Generation of monoclonal antibody that distinguishes PrPSc from PrPC and neutralizes prion infectivity.

To establish PrP(Sc)-specific mAbs, we immunized Prnp(-/-) mice with PrP(Sc) purified from prion-infected mice. Using this approach, we obtained mAb 6H10, which reacted with PrP(Sc) treated with proteinase K, but not with PrP(Sc) pretreated with more than 3 M GdnHCl. In contrast, reactivity of pan-PrP mAbs increased with increasing concentrations of GdnHCl used for pretreatment of PrP(Sc). In histoblot analysis, mAb 6H10 showed a positive reaction on a non-denatured histoblot but reactivity was lower when the histoblot was pretreated by autoclaving. Epitope analysis suggested that the extreme C-terminus of PrP is likely to be part of the epitope for mAb 6H10. MAb 6H10 immunoprecipitated PrP(Sc) from brains of mice, sheep, and cattle infected with prions. Furthermore, pretreatment of purified PrP(Sc) with mAb 6H10 reduced the infectious titer more than 1 log. Taken together, these results suggest that mAb 6H10 recognizes a conformational epitope on PrP(Sc) that is related to prion infectivity.

Conformational change in hamster scrapie prion protein (PrP27-30) associated with proteinase K resistance and prion infectivity.

The scrapie prion protein (PrP27-30) is a crucial component of the prion and is responsible for its transmissibility. Structural information on this protein is limited because it is insoluble and shows aggregated properties. In this study, PrP27-30 was effectively dispersed using sonication under the weak alkaline condition. Subsequently, the small PrP27-30 aggregates were subjected to different pH, heat, and denaturing conditions. The loss of proteinase K (PK) resistance of PrP27-30 and prion infectivity were monitored along with spectroscopic changes. Prion inactivation could not be achieved by the loss of PK resistance alone; a significant loss of the PrP27-30 amyloid structure, which was represented by a decrease in thioflavin T fluorescence, was required for the loss of transmissibility.

Accumulation of mono-glycosylated form-rich, plaque-forming PrPSc in the second atypical bovine spongiform encephalopathy case in Japan.

The recent identification of several atypical cases of bovine spongiform encephalopathy (BSE) has raised the possibility of the existence of distinct strains of BSE agents, arguing against the previous notion that BSE is caused by a single strain. To date, at least, two atypical types (L and H) of agent have been reported based on the molecular sizes of the proteinase K-resistant forms of prion protein (PrP(Sc)). These atypical agents were identified first in Japan, Italy, France, and Germany, and later in other European countries. Here, we have identified a case of BSE in a 169-month-old cow (designated as BSE/JP24), in which predominant deposition of the mono-glycosylated form of PrP(Sc) was observed by Western-blot analysis, and plaques of PrP(Sc) were detected in the brain by immunohistochemical analysis. The glycoform ratio of PrP(Sc) was different from that of the typical BSE agent, in which the di-glycosylated form is dominant; instead, the ratio resembled that of type-2 human sporadic Creutzfeldt-Jakob disease and that reported for the L-type BSE. The characteristic glycoform ratio and plaques of PrP(Sc) suggested that the agent in BSE/JP24 was relevant, if not identical, to the agent in bovine amyloidotic spongiform encephalopathy (BASE), an L-type BSE identified in Italy. It was of interest that at the level of the obex, the medulla oblongata was devoid of plaques of PrP(Sc), and a pathological phenotype similar to that of typical BSE specimens with vacuolations and coarse granular/linear deposition of PrP(Sc) were observed.

Experimental transmission of two young and one suspended bovine spongiform encephalopathy (BSE) cases to bovinized transgenic mice.

Bovine spongiform encephalopathy (BSE) is caused by a prion that primarily consists of an abnormal isoform of the prion protein (PrP(Sc)). Since PrP(Sc) is partially resistant to proteolytic digestion, the routine diagnosis of BSE is based on the immunological detection of the proteinase K (PK)-resistant moiety of PrP(Sc) (PrP(core)). However, transmission studies are indispensable in order to demonstrate prion infectivity and to analyze prion characteristics. Transmission experiments were accordingly performed on 2 young BSE cases (BSE/JP8, BSE/JP9) and 1 suspected BSE case (Suspended-1) that were detected by the BSE screening program in Japan. In this study, we attempted to transmit the prion from these 3 animals by using transgenic mice overexpressing bovine PrP (TgBoPrP). In spite of the use of BSE-sensitive transgenic mice, none of the mice developed neurological signs nor accumulated PrP(Sc) in their brains for more than 600 days post-inoculation, even with subsequent blind passages. The results of a dilution experiment using the classical BSE prion indicated that prion infectivity in these 3 cattle was below the detection limit of 10(3.0) LD(50)/g.

