Bovine herpesvirus 1 downregulates the expression of bovine MHC class I molecules

Specificity protein 1 (Sp1) and glucocorticoid receptor (GR) stimulate bovine alphaherpesvirus 1 (BoHV-1) replication and cooperatively transactivate the immediate early transcription unit 1 promoter

Bovine alphaherpesvirus 1 (BoHV-1) infections cause respiratory tract disorders and suppress immune responses, which can culminate in bacterial pneumonia. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons present in trigeminal ganglia (TG) and unknown cells in pharyngeal tonsil. Latently infected calves consistently reactivate from latency after an intravenous injection of the synthetic corticosteroid dexamethasone (DEX), which mimics the effects of stress. The immediate early transcription unit 1 (IEtu1) promoter drives expression of infected cell protein 0 (bICP0) and bICP4, two key viral transcriptional regulators. The IEtu1 promoter contains two functional glucocorticoid receptor (GR) response elements (GREs), and this promoter is transactivated by GR, DEX, and certain Krüppel transcription factors that interact with GC-rich motifs, including consensus specificity protein 1 (Sp1) binding sites. Based on these observations, we hypothesized that Sp1 stimulates productive infection and transactivates key BoHV-1 promoters. DEX treatment of latently infected calves increased the number of Sp1+ TG neurons and cells in pharyngeal tonsil indicating that Sp1 expression is induced by stress. Silencing Sp1 protein expression with siRNA or mithramycin A, a drug that preferentially binds GC-rich DNA, significantly reduced BoHV-1 replication. Moreover, BoHV-1 infection of permissive cells increased Sp1 steady-state protein levels. In transient transfection studies, GR and Sp1 cooperatively transactivate IEtu1 promoter activity unless both GREs are mutated. Co-immunoprecipitation studies revealed that GR and Sp1 interact in mouse neuroblastoma cells (Neuro-2A) suggesting this interaction stimulates IEtu1 promoter activity. Collectively, these studies suggested that the cellular transcription factor Sp1 enhances productive infection and stress-induced BoHV-1 reactivation from latency.IMPORTANCEFollowing acute infection, bovine alphaherpesvirus 1 (BoHV-1) establishes lifelong latency in sensory neurons in trigeminal ganglia (TG) and pharyngeal tonsil. The synthetic corticosteroid dexamethasone consistently induces BoHV-1 reactivation from latency. The number of TG neurons and cells in pharyngeal tonsil expressing the cellular transcription factor specificity protein 1 (Sp1) protein increases during early stages of dexamethasone-induced reactivation from latency. Silencing Sp1 expression impairs BoHV-1 replication in permissive cells. Interestingly, mithramycin A, a neuroprotective antibiotic that preferentially binds GC-rich DNA, impairs Sp1 functions and reduces BoHV-1 replication suggesting that it is a potential antiviral drug. The glucocorticoid receptor (GR) and Sp1 cooperatively transactivate the BoHV-1 immediate early transcript unit 1 (IEtu1) promoter, which drives expression of infected cell protein 0 (bICP0) and bICP4. Mithramycin A also reduced Sp1- and GR-mediated transactivation of the IEtu1 promoter. These studies revealed that GR and Sp1 trigger viral gene expression and replication following stressful stimuli.

The Bovine Herpesvirus 1 Latency-Reactivation Cycle, a Chronic Problem in the Cattle Industry

Bovine alphaherpesvirus 1 (BoHV-1) is a persistent and recurring disease that affects cattle worldwide. It is a major contributor to bovine respiratory disease and reproductive failure in the US. A major complication of BoHV-1 arises from the lifelong latent infection established in the sensory ganglia of the peripheral nervous system following acute infection. Lifelong latency is marked by periodic reactivation from latency that leads to virus transmission and transient immunosuppression. Physiological and environmental stress, along with hormone fluctuations, can drive virus reactivation from latency, allowing the virus to spread rapidly. This review discusses the mechanisms of the latency/reactivation cycle, with particular emphasis on how different hormones directly regulate BoHV-1 gene expression and productive infection. Glucocorticoids, including the synthetic corticosteroid dexamethasone, are major effectors of the stress response. Stress directly regulates BoHV-1 gene expression through multiple pathways, including β-catenin dependent Wnt signaling, and the glucocorticoid receptor. Related type 1 nuclear hormone receptors, the androgen and progesterone receptors, also drive BoHV-1 gene expression and productive infection. These receptors form feed-forward transcription loops with the stress-induced Krüppel-like transcription factors KLF4 and KLF15. Understanding these molecular pathways is critical for developing novel therapeutics designed to block reactivation and reduce virus spread and disease.

The Bacterial and Viral Agents of BRDC: Immune Evasion and Vaccine Developments

Bovine respiratory disease complex (BRDC) is a multifactorial disease of cattle which presents as bacterial and viral pneumonia. The causative agents of BRDC work in synergy to suppress the host immune response and increase the colonisation of the lower respiratory tracts by pathogenic bacteria. Environmental stress and/or viral infection predispose cattle to secondary bacterial infections via suppression of key innate and adaptive immune mechanisms. This allows bacteria to descend the respiratory tract unchallenged. BRDC is the costliest disease among feedlot cattle, and whilst vaccines exist for individual pathogens, there is still a lack of evidence for the efficacy of these vaccines and uncertainty surrounding the optimum timing of delivery. This review outlines the immunosuppressive actions of the individual pathogens involved in BRDC and highlights the key issues in the development of vaccinations against them.

