Activation of invariant natural killer T cells by synthetic glycolipid ligands suppresses autoantibody-induced arthritis

IL-18 receptor-α signalling pathway contributes to autoantibody-induced arthritis via neutrophil recruitment and mast cell activation

OBJECTIVES

The interleukin (IL)-18 signalling pathway is involved in animal models of collagen-induced arthritis, but the role of this pathway in autoantibody-induced arthritis is poorly understood. An autoantibody-induced arthritis model, K/BxN serum transfer arthritis, reflects the effector phase of arthritis and is important in innate immunity including neutrophils and mast cells. This study aimed to investigate the role of the IL-18 signalling pathway in autoantibody-induced arthritis using IL-18 receptor (IL-18R) α-deficient mice.

METHODS

K/BxN serum transfer arthritis was induced in IL-18Rα-/- and wild-type B6 (controls) mice. The severity of arthritis was graded, and histological and immunohistochemical examinations were performed on paraffin-embedded ankle sections. Total Ribonucleic acid (RNA) isolated from mouse ankle joints was analysed by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

IL-18 Rα-/- mice had significantly lower arthritis clinical scores, neutrophil infiltration, and numbers of activated, degranulated mast cells in the arthritic synovium than in controls. IL-1β, which is indispensable for the progression of arthritis, was significantly downregulated in inflamed ankle tissue in IL-18 Rα-/- mice.

CONCLUSIONS

IL-18/IL-18Rα signalling contributes to the development of autoantibody-induced arthritis by enhancing synovial tissue expression of IL-1β and inducing neutrophil recruitment and mast cell activation. Therefore, inhibition of the IL-18Rα signalling pathway might be a new therapeutic strategy for rheumatoid arthritis.

The dual role of short fatty acid chains in the pathogenesis of autoimmune disease models

Autoimmune diseases are influenced by both genetic and environmental factors. The gut environment has attracted much attention as an essential component that modulates immune responses, and therefore immune-mediated disorders, such as autoimmune diseases. Growing evidence suggests that microbiota and their metabolites are critical factors for immune modulation. Recently, we reported that the microbiome in patients with multiple sclerosis, an autoimmune disease targeting the myelin sheath of the central nervous system, is characterized by a reduction of bacteria belonging to Clostridia clusters IV and XIVa, which are potent producers of short-chain fatty acids (SCFAs) by fermentation of indigestible carbohydrates. In the present study, we investigated the role of SCFAs in the regulation of inflammation. We demonstrated that oral administration of SCFAs ameliorated the disease severity of systemic autoimmune inflammatory conditions mediated by lymphocytes such as experimental autoimmune encephalitis and collagen-induced arthritis. Amelioration of disease was associated with a reduction of Th1 cells and an increase in regulatory T cells. In contrast, SCFAs contributed to the exaggeration of K/BxN serum transfer arthritis, representing the effector phase of inflammation in rheumatoid arthritis. An increased understanding of the effect of microbiota metabolites will lead to the effective treatment and prevention of systemic inflammatory disorders.

Understanding the Regulatory Roles of Natural Killer T Cells in Rheumatoid Arthritis: T Helper Cell Differentiation Dependent or Independent?

Rheumatoid arthritis (RA) is the most common chronic systemic autoimmune disease. This disease is thought to be caused by pathogenic T cells. Th1, Th2, Th17 and Treg cells have been implicated in the pathogenesis of RA. These Th cells differentiate from CD4+ T cells primarily due to the effects of cytokines. Natural killer T (NKT) cells are a distinct subset of lymphocytes that can rapidly secrete massive amount of cytokines, including IL-2, IL-4, IL-12 and IFN-γ. Numerous studies showed that NKT cells can influence the differentiation of CD4+ T cells via cytokines in vitro. These findings suggest that NKT cells play an important role in RA by polarizing Th1, Th2, Th17 and Treg cells. In view of the complexity of RA, we discussed whether NKT cells really influence the development of RA through regulating the differentiation of Th cells.

