6-MP and its metabolite 6-TG induce NK cell apoptosis. (A) Peripheral blood NK cells isolated from healthy individuals were cultured with and without 6-MP and 1 ng mL−1 of rIL-2. Representative flow cytometry at 24, 48, and 72 h of culture. (B) Bar plot showing data from 3 experiments tabulated for % Annexin V and 7-AAD positive cells at 24, 48, and 72 h. (Student’s t-test, two-tailed. *p < 0.01, **p < 0.005) (C) Bar plot of Annexin V and 7-AAD positive NK cells at 72 h culture with 5 μmol/L 6-MP or 6-TG. Greater percentage of cells cultured with 6-MP and 6-TG were Annexin V and 7-AAD positive. Plot is representative of separate experiments from 3 healthy individuals. One way ANOVA [F(2,6) = 25.97, p = 0.001].