Marek's Disease Virus Infection Research Articles

Genome-wide identification of copy number variations between two chicken lines that differ in genetic resistance to Marek's disease.

BackgroundCopy number variation (CNV) is a major source of genome polymorphism that directly contributes to phenotypic variation such as resistance to infectious diseases. Lines 63 and 72 are two highly inbred experimental chicken lines that differ greatly in susceptibility to Marek’s disease (MD), and have been used extensively in efforts to identify the genetic and molecular basis for genetic resistance to MD. Using next generation sequencing, we present a genome-wide assessment of CNVs that are potentially associated with genetic resistance to MD.MethodsThree chickens randomly selected from each line were sequenced to an average depth of 20×. Two popular software, CNVnator and Pindel, were used to call genomic CNVs separately. The results were combined to obtain a union set of genomic CNVs in the two chicken lines. ResultsA total of 5,680 CNV regions (CNVRs) were identified after merging the two datasets, of which 1,546 and 1,866 were specific to the MD resistant or susceptible line, respectively. Over half of the line-specific CNVRs were shared by 2 or more chickens, reflecting the reduced diversity in both inbred lines. The CNVRs fixed in the susceptible lines were significantly enriched in genes involved in MAPK signaling pathway. We also found 67 CNVRs overlapping with 62 genes previously shown to be strong candidates of the underlying genes responsible for the susceptibility to MD.ConclusionsOur findings provide new insights into the genetic architecture of the two chicken lines and additional evidence that MAPK signaling pathway may play an important role in host response to MD virus infection. The rich source of line-specific CNVs is valuable for future disease-related association studies in the two chicken lines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2080-5) contains supplementary material, which is available to authorized users.

Fine mapping of QTL and genomic prediction using allele-specific expression SNPs demonstrates that the complex trait of genetic resistance to Marek's disease is predominantly determined by transcriptional regulation.

BackgroundMarek’s disease (MD) is a lymphoproliferative disease of poultry induced by Marek’s disease virus (MDV), a highly oncogenic alphaherpesvirus. Identifying the underlying genes conferring MD genetic resistance is desired for more efficacious control measures including genomic selection, which requires accurately identified genetic markers throughout the chicken genome.MethodsHypothesizing that variants located in transcriptional regulatory regions are the main mechanism underlying this complex trait, a genome-wide association study was conducted by genotyping a ~1,000 bird MD resource population derived from experimental inbred layers with SNPs containing 1,824 previously identified allele-specific expression (ASE) SNPs in response to MDV infection as well as 3,097 random SNPs equally spaced throughout the chicken genome. Based on the calculated associations, genomic predictions were determined for 200 roosters and selected sires had their progeny tested for Marek’s disease incidence.ResultsOur analyses indicate that these ASE SNPs account for more than 83 % of the genetic variance and exhibit nearly all the highest associations. To validate these findings, 200 roosters had their genetic merit predicted from the ASE SNPs only, and the top 30 and bottom 30 ranked roosters were reciprocally mated to random hens. The resulting progeny showed that after only one generation of bidirectional selection, there was a 22 % difference in MD incidence and this approach gave a 125 % increase in accuracy compared to current pedigree-based estimates.ConclusionsWe conclude that variation in transcriptional regulation is the major driving cause for genetic resistance to MD, and ASE SNPs identify the underlying genes and are sufficiently linked to the causative polymorphisms that they can be used for accurate genomic prediction as well as help define the underlying molecular basis. Furthermore, this approach should be applicable to other complex traits.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2016-0) contains supplementary material, which is available to authorized users.

Outbreak of Marek's disease in a vaccinated broiler breeding flock during its peak egg-laying period in China.

BackgroundOutbreaks of Marek’s disease (MD), caused by Marek’s disease virus (MDV), primarily occur in 10–12-week-old hens.Case presentation We report a case of MD in a breeding flock of 24–30-week-old vaccinated broilers in China. The clinical signs in the affected chickens appeared at 24 weeks, and the incidence of tumours peaked at 30 weeks. The morbidity and mortality of the hens were 5 % and 80 %, respectively. Hematoxylin–eosin staining of the tissues showed the typical characteristics of MD. MDV infection was confirmed in the hens with an agar gel diffusion precipitation assay for the MD antigen in the feather follicle epithelium. An MDV strain, designated AH1410, was isolated from the blood lymphocytes. Sequence analyses of the pp38, meq, and gB genes revealed that strain AH1410 had molecular features consistent with a virulent, previously identified MDV.ConclusionOur data provide evidence that not only is MDV becoming more virulent, but that the period of its onset in chickens is expanding. These findings provide the basis the molecular surveillance and further study of virulent MDV mutants and control strategies for MD in China.

