Analysis of bovine trigeminal ganglia following infection with bovine herpesvirus 1

A Quadruple Gene-Deleted Live BoHV-1 Subunit RVFV Vaccine Vector Reactivates from Latency and Replicates in the TG Neurons of Calves but Is Not Transported to and Shed from Nasal Mucosa

Bovine herpesvirus type 1 (BoHV-1) establishes lifelong latency in trigeminal ganglionic (TG) neurons following intranasal and ocular infection in cattle. Periodically, the latent virus reactivates in the TG due to stress and is transported anterogradely to nerve endings in the nasal epithelium, where the virus replicates and sheds. Consequently, BoHV-1 is transmitted to susceptible animals and maintained in the cattle population. Modified live BoHV-1 vaccine strains (BoHV-1 MLV) also have a similar latency reactivation. Therefore, they circulate and are maintained in cattle herds. Additionally, they can regain virulence and cause vaccine outbreaks because they mutate and recombine with other circulating field wild-type (wt) strains. Recently, we constructed a BoHV-1 quadruple mutant virus (BoHV-1qmv) that lacks immune evasive properties due to UL49.5 and glycoprotein G (gG) deletions. In addition, it also lacks the gE cytoplasmic tail (gE CT) and Us9 gene sequences designed to make it safe, increase its vaccine efficacy against BoHV-1, and restrict its anterograde neuronal transport noted above. Further, we engineered the BoHV-1qmv-vector to serve as a subunit vaccine against the Rift Valley fever virus (BoHV-1qmv Sub-RVFV) (doi: 10.3390/v15112183). In this study, we determined the latency reactivation and nasal virus shedding properties of BoHV-1qmv (vector) and BoHV-1qmv-vectored subunit RVFV (BoHV-1qmv sub-RVFV) vaccine virus in calves in comparison to the BoHV-1 wild-type (wt) following intranasal inoculation. The real-time PCR results showed that BoHV-1 wt- but not the BoHV-1qmv vector- and BoHV-1qmv Sub-RVFV-inoculated calves shed virus in the nose following dexamethasone-induced latency reactivation; however, like the BoHV-1 wt, both the BoHV-1qmv vector and BoHV-1qmv Sub-RVFV viruses established latency, were reactivated, and replicated in the TG neurons. These results are consistent with the anterograde neurotransport function of the gE CT and Us9 sequences, which are deleted in the BoHV-1qmv and BoHV-1qmv Sub-RVFV.

Evaluation of Antiviral Activity of Ivermectin against Infectious Bovine Rhinotracheitis Virus in Rabbit Model

Infectious bovine rhinotracheitis (IBR) caused by bovine herpes virus 1 (BoHV-1) can lead to enormous economic losses in the cattle industry. Vaccine immunization is preferentially used to decrease its transmission speed and resultant clinical signs, rather than to completely stop viral infection. Therefore, a drug effective in treating IBR is urgently needed. Our previous work demonstrated that ivermectin significantly inhibited viral replication in a cell infection model. This study aimed to investigate its antiviral effects in vivo by using a rabbit infection model. The viral inhibition assay was first used to confirm that ivermectin at low concentrations (6-25 nM) could reduce viral titers (TCID50) significantly (p < 0.001) at 24 h post-infection. In rabbits, ivermectin was administrated with one to three doses, based on the recommended anti-parasite treatment dosage (0.2 mg/kg bodyweight) through subcutaneous injection at different days post-infection in the treated IBRV infection groups, while non-treated infection group was used as the control. The infected rabbits showed hyperthermia and other clinical signs, but the number of high-fever rabbits in the ivermectin treatment groups was significantly lower than that in the non-treated infection group. Furthermore, in ivermectin treatment groups, the cumulative clinical scores correlated negatively with drug doses and positively with delay of administration time post-infection. The overall nasal shedding time in ivermectin-treated groups was two days shorter than the non-treated challenge group. At the same time point, the titer of neutralizing antibodies in the treatment group with triple doses was higher than the other two-dose groups, but the difference between the treatment groups decreased with the delay of drug administration. Correspondingly, the serious extent of lung lesions was negatively related to the dosage, but positively related to the delay of drug administration. The qPCR with tissue homogenates showed that the virus was present in both the lung tissues and trigeminals of the infected rabbits. In conclusion, ivermectin treatment had therapeutic effect by decreasing clinical signs and viral shedding, but could not stop virus proliferation in lung tissues and trigeminals.

The Cell-Mediated Immune Response against Bovine alphaherpesvirus 1 (BoHV-1) Infection and Vaccination

Bovine Alphaherpesvirus 1 (BoHV-1) is one of the major respiratory pathogens in cattle worldwide. Infection often leads to a compromised host immune response that contributes to the development of the polymicrobial disease known as “bovine respiratory disease”. After an initial transient phase of immunosuppression, cattle recover from the disease. This is due to the development of both innate and adaptive immune responses. With respect to adaptive immunity, both humoral and cell-mediated immunity are required to control infection. Thus, several BoHV-1 vaccines are designed to trigger both branches of the adaptive immune system. In this review, we summarize the current knowledge on cell-mediated immune responses directed against BoHV-1 infection and vaccination.

Stress Triggers Expression of Bovine Herpesvirus 1 Infected Cell Protein 4 (bICP4) RNA during Early Stages of Reactivation from Latency in Pharyngeal Tonsil

Bovine herpesvirus 1 (BoHV-1), an important pathogen of cattle, establishes lifelong latency in sensory neurons within trigeminal ganglia (TG) after acute infection. The BoHV-1 latency-reactivation cycle, like other alphaherpesvirinae subfamily members, is essential for viral persistence and transmission. Notably, cells within pharyngeal tonsil (PT) also support a quiescent or latent BoHV-1 infection. The synthetic corticosteroid dexamethasone, which mimics the effects of stress, consistently induces BoHV-1 reactivation from latency allowing early stages of viral reactivation to be examined in the natural host. Based on previous studies, we hypothesized that stress-induced cellular factors trigger expression of key viral transcriptional regulatory genes. To explore this hypothesis, RNA-sequencing studies compared viral gene expression in PT during early stages of dexamethasone-induced reactivation from latency. Strikingly, RNA encoding infected cell protein 4 (bICP4), which is translated into an essential viral transcriptional regulatory protein, was detected 30 min after dexamethasone treatment. Ninety minutes after dexamethasone treatment bICP4 and, to a lesser extent, bICP0 RNA were detected in PT. All lytic cycle viral transcripts were detected within 3 h after dexamethasone treatment. Surprisingly, the latency related (LR) gene, the only viral gene abundantly expressed in latently infected TG neurons, was not detected in PT during latency. In TG neurons, bICP0 and the viral tegument protein VP16 are expressed before bICP4 during reactivation, suggesting distinct viral regulatory genes mediate reactivation from latency in PT versus TG neurons. Finally, these studies confirm PT is a biologically relevant site for BoHV-1 latency, reactivation from latency, and virus transmission. IMPORTANCE BoHV-1, a neurotropic herpesvirus, establishes, maintains, and reactivates from latency in neurons. BoHV-1 DNA is also detected in pharyngeal tonsil (PT) from latently infected calves. RNA-sequencing studies revealed the viral infected cell protein 4 (bICP4) RNA was expressed in PT of latently infected calves within 30 min after dexamethasone was used to initiate reactivation. As expected, bICP4 RNA was not detected during latency. All lytic cycle viral genes were expressed within 3 h after dexamethasone treatment. Conversely, bICP0 and the viral tegument protein VP16 are expressed prior to bICP4 in trigeminal ganglionic neurons during reactivation. The viral latency related gene, which is abundantly expressed in latently infected neurons, was not abundantly expressed in PT during latency. These studies provide new evidence PT is a biologically relevant site for BoHV-1 latency and reactivation. Finally, we predict other alphaherpesvirinae subfamily members utilize PT as a site for latency and reactivation.

