Inhibition of T Cell Differentiation into Effectors by NKT Cells Requires Cell Contacts

The Inhibitory G Protein α-Subunit, Gαz, Promotes Type 1 Diabetes-Like Pathophysiology in NOD Mice

The α-subunit of the heterotrimeric Gz protein, Gαz, promotes β-cell death and inhibits β-cell replication when pancreatic islets are challenged by stressors. Thus, we hypothesized that loss of Gαz protein would preserve functional β-cell mass in the nonobese diabetic (NOD) model, protecting from overt diabetes. We saw that protection from diabetes was robust and durable up to 35 weeks of age in Gαz knockout mice. By 17 weeks of age, Gαz-null NOD mice had significantly higher diabetes-free survival than wild-type littermates. Islets from these mice had reduced markers of proinflammatory immune cell infiltration on both the histological and transcript levels and secreted more insulin in response to glucose. Further analyses of pancreas sections revealed significantly fewer terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL)-positive β-cells in Gαz-null islets despite similar immune infiltration in control mice. Islets from Gαz-null mice also exhibited a higher percentage of Ki-67-positive β-cells, a measure of proliferation, even in the presence of immune infiltration. Finally, β-cell-specific Gαz-null mice phenocopy whole-body Gαz-null mice in their protection from developing hyperglycemia after streptozotocin administration, supporting a β-cell-centric role for Gαz in diabetes pathophysiology. We propose that Gαz plays a key role in β-cell signaling that becomes dysfunctional in the type 1 diabetes setting, accelerating the death of β-cells, which promotes further accumulation of immune cells in the pancreatic islets, and inhibiting a restorative proliferative response.

Interleukin-13 Pathway Alterations Impair Invariant Natural Killer T-Cell-Mediated Regulation of Effector T Cells in Type 1 Diabetes

Many studies have shown that human natural killer T (NKT) cells can promote immunity to pathogens, but their regulatory function is still being investigated. Invariant NKT (iNKT) cells have been shown to be effective in preventing type 1 diabetes in the NOD mouse model. Activation of plasmacytoid dendritic cells, modulation of B-cell responses, and immune deviation were proposed to be responsible for the suppressive effect of iNKT cells. We studied the regulatory capacity of human iNKT cells from control subjects and patients with type 1 diabetes (T1D) at disease clinical onset. We demonstrate that control iNKT cells suppress the proliferation of effector T cells (Teffs) through a cell contact-independent mechanism. Of note, suppression depended on the secretion of interleukin-13 (IL-13) by iNKT cells because an antibody blocking this cytokine resulted from the abrogation of Teff suppression; however, T1D-derived iNKT cells showed impaired regulation that could be attributed to the decrease in IL-13 secretion. Thus, alteration of the IL-13 pathway at disease onset may lead to the progression of the autoimmune response in T1D. Advances in the study of iNKT cells and the selection of agonists potentiating IL-13 secretion should permit new therapeutic strategies to prevent the development of T1D.

iNKT and MAIT Cell Alterations in Diabetes

Type 1 diabetes (T1D) and type 2 diabetes (T2D) are multifactorial diseases with different etiologies in which chronic inflammation takes place. Defects in invariant natural killer T (iNKT) cell populations have been reported in both T1D and T2D patients, mouse models and our recent study revealed mucosal-associated invariant T (MAIT) cell defects in T2D and obese patients. Regarding iNKT cells many studies in non-obese diabetic mice demonstrated their protective role against T1D whereas their potential role in human T1D is still under debate. Studies in mouse models and patients suggest that iNKT cells present in adipose tissue (AT) could exert a regulatory role against obesity and associated metabolic disorders, such as T2D. Scarce data are yet available on MAIT cells; however, we recently described MAIT cell abnormalities in the blood and ATs from obese and T2D patients. These data show that a link between MAIT cells and metabolic disorders pave the way for further investigations on MAIT cells in T1D and T2D in humans and mouse models. Furthermore, we hypothesize that the gut microbiota alterations associated with T1D and T2D could modulate iNKT and MAIT cell frequency and functions. The potential role of iNKT and MAIT cells in the regulation of metabolic pathways and their cross-talk with microbiota represent exciting new lines of research.

Plasmacytoid dendritic cells license regulatory T cells, upon iNKT-cell stimulation, to prevent autoimmune diabetes

Invariant NKT (iNKT)-cell stimulation with exogenous specific ligands prevents the development of type 1 diabetes (T1D) in NOD mice. Studies based on anti-islet T-cell transfer showed that iNKT cells prevent the differentiation of these T cells into effector T cells in the pancreatic lymph nodes (PLNs). We hypothesize that this defective priming could be explained by the ability of iNKT cells to induce tolerogenic dendritic cells (DCs) in the PLNs. We evaluated the effect of iNKT-cell stimulation on T1D development by transferring naïve diabetogenic BDC2.5 T cells into proinsulin 2(-/-) NOD mice treated with a long-lasting α-galactosylceramide regimen. In this context, iNKT cells induce the conversion of BDC2.5 T cells into Foxp3(+) Treg cells in the PLNs accumulating in the pancreatic islets. Furthermore, tolerogenic plasmacytoid DCs (pDCs) characterized by low MHC class II molecule expression and TGF-β production are critical in the PLNs for the recruitment of Treg cells into the pancreatic islets by inducing CXCR3 expression. Accordingly, pDC depletion in α-galactosylceramide-treated proinsulin 2(-/-) NOD mice abrogates the protection against T1D. These findings reveal that upon repetitive iNKT-cell stimulation, pDCs are critical for the recruitment of Treg cells in the pancreatic islets and the prevention of T1D development.

