Topographical analysis of bovine herpesvirus type-1 glycoproteins: use of monoclonal antibodies to identify and characterize functional epitopes

Phylogeny and antigenic relationships of three cervid herpesviruses

Elk herpesvirus (ElkHV) from North American elk (wapiti, Cervus elaphus nelsoni) is a recently identified alphaherpesvirus related to bovine herpesvirus-1 (BHV-1). In this study, we determined its relationship with European cervid herpesviruses: cervid herpesvirus-1 (CerHV-1) from red deer and rangiferine herpesvirus (RanHV) from reindeer. For phylogenetic analysis, genes for the gC and gD proteins of these viruses were sequenced. These genes demonstrated an extremely high GC content (76-79%). Genetically, ElkHV was found to be closely related to CerHV-1 and both viruses are more closely related to BHV-1 than to RanHV. Antigenically, the same relationships were found. ElkHV shares common neutralizing epitopes with both CerHV-1 and RanHV. A total of 10 epitopes were defined on the gB, gC and gD proteins of these viruses, including a shared neutralizing epitope on gD. The results indicate that ElkHV and CerHV-1 have diverged from a common ancestor virus. Cervid herpesviruses may be useful in determination of evolutionary rates of change for alphaherpesvirus genes.

Immunization with a bovine herpesvirus 1 glycoprotein B DNA vaccine induces cytotoxic T-lymphocyte responses in mice and cattle

Virus-specific cytotoxic T lymphocytes (CTLs) are considered to be important in protection against and recovery from viral infections. In this study, several approaches to induce cytotoxicity against bovine herpesvirus 1 (BHV-1) were evaluated. Vaccination of C57BL/6 mice with BHV-1 induced a strong humoral, but no CTL, response, which may be due to downregulation of major histocompatibility complex class I molecules. In contrast, vaccinia virus expressing glycoprotein B (gB) elicited a weaker antibody response, but strong cytotoxicity, in mice. As an approach to inducing both strong humoral and cellular immune responses, a plasmid vector was then used to express gB. Both antibody and CTL responses were induced by the plasmid encoding gB in C57BL/6 and C3H mice, regardless of the type of vector backbone. This demonstrated that DNA immunization induces a broad-based immune response to BHV-1 gB. Interestingly, removal of the membrane anchor, which resulted in secretion of gB from transfected cells, did not result in reduced cytotoxicity. Here, it is shown that, compared with the cell-associated counterpart, plasmid-encoded secreted protein may induce enhanced immune responses in cattle. Therefore, calves were immunized intradermally with pMASIAtgB, a plasmid encoding the secreted form of gB (tgB), using a needle-free injection system. This demonstrated that pMASIAtgB elicited both humoral responses and activated gamma interferon-secreting CD8+ CTLs, suggesting that a DNA vaccine expressing tgB induces a CTL response in the natural host of BHV-1.

Immunization with a dicistronic plasmid expressing a truncated form of bovine herpesvirus-1 glycoprotein D and the amino-terminal subunit of glycoprotein B results in reduced gB-specific immune responses

As an approach to create a divalent DNA vaccine, a truncated secreted version of bovine herpesvirus-1 (BHV-1) glycoprotein D (tgD) and the amino-terminal subunit of glycoprotein B (gBb) were expressed from a dicistronic plasmid, designated pSLIAtgD-IRES-gBb. Intradermal immunization of mice with pSLIAtgD-IRES-gBb or a mixture of plasmids encoding tgD (pSLIAtgD) and gBb (pSLIAgBb) by needle injection or gene gun elicited strong tgD-specific immune responses. However, a significant reduction in gBb-specific immune responses was observed upon immunization of mice with pSLIAtgD-IRES-gBb or a mixture of pSLIAtgD and pSLIAgBb in comparison to immunization with pSLIAgBb alone. This reduction in gBb-specific immune responses induced by pSLIAtgD-IRES-gBb was due to production of low amounts of gBb from pSLIAtgD-IRES-gBb, inefficient processing and transport of gBb, and possibly competition for antigen-presenting cells by tgD and gBb. These results indicate that, although divalent plasmids may be used to express different antigens, the efficacy of vaccination with such plasmids may be influenced by the plasmid design and the characteristics of the expressed antigens.

Induction of immune responses in cattle with a DNA vaccine encoding glycoprotein C of bovine herpesvirus-1

A DNA vaccine expressing glycoprotein C (gC) of bovine herpesvirus-1 (BHV-1) was evaluated for inducing immunity in bovines. The plasmid encoding gC of BHV-1 was injected six times intramuscularly or intradermally into calves at monthly intervals. After immunization by both routes neutralizing antibody and lymphoproliferative responses developed. The responses in the intradermally immunized calves were better than those in calves immunized intramuscularly. However, the intradermal (i.d.) route was found to be less efficacious when protection against BHV-1 challenge was compared. Following intranasal BHV-1 challenge, all immunized calves demonstrated a rise in IgG antibody titre on day 3, indicating an anamnestic response. The control non-immunized calf developed a neutralizing antibody response on day 7 post-challenge. The immunized calves showed a slight rise in temperature and mild clinical symptoms after challenge. The intramuscularly immunized calves showed earlier clearance of challenge virus compared with intradermally immunized calves. These results indicate that DNA immunization with gC could induce neutralizing antibody and lymphoproliferative responses with BHV-1 responsive memory B cells in bovines. However, the immunity developed was not sufficient to protect calves completely from BHV-1 challenge.

Antigenic and molecular characterization of a herpesvirus isolated from a North American elk

OBJECTIVE

To determine whether a herpesvirus isolated from the semen of a North American elk was related to bovine herpesvirus 1 (BHV-1).

