Natural Killer T Cell Responses Research Articles

Migration of Invariant Natural Killer T-Cells in Response To Peritonitis is Dependent Upon Direct Ligation of PD-1:PD-L1 on These Cells and Not Indirect Actions

Migration of Invariant Natural Killer T-Cells in Response To Peritonitis is Dependent Upon Direct Ligation of PD-1:PD-L1 on These Cells and Not Indirect Actions

Raising the Roof: The Preferential Pharmacological Stimulation of Th1 and Th2 Responses Mediated by NKT Cells

Natural killer T (NKT) cells serve as a bridge between the innate and adaptive immune systems, and manipulating their effector functions can have therapeutic significances in the treatment of autoimmunity, transplant biology, infectious disease, and cancer. NKT cells are a subset of T cells that express cell-surface markers characteristic of both natural killer cells and T cells. These unique immunologic cells have been demonstrated to serve as a link between the innate and adaptive immune systems through their potent cytokine production following the recognition of a range of lipid antigens, mediated through presentation of the major histocompatibility complex (MHC) class I like CD1d molecule, in addition to the NKT cell's cytotoxic capabilities upon activation. Although a number of glycolipid antigens have been shown to complex with CD1d molecules, most notably the marine sponge derived glycolipid alpha-galactosylceramide (α-GalCer), there has been debate as to the identity of the endogenous activating lipid presented to the T-cell receptor (TCR) via the CD1d molecule on antigen-presenting cells (APCs). This review aims to survey the use of pharmacological agents and subsequent structure-activity relationships (SAR) that have given insight into the binding interaction of glycolipids with both the CD1d molecules as well as the TCR and the subsequent immunologic response of NKT cells. These studies not only elucidate basic binding interactions but also pave the way for future pharmacological modulation of NKT cell responses.

Molecular Identification of GD3 as a Suppressor of the Innate Immune Response in Ovarian Cancer

Tumors often display mechanisms to avoid or suppress immune recognition. One such mechanism is the shedding of gangliosides into the local tumor microenvironment, and a high concentration of circulating gangliosides is associated with poor prognosis. In this study, we identify ganglioside GD3, which was isolated from the polar lipid fraction of ovarian cancer-associated ascites, as an inhibitory factor that prevents innate immune activation of natural killer T (NKT) cells. Purified GD3 displayed a high affinity for both human and mouse CD1d, a molecule involved in the presentation of lipid antigens to T cells. Purified GD3, as well as substances within the ascites, bound to the CD1d antigenic-binding site and did not require additional processing for its inhibitory effect on NKT cells. Importantly, in vivo administration of GD3 inhibited α-galactosylceramide (α-GalCer)-induced NKT cell activation in a dose-dependent manner. These data therefore indicate that ovarian cancer tumors may use GD3 to inhibit the antitumor NKT cell response as an early mechanism of tumor immune evasion.

A role for Bcl-xL in CD1d-mediated Natural Killer T cell responses to B cells (46.39)

Abstract Lymphomas are a heterogeneous group of malignancies, primarily divided into Hodgkin's and non-Hodgkin's lymphomas (NHL). Unlike other cancers, the incidence of NHL is steadily rising. Natural Killer T (NKT) cells are innate-like lymphocytes that recognize glycolipid antigens in the context of CD1d, an MHC class I-like molecule. They have strong anti-tumor activity and respond by massive cytokine production and/or cytotoxicity. It is known that pro-survival factors are upregulated in B cell lymphomas, but their role in antigen processing and presentation remains unknown. The effect of Bcl-xL on CD1d-mediated antigen presentation was examined utilizing the well-characterized WEHI-231 B cell lymphoma cell line. Bcl-xL expression was modulated via genetic, pharmacologic and biological approaches. We found a concomminant increase in CD1d-mediated NKT cell responses following the induction of Bcl-xL; however, cell surface expression of CD1d molecules remained unchanged. Induction of Bcl-xL in primary B cells led to increased CD1d-mediated activation of NKT cells in response to exogenous antigens, resulting in increased Th1 not Th2 responses. Taken together, these data suggest that aberrant expression of Bcl-xL may act as a sentry system to alert the CD1d/NKT system to neoplastic transformation.

