Heparin-binding domain of bovid herpesvirus 1 glycoprotein gIII

Preliminary molecular study for DIVA trial of antigenically characterized circulating bovine herpesvirus subtype 1.1 in Egypt

Using marker vaccines to control bovine alphaherpesvirus-1 (BoHV-1) is a novel strategy for differentiation between infected and vaccinated animals (DIVA). In this study, multiplex real-time PCR targeting gD and gE genes was applied for BoHV-1 screening on 60 clinical samples from cattle with a history of vaccination, in some cases by US2-deleted marker vaccines, that were suffering from severe respiratory symptoms. Conventional PCR targeting the gC and US2 flanking region was done for molecular characterization and identification of the US2-deleted vaccine strain. Six samples were positive for BoHV-1 by both RT-PCR and conventional PCR. Surprisingly, a conventional PCR DIVA trial based on the US2 gene revealed that only one sample that exhibited the US2 gene was a wild virus, while others that did not exhibit the US2 gene were vaccine viruses. Phylogenetic characterization classifies the samples as BoHV-1.1. This finding reveals the circulation of vaccine virus in field-diseased animals, which threatens the eradication program.

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 1 infection and infectious bovine rhinotracheitis

Bovine herpesvirus 1 (BoHV-1), classified as an alphaherpesvirus, is a major pathogen of cattle. Primary infection is accompanied by various clinical manifestations such as infectious bovine rhinotracheitis, abortion, infectious pustular vulvovaginitis, and systemic infection in neonates. When animals survive, a life-long latent infection is established in nervous sensory ganglia. Several reactivation stimuli can lead to viral re-excretion, which is responsible for the maintenance of BoHV-1 within a cattle herd. This paper focuses on an updated pathogenesis based on a molecular characterization of BoHV-1 and the description of the virus cycle. Special emphasis is accorded to the impact of the latency and reactivation cycle on the epidemiology and the control of BoHV-1. Several European countries have initiated BoHV-1 eradication schemes because of the significant losses incurred by disease and trading restrictions. The vaccines used against BoHV-1 are described in this context where the differentiation of infected from vaccinated animals is of critical importance to achieve BoHV-1 eradication.

Analysis of antibody response in goats to caprine herpesvirus 1

Serum samples of goats experiencing natural and experimental infections and/or reactivation of caprine herpesvirus 1 (CpHV.1) were analysed with neutralization and Western blotting (WB) tests. WB immunological patterns resulted differently and related to neutralizing titers. In serum samples having neutralizing titer 1:2-1:4, antibodies to two proteins of Mw of 150 and 34 kDa were present. Antibodies against several proteins, two of those being characterized by monoclonal antibodies as gB and gC, were visualized by WB in sera having titer > or = 1:8. The neutralizing antibody titers and the pattern of antibody reactivity were hypothesized to modulate the reactivation and re-excretion process of CpHV.1.

The amino-terminal residue of glycoprotein B is critical for neutralization of bovine herpesvirus 1

In order to address the neutralization epitope on bovine herpesvirus 1 (BHV1) glycoprotein B (gB), a panel of monoclonal antibodies (MAbs), a series of truncation forms of the glycoprotein and an MAb-escape mutant were used in this study. Immunocytochemistry on the truncations using MAbs against the glycoprotein revealed that the neutralization epitopes recognized by the MAbs lay between residues 1 and 52 of mature gB. Comparison of the sequences among the mutant, parent, and revertant viruses demonstrated that the amino-terminal residue of mature gB of the escape mutant was changed from Arg to Gln. These findings indicate that the amino-terminal residue of gB is critical for neutralization of BHV1.

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.

