CD1d-specific NK1.1+ T cells with a transgenic variant TCR

CD1-mediated immune responses in mucosal tissues: molecular mechanisms underlying lipid antigen presentation system

The cluster of differentiation 1 (CD1) molecule differs from major histocompatibility complex class I and II because it presents glycolipid/lipid antigens. Moreover, the CD1-restricted T cells that recognize these self and foreign antigens participate in both innate and adaptive immune responses. CD1s are constitutively expressed by professional and nonprofessional antigen-presenting cells in mucosal tissues, namely, the skin, lung, and intestine. This suggests that CD1-reactive T cells are involved in the immune responses of these tissues. Indeed, evidence suggests that these cells play important roles in diverse diseases, such as inflammation, autoimmune disease, and infection. Recent studies elucidating the molecular mechanisms by which CD1 presents lipid antigens suggest that defects in these mechanisms could contribute to the activities of CD1-reactive T cells. Thus, improving our understanding of these mechanisms could lead to new and effective therapeutic approaches to CD1-associated diseases. In this review, we discuss the CD1-mediated antigen presentation system and its roles in mucosal tissue immunity.

Natural Killer T cells and the invariant subset promote atherosclerosis: A meta-analysis

AIMS

Natural Killer T (NKT) cells are reported to be both pro- and anti-atherosclerotic. With this meta-analysis, we evaluated the NKT population and their subsets in regulating the atherosclerotic disease in mice.

MAIN METHODS

Eighteen pre-clinical (mice, n = 1276) and 6 clinical observational studies (humans, n = 116) met the eligibility criteria for inclusion. Random effects model was used and standard mean difference (SMD) was calculated for the cell counts and aortic lesion area.

KEY FINDINGS

Lesion area decreased in the absence of whole NKT cell population (-1.33[95%CI, -2.14, -0.52]), and in the absence of only iNKT subset (-0.66[95%CI, -1.69, 0.37]). However, lesion area increased after over-expression/activation of iNKTs (1.40[95%CI, 0.28, 2.52]). Atherogenic diet (AD) or high fat diet (HFD) increased the number of NKT cells (2.51[95%CI, 1.42, 3.61]), whereas the iNKT cell numbers and iNKT cell-specific gene expression decreased in mice (-2.04[95%CI, -3.34, -0.75]) and atherosclerotic patients (-1.81[95 % CI, -2.89, -0.74]).

SIGNIFICANCE

Here we show that, NKT and iNKT cells promote atherosclerosis. In general, NKT cell population increases with the progression of the plaque in mice and the numbers of iNKT cells reduce once the disease is established both in mice and humans.

Type II Natural Killer T Cells Contribute to Protection Against Systemic Methicillin-Resistant Staphylococcus aureus Infection

Methicillin-resistant Staphylococcus aureus (SA) bacteremia is responsible for over 10,000 deaths in the hospital setting each year. Both conventional CD4⁺ T cells and γδ T cells play protective roles in SA infection through secretion of IFN-γ and IL-17. However, the role of other unconventional T cells in SA infection is largely unknown. Natural killer T (NKT) cells, a subset of innate-like T cells, are activated rapidly in response to a wide range of self and microbial lipid antigens presented by MHC I-like molecule CD1d. NKT cells are divided into two groups, invariant NKT (iNKT) and type II NKT cells, based on TCR usage. Using mice lacking either iNKT cells or both types of NKT cells, we show that both NKT cell subsets are activated after systemic SA infection and produce IFN-γ in response to SA antigen, however type II NKT cells are sufficient to control bacterial burden and inflammatory infiltrate in infected organs. This protective capacity was specific for NKT cells, as mice lacking mucosal associated invariant T (MAIT) cells, another innate-like T cell subset, had no increased susceptibility to SA systemic infection. We identify polar lipid species from SA that induce IFN-γ production from type II NKT cells, which requires both CD1d-TCR engagement and IL-12 production by antigen presenting cells. We also demonstrate that a population of T cells enriched for type II NKT cells are increased in PBMC of SA bacteremic patients compared to healthy controls. Therefore, type II NKT cells perform effector functions that enhance control of SA infection prior to conventional T cell activation and recognize SA-derived lipid antigens. As CD1d is highly conserved in humans, these CD1d-restricted SA lipid antigens could be used in the design of next generation SA vaccines targeting cell-mediated immunity.

Complementary approaches to study NKT cells in cancer

NKT cells are a small but influential member of the T cell family, recognizing lipids presented by the non-classical MHC-like molecule CD1d rather than peptides presented by classical MHC molecules. They bridge between the innate and adaptive immune systems, serving as rapid responders but also allowing the T cell immune system to recognize lipid antigens, for example derived from tumors or bacteria. They also serve as potent regulatory cells, controlling other immune responses. Type I NKT cells use a semi-invariant T cell receptor (TCR) whereas type II use diverse TCRs. Most often, type I NKT cells promote tumor immunity whereas type II tend to suppress it, and the two subtypes crossregulate each other, forming an immunoregulatory axis. Lack of tools to study these important cells has limited the understanding of these, but newer tools have allowed great advances, especially in mouse models. These range from transgenic and knock-out mice to CD1d tetramers carrying ligands for type I or II NKT cells, to antibodies and NKT cell hybridomas. Here we describe these complementary tools and approaches and their use to study NKT cells and their role in the immunology and immunotherapy of cancer.

Defining a novel subset of CD1d-dependent type II natural killer T cells using natural killer cell-associated markers

Natural killer T (NKT) cells are αβ T cell receptor (TCR) expressing innate‐like T cells that display natural killer (NK) cell markers. Based on TCR characteristics, they are divided into two groups restricted to the MHC class I‐like molecule CD1d. Type I NKT cells, most extensively studied, are identified by a semi‐invariant Vα14‐Jα18 (mouse, Vα24‐Jα18 in humans) TCR reactive to the prototypic ligand α‐galactosylceramide presented on CD1d. In contrast, type II NKT cells display diverse TCR reacting to different CD1d‐presented ligands. There are no reagents that identify all type II NKT cells, limiting their exploration. Here, we searched for novel type II NKT cells by comparing Jα18^−/−MHCII^−/− mice that harbour type II but not type I NKT cells, and CD1d^−/−MHCII^−/− mice, lacking all NKT cells. We identified significantly larger populations of CD4⁺ and CD4⁻CD8⁻ (double negative, DN) TCRβ⁺ cells expressing NKG2D or NKG2A/C/E in Jα18^−/−MHCII^−/− mice compared with CD1d^−/−MHCII^−/− mice, suggesting that 30%‐50% of these cells were type II NKT cells. They expressed CD122, NK1.1, CXCR3 and intermediate/low levels of CD45RB. Further, the CD4⁺ subset was CD69⁺, while the DN cells were CD49b⁺ and CD62L⁺. Both subsets expressed the NKT cell‐associated promyelocytic leukaemia zinc finger (PLZF) transcription factor and Tbet, while fewer cells expressed RORγt. NKG2D⁺ CD4⁺ and DN populations were producers of IFN‐γ, but rarely IL‐4 and IL‐17. Taken together, we identify a novel subset of primary CD4⁺ and DN type II NKT cells that expresses NKG2 receptors have typical NKT cell phenotypes and a TH1‐like cytokine production.

