Expansion and hyperactivity of CD1d-restricted NKT cells during the progression of systemic lupus erythematosus in (New Zealand Black x New Zealand White)F1 mice

Navigating the Role of CD1d/Invariant Natural Killer T-cell/Glycolipid Immune Axis in Multiple Myeloma Evolution: Therapeutic Implications

Multiple myeloma (MM) is an incurable B-cell malignancy. The immunotherapeutic approach for MM therapy is evolving. The Cd1d/invariant natural killer T-cell/glycolipid immune axis belongs to the innate immunity, and we have highlighted role in myeloma pathogenesis in the present study. The recent development of the chimeric antigen receptor (CAR19)-invariant natural killer T-cells resulted in our renewed interest in this immune system and offer new perspectives for future anti-MM immunotherapies.

Invariant NKT Cells and Rheumatic Disease: Focus on Primary Sjogren Syndrome

Primary Sjogren syndrome (pSS) is a complex autoimmune disease mainly affecting salivary and lacrimal glands. Several factors contribute to pSS pathogenesis; in particular, innate immunity seems to play a key role in disease etiology. Invariant natural killer (NK) T cells (iNKT) are a T-cell subset able to recognize glycolipid antigens. Their function remains unclear, but studies have pointed out their ability to modulate the immune system through the promotion of specific cytokine milieu. In this review, we discussed the possible role of iNKT in pSS development, as well as their implications as future markers of disease activity.

Immunoporosis: A New Role for Invariant Natural Killer T (NKT) Cells Through Overexpression of Nuclear Factor-κB Ligand (RANKL)

Background

Osteoporosis affects millions of postmenopausal women worldwide. Invariant natural killer T cells (iNKT) are important cells for bone homeostasis. The sim of this study was to investigate the contribution of invariant natural killer T cells (iNKT) in the increased receptor activator of the nuclear factor-κB ligand (RANKL) pool and bone resorption, a characteristic of patients with osteoporosis.

Material/Methods

Whole blood was collected from 79 female patients. The dual energy x-absorptiometry scan was performed in all patients, and the T-score was calculated in order to classify our patients according to the World Human Organization (WHO) criteria for diagnosis and classification of osteoporosis. Eleven patients had a T-score <−1.0 and were encompassed in our normal donors (ND) group, 46 patients had a T-score between −1 and −2.5 and were included in the osteopenia group, while 22 patients had a T-score > −2.5 and were included in the osteoporosis group. We performed a-galactosylceramide activation of iNKT cells in vitro. Surface RANKL expression was detected by multicolor flow cytometry in naive and activated lymphocytes. Beta-Crosslaps (β-CTx) levels were measured in whole blood plasma by ELISA (enzyme-linked immunosorbent assay).

Results

Although iNKT cells were not clonally expanded in patients with osteoporosis, iNKT cells from osteoporotic patients overexpressed RANKL compared to ND and osteopenic patients. This is a distinctive feature of iNKT cells and is not seen in conventional T-lymphocytes. RANKL expression in iNKT cells was not related to β-CTx levels in the blood. Finally, iNKT cell activation by the prototypal glycolipid ligand α-galactosylceramide increased by 8 times their RANKL expression.

Conclusions

In patients with osteoporosis, iNKT cells specifically overexpress RANKL, a cytokine that regulates osteoclast activity. It seems that iNKT cells have a long-standing effect of on the bone physiology, which plays an important role in the bone loss of patients with osteoporosis.

The Immunology of CD1- and MR1-Restricted T Cells

CD1- and MHC-related molecule-1 (MR1)-restricted T lymphocytes recognize nonpeptidic antigens, such as lipids and small metabolites, and account for a major fraction of circulating and tissue-resident T cells. They represent a readily activated, long-lasting population of effector cells and contribute to the early phases of immune response, orchestrating the function of other cells. This review addresses the main aspects of their immunological functions, including antigen and T cell receptor repertoires, mechanisms of nonpeptidic antigen presentation, and the current evidence for their participation in human and experimental diseases.

Different subsets of natural killer T cells may vary in their roles in health and disease

Natural killer T cells (NKT) can regulate innate and adaptive immune responses. Type I and type II NKT cell subsets recognize different lipid antigens presented by CD1d, an MHC class-I-like molecule. Most type I NKT cells express a semi-invariant T-cell receptor (TCR), but a major subset of type II NKT cells reactive to a self antigen sulphatide use an oligoclonal TCR. Whereas TCR-α dominates CD1d-lipid recognition by type I NKT cells, TCR-α and TCR-β contribute equally to CD1d-lipid recognition by type II NKT cells. These variable modes of NKT cell recognition of lipid-CD1d complexes activate a host of cytokine-dependent responses that can either exacerbate or protect from disease. Recent studies of chronic inflammatory and autoimmune diseases have led to a hypothesis that: (i) although type I NKT cells can promote pathogenic and regulatory responses, they are more frequently pathogenic, and (ii) type II NKT cells are predominantly inhibitory and protective from such responses and diseases. This review focuses on a further test of this hypothesis by the use of recently developed techniques, intravital imaging and mass cytometry, to analyse the molecular and cellular dynamics of type I and type II NKT cell antigen-presenting cell motility, interaction, activation and immunoregulation that promote immune responses leading to health versus disease outcomes.

