Large round cell granulomas induced by murine sarcoma virus (Moloney) in mouse brains

The effect of murine sarcoma virus of Moloney strain on central nervous system was examined morphologically in Swiss mice of different age. A single intracranial inoculation of cell-free virus solution resulted in the induction of characteristic intracerebral granulomas in 82.8% of the newborn to 5 day-old group, in 71.4% of the 6 to 10 day-old group, and in 68.0% of the 11 to 20 day-old group. The mean latency periods to tumor recognition were 16.5, 21.1, and 33.5 days, respectively. The granuloma consisted of inflammatory cell infilrations, reactive gliosis, and richly developed blood vessels. The lesions consistently contained numerous characteristic large round cells. In cases of long-survival, the findings included reparative changes, such as extensive gliosis, withdrawal of inflammation, and a decrease in the numbers of large round cells and blood vessels. These lesions were tentatively designated as "large round cell granuloma." The early foci of the granoloma were composed of proliferating glial cells and large round cells at the subependymal regions. Electron microscopically these large round cells had abundant intracytoplasmic fibrils quite similar to gliofibrils. Numerous C-type virus particles were present in the intercellular nad perivascular spaces, and occasionally budded from cell membranes of the large round cells and vascular endothelia. The large round cells were considered to be reactive astrocytes activated by biral infection. It was conclided that MSV-M was not a sarcomogenic but a granulomogenic virus in mice. Control animals showed no pathological changes.