Functionally distinct NK-cell subsets: developmental origins and biological implications

Mechanism of effects of nickel or nickel compounds on intestinal mucosal barrier

As an important metal in industry, national defense, and production, nickel widely exists in nature and is also a necessary trace element for human beings and animals. Nickel deficiency will affect the growth and development of animals, the contents of related active substances, enzymes and other essential elements in vivo. However, excessive nickel or longer nickel exposure can induce excessive free radicals (reactive oxygen species and reactive nitrogen) in the body, which can lead to a variety of cell damage, apoptosis and canceration, and ultimately pose negative effects on the health of the body. Among them, the intestinal tract, as the largest interface between the body and the external environment, greatly increases the contact probability between nickel or nickel compounds and the intestinal mucosal barrier, thus, the intestinal structure and function are also more vulnerable to nickel damage, leading to a series of related diseases such as enteritis. Therefore, this paper briefly analyzed the damage mechanism of nickel or its compounds to the intestinal tract from the perspective of four intestinal mucosal barriers: mechanical barrier, immune barrier, microbial barrier and chemical barrier, we hope to make a certain theoretical contribution to the further research and the prevention and treatment of nickel related diseases.

NK cell and ILC heterogeneity in colorectal cancer. New perspectives from high dimensional data

Innate lymphoid cells (ILCs) and tissue-resident natural killer (NK) cells ensure immunity at environmental interfaces and help maintain barrier integrity of the intestinal tract. This wide range of innate lymphocytes is able to provide fast and potent inflammatory responses that, when deregulated, have been associated with pathogenesis of inflammatory bowel disease (IBD) and colorectal cancer (CRC). While the presence of tumor-infiltrating NK cells is generally associated with a favorable outcome in CRC patients, emerging evidence reveals distinct roles for ILCs in regulating CRC pathogenesis and progression. Advances in next generation sequencing technology, and in particular of single-cell RNA-seq approaches, along with multidimensional flow cytometry analysis, have helped to deconvolute the complexity and heterogeneity of the ILC system both in homeostatic and pathological contexts. In this review, we discuss the protective and detrimental roles of NK cells and ILCs in the pathogenesis of CRC, focusing on the phenotypic and transcriptional modifications these cells undergo during CRC development and progression.

Natural Killer Cells and Host Defense Against Human Rhinoviruses Is Partially Dependent on Type I IFN Signaling

Rhinovirus (RV), the causative agent of the common cold, causes only mild upper respiratory tract infections in healthy individuals, but can cause longer lasting and more severe pulmonary infections in people with chronic lung diseases and in the setting of immune suppression or immune deficiency. RV-infected lung structural cells release type I interferon (IFN-I), initiating the immune response, leading to protection against viruses in conjunction with migratory immune cells. However, IFN-I release is deficient in some people with asthma. Innate immune cells, such as natural killer (NK) cells, are proposed to play major roles in the control of viral infections, and may contribute to exacerbations of chronic lung diseases, such as asthma. In this study, we characterized the NK cell response to RV infection using an in vitro model of infection in healthy individuals, and determined the extent to which IFN-I signaling mediates this response. The results indicate that RV stimulation in vitro induces NK cell activation in healthy donors, leading to degranulation and the release of cytotoxic mediators and cytokines. IFN-I signaling was partly responsible for NK cell activation and functional responses to RV. Overall, our findings suggest the involvement of NK cells in the control of RV infection in healthy individuals. Further understanding of NK cell regulation may deepen our understanding of the mechanisms that contribute to susceptibility to RV infections in asthma and other chronic lung diseases.

Role of Innate Immune Cells in Psoriasis

Psoriasis is a chronic inflammatory skin condition caused by a combination of hereditary and environmental factors. Its development is closely related to the adaptive immune response. T helper 17 cells are major IL-17-producing cells, a function that plays an important role in the pathogenesis of psoriasis. However, recent findings have demonstrated that innate immune cells also contribute to the development of psoriasis. Innate lymphoid cells, γδ T cells, natural killer T cells, and natural killer cells are activated in psoriasis, contributing to disease pathology through IL-17-dependent and -independent mechanisms. The present review provides an overview of recent findings, demonstrating a role for innate immunity in psoriasis.

Innate Lymphocytes in Psoriasis

Skin is a fundamental component of our host defense system that provides a dynamic physical and chemical barrier against pathogen invasion and environmental insults. Cutaneous barrier function is mediated by complex interactions between structural cells such as keratinocytes and diverse lineages of immune cells. In contrast to the protective role of these intercellular interactions, uncontrolled immune activation can lead to keratinocyte dysfunction and psoriasis, a chronic inflammatory disease affecting 2% of the global population. Despite some differences between human and murine skin, animal models of psoriasiform inflammation have greatly informed clinical approaches to disease. These studies have helped to identify the interleukin (IL)-23-IL-17 axis as a central cytokine network that drives disease. In addition, they have led to the recent description of long-lived, skin-resident innate lymphocyte and lymphoid cells that accumulate in psoriatic lesions. Although not completely defined, these populations have both overlapping and unique functions compared to antigen-restricted αβ T lymphocytes, the latter of which are well-known to contribute to disease pathogenesis. In this review, we describe the diversity of innate lymphocytes and lymphoid cells found in mammalian skin with a special focus on αβ T cells, Natural Killer T cells and Innate Lymphoid cells. In addition, we discuss the effector functions of these unique leukocyte subsets and how each may contribute to different stages of psoriasis. A more complete understanding of these cell types that bridge the innate and adaptive immune system will hopefully lead to more targeted therapies that mitigate or prevent disease progression.

Tissue-resident NK cells and other innate lymphoid cells

Natural killer (NK) cells are important innate effectors for their defense against pathogens and tumors without the need of prior sensitization. Along with the growing understanding of basic NK cell biology, it has been widely accepted that NK cells are a heterogeneous population of innate lymphoid cell (ILC) family. Apart from the conventional NK cell (cNK) subset that circulates throughout the body, some non-lymphoid tissues contain tissue-resident NK (trNK) cell subsets, and the composition of NK cell subsets varies greatly with different locations. Except for cNK cells, other ILCs are known as tissue-resident cells. In this review, we summarize the unique properties of trNK cells, discuss their lineage relationship with other ILCs, and highlight recent advances in our understanding of the functions of trNK cells and other ILCs.

Innate Lymphoid Cell Development: A T Cell Perspective

Innate lymphoid cells (ILCs) and natural killer (NK) cells have garnered considerable interest due to their unique functional properties in immune defense and tissue homeostasis. Our current understanding of how these cells develop has been greatly facilitated by knowledge of T cell biology. Models of T cell differentiation provided the basis for a conceptual classification of these innate effectors and inspired a scheme of their activation and regulation. In this review, we discuss NK cell and ILC development from a "T cell standpoint" in an attempt to extend the analogy between adaptive T cells and their innate ILC and NK cell counterparts.

