Human dendritic cells activate resting natural killer (NK) cells and are recognized via the NKp30 receptor by activated NK cells

NFATc2 mediates epigenetic modification of dendritic cell cytokine and chemokine responses to dectin-1 stimulation

The transcription factor NFATc2 regulates dendritic cell (DC) responses to microbial stimulation through the C-type lectin receptor dectin-1. But the genetic targets of NFATc2 and their effects on DC function remain largely unknown. Therefore we used ChIP-seq to conduct genome-wide mapping of NFATc2 target sites in dectin-1-activated DCs. By combining binding-site data with a comprehensive gene expression profile, we found that NFATc2 occupancy regulates the expression of a subset of dectin-1-activated genes. Surprisingly, NFATc2 targeted an extensive range of DC-derived cytokines and chemokines, including regulatory cytokines such as IL2, IL23a and IL12b. Furthermore, we demonstrated that NFATc2 binding is required to induce the histone 3 lysine 4 trimethylation (H3K4me3) epigenetic mark, which is associated with enhanced gene expression. Together, these data show that the transcription factor NFATc2 mediates epigenetic modification of DC cytokine and chemokine genes leading to activation of their expression.

Licensed human natural killer cells aid dendritic cell maturation via TNFSF14/LIGHT

Interactions between natural killer (NK) cells and dendritic cells (DCs) aid DC maturation and promote T-cell responses. Here, we have analyzed the response of human NK cells to tumor cells, and we identify a pathway by which NK-DC interactions occur. Gene expression profiling of tumor-responsive NK cells identified the very rapid induction of TNF superfamily member 14 [TNFSF14; also known as homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes (LIGHT)], a cytokine implicated in the enhancement of antitumor responses. TNFSF14 protein expression was induced by three primary mechanisms of NK cell activation, namely, via the engagement of CD16, by the synergistic activity of multiple target cell-sensing NK-cell activation receptors, and by the cytokines IL-2 and IL-15. For antitumor responses, TNFSF14 was preferentially produced by the licensed NK-cell population, defined by the expression of inhibitory receptors specific for self-MHC class I molecules. In contrast, IL-2 and IL-15 treatment induced TNFSF14 production by both licensed and unlicensed NK cells, reflecting the ability of proinflammatory conditions to override the licensing mechanism. Importantly, both tumor- and cytokine-activated NK cells induced DC maturation in a TNFSF14-dependent manner. The coupling of TNFSF14 production to tumor-sensing NK-cell activation receptors links the tumor immune surveillance function of NK cells to DC maturation and adaptive immunity. Furthermore, regulation by NK cell licensing helps to safeguard against TNFSF14 production in response to healthy tissues.

Pro-inflammatory role of natural killer cells in the development of allergic airway disease

BACKGROUND

Natural Killer (NK) cells have been implicated in the development of allergic airway inflammation. However, the in vivo role of NK cells has not been firmly established due to the lack of animal models with selective deficiencies in NK cells.

OBJECTIVE

To determine the specific contribution of NK cells in a murine model of allergic airway disease (AAD).

METHODS

The role of NK cells in AAD was studied using NK-deficient (NKD) mice, perforin(-/-) mice, and mice depleted of Ly49A/D/G(+) NK cell subsets in an ovalbumin-induced model of allergic airway disease (OVA-AAD).

RESULTS

Induction of OVA-AAD in C57BL/6 wild-type (WT) mice resulted in the expansion of airway NK cells and the development of pronounced airway eosinophilia. In the absence of NK cells or specific subsets of NK cells, either in NKD mice, or after the depletion of Ly49A/D/G(+) NK cells, the development of OVA-AAD was significantly impaired as seen by decreased airway inflammation and eosinophilia, decreased secretion of the Th2 cytokines IL-4, IL-5 and IL-13 and diminished OVA-specific antibody production. Furthermore, while OVA-exposure induced a dramatic expansion of dendritic cells (DCs) in WT mice, their induction was significantly attenuated in NKD mice. Development of OVA-AAD in perforin(-/-) mice suggested that the proinflammatory role of NK cells is not dependent on perforin-mediated cytotoxicity. Lastly, induction of allergic disease by OVA-specific CD4 T cells from WT but not NK-depleted or NKD mice in RAG(-/-) recipients, demonstrates that NK cells are essential for T cell priming.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data demonstrate that conventional NK cells play an important and distinct role in the development of AAD. The presence of activated NK cells has been noted in patients with asthma. Understanding the mechanisms by which NK cells regulate allergic disease is therefore an important component of treatment approaches.

IL-27 stimulates human NK-cell effector functions and primes NK cells for IL-18 responsiveness

IL-27, a member of the IL-12 family of cytokines, is produced by APCs, and displays pro- and anti-inflammatory effects. How IL-27 affects human NK cells still remains unknown. In this study, we observed that mature DCs secreted IL-27 and that blockade of IL-27R (CD130) reduced the amount of IFN-γ produced by NK cells during their coculture, showing the importance of IL-27 during DC-NK-cell crosstalk. Accordingly, human rIL-27 stimulated IFN-γ secretion by NK cells in a STAT1-dependent manner, induced upregulation of CD25 and CD69 on NK cells, and displayed a synergistic effect with IL-18. Preincubation experiments demonstrated that IL-27 primed NK cells for IL-18-induced IFN-γ secretion, which was associated with an IL-27-driven upregulation of T-bet expression. Also, IL-27 triggered NKp46-dependent NK-cell-mediated cytotoxicity against Raji, T-47D, and HCT116 cells, and IL-18 enhanced this cytotoxic response. Such NK-cell-mediated cytotoxicity involved upregulation of perforin, granule exocytosis, and TRAIL-mediated cytotoxicity but not Fas-FasL interaction. Moreover, IL-27 also potentiated Ab-dependent cell-mediated cytotoxicity against mAb-coated target cells. Taken together, IL-27 stimulates NK-cell effector functions, which might be relevant in different physiological and pathological situations.

Targeting TLR-4 with a novel pharmaceutical grade plant derived agonist, Immunomax®, as a therapeutic strategy for metastatic breast cancer

BACKGROUND

Previously we demonstrated that the resection of primary 4T1 tumors only slightly prolongs mouse survival, but importantly, creates a "window of opportunity" with attenuated suppressor cell and increased activated T cell populations. This suggests that additional activation of the immune system by immunostimulatory agents during this period may enhance anti-tumor immunity and potentially eradicate micro-metastatic disease in this stringent model. We hypothesized that the immunostimulator Immunomax®, which is comprised of a plant-derived polysaccharide, is non-toxic in humans and stimulates immune defense during the infectious diseases treatment, may have also anti-tumor activity and be beneficial in the adjuvant setting when endogenous anti-tumor responses are present and during the "window of opportunity" in post-resection metastatic breast cancer model. Here we provide the initial report that Immunomax® demonstrates the capacity to eliminate micro-metastatic disease in the post-resection, 4T1 mouse model of breast cancer.

METHODS

The efficacy of Immunomax® was evaluated by analyzing survival rate and the number of spontaneous clonogenic tumor cells in the lung homogenates of mice. The frequencies of activated NK, CD4(+) and CD8(+) cells as well as myeloid-derived suppressor cells and Treg cells were evaluated using flow cytometry. Highly purified mouse and human dendritic and NK cells were sorted and the effect of Immunomax® on activation status of these cells was assessed by flow cytometry. The property of Immunomax® as TLR-4 agonist was determined by NF-κB/SEAP reporter gene assay, WB, RT-PCR.

