Bovine herpesvirus 1 (BHV-1): biology, pathogenesis, and control

The zinc ring finger in the bICP0 protein encoded by bovine herpesvirus-1 mediates toxicity and activates productive infection

The bICP0 protein encoded by bovine herpesvirus 1 (BHV-1) is believed to activate transcription and consequently productive infection. Expression of full-length bICP0 protein is toxic in transiently transfected mouse neuroblastoma cells (neuro-2A) in the absence of other viral genes. However, bICP0 does not appear to directly induce apoptosis. Although bICP0 is believed to be functionally similar to the herpes simplex virus type 1-encoded ICP0, the only protein domain that is well conserved is a C3HC4 zinc ring finger located near the N terminus of both proteins. Site-specific mutagenesis of the zinc ring finger of bICP0 demonstrated that it was important for inducing aggregated chromatin structures in transfected cells and toxicity. The zinc ring finger was also required for stimulating productive infection in bovine cells and for trans-activating the thymidine kinase (TK) promoter of herpes simplex virus type 1. Deletion of amino acids spanning 356-677 of bICP0 altered subcellular localization of bICP0 and prevented trans-activation of the TK promoter. However, this deletion did not prevent trans-activation of the viral genome. Taken together, these studies indicated that bICP0 has several functional domains, including the zinc ring finger, which stimulate productive infection and influence cell survival.

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.

Bovine herpesvirus 1 glycoprotein G is required for prevention of apoptosis and efficient viral growth in rabbit kidney cells

In rabbit kidney (RK13) cells, gG-negative BHV-1 exhibited significant defects in plaque formation and growth compared to that of gG-positive BHV-1. RK13 cells infected with gG-negative BHV-1 exhibited a distinctive CPE and contained a larger number of cells stained with trypan blue dye compared to those infected with gG-positive strains, suggesting that gG-negative BHV-1 inflicted more damage to the infected cells than gG-positive BHV-1. Apoptotic cell death was induced in RK13 cells infected with gG-negative BHV-1 within 8 h. In contrast, the onset of apoptosis in gG-positive BHV-1-infected RK13 cells was around 12-16 h postinfection. In the presence of caspase inhibitor Z-Asp-CH2-DCB, multiplication of gG-negative minus BHV-1 was significantly increased. These results demonstrate that BHV-1 gG is involved in stabilizing the cell structure, postponing apoptotic process, and efficient BHV-1 replication in infected RK13 cells.

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.

Production of bovine herpesvirus type 1-seronegative latent carriers by administration of a live-attenuated vaccine in passively immunized calves

The consequences of the vaccination of neonatal calves with the widely used live-attenuated temperature-sensitive (ts) bovine herpesvirus type 1 (BHV-1) were investigated. The ts strain established acute and latent infections in all vaccinated calves either with or without passive immunity. Four of seven calves vaccinated under passive immunity became clearly BHV-1 seronegative by different serological tests, as did uninfected control calves after the disappearance of maternal antibodies, and they remained so for long periods. A cell-mediated immune response was detected by a BHV-1 gamma interferon assay, but this test failed to detect the seronegative latent carriers (SNLCs). While they are not detected, SNLCs represent a threat for BHV-1-free herds or countries. This study demonstrates that SNLCs can be easily obtained by inoculation with a live-attenuated BHV-1 under passive immunity and that latent carrier animals without any antibody do exist. Consequently, this situation could represent a good model to experimentally produce SNLCs.

The immunogenicity and efficacy of replication-defective and replication-competent bovine adenovirus-3 expressing bovine herpesvirus-1 glycoprotein gD in cattle

Replication-competent and replication-defective bovine adenovirus type 3 recombinants expressing the bovine herpesvirus type 1 (BHV-1) glycoprotein D (gD) were tested for induction of gD specific immune responses in calves using intratracheal (1st and 2nd immunization) and sub-cutaneous (3rd immunization) route of immunization. The replication-defective recombinant BAV501 induced systemic immune responses against gD as low titers of anti gD-IgG were detected in the serum. However, the efficacy of the replication-competent BAV3.E3gD to induce gD-specific antibodies in the serum and the nasal secretions was superior to that of replication-defective BAV501 when both viruses were given at the same dosage. Partial protection from challenge was induced in calves immunized with replication-competent BAV3.E3gD. A dramatic increase in the titers of anti-gD IgG and IgA levels, both in serum and nasal secretions, following BHV-1 challenge (anamnestic response) suggested that the animals immunized with replication-defective BAV501 had been primed for gD-specific antibody responses.