SAMPLE POPULATION

Semen from 1 healthy bull elk and 2 subtypes of BHV-1 (BHV-1.1 and BHV-1.2).

PROCEDURES

A virus with cytopathic and electron microscopic characteristics consistent with an alpha-herpesvirus was isolated from elk semen, using fetal bovine kidney cells. Cross-neutralization assays were performed with antisera against BHV-1 and the elk herpesvirus (EIkHV). Restriction endonuclease digests of EIkHV DNA were compared with digests of BHV-1.1 and BHV-1.2 DNA. A portion of the ElkHV DNA polymerase gene was amplified with consensus primers by use of the polymerase chain reaction and sequenced. Sequence was compared with known sequences of other herpesviruses. An immunoperoxidase monolayer assay was used to determine reactivities of 22 BHV-1-specific monoclonal antibodies (mAb) against ElkHV. In vitro neutralizing activities of the reactive mAb were determined by use of a microneutralization assay.

RESULTS

Results of cross-neutralization assays indicated that ElkHV was serologically related to BHV-1. Endonuclease digestion of ElkHV DNA generated fragments that were distinct from those of BHV-1. Nucleotide sequencing confirmed that ElkHV is an alphaherpesvirus closely related to but distinct from BHV-1. Six of 22 BHV-1-specific mAb reacted against ElkHV; 2 of these 6 also neutralized in vitro infectivity of ElkHV.

CONCLUSIONS AND CLINICAL RELEVANCE

ElkHV is antigenically and genetically distinguishable from BHV-1. However, the viruses are serologically related and share at least 6 antigenic determinants, one of which is a major neutralizing determinant.

An early pseudorabies virus protein down-regulates porcine MHC class I expression by inhibition of transporter associated with antigen processing (TAP)

The objectives of this study were to identify the mechanism(s) of pseudorabies virus (PrV)-induced down-regulation of porcine class I molecules and the viral protein(s) responsible for the effect. The ability of PrV to interfere with the peptide transport activity of TAP was determined by an in vitro transport assay. In this assay, porcine kidney (PK-15) cells were permeabilized with streptolysin-O and incubated with a library of 125I-labeled peptides having consensus motifs for glycosylation in the endoplasmic reticulum (ER). The efficiency of transport of peptides from the cytosol into the ER was determined by adsorbing the ER-glycosylated peptides onto Con A-coupled Sepharose beads. Dose-dependent inhibition of TAP activity was observed in PrV-infected PK-15 cells. This inhibition, which occurred as early as 2 h postinfection (h.p.i.), reached the maximum level by 6 h.p.i., indicating that TAP inhibition is one of the mechanisms by which PrV down-regulates porcine class I molecules. Infection of cells with PrV in the presence of metabolic inhibitors revealed that cycloheximide a protein synthesis inhibitor, but not phosphonoacetic acid a herpesvirus DNA synthesis inhibitor, could restore the cell surface expression of class I molecules, indicating that late proteins are not responsible for the down-regulation. Infection in the presence of cycloheximide followed by actinomycin-D, which results in accumulation of the immediate-early protein, failed to down-regulate class I, indicating that one or more early proteins are responsible for the down-regulation of class I molecules.

A chimeric protein comprised of bovine herpesvirus type 1 glycoprotein D and bovine interleukin-6 is secreted by yeast and possesses biological activities of both molecules

Bovine herpesvirus type 1 (BHV-1) glycoprotein D (gD) engenders mucosal and systemic immunity and protects cattle from viral infection. Chimerization of cytokines with gD is being explored to confer intrinsic adjuvanticity on gD. Addition of the appropriate cytokine may convert gD into an antigen that specifically engenders protective mucosal immunity. Here DNA coding for the mature bovine interleukin-6 (IL-6) protein was fused through a synthetic glycine linker to the 3' end of DNA coding for the mature BHV-1 gD (tgD) external domain. It was cloned behind the yeast alpha prepro signal sequence and transfected into Pichia pastoris which secreted the chimeric protein (tgD-IL-6) as a 100 kDa molecule. This chimera combined the immunogenic properties of native gD and the in vitro biological activity of bovine IL-6 based on the following observations. A panel of BHV-1 gD-specific monoclonal antibodies recognizing five neutralizing epitopes on native gD reacted with tgD-IL-6. Sera from yeast tgD-IL-6-immunized mice neutralized BHV-1 infection in vitro. The chimeric protein enhanced total bovine immunoglobulin production 16-fold above tgD alone in pokeweed-stimulated bovine peripheral blood mononuclear cells (P < 0.05). This chimeric protein may be a potent mucosal immunogen.

The glycoprotein D (US6) homolog is not essential for oncogenicity or horizontal transmission of Marek's disease virus

RB1BUS6lacgpt, a Marek's disease virus (MDV) mutant having a disrupted glycoprotein D (gD) homolog gene, established infection and induced tumors in chickens exposed to it by inoculation or by contact. Lymphoblastoid cell lines derived from RB1BUS6lacgpt-induced tumors harbored only the mutant virus. These results provide strong evidence that an intact gD homolog gene is not essential for oncogenicity or horizontal transmission of MDV.

