plaque burden, suggesting that plaque burden alone cannot explain the accompanying behavioral deficits. Analysis of AβPP processing revealed that elevated levels of soluble Aβ correlate with the degree of behavioral impairment in both strains. Taken together, these findings suggest that animal behavior, amyloid plaque deposition, and AβPP processing are sensitive to genetic differences between mouse strains. J. Comp. Neurol., 521:1395–1408, 2013. © 2012 Wiley Periodicals, Inc.     

Different chromogranin immunoreactivity between prion and a-beta amyloid plaque

Brain lesions in Creutzfeldt-Jakob disease (CJD) include spongiform change, neuronal loss, amyloid plaques, astrogliosis and microglial activation. Microglia are thought to play a key role in prion-induced neurodegeneration. However, the intermediate molecules supporting relationships between neurons and microglia are still unknown. Chromogranins (Cg) are soluble glycophosphoproteins that can activate microglial cells leading to a neurotoxic phenotype. The immunoreactive patterns of CgA and CgB were investigated in CJD and compared to those observed in Alzheimer's disease. We found that CgB, but not CgA, immunoreactivity was selectively associated with prion protein deposits, whereas CgA was only seen in Abeta plaques. This suggests a specific influence of the constitutive amyloid protein on chromogranin secretion and a role of CgB in the CJD neurodegenerative process.