Involvement of hydroxyl free radical, but not superoxide, in the cytolytic pathway of natural killer cells. Revision of an earlier hypothesis.

Our earlier hypothesis suggested that NK effectors, in response to tumor cells, generate superoxide anion (O2.-) which was necessary for NK cytolysis to proceed. This event could be detected by chemiluminescence. More recent data suggests that O2.- is not necessary for NK cytolysis and that chemiluminescence is the result of an NK-tumor cell-monocyte interaction. Hydroxyl radicals however do contribute to the NK-mediated cytolytic process. The source of OH. is unknown but does not appear to be generated by the NADPH oxidase system. We suggest that hydroxyl radical generation is a necessary event in NK cytolysis but we do not yet know if it acts at the level of NK activation, delivery of the lethal hit or in autolysis by the tumor cells.