Preclinical diagnosis of scrapie by immunohistochemistry of third eyelid lymphoid tissue

Ovine scrapie is a member of the transmissible spongiform encephalopathies (TSEs), a heterogeneous family of fatal neurologic disorders characterized by deposition of an abnormal isoform (prion protein [PrP] PrP-Sc) of a cellular sialoglycoprotein in neural tissue. PrP-Sc is detectable in some lymphoid tissues of infected sheep months or years before development of clinical disease. Detection of PrP-Sc in these tissues is the basis for live-animal testing. In this study, we characterize the performance of a preclinical diagnostic test for ovine scrapie based on a monoclonal antibody (MAb)-based immunohistochemistry assay of nictitating membrane ("third eyelid")-associated lymphoid tissue. The results of third eyelid immunohistochemistry assay agreed with the scrapie status of the sheep for 41 of 42 clinical suspects with confirmed scrapie and 174 of 175 sheep without scrapie. Third eyelid sampling agreed with the scrapie status for 36 of 41 clinically normal sheep positive for PrP-Sc immunostaining of brain tissue, including 27 sheep with positive biopsy specimens that progressed to clinical disease with confirmed scrapie 3 to 20 months after biopsy. The assay used MAb F89/160.1.5, which binds to residues 142 to 145 of ovine PrP. This antibody can be used in combination with MAb F99/97. 6.1, which binds to residues 220 to 225. One or both MAbs in this cocktail recognize PrP sequences conserved in most mammalian species in which natural TSEs have been reported. Immunohistochemistry assay of routinely formalin-fixed lymphoid tissues with a cocktail of pan-specific MAbs is a practical, readily standardized live-animal and preclinical test for ovine scrapie.

Use of capillary electrophoresis and fluorescent labeled peptides to detect the abnormal prion protein in the blood of animals that are infected with a transmissible spongiform encephalopathy

Transmissible spongiform encephalopathies in humans and in animals are fatal neuro-degenerative diseases with long incubation times. The putative cause of these diseases is a normal host protein, the prion protein, that becomes altered. This abnormal prion protein is found mostly in the brains of infected individuals in later stages of the disease, but also can be found in lymphoid and other tissues in lower amounts. In order to eradicate this disease in animals, it is important to develop a system that can concentrate the abnormal prion protein and an assay that is very sensitive. The sensitivity that can be achieved with capillary electrophoresis makes it possible to detect the abnormal protein in blood. A peptide from the carboxyl terminal region, amino acid positions 218-232, was labeled with fluorescein during the synthesis of the peptide at the amino terminus. Antibodies that have been produced to this peptide were affinity purified and used in a capillary electrophoresis immunoassay. The amount of fluorescein labeled peptide in the capillary was 50 amol. Blood was obtained from normal sheep and elk, from sheep infected with scrapie and elk infected with chronic wasting disease. Buffy coats and plasma were prepared by a conventional method. After treatment with proteinase K, which destroys the normal protein but not the altered one, the blood fractions were extracted and tested in the capillary electrophoresis immunoassay for the abnormal prion protein. The abnormal prion protein was detected in fractions from blood from infected animals but not from normal animals. This assay makes a pre-clinical assay possible for these diseases and could be adapted to test for the abnormal prion protein in process materials that are used for manufacture of pharmaceuticals and products for human consumption.

Intracerebral transmission of scrapie to cattle

To determine if sheep scrapie agent(s) in the United States would induce a disease in cattle resembling bovine spongiform encephalopathy, 18 newborn calves were inoculated intracerebrally with a pooled suspension of brain from 9 sheep with scrapie. Half of the calves were euthanatized 1 year after inoculation. All calves kept longer than 1 year became severely lethargic and demonstrated clinical signs of motor neuron dysfunction that were manifest as progressive stiffness, posterior paresis, general weakness, and permanent recumbency. The incubation period was 14-18 months, and the clinical course was 1-5 months. The brain from each calf was examined for lesions and for protease-resistant prion protein. Lesions were subtle, but a disease-specific isoform of the prion protein was present in the brain of all calves. Neither signs nor lesions were characteristic of those for bovine spongiform encephalopathy.

