Rapid prion neuroinvasion following tongue infection

Prion infection of oral and nasal mucosa

Centrifugal spread of the prion agent to peripheral tissues is postulated to occur by axonal transport along nerve fibers. This study investigated the distribution of the pathological isoform of the protein (PrP(Sc)) in the tongues and nasal cavities of hamsters following intracerebral inoculation of the HY strain of the transmissible mink encephalopathy (TME) agent. We report that PrP(Sc) deposition was found in the lamina propria, taste buds, and stratified squamous epithelium of fungiform papillae in the tongue, as well as in skeletal muscle cells. Using laser scanning confocal microscopy, PrP(Sc) was localized to nerve fibers in each of these structures in the tongue, neuroepithelial taste cells of the taste bud, and, possibly, epithelial cells. This PrP(Sc) distribution was consistent with a spread of HY TME agent along both somatosensory and gustatory cranial nerves to the tongue and suggests subsequent synaptic spread to taste cells and epithelial cells via peripheral synapses. In the nasal cavity, PrP(Sc) accumulation was found in the olfactory and vomeronasal epithelium, where its location was consistent with a distribution in cell bodies and apical dendrites of the sensory neurons. Prion spread to these sites is consistent with transport via the olfactory nerve fibers that descend from the olfactory bulb. Our data suggest that epithelial cells, neuroepithelial taste cells, or olfactory sensory neurons at chemosensory mucosal surfaces, which undergo normal turnover, infected with the prion agent could be shed and play a role in the horizontal transmission of animal prion diseases.

Transmission of bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) is one of several diseases known collectively as transmissible spongiform encephalopathies (TSE) and caused by prions, which are nonconventional infectious agents. The risk of human infection by exposure to a TSE agent is generally considered to be low, because of the species barrier. However, the prions causing BSE in cattle are able to cross the species barrier easily. The appearance of variant Creutzfeldt–Jakob disease (vCJD) after human exposure to BSE prions has highlighted the possible impacts of this infection on human health. Today, a major concern is that the number of BSE cases in many European countries, including the emerging eastern European countries of the EU, is growing. A further concern now emerging is the possibility that BSE could spread to other livestock species, such as sheep or goats. This paper provides an overview of BSE transmission and its potential implications for public health.

Pathological prion protein in muscles of hamsters and mice infected with rodent-adapted BSE or vCJD

Recently, pathological prion protein (PrP(TSE)) was detected in muscle from sheep infected with scrapie, the archetype of transmissible spongiform encephalopathies (TSEs). This finding has highlighted the question of whether mammalian muscle may potentially also provide a reservoir for TSE agents related to bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob Disease (vCJD). Here, results are reported from studies in hamsters and mice that provide direct experimental evidence, for the first time, of BSE- and vCJD-associated PrP(TSE) deposition in muscles. Our findings emphasize the need for further assessment of possible public-health risks from TSE involvement of skeletal muscle.

Intranasal immunization of Balb/c mice against prion protein attenuates orally acquired transmissible spongiform encephalopathy

To test whether prion protein (PrP) specific secretory immunoglobulin A (sIgA) can be induced and protect against oral transmission of spongiform encephalopathy (SE) we immunized Balb/c mice either intragastrically or intranasally (i.n.) with a recombinant PrP-fragment (PrP90-231) and cholera toxin (CT) adjuvant. Since PrP90-231 was rapidly digested in intestinal lavage, aprotinin was added to some vaccine formulations. While an anti-CT response was elicited via both routes, solely i.n. immunization without aprotinin induced PrP-specific sIgA. They recognize predominantly PrP-oligomers as the antigen was aggregated in the vaccine formulations. Challenge experiments showed that the immune response induced by our protocol could not prevent disease, but increases the median survival of the animals. We conclude that PrP-specific sIgA reduce the infectivity of the inoculum and that complete protection against transmission of SE should be achievable by optimized immunization regimens.

