Suppression Of Natural Killer Cell Activity Research Articles

High-priority communication: Ethanol suppresses polyinosinic:polycytidylic acid–induced activation of natural killer cells primarily by acting on natural killer cells, not through effects on other cell types

Natural killer (NK) cells can be activated in vitro and in vivo by polyinosinic:polycytidylic acid (poly I:C) through induction of type I interferons or other cytokines. Ethanol suppresses in vivo and ex vivo poly I:C activation of NK cell activity in a mouse model for binge drinking, but it is not known whether this effect is mediated by changes in NK cells or in other cell types (e.g., those that produce NK cell–activating cytokines). Splenocytes were obtained from C57BL/6 [NK cell–competent (NKc)] and C57BL/6 perforin knockout [NK cell–incompetent (NKi)] mice 6 h after administration of ethanol (6 g/kg) or vehicle (VH; dH 2O). Cells were incubated in vitro 18 h with poly I:C (100 μg/ml), followed by a 4-h 51Cr release assay with the use of YAC-1 target cells. Results of cell-mixing experiments involving all relevant combinations of splenocytes obtained from NKc and NKi mice treated with VH or ethanol strongly supported the suggestion that NK cells, not other cell types, are the primary target of ethanol-induced suppression of NK cell activation. For example, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice or from ethanol-treated NKc and ethanol-treated NKi mice yielded similar cytolytic function. However, mixing of splenocytes obtained from ethanol-treated NKc and VH-treated NKi mice yielded significantly less cytolytic activity than that of splenocytes from VH-treated NKc and ethanol-treated NKi mice. In addition, mixing of splenocytes obtained from VH-treated NKc and NKi mice resulted in lower cytolytic activity than when splenocytes from the NKi mice were treated with ethanol instead of with VH, demonstrating that ethanol did not decrease the function of other cell types. A strikingly similar pattern of results was observed when B6C3F1 mice, rendered NK cell deficient by administration of anti-NK 1.1 monoclonal antibody, were used instead of perforin knockout mice. These results indicate that ethanol suppresses activation of NK cells primarily by suppressing the NK cell response to poly I:C, not by acting on another cell type.

Age at onset of major depressive disorder predicts reductions in NK cell number and activity

Background: Major depressive disorder (MDD) has been associated with altered immunologic parameters including reductions in natural killer cell activity (NKCA). It remains largely unknown, however, whether alterations in immune function characterize homogeneous sub-groups of MDD. The present study addressed the question of whether age at onset of index episode and/or duration of the present episode of MDD predicted alterations in NKCA and NK cell number. Methods: Participants met DSM-IV criteria for MDD. Age at onset of MDD, duration of the present episode, demographics, and comorbidity were obtained by SCID for all subjects ( n=36). Severity and symptom pattern of MDD was assessed by the Hamilton Depression Rating Scale. NKCA was measured using a standard chromium-release cytotoxicity assay and NK number assessed by flow cytometry. Results: Age at onset of MDD significantly predicted variance in NK cell number and NKCA. Consistent with previous studies, sleep disturbance and psychomotor retardation possessed significant explanatory power for variance in NK cell number and NKCA, respectively. Limitations: Measures of age at onset of MDD and duration of the present episode were obtained by self-report and thus recall bias may attenuate the reliability of the present findings. The present study design also precludes conclusions regarding the temporal association between alterations in NK cells and MDD. Conclusions: We propose that immunologic alterations, characterized by a suppression of NKCA and NK cell number concomitant with proinflammatory processes, may constitute an immunologic phenotype unique to early-age-onset depression and may be salient factors in the pathogenesis of depression.

Influence of surgery and endotoxin-induced sepsis combined on natural killer cell activity, oxidative burst of granulocytes and antigen presentation capability of monocytes.

