Natural killer cells determine the outcome of B cell-mediated autoimmunity

Therapeutic potential of natural killer cells in neuroimmunological diseases

Natural killer (NK) cells, a major component of the innate immune system, have prominent immunoregulatory, antitumor proliferation, and antiviral activities. NK cells act as a double-edged sword with therapeutic potential in neurological autoimmunity. Emerging evidence has identified NK cells are involved in the development and progression of neuroimmunological diseases such as multiple sclerosis, neuromyelitis optica spectrum disorders, autoimmune encephalitis, Guillain-Barré Syndrome, chronic inflammatory demyelinating polyneuropathy, myasthenia gravis, and idiopathic inflammatory myopathy. However, the regulatory mechanisms and functional roles of NK cells are highly variable in different clinical states of neuroimmunological diseases and need to be further determined. In this review, we summarize the evidence for the heterogenic involvement of NK cells in the above conditions. Further, we describe cutting-edge NK-cell-based immunotherapy for neuroimmunological diseases in preclinical and clinical development and highlight challenges that must be overcome to fully realize the therapeutic potential of NK cells.

A comprehensive review of the advances in neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a rare relapsing neuroinflammatory autoimmune astrocytopathy, with a predilection for the optic nerves and spinal cord. Most cases are characterised by aquaporin-4-antibody positivity and have a relapsing disease course, which is associated with accrual of disability. Although the prognosis in NMOSD has improved markedly over the past few years owing to advances in diagnosis and therapeutics, it remains a severe disease. In this article, we review the evolution of our understanding of NMOSD, its pathogenesis, clinical features, disease course, treatment options and associated symptoms. We also address the gaps in knowledge and areas for future research focus.

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.

Circulating CXCR5+ natural killer cells are expanded in patients with myasthenia gravis

Objectives

Myasthenia gravis (MG) is a classic autoantibody-mediated disease in which pathogenic antibodies target postsynaptic membrane components, causing fluctuating skeletal muscle weakness and fatigue. Natural killer (NK) cells are heterogeneous lymphocytes that have gained increasing attention owing to their potential roles in autoimmune disorders. This study will investigate the relationship between the distinct NK cell subsets and MG pathogenesis.

Methods

A total of 33 MG patients and 19 healthy controls were enrolled in the present study. Circulating NK cells, their subtypes and follicular helper T cells were analysed by flow cytometry. Serum acetylcholine receptor (AChR) antibody levels were determined by ELISA. The role of NK cells in the regulation of B cells was verified using a co-culture assay.

Results

Myasthenia gravis patients with acute exacerbations had a reduced number of total NK cells, CD56^dim NK cells and IFN-γ-secreting NK cells in the peripheral blood, while CXCR5⁺ NK cells were significantly elevated. CXCR5⁺ NK cells expressed a higher level of ICOS and PD-1 and a lower level of IFN-γ than those in CXCR5^- NK cells and were positively correlated with Tfh cell and AChR antibody levels. In vitro experiments demonstrated that NK cells suppressed plasmablast differentiation while promoting CD80 and PD-L1 expression on B cells in an IFN-γ-dependent manner. Furthermore, CXCR5^- NK cells inhibited plasmablast differentiation, while CXCR5⁺ NK cells could more efficiently promote B cell proliferation.

Conclusion

These results reveal that CXCR5⁺ NK cells exhibit distinct phenotypes and functions compared with CXCR5^- NK cells and might participate in the pathogenesis of MG.

Interleukin-18 cytokine in immunity, inflammation, and autoimmunity: Biological role in induction, regulation, and treatment

Interleukin-18 (IL-18) is a potent pro-inflammatory cytokine involved in host defense against infections and regulates the innate and acquired immune response. IL-18 is produced by both hematopoietic and non-hematopoietic cells, including monocytes, macrophages, keratinocytes and mesenchymal cell. IL-18 could potentially induce inflammatory and cytotoxic immune cell activities leading to autoimmunity. Its elevated levels have been reported in the blood of patients with some immune-related diseases, including rheumatoid arthritis, systemic lupus erythematosus, type I diabetes mellitus, atopic dermatitis, psoriasis, and inflammatory bowel disease. In the present review, we aimed to summarize the biological properties of IL-18 and its pathological role in different autoimmune diseases. We also reported some monoclonal antibodies and drugs targeting IL-18. Most of these monoclonal antibodies and drugs have only produced partial effectiveness or complete ineffectiveness in vitro, in vivo and human studies. The ineffectiveness of these drugs targeting IL-18 may be largely due to the loophole caused by the involvement of other cytokines and proteins in the signaling pathway of many inflammatory diseases besides the involvement of IL-18. Combination drug therapies, that focus on IL-18 inhibition, in addition to other cytokines, are highly recommended to be considered as an important area of research that needs to be explored.

Exploring the Gut Microbiome in Myasthenia Gravis

The human gut microbiota is vital for maintaining human health in terms of immune system homeostasis. Perturbations in the composition and function of microbiota have been associated with several autoimmune disorders, including myasthenia gravis (MG), a neuromuscular condition associated with varying weakness and rapid fatigue of the skeletal muscles triggered by the host’s antibodies against the acetylcholine receptor (AChR) in the postsynaptic muscle membrane at the neuromuscular junction (NMJ). It is hypothesized that perturbation of the gut microbiota is associated with the pathogenesis of MG. The gut microbiota community profiles are usually generated using 16S rRNA gene sequencing. Compared to healthy individuals, MG participants had an altered gut microbiota’s relative abundance of bacterial taxa, particularly with a drop in Clostridium. The microbial diversity related to MG severity and the overall fecal short-chain fatty acids (SCFAs) were lower in MG subjects. Changes were also found in terms of serum biomarkers and fecal metabolites. A link was found between the bacterial Operational Taxonomic Unit (OTU), some metabolite biomarkers, and MG’s clinical symptoms. There were also variations in microbial and metabolic markers, which, in combination, could be used as an MG diagnostic tool, and interventions via fecal microbiota transplant (FMT) could affect MG development. Probiotics may influence MG by restoring the gut microbiome imbalance, aiding the prevention of MG, and lowering the risk of gut inflammation by normalizing serum biomarkers. Hence, this review will discuss how alterations of gut microbiome composition and function relate to MG and the benefits of gut modulation.

Increased TIM-3+PD-1+ NK cells are associated with the disease activity and severity of systemic lupus erythematosus

It is well established that natural killer (NK) cells are dysregulated in systemic lupus erythematosus (SLE) patients. However, the functions of NK cells and the mechanisms regulated by them in SLE remain incompletely understood. Patients with SLE were recruited from The First Affiliated Hospital of Nanchang University, and their clinical characteristics and treatments were recorded. The expression levels of T cell immunoglobulin mucin-3 (TIM-3) and programmed cell death protein 1 (PD-1) on NK cells were examined using flow cytometry. The correlations between the increase in TIM-3⁺PD-1⁺ NK cells in the SLE patients and clinical traits, including inflammatory markers, auto-antibodies, disease activity and severity of SLE, were examined. The TIM-3⁺NK cells, PD-1⁺NK cells and TIM-3⁺PD-1⁺ NK cells were significantly increased in the SLE patients. The increase in TIM-3⁺PD-1⁺ NK cells in the patients with SLE was associated with erythrocyte sedimentation rate, C-reactive protein, anti-double stranded DNA, anti-ribosomal P, SLE disease activity index and clinical features. The frequency of TIM-3⁺PD-1⁺NK cells in SLE patients with a cardiovascular disease (CVD) was significantly lower than that in SLE patients without a CVD. Moreover, the increased TIM-3⁺PD-1⁺ NK cells were significantly decreased in SLE patients following treatment. The present study suggested that the increased TIM-3⁺PD-1⁺ NK cells were associated with the disease activity and severity of SLE and may play a role in SLE pathogenesis.

