Prospects in Innate Immune Responses as Potential Control Strategies against Non-Primate Lentiviruses

Lentiviruses are infectious agents of a number of animal species, including sheep, goats, horses, monkeys, cows, and cats, in addition to humans. As in the human case, the host immune response fails to control the establishment of chronic persistent infection that finally leads to a specific disease development. Despite intensive research on the development of lentivirus vaccines, it is still not clear which immune responses can protect against infection. Viral mutations resulting in escape from T-cell or antibody-mediated responses are the basis of the immune failure to control the infection. The innate immune response provides the first line of defense against viral infections in an antigen-independent manner. Antiviral innate responses are conducted by dendritic cells, macrophages, and natural killer cells, often targeted by lentiviruses, and intrinsic antiviral mechanisms exerted by all cells. Intrinsic responses depend on the recognition of the viral pathogen-associated molecular patterns (PAMPs) by pathogen recognition receptors (PRRs), and the signaling cascades leading to an antiviral state by inducing the expression of antiviral proteins, including restriction factors. This review describes the latest advances on innate immunity related to the infection by animal lentiviruses, centered on small ruminant lentiviruses (SRLV), equine infectious anemia virus (EIAV), and feline (FIV) and bovine immunodeficiency viruses (BIV), specifically focusing on the antiviral role of the major restriction factors described thus far.

Prior bovine immunodeficiency virus infection does not inhibit subsequent superinfection by the acutely pathogenic Jembrana disease virus

In cattle the interaction between the two genetically and antigenically related bovine lentiviruses, the acutely pathogenic Jembrana disease virus (JDV) and the non-pathogenic Bovine immunodeficiency virus (BIV) has not been reported although both JDV and a BIV-like virus have been reported in the Bali cattle (Bos javanicus) population in Indonesia. The outcome of infection of Bali cattle with the R29 strain of BIV prior to superinfection 42 days later with JDV(TAB/87) was determined. All BIV-inoculated cattle were successfully infected and developed an antibody response to the TM and CA proteins. BIV infection did not prevent subsequent infection with JDV or ameliorate the clinical signs of Jembrana disease in the infected cattle. It did, however, modify the dynamics of the JDV infection with an earlier onset and end of the acute disease process, and a reduction in the duration of viremia that exceeded 10(6) genome copies/ml of plasma.

Recombinant Jembrana disease virus gag proteins identify several different antigenic domains but do not facilitate serological differentiation of JDV and nonpathogenic bovine lentiviruses

In Indonesia, it is suspected that there are two bovine lentiviruses circulating in the cattle population: a pathogenic Jembrana disease virus (JDV), and a nonpathogenic bovine immunodeficiency-like virus (BIV). Both viruses cross-react antigenically and cannot be differentiated by current serological tests using JDV antigens. To identify possible type-specific epitopes, a series of recombinant protein constructs including the matrix, capsid and nucleocapsid proteins were produced from JDV gag and the expressed proteins were tested by Western blot using JDV and BIV hyperimmune sera. JDV matrix and truncated capsid proteins were recognised by both JDV and BIV hyperimmune sera indicating that there were multiple cross-reactive epitopes present in JDV gag. At least three epitopic regions were identified in these constructs, including the major homology region, by monoclonal antibody binding studies. JDV nucleocapsid recombinant protein was not recognised by either JDV or BIV hyperimmune sera and none of the recombinant gag proteins were able to differentiate between JDV positive sera from Jembrana disease endemic and Jembrana disease-free areas. Additionally, a 40 amino acid recombinant subunit protein encompassing the region recently found to contain an epitope unique to BIV [Zheng, L., Zhang, S., Wood, C., Kapil, S., Wilcox, G.E., Loughin, T.A., Minocha, H.C., 2001. Differentiation of two bovine lentiviruses by a monoclonal antibody on the basis of epitope specificity. Clin. Diagn. Lab. Immunol. 8, 283-287] was tested but was not recognised by either JDV positive sera from Jembrana disease-endemic or Jembrana disease-free areas.

Estimation of sensitivity and specificity of two diagnostics tests for bovine immunodeficiency virus using Bayesian techniques

The validation of assays for bovine immunodeficiency virus (BIV) in cattle is hampered by the absence of a gold standard. Two tests that often are used to detect BIV are the indirect fluorescent-antibody assay (IFA) and the nested-set polymerase chain-reaction assay (PCR). IFA detects an antibody response whereas PCR detects the provirus in white blood cells. Using Bayesian techniques performed simultaneously on animals from two different dairy herds, we estimated the performance of the IFA and PCR assays and infection prevalence. Bayesian techniques also were used to derive posterior distributions of sensitivities, specificities, and prevalences. The Bayesian estimates were IFA sensitivity=60%, IFA specificity=88%, PCR sensitivity=80%, PCR specificity=86%, Herd A prevalence=20%, and Herd B prevalence=71%. Although PCR was the more sensitive assay, substantial misclassification of infection would be expected in epidemiological studies of BIV regardless of which assay was used.

Evidence of bovine immunodeficiency virus in cattle in Turkey

A seroepidemiological study of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) infections was conducted in four different cattle herds in Turkey. A total of 300 blood samples were analyzed and 12.3% were found to be positive for anti-BIV p26 antibodies by Western blot analysis and 1.6% positive for anti-BLV gp51 antibodies by an immunodiffusion test. BIV infection was confirmed with the detection of BIV-provirus DNA using the nested polymerase chain reaction. This is the first evidence for the presence of BIV in cattle in Turkey.

Seroprevalence of bovine immunodeficiency virus and bovine leukemia virus in dairy and beef cattle in hokkaido

Serological survey of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) infection was conducted in dairy cattle from 10 different regions of Hokkaido, Japan. Among 390 cattle, 11.0% of cattle were BIV-seropositive and 3.3% were BLV-seropositive. Moreover, in two dairy farms, where bovine leukosis has been reported, prevalence of BIV infections were 6.4 and 9.1%, respectively. In contrast, among 150 beef cattle, 16.6% were BIV-seropositive while none was BLV-seropositive. Dual infections with BLV and BIV in dairy cattle were tested by using 107 BLV-seropositive sera, and 20 sera were found BIV-positive (18.7%). These results indicate that BIV infection was widespread in Hokkaido.

