Prion Infectivity in Fat of Deer with Chronic Wasting Disease

Chronic wasting disease (CWD) is a neurodegenerative prion disease of cervids. Some animal prion diseases, such as bovine spongiform encephalopathy, can infect humans; however, human susceptibility to CWD is unknown. In ruminants, prion infectivity is found in central nervous system and lymphoid tissues, with smaller amounts in intestine and muscle. In mice, prion infectivity was recently detected in fat. Since ruminant fat is consumed by humans and fed to animals, we determined infectivity titers in fat from two CWD-infected deer. Deer fat devoid of muscle contained low levels of CWD infectivity and might be a risk factor for prion infection of other species.Prion diseases are fatal neurodegenerative diseases that include Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep, and chronic wasting disease (CWD) in cervids. Cross-species prion infection can occur and is responsible for the spread of BSE to humans (2). Since spread is likely due to exposure to infected tissues, it is vital to know which tissues contain infectivity. In animals such as cattle, sheep, and cervids, whose tissues are part of both the human and domestic-animal food chains, the central nervous system (CNS) has the highest propensity for infectivity. Lymphoid organs and muscles can also be positive for the disease agent, but this varies among species (1, 4, 7). We recently found prion infectivity in brown and white fat of scrapie agent-infected mice (13) and wanted to determine if fat from animals actually consumed by humans may also carry infectivity. To answer this question, we inoculated fat from two CWD agent-infected deer into susceptible transgenic mice expressing deer prion protein (TgDeerPrP mouse) (10).     

PrPSc accumulation in myocytes from sheep incubating natural scrapie

Because variant Creutzfeldt-Jakob disease (vCJD) in humans probably results from consumption of products contaminated with tissue from animals with bovine spongiform encephalopathy, whether infectious prion protein is present in ruminant muscles is a crucial question. Here we show that experimentally and naturally scrapie-affected sheep accumulate the prion protein PrP(Sc) in a myocyte subset. In naturally infected sheep, PrP(Sc) is detectable in muscle several months before clinical disease onset. The relative amounts of PrP(Sc) suggest a 5,000-fold lower infectivity for muscle as compared to brain.     

Correlation between Infectivity and Disease Associated Prion Protein in the Nervous System and Selected Edible Tissues of Naturally Affected Scrapie Sheep

The transmissible spongiform encephalopathies (TSEs) or prion diseases are a group of fatal neurodegenerative disorders characterised by the accumulation of a pathological form of a host protein known as prion protein (PrP). The validation of abnormal PrP detection techniques is fundamental to allow the use of high-throughput laboratory based tests, avoiding the limitations of bioassays. We used scrapie, a prototype TSE, to examine the relationship between infectivity and laboratory based diagnostic tools. The data may help to optimise strategies to prevent exposure of humans to small ruminant TSE material via the food chain. Abnormal PrP distribution/accumulation was assessed by immunohistochemistry (IHC), Western blot (WB) and ELISA in samples from four animals. In addition, infectivity was detected using a sensitive bank vole bioassay with selected samples from two of the four sheep and protein misfolding cyclic amplification using bank vole brain as substrate (vPMCA) was also carried out in selected samples from one animal. Lymph nodes, oculomotor muscles, sciatic nerve and kidney were positive by IHC, WB and ELISA, although at levels 100–1000 fold lower than the brain, and contained detectable infectivity by bioassay. Tissues not infectious by bioassay were also negative by all laboratory tests including PMCA. Although discrepancies were observed in tissues with very low levels of abnormal PrP, there was an overall good correlation between IHC, WB, ELISA and bioassay results. Most importantly, there was a good correlation between the detection of abnormal PrP in tissues using laboratory tests and the levels of infectivity even when the titre was low. These findings provide useful information for risk modellers and represent a first step toward the validation of laboratory tests used to quantify prion infectivity, which would greatly aid TSE risk assessment policies.     