Innate and adaptive stimulation of murine diverse NKT cells result in distinct cellular responses

Natural killer T (NKT) cells recognize glycolipids presented on CD1d. They share features of adaptive T lymphocytes and innate NK cells, and mediate immunoregulatory functions via rapid production of cytokines. Invariant (iNKT) and diverse (dNKT) NKT cell subsets are defined by their TCR. The immunological role of dNKT cells, that do not express the invariant TCRα‐chain used by iNKT cells, is less well explored than that of iNKT cells. Here, we investigated signals driving Toll‐like receptor (TLR) ligand activation of TCR‐transgenic murine dNKT cells. IFN‐γ production by dNKT cells required dendritic cells (DC), cell‐to‐cell contact and presence of TLR ligands. TLR‐stimulated DC activated dNKT cells to secrete IFN‐γ in a CD1d‐, CD80/86‐ and type I IFN‐independent manner. In contrast, a requirement for IL‐12p40, and a TLR ligand‐selective dependence on IL‐18 or IL‐15 was observed. TLR ligand/DC stimulation provoked early secretion of pro‐inflammatory cytokines by both CD62L⁺ and CD62L⁻ dNKT cells. However, proliferation was limited. In contrast, TCR/co‐receptor‐mediated activation resulted in proliferation and delayed production of a broader cytokine spectrum preferentially in CD62L⁻ dNKT cells. Thus, innate (TLR ligand/DC) and adaptive (TCR/co‐receptor) stimulation of dNKT cells resulted in distinct cellular responses that may contribute differently to the formation of immune memory.

Natural killer T cells and ulcerative colitis

Ulcerative colitis (UC) is one of the two major forms of inflammatory bowel disease (IBD). Both innate immunity and adaptive immunity are aberrant in IBD. The pathogenesis of UC includes abnormal inflammation and immune responses of the digestive tract. Natural killer T (NKT) cells participate in the innate and adaptive immune responses, together with a vast array of cytokines. Recent studies suggested that IL-13, IL5 and IL-4 are involved in the occurrence and the development of UC. Manipulating NKT cells may be a potential strategy to reconstruct the abnormal immune responses in UC. In this review, we explore the roles of NKT cells and cytokines in UC. Additionally, neutralizing antibodies and inhibitors of cytokines produced by NKT cells or their receptors are also discussed as novel therapeutic choices for UC.

Tissue-Specific Roles of NKT Cells in Tumor Immunity

NKT cells are an unusual population of T cells recognizing lipids presented by CD1d, a non-classical class-I-like molecule, rather than peptides presented by conventional MHC molecules. Type I NKT cells use a semi-invariant T cell receptor and almost all recognize a common prototype lipid, α-galactosylceramide (α-GalCer). Type II NKT cells are any lipid-specific CD1d-restricted T cells that use other receptors and generally don't recognize α-GalCer. They play important regulatory roles in immunity, including tumor immunity. In contrast to type I NKT cells that most have found to promote antitumor immunity, type II NKT cells suppress tumor immunity and the two subsets cross-regulate each other, forming an immunoregulatory axis. They also can promote other regulatory cells including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), and can induce MDSCs to secrete TGF-β, one of the most immunosuppressive cytokines known. In some tumors, both Tregs and type II NKT cells can suppress immunosurveillance, and the balance between these is determined by a type I NKT cell. We have also seen that regulation of tumor immunity can depend on the tissue microenvironment, so the same tumor in the same animal in different tissues may be regulated by different cells, such as type II NKT cells in the lung vs Tregs in the skin. Also, the effector T cells that protect those sites when Tregs are removed do not always act between tissues even in the same animal. Thus, metastases may require different immunotherapy from primary tumors. Newly improved sulfatide-CD1d tetramers are starting to allow better characterization of the elusive type II NKT cells to better understand their function and control it to overcome immunosuppression.

Invariant Natural Killer T and Mucosal-Associated Invariant T Cells in Asthmatic Patients

Recent studies have highlighted the heterogeneity of asthma. Distinct patient phenotypes (symptoms, age at onset, atopy, and lung function) may result from different pathogenic mechanisms, including airway inflammation, remodeling, and immune and metabolic pathways in a specific microbial environment. These features, which define the asthma endotype, may have significant consequences for the development and progression of the disease. Asthma is generally associated with Th2 cells, which produce a panel of cytokines (IL-4, IL-5, IL-13) that act in synergy to drive lung inflammatory responses, mucus secretion, IgE production, and fibrosis, causing the characteristic symptoms of asthma. In addition to conventional CD4⁺ T lymphocytes, other T-cell types can produce Th2 or Th17 cytokines rapidly. Promising candidate cells for studies of the mechanisms underlying the pathophysiology of asthma are unconventional T lymphocytes, such as invariant natural killer T (iNKT) and mucosal-associated invariant T (MAIT) cells. This review provides an overview of our current understanding of the impact of iNKT and MAIT cells on asthmatic inflammation, focusing particularly on pediatric asthma.

