The 131-amino-acid repeat region of the essential 39-kilodalton core protein of fowlpox virus FP9, equivalent to vaccinia virus A4L protein, is nonessential and highly immunogenic

Modulation of Early Host Innate Immune Response by an Avipox Vaccine Virus' Lateral Body Protein

The avian pathogen fowlpox virus (FWPV) has been successfully used as a vaccine vector in poultry and humans, but relatively little is known about its ability to modulate host antiviral immune responses in these hosts, which are replication-permissive and nonpermissive, respectively. FWPV is highly resistant to avian type I interferon (IFN) and able to completely block the host IFN-response. Microarray screening of host IFN-regulated gene expression in cells infected with 59 different, nonessential FWPV gene knockout mutants revealed that FPV184 confers immunomodulatory capacity. We report that the FPV184-knockout virus (FWPVΔ184) induces the cellular IFN response as early as 2 h postinfection. The wild-type, uninduced phenotype can be rescued by transient expression of FPV184 in FWPVΔ184-infected cells. Ectopic expression of FPV184 inhibited polyI:C activation of the chicken IFN-β promoter and IFN-α activation of the chicken Mx1 promoter. Confocal and correlative super-resolution light and electron microscopy demonstrated that FPV184 has a functional nuclear localisation signal domain and is packaged in the lateral bodies of the virions. Taken together, these results provide a paradigm for a late poxvirus structural protein packaged in the lateral bodies, capable of suppressing IFN induction early during the next round of infection.

Transient Dominant Selection for the Modification and Generation of Recombinant Infectious Bronchitis Coronaviruses

We have developed a reverse genetics system for the avian coronavirus infectious bronchitis virus (IBV) in which a full-length cDNA corresponding to the IBV genome is inserted into the vaccinia virus genome under the control of a T7 promoter sequence. Vaccinia virus as a vector for the full-length IBV cDNA has the advantage that modifications can be introduced into the IBV cDNA using homologous recombination, a method frequently used to insert and delete sequences from the vaccinia virus genome. Here, we describe the use of transient dominant selection as a method for introducing modifications into the IBV cDNA that has been successfully used for the substitution of specific nucleotides, deletion of genomic regions, and the exchange of complete genes. Infectious recombinant IBVs are generated in situ following the transfection of vaccinia virus DNA, containing the modified IBV cDNA, into cells infected with a recombinant fowlpox virus expressing T7 DNA-dependent RNA polymerase.

Comparative sequence and structural analysis of the ORF095 gene, a vaccinia virus A4L homolog of capripoxvirus in sheep and goats

Sheeppox and goatpox are important transboundary animal viral diseases of sheep and goats caused by sheeppox virus (SPPV) and goatpox virus (GTPV), respectively, of the genus Capripoxvirus, family Poxviridae. Among the proteins encoded by the capripoxvirus (CaPV) genome, ORF095 (vaccinia virus A4L homolog) is an immunodominant virion core protein that plays a pivotal role in virus assembly and morphogenesis. In the present study, sequence analysis of the ORF095 genes of 27 SPPV and GTPV isolates or field samples from different geographical regions of India was performed, and structure was prediction was done by homology modeling. A multiple sequence alignment of different CaPV isolates revealed that CaPV-A4L is highly conserved, with several species-specific signature residues, namely A93, A216, A315, G136 and G146 in GTPV, G47, A63, A168 and A276 in SPPV, and G48 and C98 in lumpy skin disease virus (LSDV). Phylogenetically, the CaPV isolates were separated into three major clusters, GTPV, SPPV and LSDV, based on the complete coding sequence of the CaPV-A4L gene. Genus-specific clustering of poxviruses was observed in phylogenetic analysis based on A4L protein homologs of chordopoxviruses. A secondary structure prediction showed the presence of six α-helices and one β-sheet as well as some coils. The signature residues identified here are potentially useful for genotyping, and the predicted characteristics of the CaPV-A4L protein make it an ideal candidate for use as an immunogenic or diagnostic antigen for the development of immunoassays in  the sero-evaluation of CaPV in target hosts.

Reverse Genetics System for the Avian Coronavirus Infectious Bronchitis Virus

We have developed a reverse genetics system for the avian coronavirus infectious bronchitis virus (IBV) in which a full-length cDNA corresponding to the IBV genome is inserted into the vaccinia virus genome under the control of a T7 promoter sequence. Vaccinia virus as a vector for the full-length IBV cDNA has the advantage that modifications can be introduced into the IBV cDNA using homologous recombination, a method frequently used to insert and delete sequences from the vaccinia virus genome. Here, we describe the use of transient dominant selection as a method for introducing modifications into the IBV cDNA that has been successfully used for the substitution of specific nucleotides, deletion of genomic regions, and exchange of complete genes. Infectious recombinant IBVs are generated in situ following the transfection of vaccinia virus DNA, containing the modified IBV cDNA, into cells infected with a recombinant fowlpox virus expressing T7 DNA-dependant RNA polymerase.

Diagnosis and phylogenetic analysis of a multifocal cutaneous orf virus with mixed bacterial infection outbreak in goats in Fujian province, China

Outbreaks of orf virus on goat farms are common in China. In this study, we investigated a severe multifocal cutaneous orf virus outbreak with a correlative mixed bacterial infection which persisted for up to 6 months, and which had a high morbidity (93.7%) and mortality (15%) among kids in a herd of crossbreed goats in Fujian province in China. The disease was diagnosed as an orf virus (ORFV XD strain) infection associating with Streptococcus pluranimalium and Staphylococcus, identified using standard virological and bacteriological techniques. Multiple sequence alignments and phylogenetic analyses of the whole ORFV 011 (B2L), 059 (F1L), 032 and 080 genes revealed that the even though the virus phylogeny was clustered in branches of conventional orf virus strains, it nonetheless evidenced high variation within this subset. Furthermore, the sequences from the ORFV 080 gene allowed us to distinguish between the different strains at a higher resolution and these observations afforded us a comparative view of the ORFV 080 gene. This is the first report describing an outbreak of severe multifocal cutaneous orf virus with associated bacterial infection in China.

Reverse Genetics of Avian Coronavirus Infectious Bronchitis Virus

We have developed a reverse genetics system for the avian coronavirus infectious bronchitis virus (IBV) in which a full-length cDNA corresponding to the IBV genome is inserted into the vaccinia virus genome under the control of a T7 promoter sequence. Vaccinia virus as a vector for the full-length IBV cDNA has the advantage that modifications can be introduced into the IBV cDNA using homologous recombination, a method frequently used to insert and delete sequences from the vaccinia virus genome. Here, we describe the use of transient dominant selection as a method for introducing modifications into the IBV cDNA; that has been successfully used for the substitution of specific nucleotides, deletion of genomic regions, and the exchange of complete genes. Infectious recombinant IBVs are generated in situ following the transfection of vaccinia virus DNA, containing the modified IBV cDNA, into cells infected with a recombinant fowlpox virus expressing T7 DNA dependant RNA polymerase.

