CD83 knockdown in monocyte-derived dendritic cells by small interfering RNA leads to a diminished T cell stimulation

MCAM+CD161- Th17 Subset Expressing CD83 Enhances Tc17 Response in Psoriasis

Recent studies have highlighted the pathogenic roles of IL-17-producing CD8+ T cells (T-cytotoxic 17 [Tc17]) in psoriasis. However, the underlying mechanisms of Tc17 induction remain unclear. In this study, we focused on the pathogenic subsets of Th17 and their mechanism of promotion of Tc17 responses. We determined that the pathogenic Th17-enriched fraction expressed melanoma cell adhesion molecule (MCAM) and CCR6, but not CD161, because this subset produced IL-17A abundantly and the presence of these cells in the peripheral blood of patients has been correlated with the severity of psoriasis. Intriguingly, the serial analysis of gene expression revealed that CCR6+MCAM+CD161-CD4+ T cells displayed the gene profile for adaptive immune responses, including CD83, which is an activator for CD8+ T cells. Coculture assay with or without intercellular contact between CD4+ and CD8+ T cells showed that CCR6+MCAM+CD161-CD4+ T cells induced the proliferation of CD8+ T cells in a CD83-dependent manner. However, the production of IL-17A by CD8+ T cells required exogenous IL-17A, suggesting that intercellular contact via CD83 and the production of IL-17A from activated CD4+ T cells elicit Tc17 responses. Intriguingly, the CD83 expression was enhanced in the presence of IL-15, and CD83+ cells stimulated with IL-1β, IL-23, IL-15, and IL-15Rα did not express FOXP3. Furthermore, CCR6+MCAM+CD161-CD4+ T cells expressing CD83 were increased in the peripheral blood of patients, and the CD83+ Th17-type cells accumulated in the lesional skin of psoriasis. In conclusion, pathogenic MCAM+CD161- Th17 cells may be involved in the Tc17 responses via IL-17A and CD83 in psoriasis.

Activation of T cell checkpoint pathways during β-cell antigen presentation by engineered dendritic cells promotes protection from type 1 diabetes

Defective immune regulation has been recognized in type 1 diabetes (T1D). Immune regulatory T cell check-point receptors, which are generally upregulated on activated T cells, have been the molecules of attention as therapeutic targets for enhancing immune response in tumor therapy. Here, we show that pancreatic β-cell antigen (BcAg) presentation by engineered tolerogenic dendritic cells (tDCs) that express CTLA4 selective ligand (B7.1wa) or a combination of CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively; multiligand-DCs) causes an increase in regulatory cytokine and T cell (Treg) responses and suppression of the effector T cell function as compared to engineered control-DCs. Non-obese diabetic (NOD) mice treated with BcAg-pulsed CTLA4-ligand-DCs and multiligand-DCs at pre-diabetic and early-hyperglycemic stages showed significantly lower degree of insulitis, higher frequencies of insulin-positive islets, profound delay in, and reversal of, hyperglycemia for a significant duration. Immune cells from the tDC treated mice not only produced lower amounts of IFNγ and higher amounts of IL10 and TGFβ1 upon BcAg challenge, but also failed to induce hyperglycemia upon adoptive transfer. While both CTLA4-ligand-DCs and multiligand-DCs were effective in inducing tolerance, multiligand-DC treatment produced an overall higher suppressive effect on effector T cell function and disease outcome. These studies show that enhanced engagement of T cell checkpoint receptors during BcAg presentation can modulate T cell function and suppress autoimmunity and progression of the disease in T1D.

Dendritic Cells of Leukemic Origin: Specialized Antigen-Presenting Cells as Potential Treatment Tools for Patients with Myeloid Leukemia

The prognosis of elderly patients with acute myeloid leukemia (AML) and high-grade myelodysplastic syndrome (MDS) is limited due to the lack of therapy options and high relapse rates. Dendritic cell (DC)-based immunotherapy seems to be a promising treatment tool. DC are potent antigen-presenting cells and play a pivotal role on the interface of the innate and the adaptive immune system. Myeloid leukemia blasts can be converted to DC of leukemic origin (DC_leu), expressing costimulatory molecules along with the whole leukemic antigen repertoire of individual patients. These generated DC_leu are potent stimulators of various immune reactive cells and increase antileukemic immunity ex vivo. Here we review the generating process of DC/DC_leu from leukemic peripheral blood mononuclear cells as well as directly from leukemic whole blood with "minimized" Kits to simulate physiological conditions ex vivo. The purpose of adoptive cell transfer of DC/DC_leu as a vaccination strategy is discussed. A new potential therapy option with Kits for patients with myeloid leukemia, which would render an adoptive DC/DC_leu transfer unnecessary, is presented. In summary, DC/DC_leu-based therapies seem to be promising treatment tools for patients with AML or MDS but ongoing research including trials in animals and humans have to be performed.

Evaluation of immunomodulatory effects of Boswellia sacra essential oil on T-cells and dendritic cells

BACKGROUND

Boswellia sacra resin has been commonly used as analgesic, antimicrobial, and anti-inflammatory properties, which reflect its immunomodulatory activity. Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) and sentinel cells that regulate the immune response. This study aims at investigating whether crude essential oil extracted from Boswellia sacra resin (BSEO), has a potential effect on the phenotype and functions of human monocyte-derived DCs.

METHODS

Oil extract from the resin of Boswellia sacra was prepared by hydrodistillation using a custom made hydrodistiller. BSEO-mediated cell viability has been initially studied on human skin dermis cells (HSD) and DC precursors using quantitative and qualitative assays before applying on DCs. Human DCs were generated from differentiated peripheral blood monocytes cultured in media containing both GM-CSF and IL-4. DCs were exposed to 5 μg/mL or 10 μg/mL of BSEO in vitro. Morphological, phonotypical, and functional properties studied with microscopy, flow cytometry, and ELISA.

RESULTS

Crude BSEO was found to interfere with the maturation and differentiation of DCs from precursor cells in the presence or absence of lipopolysaccharide (LPS). BSEO-treated DCs, cultured in the presence of LPS, reduced the ability of allogeneic T cells to proliferate compared to that co-cultured with LPS-stimulated DCs only. In addition, the endocytic capacity and secretion of IL-10 by DCs treated with BSEO was enhanced in comparison to LPS treated cells. Analysis of the chemical composition of BESO using GC-MS (Clarus 500 GC/MS, PerkinElmer, Shelton, CT) revealed the presence of compounds with several biological activities including antibacterial, antioxidant, and anti-inflammatory properties.

CONCLUSION

Results indicated that BSEO deviates the differentiation of monocytes into immature DCs. Furthermore, stimulation of immature DCs with BSEO was unable to generate full DC maturation. However, these findings may potentially be employed to generate DCs with tolerogenic properties that are able to induce tolerance in diseases with hypersensitivity, autoimmunity as well as transplantation.

Scrib and Dlg1 polarity proteins regulate Ag presentation in human dendritic cells

We recently reported, for the first time, the expression and regulation of the PDZ polarity proteins Scrib and Dlg1 in human APCs, and also described the viral targeting of these proteins by NS1 of influenza A virus in human dendritic cells (DCs). Scrib plays an important role in reactive oxygen species (ROS) production in Mϕs and uropod formation and migration in T cells, while Dlg1 is important for T cell downstream activation after Ag recognition. Nevertheless, the functions of these proteins in human DCs remain unknown. Here, we knocked-down the expression of both Scrib and Dlg1 in human DCs and then evaluated the expression of co-stimulatory molecules and cytokine production during maturation. We demonstrated that Scrib is necessary for adequate CD86 expression, while Dlg1 is important for CD83 up-regulation and IL-6 production upon maturation, suggesting that Scrib and Dlg1 participate in separate pathways in DCs. Additionally, both proteins are required for adequate IL-12 production after maturation. Furthermore, we showed that the inefficient maturation of DCs induced by Scrib or Dlg1 depletion leads to impaired T cell activation. Our results revealed the previously unknown contribution of Scrib and Dlg1 in human DCs pivotal functions, which may be able to impact innate and adaptive immune response.

Endogenous CD83 Expression in CD4+ Conventional T Cells Controls Inflammatory Immune Responses

The glycoprotein CD83 is known to be expressed by different immune cells including activated CD4+Foxp3+ regulatory T cells (Tregs) and CD4+Foxp3- conventional T cells. However, the physiological function of endogenous CD83 in CD4+ T cell subsets is still unclear. In this study, we have generated a new CD83flox mouse line on BALB/c background, allowing for specific ablation of CD83 in T cells upon breeding with CD4-cre mice. Tregs from CD83flox/flox/CD4-cretg/wt mice had similar suppressive activity as Tregs from CD83flox/flox/CD4-crewt/wt wild-type littermates, suggesting that endogenous CD83 expression is dispensable for the inhibitory capacity of Tregs. However, CD83-deficient CD4+ conventional T cells showed elevated proliferation and IFN-γ secretion as well as an enhanced capacity to differentiate into Th1 cells and Th17 cells upon stimulation in vitro. T cell-specific ablation of CD83 expression resulted in aggravated contact hypersensitivity reaction accompanied by enhanced CD4+ T cell activation. Moreover, adoptive transfer of CD4+CD45RBhigh T cells from CD83flox/flox/CD4-cretg /wt mice into Rag2-deficient mice elicited more severe colitis associated with increased serum concentrations of IL-12 and elevated CD40 expression on CD11c+ dendritic cells (DCs). Strikingly, DCs from BALB/c mice cocultured with CD83-deficient CD4+ conventional T cells showed enhanced CD40 expression and IL-12 secretion compared with DCs cocultured with CD4+ conventional T cells from CD83flox/flox/CD4-crewt/wt wild-type mice. In summary, these results indicate that endogenous CD83 expression in CD4+ conventional T cells plays a crucial role in controlling CD4+ T cell responses, at least in part, by regulating the activity of CD11c+ DCs.

