An investigation of the role of soluble cytotoxic factors and reactive oxygen intermediates in lysis by NK cells.

Using a variety of experimental approaches we have been unable to find any evidence that monoclonal CTL line, induced to express high levels of NK activity by treatment with IFN, mediates target cell lysis by secretion of a cytoxic factor. Thus, supernatant prepared in a variety of ways by incubating cloned killer cells with mycoplasma-free YAC-1 cells, or by freeze-thawing the killer cells themselves, were essentially devoid of lytic activity even when tested in 18hr assays. These findings substantiate at the clonal level our previous observations, that mouse splenic NK cells do not secrete detectable cytotoxic factors in the absence of mycoplasma (Wayner and Brooks, 1984). In addition, it appears that NK killing does not involve the participation of reactive oxygen intermediates. Neither catalase nor SOD were inhibitory. Inhibition observed with some OH. scavengers failed to correlate with their rate constants for reaction with OH., and was apparently due to the general toxicity of these compounds. A cloned cell line expressing potent NK activity failed to produce any luminol-reactive chemiluminescent species during incubation with target cells or with PMA.