Augmentation Of Natural Killer Activity Research Articles

NK Cells Augment Oncolytic Adenovirus Cytotoxicity in Ovarian Cancer

Oncolytic viruses (OVs) can trigger profound innate and adaptive immune responses, which have the potential both to potentiate and reduce the activity of OVs. Natural killer (NK) cells can mediate potent anti-viral and anti-tumoral responses, but there are no data on the role of NK cells in oncolytic adenovirus activity. Here, we have used two different oncolytic adenoviruses—the Ad5 E1A CR2-deletion mutant dl922-947 (group C) and the chimeric Ad3/Ad11p mutant enadenotucirev (group B)—to investigate the effect of NK cells on overall anti-cancer efficacy in ovarian cancer. Because human adenoviruses do not replicate in murine cells, we utilized primary human NK cells from peripheral blood and ovarian cancer ascites. Our results show that dl922-947 and enadenotucirev do not infect NK cells, but induce contact-dependent activation and anti-cancer cytotoxicity against adenovirus-infected ovarian cancer cells. Moreover, manipulation of NK receptors DNAM-1 (DNAX accessory molecule-1) and TIGIT (T cell immunoreceptor with Ig and ITIM domains) significantly influences NK cytotoxicity against adenovirus-infected cells. Together, these results indicate that NK cells act to increase the activity of oncolytic adenovirus in ovarian cancer and suggest that strategies to augment NK activity further via the blockade of inhibitory NK receptor TIGIT could enhance therapeutic potential of OVs.

HLA Mismatching Favoring Host-Versus-Graft NK Cell Activity Via KIR3DL1 Is Associated With Improved Outcomes Following Lung Transplantation.

Chronic lung allograft dysfunction (CLAD) is linked to rejection and limits survival following lung transplantation. HLA-Bw4 recipients of HLA-Bw6 grafts have enhanced host-versus-graft (HVG) natural killer (NK) cell activity mediated by killer cell immunoglobulin-like receptor (KIR)3DL1 ligand. Because NK cells maypromote tolerance by depleting antigen-presenting cells, we hypothesized improved outcomes forHLA-Bw4 recipients of HLA-Bw6 grafts. We evaluated differences in acute cellular rejection and CLAD-free survival across 252 KIR3DL1+ recipients from University of California, San Francisco (UCSF). For validation, we assessed survival and freedom from bronchiolitis obliterans syndrome (BOS), retransplantation, or death in 12845 non-KIR typed recipients from the United Network for Organ Sharing (UNOS) registry. Cox proportional hazards models were adjusted for age, gender, ethnicity, transplant type, and HLA mismatching. HVG-capable subjects in the UCSF cohort had a decreased risk of CLAD or death (hazard ratio [HR] 0.57, 95% confidence interval [CI] 0.36-0.88) and decreased early lymphocytic bronchitis. The HVG effect was not significant in subjects with genotypes predicting low KIR3DL1 expression. In the UNOS cohort, HVG-capable subjects had a decreased risk of BOS, retransplant, or death (HR 0.95, 95% CI 0.91-0.99). Survival improved with the higher-affinity Bw4-80I ligand and in Bw4 homozygotes. Improved outcomes in HVG-capable recipients are consistent with a protective NK cell role. Augmentation of NK activity could supplement current immunosuppression techniques.

Augmentation of natural killer cell activity in vitro and in vivo by sericin-derived oligopeptides

This study investigated the effects of sericin-derived oligopeptides on natural killer (NK) activity. In vitro exposure of human peripheral blood mononuclear cells with sericin-derived oligopeptides resulted in an augmentation of NK cell activity against K562 target cells and the effects appeared to be dose-related. Experiments designed to examine whether enhanced NK activity was due to direct or indirect activation of NK cells revealed that sericin oligopeptides did not induce activity of purified NK cells, and that sericin oligopeptides augmented NK activity indirectly by inducing the production of IL-2 and IFN-γ cytokines. In in vivo experimentation where mice were orally administered with sericin oligopeptides and splenic mononuclear cells tested against YAC-1 target cells, significant increase in NK activity was obtained compared to control mice. Elevated levels of IL-2 were also evident in all oligopeptides-treated groups. As demonstrated both in vitro and in vivo, these results indicate that sericin-derived oligopeptides have efficient NK-enhancing activity and suggest the potential therapeutic applications of such oligopeptides for functional improvement of NK cells, and possibly for treatment of tumor and infectious diseases in which NK activity contributes to host defense.

