Severity of arthritis is predicted by antibody response to gp135 in chronic infection with caprine arthritis-encephalitis virus

An Immunodominant Region of the Envelope Glycoprotein of Small Ruminant Lentiviruses May Function as Decoy Antigen

(1) Background: Small ruminant lentiviruses (SRLV) persist in infected goats that mount a strong humoral immune response characterized by low neutralizing titers. In this study, we characterized the antibody response to SU5, a variable, immunodominant epitope of the envelope glycoprotein of SRLV. We tested the working hypothesis that the variability of SU5 reflects escape from neutralizing antibody. (2) Methods: Affinity purified anti-SU5 antibody were tested for their neutralizing activity to the homologous lentivirus. Virus culture supernatant—in native form or following sonication and filtration—was used to test the ability of free envelope glycoproteins to compete for binding in a SU5-peptide-ELISA. (3) Results: Anti-SU5 antibodies are not neutralizing, strongly suggesting that they do not bind intact viral particles. In contrast, shed envelope glycoproteins efficiently compete for binding in a SU5-ELISA, providing convincing evidence that the SU5 epitope is exposed only on shed envelope glycoproteins. (4) Conclusions: Our results show that the antibody engaging SU5 is not neutralizing and does not appear to bind to SU expressed at the surface of virus particles. We propose that SU5 is a potential decoy epitope exposed on shaded envelope glycoproteins, luring the humoral immune response in committing an original antigenic sin to a functionally irrelevant epitope.

Use of two commercial caprine arthritis-encephalitis immunoenzymatic assays for screening of arthritic goats

Roughly one-fourth of goats infected with small ruminant lentivirus (SRLV) develop caprine arthritis-encephalitis (CAE). We compared the profile of antibody response to surface glycoprotein (SU), and combined transmembrane glycoprotein and capsid protein (TM/CA) in SRLV-infected arthritic and asymptomatic goats, and determined the ability of 2 commercial ELISAs to distinguish between arthritic and asymptomatic goats. We used sera from 312 SRLV-seropositive dairy goats in a whole-virus ELISA; 222 were collected from arthritic goats and 90 from apparently healthy goats. Sera were screened with a competitive inhibition ELISA based on SU antigen (SU-ELISA) and an indirect ELISA based on TM and CA antigens (TM/CA-ELISA). Receiver operating characteristic (ROC) curves were prepared for both ELISAs, and areas under the ROC curves (AUC) were compared. The proportion of goats with antibody response stronger to SU antigen than to TM/CA antigen was significantly higher among arthritic than asymptomatic goats (58.1% vs. 28.9%; p < 0.001). Antibody response to SU antigen was a good predictor of the arthritic form of CAE: AUC for SU-ELISA was 89.7% (95% CI: 85.2%, 94.2%), compared to 59.3% (95% CI: 51.9%, 66.8%) for TM/CA-ELISA ( p < 0.001). With the cutoff set at percentage of inhibition of 56%, SU-ELISA had sensitivity of 86.9% (95% CI: 81.9%, 90.7%) and specificity of 84.4% (95% CI: 75.6%, 90.5%) in discriminating between arthritic and asymptomatic goats.

Influence of true within-herd prevalence of small ruminant lentivirus infection in goats on agreement between serological immunoenzymatic tests

The study was conducted to evaluate influence of the true within-herd prevalence of small ruminant lentivirus (SRLV) infection on agreement beyond chance between three different types of commercial serological ELISAs. Blood samples were collected from 865 goats from 12 dairy goat herds. Serum samples were tested using three commercial ELISA kits: whole-virus indirect ELISA (wELISA), indirect ELISA based on recombined TM and CA antigens (TM/CA-ELISA), and competitive-inhibition ELISA based on SU antigen (SU-ELISA). Herds were classed into three prevalence strata of high (>50%), moderate (10-50%) and low (<10%) true within-herd prevalence of SRLV infection. The latter was estimated on the basis of results of wELISA adjusted by its sensitivity and specificity. Agreement beyond chance between the three ELISAs was assessed at two levels. First, the general agreement was determined using two coefficients corrected for chance-agreement: Cohen's kappa and Gwet's AC₁. Then, agreement between tests was evaluated using Gwet's AC₁ separately in the three prevalence strata and compared between them by computing 95% confidence intervals for differences with a Bonferroni correction for multiple comparisons. The general agreement between the three tests was very good: wELISA and TM/CA-ELISA - Cohen's kappa of 81.8% (CI 95%: 77.9% to 85.7%), Gwet's AC₁ of 82.7% (CI 95%: 79.0% to 86.4%); wELISA and SU-ELISA - Cohen's kappa of 83.2% (CI 95%: 79.4% to 86.9%), Gwet's AC₁ of 83.9% (CI 95%: 80.4% to 87.5%); TM/CA-ELISA and SU-ELISA - Cohen's kappa of 86.0% (CI 95%: 82.6% to 89.5%), Gwet's AC₁ of 86.9% (CI 95%: 83.6% to 90.1%). However, agreement between ELISAs was significantly related to the within-herd true prevalence - it was significantly lower (although still high) when within-herd true prevalence was moderate (Gwet's AC₁ between 67.2% and 78.7%), whereas remained very high, when true within-herd prevalence was either >50% (Gwet's AC₁ between 91.9% and 98.8%) or <10% (Gwet's AC₁ between 94.7% and 98.4%). Concluding, the three different commercial ELISAs for SRLV infection in goats available on the market yield highly consistent results. However, their agreement is affected by the true within-herd prevalence in a tested population, and the worse (although still high) agreement should be expected, when the percentage of infected goats is moderate.

Small ruminant lentivirus infections and diseases

Small ruminant lentiviruses include viruses with diverse genotypes that frequently cross the species barrier between sheep and goats and that display a great genetic variability. These characteristics stress the need to consider the whole host range and to perform local surveillance of the viruses to opt for optimum diagnostic tests, in order to establish control programmes. In the absence of effective vaccines, a comprehensive knowledge of the epidemiology of these infections is of major importance to limit their spread. This article intends to cover these aspects and to summarise information related to characteristics of the viruses, pathogenesis of the infection and description of the various syndromes produced, as well as the diagnostic tools available, the mechanisms involved in transmission of the pathogens and, finally, the control strategies that have been designed until now, with remarks on the drawbacks and the advantages of each one. We conclude that there are many variables influencing the expected cost and benefits of control programs that must be evaluated, in order to put into practice measures that might lead to control of these infections.

