Changes in natural killer cells activity in mice bearing subcutaneously implanted Lewis lung carcinoma

Natural killer (NK) cytotoxic activity was measured against the standard target cell line YAC-1 in a four-hour chromium release assay. Effector cells were taken from spleen and bone marrow of BDF1 mice inoculated 3, 7, 14 or 21 days earlier with 2 X 10(6) Lewis lung carcinoma (LL) cells. The peak of cytotoxic activity both in spleen and bone marrow appeared in mice 3 days after tumor inoculation. There were no differences in cytotoxic effect between tumor bearing and normal mice on day 7. The significant decrease was observed in tumor bearing mice on day 14 and 21. However, at that time the spleen cellularity increased 2.7 and 3.8 times, respectively suggesting a possible dilution effect of NK cells in mice with splenomegaly. Bone marrow cellularity remained unchanged as compared to control. The possible mechanisms of decrease in NK cytotoxic activity and its implications for progression of tumor growth are considered.