Immune Responses in Cecal Tonsils of Marek's Disease Virus-Infected Chickens.

Marek's disease (MD) is a lymphoproliferative disease of domestic chickens that is caused by a highly cell-associated oncogenic α-herpesvirus, Marek's disease virus (MDV). MDV replicates in chicken lymphocytes and establishes a latent infection within CD4+ T cells. Clinical signs of MD include depression, crippling, weight loss, bursal/thymic atrophy, neurologic disorders, and rapid onset of T cell lymphomas that infiltrate lymphoid tissues, visceral organs, and peripheral nerves. The cecal tonsils (CTs) are considered the largest lymphoid aggregates of avian gut-associated lymphoid tissue. Along with Peyer's patches, CTs elicit protective immune responses against bacterial and viral pathogens in the intestinal tract of avian species. In this study, we investigated the effect of MDV infection on toll-like receptor (TLR) gene expression in CTs of MD-susceptible (72) and resistant (63) chicken lines. Real-time PCR gene expression profiling revealed that of the 10 TLRs tested, TLR2A, TLR3, TLR5, and TLR15 displayed significant differential expression patterns at different time points postinoculation. The expression levels of the remaining six genes were minimally affected by MDV infection in either line. Immunohistochemical analysis showed a severe depletion of B cells and CD4+ T cells in the CTs of susceptible line at 5 days postinfection (dpi), which recovered by 21 dpi. The destruction of B and T cells in the CTs of the resistant line was minimal at 5 dpi, which also recovered by 21 dpi. A significant infiltration of macrophages was observed after the depletion of B and T cells in the infected birds of both lines that could account for the differential TLR gene expression in the infected birds. The data presented provide further insight into the mechanism of MDV pathogenesis and tissue-specific immunologic responses to viral infection.

Absolute quantification of a very virulent Marek's disease virus dynamic quantity and distributions in different tissues

Chickens infected with Marek's disease virus (MDV) carry the virus consistently for a long time, which increases the incidence and rate of virus-induced multi-organ tumors and increases its potential for horizontal transmission. There is a positive correlation between very virulent (vv) MDV quantity and the pathology. The purpose of this study was to determine the vvMDV loads dynamics in different phases, and the correlation between the viral quantity and tumor development. We used a SYBR Green duplex real-time quantitative PCR (q-PCR) assay to detect and quantify MDV loads and distributions in different tissues, targeting the Eco-Q protein gene (meq) of the virus and the house-keeping ovotransferrin (ovo) gene of chickens. The q-PCR was performed using different tissue DNA preparations derived from chickens which were infected with 1,000 pfu of the SDWJ1302 strain and tissue samples were collected from control and MDV-infected birds on 7, 10, 15, 21, 28, 40, 60, and 90 d post-infection (DPI). The data indicated that the MDV genome was almost quantifiable in immune organs of infected chickens as early as 7 DPI, and the number of MDV genome copies in the blood and different organs peaked by 28 DPI, but then gradually decreased by 40 DPI. The levels of viral quantity in the lymphocytes, liver, and spleen were all higher than those in other organs, and that in the feather follicles was the highest among different phases of MDV infection. The vvMDV could still be detected in peripheral blood and tissues by 90 DPI, and the vast existence of virus will stimulate tissue destruction. The data provided further evidence of viral infection involving multi-organ distribution and mainly involving immune organ proliferation, resulting in immunosuppression.

Histone modifications induced by MDV infection at early cytolytic and latency phases.

