Turned on by danger: activation of CD1d-restricted invariant natural killer T cells

CD1d-restricted invariant natural killer T (iNKT) cells bear characteristics of innate and adaptive lymphocytes, which allow them to bridge the two halves of the immune response and play roles in many disease settings. Recent work has characterized precisely how their activation is initiated and regulated. Novel antigens from important pathogens have been identified, as has an abundant self-antigen, β-glucopyranosylcaramide, capable of mediating an iNKT-cell response. Studies of the iNKT T-cell receptor (TCR)-antigen-CD1d complex show how docking between CD1d-antigen and iNKT TCR is highly conserved, and how small sequence differences in the TCR establish intrinsic variation in iNKT TCR affinity. The sequence of the TCR CDR3β loop determines iNKT TCR affinity for ligand-CD1d, independent of ligand identity. CD1d ligands can promote T helper type 1 (Th1) or Th2 biased cytokine responses, depending on the composition of their lipid tails. Ligands loaded into CD1d on the cell surface promote Th2 responses, whereas ligands with long hydrophobic tails are loaded endosomally and promote Th1 responses. This information is informing the design of synthetic iNKT-cell antigens. The iNKT cells may be activated by exogenous antigen, or by a combination of dendritic cell-derived interleukin-12 and iNKT TCR-self-antigen-CD1d engagement. The iNKT-cell activation is further modulated by recent foreign or self-antigen encounter. Activation of dendritic cells through pattern recognition receptors alters their antigen presentation and cytokine production, strongly influencing iNKT-cell activation. In a range of bacterial infections, dendritic cell-dependent innate activation of iNKT cells through interleukin-12 is the dominant influence on their activity.     

Acidification-dependent activation of CD1d-restricted natural killer T cells is intact in cystic fibrosis

CD1d‐restricted natural killer T (NKT) cells are emerging as critical regulators of the immune response to infectious agents, including Pseudomonas aeruginosa; and therapies to augment NKT‐cell activation may represent a novel approach to treat chronic, antibiotic‐resistant bacterial infections. We examined the capacity of dendritic cells (DCs) from people with cystic fibrosis (CF) to activate NKT cells. Our study was motivated by three lines of evidence: (i) NKT cells play a critical role in clearing P. aeruginosa infection; (ii) activation of NKT cells requires acidification‐dependent processing of glycolipid antigens within the endolysosomal compartment; and (iii) endolysosomal acidification may be reduced in CF. We demonstrated that NKT‐cell activation was dependent upon intact organelle acidification as inhibitors of the vacuolar (H⁺)‐ATPases prevented DCs from activating NKT cells with two glycolipid antigens, α‐galactosylceramide and galactose‐galactosylceramide. In contrast, cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel dysfunction had no significant biological impact on the capacity of DCs to activate NKT cells. Dendritic cells from subjects with CF and DCs treated with the thiazolidinone CFTR_inh‐172 inhibitor showed no reduction in their ability to activate NKT cells. Based on these data, we find no evidence for an inherent defect in glycolipid antigen presentation to NKT cells in CF subjects.     

Regulation of immune responses by CD1d-restricted natural killer T cells

Natural killer T (NKT) cells are a unique subset of T lymphocytes that share receptor structures and properties with conventional T lymphocytes and natural killer (NK) cells. NKT cells are specific for glycolipid antigens such as the marine sponge-derived agent α-galactosylceramide (α-GalCer) presented by the major histocompatibility complex (MHC) class I-like molcule CD1d. My laboratory has evaluated the function of NKT cells by generating and analyzing CD1d-deficient mice. These studies showed that CD1d expression is required for NKT cell development, but not absolutely necessary for the generation of polarized T helper (Th) cell responses. Further, we have studied the in vivo response of NKT cells toα-GalCer stimulation and the capacity of α-GalCer to modulate innate and adaptive immune responses. Our results revealed that, quickly following administration of α-GalCer, NKT cells expand and produce cytokines, trans-activate a variety of innate and adaptive immune cells, and promote Th2 responses that are capable of suppressing Th1-dominant autoimmunity. Our findings indicate that NKT cells play a regulatory role in the immune response and that specific activation of these cells may be exploited for therapeutic purposes.     