Mechanisms of innate lymphoid cell and natural killer T cell activation during mucosal inflammation

Mucosal surfaces in the airways and the gastrointestinal tract are critical for the interactions of the host with its environment. Due to their abundance at mucosal tissue sites and their powerful immunomodulatory capacities, the role of innate lymphoid cells (ILCs) and natural killer T (NKT) cells in the maintenance of mucosal tolerance has recently moved into the focus of attention. While NKT cells as well as ILCs utilize distinct transcription factors for their development and lineage diversification, both cell populations can be further divided into three polarized subpopulations reflecting the distinction into Th1, Th2, and Th17 cells in the adaptive immune system. While bystander activation through cytokines mediates the induction of ILC and NKT cell responses, NKT cells become activated also through the engagement of their canonical T cell receptors (TCRs) by (glyco)lipid antigens (cognate recognition) presented by the atypical MHC I like molecule CD1d on antigen presenting cells (APCs). As both innate lymphocyte populations influence inflammatory responses due to the explosive release of copious amounts of different cytokines, they might represent interesting targets for clinical intervention. Thus, we will provide an outlook on pathways that might be interesting to evaluate in this context.

Ly108 expression distinguishes subsets of invariant NKT cells that help autoantibody production and secrete IL-21 from those that secrete IL-17 in lupus prone NZB/W mice

Lupus is a systemic autoimmune disease characterized by anti-nuclear antibodies in humans and genetically susceptible NZB/W mice that can cause immune complex glomerulonephritis. T cells contribute to lupus pathogenesis by secreting pro-inflammatory cytokines such as IL-17, and by interacting with B cells and secreting helper factors such as IL-21 that promote production of IgG autoantibodies. In the current study, we determined whether purified NKT cells or far more numerous conventional non-NKT cells in the spleen of NZB/W female mice secrete IL-17 and/or IL-21 after TCR activation in vitro, and provide help for spontaneous IgG autoantibody production by purified splenic CD19(+) B cells. Whereas invariant NKT cells secreted large amounts of IL-17 and IL-21, and helped B cells, non-NKT cells did not. The subset of IL-17 secreting NZB/W NKT cells expressed the Ly108(lo)CD4(-)NK1.1(-) phenotype, whereas the IL-21 secreting subset expressed the Ly108(hi)CD4(+)NK1.1(-) phenotype and helped B cells secrete a variety of IgG anti-nuclear antibodies. α-galactocylceramide enhanced the helper activity of NZB/W and B6.Sle1b NKT cells for IgG autoantibody secretion by syngeneic B cells. In conclusion, different subsets of iNKT cells from mice with genetic susceptibility to lupus can contribute to pathogenesis by secreting pro-inflammatory cytokines and helping autoantibody production.

Intrinsic hyporesponsiveness of invariant natural killer T cells precedes the onset of lupus

Patients with systemic lupus erythematosus (SLE) display reduced numbers and functions of invariant natural killer T (iNK T) cells, which are restored upon treatment with corticosteroids and rituximab. It is unclear whether the iNK T cell insufficiency is a consequence of disease or is a primary abnormality that precedes the onset of disease. To address this, we analysed iNK T cell function at different stages of disease development using the genetically lupus-susceptible NZB × NZW F1 (BWF(1)) model. We found that iNK T cell in-vivo cytokine responses to an iNK T cell ligand α-galactosylceramide (α-GalCer) were lower in BWF(1) mice than in non-autoimmune BALB/c and major histocompatibility complex (MHC)-matched NZB × N/B10.PL F1 mice, although iNK T cell numbers in the periphery were unchanged in BWF(1) mice compared to control mice. Such iNK T cell hyporesponsiveness in BWF(1) mice was detected at a young age long before the animals exhibited any sign of autoimmunity. In-vivo activation of iNK T cells is known to transactivate other immune cells. Such transactivated T and B cell activation markers and/or cytokine responses were also lower in BWF(1) mice than in BALB/c controls. Finally, we show that iNK T cell responses were markedly deficient in the NZB parent but not in NZW parent of BWF(1) mice, suggesting that BWF(1) might inherit the iNK T cell defect from NZB mice. Thus, iNK T cells are functionally insufficient in lupus-prone BWF(1) mice. Such iNK T cell insufficiency precedes the onset of disease and may play a pathogenic role during early stages of disease development in SLE.

Design, synthesis, and functional activity of labeled CD1d glycolipid agonists

Invariant natural killer T cells (iNKT cells) are restricted by CD1d molecules and activated upon CD1d-mediated presentation of glycolipids to T cell receptors (TCRs) located on the surface of the cell. Because the cytokine response profile is governed by the structure of the glycolipid, we sought a method for labeling various glycolipids to study their in vivo behavior. The prototypical CD1d agonist, α-galactosyl ceramide (α-GalCer) 1, instigates a powerful immune response and the generation of a wide range of cytokines when it is presented to iNKT cell TCRs by CD1d molecules. Analysis of crystal structures of the TCR-α-GalCer-CD1d ternary complex identified the α-methylene unit in the fatty acid side chain, and more specifically the pro-S hydrogen at this position, as a site for incorporating a label. We postulated that modifying the glycolipid in this way would exert a minimal impact on the TCR-glycolipid-CD1d ternary complex, allowing the labeled molecule to function as a good mimic for the CD1d agonist under investigation. To test this hypothesis, the synthesis of a biotinylated version of the CD1d agonist threitol ceramide (ThrCer) was targeted. Both diastereoisomers, epimeric at the label tethering site, were prepared, and functional experiments confirmed the importance of substituting the pro-S, and not the pro-R, hydrogen with the label for optimal activity. Significantly, functional experiments revealed that biotinylated ThrCer (S)-10 displayed behavior comparable to that of ThrCer 5 itself and also confirmed that the biotin residue is available for streptavidin and antibiotin antibody recognition. A second CD1d agonist, namely α-GalCer C20:2 4, was modified in a similar way, this time with a fluorescent label. The labeled α-GalCer C20:2 analogue (11) again displayed functional behavior comparable to that of its unlabeled substrate, supporting the notion that the α-methylene unit in the fatty acid amide chain should be a suitable site for attaching a label to a range of CD1d agonists. The flexibility of the synthetic strategy, and late-stage incorporation of the label, opens up the possibility of using this labeling approach to study the in vivo behavior of a wide range of CD1d agonists.

