The dominantly expressed class II molecule from a resistant MHC haplotype presents only a few Marek's disease virus peptides by using an unprecedented binding motif

Viral diseases pose major threats to humans and other animals, including the billions of chickens that are an important food source as well as a public health concern due to zoonotic pathogens. Unlike humans and other typical mammals, the major histocompatibility complex (MHC) of chickens can confer decisive resistance or susceptibility to many viral diseases. An iconic example is Marek's disease, caused by an oncogenic herpesvirus with over 100 genes. Classical MHC class I and class II molecules present antigenic peptides to T lymphocytes, and it has been hard to understand how such MHC molecules could be involved in susceptibility to Marek's disease, given the potential number of peptides from over 100 genes. We used a new in vitro infection system and immunopeptidomics to determine peptide motifs for the 2 class II molecules expressed by the MHC haplotype B2, which is known to confer resistance to Marek's disease. Surprisingly, we found that the vast majority of viral peptide epitopes presented by chicken class II molecules arise from only 4 viral genes, nearly all having the peptide motif for BL2*02, the dominantly expressed class II molecule in chickens. We expressed BL2*02 linked to several Marek's disease virus (MDV) peptides and determined one X-ray crystal structure, showing how a single small amino acid in the binding site causes a crinkle in the peptide, leading to a core binding peptide of 10 amino acids, compared to the 9 amino acids in all other reported class II molecules. The limited number of potential T cell epitopes from such a complex virus can explain the differential MHC-determined resistance to MDV, but raises questions of mechanism and opportunities for vaccine targets in this important food species, as well as providing a basis for understanding class II molecules in other species including humans.

Sequence analysis of the Meq gene in the predominant Marek's disease virus strains isolated in China during 2006-2008

The main aim of the present study were to investigate sequence diversity in the Meq gene of Marek's disease viruses (MDV) isolated in China and to determine the most prevalent MDV strains. The 19 MDV strains were isolated from dead or diseased chickens from different chicken farms in China during 2006-2008, and the Meq gene was sequenced from each of these strains. Sequence analysis showed that all of the isolates contained an open reading frame of 1020 nucleotides, which encoded a 339 amino acid peptide. Compared with reference MDV strains, 12 of the 19 MDV isolates possessed two amino acid substitutions, (T → A) at position 139 and (P → R) at position 176, one isolate shared sequence similarity with the attenuated strain CVI988, and five of the other six isolates exhibited one amino acid change (P → T) at position 177 or 176. The 19 MDV isolates shared between 99.0 and 100% nucleotide sequence homology, and between 97.7 and 100% amino acid sequence homology. The nucleotide and amino acid sequence identity between the 19 MDV isolates and the 25 reference MDV strains varied from 97.6 to 100% and 94.4 to 100%, respectively. Based on the phylogenetic relationships between Meq gene sequences, Chinese MDV isolates constituted a separate clade to MDV reference strains, demonstrating that a different genotype of MDV was prevalent in China between 2006 and 2008.

Characterization of a very virulent Marek's disease virus mutant expressing the pp38 protein from the serotype 1 vaccine strain CVI988/Rispens

Marek's disease virus (MDV), a highly cell-associated oncogenic chicken herpesvirus, causes Marek's disease in domestic chickens. A unique phosphoprotein of MDV, pp38, has previously been associated with the maintenance of transformation in MDV-induced tumor cell lines. However, recently, the biological properties of a deletion mutant virus (rMd5Deltapp38) revealed that pp38 is involved in early cytolytic infection in lymphocytes but not in the induction of tumors. Thus, pp38 is important for early cytolytic infection and not for transformation. The pp38 protein of the MDV serotype 1 vaccine strain CVI988/Rispens differs by one amino acid when compared to the pathogenic strains of MDV. Monoclonal antibody, H19, recognizes all serotype 1 MDV strains except CVI988/Rispens. Previous studies have also shown that the unique pp38 epitope in CVI988/Rispens induced high antibody response. In order to study the role of this epitope in the protective properties of CVI988/Rispens, we generated a mutant rMd5 virus in which the wild type pp38 gene has been substituted with that of CVI988/Rispens (rMd5/pp38CVI). The replication properties of rMd5/pp38CVI, both in vitro and in vivo, and tumor induction were examined. We found that the biological properties of rMd5/pp38CVI were similar to the wild type rMd5 virus with regards to in vivo replication, antibody response and tumor induction. This shows that the pp38 derived from CVI988/Rispens is not involved in protective properties as was previously suggested.

