Complementary diversification of dendritic cells and innate lymphoid cells

Dendritic cell therapy for neurospoagioma: Immunomodulation mediated by tumor vaccine

Neurospagioma, arising from different glial cells such as astrocytes, oligodendrocytes, and ependymal cells, stands as the prevalent intracranial tumor within the central nervous system. Among its variants, glioblastoma (GBM) represents the most aggressive form, characterized by a notably high occurrence rate and a discouragingly low survival prognosis. The formidable challenge posed by glioblastoma underscores its critical importance as a life-threatening ailment. Currently, clinical approaches often involve surgical excision along with a combination of radiotherapy and chemotherapy. However, these treatments frequently result in a notable recurrence rate, accompanied by substantial adverse effects that significantly compromise the overall prognosis. Hence, there is a crucial need to investigate novel and dependable treatment strategies. Dendritic cells (DCs), being specialized antigen-presenting cells (APCs), hold a significant position in both innate and adaptive immune responses. Presently, DC vaccines have gained widespread application in the treatment of various tumors, including neurospoagioma. In this review, we summarize the immunomodulatory effects and related mechanisms of DC vaccines in neurospoagioma as well as the progress of clinical trials to propose possible challenges of DC vaccines and new development directions.

Reprogramming the lipid metabolism of dendritic cells in tumor immunomodulation and immunotherapy

Dendritic cells (DCs) are the most potent antigen-presenting cells in the human body. They detect and process environmental signals and communicate with T cells to bridge innate and adaptive immunity. Cell activation, function, and survival are closely associated with cellular metabolism. An increasing number of studies have revealed that lipid metabolism affects DC activation as well as innate and acquired immune responses. Combining lipid metabolic regulation with immunotherapy can strengthen the ability of antigen-presentation and T-cell activation of DCs, improve the existing anti-tumor therapy, and overcome the defects of DC-related therapies in the current stage, which has great potential in cancer therapy. This review summarizes the lipid metabolism of DCs under physiological conditions, analyzes the role of reprogramming the lipid metabolism of DCs in tumor immune regulation, and discusses potential immunotherapeutic strategies.

The show and tell of cross-presentation

Cross-presentation is the culmination of complex subcellular processes that allow the processing of exogenous proteins and the presentation of resultant peptides on major histocompatibility class I (MHC-I) molecules to CD8 T cells. Dendritic cells (DCs) are a cell type that uniquely specializes in cross-presentation, mainly in the context of viral or non-viral infection and cancer. DCs have an extensive network of endovesicular pathways that orchestrate the biogenesis of an ideal cross-presentation compartment where processed antigen, MHC-I molecules, and the MHC-I peptide loading machinery all meet. As a central conveyor of information to CD8 T cells, cross-presentation allows cross-priming of T cells which carry out robust adaptive immune responses for tumor and viral clearance. Cross-presentation can be canonical or noncanonical depending on the functional status of the transporter associated with antigen processing (TAP), which in turn influences the vesicular route of MHC-I delivery to internalized antigen and the cross-presented repertoire of peptides. Because TAP is a central node in MHC-I presentation, it is targeted by immune evasive viruses and cancers. Thus, understanding the differences between canonical and noncanonical cross-presentation may inform new therapeutic avenues against cancer and infectious disease. Defects in cross-presentation on a cellular and genetic level lead to immune-related disease progression, recurrent infection, and cancer progression. In this chapter, we review the process of cross-presentation beginning with the DC subsets that conduct cross-presentation, the signals that regulate cross-presentation, the vesicular trafficking pathways that orchestrate cross-presentation, the modes of cross-presentation, and ending with disease contexts where cross-presentation plays a role.

Type 2 Dendritic Cells Orchestrate a Local Immune Circuit to Confer Antimetastatic Immunity

The progression of transformed primary tumors to metastatic colonization is a lethal determinant of disease outcome. Although circulating adaptive and innate lymphocyte effector responses are required for effective antimetastatic immunity, whether tissue-resident immune circuits confer initial immunity at sites of metastatic dissemination remains ill defined. Here we examine the nature of local immune cell responses during early metastatic seeding in the lung using intracardiac injection to mimic monodispersed metastatic spread. Using syngeneic murine melanoma and colon cancer models, we demonstrate that lung-resident conventional type 2 dendritic cells (DC2) orchestrate a local immune circuit to confer host antimetastatic immunity. Tissue-specific ablation of lung DC2, and not peripheral DC populations, led to increased metastatic burden in the presence of an intact T cell and NK cell compartment. We demonstrate that DC nucleic acid sensing and transcription factors IRF3 and IRF7 signaling are required for early metastatic control and that DC2 serve as a robust source of proinflammatory cytokines in the lung. Critically, DC2 direct the local production of IFN-γ by lung-resident NK cells, which limits the initial metastatic burden. Collectively, our results highlight, to our knowledge, a novel DC2-NK cell axis that colocalizes around pioneering metastatic cells to orchestrate an early innate immune response program to limit initial metastatic burden in the lung.