Therapeutic manipulation of natural killer (NK) T cells in autoimmunity: are we close to reality?

T cells reactive to lipids and restricted by major histocompatibility complex (MHC) class I-like molecules represent more than 15% of all lymphocytes in human blood. This heterogeneous population of innate cells includes the invariant natural killer T cells (iNK T), type II NK T cells, CD1a,b,c-restricted T cells and mucosal-associated invariant T (MAIT) cells. These populations are implicated in cancer, infection and autoimmunity. In this review, we focus on the role of these cells in autoimmunity. We summarize data obtained in humans and preclinical models of autoimmune diseases such as primary biliary cirrhosis, type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, psoriasis and atherosclerosis. We also discuss the promise of NK T cell manipulations: restoration of function, specific activation, depletion and the relevance of these treatments to human autoimmune diseases.

NKT Cell Subsets Can Exert Opposing Effects in Autoimmunity, Tumor Surveillance and Inflammation

The innate-like natural killer T (NKT) cells are essential regulators of immunity. These cells comprise at least two distinct subsets and recognize different lipid antigens presented by the MHC class I like molecules CD1d. The CD1d-dependent recognition pathway of NKT cells is highly conserved from mouse to humans. While most type I NKT cells can recognize αGalCer and express a semi-invariant T cell receptor (TCR), a major population of type II NKT cells reactive to sulfatide utilizes an oligoclonal TCR. Furthermore TCR recognition features of NKT subsets are also distinctive with almost parallel as opposed to perpendicular footprints on the CD1d molecules for the type I and type II NKT cells respectively. Here we present a view based upon the recent studies in different clinical and experimental settings that while type I NKT cells are more often pathogenic, they may also be regulatory. On the other hand, sulfatide-reactive type II NKT cells mostly play an inhibitory role in the control of autoimmune and inflammatory diseases. Since the activity and cytokine secretion profiles of NKT cell subsets can be modulated differently by lipid ligands or their analogs, novel immunotherapeutic strategies are being developed for their differential activation for potential intervention in inflammatory diseases.

Modulatory function of invariant natural killer T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease with complex immunological and clinical manifestations. Multiple organ failure in SLE can be caused by immune dysfunction and deposition of autoantibodies. Studies of SLE-susceptible loci and the cellular and humoral immune responses reveal variable aberrations associated with this systemic disease. Invariant natural killer T (iNKT) cells are a unique subset of lymphocytes that control peripheral tolerance. Mounting evidence showing reductions in the proportion and activity of iNKT cells in SLE patients suggests the suppressive role of iNKT cells. Studies using murine lupus models demonstrate that iNKT cells participate in SLE progression by sensing apoptotic cells, regulating immunoglobulin production, and altering the cytokine profile upon activation. However, the dichotomy of iNKT cell actions in murine models implies complicated interactions within the body's milieu. Therefore, application of potential therapy for SLE using glycolipids to regulate iNKT cells should be undertaken cautiously.

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.

Epistatic suppression of fatal autoimmunity in New Zealand black bicongenic mice

Numerous mapping studies have implicated genetic intervals from lupus-prone New Zealand Black (NZB) chromosomes 1 and 4 as contributing to lupus pathogenesis. By introgressing NZB chromosomal intervals onto a non-lupus-prone B6 background, we determined that: NZB chromosome 1 congenic mice (denoted B6.NZBc1) developed fatal autoimmune-mediated kidney disease, and NZB chromosome 4 congenic mice (denoted B6.NZBc4) exhibited a marked expansion of B1a and NKT cells in the surprising absence of autoimmunity. In this study, we sought to examine whether epistatic interactions between these two loci would affect lupus autoimmunity by generating bicongenic mice that carry both NZB chromosomal intervals. Compared with B6.NZBc1 mice, bicongenic mice demonstrated significantly decreased mortality, kidney disease, Th1-biased IgG autoantibody isotypes, and differentiation of IFN-γ-producing T cells. Furthermore, a subset of bicongenic mice exhibited a paucity of CD21(+)CD1d(+) B cells and an altered NKT cell activation profile that correlated with greater disease inhibition. Thus, NZBc4 contains suppressive epistatic modifiers that appear to inhibit the development of fatal NZBc1 autoimmunity by promoting a shift away from a proinflammatory cytokine profile, which in some mice may involve NKT cells.

Invariant NKT cells inhibit autoreactive B cells in a contact- and CD1d-dependent manner

Autoantibody production is a hallmark of autoimmune diseases, such as lupus and rheumatoid arthritis. Accumulating evidence suggests a role of invariant NKT (iNKT) cells in their pathogenesis. Mechanisms underlying the role of iNKT cells in these diseases, however, remain unclear. In this study, we show that iNKT cells suppress IgG anti-DNA Ab and rheumatoid factor production and reduce IL-10-secreting B cells in a contact-dependent manner, but increase total IgG production and enhance activation markers on B cells via soluble factors. In vivo reconstitution with iNKT cells also reduces autoantibody production in iNKT-deficient mice and in SCID mice implanted with B cells. Using an anti-DNA transgenic model, we found that autoreactive B cells spontaneously produce IL-10 and are activated in vivo. In the presence of activated iNKT cells, these autoreactive B cells are selectively reduced, whereas nonautoreactive B cells are markedly activated. Because iNKTs recognize CD1d, we reasoned that CD1d might play a role in the differential regulation of autoreactive versus nonautoreactive B cells by iNKT cells. Indeed, autoreactive B cells express more CD1d than nonautoreactive B cells, and CD1d deficiency in lupus mice exacerbates autoantibody production and enhances Ab response to a self-peptide but not to a foreign peptide. Importantly, iNKT cells fail to inhibit autoantibody production by CD1d-deficient B cells. Thus, iNKT cells inhibit autoreactive B cells in a contact- and CD1d-dependent manner but activate nonautoreactive B cells via cytokines. Such ability of iNKTs to suppress autoantibody production, without causing global suppression of B cells, has important implications for the development of iNKT-based therapy for autoimmune diseases.

