Bovine herpesvirus type 1 (BHV-1) UL49.5 luminal domain residues 30 to 32 are critical for MHC-I down-regulation in virus-infected cells

An intrinsic network of polar interactions is responsible for binding of UL49.5 C-degron by the CRL2KLHDC3 ubiquitin ligase

Bovine herpesvirus type 1 (BoHV-1) is a pathogen of cattle responsible for infectious bovine rhinotracheitis. The BoHV-1 UL49.5 is a transmembrane protein that binds to the transporter associated with antigen processing (TAP) and downregulates cell surface expression of the antigenic peptide complexes with the major histocompatibility complex class I (MHC-I). KLHDC3 is a kelch domain-containing protein 3 and a substrate receptor of a cullin2-RING (CRL2) E3 ubiquitin ligase. Recently, it has been identified that CRL2KLHDC3 is responsible for UL49.5-triggered TAP degradation via a C-degron pathway and the presence of the degron sequence does not lead to the degradation of UL49.5 itself. The molecular modeling of KLHDC3 in complexes with four UL49.5 C-terminal decapeptides (one native protein and three mutants) revealed their activity to be closely correlated with the conformation which they adopt in KLHDC3 binding cleft. To analyze the interaction between UL49.5 and KLHDC3 in detail, in this work a total of 3.6 μs long molecular dynamics simulations have been performed. The complete UL49.5-KLHDC3 complexes were embedded into the fully hydrated all-atom lipid membrane model with explicit water molecules. The network of polar interactions has been proposed to be responsible for the recognition and binding of the degron in KLHDC3. The interaction network within the binding pocket appeared to be very similar between two CRL2 substrate receptors: KLHDC3 and KLHDC2.

Why does the herpes simplex 1 virus-encoded UL49.5 protein fail to inhibit the TAP-dependent antigen presentation?

Herpes simplex virus 1 (HSV-1) is a well-studied herpesvirus that causes various human diseases. Like other herpesviruses, HSV-1 produces the transmembrane glycoprotein N (gN/UL49.5 protein), which has been extensively studied, but its function in HSV-1 remains largely unknown. The amino-acid sequences and lengths of UL49.5 proteins differ between herpesvirus species. It is, therefore, crucial to determine whether and to what extent the spatial structure of UL49.5 orthologs that are transporter associated with antigen processing (TAP) inhibitors (i.e., of bovine herpesvirus 1; BoHV-1) differ from that of non-TAP inhibitors (i.e., of HSV-1). Our study aimed to examine the 3D structure of the HSV-1-encoded UL49.5 protein in an advanced model of the endoplasmic reticulum (ER) membrane using circular dichroism, 2D nuclear magnetic resonance, and multiple-microsecond all-atom molecular dynamics simulations in an ER membrane mimetic environment. According to our findings, the N-terminus of the HSV-1-encoded UL49.5 adopts a highly flexible, unordered structure in the extracellular part due to the presence of a large number of proline and glycine residues. In contrast to the BoHV-1-encoded homolog, the transmembrane region of the HSV-1-encoded UL49.5 is formed by a single long transmembrane α-helix, rather than two helices oriented perpendicularly, while the cytoplasmic part of the protein (C-terminus) has a short unordered structure. Our findings provide valuable experimental structural information on the HSV-1-encoded UL49.5 protein and offer, based on the obtained structure, insight into its lack of biological activity in inhibiting the TAP-dependent antigen presentation pathway.

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

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

Deleting UL49.5 in duck plague virus causes attachment, entry and spread defects

Duck plague is a disease with high morbidity and mortality rates, and it causes great losses for the duck breeding industry. Duck plague virus (DPV) is the causative agent of duck plague, and DPV UL49.5 protein (pUL49.5) is homologue of glycoprotein N (gN), which is conserved in herpesviruses. UL49.5 homologues are known to be involved in processes such as immune escape, virus assembly, viral fusion, transporter associated with antigen processing (TAP) inhibition and degradation, and maturation and incorporation of glycoprotein M. However, few studies have focused on the role of gN in the early stage of virus infection cells. In this study, we determined that DPV pUL49.5 was distributed in the cytoplasm and colocalized with the endoplasmic reticulum (ER). Moreover, we found that DPV pUL49.5 was a virion component and nonglycosylated protein. To better explore its function, BAC-DPV-ΔUL49.5 was constructed, and its attachment was only approximately 25 % of the revertant virus. Additionally, the penetration ability of BAC-DPV-ΔUL49.5 has only reached 73 % of the revertant virus. The plaque sizes produced by the UL49.5-deleted virus were approximately 58 % smaller than those produced by the revertant virus. Deleting UL49.5 mainly resulted in attachment and cell-to-cell-spread defects. Taken together, these findings suggest important roles for DPV pUL49.5 in viral attachment, penetration and spread.