Mesenchymal Stem Cells and Their Exocytotic Vesicles

Mesenchymal stem cells (MSCs), as a kind of pluripotent stem cells, have attracted much attention in orthopedic diseases, geriatric diseases, metabolic diseases, and sports functions due to their osteogenic potential, chondrogenic differentiation ability, and adipocyte differentiation. Anti-inflammation, anti-fibrosis, angiogenesis promotion, neurogenesis, immune regulation, and secreted growth factors, proteases, hormones, cytokines, and chemokines of MSCs have been widely studied in liver and kidney diseases, cardiovascular and cerebrovascular diseases. In recent years, many studies have shown that the extracellular vesicles of MSCs have similar functions to MSCs transplantation in all the above aspects. Here we review the research progress of MSCs and their exocrine vesicles in recent years.

The kinase p38α functions in dendritic cells to regulate Th2-cell differentiation and allergic inflammation

Dendritic cells (DCs) play a critical role in controlling T helper 2 (Th2) cell-dependent diseases, but the signaling mechanism that triggers this function is not fully understood. We showed that p38α activity in DCs was decreased upon HDM stimulation and dynamically regulated by both extrinsic signals and Th2-instructive cytokines. p38α-specific deletion in cDC1s but not in cDC2s or macrophages promoted Th2 responses under HDM stimulation. Further study showed that p38α in cDC1s regulated Th2-cell differentiation by modulating the MK2−c-FOS−IL-12 axis. Importantly, crosstalk between p38α-dependent DCs and Th2 cells occurred during the sensitization phase, not the effector phase, and was conserved between mice and humans. Our results identify p38α signaling as a central pathway in DCs that integrates allergic and parasitic instructive signals with Th2-instructive cytokines from the microenvironment to regulate Th2-cell differentiation and function, and this finding may offer a novel strategy for the treatment of allergic diseases and parasitic infection.

Mesenchymal Stem Cell Immunomodulation: A Novel Intervention Mechanism in Cardiovascular Disease

Mesenchymal stem cells (MSCs) are the member of multipotency stem cells, which possess the capacity for self-renewal and multi-directional differentiation, and have several characteristics, including multi-lineage differentiation potential and immune regulation, which make them a promising source for cell therapy in inflammation, immune diseases, and organ transplantation. In recent years, MSCs have been described as a novel therapeutic strategy for the treatment of cardiovascular diseases because they are potent modulators of immune system with the ability to modulating immune cell subsets, coordinating local and systemic innate and adaptive immune responses, thereby enabling the formation of a stable inflammatory microenvironment in damaged cardiac tissues. In this review, the immunoregulatory characteristics and potential mechanisms of MSCs are sorted out, the effect of these MSCs on immune cells is emphasized, and finally the application of this mechanism in the treatment of cardiovascular diseases is described to provide help for clinical application.

Dendritic cells in cancer immunology

The clinical success of immune checkpoint therapy (ICT) has produced explosive growth in tumor immunology research because ICT was discovered through basic studies of immune regulation. Much of the current translational efforts are aimed at enhancing ICT by identifying therapeutic targets that synergize with CTLA4 or PD1/PD-L1 blockade and are solidly developed on the basis of currently accepted principles. Expanding these principles through continuous basic research may help broaden translational efforts. With this mindset, we focused this review on three threads of basic research directly relating to mechanisms underlying ICT. Specifically, this review covers three aspects of dendritic cell (DC) biology connected with antitumor immune responses but are not specifically oriented toward therapeutic use. First, we review recent advances in the development of the cDC1 subset of DCs, identifying important features distinguishing these cells from other types of DCs. Second, we review the antigen-processing pathway called cross-presentation, which was discovered in the mid-1970s and remains an enigma. This pathway serves an essential in vivo function unique to cDC1s and may be both a physiologic bottleneck and therapeutic target. Finally, we review the longstanding field of helper cells and the related area of DC licensing, in which CD4 T cells influence the strength or quality of CD8 T cell responses. Each topic is connected with ICT in some manner but is also a fundamental aspect of cell-mediated immunity directed toward intracellular pathogens.