Advances in our understanding of the pathophysiology of Type 1 diabetes: lessons from the NOD mouse

T1D (Type 1 diabetes) is an autoimmune disease caused by the immune-mediated destruction of pancreatic β-cells. Studies in T1D patients have been limited by the availability of pancreatic samples, a protracted pre-diabetic phase and limitations in markers that reflect β-cell mass and function. The NOD (non-obese diabetic) mouse is currently the best available animal model of T1D, since it develops disease spontaneously and shares many genetic and immunopathogenic features with human T1D. Consequently, the NOD mouse has been extensively studied and has made a tremendous contribution to our understanding of human T1D. The present review summarizes the key lessons from NOD mouse studies concerning the genetic susceptibility, aetiology and immunopathogenic mechanisms that contribute to autoimmune destruction of β-cells. Finally, we summarize the potential and limitations of immunotherapeutic strategies, successful in NOD mice, now being trialled in T1D patients and individuals at risk of developing T1D.

[Regulatory role of NKT cells in the prevention of type 1 diabetes]

Type 1 diabetes is an autoimmune disease resulting from the destruction of pancreatic β cells by the immune system. NKT cells are innate-like T cells that can exert potent immuno-regulatory functions. The regulatory role of NKT cells was initially proposed after the observed decreased frequency of this subset in mouse models of type 1 diabetes, as well as in patients developing various autoimmune pathologies. Increasing NKT cell frequency and function prevent the development of type 1 diabetes in mouse models. Several mechanisms including IL-4 and IL-10 production by NKT cells and the accumulation of tolerogenic dendritic cells are critical for the dampening of pathogenic anti-islet T cell responses by NKT cells. Importantly, these cells can at the same time prevent diabetes and promote efficient immune responses against infectious agents. These results strengthen the potential role of NKT cells as a key target for the development of therapeutic strategies against type 1 diabetes.

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.

Invariant NKT cells suppress CD8(+) T-cell-mediated allergic contact dermatitis independently of regulatory CD4(+) T cells

Invariant natural killer T (iNKT) cells expressing a CD1d-restricted invariant αβTCR have key regulatory roles in autoimmunity, pathogen immunity, and tumor surveillance, but their function in the control of allergic skin diseases remains poorly documented. Using a model of contact hypersensitivity (CHS) to the hapten DNFB, we show here that iNKT cell deficiency results in enhanced skin inflammation due to augmented hapten-specific IFN-γ-producing CD8(+) effectors in skin draining lymph nodes (dLNs) and their massive recruitment into the allergen-exposed skin. Adoptive transfer and antibody depletion experiments as well as in vitro studies revealed that iNKT cells (1) reduce the severity of CHS, even in presensitized mice, (2) require hapten presentation by CD1d(+) dendritic cells (DCs) to dampen skin inflammation, and (3) produce IL-4 and IL-13 after CD1d-dependent in vitro stimulation by hapten-loaded DCs only in the presence of IFN-γ released from activated CD8(+) effector T cells. In corollary, mice double deficient in IL-4 and IL-13 exhibit an exacerbated CHS. Finally, iNKT-suppressive function is independent of Foxp3(+) regulatory T cells (Tregs). These data highlight that, besides Foxp3(+) Tregs, iNKT cells are potent downregulators of CD8(+) T cell-mediated CHS, and underscore that both cell types are important for the regulation of allergic skin inflammation.

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

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

Rapamycin combined with TGF-β converts human invariant NKT cells into suppressive Foxp3+ regulatory cells

Invariant NKT (iNKT) cells constitute a versatile T cell subset with important regulatory functions, which are thought to result essentially from their capacity to promptly produce cytokines that influence the Th1/Th2 balance. In this study, we report that these cells can also express Foxp3, an important transcriptional regulator associated with suppressive activity, once they have been exposed to TGF-β. Foxp3 was expressed by iNKT cells from both peripheral and cord blood. CD4(+) iNKT cells acquired Foxp3 expression preferentially, although a lower proportion of their CD4(-) counterpart also became positive. All Foxp3(+) iNKT cells displayed CD25 but not necessarily CTLA4 or GITR, regardless of the upregulation of these markers in the presence of TGF-β. Exposure to TGF-β decreased IL-4 and IFN-γ production while increasing IL-10, independently from Foxp3 expression. IL-17 was not detected. TGF-β induced high levels of Foxp3, but no suppressor activity, which emerged only in the presence of rapamycin. Peripheral and cord blood Foxp3(+) iNKT cells suppressed the proliferation of conventional autologous and heterologous CD4(+) T cells equally, in a cell contact-dependent and Ag-independent manner. Our findings demonstrate that human iNKT cells become suppressive in the presence of TGF-β plus rapamycin, thus adding a new facet to their complex functional properties.

NOD mice contain an elevated frequency of iNKT17 cells that exacerbate diabetes

Invariant natural killer T (iNKT) cells are a distinct lineage of innate-like T lymphocytes and converging studies in mouse models have demonstrated the protective role of iNKT cells in the development of type 1 diabetes. Recently, a new subset of iNKT cells, producing high levels of the pro-inflammatory cytokine IL-17, has been identified (iNKT17 cells). Since this cytokine has been implicated in several autoimmune diseases, we have analyzed iNKT17 cell frequency, absolute number and phenotypes in the pancreas and lymphoid organs in non-obese diabetic (NOD) mice. The role of iNKT17 cells in the development of diabetes was investigated using transfer experiments. NOD mice exhibit a higher frequency and absolute number of iNKT17 cells in the lymphoid organs as compared with C57BL/6 mice. iNKT17 cells infiltrate the pancreas of NOD mice where they express IL-17 mRNA. Contrary to the protective role of CD4(+) iNKT cells, the CD4(-) iNKT cell population, which contains iNKT17 cells, enhances the incidence of diabetes. Treatment with a blocking anti-IL-17 antibody prevents the exacerbation of the disease. This study reveals that different iNKT cell subsets play distinct roles in the regulation of type 1 diabetes and iNKT17 cells, which are abundant in NOD mice, exacerbate diabetes development.