IL-38: A new factor in rheumatoid arthritis

The newly characterized cytokine IL-38 (IL-1F10) belongs to the IL-1 family of cytokines. Previous work has demonstrated that IL-38 inhibited Candida albicans-induced IL-17 production from peripheral blood mononuclear cells. However, it is still unclear whether IL-38 is an inflammatory or an anti-inflammatory cytokine. We generated anti-human IL-38 monoclonal antibodies in order to perform immunohistochemical staining and an enzyme-linked immunosorbent assay. While human recombinant IL-38 protein was not cleaved by recombinant caspase-1, chymase, or PR3 in vitro, overexpression of IL-38 cDNA produced a soluble form of IL-38 protein. Furthermore, immunohistochemical analysis showed that synovial tissues obtained from RA patients strongly expressed IL-38 protein. To investigate the biological role of IL-38, C57BL/6 IL-38 gene-deficient (^−/−) mice were used in an autoantibody-induced rheumatoid arthritis (RA) mouse model. As compared with control mice, IL-38 ^(−/−) mice showed greater disease severity, accompanied by higher IL-1β and IL-6 gene expression in the joints. Therefore, IL-38 acts as an inhibitor of the pathogenesis of autoantibody-induced arthritis in mice and may have a role in the development or progression of RA in humans.

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The soluble form of IL-38 is detected in the sera obtained from of RA patients.

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IL-38 protein was highly expressed in the synovial lining of RA synovium.

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IL-38 expression was up-regulated during arthritis in mice at the mRNA level.

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IL-38 may attenuate joint inflammation by inhibiting the IL-1 induced inflammation.

Invariant natural killer T cells regulate anti-tumor immunity by controlling the population of dendritic cells in tumor and draining lymph nodes

BACKGROUND

Invariant natural killer T (iNKT) cells are CD1d-restricted T cells, which respond rapidly to antigen recognition and promote development of anti-tumor immunity in many tumor models. Surprisingly, we previously found that mice deficient in iNKT cells developed spontaneous CD8(+) T cells responses partially effective at inhibiting metastases in mice bearing the 4T1 mammary carcinoma, and showed a markedly improved response to treatment with local radiotherapy and anti-CTLA-4 antibody compared to wild type (WT) mice.

METHODS

To understand the mechanisms of the immunosuppressive function of iNKT cells, dendritic cells (DCs) were analyzed by immunohistochemistry and flow cytometry in WT and iNKT-deficient (iNKT(-/-)) mice. The effects of antibody-mediated blockade of CD1d on DC number and phenotype, priming of anti-tumor T cells, and tumor response to treatment with local radiotherapy and anti-CTLA-4 antibody were evaluated. To determine if the improved response to treatment in the absence of iNKT cells was independent from the immunotherapy employed, 4T1-tumor bearing WT and iNKT(-/-) mice were treated with local radiotherapy in combination with antibody-mediated CD137 co-stimulation.

RESULTS

DCs in 4T1 tumors and tumor-draining lymph nodes but not distant lymph nodes were significantly reduced in WT mice compared to iNKT(-/-) mice (p < 0.05), suggesting the selective elimination of DCs cross-presenting tumor-associated antigens by iNKT cells. Consistently, priming of T cells to a tumor-specific CD8 T cell epitope in mice treated with radiotherapy and anti-CTLA-4 or anti-CD137 was markedly enhanced in iNKT(-/-) compared to WT mice. CD1d blockade restored the number of DC in WT mice, improved T cell priming in draining lymph nodes and significantly enhanced response to treatment.

CONCLUSIONS

Here we describe a novel mechanism of tumor immune escape mediated by iNKT cells that limit priming of anti-tumor T cells by controlling DC in tumors and draining lymph nodes. These results have important implications for the design of immunotherapies targeting iNKT cells.

Therapeutic manipulation of natural killer (NK) T cells in autoimmunity: are we close to reality?

T cells reactive to lipids and restricted by major histocompatibility complex (MHC) class I-like molecules represent more than 15% of all lymphocytes in human blood. This heterogeneous population of innate cells includes the invariant natural killer T cells (iNK T), type II NK T cells, CD1a,b,c-restricted T cells and mucosal-associated invariant T (MAIT) cells. These populations are implicated in cancer, infection and autoimmunity. In this review, we focus on the role of these cells in autoimmunity. We summarize data obtained in humans and preclinical models of autoimmune diseases such as primary biliary cirrhosis, type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, psoriasis and atherosclerosis. We also discuss the promise of NK T cell manipulations: restoration of function, specific activation, depletion and the relevance of these treatments to human autoimmune diseases.