[Kinase domain analysis of MDV-1 CVI988/Rispens UL13 and preferred codon fragments expression in Escherichia coli]

OBJECTIVE

To find catalytic center of MDV-1 UL13 and express it in vitro to investigate the function of UL13 kinase.

METHODS

UL13 gene was amplified by polymerase chain reaction (PCR) from MDV-1 CVI988/Rispens strain. The codon bias and antigenicity of UL13 in Escherichia coli was analyzed by online service GENEART (www.gcua.de)and DNAstar software respectively. Then the UL13 truncated fragments were expressed in Escherichia coli, and mice were immunized with the expressed Glutathione S Transferase fusion protein. The conserved domain was analyzed with protein blast and Cn3D 4.1 online software of National Center for Biotechnology Information.

RESULTS

UL13 gene was successfully amplified. The sequence analysis suggests that 259-400 and 431-513 amino acid residues are low abundance for rare codon and strong antigenicity in UL13. Result of conserved domain analysis demonstrated that 152-297 residue iskinase catalytic center of UL13. However, conserved glycin in kinase subdomain VII for most protein kinase was replaced by serine in UL13 and proline in kinase subdomain VIII replaced by cysteine. The serum from mice immunized with truncated fragment, 259-400 amino acids, could react with recombinant UL13 protein expressed in insect cells in immunofluorenscence assay.

CONCLUSION

The 152-297 residue is kinase catalytic center of MDV-1 UL13; UL13 protein expressed in vitro induced specific antibodies against UL13.

[The N1-18 terminus of Marek's disease virus VP22 is essential for protein transduction]

We previously showed some differences in Marek's disease virus (MDV) VP22 gene between virulent and avirulent strains, in the deletion from 201aa to 206aa, namely 201TKSERT206. In this study, VP22 genes were amplified from strains: CVI988/Rispens and GA. And then the fragments were subcloned into pcDNA3.1/zeo(+), respectively, which were co-expressed with an enhancer green fluorescent protein (EGFP) after transfection into COS-1 cells. As with both human herpesvirus 1 and bovine herpesvirus 1 VP22-EGFP fusion proteins, the subcellular localization of the three MDV EGFP-VP22 products revealed few differences, which bind to microtubules and nucleus membrane, and then to heterochromatin. In addition, VP22s also bind to centrosomes and inter-membrane. During mitosis, EGFP-VP22s bind to sister chromatids, but dissociates from the centrosomes and the microtubules of the mitotic spindle. In truncated fragments' transfection experiments, stained with the specific monoclonal antibody against VP22, it concluded that the full length of VP22 was required for protein transduction, and N1-18aa was essential to VP22 translocating from cytoplasm to nucleus as a potential nucleus localization site in the absence of other viral factors in MDV-1.

Prevalence and molecular characterization of meq in feather follicular epithelial cells of Korean broiler chickens