RESULTS

Immunomax® injections significantly prolonged overall survival and cured 31% of mice. This immunostimulator activates DCs via the TLR-4, which in turn stimulates tumoricidal NK cells and in vitro, completely inhibits growth of 4T1 cells. Incubation of PBMC from healthy donors with Immunomax® activates NK cells via activation of plasmacytoid DC leading significantly higher efficacy in killing of human NK-target cells K562 compared with non-treated cells.

CONCLUSION

This is the first demonstration that Immunomax® is a TLR-4 agonist and the first report of a documented role for this pharmaceutical grade immunostimulator in augmenting anti-tumor activity, suggesting that incorporation of Immunomax® into developing breast cancer therapeutic strategies may be beneficial and with less potential toxicity than checkpoint inhibitors.

Influence of autologous dendritic cells on the in-vitro expansion and functions of peripheral blood NK cells

CONTEXT

Allogeneic reactive NK cells were previously shown to exert a graft-versus-leukemia (GVL) effect during allogeneic hematopoietic stem cell transplantation, as well as reduce the incidence of graft-versus-host disease (GVHD).

OBJECTIVE

We used autologous immature DCs as feeder cells for the in-vitro expansion of NK cells and studied the function of the NK cell cultures.

MATERIALS AND METHODS

NK cells were cultured for 15 days in the presence of autologous, immature DCs. Fold expansion, killing activity and expression of IFN-γ, perforin and granzyme B were evaluated.

RESULTS

The highest NK cell expansion efficiency was observed when the ratio of NK cells:DCs was 2:1 and when cells were cultured in a contact-dependent manner. The killing activity of NK cells was highest when the NK:DC ratio was 10:1. NK cell cultures exhibited a significant upregulation in the mRNA expression of IFN-γ, perforin and granzyme B when the ratio of NK cells to DCs was 10:1.

DISCUSSION

We successfully amplified NK cells using autologous immature DCs derived from human peripheral monocytes after induction as feeder cells. The use of autologous immature DCs for ex-vivo expansion of NK cells can be clinically applied to overcome limitations, such as the small number of NK cells in peripheral blood, and the high cost of NK cell sorting. Transfusion of allogeneic reactive NK cells has been suggested as a potential adjunctive therapeutic strategy after transplantation.

CONCLUSION

Autologous immature DCs can be used as feeder cells for ex-vivo expansion of functional NK cells.

NK cell activation in human hantavirus infection explained by virus-induced IL-15/IL15Rα expression

Clinical infection with hantaviruses cause two severe acute diseases, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). These diseases are characterized by strong immune activation, increased vascular permeability, and up to 50% case-fatality rates. One prominent feature observed in clinical hantavirus infection is rapid expansion of natural killer (NK) cells in peripheral blood of affected individuals. We here describe an unusually high state of activation of such expanding NK cells in the acute phase of clinical Puumala hantavirus infection. Expanding NK cells expressed markedly increased levels of activating NK cell receptors and cytotoxic effector molecules. In search for possible mechanisms behind this NK cell activation, we observed virus-induced IL-15 and IL-15Rα on infected endothelial and epithelial cells. Hantavirus-infected cells were shown to strongly activate NK cells in a cell-cell contact-dependent way, and this response was blocked with anti-IL-15 antibodies. Surprisingly, the strength of the IL-15-dependent NK cell response was such that it led to killing of uninfected endothelial cells despite expression of normal levels of HLA class I. In contrast, hantavirus-infected cells were resistant to NK cell lysis, due to a combination of virus-induced increase in HLA class I expression levels and hantavirus-mediated inhibition of apoptosis induction. In summary, we here describe a possible mechanism explaining the massive NK cell activation and proliferation observed in HFRS patients caused by Puumala hantavirus infection. The results add further insights into mechanisms behind the immunopathogenesis of hantavirus infections in humans and identify new possible targets for intervention.

Hantaviruses cause severe clinical infections with up to 50% case-fatality rates. The diseases represent an important global health problem as no vaccine or specific treatment is available. The most prominent hallmark in patients is strong immune activation, reflected as massive CD8 T and NK cell expansion, accompanied by severe vascular leakage. The mechanisms behind this massive immune activation are still not fully understood. Here, we first assessed the expression of several activation markers and receptors on NK cells derived from hantavirus-infected patients using flow cytometry. High NK cell activation was observed during the acute phase of clinical infection. To address possible underlying mechanisms explaining this NK cell activation, we established an in vitro hantavirus infection model using human primary endothelial cells, the natural in vivo targets of the virus. We demonstrate hantavirus-induced IL-15/IL-15Rα on infected endothelial cells, and show that this results in NK cell activation, similar to the profile found in hantavirus-infected patients. Interestingly, these activated NK cells were able to kill uninfected endothelial cells despite their normal expression of HLA class I. The present data add further insights into hantavirus-induced pathogenesis and suggest possible targets for future therapeutical interventions in these severe diseases.

Natural killer and dendritic cells collaborate in the immune response induced by the vaccine against uterine cervical cancer

Virus-like particles (VLPs) of human papillomavirus (HPV) are used as a vaccine against HPV-induced cancer, and recently we have shown that these VLPs are able to activate natural killer (NK) cells. Since NK cells collaborate with dendritic cells (DCs) to induce an immune response against viral infections and tumors, we studied the impact of this crosstalk in the context of HPV vaccination. NK cells in the presence of HPV-VLPs enhanced DC-maturation as shown by an upregulation of CD86 and HLA-DR and an increased production of IL-12p70, but not of the immunosuppressive cytokine IL-10. This activation was bidirectional. Indeed, in the presence of HPV-VLPs, DCs further activated NK cells by inducing the upregulation of cell surface activation markers (CD69 and HLA-DR). The function of NK cells was also improved as shown by an increase in IFN-γ secretion and cytotoxic activity against an HPV(+) cell line. This crosstalk between NK cells and DCs needed CD40 interaction and IL-12p70 secretion, whereas NKG2D was not implicated. Our results provide insight into how VLPs interact with innate immune cells and how NK cells and DCs play a role in the immune response induced by this vaccine agent.

TNFR2 and IL-12 coactivation enables slanDCs to support NK-cell function via membrane-bound TNF-α

Human blood NK cells exert strong cytotoxicity against transformed cells and produce different cytokines and chemokines with an important role in modulating immune responses. However, the nature of NK-cell function depends on NK-cell interaction with other immune cells. One type of immune cells that communicate with NK cells are 6-sulfo LacNAc DCs (slanDCs), which comprise a major subpopulation of proinflammatory human blood DCs. In this study, we investigated the molecular mechanisms by which slanDCs interact with NK cells. Our in vitro studies demonstrate that LPS-stimulated slanDCs enhance activation and function of NK cells essentially via membrane-bound TNF-α (mTNF-α). LPS stimulation upregulates expression of mTNF-α in slanDCs, and surface TNF receptor 2 (TNFR2) is upregulated on NK cells after coincubation with slanDCs. IL-12 secreted by slanDCs increases surface expression of TNFR2 in NK cells. TNFR2 signaling in NK cells leads to activation of NF-kB, a transcription factor for cytokines such as GM-CSF. GM-CSF provided by NK cells is responsible for enhancing IL-12 secretion in slanDCs. In conclusion, TNFR2 and IL-12 signaling, which support one another, enables slanDCs to enhance NK-cell function through mTNF-α, thereby regulating immune responses.