Heme oxygenase-1 regulates the progression of K/BxN serum transfer arthritis

Background

Heme oxygenase-1 (HO-1) is induced in many cell types as a defense mechanism against stress. We have investigated the possible role of endogenous HO-1 in the effector phase of arthritis using the K/BxN serum transfer model of arthritis in HO-1 heterozygous and homozygous knock-out mice.

Methodology/Principal Findings

Arthritis was induced in C57/Black-6 xFVB (HO-1^+/+, HO-1^+/− and HO-1^−/−) mice by intraperitoneal injection of 150 µl serum from arthritic K/BxN mice at days 0 and 2. Blood was collected and animals were sacrificed at day 10. Histological analysis was performed in ankle sections. The levels of inflammatory mediators were measured in serum and paw homogenates by enzyme-linked immunosorbent assay or Multiplex technology. The incidence of arthritis was higher in HO-1^+/− and HO-1^−/− groups compared with HO-1^+/+. The inflammatory response was aggravated in HO-1^+/− mice as shown by arthritic score and the migration of inflammatory cells that could be related to the enhancement of CXCL-1 production. In addition, the HO-1^+/− group showed proteoglycan depletion significantly higher than HO-1^+/+ mice. Serum levels of matrix metalloproteinase-3, monocyte chemotactic protein-1, plasminogen activator inhibitor-1, E-selectin and intercellular adhesion molecule-1 were increased in arthritic HO-1^−/− mice, whereas vascular endothelial growth factor and some cytokines such as interferon-γ showed a reduction compared to HO-1^+/+ or HO-1^+/− mice. In addition, down-regulated gene expression of ferritin, glutathione S-reductase A1 and superoxide dismutase-2 was observed in the livers of arthritic HO-1^+/− animals.

Conclusion/Significance

Endogenous HO-1 regulates the production of systemic and local inflammatory mediators and plays a protective role in K/BxN serum transfer arthritis.

Activation of Invariant NKT cells with glycolipid ligand α-galactosylceramide ameliorates glucose-6-phosphate isomerase peptide-induced arthritis

Objective

Invariant natural killer T (iNKT) cells regulate collagen-induced arthritis (CIA) when activated by their potent glycolipid ligand, alpha-galactosylceramide (α-GalCer). Glucose-6-phosphate isomerase (GPI)-induced arthritis is a closer model of human rheumatoid arthritis based on its association with CD4+ T cells and cytokines such as TNF-α and IL-6 than CIA. Dominant T cell epitope peptide of GPI (GPI325-339) can induce arthritis similar to GPI-induced arthritis. In this study, we investigated the roles of activation of iNKT cells by α-GalCer in GPI peptide-induced arthritis.

Methods

Arthritis was induced in susceptible DBA1 mice with GPI peptide and its severity was assessed clinically. The arthritic mice were treated with either the vehicle (DMSO) or α-GalCer. iNKT cells were detected in draining lymph nodes (dLNs) by flow cytometry, while serum anti-GPI antibody levels were measured by enzyme-linked immunosorbent assay. To evaluate GPI peptide-specific cytokine production from CD4+ T cells, immunized mice were euthanized and dLN CD4+ cells were re-stimulated by GPI-peptide in the presence of antigen-presenting cells.

Results

α-GalCer induced iNKT cell expansion in dLNs and significantly decreased the severity of GPI peptide-induced arthritis. In α-GalCer-treated mice, anti-GPI antibody production (total IgG, IgG1, IgG2b) and IL-17, IFN-γ, IL-2, and TNF-α produced by GPI peptide-specific T cells were significantly suppressed at day 10. Moreover, GPI-reactive T cells from mice immunized with GPI and α-GalCer did not generate any cytokines even when these cells were co-cultured with APC from mice immunized with GPI alone. In vitro depletion of iNKT cells did not alter the suppressive effect of α-GalCer on CD4+ T cells.