Analysis of latency in cattle after inoculation with a temperature sensitive mutant of bovine herpesvirus 1 (RLB106)

Calves were inoculated with the bovine herpes virus 1 (BHV-1) vaccine strain (RLB 106), which is a temperature sensitive mutant. The route of inoculation was intranasal instillation or intramuscular (i.m.) injection (flank or neck). As a control, five calves were given placebo by i.m. injection of the neck. Regardless of the infection route, clinical symptoms did not occur. However, BHV-1 neutralizing antibodies were detected after inoculation demonstrating that sero-conversion occurred. At 60 days post-inoculation, dexamethasone was given by i.m. injection to attempt reactivation of RLB 106. Only those calves inoculated by the intranasal route shed virus leading to an increase in BHV-1 specific antibodies. As expected, viral DNA and the latency related-RNA were detected in trigeminal ganglia (TG) of calves inoculated by the intranasal route. In contrast, viral nucleic acid was not detected in TG of calves inoculated by the i.m. route or in calves inoculated with placebo. In cervical ganglia or sacral dorsal root ganglia, viral nucleic acid was not consistently detected. This study provides evidence that efficient latency and reactivation does not occur following i.m. inoculation. Since serum-neutralizing antibodies were detected in all inoculated calves, i.m. inoculation led to sero-conversion.

Bovine herpesvirus 1 glycoprotein G is required for viral growth by cell-to-cell infection

The bovine herpesvirus 1 (BHV-1) US4 gene encodes glycoprotein G (gG), which is conserved in the majority of alphaherpesviruses. In order to identify the role of BHV-1 gG in the viral infection cycle, a gG minus BHV-1 mutant and its gG-positive revertant were constructed and their growth characteristics in Madin-Darby bovine kidney (MDBK) cells were compared. The gG minus mutant formed smaller plaques than the gG-positive BHV-1 in MDBK cells. When a monolayer culture of MDBK cells was infected with BHV-1 at a low multiplicity of infection and overlaid with semi-solid growth medium, under which adsorption of the mature virion released in the medium was inhibited, gG-positive BHV-1 multiplied, while the growth of the gG negative BHV-1 was severely inhibited. These data suggest that BHV-1 gG functions in direct cell-to-cell transmission mechanism of BHV-1 in tissue culture.

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

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

Cellular expression of alphaherpesvirus gD interferes with entry of homologous and heterologous alphaherpesviruses by blocking access to a shared gD receptor

Several human and animal alphaherpesviruses can enter cells via human herpesvirus entry mediator C (HveC), a receptor for viral glycoprotein D (gD). In previous studies with cells expressing unknown entry mediators, cellular expression of alphaherpesvirus gD was shown to inhibit entry of the homologous virus and sometimes also of heterologous alphaherpesviruses. To investigate the mechanism of gD-mediated interference and the basis for cross-interference among alphaherpesviruses, HveC was expressed in cells as the sole entry mediator, in the presence or absence of one of the gDs encoded by herpes simplex virus type 1, pseudorabies virus, or bovine herpesvirus type 1. Cells expressing HveC alone were highly susceptible to entry of all three viruses, whereas cells coexpressing HveC and any one of the gDs were at least partially resistant to infection by each virus. Coexpression of gD with HveC did not cause reduced levels of cell-surface HveC but the HveC had reduced ability to bind to exogenous gD. Coimmunoprecipitation experiments revealed that HveC was complexed with gD in lysates of cells expressing both. Thus, cellular expression of gD can interfere with alphaherpesvirus entry by blocking ligand-binding sites of the gD receptor(s) used for entry and cross-interference can occur because different forms of alphaherpesvirus gD can compete for shared entry receptors.