The split personality of NKT cells in malignancy, autoimmune and allergic disorders

NKT cells are a heterogeneous subset of specialized, self-reactive T cells, with innate and adaptive immune properties, which allow them to bridge innate and adaptive immunity and profoundly influence autoimmune and malignant disease outcomes. NKT cells mediate these activities through their ability to rapidly express pro- and anti-inflammatory cytokines that influence the type and magnitude of the immune response. Not only do NKT cells regulate the functions of other cell types, but experimental evidence has found NKT cell subsets can modulate the functions of other NKT subsets. Depending on underlying mechanisms, NKT cells can inhibit or exacerbate autoimmunity and malignancy, making them potential targets for disease intervention. NKT cells can respond to foreign and endogenous antigenic glycolipid signals that are expressed during pathogenic invasion or ongoing inflammation, respectively, allowing them to rapidly react to and influence a broad array of diseases. In this article we review the unique development and activation pathways of NKT cells and focus on how these attributes augment or exacerbate autoimmune disorders and malignancy. We also examine the growing evidence that NKT cells are involved in liver inflammatory conditions that can contribute to the development of malignancy.

NKT cells inhibit antigen-specific effector CD8 T cell induction to skin viral proteins

We recently demonstrated that CD1d-restricted NKT cells resident in skin can inhibit CD8 T cell-mediated graft rejection of human papillomavirus E7-expressing skin through an IFN-γ-dependent mechanism. In this study, we examined the role of systemically derived NKT cells in regulating the rejection of skin grafts expressing viral proteins. In lymph nodes draining transplanted skin, Ag-specific CD8 T cell proliferation, cytokine production, and cytotoxic activity were impaired by NKT cells. NKT cell suppression was mediated via CD11c(+) dendritic cells. Inhibition of CD8 T cell function did not require Foxp3(+) regulatory T cells or NKT cell-secreted IFN-γ, IL-10, or IL-17. Thus, following skin grafting or immunization with human papillomavirus-E7 oncoprotein, NKT cells reduce the capacity of draining lymph node-resident APCs to cross-present Ag to CD8 T cell precursors, as evidenced by impaired expansion and differentiation to Ag-specific CD8 T effector cells. Therefore, in the context of viral Ag challenge in the skin, systemic NKT cells limit the capacity for effective priming of adaptive immunity.

Alcohol facilitates CD1d loading, subsequent activation of NKT cells, and reduces the incidence of diabetes in NOD mice

Background

Ethanol (‘alcohol’) is a partly hydrophobic detergent that may affect the accessibility of glycolipids thereby influencing immunological effects of these molecules.

Methods

The study included cellular in vitro tests using α-galactosylceramide (αGalCer), and in vivo NOD mice experiments detecting diabetes incidence and performing behavioural and bacterial analyses.

Results

Alcohol in concentrations from 0.6% to 2.5% increased IL-2 production from NKT cells stimulated with αGalCer by 60% (p<0.05). CD1d expressed on HeLa cells contained significantly increasing amounts of αGalCer with increasing concentrations of alcohol, suggesting that alcohol facilitated the passive loading of αGalCer to CD1d. NOD mice were found to tolerate 5% ethanol in their drinking water without signs of impairment in liver function. Giving this treatment, the diabetes incidence declined significantly. Higher numbers of CD3+CD49b+ NKT cells were found in spleen and liver of the alcohol treated compared to the control mice (p<0.05), whereas the amount of CD4+Foxp3+ regulator T cells did not differ. Increased concentrations of IFN-γ were detected in 24-hour blood samples of alcohol treated mice. Behavioural studies showed no change in attitude of the ethanol-consuming mice, and bacterial composition of caecum samples was not affected by alcohol, disqualifying these as protective mechanisms.

Conclusion

Alcohol facilitates the uptake of glycolipids and the stimulation of NKT cells, which are known to counteract Type 1 diabetes development. We propose that this is the acting mechanism by which treatment with alcohol reduces the incidence of diabetes in NOD mice. This is corroborated by epidemiology showing beneficial effect of alcohol to reduce the severity of atherosclerosis and related diseases.

Role of SLAM in NKT cell development revealed by transgenic complementation in NOD mice

Allelic variation of SLAM expression on CD4(+)CD8(+) thymocytes has been proposed to play a major role in NKT cell development. In this article, this hypothesis is tested by the production of subcongenic mouse strains and Slamf1 transgenic lines. The long isoform of the C57BL/6 allele of Slamf1 was transgenically expressed on CD4(+)CD8(+) thymocytes under control of an hCD2 minigene. NOD.Nkrp1b.Tg(Slamf1)1 mice, which had a 2-fold increase in SLAM protein expression on CD4(+)CD8(+) thymocytes, had a 2-fold increase in numbers of thymic NKT cells. The additional thymic NKT cells in NOD.Nkrp1b.Tg(Slamf1)1 mice were relatively immature, with a similar subset distribution to those of congenic NOD.Nkrp1b.Nkt1 and NOD.Nkrp1b.Slamf1 mice, which also express increased levels of SLAM on CD4(+)CD8(+) thymocytes and produce larger numbers of NKT cells. Transgenic enhancement of SLAM expression also increased IL-4 and IL-17 production in response to TCR-mediated stimulation. Paradoxically, NOD.Nkrp1b.Tg(Slamf1)2 mice, which had a 7-fold increase in SLAM expression, showed no significant increase in NKT cells numbers; on the contrary, at high transgene copy number, SLAM expression levels correlated inversely with NKT cell numbers, consistent with a contribution to negative selection. These data confirm a role for SLAM in controlling NKT cell development and are consistent with a role in both positive and negative thymic selection of 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.

