Comparison of protease-resistant prion protein inhibitors in cell cultures infected with two strains of mouse and sheep scrapie

The transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases. A primary therapeutic target for TSE intervention has been a protease-resistant form of prion protein known as PrP(Sc) or PrP-res. In vitro testing of mouse scrapie-infected cell cultures has identified many PrP-res inhibitors that also have activity in vivo. Here we identify 32 new inhibitors of two strains of mouse scrapie PrP-res. Furthermore, to investigate the species-specificity of these and other PrP-res inhibitors, we have developed a high-throughput cell culture assay based on Rov9 cells chronically-infected with sheep scrapie. Of 32 inhibitors of murine PrP-res that were also tested in the Rov9 cells, only six showed inhibitory activity against sheep PrP-res. The three most potent inhibitors of both murine and ovine PrP-res formation (with 50% inhibition at < or =5 microM) were tannic acid, pentosan polysulfate and Fe(III) deuteroporphyrin 2,4-bisethyleneglycol. The latter two have anti-mouse scrapie activity in vivo. These results identify new inhibitors of murine and ovine PrP-res formation and reinforce the idea that compounds effective against PrP-res from one species or strain cannot be assumed to be active against others.     

Differences in scrapie-induced pathology of the retina and brain in transgenic mice that express hamster prion protein in neurons, astrocytes, or multiple cell types

Prion protein (PrP) is expressed in many tissues and is required for susceptibility to scrapie and other prion diseases. To investigate the role of PrP expression in different cell types on pathology in retina and brain after scrapie infection, we examined transgenic mice expressing hamster PrP from the PrP promoter (tg7), the neuron-specific enolase promoter (tgNSE), or the astrocyte-specific glial fibrillary acidic protein promoter (tgGFAP). After intraocular inoculation with hamster scrapie, clinical disease developed in tg7 and tgNSE mice by 100 days and in tgGFAP mice by 350 days. Astrogliosis and scrapie-associated protease-resistant PrP (PrP-res) were detected in retina and brain before clinical onset. Retinal PrP-res was present in high amounts in both tg7 and tgNSE mice, however only tg7 mice developed retinal degeneration and extensive apoptosis. In contrast, in all three lines of mice high levels of brain PrP-res accompanied by neurodegeneration were observed. Thus, PrP expression on neurons or astrocytes was sufficient for development of scrapie-induced degeneration in brain but not in retina. The combined effects of PrP-res production in multiple cell types was required to produce retinal degeneration, whereas in brain PrP-res production by neurons or astrocytes alone was sufficient to cause neuronal damage via direct or indirect mechanisms.     

Immunohistochemical features of PrP(d) accumulation in natural and experimental goat transmissible spongiform encephalopathies

Scrapie is a transmissible spongiform encephalopathy (TSE) or prion disease, which naturally affects sheep and goats. Immunohistochemical epitope mapping of abnormal PrP accumulations (PrP(d)) in brain can help in characterizing sheep TSE sources or strains and in identifying potential bovine spongiform encephalopathy (BSE) infections of sheep. Natural and experimental TSE infections of goats were examined to determine whether the epitope mapping approach could also be applied to aid recognition of BSE infection in goats. Goats experimentally infected with the SSBP/1 or CH1641 sheep scrapie strains or with cattle BSE, together with four field cases of natural TSE in goats, were examined immunohistochemically with six different antibodies. CH1641 and SSBP/1 infections in goats, as in sheep, showed PrP(d) accumulations which were mainly intracellular. Some differences in targeting, particularly of Purkinje cells, was evident in inter-species comparisons of CH1641 and SSBP/1. PrP(d) labelling of goat BSE experimental cases showed extensive intracellular and extracellular accumulations, also similar to those in sheep BSE. Intra-neuronal PrP(d) in both goat and sheep BSE was labelled only by antibodies recognizing epitopes located C-terminally of residue His99, whereas in natural sheep TSE sources, and in sheep and goat SSBP/1, PrP(d) was also detected by antibodies to epitopes located between residues Trp93 and His99. Testing of four natural goat TSE samples showed one case in which epitope mapping characteristics and the overall patterns of PrP(d) accumulation was identical with those of experimental goat BSE. The four natural goat scrapie cases examined showed some degree of immunohistochemical phenotype variability, suggesting that multiple strains exist within the relatively small UK goat population.     

