Bovine herpesvirus 1 glycoprotein G is necessary for maintaining cell-to-cell junctional adherence among infected cells

The biology and development of vaccines for bovine herpesvirus 1

Bovine herpesvirus type 1 (BoAHV-1) infections lead to compromised herd health and significantly reduced productivity of affected cattle. While BoAHV-1 may cause rhinotracheitis, conjunctivitis, genital infections, and abortions, respiratory tract infections constitute the predominant clinical disease. Immune suppression induced by BoAHV-1 may contribute to co-infections initiating the bovine respiratory disease complex. In this review, the emphasis is to recapitulate the biology and the vaccine technologies currently in use and in development for BoAHV-1, and to discuss the major limitations. Studies on the life cycle and host interactions of BoAHV-1 have resulted in the identification of virulence factors. While several vaccine types, such as vectored vaccines and subunit vaccines, are under investigation, modified live and inactivated BoAHV-1 vaccines are still most frequently used in most areas of the world, whereas attenuated and inactivated marker vaccines are in use in Europe. The knowledge gained from studies on the biology of BoAHV-1 can form a basis for the rational design of future vaccines.

Infectious laryngotracheitis: Etiology, epidemiology, pathobiology, and advances in diagnosis and control - a comprehensive review

Infectious laryngotracheitis (ILT) is a highly contagious upper respiratory tract disease of chicken caused by a Gallid herpesvirus 1 (GaHV-1) belonging to the genus Iltovirus, and subfamily Alphaherpesvirinae within Herpesviridae family. The disease is characterized by conjunctivitis, sinusitis, oculo-nasal discharge, respiratory distress, bloody mucus, swollen orbital sinuses, high morbidity, considerable mortality and decreased egg production. It is well established in highly dense poultry producing areas of the world due to characteristic latency and carrier status of the virus. Co-infections with other respiratory pathogens and environmental factors adversely affect the respiratory system and prolong the course of the disease. Latently infected chickens are the primary source of ILT virus (ILTV) outbreaks irrespective of vaccination. Apart from conventional diagnostic methods including isolation and identification of ILTV, serological detection, advanced biotechnological tools such as PCR, quantitative real-time PCR, next generation sequencing, and others are being used in accurate diagnosis and epidemiological studies of ILTV. Vaccination is followed with the use of conventional vaccines including modified live attenuated ILTV vaccines, and advanced recombinant vector vaccines expressing different ILTV glycoproteins, but still these candidates frequently fail to reduce challenge virus shedding. Some herbal components have proved to be beneficial in reducing the severity of the clinical disease. The present review discusses ILT with respect to its current status, virus characteristics, epidemiology, transmission, pathobiology, and advances in diagnosis, vaccination and control strategies to counter this important disease of poultry.

Equine Alphaherpesviruses Require Activation of the Small GTPases Rac1 and Cdc42 for Intracellular Transport

Viruses utilize host cell signaling to facilitate productive infection. Equine herpesvirus type 1 (EHV-1) has been shown to activate Ca2+ release and phospholipase C upon contact with α4β1 integrins on the cell surface. Signaling molecules, including small GTPases, have been shown to be activated downstream of Ca2+ release, and modulate virus entry, membrane remodeling and intracellular transport. In this study, we show that EHV-1 activates the small GTPases Rac1 and Cdc42 during infection. The activation of Rac1 and Cdc42 is necessary for virus-induced acetylation of tubulin, effective viral transport to the nucleus, and cell-to-cell spread. We also show that inhibitors of Rac1 and Cdc42 did not block virus entry, but inhibited overall virus infection. The Rac1 and Cdc42 signaling is presumably orthogonal to Ca2+ release, since Rac1 and Cdc42 inhibitors affected the infection of both EHV-1 and EHV-4, which do not bind to integrins.

Immune responses to infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is an upper respiratory tract disease in chickens caused by infectious laryngotracheitis virus (ILTV), an alphaherpesvirus. Despite the extensive use of attenuated, and more recently recombinant, vaccines for the control of this disease, ILT continues to affect the intensive poultry industries worldwide. Innate and cell-mediated, rather than humoral immune responses, have been identified as responsible for protection against disease. This review examines the current understandings in innate and adaptive immune responses towards ILTV, as well as the role of ILTV glycoprotein G in modulating the host immune response towards infection. Protective immunity induced by ILT vaccines is also examined. The increasing availability of tools and reagents for the characterisation of avian innate and cell-mediated immune responses are expected to further our understanding of immunity against ILTV and drive the development of new generation vaccines towards enhanced control of this disease.

