Monoclonal antibodies to conformational epitopes of the surface glycoprotein of caprine arthritis-encephalitis virus: potential application to competitive-inhibition enzyme-linked immunosorbent assay for detecting antibodies in goat sera

Argentinian small ruminant lentivirus (SRLV) p55gag antigen fused to maltose binding protein to use in SRLV serological confirmatory diagnosis

The complete gag gene from small ruminant lentiviruses (SRLV) encodes for a polyprotein of 55 kDa, known as p55gag. p55gag presents multiple antigenic epitopes, which can be recognized by antibodies, increasing the opportunity to detect SRLV-positive animals. Therefore, this polyprotein is considered an excellent candidate to use in diagnostic tests to detect antibodies against SRLV. Different studies have suggested that the selection of the recombinant antigen, which must be representative of the virus strains circulating in the test population, is crucial to avoid false negative results. Thus, the use of proteins from different viral strains isolated from goats or sheep of a given region or country may be a useful strategy to increase the ability to detect SRLV-infected animals. In the present study, the pMAL-p5X vector was used to express and purify p55gag (now called rp55gag for recombinant polyprotein 55 gag). The cloned gene was inserted downstream from the malE gene of Escherichia coli, which encodes a maltose-binding protein (MBP), resulting in the expression of an MBP fusion protein. The complete gag gene was amplified by RT-PCR. Finally, after digestion, the product was cloned into the pMAL-p5X vector and used to transform E. coli ER2325 cells. After the purification of MBP-rp55gag by affinity chromatography, the eluted fraction was observed by SDS-PAGE and Western Blot (WB). The WB was carried out with 85 serum samples from small ruminants previously analysed and compared by two commercial ELISAs. The results show that 76 of the serum samples were concordant with those by both ELISAs. Regarding the other nine serum samples, which showed discordant results between both ELISAs, were positive by WB. The results thus show that the rp55gag could be considered as an antigen in a confirmatory diagnostic assay to detect SRLV by WB. For this purpose, a future study with a high number of sera to determine the test specificity and sensitivity, using the p55gag of the circulating strain in Argentina will be necessary.

Degradation of C-terminal tag sequences on domain antibodies purified from E. coli supernatant

Expression of recombinant proteins often takes advantage of peptide tags expressed in fusion to allow easy detection and purification of the expressed proteins. However, as the fusion peptides most often are flexible appendages at the N- or C-terminal, proteolytic cleavage may result in removal of the tag sequence. Here, we evaluated the functionality and stability of 14 different combinations of commonly used tags for purification and detection of recombinant antibody fragments. The tag sequences were inserted in fusion with the c-terminal end of a domain antibody based on the HEL4 scaffold in a phagemid vector. This particular antibody fragment was able to refold on the membrane after blotting, allowing us to detect c-terminal tag breakdown by use of protein A in combination with detection of the tags in the specific constructs. The degradation of the c-terminal tags suggested specific sites to be particularly prone to proteolytic cleavage, leaving some of the tag combinations partially or completely degraded. This specific work illustrates the importance of tag design with regard to recombinant antibody expression in E. coli, but also aids the more general understanding of protein expression.

Generation of monoclonal antibody MS17-57 targeting secreted alkaline phosphatase ectopically expressed on the surface of gastrointestinal cancer cells

Background

Therapeutic antibody development is one of the fastest growing areas of the pharmaceutical industry. Generating high-quality monoclonal antibodies against a given therapeutic target is crucial for successful drug development. However, due to immune tolerance, making it difficult to generate antibodies using conventional approaches.

Methodology/Findings

Mixed four human gastric cancer (GC) cell lines were used as the immunogen in A/J mice; sixteen highly positive hybridoma colonies were selected via fluorescence-activated cell sorting-high throughput screening (FACS-HTS) using a total of 20,000 colonies in sixty-seven 96-well plates against live cells (mixed human GC cells versus human PBMC controls). MS17-57 and control commercial Alkaline Phosphatase (ALP) mAbs were used to confirm the target antigens (Ags), which were identified as ALPs expressed on the GC cell surface through a combination of western blot, immunoprecipitation and mass spectrometry (MS).