Preliminary findings on the experimental transmission of chronic wasting disease agent of mule deer to cattle

To determine the transmissibility of chronic wasting disease (CWD) to cattle and to provide information about clinical course, lesions, and suitability of currently used diagnostic procedures for detection of CWD in cattle, 13 calves were inoculated intracerebrally with brain suspension from mule deer naturally affected with CWD. Between 24 and 27 months postinoculation, 3 animals became recumbent and were euthanized. Gross necropsies revealed emaciation in 2 animals and a large pulmonary abscess in the third. Brains were examined for protease-resistant prion protein (PrP(res)) by immunohistochemistry and Western blotting and for scrapie-associated fibrils (SAFs) by negative-stain electron microscopy. Microscopic lesions in the brain were subtle in 2 animals and absent in the third case. However, all 3 animals were positive for PrP(res) by immunohistochemistry and Western blot, and SAFs were detected in 2 of the animals. An uninoculated control animal euthanized during the same period did not have PrP(res) in its brain. These are preliminary observations from a currently in-progress experiment. Three years after the CWD challenge, the 10 remaining inoculated cattle are alive and apparently healthy. These preliminary findings demonstrate that diagnostic techniques currently used for bovine spongiform encephalopathy (BSE) surveillance would also detect CWD in cattle should it occur naturally.

Ovine progressive pneumonia (maedi-visna) in sheep

Ovine progressive pneumonia (OPP) is a multi-systemic disease of sheep caused by a nononcogenic exogenous retrovirus belonging to the Lentiviridae subfamily. Characteristics of the disease are chronic lymphocytic pneumonitis, encephalitis, arthritis, mastitis and vasculitis associated with progressive wasting, dyspnea, lameness, indurated udder and, rarely, paralysis. Any one or all of the characteristics may be manifest. Transmission of the virus is predominantly through the colostrum to newborn lambs, however, transmission can occur by contact and in utero. Treatment of the disease is only symptomatic and prevention of infection is only by avoiding the virus.

Second passage of a US scrapie agent in cattle

Scrapie and bovine spongiform encephalopathy are similar chronic neurodegenerative diseases of sheep and cattle. An earlier study showed that, on first passage in cattle, a US scrapie agent caused an encephalopathy that was distinct from bovine spongiform encephalopathy (BSE). The present report describes a second passage in cattle, carried out because diseases caused by the spongiform encephalopathy agents often change in character with additional passages in abnormal hosts. For this work, young calves were inoculated intracerebrally with a pooled suspension of brain from cattle that had died of encephalopathy after experimental inoculation with brain from scrapie-affected sheep. The second passage disease was essentially identical with the first passage disease, as judged by clinical signs, histopathological findings and distribution of "prion protein scrapie" (PrPsc). This represents additional evidence to suggest that the US sheep scrapie agent tested is incapable of causing BSE in cattle.

Polymorphisms of the prion gene promoter region that influence classical bovine spongiform encephalopathy susceptibility are not applicable to other transmissible spongiform encephalopathies in cattle

Two regulatory region polymorphisms in the prion gene of cattle have been reported to have an association with resistance to classical bovine spongiform encephalopathy (BSE). However, it is not known if this association also applies to other transmissible spongiform encephalopathies (TSE) in cattle. In this report, we compare the relationship between these 2 polymorphisms and resistance in cattle affected with naturally occurring atypical BSE as well as in cattle experimentally inoculated with either scrapie, chronic wasting disease, or transmissible mink encephalopathy. Our analysis revealed no association between genotype and resistance to atypical BSE or experimentally inoculated TSE. This indicates the promoter polymorphism correlation is specific to classical BSE and that atypical BSE and experimentally inoculated TSE are bypassing the site of influence of the polymorphisms. This genetic discrepancy demonstrates that atypical BSE progresses differently in the host relative to classical BSE. These results are consistent with the notion that atypical BSE originates spontaneously in cattle.

