Natural Occurrence of Tumors in Mouse Strains With Different Xenotropic and Ecotropic Endogenous Viruses2

Abstract

Natural tumor incidence and type C virus expression in NIH Swiss and BALB/c mice were investigated. The BALB/c mice showed a moderate incidence of Iymphoreticular tumors containing infectious ecotropic virus. A second class of lymphoreticular tumors occurred with approximately the same incidence in both strains; though infectious virus could not be isolated from it, it contained the antigens of a common xenotropic virus. These xenotropic viral antigens were found in all NIH Swiss and BALB/c tumors examined and in normal hematopoietic tissues as well. The relationship between different classes of endogenous viruses and tumor development was discussed.