CD1d-Restricted Type II NKT Cells Reactive With Endogenous Hydrophobic Peptides

NKT cells belong to a distinct subset of T cells that recognize hydrophobic antigens presented by major histocompatibility complex class I-like molecules, such as CD1d. Because NKT cells stimulated by antigens can activate or suppress other immunocompetent cells through an immediate production of a large amount of cytokines, they are regarded as immunological modulators. CD1d-restricted NKT cells are classified into two subsets, namely, type I and type II. CD1d-restricted type I NKT cells express invariant T cell receptors (TCRs) and react with lipid antigens, including the marine sponge-derived glycolipid α-galactosylceramide. On the contrary, CD1d-restricted type II NKT cells recognize a wide variety of antigens, including glycolipids, phospholipids, and hydrophobic peptides, by their diverse TCRs. In this review, we focus particularly on CD1d-restricted type II NKT cells that recognize endogenous hydrophobic peptides presented by CD1d. Previous studies have demonstrated that CD1d-restricted type I NKT cells usually act as pro-inflammatory cells but sometimes behave as anti-inflammatory cells. It has been also demonstrated that CD1d-restricted type II NKT cells play opposite roles to CD1d-restricted type I NKT cells; thus, they function as anti-inflammatory or pro-inflammatory cells depending on the situation. In line with this, CD1d-restricted type II NKT cells that recognize type II collagen peptide have been demonstrated to act as anti-inflammatory cells in diverse inflammation-induction models in mice, whereas pro-inflammatory CD1d-restricted type II NKT cells reactive with sterol carrier protein 2 peptide have been demonstrated to be involved in the development of small vessel vasculitis in rats.

Possible Therapeutic Application of Targeting Type II Natural Killer T Cell-Mediated Suppression of Tumor Immunity

Natural killer T (NKT) cells are a unique T cell subset that exhibits characteristics from both the innate immune cells and T cells. There are at least two subsets of NKT cells, type I and type II. These two subsets of NKT cells have opposite functions in antitumor immunity. Type I NKT cells usually enhance and type II NKT cells suppress antitumor immunity. In addition, these two subsets of NKT cells cross-regulate each other. In this review, we mainly focus on immunosuppressive NKT cells, type II NKT cells. After summarizing their definition, experimental tools to study them, and subsets of them, we will discuss possible therapeutic applications of type II NKT cell pathway targeted therapies.

The Yin and Yang of Invariant Natural Killer T Cells in Tumor Immunity-Suppression of Tumor Immunity in the Intestine

CD1d-restricted invariant natural killer T (iNKT) cells are known as early responding, potent regulatory cells of immune responses. Besides their established role in the regulation of inflammation and autoimmune disease, numerous studies have shown that iNKT cells have important functions in tumor immunosurveillance and control of tumor metastasis. Tumor-infiltrating T helper 1 (TH1)/cytotoxic T lymphocytes have been associated with a positive prognosis. However, inflammation has a dual role in cancer and chronic inflammation is believed to be a driving force in many cancers as exemplified in patients with inflammatory bowel disease that have an increased risk of colorectal cancer. Indeed, NKT cells promote intestinal inflammation in human ulcerative colitis, and the associated animal model, indicating that NKT cells may favor tumor development in intestinal tissue. In contrast to other cancers, recent data from animal models suggest that iNKT cells promote tumor formation in the intestine by supporting an immunoregulatory tumor microenvironment and suppressing TH1 antitumor immunity. Here, we review the role of iNKT cells in suppression of tumor immunity in light of iNKT-cell regulation of intestinal inflammation. We also discuss suppression of immunity in other situations as well as factors that may influence whether iNKT cells have a protective or an immunosuppressive and tumor-promoting role in tumor immunity.

Crosstalk between type II NKT cells and T cells leads to spontaneous chronic inflammatory liver disease

BACKGROUND & AIM

Natural killer T (NKT) cells are CD1d-restricted innate-like T cells that modulate innate and adaptive immune responses. Unlike the well-characterized invariant/type I NKT cells, type II NKT cells with a diverse T cell receptor repertoire are poorly understood. This study defines the pathogenic role of type II NKT cells in the etiology of chronic liver inflammation.

METHODS

Transgenic mice with the Lck promoter directing CD1d overexpression on T cells in Jα18 wild-type (Lck-CD1dTgJα18⁺; type I NKT cell sufficient) and Jα18-deficient (Lck-CD1dTgJα18^o, type I NKT cell deficient) mice were analyzed for liver pathology and crosstalk between type II NKT cells and conventional T cells. CD1d expression on T cells in peripheral blood samples and liver sections from autoimmune hepatitis patients and healthy individuals were also examined.

RESULTS

Lck-CD1dTgJα18^o and Lck-CD1dTgJα18⁺ mice developed similar degrees of liver pathology resembling chronic autoimmune hepatitis in humans. Increased CD1d expression on T cells promoted the activation of type II NKT cells and other T cells. This resulted in T_h1-skewing and impaired T_h2 cytokine production in type II NKT cells. Dysfunction of type II NKT cells was accompanied by conventional T cell activation and pro-inflammatory cytokine production, leading to a hepatic T/B lymphocyte infiltration, elevated autoantibodies and hepatic injury in Lck-CD1dTg mice. A similar mechanism could be extended to humans as CD1d expression is upregulated on activated human T cells and increased presence of CD1d-expressing T cells was observed in autoimmune hepatitis patients.

CONCLUSIONS

Our data reveals enhanced crosstalk between type II NKT cells and conventional T cells, leading to a T_h1-skewed inflammatory milieu, and consequently, to the development of chronic autoimmune liver disease. Lay summary: CD1d overexpression on T cells enhances crosstalk between type II NKT cells and T cells, resulting in their aberrant activation and leading to the development of chronic autoimmune liver disease.

T-Cell-Specific Deletion of Map3k1 Reveals the Critical Role for Mekk1 and Jnks in Cdkn1b-Dependent Proliferative Expansion

MAPK signaling is important for T lymphocyte development, homeostasis, and effector responses. To better understand the role of Mekk1 (encoded by Map3k1) in T cells, we conditionally deleted Map3k1 in Lck^Cre/+Map3k1^f/f mice, and these display larger iNKT cell populations within the liver, spleen, and bone marrow. Mekk1 signaling controls splenic and liver iNKT cell expansion in response to glycolipid antigen. Lck^Cre/+Map3k1^f/f mice have enhanced liver damage in response to glycolipid antigen. Mekk1 regulates Jnk activation in iNKT cells and binds and transfers Lys63-linked poly-ubiquitin onto Carma1. Map3k1 is critical for the regulation of p27^Kip1 (encoded by Cdkn1b).