PrPTSE distribution in a primate model of variant, sporadic, and iatrogenic Creutzfeldt-Jakob disease

Human prion diseases, such as Creutzfeldt-Jakob disease (CJD), are neurodegenerative and fatal. Sporadic CJD (sCJD) can be transmitted between humans through medical procedures involving highly infected organs, such as the central nervous system. However, in variant CJD (vCJD), which is due to human contamination with the bovine spongiform encephalopathy (BSE) agent, lymphoreticular tissue also harbors the transmissible spongiform encephalopathy-associated prion protein (PrP(TSE)), which poses a particularly acute risk for iatrogenic transmission. Two blood transfusion-related cases are already documented. In addition, the recent observation of PrP(TSE) in spleen and muscle in sCJD raised the possibility that peripheral PrP(TSE) is not limited to vCJD cases. We aimed to clarify the peripheral pathogenesis of human TSEs by using a nonhuman primate model which mimics human diseases. A highly sensitive enzyme-linked immunosorbent assay was adapted to the detection of extraneural PrP(TSE). We show that affected organs can be divided into two groups. The first is peripheral organs accumulating large amounts of PrP(TSE), which represent a high risk of iatrogenic transmission. This category comprises only lymphoreticular organs in the vCJD/BSE model. The second is organs with small amounts of PrP(TSE) associated with nervous structures. These are the muscles, adrenal glands, and enteric nervous system in the sporadic, iatrogenic, and variant CJD models. In contrast to the first set of organs, this low level of tissue contamination is not strain restricted and seems to be linked to secondary centrifugal spread of the agent through nerves. It might represent a risk for iatrogenic transmission, formerly underestimated despite previous reports of low rates of transmission from peripheral organs of humans to nonhuman primates (5, 10). This study provides an additional experimental basis for the classification of human organs into different risk categories and a rational re-evaluation of current risk management measures.

Comparative evidence for a link between Peyer's patch development and susceptibility to transmissible spongiform encephalopathies

Background

Epidemiological analyses indicate that the age distribution of natural cases of transmissible spongiform encephalopathies (TSEs) reflect age-related risk of infection, however, the underlying mechanisms remain poorly understood. Using a comparative approach, we tested the hypothesis that, there is a significant correlation between risk of infection for scrapie, bovine spongiform encephalopathy (BSE) and variant CJD (vCJD), and the development of lymphoid tissue in the gut.

Methods

Using anatomical data and estimates of risk of infection in mathematical models (which included results from previously published studies) for sheep, cattle and humans, we calculated the Spearman's rank correlation coefficient, r_s, between available measures of Peyer's patch (PP) development and the estimated risk of infection for an individual of the corresponding age.

Results

There was a significant correlation between the measures of PP development and the estimated risk of TSE infection; the two age-related distributions peaked in the same age groups. This result was obtained for each of the three host species: for sheep, surface area of ileal PP tissue vs risk of infection, r_s = 0.913 (n = 19, P < 0.001), and lymphoid follicle density vs risk of infection, r_s = 0.933 (n = 19, P < 0.001); for cattle, weight of PP tissue vs risk of infection, r_s = 0.693 (n = 94, P < 0.001); and for humans, number of PPs vs risk of infection, r_s = 0.384 (n = 46, P = 0.008). In addition, when changes in exposure associated with BSE-contaminated meat were accounted for, the two age-related patterns for humans remained concordant: r_s = 0.360 (n = 46, P = 0.014).

Conclusion

Our findings suggest that, for sheep, cattle and humans alike there is an association between PP development (or a correlate of PP development) and susceptibility to natural TSE infection. This association may explain changes in susceptibility with host age, and differences in the age-susceptibility relationship between host species.

Skin-derived dendritic cells acquire and degrade the scrapie agent following in vitro exposure

The accumulation of the scrapie agent in lymphoid tissues following inoculation via the skin is critical for efficient neuroinvasion, but how the agent is initially transported from the skin to the draining lymph node is not known. Langerhans cells (LCs) are specialized antigen-presenting cells that continually sample their microenvironment within the epidermis and transport captured antigens to draining lymph nodes. We considered LCs probable candidates to acquire and transport the scrapie agent after inoculation via the skin. XS106 cells are dendritic cells (DCs) isolated from mouse epidermis with characteristics of mature LC cells. To investigate the potential interaction of LCs with the scrapie agent XS106 cells were exposed to the scrapie agent in vitro. We show that XS106 cells rapidly acquire the scrapie agent following in vitro exposure. In addition, XS106 cells partially degrade the scrapie agent following extended cultivation. These data suggest that LCs might acquire and degrade the scrapie agent after inoculation via the skin, but data from additional experiments demonstrate that this ability could be lost in the presence of lipopolysaccharide or other immunostimulatory molecules. Our studies also imply that LCs would not undergo maturation following uptake of the scrapie agent in the skin, as the expression of surface antigens associated with LC maturation were unaltered following exposure. In conclusion, although LCs or DCs have the potential to acquire the scrapie agent within the epidermis our data suggest it is unlikely that they become activated and stimulated to transport the agent to the draining lymph node.

