Comparative studies of immunoglobulin receptors and antibody dependent cell cytotoxicity (ADCC) in rat lymphoid organs

The capability of rat lymphoid cells to destroy antibody coated target cells (antibody dependent cell cytotoxicity, ADCC) and to form rosettes with immunoglobulin coated erythrocytes (EA) was compared. Because both processes require binding of a lymphoid cell to antibody associated with cellular antigen, an attempt was made to determine if both assays detect the same cell population. Peripheral blood lymphocytes, spleen and lymph node cells had both activities, but there was no correlation between the number of rosettes and the ADCC activity. Blood lymphocytes had the highest cytotoxic potential, while spleen cells produced the highest percentage of rosettes. Bone marrow cells were devoid of cytotoxic activity though many of the cells were able to form rosettes. Thymus cells were neither cytotoxic nor able to form rosettes. Following treatment of spleen cells with anti rat Ig serum or high concentrations (>1 mg/ml) of trypsin and Pronase (but not papain), or phospholipase C, the number of rosettes was strongly diminished, whereas the cytotoxic activity was unimpaired. The ADCC activity was not altered after removal of 60% of the rosette forming cells by nylon column, but was greatly reduced when 85% of the rosette forming cells were removed by anti SRBC serum. These observations indicate that there is no correlation between the percentage of EA rosette forming cells and the ADCC activity in various lymphoid tissues; these activities were not equally susceptible to enzyme action; the cytotoxic activity is mediated by a subpopulation of the EA rosette forming cells; and probably fewer immunoglobulin receptor sites per unit surface membrane are required for ADCC cytotoxicity than for rosette formation.