Evaluation of Infective Property of Recombinant Prion Protein Amyloids in Cultured Cells Overexpressing Cellular Prion Protein

Misfolded isoform of prion protein (PrP), termed scrapie PrP (PrP^Sc), tends to aggregate into various fibril forms. Previously, we reported various conditions that affect aggregation of recombinant PrP into amyloids. Because amyloidogenesis of PrP is closely associated with transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans, we investigated infectivity of recombinant PrP amyloids generated in vitro. Using cultured cell lines which overexpress cellular PrP of different species, we measured the level of de novo synthesized PrP^Sc in cells inoculated with recombinant mouse PrP amyloids. While PrP-overexpressing cells were susceptible to mouse-adapted scrapie prions used as the positive control, demonstrating the species barrier effect, infection with amyloids made of truncated recombinant PrP (PrP[89-230]) failed to form and propagate PrP^Sc even in the cells that express mouse cellular PrP. This suggests that infectivity of PrP amyloids generated in vitro is different from that of natural prions. Recombinant PrP (89-230) amyloids tested in the current study retain no or a minute level, if any, of prion infectivity.

Graphical Abstract

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Quantitative recovery of scrapie agent with minimal protein from highly infectious cultures

There are few reports on the isolation, quantitative recovery, and relative purification of infectious particles that cause scrapie, Creutzfeldt-Jakob disease (CJD) and epidemic bovine spongiform encephalopathy (BSE). Because pure prion protein (PrP) has failed to show significant infectivity, it is critical to find other molecules that are integral agent components. Only complex diseased tissues such as degenerating brain have been fractionated, and agent recoveries have been quite low in concentrated abnormal prion protein (PrP-res) preparations. To simplify the purification of infectious particles, we evaluated a monotypic cell line that continuously produced high levels of the 22L scrapie agent (N2a-22L). A new rapid and accurate GT1 culture assay was used to titrate infectivity in six representative sucrose gradients. We developed a streamlined approximately 3-h procedure that yielded full recovery of starting infectivity in fractions with only a few selected protein bands (representing <1% of starting protein). Infectious particles reproducibly sedimented through >30% sucrose steps, whereas PrP and PrP-res sedimentation varied depending on the conditions used. Both normal and abnormal PrP could be largely separated from infectivity in a single short centrifugation. Because no foreign enzymes were added to achieve reasonably purified infectious particles, these preparations may be used to elicit diagnostic antibodies to foreign agent proteins.     

Ovine infection with the agents of scrapie (CH1641 isolate) and bovine spongiform encephalopathy: immunochemical similarities can be resolved by immunohistochemistry

Immunochemical ("rapid") tests, which recognize a partly protease-resistant conformer of the prion protein (PrP(res)) are now widely used in Europe for the diagnosis of transmissible spongiform encephalopathies (TSEs). Some of these tests can be used to distinguish natural scrapie from experimental bovine spongiform encephalopathy (BSE) in sheep, on the basis of migration pattern differences of PrP(res) in Western immunoblots. However, PrP(res) from sheep inoculated with CH1641 scrapie gives an immunoblot profile similar to that of sheep inoculated with BSE. Therefore, field scrapie strains similar to CH1641 might be misclassified as ovine BSE in the rapid tests currently employed. This study confirmed that the Western blot similarities (size of the unglycosylated band and distinct reactivity with 6H4 and P4 antibodies) between CH1641 and BSE remained consistent regardless of the PrP genotype of the sheep, but the two infections resulted in accumulation of disease-associated PrP (PrP(d)) that could easily be distinguished by the immunohistochemical "peptide mapping" method. This method, which reveals conformational differences of PrP(d) by the use of a panel of antibodies, indicated that PrP(d) from the CH1641 isolate was truncated further upstream in the N terminus than was PrP(d) from other ovine TSEs, including experimental BSE. In addition, the immunohistochemical "PrP(d) profile method", which defines the phenotype of PrP(d) accumulation in the brain of affected sheep, showed that CH1641 infection leads to much more intra-neuronal and considerably less extracellular PrP(d) than does experimental BSE. The overall results demonstrate that a combined Western blotting and immunohistochemical approach is required to discriminate between different TSE strains in sheep.     

