Spatial and temporal distribution of bovine herpesvirus 1 transcripts

Herpes simplex virus type 1 and bovine herpesvirus 1 latency

Primary infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system, upper respiratory tract, and gastrointestinal tract. Recurrent ocular shedding leads to corneal scarring that can progress to vision loss. Consequently, HSV-1 is the leading cause of corneal blindness due to an infectious agent. Bovine herpesvirus 1 (BHV-1) has similar biological properties to HSV-1 and is a significant health concern to the cattle industry. Latency of BHV-1 and HSV-1 is established in sensory neurons of trigeminal ganglia, but latency can be interrupted periodically, leading to reactivation from latency and spread of infectious virus. The ability of HSV-1 and BHV-1 to reactivate from latency leads to virus transmission and can lead to recurrent disease in individuals latently infected with HSV-1. During latency, the only abundant HSV-1 RNA expressed is the latency-associated transcript (LAT). In latently infected cattle, the latency-related (LR) RNA is the only abundant transcript that is expressed. LAT and LR RNA are antisense to ICP0 or bICP0, viral genes that are crucial for productive infection, suggesting that LAT and LR RNA interfere with productive infection by inhibiting ICP0 or bICP0 expression. Numerous studies have concluded that LAT expression is important for the latency-reactivation cycle in animal models. The LR gene has recently been demonstrated to be required for the latency-reactivation cycle in cattle. Several recent studies have demonstrated that LAT and the LR gene inhibit apoptosis (programmed cell death) in trigeminal ganglia of infected animals and transiently transfected cells. The antiapoptotic properties of LAT map to the same sequences that are necessary for promoting reactivation from latency. This review summarizes our current knowledge of factors regulating the latency-reactivation cycle of HSV-1 and BHV-1.

The latency-related gene of bovine herpesvirus-1 can inhibit the ability of bICP0 to activate productive infection

Transfection of bovine cells with bovine herpesvirus-1 genomic DNA yields low levels of infectious virus. Cotransfection with the bICP0 gene enhances productive infection and virus yield because bICP0 can activate viral gene expression. Since the latency-related (LR) gene overlaps and is antisense to bICP0, the effects of LR gene products on productive infection were tested. The intact LR gene inhibited productive infection in a dose-dependent fashion but LR protein expression was not required. Further studies indicated that LR gene sequences near the 3' terminus of the LR RNA are necessary for inhibiting productive infection. When cotransfected with the bICP0 gene, the LR gene inhibited bICP0 RNA and protein expression in transiently transfected cells. Taken together, these results suggest that abundant LR RNA expression in sensory neurons is one factor that has the potential to inhibit productive infection and consequently promote the establishment and maintenance of latency.

Susceptibility of sensory neurons to apoptosis following infection by bovine herpesvirus type 1

Like other members of the alpha subfamily of herpesviruses, bovine herpesvirus type 1 (BHV-1) establishes latent infections in sensory neurons. BHV-1 induces apoptosis in lymphoid cells in vivo and in epithelial cell lines, but the ability of BHV-1 to induce apoptosis in sensory neurons remains unknown. In this report, the susceptibility of rabbit ganglionic neurons to infection by BHV-1 was examined in vitro and in vivo. Following infection of cultured neurons with BHV-1, hallmarks of apoptosis such as chromatin condensation, DNA fragmentation and membrane blebbing were detected. The appearance of these changes was preceded by active viral DNA replication as determined by in situ hybridization. When viral DNA replication was blocked by treatment of cultures with an inhibitor of eukaryotic DNA polymerases, apoptosis but not virus attachment to neurons or bICP0 gene expression was completely prevented. Taken together, these results demonstrate that sensory neurons are not intrinsically resistant to BHV-1-induced apoptosis and that viral DNA replication plays a role in triggering the apoptotic programme. Infection of rabbits with BHV-1 resulted in pathological changes in the trigeminal ganglia (TG) which included mononuclear cell infiltration and neuronophagia. Morphological evidence of apoptosis was not detected in neurons, even in cells with advanced cytophatology. Furthermore, whereas DNA fragmentation was common in infiltrating cells, it was very rare and sporadic in neurons. Therefore, mechanisms in the TG should exist to prevent neuronal apoptosis upon BHV-1 infection.