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.

BoHV-1-Vectored BVDV-2 Subunit Vaccine Induces BVDV Cross-Reactive Cellular Immune Responses and Protects against BVDV-2 Challenge

The bovine respiratory disease complex (BRDC) remains a major problem for both beef and dairy cattle industries worldwide. BRDC frequently involves an initial viral respiratory infection resulting in immunosuppression, which creates a favorable condition for fatal secondary bacterial infection. Current polyvalent modified live vaccines against bovine herpesvirus type 1(BoHV-1) and bovine viral diarrhea virus (BVDV) have limitations concerning their safety and efficacy. To address these shortcomings and safety issues, we have constructed a quadruple gene mutated BoHV-1 vaccine vector (BoHV-1 QMV), which expresses BVDV type 2, chimeric E2 and Flag-tagged Erns-fused with bovine granulocyte monocyte colony-stimulating factor (GM-CSF) designated here as QMV-BVD2*. Here we compared the safety, immunogenicity, and protective efficacy of QMV-BVD2* vaccination in calves against BVDV-2 with Zoetis Bovi-shield Gold 3 trivalent (BoHV-1, BVDV types 1 and 2) vaccine. The QMV-BVD2* prototype subunit vaccine induced the BoHV-1 and BVDV-2 neutralizing antibody responses along with BVDV-1 and -2 cross-reactive cellular immune responses. Moreover, after a virulent BVDV-2 challenge, the QMV-BVD2* prototype subunit vaccine conferred a more rapid recall BVDV-2-specific neutralizing antibody response and considerably better recall BVDV types 1 and 2-cross protective cellular immune responses than that of the Zoetis Bovi-shield Gold 3.

Investigation of the Effects of Primary Structure Modifications within the RRE Motif on the Conformation of Synthetic Bovine Herpesvirus 1-Encoded UL49.5 Protein Fragments

Herpesviruses are the most prevalent viruses that infect the human and animal body. They can escape a host immune response in numerous ways. One way is to block the TAP complex so that viral peptides, originating from proteasomal degradation, cannot be transported to the endoplasmic reticulum. As a result, a reduced number of MHC class I molecules appear on the surface of infected cells and, thus, the immune system is not efficiently activated. BoHV-1-encoded UL49.5 protein is one such TAP transporter inhibitor. This protein binds to TAP in such a way that its N-terminal fragment interacts with the loops of the TAP complex, and the C-terminus stimulates proteasomal degradation of TAP. Previous studies have indicated certain amino acid residues, especially the RRE(9-11) motif, within the helical structure of the UL49.5 N-terminal fragment, as being crucial to the protein's activity. In this work, we investigated the effects of modifications within the RRE region on the spatial structure of the UL49.5 N-terminal fragment. The introduced RRE(9-11) variations were designed to abolish or stabilize the structure of the α-helix and, consequently, to increase or decrease protein activity compared to the wild type. The terminal structure of the peptides was established using circular dichroism (CD), 2D nuclear magnetic resonance (NMR), and molecular dynamics (MD) in membrane-mimetic or membrane-model environments. Our structural results show that in the RRE(9-11)AAA and E11G peptides the helical structure has been stabilized, whereas for the RRE(9-11)GGG peptide, as expected, the helix structure has partially unfolded compared to the native structure. These RRE modifications, in the context of the entire UL49.5 proteins, slightly altered their biological activity in human cells.

