Tolerogenic Function Research Articles

Circular RNA circSnx5 Controls Immunogenicity of Dendritic Cells through the miR-544/SOCS1 Axis and PU.1 Activity Regulation

Dendritic cells (DCs) can orchestrate either immunogenic or tolerogenic responses to relay information on the functional state. Emerging studies indicate that circular RNAs (circRNAs) are involved in immunity; however, it remains unclear whether they govern DC development and function at the transcriptional level. In this study, we identified a central role for a novel circRNA, circSnx5, in modulating DC-driven immunity and tolerance. Ectopic circSnx5 suppresses DC activation and promotes the development of tolerogenic functions of DCs, while circSnx5 knockdown promotes their activation and inflammatory phenotype. Mechanistically, circSnx5 can act as a miR-544 sponge to attenuate miRNA-mediated target depression on suppressor of cytokine signaling 1 (SOCS1) and inhibit nuclear translocation of PU.1, regulating DC activation and function. Furthermore, the main splicing factors (SFs) were identified in DCs, of which heterogeneous nuclear ribonucleoprotein (hnRNP) C was essential for circSnx5 generation. Moreover, our data demonstrated that vaccination with circSnx5-conditioned DCs prolonged cardiac allograft survival in mice and alleviated experimental autoimmune myocarditis. Taken together, our results revealed circSnx5 as a key modulator to fine-tune DC function, suggesting that circSnx5 may serve as a potential therapeutic avenue for immune-related diseases.

Approaches to inducing antigen-specific immune tolerance in allergy and autoimmunity: Focus on antigen-presenting cells and extracellular vesicles.

Increasing prevalence of allergic and autoimmune diseases urges clinicians and researchers to search for new and efficient treatments. Strategies that activate antigen-specific immune tolerance and simultaneously maintain immune reactivity to all other antigens deserve special attention. Accordingly, antigen-presenting cells (APCs) seem to be the best suited for orchestrating these mechanisms by directing T cell immune responses towards a tolerant subtype. Recent advances in understanding cell-to-cell communication via extracellular vesicles (EVs) make the latter promising candidates for reprogramming APCs towards a tolerant phenotype, and for mediating tolerogenic APC function. Thus, comprehensive studies have been undertaken to describe the interactions of APCs and EVs naturally occurring during immune tolerance induction, as well as to develop EV-based manoeuvres enabling the induction of immune tolerance in an antigen-specific manner. In this review, we summarize the findings of relevant studies, with a special emphasis on future perspectives on their translation to clinical practice.

Allogeneic bone marrow derived mesenchymal stem cells outperform the autologous in modulating dendritic cells isolated from type 1 diabetic patients

Background & Aim Dendritic cells (DCs) have been implicated in the pathogenesis of type 1 diabetes mellitus (T1DM) and have potential as immunotherapeutic agents. The inhibition of DCs profile and function is part of the multi-level immunomodulatory properties displayed by human Mesenchymal Stem Cells (MSCs). Due to their potent immunoregulatory and immunomodulatory functions, MSCs have emerged as a therapeutic regimen in the management of many diseases that have no effective treatment, including T1DM. It has been shown that in T1DM patients DCs respond in terms of maturation, activation, and phenotype when co-cultured with autologous and allogeneic Bone Marrow derived MSCs (BM-MSC). In the recent study, the effect of autologous BM-MSCs in comparison with the allogeneic BM-MSCs co-cultured with monocyte-derived DCs isolated from TIDM patients was investigated for the first time. Methods, Results & Conclusion Methods Autologous and allogeneic BM-MSCs were isolated from healthy donors and T1DM patients. Then, morphology and surface markers expression were analyzed. Mature DCs (mDCs) were differentiated from CD14+ cells, obtained from newly diagnosed T1DM patients, pulsed with antigen Glutamic Acid Decarboxylase (GAD65) and co-cultured with BM-MSCs. the expression of co-stimulatory molecules and maturation markers were evaluated by flow cytometery. The level of anti-inflammatory cytokines was measured by ELISA. Autologous CD14- cells and GAD65 pulsed mDCs were co-cultured and IFN-γ ELISPOT responses were performed. Secreted level of IL-17 was measured Result autologous and allogeneic BM-MSCs have a comparable effect on GAD65 pulsed mature mDCs in terms of phenotype and maturation marker expression. Interestingly, the secretion levels of (IL-10, IL-6 and TGF-B) increased significantly in the allogeneic BM-MSCs when co-cultured with GAD65 pulsed mDCs. GAD65 pulsed-mDCs/T-cells showed decreased IFN-γ production when co-cultured with BM-MSCs. Moreover, the level of IL-17 secretion declined significantly in the allogeneic BM-MSCs compared to the autologous cells. Conclusion This research demonstrated in vitro the potent immunomodulatory effect of allogeneic BM-MSCs on pancreatic islet antigen specific T-Cells in newly-diagnosed T1DM patients through the induction of DCs’ tolerogenic function. These DCs can contribute to the suppressing T-cell mediated immunity and the promotion of anti-inflammatory responses exerted by BM-MSCs.