Search for physical interaction between BICP0 of bovine herpesvirus-1 and p53 tumor suppressor protein

The immediate-early (IE) protein BICP0 of bovine herpesvirus-1 (BHV-1) may have other functions besides transactivation of viral promoters. Recently, we observed that BICP0, delivered to cultured cells by a helpervirus-free amplicon system, forms spherical or doughnut-like structures in which the tumor suppressor protein p53 is sequestered. The objective was to determine whether BICP0 and p53 interact physically, we used both yeast and mammalian two-hybrid systems. As a bait plasmid, pVA3 which encodes a hybrid protein consisting of the Gal4 DNA binding domain fused to murine p53 was used. The BICP0 gene or its truncated versions were inserted into the prey plasmid pGAD424. Bait and prey plasmids were cotransformed into yeast strain Y153, which has LacZ and HIS3 reporter genes under the control of Gal4 upstream activating sequence. After 4-6 days, colonies were stained for beta-galactosidase activity. In the mammalian two-hybrid system, pM-53 was used as a bait where truncated p53 fused to Gal4 DNA binding domain is expressed. The BICP0 gene was cloned into prey plasmid pVP16. The interaction between p53 and SV40 T-antigen was evaluated as a positive control in both systems. Neither full-length BICP0 nor its truncated derivatives induced beta-galactosidase activity in yeast whereas the positive control turned blue under the same conditions. The mammalian two-hybrid system, in which chloramphenicol acetyltransferase (CAT) activity was used as a reporter, also failed to show an interaction between these two proteins. Co-localization of p53 with BICP0 in spherical structures is unlikely to result from a direct physical interaction between these two proteins. Mediation by additional cellular proteins may be required.

A mutation in the latency-related gene of bovine herpesvirus 1 leads to impaired ocular shedding in acutely infected calves

Bovine herpesvirus 1 (BHV-1) is an important pathogen of cattle, and infection is usually initiated in the ocular or nasal cavity. Like other alphaherpesviruses, BHV-1 establishes latency in sensory neurons but has the potential of reactivating from latency and spreading. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA, which is alternatively spliced in trigeminal ganglia during acute infection (L. R. Devireddy and C. Jones, J. Virol. 72:7294-7301, 1998). LR gene products inhibit cell cycle progression (Y. Jiang, A. Hossain, M. T. Winkler, T. Holt, A. Doster, and C. Jones, J. Virol. 72:8133-8142, 1998) and chemically induced apoptosis (J. Ciacci-Zannela, M. Stone, G. Henderson, and C. Jones. J. Virol. 73:9734-9740, 1999). Although these studies suggest that LR gene products play an important role in the latency/pathogenesis of BHV-1, construction of a mutant is necessary to test this hypothesis. Because the bICP0 gene overlaps and is antisense to the LR gene, it was necessary to mutate the LR gene without altering bICP0 expression. This was accomplished by inserting three stop codons near the beginning of the LR RNA, thus interfering with expression of proteins expressed by the LR RNA. The LR mutant virus grew with wild-type (WT) efficiency in bovine kidney (MDBK) cells and expressed bICP0 at least as efficiently as WT BHV-1 or the LR rescued virus. When calves were infected with the LR mutant, we observed a dramatic decrease (3 to 4 log units) in ocular shedding during acute infection relative to WT or the LR rescued virus. In contrast, shedding of the LR mutant from the nasal cavity was not significantly different from that of the WT or the LR rescued virus. Calves infected with the LR mutant exhibited mild clinical symptoms, but they seroconverted. Neutralizing antibody titers were lower in calves infected with the LR mutant, confirming reduced growth. In summary, this study suggests that an LR protein promotes ocular shedding during acute infection of calves.

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.

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.

BHV-1: new molecular approaches to control a common and widespread infection

BACKGROUND

Herpesviruses are widespread viruses, causing severe infections in both humans and animals. Eradication of herpesviruses is extremely difficult because of their ability to establish latent and life-long infections. However, latency is only one tool that has evolved in herpesviruses to successfully infect their hosts; such viruses display a wide (and still incompletely known) panoply of genes and proteins that are able to counteract immune responses of their hosts. Envelope glycoproteins and cytokine inhibitors are two examples of such weapons. All of these factors make it difficult to develop diagnostics and vaccines, unless they are based on molecular techniques.

MATERIALS AND METHODS

Animal herpesviruses, because of their striking similarity to human ones, are suitable models to study the molecular biology of herpesviruses and develop strategies aimed at designing neurotropic live vectors for gene therapy as well as engineered attenuated vaccines.