Altering the cellular location of an antigen expressed by a DNA-based vaccine modulates the immune response

The potential for DNA vaccines encoding mutated versions of the same antigen to modulate immune responses in C3H/HeN mice was investigated. We created expression plasmids that encoded several versions of glycoprotein D (gD) from bovine herpesvirus 1, including authentic membrane-anchored glycoprotein (pSLRSV.AgD), a secreted glycoprotein (pSLRSV.SgD), and an intracellular protein (pSLRSV.CgD). Immunization of an inbred strain of mice with these plasmids resulted in highly efficacious and long-lasting humoral and cell-mediated immunity. We also demonstrated that the cell compartment in which plasmid-encoded gD was expressed caused a deviation in the serum immunoglobulin (Ig) isotype profile as well as the predominant cytokines secreted from the draining lymph node. Immunization of C3H/HeN mice with DNA vaccines encoding cell-associated forms of gD resulted in a predominance of serum IgG2a and gamma interferon-secreting cells within the spleens and draining lymph nodes. In contrast, mice immunized with a secreted form of this same antigen displayed immune responses characterized by greater levels of interleukin 4 in the draining lymph node and IgG1 as the predominant serum isotype. We also showed evidence of compartmentalization of distinct immune responses within different lymphoid organs.

Characterization of monoclonal antibodies against bovine herpesvirus 1 gD fusion protein expressed in E. coli

A total of 20 hybridoma cell lines secreting monoclonal antibodies (MAbs) against E. coli expressed bovine herpesvirus-1 (BHV-1) gD fusion protein were produced following the fusion of Sp2/0 myeloma cells with splenocytes from BALB/c mice immunized previously with immunoaffinity purified BHV-1 gD fusion protein. An indirect fluorescent antibody test (IFAT) using BHV-1 infected MDBK cells was used for the selection of positive hybridomas secreting specific antibody. The monoclonal antibody isotypes were 11 IgM, six IgG2b, one IgG1 and two IgG3. All MAbs reacted positively with the E. coli expressed BHV-1 gD fusion protein, BHV-1 infected MDBK cell lysates and PCR BHV-1 gD transcription-translation polypeptide antigens by an ELISA.

Replication-defective bovine adenovirus type 3 as an expression vector

Although recombinant human adenovirus (HAV)-based vectors offer several advantages for somatic gene therapy and vaccination over other viral vectors, it would be desirable to develop alternative vectors with prolonged expression and decreased toxicity. Toward this objective, a replication-defective bovine adenovirus type 3 (BAV-3) was developed as an expression vector. Bovine cell lines designated VIDO R2 (HAV-5 E1A/B-transformed fetal bovine retina cell [FBRC] line) and 6.93.9 (Madin-Darby bovine kidney [MDBK] cell line expressing E1 proteins) were developed and found to complement the E1A deletion in BAV-3. Replication-defective BAV-3 with a 1.7-kb deletion removing most of the E1A and E3 regions was constructed. This virus could be grown in VIDO R2 or 6.93.9 cells but not in FBRC or MDBK cells. The results demonstrated that the E1 region of HAV-5 has the capacity to transform bovine retina cells and that the E1A region of HAV-5 can complement that of BAV-3. A replication-defective BAV-3 vector expressing bovine herpesvirus type 1 glycoprotein D from the E1A region was made. A similar replication-defective vector expressing the hemagglutinin-esterase gene of bovine coronavirus from the E3 region was isolated. Although these viruses grew less efficiently than the replication-competent recombinant BAV-3 (E3 deleted), they are suitable for detailed studies with animals to evaluate the safety, duration of foreign gene expression, and ability to induce immune responses. In addition, a replication-competent recombinant BAV-3 expressing green fluorescent protein was constructed and used to evaluate the host range of BAV-3 under cell culture conditions. The development of bovine E1A-complementing cell lines and the generation of replication-defective BAV-3 vectors is a major technical advancement for defining the use of BAV-3 as vector for vaccination against diseases of cattle and somatic gene therapy in humans.