Invariant NKT cells limit activation of autoreactive CD1d-positive B cells

Faulty activation of autoreactive B cells is a hallmark of autoimmune diseases like systemic lupus erythematosus (SLE). An important feature restricting activation of autoreactive B cells is efficient removal of apoptotic material. Mounting evidence also connects a primary defect in invariant natural killer T (iNKT) cells to autoimmune disease development. However, exactly how this unconventional T cell subset is involved remains to be defined. Here, we identify a suppressive role for iNKT cells in a model where autoantibody production is triggered by an increased load of circulating apoptotic cells, resembling the situation in SLE patients. Absence or reduction of iNKT cells as well as absence of CD1d-expression on B cells, needed for direct iNKT-B cell interaction, leads to increased autoreactive B cell activation and symptoms of disease. The suppression mediated by the iNKT cells is observed before B cell entry into germinal centers and can be rescued by transferring iNKT cells to deficient mice. This links iNKT cells to handling of dying cells and identifies a novel peripheral tolerance checkpoint relevant for autoimmune disease. Thus, these observations connect two clinical observations in SLE patients previously considered to be unrelated and define a new target for immunotherapy.

Lupus nephritis: lessons from murine models

Lupus nephritis is a challenging clinical condition for which current therapies are unsatisfactory with respect to both remission induction and unwanted toxic effects. Despite intervention, the rates of end-stage renal disease seem to be increasing in the USA. Discoveries over the past decade have greatly improved our understanding of immune activation and effector inflammatory pathways in lupus nephritis; however, this increased understanding has not yet translated into the approval of an effective new therapeutic agent. An analysis of the mechanisms of action of novel immunomodulatory drugs in multiple models of murine lupus clearly shows that interacting networks of immune and effector pathways are recruited as the disease progresses. Reversing established disease by targeting a single cell population or inflammatory pathway is, therefore, difficult once long-lived autoreactive lymphocyte populations are present and peripheral organs are inflamed. Data from murine models of lupus suggest that we need to consider new paradigms for the management of systemic lupus erythematosus that include earlier immune intervention, long-term maintenance therapies and protection of target organs.

The role of iNKT cells in the immunopathology of systemic lupus erythematosus

An increasing body of evidence suggests that CD1d-restricted invariant natural killer T (iNKT) cells play an important immunoregulatory role in a variety of autoimmune diseases in both humans and mouse models. Their role in systemic lupus erythematosus (SLE), however, is not fully determined, as SLE mouse models have yielded conflicting results demonstrating both a protective function and a pathogenic role. The reduced frequency of iNKT cells in peripheral blood of lupus patients supports the idea of a protective role for these cells in the immunopathology of SLE. Therapeutic approaches using glycolipids provide a promising tool to correct numerical iNKT cell deficiencies and to modulate their function. This review highlights the potential role of iNKT cells in lupus immunopathology and summarizes recent studies concerning iNKT cells in SLE patients, lupus-prone murine models and glycolipid therapy.

Incorporation of NKT cell-activating glycolipids enhances immunogenicity and vaccine efficacy of Mycobacterium bovis bacillus Calmette-Guerin

The attenuated strain of Mycobacterium bovis known as bacille Calmette-Guérin (BCG) has been widely used as a vaccine for prevention of disease by Mycobacterium tuberculosis, but with relatively little evidence of success. Recent studies suggest that the failure of BCG may be due to its retention of immune evasion mechanisms that delay or prevent the priming of robust protective cell-mediated immunity. In this study, we describe an approach to enhance the immunogenicity of BCG by incorporating glycolipid activators of CD1d-restricted NKT cells, a conserved T cell subset with the potential to augment many types of immune responses. A method was developed for stably incorporating two forms of the NKT cell activator alpha-galactosylceramide into live BCG organisms, and the impact of this on stimulation of T cell responses and protective antimycobacterial immunity was evaluated. We found that live BCG containing relatively small amounts of incorporated alpha-galactosylceramide retained the ability to robustly activate NKT cells. Compared with immunization with unmodified BCG, the glycolipid-modified BCG stimulated increased maturation of dendritic cells and markedly augmented the priming of Ag-specific CD8(+) T cells responses. These effects were correlated with improved protective effects of vaccination in mice challenged with virulent M. tuberculosis. These results support the view that mycobacteria possess mechanisms to avoid stimulation of CD8(+) T cell responses and that such responses contribute significantly to protective immunity against these pathogens. Our findings raise the possibility of a simple modification of BCG that could yield a more effective vaccine for control of tuberculosis.

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.