RESULTS

BHV-1 is a neurotropic herpesvirus causing infectious rhinotracheitis (IBR) in cattle. It is a major plague in zootechnics and commercial trade, because of its ability to spread through asymptomatic carrier animals, frozen semen, and embryos. Such portals of infections are also important for human herpesviruses, which mainly cause systemic, eye, and genital tract infections, leading even to the development of cancer.

CONCLUSIONS

This review covers both the genetics and molecular biology of BHV-1 and its related herpesviruses. Epidemiology and diagnostic approaches to herpesvirus infections are presented. The role of herpesviruses in gene therapy and a broad introduction to classic and engineered vaccines against herpesviruses are also provided. http://link.springer-ny. com/link/service/journals/00020/bibs/5n5p261.html

The left border of the genomic inversion of pseudorabies virus contains genes homologous to the UL46 and UL47 genes of herpes simplex virus type 1, but no UL45 gene

The genome of pseudorabies virus (PrV) is collinear with the herpes simplex virus type 1 (HSV1) genome, except for an inversion in the unique long region, the right extremity of which resides within the BamHI fragment 9 and the left within the BamHI fragment 1. We previously sequenced the right border of the inversion which is situated next to the UL44-gC gene and found that it encodes the UL24, UL25, UL26 and UL26.5 gene counterparts of HSV1. We have now sequenced 5317 base pairs of the BamHI fragment 1, upstream of the UL27-gB gene. We found two open reading frames homologous to UL46 and UL47 of HSV1 yet UL45 was absent and replaced by a set of strictly repeated sequences. PrV UL46 and UL47 are transcribed into two 3' co-terminal messenger RNAs with early and late kinetics, respectively. Comparison of the PrV UL46 and UL47 protein sequences with their counterparts from alphaherpesviruses indicated a strong similarity. The genome is rearranged in this region with respect to HSV1 and the inversion must have taken place, on the left side, within the UL46-UL27 intergenic region. Thus, the inversion should include genes UL27 to UL44.

Infectious bovine rhinotracheitis, parainfluenza-3, and respiratory coronavirus

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

Analysis of bovine herpesvirus 1 transcripts during a primary infection of trigeminal ganglia of cattle

During an infection of nonneuronal cells, bovine herpesvirus 1 (BHV-1) gene expression proceeds in a well-defined cascade. Products of immediate-early (IE) genes are expressed first, and they activate expression of early (E) and late (L) genes. Although the same cascade is assumed to occur during an infection of neurons in trigeminal ganglia (TG) of cattle, no experimental data is available to support this hypothesis. Consequently, we analyzed BHV-1 gene expression in bovine TG at 1, 2, 4, 7, and 15 days postinfection (dpi). Infectious virus was detected in ocular swabs from 1 to 7 dpi but not 15 dpi. By reverse transcription (RT)-PCR, IE (bICP4), E (thymidine kinase, ribonucleotide reductase [RR]), L (glycoprotein C, and alpha trans-inducing factor), and dual-kinetic (bICP0 and bICP22) transcripts were analyzed. When cDNA synthesis was primed with random hexamers, IE and E transcripts were detected at the same time. However, full-length and poly(A)+ (FL&P) RR or bICP22 RNAs were detected before FL&P IE RNAs. Furthermore, FL&P IE transcripts were not detected until viral DNA increased in TG. IE transcripts were detected before E or L RNAs when rabbit kidney cells were infected with a low multiplicity of infection and the same RT-PCR detection method was used. These studies suggested that expression of full-length and polyadenylated IE transcripts in trigeminal ganglia was not efficient compared to that of RR and bICP22 transcripts.

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.