The Scribble Complex PDZ Proteins in Immune Cell Polarities

hScrib and hDlg belong to the PDZ family of proteins. Since the identification of these highly phylogenetically conserved scaffolds, an increasing amount of experiments has elucidated the roles of hScrib and hDlg in a variety of cell functions. Remarkably, their participation during the establishment of polarity in epithelial cells is well documented. Although the role of both proteins in the immune system is scantly known, it has become a growing field of investigation. Here, we summarize the interactions and functions of hScrib and hDlg1, which participate in diverse functions involving cell polarization in immune cells, and discuss their relevance in the immune cell biology. The fundamental role of hScrib and hDlg1 during the establishment of the immunological synapse, hence T cell activation, and the recently described role of hScrib in reactive oxygen species production in macrophages and of hDlg1 in cytokine production by dendritic cells highlight the importance of both proteins in immune cell biology. The expression of these proteins in other leukocytes can be anticipated and needs to be confirmed. Due to their multiple interaction domains, there is a wide range of possible interactions of hScrib and hDlg1 that remains to be explored in the immune system.

The CD83 Molecule - An Important Immune Checkpoint

The CD83 molecule has been identified to be expressed on numerous activated immune cells, including B and T lymphocytes, monocytes, dendritic cells, microglia, and neutrophils. Both isoforms of CD83, the membrane-bound as well as its soluble form are topic of intensive research investigations. Several studies revealed that CD83 is not a typical co-stimulatory molecule, but rather plays a critical role in controlling and resolving immune responses. Moreover, CD83 is an essential factor during the differentiation of T and B lymphocytes, and the development and maintenance of tolerance. The identification of its interaction partners as well as signaling pathways have been an enigma for the last decades. Here, we report the latest data on the expression, structure, and the signaling partners of CD83. In addition, we review the regulatory functions of CD83, including its striking modulatory potential to maintain the balance between tolerance versus inflammation during homeostasis or pathologies. These immunomodulatory properties of CD83 emphasize its exceptional therapeutic potential, which has been documented in specific preclinical disease models.

Electroporation as a method of choice to generate genetically modified dendritic cell cancer vaccines

In the last few decades, immunotherapy has emerged as an alternative therapeutic approach to treat cancer. Immunotherapy offers a plethora of different treatment possibilities. Among these, dendritic cell (DC)-based cancer vaccines constitute one of the most promising and valuable therapeutic options. DC-vaccines have been introduced into the clinics more than 15 years ago, and preclinical studies showed their general safety and low toxic effects on patients. However, their treatment efficacy is still rather limited, demanding for novel avenues to improve vaccine efficacy. One way to potentially achieve this is to focus on improving the DC-T cell interaction to further increase T cell priming and downstream activity. A successful DC-T cell interaction requires three different signals (Figure 1): (1) Major Histocompatibility Complex (MHC) and antigen complex interaction with T cell receptor (TCR) (2) interaction between co-stimulatory molecules and their cognate ligands at the cell surface and (3) secretion of cytokines to polarize the immune response toward a Type 1 helper (Th1) phenotype. In recent years, many studies attempted to improve the DC-T cell interaction and overall cancer vaccine therapeutic outcomes by increasing the expression of mediators of signal 1, 2 and/or 3, through genetic modifications of DCs. Transfection of genes of interest can be achieved through many different methods such as passive pulsing, lipofection, viral transfection, or electroporation (EP). However, EP is currently emerging as the method of choice thanks to its safety, versatility, and relatively easy clinical translation. In this review we will highlight the potential benefits of EP over other transfection methods as well as giving an overview of the available studies employing EP to gene-modify DCs in cancer vaccines. Crucial aspects such as safety, feasibility, and gene(s) of choice will be also discussed, together with future perspectives and opportunities for DC genetic engineering.

Herpes Simplex Virus Type-2 Paralyzes the Function of Monocyte-Derived Dendritic Cells

Herpes simplex viruses not only infect a variety of different cell types, including dendritic cells (DCs), but also modulate important cellular functions in benefit of the virus. Given the relevance of directed immune cell migration during the initiation of potent antiviral immune responses, interference with DC migration constitutes a sophisticated strategy to hamper antiviral immunity. Notably, recent reports revealed that HSV-1 significantly inhibits DC migration in vitro. Thus, we aimed to investigate whether HSV-2 also modulates distinct hallmarks of DC biology. Here, we demonstrate that HSV-2 negatively interferes with chemokine-dependent in vitro migration capacity of mature DCs (mDCs). Interestingly, rather than mediating the reduction of the cognate chemokine receptor expression early during infection, HSV-2 rapidly induces β2 integrin (LFA-1)-mediated mDC adhesion and thereby blocks mDC migration. Mechanistically, HSV-2 triggers the proteasomal degradation of the negative regulator of β2 integrin activity, CYTIP, which causes the constitutive activation of LFA-1 and thus mDC adhesion. In conclusion, our data extend and strengthen recent findings reporting the reduction of mDC migration in the context of a herpesviral infection. We thus hypothesize that hampering antigen delivery to secondary lymphoid organs by inhibition of mDC migration is an evolutionary conserved strategy among distinct members of Herpesviridae.

LGR5 and Downstream Intracellular Signaling Proteins Play Critical Roles in the Cell Proliferation of Neuroblastoma, Meningioma and Pituitary Adenoma

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) has been reported to play critical roles in the proliferation of various cancer cells. However, the roles of LGR5 in brain tumors and the specific intracellular signaling proteins directly associated with it remain unknown. Expression of LGR5 was first measured in normal brain tissue, meningioma, and pituitary adenoma of humans. To identify the downstream signaling pathways of LGR5, siRNA-mediated knockdown of LGR5 was performed in SH-SY5Y neuroblastoma cells followed by proteomics analysis with 2-dimensional polyacrylamide gel electrophoresis (2D-PAGE). In addition, the expression of LGR5-associated proteins was evaluated in LGR5-inhibited neuroblastoma cells and in human normal brain, meningioma, and pituitary adenoma tissue. Proteomics analysis showed 12 protein spots were significantly different in expression level (more than two-fold change) and subsequently identified by peptide mass fingerprinting. A protein association network was constructed from the 12 identified proteins altered by LGR5 knockdown. Direct and indirect interactions were identified among the 12 proteins. HSP 90-beta was one of the proteins whose expression was altered by LGR5 knockdown. Likewise, we observed decreased expression of proteins in the hnRNP subfamily following LGR5 knockdown. In addition, we have for the first time identified significantly higher hnRNP family expression in meningioma and pituitary adenoma compared to normal brain tissue. Taken together, LGR5 and its downstream signaling play critical roles in neuroblastoma and brain tumors such as meningioma and pituitary adenoma.

CD83 orchestrates immunity toward self and non-self in dendritic cells

Dendritic cells (DCs) are crucial to balance protective immunity and autoimmune inflammatory processes. Expression of CD83 is a well-established marker for mature DCs, although its physiological role is still not completely understood. Using a DC-specific CD83-conditional KO (CD83ΔDC) mouse, we provide new insights into the function of CD83 within this cell type. Interestingly, CD83-deficient DCs produced drastically increased IL-2 levels and displayed higher expression of the costimulatory molecules CD25 and OX40L, which causes superior induction of antigen-specific T cell responses and compromises Treg suppressive functions. This also directly translates into accelerated immune responses in vivo. Upon Salmonella typhimurium and Listeria monocytogenes infection, CD83ΔDC mice cleared both pathogens more efficiently, and CD83-deficient DCs expressed increased IL-12 levels after bacterial encounter. Using the experimental autoimmune encephalomyelitis model, autoimmune inflammation was dramatically aggravated in CD83ΔDC mice while resolution of inflammation was strongly reduced. This phenotype was associated with increased cell influx into the CNS accompanied by elevated Th17 cell numbers. Concomitantly, CD83ΔDC mice had reduced Treg numbers in peripheral lymphoid organs. In summary, we show that CD83 ablation on DCs results in enhanced immune responses by dysregulating tolerance mechanisms and thereby impairing resolution of inflammation, which also demonstrates high clinical relevance.