Natural and Induced Tolerogenic Dendritic Cells.

Dendritic cells (DCs) are highly susceptible to extrinsic signals that modify the functions of these crucial APCs. Maturation of DCs induced by diverse proinflammatory conditions promotes immune responses, but certain signals also induce tolerogenic functions in DCs. These "induced tolerogenic DCs" help to moderate immune responses such as those to commensals present at specific anatomical locations. However, also under steady-state conditions, some DCs are characterized by inherent tolerogenic properties. The immunomodulatory mechanisms constitutively present in such "natural tolerogenic DCs" help to promote tolerance to peripheral Ags. By extending tolerance initially established in the thymus, these functions of DCs help to regulate autoimmune and other immune responses. In this review we will discuss the mechanisms and functions of natural and induced tolerogenic DCs and offer further insight into how their possible manipulations may ultimately lead to more precise treatments for various immune-mediated conditions and diseases.

Expression of membrane-bound human leucocyte antigen-G in systemic sclerosis and systemic lupus erythematosus

Human leucocyte antigen-G (HLA-G) is a nonclassical class I major histocompatibility complex (MHC) molecule characterized by complex immunoregulatory and tolerogenic functions. Membrane-bound HLA-G is expressed on the surface of different cell populations in both physiological and pathological conditions. Systemic sclerosis (SSc) is a multisystem autoimmune disease characterized by widespread tissue fibrosis, vascular lesions and immunological alterations. Systemic lupus erythematosus is the prototypic systemic autoimmune disease affecting virtually any organ system, such as skin, joints, central nervous system, or kidneys. In SSc and SLE patients, the membrane expression of HLA-G on monocytes (0.88 ± 1.54 and 0.43 ± 0.75, respectively), CD4+ (0.42 ± 0.78 and 0.63 ± 0.48, respectively), CD8+ (2.65 ± 3.47 and 1.29 ± 1.34, respectively) and CD4+ CD8+ double-positive cells (13.87 ± 15.97 and 3.79 ± 3.11, respectively) was significantly higher than in healthy controls (0.12 ± 0.07; 0.01 ± 0.01; 0.14 ± 0.20 and 0.32 ± 0.38, respectively) (p < 0.0001). Our results show that in SSc and SLE the membrane expression of HLA-G by different subpopulations of peripheral blood mononuclear cells (PBMC) is increased, suggesting a potential role of HLA-G molecules in the complex immunological pathogenesis of these two autoimmune disorders.

Probiotics ingestion prevents HDAC11-induced DEC205+ dendritic cell dysfunction in night shift nurses

It is known that the day-night shift-rotation has a negative impact on the immune system. The underlying mechanism remains to be further investigated. Probiotics have regulatory effects on immune functions. This study aims to investigate the role of probiotic ingestion in preventing the DEC205+ dendritic cell (decDC) dysfunction in day-night shift-engaging nurses. In this study, blood samples were collected from day-night shift-rotating nurses who took or did not take yogurt (containing C. Butyricum) during the night shift (NS). decDC functions were evaluated with pertinent immunological approaches. We observed that the immune tolerogenic functions and interleukin (IL)-10 expression were impaired in decDCs of nurses after NS. HDAC11 was detected in decDCs that was markedly up regulated after NS. The HDAC11 levels were negatively correlated with the immune tolerogenic functions in decDCs. Ingestion of probiotic-containing yogurt during NS efficiently suppressed Bmal1 and HDAC11 levels as well as up regulated the immune regulatory functions in decDCs. In conclusion, NS has a negative impact on decDC immune tolerogenic functions, which can be prevented by ingesting probiotics-containing yogurt during NS.