Immunology of bovine herpesvirus 1 infection

Immune responses to bovine herpesvirus 1 (BHV-1) have been studied following exposure of animals to virulent virus, conventional live or killed vaccines, genetically engineered live virus vaccines, subunit vaccines and, more recently, following immunization with plasmids encoding putative protective antigens. In all cases reported to date, exposure to BHV-1 or its glycoproteins induced specific responses to the virus which are capable of neutralizing virus and killing virus infected cells. These studies clearly indicate that the responses to BHV-1 are broad based, including both Th1 and Th2. In addition to inducing neutralizing antibodies, which can prevent virus attachment and penetration, these antibodies can also participate in antibody complement lysis of infected cells or in antibody dependent cell cytotoxicity. The virus also induces a myriad of specific cellular responses including the induction of cytokines, which either directly or indirectly inhibit virus replication by activation of effector cells. These activities have been associated with lymphocytes, NK-like cells, macrophages and polymorphonuclear neutrophils. These effector cells can kill virus infected cells either directly or by interacting with antibody to induce cell death by antibody dependent cell cytotoxicity. Killing of virus infected cells occurs after the expression of viral antigens on the cell surface of infected cells. Since the relationship between the time of cell killing and completion of virus assembly will influence whether the infectious cycle is aborted or results in productive viral replication any enhancement in viral killing will dramatically reduce the virus load. Based on these studies, many people conclude that antibody is critical in preventing infection and spread to susceptible contacts. In contrast, cell mediated immunity is involved in recovery from infection. However, none of these events occur in isolation in a body and a defect in one will dramatically influence the other. Furthermore, the relative importance of each effector mechanism will clearly depend on whether the animal is exposed to the virus for the first time (primary infection) or it is a secondary exposure following vaccination or infection with the field virus. Following a primary infection, where there is no antibody to interfere with the initial virus-cell interaction at the receptor level, the virus initiates an infection. These initial interactions are mediated primarily by the viral glycoproteins. Following the initial infection, viral protein synthesis induces a series of events which stimulate the nonspecific immune responses of the host. Therefore, the nonspecific immune responses (mediated primarily by viral products which induce early cytokines) are amongst the first line of defense in helping clear the infection both directly as well as indirectly by stimulating the specific immune response. The macrophage is instrumental in focusing the specific immune response by producing various cytokines and subsequently responding to cytokines produced by T-cells to kill to virus infected cells. This activity is detectable within 2 days after infection in lung parenchymal cells and 5-7 days in peripheral blood leukocytes. Interactions between various effector functions in limiting virus replication are described.

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.

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.

The distinction of serologically related ruminant alphaherpesviruses by the polymerase chain reaction (PCR) and restriction endonuclease analysis

The amplification and analysis of a 468bp fragment from the gB gene of the serologically related ruminant alphaherpesviruses bovine herpesvirus-1.1 and 1.2 (BHV-1.1 and BHV-1.2), caprine herpesvirus-1 (CapHV-1), cervine herpesvirus-1 (CerHV-1) and rangiferine herpesvirus-1 (RanHV-1) by PCR and restriction endonuclease analysis is described. As primers, 22bp oligomers selected from the BHV-1 gB gene sequences were used for the amplification of the DNA from the five viruses. The amplification product from each virus was analysed by the restriction endonuclease enzymes BglI, HinfI, SmaI and AvaI. The specific amplification obtained demonstrate the existence of the gB gene sequences for each of the five alphaherpesviruses. However, sequences from some of the fragments were found to be different from those predicted from the gB gene following restriction endonuclease analysis. All five amplification products generated the same number of fragments after digestion with HinfI except for two additional bands evident in CapHV-1. The CerHV-1 and RanHV-1 fragments contained slightly different BglI restriction sites from those of the other three. While BHV-1.1, BHV-1.2, CapHV-1 and CerHV-1 contained SmaI and AvaI restriction sites, the RanHV-1 amplification product lacked both SmaI and AvaI restriction sites.

Prediction of potential cytotoxic T lymphocyte epitopes of bovine herpesvirus 1 based on allele-specific peptide motifs and proteolytic cleavage specificities

Major histocompatibility complex (MHC) class I molecules present endogenous peptides to cytotoxic T lymphocytes (CTLs). Elucidation of CTL epitopes of intracellular pathogens helps in designing better vaccines to control economically important human and animal diseases. In this study, candidate epitopes that are potentially available for presentation to the CTLs via five bovine MHC class I molecules have been identified. This was accomplished by using the computer programs "Find-patterns" and "Peptidestructure" of GCG package and applying the information on cleavage patterns of cytosolic and endoplasmic reticulum proteases and peptidases as well as MHC class I allele-specific peptide motifs on 23 bovine herpesvirus-1 (BHV-1) proteins available on protein sequence database. Several candidate peptides were found for each of the bovine lymphocyte antigens (BoLA)-A11, -A20, -HD1, and -HD6 whereas no peptide was found for BoLA-HD7. Majority of the candidate peptides were from the viral glycoproteins. The contribution of such studies towards the identification of CTL epitopes of BHV-1 and other intracellular pathogens is discussed.