Allergen-induced activation of natural killer cells represents an early-life immune response in the development of allergic asthma

BACKGROUND

Childhood asthma in inner-city populations is a major public health burden, and understanding early-life immune mechanisms that promote asthma onset is key to disease prevention. Children with asthma demonstrate a high prevalence of aeroallergen sensitization and TH2-type inflammation; however, the early-life immune events that lead to TH2 skewing and disease development are unknown.

OBJECTIVE

We sought to use RNA sequencing of PBMCs collected at age 2 years to determine networks of immune responses that occur in children with allergy and asthma.

METHODS

In an inner-city birth cohort with high asthma risk, we compared gene expression using RNA sequencing in PBMCs collected at age 2 years between children with 2 or more aeroallergen sensitizations, including dust mite, cockroach, or both, by age 3 years and asthma by age 7 years (cases) and matched control subjects who did not have any aeroallergen sensitization or asthma by age 7 years.

RESULTS

PBMCs from the cases showed higher levels of expression of natural killer (NK) cell-related genes. After cockroach or dust mite allergen but not tetanus antigen stimulation, PBMCs from the cases compared with the control subjects showed differential expression of 244 genes. This gene set included upregulation of a densely interconnected NK cell-like gene network reflecting a pattern of cell activation and induction of inflammatory signaling molecules, including the key TH2-type cytokines IL9, IL13, and CCL17, as well as a dendritic cell-like gene network, including upregulation of CD1 lipid antigen presentation molecules. The NK cell-like response was reproducible in an independent group of children with later-onset allergic sensitization and asthma and was found to be specific to only those children with both aeroallergen sensitization and asthma.

CONCLUSION

These findings provide important mechanistic insight into an early-life immune pathway involved in TH2 polarization, leading to the development of allergic asthma.

Loss of Canonical Notch Signaling Affects Multiple Steps in NK Cell Development in Mice

Within the hematopoietic system, the Notch pathway is critical for promoting thymic T cell development and suppressing the B and myeloid lineage fates; however, its impact on NK lymphopoiesis is less understood. To study the role of Notch during NK cell development in vivo, we investigated different NK cell compartments and function in Rbp-Jk^fl/flVav-Cre^tg/+ mice, in which Rbp-Jk, the major transcriptional effector of canonical Notch signaling, was specifically deleted in all hematopoietic cells. Peripheral conventional cytotoxic NK cells in Rbp-Jk-deleted mice were significantly reduced and had an activated phenotype. Furthermore, the pool of early NK cell progenitors in the bone marrow was decreased, whereas immature NK cells were increased, leading to a block in NK cell maturation. These changes were cell intrinsic as the hematopoietic chimeras generated after transplantation of Rbp-Jk-deficient bone marrow cells had the same NK cell phenotype as the Rbp-Jk-deleted donor mice, whereas the wild-type competitors did not. The expression of several crucial NK cell regulatory pathways was significantly altered after Rbp-Jk deletion. Together, these results demonstrate the involvement of canonical Notch signaling in regulation of multiple stages of NK cell development.

Innate immunity and effector and regulatory mechanisms involved in allergic contact dermatitis

Skin's innate immunity is the initial activator of immune response mechanisms, influencing the development of adaptive immunity. Some contact allergens are detected by Toll-like receptors (TLRs) and inflammasome NLR3. Keratinocytes participate in innate immunity and, in addition to functioning as an anatomical barrier, secrete cytokines, such as TNF, IL-1β, and IL-18, contributing to the development of Allergic Contact Dermatitis. Dendritic cells recognize and process antigenic peptides into T cells. Neutrophils cause pro-inflammatory reactions, mast cells induce migration/maturation of skin DCs, the natural killer cells have natural cytotoxic capacity, the γδ T cells favor contact with hapten during the sensitization phase, and the innate lymphoid cells act in the early stages by secreting cytokines, as well as act in inflammation and tissue homeostasis. The antigen-specific inflammation is mediated by T cells, and each subtype of T cells (Th1/Tc1, Th2/Tc2, and Th17/Tc17) activates resident skin cells, thus contributing to inflammation. Skin's regulatory T cells have a strong ability to inhibit the proliferation of hapten-specific T cells, acting at the end of the Allergic Contact Dermatitis response and in the control of systemic immune responses. In this review, we report how cutaneous innate immunity is the first line of defense and focus its role in the activation of the adaptive immune response, with effector response induction and its regulation.

Interleukin (IL)-23 Stimulates IFN-γ Secretion by CD56bright Natural Killer Cells and Enhances IL-18-Driven Dendritic Cells Activation

Interleukin (IL)-23 is a member of the IL-12 family of cytokines that, as the other members of this family, is secreted by monocytes, macrophages, and dendritic cells (DC) upon recognition of bacterial, viral, and fungal components. IL-23 is critical during immunity against acute infections, and it is also involved in the development of autoimmune diseases. Although immunoregulatory effects of IL-23 on mouse natural killer (NK) cells have been described, the effect of IL-23 on human NK cells remains ill-defined. In this study, we observed that monocytes stimulated with LPS secreted IL-23 and that blockade of this cytokine during monocyte and NK cell coculture led to a diminished production of IFN-γ by NK cells. Accordingly, rIL-23-induced NK cell activation and stimulated IFN-γ production by CD56^bright NK cells. This effect involved MEK1/MEK2, JNK, PI3K, mammalian target of rapamycin, and NF-κB, but not STAT-1, STAT-3, nor p38 MAPK pathways. Moreover, while NK cell-mediated cytotoxicity remained unaltered, antibody-dependent cellular cytotoxicity (ADCC) was enhanced after IL-23 stimulation. In addition, IL-23 displayed a synergistic effect with IL-18 for IFN-γ production by both CD56^bright and CD56^dim NK cells, and this effect was due to a priming effect of IL-23 for IL-18 responsiveness. Furthermore, NK cells pre-stimulated with IL-18 promoted an increase in CD86 expression and IL-12 secretion by DC treated with LPS, and IL-23 potentiated these effects. Moreover, IL-23-driven enhancement of NK cell “helper” function was dependent on NK cell-derived IFN-γ. Therefore, our results suggest that IL-23 may trigger NK cell-mediated “helper” effects on adaptive immunity, shaping T cell responses during different pathological situations through the regulation of DC maturation.