Transient dominant selection for the modification and generation of recombinant infectious bronchitis coronaviruses

We have developed a reverse genetics system for the avian coronavirus infectious bronchitis virus (IBV) in which a full-length cDNA corresponding to the IBV genome is inserted into the vaccinia virus genome under the control of a T7 promoter sequence. Vaccinia virus as a vector for the full-length IBV cDNA has the advantage that modifications can be introduced into the IBV cDNA using homologous recombination, a method frequently used to insert and delete sequences from the vaccinia virus genome. Here, we describe the use of transient dominant selection as a method for introducing modifications into the IBV cDNA; this has been successfully used for the substitution of specific nucleotides, deletion of genomic regions, and the exchange of complete genes. Infectious recombinant IBVs are generated in situ following the transfection of vaccinia virus DNA, containing the modified IBV cDNA, into cells infected with a recombinant fowlpox virus expressing T7 DNA-dependent RNA polymerase.

Construction of FWPV Chimaeric MVA

Construction of chimaeric MVA is a useful tool with which to study gene function of related viruses. The protocol given here describes MVA chimaeras containing genes from Fowlpox virus (FWPV), although this can be applied to DNA derived from other organisms. There are a number of steps required to make the chimaeric MVA: 1) Purification of viral particles; 2) Extraction of DNA from purified viral particles; 3) Assembly of linear recombination templates; 4) Transfection of linear recombination templates; 5) Selection of chimaeric MVA. Note: This procedure uses live virus, and should be conducted using Good Microbiological Practice, in accordance with international and national biocontainment requirements. This procedure also involves Genetic Modification of microorganisms, and appropriate safety approval should be obtained before commencing.

Construction of Deletion-knockout Mutant Fowlpox Virus (FWPV)

The construction of deletion-knockout poxviruses is a useful approach to determining the function of specific virus genes. This protocol is an adaptation of the transient dominant knockout selection protocol published by Falkner and Moss (1990) for use with vaccinia virus. The protocol makes use of the dominant selectable marker Escherichia coli guanine phosphoribosyltransferase (gpt) gene (Mulligan and Berg, 1981), under the control of an early/late poxvirus promoter. The deletion viruses that are produced no longer contain a selectable marker, which may be preferable for the production of vaccines.

Fowlpox virus as a recombinant vaccine vector for use in mammals and poultry

Live vaccines against fowlpox virus, which causes moderate pathology in poultry and is the type species of the Avipoxvirus genus, were developed in the 1920s. Development of recombinant fowlpox virus vector vaccines began in the 1980s, for use not only in poultry, but also in mammals including humans. In common with other avipoxviruses, such as canarypox virus, fowlpox virus enters mammalian cells and expresses proteins, but replicates abortively. The use of fowlpox virus as a safe vehicle for expression of foreign antigens and host immunomodulators, is being evaluated in numerous clinical trials of vaccines against cancer, malaria, tuberculosis and AIDS, notably in heterologous prime-boost regimens. In this article, technical approaches to, and issues surrounding, the use of fowlpox virus as a recombinant vaccine vector in poultry and mammals are reviewed.

Genetic screen of a mutant poxvirus library identifies an ankyrin repeat protein involved in blocking induction of avian type I interferon

Mammalian poxviruses, including vaccinia virus (VACV), have evolved multiple mechanisms to evade the host type I interferon (IFN) responses at different levels, with viral proteins targeting IFN induction, signaling, and antiviral effector functions. Avian poxviruses (avipoxviruses), which have been developed as recombinant vaccine vectors for permissive (i.e., poultry) and nonpermissive (i.e., mammals, including humans) species, encode no obvious equivalents of any of these proteins. We show that fowlpox virus (FWPV) fails to induce chicken beta IFN (ChIFN2) and is able to block its induction by transfected poly(I·C), an analog of cytoplasmic double-stranded RNA (dsRNA). A broad-scale loss-of-function genetic screen was used to find FWPV-encoded modulators of poly(I·C)-mediated ChIFN2 induction. It identified fpv012, a member of a family of poxvirus genes highly expanded in the avipoxviruses (31 in FWPV; 51 in canarypox virus [CNPV], representing 15% of the total gene complement), encoding proteins containing N-terminal ankyrin repeats (ANKs) and C-terminal F-box-like motifs. Under ectopic expression, the first ANK of fpv012 is dispensable for inhibitory activity and the CNPV ortholog is also able to inhibit induction of ChIFN2. FWPV defective in fpv012 replicates well in culture and barely induces ChIFN2 during infection, suggesting that other factors are involved in blocking IFN induction and resisting the antiviral effectors. Nevertheless, unlike parental and revertant viruses, the mutants induce moderate levels of expression of interferon-stimulated genes (ISGs), suggesting either that there is sufficient ChIFN2 expression to partially induce the ISGs or the involvement of alternative, IFN-independent pathways that are also normally blocked by fpv012.

Re-emerging fowlpox: evaluation of isolates from vaccinated flocks

Vaccines of fowlpox or pigeonpox virus origin have been routinely used for more than half a century to prevent fowlpox in commercial poultry in areas where the disease is endemic. However, in recent years, outbreaks of fowlpox have occurred in previously vaccinated flocks. One possible explanation for this problem is the emergence of variant strains of fowlpox virus (FPV). A second, not mutually exclusive, postulate is that the novel FPV exhibit enhanced virulence due to the integration of avian reticuloendotheliosis virus (REV) into their genomes. To determine if immunological variance and/or the acquisition of REV nucleotide sequences could be responsible for the ineffectiveness of current vaccines, the ability of two commercial vaccine viruses and four, recently isolated, field strains to protect chickens against challenge with one of the more virulent field viruses was evaluated. Adequate protection was provided by the vaccines and two of the four field isolates. Interestingly, the two isolates that were not protective, as well as the challenge strain, failed to elicit a strong humoral antibody response. As to possible REV participation, an antibody response to this virus was only found in those chickens receiving one of the ''protective'' field strains, despite the presence of REV coding sequences in all four field viruses. While REV long terminal repeats of variable lengths were detected in the genomes of all FPV strains used in this study, only the DNAs of the field strains appeared to have intact REV provirus. This retention of foreign DNA may enhance the pathogenesis of FPV, although other factors may be involved.

Development of FPV140 antigen-specific ELISA differentiating fowlpox virus isolates from all other viral pathogens of avian origin

The FPV140 gene encodes an envelope protein of fowlpox virus (FPV). In this study, the FPV140 gene of FPV Chinese isolate HH2008 was cloned and the comparison of its sequence with other FPV isolates showed it to be highly conserved across all FPV isolates. A recombinant plasmid pET-FPV140 carrying FPV140 gene was constructed and transformed into Escherichia coli. The optimal expression condition for the FPV140 gene was developed and purified FPV140 recombinant protein was used to produce rabbit polyclonal antibody. An indirect ELISA using this anti-FPV140 polyclonal antibody was capable of distinguishing avian FPV isolates from other common avian pathogens such as mycoplasma gallisepticum, infectious laryngotracheitis virus, avian influenza virus, infectious bursal disease virus, and avian infectious bronchitis virus. This ELISA will serve as a useful diagnostic tool for the detection of FPV in clinical samples.