AntiTumor Mechanism of Recombinant Murine Interleukin-12 Vaccine

This study was designed to establish an interleukin-12 (IL-12)-expressing murine Lewis lung carcinoma (LLC) cell vaccine (LLC/murine IL-12 [mIL-12]) and assess its antitumor efficacy and mechanism in vivo. The recombinant IL-12 plasmid was transfected into LLC cells and screened by G418, and positive clones were obtained. C57BL/6 tumor-bearing mouse model was established and tumor-bearing mice were randomly divided into three groups (n = 20), that is, treated with an intratumoral injection of phosphate-buffered solution, blank plasmid, or LLC/mIL-12 vaccine, respectively, at days 0, 7, and 14. Tumor size was measured before and after treatment. Tumor growth curve was plotted, cytolytic T lymphocyte (CTL) activity assay and natural killer (NK) cell activity assay were performed, CD4(+) and CD8(+) T lymphocyte were quantitated using flow cytometry, and the expression of interferon-gamma (IFN-gamma), IL-12, and interferon-inducible protein-10 (IP-10) in serum was detected by ELISA. Microvessel density was determined by immunohistochemistry after all mice were euthanized at day 21. The study revealed suppressed tumor growth, elevated levels of IFN-gamma, IP-10, and IL-12, augmented NK and CTL cell activities, and decreased microvessel density of tumor tissues. There were abundant CD4(+) and CD8(+) T lymphocyte infiltration in the vaccine group. This study demonstrated that the antitumor mechanism of LLC/mIL-12 vaccine was to promote IFN-gamma and IL-12 secretion, augment the NK and CTL cell activities, and decrease the microvessel density of tumors.

Combination chemo-immunotherapy: kinetics of in vivo and in vitro generation of natural killer cells and lymphokine-activated killer cells in the rat

Rats received a single high dose of cyclophosphamide (Cy) (150 mg/kg), followed 48 h later (on day 0) by immunization with a T cell-dependent soluble antigen, ovalbumin in Freund's complete adjuvant (FCA). The effect of this treatment on lymphoid cell subpopulations in the spleen, natural killer (NK) cell and interleukin-2 (IL-2) induced lymphokine-activated killer (LAK) cell activity was examined. Cy (with and without ovalbumin) caused a large relative increase (by day 14) in splenic OX8+, OX19- cells with NK morphology. A marked relative increase in fresh NK cell activity was noted after Cy + ovalbumin, but not consistently after Cy alone. Elevated NK activity was Cy dose- and time-dependent, was evident within 7 days post Cy/ovalbumin and persisted for at least 28 days. Pooled splenic mononuclear cells (MNC), obtained 14 days after Cy/ovalbumin, lost all cytolytic activity against YAC-1 cells when cultured in the absence of human recombinant IL-2 (rIL-2). In contrast, similarly maintained cells from normal rats displayed NK activity higher than normal 'fresh' levels. Upon culture in medium containing 500 U/ml rIL-2, however, 'augmented' NK activity was equivalent, on a per-cell basis, in both normal and Cy/ovalbumin-pretreated groups. LAK activity generated in vitro (i.e. against NK-resistant target cells) was significantly lower in the latter group, and the overall yield of cells was reduced. By day 21 after Cy/ovalbumin, augmented NK activity was significantly greater than controls, on a per-cell and total culture yield basis. Moreover, LAK activity was now similar between groups. It is concluded that the chemotherapy/immunization protocol which we have used can greatly enhance NK activity in vivo and that these cells are responsive to induction of LAK activity by IL-2 in vitro.

