Digestion of Chromatin in Apoptotic Cell Microparticles Prevents Autoimmunity.

Antibodies to DNA and chromatin drive autoimmunity in systemic lupus erythematosus (SLE). Null mutations and hypomorphic variants of the secreted deoxyribonuclease DNASE1L3 are linked to familial and sporadic SLE, respectively. We report that DNASE1L3-deficient mice rapidly develop autoantibodies to DNA and chromatin, followed by an SLE-like disease. Circulating DNASE1L3 is produced by dendritic cells and macrophages, and its levels inversely correlate with anti-DNA antibody response. DNASE1L3 is uniquely capable of digesting chromatin in microparticles released from apoptotic cells. Accordingly, DNASE1L3-deficient mice and human patients have elevated DNA levels in plasma, particularly in circulating microparticles. Murine and human autoantibody clones and serum antibodies from human SLE patients bind to DNASE1L3-sensitive chromatin on the surface of microparticles. Thus, extracellular microparticle-associated chromatin is a potential self-antigen normally digested by circulating DNASE1L3. The loss of this tolerance mechanism can contribute to SLE, and its restoration may represent a therapeutic opportunity in the disease.

Melatonin Contributes to the Seasonality of Multiple Sclerosis Relapses.

Seasonal changes in disease activity have been observed in multiple sclerosis, an autoimmune disorder that affects the CNS. These epidemiological observations suggest that environmental factors influence the disease course. Here, we report that melatonin levels, whose production is modulated by seasonal variations in night length, negatively correlate with multiple sclerosis activity in humans. Treatment with melatonin ameliorates disease in an experimental model of multiple sclerosis and directly interferes with the differentiation of human and mouse T cells. Melatonin induces the expression of the repressor transcription factor Nfil3, blocking the differentiation of pathogenic Th17 cells and boosts the generation of protective Tr1 cells via Erk1/2 and the transactivation of the IL-10 promoter by ROR-α. These results suggest that melatonin is another example of how environmental-driven cues can impact T cell differentiation and have implications for autoimmune disorders such as multiple sclerosis.

Identification of environmental factors that promote intestinal inflammation.

Genome-wide association studies have identified risk loci linked to inflammatory bowel disease (IBD)1-a complex chronic inflammatory disorder of the gastrointestinal tract. The increasing prevalence of IBD in industrialized countries and the augmented disease risk observed in migrants who move into areas of higher disease prevalence suggest that environmental factors are also important determinants of IBD susceptibility and severity2. However, the identification of environmental factors relevant to IBD and the mechanisms by which they influence disease has been hampered by the lack of platforms for their systematic investigation. Here we describe an integrated systems approach, combining publicly available databases, zebrafish chemical screens, machine learning and mouse preclinical models to identify environmental factors that control intestinal inflammation. This approach established that the herbicide propyzamide increases inflammation in the small and large intestine. Moreover, we show that an AHR-NF-κB-C/EBPß signalling axis operates in T cells and dendritic cells to promote intestinal inflammation, and is targeted by propyzamide. In conclusion, we developed a pipeline for the identification of environmental factors and mechanisms of pathogenesis in IBD and, potentially, other inflammatory diseases.

Secreted IgD Amplifies Humoral T Helper 2 Cell Responses by Binding Basophils via Galectin-9 and CD44.

B cells thwart antigenic aggressions by releasing immunoglobulin M (IgM), IgG, IgA, and IgE, which deploy well-understood effector functions. In contrast, the role of secreted IgD remains mysterious. We found that some B cells generated IgD-secreting plasma cells following early exposure to external soluble antigens such as food proteins. Secreted IgD targeted basophils by interacting with the CD44-binding protein galectin-9. When engaged by antigen, basophil-bound IgD increased basophil secretion of interleukin-4 (IL-4), IL-5, and IL-13, which facilitated the generation of T follicular helper type 2 cells expressing IL-4. These germinal center T cells enhanced IgG1 and IgE but not IgG2a and IgG2b responses to the antigen initially recognized by basophil-bound IgD. In addition, IgD ligation by antigen attenuated allergic basophil degranulation induced by IgE co-ligation. Thus, IgD may link B cells with basophils to optimize humoral T helper type 2-mediated immunity against common environmental soluble antigens.