Interspecies transmission of chronic wasting disease prions to squirrel monkeys (Saimiri sciureus)

Chronic wasting disease (CWD) is an emerging prion disease of deer and elk. The risk of CWD transmission to humans following exposure to CWD-infected tissues is unknown. To assess the susceptibility of nonhuman primates to CWD, two squirrel monkeys were inoculated with brain tissue from a CWD-infected mule deer. The CWD-inoculated squirrel monkeys developed a progressive neurodegenerative disease and were euthanized at 31 and 34 months postinfection. Brain tissue from the CWD-infected squirrel monkeys contained the abnormal isoform of the prion protein, PrP-res, and displayed spongiform degeneration. This is the first reported transmission of CWD to primates.

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.

Anterograde axonal transport of the exogenous cellular isoform of prion protein in the chick visual system

The cellular isoform of endogenous, newly synthesized prion protein (PrPc) can be transported by axons in the anterograde direction. To determine whether a mechanism exists for secreted PrPc to be internalized and then axonally transported, we analyzed internalization and anterograde axonal transport of radiolabeled recombinant PrPc after its intraocular injection in chick embryos. Internalization and axonal transport of exogenous PrPc to the midbrain by retinal ganglion cells (RGCs) is efficient, saturable and likely receptor-mediated. Ultrastructural quantitative localization of radiolabeled PrPc within RGC soma showed significant labeling of vesicular/endosomal compartments and much less labeling present over the Golgi apparatus and lysosomes, which indicates slow degradation of exogenous PrPc in this system. These data show that a mechanism exists to internalize a secreted form of PrPc and then to axonally transport such PrPc in an anterograde direction. This may provide an additional, novel mechanism for prion protein to spread among neurons.

Mucosal vaccination delays or prevents prion infection via an oral route

In recent years major outbreaks of prion disease linked to oral exposure of the prion agent have occurred in animal and human populations. These disorders are associated with a conformational change of a normal protein, PrP(C) (prion protein cellular), to a toxic and infectious form, PrP(Sc) (prion protein scrapie). None of the prionoses currently have an effective treatment. A limited number of active immunization approaches have been shown to slightly prolong the incubation period of prion infection. Active immunization in wild-type animals is hampered by auto-tolerance to PrP and potential toxicity. Here we report that mucosal vaccination with an attenuated Salmonella vaccine strain expressing the mouse PrP, is effective at overcoming tolerance to PrP and leads to a significant delay or prevention of prion disease in mice later exposed orally to the 139A scrapie strain. This mucosal vaccine induced gut anti-PrP immunoglobulin (Ig)A and systemic anti-PrP IgG. No toxicity was evident with this vaccination approach. This promising finding suggests that mucosal vaccination may be a useful method for overcoming tolerance to PrP and preventing prion infection among animal and potentially human populations at risk.

Synaptic targeting of retrogradely transported trophic factors in motoneurons: comparison of glial cell line-derived neurotrophic factor, brain-derived neurotrophic factor, and cardiotrophin-1 with tetanus toxin

Glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and cardiotrophin-1 (CT-1) are the most potent neurotrophic factors for motoneurons, but their fate after retrograde axonal transport is not known. Internalized trophic factors may be degraded, or they may be recycled and transferred to other neurons, similar to the known route of tetanus toxin. We tested whether neonatal rat hypoglossal motoneurons target retrogradely transported trophic factors to synaptic sites on their dendrites within the brainstem and subsequently transfer these trophins across the synaptic cleft to afferent synapses (transsynaptic transcytosis). Motoneurons retrogradely transport from the tongue radiolabeled GDNF, BDNF, and CT-1 as well as tetanus toxin. Quantitative autoradiographic electron microscopy showed that GDNF and BDNF were transported into motoneuron dendrites with labeling densities similar to those of tetanus toxin. Although tetanus toxin accumulated rapidly (within 8 h) at presynaptic sites, GDNF accumulated at synapses more slowly (within 15 h), and CT-1 never associated with synapses. Thus, some retrogradely transported neurotrophic factors are trafficked similarly but not identically to tetanus toxin. Both GDNF and BDNF accumulate at the external (limiting) membrane of multivesicular bodies within proximal dendrites. We conclude that tetanus toxin, GDNF, and BDNF are released from postsynaptic sites and are internalized by afferent presynaptic terminals, thus demonstrating transsynaptic transcytosis. CT-1, however, follows a strict degradation pathway after retrograde transport to the soma. Synaptic and transcytotic trafficking thus are restricted to particular neurotrophic factors such as GDNF and BDNF.