Engineered Dendritic Cell-Directed Concurrent Activation of Multiple T cell Inhibitory Pathways Induces Robust Immune Tolerance

Inhibitory/repressor-receptors are upregulated significantly on activated T cells, and have been the molecules of attention as targets for inducing immune tolerance. Induction of effective antigen specific tolerance depends on concurrent engagement of the TCR and one or more of these inhibitory receptors. Here, we show, for the first time that dendritic cells (DCs) can be efficiently engineered to express multiple T cell inhibitory ligands, and enhanced engagement of T cell inhibitory receptors, upon antigen presentation, by these DCs can induce effective CD4+ T cell tolerance and suppress autoimmunity. Compared to control DCs, antigen presentation by DCs that ectopically express CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively) individually (mono-ligand DCs) or in combination (multi-ligand DCs) causes an inhibition of CD4+ T cell proliferation and pro-inflammatory cytokine response, as well as increase in Foxp3+ Treg frequency and immune regulatory cytokine production. Administration of self-antigen (mouse thyroglobulin; mTg) loaded multi-ligand DCs caused hyporesponsiveness to mTg challenge, suppression of autoantibody production, and amelioration of experimental autoimmune thyroiditis. Overall, this study shows that engineered DC-directed enhanced concurrent activation of multiple T cell coinhibitory pathways is an effective way to induce self-antigen specific T cell tolerance to suppress ongoing autoimmunity.

Immune reactions after modern lamellar (DALK, DSAEK, DMEK) versus conventional penetrating corneal transplantation

In the past decade, novel lamellar keratoplasty techniques such as Deep Anterior Lamellar Keratoplasty (DALK) for anterior keratoplasty and Descemet stripping automated endothelial keratoplasty (DSAEK)/Descemet membrane endothelial keratoplasty (DMEK) for posterior keratoplasty have been developed. DALK eliminates the possibility of endothelial allograft rejection, which is the main reason for graft failure after penetrating keratoplasty (PK). Compared to PK, the risk of endothelial graft rejection is significantly reduced after DSAEK/DMEK. Thus, with modern lamellar techniques, the clinical problem of endothelial graft rejection seems to be nearly solved in the low-risk situation. However, even with lamellar grafts there are epithelial, subepithelial and stromal immune reactions in DALK and endothelial immune reactions in DSAEK/DMEK, and not all keratoplasties can be performed in a lamellar fashion. Therefore, endothelial graft rejection in PK is still highly relevant, especially in the "high-risk" setting, where the cornea's (lymph)angiogenic and immune privilege is lost due to severe inflammation and pathological neovascularization. For these eyes, currently available treatment options are still unsatisfactory. In this review, we will describe currently used keratoplasty techniques, namely PK, DALK, DSAEK, and DMEK. We will summarize their indications, provide surgical descriptions, and comment on their complications and outcomes. Furthermore, we will give an overview on corneal transplant immunology. A specific focus will be placed on endothelial graft rejection and we will report on its incidence, clinical presentation, and current/future treatment and prevention options. Finally, we will speculate how the field of keratoplasty and prevention of corneal allograft rejection will develop in the future.

Endogenous Expression of the Human CD83 Attenuates EAE Symptoms in Humanized Transgenic Mice and Increases the Activity of Regulatory T Cells

The CD83 is a type I membrane protein and part of the immunoglobulin superfamily of receptors. CD83 is involved in the regulation of antigen presentation and dendritic cell dependent allogeneic T cell proliferation. A soluble form of CD83 inhibits dendritic cell maturation and function. Furthermore, CD83 is expressed on activated B cells, T cells, and in particular on regulatory T cells. Previous studies on murine CD83 demonstrated this molecule to be involved in several immune-regulatory processes, comprising that CD83 plays a key role in the development und function of different immune cells. In order to get further insights into the function of the human CD83 and to provide preclinical tools to guide the function of CD83/sCD83 for therapeutic purposes we generated Bacterial Artificial Chromosomes (BAC) transgenic mice. BACs are excellent tools for manipulating large DNA fragments and are utilized to engineer transgenic mice by pronuclear injection. Two different founders of BAC transgenic mice expressing human CD83 (BAC-hCD83tg mice) were generated and were examined for the hCD83 expression on different immune cells as well as both the in vitro and in vivo role of human CD83 (hCD83) in health and disease. Here, we found the hCD83 molecule to be present on activated DCs, B cells and subtypes of CD4+ T cells. CD8+ T cells, on the other hand, showed almost no hCD83 expression. To address the function of hCD83, we performed in vitro mixed lymphocyte reactions (MLR) as well as suppression assays and we used the in vivo model of experimental autoimmune encephalomyelitis (EAE) comparing wild-type and hCD83-BAC mice. Results herein showed a clearly diminished capacity of hCD83-BAC-derived T cells to proliferate accompanied by an enhanced activation and suppressive activity of hCD83-BAC-derived Tregs. Furthermore, hCD83-BAC mice were found to recover faster from EAE-associated symptoms than wild-type mice, encouraging the relevance also of the hCD83 as a key molecule for the regulatory phenotype of Tregs in vitro and in vivo.

Invasive Salmonella exploits divergent immune evasion strategies in infected and bystander dendritic cell subsets

Non-typhoidal Salmonella (NTS) are highly prevalent food-borne pathogens. Recently, a highly invasive, multi-drug resistant S. Typhimurium, ST313, emerged as a major cause of bacteraemia in children and immunosuppressed adults, however the pathogenic mechanisms remain unclear. Here, we utilize invasive and non-invasive Salmonella strains combined with single-cell RNA-sequencing to study the transcriptome of individual infected and bystander monocyte-derived dendritic cells (MoDCs) implicated in disseminating invasive ST313. Compared with non-invasive Salmonella, ST313 directs a highly heterogeneous innate immune response. Bystander MoDCs exhibit a hyper-activated profile potentially diverting adaptive immunity away from infected cells. MoDCs harbouring invasive Salmonella display higher expression of IL10 and MARCH1 concomitant with lower expression of CD83 to evade adaptive immune detection. Finally, we demonstrate how these mechanisms conjointly restrain MoDC-mediated activation of Salmonella-specific CD4+ T cell clones. Here, we show how invasive ST313 exploits discrete evasion strategies within infected and bystander MoDCs to mediate its dissemination in vivo.

CD83 Antibody Inhibits Human B Cell Responses to Antigen as well as Dendritic Cell-Mediated CD4 T Cell Responses

Anti-CD83 Ab capable of Ab-dependent cellular cytotoxicity can deplete activated CD83+ human dendritic cells, thereby inhibiting CD4 T cell-mediated acute graft-versus-host disease. As CD83 is also expressed on the surface of activated B lymphocytes, we hypothesized that anti-CD83 would also inhibit B cell responses to stimulation. We found that anti-CD83 inhibited total IgM and IgG production in vitro by allostimulated human PBMC. Also, Ag-specific Ab responses to immunization of SCID mice xenografted with human PBMC were inhibited by anti-CD83 treatment. This inhibition occurred without depletion of all human B cells because anti-CD83 lysed activated CD83+ B cells by Ab-dependent cellular cytotoxicity and spared resting (CD83-) B cells. In cultured human PBMC, anti-CD83 inhibited tetanus toxoid-stimulated B cell proliferation and concomitant dendritic cell-mediated CD4 T cell proliferation and expression of IFN-γ and IL-17A, with minimal losses of B cells (<20%). In contrast, the anti-CD20 mAb rituximab depleted >80% of B cells but had no effect on CD4 T cell proliferation and cytokine expression. By virtue of the ability of anti-CD83 to selectively deplete activated, but not resting, B cells and dendritic cells, with the latter reducing CD4 T cell responses, anti-CD83 may be clinically useful in autoimmunity and transplantation. Advantages might include inhibited expansion of autoantigen- or alloantigen-specific B cells and CD4 T cells, thus preventing further production of pathogenic Abs and inflammatory cytokines while preserving protective memory and regulatory cells.

Role of L-Particles during Herpes Simplex Virus Infection

Infection of eukaryotic cells with α-herpesviruses results in the formation and secretion of infectious heavy particles (virions; H-particles) and non-infectious light particles (L-particles). Herpes simplex virus type 1 (HSV-1) H-particles consist of a genome-containing capsid surrounded by tegument proteins and a glycoprotein-rich lipid bilayer. Non-infectious L-particles are composed mainly of envelope and tegument proteins and are devoid of capsids and viral DNA. L-particles were first described in the early nineties and from then on investigated for their formation and role during virus infection. The development and secretion of L-particles occur simultaneously to the assembly of complete viral particles. HSV-1 L-particles are assembled by budding of condensed tegument into Golgi-delivered vesicles and are capable of delivering their functional content to non-infected cells. Thereby, HSV-1 L-particles contribute to viral pathogenesis within the infected host by enhancing virion infectivity and providing immune evasion functions. In this review we discuss the emergence of HSV-1 L-particles during virus replication and their biological functions described thus far.