BackgroundMarek’s disease (MD) is a highly contagious, lymphomatous disease of chickens induced by a herpesvirus, Marek’s disease virus (MDV) that is the cause of major annual losses to the poultry industry. MD pathogenesis involves multiple stages including an early cytolytic phase and latency, and transitions between these stages are governed by several host and environmental factors. The success of vaccination strategies has led to the increased virulence of MDV and selective breeding of naturally resistant chickens is seen as a viable alternative. While multiple gene expression studies have been performed in resistant and susceptible populations, little is known about the epigenetic effects of infection.ResultsIn this study, we investigated temporal chromatin signatures induced by MDV by analyzing early cytolytic and latent phases of infection in the bursa of Fabricius of MD-resistant and –susceptible birds. Major global variations in chromatin marks were observed at different stages of MD in the two lines. Differential H3K27me3 marks were associated with immune-related pathways, such as MAP kinase signaling, focal adhesion and neuroactive ligand receptor interaction, and suggested varying degrees of silencing in response to infection. Immune-related microRNAs, e.g. gga-miR-155 and gga-miR-10b, bore chromatin signatures, which suggested their contribution to MD-susceptibility. Finally, several members of the focal adhesion pathway, e.g. THBS4 and ITGA1, showed marked concordance between gene expression and chromatin marks indicating putative epigenetic regulation in response to MDV infection.ConclusionOur comprehensive analysis of chromatin signatures, therefore, revealed further clues about the epigenetic effects of MDV infection although further studies are necessary to elucidate the functional implications of the observed variations in histone modifications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1492-6) contains supplementary material, which is available to authorized users.

Marek׳s disease virus-encoded analog of microRNA-155 activates the oncogene c-Myc by targeting LTBP1 and suppressing the TGF-β signaling pathway

Marek׳s disease virus (MDV) is a representative alpha herpes virus able to induce rapid-onset T-cell lymphoma in its natural host and regarded as an ideal model for the study of virus-induced tumorigenesis. Recent studies have shown that the mdv1-miR-M4-5p, a viral analog of cellular miR-155, is critical for MDV׳s oncogenicity. However, the precise mechanism whereby it was involved in MD lymphomagenesis remained unknown. We have presently identified the host mRNA targets of mdv1-miR-M4-5 and identified the latent TGF-β binding protein 1 (LTBP1) as a critical target for it. We found that during MDV infection, down-regulation of LTBP1 expression by mdv1-miR-M4-5p led to a significant decrease of the secretion and activation of TGF-β1, with suppression of TGF-β signaling and a significant activation of expression of c-Myc, a well-known oncogene which is critical for virus-induced tumorigenesis. Our findings reveal a novel and important mechanism of how mdv1-miR-M4-5p potentially contributes to MDV-induced tumorigenesis.

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

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

Marek's disease virus influences the core gut microbiome of the chicken during the early and late phases of viral replication.

Marek's disease (MD) is an important neoplastic disease of chickens caused by the Marek's disease virus (MDV), an oncogenic alphaherpesvirus. In this study, dysbiosis induced by MDV on the core gut flora of chicken was assessed using next generation sequence (NGS) analysis. Total fecal and cecum-derived samples from individual birds were used to estimate the influence of MDV infection on the gut microbiome of chicken. Our analysis shows that MDV infection alters the core gut flora in the total fecal samples relatively early after infection (2-7 days) and in the late phase of viral infection (28-35 days) in cecal samples, corresponding well with the life cycle of MDV. Principle component analyses of total fecal and cecal samples showed clustering at the early and late time points, respectively. The genus Lactobacillus was exclusively present in the infected samples in both total fecal and cecal bird samples. The community colonization of core gut flora was altered by viral infection, which manifested in the enrichment of several genera during the early and late phases of MDV replication. The results suggest a relationship between viral infection and microbial composition of the intestinal tract that may influence inflammation and immunosuppression of T and B cells in the host.

Marek's disease virus-induced transient cecal tonsil atrophy.

