Chemokines and NK cells: regulators of development, trafficking and functions

Pulmonary delivery of silver nanoparticles prevents influenza infection by recruiting and activating lymphoid cells

Silver nanoparticles (AgNPs) are a potential antiviral agent due to their ability to disrupt the viral particle or alter the virus metabolism inside the host cell. In vitro, AgNPs exhibit antiviral activity against the most common human respiratory viruses. However, their capacity to modulate immune responses during respiratory viral infections has yet to be explored. This study demonstrates that administering AgNPs directly into the lungs prior to infection can reduce viral loads and therefore virus-induced cytokines in mice infected with influenza virus or murine pneumonia virus. The prophylactic effect was diminished in mice with depleted lymphoid cells. We showed that AgNPs-treatment resulted in the recruitment and activation of lymphocytes in the lungs, particularly natural killer (NK) cells. Mechanistically, AgNPs enhanced the ability of alveolar macrophages to promote both NK cell migration and IFN-γ production. By contrast, following infection, in mice treated with AgNPs, NK cells exhibited decreased activation, indicating that these nanoparticles can regulate the potentially deleterious activation of these cells. Overall, the data suggest that AgNPs may possess prophylactic antiviral properties by recruiting and controlling the activation of lymphoid cells through interaction with alveolar macrophages.

Activin A, a Novel Chemokine, Induces Mouse NK Cell Migration via AKT and Calcium Signaling

Natural killer (NK) cells can migrate quickly to the tumor site to exert cytotoxic effects on tumors, and some chemokines, including CXCL8, CXCL10 or and CXCL12, can regulate the migration of NK cells. Activin A, a member of the transforming growth factor β (TGF-β) superfamily, is highly expressed in tumor tissues and involved in tumor development and immune cell activation. In this study, we focus on the effects of activin A on NK cell migration. In vitro, activin A induced NK cell migration and invasion, promoted cell polarization and inhibited cell adhesion. Moreover, activin A increased Ca2+, p-SMAD3 and p-AKT levels in NK cells. An AKT inhibitor and Ca2+ chelator partially blocked activin A-induced NK cell migration. In vivo, exogenous activin A increased tumor-infiltrating NK cells in NS-1 cell solid tumors and inhibited tumor growth, and blocking endogenous activin A with anti-activin A antibody reduced tumor-infiltrating NK cells in 4T-1 cell solid tumors. These results suggest that activin A induces NK cell migration through AKT signaling and calcium signaling and may enhance the antitumor effect of NK cells by increasing tumor-infiltrating NK cells.

Natural killer cells immunosenescence and the impact of lifestyle management

Natural killer cells (NKs) are lymphocytes of the innate immune system that quickly respond to viruses, infections, and tumors during their short cell life cycle. However, it was recently found that NKs undergo quantitative, distributional, structural, and functional phenotypic changes during aging that suppress immune responses, which is known as immunosenescence. The aging host environment, cytokine regulation, cytomegalovirus status, and hypothalamic‒pituitary‒adrenal axis have significant effects on NK function. Different lifestyle management interventions modulate the number and cytotoxic activity of NKs, which are essential for rebuilding the immune barrier against pathogens in elderly individuals. Based on recent studies, we review the phenotypic changes of and potential threats of NKs during aging and explore the underlying mechanisms. By summarizing the effects of lifestyle management on NKs and their application prospects, we aim to provide evidence for enhancing immune system function against immune diseases in elderly individuals.

Balancing act: the complex role of NK cells in immune regulation

Natural killer (NK) cells, as fundamental components of innate immunity, can quickly react to abnormalities within the body. In-depth research has revealed that NK cells possess regulatory functions not only in innate immunity but also in adaptive immunity under various conditions. Multiple aspects of the adaptive immune process are regulated through NK cells. In our review, we have integrated multiple studies to illuminate the regulatory function of NK cells in regulating B cell and T cell responses during adaptive immune processes, focusing on aspects including viral infections and the tumor microenvironment (TME). These insights provide us with many new understandings on how NK cells regulate different phases of the adaptive immune response.

End-Stage Idiopathic Pulmonary Fibrosis Lung Microenvironment Promotes Impaired NK Activity

Idiopathic pulmonary fibrosis (IPF) is a fibrotic age-related chronic lung disease characterized by the accumulation of senescent cells. Whether impaired immune response is responsible for the accumulation of senescent cells in the IPF lung remains unknown. In this study, we characterized the NK phenotype in IPF lungs via flow cytometry using 5-dodecanoylaminofluorescein di-β-d-galactopyranoside, markers of tissue residence, and chemokine receptors. The effect of the lung microenvironment was evaluated using lung fibroblast (LF) conditioned media (CM), and the bleomycin-induced pulmonary fibrosis mouse model was used to assess the in vivo relationship between NK cells and the accumulation of senescent cells. We found that NK cells from the lower lobe of IPF patients exhibited immune-senescent and impaired CD57-NKG2A+ phenotype. We also observed that culture of NK cells from healthy donors in CM from IPF lower lobe lung fibroblasts induced a senescent-like phenotype and impaired cytotoxic capacity. There is an impaired NK recruitment by LF, and NKs presented decreased migration toward their CM. In addition, NK cell-depleted mice treated with bleomycin showed increased collagen deposition and accumulation of different populations of senescent cells compared with controls. The IPF lung microenvironment induces a dysfunctional NK phenotype limiting the clearance of lung senescent cells and the resolution of lung fibrosis. We propose that impaired NK activity could be one of the mechanisms responsible for perpetuating the accumulation of senescent cells in IPF lungs.

Mapping the chemotactic landscape in NK cells reveals subset-specific synergistic migratory responses to dual chemokine receptor ligation

BACKGROUND

Natural killer (NK) cells have a unique capability of spontaneous cytotoxicity against malignant cells and hold promise for off-the-shelf cell therapy against cancer. One of the key challenges in the field is to improve NK cell homing to solid tumors.

METHODS

To gain a deeper understanding of the cellular mechanisms regulating trafficking of NK cells into the tumor, we used high-dimensional flow cytometry, mass cytometry, and single-cell RNA-sequencing combined with functional assays, creating a comprehensive map of human NK cell migration phenotypes.