Yeast-secreted bovine herpesvirus type 1 glycoprotein D has authentic conformational structure and immunogenicity

Bovine herpesvirus-1 (BHV-1) glycoprotein D (gD), an envelope glycoprotein, engenders mucosal and systemic immunity protecting cattle from viral infection. Production of gD with authentic immunogenicity is required for a subunit vaccine. We placed the truncated BHV-1 gD gene, lacking its putative transmembrane and cytoplasmic domains, under the control of the methanol-inducible AOX1 promoter in the yeast Pichia pastoris. Truncated BHV-1 gD (tgD) was efficiently secreted into the culture medium as a 68 kDa protein using either the yeast alpha prepro or native BHV-1 gD signal sequences. The yeast-secreted tgD had N-linked glycosylation and appears to have authentic conformational structure and immunogenicity based on the following observations A panel of monoclonal antibodies recognizing five neutralizing epitopes reacted with yeast tgD. Sera from yeast tgD-immunized mice immunoprecipitated native BHV-1 gD and neutralized BHV-1 infection in vitro. Yeast tgD competitively blocked all reaction between native gD and monospecific gD polyclonal sera from cattle. Based on these data, yeast-derived BHV-1 tgD is an excellent candidate for a subunit vaccine.

Characterization of a Marek's disease virus mutant containing a lacZ insertion in the US6 (gD) homologue gene

We report the construction of a Marek's disease virus (MDV) mutant containing the lacZ gene of Escherichia coli inserted into a homologue of the US6 (glycoprotein D, gD) gene of herpes simplex virus. The mutant was constructed using the high-passage GAatt85 MDV strain as the parent virus, since that strain grows readily in chicken embryo fibroblasts using culture conditions conducive to mutant virus construction. The lacZ insertion site was positioned one third of the way into the US6 (gD) open reading frame. Insertion of the lacZ gene disrupted a major 6.2 kb transcript that initiated approximately 2.5 kb upstream of the gD homologue gene in the vicinity of the US3 homologue and sorf4 genes, and extended into the US7 (gI) homologue gene. The mutant virus (US6lac) and the parent virus had similar growth kinetics in cell culture at 37 degrees C and 41 degrees C. Furthermore, the US6lac mutant could be reisolated from the spleens and peripheral blood of infected chickens with a frequency comparable to that of the parent virus. Our results indicate that the gene encoding the gD homologue is nonessential for growth in cell culture or for infection of chickens following intra-abdominal inoculation with an attenuated serotype-1 MDV.

Epitope-specific antibody responses in market-stressed calves to bovine herpesvirus type 1

Reciprocal competition ELISA (rcELISA) was conducted to map monoclonal antibodies (mAbs) reactive with gI, gIII and gIV glycoproteins of bovine herpesvirus type 1 (BHV-1) into epitope groups. mAbs to glycoproteins gI and gIV were divided into six epitope groups each, while gIII mAbs had been previously divided into four areas. mAbs were chosen from each epitope group to compete in cELISA wih bovine sera collected during a typical regimen of vaccination and transportation from farm to auction to feedlot. The immunodominant epitopes were identified for each BHV-1 glycoprotein. With glycoprotein gI, three epitopes defined by mAbs 1F10, D9 and 4807 were the most dominant; with glycoprotein gIII epitopes defined by mAbs G2 and 1507, and with glycoprotein gIV epitopes defined by mAbs 1102, 1106, 3C1, 3402 and 3E7 showed the maximum responses. The overall cELISA responses to each glycoprotein among two vaccination groups were also compared and it was shown that cELISA responses were significantly higher for each glycoprotein in calves receiving two vaccinations, one on the farm of origin and one at auction, than in calves receiving only one vaccination at auction.

Experimental infection of neonatal calves with neurovirulent bovine herpesvirus type 1.3

A type of bovine herpesvirus, BHV-1.3, causes encephalitis in calves, whereas BHV-1.1 causes respiratory disease. Three colostrum-deprived calves and two colostrum-fed calves were inoculated with BHV-1.3 by intranasal aerosolization. Two colostrum-deprived calves were inoculated with BHV-1.1 by intranasal aerosolization. BHV-1.3-inoculated calves demonstrated severe encephalitis with minimal respiratory lesions, and BHV-1.1-inoculated calves demonstrated severe respiratory lesions and no clinical signs of neurologic disease. Calves fed colostrum that contained virus neutralizing antibodies were protected against neurologic disease. Colostrum-fed BHV-1.3-inoculated calves did not develop disease although they did become infected; virus was shed in respiratory secretions for 10-13 days postinoculation, similar to infected colostrum-deprived calves. BHV-1.3 was reactivated from a latent state from one colostrum-fed calf after administration of dexamethasone 60 days postinoculation. Histopathologic examination of the three colostrum-deprived BHV-1.3-inoculated calves revealed severe lesions of encephalitis. One of the two BHV-1.1-inoculated calves had one focal lesion of encephalitis. Virus was isolated from brain tissue of colostrum-deprived BHV-1.3-inoculated calves and from one BHV-1.1-inoculated calf. Immunohistochemical staining for BHV-1 antigen was observed in neurons from the colostrum-deprived BHV-1.3-inoculated calves.

Bovine x murine T-cell hybridomas specific for bovine herpesvirus 1 (BHV-1) glycoproteins

Difficulties in the isolation and long-term maintenance of bovine herpesvirus-1 (BHV-1) specific T-cell clones have hindered the analysis of bovine cell-mediated immune response to this virus. In an effort to identify the T-cell epitopes of the virus, bovine murine T-cell hybridomas specific for BHV-1 were generated as an alternative to T-cell clones. Peripheral blood lymphocytes from a calf immunized with BHV-1 were restimulated in vitro with the virus to generate bulk T-cell cultures. The antigen-specific T-cell-enriched bulk culture lymphocytes were fused with the T-cell receptor-deficient mutant of the murine thymoma cell line BW 5147. T-cell hybridomas were screened for their ability to produce interferon-gamma in response to BHV-1 stimulation. Hybridomas with various specificities were obtained. One of them was specific for the BHV-1 glycoprotein gI, two were specific for gIV, while three other hybridomas were specific for gIII. One hybridoma responded to stimulation with BHV-1, but not to any of the glycoproteins gI, gIII, or gIV, suggesting that proteins other than these major glycoproteins may be involved in the bovine T-cell response to BHV-1. Of these hybridomas, one was MHC Class I restricted, while all the others were Class II restricted.