The role of innate immunity in myasthenia gravis

Myasthenia gravis (MG) is a T cell-driven, B cell-mediated and autoantibody-dependent autoimmune disorder against neuromuscular junctions (NMJ). Accumulated evidence has emerged regarding the role of innate immunity in the pathogenesis of MG. In this review, we proposed two hypothesis underlying the pathological mechanism. In the context of gene predisposition, on the one hand, Toll-like receptors (TLRs) pathways were initiated by viral infection in the thymus with MG to generate chemokines and pro-inflammatory cytokines such as Type I interferon (IFN), which facilitate the thymus to function as a tertiary lymphoid organ (TLO). On the another hand, the antibodies against acetylcholine receptors (AChR) generated by thymus then activated the classical pathways on thymus and neuromuscular junction (NMJ). Futher, we also highlight the role of innate immune cells in the pathogenic response. Finally, we provide some future perspectives in developing new therapeutic approaches particularly targeting the innate immunity for MG.

Immunopathology of Type 1 Diabetes and Immunomodulatory Effects of Stem Cells: A Narrative Review of the Literature

Type 1 Diabetes (T1D) is a complex autoimmune disorder which occurs as a result of an intricate series of pathologic interactions between pancreatic β-cells and a wide range of components of both the innate and the adaptive immune systems. Stem-cell therapy, a recently-emerged potentially therapeutic option for curative treatment of diabetes, is demonstrated to cause significant alternations to both different immune cells such as macrophages, natural killer (NK) cells, dendritic cells, T cells, and B cells and non-cellular elements including serum cytokines and different components of the complement system. Although there exists overwhelming evidence indicating that the documented therapeutic effects of stem cells on patients with T1D is primarily due to their potential for immune regulation rather than pancreatic tissue regeneration, to date, the precise underlying mechanisms remain obscure. On the other hand, immune-mediated rejection of stem cells remains one of the main obstacles to regenerative medicine. Moreover, the consequences of efferocytosis of stem-cells by the recipients' lung-resident macrophages have recently emerged as a responsible mechanism for some immune-mediated therapeutic effects of stem-cells. This review focuses on the nature of the interactions amongst different compartments of the immune systems which are involved in the pathogenesis of T1D and provides explanation as to how stem cell-based interventions can influence immune system and maintain the physiologic equilibrium.

Reduced plasmablast frequency is associated with seronegative myasthenia gravis

BACKGROUND

The immunopathology of autoimmune seronegative myasthenia gravis (SN MG) is poorly understood. Our objective was to determine immune profiles associated with a diagnosis of SN MG.

METHODS

We performed high-dimensional flow cytometry on blood samples from SN MG patients (N = 68), healthy controls (N = 46), and acetylcholine receptor antibody (AChR+) MG patients (N = 27). We compared 12 immune cell subsets in SN MG to controls using logistic modeling via a discovery-replication design. An exploratory analysis fit a multinomial model comparing AChR+ MG and controls to SN MG.

RESULTS

An increase in CD19⁺ CD20^- CD38^hi plasmablast frequencies was associated with lower odds of being a SN MG case in both the discovery and replication analyses (discovery P-value = .0003, replication P-value = .0021). Interleukin (IL) -21 producing helper T cell frequencies were associated with a diagnosis of AChR+ MG (P = .004).

CONCLUSIONS

Reduced plasmablast frequencies are strongly associated with a SN MG diagnosis and may be a useful diagnostic biomarker in the future.

Paths taken towards NK cell-mediated immunotherapy of human cancer-a personal reflection

The discovery that NK cells are able to specifically recognize cells lacking the expression of self‐MHC class I molecules provided the first insight into NK cell recognition of tumour cells. It started a flourishing field of NK cell research aimed at exploring the molecular nature of NK cell receptors involved in tumour cell recognition. While much of the important early work was conducted in murine experimental model systems, studies of human NK cells rapidly followed. Over the years, human NK cell research has swiftly progressed, aided by new detailed molecular information on human NK cell development, differentiation, molecular specificity, tissue heterogeneity and functional capacity. NK cells have also been studied in many different diseases aside from cancer, including viral diseases, autoimmunity, allergy and primary immunodeficiencies. These fields of research have all, indirectly or directly, provided further insights into NK cell‐mediated recognition of target cells and paved the way for the development of NK cell‐based immunotherapies for human cancer. Excitingly, NK cell‐based immunotherapy now opens up for novel strategies aimed towards treating malignant diseases, either alone or in combination with other drugs. Reviewed here are some personal reflections of select contributions leading up to the current state‐of‐the‐art in the field, with a particular emphasis on contributions from our own laboratory. This review is part of a series of articles on immunology in Scandinavia, published in conjunction with the 50th anniversary of the Scandinavian Society for Immunology.

Activation status of CD56dim natural killer cells is associated with disease activity of patients with systemic lupus erythematosus

OBJECTIVES

Decreased natural killer (NK) cells have been reported in systemic lupus erythematosus (SLE) patients. However, the role of NK cells in the pathogenesis of SLE is not well understood. In this study, we aimed to characterize NK cell subsets, phenotypes, and cytokine-secreting functions and investigate the clinical relevance of NK cells in SLE patients.

METHODS

Peripheral blood samples from 81 SLE patients and 59 healthy donors (HDs) were collected. The frequency and phenotype of NK cells were measured by flow cytometry. Intracellular interferon-γ (IFN-γ) production by NK cells was evaluated by flow cytometry after stimulation with interleukin-12 (IL-12) and IL-18.

RESULTS

The percentages of NK cells in the peripheral blood of SLE patients were significantly lower than those in HDs, and the percentages of CD56^dim NK cells among total NK cells showed a trend toward decrease. The CD56^dim NK cells in SLE patients showed increased production of IFN-γ and displayed relatively activated phenotypic characteristics, including significant increases in NKp44, NKp46, and CD69 and decreased expression of CD16 and CD158a/h/g. Furthermore, CD56^dim NK cells in active SLE patients had higher percentages of NKp44⁺ cells and lower percentages of CD158a/h/g⁺ cells than those in inactive SLE patients. The percentages of CD158a/h/g⁺ cells among CD56^dim NK cells were negatively correlated with the systemic lupus erythematosus disease activity index (SLEDAI) and positively correlated with C3 and C4 levels.

CONCLUSION

CD56^dim NK cells in SLE patients show a reduced proportion tendency among total NK cells and are activated, which partially reflects the disease activity. CD158a/h/g expression on CD56^dim NK cells may be considered an index of disease activity. Key Points • In patients with SLE, the proportion of CD56^dim NK cells showed a decreased trend and CD56^dim NK cells were phenotypically activated which partially reflects the disease activity. • CD158a/h/g expression on CD56^dim NK cells were decreased which may be used as an indicator for evaluating disease activity in SLE patients.

