Turning NF-κB and IRFs on and off in DC

TANK-Binding Kinase 1 in the Pathogenesis and Treatment of Inflammation-Related Diseases

TANK-binding kinase 1 (TBK1) is a key signaling kinase involved in innate immune and inflammatory responses. TBK1 drives immune cells to participate in the inflammatory response by activating the NF-κB and interferon regulatory factor signaling pathways in immune cells, promoting the expression of pro-inflammatory genes, and regulating immune cell function. Thus, it plays a crucial role in initiating a signaling cascade that establishes an inflammatory environment. In inflammation-related diseases, TBK1 acts as a bridge linking inflammation to immunity, metabolism, or tumorigenesis, playing an important role in the pathogenesis of immune-mediated inflammatory diseases, metabolic, inflammatory syndromes, and inflammation-associated cancers by regulating the activation of inflammatory pathways and the production of inflammatory cytokines in cells. In this review, we focused on the mechanisms of TBK1 in immune cells and inflammatory-related diseases, providing new insights for further studies targeting TBK1 as a potential treatment for inflammation-related diseases. Thus, optimizing and investigating highly selective cell-specific TBK1 inhibitors is important for their application in these diseases.

The ubiquitin-proteasome system in the tumor immune microenvironment: a key force in combination therapy

The ubiquitin-proteasome system (UPS) plays a crucial role in modulating the proliferation, activation, and normal functioning of immune cells through the regulation of protein degradation and function. By influencing the expression of immune checkpoint-associated proteins, the UPS modulates T cell-mediated anti-tumor immune responses and can potentially facilitate the immune escape of tumor cells. Additionally, the UPS contributes to the remodeling of the tumor immunosuppressive microenvironment (TIME) by regulating B cells, dendritic cells (DCs), macrophages, and Treg cells. Targeting the UPS in conjunction with immune checkpoint-associated proteins, and combining these with other therapeutic approaches, may significantly enhance the efficacy of combination therapies and pave the way for novel cancer treatment strategies. In this review, we first summarize the composition and alterations of the TIME, with a particular emphasis on the role of the UPS in TIME and its interactions with various immune cell types. Finally, we explore the potential of combining UPS-targeted therapies with immunotherapy to substantially improve the effectiveness of immunotherapy and enhance patient survival outcomes.

NF-κB in biology and targeted therapy: new insights and translational implications

NF-κB signaling has been discovered for nearly 40 years. Initially, NF-κB signaling was identified as a pivotal pathway in mediating inflammatory responses. However, with extensive and in-depth investigations, researchers have discovered that its role can be expanded to a variety of signaling mechanisms, biological processes, human diseases, and treatment options. In this review, we first scrutinize the research process of NF-κB signaling, and summarize the composition, activation, and regulatory mechanism of NF-κB signaling. We investigate the interaction of NF-κB signaling with other important pathways, including PI3K/AKT, MAPK, JAK-STAT, TGF-β, Wnt, Notch, Hedgehog, and TLR signaling. The physiological and pathological states of NF-κB signaling, as well as its intricate involvement in inflammation, immune regulation, and tumor microenvironment, are also explicated. Additionally, we illustrate how NF-κB signaling is involved in a variety of human diseases, including cancers, inflammatory and autoimmune diseases, cardiovascular diseases, metabolic diseases, neurological diseases, and COVID-19. Further, we discuss the therapeutic approaches targeting NF-κB signaling, including IKK inhibitors, monoclonal antibodies, proteasome inhibitors, nuclear translocation inhibitors, DNA binding inhibitors, TKIs, non-coding RNAs, immunotherapy, and CAR-T. Finally, we provide an outlook for research in the field of NF-κB signaling. We hope to present a stereoscopic, comprehensive NF-κB signaling that will inform future research and clinical practice.

Ubiquitin Signaling in the Immune System

Protein ubiquitination is a post-translational modification of proteins that is widespread in eukaryotic cells. It was identified initially while investigating the mechanisms of intracellular protein degradation. There is mounting evidence that ubiquitination and its reverse process, deubiquitination, play a critical regulatory role in the process of intrinsic and adaptive immune responses by regulating the function of various immune cell types, thereby influencing the development of a variety of major human diseases such as autoimmune diseases, infectious diseases, and malignancies. This article will discuss current advances in protein ubiquitination-mediated control of several immune cell functions and its significance in multiple sclerosis (MS).

Role of Ubiquitin Signaling in Modulating Dendritic Cell Function

As a professional antigen-presenting cell, dendritic cell (DC) plays an essential role in the connection of innate and adaptive immune responses. Ubiquitination is a post-translational mechanism of protein modification that plays a pivotal role in regulating DC maturation and function. To date, considerable progress has been made in understanding the underlying mechanisms of ubiquitination in modulating the function of DC in various diseases. Recent studies have emphasized that ubiquitin signaling in DCs plays crucial roles in regulating immune tolerance and functions, which can be promising targets for DC-based immunotherapy. In this chapter, we will focus on discussing the recent progress regarding the molecular mechanisms and functions of ubiquitination in DC-mediated immune homeostasis and responses.

Endosomal trafficking inhibitor EGA can control TLR7-mediated IFNα expression by human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDC) are the major producer of type 1 IFN in response to TLR7 agonists. Aberrant TLR7 activation and type 1 IFN expression by pDCs are linked to the pathogenesis of certain types of autoimmune diseases, including systemic lupus erythematosus (SLE). This study investigated the underlying mechanisms for TLR7-mediated cytokine expression by pDCs using a late endosome trafficking inhibitor, EGA (4-bromobenzaldehyde N-(2,6-dimethylphenyl) semicarbazone). We found that EGA treatment decreased IFNα expression by pDCs stimulated with imiquimod (R837), single-stranded RNA40, and influenza virus. EGA also decreased TNFα expression and secretion by R837-stimulated pDCs. Mechanistically, EGA treatment decreased phosphorylation of IKKα/β, STAT1, and p38, and prolonged degradation of IκBα. Furthermore, EGA treatment decreased the colocalization of 3F, a substituted adenine TLR7 agonist, with LAMP1+ compartments in pDCs. EGA was also capable of diminishing IFNα expression by SLE pDCs treated with R837 or live PR8/A/34 influenza viruses. Therefore, we concluded that trafficking of TLR7 agonists to LAMP1+ compartments is important for IFNα expression by pDCs. Data from this study support additional examinations of the potential benefits of EGA in treating type 1 IFN-associated inflammatory diseases in the future.

Role of non-coding RNAs in neuroblastoma

Neuroblastoma is known as the most prevalent extracranial malignancy in childhood with a neural crest origin. It has been widely accepted that non-coding RNAs (ncRNAs) play important roles in many types of cancer, including glioma and gastrointestinal cancers. They may regulate the cancer gene network. According to recent sequencing and profiling studies, ncRNAs genes are deregulated in human cancers via deletion, amplification, abnormal epigenetic, or transcriptional regulation. Disturbances in the expression of ncRNAs may act either as oncogenes or as anti-tumor suppressor genes, and can lead to the induction of cancer hallmarks. ncRNAs can be secreted from tumor cells inside exosomes, where they can be transferred to other cells to affect their function. However, these topics still need more study to clarify their exact roles, so the present review addresses different roles and functions of ncRNAs in neuroblastoma.