Increase in natural killer T (NKT) Cell activation in hypoxic environments via the induction of HIF1alpha (162.16)

Abstract Tumors often experience hypoxic microenvironments due to poor vascular access in the early stage of neoplastic growth and continue to experience oxygen deficits in late stage progression despite the increase in neovascularization to the primary tumor or metastasis. This persistent hypoxic state selects for tumors cells that are able to compensate for low oxygen levels by increasing use of the glycolytic cycle under aerobic conditions (The Warburg Effect), suppressing apoptosis and inducing decreased genomic stability. These effects have been shown to be mediated, at least in part, by the transcription factor hypoxia inducible factor (HIF)-1alpha. Natural Killer T (NKT) cells are a subset of T cells that recognize a wide range of lipid antigens presented by the MHC Class I-like CD1d molecule. In this study, we sought to investigate the effects of hypoxia induction on CD1d-mediated NKT cell responses. Pharmacological agents were used to induce HIF-1a in LCD1d, and then we assessed their ability to present endogenous antigen to NKT cells. It was found that the induction of HIF-1a resulted in a significant increase in CD1d-mediated NKT cell activation, as assessed by IL-2, GM-CSF, and IL-13 production. The increase in NKT function was not due to with an increase in cell surface expression of CD1d. These results suggest that hypoxia in tumor cells may alter the repertoire of endogenous lipids presented in the context of CD1d which permits their recognition by NKT cells.

The location of splenic NKT cells favours their rapid activation by blood-borne antigen.

Natural killer T (NKT) cells play an important role in mounting protective responses to blood-borne infections. However, though the spleen is the largest blood filter in the body, the distribution and dynamics of NKT cells within this organ are not well characterized. Here we show that the majority of NKT cells patrol around the marginal zone (MZ) and red pulp (RP) of the spleen. In response to lipid antigen, these NKT cells become arrested and rapidly produce cytokines, while the small proportion of NKT cells located in the white pulp (WP) exhibit limited activation. Importantly, disruption of the splenic MZ by chemical or genetic approaches results in a severe reduction in NKT cell activation indicating the need of cooperation between both MZ macrophages and dendritic cells for efficient NKT cell responses. Thus, the location of splenic NKT cells in the MZ and RP facilitates their access to blood-borne antigen and enables the rapid initiation of protective immune responses.

Retinoic acid ameliorates experimental autoimmune hepatitis and suppresses the production of cytokine in NKT cells in mice (107.4)

Abstract Retinoic acid(RA) has been demonstrated as a critical regulator of various immune cells. Especially RA regulates the response of helper T cells skewing to Th2 response during the priming. In spite of abundant studies regarding T cells, the role of RA on natural killer T(NKT) cell mediated response has not been assessed. In the present study, we demonstrated the effect of RA on the experimental autoimmune hepatitis and the response of NKT cells. We first examined whether pretreatment of RA could regulate concanavlin A(Con A)-induced hepatitis, which is initiated by NKT cells. The survival rate was increased dramatically and liver damage was ameliorated when RA was pretreated. And also the levels of IFN-gamma and IL-4 in serum were both reduced significantly in RA treated group and the cytokine expressing cells were reduced in various lymphocytes in liver, especially in NKT cells. Cytokine suppressive effects of RA were observed when NKT cell specific ligand was treated. These regulations were also detected when mononuclear cells of liver or splenocytes were treated with the stimulants in the presence of RA in vitro. These regulations are not related with the early activation of NKT cells. Rather, the apoptosis of lymphocytes in liver after the administration of con A were increased in RA-treated group. These findings implicates that RA ameliorates NKT cell mediated hepatitis and it could be used clinically to liver injury related with NKT cells.

