Passively administered neutralizing monoclonal antibodies do not protect calves against bovine herpesvirus 1 infection

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Effects of virion host shut-off activity of bovine herpesvirus 1 on MHC class I expression

Previously, we have shown that bovine herpesvirus 1 (BHV-1) down-regulates the expression of major histocompatibility complex class I molecules by interfering with transport of peptides by the transporter associated with antigen processing (TAP). Further studies revealed that BHV-1 down-regulates the expression of mRNA for class I molecules and other cellular proteins. To further elucidate the mechanisms of down-regulation of class I molecules, a virion host shut-off (vhs) deletion mutant was generated. The mutant, like the wildtype (wt) virus, interfered with transport of peptides by the TAP, and down-regulated cell surface expression of class I molecules. However, unlike the wt virus, the mutant did not impair the synthesis of class I molecules. These results indicate that down-regulation of class I molecules by BHV-1 is mediated by vhs activity of the virus, as well as mechanisms specifically directed at the class I pathway. Absence of vhs activity should result in decreased pathogenicity and enhanced immunogenicity of BHV-1 vhs deletion mutant, making it a better vaccine candidate.

Latency and reactivation of a glycoprotein E negative bovine herpesvirus type 1 vaccine: influence of virus load and effect of specific maternal antibodies

The effects of the vaccination of neonatal calves with a glycoprotein E (gE)-negative bovine herpesvirus type 1 (BHV-1) were investigated in naïve and passively immunised calves either with the recommended dose or a 5-fold concentrated one. After inoculation (PI), all calves excreted the virus vaccine except three passively immunised calves inoculated with the lower titre. No antibody response could be detected in passively immunised calves, whatever the dose used, and they all became BHV-1 seronegative and remained so after dexamethasone treatment (PDT). Nevertheless, as shown by a gamma-interferon assay, all calves that excreted the vaccine PI developed a cell-mediated immune response and a booster response was observed PDT, suggesting viral reactivation. The vaccine virus was recovered PDT from nasal secretions in two calves and BHV-1 DNA were detected in trigeminal ganglia from five calves belonging to all inoculated groups. The results show that the BHV-1 gE-negative vaccine can establish latency not only in naïve but also in passively immunised neonatal calves after a single intranasal inoculation. Moreover, this study shows for the first time that the gE-negative vaccine, when used in passively immunised calves, can lead to seronegative vaccine virus carriers.

Heat shock protein-peptide complexes elicit cytotoxic T-lymphocyte and antibody responses specific for bovine herpesvirus 1

Epitope-based vaccines offer a promising alternative to modified live vaccines against viruses such as herpesviruses which give rise to latent infections, and induce immunosuppression. The success of this approach depends on the ability to direct the CTL epitopes to the MHC class I antigen presentation pathway. The objective of this study was to evaluate the potential of the heat shock protein gp96 in this regard. A group of BALB/c mice was injected with three murine CTL epitope peptides of bovine herpesvirus 1 (BHV-1) complexed in vitro with bovine gp96 (gp96-peptides). Three other groups were injected with either the peptides alone, gp96 alone, or the peptides complexed with BSA. CTLs from mice immunized with gp96-peptides specifically lysed the peptide-pulsed syngeneic targets, as well as BHV-1-infected targets. CTLs from the other three groups did not lyse these targets. To further evaluate the utility of this approach, groups of BALB/c mice were immunized with gp96 isolated from a syngeneic cell-line transduced with BHV-1 glycoprotein D (BC-gD). Mice immunized with gp96 from BC-gD developed CTLs, as well as Abs specific for BHV-1 gD. Furthermore, in vitro stimulation of naive bovine PBMCs with gp96 from BC-gD resulted in CTLs specific for BHV-1. These results demonstrate the feasibility of using gp96-peptide complexes isolated from cells expressing BHV-1 proteins to induce CTL and Ab responses against BHV-1, without the prior knowledge of the CTL and Ab epitope sequences.