Beta-galactosylceramide alters invariant natural killer T cell function and is effective treatment for lupus

NZB/W female mice spontaneously develop systemic lupus, an autoantibody mediated disease associated with immune complex glomerulonephritis. Natural killer (NK) T cells augment anti-dsDNA antibody secretion by NZB/W B cells in vitro, and blocking NKT cell activation in vivo with anti-CD1 mAb ameliorates lupus disease activity. In the current study, we show that beta-galactosylceramide reduces the in vivo induction of serum IFN-gamma and/or IL-4 by the potent NKT cell agonist alpha-galactosylceramide and reduces NKT cell helper activity for IgG secretion. Treatment of NZB/W mice with the beta-galactosylceramide ameliorated lupus disease activity as judged by improvement in proteinuria, renal histopathology, IgG anti-dsDNA antibody formation, and survival. In conclusion, beta-galactosylceramide, a glycolipid that reduces the cytokine secretion induced by a potent NKT cell agonist ameliorates lupus in NZB/W mice.

Human CD1 dimeric proteins as indispensable tools for research on CD1-binding lipids and CD1-restricted T cells

Antigen presenting molecules play an important role in both innate and adoptive immune responses by priming and activating T cells. Among them, CD1 molecules have been identified to present both exogenous and endogenous lipid antigens to CD1-restricted T cells. The involvement of CD1-restricted T cells in autoimmune diseases and in defense against infectious diseases, however, remains largely unknown. Identifying novel antigenic lipids that bind to CD1 molecules and understanding the role of CD1-restricted T cells should lead to the successful development of vaccines, because the lipids can be used as antigens and also as adjuvants. In this paper, we have constructed functional recombinant human CD1 dimeric proteins and established a competitive ELISA assay to measure the lipid binding to CD1 molecules using the CD1 dimers. By using the competitive ELISA assay, we were able to show that the lipid extracts from murine malaria parasites can actually be loaded onto CD1 molecules. In addition, we have demonstrated that artificial antigen-presenting cells, which consist of magnetic beads coated with CD1d dimer and anti-CD28 antibody, stimulated and expanded human invariant NKT cells as efficiently as autologous immature DCs. A set of the tools presented in the current study should be valuable for screening various CD1 molecule-binding lipid antigens and for isolating CD1-restricted T cells.

NKT cell subsets mediate differential proatherogenic effects in ApoE-/- mice

OBJECTIVE

NKT cells promote atherogenesis, but the subtypes responsible have not been identified. We investigated 2 major NKT cell subtypes (CD4+ and DN NKT) in ApoE-/- mice rendered NKT cell-deficient by day-3 neonatal thymectomy (3dTx).

METHODS AND RESULTS

Atherosclerosis development was studied in thymectomized ApoE-/- mice fed a high-fat diet with/without adoptively transferred NKT cells. We demonstrate NKT cell deficiency in thymectomized mice and markedly smaller atherosclerotic lesions. The reduction in lesion size was reversed by adoptive transfer of liver-derived NKT cells. Adoptive transfer of CD4+, but not DN NKT cells, into 3dTx ApoE-/- mice increased lesion size 2.5-fold. The differential effects were not attributable to differences in homing to developing atherosclerotic lesions. DN NKT cells expressed at least 3-fold higher levels of inhibitory Ly49 receptors (Ly49A, Ly49C/I, and Ly49G2) than CD4+ NKT cells, and lesions expressed large amounts of their MHC class I ligand. In vitro these inhibitory receptors initiated greater effects in DN NKT cells. Culture of each NKT cell subset with TAP-deficient (MHC class I-deficient) dendritic cells and alpha-GalCer led to secretion of similar amounts of proatherogenic cytokines IL-2, IFN-gamma, and TNF but, when cultured with MHC class I-positive dendritic cells, CD4+ NKT cells secreted more of these cytokines.

CONCLUSIONS

CD4+ NKT cells are responsible for the proatherogenic activity of NKT cells. Expression of inhibitory Ly49 receptors by the subtypes appears responsible for regulating their secretion of proatherogenic cytokines and their differential proatherogenic effects.

Reduced proportions of natural killer T cells are present in the relatives of lupus patients and are associated with autoimmunity

Introduction

Systemic lupus erythematosus is a genetically complex disease. Currently, the precise allelic polymorphisms associated with this condition remain largely unidentified. In part this reflects the fact that multiple genes, each having a relatively minor effect, act in concert to produce disease. Given this complexity, analysis of subclinical phenotypes may aid in the identification of susceptibility alleles. Here, we used flow cytometry to investigate whether some of the immune abnormalities that are seen in the peripheral blood lymphocyte population of lupus patients are seen in their first-degree relatives.

Methods

Peripheral blood mononuclear cells were isolated from the subjects, stained with fluorochrome-conjugated monoclonal antibodies to identify various cellular subsets, and analyzed by flow cytometry.

Results

We found reduced proportions of natural killer (NK)T cells among 367 first-degree relatives of lupus patients as compared with 102 control individuals. There were also slightly increased proportions of memory B and T cells, suggesting increased chronic low-grade activation of the immune system in first-degree relatives. However, only the deficiency of NKT cells was associated with a positive anti-nuclear antibody test and clinical autoimmune disease in family members. There was a significant association between mean parental, sibling, and proband values for the proportion of NKT cells, suggesting that this is a heritable trait.

Conclusions

The findings suggest that analysis of cellular phenotypes may enhance the ability to detect subclinical lupus and that genetically determined altered immunoregulation by NKT cells predisposes first-degree relatives of lupus patients to the development of autoimmunity.

