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

The biology and development of vaccines for bovine alphaherpesvirus 1

Bovine alphaherpesvirus type 1 (BoAHV-1) infections lead to compromised herd health and significantly reduced productivity of affected cattle. While BoAHV-1 may cause rhinotracheitis, conjunctivitis, genital infections, and abortions, respiratory tract infections constitute the predominant clinical disease. Immune suppression induced by BoAHV-1 may contribute to co-infections initiating the bovine respiratory disease complex. In this review, the emphasis is to recapitulate the biology and the vaccine technologies currently in use and in development for BoAHV-1, and to discuss the major limitations. Studies on the life cycle and host interactions of BoAHV-1 have resulted in the identification of virulence factors. While several vaccine types, such as vectored vaccines and subunit vaccines, are under investigation, modified live and inactivated BoAHV-1 vaccines are still most frequently used in most areas of the world, whereas attenuated and inactivated marker vaccines are in use in Europe. The knowledge gained from studies on the biology of BoAHV-1 can form a basis for the rational design of future vaccines.

Development and evaluation of recombinant gD protein based ELISA for sero-surveillance of BoHV-1 in India

Bovine herpes virus-1 (BoHV-1) is responsible for production losses through decreased milk yields, abortions, infertility, and trade restrictions in the bovine population. The disease is endemic in many countries including India. As the virus harbors a unique feature of latency animals once infected with the virus remain sero-positive for lifetime and can re-excrete the virus when exposed to stressful conditions. Hence, identification and culling of infected animals is only the means to minimize infection-associated losses. In this study, an economical indigenous assay for the detection of BoHV-1 specific antibodies was developed to cater to the huge bovine population of the country. The viral structural gD protein, expressed in the prokaryotic system was used for optimization of an indirect ELISA for bovines followed by statistical validation of the assay. The diagnostic sensitivity and specificity of the indirect ELISA were 82.9% and 91.3% respectively. Systematically collected serum samples representing organized, unorganized and breeding farms of India were tested with the indigenously developed assay for further validation.

Bovine Herpesvirus-1 Glycoprotein M Mediates the Translocation to the Golgi Apparatus and Packaging of VP8

VP8, the most abundant tegument protein of bovine herpesvirus-1 (BoHV-1), plays an important role in viral replication. According to our previous studies, VP8 localizes to the Golgi apparatus of BoHV-1-infected cells where it can be packaged into the virus; however, Golgi localization of VP8 does not occur outside of the context of infection. The goal of this study was to identify the viral factor(s) involved in the tropism of VP8 towards the Golgi. VP8 was found to interact with glycoprotein M (gM), and the VP8 and gM domains that are essential for this interaction were identified. VP8 and gM colocalized to the Golgi apparatus in BoHV-1-infected cells. In cells co-transfected with VP8- and gM-encoding plasmids, VP8 was also found to be localized to the Golgi, suggesting gM to be sufficient. The localization of VP8 to the Golgi was lost in cells infected with a gM deletion mutant, and the amount of VP8 incorporated into mature virus was significantly reduced. However, with the restoration of gM in a revertant virus, the localization to the Golgi and the amount of VP8 incorporated in the virions were restored. These results indicate that gM plays a critical role in VP8 subcellular localization to the Golgi and packaging into mature virions.

Antigenic relationships between Caprine alphaherpesvirus 1 (CpHV-1) and Bovine alphaherpesvirus 1 (BoHV-1) and experimental CpHV-1 infection of kids and calves

Caprine alphaherpesvirus 1 (CpHV-1) is a worldwide pathogen of goats and is closely related to Bovine alphaherpevirus 1 (BoHV-1). We herein studied the antigenic relationships of CpHV-1 with BoHV-1 and investigated the pathogenesis of CpHV-1 in kids and calves. Monoclonal antibody reactivity revealed that CpHV-1 and BoHV-1 share immunogenic epitopes in the major envelope glycoproteins gB, gC and gD. The antigenic relationship was further demonstrated by virus-neutralizing assays, in which CpHV-1 and BoHV-1 antisera presented varied degrees of cross-neutralization against the respective heterologous viruses. Although cross-neutralization was observed between both viruses and the heterologous antisera, BoHV-1 antisera neutralized CpHV-1 with higher efficiency than CpHV-1 antisera neutralized BoHV-1. Hence, the antigenic cross-reactivity between CpHV-1 and BoHV-1 should be considered upon serologic testing of goats and cattle in regions where the two viruses co-circulate. Intranasal (IN) inoculation of CpHV-1 (WI13-46 isolate) in seven seronegative kids resulted in efficient viral replication in the respiratory tract. Additionally, mild to moderate systemic and respiratory signs were observed, including apathy, hyperthermia, nasal discharge and respiratory distress. Dexamethasone administration to the inoculated kids between days 36 and 40 pi did not result in virus shedding in nasal secretions. However, latent infection had been established, as evidenced by the detection of CpHV-1 DNA in trigeminal ganglia and olfactory bulbs of kids euthanized at day 67 pi. Contrasting with the outcome of infection in kids, IN inoculation of CpHV-1 in calves did not result in productive infection as no virus replication or shedding were detected, and the animals did not develop clinical signs nor seroconverted. The animal experiments demonstrated that CpHV-1 was able to produce respiratory disease in kids, but did not replicate to detectable levels in calves.

