FCs do not affect cytolytic activity of NK cells on YAC-1 cells. To evaluate whether FCs affect NK cytolytic activity as a potential mechanism of action, YAC-1 targets were cocultured with NK cells to which varying ratios of FCs or CD8⁺ T cells were added. This experiment is representative of a total of 3 performed. (A) Cytolytic activity of C3H NK cells was determined by incubating 5 × 10³ [³H]-thymidine–labeled YAC-1 cells with increasing numbers of NK cells to determine the optimal effector-target (E/T) ratio for the suppression assays. To determine maximal killing percentage, 2N HCl was added to YAC-1 cells in the absence of NK cells. (B) NK cells (500 000 per well) were preincubated in triplicate with increasing ratios of FCs or CD8⁺ T cells for 16 hours. After the coculture, 5 × 10³ labeled [³H]-labeled YAC-1 target cells (constant effector to target ratio of 100:1) was then added to each well. Function of NK cells incubated in the absence of FCs is indicated by the open bar. FC or T-cell–mediated cytolysis was measured, but no specific killing was detected (n.d. = not detected). Error bars indicate standard deviation.