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

Expanding role of deoxyribonucleic acid-sensing mechanism in the development of lifestyle-related diseases

In lifestyle-related diseases, such as cardiovascular, metabolic, respiratory, and kidney diseases, chronic inflammation plays a causal role in their pathogenesis; however, underlying mechanisms of sterile chronic inflammation are not well-understood. Previous studies have confirmed the damage of cells in these organs in the presence of various risk factors such as diabetes, dyslipidemia, and cigarette smoking, releasing various endogenous ligands for pattern recognition receptors. These studies suggested that nucleic acids released from damaged tissues accumulate in these tissues, acting as an endogenous ligand. Undamaged DNA is an integral factor for the sustenance of life, whereas, DNA fragments, especially those from pathogens, are potent activators of the inflammatory response. Recent studies have indicated that inflammatory responses such as the production of type I interferon (IFN) induced by DNA-sensing mechanisms which contributes to self-defense system in innate immunity participates in the progression of inflammatory diseases by the recognition of nucleic acids derived from the host, including mitochondrial DNA (mtDNA). The body possesses several types of DNA sensors. Toll-like receptor 9 (TLR9) recognizes DNA fragments in the endosomes. In addition, the binding of DNA fragments in the cytosol activates cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS), resulting in the synthesis of the second messenger cyclic GMP-AMP (cGAMP). The binding of cGAMP to stimulator of interferon genes (STING) activates NF-κB and TBK-1 signaling and consequently the production of many inflammatory cytokines including IFNs. Numerous previous studies have demonstrated the role of DNA sensors in self-defense through the recognition of DNA fragments derived from pathogens. Beyond the canonical role of TLR9 and cGAS-STING, this review describes the role of these DNA-sensing mechanism in the inflammatory responses caused by endogenous DNA fragments, and in the pathogenesis of lifestyle-related diseases.

Spatiotemporal NF-κB dynamics encodes the position, amplitude, and duration of local immune inputs

Infected cells communicate through secreted signaling molecules like cytokines, which carry information about pathogens. How differences in cytokine secretion affect inflammatory signaling over space and how responding cells decode information from propagating cytokines are not understood. By computationally and experimentally studying NF-κB dynamics in cocultures of signal-sending cells (macrophages) and signal-receiving cells (fibroblasts), we find that cytokine signals are transmitted by wave-like propagation of NF-κB activity and create well-defined activation zones in responding cells. NF-κB dynamics in responding cells can simultaneously encode information about cytokine dose, duration, and distance to the cytokine source. Spatially resolved transcriptional analysis reveals that responding cells transmit local cytokine information to distance-specific proinflammatory gene expression patterns, creating "gene expression zones." Despite single-cell variability, the size and duration of the signaling zone are tightly controlled by the macrophage secretion profile. Our results highlight how macrophages tune cytokine secretion to control signal transmission distance and how inflammatory signaling interprets these signals in space and time.

Emerging Roles of the Innate Immune System Regulated by DNA Sensors in the Development of Vascular and Metabolic Diseases

Sterile chronic inflammation causes cardiometabolic disorders; however, the mechanisms are not fully understood. Previous studies have demonstrated the degradation of cells/tissues in the vasculature and metabolic organs in lifestyle-associated diseases, such as diabetes and hyperlipidemia, suggesting the release and/or accumulation of nucleic acids from damaged cells. DNA is indispensable for life; however, DNA fragments, especially those from pathogens, strongly induce inflammation by the activation of DNA sensors. Growing evidence suggests that DNA-sensing mechanisms, which are normally involved in self-defense against pathogens as the innate immune system, are associated with the progression of inflammatory diseases in response to endogenous DNA fragments. There are several types of DNA sensors in our bodies. Toll-like receptor 9 (TLR9)—one of the most studied DNA sensors—recognizes DNA fragments in endosome. In addition, stimulator of interferon genes (STING), which has recently been extensively investigated, recognizes cyclic GMP-AMP (cGAMP) generated from DNA fragments in the cytosol. Both TLR9 and STING are known to play pivotal roles in host defense as the innate immune system. However, recent studies have indicated that the activation of these DNA sensors in immune cells, such as macrophages, promotes inflammation leading to the development of vascular and metabolic diseases associated with lifestyle. In this review, we discuss recent advances in determining the roles of DNA sensors in these disease contexts. Revealing a novel mechanism of sterile chronic inflammation regulated by DNA sensors might facilitate clinical interventions for these health conditions.

Central Nervous System-Endogenous TLR7 and TLR9 Induce Different Immune Responses and Effects on Experimental Autoimmune Encephalomyelitis

Innate receptors, including Toll like receptors (TLRs), are implicated in pathogenesis of CNS inflammatory diseases such as multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). TLR response to pathogens or endogenous signals includes production of immunoregulatory mediators. One of these, interferon (IFN)β, a Type I IFN, plays a protective role in MS and EAE. We have previously shown that intrathecal administration of selected TLR ligands induced IFNβ and infiltration of blood-derived myeloid cells into the central nervous system (CNS), and suppressed EAE in mice. We have now extended these studies to evaluate a potential therapeutic role for CNS-endogenous TLR7 and TLR9. Intrathecal application of Imiquimod (TLR7 ligand) or CpG oligonucleotide (TLR9 ligand) into CNS of otherwise unmanipulated mice induced IFNβ expression, with greater magnitude in response to CpG. CD45+ cells in the meninges were identified as source of IFNβ. Intrathecal CpG induced infiltration of monocytes, neutrophils, CD4+ T cells and NK cells whereas Imiquimod did not recruit blood-derived CD45+ cells. CpG, but not Imiquimod, had a beneficial effect on EAE, when given at time of disease onset. This therapeutic effect of CpG on EAE was not seen in mice lacking the Type I IFN receptor. In mice with EAE treated with CpG, the proportion of monocytes was significantly increased in the CNS. Infiltrating cells were predominantly localized to spinal cord meninges and demyelination was significantly reduced compared to non-treated mice with EAE. Our findings show that TLR7 and TLR9 signaling induce distinct inflammatory responses in the CNS with different outcome in EAE and point to recruitment of blood-derived cells and IFNβ induction as possible mechanistic links between TLR9 stimulation and amelioration of EAE. The protective role of TLR9 signaling in the CNS may have application in treatment of diseases such as MS.

Psoriatic skin inflammation is promoted by c-Jun/AP-1-dependent CCL2 and IL-23 expression in dendritic cells

Toll-like receptor (TLR) stimulation induces innate immune responses involved in many inflammatory disorders including psoriasis. Although activation of the AP-1 transcription factor complex is common in TLR signaling, the specific involvement and induced targets remain poorly understood. Here, we investigated the role of c-Jun/AP-1 protein in skin inflammation following TLR7 activation using human psoriatic skin, dendritic cells (DC), and genetically engineered mouse models. We show that c-Jun regulates CCL2 production in DCs leading to impaired recruitment of plasmacytoid DCs to inflamed skin after treatment with the TLR7/8 agonist Imiquimod. Furthermore, deletion of c-Jun in DCs or chemical blockade of JNK/c-Jun signaling ameliorates psoriasis-like skin inflammation by reducing IL-23 production in DCs. Importantly, the control of IL-23 and CCL2 by c-Jun is most pronounced in murine type-2 DCs. CCL2 and IL-23 expression co-localize with c-Jun in type-2/inflammatory DCs in human psoriatic skin and JNK-AP-1 inhibition reduces the expression of these targets in TLR7/8-stimulated human DCs. Therefore, c-Jun/AP-1 is a central driver of TLR7-induced immune responses by DCs and JNK/c-Jun a potential therapeutic target in psoriasis.