MuSK EAMG: Immunological Characterization and Suppression by Induction of Oral Tolerance

Myasthenia gravis (MG) with antibodies to the muscle-specific receptor tyrosine kinase (MuSK) is a distinct sub-group of MG, affecting 5–8% of all MG patients. MuSK, a receptor tyrosine kinase, is expressed at the neuromuscular junctions (NMJs) from the earliest stages of synaptogenesis and plays a crucial role in the development and maintenance of the NMJ. MuSK-MG patients are more severely affected and more refractory to treatments currently used for MG. Most patients require long-term immunosuppression, stressing the need for improved treatments. Ideally, preferred treatments should specifically delete the antigen-specific autoimmune response, without affecting the entire immune system. Mucosal tolerance, induced by oral or nasal administration of an auto-antigen through the mucosal system, resulting in an antigen-specific immunological systemic hyporesponsiveness, might be considered as a treatment of choice for MuSK-MG. In the present study we have characterized several immunological parameters of murine MuSK-EAMG and have employed induction of oral tolerance in mouse MuSK-EAMG, by feeding with a recombinant MuSK protein one week before disease induction. Such a treatment has been shown to attenuate MuSK-EAMG. Both induction and progression of disease were ameliorated following oral treatment with the recombinant MuSK fragment, as indicated by lower clinical scores and lower anti-MuSK antibody titers.

CXCR5-negative natural killer cells ameliorate experimental autoimmune myasthenia gravis by suppressing follicular helper T cells

Background

Recent studies have demonstrated that natural killer (NK) cells can modulate other immune components and are involved in the development or progression of several autoimmune diseases. However, the roles and mechanisms of NK cells in regulating experimental autoimmune myasthenia gravis (EAMG) remained to be illustrated.

Methods

To address the function of NK cells in experimental autoimmune myasthenia gravis in vivo, EAMG rats were adoptively transferred with splenic NK cells. The serum antibodies, and splenic follicular helper T (Tfh) cells and germinal center B cells were determined by ELISA and flow cytometry. The roles of NK cells in regulating Tfh cells were further verified in vitro by co-culturing splenocytes or isolated T cells with NK cells. Moreover, the phenotype, localization, and function differences between different NK cell subtypes were determined by flow cytometry, immunofluorescence, and ex vivo co-culturation.

Results

In this study, we found that adoptive transfer of NK cells ameliorated EAMG symptoms by suppressing Tfh cells and germinal center B cells. Ex vivo studies indicated NK cells inhibited CD4⁺ T cells and Tfh cells by inducing the apoptosis of T cells. More importantly, NK cells could be divided into CXCR5^- and CXCR5⁺ NK subtypes according to the expression of CXCR5 molecular. Compared with CXCR5^- NK cells, which were mainly localized outside B cell zone, CXCR5⁺ NK were concentrated in the B cell zone and exhibited higher expression levels of IL-17 and ICOS, and lower expression level of CD27. Ex vivo studies indicated it was CXCR5^- NK cells not CXCR5⁺ NK cells that suppressed CD4⁺ T cells and Tfh cells. Further analysis revealed that, compared with CXCR5^- NK cells, CXCR5⁺ NK cells enhanced the ICOS expression of Tfh cells.

Conclusions

These findings highlight the different roles of CXCR5^- NK cells and CXCR5⁺ NK cells. It was CXCR5^- NK cells but not CXCR5⁺ NK cells that suppressed Tfh cells and inhibited the autoimmune response in EAMG models.

The differential expression of natural killer cells in NMOSD and MS

Natural killer (NK) cells are involved in the pathogenesis of inflammatory demyelinating diseases of the central nervous system. However, the differential expressions of NK cells in the peripheral blood of patients with neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) are unknown. This study aimed to explore the differential expressions of NK cells in NMOSD and MS and evaluate the clinical implications of this difference. We performed a cross-sectional study to investigate the expression of NK cells in the peripheral blood of patients with NMOSD (n = 78) and MS (n = 24) and of healthy controls (HC, n = 27). Furthermore, we investigated the relationship between NK cell level and disease phase in 102 patients with NMOSD and MS through Spearman correlation analysis and receiver operating characteristic (ROC) analysis. Our results showed that the median (interquartile range) NK cell levels in acute-phase NMOSD patients, remission-phase NMOSD patients, acute-phase MS patients, and HC subjects were 114.10 (64.75-153.38) cells/µL, 167.60 (116.35-266.15) cells/µL, 282.55 (140.57-368.20) cells/µL, and 221.00 (170.40-269.55) cells/µL, respectively (p < 0.001). The Spearman correlation coefficient (95%) for the relationship between NK level and disease phase in NMOSD patients was 0.366 (0.150-0.550) (p < 0.001). Furthermore, ROC analysis revealed that patients with NK cell values lower than 172.200 cells/µL were more prone to have acute-phase NMOSD than MS. In conclusion, the expression of NK cells in peripheral blood was lower in patients with NMOSD than in patients with MS in the acute phase, and a low expression of NK cells may suggest having acute-phase NMOSD rather than MS.

Natural Killer Cell Regulation of B Cell Responses in the Context of Viral Infection

Secretion of both neutralizing and nonneutralizing virus-specific antibodies by B cells is a key component of immune control of many virus infections and a critical benchmark of successful preventative vaccines. Natural killer (NK) cells also play a vital role in antiviral immune defense via cytolytic elimination of infected cells and production of proinflammatory antiviral cytokines. Accumulating evidence points to multifaceted crosstalk between NK cells and antiviral B cell responses that can determine virus elimination, pathogenesis of infection, and efficacy of vaccine-elicited protection. These outcomes are a result of both positive and negative influences of NK cells on the B cell responses, as well as canonical antiviral killing of infected B cells. On one hand, NK cell-derived cytokines such as interferon-gamma (IFN-γ) may promote B cell activation and enhance immunoglobulin production. In contrast, NK cell immunoregulatory killing of CD4 T cells can limit affinity maturation in germinal centers resulting in weak infection or vaccine induction of antiviral neutralizing antibodies. In this review, we will discuss these and other dueling contributions of NK cells to B cell responses during virus infection or vaccination.

The immunogenetics of neurological disease

Genes encoding antigen-presenting molecules within the human major histocompatibility complex (MHC) account for the highest component of genetic risk for many neurological diseases, such as multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. Myriad genetic, immunological and environmental factors may contribute to an individual's susceptibility to neurological disease. Here, we review and discuss the decades long research on the influence of genetic variation at the MHC locus and the role of immunogenetic killer cell immunoglobulin-like receptor (KIR) loci in neurological diseases, including multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. The findings of immunogenetic association studies are consistent with a polygenic model of inheritance in the heterogeneous and multifactorial nature of complex traits in various neurological diseases. Future investigation is highly recommended to evaluate both coding and non-coding variation in immunogenetic loci using high-throughput high-resolution next-generation sequencing technologies in diverse ethnic groups to fully appreciate their role in neurological diseases.

Type 1 Diabetes and Its Multi-Factorial Pathogenesis: The Putative Role of NK Cells

Type 1 diabetes (T1D) affects millions of people worldwide and is the prevalent form of all pediatric diabetes diagnoses. T1D is recognized to have an autoimmune etiology, since failure in specific self-tolerance mechanisms triggers immune reactions towards self-antigens and causes disease onset. Among all the different immunocytes involved in T1D etiopathogenesis, a relevant role of natural killer cells (NKs) is currently emerging. NKs represent the interface between innate and adaptive immunity; they intervene in the defense against infections and present, at the same time, typical features of the adaptive immune cells, such as expansion and generation of memory cells. Several recent studies, performed both in animal models and in human diabetic patients, revealed aberrations in NK cell frequency and functionality in the peripheral blood and in damaged tissues, suggesting their possible redirection towards affected tissues. NKs oscillate from a quiescent to an activated state through a delicate balance of activating and inhibitory signals transduced via surface receptors. Further accurate investigations are needed to elucidate the exact role of NKs in T1D, in order to develop novel immune-based therapies able to reduce the disease risk or delay its onset.

