Molecular mechanisms of natural killer cell activation in response to cellular stress

Effects of Polar Bear and Killer Whale Derived Contaminant Cocktails on Marine Mammal Immunity

Most controlled toxicity studies use single chemical exposures that do not represent the real world situation of complex mixtures of known and unknown natural and anthropogenic substances. In the present study, complex contaminant cocktails derived from the blubber of polar bears (PB; Ursus maritimus) and killer whales (KW; Orcinus orca) were used for in vitro concentration-response experiments with PB, cetacean and seal spp. immune cells to evaluate the effect of realistic contaminant mixtures on various immune functions. Cytotoxic effects of the PB cocktail occurred at lower concentrations than the KW cocktail (1 vs 16 μg/mL), likely due to differences in contaminant profiles in the mixtures derived from the adipose of each species. Similarly, significant reduction of lymphocyte proliferation occurred at much lower exposures in the PB cocktail (EC₅₀: 0.94 vs 6.06 μg/mL; P < 0.01), whereas the KW cocktail caused a much faster decline in proliferation (slope: 2.9 vs 1.7; P = 0.04). Only the KW cocktail modulated natural killer (NK) cell activity and neutrophil and monocyte phagocytosis in a concentration- and species-dependent manner. No clear sensitivity differences emerged when comparing cetaceans, seals and PB. Our results showing lower effect levels for complex mixtures relative to single compounds suggest that previous risk assessments underestimate the effects of real world contaminant exposure on immunity. Our results using blubber-derived contaminant cocktails add realism to in vitro exposure experiments and confirm the immunotoxic risk marine mammals face from exposure to complex mixtures of environmental contaminants.

Innate immune cells for immunotherapy of autoimmune and cancer disorders

Modulation of the immune system has been widely targeted for the treatment of several immune-related diseases, such as autoimmune disorders and cancer, due to its crucial role in these pathologies. Current available therapies focus mainly on symptomatic treatment and are often associated with undesirable secondary effects. For several years, remission of disease and subsequently recovery of immune homeostasis has been a major goal for immunotherapy. Most current immunotherapeutic strategies are aimed to inhibit or potentiate directly the adaptive immune response by modulating antibody production and B cell memory, as well as the effector potential and memory of T cells. Although these immunomodulatory approaches have shown some success in the clinic with promising therapeutic potential, they have some limitations related to their effectiveness in disease models and clinical trials, as well as elevated costs. In the recent years, a renewed interest has emerged on targeting innate immune cells for immunotherapy, due to their high plasticity and ability to exert a potent and extremely rapid response, which can influence the outcome of the adaptive immune response. In this review, we discuss the immunomodulatory potential of several innate immune cells, as well as they use for immunotherapy, especially in autoimmunity and cancer.

Graft-versus-Leukemia Effect Following Hematopoietic Stem Cell Transplantation for Leukemia

The success of hematopoietic stem cell transplantation (HSCT) lies with the ability of the engrafting immune system to remove residual leukemia cells via a graft-versus-leukemia effect (GvL), caused either spontaneously post-HSCT or via donor lymphocyte infusion. GvL effects can also be initiated by allogenic mismatched natural killer cells, antigen-specific T cells, and activated dendritic cells of leukemic origin. The history and further application of this GvL effect and the main mechanisms will be discussed and reviewed in this chapter.

MYCN is an immunosuppressive oncogene dampening the expression of ligands for NK-cell-activating receptors in human high-risk neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid tumor occurring in childhood. Amplification of the MYCN oncogene is associated with poor prognosis. Downregulation on NB cells of ligands recognized by Natural Killer (NK) cell-activating receptors, involved in tumor cell recognition and lysis, may contribute to tumor progression and relapse. Here, we demonstrate that in human NB cell lines MYCN expression inversely correlates with that of ligands recognized by NKG2D and DNAM1 activating receptors in human NB cell lines. In the MYCN-inducible Tet-21/N cell line, downregulation of MYCN resulted in enhanced expression of the activating ligands MICA, ULBPs and PVR, which rendered tumor cells more susceptible to recognition and lysis mediated by NK cells. Conversely, a MYCN non-amplified NB cell line transfected with MYCN showed an opposite behavior compared with control cells. Consistent with these findings, an inverse correlation was detected between the expression of MYCN and that of ligands for NK-cell-activating receptors in 12 NB patient specimens both at mRNA and protein levels.

Taken together, these results provide the first demonstration that MYCN acts as an immunosuppressive oncogene in NB cells that negatively regulates the expression of ligands for NKG2D and DNAM-1 NK-cell-activating receptors. Our study provides a clue to exploit MYCN expression levels as a biomarker to predict the efficacy of NK-cell-based immunotherapy in NB patients.

Enriching the Housing Environment for Mice Enhances Their NK Cell Antitumor Immunity via Sympathetic Nerve-Dependent Regulation of NKG2D and CCR5

Mice housed in an enriched environment display a tumor-resistant phenotype due to eustress stimulation. However, the mechanisms underlying enriched environment-induced protection against cancers remain largely unexplained. In this study, we observed a significant antitumor effect induced by enriched environment in murine pancreatic cancer and lung cancer models. This effect remained intact in T/B lymphocyte-deficient Rag1^-/- mice, but was nearly eliminated in natural killer (NK) cell-deficient Beige mice or in antibody-mediated NK-cell-depleted mice, suggesting a predominant role of NK cells in enriched environment-induced tumor inhibition. Exposure to enriched environment enhanced NK-cell activity against tumors and promoted tumoral infiltration of NK cells. Enriched environment increased the expression levels of CCR5 and NKG2D (KLRK1) in NK cells; blocking their function effectively blunted the enriched environment-induced enhancement of tumoral infiltration and cytotoxic activity of NK cells. Moreover, blockade of β-adrenergic signaling or chemical sympathectomy abolished the effects of enriched environment on NK cells and attenuated the antitumor effect of enriched environment. Taken together, our results provide new insight into the mechanism by which eustress exerts a beneficial effect against cancer. Cancer Res; 77(7); 1611-22. ©2017 AACR.