Roles of Ubiquitination and Deubiquitination in Regulating Dendritic Cell Maturation and Function

Dendritic cells (DCs) are specialized antigen-presenting cells that play a key role in immune homeostasis and the adaptive immune response. DC-induced immune tolerance or activation is strictly dependent on the distinct maturation stages and migration ability of DCs. Ubiquitination is a reversible protein post-translational modification process that has emerged as a crucial mechanism that regulates DC maturation and function. Recent studies have shown that ubiquitin enzymes, including E3 ubiquitin ligases and deubiquitinases (DUBs), are pivotal regulators of DC-mediated immune function and serve as potential targets for DC-based immunotherapy of immune-related disorders (e.g., autoimmune disease, infections, and tumors). In this review, we summarize the recent progress regarding the molecular mechanisms and function of ubiquitination in DC-mediated immune homeostasis and immune response.

The mechanisms of hydroxychloroquine in rheumatoid arthritis treatment: Inhibition of dendritic cell functions via Toll like receptor 9 signaling

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HCQ efficiently inhibited DC phenotypic and functional maturation stimulated by serum from RA patients.

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HCQ prevented progression of arthritis by inhibiting DC maturation and migration from peripheral blood to LNs.

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HCQ inhibited CpG ODN 1826-activated BMDC maturation and migration.

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The effect of HCQ on DCs was related to the block in TLR9 signaling.

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The development of arthritis was impaired in TLR9^−/− mice.

Hydroxychloroquine (HCQ) is one of the most commonly prescribed immune-suppressants in treating rheumatoid arthritis (RA). Our previous research showed that HCQ suppressed RA development by inhibiting T follicular helper (Tfh) cells directly. Dendritic cells (DCs) serve as the link between innate and acquired immunity. Whether HCQ suppressed Tfh cell through DCs was not clear. In current study, we found that HCQ efficiently inhibited CD86, chemokine (C-X-C motif) receptor 4 (CXCR4) expression and interferon-α (IFN-α) secretion of healthy donor derived purified DCs stimulated by RA patient serum. To mimic RA, collagen-induced arthritis (CIA) mouse model was used and treated with HCQ daily for fifty-four days prior to sacrifice. We found HCQ inhibited DC maturation and migration to lymph nodes (LNs), manifested as down-regulated expression of CD40, CD80, CD86, MHCII (I-A^q) on LN DCs. In addition, HCQ reduced the level of chemokine receptor 7 (CCR7) and L-selectin on peripheral blood DCs and diminished percentage of LN DCs. Of note, HCQ only inhibited CpG ODN 1826-induced IL-12 secretion by bone marrow DCs (BMDCs) stimulated by various toll like receptor (TLR) agonists. Mechanistically, HCQ down-regulated the expression of TLR9 not only in healthy donor PBMC-derived DCs stimulated by RA patient serum, but also in LN DCs of CIA mice and CpG-activated BMDCs. Furthermore, arthritis scores in TLR9^−/− mice were much lower than that in wild type mice with impaired maturity and migration capability of DCs. Collectively, activation of DCs contributes to the pathogenesis of RA and HCQ shows protective effects on RA by inhibition of DC activation via blocking TLR9.

Emerging roles of Toll-like receptor 9 in cardiometabolic disorders

Growing evidence suggests that damage-associated molecule patterns (DAMPs) and their receptors, pattern recognition receptors (PRRs), are associated with the progression of cardiometabolic disorders, including obesity-related insulin resistance and atherosclerosis. Cardiometabolic disorders share sterile chronic inflammation as a major cause; however, the exact mechanisms are still obscure. Toll-like receptor 9 (TLR9), one of the nucleic acid-sensing TLRs, recognizes DNA fragments derived from pathogens and contributes to self-defense by activation of the innate immune system. In addition, previous studies demonstrated that TLR9 recognizes DNA fragments released from host cells, accelerating sterile inflammation, which is associated with inflammatory diseases such as autoimmune diseases. In obese adipose tissue and atherosclerotic vascular tissue, various stresses release DNA fragments and/or nuclear proteins as DAMPs from degenerated adipocytes and vascular cells. Recent studies indicated that the activation of TLR9 in immune cells including macrophages and dendritic cells by recognition of these DAMPs promotes inflammation in these tissues, which causes cardiometabolic disorders. This review discusses recent advances in understanding the role of sterile inflammation associated with TLR9 and its endogenous ligands in cardiometabolic disorders. New insights into innate immunity may provide better understanding of cardiometabolic disorders and new therapeutic options for these major health threats in recent decades.

The mechanism of action of Spi-B in the transcriptional activation of the interferon-α4 gene

Plasmacytoid dendritic cells (pDCs) are characterized by an exclusive expression of nucleic acid sensing Toll-like receptor 7 (TLR7) and TLR9, and production of high amounts of type I interferon (IFN) in response to TLR7/9 signaling. This function is crucial for both antiviral immunity and the pathogenesis of autoimmune diseases. An Ets family transcription factor, i.e., Spi-B (which is highly expressed in pDCs) is required for TLR7/9 signal-induced type I IFN production and can transactivate IFN-α promoter in synergy with IFN regulatory factor-7 (IRF-7). Herein, we analyzed how Spi-B contributes to the transactivation of the Ifna4 promoter. We performed deletion and/or mutational analyses of the Ifna4 promoter and an electrophoretic mobility shift assay (EMSA) and observed an Spi-B binding site in close proximity to the IRF-7 binding site. The EMSA results also showed that the binding of Spi-B to the double-stranded DNA probe potentiated the recruitment of IRF-7 to its binding site. We also observed that the association of Spi-B with transcriptional coactivator p300 was required for the Spi-B-induced synergistic enhancement of the Ifna4 promoter activity by Spi-B. These results clarify the molecular mechanism of action of Spi-B in the transcriptional activation of the Ifna4 promoter.

MicroRNA-429 inhibits neuroblastoma cell proliferation, migration and invasion via the NF-κB pathway

BACKGROUND

MicroRNAs (miRNAs or miRs) can participate in the development and progression of neuroblastoma. Many studies have indicated that miR-429 can participate in tumor development. However, the mechanism underlying miR-429-mediated progression of neuroblastoma remains largely unclear.

METHODS

Colony formation and apoptosis assays were used to determine the effect of miR-429 on cell proliferation. Its impact on cell migration was determined using the wound-healing and Transwell assays. The target gene of miR-429 was confirmed via western blotting and luciferase reporter assays. A nude mouse xenograft model with miR-429 overexpression was used to assess the effect on tumor growth.

RESULTS

Our findings indicate that miR-429 is downregulated in neuroblastoma cell lines. We also found that it can induce apoptosis and inhibit proliferation in cells of those lines. MiR-429 can bind to the 3'-UTR of IKKβ mRNA and overexpression of IKKβ can reverse cell proliferation, blocking the effect of miR-429. Furthermore, miR-429 overexpression inhibited neuroblastoma growth in our nude mouse xenograft model.

CONCLUSION

We provide important insight into miR-429 as a tumor suppressor through interaction with IKKβ, which is a catalytic subunit of the IKK complex that activates NF-κB nuclear transport. Our results demonstrate that miR-429 may be a new target for the treatment of neuroblastoma.

