A thymic precursor to the NK T cell lineage

Proinflammatory environment dictates the IL-17-producing capacity of human invariant NKT cells

CD1d-reactive invariant NKT (iNKT) cells have been implicated in a number of experimental models of human pathologies. Given the scope of their immunoregulatory activities mediated through distinct cytokine patterns, it has been proposed that this functional diversity originates from distinct iNKT subpopulations. In this study, we report that human CD161(+) iNKT cells are intrinsically endowed with the capacity to generate IL-17, but require TGF-β, IL-1β, and IL-23 to carry out this potential. IL-17-producing iNKT cells are already present in cord blood but, in contrast to peripheral blood iNKT cells, they cannot generate IFN-γ. These IL-17 producers respond to aryl hydrocarbon receptor stimulation and express IL-23 receptor and retinoic acid-related orphan receptor C, similar to conventional T helper 17 cells, from which they differ by their restricted ability to coproduce IL-22. In conclusion, IL-17 production by human iNKT cells depends on two critical parameters, namely an intrinsic program and a proinflammatory environment.

Transcriptional control of invariant NKT cell development

Invariant natural killer T (iNKT) cells comprise a rare lymphocyte sublineage with phenotypic and functional properties similar to T and NK cells. Akin to conventional αβ T cells, their development occurs primarily in the thymus, where they originate from CD4(+) CD8(+) double positive (DP) progenitors. However, the selection of iNKT cells is unique in that it is mediated by homotypic interactions of DP cells and recognition of glycolipid antigen-CD1d complexes. Additionally, iNKT cells acquire an activated innate-like phenotype during development that allows them to release cytokines rapidly following antigen exposure. Given their hybrid features, it is not surprising that the developmental program of iNKT cells partially overlaps with that of T and NK cells. Several recent reports have provided new and exciting insights into the developmental mechanisms that direct natural killer T (NKT) cell lineage commitment and maturation. In this review, we provide a discussion of the NKT cell developmental program with an emphasis on the signaling mechanisms and transcription factors that influence the ontogeny of this lineage. Continued investigations into the complex interplay of these transcription factors and their relationship with other extracellular and intracellular signaling molecules will undoubtedly provide important clues into the biology of this unusual T-cell lineage.

Differential requirements for the Ets transcription factor Elf-1 in the development of NKT cells and NK cells

E26 Transformation specific (Ets) family transcription factors control the expression of a large number of genes regulating hematopoietic cell development and function. Two such transcription factors, Ets-1 and myeloid Elf-1-like factor (MEF), have been shown to play critical roles in both natural killer (NK)- and NKT-cell development, but not in the development of conventional T cells. In this study, we address the role of E74-like factor 1 (Elf-1), another Ets family transcription factor that is closely related to MEF but divergent from Ets-1, in NK- and NKT-cell development using Elf-1-deficient (Elf-1(-/-)) mice. Whereas the proportion of NK cells in Elf-1(-/-) mice was normal, the proportion of NKT cells was significantly reduced in the thymus and periphery of Elf-1(-/-) mice compared with wild-type (WT) mice. Although Ets-1-deficient mice lack NKT cells altogether, Elf-1(-/-) mice exhibited only a partial block in NKT-cell development caused by a cell-intrinsic defect in the selection, survival, and maturation of NKT cells. In addition, residual NKT cells found in Elf-1(-/-) mice produced less cytokine upon antigen stimulation compared with WT NKT cells. Our data demonstrate that Elf-1 plays an important and nonredundant role in the development and function of NKT cells, but is not involved in NK-cell development.

Epigenetic reduction in invariant NKT cells following in utero vitamin D deficiency in mice

Vitamin D status changes with season, but the effect of these changes on immune function is not clear. In this study, we show that in utero vitamin D deficiency in mice results in a significant reduction in invariant NKT (iNKT) cell numbers that could not be corrected by later intervention with vitamin D or 1,25-dihydroxy vitamin D(3) (active form of the vitamin). Furthermore, this was intrinsic to hematopoietic cells, as vitamin D-deficient bone marrow is specifically defective in generating iNKT cells in wild-type recipients. This vitamin D deficiency-induced reduction in iNKT cells is due to increased apoptosis of early iNKT cell precursors in the thymus. Whereas both the vitamin D receptor and vitamin D regulate iNKT cells, the vitamin D receptor is required for both iNKT cell function and number, and vitamin D (the ligand) only controls the number of iNKT cells. Given the importance of proper iNKT cell function in health and disease, this prenatal requirement for vitamin D suggests that in humans, the amount of vitamin D available in the environment during prenatal development may dictate the number of iNKT cells and potential risk of autoimmunity.

Diverse endogenous antigens for mouse NKT cells: self-antigens that are not glycosphingolipids

NKT cells with an invariant Ag receptor (iNKT cells) represent a highly conserved and unique subset of T lymphocytes having properties of innate and adaptive immune cells. They have been reported to regulate a variety of immune responses, including the response to cancers and the development of autoimmunity. The development and activation of iNKT cells is dependent on self-Ags presented by the CD1d Ag-presenting molecule. It is widely believed that these self-Ags are glycosphingolipids (GSLs), molecules that contain ceramide as the lipid backbone. In this study, we used a variety of methods to show that mammalian Ags for mouse iNKT cells need not be GSLs, including the use of cell lines deficient in GSL biosynthesis and an inhibitor of GSL biosynthesis. Presentation of these Ags required the expression of CD1d molecules that could traffic to late endosomes, the site where self-Ag is acquired. Extracts of APCs contain a self-Ag that could stimulate iNKT cells when added to plates coated with soluble, rCD1d molecules. The Ag(s) in these extracts are resistant to sphingolipid-specific hydrolase digestion, consistent with the results using live APCs. Lyosphosphatidylcholine, a potential self-Ag that activated human iNKT cell lines, did not activate mouse iNKT cell hybridomas. Our data indicate that there may be more than one type of self-Ag for iNKT cells, that the self-Ags comparing mouse and human may not be conserved, and that the search to identify these molecules should not be confined to GSLs.