Pathological prion protein in the tongues of sheep infected with naturally occurring scrapie

Tongue involvement by prion spreading was shown to be a common outcome after oral or intracranial experimental challenge with scrapie and transmissible mink encephalopathy sources in rodent models. It is also known that bovine spongiform encephalopathy, which is pathogenic for humans, is experimentally transmissible to sheep and can lead to a disease indistinguishable from scrapie. A recent European Food Safety Authority opinion recommended research into PrPsc accumulation in the tongues of ruminants. We report on the detection of PrPsc in the tongues of seven scrapie-infected sheep by immunohistochemistry and Western blotting.

Follicular dendritic cell dedifferentiation reduces scrapie susceptibility following inoculation via the skin

Transmissible spongiform encephalopathies (TSEs) are a group of subacute infectious neurodegenerative diseases that are characterized by the accumulation in affected tissues of PrP(Sc), an abnormal isoform of the host prion protein (PrPc). Following peripheral exposure, TSE infectivity and PrP(Sc) usually accumulate in lymphoid tissues prior to neuroinvasion. Studies in mice have shown that exposure through scarified skin is an effective means of TSE transmission. Following inoculation via the skin, a functional immune system is critical for the transmission of TSEs to the brain, but until now, it has not been known which components of the immune system are required for efficient neuroinvasion. Temporary dedifferentiation of follicular dendritic cells (FDCs) by treatment with an inhibitor of the lymphotoxin-beta receptor signalling pathway (LTbetaR-Ig) 3 days before or 14 days after inoculation via the skin, blocked the early accumulation of PrP(Sc) and TSE infectivity within the draining lymph node. Furthermore, in the temporary absence of FDCs before inoculation, disease susceptibility was reduced and survival time significantly extended. Treatment with LTbetaR-Ig 14 days after TSE inoculation also significantly extended the disease incubation period. However, treatment 42 days after inoculation did not affect disease susceptibility or survival time, suggesting that the infection may have already have spread to the nervous system. Together these data show that FDCs are essential for the accumulation of PrP(Sc) and infectivity within lymphoid tissues and subsequent neuroinvasion following TSE exposure via the skin.

Shortening of the Bovine Tongue According to Regulation (EC) 999/2001 is not Complying with the Current Legal Definition of Specified Risk Material - a Macroscopical and Histological Preliminary Study

The full elimination of all specified risk material (SRM) in food of animal origin is crucial for consumer protection and is of high priority in inner EU trade. Among other tissues, the tonsils of cattle are considered as SRM. The aim of this study was to evaluate whether the 'cut at the back of the tongue just before the tongue bones' required by EC regulation is sufficient to remove tonsils and lymphatic tissue completely. Eight skulls from cattle were collected for the simulation of a vertical cut according to the EC regulation and the detection of the target at the back of the tongue. Further, specimens of the lingual mucosa were cut out from two tongues and examined microscopically. The most caudal of these specimens was from the macroscopically visible part of the lingual tonsil. The most rostral specimen contained the most caudal Papilla vallata. Simulation of the obligatory ventro-dorsal cut yielded hits at varying locations on the dorsal surface of the tongue, sometimes including tissue of the lingual tonsil. Histological examination of the lingual mucosa gave clear evidence that lymphatic tissue resembling the tissue of a tonsil in terms of its histological organization and infiltration of the mucosal epithelium could even be found in areas with no macroscopically visible lingual tonsils.

Neuroinvasion by scrapie following inoculation via the skin is independent of migratory Langerhans cells

Many natural transmissible spongiform encephalopathy (TSE) infections are likely to be acquired peripherally, and studies in mice show that skin scarification is an effective means of scrapie transmission. After peripheral exposure, TSE agents usually accumulate in lymphoid tissues before spreading to the brain. The mechanisms of TSE transport to lymphoid tissues are not known. Langerhans cells (LCs) reside in the epidermis and migrate to the draining lymph node after encountering antigen. To investigate the potential role of LCs in scrapie transportation from the skin, we utilized mouse models in which their migration was blocked either due to CD40 ligand deficiency (CD40L-/- mice) or after caspase-1 inhibition. We show that the early accumulation of scrapie infectivity in the draining lymph node and subsequent neuroinvasion was not impaired in mice with blocked LC migration. Thus, LCs are not involved in TSE transport from the skin. After intracerebral inoculation with scrapie, wild-type mice and CD40L-/- mice develop clinical disease with similar incubation periods. However, after inoculation via skin scarification CD40L-/- mice develop disease significantly earlier than do wild-type mice. The shorter incubation period in CD40L-/- mice is unexpected and suggests that a CD40L-dependent mechanism is involved in impeding scrapie pathogenesis. In vitro studies demonstrated that LCs have the potential to acquire and degrade protease-resistant prion protein, which is thought to be a component of the infectious agent. Taken together, these data suggest that LCs are not involved in scrapie transport to draining lymphoid tissues but might have the potential to degrade scrapie in the skin.