Bovine immunodeficiency virus expression in vitro is reduced in the presence of beta-chemokines, MIP-1alpha, MIP-1beta and RANTES

The inhibition of HIV expression in vitro by a cocktail of the beta-chemokines MIP-1alpha, MIP-1beta and RANTES provided the initial evidence that HIV utilizes chemokine receptors as co-receptors for infection of cells. Bovine immunodeficiency virus (BIV), a lentivirus, infects a wide variety of leukocyte populations, but the cellular receptor(s) utilized by this virus for infection of cells is not known. The purpose of this study was to determine whether MIP-1alpha, MIP-1beta and RANTES affect BIV expression in vitro, as a prelude to identifying the cellular receptors utilized by this virus. Fetal bovine lung (FBL) cells were pretreated with serial dilutions of a cocktail of the chemokines, and then the cells were infected with BIV. Virus expression in these cells was determined by counting the syncytia that had developed in the cultures by five days after infection. A significant decrease in syncytium formation, corresponding to increasing concentrations of the chemokines, was the result. Reacting the chemokines with chemokine-specific neutralizing antibodies prior to treatment of the cells neutralized the effect of the chemokines on virus replication in a dose-dependent manner, restoring viral expression to a level similar to that of untreated cells. The presence of a CCR5 homologue on the surface of FBL cells was confirmed using an anti-CCR5 monoclonal antibody and FACS analysis. Collectively, these data provide preliminary evidence that BIV may utilize the CCR5 receptor for infection of cells in vitro, but additional studies are necessary to confirm this.

Vertical transmission of bovine leukemia virus and bovine immunodeficiency virus in dairy cattle herds

Vertical transmission of bovine leukemia virus (BLV) and bovine immunodeficiency virus (BIV) was investigated in five dairy cattle herds in Hokkaido, where 36.1 and 17.0% of cattle were BLV and BIV seropositive, respectively, and 9.9% of dams were co-infected with both BIV and BLV. Twenty six cases of offspring born from dams infected with only BLV (17 cases) or with both BIV and BLV (9 cases) were examined for the presence of BLV and BIV before and after colostrum feeding by polymerase chain reaction (PCR) and syncytium assay. After birth, all calves were separated immediately from their dams. The offspring born from BLV-positive dams were BLV-negative before colostrum feeding, suggesting that no transplacental transmission had occurred. Thereafter, these offspring were fed colostrum or milk from their dams, but still remained BLV-negative. The other offspring born from BLV-positive dams were fed with BLV-negative colostrum, or with pasteurized BLV-positive colostrum. All these calves remained negative for BLV infection, suggesting that in utero transmission of BLV is negligible. In the case of offspring born from dams co-infected with BLV and BIV, calves were BIV-positive before colostrum feeding at 1 day after the birth, indicating in utero transmission of BIV. After colostrum feeding from their dams, newborn calves became BLV-positive. In addition, one calf was BLV-positive even before colostrum feeding. These results suggest that BIV can be transmitted to offspring in utero, and that BLV can be transmitted through colostrum or milk if dams are infected with both BIV and BLV.

Differentiation of two bovine lentiviruses by a monoclonal antibody on the basis of epitope specificity

Bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV) are bovine lentiviruses that are closely related genetically. A recombinant fusion protein containing the capsid protein of BIV expressed in Escherichia coli was used to immunize mice and produce monoclonal antibodies. Six hybridomas specific for BIV capsid protein were identified, and one antibody, designated 10H1, was characterized further. Competitive binding assays were performed to analyze the topography of antigenic determinants by enzyme-linked immunosorbent assay and demonstrated the existence of at least three distinct antigenic determinants on capsid protein. The monoclonal antibody reacted specifically with both BIV capsid and the recombinant fusion protein in Western immunoblot analyses. However, it did not react with the recombinant capsid fusion protein of JDV, indicating that BIV contains at least one unique epitope in the capsid protein that is absent in JDV. Further mapping of the epitope by chemical cleavage analysis identified that the epitope is located at the 6.4-kDa N terminus of the 29-kDa capsid protein. This monoclonal antibody assay will be valuable for distinguishing the two closely related lentiviruses by Western blotting.

Seroprevalence of bovine immunodeficiency virus and bovine leukemia virus in draught animals in Cambodia

Since bovine immunodeficiency virus (BIV), known as bovine lentivirus, has been detected in dairy and beef cattle in various countries around the world, a prevalence study of antibodies to BIV and bovine leukemia virus (BLV) was conducted in draught animals in five provinces in Cambodia, where protozoan parasite infections were suspected in some animals. To clarify the status of draught animals including Haryana, Brahman, mixed-breed, local breed cattle and muscle water buffaloes, a total of 544 cattle and 42 buffaloes were tested, and 26.3 and 16.7%, respectively, were found positive for anti-BIV p26 antibodies determined by Western blotting. There were 5.3% positive for anti-BLV antibodies detected by immunodiffusion test among the cattle, but no reactors among buffaloes and no dual infection for both BIV and BLV was determined in this study. Peripheral blood mononuclear cells from BIV-seropositive cattle were found to have BIV-provirus DNA, as detected by polymerase chain reaction and subsequent Southern blot hybridization. This is the first evidence for the presence of BIV and BLV infections in draught animals in tropical countries such as Cambodia. This wide distribution of BIV suggests its association with problems in animal health as reported worldwide, and that a primary BIV infection can predispose death of affected animals by other aggressive pathogens or stresses.

Antigenic and genetic stability of bovine immunodeficiency virus during long-term persistence in cattle experimentally infected with the BIV(R29) isolate

Experimental infection of cattle with bovine immunodeficiency virus (BIV) is characterized by persistent, low levels of virus replication in the absence of clinical disease. A virus neutralization (VN) assay was developed to examine the role of VN antibodies in controlling virus replication in cattle experimentally infected with the BIV(R29) isolate of BIV. All animals developed VN antibody, but there was no correlation between VN titres and restriction of virus replication in vivo. BIV infection did not induce high-titred, cross-neutralizing antibody and there was no evidence for antigenic variation through more than 4 years in vivo. Genetic comparisons among the BIV(R29) inoculum virus and viruses isolated from infected animals identified only limited genetic variation during 4 years in vivo. Moreover, there was no evidence that the observed variation was due to selection. Analyses of genetic diversity in the virus stock used for inoculation indicated a fairly homogeneous population. In the absence of high levels of virus replication and overt clinical disease, there appeared to be little selection of virus variants, resulting in antigenic and genetic stability of BIV(R29) during long-term, persistent infection.

Serological evidence of an Australian bovine lentivirus

Recombinant 26 kDa capsid (CA) proteins of bovine lentiviruses, bovine immunodeficiency virus (BIV) and Jembrana disease virus (JDV), were expressed in Escherichia coli and utilised as antigens for an enzyme-linked immunosorbent assay (ELISA) and a western immunoblot (WIB) procedure for the detection of antibody in dairy cattle in Western Australia. A total of 690 serum samples, 30 from each of 23 farms, were tested by ELISA with a JDV CA protein antigen, and antibody was detected in 3.8% (p<0.05) of the sera. Nine sera from each farm were also tested by WIB with JDV CA protein antigens and antibody was detected in 15.9% of these samples. All ELISA-positive results were also WIB-positive, and all sera antibody-positive by WIB with JDV CA protein antigens were also antibody-positive by the WIB using recombinant BIV CA antigens. This study showed that recombinant protein antigens can be used for serological tests to detect bovine lentivirus infection in Australia.