Recent advances in the role of NKT cells in allergic diseases and asthma

Asthma is the result of chronic airway inflammation that is dominated by the presence of eosinophils and CD4(+) T lymphocytes. CD4(+) T cells include several subsets and play a critical role in orchestrating the inflammation, predominantly by secreting interleukin-4 and interleukin-13. Recently, research identified a new subset of T cells, natural killer T (NKT) cells, which also express the CD4 marker. In contrast to conventional CD4(+) T cells, NKT cells do not respond to peptide antigens, but rather to glycolipids. In animal models of asthma, direct activation of NKT cells by glycolipids results in the secretion of extensive amounts of cytokines and triggers the development of airway hyperreactivity. Moreover, in patients with chronic asthma, NKT cells can be found in bronchoalveolar lavage fluids in significant amounts. These data strongly suggest that NKT cells play an important role in asthma pathogenesis.

Widespread natural variation in murine natural killer T-cell number and function

Natural killer T (NKT) cells comprise a novel T-lymphocyte subset that can influence a wide variety of immune responses through their ability to secrete large amounts of a variety of cytokines. Although variation in NKT-cell number and function has been extensively studied in autoimmune disease-prone mice, in which it has been linked to disease susceptibility, relatively little is known of the natural variation of NKT-cell number and function among normal inbred mouse strains. Here, we demonstrate strain-dependent variation in the susceptibility of C57BL/6J and BALB/cJ mice to NKT-mediated airway hyperreactivity, which correlated with significant increases in serum interleukin-4 (IL-4) and IL-13 elicited by the synthetic glycosphingolipid alpha-galactosylceramide. Examination of NKT-cell function revealed a significantly greater frequency of cytokine-producing NKT cells in C57BL/6J versus BALB/cJ mice as well as significant differences in the kinetics of NKT-cell cytokine production. Extension of this analysis to a panel of inbred mouse strains indicated that variability in NKT-cell cytokine production was widespread. Similarly, an examination of NKT-cell frequency revealed a significantly greater number of liver NKT cells in the C57BL/6J mice versus BALB/cJ mouse livers. Again, examination of a panel of inbred mouse strains revealed that liver NKT-cell numbers were quite variable, spanning over a 100-fold range. Taken together, these results demonstrate the presence of widespread natural variation in NKT-cell number and function among common inbred mouse strains, which may have implications for the examination of the influence of NKT cells in immune responses and disease pathogenesis among different genetic backgrounds.

Long-term administration of IgG2a anti-NK1.1 monoclonal antibody ameliorates lupus-like disease in NZB/W mice in spite of an early worsening induced by an IgG2a-dependent BAFF/BLyS production

The role of natural killer (NK) T cells in the development of lupus-like disease in mice is still controversial. We treated NZB/W mice with anti-NK1.1 monoclonal antibodies (mAbs) and our results revealed that administration of either an irrelevant immunoglobulin G2a (IgG2a) mAb or an IgG2a anti-NK1.1 mAb increased the production of anti-dsDNA antibodies in young NZB/W mice. However, the continuous administration of an anti-NK1.1 mAb protected aged NZB/W mice from glomerular injury, leading to prolonged survival and stabilization of the proteinuria. Conversely, the administration of the control IgG2a mAb led to an aggravation of the lupus-like disease. Augmented titres of anti-dsDNA in NZB/W mice, upon IgG2a administration, correlated with the production of BAFF/BLyS by dendritic, B and T cells. Treatment with an anti-NK1.1 mAb reduced the levels of interleukin-16, produced by T cells, in spleen cell culture supernatants from aged NZB/W. Adoptive transfer of NK T cells from aged to young NZB/W accelerated the production of anti-dsDNA in recipient NZB/W mice, suggesting that NK T cells from aged NZB/W are endowed with a B-cell helper activity. In vitro studies, using purified NK T cells from aged NZB/W, showed that these cells provided helper B-cell activity for the production of anti-dsDNA. We concluded that NK T cells are involved in the progression of lupus-like disease in mature NZB/W mice and that immunoglobulin of the IgG2a isotype has an enhancing effect on antibody synthesis due to the induction of BAFF/BLyS, and therefore have a deleterious effect in the NZB/W mouse physiology.

Natural killer T cells and innate immune B cells from lupus-prone NZB/W mice interact to generate IgM and IgG autoantibodies

Lupus-prone NZB/W F1 mice develop glomerulonephritis after T helper cell-dependent isotype switching of autoantibody secretion from IgM to IgG at about 6 months of age. We compared innate immune natural killer (NK) T cells and conventional T cells for their capacity to help spontaneous in vitro immunoglobulin and autoantibody secretion of innate immune (B-1 and marginal zone) and conventional (follicular) B cell subsets from NZB/W F1 mice. We found that purified NKT cells not only increased spontaneous secretion of IgM and IgM anti-double-stranded (ds)DNA antibodies by B-1 and marginal zone B cells, but also facilitated secretion of IgG anti-dsDNA antibodies predominantly by B-1 B cells. Few IgM or IgG anti-dsDNA antibodies were secreted by follicular B cells, and conventional T cells failed to provide potent helper activity to any B cell subset. All combinations of T and B cell subsets from normal C57BL/6 mice failed to generate vigorous IgM and IgG secretion. NZB/W NKT cell helper activity was blocked by anti-CD1 and anti-CD40L mAb. In conclusion, direct interactions between innate immune T and B cells form a pathway for the development of IgM and IgG lupus autoantibody secretion in NZB/W mice.

