Ablation of natural killer cell function by soluble cardiotoxin

A one-hour preincubation of nonadherent murine spleen cells with a soluble membrane-active cardiotoxin purified from the venom of the Thailand cobra Naja naja siamensis results in the destruction of natural killer (NK) cell activity against YAC-1 target cells in a dose-dependent manner. Prior in vivo induction of interferon production by polyinosinic/polycytidylic acid does not avert the cardiotoxin inhibition of NK function. Loss of complement-mediated lysis of cells capable of binding an NK-1.1 monoclonal antibody suggests that the cardiotoxin directly affects the integrity of the NK cell plasma membrane. Cardiotoxin which has been adsorbed to the surface of polystyrene tissue culture plates retains the ability to lyse splenic T lymphocytes, but loses the ability to interfere with NK activity, as measured either by the release of 51Cr or by the uptake of 3H-thymidine by the target lymphoma cells, suggesting that different parts of the cardiotoxin molecule are responsible for destruction of the two types of lymphocytes.     

Regulation of natural killer cell activity

Information regarding the role of natural killer (NK) cells in the response to viruses, intracellular bacteria and parasites continues to emerge. NK cells can directly lyse infected cells, secrete cytokines and interact with dendritic cells to drive the adaptive immune response. There are a large number of activating and inhibitory receptors that govern NK cell activity. Recent studies have revealed how signals are transmitted and integrated from the variety of receptors, how particular receptors influence NK development and functional status, and how NK cells access lymph nodes and sites of infection. The potential for NK cells to exhibit specific and memory-like responses has begun to blur the 'innate' definition of NK cells.     

Interleukin-12 is involved in the enhancement of human natural killer cell activity by Lactobacillus casei Shirota

We conducted a placebo-controlled, cross-over trial to examine the effect of Lactobacillus casei Shirota (LcS) on natural killer (NK) cell activity in humans. NK cell activity exhibited a declining trend during the period of placebo ingestion, but NK cell activity increased after intake for 3 weeks of fermented milk containing 4 x 10(10) live LcS. When human peripheral blood mononuclear cells were cultured in the presence of heat-killed LcS, NK cell activity was enhanced. The ability of LcS to enhance NK cell activity and induce interleukin (IL)-12 production was correlated, and the addition of anti-IL-12 monoclonal antibody reduced the enhancement of NK cell activity triggered by LcS. In addition, separation of NK cells from LcS-stimulated monocytes with membrane filter reduced NK cell activity to the intermediate level and almost deprived monocytes of the ability to produce IL-12. These results demonstrate that LcS can enhance NK cell activity in vivo and in vitro in humans, and IL-12 may be responsible for enhancement of NK cell activity triggered by LcS.     

In vivo enhancement of murine natural killer cell activity by 7-allyl-8-oxoguanosine (loxoribine).

7-Allyl-8-oxoguanosine (loxoribine) is a novel immunostimulatory compound which has been shown previously to enhance the antibody synthesis of antigen-stimulated B-lymphocytes. In this report, loxoribine was tested for the ability to activate murine natural killer (NK) cells. In studies in which mice were given a single subcutaneous (s.c.) or intravenous (i.v.) injection of loxoribine, splenic NK cell activity was increased in a dose-related manner with clear enhancement seen within 2 h of drug administration. The enhancement was optimal at 48 h but persisted for a minimum of 4 days. Slow and continuous administration of loxoribine via subcutaneously implanted infusion pumps successfully enhanced the NK activity for several days after all of the pump contents had been delivered. Peak NK responses were seen following s.c. or i.v. administration of 2-3 mg loxoribine per mouse in sesame oil, intralipid, or saline vehicles. Significant oral activity was seen after the administration of 8-10 mg/mouse in sesame oil or intralipid. The in vivo enhancement of NK activity was observed in spleen, blood, and bone marrow but was negligible in lymph nodes and thymus. Multiple injections of optimal concentrations of loxoribine did not tend to enhance the NK activity above that seen with a single injection, suggesting that the timing of injections was critical for optimal responsiveness.     