Nucleotide sequence of infectious laryngotracheitis virus (gallid herpesvirus 1) ICP4 gene

The infectious laryngotracheitis virus (ILTV) gene encoding a homologue to the ICP4 protein of herpes simplex virus (HSV) has been mapped to the inverted repeat region. The complete nucleotide sequence of ILTV ICP4 has been determined. The ILTV ORF encoding ICP4 is 4386 nucleotides long, calculated from the first of four ATG codons, and has an overall G+C content of 59%. The ILTV ICP4 contains two domains of high homology which have been reported in other studies to be conserved in the ICP4 homologues of alphaherpesviruses, and to be functionally important. Several regulatory features were identified including a serine-rich domain in region one. A more extensive serine-rich domain was located in region five which is also found in varicella-zoster virus (VZV) and bovine herpesvirus 1. A 5.4 kb immediate early transcript was identified in infected primary kidney cells.

Immediate-early gene expression and gene mapping comparisons among isolates of bovine herpesvirus 1 and 5

Bovine herpesviruses (BHV) are associated with a variety of clinical syndromes. Bovine herpesvirus 1 isolates were placed into three genome subtypes based on restriction endonuclease analyses, which were loosely associated by clinical manifestation as BHV1.1 (respiratory), BHV1.2 (genital), and BHV1.3 (encephalitic). More recently the encephalitic isolate has been classified BHV5. A comparison of the cytopathic effect (CPE) in fetal bovine lung cell cultures in the presence of cycloheximide showed that BHV1.1 and 1.2 isolates produced elongated, spindle-shaped CPE, whereas BHV5 produced more syncytial-like CPE. Each BHV-1 subtype synthesized four immediate-early transcripts. The sizes in kb were: 1.6, 3.4, 5.8, 7.5 (BHV1.1); 1.8, 3.6, 5.8, 7.5 (BHV1.2); and 1.8, 3.6, 5.8, 8.6 (BHV5). These transcripts were mapped to the inverted repeat region of each isolate by Southern blot hybridization using cDNA prepared from cycloheximide-treated BHV1-infected cellular polyA RNA. A possible unique immediate-early RNA may be produced by the BHV5 encephalitic isolate from an area of the internal repeat region unique to this isolate. Hybridization analysis using BHV1.1 cloned probes of the immediate-early protein gene, thymidine kinase gene, DNA binding/DNA polymerase gene, and glycoprotein III gene provided information for mapping of these genes to the BHV5 encephalitic isolate.

Bovine herpesvirus-1 vaccines

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

Immediate-early transcription over covalently joined genome ends of bovine herpesvirus 1: the circ gene

Herpesvirus genomes are linear molecules in virions. Prior to replication in host cells, they form circular templates by unknown mechanisms. Examining lytic infection with bovine herpesvirus 1, we observed immediate-early transcription over joined genome ends, which suggested that circles are present at the initial stage of infection. Among the transcripts was a spliced immediate-early RNA (1.5 kb) sharing exon 1 with previously described major immediate-early transcripts from the right genome end and exon 2 with a late transcript located near the left genome end. Exon 2 encodes a putative circ-encoded protein with homology to the varicella-zoster virus open reading frame 2 and equine herpesvirus 1 open reading frame 3 products. The novel features reported here for bovine herpesvirus 1 may constitute a more general property of herpesviruses.

Comparison of immediate-early transcripts among bovine herpesvirus type 1 and type 5 strains differing in neurovirulent potential

Northern (RNA) blot analysis was used to compare immediate-early (IE) transcripts among strains of bovine herpesvirus type 1 and type 5 differing in neurovirulent potential. Results obtained from the neurovirulent strain N569 were compared to those from two non-neurovirulent strains, Jura and K22. Strain N569 expressed three major IE transcripts with similar size and transcription pattern as previously reported for strain Jura and K22 (Wirth et al., 1989, 1991, 1992), except for some differences in the 5' terminal sequence common to the alternative spliced IE transcripts IER4.2 and IER2.9. More significant differences were discovered for some minor IE transcripts. Those transcribed over joined genome ends during replicative phase were found to be drastically overexpressed for strain N569 under IE condition. Among them two very long IE transcripts were detected clearly for strain N569, however hardly recognized for strain Jura and K22. These two transcripts were found to be encoded in addition to the joined terminal HindIII genome fragments by the second HindIII fragment J from the left genome end.