Natural killer T cells exacerbate liver injury in a transforming growth factor beta receptor II dominant-negative mouse model of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an organ-specific autoimmune liver disease characterized by the presence of antimitochondrial antibodies and the destruction of small intrahepatic bile ducts with portal inflammation. In previous studies, we reported that both CD1d expression and the frequency of CD1d-restricted natural killer T (NKT) cells were increased in the livers of patients with PBC. To define a specific role of CD1d-restricted NKT cells in the pathogenesis of PBC, particularly early events, we investigated the function of hepatic CD1d-restricted NKT cells in our transforming growth factor beta (TGF-beta) receptor II dominant-negative (dnTGFbetaRII) mouse model of PBC. We generated CD1d(-/-) and CD1d(+/-) dnTGFbetaRII mice and performed a comparative study of liver immunopathology. We report herein that these dnTGFbetaRII mice demonstrate a massive increase of hyperactive CD1d-restricted NKT cells within the hepatic tissues. CD1d(-/-)dnTGFbetaRII mice, which lack CD1d-restricted CD1d-restricted NKT cells, exhibit significantly decreased hepatic lymphoid cell infiltrates and milder cholangitis compared with CD1d(+/-)dnTGFbetaRII mice. Interestingly, there was a significant increase in the production of interferon-gamma in hepatic CD1d-restricted NKT cells activated by alpha-galactosylceramide in young but not older dnTGFbetaRII mice, suggesting an age-dependent role of CD1d-restricted NKT cells.

CONCLUSION

These data demonstrate that CD1d-restricted NKT cells in dnTGFbetaRII mice are a critical factor in liver injury.

The role of NKT cells in tumor immunity

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

Regulatory T cells and systemic lupus erythematosus

Regulatory T cells, especially CD4+CD25+ T cells, "natural killer" T cells and gammadelta T cells, are central in the maintenance of peripheral tolerance and the protection from the development of autoimmune diseases. Numerical or functional modifications of these cell populations were demonstrated to lead to the breakdown of tolerance and the emergence of autoimmunity. Involvement of regulatory T cells in the pathogenesis of systemic autoimmune diseases, such as systemic lupus erythematosus, might be of first importance. In murine models and patients with lupus, these regulatory T cells seem to be reduced in number. Functional deficiencies have also been described in a few studies. A better knowledge of regulatory T cell functional properties in systemic autoimmune diseases is essential to manipulate these cells and hopefully to restore immune tolerance.

The biology of NKT cells

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

Examining the role of CD1d and natural killer T cells in the development of nephritis in a genetically susceptible lupus model

OBJECTIVE

CD1d-reactive invariant natural killer T (iNKT) cells secrete multiple cytokines upon T cell receptor (TCR) engagement and modulate many immune-mediated conditions. The purpose of this study was to examine the role of these cells in the development of autoimmune disease in genetically lupus-prone (NZBxNZW)F1 (BWF1) mice.

METHODS

The CD1d1-null genotype was crossed onto the NZB and NZW backgrounds to establish CD1d1-knockout (CD1d0) BWF1 mice. CD1d0 mice and their wild-type littermates were monitored for the development of nephritis and assessed for cytokine responses to CD1d-restricted glycolipid alpha-galactosylceramide (alphaGalCer), anti-CD3 antibody, and concanavalin A (Con A). Thymus and spleen cells were stained with CD1d tetramers that had been loaded with alphaGalCer or its analog PBS-57 to detect iNKT cells, and the cells were compared between BWF1 mice and class II major histocompatibility complex-matched nonautoimmune strains, including BALB/c, (BALB/cxNZW)F1 (CWF1), and NZW.

RESULTS

CD1d0 BWF1 mice had more severe nephritis than did their wild-type littermates. Although iNKT cells and iNKT cell responses were absent in CD1d0 BWF1 mice, the CD1d0 mice continued to have significant numbers of interferon-gamma-producing NKT-like (CD1d-independent TCRbeta+,NK1.1+ and/or DX5+) cells. CD1d deficiency also influenced cytokine responses by conventional T cells: upon in vitro stimulation of splenocytes with Con A or anti-CD3, type 2 cytokine levels were reduced, whereas type 1 cytokine levels were increased or unchanged in CD1d0 mice as compared with their wild-type littermates. Additionally, numbers of thymic iNKT cells were lower in young wild-type BWF1 mice than in nonautoimmune strains.

CONCLUSION

Germline deletion of CD1d exacerbates lupus in BWF1 mice. This finding, together with reduced thymic iNKT cells in young BWF1 mice as compared with nonautoimmune strains, implies a regulatory role of CD1d and iNKT cells during the development of lupus.

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.

T cells and B cells in lupus nephritis

T and B lymphocytes play diverse roles at multiple stages in the development and progression of lupus nephritis. Disruption of T- and B-cell regulatory functions by environmental and genetic influences permits pathogenic effectors to emerge in disease. New insights into the biology of these multifunctional cells offer novel targets for intervention in lupus nephritis and systemic autoimmunity.

Immunoregulatory role of Jalpha281 T cells in aged mice developing lupus-like nephritis

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the emergence of autoreactive T cells. Humans and mice with SLE have reduced numbers of CD1d-restricted invariant natural killer T (iNKT) cells, suggesting a key role for these cells in its immunopathogenesis. This subset uses an invariant TCR constituted by Valpha14 Jalpha281 chains paired with some Vbeta domains. The regulatory role for iNKT cells in non-autoimmune mice was suggested by our previous results showing that aged Jalpha281 knockout (KO) mice produce anti-dsDNA. Here we show that old Jalpha281 KO mice have proteinuria and antibodies against dsDNA and cardiolipin. Histological analysis of Jalpha281 KO mice revealed glomeruli damage and deposition of C3c and IgG, mainly of the IgG3 subclass. In spleens of aged Jalpha281 KO mice there is an increase of activated marginal zone B cells. The evolution of lesions may depend on the age-associated increase of autoantibodies production, preferentially IgG3, mainly secreted by marginal zone B cells. Our results provide the first evidence of a lupus-like syndrome in non-autoimmune mice, supporting an age-related immunoregulatory role of Jalpha281+ cells, probably associated with the activation of marginal zone B cells.