Phenotypic alterations in pancreatic lymph node stromal cells from human donors with type 1 diabetes and NOD mice.

Tolerance induction in lymph nodes can be mediated by both haematopoietic cells (e.g. specific dendritic cells subsets) and by non-haematopoietic cells (e.g. lymph node stromal cells [LNSCs]) when they present peripheral tissue antigens to autoreactive T cells. LNSCs normally regulate T cell trafficking and survival and help to maintain peripheral tolerance by exerting immunosuppressive effects. However, whether autoimmunity can be associated with defective tolerogenic functions of LNSCs is unknown and studies aimed at characterising LNSCs in humans are lacking. We hypothesised that dysregulated T cell responses in pancreatic lymph nodes (PLNs) from donors with type 1 diabetes and from NOD mice may be associated with altered LNSC function. We analysed PLNs from donors with type 1 diabetes and NOD mice for LNSC distribution and phenotype using flow cytometry. We assessed the expression of tolerance-related genes in different subsets of LNSCs from human donors, as well as in a population of dendritic cells enriched in autoimmune regulator (AIRE)+ cells and identified as HLA-DRhigh CD45low. The relative frequency of different LNSC subsets was altered in both donors with type 1 diabetes and NOD mice, and both MHC class II and programmed death-ligand 1 (PD-L1) expression were upregulated in human type 1 diabetes. Tolerance-related genes showed similar expression profiles between mouse and human LNSCs at steady state but were generally upregulated in the context of human type 1 diabetes, while, at the same time, many such genes were downregulated in the AIRE-enriched dendritic cell population. Our study shows that LNSCs are substantially altered in type 1 diabetes, but, surprisingly, they exhibit an enhanced tolerogenic phenotype along with increased antigen-presenting potential, which may indicate an attempt to offset dendritic cell-related tolerogenic defects in tolerance. Thus, LNSCs could constitute alternative therapeutic targets in which to deliver antigens to help re-establish tolerance and prevent or treat type 1 diabetes. All data generated or analysed during this study are included in the published article (and its online supplementary files). Biomark gene expression data were deposited on the Mendeley repository at https://data.mendeley.com/datasets/d9rdzdmvyf/1 . Any other raw datasets are available from the corresponding author on reasonable request. No applicable resources were generated or analysed during the current study.

Lactate Induces Pro-tumor Reprogramming in Intratumoral Plasmacytoid Dendritic Cells.

Plasmacytoid dendritic cells are the most efficient producers of type I interferons, viz. IFNα, in the body and thus have the ability to influence anti-tumor immune responses. But repression of effective intra-tumoral pDC activation is a key immuno-evasion strategy exhibited in tumors—tumor-recruited pDCs are rendered “tolerogenic,” characterized by deficiency in IFNα induction and ability to expand regulatory T cells in situ. But the tumor-derived factors that drive this functional reprogramming of intra-tumoral pDCs are not established. In this study we aimed at exploring if intra-tumoral abundance of the oncometabolite lactate influences intra-tumoral pDC function. We found that lactate attenuates IFNα induction by pDCs mediated by intracellular Ca2+ mobilization triggered by cell surface GPR81 receptor as well as directly by cytosolic import of lactate in pDCs through the cell surface monocarboxylate transporters, affecting cellular metabolism needed for effective pDC activation. We also found that lactate enhances tryptophan metabolism and kynurenine production by pDCs which contribute to induction of FoxP3+ CD4+ regulatory T cells, the major immunosuppressive immune cell subset in tumor microenvironment. We validated these mechanisms of lactate-driven pDC reprogramming by looking into tumor recruited pDCs isolated from patients with breast cancers as well as in a preclinical model of breast cancer in mice. Thus, we discovered a hitherto unknown link between intra-tumoral abundance of an oncometabolite resulting from metabolic adaptation in cancer cells and the pro-tumor tolerogenic function of tumor-recruited pDCs, revealing new therapeutic targets for potentiating anti-cancer immune responses.

