Regulation of natural killer cell activity

Complete Rescue of HTLV-1p12KO Infectivity by Depletion of Monocytes Together with NK and CD8+ T Cells

The transient depletion of monocytes alone prior to exposure of macaques to HTLV-1 enhances both HTLV-1WT (wild type) and HTLV-1p12KO (Orf-1 knockout) infectivity, but seroconversion to either virus is not sustained over time, suggesting a progressive decrease in virus expression. These results raise the hypotheses that either HTLV-1 persistence depends on a monocyte reservoir or monocyte depletion provides a transient immune evasion benefit. To test these hypotheses, we simultaneously depleted NK cells, CD8+ T cells, and monocytes (triple depletion) prior to exposure to HTLV-1WT or HTLV-1p12KO. Remarkably, triple depletion resulted in exacerbation of infection by both viruses and complete rescue of HTLV-1p12KO infectivity. Following triple depletion, we observed rapid and sustained seroconversion, high titers of antibodies against HTLV-1 p24Gag, and frequent detection of viral DNA in the blood and tissues of all animals when compared with depletion of only CD8+ and NK cells, or monocytes alone. The infection of macaques with HTLV-1WT or HTLV-1p12KO was associated with higher plasma levels of IL-10 after 21 weeks, while IL-6, IFN-γ, IL-18, and IL-1β were only elevated in animals infected with HTLV-1WT. The repeat depletion of monocytes, NK, and CD8+ cells seven months following the first exposure to HTLV-1 did not further exacerbate viral replication. These results underscore the contribution of monocytes in orchestrating anti-viral immunity. Indeed, the absence of orf-1 expression was fully compensated by the simultaneous depletion of CD8+ T cells, NK cells, and monocytes, underlining the primary role of orf-1 in hijacking host immunity.

Fiction and Facts about BCG Imparting Trained Immunity against COVID-19

The Bacille Calmette-Guérin or BCG vaccine, the only vaccine available against Mycobacterium tuberculosis can induce a marked Th1 polarization of T-cells, characterized by the antigen-specific secretion of IFN-γ and enhanced antiviral response. A number of studies have supported the concept of protection by non-specific boosting of immunity by BCG and other microbes. BCG is a well-known example of a trained immunity inducer since it imparts ‘non-specific heterologous’ immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for the recent pandemic. SARS-CoV-2 continues to inflict an unabated surge in morbidity and mortality around the world. There is an urgent need to devise and develop alternate strategies to bolster host immunity against the coronavirus disease of 2019 (COVID-19) and its continuously emerging variants. Several vaccines have been developed recently against COVID-19, but the data on their protective efficacy remains doubtful. Therefore, urgent strategies are required to enhance system immunity to adequately defend against newly emerging infections. The concept of trained immunity may play a cardinal role in protection against COVID-19. The ability of trained immunity-based vaccines is to promote heterologous immune responses beyond their specific antigens, which may notably help in defending against an emergency situation such as COVID-19 when the protective ability of vaccines is suspicious. A growing body of evidence points towards the beneficial non-specific boosting of immune responses by BCG or other microbes, which may protect against COVID-19. Clinical trials are underway to consider the efficacy of BCG vaccination against SARS-CoV-2 on healthcare workers and the elderly population. In this review, we will discuss the role of BCG in eliciting trained immunity and the possible limitations and challenges in controlling COVID-19 and future pandemics.

Absence of MHC class Ⅱ molecules promotes natural killer cells activation in mice

The development and immune recognition of natural killer (NK) cell are regulated critically by major histocompatibility complex (MHC) class I molecules. However, it remains unclear whether the function of NK cells is regulated by MHC class II molecules. To test this, we monitored the development, phenotype and function of NK cells by using MHC class II deficient (H2^-/-) mice. The numbers and development of NK cells keep unaltered in H2^-/- mice, compared with those in wide type (H2^+/+) mice. A part of Ly49 family receptors on NK cells are down-regulated both in mRNA and protein expression in absence of MHC class II molecules. Furthermore, NK cells obtained from H2^-/- mice exhibit more expression of CD69 and IFN-γ after cross-linking with NK1.1. Also, the cytotoxicity against tumor cell lines of NK cells from H2^-/- mice was increased significantly. Taken together, our study indicates that the absence of MHC class II molecules promotes the activation and function of NK cells in mice.