The porcine humoral immune response against pseudorabies virus specifically targets attachment sites on glycoprotein gC

High titers of virus-neutralizing antibodies directed against glycoprotein gC of Pseudorabies virus (PRV) (Suid herpesvirus 1) are generally observed in the serum of immunized pigs. A known function of the glycoprotein gC is to mediate attachment of PRV to target cells through distinct viral heparin-binding domains (HBDs). Therefore, it was suggested that the virus-neutralizing activity of anti-PRV sera is directed against HBDs on gC. To address this issue, sera with high virus-neutralizing activity against gC were used to characterize the anti-gC response. Epitope mapping demonstrated that amino acids of HBDs are part of an antigenic antibody binding domain which is located in the N-terminal part of gC. Binding of antibodies to this antigenic domain of gC was further shown to interfere with the viral attachment. Therefore, these results show that the viral HBDs are accessible targets for the humoral anti-PRV response even after tolerance induction against self-proteins, which utilize similar HBDs to promote host protein-protein interactions. The findings indicate that the host's immune system can specifically block the attachment function of PRV gC. Since HBDs promote the attachment of a number of herpesviruses, the design of future antiherpesvirus vaccines should aim to induce a humoral immune response that prevents HBD-mediated viral attachment.

Effect of bovine herpesvirus-1 or bovine viral diarrhea virus on development of in vitro-produced bovine embryos

In previous experiments, zona pellucida (ZP)-intact in vitro-produced (IVP) embryos incubated for 1 hr with 10(6.3) TCID(50)/ml bovine herpes virus-1 (BHV-1), 10(5.3) TCID(50)/ml cytopathic (CP) bovine viral diarrhea virus (BVDV) or 10(5.3) TCID(50)/ml noncytopathic (NCP) BVDV showed no signs of virus replication or embryonic degeneration. The aims of the present study were to investigate whether a prolonged presence (24 hr or 8 days) of 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml BVDV in an in vitro embryo production system affected the rate of cleavage and embryonic development of ZP-intact embryos, and to point out eventual causes of adverse effects. When virus was present in each step of an IVP system, significantly lower rates of cleavage and blastocyst formation of virus-exposed embryos were observed, in comparison with control embryos (P < 0.01). When embryos were only exposed to virus during the in vitro fertilization (IVF), the rates of cleavage and blastocyst formation were significantly affected. The introduction of BHV-1 or BVDV during in vitro maturation (IVM) or in vitro culture (IVC) resulted only in significantly lower rates of blastocyst (P < 0.01). In all experiments, virus replication was not detected in the embryonic cells. On the other hand, virus replication was clearly demonstrated in oviductal cells in the co-culture system, resulting in a degeneration of these cells. In an additional experiment, synthetic oviduct fluid (SOF) without somatic cells was used as an alternative culture system. Even when SOF-embryos were exposed to 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml CP, and NCP BVDV, the rates of blastocyst formation of the BHV-1-, CP-, and NCP BVDV-exposed embryos were not different from the unexposed control embryos, 23%, 24%, and 24%, respectively, vs. 27%. Taken together, it can be concluded that the virus-induced adverse effects on embryonic development in conventional co-cultures were due to changes in the embryonic environment caused by infection of oviductal cells.

Identification and characterization of bovine herpesvirus type 5 glycoprotein H gene and gene products

Bovine herpesvirus type 5 (BHV-5) is the causative agent of a fatal meningo-encephalitis in calves and is closely related to BHV-1 which causes infectious bovine rhinotracheitis. The gene encoding BHV-5 glycoprotein gH was sequenced. A high degree of conservation was found between BHV-1 and BHV-5 deduced gH amino acid sequences (86. 4%), which is also observed for all alphaherpesvirus gH sequences. Transcriptional analysis revealed a 3.1 kb mRNA as the specific gH transcript which was detected 2 h post-infection (p.i.). Twelve out of twenty-one MAbs directed against BHV-1 gH immunoprecipitated a 108-110 kDa glycoprotein, which was then designated BHV-5 gH. Synthesis and intracellular processing of BHV- 5 gH was analysed in infected MDBK cells using gH cross-reacting MAbs. Glycoprotein gH was expressed as a beta-gamma protein, detected by radioimmunoprecipitation as early as 3 h p.i. Glycosylation studies indicated that BHV-5 gH contains N-linked carbohydrates which are essential for the recognition of the protein by the MAbs. This suggests that N-linked glycans are involved in protein folding or are targets for the gH cross-reacting MAbs. Plaque- reduction neutralization assays showed that at least one BHV-1 gH antigenic domain is lacking in BHV-5 which may possibly relate to in vivo differences in virus tropism.

