Interleukin-17A (IL-17A) and IL-17F are 2 of several cytokines produced by T helper 17 cells (Th17), which are able to indirectly induce the recruitment of neutrophils. Recently, human Th17 cells have been phenotypically characterized and shown to express discrete chemokine receptors, including CCR2 and CCR6. Herein, we show that highly purified neutrophils cultured with interferon-␥ plus lipopolysaccharide produce the CCL2 and CCL20 chemokines, the known ligands of CCR2 and CCR6, respectively. Accordingly, supernatants from activated neutrophils induced chemotaxis of Th17 cells, which was greatly suppressed by anti-CCL20 and anti-CCL2 antibodies. We also discovered that activated Th17 cells could directly chemoattract neutrophils via the release of biologically active CXCL8. Consistent with this reciprocal recruitment, neutrophils and Th17 cells were found in gut tissue from Crohn disease and synovial fluid from rheumatoid arthritis patients. Finally, we report that, although human Th17 cells can directly interact with freshly isolated or preactivated neutrophils via granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-␣, and interferon-␥ release, these latter cells cannot be activated by IL-17A and IL-17F, because of their lack of IL-17RC expression. Collectively, our results reveal a novel chemokine-dependent reciprocal cross-talk between neutrophils and Th17 cells, which may represent a useful target for the treatment of chronic inflammatory diseases. (Blood. 2010;115:335-343)

Polymorphonuclear neutrophils, besides their involvement in primary defense against infections – mainly through phagocytosis, generation of toxic molecules, release of enzymes, and formation of extracellular traps – are also becoming increasingly important for their contribution to the fine regulation in development of inflammatory and immune responses. These latter functions of neutrophils occur, in part, via their de novo production and release of a large variety of cytokines, including chemotactic cytokines (chemokines). Accordingly, the improvement in technologies for molecular and functional cell analysis, along with concomitant advances in cell purification techniques, have allowed the identification of a continuously growing list of neutrophil-derived cytokines, as well as the characterization of their biological implications in vitro and/or in vivo. This short review summarizes crucial concepts regarding the modalities of expression, release, and regulation of neutrophil-derived cytokines. It also highlights examples illustrating the potential implications of neutrophil-derived cytokines according to recent observations made in humans and/or in experimental animal models.

Bone marrow-derived mesenchymal stromal cells (BMMSCs) are stromal precursors endowed with extensive immunomodulative properties. In this study, we aimed to assess whether Toll-like receptor-3 (TLR3)-and TLR4-activated BM-MSC influence human neutrophil (PMN) responses under coculture conditions. We show that TLR3 triggering by polyinosinic:polycytidylic acid dramatically amplifies, in a more significant manner than TLR4 triggering by lipopolysaccharide, the antiapoptotic effects that resting BM-MSC constitutively exert on PMN under coculture conditions, preserving a significant fraction of viable and functional PMN up to 72 hours. In addition, TLR3-and TLR4-activated BM-MSC enhance respiratory burst ability and CD11b expression by PMN. The coculture in the absence of cell contact and the incubation of PMN in supernatants harvested from TLR3-and TLR4-activated BM-MSC yield comparable results in terms of increased survival and immunophenotypic changes, thus suggesting the involvement of endogenous soluble factors. Neutralizing experiments reveal that the biological effects exerted on PMN by TLR3-activated BM-MSC are mediated by the combined action of interleukin 6, interferon-b (IFN-b), and granulocyte macrophage colony-stimulating factor (GM-CSF), while those exerted by TLR4-activated BM-MSC mostly depend on GM-CSF. MSC isolated from thymus, spleen, and subcutaneous adipose tissue behaves similarly. Finally, the effects exerted by TLR3-or TLR4-stimulated BM-MSC on PMN are conserved even after the previous priming of BM-MSC with IFN-c and tumor necrosis factor-a. Our data highlight a novel mechanism by which MSC sustain and amplify the functions of PMN in response to TLR3-and TLR4-triggering and may consequently contribute to inflammatory disorders. STEM CELLS