Conclusion

α-GalCer significantly suppressed GPI peptide-induced arthritis through the suppression of GPI-specific CD4+ T cells.

Invariant NKT cells as novel targets for immunotherapy in solid tumors

Natural killer T (NKT) cells are a small population of lymphocytes that possess characteristics of both innate and adaptive immune cells. They are uniquely poised to respond rapidly to infection and inflammation and produce cytokines that critically shape the ensuing adaptive cellular response. Therefore, they represent promising therapeutic targets. In cancer, NKT cells are attributed a role in immunosurveillance. NKT cells also act as potent activators of antitumor immunity when stimulated with a synthetic agonist in experimental models. However, in some settings, NKT cells seem to act as suppressors and regulators of antitumor immunity. Here we briefly review current data supporting these paradoxical roles of NKT cells and their regulation. Increased understanding of the signals that determine the function of NKT cells in cancer will be essential to improve current strategies for NKT-cell-based immunotherapeutic approaches.

Mucosal-associated invariant T cells promote inflammation and exacerbate disease in murine models of arthritis

OBJECTIVE

The function of mucosal-associated invariant T (MAIT) cells remains largely unknown. We previously reported an immunoregulatory role of MAIT cells in an animal model of multiple sclerosis. The aim of this study was to use animal models to determine whether MAIT cells are involved in the pathogenesis of arthritis.

METHODS

MR1-/- and MR1+/+ DBA/1J mice were immunized with bovine type II collagen (CII) in complete Freund's adjuvant to trigger collagen-induced arthritis (CIA). To assess CII-specific T cell recall responses, lymph node cells from mice with CIA were challenged with CII ex vivo, and cytokine production and proliferation were evaluated. Serum levels of CII-specific antibodies were measured by enzyme-linked immunosorbent assay. Collagen antibody-induced arthritis (CAIA) was induced in MR1-/- and MR1+/+ C57BL/6 mice by injection of anti-CII antibodies followed by injection of lipopolysaccharide. To demonstrate the involvement of MAIT cells in arthritis, we induced CAIA in MR1-/- C57BL/6 mice that had been reconstituted with adoptively transferred MAIT cells. MAIT cell activation in response to cytokine stimulation was investigated.

RESULTS

The severity of CIA was reduced in MR1-/- DBA/1J mice. However, T and B cell responses to CII were comparable in MR1-/- and MR1+/+ DBA/1J mice. MR1-/- C57BL/6 mice were less susceptible to CAIA, and reconstitution with MAIT cells induced severe arthritis in MR1-/- C57BL/6 mice, demonstrating an effector role of MAIT cells in arthritis. MAIT cells became activated upon stimulation with interleukin-23 (IL-23) or IL-1β in the absence of T cell receptor stimuli.

CONCLUSION

These results indicate that MAIT cells exacerbate arthritis by enhancing the inflammation.

A 4-trifluoromethyl analogue of celecoxib inhibits arthritis by suppressing innate immune cell activation

Introduction

Celecoxib, a highly specific cyclooxygenase-2 (COX-2) inhibitor has been reported to have COX-2-independent immunomodulatory effects. However, celecoxib itself has only mild suppressive effects on arthritis. Recently, we reported that a 4-trifluoromethyl analogue of celecoxib (TFM-C) with 205-fold lower COX-2-inhibitory activity inhibits secretion of IL-12 family cytokines through a COX-2-independent mechanism that involves Ca²⁺-mediated intracellular retention of the IL-12 polypeptide chains. In this study, we explored the capacity of TFM-C as a new therapeutic agent for arthritis.

Methods

To induce collagen-induced arthritis (CIA), DBA1/J mice were immunized with bovine type II collagen (CII) in Freund's adjuvant. Collagen antibody-induced arthritis (CAIA) was induced in C57BL/6 mice by injecting anti-CII antibodies. Mice received 10 μg/g of TFM-C or celecoxib every other day. The effects of TFM-C on clinical and histopathological severities were assessed. The serum levels of CII-specific antibodies were measured by ELISA. The effects of TFM-C on mast cell activation, cytokine producing capacity by macophages, and neutrophil recruitment were also evaluated.