Establishment and characterization of SV40 large T antigen-immortalized cell lines derived from fetal bovine brain tissues after prolonged cryopreservation.

Bovine brain cell lines with specific characteristics are useful in vitro experimental systems for molecular and cellular investigation of the interactions between bovine specific neuropathogenic agents and the host. Here, we established two novel cell lines from cultures of cryopreserved fetal bovine brain tissue by the transfection of SV40 large T antigen. Both cell lines showed cobblestone morphology in DMEM/F12 medium supplemented with 10% fetal bovine serum, epidermal growth factor and basic fibroblast growth factor. They were immunostained with endothelial marker, Von Willebrand Factor. Endothelial properties, such as capillary-like tube formation on matrigel and the incorporation of DiI-AcLDL were confirmed with these cells. Removal of growth factors increased the number of cells expressing alpha-smooth muscle actin, suggesting the potential of these cell lines to differentiate into smooth muscle cells. This study suggests an efficient protocol to immortalize brain endothelial cell lines from fetal bovine brain tissue culture.

Microglial cell line established from prion protein-overexpressing mice is susceptible to various murine prion strains.

Several lines of evidence suggest that microglia have important roles in the pathogenesis of prion diseases. Here, we establish a novel microglial cell line (MG20) from neonatal tga20 mice that overexpress murine prion protein. After exposure to Chandler scrapie, we observed the replication and accumulation of disease-associated forms of the prion protein in MG20 cells up to the 15th passage. Furthermore, MG20 cells were susceptible to ME7, Obihiro scrapie, and bovine spongiform encephalopathy agents. Thus, MG20 cell lines persistently infected with various murine prion strains provide a useful model for the study of the pathogenesis of prion diseases.

Protein misfolding cyclic amplification as a rapid test for assessment of prion inactivation.

Abnormal isoform of prion proteins (PrP(Sc)), which are infectious agents associated with prion diseases, retain infectivity after undergoing routine sterilization processes. A sensitive method to detect the infectivity is a bioassay, and it has been used for assessing prion inactivation. However, the result is obtained after several hundred days. Here, protein misfolding cyclic amplification (PMCA) in which PrP(Sc) can be amplified in vitro was applied for assessing prion inactivation by dry heating and autoclaving. Scrapie-infected hamster brains were inactivated under various conditions, and residual infectivity and PrP(Sc) were detected by the bioassay and PMCA, respectively. The PMCA results were in good agreement with those of the bioassay. In samples autoclaved at temperatures below 150 degrees C, while infected mice died in the bioassay, protease-resistant PrP (PrP(res)) signals were detected in the second or third round of PMCA. Three rounds of PMCA require only 6 days, which means that the PMCA method is much faster than the bioassay.

A solid-phase immunoassay of protease-resistant prion protein with filtration blotting involving sodium dodecyl sulfate.

The precise diagnosis for bovine spongiform encephalopathy (BSE) is crucial for preventing new transmission to humans. Several testing procedures are reported for determining protease-resistant prion protein in various tissues as a major hallmark of prion diseases such as BSE, scrapie, and Creutzfeldt-Jakob disease. However, contamination of materials from tissues or degradation of the specimens sometimes disturbs the accuracy of the assay. Here, we have developed a novel method for solid-phase immunoassay of the disease-specific conformational isoform, PrP(Sc), using filtration blotting of protein in the presence of sodium dodecyl sulfate (SDS) followed by a filtration-based immunoassay with a single anti-prion protein antibody, together with the improved fractionation procedure involving high concentrations of surfactant/detergent. The SDS/heat treatment renders unfolded PrP(Sc) quantitative retention on a polyvinylidene difluoride filter and allows enhancement of the analyte signal with immunodetection; thus, all of the tested specimens are determined with 100% accuracy. In addition, the immunoassay is completed in approximately 1h, indicating its usefulness not only for the screening of BSE specimens but probably also for the postmortem BSE diagnosis of fallen stock as the antibody recognizes the core part of PrP(Sc). The solid-phase immunoassay method, including the filtration blotting with SDS, would be applicable to determining even more sensitively proteins other than PrP(Sc), especially those having rigid conformations.

