IL-12 or IL-4 prime human NK cells to mediate functionally divergent interactions with dendritic cells or tumors.

In the course of inflammatory responses in peripheral tissues, NK cells may be exposed to cytokines such as IL-12 and IL-4 released by other cell types that may influence their functional activities. In the present study we comparatively analyzed purified human peripheral blood NK cells that had been exposed to either IL-12 or IL-4 during short (overnight) incubation. We show that although IL-12-cultured NK cells produced abundant IFN-gamma, TNF-alpha, and GM-CSF in response to stimuli acting on the NKp46-activating receptor, IL-4-cultured NK cells did not release detectable levels of these cytokines. In contrast, IL-4-cultured NK cells produced significant levels of TNF-alpha and GM-CSF only when stimulated with PMA and ionomycin. In no instance could the production of IL-5 and IL-13 be detected. Importantly, IL-12-cultured, but not IL-4-cultured, NK cells displayed strong cytolytic activity against various tumor cells or immature dendritic cells (DCs). Moreover, only NK cells that had been cultured in IL-12 were able to induce substantial DC maturation. Our data suggest that NK cells exposed to IL-12 for a time interval compatible with in vivo responses may favor the selection of appropriate mature DCs for subsequent Th1 cell priming in secondary lymphoid organs. On the contrary, NK cells exposed to IL-4 do not exert DC selection, may impair efficient Th1 priming, and favor either tolerogenic or Th2-type responses.

DNase I behaves as a transcription factor which modulates Fas expression in human cells.

DNase I is the major nuclease present in biological fluids and is ubiquitously expressed in mammalian tissues. It is responsible for the removal of DNA from nuclear antigens, and consistently with this function, DNase I-deficient mice show features of autoimmunity. The enzyme seems also to be involved in apoptosis (programmed cell death). We demonstrate that DNase I is internalized by human cells upon binding mannose 6-phosphate receptor and gains access into the cells. Following internalization of the enzyme, the cells show an increased surface expression of Fas molecule, a key regulator of apoptosis. Here we show that DNase I up-regulates fas transcription upon interaction with the fas gene promoter. Moreover, overexpression of the DNase I gene in human cells results in a similar modulation of the fas gene expression. Our data provide the first evidence that the endonuclease DNase I behaves as a transcription factor which selectively regulates cell surface Fas expression in human cells and point towards a fundamental role of DNase I in the regulation of the apoptotic machinery.

CD59 is physically and functionally associated with natural cytotoxicity receptors and activates human NK cell-mediated cytotoxicity.

Triggering of cytotoxicity in human NK cells is induced by the combined engagement of several triggering receptors. These include primary receptors such as NKG2D and the natural cytotoxicity receptors (NCR) NKp30, NKp46 and NKp44, while other molecules, including 2B4, NTB-A and NKp80, function as co-receptors. As reported in the present study, during an attempt to identify novel NK receptors or co-receptors, we found that CD59 functions as a co-receptor in human NK cell activation; engagement of CD59 by specific mAb delivers triggering signals to human NK cells, resulting in enhancement of cytotoxicity. Similar to other NK co-receptors, the triggering function of CD59, a glycosylphosphatidylinositol (GPI)-linked protein, depends on the simultaneous engagement of primary receptors such as NCR. Accordingly, CD59-dependent triggering was virtually restricted to NK cells expressing high surface densities of NKp46, and mAb-mediated modulation of NKp46 resulted in markedly decreased responses to anti-CD59 mAb. Biochemical analysis revealed that CD59 is physically associated with NKp46 and NKp30. Moreover, engagement of CD59 resulted in tyrosine phosphorylation of CD3zeta chains associated with these NCR, but not those associated with CD16. Thus, CD59-mediated costimulation of NK cells requires direct physical interaction of this GPI-linked protein with primary triggering NK receptors.