Invariant NKT cells regulate experimental autoimmune uveitis through inhibition of Th17 differentiation

Although NKT cells have been implicated in diverse immunomodulatory responses, the effector mechanisms underlying the NKT cell-mediated regulation of pathogenic T helper cells are not well understood. Here, we show that invariant NKT cells inhibited the differentiation of CD4(+) T cells into Th17 cells both in vitro and in vivo. The number of IL-17-producing CD4(+) T cells was reduced following co-culture with purified NK1.1(+) TCR(+) cells from WT, but not from CD1d(-/-) or Jα18(-/-) , mice. Co-cultured NKT cells from either cytokine-deficient (IL-4(-/-) , IL-10(-/-) , or IFN-γ(-/-) ) or WT mice efficiently inhibited Th17 differentiation. The contact-dependent mechanisms of NKT cell-mediated regulation of Th17 differentiation were confirmed using transwell co-culture experiments. On the contrary, the suppression of Th1 differentiation was dependent on IL-4 derived from the NKT cells. The in vivo regulatory capacity of NKT cells on Th17 cells was confirmed using an experimental autoimmune uveitis model induced with human IRBP(1-20) (IRBP, interphotoreceptor retinoid-binding protein) peptide. NKT cell-deficient mice (CD1d(-/-) or Jα18(-/-) ) demonstrated an increased disease severity, which was reversed by the transfer of WT or cytokine-deficient (IL-4(-/-) , IL-10(-/-) , or IFN-γ(-/-) ) NKT cells. Our results indicate that invariant NKT cells inhibited autoimmune uveitis predominantly through the cytokine-independent inhibition of Th17 differentiation.

Mechanism of regulation of autoimmunity by iNKT cells

iNKT cells, CD1d dependent natural killer T cells are a unique population of T cells. The capacity of iNKT cells to produce regulatory cytokines first provided an indication of their regulatory potential. Later on, in experimental models as well as in patients afflicted with an auto-immune disease, such as Type 1 diabetes mellitus, multiple sclerosis, and systemic lupus erythematosus along with others, a deficit in iNKT cell number was observed, suggesting the role these cells may possibly have in the prevention of auto-immune diseases. More importantly, experimental strategies which focused on increasing the volume or stimulation of iNKT cells in laboratory animals, demonstrated an improved level of protection against the development of auto-immune diseases. This article reviews the mechanism of protection against autoimmunity by iNKT cells, discusses the obstacles against and indications for the potential use of iNKT cell manipulation in the treatment of human auto-immune diseases.

Endogenous collagen peptide activation of CD1d-restricted NKT cells ameliorates tissue-specific inflammation in mice

NKT cells in the mouse recognize antigen in the context of the MHC class I-like molecule CD1d and play an important role in peripheral tolerance and protection against autoimmune and other diseases. NKT cells are usually activated by CD1d-presented lipid antigens. However, peptide recognition in the context of CD1 has also been documented, although no self-peptide ligands have been reported to date. Here, we have identified an endogenous peptide that is presented by CD1d to activate mouse NKT cells. This peptide, the immunodominant epitope from mouse collagen type II (mCII707-721), was not associated with either MHC class I or II. Activation of CD1d-restricted mCII707-721-specific NKT cells was induced via TCR signaling and classical costimulation. In addition, mCII707-721-specific NKT cells induced T cell death through Fas/FasL, in an IL-17A-independent fashion. Moreover, mCII707-721-specific NKT cells suppressed a range of in vivo inflammatory conditions, including delayed-type hypersensitivity, antigen-induced airway inflammation, collagen-induced arthritis, and EAE, which were all ameliorated by mCII707-721 vaccination. The findings presented here offer new insight into the intrinsic roles of NKT cells in health and disease. Given the results, endogenous collagen peptide activators of NKT cells may offer promise as novel therapeutics in tissue-specific autoimmune and inflammatory diseases.

On/off TLR signaling decides proinflammatory or tolerogenic dendritic cell maturation upon CD1d-mediated interaction with invariant NKT cells

Invariant NKT (iNKT) cells play an effector/adjuvant function during antimicrobial and antitumoral immunity and a regulatory role to induce immune tolerance and prevent autoimmunity. iNKT cells that differentially modulate adaptive immunity do not bear a unique phenotype and/or specific cytokine secretion profile, thus opening questions on how a single T cell subset can exert opposite immunological tasks. In this study, we show that iNKT cells perform their dual roles through a single mechanism of action relying on the cognate interaction with myeloid dendritic cells (DCs) and leading to opposite effects depending on the presence of other maturation stimuli simultaneously acting on DCs. The contact of murine purified iNKT cells with immature autologous DCs directly triggers the tolerogenic maturation of DCs, rendering them able to induce regulatory T cell differentiation and prevent autoimmune diabetes in vivo. Conversely, the interaction of the same purified iNKT cells with DCs, in the presence of simultaneous TLR4 stimulation, significantly enhances proinflammatory DC maturation and IL-12 secretion. The different iNKT cell effects are mediated through distinct mechanisms and activation of different molecular pathways within the DC: CD1d signaling and activation of the ERK1/2 pathway for the tolerogenic action, and CD40-CD40L interaction and NF-κB activation for the adjuvant effect. Our data suggest that the DC decision to undergo proinflammatory or tolerogenic maturation results from the integration of different signals received at the time of iNKT cell contact and could have important therapeutic implications for exploiting iNKT cell adjuvant/regulatory properties in autoimmune diseases, infections, and cancer.

Type-specific human papillomavirus detection in cervical smears in Romania

To study type 1 diabetes (T1D), excellent animal models exist, both spontaneously diabetic and virus-induced. Based on knowledge from these, this review focuses on the environmental factors leading to T1D, concentrated into four areas which are: (1) The thymus-dependent immune system: T1D is a T cell driven disease and the beta cells are destroyed in an inflammatory insulitis process. Autoimmunity is breakdown of self-tolerance and the balance between regulator T cells and aggressive effector T cells is disturbed. Inhibition of the T cells (by e.g. anti-CD3 antibody or cyclosporine) will stop the T1D process, even if initiated by virus. Theoretically, the risk from immunotherapy elicits a higher frequency of malignancy. (2) The activity of the beta cells: Resting beta cells display less antigenicity and are less sensitive to immune destruction. Beta-cell rest can be induced by giving insulin externally in metabolic doses or by administering potassium-channel openers. Both procedures prevent T1D in animal models, whereas no good human data exist due to the risk of hypoglycemia. (3) NKT cells: According to the hygiene hypothesis, stimulation of NKT cells by non-pathogen microbes gives rise to less T cell reaction and less autoimmunity. Glycolipids presented by CD1 molecules are central in this stimulation. (4) Importance of the intestine and gliadin intake: Gluten-free diet dramatically inhibits T1D in animal models, and epidemiological data are supportive of such an effect in humans. The mechanisms include less subclinical intestinal inflammation and permeability, and changed composition of bacterial flora, which can also be obtained by intake of probiotics. Gluten-free diet is difficult to implement, and short-term intake has no effect. Regarding the onset of the T1D disease process, slow-acting enterovirus and gliadin deposits are speculated to be etiological in genetically susceptible individuals, followed by the mentioned four pathogenetic factors acting in concert. Neutralization of any one of these factors is capable of stopping T1D development, as lessons are learned from the animal models.