Detection of bovine herpesvirus type 1 in blood from naturally infected cattle by using a sensitive PCR that discriminates between wild-type virus and virus lacking glycoprotein E

In the present study, we report for the first time on the detection of bovine herpesvirus type 1 (BHV-1) in whole-blood samples derived from naturally infected cattle. Sensitive PCR assays specific for glycoprotein B (gB), gC, and gE of BHV-1 allow the detection of one BHV-1 DNA copy in 10(5) to 10(7) peripheral blood leukocytes (PBLs). The incidence of BHV-1-positive PBLs in naturally infected cattle appears to be quite high (92.2% positive PBLs among all samples tested), although in most cases only between 10(-5) and 10(-7) positive leukocytes were present. The results demonstrate that the viral DNA is detectable not only in the peripheral blood of acutely infected animals but, more importantly, also in the peripheral blood of subclinically infected cattle. The gE-specific PCR described in the report allows discrimination between wild-type (WT) virus-infected and vaccinated animals, which is of importance for control programs that use the recently introduced vaccination strategy with a gE-negative virus. The results further show that doubtful serological results can be verified or falsified and that individual animals can be monitored for the presence or absence of WT BHV-1 or gE-negative virus in cattle herds. The PCR protocols allow the detection of BHV-1 prior to seroconversion or in BHV-1-seronegative cattle. Finally, the results indicate the simultaneous presence of WT and gE-negative vaccine virus in the PBLs of several cattle. Therefore, investigations of viremia in naturally and experimentally infected cattle and on the identification of infected cell types of bovine PBLs can be now performed.

Immunogenicity and protective efficacy of a gE, gG and US2 gene-deleted bovine herpesvirus-1 (BHV-1) vaccine

The efficacy and safety of a gene-deleted bovine herpesvirus-1 (BHV-1) vaccine was determined in a bovine herpesvirus challenge trial in calves. Three different doses of the vaccine were administered intramuscularly at 10(5), 10(6) and 10(7) PFU/ml and compared to a commercial vaccine and non vaccinated control calves. Challenge was performed by intranasal aerosolization with the Cooper strain of BHV-1 (3 x 10(4) PFU/ml). The non-vaccinated calves shed significantly (P < 0.05) more virus than all other groups on days 4, 8 and 10 post challenge. By day 14 post challenge, antibody titers for BHV-1 of calves vaccinated with 10(7) PFU/ml were significantly (P < 0.05) higher than the commercial or non-vaccinated calves. Clinical scores of non-vaccinated calves were significantly (P < 0.05) higher than all other groups on days 4-14 post challenge. With both radioimmunoprecipitation and competitive enzyme-linked immunosorbent assays (C-ELISA), calves in the gene-deleted vaccine groups mounted comparable specific responses against gB, gC and gD post vaccination as calves in the commercial vaccine group, but in a dose dependent manner. These data suggest that the gene-deleted BHV-1 vaccine tested may be used as an effective vaccine in controlling BHV-1 infections.

Activation of caspases and p53 by bovine herpesvirus 1 infection results in programmed cell death and efficient virus release

Programmed cell death (PCD), or apoptosis, is initiated in response to various stimuli, including virus infection. Bovine herpesvirus 1 (BHV-1) induces PCD in peripheral blood mononuclear cells at the G0/G1 phase of the cell cycle (E. Hanon, S. Hoornaert, F. Dequiedt, A. Vanderplasschen, J. Lyaku, L. Willems, and P.-P. Pastoret, Virology 232:351-358, 1997). However, penetration of virus particles is not required for PCD (E. Hanon, G. Meyer, A. Vanderplasschen, C. Dessy-Doize, E. Thiry, and P. P. Pastoret, J. Virol. 72:7638-7641, 1998). The mechanism by which BHV-1 induces PCD in peripheral blood mononuclear cells is not understood, nor is it clear whether nonlymphoid cells undergo PCD following infection. This study demonstrates that infection of bovine kidney (MDBK) cells with BHV-1 leads to PCD, as judged by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling, DNA laddering, and chromatin condensation. p53 appears to be important in this process, because p53 levels and promoter activity increased after infection. Expression of proteins that are stimulated by p53 (p21(Waf1) and Bax) is also activated after infection. Cleavage of Bcl-xL, a protein that inhibits PCD, occurred after infection, suggesting that caspases (interleukin-1beta-converting enzyme-like proteases) were activated. Other caspase substrates [poly(ADP-ribose) polymerase and actin] are also cleaved during the late stages of infection. Inhibition of caspase activity delayed cytotoxic activity and virus release but increased the overall virus yield. Taken together, these results indicate that nonlymphoid cells undergo PCD near the end of productive infection and further suggest that caspases enhance virus release.