How melanoma cells inactivate NK cells

NK cells are the most potent effectors against different tumors in vitro. However, their efficacy in vivo is compromised by suppressive signals delivered by tumor or tumor-associated cells. This study unravels the molecular mechanisms by which melanomas disarm NK cells and offers clues to revert such inhibitory effect.

Dendritic cell exosomes directly kill tumor cells and activate natural killer cells via TNF superfamily ligands

Autocrine and paracrine cell communication can be conveyed by multiple mediators, including membrane-associate proteins, secreted proteins and exosomes. Exosomes are 30–100 nm endosome-derived vesicles consisting in cytosolic material surrounded by a lipid bilayer containing transmembrane proteins. We have previously shown that dendritic cells (DCs) express on their surface multiple TNF superfamily ligands (TNFSFLs), by which they can induce the apoptotic demise of tumor cells as well as the activation of natural killer (NK) cells. In the present study, we demonstrate that, similar to DCs, DC-derived exosomes (DCex) express on their surface TNF, FasL and TRAIL, by which they can trigger caspase activation and apoptosis in tumor cells. We also show that DCex activate NK cells and stimulate them to secrete interferonγ (IFNγ) upon the interaction of DCex TNF with NK-cell TNF receptors. These data demonstrate that DCex can mediate essential innate immune functions that were previously ascribed to DCs.

The use of microRNA by human viruses: lessons from NK cells and HCMV infection

Depending on ethnicity and on social conditions, between 40 and 90 % of the population is infected with human cytomegalovirus (HCMV). In immunocompetent patients, the virus may cause an acute disease and then revert to a state of latency, which enables its coexistence with the human host. However, in cases of immunosuppression or in neonatal infections, HCMV can cause serious long-lasting illnesses. HCMV has developed multiple mechanisms in order to escape its elimination by the immune system, specifically by two killer cell types of the adaptive and the innate immune systems; cytotoxic T lymphocytes (CTL) and natural killer (NK) cells, respectively. Another fascinating aspect of HCMV is that like other highly developed herpesviruses, it expresses its own unique set of microRNAs. Here, we initially describe how the activity of NK cells is regulated under normal conditions and during infection. Then, we discuss what is currently known about HCMV microRNA-mediated interactions, with special emphasis on immune modulation and NK cell evasion. We further illustrate the significant modulation of cellular microRNAs during HCMV infection. Although, the full target spectrum of HCMV microRNAs is far from being completely elucidated, it can already be concluded that HCMV uses its "multitasking" microRNAs to globally affect its own life cycle, as well as important cellular and immune-related pathways.

MHC-I molecules selectively inhibit cell-mediated cytotoxicity triggered by ITAM-coupled activating receptors and 2B4

NK cell effector functions are controlled by a combination of inhibitory receptors, which modulate NK cell activation initiated by stimulatory receptors. Most of the canonical NK cell inhibitory receptors recognize allelic forms of classical and non-classical MHC class I molecules. Furthermore, high expression of MHC-I molecules on effector immune cells is also associated with reverse signaling, giving rise to several immune-regulatory functions. Consequently, the inhibitory function of MHC class I expressed on a human NKL cell line and activated primary NK and T cells on different activating receptors are analyzed in this paper. Our results reveal that MHC-I molecules display specific patterns of “selective” inhibition over cytotoxicity and cytokine production induced by ITAM-dependent receptors and 2B4, but not on NKG2D. This contrasts with the best known “canonical” inhibitory receptors, which constitutively inhibit both functions, regardless of the activating receptor involved. Our results support the existence of a new fine-tuner inhibitory function for MHC-I molecules expressed on cytotoxic effector cells that could be involved in establishing self-tolerance in mature activated NK cells, and could also be important in tumor and infected cell recognition.

Vγ2Vδ2 T cell Costimulation Increases NK cell Killing of Monocyte-derived Dendritic Cells

Interactions between NK and dendritic cells (DC) affect maturation and function of both cell populations, including NK killing of DC (editing) that is important for controlling the quality of immune responses. We also know that antigen-stimulated Vγ2Vδ2 T cells costimulate NK cells via 4-1BB to enhance killing of tumor cell lines but we do not know what regulates 4-1BB expression or whether other NK effector functions including DC killing, might also be influenced by NK:γδ T cell cross talk. Here we show that antigen-stimulated γδ T cells costimulate NK through ICOS:ICOSL and this signal increases NK killing of autologous DC. Effects of NK:γδ T cell co-culture, which could be reproduced with soluble ICOS-Fc fusion protein, included increased CD69 and 4-1BB expression, IFN-γ, TNF-α, MIP-1β, I-309, RANTES and sFasL production, as well as elevated mRNA levels for costimulatory receptors OX40 (TNFRSF4) and GITR (TNFRSF18). Thus, ICOS/ICOSL costimulation of NK by Vγ2Vδ2 T cells had broad effects on NK phenotype and effector functions. The NK γδ T cell cross talk links innate and antigen-specific lymphocyte responses in the control of cytotoxic effector function and dendritic cell killing. This article is protected by copyright. All rights reserved.

Natural killer cells: a coherent model for their functional role in Mycobacterium tuberculosis infection

Tuberculosis is still a leading cause of bacterial infection worldwide, with an estimate of over two billion people latently infected with Mycobacterium tuberculosis (MTB). A delicate interplay between MTB and the host's innate and acquired immune system can influence the outcome of the infection, which ranges from pathogen elimination to the establishment of a latent infection or a progressive disease. Although the host cell-mediated adaptive immune response is of vital importance in the control of MTB infection, growing evidence indicates that innate immune cells may greatly influence the outcome of the interaction between the bacterium and the host. Among the cell populations likely to play a role in the host immune response to MTB, natural killer (NK) cells have recently attracted considerable interest. This review is dedicated to dissecting the role of NK cells in immunity to tuberculosis, reporting the most relevant findings and providing a working model of the possible contribution of NK cells in early and late events associated with MTB infection.

A think tank of TINK/TANKs: tumor-infiltrating/tumor-associated natural killer cells in tumor progression and angiogenesis

Tumor-infiltrating leukocytes are often induced by the cancer microenvironment to display a protumor, proangiogenic phenotype. This “polarization” has been described for several myeloid cells, in particular macrophages. Natural killer (NK) cells represent another population of innate immune cells able to infiltrate tumors. The role of NK in tumor progression and angiogenesis has not yet been fully investigated. Several studies have shown that tumor-infiltrating NK (here referred to as “TINKs”) and tumor-associated NK (altered peripheral NK cells, which here we call “TANKs”) are compromised in their ability to lysew tumor cells. Recent data have suggested that they are potentially protumorigenic and can also acquire a proangiogenic phenotype. Here we review the properties of TINKs and TANKs and compare their activities to that of NK cells endowed with a physiological proangiogenic phenotype, in particular decidual NK cells. We speculate on the potential origins of TINKs and TANKs and on the immune signals involved in their differentiation and polarization. The TINK and TANK phenotype has broad implications in the immune response to tumors, ranging from a deficient control of cancer and cancer stem cells to an altered crosstalk with other relevant players of the immune response, such as dendritic cells, to induction of cancer angiogenesis. With this recently acquired knowledge that has not yet been put into perspective, we point out new potential avenues for therapeutic intervention involving NK cells as a target or an ally in oncology.

