Search

Immunotherapy has revolutionized cancer therapy by reactivating tumour‐resident cytotoxic lymphocytes. More recently, immunotherapy has emerged to restore immunity against infectious agents, including bacterial infections. Immunotherapy primarily targets inhibitory pathways in T cells, however interest in other effector populations, such as natural killer (NK) cells, is growing. We have previously discovered that NK cell metabolism, proliferation and activation can be neutralized through the immunosuppressive transforming growth factor (TGF)‐β pathway by inducing plasticity of NK cells and differentiation into innate lymphoid cell (ILC)1‐like subsets. NK cells are also regulated through cytokine‐inducible SH2‐containing protein (CIS), which is induced by interleukin (IL)‐15 and is a potent intracellular checkpoint suppressing NK cell survival and function. Targeting these two distinct pathways to restore NK cell function has shown promise in cancer models, but their application in bacterial infection remains unknown. Here, we investigate whether enhancement of NK cell function can improve anti‐bacterial immunity, using Salmonella Typhimurium as a model. We identified conversion of NK cells to ILC1‐like for the first time in the context of bacterial infection, where TGF‐β signalling contributed to this plasticity. Future study should focus on identifying further drivers of ILC1 plasticity and its functional implication in bacterial infection model. We further describe that CIS‐deficient mice displayed enhanced pro‐inflammatory function and dramatically enhanced anti‐bacterial immunity. Inhibition of CIS may present as a viable therapeutic option to enhance immunity towards bacterial infection. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells protect against intracellular infection and cancer. These properties are exploited in oncolytic virus (OV) therapy, where antiviral responses enhance anti‐tumour immunity. We have analysed the mechanism by which reovirus, an oncolytic dsRNA virus, modulates human NK cell activity. Reovirus activates NK cells in a type I interferon (IFN‐I) dependent manner, inducing STAT1 and STAT4 signalling in both CD56dim and CD56bright NK cell subsets. Gene expression profiling revealed the dominance of IFN‐I responses and identified induction of genes associated with NK cell cytotoxicity and cell cycle progression, with distinct responses in the CD56dim and CD56bright subsets. However, reovirus treatment inhibited IL‐15 induced NK cell proliferation in an IFN‐I dependent manner and was associated with reduced AKT signalling. In vivo, human CD56dim and CD56bright NK cells responded with similar kinetics to reovirus treatment, but CD56bright NK cells were transiently lost from the peripheral circulation at the peak of the IFN‐I response, suggestive of their redistribution to secondary lymphoid tissue. Coupled with the direct, OV‐mediated killing of tumour cells, the activation of both CD56dim and CD56bright NK cells by antiviral pathways induces a spectrum of activity that includes the NK cell‐mediated killing of tumour cells and modulation of adaptive responses via the trafficking of IFN‐γ expressing CD56bright NK cells to lymph nodes. [ABSTRACT FROM AUTHOR]

Summary: Tbet‐deficient mice have reduced natural killer (NK) cells in blood and spleen, but increased NK cells in bone marrow and lymph nodes, a phenotype that is thought to be the result of defective migration. Here, we revisit the role of Tbet in NK cell bone marrow egress. We definitively show that the accumulation of NK cells in the bone marrow of Tbet‐deficient Tbx21−/− animals occurs because of a migration defect and identify a module of genes, co‐ordinated by Tbet, which affects the localization of NK cells in the bone marrow. Cxcr6 is approximately 125‐fold underexpressed in Tbx21−/−, compared with wild‐type, immature NK cells. Immature NK cells accumulate in the bone marrow of CXCR6‐deficient mice, and CXCR6‐deficient progenitors are less able to reconstitute the peripheral NK cell compartment than their wild‐type counterparts. However, the CXCR6 phenotype is largely confined to immature NK cells, whereas the Tbet phenotype is present in both immature and mature NK cells, suggesting that genes identified as being more differentially expressed in mature NK cells, such as S1pr5, Cx3cr1, Sell and Cd69, may be the major drivers of the phenotype. [ABSTRACT FROM AUTHOR]

Summary: Cytotoxic activity mediated by CD8+ T cells is the main signature of the immunopathogenesis of cutaneous leishmaniasis (CL). Here, we performed a broad evaluation of natural killer (NK) cell phenotypic and functional features during cutaneous leishmaniasis. We demonstrate for the first time that CL patients present the accumulation of circulating NK cells with multiple features of replicative senescence including low proliferative capacity and shorter telomeres, elevated expression of CD57, KLRG1 but diminished CD27 stimulatory receptor expression. Moreover, they exhibited higher cytotoxic and inflammatory potential than age‐matched controls. The accumulation of circulating senescent NK cells (CD56dim CD57bright) correlated positively with skin lesion size in the same patients, suggesting that they, like circulating senescent CD8+ T cells, may contribute to the immunopathology of CL. However, this senescent population had lower cutaneous lymphocyte antigen expression and so had diminished skin‐homing potential compared with total or senescent CD8+ T cells. This was confirmed in CL skin lesions where we found a predominance of CD8+ T cells (both senescent and non‐senescent) that correlated with the severity of the disease. Although there was also a correlation between the proportions of senescent NK cells (CD56+ CD57+) in the skin and lesion size, this was less evident. Collectively our results demonstrate first‐hand that senescent cytotoxic cells may mediate skin pathology during human cutaneous leishmaniasis. However, as senescent cytotoxic CD8+ T cells predominate in the skin lesions, they may have a greater role than NK cells in mediating the non‐specific skin damage in CL. [ABSTRACT FROM AUTHOR]

Summary: Down‐regulated chemerin expression has been reported to correlate with poor prognosis of several types of cancer including melanoma. All‐trans retinoic acid (atRA) is a potent inducer of chemerin, and we previously reported that atRA inhibited murine melanoma growth through enhancement of anti‐tumor T‐cell immunity. Here, we aimed to investigate whether loss of endogenous chemerin accelerated melanoma growth and whether chemerin was involved in the melanoma‐inhibitory effect of atRA. We demonstrated that chemerin was constitutively expressed in the skin, which was down‐regulated during murine melanoma growth. Rarres2−/− mice, which are deficient in chemerin, exhibited aggravated tumor growth and impaired tumor‐infiltrating natural killer (NK) cells that express CMKLR1, the functional receptor of chemerin. Topical treatment with atRA up‐regulated skin chemerin expression, which was primarily derived from dermal cells. Moreover, atRA treatment significantly enhanced tumor‐infiltrating NK cells, which was completely abrogated in Rarres2−/− mice and Cmklr1−/− mice, suggesting a dependency of NK cell recruitment on the chemerin–CMKLR1 axis in melanoma. Despite comparable melanoma growth detected in wild‐type mice and Cmklr1−/− mice, lack of CMKLR1 partially abrogated the melanoma‐inhibitory effect of atRA. This may be due to the inability to enhance tumor‐infiltrating NK cells in Cmklr1−/− mice following atRA treatment. Collectively, our study suggests that down‐regulation of chemerin could be a strategy used by cancers such as melanoma to impair anti‐tumor NK cell immunity and identifies a new anti‐tumor mechanism of atRA by up‐regulating chemerin to enhance CMKLR1‐dependent NK cell recruitment. [ABSTRACT FROM AUTHOR]