Enhancement of natural killer cell activity by Marek's disease vaccines

Vaccination against Marek's disease with herpesvirus of turkeys (HVT) has been reported to cause increased natural killer (NK) cell activity as detected in vitro against LSCC-RP9 target cells. The effect of vaccination with SB-1 (a nononcogenic chicken herpesvirus), HVT and the HVT/SB-1 combination on NK cell activation was compared in Marek's disease susceptible (P-2) and resistant (N-2) chickens. Birds were vaccinated at 7 days of age and NK cell activity was measured between 3 and 42 days after vaccination. Both SB-1 and HVT caused a significant increase in NK cell-induced specific release. The increase was similar in N-2 and P-2 chickens for either HVT or SB-1, while the combined vaccine induced a significantly higher increase in N-2 compared to P-2 birds. The maximal effect of vaccination on NK cells was detected at 7 days after vaccination. In contrast with the results in young birds, vaccination of birds between 31 and 45 days of age caused either no effect or a suppression rather than an enhancement in NK cell activity.     

Down-regulation of natural killer cell activity by autologous polymorphonuclear leucocytes

It has been recently reported that neutrophils are involved in the regulation of NK cell activity. However, the mechanism of such regulation is unclear. The present study was designed to investigate the mechanisms involved in the regulation of NK cytotoxicity by human neutrophils. The role of indomethacin, an anti-inflammatory drug, in this interaction was studied. NK cells were purified from peripheral blood obtained from normal individuals. NK cell cytotoxicity was tested on K 562 cell line by Cr release assay. Autologous neutrophils obtained from peripheral blood were stimulated by opsonized zymosan either in the presence or absence of indomethacin. The role of neutrophil supernatant containing oxygen radicals and prostaglandins on NK cytotoxicity was examined. It was shown that supernatants from stimulated neutrophils significantly inhibited (P less than 0.05) the autologous NK cell cytotoxicity. The presence of indomethacin in the in vitro reaction mixture, or given orally to donors, partially or completely abolished the inhibitory effect of neutrophil supernatant. Indomethacin inhibited prostaglandin E2 release, and luminol-enhanced, myeloperoxidase-mediated chemiluminescence of activated PMN. Diafiltration of neutrophil supernatant showed that the inhibitory activity was present in the fraction containing molecules lower than 5,000 daltons. In conclusion, our findings indicate that down-regulation of NK cytotoxicity is mediated by prostaglandins produced by stimulated neutrophils and possibly by oxygen radicals.     

In vitro inhibition of natural killer cell activity by doxycycline

The effect of four tetracyclines, tetracycline, rolitetracycline, oxytetracycline and doxycycline, on human natural killer (NK) cell-mediated cytotoxicity was examined in vitro. Doxycycline was the only tetracycline which inhibited the NK cell activity. At concentrations of 10 micrograms/ml the drug caused approximately 50% inhibition of NK cell mediated cytotoxicity against K562 target. The inhibition was not a result of a toxic effect of the drug on NK cells. These results support the previous findings that doxycycline shows immunosuppressive properties.     

Inhibition of human natural killer cell activity by polyclonal IgM

Pretreatment of effector cells with normal human IgM induced strong dose-dependent inhibition of NK activity. The degree of inhibition by normal IgM was stronger than that induced by monomeric IgG, which has previously been reported to be a negative regulator of NK activity. For 100% inhibition, 1.1 × 10⁻⁶ M of IgM was required, whereas 66.6 × 10⁻⁶ M of IgG was needed to abolish NK activity. This inhibitory property of polyclonal IgM appeared to be localized in the Fc region of the molecule, and also was significantly reduced upon mild reduction of disulfide bonds. Monoclonal IgM purified from sera of five patients with Waldenström's macroglobulinemia and tested in parallel with normal IgM lacked or had a decreased capacity to inhibit the cytotoxic reaction. As with IgG, IgM interfered mainly with the lytic event, after binding of effector cells to target cells. The inhibition by IgM appeared to be a direct effect on NK cells, since similar effects were observed with purified large granular lymphocytes as with non-adherent lymphocytes. These results indicate a new mechanism for negative regulation of NK cells and suggest the presence of Fcμ receptors on these effector cells.     