Regulation of neurotropic herpesvirus productive infection and latency-reactivation cycle by glucocorticoid receptor and stress-induced transcription factors

Neurotropic α-herpesvirinae subfamily members, herpes simplex virus type 1 (HSV-1) and bovine herpesvirus 1 (BoHV-1), are important viral pathogens in their respective hosts. Following acute infection on mucosal surfaces, these viruses establish life-long latency in neurons within trigeminal ganglia (TG) and central nervous system. Chronic or acute stress (physiological or psychological) increases the frequency of reactivation from latency, which leads to virus shedding, virus transmission, and recurrent disease. While stress impairs immune responses and inflammatory signaling cascades, we predict stressful stimuli directly stimulate viral gene expression and productive infection during early stages of reactivation from latency. For example, BoHV-1 and HSV-1 productive infection is impaired by glucocorticoid receptor (GR) antagonists but is stimulated by the synthetic corticosteroid dexamethasone. Promoters that drive expression of key viral transcriptional regulatory proteins are cooperatively stimulated by GR and specific Krüppel like transcription factors (KLF) induced during stress induced reactivation from latency. The BoHV-1 immediate early transcription unit 1 promoter and contains two GR response elements (GRE) that are essential for cooperative transactivation by GR and KLF15. Conversely, the HSV-1 infected cell protein 0 (ICP0) and ICP4 promoter as well as the BoHV-1 ICP0 early promoter lack consensus GREs: however, these promoters are cooperatively transactivated by GR and KLF4 or KLF15. Hence, growing evidence suggests GR and stress-induced transcription factors directly stimulate viral gene expression and productive infection during early stages of reactivation from latency. We predict the immune inhibitory effects of stress enhance virus spread at late stages during reactivation from latency.

A WIDESPREAD NOVEL GAMMAHERPESVIRUS IN APPARENTLY HEALTHY WILD QUOKKAS (SETONIX BRACHYURUS): A THREATENED AND ENDEMIC WALLABY OF WESTERN AUSTRALIA

Five genetically distinct macropodid marsupial herpesviruses have been reported [Macropodid alphaherpesviruses 1 and 2 (MaHV-1 and -2); Macropodid herpesviruses 3 to 5 (MaHV-3 to -5)]. MaHV-2 was originally isolated from an outbreak of fatal disease in captive quokkas (Setonix brachyurus) that were in contact with other macropodid species. This warranted a survey of the presence of herpesviruses in this threatened and endemic Western Australian (WA) wallaby. Blood samples from 142 apparently healthy quokkas were tested for exposure to MaHV-1 and -2 by serology. Of these 142, 121 [Rottnest Island (RI), n = 93; mainland WA, n = 28] were tested for herpesvirus infection by polymerase chain reaction (PCR). Antibodies to MaHV-1 and -2 were detected in one individual [prevalence, 0.7%; 95% confidence interval (CI), 0.1%-3.2%] from the mainland and none from RI. However, a novel gammaherpesvirus [designated Macropodid herpesvirus 6 (MaHV-6)] was detected by PCR in the blood of 13 of 121 individuals (11%; 95% CI, 6.2-17.2). Infection with MaHV-6 was significantly more prevalent on the mainland (7/28; i.e., 25%) compared with RI (6/93; i.e., 6.45%; difference in sample proportions, 95% CI, 6%-32%; P = 0.015). There was no association (P > 0.05) between infection with MaHV-6 and differences in hematology, blood chemistry, peripheral blood cell morphologies, or on clinical status. There was a significant association between infection with MaHV-6 and the presence of Theileria spp. in blood [odds ratio (OR) = 11.0; 95% CI, 2.31-52.3; P = 0.001] and yeast in the nasal lining (OR = 7.0; 95% CI, 1.54-31.8; P = 0.021), suggesting that quokkas may be more susceptible to infection with these microorganisms if also infected with MaHV-6. MaHV-6 infection may be a catalyst for vulnerability to disease with other infectious agents and may pose a significant threat to other macropods. These findings have implications for in situ and ex situ management programs of quokkas.

Regulation of Krüppel-Like Factor 15 Expression by Herpes Simplex Virus Type 1 or Bovine Herpesvirus 1 Productive Infection

Expression of Krüppel-like factor 15 (KLF15), a stress-induced transcription factor, is induced during bovine herpesvirus 1 (BoHV-1) reactivation from latency, and KLF15 stimulates BoHV-1 replication. Transient transfection studies revealed that KLF15 and glucocorticoid receptor (GR) cooperatively transactivate the BoHV-1-immediate-early transcription unit 1 (IEtu1), herpes simplex virus type 1 (HSV-1) infected cell protein 0 (ICP0), and ICP4 promoters. The IEtu1 promoter drives expression of bICP0 and bICP4, two key BoHV-1 transcriptional regulatory proteins. Based on these studies, we hypothesized infection is a stressful stimulus that increases KLF15 expression and enhances productive infection. New studies demonstrated that silencing KLF15 impaired HSV-1 productive infection, and KLF15 steady-state protein levels were increased at late stages of productive infection. KLF15 was primarily localized to the nucleus following infection of cultured cells with HSV-1, but not BoHV-1. When cells were transfected with a KLF15 promoter construct and then infected with HSV-1, promoter activity was significantly increased. The ICP0 gene, and to a lesser extent, bICP0 transactivated the KLF15 promoter in the absence of other viral proteins. In contrast, BoHV-1 or HSV-1 encoded VP16 had no effect on KLF15 promoter activity. Collectively, these studies revealed that HSV-1 and BoHV-1 productive infection increased KLF15 steady-state protein levels, which correlated with increased virus production.

Perforin and granzymes in neurological infections: From humans to cattle

Perforin and granzymes are essential components of the cytotoxic granules present in cytotoxic T lymphocytes and natural killer cells. These proteins play a crucial role in a variety of conditions, including viral infections, tumor immune surveillance, and tissue rejection. Besides their beneficial effect in most of these situations, perforin and granzymes have also been associated with tissue damage and immune diseases. Moreover, it has been reported that perforin and granzymes released during viral infections could contribute to the pathogenesis of diseases. In this review, we summarize the information available on human perforin and granzymes and their relationship with neurological infections and immune disorders. Furthermore, we compare this information with that available for bovine and present data on perforin and granzymes expression in cattle infected with bovine alphaherpesvirus types1 and -5. To our knowledge, this is the first review analyzing the impact of perforin and granzymes on neurological infections caused by bovine herpesviruses.

Typical gene expression profile of pseudorabies virus reactivation from latency in swine trigeminal ganglion

Pseudorabies virus (PRV) establishes a lifelong latent infection in swine trigeminal ganglion (TG) following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Muscle injection combined with intravenous deliver of the synthetic corticosteroid dexamethasone (DEX) consistently induces reactivation from latency in pigs. In this study, PRV-free piglets were infected with PRV. Viral shedding in nasal and ocular swabs demonstrated that PRV infection entered the latent period. The anti-PRV antibody was detected by enzyme-linked immunosorbent assay and the serum neutralization test, which suggested that the PRV could establish latent infection in the presence of humoral immunity. Immunohistochemistry and viral genome detection of TG neurons suggested that PRV was reactivated from latency. Viral gene expressions of IE180, EP0, VP16, and LLT-intron were readily detected at 3-h post-DEX treatment, but gB, a γ1 gene, was not detectable. The differentially expressed phosphorylated proteins of TG neurons were analyzed by ITRAQ coupled with LC-MS/MS, and p-EIF2S2 differentially expression was confirmed by western blot assay. Taken together, our study provides the evidence that typical gene expression in PRV reactivation from latency in TG is disordered compared with known lytic infection in epithelial cells.

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

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

The bovine herpesvirus 1 regulatory proteins, bICP4 and bICP22, are expressed during the escape from latency

Following acute infection of mucosal surfaces by bovine herpesvirus 1 (BoHV-1), sensory neurons are a primary site for lifelong latency. Stress, as mimicked by the synthetic corticosteroid dexamethasone, consistently induces reactivation from latency. Two viral regulatory proteins (VP16 and bICP0) are expressed within 1 h after calves latently infected with BoHV-1 are treated with dexamethasone. Since the immediate early transcription unit 1 (IEtu1) promoter regulates both BoHV-1 infected cell protein 0 (bICP0) and bICP4 expressions, we hypothesized that the bICP4 protein is also expressed during early stages of reactivation from latency. In this study, we tested whether bICP4 and bICP22, the only other BoHV-1 protein known to be encoded by an immediate early gene, were expressed during reactivation from latency by generating peptide-specific antiserum to each protein. bICP4 and bICP22 protein expression were detected in trigeminal ganglionic (TG) neurons during early phases of dexamethasone-induced reactivation from latency, operationally defined as the escape from latency. Conversely, bICP4 and bICP22 were not readily detected in TG neurons of latently infected calves. In summary, it seems clear that all proteins encoded by known BoHV-1 IE genes (bICP4, bICP22, and bICP0) were expressed during early stages of dexamethasone-induced reactivation from latency.