Evaluation of a non-viral vaccine in smallpox-vaccinated individuals and immunized HLA-transgenic mice

The current poxvirus vaccine is associated with rare, but serious adverse events. Therefore, we investigated a non-replicating approach to vaccine design. Peptides encoding potential HLA-binding motifs were derived from the orthopoxvirus genes, D8L, A27L, and C12L (the IL-18-binding protein [vIL18BP105]), all of which are preserved among poxviruses that infect humans, and which may be a target of host immunity. The peptides were tested with poxvirus-vaccinated human PBMC and serum for eliciting memory responses, as well as with splenocytes and serum from peptide-immunized, human HLA-DR04 transgenic (HLA tg) mice. vIL18BP105 induced 5-fold proliferation of vaccinated-donor PBMC over non-vaccinated (P<0.001), including IL-2-producing CD8+ cells. Serum IgG recognizing vIL18BP105 was detected (P<0.002 vs non-vaccinated) by ELISA. Viral peptides were conjugated to the HLA-targeting mAb, L243, for immunization of HLA tg mice. Splenocytes from vIL18BP105-L243-immunized mice proliferated upon exposure to vIL18BP105 (P<0.001). Proliferating splenocytes were interferon-γ-producing CD4(+)CD45RA(neg). vIL18BP105-L243-immunized mice generated IgG more rapidly than free-peptide-immunized mice. Peptide-specific antibody was also detected when different L243-peptide conjugates were combined. vIL18BP, by eliciting human memory responses, is a viable antigen for inclusion in a virus-free vaccine. The immunogenicity of peptides was boosted by conjugation to L243, whether administered alone or combined.

Differential effects of viral vectors on migratory afferent lymph dendritic cells in vitro predict enhanced immunogenicity in vivo

Targeting dendritic cells (DC) is key to driving effective immune responses. Lymphatic cannulation provides access to the heterogeneous populations of DC draining peripheral sites in rodents and ruminants. Afferent lymph DEC-205(+) CD11c(+) SIRPα(+) DC were preferentially infected ex vivo with three vaccine viral vectors: recombinant human replication-defective human adenovirus 5 (rhuAdV5), recombinant modified vaccinia virus Ankara (rMVA), and recombinant fowlpox virus (rFPV), all expressing green fluorescent protein (GFP). The rhuAdV5-infected cells remained viable, and peak GFP expression was observed 16 to 24 h posttransduction. Increasing the incubation period of DC with rhuAdV5 enhanced GFP expression. In contrast, DC infected with rMVA-GFP or rFPV-GFP became rapidly apoptotic and GFP expression peaked at 6 h postinfection. Delivery of foot-and-mouth disease virus (FMDV) A(22) antigen to DC by rhuAdV5-FMDV-A(22) ex vivo resulted in significantly greater CD4(+) T cell proliferation than did delivery by rFPV-FMDV-A(22). Delivery of rhuAdV5-GFP in oil adjuvant in vivo, to enhance DC-vector contact, resulted in increased GFP expression in migrating DC compared to that with vector alone. Similarly, CD4(+) T cell responses were significantly enhanced when using rhuAdV5-FMDV-A(22) in adjuvant. Therefore, the interaction between viral vectors and afferent lymph DC ex vivo can predict the outcome of in vivo immunization and provide a means of rapidly assessing the effects of vector modification.

Interaction of poxvirus intracellular mature virion proteins with the TPR domain of kinesin light chain in live infected cells revealed by two-photon-induced fluorescence resonance energy transfer fluorescence lifetime imaging microscopy

Using two-photon-induced fluorescence lifetime imaging microscopy, we corroborate an interaction (previously demonstrated by yeast two-hybrid domain analysis) of full-length vaccinia virus (VACV; an orthopoxvirus) A36 protein with the cellular microtubule motor protein kinesin. Quenching of enhanced green fluorescent protein (EGFP), fused to the C terminus of VACV A36, by monomeric red fluorescent protein (mDsRed), fused to the tetratricopeptide repeat (TPR) domain of kinesin, was observed in live chicken embryo fibroblasts infected with either modified vaccinia virus Ankara (MVA) or wild-type fowlpox virus (FWPV; an avipoxvirus), and the excited-state fluorescence lifetime of EGFP was reduced from 2.5 ± 0.1 ns to 2.1 ± 0.1 ns due to resonance energy transfer to mDsRed. FWPV does not encode an equivalent of intracellular enveloped virion surface protein A36, yet it is likely that this virus too must interact with kinesin to facilitate intracellular virion transport. To investigate possible interactions between innate FWPV proteins and kinesin, recombinant FWPVs expressing EGFP fused to the N termini of FWPV structural proteins Fpv140, Fpv168, Fpv191, and Fpv198 (equivalent to VACV H3, A4, p4c, and A34, respectively) were generated. EGFP fusions of intracellular mature virion (IMV) surface protein Fpv140 and type II membrane protein Fpv198 were quenched by mDsRed-TPR in recombinant FWPV-infected cells, indicating that these virion proteins are found within 10 nm of mDsRed-TPR. In contrast, and as expected, EGFP fusions of the IMV core protein Fpv168 did not show any quenching. Interestingly, the p4c-like protein Fpv191, which demonstrates late association with preassembled IMV, also did not show any quenching.

Integration of the reticuloendotheliosis virus envelope gene into the poultry fowlpox virus genome is not universal

Fowlpox virus (FWPV) is found worldwide in poultry and wild birds. FWPV is a natural example of recombination between viruses, as reticuloendotheliosis virus (REV) fragments have been found in all poultry FWPVs and these are implicated in virulence alteration. We aimed to determine the commonality of this phenomenon and analysed FWPVs collected from 128 poultry flocks and birds over the last 10 years. Various fragments of both viruses were amplified and sequenced at the FWPV integration site, located between FWPV open reading frames 201 and 203. Seven isolates were found to contain no REV insertions, including fragments of the REV env, gag and 5′ REV-long terminal repeat (LTR). We demonstrate here for the first time, the existence of poultry FWPVs without REV inserts (two from chickens, one from turkey FWPV and four from wild birds). The REV inserts were heterogeneous in size. In addition to poultry and wild bird isolates, three FWPV vaccine virus strains were examined and found to contain only remnant REV-LTR and no REV envelope gene fragments.

