Human Natural Killer Cell Cytotoxicity Research Articles

Effects of dexamethasone on human natural killer cell cytotoxicity, interferon production, and interleukin-2 receptor expression induced by microbial antigens

Dexamethasone inhibits the expression of the interleukin-2 receptor, the synthesis of immune interferon, and the development of natural killer cells when added to peripheral blood mononuclear cells cultured with soluble microbial antigens (purified protein derivative and a polysaccharide extract from Candida albicans [MPPS]) or human recombinant interleukin-2.

Action of novel eicosanoids lipoxin A and B on human natural killer cell cytotoxicity: effects on intracellular cAMP and target cell binding.

Lipoxin A (5,6,15L-trihydroxy-7,9,11,13-eicosatetraenoic acid) and lipoxin B (5D,14,15-trihydroxy-6,8,10,12-eicosatetraenoic acid), two newly isolated compounds derived from the oxygenation of arachidonic acid in human leukocytes, inhibit the cytotoxic activity of human natural killer (NK) cells. Dose-response studies showed that both lipoxin A and lipoxin B inhibit, at submicromolar concentrations (ID50 10(-7) M), NK cell activity assayed against K562 target cells. Prostaglandin E2 (PGE2) also inhibited cytotoxicity, whereas both 15-HETE (5(S)-hydroxy-5,8,11,13-eicosatetraenoic acid) and leukotriene B4 (synthetic and biologically derived) were ineffective. PGE2 stimulated a time- and dose-dependent increase in intracellular cAMP, which was accompanied by a decrease in NK target cell binding. Lipoxin A and lipoxin B did not elevate intracellular cAMP, nor did they inhibit target cell binding. Together these findings suggest that lipoxin A and lipoxin B abrogate NK cell cytotoxicity at a step distal to target effector cell recognition. In contrast, PGE2 appears to exert its effect, at least in part, on cytotoxicity indirectly by decreasing the binding between target and effector cells (in vitro). Moreover, they suggest that novel oxygenated derivatives of arachidonic acid (i.e., lipoxin A, lipoxin B) may regulate the activities of NK cells.

Products of the lipoxygenase pathway in human natural killer cell cytotoxicity

As earlier data suggested the importance of lipoxygenase activation for expression of human NK cell cytotoxicity, four different lipoxygenase inhibitors were tested for suppression of natural killer (NK) cell lysis. All inhibitors were found active at nontoxic concentrations with 50% inhibition at approximately 15 μ M for nordihydroguaiaretic acid (NDGA). NK cell lysis could be reconstituted to NDGA-suppressed cells with leukotriene B 4 (LTB 4), the all- trans isomers 6- trans-LTB 4 and 12-epi-6- trans-LTB 4, and 20-COOH-LTB 4. LTB 4 reconstitution was best in the concentration range 1–100 p M and near control levels at both higher and lower concentrations. Herpesvirus Ateles-transformed killer T cells could also be inhibited by NDGA. These data indicate that lipoxygenase activity is required for human NK cell lysis and that several different LTB 4-related products can restore NK activity in inhibited cells; they also suggest that the lipoxygenase pathway is present in the killer cell population.

Free oxygen radicals are not detectable by chemiluminescence during human natural killer cell cytotoxicity.

Mononuclear cells isolated from peripheral blood of normal donors produce free oxygen radicals (FR), detectable by chemiluminescence (CL), when interacting with target cells during natural killer (NK) cell lysis. FR-producing cells were found to have monocyte characteristics and gave a positive CL reaction when mixed at low concentration (0.5%) with purified NK cells. No correlation was found between susceptibility to NK cell lysis and capacity to induce CL with different target cell lines. Using high and low molecular FR scavengers, no NK cell inhibition was seen with superoxide dismutase, cytochrome c, and catalase, whereas some inhibition was seen with 4,5-dihydroxy-m- benzenedisulphonic acid (Tiron) and 2,3-dihydroxybenzoate. These compounds, however, required higher concentrations than used for inhibition of CL, suggesting an alternative action of these compounds. Normal levels of NK cell activity were found in two patients with chronic granulomatous disease, who were genetically incapable of producing detectable amounts of FR. As a result, it is concluded that human NK cells do not produce large amounts of FR during killing and that FR are unlikely to be the lytic end product. Nevertheless, neither a low degree of FR formation in NK cells nor a more subtle signal-transmitting role of FR during NK cell triggering can be excluded.

Inhibition of human NK cell cytotoxicity by induction of cyclic AMP depends on impaired target cell recognition.

Induction of cyclic AMP (cAMP) depresses natural killer (NK) cell activity. The present results demonstrate that this is dependent on a decreased capacity of the effector cells to conjugate to target cells. This was found either if dibutyryl-cAMP was used or if cAMP was induced by adenylate cyclase stimulation with prostaglandin E1 (PGE1) or by inhibition of phosphodiesterase activity with the inhibitor ZK 62711. The sites of action for cAMP-induced NK suppression and interferon (IFN)-induced NK enhancement are demonstrated to be distinct, since IFN acts by increasing the lytic efficiency and the recycling capacity without influencing target binding. Sequential treatment with cAMP/IFN and IFN/cAMP shows that IFN can neither restore target binding when added after cAMP nor protect against the cAMP-induced target binding inhibition when added before cAMP. The results are discussed in view of earlier data on cAMP in relation to cell membrane functions and cellular recognition, the mechanism underlying the cAMP-induced target binding inhibition, and the potential of the NK system as an indicator for immunosuppression. The present work also demonstrates the particular subpopulation in peripheral blood which mediates most NK activity, to respond strongly to PGE1 stimulation with regard to cAMP induction.

Influence of IgG and IgM receptor triggering on human natural killer cell cytotoxicity measured on the level of the single effector cell.

By using an agarose single cell cytotoxicity assay, in combination with rosetting with IgG- or IgM-coated ox red blood cells for detection of Fc receptors for IgG (Fc gamma R) or IgM (Fc muR), it was found that 60% of natural killer (NK) cells are Fc gamma R+ and 17% FcmuR+. This system was further used to investigate the consequence of FcmuR and FC gamma R triggering on NK killing as measured on the single effector cell level. It was found that stimulation of the Fc gamma R, but not the FCmuR, resulted in substantial NK inhibition. In order for NK cells to be inhibited by IgG-coated ox red blood cells, they must first be exposed to the IgG-containing complex prior to conjugation with the target. While exposure of the Fc gamma R to immune complexes can block up to 57% of NK activity, the particulate immune complexes do not interfere with binding of effector cells to targets. Modulation of Fc gamma R by capping at 37 degrees C does not interfere with the NK inhibition for up to 3 h, though after 20 h, when Fc gamma R+ cells are almost completely modulated, NK activity has fully returned. Although to a lesser extent, the soluble immune complex human transferrin-anti-transferrin also reduces NK cell activity when activating effector cell FC gamma R prior to target cell binding. Also, pretreatment of target cells with high concentrations of specific antibody toward membrane antigens can block NK activity while not inhibiting target cell binding as evidenced by anti-IgM IgG binding to Daudi cells. The regulatory influence of the Fc gamma R on the NK system is discussed in terms of other functions associated with this receptor and in terms of its possible biological significance.