FINDINGS

We found that the chemokine receptor repertoire of peripheral blood NK cells changes in a coordinated manner becoming progressively more diversified during NK cell differentiation and correlating tightly with the migratory response of the distinct NK cell subsets. Simultaneous ligation of CXCR1/2 and CX3CR1, synergistically potentiated the migratory response of NK cells. Analysis of 9471 solid cancers from publicly available TCGA/TARGET repositories revealed dominant chemokine patterns that varied across tumor types but with no tumor group expressing ligands for more than one chemokine receptor present on mature NK cells.

INTERPRETATION

The finding that chemokine stimulation can elicit a synergistic migratory response in NK cells combined with the identified lack of naturally occurring pairs of chemokines-chemokine receptors in human cancers may explain the systematic exclusion of NK cells from the tumor microenvironment and provides a basis for engineering next-generation NK cell therapies against malignancies.

FUNDING

The Polish Ministry of Science and Higher Education, the National Science Centre, Poland, The Norwegian Cancer Society, the Norwegian Research Council, the South-Eastern Norway Regional Health Authority, The Swedish Cancer Society, the Swedish Children's Cancer Foundation, The Swedish Research Council, The Center of Excellence: Precision Immunotherapy Alliance, Knut and Alice Wallenberg Foundation and National Cancer Institute.

The RIG-I agonist M8 triggers cell death and natural killer cell activation in human papillomavirus-associated cancer and potentiates cisplatin cytotoxicity

Although the activation of innate immunity to treat a wide variety of cancers is gaining increasing attention, it has been poorly investigated in human papillomavirus (HPV)-associated malignancies. Because these tumors harbor a severely impaired cGAS-STING axis, but they still retain a largely functional RIG-I pathway, another critical mediator of adaptive and innate immune responses, we asked whether RIG-I activation by the 5'ppp-RNA RIG-I agonist M8 would represent a therapeutically viable option to treat HPV+ cancers. Here, we show that M8 transfection of two cervical carcinoma-derived cell lines, CaSki and HeLa, both expressing a functional RIG-I, triggers intrinsic apoptotic cell death, which is significantly reduced in RIG-I KO cells. We also demonstrate that M8 stimulation potentiates cisplatin-mediated cell killing of HPV+ cells in a RIG-I dependent manner. This combination treatment is equally effective in reducing tumor growth in a syngeneic pre-clinical mouse model of HPV16-driven cancer, where enhanced expression of lymphocyte-recruiting chemokines and cytokines correlated with an increased number of activated natural killer (NK) cells in the tumor microenvironment. Consistent with a role of RIG-I signaling in immunogenic cell killing, stimulation of NK cells with conditioned medium from M8-transfected CaSki boosted NK cell proliferation, activation, and migration in a RIG-I-dependent tumor cell-intrinsic manner. Given the highly conserved molecular mechanisms of carcinogenesis and genomic features of HPV-driven cancers and the remarkably improved prognosis for HPV+ oropharyngeal cancer, targeting RIG-I may represent an effective immunotherapeutic strategy in this setting, favoring the development of de-escalating strategies.

CC group of chemokines and associated gene expression of transcription factors: Deciphering immuno-pathogenetic aspect of oral submucous fibrosis

BACKGROUND

Oral submucous fibrosis (OSMF) is a chronic disease with significantly increasing malignant transformation rate. To date the pathogenesis of OSMF has been considered to be associated with areca nut constituents and their action on fibroblasts. However, fibrosis is also associated with immunological factors such as chemokines. In-depth analysis of such factors is the need of the hour in OSMF to better understand the pathogenesis so that effective therapeutic strategies can be developed in the future.

MATERIALS AND METHOD

Clinically diagnosed cases of OSMF (n=21) and healthy individuals (n=10) were enrolled in the present study. Chemokines such as CCL2, CCL3, CCL4, CCL5, CCL11, CCL17, CCL28, CXCL1, CXCL5, CXCL8, CXCL9, CXCL10, and CXCL11 were assessed using the chemokine bead array in conjunction with the flow cytometry, along with real-time PCR (RT-PCR). The transcription factors CREB, NF-κB and NFAT5 were also studied for their expressions. The analysis of pg/ml (picogram/milliliter) values was done by using LEGENDplex™ Data Analysis Software.

RESULTS

The results obtained demonstrated early phase transient increase in CXCL-11, CCL20, CXCL9, CCL3, CCL2, CXCL10 and CXCL8. However, the expression of CCL3, CXCL10 and CXCL8 was higher in the late stage as compared to the early stage. The relative gene expression of CREB, NF-κB, NFAT5 were upregulated in the late stage of OSMF when compared to normal.

CONCLUSION

Distinctive sets of chemokine expression during the early and late stages of OSMF suggest a unique pattern of disease progression playing an important role in the pathogenesis.

NK cells and solid tumors: therapeutic potential and persisting obstacles

Natural killer (NK) cells, which are innate lymphocytes endowed with potent cytotoxic activity, have recently attracted attention as potential anticancer therapeutics. While NK cells mediate encouraging responses in patients with leukemia, the therapeutic effects of NK cell infusion in patients with solid tumors are limited. Preclinical and clinical data suggest that the efficacy of NK cell infusion against solid malignancies is hampered by several factors including inadequate tumor infiltration and persistence/activation in the tumor microenvironment (TME). A number of metabolic features of the TME including hypoxia as well as elevated levels of adenosine, reactive oxygen species, and prostaglandins negatively affect NK cell activity. Moreover, cancer-associated fibroblasts, tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells actively suppress NK cell-dependent anticancer immunity. Here, we review the metabolic and cellular barriers that inhibit NK cells in solid neoplasms as we discuss potential strategies to circumvent such obstacles towards superior therapeutic activity.

NK Cells and Other Cytotoxic Innate Lymphocytes in Colorectal Cancer Progression and Metastasis

Colorectal cancer (CRC) is one of the most common malignancies and leading causes of cancer-related deaths worldwide. Despite its complex pathogenesis and progression, CRC represents a well-fitting example of how the immune contexture can dictate the disease outcome. The presence of cytotoxic lymphocytes, both CD8⁺ T cells and natural killer (NK) cells, represents a relevant prognostic factor in CRC and is associated with a better overall survival. Together with NK cells, other innate lymphocytes, namely, innate lymphoid cells (ILCs), have been found both in biopsies of CRC patients and in murine models of intestinal cancer, playing both pro- and anti-tumor activities. In particular, several type 1 innate lymphoid cells (ILC1) with cytotoxic functions have been recently described, and evidence in mice shows a role for both NK cells and ILC1 in controlling CRC metastasis. In this review, we provide an overview of the features of NK cells and the expanding spectrum of innate lymphocytes with cytotoxic functions. We also comment on both the described and the potential roles these innate lymphocytes can play during the progression of intestinal cancer leading to metastasis. Finally, we discuss recent advances in the molecular mechanisms underlying the functional regulation of cytotoxic innate lymphocytes in CRC.