Identification of a linear heparin binding domain for human respiratory syncytial virus attachment glycoprotein G

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in infants and young children worldwide. Infection is mediated, in part, by an initial interaction between attachment protein (G) and a highly sulfated heparin-like glycosaminoglycan (Gag) located on the cell surface. Synthetic overlapping peptides derived from consensus sequences of the G protein ectodomain from both RSV subgroups A and B were tested by heparin-agarose affinity chromatography for their abilities to bind heparin. This evaluation identified a single linear heparin binding domain (HBD) for RSV subgroup A (184A-->T198) and B (183K-->K197). The binding of these peptides to Vero cells was inhibited by heparin. Peptide binding to two CHO cell mutants (pgsD-677 and pgsA-745) deficient in heparan sulfate or total Gag synthesis was decreased 50% versus the parental cell line, CHO-K1, and decreased an average of 87% in the presence of heparin. The RSV-G HBD peptides were also able to inhibit homologous and heterologous virus infectivity of Vero cells. These results indicate that the sequence 184A/183K-->198T/K197 for RSV subgroups A and B, respectively, defines an important determinant of RSV-G interactions with heparin.

Bovine herpesvirus 1-induced apoptotic cell death: role of glycoprotein D

Bovine herpesvirus 1 (BHV-1) induces apoptotic cell death in peripheral blood mononuclear cells and in bovine B lymphoma (BL-3) cells. Attachment but not penetration of BHV-1 is necessary to induce apoptosis in target cells, suggesting that one or more BHV-1 envelope glycoproteins could be involved in the activation of the apoptotic process. In the present study, we demonstrate that, although BHV-1 virions devoid of glycoprotein D (BHV-1 gD-/-) still bind to BL-3 cells, they are no longer able to induce apoptosis. In contrast, virions that contain glycoprotein D (gD) in the viral envelope but do not genetically encode gD (BHV-1 gD-/+) induce a level of apoptosis comparable to that produced by wild-type (wt) BHV-1. In addition, monoclonal antibodies directed against gD, but not against gB or gC, strongly reduced the high levels of apoptosis induced by BHV-1. These observations demonstrate that the induction of apoptosis is directly due to BHV-1 viral particles harboring gD in the viral envelope. Interestingly, binding of affinity-purified gD to BL-3 cells did not induce apoptosis but inhibited the ability of wt BHV-1 to induce apoptosis. Altogether, these results provide evidence for the direct or indirect involvement of gD in the mechanism by which BHV-1 induces apoptosis.

Attachment but not penetration of bovine herpesvirus 1 is necessary to induce apoptosis in target cells

Bovine herpesvirus 1 (BHV-1) induces apoptotic cell death in bovine peripheral blood mononuclear cells and B-lymphoma cells. Using a BHV-1 glycoprotein H null mutant, we have demonstrated that although penetration of BHV-1 is not required, attachment of BHV-1 viral particles is essential for the induction of apoptosis.

Fine mapping of bovine herpesvirus 1 (BHV-1) glycoprotein C neutralizing epitopes by type-specific monoclonal antibodies and synthetic peptides

Bovine herpesvirus glycoprotein C (gC) functions as a major virus attachment protein. Here, two BHV-1 gC-specific epitopes that are specified by complement-dependent neutralizing MAbs are mapped. The BHV-1 gC-specific peptides and MAbs were used to specifically localize continuous epitopes by direct binding to the MAbs and by blocking the Mab reactivity (competitive ELISA) to authentic viral antigen. The results of competitive ELISA indicated that the complement-dependent neutralizing epitopes recognized by MAbs F2 and 24 were located between BHV-1 gC amino acids (aa) 47-69 and (aa) 109-119, respectively.

