This study demonstrates that TLR3 expression on immune cells regulates IFN secretion by NK cells independently of the gut microbiota and is essential to control metastatic spread of cancer. Results NK cells from mice are hyporesponsive to cytokine stimulation The ability of the TLR3 ligand poly (I:C) to activate NK cells is well established.5,22 However, nothing is known about the influence of TLR3 on NK cell priming in the absence of administration of its agonist. cell responses required TLR3 Enalapril maleate sensing on radio-sensitive immune cells. Intriguingly, although CD8 DCs robustly express high levels of TLR3, we found that those cells were not necessary for efficient IFN production by NK cells. Moreover, the defective NK cell phenotype of mice appeared to be independent of the gut microbiota. Altogether, our data demonstrate a pivotal role of endogenous TLR3 activation for the acquisition of full NK cell functions and immune protection against experimental metastasis. mice compared with WT mice, supporting a protective role Enalapril maleate for endogenous triggering of TLR3.20 In humans, high levels of TLR3 expression have been associated either with Mouse monoclonal to CD20.COC20 reacts with human CD20 (B1), 37/35 kDa protien, which is expressed on pre-B cells and mature B cells but not on plasma cells. The CD20 antigen can also be detected at low levels on a subset of peripheral blood T-cells. CD20 regulates B-cell activation and proliferation by regulating transmembrane Ca++ conductance and cell-cycle progression good24,25 or poor26 prognosis, depending on the malignancies. Thus, the exact role of TLR3 in tumor immunosurveillance remains to be characterized. Among the different cellular mediators of the poly(I:C) induced-response, NK cells represent a major antitumor effector.20,21 NK cells are innate lymphocytes that recognize and directly kill transformed cells.27 In addition, activated NK cells release a myriad of pro-inflammatory Enalapril maleate factors, including interferon (IFN), tumor necrosis factor (TNF), colony stimulating factor 2 (CSF2, also known as GM-CSF), and the chemokines MIP1- (CCL3), MIP1- (CCL4) and RANTES (CCL5).28 NK cell responses are controlled by the integration of signals from germline-encoded activating and inhibitory receptors that recognize molecules expressed on the surface of the target cells. Yet, the acquisition of full effector functions by NK cells requires additional signals provided by cytokines such as interleukin (IL)-2, IL-12, IL-15, IL-18 and type I IFN or by direct contact with accessory cells, often DCs.29 Poly(I:C) has been shown to induce efficient NK cells responses, either by the direct activation of TLR3 on NK cells5,30 or via the activation of accessory cells.21-23 Here, we investigated the role of TLR3 in NK cell activation and malignancy immunosurveillance in the absence of administration of exogenous dsRNA. We showed that TLR3 modulates NK cell responses by endowing them with the ability to release high amounts of IFN in response to cytokine activation. In addition, we established that this TLR3 signaling pathway controlled the growth of Rae-1 expressing RMAS tumors as well as the metastatic spread of experimental B16F10 melanoma, both of which are known to be tightly controlled on the basis of NK cell effector function. This study demonstrates that TLR3 expression on immune cells regulates IFN secretion by NK cells independently of the gut microbiota and is essential to control metastatic spread of cancer. Results NK cells from mice are hyporesponsive to cytokine activation The ability of the TLR3 ligand poly (I:C) to activate NK cells is usually well established.5,22 However, nothing is known about the influence of TLR3 on NK cell priming in the absence of administration of its agonist. To determine whether TLR3 signaling modulates NK cell ability to respond to cytokine activation, we purified NK cells from WT or mice (Sup. Fig.?S1) and cultured them in the presence of different combinations of recombinant IL-12, Enalapril maleate IL-18 and IL-15. Interestingly, we observed that NK cells produced significantly less IFN than WT NK cells in response to cytokine activation (Fig.?1A). By contrast, when cultured with phorbol 12-myristate 13-acetate (PMA)/ionomycin, no difference between and WT NK cells was observed in terms of IFN production (Fig.?1B). Thus, the inherent ability of NK cells to produce IFN was not compromised. In addition, despite low levels of cytokine-induced IFN production, NK cells were efficiently activated upon IL-12/IL-18 activation, as assessed by their upregulation of CD69 (Fig.?1C). Immunofluorescence staining and cytofluorimetric analysis confirmed that IL-12/IL-18 stimulated NK cells produced less IFN as compared with WT NK cells since both the percentage of IFN generating cells and the fluorescence Enalapril maleate intensity of the transmission were reduced (Fig.?1D). Finally, we detected lower levels of MIP-1, MIP-1, RANTES, IL-6 and GM-CSF in the supernatant of NK cells when cultured in the presence of IL-12/IL-18 or IL-12/IL-15 (Fig.?1E and F), indicating.