Long-term subclinical carrier state precedes scrapie replication and adaptation in a resistant species: analogies to bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease in humans

Cattle infected with bovine spongiform encephalopathy (BSE) appear to be a reservoir for transmission of variant Creutzfeldt-Jakob disease (vCJD) to humans. Although just over 100 people have developed clinical vCJD, millions have probably been exposed to the infectivity by consumption of BSE-infected beef. It is currently not known whether some of these individuals will develop disease themselves or act as asymptomatic carriers of infectivity which might infect others in the future. We have studied agent persistence and adaptation after cross-species infection using a model of mice inoculated with hamster scrapie strain 263K. Although mice inoculated with hamster scrapie do not develop clinical disease after inoculation with 10 million hamster infectious doses, hamster scrapie infectivity persists in brain and spleen for the life span of the mice. In the present study, we were surprised to find a 1-year period postinfection with hamster scrapie where there was no evidence for replication of infectivity in mouse brain. In contrast, this period of inactive persistence was followed by a period of active replication of infectivity as well as adaptation of new strains of agent capable of causing disease in mice. In most mice, neither the early persistent phase nor the later replicative phase could be detected by immunoblot assay for protease-resistant prion protein (PrP). If similar asymptomatic carriers of infection arise after exposure of humans or animals to BSE, this could markedly increase the danger of additional spread of BSE or vCJD infection by contaminated blood, surgical instruments, or meat. If such subclinical carriers were negative for protease-resistant PrP, similar to our mice, then the recently proposed screening of brain, tonsils, or other tissues of animals and humans by present methods such as immunoblotting or immunohistochemistry might be too insensitive to identify these individuals.     

Widespread PrPSc accumulation in muscles of hamsters orally infected with scrapie

Scrapie, bovine spongiform encephalopathy and chronic wasting disease are orally communicable, transmissible spongiform encephalopathies (TSEs). As zoonotic transmissions of TSE agents may pose a risk to human health, the identification of reservoirs for infectivity in animal tissues and their exclusion from human consumption has become a matter of great importance for consumer protection. In this study, a variety of muscles from hamsters that were orally challenged with scrapie was screened for the presence of a molecular marker for TSE infection, PrP^Sc (the pathological isoform of the prion protein PrP). Sensitive western blotting revealed consistent PrP^Sc accumulation in skeletal muscles from forelimb and hindlimb, head, back and shoulder, and in tongue. Previously, our animal model has provided substantial baseline information about the peripheral routing of infection in naturally occurring and orally acquired ruminant TSEs. Therefore, the findings described here highlight further the necessity to investigate thoroughly whether muscles of TSE-infected sheep, cattle, elk and deer contain infectious agents.     

Extraneural prion neuroinvasion without lymphoreticular system infection

While prion infection of the lymphoreticular system (LRS) is necessary for neuroinvasion in many prion diseases, in bovine spongiform encephalopathy and atypical cases of sheep scrapie there is evidence to challenge that LRS infection is required for neuroinvasion. Here we investigated the role of prion infection of LRS tissues in neuroinvasion following extraneural inoculation with the HY and DY strains of the transmissible mink encephalopathy (TME) agent. DY TME agent infectivity was not detected in spleen or lymph nodes following intraperitoneal inoculation and clinical disease was not observed following inoculation into the peritoneum or lymph nodes, or after oral ingestion. In contrast, inoculation of the HY TME agent by each of these peripheral routes resulted in replication in the spleen and lymph nodes and induced clinical disease. To clarify the role of the LRS in neuroinvasion, the HY and DY TME agents were also inoculated into the tongue because it is densely innervated and lesions on the tongue, which are common in ruminants, increase the susceptibility of hamsters to experimental prion disease. Following intratongue inoculation, the DY TME agent caused prion disease and was detected in both the tongue and brainstem nuclei that innervate the tongue, but the prion protein PrP(Sc) was not detected in the spleen or lymph nodes. These findings indicate that the DY TME agent can spread from the tongue to the brain along cranial nerves and neuroinvasion does not require agent replication in the LRS. These studies provide support for prion neuroinvasion from highly innervated peripheral tissues in the absence of LRS infection in natural prion diseases of livestock.     

Lack of Prion Infectivity in Fixed Heart Tissue from Patients with Creutzfeldt-Jakob Disease or Amyloid Heart Disease

In most forms of prion disease, infectivity is present primarily in the central nervous system or immune system organs such as spleen and lymph node. However, a transgenic mouse model of prion disease has demonstrated that prion infectivity can also be present as amyloid deposits in heart tissue. Deposition of infectious prions as amyloid in human heart tissue would be a significant public health concern. Although abnormal disease-associated prion protein (PrP^Sc) has not been detected in heart tissue from several amyloid heart disease patients, it has been observed in the heart tissue of a patient with sporadic Creutzfeldt-Jakob Disease (sCJD), the most common form of human prion disease. In order to determine whether prion infectivity can be found in heart tissue, we have inoculated formaldehyde fixed brain and heart tissue from two sCJD patients, as well as prion protein positive fixed heart tissue from two amyloid heart disease patients, into transgenic mice overexpressing the human prion protein. Although the sCJD brain samples led to clinical or subclinical prion infection and deposition of PrP^Sc in the brain, none of the inoculated heart samples resulted in disease or the accumulation of PrP^Sc. Thus, our results suggest that prion infectivity is not likely present in cardiac tissue from sCJD or amyloid heart disease patients.     