Monocyte/Macrophage: NK Cell Cooperation-Old Tools for New Functions

Monocyte/macrophage and natural killer (NK) cells are partners from a phylogenetic standpoint of innate immune system development and its evolutionary progressive interaction with adaptive immunity. The equally conservative ways of development and differentiation of both invertebrate hemocytes and vertebrate macrophages are reviewed. Evolutionary conserved molecules occurring in macrophage receptors and effectors have been inherited by vertebrates after their common ancestor with invertebrates. Cytolytic functions of mammalian NK cells, which are rooted in immune cells of invertebrates, although certain NK cell receptors (NKRs) are mammalian new events, are characterized. Broad heterogeneity of macrophage and NK cell phenotypes that depends on surrounding microenvironment conditions and expression profiles of specific receptors and activation mechanisms of both cell types are discussed. The particular tissue specificity of macrophages and NK cells, as well as their plasticity and mechanisms of their polarization to different functional subtypes have been underlined. The chapter summarized studies revealing the specific molecular mechanisms and regulation of NK cells and macrophages that enable their highly specific cross-cooperation. Attention is given to the evolving role of human monocyte/macrophage and NK cell interaction in pathogenesis of hypersensitivity reaction-based disorders, including autoimmunity, as well as in cancer surveillance and progression.

The Development and Diversity of ILCs, NK Cells and Their Relevance in Health and Diseases

Next to T and B cells, natural killer (NK) cells are the third largest lymphocyte population. They are recently re-categorized as innate lymphocytes (ILCs), which also include ILC1, ILC2, ILC3, and the lymphoid tissue inducer (LTi) cells. Both NK cells and ILC1 cells are designated as group 1 ILCs because they secrete interferon-γ (IFN-γ) and tumor necrosis factor (TNF). However, in contrast to ILC1 and all other ILCs, NK cells possess potent cytolytic functions that resemble cytotoxic T lymphocytes (CTL). In addition, NK cells express, in a stochastic manner, an array of germ line-encoded activating and inhibitory receptors that recognize the polymorphic regions of major histocompatibility class I (MHC-I) molecules and self-proteins. Recognition of self renders NK cell tolerance to self-healthy tissues, but fail to recognize self ('missing-self') leads to activation to neoplastic transformation and infections of certain viruses. In this chapter, we will summarize the development of NK cells in the context of ILCs, describe the diversity of phenotype and function in blood and tissues, and discuss their involvement in health and diseases in humans.

Unique cytokine and chemokine responses to exertional heat stroke in mice

In heat stroke, cytokines are believed to play important roles in multiorgan dysfunction and recovery of damaged tissue. The time course of the cytokine response is well defined in passive heat stroke (PHS), but little is known about exertional heat stroke (EHS). In this study we used a recently developed mouse EHS model to measure the responses of circulating cytokines/chemokines and cytokine gene expression in muscle. A very rapid increase in circulating IL-6 was observed at maximum core temperature (T_c,max) that peaked at 0.5 h of recovery and disappeared by 3 h. IL-10 was not elevated at any time. This contrasts with PHS where both IL-6 and IL-10 peak at 3 h of recovery. Keratinocyte chemoattractant (KC), granulocyte-colony-stimulating factor (G-CSF), macrophage inflammatory protein (MIP)-2, MIP-1β, and monocyte chemoattractive factor-1 also demonstrated near peak responses at 0.5 h. Only G-CSF and KC remained elevated at 3 h. Muscle mRNA for innate immune cytokines (IL-6, IL-10, IL-1β, but not TNF-α) were greatly increased in diaphragm and soleus compared with similar measurements in PHS. We hypothesized that these altered cytokine responses in EHS may be due to a lower T_c,max achieved in EHS or a lower overall heat load. However, when these variables were controlled for, they could not account for the differences between EHS and PHS. We conclude that moderate exercise, superimposed on heat exposure, alters the pattern of circulating cytokine and chemokine production and muscle cytokine expression in EHS. This response may comprise an endocrine reflex to exercise in heat that initiates survival pathways and early onset tissue repair mechanisms.

NEW & NOTEWORTHY

Immune modulators called cytokines are released following extreme hyperthermia leading to heat stroke. It is not known whether exercise in hyperthermia, leading to EHS, influences this response. Using a mouse model of EHS, we discovered a rapid accumulation of interleukin-6 and other cytokines involved in immune cell trafficking. This response may comprise a protective mechanism for early induction of cell survival and tissue repair pathways needed for recovery from thermal injury.

The Janus Face of Death Receptor Signaling during Tumor Immunoediting

Cancer immune surveillance is essential for the inhibition of carcinogenesis. Malignantly transformed cells can be recognized by both the innate and adaptive immune systems through different mechanisms. Immune effector cells induce extrinsic cell death in the identified tumor cells by expressing death ligand cytokines of the tumor necrosis factor ligand family. However, some tumor cells can escape immune elimination and progress. Acquisition of resistance to the death ligand-induced apoptotic pathway can be obtained through cleavage of effector cell expressed death ligands into a poorly active form, mutations or silencing of the death receptors, or overexpression of decoy receptors and pro-survival proteins. Although the immune system is highly effective in the elimination of malignantly transformed cells, abnormal/dysfunctional death ligand signaling curbs its cytotoxicity. Moreover, DRs can also transmit pro-survival and pro-migratory signals. Consequently, dysfunctional death receptor-mediated apoptosis/necroptosis signaling does not only give a passive resistance against cell death but actively drives tumor cell motility, invasion, and contributes to consequent metastasis. This dual contribution of the death receptor signaling in both the early, elimination phase, and then in the late, escape phase of the tumor immunoediting process is discussed in this review. Death receptor agonists still hold potential for cancer therapy since they can execute the tumor-eliminating immune effector function even in the absence of activation of the immune system against the tumor. The opportunities and challenges of developing death receptor agonists into effective cancer therapeutics are also discussed.

Interplay Between Inflammation and Epigenetic Changes in Cancer

Immune responses can suppress tumorigenesis, but also contribute to cancer initiation and progression suggesting a complex interaction between the immune system and cancer. Epigenetic alterations, which are heritable changes in gene expression without changes to the DNA sequence, also play a role in carcinogenesis through silencing expression of tumor suppressor genes and activating oncogenic signaling. Interestingly, epithelial cells at sites of chronic inflammation undergo DNA methylation alterations that are similar to those present in cancer cells, suggesting that inflammation may initiate cancer-specific epigenetic changes in epithelial cells. Furthermore, epigenetic changes occur during immune cell differentiation and participate in regulating the immune response, including the regulation of inflammatory cytokines. Cancer cells utilize epigenetic silencing of immune-related genes to evade the immune response. This chapter will detail the interactions between inflammation and epigenetics in tumor initiation, promotion, and immune evasion and how these connections are being leveraged in cancer prevention and treatment.

