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

Cell-Specific Gene Networks and Drivers in Rheumatoid Arthritis Synovial Tissues

Rheumatoid arthritis (RA) is a common autoimmune and inflammatory disease characterized by inflammation and hyperplasia of the synovial tissues. RA pathogenesis involves multiple cell types, genes, transcription factors (TFs) and networks. Yet, little is known about the TFs, and key drivers and networks regulating cell function and disease at the synovial tissue level, which is the site of disease. In the present study, we used available RNA-seq databases generated from synovial tissues and developed a novel approach to elucidate cell type-specific regulatory networks on synovial tissue genes in RA. We leverage established computational methodologies to infer sample-specific gene regulatory networks and applied statistical methods to compare network properties across phenotypic groups (RA versus osteoarthritis). We developed computational approaches to rank TFs based on their contribution to the observed phenotypic differences between RA and controls across different cell types. We identified 18,16,19,11 key regulators of fibroblast-like synoviocyte (FLS), T cells, B cells, and monocyte signatures and networks, respectively, in RA synovial tissues. Interestingly, FLS and B cells were driven by multiple independent co-regulatory TF clusters that included MITF, HLX, BACH1 (FLS) and KLF13, FOSB, FOSL1 (synovial B cells). However, monocytes were collectively governed by a single cluster of TF drivers, responsible for the main phenotypic differences between RA and controls, which included RFX5, IRF9, CREB5. Among several cell subset and pathway changes, we also detected reduced presence of NKT cell and eosinophils in RA synovial tissues. Overall, our novel approach identified new and previously unsuspected KDG, TF and networks and should help better understanding individual cell regulation and co-regulatory networks in RA pathogenesis, as well as potentially generate new targets for treatment.

Autoimmunity in Wiskott-Aldrich Syndrome: Updated Perspectives

Wiskott–Aldrich syndrome (WAS) is an uncommon X-linked combined-immunodeficiency disorder characterized by a triad of thrombocytopenia, eczema, and immunodeficiency. Patients with WAS are also predisposed to autoimmunity and malignancy. Autoimmune manifestations have been reported in 26%–72% of patients with WAS. Autoimmunity is an independent predictor of poor prognosis and predisposes to malignancy. Development of autoimmunity is also an early pointer of the need for hematopoietic stem–cell transplantation. In this manuscript, we have collated the published data and present a narrative review on autoimmune manifestations in WAS. A summary of currently proposed immunopathogenic mechanisms and genetic variants associated with development of autoimmunity in WAS is also included.

The interaction between iNKT cells and B cells

Invariant natural killer T cells (iNKTs) bridge the innate immunity with the adaptive immunity and their interaction with B cells has been extensively studied. Here, we give a complete overview of these two cells, from their mechanism of interaction to clinical prospects and existing problems. In our introduction, we describe the relationship between iNKTs and B cells and explore the current research hotspots and future directions. We begin with how B cells interact and benefit from the innate and adaptive help of iNKTs. Next, we describe the multiple roles of these cells in infections, autoimmunity, and cancers. Lastly, we look into the potential immunotherapies that can be based on iNKTs and the possible treatments for infectious, autoimmune, and other diseases.

The Involvement of Innate and Adaptive Immunity in the Initiation and Perpetuation of Sjögren's Syndrome

Sjogren’s syndrome (SS) is a chronic autoimmune disease characterized by the infiltration of exocrine glands including salivary and lachrymal glands responsible for the classical dry eyes and mouth symptoms (sicca syndrome). The spectrum of disease manifestations stretches beyond the classical sicca syndrome with systemic manifestations including arthritis, interstitial lung involvement, and neurological involvement. The pathophysiology underlying SS is not well deciphered, but several converging lines of evidence have supported the conjuncture of different factors interplaying together to foster the initiation and perpetuation of the disease. The innate and adaptive immune system play a cardinal role in this process. In this review, we discuss the inherent parts played by both the innate and adaptive immune system in the pathogenesis of SS.

Primary Sjogren Syndrome: Focus on Innate Immune Cells and Inflammation

Primary Sjogren Syndrome (pSS) is a complex, multifactorial rheumatic disease that mainly targets salivary and lacrimal glands, inducing epithelitis. The cause behind the autoimmunity outbreak in pSS is still elusive; however, it seems related to an aberrant reaction to exogenous triggers such as viruses, combined with individual genetic pre-disposition. For a long time, autoantibodies were considered as the hallmarks of this disease; however, more recently the complex interplay between innate and adaptive immunity as well as the consequent inflammatory process have emerged as the main mechanisms of pSS pathogenesis. The present review will focus on innate cells and on the principal mechanisms of inflammation connected. In the first part, an overview of innate cells involved in pSS pathogenesis is provided, stressing in particular the role of Innate Lymphoid Cells (ILCs). Subsequently we have highlighted the main inflammatory pathways, including intra- and extra-cellular players. A better knowledge of such processes could determine the detection of new therapeutic targets that are a major need for pSS.

