Expression of Marek's Disease Virus Oncoprotein Meq During Infection in the Natural Host

•Generation of a virulent MDV that co-expresses GFP with its oncoprotein, Meq.•Dynamics of Meq expressing cells during the course of infection in vivo.•Existence of the latently infected lymphocytes that do not express Meq.•Implications to the current pathogenesis model.

Gallid herpesvirus 2 (Marek's disease virus, MDV) causes lymphoproliferative Marek's disease (MD), and is unique among alphaherpesviruses as the viral genome encodes an oncoprotein, Meq. To elucidate the temporal relationship between Meq expression and the development of MD lymphomas in infected chickens, we generated a virulent recombinant MDV that expresses GFP simultaneously with Meq. By using this virus, we monitored the dynamics of Meq expression in vivo throughout the course of infection. In peripheral blood mononuclear cells, the percentage of Meq-expressing cells dramatically increased in the early latent phase but decreased thereafter. Furthermore, we discovered evidences that indicate some of the infected lymphocytes did not express Meq during the latent phase of MDV pathogenesis. These findings provide the first insight into the temporal relationship between Meq expression and MD progression, and new clues to refine the current MD pathogenesis model.