The influence of serum from 23 patients with head and neck cancer on natural killer (NK) cell activity was analyzed using a double-layer agar assay, in which NK cells show an activity to inhibit the colony growth of K562 cells. In contrast to normal serum (or no treatment), serum from cancer patients reduced the inhibitory activity of NK cells, not only of autologous NK cells but also of allogeneic NK cells. These results suggest that the serum of patients with head and neck cancer may have some inhibitory factors on NK cell activity and may be involved in host resistance to tumor growth in vivo.