Variable patterns of distribution of PrP(CWD) in the obex and cranial lymphoid tissues of Rocky Mountain elk (Cervus elaphus nelsoni) with subclinical chronic wasting disease

Sections of medulla oblongata, taken at the level of the obex, palatine tonsil and medial retropharyngeal lymph node from 10,269 captive Rocky Mountain elk (Cervus elaphus nelsoni), were examined by immunohistochemical staining with monoclonal antibody for the prion protein associated with the transmissible spongiform encephalopathy of cervids, chronic wasting disease (PrP(CWD)). The protein was detected in 226 of them. On the basis of the anatomical location of the deposits in the brainstem of 183 elk, four distinct patterns of distribution of PrP(CWD) within the parasympathetic region of the dorsal motor nucleus of the vagus nerve and the adjacent nuclei were observed. Mild gross lesions of chronic wasting disease (serous atrophy of fat) were observed in only three elk, all with spongiform degeneration; the other elk were considered to be in the preclinical stage of the disease. In contrast with the relatively predictable distribution of prion protein (PrP) in the brain and cranial nodes of sheep and mule deer, the distribution of PrP(CWD) in the brain and nodes of the elk was more variable and unrelated to their PrP genotype. One hundred and fifty-five of the 226 positive elk had deposits of PrP(CWD) in the brainstem and lymphoid tissues, 43 had deposits only in the lymphoid tissue and 28 had deposits only in the brainstem.

Advances in the detection of prion protein in peripheral tissues of variant Creutzfeldt-Jakob disease patients using paraffin-embedded tissue blotting

The accumulation of PrP(Sc), an abnormal and disease-associated form of the normal prion protein (PrP(c)), within the central nervous system (CNS) is a key pathological feature of Creutzfeldt-Jakob disease (CJD). Following limited proteolytic digestion of PrP(Sc), the detection of PrP(res) within lymphoid tissues is a unique characteristic of variant CJD in comparison with other human prion diseases, raising fears of an increased risk of iatrogenic spread. Because levels of PrP(res) in lymphoid tissues are lower than those found in CNS tissue, there is concern that other peripheral tissues may harbour infectivity at levels that current detection systems cannot demonstrate PrP(res). We have modified the paraffin-embedded tissue blot (PET blot), a technique combining immunohistochemistry (IHC), histoblot and Western blotting, for the detection of PrP(res) in paraffin sections in peripheral tissues in variant CJD. Five cases of variant CJD were examined, using a panel of anti-PrP antibodies. In each of these five cases, spleen, tonsil, lymph nodes and dorsal root ganglia showed an increase in the sensitivity and specificity of labelling using the PET blot when compared with optimized PrP(res) IHC methods. Control cases showed no evidence of PrP accumulation in either peripheral or CNS tissues. Autopsy and biopsy brain material from sporadic CJD cases also showed an increased sensitivity of PrP(res) detection with the PET blot, confirming its value as an important diagnostic and research tool in human prion diseases.

Scrapie transmission following exposure through the skin is dependent on follicular dendritic cells in lymphoid tissues

BACKGROUND

Transmissible spongiform encephalopathies (TSEs) are chronic infectious neurodegenerative diseases that are characterized by the accumulation in affected tissues of PrP(Sc), an abnormal isoform of the host prion protein (PrP(c)). Following peripheral exposure, PrP(Sc) usually accumulates 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 via the skin, a functional immune system is critical for the transmission of scrapie to the brain as severe combined immunodeficiency (SCID) mice are refractory to infection. Until now, it was not known which components of the immune system are required for efficient scrapie neuroinvasion following skin scarification.

OBJECTIVE

To determine which cells are critical for the transmission of scrapie to the brain following inoculation via the skin.

