Natural killer cells utilize both perforin and gamma interferon to regulate murine cytomegalovirus infection in the spleen and liver

Natural killer (NK) cells are critical for innate regulation of the acute phase of murine cytomegalovirus (MCMV) infection and have been reported to utilize perforin (Pfp)- and gamma interferon (IFN-gamma)-dependent effector mechanisms in an organ-specific manner to regulate MCMV infection in the spleen and liver. In this study, we further examined the roles of NK cells, Pfp, and IFN-gamma in innate immunity to MCMV infection. With the recently described NK cell-deficient (NKD) mouse, we confirmed previous findings that NK cells, but not NKT cells, are required for control of the acute phase of MCMV infection in spleen and liver cells. Interestingly, we found that Pfp and IFN-gamma are each important for regulating MCMV replication in both the spleen and the liver. Moreover, NK cells can regulate MCMV infection in the spleens and livers of Pfp(-/-) mice in a Pfp-independent manner and can use an IFN-gamma-independent mechanism to control MCMV infection in IFN-gamma(-/-) mice. Thus, contrary to previous reports, NK cells utilize both Pfp and IFN-gamma to control MCMV infection in the spleen and liver.     

Natural killer cells regulate T-cell proliferation during human parainfluenza virus type 3 infection

Human parainfluenza virus type 3 (HPIV3) is a major respiratory pathogen in humans. Failure to induce immunological memory associated with HPIV3 infection has been attributed to inhibition of lymphocyte proliferation. We demonstrate that the inability of mixed lymphocytes to respond to virally infected antigen-presenting cells is due to an interleukin-2-dependent, nonapoptotic mechanism involving natural killer (NK) cells and their influence is exerted in a contact-dependent manner. These results suggest a novel regulatory mechanism for NK cells during HPIV3 infection, offering an explanation for viral persistence and poor memory responses.     

Natural killer cells and autoimmunity

Antibodies directed to citrullinated proteins (anti-cyclic citrullinated peptide) are highly specific for rheumatoid arthritis (RA). Recent data suggest that the antibodies may be involved in the disease process of RA and that several RA-associated genetic factors might be functionally linked to RA via modulation of the production of anti-cyclic citrullinated peptide antibodies or citrullinated antigens.     

Natural killer cells and pregnancy

The fetus is considered to be an allograft that, paradoxically, survives pregnancy despite the laws of classical transplantation immunology. There is no direct contact of the mother with the embryo, only with the extraembryonic placenta as it implants in the uterus. No convincing evidence of uterine maternal T-cell recognition of placental trophoblast cells has been found, but instead, there might be maternal allorecognition mediated by uterine natural killer cells that recognize unusual fetal trophoblast MHC ligands.     

Natural killer cells and autoimmunity

Autoimmune diseases are often characterized as clinical syndromes caused by the inappropriate activation of T or B cells resulting in systemic or organ-specific damage. However, studies support a role for the innate immune system, and in particular natural killer (NK) cells, in stimulating or suppressing autoimmunity. This review focuses on recent research elucidating a potential immunoregulatory role for NK cells in modulating T and B cell-mediated autoimmunity.     

Natural killer cells and autoimmunity

Autoimmune diseases are often characterized as clinical syndromes caused by the inappropriate activation of T or B cells resulting in systemic or organ-specific damage. However, studies support a role for the innate immune system, and in particular natural killer (NK) cells, in stimulating or suppressing autoimmunity. This review focuses on recent research elucidating a potential immunoregulatory role for NK cells in modulating T and B cell-mediated autoimmunity.     

Similarities and distinctions between murine natural killer cells and lymphokine-activated killer cells

Pretreatment of mice with rabbit anti-asialo GM1 removes both natural killer (NK) effector cells and NK cells responsive to interleukin 2 (IL-2). Spleen cells from these mice do possess normal lymphokine-activated killer (LAK) activity. Young mice (less than 3 weeks of age) do not have NK activity and do not possess IL-2-inducible NK effector cells. Similarly to anti-asialo GM1-treated mice, LAK cells can be generated from these mice. While these experiments indicate clear distinctions between a certain level of NK and LAK precursors, the distinctions are not as clear when analyzing mice congenitally deficient in NK cells. Beige mice which lack NK effector cells and IL-2-inducible NK cells also lack the ability to generate LAK cells. The relationships and differences between NK- and LAK-cell precursors and effectors are discussed.     