Cell mediated immunity is affected in the course of sepsis and following surgical stress. The natural killer (NK) cells, the granulocytes and the monocytes constitute the immediate unspecific cell mediated immunity. We therefore investigated the effect of surgery- and endotoxin-induced sepsis on NK cells, granulocytes and monocytes in a two-hit model. Three groups of 40 mice. Each group was divided into four groups of 10 mice. All the animals were anesthetized and subjected to either: laparotomy; treatment with Escherichia coli endotoxin i.p.; laparotomy followed 20 min later by endotoxin i.p.; or left untreated as a control group. In the first 40 mice the NK cell activity in the spleen and number of NK cells in the liver were measured, in the second the oxidative burst of granulocytes, and in the third the antigen presentation capacity of monocytes. Endotoxin stimulated the NK cell activity and up-regulated the antigen presentation capability on monocytes. In contrast, surgical stress reduced the NK cell activity, the number of NK cells and down-regulated the antigen presentation capability on monocytes. After surgery, followed by administration of endotoxin, the oxidative burst of granulocytes was stimulated while antigen presentation capability on monocytes was down-regulated. Endotoxin prevented or reverted the postoperative suppression of NK cell activity. Our two-hit model shows that some cell types of the unspecific immune system exhibit an excessive inflammatory response (NK cells, granulocytes) while specific functions of other cell types (monocytes) are simultaneously diminished. This diversity makes a potential therapeutic immunomodulation very complex as some cell types would need to be down-regulated while others need to be stimulated.

Immunomodulation by vitamin B12: augmentation of CD8+ T lymphocytes and natural killer (NK) cell activity in vitamin B12-deficient patients by methyl-B12 treatment.

It has been suggested that vitamin B12 (vit.B12) plays an important role in immune system regulation, but the details are still obscure. In order to examine the action of vit.B12 on cells of the human immune system, lymphocyte subpopulations and NK cell activity were evaluated in 11 patients with vit.B12 deficiency anaemia and in 13 control subjects. Decreases in the number of lymphocytes and CD8+ cells and in the proportion of CD4+ cells, an abnormally high CD4/CD8 ratio, and suppressed NK cell activity were noted in patients compared with control subjects. In all 11 patients and eight control subjects, these immune parameters were evaluated before and after methyl-B12 injection. The lymphocyte counts and number of CD8+ cells increased both in patients and in control subjects. The high CD4/CD8 ratio and suppressed NK cell activity were improved by methyl-B12 treatment. Augmentation of CD3-CD16+ cells occurred in patients after methyl-B12 treatment. In contrast, antibody-dependent cell-mediated cytotoxicity (ADCC) activity, lectin-stimulated lymphocyte blast formation, and serum levels of immunoglobulins were not changed by methyl-B12 treatment. These results indicate that vit.B12 might play an important role in cellular immunity, especially relativing to CD8+ cells and the NK cell system, which suggests effects on cytotoxic cells. We conclude that vit.B12 acts as an immunomodulator for cellular immunity.

Natural Killer Cells Express Estrogen Receptor-α and Estrogen Receptor-β and Can Respond to Estrogen Via a Non-Estrogen Receptor-α-Mediated Pathway

Natural killer (NK) cells play a crucial role in host defense against pathogens and immune surveillance against cancer. Given that estrogens have been reported to suppress NK cell activity, we sought to elucidate the mechanisms by which estrogen mediates this effect. We demonstrate by immunocytochemical staining with estrogen receptor-α (ERα)- and estrogen receptor-β (ERβ)-specific antibodies that both ERα and ERβ are expressed in murine NK cells. We also compared the ability of high doses of 17β-estradiol (∼800 pg/ml) to regulate NK cell activity in wild-type and estrogen receptor-α-deficient (ERαKO) mice. 17β-estradiol elicited a significant decrease in NK cell activity in both wild-type and ERαKO mice (P < 0.001). These data suggest that ERβ or possibly a novel receptor is involved in mediating estrogen action on NK cell activity and raise the potential for therapeutic modulation of NK cell activity with selective estrogen receptor modulators (SERMS).