Neither the RNA nor the proteins of open reading frames 3a and 3b of the coronavirus infectious bronchitis virus are essential for replication

Gene 3 of infectious bronchitis virus is tricistronic; open reading frames (ORFs) 3a and 3b encode two small nonstructural (ns) proteins, 3a and 3b, of unknown function, and a third, structural protein E, is encoded by ORF 3c. To determine if either the 3a or the 3b protein is required for replication, we first modified their translation initiation codons to prevent translation of the 3a and 3b proteins from recombinant infectious bronchitis viruses (rIBVs). Replication in primary chick kidney (CK) cells and in chicken embryos was not affected. In chicken tracheal organ cultures (TOCs), the recombinant rIBVs reached titers similar to those of the wild-type virus, but in the case of viruses lacking the 3a protein, the titer declined reproducibly earlier. Translation of the IBV E protein is believed to be initiated by internal entry of ribosomes at a structure formed by the sequences corresponding to ORFs 3a and 3b. To assess the necessity of this mechanism, we deleted most of the sequence representing 3a and 3b to produce a gene in which ORF 3c (E) was adjacent to the gene 3 transcription-associated sequence. Western blot analysis revealed that the recombinant IBV produced fivefold less E protein. Nevertheless, titers produced in CK cells, embryos, and TOCs were similar to those of the wild-type virus, although they declined earlier in TOCs, probably due to the absence of the 3a protein. Thus, neither the tricistronic arrangement of gene 3, the internal initiation of translation of E protein, nor the 3a and 3b proteins are essential for replication per se, suggesting that these proteins are accessory proteins that may have roles in vivo.

Different levels of immunogenicity of two strains of Fowlpox virus as recombinant vaccine vectors eliciting T-cell responses in heterologous prime-boost vaccination strategies

The FP9 strain of F has been described as a more immunogenic recombinant vaccine vector than the Webster FPV-M (FPW) strain (R. J. Anderson et al., J. Immunol. 172:3094-3100, 2004). This study expands the comparison to include two separate recombinant antigens and multiple, rather than single, independent viral clones derived from the two strains. Dual-poxvirus heterologous prime-boost vaccination regimens using individual clones of recombinant FP9 or FPW in combination with recombinant modified V Ankara expressing the same antigen were evaluated for their ability to elicit T-cell responses against recombinant antigens from Plasmodium berghei (circumsporozoite protein) or human immunodeficiency virus type 1 (a Gag-Pol-Nef fusion protein). Gamma interferon enzyme-linked immunospot assay and fluorescence-activated cell sorting assays of the responses to specific epitopes confirmed the approximately twofold-greater cellular immunogenicity of FP9 compared to FPW, when given as the priming or boosting immunization. Equality of transgene expression in mouse cells infected with the two strains in vitro was verified by Western blotting. Directed partial sequence analysis and PCR analysis of FPW and comparison to available whole-genome sequences revealed that many loci that are mutated in the highly attenuated and culture-adapted FP9 strain are wild type in FPW, including the seven multikilobase deletions. These "passage-specific" alterations are hypothesized to be involved in determining the immunogenicity of fowlpox virus as a recombinant vaccine vector.

Avipoxvirus phylogenetics: identification of a PCR length polymorphism that discriminates between the two major clades

Avipoxvirus infections have been observed in an extensive range of wild, captive and domesticated avian hosts, yet little is known about the genome diversity and host-range specificity of the causative agent(s). Genome-sequence data are largely restricted to Fowlpox virus (FWPV) and Canarypox virus (CNPV), which have been sequenced completely, showing considerable divergence between them. It is therefore proving difficult, by empirical approaches, to identify pan-genus, avipoxvirus-specific oligonucleotide probes for PCR and sequencing to support phylogenetic studies. A previous preliminary study used the fpv167 locus, which encodes orthologues of vaccinia virus core protein P4b (A3). PCR per se did not discriminate between viruses, but restriction-enzyme or sequence analysis indicated that the avipoxviruses clustered either with FWPV or with CNPV. Here, further study of the P4b locus demonstrated a third cluster, from psittacine birds. A newly identified locus, flanking fpv140 (orthologue of vaccinia virus H3L), confirms the taxonomic structure. This locus is particularly useful in that viruses from the fowlpox-like and canarypox-like clusters can be discriminated by PCR on the basis of fragment size, whilst sequence comparison allows discrimination for the first time between Pigeonpox virus and Turkeypox virus. Except within the psittacines, virus and avian host taxonomies do not show tight correlation, with viruses from the same species located in very different clades. Nor are all the existing recognized avipoxvirus species, defined primarily by avian host species (such as CNPV and Sparrowpox virus), resolved within the present structure.

Construction and characterization of a fowlpox virus field isolate whose genome lacks reticuloendotheliosis provirus nucleotide sequences

Fowlpox virus (FWPV) has been isolated from vaccinated chicken flocks during subsequent fowlpox outbreaks that were characterized by a high degree of mortality and significant economic losses. This inability of current vaccines to induce adequate immunity in poultry could be reflective of an antigenic and/or biologic distinctiveness of FWPV field isolates. In this regard, whereas an infectious reticuloendotheliosis virus (REV) provirus is present in the majority of the field viruses' genomes, only remnants of REV long terminal repeats (LTR) have been retained in the DNAs of each vaccine strain. Although it has not been demonstrated whether the partial LTRs can provide an avenue for FWPV to reacquire the REV provirus by homologous recombination, utilizing viruses of which genomes lack any known integrated retroviral sequences could resolve concern over this issue. Therefore, such an entity was created by genetically modifying a recently isolated field strain of FWPV. This selection, in lieu of a commercial vaccine virus, as the progenitor was based on the probability that a virus circulating in the environment would be more antigenically similar to others in this locale and thus might be a better candidate for vaccine development. A comparison in vivo of the pathogenic traits of the parental wild-type field isolate, its genetically modified progeny, and a rescue mutant in whose genome the REV provirus was inserted at its previous location, indicated that elimination of the provirus sequence correlated with reduced virulence. However, even with elimination of the parasitic REV, the modified FWPV was still slightly more invasive than a commercial vaccine virus. Interestingly, both types of attenuated FWPV elicited a similar degree of antibody production in inoculated chickens and afforded them protection against a subsequent challenge by a field virus, the origin of which was temporally and geographically distinct from that of the progenitor strain. Due to its antigenicity being retained despite a decrease in virulence, this REV-less FWPV could potentially be developed as a vaccine against fowlpox.

Gene 5 of the avian coronavirus infectious bronchitis virus is not essential for replication

The avian coronavirus Infectious bronchitis virus (IBV), like other coronaviruses, expresses several small nonstructural (ns) proteins in addition to those from gene 1 (replicase) and the structural proteins. These coronavirus ns genes differ both in number and in amino acid similarity between the coronavirus groups but show some concordance within a group or subgroup. The functions and requirements of the small ns gene products remain to be elucidated. With the advent of reverse genetics for coronaviruses, the first steps in elucidating their role can be investigated. We have used our reverse genetics system for IBV (R. Casais, V. Thiel, S. G. Siddell, D. Cavanagh, and P. Britton, J. Virol. 75:12359-12369, 2001) to investigate the requirement of IBV gene 5 for replication in vivo, in ovo, and ex vivo. We produced a series of recombinant viruses, with an isogenic background, in which complete expression of gene 5 products was prevented by the inactivation of gene 5 following scrambling of the transcription-associated sequence, thereby preventing the expression of IBV subgenomic mRNA 5, or scrambling either separately or together of the translation initiation codons for the two gene 5 products. As all of the recombinant viruses replicated very similarly to the wild-type virus, Beau-R, we conclude that the IBV gene 5 products are not essential for IBV replication per se and that they are accessory proteins.

