The induction of myeloid leukaemias by Rauscher murine leukaemia virus

A number of cloned viral preparations isolated from Rauscher virus-producing JLS-V5 cells were compared in their competence to induce different ypes of leukaemias. All preparations were able to induce myeloid leukaemias, but the induction of lymphatic or erythroid leukaemias was also observed. Serial infection of newborn mice with either cell-free extracts or serum from animals uffering from a myeloid leukaemia did not result in the occurrence of relatively more myeloid leukaemias nor did the infection with virus harvested from ascites fluid of permanent myeloid cell lines. It appears that the mechanism by which myeloid leukaemias are induced is not virus-specific. Rauscher leukaemia virus causes a rapidly developing erythroblastosis due to the presence of a defective spleen focus-forming virus (SFFV) in combination with an ecotropic lymphatic leukaemia virus (R-MuLV) (Rauscher, 1962; Steeves, 1975). Although a number of other viral components have been described in Rauscher virus preparations (van Griensven & Vogt, 1980), there has been no report of a virus strain that exclusively induces a myeloid leukaemia. In an earlier study using the culture fluid of Rauscher virus-producing JLS-V5 cells (Wright &amp