Summary: Natural killer (NK) cells are lymphocytes of the innate immune system with essential roles during viral infections. NK cell functions are mediated through a repertoire of non‐rearranging inhibitory and activating receptors that interact with major histocompatibility complex (MHC)–peptide complexes on the surface of infected cells. Recent work studying the conserved CD94–NKG2A and variable killer cell immunoglobulin‐like receptor–MHC systems suggest that these two receptor families may have subtly different properties in terms of interactions with MHC class I bound peptides, and in recognition of down‐regulation of MHC class I. In this review, we discuss how these properties generate diversity in the NK cell response to viruses. Both KIR and NKG2A recognize MHC class I. DNA and RNA viruses may interact differently with MHC class I, leading to different effects on these two systems. [ABSTRACT FROM AUTHOR]

Summary: Natural killer (NK) cells are one of the first cell types to enter inflammation sites and have been historically known as key effector cells against tumours and viruses; now, accumulating evidence shows that NK cells are also capable of direct in vitro activity and play a protective role against clinically important fungi in vivo. However, our understanding of NK cell development, maturation and activation in the setting of fungal infections is preliminary at best. Sporotrichosis is an emerging worldwide‐distributed subcutaneous mycosis endemic in many countries, affecting humans and other animals and caused by various related thermodimorphic Sporothrix species, whose prototypical member is Sporothrix schenckii. We show that following systemic infection of BALB/c mice with S. schenckii sensu stricto, NK cells displayed a more mature phenotype as early as 5 days post‐infection as judged by CD11b/CD27 expression. At 10 days post‐infection, NK cells had increased expression of CD62 ligand (CD62L) and killer cell lectin‐like receptor subfamily G member 1 (KLRG1), but not of CD25 or CD69. Depletion of NK cells with anti‐asialo GM1 drastically impaired fungal clearance, leading to a more than eightfold increase in splenic fungal load accompanied by heightened systemic inflammation, as shown by augmented production of the pro‐inflammatory cytokines tumour necrosis factor‐α, interferon‐γ and interleukin‐6, but not interleukin‐17A, in the spleen and serum. Our study is, to the best of our knowledge, the first to demonstrate that a fungal infection can drive NK cell maturation in vivo and that such cells are pivotal for in vivo protection against S. schenckii. Following systemic infection of BALB/c mice with Sporothrix schenckii ATCC 16345, natural killer (NK) cells displayed a more mature phenotype and had increased expression of CD62L and KLRG1, but not of CD25 or CD69. Depletion of NK cells with anti‐asialo GM1 drastically impaired fungal clearance, leading to a more than eightfold increase in splenic fungal load accompanied by heightened systemic inflammation. NK cells thus proved to be an essential component of the immune machinery driving the elimination of S. schenckii. [ABSTRACT FROM AUTHOR]

Summary: Dengue virus (DENV) infection is considered one of the most important mosquito‐borne diseases. It causes a spectrum of illness that could be due to qualitative and/or quantitative difference(s) of the natural killer (NK) cell responses during acute DENV infection. This view prompted us to perform a detailed phenotypic comparative characterization of NK cell subsets from DENV‐infected patients with dengue fever (DF), patients with dengue haemorrhagic fever (DHF) and healthy controls. The activation/differentiation molecules, CD69 and CD57 and a variety of tissue homing molecules were analysed on the CD56hi CD16− and CD56lo CD16+ NK cells. Although there was no increase in the frequency of the total NK cells during DENV infection compared with the healthy individuals, there was a significant increase in the frequency of the CD56hi CD16− subset and the frequency of CD69 expression by both NK cell subsets during the febrile phase of infection. We also found an increase in the frequencies of cells expressing CD69 and CD57 in the CD56lo CD16+ subset compared with those in the CD56hi CD16− subset. Moreover, although the CD56lo CD16+ subset contained a high frequency of cells expressing skin‐homing markers, the CD56hi CD16− subset contained a high frequency of cells expressing bone marrow and lymph node trafficking markers. Interestingly, no differences of these NK cell subsets were noted in samples from patients with DF versus those with DHF. These findings suggest that activation and differentiation and the patterns of tissue homing molecules of the two major NK cell subsets are different and that these might play a critical role in the immune response against acute DENV infection. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are widely distributed in lymphoid and non-lymphoid tissues, but little is known about the recirculation of NK cells between blood and tissues. This is relevant to understanding recirculation in the steady-state and also for determining the roles for NK cells in vaccine-induced immunity and responses to infection. Therefore, the percentage of NK cells and their phenotype across peripheral blood, afferent lymph and lymph nodes in steady-state conditions was investigated in cattle using the pseudo-afferent lymphatic cannulation model. CD2+ CD25lo NK cells were the predominant subset of NK cells within the blood. In contrast, CD2− CD25hi NK cells were the main subset present within the skin-draining afferent lymphatic vessels and lymph nodes, indicating that CD2− NK cells are the principal NK cell subset trafficking to lymph nodes via the afferent lymphatic vessel. Furthermore, a low percentage of NK cells were present in efferent lymph, which were predominantly of the CD2− subset, indicating that NK cells can egress from lymph nodes and return to circulation in steady-state conditions. These compartmentalization data indicate that NK cells represent a population of recirculating lymphocytes in steady-state conditions and therefore may be important during immune responses to vaccination or infection. [ABSTRACT FROM AUTHOR]

Reliable measurement of cellular cytotoxicity is essential for the characterization of immune responses and for the monitoring of antibody treatment efficacy. Until now, the standard 51Cr-release assay has remained the sole sensitive assay that measures cellular cytotoxicity. Alternative non-radioactive assays have been developed but they do not provide accurate measurement of target cell cytotoxicity. The cost and hazard of handling radioactivity are strong incentives to find alternative solutions to 51Cr. We took advantage of the recent development of cell-imaging multimode readers to develop a novel non-radioactive and real-time cytotoxic assay that demonstrates good reproducibility and sensitivity. The extent of target-cell cytotoxicity is monitored over time by imaging and quantifying live fluorescent target cells in 96-well plates. We have developed classical natural killer cell assays in the presence or absence of blocking antibodies and antibody-dependent cell-mediated cytotoxicity. We show that in these assays, cell killing occurs within the first 2 hr with half maximum killing reached after 30 min. This technology has numerous applications such as natural killer and T-cell cytotoxicity assays and can be extended to cell survival and apoptosis measurement assays. [ABSTRACT FROM AUTHOR]

The killer immunoglobulin-like receptors ( KIR) as well as their MHC class I ligands display enormous genetic diversity and polymorphism in macaque species. Signals resulting from interaction between KIR or CD94/ NKG2 receptors and their cognate MHC class I proteins essentially regulate the activity of natural killer ( NK) cells. Macaque and human KIR share many features, such as clonal expression patterns, gene copy number variations, specificity for particular MHC class I allotypes, or epistasis between KIR and MHC class I genes that influence susceptibility and resistance to immunodeficiency virus infection. In this review article we also annotated publicly available rhesus macaque BAC clone sequences and provide the first description of the CD94- NKG2 genomic region. Besides the presence of genes that are orthologous to human NKG2A and NKG2F, this region contains three NKG2C paralogues. Hence, the genome of rhesus macaques contains moderately expanded and diversified NKG2 genes in addition to highly diversified KIR genes. The presence of two diversified NK cell receptor families in one species has not been described before and is expected to require a complex MHC-dependent regulation of NK cells. [ABSTRACT FROM AUTHOR]