Dissociation of the genetic loci leading to b1a and NKT cell expansions from autoantibody production and renal disease in B6 mice with an introgressed New Zealand Black chromosome 4 interval

Previous mapping studies have linked New Zealand Black (NZB) chromosome 4 to several lupus traits, including autoantibody production, splenomegaly, and glomerulonephritis. To confirm the presence of these traits, our laboratory introgressed homozygous NZB chromosome 4 intervals extending from either 114 to 149 Mb or 32 to 149 Mb onto the lupus-resistant C57BL/6 background (denoted B6.NZBc4S and B6.NZBc4L, respectively). Characterization of aged cohorts revealed that B6.NZBc4L mice exhibited a striking increase in splenic B1a and NKT cells in the absence of high titer autoantibody production and significant renal disease. Tissue-specific expansion of these subsets was also seen in the peritoneum and liver for B1a cells and in the bone marrow for NKT cells. Staining with CD1d tetramers loaded with an alpha-galactosylceramide analog (PBS57) demonstrated that the expanded NKT cell population was mainly CD1d-dependent NKT cells. The lack of both cellular phenotypes in B6.NZBc4S mice demonstrates that the genetic polymorphism(s) that result in these phenotypes are on the proximal region of NZB chromosome 4. This study confirms the presence of a locus that promotes the expansion of B1a cells and newly identifies a region that promotes CD1d-restricted NKT cell expansion on NZB chromosome 4. Taken together, the data indicate that neither an expansion of B1a cells and/nor NKT cells is sufficient to promote autoantibody production and ultimately, renal disease.

Natural killer T cells in families of patients with systemic lupus erythematosus: their possible role in regulation of IGG production

OBJECTIVE

To determine whether there is a link between the frequency of natural killer T (NKT) cells and high levels of IgG in patients with systemic lupus erythematosus (SLE) and their relatives.

METHODS

Blood samples were obtained from patients with SLE, their first-degree relatives, patients with rheumatoid arthritis (RA), and healthy control subjects. The frequency of NKT cells (defined as CD56+ T cells) was expressed as a percentage of total blood lymphocytes. Plasma levels of total IgG and IgM, and IgG antibodies to double-stranded DNA (dsDNA) were determined.

RESULTS

The frequency of NKT cells was lower in patients with SLE than in control subjects. No such decrease was observed in the relatives of patients with SLE or in patients with RA. High levels of IgG were observed in both patients with SLE and their relatives, while low levels of IgM were observed in these same groups. In relatives of patients with SLE, an inverse correlation between the frequency of NKT cells and IgG levels was observed. Moreover, raised levels of IgG in patients with SLE and their relatives and high levels of IgG anti-dsDNA in patients were associated with low frequencies of NKT cells.

CONCLUSION

These results suggest that NKT cells have an important role in the regulation of IgG production, although NKT cells with invariant T cell receptors may not necessarily be involved. NKT cells in the setting of SLE could lack the cytokine stimulus from NK or other cells that is needed to exert control on IgG production. Enhancement of NKT cell activity may provide a novel basis for therapy in SLE.

CD1d- and MR1-restricted invariant T cells: of mice and men

CD1d-restricted natural killer T cells and MR1-restricted mucosal associated invariant T (MAIT) cells constitute two subsets of unconventional T cells that are phylogenetically conserved. Therefore, they are thought to play an essential role within the immune system. MR1-restricted MAIT cell selection is dependent upon B cells, and their accumulation in the gut lamina propria and mesenteric lymph node requires the commensal bacterial flora. These features suggest that MAIT cells could be involved in tolerance or immunity to infections in the gut. As for natural killer T cells, the recent identification of one endogenous ligand, isoglobotrihexosylceramide, and of a family of bacterial agonists is an important advance for understanding their thymic selection and their role during infections.

The role of invariant natural killer T cells in lupus and atherogenesis

Systemic lupus erythematosus (SLE) is increasingly recognized as a risk factor for the development of premature atherosclerosis. The inflammatory process in both of these diseases is controlled by a variety of cell types of the innate and adaptive immune systems. Recent studies from several groups, including ours, have revealed a critical role of a unique subset of lymphocytes, termed invariant natural killer T (iNKT) cells, in the development of lupus-like autoimmunity and atherosclerosis in animal models. iNKT cells appear to play complex and divergent roles in the development of SLE and atherosclerosis. Our findings suggest that alterations in iNKT cell functions during the development of SLE may be related to the increased risk of SLE patients to develop atherosclerosis and coronary heart disease. We found that iNKT cell activation with the sponge-derived glycolipid alpha- galactosylceramide generally protects against the development of lupus-like autoimmunity in mice, whereas it exacerbates atherosclerosis. Therefore, while our studies have identified iNKT cells as potential therapeutic targets for SLE, further studies are necessary to design drugs that will avoid the underlying harmful effects of iNKT cell activation on the development of atherosclerosis.

The diverse functions of CD1d-restricted NKT cells and their potential for immunotherapy

CD1d-restricted NKT cells have been identified as an important component of the immune system that have the capacity both to augment beneficial host immunity and to prevent harmful autoimmunity. These cells have the ability to produce a wide variety of cytokines, including both proinflammatory and antiinflammatory cytokines that can have multiple different effects on the outcome of immune reactions. The discovery that these T cells are activated by specific recognition of glycolipids in the glycosylceramide family has led to new approaches to manipulate the pleiotropic functions of these cells. Here, we review the multiple activities that have been attributed to NKT cells in a variety of different disease models, and the current state of our understanding of the mechanisms that control the functional outcome of NKT cell activation.