Evaluation of an ELISA for detection of ovine progressive pneumonia antibodies using a recombinant transmembrane envelope protein

An enzyme-linked immunosorbent assay (ELISA) was developed using a recombinant protein corresponding to the N'-terminal hydrophilic region of transmembrane glycoprotein (TM) of ovine lentivirus. This assay reproducibly detected antibodies in sera from 207 of 212 ovine progressive pneumonia (OPP) virus-infected sheep, and the recombinant TM ELISA accurately identified 26% (35 vs. 9) more seropositive samples than did the agar gel immunodiffusion test when applied to 100 sera from an infected flock. This assay also yielded no false-positive results in 14 true negative sera. Results of these experiments were further confirmed by the recombinant TM and recombinant p25 Western blot assay. A single recombinant TM antigen, as the coating antigen in ELISA, can be used successfully for the detection of OPP virus-infected animals and can improve the sensitivity and specificity for OPP diagnosis.

Detection of antibodies to ovine lentivirus using a recombinant antigen derived from the env gene

The Western blot assay was performed to characterize antibodies to the transmembrane glycoprotein (TGP) of ovine progressive pneumonia virus (OPPV) by using glutathione-S-transferase-TGP (GST-TGP) protein. The GST-TGP protein was efficiently expressed in Escherichia coli (E. coli) and was highly immunoreactive in the Western blot assay. This assay detected antibodies in 97% (103/106) of the sera from agarose gel immunodiffusion (AGID) positive OPP animals. Like human AIDS patients, antibodies to TGP appear to be one of the major serological markers in OPP infected animals.

Complexing of bacterial lipopolysaccharide with lung surfactant

Lipopolysaccharides (LPS) from Escherichia coli, Salmonella typhi, Klebsiella pneumoniae, Serratia marcescens, or Pseudomonas aeruginosa were mixed with pulmonary surfactant to investigate their in vitro interaction. After 6 h of incubation at 37 degrees C, LPS-surfactant mixtures were examined by sucrose density gradient centrifugation. The E. coli LPS-surfactant mixture was examined by immunoelectron microscopy with protein A-colloidal gold. The binding that occurred between LPS and the surfactant vesicles resulted in a complex with a density higher than the density of the surfactant alone. The protein A-colloidal gold identified LPS in the LPS-surfactant complexes. The toxicity of E. coli LPS was enhanced by complexing with the surfactant when compared with the intraperitoneal injection into CF1 mice, even at a 64:1 ratio of surfactant to LPS. The complexing of LPS and surfactant in the lung may alter the physiologic properties of surfactant that contribute to the physiopathological changes observed with some types of pneumonia.

Breed susceptibility to ovine progressive pneumonia (maedi/visna) virus

In this retrospective study of breed differences in susceptibility to disease caused by ovine progressive pneumonia (OPP) virus, 29 Border Leicester sheep were compared with 46 Columbia sheep. As judged by frequency and severity of clinical signs and lesions attributable to the infection, Border Leicester sheep were markedly more susceptible than Columbia sheep and experimentally infected sheep were slightly more susceptible than naturally infected sheep. Differences in susceptibility to infection by the virus were not determined.

Failure of experimental vaccines to protect against infection with ovine progressive pneumonia (maedi-visna) virus

Cell culture medium was harvested from cells infected with ovine progressive pneumonia (OPP) virus and used to prepare killed virus vaccines. Virus was inactivated by either heat, formalin, or ethyleneimine and used either without adjuvant, with Freund incomplete adjuvant, or with aluminum hydroxide adjuvant to vaccinate sheep. The sheep produced precipitating antibody against the virus but were not protected against infection when challenged with live OPP virus.