Use of murine bioassay to resolve ovine transmissible spongiform encephalopathy cases showing a bovine spongiform encephalopathy molecular profile

Two cases of unusual transmissible spongiform encephalopathy (TSE) were diagnosed on the same farm in ARQ/ARQ PrP sheep showing attributes of both bovine spongiform encephalopathy (BSE) and scrapie. These cases, UK-1 and UK-2, were investigated further by transmissions to wild-type and ovine transgenic mice. Lesion profiles (LP) on primary isolation and subpassage, incubation period (IP) of disease, PrP(Sc) immunohistochemical (IHC) deposition pattern and Western blot profiles were used to characterize the prions causing disease in these sheep. Results showed that both cases were compatible with scrapie. The presence of BSE was contraindicated by the following: LP on primary isolation in RIII and/or MR (modified RIII) mice; IP and LP after serial passage in wild-type mice; PrP(Sc) deposition pattern in wild-type mice; and IP and Western blot data in transgenic mice. Furthermore, immunohistochemistry (IHC) revealed that each case generated two distinct PrP(Sc) deposition patterns in both wild-type and transgenic mice, suggesting that two scrapie strains coexisted in the ovine hosts. Critically, these data confirmed the original differential IHC categorization that these UK-1 and UK-2 cases were not compatible with BSE.     

First confirmed sheep scrapie with A136R154Q171 genotype in Slovakia

The first confirmed evidence of scrapie in Slovakia was demonstrated in one sheep of the autochthonous Merino breed from the southeastern part of the country. The reported scrapie was diagnosed during compulsory transmissible spongiform encephalitis (TSE) screening of sheep over 9 months of age assigned for consumption. The positive ewe was 5-year-old, which did not show any clinical signs of scrapie. The presence of the proteinase-resistant prion protein (PrP) in brain was proved independently by two laboratories using two different immunochemical screening systems, namely the Prionics Check (Western blot analysis) and Enfer TSE enzyme-linked immunosorbent assay (ELISA). In addition, the genotyping analysis of PrP gene demonstrated the presence of PrP genotype from the high risk group R4. The affected sheep was homozygous for the allele PrP(ARQ) (ARQ/ARQ) coding for alanine (A), arginine (R) and glutamine (Q) at three most relevant codons (136, 154 and 171, respectively). The healthy sister of the positive ewe was heterozygous in the PrP locus and carried alleles ARQ/ARR.     

Reduction of protein kinase MARK4 in the brains of experimental scrapie rodents and human prion disease correlates with deposits of PrP(Sc)

Microtubule affinity-regulating kinase 4 (MARK4) belongs to a family of kinases that are able to actively phosphorylate the neuronal microtubule-associate proteins (MAPs), such as tau, MAP2 and the ubiquitous MAP4. Abnormal changes in tubulin and the profiles of tau have been previously reported in the human brain and animal transmissible spongiform encephalopathies (TSEs), which may be associated with abnormal alterations of various cellular kinases. To elucidate the possible role of MARK4 in TSE pathogenesis, the MARK4 levels in the brain tissues of scrapie-infected rodents and human prion diseases were evaluated using western blotting and immunohistochemical assays. The results revealed that at terminal stages of the diseases, MARK4 levels in the brain tissues of the scrapie 263K-infected hamsters, 139A-infected mice and a case of Creutzfeldt-Jakob disease (CJD, G114V gCJD) correlated with amounts of PrP(Sc) deposits that were almost undetectable. On the other hand MARK4 signals were noticeable in the brain tissues of a fatal familial insomnia (FFI) patient without PrP(Sc). The reduction of MARK4 was closely related to the prolonged incubation times. These results could be reproduced in SK-N-SH and PC12 cell lines after being exposed to the synthetic peptide PrP106-126. Accordingly, the levels of phosphorylated tau at Ser262 (p-tau262) in cultured cells exposed to PrP106-126, or the ratios of p-tau262/total tau in the brain tissues of 263K-infected hamsters were also significantly decreased. According to our data there is a correlation between a TSE pathological-associated decline of MARK4 in the brain tissues with the deposits of PrP(Sc). Reduction of MARK4 will result in abnormalities of tau phosphorylation, and possibly induce further detachment of microtubules and hinder microtubule transportation.     

Distinction of scrapie phenotypes in sheep by lesion profiling

Major determinants of the pathological phenotype of natural scrapie are considered to be the agent strain and host prion protein (PrP) genotype, but the relationship between these is far from clear. Little is known about the strains that produce natural scrapie. A method of brain vacuolation profiling was developed which enables this aspect of disease phenotype to be characterized in detail. This method distinguished at least two distinct pathological phenotypes in sheep of a single genotype (ARQ/ARQ) from different flocks in the UK. Great similarity was also demonstrated between one of these phenotypes and the phenotype of sheep from a flock in Sardinia. The profile of four sheep of the same ARQ/ARQ genotype experimentally infected with bovine spongiform encephalopathy (BSE) was determined for comparison. It would appear from these preliminary observations that the application of lesion profiling techniques to ovine transmissible spongiform encephalopathy (TSE) may contribute to the definition of a particular scrapie phenotype within a flock. It may, therefore, have potential for improving our understanding of current TSE phenotypes in sheep, with regard to the possibility of identifying those of bovine origin.     