MV140, a sublingual polyvalent bacterial preparation to treat recurrent urinary tract infections, licenses human dendritic cells for generating Th1, Th17, and IL-10 responses via Syk and MyD88

Recurrent urinary tract infections (RUTIs) are one of the most common bacterial infectious diseases, especially in women. Antibiotics remain the mainstay of treatment, but their overuse is associated with antibiotic-resistant infections and deleterious effects in the microbiota. Therefore, alternative approaches are fully demanded. Sublingual immunization with MV140 (Uromune), a polyvalent bacterial preparation (PBP) of whole heat-inactivated bacteria, demonstrated clinical efficacy for the treatment of RUTIs, but the involved immunological mechanisms remain unknown. Herein, we demonstrated that MV140 endorses human dendritic cells (DCs) with the capacity to generate Th1/Th17 and IL-10-producing T cells by mechanisms depending on spleen tyrosine kinase (Syk)- and myeloid differentiation primary response gene 88 (MyD88)-mediated pathways. MV140-induced activation of nuclear factor κB (NF-κB) and p38 in human DCs is essential for the generated Th1/Th17 and IL-10 immune responses whereas c-Jun N-terminal Kinase (JNK) and extracellular-signal regulated kinase (ERK) contribute to Th1 and IL-10 responses, respectively. Sublingual immunization of BALB/c mice with MV140 also induces potent systemic Th1/Th17 and IL-10 responses in vivo. We uncover immunological mechanisms underlying the way of action of MV140, which might well also contribute to understand the rational use of specific PBPs in other clinical conditions with potential high risk of recurrent infections.

Autoimmune Regulator Expression in DC2.4 Cells Regulates the NF-κB Signaling and Cytokine Expression of the Toll-Like Receptor 3 Pathway

Autoimmune regulator (Aire) mutations result in autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED), which manifests as multi-organ autoimmunity and chronic mucocutaneous candidiasis (CMC). Indendritic cells (DCs), pattern recognition receptors (PRR), such as Toll-like receptors (TLRs), are closely involved in the recognition of various pathogens, activating the intercellular signaling pathway, followed by the activation of transcription factors and the expression of downstream genes, which take part in mediating the immune response and maintaining immune tolerance. In this study, we found that Aire up-regulated TLR3 expression and modulated the downstream cytokine expression and nuclear factor-κB (NF-κB) of the TLR3 signaling pathway.

Propolis modulates miRNAs involved in TLR-4 pathway, NF-κB activation, cytokine production and in the bactericidal activity of human dendritic cells

Objectives

Dendritic cells (DCs) are antigen-presenting cells, essential for recognition and presentation of pathogens to T cells. Propolis, a resinous material produced by bees from various plants, exhibits numerous biological properties, highlighting its immunomodulatory action. Here, we assayed the effects of propolis on the maturation and function of human DCs.

Methods

DCs were generated from human monocytes and incubated with propolis and LPS. NF-κB and cytokines production were determined by ELISA. microRNA's expression was analysed by RT-qPCR and cell markers detection by flow cytometry. Colony-forming units were obtained to assess the bactericidal activity of propolis-treated DCs.

Key findings

Propolis activated DCs in the presence of LPS, inducing NF-kB, TNF-α, IL-6 and IL-10 production. The inhibition of hsa-miR-148a and hsa-miR-148b abolished the inhibitory effects on HLA-DR and pro-inflammatory cytokines. The increased expression of hsa-miR-155 may be correlated to the increase in TLR-4 and CD86 expression, maintaining LPS-induced expression of HLA-DR and CD40. Such parameters may be involved in the increased bactericidal activity of DCs against Streptococcus mutans.

Conclusion

Propolis modulated the maturation and function of DCs and may be useful in the initial steps of the immune response, providing a novel approach to the development of DC-based strategies and for the discovery of new immunomodulators.

Plasmacytoid dendritic cells orchestrate TLR7-mediated innate and adaptive immunity for the initiation of autoimmune inflammation

Endosomal toll-like receptor (TLR)-mediated detection of viral nucleic acids (NAs) and production of type I interferon (IFN-I) are key elements of antiviral defense, while inappropriate recognition of self NAs with the induction of IFN-I responses is linked to autoimmunity such as psoriasis and systemic lupus erythematosus. Plasmacytoid dendritic cells (pDCs) are cells specialized in robust IFN-I secretion by the engagement of endosomal TLRs, and predominantly express sialic acid-binding Ig-like lectin (Siglec)-H. However, how pDCs control endosomal TLR-mediated immune responses that cause autoimmunity remains unclear. Here we show a critical role of pDCs in TLR7-mediated autoimmunity using gene-modified mice with impaired expression of Siglec-H and selective ablation of pDCs. pDCs were shown to be indispensable for the induction of systemic inflammation and effector T-cell responses triggered by TLR7 ligand. pDCs aggravated psoriasiform dermatitis mediated through the hyperproliferation of keratinocytes and enhanced dermal infiltration of granulocytes and γδ T cells. Furthermore, pDCs promoted the production of anti-self NA antibodies and glomerulonephritis in lupus-like disease by activating inflammatory monocytes. On the other hand, Siglec-H regulated the TLR7-mediated activation of pDCs. Thus, our findings reveal that pDCs provide an essential link between TLR7-mediated innate and adaptive immunity for the initiation of IFN-I-associated autoimmune inflammation.

Clec4A4 is a regulatory receptor for dendritic cells that impairs inflammation and T-cell immunity

Dendritic cells (DCs) comprise several subsets that are critically involved in the initiation and regulation of immunity. Clec4A4/DC immunoreceptor 2 (DCIR2) is a C-type lectin receptor (CLR) exclusively expressed on CD8α⁻ conventional DCs (cDCs). However, how Clec4A4 controls immune responses through regulation of the function of CD8α⁻ cDCs remains unclear. Here we show that Clec4A4 is a regulatory receptor for the activation of CD8α⁻ cDCs that impairs inflammation and T-cell immunity. Clec4a4^−/−CD8α⁻ cDCs show enhanced cytokine production and T-cell priming following Toll-like receptor (TLR)-mediated activation. Furthermore, Clec4a4^−/− mice exhibit TLR-mediated hyperinflammation. On antigenic immunization, Clec4a4^−/− mice show not only augmented T-cell responses but also progressive autoimmune pathogenesis. Conversely, Clec4a4^−/− mice exhibit resistance to microbial infection, accompanied by enhanced T-cell responses against microbes. Thus, our findings highlight roles of Clec4A4 in regulation of the function of CD8α⁻ cDCs for control of the magnitude and quality of immune response.

Clec4A4 is a C-type lectin receptor highly expressed by CD8α⁻ dendritic cells. Here the authors show that its loss of function results in enhanced T cell responses and exacerbated autoimmunity, implicating Clec4A4 in limiting activation of the CD8α⁻ dendritic cells.

Apigenin, a potent suppressor of dendritic cell maturation and migration, protects against collagen-induced arthritis

This study aimed to investigate whether apigenin (API) suppresses arthritis development through the modulation of dendritic cell functions. Bone marrow-derived dendritic cells (BMDCs) were stimulated in vitro with lipopolysaccharide (LPS) and treated with API for 24 hrs; DC functions, including phenotype expressions, cytokine secretion, phagocytosis and chemotaxis, were then investigated. The effects of API on collagen-induced arthritis (CIA) were examined in vivo, and purified DCs from the lymph nodes (LNs) of API-treated CIA mice were analysed for phenotypes and subsets. In in vitro, API efficiently restrained the phenotypic and functional maturation of LPS-stimulated BMDCs while maintaining phagocytotic capabilities. Moreover, API inhibited the chemotactic responses of LPS-stimulated BMDCs, which may be related to the depressive effect on chemokine receptor 4 (CXCR4). In in vivo, API treatment delayed the onset and reduced the severity of arthritis in CIA mice, and diminished secretion of pro-inflammatory cytokines in the serum and supernatants from the LN cells of the CIA mice. Similar to the in vitro findings, the API-treated mice exhibited reduced expression of co-stimulatory molecules and major histocompatibility complex II on DCs. Furthermore, API treatment strongly down-regulated the number of Langerhans cells, but not plasmacytoid DCs (pDCs) in LNs, which may be related to the depressive effect of API on the expression of CXCR4 on DCs of peripheral blood. These data provide new insight into the mechanism of action of API on arthritis and indicate that the inhibition of maturation and migration of DCs by API may contribute to its immunosuppressive effects.