MS identified the Ags recognized by MS17-57 to be two variants of a secreted ALP, PALP and IALP (Placental and intestinal ALP). These proteins belong to a hydrolase enzyme family responsible for removing phosphate groups from many types of molecules. Immunofluorescence staining using MS17-57 demonstrated higher staining of gastrointestinal (GI) cancer tissues compared to normal GI tissues (P<0.03), and confirmed binding of MS17-57 to be restricted to a functional epitope expressed on the cancer cell surface. Proliferation assays using the PALP/IALP-expressing GC cell lines demonstrated that MS17-57 inhibited cell growth by 32±8%. Transwell cell migration assays documented that MS17-57 can inhibit PALP/IALP-expressing GI cancer cell migration by 25±5%. MS17-57 mAb inhibited tumor growth in nude mice.

Conclusions

Our findings indicate that PALP and IALP can be ectopically expressed on extracellular matrix of GI cancers, and that MS17-57 directed against PALP/IALP can inhibit GI cancer cells growth and migration invitro and invivo. This investigation provides an example of identification of cancer biomarkers representing promising therapeutic targets using mAb generated through a novel HTS technology.

Diagnostic assays used to control small ruminant lentiviruses

The serologic diagnostic tests, such as the agar gel immunodiffusion assay and various types of enzyme-linked immunosorbent assays (ELISAs), have contributed to the reduction of small ruminant lentivirus (SRLV) infections worldwide. Because there are no treatments or efficacious vaccines, the serologic diagnostic tests have supported most of the eradication efforts by testing and removal or separation of adult animals that generate antibodies to SRLVs. With the advent of molecular diagnostics, standard and quantitative polymerase chain reaction (PCR)-based assays for the detection of provirus in peripheral blood cells are becoming more common and aid in the detection of infected goats and sheep before antibody detection by ELISA in some animals. Performance of the serologic and molecular diagnostic tests is dependent upon a number of factors, including the format of the assay, the percentage of identity between the viral nucleotide sequences in a flock or herd of a certain geographic region and the sequences used to generate SRLV test reagents, and the intrinsic pathogenesis or amount of provirus and SRLV antibody generated in a species or individual small ruminant. In addition, small ruminant genomics may help with establishing genetic markers of SRLV infection and disease, which could also aid eradication or reduction of SRLVs from herds and flocks throughout the world.

MAEDI-VISNA VÍRUS: PRODUÇÃO DE ANTÍGENO, ANÁLISE PROTÉICA E ANTIGÊNICA

RESUMO A Maedi-Visna é uma doença persistente, progressiva e debilitante em ovinos causada por lentivírus que resulta primariamente em pneumonia intersticial e pode estar associada a mamite e encefalite. Este trabalho teve como objetivo produzir antígeno a partir do vírus Maedi-Visna total para utilização em ensaios imunoenzimáticos. Na produção do antígeno foram utilizados cultivos primários de células de membrana sinovial caprina, infectados com amostra padrão (MVVK1514). As suspensões virais foram tituladas e o antígeno semipurificado pela precipitação em PEG (polietilenoglicol) e ultracentrifugação. Foram realizadas eletroforese em gel de poliacrilamida (SDS-PAGE) e Western Blotting (WB). A SDS-PAGE de origem viral e do meio de cultivo resultou em várias bandas protéicas. No WB constatou-se a presença de sete proteínas imunogênicas de pesos moleculares aproximados de 16, 27, 35, 50, 42, 63 e 123 kDa. Destas, três proteínas (16, 27 e 50 kDa) apresentaram boa reação imunogênica. O trabalho abre perspectivas da utilização de testes imunoenzimáticos com maior sensibilidade para lentivírus ovino.