All major prion types recognised by a multiplex immunofluorometric assay for disease screening and confirmation in sheep

Prion diseases or transmissible spongiform encephalopathies (TSEs) in small ruminants are presented in many forms: classical scrapie, Nor98/atypical scrapie, CH1641 scrapie and bovine spongiform encephalopathy (BSE). We previously described a multiplex immunofluorometric assay (mIFMA), based on a bead array flow cytometry technology, which provided, in a single assay, discrimination between BSE (in cattle and sheep) and classical scrapie (Tang et al., 2010). In this study, we extended the mlFMA to differentiate classical scrapie, atypical scrapie, BSE (experimentally infected sheep and naturally infected cattle) and CH1641 (both experimental and natural CH1641-like infections in sheep). Three capture antibodies were used, two distinct PrP N-terminus specific antibodies 12B2 and 9A2, and a PrP core specific antibody 94B4. All three antibodies were shown to bind classical scrapie PrP(res) strongly, whereas in Nor98/atypical scrapie PrP(res) only 12B2 and 9A2 binding was observed. PrP(res) binding of 12B2 was low for both BSE and CH1641, as expected. Furthermore, analysis of serially diluted samples indicated that the assay provided a similar level of sensitivity for atypical scrapie as that found using a well established commercial test. Unexpectedly, 9A2 binding to CH1641 PrP(res) was reduced by 2.1 fold both for experimental CH1641 and CH1641-like scrapie when compared with BSE, suggesting that major cleavage of the N-terminus occurs further towards the C-terminus in CH1641 than in BSE. The ratios of 12B2/94B4 and 9A2/94B4 were similar between experimental CH1641 and CH1641-like cases, although two CH1641-like subjects displayed slightly elevated ratios of both 12B2/94B4 and 9A2/94B4. To verify this finding for PrP(res), mass spectrometry based quantification was used to determine the absolute abundance of the peptides associated with all three antibody binding regions. There was a 2.2 fold reduction of peptides containing the 9A2 epitope for experimental CH1641 PrP(res) in comparison to BSE PrP(res). Observation of reduced PrP(res) may serve as a new marker for CH1641. This mIFMA may thus provide the basis for simplified TSE diagnosis with capability for simultaneous screening and differential diagnosis.     

Differential diagnosis of infections with the bovine spongiform encephalopathy (BSE) and scrapie agents in sheep.

Scrapie, bovine spongiform encephalopathy (BSE), and variant Creutzfeldt-Jakob disease belong to the group of disorders called transmissible spongiform encephalopathies or prion diseases. The possibility that some sheep may be infected with the BSE agent is of human and animal health concern. Immunohistochemical methods were used to identify specific prion protein (PrP) peptide sequences in specific cell types of the brain and lymphoreticular system (LRS) of sheep with natural scrapie and Suffolk and Romney sheep infected experimentally with the BSE agent. Clinically affected and some pre-clinical cases of BSE infection could be distinguished from scrapie cases by the lesser amount of labelling of PrP containing the 84-102 amino-acid peptide sequences in phagocytic cells of the LRS and brain. Additionally, BSE-infected sheep had higher degrees of intra-neuronal PrP accumulation in the brain, as detected by labelling for a range of PrP peptide sequences. These results suggest that there is strain-dependent processing of PrP in specific cell types within the nervous system and LRS which can be used to distinguish BSE- and scrapie-infected sheep.     

Guanidine hydrochloride extraction and detection of prion proteins in mouse and hamster prion diseases by ELISA

Current detection of transmissible spongiform encephalopathy (TSE) relies on the proteolytic generation of a protease-resistant core from the scrapie isoform of prion protein (PrP(Sc)) followed by immunoblotting. This process is non-quantitative, time-consuming, and technically demanding. Recently, an alternative in vitro test for TSE based on the differential extraction of brain homogenates using guanidine hydrochloride followed by DELFIA (Dissociation Enhanced Lanthanide FluoroImmunoAssay) has been developed. In the present study, this approach was adopted using a panel of anti-PrP monoclonal antibodies (MAbs) in conventional sandwich enzyme-linked immunosorbent assay (ELISA) to investigate hamster and two distinct strains of mouse prion diseases. Although PrP species were present in both soluble and insoluble fractions from normal as well as TSE samples, only the PrP species in the insoluble fractions from the latter samples were protease-resistant. In addition, certain anti-PrP MAb pairs could distinguish the PrP species in infected brains from those in the normal samples. The ability to differentiate disease-associated PrP isoforms without proteinase K digestion could serve as a panacea for developing a reliable and rapid diagnostic test for prion diseases.     