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iNKT cell expansion is aberrant in Lck^Cre/+Map3k1^f/f mice

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Lck^Cre/+Map3k1^f/f mice have enhanced liver damage in response to glycolipids

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Mekk1 regulates TCR-dependent Jnk activation

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Mekk1 regulates p27^Kip1 expression to regulate proliferation

The Extended Family of CD1d-Restricted NKT Cells: Sifting through a Mixed Bag of TCRs, Antigens, and Functions

Natural killer T (NKT) cells comprise a family of specialized T cells that recognize lipid antigens presented by CD1d. Based on their T cell receptor (TCR) usage and antigen specificities, CD1d-restricted NKT cells have been divided into two main subsets: type I NKT cells that use a canonical invariant TCR α-chain and recognize α-galactosylceramide (α-GalCer), and type II NKT cells that use a more diverse αβ TCR repertoire and do not recognize α-GalCer. In addition, α-GalCer-reactive NKT cells that use non-canonical αβ TCRs and CD1d-restricted T cells that use γδ or δ/αβ TCRs have recently been identified, revealing further diversity among CD1d-restricted T cells. Importantly, in addition to their distinct antigen specificities, functional differences are beginning to emerge between the different members of the CD1d-restricted T cell family. In this review, while using type I NKT cells as comparison, we will focus on type II NKT cells and the other non-invariant CD1d-restricted T cell subsets, and discuss our current understanding of the antigens they recognize, the formation of stimulatory CD1d/antigen complexes, the modes of TCR-mediated antigen recognition, and the mechanisms and consequences of their activation that underlie their function in antimicrobial responses, anti-tumor immunity, and autoimmunity.

Natural killer T cells in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic inflammatory disease that causes demyelination of neurons in the central nervous system. Traditional therapies for MS have involved anti-inflammatory and immunosuppressive drugs with significant side effects that often only provide short-term relief. A more desirable outcome of immunotherapy would be to protect against disease before its clinical manifestation or to halt disease after its initiation. One attractive approach to accomplish this goal would be to restore tolerance by targeting immunoregulatory cell networks. Although much of the work in this area has focused on CD4(+) Foxp3(+) regulatory T cells, other studies have investigated natural killer T (NKT) cells, a subset of T cells that recognizes glycolipid antigens in the context of the CD1d glycoprotein. Studies with human MS patients have revealed alterations in the numbers and functions of NKT cells, which have been partially supported by studies with the experimental autoimmune encephalomyelitis model of MS. Additional studies have shown that activation of NKT cells with synthetic lipid antigens can, at least under certain experimental conditions, protect mice against the development of MS-like disease. Although mechanisms of this protection remain to be fully investigated, current evidence suggests that it involves interactions with other immunoregulatory cell types such as regulatory T cells and immunosuppressive myeloid cells. These studies have provided a strong foundation for the rational design of NKT-cell-based immunotherapies for MS that induce tolerance while sparing overall immune function. Nevertheless, additional pre-clinical and clinical studies will be required to bring this goal to fruition.

NKT cell networks in the regulation of tumor immunity

CD1d-restricted natural killer T (NKT) cells lie at the interface between the innate and adaptive immune systems and are important mediators of immune responses and tumor immunosurveillance. These NKT cells uniquely recognize lipid antigens, and their rapid yet specific reactions influence both innate and adaptive immunity. In tumor immunity, two NKT subsets (type I and type II) have contrasting roles in which they not only cross-regulate one another, but also impact innate immune cell populations, including natural killer, dendritic, and myeloid lineage cells, as well as adaptive populations, especially CD8⁺ and CD4⁺ T cells. The extent to which NKT cells promote or suppress surrounding cells affects the host’s ability to prevent neoplasia and is consequently of great interest for therapeutic development. Data have shown the potential for therapeutic use of NKT cell agonists and synergy with immune response modifiers in both pre-clinical studies and preliminary clinical studies. However, there is room to improve treatment efficacy by further elucidating the biological mechanisms underlying NKT cell networks. Here, we discuss the progress made in understanding NKT cell networks, their consequent role in the regulation of tumor immunity, and the potential to exploit that knowledge in a clinical setting.

The adaptor protein SAP regulates type II NKT-cell development, cytokine production, and cytotoxicity against lymphoma

CD1d-restricted NKT cells represent a unique lineage of immunoregulatory T cells that are divided into two groups, type I and type II, based on their TCR usage. Because there are no specific tools to identify type II NKT cells, little is known about their developmental requirements and functional regulation. In our previous study, we showed that signaling lymphocytic activation molecule associated protein (SAP) is essential for the development of type II NKT cells. Here, using a type II NKT-cell TCR transgenic mouse model, we demonstrated that CD1d-expressing hematopoietic cells, but not thymic epithelial cells, meditate efficient selection of type II NKT cells. Furthermore, we showed that SAP regulates type II NKT-cell development by controlling early growth response 2 protein and promyelocytic leukemia zinc finger expression. SAP-deficient 24αβ transgenic T cells (24αβ T cells) exhibited an immature phenotype with reduced Th2 cytokine-producing capacity and diminished cytotoxicity to CD1d-expressing lymphoma cells. The impaired IL-4 production by SAP-deficient 24αβ T cells was associated with reduced IFN regulatory factor 4 and GATA-3 induction following TCR stimulation. Collectively, these data suggest that SAP is critical for regulating type II NKT cell responses. Aberrant responses of these T cells may contribute to the immune dysregulation observed in X-linked lymphoproliferative disease caused by mutations in SAP.

Polyclonal type II natural killer T cells require PLZF and SAP for their development and contribute to CpG-mediated antitumor response

CD1d-restricted natural killer T (NKT) cells are innate-like T cells with potent immunomodulatory function via rapid production of both Th1 and Th2 cytokines. NKT cells comprise well-characterized type I NKT cells, which can be detected by α-galactosylceramide-loaded CD1d tetramers, and less-studied type II NKT cells, which do not recognize α-galactosylceramide. Here we characterized type II NKT cells on a polyclonal level by using a Jα18-deficient IL-4 reporter mouse model. This model allows us to track type II NTK cells by the GFP(+)TCRβ(+) phenotype in the thymus and liver. We found type II NKT cells, like type I NKT cells, exhibit an activated phenotype and are dependent on the transcriptional regulator promyelocytic leukemia zinc finger (PLZF) and the adaptor molecule signaling lymphocyte activation molecule-associated protein (SAP) for their development. Type II NKT cells are potently activated by β-D-glucopyranosylceramide (β-GlcCer) but not sulfatide or phospholipids in a CD1d-dependent manner, with the stimulatory capacity of β-GlcCer influenced by acyl chain length. Compared with type I NKT cells, type II NKT cells produce lower levels of IFN-γ but comparable amounts of IL-13 in response to polyclonal T-cell receptor stimulation, suggesting they may play different roles in regulating immune responses. Furthermore, type II NKT cells can be activated by CpG oligodeoxynucletides to produce IFN-γ, but not IL-4 or IL-13. Importantly, CpG-activated type II NKT cells contribute to the antitumor effect of CpG in the B16 melanoma model. Taken together, our data reveal the characteristics of polyclonal type II NKT cells and their potential role in antitumor immunotherapy.