Cooperative activation of bovine herpesvirus 1 productive infection and viral regulatory promoters by androgen receptor and Krüppel-like transcription factors 4 and 15

Bovine herpesvirus 1 (BoHV-1), a significant viral pathogen, establishes latency in sensory neurons. The viral genome contains more than 100 consensus glucocorticoid receptor (GR) regulatory elements (GREs): consequently, stress stimulates viral replication and reactivation from latency. The immediate early transcription unit 1 (IEtu1) and bICP0 early promoters are transactivated by GR and synthetic corticosteroid dexamethasone. The androgen receptor (AR), like GR, is a Type 1 nuclear hormone receptor that binds and stimulates certain promoters containing GREs. Consequently, we hypothesized AR and 5α-Dihydrotestosterone (DHT) stimulate productive infection and key viral promoters. New studies demonstrated AR, DHT, and Krüppel like transcription factor 4 (KLF4) cooperatively stimulated productive infection and bICP0 E promoter activity in mouse neuroblastoma cells (Neuro-2A). KLF15 also cooperated with AR and DHT to stimulate IEtu1 promoter activity. We suggest AR and testosterone increase the prevalence of virus in semen by stimulating viral gene expression and replication.

An Improved DNA Vaccine Against Bovine Herpesvirus-1 Using CD40L and a Chemical Adjuvant Induces Specific Cytotoxicity in Mice

Bovine herpesvirus-1 (BoHV-1) uses many mechanisms to elude the immune system; one of them is spreading intracellularly, even in the presence of specific antiviral antibodies. Cytotoxic T lymphocytes (CTLs) are necessary to eliminate the virus. The main preventive strategy is vaccination based on inactivated virus. These vaccines are poor inducers of cellular immune responses, and complicate serological diagnosis and determination of the real prevalence of infection. DNA vaccines are a good option because of the capacity of Differentiating Infected from Vaccinated Animals-(DIVA vaccine)-and may be the best way to induce cytotoxic responses. Although this type of vaccines leads to only weak "in vivo" expression and poor immune responses, incorporation of molecular and/or chemical adjuvants can improve the latter, both in magnitude and in direction. In this study, we have investigated the specific immune responses elicited in mice by DNA vaccines based on the BoHV-1 glycoprotein D (pCIgD) with and without two different adjuvants: a plasmid encoding for murine CD40L (pCD40L) or Montanide™ 1113101PR (101). Mice vaccinated with pCIgD⁺CD40L, pCIgD⁺101, and pCIgD⁺CD40L⁺101 developed significantly higher specific antibody titers against BoHV-1 than the pCIgD group (p < 0.01). The animals vaccinated with pCgD⁺pCD40L⁺101 raised significantly higher levels of IgG2a and IgG2b (p < 0.01 and p < 0.001, respectively) than mice vaccinated with pCIgD alone. On the contrary, when the activity of CTL against cells infected with BoHV-1 was measured, the vaccine pCgD⁺pCD40L⁺101 induced significantly higher levels of cytotoxicity activity (p < 0.001) than pCIgD alone. A significant increase in the CD4⁺ populations in the group receiving pCIgD⁺CD40L⁺101 in comparison with the pCIgD group was observed and, also, interferon gamma, interleukin (IL)-6, and IL-17A levels were higher. Considering the results obtained from this study for humoral and cellular responses in mice, the inclusion of pCD40L and 101 as adjuvants in a BoHV-1 DNA vaccine for cattle is highly recommendable.

Alphaherpesvirus gB Homologs Are Targeted to Extracellular Vesicles, but They Differentially Affect MHC Class II Molecules

Herpesvirus envelope glycoprotein B (gB) is one of the best-documented extracellular vesicle (EVs)-incorporated viral proteins. Regarding the sequence and structure conservation between gB homologs, we asked whether bovine herpesvirus-1 (BoHV-1) and pseudorabies virus (PRV)-encoded gB share the property of herpes simplex-1 (HSV-1) gB to be trafficked to EVs and affect major histocompatibility complex (MHC) class II. Our data highlight some conserved and differential features of the three gBs. We demonstrate that mature, fully processed BoHV-1 and PRV gBs localize to EVs isolated from constructed stable cell lines and EVs-enriched fractions from virus-infected cells. gB also shares the ability to co-localize with CD63 and MHC II in late endosomes. However, we report here a differential effect of the HSV-1, BoHV-1, and PRV glycoprotein on the surface MHC II levels, and MHC II loading to EVs in stable cell lines, which may result from their adverse ability to bind HLA-DR, with PRV gB being the most divergent. BoHV-1 and HSV-1 gB could retard HLA-DR exports to the plasma membrane. Our results confirm that the differential effect of gB on MHC II may require various mechanisms, either dependent on its complex formation or on inducing general alterations to the vesicular transport. EVs from virus-infected cells also contained other viral glycoproteins, like gD or gE, and they were enriched in MHC II. As shown for BoHV-1 gB- or BoHV-1-infected cell-derived vesicles, those EVs could bind anti-virus antibodies in ELISA, which supports the immunoregulatory potential of alphaherpesvirus gB.

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.

Proteogenomic Identification of a Novel Protein-Encoding Gene in Bovine Herpesvirus 1 That Is Expressed during Productive Infection

Bovine herpesvirus 1 (BoHV-1) is one of several microbes that contributes to the development of the bovine respiratory disease (BRD) and can also induce abortions in cattle. As other alpha-herpesvirinae subfamily members, BoHV-1 efficiently replicates in many cell types and subsequently establishes a life-long latent infection in sensory neurons. BoHV-1 encodes more than 70 proteins that are expressed in a well-defined manner during productive infection. However, in silico open reading frame (ORF) prediction of the BoHV-1 genome suggests that the virus may encode more than one hundred proteins. In this study we used mass spectrometry followed by proteogenomic mapping to reveal the existence of 92 peptides that map to previously un-annotated regions of the viral genome. Twenty-one of the newly termed “intergenic peptides” were predicted to have a viable ORF around them. Twelve of these produced an mRNA transcript as demonstrated by strand-specific RT-PCR. We further characterized the 5′ and 3′ termini of one mRNA transcript, ORF-A, and detected a 55 kDa protein produced during active infection using a custom-synthesized antibody. We conclude that the coding potential of BoHV-1 is underestimated.