Inflammation triggers immediate rather than progressive changes in monocyte differentiation in the small intestine

Bone marrow-derived circulating monocytes contribute to the replenishment and maintenance of the intestinal macrophage population. Intestinal monocytes undergo context-dependent phenotypic and functional adaptations to either maintain local immune balance or support intestinal inflammation. Here we use monocyte adoptive transfer to dissect the dynamics of monocyte-to-macrophage differentiation in normal and inflamed small intestine. We find that during homeostasis CCR2 and β7-integrin mediate constitutive homing of monocytes to the gut. By contrast, intestinal inflammation increases monocyte recruitment via CCR2, but not β7-integrin. In the non-inflamed intestine, monocytes gradually differentiate to express genes typically associated with tolerogenic macrophage functions. Conversely, immediately upon entry into the inflamed intestine, monocytes adapt a different expression pattern in a partly Trem-1-dependent manner. Our observations suggest that inflammation fundamentally changes the kinetics and modalities of monocyte differentiation in tissues.

Mal-deficiency impairs the tolerogenicity of dendritic cell of patients with allergic rhinitis

The tolerogenic dendritic cell dysfunction is associated with the pathogenesis of immune diseases. Microbial stimulus is required in the maintenance of immune functions. This study aims to elucidate the role of Mal signal in the maintenance of DEC205+ DC (decDC) immune tolerogenic function. In this study, peripheral DCs were collected from allergic rhinitis (AR) patients and healthy control (HC) subjects to assess the functional status of decDCs. An AR murine model was developed to test the role of Mal signals in the maintenance of decDCs’ functions. We observed that AR decDCs (decDCs obtained from AR patients) were incompetent in the induction of type 1 regulatory T cells (Tr1 cells). AR decDCs expressed less IL-10 than that in HC decDCs. IL-10 mRNA decayed spontaneously in AR decDCs. Tat-activating regulatory DNA-binding protein-43 (TDP43) protected IL-10 mRNA from decay. AR decDCs expressed lower levels of Mal than that in HC decDCs. Mal depletion resulted in IL-10 mRNA decay in HC decDCs. Reconstitution of Mal in AR decDCs restored the capacity of inducing Tr1 cells and attenuated experimental AR in mice. In conclusion, Mal plays a critical role in the maintenance of decDC’s immune tolerogenic function. The absence or insufficient Mal signal impairs decDC’s tolerogenic property. Reconstitution of Mal in AR decDCs can restore the immune tolerogenic capacity, which may have translational potential in the treatment of AR and other allergic diseases.

The Tolerogenic Function of Regulatory T Cells in Pregnancy and Cancer.

Regulatory T cells, a subpopulation of suppressive T cells, are potent mediators of self-tolerance and essential for the suppression of triggered immune responses. The immune modulating capacity of these cells play a major role in both transplantation, autoimmune disease, allergy, cancer and pregnancy. During pregnancy, low numbers of regulatory T cells are associated with pregnancy failure and pregnancy complications such as pre-eclampsia. On the other hand, in cancer, low numbers of immunosuppressive T cells are correlated with better prognosis. Hence, maternal immune tolerance toward the fetus during pregnancy and the escape from host immunosurveillance by cancer seem to be based on similar immunological mechanisms being highly dependent on the balance between immune activation and suppression. As regulatory T cells hold a crucial role in several biological processes, they may also be promising subjects for therapeutic use. Especially in the field of cancer, cell therapy and checkpoint inhibitors have demonstrated that immune-based therapies have a very promising potential in treatment of human malignancies. However, these therapies are often accompanied by adverse autoimmune side effects. Therefore, expanding the knowledge to recognize the complexities of immune regulation pathways shared across different immunological scenarios is extremely important in order to improve and develop new strategies for immune-based therapy. The intent of this review is to highlight the functional characteristics of regulatory T cells in the context of mechanisms of immune regulation in pregnancy and cancer, and how manipulation of these mechanisms potentially may improve therapeutic options.