Results

TFM-C inhibited the severity of CIA and CAIA more strongly than celecoxib. TFM-C treatments had little effect on CII-specific antibody levels in serum. TFM-C suppressed the activation of mast cells in arthritic joints. TFM-C also suppressed the production of inflammatory cytokines by macrophages and leukocyte influx in thioglycollate-induced peritonitis.

Conclusion

These results indicate that TFM-C may serve as an effective new disease-modifying drug for treatment of arthritis, such as rheumatoid arthritis.

Glucagon-like peptide-1 (GLP-1) and the regulation of human invariant natural killer T cells: lessons from obesity, diabetes and psoriasis

AIMS/HYPOTHESIS

The innate immune cells, invariant natural killer T cells (iNKT cells), are implicated in the pathogenesis of psoriasis, an inflammatory condition associated with obesity and other metabolic diseases, such as diabetes and dyslipidaemia. We observed an improvement in psoriasis severity in a patient within days of starting treatment with an incretin-mimetic, glucagon-like peptide-1 (GLP-1) receptor agonist. This was independent of change in glycaemic control. We proposed that this unexpected clinical outcome resulted from a direct effect of GLP-1 on iNKT cells.

METHODS

We measured circulating and psoriatic plaque iNKT cell numbers in two patients with type 2 diabetes and psoriasis before and after commencing GLP-1 analogue therapy. In addition, we investigated the in vitro effects of GLP-1 on iNKT cells and looked for a functional GLP-1 receptor on these cells.

RESULTS

The Psoriasis Area and Severity Index improved in both patients following 6 weeks of GLP-1 analogue therapy. This was associated with an alteration in iNKT cell number, with an increased number in the circulation and a decreased number in psoriatic plaques. The GLP-1 receptor was expressed on iNKT cells, and GLP-1 induced a dose-dependent inhibition of iNKT cell cytokine secretion, but not cytolytic degranulation in vitro.

CONCLUSIONS/INTERPRETATION

The clinical effect observed and the direct interaction between GLP-1 and the immune system raise the possibility of therapeutic applications for GLP-1 in inflammatory conditions such as psoriasis.

The dangerous liaison between iNKT cells and dendritic cells: does it prevent or promote autoimmune diseases?

Invariant natural killer T (iNKT) cells represent an important regulatory T-cell subset that perceives signals of danger and/or cellular distress and modulate the adaptive immune response accordingly. In the presence of pathogens, iNKT cells acquire an adjuvant function that is fundamental to boost anti-microbial and anti-tumor immunity. At the same time, iNKT cells can play a negative regulatory function to maintain peripheral T-cell tolerance toward self-antigens and to prevent autoimmune disease. Both these effects of iNKT cells involve the modulation of the activity of dendritic cells (DCs) through cell-cell interaction. Indeed, iNKT cells can either boost Th1 immunity by enhancing maturation of pro-inflammatory DCs or promote immune tolerance through the maturation of tolerogenic DCs. This dual action of iNKT cells opens questions on the modalities by which a single-cell subset can exert opposite effects on DCs and may even put in question the overall immunosuppressive properties of iNKT cells. This review presents the large body of evidence that shows the ability of iNKT cells to negatively regulate autoimmunity and to prevent autoimmune diseases including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus. In addition, an update is provided on the mechanisms of iNKT-DCs interactions and how this can result in inflammatory or tolerogenic responses.

In vivo protection provided by a synthetic new alpha-galactosyl ceramide analog against bacterial and viral infections in murine models

Alpha-galactosyl ceramide (α-GalCer) has been known to bind to the CD1d receptor on dendritic cells and activate invariant natural killer T (iNKT) cells, which subsequently secrete T-helper-cell 1 (Th1) and Th2 cytokines, which correlate with anti-infection activity and the prevention of autoimmune diseases, respectively. α-GalCer elicits the secretion of these two cytokines nonselectively, and thus, its effectiveness is limited by the opposing effects of the Th1 and Th2 cytokines. Reported here is the synthesis of a new α-GalCer analog (compound C34), based on the structure of CD1d, with a 4-(4-fluorophenoxy) phenyl undecanoyl modification of the N-acyl moiety of α-GalCer. Using several murine bacterial and viral infection models, we demonstrated that C34 has superior antibacterial and antiviral activities in comparison with those of several other Th1-selective glycolipids and that it is most effective by administering it to mice in a prophylactic manner before or shortly after infection.