Rotavirus induces proliferative response and augments non-specific cytotoxic activity of lymphocytes in humans

In vitro cell-mediated immune responses to rotavirus in humans were studied. Peripheral blood mononuclear cells (PBMC) of healthy adults proliferated in response to stimulation with the infectious and u.v.-inactivated Wa strain of human rotavirus, showing a maximum response on day 7 of culture; however, cord blood lymphocytes failed to respond to rotavirus. A cross-reactive proliferative response of PBMC detected by stimulation with the NCDV strain of bovine rotavirus suggests the existence of epitopes common to both human and bovine rotaviruses, which are recognized by human T lymphocytes. The phenotype of the majority of activated lymphocytes was CD3+4+8-, indicating that the cells mainly activated were helper T cells. Culture supernatants of PBMC stimulated with rotavirus contained interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In addition, PBMC stimulated with rotavirus demonstrated significantly enhanced cytotoxic activity against natural killer (NK) sensitive K562 cells as well as an NK-resistant Epstein-Barr virus-immortalized lymphoblastoid cell line (LCL). Treatment of PBMC with anti-CD16 or NKH1A monoclonal antibody, both of which react with most NK cells and lymphokine-activated killer cells and complement markedly reduced the cytotoxic activity against K562 and LCL. These results suggest that stimulation of human PBMC with rotavirus results in the production of lymphokines, such as IL-2 and IFN-gamma, by rotavirus-reactive helper T cells and that these lymphokines augment NK activity and generate other forms of non-specific cytotoxic human lymphocyte activity. These cell-mediated immune responses observed in the present in vitro study might play an important role in protection and recovery from rotavirus infection.

Differential augmentation ofin vivonatural killer cytotoxicity in normal primates with recombinant human interleukin-1 and granulocyte-macrophage colony-stimulating factor

The effect of recombinant human interleukin-1 (IL-1) alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), and combined factor therapy (CFT) on Rhesus monkey peripheral blood natural killer (NK) activity in vivo was compared. During a 14-day treatment period, IL-1-treated animals demonstrated a 170% increase in NK activity against K562 target cells by day 4, reaching maximal levels (300%) at day 16, and returning to baseline by day 30. NK activity of GM-CSF-treated monkeys increased slightly (60-100%) during days 4-12, as did saline-treated monkeys, but returned to baseline values by day 16. A delayed increase in NK activity resulted after GM-CSF treatment, reaching a peak (260%) on day 23 and remaining elevated through day 39. CFT resulted in a bimodal response pattern, with two peaks of NK activity: one at day 16 and a second at day 39. The first peak of activity (223%) was significantly less than the activity attained with IL-1 alone; the second peak (300%) was of greater duration and occurred later than the peak observed in GM-CSF-treated monkeys. Unlike IL-1, GM-CSF treatment did not lead to a immediate stimulation of NK activity; augmentation was delayed by more than 7 days post treatment. CFT results suggest that GM-CSF reduced the direct NK response to IL-1; while IL-1 led to an enhanced delayed NK response. Therefore, IL-1 and GM-CSF augment NK activity through different but interrelated pathways.

Soluble branched (1,4)‐β‐D‐glucans from Acetobacter species enhance antitumor activities against MHC class I‐negative and ‐positive malignant melanoma through augmented NK activity and cytotoxic T‐cell response