Whole-genome sequence analysis reveals unique SNP profiles to distinguish vaccine and wild-type strains of bovine herpesvirus-1 (BoHV-1)

Bovine herpesvirus-1 (BoHV-1) is a major pathogen affecting cattle worldwide causing primarily respiratory illness referred to as infectious bovine rhinotracheitis (IBR), along with reproductive disorders including abortion and infertility in cattle. While modified live vaccines (MLVs) effectively induce immune response against BoHV-1, they are implicated in disease outbreaks in cattle. Current diagnostic methods cannot distinguish between MLVs and field strains of BoHV-1. We performed whole genome sequencing of 18 BoHV-1 isolates from Pennsylvania and Minnesota along with five BoHV-1 vaccine strains using the Illumina Miseq platform. Based on nucleotide polymorphisms (SNPs) the sequences were clustered into three groups with two different vaccine groups and one distinct cluster of field isolates. Using this information, we developed a novel SNP-based PCR assay that can allow differentiation of vaccine and clinical strains and help accurately determine the incidence of BoHV-1 and the association of MLVs with clinical disease in cattle.

The Wnt Signaling Pathway Is Differentially Expressed during the Bovine Herpesvirus 1 Latency-Reactivation Cycle: Evidence That Two Protein Kinases Associated with Neuronal Survival, Akt3 and BMPR2, Are Expressed at Higher Levels during Latency

Sensory neurons in trigeminal ganglia (TG) of calves latently infected with bovine herpesvirus 1 (BoHV-1) abundantly express latency-related (LR) gene products, including a protein (ORF2) and two micro-RNAs. Recent studies in mouse neuroblastoma cells (Neuro-2A) demonstrated ORF2 interacts with β-catenin and a β-catenin coactivator, high-mobility group AT-hook 1 (HMGA1) protein, which correlates with increased β-catenin-dependent transcription and cell survival. β-Catenin and HMGA1 are readily detected in a subset of latently infected TG neurons but not TG neurons from uninfected calves or reactivation from latency. Consequently, we hypothesized that the Wnt/β-catenin signaling pathway is differentially expressed during the latency and reactivation cycle and an active Wnt pathway promotes latency. RNA-sequencing studies revealed that 102 genes associated with the Wnt/β-catenin signaling pathway were differentially expressed in TG during the latency-reactivation cycle in calves. Wnt agonists were generally expressed at higher levels during latency, but these levels decreased during dexamethasone-induced reactivation. The Wnt agonist bone morphogenetic protein receptor 2 (BMPR2) was intriguing because it encodes a serine/threonine receptor kinase that promotes neuronal differentiation and inhibits cell death. Another differentially expressed gene encodes a protein kinase (Akt3), which is significant because Akt activity enhances cell survival and is linked to herpes simplex virus 1 latency and neuronal survival. Additional studies demonstrated ORF2 increased Akt3 steady-state protein levels and interacted with Akt3 in transfected Neuro-2A cells, which correlated with Akt3 activation. Conversely, expression of Wnt antagonists increased during reactivation from latency. Collectively, these studies suggest Wnt signaling cooperates with LR gene products, in particular ORF2, to promote latency.IMPORTANCE Lifelong BoHV-1 latency primarily occurs in sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. RNA sequencing studies revealed 102 genes associated with the Wnt/β-catenin signaling pathway are differentially regulated during the latency-reactivation cycle. Two protein kinases associated with the Wnt pathway, Akt3 and BMPR2, were expressed at higher levels during latency but were repressed during reactivation. Furthermore, five genes encoding soluble Wnt antagonists and β-catenin-dependent transcription inhibitors were induced during reactivation from latency. These findings are important because Wnt, BMPR2, and Akt3 promote neurogenesis and cell survival, processes crucial for lifelong viral latency. In transfected neuroblastoma cells, a viral protein expressed during latency (ORF2) interacts with and enhances Akt3 protein kinase activity. These findings provide insight into how cellular factors associated with the Wnt signaling pathway cooperate with LR gene products to regulate the BoHV-1 latency-reactivation cycle.

Combinatorial Effects of the Glucocorticoid Receptor and Krüppel-Like Transcription Factor 15 on Bovine Herpesvirus 1 Transcription and Productive Infection

Bovine herpesvirus 1 (BoHV-1), an important bovine pathogen, establishes lifelong latency in sensory neurons. Latently infected calves consistently reactivate from latency following a single intravenous injection of the synthetic corticosteroid dexamethasone. The immediate early transcription unit 1 (IEtu1) promoter, which drives bovine ICP0 (bICP0) and bICP4 expression, is stimulated by dexamethasone because it contains two glucocorticoid receptor (GR) response elements (GREs). Several Krüppel-like transcription factors (KLF), including KLF15, are induced during reactivation from latency, and they stimulate certain viral promoters and productive infection. In this study, we demonstrate that the GR and KLF15 were frequently expressed in the same trigeminal ganglion (TG) neuron during reactivation and cooperatively stimulated productive infection and IEtu1 GREs in mouse neuroblastoma cells (Neuro-2A). We further hypothesized that additional regions in the BoHV-1 genome are transactivated by the GR or stress-induced transcription factors. To test this hypothesis, BoHV-1 DNA fragments (less than 400 bp) containing potential GR and KLF binding sites were identified and examined for transcriptional activation by stress-induced transcription factors. Intergenic regions within the unique long 52 gene (UL52; a component of the DNA primase/helicase complex), bICP4, IEtu2, and the unique short region were stimulated by KLF15 and the GR. Chromatin immunoprecipitation studies revealed that the GR and KLF15 interacted with sequences within IEtu1 GREs and the UL52 fragment. Coimmunoprecipitation studies demonstrated that KLF15 and the GR were associated with each other in transfected cells. Since the GR stimulates KLF15 expression, we suggest that these two transcription factors form a feed-forward loop that stimulates viral gene expression and productive infection following stressful stimuli.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is an important viral pathogen that causes respiratory disease and suppresses immune responses in cattle; consequently, life-threatening bacterial pneumonia can occur. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons. Reactivation from latency is initiated by the synthetic corticosteroid dexamethasone. Dexamethasone stimulates lytic cycle viral gene expression in sensory neurons of calves latently infected with BoHV-1, culminating in virus shedding and transmission. Two stress-induced cellular transcription factors, Krüppel-like transcription factor 15 (KLF15) and the glucocorticoid receptor (GR), cooperate to stimulate productive infection and viral transcription. Additional studies demonstrated that KLF15 and the GR form a stable complex and that these stress-induced transcription factors bind to viral DNA sequences, which correlates with transcriptional activation. The ability of the GR and KLF15 to synergistically stimulate viral gene expression and productive infection may be critical for the ability of BoHV-1 to reactivate from latency following stressful stimuli.

Bovine herpesvirus 1 productive infection and immediate early transcription unit 1 promoter are stimulated by the synthetic corticosteroid dexamethasone

The primary site for life-long latency of bovine herpesvirus 1 (BHV-1) is sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency; however the mechanism by which corticosteroids mediate reactivation is unclear. In this study, we demonstrate for the first time that dexamethasone stimulates productive infection, in part, because the BHV-1 genome contains more than 100 potential glucocorticoid receptor (GR) response elements (GREs). Immediate early transcription unit 1 (IEtu1) promoter activity, but not IEtu2 or VP16 promoter activity, was stimulated by dexamethasone. Two near perfect consensus GREs located within the IEtu1 promoter were necessary for dexamethasone-mediated stimulation. Electrophoretic mobility shift assays and chromatin immunoprecipitation studies demonstrated that the GR interacts with IEtu1 promoter sequences containing the GREs. Although we hypothesize that DEX-mediated stimulation of IEtu1 promoter activity is important during productive infection and perhaps reactivation from latency, stress likely has pleiotropic effects on virus-infected cells.