Enhanced co-culture and enrichment of human natural killer cells for the selective clearance of senescent cells

In the context of aging and age-associated diseases, Natural Killer (NK) cells have been revealed as a key cell type responsible for the immune clearance of senescent cells. Subsequently, NK cell-based therapies have emerged as promising alternatives to drug-based therapeutic interventions for the prevention and treatment of age-related disease and debility. Given the promise of NK cell-mediated immunotherapies as a safe and effective treatment strategy, we outline an improved method by which primary NK cells can be efficiently enriched from human peripheral blood across multiple donors (ages 20-42 years old), with a practical protocol that reliably enhances both CD56^dim and CD56^bright NK cells by 15-fold and 3-fold, respectively. Importantly, we show that our co-culture protocol can be used as an easily adaptable tool to assess highly efficient and selective killing of senescent cells by primary NK cells enriched via our method using longer co-culture durations and a low target to effector ratio, which may be more physiological than has been achieved in previous literature.

Intermediate monocytes induced by IFN-γ inhibit cancer metastasis by promoting NK cell activation through FOXO1 and interleukin-27

Background

Circulating monocytes are functionally heterogeneous and can be divided into classical (CMo), intermediate (IMo), and non-CMo/patrolling monocyte (PMo) subsets. CMo can differentiate into PMo through IMo. PMos have been shown to inhibit cancer metastasis but the role of IMo is unclear. To date, no strategy has been developed to inhibit cancer metastasis through enhancing PMo/IMo differentiation.

Methods

We screened multiple inflammatory cytokines/chemokines activity of modulating PMo/IMo associated cell markers expression using human monocyte in vitro culture system. We tested our candidate cytokine activity in vivo using multiple mice models. We identified critical key factors and cytokines for our candidate cytokine activity by using gene-knockout mice and neutralization antibodies.

Results

We identified IFN-γ as a candidate inflammatory cytokine in the regulation of human IMo/PMo marker expression. Our in vivo data demonstrated that IMo expansion was induced by short-term (3 days) IFN-γ treatment through increasing CMo-IMo differentiation and blocking IMo-PMo differentiation. The IMo induced by IFN-γ (IFN-IMo), but not IFN-γ activated CMo (IFN-CMo), inhibited cancer metastasis by 90%. Surprizing, the effect of IFN-γ is greater in PMo deficiency mice, indicating the effect of IFN-IMo is not mediated through further differentiation into PMo. We also found that IFN-IMos induced by short-term IFN-γ treatment robustly boosted NK cell expansion for threefold and promoted NK differentiation and function through IL-27 and CXCL9. Furthermore, we identified that FOXO1, a key molecule controlling cellular energy metabolism, mediated the effect of IFN-γ induced IL-27 expression, and that NR4A1, a key molecule controlling PMo differentiation and inhibiting cancer metastasis, inhibited the pro-NK cell and anti-metastasis activity of IFN-IMo by suppressing CXCL9 expression.

Conclusions

We have discovered the antimetastasis and pro-NK cell activity of IFN-IMo, identified FOXO1 as a key molecule for IFN-γ driven monocyte differentiation and function, and found NR4A1 as an inhibitory molecule for IFN-IMo activity. Our study has not only shown novel mechanisms for a classical antitumor cytokine but also provided potential target for developing superior monocytic cell therapy against cancer metastasis.

Cytomegalovirus Infection Impairs the Mobilization of Tissue-Resident Innate Lymphoid Cells into the Peripheral Blood Compartment in Response to Acute Exercise

Circulating immune cell numbers and phenotypes are impacted by high-intensity acute bouts of exercise and infection history with the latent herpesviruses cytomegalovirus (CMV). In particular, CMV infection history impairs the exercise-induced mobilization of cytotoxic innate lymphoid cells 1 (ILC1) cells, also known as NK cells, in the blood. However, it remains unknown whether exercise and CMV infection modulate the mobilization of traditionally tissue-resident non-cytotoxic ILCs into the peripheral blood compartment. To address this question, 22 healthy individuals with or without CMV (20–35 years—45% CMV^pos) completed 30 min of cycling at 70% VO₂ max, and detailed phenotypic analysis of circulating ILCs was performed at rest and immediately post-exercise. We show for the first time that a bout of high-intensity exercise is associated with an influx of ILCs that are traditionally regarded as tissue-resident. In addition, this is the first study to highlight that latent CMV infection blunts the exercise-response of total ILCs and progenitor ILCs (ILCPs). These promising data suggest that acute exercise facilitates the circulation of certain ILC subsets, further advocating for the improvements in health seen with exercise by enhancing cellular mobilization and immunosurveillance, while also highlighting the indirect deleterious effects of CMV infection in healthy adults.

Young adult binge drinkers have immunophenotypical disarrangements in peripheral natural killer cells

Alcohol consumption is an issue of worldwide relevance and a problem of national scale in Mexico. The consumption pattern of large amounts of alcohol on the weekends is rapidly increasing in young adults between 18 and 29 years. Despite various studies that have focused on the noxious effect of alcohol in immunity, the changes in the immunoprofiles of peripheral blood cells have not been completely described. Natural killer cells (NKCs) are lymphoid-origin cells of the immune system that are responsible for defense against tumors, among other functions. In homeostatic conditions, they are found to be in a state of "dynamic balance" between activation and inhibition stimuli, which, if broken, may lead to immunosuppression or activation of cytotoxic mechanisms. In this study, we evaluated the immunoprofile of peripheral NKCs of 54 young adults, 29 of whom were binge drinkers and 25 of whom were low risk (LR), as classified by validated tools. Drinking habits were assessed. Blood samples were collected to perform hematic biometry and liver enzyme tests. Peripheral NKCs were identified by FACS, and stained for CCR2, CCR4, CCR5, CXCR4, CD69, CD127, CD137, TLR4, and Granzyme B. The data were analyzed using the t test and Mann-Whitney's U test for contrasts, and the effect size was obtained in order to evaluate the impact of each immunoprofile. The binge group showed increased expression of CCR5 and PD-1 in NKCs, respective to the LR group, and decreased expression of TLR4, along with fewer CCR4⁺ cells. Moreover, the increase found in CCR5 and PD-1 expression was correlated with the number of drinks in the last drinking session. Our findings show that young binge drinkers have different immunoprofiles that could suggest an early status of immunosuppression and trafficking of NKCs to the liver, which could be related to the onset of early liver damage, early in a subject's lifespan.

