Negative regulation of Schistosoma japonicum egg-induced liver fibrosis by natural killer cells

The role of natural killer (NK) cells in infection-induced liver fibrosis remains obscure. In this study, we elucidated the effect of NK cells on Schistosoma japonicum (S. japonicum) egg-induced liver fibrosis. Liver fibrosis was induced by infecting C57BL/6 mice with 18-20 cercariae of S. japonicum. Anti-ASGM1 antibody was used to deplete NK cells. Toll-like receptor 3 ligand, polyinosinic-polycytidylic acid (poly I:C) was used to enhance the activation of NK cells. Results showed that NK cells were accumulated and activated after S. japonicum infection, as evidenced by the elevation of CD69 expression and IFN-γ production. Depletion of NK cells markedly enhanced S. japonicum egg-induced liver fibrosis. Administration of poly I:C further activated NK cells to produce IFN-γ and attenuated S. japonicum egg-induced liver fibrosis. The observed protective effect of poly I:C on liver fibrosis was diminished through depletion of NK cells. Disruption of IFN-γ gene enhanced liver fibrosis and partially abolished the suppression of liver fibrosis by poly I:C. Moreover, expression of retinoic acid early inducible 1 (RAE 1), the NKG2D ligand, was detectable at high levels on activated hepatic stellate cells derived from S. japonicum-infected mice, which made them more susceptible to hepatic NK cell killing. In conclusion, our findings suggest that the activated NK cells in the liver after S. japonicum infection negatively regulate egg-induced liver fibrosis via producing IFN-γ, and killing activated stellate cells.     

HIV infection abrogates the functional advantage of natural killer cells educated through KIR3DL1/HLA-Bw4 interactions to mediate anti-HIV antibody-dependent cellular cytotoxicity

Combinations of KIR3DL1 and HLA-Bw4 alleles protect against HIV infection and/or disease progression. These combinations enhance NK cell responsiveness through the ontological process of education. However, educated KIR3DL1(+) NK cells do not have enhanced degranulation upon direct recognition of autologous HIV-infected cells. Since antibody-dependent cellular cytotoxicity (ADCC) is associated with improved HIV infection outcomes and NK cells overcome inhibition through killer cell immunoglobulin-like receptors (KIR) to mediate ADCC, we hypothesized that KIR3DL1-educated NK cells mediate anti-HIV ADCC against autologous cells. A whole-blood flow cytometry assay was used to evaluate ADCC-induced activation of NK cells. This assay assessed activation (gamma interferon [IFN-γ] production and/or CD107a expression) of KIR3DL1(+) and KIR3DL1(-) NK cells, from HLA-Bw4(+) and HLA-Bw4(-) HIV-positive and HIV-negative individuals, in response to autologous HIV-specific ADCC targets. KIR3DL1(+) NK cells were more functional than KIR3DL1(-) NK cells from HLA-Bw4(+), but not HLA-Bw4(-), healthy controls. In HIV-infected individuals, no differences in NK cell functionality were observed between KIR3DL1(+) and KIR3DL1(-) NK cells in HLA-Bw4(+) individuals, consistent with dysfunction of NK cells in the setting of HIV infection. Reflecting the partial normalization of NK cell responsiveness following initiation of antiretroviral therapy, a significant correlation was observed between the peripheral CD4(+) T-lymphocyte counts in antiretroviral therapy-treated subjects and the functionality of NK cells. However, peripheral CD4(+) T-lymphocyte counts were not correlated with an anti-HIV ADCC functional advantage in educated KIR3DL1(+) NK cells. The abrogation of the functional advantage of educated NK cells may enhance HIV disease progression. Strategies to enhance the potency of NK cell-mediated ADCC may improve HIV therapies and vaccines.     

Expression of human T lymphocyte antigens by killer cells.

K cells, the effectors of antibody-dependent cell-mediated cytotoxicity, were found to express human T but not B lymphocyte antigens detected by rabbit anti-HTLA and anti-HBLA. Pretreatment of effector cells with anti-HTLA+C inhibited ADCC by specifically lysing K cells: no inhibition of ADCC by anti-HTLA occurred when deltaC was substituted for C. By contrast, pretreatment of effector cells with anti-HBLA nonspecifically inhibited ADCC, probably for forming antigen-antibody complexes with HBLA+ cells in effector suspensions: a) treatment with anti-HBLA deltaC was more inhibitory of ADCC than treatment with anti-HBLA+C, and b) the inhibitory effect of anti-HBLA on ADCC was either eliminated or markedly reduced if effector suspensions were first passed through a nylon fiber column, a procedure that removed most HBLA+ cells without affecting K cell activity. HTLA antigens expressed by K cells and NK cells are the same as HTLA antigens expressed by thymocytes since thymocytes completely absorb the anti-K cell and NK cell reactivity of anti-HTLA.     