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.

Protein Composition of the Bovine Herpesvirus 1.1 Virion

Bovine herpesvirus (BoHV) type 1 is an important agricultural pathogen that infects cattle and other ruminants worldwide. Acute infection of the oro-respiratory tract leads to immune suppression and allows commensal bacteria to infect an otherwise healthy lower respiratory tract. This condition is known as the Bovine Respiratory Disease (BRD). BoHV-1 latently infects the host for life and periodical stress events re-initiate BRD, translating into high morbidity and large economic losses. To gain a better understanding of the biology of BoHV-1 and the disease it causes, we elucidated the protein composition of extracellular virions using liquid chromatography-mass spectrometry analysis. We detected 33 viral proteins, including the expected proteins of the nucleocapsid and envelope as well as other regulatory proteins present in the viral tegument. In addition to viral proteins, we have also identified packaged proteins of host origin. This constitutes the first proteomic characterization of the BoHV virion.

A DNA Vaccine Formulated with Chemical Adjuvant Provides Partial Protection against Bovine Herpes Virus Infection in Cattle

Bovine herpesvirus-1 (BoHV-1) is the causative agent of bovine infectious rhinotracheitis, an important disease worldwide. Although conventional BoHV-1 vaccines, including those based on the use of modified live virus and also inactivated vaccines, are currently used in many countries, they have several disadvantages. DNA vaccines have emerged as an attractive approach since they have the potential to induce both humoral and cellular immune response; nevertheless, it is largely known that potency of naked DNA vaccines is limited. We demonstrated previously, in the murine model, that the use of adjuvants in combination with a DNA vaccine against BoHV-1 is immunologically beneficial. In this study, we evaluate the immune response and protection against challenge elicited in bovines, by a DNA vaccine carrying the sequence of secreted version of glycoprotein D (gD) of BoHV-1 formulated with chemical adjuvants. Bovines were vaccinated with formulations containing the sequence of gD alone or in combination with adjuvants ESSAI 903110 or Montanide™ 1113101PR. After prime vaccination and two boosters, animals were challenged with infectious BoHV-1. Formulations containing adjuvants Montanide™ 1113101PR and ESSAI 903110 were both, capable of increasing humoral immune response against the virus and diminishing clinical symptoms. Nevertheless, only formulations containing adjuvant Montanide™ 1113101PR was capable of improving cellular immune response and diminishing viral excretion. To our knowledge, it is the first time that a BoHV-1 DNA vaccine is combined with adjuvants and tested in cattle. These results could be useful to design a vaccine for the control of bovine rhinotracheitis.

Identification of an epitope within the Bovine herpesvirus 1 glycoprotein E cytoplasmic tail and use of a monoclonal antibody directed against the epitope for the differentiation between vaccinated and infected animals

We constructed a recombinant bovine herpesvirus type 1 triple mutant virus (BoHV-1 tmv) that lacks UL49.5 residues 30-32 and 80-96, gE cytoplasmic tail (gE CT) residues 452-575 and the entire 435 bp long Us9 ORF. To develop a gE CT-specific blocking ELISA test that is necessary to distinguish the BoHV-1 tmv vaccinated calves from the wild-type (wt) virus-infected calves, a mouse monoclonal antibody (mAb) 2H8F3 was generated by using the Escherichia coli expressed gE CT residues 452-575. Further, by performing a PEPSCAN analysis of 12 mer overlapping peptides spanning the entire gE CT, the epitope sequence recognized by the mAb2H8F3 was mapped within the gE CT residues 499SDDDGPASN507. A blocking ELISA test was then developed for detecting antibodies in wild-type BoHV-1 infected calves against the gE CT epitope specified by 499SDDDGPASN507. The assay is based on the use of HRP conjugated mAb2H8F3 and the E. coli expressed gE CT protein as an indicator antibody and a coating antigen, respectively. In this assay, serum from entire gE-deleted and BoHV-1 tmv-infected calves scored negative, whereas serum from calves infected with BoHV-1 wt scored positive. Therefore, the gE CT-ELISA, based on the mAb2H8F3 and E. coli expressed gE CT protein, is suitable for differentiating the wt virus-infected and BoHV-1 tmv-vaccinated cattle.

Oncolytic bovine herpesvirus type 1 as a broad spectrum cancer therapeutic

Oncolytic viruses selectively replicate in tumor cells and elicit antitumor effects in vivo by both direct and indirect methods. They are attractive avenues of cancer therapy due to the absence of toxic side effects often seen in current treatment modalities. Bovine herpesvirus type 1 (BHV-1) holds promise as a broad-spectrum oncolytic vector that is able to infect and kill human tumor cells from a variety of histological origins, including cancer-initiating cells. In the majority of cases, BHV-1 elicits tumor cell death in the absence of a productive infection. In vivo, BHV-1 affects the incidence of secondary lesions in cotton rats bearing subcutaneous breast adenocarcinomas. These recent studies contribute to the characterization of BHV-1 as an oncolytic virus.

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.