Bovine Herpesvirus 1 Counteracts Immune Responses and Immune-Surveillance to Enhance Pathogenesis and Virus Transmission

Infection of cattle by bovine herpesvirus 1 (BoHV-1) can culminate in upper respiratory tract disorders, conjunctivitis, or genital disorders. Infection also consistently leads to transient immune-suppression. BoHV-1 is the number one infectious agent in cattle that is associated with abortions in cattle. BoHV-1, as other α-herpesvirinae subfamily members, establishes latency in sensory neurons. Stressful stimuli, mimicked by the synthetic corticosteroid dexamethasone, consistently induce reactivation from latency in latently infected calves and rabbits. Increased corticosteroid levels due to stress have a two-pronged effect on reactivation from latency by: (1) directly stimulating viral gene expression and replication, and (2) impairing antiviral immune responses, thus enhancing virus spread and transmission. BoHV-1 encodes several proteins, bICP0, bICP27, gG, UL49.5, and VP8, which interfere with key antiviral innate immune responses in the absence of other viral genes. Furthermore, the ability of BoHV-1 to infect lymphocytes and induce apoptosis, in particular CD4+ T cells, has negative impacts on immune responses during acute infection. BoHV-1 induced immune-suppression can initiate the poly-microbial disorder known as bovine respiratory disease complex, which costs the US cattle industry more than one billion dollars annually. Furthermore, interfering with antiviral responses may promote viral spread to ovaries and the developing fetus, thus enhancing reproductive issues associated with BoHV-1 infection of cows or pregnant cows. The focus of this review is to describe the known mechanisms, direct and indirect, by which BoHV-1 interferes with antiviral immune responses during the course of infection.

Sequence analysis of the 5' third of glycoprotein C gene of South American bovine herpesviruses 1 and 5

Bovine herpesviruses 1 (BoHV-1) and 5 (BoHV-5) share high genetic and antigenic similarities, but exhibit marked differences in tissue tropism and neurovirulence. The amino-terminal region of glycoprotein C (gC), which is markedly different in each of the viruses, is involved in virus binding to cellular receptors and in interactions with the immune system. This study investigated the genetic and antigenic differences of the 5′ region of the gC (5′ gC) gene (amino-terminal) of South American BoHV-1 (n=19) and BoHV-5 (n=25) isolates. Sequence alignments of 374 nucleotides (104 amino acids) revealed mean similarity levels of 97.3 and 94.2% among BoHV-1 gC (gC1), respectively, 96.8 and 95.6% among BoHV-5 gC (gC5), and 62 and 53.3% between gC1 and gC5. Differences included the absence of 40 amino acid residues (27 encompassing predicted linear epitopes) scattered throughout 5′ gC1 compared to 5′ gC5. Virus neutralizing assays testing BoHV-1 and BoHV-5 antisera against each isolate revealed a high degree of cross-neutralization between the viruses, yet some isolates were neutralized at very low titers by heterologous sera, and a few BoHV-5 isolates reacted weakly with either sera. The virus neutralization differences observed within the same viral species, and more pronounced between BoHV-1 and BoHV-5, likely reflect sequence differences in neutralizing epitopes. These results demonstrate that the 5′ gC region is well conserved within each viral species but is divergent between BoHV-1 and BoHV-5, likely contributing to their biological and antigenic differences.