Induction of natural killer cell activity of thoracic duct lymphocytes by polyinosinic-polycytidylic acid (poly(I:C)) or interferon

Natural killer (NK) cell activity of thoracic duct lymphocytes (TDL) was examined in normal mice and in mice treated with polyinosinic-polycytidylic acid (poly(I:C) and interferon (IFN). TDL from mice treated with phosphate-buffered saline (PBS) expressed little or no NK cell activity against YAC-1 target cells at effector-to-target ratios of up to 200:1, even after in vitro treatment with murine L-cell IFN. In contrast, TDL from poly(I:C)- or IFN-treated mice expressed significant NK activity, which correlated with the significantly higher NK activity of splenocytes from these mice compared to the NK activity of splenocytes from PBS-treated mice. These data indicate that although TDL from normal mice express no detectable NK cell activity, NK cell activity can be induced in TDL by in vivo treatment with poly(I:C) or IFN.     

Restoration of TLR3-activated myeloid dendritic cell activity leads to improved natural killer cell function in chronic hepatitis B virus infection

There is increasing evidence that the function of NK cells in patients with chronic hepatitis B (CHB) infection is impaired. The underlying mechanism for the impaired NK cell function is still unknown. Since myeloid dendritic cells (mDC) are potent inducers of NK cells, we investigated the functional interaction of mDC and NK cells in CHB and the influence of antiviral therapy. Blood BDCA1(+) mDC and NK cells were isolated from 16 healthy controls or 39 CHB patients at baseline and during 6 months of antiviral therapy. After activation of mDC with poly(I · C) and gamma interferon (IFN-γ), mDC were cocultured with NK cells. Phenotype and function were analyzed in detail by flow cytometry and enzyme-linked immunosorbent assay. Our findings demonstrate that on poly(I · C)/IFN-γ-stimulated mDC from CHB patients, the expression of costimulatory molecules was enhanced, while cytokine production was reduced. In cocultures of poly(I · C)/IFN-γ-stimulated mDC and NK cells obtained from CHB patients, reduced mDC-induced NK cell activation (i.e., CD69 expression) and IFN-γ production compared to those in healthy individuals was observed. Antiviral therapy normalized mDC activity, since decreased expression of CD80 and CD86 on DC and of HLA-E on NK cells was observed, while poly(I · C)/IFN-γ-induced cytokine production by mDC was enhanced. In parallel, successful antiviral therapy resulted in improved mDC-induced NK cell activation and IFN-γ production. These data demonstrate that CHB patients display a diminished functional interaction between poly(I · C)/IFN-γ activated mDC and NK cells due to impaired mDC function, which can be partially restored by antiviral therapy. Enhancing this reciprocal interaction could reinforce the innate and thus the adaptive T cell response, and this may be an important step in achieving effective antiviral immunity.     

Characterization of a monoclonal antibody enhancing porcine natural killer cell activity (PNK-E)

A monoclonal antibody, termed PNK-E, that functionally enhances porcine natural killer (NK) cell activity but not antibody-dependent cellular cytotoxicity (ADCC) is investigated in this report. When PNK-E and K562 target cells were simultaneously added to effector cells, killing of target cells could be detected as early as 30 min, and a dramatic enhancement of killing activity was observed in short term 51Cr-release assays. When a panel of five NK-sensitive targets were tested, PNK-E enhanced the killing of K562, MOLT-4, and U937 cells, but not the killing of CEM and YAC-1. F(ab)'2 fragments of PNK-E did not enhance NK activity, indicating a requirement for the Fc portion of PNK-E to elicit enhancement of NK. Immunofluorescence analysis shows that PNK-E antigen is expressed on approximately 15% of peripheral blood lymphocytes with a relatively dull fluorescence staining pattern. PNK-E-positive sorted cells were enriched for large granular lymphocytes (LGL) and contained all detectable NK activity as compared to the PNK-E-negative sorted cells. When analyzed by polyacrylamide gel electrophoresis, PNK-E antibody immunoprecipitated a protein from 125I-labeled peripheral blood lymphocyte (PBL) cell lysates that resolved as a single band of approximately 205 kDa under nonreducing conditions and as two bands of approximately 50 kDa and 47 kDa under reducing conditions. The present data demonstrate a functional association between PNK-E antigen and NK cell activation.     