WESTERN BLOT PARA O DIAGNÓSTICO DAS INFECÇÕES PELOS LENTIVÍRUS DE PEQUENOS RUMINANTES EM CAPRINOS: UM MÉTODO SIMPLES PARA A PRODUÇÃO DE ANTÍGENO

RESUMO O sorodiagnóstico das lentiviroses de caprinos e ovinos é realizado principalmente pela imunodifusão em gel de agar (AGID) e/ou ELISA. Embora relativamente simples, esses métodos não identificam os antígenos virais reconhecidos na resposta imune do animal examinado, por isso o western blot (WB) vem ganhando maior relevância como ferramenta de diagnóstico dessas enfermidades. Neste trabalho, o antígeno utilizado no WB foi obtido através de um sistema simplificado de purificação: concentração por diálise do sobrenadante de culturas celulares infectadas, seguido de centrifugação em gradiente contínuo de sacarose. A separação das proteínas virais foi obtida por SDS-PAGE a 10% e a transferência para membranas de nitrocelulose realizada pelo sistema semi-úmido. A revelação das membranas mostrou reconhecimento pelo soro padrão positivo de cinco proteínas, com pesos moleculares de 14-16, 25, 40, 50 e 70 kDa. Todas as 8 amostras de soro caprino, positivas na ADIG, reconheceram pelo menos uma banda proteíca no immunoblot, variando contudo o número de bandas reconhecidas. Reação positiva à glícoproteína 40 (gp 40) foi observada em quatro animais, com intensidade de reação discreta em três deles. Dois animais apresentaram reação positiva à proteína 16 (p16), e dois à gp 50, de pouca intensidade. Quanto à gp 70, proteína que, embora reagisse com o soro padrão positivo, não foi reconhecida por nenhum dos soros testados. Estes resultados sugerem que o WB pode ser empregado para o sorodiagnóstico rotineiro das lentiviroses, ensejando estudos mais amplos do padrão de reconhecimento dos antígenos apresentados por este novo sistema de purificação parcial de componentes virais.

Development and validation of an ovine progressive pneumonia virus quantitative PCR

Ovine progressive pneumonia virus (OPPV) infects at least one sheep in 81% of U.S. sheep flocks, as determined by serology, and can cause viral mastitis, arthritis, dyspnea, and cachexia. Diagnostic tests that quantify OPPV proviral load in peripheral blood leukocytes (PBL) provide an additional method for identification of infected sheep and may help to further understanding of the pathogenesis of OPPV-induced disease. In this study, we compared a new OPPV real-time quantitative PCR (qPCR) assay specific for the transmembrane region of the envelope gene (tm) with a competitive inhibition enzyme-linked immunosorbent assay (cELISA) using 396 PBL samples and sera from Idaho sheep. The OPPV qPCR had a positive concordance of 96.2% +/- 2.3% and a negative concordance of 97.7% +/- 2.5% compared to the cELISA, with a kappa value of 0.93, indicating excellent agreement between the two tests. In addition, the presence of tm in the three OPPV qPCR-positive and cELISA-negative sheep and in 15 sheep with different OPPV proviral loads was confirmed by cloning and sequencing. These data indicate that the OPPV qPCR may be used as a supplemental diagnostic tool for OPPV infection and for measurement of viral load in PBLs of infected sheep.

Localization of a TNF-activated transcription site and interactions with the gamma activated site within the CAEV U3 70 base pair repeat

The cytokines TNFalpha and IFNgamma have previously been shown to activate caprine arthritis encephalitis virus (CAEV) transcription. Increased viral titers correlate with increased lesion severity. Therefore, TNFalpha and IFNgamma may augment the caprine arthritis lesion by increasing viral titers. CAEV transcription is under the control of the viral promoter within the U3 region of the long terminal repeat. A set of U3 deletion mutants was generated and used to establish stably integrated, U937-based cell lines. These cell lines were utilized to define the required promoter sequences for cytokine-induced transcriptional activation. Here we have identified a novel 17 nucleotide TNF-activated site within the U3 region 70 bp repeat which is both required and sufficient in a minimal construct for TNFalpha-induced CAEV transcriptional activation. In contrast to the results of previous studies with IFNgamma, we found that multiple sequences within the U3 region 70 bp repeat were required for IFNgamma-activation of the CAEV promoter. The results identify previously unrecognized complexity in the CAEV promoter that may be relevant to viral replication and disease.

