Bovine herpesvirus type 1 (BHV-1) mutant lacking U(L)49.5 luminal domain residues 30-32 and cytoplasmic tail residues 80-96 induces more rapid onset of virus neutralizing antibody and cellular immune responses in calves than the wild-type strain Cooper

Porcine reproductive and respiratory syndrome virus nsp4-mediated β2M downregulation contributes to SLA-I decrease and virus infection in vivo and in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) infection inhibits swine leukocyte antigen class I (SLA-I) expression in pigs, resulting in inefficient antigen presentation and subsequent low levels of cellular PRRSV-specific immunity as well as persistent viremia. We previously observed that the non-structural protein 4 (nsp4) of PRRSV contributed to inhibition of the β2-microglobulin (β2M) and SLA-I expression in cells. Here, we constructed a series of nsp4 mutants with different combination of amino acid mutations to attenuate the inhibitory effect of nsp4 on β2M and SLA-I expression. Almost all nsp4 mutants exogenously expressed in cells showed an attenuated effect on inhibition of β2M and SLA-I expression, but the recombinant PRRSV harboring these nsp4 mutants failed to be rescued with exception of the rPRRSV-nsp4-mut10 harboring three amino acid mutations. However, infection of rPRRSV-nsp4-mut10 not only enhanced β2M and SLA-I expression in both cells and pigs but also promoted the DCs to active the CD3+CD8+T lymphocytes more efficiently, as compared with its parental PRRSV (rPRRVS-nsp4-wt). These data suggested that the inhibition of nsp4-mediated β2M downregulation improved β2M/SLA-I expression in pigs.

Mapping the Key Residues within the Porcine Reproductive and Respiratory Syndrome Virus nsp1α Replicase Protein Required for Degradation of Swine Leukocyte Antigen Class I Molecules

The nonstructural protein 1α (nsp1α) of the porcine reproductive and respiratory syndrome virus (PRRSV) has been shown to target swine leukocyte antigen class I (SLA-I) for degradation, but the molecular details remain unclear. In this report, we further mapped the critical residues within nsp1α by site-directed mutagenesis. We identified a cluster of residues (i.e., Phe17, Ile81, Phe82, Arg86, Thr88, Gly90, Asn91, Phe94, Arg97, Thr160, and Asn161) necessary for this function. Interestingly, they are all located in a structurally relatively concentrated region. Further analysis by reverse genetics led to the generation of two viable viral mutants, namely, nsp1α-G90A and nsp1α-T160A. Compared to WT, nsp1α-G90A failed to co-localize with either chain of SLA-I within infected cells, whereas nsp1α-T160A exhibited a partial co-localization relationship. Consequently, the mutant nsp1α-G90A exhibited an impaired ability to downregulate SLA-I in infected macrophages as demonstrated by Western blot, indirect immunofluorescence, and flow cytometry analysis. Consistently, the ubiquitination level of SLA-I was significantly reduced in the conditions of both infection and transfection. Together, our results provide further insights into the mechanism underlying PRRSV subversion of host immunity and have important implications in vaccine development.

Characterization of BoHV-1 gG-/tk-/gE- Mutant in Differential Protein Expression, Virulence, and Immunity

Infectious bovine rhinotracheitis (IBR), caused by bovine alphaherpesvirus 1 (BoHV-1), is an important disease affecting cattle worldwide resulting in great economic losses. Marker vaccines are effective in controlling infectious diseases including IBR, because they allow the discrimination between the natural infection and the vaccination. Therefore, a triple gene deleted strain BoHV-1 gG-/tk-/gE- was developed and evaluated in vivo and in vitro as a marker vaccine. In cell culture, this triple mutant virus showed significantly slower growth kinetics and smaller plaques when compared to wild-type (wt) BoHV-1 and double mutant BoHV-1 gG-/tk- (p < 0.01). On proteomic level, it revealed downregulation of some virulence related proteins including thymidine kinase, glycoproteins G, E, I, and K when compared to the wt. In vitro, the triple mutant virus showed a significantly lower and shorter viral shedding period (p < 0.001) in calves compared to double mutant. Moreover, the immunized calves with triple mutant virus showed protection rates of 64.2% and 68.6% against wt BoHV-1 and wt BoHV-5 challenge, respectively, without reactivation of latency after dexamethasone injection. In conclusion, BoHV-1 gG-/tk-/gE- is a safer marker vaccine against IBR although its immunogenicity in calves was decreased when compared to double mutant virus.

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.

Structure determination of UL49.5 transmembrane protein from bovine herpesvirus 1 by NMR spectroscopy and molecular dynamics

The transporter associated with antigen processing (TAP) directly participates in the immune response as a key component of the cytosolic peptide to major histocompatibility complex (MHC) class I protein loading machinery. This makes TAP an important target for viruses avoiding recognition by CD8+ T lymphocytes. Its activity can be suppressed by the UL49.5 protein produced by bovine herpesvirus 1, although the mechanism of this inhibition has not been understood so far.

Therefore, the main goal of our study was to investigate the 3D structure of bovine herpesvirus 1 - encoded UL49.5 protein. The final structure of the inhibitor was established using circular dichroism (CD), 2D nuclear magnetic resonance (NMR), and molecular dynamics (MD) in membrane mimetic environments. In NMR studies, UL49.5 was represented by two fragments: the extracellular region (residues 1–35) and the transmembrane-intracellular fragment (residues 36–75), displaying various functions during viral invasion. After the empirical structure determination, a molecular docking procedure was used to predict the complex of UL49.5 with the TAP heterodimer.