Equine herpesvirus type 1 (EHV-1) open reading frame 59 encodes an early protein that is localized to the cytosol and required for efficient virus growth

Equine herpesvirus type 1 (EHV-1) ORF59 is predicted to encode a protein consisting of 180 amino acids. To determine whether ORF59 in fact encodes a protein, sequences encoding an HA epitope (YPYDVPDYA) was inserted at the carboxyterminus of the ORF59 protein in EHV-1 strain Ab4. Using anti-HA monoclonal antibodies, a 21-kDa band was specifically detected by western blot analysis in lysates of cells infected with a recombinant EHV-1 from strain Ab4 that carries the pORF59-HA but not in cells infected with parental Ab4. Further characterization of the protein using immunofluorescence and fractionation studies showed that pORF59 is an early protein that localizes to the cytosol in virus-infected cells. Recombinant EHV-1 lacking ORF59 (rAb4∆59) exhibited a small-plaque phenotype and could not be propagated. Our findings suggest that the ORF59 protein plays a major role in EHV-1 replication in vitro and likely in vivo.

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.

Bovine Herpes Virus 1 (BHV-1) and Herpes Simplex Virus Type 1 (HSV-1) Promote Survival of Latently Infected Sensory Neurons, in Part by Inhibiting Apoptosis

α-Herpesvirinae subfamily members, including herpes simplex virus type 1 (HSV-1) and bovine herpes virus 1 (BHV-1), initiate infection in mucosal surfaces. BHV-1 and HSV-1 enter sensory neurons by cell-cell spread where a burst of viral gene expression occurs. When compared to non-neuronal cells, viral gene expression is quickly extinguished in sensory neurons resulting in neuronal survival and latency. The HSV-1 latency associated transcript (LAT), which is abundantly expressed in latently infected neurons, inhibits apoptosis, viral transcription, and productive infection, and directly or indirectly enhances reactivation from latency in small animal models. Three anti-apoptosis genes can be substituted for LAT, which will restore wild type levels of reactivation from latency to a LAT null mutant virus. Two small non-coding RNAs encoded by LAT possess anti-apoptosis functions in transfected cells. The BHV-1 latency related RNA (LR-RNA), like LAT, is abundantly expressed during latency. The LR-RNA encodes a protein (ORF2) and two microRNAs that are expressed in certain latently infected neurons. Wild-type expression of LR gene products is required for stress-induced reactivation from latency in cattle. ORF2 has anti-apoptosis functions and interacts with certain cellular transcription factors that stimulate viral transcription and productive infection. ORF2 is predicted to promote survival of infected neurons by inhibiting apoptosis and sequestering cellular transcription factors which stimulate productive infection. In addition, the LR encoded microRNAs inhibit viral transcription and apoptosis. In summary, the ability of BHV-1 and HSV-1 to interfere with apoptosis and productive infection in sensory neurons is crucial for the life-long latency-reactivation cycle in their respective hosts.

Non-classical major histocompatibility complex class makes a crucial contribution to reproduction in the dairy cow

The aim of this study was to evaluate the effect of classical and non-classical major histocompatibility complex (MHC) on the reproduction in the dairy cow. Nine pairs of MHC-I genes were chosen according to their homology and possible function, and their transcription levels in maternal peripheral blood mononuclear cells (PBMCs) from all three trimesters and transcription levels in fetal tissues were compared to evaluate their contributions to cattle reproduction. The results showed that three non-classical genes were variably expressed in PBMCs of pregnant cows. MICB was downregulated in the first and second trimesters (P<0.05), but recovered back to the level in replacement heifers in the last trimester (P>0.05). BoLA-NC1* was upregulated in the first and last trimesters (P<0.001) but no different in the second trimester (P>0.05). BoLA-NC3* was upregulated in all trimesters (P<0.001). On the other hand, MICB was upregulated in fetal ear tissues (P<0.001), and BoLA-NC1* was almost silent in both fetal placenta and ear tissues (P<0.001); however, BoLA-NC3* was upregulated in both the fetal placenta and ear tissues (P<0.001). These results suggested that non-classical gene BoLA-NC1* increased maternal immunity against the fetus, which was inhibited by BoLA-NC3*. BoLA-NC3* also inhibited fetal autoimmunity. Apoptosis of the fetal placenta could reduce itself expressing MICB, and upregulated expression of MICB in ear tissues was favorable for the fetus to escape autoimmunity. On the other hand, downregulated expression of MICB in the fetal placenta allows for placental decoherence from the maternal placentome, which was beneficial to fetus delivery. Although classical genes were expressed differentially, their effects were restricted because of heavy chain deficiency.

Equine herpesvirus type 4 UL56 and UL49.5 proteins downregulate cell surface major histocompatibility complex class I expression independently of each other

Major histocompatibility complex class I (MHC-I) molecules are critically important in the host defense against various pathogens through presentation of viral peptides to cytotoxic T lymphocytes (CTLs), a process resulting in the destruction of virus-infected cells. Herpesviruses interfere with CTL-mediated elimination of infected cells by various mechanisms, including inhibition of peptide transport and loading, perturbation of MHC-I trafficking, and rerouting and proteolysis of cell surface MHC-I. In this study, we show that equine herpesvirus type 4 (EHV-4) modulates MHC-I cell surface expression through two different mechanisms. First, EHV-4 can lead to a significant downregulation of MHC-I expression at the cell surface through the product of ORF1, a protein expressed with early kinetics from a gene that is homologous to herpes simplex virus 1 UL56. The EHV-4 UL56 protein reduces cell surface MHC-I as early as 4 h after infection. Second, EHV-4 can interfere with MHC-I antigen presentation, starting at 6 h after infection, by inhibition of the transporter associated with antigen processing (TAP) through its UL49.5 protein. Although pUL49.5 has no immediate effect on overall surface MHC-I levels in infected cells, it blocks the supply of antigenic peptides to the endoplasmic reticulum (ER) and transport of peptide-loaded MHC-I to the cell surface. Taken together, our results show that EHV-4 encodes at least two viral immune evasion proteins: pUL56 reduces MHC-I molecules on the cell surface at early times after infection, and pUL49.5 interferes with MHC-I antigen presentation by blocking peptide transport in the ER.