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.

In vitro and in vivo characterization of equine herpesvirus type 1 (EHV-1) mutants devoid of the viral chemokine-binding glycoprotein G (gG)

Glycoprotein G (gG) of equine herpesvirus type 1 (EHV-1), a structural component of virions and secreted from virus-infected cells, was shown to bind to a variety of different chemokines and as such might be involved in immune modulation. Little is known, however, about its role in the replication cycle and infection of EHV-1 in vivo. Here we report on the function of gG in context of virus infection in vitro and in vivo. A gG deletion mutant of pathogenic EHV-1 strain RacL11 (vL11DeltagG) was constructed and analyzed. Deletion of gG had virtually no effect on the growth properties of vL11DeltagG in cell culture when compared to parental virus or a rescuant virus vL11DeltagGR, respectively, and virus titers and plaque formation were unaffected in the absence of the glycoprotein. Similarly, in the murine model of EHV-1 infection, no significant differences in virulence between the gG deletion mutant and RacL11 or vL11DeltagGR were found at high doses of infection. However, infection of mice at lower doses revealed that the gG deletion mutant was able to replicate to higher titers in lungs of infected mice. Additionally, these mice lost significantly more weight than those infected with RacL11 and a more pronounced inflammatory response in lungs was observed. Therefore we concluded that deletion of gG in EHV-1 seems to lead to an exacerbation of respiratory disease in the mouse.

Glycoprotein G is a virulence factor in infectious laryngotracheitis virus

Infectious laryngotracheitis virus (ILTV; Gallid herpesvirus 1) is an alphaherpesvirus that causes acute respiratory disease in chickens. The role of glycoprotein G (gG) in vitro has been investigated in a number of alphaherpesviruses, but the relevance of gG in vivo in the pathogenicity of ILTV or in other alphaherpesviruses is unknown. In this study, gG-deficient mutants of ILTV were generated and inoculated into specific-pathogen-free chickens to assess the role of gG in pathogenicity. In chickens, gG-deficient ILTV reached a similar titre to wild-type (wt) ILTV but was significantly attenuated with respect to induction of clinical signs, effect on weight gain and bird mortality. In addition, an increased tracheal mucosal thickness, reflecting increased inflammatory cell infiltration at the site of infection, was detected in birds inoculated with gG-deficient ILTV compared with birds inoculated with wt ILTV. The reinsertion of gG into gG-deficient ILTV restored the in vivo phenotype of the mutant to that of wt ILTV. Quantitative PCR analysis of the expression of the genes adjacent to gG demonstrated that they were not affected by the deletion of gG and investigations in vitro confirmed that the phenotype of gG-deficient ILTV was consistent with unaltered expression of these adjacent genes. This is the first reported study to demonstrate definitively that gG is a virulence factor in ILTV and that deletion of gG from this alphaherpesvirus genome causes marked attenuation of the virus in its natural host.

Rabies virus-induced activation of mitogen-activated protein kinase and NF-kappaB signaling pathways regulates expression of CXC and CC chemokine ligands in microglia

Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues, act as sources of chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the growth characteristics of rabies virus (RV) in microglia and the activation of cellular signaling pathways leading to chemokine expression upon RV infection. In RV-inoculated microglia, the synthesis of the viral genome and the production of virus progenies were significantly impaired, while the expression of viral proteins was observed. Transcriptional analyses of the expression profiles of chemokine genes revealed that RV infection, but not exposure to inactivated virions, strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. RV infection triggered the activation of signaling pathways mediated by mitogen-activated protein kinases, including p38, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase, and nuclear factor kappaB (NF-kappaB). RV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. In contrast, the activation of ERK1/2 was found to down-regulate CCL5 expression in RV-infected microglia, despite the fact that it was involved in partial induction of CXCL10 expression. Furthermore, NF-kappaB signaling upon RV infection was augmented via a p38-mediated mechanism. Taken together, these results indicate that the strong induction of CXCL10 and CCL5 expression in microglia is precisely regulated by the activation of multiple signaling pathways through the recognition of RV infection.