The Ninth Killer Cell Immunoglobulin-Like Receptor ( KIR) Workshop was held in Winchester, UK late in the summer of 2015. The extraordinary diversity of KIR and its functional consequences were key themes throughout the meeting. Novel sequencing technologies and new bioinformatics techniques continue to increase our understanding of the genetic diversity and evolution of the KIR; while a deeper understanding of KIR functions, including their specificity for MHC and its peptide ligands, are generating more refined models of their role in disease. Limited to 100 delegates from around the world, this intimate workshop facilitated vigorous discussion, generating new ideas for research in this ever-expanding field. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells, which can exert early and powerful anti-tumour and anti-viral responses, are important components of the innate immune system. DNAX accessory molecule-1 ( DNAM-1) is an activating receptor molecule expressed on the surface of NK cells. Recent findings suggest that DNAM-1 is a critical regulator of NK cell biology. DNAM-1 is involved in NK cell education and differentiation, and also plays a pivotal role in the development of cancer, viral infections and immune-related diseases. However, tumours and viruses have developed multiple mechanisms to evade the immune system. They are able to impair DNAM-1 activity by targeting the DNAM-1 receptor-ligand system. We have reviewed the roles of DNAM-1, and its biological functions, with respect to NK cell biology and DNAM-1 chimeric antigen receptor-based immunotherapy. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells play an important role in virus infection, their action being regulated by several activating and inhibitory receptors. The NKp30 activating receptor and its isoforms have recently emerged as important determinants of efficient NK cell responses. We determined the relative proportions of NKp30 isoforms in patients with chronic hepatitis C virus ( HCV) infection and healthy donors ( HD). NK cell function (degranulation and cytokine production) and correlations with clinical parameters were assessed following unsupervised hierarchical clustering of patients according to isoform expression. NKp30 receptor expression on NK cells and all isoforms were reduced in HCV-infected patients. Patients were clustered into two groups: the HCV-1 group had similar isoform expression to the HD group, whereas the HCV-2 group had lower expression. The latter showed a better functional activity, and a higher proportion of the activating a isoform and of the NKp30 isoform a/c ratio compared with the HCV-1 cluster. There was a positive correlation between the activating a isoform and liver stiffness and an inverse relationship between the immunosuppressive c isoform and the fibrosis 4 score, suggesting a potentially important role of NKp30 isoforms in influencing liver damage and ensuing fibrosis. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells are considered critical components of the innate and adaptive immune responses. Deficiencies in NK cell activity are common, such as those that occur in cancer patients, and they can be responsible for dysfunctional immune surveillance. Persistent oxidative stress is intrinsic to many malignant tumours, and numerous studies have focused on the effects of reactive oxygen species on the anti-tumour activity of NK cells. Indeed, investigations in animal models have suggested that one of the most important thiol-dependent antioxidant enzymes, peroxiredoxin 1 ( PRDX1), is essential for NK cell function. In this work, our analysis of the transcriptomic expression pattern of antioxidant enzymes in human NK cells has identified PRDX1 as the most prominently induced transcript out of the 18 transcripts evaluated in activated NK cells. The change in PRDX1 expression was followed by increased expression of two other enzymes from the PRDX-related antioxidant chain: thioredoxin and thioredoxin reductase. To study the role of thiol-dependent antioxidants in more detail, we applied a novel compound, adenanthin, to induce an abrupt dysfunction of the PRDX-related antioxidant chain in NK cells. In human primary NK cells, we observed profound alterations in spontaneous and antibody-dependent NK cell cytotoxicity against cancer cells, impaired degranulation, and a decreased expression of activation markers under these conditions. Collectively, our study pinpoints the unique role for the antioxidant activity of the PRDX-related enzymatic chain in human NK cell functions. Further understanding this phenomenon will prospectively lead to fine-tuning of the novel NK-targeted therapeutic approaches to human disease. [ABSTRACT FROM AUTHOR]

Host immune responses must be tightly regulated by an intricate balance between positive and negative signals while fighting pathogens; persistent pathogens may usurp these regulatory mechanisms to dampen host immunity to facilitate survival in vivo. Here we report that Tim-3, a negative signalling molecule expressed on monocytes and T cells, is up-regulated on natural killer ( NK) cells in individuals chronically infected with hepatitis C virus ( HCV). Additionally, the transcription factor T-bet was also found to be up-regulated and associated with Tim-3 expression in NK cells during chronic HCV infection. Micro RNA-155 (mi R-155), an mi RNA that inhibits signalling proteins involved in immune responses, was down-regulated in NK cells by HCV infection. This Tim-3/ T-bet over-expression and mi R-155 inhibition were recapitulated in vitro by incubating primary NK cells or NK92 cell line with Huh-7 hepatocytes expressing HCV. Reconstitution of mi R-155 in NK cells from HCV-infected patients led to a decrease in T-bet/ Tim-3 expression and an increase in interferon- γ production. Blocking Tim-3 signalling also enhanced interferon- γ production in NK cells by improving signal transducer and activator of transcription-5 phosphorylation. These data indicate that HCV-induced, mi R-155-regulated Tim-3 expression regulates NK cell function, suggesting a novel mechanism for balancing immune clearance and immune injury during chronic viral infection. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells are essential components of the immune system, and due to their rapid response potential, can have a great impact during early anti-viral immune responses. We have previously shown that interleukin-2-dependent NK and CD4+ T-cell co-operative immune responses exist in long-term simian immunodeficiency virus ( SIV) -infected controlling macaques and can be rescued in SIV-infected non-controlling macaques by a short course of antiretroviral therapy ( ART). Given that co-operative responses may play an important role in disease prevention and therapeutic treatment, in the present study we sought to determine if these responses can be enhanced in chronically SIV-infected macaques by vaccination with a single-dose of envelope protein given during ART. To this end, we treated 14 chronically SIV-infected macaques with ART for 11 weeks and gave 10 of these macaques a single intramuscular dose of SIV gp120 at week 9 of treatment. ART significantly decreased plasma and mucosal viral loads, increased the numbers of circulating CD4+ T cells in all macaques, and increased T-cell-dependent envelope- and gag-specific interferon- γ and tumour necrosis factor- α production by circulatory CD56+ NK cells. The therapeutic envelope immunization resulted in higher envelope-specific responses compared with those in macaques that received ART only. Functional T-cell responses restored by ART and therapeutic Env immunization were correlated with transiently reduced plasma viraemia levels following ART release. Collectively our results indicate that SIV-specific T-cell-dependent NK cell responses can be efficiently rescued by ART in chronically SIV-infected macaques and that therapeutic immunization may be beneficial in previously vaccinated individuals. [ABSTRACT FROM AUTHOR]

Type 2 diabetes mellitus ( DM) is associated with expanded frequencies of mycobacterial antigen-specific CD4+ T helper type 1 (Th1) and Th17 cells in individuals with active pulmonary tuberculosis ( TB). No data are available on the role of CD8+ T and natural killer ( NK) cells in TB with coincident DM. To identify the role of CD8+ T and NK cells in pulmonary TB with diabetes, we examined mycobacteria-specific immune responses in the whole blood of individuals with TB and DM ( TB- DM) and compared them with those without DM ( TB- NDM). We found that TB- DM is characterized by elevated frequencies of mycobacterial antigen-stimulated CD8+ T cells expressing type 1 [interferon- γ and interleukin-2 ( IL-2)] and type 17 ( IL-17F) cytokines. We also found that TB- DM is characterized by expanded frequencies of TB antigen-stimulated NK cells expressing type 1 (tumour necrosis factor- α) and type 17 ( IL-17A and IL-17F) cytokines. In contrast, CD8+ T cells were associated with significantly diminished expression of the cytotoxic markers perforin, granzyme B and CD107a both at baseline and following antigen or anti- CD3 stimulation, while NK cells were associated with significantly decreased antigen-stimulated expression of CD107a only. This was not associated with alterations in CD8+ T-cell or NK cell numbers or subset distribution. Therefore, our data suggest that pulmonary TB complicated with type 2 DM is associated with an altered repertoire of cytokine-producing and cytotoxic molecule-expressing CD8+ T and NK cells, possibly contributing to increased pathology. [ABSTRACT FROM AUTHOR]