We previously found that an extracellular polysaccharide, AC-1, produced by Acetobacter polysaccharogenes composed of (1,4)-beta-D-glucan with branches of glucosyl residues showed a strong activity to induce production of interleukin (IL)-12 p40 and tumor necrosis factor-alpha by macrophage cell lines in vitro via Toll-like receptor-4 signaling. In the present study, we examined the effects of oral administration of AC-1 on protection against 2 types of murine B16 melanoma lines, major histocompatibility complex (MHC) class I-negative B16L and MHC class I gene-transfected B16K(b) cells. Mice were inoculated subcutaneously with B16L or B16K(b) cells on day 0 and administrated intragastrically with AC-1 or PBS once every 5 days from 1 day before tumor inoculation. The tumor growth was severely retarded in AC-1-treated mice after subcutaneous inoculation with B16L or B16K(b) cells. The AC-1-treated mice showed augmented natural killer (NK) cell activity against B16L cells, and in vivo depletion of NK cells by antiasialoGM1 antibody (Ab) treatment abrogated the antitumor activity in AC-1-treated mice. On the other hand, AC-1-treated mice inoculated with B16K(b) cells developed a significantly higher level of cytotoxic T-lymphocyte response against B16K(b) cells, and in vivo depletion of CD8(+) T cells by anti-CD8 mAb treatment abrogated the antitumor activity. Thus, AC-1 augmented antitumor activity against different tumors via augmentation of different antitumor mechanisms. These results suggest a possible prophylactic application of AC-1 for human neoplasms irrespective of expression levels of their MHC class I molecules.

In VitroAugmentation of Natural Killer Activity and Interferon-γ Production in Murine Spleen Cells withAgaricus blazeiFruiting Body Fractions

Aqueous extracts of the Agaricus blazei fruiting body prepared at different temperatures were fractionated by ethanol precipitation with various ethanol concentrations. The original aqueous extracts of A. blazei failed to stimulate natural killer (NK) cell activity in murine spleen cells in vitro, but the strongest effect was observed in a 30% ethanol-soluble-50% ethanol-insoluble fraction prepared from the extract at 40 degrees C (fraction A-50). Fraction A-50 also showed the strongest augmenting effect on interferon (IFN)-gamma production. This augmentation of NK activity and IFN-gamma production by fraction A-50 was completely abrogated by a heat treatment.

Interleukin-21 triggers both cellular and humoral immune responses leading to therapeutic antitumor effects against head and neck squamous cell carcinoma

Interleukin-21 (IL-21) plays important roles in the regulation of T, B, and natural killer (NK) cells. We hypothesized that the cytokine may provide a novel immunotherapy strategy for cancer by stimulating both Th1 and Th2 immune responses. In this context, antitumor immunity induced by IL-21 was examined in mice bearing subcutaneous head and neck squamous cell carcinomas (HNSCC). A plasmid vector encoding murine IL-21 was injected intravenously into mice with pre-established HNSCC tumors, either alone or in combination with a vector construct expressing IL-15. Cytotoxic T lymphocyte (CTL) and NK killing activities were evaluated by chrome release assays, while HNSCC-specific antibody was examined by flow cytometry and ELISA. Significant antitumor effects were obtained by repeated transfection with either the IL-21 or the IL-15 gene. Co-administration of both cytokine genes resulted in increased suppression of tumor growth, significantly prolonging the survival periods of the animals. Thirty percent of the tumor-bearing mice that received the combination therapy survived for more than 300 days, completely rejecting rechallenge with the tumor at a distant site. IL-21 induced significant elevation of HNSCC-specific CTL activity, while IL-21 and IL-15 augmented NK activity in an additive manner. IL-21 gene transfer also promoted the production of tumor-specific IgG. In vivo transduction of the IL-21 gene elicits powerful antitumor immunity, including both humoral and cellular arms of the immune response, and results in significant suppression of pre-established HNSCC. Co-transfer of the IL-15 gene further improved the therapeutic outcome, mainly by augmenting NK tumoricidal activity. The biological effects of IL-21 may be in sharp contrast to those of conventional Th1 and Th2 cytokines, suggesting intriguing implications of this cytokine for the classical concept of Th1 vs. Th2 paradigm.