Prions in Milk from Ewes Incubating Natural Scrapie

Since prion infectivity had never been reported in milk, dairy products originating from transmissible spongiform encephalopathy (TSE)-affected ruminant flocks currently enter unrestricted into the animal and human food chain. However, a recently published study brought the first evidence of the presence of prions in mammary secretions from scrapie-affected ewes. Here we report the detection of consistent levels of infectivity in colostrum and milk from sheep incubating natural scrapie, several months prior to clinical onset. Additionally, abnormal PrP was detected, by immunohistochemistry and PET blot, in lacteal ducts and mammary acini. This PrP^Sc accumulation was detected only in ewes harbouring mammary ectopic lymphoid follicles that developed consequent to Maedi lentivirus infection. However, bioassay revealed that prion infectivity was present in milk and colostrum, not only from ewes with such lympho-proliferative chronic mastitis, but also from those displaying lesion-free mammary glands. In milk and colostrum, infectivity could be recovered in the cellular, cream, and casein-whey fractions. In our samples, using a Tg 338 mouse model, the highest per ml infectious titre measured was found to be equivalent to that contained in 6 µg of a posterior brain stem from a terminally scrapie-affected ewe. These findings indicate that both colostrum and milk from small ruminants incubating TSE could contribute to the animal TSE transmission process, either directly or through the presence of milk-derived material in animal feedstuffs. It also raises some concern with regard to the risk to humans of TSE exposure associated with milk products from ovine and other TSE-susceptible dairy species.     

Influence of water, fat, and glycerol on the mechanism of thermal prion inactivation

Extending the recent analysis of the safety of industrial bovine fat-derived products for human consumption (Müller, H., Stitz, L., and Riesner, D. (2006) Eur. J. Lip. Sci. Technol. 108, 812-826), we investigated systematically the effects of fat, fatty acids, and glycerol on the heat destruction of prions. Prion destruction was qualitatively and quantitatively evaluated in PrP 27-30, or prion rods, by the inactivation of infectivity as well as by the degradation of the polypeptide backbone. Under all conditions analyzed, inactivation of prion infectivity was achieved more efficiently than backbone degradation by several orders of magnitude. The presence of fat enhanced prion inactivation and offers a mild treatment for prion decontamination. In contrast, the presence of fat, fatty acids, and especially glycerol protected the PrP 27-30 backbone against heat-induced degradation. Glycerol also protected against heat-induced inactivation of prion infectivity. A phase distribution analysis demonstrated that prions migrated to the interphase of a fat/water mixture at room temperature and accumulated in the water phase at higher temperatures. In a systematic study of the mechanism of prion destruction, we found an intermediate structure of PrP that has fewer fibrils in beta-sheet formation, lower resistance to protease digestion, greater aggregation, and reduced solubility compared with PrP 27-30 but retains residual infectivity. These findings suggest that prion infectivity depends on beta-sheet-rich fibrillar structure and that inactivation proceeds in a stepwise manner, which explains the tailing effect frequently observed during inactivation.     

Resistance of neonatal mice to scrapie is associated with inefficient infection of the immature spleen

Previous studies demonstrated that neonatal mice up to about a week old are less susceptible than adult mice to infection by intraperitoneal inoculation with mouse-passaged scrapie. In peripherally inoculated adult mice, scrapie replicates in lymphoid tissues such as the spleen before invading the central nervous system. Here, we investigated scrapie susceptibility in neonatal mice in more detail, concentrating on spleen involvement. First, we demonstrated that neonatal mice are about 10 times less susceptible than adults to intraperitoneal scrapie inoculation. Then we injected mice intraperitoneally with a scrapie dose that produced disease in all mice inoculated at 10 days or older but in only about a third of neonatally inoculated mice. In this experiment, spleens collected 70 days after scrapie injection of mice 10 days old or older almost all contained pathological prion protein, PrPSc, and those that were bioassayed all contained high infectivity levels. In contrast, at this early stage, only two of six spleens from neonatally inoculated mice had detectable, low infectivity levels; no PrPSc was detected, even in the two spleens. Therefore, neonatal mice have an impaired ability to replicate scrapie in their spleens, suggesting that replication sites are absent or sparse at birth but mature within 10 days. The increase in susceptibility with age correlated with the first immunocytochemical detection of the normal cellular form of prion protein, PrPc, on maturing follicular dendritic cell networks. As lymphoid tissues are more mature at birth in sheep, cattle, and humans than in mice, our results suggest that in utero infection with scrapie-like agents is theoretically possible in these species.     