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

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

The preventive role of type 2 NKT cells in the development of type 1 diabetes

In the last two decades, natural killer T (NKT) cells have emerged as an important factor in preventing type 1 diabetes (T1D) when investigated in the experimental non-obese diabetic (NOD) mouse model. So far, investigations have largely focused on type 1 NKT cells with invariant T-cell receptors, whereas the role of type 2 NKT cells with diverse T-cell receptors is less well understood. However, there have been several findings which indicate that in fact type 2 NKT cells may regulate the progression of type 1 diabetes in NOD mice, including a fraction of these cells which recognize β-cell-enriched sulfatide. Therefore, the focus for this review is to present the current evidence of the effect of type 2 NKT cells on the development of T1D. In general, there is still uncertainty surrounding the mechanism of activation and function of NKT cells. Here, we present two models of the effector mechanisms, respectively, Th1/Th2 polarization and the induction of tolerogenic dendritic cells (DC). In conclusion, this review points to the importance of immunoregulation by type 2 NKT cells in preventing the development of T1D and highlights the induction of tolerogenic DC as a likely mechanism. The possible therapeutic role of type 1 and type 2 NKT cells are evaluated and future experiments concerning type 2 NKT cells and T1D are proposed.

A transgenic TCR directs the development of IL-4+ and PLZF+ innate CD4 T cells

MHC class II-expressing thymocytes can efficiently mediate positive selection of CD4 T cells in mice. Thymocyte-selected CD4 (T-CD4) T cells have an innate-like phenotype similar to invariant NKT cells. To investigate the development and function of T-CD4 T cells in-depth, we cloned TCR genes from T-CD4 T cells and generated transgenic mice. Remarkably, positive selection of T-CD4 TCR transgenic (T3) thymocytes occurred more efficiently when MHC class II was expressed by thymocytes than by thymic epithelial cells. Similar to polyclonal T-CD4 T cells and also invariant NKT cells, T3 CD4 T cell development is controlled by signaling lymphocyte activation molecule/signaling lymphocyte activation molecule-associated protein signaling, and the cells expressed both IL-4 and promyelocytic leukemia zinc finger (PLZF). Surprisingly, the selected T3 CD4 T cells were heterogeneous in that only half expressed IL-4 and only half expressed PLZF. IL-4- and PLZF-expressing cells were first found at the double-positive cell stage. Thus, the expression of IL-4 and PLZF seems to be determined by an unidentified event that occurs postselection and is not solely dependent on TCR specificity or the selection process, per se. Taken together, our data show for the first time, to our knowledge, that the TCR specificity regulates but does not determine the development of innate CD4 T cells by thymocytes.

The functions of type I and type II natural killer T cells in inflammatory bowel diseases

CD1d-restricted natural killer T (NKT) cells are a distinct subset of T cells that rapidly produce an array of cytokines on activation and play a critical role in regulating various immune responses. NKT cells are classified into 2 groups based on differences in T-cell receptor usage. Type I NKT cells have an invariant T-cell receptor α-chain and are readily detectable by α-galactosylceramide (α-GalCer)-loaded CD1d tetramers. Type II NKT cells have a more diverse T-cell receptor repertoire and cannot be directly identified. Both types of NKT cells and multiple CD1d-expressing cell types are present in the intestine, and their interactions are likely to be modulated by pathogenic and commensal microbes, which in turn contribute to the intestinal immune responses in health and disease. Indeed, in several animal models of inflammatory bowel disease, type I NKT cells have been shown to make both protective and pathogenic contributions to disease. In contrast, in patients with ulcerative colitis, and a mouse model in which both CD1d expression and the frequency of type II NKT cells are increased, type II NKT cells seem to promote intestinal inflammation. In this review, we summarize the present knowledge on the antigen recognition, activation, and function of NKT cells with a particular focus on their role in inflammatory bowel disease and discuss factors that may influence the functional outcome of NKT cell responses in intestinal inflammation.

HIV infection deregulates innate immunity to malaria despite combination antiretroviral therapy

OBJECTIVE

Malaria and HIV-1 adversely interact, with HIV-positive individuals suffering higher parasite burdens and worse clinical outcomes. However, the mechanisms underlying these disease interactions are unclear. We hypothesized that HIV coinfection impairs the innate immune response to malaria, and that combination antiretroviral therapy (cART) may restore this response. Our aim was to examine the innate inflammatory response of natural killer (NK), natural killer T (NKT), and γδ T-cells isolated from the peripheral blood of HIV-infected therapy-naive donors to malaria parasites, and determine the effect of cART on these responses.

METHODS

Freshly isolated peripheral blood mononuclear cells from 25 HIV-infected individuals pre-cART (month 0) and post-cART (months 3 and 6), and HIV-negative individuals at matched time-points, were cultured in the presence of Plasmodium falciparum parasitized erythrocytes. Supernatants and cells were collected to assess cytokine production and phenotypic changes.

RESULTS

Compared to HIV-negative participants, NKT, NK, and γδ T-cell subsets from participants with chronic HIV infection showed marked differences, including decreased production of interferon γ (IFNγ) and tumor necrosis factor (TNF) in response to malaria parasites. IFNγ production was linked to interleukin-18 receptor (IL-18R) expression in all three cell types studied. Six months of cART provided partial cellular reconstitution but had no effect on IL-18R expression, or IFNγ and TNF production.

CONCLUSION

These data suggest that HIV infection impairs the inflammatory response of innate effector cells to malaria, and that the response is not fully restored within 6 months of cART. This may contribute to higher parasite burdens and ineffective immune responses, and have implications for vaccination initiatives in coinfected individuals.

