Cytotoxicity against the K562 erythroleukemia cell line by human natural killer (NK) cells which do not bear free Fc receptors for IgG.

When Fc receptors (FcR) on normal human peripheral blood lymphocytes were induced to modulate by overnight (18 h) incubation in the presence of soluble or particulate immune complexes, the natural killer (NK) activity of the effector lymphocyte suspension, as measured against the K562 erythroleukemia cell line, was significantly, but only partially, inhibited. The NK activity which remained was always strong, and was not significantly inhibited by inclusion of antigen-antibody complexes in the cytotoxicity assay, nor was it further depleted by adsorbing the modulated cells on plastic surfaces coated with immobilized antigen-antibody complexes. Antibody-dependent cell-mediated cytotoxicity (ADCC) against rabbit antibody-sensitized Chang liver cells was totally abrogated following the modulation process, and could not be restored by exposure of modulated effector cells to trypsin, indicating that the FcR had actually been shed and were not merely being blocked with immune complexes. Although freshly isolated peripheral blood lymphocytes active in natural (or "spontaneous") cytotoxicity have been shown to bear FcR, our data indicate that NK activity against the K562 cell line can be effectively mediated by NK cells which have lost their FcR. This supports the concept that NK activity against K562 is independent of FcR, and, therefore, of IgG.