Immunological role of CD4+CD28null T lymphocytes, natural killer cells, and interferon-gamma in pediatric patients with sickle cell disease: relation to disease severity and response to therapy

Sickle cell disease (SCD) is associated with alterations in immune phenotypes. CD4⁺CD28^null T lymphocytes have pro-inflammatory functions and are linked to vascular diseases. To assess the percentage of CD4⁺CD28^null T lymphocytes, natural killer cells (NK), and IFN-gamma levels, we compared 40 children and adolescents with SCD with 40 healthy controls and evaluated their relation to disease severity and response to therapy. Patients with SCD steady state were studied, focusing on history of frequent vaso-occlusive crisis, hydroxyurea therapy, and IFN-gamma levels. Analysis of CD4⁺CD28^null T lymphocytes and NK cells was done by flow cytometry. Liver and cardiac iron overload were assessed. CD4⁺CD28^null T lymphocytes, NK cells, and IFN-gamma levels were significantly higher in patients than controls. Patients with history of frequent vaso-occlusive crisis and those with vascular complications had higher percentage of CD4⁺CD28^null T lymphocytes and IFN-gamma while levels were significantly lower among hydroxyurea-treated patients. CD4⁺CD28^null T lymphocytes were positively correlated to transfusional iron input while these cells and IFN-gamma were negatively correlated to cardiac T2* and duration of hydroxyurea therapy. NK cells were correlated to HbS and indirect bilirubin. Increased expression of CD4⁺CD28^null T lymphocytes highlights their role in immune dysfunction and pathophysiology of SCD complications.

Augmentation of Cytolytic Activity in Murine Natural Killer Cells and Inhibition of Tumor Growth by the Ethanol Fraction of Oyster Extract

A reduced number and/or reduced activity of natural killer (NK) cells, which are important for defense against a variety of cancers and viral infections, occur under various stress conditions and in patients with various diseases. In this article, we report that the 30% to 50% ethanol precipitate of oyster extract (EPOE50) dose-dependently enhanced the activity of mouse spleen NK cells in vitro and in vivo. The activity of EPOE50 was eluted with a molecular weight of about 2000 by gel filtration and was inactivated by periodate but not by proteinase K. The activity of highly purified NK cells was also augmented by EPOE50 but not by oligodeoxyribonucleotide 1585, which mimics bacterial DNA. Administration of EPOE50 to mice stimulated splenic NK cell activity without a change in splenic NK cell populations. Although the proliferation of B16 tumor cells in vitro was slightly stimulated by EPOE50, the growth of B16 melanoma in vivo was dose-dependently suppressed by administration of EPOE50. Taken together, our results indicate that EPOE50 augmented NK cell activity and that its administration to mice inhibited tumor growth presumably through the activation of NK cells and also suggest that the active substance is a sugar-containing oligomer or polymer and is not of bacterial origin.

Natural Killer Receptor 1 Dampens the Development of Allergic Eosinophilic Airway Inflammation

The function of NCR1 was studied in a model of experimental asthma, classified as a type 1 hypersensitivity reaction, in mice. IgE levels were significantly increased in the serum of OVA immunized NCR1 deficient (NCR1gfp/gfp) mice in comparison to OVA immunized wild type (NCR1+/+) and adjuvant immunized mice. Histological analysis of OVA immunized NCR1gfp/gfp mice revealed no preservation of the lung structure and overwhelming peribronchial and perivascular granulocytes together with mononuclear cells infiltration. OVA immunized NCR+/+ mice demonstrated preserved lung structure and peribronchial and perivascular immune cell infiltration to a lower extent than that in NCR1gfp/gfp mice. Adjuvant immunized mice demonstrated lung structure preservation and no immune cell infiltration. OVA immunization caused an increase in PAS production independently of NCR1 presence. Bronchoalveolar lavage (BAL) revealed NCR1 dependent decreased percentages of eosinophils and increased percentages of lymphocytes and macrophages following OVA immunization. In the OVA immunized NCR1gfp/gfp mice the protein levels of eosinophils' (CCL24) and Th2 CD4+ T-cells' chemoattractants (CCL17, and CCL24) in the BAL are increased in comparison with OVA immunized NCR+/+ mice. In the presence of NCR1, OVA immunization caused an increase in NK cells numbers and decreased NCR1 ligand expression on CD11c+GR1+ cells and decreased NCR1 mRNA expression in the BAL. OVA immunization resulted in significantly increased IL-13, IL-4 and CCL17 mRNA expression in NCR1+/+ and NCR1gfp/gfp mice. IL-17 and TNFα expression increased only in OVA-immunized NCR1+/+mice. IL-6 mRNA increased only in OVA immunized NCR1gfp/gfp mice. Collectively, it is demonstrated that NCR1 dampens allergic eosinophilic airway inflammation.

The combination of anti-NKG2D and CTLA-4 Ig therapy prolongs islet allograft survival in a murine model

Islet transplantation is an effective means of treating severe type 1 diabetes in patients with life-threatening hypoglycemia. Improvements in glycemic control with correction of HbA1C enhance quality of life irrespective of insulin independence. By antagonizing the Natural Killer Group 2, member D (NKG2D) receptor expression on NK and CD8+ T cells, in combination with blocking CTLA-4 binding sites, we demonstrate a significant delay of graft rejection in islet allotransplant. Anti-NKG2D combined with CTLA-4 Ig (n = 15) results in prolonged allograft survival, with 84.6 ± 10% of the recipients displaying insulin independence compared to controls (n = 10, p < 0.001). The effect of combination therapy on graft survival is superior to treatments alone (CTLA-4 Ig vs. combination p = 0.024, anti-NKG2D vs. combination p < 0.001) indicating an interaction between these pathways. In addition, combination treatment also improves glucose tolerance when compared to controls (n = 10, p = 0.018). Histologically, NKG2D+ cells were significantly decreased within the allograft after 7 days of combination treatment (n = 6, p = 0.029). T cell proliferation was significantly reduced with anti-NKG2D therapy and CD8+ T cell daughter fractions were also significantly decreased with mAb and combination treatment when measured by in vitro mixed lymphocyte reaction (n = 5, p = 0.015, p = 0.005 and p = 0.048). These results demonstrate that inhibition of NKG2D receptors and costimulatory pathways enhance islet allograft survival.

