Divergence in activation by poly I:C of human natural killer and killer cells

Summary Interferons consistently enhance spontaneous cellular cytotoxicity (SCC) mediated by natural killer (NK) cells. More controversial is the ability of interferons to enhance antibody-dependent cellular cytotoxicity (ADCC) mediated by killer (K) cells. Since NK and K cells appear to represent overlapping subpopulations of lymphocytes, the present study was undertaken to examine in greater detail the relationship between NK and K cell functional modulation by the potent interferon inducer, poly I:C. Utilizing peripheral mononuclear cells from a panel of 21 healthy individuals, treatment in vitro with poly I:C resulted in modulation of both SCC and ADCC. SCC was significantly enhanced in 52 of a series of 55 trials (95%), whereas ADCC was significantly enhanced in parallel in only 18 of the trials (33%). Cells which mediated enhanced ADCC were plastic-nonadherent, which is characteristic of K cells. SCC was consistently enhanced in all but two of the 14 individuals who were tested two or more times. By contrast, the ability of poly I:C to enhance ADCC varied between trials in 11 of these individuals. In the other three, ADCC enhancement never occurred. No correlation existed between SCC and ADCC augmentation despite use of the same target cell to assess the two lytic activities in parallel. Poly I:C exclusively enhanced SCC in 36 trials (65%) and exclusively enhanced ADCC in two trials (4%). Discordance between SCC and ADCC enhancement also occurred in three of eight trials (38%) in which lymphocytes were treated directly with interferon a. Results in long-term (18-h) ⁵¹Cr-release assays indicated that poly I:C accelerated the kinetics of ADCC without affecting the proportion of target cells lysed by K cells. By contrast, an increased proportion of target cells was killed by poly I:C-stimulated NK cells. These results suggest that the controversy concerning relative interferon effects upon NK and K cells derives from differences both quantitative and qualitative in nature. K cell activity is enhanced but at a relatively low frequency. Enhancement of NK cell activity is selective in the sense that it occurs independently of and with greater frequency than enhancement of K cell activity. Distinct biological mechanisms may, therefore, be involved in regulation and expression of NK and K cell activation by interferons.