OASL1-Mediated Inhibition of Type I IFN Reduces Influenza A Infection-Induced Airway Inflammation by Regulating ILC2s

Purpose

Three observations drove this study. First, 2′-5′-oligoadenylate synthetase-like protein (OASL) is a negative regulator of type I interferon (IFN). Second, type I IFN plays a central role during virus infections and the pathogenesis of various diseases, including asthma. Third, influenza A virus (IAV) causes non-eosinophilic asthma. To evaluate the potential relationships between OASL, type I IFN, and pulmonary innate immune cells in IAV-induced acute airway inflammation by using Oasl1^-/- mice.

Methods

Asthma was induced in wild-type (WT) and Oasl1^-/- mice with IAV or ovalbumin (OVA). Airway hyperreactivity (AHR) and immune cell infiltration in the bronchoalveolar lavage (BAL) fluids were measured. The immune cells in the lungs were analyzed by flow cytometry. To investigate the ability of type I IFN to shape the response of lung type 2 innate lymphoid cells (ILC2s), IFN-α was treated intratracheally. Plasmacytoid dendritic cells (pDCs) sorted from bone marrow and ILC2s sorted from lungs of naive mice were co-cultured with/without interferon-alpha receptor subunit 1 (IFNAR-1)-blocking antibodies.

Results

In the IAV-induced asthma model, Oasl1^-/- mice developed greater AHR and immune cell infiltration in the BAL fluids than WT mice. This was not observed in OVA-induced asthma, a standard model of allergen-induced asthma. The lungs of infected Oasl1^-/- mice also had elevated DC numbers and Ifna expression and depressed IAV-induced ILC2 responses, namely, proliferation and type 2 cytokine and amphiregulin production. Intratracheal administration of type I IFN in naïve mice suppressed lung ILC2 production of type 2 cytokines and amphiregulin. Co-culture of ILC2s with pDCs showed that pDCs inhibit the function of ILC2s by secreting type I IFN.

Conclusions

OASL1 may impede the IAV-induced acute airway inflammation that drives AHR by inhibiting IAV-induced type I IFN production from lung DCs, thereby preserving the functions of lung ILC2s, including their amphiregulin production.

Innate Lymphoid Cells in the Malignant Melanoma Microenvironment

Simple Summary

Innate lymphoid cells (ILCs) are the innate counterparts of adaptive immune cells. Emerging data indicate that they are also key players in the progression of multiple tumors. In this review we briefly describe ILCs’ functions in the skin, lungs and liver. Next, we analyze the role of ILCs in primary cutaneous melanoma and in its most frequent and deadly metastases, those in liver and lung. We focus on their dual anti– and pro-tumoral functions, depending on the cross-interactions among them and with the surrounding stromal cells that form the tumor microenvironment (TME) in each organ. Next, we detail the role of extracellular vesicles secreted to the TME by ILCs and melanoma on both cell populations. We conclude that the identification of markers and tools to allow the modulation of individual ILC subsets, in addition to the development of standardized protocols, is essential for addressing the therapeutic modulation of ILCs.

Abstract

The role of innate lymphoid cells (ILCs) in cancer progression has been uncovered in recent years. ILCs are classified as Type 1, Type 2, and Type 3 ILCs, which are characterized by the transcription factors necessary for their development and the cytokines and chemokines they produce. ILCs are a highly heterogeneous cell population, showing both anti– and protumoral properties and capable of adapting their phenotypes and functions depending on the signals they receive from their surrounding environment. ILCs are considered the innate counterparts of the adaptive immune cells during physiological and pathological processes, including cancer, and as such, ILC subsets reflect different types of T cells. In cancer, each ILC subset plays a crucial role, not only in innate immunity but also as regulators of the tumor microenvironment. ILCs’ interplay with other immune and stromal cells in the metastatic microenvironment further dictates and influences this dichotomy, further strengthening the seed-and-soil theory and supporting the formation of more suitable and organ-specific metastatic environments. Here, we review the present knowledge on the different ILC subsets, focusing on their interplay with components of the tumor environment during the development of primary melanoma as well as on metastatic progression to organs, such as the liver or lung.

MicroRNA-9 Fine-Tunes Dendritic Cell Function by Suppressing Negative Regulators in a Cell-Type-Specific Manner

Dendritic cells, cells of the innate immune system, are found in a steady state poised to respond to activating stimuli. Once stimulated, they rapidly undergo dynamic changes in gene expression to adopt an activated phenotype capable of stimulating immune responses. We find that the microRNA miR-9 is upregulated in both bone marrow-derived DCs and conventional DC1s but not in conventional DC2s following stimulation. miR-9 expression in BMDCs and conventional DC1s promotes enhanced DC activation and function, including the ability to stimulate T cell activation and control tumor growth. We find that miR-9 regulated the expression of several negative regulators of transcription, including the transcriptional repressor Polycomb group factor 6 (Pcgf6). These findings demonstrate that miR-9 facilitates the transition of DCs from steady state to mature state by regulating the expression of several negative regulators of DC function in a cell-type-specific manner.

