NKT cells: what's in a name?

Regulation of memory CD4 T-cell pool size and function by natural killer T cells in vivo

To develop more effective vaccines and strategies to regulate chronic inflammatory diseases, it is important to understand the mechanisms of immunological memory. Factors regulating memory CD4(+) T helper (Th)-cell pool size and function remain unclear, however. We show that activation of type I invariant natural killer T (iNKT) cells with glycolipid ligands and activation of type II natural killer T (NKT) cells with the endogenous ligand sulfatide induced dramatic proliferation and expansion of memory, but not naïve, CD4 T cells. NKT cell-induced proliferation of memory Th1 and Th2 cells was dependent largely on the production of IL-2, with Th2-cell proliferation also affected by loss of IL-4. Type II NKT cells were also required for efficient maintenance of memory CD4 T cells in vivo. Activation of iNKT cells resulted in up-regulation of IFN-γ expression by memory Th2 cells. These IFN-γ-producing memory Th2 cells showed a decreased capability to induce Th2 cytokines and eosinophilic airway inflammation. Thus, activated NKT cells directly regulate memory CD4 T-cell pool size and function via the production of cytokines in vivo.

Invariant natural killer T cells as sensors and managers of inflammation

Invariant natural killer T (iNKT) cells are a subset of innate-like lymphocytes that recognize glycolipid antigens bound by the major histocompatibility complex (MHC)-class-I-related protein CD1d. iNKT cells are activated early during a variety of infections and inflammatory diseases and contribute to the subsequent development of adaptive immune responses. Consequently, iNKT cells play a critical role in the development and resolution of inflammatory diseases and represent attractive targets for the development of immunotherapies. Recent studies have provided important insight into the mechanisms by which iNKT cells become activated in response to diverse inflammatory stimuli. These new findings should be instrumental to promote the immunomodulatory properties of iNKT cells for treatment of inflammatory diseases.

Human and mouse type I natural killer T cell antigen receptors exhibit different fine specificities for CD1d-antigen complex

Human and mouse type I natural killer T (NKT) cells respond to a variety of CD1d-restricted glycolipid antigens (Ags), with their NKT cell antigen receptors (NKT TCRs) exhibiting reciprocal cross-species reactivity that is underpinned by a conserved NKT TCR-CD1d-Ag docking mode. Within this common docking footprint, the NKT TCR recognizes, to varying degrees of affinity, a range of Ags. Presently, it is unclear whether the human NKT TCRs will mirror the generalities underpinning the fine specificity of the mouse NKT TCR-CD1d-Ag interaction. Here, we assessed human NKT TCR recognition against altered glycolipid ligands of α-galactosylceramide (α-GalCer) and have determined the structures of a human NKT TCR in complex with CD1d-4',4″-deoxy-α-GalCer and CD1d-α-GalCer with a shorter, di-unsaturated acyl chain (C20:2). Altered glycolipid ligands with acyl chain modifications did not affect the affinity of the human NKT TCR-CD1d-Ag interaction. Surprisingly, human NKT TCR recognition is more tolerant to modifications at the 4'-OH position in comparison with the 3'-OH position of α-GalCer, which contrasts the fine specificity of the mouse NKT TCR-CD1d-Ag recognition (4'-OH > 3'-OH). The fine specificity differences between human and mouse NKT TCRs was attributable to differing interactions between the respective complementarity-determining region 1α loops and the Ag. Accordingly, germline encoded fine-specificity differences underpin human and mouse type I NKT TCR interactions, which is an important consideration for therapeutic development and NKT cell physiology.

Role of gut microbiota in liver diseases

The liver constantly encounters food-derived antigens and bacterial components such as lipopolysaccharide translocated from the gut into the portal vein. Bacterial components stimulate Toll-like receptors (TLR), which are expressed on Kupffer cells, biliary epithelial cells, hepatocytes, hepatic stellate cells, endothelial cells and dendritic cells and recognize specific pathogen-associated molecular patterns. The signaling of TLR to its main ligand triggers inflammation. Usually, in order to protect against hyperactivation of the immune system and to prevent organ failure by persistent inflammation, TLR tolerance to repeated stimuli is induced. In chronic liver diseases, a breakdown in TLR tolerance occurs. Furthermore, Kupffer cells, hepatic stellate cells and natural killer T cells are key components of innate immunity. Decreased numbers and impaired ability of these cells lead to failures in immune tolerance, resulting in persistent inflammation. Recently, the activation of inflammasome was revealed to control the secretion of pro-inflammatory cytokines such as interleukin-1β in response to bacterial pathogens. Innate immunity seems to be an important contributor to the pathogenesis of fatty liver disease and autoimmune liver disease. Recently, probiotics were reported to affect various liver diseases via shifts in gut microbiota and the stability of intestinal permeability. However, many unresolved questions remain. Further analysis will be needed to gain a more comprehensive understanding of the association of innate immunity with the pathogenesis of various liver diseases.

Role of gut microbiota in liver diseases

The liver constantly encounters food-derived antigens and bacterial components such as lipopolysaccharide translocated from the gut into the portal vein. Bacterial components stimulate Toll-like receptors (TLR), which are expressed on Kupffer cells, biliary epithelial cells, hepatocytes, hepatic stellate cells, endothelial cells and dendritic cells and recognize specific pathogen-associated molecular patterns. The signaling of TLR to its main ligand triggers inflammation. Usually, in order to protect against hyperactivation of the immune system and to prevent organ failure by persistent inflammation, TLR tolerance to repeated stimuli is induced. In chronic liver diseases, a breakdown in TLR tolerance occurs. Furthermore, Kupffer cells, hepatic stellate cells and natural killer T cells are key components of innate immunity. Decreased numbers and impaired ability of these cells lead to failures in immune tolerance, resulting in persistent inflammation. Recently, the activation of inflammasome was revealed to control the secretion of pro-inflammatory cytokines such as interleukin-1β in response to bacterial pathogens. Innate immunity seems to be an important contributor to the pathogenesis of fatty liver disease and autoimmune liver disease. Recently, probiotics were reported to affect various liver diseases via shifts in gut microbiota and the stability of intestinal permeability. However, many unresolved questions remain. Further analysis will be needed to gain a more comprehensive understanding of the association of innate immunity with the pathogenesis of various liver diseases.