A Molecular Basis for the Exquisite CD1d-Restricted Antigen Specificity and Functional Responses of Natural Killer T Cells

Natural killer T (NKT) cells respond to a variety of CD1d-restricted antigens (Ags), although the basis for Ag discrimination by the NKT cell receptor (TCR) is unclear. Here we have described NKT TCR fine specificity against several closely related Ags, termed altered glycolipid ligands (AGLs), which differentially stimulate NKT cells. The structures of five ternary complexes all revealed similar docking. Acyl chain modifications did not affect the interaction, but reduced NKT cell proliferation, indicating an affect on Ag processing or presentation. Conversely, truncation of the phytosphingosine chain caused an induced fit mode of TCR binding that affected TCR affinity. Modifications in the glycosyl head group had a direct impact on the TCR interaction and associated cellular response, with ligand potency reflecting the t(1/2) life of the interaction. Accordingly, we have provided a molecular basis for understanding how modifications in AGLs can result in striking alterations in the cellular response of NKT cells.

Numerical and functional deficiencies of natural killer T cells in systemic lupus erythematosus: their deficiency related to disease activity

This study was designed to examine the frequency of natural killer T (NKT) cells and the response to α-galactosylceramide (α-GalCer) in SLE patients and to investigate the clinical relevance of NKT cell levels. Patients with SLE (n = 128) and age- and sex-matched healthy controls (HCs) (n = 92) were enrolled in the study. NKT cell and CD1d levels were measured by flow cytometry. Gene expression was determined by RT-PCR, and cytokine secretion by multiple cytokine assay. Peripheral blood mononuclear cells (PBMCs) were cultured in vitro with α-GalCer. Proliferation indices of NKT cells were estimated by flow cytometry. Percentages and absolute numbers of NKT cells were significantly lower in the peripheral blood of SLE patients than in that of HCs, whereas CD1d levels in PBMCs were comparable between these two groups. Notably, this NKT cell deficiency was found to be correlated with SLEDAI. NKT cell proliferation was found to be impaired in SLE patients, and cytokine production by NKT cells in response to α-GalCer was diminished. This poor responsiveness to α-GalCer was found to be due to NKT cell dysfunction rather than to an abnormality in CD1d-expressing cells. Our data show that NKT cell levels and functions are defective in SLE patients. Furthermore, these deficiencies were found to reflect disease activity. It would appear that these NKT cell abnormalities could contribute to immune system dysregulation in SLE.

Impact of sugar stereochemistry on natural killer T cell stimulation by bacterial glycolipids

Natural killer T (NKT) cells recognize glycolipids produced by Sphingomonas bacteria, and these glycolipids contain C6-oxidized sugars, either glucuronic acid or galacturonic acid, linked to ceramides. Glycolipids with gluco stereochemistry are the most prevalent. Multiple studies have demonstrated that galactosylceramides are more potent stimulators of NKT cells than their glucose isomers. To determine if this stereoselectivity is retained in the context of the C6-oxidized sugars found in bacterial glycolipids, we prepared two sets of gluco and galacto-glycolipids oxidized at their C6 positions and compared their NKT stimulatory properties. In the context of carboxylic acid groups at C6, gluco stereochemistry gave the more potent responses. We also prepared bacterial glycolipids containing more complex ceramide groups to determine if these chains impact NKT cell responses.

β-Glycoglycosphingolipid-Induced Alterations of the STAT Signaling Pathways Are Dependent on CD1d and the Lipid Raft Protein Flotillin-2