Immunogenicity of a bovine herpes virus I peptide expressed in tandem copies in attenuated Salmonella

A live system to release heterologous antigens using an attenuated Salmonella strain was developed. We transformed Salmonella typhimurium LVR03 (S. LVR03) with a recombinant pTECH2 vector encoding 0, 1, 2, and 4 tandem copies of an imunogenic peptide of bovine herpes virus-1 (BoHV-1) glycoprotein D (gD). The system used yielded peptides fused to the non-toxic C fragment of the tetanus toxin (TetC), which has been shown to have adjuvant properties. Inoculation of BALB/c mice with the transformed Salmonella strains gave rise to a mild self-limited infection, with primary replication of bacteria occurring in Peyer's patches, even when the bacteria was administered intranasally. Humoral and cellular immune responses directed against the BoHV-1 antigens were evaluated after oral or intranasal administration of the recombinant bacteria. The results showed that the S. LVR03-dimer vaccine induced specific humoral (IgG in serum and IgG(1) and IgA in saliva), and cellular immune responses (lymphoproliferation and lymphokine secretion), against not only the selected peptide and whole gD, but also against BoHV-1, when administered intranasally. This is the first time Salmonella has been used as an expression vector to induce immunity against BoHV-1. This work demonstrates the feasibility of using this antigen-release system and encourages future experimentation with a bovine experimental model.

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.

Localization of sequences in a protein (ORF2) encoded by the latency-related gene of bovine herpesvirus 1 that inhibits apoptosis and interferes with Notch1-mediated trans-activation of the bICP0 promoter

Bovine herpesvirus 1 (BHV-1) infection induces clinical symptoms in the upper respiratory tract, inhibits immune responses, and can result in life-threatening secondary bacterial infections. Following acute infection, BHV-1 establishes latency in sensory neurons within trigeminal ganglia. Periodically, reactivation from latency occurs, resulting in virus transmission. The latency-related (LR) RNA is abundantly expressed in latently infected sensory neurons, suggesting that LR gene products regulate the latency-reactivation cycle. An LR mutant virus with stop codons at the amino terminus of the first open reading frame (ORF) in the LR gene (ORF2) does not reactivate 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 an important role in the latency-reactivation cycle. ORF2 also interacts with Notch1 or Notch3 and consequently inhibits their ability to trans-activate the bICP0 early and glycoprotein C promoters. In this study, we identified ORF2 sequences that were necessary for inhibiting cold shock-induced apoptosis or Notch1-mediated trans-activation of the bICP0 early promoter and stimulation of productive infection. Relative to ORF2 sequences necessary for inhibiting apoptosis, distinct domains in ORF2 were important for interfering with Notch1-mediated trans-activation. Five consensus protein kinase A and/or protein kinase C phosphorylation sites within ORF2 regulate the steady-state levels of ORF2 in transfected cells. A nuclear localization signal in ORF2 was necessary for inhibiting Notch1-mediated trans-activation but not apoptosis. In summary, ORF2 has more than one functional domain that regulates its stability and functional properties.

Cytoplasmic localized infected cell protein 0 (bICP0) encoded by bovine herpesvirus 1 inhibits β interferon promoter activity and reduces IRF3 (interferon response factor 3) protein levels

Bovine herpesvirus 1 (BHV-1), an alpha-herpesvirinae subfamily member, establishes a life-long latent infection in sensory neurons. Periodically, BHV-1 reactivates from latency, infectious virus is spread, and consequently virus transmission occurs. BHV-1 acute infection causes upper respiratory track infections and conjunctivitis in infected cattle. As a result of transient immune-suppression, BHV-1 infections can also lead to life-threatening secondary bacterial pneumonia that is referred to as bovine respiratory disease. The infected cell protein 0 (bICP0) encoded by BHV-1 reduces human β-interferon (IFN-β) promoter activity, in part, by inducing degradation of interferon response factor 3 (IRF3) and interacting with IRF7. In contrast to humans, cattle contain three IFN-β genes. All three bovine IFN-β proteins have anti-viral activity: but each IFN-β gene has a distinct transcriptional promoter. We have recently cloned and characterized the three bovine IFN-β promoters. Relative to the human IFN-β promoter, each of the three IFN-β promoters contain differences in the four positive regulatory domains that are required for virus-induced activity. In this study, we demonstrate that bICP0 effectively inhibits bovine IFN-β promoter activity following transfection of low passage bovine cells with interferon response factor 3 (IRF3) or IRF7. A bICP0 mutant that localizes to the cytoplasm inhibits bovine IFN-β promoter activity as efficiently as wt bICP0. The cytoplasmic localized bICP0 protein also induced IRF3 degradation with similar efficiency as wt bICP0. In summary, these studies suggested that cytoplasmic localized bICP0 plays a role in inhibiting the IFN-β response during productive infection.