Lipid and glycolipid antigens of CD1d-restricted natural killer T cells

In spite of their relatively limited antigen receptor repertoire, CD1d-restricted NKT cells recognize a surprisingly diverse range of lipid and glycolipid antigens. Recent studies of natural and synthetic CD1d-presented antigens provide an increasingly detailed picture of how the specific structural features of these lipids and glycolipids influence their ability to be presented to NKT cells and stimulate their diverse immunologic functions. Particularly for synthetic analogues of α-galactosylceramides which have been the focus of intense recent investigation, it is becoming clear that the design of glycolipid antigens with the ability to precisely control the specific immunologic activities of NKT cells is likely to be feasible. The emerging details of the mechanisms underlying the structure–activity relationship of NKT cell antigens will assist greatly in the design and production of immunomodulatory agents for the precise manipulation of NKT cells and the many other components of the immune system that they influence.     

CD1d-restricted natural killer T cells are potent targets for human immunodeficiency virus infection

Invariant human natural killer T cells (NKT) express a restricted T-cell receptor (TCR) Valpha24Vbeta11 repertoire. These cells share both phenotypic and functional similarities between NK and T cells. Given the emerging role of NKT cells as critical cells in bridging the gap between innate and adaptive immunity, we examined their susceptibility to productive human immunodeficiency virus (HIV) infection by T-tropic, M-tropic, and primary isolates of HIV. We generated three human NKT cell clones (CA5, CA29, and CA31). Phenotypic characterization of these Valpha24+ Vbeta11+ clones indicated that they were predominately positive for CD4, CD161, HLA-DR, CD38, CD45RO, and CD95 expression. The NKT cell clones expressed significantly more surface CCR5 molecules/cell and lower CXCR4 molecules/cell than phytohaemagglutinin-stimulated peripheral blood mononuclear cells (PBMC). Consistent with the surface expression of CCR5 and CXCR4, the NKT clones were also selectively susceptible to HIV M-tropic, T-tropic, and primary isolate infection, as evaluated by both HIV p24 enzyme-linked immunosorbent assay and intracellular staining of HIV proteins. The amount of p24 production was dependent on the NKT clone studied and the HIV strain used. Clones CA29 and CA31 were also susceptible to HIV IIIB infection. The virions produced by these clones were able to productively infect PHA-stimulated PBMCs with the same kinetics as for primary infection of CD4+ blast. Collectively, this data demonstrates that NKT cells can be a target for productive HIV infection but with a lag in the time to peak p24 production.     

Role of regulatory invariant CD1d-restricted natural killer T-cells in protection against type 1 diabetes

Invariant CD1d-restricted natural killer T (iNKT) cells function during innate and adaptive immune responses. A functional and numerical deficiency of iNKT cells is well documented in both nonobese diabetic (NOD) mice and humans with autoimmune type 1 diabetes (T1D). Restoring the numerical and/or functional deficiency of iNKT cells in NOD mice by either treatment with α-galactosylceramide, transgenic induction of V α14-Jα18 expression, or transgenic expression of CD1d in NOD islets under the control of the human insulin promoter confers protection from T1D in these mice. Recently, considerable progress has been made in understanding the developmental and functional activities of iNKT cells. In this review, we discuss the role of iNKT cell deficiency and defective development in the onset of T1D in NOD mice and the different protective mechanisms known to restore these defects.     

Mechanism of CD1d-restricted natural killer T cell activation during microbial infection

CD1d-restricted natural killer T (NKT) cells are important for host defense against a variety of microbial pathogens. How and when these T cells become activated physiologically during infection remains unknown. Our data support a model in which NKT cells use a unique activation mechanism not requiring their recognition of microbial antigens. Instead, weak responses to CD1d-presented self antigens were amplified by interleukin 12 made by dendritic cells in response to microbial products, resulting in potent interferon-gamma secretion. NKT cells were among the first lymphocytes to respond during Salmonella typhimurium infection, and their activation in vivo also depended on interleukin 12 and CD1d recognition. We propose this mechanism of activation as a major pathway responsible for the rapid activation of NKT cells in different microbial infections.     