Diverse host–virus interactions following caprine arthritis-encephalitis virus infection in sheep and goats

Interspecies transmissions substantially contribute to the epidemiology of small ruminant lentiviruses (SRLVs), including caprine arthritis encephalitis virus (CAEV) and visna-maëdi virus. However, comprehensive studies of host–virus interactions during SRLV adaptation to the new host are lacking. In this study, virological and serological features were analysed over a 6 month period in five sheep and three goats experimentally infected with a CAEV strain. Provirus load at the early stage of infection was significantly higher in sheep than in goats. A broad antibody reactivity against the matrix and capsid proteins was detected in goats, whereas the response to these antigens was mostly type-specific in sheep. The humoral response to the major immunodominant domain of the surface unit glycoprotein was type-specific, regardless of the host species. These species-specific immune responses were then confirmed in naturally infected sheep and goats using sera from mixed flocks in which interspecies transmissions were reported. Taken together, these results provide evidence that SRLV infections evolve in a host-dependent manner, with distinct host–virus interactions in sheep and goats, and highlight the need to consider both SRLV genotypes in diagnosis, particularly in sheep.

Produção de antígeno e separação da proteína p28 por microfiltragem seriada para sorodiagnóstico da artrite encefalite caprina por ensaio imunoenzimático

Este estudo teve como objetivo produzir um antígeno (Ag) a partir de cultura de células de membrana sinovial caprina (MSC) infectadas com o vírus de artrite encefalite caprina (CAEV), pela técnica de microfiltração seriada, substituindo a ultracentrifugação em colchão de sacarose (UCCS) para utilização em ELISA indireto (ELISA-i). Amostras de 188 soros caprinos, que previamente foram testados pelo Western blot (WB) com Ag UCCS, foram submetidas à análise pelo ELISA-i com o novo antígeno produzido, que mostrou concordância de 92% em relação ao antígeno UCCS. A sensibilidade e a especificidade do ELISA em relação ao WB foram de 95,6% e 88,5%, respectivamente. A nova técnica, criada a partir de microfiltrações, mostrou-se efetiva e de baixo custo para o diagnóstico sorológico de anticorpos para CAEV em comparação ao antígeno ultracentrifugado, e constitui uma alternativa viável para produção de antígeno purificado de lentivírus de pequenos ruminantes.

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.

Use of B7 costimulatory molecules as adjuvants in a prime-boost vaccination against Visna/Maedi ovine lentivirus

RNA transcripts of the B7 family molecule (CD80) are diminished in blood leukocytes from animals clinically affected with Visna/Maedi virus (VMV) infection. This work investigates whether the use of B7 genes enhances immune responses and protection in immunization-challenge approaches. Sheep were primed by particle-mediated epidermal bombardment with VMV gag and env gene recombinant plasmids together with plasmids encoding both CD80 and CD86 or CD80 alone, boosted with gag and env gene recombinant modified vaccinia Ankara virus and challenged intratracheally with VMV. Immunization in the presence of one or both of the B7 genes resulted in CD4+ T cell activation and antibody production (before and after challenge, respectively), but only immunization with CD80 and CD86 genes together, and not CD80 alone, resulted in a reduced number of infected animals and increased early transient cytotoxic T lymphocytes (CTL) responses. Post-mortem analysis showed an immune activation of lymphoid tissue in challenge-target organs in those animals that had received B7 genes compared to unvaccinated animals. Thus, the inclusion of B7 genes helped to enhance early cellular responses and protection (diminished proportion of infected animals) against VMV infection.

Peripheral ovine progressive pneumonia provirus levels correlate with and predict histological tissue lesion severity in naturally infected sheep

Studies were undertaken to determine whether anti-ovine progressive pneumonia virus (OPPV) antibody responses in serum or OPP provirus levels in peripheral blood associate with the degree of histologically measured tissue lesions in naturally OPPV-infected sheep. Sections of formalin-fixed, paraffin-embedded, and hematoxylin- and eosin-stained lung, mammary gland, carpal synovial membrane, and brain tissues from 11 OPPV-infected ewes (mean age of 8.6 years) and 5 OPPV-uninfected ewes (mean age of 6 years) were evaluated for lesion severity. Ovine progressive pneumonia (OPP) provirus levels and anti-OPPV antibody titers in peripheral blood and serum samples, respectively, were measured upon euthanasia and 3 years prior to euthanasia. Both mean peripheral OPP provirus levels and mean serum anti-surface envelope glycoprotein (anti-SU) antibody titers at the time of euthanasia were significantly higher in ewes with moderate to severe histological lesions than in ewes with no to mild histological lesions. However, although mean peripheral blood OPP provirus levels at euthanasia and 3 years prior to euthanasia significantly correlated with the highest histological lesion score for any affected tissue (two-tailed P values, 0.03 and 0.02), mean serum anti-SU antibody titers, anti-capsid antibody titers, and anti-transmembrane 90 antibody titers at euthanasia did not show a significant correlation with the highest histological lesion score for any tissue (two-tailed P values, 0.32, 0.97, and 0.18, respectively). These data are the first to show that OPP provirus levels predict and correlate with the extent of OPPV-related histological lesions in various OPPV-affected tissues. These findings suggest that peripheral OPP provirus levels quantitatively contribute more to the development of histological lesions than the systemic anti-SU antibody host immune response.

Deceptive imprinting and immune refocusing in vaccine design

A large number of the world's most widespread and problematic pathogens evade host immune responses by inducing strain-specific immunity to immunodominant epitopes with high mutation rates capable of altering antigenic profiles. The immune system appears to be decoyed into reacting to these immunodominant epitopes that offer little cross protection between serotypes or subtypes. For example, during HIV-1 infection, the immune system reacts strongly to the V1, V2, and/or V3 loops of the surface envelope glycoprotein but not to epitopes that afford broad protection against strain variants. Similarly, the host mounts strain-specific immunity to immunodominant epitopes of the influenza hemagglutinin (HA) protein. A large number of pathogens appear to exploit this weakness in the host immune system by focusing antigenic attention upon highly variable epitopes while avoiding surveillance toward more highly conserved receptor binding sites or other essential functional domains. Because the propensity of the immune system to react against immunodominant strain-specific epitopes appears to be genetically hard-wired, the phenomenon has been termed "deceptive imprinting." In this review, the authors describe observations related to deceptive imprinting in multiple systems and propose strategies for overcoming this phenomenon in the design of vaccines capable of inducing protection against highly variable pathogens.

