Pathogenesis of Chronic Friend Disease in Hybrid BDF₁ Mice^1 2 Free

Friend virus induced disease in 93% of BDF₁ hybrid mice inoculated. In these mice, compared with the highly susceptible BALB/c, the disease ran a longer course and showed a period of remission between the 4th and 8th weeks postinoculation. Four phases of disease were recognized histologically; namely, proliferative, regressive, minimal focal, and advanced. Minimal focal disease was found 4 or more weeks after inoculation in apparently healthy mice without significant splenomegaly. Histologically, spleens from these mice showed up to 20 small foci of dividing stem cells in the red pulp. Eventually these progressed to advanced fatal disease. All diseased mice showed typical Friend cells in the peripheral blood although these were very scanty in mice with minimal focal disease. No virus was recovered from the spleens of mice that did not develop disease or in those with minimal focal disease, and only relatively small amounts were recovered from mice with overt disease. Comparison of the titer of neutralizing antibodies in the serum of the mice in the foregoing groups revealed no significant differences.