Beta-glucosylceramide has been shown to affect natural killer T cell function in models of inflammation. We, therefore, investigated the effects of different beta-glycosphingolipids, including beta-glucosylceramide, on STAT (signal transducers and activators of transcription) signaling pathways and determined whether these effects were mediated by lipid raft microdomains and/or CD1d molecules. The effects of alpha- and beta-structured ligands on the lipid raft protein flotillin-2 were studied in both natural killer T hybridoma cells and leptin-deficient mice. To determine whether CD1d was involved in the effects of the beta-glycosphingolipids, an anti-CD1d blocking antibody was used in a cell proliferation assay system. The downstream effects on the protein phosphorylation levels of STAT1, STAT3, and STAT6 were examined in both immune-mediated hepatitis and hepatoma models. The effects of beta-glycosphingolipids on the STAT signaling pathways were found to be dependent on CD1d. Lipid rafts were affected by both the dose and ratio of the beta-glycosphingolipids and the acyl chain length, and these effects were followed by downstream effects on STAT proteins. Our results show that beta-glycosphingolipids have beneficial effects in natural killer T cell-dependent immune-mediated metabolic and malignant animal models in vivo.

Cancellation of NKT cell immunosuppression targeting myeloid suppressor cells

CD1d-restricted natural killer T (NKT) cells are one of immunoregulatory cells. NKT cells can be specifically activated by a synthetic glycolipid, α-galactosylceramide (α-GalCer). Using some glycolipids such as α-GalCer, it is expected to develop a new NKT cell-mediated therapeutic strategy against cancer. However, it is known that, in human cancer patients, NKT cells express a degree of hyporesponsiveness to α-GalCer. For example, we have reported that, in gastrointestinal cancer patients, NKT cell proliferation and cytokine production were impaired. We have further examined the mechanism by which hyporesponsiveness to α-GalCer can be induced using cancer-bearing mice. In the animal study, α-GalCer-induced NKT cell expansion, cytokine production, cytotoxicity, and anti-metastatic effect in vivo were all significantly impaired. In fact, α-GalCer could eliminate metastatic disease in naive animals, but failed to protect cancer-bearing mice. We found that CD11b+ Gr-1+ cells were particularly increased in cancer-bearing mice and were necessary and sufficient for the suppression of NKT cells to α-GalCer. We also found that the increased CD11b+ Gr-1+ cells suppressed NKT cell function in a nitric oxide-mediated fashion. To reduce the population of CD11b+ Gr-1+ cells, we administered a retinoic acid to cancer-bearing mice. This treatment significantly reduced the population of CD11b+ Gr-1+ cells and effectively restored α-GalCer-induced NKT cell responses. These results demonstrate a novel feature of NKT cell function in cancer, and suggest a new strategy to enhance NKT cell-mediated anti-cancer immune responses by suppressing CD11b+ Gr-1+ cell functions.

NKT cell immune responses to viral infection

Background: Natural killer T (NKT) cells are a heterogeneous population of innate T cells that have attracted interest because of their potential to regulate immune responses to a variety of pathogens. The most widely studied NKT cell subset is the invariant (i)NKT cells that recognize glycolipids in the context of the CD1d molecule. The multifaceted methods of activation iNKT cells possess and their ability to produce regulatory cytokines has made them a primary target for studies. Objective/methods: To give insights into the roles of iNKT cells during infectious diseases, particularly viral infections. We also highlight mechanisms leading to iNKT cell activation in response to pathogens. Conclusions: iNKT cell's versatility allows them to detect and respond to several viruses. Therapeutic approaches to specifically target iNKT cells will require additional research. Notably, the roles of non-invariant NKT cells in response to pathogens warrant further investigation.

6′-Derivatised α-GalCer Analogues Capable of Inducing Strong CD1d-Mediated Th1-Biased NKT Cell Responses in Mice

α-Galactosyl ceramide (α-GalCer, also known as KRN 7000) is known as the prototypical antigen for invariant natural killer T (NKT) cells. Stimulation of NKT cells by CD1d-mediated α-GalCer presentation leads to rapid release of Th1 and Th2 cytokines. Since Th1 and Th2 cytokines antagonize each other’s effects, α-GalCer analogues that induce a biased Th1/Th2 response are highly awaited. With the exception of a C-glycoside (α-C-GalCer), most of the known α-GalCer analogues able to induce polarized cytokine responses are characterized by modifications of the phytosphingosine or fatty acyl chains, expected to alter the affinity for CD1d. Herein we describe the synthesis of 6′-modified α-GalCer analogues with an intact phytoceramide moiety that are capable to skew the cytokine release profile to Th1, while maintaining strong antigenic activity. These analogues are characterized by the presence of an aromatic moiety that is connected via an amide or an urea linkage to C′-6 of the galactopyranose ring.