Natural killer T cells: rapid responders controlling immunity and disease

Natural killer T (NKT) cells are a subset of T cells that share properties of natural killer cells and conventional T cells. They are involved in immediate immune responses, tumor rejection, immune surveillance and control of autoimmune diseases. Most NKT cells express both an invariant T cell antigen receptor and the NK cell receptor NK1.1, and are referred to as invariant NKT cells. This invariant T cell receptor is restricted to interactions with glycolipids presented by the non-classical MHC, CD1d. These NKT cells rapidly produce high levels of interleukin (IL)-2, IFN-gamma, TNF-alpha, and IL-4 upon stimulation through their TCR. Most also have cytotoxic activity similar to NK cells. NKT cells are involved in a number of pathological conditions, and have been shown to regulate viral infections in vivo, and control tumor growth. They may also play both protective and harmful roles in the progression of certain autoimmune diseases, such as diabetes, lupus, atherosclerosis, and allergen-induced asthma.     

Natural killer cells and natural killer T cells in Lyme arthritis

Introduction

Natural killer (NK) and natural killer T (NKT) cells provide a first line of defense against infection. However, these cells have not yet been examined in patients with Lyme arthritis, a late disease manifestation. Lyme arthritis usually resolves with antibiotic treatment. However, some patients have persistent arthritis after spirochetal killing, which may result from excessive inflammation, immune dysregulation and infection-induced autoimmunity.

Methods

We determined the frequencies and phenotypes of NK cells and invariant NKT (iNKT) cells in paired peripheral blood (PB) and synovial fluid (SF) samples from eight patients with antibiotic-responsive arthritis and fifteen patients with antibiotic-refractory arthritis using flow cytometry and cytokine analyses.

Results

In antibiotic-responsive patients, who were seen during active infection, high frequencies of CD56bright NK cells were found in SF, the inflammatory site, compared with PB (P <0.001); at both sites, a high percentage of cells expressed the activation receptor NKG2D and the chaperone CD94, a low percentage expressed inhibitory killer immunoglobulin-like receptors (KIR), and a high percentage produced IFN-γ. In antibiotic-refractory patients, who were usually evaluated near the conclusion of antibiotics when few if any live spirochetes remained, the phenotype of CD56bright cells in SF was similar to that in patients with antibiotic-responsive arthritis, but the frequency of these cells was significantly less (P = 0.05), and the frequencies of CD56dim NK cells tended to be higher. However, unlike typical NKdim cells, these cells produced large amounts of IFN-γ, suggesting that they were not serving a cytotoxic function. Lastly, iNKT cell frequencies in the SF of antibiotic-responsive patients were significantly greater compared with that of antibiotic-refractory patients where these cells were often absent (P = 0.003).

Conclusions

In patients with antibiotic-responsive arthritis, the high percentage of activated, IFN-γ-producing CD56bright NK cells in SF and the presence of iNKT cells suggest that these cells still have a role in spirochetal killing late in the illness. In patients with antibiotic-refractory arthritis, the frequencies of IFN-γ-producing CD56bright and CD56dim NK cells remained high in SF, even after spirochetal killing, suggesting that these cells contribute to excessive inflammation and immune dysregulation in joints, and iNKT cells, which may have immunomodulatory effects, were often absent.     

Natural killer and natural killer T cells in liver fibrosis

The liver lymphocyte population is enriched with natural killer (NK) cells, which play a key role in host defense against viral infection and tumor transformation. Recent evidence from animal models suggests that NK cells also play an important role in inhibiting liver fibrosis by selectively killing early or senescence activated hepatic stellate cells (HSCs) and by producing the anti-fibrotic cytokine IFN-γ. Furthermore, clinical studies have revealed that human NK cells can kill primary human HSCs and that the ability of NK cells from HCV patients to kill HSCs is enhanced and correlates inversely with the stages of liver fibrosis. IFN-α treatment enhances, while other factors (e.g., alcohol, TGF-β) attenuate, the cytotoxicity of NK cells against HSCs, thereby differentially regulating liver fibrogenesis. In addition, the mouse liver lymphocyte population is also enriched for natural killer T (NKT) cells, whereas human liver lymphocytes have a much lower percentage of NKT cells. Many studies suggest that NKT cells promote liver fibrogenesis by producing pro-fibrotic cytokines such as IL-4, IL-13, hedgehog ligands, and osteopontin; however, NKT cells may also attenuate liver fibrosis under certain conditions by killing HSCs and by producing IFN-γ. Finally, the potential for NK and NKT cells to be used as therapeutic targets for anti-fibrotic therapy is discussed. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.     