Influenza virus uses its neuraminidase protein to evade the recognition of two activating NK cell receptors

Natural Killer (NK) cells play a central role in the defense against viral infections and in the elimination of transformed cells. The recognition of pathogen-infected and tumor cells is controlled by inhibitory and activating receptors. We have previously shown that among the activating (killer) NK cell receptors the natural cytotoxicity receptors, NKp44 and NKp46, interact with the viral hemagglutinin (HA) protein expressed on the cell surface of influenza-virus-infected cells. We further showed that the interaction between NKp44/NKp46 and viral HA is sialic-acid dependent and that the recognition of HA by NKp44 and NKp46 leads to the elimination of the infected cells. Here we demonstrate that the influenza virus developed a counter-attack mechanism and that the virus uses its neuraminidase (NA) protein to prevent the recognition of HA by both the NKp44 and NKp46 receptors, resulting in reduced elimination of the infected cells by NK cells.

Models and methods for analysis of lymphocyte repertoire generation, development, selection and evolution

T and B cell receptor repertoires are diversified by variable region gene rearrangement and selected based on functionality and lack of self-reactivity. Repertoires can also be defined based on phenotype and function rather than receptor specificity - such as the diversity of T helper cell subsets. Natural killer (NK) cell repertoires, in which each cell expresses a randomly chosen subset of its inhibitory receptor genes, and is educated based on self-MHC recognition by yet unknown mechanisms, are also phenotypic repertoires. Studying the generation, development and selection of lymphocyte repertoires, and their functions during immune responses, is essential for understanding the function of the immune system in healthy individuals and in immune deficient, autoimmune or cancer patients. The study of lymphocyte repertoires will enable clinical immunologists to develop better therapeutic monoclonal antibodies, vaccines, transplantation donor-recipient matching protocols, and other immune intervention strategies. The recent development of high-throughput methods for repertoire data collection - from multicolor flow cytometry through single-cell imaging to deep sequencing - presents us now, for the first time, with the ability to analyze and compare large samples of lymphocyte repertoires in health, aging and disease. The exponential growth of these datasets, however, challenges the theoretical immunology community to develop methods for data organization and analysis. Furthermore, the need to test hypotheses regarding immune function, and generate predictions regarding the outcomes of medical interventions, necessitates the development of complex mathematical and computational models, covering processes on multiple scales, from the genetic and molecular to the cellular and system scales.

Upregulation of MHC class I expression following dengue virus infection: the mechanism at the promoter level

Unlike many other viruses that downregulate MHC class I expression on infected cell membranes, flaviviruses were reported to upregulate the MHC class I expression. Dengue virus was shown to induce HLA class I expression; however, the precise transcriptional mechanism that is used by the virus remains unclear. This article assessed the findings of a recently published report describing the mechanism used by dengue virus to induce HLA-A2 expression and characterizing the transcription factors that are involved. The study showed that p50/p65 and p65/65 NF-κB dimers bind to the class I regulatory complex within the HLA-A2 promoter. This finding and its significance for the design of possible antiviral therapeutic agents are discussed in this article.

Cellular and humoral mechanisms involved in the control of tuberculosis

Mycobacterium tuberculosis (Mtb) infection is a major international public health problem. One-third of the world's population is thought to have latent tuberculosis, a condition where individuals are infected by the intracellular bacteria without active disease but are at risk for reactivation, if their immune system fails. Here, we discuss the role of nonspecific inflammatory responses mediated by cytokines and chemokines induced by interaction of innate receptors expressed in macrophages and dendritic cells (DCs). We also review current information regarding the importance of several cytokines including IL-17/IL-23 in the development of protective cellular and antibody-mediated protective responses against Mtb and their influence in containment of the infection. Finally, in this paper, emphasis is placed on the mechanisms of failure of Mtb control, including the immune dysregulation induced by the treatment with biological drugs in different autoimmune diseases. Further functional studies, focused on the mechanisms involved in the early host-Mtb interactions and the interplay between host innate and acquired immunity against Mtb, may be helpful to improve the understanding of protective responses in the lung and in the development of novel therapeutic and prophylactic tools in TB.