Mucosal immunization against ovine lentivirus using PEI-DNA complexes and modified vaccinia Ankara encoding the gag and/or env genes

Sheep were immunized against Visna/Maedi virus (VMV) gag and/or env genes via the nasopharynx-associated lymphoid tissue (NALT) and lung using polyethylenimine (PEI)-DNA complexes and modified vaccinia Ankara, and challenged with live virus via the lung. env immunization enhanced humoral responses prior to but not after VMV challenge. Systemic T cell proliferative and cytotoxic responses were generally low, with the responses following single gag gene immunization being significantly depressed after challenge. A transient reduction in provirus load in the blood early after challenge was observed following env immunization, whilst the gag gene either alone or in combination with env resulted in significantly elevated provirus loads in lung. However, despite this, a significant reduction in lesion score was observed in animals immunized with the single gag gene at post-mortem. Inclusion of IFN-gamma in the immunization mixture in general had no significant effects. The results thus showed that protective effects against VMV-induced lesions can be induced following respiratory immunization with the single gag gene, though this was accompanied by an increased pulmonary provirus load.

Analysis of the antibody response to an immunodominant epitope of the envelope glycoprotein of a lentivirus and its diagnostic potential

The envelope glycoprotein of small ruminant lentiviruses (SRLV) is a major target of the humoral immune response and contains several linear B-cell epitopes. We amplified and sequenced the genomic segment encoding the SU5 antigenic site of the envelope glycoprotein of several SRLV field isolates. With synthetic peptides based on the deduced amino acid sequences of SU5 in an enzyme-linked immunosorbent assay (ELISA), we have (i) proved the immunodominance of this region regardless of its high variability, (ii) defined the epitopes encompassed by SU5, (iii) illustrated the rapid and peculiar kinetics of seroconversion to this antigenic site, and (iv) shown the rapid and strong maturation of the avidity of the anti-SU5 antibody. Finally, we demonstrated the modular diagnostic potential of SU5 peptides. Under Swiss field conditions, the SU5 ELISA was shown to detect the majority of infected animals and, when applied in a molecular epidemiological context, to permit rapid phylogenetic classification of the infecting virus.

Viral load, organ distribution, histopathological lesions, and cytokine mRNA expression in goats infected with a molecular clone of the caprine arthritis encephalitis virus

Caprine arthritis encephalitis virus (CAEV) is a lentivirus of goats that causes persistent infection characterized by the appearance of inflammatory lesions in various organs. To define the sites of persistence, 5 goats were infected with a molecular clone of CAEV, and the viral load was monitored by real-time-PCR and RT-PCR in different sites 8 years after infection. The lymph nodes proved to be an important virus reservoir, with moderate virus replication relative to what is reported for lentiviruses of primates. Mammary gland and milk cells were preferred sites of viral replication. The viral load varied significantly between animals, which points to an important role of the genetic background. We found a clear association between occurrence of histopathological lesions and viral load in specific sites. The mRNA expression analysis of several cytokines did not reveal differences between animals that could explain the considerable individual variations in viral load observed.

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.

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.

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.

Lentivírus de pequenos ruminantes (CAEV e Maedi-Visna): revisão e perspectivas

Os lentivírus de pequenos ruminantes (SRLV), cujos protótipos são os vírus da Artrite-Encefalite Caprina (CAEV) e Maedi-Visna, são patógenos amplamente distribuidos, os quais causam doenças degenerativas progressivas lentas em caprinos e ovinos, determinando importantes perdas econômicas. Estes vírus causam infecções persistentes com período de incubação longo e causam inflamatórias e degenerativas. As lesões são induzidas em tecidos específicos do hospedeiro como articulações, pulmões, CNS e glandulas mamárias devido à replicação viral em células da linhagem monocítico-fagocitária que são as principais células-alvo. A infecção ocorre principalmente durante os primeiros meses de vida, através da ingestão de vírus no leite ou colostro de cabras ou ovelhas infectadas. A indução da resposta imunológica é variável e não protege contra a infecção. O diagnóstico é baseado primariamente na detecção de anticorpos para SRLV, geralmente por imunodifusão em gel de agar (AGID) e enzyme linked immunosorbent assay (ELISA). O diagnóstico e separação ou descarte dos animais soropositivos associado ao uso de certas práticas de manejo, especialmente das crias, são os principais meios implementados para prevenir a disseminação de SRLV, uma vez que ainda não existe vacina contra o vírus. As estratégias adotadas pelos SRLV para enfrentar o sistema imune dificultam o diagnóstico da infecção, controle ou prevenção da disseminação de SRLV. Esta revisão apresenta alguns aspectos das lentivíroses de pequenos ruminantes baseadas em estudos filogenéticos de amostras isoladas, aspectos clínicos e imunopatológicos.

Characterization of caprine interleukin-4

Caprine interleukin-4 (IL-4) cDNA was cloned from RNA of mitogen stimulated goat peripheral blood mononuclear cells utilizing reverse transcriptase-polymerase chain reaction. The sequence of caprine IL-4 cDNA corresponds to a 535 nucleotide mRNA with 5'- and 3'-untranslated regions and a 405 nucleotide open reading frame, the first 66 nucleotides of which encode a putative signal peptide. Mature IL-4 is a 12.8kDa protein containing six cysteine residues and two potential N-linked glycosylation sites and is highly homologous with other ruminant IL-4. The predicted molecular mass of mature unglycosylated IL-4 was confirmed by western blot of recombinant caprine IL-4 expressed in bacteria with a monoclonal antibody against a carboxyterminal peptide derived from the predicted amino acid sequence of bovine IL-4. Eukaryotic expression plasmids containing caprine IL-4 cDNA were used to characterize recombinant IL-4. Transcription of IL-4 mRNA was confirmed by transfection of COS-7 and goat synovial membrane cells, and recombinant IL-4 produced by stably transfected L929 cells inhibited inducible nitric oxide synthase in macrophages. Genetic immunization of mice with a caprine IL-4 cDNA expression plasmid induced antibodies against recombinant caprine IL-4 produced in bacteria.

Immunization with plasmid DNA expressing the caprine arthritis-encephalitis virus envelope gene: quantitative and qualitative aspects of antibody response to viral surface glycoprotein

Saanen goats were vaccinated intradermally with plasmid DNA expressing caprine arthritis-encephalitis virus (CAEV) rev-env (pENV) or tat-rev-env (pTAT-ENV) or vaccinia virus expressing CAEV env (rWR-63). Sera from all vaccinated goats immunoprecipitated CAEV surface (SU) and transmembrane (TM) glycoproteins with a dominant response to SU. Antibody response to CAEV SU induced by plasmid DNA was relatively biased toward IgG2, whereas vaccinia rWR-63 induced predominantly IgG1 antibodies to SU. Differential IgG isotype bias established by immunization with plasmid or vaccinia vectors was maintained following subcutaneous boost with purified CAEV SU in Freund's incomplete adjuvant (FIA). Goats injected with pUC18 control plasmid followed by immunization with SU-FIA also had IgG2 biased responses, whereas SU-FIA immunization of a goat primed with vaccinia rWR-SC11 without the CAEV env gene induced a predominant IgG1 response. We conclude that pUC based plasmids expressing the CAEV env gene promote stable type 1 biased immune responses to plasmid encoded SU. IgG2 biased response may be due to innate type 1 priming capacity of immunostimulatory CpG motifs in the pUC ampicillin resistance gene.