Cancer-associated fibroblast suppresses killing activity of natural killer cells through downregulation of poliovirus receptor (PVR/CD155), a ligand of activating NK receptor

Cancer-associated fibroblasts (CAFs) play an important role in cancer expansion and progression in tumor microenvironment (TME), via both direct and indirect interactions. Natural killer (NK) cells play a crucial role in anticancer immunity. We investigated the inhibitory effects of CAFs on NK cell activity. CAFs were isolated from endometrial cancer tissue, while normal endometrial fibroblasts (NEFs) were obtained from normal endometrium with no pathological abnormality. NK cells were obtained from allogenic healthy volunteers. CAFs or NEFs were co-cultured at an NK/fibroblast ratio of 1:1 with or without inserted membrane. For NK cell activity, K562 cells were cultured as target cells. NK cell-killing activity was determined by calculating the ratio of PI-positive K562 cells in the presence of NK cells co-cultured with fibroblasts versus NK cells alone. To examine whether NK cell activity was suppressed by IDO pathway, we inhibited IDO activity using the IDO inhibitor 1-MT. We demonstrated that CAFs derived from endometrial cancer induced greater suppression of the killing activity of allogenic NK cells compared with normal endometrial fibroblasts (NEFs). The suppression of NK cell activity by CAFs was inhibited when a membrane was inserted between the CAFs and NK cells, but not by 1-MT, an inhibitor of IDO. We focused on receptor-ligand interactions between CAFs and NK cell and found that cell-surface poliovirus receptor (PVR/CD155), a ligand of activating NK receptor DNAM-1, was downregulated in the CAFs compared with NEFs. To confirm whether PVR downregulation results in the decrease of NK cell-killing activity, PVR expression in NEFs was knocked down using siRNA against PVR (PVRsi). NK cell activity was suppressed by co-culture with PVR-knockdown NEFs, to a similar extent than CAF-induced suppression. CAFs showed increased suppression of NK cell-killing activity compared with NEFs, due to decreased PVR cell surface expression, a ligand of an NK activating receptor. This study demonstrated a novel mechanism of suppression of NK cell activity by CAFs in the TME.

Sub-apoptotic dosages of pro-oxidant vitamin cocktails sensitize human melanoma cells to NK cell lysis

Alpha-tochopheryl succinate (αTOS), vitamin K3 (VK3) and vitamin C (ascorbic acid, AA) were previously shown to synergistically promote different death pathways in carcinoma cells, depending on their concentrations and combinations. Similar effects were observed herein in melanoma cells, although αTOS behaved as an antagonist. Interestingly, suboptimal cell death-inducing concentrations (1.5 μM αTOS/20 μM AA/0.2 μM VK3) effectively up-regulated activating Natural Killer (NK) cell ligands, including MICA (the stress-signaling ligand of the NKG2D receptor), and/or the ligands of at least one of the natural cytotoxicity receptors (NKp30, NKp44 and NKp46) in 5/6 melanoma cell lines. Only an isolated MICA down-regulation was seen. HLA class I, HLA class II, ULBP1, ULBP2, ULBP3, Nectin-2, and PVR displayed little, if any, change in expression. Ligand up-regulation resulted in improved lysis by polyclonal NK cells armed with the corresponding activating receptors. These results provide the first evidence for concerted induction of cell death by cell-autonomous and extrinsic (immune) mechanisms. Alarming the immune system much below the cell damage threshold may have evolved as a sensitive readout of neoplastic transformation and oxidative stress. Cocktails of vitamin analogues at slightly supra-physiological dosages may find application as mild complements of melanoma treatment, and in chemoprevention.

Cancer-associated fibroblast suppresses killing activity of natural killer cells through downregulation of poliovirus receptor (PVR/CD155), a ligand of activating NK receptor

Cancer-associated fibroblasts (CAFs) play an important role in cancer expansion and progression in tumor microenvironment (TME), via both direct and indirect interactions. Natural killer (NK) cells play a crucial role in anticancer immunity. We investigated the inhibitory effects of CAFs on NK cell activity. CAFs were isolated from endometrial cancer tissue, while normal endometrial fibroblasts (NEFs) were obtained from normal endometrium with no pathological abnormality. NK cells were obtained from allogenic healthy volunteers. CAFs or NEFs were co-cultured at an NK/fibroblast ratio of 1:1 with or without inserted membrane. For NK cell activity, K562 cells were cultured as target cells. NK cell-killing activity was determined by calculating the ratio of PI-positive K562 cells in the presence of NK cells co-cultured with fibroblasts versus NK cells alone. To examine whether NK cell activity was suppressed by IDO pathway, we inhibited IDO activity using the IDO inhibitor 1-MT. We demonstrated that CAFs derived from endometrial cancer induced greater suppression of the killing activity of allogenic NK cells compared with normal endometrial fibroblasts (NEFs). The suppression of NK cell activity by CAFs was inhibited when a membrane was inserted between the CAFs and NK cells, but not by 1-MT, an inhibitor of IDO. We focused on receptor-ligand interactions between CAFs and NK cell and found that cell-surface poliovirus receptor (PVR/CD155), a ligand of activating NK receptor DNAM-1, was downregulated in the CAFs compared with NEFs. To confirm whether PVR downregulation results in the decrease of NK cell-killing activity, PVR expression in NEFs was knocked down using siRNA against PVR (PVRsi). NK cell activity was suppressed by co-culture with PVR-knockdown NEFs, to a similar extent than CAF-induced suppression. CAFs showed increased suppression of NK cell-killing activity compared with NEFs, due to decreased PVR cell surface expression, a ligand of an NK activating receptor. This study demonstrated a novel mechanism of suppression of NK cell activity by CAFs in the TME.

Recognition and Regulation of T Cells by NK Cells

Regulation of T cell responses by innate lymphoid cells (ILCs) is increasingly documented and studied. Direct or indirect crosstalk between ILCs and T cells early during and after T cell activation can affect their differentiation, polarization, and survival. Natural killer (NK) cells that belong to the ILC1 group were initially described for their function in recognizing and eliminating "altered self" and as source of early inflammatory cytokines, most notably type II interferon. Using signals conveyed by various germ-line encoded activating and inhibitory receptors, NK cells are geared to sense sudden cellular changes that can be caused by infection events, malignant transformation, or cellular stress responses. T cells, when activated by TCR engagement (signal 1), costimulation (signal 2), and cytokines (signal 3), commit to a number of cellular alterations, including entry into rapid cell cycling, metabolic changes, and acquisition of effector functions. These abrupt changes may alert NK cells, and T cells might thereby expose themselves as NK cell targets. Here, we review how activated T cells can be recognized and regulated by NK cells and what consequences such regulation bears for T cell immunity in the context of vaccination, infection, or autoimmunity. Conversely, we will discuss mechanisms by which activated T cells protect themselves against NK cell attack and outline the significance of this safeguard mechanism.