异基因骨髓源间充质干细胞对BXSB小鼠T、B细胞的影响

目的：探讨异基因骨髓源间充质干细胞（Bonemarrow derived mesenchymal stem cells，BMSCs）对BXSB小鼠T、B细胞增殖、活化及功能成熟等方面的影响。方法：采用。H．TdR掺入法、FACS法、EIJSA等方法检测BMSCs对BXSB小鼠T、B细胞的影响。结果：BALB／c小鼠的BMSCs在不影响BXSB小鼠T细胞诱导活化的基础上抑制其诱导增殖；可降低由ConA诱导的CD4^＋IL^＋细胞的数量，而提高由ConA诱导的CD4^＋IFN-γ^＋细胞数量。对于B细胞，BALB／c小鼠的BMSCs可以抑制其增殖、活化及IgG的分泌。另外，BALB／c小鼠的BMSCs可以抑制BXSB小鼠B细胞上CIMOL的异位表达。结论：异基因BMSCs对自身免疫病小鼠的T、B细胞有一定的调节作用。     

Development of CD1d-restricted NKT cells in the mouse thymus

Using genetic and phenotypic analyses, we have analyzed the developmental pathway of mouse CD1d-restricted invariant NKT cells. We provide strong evidence that similar to conventional T cells, positive selection of NKT cells occurs during a CD4(+)CD8(+) stage. Later stages of NKT cell development involved the down-regulation of both TCR and CD4 levels and therefore diverge from conventional T cell development pathways. A unique and complete dependency for development on Fyn, a Src family kinase member, also distinguishes the NKT cell and conventional T cell populations.     

Therapeutic potential of CD1d-restricted invariant natural killer T cell-based treatment for autoimmune diseases

CD1d-restricted invariant natural killer T (iNKT) cells are a unique subset of T cells that recognize glycolipid antigens presented by the CD1d molecule. iNKT cells participate in various kinds of immunoregulation due to a potent ability to produce a variety of cytokines. Recent advances in studies of novel synthetic glycolipid ligands has led to new strategies to manipulate the pleiotropic functions of iNKT cells. The molecular mechanism of selective cytokine production by glycolipid ligands will be discussed. We will also focus on the possible therapeutic application of such ligands for the clinical treatment of various autoimmune diseases.     

Molecular basis of lipid antigen presentation by CD1d and recognition by natural killer T cells

Together with peptides, T lymphocytes respond to hydrophobic molecules, mostly lipids, presented by the non-classical CD1 family (CD1a–e). These molecules have evolved complex and diverse binding grooves in order to survey different cellular compartments for self and exogenous antigens, which are then presented for recognition to T-cell receptors (TCRs) on the surface of T cells. In particular, most CD1d-presented antigens are recognized by a population of lymphocytes denominated natural killer T (NKT) cells, characterized by a strong immunomodulatory potential. Among NKT cells, two major subsets (type I and type II NKT cells) have been described, based on their TCR repertoire and antigen specificity. Here we review recent structural and biochemical studies that have shed light on the molecular details of CD1d-mediated antigen recognition by type I and II NKT cells, which are in many aspects distinct from what has been observed for peptide major histocompatibility complex-reactive TCRs.     

The immunosuppressive tumour network: myeloid‐derived suppressor cells,regulatory T cells and natural killer T cells

Myeloid‐derived suppressor cells (MDSC) and regulatory T (Treg) cells are major components of the immune suppressive tumour microenvironment (TME). Both cell types expand systematically in preclinical tumour models and promote T‐cell dysfunction that in turn favours tumour progression. Clinical reports show a positive correlation between elevated levels of both suppressors and tumour burden. Recent studies further revealed that MDSCs can modulate the de novo development and induction of Treg cells. The overlapping target cell population of Treg cells and MDSCs is indicative for the importance and flexibility of immune suppression under pathological conditions. It also suggests the existence of common pathways that can be used for clinical interventions aiming to manipulate the TME. Elimination or reprogramming of the immune suppressive TME is one of the major current challenges in immunotherapy of cancer. Interestingly, recent findings suggest that natural killer T (NKT) cells can acquire the ability to convert immunosuppressive MDSCs into immunity‐promoting antigen‐presenting cells. Here we will review the cross‐talk between MDSCs and other immune cells, focusing on Treg cells and NKT cells. We will consider its impact on basic and applied cancer research and discuss how targeting MDSCs may pave the way for future immunocombination therapies.     

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.     