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

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

Loss of plasmacytoid dendritic cell function coincides with lymphopenia and viremia during foot-and-mouth disease virus infection

Foot-and-mouth disease virus (FMDV) causes an acute, highly contagious disease of livestock. Though FMDV is very sensitive to interferon-alpha (IFN-alpha), IFN-beta, and IFN-gamma, the virus has evolved mechanisms to evade such innate responses. For instance, during acute infection, FMDV suppresses IFN-alpha production by skin and myeloid dendritic cells (DCs). We have previously reported that FMDV infection induces a transient lymphopenia and interruption of T-lymphocyte responses to mitogenic stimuli. To further understand the immunopathogenesis of FMD, we have now analyzed the serum IFN-alpha response in relation to lymphopenia, and the number and function of plasmacytoid DCs (pDCs) following infection of pigs with multiple serotypes of FMDV. Serum IFN-alpha peaked 2-3 d post-infection (PI), regardless of FMDV serotype. Lymphopenia coincided with peak viremia and the serum IFN-alpha response. Circulating pDC numbers and in-vitro pDC IFN-alpha secretion transiently declined by 48 h following infection. Infection of lymphocytes or pDCs was never detected regardless of the FMDV serotype inoculated or the age of the animal infected. These data indicate that, like other DC subsets, there is suppression of interferon production by pDCs, which abrogates this important innate response. Rapid induction of serum IFN-alpha, albeit short-lived, may contribute to the rapid resolution of FMDV viremia prior to induction of specific immunity.

Regulation of Innate Immune Responses by Bovine Herpesvirus 1 and Infected Cell Protein 0 (bICP0)

Bovine herpesvirus 1 (BoHV-1) infected cell protein 0 (bICP0) is an important transcriptional regulatory protein that stimulates productive infection. In transient transfection assays, bICP0 also inhibits interferon dependent transcription. bICP0 can induce degradation of interferon stimulatory factor 3 (IRF3), a cellular transcription factor that is crucial for activating beta interferon (IFN-β) promoter activity. Recent studies also concluded that interactions between bICP0 and IRF7 inhibit trans-activation of IFN-β promoter activity. The C3HC4 zinc RING (really important new gene) finger located near the amino terminus of bICP0 is important for all known functions of bICP0. A recombinant virus that contains a single amino acid change in a well conserved cysteine residue of the C3HC4 zinc RING finger of bICP0 grows poorly in cultured cells, and does not reactivate from latency in cattle confirming that the C3HC4 zinc RING finger is crucial for viral growth and pathogenesis. A bICP0 deletion mutant does not induce plaques in permissive cells, but induces autophagy in a cell type dependent manner. In summary, the ability of bICP0 to stimulate productive infection, and repress IFN dependent transcription plays a crucial role in the BoHV-1 infection cycle.

Feline herpesvirus-1 down-regulates MHC class I expression in an homologous cell system

Cytotoxic T lymphocytes (CTLs) are an essential component of the immune defense against many virus infections. CTLs recognize viral peptides in the context of the major histocompatibility complex (MHC) class I molecules on the surface of infected cells. Many viruses have evolved mechanisms to interfere with MHC class I expression as a means of evading the host immune response. In the present research we have studied the effect of in vitro Feline Herpesvirus 1 (FeHV-1) infection on MHC class I expression. The results of this study demonstrate that FeHV-1 down regulates surface expression of MHC class I molecules on infected cells, presumably to evade cytotoxic T-cell recognition and, perhaps, attenuate induction of immunity. Sensitivity to UV irradiation and insensitivity to a viral DNA synthesis inhibitor, like phosphonacetic acid, revealed that immediate early or early viral gene(s) are responsible. Use of the protein translation inhibitor cycloheximide confirmed that an early gene is primarily responsible.

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.

Immune evasion by pathogens of bovine respiratory disease complex

Bovine respiratory tract disease is a multi-factorial disease complex involving several viruses and bacteria. Viruses that play prominent roles in causing the bovine respiratory disease complex include bovine herpesvirus-1, bovine respiratory syncytial virus, bovine viral diarrhea virus and parinfluenza-3 virus. Bacteria that play prominent roles in this disease complex are Mannheimia haemolytica and Mycoplasma bovis. Other bacteria that infect the bovine respiratory tract of cattle are Histophilus (Haemophilus) somni and Pasteurella multocida. Frequently, severe respiratory tract disease in cattle is associated with concurrent infections of these pathogens. Like other pathogens, the viral and bacterial pathogens of this disease complex have co-evolved with their hosts over millions of years. As much as the hosts have diversified and fine-tuned the components of their immune system, the pathogens have also evolved diverse and sophisticated strategies to evade the host immune responses. These pathogens have developed intricate mechanisms to thwart both the innate and adaptive arms of the immune responses of their hosts. This review presents an overview of the strategies by which the pathogens suppress host immune responses, as well as the strategies by which the pathogens modify themselves or their locations in the host to evade host immune responses. These immune evasion strategies likely contribute to the failure of currently-available vaccines to provide complete protection to cattle against these pathogens.

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.

Bovine herpesvirus 1 infection and infectious bovine rhinotracheitis

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

The cell-mediated immune response induced by plasmid encoding bovine herpesvirus 1 glycoprotein B is enhanced by plasmid encoding IL-12 when delivered intramuscularly or by gene gun, but not after intradermal injection

Bovine herpesvirus 1 (BHV-1) causes respiratory and genital infections in cattle. Previously we demonstrated that a DNA vaccine encoding a truncated, secreted form of BHV-1 glycoprotein B (tgB) induces cytotoxic T lymphocyte (CTL) responses in C3H mice. In this study we investigated the potential of interleukin 12 (IL-12) to further enhance the CTL response. C3H mice were immunized with a plasmid encoding tgB or with plasmids encoding tgB and murine IL-12. When the plasmid encoding tgB was delivered intramuscularly or epidermally by a gene gun, co-administration with IL-12 plasmid stimulated the synthesis of more IgG2a, the production of higher levels of IFN-gamma, and more effective killing by CTLs. In contrast, after intradermal delivery no effect of co-administration of IL-12 encoding plasmid was observed. Further investigation suggested that antigen and IL-12 need to be expressed in the draining lymph nodes, where IL-12 can have a direct effect on T cells.

