Helper-independent and replication-defective erythroblastosis-inducing viruses contained within anemia-inducing friend virus complex (FV-A)

Abstract Helper-independent and replication-defective viruses contained within the anemia-inducing Friend virus complex have been analyzed. Helper-independent ecotropic viruses, F-MuLV, have been isolated which produce rapid hepatosplenomegaly and anemia when injected into newborn Swiss mice, but which do not cause this disease syndrome when injected into adult NIH Swiss mice. The histology of the enlarged spleens shows many erythroblasts and some areas of clear erythroid maturation in the later stages of the disease. A replication-defective virus has also been isolated which is an env gene recombinant virus and codes for a 52,000-dalton glycoprotein which has a specific immunological relationship to the gp70 of MCF murine leukemia viruses. This replication-defective virus (SFFV FV-A ) shows many similarities to the previously studied replication-defective virus found in polycythemia-inducing Friend virus stocks (SFFV FV-P ). However, clear differences between SFFV FV-P and SFFV FV-A also exist. Pseudotypes of SFFV FV-A cause rapid proliferation of erythroid precursors when injected into either newborn or adult Swiss mice. This disease is characterized by splenomegaly, friable spleens, normal or moderately low hematocrits, and splenic foci. Pseudotypes of SFFV FV-P also cause rapid proliferation of erythroid precursors when injected into either newborn or adult Swiss mice. This disease is characterized by splenomegaly, firm spleens and large foci, and normal or elevated hematocrits. The possible relationships between F-MuLV, SFFV FV-A , and SFFV FV-P are discussed.