An electron microscopic study of the leukemia virus in AKR and hybrid mice inoculated with ascites passage or tissue-cultured leukemic cells.

Various organs and tumors from AKR and hybrid mice and leukcmic cells grown in tissue culture were studied by electron microscopy. Only spleen and thymus were examined in fetuses and newborn mice. In adults, solid tumors, lymph nodes, and ascites cells were also studied. AKR mice dying of spontaneous leukemia showed typical virus particles (Types A and C) in their lymph nodes. No virus particles could be identified in organs from newborn or 7to 10week-old mice. Virus particles were not observed in the thymus or lymph nodes of mice injected with long-term ascites transfers of the leukemia, but characteristic particles were found in all solid mesenteric and ascites tumors examined. Organs from Ft hybrids (C57B1/6 X AKR) were uniformly negative. However, in one solid tumor, produced by inoculation with tissue-cultured cells, numerous viras particles were present. All newly isolated or long-term tissue culture lines tested contained virus-like par ticles. The virulence of these lines, for AKR or hybrid mice, did not correlate with either the chromosome number or the presence of virus particles.