Cancer immunotherapy with natural killer cells

Natural killer (NK) cells were first identified for their ability to kill tumor cells of different origins. They were subsequently found to be able to kill some normal cells, especially those infected by certain viruses. Natural killer cells are a distinct lymphocytic population, with the morphology of large granular lymphocytes, and they lack surface Ig or T-cell markers. Natural killer cytotoxicity is enhanced in vitro in the presence of cytokines such as interleukin-2 and interferon-α. However, when used in immunotherapy, these cytokines have not consistently augmented NK activity or shown antitumor effects. One explanation for this divergence is that NK cell activity is suppressed in tumor tissues by various factors, including reactive oxygen species produced by infiltrating monocytes and macrophages. Agents that inhibit the generation of reactive oxygen species, such as histamine, may abrogate the suppression exerted on NK cells by monocytes/macrophages, therefore offering potential therapeutic benefit as immunoadjuvants. Semin Oncol 29 (suppl 7):27-30. Copyright 2002, Elsevier Science (USA). All rights reserved.

Interleukin-12 augments cytolytic activity of peripheral blood mononuclear cells against autologous lung cancer cells in combination with IL-2

The majority of patients with advanced lung cancer die within a few years. Accordingly, new therapeutic modalities need to be developed. Interleukin (IL)-12 was previously known as natural killer (NK) cell stimulatory factor or cytotoxic lymphocyte maturation factor. By virtue of its effects on T cells and NK cells, IL-12 seems to be one of the key cytokines that regulates cell-mediated anti tumor immune responses. Recently, there has been a substantial interest in the potential applications of IL-12 in the treatment of lung cancer. However, there have been no reports about the effect of IL-12 on peripheral blood mononuclear cells (PBMCs) obtained from lung cancer patients in an autologous setting. In this study, we examined the cytotoxicity of PBMC activated by IL-2, IL-12 or both against K562 or autologous lung cancer cells. In contrast to the effect of IL-2 on NK activity, IL-12 alone augmented NK activity against K562 cells, but not against autologous lung cancer cells. IL-12 augmented the IL-2 mediated cytotoxicity of PBMC against both K562 and autologous lung cancer cells. In the absence of IL-2, IL-12 alone cannot induce an autologous anti-tumor effect in vivo. In summary, our results clearly demonstrated that IL-12 can augment the cytolytic activity of PBMC against K562 and autologous lung cancer cells when combined with IL-2, although, IL-12 alone was unable to induce a marked increase in the cytotoxicity against autologous lung cancer cells. These results suggest that an administration of IL-12 in combination with IL-2 may be a useful therapeutic option for solid tumors.

Nigerooligosaccharides augments natural killer activity of hepatic mononuclear cells in mice

Nigerooligosaccharides (NOS), a mixture of nigerose and nigerosylmaltooligosaccharides, is immunopotentiating oligosaccharides found in foodstuffs. Augmentation of natural killer (NK) activity by NOS was studied in vitro and in vivo in mice. In vitro treatment of hepatic mononuclear cells (MNC) from normal mice with 1 μg/ml NOS 17 h or just prior to the cytotoxicity assay enhanced their cytotoxicity against YAC-1 cells. NK activity of hepatic MNC was also enhanced in mice injected intraperitoneally with 0.4 mg NOS or in mice given 1% NOS solution orally as a drinking fluid. In association with the augmentation of NK activity, increase in the liver weight induced by intravenous inoculation of EL-4 tumor cells was significantly suppressed by intraperitoneal pretreatment with 0.4 mg NOS. Moreover, drinking 1% NOS significantly improved the survival curve of mice intravenously inoculated with EL-4 cells. Our results suggest that the immunopotentiating activity of NOS is exerted partly through the augmentation of NK activity.