Bovine immunodeficiency virus and analogies with human immunodeficiency virus

After describing the results of BIV research during the past years experimental data are presented which indicate that BIV does not cause any clinical symptoms after infection and that no correlation exists with the other widely spread retrovirus in the bovine, the bovine leukosis virus (BLV). Since contact obviously did not lead to a horizontal transmission it is suggested that transmission occurs, as in the cat, vertically from dam to offspring. It was also found that a long period of time after infection can elapse before antibodies against BIV can be detected. It is also quite clear that HIV and BIV do not have much in common except that both are lentiviruses.

Development of a Western blot assay for detection of bovine immunodeficiency-like virus using capsid and transmembrane envelope proteins expressed from recombinant baculovirus

A 120-amino-acid polypeptide selected from the transmembrane protein region (tTM) and the major capsid protein p26 of bovine immunodeficiency-like virus (BIV) were expressed as fusion proteins from recombinant baculoviruses. The antigenic reactivity of both recombinant fusion proteins was confirmed by Western blot with bovine and rabbit antisera to BIV. BIV-negative bovine sera and animal sera positive for bovine syncytial virus and bovine leukemia virus failed to recognize the recombinant fusion proteins, thereby showing the specificity of the BIV Western blot. One hundred and five bovine serum samples were tested for the presence of anti-BIV antibodies by the recombinant protein-based Western blot and a reference Western blot assay using cell culture-derived virions as test antigens. There was a 100% concordance when the p26 fusion protein was used in the Western blot. However, the Western blot using the tTM fusion protein as its test antigen identified four BIV-positive bovine sera which had tested negative in both the p26 recombinant-protein-based and the reference Western blot assays. This resulted in the lower concordance of 96.2% between the tTM-protein-based and reference Western blot assays. The results of this study showed that the recombinant p26 and tTM proteins can be used as test antigens for the serodetection of BIV-infection in animals.

The antibody response of cattle infected with bovine immunodeficiency virus to peptides of the viral transmembrane protein

The development of the antibody response to peptides of the transmembrane glycoprotein of bovine immunodeficiency virus (BIV) was followed over a period of 50 weeks in six cattle experimentally infected with the BIV(FL112) isolate. Antibody was detected by an enzyme immunoassay using either a linear or a cyclized peptide with structural features common to an immunodominant region of other lentiviruses. The assay was specific for BIV, detecting antibody in bovine sera to BIV(FL112) or BIV(R29) but not to six other common viruses of cattle. Antibody was present in the sera of all cattle inoculated with BIV(FL112) within 4 weeks of infection, peaked between 10 and 30 weeks and persisted in most cattle during the 50 weeks of observation. These features indicate that this assay may be useful in identifying cattle infected with other strains of BIV in the field.

Seroprevalence and field isolation of bovine immunodeficiency virus

A seroprevalence study of bovine lentivirus, known as bovine immunodeficiency virus (BIV), was conducted in 12 different dairy herds in Hokkaido, where some herds were a high prevalence of bovine leukemia virus (BLV) infection. Amongst 611 cattle, 28.6% of cattle were BLV-seropositive, and 11.7% of cattle were seropositive for BIV, while 4.2% of cattle were seropositive for both BIV and BLV. For the isolation of BIV, 19 samples of peripheral blood mononuclear cells (PBMC) and one sample of milk-derived leukocytes were prepared from BIV-seropositive cows. These PBMC and leukocyte preparations were then co-cultivated with cc81 cells, a cat cell line transformed by mouse sarcoma virus. BIV was isolated from 17 PBMC and one milk-derived leukocyte samples. The isolated viruses showed slow replication and syncytia formation. Major core antigen, p26 from these isolates were reacted with anti-BIV (American isolate R-29) serum. In addition, proviral DNA was detected in blood and milk samples by nested polymerase chain reaction and subsequent Southern blot hybridization. Nucleotide sequence analysis of the amplified pol gene products showed its 99.0 to 99.7% homology to that of BIV R-29. These results indicate that the Japanese BIV isolates appear to be antigenically and genetically similar to the American R-29. Since BIV was isolated from milk samples, BIV could possibly be transmitted through milk. This is the first report of BIV isolation in Japan.

Effects of long-term infection with bovine immunodeficiency virus and/or bovine leukemia virus on antibody and lymphocyte proliferative responses in cattle

Immune responses were examined in cattle between 3-5 years after experimental inoculation with bovine immunodeficiency virus (BIG) and/or bovine leukemia virus (BLV). Lymphocyte proliferative responses to Con A or to allogeneic lymphocytes with foreign major histocompatibility complex molecules (allo MHC) were determined by 3H-thymidine incorporation assays. Antigen-specific antibody and lymphocyte proliferative responses were measured following vaccination with tetanus toxoid (TT) and bovine herpes virus-1 (BHV-1). Lymphocytes from BIV-infected cattle had significantly (p<0.05) reduced proliferative responses to Con A, but responses to allo-MHC and TT did not differ from those of uninfected controls. BIV infection also had little effect on TT-specific antibody responses in vivo. In contrast, BLV-infected cattle had significantly increased secondary antibody responses to vaccination with TT, as well as enhancement of antibody responses to BHV-1. Co-infection with BIV did not alter the BLV effect, suggesting a lack of significant interaction between the two viruses in vivo. Numbers of circulating mononuclear cells were also higher in BLV-infected cattle, which was attributable to increases in both T and B cell numbers. Unstimulated lymphocytes from BLV-infected cattle had significantly increased spontaneous uptake of 3H-thymidine in vitro. When differences in counts per minute were analyzed, lymphocytes from BLV-infected cattle had slightly increased proliferative responses to Con A, but no consistent alternations in responsiveness to allo-MHC, TT, or BHV-1. The observed increase in antibody responses to non-BLV antigens suggests that at least in clinically asymptomatic cattle, BLV infection may cause a non-specific B cell activation.

Investigation of the cellular tropism of bovine immunodeficiency-like virus

Bovine immunodeficiency-like virus (BIV) was first isolated from an animal showing transient leucocytosis, lymphadenopathy, lesions in the central nervous system and progressive weakness and emaciation. Similar signs are observed in other immunosuppressive lentiviral infections. BIV, like other lentiviruses, has been isolated from peripheral blood mononuclear cells and lymphoid tissue of infected animals. However, the in vivo cellular tropism of BIV remains unclear although initial studies indicate that BIV may be pantropic, infecting T cells, B cells and monocytes similar to some of the immunodeficiency-causing lentiviruses. PCR, Southern blot hybridisation, cell culture and reverse transcriptase assays were used to demonstrate the presence of BIV proviral DNA and the production of infectious virus in CD2+, WC1+, B cells and monocytes during the acute stages of infection. Western immunoblot assays were used to assess the development of antibody responses towards the virus.