Human Secretory IgM Emerges from Plasma Cells Clonally Related to Gut Memory B Cells and Targets Highly Diverse Commensals.

Secretory immunoglobulin A (SIgA) enhances host-microbiota symbiosis, whereas SIgM remains poorly understood. We found that gut IgM+ plasma cells (PCs) were more abundant in humans than mice and clonally related to a large repertoire of memory IgM+ B cells disseminated throughout the intestine but rare in systemic lymphoid organs. In addition to sharing a gut-specific gene signature with memory IgA+ B cells, memory IgM+ B cells were related to some IgA+ clonotypes and switched to IgA in response to T cell-independent or T cell-dependent signals. These signals induced abundant IgM which, together with SIgM from clonally affiliated PCs, recognized mucus-embedded commensals. Bacteria recognized by human SIgM were dually coated by SIgA and showed increased richness and diversity compared to IgA-only-coated or uncoated bacteria. Thus, SIgM may emerge from pre-existing memory rather than newly activated naive IgM+ B cells and could help SIgA to anchor highly diverse commensal communities to mucus.

IL-27 acts on DCs to suppress the T cell response and autoimmunity by inducing expression of the immunoregulatory molecule CD39.

Dendritic cells (DCs) control the balance between effector T cells and regulatory T cells in vivo. Hence, the study of DCs might identify mechanisms of disease pathogenesis and guide new therapeutic approaches for disorders mediated by the immune system. We found that interleukin 27 (IL-27) signaling in mouse DCs limited the generation of effector cells of the TH1 and TH17 subsets of helper T cells and the development of experimental autoimmune encephalomyelitis (EAE). The effects of IL-27 were mediated at least in part through induction of the immunoregulatory molecule CD39 in DCs. IL-27-induced CD39 decreased the extracellular concentration of ATP and downregulated nucleotide-dependent activation of the NLRP3 inflammasome. Finally, therapeutic vaccination with IL-27-conditioned DCs suppressed established relapsing-remitting EAE. Thus, IL-27 signaling in DCs limited pathogenic T cell responses and the development of autoimmunity.

Aiolos promotes TH17 differentiation by directly silencing Il2 expression.

CD4(+) interleukin 17 (IL-17)-producing helper T cells (T(H)17 cells) are instrumental in the immune response to pathogens. However, an overactive T(H)17 response results in tissue inflammation and autoimmunity, and therefore it is important to identify the molecular mechanisms that control the development of T(H)17 cells. IL-2 suppresses such development, but how IL-2 production is actively suppressed during T(H)7 differentiation is not understood. Here we report that under T(H)17-polarizing conditions, the transcription factors STAT3 and AhR upregulated the expression of Aiolos, a member of the Ikaros family of transcription factors. Using Aiolos-deficient mice, we demonstrated that Aiolos silenced the Il2 locus, promoting T(H)17 differentiation in vitro and in vivo. Thus, we have identified a module in the transcriptional program of T(H)17 cells that actively limits IL-2 production and promotes their differentiation.

Epigenetic control of early neurodegenerative events in diabetic retinopathy by the histone deacetylase SIRT6.

