Role Of Natural Killer Cells Research Articles

Role of natural killer cells in innate protection against lethal ebola virus infection.

Ebola virus is a highly lethal human pathogen and is rapidly driving many wild primate populations toward extinction. Several lines of evidence suggest that innate, nonspecific host factors are potentially critical for survival after Ebola virus infection. Here, we show that nonreplicating Ebola virus-like particles (VLPs), containing the glycoprotein (GP) and matrix protein virus protein (VP)40, administered 1–3 d before Ebola virus infection rapidly induced protective immunity. VLP injection enhanced the numbers of natural killer (NK) cells in lymphoid tissues. In contrast to live Ebola virus, VLP treatment of NK cells enhanced cytokine secretion and cytolytic activity against NK-sensitive targets. Unlike wild-type mice, treatment of NK-deficient or -depleted mice with VLPs had no protective effect against Ebola virus infection and NK cells treated with VLPs protected against Ebola virus infection when adoptively transferred to naive mice. The mechanism of NK cell–mediated protection clearly depended on perforin, but not interferon-γ secretion. Particles containing only VP40 were sufficient to induce NK cell responses and provide protection from infection in the absence of the viral GP. These findings revealed a decisive role for NK cells during lethal Ebola virus infection. This work should open new doors for better understanding of Ebola virus pathogenesis and direct the development of immunotherapeutics, which target the innate immune system, for treatment of Ebola virus infection.

Role of natural killer cells in the rejection process of corneal allografts in rats.

The exact mechanism of human corneal allograft rejection, which is the major cause of corneal transplant failure, remains unclear. We investigated the role of natural killer (NK) cells in rat corneal allograft rejection by examining the aqueous humor (AH) cell infiltrate on different postoperative days. Flow cytometric analysis was performed on the AH and submandibular draining lymph node (DLN) cells before transplantation and at different time points thereafter. In addition, we performed functional cytotoxicity assays with cells present in the AH during corneal rejection. We demonstrated a gradual increase in the absolute cell number of different hematopoietic subpopulations in the AH after allogeneic cornea transplantation. CD3CD4 cells, mainly monocytes and macrophages, were the predominant subpopulation 2 days after transplantation, followed by a successive relative increase of CD4 T cells, CD8 T cells, CD161 T cells, and NK cells. NK and CD161 T cells were present at a 10- to 15-fold higher percentage than in the DLN, suggestive of local expansion of these cells. A higher percentage of NK cells were CD8-negative compared with DLN NK cells. AH cells specifically lysed allogeneic cells, and this cytotoxicity was mainly attributable to NK cells but not to CD4 or CD8 T lymphocytes. These results confirm the crucial role of CD4 cells in the allogeneic corneal graft rejection process and implicate NK cells as possible mediators of the rejection.

The Emerging Role of Natural Killer Cells in Innate and Adaptive Immunity

In the early host defense system, effector function of natural killer (NK) cells results in natural killing against target cells such as microbe-infected, malignant, and certain allogenic cells without prior stimulation. NK cell cytotoxicity is selectively regulated by homeostatic prevalence between a repertoire of both activating and inhibitory receptors, and the discrimination of untransformed cells is achieved by recognition of major histocompatibility complex (MHC) class I alleles through inhibitory signals. Although it is well known that the bipotential T/NK progenitors are derived from the common precusor, functional mechanisms in terms of the development of NK cells remain to be further investigated. NK cells are mainly involved in innate immunity, but recent studies have been reported that they also play a critical role in adaptive immune responses through interaction with dendritic cells (DC). This interaction will provide effector functions and development of NK cells, and elucidation of its precise mechanism may lead to therapeutic strategies for effective treatment of several immune diseases. (Immune Network 2004;4(4):205-215)

A new role for natural killer cells, interleukin (IL)-12, and IL-18 in repeated implantation failure after in vitro fertilization