Infectious Agents in Childhood Leukemia

Acute leukemia is the most common pediatric cancer, representing one-third of all cancers that occurs in under 15 year olds, with a varied incidence worldwide. Although a number of advances have increased the knowledge of leukemia pathophysiology, its etiology remains less well understood. The role of infectious agents, such as viruses, bacteria, or parasites, in the pathogenesis of leukemia has been discussed. To date, several cellular mechanisms involving infectious agents have been proposed to cause leukemia following infections. However, although leukemia can be triggered by contact with such agents, they can also be beneficial in developing immune stimulation and protection despite the risk of leukemic clones. In this review, we analyze the proposed hypotheses concerning how infectious agents may play a role in the origin and development of leukemia, as well as in a possible mechanism of protection following infections. We review reported clinical observations associated with vaccination or breastfeeding, that support hypotheses such as early life exposure and the resulting early immune stimulation that lead to protection.

Characterizing porcine invariant natural killer T cells: A comparative study with NK cells and T cells

CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that share phenotypic characteristics of both NK and conventional T cells (Tconv). Although iNKT cells have been well characterized in mice and humans, functional CD1d and CD1d-restricted iNKT cells are not universally expressed in mammals. Swine express iNKT cells that can be detected using α-galactosylceramide (α-GalCer)-loaded CD1d tetramers. In the present study, we characterized iNKT cells from the blood, spleen, lymph node, lung and liver of commercial mixed-breed pigs, and compared their phenotype to NK cells and Tconv. The principal findings are that pig iNKT cells are CD8α and CD44 positive and CD11b and Nkp46 negative. Most are also negative for the CD4 co-receptor, which is used to distinguish functionally distinct mouse and human iNKT cells subsets. The frequency of IFN-γ-producing CD8α^bright iNKT cells was 3-4-fold higher than CD8α^dull iNKT cells, suggesting that CD8α expression identifies iNKT cells with a unique functional role in immune responses. Finally, large variability was detected among pigs in interactions between iNKT cells and monocytes when iNKT cells were activated with α-GalCer, which raises a cautionary note about manipulating iNKT cells for immunotherapy. Collectively, our study provides important phenotypic and functional information about porcine iNKT cells that will be useful for understanding how iNKT cells contribute to immune responses in swine, with potential implications for human health.

Diversity of tissue-resident NK cells

Although natural killer (NK) cells were initially named for their spontaneous tumor-killing capacity, their concept has been greatly expanded with more than 40 years of extensive investigation. Currently, NK cells are known as a heterogeneous population of innate lymphoid cell (ILC) family, consisting of different subsets with unique phenotypic and functional features. Recent studies have shown that tissue-resident NK (trNK) cells, which are distinct from conventional NK (cNK) cells, preferentially distribute in non-lymphoid tissues, such as the liver, uterus, salivary gland, and adipose. In this review, we provide a comprehensive overview of the current knowledge about the phenotype, function and development of trNK cells across different tissues and describe the similarities and differences between diverse trNK cells and cNK cells, with a particular focus on the tissue-specific characteristics of different trNK cells.

Calorie Restriction Attenuates Terminal Differentiation of Immune Cells

Immune senescence is a natural consequence of aging and may contribute to frailty and loss of homeostasis in later life. Calorie restriction increases healthy life-span in C57BL/6J (but not DBA/2J) mice, but whether this is related to preservation of immune function, and how it interacts with aging, is unclear. We compared phenotypic and functional characteristics of natural killer (NK) cells and T cells, across the lifespan, of calorie-restricted (CR) and control C57BL/6 and DBA/2 mice. Calorie restriction preserves a naïve T cell phenotype and an immature NK cell phenotype as mice age. The splenic T cell populations of CR mice had higher proportions of CD11a^-CD44^lo cells, lower expression of TRAIL, KLRG1, and CXCR3, and higher expression of CD127, compared to control mice. Similarly, splenic NK cells from CR mice had higher proportions of less differentiated CD11b^-CD27⁺ cells and correspondingly lower proportions of highly differentiated CD11b⁺CD27^-NK cells. Within each of these subsets, cells from CR mice had higher expression of CD127, CD25, TRAIL, NKG2A/C/E, and CXCR3 and lower expression of KLRG1 and Ly49 receptors compared to controls. The effects of calorie restriction on lymphoid cell populations in lung, liver, and lymph nodes were identical to those seen in the spleen, indicating that this is a system-wide effect. The impact of calorie restriction on NK cell and T cell maturation is much more profound than the effect of aging and, indeed, calorie restriction attenuates these age-associated changes. Importantly, the effects of calorie restriction on lymphocyte maturation were more marked in C57BL/6 than in DBA/2J mice indicating that delayed lymphocyte maturation correlates with extended lifespan. These findings have implications for understanding the interaction between nutritional status, immunity, and healthy lifespan in aging populations.

Natural killer cells in the development of asthma

Asthma is an immune-mediated disease of the airways characterized by reversible airway obstruction, bronchial eosinophilic inflammation, and airway hyperresponsiveness (AHR). The immune dysregulation in asthma has been attributed to the involvement of diverse immune cells that contribute to the immunopathology of the disease. Natural killer (NK) cells play critical roles in host defense against viruses and various cancers. Accumulating evidence demonstrates additional important roles for these cells in T cell priming, dendritic cell maturation, and the development of inflammation, all of which have the potential to enhance or dampen allergic responses. The ability of NK cells to produce Th2-type cytokines and their pivotal role in combating respiratory infections which cause airway dysfunction in asthmatics further suggest that they may directly contribute to the immunopathogenesis of allergic airway disease. In this review, we examine emerging evidence and discuss the putative roles of NK cells in the sensitization, progression, and resolution of asthma.

Type I interferon regulation of natural killer cell function in primary and secondary infections

The priming of natural killer (NK) cells by type I interferon (IFN) is necessary for protection against primary and secondary viral infections. However, the pathway by which type I IFN activates NK cells to elicit antiviral responses is controversial. There is evidence to suggest that type I IFN priming of NK cells occurs through both direct and indirect pathways. As with many innate mechanisms, type I IFN and NK cells also orchestrate the adaptive immune response and thus aid in protection against secondary infections. Type I IFN can shape CD4(+) T cell, B cell and humoral memory formation. In addition, long-lived NK cells can perform specific and enhanced memory-like protection in secondary infections. This review outlines the different mechanisms underlying type I IFN regulation of NK cells and how type I IFN and NK cells can be used as a therapeutic target in vaccinations.

Natural killer cell development and maturation in aged mice

The effect of aging on natural killer cell homeostasis is not well studied in humans or in animal models. We compared natural killer (NK) cells from young and aged mice to investigate age-related defects in NK cell distribution and development. Our findings indicate aged mice have reduced NK cells in most peripheral tissues, but not in bone marrow. Reduction of NK cells in periphery was attributed to a reduction of the most mature CD11b(+) CD27(-) NK cells. Apoptosis was not found to explain this specific reduction of mature NK cells. Analysis of NK cell development in bone marrow revealed that aged NK cells progress normally through early stages of development, but a smaller percentage of aged NK cells achieved terminal maturation. Less mature NK cells in aged bone marrow correlated with reduced proliferation of immature NK cells. We propose that advanced age impairs bone marrow maturation of NK cells, possibly affecting homeostasis of NK cells in peripheral tissues. These alterations in NK cell maturational status have critical consequences for NK cell function in advanced age: reduction of the mature circulating NK cells in peripheral tissues of aged mice affects their overall capacity to patrol and eliminate cancerous and viral infected cells.

