Proatherogenic Role for NK Cells Revealed

ILC in chronic inflammation, cancer and targeting with biologicals

Since their discovery, Innate Lymphoid Cells (ILC) have emerged as important effector cells, serving multiple roles in maintaining tissue homeostasis and responding to tissue insults. As such, dysregulations of their function and distribution have been observed in a variety of immune-mediated diseases, suggesting a specific role for ILC in the pathophysiology of several disorders including chronic inflammation and cancer. Here, we provide an updated view on ILC biology dissecting their pathological or protective contribution in chronic inflammatory diseases such as multiple sclerosis, inflammatory bowel diseases, psoriasis, rheumatoid arthritis, asthma and COPD, atherosclerosis, also exploring ILC role in tumor surveillance and progression. Throughout the review, we will also highlight how the potential dual role of these cells for protective or pathogenic immunity in many inflammatory diseases makes them interesting targets for the development of novel therapeutic strategies, particularly promising.

Characteristics of peripheral immune cell subsets in patients with carotid atherosclerosis undergoing carotid endarterectomy

Introduction

The role of circulating immune cells in the pathophysiology of cerebrovascular accidents is currently under debate. The aim of this study was to characterize peripheral immune cell subsets in patients undergoing carotid endarterectomy (CEA).

Material and methods

We conducted a prospective observational study in a group of 124 patients with significant carotid stenosis undergoing carotid endarterectomy, both symptomatic and asymptomatic. We compared the percentages of circulating immune cells: B lymphocytes, T lymphocytes, T helper, cytotoxic T, CD4+/CD8+ ratio, T regulatory, monocytes and NK cells before CEA and 6 h after the procedure.

Results

Total lymphocyte count and cytotoxic T lymphocyte count decreased 6 h after CEA in both subgroups. The NK cell level decrease was statistically significant only in the symptomatic subgroup (19.41 ±9.30 before CEA and 16.52 ±9.37 after CEA; p = 0.0044), but not in the asymptomatic subgroup (17.88 ±9.14 before CEA and 15.91 ±9.51 after CEA; p = 0.0886). The T lymphocyte level showed a statistically significant increase only in symptomatic patients (69.74 ±10.16 before CEA vs. 71.45 ±9.77 after CEA; p = 0.0462), and not in the asymptomatic subgroup (70.08 ±11.19 prior to CEA and 70.21 ±12.35; p = 0.9048). B lymphocyte, helper T lymphocyte and regulatory T (Treg) lymphocyte (CD4+/CD25+) levels showed a significant increase after CEA.

Conclusions

This is the first study to compare circulating immune cells in patients undergoing carotid endarterectomy. Only the symptomatic subgroup experienced a significant decrease in the NK cell level and an increase in the T lymphocyte count after CEA. This study enriches our understanding of immune cell kinetics during carotid endarterectomy.

Genetic Depletion or Hyperresponsiveness of Natural Killer Cells Do Not Affect Atherosclerosis Development

Rationale:

Chronic inflammation is central in the development of atherosclerosis. Both innate and adaptive immunities are involved. Although several studies have evaluated the functions of natural killer (NK) cells in experimental animal models of atherosclerosis, it is not yet clear whether NK cells behave as protective or proatherogenic effectors. One of the main caveats of previous studies was the lack of specificity in targeting loss or gain of function of NK cells.

Objectives:

We used 2 selective genetic approaches to investigate the role of NK cells in atherosclerosis: (1) Ncr1 iCre/+ R26 lsl− DTA/+ mice in which NK cells were depleted and (2) Noé mice in which NK cells are hyperresponsive.

Methods and Results:

No difference in atherosclerotic lesion size was found in Ldlr −/− (low-density lipoprotein receptor null) mice transplanted with bone marrow (BM) cells from Ncr1 iCre R26R lsl− DTA , Noé , or wild-type mice. Also, no difference was observed in plaque composition in terms of collagen content, macrophage infiltration, or the immune profile, although Noé chimera had more IFN (interferon)-γ–producing NK cells, compared with wild-type mice. Then, we investigated the NK-cell selectivity of anti–asialoganglioside M1 antiserum, which was previously used to conclude the proatherogenicity of NK cells. Anti–asialoganglioside M1 treatment decreased atherosclerosis in both Ldlr −/− mice transplanted with Ncr1 iCre R26R lsl− DTA or wild-type bone marrow, indicating that its antiatherogenic effects are unrelated to NK-cell depletion, but to CD8 + T and NKT cells. Finally, to determine whether NK cells could contribute to the disease in conditions of pathological NK-cell overactivation, we treated irradiated Ldlr −/− mice reconstituted with either wild-type or Ncr1 iCre R26R lsl− DTA bone marrow with the viral mimic polyinosinic:polycytidylic acid and found a significant reduction of plaque size in NK-cell–deficient chimeric mice.