The effect of specific immunotherapy on natural killer T cells in peripheral blood of house dust mite-sensitized children with asthma

To investigate the effects of specific immunotherapy on the NKT cells in peripheral blood and the ability of NKT cells to proliferate in response to alpha-galactosylceramide (alpha-GalCer) in house-dust-mite- (HDM-) sensitized asthma children, peripheral blood mononuclear cells were isolated from 42 asthmatic children, of whom 24 were on specific immunotherapy (SIT) for more than a year and 20 were healthy. Compared with control group, the ratio of peripheral blood NKT and CD4⁺NKT cells was significantly decreased (P < 0.01) and was elevated in SIT asthma group (P < 0.05), respectively, but it was still less than the normal control group (P < 0.01). The level of IL-4 in serum secreted by NKT cells in asthma group was significantly higher than that of control group (P < 0.01), particularly apparent after 72 hours. The level of IL-4 in SIT group decreased significantly (P < 0.01). The level of IL-10 in serum secreted by NKT cells in asthma group was decreased significantly than that of the control group (P < 0.01) especially in 48 hours, while that of SIT group was increased significantly (P < 0.01). These results suggest that the pathogenesis of asthma may be related to the ratio and dysfunction of NKT and CD4⁺NKT cells.

The bovine CD1D gene has an unusual gene structure and is expressed but cannot present α-galactosylceramide with a C26 fatty acid

Although CD1d and NKT cells have been proposed to have highly conserved functions in mammals, data on functions of CD1d and NKT cells in species other than humans and rodents are lacking. Upon stimulation with the CD1d-presented synthetic antigen α-galactosylceramide, human and rodent type I invariant NKT cells release large amounts of cytokines. The two bovine CD1D (boCD1D) genes have structural features that suggest that they cannot be translated into functional proteins expressed on the cell surface. Here we provide evidence that despite an intron-exon structure and signal peptide that are different from all other known CD1 genes, boCD1D can be translated into a protein that is expressed on the cell surface. However, in vivo treatment of cattle (Bos taurus) with 0.1, 1, or 10 µg kg⁻¹ of the most commonly used α-galactosylceramide, which has a C26 fatty acid, did not lead to an increase in body temperature and serum cytokine levels of the animals. This lack of reactivity is not due to a complete inability of boCD1d to present glycosphingolipids because α-galactosylceramide variants with shorter fatty acids could be presented by boCD1d to human NKT cells in vitro. This suggests that the natural ligands of boCD1d are smaller lipids.

Type II natural killer T cells use features of both innate-like and conventional T cells to recognize sulfatide self antigens

Glycolipids presented by the major histocompatibility complex (MHC) class I homolog CD1d are recognized by natural killer T cells (NKT cells) characterized by either a semi-invariant T cell antigen receptor (TCR) repertoire (type I NKT cells or iNKT cells) or a relatively variable TCR repertoire (type II NKT cells). Here we describe the structure of a type II NKT cell TCR in complex with CD1d-lysosulfatide. Both TCR α-chains and TCR β-chains made contact with the CD1d molecule with a diagonal footprint, typical of MHC-TCR interactions, whereas the antigen was recognized exclusively with a single TCR chain, similar to the iNKT cell TCR. Type II NKT cell TCRs, therefore, recognize CD1d-sulfatide complexes by a distinct recognition mechanism characterized by the TCR-binding features of both iNKT cells and conventional peptide-reactive T cells.

Expression of the promyelocytic leukemia zinc-finger in T-lymphoblastic lymphoma and leukemia has strong implications for their cellular origin and greater association with initial bone marrow involvement

The promyelocytic leukemia zinc-finger (PLZF) is essential for the development of innate T cells (as represented by natural killer T cells) for acquisition of their unique innate immune properties. We evaluated the PLZF protein expression in a variety of immature and mature lymphoid malignancies. PLZF was preferentially expressed in T-lymphoblastic lymphoma/acute lymphoblastic leukemia (T-LBL/ALL) in 50% of the 54 cases. Among 51 cases of peripheral T-cell lymphoma not otherwise specified, only one (2%) expressed PLZF. One mycosis fungoides case expressed PLZF in lymph node involved by tumor. Otherwise, PLZF was not detected in any other type of lymphoma. In T-LBL/ALL, PLZF expression was more common in CD4/CD8 double-negative (67%) or CD8 single-positive subtypes (73%) than in CD4/CD8 double-positive (13%) and CD4 single-positive subtypes (0%) (P=0.001). Importantly, PLZF and CD1a expression were mutually exclusive in T-LBL/ALL (P=0.001). This was also the case for T-cell receptor βF1 expression (P=0.000). Most (96%) of the PLZF-positive T-LBL/ALL cases showed initial bone marrow involvement compared with 39% of PLZF-negative cases (P=0.000). Based on these findings, we suggest that T-LBL/ALLs that express PLZF arise from early immature double-negative thymocytes when the T-cell receptor β chain has not yet expressed or innate T-cell precursors, and strongly imply bone marrow involvement.

Immature murine NKT cells pass through a stage of developmentally programmed innate IL-4 secretion

We assessed the production of the canonical Th2 cytokine IL-4 by NKT cells directly in vivo using IL-4-substituting strains of reporter mice that provide faithful and sensitive readouts of cytokine production without the confounding effects of in vitro stimulation. Analysis in naïve animals revealed an "innate" phase of IL-4 secretion that did not need to be triggered by administration of a known NKT cell ligand. This secretion was by immature NKT cells spanning Stage 1 of the maturation process in the thymus (CD4(+) CD44(lo) NK1.1(-) cells) and Stage 2 (CD4(+) CD44(hi) NK1.1(-) cells) in the spleen. Like ligand-induced IL-4 production by mature cells, this innate activity was independent of an initial source of IL-4 protein and did not require STAT6 signaling. A more sustained level of innate IL-4 production was observed in animals on a BALB/c background compared with a C57BL/6 background, suggesting a level of genetic regulation that may contribute to the "Th2-prone" phenotype in BALB/c animals. These observations indicate a regulated pattern of IL-4 expression by maturing NKT cells, which may endow these cells with a capacity to influence the development of surrounding cells in the thymus.

A comprehensive review of the phenotype and function of antigen-specific immunoregulatory double negative T cells

Double negative T cells that lack the expression of both CD4 and CD8 T cell co-receptors exhibit a most unique antigen-specific immunoregulatory potential first described over a decade ago. Due to their immunoregulatory function, this rare T cell population has been studied in both mice and humans for their contribution to peripheral tolerance and disease prevention. Consequently, double negative cells are gaining interest as a potential cellular therapeutic. Herein, we review the phenotype and function of double negative T cells with emphasis on their capacity to induce antigen-specific immune tolerance. While the phenotypic and functional similarities between double negative T cells identified in mouse and humans are highlighted, we also call attention to the need for a specific marker of double negative T cells, which will facilitate future studies in humans. Altogether, due to their unique properties, double negative T cells present a promising therapeutic potential in the context of various disease settings.

iNKT cells suppress the CD8+ T cell response to a murine Burkitt's-like B cell lymphoma