Feruloylated Oligosaccharides Alleviate Dextran Sulfate Sodium-Induced Colitis in Vivo

The imbalance of T lymphocyte subsets substantially conduces to disturbed intestinal immune system and succeeding colonic tissue damage in inflammatory bowel diseases. It is considered that regulation of phytochemicals on cytokine production potentially provides a broad prospect for the exploitation of immunomodulatory agents. Here, we reported that oral administration of feruloylated oligosaccharides (FOs) effectively alleviated mice colitis disease induced by dextran sulfate sodium (DSS). FOs decreased the percentage of T helper (Th)17 cells and downregulated the production of Th17-specific cytokines. In contrast, FOs increased the percentage of regulatory T (Treg) cells and elevated the production of Treg-specific cytokines in colons of DSS-challenged mice. These results indicated that FOs restored the immunologic equilibrium of Th17 and Treg subsets, hereby ameliorating the deterioration of colitis. Furthermore, FOs diminished the secretion of interleukin (IL)-23 and IL-6 but enhanced the transforming growth factor-β1 (TGF-β1) in dendritic cells in vitro and in vivo, which contributed to the restoration of Th17 and Treg cells immune balance. The mechanistic analysis showed that the regulation of FOs on IL-23 and IL-6 was associated with the nuclear factor-κ-gene binding signaling pathway and TGF-β1 with mitogen-activated protein kinase-activator protein 1 signaling pathway. Taken together, oral administration of FOs exerted potent immunomodulatory effects against mice colitis via restoring the immune balance of Th17 and Treg cells.

Dendritic Cell Accumulation in the Gut and Central Nervous System Is Differentially Dependent on α4 Integrins

Homing of pathogenic CD4⁺ T cells to the CNS is dependent on α4 integrins. However, it is uncertain whether α4 integrins are also required for the migration of dendritic cell (DC) subsets, which sample Ags from nonlymphoid tissues to present it to T cells. In this study, after genetic ablation of Itga4 in DCs and monocytes in mice via the promoters of Cd11c and Lyz2 (also known as LysM), respectively, the recruitment of α4 integrin-deficient conventional and plasmacytoid DCs to the CNS was unaffected, whereas α4 integrin-deficient, monocyte-derived DCs accumulated less efficiently in the CNS during experimental autoimmune encephalomyelitis in a competitive setting than their wild-type counterparts. In a noncompetitive setting, α4 integrin deficiency on monocyte-derived DCs was fully compensated. In contrast, in small intestine and colon, the fraction of α4 integrin-deficient CD11b⁺CD103⁺ DCs was selectively reduced in steady-state. Yet, T cell-mediated inflammation and host defense against Citrobacter rodentium were not impaired in the absence of α4 integrins on DCs. Thus, inflammatory conditions can promote an environment that is indifferent to α4 integrin expression by DCs.

A Subset of Type I Conventional Dendritic Cells Controls Cutaneous Bacterial Infections through VEGFα-Mediated Recruitment of Neutrophils

Skin conventional dendritic cells (cDCs) exist as two distinct subsets, cDC1s and cDC2s, which maintain the balance of immunity to pathogens and tolerance to self and microbiota. Here, we examined the roles of dermal cDC1s and cDC2s during bacterial infection, notably Propionibacterium acnes (P. acnes). cDC1s, but not cDC2s, regulated the magnitude of the immune response to P. acnes in the murine dermis by controlling neutrophil recruitment to the inflamed site and survival and function therein. Single-cell mRNA sequencing revealed that this regulation relied on secretion of the cytokine vascular endothelial growth factor α (VEGF-α) by a minor subset of activated EpCAM+CD59+Ly-6D+ cDC1s. Neutrophil recruitment by dermal cDC1s was also observed during S. aureus, bacillus Calmette-Guérin (BCG), or E. coli infection, as well as in a model of bacterial insult in human skin. Thus, skin cDC1s are essential regulators of the innate response in cutaneous immunity and have roles beyond classical antigen presentation.