Characterization of promoters integrated in the genome of bovine herpesvirus-1 (BHV-1)

Bovine herpesvirus-1 (BHV-1) has been used as a vector of live recombinant vaccines for cattle which express the genes of other pathogens. Because of the importance of the choice of the promoter which allows the efficient expression of the foreign genes in the BHV-1 vector, we compared the relative efficacy of various promoters integrated in the BHV-1 genome. The promoter sequences of the BHV-1 thymidine kinase (tk), gB, gC, SV40 early, and pseudorabies virus (PRV) immediate early (IE) genes were placed at the upstream of the open reading frame of the chloramphenycol acetyl transferase (CAT) gene and the promoter-CAT sequences were integrated into the tk gene of BHV-1 by homologous recombination. The promoter activity was assayed by measuring the CAT activity in the extracts of Madin Darby bovine kidney (MDBK) cells infected with the recombinant BHV-1. The PRV IE promoter was activated earlier and maintained at a higher level activity than the BHV-1 gB or gC promoters throughout the most of the growth phase of BHV-1. At the late phase, however, the activities of the BHV-1 gB and gC promoters reached the higher level. The BHV-1 tk promoter activity was low and the SV40 early promoter was hardly activated when integrated into the BHV-1 genome. promoter, recombinant BHV-1.

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.

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.

CD4(+) cytotoxic T-lymphocyte activity against macrophages pulsed with bovine herpesvirus 1 polypeptides

Bovine herpesvirus 1 (BHV-1) induces immune suppression, but the mechanisms for suppression are not well identified. We examined the induction and activity of BHV-1-specific cytolytic CD4(+) T lymphocytes (CTL) by stimulating peripheral blood mononuclear cells (PBMC) of cattle immunized with attenuated live BHV-1. Cytolytic effector cells were primarily CD4(+) T lymphocytes and lysed autologous, but not allogeneic, macrophages infected with BHV-1 or pulsed with BHV-1 polypeptides. Apoptosis of BHV-1-expressing target cells was observed in CD4(+) CTL assays by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) analysis. To determine if apoptosis was mediated by a perforin- or Fas-mediated pathway, EGTA, a known selective inhibitor of the perforin pathway, was used. EGTA did not inhibit CD4(+)-T-cell-mediated cytotoxic activity, but it did limit the NK cell cytotoxicity of virus infected cells. These findings support the concept that CD4(+) CTL lyse macrophages pulsed with BHV-1 polypeptides through a Fas-mediated lytic pathway by inducing apoptosis in the target cells. The prominent cytotoxicity mediated by CD4(+) CTL suggests a mechanism of selective removal of viral antigen-associated antigen-presenting cells.

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.

Evaluation of baculovirus-expressed bovine herpesvirus-1 (BHV-1) glycoproteins for detection and analysis of BHV-1-specific antibody responses

Baculovirus (Autographa californica nuclear polyhedrosis)-expressed bovine herpesvirus-1 (BHV-1) glycoproteins B (gB), gC, and gD were developed and characterized. The recombinant proteins retained their antigenic properties as determined by immunoblotting against monoclonal antibodies. The proteins were examined as antigens for detection of BHV-1 infection and for the analysis of antibody responses to the individual viral proteins. A total of 115 bovine serum samples were tested for their reactivity with individual recombinant proteins from baculovirus-infected Spodoptera frugiperda (SF-9) cell lysates by enzyme-linked immunosorbent assay (ELISA), western blotting, and dot blotting assays. These serum samples were previously tested for BHV-1-specific antibodies by virus neutralization (VN) at the veterinary diagnostic laboratory. All 90 serum samples tested positive with VN were positive by ELISA against gC and gD, separately. However, reactivities of sera against gB were generally low and inconsistent. On the other hand, out of 25 sera that were negative with VN, 22 sera were consistent and gave negative results against gC or gD by ELISA, whereas reactivities with gB were inconsistent. Similar results were obtained when the sera were tested by western blotting and dot blotting. The positive sera consistently reacted strongly against gC and to a lesser extent gD. These results suggest that baculovirus expressed gC from infected cell lysate can be used as a potential diagnostic antigen for detection of anti-gC-specific antibody responses in BHV-1 infected cattle.

