ISOLATION OF SEROTYPE-2 MAREKS-DISEASE VIRUS FROM A CELL-LINE OF AVIAN LYMPHOID LEUKOSIS

To determine a serotype of Marek's disease virus (MDV) persistently in fected in a lympohoid leukosis (LL)-cell line, LSCC-BK3, clone A (BK3A ), and to examine the pathogenicity of the virus, an attempt was made to isolate MDV from culture fluid of the LL-cell line, using chick emb ryo fibroblast cultures resistant to infection with subgroup A avian l eukosis virus (ALV) to eliminate subgroup A ALV. The MDV isolate, sero logically identified as serotype 2 MDV and designated as the 2H strain , was free from ALV and reticuloendotheliosis virus. A serotype 2-spec ific antigen of MDV was detected in 44% of BK3A, but antigens of serot ypes 1 and 3 were not detected in this cell line, by the indirect immu nofluorescent antibody test using serotype-specific monoclonal antibod ies. MDV antigens were undetectable in LSCC-BK3, clone 2C; both cell l ines were established from the same chicken. Neither clinical signs no r macroscopic lesions were observed in any of 19 chicks inoculated wit h the 2H strain. Three out of 19 chicks histopathologically examined h ad no lesions. These results suggest that serotype 2 MDV can persist i n B cells transformed by ALV without cytopathic effect at a high rate, and the isolate may become a candidate for MD vaccine strains.