Molecular virology of ruminant herpesviruses

Molecular virology has served to establish bovine herpesvirus 1 (BHV-1) as the prototype member of ruminant herpesviruses. Based on the genomic sequence of the virus, we aim to identify and characterize virus-specified components, to explain their concerted action, and to predict how the chain of events during the lytic and latent phases of the viral life cycle may be interrupted. The nucleotide sequence of the BHV-1 genome (136 kb) has just been completed by international cooperation (July 1995; except for a small gap in UL36). It comprises 67 unique genes and 2 genes, both duplicated, in the inverted repeats. In general, these genes exhibit strong homology at the amino acid sequence level to those of other alphaherpesviruses (HSV-1, VZV, EHV-1) and are arranged in similar order. A few genes are peculiar to only one or two herpesviruses, e.g. in BHV-1 the circ, UL0.5, UL3.5 and US1.5 genes. Not long ago, the repertoire of BHV-1 proteins under study was restricted to the three major glycoproteins (gB, gC, and gD) and thymidine kinase. The repertoire is now growing rapidly and includes 7 additional glycoproteins (gE, gI, gH, gL, gG, gK and gM), a number of enzymes (e.g. ribonucleotide reductase, DNA Polymerase, dUTPase), and a group of regulatory proteins (BICPO, 4, 22, and 27, alpha TIF). Investigations into the functions of these proteins and comparison with their counterparts in other herpesviruses should reveal which are useful targets for diagnosis, prevention or antiviral treatment. Recombinant viruses containing deletions or replacements of individual genes are being created, aiming at vaccine development and insights into pathogenesis, notably latency, neurotropism, and interference with host functions. Molecular analysis of other ruminant herpesviruses is much less advanced. Over a dozen virus species have been described; most share basic properties with BHV-1 and may be classified as alphaherpesviruses. The gammaherpesviruses are represented by the proposed agent of malignant catarrhal fever, alcelaphine herpesvirus 1, and by bovine herpesvirus 4, whose partial sequences exhibit similarity to herpesvirus saimiri.

The receptor-binding domain of pseudorabies virus glycoprotein gC is composed of multiple discrete units that are functionally redundant

Many herpesviruses attach to cells in a two-step process, using the glycoprotein gC family of homologs to bind the primary receptor, heparan sulfate (HS) proteoglycan, and glycoprotein gD homologs to bind an unknown secondary receptor. We have previously shown by deletion analysis that the amino-terminal one-third of gC from pseudorabies virus (PRV), a swine herpesvirus, includes at least the principal HS receptor-binding domain. This portion of PRV gC contains three discrete clusters of basic residues that exactly or nearly match proposed consensus sequences for heparin-binding domains (HBDs); four additional potential HBDs lie in the distal two-thirds of the glycoprotein. We now specifically implicate each of the three amino-terminal HBDs in virus attachment. Mutational analysis demonstrated that any one of the three HBDs could mediate efficient virus infectivity; HS-dependent PRV attachment to cells was eliminated only after all three amino-terminal HBDs were altered. Furthermore, the binding dysfunction was due to a disruption of the specific HBDs and not to total charge loss. Thus, unlike previously described viral receptor-binding domains, the PRV gC receptor-binding domain is composed of multiple, discrete units that can function independently of one another. These units may function redundantly either to increase binding affinity or perhaps to effectively increase the virus's host range.

Interaction of heparin with synthetic peptides corresponding to the C-terminal domain of intestinal mucins

Unlike most other mucins described to date, two intestinal mucins, rat MLP (rat Muc 2) and human MUC2 have a C-terminal tail that is enriched in cationic amino acids. The distribution of charge in each case resembles that of several well known heparin binding proteins. Peptides designated E20-14 and F13-15, corresponding to the C-terminal 14 amino acids of the two mucins, were synthesized and shown to bind 3 H-labelled heparin by a process that was saturable and mediated by strong electrostatic interactions, giving Kd values of 10 (-7) to 10 (-8) M. Using turbidometric analyses and native gel electrophoresis, we observed that peptide-heparin mixtures formed polydisperse aggregates that dissociated with a progressive increase in the concentration of heparin. Under certain conditions heparin protected the peptide from proteolysis by trypsin. Both heparin and dextran sulfate, the latter a highly sulfated synthetic polysaccharide, were potent inhibitors of 3 H-heparin binding to peptide E20-14, while less sulfated glycosaminoglycans were poorly- or non-inhibitory. Mucin in tissue dispersions and homogenates, or purified from rat intestine, did not bind to heparin, and failed to interact with an antibody specific for the peptide E20-14. Both mucin samples however, reacted with antibodies that recognize regions upstream of the C-terminal 14 amino acids. Immunofluorescent localization of E20-14 was confined to the basal perinuclear regions of goblet cells, whereas localization of an antibody to a flanking sequence on the N-terminal side of the C-tail, localized to mature mucin storage granules. These findings suggest that the heparin -binding C-tail of the mucin may be removed at an early stage of biosynthesis. Heparin-mucin complexes, if they form in vivo, are thus likely to be confined to the ER and/or Golgi compartments.

