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Title: CHARACTERIZATION OF A VERY VIRULENT MAREK'S DISEASE VIRUS MUTANT EXPRESSING THE PP38 PROTEIN FROM THE SEROTYPE 1 VACCINE STRAIN CVI988/RISPENS

Author
item Lee, Lucy
item CUI, XIAOPING - MICHIGAN STATE UNIV
item CUI, ZHIZHONG - SHANDONG AGRIC UNIV CHINA
item Gimeno, Isabel
item LUPIANI, BLANCA - TEXAS A & M UNIV
item REDDY, SANJAY - TEXAS A & M UNIV

Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2005
Publication Date: 7/1/2005
Citation: Lee, L.F., Cui, X., Cui, Z., Gimeno, I.M., Lupiani, B., Reddy, S.M. 2005. Characterization of a very virulent Marek's disease virus mutant expressing the PP38 protein from the serotype 1 vaccine strain CVI988/Rispens. Virus Genes. 31(1):73-80.

Interpretive Summary: Marek's disease (MD), a virus-induced cancer-like disease of chickens, is considered as a major disease problem in commercial poultry. Vaccination has dramatically reduced the incidence of the disease, but more virulent viruses are emerging and development of new control strategies is needed. The objective of this research was to characterize the function of the pp38 gene of the Marek's disease virus (MDV) that has been associated with important events in the development of MD, such as replication, reactivation from latency and tumor formation. We have shown that insertion of pp38 gene from CVI988 vaccine strain into a pp38 deleted rMd5 mutant results in virulence and tumor induction. This is a critical step in demonstrating the function of pp38 gene involved in virus replication in chickens. This important information about the pp38 gene of MDV will help scientists in academia and industry understand MD and eventually lead to better control of the disease.

Technical Abstract: Marek's disease virus (MDV), a highly cell-associated oncogenic chicken herpesvirus, causes Marek's disease in domestic chickens. A unique phosphoprotein of MDV, pp38, has previously been associated with the maintenance of transformation in MDV-induced tumor cell lines. However, recently, the biological properties of a deletion mutant virus (rMd5'pp38) revealed that pp38 is involved in early cytolytic infection in lymphocytes but not in the induction of tumors. Thus, pp38 is essential for replication and not for transformation. The pp38 protein of the MDV serotype 1 vaccine strain CVI988/Rispens differs by one amino acid when compared to the pathogenic strains of MDV. Monoclonal antibody, H19, recognizes all serotype 1 MDV strains except CVI988/Rispens. Previous studies have also shown that the unique pp38 epitope in CVI988/Rispens induced high antibody response. In order to study the role of this epitope in the protective properties of CVI988/Rispens, we generated a mutant rMd5 virus in which the wild type pp38 gene has been substituted with that of CVI988/Rispens (rMd5/pp38CVI). The replication properties of rMd5/pp38CVI, both in vitro and in vivo, and tumor induction were examined. We found that the biological properties of rMd5/pp38CVI were similar to the wild type Md5 virus with regards to in vivo replication, antibody response and tumor induction. This showed that the pp38 derived from CVI988/Rispens is not involved in protective properties as was previously suggested.