Bovine herpesvirus 1 regulatory proteins are detected in trigeminal ganglionic neurons during the early stages of stress-induced escape from latency

Bovine herpesvirus 1 (BHV-1) establishes latency in sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency. Within 90 min after latently infected calves are treated with dexamethasone, two BHV-1 regulatory proteins, BHV-1-infected cell protein 0 (bICP0) and viral protein 16 (VP16), are expressed in the same neuron. In this study, we demonstrate that VP16 and bICP0 can be detected at 22 and 33 min after dexamethasone (DEX) treatment of latently infected calves. However, we were unable to discern whether VP16 or bICP0 was expressed at early times after reactivation. VP16+ neurons consistently express the glucocorticoid receptor suggesting corticosteroid-mediated activation of its receptor rapidly stimulates reactivation from latency.

Bovine herpesvirus 1 productive infection stimulates inflammasome formation and caspase 1 activity

Bovine herpesvirus 1 (BoHV-1), a significant viral pathogen of cattle, causes inflammation in affected tissue during acute infection. Consequently, we tested whether productively infected bovine cells stimulate inflammasome formation. Expression of two components required for inflammasome formation, the DNA sensor IFI16 (gamma-interferon-inducible protein 16) and NLRP3 (NOD-like receptor family, pyrin domain containing 3), were induced in bovine kidney cells by eight hours after infection. IFI16 was detected in punctate granules localized to the cytoplasm and nucleus. During productive infection, more than ten times more cells were caspase 1 positive, which is activated following inflammasome formation. Two caspase 1 inhibitors had no effect on productive infection. Conversely, another caspase 1 inhibitor, glyburide, significantly inhibited virus infection suggesting it had off-target effects on related enzymes or interfered with infection via non-enzymatic mechanisms. Collectively, these studies demonstrated that BoHV-1 infection stimulated inflammasome formation, which we predict is important for clinical symptoms in cattle.

Ocular and neural distribution of feline herpesvirus-1 during active and latent experimental infection in cats

BACKGROUND

Herpes simplex virus 1 (HSV-1) and varicella zoster virus (VZV) cause extensive intra-ocular and neural infections in humans and are closely related to Felid herpes virus 1 (FeHV-1). We report the extent of intra-ocular replication and the extent and morphological aspects of neural replication during the acute and latent phases of FeHV-1 infection. Juvenile, SPF cats were inoculated with FeHV-1. Additional cats were used as negative controls. Cats were euthanized on days 6, 10, and 30 post-inoculation.

RESULTS

FeHV-1 was isolated from the conjunctiva, cornea, uveal tract, retina, optic nerve, ciliary ganglion (CG), pterygopalatine ganglion (PTPG), trigeminal ganglion (TG), brainstem, visual cortex, cerebellum, and olfactory bulb of infected cats during the acute phase, but not the cranial cervical ganglion (CCG) and optic chiasm. Viral DNA was detected in all tissues during acute infection by a real-time quantitative PCR assay. On day 30, viral DNA was detected in all TG, all CCG, and 2 PTPG. Histologically mild inflammation and ganglion cell loss were noted within the TG during acute, but not latent infection. Using linear regression, a strong correlation existed between clinical score and day 30 viral DNA copy number within the TG.

CONCLUSIONS

The correlation between clinical score and day 30 viral DNA copy number suggests the severity of the acute clinical infection is related to the quantity of latent viral DNA. The histologic response was similar to that seen during HSV-1 or VZV infection. To the author's knowledge this is the first report of FeHV-1 infection involving intraocular structures and autonomic ganglia.

Stress-induced cellular transcription factors expressed in trigeminal ganglionic neurons stimulate the herpes simplex virus 1 ICP0 promoter

Alphaherpesvirinae family members can reactivate from latency following stress. The synthetic corticosteroid dexamethasone induces certain cellular transcription factors in murine and bovine trigeminal ganglionic neurons. Three dexamethasone-induced transcription factors, Krüppel-like factor 15, Slug, and SPDEF, stimulated the herpes simplex virus type 1-infected cell protein 0 (ICP0) promoter more than 150-fold. Conversely, other viral promoters (VP16 and ICP4) were not strongly stimulated, suggesting that the ICP0 promoter is preferentially activated by dexamethasone-simulated stress.

Bovine herpesvirus 1 regulatory proteins bICP0 and VP16 are readily detected in trigeminal ganglionic neurons expressing the glucocorticoid receptor during the early stages of reactivation from latency

Bovine herpesvirus 1 (BHV-1) establishes a lifelong latent infection in sensory neurons following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Within minutes, corticosteroids activate the glucocorticoid receptor and transcription of promoters containing a glucocorticoid receptor element. A single intravenous injection of the synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. Lytic cycle viral gene expression is detected within 6 h after dexamethasone treatment of calves latently infected with BHV-1. Cellular transcription factors are induced by dexamethasone in trigeminal ganglionic neurons within 1.5 h after dexamethasone treatment, suggesting they promote viral gene expression during the early phases of reactivation from latency, which we operationally defined as the escape from latency. In this study, immunohistochemistry was utilized to examine viral protein expression during the escape from latency. Within 1.5 h after dexamethasone treatment, bICP0 and a late protein (VP16) were consistently detected in a subset of trigeminal ganglionic neurons. Most neurons expressing bICP0 also expressed VP16. Additional studies revealed that neurons expressing the glucocorticoid receptor also expressed bICP0 or VP16 at 1.5 h after dexamethasone treatment. Two other late proteins, glycoprotein C and D, were not detected until 6 h after dexamethasone treatment and were detected in only a few neurons. These studies provide evidence that VP16 and the promiscuous viral trans-activator (bICP0) are expressed during the escape from latency, suggesting they promote the production of infectious virus in a small subset of latently infected neurons.

A bovine herpesvirus 1 protein expressed in latently infected neurons (ORF2) promotes neurite sprouting in the presence of activated Notch1 or Notch3

Bovine herpesvirus 1 (BHV-1) infection induces clinical symptoms in the upper respiratory tract, inhibits immune responses, and can lead to life-threatening secondary bacterial infections. Following acute infection, BHV-1 establishes latency in sensory neurons within trigeminal ganglia, but stress can induce reactivation from latency. The latency-related (LR) RNA is the only viral transcript abundantly expressed in latently infected sensory neurons. An LR mutant virus with stop codons at the amino terminus of the first open reading frame (ORF) in the LR gene (ORF2) is not reactivated from latency, in part because it induces higher levels of apoptosis in infected neurons. ORF2 inhibits apoptosis in transiently transfected cells, suggesting that it plays a crucial role in the latency-reactivation cycle. ORF2 also interacts with Notch1 or Notch3 and inhibits its ability to trans activate certain viral promoters. Notch3 RNA and protein levels are increased during reactivation from latency, suggesting that Notch may promote reactivation. Activated Notch signaling interferes with neuronal differentiation, in part because neurite and axon generation is blocked. In this study, we demonstrated that ORF2 promotes neurite formation in mouse neuroblastoma cells overexpressing Notch1 or Notch3. ORF2 also interfered with Notch-mediated trans activation of the promoter that regulates the expression of Hairy Enhancer of Split 5, an inhibitor of neurite formation. Additional studies provided evidence that ORF2 promotes the degradation of Notch3, but not that of Notch1, in a proteasome-dependent manner. In summary, these studies suggest that ORF2 promotes a mature neuronal phenotype that enhances the survival of infected neurons and consequently increases the pool of latently infected neurons.