Objective To investigate the endometrial immunohistochemical staining of interleukin (IL)-12 and IL-18 and to quantify the CD56 bright natural killer (NK) cells in relation to Doppler vascular disorders. Design Controlled clinical study. Setting Research unit of a university hospital. Patient(s) Thirty-five women with repeated implantation failure after ET in IVF and 12 fertile control patients. Intervention(s) Ultrasound evaluation and endometrial biopsy on day 20. Main outcome measure(s) The balance between IL-12 and IL-18, the number of NK cells, and the vascular status among fertile and implantation failure patients. Result(s) The control patients displayed normal vascular parameters, a weak anti–IL-12 staining, a consistent moderate stromal anti–IL-18 staining, and fewer than 15 NK cells/field. This pattern was observed among only 17% (6/35) of the implantation failure group. The remaining patients fit into one of two patterns: [1] 37% (13/35) had more than 40 NK cells/field with a strong anti–IL-12 and/or anti–IL-18 staining, and [2] the remaining 46% (16/35) had a marked local depletion of IL-18 and IL-12. Respectively, 85% and 31% of two groups displayed abnormal vascular parameters. Conclusion(s) Distinctions between the different local dysregulations of the cytokine network may provide clues for further exploration and treatment.

A role for natural killer cells in the rapid death of cultured donor myoblasts after transplantation.

The rapid and massive death of cultured donor myoblasts after injection in vivo is a major problem for clinical myoblast transfer therapy (MTT). This study shows blood-borne factors are responsible and that ablating the host natural killer (NK) cell response greatly enhances the survival of such donor myoblasts. Cultured male donor myoblasts were injected into muscles of female host mice and surviving donor male DNA (myoblasts) quantified using a Y-chromosome specific (Y1) probe. Survival of donor myoblasts transfected with m144, a murine major histocompatibility complex (MHC) class I homologue that protects against NK attack, was quantified. In addition, donor myoblast survival was investigated in host mice following initial (before MTT) and sustained (repeatedly for 3 weeks after MTT) depletion of host NK1.1+ and CD4+/CD8+ cells using specific monoclonal antibodies (either alone or in combination) for up to 3 weeks after MTT, as well as in beige (deficient in NK activity) and in perforin-deficient mdx host mice. A major role for blood-borne factors (especially cells) was confirmed by MTT experiments in irradiated and perfused host mice. Substantially enhanced myoblast survival was seen with donor myoblasts modified by transfection with the m144 molecule or following antibody depletion of host NK1.1+ cells and in beige host mice. Other studies support some role for CD8+ but not CD4+ cells. These combined data support a central role for host NK cells in the rapid initial death of donor myoblasts. The demonstrated role of NK cells provides strategies to enhance the efficacy of clinical myoblast transplantation.

Natural killer cells in human peripheral blood and primary cutaneous natural killer cell lymphomas may express cutaneous lymphocyte antigen.

In normal human peripheral blood, cutaneous lymphocyte antigen is expressed by memory T cells, suggesting a specific tissue-homing population of T cells. In this study it is demonstrated that 6% of CD56 + natural killer cells in peripheral blood also express cutaneous lymphocyte antigen (CLA). It was also detected that most of the tumor cells in primary cutaneous nasal-type natural killer cell lymphomas were CLA-positive, whereas primary nasal natural killer cell lymphomas were CLA-negative. Although natural killer cells traditionally are known to be non-specific immune cells without antigen specificity and little is known about the role of natural killer cells in skin diseases, the results of this study suggest the existence of a subset of skin-associated CLA+ CD56+ natural killer cells. These natural killer cells may be related to the pathogenesis of primary cutaneous natural killer cell lymphomas.

An immunoregulatory role for natural killer cells in transplanted patients

An immunoregulatory role for natural killer cells in transplanted patients

Natural Killer and Dendritic Cell Contact in Lesional Atopic Dermatitis Skin –Malassezia-Influenced Cell Interaction