Human NK cells require caspases for activation-induced proliferation and cytokine release but not for cytotoxicity

Natural killer (NK) cells are innate immune cells involved in antiviral defence and tumour surveillance. To fulfil these tasks, NK cells make use of two major effector functions, cytokine and chemokine release and cytotoxicity. In addition, NK cells proliferate in response to cytokines such as IL-2. NK cells possess a large array of activating and inhibitory receptors and their activation demands a complex crosstalk between those receptors. The signalling pathways leading to NK-cell activation are a field of intensive research. The first clue for signal specificity was provided by studies showing that a pathway leading to NF-κB activation selectively induces cytokine release, but is dispensable for cytotoxicity. Here, we demonstrate that in human NK cells caspase activity is required for the upregulation of select activation markers and IFN-γ and TNF production, but not for cytotoxicity. Interestingly, caspases have previously been linked in T cells to the same mechanism of NF-κB induction that is active in NK cells. Moreover, we provide evidence that caspases are involved in IL-2-induced proliferation. Thus, our data provide the basis for a novel approach using caspase inhibitors to generate cytotoxic NK cells, while simultaneously suppressing cytokine release.

Natural cytotoxicity of NC-2+ cells against the growth and metastasis of WEHI-164 fibrosarcoma

We have previously reported a new receptor (NC-2) for natural cytotoxicity (NC) on murine leucocytes, identified by monoclonal antibody D9 (mAb D9). Pretreatment of mouse spleen cells with different concentrations of mAb D9 in vitro blocked NC against WEHI-164, whereas natural killing (NK) activity against YAC-1 was unaffected. This paper reports the immune surveillance against the growth of WEHI-164 tumour cells in mice by NC-2(+) Cells. The kinetics of in vivo reduction in NC activity were investigated by treating BALB/c and (CBA × C57BL/6) F1 mice with a single injection of 40 μg of mAb D9 and monitoring splenic NC activity by (51) Cr-release assay at intervals from 24 h to 3 weeks. Control mice were injected with OKT8 irrelevant antibody. Results showed a significant (P < 0.05) reduction in splenic NC activity within 24 h which persisted for up to 1 week. Similar results were also obtained when (CBA × C57BL/6) F1 mice were employed (P<0.001). In vivo tumour studies were undertaken to investigate the role of NC-2(+) cells in surveillance against tumour growth and metastasis of the WEHI-164 fibrosarcoma. When syngeneic BALB/c mice were injected with 40 μg of mAb D9 and then challenged with 5 × 10(5) WEHI-164 cells, results showed significantly increased growth rate of the transplanted WEHI-164 fibrosarcoma and tumour nodules in the lungs of animals, when compared to control mice with normal NC activity. Our data support an innate surveillance in metastasis and growth of WEHI-164 fibrosarcoma in mice.

Hepatitis B immunology for clinicians

Hepatitis B virus (HBV) is a hepatotrophic DNA virus that causes acute and chronic hepatitis. Despite an effective vaccine, more than 350 million people are chronically infected with HBV worldwide and are at risk for progressive liver disease. There are marked geographic variations in HBV prevalence (ranging from 0.1% to 2% in low prevalence areas and 10% to 20% in high prevalence areas) related to the timing and mode of HBV exposure. In many developed countries, HBV exposure typically occurs in adults via sexual transmission with a low chronicity rate (5%). In regions with high HBV prevalence (eg, Asia, sub-Saharan Africa), HBV exposure tends to occur in the perinatal period (eg, vertical transmission from mother to infant) with a high rate of persistence in the absence of timely vaccination. The course of viral infection is defined by the interplay between the virus and host immune defense. This article introduces the innate and adaptive immune defense mechanisms in general and as related to HBV. In particular, the current concepts regarding the innate and adaptive immune components contributing to the clinical, virologic and therapeutic outcome in acute and chronic hepatitis B are examined.

Influence of human cytomegalovirus infection on the NK cell receptor repertoire in children

Human cytomegalovirus (hCMV) infection is usually asymptomatic but may cause disease in immunocompromised hosts. It has been reported that hCMV infection may shape the NK cell receptor (NKR) repertoire in adult individuals, promoting a variable expansion of the CD94/NKG2C+ NK cell subset. We explored the possible relationship between this viral infection and the expression pattern of different NKR including CD94/NKG2C, CD94/NKG2A, immunoglobulin-like transcript 2 (ILT2, CD85j), KIR2DL1/2DS1, KIR3DL1, and CD161 in peripheral blood lymphocytes from healthy children, seropositive (n=21) and seronegative (n=20) for hCMV. Consistent with previous observations in adults, a positive serology for hCMV was associated with increased numbers of NKG2C+ NK and T cells as well as with ILT2+ T lymphocytes. Moreover, the proportions of CD161+ and NKG2C+CD56-CD3- NK cells also tended to be increased in hCMV+ individuals. Excretion of the virus was associated with higher proportions of NKG2C+ NK cells. Altogether, these data reveal that hCMV may have a profound influence on the NKR repertoire in early childhood.

Distinct roles for the actin nucleators Arp2/3 and hDia1 during NK-mediated cytotoxicity

BACKGROUND

Several actin nucleators, including Arp2/3 and various formins, control numerous cytoskeletal-based functions in vivo.