The activating receptor NKG2D of natural killer cells promotes resistance against enterovirus-mediated inflammatory cardiomyopathy

In enterovirus-induced cardiomyopathy, information regarding the detailed impact of natural killer (NK) cells on the outcome of the disease is limited. We therefore hypothesized that NK cells and certain NK cell receptors determine the different outcome of coxsackievirus B3 (CVB3) myocarditis. Here, we demonstrate in murine models that resistance to chronic CVB3 myocarditis in immunocompetent C57BL/6 mice is characterized by significantly more mature CD11b(high) NK cells, the presence of NKG2D on NK cells, and enhanced NKG2D-dependent cytotoxicity compared to CVB3-susceptible A.BY/SnJ mice. The highly protective role of NKG2D in myocarditis was further proven by in vivo neutralization of NKG2D as well as in NKG2D-deficient mice but was shown to be independent of CD8(+) T-cell-dependent immunity. Moreover, the adoptive transfer of immunocompetent C57BL/6 NK cells pre- (day -1) as well as post-infectionem (day +2) displayed the potential to prevent permissive A.BY/SnJ mice from a progressive outcome of CVB3 myocarditis reflected by significantly improved cardiopathology and heart function. Altogether, our results provide firm evidence for a protective role of NKG2D-activated NK cells in CVB3 myocarditis leading to an effective virus clearance, thus offering novel therapeutic options in the treatment of virus-induced myocarditis.

Phenotypic and functional activation of hyporesponsive KIRnegNKG2Aneg human NK-cell precursors requires IL12p70 provided by Poly(I:C)-matured monocyte-derived dendritic cells

A functionally responsive natural killer (NK)-cell repertoire requires the acquisition of inhibitory NKG2A and killer immunoglobulin-like receptors (KIR) through pathways that remain undefined. Functional donor NK cells expressing KIRs for non-self class I MHC ligands contribute to a positive outcome after allogeneic hematopoietic stem cell transplantation (alloHSCT) by targeting HLA-matched recipient leukemic cells. Insofar as circulating donor conventional dendritic cells (DC) reconstitute with comparable kinetics with donor NK cells after alloHSCT, we used hyporesponsive KIRnegNKG2Aneg precursor cells to evaluate how specific DC subtypes generate a functionally active NK-cell repertoire. Both monocyte-derived DCs (moDC) and Langerhans-type DCs (LC) induce KIRnegNKG2Aneg precursor cells to express the inhibitory receptors NKG2A and KIR, without requiring cell proliferation. Poly(I:C)-matured moDCs significantly augmented the expression of NKG2A, but not KIR, in an IL12p70-dependent manner. Although all DC-stimulated KIRnegNKG2Aneg cells were able to acquire cytolytic activity against class I MHC-negative targets, the ability to secrete IFNγ was restricted to cells that were stimulated by IL12p70-producing, poly(I:C)-matured moDCs. This critical ability of poly(I:C)-matured moDCs to provide IL12p70 to developing KIRnegNKG2Aneg precursors results in a dom4inant, multifunctional, NKG2Apos NK-cell population that is capable of both cytolysis and IFNγ production. Poly(I:C)-matured moDCs are, therefore, the most effective conventional DC subtype for generating a functionally competent NK-cell repertoire by an IL12p70-dependent mechanism.

Liaison between natural killer cells and dendritic cells in human gestation

A successful pregnancy relies on immunological adaptations that allow the fetus to grow and develop in the uterus, despite being recognized by maternal immune cells. Among several immunocompetent cell types present within the human maternal/fetal interface, DC-SIGN(+) dendritic cells (DCs) and CD56(+) natural killer (NK) cells are of major importance for early pregnancy maintenance, not only generating maternal immunological tolerance but also regulating stromal cell differentiation. Previous reports show the presence of NK-DC cell conjugates in first trimester human decidua, suggesting that these cells may play a role in the modulation of the local immune response within the uterus. While effective immunity is necessary to protect the mother from harmful pathogens, some form of tolerance must be activated to avoid an immune response against fetal antigens. This review article discusses current evidence concerning the functions of DC and NK cells in pregnancy and their liaison in human decidua.

Dendritic cells during Epstein Barr virus infection

Epstein Barr virus (EBV) causes persistent infection in more than 90% of the human adult population and is associated with 2% of all tumors in humans. This γ-herpes virus infects primarily human B and epithelial cells, but it has been reported to be sensed by dendritic cells (DCs) during primary infection. These activated DCs are thought to contribute to innate restriction of EBV infection and initiate EBV-specific adaptive immune responses via cross-priming. The respective evidence and their potential importance for EBV-specific vaccine development will be discussed in this review.

NK cell receptor NKp46 regulates graft-versus-host disease

Hematopoietic stem cell transplantation (HSCT) is often the only curative treatment for a wide variety of hematologic malignancies. Donor selection in these diseases is crucial, given that transplanted cells can mediate not only the desired graft-versus-leukemia effect but also graft-versus-host disease (GVHD). Here, we demonstrate that in the absence of NKp46, a major killer receptor expressed by human and mouse natural killer (NK) cells, GVHD is greatly exacerbated, resulting in rapid mortality of the transplanted animals because of infection with commensal bacteria. Furthermore, we demonstrate that the exacerbated GVHD is the result of an altered ability of immune cells to respond to stimulation by immature dendritic cells. Because high and low expression of NKp46 on NK cells is observed in different individuals, our data indicate that choosing NKp46-high donors for the treatment of different hematologic malignancies might lead to better tumor eradication while minimizing GVHD.

Role of CD8+ T cells and lymphoid dendritic cells in protection from ocular herpes simplex virus 1 challenge in immunized mice

The development of immunization strategies to protect against ocular infection with herpes simplex virus 1 (HSV-1) must address the issue of the effects of the strategy on the establishment of latency in the trigeminal ganglia (TG). It is the reactivation of this latent virus that can cause recurrent disease and corneal scarring. CD8(+) T cells and dendritic cells (DCs) have been implicated in the establishment and maintenance of latency through several lines of inquiry. The objective of the current study was to use CD8α(-/-) and CD8β(-/-) mice to further evaluate the contributions of CD8(+) T cells and the CD8α(+) and CD8α(-) subpopulations of DCs to the protection afforded against ocular infection by immunization against HSV-1 and their potential to increase latency. Neutralizing antibody titers were similar in immunized CD8α(-/-), CD8β(-/-), and wild-type (WT) mice, as was virus replication in the eye. However, on day 3 postinfection (p.i.), the copy number of HSV-1 glycoprotein B (gB) was higher in the corneas and TG of CD8α(-/-) mice than those of WT mice, whereas on day 5 p.i. it was lower. As would be anticipated, the lack of CD8α(+) or CD8β(+) cells affected the levels of type I and type II interferon transcripts, but the effects were markedly time dependent and tissue specific. The levels of latent virus in the TG, as estimated by measurement of LAT transcripts and in vitro explant reactivation assays, were lower in the immunized, ocularly challenged CD8α(-/-) and WT mice than in their CD8β(-/-) counterparts. Immunization reduced the expression of PD-1, a marker of T-cell exhaustion, in the TG of ocularly challenged mice, and mock-immunized CD8α(-/-) mice had lower levels of PD-1 expression and latency than mock-immunized WT or CD8β(-/-) mice. The expansion of the CD8α(-) subpopulation of DCs through injection of WT mice with granulocyte-macrophage colony-stimulating factor (GM-CSF) DNA reduced the amount of latency and PD-1 expression in the TG of infected mice. In contrast, injection of FMS-like tyrosine kinase 3 ligand (Flt3L) DNA, which expanded both subpopulations, was less effective. Our results suggest that the absence of both CD8α(+) T cells and CD8α(+) DCs does not reduce vaccine efficacy, either directly or indirectly, in challenged mice and that administration of GM-CSF appears to play a beneficial role in reducing latency and T-cell exhaustion. Importance: In the past 2 decades, two large clinical HSV vaccine trials were performed, but both vaccine studies failed to reach their goals. Thus, as an alternative to conventional vaccine studies, we have used a different strategy to manipulate the host immune responses in an effort to induce greater protection against HSV infection. In lieu of the pleiotropic effect of CD8α(+) DCs in HSV-1 latency, in this report, we show that the absence of CD8α(+) T cells and CD8α(+) DCs has no adverse effect on vaccine efficacy. In line with our hypothesis, we found that pushing DC subpopulations from CD8α(+) DCs toward CD8α(-) DCs by injection of GM-CSF reduced the amount of latent virus and T-cell exhaustion in TG. While these studies point to the lack of a role for CD8α(+) T cells in vaccine efficacy, they in turn point to a role for GM-CSF in reducing HSV-1 latency.