Functional Impairment of Myeloid Dendritic Cells during Advanced Stage of HIV-1 Infection: Role of Factors Regulating Cytokine Signaling

INTRODUCTION

Severely immunocompromised state during advanced stage of HIV-1 infection has been linked to functionally defective antigen presentation by dendritic cells (DCs). The molecular mechanisms behind DC impairment are still obscure. We investigated changes in DC function and association of key regulators of cytokine signaling during different stages of HIV-1 infection and following antiretroviral therapy (ART).

METHODS

Phenotypic and functional characteristics of circulating myeloid DCs (mDCs) in 56 ART-naive patients (23 in early and 33 in advanced stage of disease), 36 on ART and 24 healthy controls were evaluated. Sixteen patients were studied longitudinally prior-to and 6 months after the start of ART. For functional studies, monocyte-derived DCs (Mo-DCs) were evaluated for endocytosis, allo-stimulation and cytokine secretion. The expression of suppressor of cytokine signaling (SOCS)-1 and other regulators of cytokine signaling was evaluated by real-time RT-PCR.

RESULTS

The ability to respond to an antigenic stimulation was severely impaired in patients in advanced HIV-1 disease which showed partial recovery in the treated group. Mo-DCs from patients with advanced HIV-disease remained immature with low allo-stimulation and reduced cytokine secretion even after TLR-4 mediated stimulation ex-vivo. The cells had an increased expression of negative regulatory factors like SOCS-1, SOCS-3, SH2-containing phosphatase (SHP)-1 and a reduced expression of positive regulators like Janus kinase (JAK)2 and Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)1. A functional recovery after siRNA mediated silencing of SOCS-1 in these mo-DCs confirms the role of negative regulatory factors in functional impairment of these cells.

CONCLUSIONS

Functionally defective DCs in advanced stage of HIV-1 infection seems to be due to imbalanced state of negative and positive regulatory gene expression. Whether this is a cause or effect of increased viral replication at this stage of disease, needs further investigation. The information may be useful in design of novel therapeutic targets for better management of disease.

Primary biliary cirrhosis: From bench to bedside

Primary biliary cirrhosis (PBC) is a chronic non-suppurative destructive intrahepatic cholangitis leading to cirrhosis after a protractive non cirrhotic stage. The etiology and pathogenesis are largely unknown and autoimmne mechanisms have been implicated to explain the pathological lesions. Many epitopes and autoantigens have been reported as crucial in the pathophysiology of the disease and T and B cells abnormalities have been described, the exact pathways leading to the destruction of small intrahepatic ductules are mostly speculative. In this review we examined the various epidemiologal and geoepidemiological data as well as the complex pathogenetic aspects of this disease, focusing on recent in vivo and in vitro studies in this field. Initiation and progression of PBC is believed to be a multifactorial process with strong infuences from the patient’s genetic background and by various environmental factors. The role of innate and adaptive immunity, including cytokines, chemokines, macrophages and the involvement of apoptosis and reactive oxygen species are outlined in detailed. The current pathogenetic aspects are presented and a novel pathogenetic theory unifying the accumulated clinical information with in vitro and in vivo data is formulated. A review of clinical manifestations and immunological and pathological diagnosis was presented. Treatment modalities, including the multiple mechanisms of action of ursodeoxycholate were finally discussed.

Irisflorentin Modifies Properties of Mouse Bone Marrow-Derived Dendritic Cells and Reduces the Allergic Contact Hypersensitivity Responses

Irisflorentin is an isoflavone component derived from the roots of Belamcanda chinensis (L.) DC. In traditional Chinese medicine, this herb has pharmacological properties to treat inflammatory disorders. Dendritic cells (DCs) are crucial modulators for the development of optimal T-cell immunity and maintenance of tolerance. Aberrant activation of DCs can induce harmful immune responses, and so agents that effectively improve DC properties have great clinical value. We herein investigated the effects of irisflorentin on lipopolysaccharide (LPS)-stimulated maturation of mouse bone marrow-derived DCs in vitro and in the contact hypersensitivity response (CHSR) in vivo. Our results demonstrated that treatment with up to 40 μM irisflorentin does not cause cellular toxicity. Irisflorentin significantly lessened the proinflammatory cytokine production (tumor necrosis factor-α, interleukin-6, and interleukin-12p70) by LPS-stimulated DCs. Irisflorentin also inhibited the expression of LPS-induced major histocompatibility complex class II and costimulatory molecules (CD40 and CD86) on LPS-stimulated DCs. In addition, irisflorentin diminished LPS-stimulated DC-elicited allogeneic T-cell proliferation. Furthermore, irisflorentin significantly interfered with LPS-induced activation of IκB kinase, c-Jun N-terminal kinase, and p38, as well as the nuclear translocation of NF-κB p65. Subsequently, treatment with irisflorentin obviously weakened 2,4-dinitro-1-fluorobenzene-induced delayed-type hypersensitivity. These findings suggest new insights into the role of irisflorentin as an immunotherapeutic adjuvant through its capability to modulate the properties of DCs.

[Expression and significance of IKBKB in pulmonary adenocarcinoma A549 cells and its cisplatin-resistant variant A549/DDP]

背景与目的

肺癌顺铂耐药在临床治疗中广泛存在，严重影响了肺癌患者的治疗效果，因此研究肺癌耐药机制对新药的研发和解决临床肿瘤耐药有十分重要的意义。IKBKB是组成IKK复合物重要的催化亚基之一，其对核转录因子NF-κB的激活起到重要调控作用。本研究旨在探讨IKBKB基因在肺腺癌顺铂耐药细胞株（A549/DDP）与其亲本肺腺癌A549细胞株中的表差异及其调控肺腺癌顺铂耐药的机制。

方法

应用MTT法检测A549和A549/DDP细胞株顺铂敏感性及IKBKB基因对A549细胞株顺铂耐药性的影响。Real-time PCR检测肿瘤细胞中IKBKB基因mRNA变化，流式细胞学检测肿瘤细胞凋亡率，双荧光素酶报告基因实验检测NF-κB的活性。

结果

A549细胞与A549/DDP细胞在IC₅₀和凋亡率方面均有统计学差异，IKBKB基因在A549/DDP细胞株中mRNA表达水平明显高于A549。与对照组比较，pcDNA3.1/IKBKB转染A549细胞后，IKBKB基因在mRNA水平明显升高，A549细胞顺铂耐药性明显增加，IC₅₀增加2.85倍，凋亡率减少59%，NF-κB的活性明显升高。

结论

IKBKB基因通过激活NF-κB信号通路抑制细胞凋亡，从而导致细胞耐药性增加，这一研究结果对新抗肿瘤药物的研发和解决肿瘤耐药难题有重要意义。

Dryocrassin Suppresses Immunostimulatory Function of Dendritic Cells and Prolongs Skin Allograft Survival

Dendritic cells (DCs) are the major specialized antigen-presenting cells for the development of optimal T-cell immunity. DCs can be used as pharmacological targets to monitor novel biological modifiers for the cure of harmful immune responses, such as transplantation rejection. Dryopteris crassirhizoma Nakai (Aspiadaceae) is used for traditional herbal medicine in the region of East Asia. The root of this fern plant has been listed for treating inflammatory diseases. Dryocrassin is the tetrameric phlorophenone component derived from Dryopteris. Here we tested the immunomodulatory potential of dryocrassin on lipopolysaccharide (LPS)-stimulated activation of mouse bone marrow-derived DCs in vitro and in skin allograft transplantation in vivo. Results demonstrated that dryocrassin reduced the emission of tumor necrosis factor-α, interleukin-6, and interleukin-12p70 by LPS-stimulated DCs. The expression of LPS-induced major histocompatibility complex class II, CD40, and CD86 on DCs was also blocked by dryocrassin. Moreover, LPS-stimulated DC-elicited allogeneic T-cell proliferation was alleviated by dryocrassin. In addition, dryocrassin inhibited LPS-induced activation of IkB kinase, JNK/p38 mitogen-activated protein kinase, and the translocation of NF-κB. Treatment with dryocrassin noticeably diminished 2,4-dinitro-1-fluorobenzene-reduced delayed-type hypersensitivity and extended skin allograft survival. Dryocrassin may be one of the potent immunosuppressive agents for transplant rejection via the destruction of DC maturation and function.

