STUDIES OF GENETIC TRANSMISSION OF MURINE LEUKEMIA VIRUS BY AKR MICE : II. CROSSES WITHFv-1b STRAINS OF MICE

The transmission of murine leukemia virus (MLV) to hybrids between AKR and Fv-1b mice was studied in order to evaluate the effect of the Fv-1 gene on endogenous MLV infection and to attempt to determine if the genetic loci contributed by AKR carry viral genetic determinants. Fv-1 was shown to have a marked suppressive effect on time of appearance of detectable infectious virus and on the titers attained in vivo, but did not affect the ability of the cells to produce virus in vitro after induction with 5-iododeoxyuridine. The host range type of the virus detected in the hybrid mice was almost always of the type carried by AKR, although the low-virus Fv-1b parents carry the genome of a different host range type. This finding provides strong, but not conclusive, evidence that the virus-inducing loci of AKR contain MLV genetic determinants

A MAJOR GENETIC LOCUS AFFECTING RESISTANCE TO INFECTION WITH MURINE LEUKEMIA VIRUSES : I. TISSUE CULTURE STUDIES OF NATURALLY OCCURRING VIRUSES

Previous studies have indicated that all naturally occurring murine leukemia viruses propagate significantly more efficiently on embryo cells of either NIH Swiss or BALB/c mice. Studies of the plaquing efficiency of representative viruses on embryo cells of various inbred and hybrid mice indicate that the pattern of sensitivity of the cells is genetically determined. All of 23 strains tested were found to resemble either NIH Swiss (N-type) or BALB/c (B-type) with respect to plaquing efficiency of these viruses. Virus growth on embryo cells derived from (N-type x B-type)F1 hybrids indicated dominance of resistance to both types of viruses. Backcross hybrid studies indicated that a single locus is the primary determinant of the host-range patterns observed. This locus has no effect on growth of certain laboratory-passaged leukemia viruses which propagate equally well on embryo cells of all mouse strains, F1, and backcross hybrids. Though other genetic and nongenetic factors influence viral growth or expression in vitro and in vivo, the genetic locus described appears of major significance in the biology of murine leukemia

Expression of infectious murine leukemia viruses by RAW264.7 cells, a potential complication for studies with a widely used mouse macrophage cell line

The mouse macrophage-like cell line RAW264.7, the most commonly used mouse macrophage cell line in medical research, was originally reported to be free of replication-competent murine leukemia virus (MuLV) despite its origin in a tumor induced by Abelson MuLV containing Moloney MuLV as helper virus. As currently available, however, we find that it produces significant levels of ecotropic MuLV with the biologic features of the Moloney isolate and also MuLV of the polytropic or MCF class. Newborn mice developed lymphoma following inoculation with the MuLV mixture expressed by these cells. These findings should be considered in interpretation of increasingly widespread use of these cells for propagation of other viruses, studies of biological responses to virus infection and use in RNA interference and cell signalling studies