Cellular transcription factors induced in trigeminal ganglia during dexamethasone-induced reactivation from latency stimulate bovine herpesvirus 1 productive infection and certain viral promoters

Bovine herpesvirus 1 (BHV-1), an alphaherpesvirinae subfamily member, establishes latency in sensory neurons. Elevated corticosteroid levels, due to stress, reproducibly triggers reactivation from latency in the field. A single intravenous injection of the synthetic corticosteroid dexamethasone (DEX) to latently infected calves consistently induces reactivation from latency. Lytic cycle viral gene expression is detected in sensory neurons within 6 h after DEX treatment of latently infected calves. These observations suggested that DEX stimulated expression of cellular genes leads to lytic cycle viral gene expression and productive infection. In this study, a commercially available assay-Bovine Gene Chip-was used to compare cellular gene expression in the trigeminal ganglia (TG) of calves latently infected with BHV-1 versus DEX-treated animals. Relative to TG prepared from latently infected calves, 11 cellular genes were induced more than 10-fold 3 h after DEX treatment. Pentraxin three, a regulator of innate immunity and neurodegeneration, was stimulated 35- to 63-fold after 3 or 6 h of DEX treatment. Two transcription factors, promyelocytic leukemia zinc finger (PLZF) and Slug were induced more than 15-fold 3 h after DEX treatment. PLZF or Slug stimulated productive infection 20- or 5-fold, respectively, and Slug stimulated the late glycoprotein C promoter more than 10-fold. Additional DEX-induced transcription factors also stimulated productive infection and certain viral promoters. These studies suggest that DEX-inducible cellular transcription factors and/or signaling pathways stimulate lytic cycle viral gene expression, which subsequently leads to successful reactivation from latency in a small subset of latently infected neurons.

Regulation of the latency-reactivation cycle by products encoded by the bovine herpesvirus 1 (BHV-1) latency-related gene

Like other α-herpesvirinae subfamily members, the primary site for bovine herpesvirus 1 (BHV-1) latency is ganglionic sensory neurons. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Transcription from the latency-related (LR) gene is readily detected in neurons of trigeminal ganglia (TG) of calves or rabbits latently infected with BHV-1. Two micro-RNAs and a transcript encompassing a small open reading frame (ORF-E) located within the LR promoter can also be detected in TG of latently infected calves. A BHV-1 mutant that contains stop codons near the beginning of the first open reading frame (ORF2) within the major LR transcript (LR mutant virus) has been characterized. The LR mutant virus does not express ORF2, a reading frame that lacks an initiating ATG (reading frame B), and has reduced expression of ORF1 during productive infection. The LR mutant virus does not reactivate from latency following dexamethasone treatment suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG neurons of calves infected with the LR mutant viruses when compared to wild-type BHV-1 indicating that the anti-apoptotic properties of the LR gene is necessary for the latency-reactivation cycle. ORF2 inhibits apoptosis and regulates certain viral promoters, in part, because it interacts with three cellular transcription factors (C/EBP-alpha, Notch1, and Notch3). Although ORF2 is important for the latency-reactivation cycle, we predict that other LR gene products play a supportive role during life-long latency in cattle.

Two microRNAs encoded within the bovine herpesvirus 1 latency-related gene promote cell survival by interacting with RIG-I and stimulating NF-κB-dependent transcription and beta interferon signaling pathways

Sensory neurons latently infected with bovine herpesvirus 1 (BHV-1) abundantly express latency-related (LR) RNA (LR-RNA). Genetic evidence indicates that LR protein expression plays a role in the latency-reactivation cycle, because an LR mutant virus that contains three stop codons downstream of the first open reading frame (ORF2) does not reactivate from latency. The LR mutant virus induces higher levels of apoptotic neurons in trigeminal ganglia, and ORF2 interferes with apoptosis. Although ORF2 is important for the latency-reactivation cycle, other factors encoded by the LR gene are believed to play a supportive role. For example, two microRNAs (miRNAs) encoded within the LR gene are expressed in trigeminal ganglia of latently infected calves. These miRNAs interfere with bICP0 protein expression and productive infection in transient-transfection assays. In this report, we provide evidence that the two LR miRNAs cooperate with poly(I·C), interferon (IFN) regulatory factor 3 (IRF3), or IRF7 to stimulate beta interferon (IFN-β) promoter activity. Both miRNAs also stimulated IFN-β promoter activity and nuclear factor-kappa B (NF-κB)-dependent transcription when cotransfected with a plasmid expressing retinoic acid-inducible gene I (RIG-I). In the presence of RIG-I, the LR miRNAs enhanced survival of mouse neuroblastoma cells, which correlated with activation of the antiapoptosis cellular transcription factor, NF-κB. Immunoprecipitation assays demonstrated that both miRNAs stably interact with RIG-I, suggesting that this interaction directly stimulates the RIG-I signaling pathway. In summary, the results of these studies suggest that interactions between LR miRNAs and RIG-I promote the establishment and maintenance of latency by enhancing survival of infected neurons.

Identification of herpes simplex virus type 1 proteins encoded within the first 1.5 kb of the latency-associated transcript

Expression of the first 1.5 kb of the latency-associated transcript (LAT) that is encoded by herpes simplex virus type 1 (HSV-1) is sufficient for wild-type (wt) levels of reactivation from latency in small animal models. Peptide-specific immunoglobulin G (IgG) was generated against open reading frames (ORFs) that are located within the first 1.5 kb of LAT coding sequences. Cells stably transfected with LAT or trigeminal ganglionic neurons of mice infected with a LAT expressing virus appeared to express the L2 or L8 ORF. Only L2 ORF expression was readily detected in trigeminal ganglionic neurons of latently infected mice.

Experimental infection of reindeer with cervid herpesvirus 2

Cervid herpesvirus 2 (CvHV2) has been isolated from reindeer (Rangifer tarandus tarandus), and serological data indicate that in reindeer this virus is endemic in Fennoscandia, Alaska, Canada, and Greenland. CvHV2 has been described as a cause of subclinical genital infections in reindeer, but little information on primary infections exists. In this study, six seronegative and presumably pregnant reindeer were allocated to one of two groups. Two animals were inoculated with CvHV2 intratracheally, and two animals intravaginally, with one control animal in each group receiving sterile water. Mild hyperthermia and serous discharges from the vagina and nose were observed. No abortions were recorded, but one calf died shortly after birth. Inoculated animals seroconverted and had neutralizing antibodies after days 7 to 10 postinfection. CvHV2 was detected by PCR in nasal and vaginal swabs from animals in both groups but could be isolated only from nasal swabs in the respiratory group and from vaginal swabs in the genital group. CvHV2 was detected by PCR in various organs and tissues postmortem. In control animals, the virus could not be isolated in spite of PCR-positive nasal and vaginal swab samples and some degree of positive immunostaining. One of the animals that were inoculated intratracheally developed a hemorrhagic, necrotizing bronchopneumonia, which was CvHV2 positive by PCR and immunohistochemistry. We conclude that CvHV2 can cause systemic infection, that both genital and respiratory inoculations can lead to virus shedding, and that the virus can infect the fetus in utero.

Identification of a novel herpes simplex virus type 1 transcript and protein (AL3) expressed during latency

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is abundantly expressed in latently infected sensory neurons. In small animal models of infection, expression of the first 1.5 kb of LAT coding sequences is necessary and sufficient for wild-type reactivation from latency. The ability of LAT to inhibit apoptosis is important for reactivation from latency. Within the first 1.5 kb of LAT coding sequences and LAT promoter sequences, additional transcripts have been identified. For example, the anti-sense to LAT transcript (AL) is expressed in the opposite direction to LAT from the 5' end of LAT and LAT promoter sequences. In addition, the upstream of LAT (UOL) transcript is expressed in the LAT direction from sequences in the LAT promoter. Further examination of the first 1.5 kb of LAT coding sequences revealed two small ORFs that are anti-sense with respect to LAT (AL2 and AL3). A transcript spanning AL3 was detected in productively infected cells, mouse neuroblastoma cells stably expressing LAT and trigeminal ganglia (TG) of latently infected mice. Peptide-specific IgG directed against AL3 specifically recognized a protein migrating near 15 kDa in cells stably transfected with LAT, mouse neuroblastoma cells transfected with a plasmid containing the AL3 ORF and TG of latently infected mice. The inability to detect the AL3 protein during productive infection may have been because the 5' terminus of the AL3 transcript was downstream of the first in-frame methionine of the AL3 ORF during productive infection.