TNFα and GM-CSF-induced activation of the CAEV promoter is independent of AP-1

Caprine arthritis encephalitis virus transcription is under the control of the viral promoter within the long terminal repeat. Previous studies with the closely related maedi visna lentivirus have indicated that viral transcription is dependent upon the AP-1 transcription factor. Other studies have indicated a potential role for the cytokines TNFalpha and GM-CSF in CAEV pathogenesis by increasing viral loads in infected tissues. The hypotheses that AP-1 transcription factors are necessary for transcriptional activation of the CAEV promoter and that CAEV transcriptional activation results from treatment with the cytokines GM-CSF and TNFalpha were tested with a stably transduced U937 cell line. Here, we found that TNFalpha and GM-CSF activated CAEV transcription in U937 cells. However, this activation effect was not blocked by SP600125, an inhibitor of Jun N-terminal kinase. SP600125 effectively prevented Jun phosphorylation in cells subsequently treated with cytokines. The cytokines TNFalpha and GM-CSF therefore activate CAEV transcription, and this effect occurs independently of AP-1. A set of progressive deletion mutants was utilized to show that TNFalpha-induced expression depends on an element or elements within the U3 70-bp repeat.

Surface envelope glycoprotein is B-lymphocyte immunodominant in sheep naturally infected with ovine progressive pneumonia virus

The B-lymphocyte-immunodominant antigen involved in naturally ovine progressive pneumonia virus (OPPV)-infected mature sheep remains unknown. Therefore, the amount of antibody in sera from 10 naturally OPPV-infected sheep was evaluated by immunoprecipitation (IP) of the major viral proteins in [(35)S]methionine/cysteine-labeled OPPV (whole virus) lysate. Using an excess of OPPV proteins in whole-virus lysate, 8 out of 10 sheep had the highest serum antibody IP endpoint titers to the gp135 surface envelope glycoprotein (SU). Also, 2 out of 10 sheep had equivalent serum antibody IP endpoint titers to the transmembrane glycoprotein oligomer (TM90) and SU. Since these data indicate that SU is the immunodominant protein in most mature sheep persistently infected with OPPV, SU-specific diagnostic serological assays can be utilized for OPPV diagnosis.

Mutations increasing exposure of a receptor binding site epitope in the soluble and oligomeric forms of the caprine arthritis-encephalitis lentivirus envelope glycoprotein

The caprine arthritis-encephalitis (CAEV) and ovine maedi-visna (MVV) viruses are resistant to antibody neutralization, a feature shared with all other lentiviruses. Whether the CAEV gp135 receptor binding site(s) (RBS) in the functional surface envelope glycoprotein (Env) is protected from antibody binding, allowing the virus to resist neutralization, is not known. Two CAEV gp135 regions were identified by extrapolating a gp135 structural model that could affect binding of antibodies to the RBS: the V1 region and a short sequence analogous in position to the human immunodeficiency virus type 1 gp120 loop B postulated to be located between two major domains of CAEV gp135. Mutation of isoleucine-166 to alanine in the putative loop B of gp135 increased the affinity of soluble gp135 for the CAEV receptor(s) and goat monoclonal antibody (Mab) F7-299 which recognizes an epitope overlapping the gp135 RBS. The I166A mutation also stabilized or exposed the F7-299 epitope in anionic detergent buffers, indicating that the I166A mutation induces conformational changes and stabilizes the RBS of soluble gp135 and enhances Mab F7-299 binding. In contrast, the affinity of a V1 deletion mutant of gp135 for the receptor and Mab F7-299 and its structural stability did not differ from that of the wild-type gp135. However, both the I166A mutation and the V1 deletion of gp135 increased cell-to-cell fusion activity and binding of Mab F7-299 to the oligomeric Env. Therefore, the CAEV gp135 RBS is protected from antibody binding by mechanisms both dependent and independent of Env oligomerization which are disrupted by the V1 deletion and the I166A mutation, respectively. In addition, we found a correlation between side-chain beta-branching at amino acid position 166 and binding of Mab F7-299 to oligomeric Env and cell-to-cell fusion, suggesting local secondary structure constraints in the region around isoleucine-166 as one determinant of gp135 RBS exposure and antibody binding.

