Quantitative comparison of K cell potential in human T and null cells

Using a short‐term quantitative assay of the antibody‐dependent cell‐mediated cytotoxicity (ADCC) of human peripheral blood lymphocytes towards 51Cr‐labeled mouse lymphoma cells, it is possible to estimate the relative involvement of various lymphocyte populations in the overall ADCC potential displayed by unfractioned lymphocytes. Lymphocytes were separated by means of an anti‐F(ab')2 column combined with sedimentation of E rosette‐forming cells or EA rosette‐forming cells, and a discontinuous serum albumin gradient, and were characterized by several surface markers. ADCC results were expressed as the cytotoxic capacity of 106 cells of each population (lytic units/106 cells) as well as as the cytotoxic potential of each population by taking into account their relative numerical sizes. Although the null cells had the highest cytotoxic capacity, highly purified T cells also disclosed a cytotoxic capacity which, because of the large numerical excess of T cells over null cells, could account for closely equivalent cytotoxic potentials of these two populations. ADCC was entirely abolished by further removal of Fc receptor‐bearing cells, in all the subsets studied. Our data underline the role that the small proportion of Fc receptor‐carrying T cells might play in ADCC.