Diabetic retinopathy (DR) is one of the common complications associated with diabetes mellitus and the leading cause of blindness worldwide. Recent research has demonstrated that DR is not only a microvascular disease but may be a result of neurodegenerative processes. Moreover, glucose-induced neuron and glial cell damage may occur shortly after the onset of diabetes which makes the disease hard to diagnose at early stages. SIRT6, a NAD-dependent sirtuin deacylase, modulates aging, energy metabolism, and neurodegeneration. In previous studies we showed that SIRT6 deficiency causes major retinal transmission defects, changes in the expression of glycolytic genes, and elevated levels of apoptosis. Given the importance of glucose availability for retinal function and the critical role of SIRT6 in modulating glycolysis, we aimed to analyze SIRT6 participation in the molecular machinery that regulates the development of experimental DR. Using non-obese diabetic mice, we determined by western blot that 2 weeks after the onset of the disease, high glucose concentrations induced retinal increase in a neovascularization promoting factor (vascular endothelial growth factor, VEGF), and the loss of a neuroprotective factor (brain-derived neurotrophic factor, BDNF) associated with reduced levels of SIRT6 and increased acetylation levels of its substrates (H3K9 and H3K56) suggesting a deregulation of key neural factors. Noteworthy, retinas from CNS conditionally deleted SIRT6 mice showed a resemblance to diabetic retinas exhibiting lower protein levels of BDNF factor and increased protein levels of VEGF. Moreover, cultured Müller glial cells subjected to high glucose concentrations exhibited decreased levels of SIRT6 and increased levels of H3K56 acetylation. In addition, the increment of VEGF levels induced by high glucose was reverted by the over-expression of SIRT6 in this cell type. Accordingly, siRNA experiments showed that, when SIRT6 was silenced, VEGF levels increased. Our findings suggest that epigenetically regulated neurodegenerative events may occur at an early diabetic stage prior to the characteristic proliferative and vascular changes observed at a later diabetic stage.

Fatal autoimmunity in mice reconstituted with human hematopoietic stem cells encoding defective FOXP3.

Mice reconstituted with a human immune system provide a tractable in vivo model to assess human immune cell function. To date, reconstitution of murine strains with human hematopoietic stem cells (HSCs) from patients with monogenic immune disorders have not been reported. One obstacle precluding the development of immune-disease specific "humanized" mice is that optimal adaptive immune responses in current strains have required implantation of autologous human thymic tissue. To address this issue, we developed a mouse strain that lacks murine major histocompatibility complex class II (MHC II) and instead expresses human leukocyte antigen DR1 (HLA-DR1). These mice displayed improved adaptive immune responses when reconstituted with human HSCs including enhanced T-cell reconstitution, delayed-type hypersensitivity responses, and class-switch recombination. Following immune reconstitution of this novel strain with HSCs from a patient with immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, associated with aberrant FOXP3 function, mice developed a lethal inflammatory disorder with multiorgan involvement and autoantibody production mimicking the pathology seen in affected humans. This humanized mouse model permits in vivo evaluation of immune responses associated with genetically altered HSCs, including primary immunodeficiencies, and should facilitate the study of human immune pathobiology and the development of targeted therapeutics.

Nanoparticle-mediated codelivery of myelin antigen and a tolerogenic small molecule suppresses experimental autoimmune encephalomyelitis.

The immune response is normally controlled by regulatory T cells (Tregs). However, Treg deficits are found in autoimmune diseases, and therefore the induction of functional Tregs is considered a potential therapeutic approach for autoimmune disorders. The activation of the ligand-activated transcription factor aryl hydrocarbon receptor by 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) or other ligands induces dendritic cells (DCs) that promote FoxP3(+) Treg differentiation. Here we report the use of nanoparticles (NPs) to coadminister ITE and a T-cell epitope from myelin oligodendrocyte glycoprotein (MOG)(35)(-55) to promote the generation of Tregs by DCs. NP-treated DCs displayed a tolerogenic phenotype and promoted the differentiation of Tregs in vitro. Moreover, NPs carrying ITE and MOG(35-55) expanded the FoxP3(+) Treg compartment and suppressed the development of experimental autoimmune encephalomyelitis, an experimental model of multiple sclerosis. Thus, NPs are potential new tools to induce functional Tregs in autoimmune disorders.

Defect in regulatory B-cell function and development of systemic autoimmunity in T-cell Ig mucin 1 (Tim-1) mucin domain-mutant mice.