Decreased percentage of NKG2D+NK cells in patients with incident onset of Type 1 Diabetes

Type 1 diabetes mellitus (T1DM) is characterized by absolute insulin deficiency owing to autoimmune destruction of the pancreatic β cells. A significant decrease in natural killer (NK) cells in peripheral blood has been observed in patients with untreated T1DM. In the present study, we aimed to explore the role of NK cells and their subsets in young T1DM patients. A total of 30 children and adolescents with untreated T1DM and 27 healthy controls (HC) were recruited in this study. Flow cytometry analysis indicated that the percentage of peripheral blood CD3-CD56+ NK cells and NK cells subsets (CD56bright, CD56dim and CD56neg), were significantly decreased in the T1DM patients compared to healthy controls. In addition, the percentage of inducible CD107a+ and IFN-γ-secreting NK cells was significantly decreased compared to HC. Interestingly, the percentage of NKG2D+ NK cells negatively correlated with the level of serum TCHOL and TG in T1DM patients. Our data indicate that decreased number and impaired function of NK cells may have a role in the pathogenesis of T1DM.

CD86 Blockade in Genetically Modified Porcine Cells Delays Xenograft Rejection by Inhibiting T-Cell and NK-Cell Activation

Porcine xenografts transplanted into primates are rejected in spite of immunosuppression. Identification of the triggering mechanisms and the strategies to overcome them is crucial to achieve long-term graft survival. We hypothesized that porcine CD86 (pCD86) contributes to xenograft rejection by direct activation of host T cells and NK cells. Formerly, we designed the human chimeric molecule hCD152-hCD59 to block pCD86 in cis. To test the efficacy in vivo, we have utilized a pig-to-mouse xenotransplant model. First, we showed that hCD152-hCD59 expression prevents the binding of murine CD28Ig to pCD86 on porcine aortic endothelial cells (PAEC) and dramatically reduces IL-2 secretion by Con A-stimulated mouse splenocytes in coculture. Moreover, IFN-γ secretion by IL-12-stimulated mouse NK cells was averted after coculture with hCD152-hCD59 PAEC. In vivo, control PAEC implanted under the kidney capsule were rapidly rejected (2–4 weeks) in BALB/c and BALB/c SCID mice. Rejection of hCD152-hCD59 PAEC was significantly delayed in both cases. Signs of immune modulation in the hCD152-hCD59-PAEC BALB/c recipients were identified such as early hyporesponsiveness and diminished antibody response. Thus, simply modifying the donor xenogeneic cell can diminish both T cell and NK cell immune responses. We specifically demonstrate that pCD86 contributes to rejection of porcine xenografts.

Astrocyte-derived interleukin-15 exacerbates ischemic brain injury via propagation of cellular immunity

Astrocytes are believed to bridge interactions between infiltrating lymphocytes and neurons during brain ischemia, but the mechanisms for this action are poorly understood. Here we found that interleukin-15 (IL-15) is dramatically up-regulated in astrocytes of postmortem brain tissues from patients with ischemic stroke and in a mouse model of transient focal brain ischemia. We generated a glial fibrillary acidic protein (GFAP) promoter-controlled IL-15-expressing transgenic mouse (GFAP-IL-15^tg) line and found enlarged brain infarcts, exacerbated neurodeficits after the induction of brain ischemia. In addition, knockdown of IL-15 in astrocytes attenuated ischemic brain injury. Interestingly, the accumulation of CD8⁺ T and natural killer (NK) cells was augmented in these GFAP-IL-15^tg mice after brain ischemia. Of note, depletion of CD8⁺ T or NK cells attenuated ischemic brain injury in GFAP-IL-15^tg mice. Furthermore, knockdown of the IL-15 receptor α or blockade of cell-to-cell contact diminished the activation and effector function of CD8⁺ T and NK cells in GFAP-IL-15^tg mice, suggesting that astrocytic IL-15 is delivered in trans to target cells. Collectively, these findings indicate that astrocytic IL-15 could aggravate postischemic brain damage via propagation of CD8⁺ T and NK cell-mediated immunity.

The Expanding Role of Natural Killer Cells in Type 1 Diabetes and Immunotherapy

Treatments for autoimmune diseases including type 1 diabetes (T1D) are aimed at resetting the immune system, especially its adaptive arm. The innate immune system is often ignored in the design of novel immune-based therapies. There is increasing evidence for multiple natural killer (NK) subpopulations, but their role is poorly understood in autoimmunity and likely is contributing to the controversial role reported for NKs. In this review, we will summarize NK subsets and their roles in tolerance, autoimmune diabetes, and immunotherapy.

NK Cell Subtypes as Regulators of Autoimmune Liver Disease

As major components of innate immunity, NK cells not only exert cell-mediated cytotoxicity to destroy tumors or infected cells, but also act to regulate the functions of other cells in the immune system by secreting cytokines and chemokines. Thus, NK cells provide surveillance in the early defense against viruses, intracellular bacteria, and cancer cells. However, the effecter function of NK cells must be exquisitely controlled to prevent inadvertent attack against normal “self” cells. In an organ such as the liver, where the distinction between immunotolerance and immune defense against routinely processed pathogens is critical, the plethora of NK cells has a unique role in the maintenance of homeostasis. Once self-tolerance is broken, autoimmune liver disease resulted. NK cells act as a “two-edged weapon” and even play opposite roles with both regulatory and inducer activities in the hepatic environment. That is, NK cells act not only to produce inflammatory cytokines and chemokines, but also to alter the proliferation and activation of associated lymphocytes. However, the precise regulatory mechanisms at work in autoimmune liver diseases remain to be identified. In this review, we focus on recent research with NK cells and their potential role in the development of autoimmune liver disease.

Neural stem cells sustain natural killer cells that dictate recovery from brain inflammation

Recovery from organ-specific autoimmune diseases largely relies on the mobilization of endogenous repair mechanisms and local factors that control them. Natural killer (NK) cells are swiftly mobilized to organs targeted by autoimmunity and typically undergo numerical contraction when inflammation wanes. We report the unexpected finding that NK cells are retained in the brain subventricular zone (SVZ) during the chronic phase of multiple sclerosis in humans and its animal model in mice. These NK cells were found preferentially in close proximity to SVZ neural stem cells (NSCs) that produce interleukin-15 and sustain functionally competent NK cells. Moreover, NK cells limited the reparative capacity of NSCs following brain inflammation. These findings reveal that reciprocal interactions between NSCs and NK cells regulate neurorepair.

