Susceptibility of natural killer (NK) cells to reactive oxygen species (ROS) and their restoration by the mimics of superoxide dismutase (SOD)

Natural killer (NK) cells are susceptible to reactive oxygen species (ROS), and lose the activity by the effects of ROS. Cancer bearing hosts usually suffer from oxidative stress (OS), and the NK-activity decreases to a significantly lower level than normal controls. Superoxide dismutase (SOD)-mimicking substances, such as protein-bound polysaccharide of Coriolus versicolor (Fr) QUEL (PSK) and iron-chelating chlorin e6-Na (FeCNa), can restore the NK-activity of cancer bearing hosts, when collaborating with catalase. Incorporation of H-3-thymidine by ROS-treated NK-cells is not affected, indicating that these cells are still active in the nucleic acid metabolism. Intraperitoneal administration of anti-Asialo GM1 antibody extinguished the NK-activity. NK-cells affected by ROS lost the adherence to target cancer cells in both in vitro and in vivo. ROS may change the surface charge of NK-cells to anionic, resulting in an inability of adhesion to target cancer cells which usually show the negative surface charge.