Rapid PrP(Sc) detection in lymphoid tissue and application to scrapie surveillance of fallen stock in Japan: variable PrP(Sc) accumulation in palatal tonsil in natural scrapie.

Rapid western blot (WB) procedure for an abnormal isoform of prion protein (PrP(Sc) ) detection in lymphoid tissues was established and has been applied to the surveillance of fallen stock. In this program, brain and palatal tonsil were examined by WB and three cases of sheep scrapie were detected. While one clinically scrapie-infected sheep harbored PrP(Sc) in the brain and palatal tonsil, the two sheep in the pre-clinical stage harbored PrP(Sc) in the brain, but not in the palatal tonsil. This study shows that PrP(Sc) accumulation in palatal tonsil is variable in natural scrapie, even among genetically susceptible sheep.

Polymorphisms of caprine PrP gene detected in Japan.

Polymorphism of the PrP gene is a primary factor influencing susceptibility and incubation period in natural and experimental scrapie in sheep and goats. Polymorphisms of the caprine PrP gene in Japan were examined in 118 goats. Eight allelic variants and 19 genotypes were obtained. Amino acid polymorphisms were observed at 7 codons: 102, 142, 143, 240, 127, 146 and 211 (the latter 3 are novel polymorphisms). The polymorphisms at codons 142M and 143R, which are associated with the resistance to scrapie, were relatively rare in the present study. Thus, the present results provide information about the caprine PrP gene that may be useful for assessing the risk of goat scrapie.

The N-terminal cleavage site of PrPSc from BSE differs from that of PrPSc from scrapie.

Heterogeneity in transmissible spongiform encephalopathy is thought to have derived from conformational variation in an abnormal isoform of the prion protein (PrPSc). To characterize PrPSc in bovine spongiform encephalopathy (BSE) and scrapie, we analyzed the newly generated N-terminus of PrPSc isoforms by digestion with proteinase K (PK). With a lower concentration of PK, the terminal amino acid of BSE PrPSc converged at N96. Under the same conditions, however, the terminal amino acid of scrapie PrPSc was G81 or G85. Furthermore, with an increase of PK concentration, the N-terminal amino acid was shifted and converged at G89. The results suggest that the PK cleavage site of BSE PrPSc is uniform and is different from the cleavage site of scrapie PrPSc.

Effective antigen-retrieval method for immunohistochemical detection of abnormal isoform of prion proteins in animals.

For immunohistochemistry of the prion diseases, several pretreatment methods to enhance the immunoreactivity of human and animal abnormal proteinase-resistant prion protein (PrP(Sc)) on the tissue sections have been employed. The method of 121 degree C hydrated autoclaving pretreatment or the combination method of 121 degree C hydrated autoclaving with a certain chemical reagent (formic acid or proteinase K, etc) are now widely used. We found that an improved hydrated autoclaving method at 135 degrees C, more effectively enhanced PrP(Sc) immunoreactivity for the antibodies recognizing the linear epitope. In addition, this method was more effective for the long-term fixation samples as compared with other previous methods. However, this modified method could not retrieve PrP(Sc) antigenic epitopes composed of conformational structures or several discontinuous epitopes. We describe the comparative studies between our improved method and other antigen-retrieval procedures reported previously. Based on the differences of reaction among the antibodies, we also discuss the mechanisms of the hydrated autoclaving methods to retrieve PrP(Sc) immunoreactivity.

Unique amino acid polymorphisms of PrP genes in Mongolian sheep breeds.

To characterize amino acid polymorphisms of sheep prion protein (PrP) gene, DNA from 740 sheep of nine breeds raised in Mongolia was isolated and analyzed. A total of 16 genotypes and seven allelic variants of the PrP gene at codons 112, 136, 154, and 171 were found. The MARQ/MARQ genotype associated with susceptibility to scrapie was found in 82.6% of the sheep while the MARR/MARR genotype associated with resistance to scrapie was found in 1.8% of the sheep. The polymorphisms of valine and serine at codon 127, and leucine and arginine at codon 189 were detected in eight Mongolian sheep breeds, suggesting that these polymorphisms are a common feature among Mongolian sheep breeds.

Cell-surface retention of PrPC by anti-PrP antibody prevents protease-resistant PrP formation.