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

Four immunoglobulin G1 monoclonal antibodies (MAbs) to the gp135 surface envelope glycoprotein (SU) of the 79-63 isolate of caprine arthritis-encephalitis virus (CAEV), referred to as CAEV-63, were characterized and evaluated for their ability to compete with antibody from CAEV-infected goats. Three murine MAbs (MAbs GPB16A, 29A, and 74A) and one caprine MAb (MAb F7-299) were examined. All MAbs reacted in nitrocellulose dot blots with native CAEV-63 SU purified by MAb F7-299 affinity chromatography, whereas none reacted with denatured and reduced SU. All MAbs reacted in Western blots with purified CAEV-63 SU or the SU component of whole-virus lysate following denaturation in the absence of reducing agent, indicating that intramolecular disulfide bonding was essential for epitope integrity. Peptide-N-glycosidase F digestion of SU abolished the reactivities of MAbs 74A and F7-299, whereas treatment of SU with N-acetylneuraminate glycohydrolase (sialidase A) under nonreducing conditions enhanced the reactivities of all MAbs as well as polyclonal goat sera. MAbs 29A and F7-299 were cross-reactive with the SU of an independent strain of CAEV (CAEV-Co). By enzyme-linked immunosorbent assay (ELISA), the reactivities of horseradish peroxidase (HRP)-conjugated MAbs 16A and 29A with homologous CAEV-63 SU were <10% of that of HRP-conjugated MAb 74A. The reactivity of HRP-conjugated MAb 74A was blocked by sera from goats immunized with CAEV-63 SU or infected with CAEV-63. The reactivity of MAb 74A was also blocked by sera from goats infected with a CAEV-Co molecular clone, although MAb 74A did not react with CAEV-Co SU in Western blots. Thus, goats infected with either CAEV-63 or CAEV-Co make antibodies that inhibit binding of MAb 74A to CAEV-63 SU. A competitive-inhibition ELISA based on displacement of MAb 74A reactivity has potential applicability for the serologic diagnosis of CAEV infection.

B-cell epitopes of the envelope glycoprotein of caprine arthritis-encephalitis virus and antibody response in infected goats

Goats infected with caprine arthritis-encephalitis virus (CAEV) develop high titres of antibodies to Env. Not only is no consistent neutralizing response found but anti-Env antibodies have even been associated with disease in infected goats. To identify the continuous antigenic determinants involved in this atypical anti-Env response, we mapped CAEV-CO Env by screening an epitope expression library with infected goat sera. In addition to the four previously described epitopes, seven novel antigenic sites were identified, of which five were located on the surface (SU) and two in the transmembrane (TM) subunits of Env. The SU antibody-binding domains located in the variable regions of the C-terminal part of the molecule (SU3 to SU5) showed the strongest reactivity and induced a rapid seroconversion in six experimentally infected goats. However, the response to these immunodominant epitopes did not appear to be associated with any neutralizing activity. The pattern of serum reactivity of naturally infected goats with these epitopes was restricted, suggesting a type-specific reaction. Interestingly, the reactivity of peptides representing SU5 sequences derived from CAEV field isolates varied with the geographical and/or breeding origin of the animals. This suggests that peptides corresponding to the immunodominant SU epitopes may well be useful in the serotyping of CAEV isolates. Furthermore, the identification of the CAEV Env epitopes will permit us to functionally dissect the antibody response and to address the role of anti-Env antibodies either in the protection from or in the pathogenesis of CAEV infection.

Variability and immunogenicity of caprine arthritis-encephalitis virus surface glycoprotein

The complete surface glycoprotein (SU) nucleotide sequences of three French isolates of caprine arthritis-encephalitis virus (CAEV) were determined and compared with those of previously described isolates: three American isolates and one French isolate. Phylogenetic analyses revealed the existence of four distinct and roughly equidistant evolutionary CAEV subtypes. Four conserved and five variable domains were identified in the SU. The fine specificities of antibodies produced against these domains during natural infection were examined using a pepscan analysis. Nine immunogenic segments were delineated throughout the conserved and variable domains of SU, two of them corresponding to conserved immunodominant epitopes. Antigenic determinants which may be involved in the immunopathogenic process induced by CAEV were identified. These results also provide sensitive and specific antigen peptides for the serological detection and differentiation of CAEV and visna/maedi virus infections.

Immune response to caprine arthritis-encephalitis virus surface protein induced by coimmunization with recombinant vaccinia viruses expressing the caprine arthritis-encephalitis virus envelope gene and caprine interleukin-12

The objective of this study was to determine if interleukin (IL)-12 can focus an antigen specific type 1 immune response characterized by activation of Th1 lymphocytes and production of IgG2 antibodies in vivo. Saanen goats co-immunized with recombinant vaccinia viruses expressing caprine IL-12 (rRB-IL12) and the caprine arthritis-encephalitis virus (CAEV) envelope (env) gene (rWR-63) were evaluated for development of immune responses to the CAEV env encoded surface glycoprotein (SU). Immune responses were defined by: (i) SU antibody titers; (ii) the ratio of SU IgG1 and IgG2 antibodies; (iii) interferon gamma (IFNgamma) and IL-4 gene expression and proliferative response of SU stimulated lymph node mononuclear cells (LNMC). Apart from enhancement of IFNgamma and IL-4 gene expression in SU stimulated LNMC, rRB-IL12 did not affect the immune response to rWR-63 encoded SU. Thus, localized production of exogenous species specific IL-12 at the site of immunization did not focus initial priming of antigen reactive Th lymphocytes. These results are in contrast to previous studies using inbred mice and raise questions regarding the use of cytokine adjuvants to focus immune responses in outbred animals.