Capillary isoelectric focusing of the scrapie prion protein

Prion diseases or transmissible spongiform encephalopathies belong to a group of neurodegenerative diseases that infect both animals and humans. These diseases are associated with an accumulation of fibrils in the brains of infected individuals. These fibrils are composed of an abnormal isoform of a host-encoded glycoprotein that is characterized by its insolubility and partial resistance to proteases. Another characteristic of the scrapie prion protein (PrPsc) is the wide range of isoelectric points (pI values) that have been observed on conventional isoelectrofocusing gels. In this study, we explored the use of capillary isoelectric focusing (cIEF) to characterize the pI values for PrPsc isolated from sheep and hamster brain. We used a Beckman 5500 P/ACE using UV detection at 280 nm. A cIEF 3-10 Kit from Beckman Instruments was used to perform the analysis. The PrPsc was solubilized in 0.01 M Tris-HCl, pH 8.00 containing 2 mM EDTA. 5% SDS and 10% hexafluoroisopropanol at 100 degrees C for 10 min. The solubilized PrPsc was placed over a high-performance hydrophilic interaction column. After elution, the peaks were concentrated and assayed for immunoreactivity with specific antisera. The peaks that contained immunoreactivity were then placed on the cIEF capillary. The samples containing PrPsc were solubilized in 1% n-octylglucoside before isoelectric focusing. The scrapie infected sheep sample had peaks with pI values ranging from 5.2 to 3.00 with a major peak at 3.09. The normal sheep brain had pI values that were higher. The hamster adapted scrapie strain had peaks with pI values ranging from 6.47 to 3.8. These pI values were slightly higher than those obtained for the sheep samples. The use of cIEF to determine the pI values of PrPsc led to the identification of a major species of PrPsc from sheep with a very acidic pI.

Response of sheep after localized deposition of lipopolysaccharide in the lung

Deposition by fiberoptic bronchoscopy of lipopolysaccharide (LPS) from Pasteurella haemolytica (Type 1A) or Escherichia coli (Type 026:B6) into the lungs of sheep elicited a variety of clinical and pathologic reactions. Sheep given P. haemolytica LPS developed a biphasic hematologic response: a marked decline in leukocyte counts in 4 h that was followed in 18 h by a mild leukocytosis. A gradual rise in leukocyte counts was seen in sheep given E. coli LPS. Neutrophil counts gradually increased after deposition with either LPS, but lymphocyte counts fluctuated with the total leukocyte counts. Body temperature remained normal after LPS deposition. A marked increase in total lung lavage cell counts was observed 22 h after LPS deposition. Up to 83% of the lavage cells were neutrophils. Both LPS induced diffuse fibrinopurulent inflammation, edema, hyperemia, and hemorrhage in the lungs. LPS from P. haemolytica also caused foci of necrosis. In contrast, distilled water caused diffuse edema and hyperemia, with a limited number of neutrophils. Deposition of P. haemolytica or E. coli LPS into the lungs of sheep resulted in lesions similar to those reported in animals with an acute pneumonia experimentally induced with gram-negative bacteria.

Use of capillary sodium dodecyl sulfate gel electrophoresis to detect the prion protein extracted from scrapie-infected sheep

Scrapie in sheep and in goats is the prototype of a group of transmissible spongiform encephalopathies (TSE). A feature of these diseases is the accumulation in the brain of rod shaped fibrils that form from an aggregated protein that is a protease-resistant form of a modified normal host cell protein. In this study, we compared SDS gel capillary electrophoresis to conventional SDS-PAGE and Western blot to detect the monomer of this aggregated protein. This prion protein was extracted from the sheep brain by homogenizing the brain stem (10%, w/v) in 0.32 M sucrose and by using a series of ultracentrifugation steps and treatment with sodium lauroyl sarcosine and proteinase K. After the final centrifugation step, the pellet was resuspended in 0.01 M Tris pH 7.4 in a volume equivalent to 0.1 ml/g of brain used. This resuspended pellet was treated with 1% SDS and 5% 2-mercaptoethanol and boiled for 10 min. The analysis was done in a Beckman P/ACE 5500 using a SDS gel capillary (eCap SDS14-200 Beckman capillary). In infected sheep brain samples, but not normal sheep, a major peak at a molecular mass of 16.1 kDa and a minor peak with a leading shoulder were observed. Since the molecular mass determined for this protein was lower than that estimated on Western blot (22.4 kDa), a Ferguson plot was made to determine if there were abberations in the molecular mass determination. After correction, the major peak was estimated to be 19.2 kDa. This has a better correlation with that determined by SDS-PAGE and Western blot. The equivalent amount of brain sample in the capillary was approximately 50 micrograms. For Western blot, the amount of brain sample was approximately 20 mg. For this assay, this is approximately 100 times less than that needed for Western blot for sheep samples.

