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-α) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-α and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-α 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.     

Enhancement of natural killer cell activation and antibody-dependent cellular cytotoxicity by interferon-alpha and interleukin-12 in vaginal mucosae Sivmac251-infected Macaca fascicularis

We studied the innate immune system of Cynomolgus monkeys (Macaca fascicularis) experimentally infected via the vaginal mucosae with a virulent simian immunodeficiency virus isolate SIVmac251. Animals were evaluated for their natural killer (NK) cell activity, and for their antibody-dependent cellular cytotoxicity. NK cells from SIVmac251-infected macaques show impaired NK cell activity compared to cells from uninfected animals. Subsequent treatment of NK cells with interferon-a (IFN-alpha) or interleukin-12 (IL-12) alone partially restored the NK activity. However, either treatment of NK cells with both IFN-alpha and IL-12 completely reversed the impairment of cytotoxicity induced by simian immunodeficiency virus (SIV) infection. Incubation of NK cells from infected but not from uninfected monkeys with IFN-alpha and IL-12 for 8 days increased the percentage of CD16+/CD56+ cells twofold to five-fold and enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. Thus IFN-alpha and IL-12 greatly enhance both the NK cell and ADCC activities of peripheral blood cells from SIVmac251-infected animals and increase the number of NK cells in longer term culture. The combined effect of IFN-alpha and IL-12 in enhancing NK cell activity may provide a novel therapeutic approach for the restoration of depressed NK cell activity observed in human immunodeficiency virus (HIV)-infected patients.     

Interleukin 2-activated large granular lymphocytes: cytotoxic efficiency and mechanism of killing of tumor cell lines

We have compared the effects of interleukin 2 (IL-2) on the proliferative and cytolytic activity of human peripheral blood lymphocytes (PBL) and natural killer (NK) cell-enriched large granular lymphocyte (LGL) subpopulations. Both populations displayed enhanced cytolytic activity against various cell lines following culture with IL-2; the killing capacity and growth of IL-2 activated LGL was, however, superior to that of PBL. Analysis of the mechanisms of action of IL-2 indicated that the percentage of cells binding to tumor targets as well as the frequency of killer cells in both lymphocyte populations was increased after culture with IL-2; however, the LGL displayed 1.5-2.5-fold greater increase in all parameters of cytotoxicity. Additionally, the rate of tumor cell killing and the recycling capacity of LGL were substantially increased (63-76-fold and 4-9-fold, respectively), following IL-2 activation. These data indicate that IL-2-induced potentiation of cytolytic activity is due to an increase in all parameters of the lytic process, and suggest that NK-enriched LGL may be a more powerful antitumor effector population for use in adoptive therapy.     

Concomitant Effect of 2''-Deoxycoformycin on Natural Killer Cell Activity and Tumour Cell Sensitivity to Lysis in Hairy Cell Leukaemia—Discordant Effects of Alpha Interferon

The effects of 2'-deoxycoformycin (dCF) and alpha interferon (IFN-alpha) on natural killer (NK) cell-enriched fractions and hairy cell (HC) targets from three patients with HC leukaemia (HCL) were investigated. There was no significant increase in NK activity when either the HC targets or NK-enriched cells were preincubated with dCF. However, preincubation of both HC and NK cells with dCF resulted in increased NK activity. Culture of enriched NK cells with IFN-alpha enhanced their activity. However, preincubation of HC targets with this drug in the presence or absence of dCF resulted in a protective effect. Maximal NK activity towards HCL was obtained when the target tumour cells were separately precultured with dCF and the NK-enriched effectors precultured with dCF + IFN-alpha. The effect of dCF and IFN-alpha was also measured using the standard K562 cells as targets for NK activity. dCF enhanced NK activity following preculture of both effector and target K562 cells, but IFN-alpha did not reduce K562 cell susceptibility to NK lysis as it did for HC cells. Our findings suggest that (a) dCF and IFN-alpha, which are used to treat HC, could function via activation of NK cells, (b) effects on both effector and tumour target cells should be taken into account, and (c) caution should be exercised in extrapolating the effects of NK-cell activity against K562 cells to those on HC targets.     

Defective NK cell activity following thermal injury.