Genetic and environmental determinants of human NK cell diversity revealed by mass cytometry

Natural killer (NK) cells play critical roles in immune defense and reproduction, yet remain the most poorly understood major lymphocyte population. Because their activation is controlled by a variety of combinatorially expressed activating and inhibitory receptors, NK cell diversity and function are closely linked. To provide an unprecedented understanding of NK cell repertoire diversity, we used mass cytometry to simultaneously analyze 37 parameters, including 28 NK cell receptors, on peripheral blood NK cells from 5 sets of monozygotic twins and 12 unrelated donors of defined human leukocyte antigen (HLA) and killer cell immunoglobulin-like receptor (KIR) genotype. This analysis revealed a remarkable degree of NK cell diversity, with an estimated 6000 to 30,000 phenotypic populations within an individual and >100,000 phenotypes in the donor panel. Genetics largely determined inhibitory receptor expression, whereas activation receptor expression was heavily environmentally influenced. Therefore, NK cells may maintain self-tolerance through strictly regulated expression of inhibitory receptors while using adaptable expression patterns of activating and costimulatory receptors to respond to pathogens and tumors. These findings further suggest the possibility that discrete NK cell subpopulations could be harnessed for immunotherapeutic strategies in the settings of infection, reproduction, and transplantation.

Fc receptor-mediated immune responses: new tools but increased complexity in HIV prevention

The modest success of the RV144 HIV vaccine trial in Thailand and the ensuing suggestion that a Fc-receptormediated antibody activity might have played a role in the protection observed have intensified investigations on Fcrelated immune responses. HIV neutralizing antibodies have been and continue to be the focal point of research into humoral immune protection. However, recent knowledge that their protective efficacy can be augmented by Fc-FcR interactions has increased the complexity of identifying immune correlates of protection. If anything, continued studies of both humoral and cellular immune mechanisms point to the lack of a single protective anti-HIV immune response. Here we focus on humoral immunity, analyzing the role played by Fc receptor-related responses and discussing how new knowledge of their interactions requires further investigation, but may also spur novel vaccination approaches. We initially address classical Fc-receptor mediated anti-viral mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cell mediated viral inhibition (ADCVI), and antibody-dependent cellular phagocytosis (ADCP), as well as the effector cells that mediate these functions. Next, we summarize key aspects of FcR-Fc interactions that are important for potential control of HIV/SIV such as FcR polymorphisms and post-transcriptional modifications. Finally we discuss less commonly studied non-mechanistic anti-HIV immune functions: antibody avidity and envelopespecific B cell memory. Overall, a spectrum of immune responses, reflecting the immune system's redundancy, will likely be needed to prevent HIV infection and/or disease progression. Aside from elicitation of critical immune mechanisms, a successful vaccine will need to induce mature B cell responses and long-lasting immune memory.

Brief Exercise Increases Peripheral Blood NK Cell Counts without Immediate Functional Changes, but Impairs their Responses to ex vivo Stimulation

Physical as well as psychological stress increases the number of circulating peripheral blood NK cells. Whereas some studies found a positive correlation between exercise and NK cell counts and cytotoxic activity, others showed that, for example, heavy training leads to a decrease in per cell NK cytotoxicity. Thus, the impact of exercise on NK cell function and eventually on altered immunocompetence remains to be elucidated. Here, we investigated whether a single bout of brief exercise, consisting in running up and down 150 stair-steps, affects the number and function of circulating NK cells. NK cells, obtained from 29 healthy donors, before and immediately after brief exercise, were assessed for numbers, phenotype, IFNγ production, degranulation, cytotoxicity, and in vitro response to stimulation with IL-2, IL-2/IL-12, or TLR2 agonists. Running resulted in a sixfold increase in the number of CD3⁻/CD56⁺ NK cells, but decreased the frequency of CD56^bright NK cells about twofold. Brief exercise did not significantly interfere with baseline IFNγ secretion or NK cell cytotoxicity. In vitro stimulation with IL-2 and TLR2 agonists (lipoteichoic acid, and synthetic triacylated lipopeptide Pam3CSK4) enhanced IFNγ-secretion, degranulation, and cytotoxicity mediated by NK cells isolated pre-exercise, but had less effect on NK cells isolated following exercise. There were no differences in response to combined IL-2/IL-12 stimulation. In conclusion, having no obvious impact on baseline NK functions, brief exercise might be used as a simple method to significantly increase the number of CD56^dim NK cell available for in vitro experiments. Nevertheless, the observed impaired responses to stimulation suggest an alteration of NK cell-mediated immunity by brief exercise which is at least in part explained by a concomitant decrease of the circulating CD56^bright NK cell fraction.

Natural killer cells regulate diverse T cell responses

Natural killer (NK) cells are important mediators of the immune response against microbial pathogens and tumors. There is growing evidence from mouse and human studies that, NK cells exhibit immunoregulatory functions and can limit T cell immunity. NK cell regulatory activity has been demonstrated in a variety of disease models including chronic viral infection, autoimmunity, and transplantation. Depending on the nature of the immune challenge, NK cells use different strategies to limit T cell function, including via cytokines, interactions with NK receptors NKG2D and NKp46, or by perforin-mediated T cell death. Future work should address whether specific subsets of NK cells inhibit T cell responses, and how NK cells acquire immunosuppressive functions.

CD11b(-)CD27(-) NK cells are associated with the progression of lung carcinoma

NK cells are a major component of the antitumour immune response that limits tumour progression. However, it has been reported that tumour-infiltrating NK (TINK) cells from patients with non-small-cell lung carcinoma (NSCLC) exhibit profound defects in degranulation and IFN-γ production. In support of this notion, we report a novel mechanism associated with tumour escape from NK cell-mediated antitumour immunity in lung carcinoma. In this study, we investigated the phenotypic profile of TINK cells based on the expression of the NK-cell maturation markers CD11b and CD27. Interestingly, we found a substantial CD11b⁻CD27⁻ (DN) NK-cell population harboured within the tumour tissues. The presence of this CD11b⁻CD27⁻ NK subset indicated that the TINK cells were of an immature and inactive phenotype. Remarkably, we determined that the presence of DN NK cells had an impact on the clinical outcomes of patients with NSCLC, as the frequency of tumour-infiltrating DN NK cells was positively correlated with the tumour stage and tumour size. We further used a murine Lewis lung cancer (LLC) model to confirm the correlation between the frequency of tumour-infiltrating DN NK cells and the progression of lung carcinoma. Together, our findings demonstrate that the tumour microenvironment may render TINK cells less tumouricidal and thereby contribute to cancer progression.