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.

Characterization of cell-binding properties of bovine herpesvirus 1 glycoproteins B, C, and D: identification of a dual cell-binding function of gB

Previous studies have suggested that the attachment of bovine herpesvirus 1 (BHV-1) to permissive cells is mediated by its major glycoproteins B (gB), C (gC), and D (gD). In order to gain further insight into the mechanism of the BHV-1 attachment process, we purified authentic gB, gC, and gD from BHV-1-infected cells and membrane anchor-truncated, soluble gB, gC, and gD from stably transfected cell lines by affinity chromatography and examined their cell-binding properties on Madin-Darby bovine kidney cells. All of the glycoproteins tested exhibited saturable binding to Madin-Darby bovine kidney cells. All of the glycoproteins tested exhibited saturable binding to Madin-Darby bovine kidney cells. Addition of exogenous heparin or treatment of cells with heparinase to remove cellular heparan sulfate (HS) prevented both gC and gB from binding to cells but had no effect on gD binding. An assessment of competition between gB, gC, and gD for cell binding revealed that gC was able to inhibit gB binding, whereas other combinations showed no effect. Cell-bound gC could be dissociated by heparin or heparinase treatment. The response of bound gB to heparin and heparinase treatments differed for the authentic and soluble forms; while soluble gB was susceptible to the treatment, a significant portion of cell-bound authentic gB was resistant to the treatment. Binding affinity analysis showed that soluble gB and both forms of gC and gD each had single binding kinetics with comparable dissociation constants (Kds), ranging from 1.5 x 10(-7) to 5.1 x 10(-7) M, whereas authentic gB exhibited dual binding kinetics with Kd1 = 5.2 x 10(-7) M and Kd2 = 4.1 x 10(-9) M. These results demonstrate that BHV-1 gC binds only to cellular HS, gD binds to a non-HS component, and gB initially binds to HS and then binds with high affinity to a non-HS receptor. Furthermore, we found that while authentic gB was able to inhibit viral plaque formation, soluble gB, which retains the HS-binding property but lacks the high-affinity binding property, was defective in this respect. These results suggest that the interaction between gB and its high-affinity receptor may play a critical role in the virus entry process.

A heterologous heparin-binding domain can promote functional attachment of a pseudorabies virus gC mutant to cell surfaces

The efficient attachment of pseudorabies virus to cultured cells is dependent on an electrostatic interaction between negatively charged cell surface heparan sulfate and the viral envelope glycoprotein gC. Deletion of the first one-third of gC severely impairs virus attachment, but the mutant virions are still capable of entering cells and establishing an infection via a gC-independent pathway. This region of gC contains three clusters of positively charged amino acids that exactly or nearly conform to proposed consensus motifs for heparin-binding domains (HBDs), and the loss of one or more of these potential HBDs may be responsible for the observed attachment defect. To more directly show the involvement of HBDs in pseudorabies virus attachment to cells, we replaced the first one-third of gC with a single, biochemically defined HBD from apolipoprotein B-100. On the basis of the results of attachment, penetration, and heparin competition assays, the heterologous HBD mediated heparan sulfate-dependent virus attachment, but not to fully wild-type levels. Although the intermediate phenotype is not understood, the apolipoprotein B-100 HBD may represent the smallest defined amino acid sequence that promotes functional herpesvirus attachment to cultured cells.