IL-33 induces a metabolic programming supporting dendritic cells tolerogenicity

Abstract Objective Delivery of the stromal cell-derived cytokine IL-33 protects allografts from rejection by acting on CD11c+ DC that facilitate the expansion of regulatory T cells (Treg). IL-33 administration also permits tolerance induction at doses of co-stimulatory blockade that fails on their own. Based on these data we hypothesized that IL-33-stimulated DC represent a tolerogenic DC subset and their precise examination will define biochemical pathways that contribute to tolerogenic DC functions. Methods Mouse bone marrow-derived CD11c+ DCs were treated with lipopolysaccharide (LPS) or IL-33 before nitric oxide (NO) generation, glucose and fatty acid uptake, and mitochondrial function and potential were assessed by EPR spectroscopy, flow cytometry, and Seahorse analysis. Results DC responded to the TLR4 ligand LPS by generating high levels of NO and shifting their metabolic activity to aerobic glycolysis. This was in stark contrast to IL-33, which caused a metabolic reprogramming in DC that involved augmented mitochondrial basal respiration, ATP production, and maximum respiration. IL-33-stimulated DC also displayed increase mitochondrial potential and a profound increase in the uptake of fatty acids. Conclusions It has emerged that immunogenic DCs undergo metabolic changes that enables their pro-inflammatory functions. The metabolic underpinnings of tolerogenic DCs is less understood. Here we show that IL-33-stimulated DC, which potently expand Treg, rely on oxidative phosphorylation and uptake fatty acids. These data suggest IL-33 initiates metabolic reprogramming matching those found in regulatory myeloid populations, including tumor associated DC and alternatively activated macrophages.

Genetic Restoration of Heme Oxygenase-1 Expression Protects from Type 1 Diabetes in NOD Mice.

Antigen-presenting cells (APCs) including dendritic cells (DCs) play a critical role in the development of autoimmune diseases by presenting self-antigen to T-cells. Different signals modulate the ability of APCs to activate or tolerize autoreactive T-cells. Since the expression of heme oxygenase-1 (HO-1) by APCs has been associated with the tolerization of autoreactive T-cells, we hypothesized that HO-1 expression might be altered in APCs from autoimmune-prone non-obese diabetic (NOD) mice. We found that, compared to control mice, NOD mice exhibited a lower percentage of HO-1-expressing cells among the splenic DCs, suggesting an impairment of their tolerogenic functions. To investigate whether restored expression of HO-1 in APCs could alter the development of diabetes in NOD mice, we generated a transgenic mouse strain in which HO-1 expression can be specifically induced in DCs using a tetracycline-controlled transcriptional activation system. Mice in which HO-1 expression was induced in DCs exhibited a lower Type 1 Diabetes (T1D) incidence and a reduced insulitis compared to non-induced mice. Upregulation of HO-1 in DCs also prevented further increase of glycemia in recently diabetic NOD mice. Altogether, our data demonstrated the potential of induction of HO-1 expression in DCs as a preventative treatment, and potential as a curative approach for T1D.

Engineering release kinetics with polyelectrolyte multilayers to modulate TLR signaling and promote immune tolerance.

Autoimmune disorders, such as multiple sclerosis and type 1 diabetes, occur when immune cells fail to recognize "self" molecules. Recently, studies have revealed aberrant inflammatory signaling through pathogen sensing pathways, such as toll-like receptors (TLRs), during autoimmune disease. Therapeutic inhibition of these pathways might attenuate disease development, skewing disease-causing inflammatory cells towards cell types that promote tolerance. Delivering antagonistic ligands to a TLR upstream of an inflammatory signaling cascade, TLR9, has demonstrated exciting potential in a mouse model of MS; however, strategies that enable sustained delivery could reduce the need for repeated administration or enhance therapeutic efficacy. We hypothesized that GpG - an oligonucleotide TLR9 antagonist - which is inherently anionic, could be self-assembled into polyelectrolyte multilayers (PEMs) with a cationic, degradable poly(β-amino ester) (Poly1). We hypothesized that degradable Poly1/GpG PEMs could promote sustained release of GpG and modulate inflammatory immune cell functions. Here we demonstrate layer-by-layer assembly of degradable PEMs, as well as subsequent degradation and release of GpG. Following assembly and release, GpG maintains the ability to reduce dendritic cell activation and inflammatory cytokine secretion, restrain TLR9 signaling, and polarize myelin specific T cells towards regulatory phenotypes and functions in primarily immune cells. These results indicate that degradable PEMs may be able to promote tolerogenic immune function in the context of autoimmunity.