Effects of bovine herpesvirus type 1 infection in calves with maternal antibodies on immune response and virus latency

The presence of maternally derived antibodies can interfere with the development of an active antibody response to antigen. Infection of seven passively immunized young calves with a virulent strain of bovine herpesvirus type 1 (BHV-1) was performed to determine whether they could become seronegative after the disappearance of maternal antibodies while latently infected with BHV-1. Four uninfected calves were controls. All calves were monitored serologically for 13 to 18 months. In addition, the development of a cell-mediated immune response was assessed by an in vitro antigen-specific gamma interferon (IFN-gamma) production assay. All calves had positive IFN-gamma responses as early as 7 days until at least 10 weeks after infection. However, no antibody rise was observed after infection in the three calves with the highest titers of maternal antibodies. One of the three became seronegative by virus neutralization test at 7 months of age like the control animals. This calf presented negative IFN-gamma results at the same time and was classified seronegative by enzyme-linked immunosorbent assay at around 10 months of age. This calf was latently infected, as proven by virus reexcretion after dexamethasone treatment at the end of the experiment. In conclusion, this study demonstrated that BHV-1-seronegative latent carriers can be obtained experimentally. In addition, the IFN-gamma assay was able to discriminate calves possessing only passively acquired antibodies from those latently infected by BHV-1, but it could not detect seronegative latent carriers. The failure to easily detect such animals presents an epidemiological threat for the control of BHV-1 infection.

Mapping T and B lymphocyte epitopes of bovine herpesvirus-1 glycoprotein B

Glycoprotein B (gB) is a major envelope protein of bovine herpesvirus-1 (BHV-1). As a subunit vaccine, the extracellular domain of recombinant gB induces neutralizing antibody and T cell responses that engender protection against virus challenge. Here, lymphocytes from animals of different parentage were analysed for T cell proliferation to the gB extracellular domain for immune recognition. Four truncated overlapping gB gene segments encoding 742 amino acids were expressed from a baculovirus vector to identify antigenic regions. One immunodominant region (amino acids 254-532) was recognized by T cells from immune individuals of different parentage. Serial synthetic peptides spanning this region localized the T cell (amino acids 319-340 and 415-436) and B cell (amino acids 331-352, 475-496 and 487-508) epitopes. Elucidation of gB epitopes indicates the diverse and distinctive recognition by T cells and antibodies of this envelope glycoprotein by cattle, the natural host of BHV-1.

Bovine herpesvirus-1 infection affects the peptide transport activity in bovine cells

Infection of cattle with bovine herpesvirus-1 (BHV-1) impairs the cell-mediated immune response (CMI) of the affected host. We investigated the location of interference of BHV-1 with the major histocompatibility complex (MHC) class I antigen presentation pathway by employing an assay that allows assessment of the peptide transport activity of the Transporter associated with Antigen Presentation (TAP) from the cytoplasm into the endoplasmic reticulum (ER). We found a considerable down-regulation of the peptide transport activity in bovine epithelial cells, taking place as early as 2 h after virus infection. This down-regulation was also dose-dependent, and, at high multiplicities of infection (moi), led to an almost complete shutdown of TAP. By inhibiting peptide transport into the ER, the virus impairs loading of MHC class I molecules and their subsequent egress from the ER to the cell surface. This may lead to defective priming of cytotoxic T lymphocytes. Thus, BHV-1 is yet another member of its family Herpesviridae that selectively interferes with the host's antigen presentation machinery to evade the host's immune response in vivo.

Infectious bovine rhinotracheitis, parainfluenza-3, and respiratory coronavirus

A number of viruses have been proven to be primary respiratory pathogens of cattle. Viruses may play an important role in making cattle susceptible to secondary respiratory bacterial pathogens. Epidemiology, pathogenesis, laboratory diagnosis, and important properties in infectious bovine rhinotracheitis (IBR), parainfluenza-3 (PI-3), and bovine respiratory coronavirus (BRCV) are described in this article.