Localization of sequences within the latency-related gene of bovine herpesvirus 1 that inhibit mammalian cell growth

The latency-related (LR) RNA of bovine herpes virus 1 (BHV-1) is abundantly expressed in sensory neurons of latently infected cattle. Wild-type expression of LR gene products is required for the latency-reactivation cycle. LR gene products inhibit apoptosis, bICP0 expression, and mammalian cell growth. The cell growth inhibitory function of the LR gene maps to a 463-bp XbaI-PstI fragment. Introduction of stop codons into the XbaI-PstI fragment had no effect on inhibiting growth. Expression of a LR strand-specific transcript correlates with growth inhibition in bovine fibroblasts and mouse neuroblastoma cells.

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.

Viral interference with MHC class I antigen presentation pathway: the battle continues

CD8+ cytotoxic T lymphocytes (CTLs) play a critical role in the defense against viral infections. In general, CD8+ CTLs recognize antigenic peptides in the context of the major histocompatibility complex (MHC) class I molecule. The MHC class I molecules are expressed on almost all the nucleated cells in the body. The trimolecular complex consisting of the class I heavy chain, beta2-microglobulin and the peptide are generated by the MHC class I antigen presentation pathway. This pathway is designed to sample the intracellular milieu and present the information to the CTLs trafficking the area. This rigorous sampling of intracellular environment enables the CTLs to quickly identify and eliminate the cells that synthesize non-self proteins as a result of a viral infection. Many viruses, including several viruses of veterinary importance, have evolved astounding strategies to interfere with the MHC class I antigen presentation pathway, as a means of evading the CTL response of the host. This review focuses on the diverse mechanisms of viral evasion of the MHC class I antigen presentation pathway with particular emphasis on viruses of veterinary importance.

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.

Immunization with a bovine herpesvirus 1 glycoprotein B DNA vaccine induces cytotoxic T-lymphocyte responses in mice and cattle

Virus-specific cytotoxic T lymphocytes (CTLs) are considered to be important in protection against and recovery from viral infections. In this study, several approaches to induce cytotoxicity against bovine herpesvirus 1 (BHV-1) were evaluated. Vaccination of C57BL/6 mice with BHV-1 induced a strong humoral, but no CTL, response, which may be due to downregulation of major histocompatibility complex class I molecules. In contrast, vaccinia virus expressing glycoprotein B (gB) elicited a weaker antibody response, but strong cytotoxicity, in mice. As an approach to inducing both strong humoral and cellular immune responses, a plasmid vector was then used to express gB. Both antibody and CTL responses were induced by the plasmid encoding gB in C57BL/6 and C3H mice, regardless of the type of vector backbone. This demonstrated that DNA immunization induces a broad-based immune response to BHV-1 gB. Interestingly, removal of the membrane anchor, which resulted in secretion of gB from transfected cells, did not result in reduced cytotoxicity. Here, it is shown that, compared with the cell-associated counterpart, plasmid-encoded secreted protein may induce enhanced immune responses in cattle. Therefore, calves were immunized intradermally with pMASIAtgB, a plasmid encoding the secreted form of gB (tgB), using a needle-free injection system. This demonstrated that pMASIAtgB elicited both humoral responses and activated gamma interferon-secreting CD8+ CTLs, suggesting that a DNA vaccine expressing tgB induces a CTL response in the natural host of BHV-1.

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.

Bovine herpesvirus 1 VP22 enhances the efficacy of a DNA vaccine in cattle

For this study, the intercellular trafficking ability of bovine herpesvirus 1 (BHV-1) VP22 was applied to improve the efficacy of a DNA vaccine in calves. A plasmid encoding a truncated version of glycoprotein D (tgD) fused to VP22 was constructed. The plasmid encoding tgD-VP22 elicited significantly enhanced and more balanced immune responses than those induced by a plasmid encoding tgD. Furthermore, protection against a BHV-1 challenge was obtained in calves immunized with the plasmid encoding tgD-VP22, as shown by significant reductions in viral excretion. However, less significant protection was observed for animals vaccinated with the tgD-expressing plasmid, correlating with the lower level of immunity observed prechallenge. This is the first report of the use of VP22 as a transport molecule in the context of a DNA vaccine for a large animal species.

BHV-1 infection and inflammatory cytokines amplify the interaction of Mannheimia haemolytica leukotoxin with bovine peripheral blood mononuclear cells in vitro

Bovine herpesvirus-1 (BHV-1) has been reported to increase the susceptibility of cattle to respiratory disease caused by Mannheimia (Pasteurella) haemolytica A1. The principal virulence factor of M. haemolytica is a leukotoxin (LKT) that can specifically kill ruminant leukocytes following its binding to the beta2-integrin CD11a/CD18 (lymphocyte function-associated antigen 1 (LFA-1)). In this study, we investigated the effects of experimental infection of bovine peripheral blood mononuclear cells (MNCs) with BHV-1 in vitro, on the subsequent interaction of these cells with the M. haemolytica LKT. We found that BHV-1 infection increased LFA-1 expression (as assessed by flow cytometry), and subsequently enhanced LKT binding and cytotoxicity to bovine MNCs. We also found that BHV-1 infection increased CD18, IL-1beta, and IFN-gamma mRNA expression by MNCs. As previously reported for bovine polymorphonuclear neutrophils (PMNs), MNCs increased their expression of LFA-1, and their LKT binding and cytotoxicity, following exposure to IL-1beta, TNF-alpha, and IFN-gamma. These findings suggest that BHV-1 infection, and the resulting release of inflammatory cytokines, can stimulate expression of LFA-1 in bovine MNCs, thus enhancing the binding and biological effects of LKT. If such a mechanism occurs in vivo it might explain, in part, the increased susceptibility of BHV-1 infected cattle to bovine pasteurellosis.

