Spontaneous human lymphocyte‐mediated cytotoxicity against tumor target cells. II. Is the complement receptor necessarily present on the killer cells?

The effect of various lymphocyte depletion techniques on SLMC effector cell activity against the cell line K562 could be attributed t o the effects that these procedures had on the proportions of FclC3 receptor‐bearing cells in the preparations. Depletion of cytotoxic activity by removal of Fc receptor‐bearing cells could be augmented by the presence of complement on the 7S‐EA indicator cells used for rosette depletion. Two methods of assessing the presence of surface receptors on cytotoxic cells are presented: (1) linear regression analysis of spontaneous cytotoxicity plotted as a function of the proportions of receptor‐bearing cells remaining after various depletion techniques; and (2) the use of a mathematical formula t o estimate the proportion o f cytotoxic cells with any particular receptor, based on the effects of receptor‐bearing cell depletion. Linear regression analysis of cytotoxicity vs the proportions of SRBC, Fc o r C3 receptor‐bearing cells demonstrated that all cytotoxic cells had the Fc receptor, but that cytotoxicity could s t i l l occur in the absence of cells with the C3 receptor. This indicated that the C3 recepor is not necessary for the demonstration of SLMC activity. The mathematical formula to predict cytotoxicity after depletion of C3 receptor‐bearing lymphocytes showed, however, that a significant proportion of the Fc receptor‐positive killer cells were also C3 receptor‐positive. No direct evidence was found t o support a role for T cells in SLMC, although E rosette depletion resulted in lower than expected cytotoxicity i n view of the number of Fc receptor‐bearing cells remaining in the preparation.