Dexamethasone treatment of calves latently infected with bovine herpesvirus 1 leads to activation of the bICP0 early promoter, in part by the cellular transcription factor C/EBP-alpha

Sensory neurons within trigeminal ganglia (TG) are the primary site for bovine herpesvirus 1 (BHV-1) latency. During latency, viral gene expression is restricted to the latency-related (LR) gene and the open reading frame ORF-E. We previously constructed an LR mutant virus that expresses LR RNA but not any of the known LR proteins. In contrast to calves latently infected with wild-type (wt) BHV-1 or the LR rescued virus, the LR mutant virus does not reactivate from latency following dexamethasone (DEX) treatment. In this study, we demonstrated that bICP0, but not bICP4, transcripts were consistently detected in TG of calves infected with the LR mutant or LR rescued virus following DEX treatment. Calves latently infected with the LR rescued virus but not the LR mutant virus expressed late transcripts, which correlated with shedding of infectious virus following DEX treatment. The bICP4 and bICP0 genes share a common immediate-early promoter, suggesting that this promoter was not consistently activated during DEX-induced reactivation from latency. The bICP0 gene also contains a novel early promoter that was activated by DEX in mouse neuroblastoma cells. Expression of a cellular transcription factor, C/EBP-alpha, was stimulated by DEX, and C/EBP-alpha expression was necessary for DEX induction of bICP0 early promoter activity. C/EBP-alpha directly interacted with bICP0 early promoter sequences that were necessary for trans activation by C/EBP-alpha. In summary, DEX treatment of latently infected calves induced cellular factors that stimulated bICP0 early promoter activity. Activation of bICP0 early promoter activity does not necessarily lead to late gene expression and virus shedding.

The zinc RING finger of bovine herpesvirus 1-encoded bICP0 protein is crucial for viral replication and virulence

Bovine herpesvirus 1 (BHV-1) infected cell protein 0 (bICP0) stimulates productive infection, in part by activating viral gene expression. The C(3)HC(4) zinc RING finger of bICP0 is crucial for activating viral transcription and productive infection. In this study, we used a bacterial artificial chromosome containing a wild-type (wt) virulent BHV-1 strain to generate a single amino acid mutation in the C(3)HC(4) zinc RING finger of bICP0. This virus (the 51g mutant) contains a cysteine-to-glycine mutation (51st amino acid) in the C(3)HC(4) zinc RING finger of bICP0. A plasmid expressing the 51g mutant protein did not transactivate viral promoter activity as efficiently as wt bICP0. The 51g mutant virus expressed higher levels of the bICP0 protein than did the 51g rescued virus (51gR) but yielded reduced virus titers following infection of permissive bovine cells. The 51g mutant virus, but not the 51gR virus, grew poorly in bovine cells pretreated with imiquimod to stimulate interferon production. During acute infection of calves, levels of infectious virus were 2 to 3 logs lower in ocular or nasal swabs with 51g than with 51gR. Calves latently infected with the 51g mutant did not reactivate from latency because virus shedding did not occur in ocular or nasal cavities. As expected, calves latently infected with 51gR reactivated from latency following dexamethasone treatment. These studies demonstrate that mutation of a single well-conserved cysteine residue in the C(3)HC(4) zinc RING finger of bICP0 has dramatic effects on the growth properties of BHV-1.

Open reading frame 2, encoded by the latency-related gene of bovine herpesvirus 1, has antiapoptotic activity in transiently transfected neuroblastoma cells

The latency-related (LR) RNA encoded by bovine herpesvirus 1 is abundantly expressed in the trigeminal ganglia of latently infected calves. Expression of LR proteins is necessary for reactivation from latency and the protection of infected neurons from apoptosis. In this study, we demonstrated that an LR-encoded protein, open reading frame 2 (ORF-2), or ORF-2 fusion proteins encoded by alternatively spliced LR transcripts inhibit cold shock or Fas ligand-induced apoptosis in mouse neuroblastoma (neuro-2A) cells. Frameshift mutants of ORF-2 do not inhibit apoptosis, which suggests that protein expression, not LR RNA expression, mediates the antiapoptotic activity of the LR gene in transfected neuro-2A cells.

Premature expression of the latency-related RNA encoded by bovine herpesvirus type 1 correlates with higher levels of beta interferon RNA expression in productively infected cells

Bovine herpesvirus type 1 (BHV-1) is an important pathogen that can initiate bovine respiratory disease complex. Like other members of the subfamily Alphaherpesvirinae, BHV-1 establishes latency in sensory neurons. The latency-related (LR) gene expresses a family of alternatively spliced transcripts in infected sensory neurons that have the potential to encode several LR proteins. An LR mutant virus that contains three stop codons near the 5' terminus of the first open reading frame in the LR gene does not express two LR proteins or reactivate from latency. In addition, the LR mutant virus induces higher levels of apoptosis in trigeminal ganglionic neurons and grows less efficiently in certain tissues of infected calves. In spite of the reduced pathogenesis, the LR mutant virus, wild-type BHV-1 and the LR rescued virus exhibit identical growth properties in cultured bovine cells. In this study, we demonstrated that during early phases of productive infection the LR mutant virus expressed higher levels of LR-RNA relative to the LR rescued virus or wt BHV-1. Bovine kidney cells infected with the LR mutant virus also induced higher levels of beta interferon RNA and interferon response genes. These results suggest that inappropriate expression of LR-RNA, in the absence of LR protein expression, may influence the latency-reactivation cycle and pathogenic potential of BHV-1.

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

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

Identification of a novel protein encoded by the latency-related gene of bovine herpesvirus 1

The latency-related (LR) RNA encoded by bovine herpesvirus 1 (BHV-1) is abundantly expressed and alternatively spliced in trigeminal ganglia. A mutant BHV-1 strain that contains three stop codons at the beginning of LR open reading frame (ORF)-2 (LR mutant virus) does not express ORF-2 or an adjacent reading frame that lacks an initiating ATG (RF-C). Calves latently infected with wild-type (wt) BHV-1, but not with the LR mutant virus, reactivate from latency, indicating that proteins encoded by the LR gene regulate the latency-reactivation cycle. The LR gene also contains another large ORF (ORF-1) that is approximately 200 bp downstream of stop codons inserted at the N-terminus of ORF-2. To test whether the LR mutant virus can expresses ORF-1, the authors developed antiserum directed against ORF-1. The ORF-1 antiserum recognizes specific proteins in bovine cells productively infected with wt BHV-1. ORF-1 protein expression is reduced, but not blocked, when bovine cells are infected with the LR mutant virus. Confocal microscopy demonstrated ORF-1 is present in the cytoplasm and nucleus of productively infected cells, whereas RF-C or a fusion protein containing RF-C localizes to the cytoplasm. Trigeminal ganglia from calves latently infected with wt BHV-1 contain neurons specifically stained with the ORF-1 antiserum. These studies suggest ORF-1 expression may be important for the BHV-1 latency-reactivation cycle.

Bovine herpesvirus type 1 induces cell death by a cell-type-dependent fashion

Bovine herpesvirus 1 (BHV-1), a member of the alpha-herpesvirinae sub-family, causes significant losses to the cattle industry. BHV-1 establishes latency in trigeminal ganglionic sensory neurons, but periodically reactivates from latency. Previous studies suggested that infection with BHV-1-induced novel morphological changes in rabbit skin (RS) cells versus bovine kidney cells (MDBK). Consequently, we hypothesized that viral infection led to a novel form of cell death in RS cells compared to MDBK cells. To test this hypothesis, we examined the levels of apoptosis in these cell types following infection with BHV-1. Infection of RS, but not MDBK, cells leads to high levels of apoptosis compared to mock-infected cells. Previous studies indicated that a BHV-1 recombinant virus that does not express the bICP0 protein grows poorly in permissive cells and induces a persistent-like infection. This suggested that bICP0 played an important role in regulating cell death following infection. To test this hypothesis, we compared the levels of apoptosis in cells infected with the bICP0 null mutant versus viral strains that expressed bICP0. The bICP0 null mutant induces low levels of apoptosis in RS or MDBK cells. When MDBK cells are treated with UV light prior to infection, bICP0 expressing viral strains, but not the bICP0 null mutant, inhibited UV-induced apoptosis. Infection of MDBK cells with the bICP0 null mutant, leads to an accumulation of autophagosomes that are not detected following infection with bICP0 expressing viruses. These studies suggest that the bICP0 null mutant induces autophagy in MDBK cells, and bICP0 protein expression mediates cell-type specific cytotoxicity.