Role of NKp46 expression in cytokine production by CD56-positive NK cells in the peripheral blood and the uterine endometrium

PROBLEM

To investigate the role of natural cytotoxicity receptor, NKp46 expression in cytokine-producing NK cells.

METHOD OF STUDY

CD56(+) /NKp46(+) NK cells from the peripheral blood and the uterine endometrium were magnetically separated. IFN-γ, TNF-α, IL-4, IL-10, and TGF-β(1) expressions on NK cells were investigated using multicolor flow cytometry.

RESULTS

Peripheral blood and uterine endometrial NK cells were grouped into 4 subpopulations based upon the degree of CD56 and NKp46 expressions. NKp46 expression was associated with higher frequency of cytokine-producing NK cells, including CD56(dim) NK cells. The percentage of TNF-α(+) and IL-10(+) NK cells per total CD56(+) /NKp46(+) NK cells in the uterine endometrium showed a significant correlation with those of the peripheral blood in all subpopulations, but that of IFN-γ(+) , IL-4(+,) and TGF-β(1) (+) NK cells showed partial correlation.

CONCLUSION

Expression of NKp46 is involved in cytokine production of CD56(+) NK cells in the peripheral blood and the uterine endometrium.

The role of innate immunity in the host defense against intestinal bacterial pathogens

Eradication of infectious disease is our global health challenge. After encountering intestinal infection with a bacterial pathogen, the host defense program is initiated by local antigen-presenting cells (APCs) that eliminate invading pathogens by phagocytosis and establish localized inflammation by secreting cytokines and chemokines. These pathogen-experienced APCs migrate to the mesenteric lymph nodes, where host immune responses are precisely orchestrated. Initiation and regulation of this defense program appear to be largely dependent on innate immunity which is antigen non-specific and provides a rapid defense against broader targets. On the other hand, many bacterial enteropathogens have evoked abilities to modify the host defense program to their advantage. Therefore, better understanding of the host-pathogen interactions is essential to establish effective eradication strategies for enteric infectious diseases. In this review, we will discuss the current understanding of innate immune regulation of the host defense mechanisms against intestinal infection by bacterial pathogens.

NK and CD4+ T cell cooperative immune responses correlate with control of disease in a macaque simian immunodeficiency virus infection model

Control of infectious disease may be accomplished by successful vaccination or by complex immunologic and genetic factors favoring Ag-specific multicellular immune responses. Using a rhesus macaque model, we evaluated Ag-specific T cell-dependent NK cell immune responses in SIV-infected macaques, designated "controlling" or "noncontrolling" based on long-term chronic viremia levels, to determine whether NK cell effector functions contribute to control of SIV infection. We observed that Gag stimulation of macaque PBMCs induced subset-specific NK cell responses in SIV-controlling but not SIV-noncontrolling animals, as well as that circulatory NK cell responses were dependent on Ag-specific IL-2 production by CD4(+) central memory T cells. NK cell activation was blocked by anti-IL-2-neutralizing Ab and by CD4(+) T cell depletion, which abrogated the Gag-specific responses. Among tissue-resident cells, splenic and circulatory NK cells displayed similar activation profiles, whereas liver and mucosal NK cells displayed a decreased activation profile, similar in SIV-controlling and -noncontrolling macaques. Lack of T cell-dependent NK cell function was rescued in SIV-noncontrolling macaques through drug-mediated control of viremia. Our results indicate that control of disease progression in SIV-controlling macaques is associated with cooperation between Ag-specific CD4(+) T cells and NK cell effector function, which highlight the importance of such cell-to-cell cooperativity in adaptive immunity and suggest that this interaction should be further investigated in HIV vaccine development and other prophylactic vaccine approaches.

[Homeostasis of natural killer cells]

Natural killer (NK) cells are important players of innate immunity, dedicated to the host defense against viruses and also involved in the immune surveillance of tumors. NK cells are widely distributed in the body and their number may increase locally during infection. They develop mainly in the bone marrow and perhaps in other lymphoid organs. They are constantly renewed, with a half-life of about 17 days at the periphery. In this article, we review the factors that regulate the homeostasis of NK cells including their development, differentiation, export to the periphery, their turnover, their homeostatic or antigen-induced proliferation and their survival before or after activation. In addition, we discuss the homeostasis of recently described so-called "memory" NK cells.

A CD8α(-) subpopulation of macaque circulatory natural killer cells can mediate both antibody-dependent and antibody-independent cytotoxic activities

Natural killer (NK) cells are important components of the innate immune system that mediate effector and regulatory functions. As effector cells, NK cells help control virus-infected cells through cell-mediated antibody-dependent mechanisms such as antibody-dependent cellular cytotoxicity (ADCC). Although macaques are an important and reliable animal model for the study of retrovirus-induced human diseases, and despite the crucial role played by NK cells in innate and adaptive immune responses against simian immunodeficiency virus (SIV), only a few studies have attempted to characterize different macaque NK cell subpopulations. In the present study, we identified a subpopulation of circulatory CD8α(-) macaque NK cells that express NK lineage markers and exhibit cytotoxic potential. CD8α(-) NK cells were phenotypically characterized as CD3(-) CD14(-) CD20(-) CD8α(-) cells that express NK cell markers including CD16, CD56, granzyme B, perforin, NKG2D and KIR2D. Based on their CD56/CD16 expression patterns, cells within the CD8α(-) gate can be divided into four subpopulations: CD56(dim) CD16(bright) , CD56(dim) CD16(-) , CD56(bright) CD16(-) , and CD56(-) CD16(-) cells. In contrast, CD8α(+) NK cells are 95% CD56(dim) CD16(bright) , which correlates with their high cytotoxic potential. Upon interleukin-15 activation, CD8α(-) cells up-regulated CD69 expression and produced low levels of interferon-γ and tumour necrosis factor-α. Sorted CD8α(-) NK cells were capable of killing MHC-I-devoid target cells and mediated ADCC responses against SIV gp120-coated target cells in the presence of macaque anti-gp120 antibodies. Taking into account CD8α(-) myeloid dendritic cells, we show that about 35% of macaque CD8α(-) cells represent a novel, functional population of circulatory NK cells that possesses cytotoxic potential and is capable of mediating anti-viral immune responses.

Natural killer-22 cells in the synovial fluid of patients with rheumatoid arthritis are an innate source of interleukin 22 and tumor necrosis factor-α

OBJECTIVE

To determine the role of natural killer (NK)-22 cells in the pathogenesis of rheumatoid arthritis (RA).

