Absence of activated murine leukaemia virus in x-irradiated CBA/H-T6crc mice

CBA/H-T6Crc mice, a substrain that does not normally express demonstrable levels of murine leukaemia virus (MuLV) and has a low natural incidence of leukaemia, were examined for evidence of virus activation at various times following X-irradiation. Although X-irradiation caused a high incidence of leukaemia, no ecotropic, xenotropic or recombinant MuLV was detected by in vitro co-cultivation of bone marrow, spleen and thymus cells from pre-leukaemic and leukaemic animals with selectively permissive cell lines followed by indirect immunofluorescence for MuLV group-specific (gs) antigen. These results, therefore, are not consistent with the hypothesis that endogenous viruses are the universal aetiological agents of leukaemia.