An NK Cell Perforin Response Elicited via IL-18 Controls Mucosal Inflammation Kinetics during Salmonella Gut Infection

Salmonella Typhimurium (S.Tm) is a common cause of self-limiting diarrhea. The mucosal inflammation is thought to arise from a standoff between the pathogen's virulence factors and the host's mucosal innate immune defenses, particularly the mucosal NAIP/NLRC4 inflammasome. However, it had remained unclear how this switches the gut from homeostasis to inflammation. This was studied using the streptomycin mouse model. S.Tm infections in knockout mice, cytokine inhibition and –injection experiments revealed that caspase-1 (not -11) dependent IL-18 is pivotal for inducing acute inflammation. IL-18 boosted NK cell chemoattractants and enhanced the NK cells' migratory capacity, thus promoting mucosal accumulation of mature, activated NK cells. NK cell depletion and Prf^-/- ablation (but not granulocyte-depletion or T-cell deficiency) delayed tissue inflammation. Our data suggest an NK cell perforin response as one limiting factor in mounting gut mucosal inflammation. Thus, IL-18-elicited NK cell perforin responses seem to be critical for coordinating mucosal inflammation during early infection, when S.Tm strongly relies on virulence factors detectable by the inflammasome. This may have broad relevance for mucosal defense against microbial pathogens.

Salmonella Typhimurium is a common cause of foodborne diarrhea. The disease symptoms arise already a few hours after infection. However, it had remained unclear how the immune system can mount the responses eliciting the disease symptoms so quickly. Earlier work in a mouse model had shown that the gut epithelium expresses a sensor, called NAIP/NLRC4/caspase-1 inflammasome that can detect the pathogen and mount a defense by 12-18h p.i. However, it has remained uncharacterized how inflammasome sensing drives the initial gut inflammation. Here, we found that the caspase-1 inflammasome triggers the production of IL-18, a pro-inflammatory cytokine that appears essential for the early onset of inflammation. IL-18 is driving the accumulation of NK cells into the infected mucosa, via the upregulation of NK cell chemoattractants and by the stimulation of their migratory capacity. Mature NK cells seem to induce mucosal inflammation via a perforin-mediated cytotoxic response. These data suggest that the inflammasome/IL-18/NK cell axis is a driver of early mucosal inflammation via a perforin-dependent cytotoxic NK cell response. Future work will have to address, if this mechanism is equally potent in the human gut and may contribute to ramping up the host's response during the first hours of infection. This may have implications for other gut infections and might provide leads for developing therapies.

UV-inactivated HSV-1 potently activates NK cell killing of leukemic cells

Herein we demonstrate that oncolytic herpes simplex virus-1 (HSV-1) potently activates human peripheral blood mononuclear cells (PBMCs) to lyse leukemic cell lines and primary acute myeloid leukemia samples, but not healthy allogeneic lymphocytes. Intriguingly, we found that UV light-inactivated HSV-1 (UV-HSV-1) is equally effective in promoting PBMC cytolysis of leukemic cells and is 1000- to 10 000-fold more potent at stimulating innate antileukemic responses than UV-inactivated cytomegalovirus, vesicular stomatitis virus, reovirus, or adenovirus. Mechanistically, UV-HSV-1 stimulates PBMC cytolysis of leukemic cells, partly via Toll-like receptor-2/protein kinase C/nuclear factor-κB signaling, and potently stimulates expression of CD69, degranulation, migration, and cytokine production in natural killer (NK) cells, suggesting that surface components of UV-HSV-1 directly activate NK cells. Importantly, UV-HSV-1 synergizes with interleukin-15 (IL-15) and IL-2 in inducing activation and cytolytic activity of NK cells. Additionally, UV-HSV-1 stimulates glycolysis and fatty acid oxidation-dependent oxygen consumption in NK cells, but only glycolysis is required for their enhanced antileukemic activity. Last, we demonstrate that T cell-depleted human PBMCs exposed to UV-HSV-1 provide a survival benefit in a murine xenograft model of human acute myeloid leukemia (AML). Taken together, our results support the preclinical development of UV-HSV-1 as an adjuvant, alone or in combination with IL-15, for allogeneic donor mononuclear cell infusions to treat AML.

Deep sequencing of the MHC region in the Chinese population contributes to studies of complex disease

The human major histocompatibility complex (MHC) region has been shown to be associated with numerous diseases. However, it remains a challenge to pinpoint the causal variants for these associations because of the extreme complexity of the region. We thus sequenced the entire 5-Mb MHC region in 20,635 individuals of Han Chinese ancestry (10,689 controls and 9,946 patients with psoriasis) and constructed a Han-MHC database that includes both variants and HLA gene typing results of high accuracy. We further identified multiple independent new susceptibility loci in HLA-C, HLA-B, HLA-DPB1 and BTNL2 and an intergenic variant, rs118179173, associated with psoriasis and confirmed the well-established risk allele HLA-C*06:02. We anticipate that our Han-MHC reference panel built by deep sequencing of a large number of samples will serve as a useful tool for investigating the role of the MHC region in a variety of diseases and thus advance understanding of the pathogenesis of these disorders.

Celiac Disease-Related Inflammation Is Marked by Reduction of Nkp44/Nkp46-Double Positive Natural Killer Cells

INTRODUCTION AND AIM

Natural killer (NK) cells are a first line of defence against viruses and down-regulation of NK cell cytotoxic receptors represents one of the strategies by which viruses escape the host's immune system. Since onset of celiac disease (CD), a gluten-driven enteropathy, has been associated with viral infections, we examined whether CD-associated inflammation is characterized by abnormal distribution of NK cell receptors involved in recognition of viral-infected cells.

MATERIALS AND METHODS

Intraepithelial mononuclear cells, isolated from duodenal biopsies of active and inactive CD patients and healthy controls (CTR) and jejunal specimens of obese subjects undergoing gastro-intestinal bypass, were analysed for NK cell markers by flow-cytometry. Expression of granzyme B, interleukin (IL)-22 and tumor necrosis factor (TNF)-α was as assessed in freshly isolated and toll-like receptor (TLR) ligand-stimulated cells.

RESULTS

The percentages of total NK cells and NKT cells did not significantly differ between CD patients and CTR. In active CD, the fractions of NKp30+ NK cells, NKG2D+ NK cells and NKG2D+ NKT cells were significantly increased as compared to inactive CD patients and CTR. In contrast, CD-associated inflammation was marked by diminished presence of NKG2A+ NK cells and NKG2A+ NKT cells. The fractions of NK cells and NKT cells expressing either NKp44 or NKp46 did not differ between CD and controls, but in CD less NK cells and NKT cells co-expressed these receptors. NKp44/NKp46-double positive cells produced granzyme B and IL-22 but not TNF-α and responded to TLR ligands with enhanced expression of granzyme B.