Marek's disease (MD) is a lymphoproliferative disease of domestic chickens that is caused by a highly cell-associated oncogenic alpha-herpesvirus, Marek's disease virus (MDV). MDV replicates in chicken lymphocytes and establishes a latent infection within CD4+ T cells. MD is characterized by bursal and thymic atrophy and rapid onset of T cell lymphomas that infiltrate lymphoid tissues, visceral organs, and peripheral nerves with severe clinical symptoms that include transient paralysis, anemia, weight loss, and neurologic disorders. The cecal tonsils (CT) are considered the largest lymphoid aggregates of avian gut-associated lymphoid tissue (GALT). Along with Peyer's patches, CT elicits protective immune responses against bacterial and viral pathogens in the intestinal tract of avian species. In this study we investigated the effect of MDV infection on CT structural changes and cytokine gene expression in two MD-susceptible and resistant chicken lines. The histopathologic analysis revealed that MDV causes the loss of germinal follicular centers within the CT of the resistant line while inducing a severe, near-total lymphoid depletion in the susceptible line during cytolytic infection. The lymphoid depletion, however, recovered approximately 2 wk postinfection but the loss of germinal centers persisted during the latent phase of infection in both lines. The atrophy of this important GALT was transient and there were no visible differences between the CT of the infected and control birds of either line by 21 days postinfection. Of the genes tested, IFN-beta and IFN-gamma were up regulated in the CT of both infected lines during lytic infection. The expression levels of both genes were much higher in the susceptible line than in the resistant line. A similar pattern of expression was observed for IL-6, IL-10, IL-13, and iNOS. IL-12 was up regulated in the CT of birds of the susceptible line during all three phases of infection. An over expression of IL-18 was also observed in CT of the susceptible line during lytic and latent phases of infection. IL-8 was the only cytokine expressed at higher levels in the CT of the resistant line during the lytic and reactivation phases of infection. The histopathologic observations and gene expression profiling are further discussed.

Gga-miR-26a targets NEK6 and suppresses Marek's disease lymphoma cell proliferation

MicroRNA (miRNA) are a class of highly conserved, small noncoding RNA that emerge as key posttranscriptional regulators in various neoplastic transformations. Our previous study profiling the miRNA transcriptome in Marek's disease virus (MDV)-induced lymphoma revealed many novel and differentially expressed miRNA, including gga-miR-26a, which was downregulated in MDV-infected spleens of chickens. In this study, differential expression of gga-miR-26a between MDV-infected and noninfected spleens at 4, 7, 14, 21, and 28 d postinfection was analyzed by real-time PCR. The results showed gga-miR-26a were downregulated in MDV-infected spleens at cytolytic infection, latency, and tumor transformation phases. Subsequent cell proliferation assay revealed cell viability was lower in gga-miR-26a mimic transfection group than that in negative controls. Target genes of gga-miR-26a were identified by luciferase reporter gene assay. The results showed significant interaction between gga-miR-26a and Never In Mitosis Gene A (NIMA)-related kinase 6 (NEK6) gene. Subsequent gain of function experiment and Western blot assay showed that mRNA and protein levels of NEK6 were downregulated after gga-miR-26 mimic was transfected into MDV-transformed lymphoid cell line (MSB-1), indicating that NEK6 was modulated by gga-miR-26a. The expression of NEK6 showed a higher trend in MDV-infected samples including tumorous spleen and MD lymphoma from liver than that in noninfected controls. The results suggested that gga-miR-26a inhibited MSB-1 cell proliferation. Gga-miR-26a and its direct target, NEK6, might play important roles in MDV infection.

Distinct expression pattern of miRNAs in Marek's disease virus infected-chicken splenic tumors and non-tumorous spleen tissues

MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression. Emerging evidence suggests that differential miRNA expression is associated with viral infection and tumorigenesis. Recently discovered microRNAs in the Marek's disease virus (MDV) genome have been suggested to have regulatory roles during MDV oncogenesis. To gain more insight into the molecular mechanisms of the tumorigenesis of MDV, we used microarrays to screen host and viral miRNAs that were sensitive to infection by MDV. Microarray analysis showed significant differential expression of 79 miRNAs, which was confirmed by qRT-PCR analysis. These data suggest that differentially expressed miRNAs may have major roles in MDV-induced tumorigenesis. In addition, we found two clades of chicken miRNAs had increased expression in splenic tumors and non-tumorous spleen tissues from GA-infected chickens. Thus, the expression of these miRNAs can be considered signatures for MDV infection and tumorigenesis.