NIK signaling axis regulates dendritic cell function in intestinal immunity and homeostasis

Dendritic cells (DCs) play an integral role in regulating mucosal immunity and homeostasis, but the signaling network mediating this function of DCs is poorly defined. We identified the noncanonical NF-κB-inducing kinase (NIK) as a crucial mediator of mucosal DC function. DC-specific NIK deletion impaired intestinal immunoglobulin A (IgA) secretion and microbiota homeostasis, rendering mice sensitive to an intestinal pathogen, Citrobacter rodentium. DC-specific NIK was required for expression of the IgA transporter polymeric immunoglobulin receptor (pIgR) in intestinal epithelial cells, which in turn relied on the cytokine IL-17 produced by TH17 cells and innate lymphoid cells (ILCs). NIK-activated noncanonical NF-κB induced expression of IL-23 in DCs, contributing to the maintenance of TH17 cells and type 3 ILCs. Consistent with the dual functions of IL-23 and IL-17 in mucosal immunity and inflammation, NIK deficiency also ameliorated colitis induction. Thus, our data suggest a pivotal role for the NIK signaling axis in regulating DC functions in intestinal immunity and homeostasis.

Notch2-dependent DC2s mediate splenic germinal center responses

CD4⁺ T follicular helper (T_FH) cells support germinal center (GC) reactions promoting humoral immunity. Dendritic cell (DC) diversification into genetically distinct subsets allows for specialization in promoting responses against several types of pathogens. Whether any classical DC (cDC) subset is required for humoral immunity is unknown, however. We tested several genetic models that selectively ablate distinct DC subsets in mice for their impact on splenic GC reactions. We identified a requirement for Notch2-dependent cDC2s, but not Batf3-dependent cDC1s or Klf4-dependent cDC2s, in promoting T_FH and GC B cell formation in response to sheep red blood cells and inactivated Listeria monocytogenes This effect was mediated independent of Il2ra and several Notch2-dependent genes expressed in cDC2s, including Stat4 and Havcr2 Notch2 signaling during cDC2 development also substantially reduced the efficiency of cDC2s for presentation of MHC class II-restricted antigens, limiting the strength of CD4 T cell activation. Together, these results demonstrate a nonredundant role for the Notch2-dependent cDC2 subset in supporting humoral immune responses.

Clec9a-Mediated Ablation of Conventional Dendritic Cells Suggests a Lymphoid Path to Generating Dendritic Cells In Vivo

Conventional dendritic cells (cDCs) are versatile activators of immune responses that develop as part of the myeloid lineage downstream of hematopoietic stem cells. We have recently shown that in mice precursors of cDCs, but not of other leukocytes, are marked by expression of DNGR-1/CLEC9A. To genetically deplete DNGR-1-expressing cDC precursors and their progeny, we crossed Clec9a-Cre mice to Rosa-lox-STOP-lox-diphtheria toxin (DTA) mice. These mice develop signs of age-dependent myeloproliferative disease, as has been observed in other DC-deficient mouse models. However, despite efficient depletion of cDC progenitors in these mice, cells with phenotypic characteristics of cDCs populate the spleen. These cells are functionally and transcriptionally similar to cDCs in wild type control mice but show somatic rearrangements of Ig-heavy chain genes, characteristic of lymphoid origin cells. Our studies reveal a previously unappreciated developmental heterogeneity of cDCs and suggest that the lymphoid lineage can generate cells with features of cDCs when myeloid cDC progenitors are impaired.

Chemokine and chemotactic signals in dendritic cell migration

Dendritic cells (DCs) are professional antigen-presenting cells responsible for the activation of specific T-cell responses and for the development of immune tolerance. Immature DCs reside in peripheral tissues and specialize in antigen capture, whereas mature DCs reside mostly in the secondary lymphoid organs where they act as antigen-presenting cells. The correct localization of DCs is strictly regulated by a large variety of chemotactic and nonchemotactic signals that include bacterial products, DAMPs (danger-associated molecular patterns), complement proteins, lipids, and chemokines. These signals function both individually and in concert, generating a complex regulatory network. This network is regulated at multiple levels through different strategies, such as synergistic interactions, proteolytic processing, and the actions of atypical chemokine receptors. Understanding this complex scenario will help to clarify the role of DCs in different pathological conditions, such as autoimmune diseases and cancers and will uncover new molecular targets for therapeutic interventions.

Functions of Murine Dendritic Cells

Dendritic cells (DCs) play critical roles in activating innate immune cells and initiating adaptive immune responses. The functions of DCs were originally obscured by their overlap with other mononuclear phagocytes, but new mouse models have allowed for the selective ablation of subsets of DCs and have helped to identify their non-redundant roles in the immune system. These tools have elucidated the functions of DCs in host defense against pathogens, autoimmunity, and cancer. This review will describe the mouse models generated to interrogate the role of DCs and will discuss how their use has progressively clarified our understanding of the unique functions of DC subsets.