CONCLUSIONS

These data indicate that active phase of CD associates with reduced presence of NKp44/NKp46-double positive NK cells and NKT cells in the epithelial compartment.

Transcription factor KLF2 regulates homeostatic NK cell proliferation and survival

Natural killer (NK) cells are innate lymphocytes that recognize and lyse virally infected or transformed cells. This latter property is being pursued in clinics to treat leukemia with the hope that further breakthroughs in NK cell biology can extend treatments to other cancers. At issue is the ability to expand transferred NK cells and prolong their functionality within the context of a tumor. In terms of NK cell expansion and survival, we now report that Kruppel-like factor 2 (KLF2) is a key transcription factor that underpins both of these events. Excision of Klf2 using gene-targeted mouse models promotes spontaneous proliferation of immature NK cells in peripheral tissues, a phenotype that is replicated under ex vivo conditions. Moreover, KLF2 imprints a homeostatic migration pattern on mature NK cells that allows these cells to access IL-15-rich microenvironments. KLF2 accomplishes this feat within the mature NK cell lineage via regulation of a subset of homing receptors that respond to homeostatic ligands while leaving constitutively expressed receptors that recognize inflammatory cytokines unperturbed. Under steady-state conditions, KLF2-deficient NK cells alter their expression of homeostatic homing receptors and subsequently undergo apoptosis due to IL-15 starvation. This novel mechanism has implications regarding NK cell contraction following the termination of immune responses including the possibility that retention of an IL-15 transpresenting support system is key to extending NK cell activity in a tumor environment.

Nutritional deprivation and LPS exposure as feasible methods for induction of cellular - A methodology to validate for vitro photobiomodulation studies

Previous studies have demonstrated that high biostimulation takes place when cells under stress are subjected to phototherapy by laser or light-emitting-diode (LED) devices. Several studies selected nutritional deprivation by reducing the concentration of fetal bovine serum (FBS) in the culture medium or the exposure of cultured cells to lipopolysaccharide (LPS) as an in vitro cellular stress condition. However, there are no data certifying that these stimuli cause stressful conditions for cultured cells. This investigation assessed the induction of cellular stress by decreasing the concentration of FBS or adding LPS to culture medium. Odontoblast-like cells (MDPC-23) were cultured in complete culture medium (DMEM) containing 10% FBS. After a 12-hour incubation period, the DMEM was replaced by fresh medium containing 10% FBS (control), low concentrations of FBS (0, 0.2, 0.5, 2, or 5%) or LPS from Escherichia coli (10μg/ml). After an additional 12-hour incubation, cell viability, total cell-counting, total protein production, and gene expression of heat shock protein 70 (HSP70) were assessed. Data were statistically analyzed by ANOVA complemented by the Tukey test, with 5% considered significant. Cell viability was negatively affected only for 0% FBS, while reduced viable cell numbers and total protein production were detected for FBS concentrations lower than 2%. Higher HSP70 gene expression was also observed for FBS concentrations lower than 2% and for cells exposed to LPS. The nutritional deprivation model with culture medium lower than 2% of FBS can be safely used to induce cellular stress for in vitro photobiomodulation studies.

Suppression of Metastases Using a New Lymphocyte Checkpoint Target for Cancer Immunotherapy

CD96 has recently been shown as a negative regulator of mouse natural killer (NK)-cell activity, with Cd96(-/-)mice displaying hyperresponsive NK cells upon immune challenge. In this study, we have demonstrated that blocking CD96 with a monoclonal antibody inhibited experimental metastases in three different tumor models. The antimetastatic activity of anti-CD96 was dependent on NK cells, CD226 (DNAM-1), and IFNγ, but independent of activating Fc receptors. Anti-CD96 was more effective in combination with anti-CTLA-4, anti-PD-1, or doxorubicin chemotherapy. Blocking CD96 in Tigit(-/-)mice significantly reduced experimental and spontaneous metastases compared with its activity in wild-type mice. Co-blockade of CD96 and PD-1 potently inhibited lung metastases, with the combination increasing local NK-cell IFNγ production and infiltration. Overall, these data demonstrate that blocking CD96 is a new and complementary immunotherapeutic strategy to reduce tumor metastases.

SIGNIFICANCE

This article illustrates the antimetastatic activity and mechanism of action of an anti-CD96 antibody that inhibits the CD96-CD155 interaction and stimulates NK-cell function. Targeting host CD96 is shown to complement surgery and conventional immune checkpoint blockade.

Differential loss of natural killer cell activity in patients with acute myocardial infarction and stable angina pectoris

BACKGROUND

To evaluate the activity of natural killer cells through their inhibitory and activating receptors and quantity in peripheral blood mononuclear cells extracted from patients with acute myocardial infarction, stable angina pectoris and the controls.

METHODS

100 patients with myocardial infarction, 100 with stable angina, and 20 healthy volunteers were recruited into the study. 20 randomly chosen people per group were examined for the whole human genome microarray analysis to detect the gene expressions of all 40 inhibitory and activating natural killer cell receptors. Flow cytometry analysis was applied to all 200 patients to measure the quantity of natural killer cells.

RESULTS

In myocardial infarction group, the mRNA expressions of six inhibitory receptors KIR2DL2, KIR3DL3, CD94, NKG2A, KLRB1, KLRG1, and eight activating receptors KIR2DS3, KIR2DS5, NKp30, NTB-A, CRACC, CD2, CD7 and CD96 were significantly down-regulated (P<0.05) compared with both angina patients and the controls. There was no statistical difference in receptor expressions between angina patients and control group. The quantity of natural killer cells was significantly decreased in both infarction and angina patients compared with normal range (P<0.001).

CONCLUSIONS

The significant mRNAs down-regulation of several receptors in myocardial infarction group and reduction in the quantity of natural killer cells in both myocardial infarction and angina patients showed a quantitative loss and dysfunction of natural killer cells in myocardial infarction patients.

HTLV-1 ORF-I Encoded Proteins and the Regulation of Host Immune Response: Viral Induced Dysregulation of Intracellular Signaling

The human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus associated with both proliferative and inflammatory disorders. This virus causes a persistent infection, mainly in CD4+ T lymphocyte. The ability to persist in the host is associated with the virus capacity to evade the immune response and to induce infected T-cell proliferation, once the HTLV-1 maintains the infection mainly by clonal expansion of infected cells. There are several evidences that ORF-I encoded proteins, such as p12 and p8, play an important role in this context. The present study will review the molecular mechanisms that HTLV-1 ORF-I encoded proteins have to induce dysregulation of intracellular signaling, in order to escape from immune response and to increase the infected T-cell proliferation rate. The work will also address the impact of ORF-I mutations on the human host and perspectives in this study field.