Ultrastructure and frequency of mastitis caused by ovine progressive pneumonia virus infection in sheep

Twenty-five sheep, experimentally (n = 15) or naturally (n = 6) infected with ovine progressive pneumonia virus and noninfected controls (n = 4), were evaluated for histological and ultrastructural lesions of mastitis. Histologically, nine of 15 experimentally infected sheep and all six naturally infected sheep had lympho-plasmacytic mastitis. Severity of the lesion increased with length of time after infection. Periductal lymphatic nodules were seen in five sheep experimentally infected for 2.8 years or longer and in five naturally infected sheep that were 3.7 years old or older. Ultrastructurally, responses to ovine progressive pneumonia virus were diffuse lympho-plasmacytic infiltrates in glandular interstitium, lymphocytic and occasional plasmacytic infiltrates in ductal walls and lumens, lymphoblasts surrounded by small lymphocytes in glandular interstitium, and degeneration of epithelium releasing cells and cellular debris into the lumen. Based on the prevalence of lesions, the mammary tissue was more susceptible to ovine progressive pneumonia virus than other target organs: lung, brain, and synovium. Lesions did not differ between breeds of sheep. Ovine progressive pneumonia virus was not seen in the mammary tissue but was isolated from 15 of 17 mammary glands.

Capillary electrophoresis of the scrapie prion protein from sheep brain

Scrapie in sheep and goats causes a progressive, degenerative disease of the central nervous system and is the prototype of other transmissible spongiform encephalopathies (TSE) found in humans and in animals. In samples of TSE-affected brains, unique rod-shaped structures are found and are infectious. These rods are composed of a protease-resistant, post-translationally modified cellular protein (PrPsc) that has a molecular mass of ca. 27,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Laboratory tests used for the diagnosis of scrapie detect PrPsc. The overall concentration of PrPsc in tissues is low. The present methods to diagnose scrapie are lengthy, require relatively large quantities of starting material to detect PrPsc and lack sensitivity. We explored the use of free zone capillary electrophoresis and immunocomplex formation to detect PrPsc in the brain tissue of infected sheep. Brain tissue from both infected (as confirmed by histological and biological tests) and from normal animals was used to prepare the PrPsc. After treatment with proteinase K and non-ionic detergents, PrPsc was solubilized and reacted with a rabbit antiserum specific for a peptide of the prion protein. Immunocomplex formation was observed for the samples from scrapie-infected brain but not for samples from normal brain. When a fluorescein-labeled goat anti-rabbit immunoglobulin was used as a second antibody, the detection of immunocomplex formation was enhanced both by the immunological technique and by using laser-induced fluorescence for detection. This same rabbit antiserum was used on immunoblot analysis. Three bands were observed for material from an infected sheep but none in preparations from brain material from normal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of antibody response to ovine lentivirus by using viral gene products expressed in a prokaryotic system

The polymerase chain reaction (PCR) was used to amplify, clone, and express eight DNA fragments encoding p25, p16, reverse transcriptase (RT) core, C'-terminal RT, N'- and C'-terminals of external (gp70), and transmembrane (gp40) envelope proteins from visna virus infectious recombinant DNA. Efforts were focused on characterizing the nature of the humoral immune response of ovine progressive pneumonia (OPP) virus infected animals and identifying the conserved and prime-reactive antigenic determinants that have potential diagnostic value. This communication reports that the N'-terminal region of gp40 appeared to be the most immunoreactive of the bacterially expressed proteins and could serve as a sensitive immunodiagnostic antigen for the detection of OPP infection.