Herpes simplex virus type 1 ( HSV-1), a member of the herpes virus family, is characterized by a short replication cycle, high cytopathogenicity and distinct neurotropism. Primary infection and reactivation may cause severe diseases in immunocompetent and immunosuppressed individuals. This study investigated the role of human plasmacytoid dendritic cells (p DC) in the activation of natural killer ( NK) cells for the control of herpesviral infections. Within peripheral blood mononuclear cells, UV-inactivated HSV-1 and Cp G- A induced CD69 up-regulation on NK cells, whereas infectious HSV-1 was particularly active in inducing NK cell effector functions interferon- γ ( IFN- γ) secretion and degranulation. The p DC-derived IFN- α significantly contributed to NK cell activation, as evident from neutralization and cell depletion experiments. In addition, monocyte-derived tumour necrosis factor- α ( TNF- α) induced after exposure to infectious HSV-1 was found to stimulate IFN- γ secretion. A minority of monocytes was shown to be non-productively infected in experiments using fluorescently labelled viruses and quantitative PCR analyses. HSV-1-exposed monocytes up-regulated classical HLA- ABC and non-classical HLA- E molecules at the cell surface in an IFN- α-dependent manner, whereas stress molecules MICA/ B were not induced. Notably, depletion of monocytes reduced NK cell effector functions induced by infectious HSV-1 ( P < 0·05). Altogether, our data suggest a model in which HSV-1-stimulated p DC and monocytes activate NK cells via secretion of IFN- α and TNF- α. In addition, infection of monocytes induces NK cell effector functions via TNF- α-dependent and TNF- α-independent mechanisms. Hence, p DC and monocytes, which are among the first cells infiltrating herpetic lesions, appear to have important bystander functions for NK cells to control these viral infections. [ABSTRACT FROM AUTHOR]

The importance of Fc-mediated effector function in protective immunity to HIV-1 (hereafter referred to simply as HIV) is becoming increasingly apparent. A large of number of studies in natural infection cohorts, spanning the last 26 years, have associated Fc-mediated effector function, particularly antibody-dependent cellular cytotoxicity, with a favourable clinical course. These studies strongly suggest a role for Fc-mediated effector function in the post-infection control of viraemia. More recently, studies in both humans and non-human primates ( NHPs) also implicate Fc-mediated effector function in blocking HIV acquisition. Accordingly, this review will discuss the results supporting a role of Fc-mediated effector function in both blocking acquisition and post-infection control of viraemia. Parallel studies in NHPs and humans will be compared for common themes. Context for this discussion will be provided by summarizing the temporal emergence of key host and virological events over the course of an untreated HIV infection framing where, when and how Fc-mediated effector function might be protective. A hypothesis that Fc-mediated effector function protects primarily in the early stages of both acquisition and post-infection control of viraemia will be developed. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells contribute to the effector phase of vaccine-induced adaptive immune responses, secreting cytokines and releasing cytotoxic granules. The proportion of responding NK cells varies between individuals and by vaccine, suggesting that functionally discrete subsets of NK cells with different activation requirements may be involved. Here, we have used responses to individual components of the DTP vaccine [tetanus toxoid ( TT), diphtheria toxoid ( DT), whole cell inactivated pertussis] to characterize the NK cell subsets involved in interleukin-2-dependent recall responses. Culture with TT, DT or pertussis induced NK cell CD25 expression and interferon- γ production in previously vaccinated individuals. Responses were the most robust against whole cell pertussis, with responses to TT being particularly low. Functional analysis of discrete NK cell subsets revealed that transition from CD56bright to CD56dim correlated with increased responsiveness to CD16 cross-linking, whereas increasing CD57 expression correlated with a loss of responsiveness to cytokines. A higher frequency of CD56dim CD57− NK cells expressed CD25 and interferon- γ following stimulation with vaccine antigen compared with CD56dim CD57+ NK cells and made the largest overall contribution to this response. CD56dim CD57int NK cells represent an intermediate functional phenotype in response to vaccine-induced and receptor-mediated stimuli. These findings have implications for the ability of NK cells to contribute to the effector response after vaccination and for vaccine-induced immunity in older individuals. [ABSTRACT FROM AUTHOR]

Early phases of human pregnancy are associated with the accumulation of a unique subset of natural killer (NK) cells in the maternal decidua. Decidual NK ( dNK) cells that are devoid of cytotoxicity play a pivotal role in successful pregnancy. By secreting large amounts of cytokines/chemokines and angiogenic factors, dNK cells participate in all steps of placentation including trophoblast invasion into the maternal endometrium and vascular remodelling. In this review, we summarize some of dNK cell features and discuss more recent exciting data that challenge the conventional view of these cells. Our new data demonstrate that dNK cells undergo fine tuning or even subvert their classical inhibitory machinery and turn into a real defence force in order to prevent the spread of viruses to fetal tissue. Today it is not clear how these phenotypic and functional adaptations impact cellular cross-talk at the fetal-maternal interface and tissue homeostasis. Ultimately, precise understanding of the molecular mechanisms that govern dNK cell plasticity during congenital human cytomegalovirus infection should lead to the design of more robust strategies to reverse immune escape during viral infection and cancer. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cell-mediated contact sensitivity was recently described in mice. Here, we confirm NK cell-mediated contact sensitivity ( CS) in SCID and RAG1−/− mice but not in SCIDbeige mice, which have non-functional NK cells that lack NK cell granules. NK cell-mediated CS was transferred by liver mononuclear cells and the DX5+ fraction of liver cells, confirming that NK cells mediate CS in the absence of T and B cells. Participation of NKT cells and B-1 cells was ruled out using Jα18−/− and JH−/− mice, respectively. Remarkably, NK cell-mediated CS was observed just 1 hr after immunization and was detectable as early as 30 min after challenge. Further, we examined cytokine requirements for NK cell-mediated CS, and found that liver mononuclear cells from interleukin-12−/−, interferon-γ−/− and interferon-α receptor−/− donors fail to transfer NK cell-mediated CS to naive hosts. Our studies clearly show that dinitrofluorobenzene sensitized NK cells mediate very rapid, antigen-specific cell-mediated immunity, with features of both innate and acquired immune responses. [ABSTRACT FROM AUTHOR]

Innate lymphoid cells ( ILCs) is the collective term for a group of related innate lymphocytes, including natural killer ( NK) cells and the more recently discovered non- NK ILCs, which all lack rearranged antigen receptors such as those expressed by T and B cells. Similar to NK cells, the newly discovered ILCs depend on the transcription factor Id2 and the common γ-chain of the interleukin-2 receptor for development. However, in contrast to NK cells, non- NK ILCs also require interleukin-7. In addition to the cytotoxic functions of NK cells, assuring protection against tumour development and viruses, new data indicate that ILCs contribute to a wide range of homeostatic and pathophysiological conditions in various organs via specialized cytokine production capabilities. Here we summarize current knowledge on ILCs with a particular emphasis on their tissue-specific effector functions, in the gut, liver, lungs and uterus. When possible, we try to highlight the role that these cells play in humans. [ABSTRACT FROM AUTHOR]