beta-Endorphin augments the cytolytic activity and interferon production of natural killer cells

We have investigated the in vitro effects of the neurohormone beta-endorphin (b-end) on natural killer (NK) activity and interferon (IFN) production mediated by large granular lymphocytes (LGL). LGL-enriched fractions from peripheral blood mononuclear cells (PBMC) from normal human volunteers were obtained by fractionation over discontinuous Percoll gradients. LGL were preincubated with or without various concentrations of b-end or the closely related peptides alpha-endorphin (a-end), gamma-endorphin (g-end), or D-ALA2-beta-endorphin (D-ALA2-b-end), a synthetic b-end analogue. NK activity was assayed on 51Cr-labeled K562 target cells. Preincubation of LGL effectors (but not K562 targets) for 2 to 18 hr with concentrations of b-end between 10(-7) M and 10(-10) M produced significant augmentation of NK cytolytic activity (mean percentage increase: 63%). The classic opiate antagonist naloxone blocked the enhancing effect when used at a 100-fold molar excess relative to b-end. Neither a-end nor g-end could augment NK activity, whereas D-ALA2-b-end produced an enhancement comparable with that produced by b-end. In addition, incubation of LGL with b-end in the presence of phytohemagglutinin or poly I:C significantly augmented IFN production. These findings demonstrate that b-end enhances NK activity and IFN production of purified LGL, and suggests that b-end might bind to an opioid receptor on LGL that can be blocked by naloxone. These results lend support to the concepts of regulation of the immune response by neurohormones and the functional relationship between the nervous and immune systems.     

Association of decreased natural and antibody-dependent cellular cytotoxicity and production of natural killer cytotoxic factor and interferon in neonates

Cord blood lymphocytes (CBL) were compared with adult peripheral blood lymphocytes (a-PBL) for their: (i) natural killer (NK) and antibody-dependent cellular cytotoxic (ADCC) activities, (ii) target-binding capacity, (iii) ability to induce soluble natural killer cytotoxic factor (NKCF), (iv) interferon (IFN)-, interleukin 2 (IL-2)-, and lectin-induced augmentation of NK activity, and (v) ability to produce IFN against tumor targets in vitro. CBL depleted of adherent cells and Percoll-separated, NK-enriched subpopulations demonstrated significantly lower NK, ADCC, and target-binding activities compared to a-PBL. CBL produced significantly lower levels of NKCF directed against K562 tumor targets in comparison with a-PBL. Although the NK activity of CBL was not stimulated by either IFN or IL-2 to the same levels shown by a-PBL, the percentage enhancement of cytotoxicity of CBL by IFN and IL-2 was greater than that of a-PBL. Lectin-induced enhancement of cytotoxicity was significantly greater for CBL in comparison with a-PBL. Further, the ability of CBL lymphocytes to produce IFN-gamma in vitro against K562 target cells was significantly lower than that of adult PBL. These studies suggest an association between decreased NK, ADCC, and target-binding activities, induction of NKCF and IFN production by CBL, and increased susceptibility of neonates to infection.     

Immunoregulation by natural killer cells

Polyinosinic-polycytidilic acid (poly (I:C], a synthetic analog of viral double-stranded RNA (dsRNA), activates natural killer (NK) cells and inhibits induction or promotes termination of the primary IgM response in vivo. Suppression of responses was reproduced in vivo by interferons (IFN) which activate NK cells and in vitro by cells enriched for NK cells. The likelihood that NK cells may be involved in the normal regulation of IgM responses is supported by the following observations: immunization itself induces NK activity at times appropriate to account for termination, NK cells activated by immunization suppress in vitro, mice with high NK activity induced by immunization with one antigen have reduced responses to immunization with a second antigen, and mice with induced loss of NK activity fail to down-regulate IgM antibody responses normally.     