Invariant NKT cell development and function in microRNA-223 knockout mice

Invariant natural killer T (iNKT) cells, potent regulators of diverse immune responses, have been implicated in a number of diseases. The detailed mechanisms that drive iNKT cell development and maturation are still not completely understood. MicroRNAs (miRNAs) are small noncoding RNAs that regulate vast networks of genes that share miRNA target sequences. Our previous studies indicate that Dicer-dependent miRNAs play important roles in iNKT cell development, maturation, and function, but the roles of specific single miRNAs in this context are still lacking. Accumulated studies indicated that the miRNA miR-223 is a myeloid-specific miRNA. Here we report that miR-223 is highly expressed in thymic immature and activated splenic iNKT cells. To identify the role of miR-223 in iNKT cell development and function, miRNA-223-deficient mice were used. We have found that miR-223 deletion does not significantly interrupt iNKT cell development in the thymus, and miR-223-deficient mice have a normal frequency and number of iNKT cells in the thymus and peripheral immune organs. Furthermore, cytokine production of iNKT cells activated in vivo and in vitro shows no significant differences between miR-223 deficient mice and wild-type control. Thus, our data suggest that miR-223 may not be required for iNKT cell development and function.

Temporal differences in the dependency on phosphoinositide-dependent kinase 1 distinguish the development of invariant Valpha14 NKT cells and conventional T cells

This study uses two independent genetic strategies to explore the requirement for phosphoinositide-dependent kinase-1 (PDK1) in the development of mature T cell populations from CD4/CD8 double-positive thymocytes. The data show that CD4/CD8 double-positive thymocytes that do not express PDK1 or express a catalytically inactive PDK1 mutant fail to produce mature invariant Vα14 NKT cells but can differentiate to conventional CD4, CD8, or regulatory T cell subsets in the thymus. The PDK1 requirement for Vα14 NKT cell development reflects that these cells require the PDK1 substrate protein kinase B to meet the metabolic demands for proliferative expansion in response to IL-15 or AgR stimulation. There is also constitutive PDK1 signaling in conventional α/β T cells that is not required for lineage commitment of these cells but fine-tunes the expression of coreceptors and adhesion molecules. Also, although PDK1 is dispensable for thymic development of conventional α/β T cells, peripheral cells are reduced substantially. This reflects a PDK1 requirement for lymphopenia-induced proliferation, a process necessary for initial population of the peripheral T cell niche in neonatal mice. PDK1 is thus indispensable for T cell developmental programs, but the timing of the PDK1 requirement is unique to different T cell subpopulations.

Invariant NKT cells modulate the suppressive activity of IL-10-secreting neutrophils differentiated with serum amyloid A

Neutrophils are the main effector cells during inflammation, but they can also control excessive inflammatory responses by secreting anti-inflammatory cytokines. However, the mechanisms that modulate their plasticity remain unclear. We now show that systemic serum amyloid A 1 (SAA-1) controls the plasticity of neutrophil differentiation. SAA-1 not only induced anti-inflammatory interleukin 10 (IL-10)-secreting neutrophils but also promoted the interaction of invariant natural killer T cells (iNKT cells) with those neutrophils, a process that limited their suppressive activity by diminishing the production of IL-10 and enhancing the production of IL-12. Because SAA-1-producing melanomas promoted differentiation of IL-10-secreting neutrophils, harnessing iNKT cells could be useful therapeutically by decreasing the frequency of immunosuppressive neutrophils and restoring tumor-specific immune responses.

Thymic and peripheral microenvironments differentially mediate development and maturation of iNKT cells by IL-15 transpresentation

Invariant NKT (iNKT) cells are an innate type of T cells, which respond rapidly on activation. iNKT cells acquire these innate-like abilities during development; however, the signals driving development and functional maturation remain only partially understood. Because interleukin-15 (IL-15) is crucial for iNKT development and is delivered by transpresentation, we set out to identify the cell types providing IL-15 to developing iNKT cells and determine their role at the various states of development and maturation. We report here that transpresentation of IL-15 by parenchymal cells was crucial for generating normal number of iNKTs in the thymus, whereas both hematopoietic and parenchymal cells regulated iNKT cell numbers in the periphery, particularly in the liver. Specifically, dendritic cells contributed to peripheral iNKT cell numbers by up-regulating Bcl-2 expression and promoting extrathymic iNKT cell ex-pansion and their homeostatic proliferation. Whether IL-15 affects functional maturation of iNKT cells was also examined. In IL-15Rα(-/-) mice, CD44(High)NK1.1(+) iNKT cells displayed decreased T-bet expression and in response to α-galactosylceramide, had deficient interferon-γ expression. Such defects could be reversed by exogenous IL-15 signals. Overall, these studies identify stage-specific functions of IL-15, which are determined by the tissue microenvironment and elucidate the importance of IL-15 in functional maturation.

NKT cells are necessary for maximal expression of allergic conjunctivitis

Allergic conjunctivitis (AC) is elicited by immediate hypersensitivity responses to environmental agents. It is initiated by a T(h)2-dominated immune response that is characterized by production of IgE antibodies and eosinophilic infiltration. By using an experimental mouse model of AC induced by short ragweed (SRW) pollen, we show that sensitized Jalpha18(-/-) mice, which lack type I NKT cells, and CD1d(-/-) mice, which lack type I and type II NKT cells, exhibited a decrease in tearing, lid edema, conjunctival edema and vasodilatation and eosinophil infiltration into the conjunctiva when compared with wild-type (WT) mice in both T(h)1- and T(h)2-prone hosts (C57BL/6 and BALB/c mice, respectively). This demonstrates that NKT cells are needed for both the early and late phases of AC. Adoptive transfer of SRW-primed CD4(+) T cells from Jalpha18(-/-) mice into naive WT BALB/c mice revealed that NKT cells were needed for the maximal induction of allergen-specific T(h)2 cells. Results from adoptive transfer of SRW-primed CD4(+) T cells from WT BALB/c mice to naive Jalpha18(-/-) mice indicated that NKT cells were also needed for the expression of AC produced by allergen-primed CD4(+) T cells. The decreased expression of AC in NKT cell-deficient mice was correlated with significant reduction in the production of T(h)2 cytokines in SRW pollen-sensitized mice compared with WT mice and in the capacity of SRW pollen-sensitized CD4(+) T cells to mediate ocular inflammation when the hosts were confronted with SRW pollen at the ocular surface.

