Cytotoxic Reactivity of Human Lymphocytes Cultured in Vitro

Abstract

Recent evidence indicates that both natural killer and killer cells active in antibody-dependent cell-mediated cytotoxicity are cell types that bear Fc receptors. Natural killer and antibody-dependent cell-mediated cytotoxicity have also been shown to be in a SRBC-rosetting subpopulation. Human mononuclear peripheral blood leukocytes were cultured under various conditions to examine natural killing and antibody-dependent cell-mediated cytotoxicity. It was of interest to determine if these activities would be maintained or augmented under various culture conditions. Before culture, normal mononuclear peripheral blood leukocytes were tested in a 4-hr ⁵¹Cr release assay against K-562 to measure natural killer activity, and against antibody-coated Chang liver cells to measure antibody-dependent cell-mediated cytotoxicity. Fc receptor-bearing cells were removed by adsorption to immobilized antigen-antibody complexes. When lymphocytes were cultured alone, we often observed what we call cytotoxicity from cultured cells (CCC). The amount of cytotoxicity against K-562 and in antibody-dependent cell-mediated cytotoxicity was dependent on the presence of FBS and proportional to its concentration in the cultures. The presence of FCS resulted in high levels of CCC whereas human serum demonstrated low or negligible activities. This CCC was not directed against FBS-associated antigens. These CCC cannot be called NK since their extensive characteristics are not known. As was characteristic on day 0 for natural killing and antibody-dependent cell-mediated cytotoxicity, the cultured effector cells also contained an Fc receptor. Therefore, the presence of CCC with features of natural killer and killer cell activities and its regeneration in culture indicate that it must be distinguished from specific tumor reactivity or alloreactivity in mixed lymphocyte and mixed lymphocyte-tumor reactions, particularly when tumor cell lines are used as targets.