Inhibition of Lung Natural Killer Cell Activity by Smoking: The Role of Alveolar Macrophages

Background: It is known that natural killer (NK) cell activity in the lung of smokers (SM) is lower than in non-smokers (NS). However, little is known about the underlying mechanisms. Objective: The purpose of this work was to investigate the mechanisms of the inhibition of NK cell activity by alveolar macrophages (AM) in SM. Methods: Lung effector cells and AM were obtained using bronchoalveolar lavage. The NK cell activity was assayed by ⁵¹Cr release method after incubation of 4 and 24 h, using K562 as target cell. AM were added at a concentration of 25% to effector cells. Results: Following 24-hour culture, NK cell activity significantly increased in the NS but not in the SM. Lung NK cell activity was significantly augmented by interleukin-2 in the NS but not in the SM. Addition of AM to the NK cell preparation from SM exerted a significantly greater suppressive effect on autologous blood NK cell activity than in the NS. Indomethacin, catalase or thiourea did not prevent AM-mediated suppression of NK cell activity, in contrast to superoxide dismutase. Conclusions: These results suggest that the suppression of NK cell activity by AM in SM may be caused by O^–₂ release rather than by prostaglandins, H₂O₂ or OH release from AM.

Effects of mycotoxins on human immune functions in vitro

Immunosuppressive and carcinogenic Fusarium mycotoxins may appear in domestic food products. Therefore, the immunological effects of Fusarium mycotoxins were tested on human peripheral blood mononuclear cells from different blood donors. In the present study we investigated deoxynivalenol (DON), 3-acetyldeoxynivalenol, fusarenon-X, T-2 toxin, zearalenone, α-zearalenol, β-zearalenol and nivalenol for their effects on T and B cells in a proliferation assay, antibody-dependent cellular cytotoxicity (ADCC) and natural killer (NK) cell activity on human peripheral blood mononuclear cells. The concentrations applied in our experiments were similar to those which can be found in normal human peripheral blood system (0.2–1800 ng/ml). Among the eight mycotoxins tested, T-2 toxin, fusarenon X, nivalenol and deoxynivalenol exerted the highest immunosuppressing effect on human peripheral blood mononuclear cells in vitro. Mycotoxin-induced immunosupression was manifested as depressed T or B lymphocyte activity. Furthermore, by virtue of inhibition of NK cell activity, the protection against tumor development may also be attenuated.

Effects of morphine on immune response in rats with sciatic constriction injury

We investigated the effects of acute and of chronic morphine treatment on T-lymphocyte function and natural killer (NK) cell activity in rats receiving chronic constriction injury (CCI) of the sciatic nerve. T-Lymphocyte function was evaluated based on concanavalin-A (ConA)- and phytohemagglutinin (PHA)-induced splenocyte proliferation. The effects of morphine on thermal hyperalgesia were also assessed by measuring paw withdrawal latency (PWL) in rats. All of the rats that received CCI developed thermal hyperalgesia while sham-operated rats did not. Thermal hyperalgesia was dose-dependently reversed after acute (single injection) and after chronic (daily injection for 7 days) administration of morphine but persisted in saline-treated CCI rats. There was no significant difference between sham and saline-treated CCI groups in splenocyte proliferation and NK cell activity. NK cell activity and splenocyte proliferation induced by ConA and PHA were significantly suppressed by acute morphine treatment in a dose-dependent manner. The reversal of the thermal hyperalgesia persisted throughout the period of chronic morphine treatment. No tolerance to the suppression of NK cell activity and splenocyte proliferation was observed after chronic morphine treatment. These data suggest that both acute and chronic morphine treatment can cause a dose-dependent reversal of thermal hyperalgesia and inhibition of NK cell activity and splenocyte proliferation in rats with sciatic CCI, without concomitant development of tolerance. Opioid therapy for chronic neuropathic pain should be used cautiously, especially in immune-compromised cases.