Envelope protein Us9 is required for the anterograde transport of bovine herpesvirus type 1 from trigeminal ganglia to nose and eye upon reactivation

In this study, the authors examined the role of bovine herpesvirus type 1 (BHV-1) Us9 in the anterograde transport of the virus from trigeminal ganglia (TG) to nose and eye upon reactivation from latency. During primary infection, both BHV-1 Us9-deleted and BHV-1 Us9-rescued viruses replicated efficiently in the nasal and ocular epithelium. However, upon reactivation from latency, only the BHV-1 Us9-rescued virus could be isolated in the nasal and ocular shedding. By real-time polymerase chain reaction, comparable DNA copy numbers were detected in the TGs during latency and reactivation for both the viruses. Therefore, Us9 is essential for reactivation of the virus in the TG and anterograde axonal transport from TG to nose and eye.

A protein encoded by the bovine herpesvirus 1 open reading frame E gene induces neurite-like morphological changes in mouse neuroblastoma cells and is expressed in trigeminal ganglionic neurons

Bovine herpes virus 1 (BHV-1), like other alpha-herpesvirinae subfamily members, establishes latency in sensory neurons. Periodically BHV-1 reactivates from latency, resulting in virus shedding and spread to uninfected cattle. Although reactivation from latency does not usually lead to recurrent disease, the latency-reactivation cycle is crucial for virus transmission. The latency-related (LR) RNA is abundantly expressed during latency, and expression of a LR encoded protein is necessary for dexamethasone-induced reactivation from latency in cattle. Within LR promoter sequences, a small open reading frame (ORF) was identified (ORF-E) that is antisense to the LR-RNA, and downstream of the bICP0 gene. ORF-E transcription is consistently detected in trigeminal ganglia (TG) of latently infected calves, suggesting ORF-E expression plays a role in the latency-reactivation cycle. Polyclonal antiserum directed against an ORF-E peptide or the entire ORF-E protein specifically recognizes the nucleus of sensory neurons in TG of latently infected calves. The ORF-E peptide-specific antiserum also recognizes a protein when mouse neuroblastoma cells (neuro-2A) are transfected with an ORF-E expression construct. In contrast to the growth inhibiting properties of the LR gene, stably transfected ORF-E-expressing cells were obtained. Neuro-2A cells stably transfected with a plasmid expressing ORF-E induced morphological changes that resembled neurite-like projections. In contrast, neurite-like projections were not observed following transfection of neuro-2A cells with an empty vector. These studies suggest that a protein encoded by ORF-E has the potential to alter the physiology or metabolism of neuronal cell types, which may be important for long-term latency.

Comparison of inflammatory infiltrates in trigeminal ganglia of cattle infected with wild-type Bovine herpesvirus 1 versus a virus strain containing a mutation in the LR (latency-related) gene

During latency, the bovine herpesvirus 1 (BHV-1) latency-related (LR) RNA is abundantly expressed in neurons within trigeminal ganglia (TG). A LR mutant virus that does not express two LR proteins is unable to reactivate from latency following dexamethasone treatment. Increased infiltration of inflammatory cells occurs in TG of calves acutely infected with the LR mutant virus. Throughout acute infection, wild-type BHV-1 DNA is detected in neurons surrounded by mononuclear infiltrates and in non-neuronal cells comprising the infiltrate. Conversely, LR mutant DNA is only detected in neurons near the end of acute infection, suggesting LR gene products promote virus spread in TG.

A protein encoded by the bovine herpesvirus 1 latency-related gene interacts with specific cellular regulatory proteins, including CCAAT enhancer binding protein alpha

Following acute infection, bovine herpesvirus 1 establishes latency in sensory neurons of trigeminal ganglia (TG). Reactivation from latency occurs periodically, resulting in the shedding of infectious virus. The latency-related (LR) RNA is abundantly expressed in TG of latently infected calves, and the expression of LR proteins is necessary for dexamethasone-induced reactivation from latency. Previously published studies also identified an alternatively spliced LR transcript which is abundantly expressed in TG at 7 days after infection and has the potential to encode a novel LR fusion protein. Seven days after infection is when extensive viral gene expression is extinguished in TG and latency is established, suggesting that LR gene products influence the establishment of latency. In this study, we used a bacterial two-hybrid assay to identify cellular proteins that interact with the novel LR fusion protein. The LR fusion protein interacts with two proteins that can induce apoptosis (Bid and Cdc42) and with CCAAT enhancer binding protein alpha (C/EBP-alpha). Additional studies confirmed that the LR fusion protein interacts with human or insect C/EBP-alpha. C/EBP-alpha protein expression is induced in TG neurons of infected calves and after dexamethasone-induced reactivation from latency. Wild-type C/EBP-alpha, but not a DNA binding mutant of C/EBP-alpha, enhances plaque formation in bovine cells. We hypothesize that interactions between the LR fusion protein and C/EBP-alpha promote the establishment of latency.

Functional analysis of bovine herpesvirus 1 (BHV-1) genes expressed during latency

Bovine herpes virus 1 (BHV-1) establishes latency in sensory neurons of trigeminal ganglia (TG), and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two transcripts, the latency related (LR) RNA and ORF-E, are abundantly expressed in TG of latently infected cattle. A LR mutant strain of BHV-1 was constructed that contains stop codons near the beginning of the LR-RNA. The LR mutant virus does not express two proteins encoded by the LR gene, or reactivate from latency suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG of calves infected with the LR mutant versus wild type BHV-1 indicating that the anti-apoptotic properties of the LR gene regulate the latency-reactivation cycle. The LR gene also inhibits bICP0 expression and mammalian cell growth, but these functions do not require LR protein expression. In contrast, the ability of the LR gene to inhibit apoptosis appears to require LR protein expression. A small open reading frame (ORF-E) that is located within the LR promoter is expressed in the nucleus of neuroblastoma cells. We predict that the LR gene and ORF-E regulate the BHV-1 latency-reactivation cycle.

Positional and functional characterisation of apoptosis related genes belonging to the BCL2 family in sheep

Apoptosis is a process whereby cells die in a controlled manner and it is involved in animal development, tissue homeostasis and a variety of diseases. The B-cell lymphoma 2 family proteins are central regulators of intracellular apoptotic signalling cascades. This work describes the isolation of cDNA and genomic fragments from five sheep BCL2 related genes: BCL2, BCL2L1, BCL2L2, BAX and MCL1. Transcript sequences showed a high homology with BCL2 related genes from other species. Three cattle BAC probes containing the homologous BCL2, BCL2L1 and BCL2L2 genes were identified and used for comparative FISH mapping in sheep. BCL2 was localised in OAR23q27, BCL2L1 in OAR13q22 and BCL2L2 in OAR7q15-->q21. Intron polymorphisms were used for linkage mapping of BAX and MCL1, which were mapped on OAR14 and OAR1 respectively. Moreover, a BCL2L1 pseudogene was also identified and linkage mapped on OAR2. The expression of these genes was analysed in mammary gland, ovary, intestine and brain which are target tissues for sheep pathological processes where apoptosis is involved.

Analysis of a bovine herpesvirus 1 recombinant virus that does not express the bICP0 protein

Bovine herpesvirus 1 (BHV-1) infected-cell protein 0 (bICP0) stimulates productive infection by activating viral gene expression. In this study, an attempt was made to construct a recombinant virus with point mutations in the C3HC4zinc RING finger of bICP0, as this domain is necessary for activating viral transcription and productive infection. A virus was identified in bovine cells that induced small clusters of infected cells resembling a small plaque. Instead of the expected mutations within the zinc RING finger, this virus contained a point mutation within the initiating ATG of bICP0, a point mutation two bases downstream from the ATG mutation and deletion of flanking plasmid sequences used for homologous recombination. The bICP0 mutant was rescued with wild-type (wt) bICP0 sequences and the bICP0-rescued virus produced wt plaques. The bICP0-rescued virus and wt BHV-1, but not the mutant, expressed the bICP0 protein during productive infection of bovine cells, suggesting that the mutant virus was a null mutant. Consequently, the mutant was designated the bICP0 null mutant. Infection of bovine cells with the bICP0 null mutant resulted in at least 100-fold lower virus titres, indicating that bICP0 protein expression is important, but not required, for virus production. When bovine cells infected with the bICP0 null mutant virus were subcultured, the cells continued to divide, but viral DNA could be detected after more than 35 passages, suggesting that the bICP0 null mutant induced a persistent-like infection in bovine cells and that it may be useful for generating additional bICP0 mutants.