Conclusions:

Our findings, using state-of-the-art mouse models, demonstrate that NK cells have no direct effect on the natural development of hypercholesterolemia-induced atherosclerosis, but may play a role when an additional systemic NK-cell overactivation occurs.

Natural Killer Cells in the Orchestration of Chronic Inflammatory Diseases

Inflammation, altered immune cell phenotype, and functions are key features shared by diverse chronic diseases, including cardiovascular, neurodegenerative diseases, diabetes, metabolic syndrome, and cancer. Natural killer cells are innate lymphoid cells primarily involved in the immune system response to non-self-components but their plasticity is largely influenced by the pathological microenvironment. Altered NK phenotype and function have been reported in several pathological conditions, basically related to impaired or enhanced toxicity. Here we reviewed and discussed the role of NKs in selected, different, and “distant” chronic diseases, cancer, diabetes, periodontitis, and atherosclerosis, placing NK cells as crucial orchestrator of these pathologic conditions.

Natural killer cells in placentation and cancer: Implications for hypertension during pregnancy

Hypertension during pregnancy is the most common medical condition encountered during gestation. Despite this, knowledge of the mechanisms that underlie the disease and the development of new therapies are limited. Hypertension during pregnancy and some forms of cancer confer an increased risk to the development of cardiovascular disease later in life; one mechanism which may link these conditions is the involvement of natural killer (NK) cells. Whilst immunology and immunotherapy are well-developed areas in oncology; the complex mechanisms of the immune system in health and disease at the maternal-fetal interface are less well-defined. Natural killer (NK) cells have emerged as key immune cells involved in physiology and pathology of pregnancy. These small lymphocytes are present in the decidua (the uterine-specific uNK cells) and are distinct from peripheral NK cells. The uNK cell population plays a vital role in mediating trophoblast invasion and affecting decidual vascular remodelling whereas the role of the peripheral NK cell population during pregnancy is less well-defined. This review will give an overview of NK cell biology followed by a discussion of the current evidence for the role of uterine and peripheral NK cells at the maternal-fetal interface in health and disease. Furthermore, examples of NK cell research from cancer biology will be employed to inform future directions of research. By combining this knowledge from oncology where the field of immunotherapy has now matured into clinical trials; it is hopeful that new mechanisms can be elucidated to generate targets for similar therapeutic strategies for women with hypertensive pregnancies where interventions are needed.

Peripheral Blood Lymphocyte Subsets (CD4+, CD8+ T Cells, NK Cells) in Patients with Cardiovascular and Neurological Complications after Carotid Endarterectomy

Background: The aim of the study was to evaluate the differences in the circulating immune cells’ subgroups after the atherosclerotic plaque removal in patients presenting with postoperative complications as compared to the patients without complications after carotid endarterectomy (CEA). Methods: Patients with significant carotid atherosclerosis (n = 124, age range: 44 to 87 years) who underwent CEA were enrolled in a prospective study. The immunology study using flow cytometry was performed to determine the percentages of peripheral blood T cells (CD4⁺, CD8⁺, Treg—CD4⁺/CD25⁺) and NK (natural killer) cells before and after the procedure. The data were expressed as the percentage of total lymphocytes ± the standard error of mean. Results: The mean percentage of lymphocytes (61.54% ± 17.50% vs. 71.82% ± 9.68%, p = 0.030) and CD4 T lymphocytes (T helper, 38.13% ± 13.78% vs. 48.39% ± 10.24%, p = 0.027) was significantly lower six hours after CEA in patients with postoperative 30-day cardiovascular and neurological complications as compared to the group without complications. On the other hand the mean NK level in the group with complications was significantly higher (21.61% ± 9.00% vs. 15.80% ± 9.31%, p = 0.048). Conclusions: The results of this study suggest that after carotid endarterectomy the percentages of circulating immune cells subsets differ in patients with and without postoperative complications.

Innate immune system cells in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall characterized by innate and adaptive immune system involvement. A key component of atherosclerotic plaque inflammation is the persistence of different innate immune cell types including mast cells, neutrophils, natural killer cells, monocytes, macrophages and dendritic cells. Several endogenous signals such as oxidized low-density lipoproteins, and exogenous signals such as lipopolysaccharides, trigger the activation of these cells. In particular, these signals orchestrate the early and late inflammatory responses through the secretion of pro-inflammatory cytokines and contribute to plaque evolution through the formation of foam cells, among other events. In this review we discuss how innate immune system cells affect atherosclerosis pathogenesis.