Longitudinal studies of immune function in cattle experimentally infected with bovine immunodeficiency-like virus and/or bovine leukemia virus

The effects of single or dual infection with bovine immunodeficiency-like virus (BIV) and/or, bovine leukemia virus (BLV) on bovine immune function were examined over a 4 year period. Holstein calves were infected with BIV (four calves), BLV (five calves), BIV and BLV (five calves), or sham inoculated (three calves). Lymphocyte blastogenesis to mitogens, seven tests of neutrophil function, and mononuclear cell subset analysis by flow cytometry (BoCD4, BoCD8, BoCD2, BoWC1, sIgM+, and monocytes) were performed at regular intervals to 49 months post-infection. These data were analyzed for main effects of each virus and interaction as a 2 x 2 factorial. BIV infected cattle had lower neutrophil antibody-dependent cell-mediated cytotoxicity and iodination responses during 2 of the 4 years post-infection (P < 0.05). BIV infection was not associated with any long-term significant changes in lymphocyte blastogenesis to mitogens or changes in mononuclear cell subset numbers in blood. There was a tendency for animals infected with BIV alone to have decreased lymphocyte blastogenic responses to mitogens, but this was not statistically significant. BLV infection caused an increase in total mononuclear cells with no dramatic shift in the relative proportions of the various subsets. Co-infection with BIV and BLV did not consistently cause a different response than either virus did individually. One BIV infected animal died of non-BLV lymphosarcoma 7 months after infection. All other animals had no unusual clinical signs. In summary, infection with BIV caused a significant, temporary decrease in neutrophil function with no consistent statistically significant alteration in lymphocyte blastogenesis or mononuclear cell numbers during the first 4 years after infection. BLV infection caused an increase in lymphocyte numbers, and there appeared to be no synergism between the viruses.

Immune suppression in calves with bovine immunodeficiency virus

The present study was designed to evaluate the effect of bovine immunodeficiency virus (BIV) infection on immune functions and possible interactions between BIV and other bovine viruses in calves. Ten calves were inoculated intravenously with BIV, and five served as controls. An increased lymphocyte proliferation to BIV gag protein was demonstrated 2 to 6 weeks after BIV inoculation (P < 0.05). Lymphocyte subset differentiation revealed a decreased CD4/CD8 ratio (P < 0.05) during weeks 2 to 7, suggesting a possible immune dysfunction in BIV-infected calves. When the calves were inoculated with bovine herpesvirus type 1 (BHV-1), the antibody response to BHV-1 in BIV-infected calves was delayed and the antibody titers were significantly lower (P < 0.05). Injection of bovine viral diarrhea virus vaccine also elicited a lower neutralizing antibody response in BIV-infected calves. The results indicated that immune suppression occurred in BIV-infected calves.

Immunomodulative effects of bovine immunodeficiency-like virus (BIV)-infection and mixed infection of BIV and bovine leukemia virus on sheep

Experimental bovine immunodeficiency-like virus (BIV)-infection and mixed infection of BIV and bovine leukemia virus (BLV) were performed on sheep. BIV proviral DNA and anti-BIV antibodies were persistently detected in all BIV-inoculated sheep. A slight increase in lymphocyte counts was observed in BIV-infected sheep, but the percentages of CD4+ and CD8+ cells in sheep peripheral blood mononuclear cells (PBMCs) were not significantly changed. A transient decrease in lymphocyte blastogenic response to concanavalin. A was observed in two of three BIV-infected sheep at 3-6 months after inoculation. From 6 months after BLV-inoculation to sheep which were previously infected with BIV, the numbers of lymphocytes expressing a tumor-associated antigen (TAA) of bovine leukosis were increased compared to those of a sheep inoculated with BLV alone. The BLV titers in PBMCs and the antibody titers against BLV from sheep infected with both BIV and BLV were higher than those of a sheep inoculated with BLV alone.

Lymphoproliferation assays in cattle naturally infected with bovine leukaemia virus (BLV) and bovine immunodeficiency-like virus (BIV)

Experiments were designed to evaluate the effect of BLV on mitogen-stimulated peripheral blood mononuclear cells (PBMC) from naturally infected cattle. BIV was also taken into consideration due to a recent report showing that in Costa Rica, most of the BLV-infected animals are also seropositive for BIV. The methodology was based on a non-radioactive technique to determine lymphoproliferation. A colorimetric assay using XTT (formazan salt) to measure cell multiplication was adapted for bovine PBMC. ELISA and Western blotting were used to determine the serologic status of the cattle. PCR was only available for BIV detection. Our results show clearly that, dually-infected cattle (BIV-BLV) have reduced lymphoproliferative responses to the mitogen Con A. Haematological abnormalities associated with viral infections were also observed, specially leukocytosis and lymphocytosis. Cows with lymphosarcomas are severely affected. The specific antibody response to different viral proteins could not be associated with the suppressive status of the animals. Due to the high rate of dual infections observed in Costa Rica, these results are not sufficient to clarify which virus is responsible for the suppressive activity, if one or both viruses are necessary, or if they act synergistically.

Detection of antibodies against bovine immunodeficiency-like virus in daily cattle in Hokkaido

Serological survey of bovine immunodeficiency-like virus (BIV) infection was performed in cattle of 3 different farms in Hokkaido, where a relatively high seroprevalence was recorded for bovine leukemia virus (BLV). About a half of 120 cattle tested were seropositive for BLV, while 7.5% of the cattle were seropositive for BIV. Though increased numbers of leukocytes were frequently observed in BLV-seropositive cows, no such changes were observed in BIV-positive but BLV-negative cows. No correlation was demonstrated between BIV- and BLV-seroprevalence of the cattle.

Serologic evidence for bovine immunodeficiency virus infection in France

We report herein on the first serologic detection of antibodies to bovine immunodeficiency virus (BIV) in France. Serum samples from dairy and beef cattle from southwestern and western France (Landes and Vendée) were tested using a western blot assay with a recombinant 53 kDa gag precursor derived from the Louisiana BIV R29 isolate. We performed our study on the oldest animals from 37 different herds that were under serologic follow up for previous bovine leukemia virus infection. Overall, 398 selected bovine sera were assayed and 15 serum samples from 8 herds reacted with the recombinant 53 kDa BIV R29 gag. Interestingly, reactions obtained with French sera were weaker than with positive Louisiana sera, a finding that may indicate the occurrence of distinct French and Louisiana BIV variants.