METHODS

Using flow cytometry, the proportions of NK-22 cells and intracellular contents of perforin, granzyme B, and interferon-γ (IFN-γ) were determined in the peripheral blood (PB) and synovial fluid (SF) of patients with RA and healthy individuals. The levels of interleukin 22 (IL-22) and tumor necrosis factor-α (TNF-α) in the NK-22 supernatant and gene expressions were measured using ELISA and QuantiGene Plex assay, respectively. The effect of NK-22 supernatant on the proliferation of fibroblast-like synoviocytes (FLS) and recombinant human IL-22 (rhIL-22) on the production of monocyte chemoattractant protein 1 (MCP-1) by RA FLS was detected using the yellow tetrazolium salt method and ELISA, respectively. The relationship between the proportions of NK-22 cells and disease activity was analyzed.

RESULTS

NKp44 and CCR6 were expressed in a larger population of SF NK cells than in the PB NK cells of patients with RA. NK-22 cells produce low content of perforin, granzyme B, and IFN-γ. NK-22 cells in vitro can secrete IL-22 and TNF-α and there was increased messenger RNA coding for IL-22 and TNF-α. NK-22 supernatant can induce the proliferation of RA FLS. Addition of IL-22 antibody plus TNF-α antibody inhibited the proliferation of FLS induced by the NK-22 supernatant. Both rhIL-22 1 ng/ml and rhIL-22 10 ng/ml induced the production of MCP-1 by RA FLS. The NK-22 proportions were positively correlated with disease activity.

CONCLUSION

NK-22 cells are increased in patients with RA and might play a role in the pathogenesis of RA through the production of IL-22 and TNF-α. The proportion of NK-22 cells and disease activity were highly correlated.

Plasmid vector-linked maturation of natural killer (NK) cells is coupled to antigen-dependent NK cell activation during DNA-based immunization in mice

Plasmid DNA vaccines serve in a wide array of applications ranging from prophylactic vaccines to potential therapeutic tools against infectious diseases and cancer. In this study, we analyzed the mechanisms underlying the activation of natural killer (NK) cells and their potential role in adaptive immunity during DNA-based immunization against hepatitis B virus surface antigen in mice. We observed that the mature Mac-1(+) CD27(-) NK cell subset increased in the liver of mice early after DNA injection, whereas the number of the less mature Mac-1(+) CD27(+) NK cells in the liver and spleen was significantly reduced. This effect was attributed to bacterial sequences present in the plasmid backbone rather than to the encoded antigen and was not observed in immunized MyD88-deficient mice. The activation of NK cells by plasmid-DNA injection was associated with an increase in their effector functions that depended on the expressed antigen. Maturation of NK cells was abrogated in the absence of T cells, suggesting that cross talk exists between NK cells and antigen-specific T cells. Taken together, our data unravel the mechanics of plasmid vector-induced maturation of NK cells and plasmid-encoded antigen-dependent activation of NK cells required for a crucial role of NK cells in DNA vaccine-induced immunogenicity.

IL-1β regulates a novel myeloid-derived suppressor cell subset that impairs NK cell development and function

Chronic inflammation is associated with promotion of malignancy and tumor progression. Many tumors enhance the accumulation of myeloid-derived suppressor cells (MDSC), which contribute to tumor progression and growth by suppressing anti-tumor immune responses. Tumor-derived IL-1β secreted into the tumor microenvironment has been shown to induce the accumulation of MDSC possessing an enhanced capacity to suppress T cells. In this study, we found that the enhanced suppressive potential of IL-1β-induced MDSC was due to the activity of a novel subset of MDSC lacking Ly6C expression. This subset was present at low frequency in tumor-bearing mice in the absence of IL-1β-induced inflammation; however, under inflammatory conditions, Ly6C(neg) MDSC were predominant. Ly6C(neg) MDSC impaired NK cell development and functions in vitro and in vivo. These results identify a novel IL-1β-induced subset of MDSC with unique functional properties. Ly6C(neg) MDSC mediating NK cell suppression may thus represent useful targets for therapeutic interventions.

Heat-killed Lactobacillus acidophilus La205 enhances NK cell cytotoxicity through increased granule exocytosis

Heat-killed lactic acid bacteria (LAB) are known to be important immunomodulators that stimulate tumor necrosis factor-α (TNF-α) and nitric oxide (NO) production as well as increase phagocytic activity in macrophages. NK cells play a critical role in innate immune response and induce spontaneous killing of tumor cells and virus-infected cells. However, the effect of heat-killed LAB on NK cells is still unclear. In this study, we investigated the effect of heat-killed Lactobacillus acidophilus La205 (La205) on NK cytolytic activity. We found that heat-killed La205 directly stimulated NK cytolytic activity in dose- and time-dependent manners. To determine the mechanism underlying heat-killed La205-enhanced NK cytotoxicity, the expression of NK activating receptors was tested. Heat-killed La205 did not affect the expression of NK activating receptors. To investigate whether NK degranulation is related to heat-killed La205-enhanced NK cytotoxicity, NK degranulation inhibitor concanamycin A (CMA) was used. CMA effectively blocked heat-killed La205-induced NK cytotoxicity, and an assay for detection of a degranulation marker, CD107a, showed that heat-killed La205 increased granule exocytosis approximately 2-fold in comparison to non-treated NK cells. In addition, heat-killed La205 dramatically elevated mRNA expression of granulysin, a component of the cytolytic granule contents, in NK cells. However, other granule contents, including perforin and granzymes, were not changed by heat-killed La205. From these data, we concluded that heat-killed La205 stimulated NK cytolytic activity through enhancement of granule exocytosis, and granulysin may be a critical mediator in heat-killed La205-induced granule exocytosis.

Persistence of decidual NK cells and KIR genotypes in healthy pregnant and preeclamptic women: a case-control study in the third trimester of gestation

BACKGROUND

Natural Killer (NK) cells are the most abundant lymphocytes in the decidua during early gestation. The interactions of NK cells with the extravillous cytotrophoblast have been associated with a normal spiral artery remodeling process, an essential event for a successful pregnancy. Recent data indicate that alterations in the amount of decidual NK (dNK) cells contribute to the development of preeclampsia (PE). Moreover, genetic studies suggest that Killer Immunoglobulin-like Receptors (KIR) expressed in dNK cells influence the susceptibility to PE. Although dNK cells have been well characterized during early pregnancy, they have been scarcely studied in the third trimester of gestation. The aim of this work was to characterize dNK cells at the last trimester of gestation and to analyze the KIR genotype of healthy and PE women.

