Production of cytotoxin to a tumor cell in co-cultures of macrophage cell line with bovine leukemia virus producing cell line

J 774 cells (macrophage cell line) were co-cultured with fetal lamb kidney cells which permanently produce Bovine leukemia virus (BLV-FLK cells) and after co-culture, the cells removed by scraping were subcultured once every for 2-4 days. Strong cytotoxicity to a cell (C8 cells; a clone of F81 cell line which contains mouse sarcoma virus genome) was found in culture of cells from generations 11 after the passages of co-cultures. The activity to the cells was continuously found in the fluid without any other addition of stimulants. The above results show that J 774 cells were activated by the co-culture with BLV-FLK cells and produced the cytotoxic factor which revealed strong cytotoxicity to a C8 cells.