PLZF induces the spontaneous acquisition of memory/effector functions in T cells independently of NKT cell-related signals

The broad complex, tramtrack, bric-a-brac-zinc finger (BTB-ZF) transcription factor promyelocytic leukemia zinc finger (PLZF) is required for development of the characteristic innate/effector functions of NKT cells. In this study, we report the characterization and functional analysis of transgenic mouse T cells with forced expression of PLZF. PLZF expression was sufficient to provide some memory/effector functions to T cells without the need for Ag stimulation or proliferation. The acquisition of this phenotype did not require the proliferation typically associated with T cell activation. Furthermore, PLZF transgenic cells maintained a diverse TCR repertoire, indicating that there was no preferential expansion of specific clones. Functionally, PLZF transgenic CD4 and CD8 lymphocytes were similar to wild type memory cells, in that they had similar requirements for costimulation and exhibited a similar pattern of cytokine secretion, with the notable exception that transgenic T cells produced significantly increased levels of IL-17. Whereas transgene-mediated PLZF expression was not sufficient to rescue NKT cell development in Fyn- or signaling lymphocytic activation-associated protein (SAP)-deficient mice, the acquisition of memory/effector functions induced by PLZF in conventional T cells was independent of Fyn and SAP. These data show that PLZF is sufficient to promote T cell effector functions and that PLZF acts independently of SAP- and Fyn-mediated signaling pathways.

Co-receptor choice by V alpha14i NKT cells is driven by Th-POK expression rather than avoidance of CD8-mediated negative selection

Mouse natural killer T (NKT) cells with an invariant Vα14-Jα18 rearrangement (Vα14 invariant [Vα14i] NKT cells) are either CD4⁺CD8⁻ or CD4⁻CD8⁻. Because transgenic mice with forced CD8 expression in all T cells exhibited a profound NKT cell deficit, the absence of CD8 has been attributed to negative selection. We now present evidence that CD8 does not serve as a coreceptor for CD1d recognition and that the defect in development in CD8 transgene homozygous mice is the result of a reduction in secondary T cell receptor α rearrangements. Thymocytes from mice hemizygous for the CD8 transgene have a less severe rearrangement defect and have functional CD8⁺ Vα14i NKT cells. Furthermore, we demonstrate that the transcription factor Th, Poxviruses and Zinc finger, and Krüppel family (Th-POK) is expressed by Vα14i NKT cells throughout their differentiation and is necessary both to silence CD8 expression and for the functional maturity of Vα14i NKT cells. We therefore suggest that Th-POK expression is required for the normal development of Vα14i NKT cells and that the absence of CD8 expression by these cells is a by-product of such expression, as opposed to the result of negative selection of CD8-expressing Vα14i NKT cells.

Regulation of natural killer T-cell development by deubiquitinase CYLD

Natural killer T (NKT) cells modulate immune responses against pathogens and tumours, as well as immunological tolerance. We show here that CYLD, a tumour suppressor with deubiquitinase function, has a pivotal and cell-intrinsic function in NKT cell development. Unlike other known NKT regulators, CYLD is dispensable for intrathymic NKT cell maturation but is obligatory for the survival of immature NKT cells. Interestingly, CYLD deficiency impairs the expression of ICOS, a costimulatory molecule required for the survival and homeostasis of NKT cells, and this molecular defect is associated with attenuated response to an NKT-survival cytokine, IL-7, due to reduced expression of IL-7 receptor. We show, for the first time, that IL-7 induces the expression of ICOS in NKT cells, which is largely dependent on CYLD. Interestingly, loss of CYLD causes constitutive NF-kappaB activation in developing NKT cells, which contributes to their defective IL-7 response and attenuated ICOS expression. These findings establish CYLD as a critical regulator of NKT cell development and provide molecular insights into this novel function of CYLD.

Retroviral infection in vivo requires an immune escape virulence factor encrypted in the envelope protein of oncoretroviruses

We previously delineated a highly conserved immunosuppressive (IS) domain within murine and primate retroviral envelope proteins (Envs). The envelope-mediated immunosuppression was manifested by the ability of the proteins, when expressed by allogeneic tumor cells normally rejected by engrafted mice, to allow these cells to escape, at least transiently, immune rejection. Using this approach, we identified key residues whose mutation specifically abolishes IS activity without affecting the "mechanical" fusogenic function of the entire envelope. Here, we genetically "switched off' the envelope-mediated immunosuppression of an infectious retrovirus, the Friend murine leukemia virus, while preserving mutant envelope infectivity both ex vivo and in vivo, thus allowing us to test the functional importance of envelope-mediated immunosuppression in retrovirus physiology. Remarkably, we show, in vivo, that the non-IS mutant virus displays the same propagation kinetics as its WT counterpart in irradiated immunocompromised mice but that it is rapidly and totally cleared from normal immunocompetent mice, which become fully protected against a challenge with the WT retrovirus. Using cell depletion strategies, we further establish that envelope-mediated immunosuppression enables the retrovirus to escape innate (natural killer cells) and adaptive (CD8 T cells) antiviral effectors. Finally, we show that inactivated mutant virions induce higher humoral and cellular responses than their WT counterparts. In conclusion, our work demonstrates the critical role of Env-induced immunosuppression for retrovirus propagation in vivo and identifies a unique definite target for antiretroviral therapies and vaccine strategies, also characterized in the human T-cell leukemia virus (HTLV) and xenotropic murine leukemia virus-related virus (XMRV) retroviruses, opening unprecedented prospects for the treatment of retroviral diseases.

Raising the NKT cell family

Natural killer T cells (NKT cells) are CD1d-restricted, lipid antigen-reactive, immunoregulatory T lymphocytes that can promote cell-mediated immunity to tumors and infectious organisms, including bacteria and viruses, yet paradoxically they can also suppress the cell-mediated immunity associated with autoimmune disease and allograft rejection. Furthermore, in some diseases, such as atherosclerosis and allergy, NKT cell activity can be deleterious to the host. Although the precise means by which these cells carry out such contrasting functions is unclear, recent studies have highlighted the existence of many functionally distinct NKT cell subsets. Because their frequency and number vary widely between individuals, it is important to understand the mechanisms that regulate the development and maintenance of NKT cells and subsets thereof, which is the subject of this review.

AIRE deficiency leads to impaired iNKT cell development

Autoimmune Polyendocrine Syndrome type I (APS I) is caused by mutations in the Autoimmune Regulator gene (AIRE), and results in the immunological destruction of endocrine organs. Herein we have characterized the CD1d-restricted invariant NKT cells (iNKT) and NK cells in APS I patients and Aire(-/-) mice, two cell populations known to play a role in the regulation of autoimmune disease. We show that the frequency of circulating iNKT cells is reduced in APS I patients compared to healthy controls. In accordance with this, iNKT cells are significantly reduced in the thymus and peripheral organs of Aire(-/-) mice. Bone marrow transfer from wild type donors into lethally irradiated Aire(-/-) recipients led to a decreased iNKT cell population in the liver, suggesting an impaired development of iNKT cells in the absence of Aire expression in radio-resistant cells. In contrast to the iNKT cells, both conventional NK cells and thymus-derived NK cells were unaffected by Aire deficiency and differentiated normally in Aire(-/-) mice. Our results show that expression of Aire in radio-resistant cells is important for the development of iNKT cells, whereas NK cell development and function does not depend on Aire.