Chemokine regulation of inflammation during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infections especially in infants, immunocompromised individuals and the elderly and is the most common cause of infant hospitalisation in the developed world. The immune responses against RSV are crucial for viral control and clearance but, if dysregulated, can also result in immunopathology and impaired gas exchange. Lung immunity to RSV and other respiratory viruses begins with the recruitment of immune cells from the bloodstream into the lungs. This inflammatory process is controlled largely by chemokines, which are small proteins that are produced in response to innate immune detection of the virus or the infection process. These chemokines serve as chemoattractants for granulocytes, monocytes, lymphocytes and other leukocytes. In this review, we highlight recent advances in the field of RSV infection and disease, focusing on how chemokines regulate virus-induced inflammation.

Senescent hepatocytes enhance natural killer cell activity via the CXCL-10/CXCR3 axis

Cellular senescence and natural killer (NK) cells play an important role in liver diseases. Chemokines, a component of the senescence-associated secretory phenotype, can recruit NK cells and are involved in the development of various liver diseases. The effect of the C-X-C motif chemokine ligand (CXCL)-9, −10, −11/C-X-C motif chemokine receptor (CXCR)3 axis in senescent hepatocytes remains unknown. The chemokines secreted by senescent hepatocytes, the contribution of the CXCL-9, −10, −11/CXCR3 axis to the migration of NK cells, and the effect of senescent hepatocytes on the function of NK cells were investigated in the present study. The results demonstrated significantly increased levels of C-C motif chemokine ligand 2 and CXCL-1, −2 and −10 in the supernatant of senescent AML12 cells. Despite increased mRNA expression of CXCL-9, −10, and −11 in these cells, western blotting revealed significantly enhanced expression of only CXCL-10. The expression of CXCR3 on the surface of NK cells stimulated by senescent AML12 cells was upregulated (fold change, >3). Following incubation with the supernatant of senescent hepatocytes, both CD107a and interferon γ expression in NK cells increased by >2.5-fold. The cytotoxic effect of NK cells was notably higher stimulated by senescent AML12 cells. Chemotaxis and blocking assays demonstrated that the senescent hepatocytes enhanced the migration of NK cells via the CXCL-10/CXCR3 axis. The present study suggests that senescent hepatocytes secrete various chemokines, including CXCL-10, resulting in the upregulation and activation of CXCR3 in NK cells and the enhancement of NK cell migration via the CXCL-10/CXCR3 axis.

Innate lymphocyte-induced CXCR3B-mediated melanocyte apoptosis is a potential initiator of T-cell autoreactivity in vitiligo

T-cells play a crucial role in progression of autoimmunity, including vitiligo, yet the initial steps triggering their activation and tissue damage remain unknown. Here we demonstrate increased presence of type-1 innate lymphoid cells (NK and ILC1)-producing interferon gamma (IFNγ) in the blood and in non-lesional skin of vitiligo patients. Melanocytes of vitiligo patients have strong basal expression of chemokine-receptor-3 (CXCR3) isoform B which is directly regulated by IFNγ. CXCR3B activation by CXCL10 at the surface of cultured human melanocytes induces their apoptosis. The remaining melanocytes, activated by the IFNγ production, express co-stimulatory markers which trigger T-cell proliferation and subsequent anti-melanocytic immunity. Inhibiting the CXCR3B activation prevents this apoptosis and the further activation of T cells. Our results emphasize the key role of CXCR3B in apoptosis of melanocytes and identify CXCR3B as a potential target to prevent and to treat vitiligo by acting at the early stages of melanocyte destruction.

Tissue signals that prime autoreactive T cells at the onset of autoimmunity remain enigmatic. Here the authors show NK and ILC1 cells are increased in vitiligo patients, and induce melanocyte apoptosis via CXCR3B, which in turn leads to increased priming of T cell responses in cell culture.

Immunosenescence of Natural Killer Cells, Inflammation, and Alzheimer's Disease

Alzheimer's disease (AD) represents the most common cause of dementia in the elderly. AD is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although the aetiology of AD is not clear, both environmental factors and heritable predisposition may contribute to disease occurrence. In addition, inflammation and immune system alterations have been linked to AD. The prevailing hypothesis as cause of AD is the deposition in the brain of amyloid beta peptides (Aβ). Although Aβ have a role in defending the brain against infections, their accumulation promotes an inflammatory response mediated by microglia and astrocytes. The production of proinflammatory cytokines and other inflammatory mediators such as prostaglandins and complement factors favours the recruitment of peripheral immune cells further promoting neuroinflammation. Age-related inflammation and chronic infection with herpes virus such as cytomegalovirus may also contribute to inflammation in AD patients. Natural killer (NK) cells are innate lymphoid cells involved in host defence against viral infections and tumours. Once activated NK cells secrete cytokines such as IFN-γ and TNF-α and chemokines and exert cytotoxic activity against target cells. In the elderly, changes in NK cell compartment have been described which may contribute to the lower capacity of elderly individuals to respond to pathogens and tumours. Recently, the role of NK cells in the immunopathogenesis of AD is discussed. Although in AD patients the frequency of NK cells is not affected, a high NK cell response to cytokines has been described together with NK cell dysregulation of signalling pathways which is in part involved in this altered behaviour.

Beyond migration-Chemokines in lymphocyte priming, differentiation, and modulating effector functions

Chemokines and their receptors coordinate the positioning of leukocytes, and lymphocytes in particular, in space and time. Discrete lymphocyte subsets, depending on their activation and differentiation status, express various sets of chemokine receptors to be recruited to distinct tissues. Thus, the network of chemokines and their receptors ensures the correct localization of specialized lymphocyte subsets within the appropriate microenvironment enabling them to search for cognate antigens, to become activated, and to fulfill their effector functions. The chemokine system therefore is vital for the initiation as well as the regulation of immune responses to protect the body from pathogens while maintaining tolerance towards self. Besides the well investigated function of orchestrating directed cell migration, chemokines additionally act on lymphocytes in multiple ways to shape immune responses. In this review, we highlight and discuss the role of chemokines and chemokine receptors in controlling cell-to-cell contacts required for lymphocyte arrest on endothelial cells and immunological synapse formation, in lymphocyte priming and differentiation, survival, as well as in modulating effector functions.