Tim-1, a type I transmembrane glycoprotein, consists of an IgV domain and a mucin domain. The IgV domain is essential for binding Tim-1 to its ligands, but little is known about the role of the mucin domain, even though genetic association of TIM-1 with atopy/asthma has been linked to the length of mucin domain. We generated a Tim-1-mutant mouse (Tim-1(Δmucin)) in which the mucin domain was deleted genetically. The mutant mice showed a profound defect in IL-10 production from regulatory B cells (Bregs). Associated with the loss of IL-10 production in B cells, older Tim-1(Δmucin) mice developed spontaneous autoimmunity associated with hyperactive T cells, with increased production of IFN-γ and elevated serum levels of Ig and autoantibodies. However, Tim-1(Δmucin) mice did not develop frank systemic autoimmune disease unless they were crossed onto the Fas-mutant lpr mice on a C57BL/6 background. Tim-1(Δmucin)lpr mice developed accelerated and fulminant systemic autoimmunity with accumulation of abnormal double-negative T cells and autoantibodies to a number of lupus-associated autoantigens. Thus, Tim-1 plays a critical role in maintaining suppressive Breg function, and our data also demonstrate an unexpected role of the Tim-1 mucin domain in regulating Breg function and maintaining self-tolerance.

Antigen microarrays for the study of autoimmune diseases.

BACKGROUND: The immune response involves the activation of heterogeneous populations of T cells and B cells that show different degrees of affinity and specificity for target antigens. Although several techniques have been developed to study the molecular pathways that control immunity, there is a need for high-throughput assays to monitor the specificity of the immune response. CONTENT: Antigen microarrays provide a new tool to study the immune response. We reviewed the literature on antigen microarrays and their advantages and limitations, and we evaluated their use for the study of autoimmune diseases. Antigen arrays have been successfully used for several purposes in the investigation of autoimmune disorders: for disease diagnosis, to monitor disease progression and response to therapy, to discover mechanisms of pathogenesis, and to tailor antigen-specific therapies to the autoimmune response of individual patients. In this review we discuss the use of antigen microarrays for the study of 4 common autoimmune diseases and their animal models: type 1 diabetes, systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. CONCLUSIONS: Antigen microarrays constitute a new tool for the investigation of the immune response in autoimmune disorders and also in other conditions such as tumors and allergies. Once current limitations are overcome, antigen microarrays have the potential to revolutionize the investigation and management of autoimmune diseases.

A cell-based drug delivery platform for treating central nervous system inflammation.

Mesenchymal stem cells (MSCs) are promising candidates for the development of cell-based drug delivery systems for autoimmune inflammatory diseases, such as multiple sclerosis (MS). Here, we investigated the effect of Ro-31-8425, an ATP-competitive kinase inhibitor, on the therapeutic properties of MSCs. Upon a simple pretreatment procedure, MSCs spontaneously took up and then gradually released significant amounts of Ro-31-8425. Ro-31-8425 (free or released by MSCs) suppressed the proliferation of CD4+ T cells in vitro following polyclonal and antigen-specific stimulation. Systemic administration of Ro-31-8425-loaded MSCs ameliorated the clinical course of experimental autoimmune encephalomyelitis (EAE), a murine model of MS, displaying a stronger suppressive effect on EAE than control MSCs or free Ro-31-8425. Ro-31-8425-MSC administration resulted in sustained levels of Ro-31-8425 in the serum of EAE mice, modulating immune cell trafficking and the autoimmune response during EAE. Collectively, these results identify MSC-based drug delivery as a potential therapeutic strategy for the treatment of autoimmune diseases. KEY MESSAGES: MSCs can spontaneously take up the ATP-competitive kinase inhibitor Ro-31-8425. Ro-31-8425-loaded MSCs gradually release Ro-31-8425 and exhibit sustained suppression of T cells. Ro-31-8425-loaded MSCs have more sustained serum levels of Ro-31-8425 than free Ro-31-8425. Ro-31-8425-loaded MSCs are more effective than MSCs and free Ro-31-8425 for EAE therapy.

Chi3l3 induces oligodendrogenesis in an experimental model of autoimmune neuroinflammation.