The dangerous liaison between iNKT cells and dendritic cells: does it prevent or promote autoimmune diseases?

Invariant natural killer T (iNKT) cells represent an important regulatory T-cell subset that perceives signals of danger and/or cellular distress and modulate the adaptive immune response accordingly. In the presence of pathogens, iNKT cells acquire an adjuvant function that is fundamental to boost anti-microbial and anti-tumor immunity. At the same time, iNKT cells can play a negative regulatory function to maintain peripheral T-cell tolerance toward self-antigens and to prevent autoimmune disease. Both these effects of iNKT cells involve the modulation of the activity of dendritic cells (DCs) through cell-cell interaction. Indeed, iNKT cells can either boost Th1 immunity by enhancing maturation of pro-inflammatory DCs or promote immune tolerance through the maturation of tolerogenic DCs. This dual action of iNKT cells opens questions on the modalities by which a single-cell subset can exert opposite effects on DCs and may even put in question the overall immunosuppressive properties of iNKT cells. This review presents the large body of evidence that shows the ability of iNKT cells to negatively regulate autoimmunity and to prevent autoimmune diseases including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus. In addition, an update is provided on the mechanisms of iNKT-DCs interactions and how this can result in inflammatory or tolerogenic responses.

Regulation of type 1 diabetes, tuberculosis, and asthma by parasites

Helminth infection is a worldwide health problem. In addition to directly causing disease, helminthic infection also affects the incidence and progression of other diseases by exerting immune modulatory effects. In animal models, infection with helminthic parasites can prevent autoimmune diseases and allergic inflammatory diseases, but worsens protective immunity to certain infectious pathogens. In this review, we summarize current findings regarding the effects of helminth infection on type 1 diabetes, tuberculosis, and asthma and discuss possible mechanisms through which helminthic parasites modulate host immunity. Investigating these mechanisms could lead to treatment strategies that specifically modulate the immune response as well as address fundamental questions in immunobiology.

Therapeutic Potential of CD1d-Restricted Invariant Natural Killer T Cell–based Treatment for Autoimmune Diseases

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

Clinical application of NKT cell biology in type I (autoimmune) diabetes mellitus

Type 1 natural killer T (NKT) cells are a population of CD1d-restricted, regulatory T cells that exhibit various NK cell characteristics and rapidly produce cytokines on stimulation with glycolipid antigen. In type I diabetes (TID), NKT cells are thought to have a tolerogenic function, evidenced by NKT cell numerical and functional deficiencies in the nonobese diabetic (NOD) mouse, which when corrected, can ameliorate disease. The mechanisms by which NKT cells can mediate their immunosuppressive effects in NOD mice are still poorly understood, which makes successful clinical translation of NKT- cell-based therapies challenging. However, new insights into the genetic control of NKT cell deficiencies have provided some understanding of the genes that may control NKT cell number and function, potentially offering a new avenue for assessing TID risk in humans. Here, we review the mechanisms by which NKT cells are thought to prevent TID, discuss the evidence for involvement of NKT cells in the regulation of human TID and examine the genetic control of NKT cell number and function. A greater understanding of these areas will increase the chances of successful clinical manipulation of NKT cells to prevent or treat TID.

Activation of invariant NKT cells ameliorates experimental ocular autoimmunity by a mechanism involving innate IFN-gamma production and dampening of the adaptive Th1 and Th17 responses

Invariant NKT cells (iNKT cells) have been reported to play a role not only in innate immunity but also to regulate several models of autoimmunity. Furthermore, iNKT cells are necessary for the generation of the prototypic eye-related immune regulatory phenomenon, anterior chamber associated immune deviation (ACAID). In this study, we explore the role of iNKT cells in regulation of autoimmunity to retina, using a model of experimental autoimmune uveitis (EAU) in mice immunized with a uveitogenic regimen of the retinal Ag, interphotoreceptor retinoid-binding protein. Natural strain-specific variation in iNKT number or induced genetic deficiencies in iNKT did not alter baseline susceptibility to EAU. However, iNKT function seemed to correlate with susceptibility and its pharmacological enhancement in vivo by treatment with iNKT TCR ligands at the time of uveitogenic immunization reproducibly ameliorated disease scores. Use of different iNKT TCR ligands revealed dependence on the elicited cytokine profile. Surprisingly, superior protection against EAU was achieved with alpha-C-GalCer, which induces a strong IFN-gamma but only a weak IL-4 production by iNKT cells, in contrast to the ligands alpha-GalCer (both IFN-gamma and IL-4) and OCH (primarily IL-4). The protective effect of alpha-C-GalCer was associated with a reduction of adaptive Ag-specific IFN-gamma and IL-17 production and was negated by systemic neutralization of IFN-gamma. These data suggest that pharmacological activation of iNKT cells protects from EAU at least in part by a mechanism involving innate production of IFN-gamma and a consequent dampening of the Th1 as well as the Th17 effector responses.