Chemokine regulation of innate lymphoid cell tissue distribution and function

Three groups of innate lymphoid cells (ILCs) can be defined based on transcription factor requirements, cytokine production profiles, and roles in immunity. Given their strategic anatomical location into barrier tissues and the ability to rapidly produce cytokines and to cross-talk with other immune and non-immune cells, ILCs play fundamental functions in tissue homeostasis and regulation of immune responses. Several members of the chemokine family influence ILC tissue localization in the correct microenvironment by regulating their release from the bone marrow as well as their homing and retention in the tissues. In this review, we discuss the recent advances on how chemokine regulation of ILC tissue-positioning and functional interaction with other cells play essential roles in tissue-specific regulation of innate and adaptive immune responses.

Understanding the Progression of Bone Metastases to Identify Novel Therapeutic Targets

Bone is one of the most preferential target site for cancer metastases, particularly for prostate, breast, kidney, lung and thyroid primary tumours. Indeed, numerous chemical signals and growth factors produced by the bone microenvironment constitute factors promoting cancer cell invasion and aggression. After reviewing the different theories proposed to provide mechanism for metastatic progression, we report on the gene expression profile of bone-seeking cancer cells. We also discuss the cross-talk between the bone microenvironment and invading cells, which impacts on the tumour actions on surrounding bone tissue. Lastly, we detail therapies for bone metastases. Due to poor prognosis for patients, the strategies mainly aim at reducing the impact of skeletal-related events on patients' quality of life. However, recent advances have led to a better understanding of molecular mechanisms underlying bone metastases progression, and therefore of novel therapeutic targets.

Leukocyte trafficking in tumor microenvironment

The tumor microenvironment consists of both malignant and non-malignant cells and a plethora of soluble mediators. Different types of tumors have specific tumor microenvironments characterized by distinct chemokines and chemotactic factors that influence leukocyte recruitment. The immune cell infiltrate continuously interacts with stroma cells and influence tumor growth. Emerging evidence suggests that the regulation of the composition and the metabolic state of tumor-associated leukocytes may represent a new promising intervention strategy. Here we summarize the current knowledge on the role of tumor-associated immune cells in tumor growth and dissemination, with a specific focus on the nature of the chemotactic factors responsible for their accumulation and activation in tumors.

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.

NKG2D ligands mediate immunosurveillance of senescent cells

Cellular senescence is a stress response mechanism that limits tumorigenesis and tissue damage. Induction of cellular senescence commonly coincides with an immunogenic phenotype that promotes self-elimination by components of the immune system, thereby facilitating tumor suppression and limiting excess fibrosis during wound repair. The mechanisms by which senescent cells regulate their immune surveillance are not completely understood. Here we show that ligands of an activating Natural Killer (NK) cell receptor (NKG2D), MICA and ULBP2 are consistently up-regulated following induction of replicative senescence, oncogene-induced senescence and DNA damage - induced senescence. MICA and ULBP2 proteins are necessary for efficient NK-mediated cytotoxicity towards senescent fibroblasts. The mechanisms regulating the initial expression of NKG2D ligands in senescent cells are dependent on a DNA damage response, whilst continuous expression of these ligands is regulated by the ERK signaling pathway. In liver fibrosis, the accumulation of senescent activated stellate cells is increased in mice lacking NKG2D receptor leading to increased fibrosis. Overall, our results provide new insights into the mechanisms regulating the expression of immune ligands in senescent cells and reveal the importance of NKG2D receptor-ligand interaction in protecting against liver fibrosis.

NK cells regulate CXCR2+ neutrophil recruitment during acute lung injury

A critical step in the pathogenesis of acute lung injury (ALI) is excessive recruitment of polymorphonuclear neutrophils (PMNs) into the lungs, causing significant collateral tissue damage. Defining the molecular and cellular steps that control neutrophil infiltration and activation during ALI is therefore of important therapeutic relevance. Based on previous findings implicating the transcription factor Tbet in mucosal Th1-inflammation, we hypothesized a detrimental role for Tbet during ALI. In line with our hypothesis, initial studies of endotoxin-induced lung injury revealed a marked protection of Tbet^-/- mice, including attenuated neutrophilia compared to WT counterparts. Surprisingly, subsequent studies identified natural killer (NK) cells as the major source of pulmonary Tbet during ALI. In addition, a chemokine screen suggested that mature Tbet⁺ NK-cells are critical for the production of pulmonary CXCL1 and -2, thereby contributing to pulmonary PMN recruitment. Indeed, both NK-cell Ab depletion and adoptive transfer studies provide evidence for NK cells in the orchestration of neutrophil recruitment during endotoxin-induced ALI. Taken together, these findings identify a novel role for Tbet⁺ NK-cells in initiating the early events of noninfectious pulmonary inflammation.

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.

NK Cells, Tumor Cell Transition, and Tumor Progression in Solid Malignancies: New Hints for NK-Based Immunotherapy?

Several evidences suggest that NK cells can patrol the body and eliminate tumors in their initial phases but may hardly control established solid tumors. Multiple factors, including the transition of tumor cells towards a proinvasive/prometastatic phenotype, the immunosuppressive effect of the tumor microenvironment, and the tumor structure complexity, may account for limited NK cell efficacy. Several putative mechanisms of NK cell suppression have been defined in these last years; conversely, the cross talk between NK cells and tumor cells undergoing different transitional phases remains poorly explored. Nevertheless, recent in vitro studies and immunohistochemical analyses on tumor biopsies suggest that NK cells could not only kill tumor cells but also influence their evolution. Indeed, NK cells may induce tumor cells to change the expression of HLA-I, PD-L1, or NKG2D-L and modulate their susceptibility to the immune response. Moreover, NK cells may be preferentially located in the borders of tumor masses, where, indeed, tumor cells can undergo Epithelial-to-Mesenchymal Transition (EMT) acquiring prometastatic phenotype. Finally, the recently highlighted role of HMGB1 both in EMT and in amplifying the recruitment of NK cells provides further hints on a possible effect of NK cells on tumor progression and fosters new studies on this issue.