IL-17-producing CD4(+) T cells contribute to the loss of B-cell tolerance in experimental autoimmune myasthenia gravis

The role of Th17 cells in the pathogenesis of autoantibody-mediated diseases is unclear. Here, we assessed the contribution of Th17 cells to the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), which is induced by repetitive immunizations with Torpedo californica acetylcholine receptor (tAChR). We show that a significant fraction of tAChR-specific CD4(+) T cells is producing IL-17. IL-17(ko) mice developed fewer or no EAMG symptoms, although the frequencies of tAChR-specific CD4(+) T cells secreting IL-2, IFN-γ, or IL-21, and the percentage of FoxP3(+) Treg cells were similar to WT mice. Even though the total anti-tAChR antibody levels were equal, the complement fixating IgG2b subtype was reduced in IL-17(ko) as compared to WT mice. Most importantly, pathogenic anti-murine AChR antibodies were significantly lower in IL-17(ko) mice. Furthermore, we confirmed the role of Th17 cells in EAMG pathogenesis by the reconstitution of TCR β/δ(ko) mice with WT or IL-17(ko) CD4(+) T cells. In conclusion, we show that the level of IgG2b and the loss of B-cell tolerance, which results in pathogenic anti-murine AChR-specific antibodies, are dependent on IL-17 production by CD4(+) T cells. Thus, we describe here for the first time how Th17 cells are involved in the induction of classical antibody-mediated autoimmunity.

Natural killer cells limit cardiac inflammation and fibrosis by halting eosinophil infiltration

Myocarditis is a leading cause of sudden cardiac failure in young adults. Natural killer (NK) cells, a subset of the innate lymphoid cell compartment, are protective in viral myocarditis. Herein, we demonstrated that these protective qualities extend to suppressing autoimmune inflammation. Experimental autoimmune myocarditis (EAM) was initiated in BALB/c mice by immunization with myocarditogenic peptide. During EAM, activated cardiac NK cells secreted interferon γ, perforin, and granzyme B, and expressed CD69, tumor necrosis factor-related apoptosis-inducing ligand treatment, and CD27 on their cell surfaces. The depletion of NK cells during EAM with anti-asialo GM1 antibody significantly increased myocarditis severity, and was accompanied by elevated fibrosis and a 10-fold increase in the percentage of cardiac-infiltrating eosinophils. The resultant influx of eosinophils to the heart was directly responsible for the increased disease severity in the absence of NK cells, because treatment with polyclonal antibody asialogangloside GM-1 did not augment myocarditis severity in eosinophil-deficient ΔdoubleGATA1 mice. We demonstrate that NK cells limit eosinophilic infiltration both indirectly, through altering eosinophil-related chemokine production by cardiac fibroblasts, and directly, by inducing eosinophil apoptosis in vitro. Altogether, we define a new pathway of eosinophilic regulation through interactions with NK cells.

Alterations of natural killer cells in traumatic brain injury

To investigate the relationship between natural killer (NK) cells and traumatic brain injury (TBI), we tracked an established phenotype of circulating NK cells at several time points in patients with different grades of TBI. In serial peripheral blood samples, NK cells were prospectively measured by flow cytometry of CD3(-) CD56(+) lymphocytes. Compared to healthy controls, TBI patients had reductions in both the percentage and the absolute number of NK cells. Furthermore, the magnitude of NK cell reduction correlated with the degree of TBI severity at several time points. That is, NK cell population size was independently associated with lower Glasgow Coma Scale scores. In addition, at some time points, a positive correlation was found between the NK cell counts and Glasgow Outcome Scale scores. Our results indicate that TBI induces a reduction in the number of NK cells, and the magnitude of the reduction appears to parallel the severity of TBI.

NKG2A expression and impaired function of NK cells in patients with new onset of Graves' disease

BACKGROUND

Graves' disease (GD) is an organ-specific autoimmune disease. A significant decrease of the distribution of NK cells in the peripheral blood in children and adolescents with untreated GD has been observed. However, the role of NK and its subsets in adults with GD remains unclear.

METHODS

A total of 28 adult patients with new onset of GD and 23 healthy controls (HC) were recruited. The number of activated inhibitory NK cells in peripheral blood of individual subjects was determined by flow cytometry.

RESULTS

The number of CD3(-)CD56(+) and CD3(-)CD16(+)NK cells in peripheral blood was significantly decreased in the GD patients than the HC. Compared to the HCs, decreased number of NKG2D(+), NKG2C(+), NKp30(+) and NKG2A(+) NK cells and increased number of KIR3DL1(+) NK cells were detected in the GD patients. Moreover, the number of inducible CD107a(+) and IFN-γ-secreting NK cells in GD patients significantly decreased than those in HC. Interestingly, the number of NKG2A(+)NK cells was negatively correlated with the level of serum TRAb in GD patients.

CONCLUSION

Our data indicate that decreased number and impaired function of NK cells may contribute to the pathogenesis of GD.

Collagen-induced arthritis: severity and immune response attenuation using multivalent N-acetyl glucosamine

Rheumatoid arthritis is an autoimmunity leading to considerable impairment of quality of life. N-acetyl glucosamine (GlcNAc) has been described previously as a potent modulator of experimental arthritis in animal models and is used for osteoarthritis treatment in humans, praised for its lack of adverse effects. In this study we present a comprehensive immunological analysis of multivalent GlcNAc-terminated glycoconjugate (GC) application in the treatment of collagen-induced arthritis (CIA) and its clinical outcome. We used immunohistochemistry and FACS to describe conditions on the inflammation site. Systemic and clinical effects were evaluated by FACS, cytotoxicity assay, ELISA, cytometric bead array (CBA), RT-PCR and clinical scoring. We found reduced inflammatory infiltration, NKG2D expression on NK and suppression of T, B and antigen-presenting cells (APC) in the synovia. On the systemic level, GCs prevented the activation of monocyte- and B cell-derived APCs, the rise of TNF-α and IFN-γ levels, and subsequent type II collagen (CII)-specific IgG2a formation. Moreover, we detected an increase of anti-inflammatory IL-4 mRNA in the spleen. Similar to the synovia, the GCs caused a significant reduction of NKG2D-expressing NK cells in the spleen without influencing their lytic function. GCs effectively postponed the onset of arthritic symptoms, reduced their severity and in 18% (GN8P) and 31% (GN4C) of the cases completely prevented their appearance. Our data prove that GlcNAc glycoconjugates prevent the inflammatory response, involving proinflammatory cytokine rise, APC activation and NKG2D expression, leading to the attenuation of clinical symptoms. These results support the glycobiological approach to the treatment of collagen-induced arthritis/rheumatoid arthritis (CIA/RA) as a way of bringing new prospects for more effective therapeutic interventions.

Presence of more activating KIR genes is associated with Hashimoto's thyroiditis

Killer cell immunoglobulin-like receptors (KIR) regulate the effector function of natural killer (NK) cells and the subset of T cells with memory phenotype. The number and type of genes that encode KIR receptors substantially varied between individuals and between populations. Specific KIR receptors are known to be associated with certain diseases. The present study was undertaken to investigate if any specific KIR gene(s) is associated with the susceptibility to Hashimoto's thyroiditis (HT), an inflammatory disease characterized by lymphocytic infiltration of the thyroid gland and the presence of autoantibodies directed against thyroglobulin and/or thyroid peroxidase. DNA from 118 patients with HT and 120 healthy controls was characterized for the presence and absence of 11 variable KIR genes using a gene-specific PCR typing system. Although no significant difference in the frequency of individual KIR genes between patients and controls was detected, more patients carry the six activating KIR genes compared with the control group (11.8 vs. 4.1 %, p = 0.032, OR = 3.09, 95 % CI 1.07-8.89). The data suggest that augmented signals from multiple activating KIR receptors might exacerbate the activation of NK cells and T cell subsets against self-antigens, thus contributing to the pathogenesis of HT.

Acute clearance of human metapneumovirus occurs independently of natural killer cells

Human metapneumovirus (HMPV) is a major cause of respiratory disease. The role of NK cells in protection against HMPV is unclear. We show that while HMPV-infected C57BL/6 mice had higher numbers of functional lung NK cells than mock-treated mice, comparing NK cell-depleted and control mice did not reveal differences in lung viral titers, histopathology, cytokine levels, or T cell numbers or function. These data indicate that NK cells are not required for host control of HMPV.