Interferon response factor-3 promotes the pro-Th2 activity of mouse lung CD11b+ conventional dendritic cells in response to house dust mite allergens

Very few transcription factors have been identified that are required by antigen-presenting cells (APCs) to induce T helper type 2 (Th2) responses. Because lung CD11b⁺ conventional dendritic cells (CD11b⁺ cDCs) are responsible for priming Th2 responses in house-dust mite (HDM)-induced airway allergy, we used them as a model to identify transcriptional events regulating the pro-Th2 activity of cDCs. Transcriptomic profiling of lung CD11b⁺ cDCs exposed to HDM in vivo revealed first that HDM triggers an antiviral defence-like response, and second that the majority of HDM-induced transcriptional changes depend on the transcription factor Interferon Response Factor-3 (Irf3). Validating the functional relevance of these observations, Irf3-deficient CD11b⁺ cDCs displayed reduced pro-allergic activity. Indeed, Irf3-deficient CD11b⁺ cDCs induced less Th2, more regulatory T cell, and similar Th1 differentiation in naïve CD4⁺ T cells compared to their wild-type counterparts. The altered APC activity of Irf3 CD11b⁺ cDCs was associated with reduced expression of CD86 and was phenocopied by blocking CD86 activity in wild-type CD11b⁺ cDCs. Altogether, these results establish Irf3, known mostly for its role in antiviral responses, as a transcription factor involved in the induction of Th2 responses through the promotion of pro-Th2 costimulation in CD11b⁺ DCs.

Cigarette smoke alters the ability of human dendritic cells to promote anti-Streptococcus pneumoniae Th17 response

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is associated with chronic inflammation and impaired immune response to pathogens leading to bacteria-induced exacerbation of the disease. A defect in Th17 cytokines in response to Streptococcus pneumoniae, a bacteria associated with COPD exacerbations, has been recently reported. Dendritic cells (DC) are professional antigen presenting cells that drive T-cells differentiation and activation. In this study, we hypothesized that exposure to cigarette smoke, the main risk factor of COPD, might altered the pro-Th17 response to S. pneumoniae in COPD patients and human DC.

METHODS

Pro-Th1 and -Th17 cytokine production by peripheral blood mononuclear cells (PBMC) from COPD patients was analyzed and compared to those from smokers and non-smokers healthy subjects. The effect of cigarette smoke extract (CSE) was analyzed on human monocyte-derived DC (MDDC) from controls exposed or not to S. pneumoniae. Bacteria endocytosis, maturation of MDDC and secretion of cytokines were assessed by flow cytometry and ELISA, respectively. Implication of the oxidative stress was analyzed by addition of antioxidants and mitochondria inhibitors. In parallel, MDDC were cocultured with autologous T-cells to analyze the consequence on Th1 and Th17 cytokine production.

RESULTS

PBMC from COPD patients exhibited defective production of IL-1β, IL-6, IL-12 and IL-23 to S. pneumoniae compared to healthy subjects and smokers. CSE significantly reduced S. pneumoniae-induced MDDC maturation, secretion of pro-Th1 and -Th17 cytokines and activation of Th1 and Th17 T-cell responses. CSE exposure was also associated with sustained CXCL8 secretion, bacteria endocytosis and mitochondrial oxidative stress. Antioxidants did not reverse these effects. Inhibitors of mitochondrial electron transport chain partly reproduced inhibition of S. pneumoniae-induced MDDC maturation but had no effect on cytokine secretion and T cell activation.

CONCLUSIONS

We observed a defective pro-Th1 and -Th17 response to bacteria in COPD patients. CSE exposure was associated with an inhibition of DC capacity to activate antigen specific T-cell response, an effect that seems to be not only related to oxidative stress. These results suggest that new therapeutics boosting this response in DC may be helpful to improve treatment of COPD exacerbations.

Molecular events by which dendritic cells promote Th2 immune protection in helmith infection

Helminth parasites are a major cause of global infectious diseases, affecting nearly one quarter of the world's population. The common feature of helminth infections is to skew the immune system towards a T-helper 2 (Th2) response that helps to control disease. Dendritic cells (DCs), which are professional antigen-presenting cells, play a critical role for Th2 skewing against helminth parasites. However, the molecular mechanisms by which helminth antigens activate DCs for Th2 polarization have not yet been clearly defined. This review provides a focused update on the major role of DCs for inducing and/or enhancing Th2 immune responses in helminthic infection and will discuss the main signalling-dependent and independent mechanisms by which helminth antigens activate DCs for Th2 skewing.