Reduced NK activity in pulmonary tuberculosis patients with/without HIV infection: identifying the defective stage and studying the effect of interleukins on NK activity

Setting: A study was undertaken to understand the non-major histocompatibility restricted cytotoxicity in order to delineate the role of natural killer (NK) cells towards the development of host immunity to tuberculosis.Objective: (a) Enumeration of NK cell numbers and activity in normal individuals (35), pulmonary tuberculosis patients (32), HIV-infected TB patients (20) and patient contacts (10), (b) effect of treatment on NK status, (c) enumeration of effector-target conjugates and (d) effect of in vitro cytokine stimulation on NK activity.Design: NK cells were enumerated by flowcytometry. NK activity was assessed by chromium release assay before and after treatment for tuberculosis and after stimulation with IL-2/IL-12. Novel flow cytometric method was standardized to enumerate effector-–target conjugates.Results: No changes were seen between different groups as far as number of NK cells and relative proportions of different conjugate types were concerned, but there was a decrease in NK activity in TB patients which increased after treatment. Augmentation of NK activity was observed after cytokine stimulation.Conclusion: Lowered NK activity during tuberculosis infection is probably the ‘effect’ and not the ‘cause’ for the disease as demonstrated by the follow-up study. Similar number of conjugates in both groups indicates no defect in the recognition/binding step but probably at subsequent steps of the cytotoxic process. Augmentation of NK activity with cytokines implicates them as potential adjuncts to tuberculosis chemotherapy.

Simultaneous exposure to interleukin-18 and interleukin-10 in vitro synergistically augments murine spleen natural killer cell activity.

Interleukin-18 (IL-18) enhances interferon gamma (IFNgamma) production and natural killer (NK) cell activity, and elicits protective antitumor effects in vivo. IL-18 and IL-12 synergistically augment IFNgamma production reportedly because IL-12 enhances IL-18 receptor (IL-18R) expression. We now show that IL-18 also synergizes with IL-10 to augment murine splenic NK activity against Yac-1 cells in a standard 4-h chromium-release assay, but IFNgamma production is only slightly enhanced. This pattern of NK activity was also observed with severe combined immunodeficient (SCID) mouse spleen cells indicating that the cytokines were not acting on T or B cells. The cytokines had no priming activity on the spleen cells and, when cells were left unstimulated for 24 h in culture, little NK activity was induced when IL-18 was added for the next 24 h. The reverse transcriptase/polymerase chain reaction revealed that IL-18 receptor (IL-18R) mRNA was expressed early during in vitro spleen cell culture but none was expressed after culture for 24 h regardless of the stimulus. Binding of 125I-labeled IL-18 revealed that exposure to IL-10 only slightly increased IL-18R expression. Expression of perforin mRNA was constitutive and was unaffected by the cytokines; however, Fas ligand (FasL) mRNA expression was strong in cultures with IL-18 alone or combined with IL-10. When Fas-expressing cells and their parental cells were used as targets, weak Fas-mediated cytolytic activity was observed after exposure to IL-18, and this was further enhanced by combination with IL-10. Finally, the augmentation of NK activity was abrogated by the inhibitor concanamycin A, indicating that the enhanced NK activity is perforin-dependent.

Age-dependent effect of pituitary transplants on immune responses in rat spleen: modulatory effect of cyclosporine.