Bovine herpesvirus glycoprotein D: a review of its structural characteristics and applications in vaccinology

The viral envelope glycoprotein D from bovine herpesviruses 1 and 5 (BoHV-1 and -5), two important pathogens of cattle, is a major component of the virion and plays a critical role in the pathogenesis of herpesviruses. Glycoprotein D is essential for virus penetration into permissive cells and thus is a major target for virus neutralizing antibodies during infection. In view of its role in the induction of protective immunity, gD has been tested in new vaccine development strategies against both viruses. Subunit, DNA and vectored vaccine candidates have been developed using this glycoprotein as the primary antigen, demonstrating that gD has the capacity to induce robust virus neutralizing antibodies and strong cell-mediated immune responses, as well as protection from clinical symptoms, in target species. This review highlights the structural and functional characteristics of BoHV-1, BoHV-5 and where appropriate, Human herpesvirus gD, as well as its role in viral entry and interactions with host cell receptors. Furthermore, the interactions of gD with the host immune system are discussed. Finally, the application of this glycoprotein in new vaccine design is reviewed, taking its structural and functional characteristics into consideration.

Cell-mediated immune responses induced by BHV-1: rational vaccine design

Bovine herpesvirus-1 (BHV-1) is one of the major respiratory pathogens in cattle worldwide. Although antibodies have been correlated with protection and recovery from BHV-1 infection, the cell-mediated immune response is also a critical defense mechanism because cell-to-cell spread occurs before hematogenous spread. Furthermore, induction of robust T-cell memory is critical for the long-term duration of immunity. Among current commercial vaccines, the attenuated conventional vaccines induce a balanced immune response and long-term memory but may result in viral shedding. By contrast, inactivated vaccines primarily elicit a humoral immune response and relative short-term memory. These vaccines do not allow differentiation of vaccinated from infected cattle. Recent efforts are focusing on the development of vaccines that induce a balanced immune response and long-term memory, as well as having differentiation markers. This includes well-defined genetically engineered gene-deleted, subunit and vectored vaccines.

Induction of humoral responses to BHV-1 glycoprotein D expressed by HSV-1 amplicon vectors

Herpes simplex virus type-1 (HSV-1) amplicon vectors are versatile and useful tools for transferring genes into cells that are capable of stimulating a specific immune response to their expressed antigens. In this work, two HSV-1-derived amplicon vectors were generated. One of these expressed the full-length glycoprotein D (gD) of bovine herpesvirus 1 while the second expressed the truncated form of gD (gDtr) which lacked the trans-membrane region. After evaluating gD expression in the infected cells, the ability of both vectors to induce a specific gD immune response was tested in BALB/c mice that were intramuscularly immunized. Specific serum antibody responses were detected in mice inoculated with both vectors, and the response against truncated gD was higher than the response against full-length gD. These results reinforce previous findings that HSV-1 amplicon vectors can potentially deliver antigens to animals and highlight the prospective use of these vectors for treating infectious bovine rhinotracheitis disease.

Molecular and in vitro characterization of field isolates of bovine herpesvirus-1

Bovine Herpesvirus-1 (BoHV-1) is distributed worldwide and is a major pathogen in cattle, being the causal agent of a variety of clinical syndromes. The aim of this study was to isolate and to characterize (molecular and biological characterization) BoHV-1 from 29 immunosuppressed animals. It was possible to obtain 18 isolates, each from a different animal, such as from the respiratory and reproductive tracts. In some cases the cytopathic effect was visible 12 hours post-inoculation, and became characteristic after 36-48 hours. Biological characteristics were evaluated and compared with Iowa and Colorado-1 reference strains, and differences were found in plaque size, virus titer measured by TCID50 and PFU/mL, and one step virus curves. These results showed that some isolates had a highly virulent-like behavior in vitro, compared to the reference strains, with shorter eclipse periods, faster release of virus into the supernatants, and higher burst size and viral titer. There were no differences in glycoprotein expression of BoHV-1 isolates, measured by Western blot on monolayers. Moreover, using restriction endonucleases analysis, most of the viruses were confirmed as BoHV-1.1 and just one of them was confirmed as BoHV-1.2a subtype. These findings suggest that some wild-type BoHV-1 isolates could be useful as seeds to develop new monovalent vaccines.

Bovine herpesvirus type 1 (BHV-1) is an important cofactor in the bovine respiratory disease complex

BHV-1 is an important pathogen of cattle. Because of its ability to induce immune suppression, BHV-1 is an important agent in the multifactorial disorder, bovine respiratory disease complex (BRDC). BHV-1 encodes several proteins that inhibit various arms of the immune system suggesting that these proteins are important in the development of BRDC.