Dietary fat and natural killer cell activity

Evidence from a number of sources implicates dietary fat in the etiology of various human cancers. We hypothesize a possible mechanism by which fat might increase tumorigenesis. Specifically, we discuss the connection between polyunsaturated fatty acids, prostaglandin synthesis, and the potential effect on Natural Killer (NK) cell activity. Polyunsaturated fatty acid-induced increases in series-2 prostaglandin synthesis could result in depressing NK-cell activity. As the first line of defense against tumor cells, NK-cell function may be particularly important in modifying cancer risk.     

Increased natural killer cell activity in sarcoidosis

We have studied NK cell activity in 32 patients with sarcoidosis and in 29 control subjects. Cytotoxicity was increased in both active and inactive sarcoids, the lytic activity of sarcoid peripheral blood mononuclear cells (PBMC) being approximately 50% higher than that of control subjects. The number of lymphocytes bearing Fc receptors for IgG (FcR-IgG) was correlated with NK cell activity, both parameters being increased in the sarcoid group. Sarcoid NK cell activity was reduced to control levels after depletion of plastic adherent cells, whilst inhibition of cytotoxicity by PGE2 was increased using non-adherent sarcoid PBMC. Plastic depletion had no effect on NK cell activity or its inhibition by PGE2 using PBMC from control subjects. The results demonstrate the presence of a weakly adherent, PGE2 insensitive NK cell in sarcoid PBMC preparations.     

Differential staphylococcal protein A-induced enhancement of natural killer cell activity of lymphocytes from HIV-seropositive individuals.

A decrease in Natural Killer (NK) cell activity is a common feature of the immune dysfunction found in patients with HIV-induced acquired immune deficiency syndrome (AIDS). We and others have shown earlier that staphylococcal protein A (SpA) preparations enhance NK cell activity against tumor targets. The present study was aimed at exploring whether the decreased NK activity of lymphocytes from HIV seropositive subjects could be modulated or restored in vitro by SpA. Two types of HIV-seropositive subjects were studied: hemophiliac and non-hemophiliac; matched controls were chosen among hospital staff and HIV-seronegative hemophiliac volunteers. In vitro proliferation and interleukin-2(IL-2)/interferon gamma (IFN gamma) release in response to mitogens were also studied. NK cell responses of peripheral blood lymphocytes (PBL) of HIV-seropositives were lower than those of seronegatives. However, exposure of PBL from HIV-seropositive individuals to SpA boosted their NK cell responses against NK-resistant target cells of tumor origin. The decrease in NK activity could not be attributed to the low number of NK cells, since no significant difference in NK cell number was observed between HIV-seropositive individuals and controls. Mitogen-induced blastogenic responses were present in all four groups, as was the mitogen-induced IFN gamma release. We conclude that impaired NK activity and its boosting against NK-resistant targets after SpA induction is an important characteristic of lymphocytes of HIV-seropositive individuals regardless of the disease state and that this NK defect may not be irreversible.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of terbutaline on natural killer cell activity

Studies on the effect of cAMP-inducing agents on NK activity have been contradictory. The aim of this study was to investigate the acute effects of beta-agonists on NK activity in vivo in 15 asthmatics and 3 healthy volunteers. Blood samples of NK activity were taken at regular intervals after placebo and after subcutaneous injection of 7 micrograms/kg of terbutaline. NK activity was measured by the standard 4-h Chromium51 release assay against the leukemic line K 562 at a 50:1 effector/target cell ratio. Compared with placebo, terbutaline induced within 30-60 min a significant increase in NK activity which lasted less than 2 h. Further studies are necessary to investigate the effect of long-term beta-agonist treatment on NK activity.     