Peripheral blood mononuclear lymphocytes (PBL) from thermal injury patients were examined for their ability to mediate natural killer (NK) cell activity against K562 tumour cells and against herpes simplex virus type 1 (HSV-1) infected Raji tumour cells. Using fluorescein isothiocyanate-conjugated monoclonal antibodies, the number of T3, T4, T8, Leu11, and Leu7 positive cells in PBL obtained from patients and normal controls was determined. Thermal injury patients had decreased levels of T3+ cells and a T4:T8 ratio which was significantly lower than that found in normal control individuals. Although patients had normal percentages of Leu7+ and Leu11+ cells, they had depressed NK cell activity against both K562 tumour cells and HSV-1 infected Raji cells. NK cell activity against K562 tumour cells was severely depressed during the first 20 days after injury. This defective NK cell activity did not appear to be due to a defect in PBL binding to the K562 tumour cells. In patients, the level of NK cell activity against HSV-1 infected cells did not correlate with the level of NK cell activity against K562 tumour cells. This finding further supports previous reports showing that NK cells which kill K562 tumour cells are different from the NK cell population which kills HSV-1 infected cells. Pretreatment of PBL obtained from patients with IL-2 or IFN-alpha, in some cases greatly enhanced NK cell killing of K562 tumour cells. However, IL-2 or IFN-alpha did not enhance NK cell activity in patients who had severely depressed levels of NK cell activity. Interestingly, in some patients, differential responsiveness to IL-2 and IFN-alpha was observed. In some patients, NK cell activity was enhanced by IL-2 but not by IFN-alpha. These results, while only suggestive, may indicate that different populations of NK cells respond preferentially to IL-2 and that IFN-alpha and/or IL-2 enhance NK cell activity in PBL obtained from some, but not all, thermal injury patients. Finally, this study clearly shows that thermal injury patients have defective NK cell activity not only against K562 tumour cells but also against virus-infected cells.     

Effect of Pseudomonas aeruginosa exotoxin A on IFN-gamma synthesis: expression of costimulatory molecules on monocytes and activity of NK cells.

The aim of the study was (1) to evaluate the effect of Pseudomonas aeruginosa Exotoxin A (P-ExA) on the production of IFN-gamma in anti-CD3 induced human peripheral blood mononuclear cells (PBMC) and (2) to establish the effect of P-ExA on the IFN-gamma dependent cellular activities such as the expression of costimulatory molecules on monocytes and cytotoxicity of NK cells. The toxin in a high dose (100 ng/ml) inhibited IFN-gamma synthesis. Inhibitory effect of P-ExA was abolished by IL-1alpha which in a combination with P-ExA exerted a strong synergistic effect on IFN-gamma synthesis. Other monokines such as IL-1beta, IL-6, TNF-alpha neither reversed the inhibitory effect of P-ExA nor induced production of IFN-gamma. P-ExA also inhibited IFN-gamma-induced cellular events: (1) expression of costimulatory molecules on monocytes (CD80, CD86, ICAM-1, HLA-DR); (2) cytotoxic activity of NK cells. Inhibition of NK cells activity by P-ExA was not reversed by cytokines such as IL-2, IFN-alpha and TNF-alpha, which are known to enhance effector functions of NK cells. From these results we conclude that: (1) inhibition of IFN-gamma synthesis, as well as IFN-gamma-induced expression of costimulatory molecules and NK-cell effector functions may lead to suppression of specific and non-specific defense mechanisms, respectively, which are necessary for elimination of PA bacteria; (2) enhancement of IFN-gamma synthesis induced by P-ExA in a combination with IL-1alpha may cause harmful, Th1 cells dependent, inflammatory reactions of the host (septic shock, tissue damage) during infection with Pseudomonas aeruginosa.     

Suppression of human immunoglobulin synthesis by interleukin-4 in tandem with interleukin-2 through large granular lymphocytes

Recent studies have shown that interleukin (IL)-4 can affect secretion of immunoglobulins (Igs) or activation of cytotoxic cells by IL-2, while other studies have shown that natural killer (NK) cells/large granular lymphocytes (LGLs) can also affect Ig synthesis. Therefore, we examined the effect of IL-4 with and without IL-2 or human NK/LGLs on pokeweed mitogen (PWM)-stimulated production of IgM and IgG. We found that when IL-4 and/or IL-2 were incubated with peripheral blood lymphocytes and PWM for 7 days and an enzyme-linked immunosorbent assay was run to measure Ig synthesis, IL-4 with IL-2 caused a greater suppression of Ig synthesis than either cytokine alone. A further experiment was done to determine the effect IL-4 and IL-2 would have on LGL suppression of Ig synthesis. IL-4 and IL-2 alone and in combination, when added to LGL, caused the LGL to suppress Ig synthesis to a greater extent than alone. We conclude that IL-4 acts on NK/LGLs separately and jointly with IL-2, to suppress Ig synthesis (IgM and IgG).     