A review of the biology of bovine herpesvirus type 1 (BHV-1), its role as a cofactor in the bovine respiratory disease complex and development of improved vaccines

Infection of cattle by bovine herpesvirus type 1 (BHV-1) can lead to upper respiratory tract disorders, conjunctivitis, genital disorders and immune suppression. BHV-1-induced immune suppression initiates bovine respiratory disease complex (BRDC), which costs the US cattle industry approximately 3 billion dollars annually. BHV-1 encodes at least three proteins that can inhibit specific arms of the immune system: (i) bICP0 inhibits interferon-dependent transcription, (ii) the UL41.5 protein inhibits CD8+ T-cell recognition of infected cells by preventing trafficking of viral peptides to the surface of the cells and (iii) glycoprotein G is a chemokine-binding protein that prevents homing of lymphocytes to sights of infection. Following acute infection of calves, BHV-1 can also infect and induce high levels of apoptosis of CD4+ T-cells. Consequently, the ability of BHV-1 to impair the immune response can lead to BRDC. Following acute infection, BHV-1 establishes latency in sensory neurons of trigeminal ganglia (TG) and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two viral genes, the latency related gene and ORF-E are abundantly expressed during latency, suggesting that they regulate the latency-reactivation cycle. The ability of BHV-1 to enter permissive cells, infect sensory neurons and promote virus spread from sensory neurons to mucosal surfaces following reactivation from latency is also regulated by several viral glycoproteins. The focus of this review is to summarize the biology of BHV-1 and how this relates to BRDC.

Inhibition of bovine sperm–zona binding by bovine herpesvirus-1

The purpose of the present study was to identify a potential interference of bovine herpesvirus-1 (BoHV-1) with sperm–oocyte interactions during bovinein vitrofertilization. An inhibition of almost 70% of sperm–zona binding was observed when bovine cumulus-denuded oocytes were inseminated in the presence of 10750% tissue culture infective dose/ml BoHV-1. The inhibitory effect of BoHV-1 on sperm–zona binding was mediated by an interaction of the virus with spermatozoa, but not with oocytes. Treatment of spermatozoa with BoHV-1, however, did not affect sperm motility and acrosomal status. Antiserum against BoHV-1 prevented the virus-induced inhibition of sperm–zona binding, indicating that BoHV-1 itself affects the fertilization process. In order to investigate which BoHV-1 glycoprotein(s) are responsible for the virus–sperm interaction, BoHV-1 was treated with monoclonal antibodies against the viral glycoproteins gB, gC, gD and gH prior to insemination. Anti-gC completely prevented the inhibitory effect of BoHV-1 on sperm–zona binding, while anti-gD caused a reduction of this inhibition. Further evidence for the involvement of gC and gD in the virus–sperm interaction was provided by the fact that purified gC and gD decreased sperm–zona binding in a dose-dependent way with gC being more effective than gD. These results indicated that BoHV-1 inhibits bovine sperm–zona binding by interacting with spermatozoa. The binding of BoHV-1 to a spermatozoon is mediated by the viral glycoproteins gC and gD, and therefore seems to be comparable with the mechanisms of BoHV-1 attachment to its natural host cell.

Rise and survival of bovine herpesvirus 1 recombinants after primary infection and reactivation from latency

Recombination is thought to be an important source of genetic variation in herpesviruses. Several studies, performed in vitro or in vivo, detected recombinant viruses after the coinoculation of two distinguishable strains of the same herpesvirus species. However, none of these studies investigated the evolution of the relative proportions of parental versus recombinant progeny populations after coinoculation of the natural host, both during the excretion and the reexcretion period. In the present study, we address this by studying the infection of cattle with bovine herpesvirus 1 (BoHV-1). The recombination of two BoHV-1 mutants lacking either glycoprotein C (gC(-)/gE(+)) or E (gC(+)/gE(-)) was investigated after inoculation of cattle by the natural route of infection. The results demonstrated that (i) recombination is a frequent event in vivo since recombinants (gC(+)/gE(+) and gC(-)/gE(-)) were detected in all coinoculated calves, (ii) relative proportions of progeny populations evolved during the excretion period toward a situation where two populations (gC(+)/gE(+) and gC(-)/gE(+)) predominated without fully outcompeting the presence of the two other detected populations (gC(+)/gE(-) and gC(-)/gE(-)), and (iii) after reactivation from latency, no gC(+)/gE(-) and gC(-)/gE(-) progeny viruses were detected, although gC(+)/gE(-) mutants, when inoculated alone, were detected after reactivation treatment. In view of these data, the importance of gE in the biology of BoHV-1 infection and the role of recombination in herpesvirus evolution are discussed.