Foxp1 is an essential transcriptional regulator for the generation of quiescent naive T cells during thymocyte development

Proper thymocyte development is required to establish T-cell central tolerance and to generate naive T cells, both of which are essential for T-cell homeostasis and a functional immune system. Here we demonstrate that the loss of transcription factor Foxp1 results in the abnormal development of T cells. Instead of generating naive T cells, Foxp1-deficient single-positive thymocytes acquire an activated phenotype prematurely in the thymus and lead to the generation of peripheral CD4(+) T and CD8(+) T cells that exhibit an activated phenotype and increased apoptosis and readily produce cytokines upon T-cell receptor engagement. These results identify Foxp1 as an essential transcriptional regulator for thymocyte development and the generation of quiescent naive T cells.

Generation of functional NKT cells in vitro from embryonic stem cells bearing rearranged invariant Vα14-Jα18 TCRα gene

Establishment of a system with efficient generation of natural killer T (NKT) cells from embryonic stem (ES) cells would enable us to identify the cells with NKT-cell potential and obtain NKT cells with desired function. Here, using cloned ES (NKT-ES) cells generated by the transfer of nuclei from mature NKT cells, we have established a culture system that preferentially developed functional NKT cells and also identified early NKT progenitors, which first appeared on day 11 as a c-kit+ population in the cocultures on OP9 cells with expression of Notch ligand, delta-like1 (OP9/Dll-1) and became c-kitlo/− on day 14. Interestingly, in the presence of Notch signals, NKT-ES cells differentiated only to thymic CD44lo CD24hi NKT cells producing mainly interleukin-4 (IL-4), whereas NKT cells resembling CD44hi CD24lo liver NKT cells producing mainly interferon γ (IFN-γ) and exhibiting strong adjuvant activity in vivo were developed in the switch culture starting at day 14 in the absence of Notch. The cloned ES culture system offers a new opportunity for the elucidation of the molecular events on NKT-cell development and for the establishment of NKT-cell therapy.

Development of promyelocytic zinc finger and ThPOK-expressing innate gamma delta T cells is controlled by strength of TCR signaling and Id3

The broad-complex tramtrack and bric a brac-zinc finger transcriptional regulator (BTB-ZF), promyelocytic leukemia zinc finger (PLZF), was recently shown to control the development of the characteristic innate T cell phenotype and effector functions of NK T cells. Interestingly, the ectopic expression of PLZF was shown to push conventional T cells into an activated state that seems to be proinflammatory. The factors that control the normal expression of PLZF in lymphocytes are unknown. In this study, we show that PLZF expression is not restricted to NK T cells but is also expressed by a subset of gammadelta T cells, functionally defining distinct subsets of this innate T cell population. A second BTB-ZF gene, ThPOK, is important for the phenotype of the PLZF-expressing gammadelta T cells. Most importantly, TCR signal strength and expression of inhibitor of differentiation gene 3 control the frequency of PLZF-expressing gammadelta T cells. This study defines the factors that control the propensity of the immune system to produce potentially disease-causing T cell subsets.

Inflammation and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the hepatic component of the metabolic syndrome. The metabolic syndrome represents a chronic inflammatory state, and individuals with the disorder demonstrate various immunologic abnormalities. Innate immune dysfunction in adipose tissue leads to abnormal production of adipose-derived factors, some of which can inhibit hepatic fat disposal and promote lipid accumulation within hepatocytes. The latter induces generation of excessive proinflammatory cytokines, particularly when the hepatic innate immune system becomes Th-1 polarized, thus promoting the development of nonalcoholic steatohepatitis (NASH). Although sustained exposure to these inflammatory mediators generally promotes the generation of various profibrogenic factors, progression from NASH to cirrhosis is actually relatively uncommon due to reduced production of other cytokines such as Th-2 cytokines.

Fatty liver and lipotoxicity

Fatty liver disease comprises a spectrum ranging from simple steatosis to steatohepatitis which can progress to liver cirrhosis and hepatocellular cancer. Hepatic lipotoxicity may ensue when the hepatic capacity to utilize, store and export fatty acids (FA) as triglycerides is overwhelmed. Additional mechanisms of hepatic lipotoxicity include abnormal FA oxidation with formation of reactive oxygen species, disturbances in cellular membrane FA and phospholipid composition, alterations of cholesterol content and ceramide signalling. Lipotoxicity is a key factor for the progression of fatty liver disease by inducing hepatocellular death, activating Kupffer cells and an inflammatory response, impairing hepatic insulin signalling resulting in insulin resistance, and activation of a fibrogenic response in hepatic stellate cells that can ultimately lead to cirrhosis. Therefore, the concept of hepatic lipotoxicity should be considered in future therapeutic concepts for fatty liver disease.

Dicer-dependent microRNA pathway controls invariant NKT cell development

Invariant NK T (iNKT) cells are a separate lineage of T lymphocytes with innate effector functions. They express an invariant TCR specific for lipids presented by CD1d and their development and effector differentiation rely on a unique gene expression program. We asked whether this program includes microRNAs, small noncoding RNAs that regulate gene expression posttranscriptionally and play a key role in the control of cellular differentiation programs. To this aim, we investigated iNKT cell development in mice in which Dicer, the RNase III enzyme that generates functional microRNAs, is deleted in cortical thymocytes. We find that Dicer deletion results in a substantial reduction of iNKT cells in thymus and their disappearance from the periphery, unlike mainstream T cells. Without Dicer, iNKT cells do not complete their innate effector differentiation and display a defective homeostasis due to increased cell death. Differentiation and homeostasis of iNKT cells require Dicer in a cell-autonomous fashion. Furthermore, we identify a miRNA profile specific for iNKT cells, which exhibits features of activated/effector T lymphocytes, consistent with the idea that iNKT cells undergo agonist thymic selection. Together, these results define a critical role of the Dicer-dependent miRNA pathway in the physiology of iNKT cells.

