Mice treated with strontium 90: an animal model deficient in NK cells.

Treatment of BALB/c mice with radioactive isotopes of the bone-seeking element strontium reduces the percentage of specific NK-cell cytotoxicity to only 2.6%, compared with 13.6% for normal BALB/c and 36.3% for athymic (nude) BALB/c. The syngeneic plasmacytoma NS-1 was used as target in a 4th in vitro NK-cell microassay. Marrow cellularity in treated mice is reduced to 12.5% of controls, but haemopoietic and stem-cell functions are taken over by the spleen and the peripheral blood picture remains relatively normal. Allogenic (H-2k) tumour transplants are rejected normally with good anti-H-2k alloantibody response. Haemopoietic and T- and B-cell functions are therefore substantially intact, and the defect seems confined to NK cells. In vivo, after s.c. inoculation of 10(6) NS-1 cells, 8/12 controls grew a solid tumour after a mean delay of 30.5 +/- 1.25 (s.e.) days, whereas 5/6 90Sr-treated mice grew the tumours after a delay of only 10.5 +/- 1.8 days. This markedly reduced delay in the 90Sr-treated mice lends support to suggestions that NK cells play an important role in resisting the establishment of tumour foci (i.e. in antitumour surveillance). Mice treated with 90Sr could be useful in evaluating the in vitro role of NK cells.