Carola Prato

Crosstalk between decidual NK and CD14+ myelomonocytic cells results in induction of Tregs and immunosuppression

Regulatory T cells (Tregs) are thought to play a major role in pregnancy by inhibiting the maternal immune system and preventing fetal rejection. In decidual tissues, NK cells (dNK) reside in close contact with particular myelomonocytic CD14+ (dCD14+) cells. Here we show that the interaction between dNK and dCD14+ cells results in induction of Tregs. The interaction is mediated by soluble factors as shown by transwell experiments, and the prominent role of IFN-γ is revealed by the effect of a neutralizing monoclonal antibody. Following interaction with dNK cells, dCD14+ cells express indoleamine 2,3-dioxygenase (IDO), which, in turn, induces Tregs. Notably, unlike peripheral blood NK (pNK) cells, dNK cells are resistant to inhibition by the IDO metabolite L-kynurenine. “Conditioned” dCD14+ cells also may induce Tregs through transforming growth factor-β (TGF-β) production or CTLA-4–mediated interactions, as indicated by the effect of specific neutralizing Abs. Remarkably, only the interaction between dNK and dCD14+ cells results in Treg induction, whereas other coculture combinations involving either NK or CD14+ cells isolated from peripheral blood are ineffective. Our study provides interesting clues to understanding how the crosstalk between decidual NK and CD14+ cells may initiate a process that leads to Treg induction and immunosuppression. Along this line, it is conceivable that an impaired function of these cells may result in pregnancy failure.

Regulatory role of NKp44, NKp46, DNAM-1 and NKG2D receptors in the interaction between NK cells and trophoblast cells. Evidence for divergent functional profiles of decidual versus peripheral NK cells

During the first trimester of pregnancy NK cells represent >50% of the lymphoid cells present in the human decidua where they reside in close contact with trophoblast cells. Because in decidual tissues NK cell activation and function may be induced by this interaction, we analyzed the cellular ligands recognized by activating NK receptors expressed on trophoblast cells. We show that these cells primarily express the NKp44 and DNAM-1 ligands and that interaction between these ligands and their corresponding receptors results in NK cell triggering. While activated peripheral blood NK (pNK) cells lysed the trophoblast cell lines JAR and JEG3, decidual NK (dNK) cells did not. On the other hand, they released VEGF, SDF-1, IP10 and large amounts of IL-8. Interaction with K562 target cells was exploited to induce optimal NK cell triggering, allowing a parallel, quantitative assessment of both cytolytic activity and cytokine production elicited by dNK cells. While dNK cells were unable to kill K562 even at high effector:target (E:T) ratios, they released large amounts of IL-8 also at low E:T ratios, a scenario compatible with dNK trophoblast cells interaction occurring within decidual tissues.

Human NK Cells Induce Neutrophil Apoptosis via an NKp46- and Fas-Dependent Mechanism

Polymorphonuclear neutrophils (PMN) are potent inflammatory effector cells essential to host defense, but at the same time they may cause significant tissue damage. Thus, timely induction of neutrophil apoptosis is crucial to avoid tissue damage and induce resolution of inflammation. NK cells have been reported to influence innate and adaptive immune responses by multiple mechanisms including cytotoxicity against other immune cells. In this study, we analyzed the effect of the interaction between NK cells and neutrophils. Coculture experiments revealed that human NK cells could trigger caspase-dependent neutrophil apoptosis in vitro. This event was dependent on cell–cell contact, and experiments using blocking Abs indicated that the effect was mediated by the activating NK cell receptor NKp46 and the Fas pathway. CD56-depleted lymphocytes had minimal effects on neutrophil survival, suggesting that the ability to induce neutrophil apoptosis is specific to NK cells. Our findings provide evidence that NK cells may accelerate neutrophil apoptosis, and that this interaction may be involved in the resolution of acute inflammation.

Role of the calpain-calpastatin system in the density-dependent growth arrest.

In dividing cells calpastatin diffuses from aggregates into cytosol, indicating the requirement for a tight regulation of calpain. Accordingly, the involvement of the calpain-calpastatin system in cell proliferation and in the density-dependent growth arrest was studied in JA3 cells stably transfected with a calpastatin form permanently localized in cytosol. In calpastatin overexpressing cells, cell cycle rate is 50% reduced, and cells enter the ungrowing, still fully reversible, stage at a 3-fold higher cell density. Furthermore, in cell density growth arrest phase, down regulation of alpha- and theta-PKC isoforms, as well as FAK and talin occurs. In calpastatin overexpressing cells, degradation of these calpain substrate proteins is prevented and delayed. Thus, calpain activity plays a crucial role in inducing the cell entry into a functional quiescent phase.

