A novel strategy for determining protective antigens of the parapoxvirus, orf virus

ORFV can carry TRAP gene expression via intracellular CRISPR/Cas9 gene editing technology

Orf is an acute and highly contracted human and animal infection caused by orf virus (ORFV), which mainly affects sheep, goats, and other species. Clinically, opportunistic or conditional pathogens such as Staphylococcus aureus (S. aureus) are often detected in cases of orf, which greatly increases the risk of disease progression and clinical death. It has been reported that TRAP gene products of S. aureus can broadly influence bacterial life and pathogenicity in vivo, and introduction of exogenous TRAP genes may help to inhibit the proliferation of bacteria. In order to achieve the combined control of ORFV and S. aureus, a novel approach to design a S. aureus TRAP gene vaccine using a live attenuated ORFV vector is proposed. In this study, CRISPR/Cas9 gene editing technology was used to disable vascular endothelial growth factor E of ORFV (VEGF-v) and introduced TRAP gene into this position. TRAP gene expression was detected in keratinocytes infected with recombinant virus. The construction and experimental verification of recombinant ORFV (ORFV-v/TRAP) will provide a reference for in-depth studies on the prevention and control of mixed infectious disease.

The parapoxvirus Orf virus inhibits IFN-β expression induced by dsRNA

Orf virus (ORFV) is the type species of the Parapoxvirus genus that belongs to the Poxviridae family. Type I interferons (IFN) are critical in the host defence against viruses. They induce hundreds of interferon stimulated genes (ISGs) many of which have an antiviral role. The ability of ORFV to modulate type I IFN production was undertaken to investigate whether ORFV could inhibit IFN-β expression via dsRNA dependant signalling pathways. HEK293 cells are known to lack DNA pattern-recognition receptors and Toll-like receptors however, they do express the cytosolic dsRNA receptors RIG-I and MDA5. HEK293 cells were shown to produce high levels of IFN-β when cells were stimulated with poly(I:C) and this was shown to be predominantly via RIG-I-dependant signalling as confirmed by siRNA knock-down of RIG-I. Further we showed that HEK293 cells are permissive for ORFV and caused potent inhibition of IFN-β transcription when cells were stimulated with poly(I:C) post-viral infection. Studies using heat inactivated ORFV suggested that de novo synthesis of early genes was required. In addition our findings showed that the ORFV encoded factor ORF020, that is known to bind dsRNA, is involved in antagonising IFN expression. Overall, this study has shown for first time the ability of ORFV to counteract type I IFN expression by antagonising dsRNA-activated RIG-I signalling.

Animal poxvirus vaccines: a comprehensive review

The family Poxviridae includes several viruses of medical and veterinary importance. Global concerted efforts combined with an intensive mass-vaccination campaign with highly efficaceious live vaccine of vaccinia virus have led to eradication of smallpox. However, orthopoxviruses affecting domestic animals continue to cause outbreaks in several endemic countries. Different kinds of vaccines starting from conventional inactivated/attenuated to recombinant protein-based vaccines have been used for control of poxvirus infections. Live virus homologous vaccines are currently in use for diseases including capripox, parapox, camelpox and fowlpox, and these vaccines are highly effective in eliciting (with the exception of parapoxviruses) long-lasting immunity. Attenuated strains of poxviruses have been exploited as vectored vaccines to deliver heterologous immunogens, many of them being licensed for use in animals. Worthy of note are vaccinia virus, fowlpox virus, capripoxvirus, parapoxvirus and canary pox, which have been successfully used for developing new-generation vaccines targeting many important pathogens. Remarkable features of these vaccines are thermostability and their ability to engender both cellular and humoral immune responses to the target pathogens. This article updates the important vaccines available for poxviruses of livestock and identifies some of the research gaps in the present context of poxvirus research.

Evaluation of homologous and heterologous protection induced by a virulent field strain of orf virus and an orf vaccine in goats

OBJECTIVE

To evaluate cross protection provided by administration of contagious ecthyma vaccines against strains of orf virus in goats.

ANIMALS

126 Boer-Spanish crossbred goats (3 to 20 days old).

PROCEDURES

85 goats were vaccinated with a goat-derived contagious ecthyma vaccine. Of these, 41 were challenge exposed with the virus strain for the contagious ecthyma vaccine, 40 were challenge exposed with a more virulent field strain of orf virus, and 4 were lost to predation or died. Another 41 goats were vaccinated with a vaccine produced from a more virulent field strain of orf virus; of these, 18 were challenge exposed with the virus strain of the goat-derived contagious ecthyma vaccine, 18 were challenge exposed with the more virulent field strain of orf virus, and 5 were lost to predation or died.