What Goes Around, Comes Around - HSV-1 Replication in Monocyte-Derived Dendritic Cells

HSV-1 is a very successful human pathogen, known for its high sero-prevalence and the ability to infect a wide range of different cell types, including dendritic cells (DCs). As very potent antigen-presenting cells DCs play an important role in the induction of antiviral immune responses and therefore represent a strategic target for viral-mediated immune escape mechanisms. It is known that HSV-1 completes its gene expression profile in immature as well as in mature DCs, while lytic infection is only found in immature DCs (iDCs). Notably, HSV-1 infected mature DCs (mDCs) fail to release infectious progeny virions into the supernatant. Apart from HSV-1 dissemination via extracellular routes cell-to-cell spread counteracts a yet unknown mechanism by which the virus is trapped in mDCs and not released into the supernatant. The dissemination in a cell-cell contact-dependent manner enables HSV-1 to infect bystander cells without the exposure toward the extracellular environment. This supports the virus to successfully infect the host and establish latency. In this review the mechanism of HSV-1 replication in iDCs and mDCs and its immunological as well as virological implications, will be discussed.

Butyrate and propionate inhibit antigen-specific CD8+ T cell activation by suppressing IL-12 production by antigen-presenting cells

Short chain fatty acids (SCFAs), such as acetate, butyrate and propionate, are products of microbial macronutrients fermentation that distribute systemically and are believed to modulate host immune responses. Recent data have indicated that certain SCFAs, such as butyrate and propionate, directly modulate human dendritic cell (DC) function. Given the role of DCs in initiating and shaping the adaptive immune response, we now explore how SCFAs affect the activation of antigen-specific CD8⁺ T cells stimulated with autologous, MART1 peptide-pulsed DC. We show that butyrate reduces the frequency of peptide-specific CD8⁺ T cells and, together with propionate, inhibit the activity of those cells. On the contrary, acetate does not affect them. Importantly, butyrate and propionate inhibit the production of IL-12 and IL-23 in the DCs and exogenous IL-12 fully restores the activation of the MART-1-specific CD8⁺ T cells, whereas IL-23 has no effect. In conclusion, these results point to a pivotal role of butyrate and propionate in modulating CD8⁺ T cell activation via the inhibition of IL-12 secretion from DCs. These findings reveal a novel mechanism whereby bacterial fermentation products may modulate CD8⁺ T cell function with possible implications in anti-cancer immunotherapy.

Different capacity of in vitro generated myeloid dendritic cells of newborns of healthy and allergic mothers to respond to probiotic strain E. coli O83:K24:H31

Allergic diseases belong to one of the most common diseases with steadily increasing incidence even among young children. There is an urgent need to identify a prognostic marker pointing to increased risk of allergy development enabling early preventive measures introduction. It has been shown that administration of selected probiotic strains or mixtures could prevent allergy development. In our study, we have tested the capacity of probiotic strain Escherichia coli O83:K24:H31 (E. coli O83) to promote dendritic cell (DC) maturation and polarisation of immune responses. Increased presence of activation marker CD83 was observed on DC stimulated by E. coli O83 and DC of newborns of allergic mothers have significantly more increased cell surface presence of CD83 in comparison to children of healthy mothers. Increased gene expression and secretion of IL-10 was detected in DC stimulated with E. coli O83 being higher in DC of newborns of healthy mothers in comparison to allergic ones. Generally, increased presence of intracellular cytokines (IL-4, IL-13, IFN-gamma, IL-17A, IL-22, IL-10) was detected in CD4+ T cells cocultured with DC of children of allergic mothers in comparison to healthy ones. E. coli O83 primed DC significantly increased IL-10 and IL-17A in CD4 T cells of newborns of healthy mothers in comparison to the levels detected in CD4 T cells cocultured with control non-stimulated DC. We can conclude E. coli O83 induces dendritic cell maturation and IL-10 production in DC. Newborns of allergic mothers have generally increased reactivity of both DC and CD4 T cells which together with decreased capacity of DC of newborns of allergic mothers to produce IL-10 could support inappropriate immune responses development after allergen encounter.

Expression of soluble CD83 in plasma from early-stage rheumatoid arthritis patients is not modified by anti-TNF-α therapy

Rheumatoid arthritis (RA) is an autoimmune disease which may lead to severe disabilities due to structural joint damage and extraarticular manifestations The dendritic cell marker CD83 belongs to the immunoglobulin superfamily and has previously been associated with autoimmune diseases. In RA the levels of soluble CD83 (sCD83) are elevated in synovial fluid, however little is known about CD83 expression and regulation in RA. Therefore, we studied how CD83 is expressed in RA and further evaluated the effect of anti-TNF-α therapy hereon. Early RA patients were randomized to conventional disease modifying anti-rheumatic drugs with or without additional anti-TNF-α therapy. Rheumatoid arthritis patients had increased levels of sCD83 in plasma compared with healthy volunteers. The increase in sCD83 plasma levels were unaffected by anti-TNF-α therapy. In chronic RA patients the levels of sCD83 were higher in synovial fluid than in plasma, and only a limited amount of membrane bound CD83 expression was detected on the surface of cells from peripheral blood and synovial fluid. Finally, confocal microscopy of RA synovial membranes revealed that CD83 was mainly localized intracellularly in a group of cells with diverse morphology including both antigen-presenting cells and non-antigen-presenting cells. Our findings demonstrate that early-stage RA patients have elevated levels of sCD83 in plasma and that anti-TNF-α treatment has no effect on the sCD83 plasma level. This suggest that in RA patients sCD83 regulation is beyond control of TNF-α.

A new marine-derived sulfoglycolipid triggers dendritic cell activation and immune adjuvant response

Dendritic Cells (DCs) recognize infectious non-self molecules and engage the adaptive immune system thereby initiating long lasting, antigen-specific responses. As such, the ability to activate DCs is considered a key tool to enhance the efficacy and quality of vaccination. Here we report a novel immunomodulatory sulfolipid named β-SQDG18 that prototypes a class of natural-derived glycolipids able to prime human DCs by a TLR2/TLR4-independent mechanism and trigger an efficient immune response in vivo. β-SQDG18 induces maturation of DC with the upregulation of MHC II molecules and co-stimulatory proteins (CD83, CD86), as well as pro-inflammatory cytokines (IL-12 and INF-γ). Mice immunized with OVA associated to β-SQDG18 (1:500) produced a titer of anti-OVA Ig comparable to traditional adjuvants. In an experimental model of melanoma, vaccination of C57BL/6 mice with β-SQDG18-adjuvanted hgp10 peptide elicited a protective response with a reduction in tumour growth and increase in survival.

Influence of nanoparticle-mediated transfection on proliferation of primary immune cells in vitro and in vivo

INTRODUCTION

One of the main obstacles in the widespread application of gene therapeutic approaches is the necessity for efficient and safe transfection methods. For the introduction of small oligonucleotide gene therapeutics into a target cell, nanoparticle-based methods have been shown to be highly effective and safe. While immune cells are a most interesting target for gene therapy, transfection might influence basic immune functions such as cytokine expression and proliferation, and thus positively or negatively affect therapeutic intervention. Therefore, we investigated the effects of nanoparticle-mediated transfection such as polyethylenimine (PEI) or magnetic beads on immune cell proliferation.

METHODS

Human adherent and non-adherent PBMCs were transfected by various methods (e.g. PEI, Lipofectamine® 2000, magnetofection) and stimulated. Proliferation was measured by lymphocyte transformation test (LTT). Cell cycle stages as well as expression of proliferation relevant genes were analyzed. Additionally, the impact of nanoparticles was investigated in vivo in a murine model of the severe systemic immune disease GvHD (graft versus host disease).

RESULTS

The proliferation of primary immune cells was influenced by nanoparticle-mediated transfection. In particular in the case of magnetic beads, proliferation inhibition coincided with short-term cell cycle arrest and reduced expression of genes relevant for immune cell proliferation. Notably, proliferation inhibition translated into beneficial effects in a murine GvHD model with animals treated with PEI-nanoparticles showing increased survival (pPEI = 0.002) most likely due to reduced inflammation.

CONCLUSION

This study shows for the first time that nanoparticles utilized for gene therapeutic transfection are able to alter proliferation of immune cells and that this effect depends on the type of nanoparticle. For magnetic beads, this was accompanied by temporary cell cycle arrest. Notably, in GvHD this nonspecific anti-proliferative effect might contribute to reduced inflammation and increased survival.