Autoimmunity and mast cell-related diseases

Allergy and autoimmunity are complex inflammatory processes caused by dysregulation of the immune system. There are select situations in which allergy and autoimmunity coexist pathologically. Traditionally considered unrelated, recent evidence suggests unexpected roles for allergic mediators in several autoimmune diseases. This review presents updated evidence for allergic mediators in several autoimmune diseases, as well as autoimmune phenomena in mast cell-related conditions. We will describe the concomitant manifestation of these conditions in patients and in animal models. The involvement of the main effectors of the immune system - mast cells, T lymphocytes, antibodies and cytokines - in both conditions is also discussed.

Early activation of invariant natural killer T cells in a rheumatoid arthritis model and application to disease treatment

Invariant NKT (iNKT) cells are a distinctive subtype of CD1d-restricted T cells involved in regulating autoimmunity and capable of producing various T helper type 1 (Th1), Th2 and Th17 cytokines. Activation of iNKT cells by their exogenous ligand alpha-galactosylceramide (alpha-GalCer) exerts therapeutic effects in autoimmune diseases such as rheumatoid arthritis (RA). However, the pathophysiological role of iNKT cells in RA, in the absence of exogenous stimulation, is incompletely understood. We investigated the potential pathophysiological effects of iNKT cells in mice with collagen-induced arthritis (CIA), a model of RA. We found that iNKT cells underwent activation only in the early phases of the disease (6 days post-induction). In the liver, but not the spleen or lymph nodes, this early activation led to the release of interleukins -4, -17A and -10 and of interferon-gamma; and an increased CD69 expression. Importantly, clinical and histological signs of arthritis were improved by the functional blockade of iNKT cells by a monoclonal antibody to CD1d at the early phase of the disease. This improvement was associated on day 6 post-induction with decreased expression of co-stimulatory molecules (CD80, CD86, CD40) on splenic dendritic cells and macrophages, whereas regulatory T-cell suppressive effects and proportions were not modified. Taken in concert, these findings suggest that iNKT cells are activated early in the course of CIA and contribute to the pathogenesis of arthritis. Therefore, iNKT-cell activation may be a valid treatment target in RA.

High doses of alpha-galactosylceramide potentiate experimental autoimmune encephalomyelitis by directly enhancing Th17 response

Alpha-galactosylceramide (alpha-GC) is widely known to activate invariant natural killer T (iNKT) cells to suppress myelin antigen-specific Th1 responses, protecting susceptible mice against experimental autoimmune encephalomyelitis (EAE). Here, we demonstrate an unexpected finding that high doses of alpha-GC exacerbated, rather than ameliorated, EAE. Similar results were observed when MOG(35-55)-specific T cells treated with high-dose alpha-GC were transferred into naïve syngeneic recipient mice. Further study showed that high doses of alpha-GC directly enhance the Th17 and Th1 response by activation of CD4(+)CD44(+) memory T cells through phosphorylation of STAT3 and activation of NF-kappaB. Unlike the activation of iNKT cells by low doses of alpha-GC, high doses of alpha-GC directly interacted with CD1d expressed on T cells and activated Th17 and Th1 cells. Furthermore, antigen-presenting cells (APCs) predominantly express CD1d1, whereas the majority of CD4(+) T cells express CD1d2. Knockdown of CD1d1 or CD1d2 gene expression by RNAi interfered with the activation of iNKT or Th17/Th1 cells, respectively. Therefore, alpha-GC treatment could improve or worsen EAE by engaging either APCs or Th17/Th1 cells depending on the dose used.

