Dendritic cells in the periphery control antigen-specific natural and induced regulatory T cells

Short-term administration of Qipian®, a mixed bacterial lysate, inhibits airway inflammation in ovalbumin-induced mouse asthma by modulating cellular, humoral and neurogenic immune responses

AIMS

Qipian® is a commercialized agent composed of extracts of three genera of commensal bacteria, and its mechanism of action on asthma is unclear. This study aimed to examine the impact of Qipian® on airway inflammation and investigate the underlying mechanisms.

MATERIALS AND METHODS

Qipian® or dexamethasone (DEX) was administered before OVA challenge in an ovalbumin-induced asthma mouse model, and then asthmatic symptoms were observed and scored. Samples of lung tissues, blood, and bronchoalveolar lavage fluid (BALF) were collected, and eosinophils (Eos), immunoglobins (Igs), and type 1 T helper (Th1)/Th2 cell cytokines were measured. Mucus production in the lung was assessed by periodic acid-Schiff (PAS) staining. The effects of Qipian® on dendritic and T regulatory (Treg) cells were investigated using flow cytometry.

KEY FINDINGS

The short-term administration of Qipian® significantly inhibited the cardinal features of allergic asthma, including an elevated asthmatic behaviour score, airway inflammation and immune response. Histological analysis of the lungs showed that Qipian® attenuated airway inflammatory cell infiltration and mucus hyperproduction. Qipian® restored Th1/Th2 imbalance by decreasing interleukin (IL)-4, IL-5, and IL-13 while increasing interferon (IFN)-γ and IL-10. Further investigation revealed that Qipian® treatment induced the upregulation of CD4+CD25+Foxp3+ Treg cells and CD103+ DCs and downregulation of tachykinins neurokinin A (NKA) and NKB in the lung.

SIGNIFICANCE

Our findings suggested that short-term treatment with Qipian® could alleviate inflammation in allergic asthma through restoring the Th1/Th2 balance by recruiting Treg cells to airways and inducing the proliferation of CD103+ DCs, which actually provides a new treatment option for asthma.

A novel peanut allergy immunotherapy: Plant-based enveloped Ara h 2 Bioparticles activate dendritic cells and polarize T cell responses to Th1

Introduction

As the only market-authorized allergen immunotherapy (AIT) for peanut allergy is accompanied by a high risk of side effects and mainly induces robust desensitization without sustained efficacy, novel treatment options are required. Peanut-specific plant-derived eBioparticles (eBPs) surface expressing Ara h 2 at high density have been shown to be very hypoallergenic. Here, we assessed the dendritic cell (DC)-activating and T cell polarization capacity of these peanut-specific eBPs.

Methods

Route and kinetics of eBP uptake were studied by (imaging) flow cytometry using monocyte-derived DCs incubated with fluorescently-labelled Ara h 2 eBPs or natural Ara h 2 (nAra h 2) in the presence or absence of inhibitors that block pathways involved in macropinocytosis, phagocytosis, and/or receptor-mediated uptake. DC activation was monitored by flow cytometry (maturation marker expression) and ELISA (cytokine production). T cell polarization was assessed by co-culturing DCs exposed to Ara h 2 eBPs or nAra h 2 with naïve CD4+ T cells, followed by flow cytometry assessment of intracellular IFNγ+ (Th1) and IL-13+ (Th2), and CD25+CD127-Foxp3+ regulatory T cells (Tregs). The suppressive activity of Tregs was tested using a suppressor assay.

Results

Ara h 2 eBPs were taken up by DCs through actin-dependent pathways. They activated DCs demonstrated by an induced expression of CD83 and CD86, and production of TNFα, IL-6, and IL-10. eBP-treated DCs polarized naïve CD4+ T cells towards Th1 cells, while reducing Th2 cell development. Furthermore, eBP-treated DCs induced reduced the frequency of Foxp3+ Tregs but did not significantly affect T cell IL-10 production or T cells with suppressive capacity. In contrast, DC activation and Th1 cell polarization were not observed for nAra h 2.