A serological survey of bovine syncytial virus in Ontario: associations with bovine leukemia and immunodeficiency-like viruses, production records, and management practices

Of the 920 cows tested, 56.7% showed antiretroviral serological reactivity. Prevalence rates (95% confidence interval) of antiretroviral antibodies among individual dairy cows in Ontario were: BIV 5.5% (4.0-7.0), BLV 25.7% (22.9-28.6), and BSV 39.6% (36.4-42.8). The following percentages of cows showed serological reactivity against the specified retroviruses: BIV 2.3%, BLV 14.0%, BSV 27.5%, BIV and BSV 1.3%, BIV and BLV 0.9%, BLV and BSV 9.9%, BIV and BLV and BSV 0.9%. These rates of sero-positivity are similar to those found in other countries. Serological test results were not adjusted for sensitivity and specificity. The prevalence rates of antibodies to the three retroviruses (BIV, BLV, and BSV) were significantly different, but no associations were observed between specific retroviral serological test results among individual cows. The prevalence rates of BIV and BSV seropositivity were constant across Ontario, whereas, there was a significant trend for the prevalence rate of BLV seropositivity to decrease going from southwestern to eastern Ontario; cows in eastern Ontario had approximately half the prevalence rate of those in southwestern Ontario. Cows that were seropositive for BSV were significantly older than BSV seronegative cows. There was no association between culling rate and BSV serology. Significant negative associations were found with winter or summer housing of calves separate from adults and summer outdoor exercise for dry cows. The use of calf hutches in the summer had a significant positive association with BSV seropositivity. Regression analyses were done to assess the association of retroviral (BIV, BLV, and BSV) seropositivity on calving interval, milk somatic cell count, and milk production. Serological test results for BIV, BLV, and BSV were entered into all models and all models were adjusted for intra-cluster (intraherd) correlation. Herd size and age were found to be important confounding variables. BIV seropositivity was not associated with any changes in production using this approach, however when considered in isolation BIV seropositivity remained associated with decreased milk production. BLV seropositivity was significantly associated with longer calving intervals and higher somatic cell counts in older cows. As well, in older cows, BSV seropositivity was significantly associated with higher milk production.

Two retroviral infections of periparturient Holstein cattle: a phenotypic and genetic study

Environmental and genetic factors affecting prevalences of antibodies to bovine leukosis virus and bovine immunodeficiency-like virus were studied on 137 periparturient Holstein cows selected for milk production. Environmental effects were obtained by logistic regression, and genetic parameters were determined using threshold animal models. Cows selected for high predicted transmitting ability for kilograms of milk fat plus protein had the highest prevalence of antibodies to bovine immunodeficiency-like virus and the lowest prevalence of antibodies to bovine leukosis virus. Heritability estimates for susceptibility to retroviral infections were close to zero.

Possible role of bovine immunodeficiency virus in bovine paraplegic syndrome: evidence from immunochemical, virological and seroprevalence studies

Bovine paraplegic syndrome (BPS) is a debilitating cattle disease of unknown origin that is characterized by leukocytosis, lymphocytopenia and monocytopenia. The major clinical signs are difficulties in locomotion affecting hind limbs, hypoalgesia in the hind quarters, posterior paralysis and death within 72 to 96 hours after recumbency. To investigate the aetiological basis of BPS, we examined a possible association of the syndrome with infection by bovine immunodeficiency virus (BIV), a lentivirus implicated in immune system dysfunction and central nervous system lesions in cattle. Serum samples (n = 1,278) were collected from both healthy and BPS-prevalent cattle herds in Venezuela, and organ extracts were prepared from euthanized animals (n = 11) suspected of having BPS. Sera were analysed for reactivity to recombinant BIV and bovine leukaemia virus gag precursor proteins by immunoblot procedures. Serum reactivity to BIV ranged from 12 to 66% between groups of BPS prevalent herds. The percentage of samples reactive to BLV antigen was much lower (2 to 17%). Rabbits inoculated with extracts from BPS-afflicted animals exhibited an anamnestic immune response to BIV antigens as well as the presence of BIV gag antigens in their tissues. We present evidence for a possible association between BPS disease and a viral agent related to BIV. The role of BIV, in combination with malnutrition, in BPS is discussed.

Loss of Gag-specific antibody reactivity in cattle experimentally infected with bovine immunodeficiency-like virus

The development and persistence of virus-specific antibodies were investigated in eight cattle experimentally infected with the R29 isolate of bovine immunodeficiency-like virus (BIV). By 4 weeks postinoculation (p.i.), antibodies reactive to BIV gag- and env-encoded recombinant fusion proteins were detectable by immunoblotting in all animals. By 40 weeks p.i., seven of eight cattle had dramatically decreased Gag-specific antibodies, and anti-Gag reactivity remained very low or undetectable through 190 weeks p.i. Immunoprecipitation experiments revealed a similar loss of reactivity to nondenatured BIV Gag in these animals. In contrast, antibodies to a recombinant BIV Env protein were readily detectable throughout the study in all eight cattle. During the period of declining Gag antibody, infectious virus was recoverable from peripheral blood mononuclear cells of each animal. However, there was no evidence for sufficient amounts of BIV p26-containing immune complexes to explain the loss of anti-Gag reactivity. Interestingly, the single animal that maintained detectable anti-Gag reactivity throughout the study was repeatedly negative for virus recovery beyond 17 weeks p.i. All animals have remained clinically normal for over 4 years p.i., with no evidence of consistent changes in mononuclear cell subsets. These findings provide evidence that in BIV infection an early decline in Gag-specific antibody reactivity can occur without evidence of increasing viral replication or progression to overt clinical disease.

Acquired immune dysfunction in rabbits experimentally infected with an infectious molecular clone of the bovine immunodeficiency virus (BIV127)

To investigate the effect of bovine immunodeficiency virus (BIV) infection on the rabbit immune system, we studied the proliferative responses of peripheral blood lymphocytes (PBLs) of rabbits experimentally inoculated with BIV. All BIV127-inoculated rabbits seroconverted after 6 weeks and remained seropositive over a prolonged period of time. Assays for specific lymphocyte reactivity to concanavalin A (Con A) were performed monthly for over 1 year. One-hundred percent of infected rabbits developed abnormally low T cell responses, as measured by Con A stimulation. By 3 months postinoculation, the PBL response to Con A was diminished and remained depressed for 6 months. All animals were clinically asymptomatic within 14 months of BIV inoculation. By 15 and 16 months postinoculation, two of three infected rabbits exhibited recurrent lowering of the T cell responsiveness including a decrease in absolute PBL counts. One of these animals died unexpectedly. Our results further confirmed that a functional impairment of lymphocytes was induced early in the course of BIV infection, prior to clinical disease. These findings suggested that BIV infection may mimic asymptomatic infection of human immunodeficiency virus (HIV) and provided further evidence of the importance of BIV-induced disease in rabbits as a relevant model for the study of AIDS.