Bovine herpesvirus 1 (BHV-1) envelope protein gE subcellular trafficking is contributed by two separate YXXL/Φ motifs within the cytoplasmic tail which together promote efficient virus cell-to-cell spread

Bovine herpesvirus envelope glycoprotein E (gE) and, in particular, the gE cytoplasmic tail (CT) is a virulence determinant in cattle. Also, the gE CT contributes to virus cell-to-cell spread and anterograde neuronal transport. In this study, our goal was to map the gE CT sub-domains that contribute to virus cell-to-cell spread property. A panel of gE-CT specific mutant viruses was constructed and characterized, in vitro, with respect to their plaque phenotypes, gE recycling and gE basolateral membrane targeting. The results revealed that disruption of the tyrosine-based motifs, ₄₆₇YTSL₄₇₀ and ₅₆₃YTVV₅₆₆, individually produced smaller plaque phenotypes than the wild type. However, they were slightly larger than the gE CT-null virus plaques. The Y467A mutation affected the gE endocytosis, gE trans-Golgi network (TGN) recycling, and gE virion incorporation properties. However, the Y563A mutation affected only the gE basolateral cell-surface redistribution function. Notably, the simultaneous Y467A/Y563A mutations produced gE CT-null virus-like plaque phenotypes.

Anti-viral immunity in the tumor microenvironment: implications for the rational design of herpes simplex virus type 1 oncolytic virotherapy

Purpose of review

The design of novel herpes simplex type I (HSV-1)-derived oncolytic virotherapies is a balancing act between safety, immunogenicity and replicative potential. We have undertaken this review to better understand how these considerations can be incorporated into rational approaches to the design of novel herpesvirus oncolytic virotherapies.

Recent findings

Several recent papers have demonstrated that enhancing the potential of HSV-1 oncolytic viruses to combat anti-viral mechanisms present in the tumor microenvironment leads to greater efficacy than their parental viruses.

Summary

It is not entirely clear how the immunosuppressive tumor microenvironment affects oncolytic viral replication and spread within tumors. Recent work has shown that the manipulation of specific cellular and molecular mechanisms of immunosuppression operating within the tumor microenvironment can enhance the efficacy of oncolytic virotherapy. We anticipate that future work will integrate greater knowledge of immunosuppression in tumor microenvironments with design of oncolytic virotherapies.

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

Bovine Herpesvirus 1 UL49.5 Interacts with gM and VP22 To Ensure Virus Cell-to-Cell Spread and Virion Incorporation: Novel Role for VP22 in gM-Independent UL49.5 Virion Incorporation

Alphaherpesvirus envelope glycoprotein N (gN) and gM form a covalently linked complex. Bovine herpesvirus type 1 (BHV-1) U_L49.5 (a gN homolog) contains two predicted cysteine residues, C42 and C78. The C42 is highly conserved among the alphaherpesvirus gN homologs (e.g., herpes simplex virus 1 and pseudorabies virus). To identify which cysteine residue is required for the formation of the U_L49.5/gM complex and to characterize the functional significance of the U_L49.5/gM complex, we constructed and analyzed C42S and C78S substitution mutants in either a BHV-1 wild type (wt) or BHV-1 U_L49.5 cytoplasmic tail-null (CT-null) virus background. The results demonstrated that BHV-1 U_L49.5 residue C42 but not C78 was essential for the formation of the covalently linked functional U_L49.5/gM complex, gM maturation in the Golgi compartment, and efficient cell-to-cell spread of the virus. Interestingly, the C42S and CT-null mutations separately did not affect mutant U_L49.5 virion incorporation. However, when both of the mutations were introduced simultaneously, the U_L49.5 C42S/CT-null protein virion incorporation was severely reduced. Incidentally, the anti-VP22 antibody coimmunoprecipitated the U_L49.5 C42S/CT-null mutant protein at a noticeably reduced level compared to that of the individual U_L49.5 C42S and CT-null mutant proteins. As expected, in a dual U_L49.5 C42S/VP22Δ virus with deletion of VP22 (VP22Δ), the U_L49.5 C42S virion incorporation was also severely reduced while in a gMΔ virus, U_L49.5 virion incorporation was affected only slightly. Together, these results suggested that U_L49.5 virion incorporation is mediated redundantly, by both U_L49.5/gM functional complex and VP22, through a putative gM-independent novel U_L49.5 and VP22 interaction.IMPORTANCE Bovine herpesvirus 1 (BHV-1) envelope protein U_L49.5 is an important virulence determinant because it downregulates major histocompatibility complex class I (MHC-I). U_L49.5 also forms a covalently linked complex with gM. The results of this study demonstrate that U_L49.5 regulates gM maturation and virus cell-to-cell spread since gM maturation in the Golgi compartment depends on covalently linked U_L49.5/gM complex. The results also show that the U_L49.5 residue cysteine 42 (C42) mediates the formation of the covalently linked U_L49.5-gM interaction. Furthermore, a C42S mutant virus in which U_L49.5 cannot interact with gM has defective cell-to-cell spread. Interestingly, U_L49.5 also interacts with the tegument protein VP22 via its cytoplasmic tail (CT). The putative U_L49.5 CT-VP22 interaction is essential for a gM-independent U_L49.5 virion incorporation and is revealed when U_L49.5 and gM are not linked. Therefore, U_L49.5 virion incorporation is mediated by U_L49.5-gM complex interaction and through a gM-independent interaction between U_L49.5 and VP22.