In monoclonal gammopathies (MG) and multiple myeloma (MM), normal natural cytotoxicity receptors (NCR) expression (NCR1/NKp46, NCR2/NKp44, NCR3/NKp30) is observed in natural killer (NK) cells. Nonetheless, except in plasma cell leukemia, few tumor plasmocytes are present in PB, while NK studies have been performed on peripheral blood (PB). For this reason we focused our attention on NK from bone marrow (BM). Our study demonstrates that the down-regulation of NCR3/NKp30 is only detectable in NK from BM but not in PB, and shows a drastic decrease of both NKG2D and CD244/2B4/p38 expression in NK from BM in comparison with PB. In conclusion, our data more precisely describe the mechanism of immune escape of MG/MM from innate immunity since we show a drastic down regulation of 3 major activating NK receptors (NCR3/NKp30, NKG2D and CD244/2B4/p38) at the site of tumor, i.e BM, that was undetectable in PB. Further studies regarding immune regulatory drugs in MG/MM will imperiously require the assessment of immune cell status not only in PB but also in BM to obtain more relevant data regarding anti-tumor efficacy. [ABSTRACT FROM AUTHOR]

NKG2D ligands are cell surface proteins that activate NKG2D, a receptor used by natural killer ( NK) cells to detect virus-infected and transformed cells. When tumour cells express high levels of NKG2D ligands, they are rejected by the immune system. Hence, reagents that increase NKG2D ligand expression on tumour cells can be important for tumour immunotherapy. To identify genes that regulate the NKG2D ligand H60a, we performed a microarray analysis of 3′-methylcholanthrene-induced sarcoma cell lines expressing high versus low H60a levels. A20, an inhibitor of nuclear factor-κB ( NF-κB) activation, was differentially expressed in H60a-hi sarcoma cells. Correspondingly, treatment of tumour cells with inhibitors of NF-κB activation, such as sulfasalazine (slz), BAY-11-7085, or a non-phosphorylatable IκB, led to increased levels of H60a protein, whereas transduction of cells with an active form of IκB kinase-β ( IKKβ) led to decreased levels of H60a. The regulation probably occurred at the transcriptional level, because NF-κB pathway inhibition led to increased H60a transcripts and promoter activity. Moreover, treatment of tumour cells with slz enhanced their killing by NK cells in vitro, suggesting that NF-κB inhibition can lead to tumour cell rejection. Indeed, when we blocked the NF-κB pathway specifically in tumour cells, there was decreased tumour growth in wild-type but not immune-deficient mice. Our results suggest that reagents that can block NF-κB activity specifically in the tumour and not the host immune cells would be efficacious for tumour therapy. [ABSTRACT FROM AUTHOR]

Natural killer ( NK) cells provide an immediate first line of defence against viral infections. Memory responses, maintained by CD4+ T cells, require exposure to viral antigen and provide long-term protection against future infections. It is known that NK cells can promote the development of the adaptive response through cytokine production and cross-talk with antigen-presenting cells. In this paper however, we summarize a series of recent publications, in mouse models and for the first time in man, with the unifying message that rapid viral antigen control by the innate immune system limits antigen exposure to CD4+ cells thereby abrogating the development of a memory response. We discuss the significant implication of these studies on viral treatment strategies and immunization models. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells protect against intracellular infection and cancer. These properties are exploited in oncolytic virus (OV) therapy, where antiviral responses enhance anti-tumour immunity. We have analysed the mechanism by which reovirus, an oncolytic dsRNA virus, modulates human NK cell activity. Reovirus activates NK cells in a type I interferon (IFN-I) dependent manner, inducing STAT1 and STAT4 signalling in both CD56 dim and CD56 bright NK cell subsets. Gene expression profiling revealed the dominance of IFN-I responses and identified induction of genes associated with NK cell cytotoxicity and cell cycle progression, with distinct responses in the CD56 dim and CD56 bright subsets. However, reovirus treatment inhibited IL-15 induced NK cell proliferation in an IFN-I dependent manner and was associated with reduced AKT signalling. In vivo, human CD56 dim and CD56 bright NK cells responded with similar kinetics to reovirus treatment, but CD56 bright NK cells were transiently lost from the peripheral circulation at the peak of the IFN-I response, suggestive of their redistribution to secondary lymphoid tissue. Coupled with the direct, OV-mediated killing of tumour cells, the activation of both CD56 dim and CD56 bright NK cells by antiviral pathways induces a spectrum of activity that includes the NK cell-mediated killing of tumour cells and modulation of adaptive responses via the trafficking of IFN-γ expressing CD56 bright NK cells to lymph nodes., (© 2022 The Authors. Immunology published by John Wiley & Sons Ltd.)

Natural killer ( NK) cells have a specialized function in peripheral organs, which is determined by the organ-specific niches. We have attempted to explore whether lung NK cells display a particular phenotype according to their function in the unique pulmonary environment in health or during respiratory infection in mice. In healthy mice, higher frequencies of NK cells among lymphocytes were detected in the lung than in other tissues (lymph node, bone marrow, spleen, blood and liver), and lung NK cells maintained a more mature phenotype, implying that lung NK cells were critical for the pulmonary immune response. However, lung NK cells expressed higher levels of inhibitory receptors and lower levels of activating receptors, migration/adhesion-associated molecules and co-stimulatory molecules than splenic NK cells, implying that lung NK cells were quiescent, and the activation of lung NK cells was tightly regulated by the pulmonary environment in health. During respiratory infection, lung NK cells could be activated and express functional molecules ( CD107a and interferon-γ) to take part in the response to infection quickly. These results suggested that the unique pulmonary environment promotes the development of NK cells with a lung-specific phenotype. [ABSTRACT FROM AUTHOR]

Streptococcus pyogenes is the causative agent of numerous diseases ranging from benign infections (pharyngitis and impetigo) to severe infections associated with high mortality (necrotizing fasciitis and bacterial sepsis). As with other bacterial infections, there is considerable interest in characterizing the contribution of interleukin-17A (IL-17A) responses to protective immunity. We here show significant il17a up-regulation by quantitative real-time PCR in secondary lymphoid organs, correlating with increased protein levels in the serum within a short time of S. pyogenes infection. However, our data offer an important caveat to studies of IL-17A responsiveness following antigen inoculation, because enhanced levels of IL-17A were also detected in the serum of sham-infected mice, indicating that inoculation trauma alone can stimulate the production of this cytokine. This highlights the potency and speed of innate IL-17A immune responses after inoculation and the importance of proper and appropriate controls in comparative analysis of immune responses observed during microbial infection. [ABSTRACT FROM AUTHOR]