Update on Pathogenesis, Diagnosis, and Treatment of Feline Herpesvirus Type 1

Feline herpesvirus type 1 (FHV-1) infection, but not necessarily chronic or recurrent disease, is common throughout domestic cat populations worldwide. Knowledge of a few essential virological facts permits practitioners to provide appropriate advice to owners of individual pet cats infected with this virus and to assist in the management of shelters and other multicat households in which the virus is enzootic. This article discusses pathogenesis, diagnostic techniques, and clinical signs considered characteristic of infection with FHV-1. Treatment options are considered under the broad categories of supportive care, antiviral agents, and adjunctive therapies.

The locus encompassing the latency-associated transcript of herpes simplex virus type 1 interferes with and delays interferon expression in productively infected neuroblastoma cells and trigeminal Ganglia of acutely infected mice

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is the only abundant viral transcript expressed in latently infected neurons. LAT inhibits apoptosis, suggesting that it regulates latency by promoting the survival of infected neurons. The LAT locus also contains a newly described gene (AL), which is antisense to LAT and partially overlaps LAT encoding sequences. When human (SK-N-SH) or mouse (neuro-2A) neuroblastoma cells were infected with a virus that does not express LAT or AL gene products (dLAT2903), beta interferon (IFN-beta) and IFN-alpha RNA expression was detected earlier relative to the same cells infected with HSV-1 strains that express LAT and AL. Infection of neuro-2A cells with dLAT2903 also led to higher levels of IFN-beta promoter activity than in cells infected with wild-type (wt) HSV-1. In contrast, IFN RNA expression was the same when human lung fibroblasts were infected with dLAT2903 or wt HSV-1. When BALB/c mice were infected with dLAT2903, IFN-alpha and IFN-beta RNA expression was readily detected in trigeminal ganglia (TG) 4 days after infection. These transcripts were not detected in TG of mice infected with wt HSV-1 or dLAT2903R (marker-rescued dLAT2903) until 6 days postinfection. When TG single-cell suspensions from infected BALB/c mice were prepared and incubated in vitro with wt HSV-1 as a source of antigen, TG cultures prepared from mice infected with dLAT2903 produced and secreted higher levels of IFN protein than wt HSV-1 or dLAT2903R. Collectively, these studies suggest that the LAT locus interferes with and delays IFN expression.

Latency-related gene encoded by bovine herpesvirus 1 promotes virus growth and reactivation from latency in tonsils of infected calves

Infection of calves with bovine herpesvirus 1 (BHV-1) results in transient immunosuppression that may lead to bacterium-induced pneumonia and, occasionally, death. Although sensory neurons in the trigeminal ganglia (TG) are the primary site of BHV-1 latency, viral genomes are detected in the tonsils of latently infected calves. Dexamethasone (DEX) consistently induces reactivation from latency, and viral gene expression is detected in TG and tonsils. In sensory neurons of latently infected calves, the latency-related (LR) gene is abundantly expressed and is required for reactivation from latency. In the present study, we compared the abilities of wild-type (wt) BHV-1 and a strain with a mutation in the LR gene (the LR mutant strain) to grow in the tonsils of infected calves and reactivate from latency. Lower levels of the LR mutant virus were detected in the tonsils of acutely infected calves. LR mutant viral DNA was consistently detected by PCR in the tonsils of latently infected calves, suggesting that the establishment of a latent or persistent infection occurred. Although the LR mutant did not reactivate from latency in vivo after DEX treatment, explantation of tonsil tissue from calves latently infected with the LR mutant yielded infectious virus. Relative to wt BHV-1, the LR mutant did not induce explant-induced reactivation as efficiently. These studies indicate that the LR gene promotes virus shedding from tonsil tissue during acute infection and reactivation from latency in tonsil tissue in vivo. We suggest that incorporation of the LR gene mutation into existing modified live vaccines would prevent reactivation from latency in neural and nonneural sites and would thus prevent transmission to other animals.

Effects of hypervaccination with bovine herpesvirus type 1 gE-deleted marker vaccines on the serological response and virological status of calves challenged with wild-type virus

Twenty-four calves were immunised four times with gE-deleted infectious bovine rhinotracheitis marker vaccines before being challenged with small doses of wild-type bovine herpesvirus type 1 (BHV-1). The repeated vaccinations induced strong immunity that prevented detectable virus replication and gE-seroconversion after the challenge infection in most of the calves. The hypervaccinated calves that shed virus after the challenge infection showed no delay in gE-seroconversion compared with unvaccinated control calves. Using a sensitive nested PCR, BHV-1 gE sequences could be detected in the trigeminal ganglia of several of the gE-seronegative, challenge-infected calves, possibly indicating the presence of wild-type BHV-1 DNA.

Identification of a novel bovine herpesvirus 1 transcript containing a small open reading frame that is expressed in trigeminal ganglia of latently infected cattle

Bovine herpesvirus 1 (BHV-1), like other Alphaherpesvirinae subfamily members, establishes latency in sensory neurons. The latency-related (LR) RNA is abundantly expressed during latency, and expression of an LR protein is required for the latency reactivation cycle in cattle. Within LR promoter sequences, a 135-amino-acid open reading frame (ORF) was identified, ORF-E, that is antisense to the LR RNA. ORF-E is also downstream of the gene encoding the major viral transcriptional activator, bICP0. Strand-specific reverse transcription-PCR demonstrated that a transcript containing ORF-E was consistently expressed in trigeminal ganglia (TG) of latently infected calves, productively infected cultured cells, and acutely infected calves. As expected, a late transcript encoding glycoprotein C was not detected in TG of latently infected calves. The ORF-E transcript is polyadenylated and is expressed early when cultured bovine cells are productively infected. Protein coding sequences containing ORF-E were fused to green fluorescent protein (GFP) to examine the cellular localization of the putative protein. In transiently transfected mouse neuroblastoma (neuro-2A) and human neuroblastoma (SK-N-SH) cells, the ORF-E/GFP fusion protein was detected in discreet domains within the nucleus. In contrast, the ORF-E/GFP fusion protein was detected in the cytoplasm and nucleus of rabbit skin cells and bovine kidney cells. As expected, the GFP protein was expressed in the cytoplasm and nucleus of transfected cells. These studies indicate that the ORF-E transcript is consistently expressed during latency. We suggest that the ORF-E gene regulates some aspect of the latency reactivation cycle.

Infection of cattle with a bovine herpesvirus 1 strain that contains a mutation in the latency-related gene leads to increased apoptosis in trigeminal ganglia during the transition from acute infection to latency

Bovine herpesvirus 1 (BHV-1) is an important pathogen of cattle and infection is usually initiated via the ocular or nasal cavity. After acute infection, the primary site for BHV-1 latency is sensory neurons in the trigeminal ganglia (TG). Reactivation from latency occurs sporadically, resulting in virus shedding and transmission to uninfected cattle. The only abundant viral transcript expressed during latency is the latency-related (LR) RNA. An LR mutant was constructed by inserting three stop codons near the beginning of the LR RNA. This mutant grows to wild-type (wt) efficiency in bovine kidney cells and in the nasal cavity of acutely infected calves. However, shedding of infectious virus from the eye and TG was dramatically reduced in calves infected with the LR mutant. Calves latently infected with the LR mutant do not reactivate after dexamethasone treatment. In contrast, all calves latently infected with wt BHV-1 or the LR rescued mutant reactivate from latency after dexamethasone treatment. In the present study, we compared the frequency of apoptosis in calves infected with the LR mutant to calves infected with wt BHV-1 because LR gene products inhibit apoptosis in transiently transfected cells. A sensitive TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay and an antibody that detects cleaved caspase-3 were used to identify apoptotic cells in TG. Both assays demonstrated that calves infected with the LR mutant for 14 days had higher levels of apoptosis in TG compared to calves infected with wt BHV-1 or to mock-infected calves. Viral gene expression, except for the LR gene, is extinguished by 14 days after infection, and thus this time frame is operationally defined as the establishment of latency. Real-time PCR analysis indicated that lower levels of viral DNA were present in the TG of calves infected with the LR mutant throughout acute infection. Taken together, these results suggest that the antiapoptotic properties of the LR gene play an important role during the establishment of latency.

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.