Tumour cell toxicity for the targets of natural killer cells

Cells of intraperitoneally transplanted murine leukaemias and sarcomas (L-1210, EL-4, MC-11 and SA-1), were found to be toxic for target cells usually employed for assaying NK cells (K-562, EL-4, YAC-1). The 3H-uridine-ribonuclease method used in our study, in contrast to the 51Cr assay, revealed not only cytotoxicity but also reversible damage to target cell membrane (membrane toxicity). This damage became irreversible if target cells had been pretreated with actinomycin D. To exclude the possible role of an admixture of NK, macrophages and T killer cells, contaminants were removed from suspensions of peritoneal tumour cells from syngeneic mice by adherence to plastic surfaces and separation on Hypaque-Ficoll, and from tumour cells grown in vivo or in vitro and then maintained in allogeneic animals by additional treatment with anti-H-2 sera and complement. The toxic effect depended directly on the dosage of tumour cells. Unlabelled target cells inhibited tumour cell toxicity. The medium used for incubating tumour cells was not toxic for target cells.