The T cell response to B cell lymphomas differs from the majority of solid tumors in that the malignant cells themselves are derived from B lymphocytes, key players in immune response. B cell lymphomas are therefore well situated to manipulate their surrounding microenvironment to enhance tumor growth and minimize anti-tumor T cell responses. We analyzed the effect of T cells on the growth of a transplantable B cell lymphoma and found that iNKT cells suppressed the anti-tumor CD8⁺ T cell response. Lymphoma cells transplanted into syngeneic wild type (WT) mice or Jalpha18^−/− mice that specifically lack iNKT cells grew initially at the same rate, but only the mice lacking iNKT cells were able to reject the lymphoma. This effect was due to the enhanced activity of tumor-specific CD8⁺ T cells in the absence of iNKT cells, and could be partially reversed by reconstitution of iNKT cells in Jalpha 18^−/− mice. Treatment of tumor-bearing WT mice with alpha -galactosyl ceramide, an activating ligand for iNKT cells, reduced the number of tumor-specific CD8⁺ T cells. In contrast, lymphoma growth in CD1d1^−/− mice that lack both iNKT and type II NKT cells was similar to that in WT mice, suggesting that type II NKT cells are required for full activation of the anti-tumor immune response. This study reveals a tumor-promoting role for iNKT cells and suggests their capacity to inhibit the CD8⁺ T cell response to B cell lymphoma by opposing the effects of type II NKT cells.

Dendritic cell sphingosine 1-phosphate receptor-3 regulates Th1-Th2 polarity in kidney ischemia-reperfusion injury

Dendritic cells (DCs) are central to innate and adaptive immunity of early kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in S1P3-deficient mice. Through a series of experiments we determined that this protective effect was owing in part to differences between S1P3-sufficient and -deficient DCs. Mice lacking S1P3 on bone marrow cells were protected from IRI, and S1P3-deficient DCs displayed an immature phenotype. Wild-type (WT) but not S1P3-deficient DCs injected into mice depleted of DCs prior to kidney IR reconstituted injury. Adoptive transfer (i.e., i.v. injection) of glycolipid (Ag)-loaded WT but not S1P3-deficient DCs into WT mice exacerbated IRI, suggesting that WT but not S1P3-deficient DCs activated NKT cells. Whereas WT DC transfers activated the Th1/IFN-γ pathway, S1P3-deficient DCs activated the Th2/IL-4 pathway, and an IL-4-blocking Ab reversed protection from IRI, supporting the concept that IL-4 mediates the protective effect of S1P3-deficient DCs. Administration of S1P3-deficient DCs 7 d prior to or 3 h after IRI protected mice from IRI and suggests their potential use in cell-based therapy. We conclude that absence of DC S1P3 prevents DC maturation and promotes a Th2/IL-4 response. These findings highlight the importance of DC S1P3 in modulating NKT cell function and IRI and support development of selective S1P3 antagonists for tolerizing DCs for cell-based therapy or for systemic administration for the prevention and treatment of IRI and autoimmune diseases.

Natural killer T cells are required for lipopolysaccharide-mediated enhancement of atherosclerosis in apolipoprotein E-deficient mice

Lipopolysaccharide (LPS) has been shown to accelerate atherosclerosis and to increase the prevalence of IL-4-producing natural killer T (NKT) cells in various tissues. However, the role of NKT cells in the development of LPS-induced atherosclerotic lesions has not been fully tested in NKT cell-deficient mice. Here, we examined the lesion development in apolipoprotein E knockout (apoE-KO) mice and apoE-KO mice on an NKT cell-deficient, CD1d knockout (CD1d-KO) background (apoE-CD1d double knockout; DKO). LPS (0.5 μg/g body weight/wk) or phosphate-buffered saline (PBS) was intraperitoneally administered to apoE-KO and DKO mice (8-wk old) for 5 wk and atherosclerotic lesion areas were quantified thereafter. Consistent with prior reports, NKT cell-deficient DKO mice showed milder atherosclerotic lesions than apoE-KO mice. Notably, LPS administration significantly increased the lesion size in apoE-KO, but not in DKO mice, compared to PBS controls. Our findings suggest that LPS, and possibly LPS-producing bacteria, aggravate the development of atherosclerosis primarily through NKT cell activation and subsequent collaboration with NK cells.

Prevention and treatment of type 1 diabetes mellitus by the manipulation of invariant natural killer T cells

Invariant natural killer T (iNKT) cells are CD1d-restricted T cells with regulatory functions. iNKT cells are numerically and functionally deficient in experimental models of type 1 diabetes mellitus (T1DM). Moreover, various experimental strategies correcting the defect of or stimulating iNKT cells prevent T1DM. Here, we review the data on the role of iNKT cells in the development of T1DM and discuss indications, obstacles and prospects of the use of iNKT cell manipulations in the prevention and treatment of human T1DM.

New CD1d agonists: synthesis and biological activity of 6″-triazole-substituted α-galactosyl ceramides

Huisgen [3+2] dipolar cycloaddition of 6″-azido-6″-deoxy-α-galactosyl ceramide 11 with a range of alkynes (or a benzyne precursor) yielded a series of triazole-containing α-galactosyl ceramide (α-GalCer) analogues in high yield. These α-GalCer analogues and the precursor azide 11 were tested for their ability to activate iNKT cells and stimulate IL-2 cytokine secretion in vitro, and IFN-γ and IL-4 cytokine secretion in vivo. Some of these analogues, specifically 11, 12b, 12f and 13, were more potent IL-2 stimulators than the prototypical CD1d agonist, α-GalCer 1. In terms of any cytokine bias, most of the triazole-containing analogues exhibited a small Th2 cytokine-biasing response relative to that shown by α-GalCer 1. In contrast, the cycloaddition precursor, namely azide 11, provided a small Th1 cytokine-biasing response.

The glycolipid exoantigen derived from Chlamydia muridarum activates invariant natural killer T cells

The chlamydial glycolipid exoantigen (GLXA), a glycolipid antigen derived from Chlamydia muridarum, has been implicated in chlamydial-host cell interaction. Although glycolipid antigens from Sphingomonas and related bacteria have been shown to activate invariant natural killer T (iNKT) cells, it is not yet known whether GLXA can activate these cells. In this study, we have for the first time investigated the role of GLXA in iNKT cell activation using in vitro as well as in vivo settings. First, we examined the effect of GLXA on iNKT cell activation in a cell-free antigen-presentation assay, and found that GLXA specifically stimulated iNKT1.4 hybridoma cell produce enhanced amounts of IL-2. Next, we analyzed the effect of pharmacological activation of iNKT cells by GLXA using iNKT cell-deficient (iNKT knockout (KO)) mice and bone marrow-derived dendritic cell (BMDC)-liver mononuclear cell (LMC) coculture system. On stimulation with GLXA, iNKT cells produced higher quantities of cytokines in a CD1d-dependent fashion. More importantly, iNKT cells from GLXA-treated, but not from cell mock-treated, mice showed higher expression of activation marker, CD69, and enhanced production of interferon (IFN)-γ and IL-4 in vivo. Cumulatively, these data provide evidence on the pharmacological ability of GLXA in specifically activating iNKT cells.