Marek's disease (MD) is a highly contagious lymphoproliferative disease of chickens. Meq is the relevant oncogene and four isoforms, long (L)-meq, meq, short (S)-meq and very short (VS)-meq, have been identified. Although MD is important in the poultry industry, the prevalence and molecular properties of Korean MD virus (MDV) among broiler chickens remain unclear. Therefore, we characterized meq in pooled feather tips sampled at 3- and 5-week-old chickens from 21 unvaccinated and 22 vaccinated broiler farms via nested-PCR and nucleotide sequence analysis. Multiple bands consisting of L-meq, meq, and S-meq amplicons were observed in a commercial vaccine (CVI988 + HVT), 1 (4.8%) and 5 samples (22.7%) from unvaccinated and vaccinated farms, respectively. A strong meq amplicon was observed in a MD-related tumor tissue, 6 (28.6%) and 1 (4.5%) samples from unvaccinated and vaccinated farms, respectively. Six and one amplicons from unvaccinated (28.6%) and vaccinated farms (4.5%), respectively, were differentiated from CVI988 by nucleotide sequence analysis. Therefore, the relatively high rate of meq in the unvaccinated broiler farms constitutes support for vaccination. However, the existence of CVI988-related meq in unvaccinated chickens necessitates further study regarding the origins and pathoimmunological effects of the viruses on chickens.

Marek's disease virus-encoded Meq gene is involved in transformation of lymphocytes but is dispensable for replication

Marek's disease virus (MDV) causes an acute lymphoproliferative disease in chickens, resulting in T cell lymphomas in visceral organs and peripheral nerves. Earlier studies have determined that the repeat regions of oncogenic serotype 1 MDV encode a basic leucine zipper protein, Meq, which structurally resembles the Jun/Fos family of transcriptional activators. Meq is consistently expressed in MDV-induced tumor cells and has been suggested as the MDV-associated oncogene. To study the function of Meq, we have generated an rMd5DeltaMeq virus by deleting both copies of the meq gene from the genome of a very virulent strain of MDV. Growth curves in cultured fibroblasts indicated that Meq is dispensable for in vitro virus replication. In vivo replication in lymphoid organs and feather follicular epithelium was also not impaired, suggesting that Meq is dispensable for lytic infection in chickens. Reactivation of the rMd5DeltaMeq virus from peripheral blood lymphocytes was reduced, suggesting that Meq is involved but not essential for latency. Pathogenesis experiments showed that the rMd5DeltaMeq virus was fully attenuated in chickens because none of the infected chickens developed Marek's disease-associated lymphomas, suggesting that Meq is involved in lymphocyte transformation. A revertant virus that restored the expression of the meq gene, showed properties similar to those of the parental virus, confirming that Meq is involved in transformation but not in lytic replication in chickens.

Sequence and initial characterization of the U(L)10 (glycoprotein M) and U(L)11 homologous genes of serotype 1 Marek's Disease Virus

The nucleotide sequence of the U(L)10 (glycoprotein M) and the U(L)11 homologs of Marek's Disease Virus 1 strain GA was determined. The U(L)10 open reading frame encodes a type III membrane protein of 424 amino acids that contains eight hydrophobic domains and two consensus N-linked glycosylation sites. The U(L)11 homologous gene encodes an 84 amino acid polypeptide, and contains a highly conserved myristylation site at its aminoterminus. By analysis of infected-cell RNA with strand-specific RNA probes, transcription of both U(L)10 and U(L)11 in infected cells was demonstrated. Coupled in vitro transcription-translation confirmed that the U(L)10 product is a 47 kD N-glycosylated viral protein that aggregated upon boiling, whereas the U(L)11 protein exhibited a size of 12 kD after in vitro translation.

Identification of the Marek's disease virus serotype 2 genes homologous to the glycoprotein B (UL27), ICP18.5 (UL28) and major DNA-binding protein (UL29) genes of herpes simplex virus type 1

We determined the nucleotide sequence of non-pathogenic Marek's disease virus serotype 2 (MDV2) strain HPRS24 glycoprotein B (gB) (UL27), ICP18.5 (UL28) and major DNA-binding protein (MDBP) (UL29) genes homologous to herpes simplex virus type 1 (HSV-1). The sequence data revealed that important motives in the proteins are conserved in MDV2 ICP18.5 and MDBP, however the sequence of viral DNA replication origin which exists in the regions between the UL29 and UL30 genes of other alphaherpesviruses was not found in the regions of the MDV2 genome. By northern blot analyses, we also demonstrated that 8.9, 5.0 and 2.6 kb transcripts were actually transcribed from the sequenced region in MDV2-infected cells. The MDV2 UL28 and UL29 genes have not been reported in other serotypes of MDV.