The regulation of dendritic cells is far from fully understood. Interestingly, several recent reports have suggested a role for natural killer cells in affecting dendritic cell maturation and function upon direct contact between the cells. It is not known if this interaction takes place also in vivo, or if a potential interaction of natural killer cells and dendritic cells would be affected by allergen exposure of the dendritic cells. The yeast Malassezia can act as an allergen in atopic eczema/dermatitis syndrome, and induce maturation of dendritic cells. Our aims were to study the distribution of natural killer cells in the skin from atopic eczema/dermatitis syndrome patients with the emphasis on possible natural killer cell-dendritic cell interaction, and to assess whether the interaction of Malassezia with dendritic cells would affect subsequent interaction between dendritic cells and natural killer cells. A few scattered natural killer (CD56+/CD3-) cells were found in the dermis of healthy individuals and in nonlesional skin from atopic eczema/dermatitis syndrome patients. In lesional skin and in biopsies from Malassezia atopy-patch-test-positive skin, however, natural killer cells were differentially distributed and for the first time we could show close contact between natural killer cells and CD1a+ dendritic cells. Dendritic cells preincubated with Malassezia became less susceptible to natural-killer-cell-induced cell death, suggesting a direct effect imposed by Malassezia upon interaction of dendritic cells with natural killer cells. These findings indicate that natural killer cells and dendritic cells can interact in the skin and that Malassezia affects the interaction between natural killer cells and dendritic cells. Our data suggest that natural killer cells may play a role in regulating dendritic cells in atopic eczema/dermatitis syndrome.

Inhibition Of Natural, Interleukin-2 Stimulated and Bacillus Calmette-Guerin Enhanced Cytotoxicity With Anti-CD16 Antibodies

We studied the cytolytic mechanism of nonstimulated, bacillus Calmette-Guerin (BCG) stimulated and interleukin (IL)-2 (Chiron Corp., Amsterdam, The Netherlands) stimulated peripheral blood mononuclear cells. We inhibited the cytotoxicity of nonstimulated, BCG stimulated and IL-2 stimulated peripheral blood mononuclear cells against various target cells using 3 monoclonal antibodies directed against the CD16 receptor of natural killer cells or alternatively monoclonal antibodies against the alpha and beta subunits of the IL-2 receptor complex (IL-2R). The main target cell was the poorly differentiated transitional cell line T24. Of the 3 anti-CD16 antibodies tested only CLB FcR-gran/1 effectively inhibited natural, IL-2 stimulated and BCG enhanced cytotoxicity. Cytotoxicity was also markedly diminished after depletion of CD16+CD56+/- cells with CLB FcR-gran/1. An hour of pretreatment with CLB FcR-gran/1 was enough to reduce significantly the level of cytotoxicity evoked by overnight stimulation with BCG or IL-2. Simultaneous administration of anti-IL-2Ralpha and anti-IL-2Rbeta significantly decreased the killing of target cells by BCG stimulated and IL-2 stimulated peripheral blood mononuclear cells. Within the stimulation times chosen the same killing mechanisms seemed to explain the nonstimulated, BCG stimulated and IL-2 stimulated cytotoxicity with CD16 positive cells as central effectors. Anti-CD16 antibodies may deliver a target cell independent down-regulatory signal to natural killer cells or alternatively mimic a nonIg ligand and block the detection of the target cell.

Functional analyses of natural killer cells in macaques infected with neurovirulent simian immunodeficiency virus

Clearance of HIV and SIV from the peripheral blood by the cellular immune system lessens the viral burden in infected individuals and may have an impact on virus infection of the CNS and the development of CNS lesions. However, the role of immune responses in preventing or limiting CNS infection has not been clearly defined. We investigated the role of natural killer cells in the outcome of SIV infection of macaques as a model for humans with AIDS and HIV encephalitis. In our study, six pig-tailed macaques were infected with the neurovirulent virus, SIV/17E-Fr, and the immunosuppressive virus, SIV/ DeltaB670, in a model system that causes rapid progression to AIDS and a high frequency of CNS lesions. NK lytic activity in each macaque was monitored longitudinally. In addition, we enumerated NK cells and tested macaque PBMC for the ability to lyse SIV-infected target cells. We found that there was a significant inverse correlation (P=0.02) between the robustness of NK response and the development of CNS lesions. Animals lacking strong NK cell responses developed more severe CNS lesions than those with robust NK responses did. Furthermore, pre-infection levels of NK activity were predictive of CNS lesion severity. The macaque with the most robust pre-infection NK activity developed no CNS lesions. In these infected macaques, NK activity was shown to be directed against SIV-infected cells. We extended these in vivo findings to delineate precisely which cell type was mediating this SIV-directed lysis. We used both macaque and human cells to demonstrate that the population that mediated anti-SIV and anti-HIV cytolytic effects was NK cells. Furthermore, we showed that this anti-SIV and anti-HIV cytolytic effect was directed at the envelope protein and not gag proteins. Thus, NK cells have the capacity to recognize and lyse cells expressing SIV and HIV antigens. These data support a role for NK cells in the modulation of CNS disease.

