Antibody-dependent cell-mediated cytotoxicity (ADCC) of human peripheral leukocytes was investigated using (51)Cr-labelled sheep red blood cells (SRBC) sensitized with rabbit anit-SRBC antibody as target cells. ADCC (lysis of target cells without erythrophagocytosis) was mediated by the lymphocytes. On the other hand, phagocytes including monocytes and granulocytes showed antibody-dependent erythrophagocytosis (ADEP). ADCC of the lymphocytes was augumented by the enrichment of Fc-receptor bearing or Nylon-wool column passing cells. Phagocytes showed rapid ADEP, and granulocytes released (51)Cr-radioactivity originating from target cells into the culture medium in a short time, whereas the monocytes released little radioactivity during the incubation period. The monocytes inhibited ADCC of the lymphocytes competitivelly through ADEP, since decreased ADCC activity of monocyte-contaminated crude lymphocyte fraction was recovered by elimination of contaminating monocytes. Antibody-independent erythrophagocytosis of SRBC was mediated by monocytes, but not by granulocytes. Both ADCC of lymphocytes and ADEP of phagocytes were dependent on IgG-antibody, IgM-antibody did not participate in these phenomena. ADEP of monocytes was detected at 10(-2)-10(-6) dilution of IgG-antibody fraction (original hemmagglutination titer; × 1600), and ADCC of lymphocytes and ADEP of granulocytes were detected at 10(-2)-10(-4) and 10(-2)-10(-3) dilution of this antibody fraction, respectively. Soluble cytotoxic factors were not released from lymphocytes, monocytes or granulocytes in this assay system, because no cytotoxic activity on (51)Cr-labelled human erythrocytes used as an adjacent cell was demonstrated by any leukocyte fraction in the presence of antibody-coated SRBC.
sheep red blood cells