Evaluation of the human transmission risk of an atypical bovine spongiform encephalopathy prion strain

Bovine spongiform encephalopathy (BSE), the prion disease in cattle, was widely believed to be caused by only one strain, BSE-C. BSE-C causes the fatal prion disease named new variant Creutzfeldt-Jacob disease in humans. Two atypical BSE strains, bovine amyloidotic spongiform encephalopathy (BASE, also named BSE-L) and BSE-H, have been discovered in several countries since 2004; their transmissibility and phenotypes in humans are unknown. We investigated the infectivity and human phenotype of BASE strains by inoculating transgenic (Tg) mice expressing the human prion protein with brain homogenates from two BASE strain-infected cattle. Sixty percent of the inoculated Tg mice became infected after 20 to 22 months of incubation, a transmission rate higher than those reported for BSE-C. A quarter of BASE strain-infected Tg mice, but none of the Tg mice infected with prions causing a sporadic human prion disease, showed the presence of pathogenic prion protein isoforms in the spleen, indicating that the BASE prion is intrinsically lymphotropic. The pathological prion protein isoforms in BASE strain-infected humanized Tg mouse brains are different from those from the original cattle BASE or sporadic human prion disease. Minimal brain spongiosis and long incubation times are observed for the BASE strain-infected Tg mice. These results suggest that in humans, the BASE strain is a more virulent BSE strain and likely lymphotropic.     

Failure of fallow deer (Dama dama) to develop chronic wasting disease when exposed to a contaminated environment and infected mule deer (Odocoileus hemionus)

We monitored a herd of fallow deer (Dama dama) for evidence of prion infection for 7 yr by periodic postmortem examination of animals from the herd. The fallow deer were exposed to the chronic wasting disease (CWD) agent from mule deer by living in a paddock considered contaminated with infectivity from its history of housing CWD infected deer and, after the first year of the study, by comingling with infected mule deer (Odocoileus hemionus). At least 8 of 12 mule deer serving as sentinels for prion transmission and 25 additional mule deer serving as sources of infectivity developed clinical CWD or were otherwise confirmed to be infected with CWD via lymphoid tissue immunohistochemistry (IHC). In contrast, none of the 41 exposed fallow deer showed clinical signs suggestive of CWD, IHC staining of disease-associated prion in lymphoid or brain tissues, or evidence of spongiform degeneration in sections of brain stem at the level of the obex when sampled 18 mo to 7 yr after entering the mule deer paddock. The absence of clinical disease and negative IHC results in fallow deer housed in the same contaminated paddock for up to 7 yr and almost continuously exposed to CWD-infected mule deer for up to 6 yr suggests a species barrier or other form of resistance preventing fallow deer infection by the CWD agent or delaying progression of the disease in this species.     

Follicular dendritic cell of the knock-in mouse provides a new bioassay for human prions

Infectious prion diseases initiate infection within lymphoid organs where prion infectivity accumulates during the early stages of peripheral infection. In a mouse-adapted prion infection, an abnormal isoform (PrP(Sc)) of prion protein (PrP) accumulates in follicular dendritic cells within lymphoid organs. Human prions, however, did not cause an accumulation of PrP(Sc) in the wild type mice. Here, we report that knock-in mouse expressing humanized chimeric PrP demonstrated PrP(Sc) accumulations in follicular dendritic cells following human prion infections, including variant Creutzfeldt-Jakob disease. The accumulated PrP(Sc) consisted of recombinant PrP, but not of the inoculated human PrP. These accumulations were detectable in the spleens of all mice examined 30 days post-inoculation. Infectivity of the spleen was also evident. Conversion of humanized PrP in the spleen provides a rapid and sensitive bioassay method to uncover the infectivity of human prions. This model should facilitate the prevention of infectious prion diseases.     