Monoclonal antibodies that distinguish between encephalitogenic bovine herpesvirus type 1.3 and respiratory bovine herpesvirus type 1.1

Seven mouse hybridoma cell lines producing monoclonal antibodies (MAb) against an encephalitogenic strain of bovine herpesvirus type 1.3 (BHV-1.3) were established. The clones producing MAb were selected to be specific for BHV-1.3 by enzyme-linked immunosorbent assay. Only L1B neutralized virus without complement. With the addition of complement, five of the MAb neutralized BHV-1.3 but not the respiratory strain BHV-1.1. The anti-BHV-1.3-specific MAb Q10B, L6G, and L1B precipitated glycoproteins from BHV-1.3 that were analogous to the gI, GIII, and gIV glycoproteins of BHV-1.1, respectively. The other four MAb precipitated unknown proteins. None of the anti-BHV-1.3 MAb precipitated BHV-1.1 glycoproteins. The majority of the anti-BHV-1.3 MAb did not react with BHV-1.1 by immunoblotting, but O7E (unknown protein pattern by radioimmunoprecipitation) was reactive with five proteins (M(r)s of 33,000, 43,000, 70,000, 141,000, and 190,000) of BHV-1.3 and with a different pattern of proteins of BHV-1.1 (M(r)s of 30,000, 38,000, 83,000 and 144,000). Two of the MAb, L6G and O7E, conjugated with peroxidase were found to be useful for detecting BHV-1.3 antigen by immunochemistry in Formalin-fixed brain tissue from experimentally infected calves.

Bovine herpesvirus-1 vaccines

Vaccination has been important in controlling a wide variety of viral and bacterial infections of man and animals. Vaccines to herpesvirus infection of cattle are no exception. The present review describes the different types of conventional vaccines that have been used to date and furthermore describes the novel approaches which are presently being implemented to develop more effective vaccines. These include subunit vaccines as well as genetically engineered modified live deletion mutants. Both these novel vaccine approaches appear to be more efficacious than conventional vaccines. Furthermore, these vaccines provide an additional dimension for control and eradication of infection by providing an opportunity to develop companion diagnostic tests to differentiate infected animals from vaccinated animals. This review summarizes these developments as well as present knowledge regarding the important host defence mechanisms required for preventing infection and aiding recovery from infection.

Protection of cattle from BHV-1 infection by immunization with recombinant glycoprotein gIV

High levels of recombinant bovine herpesvirus-1 (BHV-1) glycoprotein IV were produced in baculovirus, adenovirus, vaccinia virus and Escherichia coli expression systems. The different recombinant forms as well as authentic gIV were injected intramuscularly into seronegative calves. With the exception of E. coli-produced gIV, all forms of gIV induced high levels of neutralizing antibodies both in the serum and in the nasal superficial mucosa. Animals immunized with gIV produced in insect or mammalian cells were completely protected from infection with BHV-1, as demonstrated by the absence of temperature responses, clinical signs or detectable virus in the nasal secretions after challenge exposure. The E. coli-derived gIV induced partial protection from clinical disease, even though it was not glycosylated and did not induce appreciable levels of neutralizing antibodies. This study demonstrated that all forms of glycosylated gIV, whether authentic or recombinant, confer protection from BHV-1 infection and thus may be useful as an effective subunit vaccine.

Structural, functional, and immunological characterization of bovine herpesvirus-1 glycoprotein gl expressed by recombinant baculovirus

The major glycoprotein complex gl of bovine herpesvirus-1 was expressed at high levels (36 micrograms per 1 x 10(6) cells) in insect cells using a recombinant baculovirus. The recombinant gl had an apparent molecular weight of 116 kDa and was partially cleaved to yield 63-kDa (glb) and 52-kDa (glc) subunits. This processing step was significantly less efficient in insect cells than the analogous step in mammalian cells, even though the cleavage sites of authentic and recombinant gl were shown to be identical. The oligosaccharide linkages were mostly endoglycosidase-H-sensitive, in contrast to those of authentic gl, which has mostly endoglycosidase-H-resistant linkages and an apparent molecular weight of 130/74/55 kDa. Despite the reduced cleavage and altered glycosylation, the recombinant glycoprotein was transported and expressed on the surface of infected insect cells. These surface molecules were biologically active as demonstrated by their ability to induce cell-cell fusion. Fusion was inhibited by three monoclonal antibodies specific for antigenic domains I and IV on gl. Domain I maps to the extracellular region of the carboxy terminal fragment glc and domain IV to the very amino terminus of the glb fragment, indicating that domains mapping in two distinct regions of gl function in cell fusion. Monoclonal antibodies specific for eight different epitopes recognized recombinant gl, indicating that the antigenic characteristics of the recombinant and authentic glycoproteins are similar. In addition, the recombinant gl was as immunogenic as the authentic gl, resulting in the induction of gl-specific antibodies in cattle.