The outcome of dendritic cell (DC) presentation of P815AB, a tolerogenic tumor/self peptide, depends on a balance between the respective immunogenic and tolerogenic properties of myeloid (CD8α−) and lymphoid (CD8α+) DC. We have previously shown that CD8− DC can be primed by IL-12 to overcome inhibition by the CD8+ subset and initiate immunogenic presentation in vivo when the two types of peptide-pulsed DC are cotransferred into recipient hosts. IFN-γ enhances the inhibitory activity of CD8+ DC on Ag presentation by the other subset, blocking the ability of IL-12-treated CD8− DC to overcome suppression. We report here that CD40 ligation on lymphoid DC ablated their inhibitory function on Ag presentation as well as IFN-γ potentiation of the effect. CD40 modulation of IFN-γ action on lymphoid DC involved a reduction in IFN-γR expression and tryptophan-degrading ability. This effect was accompanied in vitro by an impaired capacity of the CD40-modulated and IFN-γ-treated DC to initiate T cell apoptosis. In vivo, not only did CD40 triggering on lymphoid DC abrogate their tolerogenic activity, but it also induced the potential for immunogenic presentation of P815AB. Importantly, a pattern similar to P815AB as well as CD40 modulation of lymphoid DC function were observed on testing reactivity to NRP, a synthetic peptide mimotope recognized by diabetogenic CD8+ T cells in nonobese diabetic mice.

Murine dendritic cells (DCs) can present Ag in an immunogenic or tolerogenic fashion, the distinction depending on either the occurrence of specialized DC subsets or the maturation or activation state of the DC. Although DC subsets may be programmed to direct either tolerance or immunity, it is not known whether appropriate environmental stimulation can result in complete flexibility of a basic program. Using splenic CD8− and CD8+ DCs that mediate the respective immunogenic and tolerogenic presentation of self peptides, we show that both the in vivo and in vitro activities of either subset can be altered by ligation of specific surface receptors. Otherwise immunogenic CD8− DCs become tolerogenic upon B7 ligation by soluble CTLA-4, a maneuver that initiates immunosuppressive tryptophan catabolism. In contrast, CD40 ligation on tolerogenic CD8+ DCs makes these cells capable of immunogenic presentation. Thus, environmental conditioning by T cell ligands may alter the default function of DC subsets to meet the needs of flexibility and redundancy.

It is increasingly evident that neutrophils are able to cross-talk with other leukocytes to shape ongoing inflammatory and immune responses. In this study, we analyzed whether human NK cells may influence the survival and activation of neutrophils under co-culture conditions. We report that NK cells exposed to either IL-15 or IL-18 alone strongly protect the survival of neutrophils via the release of IFNγ and granulocyte macrophage colony-stimulating factor (GM-CSF) plus IFNγ, respectively, and cause a slight up-regulation of neutrophil CD64 and CD11b expression. In comparison, NK cells exposed to both IL-15 and IL-18 show a lesser ability to increase the survival of neutrophils but can more potently up-regulate CD64 and CD11b expression, as well as induce the de novo surface expression of CD69, in neutrophils. Analysis of the events occurring in neutrophil/NK co-cultures exposed to IL-15 plus IL-18 revealed that (i) neutrophil survival is positively affected by NK-derived GM-CSF but negatively influenced by a CD18-dependent neutrophil/NK contact, (ii) NK-derived IFNγ is almost entirely responsible for the induction of CD64, (iii) both soluble factors (primarily GM-CSF) and direct cell-cell contact up-regulate CD11b and CD69 and (iv) NK-derived GM-CSF induces the expression of biologically active heparin-binding EGF-like growth factor (HB-EGF) in neutrophils. Finally, we demonstrate that NK cells can also express HB-EGF when stimulated with either IL-2 or IL-15, yet independently of endogenous GM-CSF. Altogether, our results define a novel interaction within the innate immune system whereby NK cells, by directly modulating neutrophil functions, might contribute to the pathogenesis of inflammatory diseases.