Recognition of microbial and mammalian phospholipid antigens by NKT cells with diverse TCRs

CD1d-restricted natural killer T (NKT) cells include two major subgroups. The most widely studied are Vα14Jα18(+) invariant NKT (iNKT) cells that recognize the prototypical α-galactosylceramide antigen, whereas the other major group uses diverse T-cell receptor (TCR) α-and β-chains, does not recognize α-galactosylceramide, and is referred to as diverse NKT (dNKT) cells. dNKT cells play important roles during infection and autoimmunity, but the antigens they recognize remain poorly understood. Here, we identified phosphatidylglycerol (PG), diphosphatidylglycerol (DPG, or cardiolipin), and phosphatidylinositol from Mycobacterium tuberculosis or Corynebacterium glutamicum as microbial antigens that stimulated various dNKT, but not iNKT, hybridomas. dNKT hybridomas showed distinct reactivities for diverse antigens. Stimulation of dNKT hybridomas by microbial PG was independent of Toll-like receptor-mediated signaling by antigen-presenting cells and required lipid uptake and/or processing. Furthermore, microbial PG bound to CD1d molecules and plate-bound PG/CD1d complexes stimulated dNKT hybridomas, indicating direct recognition by the dNKT cell TCR. Interestingly, despite structural differences in acyl chain composition between microbial and mammalian PG and DPG, lipids from both sources stimulated dNKT hybridomas, suggesting that presentation of microbial lipids and enhanced availability of stimulatory self-lipids may both contribute to dNKT cell activation during infection.

Immunomodulatory type II natural killer T lymphocytes in health and disease

Natural killer T (NKT) lymphocytes are αβ T cells activated by lipid-based ligands presented on the non-polymorphic CD1d-molecule. Type I NKT cells that carry an invariant Vα14 (in the mouse) or Vα24 (in humans) T cell receptor α-chain rearrangement have received significant attention for their involvement in a diversity of immune reactions. Their sister population, CD1d-restricted type II NKT cells, has been more difficult to study because of the lack of molecular markers that specify these cells. In the last few years, however, significant progress has been made, demonstrating that type II NKT cells have unique functions in immune responses to tumours and infections, in autoimmunity, obesity and graft-versus-host disease. Type II NKT cells appear more frequent than type I NKT cells in humans and accumulate in certain diseases such as ulcerative colitis, hepatitis and multiple myeloma. Recently, novel type II NKT cell ligands have been identified, and it is becoming clear that the type II NKT cell population may be oligoclonal. Here, we review the recent progress in the study of type II NKT cells, supporting the view that type II NKT cells may be attractive targets for immunotherapy.

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.

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.

NKT and tolerance

NKT cells are innate-like αβ T cells that are conserved between humans and mice. They are distinct from conventional T cells as they recognize lipid antigens presented by the CD1d molecule. Most NKT cells expressed a highly restricted TCR repertoire and can be activated by α-galactosylceramide (α-GalCer) and detected by α-GalCer-loaded-CD1d tetramers. Upon activation, NKT cells respond in few hours by producing cytokines and stimulating many other cells of the innate and adaptive immune system. Over the last decade, many studies have analyzed the regulatory role of NKT cells that can either suppress or exacerbate immune functions. This chapter describes the tools and techniques required to study in vivo and in vitro the regulatory role of NKT cells in mouse as well as from human blood.

B7-H1-deficiency enhances the potential of tolerogenic dendritic cells by activating CD1d-restricted type II NKT cells

Background

Dendritic cells (DC) can act tolerogenic at a semi-mature stage by induction of protective CD4⁺ T cell and NKT cell responses.

Methodology/Principal Findings

Here we studied the role of the co-inhibitory molecule B7-H1 (PD-L1, CD274) on semi-mature DC that were generated from bone marrow (BM) cells of B7-H1^−/− mice and applied to the model of Experimental Autoimmune Encephalomyelitis (EAE). Injections of B7-H1-deficient DC showed increased EAE protection as compared to wild type (WT)-DC. Injections of B7-H1^−/− TNF-DC induced higher release of peptide-specific IL-10 and IL-13 after restimulation in vitro together with elevated serum cytokines IL-4 and IL-13 produced by NKT cells, and reduced IL-17 and IFN-γ production in the CNS. Experiments in CD1d^−/− and Jα281^−/− mice as well as with type I and II NKT cell lines indicated that only type II NKT cells but not type I NKT cells (invariant NKT cells) could be stimulated by an endogenous CD1d-ligand on DC and were responsible for the increased serum cytokine production in the absence of B7-H1.

Conclusions/Significance

Together, our data indicate that BM-DC express an endogenous CD1d ligand and B7-H1 to ihibit type II but not type I NKT cells. In the absence of B7-H1 on these DC their tolerogenic potential to stimulate tolerogenic CD4⁺ and NKT cell responses is enhanced.

Multiple tissue-specific isoforms of sulfatide activate CD1d-restricted type II NKT cells

The glycosphingolipid sulfatide (SO(3)-3Galbeta1Cer) is a demonstrated ligand for a subset of CD1d-restricted NKT cells, which could regulate experimental autoimmune encephalomyelitis, a murine model for multiple sclerosis, as well as tumor immunity and experimental hepatitis. Native sulfatide is a mixture of sulfatide isoforms, i.e. sulfatide molecules with different long-chain bases and fatty acid chain lengths and saturation. Here, we demonstrate that sulfatide-specific CD1d-restricted murine NKT hybridomas recognized several different sulfatide isoforms. These included the physiologically relevant isoforms C24:1 and C24:0, major constituents of the myelin sheet of the nervous system, and C16:0, prominent in the pancreatic islet beta-cells. The most potent sulfatide isoform was lysosulfatide (lacking a fatty acid). Shortened fatty acid chain length (C24:1 versus C18:1), or saturation of the long fatty acid (C24:0), resulted in reduced stimulatory capacity, and fatty acid hydroxylation abolished the response. Moreover, sulfatide was not responsible for the natural autoreactivity toward splenocytes by XV19 T hybridoma cells. Our results reveal a promiscuity in the recognition of sulfatide isoforms by a CD1d-restricted NKT-cell clone, and suggest that sulfatide, a major component of the myelin sheet and pancreatic beta-cells, is one of several natural ligands for type II CD1d-restricted NKT cells.

Polymorphisms in CD1d affect antigen presentation and the activation of CD1d-restricted T cells

CD1 proteins constitute a distinct lineage of antigen-presenting molecules specialized for the presentation of lipid antigens to T cells. In contrast to the extensive sequence polymorphism characteristic of classical MHC molecules, CD1 proteins exhibit limited sequence diversity. Here, we describe the identification and characterization of CD1d alleles in wild-derived mouse strains. We demonstrate that polymorphisms in CD1d affect the presentation of endogenous and exogenous ligands to CD1d-restricted T cells, including type I (Valpha14i) and type II (non-Valpha14i) natural killer T (NKT) cells. Using congenic mice, we found CD1d polymorphisms affect the thymic selection of type I NKT cells and induce allogeneic T cell responses. Collectively, results from these studies demonstrate a role for polymorphisms in influencing the development and function of CD1d-restricted T cells.

