ABSTRACT
The objective of this study was to investigate the effect of dendritic cells (DCs) on expansion and function of autologous natural killer (NK) cells and its mechanism in vitro. NK cells were expanded from peripheral blood mononuclear cells (PBMNCs) of healthy volunteers in stem cell growth medium (SCGM) supplemented with rhIL-2 (control group) in 24-well culture plates at 37 degrees C in a humidified CO(2)-containing atmosphere. NK cells were cultured with autologous DCs in the ratio of 5 to 1 (group 5:1) or 1 to 1 (group 1:1) from day 10 after expansion. Total cells of every group were counted and the expression of CD3, CD16/56 on the surface of NK cells was assayed by flow cytometry on days 7, 14 and 21 to calculate the expansion of NK cells. Cytotoxicity of expanded NK cells against K562 cells was assayed by MTT method. TNF-alpha and IL-12p70 were detected in culture supernatants by sandwich ELISA. The results indicated that the expansion and cytotoxicity of NK cells were improved after mixed with autologous DCs. Furthermore, when DCs were mixed with NK cells, the ratio of DCs to NK cells was higher, the expansion and cytotoxicity NK cells were higher. On day 14, the expansion multiple in control, group 5:1 and group 1:1 were 16.26 +/- 1.58, 29.25 +/- 4.01 and 21.23 +/- 2.91 respectively. The expansion multiple of group 5:1 was much higher than that of the other two groups (p < 0.05). The expressions of CD3(-), CD56/16(+) on surface of NK cells in control, group 5:1, group 1:1 were (34.8 +/- 5.1)%, (64.6 +/- 7.8)% and (50.6 +/- 8.7)% respectively and that of group 5:1 was the highest (p < 0.05). The cytotoxicities against K562 cells in control, group 5:1 and group 1:1 were (63.7 +/- 3.8)%, (87.4 +/- 6.8)% and (75.4 +/- 6.3)% respectively. The cytotoxicity of group 5:1 was higher than that in the other two groups also (p < 0.05). TNF-alpha and IL-12p70 levels in culture supernatants when DCs and NK cells were mixed in the ratio of 5 to 1 were much higher than those in culture supernatants of DCs and NK cells alone or in culture supernatants when DCs and NK cells were mixed in the ratio of 1 to 1 (p < 0.05). It is concluded that the expansion and cytotoxicity of NK cells can be improved by DCs and it depended on the mixed ratio of DCs to NK cells. The elevated expansion of NK cells by DCs bears relation to IL-12 produced by DCs. The enhanced cytotoxicity of NK cells is associated with TNF-alpha secreted by NK cells.