Lack of ecotropic virus involvement in induction of lymphomas in DBA/2J mice by 7,12-dimethylbenz(a)anthracene

Retrovirus-induced lymphoproliferation as a model for developing diagnostic criteria for malignant lymphoma in mice

Several methods for evaluating lymphoproliferative lesions in mice were compared. The model systems included spontaneous lymphomas arising in CWD mice and NFS mice congenic for ecotropic murine leukemia virus (MuLV) induction loci and a series of transplants in mice with severe combined immunodeficiency disease mutation of cells derived from mice infected with LP-BM5 MuLV. Primary lymphomas and donor tissues and transplants were examined using histopathology, flow cytometry, and Southern blot analysis of DNA for rearrangements of immunoglobulin and T-cell receptor genes and for viral integrations. The use of flow cytometric analysis, to establish cell lineage and define population size, and DNA analysis, for cell lineage and clonality determination, allowed the identification of malignant lymphoproliferations. Histologic evaluation did not define clonal populations of particular lineage but did provide other indications of malignancy such as invasiveness and presence of a dominant morphologic cell type. Thus, the precision of diagnosis of mouse lymphomas can be considerably enhanced by augmenting histopathologic examination with antigenic and molecular characterizations that can define malignant populations.

Influence of murine leukemia proviral integrations on development of N-methyl-N-nitrosourea-induced thymic lymphomas in AKR mice

The AKR mouse strain is characterized by a high incidence of spontaneous thymic lymphoma that appears in older animals (greater than 6 months of age) and is associated with novel provirus integrations of ecotropic and recombinant murine leukemia viruses (MuLVs). Treatment of 4- to 6-week-old AKR/J mice with the carcinogen N-methyl-N-nitrosourea (MNU) results in thymic lymphomas that arise as early as 3 to 4 months of age and contain novel somatically acquired MuLV provirus integrations. The AKR/J strain develops MNU-induced lymphoma with a higher incidence and shorter latency than has been observed for other inbred mouse strains. To determine whether provirus integrations of endogenous MuLV account for the enhanced susceptibility of the AKR strain, the incidence and latency of MNU-induced lymphoma development was compared in AKR/J and AKR.Fv-1b mice. The restrictive b allele of the Fv-1 locus restricts integration and replication of endogenous N-tropic MuLV; therefore, AKR-Fv-1b mice have a very low incidence of spontaneous lymphoma. In contrast, AKR.Fv-1b mice develop MNU-induced lymphomas with an incidence and latency similar to those of the AKR/J strain. Furthermore, thymic lymphomas from both strains express an immature CD4-8+ phenotype, indicating neoplastic transformation of the same thymocyte subset. Southern blot analysis confirmed that lymphoma DNA from AKR.Fv-1b mice did not contain somatically acquired provirus integrations. These results demonstrate that provirus integration does not contribute to the predisposition of AKR mice to develop a high incidence of early MNU-induced lymphomas. Nevertheless, MNU treatment stimulated high-level expression of infectious ecotropic MuLV in AKR.Fv-1b as well as in AKR/J mice, suggesting that viral gene products might enhance lymphoma progression.