Role of immunodeficient animal models in the development of fructose induced NAFLD

Cellular and humoral immunity had been implicated in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). This study was designed to assess if T, B and natural killer (NK) cells are involved in the progress of NAFLD in mouse models after chronic fructose treatment. Mouse models that are deficient in either T cells, B cells or NK cells or lacking both T and B cells were fed with 30% fructose solution for 12 weeks. Typical features of NAFLD, including the relative body weight, food and water intake, biochemical analytes, liver histology, NAFLD activity score, and glucose tolerance and insulin tolerance test were characterized. Further, the percentage of CD3, B220 and NK cells in peripheral-blood mononuclear cell, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, immunodetection for hepatic apoptosis (p53) and for inflammation (TNFα) and quantitative real-time polymerase chain reaction for putative and inflammatory genes involved were determined. Our results conclude that mice deficient in T cells or NK cells fail to develop fructose induced NAFLD whereas the immunocompetent mice and mice with B-cell-specific defect developed NAFLD. Taken together, these data support that the onset of fructose-induced NAFLD is associated with involvement of T cells and NK cells in mice.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Increased expression of T cell immunoglobulin- and mucin domain-containing molecule-3 on natural killer cells in atherogenesis

OBJECTIVE

Atherosclerosis (AS) has many features of a chronic inflammatory disease in which both adaptive and innate immune cells play roles. Increasing evidence has demonstrated the impairment of circulating natural killer (NK) cells in atherosclerosis. However, the mechanisms of this impairment remain unclear. We previously reported the suppression of NK cell functions by T cell immunoglobulin- and mucin domain-containing molecule (Tim)-3. Here, we investigated the expression of Tim-3 on NK cells and assessed its possible roles in NK loss during atherogenesis.

METHODS AND RESULTS

Flow cytometry analysis showed increased Tim-3 expression on peripheral NK cells from patients with AS. This increased expression of Tim-3 was significantly related to the levels of serum lipids and inflammation markers, C-reactive protein (CRP) and tumor necrosis factor (TNF)-α, which are risk factors for atherogenesis. We detected decreased peripheral NK cell number in patients with AS. The NK cell number showed significant inverse correlations with Tim-3 expression levels on NK cells and the level of serum TNF-α. Consistently, Tim-3 overexpression reduced NK92 cell number. Blockade of Tim-3 protected NK92 cells from TNF-α-induced cell death. Similar results were obtained with peripheral NK cells from patients with AS.

CONCLUSIONS

To the best of our knowledge, for the first time, the data from our study provide evidence that augmented Tim-3 expression on NK cells plays an important role in NK cell loss in atherosclerosis. The augmented Tim-3 expression on NK cells might be used as an indicator for disease progression.

Anti-phosphorylcholine-opsonized low-density lipoprotein promotes rapid production of proinflammatory cytokines by dendritic cells and natural killer cells

BACKGROUND AND OBJECTIVE

Epidemiological and animal studies suggest that periodontal infections increase atherosclerosis risk. Periodontitis patients have elevated levels of anti-phosphorylcholine (anti-PC) reactive not only with numerous periodontal organisms but also with minimally modified low-density lipoprotein (mmLDL). Dendritic cells (DCs) reside in arterial walls and accumulate in atherosclerotic lesions. The ability of anti-PC to bind mmLDL prompted the hypothesis that opsonized mmLDL would stimulate DCs and enhance the production of proinflammatory cytokines that promote atherogenic plaque development.

MATERIAL AND METHODS

Monocyte-derived DCs (mDCs) were generated using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4, then stimulated with mmLDL or with anti-PC-opsonized mmLDL. The anti-PC effect was determined using flow cytometry, cofocal microscopy and cytokine assays. The production of CD83, IL-12p35 mRNA, IL-12p40 mRNA, IL-12p70 and IL-10 by DCs was monitored.

RESULTS

Dendritic cells stimulated with mmLDL expressed little CD83 and produced little IL-12p70. However, anti-PC-opsonized mmLDL enhanced DC maturation, as indicated by upregulated CD83 and rapid (≤ 48 h) production of IL-12p70 if a source of interferon-γ (IFN-γ) was available. In leukocyte cultures, natural killer (NK) cells rapidly produced IFN-γ (≤ 48 h) when interacting with IL-12-producing DCs activated by anti-PC-opsonized mmLDL. Moreover, IFN-γ promoted DC IL-12 responses that were further augmented when mmLDL was opsonized with anti-PC.

CONCLUSION

Minimally modified LDL-stimulated DCs and NK cells were mutually stimulatory, with DC IL-12p70 needed by NK cells and with NK cell IFN-γ needed by DCs. Moreover, production of these proinflammatory cytokines was markedly enhanced when LDL was opsonized by anti-PC. In short, the data suggest that the elevated anti-PC levels in periodontitis patients could promote a mechanism that facilitates atherosclerosis.