Human interleukin 17-producing cells originate from a CD161+CD4+ T cell precursor

We demonstrate that CD161 is a highly up-regulated gene in human interleukin (IL) 17 T helper cell (Th17) clones and that all IL-17-producing cells are contained in the CD161(+) fraction of CD4(+) T cells present in the circulation or in inflamed tissues, although they are not CD1-restricted natural killer T cells. More importantly, we show that all IL-17-producing cells originate from CD161(+) naive CD4(+) T cells of umbilical cord blood, as well as of the postnatal thymus, in response to the combined activity of IL-1 beta and IL-23. These findings implicate CD161 as a novel surface marker for human Th17 cells and demonstrate the exclusive origin of these cells from a CD161(+)CD4(+) T cell progenitor.

The genetics of immunoregulatory T cells

The immune repertoire of normal, healthy individuals contains autoreactive T cells and natural antibodies that, under normal conditions, are controlled, either through central tolerance or by the activity of immunoregulatory T cells to prevent the onset of autoimmune diseases. Over the years, several types of immunoregulatory T cells have been identified. These include natural CD4+CD25+Foxp3+T (Treg) cells and type 1 NKT cells, which develop in the thymus, as well as acquired immunoregulatory T cells, such as type 1 cells (Tr1), Th3 cells, Ts cells and anergic CD4 T cells, which all appear to be products of peripheral immune activation. While little is understood about the genetics of most types of immunoregulatory T cell, detailed information on the genetic control of NKT and Treg cells is now available and may contribute significantly to our understanding of the aetiology of autoimmune disease.

Killer cells in chronic obstructive pulmonary disease

COPD (chronic obstructive pulmonary disease) is a treatable and preventable disease state, characterized by progressive airflow limitation that is not fully reversible. It is a current and growing cause of mortality and morbidity worldwide, with the WHO (World Health Organization) projecting that total deaths attributed to COPD will increase by more than 30% in the next 10 years. The pathological hallmarks of COPD are destruction of the lung parenchyma (pulmonary emphysema), inflammation of the central airways (chronic bronchitis) and inflammation of the peripheral airways (respiratory bronchiolitis). The destructive changes and tissue remodelling observed in COPD are a result of complex interactions between cells of the innate and adaptive immune systems. The focus of the present review is directed towards the role of CD8(+) T-lymphocytes, NK (natural killer) cells and NKT cells (NK T-cells). These three classes of killer cell could all play an important part in the pathogenesis of COPD. The observed damage to the pulmonary tissue could be caused in three ways: (i) direct cytotoxic effect against the lung epithelium mediated by the activities of perforin and granzymes, (ii) FasL (Fas ligand)-induced apoptosis and/or (iii) cytokine and chemokine release. The present review considers the role of these killer cells in COPD.

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.

Deficiency of invariant V alpha 14 natural killer T cells decreases atherosclerosis in LDL receptor null mice

Aims

CD1d-restricted natural killer T (NKT) cells function by regulating numerous immune responses during innate and adaptive immunity. Depletion of all populations of CD1d-dependent NKT cells has been shown by several groups to reduce atherosclerosis in two different mouse models of the disease. In this study, we determined if removal of a single (Vα14) NKT cell population protects mice from the disease.

Methods and results

Targeted deletion of the Jα18 gene results in selective depletion of CD1d-dependent Vα14 NKT cells in C57BL/6 mice without affecting the population of other NKT, NK, and conventional T cells. Therefore, to study the effect of Vα14 NKT cell depletion on the progression of atherosclerosis, we examined the extent of lesion formation using paired littermate LDL receptor null mice that were either ^+/+ or ^−/− for the Jα18 gene following the feeding of these mice a cholesterol- and fat-enriched diet for 8 weeks. At the end of the study, we found no difference in either serum total- or lipoprotein-cholesterol distributions between groups. However, quantification of atherosclerosis revealed that Vα14 NKT cell deficiency significantly decreased lesion size in the aortic root (20–28%) and arch (28–38%) in both genders of mice. By coupling the techniques of laser capture microdissection with quantitative real-time RT–PCR, we found that expression of the proatherogenic cytokine interferon (IFN)-γ was significantly reduced in lesions from Jα18^−/− mice.

Conclusion

This study is the first to identify a specific subpopulation of NKT cells that promotes atherosclerosis via a mechanism appearing to involve IFN-γ expression.

The role of NKT cells in tumor immunity

NKT cells are a relatively newly recognized member of the immune community, with profound effects on the rest of the immune system despite their small numbers. They are true T cells with a T cell receptor (TCR), but unlike conventional T cells that detect peptide antigens presented by conventional major histocompatibility (MHC) molecules, NKT cells recognize lipid antigens presented by CD1d, a nonclassical MHC molecule. As members of both the innate and adaptive immune systems, they bridge the gap between these, and respond rapidly to set the tone for subsequent immune responses. They fill a unique niche in providing the immune system a cellular arm to recognize lipid antigens. They play both effector and regulatory roles in infectious and autoimmune diseases. Furthermore, subsets of NKT cells can play distinct and sometimes opposing roles. In cancer, type I NKT cells, defined by their invariant TCR using Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans, are mostly protective, by producing interferon-gamma to activate NK and CD8(+) T cells and by activating dendritic cells to make IL-12. In contrast, type II NKT cells, characterized by more diverse TCRs recognizing lipids presented by CD1d, primarily inhibit tumor immunity. Moreover, type I and type II NKT cells counter-regulate each other, forming a new immunoregulatory axis. Because NKT cells respond rapidly, the balance along this axis can greatly influence other immune responses that follow. Therefore, learning to manipulate the balance along the NKT regulatory axis may be critical to devising successful immunotherapies for cancer.

