Susceptibility to two strains of Friend leukemia virus in mice.

A mutant strain of the Friend leukemia virus is described. The parental virus strain, passaged through ICR/Ha mice, shows no or very little activity by the spleen-focus assay in BALB/c mice (by comparison with highly susceptible DBA/2 and ICR/Ha mice) and produces typical Friend disease in these mice only exceptionally; susceptibility to this strain of virus is recessive in the (C57BL/6 x DBA/2) F(1). By contrast, the mutant virus strain is as active in BALB/c mice as in DBA/2 or ICR/Ha mice; susceptibility to the mutant virus strain is dominant in the (C57BL/6 x DBA/2) F(1).