Fucose-activated killer (FAK) cells: anomalous killers with augmented cytotoxic activity

The effects of monosaccharides on various lymphocyte functions have provided useful probes for the study of cell-cell interactions. In this report, we show that a monosaccharide, alpha-L-fucose, significantly enhances the cytolytic capacity of MLC-induced or preincubated effector cells. The increase in activity was seen against cytotoxic T lymphocyte (CTL) targets (:relevant PHA blasts), natural killer cell (NK) targets (:K562), and natural cytotoxic cell (NC) targets (:MA-160). In addition, traditionally NK-insensitive targets (Raji cells, irrelevant and autologous PHA blasts) were lysed after preincubation of effector cells with fucose. Conversely, ADCC activity was not significantly increased with fucose induction. The addition of fucose directly to assay cultures did not enhance NK or CTL activity, whereas other sugars, such as alpha-methyl-D-mannoside and D-fructose, were inhibitory. The proportion of target-binding cells was not affected by preincubation with fucose, but the percentage of lytic conjugates was doubled. Significant augmentation of NK activity could be observed within 24 hr of incubation with alpha-L-fucose. Conversely, when fucose was added more than 24 hr after initiation of the culture, the increase in cytolytic activity was not observed. Parallel to the increase in cytolytic activity, after preincubation with alpha-L-fucose, an increase in the expression of a newly defined human NC cell marker, HNC-1A3, was observed. The HNC-1A3+ cells were not the major subpopulation responsible for fucose-induced activity, as ascertained by the use of positively sorted cells. The populations expressing antigens defined by the antibodies OKT8 and Leu-7 showed no quantitative change. The treatment of cells with OKM1 and complement (C) before culture eliminated fucose-enhanced killing, whereas similar treatment with OKT8 and C had no significant effect. The induction of fucose-activated killers (FAK) does not result in higher concentrations of interferon (IFN) in culture supernatants, in contrast to poly I:C, which induced both higher cytolytic activity and high titers of IFN. In addition, the induction of FAK was not sensitive to 100 ng/ml of cyclosporin A, suggesting that IL 2 did not play a major role in fucose activation of killing. These results provide strong evidence that alpha-L-fucose is capable of augmenting nonspecific activity by acting on OKM1+ precursors of cytotoxic cells and influencing a postbinding event.     

Augmentation of mouse natural killer cell activity by LS 2616, a new immunomodulator

The quinoline-3-carboxamide LS 2616 administered to mice in drinking water increased spontaneous cytotoxicity against YAC-1 cells in a dose-dependent manner. The enhancement of spontaneous cytotoxicity was found to be mediated by NK cells, as judged by their lack of adherence to nylon wool columns, relative resistance to treatment with antibodies to Thy-1.2 and complement, and almost total abrogation after depletion of asialo-GM1+ cells. Enhancement of NK activity was evident after 2 days of treatment, was maximal after 4 days, and remained elevated during the 14-day exposure period studied. NK activity returned to control levels 4 days after cessation of treatment. NK activity was significantly increased in spleen, peripheral blood, lymph nodes, and bone marrow of LS 2616-treated mice, while activity in peritoneal exudate cells and thymus remained low. LS 2616 was able to elevate NK activity in several mouse strains studied, including mice homozygous for the beige gene. Serum interferon levels were not increased during treatment with LS 2616. Combined injection of the interferon inducer Poly I:C and LS 2616 did not increase NK activity above that of animals injected with Poly I:C alone. However, Poly I:C, in contrast to LS 2616, increased NK activity in peritoneal exudate cells. Studies at the single cell level revealed that LS 2616 increased NK activity by increasing the number of lytically active cells via recruitment of new target-binding cells and not by increasing the lytic activity of pre-existing binders.     