Lipid tails dictate NKT cell response

Short lipid chains tweak the responses of natural killer T (NKT) cells by weakening the binding between the T cell receptor (TCR) and the lipid-presenting protein, report McCarthy et al. on page 1131. Figure 1 Lipid antigens have to be long enough for cytotoxic granules (green) to move from the rear of NKT cells to the immunological synapse (left to right). Lipid antigens are presented to NKT cells by the surface glycoprotein CD1d. These fatty antigens are composed of a hydrophilic head that is exposed to the TCR on the NKT cells, and two hydrophobic tails. Each tail—an acyl chain and a fatty acid chain—is tucked away inside separate grooves within the CD1d molecule. Previous studies showed that shorter lipid chains destabilize the binding of the lipid antigen to CD1d. Whereas some of these short ligands simply reduce the ability of CD1d to activate an NKT cell, others switch the NKT response from interferonγ to interleukin-4 production. McCarthy et al. now find that shortening either the acyl or the fatty acid chain destabilizes the CD1d-lipid complex. The shorter fatty acid chain, however, also reduces the binding affinity between the CD1d-lipid complex and the TCR. The NKT cells are therefore unable to induce clustering of CD1d-lipid complexes and fail to form a productive synapse with the antigen presenting cell. The authors propose that the stumpy fatty acid chain doesn't completely fill its CD1d groove, which consequently collapses. This new conformation might lead to a less stable interaction between the complex and the TCR.

Natural killer T cells recognize diacylglycerol antigens from pathogenic bacteria

Natural killer T (NKT) cells recognize glycosphingolipids presented by CD1d molecules and have been linked to defense against microbial infections. Previously defined foreign glycosphingolipids recognized by NKT cells are uniquely found in nonpathogenic sphingomonas bacteria. Here we show that mouse and human NKT cells also recognized glycolipids, specifically a diacylglycerol, from Borrelia burgdorferi, which causes Lyme disease. The B. burgdorferi-derived, glycolipid-induced NKT cell proliferation and cytokine production and the antigenic potency of this glycolipid was dependent on acyl chain length and saturation. These data indicate that NKT cells recognize categories of glycolipids beyond those in sphingomonas and suggest that NKT cell responses driven by T cell receptor-mediated glycolipid recognition may provide protection against diverse pathogens.

Enhancement of ligand-dependent activation of human natural killer T cells by lenalidomide: therapeutic implications

Natural killer T (NKT) cells are CD1d-restricted glycolipid reactive innate lymphocytes that play an important role in protection from pathogens and tumors. Pharmacologic approaches to enhance NKT cell function will facilitate specific NKT targeting in the clinic. Here we show that lenalidomide (LEN), a novel thalidomide (Thal) analog, enhances antigen-specific expansion of NKT cells in response to the NKT ligand alpha-galactosylceramide (alpha-GalCer) in both healthy donors and patients with myeloma. NKT cells activated in the presence of LEN have greater ability to secrete interferon-gamma. Antigen-dependent activation of NKT cells was greater in the presence of dexamethasone (DEX) plus LEN than with DEX alone. Therapy with LEN/Thal also led to an increase in NKT cells in vivo in patients with myeloma and del5q myelodysplastic syndrome. Together these data demonstrate that LEN and its analogues enhance CD1d-mediated presentation of glycolipid antigens and support combining these agents with NKT targeted approaches for protection against tumors.