Reversal of human immunodeficiency virus type 1 protein-induced inhibition of natural killer cell activity by alpha interferon and interleukin-2.

A recombinant fusion peptide, Env-Gag, derived from the human immunodeficiency virus type 1 (HIV-1) genome corresponding to a defined portion of the envelope (Env) and internal core (Gag) proteins was examined for immunoregulatory effects on the cytotoxic activity of natural killer (NK) cell-enriched, large granular lymphocytes (LGL) from healthy donors. Percoll-separated, NK cell-enriched LGL precultured for 24 h with Env-Gag at 10- and 50-ng/ml concentrations, which significantly stimulated lymphocyte proliferation, caused significant suppression of NK cell activity. Denatured Env-Gag did not cause any effect on the NK cell activity of LGL. Two other control peptides, one derived from the Escherichia coli vector used to clone the HIV Env-Gag fusion peptide and the other derived from a non-HIV-1 viral antigen (rubeola virus), did not produce any observable effect on the NK cell activity of LGL, demonstrating the specificity of the effect produced by Env-Gag. Subsequent treatment of LGL with alpha interferon (IFN-alpha) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-alpha and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-alpha and IL-2 in enhancing NK cell activity may provide a novel therapeutic approach to the restoration of depressed NK cell activity observed in HIV-infected patients.

Crystal structure of a lectin-like natural killer cell receptor bound to its MHC class I ligand.

Natural killer (NK) cell function is regulated by NK receptors that interact with MHC class I (MHC-I) molecules on target cells. The murine NK receptor Ly49A inhibits NK cell activity by interacting with H-2D(d) through its C-type-lectin-like NK receptor domain. Here we report the crystal structure of the complex between the Ly49A NK receptor domain and unglycosylated H-2D(d). The Ly49A dimer interacts extensively with two H-2D(d) molecules at distinct sites. At one interface, a single Ly49A subunit contacts one side of the MHC-I peptide-binding platform, presenting an open cavity towards the conserved glycosylation site on the H-2D(d) alpha2 domain. At a second, larger interface, the Ly49A dimer binds in a region overlapping the CD8-binding site. The smaller interface probably represents the interaction between Ly49A on the NK cell and MHC-I on the target cell, whereas the larger one suggests an interaction between Ly49A and MHC-I on the NK cell itself. Both Ly49A binding sites on MHC-I are spatially distinct from that of the T-cell receptor.

Heatstroke induces a reduction of natural killer cell activity in rats

Experiments were carried out to determine the changes of natural killer (NK) cell activity that occurred during heatstroke in rats pretreated with or without interleukin-1 (IL-1) receptor antagonist (IL-1ra). After the onset of heatstroke, all the splenic NK cell activity, the effector-target cell conjugation, and the NK cell numbers were decreased in rats. Additionally, an increase in the plasma IL-1 level was associated with arterial hypotension, cerebral ischemia and hyperthermia during rat heatstroke. Pretreatment with an IL-1ra reversed in part the heatstroke-induced inhibition of NK cell activity. Thus it appears that the inhibition of NK cell activity produced by activation of IL-1 receptor mechanism is associated with the increased susceptibility to infection that is well described in heatstroke.

The Effect of Butylated Hydroxytoluene on Selected Immune Surveillance Parameters in Rats bearing Enzyme-altered Hepatic Preneoplastic Lesions