Alteration of immune responses of rabbits infected with bovine immunodeficiency-like virus

Nine 3-month-old rabbits were inoculated with bovine immunodeficiency-like virus (BIV) to study the pathogenesis of BIV and alteration of the immune responses in experimentally infected rabbits. BIV proviral DNA and anti-BIV antibodies were detected from all rabbits inoculated with BIV-infected bovine embryo spleen (BESP) cells. Rabbits inoculated with spleen cells of the BIV-infected rabbit also converted to proviral DNA-positive and BIV-antibody-positive. The blastogenic responses to concanavalin A of peripheral blood mononuclear cells prepared from BIV-infected rabbits were not significantly different from those from uninfected controls at 2 and 4 months post-inoculation (PI). The humoral immune responses against bovine serum albumin (BSA) were depressed in two of four BIV-infected rabbits at 1 to 3 months PI. The antibody responses against sheep red blood cells (SRBCs) were significantly depressed in all BIV-infected rabbits at 2 to 4 months PI. BIV was rescued by cocultivation of spleen cells of infected rabbits with BESP cells. Distinct development of lymphoid follicle was observed in lymph nodes and spleens of uninfected rabbits which received BSA and SRBCs. In contrast, moderate lymphoid cell depletion was observed in BIV-infected rabbits which received the same immunogens.

Seroprevalence of bovine immunodeficiency-virus (BIV) antibodies in the cattle population in Germany

Serum samples from 380 cattle were analysed for the presence of bovine immunodeficiency-virus (BIV) antibodies by focus immunoassay (cell-ELISA) and immunofluorescence assay (IFA). All specimens originated from dairy farms in the eastern part of Germany, which had been randomly collected during the period 1989-1991. The cattle were clinically healthy and free of bovine leukaemia virus (BLV) and bovine-virus diarrhoea-virus (BVDV) antibodies. Infection of cell lines with BIV was monitored by syncytia formation, cell-ELISA, and immunofluorescence. The seroprevalence of BIV antibodies was 6.6%, as determined by cell-ELISA. Comparison of IFA and cell-ELISA showed that all IFA positive sera were also positive in cell-ELISA. However, additional sera were reactive only in cell-ELISA. This first report suggests that BIV infection may cause minor problems in German cattle, while BIV is present in a similar prevalence to that reported from other countries.

Bovine immunodeficiency virus: incidence of infection in Mississippi dairy cattle

Bovine immunodeficiency virus (BIV), a lentivirus, was originally derived from a Holstein cow with persistent lymphocytosis and severe wasting. The virus is known to occur sporadically throughout the United States and perhaps across the globe, but epidemiological data concerning the incidence of BIV are meager and the virus was previously unreported in Mississippi animals. This study examined the seroepidemiology of BIV infection from two Mississippi dairy herds (Coastal Plains and MSU). Serology revealed a 38% incidence of BIV infection in Coastal Plains animals and a 58% incidence in MSU animals. A cumulative BIV seroprevalence of 50% was found in the Mississippi animals, and BIV seroprevalence increased with increasing age of the animals. Peripheral blood leukocytes of age matched BIV seropositive and seronegative animals were enumerated to assess any effect of BIV infection on leukocyte populations. No significant differences were found in total leukocyte populations or leukocyte subpopulations between BIV seropositive or seronegative animals. These data indicate that BIV infection is prevalent in Mississippi animals, but the role of BIV in bovine disease remains unclear.

Haematological and lymphocyte subset analyses in sheep inoculated with bovine immunodeficiency-like virus

Bovine immunodeficiency-like virus (BIV) was passaged in vivo by intraperitoneal transfusion of ovine whole blood. Prior to transfusion, the recipient sheep were given sodium thioglycolate intraperitoneally to induce mild non-suppurative inflammation. The anti-BIV antibody response, haematology, and peripheral blood lymphocyte subsets (B, gamma delta, CD2+, CD4+ and CD8+) of recipient sheep were assessed for one year following transfusion. Passaging was successful since serum anti-BIV antibody responses were detected in 5 of the 6 recipient sheep; 1 of the 5 remained seropositive throughout the study. Lentivirus was not isolated from the recipient sheep, but provirus was detected by the polymerase chain reaction in DNA from peripheral blood leukocytes in 3 of the 5 sheep that seroconverted. In the BIV-inoculated sheep, neutrophils and eosinophils were significantly increased (p < or = 0.05) at 3 months and between 6 and 8 months postinoculation, respectively. B, CD2+ and CD4+ cells and the CD4+/CD8+ ratios were significantly increased (p < or = 0.05) 2 months postinoculation. Mild, transient haematological changes occurred in BIV-exposed sheep, but illness was not detected in the year.

Use of TrpE fusion protein to identify antigenic domains within the BIV envelope protein

Nine different recombinant clones spanning various regions of the bovine immunodeficiency-like virus (BIV) envelope gene open reading frame were generated. These clones span the entire external glycoprotein as well as the transmembrane glycoprotein region. These proteins were expressed as fusions to the TrpE protein in E. coli. The levels of recombinant protein expressed varied, some clones expressed enough protein that can be detected in a Coomassie blue-stained gel, whereas other proteins could only be detected by Western blot analyses. A recombinant env protein representing the extracellular domain of the env protein was detected by BIV-infected bovine sera. In addition, a 134 amino acid peptide which may represent a major immunoreactive epitope was identified. This peptide is located at the amino terminus of the transmembrane glycoprotein and was specifically recognized by all BIV-infected calf sera tested. The identification of this epitope and the use of recombinant envelope protein will enable us to develop a more effective screening test to study the epidemiology of BIV infection.

Cell-mediated and humoral immunity in sheep exposed to bovine immunodeficiency-like virus

Six sheep were transfused intraperitoneally with whole blood from two sheep chronically infected with the bovine immunodeficiency-like virus (BIV). Five sheep were transfused intraperitoneally (i.p.) with normal ovine whole blood and served as controls. Five of six BIV-inoculated sheep seroconverted; four were transiently seropositive while one remained seropositive for the duration of the experiment. Tests for nonspecific lymphocyte reactivity to mitogens were performed monthly for one year. At approximately 10 months postinoculation, all sheep were immunized with chicken ovalbumin, canine red blood cells, and tuberculin. There were no significant associations between BIV exposure and deficits in antibody production to chicken ovalbumin and canine red blood cells; nonspecific lymphoproliferative responses to concanavalin-A, lipopolysaccharide, and pokeweed mitogen; specific lymphoproliferative responses to ovalbumin and tuberculin purified protein derivative; or cutaneous delayed type hypersensitivity to tuberculin purified protein derivative. Exposure to BIV did not alter the humoral or cell mediated immune responses of sheep in the first year of exposure.

Serological evidence of bovine immunodeficiency-like virus infection in a sheep

A six month-old sheep was entered into a control group in an experiment designed to study the effects of exposure to the bovine immunodeficiency-like virus (BIV). Anti-BIV antibodies were detected in the serum of this sheep prior to the start of the study; these antibodies persisted for 12 months at which time the animal was destroyed. The sheep was normal clinically and was grossly normal at postmortem examination. Blood from this sheep was inoculated into a recipient sheep which subsequently showed a transient anti-BIV antibody response beginning two months postinoculation. Sheep have been previously shown to produce anti-BIV antibodies after experimental inoculation with infected cell culture material or infected bovine blood and BIV infection was found in a sheep pastured with BIV-infected cattle. In the present case there was no contact with cattle; the source of the infection was not identified.