Purification and target cell range of in vivo elicited blast natural killer cells

Blast natural killer (NK) cells were elicited in the spleens of mice by treatments with the interferon inducers lymphocytic choriomeningitis virus (LCMV) or polyinosinic-polycytidylic acid (poly I:C). The blast-NK cells, separated on the basis of size by centrifugal elutriation, were compared with blast cytotoxic T lymphocytes (CTL) generated during infection with LCMV. In vivo treatments with antibody to asialo GM1 (AGM1) blocked the appearance of blast-NK cells but not blast-CTL. Antibody and complement depletion experiments indicated that the blast-NK cells were AGM1+, NK 1.2+/-, Lyt-5+/-, Thy+/-, Qa-5/NK 1.1+, Lyt-2-, B23.1-, and J11d-. Blast-NK cells could be unequivocally distinguished from blast-CTL, because the blast-CTL were completely sensitive to treatments with anti-Lyt-2 and complement, whereas the blast-NK cells were completely resistant. The blast-NK cells were purified from populations of large-size cells by antibody and complement treatments that depleted the co-eluting monocyte/macrophages and polymorphonuclear leukocytes. The population resulting after separation from dead cells over Percoll gradients represented approximately 1% of the total spleen cells, contained greater than 60% large granular lymphocytes and mediated greater than 15% killing of YAC-1 target cells in a 4-hr 51Cr release assay at an effector to target cell ratio of 1:1. The purified blast-NK cells lysed a broad range of target cells at relatively low effector to target cell ratios. The order of sensitivity of the target cells was YAC-1 much greater than K562 approximately equal to L-929 much greater than P815, consistent with that reported for NK cell-mediated lysis. The ability of the blast-NK cells to mediate lysis of NK cells also was examined. The purified NK cells mediated significant levels of lysis against the NK-like cloned line, NK1B6B10, in a 51Cr release assay. Furthermore, the purified blast-NK cells mediated lysis of bound blast-NK cells in a single-cell agarose assay. These results indicate that highly purified blast-NK cells are exceptionally efficient at mediating lysis and suggest that NK cells may act to negatively regulate the proliferation of NK cells by lysing other NK cells.     

Regulation of human natural killing. II. Protective effect of interferon on NK cells from suppression by PGE2

Activation of human natural killer (NK) cells in vitro with interferon (IFN) and poly I:C results in a partial loss of sensitivity of these cells to suppression by PGE2. The acquired resistance to suppression can be induced with the large granular lymphocytes (LGL) in the absence of monocytes. With K562, HSB, and CEM used as NK target cells, the IFN-induced resistance to suppression by PGE2 is observed with all three target cells. Furthermore, ADCC activity of IFN-activated cells against tumor (SB-TNP) and erythroid (CRC-TNP) target cells is also less susceptible to suppression by PGE2. The dual effect of IFN on NK cells is prompt; the augmentation of NK activity and the acquired resistance to suppression by PGE2 can be seen after 3 hr of treatment with IFN. Both of these characteristics seem to be quite stable for at least 24 hr. Spleen cells from mice (CBA, C3H, and BALB/c nude) treated in vivo with poly I:C also acquire partial resistance to suppression by PGE2. Our data therefore suggest that IFN-stimulated NK cells are protected from suppression by PGE2. Biologically, the IFN-induced protective effect may be beneficial to host resistance to neoplasia.     

Human epidermal cells and squamous carcinoma cells synthesize a cytokine that augments natural killer cell activity

Normal as well as transformed epidermal cells (EC) have recently been reported to produce a cytokine--EC-derived thymocyte-activating factor (ETAF), which according to its biologic as well as biochemical properties is indistinguishable from macrophage-derived interleukin 1 (IL 1). In the present study, the effect of supernatants (SN) derived from normal EC and a human squamous carcinoma cell (SCC) line were tested for their effects on natural killer (NK) cell activity. EC- as well as SCC-derived SN were able to augment in vitro NK cell activity of peripheral blood lymphocytes against K 562 cells. In contrast, adherent cell-derived, IL 1-containing SN did not affect NK cell activity. Upon high-pressure liquid chromatography (HPLC) gel filtration, ETAF and the EC-derived NK cell activity-augmenting factor (ENKAF) exhibited a similar m.w. However, by using reverse-phase HPLC, ETAF and ENKAF eluted as distinct peaks of activity, indicating that SCC cell-derived ENKAF is different from ETAF. Furthermore, ENKAF does not contain interleukin 2 (IL 2) or interferon (IFN) activity. The enhancement of NK cell activity was dose dependent and evident after 20 hr of preincubation of effector cells. Pretreatment of target cells with ENKAF did not affect the susceptibility of the target cells. The NK activity of large granular lymphocytes (LGL) purified by discontinuous Percoll gradient centrifugation and further depleted of high-affinity sheep erythrocyte rosetting cells was enhanced by ENKAF. In contrast, no NK cell activity was expressed by LGL-depleted T cell populations before or after treatment with ENKAF. In a single cell cytotoxicity assay in agarose, the number of lymphocyte binding to K 562 was not affected by ENKAF, but the frequency of dead conjugated target cells and presumably of active killer cells was increased by pretreatment with ENKAF. Additional incubation of LGL with ETAF did not further increase ENKAF-mediated augmentation of NK activity. In contrast to ETAF, ENKAF was not chemotactic for polymorphonuclear leukocytes. These results indicate that normal as well as transformed EC release a unique cytokine--ENKAF--which augments NK cell activity of LGL but is distinct from ETAF, IL 2, and IFN.     