CD2 and other surface molecules in the regulation of non-MHC-restricted cytolytic function.

The effect of anti-CD2 and Fc receptor binding molecules on the cytolytic function of a highly enriched population of CD3- large granular lymphocytes (LGL) was studied. These cells could mediate natural killer (NK) activity, antibody-dependent cellular cytotoxicity (ADCC) and lectin-dependent cellular cytotoxicity (LDCC). Both ADCC and LDCC were enhanced by anti-CD2. The enhanced LDCC could also be observed with IL-2-activated LGL. However, NK cell activity was usually slightly diminished or unaffected by anti-CD2 binding. Immune complex and aggregated human IgG had no effect on ADCC but an anti-CD16 showed a dose-dependent inhibition of ADCC, reversible by anti-HLA-ABC and anti-CD2. Cross-linking of LGL surface-bound anti-CD2 caused an almost complete inhibition of LDCC and ADCC but had much less effect on NK activity. These experiments show that ADCC and LDCC mediated by CD3- LGL can be influenced by perturbing the CD2 molecule. NK activity was, however, affected differently, suggesting some basic differences in the pathway of ADCC and NK function.     

The proliferation and life-span of rat large granular lymphocytes: effects of cytokines

Pulse labeling of large granular lymphocytes (LGL) with [3H]thymidine for 1 h in vitro showed that 1%-7% of LGL were in S phase in the blood, spleen and liver of unstimulated euthymic and athymic rats as scored with autoradiography. Repetitive injections of [3H]thymidine over 2-7 days revealed that about half of the blood and spleen LGL had formed by division of precursors during this week. Stimulation of rats with the interferon inducer poly(I).poly(C) increased the proportion of S phase LGL rapidly and simultaneously in the blood, spleen and liver, so that by 20 h after stimulation ca 30% of LGL were in the S phase in these organs. This LGL proliferation was accompanied by an increased number of LGL in all three compartments 48-96 h after poly(I).poly(C) injection. Blood LGL cultured in cell impermeable diffusion chambers in the peritoneal cavity of poly(I).poly(C)-stimulated rats exhibited enhanced natural killer (NK) activity but no proliferative response, indicating that mature LGL were not induced to undergo blastogenesis by poly(I).poly(C) in vivo. Pretreatment of NK cells with rat interferon (IFN-alpha/beta) and with human recombinant interleukin 2 (rIL 2) in vitro, showed that these two cytokines, when combined, had opposing effects on NK activity and proliferation: whereas rIL 2 inhibited the IFN-induced augmentation in NK activity, IFN inhibited the rIL 2-induced LGL proliferation.     

Multiplication of Herpes Simplex Virus in Large Granular Lymphocytes that Co-Fractionate with Human Natural Killer Cell Activity

Highly enriched preparations of human large granular lymphocytes (LGL) cells, isolated from peripheral blood of normal adult donors, showed partial intrinsic resistance to infection with herpes simplex virus type 1 (HSV-1). Three subsets of LGL cells were identified on the basis of susceptibility to this virus: 1) resistant cells: 2) abortively infected cells; and 3) permissive cells. An average of 25% of LGL cells were completely resistant to infection. The majority (approximately 75%) could be infected as estimated by immunofluorescence. Only 5% of the original cell suspensions were productively infected as determined by infections center assay and transmission electron microscopy. These results have been reproduced in multiple experiments from 8 different donors consisting of both males and females. No significant difference in LGL cell responses to HSV-1 were detected within this population. Enriched LGL preparations exhibited enhanced natural killer (NK) cell activity. These findings raise several questions concerning the biological significance of LGL susceptibility to infection with HSV-1, relative to virus transport and/or immune surveillance by NK cells.     

Effects of anti-Tac antibody on the response of large granular lymphocytes to interleukin-2.

Large granular lymphocytes (LGL), which consist of a unique population comprising almost all of the natural killer (NK) cell activity, were separated from peripheral blood mononuclear cells by sequential depletion of monocytes and conventional discontinuous Percoll density gradient sedimentation. The LGL populations thus obtained exhibited significant levels of interferon-gamma (IFN-gamma) production and proliferation, as well as augmentation of NK cell activity in response to interleukin-2 (IL-2). Among these IL-2-driven phenomena, only IFN-gamma production was markedly inhibited by the monoclonal anti-Tac antibody, which presumably recognized the IL-2 receptor, whereas the proliferative response and the augmentation of NK cell activity were only minimally affected by the same antibody, even at the higher concentration. The dissociation of the effects of anti-Tac antibody on these IL-2-driven events gives us some insight on the role of IL-2 receptors involved in these immunologically interesting functions of IL-2.     