Natural killer cells induce eosinophil activation and apoptosis

Eosinophils are potent inflammatory cells with numerous immune functions, including antigen presentation and exacerbation of inflammatory responses through their capacity to release a range of largely preformed cytokines and lipid mediators. Thus, timely regulation of eosinophil activation and apoptosis is crucial to develop beneficial immune response and to avoid tissue damage and induce resolution of inflammation. Natural Killer (NK) cells have been reported to influence innate and adaptive immune responses by multiple mechanisms including cytotoxicity against other immune cells. In this study, we analyzed the effect of the interaction between NK cells and eosinophils. Co-culture experiments revealed that human NK cells could trigger autologous eosinophil activation, as shown by up-regulation of CD69 and down-regulation of CD62L, as well as degranulation, evidenced by increased CD63 surface expression, secretion of eosinophil cationic protein (ECP) and eosinophil derived neurotoxin (EDN). Moreover, NK cells significantly and dose dependently increased eosinophil apoptosis as shown by annexin V and propidium iodide (PI) staining. Direct contact was necessary for eosinophil degranulation and apoptosis. Increased expression of phosphorylated extracellular signal-regulated kinase (ERK) in cocultured eosinophils and inhibition of eosinophil CD63 expression by pharmacologic inhibitors suggest that MAPK and PI3K pathways are involved in NK cell-induced eosinophil degranulation. Finally, we showed that NK cells increased reactive oxygen species (ROS) expression by eosinophils in co-culture and that mitochondrial inhibitors (rotenone and antimycin) partially diminished NK cell-induced eosinophil apoptosis, suggesting the implication of mitochondrial ROS in NK cell-induced eosinophil apoptosis. Pan-caspase inhibitor (ZVAD-FMK) only slightly decreased eosinophil apoptosis in coculture. Altogether, our results suggest that NK cells regulate eosinophil functions by inducing their activation and their apoptosis.

Cross-Talks between Natural Killer Cells and Distinct Subsets of Dendritic Cells

In recent years, the essential role of bi-directional cross-talk between natural killer (NK) and dendritic cells (DC) during immune responses has been clearly elucidated. In particular, this cross-talk results in the development of an efficient innate response, through DC-mediated NK cell activation, and a potent adaptive immune response, through NK-mediate DC editing and maturation. Recently, some novel human DC subsets have been identified: migratory DCs in afferent lymph and draining lymph nodes; CLEC9A⁺/BDCA3⁺ (CD141) DCs in interstitial dermis, liver, lung; inflammatory DCs in several inflammatory fluids. At the same time, it has been shown that also human NK cells are present in these compartments. Here, we will review the most recent findings on NK/DC cross-talk and we will discuss the necessity of acquiring more complete knowledge about these interactions in view of the new information available on both DC and NK cell subsets.

In vivo immunological antitumor effect of OK-432-stimulated dendritic cell transfer after radiofrequency ablation

Radiofrequency ablation therapy (RFA) is a radical treatment for liver cancers and induces tumor antigen-specific immune responses. In the present study, we examined the antitumor effects of focal OK-432-stimulated dendritic cell (DC) transfer combined with RFA and analyzed the functional mechanisms involved using a murine model. C57BL/6 mice were injected subcutaneously with colon cancer cells (MC38) in their bilateral flanks. After the establishment of tumors, the subcutaneous tumor on one flank was treated using RFA, and then OK-432-stimulated DCs were injected locally. The antitumor effect of the treatment was evaluated by measuring the size of the tumor on the opposite flank, and the immunological responses were assessed using tumor-infiltrating lymphocytes, splenocytes and draining lymph nodes. Tumor growth was strongly inhibited in mice that exhibited efficient DC migration after RFA and OK-432-stimulated DC transfer, as compared to mice treated with RFA alone or treatment involving immature DC transfer. We also demonstrated that the antitumor effect of this treatment depended on both CD8-positive and CD4-positive cells. On the basis of our findings, we believe that combination therapy for metastatic liver cancer consisting of OK-432-stimulated DCs in combination with RFA can proceed to clinical trials, and it is anticipated to be markedly superior to RFA single therapy.

CTLA-4 is expressed by activated mouse NK cells and inhibits NK Cell IFN-γ production in response to mature dendritic cells

NK cells express an array of activating and inhibitory receptors that determine NK cell responses upon triggering by cognate ligands. Although activating NK cell receptors recognize mainly ligands expressed by stressed, virus-infected, or transformed cells, most inhibitory receptors engage MHC class I, preventing NK cell activation in response to healthy cells. In this study, we provide insight into the regulation and function of additional receptors involved in mouse NK cell responses: CTLA-4 and CD28. CTLA-4 and CD28 engage the same ligands, B7-1 and B7-2, which are primarily expressed by APCs, such as dendritic cells. Our data demonstrate that activation of mouse NK cells with IL-2 induces the expression of CTLA-4 and upregulates CD28. CTLA-4 expression in IL-2-expanded NK cells was further up- or downregulated by IL-12 or TGF-β, respectively. Using gene-deficient NK cells, we show that CD28 induces, and CTLA-4 inhibits, IFN-γ release by NK cells upon engagement by the recombinant ligand, B7-1, or upon coculture with mature dendritic cells. Notably, we show that mouse NK cells infiltrating solid tumors express CD28 and CTLA-4 and respond to stimulation with recombinant B7-1, suggesting that the NK cell responses mediated by the CD28/CTLA-4:B7-1/B7-2 system could be of importance during malignant disease. Accordingly, our study might have implications for immunotherapy of cancer based on blocking anti-CTLA-4 mAbs.