Male rats were grafted an anterior pituitary within breast muscles on day 5 or under the kidney capsule on day 30 or 60 of life. On the 70th day of life (rats operated on the 5th or 30th day) or on the 100th day of life (rats operated on the 60th day), rats were injected subcutaneously with Freund's complete adjuvant, being killed 2 days later. Rats that had received a pituitary graft on the 30th day showed a greater degree of hyper-prolactinemia than rats grafted on the 5th or 60th day. Analyzed as main factors in a factorial analysis of variance (ANOVA), pituitary transplants augmented splenic natural killer (NK) activity and lipopolysaccharide (LPS)- and concanavalin A (Con A)-induced cell proliferation, and decreased splenic cell number. As indicated by significant interactions between treatment and age of transplantation in a factorial ANOVA, splenic NK activity augmented in rats grafted on the 30th day of life, while LPS and Con A splenic cell proliferation augmented in rats grafted neonatally. Spleen cellularity decreased after pituitary transplants in 30- and 60-day-old rats. In a second study, the effect of cyclosporine on spleen immune responses was tested by administering cyclosporine (5 mg/kg) or vehicle to rats grafted as in experiment 1 for 5 days before sacrifice. Cyclosporine decreased splenic NK activity and LPS- and Con A-induced cell proliferation regardless of the presence of a pituitary graft. In rats grafted on the 30th day of life, cyclosporine reversed the effect of pituitary grafts on splenic NK activity, and ectopic pituitary augmenting NK activity in vehicle-treated rats while decreasing it in cyclosporine-injected rats. Cyclosporine reversed the inhibitory effect of pituitary transplants on spleen cell number. The high circulating prolactin levels found in rats with pituitary grafts were decreased by cyclosporine administration. The results are compatible with age-dependent promoting and inhibitory effects of hyperprolactinemia on the immune responses of the spleen, which were antagonized by cyclosporine immunosuppression.

Antiviral activity of biological response modifiers in a murine model of aids. requirement for augmentation of natural killer cell activity and synergy with oral AZT

We employed the Rauscher murine leukemia virus (RMuLV) as a murine retrovirus model of AIDS, to test biological response modifiers (BRM) and antiviral agents for potential therapeutic activity against the human immunodeficiency virus (HIV). We examined the relationship between the augmentation of natural killer (NK) cell activity and antiviral efficacy of a series of BRM, most of which are known inducers of interferon, in this model. Poly [I,C]-LC, MVE-2, and CL 246,738, but not Ampligen, soluble glucan, or 7-thia-8-oxoguanosine, consistently produced antiviral activity. In addition, the combination of suboptimal doses of oral 3'-azido-3'-deoxythymidine (AZT) (in drinking water) and poly [1,C]-LC produced a synergistic antiviral effect. With all the BRM tested, a consistent pattern emerged, namely that antiviral activity always correlated with the augmentation of splenic NK cell activity in infected animals. For instance, poly [I,C]-LC boosted NK activity much more in infected mice treated therapeutically (treatment initiated after infection) than prophylactically (treatment initiated before infection), and it had greater antiviral activity therapeutically than prophylactically. For the BRM tested, antiviral activity did not occur without augmentation of NK activity in infected mice. In contrast, augmentation of NK activity in uninfected mice bore no relationship to antiviral activity. Furthermore, elimination of NK cells by treating mice with anti-asialo GM 1 abolished the antiviral activity of poly [I,C]-LC. Although splenic NK activity was ablated by anti-asialo GM, serum interferon levels were not affected by this treatment. These results point to a causal connection between the augmentation of NK cell activity and the antiviral efficacy of these BRM in this murine AIDS model. NK cells thus appear to play a key role in resistance to this retrovirus, as has been suggested for HIV.

The concurrent administration of OK432 augments the antitumor vaccination effect with tumor cells by sustaining locally infiltrating natural killer cells.

The effect of a local injection with a streptococcal preparation OK432 on the antitumor vaccination with tumor cells was investigated. Natural killer (NK) cells, which were detected by anti-NK1.1 monoclonal antibody (mAb), increased in the peritoneal exudate cells after an intraperitoneal (i.p.) injection with syngeneic B16 melanoma cells. Furthermore, a concurrent i.p. injection with OK432 efficiently sustained the locally infiltrating NK cells. The OK432 treatment also sustained the augmented NK and lymphokine-activated killer activities in the peritoneal exudate cells. This treatment also increased the ability of the locally infiltrating NK cells to produce interferon gamma in response to the tumor cells. In addition, the concurrent i.p. injection with OK432 in combination with the tumor cells enhanced the capacity of the spleen cells to turn into anti-(B16 melanoma) cytotoxic T lymphocytes after in vitro restimulation. This augmenting effect of OK432 was dependent on NK cells. Moreover, the concurrent injection with OK432 at the time of anti-tumor vaccination significantly enhanced the protective immunity against B16 melanoma at the rechallenge. Taken together, these findings indicate that a concurrent local injection with OK432 in combination with tumor cells efficiently augments the antitumor vaccination effect, in part, by sustaining the locally infiltrating activated NK cells.