Isolation of a glycoprotein E-deleted bovine herpesvirus type 1 strain in the field

During a field trial to evaluate the efficacy of repeated vaccinations with bovine herpesvirus type 1 (BHV-1) marker vaccines, a glycoprotein E (gE)-negative BHV-1 strain was isolated from the nasal secretions of two cows, eight months after vaccination with a gE-negative live-attenuated vaccine, initially given intranasally, then intramuscularly. The strain isolated was characterised using immunofluorescence, restriction analysis and PCR. All the techniques used identified the isolated virus as a gE-negative BHV-1 phenotypically and genotypically identical to the Za strain used as a control.

Use of epitope mapping to identify a PCR template for protein amplification and detection by enzyme-linked immunosorbent assay of bovine herpesvirus type 1 glycoprotein D

Infection with bovine herpesvirus type 1 (BHV-1) occurs worldwide and causes serious economic losses due to the deaths of animals, abortions, decreased milk production, and loss of body weight. BHV-1 is frequently found in bovine semen and is transmitted through natural service and artificial insemination. The detection of BHV-1 in bovine semen is a long-standing problem in veterinary virology which is important in disease control schemes. In the present study, ordered deletions of the full-length BHV-1 glycoprotein open reading frame were used to identify an epitope recognized by a specific monoclonal antibody (MAb). A glycoprotein D fragment containing this epitope was then amplified using an in vitro protein amplification assay developed previously (J. Zhou, J. Lyaku, R. A. Fredrickson, and F. S. Kibenge, J. Virol. Methods 79:181-189, 1999), and the resulting peptide was detected by indirect enzyme-linked immunosorbent assay (ELISA) with the specific MAb. This method detected 0.0395 50% tissue culture infective dose of BHV-1 in raw bovine semen, which was 1,000-fold more sensitive than traditional PCR. We therefore conclude that this in vitro protein amplification assay combined with ELISA has superior sensitivity for direct virus detection in clinical samples.

Characterization of the glycoprotein B gene from ruminant alphaherpesviruses

The complete open reading frame and promoter region of the glycoprotein B (gB) gene has been identified and sequenced from five poorly characterized alphaherpesviruses of ruminants, bovine herpesvirus 5 (BHV-5), buffalo herpesvirus 1 (BuHV-1), cervine herpesvirus 1 (CerHV-1), rangiferine herpesvirus 1 (RanHV-1), and caprine herpesvirus 1 (CapHV-1). One of the two regions identified with considerable sequence and length variation is also target of the immune system, as two B cell epitopes have been identified in this location. Features shared with bovine herpesvirus 1 (BHV-1) gB include two broad hydrophobic regions, six N-glycosylation sites and ten conserved cysteine residues in the gB extracellular domain. Phylogenetic analysis showed that the studied ruminant alphaherpesviruses form, together with BHV-1, a consistent group within the alpha2 subgroup of the herpesviruses. BHV-5 and BuHV-1 are most closely related to BHV-1, followed by CerHV-1, RanHV-1 and more distantly by CapHV-1. A remarkable high degree of sequence similarity was observed between BuHV-1 and the neuropathogenic BHV-5.

Detection of bovine herpesvirus-1 in peripheral blood mononuclear cells eight months postinfection

Peripheral blood mononuclear cells (PBMCs) from 5 calves (3 controls and 2 vaccinates) used in a bovine herpesvirus 1 (BHV-1) vaccine study with a BHV-1 Cooper strain challenge were collected 6 months after challenge. The PBMCs from the control animals were positive by immunofluorescence for the BHV-1 glycoprotein D (gD) while the vaccinates were negative. The PBMC samples from 4 of the 5 animals were examined for BHV-1 DNA by polymerase chain reaction (PCR) and for gD immunofluorescence at 8 months after challenge. The BHV-1 DNA and viral antigen were detected in PBMC samples at 8 months postinfection, but no virus was isolated.

Glycoprotein D homologs in herpes simplex virus type 1, pseudorabies virus, and bovine herpes virus type 1 bind directly to human HveC(nectin-1) with different affinities