Possible role of natural killer cells in negative selection of mutant lymphocytes that fail to express the human leukocyte antigen-A2 allele

Increased frequencies of cells carrying mutations at several loci have been found in the blood cells of atomic-bomb (A-bomb) survivors upon testing four or five decades after the bombing. Interestingly, though, we have been unable to demonstrate any radiation-associated increases in the frequencies of mutant blood cells in which human leukocyte antigen (HLA)-A expression has been disrupted; this is true both of preliminary tests on the T cells of a small subset of A-bomb survivors and of the much more extensive study reported here in which we screened a much larger group of survivors for HLA-A2 loss mutations in B cells and granulocytes as well as in T cells. In attempting to explain our inability to detect any increases in HLA-A2-negative cell numbers in HLA-A2 heterozygous individuals exposed to A-bomb irradiation, we decided to test the hypothesis that HLA-A mutant lymphocytes might well have been induced by radiation exposure in much the same way as every other type of mutant we encountered, but may subsequently have been eliminated by the strong negative selection associated with their almost inevitable exposure to autologous natural killer (NK) cells in the bloodstream of each of the individuals concerned. We now report that mutant B lymphocyte cell lines that have lost the ability to express the HLA-A2 antigen do indeed appear to be much more readily eliminated than their parental heterozygous counterparts during co-culture in vitro with autologous NK cells. We make this claim first because we have observed that adding autologous NK cells to in vitro cultures of HLA-A2 heterozygous B or T cell lines appeared to cause a dose-dependent decrease in the numbers of HLA-A2-negative mutants that could be detected over a period of 3 days, and second because when we used peripheral blood HLA-A2 heterozygous lymphocyte cultures from which most of the autologous NK cells had been removed we found that we were able to detect newly-arising HLA-A2 mutant T cells in substantial numbers. Taken together, these results strongly support the hypothesis that autologous NK cells are responsible for eliminating mutant lymphocytes that have lost the ability to express self-HLA class I molecules in vivo, and may well therefore explain why we have been unable to detect increased frequencies of HLA-A2 mutants in samples from any of the 164 A-bomb survivors whose HLA-A2 heterozygote status made their lymphocytes suitable for our tests.

Enhanced Survival of Porcine Neural Xenografts in Mice Lacking CD1d1, But No Effect of NK1.1 Depletion.

Transplantation of embryonic porcine neurons may restore neurological function in patients with Parkinson's disease, if immunological rejection could be prevented. This study was performed to investigate the role of natural killer cells (NK cells) and NK1.1+ T cells (NK T cells) in the rejection of neural xenografts. A cell suspension was prepared from the ventral mesencephalon of 26 - 27-day-old pig embryos, and 2 μl was implanted in the right striata of mutant CD1d1 null (CD1.1-/-) mice, NK1.1-depleted mice, and controls. The CD1.1-/- mice are deficient in NK T cells and the antigen-presenting molecule CD1d1. Graft survival and host responses were determined immunohistochemically using markers for dopamine neurons, CD4-, CD8- cells, microglia, and macrophages. At 2 weeks, the grafts were significantly larger in CD1.1-/- mice, 0.09 ± 0.02 μl (mean ± SEM), compared with controls, 0.05 ± 0.01 μl. There was no significant difference between NK1.1-depleted mice, 0.02 ± 0.01 μl, and controls. At 5 weeks, two grafts were still present in the CD1-/- mice, whereas only scars remained in the controls and in the NK1.1-depleted mice. Immune reactions were strong at 2 weeks and less pronounced at 5 weeks in all groups. Microglial activation was lower in NK-depleted mice than in the controls at 2 weeks. In contrast to organ xenografting, NK1.1+ cells do not seem to be important mediators of the rejection of discordant cellular neural xenografts. However, our results suggest that the antigen-presenting molecule CD1d1 may be involved in the rejection process.