Cross-regulation between type I and type II NKT cells in regulating tumor immunity: a new immunoregulatory axis

Negative immunoregulation is a major barrier to successful cancer immunotherapy. The NKT cell is known to be one such regulator. In this study we explored the roles of and interaction between the classical type I NKT cell and the poorly understood type II NKT cell in the regulation of tumor immunity. Selective stimulation of type II NKT cells suppressed immunosurveillance, whereas stimulation of type I NKT cells protected against tumor growth even when responses were relatively skewed toward Th2 cytokines. When both were stimulated simultaneously, type II NKT cells appeared to suppress the activation in vitro and protective effect in vivo of type I NKT cells. In the absence of type I, suppression by type II NKT cells increased, suggesting that type I cells reduce the suppressive effect of type II NKT cells. Thus, in tumor immunity type I and type II NKT cells have opposite and counteractive roles and define a new immunoregulatory axis. Alteration of the balance between the protective type I and the suppressive type II NKT cell may be exploited for therapeutic intervention in cancer.

A novel mouse model for invariant NKT cell study

We have generated a novel mouse model harboring the in-frame rearranged TCRValpha specific for invariant NKT (iNKT) cells (Valpha14-Jalpha18) on one allele by crossing the mouse cloned from NKT cells with wild-type mice. This genomic configuration would ensure further rearrangement and expression of TCRValpha14-Jalpha18 under the endogenous promoters and enhancers. Mice harboring such an in-frame rearranged TCRValpha (Valpha14-Jalpha18 mouse) possessed an increase in iNKT cells in the thymus, liver, spleen, and bone marrow. Intriguingly, both Th1- and Th2-type cytokines were produced upon stimulation with alphaGalactosylceramide, an agonist of iNKT cells, and the IgE level in the serum remained unaffected in the Valpha14-Jalpha18 mouse. These features markedly distinguish the nature of iNKT cells present in the Valpha14-Jalpha18 mouse from that of iNKT cells found in the Valpha14-Jalpha18 transgenic mouse. Besides these, the expression of TCRVgammadelta cells remained intact, and the use of the TCRVbeta repertoire in iNKT cells was highly biased to TCRVbeta8 in the Valpha14-Jalpha18 mouse. Furthermore, alphaGalactosylceramide-CD1d dimer-reactive immature iNKT cells expressed less Rag2 as compared with the conventional immature T cells at the positive selection stage. Cell cycle analysis on the thymocytes revealed that no particular subset proliferated more vigorously than the others. Crossing the Valpha14-Jalpha18 mouse with the CD1d knockout mouse revealed a novel population of iNKT cells whose coreceptor expression profile was similar to that assigned to iNKT precursor cells. These mice will be useful for the study on the development of iNKT cells as well as on their functions in the immune system.

Natural killer T-cell characterization through gene expression profiling: an account of versatility bridging T helper type 1 (Th1), Th2 and Th17 immune responses

Natural killer T (NKT) cells constitute a distinct lymphocyte lineage at the interface between innate and adaptive immunity, yet their role in the immune response remains elusive. Whilst NKT cells share features with other conventional T lymphocytes, they are unique in their rapid, concomitant production of T helper type 1 (Th1) and Th2 cytokines upon T-cell receptor (TCR) ligation. In order to characterize the gene expression of NKT cells, we performed comparative microarray analyses of murine resting NKT cells, natural killer (NK) cells and naïve conventional CD4+ T helper (Th) and regulatory T cells (Treg). We then compared the gene expression profiles of resting and alpha-galactosylceramide (alphaGalCer)-activated NKT cells to elucidate the gene expression signature upon activation. We describe here profound differences in gene expression among the various cell types and the identification of a unique NKT cell gene expression profile. In addition to known NKT cell-specific markers, many genes were expressed in NKT cells that had not been attributed to this population before. NKT cells share features not only with Th1 and Th2 cells but also with Th17 cells. Our data provide new insights into the functional competence of NKT cells which will facilitate a better understanding of their versatile role during immune responses.

The biology of NKT cells

Recognized more than a decade ago, NKT cells differentiate from mainstream thymic precursors through instructive signals emanating during TCR engagement by CD1d-expressing cortical thymocytes. Their semi-invariant alphabeta TCRs recognize isoglobotrihexosylceramide, a mammalian glycosphingolipid, as well as microbial alpha-glycuronylceramides found in the cell wall of Gram-negative, lipopolysaccharide-negative bacteria. This dual recognition of self and microbial ligands underlies innate-like antimicrobial functions mediated by CD40L induction and massive Th1 and Th2 cytokine and chemokine release. Through reciprocal activation of NKT cells and dendritic cells, synthetic NKT ligands constitute promising new vaccine adjuvants. NKT cells also regulate a range of immunopathological conditions, but the mechanisms and the ligands involved remain unknown. NKT cell biology has emerged as a new field of research at the frontier between innate and adaptive immunity, providing a powerful model to study fundamental aspects of the cell and structural biology of glycolipid trafficking, processing, and recognition.

Regulation of type 1 diabetes by NKT cells

Type 1 diabetes is an autoimmune disease due to the destruction of insulin-producing pancreatic beta cells. Natural Killer T (NKT) cells are a T-cell subset that links the innate and adaptive immune systems. NKT cells play a key regulatory role in type 1 diabetes. The absence of NKT cells correlates with exacerbation of type 1 diabetes, whereas an increased frequency and/or activation of NKT cells prevents beta-cell autoimmunity. Various mechanisms are involved in the protective effect of NKT cells. The goal is now to translate knowledge gained from mouse models into human therapeutics.

The natural killer T lymphocyte: a player in the complex regulation of autoimmune diabetes in non-obese diabetic mice

Manipulation of the immune response to specifically prevent autoaggression requires an understanding of the complex interactions that occur during the pathogenesis of autoimmunity. Much attention has been paid to conventional T lymphocytes recognizing peptide antigens presented by classical major histocompatibility complex (MHC) class I and II molecules, as key players in the destructive autoreactive process. A pivotal role for different types of regulatory T lymphocytes in modulating the development of disease is also well established. Lately, CD1d-restricted natural killer T (NKT) lymphocytes have been the subject of intense investigation because of their ability to regulate a diversity of immune responses. The non-classical antigen presenting molecule CD1d presents lipids and glycolipids to this highly specialized subset of T lymphocytes found in both humans and mice. From experimental models of autoimmunity, evidence is accumulating that NKT cells can protect from disease. One of the best studied is the murine type 1 diabetes model, the non-obese diabetic (NOD) mouse. While the NKT cell population was first recognized to be deficient in NOD mice, augmenting NKT cell activity has been shown to suppress the development of autoimmune disease in this strain. The mechanism by which CD1d-restricted T cells exert this function is still described incompletely, but investigations in NOD mice are starting to unravel specific effects of NKT cell regulation. This review focuses on the role of CD1d-restricted NKT cells in the control of autoimmune diabetes.