Increased frequency of circulating invariant natural killer T cells in malignant pleural mesothelioma patients

Invariant natural killer T (iNKT) cells are a distinct subset of human T cells, which expresses an invariant T cell receptor Vα24 Jα18 and recognizes glycolipid antigens in the context of CD1d molecules. iNKT cells exert pivotal regulatory roles in many immune responses, including antitumor immune responses. Alterations in iNKT cell frequency, phenotype, and activation state have been reported in cancer patients. No data are available on the iNKT cells in malignant pleural mesothelioma (MPM), a rare, but very aggressive, malignancy of the pleura with a very poor prognosis. Here, we studied the frequency, phenotype, and cytokine profile of circulating iNKT cells in MPM patients, and correlated results with tumor histological types (epithelioid, sarcomatoid, biphasic) and clinical stages (I-III). We found that the iNKT cell frequency was significantly increased in MPM patients with epithelioid and sarcomatoid types in comparison with healthy volunteers (HV); only three biphasic mesotheliomas were available in this study, thus no conclusions can be drawn for this MPM type. The increased frequency significantly correlates with the clinical stage of tumor with the highest value at the stage III in both epithelioid and sarcomatoid subtypes. According to the histological types, we measured changes in the frequencies of CD4⁺ CD8⁺ (DP) and CD4⁻CD8⁻ (DN), but not in the cytokine profiles (IFN-γ/IL-4 expression). These results demonstrate that the frequency of iNKT cells is increased in MPM patients and that this increase correlates with MPM type and stage.

Structure-activity relationship studies of novel glycosphingolipids that stimulate natural killer T-cells

KRN7000, an anticancer drug candidate developed by Kirin Brewery Co. in 1995, is an α-galactosyl ceramide. It is a ligand making a complex with CD1d protein, and it stimulates invariant natural killer T (NKT) cells, which are one of the lineages of immunocytes. NKT cells activated by recognition of the CD1d/KRN7000 complex with its invariant T-cell receptor (TCR) can induce both protective and regulatory immune responses. To determine the recognition and activation mechanisms of NKT cells and to develop drug candidates more effective than KRN7000, a large number of analogs of KRN7000 have been synthesized. Some of them show potent bioactivities and have the potential of being utilized as therapeutic agents. In this review, structure-activity relationship studies of novel glycolipids which stimulate NKT cells efficiently are summarized.

Reduced frequency of NKT-like cells in patients with progressive chronic lymphocytic leukemia

Natural killer T (NKT) cells are a subset of innate immune cells displaying a limited repertoire of antigen specificities and CD1d restriction. Little is known about contribution of NKT cells in cancer initiation and progression. In this study, the frequencies of NKT-like cells, B cells expressing CD1d molecule and CD4(+) regulatory (Treg) cells were analyzed in 40 patients with chronic lymphocytic leukemia (CLL) and 15 healthy subjects by flow cytometry. Our results showed that the frequency of CD3(+)CD56(+) NKT-like cells is significantly decreased in progressive (4.9 ± 0.8 % of total CD3(+) T cells) compared with indolent (8.1 ± 1.2 %, p = 0.036) patients and healthy subjects (10.6 ± 1.7 %, p = 0.003). However, no association was found between NKT-like cell frequency and immunoglobulin heavy chain variable region gene (IGHV) mutation or CD38 and ZAP70 expression. On the other hand, expression of CD1d molecule was significantly higher in leukemic B cells of patients with CLL (75 ± 1.5 % of total CD19(+) B cells) compared to B cells from healthy subjects (59.6 ± 2.2 %, p < 0.001), with no significant difference between progressive and indolent patients. Interestingly, the frequency of Treg cells was inversely correlated with that of NKT-like cells in patients with CLL (r = -0.4, p = 0.002). Our results suggest a protective role for NKT-like cells in patients with CLL, which seems to be downregulated presumably by Treg cells.

The ROS scavenger, NAC, regulates hepatic Vα14iNKT cells signaling during Fas mAb-dependent fulminant liver failure

Uncontrolled systemic activation of the immune system is an early initiating event that leads to development of acute fulminant liver failure (FLF) in mice after treatment with agonistic Fas mAb. In this study, we demonstrate that treatment of mice with N-acetylcysteine (NAC), an ROS scavenger and glutathione (GSH) precursor, almost completely abolished Fas mAb-induced FLF through suppression of Vα14iNKT cell activation, IFN-γ signaling, apoptosis and nitrotyrosine formation in liver. In addition, enrichment of the liver with GSH due to Vα14iNKT cells deficiency, induced an anti-inflammatory response in the liver of Jα18(-/-) mice that inhibited apoptosis, nitrotyrosine formation, IFN-γ signaling and effector functions. In summary, we propose a novel and previously unrecognized pro-inflammatory and pro-apoptotic role for endogenous ROS in stimulating Th1 signaling in Vα14iNKT cells to promote the development of FLF. Therefore, our study provides critical new insights into how NAC, a ROS scavenger, regulates Th1 signaling in intrahepatic Vα14iNKT cells to impact inflammatory and pathological responses.

Therapeutic potential of semi-mature dendritic cells for tolerance induction

Dendritic cells (DCs) are major players in the control of adaptive tolerance and immunity. Therefore, their specific generation and adoptive transfer into patients or their in vivo targeting is attractive for clinical applications. While injections of mature immunogenic DCs are tested in clinical trials, tolerogenic DCs still are awaiting this step. Besides the tolerogenic potential of immature DCs, also semi-mature DCs can show tolerogenic activity but both types also bear unfavorable features. Optimal tolerogenic DCs, their molecular tool bar, and their use for specific diseases still have to be defined. Here, the usefulness of in vitro generated and adoptively transferred semi-mature DCs for tolerance induction is outlined. The in vivo targeting of semi-mature DCs as represented by steady state migratory DCs are discussed for treatment of autoimmune diseases and allergies. First clinical trials with transcutaneous allergen application may point to their therapeutic use in the future.

The sterile immune response during hepatic ischemia/reperfusion

Hepatic ischemia and reperfusion elicits an immune response that lacks a microbial constituent yet poses a potentially lethal threat to the host. In this sterile setting, the immune system is alarmed by endogenous danger signals that are release by stressed and dying liver cells. The detection of these immunogenic messengers by sentinel leukocyte populations constitutes the proximal trigger for a self-perpetuating cycle of inflammation, in which consecutive waves of cytokines and chemokines orchestrate the influx of various leukocyte subsets that ultimately confer tissue destruction. This review focuses on the temporal organization of sterile hepatic inflammation, using surgery-induced trauma as a template disease state.