Cervical cancer cell-derived interleukin-6 impairs CCR7-dependent migration of MMP-9-expressing dendritic cells

Cervical carcinogenesis is a consequence of persistent infection with high-risk human papillomaviruses (HPVs). Recent studies indicate that HPV-transformed cells actively instruct their microenvironment to promote carcinogenesis. Here, we demonstrate that cervical cancer cells activate monocytes to produce their own CCL2 for further monocyte recruitment and reprogram their function during differentiation and maturation to dendritic cells (DCs). Our data show that cervical cancer cells suppress the induction of the chemokine receptor CCR7 in phenotypically mature DCs and impair their migration toward a lymph node homing chemokine, required to initiate adaptive immune responses. We confirmed the presence of CD83(+)CCR7(low) DCs in cancer biopsies. The second factor essential for DC migration, matrix-metalloproteinase MMP-9, which also has vasculogenic and protumorigenic properties, is not suppressed but upregulated in immature as well as mature DCs. We identified interleukin-6 (IL-6) as a crucial cervical cancer cell-derived mediator and nuclear factor kappaB (NF-jB) as the central signaling pathway targeted in DCs. Anti-IL-6 antibodies reverted not only NF-jB inhibition and restored CCR7-dependent migration but also blocked MMP-9 induction. This is the first report demonstrating the dissociation of CCR7 and MMP-9 expression in phenotypically mature CD83(+) DCs by cancer cells. Our results show that cervical cancer cells actively shape the local microenvironment. They induce the accumulation of myeloid cells and skew their function from immune activation to local production of protumorigenic MMP-9. Neutralizing anti-IL-6 antibodies can counteract this functional dysbalance and should therefore be considered for adjuvant cervical cancer therapy.

Geldanamycin-mediated inhibition of heat shock protein 90 partially activates dendritic cells, but interferes with their full maturation, accompanied by impaired upregulation of RelB

Background

The chaperon heat shock protein 90 (HSP90) constitutes an important target for anti-tumor therapy due to its essential role in the stabilization of oncogenes. However, HSP90 is ubiquitously active to orchestrate protein turnover, chemotherapeutics that target HSP90 may affect immune cells as a significant side effect. Therefore, we asked for potential effects of pharmacological HSP90 inhibition at a therapeutically relevant concentration on human dendritic cells (DCs) as main inducers of both cellular and humoral immune responses, and on human CD4⁺ T cells as directly activated by DCs and essential to confer B cell help.

Methods

Unstimulated human monocyte-derived DCs (MO-DCs) were treated with the prototypical HSP90 inhibitor geldanamycin (GA). Based on dose titration studies performed to assess cytotoxic effects, GA was applied at a rather low concentration, comparable to serum levels of clinically used HSP90 inhibitors. The immuno-phenotype (surface markers, cytokines), migratory capacity, allo T cell stimulatory and polarizing properties (proliferation, cytokine pattern) of GA-treated MO-DCs were assessed. Moreover, effects of GA on resting and differentially stimulated CD4⁺ T cells in terms of cytotoxicity and proliferation were analysed.

Results

GA induced partial activation of unstimulated MO-DCs. In contrast, when coapplied in the course of MO-DC stimulation, GA prevented the acquisition of a fully mature DC phenotype. Consequently, this MO-DC population exerted lower allo CD4⁺ T cell stimulation and cytokine production. Furthermore, GA exerted no cytotoxic effect on resting T cells, but abrogated proliferation of T cells stimulated by MO-DCs at either state of activation or by stimulatory antibodies.

Conclusion

HSP90 inhibitors at clinically relevant concentrations may modulate adaptive immune responses both on the level of DC activation and T cell proliferation. Surprisingly, unstimulated DCs may be partially activated by that agent. However, due to the potent detrimental effects of HSP90 inhibitors on stimulated CD4⁺ T cells, as an outcome a patients T cell responses might be impaired. Therefore, HSP90 inhibitors most probably are not suitable for treatment in combination with immunotherapeutic approaches aimed to induce DC/T cell activation.

Self-antigen presentation by dendritic cells in autoimmunity

The operation of both central and peripheral tolerance ensures the prevention of autoimmune diseases. The maintenance of peripheral tolerance requires self-antigen presentation by professional antigen presenting cells (APCs). Dendritic cells (DCs) are considered as major APCs involved in this process. The current review discusses the role of DCs in autoimmune diseases, the various factors involved in the induction and maintenance of tolerogenic DC phenotype, and pinpoints their therapeutic capacity as well as potential novel targets for future clinical studies.

Transcriptional control of dendritic cell differentiation

Dendritic cells (DCs) are professional antigen presenting cells involved critically not only in provoking innate immune responses but also in establishing adaptive immune responses. Dendritic cells are heterogenous and divided into several subsets, including plasmactyoid DCs (pDCs) and several types of conventional DCs (cDCs), which show subset-specific functions. Plasmactyoid DCs are featured by their ability to produce large amounts of type I interferons (IFNs) in response to nucleic acid sensors, TLR7 and TLR9 and involved in anti-viral immunity and pathogenesis of certain autoimmune disorders such as psoriasis. Conventional DCs include the DC subsets with high crosspresentation activity, which contributes to anti-viral and anti-tumor immunity. These subsets are generated from hematopoietic stem cells (HSCs) via several intermediate progenitors and the development is regulated by the transcriptional mechanisms in which subset-specific transcription factors play major roles. We have recently found that an Ets family transcription factor, SPI-B, which is abundantly expressed in pDCs among DC subsets, plays critical roles in functions and late stage development of pDCs. SPI-B functions in cooperation with other transcription factors, especially, interferon regulatory factor (IRF) family members. Here we review the transcription factor-based molecular mechanisms for generation and functions of DCs, mainly by focusing on the roles of SPI-B and its relatives.

High doses of CpG oligodeoxynucleotides stimulate a tolerogenic TLR9-TRIF pathway

CpG-rich oligodeoxynucleotides activate the immune system, leading to innate and acquired immune responses. The immune-stimulatory effects of CpG-rich oligodeoxynucleotides are being exploited as a therapeutic approach. Here we show that at high doses, CpG-rich oligodeoxynucleotides promote an opposite, tolerogenic response in mouse plasmacytoid dendritic cells in vivo and in a human in vitro model. Unveiling a previously undescribed role for TRIF and TRAF6 proteins in Toll-like receptor 9 (TLR9) signalling, we demonstrate that physical association of TLR9, TRIF and TRAF6 leads to activation of noncanonical NF-κB signalling and the induction of IRF3- and TGF-β-dependent immune-suppressive tryptophan catabolism. In vivo, the TLR9-TRIF circuit--but not MyD88 signalling--was required for CpG protection against allergic inflammation. Our findings may be relevant to an increased understanding of the complexity of Toll-like receptor signalling and optimal exploitation of CpG-rich oligodeoxynucleotides as immune modulators.