Diagnostic tests for small ruminant lentiviruses

Maedi visna virus and caprine arthritis encephalitis virus are closely related retroviruses that cause chronic inflammatory disease in small ruminants. The infections are characterised by insidious onset and slow progression. Diagnosis of infection is usually by serological testing. A variety of assays are available for this purpose, though the relative sensitivity and specificity of these assays has not been compared systematically. Here we review recent developments in laboratory diagnostic methods and their use in field diagnosis. The results suggest that a combination of ELISA and PCR might afford optimal detection of SRLV infection.

Glycosylation of immunodominant linear epitopes in the carboxy-terminal region of the caprine arthritis-encephalitis virus surface envelope enhances vaccine-induced type-specific and cross-reactive neutralizing antibody responses

This study evaluated type-specific and cross-reactive neutralizing antibodies induced by immunization with modified surface glycoproteins (SU) of the 63 isolate of caprine arthritis-encephalitis lentivirus (CAEV-63). Epitope mapping of sera from CAEV-infected goats localized immunodominant linear epitopes in the carboxy terminus of SU. Two modified SU (SU-M and SU-T) and wild-type CAEV-63 SU (SU-W) were produced in vaccinia virus and utilized to evaluate the effects of glycosylation or the deletion of immunodominant linear epitopes on neutralizing antibody responses induced by immunization. SU-M contained two N-linked glycosylation sites inserted into the target epitopes by R539S and E542N mutations. SU-T was truncated at 518A, upstream from the target epitopes, by introduction of termination codons at 519Y and 521Y. Six yearling Saanen goats were immunized subcutaneously with 30 microg of SU-W, SU-M, or SU-T in Quil A adjuvant and boosted at 3, 7, and 16 weeks. SU antibody titers determined by indirect enzyme-linked immunosorbent assay demonstrated anamnestic responses after each boost. Wild-type and modified SU-induced type-specific CAEV-63 neutralizing antibodies and cross-reactive neutralizing antibodies against CAEV-Co, a virus isolate closely related to CAEV-63, and CAEV-1g5, an isolate geographically distinct from CAEV-63, were determined. Immunization with SU-T resulted in altered recognition of SU linear epitopes and a 2.8- to 4.6-fold decrease in neutralizing antibody titers against CAEV-63, CAEV-Co, and CAEV-1g5 compared to titers of SU-W-immunized goats. In contrast, immunization with SU-M resulted in reduced recognition of glycosylated epitopes and a 2.4- to 2.7-fold increase in neutralizing antibody titers compared to titers of SU-W-immunized goats. Thus, the glycosylation of linear immunodominant nonneutralization epitopes, but not epitope deletion, is an effective strategy to enhance neutralizing antibody responses by immunization.

Antibody response to the surface envelope of caprine arthritis-encephalitis lentivirus: disease status is predicted by SU antibody isotype

This study evaluated the hypothesis that the disease status of Saanen goats infected with caprine arthritis-encephalitis lentivirus (CAEV) is associated with the focus of immune responses to viral antigens, particularly the surface envelope glycoprotein (SU). Specifically, we have proposed that Th2 responses promote progressive immune-mediated arthritis, whereas Th1 responses restrict virus replication and development of clinical disease. The present study determined the isotype of SU antibodies associated with progressor and long-term nonprogressor (LTNP) status. We show that chronically infected goats that develop clinical arthritis have predominantly IgG1 antibodies to SU during both preclinical and clinical stages of disease, whereas SU antibodies of LTNP goats are relatively biased toward IgG2. Additional studies determined the isotype of SU antibodies induced initially by CAEV infection. These experiments show that initial IgG1-dominated responses to SU are associated with subsequent development of preclinical inflammatory joint lesions, whereas lack of joint pathology is associated with an IgG2 bias of initial responses to SU. Our results using the CAEV model suggest that isotype bias of SU antibodies is a reliable indicator of clinical disease caused by lentiviruses. Isotype analysis may be a useful method to screen candidate lentiviral vaccines intended to prevent disease progression.