Towards cellular receptors for prions

Transmissible spongiform encephalopathies (TSE) are attributed to the conversion of the cellular prion protein (PrP(c)) into an abnormal isoform (PrP(sc)). This can be caused by the invasion of living organisms by infectious particles, or be inherited due to mutations on the PrP(c) gene. One of the most intriguing problems of prion biology is the inability to generate the infectious agent in vitro. This argues strongly that other cellular proteins besides those added in test tubes or found in cellular preparations are necessary for infection. Despite recent progress in the understanding of prion pathology, the subcellular compartments in which the interaction and conversion of PrP(c) into PrP(sc) take place are still controversial. PrP(c) interacts with various macromolecules at the cell membrane, in endocytic compartments and in the secretory pathway, all of which may play specific roles in the internalisation of PrP(sc) and conversion of PrP(c). A specific interacting protein required for the propagation of prions was originally proposed as a prion receptor, and later referred to as a ligand, a cofactor, protein X, or a partner. However, current studies indicate that PrP(c) associates with multi-molecular complexes, which mediate a variety of functions in distinct cellular compartments. It is proposed that a deeper understanding of the mechanics of such interactions, coupled to a better knowledge of the corresponding signalling pathways and ensuing cellular responses, will have a major impact on the prevention and treatment of TSE.     

Overexpression of Shadoo protein in transgenic mice does not impact the pathogenesis of scrapie

Shadoo is a glycoprotein expressed in the adult brain that is an interacting protein of prion protein; however, its function remains to be determined. To elucidate its role in prion pathogenesis, we generated transgenic mice overexpressing wild-type (wt) Shadoo driven by the murine PrP promoter. Expression of the murine Sprn transgene significantly increased brain Shadoo protein levels in all three mouse lines generated. Following infection with mouse-adapted scrapie strain 22L, all transgenic mice tested exhibited characteristics of scrapie disease. Importantly, there was no correlation between the expression level or incubation time of Shadoo with disease phenotype. We therefore conclude that Shadoo has little or no influence on the outcome of transmissible spongiform encephalopathy (TSE) disease in transgenic mice.     

Disease-associated prion protein is not detectable in human systemic amyloid deposits

Cerebral and cardiac amyloid deposits have been reported after scrapie infection in transgenic mice expressing variant prion protein (PrP(C)) lacking the glycophosphatidylinositol anchor. The amyloid fibril protein in the systemic amyloid deposits was not characterized, and there is no clinical or pathological association between prion diseases and systemic amyloidosis in humans. Nevertheless, in view of the potential clinical significance of these murine observations, we tested both human amyloidotic tissues and isolated amyloid fibrils for the presence of PrP(Sc), the prion protein conformation associated with transmissible spongiform encephalopathy (TSE). We also sequenced the complete prion protein gene, PRNP, in amyloidosis patients. No specific immunohistochemical staining for PrP(Sc) was obtained in the amyloidotic cardiac and other visceral tissues of patients with different types of systemic amyloidosis. No protease-resistant prion protein, PrP(res), was detectable by Western blotting of amyloid fibrils isolated from cardiac and other systemic amyloid deposits. Only the complete normal wild-type PRNP gene sequence was identified, including the usual distribution of codon 129 polymorphisms. These reassuringly negative results do not support the idea that there is any relationship of prions or TSE with human systemic amyloidosis, including cardiac amyloid deposition.     

