Differentially-expressed genes during spontaneous reactivation of Marek’s disease virus in lymphoblastoid cell lines determined by global gene expression profiling

Marek’s Disease Virus (MDV) is a widespread alphaherpesvirus of poultry that causes Marek’s disease (MD) characterised by fatal visceral CD4+ TCRαβ+ T cell tumours at high incidence in susceptible hosts. As is the case with many virus-induced tumours, immortal cell lines harbouring viral genome have been generated from ex vivo cultures of MD tumours. As readily-available sources of large numbers of cells of a uniform type, MDV-transformed lymphoblastoid cell lines (LCL) have proved extremely valuable in studying virus-host interaction. While the viral genome is held in a latent state in most of the cells, a minor population of cells display spontaneous reactivation identifiable by the expression of lytic viral genes such as pp38. The process of spontaneous reactivation in these cell populations offers the opportunity for investigating the biological processes involved in the reactivation events. For this, we used two lymphoblastoid cell lines derived from lymphomas induced by pRB1B-UL47eGFP, a recombinant MDV engineered to express EGFP fused with the UL47. We used Fluorescence-activated cell sorting (FACS) to purify the rare EGFP-positive cell population with spontaneously activating viral genome from the majority EGFP-negative cells and analysed their gene expression profiles by RNA-sequencing using Illumina HiSeq2500. The reads generated were mapped using TopHat and gene expression levels were analysed by edgeR. Ingenuity pathway analysis software on more than 2000 differentially-expressed genes between the lytically infected (EGFP-positive) and latently infected (EGFP-negative) cell populations was used identify major biological pathways involved in the reactivation. These studies revealed that amongst others, transcripts directly involved in T activation such as CD3 complex, CD28, ICOS, phospholipase C, CD3 complex were down-regulated following reactivation of the virus in the LCL.

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