Type-C RNA viruses and leukemogenesis: relation of type-C virus infectivity and leukemogenesis induced by nitrosourea compounds in mice.

Correlation between infectivity of type-C RNA virus) murine leukemia virus, MLV) and development of leukemia was tested in female ICR/JCL mice treated with either 1-ethyl-1-nitrosourea (ENU) or 1-butyl-1-nitrosourea (BNU). Continuous administration of either chemicals resulted in the occurrence of thymic lymphoma in every mouse with a short latent period. The time of appearance and distribution pattern of MLV infectivity in various tissues were examined by the XC plaque assay technique at fixed intervals during the leukemogenic treatment. In ENU- or BNU-treated mice, only a few samples of the thymus showed MLV infectivity with rather low titers during incubation period and the presence of MLV was not consistent even in leukemic cases though the thymus was almost invariably the target of leukemogenesis. On the other hand, many samples of the uterus, spleen, and mesenteric node from non-leukemic and leukemic mice harbored a good quantity of MLV. In tissues such as the liver, kidney, bone marrow, and muscle, positive cases occurred only sporadically. Observations on the MLV infectivity in untreated controls were almost comparable with those in leukemogen-treated mice. These results indicate that the infectivity of MLV, detected by the XC plaque assay technique, is not necessarily related to the induction of leukemia in mice by exogenous agents.