Characterization of cytotoxic human lymphocyte subpopulations: the role of Fc-receptor-carrying cells.

Natural cytotoxicity against tumor-derived monolayer and lymphoblastoid cell lines was found to be most marked in the non-T non-B subpopulation of human lymphocytes. A high proportion of cells in this population were Fc receptor positive. This receptor seems to be important in exerting the cytotoxic effect. The T-cell fraction had a weak cytotoxic activity for which Fc-positive T cells were responsible. Steps in the cell separation procedure such as EA resetting and ammonium chloride treatment impaired cytotoxic activity. However, the cells recovered to a large degree during the 48-hr assay. Cells incubated at 37 °C prior to the functional test regained part of the activity and could thus be used in a short-term, 8-hr assay. Within a certain effector cell range, the dose-response curves were linear. Thus, it was possible to express the efficiency of a certain fraction in lytic units (the cells which cause 50% lysis of the target cell). Considering the representativeness of the cell type in the total population, the non-T non-B cells were calculated to be responsible for 24% of the total activity though their proportion was only 7%.