Distinct subsets of human receptors for alphaherpesviruses mediate the entry of herpes simplex virus (HSV), pseudorabies virus (PrV), or bovine herpes virus type 1 (BHV-1) into cells. Glycoprotein D (gD) is essential for receptor-mediated entry of all three viruses into cells. However, the gD homologs of these viruses share only 22-33% amino acid identity. Several entry receptors for HSV have been identified. Two of these, HveA (HVEM) and HveC (nectin-1), mediate entry of most HSV-1 and HSV-2 strains and are bound directly by HSV gD. A third receptor, HveB (nectin-2), mediates entry of HSV-2 and only a limited number of HSV-1 strains. HveB and HveC can also serve as entry receptors for PrV, whereas only HveC can serve this function for BHV-1. We show here that gD from PrV and BHV-1 binds directly to the human receptors that mediate PrV and BHV-1 entry. We expressed soluble forms of PrV gD and BHV-1 gD using recombinant baculoviruses and purified each protein. Using ELISA, we detected direct binding of PrV gD to HveB and HveC and direct binding of BHV-1 gD to HveC. Biosensor analysis revealed that PrV gD had a 10-fold higher affinity than HSV-1 gD for human HveC. In contrast, the binding of BHV-1 gD to HveC was weak. PrV gD and HSV-1 gD competed for binding to the V domain of HveC and both inhibited entry of the homologous and heterologous viruses. These data suggest that the two forms of gD bind to a common region on human HveC despite their low amino acid similarity. Based on affinities for human HveC, we predict a porcine HveC homolog may be important for PrV infection in its natural host, whereas a BHV-1 infection in its natural host may be mediated by a receptor other than a bovine HveC homolog.

Reverse immunogenetic and polyepitopic approaches for the induction of cell-mediated immunity against bovine viral pathogens

The control of several infectious diseases of animals by vaccination is perhaps the most outstanding accomplishment of veterinary medicine in the last century. Even the eradication of some pathogens is in sight, at least in some parts of the world. However, infectious diseases continue to cost millions of dollars to the livestock industry. One of the reasons for the failure to control certain pathogens is the limited emphasis placed on cell-mediated immunity (CMI) in the design of vaccines against these pathogens. Traditionally, vaccine-induced immunity has been studied in relation to antibody-mediated protection. More recent studies, however, have focused on understanding CMI and developing means of inducing CMI. This review focuses on recent advances made in the study of CMI in general and of cytotoxic T lymphocytes in particular. Parallels from studies in human and mouse immunology are drawn in order to point out implications to bovine immunology, specifically for immunity against bovine herpesvirus 1.

The bovine herpesvirus type 1 UL3.5 open reading frame encodes a virion structural protein

The bovine herpesvirus type 1 (BHV-1) open reading frame (ORF) UL3.5 is similar to ORFs found in pseudorabies virus, infectious laryngotracheitis virus, equine herpesvirus type 1, and varicella zoster virus, but clearly absent from herpes simplex virus. The published sequence for this ORF predicts a 126-amino-acid (13.2 kDa) protein product with an isoelectric point of 12.3. We confirmed the UL3.5 sequence, expressed the ORF as a glutathione-S-transferase fusion protein, and made rabbit antibodies against the purified fusion protein. The antiserum detected a 13-kDa protein in Western blots of MDBK cells infected with BHV-1, but not with other herpesviruses or uninfected cells. The BHV-1 UL3.5 protein was characterized as a component of the virion envelope or tegument because it was expressed as a late protein, it was present in the cytoplasm but not the nucleus of infected cells, and it was removed from purified virions by detergent extraction.

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.

Molecular basis of antigenic variation between the glycoproteins C of respiratory bovine herpesvirus 1 (BHV-1) and neurovirulent BHV-5

Herpesvirus glycoprotein C (gC) functions as a major virus attachment protein. The gC sequence of the neurovirulent bovine herpesvirus type 5 (BHV-5) virus was determined and compared with the gC sequence of the nonneurovirulent BHV-1. Alignment of the predicted amino acid sequences of BHV-1 and BHV-5 gC ORFs showed that the amino-terminal third of the protein differed between the two viruses. Whole or subgenomic fragments of gC coding regions from both viruses were expressed as trpE-gC fusion proteins in Escherichia coli to map linear epitopes defined by type-specific murine monoclonal antibodies (MAbs). Based on the reactivity of BHV-1-specific MAbs with the recombinant proteins, two epitopes were mapped between BHV-1 gC residues 22 and 172. Undirectional deletion of these residues at the carboxy end mapped one within residues 22-69 and the other within residues 103-122. Two BHV-5-specific MAbs identified an epitope coding region within BHV-5 gC residues 31-78. Bovine antisera against BHV-1 and BHV-5 showed specificity to BHV-1 gC residues 22-69 and to BHV-5 gC residues 31-78, respectively, in a type-specific manner.