In vitro expression and analysis of secreted fowlpox virus CC chemokine-like proteins Fpv060, Fpv061, Fpv116 and Fpv121

The four CC chemokine-like proteins (Fpv060, Fpv061, Fpv116 and Fpv121) of fowlpox virus (FWPV) were over-expressed as His-tagged versions from a T7 promoter/EMCV IRES construct in vitro, by coupled transcription/translation, or in cell culture, by co-infection with two recombinant FWPVs (one expressing the chemokine-like protein and one expressing T7 RNA polymerase). All, except Fpv116, appeared to be glycosylated in the presence of microsomal membranes in vitro. In culture, all were secreted (even though secretion of Fpv061 was not predicted). Secreted forms of Fpv060 and Fpv121 were the most abundant forms of those two proteins. Glycosidase analysis of cellular and secreted forms confirmed that Fpv060, Fpv061 and Fpv121 were N-glycosylated and that the most abundant, cellular form of Fpv061 had been glycosylated but remained Endo H-sensitive (retained in the endoplasmic reticulum or Golgi). N-terminal sequence analysis of His-tagged Fpv060 and Fpv121 showed that they were processed at the predicted signal cleavage sites. Fpv060- and Fpv061-specific antipeptide sera allowed confirmation that the expression, processing and secretion of the native proteins were as determined for the His-tagged proteins. Isolation of knock-out mutants showed that all four proteins were non-essential for replication in tissue culture.

Avipoxvirus multiplication in a mammalian cell line

Avipoxviruses have many advantages and are being increasingly employed as recombinant vaccine vectors. One attractive feature is that while inserted transgenes are expressed in immunologically favourable ways, avipoxvirus infections of mammalian cells are believed to be abortive. The experimental evidence supporting this belief is, however, based on a limited number of mammalian cell-types and a few avipoxvirus species. We evaluated two avian and eight mammalian cell lines for permissivity to three avipoxvirus strains, one reference fowlpoxvirus and two newly isolated strains from sparrow and pigeon, respectively. Both avian cell lines were, as expected, permissive for all three avipoxvirus strains. However, by multiplication assays, we found to our surprise that Syrian baby hamster kidney (BHK-21) cells were equally permissive to all virus strains. Results from electron microscopy of infected BHK-21 cells revealed viral morphogenesis proceeding to various forms of infectious viruses. These results were supported by the demonstration of avipoxvirus specific late gene expression and avipoxvirus specific DNA restriction pattern in BHK-21 infected cells.

Generation of a recombinant avian coronavirus infectious bronchitis virus using transient dominant selection

A reverse genetics system for the avian coronavirus infectious bronchitis virus (IBV) has been described in which a full-length cDNA, corresponding to the IBV (Beaudette-CK) genome, was inserted into the vaccinia virus genome following in vitro assembly of three contiguous cDNAs [Casais, R., Thiel, V., Siddell, S.G., Cavanagh, D., Britton, P., 2001. Reverse genetics system for the avian coronavirus infectious bronchitis virus. J. Virol. 75, 12359-12369]. The method has subsequently been used to generate a recombinant IBV expressing a chimaeric S gene [Casais, R., Dove, B., Cavanagh, D., Britton, P., 2003. Recombinant avian infectious bronchitis virus expressing a heterologous spike gene demonstrates that the spike protein is a determinant of cell tropism. J. Virol. 77, 9084-9089]. Use of vaccinia virus as a vector for the full-length cDNA of the IBV genome has the advantage that modifications can be made to the IBV cDNA using homologous recombination, a method frequently used to insert and delete sequences from the vaccinia virus genome. We describe the use of homologous recombination as a method for modifying the Beaudette full-length cDNA, within the vaccinia virus genome, without the requirement for in vitro assembly of the IBV cDNA. To demonstrate the feasibility of the method we exchanged the ectodomain of the Beaudette spike gene for the corresponding region from IBV M41 and generated two recombinant infectious bronchitis viruses (rIBVs) expressing the chimaeric S protein, validating the method as an alternative way for generating rIBVs.

Comparison of the genome sequence of FP9, an attenuated, tissue culture-adapted European strain of Fowlpox virus, with those of virulent American and European viruses

The 266 kbp genome sequence of plaque-purified, tissue culture-adapted, attenuated EuropeanFowlpox virusFP9 has been determined and compared with the 288 kbp sequence of a pathogenic US strain (FPVUS). FP9 carries 244 of the 260 reported FPVUS ORFs (both viruses also have an unreported orthologue of conserved poxvirus gene A14.5L). Relative to FPVUS, FP9 differed by 118 mutations (26 deletions, 15 insertions and 77 base substitutions), affecting FP9 equivalents of 71 FPVUS ORFs. To help to identify mutations involved in adaptation and attenuation, the virulent parent of FP9, HP1, was sequenced at positions where FP9 differed from FPVUS. At 68 positions, FP9 and HP1 sequences were identical, reflecting differences between American and European lineages. Mutations at the remaining 50 positions in FP9 relative to FPVUS and HP1, involving 46 ORFs, therefore accounted for adaptation and attenuation. ORFs deleted during passage included those encoding members of multigene families: 12 ankyrin repeat proteins, three C-type lectin-like proteins, two C4L/C10L-like proteins, one G-protein coupled receptor protein, one V-type Ig domain protein, two N1R/p28 proteins and one EFc family protein. Tandem ORFs encodingVariola virusB22R orthologues were fused by a 5·8 kbp deletion. Single-copy genes disrupted or deleted during passage included those encoding a homologue of murine T10, a conserved DNA/pantothenate metabolism flavoprotein, photolyase, the A-type inclusion protein and an orthologue of vaccinia A47L. Gene assignments have been updated for DNase II/DLAD, binding proteins for IL-18 and interferon-γ, phospholipid hydroperoxide glutathione peroxidase (PHGPX/GPX-4) and for a highly conserved homologue of ELOVL4.