RESULTS

Vaccination with the goat-derived contagious ecthyma vaccine did not significantly reduce the number of goats with lesions or lesion severity caused by challenge exposure with the more virulent field strain of orf virus. Vaccination with the vaccine produced from the more virulent field strain of orf virus significantly reduced the number of goats with lesions attributable to challenge exposure with the virus strain of the goat-derived contagious ecthyma vaccine, but it failed to significantly reduce lesion severity.

CONCLUSIONS AND CLINICAL RELEVANCE

Vaccination did not result in cross protection for the 2 strains of orf virus. This may have been attributable to antigenic differences and may be a factor in outbreaks of contagious ecthyma in vaccinated goats.

Characterization of immunostimulatory components of orf virus (parapoxvirus ovis)

Inactivated orf virus (ORFV, parapoxvirus ovis) induces antiviral activity in animal models of acute and chronic viral infections and exerts strong effects on human immune cells. ORFV activates antigen presenting cells (APC) via CD14 and, probably, Toll-like receptor signalling, and triggers the release of IFN-γ that has been identified as the key mediator of the antiviral activity. After delineating virus proteins as being the most likely active constituent, we aimed to characterize the ORFV proteins responsible for the therapeutic effect. By using a vaccinia virus/ORFV expression library we identified several multi-gene DNA fragments with strong immunomodulatory activity. Together these fragments contain 27 ORFs. The encoded proteins are related to virion structure and transcription but are otherwise unrelated. Two proteins were separately expressed and purified, and demonstrated immunostimulatory activity. Gene expression profiles induced by ORFV and the identified fragments were investigated by microarray analysis. Interestingly, all active fragments induced a similar gene-expression pattern, differing only in quantitative aspects. Obviously, several proteins of ORFV activate similar cellular pathways, modulating APC to generate a strong T-helper 1-dominated immune response. This was balanced by additional induction of immune dampening mechanisms, suggesting regulatory differences compared to single cytokine therapies. We conclude that ORFV may have the potential to enrich the armamentarium of antiviral therapies.

Cell cycle deregulation by a poxvirus partial mimic of anaphase-promoting complex subunit 11

The anaphase-promoting complex (APC), or cyclosome, is a ubiquitin ligase with major roles in cell cycle regulation. It is required for mitotic exit, but must be deactivated for the G(1)/S phase transition to occur. APC consists of at least 12 subunits with the catalytic core formed by a scaffold protein, APC2, and a RING-H2 protein, APC11. APC11 facilitates ubiquitin chain formation by recruiting ubiquitin-charged conjugating enzymes through its RING-H2 domain. We report that a small number of poxviruses encode RING-H2 proteins with sequence similarities to APC11. We show that a representative of these viral proteins mimics APC11 in its interactions with APC, but unlike APC11, the viral protein fails to promote ubiquitin chain formation. This absence of ubiquitin ligase activity is linked to a distinctive sequence variation within its RING-H2 domain. Expression of the viral protein led to cell cycle deregulation and the accumulation of APC substrates in a manner consistent with impaired APC function. Our data characterize this protein as a regulator of APC activity, and consequently, we have called it PACR (poxvirus APC/cyclosome regulator). Deletion of the PACR gene substantially reduced viral replication. Here, we report a viral mimic of an APC component and reveal an intriguing mechanism by which viruses can manipulate cell cycle progression and, thereby, promote their own replication.

A novel Bcl-2-like inhibitor of apoptosis is encoded by the parapoxvirus ORF virus

Apoptotic cell death forms part of the host defense against virus infection. We tested orf virus, a member of the poxvirus family, for the ability to inhibit apoptosis and found that orf virus-infected cells were fully resistant to UV-induced changes in cell morphology, caspase activation, and DNA fragmentation. By using a library of vaccinia virus-orf virus recombinants, we identified an orf virus gene (ORFV125) whose presence was linked with the inhibition of apoptosis. The 173-amino-acid predicted protein had no clear homologs in public databases other than those encoded by other parapoxviruses. However, ORFV125 possessed a distinctive C-terminal domain which was necessary and sufficient to direct the protein to the mitochondria. We determined that ORFV125 alone could fully inhibit UV-induced DNA fragmentation, caspase activation, and cytochrome c release and that its mitochondrial localization was required for its antiapoptotic function. In contrast, ORFV125 did not prevent UV-induced activation of c-Jun NH2-terminal kinase, an event occurring upstream of the mitochondria. These features are comparable to the antiapoptotic properties of the mitochondrial regulator Bcl-2. Furthermore, bioinformatic analyses revealed sequence and secondary-structure similarities to Bcl-2 family members, including characteristic residues of all four Bcl-2 homology domains. Consistent with this, the viral protein inhibited the UV-induced activation of the proapoptotic Bcl-2 family members Bax and Bak. ORFV125 is the first parapoxvirus apoptosis inhibitor to be identified, and we propose that it is a new antiapoptotic member of the Bcl-2 family.