Dendritic cell (DC)-mediated vaccination against Leishmania major induces a parasite-specific T helper 1 (Th1) response and long-lasting protective immunity in susceptible mice. As the cytokine interleukin-12 required for induction of this Th1 response is not derived from the transferred DC, but has to be produced by the vaccinated host, we examined cross-presentation of transferred DC via resident DC of the host and cross-activation with natural killer (NK) cells as mechanisms supporting the induction of protective immunity after DC-mediated vaccination. Co-culture with DC that had been conditioned ex vivo by loading with L. major lysate and stimulation with CpG-containing oligodeoxynucleotides did not result in the activation of naive DC in vitro. Furthermore, L. major antigen from conditioned DC was not cross-presented to a significant extent in vivo. In contrast, co-culture of DC with NK cells led to cross-activation of both cell populations with induction of interferon-γ, which was dependent on the activation status of the conditioned DC. Transient depletion of NK cells during vaccination of L. major-susceptible mice with conditioned DC resulted in reduced protection. Our findings indicate that cross-presentation of conditioned DC after DC-based vaccination against L. major plays a minor role in the induction of protective immunity. However, we demonstrated for the first time that the capacity of DC to mediate protection against L. major is supported by cross-activation with NK cells of the host and NK-cell-derived interferon-γ. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells have been implicated in tumour surveillance and in the early control of several microbial infections. In autoimmune disease their involvement in these processes has been evaluated in animal models, with conflicting results. Both a disease-controlling and a disease-promoting role have been suggested. In human autoimmune disease only a few studies, mainly descriptive, have demonstrated qualitative and quantitative modification of NK cells. These changes were observed on blood- or tissue-infiltrating NK cells. Taken together with our expanding knowledge of the genetical variability of NK cell receptors and NK cell physiology, these findings pave the way for the dissection of the role of NK cells in human autoimmune diseases. NK cells may be directly involved in these diseases through their potential autoreactivity or through their interaction with dendritic cells, macrophages or T lymphocytes, thereby inducing excessive inflammation or favouring the adaptive autoimmune response. Thus, NK cells may be implicated in the onset, the maintenance or the progression of autoimmune diseases. Some reports also suggest the involvement of NK cells in the treatment of human autoimmune disease by biotherapies. All these observations suggest that NK cells are involved in the complex processes of autoimmune diseases. Nevertheless, further careful analysis of NK cells at different steps of these diseases, in different tissues and through combined genetical and functional studies will contribute to a better understanding of their role in autoimmune diseases. This knowledge might allow the development of new therapeutic strategies based on NK cells for the treatment of some autoimmune diseases. [ABSTRACT FROM AUTHOR]

The pore-forming protein perforin is synthesized as an inactive precursor in natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), and becomes active when a short C-terminal peptide is cleaved within acidic lysosome-like cytotoxic granules. Although it was shown more than a decade ago that this cleavage is pH dependent and can be inhibited by the generic cysteine cathepsin inhibitor E-64d, no protease capable of processing the perforin C terminus has been identified. Neither is it known whether a single protease is responsible or the processing has inbuilt redundancy. Here, we show that incubation of human NK cells and primary antigen-restricted mouse CTLs with the cathepsin L (CatL) inhibitor L1 resulted in a marked inhibition of perforin-dependent target cell death and reduced perforin processing. In vitro, CatL preferentially cleaved a site on full-length recombinant perforin close to its C terminus. The NK cells of mice deficient in CatL showed a reduction but not a complete absence of processed perforin, indicating that cysteine proteases other than CatL are also able to process perforin. We conclude that granule-bound cathepsins are essential for processing perforin to its active form, and that CatL is an important, but not exclusive, participant in this process. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells bridge the interface between innate and adaptive immunity and are implicated in the control of herpes simplex virus 2 (HSV-2) infection. In subjects infected with human immunodeficiency virus 1 (HIV-1), the critical impact of the innate immune response on disease progression has recently come into focus. Higher numbers of NK cells are associated with lower HIV-1 plasma viraemia. Individuals with the compound genotype of killer cell immunoglobulin-like receptor ( KIR) 3DS1 and human leucocyte antigen ( HLA)- Bw4-80I, or who have alleles of KIR3DL1 that encode proteins highly expressed on the NK cell surface, have a significant delay in disease progression. We studied the effect of HSV-2 co-infection in HIV-1-infected subjects, and show that HSV-2 co-infection results in a pan-lymphocytosis, with elevated absolute numbers of CD4+ and CD8+ T cells, and NK cells. The NK cells in HSV-2 co-infected subjects functioned more efficiently, with an increase in degranulation after in vitro stimulation. The number of NK cells expressing the activating receptors NKp30 and NKp46, and expressing KIR3DL1 or KIR3DS1, was inversely correlated with HIV-1 plasma viral load in subjects mono-infected with HIV-1, but not in subjects co-infected with HSV-2. This suggests that HSV-2 infection mediates changes within the NK cell population that may affect immunity in HIV-1 infection. [ABSTRACT FROM AUTHOR]

We investigated the distribution of natural killer (NK) cell subsets, their activating and inhibitory receptors, and their cytolytic potential, in primary human immunodeficiency virus (HIV)-infected (PHI) individuals at baseline and during 1 year of follow-up with or without antiretroviral therapy, and compared the results with those obtained in treatment-naïve, chronically HIV-infected (CHI) individuals, and HIV-seronegative (HN) healthy individuals. The proportion of the CD56dim and CD56bright subsets decreased with disease progression, whereas that of the CD56− CD16+ subset increased. In the CD56dim subset, the proportion of cells with natural cytotoxicity receptors (NCRs) decreased with disease progression, and their cytolytic potential was reduced. Conversely, the CD56bright subset was characterized by a high proportion of NCR-positive, killer cell immunoglobulin-like receptor (KIR)-positive NKG2A+ cells in both CHI and PHI individuals, which was associated with an increase in their cytolytic potential. During the 1 year of follow-up, the PHI individuals with high viraemia levels and low CD4+ T-cell counts who received highly active antiretroviral therapy (HAART) had a similar proportion of NK subsets to CHI individuals, while patients with low viraemia levels and high CD4+ T-cell counts who remained untreated had values similar to those of the HN individuals. Our results indicate a marked perturbation of the NK cell compartment during HIV-1 infection that is multifaceted, starts early and is progressive, primarily involves the CD56bright subset, and is partially corrected by effective HAART. [ABSTRACT FROM AUTHOR]

In mice expressing a transgenic T-cell receptor (TCR; TCRP1A) of DBA/2 origin with reactivity towards a cancer-germline antigen P1A, the number of TCRP1A CD8+ T cells in lymphoid organs is lower in DBA/2 than in B10.D2 or B10.D2(× DBA/2)F1 mice. This reduction results from haemopoietic cell autonomous differences in the differentiation of the major histocompatibility complex class I-restricted TCRP1A thymocytes controlled by DBA/2 versus B10.D2-encoded genes. We report here that the lower number of TCRP1A CD8+ T cells in DBA/2 mice correlated with their poor resistance to P1A-expressing mastocytoma solid tumours. Functional potency of CD8+ cytolytic T lymphocytes (CTL) from the above strains was not compromised, but their number after expansion appeared to be influenced by their genetic background. Intriguingly, non-transgenic DBA/2 mice resisted P1A+ tumours more efficiently despite poor representation of P1A-specific CTL. This was partly the result of their more heterogeneous TCR repertoire, including reactivity to non-P1A tumour antigens because mice that had rejected a P1A+ tumour became resistant to a P1A− variant of the tumour. Such ‘cross-resistance’ did not develop in the TCRP1A transgenic mice. Nonetheless, reconstitution of RAGº/º mice with TCRP1A CD8+ T cells, with or without CD4+ T cells, or exclusive representation of TCRP1A CD8+ T cells in RAGº/º TCRP1A transgenic mice efficiently resisted the growth of P1A-expressing tumours. Natural killer cells present at a higher number in RAGº/º mice also contributed to tumour resistance, in part through an NKG2D-dependent mechanism. Hence, in the absence of a polyclonal T-cell repertoire, precursor frequencies of natural killer cells and tumour-specific CTL affect tumour resistance. [ABSTRACT FROM AUTHOR]