Genomes of the parapoxviruses ORF virus and bovine papular stomatitis virus

Bovine papular stomatitis virus (BPSV) and orf virus (ORFV), members of the genus Parapoxvirus of the Poxviridae, are etiologic agents of worldwide diseases affecting cattle and small ruminants, respectively. Here we report the genomic sequences and comparative analysis of BPSV strain BV-AR02 and ORFV strains OV-SA00, isolated from a goat, and OV-IA82, isolated from a sheep. Parapoxvirus (PPV) BV-AR02, OV-SA00, and OV-IA82 genomes range in size from 134 to 139 kbp, with an average nucleotide composition of 64% G+C. BPSV and ORFV genomes contain 131 and 130 putative genes, respectively, and share colinearity over 127 genes, 88 of which are conserved in all characterized chordopoxviruses. BPSV and ORFV contain 15 and 16 open reading frames (ORFs), respectively, which lack similarity to other poxvirus or cellular proteins. All genes with putative roles in pathogenesis, including a vascular endothelial growth factor (VEGF)-like gene, are present in both viruses; however, BPSV contains two extra ankyrin repeat genes absent in ORFV. Interspecies sequence variability is observed in all functional classes of genes but is highest in putative virulence/host range genes, including genes unique to PPV. At the amino acid level, OV-SA00 is 94% identical to OV-IA82 and 71% identical to BV-AR02. Notably, ORFV 006/132, 103, 109, 110, and 116 genes (VEGF, homologues of vaccinia virus A26L, A33R, and A34R, and a novel PPV ORF) show an unusual degree of intraspecies variability. These genomic differences are consistent with the classification of BPSV and ORFV as two PPV species. Compared to other mammalian chordopoxviruses, PPV shares unique genomic features with molluscum contagiosum virus, including a G+C-rich nucleotide composition, three orthologous genes, and a paucity of nucleotide metabolism genes. Together, these data provide a comparative view of PPV genomics.

The HIV-1 chimeric protein CR3 expressed by poxviral vectors induces a diverse CD8+ T cell response in mice and is antigenic for PBMCs from HIV+ patients

Recombinant avipoxvirus vectors are attractive for vaccination against human immunodeficiency virus type 1 (HIV-1), where induction of a cytotoxic CD8(+) T cell (CTL) response seems to be an important component of protective immunity. We expressed the chimeric protein CR3, composed by CTL epitopes rich regions from, RT, Gag and Nef and conserved Th cell epitopes from gp120, gp41 and Vpr of HIV-1 in a fowlpox virus (FWPV) vector (FPCR3), and used this vector to induce HIV-specific CTL responses in mice. Mice immunised twice intraperitoneally with FPCR3, developed a CD8(+) T cell response measured as production of IFN-gamma by splenocytes in response to stimulation with P815 cells infected with recombinant vaccinia viruses (rVV) expressing CR3, Gag and Nef. The number of IFN-gamma secreting cells was markedly higher when a P815 cell line constitutively expressing CR3 was used as target cells for Enzyme-linked-immunospot (ELISPOT). CR3 epitopes were also specifically recognised by human PBMCs from three HIV(+) patients with different haplotypes. These results confirm the potential of FWPV vectors expressing these novel HIV-1 chimeric proteins to induce a simultaneous CD8(+) T cell response against conserved viral targets and early expressed regulatory proteins.

Poxvirus orthologous clusters: toward defining the minimum essential poxvirus genome

Increasingly complex bioinformatic analysis is necessitated by the plethora of sequence information currently available. A total of 21 poxvirus genomes have now been completely sequenced and annotated, and many more genomes will be available in the next few years. First, we describe the creation of a database of continuously corrected and updated genome sequences and an easy-to-use and extremely powerful suite of software tools for the analysis of genomes, genes, and proteins. These tools are available free to all researchers and, in most cases, alleviate the need for using multiple Internet sites for analysis. Further, we describe the use of these programs to identify conserved families of genes (poxvirus orthologous clusters) and have named the software suite POCs, which is available at www.poxvirus.org. Using POCs, we have identified a set of 49 absolutely conserved gene families-those which are conserved between the highly diverged families of insect-infecting entomopoxviruses and vertebrate-infecting chordopoxviruses. An additional set of 41 gene families conserved in chordopoxviruses was also identified. Thus, 90 genes are completely conserved in chordopoxviruses and comprise the minimum essential genome, and these will make excellent drug, antibody, vaccine, and detection targets. Finally, we describe the use of these tools to identify necessary annotation and sequencing updates in poxvirus genomes. For example, using POCs, we identified 19 genes that were widely conserved in poxviruses but missing from the vaccinia virus strain Tian Tan 1998 GenBank file. We have reannotated and resequenced fragments of this genome and verified that these genes are conserved in Tian Tan. The results for poxvirus genes and genomes are discussed in light of evolutionary processes.

Reticuloendotheliosis virus sequences within the genomes of field strains of fowlpox virus display variability

Nine field strains of fowlpox virus (FPV) isolated during a 24-year span from geographically diverse outbreaks of fowlpox in the United States were screened for the presence of reticuloendotheliosis virus (REV) sequences in their genomes by PCR. Each isolate appeared to be heterogeneous in that either a nearly intact provirus or just a 248- or 508-nucleotide fusion of portions of the integrated REV 5' and 3' long terminal repeats (LTRs) was exclusively present at the same genomic site. In contrast, four fowlpox vaccines of FPV origin and three originating from pigeonpox virus were genetically homogeneous in having retained only the 248-bp LTR fusion, whereas two other FPV-based vaccines had only the larger one. These remnants of integrated REV presumably arose during homologous recombination at one of the two regions common to both LTRs or during retroviral excision from the FPV genome. Loss of the provirus appeared to be a natural event because the tripartite population could be detected in a field sample (tracheal lesion). Moreover, the provirus was also readily deleted during propagation of FPV in cultured cells, as evidenced by the detection of truncated LTRs after one passage of a plaque-purified FPV recombinant having a "genetically marked" provirus. However, the deletion mutants did not appear to have a substantial replicative advantage in vitro because even after 55 serial passages the original recombinant FPV was still prevalent. As to the in vivo environment, retention of the REV provirus may confer some benefit to FPV for infection of poultry previously vaccinated against fowlpox.

Recognition of bovine respiratory syncytial virus proteins by bovine CD8+ T lymphocytes

CD8+ T lymphocytes play a major role in the clearance of bovine respiratory syncytial virus (BRSV), an important respiratory pathogen of young calves that shares many of the epidemiological and pathological features of human respiratory syncytial virus (HRSV) in infants. Recombinant vaccinia virus (rVV) and recombinant fowlpox virus (rFPV), expressing individual BRSV proteins, were used to demonstrate that the F, N and M2 proteins were the major antigens recognized by bovine CD8+ T cells in major histocompatibility complex (MHC)-defined cattle. BRSV protein recognition by CD8+ T cells was analysed using cytotoxic T lymphocyte (CTL) assays or by the production of interferon-gamma (IFN-gamma) following restimulation with BRSV proteins. Strong recognition of the G protein by CD8+ T cells was observed in cattle that had been vaccinated with rVV expressing this protein and subsequently challenged with BRSV. Although there is variation in the number of expressed MHC genes in cattle with different class I haplotypes, this did not appear to influence BRSV protein recognition by CD8+ T cells. Knowledge of the antigenic specificity of BRSV-specific CD8+ T cells will facilitate the qualitative and quantitative analysis of BRSV-specific CD8+ T-cell memory in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8+ T-cell response.