METHODS

Decidual samples were obtained during Caesarean section from control (n = 10) and PE (n = 9) women. Flow cytometric analysis of CD3, CD56, CD16 and CD9 was used to characterize and quantify dNK cells in both groups. Cell surface markers from decidual leukocytes were compared with PBMC from healthy donors.KIR genotyping was performed in genomic DNA (control, n = 86; PE, n = 90) using PCR-SSP.

RESULTS

The results indicate that dNK cells persist throughout pregnancy. They represented 20% of total leukocytes in control and PE groups, and they expressed the same cell surface markers (CD3-, CD56+, CD16- and CD9+) as dNK in the first trimester of gestation. There were no significant differences in the percentage of dNK cells between control and PE groups. The analysis of KIR gene frequencies and genotypes was not statistically different between control and PE groups. The ratio of activating to inhibitory genes indicated that the overall inhibitory balance (0.2-0.5) was more frequent in the PE group (control, 31.3% vs PE, 45.5%), and the activating balance (0.6-1.1) was more frequent in the control group (control, 68.6% vs PE, 54.4%). However this difference was not significant.

CONCLUSION

We demonstrated the persistence of dNK cells in PE and control women at the third trimester of pregnancy; these dNK cells had a similar phenotype to those found during early pregnancy. The predominance of a KIR inhibitory balance in the PE group could be associated to the physiopathology of PE.

Next-generation sequencing identifies the natural killer cell microRNA transcriptome

Natural killer (NK) cells are innate lymphocytes important for early host defense against infectious pathogens and surveillance against malignant transformation. Resting murine NK cells regulate the translation of effector molecule mRNAs (e.g., granzyme B, GzmB) through unclear molecular mechanisms. MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate the translation of their mRNA targets, and are therefore candidates for mediating this control process. While the expression and importance of miRNAs in T and B lymphocytes have been established, little is known about miRNAs in NK cells. Here, we used two next-generation sequencing (NGS) platforms to define the miRNA transcriptomes of resting and cytokine-activated primary murine NK cells, with confirmation by quantitative real-time PCR (qRT-PCR) and microarrays. We delineate a bioinformatics analysis pipeline that identified 302 known and 21 novel mature miRNAs from sequences obtained from NK cell small RNA libraries. These miRNAs are expressed over a broad range and exhibit isomiR complexity, and a subset is differentially expressed following cytokine activation. Using these miRNA NGS data, miR-223 was identified as a mature miRNA present in resting NK cells with decreased expression following cytokine activation. Furthermore, we demonstrate that miR-223 specifically targets the 3' untranslated region of murine GzmB in vitro, indicating that this miRNA may contribute to control of GzmB translation in resting NK cells. Thus, the sequenced NK cell miRNA transcriptome provides a valuable framework for further elucidation of miRNA expression and function in NK cell biology.

Natural killer cells: versatile roles in autoimmune and infectious diseases

Natural killer (NK) cells are essential members of innate immunity and they rapidly respond to a variety of insults via cytokine secretion and cytolytic activity. Effector functions of NK cells form an important first line of innate immunity against viral, bacterial and parasitic infections, as well as an important bridge for the activation of adaptive immune responses. The control of NK-cell activation and killing is now understood to be a highly complex system of diverse inhibitory and activatory receptor-ligand interactions, sensing changes in MHC expression. NK cells have a functional role in innate immunity as the primary source of NK-cell-derived immunoregulatory cytokines, which have been identified in target organs of patients suffering from autoimmune diseases, and play a critical role in early defense against infectious agents. This review focuses on recent research of NK cells, summarizing their potential immunoregulatory role in modulating autoimmunity and infectious diseases.

Murine CXCR3+CD27bright NK cells resemble the human CD56bright NK-cell population

Human NK cells can be subdivided into CD56(dim) and CD56(bright) NK cells, which exhibit different phenotypical and functional characteristics. As murine NK cells lack CD56 or a distinct correlate, direct comparative studies of NK cells in mice and humans are limited. Although CD27 is currently proposed as a feasible subset marker in mice, we assume that the usage of this marker alone is insufficient. We rather investigated the expression of the chemokine receptor CXCR3 for its suitability for distinguishing murine NK-cell subsets with simultaneous consideration of CD27. Compared with CXCR3(-) NK cells, exerting stronger cytotoxic capability, CXCR3+ NK cells displayed an activated phenotype with a lower expression of Ly49 receptors, corresponding to human CD56(bright) NK cells. Also in common with human CD56(bright) NK cells, murine CXCR3+ NK cells exhibit prolific expansion as well as robust IFN-gamma, TNF-alpha and MIP-1alpha production. We additionally demonstrated changes in both CXCR3 and CD27 expression upon NK-cell activation. In summary, CXCR3 serves as an additional applicable marker for improved discrimination of functionally distinct murine NK-cell subsets that comply with those in humans.

NK cell regulation of CD4 T cell-mediated graft-versus-host disease

CD3-negative NK cells are granular lymphocytes capable of producing inflammatory cytokines and killing malignant, infected, or stressed cells. We have recently observed a new role for NK cells in the control of the proliferation of CD4 T cells under persistent antigenic stimulation. Monoclonal anti-male CD4 T cells transferred into Rag2-/- male recipients did not expand or were rapidly eliminated. Remarkably, T cells transferred into NK cell-deficient Rag2-/- Il-2Rgammac-/- male hosts expanded extensively and mediated tissue lesions usually observed in chronic graft-versus-host disease (GVHD). T cell failure to proliferate and to induce chronic GVHD was the result of NK cell activity, because depletion of the recipient's NK1.1+ cells by Ab treatment induced T cell expansion and chronic GVHD. T cells under chronic Ag stimulation upregulated ligands of the activating receptor NKG2D, and regulatory activity of NK cells was inhibited by the injection of Abs directed to NKG2D. On the contrary, blocking NKG2A inhibitory receptors did not increase NK cell regulatory activity. Finally, we show that NK regulation of T cell expansion did not involve perforin-mediated lytic activity of NK cells, but depended on T cell surface expression of a functional Fas molecule. These results highlight the potential role played by NK cells in controlling the Ag-specific CD4+ T cells responsible for chronic GVHD.

Multiple hats for natural killers

Natural killer (NK) cells are a subset of lymphocytes that kill virus-infected or cancerous cells and influence adaptive immune responses via production of inflammatory cytokines. Unlike B and T lymphocytes, no transcription factors have been identified that are essential for the emergence of NK cell progenitors from their multipotent precursors. We argue that this dearth of essential factors is because of the expression of redundant transcription factors that function at the earliest stages of development. However, multiple essential transcription factors have been identified at later stages of development. Recent studies have revealed novel subsets of NK cells with differing potential for target cell lysis and cytokine production. How these subsets arise from the conventional pathway of NK cell development and identification of the transcriptional networks that control their development are major challenges for future studies.