Innate Immune Activity Correlates with CD4 T Cell-Associated HIV-1 DNA Decline during Latency-Reversing Treatment with Panobinostat

The pharmaceutical reactivation of dormant HIV-1 proviruses by histone deacetylase inhibitors (HDACi) represents a possible strategy to reduce the reservoir of HIV-1-infected cells in individuals treated with suppressive combination antiretroviral therapy (cART). However, the effects of such latency-reversing agents on the viral reservoir size are likely to be influenced by host immune responses. Here, we analyzed the immune factors associated with changes in proviral HIV-1 DNA levels during treatment with the potent HDACi panobinostat in a human clinical trial involving 15 cART-treated HIV-1-infected patients. We observed that the magnitude, breadth, and cytokine secretion profile of HIV-1-specific CD8 T cell responses were unrelated to changes in HIV-1 DNA levels in CD4 T cells during panobinostat treatment. In contrast, the proportions of CD3(-) CD56(+) total NK cells and CD16(+) CD56(dim) NK cells were inversely correlated with HIV-1 DNA levels throughout the study, and changes in HIV-1 DNA levels during panobinostat treatment were negatively associated with the corresponding changes in CD69(+) NK cells. Decreasing levels of HIV-1 DNA during latency-reversing treatment were also related to the proportions of plasmacytoid dendritic cells, to distinct expression patterns of interferon-stimulated genes, and to the expression of the IL28B CC genotype. Together, these data suggest that innate immune activity can critically modulate the effects of latency-reversing agents on the viral reservoir and may represent a target for future immunotherapeutic interventions in HIV-1 eradication studies.

IMPORTANCE

Currently available antiretroviral drugs are highly effective in suppressing HIV-1 replication, but the virus persists, despite treatment, in a latent form that does not actively express HIV-1 gene products. One approach to eliminate these cells, colloquially termed the "shock-and-kill" strategy, focuses on the use of latency-reversing agents that induce active viral gene expression in latently infected cells, followed by immune-mediated killing. Panobinostat, a histone deacetylase inhibitor, demonstrated potent activities in reversing HIV-1 latency in a recent pilot clinical trial and reduced HIV-1 DNA levels in a subset of patients. Interestingly, we found that innate immune factors, such as natural killer cells, plasmacytoid dendritic cells, and the expression patterns of interferon-stimulated genes, were most closely linked to a decline in the HIV-1 DNA level during treatment with panobinostat. These data suggest that innate immune activity may play an important role in reducing the residual reservoir of HIV-1-infected cells.

NKG2D Signaling Leads to NK Cell Mediated Lysis of Childhood AML

Natural killer cells have been shown to be relevant in the recognition and lysis of acute myeloid leukemia. In childhood acute lymphoblastic leukemia, it was shown that HLA I expression and KIR receptor-ligand mismatch significantly impact ALL cytolysis. We characterized 14 different primary childhood AML blasts by flow cytometry including NKG2D ligands. Further HLA I typing of blasts was performed and HLA I on the AML blasts was quantified. In two healthy volunteer NK cell donors HLA I typing and KIR genotyping were done. Blasts with high NKG2D ligand expression had significantly higher lysis by isolated NK cells. Grouping the blasts by NKG2D ligand expression led to a significant inverse correlation of HLA I expression and cytolysis in NKG2D low blasts. Furthermore, a significant positive correlation of NKG2D ligand expression and blast cytolysis was shown. No impact of KIR ligand-ligand mismatch was found but a significantly increased lysis of homozygous C2 blasts by KIR2DL1 negative NK cells (donor B) was revealed. In conclusion, NKG2D signaling leads to NK cell mediated lysis of childhood AML despite high HLA I expression.

NK cells require IL-28R for optimal in vivo activity

Natural killer (NK) cells are naturally circulating innate lymphoid cells that protect against tumor initiation and metastasis and contribute to immunopathology during inflammation. The signals that prime NK cells are not completely understood, and, although the importance of IFN type I is well recognized, the role of type III IFN is comparatively very poorly studied. IL-28R-deficient mice were resistant to LPS and cecal ligation puncture-induced septic shock, and hallmark cytokines in these disease models were dysregulated in the absence of IL-28R. IL-28R-deficient mice were more sensitive to experimental tumor metastasis and carcinogen-induced tumor formation than WT mice, and additional blockade of interferon alpha/beta receptor 1 (IFNAR1), but not IFN-γ, further enhanced metastasis and tumor development. IL-28R-deficient mice were also more susceptible to growth of the NK cell-sensitive lymphoma, RMAs. Specific loss of IL-28R in NK cells transferred into lymphocyte-deficient mice resulted in reduced LPS-induced IFN-γ levels and enhanced tumor metastasis. Therefore, by using IL-28R-deficient mice, which are unable to signal type III IFN-λ, we demonstrate for the first time, to our knowledge, the ability of IFN-λ to directly regulate NK cell effector functions in vivo, alone and in the context of IFN-αβ.

Immunosurveillance and therapy of multiple myeloma are CD226 dependent

Multiple myeloma (MM) is an age-dependent hematological malignancy. Evaluation of immune interactions that drive MM relies on in vitro experiments that do not reflect the complex cellular stroma involved in MM pathogenesis. Here we used Vk*MYC transgenic mice, which spontaneously develop MM, and demonstrated that the immune system plays a critical role in the control of MM progression and the response to treatment. We monitored Vk*MYC mice that had been crossed with Cd226 mutant mice over a period of 3 years and found that CD226 limits spontaneous MM development. The CD226-dependent anti-myeloma immune response against transplanted Vk*MYC MM cells was mediated both by NK and CD8+ T cells through perforin and IFN-γ pathways. Moreover, CD226 expression was required for optimal antimyeloma efficacy of cyclophosphamide (CTX) and bortezomib (Btz), which are both standardly used to manage MM in patients. Activation of costimulatory receptor CD137 with mAb (4-1BB) exerted strong antimyeloma activity, while inhibition of coinhibitory receptors PD-1 and CTLA-4 had no effect. Taken together, the results of this study provide in vivo evidence that CD226 is important for MM immunosurveillance and indicate that specific immune components should be targeted for optimal MM treatment efficacy. As progressive immunosuppression associates with MM development, strategies aimed to increase immune functions may have important therapeutic implications in MM.