Our results revealed that UL49.5 adopted a highly flexible membrane-proximal helical structure in the extracellular part. In the transmembrane region, we observed two short α-helices. Furthermore, the cytoplasmic part had an unordered structure. Finally, we propose three different orientations of UL49.5 in the complex with TAP. Our studies provide, for the first time, the experimental structural information on UL49.5 and structure-based insight in its mechanism of action which might be helpful in designing new drugs against viral infections.

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The UL49.5 viral protein forms a helical structure in the biological membrane

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Our NMR-based 3D structure of UL49.5 differs from the theoretical predictions

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Apart from the protruding N-terminal helix the structure is buried in the membrane

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Attention should be paid to the turns in the external and transmembrane domains

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Molecular docking proposes three possible structures of the UL49.5/TAP complexes

Transmembrane regions of bovine herpesvirus 1-encoded UL49.5 and glycoprotein M regulate complex maturation and ER-Golgi trafficking

Bovine herpesvirus 1 (BoHV-1)-encoded UL49.5 (a homologue of herpesvirus glycoprotein N) can combine different functions, regulated by complex formation with viral glycoprotein M (gM). We aimed to identify the mechanisms governing the immunomodulatory activity of BoHV-1 UL49.5. In this study, we addressed the impact of gM/UL49.5-specific regions on heterodimer formation, folding and trafficking from the endoplasmic reticulum (ER) to the trans-Golgi network (TGN) - events previously found to be responsible for abrogation of the UL49.5-mediated inhibition of the transporter associated with antigen processing (TAP). We first established, using viral mutants, that no other viral protein could efficiently compensate for the chaperone function of UL49.5 within the complex. The cytoplasmic tail of gM, containing putative trafficking signals, was dispensable either for ER retention of gM or for the release of the complex. We constructed cell lines with stable co-expression of BoHV-1 gM with chimeric UL49.5 variants, composed of the BoHV-1 N-terminal domain fused to the transmembrane region (TM) from UL49.5 of varicella-zoster virus or TM and the cytoplasmic tail of influenza virus haemagglutinin. Those membrane-anchored N-terminal domains of UL49.5 were sufficient to form a complex, yet gM/UL49.5 folding and ER-TGN trafficking could be affected by the UL49.5 TM sequence. Finally, we found that leucine substitutions in putative glycine zipper motifs within TM helices of gM resulted in strong reduction of complex formation and decreased ability of gM to interfere with UL49.5-mediated major histocompatibility class I downregulation. These findings highlight the importance of gM/UL49.5 transmembrane domains for the biology of this conserved herpesvirus protein complex.

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.

An MHC class I immune evasion gene of Marek׳s disease virus

Marek׳s disease virus (MDV) is a widespread α-herpesvirus of chickens that causes T cell tumors. Acute, but not latent, MDV infection has previously been shown to lead to downregulation of cell-surface MHC class I (Virology 282:198-205 (2001)), but the gene(s) involved have not been identified. Here we demonstrate that an MDV gene, MDV012, is capable of reducing surface expression of MHC class I on chicken cells. Co-expression of an MHC class I-binding peptide targeted to the endoplasmic reticulum (bypassing the requirement for the TAP peptide transporter) partially rescued MHC class I expression in the presence of MDV012, suggesting that MDV012 is a TAP-blocking MHC class I immune evasion protein. This is the first unique non-mammalian MHC class I immune evasion gene identified, and suggests that α-herpesviruses have conserved this function for at least 100 million years.

A triple gene mutant of BoHV-1 administered intranasally is significantly more efficacious than a BoHV-1 glycoprotein E-deleted virus against a virulent BoHV-1 challenge

Bovine herpesvirus 1 (BoHV-1) causes respiratory infections and abortions in cattle, and is an important component of bovine respiratory disease complex, which causes a considerable economic loss worldwide. Several efforts have been made to produce safer and more effective vaccines. One of these vaccines is a glycoprotein E (gE)-deleted marker vaccine which is currently mandated for use in EU countries. In the present study, we have constructed a three-gene-mutated BoHV-1 vaccine virus (UL49.5 luminal domain residues 30-32 and cytoplasmic tail residues 80-96 deleted, gE cytoplasmic tail- and entire Us9-deleted) and compared its protective vaccine efficacy in calves after intranasal vaccination with that of a gE-deleted virus. Following vaccination, both the triple mutant and gE-deleted vaccine virus replicated well in the nasal epithelium of the calves. The vaccinated calves did not show any clinical signs. Four weeks post-vaccination, the animals were challenged intranasally with a virulent BoHV-1 wild-type virus. Based on clinical signs, both the gE-deleted and triple mutant group were protected equally against the virulent BoHV-1 challenge. However, based on the quantity and duration of nasal viral shedding, virus neutralizing antibody and cellular immune responses, the triple mutant virus vaccine induced a significantly better protective immune response than the gE-deleted virus vaccine. Notably, after the virulent BoHV-1 challenge, the triple mutant virus vaccinated group cleared the challenge virus three days earlier than the BoHV-1 gE-deleted virus vaccinated group.

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Felid herpesvirus type 1 infection in cats: a natural host model for alphaherpesvirus pathogenesis

Feline herpesvirus 1 (FeHV-1) is an alphaherpesvirus that causes feline viral rhinotracheitis, an important viral disease of cats on a worldwide basis. Acute FeHV-1 infection is associated with both upper respiratory and ocular signs. Following the acute phase of the disease lifelong latency is established, primarily in sensory neuronal cells. As is the case with human herpes simplex viruses, latency reactivation can result in recrudescence, which can manifest itself in the form of serious ocular lesions. FeHV-1 infection in cats is a natural host model that is useful for the identification of viral virulence genes that play a role in replication at the mucosal portals of entry or are mediators of the establishment, maintenance, or reactivation of latency. It is also a model system for defining innate and adaptive immunity mechanisms and for immunization strategies that can lead to better protection against this and other alphaherpesvirus infections.