Caprine arthritis-encephalitis virus envelope surface glycoprotein regions interacting with the transmembrane glycoprotein: structural and functional parallels with human immunodeficiency virus type 1 gp120

A sequence similarity between surface envelope glycoprotein (SU) gp135 of the lentiviruses maedi-visna virus and caprine arthritis-encephalitis virus (CAEV) and human immunodeficiency virus type 1 (HIV-1) gp120 has been described. The regions of sequence similarity are in the second and fifth conserved regions of gp120, and the similarity is highest in sequences coinciding with beta-strands 4 to 8 and 25, which are located in the most virion-proximal region of the gp120 inner domain. A subset of this structure, formed by gp120 beta-strands 4, 5, and 25, is conserved in most or all lentiviruses. Because of the orientation of gp120 on the virion, this highly conserved virion-proximal region of the gp120 core may interact with the transmembrane glycoprotein (TM) together with the amino and carboxy termini of full-length gp120. Therefore, interactions between SU and TM of lentiviruses may be structurally related. Here we tested whether the amino acid residues in the putative virion-proximal region of CAEV gp135 comprising putative beta-strands 4, 5, and 25, as well as its amino and carboxy termini, are important for stable interactions with TM. An amino acid change at gp135 position 119 or 521, located in the turn between putative beta-strands 4 and 5 and near beta-strand 25, respectively, specifically disrupted the epitope recognized by monoclonal antibody 29A. Thus, similar to the corresponding gp120 regions, these gp135 residues are located in close proximity to each other in the folded protein, supporting the hypothesis of a structural similarity between the gp120 virion-proximal inner domain and gp135. Amino acid changes in the amino- and carboxy-terminal and putative virion-proximal regions of gp135 increased gp135 shedding from the cell surface, indicating that these gp135 regions are involved in interactions with TM. Our results indicate structural and functional parallels between CAEV gp135 and HIV-1 gp120 that may be more broadly applicable to the SU of other lentiviruses.

Caprine arthritis-encephalitis virus-infected goats can generate human immunodeficiency virus-gp120 cross-reactive antibodies(1)

Lentiviruses display surprisingly disparate clinical manifestations in their specific hosts, share complex genetic structures, and exhibit extensive diversity, particularly in their envelope genes. The envelope protein, gp135, of caprine arthritis-encephalitis virus (CAEV) has minimal primary sequence homology to gp120, the envelope protein of human immunodeficiency virus (HIV). Nevertheless, they bear certain similarities in that they both possess five variable regions, both are heavily glycosylated, and both share short sequence motifs. We establish a further relationship and demonstrate that some goats, infected with CAEV, possess gp135-specific antibodies which cross-react with gp120 from several HIV strains, provided the protein is expressed in insect cells. We show that, although the cross-reactivity of these immunoglobulins depends on the level of glycosylation, nevertheless, some antibodies recognize the protein epitopes on gp120, at least some of which are linear in character. Further characterization of this unexpected cross-reaction will define its potential therapeutic utility.

Actinobacillus actinomycetemcomitans serotype d-specific antigen contains the O antigen of lipopolysaccharide

Actinobacillus actinomycetemcomitans is a gram-negative, facultatively anaerobic bacterium which is associated especially with aggressive forms of periodontitis. Contradictory results on the localization of the A. actinomycetemcomitans serotype-specific antigen have been reported. The aim of the present study was to characterize the A. actinomycetemcomitans serotype d-specific antigen. The antigen was isolated by affinity chromatography. The affinity column was prepared from immunoglobulin G isolated from rabbit antiserum raised against A. actinomycetemcomitans serotype d. The isolated antigen was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and silver staining, all of which revealed a ladder-like structure typical for the O antigen of lipopolysaccharide (LPS). In a displacement enzyme-linked immunosorbent assay (ELISA), the isolated antigen displaced in a concentration-dependent manner the binding of the polyclonal rabbit antiserum raised against A. actinomycetemcomitans serotype d to the competing whole-cell serotype d antigen. The isolated antigen contained LPS, and an equal concentration of LPS isolated from A. actinomycetemcomitans serotype d gave a similar displacement curve in the ELISA. In order to test the immunogenic properties of the isolated antigen, it was used to immunize a rabbit. The antiserum raised against the isolated antigen displayed specificity in Western blotting and ELISA similar to that of antibody raised against LPS isolated from A. actinomycetemcomitans serotype d. In conclusion, our results show that the A. actinomycetemcomitans serotype d-specific antigen contains the O-antigenic structure of LPS.