Cellular responses in chickens treated with IFN-alpha orally or inoculated with recombinant Marek's disease virus expressing IFN-alpha.

Mammalian type I interferons (IFN-alpha/beta) are potent mediators of innate antiviral immune responses, in particular through enhancement of natural killer (NK) cell cytotoxicity. Recently, chicken IFN-alpha (ChIFN-alpha) has been identified and shown to ameliorate Newcastle disease virus (NDV) infection when given to chickens at relatively high concentrations in the drinking water. In this report, the effect of recombinant ChIFN-alpha (rChIFN-alpha) on NK cell cytotoxicity was examined using (51)Cr-release assays. NK cell cytotoxic activity was also analyzed following inoculation with attenuated Marek's disease virus (MDV) serotype 1 strain R2/23 and a recombinant MDV (parent strain R2/23)-expressing ChIFN-alpha [rMDV(IFN-alpha)]. Treatment of chickens with high doses of rChIFN-alpha in the drinking water significantly decreased NK cell cytotoxicity compared with untreated chickens over a 7-day period. Inoculation of chickens with R2/23 significantly decreased NK cell cytotoxicity as well, whereas the rMDV(IFN-alpha) had no effect on NK cell cytotoxicity. Treatment of chicken embryo cell cultures with rChIFN-alpha inhibited replication of the very virulent MDV RB-1B strain in vitro, and oral treatment of chickens with rChIFN-alpha reduced MDV R2/23 replication in vivo.     

Multiplication of Herpes Simplex Virus in Large Granular Lymphocytes that Co-Fractionate with Human Natural Killer Cell Activity

Highly enriched preparations of human large granular lymphocytes (LGL) cells, isolated from peripheral blood of normal adult donors, showed partial intrinsic resistance to infection with herpes simplex virus type 1 (HSV-1). Three subsets of LGL cells were identified on the basis of susceptibility to this virus: 1) resistant cells: 2) abortively infected cells; and 3) permissive cells. An average of 25% of LGL cells were completely resistant to infection. The majority (approximately 75%) could be infected as estimated by immunofluorescence. Only 5% of the original cell suspensions were productively infected as determined by infections center assay and transmission electron microscopy. These results have been reproduced in multiple experiments from 8 different donors consisting of both males and females. No significant difference in LGL cell responses to HSV-1 were detected within this population. Enriched LGL preparations exhibited enhanced natural killer (NK) cell activity. These findings raise several questions concerning the biological significance of LGL susceptibility to infection with HSV-1, relative to virus transport and/or immune surveillance by NK cells.     

Antiviral effects of apolipoprotein A-I and its synthetic amphipathic peptide analogs

Apolipoprotein A-I (apo A-I), the major protein component of serum high density lipoproteins, was found to inhibit herpes simplex virus (HSV)-induced cell fusion at physiological (approximately 1 microM) concentrations. An 18 amino acid-long synthetic amphipathic alpha-helical peptide analog of apo A-I (18A) was also found to inhibit HSV-induced cell fusion at similar concentration (approximately 2 microM). Dimers of 18A connected via a proline (37pA) or an alanine (37aA) residue also inhibited virus-induced cell fusion at similar concentration, suggesting that the presence of a proline turn does not influence the antiviral activity of the amphipathic peptides. However, a peptide analog 18R, in which the distribution of charged residues was reversed, inhibited virus-induced cell fusion only at a higher (approximately 125 microM) concentration, suggesting that the anti-viral activity of the amphipathic peptide is strongly influenced by the nature of the charge distribution at the polar-nonpolar interface. Consistent with their ability to inhibit virus-induced cell fusion, the peptides inhibited the spread of HSV infection as demonstrated by a 10-fold reduction in the virus yield, when virus-infected cells were maintained in the presence of amphipathic peptides. The amphipathic peptides also inhibited penetration of virus into cells, but did not exert any effect on virus adsorption. A nearly complete inhibition of virus penetration was observed when the virus, or both virus and cells, was pretreated with the peptide, suggesting that the peptides may have a direct effect on the virus. The results indicate that amphipathic helices may be useful in designing novel antiviral agents that inhibit penetration and spread of enveloped viruses.     