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.

Inhibition of Rho-Kinase Downregulates Th17 Cells and Ameliorates Hepatic Fibrosis by Schistosoma japonicum Infection

BACKGROUND

Schistosomiasis is an immunopathogenic disease in which Th17 cells play vital roles. Hepatic granuloma formation and subsequent fibrosis are its main pathologic manifestations and the leading causes of hepatic cirrhosis, and effective therapeutic interventions are lacking. In this study, we explored the effects of fasudil, a selective RhoA-Rho-associated kinase (ROCK) inhibitor, on Th17 cells and the pathogenesis of schistosomiasis.

METHODS

Mice were infected with Schistosoma japonicum and treated with fasudil. The worm burden, hepatic granuloma formation, and fibrosis were evaluated. The roles of fasudil on Th17, Treg, and hepatic stellate cells were analyzed.

RESULTS

Fasudil therapy markedly reduced the granuloma size and collagen deposit in livers from mice infected with S. japonicum. However, fasudil therapy did not affect the worm burden in infected mice. The underlying cellular and molecular mechanisms were investigated. Fasudil suppressed the activation and induced the apoptosis of CD4⁺ T cells. Fasudil inhibited the differentiation and effector cytokine secretion of Th17 cells, whereas it upregulated Treg cells in vitro. It also restrained the in vivo interleukin (IL)-4 and IL-17 levels in infected mice. Fasudil directly induced the apoptosis of hepatic stellate cells and downregulated the expressions of hepatic fibrogenic genes, such as collagen type I (Col-I), Col-III, and transforming growth factor-1 (TGF-β1). These effects may contribute to its anti-pathogenic roles in schistosomiasis.

CONCLUSIONS

Fasudil inhibits hepatic granuloma formation and fibrosis with downregulation of Th17 cells. Fasudil might serve as a novel therapeutic agent for hepatic fibrosis due to schistosome infections and perhaps other disorders.

Antiphospholipid Antibodies Overlapping in Isolated Neurological Syndrome and Multiple Sclerosis: Neurobiological Insights and Diagnostic Challenges

Antiphospholipid syndrome (APS) is characterized by arterial and venous thrombosis, pregnancy morbidity and fetal loss caused by pathogenic autoantibodies directed against phospholipids (PL) and PL-cofactors. Isolated neurological APS may represent a significant diagnostic challenge, as epidemiological, clinical and neuroimaging features may overlap with those of multiple sclerosis (MS). In an open view, MS could be considered as an organ-specific anti-lipid (phospholipid and glycosphingolipid associated proteins) disease, in which autoreactive B cells and CD8+ T cells play a dominant role in its pathophysiology. In MS, diverse autoantibodies against the lipid-protein cofactors of the myelin sheath have been described, whose pathophysiologic role has not been fully elucidated. We carried out a review to select clinical studies addressing the prevalence of antiphospholipid (aPL) autoantibodies in the so-called MS-like syndrome. The reported prevalence ranged between 2% and 88%, particularly aCL and aβ2GPI, with predominant IgM isotype and suggesting worse MS prognosis. Secondarily, an updated summary of current knowledge on the pathophysiological mechanisms and events responsible for these conditions is presented. We draw attention to the clinical relevance of diagnosing isolated neurological APS. Prompt and accurate diagnosis and antiaggregant and anticoagulant treatment of APS could be vital to prevent or at least reduce APS-related morbidity and mortality.

Self-glycerophospholipids activate murine phospholipid-reactive T cells and inhibit iNKT cell activation by competing with ligands for CD1d loading

Glycosphingolipids and glycerophospholipids bind CD1d. Glycosphingolipid-reactive invariant NKT-cells (iNKT) exhibit myriad immune effects, however, little is known about the functions of phospholipid-reactive T cells (PLT). We report that the normal mouse immune repertoire contains αβ T cells, which recognize self-glycerophospholipids such as phosphatidic acid (PA) in a CD1d-restricted manner and don't cross-react with iNKT-cell ligands. PA bound to CD1d in the absence of lipid transfer proteins. Upon in vivo priming, PA induced an expansion and activation of T cells in Ag-specific manner. Crystal structure of the CD1d:PA complex revealed that the ligand is centrally located in the CD1d-binding groove opening for TCR recognition. Moreover, the increased flexibility of the two acyl chains in diacylglycerol ligands and a less stringent-binding orientation for glycerophospholipids as compared with the bindings of glycosphingolipids may allow glycerophospholipids to readily occupy CD1d. Indeed, PA competed with α-galactosylceramide to load onto CD1d, leading to reduced expression of CD1d:α-galactosylceramide complexes on the surface of dendritic cells. Consistently, glycerophospholipids reduced iNKT-cell proliferation, expansion, and cytokine production in vitro and in vivo. Such superior ability of self-glycerophospholipids to compete with iNKT-cell ligands to occupy CD1d may help maintain homeostasis between the diverse subsets of lipid-reactive T cells, with important pathogenetic and therapeutic implications.