Natural killer T cells promote collagen-induced arthritis in DBA/1 mice

The role of NKT cells in the pathogenesis of collagen-induced arthritis (CIA) remains unclear since most studies have used C57BL/6 (B6) mice, which are less susceptible to CIA than mice with a DBA/1 background. To clarify the immunological functions of NKT cells in CIA, it is necessary to analyze in detail the effects of NKT cell deficiency on CIA development in DBA/1 mice. The incidence and severity of CIA were significantly exacerbated in DBA/1CD1d(+/-) mice as compared to DBA/1CD1d(-/-) mice. In DBA/1CD1d(+/-) mice, antigen-specific responses of B and T cells against CII were remarkably increased and inflammatory cytokine levels were also increased in vivo and in vitro. The number of IL-17-producing NKT cells significantly increased in DBA/1CD1d(+/-) mice as the disease progressed. Our results clearly show that NKT cells are involved not only in accelerating the severity and incidence of CIA but also in perpetuating the disease progression.

[Immunoregulation by iNKT cells]

NKT cells are defined as cells co-expressing of the natural killer receptors such as NK1.1 or NKR-P1A (CD161) and a T cell receptor (TCR). Although NK1.1(+) TCR(+) lymphocytes are heterogeneous, we focus on two distinct T cell subsets express invariant T cell receptor alpha chains, Valpha14-Jalpha18(Valpha14i) and Valpha19-Jalpha33(Valpha19i). Valpha14i NKT cells (Valpha24i NKT cells for human) are restricted by CD1d and Valpha19i NKT cells (Valpha7.2i NKT cells for human) are restricted by MR1 molecule. These cells emerge as an unique lymphocytes subset to bridge innate and acquired immunity. Here in this review, we discuss on the role of these cells in the regulation of autoimmunity and on the potential of therapeutic target for autoimmune diseases.

Impaired SLAM-SLAM homotypic interaction between invariant NKT cells and dendritic cells affects differentiation of IL-4/IL-10-secreting NKT2 cells in nonobese diabetic mice

The regulatory function of invariant NKT (iNKT) cells for tolerance induction and prevention of autoimmunity is linked to a specific cytokine profile that comprises the secretion of type 2 cytokines like IL-4 and IL-10 (NKT2 cytokine profile). The mechanism responsible for iNKT cell differentiation toward a type 2 phenotype is unknown. Herein we show that costimulatory signals provided by the surface receptor signaling lymphocytic activation molecule (SLAM) on myeloid dendritic cells (mDC) to iNKT cells is crucial for NKT2 orientation. Additionally, we demonstrate that the impaired acquisition of an NKT2 cytokine phenotype in nonobese diabetic (NOD) mice that spontaneously develop autoimmune diabetes is due to defective SLAM-induced signals generated by NOD mDC. Mature mDC of C57BL/6 mice express SLAM and induce C57BL/6 or NOD iNKT cells to acquire a predominant NKT2 cytokine phenotype in response to antigenic stimulation with the iNKT cell-specific Ag, the alpha-galactosylceramide. In contrast, mature NOD mDC express significantly lower levels of SLAM and are unable to promote GATA-3 (the SLAM-induced intracellular signal) up-regulation and IL-4/IL-10 production in iNKT cells from NOD or C57BL/6 mice. NOD mice carry a genetic defect of the Slamf1 gene that is associated with reduced SLAM expression on double-positive thymocytes and altered iNKT cell development in the thymus. Our data suggest that the genetic Slamf1 defect in NOD mice also affects SLAM expression on other immune cells such as the mDC, thus critically impairing the peripheral differentiation of iNKT cells toward a regulatory NKT2 type.

NKT cells and autoimmune diseases: unraveling the complexity

CDld-restricted invariant natural killer T (NKT) cells emerge as unique lymphocyte subsets implicated in the regulation of autoimmunity. Abnormalities in the numbers and functions of NKT cells have been observed in patients with diverse autoimmune diseases as well as in animal models of autoimmune diseases. NKT cells recognize glycolipid antigens presented by the nonpolymorphic MHC class I-like protein CD1d and participate in various kinds of immunoregulation due to a potent ability to produce a variety of cytokines. In this review, we examine the potential roles of NKT cells in the regulation and pathogenesis of autoimmune disease and the recent advances in glycolipid therapy for autoimmune disease models.