In vitro detection of bovine immunodeficiency-like virus using monoclonal antibodies generated to a recombinant gag fusion protein

An Escherichia coli recombinant fusion protein containing the major core protein of bovine immunodeficiency-like virus (BIV) was used to immunize mice for generation of monoclonal antibodies to BIV p26. Eight hybridomas specific for BIV p26 were identified and two antibodies, designated 104 and 142, were further characterized. Both 104 and 142 antibodies were isotyped as IgG1; they reacted specifically with both BIV p26 and the recombinant fusion protein in Western immunoblot analyses. However, the epitope specificity of the antibodies was different. Immunoperoxidase assays were used to determine if antibodies 104 and/or 142 could detect BIV replication in cell culture. Both antibodies were found to react with BIV-induced syncytia and individual BIV-infected cells. The antibodies were also used successfully in a focal immunoassay for quantitation of BIV-infected cells. These antibodies will provide valuable reagents for detection and quantitation of BIV replication in studies of viral pathogenesis and immunity.

Effect of bovine immunodeficiency-like virus infection on immune function in experimentally infected cattle

Bovine immunodeficiency-like virus (BIV) is a bovine lentivirus that has antigenic and genetic homology with the human immunodeficiency virus. Little work has been reported on the effect of BIV infection on bovine immune function. This study was designed to evaluate lymphocyte blastogenesis, mononuclear cell subset numbers, neutrophil function, hematology, and clinical signs in three groups of cattle. These groups were evaluated at 0-2 months post inoculation (PI, Group 1), 4-5 months PI (Group 2), or 19-27 months PI (Group 3). BIV infected animals were inoculated with the R-29 isolate of BIV in tissue culture cells, peripheral blood mononuclear cells from a R-29 infected calf, or a molecular clone of the R-29 isolate. Most inoculated animals seroconverted to BIV by Western immunoblot. BIV was reisolated from most of the animals inoculated. BIV infection was associated with an increase in the lymphocyte blastogenic response to the mitogen phytohemagglutinin in Groups 2 and 3. Neutrophil antibody dependent cell mediated cytotoxicity and neutrophil iodination were decreased (P < 0.05) in BIV infected cattle (Groups 2 and 3 and Group 3, respectively). All animals were clinically normal during the evaluation periods. Notable differences were not observed in the other assessments performed. Work with additional BIV isolates and over longer time frames is warranted.

Immunological characterization of the gag gene products of bovine immunodeficiency virus

The bovine immunodeficiency virus (BIV) gag gene encodes a 53-kDa precursor (Pr53gag) that is involved in virus particle assembly and is further processed into the putative matrix (MA), capsid (CA), and nucleocapsid (NC) functional domains in the mature virus. Gag determinants are also found in the Gag-Pol polyprotein precursor. To immunologically identify the major precursors and processed products of the BIV gag gene, monospecific rabbit sera to recombinant BIV MA protein and Pr53gag and peptides predicted to correspond to the CA and NC proteins and the MA-CA cleavage site were developed and used in immunoprecipitations and immunoblots of BIV antigens. Monospecific antisera to native and recombinant human immunodeficiency virus type 1 proteins were also used to identify analogous BIV Gag proteins and to determine whether cross-reactive epitopes were present in the BIV Gag precursors or processed products. The BIV MA, CA, and NC Gag proteins were identified as p16, p26, and p13, respectively. In addition to BIV Pr53gag, the major Gag precursor, two other Gag-related precursors of 170 and 49 kDa were identified that have been designated pPr170gag-pol and Pr49gag, respectively; pPr170gag-pol is the Gag-Pol polyprotein precursor, and Pr49gag is the transframe Gag precursor present in pPr170gag-pol. Several alternative Gag cleavage products were also observed, including p23, which contains CA and NC determinants, and p10, which contains a peptide sequence conserved in the CA proteins of most lentiviruses. The monospecific antisera to human immunodeficiency virus type 1 CA (p24) and NC (p7) proteins showed cross-reactivity to and aided in the identification of analogous BIV proteins. Based on the present data, a scheme for the processing of BIV Gag precursors is proposed.

Detection of multiple retroviral infections in cattle and cross-reactivity of bovine immunodeficiency-like virus and human immunodeficiency virus type 1 proteins using bovine and human sera in a western blot assay

Bovine antibovine immunodeficiency-like virus (BIV) antibodies were detected by Western blot analysis (WBA) using a chemiluminescence protocol. Bovine sera with anti-BIV activity, obtained from cows in two dairy herds, had antibodies directed against a variety of BIV-specific antigens indicating chronic infections. These sera were also tested for serological reactivity against bovine leukemia virus (BLV) and bovine syncytial virus (BSV). Cows most commonly had anti-BSV antibodies (12 of 39). Evidence for infection with BSV and BIV or BSV and BLV occurred with almost equal frequency (5 of 39 and 4 of 39, respectively) while only one instance of BIV and BLV coseropositivity was detected. The high prevalence of BSV seropositivity is consistent with a relatively infectious virus, which, as is known, may be transferred congenitally. Similar rates of coseropositivity of BIV or BLV with BSV in this population suggest that BIV is no more infectious than BLV and probably requires prolonged close contact for transmission. Seven of nine cows with anti-BIV antibodies detected primarily human immunodeficiency virus type 1 (HIV-1) p51 and p63 antigens by WBA using an alkaline phosphatase detection system, suggesting that HIV-1 proteins have potential usefulness in screening cattle for BIV seropositivity. Six human sera that showed strong reactivity against multiple HIV-1 proteins and the serum from one of three patients considered to be an "indeterminate" HIV-1 reactor, cross-reacted primarily with BIV p26. This is the first report of human sera with antibody to BIV-specific proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Infection and dysfunction of monocytes induced by experimental inoculation of calves with bovine immunodeficiency-like virus

Three calves were experimentally inoculated with bovine immunodeficiency-like virus (BIV) to examine BIV pathogenesis. Inoculated calves produced specific antibody that could be detected from 3 to 5 weeks up to 1 year postinoculation (pi). Virus was isolated from peripheral blood mononuclear cells (PBMC) 3-4 weeks pi by syncytia assay. Thereafter, the virus could be continually isolated. BIV could be isolated from monocytes but not from T cells. Likewise, monocytes could be infected with BIV in vitro. Various monocyte functions of these BIV-infected calves and age-matched uninfected calves were tested; superoxide anion release, phagocytic activity, and chemotactic responsiveness of monocytes were depressed in BIV-infected calves compared with control calves. A slight delay in the humoral immune response against mouse serum protein was also evident. During the observation period of approximately 1 year, no significant clinical symptoms could be observed. One calf, however, was killed at 15 months pi. At the time of necropsy, BIV could be isolated from PBMC as well as from cells of the spleen, liver, and lymph nodes.