Heat shock protein vaccination and directed IL-2 therapy amplify tumor immunity rapidly following bone marrow transplantation in mice

Tumor relapse is the primary cause of mortality in patients with hematologic cancers following autologous hematopoietic stem cell transplantation (HSCT). Vaccination early after HSCT can exploit both the state of lymphopenia and minimal residual disease for generating antitumor immunity. Here, multiple vaccinations using lymphoma cells engineered to secrete heat shock protein fusion gp96-Ig within 2 weeks of T cell-replete syngeneic HSCT led to cross-presentation and increased survival of lymphoma-bearing mice. To enhance vaccine efficacy, interleukin (IL)-2 was directed to predominantly memory phenotype CD8(+) T lymphocytes and natural killer (NK) cells via administration bound to anti-IL-2 monoclonal antibody clone S4B6 (IL-2S4B6). Combination therapy with gp96-Ig vaccination and coordinated infusions of IL-2S4B6 resulted in marked prolongation of survival, which directly correlated with ~500% increase in effector CD8(+) T-cell numbers. Notably, this dual regimen elicited large increases in both donor CD8(+) T and NK cells, but not CD4(+) T lymphocytes; the former 2 populations are essential for both vaccine efficacy and protection against opportunistic infections after HSCT. Indeed, IL-2S4B6-treated HSCT recipients infected with Listeria monocytogenes exhibited decreased bacterial levels. These preclinical studies validate a new strategy particularly well suited to the post-HSCT environment, which may augment adaptive and innate immune function in patients with malignant disease receiving autologous HSCT.

Human NK cells: from surface receptors to the therapy of leukemias and solid tumors

Natural Killer (NK) cells are major effector cells of the innate immunity. The discovery, over two decades ago, of major histocompatibility complex-class I-specific inhibitory NK receptors and subsequently of activating receptors, recognizing ligands expressed by tumor or virus-infected cells, paved the way to our understanding of the mechanisms of selective recognition and killing of tumor cells. Although NK cells can efficiently kill tumor cells of different histotypes in vitro, their activity may be limited in vivo by their inefficient trafficking to tumor lesions and by the inhibition of their function induced by tumor cells themselves and by the tumor microenvironment. On the other hand, the important role of NK cells has been clearly demonstrated in the therapy of high risk leukemias in the haploidentical hematopoietic stem cell (HSC) transplantation setting. NK cells derived from donor HSC kill leukemic cells residual after the conditioning regimen, thus preventing leukemia relapses. In addition, they also kill residual dendritic cells and T lymphocytes, thus preventing both GvH disease and graft rejection.

NCR3/NKp30 contributes to pathogenesis in primary Sjogren's syndrome

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease characterized by a lymphocytic exocrinopathy. However, patients often have evidence of systemic autoimmunity, and they are at markedly increased risk for the development of non- Hodgkin's lymphoma. Similar to other autoimmune disorders, a strong interferon (IFN) signature is present among subsets of pSS patients, although the precise etiology remains uncertain. NCR3/NKp30 is a natural killer (NK)-specific activating receptor regulating the cross talk between NK and dendritic cells and type II IFN secretion. We performed a case-control study of genetic polymorphisms of the NCR3/NKp30 gene and found that rs11575837 (G>A) residing in the promoter was associated with reduced gene transcription and function as well as protection to pSS. We also demonstrated that circulating levels of NCR3/NKp30 were significantly increased among pSS patients compared with controls and correlated with higher NCR3/NKp30 but not CD16-dependent IFN-γ secretion by NK cells. Excess accumulation of NK cells in minor salivary glands correlated with the severity of the exocrinopathy. B7H6, the ligand of NKp30, was expressed by salivary epithelial cells. These findings suggest that NK cells may promote an NKp30-dependent inflammatory state in salivary glands and that blockade of the B7H6/NKp30 axis could be clinically relevant in pSS.

NK cell autoreactivity and autoimmune diseases

Increasing evidences have pointed out the relevance of natural killer (NK) cells in organ-specific and systemic autoimmune diseases. NK cells bear a plethora of activating and inhibiting receptors that can play a role in regulating reactivity with autologous cells. The activating receptors recognize natural ligands up-regulated on virus-infected or stressed or neoplastic cells. Of note, several autoimmune diseases are thought to be linked to viral infections as one of the first event in inducing autoimmunity. Also, it is conceivable that autoimmunity can be triggered when a dysregulation of innate immunity occurs, activating T and B lymphocytes to react with self-components. This would imply that NK cells can play a regulatory role during adaptive immunity; indeed, innate lymphoid cells (ILCs), comprising the classical CD56(+) NK cells, have a role in maintaining or alternating tissue homeostasis secreting protective and/or pro-inflammatory cytokines. In addition, NK cells display activating receptors involved in natural cytotoxicity and the activating isoforms of receptors for HLA class I that can interact with healthy host cells and induce damage without any evidence of viral infection or neoplastic-induced alteration. In this context, the interrelationship among ILC, extracellular-matrix components, and mesenchymal stromal cells can be considered a key point for the control of homeostasis. Herein, we summarize evidences for a role of NK cells in autoimmune diseases and will give a point of view of the interplay between NK cells and self-cells in triggering autoimmunity.

Activin A as a mediator of NK-dendritic cell functional interactions

The interaction of NK cells with dendritic cells (DCs) results in reciprocal cell activation through the interaction of membrane proteins and the release of soluble factors. In this article, we report that in NK-DC cocultures, among a set of 84 cytokines investigated, activin A was the second highest induced gene, with CXCL8 being the most upregulated one. Activin A is a member of the TGF-β superfamily and was previously shown to possess both proinflammatory and anti-inflammatory activities. In NK-DC cocultures, the induction of activin A required cell contact and was dependent on the presence of proinflammatory cytokines (i.e., IFN-γ, TNF-α, and GM-CSF), as well as on NK cell-mediated DC killing. CD1(+) DCs were the main activin A producer cells among myeloid blood DC subsets. In NK-DC cocultures, inhibition of activin A by follistatin, a natural inhibitory protein, or by a specific blocking Ab, resulted in the upregulation of proinflammatory cytokine release (i.e., IL-6, IL-8, TNF-α) by DCs and in the increase of DC maturation. In conclusion, our study reports that activin A, produced during NK-DC interactions, represents a relevant negative feedback mechanism that might function to prevent excessive immune activation by DCs.

Immunotherapy of multiple myeloma: the start of a long and tortuous journey

The field of tumor immunotherapy is still in its infancy. It is becoming clear that the human immune response is the result of highly complex, continuously evolving interactions between cells of the adaptive and innate arms of the immune system, the internal and external environments, and normal and abnormal cells (e.g., myeloma plasma cells). Despite the considerable advances in our knowledge over the past 30 years, we have still only scratched the surface of the immune system's interaction with malignant diseases such as myeloma and to date, this has not translated into significantly better outcomes for patients with this disease. This review will summarize our current knowledge of the fundamental immunology of myeloma, review immunotherapy trials reported to date and discuss whether, in light of the current information, immunotherapy of multiple myeloma is an achievable goal.

Hypersensitivity reactions to beta-lactams

Beta-lactam antibiotics (BLs) are the most frequent cause of hypersensitivity reactions mediated by specific immunological mechanisms, with two main types, IgE reactions or T-cell-dependent responses. From a practical point of view, these reactions can be classified into immediate, for those appearing within 1 h after drug intake, and non-immediate, for those appearing at least 1 h after and usually within 24 h of BL administration. The clinical symptoms differ according to this classification. Urticaria and anaphylaxis are the most frequently recorded symptoms in immediate reactions and maculopapular exanthema and delayed urticaria in non-immediate reactions. Although the exact diagnostic approach differs depending on the underlying mechanism, it is based on the performance of skin testing, laboratory tests, and drug provocation tests.T cells are a key factor in all types of hypersensitivity reactions to BLs, regulating both IgE production or acting as effector cells, with a different profile of cytokine production. A Th1 pattern is observed in both CD4(+) and CD8(+) peripheral T cells in non-immediate reactions, whereas a Th2 pattern is expressed in CD4(+) T cells in immediate reactions.

