Figure 1.

Hypoxic NK cells show lower cytotoxicity against tumor cells. (a, b) Flow cytometric analysis of KHYG-1 cells cytotoxicity against tumor cells. KHYG-1 cells were incubated with K562 (a) or MM.1S (b) tumor cells for 4 h at different E : T ratios after cultivation at normoxic (20% O₂) and hypoxic (1% O₂) conditions for 24 h. Left panel: a representation of results from three experiments; Right panel: statistical analysis showing the percentage of tumor cells killed by NK cells (n = 3, ^∗P < 0.05). (c) Western blotting analysis of the effects of hypoxia on the expression of hypoxia marker HIF-1α. NK cells were cultured in 20% or 1% O₂ for 24 h, and then Western blotting analysis was performed. Representative Western blot images are shown in the upper panel; the densitometric analysis is shown in bottom panel (n = 3, ^∗P < 0.05, ∗∗∗P < 0.001). (d) Flow cytometric analysis of the effects of hypoxia on NK cell viability by performing Annexin V-FITC/7-AAD staining. NK cells were cultured in 20% or 1% O₂ for 24 h, then flow cytometric staining was performed (n = 3, ns: no significance).