Persistent infection of rabbits with bovine immunodeficiency-like virus

Chronic infection of rabbits was induced by a single intraperitoneal injection of bovine immunodeficiency-like virus (BIV)-infected cells. Ten BIV-infected animals were monitored serologically for up to 2 years. Results of serologic and virus rescue assays indicated that all animals became infected and demonstrated a rapid and sustained BIV-specific humoral response. BIV was rescued by cocultivation from spleen, lymph nodes, and peripheral blood leukocytes of infected animals. Viral DNA in immune tissues was confirmed by polymerase chain reaction amplification of BIV sequences. These data and specific immunohistochemical staining of mononuclear cells of the spleen for BIV antigen suggest that the infection is targeted to immune system cells.

Seroprevalence of bovine immunodeficiency-like virus and bovine leukemia virus in a dairy cattle herd

To determine the prevalence of single vs. dual infection with bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV), sera (n = 95) from a dairy cattle herd were analyzed for anti-BIV and anti-BLV antibodies by an enzyme linked immunosorbent assay. Twenty-one percent (20/95) of samples were BIV-seropositive, while 52% (49/95) of the same samples were BLV-seropositive. A significantly greater percentage of BIV-seronegative samples were BLV-seropositive, 57% (43/75), than were BIV-seropositive samples, 30% (6/20). There was no significant correlation between data ranked from least to greatest amount of anti-viral antibody. Five cattle had persistent lymphocytosis (PL); all five were BLV-seropositive and two were BIV-positive. The mean anti-BLV titer was significantly greater in PL cattle, as compared at non-PL cattle, whereas there was no significant difference between the mean anti-BIV titer in PL cattle, as compared with non-PL cattle. These results provide additional information on the seroprevalence of naturally occurring BIV infection, and indicate that BIV can exist independent of other common infectious agents, such as BLV. Further, the results suggest that infection with BIV is not associated with an increased rate of infection with other infectious agents such as BLV.

Examination of whether persistently indeterminate human immunodeficiency virus type 1 Western immunoblot reactions are due to serological reactivity with bovine immunodeficiency-like virus

The bovine lentivirus, known as bovine immunodeficiency-like virus (BIV), is genetically, structurally, and antigenically related to human immunodeficiency virus type 1 (HIV-1). It is not known whether sera from persons exposed to BIV proteins would show either positive or indeterminate reactivity on HIV-1 antibody tests. We used a BIV Western blot (immunoblot) analysis to examine human sera characterized as HIV-1 antibody positive, HIV-1 antibody negative, HIV-1 persistently indeterminate, HIV-1 p17 antibody positive only, HIV-1 p24 antibody positive only, human T-cell leukemia virus type 1 (HTLV-1) p19 antibody positive only, or HTLV-1 p24 antibody positive only. None of these sera were positive by Western blot to BIV-specific proteins. Many of these sera, however, displayed strong reactivities to bovine cell culture antigens on blots prepared from both mock-infected and BIV-infected cell cultures. The HIV-1 p17 and p24 antibody-positive and the HTLV-1 p19 and p24 antibody-positive sera were further examined by Western blot to bovine leukemia virus (BLV) and were found to be negative. We examined sera from laboratory personnel at risk for BIV exposure, including two laboratory workers who were exposed to BIV by accidental injection with BIV-infected cell culture material, and found no evidence of seroconversion to BIV-specific proteins. We tested 371 samples of fetal bovine sera, each sample representing serum pooled from one to three fetuses. All samples were negative by BIV Western blot. To date, we have not detected any human sera with antibody to BIV-specific proteins. Our data indicate that persistently indeterminate results on HIV-1 Western blot are not caused by a human antibody response to BIV proteins.

Use of bacterial trpE fusion vectors to express and characterize the bovine immunodeficiency-like virus core protein

The gag coding region from Bovine Immunodeficiency-like Virus (BIV) was cloned into E. coli and expressed as a bacterial fusion protein. Six different clones spanning various regions of the gag open reading frame were generated. The resulting fusion proteins were expressed at high concentrations and readily purified. A panel of bovine immune sera specifically recognized the recombinant Gag proteins, as did immune sera from animals infected or immunized with lentiviruses related to BIV, such as Equine Infectious Anemia Virus (EIAV) and Human Immunodeficiency Virus (HIV). Analysis of the deletion clones, using the bovine immune sera panel, enabled us to identify at least one major epitope which was specifically recognized by all bovine sera examined. The ease of expression, purification, and specificity of these fusion proteins should enable a thorough study of the epidemiology of BIV infection.

Bovine immunodeficiency virus: immunochemical characterization and serological survey

Bovine immunodeficiency virus (BIV) was purified by isodensity centrifugation; viral activities were monitored in gradient fractions using the reverse transcriptase assay and a p26-specific monoclonal antibody ELISA. In the coincident peak fractions (density about 1.17 g/ml) proteins with Mr values of 26K, 17K, 53K, 14K and 100K (with decreasing intensity) were detected by Western blotting using serum of a calf after experimental BIV infection. When 957 randomly collected cattle sera from The Netherlands were tested by indirect immunofluorescence and confirmed using Western blot and/or radioimmunoprecipitation, 1.4% appeared seropositive. Thus BIV infection is not uncommon in one European cattle population.

A western blot assay for the detection of antibodies to bovine immunodeficiency-like virus in experimentally inoculated cattle, sheep, and goats

A cocultivation method was used to establish a cytocidal bovine immunodeficiency-like virus (BIV) infection in primary fetal bovine lung (FBL) cell cultures. Cultures were monitored for virus production using radial immunodiffusion and agar gel immunodiffusion. Pelleted virus and detergent (CHAPS)-solubilized infected cell lysates from BIV-infected cell cultures were compared as sources of antigen for Western blots. Pelleted virus preparations from FBL-BIV cell cultures produced the best antigen for Western blot. Sheep and goats were inoculated with BIV and serum antibody responses were monitored up to 1 year post inoculation (PI). Sera from experimentally infected cattle, sheep, and goats reacted in Western blot assay with BIV viral induced polypeptides gp 110, p 72, p 55, p 50, gp 42, p 38, p 26, p 24, p 18, p 15, and p 13. Antibodies to p 26 were detected as early as 2 weeks PI in cattle, sheep, and goats. Antibodies to gp 110 were detected by 4 to 6 weeks PI in cattle, and by 9 months PI in sheep and goats. Antibodies to BIV proteins were still evident in cattle sera 2 1/2 years PI, and in sheep and goat sera 1 year PI.