Involvement of exon 6-mediated calpastatin intracellular movements in the modulation of calpain activation

BACKGROUND To establish the physiological role of calpain, it is necessary to define how the protease can escape from the effect of its natural inhibitor calpastatin, since both proteins co-localize into the cell cytosol. METHODS To answer this question, we have overexpressed four fluorescent calpastatin constructs, differing in the composition of their XL- and L-domains, and the intracellular trafficking of this protein inhibitor has been followed by single cell fluorescence imaging. RESULTS AND CONCLUSIONS By the use of these calpastatin forms differing in the type of exon-derived sequences contained in the XL- and L-domains, we have demonstrated that the sequence coded by exon 6, containing multiple phosphorylation sites, is directly involved in determining the cell localization of calpastatin. In fact, exposure to cAMP promotes the recruitment into aggregates of those calpastatin forms containing the exon 6 sequence. These protein movements are directly related to the level of cytosolic inhibitory capacity and thereby to the extent of intracellular calpain activation. GENERAL SIGNIFICANCE The recruitment of calpastatin into aggregates allows the translocation and activation of the protease to the membranes; on the contrary, the presence of large amounts of calpastatin in the cytosol prevents both processes, protecting the cell from undesired proteolysis.

Nidogen-1 is a novel extracellular ligand for the NKp44 activating receptor

ABSTRACT The release of soluble ligands of activating Natural Killer (NK) cell receptors may represent a regulatory mechanism of NK cell function both in physiologic and in pathologic conditions. Here, we identified the extracellular matrix protein Nidogen-1 (NID1) as a ligand of NKp44, an important activating receptor expressed by activated NK cells. When released as soluble molecule, NID1 regulates NK cell function by modulating NKp44-induced IFN-γ production or cytotoxicity. In particular, it also modulates IFN-γ production induced by Platelet-Derived Growth Factor (PDGF)-DD following NKp44 engagement. We also show that NID1 may be present at the cell surface. In this form or when bound to a solid support (bNID1), NID1 fails to induce NK cell cytotoxicity or cytokine release. However, analysis by mass spectrometry revealed that exposure to bNID1 can induce in human NK cells relevant changes in the proteomic profiles suggesting an effect on different biological processes.

The Innate Immune Cross Talk between NK Cells and Eosinophils Is Regulated by the Interaction of Natural Cytotoxicity Receptors with Eosinophil Surface Ligands

Previous studies suggested that the cross talk between NK cells and other cell types is crucial for the regulation of both innate and adaptive immune responses. In the present study, we analyzed the phenotypic and functional outcome of the interaction between resting or cytokine-activated NK cells and eosinophils derived from non-atopic donors. Our results provide the first evidence that a natural cytotoxicity receptor (NCR)/NCR ligand-dependent cross talk between NK cells and eosinophils may be important to upregulate the activation state and the effector function of cytokine-primed NK cells. This interaction also promotes the NK-mediated editing process of dendritic cells that influence the process of Th1 polarization. In turn, this cross talk also resulted in eosinophil activation and acquisition of the characteristic features of antigen-presenting cells. At higher NK/eosinophil ratios, cytokine-primed NK cells were found to kill eosinophils via NKp46 and NKp30, thus suggesting a potential immunoregulatory role for NK cells in dampening inflammatory responses involving eosinophils.

The innate immune cross talk between NK cells and eosinophils is regulated by the interaction of Natural Cytotoxicity Receptors with eosinophil surface ligands

Previous studies suggested that the cross talk between NK cells and other cell types is crucial for the regulation of both innate and adaptive immune responses [1,2]. In the present study, we analyzed the phenotypic and functional outcome of the interaction between resting or cytokine-activated NK cells and eosinophils derived from non-atopic donors. Our results provide the first evidence that an NCR/NCR ligand-dependent cross talk between NK cells and eosinophils may be important to up regulate the activation state and the effector function of cytokine-primed NK cells. This interaction also promotes the NK-mediated editing process of DCs that influences the process of Th1 polarization. In turn, this cross talk also resulted in eosinophil activation and acquisition of the characteristic features of antigen presenting cells. At higher NK/eosinophil ratios, cytokine-primed NK cells were found to kill eosinophils via NKp46 and NKp30, thus suggesting a potential immunoregulatory role for NK cells in dampening inflammatory responses involving eosinophils.