Mycoplasma arthritidis mitogen up-regulates human NK cell activity.

While the effects of superantigens on T lymphocytes are well characterized, how superantigens interact with other immune cells is less clear. This report examines the effects of Mycoplasma arthritidis mitogen (MAM) on human natural killer (NK) cell activity. Incubation of peripheral blood mononuclear cells (PBMC) with MAM for 16 to 20 h augmented NK cytotoxicity (against K562) in a dose-dependent manner (P < or = 0.05). Superantigen-dependent cellular cytotoxicity, an activity of superantigen-activated cytotoxic T cells, was not involved in lysis of K562 cells because the erythroleukemic tumor target cells expressed no class II major histocompatibility complex by fluorescence-activated cell sorter analysis. Kinetic experiments showed that the largest increase in NK activity induced by MAM occurred within 48 h. Incubation with MAM caused a portion of NK cells to become adherent to tissue culture flasks, a quality associated with activation, and augmented NK activity was found in both adherent and nonadherent subpopulations. Experiments using cytokine-specific neutralizing antibodies showed that interleukin-2 contributed to enhancement of the NK activity observed in superantigen-stimulated PBMC. Interestingly, MAM was able to augment NK lysis of highly purified NK (CD56+) cells in the absence of other immune cells in 9 of 12 blood specimens, with the augmented lytic activity ranging from 110 to 170% of unstimulated NK activity. In summary, data presented in this report show for the first time that MAM affects human NK cells directly by increasing their lytic capacity and indirectly in PBMC as a consequence of cytokines produced by T cells. Results of this work suggest that, in vivo, one consequence of interaction with superantigen-secreting microorganisms may be up-regulation of NK lytic activity. These findings may have clinical application as a means of generating augmented NK effector cells useful in the immunotherapy of parasitic infections or neoplasms.

Silicone-induced modulation of natural killer cell activity.

Current controversy regarding the effects of silicone gel mammary implants on the immune system has led to increased focus on the potential biological activity of silicone materials. Studies were undertaken in the B6C3F1 mouse to evaluate the immunotoxicological effects of the following components of a mammary gel prosthesis: polydimethylsiloxane fluid, silicone gel, elastomer shell and a polyurethane implant cover. Material was implanted subcutaneously (s.c.) for either 10 or 180 days. The only toxicological or immunological parameter which differed from control values was the natural killer (NK) cell activity in gel implanted mice. In these animals, basal NK activity was decreased. NK activity was comparably inhibited in female Fischer 344 rats implanted with silicone gel following short term (14 or 30 days) as well as chronic (1 year) exposure. The response was variable in both the rat and mouse. Host resistance to B16F10 melanoma in the mouse is known to be related to NK activity. Despite suppression of NK activity following gel implantation, host resistance was unaltered. Inhibition of NK activity by the administration of anti-asialo GM1 indicated that resistance was not adversely affected until NK activity was decreased by 40 to 50%. As with basal NK activity, augmented NK activity was inhibited in gel implanted rats when compared to controls. Administration of polyinosinic:polycytidylic acid to gel implanted rats resulted in an increase of approximately 65% in NK activity compared to gel implanted controls. This level of augmented NK activity was significantly less than the level of augmented NK activity in vehicle implanted animals where 100% enhancement in NK activity was noted. The results of these studies indicate that (1) NK cytolytic activity is altered in two animal models, the mouse and rat, although the results were variable, that (2) the level of suppression noted in the mouse is ineffective when compared to the level of suppression required to alter host resistance to B16F10 melanoma and that (3) the gel implanted animals exhibit a suppressed response to NK augmentation.