Efficacy of DHMEQ, a NF-κB inhibitor, in islet transplantation: II. Induction DHMEQ treatment ameliorates subsequent alloimmune responses and permits long-term islet allograft acceptance

BACKGROUND

Long-term graft deterioration remains a major obstacle in the success of pancreatic islet transplantation (PITx). Antigen-independent inflammatory and innate immune responses strengthen subsequent antigen-dependent immunity; further, activation of nuclear factor (NF)-κB plays a key role during these responses. In this study, we tested our hypothesis that, by the inhibition of NF-κB activation, the suppression of these early responses after PITx could facilitate graft acceptance.

METHODS

Full major histocompatibility complex (MHC)-mismatched BALB/c (H-2) mice islets were transplanted into streptozotocin-induced diabetic C57BL/6 (B6: H-2) mice. The NF-κB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ) was administered for either 3 or 14 days after PITx. To some PITx recipients, tacrolimus was also administered. Islet allograft survival, alloimmune responses, and in vitro effects of DHMEQ on dendritic cells (DCs) were assessed.

RESULTS

With a vehicle treatment, 600 islet allografts were promptly rejected after PITx. In contrast, 3-day treatment with DHMEQ, followed by 2-week treatment with tacrolimus, allowed permanent acceptance of islet allografts. The endogenous danger-signaling molecule high mobility group complex 1 (HMGB1) was elevated in sera shortly after PITx, whereas DHMEQ administration abolished this elevation. DHMEQ suppressed HMGB1-driven cellular activation and proinflammatory cytokine secretion in mouse bone marrow-derived DCs and significantly reduced the capacity of DCs to prime allogeneic T-cell proliferation in vitro. Finally, the DHMEQ plus tacrolimus regimen reverted the diabetic state with only 300 islet allografts.

CONCLUSIONS

Inhibition of NF-κB activation by DHMEQ shortly after PITx suppresses HMGB1, which activates DCs and strengthens the magnitude of alloimmune responses; this permits long-term islet allograft acceptance, even in case of fewer islet allografts.

Nucleic acid scavenging polymers inhibit extracellular DNA-mediated innate immune activation without inhibiting anti-viral responses

Toll-like receptor (TLR) family members, 3, 7 and 9 are key components in initiation and progression of autoimmune disorders such as systemic lupus erythematosus (SLE). These TLRs are often referred to as nucleic acid-sensing TLRs based on their ability to recognize DNAs or RNAs produced by pathogens or damaged cells. During autoimmune disease progression these receptors recognize self nucleic acids as well as self nucleic acid-containing complexes and contribute to inflammatory cytokine production and subsequent enhancement of serum autoantibody levels. We have recently discovered that nucleic-acid scavenging polymers (NASPs) can neutralize the proinflammatory effects of nucleic acids. Here, we begin to explore what effects such NASPs have on normal immune function. We show that such NASPs can inhibit TLR activation without affecting nucleic acid-independent T cell activation. Moreover, we observe that stimulation of immune cells by encapsulated nucleic acids, such as those found in viral particles, is unaffected by NASPs. Thus NASPs only limit the activation of the immune system by accessible extra-cellular nucleic acid and do not engender non-specific immune suppression. These important findings suggest that NASPs represent a new approach toward anti-inflammatory drug development as these agents can potentially be utilized to block overt autoimmune disorders and inflammation while allowing normal immune responses to occur.

Acetylcorynoline impairs the maturation of mouse bone marrow-derived dendritic cells via suppression of IκB kinase and mitogen-activated protein kinase activities

Background

Dendritic cells (DCs) are major modulators in the immune system. One active field of research is the manipulation of DCs as pharmacological targets to screen novel biological modifiers for the treatment of inflammatory and autoimmune disorders. Acetylcorynoline is the major alkaloid component derived from Corydalis bungeana herbs. We assessed the capability of acetylcorynoline to regulate lipopolysaccharide (LPS)-stimulated activation of mouse bone marrow-derived DCs.

Methodology/Principal Findings

Our experimental data showed that treatment with up to 20 µM acetylcorynoline does not cause cytotoxicity in cells. Acetylcorynoline significantly inhibited the secretion of tumor necrosis factor-α, interleukin-6, and interleukin-12p70 by LPS-stimulated DCs. The expression of LPS-induced major histocompatibility complex class II, CD40, and CD86 on DCs was also decreased by acetylcorynoline, and the endocytic capacity of LPS-stimulated DCs was restored by acetylcorynoline. In addition, LPS-stimulated DC-elicited allogeneic T-cell proliferation was blocked by acetylcorynoline, and the migratory ability of LPS-stimulated DCs was reduced by acetylcorynoline. Moreover, acetylcorynoline significantly inhibits LPS-induced activation of IκB kinase and mitogen-activated protein kinase. Importantly, administration of acetylcorynoline significantly attenuates 2,4-dinitro-1-fluorobenzene-induced delayed-type hypersensitivity.

Conclusions/Significance

Acetylcorynoline may be one of the potent immunosuppressive agents through the blockage of DC maturation and function.

Molecular control of steady-state dendritic cell maturation and immune homeostasis

Dendritic cells (DCs) are specialized sentinels responsible for coordinating adaptive immunity. This function is dependent upon coupled sensitivity to environmental signs of inflammation and infection to cellular maturation-the programmed alteration of DC phenotype and function to enhance immune cell activation. Although DCs are thus well equipped to respond to pathogens, maturation triggers are not unique to infection. Given that immune cells are exquisitely sensitive to the biological functions of DCs, we now appreciate that multiple layers of suppression are required to restrict the environmental sensitivity, cellular maturation, and even life span of DCs to prevent aberrant immune activation during the steady state. At the same time, steady-state DCs are not quiescent but rather perform key functions that support homeostasis of numerous cell types. Here we review these functions and molecular mechanisms of suppression that control steady-state DC maturation. Corruption of these steady-state operatives has diverse immunological consequences and pinpoints DCs as potent drivers of autoimmune and inflammatory disease.

Myricetin attenuates lipopolysaccharide-stimulated activation of mouse bone marrow-derived dendritic cells through suppression of IKK/NF-κB and MAPK signalling pathways

BACKGROUND

Myricetin is a naturally occurring flavonoid that is found in many fruits, vegetables, teas and medicinal herbs. It has been demonstrated to have anti-inflammatory properties, but, to date, no studies have described the immunomodulatory effects of myricetin on the functions of dendritic cells (DCs). The aim of this study was to evaluate the potential for myricetin to modulate lipopolysaccharide (LPS)-stimulated activation of mouse bone marrow-derived DCs.

RESULTS

Our experimental data showed that treatment with myricetin up to 10 µg mL(-1) does not cause cytotoxicity in cells. Myricetin significantly decreased the secretion of tumour necrosis factor-α, interleukin-6 and interleukin-12p70 by LPS-stimulated DCs. The expression of LPS-induced major histocompatibility class II, CD40 and CD86 on DCs was also inhibited by myricetin, and the endocytic and migratory capacity of LPS-stimulated DCs was blocked by myricentin. In addition, LPS-stimulated DC-elicited allogeneic T-cell proliferation was reduced by myricetin. Moreover, our results confirmed that myricetin attenuates the responses of LPS-stimulated activation of DCs via suppression of IκB kinase/nuclear factor-κB and mitogen-activated protein kinase-dependent pathways.

CONCLUSION

Myricetin has novel immunopharmacological activity, and modulation of DCs by myricetin may be an attractive strategy for the treatment of inflammatory and autoimmune disorders, and for transplantation.