RESULTS

We investigated the relative roles of these nucleators. As a model system, we used natural killer (NK) lymphocytes, which display a wide range of cytoskeletal-based functions that culminate in the lysis of target cells. NK cells lacking either Arp2/3 or the formin hDia1 were ineffective in target cell lysis, but for distinct reasons. Loss of Arp2/3 function led to defects in cell adhesion and actin assembly at the junction with the target cell (the lytic synapse). In contrast, loss of hDia1 did not disrupt actin assembly at the lytic synapse. Instead, loss of hDia1 led to perturbations in the microtubule cytoskeleton, including the targeting of microtubules to the lytic synapse.

CONCLUSIONS

These studies reveal novel distinctions and relationships among the functions of Arp2/3, formins, and microtubules in cells. Notably, a formin mediates the capture of microtubules at the cell periphery.

Innate immune signaling pathways in animals: beyond reductionism

The immune system plays a crucial role in the maintenance of the stability and equilibrium of the internal environment in living organisms. The field of animal innate immunity has been the global focus of immunological research for decades. It is now known that the functions of innate immunity inevitably rely on the action of the molecular machines of the cascades or network of immune signaling pathways. Up to date, many researches on the immune signaling pathways in animals were focused on identifying the component functions or cascade molecules in details, which essentially followed a reductionist paradigm without paying high attention to the integrated features. The main purpose of this article was dedicated to accentuating the shift of this field from a reductionist to a systemic view. First, the former part of this article made efforts to summarize the main aspects of the signaling pathways of animal innate immunity including the web resources, the recapitulation of highlighted pathways, the cross-talks, and the evolutionary considerations, which heavily emphasized the integrated characteristics of the immune signaling pathways. Subsequently, the later part of this article was based on the holistic feature of the immune signaling pathways, mainly dedicated to propose a novel hypothesis. From a whole perspective, the oscillating balance hypothesis was deliberately formulated to characterize the holistic pattern of the signaling transduction network of animal innate immune system, which might help to understand some immunological phenomena through the integral principle of the immune network.

[Could anaesthesia, analgesia and sympathetic modulation affect neoplasic recurrence after surgery? A systematic review centred over the modulation of natural killer cells activity]

OBJECTIVE

The Natural Killer cells (NK) are an important part of non-specific cellular-mediated and antitumoral immunity. The goal of this review is to recapitulate data published over NK activity during the perioperative period and the influence of anaesthesia, analgesia and modulation of sympathetic system.

DATA SOURCES

Pubmed/Medline database.

STUDY SELECTION AND DATA EXTRACTION

Keywords-based selection, without limit of date: fundamental studies, randomized controlled trials and non-randomized comparative studies.

DATA SYNTHESIS

In human as in animal studies, an important correlation exists between NK activity and prognosis linked to the development of metastasis. The great depression of this cytotoxicity during the perioperative period could be able to compromise host defenses. The influence of anaesthetics and analgesics is important. The effects of the opioids, the agonists and the antagonists of the sympathetic nervous system, the prostaglandins, the NSAIDs, the ketamine, the hypnotics and the locoregional anaesthesia are systematically reviewed. The limits of experimental model presented are covered.

CONCLUSION

The effects of anaesthetic/analgesic drugs and techniques, the consequences of sympathomodulation on NK activity are numerous and sometimes opposite. It is important for the anaesthesiologist to keep in mind that the long term consequences of his techniques on the patients' outcome must be clarified.

Mechanism of human natural killer cell activation by Haemophilus ducreyi

The role of natural killer (NK) cells in the host response to Haemophilus ducreyi infection is unclear. In pustules obtained from infected human volunteers, there was an enrichment of CD56bright NK cells bearing the activation markers CD69 and HLA-DR, compared with peripheral blood. To study the mechanism by which H. ducreyi activated NK cells, we used peripheral blood mononuclear cells from uninfected volunteers. H. ducreyi activated NK cells only in the presence of antigen-presenting cells. H. ducreyi-infected monocytes and monocyte-derived macrophages activated NK cells in a contact- and interleukin-18 (IL-18)-dependent manner, whereas monocyte-derived dendritic cells induced NK activation through soluble IL-12. More lesional NK cells than peripheral blood NK cells produced IFN-gamma in response to IL-12 and IL-18. We conclude that NK cells are recruited to experimental lesions and likely are activated by infected macrophages and dendritic cells. IFN-gamma produced by lesional NK cells may facilitate phagocytosis of H. ducreyi.

NKp44 receptor mediates interaction of the envelope glycoproteins from the West Nile and dengue viruses with NK cells

Dengue virus (DV) and West Nile virus (WNV) have become a global concern due to their widespread distribution and their ability to cause a variety of human diseases. Antiviral immune defenses involve NK cells. In the present study, we investigated the interaction between NK cells and these two flaviviruses. We show that the NK-activating receptor NKp44 is involved in virally mediated NK activation through direct interaction with the flavivirus envelope protein. Recombinant NKp44 directly binds to purified DV and WNV envelope proteins and specifically to domain III of WNV envelope protein; it also binds to WNV virus-like particles. These WNV-virus-like particles and WNV-domain III of WNV envelope protein directly bind NK cells expressing high levels of NKp44. Functionally, interaction of NK cells with infective and inactivated WNV results in NKp44-mediated NK degranulation. Finally, WNV infection of cells results in increased binding of rNKp44 that is specifically inhibited by anti-WNV serum. WNV-infected target cells induce IFN-gamma secretion and augmented lysis by NKp44-expressing primary NK cells that are blocked by anti-NKp44 Abs. Our findings show that triggering of NK cells by flavivirus is mediated by interaction of NKp44 with the flavivirus envelope protein.

