Radiation Sensitivity of Resting and Activated Nonspecific Cytotoxic Cells of T Lineage and NK Lineage

Natural killer (NK) cell-mediated killing of tumor cells is a radiation-sensitive function that in most subjects is completely abrogated by treatment of the effector cells with 3,000 cGy. The radiation sensitivity of LAK (lymphokine-activated killer) cells and their precursors, the bulk of which are NK cells, is undetermined. In this study, functional cytotoxicity assays and electron microscopy were used to determine the effect of radiation on the cytotoxic function of NK cells, LAK cells (generated by three-day culture of peripheral blood lymphocytes with IL-2), and LAK cell precursors (lymphocytes irradiated prior to culture with IL-2). For comparison, we analyzed the radiation sensitivity of lectin-dependent cell-mediated cytotoxicity (LDCC), which is primarily a function of CD3+CD8+ granular lymphocytes. We also analyzed the radiation sensitivity of nonspecific cytotoxicity mediated by mitogen-activated T cells (AK activity). Following 3,000 cGy irradiation, NK cells retained their ability to bind to tumor cell targets but, as shown by both morphologic and functional analyses, they did not undergo activation after conjugate formation, and were unable to release the content of their granules. In order to evaluate LDCC, lymphocytes were depleted of CD16+ cells and tested in a cytotoxicity assay in the presence of Con A. The radiation sensitivity curve was comparable to that of NK cell-mediated cytotoxicity. IL-2-treated lymphocytes (LAK cells) were relatively radioresistant as compared with untreated NK cells, and their cytotoxic function was not abrogated until treatment with >10,000 cGy. Cells receiving such radiation doses displayed cytoplasmic blebbing and damage of their cyto-skeletal structures, with disruption of centrioles and microtubules, and disarray of the intermediate filaments. As was shown with NK cells, irradiated LAK cells formed conjugates with tumor targets but failed to degranulate. The radiation sensitivity of nonspecific cytotoxicity mediated by mitogen-activated T cells was identical to that of LAK effector cells. Doses up to 2,000 cGy did not prevent generation of LAK cells from blood lymphocytes, but 3,000 cGy did so. Blast transformation similar to that observed in IL-2-stimulated controls occurred when lymphocytes irradiated with 3,000 cGy were cultured with IL-2. These transformed cells were not cytotoxic and displayed a normal cytoskeletal apparatus but did not bear electron-dense granules. The similar pattern of radiation se