A Kinetic Study of CD83 Reveals an Upregulation and Higher Production of sCD83 in Lymphocytes from Pregnant Mice

For the normal development of pregnancy, a balance between immune tolerance and defense is crucial. However, the mechanisms mediating such a balance are not fully understood. CD83 is a transmembrane protein whose expression has been linked to anti-inflammatory functions of T and B cells. The soluble form of CD83, released by cleavage of the membrane-bound protein, has strong anti-inflammatory properties and was successfully tested in different mouse models. It is assumed that this molecule contributes to the establishment of immune tolerance. Therefore, we postulated that the expression of CD83 is crucial for immune tolerance during pregnancy in mice. Here, we demonstrated that the membrane-bound form of CD83 was upregulated in T and B cells during allogeneic murine pregnancies. An upregulation was also evident in the main splenic B cell subtypes: marginal zone, follicular zone, and transitional B cells. We also showed that there was an augmentation in the number of CD83⁺ cells toward the end of pregnancy within splenic B and CD4⁺ T cells, while CD83⁺ dendritic cells were reduced in spleen and inguinal lymph nodes of pregnant mice. Additionally, B lymphocytes in late-pregnancy presented a markedly higher sensitivity to LPS in terms of CD83 expression and sCD83 release. Progesterone induced a dosis-dependent upregulation of CD83 on T cells. Our data suggest that the regulation of CD83 expression represents a novel pathway of fetal tolerance and protection against inflammatory threats during pregnancy.

Crystal Structure of the Extracellular Domain of the Human Dendritic Cell Surface Marker CD83

CD83 is a type-I membrane protein and an efficient marker for identifying mature dendritic cells. Whereas membrane-bound, full-length CD83 co-stimulates the immune system, a soluble variant (sCD83), consisting of the extracellular domain only, displays strong immune-suppressive activities. Besides a prediction that sCD83 adopts a V-set Ig-like fold, however, little is known about the molecular architecture of CD83 and the mechanism by which CD83 exerts its function on dendritic cells and additional immune cells. Here, we report the crystal structure of human sCD83 up to a resolution of 1.7Å solved in three different crystal forms. Interestingly, β-strands C', C″, and D that are typical for V-set Ig-domains could not be traced in sCD83. Mass spectrometry analyses, limited proteolysis experiments, and bioinformatics studies show that the corresponding segment displays enhanced main-chain accessibility, extraordinary low sequence conservation, and a predicted high disorder propensity. Chimeric proteins with amino acid swaps in this segment show unaltered immune-suppressive activities in a TNF-α assay when compared to wild-type sCD83. This strongly indicates that this segment does not participate in the biological activity of CD83. The crystal structure of CD83 shows the recurrent formation of dimers and trimers in the various crystal forms and reveals strong structural similarities between sCD83 and B7 family members and CD48, a signaling lymphocyte activation molecule family member. This suggests that CD83 exerts its immunological activity by mixed homotypic and heterotypic interactions as typically observed for proteins present in the immunological synapse.

Soluble CD83 Inhibits T Cell Activation by Binding to the TLR4/MD-2 Complex on CD14+ Monocytes

The transmembrane protein CD83, expressed on APCs, B cells, and T cells, can be expressed as a soluble form generated by alternative splice variants and/or by shedding. Soluble CD83 (sCD83) was shown to be involved in negatively regulating the immune response. sCD83 inhibits T cell proliferation in vitro, supports allograft survival in vivo, prevents corneal transplant rejection, and attenuates the progression and severity of autoimmune diseases and experimental colitis. Although sCD83 binds to human PBMCs, the specific molecules that bind sCD83 have not been identified. In this article, we identify myeloid differentiation factor-2 (MD-2), the coreceptor within the TLR4/MD-2 receptor complex, as the high-affinity sCD83 binding partner. TLR4/MD-2 mediates proinflammatory signal delivery following recognition of bacterial LPSs. However, altering TLR4 signaling can attenuate the proinflammatory cascade, leading to LPS tolerance. Our data show that binding of sCD83 to MD-2 alters this signaling cascade by rapidly degrading IL-1R-associated kinase-1, leading to induction of the anti-inflammatory mediators IDO, IL-10, and PGE2 in a COX-2-dependent manner. sCD83 inhibited T cell proliferation, blocked IL-2 secretion, and rendered T cells unresponsive to further downstream differentiation signals mediated by IL-2. Therefore, we propose the tolerogenic mechanism of action of sCD83 to be dependent on initial interaction with APCs, altering early cytokine signal pathways and leading to T cell unresponsiveness.

The Major Immediate-Early Protein IE2 of Human Cytomegalovirus Is Sufficient to Induce Proteasomal Degradation of CD83 on Mature Dendritic Cells

Human cytomegalovirus (HCMV) is the prototypic beta-herpesvirus and widespread throughout the human population. While infection is asymptomatic in healthy individuals, it can lead to high morbidity and mortality in immunocompromised persons. Importantly, HCMV evolved multiple strategies to interfere with immune cell function in order to establish latency in infected individuals. As mature DCs (mDCs) are antigen-presenting cells able to activate naïve T cells they play a crucial role during induction of effective antiviral immune responses. Interestingly, earlier studies demonstrated that the functionally important mDC surface molecule CD83 is down-regulated upon HCMV infection resulting in a reduced T cell stimulatory capacity of the infected cells. However, the viral effector protein and the precise mechanism of HCMV-mediated CD83 reduction remain to be discovered. Using flow cytometric analyses, we observed significant down-modulation of CD83 surface expression becoming significant already 12 h after HCMV infection. Moreover, Western bot analyses revealed that, in sharp contrast to previous studies, loss of CD83 is not restricted to the membrane-bound molecule, but also occurs intracellularly. Furthermore, inhibition of the proteasome almost completely restored CD83 surface expression during HCMV infection. Results of infection kinetics and cycloheximide-actinomycin D-chase experiments, strongly suggested that an HCMV immediate early gene product is responsible for the induction of CD83 down-modulation. Consequently, we were able to identify the major immediate early protein IE2 as the viral effector protein that induces proteasomal CD83 degradation.

IL-10-Modulated Human Dendritic Cells for Clinical Use: Identification of a Stable and Migratory Subset with Improved Tolerogenic Activity

Dendritic cells (DCs) are key regulators of protective immune responses and tolerance to (self-)Ags. Therefore, the scientific rationale for the use of tolerogenic DC therapy in the fields of allergies, autoimmunity, and transplantation medicine is strong. In this study, we analyzed the tolerogenic capacity of IL-10-modulated DC (IL-10DC) subpopulations to identify a DC subset that combines potent immunosuppressive activities with valuable immune properties for clinical implementation. IL-10DCs consist of two phenotypically distinct subpopulations: CD83highCCR7+ IL-10DCs and CD83lowCCR7- IL-10DCs. Suppressor assays with activated effector T cells revealed that CD4+ regulatory T cells generated by CD83high IL-10DCs (iTreg+) exhibited a significantly higher suppressive capacity compared with CD4+ regulatory T cells generated by CD83low IL-10DCs (iTreg-). In this context, iTreg+ displayed a more activated phenotype (proliferation, cytokine production) compared with iTreg- In contrast to CD83low IL-10DCs, CD83high IL-10DCs exerted a strong migratory capacity toward the secondary lymphoid organ chemokine CCL21 and retained a functionally stable phenotype under inflammatory conditions. In addition, CD83high IL-10DCs expressed significantly higher levels of surface and soluble CD25. Functional analysis demonstrated that IL-10DC-related soluble CD25 efficiently inhibited the proliferation of activated T cells and that blockade of CD25 function abolished the induction of regulatory T cells by IL-10DCs, indicating a critical role for IL-10DC-related CD25 in shifting the immune response toward an iTreg- controlled tolerance reaction. In conclusion, the selective use of the CD83high IL-10DC subset may result in a higher efficacy of tolerance induction in vivo and may support the development of novel DC vaccination strategies for transplantations, as well as for allergic and autoimmune diseases.

Human 15-lipoxygenase-1 is a regulator of dendritic-cell spreading and podosome formation

Dendritic cells (DCs) involved in proinflammatory immune responses derive mainly from peripheral monocytes, and the cells subsequently mature and migrate into the inflammatory micromilieu. Here we report that suppressing of 15-lipoxygenase-1 led to a substantial reduction in DC spreading and podosome formation in vitro. The surface expression of CD83 was significantly lower in both sh-15-lipoxygenase-1 (15-LOX-1)-transduced cells and DCs cultivated in the presence of a novel specific 15-LOX-1 inhibitor. The T-cell response against tetanus-pulsed DCs was only affected to a minor extent on inhibition of 15-LOX-1. In contrast, endocytosis and migration ability of DCs were significantly suppressed on 15-LOX-1 inhibition. The expression of 15-LOX-1 in DCs was also demonstrated in affected human skin in atopic and contact dermatitis, showing that the enzyme is indeed expressed in inflammatory diseases in vivo. This study demonstrated that inhibiting 15-LOX-1 led to an impaired podosome formation in DCs, and consequently suppressed antigen uptake and migration capacity. These results indicated that 15-LOX-1 is a potential target for inhibiting the trafficking of DCs to lymphoid organs and inflamed tissues and decreasing the inflammatory response attenuating symptoms of certain immunologic and inflammatory disorders such as dermatitis.-Han, H., Liang, X., Ekberg, M., Kritikou, J. S., Brunnström, Å., Pelcman, B., Matl, M., Miao, X., Andersson, M., Yuan, X., Schain, F., Parvin, S., Melin, E., Sjöberg, J., Xu, D., Westerberg, L. S., Björkholm, M., Claesson, H.-E. Human 15-lipoxygenase-1 is a regulator of dendritic-cell spreading and podosome formation.