Intraepithelial vibrio associated with acute typhlitis of young rabbits

A retrospective morphologic study was conducted on tissues from weanling laboratory rabbits with diarrheal disease of unknown cause. The consistent lesion was in the cecum and consisted of exaggerated degeneration and loss and replacement of surface absorptive cells. This was accompanied by hyperplasia of crypt epithelial cells and acute diffuse inflammation of the lamina propria and submucosa. Numerous bacteria, identified morphologically as vibrio sp., were in surface epithelial cells in the cecum of affected rabbits. This was demonstrated in 10 of 12 affected rabbits via light microscopic examination of Levaditi-stained histologic sections. The occurrence, intraepithelial location, and identification of the vibrio, as well as the associated cytopathology, was confirmed in four of the six ceca from affected rabbits examined by electron microscopy. Lesions were not seen in cecal mucosa of six healthy weanlings from the colony. Vibrio was seen in the intestinal and cecal lumina of one control by both Levaditi and electron microscopic methods; none had invaded the mucosa, however. The possibilities that vibrio had either a primary or secondary causal association with acute typhlitis and that the disease had a pathogenesis similar to that of primate shigellosis are discussed.

Cilia-associated respiratory bacillus in wild rats in central Iowa

Twenty-eight wild rats were live-trapped in central Iowa (USA) to estimate the prevalence of the cilia-associated respiratory (CAR) bacillus. Both light and electron microscopy were used to look for the Gram-negative, filamentous bacterium among cilia in tracheal and lung tissue sections. The organism was observed in the trachea of 20 rats with chronic respiratory disease and in the trachea of three of eight normal rats. Therefore, the organism appears to be common among wild rats in central Iowa.

Morphogenesis and structure of caprine respiratory syncytial virus

Cell cultures inoculated with caprine respiratory syncytial virus (RSV) were studied with light, fluorescent, and electron microscopy to determine the morphogenesis and structure of the virus. Small syncytia were seen after 36 hours in culture. After 48 hours in culture, syncytia were large and numerous and pleomorphic cytoplasmic inclusions were seen. These inclusions were more pronounced and numerous later in the infection cycle. Indirect immunofluorescence revealed a diffuse to granular cytoplasmic fluorescence with fluorescing fibrils on the cell surface. With the electron microscope, filamentous (100-160 nm) and spherical (90-160 nm) particles were seen budding off the cell membrane. The number of virus buds diminished with increased size of syncytia. Granular pleomorphic cytoplasmic inclusions were seen near the nucleus, and electron dense masses were seen just beneath the cytoplasmic membrane where large quantities of virus were budding from the cell surface. The first type of inclusion had distinct borders; the second diffuse borders and appeared to contain viral nucleoprotein. Negative staining revealed spherical, pleomorphic, and filamentous forms of the virus; the last form predominated. The virions were covered with club-shaped projections, and the nucleocapsids were seen as fragile strands frequently broken into fragments or as isolated rings. Morphogenesis and structure of the caprine RSV places this virus with the Pneumovirus genus of the Paramyxoviridae family.

Improvements in a competition assay to detect scrapie prion protein by capillary electrophoresis

Scrapie in sheep and goats is the prototype of transmissible spongiform encephalopathies found in humans and animals. A feature of these diseases is the accumulation of rod-shaped fibrils in the brain that form from an aggregated protein. This protein is a protease-resistant form of a normal host cell protein. When the aggregated protein is denatured in SDS and beta-mercaptoethanol, a monomer form (prion protein) with a molecular mass of 27 kDa is observed. Free zone capillary electrophoresis and peptides labeled with fluorescein were used to detect the prion protein through competition for a labeled peptide in immune complex formation. The separation of the immune complexes from the unbound peptide using 200 mM Tricine (pH 8.0) was faster and was better resolved than that obtained with phosphate or borate buffer systems. The amount of immune complex formation was dependent on the amount of antibody in the assay. The amount of bound labeled peptide and unbound labeled peptide could be measured directly by calculating the area of each respective peak. As increasing amounts of unlabeled peptide were added to the assay, a concentration dependent reduction in the immune complex peak was observed. The assay could detect less than 10.0 fmol of unlabeled peptide. There was a quantitative difference in the competition of preparations from scrapie infected sheep brain and normal sheep brain.