Activation of invariant natural killer T cells by lipid excess promotes tissue inflammation, insulin resistance, and hepatic steatosis in obese mice

Obesity triggers a low-grade systemic inflammation, which plays an important role in the development of obesity-associated metabolic diseases. In searching for links between lipid accumulation and chronic inflammation, we examined invariant natural killer T (iNKT) cells, a subset of T lymphocytes that react with lipids and regulate inflammatory responses. We show that iNKT cells respond to dietary lipid excess and become activated before or at the time of tissue recruitment of inflammatory leukocytes, and that these cells progressively increase proinflammatory cytokine production in obese mice. Such iNKT cells skew other leukocytes toward proinflammatory cytokine production and induce an imbalanced proinflammatory cytokine environment in multiple tissues. Further, iNKT cell deficiency ameliorates tissue inflammation and provides protection against obesity-induced insulin resistance and hepatic steatosis. Conversely, chronic iNKT cell stimulation using a canonical iNKT cell agonist exacerbates tissue inflammation and obesity-associated metabolic disease. These findings place iNKT cells into the complex network linking lipid excess to inflammation in obesity and suggest new therapeutic avenues for obesity-associated metabolic disorders.

Invariant natural killer T cells contribute to the allergic response in cow's milk protein-sensitized mice

BACKGROUND

Little is known about the contribution of the invariant natural killer T (iNKT) cells in the onset of food allergy. Using a mouse model for cow's milk allergy the function of iNKT cells was investigated.

METHODS

Mice were sensitized orally with casein or whey proteins. One hour before the sensitizations the mice were injected intraperitoneally with α-galactosylceramide (αGalCer) or control. One week after the last sensitization acute allergic skin reactions were measured. Furthermore, in the liver, spleen and mesenteric lymph nodes (MLN) percentages of iNKT cells were analyzed and liver lymphocyte restimulation assays were performed.

RESULTS

Whey- or casein-sensitized mice treated with αGalCer showed enhanced acute allergic skin reactions. The percentage of iNKT cells in the liver of sensitized mice was reduced compared to sham-sensitized mice. αGalCer treatment was found to deplete iNKT cells in the liver of sensitized as well as sham-sensitized mice, and these hepatocytes did not respond to ex vivo restimulation with αGalCer. αGalCer treatment did not reduce iNKT cell percentages in the spleen and MLN of sham-sensitized mice but abrogated the increase in iNKT cell percentage in the spleen upon whey sensitization, whereas it enhanced the iNKT cell percentage in the MLN of casein-sensitized mice. Due to the repeated application of αGalCer, livers were functionally depleted of iNKT cells. This resulted in an increased allergic effector response which was most pronounced in whey-sensitized mice and associated with enhanced whey-specific immunoglobulin levels.

CONCLUSION

iNKT cells may suppress cow's milk allergic symptoms in mice and may differentially regulate oral sensitization for casein and whey.

Double negative Treg cells promote nonmyeloablative bone marrow chimerism by inducing T-cell clonal deletion and suppressing NK cell function

The establishment of immune tolerance and prevention of chronic rejection remain major goals in clinical transplantation. In bone marrow (BM) transplantation, T cells and NK cells play important roles for graft rejection. In addition, graft-versus-host-disease (GVHD) remains a major obstacle for BM transplantation. In this study, we aimed to establish mixed chimerism in an irradiation-free condition. Our data indicate that adoptive transfer of donor-derived T-cell receptor (TCR) αβ(+) CD3(+) CD4(-) CD8(-) NK1.1(-) (double negative, DN) Treg cells prior to C57BL/6 to BALB/c BM transplantation, in combination with cyclophosphamide, induced a stable-mixed chimerism and acceptance of C57BL/6 skin allografts but rejection of third-party C3H (H-2k) skin grafts. Adoptive transfer of CD4(+) and CD8(+) T cells, but not DN Treg cells, induced GVHD in this regimen. The recipient T-cell alloreactive responsiveness was reduced in the DN Treg cell-treated group and clonal deletions of TCRVβ2, 7, 8.1/2, and 8.3 were observed in both CD4(+) and CD8(+) T cells. Furthermore, DN Treg-cell treatment suppressed NK cell-mediated BM rejection in a perforin-dependent manner. Taken together, our results suggest that adoptive transfer of DN Treg cells can control both adoptive and innate immunities and promote stable-mixed chimerism and donor-specific tolerance in the irradiation-free regimen.

Intravenous immunoglobulin treatment increased live birth rate in a Spanish cohort of women with recurrent reproductive failure and expanded CD56(+) cells

PROBLEM

Natural killer (NK, CD3(-)CD56(+)/CD16(+)) and NKT-like cells (CD3(+)CD56(+)/CD16(+)) activity is considered among the key factors for reproductive success. In the absence of immunological screening, beneficial effects of intravenous immunoglobulin (IVIG) in preventing recurrent reproductive failure (RRF) have not been reported. Here, we analyse the IVIG influence on pregnancy success in women with RRF and circulating NK or/and NKT-like cells expansion.

METHOD OF STUDY

One hundred fifty-seven women with previous recurrent miscarriage and/or recurrent implantation failure after in vitro fertilization were consecutively studied. Sixty-four patients with CD56(+) cell expansion, no apparent underlying disease and who maintained their desire to conceive were selected. Forty of them received IVIG during pregnancy.

RESULTS

Overall, the clinical pregnancy rate for the women under IVIG therapy was 92.5% and the live birth rate was 82.5%. Significantly lower pregnancy and live birth rates (25% and 12.5%, respectively) were observed for the patients with recurrent pregnancy loss and NK/NKT-like cells expansion without IVIG. After three cycles of IVIG, NK cell percentages decreased significantly and these values persisted throughout gestation.

CONCLUSION

Intravenous immunoglobulin therapy for women with RRF and NK or NKT-like cell expansion was a safe and beneficial therapeutic strategy that associated with high clinical pregnancy and live birth rates.

Differential requirements for IRF-2 in generation of CD1d-independent T cells bearing NK cell receptors

NK cell receptors (NKRs) such as NK1.1, NKG2D, and Ly49s are expressed on subsets of CD1d-independent memory phenotype CD8(+) and CD4(-)CD8(-) T cells. However, the mechanism for the generation and functions of these NKR(+) T cells remained elusive. In this study, we found that CD1d-independent Ly49(+) T cells were reduced severely in the spleen, bone marrow, and liver, but not thymus, in mice doubly deficient for IFN regulatory factor-2 (IRF-2) and CD1d, in which the overall memory phenotype T cell population was contrastingly enlarged. Because a large fraction of Ly49(+) T cells coexpressed NK1.1 or NKG2D, the reduction of Ly49(+) T cells resulted indirectly in underrepresentation of NK1.1(+) or NKG2D(+) cells. Ly49(+) T cell deficiency was observed in IRF-2(-/-) mice additionally lacking IFN-α/βR α-chain (IFNAR1) as severely as in IRF-2(-/-) mice, arguing against the involvement of the accelerated IFN-α/β signals due to IRF-2 deficiency. Rather, mice lacking IFN-α/βR alone also exhibited relatively milder Ly49(+) T cell reduction, and IL-2 could expand Ly49(+) T cells from IFNAR1(-/-), but not from IRF-2(-/-), spleen cells in vitro. These results together indicated that IRF-2 acted in Ly49(+) T cell development in a manner distinct from that of IFN-α/β signals. The influence of IRF-2 deficiency on Ly49(+) memory phenotype T cells observed in this study suggested a unique transcriptional program for this T cell population among other NKR(+) T and memory phenotype T cells.