CD11c/CD18 Dominates Adhesion of Human Monocytes, Macrophages and Dendritic Cells over CD11b/CD18

Complement receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) belong to the family of beta2 integrins and are expressed mainly by myeloid cell types in humans. Previously, we proved that CR3 rather than CR4 plays a key role in phagocytosis. Here we analysed how CD11b and CD11c participate in cell adhesion to fibrinogen, a common ligand of CR3 and CR4, employing human monocytes, monocyte-derived macrophages (MDMs) and monocyte-derived dendritic cells (MDDCs) highly expressing CD11b as well as CD11c. We determined the exact numbers of CD11b and CD11c on these cell types by a bead-based technique, and found that the ratio of CD11b/CD11c is 1.2 for MDDCs, 1.7 for MDMs and 7.1 for monocytes, suggesting that the function of CD11c is preponderant in MDDCs and less pronounced in monocytes. Applying state-of-the-art biophysical techniques, we proved that cellular adherence to fibrinogen is dominated by CD11c. Furthermore, we found that blocking CD11b significantly enhances the attachment of MDDCs and MDMs to fibrinogen, demonstrating a competition between CD11b and CD11c for this ligand. On the basis of the cell surface receptor numbers and the measured adhesion strength we set up a model, which explains the different behavior of the three cell types.

Thymic CD4 T cell selection requires attenuation of March8-mediated MHCII turnover in cortical epithelial cells through CD83

Deficiency of CD83 in thymic epithelial cells (TECs) dramatically impairs thymic CD4 T cell selection. CD83 can exert cell-intrinsic and -extrinsic functions through discrete protein domains, but it remains unclear how CD83's capacity to operate through these alternative functional modules relates to its crucial role in TECs. In this study, using viral reconstitution of gene function in TECs, we found that CD83's transmembrane domain is necessary and sufficient for thymic CD4 T cell selection. Moreover, a ubiquitination-resistant MHCII variant restored CD4 T cell selection in Cd83(-/-) mice. Although during dendritic cell maturation CD83 is known to stabilize MHCII through opposing the ubiquitin ligase March1, regulation of March1 did not account for CD83's TEC-intrinsic role. Instead, we provide evidence that MHCII in cortical TECs (cTECs) is targeted by March8, an E3 ligase of as yet unknown physiological substrate specificity. Ablating March8 in Cd83(-/-) mice restored CD4 T cell development. Our results identify CD83-mediated MHCII stabilization through antagonism of March8 as a novel functional adaptation of cTECs for T cell selection. Furthermore, these findings suggest an intriguing division of labor between March1 and March8 in controlling inducible versus constitutive MHCII expression in hematopoietic antigen-presenting cells versus TECs.

A novel liposomal recombinant lipoimmunogen enhances anti-tumor immunity

Synthetic liposomes provide a biocompatible and biodegradable approach for delivering drugs and antigens. In addition, self-adjuvanting recombinant lipoproteins (rlipoproteins) can enhance Th1 anti-tumor immune responses via the TLR2 signaling pathway. To generate a liposomal rlipoprotein for a cancer immunotherapeutic vaccine, we assessed 3 types of synthetic liposomes for use with the rlipoproteins rlipoE7m and rlipoOVA. We determined that the cationic liposome DOTAP could stabilize anionic rlipoproteins and delay rlipoprotein release. Surprisingly, rlipoproteins and DOTAP could synergistically up-regulate CD83 expression in bone marrow-derived dendritic cells (BMDCs). Compared with other liposome formulations, the rlipoprotein/DOTAP formulation elicited higher cytotoxic T-lymphocyte (CTL) responses. To explore the mechanism of BMDC activation by rlipoprotein/DOTAP, we assessed the production of reactive oxygen species (ROS) and the TNF-α secretion of BMDCs. We observed that rlipoprotein/DOTAP induced ROS to the same extent as DOTAP did. In addition, TLR2 signaling was also required for the TNF-α secretion of rlipoprotein/DOTAP-treated BMDCs. Moreover, compared with rlipoOVA-treated BMDCs, rlipoOVA/DOTAP-treated BMDCs increased the levels of IFN-γ produced by OVA-specific T cells. We also observed that rlipoE7m/DOTAP treatment but not rlipoE7m treatment delayed tumor growth. These results indicate that the rlipoprotein/DOTAP formulation can synergistically activate BMDCs via ROS and the TLR2 signaling pathway. In summary, rlipoprotein/DOTAP is a novel and stable formulation for cancer immunotherapy.

Gut dendritic cell activation links an altered colonic microbiome to mucosal and systemic T-cell activation in untreated HIV-1 infection

HIV-1-associated disruption of intestinal homeostasis is a major factor contributing to chronic immune activation and inflammation. Dendritic cells (DCs) are crucial in maintaining intestinal homeostasis, but the impact of HIV-1 infection on intestinal DC number and function has not been extensively studied. We compared the frequency and activation/maturation status of colonic myeloid DC (mDC) subsets (CD1c(+) and CD1c(neg)) and plasmacytoid DCs in untreated HIV-1-infected subjects with uninfected controls. Colonic mDCs in HIV-1-infected subjects had increased CD40 but decreased CD83 expression, and CD40 expression on CD1c(+) mDCs positively correlated with mucosal HIV-1 viral load, with mucosal and systemic cytokine production, and with frequencies of activated colon and blood T cells. Percentage of CD83(+)CD1c(+) mDCs negatively correlated with frequencies of interferon-γ-producing colon CD4(+) and CD8(+) T cells. CD40 expression on CD1c(+) mDCs positively associated with abundance of high prevalence mucosal Prevotella copri and Prevotella stercorea but negatively associated with a number of low prevalence mucosal species, including Rumminococcus bromii. CD1c(+) mDC cytokine production was greater in response to in vitro stimulation with Prevotella species relative to R. bromii. These findings suggest that, during HIV infection, colonic mDCs become activated upon exposure to mucosal pathobiont bacteria leading to mucosal and systemic immune activation.

Identification of Interleukin-1β-Producing Monocytes That Are Susceptible to Pyronecrotic Cell Death in Patients With Neonatal-Onset Multisystem Inflammatory Disease

OBJECTIVE

Spontaneous inflammatory responses initiated by NLRP3 mutations promote inflammasome-mediated interleukin-1β (IL-1β) processing and release and can induce rapid necrotic cell death. The cells that produce IL-1β in neonatal-onset multisystem inflammatory disease (NOMID) have not been clearly identified, nor have the mechanisms mediating IL-1β release and cell death been completely elucidated.

METHODS

Whole blood cells were stimulated with lipopolysaccharide (LPS) in the presence of cathepsin B and caspase 1 inhibitors, followed by ATP treatment. Supernatants were collected and incubated with IL-1β-capturing beads. Cells were fixed, permeabilized, and stained for a combination of cell surface and intracellular markers, and a novel flow cytometry bead-based assay was used to measure secreted IL-1β. LPS-stimulated cells were also evaluated using immunofluorescence microscopy.

RESULTS

Monocytes characterized by CD14(high) -CD16(low) expression and intracellular CD83 were increased in NOMID patients and were responsible for the majority of IL-1β production in response to LPS stimulation. This population of monocytes also underwent a rapid death response with LPS alone that is temporally associated with IL-1β and ASC release and has characteristic features of pyronecrotic but not pyroptotic cell death. Inhibition of cell death reduced IL-1β production from NOMID patient cells. In addition, IL-1 triggered cell death in monocytes from NOMID patients.

CONCLUSION

Our findings indicate that monocytes are the predominant IL-1β-producing cell population in the peripheral blood of NOMID patients. Furthermore, they suggest that IL-1 receptor blockade may work in part by preventing pyronecrotic cell death, which may be an important target in NOMID and other forms of cryopyrin-associated periodic syndromes.

The Polyunsaturated Fatty Acids Arachidonic Acid and Docosahexaenoic Acid Induce Mouse Dendritic Cells Maturation but Reduce T-Cell Responses In Vitro

Long-chain polyunsaturated fatty acids (PUFAs) might regulate T-cell activation and lineage commitment. Here, we measured the effects of omega-3 (n-3), n-6 and n-9 fatty acids on the interaction between dendritic cells (DCs) and naïve T cells. Spleen DCs from BALB/c mice were cultured in vitro with ovalbumin (OVA) with 50 μM fatty acids; α-linolenic acid, arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), linoleic acid or oleic acid and thereafter OVA-specific DO11.10 T cells were added to the cultures. Fatty acids were taken up by the DCs, as shown by gas chromatography analysis. After culture with arachidonic acid or DHA CD11c⁺ CD11b⁺ and CD11c⁺ CD11b^neg DCs expressed more CD40, CD80, CD83, CD86 and PDL-1, while IA^d remained unchanged. However, fewer T cells co-cultured with these DCs proliferated (CellTrace Violet^low) and expressed CD69 or CD25, while more were necrotic (7AAD⁺). We noted an increased proportion of T cells with a regulatory T cell (Treg) phenotype, i.e., when gating on CD4⁺ FoxP3⁺ CTLA-4⁺, CD4⁺ FoxP3⁺ Helios⁺ or CD4⁺ FoxP3⁺ PD-1⁺, in co-cultures with arachidonic acid- or DHA-primed DCs relative to control cultures. The proportion of putative Tregs was inversely correlated to T-cell proliferation, indicating a suppressive function of these cells. With arachidonic acid DCs produced higher levels of prostaglandin E₂ while T cells produced lower amounts of IL-10 and IFNγ. In conclusion arachidonic acid and DHA induced up-regulation of activation markers on DCs. However arachidonic acid- and DHA-primed DCs reduced T-cell proliferation and increased the proportion of T cells expressing FoxP3, indicating that these fatty acids can promote induction of regulatory T cells.