Selected immune function parameters were examined in male Fischer 344 rats following (a) induction of enzyme-altered preneoplastic liver foci (EAF), and (b) growth modulation of EAF by 30-day feeding with the food antioxidant butylated hydroxytoluene (BHT). Glutathione S-transferase-P (GSTP)-positive EAF were observed in livers of rats receiving diethylnitrosamine (DEN), 2-acetylaminofluorene (2-AAF) and partial hepatectomy (PH) (Solt-Farber procedure), with or without BHT treatment. The induction of EAF and/or 0.5% BHT treatment resulted in a significant reduction in the natural killer (NK) cell activity of splenocytes. PH did not affect NK activity significantly compared with control (no PH) rats. The concanavalin A-induced lymphoproliferative activity of splenocytes was increased in rats with PH compared with those without. A lag in time needed to attain maximum calcium release was observed only in the rats with PH compared with those without PH. None of the treatments affected the phagocytic activity of resident peritoneal macrophages. Only EAF-bearing rats without BHT treatment had increased granulocyte and monocyte levels, while the leucocyte and lymphocyte levels were reduced by the initiator DEN, but not by BHT treatment. Further investigations are necessary to determine whether the observed suppression of NK cell activity during EAF induction and growth modulation by BHT is a contributing factor in enhancement of rodent liver neoplasia by this non-genotoxic food antioxidant.

Immune function and psychological factors in patients with coronary heart disease (I).

As part of studies on the effects, especially the preventive effects, of exercise and psychological factors on cardiovascular diseases, the association between psychological tendencies and immune response was evaluated in patients with coronary heart disease who were receiving exercise therapy. The Pearson's product-moment correlation coefficients between natural killer (NK) cell activity and various psychological scales were obtained. For the Moudsley Personality Inventory, NK cell activity had a significant positive correlation with the extraversion scale and a significant negative correlation with the neuroticism scale. NK cell activity also had a significant positive correlation with the playful humor scale and a significantly negative correlation with the Self-rating Depression Scale. The positive correlation of NK cell activity with the extraversion scale and the humor scale and its negative correlation with the neuroticism scale suggest an association between a positive-feeling tendency and high NK cell activity. The negative correlations of NK activity with the depression scale and neuroticism scale indicate that decreased or excessive expression of feelings inhibits NK cell activity. Thus, high NK activity appears to be associated with optimal expression of feelings.

Differential tolerance to morphine's immunomodulatory effects following continuous administration

Rats were continuously infused with either morphine or saline via an osmotic minipump for 20 consecutive days. Effects on immune status were assessed on the twentieth day of the chronic administration period following a bolus injection of morphine administered 1 h prior to sacrifice. The morphine injection suppressed measures of splenic natural killer (NK) cell activity, mitogen-stimulated T-cell proliferation, and γ-interferon (IFN) production in rats that received saline via the minipump. In rats that received chronic morphine via the minipump, the morphine injection also suppressed mitogen-stimulated splenocyte proliferation and γ-IFN production but did not suppress NK cell activity. These data indicate that chronic morphine administration via osmotic minipumps leads to differential tolerance to the immunomodulatory effects of morphine. These findings support previous results indicating differential tolerance development within the immune system following chronic morphine administration via the drinking water.

Modulation of orphanin FQ or electroacupuncture (EA) on immune function of traumatic rats.

Orphanin FQ(OFQ) is a recently discovered 17-amino acid neuropeptide[1-2]. In present paper, influence of intracerebroventricular(ICV) administration of OFQ or electroacupuncture(EA) on the surgical trauma-induced inhibition of the splenic natural killer(NK) cell activity in rat was observed. The results showed that administration of 0.1 microgram(0.0055 nmol) and 1 microgram (0.055 nmol) OFQ had no effect on the NK cell activity, while 5 micrograms(2.75 nmol) OFQ reduced the NK cell activity in normal rats. However, 0.1 microgram, 1 microgram or 5 micrograms OFQ were found to antagonise the immune function depression caused by surgical trauma. The NK cell activity was reduced in normal rats after repeated ICV treatment with antisense oligonucleotide (ASO) complementary to bases of translated region of rat OFQ receptor mRNA to block the translation of OFQ receptor mRNA into protein. EA stimulation of Zusanli(St. 36) and Lanwei(Extra. 37) points also obviously improved the immunosuppression produced by trauma. OFQ combined with EA showed antagonism on the suppression, but there was no significant differences compared with OFQ(ICV) or EA alone. When blocking the translation of OFQ receptor mRNA with the ASO, the OFQ induced anti-immunosuppression effect was completely reversed, but EA still improved the inhibition on NK cell activity. The results suggested that the OFQ played a role in the regulation of immunosuppression. EA could modulate the suppression of NK cell activity induced by surgical trauma. The mechanisms of the modulation of OFQ or EA on the immunosuppression induced by surgical trauma need further study.