Role of natural killer cells in resistance against friend retrovirus-induced leukemia.

We have previously shown that immunization with a synthetic peptide that contains a single CD4(+) T-cell epitope protects mice against immunosuppressive Friend retrovirus infection. Cells producing infectious Friend virus were rapidly eliminated from the spleens of mice that had been immunized with the single-epitope peptide. However, actual effector mechanisms induced through T-helper-cell responses after Friend virus inoculation were unknown. When cytotoxic effector cells detected in the early phase of Friend retrovirus infection were separated based on their expression of cell surface markers, those lacking CD4 and CD8 but expressing natural killer cell markers were found to constitute the majority of effector cells that lysed Friend virus-induced leukemia cells. Depletion of natural killer cells by injecting anti-asialo-ganglio-N-tetraosylceramide antibody did not affect the number of CD4(+) or CD8(+) T cells in the spleen, virus antigen-specific proliferative responses of CD4(+) T cells, or cytotoxic activity against Friend virus-induced leukemia cells exerted by CD8(+) effector cells. However, the same treatment markedly reduced the killing activity of CD4(-) CD8(-) effector cells and completely abolished the effect of peptide immunization. Although the above enhancement of natural killer cell activity in the early stage of Friend virus infection was also observed in mice given no peptide, these results have demonstrated the importance and requirement of natural killer cells in vaccine-induced resistance against the retroviral infection.

The Role of Natural Killer Cells in the Induction of Autoimmune Gastritis

A number of experimental models of organ-specific autoimmunity involve a period of peripheral T cell lymphopenia prior to disease onset. In particular, experimental autoimmune gastritis, induced in susceptible mouse strains by neonatal thymectomy, is a CD4+ T cell mediated autoimmune disease. We have previously demonstrated that this disease displays the hallmarks of a Thl-mediated DTH inflammatory response with an essential role for IFN-γ very early in the pathogenesis of disease. Given the interplay between the innate and adaptive immune responses, a potential source of early IFN–γ production in these lymphopenic mice is the innate immune response. Here we have assessed the contribution of innate immunity to the induction of experimental autoimmune gastritis, in particular, the role of natural killer (NK) cells in production of IFN–γ. Analysis of NK cells and macrophages revealed no difference in either the number or activation status between euthymic and neonatally thymectomised mice. Furthermore, in vivo depletion of NK cells immediately after neonatal thymectomy of (BALB/cCrSlcxC57BL/6) Fl mice demonstrated no reduction in disease incidence compared to control groups of neonatally thymectomised mice. Therefore, we conclude that NK cells are not the primary source of IFN-γ required for the pathogenesis of autoimmune gastritis following neonatal thymectomy but rather the small cohort of T cells in the periphery of lymphopenic mice are likely to be responsible for the IFN-γ production.

Functional analyses of natural killer cells in macaques infected with neurovirulent simian immunodeficiency virus.

Clearance of HIV and SIV from the peripheral blood by the cellular immune system lessens the viral burden in infected individuals and may have an impact on virus infection of the CNS and the development of CNS lesions. However, the role of immune responses in preventing or limiting CNS infection has not been clearly defined. We investigated the role of natural killer cells in the outcome of SIV infection of macaques as a model for humans with AIDS and HIV encephalitis. In our study, six pig-tailed macaques were infected with the neurovirulent virus, SIV/17E-Fr, and the immunosuppressive virus, SIV/ DeltaB670, in a model system that causes rapid progression to AIDS and a high frequency of CNS lesions. NK lytic activity in each macaque was monitored longitudinally. In addition, we enumerated NK cells and tested macaque PBMC for the ability to lyse SIV-infected target cells. We found that there was a significant inverse correlation (P=0.02) between the robustness of NK response and the development of CNS lesions. Animals lacking strong NK cell responses developed more severe CNS lesions than those with robust NK responses did. Furthermore, pre-infection levels of NK activity were predictive of CNS lesion severity. The macaque with the most robust pre-infection NK activity developed no CNS lesions. In these infected macaques, NK activity was shown to be directed against SIV-infected cells. We extended these in vivo findings to delineate precisely which cell type was mediating this SIV-directed lysis. We used both macaque and human cells to demonstrate that the population that mediated anti-SIV and anti-HIV cytolytic effects was NK cells. Furthermore, we showed that this anti-SIV and anti-HIV cytolytic effect was directed at the envelope protein and not gag proteins. Thus, NK cells have the capacity to recognize and lyse cells expressing SIV and HIV antigens. These data support a role for NK cells in the modulation of CNS disease.