In demyelinating diseases including multiple sclerosis (MS), neural stem cells (NSCs) can replace damaged oligodendrocytes if the local microenvironment supports the required differentiation process. Although chitinase-like proteins (CLPs) form part of this microenvironment, their function in this differentiation process is unknown. Here, we demonstrate that murine Chitinase 3-like-3 (Chi3l3/Ym1), human Chi3L1 and Chit1 induce oligodendrogenesis. In mice, Chi3l3 is highly expressed in the subventricular zone, a stem cell niche of the adult brain, and in inflammatory brain lesions during experimental autoimmune encephalomyelitis (EAE). We find that silencing Chi3l3 increases severity of EAE. We present evidence that in NSCs Chi3l3 activates the epidermal growth factor receptor (EGFR), thereby inducing Pyk2-and Erk1/2- dependent expression of a pro-oligodendrogenic transcription factor signature. Our results implicate CLP-EGFR-Pyk2-MEK-ERK as a key intrinsic pathway controlling oligodendrogenesis.

Bilirubin suppresses Th17 immunity in colitis by upregulating CD39.

Unconjugated bilirubin (UCB), a product of heme oxidation, has known immunosuppressant properties but the molecular mechanisms, other than antioxidant effects, remain largely unexplored. We note that UCB modulates T helper type 17 (Th17) immune responses, in a manner dependent upon heightened expression of CD39 ectonucleotidase. UCB has protective effects in experimental colitis, where it enhances recovery after injury and preferentially boosts IL-10 production by colonic intraepithelial CD4+ cells. In vitro, UCB confers immunoregulatory properties on human control Th17 cells, as reflected by increased levels of FOXP3 and CD39 with heightened cellular suppressor ability. Upregulation of CD39 by Th17 cells is dependent upon ligation of the aryl hydrocarbon receptor (AHR) by UCB. Genetic deletion of CD39, as in Entpd1-/- mice, or dysfunction of AHR, as in Ahrd mice, abrogates these UCB salutary effects in experimental colitis. However, in inflammatory bowel disease (IBD) samples, UCB fails to confer substantive immunosuppressive properties upon Th17 cells, because of decreased AHR levels under the conditions tested in vitro. Immunosuppressive effects of UCB are mediated by AHR resulting in CD39 upregulation by Th17. Boosting downstream effects of AHR via UCB or enhancing CD39-mediated ectoenzymatic activity might provide therapeutic options to address development of Th17 dysfunction in IBD.

Serum lipid antibodies are associated with cerebral tissue damage in multiple sclerosis.

OBJECTIVE: To determine whether peripheral immune responses as measured by serum antigen arrays are linked to cerebral MRI measures of disease severity in multiple sclerosis (MS). METHODS: In this cross-sectional study, serum samples were obtained from patients with relapsing-remitting MS (n = 21) and assayed using antigen arrays that contained 420 antigens including CNS-related autoantigens, lipids, and heat shock proteins. Normalized compartment-specific global brain volumes were obtained from 3-tesla MRI as surrogates of atrophy, including gray matter fraction (GMF), white matter fraction (WMF), and total brain parenchymal fraction (BPF). Total brain T2 hyperintense lesion volume (T2LV) was quantified from fluid-attenuated inversion recovery images. RESULTS: We found serum antibody patterns uniquely correlated with BPF, GMF, WMF, and T2LV. Furthermore, we identified immune signatures linked to MRI markers of neurodegeneration (BPF, GMF, WMF) that differentiated those linked to T2LV. Each MRI measure was correlated with a specific set of antibodies. Strikingly, immunoglobulin G (IgG) antibodies to lipids were linked to brain MRI measures. Based on the association between IgG antibody reactivity and each unique MRI measure, we developed a lipid index. This comprised the reactivity directed against all of the lipids associated with each specific MRI measure. We validated these findings in an additional independent set of patients with MS (n = 14) and detected a similar trend for the correlations between BPF, GMF, and T2LV vs their respective lipid indexes. CONCLUSIONS: We propose serum antibody repertoires that are associated with MRI measures of cerebral MS involvement. Such antibodies may serve as biomarkers for monitoring disease pathology and progression.

AHR Activation Is Protective against Colitis Driven by T Cells in Humanized Mice.