The unique neonatal NK cells: a critical component required for neonatal autoimmune disease induction by maternal autoantibody

Human maternal autoantibodies can trigger autoimmune diseases such as congenital heart block (CHB) in the progeny of women with lupus or Sjogren’s disease. The pathogenic effect of early autoantibody (autoAb) exposure has been investigated in a murine neonatal autoimmune ovarian disease (nAOD) model triggered by a unique ZP3 antibody. Although immune complexes (IC) are formed in adult and neonatal ovaries, ZP3 antibody triggers severe nAOD only in <7-day-old neonatal mice. Propensity to nAOD is due to the uniquely hyper-responsive neonatal natural killer (NK) cells that lack the inhibitory Ly49C/I receptors. In nAOD, the neonatal NK cells directly mediate ovarian inflammation and oocyte depletion while simultaneously promoting de novo pathogenic ovarian-specific T cell responses. Resistance to nAOD in older mice results from the emergence of the Ly49C/I⁺ NK cells that regulate effector NK cells and from CD25⁺ regulatory T cell control. In preliminary studies, FcγRIII⁺ NK cells as well as the ovarian resident FcγRIII⁺ macrophages and/or dendritic cells were found to be as indispensable players. Activated by ovarian IC, they migrate to lymphoid organs where NK cell priming occurs. Remarkably, the findings in nAOD are very similar to those reported for neonatal responses to a retrovirus and its cognate antibody that lead to long-lasting immunity. Studies on nAOD therefore provide insights into maternal autoAb-mediated neonatal autoimmunity, including CHB, while simultaneously uncovering new properties of the neonatal innate and adaptive responses, lethality of premature infant infection, and novel neonatal antiviral vaccine design.

Differential expression of natural killer activating and inhibitory receptors in patients with newly diagnosed systemic lupus erythematosus

AIM

Systemic lupus erythematosus (SLE) presents as the abnormal activation and over-proliferation of immune competent cells. Few studies have characterized the role of natural killer (NK) and NK T (NKT) cells in the pathogenesis of SLE, and therefore a consensus has not been reached as yet.

METHOD

Thirty-two patients with new-onset SLE and 15 healthy controls were recruited. Activated and inhibitory NK and NKT cells in peripheral blood were quantified by flow cytometry. The proportions of spontaneous and stimulated interferon (IFN)-γ(+) NK and NKT cells and CD107a(+) NK cells was examined. Finally, the potential relationship between the cell subsets and clinical indexes was analyzed.

RESULTS

The proportions of NK and NKT cells (P = 0.002 and 0.004, respectively) as well as the proportions of NKG2C(+) NK cells, inhibitory NK and NKT cell subsets (P = 0.016, P = 0.019, P = 0.049, and P = 0.028, respectively) in SLE patients were significantly lower than those in controls. In contrast, the proportions of activated NK cells and NKT cell subsets were significantly higher (P = 0.036, P = 0.034, P = 0.005, and P = 0.007, respectively). Moreover, the proportions of stimulated IFN-γ(+) NKT cells were significantly higher than in the controls, and the proportions of stimulated CD107a(+) NKT cells in SLE patients were significantly lower than in the controls (P = 0.032 and P = 0.02, respectively).

CONCLUSION

Lower proportions of NK and NKT cells, higher proportions of activated NK cells and activated NKT cells, lower proportions of inhibitory NK and NKT cells, higher NKT cell activity, and lower NKT cell degranulation may induce the autoimmune reaction involved in the pathogenesis of SLE.

Ischemic neurons recruit natural killer cells that accelerate brain infarction

Brain ischemia and reperfusion activate the immune system. The abrupt development of brain ischemic lesions suggests that innate immune cells may shape the outcome of stroke. Natural killer (NK) cells are innate lymphocytes that can be swiftly mobilized during the earliest phases of immune responses, but their role during stroke remains unknown. Herein, we found that NK cells infiltrated the ischemic lesions of the human brain. In a mouse model of cerebral ischemia, ischemic neuron-derived fractalkine recruited NK cells, which subsequently determined the size of brain lesions in a T and B cell-independent manner. NK cell-mediated exacerbation of brain infarction occurred rapidly after ischemia via the disruption of NK cell tolerance, augmenting local inflammation and neuronal hyperactivity. Therefore, NK cells catalyzed neuronal death in the ischemic brain.

The immunoregulatory role of type I and type II NKT cells in cancer and other diseases

NKT cells are CD1d-restricted T cells that recognize lipid antigens. They also have been shown to play critical roles in the regulation of immune responses. In the immune responses against tumors, two subsets of NKT cells, type I and type II, play opposing roles and cross-regulate each other. As members of both the innate and adaptive immune systems, which form a network of multiple components, they also interact with other immune components. Here, we discuss the function of NKT cells in tumor immunity and their interaction with other regulatory cells, especially CD4(+)CD25(+)Foxp3(+) regulatory T cells.

Circulating miRNAs in myasthenia gravis: miR-150-5p as a new potential biomarker

Objective

Myasthenia gravis (MG) is a chronic autoimmune disorder where autoantibodies target the nicotinic acetylcholine receptors (AChR+) in about 85% of cases, in which the thymus is considered to play a pathogenic role. As there are no reliable biomarkers to monitor disease status in MG, we analyzed circulating miRNAs in sera of MG patients to find disease-specific miRNAs.

Methods

Overall, 168 miRNAs were analyzed in serum samples from four AChR+ MG patients and four healthy controls using Exiqon Focus miRNA polymerase chain reaction (PCR) Panel I + II. Specific accumulation pattern of 13 miRNAs from the discovery set was subsequently investigated in the sera of 16 AChR+ MG patients and 16 healthy controls. All patients were without immunosuppressive treatment. Selected specific miRNAs were further analyzed in the serum of nine MG patients before and after thymectomy to assess the effect of thymus removal on the accumulation of the candidate miRNAs in patient sera.

Results

Three miRNAs were specifically dysregulated in AChR+ MG patient sera samples. Hsa-miR150-5p, which induces T-cell differentiation, as well as hsa-miR21-5p, a regulator of Th1 versus Th2 cell responses, were specifically elevated in MG sera. Additionally, hsa-miR27a-3p, involved in natural killer (NK) cell cytotoxicity, was decreased in MG. Hsa-miR150-5p levels had the highest association with MG and were significantly reduced after thymus removal in correlation with disease improvement.

Interpretation

We propose that the validated miRNAs: hsa-miR150-5p, hsa-miR21-5p, and hsa-miR27a-3p can serve as novel serum biomarkers in AChR+ MG. Hsa-miR-150-5p could be a helpful marker to monitor disease severity.

IL-18 in inflammatory and autoimmune disease

Inflammation serves as the first line of defense in response to tissue injury, guiding the immune system to ensure preservation of the host. The inflammatory response can be divided into a quick initial phase mediated mainly by innate immune cells including neutrophils and macrophages, followed by a late phase that is dominated by lymphocytes. Early in the new millennium, a key component of the inflammatory reaction was discovered with the identification of a number of cytosolic sensor proteins (Nod-like receptors) that assembled into a common structure, the 'inflammasome'. This structure includes an enzyme, caspase-1, which upon activation cleaves pro-forms of cytokines leading to subsequent release of active IL-1 and IL-18. This review focuses on the role of IL-18 in inflammatory responses with emphasis on autoimmune diseases.

