Natural cell-mediated cytotoxicity in Ehrlich ascites tumor-bearing mice

The level of NCMC (natural cell-mediated cytotoxicity) in the spleen of Ehrlich ascites tumor-bearing mice at every 5 days after i. p. tumor transplantation, and the effect of cell-free ascitic fluid or serum of tumor bearers on natural cytotoxicity in vitro, were assessed. Spleen lymphocytes were used as effectors and 51Cr-labeled YAC1 cells as targets at the effector: target ratio of 200 : 1. In tumor bearers, the NCMC increased in the first days after i. p. inoculation of 1 X 10(6) Ehrlich cells with a maximum peak on day 5. Thereafter, the activity decreased continuously, on day 20 representing about half of normal value. Ascitic fluid and serum of tumor bearing mice significantly depressed the NCMC activity exerted in vitro by spleen lymphocytes of normal mice.