Congenic analysis of the NKT cell control gene Nkt2 implicates the peroxisomal protein Pxmp4

Type 1 NKT cells play a critical role in controlling the strength and character of adaptive and innate immune responses. We have previously reported deficiencies in the numbers and function of NKT cells in the NOD mouse strain, which is a well-validated model of type 1 diabetes and systemic lupus erythematosus. Genetic control of thymic NKT cell numbers was mapped to two linkage regions: Nkt1 on distal chromosome 1 and Nkt2 on chromosome 2. Herein, we report the production and characterization of a NOD.Nkrp1(b).Nkt2b(b) congenic mouse strain, which has increased thymic and peripheral NKT cells, a decreased incidence of type 1 diabetes, and enhanced cytokine responses in vivo and increased proliferative responses in vitro following challenge with alpha-galactosylceramide. The 19 highly differentially expressed candidate genes within the congenic region identified by microarray expression analyses included Pxmp4. This gene encodes a peroxisome-associated integral membrane protein whose only known binding partner is Pex19, an intracellular chaperone and component of the peroxisomal membrane insertion machinery encoded by a candidate for the NKT cell control gene Nkt1. These findings raise the possibility that peroxisomes play a role in modulating glycolipid availability for CD1d presentation, thereby influencing NKT cell function.

Impaired SLAM-SLAM homotypic interaction between invariant NKT cells and dendritic cells affects differentiation of IL-4/IL-10-secreting NKT2 cells in nonobese diabetic mice

The regulatory function of invariant NKT (iNKT) cells for tolerance induction and prevention of autoimmunity is linked to a specific cytokine profile that comprises the secretion of type 2 cytokines like IL-4 and IL-10 (NKT2 cytokine profile). The mechanism responsible for iNKT cell differentiation toward a type 2 phenotype is unknown. Herein we show that costimulatory signals provided by the surface receptor signaling lymphocytic activation molecule (SLAM) on myeloid dendritic cells (mDC) to iNKT cells is crucial for NKT2 orientation. Additionally, we demonstrate that the impaired acquisition of an NKT2 cytokine phenotype in nonobese diabetic (NOD) mice that spontaneously develop autoimmune diabetes is due to defective SLAM-induced signals generated by NOD mDC. Mature mDC of C57BL/6 mice express SLAM and induce C57BL/6 or NOD iNKT cells to acquire a predominant NKT2 cytokine phenotype in response to antigenic stimulation with the iNKT cell-specific Ag, the alpha-galactosylceramide. In contrast, mature NOD mDC express significantly lower levels of SLAM and are unable to promote GATA-3 (the SLAM-induced intracellular signal) up-regulation and IL-4/IL-10 production in iNKT cells from NOD or C57BL/6 mice. NOD mice carry a genetic defect of the Slamf1 gene that is associated with reduced SLAM expression on double-positive thymocytes and altered iNKT cell development in the thymus. Our data suggest that the genetic Slamf1 defect in NOD mice also affects SLAM expression on other immune cells such as the mDC, thus critically impairing the peripheral differentiation of iNKT cells toward a regulatory NKT2 type.

Induction of active tolerance and involvement of CD1d-restricted natural killer T cells in anti-CD3 F(ab')2 treatment-reversed new-onset diabetes in nonobese diabetic mice

The application of anti-CD3 F(ab')(2) monoclonal antibodies has recently been expanded to treat established autoimmune diseases, including type 1 diabetes. However, the mechanism underlying their effect remains largely unclear. We report that short-phase administration of anti-CD3 F(ab')(2) antibodies efficiently allowed 80% of new-onset, nonobese diabetic (NOD) mice to significantly regain both normoglycemia and pancreatic beta cell-specific autoantigen (ie, glutamic acid decarboxylase and insulin) tolerance, with both effects lasting more than 40 weeks. The responsible mechanism appears to involve the induction and maintenance of a population of immunoregulatory CD1d-restricted natural killer T (NKT) cells, which were marked by an enhanced Th2 response and secretion of elevated levels of interleukin-10. In vivo neutralization of interleukin-4 and/or interleukin-10 bioactivity abrogated this anti-CD3-mediated effect. Importantly, when the cotransfer of NKT cells from the livers of anti-CD3-treated mice and splenocytes from untreated, acutely diabetic NOD mice was performed in NOD-severe combined immunodeficient mice, the NKT cells were sufficient to either delay or prevent the onset of diabetes compared with controls where only splenocytes were introduced. These data suggest that CD1d-restricted NKT cells may play a critical role in anti-CD3 antibody-induced diabetes remission and the restoration of immune tolerance.

Human invariant Valpha24+ natural killer T cells acquire regulatory functions by interacting with IL-10-treated dendritic cells

Glycolipid-reactive Valpha24(+) invariant natural killer T (iNKT) cells have been implicated in regulating a variety of immune responses and in the induction of immunologic tolerance. Activation of iNKT cells requires interaction with professional antigen-presenting cells, such as dendritic cells (DCs). We have investigated the capacity of distinct DC subsets to modulate iNKT cell functions. We demonstrate that tolerogenic DCs (tolDCs), generated by treatment of monocyte-derived DC with interleukin (IL)-10, induced regulatory functions in human iNKT cells. tolDCs, compared with immunogenic DCs, had reduced capacity to induce iNKT-cell proliferation, but these cells produced large amounts of IL-10 and acquired an anergic phenotype. These anergic Valpha24(+) iNKT cells were able to potently inhibit allogeneic CD4(+) T-cell proliferation in vitro. Furthermore, the anergic Valpha24(+) iNKT cells could suppress DC maturation in vitro. We conclude that the interaction of iNKT cells with tolDCs plays an important role in the immune regulatory network, which might be exploited for therapeutic purposes.

