The effect of oxidant stress on human lymphocyte cytotoxicity

We have studied the effect of oxidant stress on human lymphocyte cytotoxicity. Lymphocyte cultures maintained good viability after incubation with xanthine and xanthine oxidase, an enzyme system known to generate several highly reactive oxygen compounds. We demonstrated that these lymphocytes were viable after exposure to an in vitro oxidant stress but had a significant impairment in both antibody-dependent and nonantibody-mediated cytotoxicity against the CEM lymphoblast target cell. Specific scavengers of reactive oxygen species were examined for a potential protective effect on lymphocyte function. Cultures supplemented with catalase demonstrated highly significant but incomplete protection from oxidant injury. In contrast, cultures supplemented with superoxide dismutase and mannitol were not protected. The impairment of lymphocyte function that resulted from the in vitro exposure to the xanthine and xanthine oxidase was mediated primarily through the generation of hydrogen peroxide. The scavenger studies indicated that superoxide, hydroxyl radical and singlet oxygen were probably not involved in producing the oxidant injury. Incubation of lymphocytes directly with hydrogen peroxide produced a similar functional impairment. Heat inactivation or chemical inhibition of the enzyme xanthine oxidase with allopurinol prevented oxidant injury and implied that the intact enzyme was necessary to produce the injury. Similar alterations of lymphocyte function may occur in vivo during an inflammatory reaction or in patients receiving ionizing radiation as treatment for neoplasia.