Existing therapies for inflammatory bowel disease that are based on broad suppression of inflammation result in variable clinical benefit and unwanted side effects. A potential therapeutic approach for promoting immune tolerance is the in vivo induction of regulatory T cells (Tregs). Here we report that activation of the aryl hydrocarbon receptor using the non-toxic agonist 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) induces human Tregs in vitro that suppress effector T cells through a mechanism mediated by CD39 and Granzyme B. We then developed a humanized murine system whereby human CD4+ T cells drive colitis upon exposure to 2,4,6-trinitrobenzenesulfonic acid and assessed ITE as a potential therapeutic. ITE administration ameliorated colitis in humanized mice with increased CD39, Granzyme B, and IL10-secreting human Tregs. These results develop an experimental model to investigate human CD4+ T responses in vivo and identify the non-toxic AHR agonist ITE as a potential therapy for promoting immune tolerance in the intestine.

Tolerogenic nanoparticles inhibit T cell-mediated autoimmunity through SOCS2.

Type 1 diabetes (T1D) is a T cell-dependent autoimmune disease that is characterized by the destruction of insulin-producing ß cells in the pancreas. The administration to patients of ex vivo-differentiated FoxP3(+) regulatory T (Treg) cells or tolerogenic dendritic cells (DCs) that promote Treg cell differentiation is considered a potential therapy for T1D; however, cell-based therapies cannot be easily translated into clinical practice. We engineered nanoparticles (NPs) to deliver both a tolerogenic molecule, the aryl hydrocarbon receptor (AhR) ligand 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE), and the ß cell antigen proinsulin (NPITE+Ins) to induce a tolerogenic phenotype in DCs and promote Treg cell generation in vivo. NPITE+Ins administration to 8-week-old nonobese diabetic mice suppressed autoimmune diabetes. NPITE+Ins induced a tolerogenic phenotype in DCs, which was characterized by a decreased ability to activate inflammatory effector T cells and was concomitant with the increased differentiation of FoxP3(+) Treg cells. The induction of a tolerogenic phenotype in DCs by NPs was mediated by the AhR-dependent induction of Socs2, which resulted in inhibition of nuclear factor κB activation and proinflammatory cytokine production (properties of tolerogenic DCs). Together, these data suggest that NPs constitute a potential tool to reestablish tolerance in T1D and potentially other autoimmune disorders.

Metabolic control of type 1 regulatory T cell differentiation by AHR and HIF1-α.

Our understanding of the pathways that regulate lymphocyte metabolism, as well as the effects of metabolism and its products on the immune response, is still limited. We report that a metabolic program controlled by the transcription factors hypoxia inducible factor-1α (HIF1-α) and aryl hydrocarbon receptor (AHR) supports the differentiation of type 1 regulatory T cell (Tr1) cells. HIF1-α controls the early metabolic reprograming of Tr1 cells. At later time points, AHR promotes HIF1-α degradation and takes control of Tr1 cell metabolism. Extracellular ATP (eATP) and hypoxia, linked to inflammation, trigger AHR inactivation by HIF1-α and inhibit Tr1 cell differentiation. Conversely, CD39 promotes Tr1 cell differentiation by depleting eATP. CD39 also contributes to Tr1 suppressive activity by generating adenosine in cooperation with CD73 expressed by responder T cells and antigen-presenting cells. These results suggest that HIF1-α and AHR integrate immunological, metabolic and environmental signals to regulate the immune response.

IL-21 induces IL-22 production in CD4+ T cells.

Interleukin (IL)-22 produced by innate lymphoid cells (ILCs) and CD4+ T cells plays an important role in host defence and mucosal homeostasis, thus it is important to investigate the mechanisms that regulate IL-22 production. We investigated the regulation IL-22 production by CD4+ T cells. Here we show that IL-21 triggers IL-22, but not IL-17 production by CD4+ T cells. STAT3, activated by IL-21, controls the epigenetic status of the il22 promoter and its interaction with the aryl hydrocarbon receptor (AhR). Moreover, IL-21 and AhR signalling in T cells control IL-22 production and the development of dextran sodium sulphate-induced colitis in ILC-deficient mice. Thus, we have identified IL-21 as an inducer of IL-22 production in CD4+ T cells in vitro and in vivo.