Comparative analysis of genome sequences of three isolates of Orf virus reveals unexpected sequence variation

Orf virus (ORFV) is the type species of the Parapoxvirus genus. Here, we present the genomic sequence of the most well studied ORFV isolate, strain NZ2. The NZ2 genome is 138 kbp and contains 132 putative genes, 88 of which are present in all analyzed chordopoxviruses. Comparison of the NZ2 genome with the genomes of 2 other fully sequenced isolates of ORFV revealed that all 3 genomes carry each of the 132 genes, but there are substantial sequence variations between isolates in a significant number of genes, including 9 with inter-isolate amino acid sequence identity of only 38-79%. Each genome has an average of 64% G+C but each has a distinctive pattern of substantial deviation from the average within particular regions of the genome. The same pattern of variation was also seen in the genome of another parapoxvirus species and was clearly unlike the uniform patterns of G+C content seen in all other genera of chordopoxviruses. The availability of genomic sequences of three orf virus isolates allowed us to more accurately assess likely coding regions and thereby revise published data for 24 genes and to predict two previously unrecognized genes.

Immunity and counter-immunity during infection with the parapoxvirus orf virus

Orf virus is a DNA parapoxvirus that causes orf, an acute debilitating skin disease of sheep, goats and humans. In sheep, a vigorous immune response involving neutrophils, dermal dendritic cells, T cells, B cells and antibody is generated after infection. CD4(+) T cells, IFN-gamma and to a lesser extent CD8(+) T cells are involved in partial protection against infection. In spite of this, orf virus can repeatedly infect sheep albeit with reduced lesion size and time to resolution compared to primary infection. This is due at least in part to the action of virus immuno-modulator proteins that interfere with host immune and inflammatory responses. These include: an interferon resistance protein; a viral orthologue of mammalian IL-10 (vIL-10) that is an anti-inflammatory cytokine; and a novel inhibitor of the cytokines GM-CSF and IL-2 (GIF). The virus also encodes a virulence protein that is an orthologue of mammalian vascular endothelial growth factor. The study of the immuno-modulator proteins provides an insight into disease pathogenesis and important elements of a host protective response. This information will be used to devise a rational disease control strategy.

Parapoxviruses: from the lesion to the viral genome

Viruses of the genus parapoxvirus from the family poxviridae cause widespread but localized diseases of small and large ruminants. The economically most important disease is contagious pustular dermatitis or contagious ecthyma among sheep and goats, often simply called orf. The parapoxviruses (PPV) can be transmitted to man leading to localized lesions that are named pseudocowpox or milkers' node as being mostly restricted to the hands and fingers. In cattle two forms of PPV manifestation are commonly observed, the bovine papular stomatitis in young calves and the occurrence of lesions at the udder of cows. We here report about the recent efforts in molecular characterization of orf viruses and the state of the art about the generation of orf virus recombinants. In addition the current knowledge on immune responses against orf viruses and some new data on the behaviour of orf virus recombinants under non-permissive conditions are reported.

Evidence for a parapox ovis virus-associated superantigen

As shown in a number of species, susceptibility to infectious diseases can be efficiently reduced following application of inactivated parapox ovis viruses (iPPOV). However, the basic mechanism for this stimulating capacity of iPPOV remains unclear. When analyzed, the interaction of iPPOV with porcine peripheral blood mononuclear cells was seen to involve T helper cells as the main target cell population responding to iPPOV. These cells displayed a strong proliferation, and were the major source for the observed increased levels of IL-2. Activation of the T helper cells was MHC class II dependent, but not MHC class II restricted: cellular processing of iPPOV was not required for presentation by autologous, allogeneic or xenogeneic MHC class II molecules. Furthermore, CD3 and CD4 molecules were involved in the stimulation, indicating a receptor-mediated activation of T helper cells. The results demonstrated typical characteristics of a superantigen-induced response providing evidence for a viral component within PPOV functioning as superantigen(s) in swine.

Orf virus encodes a novel secreted protein inhibitor of granulocyte-macrophage colony-stimulating factor and interleukin-2

The parapoxvirus orf virus encodes a novel soluble protein inhibitor of ovine granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2). The GM-CSF- and IL-2-inhibitory factor (GIF) gene was expressed as an intermediate-late viral gene in orf virus-infected cells. GIF formed homodimers and tetramers in solution, and it bound ovine GM-CSF with a K(d) of 369 pM and ovine IL-2 with a K(d) of 1.04 nM. GIF did not bind human GM-CSF or IL-2 in spite of the fact that orf virus is a human pathogen. GIF was detected in afferent lymph plasma draining the skin site of orf virus reinfection and was associated with reduced levels of lymph GM-CSF. GIF expression by orf virus indicates that GM-CSF and IL-2 are important in host antiviral immunity.