Natural killer cells, viruses and cancer

Natural killer cells are innate immune cells that control certain microbial infections and tumours. The function of natural killer cells is regulated by a balance between signals transmitted by activating receptors, which recognize ligands on tumours and virus-infected cells, and inhibitory receptors specific for major histocompatibility complex class I molecules. Here, we review the emerging evidence that natural killer cells have an important role in vivo in immune defence.     

Natural killer cells in meningiomas.

A monoclonal antibody against the surface marker IOT-10 of natural killer (NK) cells was used to investigate the presence of these cells in a series of twenty intracranial meningiomas. In all of these tumours, IOT-10 positive NK cells were found in small numbers, mainly distributed among the tumor cells. Two recurrent tumors showed a relatively high number of immunostained cells. The data obtained in the present study suggest that a NK-cell-mediated immunological response can occur in meningioma tissue.     

Natural killer cells in human colostrum

The presence of natural killer cells in human colostrum was disclosed with the use of a fluorochrome-labeled monoclonal antibody HNK-1 (Leu-7) that recognizes cells with natural killer and killer activity. Approximately 0.5% of total colostral cells were stained with this reagent. These cells were separated by the fluorescence-activated cell sorter and examined for their morphology by electron microscopy and for their cytotoxic activity against 51Cr-labeled K562 target cells. Two morphological types of natural killer cells were observed in colostrum: the first was represented by large cells with numerous vacuoles but without dense cytoplasmic granules; the second type, which occurred with lower frequency, resembled the large granular lymphocytes associated with natural killer activity in peripheral blood. The HNK-1-positive cells from colostrum displayed low cytotoxic activity against K562 target cells. Incubation of HNK-1-positive cells from peripheral blood with cell-free colostrum resulted in a dose-dependent inhibition of the cytotoxic activity. The functional changes were accompanied by morphological alterations which included degranulation and the formation of numerous vacuoles. The variances in the cytotoxic activity of peripheral blood HNK-1-positive cells suspended in different dilutions of colostrum suggest that this fluid contains humoral factors which modify morphology and function depending on their concentrations.     

Lysis of fresh murine mammary tumor cells by syngeneic natural killer cells and lymphokine-activated killer cells

Summary We have compared the ability of natural killer (NK) cells from two substrains of C3H mice that differ with respect to their susceptibility to the development of mammary adenocarcinomas to lyse fresh syngeneic mammary tumor cells. Single cell suspensions of mammary tumors from retired breeder females were used as targets in 22-h ⁵¹Cr-release cytotoxicity assays with syngeneic NK cells. Tumor cell suspensions were prepared by enzymatic digestion of finely minced tissue followed by centrifugation through a discontinuous Percoll gradient. Effector cells were prepared by passing spleen cells over nylon wool followed by centrifugation through Percoll fraction 7. Syngeneic NK cells had significant levels of lysis against 5/8 tumors studied. NK cells from low risk animals (C3Heb/FeJ) consistently demonstrated greater cytotoxicity against tumor cell preparations than did effectors from the high tumor substrain (C3H/OuJ). Study of cytocentrifuge preparations stained with Wright-Giemsa revealed that the two substrains were identical with respect to the number of azurophilic granules present in the cytoplasm of their NK cells. We have also shown that lymphokine-activated killer (LAK) cells can be generated from splenocytes in C3H mice. While LAK cells from both substrains were capable of lysing fresh syngeneic mammary tumor cells in vitro, LAK cells from the animals at high risk for the formation of mammary adenocarcinomas had greater cytotoxicity against tumor cell suspensions than LAK cells from the low tumor substrain.