The tyrosine kinase inhibitor dasatinib suppresses cytokine production by plasmacytoid dendritic cells by targeting endosomal transport of CpG DNA

Plasmacytoid dendritic cells (pDCs) produce a vast amount of interferon (IFN)-α in response to nucleic acids from viruses and damaged self-cells through Toll-like receptor (TLR)7 and TLR9. Pharmaceutical agents that suppress IFN-α production by pDCs are instrumental in elucidating the mechanisms behind IFN-α production, and in developing novel therapies for inflammatory disorders that involve pDCs. Here, we show that a tyrosine kinase inhibitor for chronic myeloid leukemia with multiple targets, dasatinib, strongly suppresses production of IFN-α and proinflammatory cytokines by human pDCs stimulated with multimeric CpG oligodeoxynucleotides (CpG-A) without reducing viability. In contrast, other tyrosine kinase inhibitors, imatinib, and nilotinib, did not suppress the cytokine production at clinically relevant concentrations. Inhibitors of SRC family kinases (SFKs), which are prominent targets of dasatinib, also suppressed the cytokine production. Notably, however, dasatinib, but not SFK inhibitors, abrogated prolonged localization of CpG-A in early endosomes, which is a critical step for pDCs to produce a large amount of IFN-α. This study suggests that dasatinib suppresses IFN-α production by pDCs by inhibiting SFK-dependent pathways and SFK-independent endosomal retention of CpG DNA. Kinases controlling the distinctive endosomal trafficking in pDCs may be exploited as targets to develop novel therapies for pDC-related inflammatory disorders.

Regulation and dysregulation of innate immunity by NFAT signaling downstream of pattern recognition receptors (PRRs)

Innate immunity is the most ancient form of response to pathogens and it relies on evolutionary conserved signaling pathways, i.e. those involving the NF-κB pathway. Nevertheless, increasing evidence suggests that factors that have appeared more recently in evolution, such as the nuclear factor of activated T-cell transcription factor family (NFATc), also contribute to innate immune-response regulation in vertebrates. Exposure to inflammatory stimuli induces the activation of NFATc factors in innate immune cells, including conventional dendritic cells (DCs), granulocytes, mast cells and under pathological circumstances, also macrophages. While the evolutionary conserved functions of innate immunity, such as direct microbial killing and interferon production, are expected to be NFATc independent, other aspects of innate immunity, including collaboration with adaptive immunity and mechanisms to limit the tissue damage generated by the inflammatory process, are presumably controlled by NFATc members in collaboration with other transcription factors. In this article, we discuss the recent advances regarding the role of the NFATc signaling pathway in regulating DC, neutrophil and macrophage responses to specific inflammatory stimuli, including lipopolysaccharide and β-glucan-bearing microorganisms. We also discuss how NFATc signaling influences the interactions of myeloid cells with lymphocytes.

Spi-B is critical for plasmacytoid dendritic cell function and development

Plasmacytoid dendritic cells (pDCs), originating from hematopoietic progenitor cells in the BM, are a unique dendritic cell subset that can produce large amounts of type I IFNs by signaling through the nucleic acid-sensing TLR7 and TLR9 (TLR7/9). The molecular mechanisms for pDC function and development remain largely unknown. In the present study, we focused on an Ets family transcription factor, Spi-B, that is highly expressed in pDCs. Spi-B could transactivate the type I IFN promoters in synergy with IFN regulatory factor 7 (IRF-7), which is an essential transcription factor for TLR7/9-induced type I IFN production in pDCs. Spi-B-deficient pDCs and mice showed defects in TLR7/9-induced type I IFN production. Furthermore, in Spi-B-deficient mice, BM pDCs were decreased and showed attenuated expression of a set of pDC-specific genes whereas peripheral pDCs were increased; this uneven distribution was likely because of defective retainment of mature nondividing pDCs in the BM. The expression pattern of cell-surface molecules in Spi-B-deficient mice indicated the involvement of Spi-B in pDC development. The developmental defects of pDCs in Spi-B-deficient mice were more prominent in the BM than in the peripheral lymphoid organs and were intrinsic to pDCs. We conclude that Spi-B plays critical roles in pDC function and development.

Different partners, opposite outcomes: a new perspective of the immunobiology of indoleamine 2,3-dioxygenase

Indoleamine 2,3-dioxygenase (IDO), a metabolic enzyme that catalyzes tryptophan conversion into kynurenines, is a crucial regulator of immunity. Altered IDO activity is often associated with pathology, including neoplasia and autoimmunity. IDO is highly expressed in dendritic cells (DCs) that exploit the enzyme's activity and the production of tryptophan catabolites to regulate immune responses by acting on several cell types, including T lymphocytes, of which they promote a regulatory phenotype. IDO also contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that, once bound by distinct molecular partners, will either promote degradation or initiate signaling activity and self-maintenance of the enzyme. We here discuss how ITIM-dependent molecular events can affect the functional plasticity of IDO by modifying the protein half-life and its enzymic and nonenzymic functions.

FOXO3 as a new IKK-ε-controlled check-point of regulation of IFN-β expression

Cell survival transcription factor FOXO3 has been recently implicated in moderating pro-inflammatory cytokine production by dendritic cells (DCs), but the molecular mechanisms are unclear. It was suggested that FOXO3 could antagonize NF-κB activity, while IKK-β was demonstrated to inactivate FOXO3, suggesting a cross-talk between the two pathways. Therefore, FOXO3 activity must be tightly regulated to allow for an appropriate inflammatory response. Here, we show that in human monocyte-derived DCs (MDDCs), FOXO3 is able to antagonize signaling intermediates downstream of the Toll-like receptor (TLR) 4, such as NF-κB and interferon regulatory factors (IRFs), resulting in inhibition of interferon (IFN)-β expression. We also demonstrate that the activity of FOXO3 itself is regulated by IKK-ε, a kinase involved in IFN-β production, which phosphorylates and inactivates FOXO3 in response to TLR4 agonists. Thus, we identify FOXO3 as a new IKK-ε-controlled check-point of IRF activation and regulation of IFN-β expression, providing new insight into the role of FOXO3 in immune response control.

Targeting of macrophage galactose-type C-type lectin (MGL) induces DC signaling and activation

Dendritic cells (DCs) sense the microenvironment through several types of receptors recognizing pathogen-associated molecular patterns. In particular, C-type lectins, expressed by distinct subsets of DCs, recognize and internalize specific carbohydrate antigen in a Ca(2+) -dependent manner. Targeting of these receptors is becoming an efficient strategy of delivering antigens in DC-based anticancer immunotherapy. Here we investigated the role of the macrophage galactose type C-lectin receptor (MGL), expressed by immature DCs (iDCs), as a molecular target for α-N-acetylgalactosamine (GalNAc or Tn)-carrying tumor-associated antigens to improve DC performance. MGL expressed by ex vivo-generated iDCs from healthy donors was engaged by a 60-mer MUC1(9Tn) -glycopeptide as a Tn-carrying tumor-associated antigen, and an anti-MGL antibody, as a specific MGL binder. We demonstrated that MGL engagement induced homotrimers and homodimers, triggering the phosphorylation of extracellular signal-regulated kinase 1,2 (ERK1,2) and nuclear factor-κB activation. Analysis of DC phenotype and function demonstrated that MGL engagement improved DC performance as antigen-presenting cells, promoting the upregulation of maturation markers, a decrease in phagocytosis, an enhancement of motility, and most importantly an increase in antigen-specific CD8(+) T-cell activation. These results demonstrate that the targeting of MGL receptor on human DCs has an adjuvant effect and that this strategy can be used to design novel anticancer vaccines.