Connexin43 knockdown in bone marrow‑derived dendritic cells by small interfering RNA leads to a diminished T-cell stimulation

Dendritic cells, the most powerful type of antigen‑presenting cells, have the unique ability to induce primary immune responses. Connexin43 expression is upregulated to increase gap junctions when immune cells are exposed to inflammatory factors. The present study applied small‑interfering RNA (siRNA) to decrease connexin43 expression. The results showed that silencing of connexin43 using siRNA resulted in arrest of bone marrow‑derived dendritic cell (BM‑DC) maturation as evidenced by reduced expression of major histocompatibility complex II, CD40, CD80 and CD86. Functionally, connexin43‑silenced BM‑DC showed a markedly decreased capability to induce T-cell stimulation. In conclusion, the present study demonstrated that antigens present on BM‑DCs can be suppressed by connexin43 knockdown in BM‑DCs. The present study therefore presented an effective method to modulate the immunology of BM‑DCs.

Nonspreading Rift Valley Fever Virus Infection of Human Dendritic Cells Results in Downregulation of CD83 and Full Maturation of Bystander Cells

Vaccines based on nonspreading Rift Valley fever virus (NSR) induce strong humoral and robust cellular immune responses with pronounced Th1 polarisation. The present work was aimed to gain insight into the molecular basis of NSR-mediated immunity. Recent studies have demonstrated that wild-type Rift Valley fever virus efficiently targets and replicates in dendritic cells (DCs). We found that NSR infection of cultured human DCs results in maturation of DCs, characterized by surface upregulation of CD40, CD80, CD86, MHC-I and MHC-II and secretion of the proinflammatory cytokines IFN-β, IL-6 and TNF. Interestingly, expression of the most prominent marker of DC maturation, CD83, was consistently downregulated at 24 hours post infection. Remarkably, NSR infection also completely abrogated CD83 upregulation by LPS. Downregulation of CD83 was not associated with reduced mRNA levels or impaired CD83 mRNA transport from the nucleus and could not be prevented by inhibition of the proteasome or endocytic degradation pathways, suggesting that suppression occurs at the translational level. In contrast to infected cells, bystander DCs displayed full maturation as evidenced by upregulation of CD83. Our results indicate that bystander DCs play an important role in NSR-mediated immunity.

L Particles Transmit Viral Proteins from Herpes Simplex Virus 1-Infected Mature Dendritic Cells to Uninfected Bystander Cells, Inducing CD83 Downmodulation

Mature dendritic cells (mDCs) are known as the most potent antigen-presenting cells (APCs) since they are also able to prime/induce naive T cells. Thus, mDCs play a pivotal role during the induction of antiviral immune responses. Remarkably, the cell surface molecule CD83, which was shown to have costimulatory properties, is targeted by herpes simplex virus 1 (HSV-1) for viral immune escape. Infection of mDCs with HSV-1 results in downmodulation of CD83, resulting in reduced T cell stimulation. In this study, we report that not only infected mDCs but also uninfected bystander cells in an infected culture show a significant CD83 reduction. We demonstrate that this effect is independent of phagocytosis and transmissible from infected to uninfected mDCs. The presence of specific viral proteins found in these uninfected bystander cells led to the hypothesis that viral proteins are transferred from infected to uninfected cells via L particles. These L particles are generated during lytic replication in parallel with full virions, called H particles. L particles contain viral proteins but lack the viral capsid and DNA. Therefore, these particles are not infectious but are able to transfer several viral proteins. Incubation of mDCs with L particles indeed reduced CD83 expression on uninfected bystander DCs, providing for the first time evidence that functional viral proteins are transmitted via L particles from infected mDCs to uninfected bystander cells, thereby inducing CD83 downmodulation.

IMPORTANCE

HSV-1 has evolved a number of strategies to evade the host's immune system. Among others, HSV-1 infection of mDCs results in an inhibited T cell activation caused by degradation of CD83. Interestingly, CD83 is lost not only from HSV-1-infected mDCs but also from uninfected bystander cells. The release of so-called L particles, which contain several viral proteins but lack capsid and DNA, during infection is a common phenomenon observed among several viruses, such as human cytomegalovirus (HCMV), Epstein-Barr virus, and HSV-1. However, the detailed function of these particles is poorly understood. Here, we provide for the first time evidence that functional viral proteins can be transferred to uninfected bystander mDCs via L particles, revealing important biological functions of these particles during lytic replication. Therefore, the transfer of viral proteins by L particles to modulate uninfected bystander cells may represent an additional strategy for viral immune escape.

Toscana virus infects dendritic and endothelial cells opening the way for the central nervous system

Toscana virus (TOSV) is a Phlebovirus responsible for human neurological infections in endemic Mediterranean areas. The main viral target is the central nervous system, with viremia as a way of dissemination throughout the host. This study was aimed at understanding the spread of TOSV in the host by identifying the cell population infected by the virus and the vehicle to the organs. In vivo studies provided evidence that endothelial cells are infected by TOSV, indicating their potential role in the diffusion of the virus following viremic spread. These results were further confirmed in vitro. Human peripheral mononuclear blood cells were infected with TOSV; only monocyte-derived dendritic cells were identified as susceptible to TOSV infection. Productive viral replication was then observed in human monocyte-derived dendritic cells (moDCs) and in human endothelial cells by recovery of the virus from a cell supernatant. Interleukin-6 was produced by both cell types upon TOSV infection, mostly by endothelial cells, while moDCs particularly expressed TNF-α, which is known to induce a long-lasting decrease in endothelial cell barrier function. These cells could therefore be implicated in the spread of the virus in the host and in the infection of tissues that are affected by the disease, such as the central nervous system. The identification of in vitro and in vivo TOSV cell targets is an important tool for understanding the pathogenesis of the infection, providing new insight into virus-cell interaction for improved knowledge and control of this viral disease.

Effect of thymosin α₁ on the phenotypic and functional maturation of dendritic cells from children with acute lymphoblastic leukemia

To determine the effect of thymosin α1 (Tα1) on the phenotypic and functional maturation of HL‑60 cells, freeze‑thaw antigen‑loaded dendritic cells (DCs) were derived from peripheral blood mononuclear cells (PBMCs) of children with acute lymphoblastic leukemia (ALL). The DCs were generated from the PBMC samples that were collected from the PB of 10 consecutive ALL children. On day 3 of culturing, the cells in the antigen + no Tα1 (AN) and antigen + Tα1 (AT) groups were incubated with 100 µl lysates obtained from freeze‑thaw cycling. After 5 days of incubation, the AT group was administered with 100 ng/ml Tα1. On day 8, the DCs were stained with fluorescein isothiocyanate‑conjugated cluster of differentiation (CD)1a, CD83 and HLA‑DR antibodies and analyzed by flow cytometry. In addition, the killing activity of cytotoxic T lymphocytes (CTLs) from the different groups on wild‑type leukemia cells was measured. The DCs in the AT group exhibited more apparent, characteristic dendritic morphologies than the control and AN group DCs. Furthermore, the lowest expression level of CD1a, and the highest expression of CD83 and HLA‑DR were observed in the AT group when compared with the AN and control groups (P<0.05). The lactate dehydrogenase release assay demonstrated that the killing rate of CTL in the AT group was significantly higher than that in the control and AN groups (P<0.01). Thus, Tα1 may markedly promote the phenotypic and functional maturation of DCs, and may serve as a suitable immunomodulator of DC‑based immunotherapy for treatment of hematological malignancies.