XCR1+ dendritic cells promote memory CD8+ T cell recall upon secondary infections with Listeria monocytogenes or certain viruses

Alexandre et al. demonstrate the XCR1⁺ DCs are instrumental in memory CD8⁺ T cell responses to Listeria, VSV or vaccinia virus infection, but not CMV. Depending on the infection, robust memory CTL responses require cytokine- and chemokine-dependent cross-talk between XCR1⁺ DCs and NK cells or other IFN-γ–producing lymphocytes.

Naive CD8⁺ T cell priming during tumor development or many primary infections requires cross-presentation by XCR1⁺ dendritic cells (DCs). Memory CD8⁺ T lymphocytes (mCTLs) harbor a lower activation threshold as compared with naive cells. However, whether their recall responses depend on XCR1⁺ DCs is unknown. By using a new mouse model allowing fluorescent tracking and conditional depletion of XCR1⁺ DCs, we demonstrate a differential requirement of these cells for mCTL recall during secondary infections by different pathogens. XCR1⁺ DCs were instrumental to promote this function upon secondary challenges with Listeria monocytogenes, vesicular stomatitis virus, or Vaccinia virus, but dispensable in the case of mouse cytomegalovirus. We deciphered how XCR1⁺ DCs promote mCTL recall upon secondary infections with Listeria. By visualizing for the first time the in vivo choreography of XCR1⁺ DCs, NK cells and mCTLs during secondary immune responses, and by neutralizing in vivo candidate molecules, we demonstrate that, very early after infection, mCTLs are activated, and attracted in a CXCR3-dependent manner, by NK cell–boosted, IL-12–, and CXCL9-producing XCR1⁺ DCs. Hence, depending on the infectious agent, strong recall of mCTLs during secondary challenges can require cytokine- and chemokine-dependent cross-talk with XCR1⁺ DCs and NK cells.

Multifunctional T Lymphocytes Generated After Therapy With an Antitumor Gallotanin-Rich Normalized Fraction Are Related to Primary Tumor Size Reduction in a Breast Cancer Model

Natural compounds are promising sources for anticancer therapies because of their multifunctional activity and low toxicity. Although the host immune response (IR) is clearly implicated in tumor control, the relationship between natural therapies and IR has not yet been elucidated. The present work evaluates IR induction after treatment with a gallotannin-rich fraction from Caesalpinia spinosa (P2Et). Breast tumor 4T1 cells were used to evaluate antitumor properties and IR activation. Apoptosis and expression of immunogenic cell death (ICD) markers were assessed in vitro, whereas IR and postvaccination tumor evolution were assessed in vivo. P2Et fraction induced apoptotic cell death, displaying phosphatidylserine externalization and DNA fragmentation. ICD markers such as calreticulin, high-mobility group box 1 translocation from nuclei to cytoplasm, and ATP secretion were observed. Primary tumor control was improved by vaccination with P2Et-pretreated 4T1 cells (t-P2Et), yielding long-lasting ex vivo multifunctional CD4+ and CD8+ T lymphocytes (interleukin [IL]-2+, tumor necrosis factor [TNF]-α+, interferon [IFN]-γ+) that secrete IL-2, TNF-α, IL-4, IL-5, and IFN-γ after specific 4T1 cell stimulation. The present study constitutes the first demonstration of a long-lasting antitumor IR induction and primary tumor reduction induced by a complex natural fraction. These data reveal the potential use of this fraction as an adjuvant in breast cancer treatment.

Multifunctional T Lymphocytes Generated After Therapy With an Antitumor Gallotanin-Rich Normalized Fraction Are Related to Primary Tumor Size Reduction in a Breast Cancer Model

Natural compounds are promising sources for anticancer therapies because of their multifunctional activity and low toxicity. Although the host immune response (IR) is clearly implicated in tumor control, the relationship between natural therapies and IR has not yet been elucidated. The present work evaluates IR induction after treatment with a gallotannin-rich fraction from Caesalpinia spinosa (P2Et). Breast tumor 4T1 cells were used to evaluate antitumor properties and IR activation. Apoptosis and expression of immunogenic cell death (ICD) markers were assessed in vitro, whereas IR and postvaccination tumor evolution were assessed in vivo. P2Et fraction induced apoptotic cell death, displaying phosphatidylserine externalization and DNA fragmentation. ICD markers such as calreticulin, high-mobility group box 1 translocation from nuclei to cytoplasm, and ATP secretion were observed. Primary tumor control was improved by vaccination with P2Et-pretreated 4T1 cells (t-P2Et), yielding long-lasting ex vivo multifunctional CD4+ and CD8+ T lymphocytes (interleukin [IL]-2+, tumor necrosis factor [TNF]-α+, interferon [IFN]-γ+) that secrete IL-2, TNF-α, IL-4, IL-5, and IFN-γ after specific 4T1 cell stimulation. The present study constitutes the first demonstration of a long-lasting antitumor IR induction and primary tumor reduction induced by a complex natural fraction. These data reveal the potential use of this fraction as an adjuvant in breast cancer treatment.

Modulation of the immune system during postpartum uterine inflammation

Postpartum uterine inflammation (endometritis) in the dairy cow is associated with lower fertility at both the time of infection and after the inflammation has resolved. We hypothesized that aberrant DNA methylation may be involved in the subfertility associated with uterine inflammation. The objective of this study was to characterize genome-wide DNA methylation and gene expression in the endometrium of dairy cows with subclinical endometritis (SCE). Endometrial tissues were obtained at 29 days postpartum ( n = 12), and microarrays were used to characterize transcription and DNA methylation. Analyses revealed 1,856 probes differentially expressed in animals with SCE ( n = 6) compared with controls (CON, n = 6, P < 0.05, Storey Multiple testing correction) and 2,976 probes with significant correlation between gene expression and bacteriology score. No significant associations among DNA methylation and gene expression were detected. Analysis of transcription data using the Database for Annotation, Visualization, and Integrated Discovery and Gene Set Enrichment Analysis identified several pathways and processes enriched in SCE cows, with the majority related to the immune response. Furthermore, the top ontology terms enriched in genes that had expression data correlated to bacteriology score were: Defense response, inflammatory response, and innate immune response. Gene expression profiles in cows with subclinical endometritis in this study indicate that the immune response is activated, potentially resulting in a local proinflammatory environment in the uterus. If this period of inflammation is prolonged it could result in tissue damage or failure to complete involution of the uterus, which may create a suboptimal environment for future pregnancy.