The emerging role of autoimmunity in myalgic encephalomyelitis/chronic fatigue syndrome (ME/cfs)

The World Health Organization classifies myalgic encephalomyelitis/chronic fatigue syndrome (ME/cfs) as a nervous system disease. Together with other diseases under the G93 heading, ME/cfs shares a triad of abnormalities involving elevated oxidative and nitrosative stress (O&NS), activation of immuno-inflammatory pathways, and mitochondrial dysfunctions with depleted levels of adenosine triphosphate (ATP) synthesis. There is also abundant evidence that many patients with ME/cfs (up to around 60 %) may suffer from autoimmune responses. A wide range of reported abnormalities in ME/cfs are highly pertinent to the generation of autoimmunity. Here we review the potential sources of autoimmunity which are observed in people with ME/cfs. The increased levels of pro-inflammatory cytokines, e.g., interleukin-1 and tumor necrosis factor-α, and increased levels of nuclear factor-κB predispose to an autoimmune environment. Many cytokine abnormalities conspire to produce a predominance of effector B cells and autoreactive T cells. The common observation of reduced natural killer cell function in ME/cfs is a source of disrupted homeostasis and prolonged effector T cell survival. B cells may be pathogenic by playing a role in autoimmunity independent of their ability to produce antibodies. The chronic or recurrent viral infections seen in many patients with ME/cfs can induce autoimmunity by mechanisms involving molecular mimicry and bystander activation. Increased bacterial translocation, as observed in ME/cfs, is known to induce chronic inflammation and autoimmunity. Low ATP production and mitochondrial dysfunction is a source of autoimmunity by inhibiting apoptosis and stimulating necrotic cell death. Self-epitopes may be damaged by exposure to prolonged O&NS, altering their immunogenic profile and become a target for the host's immune system. Nitric oxide may induce many faces of autoimmunity stemming from elevated mitochondrial membrane hyperpolarization and blockade of the methionine cycle with subsequent hypomethylation of DNA. Here we also outline options for treatment involving rituximab and endotherapia.

Cutting edge: Ly49C/I⁻ neonatal NK cells predispose newborns to autoimmune ovarian disease induced by maternal autoantibody

NK cells are critical in immune responses against pathogens. However, their role in autoimmunity is still controversial. In this study, we demonstrate that neonatal NK cells render newborns more susceptible to neonatal autoimmunity induced by maternal autoantibodies (neonatal autoimmune ovarian disease); thus, neonatal but not adult NK cells are pathogenic after transfer into NK cell-deficient pups. The inhibitory receptors Ly49C/I are expressed in ∼5% of neonatal and ∼50% of adult NK cells. In this study, we show that the presence of Ly49C/I⁺ adult NK cells inhibits neonatal autoimmune ovarian disease induction. Thus, the ontogenetic regulation of Ly49C/I expression determines the propensity to autoantibody-induced autoimmunity. In summary, this study provides definitive evidence of a pathogenic role of NK cells in neonatal autoimmunity and also elucidates a novel mechanism by which neonatal NK cells render newborns more susceptible to autoantibody-induced autoimmunity.

Mechanisms of obesity-induced inflammation and insulin resistance: insights into the emerging role of nutritional strategies

Obesity and associated chronic inflammation initiate a state of insulin resistance (IR). The secretion of chemoattractants such as MCP-1 and MIF and of cytokines IL-6, TNF-α, and IL-1β, draw immune cells including dendritic cells, T cells, and macrophages into adipose tissue (AT). Dysfunctional AT lipid metabolism leads to increased circulating free fatty acids, initiating inflammatory signaling cascades in the population of infiltrating cells. A feedback loop of pro-inflammatory cytokines exacerbates this pathological state, driving further immune cell infiltration and cytokine secretion and disrupts the insulin signaling cascade. Disruption of normal AT function is causative of defects in hepatic and skeletal muscle glucose homeostasis, resulting in systemic IR and ultimately the development of type 2 diabetes. Pharmaceutical strategies that target the inflammatory milieu may have some potential; however there are a number of safety concerns surrounding such pharmaceutical approaches. Nutritional anti-inflammatory interventions could offer a more suitable long-term alternative; whilst they may be less potent than some pharmaceutical anti-inflammatory agents, this may be advantageous for long-term therapy. This review will investigate obese AT biology, initiation of the inflammatory, and insulin resistant environment; and the mechanisms through which dietary anti-inflammatory components/functional nutrients may be beneficial.

NK cells inhibit T-bet-deficient, autoreactive Th17 cells

The differentiation and maintenance of Th17 cells require a unique cytokine milieu and activation of lineage-specific transcription factors. This process appears to be antagonized by the transcription factor T-bet, which controls the differentiation of Th1 cells. Considering that T-bet-deficient (T-bet(-/-) ) mice are largely devoid of natural killer (NK) cells due to a defect in the terminal maturation of these cells, and because NK cells can influence the differentiation of T helper cells, we investigated whether the absence of NK cells in T-bet-deficient mice contributes to the augmentation of autoreactive Th17 cell responses. We show that the loss of T-bet renders the transcription factors Rorc and STAT3 highly responsive to activation by stimuli provided by NK cells. Furthermore, reconstitution of T-bet(-/-) mice with wild-type NK cells inhibited the development of autoreactive Th17 cells through NK cell-derived production of IFN-γ. These results identify NK cells as critical regulators in the development of autoreactive Th17 cells and Th17-mediated pathology.

Myasthenia gravis: a review

Acquired myasthenia gravis is a relatively uncommon disorder, with prevalence rates that have increased to about 20 per 100,000 in the US population. This autoimmune disease is characterized by muscle weakness that fluctuates, worsening with exertion, and improving with rest. In about two-thirds of the patients, the involvement of extrinsic ocular muscle presents as the initial symptom, usually progressing to involve other bulbar muscles and limb musculature, resulting in generalized myasthenia gravis. Although the cause of the disorder is unknown, the role of circulating antibodies directed against the nicotinic acetylcholine receptor in its pathogenesis is well established. As this disorder is highly treatable, prompt recognition is crucial. During the past decade, significant progress has been made in our understanding of the disease, leading to new treatment modalities and a significant reduction in morbidity and mortality.

Immunoregulatory natural killer cells suppress autoimmunity by down-regulating antigen-specific CD8+ T cells in mice

Natural killer (NK) cells belong to the innate immune system. Besides their role in antitumor immunity, NK cells also regulate the activity of other cells of the immune system, including dendritic cells, macrophages, and T cells, and may, therefore, be involved in autoimmune processes. The aim of the present study was to clarify the role of NK cells within this context. Using two mouse models for type 1 diabetes mellitus, a new subset of NK cells with regulatory function was identified. These cells were generated from conventional NK cells by incubation with IL-18 and are characterized by the expression of the surface markers CD117 (also known as c-Kit, stem cell factor receptor) and programmed death (PD)-ligand 1. In vitro analyses demonstrated a direct lysis activity of IL-18-stimulated NK cells against activated insulin-specific CD8(+) T cells in a PD-1/PD-ligand 1-dependent manner. Flow cytometry analyses revealed a large increase of splenic and lymphatic NK1.1(+)/c-Kit(+) NK cells in nonobese diabetic mice at 8 wk of age, the time point of acceleration of adaptive cytotoxic immunity. Adoptive transfer of unstimulated and IL-18-stimulated NK cells into streptozotocin-treated mice led to a delayed diabetes development and partial disease prevention in the group treated with IL-18-stimulated NK cells. Consistent with these data, mild diabetes was associated with increased numbers of NK1.1(+)/c-Kit(+) NK cells within the islets. Our results demonstrate a direct link between innate and adaptive immunity in autoimmunity with newly identified immunoregulatory NK cells displaying a potential role as immunosuppressors.