The Role of Invariant NKT in Autoimmune Liver Disease: Can Vitamin D Act as an Immunomodulator?

Natural killer T (NKT) cells are a distinct lineage of T cells which express both the T cell receptor (TCR) and natural killer (NK) cell markers. Invariant NKT (iNKT) cells bear an invariant TCR and recognize a small variety of glycolipid antigens presented by CD1d (nonclassical MHC-I). CD1d-restricted iNKT cells are regulators of immune responses and produce cytokines that may be proinflammatory (such as interferon-gamma (IFN-γ)) or anti-inflammatory (such as IL-4). iNKT cells also appear to play a role in B cell regulation and antibody production. Alpha-galactosylceramide (α-GalCer), a derivative of the marine sponge, is a potent stimulator of iNKT cells and has been proposed as a therapeutic iNKT cell activator. Invariant NKT cells have been implicated in the development and perpetuation of several autoimmune diseases such as multiple sclerosis and systemic lupus erythematosus (SLE). Animal models of SLE have shown abnormalities in iNKT cells numbers and function, and an inverse correlation between the frequency of NKT cells and IgG levels has also been observed. The role of iNKT cells in autoimmune liver disease (AiLD) has not been extensively studied. This review discusses the current data with regard to iNKT cells function in AiLD, in addition to providing an overview of iNKT cells function in other autoimmune conditions and animal models. We also discuss data regarding the immunomodulatory effects of vitamin D on iNKT cells, which may serve as a potential therapeutic target, given that deficiencies in vitamin D have been reported in various autoimmune disorders.

Activation and Regulation of B Cell Responses by Invariant Natural Killer T Cells

CD1d-restricted invariant natural killer T (iNKT) cells play central roles in the activation and regulation of innate and adaptive immunity. Cytokine-mediated and CD1d-dependent interactions between iNKT cells and myeloid and lymphoid cells enable iNKT cells to contribute to the activation of multiple cell types, with important impacts on host immunity to infection and tumors and on the prevention of autoimmunity. Here, we review the mechanisms by which iNKT cells contribute to B cell maturation, antibody and cytokine production, and antigen presentation. Cognate interactions with B cells contribute to the rapid production of antibodies directed against conserved non-protein antigens resulting in rapid but short-lived innate humoral immunity. iNKT cells can also provide non-cognate help for the generation of antibodies directed against protein antigens, by promoting the activation of follicular helper T cells, resulting in long-lasting adaptive humoral immunity and B cell memory. iNKT cells can also regulate humoral immunity by promoting the development of autoreactive B cells into regulatory B cells. Depletions and functional impairments of iNKT cells are found in patients with infectious, autoimmune and malignant diseases associated with altered B cell function and in murine models of these conditions. The adjuvant and regulatory activities that iNKT cells have for B cells makes them attractive therapeutic targets for these diseases.

Repeated administration of alpha-galactosylceramide ameliorates experimental lupus nephritis in mice

Lupus nephritis is a crucial complication of systemic lupus erythematosus. In this study, we investigated the roles of mouse natural killer T (NKT) cells in lupus nephritis. From 24 weeks of age, NZB/NZW F1 mice were injected with alpha-galactosylceramide (α-GalCer) or vehicle once a week for four weeks. In the α-GalCer group, the levels of proteinuria and blood urea nitrogen were significantly lower than those in the vehicle group. The histological evaluation showed a decrease in glomerular immune complex deposits and an alleviation of podocyte injury. The proportion of NKT cells in the mononuclear cell (MNC) fraction in the α-GalCer group was significantly decreased in the liver, kidney, and spleen. The proliferation and cytokine production in α-GalCer-stimulated liver MNCs were markedly diminished in the α-GalCer group (anergy). The IFN-γ production in liver MNCs stimulated by concanavalin A or an anti-CD3 antibody did not differ between the two groups, whereas the IL-4 production was significantly lower in the α-GalCer group. In addition, the IgM production in CpG-oligodeoxynucleotide-stimulated spleen MNCs was significantly lower in the α-GalCer group. These results suggest that α-GalCer suppressed Th2 immune responses in NKT cells and B cell function, thereby slowing the progression of lupus nephritis.