Involvement of Catecholamines and Glucocorticoids in Ethanol‐Induced Suppression of Splenic Natural Killer Cell Activity in a Mouse Model for Binge Drinking

Ethanol (EtOH) suppresses splenic natural killer (NK) cell activity in a mouse binge drinking model. Direct effects of EtOH and its metabolites are not the major cause of this suppression. Also, catecholamines do not completely explain this suppression. This implicates the involvement of other neuroendocrine mediators in this suppression. Previous studies in this laboratory have shown that RU 486 at a dosage of 100 mg/kg did not affect EtOH-induced suppression of NK cell activity. However, in the present study, RU 486 at a dosage of 200 mg/kg partially blocked the suppression of NK cell activity induced by EtOH. Moreover, corticosterone at levels expected in the free (unbound) form in EtOH-treated mice decreased NK cell activity in vitro. Nadolol in combination with RU 486 blocked the suppression of NK cell activity in EtOH-treated mice. Although there were reasons to suspect that EtOH-induced changes in the levels of growth hormone or prolactin might also contribute to the suppression of NK cell activity; evidence obtained herein did not indicate such involvement. Thus, glucocorticoids and catecholamines seem to be involved in EtOH-induced suppression of NK cell activity. Together, with the direct effects of EtOH, these neuroendocrine mediators seem to be sufficient to explain all of the suppression of NK cell activity caused by EtOH.

Local inhibition of natural killer cell activity promotes the progressive growth of intraocular tumors.

Purpose. To study the effect of aqueous humor (AH)-mediated inhibition of natural killer (NK) cell activity on intraocular tumor progression. Methods. Two NK-sensitive tumors, RMA-S lymphoma and OCM-3 uvcal melanoma, were tested in vitro for susceptibility to NK cell-mediated lysis in the presence or absence of AH in conventional cytotoxicity assays. Various numbers of RMA-S and OCM-3 tumor cells were injected either subcutaneously or intracamerally into C157BL/6 severe combined immunodeficiency mice and BALB/c nude mice respectively and tumor growth was monitored. The role of NK cell-mediated cytotoxicity in controlling tumor growth was confirmed by depleting NK cells in severe combined immunodeficiency mice by administering anti-asialo GM1 antibodies before subcutaneous tumor injection. Results. AH significantly inhibited NK cell-mediated lysis of RMA-S and OCM-3 tumor cells in vitro and in vivo. NK sensitive RMA-S (1 x 10 4 cells) and OCM-3 tumors (I X 10 6 , 5 X 10 6 Cells) were rejected after subcutaneous injection in C57BL/6 mice, whereas the same or even lower numbers of cells grew progressively in the eye. In vivo NK cell depletion resulted in progressive growth of subcutaneously injected RMA-S tumors at a dose rejected by mice with normal NK cell activity. Conclusions. AH inhibits NK cell activity in vitro and within the interior of the eye and prevents the rejection of NK-sensitive intraocular tumors.

Tolerance development to morphine-induced alterations of immune status

A variety of in vitro immune measures were examined in groups of Lewis rats that chronically consumed either tap water or a 0.2, 0.4, or 0.6 mg/ml morphine drinking solution. Rats received a subcutaneous injection of either saline or 15 mg/kg morphine sulfate 1 h before sacrifice. In the water drinking groups, the acute morphine injection significantly suppressed splenic natural killer (NK) cell activity, mitogen-stimulated splenic T- and B-cell proliferation and γ-interferon (γ-IFN) production. A single, acute injection of morphine did not suppress NK cell activity in rats that drank the two highest concentrations of morphine, whereas it did suppress the mitogen-stimulated splenic T- and B-cell proliferation and γ-IFN production. These results suggest that rats that drank morphine for 20 days developed tolerance to morphine's suppressive effect on NK cell activity but not to other measures of immune status. Morphine drinking rats also developed tolerance to morphine's antinociceptive effects and revealed signs of physical dependence when the morphine solution was withdrawn or when naltrexone was administered.