Complete nucleotide sequence of the Marek's disease virus ICP4 gene

The Marek's disease virus (MDV) gene encoding a homologue to the ICP4 protein of herpes simplex virus has been mapped to BamHl fragment A based on the physical map of the MDV genome (Fukuchi et al., 1984). The gene lies completely within the inverted repeat flanking the unique short region of the genome. The complete nucleotide sequence of the MDV ICP4 gene has been determined. The coding region is 4245 nucleotides long and has an overall G+C content of 52%. The MDV ICP4 protein is predicted to have a structure similar to that of ICP4-like proteins of other herpesviruses in that it has five distinct regions, the second and fourth of which are highly conserved. In addition, the protein contains the characteristic run of serine residues located toward its amino terminus. The MDV ICP4 gene is expressed in MDV-infected chicken embryo fibroblasts.

Relationship of bovine herpesvirus 1 immediate-early, early, and late gene expression to host cellular gene transcription

Bovine herpesvirus 1 (BHV-1) gene expression was examined by RNA blot hybridization using clones representing immediate-early, early, and late genes. An immediate-early protein gene probe hybridized with two transcripts, 3.4 and 5.8 kb, expressed by infected cells in the presence of cycloheximide (CH). During infection of cells without metabolic inhibitors these transcripts were detected as early as 2 hr postinfection (p.i.) and accumulated to 8 hr p.i. The early gene probe, thymidine kinase, hybridized with a 4.3-kb RNA that was detected in the presence of phosphonoacetic acid (PAA), but not in the presence of CH. The late gene probe, glycoprotein III, (gIII) hybridized with a 1.6-kb transcript that was not expressed by infected cells treated with CH and only in very reduced amounts by infected cells treated with PAA. The gIII RNA was not detected until 4 hr p.i. in total cell RNA. Transcripts for the bovine actin and beta-galactosyltransferase genes did not decrease in BHV-1-infected cells until 6 hr p.i., coincident with the increase of BHV-1 DNA and RNA synthesis. Consequently, shutoff of host cell transcription by BHV-1 may be different than what has been described for herpes simplex virus.

Immediate-early RNA 2.9 and early RNA 2.6 of bovine herpesvirus 1 are 3' coterminal and encode a putative zinc finger transactivator protein

Bovine herpesvirus 1 (BHV-1) contains three major immediate-early (IE) genes involved in regulation of the productive cycle of replication. Two spliced IE RNAs, IER4.2 (4.2 kb) and IER2.9 (2.9 kb), are under the control of a single promoter; IER1.7 (1.7 kb) is transcribed from a different promoter in the opposite direction. Examining the kinetics of transcription, we found that the IER4.2/2.9 promoter was turned off at the end of the IE period. An alternative promoter became active, directing synthesis of an unspliced early RNA, ER2.6 (2.6 kb), which was colinear with the second exon of IER2.9 except for its 5' end in the intron about 10 bases upstream of the splice site. Sequence analysis revealed a single open reading frame common to IER2.9 and ER2.6 with a coding potential of 676 amino acids. The putative protein, named p135, contained a cysteine-rich zinc finger domain near the N terminus with homology to ICP0 of herpes simplex virus type 1, to protein 61 of varicella-zoster virus, to early protein 0 of pseudorabies virus, and to other viral and cellular proteins. The remaining parts of p135 exhibited only limited homology, mainly with pseudorabies virus protein 0, but the entire sequence was highly conserved between two strains of BHV-1 (K22 and Jura). The latency-related antisense transcript covered a large portion of ER2.6 excluding the zinc finger coding region. In transient expression assays, p135 activated a variety of promoters, including that for ER2.6, but repressed the IER1.7 promoter. Thus, p135 combines functional characteristics of ICP0, a strong transactivator, and of protein 61, a repressor. BHV-1 seems to have evolved a subtle mechanism to ensure the continued synthesis of p135 while turning off IER4.2, which encodes p180, the herpes simplex virus type 1 ICP4 homolog.

Characterization of dexamethasone-induced reactivation of latent bovine herpesvirus 1

Synchronous reactivation of bovine herpesvirus type 1 in all latently infected rabbits was achieved following a single intravenous dose of dexamethasone. Reactivated latent virus was first present in ocular secretions between 48 and 72 h post-dexamethasone treatment (PT). Cell-free infectious virus, viral-antigen-containing neurons, and pathologic changes were detectable in trigeminal ganglia (TG) by 48 h PT. A shift from the viral transcriptional pattern characteristic of the latent state (latency-related RNA [LR RNA]) to one typical of that seen during acute infection was detected in a small number of neurons in latently infected TG between 15 and 18 h PT, with viral DNA first detectable by in situ hybridization at 18 to 21 h PT. The number of LR RNA-containing neurons in latently infected TG decreased significantly at 24 and 48 h PT but returned to near-normal levels by 72 h PT. Correlation of this decrease with viral reactivation suggests that altered regulation of LR RNA transcription is a significant event in the process of viral reactivation.