Marek’s disease virus may interfere with T cell immunity by TLR3 signals

Marek's disease virus (MDV) is a highly oncogenic alpha-herpesvirus that causes T cell immune suppression and malignant lymphomas in chickens. Toll-like receptor (TLR) plays a dominant role in antiviral T cell immunity. However, it is unclear whether MDV induced T cell immunity is associated with TLR-mediated immunity. In this study, the expression of 28 host genes that are involved in TLR-mediated immunity and MHC-medicated T cell immunity was evaluated in chicken thymus at 7, 14, 21 and 28days post-infection (dpi). Our results demonstrated that 24 host immune-related genes were upregulated during MDV infection at 7dpi; however, the expression of most of these genes decreased at 21 and 28dpi. Notably, a positive correlation was found between the down-regulation of CD4, CD8 and TLR3 signals but not the MyD88-dependent TLR pathway. The present study expanded our knowledge of host immune responses against MDV infection and our results might provide a clue that MDV may interfere with T cell immune response through TLR3 signals.

Differential expression of Toll-like receptor pathway genes in chicken embryo fibroblasts from chickens resistant and susceptible to Marek's disease

The Toll-like receptor (TLR) signaling pathway is one of the innate immune defense mechanisms against pathogens in vertebrates and invertebrates. However, the role of TLR in non-MHC genetic resistance or susceptibility to Marek's disease (MD) in the chicken is yet to be elucidated. Chicken embryo fibroblast (CEF) cells from MD susceptible and resistant lines were infected either with Marek's disease virus (MDV) or treated with polyionosinic-polycytidylic acid, a synthetic analog of dsRNA, and the expression of TLR and pro-inflammatory cytokines was studied at 8 and 36 h posttreatment by quantitative reverse transcriptase PCR. Findings of the present study reveal that MDV infection and polyionosinic-polycytidylic acid treatment significantly elevated the mRNA expression of TLR3, IL6, and IL8 in both susceptible and resistant lines. Furthermore, basal expression levels in uninfected CEF for TLR3, TLR7, and IL8 genes were significantly higher in resistant chickens compared with those of susceptible chickens. Our results suggest that TLR3 together with pro-inflammatory cytokines may play a significant role in genetic resistance to MD.

In vitro and in vivo broad antiviral activity of peptides homologous to fusion glycoproteins of Newcastle disease virus and Marek's disease virus

Newcastle disease virus (NDV) of paramyxovirus and Marek's disease virus (MDV) of herpesvirus, two of the most serious threats to the poultry industry, can give rise to complex co-infections that hinder diagnosis and prevention. In the current study, two different peptides, derived from the MDV gH (gHH2L) and gB (gBH3), respectively, exhibit antiviral activity against NDV in vitro. The potent inhibitory effect of heptad repeat 2 from fusion glycoprotein of the NDV on MDV infection also has been demonstrated. Plaque formation and embryo infectivity assays confirmed these antiviral results. Furthermore, each tandem peptide consisting of two motifs from different viruses exhibits more potent antiviral activity than the constituent peptides. The current work provides a new strategy for developing novel peptides and vaccines against virus infection and co-infections.

Sequence variations of the MHC class I gene exon 2 and exon 3 between infected and uninfected chickens challenged with Marek’s disease virus

The major histocompatibility complex (MHC) among chickens has been well established as being associated with disease resistance and pathogens infection, but the genetic differences in MHC between chickens susceptible to certain infections and those chickens that remain uninfected have not been sufficiently determined. In this study, we sought the genetic basis that may underlie differences in susceptibility to infection among chickens by challenging four groups of broilers with Marek’s disease virus (MDV). Over the course of the experiment, lesions began to appear between 21 and 35days post challenge (dpc), and commercial broilers were not necessarily better than indigenous chickens in terms of disease resistance. The four groups showed neutral resistance to MDV infection validated by challenge results and evolutionary analysis of exons 2 and 3 of the MHC class I region. Several variable sites in exon 2 and exon 3 were exclusively appeared in infected chickens. Exon 3 was likely more crucial than exon 2 in disease resistance. Our observations offered a support for a potential association between promiscuous pathogens and conspicuous genetic diversity in the MHC class I region.