The functions of human natural killer (NK) cells are controlled by diverse families of antigen receptors. Prominent among these are the killer cell immunoglobulin-like receptors (KIR), a family of genes clustered in one of the most variable regions of the human genome. Within this review we discuss the vast polymorphism of the KIR gene complex which rivals that of the human leucocyte antigen (HLA) complex. There are several aspects to this polymorphism. Initially there is presence/absence of individual KIR genes, with four of these genes, termed framework genes, being present in all individuals tested to date, except on those very occasional instances when the gene has been deleted. Within each gene, alleles are present at different frequencies. We provide details of a new website that enables convenient searching for data on KIR gene, allele and genotype frequencies in different populations and show how these frequencies vary in different worldwide populations and the high probability of individuals differing in their KIR repertoire when both gene and allele polymorphism is considered. The KIR genes present in an individual may be classified into A and/or B haplotypes, which respectively have a more inhibitory role or a more activating role on the function of the NK cell. Family studies have been used to ascertain the make-up of these haplotypes, inclusion of allele typing enabling determination of whether one or two copies of a particular gene is present. In addition to genetic diversification the KIR gene complex shows differences at the functional level with different alleles having different protein expression levels and different avidity with their HLA ligand. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are key components of the innate anti-viral and anti-tumour immune responses. NK cell function is regulated by the interaction of killer cell immunoglobulin-like receptors (KIR) with human leucocyte antigen (HLA) class I molecules. In this study, we report on the generation of KIR-specific antibodies allowing for discrimination between activating and inhibitory KIR. For this purpose, BALB/c mice were immunized with human KIR2DS2 recombinant protein. The precise specificity of KIR2DS2-specific clones was determined on KIR-transfected BW cells and KIR-genotyped NK cells. When used in combination with EB6 (KIR2DL1/2DS1) or GL183 (KIR2DL2/2DL3/2DS2), two KIR-specific monoclonal antibodies (mAbs), 8C11 (specific for KIR2DL1/2DL2/2DL3/2DS2) and 1F12 (specific for KIR2DL3/2DS2), discriminated activating KIR2DS1 (8C11− EB6+) from inhibitory KIR2DL1 (8C11+ GL183−) and KIR2DL2 (1F12− GL183+), while excluding the main HLA-Cw-specific KIR. Using these mAbs, KIR2DS1 was shown to be expressed on the surface of NK cells from all individuals genotyped as KIR2DS1+ ( n = 23). Moreover, KIR2DS1 and KIR2DL1 were independently expressed on NK cells. We also determined the amino acid position recognized by the 8C11 and 1F12 mAbs, which revealed that some KIR2DL1 allele-encoded proteins are not recognized by 8C11. Because most available anti-KIR mAbs recognize both inhibitory and activating forms of KIR, these newly characterized antibodies should help assess the expression of activating and inhibitory KIR and their functional relevance to NK biology. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells target and kill aberrant cells, such as virally infected and tumorigenic cells. Killing is mediated by cytotoxic molecules which are stored within secretory lysosomes, a specialized exocytic organelle found in NK cells. Target cell recognition induces the formation of a lytic immunological synapse between the NK cell and its target. The polarized exocytosis of secretory lysosomes is then activated and these organelles release their cytotoxic contents at the lytic synapse, specifically killing the target cell. The essential role that secretory lysosome exocytosis plays in the cytotoxic function of NK cells is highlighted by immune disorders that are caused by the mutation of critical components of the exocytic machinery. This review will discuss recent studies on the molecular basis for NK cell secretory lysosome exocytosis and the immunological consequences of defects in the exocytic machinery. [ABSTRACT FROM AUTHOR]

NKG2D is one of the best characterized activating receptors and is expressed on natural killer cells and on various T-cell subsets. This receptor recognizes several different ligands that are induced by cellular stresses. In this review, we described the mechanisms controlling the expression of NKG2D ligands, with the emphasis on post-transcriptional and post-translational regulation. [ABSTRACT FROM AUTHOR]

Human natural killer (NK) cells can be subdivided into different populations based on the relative expression of the surface markers CD16 and CD56. The two major subsets are CD56bright CD16dim/− and CD56dim CD16+, respectively. In this review, we will focus on the CD56bright NK cell subset. These cells are numerically in the minority in peripheral blood but constitute the majority of NK cells in secondary lymphoid tissues. They are abundant cytokine producers but are only weakly cytotoxic before activation. Recent data suggest that under certain conditions, they have immunoregulatory properties, and that they are probably immediate precursors of CD56dim NK cells. CD56bright NK cell percentages are expanded or reduced in a certain number of diseases, but the significance of these variations is not yet clear. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells belong to the innate immune system but can also affect adaptive immune reactions. This immune regulatory function is often ascribed to the CD56bright subpopulation of NK cells that is prevalent in secondary lymphoid tissues and has potent cytokine-producing ability. The NK cells have been described as affecting autoimmune disease and stimulating B-cell production of antibodies, but their role in systemic lupus erythematosus (SLE) pathology has not been extensively studied. We have studied NK cells in SLE, a B-cell-driven systemic autoimmune disease, and phenotypically characterized peripheral blood NK cells in comparison to NK cells from patients with immunoglobulin A nephritis, rheumatoid arthritis and healthy individuals. We have found an increased proportion of CD56bright NK cells in SLE, regardless of disease activity. We detected a somewhat increased expression of the activating receptor NKp46/CD335 on NK cells from SLE patients, although neither the percentage of NK cells of all lymphocytes nor the expression of other NK receptors analysed (LIR-1/CD85j, CD94, NKG2C/CD159c, NKG2D/CD314, NKp30/CD337, NKp44/CD336, CD69) differed between patient groups. We show that type I interferon, a proinflammatory cytokine known to be abundant in SLE, can cause increases of CD56bright NK cells in vitro. We confirmed that serum levels of interferon-α were increased in active, but not in inactive, disease in the SLE patient group. In conclusion, we found an increased proportion of CD56bright NK cells in the blood of SLE patients, although it remains to be examined whether and how this relates to the disease process. [ABSTRACT FROM AUTHOR]

CD66a (CEACAM1), an adhesion molecule that has regulatory function on T lymphocytes, was found to be expressed on a minority of mouse natural killer (NK) cells, especially in the liver. CD66a expression on NK cells depended on their differentiation stage, with highest levels on immature CD49b−NK cells. Expression of CD66a on NK cells was strongly enhanced by in vitro activation with interleukin-12 (IL-12) and IL-18. However, in vivo NK cell stimulation by infection with lactate dehydrogenase-elevating virus did not lead to strong CD66a expression, even on activated interferon--γ-producing NK cells. These results indicate that CD66a expression is differently regulated, depending on the NK cell activation pathway, which may lead to distinct regulatory mechanisms of the functional subpopulations of these cells. [ABSTRACT FROM AUTHOR]

Interleukin (IL)-21 is a novel cytokine that has been shown to enhance proliferation and activation of CD8+ T cells, enhance natural killer (NK) cell activity and costimulate anti-CD40-driven B-cell proliferation in mice. Several studies have furthermore demonstrated antitumour effects of IL-21 administration in mouse models. In this study we have investigated how IL-21 affects the survival and cytotoxicity of human NK cells and modulates their expression of surface receptors and of the effector molecules granzyme B and perforin. In contrast to murine NK cells, where IL-21 alone cannot sustain survival, IL-21 and IL-2 were equally efficient in sustaining survival of human NK cells. In the absence of other cytokines, IL-21 had little effect on expression of a panel of surface receptors on human NK cells. However, IL-21 synergized with IL-2 to up-regulate several surface receptors, including NKG2A, CD25, CD86 and CD69. The CD25+ CD86+ NK cells were CD56bright and were large and granular. Expression of the effector molecules perforin and granzyme A and B was up-regulated by IL-21 at both mRNA and protein levels. Furthermore, IL-21 increased the cytotoxicity of NK cells against K562 target cells. These findings suggest that IL-21 modulates NK cell activity through induction of intracellular effector molecules as well as modulation of surface receptor expression. [ABSTRACT FROM AUTHOR]