EAE tolerance induction with Hsp70-peptide complexes depends on H60 and NKG2D activity

Inflammation leads to induction of tissue stress conditions that might contribute to the generation of mechanisms limiting ongoing immune responses. We have shown previously that peptides derived from brain tissue of mice with experimental autoimmune encephalomyelitis (EAE) complexed with the chaperone heat shock protein 70 (Hsp70-pc) induce an NK-cell-dependent tolerance for subsequent EAE sensitization. We now present data that showed that the MHC class I-related glycoprotein H60 determines Hsp70-pc-induced EAE inhibition. Hsp70-pc led to significant and selective up-regulation of H60 expression in SJL/J mice, and Ab-blocking of H60 expression led to loss of EAE tolerance. Similarly, blocking of the NK cell receptor for H60, NKG2D, also reversed the Hsp70-pc-induced EAE inhibition. In contrast, in C57BL/6 mice H60 was not expressed, and Hsp70-pc-induced tolerance was not detected. The NK cell mediated Hsp70-pc-induced tolerance to EAE was dependent on modulation of dendritic cells function leading to diminished T cell reactivity to PLP. As, no increase of H60 expression on T cells from EAE mice immunized with PLP was detected, and no enhanced loss of CD3+ H60+ over CD3+ H60- cells in Hsp70-pc-induced EAE tolerance was found direct killing of H60+ PLP-reactive cells seems not to be involved in the Hsp70-pc-induced tolerance induction. We have provided evidence that Hsp70-pc-induced tolerance for EAE, mediated by NK cells, involves induction of H60 ligand and its interaction with NKG2D receptor. NK cells tolerization of EAE depends on altered dendritic cells activity leading to enhanced death of Ag reactive cells.

Role of NKT cells in allogeneic islet graft survival

Although NKT cells expressing CD1d-reactive TCR exerted protective role in autoimmune diseases, the regulatory function of CD1d-dependent NKT cells in alloimmune responses has not been investigated thoroughly. Here, we demonstrated the regulatory effects of NKT cells using a pancreas islet transplantation model. CD40/CD154 blocking induced long-term graft survival in most B6 recipients, but B6.CD1d(-/-) recipients showed co-stimulation blockade-resistant rejection. Adoptive transfer of NKT cells into B6.CD1d(-/-) restored tolerizing capacity of co-stimulatory blockade. Activation of NKT cells was effective for the prolongation of graft survival and up-regulated membrane-bound TGF-beta expression transiently on their cell surface. The activated CD1d-dependent NKT cells inhibited alloantigen-driven cell proliferation through cell contacts and the beneficial effect of CD154 blocking for allograft survival was related to TGF-beta pathway. Thus, we can conclude that NKT cells are essential for the stable allograft survival and the regulatory function is dependent on, at least in part, TGF-beta engagement.

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.

NKT cells and autoimmune diseases: unraveling the complexity

CDld-restricted invariant natural killer T (NKT) cells emerge as unique lymphocyte subsets implicated in the regulation of autoimmunity. Abnormalities in the numbers and functions of NKT cells have been observed in patients with diverse autoimmune diseases as well as in animal models of autoimmune diseases. NKT cells recognize glycolipid antigens presented by the nonpolymorphic MHC class I-like protein CD1d and participate in various kinds of immunoregulation due to a potent ability to produce a variety of cytokines. In this review, we examine the potential roles of NKT cells in the regulation and pathogenesis of autoimmune disease and the recent advances in glycolipid therapy for autoimmune disease models.

IL-4 inducibility in NKT cells, naïve CD4+ T cells and TCR-gamma delta T cells

NKT cells, naïve CD4(+) T cells, and TCR-gammadelta T cells belong to distinct T cell lineages but all express T cell receptors generated through random combinatorial joining of V-(D)-J genes. These distinct lineage T cells also possess the property of promptly activating the IL-4 gene upon T cell receptor stimulation. A comparative accounting of features as they pertain to IL-4 inducibility in these three distinct lineage T cells is provided here.

Prevention of type 1 diabetes by invariant NKT cells is independent of peripheral CD1d expression

Invariant NKT (iNKT) cells can prevent diabetes by inhibiting the differentiation of anti-islet T cells. We recently showed that neither iNKT cell protection against diabetes nor iNKT cell inhibition of T cell differentiation in vitro requires cytokines such as IL-4, IL-10, IL-13, and TGF-beta. In contrast, cell-cell contacts were required for iNKT cell inhibition of T cell differentiation in vitro. The present study was designed to determine whether the CD1d molecule is involved in the inhibitory function of iNKT cells. Experiments were performed in vitro and in vivo, using cells lacking CD1d expression. The in vivo experiments used CD1d-deficient mice that were either reconstituted with iNKT cells or expressed a CD1d transgene exclusively in the thymus. Both mouse models had functional iNKT cells in the periphery, even though CD1d was not expressed in peripheral tissues. Surprisingly, both in vitro inhibition of T cell differentiation by iNKT cells and mouse protection against diabetes by iNKT cells were CD1d-independent. These results reveal that iNKT cells can exert critical immunoregulatory effects in the absence of CD1d recognition and that different molecular interactions are involved in iNKT cell functions.

Protection from Type 1 Diabetes by Invariant NK T Cells Requires the Activity of CD4+CD25+ Regulatory T Cells

Invariant NK T (iNKT) cells regulate immune responses, express NK cell markers and an invariant TCR, and recognize lipid Ags in a CD1d-restricted manner. Previously, we reported that activation of iNKT cells by alpha-galactosylceramide (alpha-GalCer) protects against type 1 diabetes (T1D) in NOD mice via an IL-4-dependent mechanism. To further investigate how iNKT cells protect from T1D, we analyzed whether iNKT cells require the presence of another subset(s) of regulatory T cells (Treg), such as CD4+ CD25+ Treg, for this protection. We found that CD4+ CD25+ T cells from NOD.CD1d(-/-) mice deficient in iNKT cell function similarly in vitro to CD4+ CD25+ T cells from wild-type NOD mice and suppress the proliferation of NOD T responder cells upon alpha-GalCer stimulation. Cotransfer of NOD diabetogenic T cells with CD4+ CD25+ Tregs from NOD mice pretreated with alpha-GalCer demonstrated that activated iNKT cells do not influence the ability of T(regs) to inhibit the transfer of T1D. In contrast, protection from T1D mediated by transfer of activated iNKT cells requires the activity of CD4+ CD25+ T cells, because splenocytes pretreated with alpha-GalCer and then inactivated by anti-CD25 of CD25+ cells did not protect from T1D. Similarly, mice inactivated of CD4+ CD25+ T cells before alpha-GalCer treatment were also not protected from T1D. Our data suggest that CD4+ CD25+ T cells retain their function during iNKT cell activation, and that the activity of CD4+ CD25+ Tregs is required for iNKT cells to transfer protection from T1D.