Decreased CD1d level is associated with CD86 over-expression in B cells from systemic lupus erythematosus

The disorder of B cells is one of the hallmarks of systemic lupus erythematosus (SLE). The activation state indicated by CD86 of B cells from SLE is well known, while the defect of regulatory B cells mediated by CD1d is also responsible for the process of SLE. In the present study, we focused on the relationship between B cell activation mediated by CD86 and B cell regulatory function mediated by CD1d. Our results showed that the level of CD1d in B cells was decreased during the early stages of B6.MRLlpr SLE mice and imiquimod-treated (IMQ-treated) mice, while the level of CD86 was significantly increased at the late stage. Moreover, the expression of CD1d showed a significantly negative correlation with CD86 level in B cells from IMQ-treated mice (r = -05741; P = 0.0022), B6.MRLlpr mice (r = -0.7091; P = 0.0268), and SLE patients (r = -0.4125; P = 0.0404). The in vivo and in vitro experiments with splenocytes demonstrated that CD1d signaling pathway could inhibit toll-like receptor 7 (TLR7)-induced CD86 expression of B cells. Further studies showed that this relationship also affected antibody production. Thus, our results confirmed the association of CD1d and CD86 levels in B cells from SLE, and demonstrated the importance to preserve the immunoregulatory function of B cells mediated by CD1d in the progression of SLE.

The Clonal Invariant NKT Cell Repertoire in People with Type 1 Diabetes Is Characterized by a Loss of Clones Expressing High-Affinity TCRs

Invariant NKT (iNKT) cells in healthy people express iNKT-TCRs with widely varying affinities for CD1d, suggesting different roles for high- and low-affinity iNKT clones in immune regulation. However, the functional implications of this heterogeneity have not yet been determined. Functionally aberrant iNKT responses have been previously demonstrated in different autoimmune diseases, including human type 1 diabetes, but their relationship to changes in the iNKT clonal repertoire have not been addressed. In this study, we directly compared the clonal iNKT repertoire of people with recent onset type 1 diabetes and age- and gender-matched healthy controls with regard to iNKT-TCR affinity and cytokine production. Our results demonstrate a selective loss of clones expressing high-affinity iNKT-TCRs from the iNKT repertoire of people with type 1 diabetes. Furthermore, this bias in the clonal iNKT repertoire in type 1 diabetes was associated with increased GM-CSF, IL-4, and IL-13 cytokine secretion among Ag-stimulated low-affinity iNKT clones. Thus, qualitative changes of the clonal iNKT repertoire with the potential to affect the regulatory function of this highly conserved T cell population are already established at the early stages in type 1 diabetes. These findings may inform future rationales for the development of iNKT-based therapies aiming to restore immune tolerance in type 1 diabetes.

B cells interactions in lipid immune responses: implications in atherosclerotic disease

Atherosclerosis is considered as an inflammatory and chronic disorder with an important immunologic component, which underlies the majority of cardiovascular diseases; condition that belongs to a group of noncommunicable diseases that to date and despite of prevention and treatment approaches, they remain as the main cause of death worldwide, with 17.5 million of deaths every year. The impact of lipids in human health and disease is taking center stage in research, due to lipotoxicity explained by elevated concentration of circulating lipids, in addition to altered adipose tissue metabolism, and aberrant intracellular signaling. Immune response and metabolic regulation are highly integrated systems and the proper function of each one is dependent on the other. B lymphocytes express a variety of receptors that can recognize foreign, endogenous or modified self-antigens, among them oxidized low density lipoproteins, which are the main antigens in atherosclerosis. Mechanisms of B cells to recognize, remove and present lipids are not completely clear. However, it has been reported that B cell can recognize/remove lipids through a range of receptors, such as LDLR, CD1d, FcR and SR, which might have an atheroprotector or proatherogenic role during the course of atherosclerotic disease. Pertinent literature related to these receptors was examined to inform the present conclusions.

Cellular and Molecular Mechanisms of Autoimmunity and Lupus Nephritis

Autoimmunity involves immune responses directed against self, which are a result of defective self/foreign distinction of the immune system, leading to proliferation of self-reactive lymphocytes, and is characterized by systemic, as well as tissue-specific, inflammation. Numerous mechanisms operate to ensure the immune tolerance to self-antigens. However, monogenetic defects or genetic variants that weaken immune tolerance render susceptibility to the loss of immune tolerance, which is further triggered by environmental factors. In this review, we discuss the phenomenon of immune tolerance, genetic and environmental factors that influence the immune tolerance, factors that induce autoimmunity such as epigenetic and transcription factors, neutrophil extracellular trap formation, extracellular vesicles, ion channels, and lipid mediators, as well as costimulatory or coinhibitory molecules that contribute to an autoimmune response. Further, we discuss the cellular and molecular mechanisms of autoimmune tissue injury and inflammation during systemic lupus erythematosus and lupus nephritis.

