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Abstract The specificity and the cells involved in natural cytotoxicity against tumor cells by fresh normal human peripheral blood mononuclear leukocytes have been extensively examined. Recently we have observed that removal of Fc receptor-positive cells from peripheral blood mononuclear leukocytes on day 0 removed all natural cytotoxic activity against K-562 (a myeloid leukemia cell line that is particularly susceptible to natural cytotoxicity) but after in vitro culture for 7 days, cytotoxic activity against K-562 had regenerated to near its original level. In the present study, we examined the specificity of the cytotoxicity of both fresh and cultured peripheral blood mononuclear leukocytes against a panel of target cells susceptible to natural killing and the characteristics of the cultured effector cells. By testing various donors against a checkerboard panel of labeled target and cold target inhibitor cells, it was found that the reactivity after culture was similar to that seen on day 0. Small variation in rank order of the level of inhibition was observed in most experiments, but none of the reactivity patterns of the donor lymphocytes demonstrated major changes after culture. Furthermore, the surface characteristics of the effector cells before and after culture were similar with regard to surface immunoglobulin, Fc receptors, complement receptors, sensitivity to trypsin and to specific anti-T antiserum. However, the cultured effector cells did have some distinctive characteristics, rosetting less with sheep red blood cells, adhering to some extent to rayon wool, and being partially sensitive to an anti-Ia-like antiserum. These features may indicate that the cultured cells are at a different stage of differentiation than in vivo generated natural killer (NK) cells. These results indicate that the natural cytotoxicity of human lymphocytes and the reactivity of cultured cells are mediated by similar effector cells, i.e., NK cells, and are directed against similar specificities.
Ortaldo et al. (1979) studied this question.