In Vivo Activation of Human NK Cells by Treatment with an Interleukin-15 Superagonist Potently Inhibits Acute In Vivo HIV-1 Infection in Humanized Mice

Natural killer (NK) cells with anti-HIV-1 activity may inhibit HIV-1 replication and dissemination during acute HIV-1 infection. We hypothesized that the capacity of NK cells to suppress acute in vivo HIV-1 infection would be augmented by activating them via treatment with an interleukin-15 (IL-15) superagonist, IL-15 bound to soluble IL-15Rα, an approach that potentiates human NK cell-mediated killing of tumor cells. In vitro stimulation of human NK cells with a recombinant IL-15 superagonist significantly induced their expression of the cytotoxic effector molecules granzyme B and perforin; their degranulation upon exposure to K562 cells, as indicated by cell surface expression of CD107a; and their capacity to lyse K562 cells and HIV-1-infected T cells. The impact of IL-15 superagonist-induced activation of human NK cells on acute in vivo HIV-1 infection was investigated by using hu-spl-PBMC-NSG mice, NOD-SCID-IL2rγ(-/-) (NSG) mice intrasplenically injected with human peripheral blood mononuclear cells (PBMCs) which develop productive in vivo infection after intrasplenic inoculation with HIV-1. IL-15 superagonist treatment potently inhibited acute HIV-1 infection in hu-spl-PBMC-NSG mice even when delayed until 3 days after intrasplenic HIV-1 inoculation. Removal of NK cells from human PBMCs prior to intrasplenic injection into NSG mice completely abrogated IL-15 superagonist-mediated suppression of in vivo HIV-1 infection. Thus, the in vivo activation of NK cells, integral mediators of the innate immune response, by treatment with an IL-15 superagonist increases their anti-HIV activity and enables them to potently suppress acute in vivo HIV-1 infection. These results indicate that in vivo activation of NK cells may represent a new immunotherapeutic approach to suppress acute HIV-1 infection.

IMPORTANCE

Epidemiological studies have indicated that NK cells contribute to the control of HIV-1 infection, and in vitro studies have demonstrated that NK cells can selectively kill HIV-1-infected cells. We demonstrated that in vivo activation of NK cells by treatment with an IL-15 superagonist that potently stimulates the antitumor activity of NK cells markedly inhibited acute HIV-1 infection in humanized mice, even when activation of NK cells by IL-15 superagonist treatment is delayed until 3 days after HIV-1 inoculation. NK cell depletion from PBMCs prior to their intrasplenic injection abrogated the suppression of in vivo HIV-1 infection observed in humanized mice treated with the IL-15 superagonist, demonstrating that activated human NK cells were mediating IL-15 superagonist-induced inhibition of acute HIV-1 infection. Thus, in vivo immunostimulation of NK cells, a promising therapeutic approach for cancer therapy, may represent a new treatment modality for HIV-1-infected individuals, particularly in the earliest stages of infection.

Balancing natural killer cell activation through paired receptors

Natural killer (NK) cells are innate lymphocytes that are crucial for the control of infections and malignancies. NK cells express a variety of inhibitory and activating receptors that facilitate fine discrimination between damaged and healthy cells. Among them, a family of molecules that bind nectin and nectin-like proteins has recently emerged and has been shown to function as an important regulator of NK cell functions. These molecules include CD226, T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT), CD96, and cytotoxic and regulatory T cell molecule (CRTAM). In this Review, we focus on the recent advances in our understanding of how these receptors regulate NK cell biology and of their roles in pathologies such as cancer, infection and autoimmunity.

MICA SNPs and the NKG2D system in virus-induced HCC

Hepatocellular carcinoma (HCC) is one of the most frequent causes of cancer-related death globally. Above well-known risk factors for HCC development ranging from various toxins to diseases such as diabetes mellitus, chronic infection with hepatitis B virus and hepatitis C virus (HCV) poses the most serious threat, constituting the cause in more than 80 % of cases. In addition to the viral genes intensively investigated, the pathophysiological importance of host genetic factors has also been greatly and increasingly appreciated. Genome-wide association studies (GWAS) comprehensively search the host genome at the single-nucleotide level, and have successfully identified the genomic region associated with a whole variety of diseases. With respect to HCC, there have been reports from several groups on single nucleotide polymorphisms (SNPs) associated with hepatocarcinogenesis, among which was our GWAS discovering MHC class I polypeptide-related sequence A (MICA) as a susceptibility gene for HCV-induced HCC. MICA is a natural killer (NK) group 2D (NKG2D) ligand, whose interaction with NKG2D triggers NK cell-mediated cytotoxicity toward the target cells, and is a key molecule in tumor immune surveillance as its expression is induced on stressed cells such as transformed tumor cells for the detection by NK cells. In this review, the latest understanding of the MICA-NKG2D system in viral HCC, particularly focused on its antitumor properties and the involvement of MICA SNPs, is summarized, followed by a discussion of targets for state-of-the-art cancer immunotherapy with personalized medicine in view.

Metastatic colon cancer cell populations contain more cancer stem-like cells with a higher susceptibility to natural killer cell-mediated lysis compared with primary colon cancer cells

In the present study, the soft agar clonogenicity and the susceptibility of clonogenic cancer cells to natural killer (NK) cells were compared between primary colon cancer cells (KM12C) and metastatic colon cancer cells (KM12L4a and KM12SM) to determine whether the metastatic cancer cells consisted of more cancer stem-like cells and were resistant to NK cell-mediated lysis. The majority of colon cancer cells were positive for putative cancer stem cell markers, including CD44, CD133 and EpCAM, with the exception of KM12C cells, of which only ~55% were positive for CD133. In addition, the expression levels of sex determining region Y-box 2, Nanog and octamer-binding transcription factor 4, which are essential for maintaining self-renewal, were higher in KM12L4a and KM12SM compared with that in KM12C cells. Consistently, an increased clonogenicity of KM12L4a and KM12SM compared with KM12C cells in soft agar was observed. The expression levels of NKG2D ligands, including major histocompatibility complex class I polypeptide-related sequence A/B and UL16 binding protein 2, and of death receptor 5 were significantly higher in KM12L4a and KM12SM than in KM12C cells. Furthermore, the results indicated an increased susceptibility of KM12L4a and KM12SM to NK cell-mediated cytotoxicity in comparison with KM12C cells. These results indicated that metastatic colon cancer cell populations may consist of more cancer stem-like cells, and have greater susceptibility to NK cell-mediated lysis compared with that of primary colon cancers.

