Human NK Cell Function Research Articles

Prostaglandin E2 suppressed IL-15-mediated human NK cell function through down-regulation of common gamma-chain.

NK cell function is regulated by cytokines and certain biochemical mediators in a positive or negative manner. This study was performed to investigate the suppressive effects of PGE(2) on IL-15-activated human NK cell function. Purified NK cells were cultured with 200 ng/ml IL-15 for 2 days in the presence or absence of 10-200 ng/ml PGE(2). PGE(2) significantly suppressed NK cell-mediated cytotoxicity and IFN-gamma production at the secretional and the transcriptional levels. We also evaluated the effect of PGE(2) on the IL-15R complex that consists of IL-2Rbeta, common gamma-chain (gamma(c)-chain), and a specific chain IL-15Ralpha. Percentage of positive cells and number of binding sites for gamma(c)-chain were significantly increased after IL-15 treatment; however, a substantial decrease was observed with PGE(2) cotreatment. In contrast, constitutive expression of IL-2Rbeta was significantly decreased after IL-15 treatment, with no change detected in the presence of PGE(2.) At the transcriptional level, neither IL-15 nor PGE(2) had significant effects on the expression of beta- or gamma(c)-chains. There was a 3-fold increase in the expression of IL-15Ralpha at the transcriptional level that peaked at 8 h after IL-15 treatment; however, PGE(2) had no significant effect. Suppression of NK function by PGE(2) was not due to the endogenous production of IL-4, IL-10, or TGF-beta(1) by NK cells. These results suggest that down-regulation of surface expression of gamma(c)-chain on NK cells may be one mechanism through which PGE(2) mediates suppression of IL-15-activated NK cell function.

Surface receptors delivering opposite signals regulate the function of human NK cells

The effector function of NK cells is regulated by a number of positive and negative signals. The receptors involved in the negative regulation of NK cells are known since several years: they are represented by different families of MHC-specific receptors characterized by ITIM sequences in their cytoplasmic tail. In contrast, the surface molecules responsible for NK cell activation in the process of natural cytotoxicity and tumor cell lysis have remained elusive until recently. Three distinct NK-specific molecules termed `natural cytotoxicity receptors' (NCR) have recently been identified and cloned. They play a complementary role in mediating NK cell activation in the interaction and lysis of most tumor cells. They are associated with different ITAM-containing adaptor proteins mediating signal transduction. Molecular cloning revealed novel members of the Ig superfamily displaying a limited homology with known human receptors.

Inhibition of human NK cell function by valinomycin, a toxin from Streptomyces griseus in indoor air.

Streptomyces griseus strains isolated from indoor dust have been shown to synthesize valinomycin. In this report, we show that human peripheral blood lymphocytes treated with small doses (30 ng ml(-1)) of pure valinomycin or high-pressure liquid chromatography-pure valinomycin from S. griseus quickly show mitochondrial swelling and reduced NK cell activity. Larger doses (>100 ng/ml(-1)) induced NK cell apoptosis within 2 days. Within 2 h, the toxin at 100 ng ml(-1) dramatically inhibited interleukin-15 (IL-15)- and IL-18-induced granulocyte-macrophage colony-stimulating factor and gamma interferon (IFN-gamma) production by NK cells. However, IFN-gamma production induced by a combination of IL-15 and IL-18 was somewhat less sensitive to valinomycin, suggesting a protective effect of the cytokine combination against valinomycin. Thus, valinomycin in very small doses may profoundly alter the immune response by reducing NK cell cytotoxicity and cytokine production.

CD94/NKG2-A Inhibitory Complex Blocks CD16-Triggered Syk and Extracellular Regulated Kinase Activation, Leading to Cytotoxic Function of Human NK Cells

The CD94/NKG2-A complex is the inhibitory receptor for the nonclassical MHC class I molecule HLA-E on human NK cells. Here we studied the molecular mechanisms underlying the inhibitory activity of CD94/NKG2-A on NK cell functions by analyzing its interference on CD16-initiated signaling pathways involved in the control of cytolytic activity. Both tyrosine phosphorylation and activation of Syk kinase together with tyrosine phosphorylation of CD16 receptor zeta subunit are markedly inhibited by the coengagement of CD94/NKG2-A complex. As a downstream consequence, CD94/NKG2-A cross-linking impairs the CD16-induced activation of extracellular regulated kinases (ERKs), a pathway involved in NK cytotoxic function. The block of ERK activation is exerted at an early, PTK-dependent stage in the events leading to p21ras activation, as the CD16-induced tyrosine phosphorylation of Shc adaptor protein and the formation of Shc/Grb-2 complex are abrogated by CD94/NKG2-A simultaneous engagement. Our observations indicate that CD94/NKG2-A inhibits the CD16-triggered activation of two signaling pathways involved in the cytotoxic activity of NK cells. They thus provide molecular evidence to explain the inhibitory function of CD94/NKG2-A receptor on NK effector functions.

Functions of human decidual NK cells.

The main population of lymphocytes found in the human decidua during early pregnancy are NK-like cells with a distinctive phenotype, CD56bright CD16- CD3-. These cells are in close association with invading trophoblast that may be their in vivo target. We have examined three aspects of decidual NK function in vitro: cytotoxicity, proliferation, and cytokine production. The functional assays indicate uterine lymphocytes differ fundamentally from both PBL and even from classical circulating NK cells. Their role in the establishment of normal pregnancy remains unknown.