The C-terminal portion of the prion protein (PrP), corresponding to a protease-resistant core fragment of the abnormal isoform of the prion protein (PrP(Sc)), is essential for prion propagation. Antibodies to the C-terminal portion of PrP are known to inhibit PrP(Sc) accumulation in cells persistently infected with prions. Here it was shown that, in addition to monoclonal antibodies (mAbs) to the C-terminal portion of PrP, a mAb recognizing the octapeptide repeat region in the N-terminal part of PrP that is dispensable for PrP(Sc) formation reduced PrP(Sc) accumulation in cells persistently infected with prions. The 50% effective dose was as low as approximately 1 nM, and, regardless of their epitope specificity, the inhibitory mAbs shared the ability to bind cellular prion protein (PrP(C)) expressed on the cell surface. Flow cytometric analysis revealed that mAbs that bound to the cell surface during cell culture were not internalized even after their withdrawal from the growth medium. Retention of the mAb-PrP(C) complex on the cell surface was also confirmed by the fact that internalization was enhanced by treatment of cells with dextran sulfate. These results suggested that anti-PrP mAb antagonizes PrP(Sc) formation by interfering with the regular PrP(C) degradation pathway.

Effect of tissue deterioration on postmortem BSE diagnosis by immunobiochemical detection of an abnormal isoform of prion protein.

Surveillance for bovine spongiform encephalopathy (BSE) in fallen stock in Japan is conducted with a commercial enzyme-linked immunosorbent assay (ELISA) for mass screening, with Western blotting (WB) and immunohistochemistry performed for confirmation of the ELISA. All tests are based on immunological detection of an abnormal isoform of the prion protein (PrP(Sc)) in brain tissues, which have sometimes deteriorated by the time samples from fallen stock reach a diagnostic laboratory. To evaluate BSE surveillance procedures for fallen stock, we examined PrP(Sc) detection from artificially deteriorated BSE-affected bovine brain tissues with a commercial ELISA kit and compared the results with those of WB. The optical density (OD) values of the ELISA decreased with advancing deterioration of the tissues, whereas no reduction in the signal for PrP(Sc) was observed in WB, even when performed after 4 days of incubation at 37 degrees C. The progressive decrease in the OD values in the ELISA appear to be caused by a partial loss of the N-terminal moiety of PrP(Sc) due to digestion by endogeneous and/or contaminated microbial enzymes, and by the presence of ELISA inhibitors that are generated in deteriorated tissues. These results suggest that WB is the most reliable test for fallen stock, especially for cattle brains within decaying carcasses.

Antigenic characterization of an abnormal isoform of prion protein using a new diverse panel of monoclonal antibodies.

We established a panel of monoclonal antibodies (mAbs) against prion protein (PrP) by immunizing PrP gene-ablated mice with the pathogenic isoform of prion protein (PrPSc) or recombinant prion protein (rPrP). The mAbs could be divided into at least 10 groups by fine epitope analyses using mutant rPrPs and pepspot analysis. Seven linear epitopes, lying within residues 56-90, 119-127, 137-143, 143-149, 147-151, 163-169, and 219-229, were defined by seven groups of mAbs, although the remaining three groups of mAbs recognized discontinuous epitopes. We attempted to examine whether any of these epitopes are located on the accessible surface of PrPSc. However, no mAbs reacted with protease-treated PrPSc purified from scrapie-affected mice, even when PrPSc was dispersed into a detergent-lipid protein complex, to reduce the size of PrPSc aggregates. In contrast, denaturation of PrPSc by guanidine hydrochloride efficiently exposed all of the epitopes. This suggests that any epitope recognized by this panel of mAbs is buried within the PrPSc aggregates. Alternatively, if the corresponding region(s) are on the surface of PrPSc, the region(s) may be folded into conformations to which the mAbs cannot bind. The reactivity of a panel of mAb also showed that the state of PrPSc aggregation influenced the denaturation process, and the sensitivity to denaturation appeared to vary between epitopes. Our results demonstrate that this new panel of well-characterized mAbs will be valuable for studying the biochemistry and biophysics of PrP molecules as well as for the immuno-diagnosis of prion diseases.

Susceptibility of transgenic mice expressing chimeric sheep, bovine and human PrP genes to sheep scrapie.