Interplay between carbohydrate and lipid in recognition of glycolipid antigens by natural killer T cells

Natural killer T (NKT) cells are a T cell subpopulation that were named originally based on coexpression of receptors found on natural killer (NK) cells, cells of the innate immune system, and by T lymphocytes. The maturation and activation of NKT cells requires presentation of glycolipid antigens by CD1d, a cell surface protein distantly related to the major histocompatibility complex (MHC)-encoded antigen presenting molecules. This specificity distinguishes NKT cells from most CD4(+) and CD8(+) T cells that recognize peptides presented by MHC class I and class II molecules. The rapid secretion of a large amount of both Th1 and Th2 cytokines by activated NKT cells endows them with the ability to play a vital role in the host immune defense against various microbial infections. In this review, we summarize progress on identifying the sources of microbe-derived glycolipid antigens recognized by NKT cells and the biochemical basis for their recognition.

Dysfunction of natural killer T cells in patients with active Mycobacterium tuberculosis infection

Natural killer T (NKT) cells are known to play a protective role in the immune responses of mice against a variety of infectious pathogens. However, little is known about the detailed information of NKT cells in patients with Mycobacterium tuberculosis infection. The aims of this study were to examine NKT cell levels and functions in patients with active M. tuberculosis infection, to investigate relationships between NKT cell levels and clinical parameters, and to determine the mechanism responsible for the poor response to α-galactosylceramide (α-GalCer). NKT cell levels were significantly lower in the peripheral blood of pulmonary tuberculosis and extrapulmonary tuberculosis patients, and the proliferative responses of NKT cells to α-GalCer were also lower in patients, whereas NKT cell levels and responses were comparable in latent tuberculosis infection subjects and healthy controls. Furthermore, this NKT cell deficiency was found to be correlated with serum C-reactive protein levels. In addition, the poor response to α-GalCer in M. tuberculosis-infected patients was found to be due to increased NKT cell apoptosis, reduced CD1d expression, and a defect in NKT cells. Notably, M. tuberculosis infection was associated with an elevated expression of the inhibitory programmed death-1 (PD-1) receptor on NKT cells, and blockade of PD-1 signaling enhanced the response to α-GalCer. This study shows that NKT cell levels and functions are reduced in M. tuberculosis-infected patients and these deficiencies were found to reflect the presence of active tuberculosis.

Protective role of α-galactosylceramide-stimulated natural killer T cells in genital tract infection with Chlamydia muridarum

Natural killer T (NKT) cells are a unique lymphocyte subpopulation which has an important role in the response to microbial pathogens. In this study, we used α-galactosylceramide (α-GalCer), a specific ligand of NKT cells, to enhance NKT response and examine its effect on host defense against genital tract Chlamydia muridarum infection. The results showed that α-GalCer treatment before infection led to reduced pathological changes and bacterial burden in the genital tract. Moreover, α-GalCer-treated mice showed greater local Th1 cytokine production [interferon γ (IFN-γ) and interleukin 12 (IL-12)] in local lymph node cells and genital tissues following challenge infection compared with untreated mice, as well as an enhanced level of IFN-γ production by NK and T cells. In addition, NKT cells in the mice with genital tract C. muridarum infection, unlike those from naïve mice, showed a polarized IFN-γ production. These results suggest a promoting role of NKT cells on type 1 T cell immune response and host resistance to Chlamydia in genital tract infection.

CD4(+) type II NKT cells mediate ICOS and programmed death-1-dependent regulation of type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease that results from T cell-mediated destruction of pancreatic β cells. CD1d-restricted NKT lymphocytes have the ability to regulate immunity, including autoimmunity. We previously demonstrated that CD1d-restricted type II NKT cells, which carry diverse TCRs, prevented T1D in the NOD mouse model for the human disease. In this study, we show that CD4(+) 24αβ type II NKT cells, but not CD4/CD8 double-negative NKT cells, were sufficient to downregulate diabetogenic CD4(+) BDC2.5 NOD T cells in adoptive transfer experiments. CD4(+) 24αβ NKT cells exhibited a memory phenotype including high ICOS expression, increased cytokine production, and limited display of NK cell markers, compared with double-negative 24αβ NKT cells. Blocking of ICOS or the programmed death-1/programmed death ligand 1 pathway was shown to abolish the regulation that occurred in the pancreas draining lymph nodes. To our knowledge, these results provide for the first time cellular and molecular information on how type II CD1d-restricted NKT cells regulate T1D.

Enrichment of invariant natural killer T cells in the bone marrow of visceral leishmaniasis patients

Lipid antigens of Leishmania donovani like lipophosphoglycans are shown as a potent ligand for the activation of invariant natural killer T (iNKT) cells. It is reported that activation of iNKT cells augments the disease pathology in experimental visceral leishmaniasis (VL). In this study, we demonstrate the enrichment of iNKT cells in the bone marrow, one of the disease sites among patients with VL.

Role of natural killer T cells in the mouse colitis-associated colon cancer model

Invariant natural killer T (iNKT) cells are considered innate-like lymphocytes, and regulate the immunity against inflammation and tumorigenesis. However, the impact of iNKT cells in inflammation-associated tumorigenesis remains unclear. In this study, we examined the physiological role of iNKT cells in a mouse colitis-associated colorectal cancer model. C57BL/6 (B6) and Jα18 NKT cell-deficient KO (KO) mice were used. Colitis-associated colorectal cancer was induced by azoxymethane (AOM) and dextran sodium sulfate (DSS). The resulting inflammation and tumours were examined. The surface markers of mononuclear cells from the liver and the colon were assessed by FACS. The levels of IL-13 from the colon were measured by ELISA. α-galactosylceramide (GC), or its close analog OCH, was administered intraperitoneally on the first day of each cycle of DSS-administration. In the AOM/DSS model, hepatic iNKT cells were significantly decreased. In KO mice there were significantly greater numbers of colon tumours and more severe inflammation than in B6 mice. FACS analysis revealed that the population of NK1.1 (+) T cells (non-invariant NKT cells) in the colon was increased when compared to B6 mice. The secretion of IL-13 was increased in the colon of KO mice after AOM/DSS. The number of colon tumours was significantly decreased in the GC-treated group compared to the control group. GC-treatment significantly inhibited IL-13 secretion from the colonic mononuclear cells and the number of colonic NK1.1 (+) T cells was significantly decreased. These results suggest that iNKT cells may play a critical role in the prevention of tumour progression and inflammation in the AOM/DSS model.