Inhibition of bovine sperm–zona binding by bovine herpesvirus-1

The purpose of the present study was to identify a potential interference of bovine herpesvirus-1 (BoHV-1) with sperm–oocyte interactions during bovinein vitrofertilization. An inhibition of almost 70% of sperm–zona binding was observed when bovine cumulus-denuded oocytes were inseminated in the presence of 10750% tissue culture infective dose/ml BoHV-1. The inhibitory effect of BoHV-1 on sperm–zona binding was mediated by an interaction of the virus with spermatozoa, but not with oocytes. Treatment of spermatozoa with BoHV-1, however, did not affect sperm motility and acrosomal status. Antiserum against BoHV-1 prevented the virus-induced inhibition of sperm–zona binding, indicating that BoHV-1 itself affects the fertilization process. In order to investigate which BoHV-1 glycoprotein(s) are responsible for the virus–sperm interaction, BoHV-1 was treated with monoclonal antibodies against the viral glycoproteins gB, gC, gD and gH prior to insemination. Anti-gC completely prevented the inhibitory effect of BoHV-1 on sperm–zona binding, while anti-gD caused a reduction of this inhibition. Further evidence for the involvement of gC and gD in the virus–sperm interaction was provided by the fact that purified gC and gD decreased sperm–zona binding in a dose-dependent way with gC being more effective than gD. These results indicated that BoHV-1 inhibits bovine sperm–zona binding by interacting with spermatozoa. The binding of BoHV-1 to a spermatozoon is mediated by the viral glycoproteins gC and gD, and therefore seems to be comparable with the mechanisms of BoHV-1 attachment to its natural host cell.

Human cytomegalovirus cell-to-cell spread in the absence of an essential assembly protein

The human cytomegalovirus UL99-coded pp28 is a myristoylated phosphoprotein located in the virion tegument domain, which resides between the capsid and envelope. A previous study has demonstrated that BADsubUL99, a pp28-deficient mutant virus, fails to assemble enveloped virus particles. Capsids, coated with tegument proteins, accumulate in the cytoplasm of mutant virus-infected cells. This phenotype indicates that pp28 is required for the acquisition of an envelope; it presumably acts by directing tegument-associated capsids to bud through an intracellular membrane derived from the cell's secretory apparatus that has been modified to contain viral transmembrane glycoproteins. Here we demonstrate that BADsubUL99 can spread from cell to cell, even though highly sensitive assays fail to detect infectious virus progeny in cultures of infected fibroblasts. We propose that, in the absence of pp28, tegument-coated capsids might nevertheless bud through cellular membranes, including the plasma membrane. If this suggestion is correct, the enveloped particle could potentially infect an adjacent cell to mediate the cell-to-cell spread that is observed. This mode of spread might also occur after infection with wild-type virus, and it could facilitate immune evasion, assuming that the resulting particles do not have a normal complement of virus-coded envelope glycoproteins.

Rabies virus stimulates nitric oxide production and CXC chemokine ligand 10 expression in macrophages through activation of extracellular signal-regulated kinases 1 and 2

Macrophages represent an essential part of innate immunity, and the viral infection of macrophages results in the release of multiple proinflammatory mediators, such as nitric oxide (NO), cytokines, and chemokines. This study was undertaken to define the molecular mechanism of macrophage activation in response to rabies virus (RV) infection. In RAW264 murine macrophage cells, a well-characterized macrophage model, RV replication was strictly restricted, whereas cell proliferation was significantly enhanced upon RV inoculation. Transcriptional analyses for the expression of inducible forms of NO synthase (iNOS), cytokines, and chemokines revealed that RV virions potentiate the gene expression of iNOS and CXC chemokine ligand 10 (CXCL10), a major chemoattractant of T helper cell type 1. However, RV stimulation had little or no effect on the expression profiles of proinflammatory cytokines and other types of chemokines. In macrophages stimulated with UV-inactivated RV virions, as well as infectious viruses, the phosphorylation of extracellular signal-regulated kinase (ERK) 1 and 2, members of the mitogen-activated protein kinase family, was significantly induced. Specific inhibitors of MAPK/ERK kinase reduced the RV-induced production of NO and CXCL10. Furthermore, the RV-induced activation of the ERK1/2 pathway was severely impaired by the neutralization of the endosomal and lysosomal pH environment with lysosomotropic agents, indicating that endocytosis is a key step leading to the activation of ERK1/2 signaling. Taken together, these results suggest that the ERK1/2-mediated signaling pathway plays a cardinal role in the selective activation of macrophages in response to RV virions, thereby regulating cellular functions during virus infection.