Establishment of a reference interval for natural killer cell activity through flow cytometry and its clinical application in the diagnosis of hemophagocytic lymphohistiocytosis

Recently, the Histiocyte Society revised the diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH) to include low or absent natural killer (NK) cell activity, according to local laboratory reference. The aim of this study was to establish reference interval for functional NK-cell activity in 63 healthy Korean individuals using a flow-cytometric assay. We used peripheral blood mononuclear cells (PBMCs) as effector cells and Fluorescein isothiocyanate-labeled K562 cells as target cells. NK-cell activity was calculated using the following equation: NK-cell activity (%) = (test lysis - spontaneous lysis) x 100/(maximum lysis - spontaneous lysis). NK-cell activity was analyzed in 13 known HLH patients and 16 suspected non-HLH patients using a flow-cytometric assay. The mean (+/-SD) cytotoxicity of PBMCs from healthy individuals was 20.9 +/- 5.3% and the reference interval was 11.8-31.9%. The mean NK-cell activity of HLH patients (8.3 +/- 8.9%) was significantly lower (P = 0.001) than that of non-HLH patients (20.1 +/- 7.8%). The sequential changes in NK-cell activity in the HLH group corresponded to clinical and laboratory findings following treatment. We successfully developed a functional NK-cell activity test for use in the clinical laboratory and obtained a reference interval of NK-cell activity from healthy donors. This assay, and associated reference interval, was used to analyze 30 clinically relevant specimens and the results were shown to be well correlated.

Biochemical signaling pathways for memory T cell recall

Memory T cells exhibit low activation thresholds and rapid effector responses following antigen stimulation, contrasting naive T cells with high activation thresholds and no effector responses. Signaling mechanisms for the distinct properties of naive and memory T cells remain poorly understood. Here, I will discuss new results on signal transduction in naive and memory T cells that suggest proximal control of activation threshold and a distinct biochemical pathway to rapid recall. The signaling and transcriptional pathways controlling immediate effector function in memory T cells closely resemble pathways for rapid effector cytokine production in innate immune cells, suggesting memory T cells use innate pathways for efficacious responses.

Are natural killer cells protecting the metabolically healthy obese patient?

With the emerging obesity pandemic, identifying those who appear to be protected from adverse consequences such as type 2 diabetes and certain malignancies will become important. We propose that the circulating immune system plays a role in the development of these comorbidities. Clinical data and blood samples were collected from 52 patients with severe obesity attending a hospital weight-management clinic and 11 lean healthy controls. Patients were classified into metabolically "healthy obese" (n = 26; mean age 42.6 years, mean BMI 46.8 kg/m(2)) or "unhealthy obese" (n = 26; mean age 45 years, mean BMI 47.5 kg/m(2)) groups, based upon standard cutoff points for blood pressure, lipid profile, and fasting glucose. Circulating lymphoid populations and phenotypes were assessed by flow cytometry. Obese patients had significantly less circulating natural killer (NK) and cytotoxic T lymphocytes (CTL) compared to lean controls. There were significantly higher levels of NK cells and CTLs in the healthy obese group compared to the unhealthy obese group (NK: 11.7% vs. 6.5%, P < 0.0001, CD8 13.4% vs. 9.3%, P = 0.04), independent of age and BMI and these NK cells were also less activated in the healthy compared to the unhealthy group (CD69, 4.1% vs. 11.8%, P = 0.03). This is the first time that quantitative differences in the circulating immune system of obese patients with similar BMI but different metabolic profiles have been described. The significantly higher levels of CTLs and NK cells, which express fewer inhibitory molecules, could protect against malignancy, infection, and metabolic disease seen in obesity.

Role of NK cells and invariant NKT cells in multiple sclerosis

Natural killer (NK) cells and invariant natural killer T (iNKT) cells are two distinctive lymphocyte populations, each possessing its own unique features. Although NK cells are innate lymphocytes with cytotoxic property, they play an immunoregulatory role in the pathogenesis of autoimmune diseases. NKT cells are T cells expressing invariant TCR a-chains, which are known to bridge innate and adaptive arms of the immune system. Accumulating data now support active involvement of these cells in multiple sclerosis (MS). However, unlike professionally committed regulatory cells such as Foxp3(+) regulatory T cells, NK, and iNKT cells have dual potential of acting as either protective or pathogenic lymphocytes depending on the disease setting, adding complexity to the interpretation of data obtained from human and rodent studies. They are potential therapeutic targets in MS, and further in-depth understanding of these cells will lead to designing new strategies to overcome the disabling disease MS.