Mechanisms of Leptin and Ghrelin Action on Maturation and Functions of Dendritic Cells.

Molecular mechanisms of the immunomodulatory effects of leptin and ghrelin in concentrations typical for pregnancy on the maturation and functional activity of dendritic cells (DCs) generated from the peripheral blood monocytes of women are investigated. The presence of leptin during DC maturation did not affect the levels of CD83+CD1c+, CD86+CD1c+, and HLA-DR+CD1c+ DCs, but increased the amount and the activity of the enzyme indoleamine 2,3-dioxygenase (IDO). Cell culturing in the presence of ghrelin or combination of leptin and ghrelin reduced the percentage of CD86+CD1c+ DCs but did not affect the levels of CD83+CD1c+ and HLA-DR+CD1c+ DCs. In addition, ghrelin reduced the number of IDO molecules without affecting its activity. Simultaneous presence of leptin and ghrelin increased induced IDO activity without affecting the amount of the enzyme in DCs. The effects of leptin and ghrelin on the investigated functions of DCs in some cases correlated with high levels of cAMP. New mechanisms for leptin and ghrelin regulation of tolerogenic functions of DCs in pregnancy are proposed.

Knockdown of NEAT1 induces tolerogenic phenotype in dendritic cells by inhibiting activation of NLRP3 inflammasome.

Rationale: Tolerogenic dendritic cells (tol-DCs) play essential roles in immune-related diseases and induce immune tolerance by shaping T-cell responses. Accumulating evidence suggests that long noncoding RNAs (lncRNAs) play important regulatory roles in the immune system. However, the potential roles and underlying mechanisms of lncRNAs in tol-DCs remain unclear.Methods: RNA in-situ hybridization, histochemistry, and qRT-PCR were performed to determine the distribution and expression of NEAT1 in DCs. Flow cytometry was used to analyze the tolerogenic function of DCs. Small sequencing, followed by bioinformatic analysis, was performed to determine the target genes of NEAT1. The mechanism of NEAT1 was explored using a luciferase reporter, chromatin immunoprecipitation assays, and Immunofluorescence. In-vivo experiments were used to investigate the induction of immune tolerance via NEAT1-knockdown DCs.Results: Our results show that lncRNA NEAT1 can induce tolerogenic phenotype in DCs. Mechanistically, small RNA-seq analysis revealed that NEAT1 knockdown preferentially affected the expression of miR-3076-3p. Furthermore, NEAT1 used the NLRP3 inflammasome as a molecular decoy for miR-3076-3p, thus facilitating the expression of tolerogenic phenotype in DCs. Moreover, the transcription factor E2F1 acted as a repressor of NEAT1 transcription via activity of H3K27ac. Our results also indicate that NEAT1 knockdown in DCs can induce immune tolerance in models of experimental autoimmune myocarditis and heart transplantation.Conclusions: Taken together, our study shows the mechanism used by NEAT1 in inducing tol-DCs and highlights the therapeutic potential of targeting NEAT1 for the treatment of immune-related diseases.

Role of the p38 MAPK/C/EBPβ Pathway in the Regulation of Phenotype and IL-10 and IL-12 Production by Tolerogenic Bone Marrow-Derived Dendritic Cells.

