Type-C virus antigen detection in co-cultures of human leukaemic bone marrow and dog cells

Bone marrow of leukaemic patients, non-leukaemic patients and normal individuals were co-cultivated with the canine cell line A7573. These co-cultures were screened for retrovirus antigens by means of the indirect cytoplasmic immunofluorescence assay (IFA). Rabbit antisera directed against the major structural protein (p30) of woolly monkey (simian) sarcoma leukaemia virus (grown in human lymphoid cells) and Rauscher murine leukaemia virus were used for testing. After 2 months in culture, 6 of 17 co-cultures containing cells from leukaemic patients showed positive staining in the IFA with the anti-simian virus serum. In control dog cells fluorescence was never observed. Five of the six positive cultures were derived from leukaemic children. One of 12 co-cultures of the non-leukaemic group and one of nine normal bone marrow co-cultures were positive with the simian virus antiserum. None of the 38 co-cultures stained positive in the IFA with Rauscher virus antiserum. Absorption of the simian virus antiserum with calf serum or mouse mammary tumour virus had no dramatic effect in the IFA on positive control cells or on cells of a positive co-culture. However, absorption with purified simian virus (grown in rat cells) completely abolished these fluorescence reactions. The results provide evidence that simian sarcoma-leukaemia virus related information was present in the original bone marrow samples and that co-cultivation with permissive mammalian cells enabled the detection of virus footprints.