The synergistic neutralization of Rift Valley fever virus by monoclonal antibodies to the envelope glycoproteins

A panel of monoclonal antibodies (MAbs) mapping to different antigenic sites on the RVFV G1 and G2 proteins were used to examine the mechanisms involved in neutralization of the virus. Three types of synergistic neutralization of RVFV were observed on mixing various pairs of MAbs. Firstly, enhanced neutralization occurred for two MAb pairs that showed augmented binding for G2. These comprised a combination of a neutralizing MAb with a non-neutralizing antibody, as well as two antibodies which were non-neutralizing individually. In the second category, synergistic neutralization was observed between combinations of MAbs for which increased binding had not been detected. Lastly, mixtures of G1 and G2-specific MAbs were also capable of enhancing neutralization. Post-adsorption neutralization assays revealed that some MAbs neutralized cell-attached virus efficiently, indicating that they can neutralize by inhibiting the infection process after virus attachment. MAbs mapping to G1 IIe, G2I b and G2I c were unable to neutralize adsorbed virus and thus probably neutralize by preventing virus attachment to cells. Several G1-reactive MAbs displayed low level post-adsorption activity, suggesting they may be capable of inhibiting RVFV infectivity at different stages of the replication cycle.

Anti-idiotypic antibodies to bovine herpesvirus-1 inhibit virus infection in cell cultures

A panel of murine monoclonal antibodies (MAbs) to bovine herpesvirus-1 (BHV-1) was prepared. Three of them were neutralizing MAbs and reacted against 130/75/50 kDa, 77 kDa, or 97 kDa glycoproteins (gp). A fourth non-neutralizing MAb recognized the 97 kDa gp. Competition radioimmunoassay demonstrated that each of the four MAbs reacted against a different virus epitope. Anti-idiotypic antibodies (anti-id) to the four MAbs were produced in rabbits and purified by sequential immunoaffinity chromatography. Each anti-id inhibited the binding of its respective MAb to BHV-1 in competitive ELISA and blocked BHV-1 neutralizing activity of the MAb. This inhibition suggested that the anti-ids were specific for the antigen binding site of the MAbs. Treatment of MDBK cells with anti-ids inhibited BHV-1 infection, which suggested that the anti-ids block a cellular component essential for virus infection. Absence of significant cross-reactivity among the anti-ids for heterologous MAbs indicated that they recognized unique determinants on the antigen binding site of the homologous MAb.

Expression of bovine herpesvirus 1 glycoprotein gIV by recombinant baculovirus and analysis of its immunogenic properties

The gene encoding the gIV glycoprotein of bovine herpesvirus 1 has been inserted into the genome of Autographa californica baculovirus in lieu of the coding region of the A. californica baculovirus polyhedrin gene. Recombinant protein was identified by its reactivity with gIV-specific monoclonal antibodies and expressed at high levels (about 85 micrograms per 2.5 x 10(6) cells) in Spodoptera frugiperda (SF9) cells. The recombinant glycoprotein had an apparent molecular mass of 63 kDa, indicating that it was incompletely glycosylated. However, it was transported to and expressed on the cell surface of infected SF9 cells. Furthermore, reactivity with polyclonal and monoclonal antibodies specific for gIV suggested that most epitopes were functionally unaltered on the recombinant gIV. Immunization of cattle with recombinant gIV in crude, partially purified, or pure form resulted in the induction of neutralizing antibodies to BHV-1, which were reactive with authentic gIV. However, the neutralizing antibody titers were lower than those elicited by an equivalent amount of affinity-purified authentic gIV, which appeared to be mainly due to reduced recognition of one of the neutralizing antigenic domains of gIV, designated domain I. The potential use of this recombinant gIV glycoprotein as a vaccine to bovine herpesvirus 1 infection in cattle is discussed.

Bovine cells expressing bovine herpesvirus 1 (BHV-1) glycoprotein IV resist infection by BHV-1, herpes simplex virus, and pseudorabies virus

We expressed the bovine herpesvirus 1 (BHV-1) glycoprotein IV (gIV) in bovine cells. The protein expressed was identical in molecular mass and antigenic reactivity to the native gIV protein but was localized in the cytoplasm. Expressing cells were partially resistant to BHV-1, herpes simplex virus, and pseudorabies virus, as shown by a 10- to 1,000-fold-lower number of plaques forming on these cells than on control cells. The level of resistance depended on the level of gIV expression and the type and amount of challenge virus. These data are consistent with previous reports by others that cellular expression of the BHV-1 gIV homologs, herpes simplex virus glycoprotein D, and pseudorabies virus glycoprotein gp50 provide partial resistance against infection with these viruses. We have extended these findings by showing that once BHV-1 enters gIV-expressing cells, it replicates and spreads normally, as shown by the normal size of BHV-1 plaques and the delayed but vigorous synthesis of viral proteins. Our data are consistent with the binding of BHV-1 gIV to a cellular receptor required for initial penetration by all three herpesviruses and interference with the function of that receptor molecule.

Epitope specificity of the protective immune response induced by individual bovine herpesvirus-1 glycoproteins

Affinity-purified bovine herpesvirus-1 (BHV-1) glycoproteins gI, gIII and gIV, as well as a virus-free BHV-1-infected cell lysate were injected intramuscularly into seronegative calves. All immunized animals developed specific serum-neutralizing antibodies and they were fully protected from disease, using a BHV-1/Pasteurella haemolytica challenge model. After challenge, viral replication in the nasal passages was significantly reduced in animals vaccinated with gIV (10,000-fold) or BHV-1-infected cell lysate (450,000-fold) but just slightly reduced in animals immunized with gI (500-fold) or gIII (25-fold). All of the known epitopes of the glycoproteins were retained during the affinity-purification or preparation of the cell lysate. The high level of protection induced by gIV and the virus-infected cell lysate in particular indicates the potential of glycoprotein gIV as a subunit vaccine, ideally in combination with component(s) from the cell lysate, which may mediate cellular immune responses.