Regulation of human natural killer cell activity by an interferon inhibitor

Laboratory of Immunochemistry and Department of Interferons, N. F. Gamaleya Research Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 112, No. 10, pp. 395–397, October, 1991.     

In vivo augmentation of natural killer cell activity by Candida albicans

We determined in vivo effects of Candida albicans (CA) on murine natural killer (NK) cell activity. C3H mice were treated with heat-killed CA and splenic NK cell activity assayed at 2, 7, 30 and 50 days post treatment. A single injection of CA caused enhancement of splenic NK activity as measured in a 4 h 51Cr-release assay. Peak NK activity was detected at day 7 and persisted for up to 30 days, after which it declined to control values at 50 days. Augmentation of NK activity by CA resulted from enhanced lytic effects of NK cells, which was independent of effector cell binding capacity. Moreover, enhanced NK activity was associated with an increase in the proliferative response to CA antigen and in splenic cellularity when compared to saline injected controls. Thus, CA seems to act as an immunomodulator causing an augmentation of NK cell activity. Since other biological response modifiers (BRMs) do not show the same strength of augmentation, CA could be used as a new BRM having possible anticancer effects.     

Neuroimmunomodulation with enkephalins: enhancement of human natural killer (NK) cell activity in vitro

To further define the effects of enkephalins on immune function, the effect of methionine-enkephalin and leucine-enkephalin on natural killer cell (NK) activity in isolated human peripheral blood lymphocytes was investigated. Incubation of lymphocytes with either enkephalin resulted in significant increases in natural killer cell activity. At effector:target cell ratios of 11:1 methionine-enkephalin significantly (P less than 0.05) enhanced NK activity at dilutions of 10(-6), 10(-8), 10(-10), and 10(-14) mg/ml, while leucine-enkephalin significantly (P less than 0.05) enhanced NK activity at dilutions of 10(-4), 10(-6), 10(-8), 10(-10), and 10(-14) mg/ml. Cells from individuals with low NK activity showed greater percentage increases in NK activity following enkephalin than did cells from individuals with high NK activity.     

Modulation of human natural killer cell activity by pharmacological mediators.

We have studied the effects of various pharmacological mediators on human NK cell activity. Prostaglandin E2 (PGE2) inhibits NK cell activity in a dose-dependent fashion, whereas PGF2 alpha has no significant effect over the same concentration range. Histamine at high doses (10(-4) M) induced a small but significant inhibition of NK cell activity which was mimicked by both H1 and H2 specific histamine receptor agonists. Inhibition of endogenous prostaglandin production by indomethacin did not alter NK cell activity. Inhibition of NK activity by cAMP but not cGMP analogues, together with other data presented suggests that the mechanism of PGE2-induced inhibition of NK cell activity is not due to impairment of effector cell movement or effector: target cell interaction, but through the adenylate cyclase system which modulates the killing process.     

Inhibition of human natural killer cell activity by prostaglandin D2

We have studied the effect of prostaglandin (PG) D₂ on human natural killer (NK) cell activity using ⁵¹Cr-labelled K562 target cells. PGD₂ caused a dose dependant inhibition of NK cell activity, producing maximal, non-toxic inhibition at a concentration of 1 × 10⁻⁶ M. This inhibition was not due to interference with effector target cell binding (E:TCB) and was seen using Percoll-enriched NK cells. A time dependent inhibition of NK cell activity was seen when dibutyryl cyclic AMP (DiBcAMP) and PGD₂ were added in parallel to the NK cell assay suggesting that PGD₂ directly inhibits NK cell activity via the adenylate cyclase system which modulates the killing process.