Development and function of invariant natural killer T cells producing T(h)2- and T(h)17-cytokines

Four distinct subsets of invariant natural killer T (NKT) cells are shown to differentiate in the thymus, then migrate to peripheral tissues where they retain their phenotypic and functional characteristics.

There is heterogeneity in invariant natural killer T (iNKT) cells based on the expression of CD4 and the IL-17 receptor B (IL-17RB), a receptor for IL-25 which is a key factor in T_H2 immunity. However, the development pathway and precise function of these iNKT cell subtypes remain unknown. IL-17RB⁺iNKT cells are present in the thymic CD44^+/− NK1.1⁻ population and develop normally even in the absence of IL-15, which is required for maturation and homeostasis of IL-17RB⁻iNKT cells producing IFN-γ. These results suggest that iNKT cells contain at least two subtypes, IL-17RB⁺ and IL-17RB⁻ subsets. The IL-17RB⁺iNKT subtypes can be further divided into two subtypes on the basis of CD4 expression both in the thymus and in the periphery. CD4⁺ IL-17RB⁺iNKT cells produce T_H2 (IL-13), T_H9 (IL-9 and IL-10), and T_H17 (IL-17A and IL-22) cytokines in response to IL-25 in an E4BP4-dependent fashion, whereas CD4⁻ IL-17RB⁺iNKT cells are a retinoic acid receptor-related orphan receptor (ROR)γt⁺ subset producing T_H17 cytokines upon stimulation with IL-23 in an E4BP4-independent fashion. These IL-17RB⁺iNKT cell subtypes are abundantly present in the lung in the steady state and mediate the pathogenesis in virus-induced airway hyperreactivity (AHR). In this study we demonstrated that the IL-17RB⁺iNKT cell subsets develop distinct from classical iNKT cell developmental stages in the thymus and play important roles in the pathogenesis of airway diseases.

T cells are a diverse group of immune cells involved in cell-mediated acquired immunity. One subset of T cells is the innate-like invariant natural killer T (iNKT) cells that recognize glycolipid ligands on target cells instead of peptides. We know that functionally distinct subtypes of iNKT cells are involved in specific pathologies, yet their development, phenotypes, and functions are not well understood. Here, we determine the relationship between various mouse iNKT cell subsets, identify reliable molecular markers for these subsets, and show that these contribute to their functional differences. We identify four iNKT cell subsets that we show arise via different developmental pathways and exhibit different cytokine profiles. Importantly, we show that these subsets can be isolated from the thymus (the organ of all T cells), as well as from peripheral tissues such as spleen, liver, lung, and lymph nodes. Contrary to the general understanding that iNKT cells mature after their exit from the thymus and their migration into peripheral tissues, we conclude that distinct phenotypic and functional iNKT cell subsets can be distinguished in the thymus by virtue of the presence or absence of the cytokine receptor IL-17RB and another cell surface molecule called CD4, and these subsets then migrate to peripheral tissues where they retain their phenotypic and functional characteristics. Regarding functional significance, we show that those iNKT cell subsets that lead to airway hyper-responsiveness to respiratory viruses are different to those that lead to allergen-induced airway hyperreactivity, which will enable researchers to focus on specific subsets as potential targets for therapeutic intervention.

dysregulation of CD1d-restricted type ii natural killer T cells leads to spontaneous development of colitis in mice

BACKGROUND & AIMS

CD1d-restricted natural killer (NK) T cells are a subset of immunoregulatory T cells that comprise type I (express the semi-invariant T-cell receptor [TCR] and can be detected using the α-galactosylceramide/CD1d tetramer) and type II (express diverse TCRs and cannot be directly identified). Studies in mouse models of inflammatory bowel disease revealed a complex role for type I NKT cells in the development of colitis. Type II NKT cells have been associated with intestinal inflammation in patients with ulcerative colitis.

METHODS

To investigate whether dysregulation of type II NKT cells, caused by increased expression of CD1d, can contribute to colitis, we generated transgenic mice that express high levels of CD1d and a TCR from an autoreactive, type II NKT cell (CD1dTg/24αβTg mice).

RESULTS

CD1dTg/24αβTg mice had reduced numbers of 24αβ T cells compared with 24αβTg mice, indicating that negative selection increases among type II NKT cells engaged by abundant self-antigen. The residual 24αβ T cells in CD1dTg/24αβTg mice had an altered surface phenotype and acquired a cytokine profile distinct from that of equivalent cells in 24αβTg mice. Interestingly, CD1dTg/24αβTg mice spontaneously developed colitis; adoptive transfer experiments confirmed that type II NKT cells that develop in the context of increased CD1d expression are pathogenic.

CONCLUSIONS

Aberrant type II NKT cell responses directly contribute to intestinal inflammation in mice, indicating the importance of CD1d expression levels in the development and regulation of type II NKT cells.

Primary immunodeficiency associated with defects in CD1 and CD1-restricted T cells

CD1 is a family of atypical MHC class I molecules that present various endogenous and exogenous lipid antigens to CD1-restricted T cells. While little is known about the function of CD1a-, CD1b-, and CD1c-restricted lipid-reactive T cells due to their absence in mice, CD1d-restricted natural killer T (NKT) cells have been extensively studied since their description almost 20 years ago. NKT cells, effector memory cells that share characteristics of innate and adaptive lymphocytes, are among the earliest responders in immune reactions and have broad effects on the activation of other immune cell lineages, including NK cells, T cells, and B cells. Accordingly, studies in mice have revealed critical roles of NKT cells in infectious, malignant, and autoimmune diseases. The recent description of primary immunodeficiencies associated with defects in CD1 and CD1-restricted T cells has provided a unique opportunity to study the biological role of lipid antigen presentation in human disease. Intriguingly, these studies revealed that defects in lipid immunity are associated with susceptibility to selected infectious and malignant diseases but not with broad immunodeficiency.

Sulfatide inhibits α-galactosylceramide presentation by dendritic cells

Sulfatide-reactive type II NKT cells, the so-called non-invariant NKT (non-iNKT) cells, have been shown to counteract invariant NKT (iNKT) cell activity. However, the effects of sulfatide on activation of iNKT cells by α-galactocylceramide (αGC) in the context of CD1d have not been studied in detail. Therefore, we studied the blocking effect of sulfatide on αGC-induced iNKT cell activation by dendritic cells (DCs). Even in the absence of non-iNKT cells, sulfatide inhibited αGC-mediated iNKT cell activation by reducing αGC/CD1d complex formations in a dose-dependent manner. This was also confirmed in a cell-free setting using immobilized CD1d-Ig. Moreover, simultaneous injection of αGC with sulfatide decreased αGC/CD1d complex formations on DCs, accompanied by the reduced CD40L-up-regulation and IFN-γ production by iNKT cells and IL-12p70 production by DCs. However, sulfatide by itself did not interfere with the presentation of MHC class II-mediated antigen presentation to specific T cells. These results demonstrate that sulfatide competes with αGC to be loaded onto CD1d along the endocytic pathway in DCs, thereby inhibiting the iNKT cell response.