Study of neutralizing monoclonal antibodies to bovine herpes virus type-1 (Cooper strain) by immunoperoxidase and immunoelectron microscopy

Three neutralizing monoclonal antibodies (mAbs) that are specific against bovine herpes virus Type-1 (BHV-1) were studied as to their viral specificity by immunoperoxidase and immunoelectron microscopy. Microscopic examination of GBK BHV-1 infected cells revealed peroxidase activity represented by red-brown granular deposits in the nucleus and cytoplasm. No immunoperoxidase activity was observed in negative controls. For the ultrastructural observations, two approaches were used. Firstly we tested a pre-embedding technique using GBK infected cells, mAbs and gold conjugated-protein A. Gold particles were observed linked to the viral envelopes and to the host cell membrane. Alternatively, a second technique employed BHV-1 purified by potassium tartrate gradients, mAbs and gold conjugated-protein A. After performing the immune reaction, the samples were adsorbed to formvar-coated grids, stained with phosphotungstic acid and observed in a transmission electron microscope. Gold particles were mainly attached to the virion envelope.

Fine mapping of bovine herpesvirus-1 (BHV-1) glycoprotein D (gD) neutralizing epitopes by type-specific monoclonal antibodies and sequence comparison with BHV-5 gD

Overlapping fragments of the bovine herpesvirus-1 (BHV-1) glycoprotein (gD) ORF were expressed as trpE-gD fusion proteins in Escherichia coli to map linear neutralizing epitopes defined by BHV-1-specific MAbs. The MAbs 3402 and R54 reacted with the expressed fragments on Western blots that located the epitopes between the amino acids 52-126 and 165-216, respectively, of gD. Bovine covalescent sera with high neutralizing antibody titers against BHV-1 reacted with these bacterially expressed proteins containing both of the epitopes. Alignment of these sequences from BHV-1 with the corresponding region of the BHV-5 gD ORF sequences (reported here) identified several amino acid mismatches. Since the MAbs 3402 and R54 neutralize the BHV-1 and not BHV-5, it was presumed that these were important amino acids in defining the epitope. To further localize the neutralizing epitopes, synthetic peptides corresponding to these regions in the BHV-1 gD ORF were tested for their capacity to block monoclonal antibody neutralization of BHV-1 infectivity. The peptides encompassing amino acids 92-106 (3402 epitope) and amino acids 202-213 (R54 epitope) of the BHV-1 gD competed with BHV-1 for the binding by MAbs 3402 and R54, respectively, in a dose-dependent manner. Antisera produced in rabbits to these peptides conjugated to a carrier reacted strongly with a 30-kDa protein by Western blotting and had neutralizing antibody titers against BHV-1.

Synthesis and processing of bovine herpesvirus-1 glycoprotein H

The translation product of the bovine herpesvirus-1 (BHV-1) gH gene was identified and characterized. Synthetic peptides were used to generate specific antisera and a glycoprotein of 108K was precipitated by one of the antisera. Cross-immunoprecipitations with monoclonal antibodies to BHV-1 glycoprotein gp108 and the anti-gH peptide antiserum demonstrated that gp108 is the translation product of the gH open reading frame. Glycoprotein gH synthesis and intracellular processing was analyzed in infected Madin-Darby bovine kidney cells using anti-gp 108 monoclonal antibodies. Glycoprotein gH is expressed as a beta-gamma protein and could be detected by radioimmunoprecipitation as early as 2 hr postinfection. Cotranslational N-glycosylation of gH is essential for the recognition by monoclonal antibodies, suggesting that N-linked glycans are involved in protein folding or that they are targets for most of monoclonal antibodies used in this study.

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.

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.

Identification of 108K, 93K, and 42K glycoproteins of bovine herpesvirus-1 by monoclonal antibodies

Three glycoproteins of bovine herpesvirus-1 (BHV-1) other than glycoproteins gI, gIII, and gIV were identified by monoclonal antibody (MAb) analyses. Monoclonal antibodies were obtained by immunization of mice with either BHV-1 envelope or virus infected cells, from which the glycoproteins gI, gIII, and gIV were removed by immunoaffinity. In the latter immunization procedure mice were tolerized either against normal cellular antigens with or without glycoproteins gI, gIII, gIV, and nucleocapsid. From 154 anti-BHV-1 hybridomas isolated, 39 MAbs precipitated a 108K glycoprotein. Two other glycoproteins of respectively 42K and 93K were precipitated each by one MAb. These three glycoproteins were detected in infected cell lysate. Nine anti-108K glycoprotein MAbs neutralized BHV-1 infectivity and three non-neutralizing MAbs were able to reduce plaque development when virus was grown in the presence of these MAbs. It is therefore suggested that this glycoprotein is involved in viral entry into the cell and in cell-to-cell spread of the virus.