Further investigations on the efficacy of a non-specific defence inducer evaluated in calves exposed to infectious bovine rhinotracheitis virus

Six calves were given the immunomodulator Baypamun and housed together with another six calves of which, three were experimentally infected with bovine herpesvirus-1 (BHV-1), whereas the remaining three served as untreated controls. The three experimentally infected calves as well as the three controls developed clinical signs of the typical acute form of infectious bovine rhinotracheitis (IBR). Of the calves treated with Baypamun, those that had only one injection of the immunomodulator, either at the start of the experiment (time 0) or 2 days later, underwent a much milder form of IBR and recovered in a shorter time than the experimentally infected calves or the controls. The calves that received four injections of the immunomodulator, i.e. at time 0 and subsequently for the next 3 days, remained healthy throughout the 30 days of observation. Moreover, the virus shedding by the Baypamun treated calves was significantly reduced. It was speculated that the use of an immunomodulator, eventually associated with a vaccination programme, would be a feasible approach to reduce significantly the onset of outbreaks of BHV-1, one of the main infectious agent initiating the respiratory disease in cattle.

A serological survey of bovine herpesvirus-1 infection in selected dairy herds in northern and central Italy

Serum samples from a total of 6979 dairy cattle from 55 herds in northern Italy (51 herds) and central Italy (4 herds), were examined by the serum neutralization test for the presence of antibody to bovine herpesvirus-1 (BHV-1). It was found that 84.31% of the farms selected in northern Italy and all the farms from central Italy had seropositive animals at titers of 1:4 or higher. The prevalence of infection was essentially the same among the cattle populations of the two selected areas of the country, being of 34.99% in the north and of 38.65% in central regions. A comparison of the data from the present study with those obtained in a serological survey conducted in Italy in 1966, shows that the rate of seropositive cattle to BHV-1 has increased by about 5.0% in the last 30 years.

Recombinant viral vector vaccines for the veterinary use

Recently, genetically engineering using recombinant DNA techniques has been applied to design new viral vaccines in order to reduce some problems which present viral vaccines have. Up to now, many viruses have been investigated for development of recombinant attenuated vaccines or live viral vectors for delivery of foreign immunogenic antigens. In this review, we introduced three kind of viruses; herpesviruses, vaccinia viruses, and adenoviruses, which have best widely been studied as recombinant vaccines or delivery vaccines for the veterinary use.

Pseudorabies virus recombinants expressing functional virulence determinants gE and gI from bovine herpesvirus 1.1

In the Alphaherpesvirinae subfamily, the gE and gI genes are conserved and encode membrane glycoproteins required for efficient pathogenesis (virulence). The molecular mechanism(s) responsible is not well understood, but the existence of similar phenotypes of gE and gI mutations in diverse Alphaherpesvirinae implies conservation of function(s). In this report, we describe construction of pseudorabies virus (PRV) recombinants that efficiently express the bovine herpesvirus 1 (BHV-1) membrane proteins gI and gE at the PRV gG locus. Each BHV-1 gene was cloned in a PRV mutant lacking both the PRV gI and gE coding sequences. All recombinant viruses expressed the BHV-1 proteins at levels similar to or greater than that observed after infection with parental BHV-1, and there were no observable differences in processing or ability to form gE-gI oligomers. The important observation resulting from this report is that the BHV-1 gE and gI proteins functioned together to complement the virulence defect of PRV lacking its own gE and gI genes in a rodent model, despite being derived from a highly restricted host range virus with a different pathogenic profile.

