C-type virus particles in spontaneous and virus-induced leukemia and malignant lymphomas in mice and rats

The presence and numbers of C-type virus particles in an animal model consisting of mice and rats with either spontaneous or virus-induced leukemia and lymphomas were studied, in order to determine the relation of the appearance of virus particles to viral etiology of such neoplasms. The numbers and distribution of C-type virus particles in organs from 13 mice with spontaneous leukemia and lymphomas were compared with the presence of virus particles in organs of 13 mice with leukemia and lymphomas induced by passage A (Gross) virus inoculation. C-type virus particles were present in organs of all mice with either spontaneous leukemia or leukemia and lymphomas induced by virus inoculation. However, the number of particles observed was significantly higher in those mice in which leukemia was induced by virus inoculation. Virus particles were also observed, but in substantially smaller numbers, in organs of 13 of 25 untreated, healthy mice of the nonleukemic C3H(f) inbred line. In contrast to mice, C-type, or any other virus particles, were not found in organs of 10 Sprague-Dawley, Long-Evans or Sprague-Dawley X Long-Evans F1 hybrid rats with spontaneous leukemia. However, C-type virus particles were consistently present in organs of 11 Sprague-Dawley rats with leukemia induced by rat-adapted passage A (Gross) mouse leukemia inoculation. The virus particles appeared in the organs of the inoculated rats 5 days after i.p., and 11 days after s.c. inoculation. Virus particles were not found in organs of 10 healthy untreated Sprague-Dawley rats. The implications of these observations are discussed.