What rheumatologists need to know about innate lymphocytes

Many rheumatic diseases are characterized by having an autoimmune background. Determining the mechanisms underlying autoimmunity is, therefore, important to further understand these diseases and to inform future lines of research aimed at developing new treatments and cures. As fast responders, innate lymphocytes have protective or pathogenic roles in the initiation as well as the maintenance of immune responses in general, and they contribute to tissue homeostasis, among other functions. Innate lymphocytes also seem to be involved in autoimmunity in particular. Since 2010, accumulating evidence clearly shows that different populations of innate lymphocytes have roles in responding to antigen-specific autoantibody and autoreactive T cells, thereby amplifying or attenuating disease processes. Cytotoxicity is a cardinal feature of many innate lymphocytes and can contribute to inflammatory tissue damage. Finally, innate lymphocytes can respond to biologic therapies for autoimmune diseases. Consequently, like TNF and other effector molecules, certain innate lymphocyte subsets might be appropriate therapeutic targets to ameliorate various autoimmune diseases. In this Review, we summarize the main characteristics and functions of innate lymphocyte subsets, and describe their roles in autoimmune disease. We also discuss how biologic therapies influence innate lymphocyte function and consider the potential for these cell subsets to act as future therapeutic targets.

Effects of Invariant NKT Cells on Parasite Infections and Hygiene Hypothesis

Invariant natural killer T (iNKT) cells are unique subset of innate-like T cells recognizing glycolipids. iNKT cells can rapidly produce copious amounts of cytokines upon antigen stimulation and exert potent immunomodulatory activities for a wide variety of immune responses and diseases. We have revealed the regulatory effect of iNKT cells on autoimmunity with a serial of publications. On the other hand, the role of iNKT cells in parasitic infections, especially in recently attractive topic “hygiene hypothesis,” has not been clearly defined yet. Bacterial and parasitic cell wall is a cellular structure highly enriched in a variety of glycolipids and lipoproteins, some of which may serve as natural ligands of iNKT cells. In this review, we mainly summarized the recent findings on the roles and underlying mechanisms of iNKT cells in parasite infections and their cross-talk with Th1, Th2, Th17, Treg, and innate lymphoid cells. In most cases, iNKT cells exert regulatory or direct cytotoxic roles to protect hosts against parasite infections. We put particular emphasis as well on the identification of the natural ligands from parasites and the involvement of iNKT cells in the hygiene hypothesis.

Cd1d regulates B cell development but not B cell accumulation and IL10 production in mice with pathologic CD5(+) B cell expansion

Background

CD1d is a widely expressed lipid antigen presenting molecule required for CD1d-restricted invariant natural killer T (iNKT) cell development. Elevated CD1d expression is detected in CD5⁺ IL10-producing B cells, called B10 B cells, and is correlated with poorer prognosis in chronic lymphocytic leukemia (CLL), a CD5⁺ B cell malignancy with B10-like functional properties. Whether CD1d expression regulates CD5⁺ B cell accumulation, IL10 competence, and antibody production in naïve mice with pathologic CD5⁺ B cell expansion remains untested.

Results

Using three different transgenic mouse models of benign or leukemic CD5⁺ B cell expansion, we found that CD1d was differentially expressed on CD5⁺ B cells between the three models, but loss of CD1d expression had no effect on CD5⁺ B cell abundance or inducible IL10 expression in any of the models. Interestingly, in the CLL-prone Eμ-TCL1 model, loss of CD1d expression suppressed spontaneous IgG (but not IgM) production, whereas in the dnRAG1xEμ-TCL1 (DTG) model of accelerated CLL, loss of CD1d expression was associated with elevated numbers of splenic CD4⁺ and CD8⁺ T cells and an inverted CD4⁺:CD8⁺ T cell ratio. Unexpectedly, before leukemia onset, all three transgenic CD1d-deficient mouse strains had fewer splenic transitional B cells than their CD1d-proficient counterparts.

Conclusions

The results show that CD1d expression and iNKT cells are dispensable for the development, accumulation, or IL10 competence of CD5⁺ B cells in mice prone to benign or leukemic CLL-like B cell expansion, but reveal a novel role for iNKT cells in supporting B cell progression through the transitional stage of development in these animals. These results suggest CD1d-directed therapies to target CLL could be evaded by downregulating CD1d expression with little effect on continued leukemic CD5⁺ B cell survival. The data also imply that iNKT cells help restrain pro-leukemic CD8⁺ T cell expansion in CLL, potentially explaining a reported correlation in human CLL between disease progression, the loss of NKT cells, and a paradoxical increase in CD8⁺ T cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0130-z) contains supplementary material, which is available to authorized users.