Conclusion

Ara h 2 eBPs activate DCs that subsequently promote Th1 cell polarization and reduce Th2 cell polarization. These characteristics mark Ara h 2 eBPs as a promising novel candidate for peanut AIT.

Comprehensive insights into the function and molecular and pharmacological regulation of neuron-derived orphan receptor 1, an orphan receptor

Neuron-derived orphan receptor 1 (NOR1), also called nuclear receptor subfamily 4 group A member 3 (NR4A3), is a nuclear receptor belonging to the NR4A family. Since no endogenous ligand has been identified to date, NOR1 is also referred to as an orphan receptor. NOR1 is expressed in a variety of cells and tissues, including neurons, vascular smooth muscle cells, T lymphocytes, dendritic cells, tumor cells, heart, liver, and pancreas. Because NOR1 was first identified in apoptotic neurons, it is functionally associated with the regulation of cell migration and the growth of neuronal synapses. In-depth studies have shown that NOR1 can be edited by the immediate early gene and functions as a transcription factor. NOR1 has been shown to be rapidly induced by a number of stimulants including growth factors, fatty acids, and neurotransmitters. Elevated NOR1 levels may be involved in a number of pathophysiological processes. These include regulation of cellular apoptosis and regeneration, neuron formation, contextual fearing memory, inflammation, vascular smooth muscle proliferation, insulin secretion, and tumor development, whereby NOR1 mediates the pathogenesis of numerous diseases such as cerebral ischemia, depression, post-traumatic stress disorder, atherosclerosis, abdominal aortic aneurysm, cardiac hypertrophy, diabetes, osteoarthritis, rheumatoid arthritis, and cancer. However, to date, comprehensive insights into the function of NOR1 are not available in sources published online. In this review, we provide a brief overview of the function and molecular and pharmacological regulation of NOR1 in various pathological or physiological conditions to advance the development of NOR1 as a novel target for disease treatment.

Tolerogenic Immunotherapy: Targeting DC Surface Receptors to Induce Antigen-Specific Tolerance

Dendritic cells (DCs) are well-established as major players in the regulation of immune responses. They either induce inflammatory or tolerogenic responses, depending on the DC-subtype and stimuli they receive from the local environment. This dual capacity of DCs has raised therapeutic interest for their use to modify immune-activation via the generation of tolerogenic DCs (tolDCs). Several compounds such as vitamin D3, retinoic acid, dexamethasone, or IL-10 and TGF-β have shown potency in the induction of tolDCs. However, an increasing interest exists in defining tolerance inducing receptors on DCs for new targeting strategies aimed to develop tolerance inducing immunotherapies, on which we focus particular in this review. Ligation of specific cell surface molecules on DCs can result in antigen presentation to T cells in the presence of inhibitory costimulatory molecules and tolerogenic cytokines, giving rise to regulatory T cells. The combination of factors such as antigen structure and conformation, delivery method, and receptor specificity is of paramount importance. During the last decades, research provided many tools that can specifically target various receptors on DCs to induce a tolerogenic phenotype. Based on advances in the knowledge of pathogen recognition receptor expression profiles in human DC subsets, the most promising cell surface receptors that are currently being explored as possible targets for the induction of tolerance in DCs will be discussed. We also review the different strategies that are being tested to target DC receptors such as antigen-carbohydrate conjugates, antibody-antigen fusion proteins and antigen-adjuvant conjugates.

The Long Noncoding RNA MALAT1 Induces Tolerogenic Dendritic Cells and Regulatory T Cells via miR155/Dendritic Cell-Specific Intercellular Adhesion Molecule-3 Grabbing Nonintegrin/IL10 Axis