Neutralizing antibody responses and evolution of antigenic variants in monozygotic twin lambs infected with phenotypically distinct ovine lentiviruses

Ovine lentivirus (OvLV) isolates 85/34 (OvLV 34) and 84/28 (OvLV 28) were initially characterized as phenotypically distinct "rapid/high" and "slow/low" strains based on replication kinetics, syncytiogenesis, and cell lysis in vitro. In the present study, sera from OvLV-34- or OvLV-28-infected monozygotic twin lambs defined these virus strains as distinct neutralization serotypes. We also show that immune recognition of at least one OvLV neutralization epitope is influenced by genetic differences between lambs. Additional studies determined the neutralization phenotype of virus isolates from alveolar macrophages of OvLV-34- or OvLV-28-infected lambs, evaluated the role of neutralizing antibodies in selection and persistence of antigenic variants, and related the severity of OvLV-induced lymphoid interstitial pneumonia (LIP) to the evolution of neutralization variants. These studies demonstrate that (i) macrophage-associated OvLV neutralization variants can arise in the presence or the absence of neutralizing antibodies directed to inoculum viruses, (ii) OvLV variants persist in macrophages in the presence of serum neutralizing antibodies, and (iii) the emergence of OvLV variants is apparently unrelated to the severity of LIP.

Priming with tat-deleted caprine arthritis encephalitis virus (CAEV) proviral DNA or live virus protects goats from challenge with pathogenic CAEV

We previously reported that infection of goats with caprine arthritis encephalitis virus (CAEV) tat- proviral DNA or virus results in persistent infection, since the animals seroconverted and direct virus isolation from cultures of blood-derived macrophages was positive. In this study we wanted to determine whether goats injected with CAEV tat- proviral DNA or virus were protected against challenge with the pathogenic homologous virus and to investigate whether CAEV tat- was still pathogenic. All animals injected with CAEV tat- became infected as indicated by seroconversion and virus isolation. Challenge at 8 or 9 months postinfection demonstrated protection in four of four animals injected with CAEV tat- but did not in three of three mock-inoculated challenged goats. Challenge virus was undetectable in the blood macrophages of protected animals during a period of 6 or 10 months postchallenge. In two of four protected animals, however, we were able to detect the challenge wild-type virus by reverse transcriptase PCR on RNA directly extracted from synovial membrane cells surrounding the inoculation site. This result suggests that protection was achieved without complete sterilizing immunity. Animals injected with CAEV tat- and mock challenged developed inflammatory lesions in the joints, although these lesions were not as severe as those in CAEV wild-type-injected goats. These results confirm the dispensable role of Tat in CAEV replication in vivo for the establishment of infection and pathogenesis and demonstrate in another lentivirus infection model the efficacy of live attenuated viruses to induce resistance to superinfection.

Immune response to recombinant visna virus Gag and Env precursor proteins synthesized in insect cells

Two different recombinant visna virus (VV) gag-baculoviruses were constructed for the expression of precursor VV Gag in insect cells. Both recombinant Gag viruses expressed proteins migrating on SDS PAGE at the predicted rate for VV Gag precursor, Pr50gag. However, differences were seen in the morphology of the virus-like particles produced. Monoclonal antibody directed against the VV Gag capsid protein (p25) and sera from sheep infected with ovine lentiviruses reacted to both 50-kDa proteins. A recombinant VV env-baculovirus was constructed, substituting sequences encoding the signal peptide of VV Env with the murine IFN-gamma analogue. Sera from ovine lentivirus infected sheep reacted in immunoblots with two proteins of approximately 100 and 200 kDa found in the plasma membrane of insect cells infected with env-recombinant virus. Sheep immunized with either the recombinant Gag or the Env proteins developed high antibody titers to VV in ELISA. The serum of sheep and ascitic fluid of mice immunized with the recombinant Gag reacted with native Pr50gag and the processed Gag proteins in immunoblots, whereas serum of the recombinant Env immunized sheep reacted with VV gp135 and a putative oligomer of gp135. The immunized sheep responded specifically to visna virus by lymphocyte proliferation in vitro.

Immunohistology of the early course of lentivirus-induced arthritis

Caprine arthritis encephalitis (CAE) is a lentiviral infection of goats characterized by mononuclear cell infiltration of various tissues, most prominently the joints, mammary glands and, in young animals, the brain. We have investigated the early stages of arthritis induced by intracarpal and intravenous infection with molecularly cloned CAE virus. Analysis of the synovial membranes by immunohistological methods showed that the proportion of CD8+ T cells peaked around day 12 post-infection. CD4+ T cells increased to a lesser degree. The relative proportion of B cells rose steadily post-infection. At 33 days post-infection, plasma cells accounted for over one third of all inflammatory cells in the inflamed synovium. Histopathologically, the arthritic lesions in the synovial membranes closely resembled those in membranes of animals with a 2-year history of chronic arthritis. Our observations indicate that this type of short-term experimental infection is particularly suitable for studying the pathogenesis of goat lentiviral infection. In addition, our observations support the view that a predominantly humoral (type 2) immune response may contribute to the pathogenesis of CAE.

Antibody reactivity to the transmembrane protein of the caprine arthritis encephalitis virus correlates with severity of arthritis: no evidence for the involvement of epitope mimicry

Serum and synovial antibody reactivities of caprine arthritis encephalitis virus (CAEV) infected goats were assessed by Western blotting against purified CAEV antigen and the greatest intensity of reactivity in the serum of arthritic goats was to the gp45 transmembrane protein (TM). The extracytoplasmic domain of the TM gene was cloned into a pGEX vector and expressed in Escherichia coli as a glutathione S transferase fusion protein (GST-TM). This clone was found to be 90.5 and 89.2% homologous to published sequences of CAEV TM gene. Serum of 16 goats naturally infected with CAEV were examined by Western blotting for reactivity to the fusion protein. Antibody reactivity to the GST-TM correlated with clinically detectable arthritis (R = 0.642, P < or = 0.007). The hypothesis that the immune response to the envelope proteins of the CAEV contributes to the severity of arthritis in goats naturally infected with CAEV via epitope mimicry was tested. Antibodies from 5 CAEV infected goats were affinity purified against the GST-TM fusion protein and tested for cross-reactivity with a series of goat synovial extracts and proteogylcans. No serum antibody response or cross-reactivity of affinity purified antibodies could be detected. Peptides of the CAEV SU that were predicted to be linear epitopes and a similar heat shock protein 83 (HSP) peptide identified by database searching, were synthesized and tested for reactivity in CAEV goats using ELISA, in vitro lymphocyte proliferation and delayed type hypersensitivity (DTH) assays. Peripheral blood lymphocytes from 10 of 17 goats with long term natural CAEV infections proliferated in vitro in response to CAEV and in vivo 3 of 7 CAEV infected goats had a DTH reaction to CAEV antigen. However, none of the peptides elicited significant cell mediated immune responses from CAEV infected goats. No antibody reactivity to the SU peptides or HSP peptide was found. We observed that the antibody reactivity to the CAEV TM protein associated with severity of arthritis however epitope mimicry by the envelope proteins of CAEV is unlikely to be involved.