Sodium Tanshinone IIA Sulfonate Inhibits the MEQ, Ul49 and VP22 Expression of Marek's Disease Virus

Our previous studies have demonstrated that sodium tanshinone IIA sulfonate (STS), a natural compound derived from Salviae Miltiorrhizae Radix et Rhizoma (Danshen), could effectively inhibit Marek's disease virus (MDV) infection both in vitro and in vivo, but the underlying mechanisms remain unclear. The main objective of the study was to explore the effect of STS on the meq, ul49 and VP22 expression of MDV in vitro. Quantitative real-time PCR (qRT-PCR) was used to analyse the effect of STS on meq and ul49 expression at both the DNA and messenger RNA (mRNA) level, and the effect of STS on VP22 was assessed by immunofluorescence assay and western blotting. The DNA and mRNA copy numbers of meq and ul49 significantly decreased in the groups treated with STS compared with MDV control (P<0.05), which indicated that STS could inhibit the expression of meq and ul49 at both the DNA and mRNA level. Moreover, the expression of VP22 encoded by ul49 was also significantly inhibited (P<0.05). STS possessed anti-MDV activity in chicken embryo fibroblasts. Its antiviral mechanisms may be ascribed to inactivating MDV directly, disturbing meq and ul49 replication and inhibiting the expression of VP22 encoded by ul49. These results suggested that STS is a promising natural compound to be further developed as an antiviral agent against MDV infection.

Transcriptional Profiling of MEq-Dependent Genes in Marek’s Disease Resistant and Susceptible Inbred Chicken Lines

Marek’s disease (MD) is an economically significant disease in chickens caused by the highly oncogenic Marek’s disease virus (MDV). Understanding the genes and biological pathways that confer MD genetic resistance should lead towards the development of more disease resistant commercial poultry flocks or improved MD vaccines. MDV mEq, a bZIP transcription factor, is largely attributed to viral oncogenicity though only a few host target genes have been described, which has impeded our understanding of MDV-induced tumorigenesis. Given the importance of mEq in MDV-induced pathogenesis, we explored the role of mEq in genetic resistance to MDV. Using global transcriptome analysis and cells from MD resistant or susceptible birds, we compared the response to infection with either wild type MDV or a nononcogenic recombinant lacking mEq. As a result, we identified a number of specific genes and pathways associated with either MD resistance or susceptibility. Additionally, integrating prior information from ChIP-seq, microarray analysis, and SNPs exhibiting allele-specific expression (ASE) in response to MDV infection, we were able to provide evidence for 24 genes that are polymorphic within mEq binding sites are likely to account for gene expression in an allele-specific manner and potentially for the underlying genetic differences in MD incidence.

Expression kinetics of chicken β2-microglobulin and Class I MHC in vitro and in vivo during Marek’s disease viral infections

Marek's disease virus (MDV) is a highly cell-associated herpesvirus that causes a disease in chickens characterized by tumor formation and immunosuppression. The changes of major histocompatibility complex (MHC) expression in different MDV-infected cells are not completely understood. In this study, we investigated the expression of the Class I MHC and β2-microglobulin (β2m) genes in response to MDV infection at different time points by real-time PCR. In both in vitro and in vivo, the expression levels of Class I MHC and β2m genes were upregulated during early MDV infections in comparison to control cells; We also found that the expression of Class I MHC gene was downregulated in BudR (5-bromo-2'-deoxyuridine)-treated MSB1 cells at 48 h and MDV-infected chicken embryo fibroblast cells (CEF) at 120 and 168 h post infection (hpi); Furthermore, compared to control groups, Class I MHC and β2m expression levels were downregulated in peripheral blood lymphocytes (PBLC) from MDV-infected chickens at 14 and 28 days post infection (dpi); Interestingly, both Class I MHC and β2m gene expression levels increased again in PBLC from MDV RB1B-infected chickens at 35 dpi, in which MDV was in the latent or transformed infection stages. In addition, Class I MHC expression was clearly decreased in MDV-infected CEF at 120 hpi although β2m expression was significantly increased. These changes in Class I MHC and β2m gene expression might provide more insights into host-virus interaction.

DNA Methylation Down-Regulates EGFR Expression in Chickens

The epidermal growth factor receptor (EGFR), a growth-factor-receptor tyrosine kinase, is up-regulated in numerous tumors, which provides a good target for cancer therapy. Although it has been documented that oncoviruses are responsible for the activation of EGFR in tumors, the impact of Marek's disease virus (MDV) infection on EGFR has not yet been studied. We performed quantitative reverse transcriptase (RT)-PCR to check EGFR expression and found that it was significantly down-regulated after MDV infection. To explore the mechanism of EGFR repression, we examined the level of methylation of the EGFR promoter. The methylation level was significantly increased at 21 days postinfection, indicating a potential role of promoter methylation in EGFR repression.