Critical proinflammatory and anti-inflammatory functions of different subsets of CD1d-restricted natural killer T cells during Trypanosoma cruzi infection

Trypanosoma cruzi infects 15 to 20 million people in Latin America and causes Chagas disease, a chronic inflammatory disease with fatal cardiac and gastrointestinal sequelae. How the immune response causes Chagas disease is not clear, but during the persistent infection both proinflammatory and anti-inflammatory responses are critical. Natural killer T (NKT) cells have been shown to regulate immune responses during infections and autoimmune diseases. We report here that during acute T. cruzi infection NKT-cell subsets provide distinct functions. CD1d(-/-) mice, which lack both invariant NKT (iNKT) cells and variant NKT (vNKT) cells, develop a mild phenotype displaying an increase in spleen and liver mononuclear cells, anti-T. cruzi antibody response, and muscle inflammation. In contrast, Jalpha18(-/-) mice, which lack iNKT cells but have vNKT cells, develop a robust phenotype involving prominent spleen, liver, and skeletal muscle inflammatory infiltrates comprised of NK, dendritic, B and T cells. The inflammatory cells display activation markers; produce more gamma interferon, tumor necrosis factor alpha, and nitric oxide; and show a diminished antibody response. Strikingly, most Jalpha18(-/-) mice die. Thus, in response to the same infection, vNKT cells appear to augment a robust proinflammatory response, whereas the iNKT cells dampen this response, possibly by regulating vNKT cells.     

Low-dose cyclophosphamide combined with IL-2 inhibits tumor growth by decreasing regulatory T cells and increasing CD8+ T cells and natural killer cells in mice

Interleukin-2 (IL-2) benefits some cancer patients by promoting the proliferation of cytotoxic effector T cells, but this process is limited by the expansion of regulatory T cells (Tregs). Low-dose cyclophosphamide (CTX) can inhibit the number and function of Tregs. We treated carcinoma-bearing mice with Vehicle, CTX, IL-2 and CTX + IL-2 to investigate the effects of low-dose CTX combined with IL-2 in antitumor treatment. In comparison to monotherapy, CTX + IL-2 significantly limited tumor growth, via tumor cell proliferation inhibition and increased apoptosis. The infiltration of CD8⁺ T cells in tumor tissues was significantly increased in the CTX + IL-2 group. CTX + IL-2 safely increased CD8⁺ T and natural killer cells in the spleen, lymph nodes and peripheral blood, and CTX attenuated the increase in Tregs induced by IL-2 in the spleen.     

Co-inhibitory roles for glucocorticoid-induced TNF receptor in CD1d-dependent natural killer T cells

Invariant natural killer T (iNKT) cells are a special subset of alphabeta T cells with invariant TCR, which recognize alpha-galactosylceramide (alpha-GalCer) presented by CD1d. In addition to signals through the invariant TCR upon stimulation with alpha-GalCer, costimulatory signals, such as signals through CD28 and OX40, are indispensable for full activation of iNKT cells. In this study, we investigated the functions of a well-known costimulatory molecule, glucocorticoid-induced TNF receptor (GITR), on Ag-induced iNKT cell activation. Unexpectedly, engagement of GITR by agonistic mAb DTA-1 suppressed proliferation and cytokine production of iNKT cells upon alpha-GalCer stimulation. In addition, GITR signals in iNKT cells during only the Ag-priming phase was sufficient to inhibit the iNKT cell activation. Consistent with these results, the GITR-deficient iNKT cells showed enhanced proliferation and increased cytokine production upon alpha-GalCer stimulation both in vitro and in vivo. Furthermore, the in vivo administration of alpha-GalCer suppressed tumor metastasis more efficiently in GITR-deficient mice than in wild-type mice. Collectively, GITR plays a co-inhibitory role in Ag-induced iNKT cell activation.     

A role for CD1d-restricted NKT cells in injury-associated T cell suppression

Natural killer T (NKT) cells are known to modulate T cell responses during autoimmunity, tolerance, and antitumor immunity; however, their potential role in regulating the immune response to injury has not been reported. Using a murine model of burn injury, we investigated whether CD1d-restricted NKT cells played a role in the T cell suppression that occurs early after injury. A functional role for CD1d stimulation of NKT cells in the injury-related immune suppression was demonstrated by experiments in which the suppression of antigen (Ag)-specific delayed-type hypersensitivity and in vitro T cell-proliferative responses were prevented if mice were given anti-CD1d monoclonal antibody (mAb) systemically just before injury. The CD1d-NKT cell-dependent suppression of the T cell response after injury occurred in the absence of quantitative changes in NKT cells themselves or CD1d(+) Ag-presenting cells. We observed that elevated production of the immunosuppressive cytokine interleukin (IL)-4 correlated with burn-induced immune dysfunction, and we found that NKT cells but not conventional T cells were the source of IL-4 early after injury. Lastly, we observed that the injury-induced production of NKT cell-derived IL-4 could be blocked by systemic treatment of burn-injured mice with anti-CD1d mAb. Together, our results reveal a novel mechanism involving CD1d stimulation of NKT cells in the onset of T cell suppression that occurs subsequent to injury.     

