Cytokine production and killer activity of NK/T-NK cells derived with IL-2, IL-15, or the combination of IL-12 and IL-18

NK cell populations were derived from murine splenocytes stimulated by IL-2, IL-15, or the combination of IL-12 and IL-18. Whereas NK cells derived with the latter cytokines consisted of an homogeneous population of NK cells (DX5+CD3-), those derived with IL-2 or IL-15 belonged to two different populations, namely NK cells (DX5+CD3-) and T-NK cells (DX5+CD3+). Among NK cells, only those derived with IL-12/IL-18 produced detectable levels of cytokines, namely IFN-gamma, IL-10, and IL-13 (with the exception of IL-13 production by NK cells derived with IL-2). As for T-NK cells, IL-2-stimulated cells produced a wide range of cytokines, including IL-4, IL-5, IL-9, IL-10, and IL-13, but no IFN-gamma, whereas IL-15-derived T-NK cells failed to produce any cytokine. Switch-culture experiments indicated that T-NK cells derived in IL-2 and further stimulated with IL-12/IL-18 produced IFN-gamma and higher IL-13 levels. Next, we observed that NK/T-NK cell populations exerted distinct effects on Ig production by autologous splenocytes according to the cytokines with which they were derived. Thus, addition of NK cells derived in IL-12/IL-18 inhibited Ig production and induced strong cytotoxicity against splenocytes, whereas addition of NK or T-NK cells grown in IL-2 or IL-15 did not. Experiments performed in IFN-gammaR knockout mice demonstrated that IFN-gamma was not involved in the killer activity of IL-12/IL-18-derived NK cells. The hypothesis that their cytotoxic activity was related to the induction of target apoptosis was confirmed on murine A20 lymphoma cells. Experiments performed in MRL/lpr mice indicated that IL-12/IL-18-derived NK cells displayed their distinct killer activity through a Fas-independent pathway. Finally, perforin was much more expressed in IL-12/IL-18-derived NK cells as compared with IL-2- or IL-15-derived NK cells, an observation that might explain their unique cytotoxicity.