Invariant natural killer T cells in lupus patients promote IgG and IgG autoantibody production

IgG autoantibodies, including antibodies to double-stranded DNA (dsDNA), are pathogenic in systemic lupus erythematosus (SLE), but the mechanisms controlling their production are not understood. To assess the role of invariant natural killer T (iNKT) cells in this process, we studied 44 lupus patients. We took advantage of the propensity of PBMCs from patients with active disease to spontaneously secrete IgG in vitro. Despite the rarity of iNKT cells in lupus blood (0.002-0.05% of CD3-positive T cells), antibody blockade of the conserved iNKT TCR or its ligand, CD1d, or selective depletion of iNKT cells, inhibited spontaneous secretion of total IgG and anti-dsDNA IgG by lupus PBMCs. Addition of anti-iNKT or anti-CD1d antibody to PBMC cultures also reduced the frequency of plasma cells, suggesting that lupus iNKT cells induce B-cell maturation. Like fresh iNKT cells, expanded iNKT-cell lines from lupus patients, but not healthy subjects, induced autologous B cells to secrete antibodies, including IgG anti-dsDNA. This activity was inhibited by anti-CD40L antibody, as well as anti-CD1d antibody, confirming a role for CD40L-CD40 and TCR-CD1d interactions in lupus iNKT-cell-mediated help. These results reveal a critical role for iNKT cells in B-cell maturation and autoantibody production in patients with lupus.

Aberrant presentation of self-lipids by autoimmune B cells depletes peripheral iNKT cells

Invariant natural killer T (iNKT) cells provide cognate help via CD1d to lipid antigen-presenting B cells for antibody production, but whether B cells reciprocally regulate iNKT cells remains largely unexplored. Here, we found peripheral, but not thymic, iNKT cells to be numerically reduced in autoimmune mice lacking Fas specifically in B cells. The residual iNKT cells were antigenically overstimulated, had altered cytokine production, and manifested enhanced proliferation and apoptosis. B cell-specific ablation of CD1d ameliorated these iNKT defects, suggesting that inappropriate presentation of CD1d-restricted self-lipids by autoimmune B cell-depleted peripheral iNKT cells. CD1d(+) autoimmune B cells have reduced α-galactosidase A expression and, as revealed by lipidomic profiling, altered lipidome with aberrant accumulation of certain self-lipids and reduction of others. These findings unveil a critical link between autoimmunity, B cell lipidome, and the maintenance of peripheral iNKT cells and highlight an essential homeostatic function of B cells beyond antibody production.

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.

Blockade of invariant TCR-CD1d interaction specifically inhibits antibody production against blood group A carbohydrates

Previously, we detected B cells expressing receptors for blood group A carbohydrates in the CD11b(+)CD5(+) B-1a subpopulation in mice, similar to that in blood group O or B in humans. In the present study, we demonstrate that CD1d-restricted natural killer T (NKT) cells are required to produce anti-A antibodies (Abs), probably through collaboration with B-1a cells. After immunization of wild-type (WT) mice with human blood group A red blood cells (A-RBCs), interleukin (IL)-5 exclusively and transiently increased and the anti-A Abs were elevated in sera. However, these reactions were not observed in CD1d(-/-) mice, which lack NKT cells. Administration of anti-mouse CD1d blocking monoclonal Abs (mAb) prior to immunization abolished IL-5 production by NKT cells and anti-A Ab production in WT mice. Administration of anti-IL-5 neutralizing mAb also diminished anti-A Ab production in WT mice, suggesting that IL-5 secreted from NKT cells critically regulates anti-A Ab production by B-1a cells. In nonobese diabetic/severe combined immunodeficient (NOD/SCID/γc(null)) mice, into which peripheral blood mononuclear cells from type O human volunteers were engrafted, administration of anti-human CD1d mAb prior to A-RBC immunization completely inhibited anti-A Ab production. Thus, anti-CD1d treatment might constitute a novel approach that could help in evading Ab-mediated rejection in ABO-incompatible transplant recipients.

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.

Germline deletion of β2 microglobulin or CD1d reduces anti-phospholipid antibody, but increases autoantibodies against non-phospholipid antigens in the NZB/W F1 model of lupus

Introduction

β2-microglobulin (β2m) is required for the surface expression of MHC class I and class I-like proteins such as CD1d, Qa1 and neonatal Fc receptor (FcRn), all of which may impact the development of autoimmunity. Since CD1d is known to bind and present phospholipid antigens to T cells, we asked if the deficiency of β2m or CD1d will impact the development of anti-phospholipid antibodies as compared to other aspects of lupus autoimmunity.

