Cell-associated mammary tumor virus in blood of BALB-cf C3H mice

SUMMARY-The nodule assay of mammary tumor virus (MN or Bittner virus) was used to detect viral activity in intact cells and/or in cell-free preparations of tissues of hematopoietic and mammary gland origin. MTV activity was easily found in intact mammary tumor cells and cell-free preparations of tumor cells and lactating mammary tissues from (3H and BALB/dC3H «(+) mice. In contrast, MTV activity in (+ blood cells and (+ hematopoietic colony cells in spleens of irradiated BALB/c mice was always cell-associated. All preparations of cells of hematopoietic origin com-pletely lost their MTV activity when they were freed of intact cells by centrifugation or filtration. The results suggest that, in our (+ mice, Bittner virus may pass through a cell-associated form in the cells of hematopoietic origin and through a cell-free form in the cells of mammary origin.- J Nat (ancer Inst 48: 1085-1088, 1972. A CELL-FREE form of infectious mammary tumor virus (MTV or Bittner virus) can readily b