Identification and characterization of glycoprotein H of MDV-1 GA strain

A 2439 bp open reading frame (ORF) was identified from the DNA sequence of BamHI-F and -K2 fragments of Marek's disease virus of serotype 1 (MDV-1) GA strain, which predicts an 813 amino acid polypeptide. This peptide is homologous to HSV-1 gH, and has typical glycoprotein features. There are nine potential N-linked glycosylation sites within the extracellular domain. A fragment of the gH ORF was cloned into pGEX vector in frame with glutathione S-transferase (GST) to produce a GST-gH fusion protein in Escherichia coli. The GST-gH fusion protein was used to develop gH monoclonal and polyclonal antibodies. Expression of gH was detected in duck embryo fibroblasts (DEFs) infected with MDV-1 GA strain by immunofluorescence assay (IFA) with these antibodies. Virus neutralization and plaque-forming inhibition analyses were conducted with the gH antiserum. There were no neutralization and plaque-forming inhibition activities of gH antiserum. Comparison of the DNA sequence of gH gene between GA and RB1B strains of MDV-1 revealed major difference in the upstream control elements of gH ORF.

Construction and characterization of a H19 epitope point mutant of MDV CVI988/Rispens strain

A recombinant virus, CVI/rpp38, was developed from the Marek's disease virus (MDV) CVI988/Rispens vaccine strain. This recombinant was obtained by transfection of CVI988/Rispens-infected chick embryo fibroblasts (CEFs) with plasmid pHA25 DNA containing pp38 gene from GA strain of MDV. Monoclonal antibody (MAb) H19 which reacts with pp38 from GA but not with that from CVI988 was used to screen for recombinant viruses in transfected cell culture plates by immunofluorescent assay (IFA). A positive plaque was isolated, propagated, and purified from cell-free virus particles after sonication of infected CEFs. The mutant CVI/rpp38 was not only reactive with MAb H19 in IFA but also in immunoprecipitation. A 38 kDa protein was immunoprecipitated from the CVI/rpp38 mutant virus but not from parental CVI988 virus. DNA sequence of the mutant virus showed a substitution of G at position 320 by a resulting in a change of an amino acid residue from arginine to glutamine. Comparison of nucleotide sequence of pp38 from strains GA, Md5 and Md11/75c/R2 and CVI988 revealed change to glutamine in this position. The result of this study provides a direct evidence for the location of the identified H19 epitope in pp38. This mutant is potentially useful to further explore the biological function of pp38 and its H19 epitope.

Characterization and expression of the Marek's disease virus serotype 2 glycoprotein E in recombinant baculovirus-infected cells: initial analysis of its DNA sequence and antigenic properties

In Marek's disease virus (MDV) serotype 2 (MDV2) genome, a gene equivalent to the glycoprotein E (gE) of other alphaherpesviruses was identified and sequenced. The primary translation product comprises 488 amino acids with a M(r) of 54.3 kDa. The predicted amino acid sequence possesses several characteristics typical of membrane glycoproteins, including a N-terminal hydrophobic signal sequence, C-terminal transmembrane and cytoplasmic domains, and extra-cellular region containing four potential N-linked glycosylation sites. Compared with other MDV serotypes, MDV2 gE showed 47.3% identity with MDV1 gE, and 38.9% identity with HVT gE at the amino acid level. In transcriptional analyses, a 2.0 kb mRNA which starts between 65 and 86 bps upstream of the potential translational initiation codon of gE was identified as the gE-specific transcript. By a recombinant baculovirus, this potential gE coding region was expressed as several specific products from 66 to 72 kDa. These products were susceptible to tunicamycin treatment, indicating that they were glycoprotein in nature. Further, the expressed gE reacted with all chicken-antisera raised to each of the three serotypes of MDV (strains GA, SB-1, and FC126), suggesting that gE is expressed by all three serotypes of MDV in infected cells and conserves common antigenic epitope(s) beyond those that are serotype specific.

