Cytopathogenic XC assay for bone marrow from mice infected with murine leukemia viruses.

Virus production "in vitro" by bone marrow cells of murine leukemia virus-infected BALB/c mice was determined with a modified reverse XC cell assay. Bone marrow of mice infected by either Rauscher leukemia virus or Soulé myeloid leukemia virus was cocultivated with XC cells and quantification was done by counting syncytia. During the development of both erythroblastosis and myeloid leukemia, the number of syncytia induced by cocultivation increased. High numbers of syncytia were especially obtained with myeloid leukemia cells; the phenomenon was evident as early as one month following inoculation with virus and before the onset of conspicuous clinical signs of disease.