Diverse CD1d-restricted T cells: diverse phenotypes, and diverse functions

Invariant CD1d-restricted T cells express NK cell markers and use a limited TCR repertoire. Here, we describe a second CD1d-restricted T cell subset that uses a diverse TCR repertoire. These T cells can also express NK cell markers and function similarly to invariant T cells. The antigens recognized by the diverse subset are likely to be different from those recognized by invariant TCRs. The variable NK1.1 antigen expression on these T cell populations limits its usefulness in identifying CD1d-restricted T cells. Lastly, the discovery of antigens recognized by diverse CD1d-restricted T cells will provide insight into their role in normal and pathological immune responses.     

多发性骨髓瘤患者骨髓间充质干细胞免疫调节功能异常及其在骨髓瘤骨病中的作用

目的 探讨多发性骨髓瘤(MM)患者骨髓间充质干细胞(MSCs)免疫调节功能及其对骨髓瘤骨病的影响.方法 分离MM患者和正常对照MSCs,流式细胞技术比较二者的免疫表型.Real-time PCR检测实验组及对照组MSCs的TGF-β1、TGF-β2、TGF-β3、IL-6、IL-3、TNF-α、FasL和NF-κB配体的受体激活物(RANKL)表达量.共培养系统与流式细胞术检测MSCs对T细胞增殖、凋亡和早期活化标志CD25和CD69表达的影响.Von kossa染色、real-time PCR和Western blot等技术检测T细胞对正常对照MSCs向成骨细胞分化的影响.结果 MM来源和正常对照MSCs具有相似的形态学和免疫表型.MM来源的MSCs表达TGF-β1、IL-6、IL-3、TNF-α和RANKL较正常对照MSCs增加,而TGF-β2、TGF-β3和FasL的表达下降.MM来源的MSCs对T细胞增殖的抑制作用明显减弱.正常对照MSCs较MM来源MSCs使更多T细胞静止于G0/G1期.正常对照MSCs明显促进T细胞凋亡,而MM来源的MSCs对T细胞的促凋亡作用减弱.正常对照MSCs明显抑制T细胞活化分子表达,而MM患者的MSCs此抑制作用明显降低.与MM患者的MSCs共培养后的T细胞以及直接来源于MM患者的T细胞均可以明显抑制正常对照MSCs向成骨细胞分化.结论 MM患者的MSCs免疫调节功能较正常对照MSCs降低,主要表现为抑制T细胞活化的功能减弱,而活化的T细胞可抑制MSCs向成骨细胞分化,此可能为骨髓瘤骨病发病机制之一.     

Molecular profiling reveals distinct functional attributes of CD1d-restricted natural killer (NK) T cell subsets

CD1d-restricted natural killer T (NKT) cells can have multiple effects on an immune response, including the activation, regulation and attraction of innate immune cells, and modulation of adaptive immunity. Recent studies reveal that there are distinct subsets of NKT cells which selectively perform some of the functions attributed to CD1d-restricted cells, but the mechanisms underlying these functional differences have not been resolved. Our aim in this study was to identify novel NKT cell associated traits that would provide important insight into NKT cell activation and function. To this end, we have performed gene expression profiling of two separate subsets of NKT cells, analyzing genes differentially expressed in these cells compared to conventional CD4(+)NK1.1(-) T cells. We identify different sets of genes over expressed in each of the two NKT cell types, as well as genes that are common to the two CD1d-restricted NKT cell populations analyzed. A large number of these genes are highly relevant for NKT cell development, activation and function. Each NKT subtype displayed a unique set of chemokine receptors, integrins and molecules related to effector function, supporting the notion that distinct NKT cells can be selectively engaged and have diverse functions in different types of immune reactions.