Immune evasion of natural killer cells by viruses

Natural killer (NK) cells are important in the host resistance to viral infections. They are among the first cells to sense the release of proinflammatory cytokines, as well as the downregulation of surface MHC class I molecules and molecules induced by viral invasion of cells. Various viral functions have evolved to counter NK cell responses illustrating the evolutionary struggles between viruses and NK cells. Ligands for NK cell receptors are primary targets for viral immunoevasion. In order to counteract NK cell activation via the 'missing self'-axis, viruses encode proteins which serve as ligands for inhibitory NK cell receptors. Viruses also downmodulate the ligands for the activating NK cell receptors and encode soluble ligands which block these receptors. In addition to viral immunoregulatory proteins, regulatory RNAs can also inhibit the expression of ligands for NK cell receptors. Improving our understanding of viral regulation of NK cell function could be essential for designing more efficient measures in the prophylaxis and treatment of virus-induced pathology.

Interaction of NK inhibitory receptor genes with HLA-C and MHC class II alleles in Hepatitis C virus infection outcome

Natural killer cells are important in innate defense against viral infections. The interplay between stimulatory and inhibitory natural killer cell receptors and their corresponding human leukocyte antigen ligands are known to influence the outcome of acute Hepatitis C virus infection. Frequencies of NK receptor genes (8 inhibitory, 6 activating and 2 pseudogenes) and HLA class II alleles (DRB1, DQB1) were analyzed in 160 Puerto-Rican American drug users with Hepatitis C virus infection; 121 had chronic viremia (CV) and 39 were spontaneous clearance (SC). We further ruled out genetic stratification using short tandem repeats. Interaction between KIR gene receptor 2DL3/2DL3 and its ligand, C1/C1 of HLA-Cw alleles and spontaneous clearance was confirmed (p=0.03, OR=3.05). We also found a new interaction between the KIR receptor gene 2DL3 with HLA-DRB1*1201 (p=0.0001, OR=22) associated with SC, and an association of HLA DQB1*0501 (p=0.05, OR=0.30) with CV. Our findings suggested a role for MHC class II alleles in Hepatitis C virus peptide presentation to T cells together with NK ligand interaction involving pathways that will be useful for the development of immunotherapeutic interventions.

Influence of Hsp70 and HLA-E on the killing of leukemic blasts by cytokine/Hsp70 peptide-activated human natural killer (NK) cells

This study compared the effects of the human 70-kDa stress protein (Hsp70) peptide, TKDNNLLGRFELSG (TKD), proinflammatory cytokines, or a combination of both on the repertoire of receptors expressed by human natural killer (NK) cells and their capacity to kill human CX colon carcinoma cells, K562 erythroleukemic cells, and leukemic blasts from two patients with acute myelogenous leukemia. Low-dose interleukin (IL) 2/IL-15 and TKD increase the expression density of activatory (NKG2D, NKp30, NKp44, NKp46, CD94/NKG2C) and inhibitory (CD94/NKG2A) receptors on NK cells. Concomitantly, IL-2/TKD treatment enhances the cytotoxicity of NK cells (as reflected by their secretion of granzyme B) against Hsp70 membrane-positive and human leukocyte antigen (HLA)-E membrane-negative (Hsp70(+)/HLA-E(-)) CX(+) and K562 cells. However, it had no effect on the responsiveness to Hsp70(-)/HLA-E(-) CX(-) cells over that induced by IL-2 alone. The cytotoxicity of IL-2/TKD-activated, purified NK cells and peripheral blood mononuclear cells against Hsp70(+)/HLA-E(+) leukemic blasts was weaker than that against Hsp70(+)/HLA-E(-) K562 cells. Hsp70-blocking and HLA-E transfection experiments confirmed membrane-bound Hsp70 as being a recognition/activatory ligand for NK cells, as cytotoxicity was reduced by the presence of the anti-Hsp70 monoclonal antibody cmHsp70.2 and by inhibiting Hsp70 synthesis using short interference ribonucleic acid. HLA-E was confirmed as an inhibitory ligand, as the extent of NK cell-mediated lysis of K562 cell populations that had been transfected with HLA-E(R) or HLA-E(G) alleles was dependent on the proportion of HLA-E-expressing cells. These findings indicate that Hsp70 (as an activatory molecule) and HLA-E (as an inhibitory ligand) expression influence the susceptibility of leukemic cells to the cytolytic activities of cytokine/TKD-activated NK cells.

Murine cytomegalovirus regulation of NKG2D ligands

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that causes morbidity risk in immunologically suppressed and immunodeficient patients including congenital infections. Approaches to curb the consequences of HCMV infections are restricted by a lack of complete understanding of viral pathogenesis. The infection of mice with murine cytomegalovirus (MCMV) as a model of HCMV infection has been particularly useful in elucidating the role of innate and adaptive immune response mechanisms. A large number of cytomegalovirus genes modulate the innate and the adaptive host immune response. The products of several MCMV genes are involved in subverting the natural killer (NK) cell response by down-modulating cellular ligands for the NKG2D receptor expressed on NK cells and CD8(+) T cells. Mutant viruses lacking these immunoevasion genes are attenuated with respect to virus growth in vivo. Given the importance of the NKG2D receptor in controlling both NK- and T cell-mediated immunity, it is of tremendous importance to understand the molecular mechanisms and consequences of viral regulation of the NKG2D ligands.