Reduction of intracellular ph by inhibitors of natural killer cell activity, nicardipine, methyl 2-( n-benzyl- n-methylamino)ethyl-2,6-dimethyl-4-(2-isopropyl-pyrazolo[1,5- a] pyridine-3-yl)-1,4-dihydro-pyridine-3,5-dicarboxylate (ahc-52), and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS)

Our previous study showed that nicardipine and its structural analog, methyl 2-( N-benzyl- N-methylamino)ethyl-2,6-dimethyl-4-(2-isopropyl-pyrazolo[l,5- a]pyridine-3-yl)-l,4-dihydro-pyridine-3,5-dicarboxylate (AHC-52), which is devoid of calcium channel blocking activity, were equally effective in inhibiting natural killer (NK) cell activity, perhaps through inhibition of P-glycoprotein. In this study, we confirmed this finding using a human NK-like cell line, YTN, which is highly cytotoxic to JY cells. The YTN cell-mediated cytotoxicity toward JY cells was inhibited by nicardipine and AHC-52 in a concentration-dependent manner, the concentrations required for 50% inhibition being 14 and 7 μM, respectively. We then examined by flow cytometry whether these reagents modulate the intracellular pH (pH i), since P-glycoprotein reportedly plays a role in pH i homeostasis, perhaps by altering chloride translocation. Both reagents reduced pH i at concentrations similar to those required for inhibition of the cytotoxicity. In addition, 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS), an inhibitor of anion exchangers, also inhibited NK cell activity, with an IC 50 value of 160 μM, and reduced pH i at a similar concentration, although it is not a P-glycoprotein blocker. Thus, the inhibitory activities of nicardipine, AHC-52, and DIDS toward NK cell activity paralleled their lowering activities of pH i, suggesting the possibility that disregulation of pH i is related to inhibition of NK cell activity.

Natural killer cell activity during UVR-induced skin tumor formation in the Skh hairless mouse.

We analyzed natural killer (NK) cell activity in the hairless albino Skh/HR1 mouse, to study whether the NK cell activity plays a role during UV radiation (UVR)-induced carcinogenesis. In 4 h 51Cr-release assays, spleen lymphocytes of specific pathogen-free (spf) Skh/HR1 mice displayed 5-10% spontaneous NK cell activity. This was comparable to NK cell activity in C57B1/6, C3H and athymic NMRI nu/nu mice, which were also kept under spf conditions. In all strains investigated, the low spontaneous NK cell activity could be increased up to 20-30% by intraperitoneal administration of polyinosinic:polycytidylic acid (polyI:C), a standardized in vivo NK cell induction method. The polyI:C potentiation of NK cells in Skh/HR1 mice was similar to that in C57B1/6 and NMRI, but significantly less than in C3H mice. Chronic daily UV irradiation according to a protocol that was also used for induction of carcinogenesis (11-12 weeks, 95 mJ/cm2 of UV exposure from FS40 sunlamps) did not decrease NK cell activity on a cell for cell basis. Neither was the inducibility of NK spleen cell activity with polyI:C in Skh/HR1 mice during UV exposure reduced. Based on total organ basis, the pooled lymph node cells (axillary, mandibulary and inguinal lymph node) showed a doubling of NK cell activity (P < 0.001), mainly due to an almost 100% increase in the number of lymph node cells. In conclusion, UVR does not suppress the normal or inducible NK cell activity at the time of clinical appearance of skin tumors. This suggests that such suppression of NK cell activity is not likely to contribute to UVR-induced carcinogenesis in the Skh/HR1 strain.