Distinct Transcriptional Programs Control Cross-Priming in Classical and Monocyte-Derived Dendritic Cells

Both classical DCs (cDCs) and monocyte-derived DCs (Mo-DCs) are capable of cross-priming CD8(+) T cells in response to cell-associated antigens. We found that Ly-6C(hi)TREML4(-) monocytes can differentiate into Zbtb46(+) Mo-DCs in response to granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) but that Ly-6C(hi)TREML4(+) monocytes were committed to differentiate into Ly-6C(lo)TREML4(+) monocytes. Differentiation of Zbtb46(+) Mo-DCs capable of efficient cross-priming required both GM-CSF and IL-4 and was accompanied by the induction of Batf3 and Irf4. However, monocytes require IRF4, but not BATF3, to differentiate into Zbtb46(+) Mo-DCs capable of cross-priming CD8(+) T cells. Instead, Irf4(-/-) monocytes differentiate into macrophages in response to GM-CSF and IL-4. Thus, cDCs and Mo-DCs require distinct transcriptional programs of differentiation in acquiring the capacity to prime CD8(+) T cells. These differences may be of consideration in the use of therapeutic DC vaccines based on Mo-DCs.

Dendritic cell development-History, advances, and open questions

Dendritic cells (DCs) are uniquely potent in orchestrating T cell immune response, thus they are indispensable immune sentinels. They originate from progenitors in the bone marrow through hematopoiesis, a highly regulated developmental process involving multiple cellular and molecular events. This review highlights studies of DC development-from the discovery of DCs as glass-adherent antigen presenting cells to the debate and resolution of their origin and lineage map. In particular, we summarize the roles of lineage-specific cytokines, the placement of distinct hematopoietic progenitors within the DC lineage and transcriptional programs governing DC development, which together have allowed us to diagram the current view of DC hematopoiesis. Important open questions and debates on the DC development and relevant models are also discussed.

Crucial roles of XCR1-expressing dendritic cells and the XCR1-XCL1 chemokine axis in intestinal immune homeostasis

Intestinal immune homeostasis requires dynamic crosstalk between innate and adaptive immune cells. Dendritic cells (DCs) exist as multiple phenotypically and functionally distinct sub-populations within tissues, where they initiate immune responses and promote homeostasis. In the gut, there exists a minor DC subset defined as CD103(+)CD11b(-) that also expresses the chemokine receptor XCR1. In other tissues, XCR1(+) DCs cross-present antigen and contribute to immunity against viruses and cancer, however the roles of XCR1(+) DCs and XCR1 in the intestine are unknown. We showed that mice lacking XCR1(+) DCs are specifically deficient in intraepithelial and lamina propria (LP) T cell populations, with remaining T cells exhibiting an atypical phenotype and being prone to death, and are also more susceptible to chemically-induced colitis. Mice deficient in either XCR1 or its ligand, XCL1, similarly possess diminished intestinal T cell populations, and an accumulation of XCR1(+) DCs in the gut. Combined with transcriptome and surface marker expression analysis, these observations lead us to hypothesise that T cell-derived XCL1 facilitates intestinal XCR1(+) DC activation and migration, and that XCR1(+) DCs in turn provide support for T cell survival and function. Thus XCR1(+) DCs and the XCR1/XCL1 chemokine axis have previously-unappreciated roles in intestinal immune homeostasis.

The induction of antigen-specific CTL by in situ Ad-REIC gene therapy

An adenovirus vector carrying the human Reduced Expression in Immortalized Cell (REIC)/Dkk-3 gene (Ad-REIC) mediates simultaneous induction of cancer-selective apoptosis and augmentation of anticancer immunity. In our preclinical and clinical studies, in situ Ad-REIC gene therapy showed remarkable direct and indirect antitumor effects to realize therapeutic cancer vaccines. We herein aimed to confirm the induction of tumor-associated antigen-specific cytotoxic T lymphocytes (CTLs) by Ad-REIC. Using an ovalbumin (OVA), a tumor-associated antigen, expressing E.G7 tumor-bearing mouse model, we investigated the induction and expansion of OVA-specific CTLs responsible for indirect, systemic effects of Ad-REIC. The intratumoral administration of Ad-REIC mediated clear antitumor effects with the accumulation of OVA-specific CTLs in the tumor tissues and spleen. The CD86-positive dendritic cells (DCs) were upregulated in the tumor draining lymph nodes of Ad-REIC-treated mice. In a dual tumor-bearing mouse model in the left and right back, Ad-REIC injection in one side significantly suppressed the tumor growth on both sides and significant infiltration of OVA-specific CTLs into non-injected tumor was also detected. Consequently, in situ Ad-REIC gene therapy is expected to realize a new-generation cancer vaccine via anticancer immune activation with DC and tumor antigen-specific CTL expansion.