Genome of bovine herpesvirus 5

Here we present the complete genomic sequence of bovine herpesvirus 5 (BHV-5), an alphaherpesvirus responsible for fatal meningoencephalitis in cattle. The 138390-bp genome encodes 70 putative proteins and resembles the alpha2 subgroup of herpesviruses in genomic organization and gene content. BHV-5 is very similar to BHV-1, the etiological agent of infectious bovine rhinotracheitis, as reflected by the high level of amino acid identity in their protein repertoires (average, 82%). The highest similarity to BHV-1 products (>or=95% amino acid identity) is found in proteins involved in viral DNA replication and processing (UL5, UL15, UL29, and UL39) and in virion proteins (UL14, UL19, UL48, and US6). Among the least conserved ( Collapse

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MESH Headings

• Amino Acid Sequence
• Base Sequence
• Genes, Immediate-Early
• Genome, Viral
• Herpesvirus 5, Bovine/genetics
• Molecular Sequence Data
• Promoter Regions, Genetic
• Repetitive Sequences, Nucleic Acid
• Virus Latency/genetics

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Affiliation(s)

G Delhon Plum Island Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944, USA
M P Moraes
Z Lu
C L Afonso
E F Flores
R Weiblen
G F Kutish
D L Rock

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Glycoprotein G isoforms from some alphaherpesviruses function as broad-spectrum chemokine binding proteins

Mimicry of host chemokines and chemokine receptors to modulate chemokine activity is a strategy encoded by beta- and gammaherpesviruses, but very limited information is available on the anti-chemokine strategies encoded by alphaherpesviruses. The secretion of chemokine binding proteins (vCKBPs) has hitherto been considered a unique strategy encoded by poxviruses and gammaherpesviruses. We describe a family of novel vCKBPs in equine herpesvirus 1, bovine herpesvirus 1 and 5, and related alphaherpesviruses with no sequence similarity to chemokine receptors or other vCKBPs. We show that glycoprotein G (gG) is secreted from infected cells, binds a broad range of chemokines with high affinity and blocks chemokine activity by preventing their interaction with specific receptors. Moreover, gG also blocks chemokine binding to glycosaminoglycans, an interaction required for the correct presentation and function of chemokines in vivo. In contrast to other vCKBPs, gG may also be membrane anchored and, consistently, we show chemokine binding activity at the surface of cells expressing full-length protein. These alphaherpesvirus vCKBPs represent a novel family of proteins that bind chemokines both at the membrane and in solution.

Mutagenesis of a bovine herpesvirus type 1 genome cloned as an infectious bacterial artificial chromosome: analysis of glycoprotein E and G double deletion mutants

The genome of bovine herpesvirus type 1 Schönböken was cloned as a bacterial artificial chromosome (BAC) by inserting mini F plasmid sequences into the glycoprotein (g) E gene. The resulting BAC clone, pBHV-1DeltagE, was transfected into bovine kidney cells and viable gE-negative BHV-1 (BHV-1DeltagE) was recovered. By RecE/T mutagenesis in Escherichia coli, the gG open reading frame was deleted from pBHV-1DeltagE. From the mutated BAC, double negative BHV-1DeltagE-gG was reconstituted and its growth properties were compared to those of rescuant viruses in which the gE gene was restored (BHV-1rev, BHV-1DeltagG). The mutant viruses did not exhibit markedly lowered virus titres. Plaque sizes of BHV-1DeltagE, BHV-1DeltagE-gG and BHV-1DeltagG, however, were reduced by 19 to 55 % compared to parental strain Schönböken or BHV-1rev. Our results suggested that gE and gG function independently from each other in cell-to-cell spread, because an additive effect on plaque formation was observed in the gE/gG double deletion mutant.