METHODS

A chimeric mouse model was used, which had a mismatch in PrP(c) expression between FDCs and other bone marrow-derived cells within lymphoid tissues. These chimeric mice were challenged with scrapie by skin scarification to allow the separate roles of FDCs and lymphocytes in peripheral scrapie pathogenesis to be determined.

RESULTS

We show that mature FDCs are essential for the accumulation of scrapie within lymphoid tissues and the subsequent transmission of infection to the brain following TSE exposure by this route. Furthermore, we show that the accumulation of PrP(Sc) and infectivity in the spleen is independent of PrP expression by lymphocytes or other bone marrow-derived cells.

CONCLUSION

Following inoculation with scrapie by skin scarification, replication in the spleen and subsequent neuroinvasion is critically dependent upon mature FDCs.

Prion infection of skeletal muscle cells and papillae in the tongue

The presence of the prion agent in skeletal muscle is thought to be due to the infection of nerve fibers located within the muscle. We report here that the pathological isoform of the prion protein, PrP(Sc), accumulates within skeletal muscle cells, in addition to axons, in the tongue of hamsters following intralingual and intracerebral inoculation of the HY strain of the transmissible mink encephalopathy agent. Localization of PrP(Sc) to the neuromuscular junction suggests that this synapse is a site for prion agent spread between motor axon terminals and muscle cells. Following intracerebral inoculation, the majority of PrP(Sc) in the tongue was found in the lamina propria, where it was associated with sensory nerve fibers in the core of the lingual papillae. PrP(Sc) staining was also identified in the stratified squamous epithelium of the lingual mucosa. These findings indicate that prion infection of skeletal muscle cells and the epithelial layer in the tongue can be established following the spread of the prion agent from nerve terminals and/or axons that innervate the tongue. Our data suggest that ingestion of meat products containing prion-infected tongue could result in human exposure to the prion agent, while sloughing of prion-infected epithelial cells at the mucosal surface of the tongue could be a mechanism for prion agent shedding and subsequent prion transmission in animals.

Polymorphisms in the prion precursor functional gene but not the pseudogene are associated with susceptibility to chronic wasting disease in white-tailed deer

Chronic wasting disease (CWD) status and PrP genotypes were determined for a group of 133 wild white-tailed deer in a 780 acre enclosure in western Nebraska, USA. Approximately half of the deer tested showed evidence of PrPd in the brainstem or lymphoid tissues. Four PRNP alleles encoding amino acid substitutions were identified, with substitutions at residues 95 (Q-->H), 96 (G-->S) or 116 (A-->G), each with serine (S) at residue 138. In addition, a processed pseudogene with two alleles encoding five or six copies of the octapeptide repeat was identified in 26 % of the deer. Both alleles encoded asparagine (N) at residue 138. The functional gene alleles sorted into five major diploid genotypes and four rare genotypes. Although all five major diploid genotypes were found in deer with CWD, unaffected deer were less likely to have the allele QGAS and more likely to have QSAS compared with CWD-affected deer. Late-stage disease (PrPd in brainstem) was noted in deer less than 1 year of age, although no single genotype was associated with this rapid neuroinvasion. Early-stage disease (PrPd distribution limited to the lymphoid system) was observed in deer estimated to be more than 5 years old, suggesting that they were infected as adults or that the incubation time might be extremely long in some individuals. The pseudogene was found in deer of all major PRNP genotypes and was not correlated with CWD status. The large number of susceptible genotypes and the possibility of adult-to-adult transmission suggest that much of the white-tailed deer population may be at risk for disease following exposure to CWD, despite the association of specific genotypes with CWD noted here.

Preclinical deposition of pathological prion protein PrPSc in muscles of hamsters orally exposed to scrapie

Recently, pathological prion protein PrP(Sc), the putative key constituent of infectious agents causing transmissible spongiform encephalopathies (TSEs), was found in muscles of rodents experimentally infected with scrapie and in patients with Creutzfeldt-Jakob disease (CJD). For the assessment of risk scenarios originating from these findings (e.g., alimentary transmission of pathogens associated with bovine spongiform encephalopathy [BSE] and chronic wasting disease [CWD] via tainted beef and game or iatrogenic dissemination of CJD agent through contaminated surgical instruments) more detailed information about the time course of PrP(Sc) accumulation in muscles at preclinical and clinical stages of incubation is needed. Here we show that PrP(Sc) in muscles of hamsters fed with scrapie can be detected prior to the onset of clinical symptoms, but that the bulk of PrP(Sc) was deposited late in clinical disease. Additionally, regarding the question of how muscles become invaded, we report on the intramuscular location of PrP(Sc) and substantial indications for centrifugal spread of infection from spinal motor neurons to myofibers. Our findings in a well-established animal model for TSEs contribute to a better assessment of the risks for public health emanating from "Prions in skeletal muscle" and provide new insights into the pathophysiological spread of TSE agents through the body.