Inhibition of the calpain-mediated proteolysis of protein kinase C enhances lytic activity in human NK cells

Recent evidence from our laboratory has demonstrated that NK/LAK cell activation of human lymphocytes is protein kinase C (PKC)-dependent. Here, we have investigated the translocation of PKC in human NK cells exposed to sensitive targets or to PMA, a phorbol ester. In NK cells exposed to K562 for 6 hr, we observed a weak translocation of PKC whereas in NK cells exposed to PMA more than 90% of cytosolic PKC was translocated to the membrane in less than 5 min. Stimulation of NK cells with an NK-resistant target, however, did not translocate PKC even after 6 hr. Translocation of PKC to the membrane was followed by the appearance of PKM, the cytosolic calcium/phospholipid (Ca2+/PL)-independent form of PKC. The conversion of PKC to PKM was mediated by calpain, an intracellular calcium-dependent thiol proteinase. When we used two inhibitors of calpain, calpain inhibitor I (CI-I) and calpain inhibitor II (CI-II), both caused a dose-related enhancement of NK-CMC when the inhibitors were present throughout the 3-hr chromium release assay. This enhancement could be circumvented by PMA or by the PKC inhibitor H-7. CI-I and CI-II added together caused a greater increase in NK-CMC than when each was added alone. CI-I and CI-II also enhanced antibody-dependent cell-mediated cytotoxicity (ADCC), substantiating further our previous contention that the activation of both NK-CMC and ADCC may involve a common lytic pathway. Activation of NK cells with IL-2 for 18 hr at 37 degrees C was inhibited in the presence of CI-I. To investigate a possible feedback inhibition mechanism due to the buildup of PKC, we examined phosphatidylinositol (PI) metabolism in NK cells activated by IL-2 in either the presence or the absence of CI-I. We observed a significant decrease in PI turnover when NK cells, activated in the presence of IL-2 and CI-I, were stimulated with K562 as compared to NK cells activated by IL-2 alone, then stimulated with K562.     

Influence of cytokines on HIV-specific antibody-dependent cellular cytotoxicity activation profile of natural killer cells

There is growing interest in HIV-specific antibody-dependent cellular cytotoxicity (ADCC) as an effective immune response to prevent or control HIV infection. ADCC relies on innate immune effector cells, particularly NK cells, to mediate control of virus-infected cells. The activation of NK cells (i.e., expression of cytokines and/or degranulation) by ADCC antibodies in serum is likely subject to the influence of other factors that are also present. We observed that the HIV-specific ADCC antibodies, within serum samples from a panel of HIV-infected individuals induced divergent activation profiles of NK cells from the same donor. Some serum samples primarily induced NK cell cytokine expression (i.e., IFNγ), some primarily initiated NK cell expression of a degranulation marker (CD107a) and others initiated a similar magnitude of responses across both effector functions. We therefore evaluated a number of HIV-relevant soluble factors for their influence on the activation of NK cells by HIV-specific ADCC antibodies. Key findings were that the cytokines IL-15 and IL-10 consistently enhanced the ability of NK cells to respond to HIV-specific ADCC antibodies. Furthermore, IL-15 was demonstrated to potently activate "educated" KIR3DL1(+) NK cells from individuals carrying its HLA-Bw4 ligand. The cytokine was also demonstrated to activate "uneducated" KIR3DL1(+) NK cells from HLA-Bw6 homozygotes, but to a lesser extent. Our results show that cytokines influence the ability of NK cells to respond to ADCC antibodies in vitro. Manipulating the immunological environment to enhance the potency of NK cell-mediated HIV-specific ADCC effector functions could be a promising immunotherapy or vaccine strategy.     

