ABSTRACT
Type C RNA viruses can be induced by certain chemicals from cells of many mouse strains. Both C58 and BALB/c cells have been shown to contain endogenous viruses that are designated N-tropic because they grow preferentially in cells of NIH Swiss mouse origin. While demonstrating many similar biological and immunological properties, the C58-induced virus is around 10-fold more infectious per physical particle than the N-tropic virus of BALB/c cells. In the present studies, inoculation of these viruses into newborn NIH Swiss mice led to the development of diseases associated with splenomegaly and lymphadenopathy at similar frequency in each group. The disease induced by C58-MuLV was histophathologically diagnosed as lymphoblastic leukemia and was highly malignant following transplantation into newborn mice. The histopathological appearance of spleens from BALB/c virus-affected animals was distinguishable, demonstrating instead myeloid metaplasia or myelogenous leukemia. These findings provide evidence that different endogenous mouse type C viruses can induce distinct diseases in the same mouse strain. Furthermore, they implicate the N-tropic virus endogenous to C58 cells as a major factor in the development of lymphoblastic leukemia that occurs at high frequency in that strain.