Detection of serum antibodies to ovine progressive pneumonia virus in sheep by using a caprine arthritis-encephalitis virus competitive-inhibition enzyme-linked immunosorbent assay

A competitive-inhibition enzyme-linked immunosorbent assay (cELISA) for detection of antibodies to the surface envelope (SU) of caprine arthritis-encephalitis virus (CAEV) was recently reported (L. M. Herrmann, W. P. Cheevers, T. C. McGuire, D. Scott Adams, M. M. Hutton, W. G. Gavin, and D. P. Knowles, Clin. Diagn. Lab. Immunol. 10:267-271, 2003). The cELISA utilizes CAEV-63 SU captured on microtiter plates using the monoclonal antibody (MAb) F7-299 and measures competitive displacement of binding of the anti-CAEV MAb GPB 74A by goat serum. The present study evaluated the CAEV cELISA for detection of antibodies to ovine progressive pneumonia virus (OPPV) in sheep. Three hundred thirty-two sera were randomly selected from 21,373 sheep sera collected throughout the United States to determine the sensitivity and specificity of cELISA and agar gel immunodiffusion (AGID) based on immunoprecipitation (IP) of [35S]methionine-labeled OPPV antigens as a standard of comparison. A positive cELISA test was defined as >20.9 percent inhibition (% I) of MAb 74A binding based on two standard deviations above the mean % I of 191 IP-negative sheep sera. At this cutoff, there were 2 of 141 false-negative sera (98.6% sensitivity) and 6 of 191 false-positive sera (96.9% specificity). Sensitivity and specificity values for IP-monitored AGID were comparable to those for cELISA for 314 of 332 sera with unambiguous AGID results. Concordant results by cELISA and IP resolved 16 of the 18 sera that were indeterminate by AGID. Additional studies evaluated cELISA by using 539 sera from a single OPPV-positive flock. Based on IP of 36 of these sera, there was one false-negative by cELISA among 21 IP-positive sera (95.5% sensitivity) and 0 of 15 false-positives (100% specificity). We conclude that the CAEV cELISA can be applied to detection of OPPV antibodies in sheep with high sensitivity and specificity.

Competitive-inhibition enzyme-linked immunosorbent assay for detection of serum antibodies to caprine arthritis-encephalitis virus: diagnostic tool for successful eradication

A competitive-inhibition enzyme-linked immunosorbent assay (cELISA) was evaluated for the detection of serum antibodies to the surface envelope (SU) of caprine arthritis-encephalitis virus (CAEV) in goats. This assay utilized 96-well microtiter plates containing CAEV-63 SU captured by monoclonal antibody (MAb) F7-299 and measured the competitive displacement of horseradish peroxidase-conjugated MAb GPB 74A binding by undiluted goat sera (F. Ozyörük, W. P. Cheevers, G. A. Hullinger, T. C. McGuire, M. Hutton, and D. P. Knowles, Clin. Diagn. Lab. Immunol. 8:44-51, 2001). Two hundred serum samples from goats in the United States were used to determine the sensitivity and specificity of cELISA based on the immunoprecipitation (IP) of [(35)S]methionine-labeled viral antigens as a standard of comparison. A positive cELISA was defined as >33.2% inhibition of MAb 74A binding based on 2 standard deviations above the mean percent inhibition of 140 IP-negative serum samples. At this cutoff value, there were 0 of 60 false-negative sera (100% sensitivity) and 5 of 140 false-positive sera (96.4% specificity). Additional studies utilized IP-monitored cELISA to establish a CAEV-free herd of 1,640 dairy goats.