Baseline and Dynamic Expression of Activating NK Cell Receptors in the Control of Chronic Viral Infections: The Paradigm of HIV-1 and HCV

Natural killer (NK) cell function is regulated by a balance between the triggering of activating and inhibitory receptors expressed on their surface. A relevant effort has been focused so far on the study of KIR carriage/expression setting the basis for NK cell education and self-tolerance. Focus on the evolution and regulation of activating NK receptors has lagged behind so far. Our understanding of activating receptor expression and regulation has recently improved by evidences derived from in vitro and in vivo studies. Virus infection - either acute or chronic - determines preferential expansion of NK cells with specific phenotype, activating receptors, and with recall-like functional activity. Studies on patients with viral infection (HIV and HCV) and specific diverging clinical courses confirm that inter-individual differences may exist in baseline expression of natural cytotoxicity receptors (NKp46 and NKp30). The findings that patients with divergent clinical courses have different kinetics of activating receptor density expression upon NK cell activation in vitro provide an additional, time-dependent, functional parameter. Kinetic changes in receptor expression thus represent an additional parameter to basal receptor density expression. Different expression and inducibilities of activating receptors on NK cells contribute to the high diversity of NK cell populations and may help our understanding of the inter-individual differences in innate responses that underlie divergent disease courses.

Gap junction intercellular communications regulate NK cell activation and modulate NK cytotoxic capacity

Gap junctions (GJs) mediate intercellular communication between adjacent cells. Previously, we showed that connexin 43 (Cx43), the main GJ protein in the immune system, mediates Ag transfer between human dendritic cells (DCs) and is recruited to the immunological synapse during T cell priming. This crosstalk contributed to T cell activation, intracellular Ca(2+) responses, and cytokine release. However, the role of GJs in NK cell activation by DCs and NK cell-mediated cytotoxicity against tumor cells remains unknown. In this study, we found polarization of Cx43 at the NK/DC and NK/tumor cell-contact sites, accompanied by the formation of functional GJs between NK/DCs and NK/tumor cells, respectively. Cx43-GJ-mediated intercellular communication (GJIC) between human NK and DCs was bidirectional. Blockage of Cx43-GJIC inhibited NK cell activation, though it affected neither the phenotype nor the function of DCs. Cx43 knockdown or inhibition using mimetic peptides greatly reduced CD69 and CD25 expression and IFN-γ release by DC-stimulated NK cells. Moreover, blocking Cx43 strongly inhibited the NK cell-mediated tumor cell lysis associated with inhibition of granzyme B activity and Ca(2+) influx. Our data identify a novel and active role for Cx43-GJIC in human NK cell activation and antitumor effector functions that may be important for the design of new immune therapeutic strategies.

Natural cytotoxicity receptors and their ligands

Natural killer (NK) cells are innate lymphoid cells (ILCs) that participate to the clearance of pathogen-infected cells and tumour cells. NK cells and subsets of ILCs express the natural cytotoxicity receptors (NCRs) NKp46, NKp44 and NKp30 at their surface. NCRs have been shown to recognize a broad spectrum of ligands ranging from viral-, parasite- and bacterial-derived ligands to cellular ligands; however, the full identification of NCR ligands remains to be performed and will undoubtedly contribute to a better understanding of NK cell and ILC biology.

Natural killer cells in patients with allergic diseases

Natural killer (NK) cells not only exert cytotoxic activity against tumor cells or infected cells but also act to regulate the function of other immune cells through secretion of cytokines and chemokines or cell contact-dependent mechanisms. NK cells are able to polarize in vitro into 2 functional distinct subsets, NK1 or NK2 cells, which are analogous to the T-cell subsets TH1 or TH2. In addition, a regulatory NK cell subset has been described that secretes IL-10, shows antigen-specific T-cell suppression, and suppresses IgE production. Although it has been demonstrated that NK cells play important roles in autoimmunity, cancer, transplantation, and pregnancy, the role of NK cells in allergy has not been extensively discussed. This review aims to discuss our understanding of NK cells and NK cell subsets in allergic inflammation and IgE regulation.

Dendritic cell derived cytokines in human natural killer cell differentiation and activation

Dendritic cells (DCs) and natural killer (NK) cells shape each other’s functions early during immune responses. DCs activate NK cells and NK cells can mature or kill DCs. In this review we will discuss which DC and NK cell subsets are mainly affected by this interaction, where these encounters might take place and which signals are exchanged. Finally, we will point out what the clinical benefit of understanding this interaction might be and how it changed our view on NK cells as innate lymphocytes.

Innate immune responses in hepatitis C virus-exposed healthcare workers who do not develop acute infection

Hepatitis C virus (HCV) infection typically results in chronic disease with HCV outpacing antiviral immune responses. Here we asked whether innate immune responses are induced in healthcare workers who are exposed to small amounts of HCV, but do not develop systemic infection and acute liver disease. Twelve healthcare workers with accidental percutaneous exposure to HCV-infected blood were prospectively studied for up to 6 months for phenotype and function of natural killer T (NKT) and NK cells, kinetics of serum chemokines, and vigor and specificity of HCV-specific T-cell responses. Eleven healthcare workers tested negative for HCV RNA and HCV antibodies. All but one of these aviremic cases displayed NKT cell activation, increased serum chemokines levels, and NK cell responses with increased CD122, NKp44, NKp46, and NKG2A expression, cytotoxicity (as determined by TRAIL and CD107a expression), and interferon-gamma (IFN-γ) production. This multifunctional NK cell response appeared a month earlier than in the one healthcare worker who developed high-level viremia, and it differed from the impaired IFN-γ production, which is typical for NK cells in chronic HCV infection. The magnitude of NKT cell activation and NK cell cytotoxicity correlated with the magnitude of the subsequent HCV-specific T-cell response. T-cell responses targeted nonstructural HCV sequences that require translation of viral RNA, which suggests that transient or locally contained HCV replication occurred without detectable systemic viremia.

CONCLUSION

Exposure to small amounts of HCV induces innate immune responses, which correlate with the subsequent HCV-specific T-cell response and may contribute to antiviral immunity.

NKp46 regulates allergic responses

Natural killer (NK) cells are cytotoxic cells that are able to rapidly kill viruses, tumor cells, parasites, bacteria, and even cells considered "self". The activity of NK cells is controlled by a fine balance of inhibitory and activating signals mediated by a complex set of different receptors. However, the function of NK cells is not restricted only to the killing of target cells, NK cells also possess other properties such as the secretion of proangiogenic factors during pregnancy. Here, we demonstrate another unique NK-cell activity, namely the regulation of T-cell mediated allergic responses, which is dependent on the NK-cell specific receptor NKp46 (Ncr1 in mice). Using mice in which the Ncr1 gene has been replaced with a green fluorescent protein, we demonstrate reduced delayed-type hypersensitivity and airway hypersensitivity. Interestingly, we show that this reduction in airway hypersensitivity is due to differences in the stimulation of T cells resulting in an altered cytokine profile.