Natural killer (NK) cells are present in mice with severe combined immunodeficiency (scid)

Spleen cells from C.B- 17 scid mice with severe combined immunodeficiency disease exhibit natural killer cell (NK) activity against YAC lymphoma targets in a standard 4-hr 51Cr release assay. The cytolytic activity is demonstrable only at high effector to target ratios but can be augmented at least sevenfold by the interferon inducer poly I:C. The pattern of target lysis is specific, because splenocytes from poly I:C-primed C.B-17 scid mice lyse NK-sensitive YAC cells and not the insensitive P815 mastocytoma. The presence of several NK-associated antigens on C.B-17 scid splenocytes was tested by pretreating cells with the appropriate antiserum plus complement before testing for NK activity. The results indicate that a proportion of NK effectors in C.B-17 scid mice bear surface NK 2.1 and Asialo GM1 but are negative for Thy-1.     

Modulation of stimulatory effects of poly(I:C) on natural cytotoxicity by anti-interferon

The effect of polyinosinic . polycytidylic acid [poly(I:C)] on tumor inhibition in the context of natural cytotoxicity enhancement prompted further assessment of mechanisms underlying these effects. In vivo inoculations of poly(I:C) led to dose-dependent cytotoxicity enhancement in splenic lymphocytes and nonrecruited peritoneal exudate cells (monocytes). Although cytotoxicity of macrophages and lymphocytes together was less than that seen with lymphocytes alone, addition of indomethacin to these samples did not enhance cytotoxicity. In vivo inoculation of anti-interferon prior to poly(I:C) treatment prevented poly(I:C)-induced enhancement of natural cytotoxicity. Tumor growth was significantly inhibited by poly(I:C) treatment. Prior inoculation of anti-interferon antiserum partially prevented such tumor inhibition. Taken together, the tumor-inhibitory effect of poly(I:C) in this model may be mediated by interferon production and, at least in part, by interferon-induced enhancement of natural cytotoxicity.     

Effect of human recombinant interferon on cytotoxic activity of natural killer (NK) cells and monocytes

Studies have been performed on the in vitro immunologic effects of homogeneous recombinant human leukocyte interferon, IFLrA. Large granular lymphocytes, enriched for natural killer (NK) cell activity, were pretreated wtih IFLrA or natural interferon preparations and then tested for augmentation of NK activity and of antibody-dependent cell-mediated cytoxicity (ADCC). Monocytes were tested for cytolytic and cytostatic activity in 48–72 hr radioisotopic assays performed in the presence or absence of interferon. Treatment with IFLrA caused significant augmentation of NK, ADCC, and monocyte-mediated cytotoxic activities. Even 10 units of IFLrA induced augmentation of NK activity, and 100 units or more boosted monocyte-mediated activity. The effects in each of these assays were species-specific, with no detectable effects on the activity of mouse effector cells. These results indicate that homogeneous recombinant interferon has potent in vitro immunomodulating effects and thus provide a basis for carefully examining the in vivo effects of this protein on host defenses in forthcoming clinical trials with cancer patients.     

Modulation of ongoing human immunoglobulin synthesis by natural killer cells

Freshly separated human NK cells (NKH-1+) inhibited IgE synthesis from IgE myeloma U266/AF-10 as much as 70% whereas they enhanced IgG and IgA synthesis 200 and 500% from the lymphoblastoid cell lines GM-1500 and GM-1056, respectively. The inhibition of IgE synthesis by NK cells was due to a direct cytolytic effect on AF-10. This could be reversed using K562 cells in a cold target competition assay. NK cells also inhibited spontaneous IgE as well as IgG and IgA synthesis from B cells of highly atopic donors. On the other hand the enhancement of Ig secretion by NKH-1+ cells was shown to be mediated by soluble factors released from NK cells. Furthermore when NK cells were preincubated with immune complexes (IgE-IC) constructed of human IgE and mouse IgG1 monoclonal anti-human IgE, inhibition of IgE synthesis was reversed, and in some cases actual enhancement of IgE synthesis was observed, while enhancement of IgG and IgA synthesis was not affected. In contrast to NK cells, T cells depleted of NK cells (T-NK), when activated by IgE-IC, suppressed IgE synthesis in an isotype specific fashion. Thus, NK and T-cell modulation of ongoing Ig synthesis involve distinct mechanisms.