Molecular pathogenesis of Marek's disease—recent developments

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Abstract
Marek's disease (MD) is a lymphoproliferative disorder induced by a herpesvirus in chickens, its natural host. After an early cytolytic infection, the virus induces lymphomas in T‐cells. These cells are latently infected with the virus, but very few viral transcripts or proteins are detectable. Although there are indications that some of these virus‐encoded transcripts may be involved in tumourigenesis, the exact nature of the virus‐cell interaction contributing towards the transformed phenotype is not completely understood. Among the transcripts the meq protein with basic leucine zipper (bZIP) characteristic of the fos/jun family of transcriptional activators is thought to play a major role in MDV‐induced oncogenesis. Similarly the MDV‐en‐coded immediate early transcripts, ICP4, also seems to play an important role in latency and transformation. Apart from the virally‐encoded factors, various host cell factors may be involved in the induction of tumours. Although not much work has been done in elucidating these factors, the possible role of tumour suppressor genes like p53, proto‐oncogenes like Bcl‐2 capable of blocking apoptosis, and telomerases in the induction of lymphomas are discussed. Some of the recent findings concerning the molecular mechanisms of interactions between MD virus and retroviruses are also presented.