Distinct requirements for CD1d intracellular transport for development of V(alpha)14 iNKT cells

The positive selection of V(alpha)14 invariant (i)NKT cells in mice requires CD1d-mediated Ag presentation by CD4(+)CD8(+) thymocytes. Maturation of newly selected iNKT cells continues in the periphery and also involves CD1d expression. CD1d molecules acquire Ags for presentation in endosomal compartments, to which CD1d molecules have access through an intrinsic CD1d-encoded tyrosine motif and by association with the class II MHC chaperone, invariant chain. In this study, we report the generation of mice in which all CD1d is replaced by CD1d-enhanced yellow fluorescent fusion protein (EYFP). CD1d-EYFP molecules are stable, present lipid Ags, and have near normal subcellular distribution. CD1d-EYFP molecules mediated positive selection of V(alpha)14 iNKT cell precursors at decreased efficiency, caused a delay in their terminal maturation, and did not invoke V(alpha)14iNKT cell effector function as wild-type CD1d could. Using these mice, we show that the intrinsic CD1d-encoded sorting motif mediates thymic selection and activation of V(alpha)14 iNKT cells by professional APCs, while for peripheral terminal differentiation the intrinsic CD1d sorting motif is dispensable.

Cutting edge: the chemokine receptor CXCR3 retains invariant NK T cells in the thymus

The current model used to define T cell export from the thymus suggests that emigrating lymphocytes seed the peripheral organs as functionally mature cells. This model holds true for the majority of T cells exported from the thymus with the exception of invariant NK T (iNKT) cells. iNKT cells undergo lineage expansion after positive selection and acquire NK receptor expression once fully mature; yet, the majority of mature iNKT cells are retained in the thymus by an as of yet unidentified mechanism. In this study we demonstrate that mature iNKT cells are retained in the thymus by the chemokine receptor CXCR3. We propose that the expression of CXCR3 ligands in the thymic medullary epithelium promotes the chemotactic retention of mature iNKT thymocytes and prevents leakage of iNKT cells into the peripheral circulation.

Skin and peripheral lymph node invariant NKT cells are mainly retinoic acid receptor-related orphan receptor (gamma)t+ and respond preferentially under inflammatory conditions

Lymph nodes (LNs) have been long considered as comprising few invariant NKT (iNKT) cells, and these cells have not been studied extensively. In this study, we unravel the existence of stable rather than transitional LN-resident NK1.1(-) iNKT cell populations. We found the one resident in peripheral LNs (PLNs) to comprise a major IL-17-producing population and to express the retinoic acid receptor-related orphan receptor (gamma)t (ROR(gamma)t). These cells respond to their ligand alpha-galactosylceramide (alpha-GalCer) in vivo by expanding dramatically in the presence of LPS, providing insight into how this rare population could have an impact in immune responses to infection. PLN-resident ROR(gamma)t(+) NK1.1(-) iNKT cells express concomitantly CCR6, the integrin alpha-chain alpha(E) (CD103), and IL-1R type I (CD121a), indicating that they might play a role in inflamed epithelia. Accordingly, skin epithelia comprise a major ROR(gamma)t(+) CCR6(+)CD103(+)CD121a(+) NK1.1(-) cell population, reflecting iNKT cell composition in PLNs. Importantly, both skin and draining PLN ROR(gamma)t(+) iNKT cells respond preferentially to inflammatory signals and independently of IL-6, indicating that they could play a nonredundant role during inflammation. Overall, our study indicates that ROR(gamma)t(+) iNKT cells could play a major role in the skin during immune responses to infection and autoimmunity.

Role for hedgehog pathway in regulating growth and function of invariant NKT cells

Lymphocyte accumulation is characteristic of chronic hepatitis, but the mechanisms regulating lymphocyte numbers and their roles in liver disease progression are poorly understood. The Hedgehog (Hh) pathway regulates thymic development and lymphopoeisis during embryogenesis, and is activated in fibrosing liver disease in adults. Our objective was to determine if Hh ligands regulate the viability and phenotype of NKT cells, which comprise a substantial sub-population of resident lymphocytes in healthy adult livers and often accumulate during liver fibrosis. The results demonstrate that a mouse invariant NKT cell line (DN32 iNKT cells), mouse primary liver iNKT cells, and human peripheral blood iNKT cells are all responsive to sonic hedgehog (Shh). In cultured iNKT cells, Shh enhances proliferation, inhibits apoptosis, induces activation, and stimulates expression of the pro-fibrogenic cytokine, IL-13. Livers of transgenic mice with an overly active Hh pathway harbor increased numbers of iNKT cells. iNKT cells also express Shh. These results demonstrate that iNKT cells produce and respond to Hh ligands, and that Hh pathway activation regulates the size and cytokine production of liver iNKT cell populations. Therefore, Hh pathway activation may contribute to the local expansion of pro-fibrogenic iNKT cell populations during certain types of fibrosing liver damage.

Wiskott-Aldrich syndrome protein is required for homeostasis and function of invariant NKT cells

NKT cells comprise a separate T lineage expressing semi-invariant T cell receptors. Canonical invariant NKT (iNKT) cells specifically recognize lipid Ags presented by CD1d, a MHC class I-like molecule. iNKT cells function, in part, as initial responders to bacterial infection and play a role in immune surveillance and tumor rejection. The Wiskott-Aldrich Syndrome protein (WASp) serves as a crucial link between cellular stimuli and cytoskeletal rearrangements. Although we and others have identified a key role for WASp in homeostasis of T-regulatory and marginal zone B cells, little data exist regarding the role for WASp within the iNKT lineage. Analysis of WASp-expressing cell populations in heterozygous female WASp mice revealed a substantial selective advantage for WASp(+) vs WASp(-) iNKT cells. Although adult WASp-deficient (WASp(-/-)) mice had normal thymic and bone marrow iNKT numbers, we observed 2- to 3-fold reduction in the numbers of iNKT cells in the spleen and liver. This peripheral iNKT deficit is manifested, in part, due to defective iNKT homeostasis. WASp(-/-) iNKT cells exhibited reduced levels of integrin surface expression and decreased homing and/or retention within peripheral tissues in a competitive repopulation model. In addition, analysis of young mice showed that WASp is important for both maturation and egress of thymic iNKT cells. WASp(-/-) iNKT cells also exhibited a marked reduction in Ag-induced proliferation and cytokine production. Our findings highlight the crucial role for WASp in iNKT development, homeostasis, and activation, and identify iNKT dysfunction as an additional factor likely to contribute to the clinical features observed in WAS patients.