Dendritic cells (DCs) play a major role in innate and adaptive immunity and self-immune tolerance. Immunogenic versus tolerogenic DC functions are dictated by their levels of costimulatory molecules and their cytokine expression profile. The transcription factor C/EBPβ regulates the expression of several inflammatory genes in many cell types including macrophages. However, little is known regarding the role of C/EBPβ in tolerogenic versus immunogenic DCs functions. We have previously reported that bone marrow-derived DCs generated with GM-CSF (GM/DCs) acquire the signature of semi-mature tolerogenic IL-10-producing DCs as opposed to immunogenic DCs generated with GM-CSF and IL-4 (IL-4/DCs). Here, we show that tolerogenic GM/DCs exhibit higher levels of phosphorylation and enhanced DNA binding activity of C/EBPβ and CREB than immunogenic IL-4/DCs. We also show that the p38 MAPK/CREB axis and GSK3 play an important role in regulating C/EBPβ phosphorylation and DNA binding activity. Inhibition of p38 MAPK in GM/DCs resulted in a drastic decrease of C/EBPβ and CREB DNA binding activities, a reduction of their IL-10 production and an increase of their IL-12p70 production, a characteristic of immunogenic IL-4/DCs. We also present evidence that GSK3 inhibition in GM/DCs reduced C/EBPβ DNA binding activity and increased expression of costimulatory molecules in GM/DCs and their production of IL-10. Analysis of GM/DCs of C/EBPβ−/− mice showed that C/EBPβ was essential to maintain the semimature phenotype and the production of IL-10 as well as low CD4+ T cell proliferation. Our results highlight the importance of the p38MAPK-C/EBPβ pathway in regulating phenotype and function of tolerogenic GM/DCs.

Human Leukocyte Antigen-G Restores Immune Tolerance in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a common autoimmune bleeding disorder in which loss of immune tolerance leads to platelet destruction. Human leukocyte antigen-G (HLA-G) is a non-classical major histocompatibility complex class I antigen including four membrane-bound (mHLA-G, HLA-G1 to -G4) and three soluble (sHLA-G, HLA-G5 to -G7) isoforms due to alternative splicing of the HLA-G primary transcript. HLA-G exerts immunosuppressive functions by interacting with its inhibitory receptors, immunoglobulin-like transcripts (ILTs), expressing differentially on natural killer cells, T cells, and antigen presenting cells.Upon binding to ILTs, HLA-G suppressed lymphocyte proliferation, promoted apoptosis of cytotoxic lymphocytes and natural killer cells, inhibited antibody secretion from activated B cells, and induced expansion of suppressive T cells, tolerogenic dendritic cells and myeloid-derived suppressor cells. HLA-G supports immune escape, and high level of HLA-G is associated with unfavorable outcomes in cancer patients. Meanwhile, HLA-G-induced tolerance can benefit human allotransplantation and autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, but the role of HLA-G in the treatment of ITP is still unclear.Here we observed significantly less soluble HLA-G in plasma from ITP patients positive for anti-glycoprotein (GP) IIb/IIIa and/or anti-GPIb/IX autoantibodies compared with autoantibody-negative patients or healthy controls. However, no significant difference was found in the sHLA-G levels between anti-glycoprotein (GP) IIbIIIa and anti-GPIb-IX autoantibodies groups. Interestingly, sHLA-G is positively correlated with platelet counts in ITP patients both with and without autoantibodies, suggesting that HLA-G can also protect platelets from destruction through other mechanisms. To elucidate this, we then analyzed both expression of membrane HLA-G and ILTs on PBMCs. Our data found less membrane-bound HLA-G and ILTs on CD4+T cells and CD14+cells in ITP patients. Moreover, recombinant human HLA-G (rhHLA-G) upregulated expression of ILT2 on CD4+and ILT4 on CD14+cells. The upregulation of ILT by rhHLA-G indicates that sHLA-G might also benefit ITP patients negative for anti-platelet autoantibodies.To determine whether rhHLA-G affects T cell differentiation, we tested 17 cytokines by ELISA to investigate the immune environment with or without rhHLA-G, and found that rhHLA-G upregulated Interleukin (IL)-4 and IL-10, and downregulated tumor necrosis factor-α, IL-12, and IL-17 secreted by ITP patient peripheral blood mononuclear cells (PBMCs), indicating a promotion of helper T(Th)2 and inhibition of Th1 and Th17 differentiation. However, our results indicated that rhHLA-G did not expand the CD4+CD25+Foxp3+regulatory T cells(Tregs). In addition, rhHLA-G exerted their immunosuppressive effects by upregulating IL-1β, IL-2, Granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony stimulating factor (GM-CSF). By reprogramming the cytokine profile in ITP patients, HLA-G established an optimal environment for the impaired cell populations, such as dendritic cells (DCs), to regain their tolerogenic function. Our results showed that rhHLA-G inhibited monocyte-derived DCs maturation by downregulating CD80 and CD86 expression. To further assess whether the rhHLA-G modulated-DCs were functionally tolerogenic, PBMCs were then cocultured with rhHLA-G modulated-DCs. Our results showed that rhHLA-G-modulated DCs from ITP patients suppressed CD4+T cell proliferation by 38.8% compared to unmodulated cells. Besides, PBMCs exposed to rhHLA-G were less cytotoxic toward plateletsfrom ITP patients or healthy subjects. This study provides a potential strategy to protect exogenous platelets from destruction in ITP patients.In conclusion, our data demonstrated that impaired expression of HLA-G and/or ILT is involved in the pathogenesis of ITP, and recombinant human HLA-G can restore immune tolerance in ITP patients via upregulation of ILTs, which indicates that HLA-G can be a diagnostic marker and also a therapeutic option for ITP treatment. DisclosuresNo relevant conflicts of interest to declare.