Activating KIR and HLA Bw4 ligands are associated to decreased susceptibility to pemphigus foliaceus, an autoimmune blistering skin disease

The KIR genes and their HLA class I ligands have thus far not been investigated in pemphigus foliaceus (PF) and related autoimmune diseases, such as pemphigus vulgaris. We genotyped 233 patients and 204 controls for KIR by PCR-SSP. HLA typing was performed by LABType SSO reagent kits. We estimated the odds ratio, 95% confidence interval and performed logistic regression analyses to test the hypothesis that KIR genes and their known ligands influence susceptibility to PF. We found significant negative association between activating genes and PF. The activating KIR genes may have an overlapping effect in the PF susceptibility and the presence of more than three activating genes was protective (OR = 0.49, p = 0.003). A strong protective association was found for higher ratios activating/inhibitory KIR (OR = 0.44, p = 0.001). KIR3DS1 and HLA-Bw4 were negatively associated to PF either isolated or combined, but higher significance was found for the presence of both together (OR = 0.34, p<10⁻³) suggesting that the activating function is the major factor to interfere in the PF pathogenesis. HLA-Bw4 (80I and 80T) was decreased in patients. There is evidence that HLA-Bw4(80T) may also be important as KIR3DS1 ligand, being the association of this pair (OR = 0.07, p = 0.001) stronger than KIR3DS1-Bw4(80I) (OR = 0.31, p = 0.002). Higher levels of activating KIR signals appeared protective to PF. The activating KIR genes have been commonly reported to increase the risk for autoimmunity, but particularities of endemic PF, like the well documented influence the environmental exposure in the pathogenesis of this disease, may be the reason why activated NK cells probably protect against pemphigus foliaceus.

Regulatory NK cells in autoimmune disease

As major components of innate immunity, NK cells not only exert cell-mediated cytotoxicity against tumor cells or infected cells, but also act to regulate the function of other immune cells by secretion of cytokines and chemokines, thus providing surveillance in early defense against viruses, intracellular bacteria and cancer cells. However, the effector function of NK cells must be exquisitely controlled in order to prevent inadvertent attack against self normal cells. The activity of NK cells is defined by integration of signals coming from inhibitory and activation receptors. Inhibitory receptors not only distinguish healthy from diseased cells by recognize self-MHC class I molecules on cell surfaces with "missing-self" model, but also provide an educational signal that generates functional NK cells. NK cells enrich in immunotolerance organ and recent findings of different regulatory NK cell subsets have indicated the unique role of NK cells in maintenance of homeostasis. Once the self-tolerance is broken, autoimmune response may occur. Although data has demonstrated that NK cells play important role in autoimmune disorders, NK cells seemed to act as a two edged weapon and play opposite roles with both regulatory and inducer activity even in the same disease. The precise role and regulatory mechanisms need to be further determined. In this review, we focus on recent research on the association of NK cells and antoimmune diseases, particularly the genetic correlation, the immune tolerance and misrecognition of NK cells, the regulatory function of NK cells, and their potential role in autoimmunity.

Natural killer cells: role in local tumor growth and metastasis

Historically, the name of natural killer (NK) cells came from their natural ability to kill tumor cells in vitro. From the 1970s to date, accumulating data highlighted the importance of NK cells in host immune response against cancer and in therapy-induced antitumor response. The recognition and the lysis of tumor cells by NK cells are regulated by a complex balance of inhibitory and activating signals. This review summarizes NK cell mechanisms to kill cancer cells, their role in host immune responses against tumor growth or metastasis, and their implications in antitumor immunotherapies via cytokines, antibodies, or in combination with other therapies. The regulatory role of NK cells in autoimmunity is also discussed.

Ocular surface immunity: homeostatic mechanisms and their disruption in dry eye disease

The tear film, lacrimal glands, corneal and conjunctival epithelia and Meibomian glands work together as a lacrimal functional unit (LFU) to preserve the integrity and function of the ocular surface. The integrity of this unit is necessary for the health and normal function of the eye and visual system. Nervous connections and systemic hormones are well known factors that maintain the homeostasis of the ocular surface. They control the response to internal and external stimuli. Our and others' studies show that immunological mechanisms also play a pivotal role in regulating the ocular surface environment. Our studies demonstrate how anti-inflammatory factors such as the expression of vascular endothelial growth factor receptor-3 (VEGFR-3) in corneal cells, immature corneal resident antigen-presenting cells, and regulatory T cells play an active role in protecting the ocular surface. Dry eye disease (DED) affects millions of people worldwide and negatively influences the quality of life for patients. In its most severe forms, DED may lead to blindness. The etiology and pathogenesis of DED remain largely unclear. Nonetheless, in this review we summarize the role of the disruption of afferent and efferent immunoregulatory mechanisms that are responsible for the chronicity of the disease, its symptoms, and its clinical signs. We illustrate current anti-inflammatory treatments for DED and propose that prevention of the disruption of immunoregulatory mechanisms may represent a promising therapeutic strategy towards controlling ocular surface inflammation.

Changes in immune cell frequencies after cyclophosphamide or mycophenolate mofetil treatments in patients with systemic lupus erythematosus

This study was designed to explore the profile of immune cell subsets, including T, B, natural killer (NK), and NKT cells, in systemic lupus erythematosus (SLE) patients, and to determine their relationships with the clinical index and the effects of cyclophosphamide (CYC) and mycophenolate mofetil (MMF) treatment. SLE patients (n = 28) and age/sex-matched healthy controls (n = 28) were evaluated. The patients were equally divided into two treatment groups: intravenous drip (IVD) with CYC and prednisolone, and oral MMF and IVD with prednisolone. SLE peripheral blood samples were taken immediately prior to treatment and after 4 weeks of drug treatment. T, B, NK, and NKT cell subsets were measured by flow cytometry. Double-stranded DNA antibody and Sm antibody were detected by indirect immunofluorescence. Serum C3, C4, and C-reactive protein were determined by scatter turbidimetry. The percentages of CD3+CD4+ T, CD3-CD16CD56+ NK, and CD3+CD16CD56+ NKT cells and the CD4+/CD8+ ratio were significantly lower in SLE patients, while CD3+CD8+ T and CD3-CD19+ B cells were higher than the controls. The lymphocyte subsets were significantly correlated with the SLE disease activity index (SLEDAI) and complement factors (C3, C4). Four weeks of CYC or MMF treatment led to a significant increase in CD3+CD4+ T cells (P < 0.05). In addition, both CYC and MMF treatments led to increases in CD3+ T and CD3-CD16CD56+NKT cells and decreases in CD3-CD16CD56+ NK and CD3+CD8+ T cells, but these changes were not obvious. The significant correlation that exists between lymphocytes subsets and SLEDAI activity scores suggests that the lymphocyte subsets may reflect SLE severity. Our results indicate that both the traditional cyclophosphamide agent and the new mycophenolate mofetil agent can regulate the lymphocyte subsets and consequent abnormal immunity, suggesting that MMF, which is known to produce less side-effects than CYC, may be used as an effective treatment of SLE.