Subcellular Trafficking and Functional Relationship of the HSV-1 Glycoproteins N and M

The herpes simplex virus type 1 (HSV-1) glycoprotein N (gN/UL49.5) is a type I transmembrane protein conserved throughout the herpesvirus family. gN is a resident of the endoplasmic reticulum that in the presence of gM is translocated to the trans Golgi network. gM and gN are covalently linked by a single disulphide bond formed between cysteine 46 of gN and cysteine 59 of gM. Exit of gN from the endoplasmic reticulum requires the N-terminal core of gM composed of eight transmembrane domains but is independent of the C-terminal extension of gM. Co-transport of gN and gM to the trans Golgi network also occurs upon replacement of conserved cysteines in gM and gN, suggesting that their physical interaction is mediated by covalent and non-covalent forces. Deletion of gN/UL49.5 using bacterial artificial chromosome (BAC) mutagenesis generated mutant viruses with wild-type growth behaviour, while full deletion of gM/UL10 resulted in an attenuated phenotype. Deletion of gN/UL49.5 in conjunction with various gM/UL10 mutants reduced average plaque sizes to the same extent as either single gM/UL10 mutant, indicating that gN is nonessential for the function performed by gM. We propose that gN functions in gM-dependent as well as gM-independent processes during which it is complemented by other viral factors.

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.

CD8(+) T-cell Immune Evasion Enables Oncolytic Virus Immunotherapy

Although counteracting innate defenses allows oncolytic viruses (OVs) to better replicate and spread within tumors, CD8(+) T-cells restrict their capacity to trigger systemic anti-tumor immune responses. Herpes simplex virus-1 (HSV-1) evades CD8(+) T-cells by producing ICP47, which limits immune recognition of infected cells by inhibiting the transporter associated with antigen processing (TAP). Surprisingly, removing ICP47 was assumed to benefit OV immuno-therapy, but the impact of inhibiting TAP remains unknown because human HSV-1 ICP47 is not effective in rodents. Here, we engineer an HSV-1 OV to produce bovine herpesvirus UL49.5, which unlike ICP47, antagonizes rodent and human TAP. Significantly, UL49.5-expressing OVs showed superior efficacy treating bladder and breast cancer in murine models that was dependent upon CD8(+) T-cells. Besides injected subcutaneous tumors, UL49.5-OV reduced untreated, contralateral tumor size and metastases. These findings establish TAP inhibitor-armed OVs that evade CD8(+) T-cells as an immunotherapy strategy to elicit potent local and systemic anti-tumor responses.

Equine Herpesvirus 1 Multiply Inserted Transmembrane Protein pUL43 Cooperates with pUL56 in Downregulation of Cell Surface Major Histocompatibility Complex Class I

Herpesviruses have evolved an array of strategies to counteract antigen presentation by major histocompatibility complex class I (MHC-I). Previously, we identified pUL56 of equine herpesvirus 1 (EHV-1) as one major determinant of the downregulation of cell surface MHC-I (G. Ma, S. Feineis, N. Osterrieder, and G. R. Van de Walle, J. Virol. 86:3554-3563, 2012, http://dx.doi.org/10.1128/JVI.06994-11; T. Huang, M. J. Lehmann, A. Said, G. Ma, and N. Osterrieder, J. Virol. 88:12802-12815, 2014, http://dx.doi.org/10.1128/JVI.02079-14). Since pUL56 was able to exert its function only in the context of virus infection, we hypothesized that pUL56 cooperates with another viral protein. Here, we generated and screened a series of EHV-1 single-gene deletion mutants and found that the pUL43 orthologue was required for downregulation of cell surface MHC-I expression at the same time of infection as when pUL56 exerts its function. We demonstrate that the absence of pUL43 was not deleterious to virus growth and that expression of pUL43 was detectable from 2 h postinfection (p.i.) but decreased after 8 h p.i. due to lysosomal degradation. pUL43 localized within Golgi vesicles and required a unique hydrophilic N-terminal domain to function properly. Finally, coexpression of pUL43 and pUL56 in transfected cells reduced the cell surface expression of MHC-I. This process was dependent on PPxY motifs present in pUL56, suggesting that late domains are required for pUL43- and pUL56-dependent sorting of MHC class I for lysosomal degradation.

