Cell Proliferation during the Maturation of Natural Killer Cells

The requirement for cell division during the maturation of natural killer (NK) cells was studied by following the appearance of donor-type NK cells in irradiated mice injecied with bone marrow cells and by blocking the cell division at different times during this development. Irradiation (700 rad) or treatment with hydroxyurea (1 mg/g body weight, twice daily) of the recipieni mice 7 days after the bone marrow cell inoculation inhibited the appearance of normal NK cell levels, suggesting that the NK cell progenitors are dividing cells. Blocking of the cell division in chimeras that had already developed high NK levels decreased the splenic NK activity, indicating the presence of a dividing NK cell population at this stage of maturation. These results are in accordance with the concept that mature NK cells are nondividing cells but are derived from actively proliferating progenitors in the bone marrow, and some of the first NK cells appearing in the spleen from the bone marrow can still be dividing.