Mapping of 10 epitopes on bovine herpesvirus type 1 glycoproteins gI and gIII

In order to map some of the immunologically important sites on bovine herpesvirus type 1 (BHV-1), deleted, truncated, and hybrid forms of glycoproteins gI and gIII were expressed in transfected murine LMTK- cells. The cells were tested for reactivity with a panel of 16 gI- or gIII-specific monoclonal antibodies (MAbs) possessing conformation-independent antigen binding properties. This panel represented five epitopes on gI and five epitopes on gIII. For gI, two epitopes were mapped between residues 68 and 119, one epitope was mapped between residues 370 and 440, one epitope was mapped to the vicinity of residue 487, and one epitope was mapped between residues 744 and 763. For gIII, three epitopes were mapped between residues 22 and 150, one epitope was mapped between residues 140 and 240, and one epitope was mapped between residues 230 and 287. The location of the gI epitope in the vicinity of residue 487, which was recognized by a virus-neutralizing MAb, was verified by synthetic peptide binding studies. The epitope locations were consistent with proposed models for the structure of gI and gIII, and comparable to some of the epitope locations reported for the homologous glycoproteins of herpes simplex virus type 1. The implications of these results for development of a subunit vaccine against BHV-1 are discussed.

Synthesis, cellular location, and immunogenicity of bovine herpesvirus 1 glycoproteins gI and gIII expressed by recombinant vaccinia virus

Two of the major glycoproteins of bovine herpesvirus 1 (BHV-1) are gI, a polypeptide complex with apparent molecular weights of 130,000, 74,000, and 55,000, and gIII (a 91,000-molecular-weight [91K] glycoprotein), which also exists as a 180K dimer. Vaccinia virus (VAC) recombinants were constructed which carry full-length gI (VAC-I) or gIII (VAC-III) genes. The genes for gI and gIII were each placed under the control of the early VAC 7.5K gene promoter and inserted within the VAC gene for thymidine kinase. The recombinant viruses VAC-I and VAC-III retained infectivity and expressed both precursor and mature forms of glycoproteins gI and gIII. The polypeptide backbones, partially glycosylated precursors, and mature gI and gIII glycoproteins were indistinguishable from those produced in BHV-1-infected cells. Consequently, they were apparently cleaved, glycosylated, and transported in a manner similar to that seen during authentic BHV-1 infection, although the processing efficiencies of both gI and gIII were generally higher in recombinant-infected cells than in BHV-1-infected cells. Immunofluorescence studies further demonstrated that the mature gI and gIII glycoproteins were transported to and expressed on the surface of cells infected with the respective recombinants. Immunization of cattle with recombinant viruses VAC-I and VAC-III resulted in the induction of neutralizing antibodies to BHV-1, which were reactive with authentic gI and gIII. These data demonstrate the immunogenicity of VAC-expressed gI and gIII and indicate the potential of these recombinant glycoproteins as a vaccine against BHV-1.

Expression of bovine herpesvirus 1 glycoproteins gI and gIII in transfected murine cells

Genes encoding two of the major glycoproteins of bovine herpesvirus 1 (BHV-1), gI and gIII, were cloned into the eucaryotic expression vectors pRSVcat and pSV2neo and transfected into murine LMTK- cells, and cloned cell lines were established. The relative amounts of gI or gIII expressed from the two vectors were similar. Expression of gI was cell associated and localized predominantly in the perinuclear region, but nuclear and plasma membrane staining was also observed. Expression of gI was additionally associated with cell fusion and the formation of polykaryons and giant cells. Expression of gIII was localized predominantly in the nuclear and plasma membranes. Radioimmunoprecipitation in the presence or absence of tunicamycin revealed that the recombinant glycoproteins were proteolytically processed and glycosylated and had molecular weights similar to those of the forms of gI and gIII expressed in BHV-1-infected bovine cells. However, both recombinant glycoproteins were glycosylated to a lesser extent than were the forms found in BHV-1-infected bovine cells. For gI, a deficiency in N-linked glycosylation of the amino-terminal half of the protein was identified; for gIII, a deficiency in O-linked glycosylation was implicated. The reactivity pattern of a panel of gI- and gIII-specific monoclonal antibodies, including six which recognize conformation-dependent epitopes, was found to be unaffected by the glycosylation differences and was identical for transfected or BHV-1-infected murine cells. Use of the transfected cells as targets in immune-mediated cytotoxicity assays demonstrated the functional recognition of recombinant gI and gIII by murine antibody and cytotoxic T lymphocytes. Immunization of mice with the transfected cells elicited BHV-1-specific virus-neutralizing antibody, thus verifying the antigenic authenticity of the recombinant glycoproteins and the important role of gI and gIII as targets of the immune response to BHV-1 in this murine model system.

Effects of immunization with bovine herpesvirus-1 glycoproteins on bovine herpesvirus-1-induced alteration of bovine neutrophil chemotactic and anti-Pasteurella haemolytica activities

It has been reported previously that active bovine herpesvirus-1 (BHV-1) infection greatly enhances the susceptibility of cattle to secondary bacterial pneumonia involving Pasteurella haemolytica. The present study examines the possibility that immunization of BHV-1 naive calves with purified BHV-1 glycoproteins would protect them against changes in neutrophil function that might compromise their ability to eliminate P. haemolytica during an active BHV-1 infection. The results show that circulating neutrophil chemotactic activity was generally reduced at 7-8 days after BHV-1 challenge; immunization with a 77 kilodalton BHV-1 glycoprotein (gIV) prevented impairment of neutrophil chemotaxis. BHV-1 infection did not markedly affect the ability of neutrophils to ingest and kill P. haemolytica in vitro. Immunization and challenge with BHV-1 had little effect on the chemiluminescence response of bovine neutrophils to opsonized P. haemolytica in vitro, although in one experiment a marked increase in baseline neutrophil chemiluminescence was observed which may be relevant to understanding the pathogenesis of pulmonary damage that occurs in BHV-1 infected calves.