Enhancement of feline immunodeficiency virus (FIV) infection after DNA vaccination with the FIV envelope

Despite intensive experimentation to develop effective and safe vaccines against the human immunodeficiency viruses and other pathogenic lentiviruses, it remains unclear whether an immune response that does not afford protection may, on the contrary, produce adverse effects. In the present study, the effect of genetic immunization with the env gene was examined in a natural animal model of lentivirus pathogenesis, infection of cats by the feline immunodeficiency virus (FIV). Three groups of seven cats were immunized by intramuscular transfer of plasmid DNAs expressing either the wild-type envelope or two envelopes bearing mutations in the principal immunodominant domain of the transmembrane glycoprotein. Upon homologous challenge, determination of plasma virus load showed that the acute phase of viral infection occurred earlier in the three groups of cats immunized with FIV envelopes than in the control cats. Genetic immunization, however, elicited low or undetectable levels of antibodies directed against envelope glycoproteins. These results suggest that immunization with the FIV env gene may result in enhancement of infection and that mechanisms unrelated to enhancing antibodies underlay the observed acceleration.

Caprine arthritis encephalitis virus dysregulates the expression of cytokines in macrophages

Caprine arthritis encephalitis virus (CAEV) is a lentivirus of goats that leads to chronic mononuclear infiltration of various tissues, in particular, the radiocarpal joints. Cells of the monocyte/macrophage lineage are the major host cells of CAEV in vivo. We have shown that infection of cultured goat macrophages with CAEV results in an alteration of cytokine expression in vitro. Constitutive expression of interleukin 8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) was increased in infected macrophages, whereas transforming growth factor beta1 (TGF-beta1) mRNA was down-regulated. When macrophages were infected with a CAEV clone lacking the trans-acting nuclear regulatory gene tat, IL-8 and MCP-1 were also increased. No significant differences from cells infected with the wild-type clone were observed, suggesting that Tat is not required for the increased expression of IL-8 and MCP-1 in infected macrophages. Furthermore, infection with CAEV led to an altered pattern of cytokine expression in response to lipopolysaccharide (LPS), heat-killed Listeria monocytogenes plus gamma interferon, or fixed cells of Staphylococcus aureus Cowan I. In infected macrophages, tumor necrosis factor alpha, IL-1beta, IL-6, and IL-12 p40 mRNA expression was reduced in response to all stimuli tested whereas changes in expression of granulocyte-macrophage colony-stimulating factor depended on the stimulating agent. Electrophoretic mobility shift assays demonstrated that, in contrast to effects of human immunodeficiency virus infection of macrophages, CAEV infection had no effect on the level of constitutive nuclear factor-kappaB (NF-kappaB) activity or on the level of LPS-stimulated NF-kappaB activity, suggesting that NF-kappaB is not involved in altered regulation of cytokine expression in CAEV-infected cells. In contrast, activator protein 1 (AP-1) binding activity was decreased in infected macrophages. These data show that CAEV infection may result in a dysregulation of expression of cytokines in macrophages. This finding suggests that CAEV may modulate the accessory functions of infected macrophages and the antiviral immune response in vivo.

Type 1 and type 2 cytokine gene expression by viral gp135 surface protein-activated T lymphocytes in caprine arthritis-encephalitis lentivirus infection

Peripheral blood mononuclear cells (PBMC) from Saanen goats experimentally infected with the lentivirus caprine arthritis-encephalitis virus (CAEV) were evaluated by semiquantitative reverse transcriptase PCR for gamma interferon (IFN-gamma), interleukin-4 (IL-4), and IL-2 gene expression following in vitro stimulation with purified CAEV gp135 surface protein (SU). Studies examined three goats with chronic arthritis and four clinically asymptomatic goats at 5 years postinfection. SU-responsive IFN-gamma mRNA-positive cells and IL-4 mRNA-positive cells in PBMC from infected goats reflected differences in lymphokine balance associated with disease status. IFN-gamma mRNA-positive cells were dominant in PBMC from asymptomatic goats, whereas SU-responsive IL-4 mRNA-positive cells were dominant in PBMC from goats with arthritis. IL-2 gene expression was not responsive to SU stimulation of PBMC from either asymptomatic or arthritic goats. Lymphokine mRNA profiles in SU-stimulated PBMC were dependent on the presence of CD4+ T lymphocytes. The results indicate that asymptomatic goats have a dominant population of CAEV SU-reactive T-helper 1 (Th1)-like lymphocytes in PBMC whereas goats with clinical arthritis have a dominant population of SU-reactive Th2-like lymphocytes.

A long term study of goats naturally infected with caprine arthritis-encephalitis virus

The caprine arthritis-encephalitis virus (CAEV) is a big problem in dairy goat industry. Little is known about its characteristics in naturally infected goat herds. The aims of this study were: 1) to study how antibody expression, measured by agar gel immunodiffusion test (AGIDT), varied over time in naturally infected, seropositive goats, 2) to observe clinical signs in seropositive adult goats and 3) to follow seroconversion and gamma globulin concentration in goat kids artificially reared on cow milk replacement product only, compared to kids reared on untreated goat milk. The antibody expression pattern to the viral proteins gp135 and p28 varied in the individual goat and intermittent negative reactions were seen in 19 adult animals followed for 30-91 weeks. Four seropositive goats developed clinical symptoms with difficulties to move. However, no correlation between clinical signs and antibody expression pattern was seen. During the first 27 weeks of age no kid in the milk replacement reared group (N = 4) seroconverted, but 5 of the 7 kids fed goat milk occasionally showed a positive antibody reaction. The gamma globulin concentration was significantly higher in the goat milk fed group until the kids had become more than 19 weeks old. The results show that a great variation of the antibody pattern in individual goats occurs, and therefore the AGIDT is only reliable as a herd screening test. Frequent sampling is necessary to get reliable information about spreading of the CAEV in a naturally infected goat herd. Removing kids from their dams immediately after birth combined with segregation and artificial rearing protected them from CAEV infection. However their gamma globulin concentration was initially low.