Expression of porcine pseudorabies virus genes by a bovine herpesvirus-1 (infectious bovine rhinotracheitis virus) vector

Recombinant DNA techniques were used to insert foreign genes into bovine herpesvirus-1 [infectious bovine rhinotracheitis virus (IBRV)] vectors which were attenuated by deletion and/or insertion mutations in the IBRV thymidine kinase (tk) gene. In one recombinant, the regulatory and coding sequences of the late pseudorabies virus (PRV) glycoprotein gIII gene, were inserted into the early IBRV tk gene. This recombinant efficiently expressed the PRV gIII gene indicating that immediate early IBRV proteins were competent to transactivate the late PRV gIII gene. IBRV vector viruses were also prepared in which the coding sequences of the early PRV tk gene, the late PRV gIII gene, and the E. coli beta-galactosidase gene were ligated to the late IBRV gIII promoter. Genotypes and phenotypes of the recombinant viruses were verified by restriction endonuclease and molecular hybridization experiments, thymidine plaque autoradiography, beta-gal plaque assays, and by immunoprecipitation experiments on extracts from 3H-mannose-labelled cells. The recombinant IBRV expressing beta-gal from the IBRV gIII promoter has been useful as an intermediate in the construction of IBRV vectors harboring foreign DNA sequences. The infectivity of the IBRV recombinant that expressed PRV gIII from the IBRV gIII promoter, was neutralized by polyclonal PRV antisera and by monoclonal antibodies to PRV gIII. The PRV gIII glycoprotein synthesized by the preceding recombinant has been used to coat microtiter test plate wells in a PRV gIII differential diagnostic test kit.

Glycoprotein IV of bovine herpesvirus 1-expressing cell line complements and rescues a conditionally lethal viral mutant

Glycoprotein IV (gIV) of bovine herpesvirus 1 (BHV-1), a homolog of herpes simplex virus glycoprotein D, represents a major component of the viral envelope and a dominant immunogen. To analyze the functional role of gIV during BHV-1 replication, cell line BUIV3-7, which constitutively expresses gIV, was constructed and used for the isolation of gIV- BHV-1 mutant 80-221, in which the gIV gene was replaced by a lacZ expression cassette. On complementing gIV-expressing cells, the gIV- BHV-1 replicated normally but was unable to form plaques and infectious progeny on noncomplementing cells. Further analysis showed that gIV is essential for BHV-1 entry into target cells, whereas viral gene expression, DNA replication, and envelopment appear unchanged in both noncomplementing and complementing cells infected with phenotypically complemented gIV- BHV-1. The block in entry could be overcome by polyethylene glycol-induced membrane fusion. After passaging of gIV- BHV-1 on complementing cells, a rescued variant, BHV-1res, was isolated and shown to underexpress gIV in comparison with its wild-type parent. Comparison of the penetration kinetics of BHV-1 wild type, phenotypically complemented gIV- BHV-1, and BHV-1res indicated that penetration efficiency correlated with the amount of gIV present in virus particles. In conclusion, we show that gIV of BHV-1 is an essential component of the virion involved in virus entry and that the amount of gIV in the viral envelope modulates the penetration efficiency of the virus.

Transcriptional analysis of the bovine herpesvirus 1 Cooper isolate. Temporal analysis and characterization of immediate-early, early, and late RNA

Blot hybridization analysis of infected bovine herpesvirus 1 (BHV-1) cellular RNA isolated at various times post infection and after treatment with specific metabolic inhibitors was used to characterize transcription of the BHV-1 Cooper isolate. Synthesis of BHV-1 RNA was detected as early as 3 h post infection and reached a maximum at six to eight hours post infection. The most transcriptionally active area of the genome was between map units 0.110 to 0.195, within the HindIII I fragment. From the entire genome a total of 59 transcripts ranging in size from approximately 0.6 to 10 kilobases were characterized as belonging to one of three distinct classes. Using the protein synthesis inhibitor cycloheximide, three immediate-early transcripts were identified as originating from the internal inverted repeat region between map units 0.734 and 0.842, corresponding to the HindIII D fragment. Using phosphonoacetic acid to prevent virus DNA synthesis by inhibition of the BHV-1 DNA polymerase, 28 early transcripts were recognized. The remaining 28 transcripts, classified as late RNA, were detected without the use of metabolic inhibitors at 6 to 8 h post infection. Transcription of early and late RNA was not restricted to any specific area of the genome. Eighty percent of the transcripts from both the HindIII A fragment, between map units 0.381 to 0.537 within the unique long segment, and the HindIII K fragment, between map units 0.840 to 0.907 of the unique short segment, were designated as belonging to the early class.