The use of Transgenic (Tg) mice expressing chimeric sheep/mouse (Sh/Mo) prion protein (PrP) and chimeric bovine/mouse (Bo/Mo) PrP genes was evaluated as a sheep scrapie model. We also investigated the potential for the transmission of sheep scrapie to a human/mouse (Hu/Mo) PrP Tg mouse line. The Sh/Mo PrP and Bo/Mo PrP Tg Prnp(+/+) or Prnp(0/0) mouse lines were inoculated intracerebrally with brain homogenates from three sheep with natural scrapie (KU, Y5 or S2). Incubation periods were slightly shorter in Sh/Mo PrP Tg Prnp(+/+), than in non-Tg mice inoculated with KU brain homogenate. In contrast, the incubation period was significantly prolonged (p<0.05) in Bo/Mo PrP Tg Prnp(+/+) mice inoculated with KU brain homogenate. The incubation period was significantly longer in all Tg Prnp(+/+) and Prnp(0/0), than in non-Tg mice (p<0.01) inoculated withY5 brain homogenate. None of the Tg Prnp(0/0) mice inoculated with S2 brain homogenate developed clinical signs and PrP(Sc) was undetectable in their brains. These results suggested that expression of the Sh/Mo PrP or Bo/Mo PrP transgenes does not confer susceptibility to sheep prions upon mice, and thus none of the Tg mouse lines could be a suitable model of sheep scrapie. Hu/Mo PrP Tg Prnp(0/0) mice inoculated with natural and experimental scrapie or mouse prions did not develop clinical signs of scrapie and PrP(Sc) was undetectable. These results suggested that neither sheep nor mouse strains of scrapie are highly transmissible to humans.

Amino acid polymorphisms of PrP gene in Mongolian sheep.

To characterize amino acid polymorphisms in sheep prion protein (PrP), we analyzed the PrP genes from 271 sheep of 4 breeds (Khalkh, Yeroo, Orkhon and Khangai) raised in central Mongolia (Tuv, Uvurkhangai and Selenge prefectures). A total of 16 genotypes and 8 allelic variants of the PrP gene at codons 112, 136, 154 and 171 were found. At codon 171, 1.8% of the sheep had arginine/arginine (R/R) (resistant to scrapie) and 66.8% had glutamine/glutamine (Q/Q) (susceptible to scrapie). Several Yeroo and Orkhon sheep raised in Selenge prefecture had valine at codon 136 (136V) (highly susceptible to scrapie). Several Yeroo, Orkhon and Khangai sheep raised in Selenge prefecture had histidine at codon 154 (154H). Novel polymorphisms of valine (V) and serine (S) at codon 127, lysine (K) at codon 171, and leucine (L) and arginine (R) at codon 189 were also found in Khalkh, Yeroo and Orkhon sheep. It is not known whether these novel polymorphisms affect scrapie susceptibility.

Bacteriological and genetic assessment of game meat from Japanese wild boars.

Bacterial tests were used to assess bacterial contamination of game meat from Japanese wild boars. The bacterial contamination of wild boar meat was less than that of domestic pork, as determined by aerobic plate counts (APC) and coliform counts. None of the meat examined in this study was contaminated by Salmonella or E. coli O-157. To detect adulteration by domestic pig meat or European wild boar meat, 46 samples of game meat sold as Japanese wild boar were examined genetically. A total of 17 samples showed genetic haplotypes of European and Asian domestic pigs in the D-loop of mitochondrial DNA (mtDNA), and 16 samples showed nuclear glucosephosphate isomerase-processed pseudogene (GPIP) genotypes of European domestic pigs. The European GPIP genotypes of these samples were confirmed by PCR-RFLP analysis. These results indicate that some game meat sold as Japanese wild boar is adulterated by cross-breeding between pigs and wild boars or by contamination with meat from domestic pigs or European wild boars.

A genetic method to distinguish crossbred Inobuta from Japanese wild boars.

To distinguish pig-wild boar crossbred Inobuta from Japanese wild boar populations, a genetic method by using mitochondrial DNA (mtDNA) haplotypes and the nuclear glucosephosphate isomerase-processed pseudogene (GPIP) was developed. Sixteen mtDNA haplotypes from 152 wild boars from Kyushu, Shikoku and Honshu islands of Japan were distinct from those from Asian and European domestic pigs. Five alleles of GPIP were classified into two groups: 1). alleles GPIP*1, GPIP*3 and GPIP*3a from Japanese wild boars, Asian wild boars and domestic pigs; 2). alleles GPIP*4 and GPIP*4a from European wild boars and domestic pigs. An extensive genetic survey was done to distinguish the crossbred Inobuta from 60 wild boars hunted on Tsushima Island, Goto Islands, and Nagasaki and Ooita Prefectures. The mtDNA haplotypes from the 60 samples showed Japanese wild boars, but four wild boar samples from Nagasaki Prefecture had the European GPIP allele, GPIP*4. These results showed that nuclear DNA polymorphism analysis is useful, in addition to mtDNA haplotype assay, to detect "Inobuta" having the European genotype from Japanese wild boar populations.