Role of natural killer cells in allograft rejection

Role of natural killer cells in allograft rejection

Role of natural killer cells in the rejection of transplanted hearts in the mouse model

Role of natural killer cells in the rejection of transplanted hearts in the mouse model

Early nonspecific immune responses and immunity to blood-stage nonlethal Plasmodium yoelii malaria.

The early role of natural killer cells and gamma delta T cells in the development of protective immunity to the blood stage of nonlethal Plasmodium yoelii infection was studied. Splenic cytokine levels were measured 24 h after infection of natural killer cell-depleted immunodeficient and littermate mice or transiently T-cell-depleted normal mice. Splenic gamma interferon levels were significantly increased above background in immunodeficient and littermate mice 24 h after infection. Depletion of natural killer cells resulted in markedly depressed gamma interferon levels and poor control of parasitemia, particularly in severe combined immunodeficient mice. In the littermates, gamma interferon levels were partially reduced, but parasitemias were resolved normally. However, in athymic mice, natural killer cell depletion had no effect on gamma interferon production. Levels of tumor necrosis factor alpha were increased in all animals 24 h after infection, and responses were not affected by natural killer cell depletion. However, in T-cell-depleted animals, both gamma interferon and tumor necrosis factor alpha levels were decreased 24 h after infection, and depleted mice were unable to control their parasitemia. These results suggest that the early production of both cytokines is important in the early control of parasitemia and that both natural killer and gamma delta T cells contribute equally towards their production. The data also suggest that the subsequent resolution of infection requires early production of gamma interferon, which might act by switching on the appropriate T-helper-cell subsets and other essential parasitotoxic effector mechanisms.

Vaccination with B16 melanoma cells expressing a secreted form of interleukin-1beta induces tumor growth inhibition and an enhanced immunity against the wild-type B16 tumor.

We have demonstrated previously that gene transfer of the mature human interleukin-1beta (IL-1beta) gene, fused to a signal sequence (ss), into mouse B16 melanoma cells results in an inhibition of their growth in vivo compared with control B16 cells. We here extend these results to show that intraperitoneal vaccinations with irradiated IL-1beta-secreting cells result in protection against subsequent subcutaneous challenge with wild-type (wt) B16 tumor cells in syngeneic C57BL/6 mice. This protection appears to be long-lasting, because rechallenge of cured mice 4 months after the first challenge also demonstrated resistance. In addition, we demonstrate that mice with established wt tumors subjected to therapeutic vaccinations with irradiated B16/ssIL-1beta cells starting 3 days after challenge isografting have a significantly inhibited tumor growth and 25-40% survival at the challenge doses given. In vitro coculture of spleen cells from B16/ssIL-1beta vaccinated animals and wt B16 cells induced an enhanced proliferative response, which correlated with elevated production of IL-2 and interferon-gamma. A significantly enhanced cytolytic activity against B16 wt target tumor cells was observed when spleen cells from B16/ssIL-1beta vaccinated mice were used as effector cells compared with spleen cells from control vaccinated mice. In vitro depletion experiments using anti-asialo GM1 revealed a prominent role for natural killer cells as effector cells. The data suggest that local IL-1beta secretion during the vaccination phase can provoke or augment protective immune responses to B16 melanoma cells, which are otherwise not recorded in mice bearing B16 tumors.

Role of natural killer cells and T cells in immune surveillance

A 61-year-old woman with extensive cutaneous vasculitis and hairy cell leukemia treated with cladribine is described. She achieved a dramatic hematological and dermatological response which has lasted more than 6 years. © 2000 Elsevier Science Ltd. All rights reserved.