Bovine Immunodeficiency-like Virus Infection Research Articles

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.

Monocyte function in cattle experimentally infected with bovine immunodeficiency-like virus

The effects of bovine immunodeficiency-like virus (BIV) on monocyte function were examined in experimentally infected cattle and in monocytes infected in vitro. Infection with the R29 isolate of BIV appeared to have relatively little effect on monocyte function in cattle during the first 2 years postinfection (PI). For the first 4 to 8 months post infection, monocyte phagocytosis of Staphylococcus aureus tended to be lower ( P=0.06) in BIV infected calves than in control animals. After 8 months PI, however, phagocytosis became equal between the two groups. Random and chemotactic migration and antibody-dependent cell-mediated cytotoxicity (ADCC) did not appear to be affected by BIV infection. Monocytes from BIV infected cattle were able to respond to in vitro treatment with interferon γ similarly to monocytes from control cattle. Although experimental infection with BIV R29 resulted in minimal effects on monocyte function, this result could have been due either to a low virus burden in vivo or because BIV is intrinsically unable to affect monocyte function. To distinguish between these possibilities, monocytes from control, uninfected cattle were treated with BIV virus in vitro. Treatment of normal monocytes with cell-free virus significantly ( P<0.05) increased phagocytosis and random and chemotactic migration and decreased ADCC, in a dose-dependent manner. It appears, therefore, that the normal function of peripheral blood monocytes in the BIV R29 infected animals may be due to a low virus burden rather than to the inability of BIV to affect monocyte function. The in vitro infection results also raise the possibility that the function of monocyte derived cells at local sites of BIV replication may be altered.

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.

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.

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.

Bovine immunodeficiency-like virus encodes factors which trans activate the long terminal repeat

Lentiviruses are known to encode factors which trans activate expression from the viral long terminal repeat (LTR); the primary trans activator is the tat gene product. One of the putative accessory genes (tat) of the bovine immunodeficiency-like virus (BIV) bears sequence similarity to other lentivirus tat genes. This finding suggests that BIV may encode a trans-activating protein capable of stimulating LTR-directed gene expression. To test this hypothesis in vitro, BIV LTR-chloramphenicol acetyltransferase (CAT) reporter gene plasmids were constructed and transfected into three cell lines established from canine, bovine, or lapine tissues that are susceptible to BIV infection. The level of BIV LTR-directed CAT gene expression was significantly elevated in BIV-infected cells compared with uninfected cells. The relatively high basal-level expression of BIV LTR-CAT in uninfected canine and bovine cell lines suggests that cellular factors play a role in regulating BIV LTR-directed gene expression. Additionally, by using a clonal canine cell line in which the BIV LTR-CAT plasmid is stably expressed, BIV LTR-directed CAT expression is elevated 15- to 80-fold by cocultivation with BIV-infected cells, supporting the notion that BIV encodes a trans activator. The relative specificity of this viral activation was assessed by coculturing the clonal BIV LTR-CAT cell line with bovine leukemia virus- or bovine syncytial virus-infected cells; these bovine retroviruses increased expression from the BIV LTR only two- to threefold. Thus, BIV LTR regulatory elements in infected cells, like those of human immunodeficiency virus type 1 and other lentiviruses, are trans activated, presumably through the action of a Tat-like protein and cellular factors.

Infection of rabbits with bovine immunodeficiency-like virus

New Zealand White rabbits, which had been prepared for inoculation by intraperitoneal treatment with thioglycollate, were inoculated intraperitoneally with bovine immunodeficiency-like virus (BIV). Infected materials from various sources were used including cultured cells and culture fluids, peripheral blood leukocytes from infected cattle and spleen tissue tissue from previously infected rabbits. Virus isolations and serological responses detected by western blotting provided clear evidence that infections had been established in inoculated rabbits and that the spleen was an important site of BIV infectivity. These results indicate that rabbits may be a useful species when testing for BIV infectivity in materials too toxic or highly contaminated to be inoculated directly into cell cultures. Furthermore, rabbits may also be useful in testing effects of coinfections with other bovine viruses on progression of BIV infection and for the initial evaluation of therapeutic regimens designed to suppress or eliminate BIV infections.

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.

Lymphocyte transformation abnormalities in bovine immunodeficiency-like virus infected calves

Bovine immunodeficiency-like virus (BIV) is a lentiviral pathogen of cattle which is genetically and antigenically related to the human immunodeficiency virus (HIV-1). To determine the impact of BIV infection on the bovine immune system we studied the lymphocyte transformation responses of male Holstein calves inoculated with BIV strain R-29 to three mitogens: pokeweed mitogen (PWM), concanavalin A (Con A), and phytohemagglutinin (PHA) at two and six months post-infection. By six months post-inoculation the response to all three mitogens was diminished compared to control animals and remained depressed 10 months post-inoculation. These results demonstrate that a functional impairment of lymphocytes can be observed early in the course of BIV infection, and prior to the onset of overt clinical disease.