The three major immediate-early transcripts of bovine herpesvirus 1 arise from two divergent and spliced transcription units

Among 54 transcripts expressed in a temporal cascade during lytic infection with bovine herpesvirus 1, we have previously identified three major immediate-early (IE) RNAs, IER4.2 (4.2 kb), IER2.9 (2.9 kb), and IER1.7 (1.6 to 1.8 kb depending on the virus strain) transcribed from the HindIII C genome region (U. V. Wirth, K. Gunkel, M. Engels, and M. Schwyzer, J. Virol. 63:4882-4889, 1989). Northern (RNA) blot, S1 nuclease protection, and primer extension analysis used in the present study demonstrated that all three IE transcripts were spliced and originated from two divergent transcription units with start sites located in the inverted repeat. Transcription unit 1 encoded two alternative spliced transcripts, IER4.2 and IER2.9, with a common exon 1 located at 0.797 to 0.795 map units (m.u.) and an exon 2 for IER4.2 (0.792 to 0.762 m.u.) in the inverted repeat; exon 2 for IER2.9 (0.754 to 0.738 m.u.) was located in the unique long sequence and transcribed in antisense orientation to latency-related RNA. Transcription unit 2 (0.818 to 0.836 m.u.), further characterized by cDNA cloning, encoded the spliced IER1.7 with three exons in the inverted repeat. Additional minor IE transcripts were interpreted as unspliced precursors and splicing variants. With regard to the number and layout of IE genes, bovine herpesvirus 1 occupies an intermediate position between pseudorabies virus and equine herpesvirus 1 on the one hand and varicella-zoster virus and herpes simplex virus type 1 on the other.

Characterization of the latency-related transcriptionally active region of the bovine herpesvirus 1 genome

Approximate 5' and 3' ends of the bovine herpesvirus 1 (BHV-1) latency-related RNA (LR RNA) were mapped in rabbit trigeminal ganglia (TG) by in situ hybridization. The data provide a size estimate of 0.77 to 1.16 kb for the LR RNA. An LR RNA mapping to a similar location was also detected in TG of cattle latently infected with BHV-1. The BHV-1 LR region is transcriptionally active in bovine cell cultures lytically infected with BHV-1. A 1.15-kb transcript, present at early and late times postinfection, of the same sense and approximate size that seen in latently infected TG overlaps a 2.9-kb immediate-early and a 2.6-kb early and late transcription unit present on the complementary strand. Sequence analysis of the LR RNA sense strand indicates the presence of a potential polymerase II promoter in close proximity to the 5' terminus of the LR RNA and two open reading frames within its map positions. The complementary strand contains the 3' portion of a large open reading frame that almost completely overlaps the map position of the LR RNA present on the opposite strand.

Pseudorabies virus immediate-early gene overlaps with an oppositely oriented open reading frame: characterization of their promoter and enhancer regions

The immediate-early (IE) gene of pseudorabies virus (PRV) has recently been sequenced for two virus strains. To investigate IE gene regulation and to examine the genome segment reported to encode latency-related transcripts in opposite polarity to the IE gene, sequence analysis has been extended by 5 kb from each end of the IE gene. The IE promoter (P1) was found to be more complex than previously recognized: it consisted of nine imperfect repeats, each containing five to six different consensus elements for transcription factor binding. A second promoter (P2) was discovered downstream of the IE gene. It contained numerous octamer consensus sequences (ATGCAAAT) and recognition sites for transcription factor Sp1; specific binding of nuclear proteins to four Sp1 sites was detected. An open reading frame (ORF3) bordering on P2 was identified, oriented antiparallel to the IE gene. Potential enhancer elements (E3 and E4) were isolated by the enhancer trap technique. Linked to P1 and a CAT indicator gene, E3 acted as an enhancer and E4 as a silencer. The PRV IE gene product repressed transcription from its own promoter and activated the SV40 early promoter. The transactivating virion protein Vmw65 of HSV1 had an opposite effect on these promoters.