Intrathymic proliferation wave essential for Valpha14+ natural killer T cell development depends on c-Myc

The molecular requirements for invariant Valpha14-bearing natural killer T cells (iNKT) in the thymus are poorly understood. A minute population of approximately 500 newly selected CD69(+)CD24(+) stage 0 (ST0) iNKT cells gives rise to approximately 100 times more CD44(neg/lo)CD24(-) stage 1 (ST1) cells, which then generate similar frequencies of CD44(hi)CD24(-) stage 2 (ST2) and mature iNKT cells. Although the increased number of ST1 compared with ST0 cells indicates the initiation of a proliferation wave in the very early stages of iNKT cell development, details about the controlling mechanism are currently lacking. Here, we show that the transcription factor c-Myc is required for iNKT cell development. Conditional ablation of c-Myc in double-positive thymocytes specifically impacted iNKT but not conventional T cell development. Within the iNKT population, a progressive reduction of iNKT cells was observed starting at ST1 (approximately 50-fold) and ST2 (approximately 350-fold), with a complete lack of mature cells in thymus, spleen, and liver. ST0/ST1 c-Myc-deficient iNKT cells showed reduced proliferation. In contrast, annexin V staining did not reveal increased apoptosis, and transgenic overexpression of BCL-2 did not rescue iNKT cell development in c-Myc-deficient mice. Moreover, expression of known iNKT differentiation factors such as Plzf and Gata3 was not dramatically altered. These, findings provide compelling evidence that c-Myc mediates an intrathymic proliferation wave immediately after agonist selection of iNKT cells and illustrate the importance of this expansion for the generation of mature iNKT cells in vivo.

iNKT cell development is orchestrated by different branches of TGF-beta signaling

Invariant natural killer T (iNKT) cells constitute a distinct subset of T lymphocytes exhibiting important immune-regulatory functions. Although various steps of their differentiation have been well characterized, the factors controlling their development remain poorly documented. Here, we show that TGF-beta controls the differentiation program of iNKT cells. We demonstrate that TGF-beta signaling carefully and specifically orchestrates several steps of iNKT cell development. In vivo, this multifaceted role of TGF-beta involves the concerted action of different pathways of TGF-beta signaling. Whereas the Tif-1gamma branch controls lineage expansion, the Smad4 branch maintains the maturation stage that is initially repressed by a Tif-1gamma/Smad4-independent branch. Thus, these three different branches of TGF-beta signaling function in concert as complementary effectors, allowing TGF-beta to fine tune the iNKT cell differentiation program.

Cd1d-dependent regulation of bacterial colonization in the intestine of mice

The accumulation of certain species of bacteria in the intestine is involved in both tissue homeostasis and immune-mediated pathologies. The host mechanisms involved in controlling intestinal colonization with commensal bacteria are poorly understood. We observed that under specific pathogen-free or germ-free conditions, intragastric administration of Pseudomonas aeruginosa, E. coli, Staphylococcus aureus, or Lactobacillus gasseri resulted in increased colonization of the small intestine and bacterial translocation in mice lacking Cd1d, an MHC class I-like molecule, compared with WT mice. In contrast, activation of Cd1d-restricted T cells (NKT cells) with alpha-galactosylceramide caused diminished intestinal colonization with the same bacterial strains. We also found prominent differences in the composition of intestinal microbiota, including increased adherent bacteria, in Cd1d-/- mice in comparison to WT mice under specific pathogen-free conditions. Germ-free Cd1d-/- mice exhibited a defect in Paneth cell granule ultrastructure and ability to degranulate after bacterial colonization. In vitro, NKT cells were shown to induce the release of lysozyme from intestinal crypts. Together, these data support a role for Cd1d in regulating intestinal colonization through mechanisms that include the control of Paneth cell function.

The surprising diversity of lipid antigens for CD1-restricted T cells

CD1 proteins have been conserved throughout mammalian evolution and function to present lipid antigens to T cells. Crystal structures of CD1-lipid complexes show that CD1 antigen-binding grooves are composed of four pockets and two antigen entry portals. This structural information now provides a detailed understanding of how CD1-binding grooves capture a surprisingly diverse array of lipid ligands. CD1-expressing APCs are able to acquire lipid antigens from their own pool of lipids and from exogenous sources, including microbial pathogens, bystander cells, or even the systemic circulation. CD1 proteins bind to certain antigens using high stringency loading reactions within endosomes that involve low pH, glycosidases, and lipid transfer proteins. Other antigens can directly load onto CD1 proteins using low stringency mechanisms that are independent of cellular factors. New evidence from in vivo systems shows that CD1-restricted T cells influence outcomes in infectious, autoimmune, and allergic diseases. These studies lead to a broader view of the natural function of alphabeta T cells, which involves recognition of both cellular proteins and lipids.

NKT cells: from totipotency to regenerative medicine

The recent discovery that natural killer T (NKT) cell nuclei are totipotent opens a novel avenue for further understanding NKT cell function in normal and diseased states. The progeny of a cloned mouse harboring the in-frame rearranged Valpha14-Jalpha18 T cell receptor in one allele showed a significant increase in NKT cell number compared with wild-type or littermate control mice that possessed a different TCR. Importantly, NKT cells from such progeny produced both interferon-gamma and interleukin-4, a hallmark of NKT cells. In these progeny, NKT cell development appeared to be instructively, rather than permissively, determined. Using embryonic stem cells prepared via the somatic cell nuclear transfer of NKT nuclei, relatively mature NKT cells were induced under conditions permissible for T cell induction. Furthermore, these NKT cells matured autonomously upon injection into mice, resulting in an antigen-specific adjuvant effect.

The gene encoding early growth response 2, a target of the transcription factor NFAT, is required for the development and maturation of natural killer T cells

The influence of signals transmitted by the phosphatase calcineurin and the transcription factor NFAT on the development and function of natural killer T (NKT) cells is unclear. In this report, we demonstrate that the transcription factor early growth response 2 (Egr2), a target gene of NFAT, was specifically required for the ontogeny of NKT cells but not that of conventional CD4(+) or CD8(+) T cells. NKT cells developed normally in the absence of Egr1 or Egr3, which suggests that Egr2 is a specific regulator of NKT cell differentiation. We found that Egr2 was important in the selection, survival and maturation of NKT cells. Our findings emphasize the importance of the calcineurin-NFAT-Egr2 pathway in the development of the NKT lymphocyte lineage.