Methods

We introgressed the β2m-null genotype onto the NZB and NZW backgrounds for 12 to 14 generations to generate genetically lupus-susceptible (NZB/NZW)F1 (BWF1) mice that are β2m-deficient (β2m°). Circulating immunoglobulins (Ig), rheumatoid factor (RF), anti-DNA and anti-cardiolipin (anti-CL) antibodies, and renal disease were analyzed in these and CD1d-deficient (CD1d°) BWF1 mice that we had previously generated.

Results

Whereas β2m° BWF1 mice had reduced serum IgG, they had increased mortality, nephritis, serum IgG anti-DNA antibody and RF as compared to heterozygous and wild-type littermates. These effects were recapitulated in CD1d° BWF1 mice, except that they also had increased serum IgG as compared to control littermates. Intriguingly, both β2m° and CD1d° mice had lower serum anti-CL antibody levels than in control littermates. Such CD1d dependence of anti-CL antibody production is not mediated by CD1d/glycolipid-reactive iNKT cells, as these cells reduced the production of RF and anti-DNA antibodies but had no effect on anti-CL antibodies.

Conclusions

We report a novel dichotomous role of β2m and CD1d, whereby these molecules differently regulate autoimmunity against phospholipid versus non-phospholipid autoantigens.

Autoimmunity in wiskott-Aldrich syndrome: an unsolved enigma

Wiskott-Aldrich Syndrome (WAS) is a severe X-linked Primary Immunodeficiency that affects 1-10 out of 1 million male individuals. WAS is caused by mutations in the WAS Protein (WASP) expressing gene that leads to the absent or reduced expression of the protein. WASP is a cytoplasmic protein that regulates the formation of actin filaments in hematopoietic cells. WASP deficiency causes many immune cell defects both in humans and in the WAS murine model, the Was(-/-) mouse. Both cellular and humoral immune defects in WAS patients contribute to the onset of severe clinical manifestations, in particular microthrombocytopenia, eczema, recurrent infections, and a high susceptibility to develop autoimmunity and malignancies. Autoimmune diseases affect from 22 to 72% of WAS patients and the most common manifestation is autoimmune hemolytic anemia, followed by vasculitis, arthritis, neutropenia, inflammatory bowel disease, and IgA nephropathy. Many groups have widely explored immune cell functionality in WAS partially explaining how cellular defects may lead to pathology. However, the mechanisms underlying the occurrence of autoimmune manifestations have not been clearly described yet. In the present review, we report the most recent progresses in the study of immune cell function in WAS that have started to unveil the mechanisms contributing to autoimmune complications in WAS patients.

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.

Lipid-antigen presentation by CD1d(+) B cells is essential for the maintenance of invariant natural killer T cells

B cells perform many immunological functions, including presenting lipid antigen to CD1d-restricted invariant natural killer T (iNKT) cells, known to contribute to maintaining tolerance in autoimmunity. Patients with systemic lupus erythematous (SLE) display dysregulated B cell responses and reduced peripheral iNKT cell frequencies. The significance of these defects and how they relate to SLE pathogenesis remain elusive. We report that B cells are essential for iNKT cell expansion and activation in healthy donors but fail to exert a similar effect in SLE patients. Defective B cell-mediated stimulation of iNKT cells in SLE patients was associated with altered CD1d recycling, a defect recapitulated in B cells from healthy donors after stimulation with interferon-α (IFN-α) and anti-immunoglobulin (Ig). iNKT cell number and function were restored in SLE patients responding to anti-CD20 treatment upon normalization of CD1d expression exclusively in repopulated immature B cells. We propose that healthy B cells are pivotal for iNKT cell homeostasis.

The inflammatory cytokine IL-18 induces self-reactive innate antibody responses regulated by natural killer T cells

Inflammatory responses initiate rapid production of IL-1 family cytokines, including IL-18. This cytokine is produced at high levels in inflammatory diseases, including allergy and autoimmunity, and is known to induce IgE production in mice. Here we provide evidence that IL-18 is directly coupled to induction of self-reactive IgM and IgG antibody responses and recruitment of innate B2 B cells residing in the marginal zone of the spleen. Moreover, the data suggest that the B-cell activation occurs predominantly in splenic extrafollicular plasma cell foci and is regulated by natural killer T (NKT) cells that prevent formation of mature germinal centers. We also find evidence that NKT cells control this type of B-cell activation via cytotoxicity mediated by both the perforin and CD95/CD178 pathways. Thus, NKT cells regulate innate antibody responses initiated by an inflammatory stimulus, suggesting a general mechanism that regulates B-cell behavior in inflammation and autoreactivity.