Prime-boost vaccination with plasmid DNA encoding caprine-arthritis encephalitis lentivirus env and viral SU suppresses challenge virus and development of arthritis

This study evaluated the efficacy of prime-boost vaccination for immune control of caprine arthritis-encephalitis virus (CAEV), a macrophage tropic lentivirus that causes progressive arthritis in the natural host. Vaccination of Saanen goats with pUC-based plasmid DNA expressing CAEV env induces T helper type 1 (Th1) biased immune responses to vector-encoded surface envelope (SU), and the plasmid-primed Th1 response is expanded following boost with purified SU in Freund's incomplete adjuvant (SU-FIA) (J. C. Beyer et al., 2001, Vaccine 19, 1643-1651). Four goats vaccinated with env expression plasmids and boosted with SU-FIA were challenged intravenously with 1 x 10(4) TCID(50) of CAEV at 428 days after SU-FIA boost and evaluated by immunological, virological, and disease criteria. Controls included two goats primed with pUC18 and eight unvaccinated goats. Goats receiving prime-boost vaccination with CAEV env plasmids and SU-FIA became infected but suppressed postchallenge virus replication, provirus loads in lymph node, and development of arthritis for at least 84 weeks.

Effect of caprine arthritis-encephalitis virus infection on expression of interleukin-16 in goats

OBJECTIVE

To determine the effect of caprine arthritis-encephalitis virus (CAEV) infection on expression of interleukin-16 (IL-16).

ANIMALS

6 goats experimentally infected with CAEV and 6 age-matched healthy uninfected control goats.

PROCEDURE

Peripheral blood mononuclear cells (PBMCs) and synovial membrane cells from infected and control goats cultured with or without phytohemagglutinin were analyzed for IL-16 mRNA by use of a reverse transcriptase-polymerase chain reaction assay with goat-specific primers, after cloning and sequencing of a 384-bp fragment of the goat IL-16 gene. Synovial fluid, serum, and culture supernatants of PBMCs and synovial cells of control and CAEV-infected goats were analyzed for IL-16 by use of an ELISA.

RESULTS

The 384-bp product was 86% homologous to the corresponding human IL-16 nucleotide sequence. Higher expression of IL-16 mRNA in PBMCs (unstimulated or stimulated with phytohemagglutinin) was detected in samples from CAEV-infected goats, compared with control goats, but the difference was not significant. Synovial membrane cells infected in vitro had higher expression than uninfected control cells. Higher IL-16 concentration was detected in synovial fluid, serum, and culture supernatants of PBMCs of infected goats than in samples from control goats.

CONCLUSIONS AND CLINICAL RELEVANCE

infection with CAEV increases expression of IL-16, a proinflammatory and chemotactic cytokine. This cytokine appears to be constitutively expressed at low concentrations in normal uninfected PBMCs and synovial membrane cells. Increased production of IL-16 in CAEV infection may partly be responsible for increased lymphoid cell infiltrations observed in arthritic joints and other tissues of CAEV-infected goats.

Differential receptor usage of small ruminant lentiviruses in ovine and caprine cells: host range but not cytopathic phenotype is determined by receptor usage

The ovine maedi-visna (MVV) and caprine arthritis-encephalitis (CAEV) small ruminant lentiviruses (SRLV) exhibit differential species tropism and cytopathic effects in vitro. Icelandic MVV-K1514 is a lytic SRLV which can infect cells from many species in addition to ruminants, whereas a lytic North American MVV strain (85/34) as well as nonlytic MVV strain S93 and CAEV can infect only ruminant cells. In the present study, we determined if differential receptor usage in sheep and goat cells is the basis of differential species tropism or cytopathic phenotype of SRLV. Infection interference assays in sheep and goat synovial membrane cells using pseudotyped CAEV vectors showed that North American MVV strains 85/34 and S93 and CAEV use a common receptor (SRLV receptor A), whereas MVV-K1514 uses a different receptor (SRLV receptor B). In addition, human 293T cells expressing CAEV but not MVV-K1514 envelope glycoproteins fused with a goat cell line persistently infected with MVV-K1514, indicating that MVV-K1514 does not use SRLV receptor A for cell-to-cell fusion. Therefore, our results indicate that the differential species tropism of SRLV is determined by receptor usage. However, receptor usage is unrelated to cytopathic phenotype.