Intracellular bacterial infection and invariant NKT cells

The invariant (i) natural killer (NK)T cells represent a unique subset of T lymphocytes which express the V alpha 14 chain of the T cell receptor (TCR), that recognizes glycolipid antigens presented by the nonpolymorphic major histocompatibility complex (MHC) class I-like antigen presentation molecule CD1d, and they participate in protection against some microbial pathogens. Although iNKT cells have originally been regarded as T cells co-expressing NKR-P1B/C (NK1.1: CD 161), they do not seem to consistently express this marker, since NK1.1 surface expression on iNKT cells undergoes dramatic changes following facultative intracellular bacterial infection, which is correlated with functional changes of this cell population. Accumulating evidence suggests that NK1.1 allows recognition of "missing-self", thus controlling activation/inhibition of NK1.1-expressing cells. Therefore, it is tempting to suggest that iNKT cells participate in the regulation of host immune responses during facultative intracellular bacterial infection by controlling NK1.1 surface expression. These findings shed light not only on the unique role of iNKT cells in microbial infection, but also provide evidence for new aspects of the NK1.1 as a regulatory molecule on these cells.

V alpha14 i NKT cells are innate lymphocytes that participate in the immune response to diverse microbes

Natural Killer T (NKT) cells constitute a conserved T lymphocyte sublineage that has been implicated in the regulation of various immune responses, including the responses to viruses, bacteria, and parasites. NKT cells recognize self and foreign glycolipids presented by CD1d, a non-classical antigen-presenting molecule, and they rapidly produce various cytokines. Many studies have shown that NKT cells have protective roles following microbial infection through the amplification of innate and adaptive immunity, although NKT cells have detrimental roles in some cases. Recent studies have shed light on the natural antigens recognized by NKT cells and the mechanisms whereby they contribute to host defense, and they suggest that these unique T cells have evolved to jump start the immune response to microbes.

Allergic airway hyperresponsiveness-enhancing gammadelta T cells develop in normal untreated mice and fail to produce IL-4/13, unlike Th2 and NKT cells

Allergic airway hyperresponsiveness (AHR) in OVA-sensitized and challenged mice, mediated by allergen-specific Th2 cells and Th2-like invariant NKT (iNKT) cells, develops under the influence of enhancing and inhibitory gammadelta T cells. The AHR-enhancing cells belong to the Vgamma1(+) gammadelta T cell subset, cells that are capable of increasing IL-5 and IL-13 levels in the airways in a manner like Th2 cells. They also synergize with iNKT cells in mediating AHR. However, unlike Th2 cells, the AHR enhancers arise in untreated mice, and we show here that they exhibit their functional bias already as thymocytes, at an HSA(high) maturational stage. In further contrast to Th2 cells and also unlike iNKT cells, they could not be stimulated to produce IL-4 and IL-13, consistent with their synergistic dependence on iNKT cells in mediating AHR. Mice deficient in IFN-gamma, TNFRp75, or IL-4 did not produce these AHR-enhancing gammadelta T cells, but in the absence of IFN-gamma, spontaneous development of these cells was restored by adoptive transfer of IFN-gamma-competent dendritic cells from untreated donors. The i.p. injection of OVA/aluminum hydroxide restored development of the AHR enhancers in all of the mutant strains, indicating that the enhancers still can be induced when they fail to develop spontaneously, and that they themselves need not express TNFRp75, IFN-gamma, or IL-4 to exert their function. We conclude that both the development and the cytokine potential of the AHR-enhancing gammadelta T cells differs critically from that of Th2 cells and NKT cells, despite similar influences of these cell populations on AHR.

Rel/NF-kappaB family member RelA regulates NK1.1- to NK1.1+ transition as well as IL-15-induced expansion of NKT cells

Development of NKT cells was shown to depend on lymphotoxin (LT) and IL-15 signaling pathways as well as on cytokine receptor common gamma chain. After positive selection, NKT-cell precursors transit through progressive maturation stages including proliferative expansion within the NK1.1(-) window. The transcription factors that integrate different signaling pathways into different stages of NKT-cell development are not well characterized. Here, we show that the Rel/NF-kappaB family member RelA regulates the NK1.1(-) to NK1.1(+) transition during NKT-cell development. RelA is also required for both IL-15- and IL-7-induced proliferation of CD44(hi)NK1.1(-) NKT-cell precursors. Activation of the invariant NKT-cell receptor induces both IL-15 receptor alpha and gamma chains' expression in an NF-kappaB-dependent manner, suggesting a molecular mechanism by which NF-kappaB regulates NKT-cell development. NF-kappaB also regulates TCR-induced expression of LT-alpha and LT-beta within NKT cells. In contrast to previous reports, however, we show that LT signaling is dispensable for thymic NKT-cell development but is essential for their colonization of peripheral organs such as liver.

The adaptor molecule signaling lymphocytic activation molecule-associated protein (SAP) regulates IFN-gamma and IL-4 production in V alpha 14 transgenic NKT cells via effects on GATA-3 and T-bet expression

NKT cells comprise a rare regulatory T cell population of limited TCR diversity, with most cells using a Valpha14 Jalpha18 TCR. These cells exhibit a critical dependence on the signaling adapter molecule, signaling lymphocytic activation molecule-associated protein (SAP), for their ontogeny, an aspect not seen in conventional alphabeta T cells. Prior studies demonstrate that SAP enhances TCR-induced activation of NF-kappaB in CD4(+) T cells. Because NF-kappaB is required for NKT cell development, SAP might promote the ontogeny of this lineage by signaling to NF-kappaB. In this study, we demonstrate that forced expression of the NF-kappaB target gene, Bcl-x(L), or inhibitory NF-kappaB kinase beta, a catalytic subunit of the IkappaB kinase complex essential for NF-kappaB activation, fails to restore NKT cell development in sap(-/-) mice, suggesting that SAP mediates NKT cell development independently of NF-kappaB. To examine the role of SAP in NKT cell function, we generated NKT cells in sap(-/-) mice by expressing a transgene encoding the Valpha14 Jalpha18 component of the invariant TCR. These cells bound alpha-galactosylceramide-loaded CD1d tetramers, but exhibited a very immature CD24(+)NK1.1(-) phenotype. Although sap(-/-) tetramer-reactive cells proliferated in response to TCR activation, they did not produce appreciable levels of IL-4 or IFN-gamma. The reduction in cytokine production correlated with the near absence of GATA-3 and T-bet, key transcription factors regulating cytokine expression and maturation of NKT cells. Ectopic expression of GATA-3 partially restored IL-4 production by the NKT cells. Collectively, these data suggest that by promoting GATA-3 and T-bet expression, SAP exerts control over NKT cell development and mature NKT cell cytokine production.

