Rat natural killer cell activity against lymphoid and nonlymphoid tumor cells and normal rat cell lines

Natural cytotoxicity in the rat was assessed against solid tumors and normal and embryonic rat monolayer culture lines, and the results were compared with rat natural killer activity towards syngeneic, allogeneic, and xenogeneic lymphoma targets. The targets tested showed a very wide range of susceptibility to lysis by peripheral blood and spleen effector cells in both 4- and 18-hr cytotoxicity assays. Cytotoxicity toward the mouse lymphoma, YAC-1, and rat sarcoma LT1 targets was relatively high in a 4-hr assay, compared with that toward the other cell lines used in the study. At 18 hr, increased killing was seen against YAC-1, LT1, SP3 (rat pheochromoblastoma), F2304 (rat embryonic cells), and normal rat kidney cells, while a significant increase in susceptibility with time was not observed with other rat targets: W/Fu-T (sarcoma); ERTh/V-G (sarcoma); R35 (mammary tumor); and W/Fu-P21 (embryo fibroblasts) targets. The cytotoxicity against all of the targets tested was not age restricted and was potentiated by rat interferon. Natural cytotoxic reactivity was seen with effector cells from the blood, spleen, and peritoneal cavity of both W/Fu (euthymic) and Rowett nude (congenitally athymic) rats. Cytotoxic effector cells from the blood were present in the low-density fractions recovered from discontinuous Percoll density gradients and, as shown previously for lymphoma target cells, a strong correlation was observed between the killing of embryonic, normal, and solid tumor targets and the presence of large granular lymphocytes. These results indicate that the naturally cytotoxic rat effector cells for normal fibroblast and bone marrow targets, lymphomas-leukemias, embryonic cell lines, and solid tumor targets are all included in the large granular lymphocyte subpopulation.