Recombinant bovine herpesvirus-1 (BHV-1) lacking transactivator protein BICPO entails lack of glycoprotein C and severely reduced infectivity

The immediate-early transactivator protein BICPO is a key regulatory element of bovine herpesvirus 1 (BHV-1) replication based on transient expression assays. To examine BICPO function in the context of the viral genome, we created recombinant BHV-1 expressing beta-galactosidase instead of BICPO. To complement the defect, a neomycin resistant MDBK cell line (M164) expressing BICPO was established, permitting selection of a blue-staining BHV-1 recombinant (A2G2). Southern blot and PCR analysis confirmed that the BICPO gene was interrupted by the beta-galactosidase gene and that wt progeny was absent. Compared with wt BHV-1, A2G2 reached lower titers in M164 cells but replicated with similar kinetics. Once isolated, A2G2 also grew in MDBK cells although the titer was reduced a further 10-fold and the virus remained strongly cell-associated. Thus, BICPO is not absolutely required for replication in cell culture. Gene expression of A2G2 was investigated by Western blots and immunofluorescence. Surprisingly, not only was BICPO absent, but glycoprotein C (gC) was also missing. Other viral genes were expressed normally. Semiquantitative PCR showed that A2G2 produced similar amounts of viral DNA as wt but a much smaller number of infectious particles. Cotransfection of A2G2 DNA and a plasmid containing the BICPO gene yielded revertant virus with fully restored wt properties. We conclude that BICPO is required for gC expression, and that the missing gC partly accounts for the reduced A2G2 infectivity.

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.

Structural and functional analysis of bovine herpesvirus 1 minor glycoproteins

This paper focuses on the structure and functions of bovine herpesvirus 1 minor glycoproteins gH, gE, gG and gp42. It reviews the progress which has been made in their identification and characterization, in the study of their temporal expression and processing in infected cells, and finally in the understanding of their biological activities. In addition, aspects discussed include a comparison with two other alphaherpesviruses, namely herpes simplex virus and pseudorabies virus.

Gene contents in a 31-kb segment at the left genome end of bovine herpesvirus-1

We report the nucleotide sequence of a 31-kb segment at the left genome end of bovine herpesvirus-1 (BHV-1) and show that it comprises 19 different open reading frames (ORFs), including seven which have been described previously (circ, dUTPase, UL49.5, alpha TIF, VP8, glycoprotein C, and ribonucleotide reductase small subunit). The new sequence resulted in a correction at the C-terminus of glycoprotein C. All 19 ORFs exhibited strong amino acid sequence homology to the gene products of other alphaherpesviruses. The BHV-1 ORFs were arranged colinearly with the prototype sequence of herpes simplex virus 1 (HSV-1) in the range of the UL54 to UL37 genes. No BHV-1 homologs of the HSV-1 UL56, UL55, and UL45 genes were identified. The BHV-1 circ gene was the only gene without a HSV-1 counterpart. The additional ORFs 1 and 2 found at the left genome end of equine herpesvirus-1 (EHV-1) were absent in BHV-1. Among the newly sequenced BHV-1 ORFs are homologs of ICP27 (UL54), glycoprotein K (UL53), helicase-primase (UL52), DNA polymerase accessory protein (UL42), ribonucleotide reductase large subunit (UL39), and several virion proteins (UL49, UL46, UL43, UL41, UL38, UL37), most of which are strongly conserved in all herpesviruses. The possible functions of the proteins encoded within the sequenced region are assessed and features found are discussed.