Identification of CD25+ gamma delta T cells as fetal thymus-derived naturally occurring IL-17 producers

We previously reported that resident gammadelta T cells in the peritoneal cavity rapidly produced IL-17 in response to Escherichia coli infection to mobilize neutrophils. We found in this study that the IL-17-producing gammadelta T cells did not produce IFN-gamma or IL-4, similar to Th17 cells. IL-17-producing gammadelta T cells specifically express CD25 but not CD122, whereas CD122(+) gammadelta T cells produced IFN-gamma. IL-17-producing gammadelta T cells were decreased but still present in IL-2- or CD25-deficient mice, suggesting a role of IL-2 for their maintenance. IFN-gamma-producing CD122(+) gammadelta T cells were selectively decreased in IL-15-deficient mice. Surprisingly, IL-17-producing gammadelta T cells were already detected in the thymus, although CD25 was not expressed on the intrathymic IL-17-producing gammadelta T cells. The number of thymic IL-17-producing gammadelta T cells was peaked at perinatal period and decreased thereafter, coincided with the developmental kinetics of Vgamma6(+) Vdelta1(+) gammadelta T cells. The number of IL-17-producing gammadelta T cells was decreased in fetal thymus of Vdelta1-deficient mice, whereas Vgamma5(+) fetal thymocytes in normal mice did not produce IL-17. Thus, it was revealed that the fetal thymus-derived Vgamma6(+) Vdelta1(+) T cells functionally differentiate to produce IL-17 within thymus and thereafter express CD25 to be maintained in the periphery.

Critical role of ROR-γt in a new thymic pathway leading to IL-17-producing invariant NKT cell differentiation

Invariant natural killer T (iNKT) cells constitute a subpopulation of T cells that recognize glycolipids presented by CD1d molecules. They are characterized by their prompt production of interleukin-4 (IL-4) and interferon-gamma (IFN-gamma), which enables them to modulate diverse immune responses. Recently, we enlarged this concept by identifying a distinct IL-17-producing iNKT cell subset, named iNKT17 cells. The mechanisms leading to the acquisition of this new iNKT cell activity are unknown. Herein we show that IL-17-producing iNKT cells are already present in the thymus, predominantly among a subset regarded so far as an immature stage of thymic iNKT cell development, the CD1d tetramer(pos)CD44(pos)NK1.1(neg)CD4(neg) cells. Using EGFP reporter mice, we demonstrate that the transcription factor ROR-gammat is critical for the thymic differentiation of this subset because only ROR-gammat(pos) iNKT cells are capable of massively secreting IL-17. Moreover, IL-17-producing CD1d tetramer(pos)CD44(pos)NK1.1(neg)CD4(neg) thymic iNKT cells have reached a mature differentiation stage because they fail to generate other cell subsets in fetal thymic organ culture. Conversely, thymic ROR-gammat(neg) iNKT cell precursors give rise to progeny, but acquire neither ROR-gammat expression nor the ability to secrete IL-17. In conclusion, our findings demonstrate an alternative thymic pathway leading to the development of iNKT17 cells that requires ROR-gammat expression.

Glycolipid ligands of invariant natural killer T cells as vaccine adjuvants

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that recognize glycolipid antigens in the context of the antigen-presenting molecule CD1d. Upon glycolipid antigen stimulation, iNKT cells rapidly produce copious amounts of immunomodulatory cytokines, leading to potent activation of a variety of innate and adaptive immune cells. These immune-potentiating properties of iNKT cells hold great promise for the development of vaccine adjuvants. This review aims to summarize the immunomodulatory activities of iNKT cell ligands and to discuss prospects for developing iNKT cell-based vaccine adjuvants.

MHC class II-dependent T-T interactions create a diverse, functional and immunoregulatory reaction circle

Unlike conventional T cells, innate-like T cells such as natural killer (NK) T cells are selected by homotypic T-cell interactions. Recently, a few reports have shown that T-T CD4(+) T cells can be generated in a similar manner to that for NKT cells. These two types of cells share common functional properties such as rapid response to antigenic encounters and the potential for a panoply of cytokine secretion. However, T-T CD4(+) T cells differ from NKT cells in that they are restricted by highly polymorphic major histocompatibility complex (MHC) II molecules and have a diverse T-cell receptor repertoire. Additional example of T-T interactions was recently reported in which peripheral T cells re-circulate to the thymus and participate in the thymocyte selection process. In this review, we dissect the cellular mechanisms underlying the production of T-T CD4(+) and NKT cells, with particular emphasis on the differences between these two T-cell prototypes. Finally, we propose that T-T CD4(+) T cells serve two major functions: one as an acute-phase reactant against viral infection and the other is the generation of anti-ergotypic CD4(+) T cells for regulatory purposes. All of these features make it possible to create a diverse set of functional cells through MHC class II-restricted T-T interactions.

Invariant NKT cells regulate experimental autoimmune encephalomyelitis and infiltrate the central nervous system in a CD1d-independent manner

Invariant NKT cells are CD1d-restricted T cells specific for glycolipid Ags. Their activation or transgenic enrichment abrogates the development of experimental autoimmune encephalomyelitis (EAE). Herein, we demonstrate that in NKT-enriched mice the protection from EAE is associated with the infiltration of NKT cells in the CNS and the local expression of CD1d. This indicates that the CNS acquires the potential for local glycolipid presentation when exposed to inflammatory stress, permitting the triggering of NKT cells. To address the importance of CD1d-mediated Ag presentation, we used transgenic mice that express CD1d solely in the thymus. Interestingly, enrichment of NKT cells in these mice also conferred resistance to EAE, with an efficacy indistinguishable from that of NKT-enriched CD1d-sufficient mice. This protection was due to an abrogation of the encephalitogenic Th1 and Th17 response in the spleen, revealing that endogenous glycolipid presentation is dispensable for the regulatory function of NKT cells in EAE. Moreover, abrogating extrathymic CD1d expression failed to affect both the recruitment of NKT cells and their effector phenotype. CNS-infiltrating NKT cells were characterized by a cytotoxic IFN-gamma(high)IL-4(low)IL-10(low)granzyme B(high) profile, irrespective of the local expression of CD1d. Glycolipid Ag presentation is therefore dispensable for the control of autoimmune demyelination by NKT cells, underlining the importance of alternative cognate and/or soluble factors in the control of NKT cell function.