Deficiency of invariant V alpha 14 natural killer T cells decreases atherosclerosis in LDL receptor null mice

Aims

CD1d-restricted natural killer T (NKT) cells function by regulating numerous immune responses during innate and adaptive immunity. Depletion of all populations of CD1d-dependent NKT cells has been shown by several groups to reduce atherosclerosis in two different mouse models of the disease. In this study, we determined if removal of a single (Vα14) NKT cell population protects mice from the disease.

Methods and results

Targeted deletion of the Jα18 gene results in selective depletion of CD1d-dependent Vα14 NKT cells in C57BL/6 mice without affecting the population of other NKT, NK, and conventional T cells. Therefore, to study the effect of Vα14 NKT cell depletion on the progression of atherosclerosis, we examined the extent of lesion formation using paired littermate LDL receptor null mice that were either ^+/+ or ^−/− for the Jα18 gene following the feeding of these mice a cholesterol- and fat-enriched diet for 8 weeks. At the end of the study, we found no difference in either serum total- or lipoprotein-cholesterol distributions between groups. However, quantification of atherosclerosis revealed that Vα14 NKT cell deficiency significantly decreased lesion size in the aortic root (20–28%) and arch (28–38%) in both genders of mice. By coupling the techniques of laser capture microdissection with quantitative real-time RT–PCR, we found that expression of the proatherogenic cytokine interferon (IFN)-γ was significantly reduced in lesions from Jα18^−/− mice.

Conclusion

This study is the first to identify a specific subpopulation of NKT cells that promotes atherosclerosis via a mechanism appearing to involve IFN-γ expression.

Participatory role of natural killer and natural killer T cells in atherosclerosis: lessons learned from in vivo mouse studies

Atherosclerosis is a multifactor, highly complex disease with numerous aetiologies that work synergistically to promote lesion development. One of the emerging components that drive the development of both early- and late-stage atherosclerotic lesions is the participation of both the innate and acquired immune systems. In both humans and animal models of atherosclerosis, the most prominent cells that infiltrate evolving lesions are macrophages and T lymphocytes. The functional loss of either of these cell types reduces the extent of atherosclerosis in mice that were rendered susceptible to the disease by deficiency of either apolipoprotein E or the LDL (low density lipoprotein) receptor. In addition to these major immune cell participants, a number of less prominent leukocyte populations that can modulate the atherogenic process are also involved. This review will focus on the participatory role of two "less prominent" immune components, namely natural killer (NK) cells and natural killer T (NKT) cells. Although this review will highlight the fact that both NK and NKT cells are not sufficient for causing the disease, the roles played by both these cells types are becoming increasingly important in understanding the complexity of this disease process.

NK Cells Can Trigger Allograft Vasculopathy: The Role of Hybrid Resistance in Solid Organ Allografts

Progressive arterial stenosis (cardiac allograft vasculopathy (CAV)) is a leading cause of long-term failure of organ transplants. CAV remains intractable, in part because its mechanisms are insufficiently understood. A central proposition is that MHC-driven alloimmune processes play a necessary role in CAV, as shown by the absolute requirement for histoincompatibility between donor and recipient for its production. Two immunological pathways have been implicated involving reactivity to donor MHC Ags by either T or B cells. In this study, we use a novel system of semiallogeneic cardiac transplants between parental donors and F1 hybrid recipients to provide evidence that NK cells, members of the innate immune system, also contribute to the generation of CAV in mice. This finding marks the first demonstration that the hybrid resistance phenomenon occurs in solid organ allografts. Extension of these experiments to recipients deficient in T cells demonstrates that this third pathway of CAV, the NK cell-triggered pathway, involves the recruitment of T cells not responsive to donor alloantigens. Finally, transplants performed with donors or recipients deficient in IFN-gamma revealed that recipient-derived IFN-gamma is necessary for CAV formation in parental to F1 transplants, suggesting a possible effector mechanism by which NK cells can promote CAV. Together, these results define a previously unknown pathway toward CAV and assign a novel role to NK cells in organ allograft rejection.

Thematic review series: the immune system and atherogenesis. Immune function in atherogenesis

In this overview to a new thematic series on the immune system and atherogenesis, I provide a very brief summary of current conceptions of atherogenesis, of the innate and adaptive immune systems, and of the participation of the latter in atherogenesis, with particular emphasis on studies of the involvement of the immune system in atherosclerosis reported in the last 2 years. This is followed by a short outline of the eight reviews that will make up this thematic series. The overview is concluded with some caveats that should be considered in the analysis of atherosclerosis in experimental animals.