By shaping T cell immunity, tolerogenic dendritic cells (tDCs) play critical roles in the induction of immune tolerance after transplantation. However, the role of long noncoding RNAs (lncRNAs) in the function and immune tolerance of dendritic cells (DCs) is largely unknown. Here, we found that the lncRNA MALAT1 is upregulated in the infiltrating cells of tolerized mice with cardiac allografts and activated DCs. Functionally, MALAT1 overexpression favored a switch in DCs toward a tolerant phenotype. Mechanistically, ectopic MALAT1 promoted dendritic cell-specific intercellular adhesion molecule-3 grabbing nonintegrin (DC-SIGN) expression by functioning as an miR155 sponge, which is essential for the tolerogenic maintenance of DCs and the DC-SIGN-positive subset with more potent tolerogenic ability. The adoptive transfer of MALAT1-overexpressing DCs promoted cardiac allograft survival and protected from the development of experimental autoimmune myocarditis, accompanied with increasing antigen-specific regulatory T cells. Therefore, overexpressed MALAT1 induces tDCs and immune tolerance in heart transplantation and autoimmune disease by the miRNA-155/DC-SIGH/IL10 axis. This study highlights that the lncRNA MALAT1 is a novel tolerance regulator in immunity that has important implications in settings in which tDCs are preferred.

Targeting DEC-205-DCIR2+ dendritic cells promotes immunological tolerance in proteolipid protein-induced experimental autoimmune encephalomyelitis

Background

Dendritic cells (DC) induce adaptive responses against foreign antigens, and play an essential role in maintaining peripheral tolerance to self-antigens. Therefore they are involved in preventing fatal autoimmunity. Selective delivery of antigens to immature DC via the endocytic DEC-205 receptor on their surface promotes antigen-specific T cell tolerance, both by recessive and dominant mechanisms. We provide evidence that the induction of antigen-specific T cell tolerance is not a unique property of CD11c⁺CD8⁺DEC-205⁺ DCs.

Methods

We employed a fusion between αDCIR2 antibodies and the highly encephalitogenic peptide 139–151 of myelin-derived proteolipid protein (PLP_139–151), to target CD11c ⁺CD8^- DCs with a DEC-205−DCIR2⁺ phenotype in vivo, and to substantially improve clinical symptoms in the PLP_139–151-induced model of experimental autoimmune encephalomyelitis (EAE).

Results

Consistent with previous studies targeting other cell surface receptors, EAE protection mediated by αDCIR2-PLP_139–151 fusion antibody (Ab) depended on an immature state of targeted DCIR2⁺ DCs. The mechanism of αDCIR2-PLP_139–151 mAb function included the deletion of IL-17- and IFN-γ-producing pathogenic T cells, as well as the enhancement of regulatory T (Treg) cell activity. In contrast to the effect of αDEC-205⁺ fusion antibodies, which involves extrathymic induction of a Foxp3⁺ Treg cell phenotype in naïve CD4⁺Foxp3^- T cells, treatment of animals with DCIR2⁺ fusion antibodies resulted in antigen-specific activation and proliferative expansion of natural Foxp3⁺ Treg cells.

Conclusions

These results suggest that multiple mechanisms can lead to the expansion of the Treg population, depending on the DC subset and receptor targeted.

Electronic supplementary material

The online version of this article (10.1186/s10020-018-0017-6) contains supplementary material, which is available to authorized users.

The similarities between smDCs and regDCs in alleviating the immune injury caused by transplantation of hepatocytes differentiated from ESCs

Background

This study aimed to investigate the tolerogenic mechanisms induced by semimature dendritic cells (smDCs) and regulatory dendritic cells (regDCs) after transplantation of hepatocytes differentiated from mouse embryonic stem cells (ESCs) and to confirm the low immunogenicity of hepatocytes differentiated from ESCs.

Methods

Green fluorescent protein-labeled ESCs collected from 129 mice were cultured to differentiate into hepatocytes. smDCs and regDCs were cultured in vitro. The hepatocytes were cultured after being extracted from the livers of 129 mice. After injecting smDCs or regDCs 3 days in advance, these differentiated hepatocytes and normal hepatocytes were transplanted into the livers of BALB/c mice separately. Subsequently, the histopathological features and cytokines in transplant tissues as well as the Foxp3 expression in peripheral blood CD4⁺ T cells of the recipients were examined.