Prion diseases: from protein to cell pathology

Prion diseases or transmissible spongiform encephalopathies are fatal neurodegenerative conditions in humans and animals that originate spontaneously, genetically or by infection. Conformational change of the normal (cellular) form of prion protein (PrP c) to a pathological, disease-associated form (PrP TSE) is considered central to pathogenesis and formation of the infectious agent or prion. Neuronal damage is central to clinical manifestation of prion diseases but poorly understood. In this review, we analyze the major pathogenetic pathways that lead to tissue pathology in different forms of disease. Neuropathogenesis of prion diseases evolves in complex ways on several front lines, most but not all of which exist also in other neurodegenerative as well as infectious diseases. Whereas intracellular accumulation of PrP forms might significantly impair cell function and lead to cytopathology, mere extracellular deposition of PrP TSE is questionable as a direct cytotoxic factor. Tissue damage may result from several parallel, interacting, or subsequent pathways. Future studies should clarify the trigger(s) and sequence of these processes and whether, and which, one is dominating or decisive.     

Prion: toxic or infectious agent?

Prions are proteins that cause a number of invariably fatal neuro-degenerative diseases, which can be classified into two groups: genetic or sporadic diseases (GSD) and transmissible spongiform encephalopathies (TSE). Both types of disease require the development of both normal prion (PrP) and abnormal prion (PrP(sc)) which differs from PrP in having a tertiary structure rich in beta-sheets. In fact, PrP(sc) is a totally dehydrated protein with an anhydrous environment, probably a thin carbon dioxide gas gap, that is why it appears highly resistant to proteases, to chemical disinfectants in water phase except in certain conditions to sodium hydroxide and sodium hypochlorite, to heat and to radiation. GSD and TSE diseases differ in incubation time, primary symptoms, and nature of CNS lesions. This paper argues that diseases of the GSD type as inherited or hereditary metabolic disorders and diseases of the TSE type could be regarded as chemical poisonings. TSE is caused by a deficiency in the chemo-defense system (CDS), which is unable to destroy or eliminate PrP(sc). As a result, the immune defense system (IDS) accommodates PrP(sc) as an inert particle if not a virus lure and routes it through to the nervous central system and the brain via the body's lymphoreticular system. In TSE PrP(sc) acts inside the cells as a toxic disruptor of post-translational phase of PrP biosynthesis. Unfortunately, CDS and IDS appear unable to neutralize PrP(sc).     

Protease-resistant prion protein in brain and lymphoid organs of sheep within a naturally scrapie-infected flock

The hallmark of transmissible spongiform encephalopathies (TSE), such as scrapie in sheep, is the accumulation in tissues of an insoluble and protease resistant form (PrPres) of the cellular prion protein. In this study, we evaluated whether the diversity in both the clinical pattern and the PrP genotypes of scrapied sheep from the same flock was connected with different levels and/or glycoform patterns of the PrPres in the brain and lymphoid organs of the animals. Whereas the PrPres levels in spleen, lymph nodes and tonsils from sheep of different PrP genotypes and clinical status appeared comparable, they were highly variable in brain, particularly in the brain stem and the cerebellum. PrPres was only detected in sheep bearing at least one VRQ allele, including three asymptomatic sheep and the highest PrPres load was found in the cerebellum of VRQ/VRQ animals. All together, levels of PrPres in brain did not necessarily correlate with the severity of the clinical disease but might depend on the PrP genotype of the animals. Different brain regions from a given sheep displayed a similar glycopattern of PrPres, whereas the apparent molecular sizes of the unglycosylated and diglycosylated forms of the protein differed between brain and lymphoid tissues. We did not find any notifiable differences in the glycopattern of PrPres in brain from sheep of different PrP genotypes or different clinical status and this PrPres glycotype was also similar to that found in brain from four cattle BSE.     

Role of the draining lymph node in scrapie agent transmission from the skin

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases that affect humans and animals. Diseases include scrapie in sheep and Creutzfeldt-Jakob disease in humans. Following peripheral exposure, TSE agents usually accumulate on follicular dendritic cells (FDCs) in lymphoid tissues before neuroinvasion. Studies in mice have shown that TSE exposure through scarified skin is an effective means of transmission. Following inoculation by this route TSE agent accumulation upon FDCs is likewise essential for the subsequent transmission of disease to the brain. However, which lymphoid tissues are crucial for TSE pathogenesis following inoculation via the skin was not known. Mice were therefore created that lacked the draining inguinal lymph node (ILN), but had functional FDCs in remaining lymphoid tissues such as the spleen. These mice were inoculated with the scrapie agent by skin scarification to allow the role of draining ILN in scrapie pathogenesis to be determined. We show that following inoculation with the scrapie agent by skin scarification, disease susceptibility was dramatically reduced in mice lacking the draining ILN. These data demonstrate that following inoculation by skin scarification, scrapie agent accumulation upon FDCs in the draining lymph node is critical for the efficient transmission of disease to the brain.