A long term study of goats naturally infected with caprine arthritis-encephalitis virus

The caprine arthritis-encephalitis virus (CAEV) is a big problem in dairy goat industry. Little is known about its characteristics in naturally infected goat herds. The aims of this study were: 1) to study how antibody expression, measured by agar gel immunodiffusion test (AGIDT), varied over time in naturally infected, seropositive goats, 2) to observe clinical signs in seropositive adult goats and 3) to follow seroconversion and gamma globulin concentration in goat kids artificially reared on cow milk replacement product only, compared to kids reared on untreated goat milk. The antibody expression pattern to the viral proteins gp135 and p28 varied in the individual goat and intermittent negative reactions were seen in 19 adult animals followed for 30-91 weeks. Four seropositive goats developed clinical symptoms with difficulties to move. However, no correlation between clinical signs and antibody expression pattern was seen. During the first 27 weeks of age no kid in the milk replacement reared group (N = 4) seroconverted, but 5 of the 7 kids fed goat milk occasionally showed a positive antibody reaction. The gamma globulin concentration was significantly higher in the goat milk fed group until the kids had become more than 19 weeks old. The results show that a great variation of the antibody pattern in individual goats occurs, and therefore the AGIDT is only reliable as a herd screening test. Frequent sampling is necessary to get reliable information about spreading of the CAEV in a naturally infected goat herd. Removing kids from their dams immediately after birth combined with segregation and artificial rearing protected them from CAEV infection. However their gamma globulin concentration was initially low.

Evaluation of two recombinant Maedi-visna virus proteins for use in an enzyme-linked immunosorbent assay for the detection of serum antibodies to ovine lentiviruses

Defined segments of the gag polyprotein and transmembrane envelope glycoprotein from Maedi-visna virus were expressed as glutathione S-transferase fusion proteins in Escherichia coli and evaluated singly and in combination for use in an enzyme-linked immunosorbent assay (ELISA). Two hundred sixty field serum specimens from 15 sheep flocks were tested in parallel with recombinant and whole-virus antigens, and the relative sensitivities and specificities of the recombinant antigens were calculated. When the recombinant gag and transmembrane proteins were used in combination, a sensitivity of 97.4% and a specificity of 99.4% relative to whole-virus antigen were observed, indicating the utility of these proteins in diagnostic testing.

Immunopathology of chronic lentivirus-induced arthritis

This study evaluated histopathology and mononuclear cell phenotypes in synovial lesions of chronic arthritis induced by experimental infection of Saanen goats with caprine arthritis-encephalitis lentivirus. Histological examination of carpal joint synovium of three infected goats with clinical arthritis revealed progressive lesions consisting of membrane villus hypertrophy with extensive angiogenesis and mononuclear cell infiltration and degenerative changes of membrane villus necrosis associated with loss of vasculature and infiltrates. Changes in synovial tissue of five age-matched infected goats without clinical arthritis were limited to moderate synovial membrane hyperplasia also noted in an age-matched uninfected goat. Immunohistochemistry identified CD45R+ CD5- B lymphocytes as the principal component of most perivascular infiltrates in arthritic synovium. Other mononuclear cells included perivascular CD4+ and CD8+ T lymphocytes and macrophages with a prominent accumulation of CD8+ T lymphocytes at the lining surface of inflamed villi. T lymphocytes and macrophages as well as synovial lining cells were activated with respect to MHC class II but not for interleukin-2 receptors. Inflamed villi also contained lymphoid aggregates comprised of B cell germinal centers and activated T-cell mantles. B cells expressing immunoglobulin occurred around follicles and throughout inflamed villi. These findings indicate that memory immune responses that favor expansion and maturation of B cells and immunoglobulin production contribute to the immunopathology of chronic arthritis.

Immunoglobulin deposits in synovial membrane and cartilage and phenotype analysis of chondrocyte antigens in sheep infected with the visna retrovirus

Synovial membranes and cartilage slices from sheep infected with the maedi-visna retrovirus were examined for immunoglobulin deposits by immunohistology. Granular deposits of IgM and IgG were observed in the synovial membranes and upper layers of cartilage from about 40% of virus-infected sheep. These deposits were present in animals with subclinical joint disease, as well as those affected clinically. No significant deposits were found in the synovial membrane or cartilage from normal sheep. Infected animals tended to have reduced cartilage proteoglycan staining. Altered expression of MHC class II, CD1 and adhesion molecules by chondrocytes in cartilage from infected sheep with clinical or subclinical synovitis was observed suggesting that in vivo cell activation is an early event in cartilage degradation in these infections. Exogenously derived antiviral antibodies exhibited molecular mimicry towards chondrocyte antigens, but no in vivo evidence for cross-reactivity was observed. The results showed that IgM and IgG deposits, putatively containing either virus/antivirus immune complexes or autoantibodies were formed in the joints of sheep with clinical or subclinical synovitis. These immune deposits may initiate and perpetuate chronic inflammation with concomitant activation of chondrocytes leading to pannus formation and cartilage destruction.

Antibody reactivity to the immunodominant epitopes of the caprine arthritis-encephalitis virus gp38 transmembrane protein associates with the development of arthritis

High titers of antibodies to caprine arthritis-encephalitis virus (CAEV) envelope (Env) glycoproteins are found in infected goats developing a progressive arthritis. In order to identify linear B epitopes of the CAEV Env, which may be involved in the immunopathology of arthritis, we constructed a lambda gt11 Env expression library. By combining library screening with sera from naturally infected Swiss goats with an enzyme immunoassay with overlapping peptides (pepscan), four group-specific epitopes could be precisely defined in the transmembrane envelope proteins: TM1 to TM4, including a conserved structure (TM3) that corresponds to the immunodominant epitope of human immunodeficiency virus type 1 and other lentiviruses. A panel of 190 CAEV naturally infected goat serum samples, obtained from animals with defined clinical status, was tested for reactivity to synthetic peptides corresponding to the TM epitopes in an enzyme-linked immunosorbent assay. Antibody reactivity to two epitopes was highly associated (TM3, P = 0.002, and TM4, P < 0.001) with the presence of clinically detectable arthritis. Such an association is absent for anti-Gag antibody. Antibodies to the immunodominant structures of the TM glycoprotein could thus have an important role in the immunopathogenic process leading to disease.

Caprine arthritis-encephalitis lentivirus (CAEV) challenge of goats immunized with recombinant vaccinia virus expressing CAEV surface and transmembrane envelope glycoproteins

This study evaluated infection and disease following caprine arthritis-encephalitis lentivirus (CAEV) challenge of goats with existent immune response to CAEV surface and transmembrane envelope glycoproteins. Six Saanen goats were vaccinated three times with recombinant vaccinia virus rWR63 expressing glycoproteins encoded by the CAEV-63 envelope gene. Two goats were immunized with rWRSC11, a control vaccinia virus derived from the pSC11 vaccinia expression plasmid without the CAEV envelope gene. One pair of rWR63 vaccinated goats received a booster immunization with recombinant surface glycoprotein in Freund's complete adjuvant, a second pair was boosted by intravenous inoculation with rWR63, and the third pair was boosted by immunization with HPLC purified native CAEV surface glycoprotein in Freund's complete adjuvant. All six goats vaccinated with rWR63 developed antibody responses to CAEV envelope glycoproteins; however, CAEV-63 neutralizing antibody was not detected. Neither of the rWRSC11-vaccinated goats developed CAEV reactive antibody. All goats were challenged by intravenous inoculation with 10(6) TCID50 CAEV-63. All goats became infected following challenge infection, shown by detection of serum antibody to CAEV core proteins and virus isolation. Existent CAEV-63 immune responses did not detectably alter the severity of inflammatory joint lesions at 24 weeks postchallenge.