Expression of vitronectin receptor on human NK cells and its role in protein phosphorylation, cytokine production, and cell proliferation.

In this paper, we provide evidence that the vitronectin receptor (VNR) alpha v beta 3 is expressed on human NK cells. The presence of this VNR on freshly purified NK cells was demonstrated by flow cytometry analysis, as well as biochemically, after 125I-labeled surface lactoperoxidase labeling and immunoprecipitation. mAbs LM142 and LM609 specific for alpha v and alpha v beta 3, respectively, precipitated a heterodimer of alpha- and beta-chains with approximate molecular masses of 155 and 110 kDa under nonreducing conditions. Under reducing conditions, there was an apparent decrease in the molecular mass of the alpha-chain, which is likely to result from the release of a protein of 20 to 30 kDa linked by internal disulfide bond to the alpha v-chain. Integrin alpha v beta 3 expressed on NK cells became functional, i.e., was able to bind its ligand, vitronectin (VN), only after cellular activation or when costimulation with an additional signal was provided. Thus, NK cells adhered to plastic-immobilized VN only after IL-2 activation, and RGD-containing synthetic peptides or mAbs specific for alpha v beta 3 complex inhibited this binding. To assess the role of the VNR in signal transduction, anti-beta 3 mAb was used to cluster the VNR on NK cells and, thereby, mimic the process that occurs during formation of adhesive contacts. Cross-linking of VNR on fresh NK cells stimulated phosphorylation on tyrosine residues of several intracellular proteins. The major increase in tyrosine phosphorylation was observed in proteins of approximate molecular masses of 75 and 120 kDa. Therefore, signal transduction by the VNR on NK cells induced activation of intracellular protein kinases. Ligand engagement of the VNR on NK cells also costimulated cytokine production and proliferation of NK cells. Binding of NK cells to plastic-immobilized VN served as a costimulus with either anti-Fc gamma RIII or IL-2 to produce IFN-gamma, TNF-alpha, and cell proliferation. Our findings suggest that occupancy and subsequent clustering of VNRs play a role in the activation and function of human NK cells.

Histaminergic regulation of NK cells. Role of monocyte-derived reactive oxygen metabolites.

Monocytes, recovered by centrifugal elutriation, effectively inhibit functions of human NK cells in vitro. Histamine, acting via monocyte H2-type histamine receptors, abrogates the inhibitory signal. The aim of this study was to define the histamine-reversible mechanism by which monocytes inhibit NK cells with special reference to the respiratory burst activity of monocytes. Monocytes recovered from patients with chronic granulomatous disease did not suppress NK cell function, indicating the requirement of intact nicotinamide-adenine dinucleotide phosphate (NAPDH) oxidase activity of monocytes to inhibit NK cells. Furthermore, catalase, a scavenger of hydrogen peroxide (H2O2), was found to potently reverse the monocyte-induced inhibition of NK cell function; on the other hand, superoxide dismutase (a scavenger of superoxide anion), hydroxyl radical scavengers such as mannitol and deferoxamine, the hypochlorous acid scavenger taurin, or the nitric oxide synthetase inhibitor NG-monomethyl-L-arginine (L-NMMA) did not affect the monocyte-derived, suppressive signal. H2O2, at micromolar concentrations, reconstituted the inhibitory effects of monocytes on NK cell function. Histamine had no scavenger activity but effectively suppressed the generation of H2O2 in isolated monocytes. This effect of histamine was transduced by H2-type histamine receptors. We conclude that the histamine-reversible, inhibitory effect of elutriated monocytes on NK cells is dependent on the formation of reactive oxygen metabolites by monocytes and that H2O2 is a pivotal mediator of the suppressive signal.

CD44 triggering enhances human NK cell cytotoxic functions.

CD44, a major hyaluronate receptor, is involved in a variety of lymphocyte functions including lympho-hemopoiesis, adhesion to high endothelial venules or the extracellular matrix, and T cell activation. Here we investigated the ability of CD44 to affect the cytotoxic functions of human NK cells. Ligation of CD44 by selected mAb (J173 and F10442) resulted in a rapid, dose-response-dependent enhancement of NK cytotoxic activity against a panel of tumor target cells that varied in their sensitivity to NK killing. Neither enhanced killing against NK-resistant target cells nor CD44 mAb-mediated redirected lysis was not observed. CD44 cross-linking also was found to up-regulate CD16-mediated lysis. In an attempt to investigate the early biochemical events that occur after CD44 ligation, we found that optimal cross-linking conditions induce a rapid increase of intracellular free calcium levels, which is abrogated by extracellular Ca2+ chelation. Moreover, enhanced and more sustained Ca2+ rise resulted from CD16 and CD44 coengagement. In contrast, no inositol 1,4,5-trisphosphate generation was found after optimal CD44 cross-linking. These results suggest that although CD44 is not capable of delivering a lytic signal in human NK cells, it coactivates spontaneous or CD16-mediated NK cytotoxicity. The variation in intracellular free calcium may be one of the signals that account for the costimulation of the lytic activity.

A new family of NK-specific surface molecules involved in human NK cell function : [formula omitted]. 1st. Istologia ed Embriologia — University of Genova

A new family of NK-specific surface molecules involved in human NK cell function : [formula omitted]. 1st. Istologia ed Embriologia — University of Genova