A mutation in the latency-related gene of bovine herpesvirus 1 inhibits protein expression from open reading frame 2 and an adjacent reading frame during productive infection

The latency-related (LR) gene of bovine herpesvirus 1 (BHV-1) is abundantly expressed during latency. A mutant BHV-1 strain that contains three stop codons at the 5' terminus of the LR gene (LR mutant) does not reactivate from latency. This study demonstrates that the LR mutant does not express open reading frame 2 or an adjacent reading frame that lacks an initiating ATG (reading frame C). Since the LR mutant and wild-type BHV-1 express similar levels of LR RNA, we conclude that LR protein expression plays an important role in regulating the latency reactivation cycle in cattle.

Inhibition of TAP by pseudorabies virus is independent of its vhs activity

Previously we have shown that pseudorabies virus (PrV) down-regulates the expression of porcine MHC class I molecules by interfering with the transporter associated with antigen processing (TAP). During lytic PrV infection, the half-lives of both host and viral mRNA are regulated by the product of virion host shut-off (vhs) gene, UL41. PrV vhs protein induces degradation of cellular mRNA including those encoding class I and TAP. Therefore, further elucidation of specific mechanisms of down-regulation of class I molecules by PrV necessitates construction of a vhs deletion mutant. Two such mutants (vhsDelta1 and vhsDelta2) were generated by homologous recombination between the wild type (wt) PrV Indiana-F strain, and plasmids containing truncated UL41 gene of PrV into which the enhanced green fluorescent protein (EGFP) cassette was inserted. Compared with the wt virus, both the vhs mutants exhibited slower in vitro growth kinetics. The mutants, like the wt virus, inhibited the peptide transport activity of TAP and down-regulated cell surface expression of class I molecules. These findings suggest that, inhibition of TAP activity in PrV-infected cells is due to mechanism(s) specifically directed at class I pathway and not due to the non-specific vhs activity of the virus.

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.

Stimulation of bovine herpesvirus-1 productive infection by the adenovirus E1A gene and a cell cycle regulatory gene, E2F-4

Identifying cellular genes that promote bovine herpesvirus-1 (BHV-1) productive infection is important, as BHV-1 is a significant bovine pathogen. Previous studies demonstrated that BHV-1 DNA is not very infectious unless cotransfected with a plasmid expressing bICP0, a viral protein that stimulates expression of all classes of viral promoters. Based on these and other studies, we hypothesize that the ability of bICP0 to interact with and modify the function of cellular proteins stimulates virus transcription. If this prediction is correct, cellular proteins that activate virus transcription could, in part, substitute for bICP0 functions. The adenovirus E1A gene and bICP0 encode proteins that are potent activators of viral gene expression, they do not specifically bind DNA and both proteins interact with chromatin-remodelling enzymes. Because of these functional similarities, E1A was tested initially to see if it could stimulate BHV-1 productive infection. E1A consistently stimulates BHV-1 productive infection, but not as efficiently as bICP0. The ability of E1A to bind Rb family members plays a role in stimulating productive infection, suggesting that E2F family members activate productive infection. E2F-4, but not E2F-1, E2F-2 or E2F-5, activates productive infection with similar efficiency as E1A. Next, E2F family members were examined for their ability to activate the BHV-1 immediate-early (IE) transcription unit 1 (IEtu1) promoter, as it regulates IE expression of bICP0 and bICP4. E2F-1 and E2F-2 strongly activate the IEtu1 promoter, but not a BHV-1 IEtu2 promoter or a herpes simplex virus type 1 ICP0 promoter construct. These studies suggest that E2F family members can stimulate BHV-1 productive infection.

Effects of virion host shut-off activity of bovine herpesvirus 1 on MHC class I expression

Previously, we have shown that bovine herpesvirus 1 (BHV-1) down-regulates the expression of major histocompatibility complex class I molecules by interfering with transport of peptides by the transporter associated with antigen processing (TAP). Further studies revealed that BHV-1 down-regulates the expression of mRNA for class I molecules and other cellular proteins. To further elucidate the mechanisms of down-regulation of class I molecules, a virion host shut-off (vhs) deletion mutant was generated. The mutant, like the wildtype (wt) virus, interfered with transport of peptides by the TAP, and down-regulated cell surface expression of class I molecules. However, unlike the wt virus, the mutant did not impair the synthesis of class I molecules. These results indicate that down-regulation of class I molecules by BHV-1 is mediated by vhs activity of the virus, as well as mechanisms specifically directed at the class I pathway. Absence of vhs activity should result in decreased pathogenicity and enhanced immunogenicity of BHV-1 vhs deletion mutant, making it a better vaccine candidate.

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.

Down-regulation of surface major histocompatibility complex class I by guinea pig cytomegalovirus

Live attenuated strains of human cytomegalovirus are under development as vaccines to prevent birth defects resulting from congenital infections. These strains encode four proteins that inhibit surface expression of MHC class I, presumably to evade cytotoxic T-cell recognition and, perhaps, attenuate induction of immunity. To initiate studies of the role of class I down-regulation on congenital infection and vaccine efficacy, the ability of guinea pig cytomegalovirus to down-regulate class I was examined. Surface class I was specifically down-regulated on infected cells up to 8-fold. Sensitivity to UV irradiation and insensitivity to a viral DNA synthesis inhibitor revealed that immediate early or early viral gene(s) are responsible. Identification of these genes will permit future experiments to evaluate the role of class I down-regulation in congenital cytomegalovirus disease and its impact on vaccine efficacy. These findings should be pertinent to understanding human cytomegalovirus disease and may help guide the design of candidate vaccines.