Evaluation of agar gel immunodiffusion serology using caprine and ovine lentiviral antigens for detection of antibody to caprine arthritis-encephalitis virus

The sensitivity of the agar gel immunodiffusion (AGID) test for the detection of antibody to caprine arthritis-encephalitis virus (CAEV) was investigated with CAEV or ovine progressive pneumonia virus (OPPV) as the source of antigen. A total of 218 goat serum specimens were tested for anti-CAEV antibody by AGID and immunoprecipitation of [35S]methionine-labeled CAEV. In comparison with that of immunoprecipitation, the sensitivity of the CAEV AGID test was 0.91, and that of the OPPV AGID test was 0.56. The AGID test with either antigen was 100% specific. The lower sensitivity of the OPPV AGID test in detecting caprine antibody to CAEV indicates that OPPV antigen is of limited value for use in CAEV diagnosis and control programs.

Host-virus interaction as defined by amplification of viral DNA and serology in lentivirus-infected sheep

To correlate the presence of ovine lentivirus (OvLV) as detected by polymerase chain reaction (PCR) with detection of antibody, 42 sheep from a flock with enzootic OvLV infection were studied. The results of agar gel immunodiffusion (AGID), ELISA, and immunoblotting assays were compared, and leukocytes (blood, bone marrow, lymph node, and lung cells) were assessed for viral DNA by PCR using pol and LTR primers; amplified products were detected by specific DNA and RNA probes. Based on the number of animals that had detectable viral DNA, the specificities of AGID, ELISA, and immunoblotting were 77%, 92%, and 95 or 100% (depending on which criterion was used to interpret immunoblot results), respectively. Only in animals with OvLV-associated disease was OvLV DNA detected in leukocyte DNA prior to the amplification of virus in culture and only in this group was high titer antibody detected to the OvLV major surface (gp 105) and transmembrane (gp 55) antigens. Animals that were both antibody and PCR-negative lacked histopathologic evidence of disease. From this study there was no indication that OvLV infection without the development of antibody occurs, and detection of OvLV DNA in animals with weak or partial serological reactions likely indicates early OvLV infection rather than false-positive PCR results.

The biology of maedi-visna virus--an overview

This review aims to summarize the current understanding of the biology of maedi-visna virus (MVV), the prototype virus of the family lentivirinae. The paper provides a short overview of the historical background to the discovery of MVV. Detailed descriptions of the structure and organization of the MVV genome and of the virion encoded polypeptides are given and the MVV life cycle in vitro and in vivo are compared and contrasted and the tropism of the virus discussed. The clinical consequences of infection are considered and the mode of transmission, immune response to the virus and possible mechanisms of pathogenesis are discussed.

Occurrence of caprine leucocyte class I and II antigens in Saanen goats affected by caprine arthritis (CAE)

The distribution of CLA class I and II antigens in CAE virus-infected, diseased and healthy Saanen goats has been investigated. Three class I antigens and two class II antigens showed a statistically different frequency in the two groups.

Efficacy of inactivated whole-virus and subunit vaccines in preventing infection and disease caused by equine infectious anemia virus

We report here on a series of vaccine trials to evaluate the effectiveness of an inactivated equine infectious anemia virus (EIAV) whole-virus vaccine and of a subunit vaccine enriched in EIAV envelope glycoproteins. The inactivated vaccine protected 14 of 15 immunized ponies from infection after challenge with at least 10(5) 50% tissue culture-infective doses of the homologous prototype strain of EIAV. In contrast, it failed to prevent infection in any of 15 immunized ponies that were challenged with the heterologous PV strain. Levels of PV virus replication and the development of disease, however, were significantly reduced in 12 of the 15 ponies so challenged. The subunit vaccine prevented infection from homologous challenge in four of four ponies tested but failed to prevent infection in all four challenged with the PV strain. Two of the four subunit vaccinates had more severe symptoms of equine infectious anemia than nonimmunized ponies infected in parallel. Both vaccines stimulated EIAV-specific cell-mediated immunity. The in vitro lymphoproliferative response was shown to be mediated by T lymphocytes and appeared to be indistinguishable from that induced by EIAV infection. Significant differences were observed in the in vivo lymphocyte responses following challenge with the two virus strains. While peripheral blood mononuclear cells from the inactivated virus vaccinates were equally stimulated by both the prototype and PV strains, the subunit vaccinates challenged with PV exhibited lower levels of spontaneous proliferation and serine esterase activity. This diminished cellular response to PV was correlated with more severe clinical disease in the same ponies. These studies demonstrate for the first time that both an EIAV inactivated whole-virus vaccine and a viral envelope glycoprotein-based subunit vaccine can provide protection against rigorous challenge levels of homologous virus but are unable to protect against similar challenge levels of a heterologous virus. Moreover, the data demonstrate that protection can be achieved in the absence of detectable levels of virus-specific neutralizing antibody in the vaccine recipients at the time of virus challenge. While vaccine-induced virus-specific cell-mediated immune responses were detected, their role in conferring protection was not obvious. Nevertheless, protection from disease appeared to be correlated with the induction of high levels of serine esterase activity following challenge. A significant observation is that while the whole-virus vaccine was usually capable of preventing or markedly moderating disease in the PV-infected ponies, the subunit vaccine appeared to have a high potential to enhance the disease induced by PV infection.(ABSTRACT TRUNCATED AT 400 WORDS)

Transmembrane protein oligomers of caprine arthritis-encephalitis lentivirus are immunodominant in goats with progressive arthritis

To dissect mechanisms of caprine arthritis-encephalitis lentivirus-induced arthritis, an undefined immunodominant viral glycoprotein, gp90 (G. C. Johnson, A. F. Barbet, P. Klevjer-Anderson, and T. C. McGuire, Infect. Immun. 41:657-665, 1983), was characterized. Monoclonal antibody to gp90 and specific antiserum to env gene products demonstrated that gp90 was a transmembrane protein (TM) dimer. Goats with progressive arthritis had high antibody titers to oligomeric and monomeric (38-kDa) TM.