Innate Immune Cells in Immune Tolerance After Liver Transplantation.

Currently, liver transplantation is the most effective treatment for end-stage liver disease. Immunosuppressive agents are required to be taken after the operations, which have significantly reduced rejection rates and improved the short-term (<1 year) survival rates. However, post-transplant complications related to the immunosuppressive therapy have led to the development of new protocols aimed at protecting renal function and preventing de novo cancer and dysmetabolic syndrome. Donor specific immune tolerance, which means the mature immune systems of recipients will not attack the grafts under the conditions without any immunosuppression therapies, is considered the optimal state after liver transplantation. There have been studies that have shown that some patients can reach this immune tolerance state after liver transplantation. The intrahepatic immune system is quite different from that in other solid organs, especially the innate immune system. It contains a variety of liver specific cells, such as liver-derived dendritic cells, Kupffer cells, liver sinusoidal endothelial cells, liver-derived natural killer (NK) cells, natural killer T (NKT) cells, and so on. Depending on their specific structures and functions, these intrahepatic innate immune cells play important roles in the development of intrahepatic immune tolerance. In this article, in order to have a deeper understanding of the tolerogenic functions of liver, we summarized the molecular mechanisms of immune tolerance induced by intrahepatic innate immune cells after liver transplantation.

A Chromatin-Mimetic Nanomedicine for Therapeutic Tolerance Induction.

The undesirable immune response poses a life-threatening challenge to human health. It not only deteriorates the therapeutic performance of biologic drugs but also contributes to various diseases such as allergies and autoimmune diseases. Inspired by the role of chromatin in the maintenance of natural immune tolerance, here we report a DNA-protein polymeric nanocomplex that can mimic the tolerogenic function of chromatin and induce an immune tolerance to its protein cargos. We first proved that the chromatin-mimetic nanomedicine loaded with keyhole limpet hemocyanin (KLH), a highly immunogenic model protein, could elicit a durable antigen-specific immune tolerance to KLH lasting for at least five weeks in mice. Following the proof-of-concept study, we demonstrated that this nanomedicine could be applied to improve the safety and efficacy of a biologic drug, PEGylated uricase, by attenuating the relevant antibody (Ab) responses. Moreover, we also demonstrated that prophylactic treatments with this nanomedicine could tolerize the immune system with the allergen of ovalbumin (OVA) and thus inhibit the occurrence of airway inflammation in an OVA-induced allergic asthma murine model. Collectively, our work illustrates a nature-inspired concept of immune tolerance induction and establishes a useful tool to specifically suppress unwanted immune responses for therapeutic purposes.