Natural killer T (NKT) cells constitute a distinct lymphocyte lineage at the interface between innate and adaptive immunity, yet their role in the immune response remains elusive. Whilst NKT cells share features with other conventional T lymphocytes, they are unique in their rapid, concomitant production of T helper type 1 (Th1) and Th2 cytokines upon T-cell receptor (TCR) ligation. In order to characterize the gene expression of NKT cells, we performed comparative microarray analyses of murine resting NKT cells, natural killer (NK) cells and naïve conventional CD4+ T helper (Th) and regulatory T cells (Treg). We then compared the gene expression profiles of resting and alpha-galactosylceramide (αGalCer)-activated NKT cells to elucidate the gene expression signature upon activation. We describe here profound differences in gene expression among the various cell types and the identification of a unique NKT cell gene expression profile. In addition to known NKT cell-specific markers, many genes were expressed in NKT cells that had not been attributed to this population before. NKT cells share features not only with Th1 and Th2 cells but also with Th17 cells. Our data provide new insights into the functional competence of NKT cells which will facilitate a better understanding of their versatile role during immune responses. [ABSTRACT FROM AUTHOR]

It is still controversial whether malaria protection is mediated by conventional immunity associated with T and B cells or by innate immunity associated with extrathymic T cells and autoantibody-producing B cells. Given this situation, it is important to examine the mechanism of malaria protection in β2-microglobulin-deficient (β2m(–/–)) mice. These mice lack major histocompatibility complex class I and CD1d antigens, which results in the absence of CD8+ T cells and natural killer T (NKT) cells. When C57BL/6 and β2m(–/–) mice were injected with parasitized ( Plasmodium yoelii 17XNL) erythrocytes, both survived from the infection and showed a similar level of parasitaemia. The major expanding T cells were NK1.1– αβΤ-cell receptorint cells in both mice. The difference was a compensatory expansion of NK and γδT cells in β2m(–/–) mice, and an elimination experiment showed that these lymphocytes were critical for protection in these mice. These results suggest that malaria protection might be events of the innate immunity associated with multiple subsets with autoreactivity. CD8+ T and NKT cells may be partially related to this protection. [ABSTRACT FROM AUTHOR]

Interleukin-21 (IL-21) is a cytokine with pleiotropic effects on various cell types including dendritic cells, B cells, T cells and natural killer (NK) cells. To evaluate if IL-21 affects human NK cell subpopulations in a similar fashion, functional studies were performed on CD56dim and CD56bright NK cells, both bearing IL-21 receptors at identical densities. Stimulation with IL-21 strongly induced proliferation of CD56bright NK cells and cytotoxicity against K562 target cells was preferentially augmented in CD56dim NK cells. In contrast, stimulation with IL-2 and IL-21 alone or in combination failed to induce interferon-γ and tumour necrosis factor-α production in the two NK cell subsets. Intracellular analysis of signal transducer and activator of transcription (STAT) proteins revealed that IL-21 by itself induces phosphorylation of STAT1 and STAT3 in CD56dim NK cells, and to an even higher degree in CD56bright NK cells. In this CD56bright NK cell population alone, IL-2 weakly phosphorylated STAT1 and STAT3, which was further increased when cells were treated with the combination of both cytokines. In contrast, STAT5 was strongly phosphorylated only in CD56bright NK cells by low-dose IL-2, while IL-21 did not affect STAT5 at all. In summary, we present data indicating that the NK-cell-directed cytokines IL-2 and IL-21 not only affect functions in NK cell subpopulations differently but can also act additively. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are activated early during inflammatory events and contribute to the shaping of the ensuing adaptive immune response. To further understand the role for NK cells in inflammation, we investigated the phenotype and function of synovial fluid (SF) NK cells from patients with chronic joint inflammation, as well as from patients with transient inflammation of the knee following trauma. We confirm that synovial NK cells are similar to the well-characterized CD56bright peripheral blood (PB) NK-cell subset present in healthy individuals. However, compared to this PB subset the synovial NK cells express a higher degree of activation markers including CD69 and NKp44, the latter being up-regulated also on CD56bright NK cells in the PB of patients. Activated synovial NK cells produced interferon-γ and tumour necrosis factor, and the production was further up-regulated by antibody masking of CD94/NKG2A, and down-regulated by target cells expressing human leucocyte antigen-E in complex with peptides known to engage CD94/NKG2A. We conclude that synovial NK cells have an activated phenotype and that CD94/NKG2A is a key regulator of synovial NK-cell cytokine synthesis. [ABSTRACT FROM AUTHOR]

Human natural killer (NK) cells form a circulating population in a state of dynamic homeostasis. We investigated NK cell homeostasis by labelling dividing cells in vivo using deuterium-enriched glucose in young and elderly healthy subjects and patients with viral infection. Following a 24-hr intravenous infusion of 6,6-D2-glucose, CD3– CD16+ NK cells sorted from peripheral blood mononuclear cells (PBMC) by fluorescence-activated cell sorter (FACS) were analysed for DNA deuterium content by gas chromatography mass spectrometry to yield minimum estimates for proliferation rate ( p). In healthy young adults ( n = 5), deuterium enrichment was maximal ∼ 10 days after labelling, consistent with postmitotic maturation preceding circulation. The mean (± standard deviation) proliferation rate was 4·3 ± 2·4%/day (equivalent to a doubling time of 16 days) and the total production rate was 15 ± 7·6 × 106 cells/l/day. Labelled cells disappeared from the circulation at a similar rate [6·9 ± 4·0%/day; half-life ( T½) < 10 days]. Healthy elderly subjects ( n = 8) had lower proliferation and production rates ( P = 2·5 ± 1·0%/day and 7·3 ± 3·7 × 106 cells/l/day, respectively; P = 0·04). Similar rates were seen in patients chronically infected with human T-cell lymphotropic virus type I (HTLV-I) ( P = 3·2 ± 1·9%/day). In acute infectious mononucleosis ( n = 5), NK cell numbers were increased but kinetics were unaffected ( P = 2·8 ± 1·0%/day) a mean of 12 days after symptom onset. Human NK cells have a turnover time in blood of about 2 weeks. Proliferation rates appear to fall with ageing, remain unperturbed by chronic HTLV-I infection and normalize rapidly following acute Epstein–Barr virus infection. [ABSTRACT FROM AUTHOR]

Strains of mice with maximal and minimal acute inflammatory responsiveness (AIRmax and AIRmin, respectively) were developed through selective breeding based on their high- or low-acute inflammatory responsiveness. Previous reports have shown that AIRmax mice are more resistant to the development of a variety of tumours than AIRmin mice, including spontaneous metastasis of murine melanoma. Natural killer activity is involved in immunosurveillance against tumour development, so we analysed the number and activity of natural killer cells (CD49b+), T-lymphocyte subsets and in vitro cytokine production by spleen cells of normal AIRmax and AIRmin mice. Analysis of lymphocyte subsets by flow cytometry showed that AIRmax mice had a higher relative number of CD49b+ cells than AIRmin mice, as well as cytolytic activity against Yac.1 target cells. The number of CD3+ CD8+ cells was also higher in AIRmax mice. These findings were associated with the ability of spleen cells from AIRmax mice in vitro to produce higher levels of the pro-inflammatory cytokines tumour necrosis factor-α, interleukin-12p40 and interferon-γ but not the anti-inflammatory interleukin-10. Taken together, our data suggest that the selective breeding to achieve the AIRmax and AIRmin strains was able to polarize the genes associated with cytotoxic activity, which can be responsible for the antitumour resistance observed in AIRmax mice. [ABSTRACT FROM AUTHOR]