Infectivity in skeletal muscle of cattle with atypical bovine spongiform encephalopathy

The amyloidotic form of bovine spongiform encephalopathy (BSE) termed BASE is caused by a prion strain whose biological properties differ from those of typical BSE, resulting in a clinically and pathologically distinct phenotype. Whether peripheral tissues of BASE-affected cattle contain infectivity is unknown. This is a critical issue since the BASE prion is readily transmissible to a variety of hosts including primates, suggesting that humans may be susceptible. We carried out bioassays in transgenic mice overexpressing bovine PrP (Tgbov XV) and found infectivity in a variety of skeletal muscles from cattle with natural and experimental BASE. Noteworthy, all BASE muscles used for inoculation transmitted disease, although the attack rate differed between experimental and natural cases (～70% versus ～10%, respectively). This difference was likely related to different prion titers, possibly due to different stages of disease in the two conditions, i.e. terminal stage in experimental BASE and pre-symptomatic stage in natural BASE. The neuropathological phenotype and PrP(res) type were consistent in all affected mice and matched those of Tgbov XV mice infected with brain homogenate from natural BASE. The immunohistochemical analysis of skeletal muscles from cattle with natural and experimental BASE showed the presence of abnormal prion protein deposits within muscle fibers. Conversely, Tgbov XV mice challenged with lymphoid tissue and kidney from natural and experimental BASE did not develop disease. The novel information on the neuromuscular tropism of the BASE strain, efficiently overcoming species barriers, underlines the relevance of maintaining an active surveillance.     

Fatal Transmissible Amyloid Encephalopathy: A New Type of Prion Disease Associated with Lack of Prion Protein Membrane Anchoring

Prion diseases are fatal neurodegenerative diseases of humans and animals characterized by gray matter spongiosis and accumulation of aggregated, misfolded, protease-resistant prion protein (PrPres). PrPres can be deposited in brain in an amyloid-form and/or non-amyloid form, and is derived from host-encoded protease-sensitive PrP (PrPsen), a protein normally anchored to the plasma membrane by glycosylphosphatidylinositol (GPI). Previously, using heterozygous transgenic mice expressing only anchorless PrP, we found that PrP anchoring to the cell membrane was required for typical clinical scrapie. However, in the present experiments, using homozygous transgenic mice expressing two-fold more anchorless PrP, scrapie infection induced a new fatal disease with unique clinical signs and altered neuropathology, compared to non-transgenic mice expressing only anchored PrP. Brain tissue of transgenic mice had high amounts of infectivity, and histopathology showed dense amyloid PrPres plaque deposits without gray matter spongiosis. In contrast, infected non-transgenic mice had diffuse non-amyloid PrPres deposits with significant gray matter spongiosis. Brain graft studies suggested that anchored PrPsen expression was required for gray matter spongiosis during prion infection. Furthermore, electron and light microscopic studies in infected transgenic mice demonstrated several pathogenic processes not seen in typical prion disease, including cerebral amyloid angiopathy and ultrastructural alterations in perivascular neuropil. These findings were similar to certain human familial prion diseases as well as to non-prion human neurodegenerative diseases, such as Alzheimer''s disease.     

Prion formation,but not clearance,is supported by protein misfolding cyclic amplification

Prion diseases are fatal transmissible neurodegenerative disorders that affect animals including humans. The kinetics of prion infectivity and PrP^Sc accumulation can differ between prion strains and within a single strain in different tissues. The net accumulation of PrP^Sc in animals is controlled by the relationship between the rate of PrP^Sc formation and clearance. Protein misfolding cyclic amplification (PMCA) is a powerful technique that faithfully recapitulates PrP^Sc formation and prion infectivity in a cell-free system. PMCA has been used as a surrogate for animal bioassay and can model species barriers, host range, strain co-factors and strain interference. In this study we investigated if degradation of PrP^Sc and/or prion infectivity occurs during PMCA. To accomplish this we performed PMCA under conditions that do not support PrP^Sc formation and did not observe either a reduction in PrP^Sc abundance or an extension of prion incubation period, compared to untreated control samples. These results indicate that prion clearance does not occur during PMCA. These data have significant implications for the interpretation of PMCA based experiments such as prion amplification rate, adaptation to new species and strain interference where production and clearance of prions can affect the outcome.     