Disparate effects of depletion of CD1d-reactive T cells during early versus late stages of disease in a genetically susceptible model of lupus

Some T cells react with lipid antigens bound to antigen-presenting molecule CD1d. Numbers and functions of a subset of such lipid-reactive T cells are reduced in patients with systemic lupus erythematosus (SLE) and their relatives, as well as in genetically susceptible and chemically induced animal models of lupus-like disease. We have reported that the germline deletion of CD1d exacerbates lupus, suggesting a protective role of these cells in the development of lupus. The use of a knockout mouse model in this study, however, did not allow examination of the role of these cells at different stages of disease. Here, we describe an approach to deplete CD1d-dependent T cells, which allowed us to investigate the role of these cells at different stages of disease in genetically lupus-prone NZB/NZW F1 (BWF1) mice. Repeated intravenous injections of large numbers of CD1d-transfected cells resulted in ∼50-75% reduction in these cells, as defined by the expression of CD4, NK1.1 and CD122, and lack of expression of CD62 ligand. TCR γδ (+)NK1.1(+) cells were also reduced in the recipients of CD1d-transfected cells as compared with control recipients. Such depletion of CD1d-reactive T cells in preclinical BWF1 mice resulted in disease acceleration with a significant increase in proteinuria and mortality. In older BWF1 mice having advanced nephritis, however, such depletion of CD1d-reactive T cells resulted in some disease improvement. Taken together, these data as well as our published studies suggest that CD1d-reactive T cells protect against the development of lupus in animal models. However, these cells appear to be unable to suppress established lupus nephritis in these animals, and might even play a disease aggravating role in late stages of disease.

Homeostatic regulation of marginal zone B cells by invariant natural killer T cells

Marginal zone B cells (MZB) mount a rapid antibody response, potently activate naïve T cells, and are enriched in autoreactive B cells. MZBs express high levels of CD1d, the restriction element for invariant natural killer T cells (iNKT). Here, we examined the effect of iNKT cells on MZB cell activation and numbers in vitro and in vivo in normal and autoimmune mice. Results show that iNKT cells activate MZBs, but restrict their numbers in vitro and in vivo in normal BALB/c and C57/BL6 mice. iNKT cells do so by increasing the activation-induced cell death and curtailing proliferation of MZB cells, whereas they promote the proliferation of follicular B cells. Sorted iNKT cells can directly execute this function, without help from other immune cells. Such MZB regulation by iNKTs is mediated, at least in part, via CD1d on B cells in a contact-dependent manner, whereas iNKT-induced proliferation of follicular B cells occurs in a contact- and CD1d-independent manner. Finally, we show that iNKT cells reduce 'autoreactive' MZB cells in an anti-DNA transgenic model, and limit MZB cell numbers in autoimmune-prone (NZB×NZW)F1 and non-obese diabetic mice, suggesting a potentially new mechanism whereby iNKT cells might regulate pathologic autoimmunity. Differential regulation of follicular B cells versus potentially autoreactive MZBs by iNKT cells has important implications for autoimmune diseases as well as for conditions that require a rapid innate B cell response.

Brief treatment with iNKT cell ligand α-galactosylceramide confers a long-term protection against lupus

CD1d presents glycolipid antigens such as α-galactosylceramide (αGalCer) to invariant natural killer T cells (iNKT). We have reported that activated iNKTs inhibit IL-10-producing autoreactive B cells, while promoting or leaving intact the normal B cell responses, making iNKT modulation an attractive therapeutic modality. Here, we report that a brief treatment of young lupus-prone (NZB/NZW)F1 (BWF1) mice with two injections of αGalCer conferred a long-term protection against lupus. Long-term repeated administrations of αGalCer, however, afforded no clinical benefit. These disparate clinical effects correlated with iNKT responsiveness. While a brief treatment with αGalCer enhanced iNKT responses upon in vitro recall, the long-term αGalCer treatment resulted in reduced iNKT responses in BWF1 mice. The improvement in disease with αGalCer treatment was associated with the reduced IL-10 production. Furthermore, iNKTs directly inhibited IL-10-secreting cells in vivo in reconstituted SCID mice and inhibited IL-10-secreting B cells in vitro in co-cultures. Thus, a brief treatment with a CD1d-binding glycolipid enhances iNKT responses, reduces IL-10 production, and delays the onset of lupus, whereas long-term repeated treatments induce marked iNKT hyporesponsiveness and do not affect disease outcome in BWF1 mice. Identifying glycolipid regimens that can modulate iNKT responsiveness will have important implications for developing iNKT-based therapies for autoimmune diseases.

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.