Cloning, recombinant expression and biochemical characterization of the murine CD83 molecule which is specifically upregulated during dendritic cell maturation

Characterization of CD83 homologs differently expressed during monocytes differentiation in ginbuna crucian carp, Carassius auratus langsdorfii

CD83 is a costimulatory molecule of antigen-presenting cells (APCs) that plays an important role in eliciting adaptive responses. It is also a well-known surface protein on mature dendritic cells (DCs). Furthermore, monocytes have been reported to differentiate into macrophages and monocyte-derived dendritic cells, which play an important role in innate immunity. CD83 expression affects the activation and maturation of DCs and stimulates cell-mediated immune responses. This study aims to reveal the CD83 expression during monocyte differentiation in teleosts, and the CD83 homologs evolutionary relationship. This study found two distinct CD83 homologs (GbCD83 and GbCD83-L) in ginbuna crucian carp (Gb) and investigated the evolutionary relationship among GbCD83 homologs and other vertebrates and the gene and protein expression levels of the homologs during 4 days of monocyte culture. The phylogenetic tree showed that the two GbCD83 homologs are classified into two distinct branches. Interestingly, only ostariophysians (Gb, common carp, rohu, fathead minnow and channel catfish), but not neoteleosts, mammals, and others, have two CD83 homologs. Morphological observation and colony-stimulating factor-1 receptor (CSF-1R), CD83, CD80/86, and CCR7 gene expressions illustrated that there is a differentiation of monocytes isolated from peripheral blood leukocytes after 4 days. Specifically, gene expression and immunocytochemistry revealed that GbCD83 is mainly expressed on monocytes at the early stage of cell culture, whereas GbCD83-L is expressed in the latter stage. These findings provided the first evidence of differential expression of CD83 homologs during monocytes differentiation in teleost.

Tilting the Balance: Therapeutic Prospects of CD83 as a Checkpoint Molecule Controlling Resolution of Inflammation

Chronic inflammatory diseases and transplant rejection represent major challenges for modern health care. Thus, identification of immune checkpoints that contribute to resolution of inflammation is key to developing novel therapeutic agents for those conditions. In recent years, the CD83 (cluster of differentiation 83) protein has emerged as an interesting potential candidate for such a "pro-resolution" therapy. This molecule occurs in a membrane-bound and a soluble isoform (mCD83 and sCD83, respectively), both of which are involved in resolution of inflammation. Originally described as a maturation marker on dendritic cells (DCs), mCD83 is also expressed by activated B and T cells as well as regulatory T cells (Tregs) and controls turnover of MHC II molecules in the thymus, and thereby positive selection of CD4+ T cells. Additionally, it serves to confine overshooting (auto-)immune responses. Consequently, animals with a conditional deletion of CD83 in DCs or regulatory T cells suffer from impaired resolution of inflammation. Pro-resolving effects of sCD83 became evident in pre-clinical autoimmune and transplantation models, where application of sCD83 reduced disease symptoms and enhanced allograft survival, respectively. Here, we summarize recent advances regarding CD83-mediated resolution of inflammatory responses, its binding partners as well as induced signaling pathways, and emphasize its therapeutic potential for future clinical trials.

Eubacterium rectale Attenuates HSV-1 Induced Systemic Inflammation in Mice by Inhibiting CD83

The purpose of this study was to determine whether administration of the microorganism Eubacterium rectale (E. rectale) could regulate dendritic cell (DC) activation and systemic inflammation in herpes simplex virus type 1-induced Behçet's disease (BD). E. rectale, butyrate-producing bacteria, was administered to BD mice. Peripheral blood leukocytes (PBL) and lymph node cells were isolated and analyzed by flow cytometry. 16S rRNA metagenomic analysis was performed in the feces of mice to determine the differences in the composition of the microbial population between normal and BD mice. Serum cytokine levels were measured by enzyme-linked immunosorbent assay. The frequency of DC activation marker CD83 positive cells was significantly increased in PBL of BD mice. Frequencies of CD83+ cells were also significantly increased in patients with active BD. 16S rRNA metagenomic analysis revealed different gut microbiota composition between normal and BD mice. The administration of E. rectale to BD mice reduced the frequency of CD83+ cells and significantly increased the frequency of NK1.1+ cells with the improvement of symptoms. The co-administration of colchicine and E. rectale also significantly reduced the frequency of CD83+ cells. Differences in gut microbiota were observed between normal mice and BD mice, and the administration of E. rectale downregulated the frequency of CD83, which was associated with BD deterioration. These data indicate that E. rectale could be a new therapeutic adjuvant for BD management.