Characterization of an antigenic site on glycoprotein 13 (gC) of equid herpesvirus type-1

Six monoclonal antibodies directed against EHV-1 glycoprotein 13 were characterized. Five antibodies neutralized EHV-1 and were directed against a single antigenic site which comprised type-specific and type cross-reactive epitopes. Inhibition of monoclonal antibody binding to this site by post-infection equine sera suggests that it is a target of host antibody during natural infection with either EHV-1 or EHV-4.

Induction of a mucosal barrier to bovine herpesvirus 1 replication in cattle

Current vaccines for human and animal herpesviruses engender an immunity that may ameliorate disease but generally fails to prevent infection, latency, reactivation from latency, or spread through a population. By administering intranasally to cattle bovine herpesvirus type 1 virion envelope proteins combined with the potent mucosal immune system adjuvant, cholera toxin B subunit, we engendered a local antibody response that acted as a barrier to infection of mucosal epithelial cells and thereby prevented viral replication, consequently precluding disease, latency, and spread.

Induction of immune response to bovine herpesvirus-1 with anti-idiotypic antibodies

Previously, we prepared rabbit anti-idiotypic (anti-Id) antibodies against murine monoclonal antibodies (MAbs) specific for the major bovine herpesvirus-1 (BHV-1) envelope glycoproteins. Glycoprotein III (gIII) contains neutralization epitopes and may be the virus attachment protein. Anti-Id antibodies to a neutralizing MAb that reacts with gIII were purified by sequential immunoaffinity chromatography. Immune responses to the purified anti-Id reagent and BHV-1 were compared in mice. Both groups of mice produced BHV-1-specific neutralizing antibodies. However, lymphocyte proliferative responses and interferon and interleukin-2 production were specific for the respective immunizing antigens. These results suggest that the anti-Id reagent may bear an internal image of a B-cell-stimulating epitope of glycoprotein gIII; however, this epitope does not stimulate a virus-specific cellular immune response in mice.

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.

Identification of a neutralizing epitope on glycoprotein gp58 of human cytomegalovirus

Human cytomegalovirus contains an envelope glycoprotein of 58 kilodaltons (gp58). The protein, which is derived from a glycosylated precursor molecule of 160 kilodaltons via proteolytic cleavage, is capable of inducing neutralizing antibodies. We have mapped the epitopes recognized by the neutralizing monoclonal antibody 7-17 and a second antibody (27-287) which is not neutralizing. Overlapping fragments of the carboxy-terminal part of the open reading frame coding for gp58 were expressed in Escherichia coli as beta-galactosidase fusion proteins. The reactivities of antibodies 7-17 and 27-287 were determined by Western blot (immunoblot) analysis. Both antibodies recognized sequences between amino acids 608 and 625 of the primary gp58 translation product. The antibodies almost completely inhibited one another in a competitive binding assay with intact virus as antigen. Moreover, antibody 27-287 was able to inhibit the complement-independent neutralizing activity of antibody 7-17.

Preincubation of bovine blood neutrophils with bovine herpesvirus-1 does not impair neutrophil interaction with Pasteurella haemolytica A1 in vitro

In this study we examined the direct effects of bovine herpesvirus-1 on the interaction of bovine blood neutrophils with Pasteurella haemolytica A1. Preincubation of neutrophils for approximately 2 h in vitro with BHV-1 at a multiplicity of infection of 5:1 had no effect on neutrophil random migration and directed migration to zymosan-activated bovine serum. Neutrophils also were unimpaired in their ability to ingest and kill P. haemolytica A1. Preincubation of neutrophils with BHV-1 did not elicit an oxidative burst, as measured by luminol-enhanced chemiluminescence, nor did it alter neutrophil chemiluminescence in response to opsonized P. haemolytica A1. Prolonged preincubation with BHV-1 for 18-24 h similarly did not affect neutrophil chemiluminescence in response to opsonized P. haemolytica A1. The susceptibility of neutrophils to the lethal effects of crude P. haemolytica cytotoxin also was unaltered by preincubation with BHV-1. We observed no evidence of BHV-1 replication in bovine neutrophils as determined by indirect immunofluorescence and electron microscopy. Previous reports have indicated that active BHV-1 infection alters certain neutrophil functions and results in hypersusceptibility to pulmonary pasteurellosis. Our results suggest that these effects are unlikely to be mediated directly by BHV-1, but instead may reflect the action of endogenous mediators that are released during active BHV-1 infection.

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.