Synthesis of C-glycoside analogues of α-galactosylceramide via linear allylic C-H oxidation and allyl cyanate to isocyanate rearrangement

C-Glycoside analogues of α-galactosylceramide were synthesized in which several significant modifications known to promote Th-1 cytokine production were included. The key transformations include C-H oxidation, Sharpless asymmetric epoxidation, olefin cross metathesis, and an allyl cyanate to isocyanate rearrangement.

Natural killer T cells in pulmonary disorders

Natural killer T (NKT) cells, a unique subgroup of lymphocytes with features of both T and natural killer (NK) cells, represent a bridge between innate and adaptive immunity. They have the ability to either promote or suppress immune responses. With these immunoregulatory functions, NKT cells have emerged as an important subset of lymphocytes with a protective role in some disorders, such as infections, cancer, and possibly sarcoidosis, and a pathogenic role in others, such as asthma, chronic obstructive pulmonary disease and hypersensitivity pneumonitis. Immunotherapeutic interventions to modulate the immune response by targeting iNKT cell functions has become a challenging field and has shown promising results for the development of new therapies.

Natural killer T cell based Immunotherapy

Natural killer T (NKT) cells play an important immunoregulatory role and are thought to bridge the innate and adaptive immune responses. Following activation through cognate interactions with lipid antigen presented in the context of CD1d molecules, NKT cells rapidly produce a plethora of cytokines and can also mediate cytotoxicity. Due to their potent effector functions, extensive research has been performed to increase our understanding on how to effectively modulate these cells. In fact, NKT cell agonists have been used as vaccine adjuvants to enhance antigen specific T and B cell responses to infections and malignancy. In this review, we will focus on recent advances in NKT cell-based vaccination strategies. Given the role that NKT cells play in autoimmune disease, infectious diseases, cancer, transplant immunology and dermatology, it is important to understand how to effectively guide their effector functions in order to develop novel immunotherapeutic strategies.

A pivotal role for antigen-presenting cells overexpressing SOCS3 in controlling invariant NKT cell responses during collagen-induced arthritis

OBJECTIVE

Suppressor of cytokine signalling (SOCS) proteins constitute a class of intracellular proteins that are key physiological regulators of immune cell function. It has previously been shown that antigen-presenting cells (APCs) overexpressing SOCS3 steer T helper immune responses and protect against experimental arthritis. A study was undertaken to investigate the contribution of SOCS3 in regulating invariant natural killer T (iNKT) cell responses during collagen-induced arthritis (CIA).

METHODS

DBA/1 mice were immunised with type II collagen and adenoviruses encoding SOCS3 were administered intravenously before the clinical onset of arthritis. Murine APCs overexpressing SOCS3 were co-cultured with an iNKT cell hybridoma and interleukin 2 (IL-2) release was measured by Luminex multi-analyte technology. The frequency and activation of primary iNKT cells was assessed by flow cytometry. Murine APCs were analysed for cytokine and CD1d expression following viral SOCS3 gene transfer.

RESULTS

Viral overexpression of SOCS3 in APCs resulted in reduced activation of the iNKT cell hybridoma. Importantly, during initiation of CIA, adenovirus-mediated overexpression of SOCS3 in hepatic and splenic APCs inhibited iNKT cell expansion in both organs. The iNKT cell population from SOCS3-treated mice showed low expression of the early activation marker CD69 and primary liver iNKT cells produced less interferon γ and IL-4 upon α-galactosylceramide stimulation. No differences in CD1d surface expression were observed, but SOCS3-transduced APCs produced decreased levels of proinflammatory cytokines and increased levels of IL-10.

CONCLUSION

These results demonstrate a critical role for SOCS3 in controlling the immunostimulatory capacities of APCs, which has direct implications for the effector function of iNKT cells during arthritis.

Invariant natural killer T cells direct B cell responses to cognate lipid antigen in an IL-21-dependent manner

Mouse invariant natural killer T cells (iNKT cells) provide cognate and noncognate help for lipid and protein-specific B cells, respectively. However, the long-term outcome for B cells after cognate help is provided by iNKT cells is unknown at present. Here we found that cognate iNKT cell help resulted in a B cell differentiation program characterized by extrafollicular plasmablasts, germinal-center formation, affinity maturation and a robust primary immunoglobulin G (IgG) antibody response that was uniquely dependent on iNKT cell-derived interleukin 21 (IL-21). However, cognate help from iNKT cells did not generate an enhanced humoral memory response. Thus, cognate iNKT cell help for lipid-specific B cells induces a unique signature that is a hybrid of classic T cell-dependent and T cell-independent type 2 B cell responses.

Structural basis for the recognition of C20:2-αGalCer by the invariant natural killer T cell receptor-like antibody L363

Natural killer T (NKT) cells express a semi-invariant Vα14 T cell receptor (TCR) and recognize structurally diverse antigens presented by the antigen-presenting molecule CD1d that range from phosphoglycerolipids to α- and β-anomeric glycosphingolipids, as well as microbial α-glycosyl diacylglycerolipids. Recently developed antibodies that are specific for the complex of the prototypical invariant NKT (iNKT) cell antigen αGalCer (KRN7000) bound to mouse CD1d have become valuable tools in elucidating the mechanism of antigen loading and presentation. Here, we report the 3.1 Å resolution crystal structure of the Fab of one of these antibodies, L363, bound to mCD1d complexed with the αGalCer analog C20:2, revealing that L363 is an iNKT TCR-like antibody that binds CD1d-presented αGalCer in a manner similar to the TCR. The structure reveals that L363 depends on both the L and H chains for binding to the glycolipid-mCD1d complex, although only the L chain is involved in contacts with the glycolipid antigen. The H chain of L363 features residue Trp-104, which mimics the TCR CDR3α residue Leu-99, which is crucial for CD1d binding. We characterized the antigen-specificity of L363 toward several different glycolipids, demonstrating that whereas the TCR can induce structural changes in both antigen and CD1d to recognize disparate lipid antigens, the antibody L363 can only induce the F' roof formation in CD1d but fails to reorient the glycolipid headgroup necessary for binding. In summary, L363 is a powerful tool to study mechanism of iNKT cell activation for structural analogs of KRN7000, and our study can aid in the design of antibodies with altered antigen specificity.