Results

The morphological phenotypes of smDCs and regDCs were similar. They both expressed medium levels of MHC-II, CD40, CD80, and CD86, high levels of TGF-β and IL-10, and low levels of IL-2. The survival of differentiated hepatocytes was prolonged and inflammatory infiltration in transplant tissues was reduced in both the smDC and regDC groups. Foxp3 expression in peripheral blood CD4⁺ T cells of the smDC group increased to 5.38% and that of the regDC group also rose to 3.87%. Moreover, the inflammatory infiltration in the tissues receiving transplanted hepatocytes was more obvious.

Conclusions

smDCs and regDCs were similar tolerogenic dendritic cells. They both could alleviate the immune injury by inducing CD4⁺CD25⁺Foxp3⁺ regulatory T cells through the medium expression of MHC-II, CD40, CD80, and CD86 and the appropriate secretion of cytokines. Hepatocytes differentiated from ESCs displayed low immunogenicity.

Synergistic effects of dendritic cell targeting and laser-microporation on enhancing epicutaneous skin vaccination efficacy

Due to its unique immunological properties, the skin is an attractive target tissue for allergen-specific immunotherapy. In our current work, we combined a dendritic cell targeting approach with epicutaneous immunization using an ablative fractional laser to generate defined micropores in the upper layers of the skin. By coupling the major birch pollen allergen Bet v 1 to mannan from S. cerevisiae via mild periodate oxidation we generated hypoallergenic Bet-mannan neoglycoconjugates, which efficiently targeted CD14⁺ dendritic cells and Langerhans cells in human skin explants. Mannan conjugation resulted in sustained release from the skin and retention in secondary lymphoid organs, whereas unconjugated antigen showed fast renal clearance. In a mouse model, Bet-mannan neoglycoconjugates applied via laser-microporated skin synergistically elicited potent humoral and cellular immune responses, superior to intradermal injection. The induced antibody responses displayed IgE-blocking capacity, highlighting the therapeutic potential of the approach. Moreover, application via micropores, but not by intradermal injection, resulted in a mixed TH1/TH17-biased immune response. Our data clearly show that applying mannan-neoglycoconjugates to an organ rich in dendritic cells using laser-microporation is superior to intradermal injection. Due to their low IgE binding capacity and biodegradability, mannan neoglycoconjugates therefore represent an attractive formulation for allergen-specific epicutaneous immunotherapy.

Critical role of CCL22/CCR4 axis in the maintenance of immune homeostasis during apoptotic cell clearance by splenic CD8α(+) CD103(+) dendritic cells

Macrophages and dendritic cells (DCs) in murine spleen are essential for the maintenance of immune homeostasis by elimination of blood-borne foreign particles and organisms. It has been reported that splenic DCs, especially CD8α(+) CD103(+) DCs, are responsible for tolerance to apoptosis-associated antigens. However, the molecular mechanism by which these DCs maintain immune homeostasis by blood-borne apoptotic cell clearance remains elusive. Here, we found that the CCL22/CCR4 axis played a critical role in the maintenance of immune homeostasis during apoptotic cell clearance by splenic CD8α(+) CD103(+) DCs. The present results revealed that systemic administration of apoptotic cells rapidly induced a large number of CCL22 and CCR4(+) regulatory T (Treg) cells in the spleen of C57BL/6J mice. Further study demonstrated that CD8α(+) CD103(+) DCs dominantly produce much higher CCL22 than CD8α(+) CD103(-) DCs. Moreover, the transient deletion of CD8α(+) CD103(+) DCs caused a decrease in CCL22 levels together with CCR4(+) Treg cell percentage. Subsequently, the levels of some pro-inflammatory cytokines, such as interleukin-17 and interferon-γ in the spleen with the absence of CD8α(+) CD103(+) DCs increased in response to the administration of apoptotic cells. Hence, intravenous injection of apoptotic cells induced a subsequent increase in CCL22 expression and CCR4(+) Treg cells, which contribute to the maintenance of immune homeostasis at least partially by splenic CD8α(+) CD103(+) DCs.