Supplementary cleaning does not remove protein deposits from re-usable laryngeal mask devices

PURPOSE

To test the hypothesis that supplementary cleaning facilitates removal of protein deposits from the laryngeal mask airway (LMA).

METHODS

Twenty previously used Classic) and Flexible LMAs were hand washed, machine washed, dried, autoclaved and then randomly allocated into four groups for supplementary cleaning. In Group A, the dorsal surface was immersed in water and the surface scrubbed with a high-speed rotating brush. In Group B, the dorsal surface was immersed in a plaque removing solution. In Group C, the dorsal surface was immersed in a protein removing solution. In Group D (controls), the dorsal surface was immersed in water. Before and after supplementary cleaning the LMAs were immersed in a protein staining solution, rinsed and a high-resolution digital image taken of the dorsal surface. The location and severity of staining were scored by two observers blinded to group assignment.

RESULTS

Staining was similar before and after supplementary cleaning for all groups. Mild, moderate and severe staining occurred in 31%, 7% and 2% of zones respectively; 60% were unstained. Staining was less common on the cuff than on the backplate and distal tube (both: P < 0.00001). Staining was less common on the backplate than on the distal tube (P = 0.001). Staining was always present on the mid-portion of the backplate or distal tube.

CONCLUSION

Supplementary cleaning using a rotating brush, plaque or protein removing solution does not facilitate removal of protein deposits from re-usable LMAs; however, the infectious risk associated with the protein deposits remains to be determined.

Failure to detect prion protein (PrPres) by immunohistochemistry in striated muscle tissues of animals experimentally inoculated with agents of transmissible spongiform encephalopathy

Transmissible spongiform encephalopathies (TSEs) are fatal neurologic diseases. Infection by the causative agent, a prion, induces accumulations of an abnormal form of prion protein (PrP(res)) in tissues of nervous and lymphoid systems. Presence of characteristic histopathologic changes (spongiform encephalopathy) and detection of protease-resistant PrP(res) in neural and lymphoid tissues are the basis of currently available methods for diagnosis of TSEs. In this study, samples of striated muscle tissues (tongue, heart, diaphragm, and masseter muscle) from 20 animals (cattle, sheep, elk, and raccoons) were examined for PrP(res) by immunohistochemistry (IHC). All the animals had developed a TSE after experimental inoculation. PrP(res) was found by IHC in the brain but not in the muscle tissues of all the animals examined. These findings are contradictory to recently published reports of laboratory animals with TSEs, where these altered prion proteins were detected in tongue and other striated muscles. Further testing of muscle tissues is needed to confirm the findings of the present study.

Cultured peripheral neuroglial cells are highly permissive to sheep prion infection

Transmissible spongiform encephalopathies arise as a consequence of infection of the central nervous system (CNS) by prions. Spreading of the infectious agent through the peripheral nervous system (PNS) may represent a crucial step toward CNS neuroinvasion, but the modalities of this process have yet to be clarified. Here we provide further evidence that PNS glial cells are likely targets for infection by prions. Glial cell clones originating from dorsal root ganglia of transgenic mice expressing ovine PrP (tgOv) and simian virus 40 T antigen were found to be readily infectible by sheep scrapie agent. This led us to establish two stable cell lines that exhibited features of Schwann cells. These cells were shown to sustain an efficient and stable replication of sheep prion based on the high level of accumulation of abnormal PrP and infectivity in exposed cultures. We also provide evidence for abnormal PrP deposition in peripheral neuroglial cells from scrapie-infected tgOv mice and sheep. These findings have potential implications in terms of designing new cell systems permissive to prions and of peripheral pathobiology of prion infections.

Investigation of PrPres in dental tissues in variant CJD

OBJECTIVES

To study the distribution of disease-associated prion protein (PrP) in oral and dental tissues in variant CJD.

DESIGN

Prospective single centre autopsy based study.

SETTING

Within the National CJD Surveillance Unit, UK, 2000-2002.