Identification of a potential Marek's disease virus serotype 2 glycoprotein D gene with homology to herpes simplex virus glycoprotein D

The gene of Marek's disease virus (MDV) serotype 2 (MDV2) homologous to glycoprotein D (gD) of herpes simplex virus (HSV) was identified and characterized by its nucleotide and predicted amino acid sequences. The MDV2 gD homologous gene contains an open reading frame capable of specifying a polypeptide of 385 amino acids, which include N- and C-terminal hydrophobic domains consistent with signal and anchor regions, respectively, and two potential N-linked glycosylation sites, one of which was located in a highly conserved region when compared to MDV serotype 1 (MDV1) and herpesvirus of turkeys (HVT). By northern blot analysis using a MDV2 gD-specific DNA probe, two highly abundant polycistronic 6.0 and 4.2 kb transcripts were detected in MDV2-infected cells. The genes encoding MDV2 protein kinase (PK), gD, and glycoprotein I (gI) homologues are transcribed to form 3' coterminal mRNAs of 6.0 kb (encoding PK, gD and gI) and 4.2 kb (encoding gD and gI), respectively. By using rapid amplification cDNA end (RACE) method, several RNA start sites, to be thought those of the 4.2 kb mRNA, were detected in the upstream of MDV2 gD homologue.

Identification and characterization of a Marek's disease virus gene homologous to glycoprotein L of herpes simplex virus

We have identified three Marek's disease virus (MDV) open reading frames (ORFs) within the BamHI D fragment of MDV genome. The predicted polypeptides are homologous to UL1 (glycoprotein L, gL), UL2 (uracil-DNA glycosylase), and UL3 (nuclear localizing phosphoprotein) of herpes simplex virus type 1 (HSV-1). Comparison of the deduced amino acid sequences of these three ORFs with HSV-1 counterparts revealed overall identities of 18, 43, and 49%, respectively. In spite of the low overall amino acid identity with HSV-1 gL, the first open reading frame was identified as a gL homolog of HSV-1 based not only on the gene arrangement but also on a limited amino acid conservation among gL homologs of alpha-herpesviruses. To characterize the expression of the MDV gL gene, an antiserum to a hydrophilic region of the gene expressed in a bacterial expression vector was produced. Immunoprecipitation with this antiserum revealed a 25,000-Da polypeptide in MDV-infected cells. Furthermore, the 25,000-Da polypeptide migrated as a 18,000-Da polypeptide following PNGase F treatment. This result is consistent with the predicted molecular weight of MDV gL, considering the two potential N-glycosylation sites and the predicted N-terminal signal sequence. A recombinant fowlpox virus expressing the MDV gL gene was generated to characterize this glycoprotein. Unlike gL in MDV-infected cells, gL expressed by recFPV-gL was highly sensitive to Endo H, indicating that it was probably retained in the endoplasmic reticulum and was not properly processed to a mature form. Therefore, similar to HSV-1 coexpression and complex formation of MDV gL and gH may be required for proper processing and transport of gL to the cell surface.

Nucleosomal structure of Marek's disease virus genome in transformed lymphoblastoid cell lines, MDCC-MSB1 and MDCC-RP1

The latent MDV (Marek's disease virus) genomes are folded into nucleosomal structures in both virus-productive and -nonproductive lymphoblastoid cell lines, MDCC-MSB1 (MSB-1) and -RP1 (RP-1), respectively. There was no difference between transcriptionally active and inactive regions of MDV genome with regard to nucleosomal patterns. In order to investigate whether nucleosomal structure is correlated with the repression of the transcription of MDV genome in lymphoblastoid cells, we examined the DNaseI sensitivity of nucleosomal MDV DNA in lymphoblastoid cell lines, MSB-1 and RP-1. No difference in the DNaseI sensitivity between transcriptionally active and inactive MDV DNA regions in lymphoblastoid cells was observed.