Effect of surgery on pancreatic tumor-dependent lymphocyte asset: modulation of natural killer cell frequency and cytotoxic function

OBJECTIVES

Tumor burden and invasiveness establish a microenvironment that surgery could alter. This study shows a comprehensive analysis of size, dynamics, and function of peripheral lymphocyte subsets in pancreatic cancer patients before and at different times after duodenopancreatectomy.

METHODS

Lymphocyte frequency and natural cytotoxicity were evaluated by flow cytometry and in vitro assay on peripheral blood from initial and advanced-stage pancreatic cancer patients before (BS), at day 7 (PS7), and at day 30 (PS30) after surgery.

RESULTS

An increase in natural killer (NK) cells and the diminution of B-cells occurred at PS30, whereas cytotoxicity decreased at PS7. The positive correlation between NK frequency and cytotoxicity at BS and PS7 revealed an altered NK behavior. The elevation of NK cell frequency at PS30, an initial defect in CD56bright NK, and the aberrant correlation between NK frequency and cytotoxicity remained significant in advanced-stage patients, whereas the diminution of NK cytotoxicity only affected initial stage patients.

CONCLUSIONS

The NK cell functional ability is altered in presurgery patients; duodenopancreatectomy is associated with short-term impairment of NK function and with a long-term NK cell augmentation and reversion of the aberrant NK behavior, which may impact on immunosurveillance against residual cancer.

Multifunctional human CD56 low CD16 low natural killer cells are the prominent subset in bone marrow of both healthy pediatric donors and leukemic patients

We phenotypically and functionally characterized a distinct CD56(low) natural killer cell subset based on CD16 expression levels in bone marrow and peripheral blood of healthy children and pediatric patients with acute lymphoblastic leukemia. Our findings demonstrate for the first time that CD56(low)CD16(low) natural killer cells are more abundant in bone marrow than in peripheral blood and that their frequency is further increased in children with acute lymphoblastic leukemia. Bone marrow and peripheral blood CD56(low)CD16(low) natural killer cells compared with CD56(low)CD16(high) natural killer cells express lower levels of killer inhibitory receptors, higher levels of CD27, CD127, CD122, CD25, but undetectable levels of CD57, suggesting that they have a higher proliferative and differentiation potential. Moreover, CD56(low)CD16(low) natural killer cells display higher levels of CXCR4 and undetectable levels of CX3CR1 and can be consistently and rapidly mobilized in peripheral blood in response to CXCR4 antagonist. Unlike CD56(low)CD16(high), both bone marrow and peripheral blood CD56(low)CD16(low) natural killer cells release IFNγ following cytokine stimulation, and represent the major cytotoxic natural killer cell population against K562 or acute lymphoblastic leukemia target cells. All these data suggest that CD56(low)CD16(low) natural killer cells are multifunctional cells, and that the presence of hematologic malignancies affects their frequency and functional ability at both tumor site and in the periphery.

Subsets of human natural killer cells and their regulatory effects

Human natural killer (NK) cells have distinct functions as NK(tolerant) , NK(cytotoxic) and NK(regulatory) cells and can be divided into different subsets based on the relative expression of the surface markers CD27 and CD11b. CD27⁺ NK cells, which are abundant cytokine producers, are numerically in the minority in human peripheral blood but constitute the large population of NK cells in cord blood, spleen, tonsil and decidua tissues. Recent data suggest that these NK cells may have immunoregulatory properties under certain conditions. In this review, we will focus on these new NK cell subsets and discuss how regulatory NK cells may serve as rheostats or sentinels in controlling inflammation and maintaining immune homeostasis in various organs.

Multiple levels of chemokine receptor regulation in the control of mouse natural killer cell development

Chemokines play a fundamental role in lymphocyte development, mainly attributable to the control of the correct localization in the proper microenvironments of cells undergoing maturation. Natural killer (NK) cell development occurs in the bone marrow (BM) where their localization is regulated by the balance of chemokine function in cell retention into tissues and mobilization into circulation. In addition, NK cells from several extra-medullary tissues are phenotypically and functionally different from their circulating counterpart suggesting that maturation can be completed in organs other than BM. Indeed, a role of chemokines in NK cell localization into tissues during homeostatic conditions is also documented. In this review, we summarize the current notion related to the relevance of several chemokine/chemokine receptor axes in NK cell development with a focus on the regulation of their expression and function.

NK cells in hepatitis B virus infection: a potent target for immunotherapy

Viruses, including hepatitis B virus (HBV), are the most prevalent and infectious agents that lead to liver disease in humans. Hepatocellular carcinoma (HCC) and cirrhosis of the liver are the most serious complications arising from prolonged forms of hepatitis B. Previous studies demonstrated that patients suffering from long-term HBV infections are unable to eradicate HBV from hepatocytes completely. The mechanisms responsible for progression of these forms of infection have not yet been clarified. However, it seems that there are differences in genetic and immunological parameters when comparing patients to subjects who successfully clear HBV infections, and these may represent the causes of long-term infection. Natural killer (NK) cells, the main innate immune cells that target viral infections, play important roles in the eradication of HBV from hepatocytes. NK cells carry several stimulatory and inhibitor receptors, and binding of receptors with their ligands results in activation and suppression of NK cells, respectively. The aim of this review is to address the recent information regarding NK cell phenotype, functions and modifications in hepatitis B. This review addresses the recent data regarding the roles of NK cells as novel targets for immunotherapies that target hepatitis B infection. It also discusses the potential to reduce the risk of HCC or cirrhosis of the liver by targeting NK cells.

Chemokines and chemokine receptors: positioning cells for host defense and immunity

Chemokines are chemotactic cytokines that control the migratory patterns and positioning of all immune cells. Although chemokines were initially appreciated as important mediators of acute inflammation, we now know that this complex system of approximately 50 endogenous chemokine ligands and 20 G protein-coupled seven-transmembrane signaling receptors is also critical for the generation of primary and secondary adaptive cellular and humoral immune responses. Recent studies demonstrate important roles for the chemokine system in the priming of naive T cells, in cell fate decisions such as effector and memory cell differentiation, and in regulatory T cell function. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the organismic level in homeostasis, in acute inflammation, and during the generation and regulation of adoptive primary and secondary immune responses in the lymphoid system and peripheral nonlymphoid tissue.