The IL-2 receptor beta subunit is absolutely required for mediating the IL-2-induced activation of NK activity and proliferative activity of human large granular lymphocytes.

TU27 monoclonal antibody reacts with the cellular receptor to the beta subunit of the interleukin-2 receptor (IL-2R) (p70-75). This reagent has been utilized to demonstrate directly that the IL-2R beta is the IL-2-binding protein that mediates the activation of large granular lymphocytes (LGL) to proliferate and increase cytolytic activity in response to IL-2. The results presented here show that (i) the frequency of TU27+ cells paralleled the frequency of CD16+ (Leu-11+) cells; (ii) TU27 completely abrogated the proliferative response of LGL to IL-2, while GL439, an anti-IL-2R alpha (anti-Tac) reagent, had a much smaller effect, and the effect of the two together was no different from the effect of TU27 alone; (iii) TU27 abolished the IL-2-induced activation of natural killer (NK) activity and inhibited the development of LAK activity, while GL439 had no effect; and (iv) TU27 also inhibited naive NK activity. Therefore, these data clearly show that the IL-2-IL-2R beta interaction is responsible, and probably completely so, for the proliferative and cytolytic-promoting effects of IL-2 on LGL. In addition, they also suggest a role for this interaction in autocrine effects on native NK activity.     

In vivo treatment with interferon causes augmentation of IL-2 induced lymphokine-activated killer cells in the organs of mice.

Interferon-alpha (IFN-alpha) has been shown to synergize with IL-2 in the regression of a variety of established murine tumours and studies are underway to explore this combination in patients with advanced cancers as well. To understand the mechanism of synergy we have studied lymphokine-activated killer (LAK) cell activity in various compartments of mice in response to IFN-alpha and IL-2 administration. The effects of IFN-gamma, TNF-alpha and IL-4 were also examined. C57BL/6 mice were injected intraperitoneally with HBSS, IL-2 alone, IFN-alpha alone or both, two times a day for 7 days. On days 4 and 8, LAK activity was tested in a 4-h chromium release in cells obtained from lungs, spleen, and liver using fresh MCA-102 tumour cells as targets. The cells from control mice failed to lyse the MCA-102 target. IL-2 caused the generation of LAK activity and an increase in total cell yield in all the organs after 3 days of injection. IFN-alpha failed to generate LAK activity but when administered along with IL-2, caused synergistic enhancement of LAK lysis of MCA-102 target cells. Cell yield in this group was lower as compared with the IL-2-treated group. LAK activity tested after 7 days of IL-2 therapy was significantly decreased compared with that observed after 3 days. However, activity remained at as high a level after 7 days of therapy as after 3 days of therapy in animals treated with IFN-alpha and IL-2. FACS analysis revealed that asialo GM-1+ (ASGM-1) and NK1.1+ cells were increased in number in IL-2 and IL-2 plus IFN-alpha-treated spleen; however, the number of these cells was similar in both groups. In the liver, ASGM-1+ cells were higher in the IL-2 plus IFN-alpha group than in the group treated with IL-2 alone. By in vitro depletion utilizing antibody and Rbc' experiments, it was clear that both ASGM-1+ and NK1.1+ cells from the spleen mediated most of the cytotoxicity of MCA-102 targets. Pre-treatment irradiation (5 Gy) of mice completely abrogated the capability of IL-2 or IL-2 plus IFN-alpha to generate LAK activity. IFN-gamma also had a stimulatory effect on IL-2 induction of LAK activity. Tumour necrosis factor-alpha (TNF-alpha) and IL-4 failed to generate LAK activity and, in combination with IL-2, no additional stimulatory effect was observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Serum factors which suppress natural cytotoxicity in cancer patients

Spontaneous cytotoxicity mediated by natural killer (NK) cells is potentially an important mechanism of immunosurveillance against tumor or virus-infected cells. NK activity is impaired in many cancer patients. This study investigated the possibility that humoral factors are responsible for depressed NK activity in cancer patients and examined whether these factors were anti-lymphocyte antibodies (ALA) or immune complexes. The degree of NK suppression induced by 20 cancer patients' sera was determined by preincubating normal peripheral blood mononuclear cells with cancer sera. Eight of the 20 serum samples from cancer patients had NK-suppressive humoral factors. Elimination of immune aggregates by ultracentrifugation did not remove the inhibitory factors. The degree of NK suppression induced by cancer sera correlated with the extent of NK impairment in the serum donors (p less than 0.05). The cancer sera was examined for the presence of ALAs using flow cytometry. All cancer sera tested contained only low ALA reactivity to NK cell-enriched suspensions (less than 15%). This is in marked contrast to previous reports regarding NK-inhibitory systemic lupus erythematosus sera which contained large amounts of large granular lymphocyte (LGL) reactive ALAs. This study demonstrates that certain cancer sera suppress NK cell function. These inhibitory serum factors do not appear to be LGL-reactive ALAs or immune aggregates.     