Introduction

The advent of biologic agents has brought about an accelerated growth in therapies available to clinicians for treatment of various dermatoses. Psoriasis is a good example of a disease in which our knowledge of its pathophysiology has increased dramatically with the introduction of therapeutics such as tumor necrosis factor (TNF) antagonists and agents that block T-cell interactions. Activated T cells and dendritic cells are important in the development and maintenance of psoriasis through the release of cytokines such as TNF, chemokines, proteases, and other inflammatory mediators. 1 Gottlieb A.B. Psoriasis: emerging therapeutic strategies. Nat Rev Drug Discov. 2005; 4: 19-34 Crossref PubMed Scopus (130) Google Scholar In a review on the pathophysiology of psoriasis, Gaspari discusses the innate and adaptive components of the immune response involved in this disease, as well as the emerging roles of defective regulatory T-cell suppressor function, natural killer T-cell response, and toll-like receptors.

Changes in natural killer T cells subsets during therapy in type C hepatitis and hepatocellular carcinoma

Natural killer T (NKT) cells share features of both classical T cells and NK cells. NKT are heterogenous populations, and recognize glycolipids associated with CD1d molecule. We investigated Th1/Th2 cytokine production as well as frequency and phenotype of circulating NKT cells in 14 healthy subjects and in patients during therapy with type C chronic hepatitis (CH; 14 cases) and hepatocellular carcinoma (HCC; 13 cases). Peripheral blood mononuclear cells (PBMC) were obtained before and 2 weeks later interferon (IFN)/ribavirin and radiofrequency ablation therapy for CH and HCC, respectively. PBMC were cultured for 10 days with alpha-galactosylceramide (alpha-GalCer) and interleukin-2 (IL-2). Frequencies and IFN-gamma/IL-4 production of NKT cells were analyzed using flow cytometry. Intrahepatic lymphocytes were analyzed in seven CH patients with liver biopsy specimen. Prevalence of circulating Valpha24+CD3+ T cells was 0.9+/-0.9% of PBMC for controls and increased to 8.5+/-8.9% (p<0.001) in response to alpha-GalCel. Similar frequency and expansion were noted in CH. The frequency increased during therapy. The prevalence in HCC tended to be high compared to controls and response to alpha-GalCel was well. Although frequency of Valpha24+Vbeta11+CD3+ T cells was low in all groups, the distribution pattern was similar to Valpha24+Vbeta11-CD3+ T cells. Prevalence of CD56+CD3+ T cells was low independent of therapy in CH (2-3%) compared to 5.0+/-4.0% of controls, although response to alpha-GalCel was not impaired. IFN-gamma production of Valpha24+CD3+ T cells did not differ among groups, but became greater after treatment in contrast to lowered IL-4 production. Frequencies of NKT populations were higher in liver than in peripheral blood. Our study suggests that CD1d-reactive T cells have distinct distribution in different populations and therapy for patients alters cytokine response of NKT cells.

Quantitative and qualitative differences in proatherogenic NKT cells in apolipoprotein E-deficient mice.

Atherosclerosis is a disease marked by lipid accumulation and inflammation. Recently, atherosclerosis has gained recognition as an autoimmune-type syndrome characterized by increased activation of the innate and acquired immune systems. Natural killer T (NKT) cells have characteristics of both conventional T cells and NK cells and recognize glycolipid antigens presented in association with CD1d molecules on antigen-presenting cells. The capacity of NKT cells to respond to lipid antigens and modulate innate and acquired immunity suggests that they may play a role in atherogenesis. We examined the role of NKT cells in atherogenesis and how the atherosclerotic environment affects the NKT cell population itself. The data show that CD1d-deficiency in male apolipoprotein E-deficient (apoE(0)) mice results in reduction in atherosclerosis, and treatment of apoE(0) mice with alpha-galactosylceramide, a potent and specific NKT cell activator, results in a 2-fold increase in atherosclerosis. Interestingly, we demonstrate that alpha-galactosylceramide-induced interferon-gamma responses and numbers of NKT cells in apoE(0) mice show age-dependent qualitative and quantitative differences as compared with age-matched wild-type mice. Collectively, these findings reveal that hyperlipidemia and atherosclerosis have significant effects on NKT cell responses and that these cells are proatherogenic.