Protective effect of polysaccharides on simulated microgravity-induced functional inhibition of human NK cells

Polysaccharides are believed to be strong immunostimulants that can promote the proliferation and activity of T cells, B cells, macrophages and natural killer (NK) cells. This study aimed to investigate the effects of five polysaccharides (Grifola frondosa polysaccharide (GFP), lentinan (LNT), G. lucidum polysaccharide (GLP), Lycium barbarum polysaccharide (LBP) and yeast glucan (YG)) on primary human NK cells under normal or simulated microgravity (SMG) conditions. Our results demonstrated that polysaccharides markedly promoted the cytotoxicity of NK cells by enhancing IFN-γ and perforin secretion and increasing the expression of the activating receptor NKp30 under normal conditions. Meanwhile polysaccharides can enhance NK cell function under SMG conditions by restoring the expression of the activating receptor NKG2D and reducing the early apoptosis and late apoptosis/necrosis. Moreover, the antibody neutralization test showed that CR3 may be the critical receptor involved in polysaccharides induced NK cells activation. These findings indicated that polysaccharides may be used as immune regulators to promote the health of the public and astronauts during space missions.

Kinetics of myeloid dendritic cell trafficking and activation: impact on progressive, nonprogressive and controlled SIV infections

We assessed the role of myeloid dendritic cells (mDCs) in the outcome of SIV infection by comparing and contrasting their frequency, mobilization, phenotype, cytokine production and apoptosis in pathogenic (pigtailed macaques, PTMs), nonpathogenic (African green monkeys, AGMs) and controlled (rhesus macaques, RMs) SIVagmSab infection. Through the identification of recently replicating cells, we demonstrated that mDC mobilization from the bone marrow occurred in all species postinfection, being most prominent in RMs. Circulating mDCs were depleted with disease progression in PTMs, recovered to baseline values after the viral peak in AGMs, and significantly increased at the time of virus control in RMs. Rapid disease progression in PTMs was associated with low baseline levels and incomplete recovery of circulating mDCs during chronic infection. mDC recruitment to the intestine occurred in all pathogenic scenarios, but loss of mucosal mDCs was associated only with progressive infection. Sustained mDC immune activation occurred throughout infection in PTMs and was associated with increased bystander apoptosis in blood and intestine. Conversely, mDC activation occurred only during acute infection in nonprogressive and controlled infections. Postinfection, circulating mDCs rapidly became unresponsive to TLR7/8 stimulation in all species. Yet, stimulation with LPS, a bacterial product translocated in circulation only in SIV-infected PTMs, induced mDC hyperactivation, apoptosis and excessive production of proinflammatory cytokines. After infection, spontaneous production of proinflammatory cytokines by mucosal mDCs increased only in progressor PTMs. We thus propose that mDCs promote tolerance to SIV in the biological systems that lack intestinal dysfunction. In progressive infections, mDC loss and excessive activation of residual mDCs by SIV and additional stimuli, such as translocated microbial products, enhance generalized immune activation and inflammation. Our results thus provide a mechanistic basis for the role of mDCs in the pathogenesis of AIDS and elucidate the causes of mDC loss during progressive HIV/SIV infections.

Myeloid dendritic cells (mDCs) are potent antigen-presenting cells that regulate both innate and adaptive immune responses and act as “watch-dogs”, sensing and controlling aberrant immune activation; as such, they may significantly impact the outcome of HIV/SIV infection. By comparing and contrasting the frequency, function, migration to tissues and levels of activation and apoptosis in progressive, nonprogressive and elite-controlled SIV infections, we investigated the mechanisms responsible for mDC loss in HIV/SIV infection and their role in driving progression to AIDS. We report that progression to AIDS is associated with low mDC preinfection levels and depletion throughout infection, due to massive migration of these cells to mucosal sites and excessive cell death by apoptosis. We also show that residual mDCs from blood and intestine have a high capacity to produce proinflammatory cytokines, thus contributing to the increased immune activation and inflammation characteristic of progressive infections.

Novel perspectives on dendritic cell-based immunotherapy of cancer

Advances in immunobiology knowledge as well as in cell culture processes that generate large numbers of purified and functionally mature dendritic cells (DCs) have raised the possibility that DCs might represent promising clinical agents to generate effective immune responses against cancer. Here, we discuss the present pitfalls of dendritic cell vaccines for the treatment of human cancer with regard to the most recent knowledge in the biology of DCs. In particular, we highlight the relevance of improving our current understanding of DC trafficking, functions and interactions with other cells of innate immunity for the development of more effective cancer vaccines.

The impact of ageing on natural killer cell function and potential consequences for health in older adults

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Roles are emerging for natural killer (NK) cells beyond removing transformed cells.

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These include immune regulation and the elimination of senescent cells.

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Human ageing is associated with a decline in NK cell function.

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We propose some aspects of human ageing are due in part to reduced NK cell function.

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These include reduced vaccination efficacy and delayed resolution of inflammation.

Forming the first line of defence against virally infected and malignant cells, natural killer (NK) cells are critical effector cells of the innate immune system. With age, significant impairments have been reported in the two main mechanisms by which NK cells confer host protection: direct cytotoxicity and the secretion of immunoregulatory cytokines and chemokines. In elderly subjects, decreased NK cell activity has been shown to be associated with an increased incidence and severity of viral infection, highlighting the clinical implications that age-associated changes in NK cell biology have on the health of older adults. However, is an increased susceptibility to viral infection the only consequence of these age-related changes in NK cell function? Recently, evidence has emerged that has shown that in addition to eliminating transformed cells, NK cells are involved in many other biological processes such as immune regulation, anti-microbial immune responses and the recognition and elimination of senescent cells, novel functions that involve NK-mediated cytotoxicity and/or cytokine production. Thus, the decrease in NK cell function that accompanies physiological ageing is likely to have wider implications for the health of older adults than originally thought. Here, we give a detailed description of the changes in NK cell biology that accompany human ageing and propose that certain features of the ageing process such as: (i) the increased reactivation rates of latent Mycobacterium tuberculosis, (ii) the slower resolution of inflammatory responses and (iii) the increased incidence of bacterial and fungal infection are attributable in part to an age-associated decline in NK cell function.

Natural killer cells: multifaceted players with key roles in hepatitis C immunity

Natural killer cells (NKs) are involved in every stage of hepatitis C viral (HCV) infection, from protection against HCV acquisition and resolution in the acute phase to treatment-induced clearance. In addition to their direct antiviral actions, NKs are involved in the induction and priming of appropriate downstream T-cell responses. In the setting of chronic HCV, overall NK cell levels are decreased, subset distribution is altered, and changes in NK receptor (NKR) expression have been demonstrated, although the contribution of individual NKRs to viral clearance or persistence remains to be clarified. Enhanced NK cell cytotoxicity accompanied by insufficient interferon-γ production may promote liver damage in the setting of chronic infection. Treatment-induced clearance is associated with activation of NK cells, and it will be of interest to monitor NK cell responses to triple therapy. Activated NK cells also have anti-fibrotic properties, and the same hepatic NK cell populations that are actively involved in control of HCV may also be involved in control of HCV-associated liver damage. We still have much to learn, in particular: how do liver-derived NKs influence the outcome of HCV infection? Do NK receptors recognize HCV-specific components? And, are HCV-specific memory NK populations generated?