Pathogenesis of ruminant herpesvirus infections

Ruminants are hosts for members of both Alpha- and Gamma-herpesvirinae. A wide range of disease syndromes is associated with infections by these agents. The associated diseases reflect the biological nature of the causative viruses. Clinically, the symptoms may be mild and localized or include severe generalized disease, leading eventually to death. Much knowledge has been gained concerning the pathogenesis of some alpha-herpesviruses. Initially, these viruses replicate in epithelial cells at the portal of entry. The symptoms of the acute diseases are often associated with the destruction of those epithelial cells. However, as in the case of bovine herpesvirus 1 (BHV-1), the virus may spread in the infected host by viremia, gaining access to a broader range of tissues and organs, and causing a broader variety of diseases. Furthermore, many herpesviruses are capable of entering neuronal cells. There, they may replicate, which may lead to neuronal diseases, for example, encephalitis. In addition, the herpesviruses may establish latency in neuronal or lymphoid cells. During latency, apparently no viral antigens are synthesized but the genomes of the latent viruses are present in the nuclei of long living cells, such as, e.g., neurones of the ganglia corresponding to the sites of peripheral replication. Upon reactivation, the viruses re-establish the lytic cycle of replication. Shielded from the effectors of the immune system, they migrate back to the peripheral tissues where they are excreted and may be transmitted. Although a strong immune response is provoked during primary viral replication, these mechanisms help the herpesviruses to escape from immune surveillance during latency and to a lesser degree during reactivation. It has been observed that certain herpesviruses may behave differently upon infection of different hosts. Relatively little progress has been made concerning the understanding of the pathogenesis of ruminant herpesviruses but much has been learned about viral molecular biology. Many viral proteins have been identified and characterized and the technology to create recombinant viruses has been established. With these tools in our hands, it is now possible to address the really interesting questions concerning pathogenesis. We postulate that herpesviruses contain at least two sets of genes, a first set involved in gene expression and viral replication, and a second set responsible for functions, which may affect pathogenesis, latency, and virus/host interactions. Using recombinant virus technology, it will be possible in the future to design targeted deletions and gene transfers in ruminant herpesviruses in order to study the viral and host factors involved in pathogenesis on the molecular level.

A non-specific defence inducer in preventing clinical signs of infectious bovine rhinotracheitis in calves

One calf was infected with bovine herpesvirus-1 (BHV-1) and mixed with five other calves, of which one had been vaccinated with a BHV-1 modified live vaccine one month earlier. The other four calves were vaccinated at the time the experimentally infected calf developed the first signs of the disease (fever, depression, nasal discharge), i.e. on post infection day (PID) 2. In addition to the vaccine, two of the four PID 2 vaccinated calves also received a non-specific defence (NSD) inducer (Baypamun, Bayer AG) at the same time as the vaccine. The calf that was vaccinated 1 month before the start of the experiment, as expected, did not show any signs of the disease. Of the remaining four, the two vaccine-only calves experienced a classical form of infectious bovine rhinotracheitis. However, the two calves that had also received the NSD inducer remained generally healthy during the entire observation period of 30 days. It was speculated that the use of a NSD inducer once an outbreak of a respiratory disease has started on a farm could be of significant help in an emergency in reducing the clinical manifestations in those animals that may subsequently be infected.

The UL2 open reading frame of bovine herpesvirus 1 encodes a uracil-DNA glycosylase

Sequence analysis within the unique long segment of the bovine herpesvirus 1 (BHV-1) genome previously identified an open reading frame (ORF), designated UL2, whose deduced polypeptide of 204 amino acids contained a consensus uracil-DNA glycosylase (UDGase) signature sequence. To determine whether the BHV-1 UL2 ORF product has UDGase activity, we positioned the UL2 sequence down-stream of the T7 promoter on the vector pET-28b(+) and expressed it in Escherichia coli. Upon induction with isopropyl beta-D-thiogalactopyranoside these cells produced a 23-kDa protein, the molecular mass of which was in accordance with the prediction from the nucleotide sequence. A one-step purification procedure using nickel-chelating affinity chromatography resulted in a homogeneous preparation of this protein, which displayed specific UDGase activity in an in vitro enzyme assay. These results provide evidence that the BHV-1 UL2 gene does encode a UDGase.

Lymphocyte proliferative responses to recombinant bovine herpes virus type 1 (BHV-1) glycoprotein gD (gIV) in immune cattle: identification of a T cell epitope

The lymphocyte proliferative response to BHV-1 in immune cattle was compared to recombinant wild-type gD and truncated gD produced from recombinant vaccinia viruses. The response exhibited by recombinant proteins was comparable to the response induced by BHV-1 suggesting that gD is the major target structure for stimulation of bovine lymphocytes. Analysis of the proliferative response using vaccinia virus vectors expressing various modified forms of gD identified a region between residues 165 and 216 recognized by T-lymphocytes of immune cattle. Further analysis by overlapping peptides in this region localized the T cell epitope to residues 161-172. Antibody-blocking studies demonstrated that lymphocytes responding to this epitope are CD4+. In addition, lymphocytes stimulated with gD or peptide 77 (residues 161-172) also produced IFN-gamma and IL-2.