IVIg treatment increases the susceptibility of matured DCs for NK-mediated killing. (A) After maturation with IL-1β and TNF-α, DCs were cultured with allogeneic NK cells at the ratio of 1:6. Eight hours thereafter, intracellular expression of active caspase-3 in CTRL-DCs (■), IVIg-DCs (▴), and HSA-DCs (▾) was determined (N = 6; Wilcoxon test for paired data, *P < .05 compared with CTRL-DCs; NS indicates not significant). (B) After 18 hours of coculture, DC death was monitored by 7-AAD uptake in CTRL-DCs (■), IVIg-DCs (▴), and HSA-DCs (▾) (N = 9; Wilcoxon test for paired data, **P < .01 compared with CTRL-DCs; NS indicates not significant). (C,D) After 18 hours of coculture of matured DCs with allogeneic NK cells, DC apoptosis was monitored by annexin V staining combined with 7-AAD. (N = 6; Wilcoxon test for paired data, §P < .08, *P < .05 compared with CTRL-DCs; NS indicates not significant.) Error bars are SD. Panel D shows plots of 1 representative experiment of 6 experiments. Numbers below panel D are the percentages of cells in each quadrant. (E) After 18 and 48 hours of coculture of 40 000 matured DCs with allogeneic NK cells (DC/NK ratio, 1:6), cells were harvested from the cultures and fixed numbers of Calibrite beads were added. Absolute numbers of viable DCs were calculated by determining the ratio of 7-AAD⁻ DCs to beads and then multiplying this ratio by the number of beads in the tube. Data are depicted as mean with SE (N = 7; *P < .05, Wilcoxon test for paired data).