Regulatory Rebound in IL-12-Treated Tumors Is Driven by Uncommitted Peripheral Regulatory T Cells

IL-12 promotes a rapid reversal of immune suppression in the tumor microenvironment. However, the adjuvant activity of IL-12 is short-lived due to regulatory T cell (Treg) reinfiltration. Quantitative analysis of Treg kinetics in IL-12-treated tumors and tumor-draining lymph nodes revealed a transient loss followed by a rapid 4-fold expansion of tumor Treg between days 3 and 10. Subset-specific analysis demonstrated that the posttreatment rebound was driven by the CD4(+)CD25(+)Foxp3(+) neuropilin-1(low) peripheral Treg (pTreg), resulting in a 3-5-fold increase in the pTreg to CD4(+)CD25(+)Foxp3(+) neuropilin-1(high) thymic Treg ratio by day 10. The expanding pTreg displayed hypermethylation of the CpG islands in Treg-specific demethylated region, CTLA-4 exon 2, and glucocorticoid-induced TNFR exon 5, were phenotypically unstable, and exhibited diminished suppressive function consistent with an uncommitted in vitro-induced Treg-like phenotype. In vitro culture of posttherapy Treg populations under Th1-promoting conditions resulted in higher levels of IFN-γ production by pTreg compared with thymic Treg, confirming their transitional state. Blockade of selected molecular mechanisms that are known to promote Treg expansion identified IDO-positive dendritic cells as the primary mediator of post-IL-12 pTreg expansion. Clinical implications of these findings are discussed.

IFNγ signaling endows DCs with the capacity to control type I inflammation during parasitic infection through promoting T-bet+ regulatory T cells

IFNγ signaling drives dendritic cells (DCs) to promote type I T cell (Th1) immunity. Here, we show that activation of DCs by IFNγ is equally crucial for the differentiation of a population of T-bet+ regulatory T (Treg) cells specialized to inhibit Th1 immune responses. Conditional deletion of IFNγ receptor in DCs but not in Treg cells resulted in a severe defect in this specific Treg cell subset, leading to exacerbated immune pathology during parasitic infections. Mechanistically, IFNγ-unresponsive DCs failed to produce sufficient amount of IL-27, a cytokine required for optimal T-bet induction in Treg cells. Thus, IFNγ signalling endows DCs with the ability to efficiently control a specific type of T cell immunity through promoting a corresponding Treg cell population.

Dendritic cells during Staphylococcus aureus infection: subsets and roles

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play a crucial role in both innate and adaptive immune responses. DCs orient the immune responses by modulating the balance between protective immunity to pathogens and tolerance to self-antigens. Staphylococcus aureus (S. aureus) is a common member of human skin microbiota and can cause severe infections with significant morbidity and mortality. Protective immunity to pathogens by DCs is required for clearance of S. aureus. DCs sense the presence of the staphylococcal components using pattern recognition receptors (PRRs) and then orchestrate immune systems to resolve infections. This review summarizes the possible roles of DCs, in particular their Toll-like receptors (TLRs) involved in S. aureus infection and strategies by which the pathogen affects activation and function of DCs.

Homeostasis of thymus-derived Foxp3+ regulatory T cells is controlled by ultraviolet B exposure in the skin

Accumulating evidence shows that immunological tolerance induced by Ag administration together with UVB irradiation is dependent on Foxp3(+) CD4(+) regulatory T (Treg) cells. However, the mechanisms by which UVB controls Treg cells in the skin are currently unclear. In this study, we have shown that exposure to UVB induced expansion of Treg cells up to 50-60% of the CD4(+) T cells in the irradiated skin. The Treg cell expansion in the skin lasted for 2 wk after exposure, which contributed to homeostasis of Treg cells in the periphery later. UVB-expanded Treg cells formed clusters with dendritic cells and proliferated in situ. Furthermore, the expanded Treg cells appeared to derive from neuropilin 1(+) thymus-derived Treg (tTreg) cells in the periphery because UVB-expanded Treg cells possessed Treg cell-specific CpG hypomethylation pattern, as seen in tTreg cells. These results collectively indicate that homeostasis of tTreg cells is controlled by UVB exposure in the skin. UVB therapy may be useful for not only inflammatory skin disorders, but also autoimmunity, transplantation, and allergy.