Enhancement of NKT Cells and Increase in Regulatory T Cells Results in Improved Allograft Survival

BACKGROUND

Natural killer T (NKT) cells can serve as regulatory cells important in peripheral tolerance. In an experimental colitis model, it was shown that FK506 enhances the tolerizing effect of regulatory NKT cells induced by oral tolerance. We explored whether a subtherapeutic dose of FK506 could enhance the tolerizing effect of NKT cells induced by oral administration of donor spleen cells (SCs) in the pre-transplant period to prolong heart allograft survival.

METHODS

Heterotopic heart transplantation was performed from BALB/c to B6 mice. The B6 recipients were pre-treated with either BALB/c SCs (2 x 10(7)/mouse), or FK506 (1.0 mg/kg/d), or BALB/c SCs + FK506 by gavage every other day for a total of five feedings before transplantation.

RESULTS

Heart allograft survival was only significantly prolonged in the BALB/c SC + FK506 pre-fed mice. This was associated with a marked increase of NKT cells in both the liver and spleen of the recipients, and most importantly, 7 days after transplantation, an increase in CD25+CD4+ T cells expressing CTLA4 in the spleen.

CONCLUSIONS

In our model it appears that a subtherapeutic dose of FK506 enhanced the tolerizing effect of NKT cells induced by oral tolerance, prolonging allograft survival by generating CD25+CD4+ CTLA4 T cells. This appears to be an excellent in vivo model to generate regulatory T cells to allospecific transplant antigens.

Genetic and functional analysis of the Nkt1 locus using congenic NOD mice: improved Valpha14-NKT cell performance but failure to protect against type 1 diabetes

Defective invariant natural killer T-cells (iNKT cells) have been implicated in the etiology of type 1 diabetes in nonobese diabetic (NOD) mice. In a genome scan of a cross between NOD and C57BL/6 mice, the most significant locus controlling the number of iNKT cells, referred to as Nkt1, was recently mapped to distal chromosome 1. Here, using congenic mice for this chromosomal segment, we definitively demonstrate the existence of Nkt1 and show that introgression of the C57BL/6 allele onto the NOD background improves both the number of iNKT cells and their rapid production of cytokines elicited by alpha-galactosylceramide treatment, explaining at least half of the difference between the NOD and C57BL/6 strains. Using new subcongenic lines, we circumscribed the Nkt1 locus to a 8.7-cM segment, between the NR1i3 and D1Mit458 markers, that notably includes the SLAM (signaling lymphocytic activation molecule) gene cluster, recently involved in murine lupus susceptibility. However, despite a significant correction of the iNKT cell defect, the Nkt1 locus did not alter the course of spontaneous diabetes in congenic mice. Our findings indicate a complex relationship between iNKT cells and autoimmune susceptibility. Congenic lines nonetheless provide powerful models to dissect the biology of iNKT cells.

NKT cells and IFN-gamma establish the regulatory environment for the control of diabetogenic T cells in the nonobese diabetic mouse

In type 1 diabetes mellitus (T1DM), T cell-mediated destruction of insulin-producing pancreatic beta cells leads to the acute onset of hyperglycemia. The nonobese diabetic mouse model of human T1DM reveals that T cells capable of inducing diabetes can escape normal central tolerance, and can cause T1DM if left unchecked. However, several regulatory T cell subsets can temper autoaggressive T cells, although it remains undetermined when and how, and by which subset, homeostatic control of diabetogenic T cells is normally achieved in vivo. Using a cotransfer model, we find that NKT cells efficiently dampen the action of diabetogenic CD4+ T cells, and do so in an indirect manner by modifying the host environment. Moreover, the NKT cell-containing population modifies the host via production of IFN-gamma that is necessary for driving the inhibition of diabetogenic T cells in vivo.

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.

Immunoregulation of Autoimmunity by Natural Killer T Cells

Natural killer T (NKT) cells are a conserved subpopulation of lymphocytes that recognize glycolipid antigens in a CD1d context. Upon activation through their semi-invariant T cell receptor, these cells rapidly release large amounts of immunomodulating Th1 and Th2 cytokines. NKT cells have therefore been implicated in immune responses controlling various diseases, including infection, cancer, transplantation, and autoimmunity. Stimulation of the immunoregulatory capacity of NKT cells by the prototypical antigen alpha-galactosylceramide results in amelioration of disease in several animal models. This review will focus on the current knowledge of human NKT cells and their role in autoimmune diseases. The features of these cells and their importance in regulation of autoimmunity suggest that NKT cell-based therapies might be an interesting approach for the treatment of autoimmune diseases.

Invariant NKT cells exacerbate type 1 diabetes induced by CD8 T cells

Invariant NKT (iNKT) cells have been implicated in the regulation of autoimmune diseases. In several models of type 1 diabetes, increasing the number of iNKT cells prevents the development of disease. Because CD8 T cells play a crucial role in the pathogenesis of diabetes, we have investigated the influence of iNKT cells on diabetogenic CD8 T cells. In the present study, type 1 diabetes was induced by the transfer of CD8 T cells specific for the influenza virus hemagglutinin into recipient mice expressing the hemagglutinin Ag specifically in their beta pancreatic cells. In contrast to previous reports, high frequency of iNKT cells promoted severe insulitis and exacerbated diabetes. Analysis of diabetogenic CD8 T cells showed that iNKT cells enhance their activation, their expansion, and their differentiation into effector cells producing IFN-gamma. This first analysis of the influence of iNKT cells on diabetogenic CD8 T cells reveals that iNKT cells not only fail to regulate but in fact exacerbate the development of diabetes. Thus, iNKT cells can induce opposing effects dependent on the model of type 1 diabetes that is being studied. This prodiabetogenic capacity of iNKT cells should be taken into consideration when developing therapeutic approaches based on iNKT cell manipulation.