Dendritic Cells

T cells are an essential element that regulates the balance in immunity, by killing infected cells, helping antibody formation and suppressing autoimmune responses. However, T cells are incapable of recognizing native antigens. Instead, they recognize processed peptides presented by MHC molecules. Dendritic cells (DCs) are professional antigen presenting cells that inform the fight against invasive pathogens while enforcing tolerance to self and harmless environmental antigens. They capture pathogens and receive signals from pathogens that influence the outcome of immune responses. On the basis of these signals, DCs orchestrate antigen specific T cell differentiation. Alternatively they can silence self-reactive T cells by inducing deletion, anergy or regulation (Treg). This article will discuss the discovery, function and development of DCs and the mechanisms by which they link innate immunity to adaptive immunity.

Control of adaptive immunity by the innate immune system

Microbial infections are recognized by the innate immune system both to elicit immediate defense and to generate long-lasting adaptive immunity. To detect and respond to vastly different groups of pathogens, the innate immune system uses several recognition systems that rely on sensing common structural and functional features associated with different classes of microorganisms. These recognition systems determine microbial location, viability, replication and pathogenicity. Detection of these features by recognition pathways of the innate immune system is translated into different classes of effector responses though specialized populations of dendritic cells. Multiple mechanisms for the induction of immune responses are variations on a common design principle wherein the cells that sense infections produce one set of cytokines to induce lymphocytes to produce another set of cytokines, which in turn activate effector responses. Here we discuss these emerging principles of innate control of adaptive immunity.

T helper subsets in allergic eye disease

PURPOSE OF REVIEW

Ocular allergy is an IgE-mediated disease that results in inflammation of the conjunctiva and, in more severe cases, the cornea. This is driven by an immediate hypersensitivity response via mast cells, followed by a late phase response mediated by eosinophils both of which are indeed dependent on T helper (Th) lymphocyte activity. Here, we provide an update on Th subsets [Th1, Th2, Th17, and T regulatory (Treg)] and their relevance in ocular allergy.

RECENT FINDINGS

Recent evidence in ocular allergy points to an involvement of other Th subsets, in addition to Th2. However, how these subsets are activated and their role in mediating the different clinical forms is poorly understood. Novel mouse models may facilitate addressing such unknowns, and future challenges will involve how to translate such findings into more effective and 'patho-specific' treatments.

SUMMARY

Ocular allergy, especially in severe forms, involves subsets other than Th2. Th1 cells have been detected in mild and severe forms, and recent evidence points to a possible role for IL-17 in severe disease. Tregs, on the other hand, dampen pathogenic Th cell function and allergy immunotherapy is associated with Treg augmentation in disease management. Further understanding of Th biology is warranted and may lead to better therapies.

Fate mapping of dendritic cells

Dendritic cells (DCs) are a heterogeneous group of mononuclear phagocytes with versatile roles in immunity. They are classified predominantly based on phenotypic and functional properties, namely their stellate morphology, expression of the integrin CD11c, and major histocompatibility class II molecules, as well as their superior capacity to migrate to secondary lymphoid organs and stimulate naïve T cells. However, these attributes are not exclusive to DCs and often change within inflammatory or infectious environments. This led to debates over cell identification and questioned even the mere existence of DCs as distinct leukocyte lineage. Here, we review experimental approaches taken to fate map DCs and discuss how these have shaped our understanding of DC ontogeny and lineage affiliation. Considering the ontogenetic properties of DCs will help to overcome the inherent shortcomings of purely phenotypic- and function-based approaches to cell definition and will yield a more robust way of DC classification.

Priming dendritic cells for th2 polarization: lessons learned from helminths and implications for metabolic disorders

Nearly one quarter of the world's population is infected with helminth parasites. A common feature of helminth infections is the manifestation of a type 2 immune response, characterized by T helper 2 (Th2) cells that mediate anti-helminth immunity. In addition, recent literature describes a close association between type 2 immune responses and wound repair, suggesting that a Th2 response may concurrently mediate repair of parasite-induced damage. The molecular mechanisms that govern Th2 responses are poorly understood, although it is clear that dendritic cells (DCs), which are the most efficient antigen-presenting cells in the immune system, play a central role. Here, we review the molecular mechanisms by which DCs polarize Th2 cells, examining both helminth antigens and helminth-mediated tissue damage as Th2-inducing triggers. Finally, we discuss the implication of these findings in the context of metabolic disorders, as recent literature indicates that various aspects of the Th2-associated inflammatory response contribute to metabolic homeostasis.