IMPORTANCE

We describe here that the poorly characterized herpesviral protein pUL43 is involved in downregulation of cell surface MHC-I. pUL43 is an early protein and degraded in lysosomes. pUL43 resides in the Golgi vesicles and needs an intact N terminus to induce MHC-I downregulation in infected cells. Importantly, pUL43 and pUL56 cooperate to reduce MHC-I expression on the surface of transfected cells. Our results suggest a model for MHC-I downregulation in which late domains in pUL56 are required for the rerouting of vesicles containing MHC-I, pUL56, and pUL43 to the lysosomal compartment.

Effect of Antimuscarinic Autoantibodies in Primary Sjögren's Syndrome

The presence of functional autoantibodies against the muscarinic type 3 receptor (M3R) has been reported in primary Sjögren's syndrome (pSS). However, the pathogenic role of these autoantibodies in pSS development remains to be elucidated. In this experiment, we investigated a pathologic role of pSS autoantibodies (pSS IgG) associated with downregulation of the major histocompatibility complex I (MHC I) molecule with M3R through internalization. Anti-M3R autoantibodies in purified control and pSS IgG were detected using 4 synthesized cyclic M3R peptides by enzyme-linked immunosorbent assay. The binding reactivity of pSS IgG to M3R in situ was analyzed by a dual immunostaining method. Surface expression, interaction, and internalization of M3R with MHC I were analyzed by immunofluorescence confocal microscopy and biochemical assays. Synthetic cyclic peptides M3RP(205-221) and M3RP(520-527) showed significantly high reactivity with pSS IgG compared to the control IgG or the other 3 peptides (P < 0.05). Significantly high reactivity of pSS IgG to M3R in situ was observed. PSS IgG increased the interaction of membrane M3R with MHC I and induced their internalization in primary human submandibular gland cells. The pSS IgG-induced internalization of M3R with MHC I was significantly inhibited by the cholesterol-sequestering drug filipin. Our novel finding-namely, strong downregulation of the membrane MHC I with M3R through internalization of the cholesterol-rich microdomain associating with anti-M3R autoantibodies-could be an important mechanism contributing to the impaired salivation seen in pSS and linking secretory hypofunction to autoimmune pathogenesis.

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.

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

Bovine herpesvirus type 1 (BHV-1) envelope protein U(L)49.5 inhibits transporter associated with antigen processing (TAP) and down-regulates cell-surface expression of major histocompatibility complex (MHC) class I molecules to promote immune evasion. Earlier, we have constructed a BHV-1U(L)49.5Δ30-32 CT-null virus and determined that in the infected cells, TAP inhibition and MHC-I down regulation properties of the virus are abolished. In this study, we compared the pathogenicity and immune responses in calves infected with BHV-1U(L)49.5Δ30-32 CT-null and BHV-1 wt viruses. Following primary infection, both BHV-1 wt and BHV-1U(L)49.5Δ30-32 CT-null virus replicated in the nasal epithelium with very similar yields. BHV-1 antigen-specific CD8+ T cell proliferation as well as CD8+ T cell cytotoxicity in calves infected with the BHV-1U(L)49.5Δ30-32 CT-null virus peaked by 7 dpi (P<0.05) which is 7 days earlier than that of BHV-1 wt-infected calves. Further, virus neutralizing antibody (VN Ab) titers and IFN-γ producing peripheral blood mononuclear cells (PBMCs) in the U(L)49.5 mutant virus-infected calves, also peaked 7 days (IFN-γ; P<0.05) and 14 days (VN Ab; P<0.05) earlier, respectively. Therefore, relative to wt in the BHV-1U(L)49.5 mutant virus-infected calves, primary neutralizing antibody and cellular immune responses were induced significantly more rapidly.