ADCC activity of spleen cells in mice after tumor inoculation. ⁵¹Cr-labeled RPMI 8226 cells were incubated with nonactivated or IL-2–activated spleen cells at an E/T ratio of 50 in the presence of 1 μg/mL control IgG or anti-HM1.24 IgG. Data represent the mean ± SD of triplicate determinants. *P < .02, †P < .005, compared with the data of nonactivated spleen cells in the presence of anti-HM1.24 IgG. Results are shown for a single experiment, but have been confirmed in two further experiments.