Antibody-Dependent Cytotoxicity Mediated by Human Fc-Receptor-Bearing Cells Lacking Markers for B- and T-Lymphocytes

Abstract

The effector cell in human antibody-dependent cytotoxicity was studied by means of various cell fractionation methods. A strong decrease of cytotoxicity was observed in cell suspensions depleted of lymphocytes forming rosettes with human erythrocytes sensitized with human IgG (EA-RFC) either by gradient centrifugation of rosettes or by fractionation on immune complex Degalan columns. The EA-RFC-depleted, ineffective cell suspensions contained considerable proportions of Ig-positive lymphocytes. In contrast, a marked increase in both cytotoxicity and the proportion of EA-RFC was observed after depletion of T-lymphocytes forming rosettes with sheep erythrocytes by gradient centrifugation. The net effect of the presence of monocytes was to diminish cytotoxicity as measured by chromium release, probably because phagocytized target cells were protected from extracellular lysis. It is concluded that antibody-dependent cytotoxicity in man is mediated by a lymphocyte-like cell that has receptors for the Fc part of IgG but lacks conventional B- and T-lymphocyte markers.