The role of neutrophils as key players in the regulation of innate and adaptive immune responses is increasingly being recognized. We report that human neutrophils establish a network with both natural killer (NK) cells and 6-sulfo LacNAc ؉ dendritic cells (slanDCs), which ultimately serves to up-regulate NK-derived interferon␥ (IFN␥). This network involves direct reciprocal interactions and positive amplification loops mediated by cellderived cytokines. Accordingly, we show that after lipopolysaccharide ؉ interleu- IntroductionPolymorphonuclear neutrophil leukocytes are known as "professional" phagocytic cells of the innate immune system. However, numerous observations regarding their capacity to respond to and produce a wide variety of cytokines and chemotactic molecules and to change phenotype under specific circumstances also position them as key regulators of various cross talks. 1,2 The outcome(s) of potential interactions between neutrophils and other leukocytes, including macrophages, monocyte-derived dendritic cells (DCs), and T lymphocytes, have been addressed in recent studies [3][4][5][6] and reveal that neutrophils may participate in shaping not only the innate but also the adaptive immune response. 7 For example, activated neutrophils were shown to recruit T-helper 17 (Th17) cells 8 and to trigger T-cell proliferation and strong Th1-cell responses by inducing the maturation of monocyte-derived DCs in in vitro cocultures. 9 Natural killer (NK) cells are effector lymphocytes of the innate immune system endowed with cytotoxic and cytokine-producing capacities, typically recognized for their role in cancer immunosurveillance and pathogen clearance. 10 Although NK cells can directly recognize some pathogens, it is becoming increasingly clear that NK-cell activation requires the presence of accessory cells 11 such as monocytes, 12-14 macrophages, 15,16 and DCs. 17,18 While recent evidence for a potential role of neutrophils in NK-cell activation has been found in mice, 19 it remains unknown whether human neutrophils exert similar effects. Early investigations have focused on a putative inhibitory function of human neutrophils directed toward the cytotoxic activity of cocultured NK cells, 20,21 whereas most subsequent research has delineated the suppressive role of neutrophil-derived reactive oxygen species on NK-cell survival, expression of selected activating receptors, and cytotoxic activity. 22,23 It should also be emphasized that the neutrophil preparations used in most of these studies were not pure (containing approximately 5% of contaminant cells), which might well explain some of the controversial results. 20,21 Based on these premises, we examined whether human neutrophils can activate NK cells either by functioning as and/or modulating the activity of accessory cells. We report that neutrophils potently enhance the release of interferon␥ (IFN␥) by NK cells when cocultured with 6-sulfo LacNAc ϩ dendritic cells (slanDCs), but not CD1c ϩ DCs or plasmacytoid DCs (pDCs), in the presence of lipopoly...

Dendritic cells (DCs) initiate adaptive immune responses to cancer cells by activating naive T lymphocytes. 6-sulfo LacNAc þ DCs (slanDCs) represent a distinct population of circulating and tissue proinflammatory DCs, whose role in cancer immune surveillance is unknown. Herein, by screening a large set of clinical samples, we demonstrate accumulation of slanDCs in metastatic tumour-draining lymph nodes (M-TDLN) from carcinoma patients. Remarkably, slanDCs are absent at the primary carcinoma site, while their selective nodal recruitment follows the arrival of cancer cells to M-TDLN. slanDCs surround metastatic carcinoma deposits in close proximity to dead cells and efficiently phagocytose tumour cells. In colon carcinoma patients, the contingent of circulating slanDCs remains intact and competent in terms of IL-12p70 and tumour necrosis factor alpha production, induction of T-cell proliferation and migratory capacity to a set of chemokines produced in M-TDLN. We conclude that activated slanDCs represent previously unrecognized players of nodal immune responses to cancer cells.