Processing of high-titer prions for mass spectrometry inactivates prion infectivity

Prions represent a class of universally fatal and transmissible neurodegenerative disorders that affect humans and other mammals. The prion agent contains a pathologically aggregated form of the host prion protein that can transmit infectivity without any bacterial or viral component and is thus difficult to inactivate using disinfection protocols designed for infectious microorganisms. Methods for prion inactivation include treatment with acids, bases, detergents, bleach, prolonged autoclaving and incineration. During these procedures, the sample is often either destroyed or damaged such that further analysis for research purposes is compromised. In this study we show that a straightforward denaturation and in-gel protease digestion protocol used to prepare prion-infected samples for mass spectroscopy leads to the loss of at least 7 logs of prion infectivity, yielding a final product that fails to transmit prion disease in vivo. We further show that the resultant sample remains suitable for mass spectrometry-based protein identifications. Thus, the procedure described can be used to prepare prion-infected samples for mass spectrometry analysis with greatly reduced biosafety concerns.     

Subclinical prion disease induced by oral inoculation

Natural transmission of prion disease is believed to occur by peripheral infection such as oral inoculation. Following this route of inoculation, both the peripheral nervous system and the lymphoreticular system may be involved in the subsequent neuroinvasion of the central nervous system by prions, which may not necessarily result in clinical signs of terminal disease. Subclinical prion disease, characterized by the presence of infectivity and PrP(Sc) in the absence of overt clinical signs, may occur. It is not known which host factors contribute to whether infection with prions culminates in a terminal or subclinical disease state. We have investigated whether the level of host PrP(c) protein expression is a factor in the development of subclinical prion disease. When RML prion inoculum was inoculated by either the i.c. or intraperitoneal route, wild-type and tga20 mice both succumbed to terminal prion disease. In contrast, orally inoculated tga20 mice succumbed to terminal prion disease, whereas wild-type mice showed no clinical signs. However, wild-type mice sacrificed 375 or 525 days after oral inoculation harbored significant levels of brain PrP(Sc) and infectivity. These data show that same-species transmission of prions by the oral route in animals that express normal levels of PrP(c) can result in subclinical prion disease. This indicates that the level of host PrP(c) protein expression is a contributing factor to the regulation of development of terminal prion disease. Events that increase PrP(c) expression may predispose a prion-infected animal to the more deleterious effects of prion pathology.     

Temporary depletion of complement component C3 or genetic deficiency of C1q significantly delays onset of scrapie

Following peripheral exposure to transmissible spongiform encephalopathies (TSEs), infectivity usually accumulates in lymphoid tissues before neuroinvasion. The host prion protein (PrPc) is critical for TSE agent replication and accumulates as an abnormal, detergent insoluble, relatively proteinase-resistant isoform (PrPSc) in diseased tissues. Early PrPSc accumulation takes place on follicular dendritic cells (FDCs) within germinal centers in lymphoid tissues of patients with variant Creutzfeldt-Jakob disease (vCJD), sheep with natural scrapie or rodents following experimental peripheral infection with scrapie. In mouse scrapie models, the absence of FDCs blocks scrapie replication and PrPSc accumulation in the spleen, and neuroinvasion is significantly impaired. The mechanisms by which the TSE agent initially localizes to lymphoid follicles and interacts with FDCs are unknown. Antigens are trapped and retained on the surface of FDCs through interactions between complement and cellular complement receptors. Here we show that in mice, both temporary depletion of complement component C3 or genetic deficiency of C1q significantly delays the onset of disease following peripheral infection, and reduces the early accumulation of PrPSc in the spleen. Thus, in the early stages of infection, C3 and perhaps C1q contribute to the localization of TSE infectivity in lymphoid tissue and may be therapeutic targets.     

Ovine recombinant PrP as an inhibitor of ruminant prion propagation in vitro

Prion diseases are fatal and incurable neurodegenerative diseases of humans and animals. Despite years of research, no therapeutic agents have been developed that can effectively manage or reverse disease progression. Recently it has been identified that recombinant prion proteins (rPrP) expressed in bacteria can act as inhibitors of prion replication within the in vitro prion replication system protein misfolding cyclic amplification (PMCA). Here, within PMCA reactions amplifying a range of ruminant prions including distinct Prnp genotypes/host species and distinct prion strains, recombinant ovine VRQ PrP displayed consistent inhibition of prion replication and produced IC50 values of 122 and 171 nM for ovine scrapie and bovine BSE replication, respectively. These findings illustrate the therapeutic potential of rPrPs with distinct TSE diseases.