Natural killer cells in infection and inflammation of the lung

The lungs are a major site of entry of pathogens into the body and thus require rapid and effective innate responses to prevent pathogens establishing infection and to limit their spread. Additionally, the immune response in the lung must be tightly regulated such that pathogens are cleared, but immunopathology and chronic inflammation are prevented. In this review, I consider the role of natural killer (NK) cells in pulmonary infection and inflammation, specifically their contributions to influenza, tuberculosis, asthma and chronic obstructive pulmonary disease (COPD), which are major causes of morbidity and mortality world-wide. Despite evidence of the importance of NK cells in these diseases, there are still major gaps in our understanding of how their function is regulated in this unique tissue environment. Understanding how different beneficial and detrimental effector functions of NK cells are triggered will be crucial if NK cells are to be exploited therapeutically in respiratory disease.

CD56highCD16-CD62L- NK cells accumulate in allergic contact dermatitis and contribute to the expression of allergic responses

Allergic contact dermatitis is a common disease caused by an exaggerated T cell-mediated immune response to skin-applied haptens. We show in this study that NK cells affect skin immune responses to haptens by releasing type 1 cytokines and inducing keratinocytes apoptosis. Immunohistochemical stainings demonstrated that NK lymphocytes constitute approximately 10% of the inflammatory infiltrate mostly distributed in the superficial dermis and in the epidermis at the site of intense spongiotic changes. More than 90% of NK cells isolated from allergic contact dermatitis skin showed a CD3-CD56(high)CD16- phenotype by FACS analysis. In addition, they uniformly expressed NKG2A, intermediate to high levels of perforin, and the activating receptors, NKG2D, NKp44, and NKp46, but lacked NKp30 and killer Ig-related receptors. Skin NK lymphocytes displayed a CXCR3+CCR6+CCR5+ chemokine receptor asset for homing into inflamed skin, but not CD62L and CCR7 for lymph node homing. When NK cells from nickel-allergic donors were exposed in vitro to the metal, they failed to proliferate, to upregulate CD69, and to release IFN-gamma, thus indicating that NK lymphocytes do not exhibit memory-like properties to haptens. However, IL-2 released by hapten-driven T lymphocytes rapidly induced the release of IFN-gamma by NK cells and promoted the NK-mediated apoptosis of autologous keratinocytes in a hapten-independent manner. Our findings underline the importance of the interaction between innate and adaptive immune mechanisms for amplification of skin allergic responses to haptens and full expression of allergic contact dermatitis.

Regulation of human NK-cell cytokine and chemokine production by target cell recognition

Natural killer (NK)-cell recognition of infected or neoplastic cells can induce cytotoxicity and cytokine secretion. So far, it has been difficult to assess the relative contribution of multiple NK-cell activation receptors to cytokine and chemokine production upon target cell recognition. Using Drosophila cells expressing ligands for the NK-cell receptors LFA-1, NKG2D, DNAM-1, 2B4, and CD16, we studied the minimal requirements for secretion by freshly isolated, human NK cells. Target cell stimulation induced secretion of predominately proinflammatory cytokines and chemokines. Release of chemokines MIP-1alpha, MIP-1beta, and RANTES was induced within 1 hour of stimulation, whereas release of TNF-alpha and IFN-gamma occurred later. Engagement of CD16, 2B4, or NKG2D sufficed for chemokine release, whereas induction of TNF-alpha and IFN-gamma required engagement of additional receptors. Remarkably, our results revealed that, upon target cell recognition, CD56(dim) NK cells were more prominent cytokine and chemokine producers than CD56(bright) NK cells. The present data demonstrate how specific target cell ligands dictate qualitative and temporal aspects of NK-cell cytokine and chemokine responses. Conceptually, the results point to CD56(dim) NK cells as an important source of cytokines and chemokines upon recognition of aberrant cells, producing graded responses depending on the multiplicity of activating receptors engaged.

Non-classical natural killer T cells modulate plasmid DNA vaccine antigen expression and vaccine-elicited immune responses by MCP-1 secretion after interaction with a beta2-microglobulin-independent CD1d

The magnitude and durability of a plasmid DNA vaccine-induced immune response is shaped by immune effector molecules at the site of vaccination. In the present study, we show that antigen expression is modified by type II NKT cells, after interaction with a beta2-microglobulin-independent CD1d receptor. After activation, during the first days following plasmid DNA vaccination, NKT cells release IL-5 and MCP-1, leading to a T helper 0 (T(H)0) cytokine/chemokine profile and a stronger CD8(+)/CD4(+) T cell immune response. Our data indicate that this phenomenon was induced through the strong T(H)1 chemokine MCP-1 during the early phases of plasmid DNA vaccination because injecting the type II NKT cell-associated MCP-1 during the first 5 days led to 2-3-fold increases in vaccine-elicited T cell responses. This study demonstrates a critical role for NKT cells in plasmid DNA vaccine-induced immune responses. Manipulation of NKT cell function or co-administration of MCP-1 may represent novel methods for enhancing immune responses to plasmid DNA vaccines.

Interleukin-22-producing natural killer cells and lymphoid tissue inducer-like cells in mucosal immunity

Blood, lymphoid tissues, and placenta contain diverse subpopulations of natural killer (NK) cells that possess distinct immune functions. Recent studies have shown that human and mouse gut-associated lymphoid tissues harbor a unique NK cell subset that specializes in production of interleukin (IL)-22. This cytokine plays a role in host defense of mucosal barriers, although dysregulated secretion may cause autoimmune disease. In parallel, human fetal lymphoid tissue inducer (LTi) cells and mouse adult LTi-like cells in secondary lymphoid tissues were found to release IL-22, as well as IL-17, a proinflammatory cytokine that mediates host defense against extracellular pathogens. Here, we compare these recently identified immune cells, reviewing what is known about their anatomical location, differentiation requirements, function, and potential involvement in host defense and autoimmunity. Finally, we discuss the challenges faced in furthering our understanding of the developmental relationships and role of NK and LTi-like cells in mucosal immune responses.

NK cells: new issues and challenges. Preface

NK cells are innate lymphocytes crucial for surveillance against pathogens and tumors. Although the basic mechanisms through which NK cells operate have been established, many questions are still unresolved. Are all NK cells equal or can we identify subsets with distinct developmental origin and function? How do NK cells interact with other components of the immune system, such as DC, effector T cells, and Treg cells to elicit effective immune responses? How do NK cells become tolerant to self and preclude autoimmunity? Finally, can we design novel therapeutic avenues for cancer treatment based on NK cells? The editorial team of the European Journal of Immunology asked the opinion of some of the leading experts in the NK-cell field regarding the new challenges and opportunities facing this area of research and the thoughts of the experts are presented in this viewpoint series. This introduction to the series brings together some of the novel concepts emerging from the experts' discussions.