Bovine herpesvirus 1 downregulates the expression of bovine MHC class I molecules

The mechanism of immunosuppression induced by bovine herpesvirus 1 (BHV-1) was investigated by studying the effects of the virus on the expression of major histocompatibility complex (MHC) class I molecules. After infection with the virus, the expression of class I molecules was detected by flow cytometry and pulse-chase analysis. A selective downregulation of expression of class I molecules was seen in the infected cells, while the class II expression remained unaffected. The reduction in surface expression was evident as early as 8 hours postinfection, reaching significant levels by 12 hours. The downregulation was seen with a multiplicity of infection as low as 0.1. A modified live vaccine strain of BHV-1 also induced the downregulation of class I expression. Analysis of the viral proteins(s) involved in this downregulation with metabolic inhibitors (cycloheximide or phosphonoacetic acid), suggested that the immediate early and/or early proteins of the virus mediate this effect. Pulse-chase analysis revealed that the synthesis of the class I heavy chain, and the assembly/transport of class I molecules were affected by the virus infection. These results suggest that BHV-1 interferes with the molecular mechanisms involved in the synthesis, and assembly/transport of MHC-class I molecules. This interference with the class I antigen processing pathway might help the virus to evade the cytotoxic T-lymphocyte response of the host.

Failure of an in vitro lymphoproliferative assay specific for bovine herpes virus type 1 to detect immunised or latently infected animals

The in vitro lymphoproliferative assay specific for bovine herpes virus type 1 (BHV1) was tested for its ability to predict whether an animal was protected against challenge with virulent BHV1 and for its ability to identify animals latently infected with the virus. Three animals that had been in contact with a field strain of the virus, three that had been vaccinated with a modified live-virus vaccine seven weeks previously, six that had been vaccinated in the same way five months previously, and seven control animals that had had no previous contact with the virus were challenged with virulent BHV1. The 12 animals that had had previous contact with BHV1 all resisted the challenge well or fairly well, but six of them did not react positively in the in vitro lymphoproliferative assay. It was concluded that the assay did not give consistent evidence of the immune status of the animals. Four animals that had had previous contact with a field strain of BHV1 were treated with dexamethasone; they excreted BHV1 irrespective of whether they showed a positive response in the in vitro lymphoproliferative assay.

Identification of two independent MHC class II antigens in a bovine lymphoblastoid cell line

Bovine major histocompatibility complex (MHC) class II antigens were investigated using monoclonal antibodies (MoAbs) with known MHC class II specificities in other species. Thirty-four MoAbs were tested for reactivity with bovine peripheral blood mononuclear (PBM) cells and the bovine lymphoblastoid cell line, BL3, by flow cytometry. Twenty-seven of 31 MoAbs tested, reacted with BL3 cells, and 22 of 25 MoAbs tested with PBM cells were reactive. MoAbs that reacted with BL3 cells were used to immunoprecipitate class II molecules from BL3 lysate labeled with [35S]methionine. Using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography, many MoAbs were found to immunoprecipitate a single band of approximately 31,000 relative mass (Mr). MoAbs yielding successful immunoprecipitations and with known antigen specificity in other species were then used in sequential immunoprecipitations and two dimensional (2-D) non-equilibrium pH gradient electrophoresis (NEPHGE). The HLA-DR specific MoAb H4 and the predominantly HLA-DQ specific MoAb CC11.23 were used to identify the presence of two independent antigens in BL3 cell lysate. These class II molecules consist of alpha and beta chains.

Epitope specificity and protective efficacy of the bovine immune response to bovine herpesvirus-1 glycoprotein vaccines

Bovine herpesvirus-1 (BHV-1) envelope glycoproteins gI, gIII and gIV were individually purified on monoclonal antibody affinity columns and injected intradermally into BHV-1 seronegative calves. The calves developed serum neutralizing antibodies that monospecifically precipitated the immunizing glycoprotein from a preparation of 125I-labelled BHV-1 envelope proteins. A competitive radioimmunoassay using the bovine antisera demonstrated that known functional epitopes had been retained in the glycoprotein vaccines. Calves immunized with the gI, gIII or gIV glycoproteins were not protected from intranasal challenge with BHV-1 and had levels and duration of viral shedding in their nasal secretions similar to those of non-immunized control calves.