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.

CX3CR1 regulates the maintenance of KLRG1+ NK cells into the bone marrow by promoting their entry into circulation

NK cell differentiation mainly occurs in the bone marrow (BM) where a critical role in the regulation of developing lymphocyte distribution is played by members of the chemokine receptor family. In mouse, the chemokine receptor CX3CR1 identifies a late stage of NK cell development characterized by decreased effector functions and expression of the inhibitory receptor KLRG1. The role of CX3CR1 in the regulation of differentiation and positioning of NK cell subsets in the BM is not known. In this study, we found that CX3CR1 deficiency leads to accumulation of KLRG1(+) NK cells in BM during steady-state conditions. The NK cell subset that expresses the receptor in wild-type mice was expanded in several tissues of CX3CR1-deficient mice, and NK cell degranulation in response to sensitive target cell stimulation was enhanced, suggesting a regulatory role of CX3CR1 in NK cell positioning and differentiation in BM. Indeed, the observed NK cell expansion was not due to altered turnover rate, whereas it was associated with preferential accumulation in the BM parenchyma. In addition, a role of CX3CR1 in NK cell trafficking from BM and spleen was evidenced also during inflammation, as CX3CR1-deficient NK cells were more prompt to exit the BM and did not decrease in spleen in response to polyinosinic-polycytidylic acid-promoted hepatitis. Overall, our results evidenced a relevant role of CX3CR1 in the regulation of NK cell subset exit from BM during homeostasis, and suggest that defect in the CX3CR1/CX3CL1 axis alters NK cell trafficking and functional response during inflammatory conditions.

Location and cellular stages of natural killer cell development

The identification of distinct tissue-specific natural killer (NK) cell populations that apparently mature from local precursor populations has brought new insight into the diversity and developmental regulation of this important lymphoid subset. NK cells provide a necessary link between the early (innate) and late (adaptive) immune responses to infection. Gaining a better understanding of the processes that govern NK cell development should allow us to harness better NK cell functions in multiple clinical settings, as well as to gain further insight into how these cells undergo malignant transformation. In this review, we summarize recent advances in understanding sites and cellular stages of NK cell development in humans and mice.

Differential chemotactic receptor requirements for NK cell subset trafficking into bone marrow

Responsiveness of maturing natural killer (NK) cells to chemotactic molecules directly affect their retention and relocation in selected bone marrow (BM) microenvironment during development, as well as their localization at sites of immune response during inflammatory diseases. BM is the main site of NK cell generation, providing microenvironmental signals required to sustain cell proliferation and differentiation. Drastic changes of expression and function of several chemoattractant receptors can be observed during progression from precursor NK cells to immature and mature NK cells. Indeed, the gradual decrease of CXCR4 expression parallels the increased expression of CXCR3, CCR1, and CX3CR1 and S1P₅ (Sphingosine-1-phosphate receptor 5) on mature DX5⁺ NK cells. The chemokine CXCL12 is produced constitutively in the BM and, acting via CXCR4, is critical for retaining immature and mature NK cell subsets in the BM. During steady-state, the maintenance of NK cells into BM parenchyma depends on the equilibrium of CXCR4 retention and S1P₅ mobilizing functions, as the gradient of S1P coming from the sinusoids facilitates mature NK cell egress into circulation via S1P₅, when CXCR4/CXCL12-mediated retention decreases. Chemoattractants are also key factors for the response to inflammatory or infection conditions that promote mobilization of effector NK cells from storage compartments (including BM) to sites of disease or for NK cell recruitment/response during pathological conditions that affect BM integrity, including hematopoietic malignancies. In this review, we summarize what is known about the requirement for NK cell localization and exit from BM and how chemokine-mediated functions may affect BM NK cell development and immune responses.

Impact of brief exercise on peripheral blood NK cell gene and microRNA expression in young adults

Natural killers (NK) cells are unique innate immune cells that increase up to fivefold in the circulating blood with brief exercise and are known to play a key role in first-response defense against pathogens and cancer immunosurveillance. Whether exercise alters NK cell gene and microRNA (miRNA) expression is not known. Thirteen healthy men (20-29 yr old) performed ten 2-min bouts of cycle ergometer exercise at a constant work equivalent to an average of 77% of maximum O2 consumption interspersed with 1-min rest. Blood was drawn before and immediately after the exercise challenge. NK cells were isolated from peripheral blood mononuclear cells using a negative magnetic cell separation method. We used Affymetrix U133+2.0 arrays for gene expression and Agilent Human miRNA V2 Microarray for miRNAs. A stringent statistical approach (false discovery rate < 0.05) was used to determine that exercise significantly altered the expression of 986 genes and 23 miRNAs. Using in silico analysis, we found exercise-related gene pathways where there was a high likelihood of gene-miRNA interactions. These pathways were predominantly associated with cancer and cell communication, including p53 signaling pathway, melanoma, glioma, prostate cancer, adherens junction, and focal adhesion. These data support the hypothesis that exercise affects the gene and miRNA expression pattern in the population of NK cells in the circulation and suggest mechanisms through which physical activity could alter health through the innate immune system.

CCR2 defines a distinct population of NK cells and mediates their migration during influenza virus infection in mice

Natural killer (NK) cells are innate lymphocytes that play an important role in control of viral infections. We recently showed that intranasal infection of mice with influenza virus induced the accumulation of NK cells in the airways. NK cells however did not proliferate in the airways or in the draining lymph node, but in the bone marrow mainly. As also monocyte-precursors undergo vigorous proliferation in the bone marrow (BM) during infections and then egress CCR2-dependently, we decided to determine the role of CCR2 in NK cell migration during intranasal influenza virus infection. We show that a unique population of NK cells in the BM expressed CCR2 and that monocyte chemotactic protein-1 (MCP-1), one of the CCR2 ligands, was produced in the airways of influenza virus infected mice. Analysis of BM chimeric mice reconstituted with a mix of wild-type (wt) and CCR2-deficient BM cells showed that upon influenza virus infection, a significantly lower proportion of CCR2-deficient than wt NK cells was recovered from the bronchoalveolar lavage (BAL). Taken together, our data demonstrate that during influenza virus infection a proportion of NK cells migrate in a CCR2-dependent fashion.