DNA of the oncogenic strain BC-1 of Marek's disease virus contains three units of tandem direct repeats with 132 base pairs in the terminal repeat and internal repeat, respectively, of the long region of the Marek's disease virus genome, whereas the attenuated, nononcogenic viral DNA contains multiple units of the tandem direct repeats.

No abstract

Continuously proliferating T-lymphoblastoid cells, named MDCC-MTB1, were obtained by infection of chick embryo lymphocytes with Marek's disease virus serotype I (MDV1) in culture and subsequent cultivation in the presence of human interleukin 2 (IL-2). The MTB1 cells have now been growing well for at least 4 months with a doubling time of about 10 hr, irrespective of the presence of IL-2. The MTB1 cells show lymphoblastoid morphology, and carry T-lymphocyte marker surface antigens and a karyotype of female chick origin with several abnormal chromosomes. Southern blot hybridization showed that they contain about 10 virus genome equivalents/cell of almost the whole MDV genome. Infectious virus could not be rescued from MTB1 cells by co-cultivation of these with chick embryo fibroblasts. In addition, no virus particles were found in thin-sectioned MTB1 cells by electron microscopy. An immunofluorescence test with monoclonal antibody (MAb) to MDV-specific phosphorylated proteins showed that MTB1 cells expressed the MDV-specific antigen in the cytoplasm only after the cells had been treated with 5-iodo-2-deoxyuridine for 48 hr at 41 degrees C. MTB1 cells can form colonies in 0.33% soft agar, and can be transplanted into chicks by i.p. injection. Thus, continuously growing lymphoblastoid cells were obtained by in vitro infection of chick embryo lymphocytes with oncogenic MDV1 and cultivation of the cells in the presence of human IL-2 during the transformation step. These cells appear to show a similar phenotype to an MD lymphoma-derived cell line.