Natural killer (NK) cells play an important role in many immune functions, including the lysis of tumor cells. In this study, we analyzed the influence of serum from 40 patients with head and neck cancer on NK cell activity using a double-layer agar assay. NK cell activity can be express as the inhibitory effect of NK cells on colony growth of K562 cells in the double-layer agar assay. When serum from cancer patients was added in this assay, we observed the reduction of the inhibitory activity of NK cells, not only of autologous NK cells but also of allogeneic NK cells in 24 out of 40 patients. In addition, we compared the TNM staging and survival rate between the reduction group and no-reduction group of NK cell activity. These results suggest that the serum of some patients with head and neck cancer may be an inhibitory factor on NK cell activity and may be involved in host resistance to tumor growth.
