Propagation and assay of virulent and attenuated JMV Marek's disease‐associated tumour cells

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Abstract
JMV tumour cells were shown to cause a lethal lymphoblastic leukaemia in young chickens as well as in chicken embryos. The incubation period was very short but dose‐dependent. Chickens died in 4 to 12 days, embryos in 7 to 14 days, after inoculation. Embryo‐passaged attenuated JMV (JMV‐A) caused the same lesions in embryos as virulent JMV. The dose‐response relationship depended on the route of inoculation and on the quality of the tumour cell preparation. Intramuscular (i.m.) inoculation of leukaemic blood or embryo lymphoblasts provided the most satisfactory response. Intraperitoneal (i.p.) inoculation and lymphoblastic chicken spleens as a source of JMV were definitely less suitable. The dose‐response curves obtained in yolk sac‐inoculated embryos were similar to the curves obtained by i.m. inoculation of chickens. Only 4 to 10 lymphoblasts were needed per lethal dose (50%) in chickens and 50 to 80 in embryos. The pathogenicity and antigenicity of JMV and JMV‐A were strictly cell‐associated. No Marek's disease (MD) virus or any other avian virus could be detected, either by various virus isolation procedures, or by serological methods. Contact transmission of JMV to other chickens did not occur. Antibodies against surface antigens on JMV lymphoblasts were detected in JMV and JMV‐A chicken hyperimmune sera. These sera reacted against MD lymphoblastoid cell lines (HPRS‐1 & 2, MSB‐1) as well as MSB‐1 anti‐serum, but all sera reacted also against thymus lymphocytes from normal chickens. The results of absorption tests suggested that the surface antigens of JMV lymphoblasts and of the tested cell lines were not identical. The majority of tumour cell surface antigens appeared to represent genetically specific histocompatibility or lymphocyte antigens. A common MD tumour‐associated surface antigen (MATSA) could not be identified serologically (FA test) on the tumour cells studied.