Induction of a strong HIV-specific CD8+ T cell response in mice using a fowlpox virus vector expressing an HIV-1 multi-CTL-epitope polypeptide

Recombinant avipoxvirus vectors are attractive candidates for use in vaccination strategies for infections such as human immunodeficiency virus type 1 (HIV-1), where induction of a CD8+ T cell response is thought to be an important component of protective immunity. Here, we report the expression of a multiepitope polypeptide (TAB9) composed of the central 15 amino acids of the V3 loop from six different isolates of HIV-1 in a fowlpox virus (FWPV) vector, and the use of this vector (FPTAB9LZ) to induce strong HIV-specific CD8+ T cell responses in mice. In animals immunized twice intravenously with FPTAB9LZ, almost 2% of the CD8+ T cells in the spleen were shown to produce IFN-gamma in response to stimulation with HIV-1 peptides 1 week after the second immunization. The most dominant response was to the HIV-1 IIIB peptide. A strong HIV-specific response was also induced by intraperitoneal immunization of mice with FPTAB9LZ, whilst subcutaneous immunization elicited a weaker response. Intraperitoneal immunization with FPTAB9LZ was also shown to provide protection against challenge with a recombinant vaccinia virus expressing antigens, including those in TAB9. These results confirm the potential of FWPV vectors for use in HIV vaccination strategies.

Identification and characterization of fowlpox virus strains using monoclonal antibodies

The use of 2 monoclonal antibodies (MAbs), P1D9 and P2D4, which recognize different fowlpox virus (FPV) antigens, for the identification and characterization of FPV strains was evaluated. Initially, the MAbs were used in conjunction with a dot blot assay that enabled FPV to be differentiated from the avian herpesvirus, infectious laryngotracheitis virus. Confirmation of the specificity of these MAbs was provided by the demonstration that only FPV antigens were recognized by a combination of both antibodies when used for immunoblotting proteins contained in various avipoxviruses. Later, an antigenic characterization of 11 FPV field isolates, 6 FPV vaccine strains, and 3 pigeonpox virus vaccines was performed by Western blotting with the individual MAbs. Whereas MAb P2D4 consistently recognized a protein with an apparent molecular weight of 60 kD, there was variability in the size of the antigen that was immunoreactive with the other MAb. For example, MAb P1D9 recognized an antigen of apparent molecular weight of 46 kD in all vaccine strains except 2 of FPV origin. In these exceptions, either only a 39-kD or both a 42- and 46-kD protein were immunoreactive. As for the field isolates, a 39-kD antigen was recognized in 8 of them, whereas a 42-kD antigen was detected in the remaining 3. Therefore, the more extensive immunoblotting technique may facilitate FPV strain differentiation, whereas routine diagnosis of fowlpox could be accomplished by using the MAb-based dot blot assay.

Generation of recombinant fowlpox virus using the non-essential F11L orthologue as insertion site and a rapid transient selection strategy

Avipoxviruses show an abortive replication phenotype in mammalian cells and are under evaluation as safe vectors for vaccination. Non-essential gene sequences located in highly conserved regions of virus genomes are considered particularly useful to integrate heterologous DNA. Fowlpox virus F11L orthologue is described in this paper as a suitable locus for insertion into fowlpox virus genome. Disruption of the F11L coding sequence by integration of an expression cassette for the Escherichia coli lacZ and guanine phosphoribosyltransferase marker genes resulted in the isolation of replication competent knockout viruses. Growth of F11L-knockout viruses in primary chicken embryo fibroblasts was unimpaired in comparison to wild type-virus. To test the generation of vector viruses, an insertion plasmid was constructed that contains F11L-specific sequences for homologous recombination, the E. coli lacZ and gpt genes as transient selectable marker, and the vaccinia virus early/late promoter P7.5 for transcriptional control of target gene expression. The coding sequence of the melanoma-associated antigen tyrosinase was chosen as model recombinant gene. Isolation of tyrosinase-recombinant viruses, which produced stably the insert, demonstrated the usefulness of the F11L-insertion site for the generation of fowlpox vectors. Rapid isolation of those recombinants was achieved by using a double selective system and linearising the vector plasmid before transfection.

Identification and characterization of three immunodominant structural proteins of fowlpox virus

Genes encoding fowlpox virus (FWPV) structural proteins have been identified mainly by sequence homology with those from vaccinia virus (VACV), but little is known about the encoded proteins. Production of monoclonal antibodies (MAbs) against Poxine and HP1-440 (Munich) clone FP9 allowed the identification of three immunodominant FWPV proteins: the 39-kDa core protein (encoded by FPV168, homologous to VACV A4L), a 30- and 35-kDa protein doublet, and an abundant 63-kDa protein. The 30- and 35-kDa proteins are nonglycosylated, antigenically related proteins present in the intracellular mature virus membrane and localizing closely with the viral factories. N-terminal sequencing identified the 35-kDa protein as encoded by FPV140 (the FWPV homolog of VACV H3L). The 63-kDa protein forms covalently linked dimers and oligomers. It remained mainly insoluble upon detergent treatment of purified virus but did not localize closely with the viral factory. N-terminal sequencing was unsuccessful, suggesting N-terminal blocking. CNBr digestion generated a peptide encoded by FPV191, predicted to encode one of two FWPV A-type inclusion (ATI) proteins. The characteristics of the 63-kDa protein were inconsistent with published observations on cowpox or VACV ATI proteins (it appears to be essential). The 63-kDa protein, however, shares characteristics with both VACV p4c virus occlusion and 14-kDa fusion proteins. Gene assignment at the poxvirus ATI locus (between VACV A24R and A28L) is complicated by sequence redundancies and variations, often due to deletions and multiple frameshift mutations. The identity of FPV191 in relation to genes at this locus is discussed.

Development of a monoclonal blocking ELISA for the detection of antibodies against fowlpox virus

To provide a fast and easy method to detect antibodies against fowlpox virus (FWPV) particularly in high numbers of chicken sera we established a monoclonal blocking enzyme-linked immunosorbent assay (ELISA). We chose two different monoclonal antibodies (mAb), anti-FWPV 3D9/2B3 and anti-FWPV 8F3/2E11, which are both directed against the 39-kDa protein of FWPV strain HP-1. The blocking ELISA depends on the blocking of mAb binding to solid-phase antigen in the presence of positive serum. For an epidemiological study a total of 184 serum samples from Gambian chicken flocks were analysed against each of the mAbs. Four of the sera were shown to contain FWPV antibodies. These four sera showed a positive cut-off value of more than 50% inhibition exclusively in the test against the mAb anti-FWPV 8F3/2E11. This phenomenon can be explained by the binding of the mAbs to distinct epitopes on the same protein.