MATERIALS AND METHODS

Patients with suspected variant CJD undergoing autopsy where permission to remove tissues for research purposes had been obtained from the relatives. Fixed and frozen autopsy tissues from the brain, trigeminal ganglion, alveolar nerve, dental pulp, gingiva, salivary gland, tongue and tonsils were studied by Western blot, PET blot and immunocytochemistry to detect disease-associated PrP.

RESULTS

Disease-associated PrP was only detected in the brain, trigeminal ganglia and tonsils.

CONCLUSIONS

The failure to detect disease-associated PrP in most dental and oral tissues will help inform ongoing risk assessments for dental surgery in relation to the possible iatrogenic transmission of variant CJD via dental instruments.

Enhanced detection and retrograde axonal transport of PrPc in peripheral nerve

Neuroinvasion of the CNS during orally acquired transmissible spongiform encephalopathies (TSEs) may involve the transport of the infectious agent from the periphery to the CNS via the peripheral nerves. If this occurs within axons, the mechanism of axonal transport may be fundamental to the process. In studies of peripheral nerve we observed that the cellular prion protein (PrPc) is highly resistant to detergent extraction. The implication of this is an underestimation of the abundance of PrPc in peripheral nerve. We have developed nerve extraction conditions that enhance the quantification of the protein in nerve 16-fold. Application of these conditions to evaluate the accumulation of PrPc distal to a cut nerve now reveals that PrPc is retrogradely transported from the axon ending. These results provide a potential cellular mechanism for TSE infectivity to gain entry to the CNS from the periphery.

Routine Cleaning and Autoclaving Does Not Remove Protein Deposits from Reusable Laryngeal Mask Devices

We tested the hypothesis that routine cleaning and autoclaving does not remove protein deposits from reusable laryngeal mask airways (LMAs). All previously used classic and flexible LMAs from a single hospital were tested. Each LMA was hand-washed in an enzymatic solution for 3 min, machine-washed with a disinfectant for 14 min at up to 85 degrees C; dried for 30 min at 75 degrees C, packaged in porous film, and autoclaved for 4 min at 134 degrees C. Protein deposits were detected by immersion in a 1.2% erythrosin B solution, which stains for proteins present on surfaces. The outer surface, inner surface, and edges of the cuff, and the outer and inner surface of the airway tube were examined for the uptake of stain. The severity of staining was scored according to the percentage of surface area stained: nil, mild (>0%-20%), moderate (>20%-80%), and severe (>80%-100%). Fifty-nine LMAs were collected (16 classic and 43 flexible). Staining was detected on 15 (94%) classic LMAs and 39 (91%) flexible LMAs. All staining was graded as mild. Staining was less common on the inner surface than the outer surface or edges for both devices (all P < 0.004). Staining was less common with the airway tube than any location on the cuff (all P < 0.02). Two unused LMAs used as controls were without staining. We conclude that routine cleaning and autoclaving does not remove protein material from reusable LMAs.

IMPLICATIONS

Routine cleaning and autoclaving does not remove protein material from reusable laryngeal mask airway devices.

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, PrPSc (the pathological isoform of the prion protein PrP). Sensitive western blotting revealed consistent PrPSc 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.

Axonal transport and neuronal transcytosis of trophic factors, tracers, and pathogens

Neurons can specifically internalize macromolecules, such as trophic factors, lectins, toxins, and other pathogens. Upon internalization in terminals, proteins can move retrogradely along axons, or, upon internalization at somatodendritic domains, they can move into an anterograde axonal transport pathway. Release of internalized proteins from neurons after either retrograde or anterograde axonal transport results in transcytosis and trafficking of proteins across multiple synapses. Recent studies of binding properties of several such proteins suggest that pathogens and lectins may utilize existing transport machineries designed for trafficking of trophic factors. Specific pathways may protect trophic factors, pathogens, and toxins from degradation after internalization and may target the trophic or pathogenic cargo for transcytosis after either retrograde or anterograde transport along axons. Elucidating the molecular mechanisms of sorting steps and transport pathways will further our understanding of trophic signaling and could be relevant for an understanding and possible treatment of neurological diseases such as rabies, Alzheimer's disease, and prion encephalopathies. At present, our knowledge is remarkably sparse about the types of receptors used by pathogens for trafficking, the signals that sort trophins or pathogens into recycling or degradation pathways, and the mechanisms that regulate their release from somatodendritic domains or axon terminals. This review intends to draw attention to potential convergences and parallels in trafficking of trophic and pathogenic proteins. It discusses axonal transport/trafficking mechanisms that may help to understand and eventually treat neurological diseases by targeted drug delivery.