Marek's disease virus-induced immunosuppression: array analysis of chicken immune response gene expression profiling

Marek's disease (MD) is a lymphoproliferative disease of chickens induced by a highly cell-associated oncogenic alpha-herpesvirus, Marek's disease virus (MDV). MDV replicates in chicken lymphocytes and establishes a latency infection within CD4(+) T cells. Host-virus interaction, immune responses to infection, and transcriptional profiling of chicken gene expression in MD are poorly understood. In this study we conducted a global host gene expression analysis in the splenocytes of MDV-infected chickens using oligonucleotide-based Affymetrix GeneChip Chicken Genome Arrays. These arrays contain probes for more than 32,000 chicken transcripts and most of the known MDV genes and open reading frames. Two-week-old MD-susceptible chickens were inoculated with an oncogenic strain of MDV, and spleen samples were collected 5 and 15 days post-infection (dpi) for RNA isolation and microarray analysis. Array results displayed a significant differential pattern of immune response transcriptome between the two phases of MDV infection. The expression levels of more than 22 immune-response and related genes were downregulated, while the expression levels of at least 58 genes were increased at 5 dpi (cytolytic infection), compared to age-matched control birds. In comparison, out of 73 immune-response and related genes, 67 genes were downregulated, with only 6 genes having higher expression levels at 15 dpi (latency infection). Cytokines, chemokines, MHC molecules and related receptors, and adhesion molecules were among the many MDV-induced downregulated genes that are critical for an effective antiviral immune response. In addition, several apoptosis-associated genes were decreased in expression during latent infection, suggesting an MDV-induced blocking of initiation or progression of programmed cell death processes. These chicken arrays are valuable tools in understanding the molecular mechanisms behind viral pathogenesis and chicken gene expression patterns, and associated biological pathways in response to MDV infection.