Multiple ITAM-coupled NK-cell receptors engage the Bcl10/Malt1 complex via Carma1 for NF-kappaB and MAPK activation to selectively control cytokine production

Natural killer (NK) cells are innate immune cells that mediate resistance against viruses and tumors. They express multiple activating receptors that couple to immunoreceptor tyrosine-based activation motif (ITAM)-containing signaling chains for downstream cell activation. Ligation of activating NK-cell receptors induces NK-cell cytotoxicity and cytokine release. How these distinct events are selectively controlled is not well defined. Here we report the identification of a specific signaling pathway that operates downstream of the ITAM-coupled NK-cell receptors NK1.1, Ly49D, Ly49H, and NKG2D. Using primary NK cells from Bcl10(-/-), Malt1(-/-), Carma1(-/-), and Card9(-/-) mice, we demonstrate a key role for Bcl10 signalosomes in the activation of canonical NF-kappaB signaling as well as JNK and p38 MAPK upon NK-cell triggering. Bcl10 directly cooperates with Malt1 and depends on Carma1 (Card11) but not on Card9 for NK-cell activation. These Bcl10-dependent cascades selectively control cytokine and chemokine production but do not affect NK-cell differentiation or killing. Thus, we identify a molecular basis for the segregation of NK-cell receptor-induced signals for cytokine release and target cell killing and extend the previously recognized roles for CARD-protein/Bcl10/Malt1 complexes in ITAM receptor signaling in innate and adaptive immune cells.

IFN-gamma production dominates the early human natural killer cell response to Coxsackievirus infection

Coxsackieviruses (CV) are important human pathogens that have been implicated in the pathogenesis of several diseases, including myocarditis and pancreatitis. How the human immune system recognizes and controls CV infections is not well understood. Studies in mice suggest that natural killer (NK) cells play a critical role in viral clearance and host survival, but the mechanism(s) by which human NK cells may contribute to the host anti-CV defence has not been investigated. Here we show that CVB3 infection markedly reduces HLA class I cell surface expression but does not increase the expression of the activating NK cell receptor ligands MICA/B and ULBP1-3 on human cells. We also demonstrate that the lowered target cell HLA class I surface expression does not correlate with an increased susceptibility to NK cell-mediated killing. However, NK cells responded with a robust production of interferon gamma (IFN-gamma) when peripheral blood mononuclear cells were cocultured with infected cells. In summary, this study shows that CVB3 interferes with the expression of NK cell receptor ligands on infected cells and indicates that IFN-gamma production, rather than cytotoxicity, marks the early human NK cell response to CVB3 infection.

Filarial parasites induce NK cell activation, type 1 and type 2 cytokine secretion, and subsequent apoptotic cell death

NK cells are an important source of early cytokine production in a variety of intracellular viral, bacterial, and protozoan infections; however, the role of NK cells in extracellular parasitic infections such as filarial infections is not well-defined. To investigate the role of NK cells in filarial infections, we have used an in vitro model system of culturing live infective-stage larvae (L3) or live microfilariae (Mf) of Brugia malayi, a causative agent of human lymphatic filariasis, with PBMC of normal individuals. We found that NK cells undergo early cell activation and produce IFN-gamma and TNF-alpha within 24 h after stimulation with both live L3 and Mf. Interestingly, NK cells also express IL-4 and IL-5 at this time point in response to live Mf but not L3. This is accompanied by significant alterations in NK cell expression of costimulatory molecules and natural cytotoxicity receptors. This activation is dependent on the presence of monocytes in the culture, IL-12, and direct contact with live parasites. The early activation event is subsequently followed by apoptosis of NK cells involving a caspase-dependent mechanism in response to live L3 but not live Mf. Thus, the NK cell-parasite interaction is complex, with filarial parasites inducing NK cell activation and cytokine secretion and finally NK cell apoptosis, which may provide an additional mechanism of down-regulating the host immune response.

The role of natural killer cells in curbing neuroinflammation

Natural killer (NK) cells are evolutionarily early lymphocytes that lack antigen-specific receptors and, hence, are considered to be part of the innate immune system. The majority of research on NK cells has focused on their ability to lyse "target cells", generally identified by low or absent MHC Class I expression, such as tumor cells and virus infected cells. However, an alternative role of these leukocytes as regulators of adaptive (and potentially destructive) immune responses, in particular organ-specific autoimmune diseases, has been increasingly recognized. Here we discuss the growing body of evidence that NK cells limit damage in autoimmune demyelinating disease by inhibiting autoreactive T cell responses without harming resident neurons or glia.

Real and artificial immune systems: computing the state of the body

Here I present the idea that the immune system uses a computational strategy to carry out its many functions in protecting and maintaining the body. Along the way, I define the concepts of computation, Turing machines and system states. I attempt to show that reframing our view of the immune system in computational terms is worth our while.