Continuous expression of CD83 on activated human CD4⁺ T cells is correlated with their differentiation into induced regulatory T cells

CD83 is a widely recognized surface marker for mature dendritic cells, which are essential for priming naïve CD4+ T cells into effector cells. However, CD83 is also expressed on activated CD4+ T cells, which remains an enigma in T‑cell mediated immunity. Therefore, the identification of the biological features and regulation of the expression of CD83 on activated CD4+ T cells is important in understanding the function of CD83 in the adaptive immune response. The present study revealed a time‑dependent manner of the expression of CD83 on anti‑CD3/CD28‑stimulated human CD4+ T cells, which is characterized by the maximum expression at day 2 and a significant decrease at day 3. The reduced expression is not a result of a reduced rate of cell proliferation. The activation of interleukin‑2 and secretion of interferon‑γ accumulated progressively from day 1 to 3. Of note, sustained expression of CD83 was observed when CD4+ T cells were induced by transforming growth factor-β to differentiate into CD4+CD25+ forkhead box P3+ regulatory T (iTreg) cells. Confocal immunofluorescence microscopy analysis demonstrated that CD83 was highly co‑localized with CD25 on activated CD4+ T cells. In conclusion, the findings of the present study suggested that the continuous expression of CD83 on activated human CD4+ T cells is correlated with their differentiation into iTreg cells.

CD83 and GRASP55 interact in human dendritic cells

CD83 is one of the best known surface markers for mature human dendritic cells (DCs). The full-length 45 kDa type-I membrane-bound form (mbCD83) is strongly glycosylated upon DCs maturation. As co-stimulatory properties of CD83 are attributed to mbCD83 surface expression is required for efficient T-cell stimulation by mature DCs. By yeast two-hybrid screening, we were able to identify GRASP55 as interaction partner of CD83. DCs maturation induces endogenous CD83 protein expression with simultaneous regulation of CD83 glycosylation, interaction and co-localization with GRASP55 and CD83 surface exposure. GRASP55 is especially known for its role in maintaining Golgi architecture, but also plays a role in Golgi transport of specific cargo proteins bearing a C-terminal valine residue. Here we additionally demonstrate that binding of CD83 and GRASP55 rely on the C-terminal TELV-motif of CD83. Mutation of this TELV-motif not only disrupted binding to GRASP55, but also altered the glycosylation pattern of CD83 and reduced its membrane expression. Here we show for the first time that GRASP55 interacts with CD83 shortly after induction of DC maturation and that this interaction plays a role in CD83 glycosylation as well as in surface expression of CD83 on DCs.

Induction of indoleamine 2,3-dioxygenase by Borrelia burgdorferi in human immune cells correlates with pathogenic potential

Borrelia burgdorferi, the bacterial agent of Lyme disease, induces the production of type I IFNs by human DCs through TLR7 and TLR9 signaling. This type I IFN response occurs in a genotype-dependent manner, with significantly higher levels of IFN-α elicited by B. burgdorferi strains that have a greater capacity for causing disseminated infection. A B. burgdorferi strain that was previously shown to induce IFN-α was found to elicit significantly higher levels of IDO1 protein and its downstream metabolite, kynurenine, compared with a B. burgdorferi mutant that lacks a single linear plasmid (lp36); this mutant is unable to induce IFN-α and is severely attenuated for infectivity in mice. Production of IDO by mDC and pDC populations, present within human PBMCs, was concomitant with increased expression of the DC maturation markers, CD83 and CCR7. The defects in IDO production and expression of CD83 and CCR7 could be restored by complementation of the mutant with lp36. Maximal IDO production in response to the wild-type strain was dependent on contributions by both type I IFN and IFN-γ, the type II IFN. Induction of IDO was mediated by the same TLR7-dependent recognition of B. burgdorferi RNA that contributes to the production of type I IFNs by human DCs. The ability of IFN-α-inducing B. burgdorferi strains to stimulate production of IDO and kynurenines may be a mechanism that is used by the pathogen to promote localized immunosuppression and facilitate hematogenous dissemination.

Soluble CD83 ameliorates experimental colitis in mice

The physiological balance between pro- and anti-inflammatory processes is dysregulated in inflammatory bowel diseases (IBD) as in Crohn's disease and ulcerative colitis. Conventional therapy uses anti-inflammatory and immunosuppressive corticosteroids to treat acute-phase symptoms. However, low remission rate and strong side effects of these therapies are not satisfying. Thus, there is a high medical need for new therapeutic strategies. Soluble CD83, the extracellular domain of the transmembrane CD83 molecule, has been reported to have interesting therapeutic and immunosuppressive properties by suppressing dendritic cell (DC)-mediated T-cell activation and inducing tolerogenic DCs. However, the expression and function of CD83 in IBD is still unknown. Here, we show that CD83 expression is upregulated by different leukocyte populations in a chemical-induced murine colitis model. Furthermore, in this study the potential of sCD83 to modulate colitis using an experimental murine colitis model was investigated. Strikingly, sCD83 ameliorated the clinical disease symptoms, drastically reduced mortality, and strongly decreased inflammatory cytokine expression in mesenteric lymph nodes and colon. The infiltration of macrophages and granulocytes into colonic tissues was vigorously inhibited. Mechanistically, we could show that sCD83-induced expression of indolamine 2,3-dioxygenase is essential for its protective effects.

Herpes simplex virus type 1 ICP0 induces CD83 degradation in mature dendritic cells independent of its E3 ubiquitin ligase function

Mature dendritic cells (mDCs) are the most potent antigen-presenting cells known today, as they are the only antigen-presenting cells able to induce naïve T-cells. Therefore, they play a crucial role during the induction of effective antiviral immune responses. Interestingly, the surface molecule CD83 expressed on mDCs is targeted by several viruses. As CD83 has been shown to exert co-stimulatory functions on mDCs, its downmodulation represents a viral immune escape mechanism. Mechanistically, it has been shown that herpes simplex virus type 1 infection leads to proteasomal degradation of CD83, resulting in a strongly diminished T-cell stimulatory capacity of the infected mDC. Previous data suggest that the viral immediate-early protein ICP0 (infected-cell protein 0) plays an important role in this process. In the present study, we showed that ICP0 is sufficient to induce CD83 degradation in the absence of any other viral factor. However, the mechanism of ICP0-mediated CD83 degradation is not yet understood. Here, we provide evidence that ubiquitination of lysine residues is, despite the published E3 ubiquitin ligase activity of ICP0, not necessary for CD83 degradation. This finding was underlined by the observation that expression of an ICP0 mutant lacking the E3 ubiquitin ligase domain in mDCs still induced CD83 degradation. Finally, inhibition of E1 activating enzyme using the specific inhibitor 4[4-(5-nitro-furan-2-ylmethylene)-3.5-dioxo-pyrazolidin-1-yl]-benzoic acid ethyl ester did not prevent CD83 degradation. Taken together, our data provide strong evidence that ICP0 alone induces CD83 degradation independent of its E3 ubiquitin ligase function and of the ubiquitin machinery.

Dendritic cell membrane CD83 enhances immune responses by boosting intracellular calcium release in T lymphocytes

CD83 is a marker of mDCs directly related to their lymphostimulatory ability. Some data suggest that it has a central role in the immune system regulation, but how this function is performed remains to be determined. This work aimed to analyze the influence of CD83, present in mDCs, in the modulation of calcium signaling in T lymphocytes. Mo were differentiated into iDCs and activated with TNF-α. iDCs were treated, 4 h before activation, with siRNACD83, to reduce CD83 expression. Purified allogeneic T lymphocytes were labeled with the calcium indicator Fluo-4-AM, and calcium mobilization in the presence of mDCs was analyzed. CD83 knockdown mDCs induced lower calcium signal amplitude in T lymphocytes (29.0±10.0) compared with siRNAscr-treated mDCs (45.5±5.3). In another set of experiments, surface mDC CD83 was blocked with a specific mAb, and again, decreased calcium signaling in T lymphocytes was detected by flow cytometry and microscopy (fluorescence and confocal). In the presence of antibody, the percentage of responding T cells was reduced from 58.14% to 34.29%. As expected, anti-CD83 antibodies also reduced the proliferation of T lymphocytes (as assessed by CFSE dilution). Finally, in the absence of extracellular calcium, CD83 antibodies abrogated T cell signaling induced by allogeneic mDCs, suggesting that the presence of CD83 in mDC membranes enhances T lymphocyte proliferation by boosting calcium release from intracellular stores in these cells.

The expression and characterization of functionally active soluble CD83 by Pichia pastoris using high-density fermentation

CD83 is a highly glycosylated type I transmembrane glycoprotein that belongs to the immunoglobulin superfamily. CD83 is upregulated during dendritic cell (DC) maturation, which is critical for the initiation of adaptive immune responses. The soluble isoform of CD83 (sCD83) is encoded by alternative splicing from full-length CD83 mRNA and inhibits DC maturation, which suggests that sCD83 acts as a potential immune suppressor. In this study, we developed a sound strategy to express functional sCD83 from Pichia pastoris in extremely high-density fermentation. Purified sCD83 was expressed as a monomer at a yield of more than 200 mg/L and contained N-linked glycosylation sites that were characterized by PNGase F digestion. In vitro tests indicated that recombinant sCD83 bound to its putative counterpart on monocytes and specifically blocked the binding of anti-CD83 antibodies to cell surface CD83 on DCs. Moreover, sCD83 from yeast significantly suppressed ConA-stimulated PBMC proliferation. Therefore, sCD83 that was expressed from the P. pastoris was functionally active and may be used for in vivo and in vitro studies as well as future clinical applications.