Spleen foci and polycythemia in C57B1 mice infected with host-adapted Friend leukemia virus.

Abstract

AbstractThe host range of Friend leukemia virus was altered significantly by passage in newborn C57Bl mice. Two virus isolates (BSB and BB6), derived from the original Friend virus stock, induced the familiar “Friend disease” and polycythemia in suckling or adult C57Bl mice. However, both isolates differed from the parent virus in Swiss mice by their longer latent period and lower mortality in adult C57Bl mice. Replication of spleen focus‐forming virus (SFFV) from either isolate was limited in suckling mice and barely detectable in adult C57Bl mice. Host susceptibility to SFFV in the BSB isolate varied according to age in young adult C57Bl mice, and was also affected by a gene closely linked with or at the Histocompatibility‐2 locus. Spleen focus formation by either BSB or BB6 in adult BALB/c mice gave one‐hit dose‐response relationships, in contrast to the multiple‐hit relationship obtained with the parent virus. Thus, infection of C57Bl mice with either of two host‐adapted viruses resulted in the development of polycythemia and splenomegaly without extensive SFFV replication, in contrast to earlier observations with the original Friend virus preparation in Swiss mice. Even with the present virus‐host system, however, there was an association between virus replication and the virulence of the induced disease. In addition, there was an association between adaptation of SFFV to the C57Bl strain and an increased concentration of either helper virus or competent virions. Reasons for the low virus titers in several mouse strains and for the limited virus replication in the two strains tested were not apparent.