Functional characterization of a conserved pair of NKR-P1 receptors expressed by NK cells and T lymphocytes in liver and gut

Natural killer cell receptor protein 1 (NKR-P1) molecules are C-type lectin-like receptors modulating cellular responses toward target cells expressing C-type lectin-like related (Clr) molecules. Although the function of the prototypic rat NKR-P1A receptor and its inhibitory counterpart NKR-P1B are known, little is known about NKR-P1F and NKR-P1G apart from their promiscuity for Clr ligands. Here we generated mAbs against both receptors for phenotypic and functional analyses in rat tissues. NKR-P1F induced redirected lysis and robust Ca(2+) signaling in NK cells, which were prevented by simultaneous engagement of NKR-P1G. NKR-P1G also inhibited NK-cell lysis of Clr transfectants. NKR-P1F was expressed by most NK cells and NKR-P1A(+) T cells in all tissues analyzed, and by many NKR-P1A(-) intestinal T cells, while NKR-P1G was expressed by subsets of these cells with highest prevalence in gut and liver. In the intraepithelial compartment, the proportion of NKR-P1A(+) and NKR-P1F(+) cells was high at birth and thereafter declined, while NKR-P1B(+) and NKR-P1G(+) cells increased with age. Expression levels were also modulated by cytokines, with an increase of NKR-P1B and NKR-P1G induced by inflammatory cytokines, and a reduction of NKR-P1A by TGF-β. The physiological impact of NKR-P1 receptors might thus be dependent on age, tissue, and inflammatory status.

Natural killer cells are essential for the ability of BRAF inhibitors to control BRAFV600E-mutant metastatic melanoma

BRAF(V600E) is a major oncogenic mutation found in approximately 50% of human melanoma that confers constitutive activation of the MAPK pathway and increased melanoma growth. Inhibition of BRAF(V600E) by oncogene targeting therapy increases overall survival of patients with melanoma, but is unable to produce many durable responses. Adaptive drug resistance remains the main limitation to BRAF(V600E) inhibitor clinical efficacy and immune-based strategies could be useful to overcome disease relapse. Tumor microenvironment greatly differs between visceral metastasis and primary cutaneous melanoma, and the mechanisms involved in the antimetastatic efficacy of BRAF(V600E) inhibitors remain to be determined. To address this question, we developed a metastatic BRAF(V600E)-mutant melanoma cell line and demonstrated that the antimetastatic properties of BRAF inhibitor PLX4720 (a research analogue of vemurafenib) require host natural killer (NK) cells and perforin. Indeed, PLX4720 not only directly limited BRAF(V600E)-induced tumor cell proliferation, but also affected NK cell functions. We showed that PLX4720 increases the phosphorylation of ERK1/2, CD69 expression, and proliferation of mouse NK cells in vitro. NK cell frequencies were significantly enhanced by PLX4720 specifically in the lungs of mice with BRAF(V600E) lung metastases. Furthermore, PLX4720 also increased human NK cell pERK1/2, CD69 expression, and IFNγ release in the context of anti-NKp30 and IL2 stimulation. Overall, this study supports the idea that additional NK cell-based immunotherapy (by checkpoint blockade or agonists or cytokines) may combine well with BRAF(V600E) inhibitor therapy to promote more durable responses in melanoma.

Reactive oxygen species- and DNA damage response-dependent NK cell activating ligand upregulation occurs at transcriptional levels and requires the transcriptional factor E2F1

Increasing evidence indicates that cancer cell stress induced by chemotherapeutic agents promote antitumor immune responses and contribute to their full clinical efficacy. In this article, we identify the signaling events underlying chemotherapy-induced NKG2D and DNAM-1 ligand expression on multiple myeloma (MM) cells. Our findings indicate that sublethal doses of doxorubicin and melphalan initiate a DNA damage response (DDR) controlling ligand upregulation on MM cell lines and patient-derived malignant plasma cells in Chk1/2-dependent and p53-independent manner. Drug-induced MICA and PVR gene expression are transcriptionally regulated and involve DDR-dependent E2F1 transcription factor activity. We also describe the involvement of changes in the redox state in the control of DDR-dependent upregulation of ligand surface expression and gene transcriptional activity by using the antioxidant agent N-acetyl-L-cysteine. Finally, in accordance with much evidence indicating that DDR and oxidative stress are major determinants of cellular senescence, we found that redox-dependent DDR activation upon chemotherapeutic treatment is critical for MM cell entry in premature senescence and is required for the preferential ligand upregulation on senescent cells, which are preferentially killed by NK cells and trigger potent IFN-γ production. We propose immunogenic senescence as a mechanism that promotes the clearance of drug-treated tumor cells by innate effector lymphocytes, including NK cells.

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.

DNAM-1 control of natural killer cells functions through nectin and nectin-like proteins

Natural killer (NK) cells represent key innate immune cells that restrain viral infection and malignant transformation and help mount an adaptive immune response. To perform such complicated tasks, NK cells express a wide set of inhibitory and activating receptors that alert them against cellular stress without damaging healthy cells. A new family of receptors that recognize nectin and nectin-like molecules has recently emerged as a critical regulator of NK cell functions. The most famous member of this family, DNAX accessory molecule (DNAM-1, CD226), is an adhesion molecule that control NK cell cytotoxicity and interferon-γ production against a wide range of cancer and infected cells. Its ligands CD112 and CD155 have been described in different pathological conditions, and recent evidence indicates that their expression is regulated by cellular stress. Additional receptors have been shown to bind DNAM-1 ligands and modulate NK cell functions bringing another level of complexity. These include CD96 (TACTILE) and TIGIT (WUCAM, VSTM3). Here, we review the role of DNAM-1, TIGIT and CD96 in NK cell biology summarizing the recent advances made on the role of these receptors in various pathologies, such as cancer, viral infections and autoimmunity.

Mesenchymal stem cell therapy for cardiac inflammation: immunomodulatory properties and the influence of toll-like receptors

BACKGROUND

After myocardial infarction (MI), the inflammatory response is indispensable for initiating reparatory processes. However, the intensity and duration of the inflammation cause additional damage to the already injured myocardium. Treatment with mesenchymal stem cells (MSC) upon MI positively affects cardiac function. This happens likely via a paracrine mechanism. As MSC are potent modulators of the immune system, this could influence this postinfarct immune response. Since MSC express toll-like receptors (TLR), danger signal (DAMP) produced after MI could influence their immunomodulatory properties.

SCOPE OF REVIEW

Not much is known about the direct immunomodulatory efficiency of MSC when injected in a strong inflammatory environment. This review focuses first on the interactions between MSC and the immune system. Subsequently, an overview is provided of the effects of DAMP-associated TLR activation on MSC and their immunomodulative properties after myocardial infarction.

MAJOR CONCLUSIONS

MSC can strongly influence most cell types of the immune system. TLR signaling can increase and decrease this immunomodulatory potential, depending on the available ligands. Although reports are inconsistent, TLR3 activation may boost immunomodulation by MSC, while TLR4 activation suppresses it.

GENERAL SIGNIFICANCE

Elucidating the effects of TLR activation on MSC could identify new preconditioning strategies which might improve their immunomodulative properties.