Immunomodulatory activities of IFN-gamma1b in combination with type I IFN: implications for the use of IFN-gamma1b in the treatment of chronic HCV infections.

The standard of care for chronic hepatitis C, pegylated interferon-alpha (IFN-alpha) and ribavirin (RBV), causes a sustained virologic response (SVR) in approximately 50% of patients. SVR is correlated with innate and adaptive immune system responses, such as natural killer (NK) cell activation, production of IFN-alpha from immature plasmocytoid dendritic cells (pDC), and polarization of CD4(+) cells to a T helper 1 (Th1) cell phenotype. To examine how these immunologic responses vary with currently available regimens for chronic hepatitis C, cell populations purified from human peripheral blood mononuclear cells (PBMC) were treated with the clinically available combinations of pegylated IFN-alpha2b (PEG-IFN-alpha2b) + RBV, IFN-alphacon1 + RBV, or IFN- alphacon1 + IFN-gamma1b, and activation of cellular immune system components was monitored. The magnitude of NK cell activation depended on regimen, with IFN-alphacon1 + IFN-gamma1b > IFN-alphacon1 + RBV > PEG-IFN- alphaa2b + RBV. The maximum human serum concentrations of IFN-alphacon1 + IFN-gamma1b saturated NK cell activation, whereas the maximum human serum concentrations of IFN-alphacon1 + RBV or PEG-IFN-alpha2b + RBV did not. IFN-gamma1b also enhanced the production of IFN-alpha from immature pDCs, which are the dominant source of IFN-alpha upon viral infection. The rank order for induction of Th1 cell phenotype and repression of Th2 cell phenotype by the cocktails described was identical to that observed for NK cell activation. Additionally, IFN- gamma1b suppressed the ability of the hepatitis C virus (HCV) NS4 protein to enhance monocyte secretion of interleukin- 10 (IL-10), a cytokine whose expression level is correlated with viral persistence. These results suggest that addition of IFN-gamma1b to HCV treatment regimens may provide unique benefits.     

Down-regulation of interleukin-2 receptor expression on natural killer cells/large granular lymphocytes by interleukin-4.

It has recently been demonstrated that IL-4 inhibits IL-2 receptor expression on T cells. Studies have also shown that IL-4 can inhibit IL-2-induced natural killer cell (NK) cytotoxicity, and that IL-4 in combination with IL-2 and large granular lymphocyte (NK/LGL) cells suppresses Ig synthesis. Therefore, we examine whether IL-2 receptor expression on NK/LGL cells is affected with or without IL-4, using fluorescent receptor analysis. Our results demonstrate that IL-4 inhibits/down-regulates the expression of IL-2 receptors on either phytohemagglutinin or IL-2-stimulated NK/LGL cells.     

Suppression of Natural Killer Cell Activity and Interleukin-2 Concentration of Serum Obtained from In Vitro Fertilization-Embryo Transfer Patients

PROBLEM: The effect of serum obtained from in vitro fertilization-embryo transfer (IVF-ET) patients on healthy volunteers' natural killer (NK) cell activity was evaluated. We also measured interleukin (IL)-2 concentration with IVF-ET patients' serum and clarified the relationship between IL-2 levels and the suppressive effect on NK cell activity. METHOD OF STUDY: A retrospective nonrandomized clinical study was performed. The suppressive effect on NK cell activity and IL-2 concentrations was measured with serum obtained from 30 pregnant and 30 nonpregnant women during an IVF-ET procedure. The suppressive effect of the serum on NK cell activity was evaluated by the formula that we defined in our previous study. RESULTS: The suppression of NK cell activity was significantly higher in the nonpregnant women than in the pregnant women (P < 0.05); however, IL-2 concentration did not differ. There was a positive correlation between the suppression of NK cell activity and IL-2 levels in the pregnant women, but no significant correlation in the nonpregnant women. CONCLUSIONS: These results suggest that the suppression of NK cell activity may be one of the prognostic factors for IVF-ET. In addition, we speculate that an unidentified humoral factor other than IL-2, which could increase NK cell activity, might exist in the serum of the nonpregnant patient.