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

Monoclonal antibodies specific for defined epitopes on the gI, gIII and gIV envelope glycoproteins of BHV-1 were used individually or in glycoprotein-monospecific pools for passive immunization of young calves. Although serum antibody titres comparable to those found in naturally infected and recovered calves were achieved, passive immunization failed to prevent the growth of BHV-1 in nasal and ocular mucosa and did not decrease the duration of viral shedding.

Characterization of an equine herpesvirus type 1 gene encoding a glycoprotein (gp13) with homology to herpes simplex virus glycoprotein C

The molecular structure of the equine herpesvirus type 1 (EHV-1) gene encoding glycoprotein 13 (gp13) was analyzed. The gene is contained within a 1.8-kilobase AccI-EcoRI restriction fragment mapping at map coordinates 0.136 to 0.148 in the UL region of the EHV-1 genome and is transcribed from right to left. Determination of the nucleotide sequence of the DNA fragment revealed a complete transcriptional unit composed of typical regulatory promoter elements upstream to a long open reading frame (1,404 base pairs) that encoded a 468-amino-acid primary translation product of 51 kilodaltons. The predicted protein has the characteristic features of a membrane-spanning protein: an N-terminal signal sequence, a hydrophobic membrane anchor region, a charged C-terminal cytoplasmic tail, and an exterior domain with nine potential N-glycosylation sites. The EHV-1 DNA sequences expressed in lambda gt11 as gp13 epitopes were present in the open reading frame. Amino acid sequences composing a major antigenic site, recognized by 35% of a panel of 42 anti-gp13 monoclonal antibodies, were identified in the N-terminal surface domain of the deduced gp13 molecule. Comparison of the EHV-1 gp13 DNA sequence with that encoding glycoproteins of other alphaherpesviruses revealed no detectable homology. However, a search for homology at the amino acid level showed regions of significant sequence similarity between the amino acids of the carboxy half of EHV-1 gp13 and those of the same region of gC-like glycoproteins of herpes simplex virus (gC-1 and gC-2), pseudorabies herpesvirus (gIII), and varicella-zoster virus (gp66). The sequences of the N-terminal portion of gp13, by contrast, were much less conserved. The results of these studies indicate that EHV-1 gp13 is the structural homolog of herpes simplex virus glycoprotein C and further suggest that the epitope-containing N-terminal amino acid sequences of the herpesvirus gC-like glycoproteins have undergone more extensive evolutionary divergence than the C-terminal sequences.

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.

Monoclonal antibody analysis of bovine herpesvirus-1 glycoprotein antigenic areas relevant to natural infection

Neutralizing antigenic areas on the glycoproteins of bovine herpesvirus-1 (BHV-1) were identified by reciprocal competition radioimmunoassays using monoclonal antibodies. Three interrelated and two independent antigenic areas were identified on the 77-kDa (K) gIV envelope glycoprotein. Antigenic analysis of this protein has not been previously described. Four interrelated and one independent antigenic areas were found on the 97K gIII envelope glycoprotein. A third group of monoclonal antibodies reacting in Western blot with the 74K subunit of gI, a 130K disulfide-linked 74K/55K heterodimer, revealed four interrelated antigenic areas. All of the antigenic areas on all three glycoproteins were reactive with neutralizing monoclonal antibodies and all were targets for antibody-complement lysis. However, antibodies against gIV were the most efficient at neutralizing the virus and rendering infected cells susceptible to antibody-complement lysis. Convalescent sera from experimentally infected calves were used in a competitive radioimmunoassay to confirm that each antigenic area on the gI, gIII, or gIV glycoproteins was a target for bovine antibodies during primary infection with BHV-1.

Functional and topographical analyses of epitopes on bovine herpesvirus type 1 glycoprotein IV

Bovine herpesvirus type 1 (BHV-1) glycoprotein gIV was purified by affinity chromatography. Purified preparations showed two distinct components of 71 K and 140 K following electrophoresis in sodium dodecyl sulphate polyacrylamide gels. The polypeptides were separated, excised from the gel and used to immunize rabbits; the resulting antisera showed a high degree of cross reactivity indicating that these polypeptides represent monomeric and dimeric forms of the same glycoprotein. Purified gIV was also used to develop a gIV-specific panel of monoclonal antibodies. Neutralizing monoclonal antibodies directed against gIV were conjugated to horseradish peroxidase and subjected to competition binding assays by ELISA. Three distinct neutralizing antigenic domains on gIV were identified. Domain 1 comprised two overlapping epitopes, whereas domain 2 was represented by a single monoclonal antibody. The third antigenic domain was made up of a complex of four identical or overlapping epitopes designated 3a, b, c, and d. Evidence is presented suggesting that domain 1 of gIV may be involved in penetration of the virus into the cell.

Epitopes on the peplomer protein of infectious bronchitis virus strain M41 as defined by monoclonal antibodies

Sixteen monoclonal antibodies (Mcabs) were prepared against infectious bronchitis virus strain M41, all of them reacting with the peplomer protein. One of them, Mcab 13, was able to neutralize the virus and to inhibit hemagglutination. Competition binding assays allowed the definition of five epitopes, designated as A, B, C, D, and E, of which epitopes A and B are overlapping. Furthermore, the binding of Mcab 13 (epitope E) could be enhanced by the addition of Mcabs from group B, C, and D. A dot immunoblot assay was used to analyze the effect of denaturation on antibody recognition of the epitopes. Only the binding of Mcab 13 was affected, indicating that the epitope involved in neutralization and hemagglutination is conformation dependent. The epitopes A to D were highly conserved among IBV strains, while epitope E was specific for strains M41 and D3896. In this last strain, however, this epitope was not involved in neutralization.