Utilizing fowlpox virus recombinants to generate defective RNAs of the coronavirus infectious bronchitis virus

Coronavirus defective RNAs (D-RNAs) have been used as RNA vectors for the expression of heterologous genes and as vehicles for reverse genetics by modifying coronavirus genomes by targetted recombination. D-RNAs based on the avian coronavirus infectious bronchitis virus (IBV) D-RNA CD-61 have been rescued (replicated and packaged into virions) in a helper virus-dependent manner following electroporation of in vitro-generated T7 transcripts into IBV-infected cells. In order to increase the efficiency of rescue of IBV D-RNAs, cDNAs based on CD-61, under the control of a T7 promoter, were integrated into the fowlpox virus (FPV) genome. The 3'-UTR of the D-RNAs was flanked by a hepatitis delta antigenomic ribozyme and T7 terminator sequence to generate suitable 3' ends for rescue by helper IBV. Cells were co-infected simultaneously with IBV, the recombinant FPV (rFPV) containing the D-RNA sequence and a second rFPV expressing T7 RNA polymerase for the initial expression of the D-RNA transcript, subsequently rescued by helper IBV. Rescue of rFPV-derived CD-61 occurred earlier and with higher efficiency than demonstrated previously for electroporation of in vitro T7-generated RNA transcripts in avian cells. Rescue of CD-61 was also demonstrated for the first time in mammalian cells. The rescue of rFPV-derived CD-61 by M41 helper IBV resulted in leader switching, in which the Beaudette-type leader sequence on CD-61 was replaced with the M41 leader sequence, confirming that helper IBV virus replicated the rFPV-derived D-RNA. An rFPV-derived D-RNA containing the luciferase gene under the control of an IBV transcription-associated sequence was also rescued and expressed luciferase on serial passage.

The genome of fowlpox virus

Here we present the genomic sequence, with analysis, of a pathogenic fowlpox virus (FPV). The 288-kbp FPV genome consists of a central coding region bounded by identical 9.5-kbp inverted terminal repeats and contains 260 open reading frames, of which 101 exhibit similarity to genes of known function. Comparison of the FPV genome with those of other chordopoxviruses (ChPVs) revealed 65 conserved gene homologues, encoding proteins involved in transcription and mRNA biogenesis, nucleotide metabolism, DNA replication and repair, protein processing, and virion structure. Comparison of the FPV genome with those of other ChPVs revealed extensive genome colinearity which is interrupted in FPV by a translocation and a major inversion, the presence of multiple and in some cases large gene families, and novel cellular homologues. Large numbers of cellular homologues together with 10 multigene families largely account for the marked size difference between the FPV genome (260 to 309 kbp) and other known ChPV genomes (178 to 191 kbp). Predicted proteins with putative functions involving immune evasion included eight natural killer cell receptors, four CC chemokines, three G-protein-coupled receptors, two beta nerve growth factors, transforming growth factor beta, interleukin-18-binding protein, semaphorin, and five serine proteinase inhibitors (serpins). Other potential FPV host range proteins included homologues of those involved in apoptosis (e.g., Bcl-2 protein), cell growth (e.g., epidermal growth factor domain protein), tissue tropism (e.g., ankyrin repeat-containing gene family, N1R/p28 gene family, and a T10 homologue), and avian host range (e.g., a protein present in both fowl adenovirus and Marek's disease virus). The presence of homologues of genes encoding proteins involved in steroid biogenesis (e.g., hydroxysteroid dehydrogenase), antioxidant functions (e.g., glutathione peroxidase), vesicle trafficking (e.g., two alpha-type soluble NSF attachment proteins), and other, unknown conserved cellular processes (e.g., Hal3 domain protein and GSN1/SUR4) suggests that significant modification of host cell function occurs upon viral infection. The presence of a cyclobutane pyrimidine dimer photolyase homologue in FPV suggests the presence of a photoreactivation DNA repair pathway. This diverse complement of genes with likely host range functions in FPV suggests significant viral adaptation to the avian host.

Morphogenesis and release of fowlpox virus

Release of fowlpox virus (FWPV) as extracellular enveloped virus (EEV) appears to proceed both by the budding of intracellular mature virus (IMV) through the plasma membrane and by the fusion of intracellular enveloped virus (IEV) with the plasma membrane. Based on the frequency of budding events compared to wrapping events observed by electron microscopy, FWPV FP9 strain seems to exit chick embryo fibroblast cells predominantly by budding. In contrast to vaccinia virus (VV), the production of FWPV extracellular virus particles is not affected by N(1)-isonicotinoyl-N(2)-3-methyl-4-chlorobenzoylhydrazine (IMCBH). Comparison of the sequence of the VV F13L gene product with its FWPV orthologue showed a mutation, in the fowlpox protein, at the residue involved in IMCBH resistance in a mutant VV. Glucosamine, monensin or brefeldin A did not have any specific effect on FWPV extracellular virus production. Cytochalasin D, which inhibits the formation of actin filaments, reduces the production of extracellular virus particles by inhibiting the release of cell-associated enveloped virus (CEV) particles from the plasma membrane. Involvement of actin filaments in this mechanism is further supported by the co-localization of actin with viral particles close to the plasma membrane in the absence of cytochalasin D. Actin is also co-localized with virus factories.

The vaccinia virus 39-kDa protein forms a stable complex with the p4a/4a major core protein early in morphogenesis

The vaccinia virus (VV) 39-kDa protein, the product of the A4L gene, is a highly antigenic protein of the viral core. Pulse-chase and immunoprecipitation experiments have shown that the 39-kDa protein interacts with p4a (encoded by the A10L gene), the precursor of the most abundant virion protein. This interaction is maintained with the processed 4a form that arises during virion maturation. The controlled disruption of mature viral particles showed that the 39-kDa and 4a proteins are tightly bound within the virion. Immunoelectron microscopy showed that both proteins first localize within the cytoplasm and later accumulate inside the viral factories, reaching these locations via a mechanism apparently unrelated to cellular membranes. Double labeling experiments showed a colocalization of both proteins in all virus-induced structures.

Fowlpox virus encodes nonessential homologs of cellular alpha-SNAP, PC-1, and an orphan human homolog of a secreted nematode protein

The genome of fowlpox virus (FWPV), type species of the Avipoxviridae, is considerably rearranged compared with that of vaccinia virus (the prototypic poxvirus and type species of the Orthopoxviridae) and is 30% larger. It is likely that the genome of FWPV contains genes in addition to those found in vaccinia virus, probably involved with its replication and survival in the chicken. A 7,470-bp segment of the FWPV genome has five open reading frames (ORFs), two of which encode ankyrin repeat proteins, many examples of which have been found in poxviruses. The remaining ORFs encode homologs of cellular genes not reported in any other virus. ORF-2 encodes a homolog of the yeast Sec17p and mammalian SNAP proteins, crucial to vesicular transport in the exocytic pathway. ORF-3 encodes a homolog of an orphan human protein, R31240_2, encoded on 19p13.2. ORF-3 is also homologous to three proteins (YLS2, YMV6, and C07B5.5) from the free-living nematode Caenorhabditis elegans and to a 43-kDa antigen from the parasitic nematode Trichinella spiralis. ORF-5 encodes a homolog of the mammalian plasma cell antigen PC-1, a type II glycoprotein with exophosphodiesterase activity. The ORFs are present in the virulent precursor, HP1, of the sequenced attenuated virus (FP9) and are conserved in other strains of FWPV. They were shown, by deletion mutagenesis, to be nonessential to virus replication in tissue culture. RNA encoding the viral homolog of PC-1 is expressed strongly early and late in infection, but RNAs encoding the homologs of SNAP and R31240_2 are expressed weakly and late.