H-2-dependent regulation of the high level of expression of ecotropic murine leukemia virus.

Adult B10.Y mice, which are congenic with C57BL/10ScSn ((B10) mice for the H-2 region, expressed a high titer of infectious ecotropic virus in the spleen. F1 hybrids between B10.Y and B10 mice were negative or had very low levels of virus expression. In (B10.Y x B10)F2 segregant mice, the high virus phenotype segregated with the H-2pa haplotype of B10.Y, whereas the virus-negative phenotype was associated with the H-2b haplotype of B10. Molecular hybridization experiments with a selected ecotropic AKR murine leukemia virus cyclic DNA probe indicated that both partner strains possessed ecotropic virus sequences and that the number of sequences present was the same in B10.Y mice as in B10 mice. This finding excluded the possibility that the H-2-related effect might be due to the presence of additional viral structural genes within or close to the H-2 region of B10.Y mice. The level of expression of this endogenous ecotropic virus was therefore affected by regulatory genes of the H-2 region.