Temporal control of bovine herpesvirus 1 glycoprotein synthesis

The gI, gIII, and gIV glycoproteins are major bovine herpesvirus 1 antigens involved in virus neutralization. Results indicate that the gI and gIV glycoproteins were expressed as beta proteins, whereas the gIII glycoprotein was expressed strictly as a gamma protein. These findings suggest that gI and gIV may be superior to gIII as vaccine candidates.

Protection of cattle from bovine herpesvirus type I (BHV-1) infection by immunization with individual viral glycoproteins

The major glycoproteins gI, gIII, and gIV of bovine herpesvirus-1 (BHV-1) were found to induce high levels of antibody in cattle which could neutralize virus and participate in antibody-dependent cell cytotoxicity of BHV-1-infected cells. Immunized animals were fully protected from disease, using a BHV-1/Pasteurella haemolytica aerosol challenge model but not from infection with the virus. Thus, virus could still replicate in the nasal passages of immunized animals, although to a lesser extent than in placebo-treated animals or animals immunized with a commercial killed whole virus vaccine. Systemic spread of the virus in immunized animals did not appear to occur since there was not a dramatic alteration of leukocyte function following challenge. These results suggest that any one of the three major BHV-1 glycoproteins may be useful as a subunit vaccine either individually or in combination.

Hemagglutination inhibition and virus neutralizing response of rabbits inoculated with bovine herpesvirus 1 subunit vaccine

The immunogenicity of bovine herpesvirus type 1 (BHV-1) hemagglutinin has been investigated. Both live and nonionic detergent solubilized vaccines were prepared and 5000 hemagglutinating units (HAU) were injected subcutaneously into rabbits. Both types of vaccine induced a good antibody response but live virus was four times more efficient in inducing hemagglutination inhibiting and neutralizing antibodies than either Triton X-100- or octylglucoside-solubilized subunit vaccine. Blotting analysis revealed that five proteins, of 105,000, 90,000, 74,000, 64,000 and 54,000 mol. wt, were recognized by the serum of vaccinated animals. Triton X-100-solubilized vaccine did not induce antibodies against the 105,000 and 64,000 mol. wt proteins, indicating the important role of VP 90,000 and VP 74,000 in hemagglutination and neutralization. The order in which antibodies to the different viral proteins were induced was VP 90,000, (VP 105,000, VP 64,000, VP 54,000) and VP 74,000. Our data indicate that VP 90,000 is the hemagglutinin. Using convalescent serum from intranasally infected animals, we could identify nine structural proteins for BHV-1; VP 105,000, VP 90,000, VP 74,000, VP 64,000, VP 54,000, VP 50,000, VP 47,000, VP 40,000 and VP 31,000.

Critical epitopes in transmissible gastroenteritis virus neutralization

Purified transmissible gastroenteritis (TGE) virus was found to be composed of three major structural proteins having relative molecular weights of 200,000, 48,000, and 28,000. The peplomer glycoprotein was purified by affinity chromatography with the monoclonal antibody (MAb) 1D.G3. A collection of 48 MAbs against TGE virus was developed from which 26, 10, and 3 were specific for proteins E2, N, and E1, respectively. A total of 14 neutralizing MAbs of known reactivity were E2 protein specific. In addition, MAb 1B.C11, of unknown specificity, was also neutralizing. These MAbs reduced the virus titer 10(2)- to 10(9)-fold. Six different epitopes critical in TGE virus neutralization were found, all of which were conformational based on their immunogenicity and antigenicity. Only the epitope defined by MAb 1G.A7 was resistant to sodium dodecyl sulfate treatment, although it was destroyed by incubation in the presence of both the detergent and beta-mercaptoethanol. The frequency of MAb-resistant (mar) mutants selected with four MAbs (1G.A7, 1B.C11, 1G.A6, and 1E.F9) ranged from 10(-6) to 10(-7), whereas the frequency of the putative mar mutant defined by MAb 1B.B11 was lower than 10(-9). Furthermore, the epitopes defined by these MAbs and by MAbs 1H.C2 and 1A.F10, were present in 11 viral isolated with different geographical locations, years of isolation, and passage numbers (with the exception of two epitopes absent or modified in the TOY 56 viral isolate), suggesting that the critical epitopes in TGE virus neutralization were highly conserved.

Bovine herpesvirus 1: strain comparison of polypeptides and identification of a neutralization epitope on the 90-kilodalton hemagglutinin

The intracellular and structural polypeptides of the Los Angeles and Cooper 1 reference strains of bovine herpesvirus 1, together with 12 other Canadian field isolates, were analyzed by polyacrylamide gel electrophoresis. Although a few minor differences were noted among some isolates in regard to intracellular viral protein content, analysis of partly purified virus showed strikingly similar polypeptide profiles among 19 proteins with molecular masses of 14 to 145 kilodaltons (kDa). Moreover, a neutralizing monoclonal antibody produced against the Cooper 1 strain also neutralized all of the other 13 strains tested in this study and immunoprecipitated the major 90-kDa glycoprotein. A second monoclonal antibody with a high hemagglutination inhibition titer prevented hemagglutination of other strains tested and also reacted against the 90-kDa glycoprotein by immunoprecipitation, indicating that this glycoprotein is responsible for the hemagglutinating activity of the viral particle and carries an important neutralization epitope.