Porcine soluble CD83 alleviates LPS-induced abortion in mice by promoting Th2 cytokine production, Treg cell generation and trophoblast invasion

CD83, either in its membrance-bound form (mCD83) or soluble form (sCD83), is an important immunomodulatory molecule in humans and mice. While mCD83 is immunostimulatory, sCD83 exhibits striking immunosuppressive activities, suggesting that sCD83 may be used to combat inflammatory diseases, such as rheumatoid arthritis, graft-versus-host disease and habitual abortion. Although many studies had shed lights on the role of CD83 in humans and mice, little is known about CD83 in other animals. Recently, we showed that porcine CD83 had similar biochemical characteristics and immunoregulatory functions as its human counterpart. However, whether porcine sCD83 (psCD83) is involved in maintaining the immunological tolerance at the maternal-fetal interface and thereby prevents embryo loss and abortion during pregnancy is unclear. In this study, we used LPS-induced animal model to analyze the effect of porcine sCD83 on the mouse abortion. Results showed that psCD83 could significantly alleviate LPS-induced abortion in mice, indicating that the psCD83 had the function of fetal protection. Mechanically, psCD83-mediated fetal protection was related to the promotion on Th2 cytokine production, Treg cell differentiation and trophoblast invasion. This study provides a molecular basis for the fetal protection of psCD83, as well as a potential target for the regulation of maternal-fetal interfacial immune tolerance.

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 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.

Membrane-bound and soluble porcine CD83 functions antithetically in T cell activation and dendritic cell differentiation in vitro

Emerging evidence suggests that CD83, a dendritic cells (DCs) maturation marker in humans and mice, may prossess immunomodulatory capacities. Although porcine CD83 shares ∼75% sequence homology with its human counterpart, whether it functions as an immunoregulatory molecule remains unknown. To investigate porcine CD83 function, we deleted it in porcine DCs by RNA intereference. Results show that membrane-bound CD83 (mCD83) promotes DC-mediated T cell proliferation and cytokine production, thus confirming its immunoregulatory capacity. Intriguingly, porcine soluble CD83 (sCD83) treatment instead led to inhibition of DC-mediated T cell activation. Moreover, porcine sCD83 also inhibited differentiation of prepheral blood mononuclear cells (PBMCs) into DCs. These results collectively indicate that in addition to being a DC maturation maker, both membrane bound and souble porcine CD83 serve as immunoregulatory molecules with opposite effects on DC-mediated T cell activation and DC differentiation.

Inhibition of CD83 Alleviates Systemic Inflammation in Herpes Simplex Virus Type 1-Induced Behçet's Disease Model Mouse

Behçet's disease (BD) is an autoinflammatory disease that can lead to life- and sight-threating complications. Dendritic cells (DCs) are the most potent antigen-presenting cells that can regulate multiple inflammatory pathways. The objective of this study was to investigate the association of the DC stimulatory molecule CD83 with BD. Frequencies of costimulatory molecules expressing DCs in peripheral blood leukocytes (PBL) were measured by flow cytometry (FACS). The severity of symptoms in HSV-1-induced BD symptomatic mice was also assessed. Frequencies of CD83-positive cells were significantly increased in mice exhibiting BD symptoms, compared to those in asymptomatic mice. Abatacept, a CD80/86 blocker, significantly decreased the frequencies of CD83-positive cells in a time- and dose-dependent manner. BD symptomatic mice treated with Abatacept showed gradual reduction in the severity score of symptoms. Intraperitoneal injection of CD83 siRNA significantly reduced the frequencies of CD83-positive cells in PBL and peritoneal macrophages. After CD83 siRNA injection, BD symptoms of mice were improved and disease severity was decreased. Discontinuation of CD83 siRNA deteriorated symptoms while readministration of CD83 siRNA again improved BD symptoms of mice. These results clearly indicate the involvement of CD83-expressing cells in the inflammatory symptoms of BD. Therefore, CD83 might be useful as a therapeutic target for BD.

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.

Rainbow Trout Red Blood Cells Exposed to Viral Hemorrhagic Septicemia Virus Up-Regulate Antigen-Processing Mechanisms and MHC I&II, CD86, and CD83 Antigen-presenting Cell Markers

Nucleated teleost red blood cells (RBCs) are known to express molecules from the major histocompatibility complex and peptide-generating processes such as autophagy and proteasomes, but the role of RBCs in antigen presentation of viruses have not been studied yet. In this study, RBCs exposed ex vivo to viral hemorrhagic septicemia virus (VHSV) were evaluated by means of transcriptomic and proteomic approaches. Genes and proteins related to antigen presentation molecules, proteasome degradation, and autophagy were up-regulated. VHSV induced accumulation of ubiquitinated proteins in ex vivo VHSV-exposed RBCs and showed at the same time a decrease of proteasome activity. Furthermore, induction of autophagy was detected by evaluating LC3 protein levels. Sequestosome-1/p62 underwent degradation early after VHSV exposure, and it may be a link between ubiquitination and autophagy activation. Inhibition of autophagosome degradation with niclosamide resulted in intracellular detection of N protein of VHSV (NVHSV) and p62 accumulation. In addition, antigen presentation cell markers, such as major histocompatibility complex (MHC) class I & II, CD83, and CD86, increased at the transcriptional and translational level in rainbow trout RBCs exposed to VHSV. In summary, we show that nucleated rainbow trout RBCs can degrade VHSV while displaying an antigen-presenting cell (APC)-like profile.

Porcine CD83 is a glycosylated dimeric protein existing naturally in membrane-bound and soluble forms

Human and mouse CD83 have been well characteized, however, the other mammalian CD83 genes have not been cloned and characterized. In this study, the porcine CD83 (pCD83) was cloned, expressed and characterized, and showed that the pCD83 gene has 81% and 74% homologies with humans and mice, respectively, which was identified to be glycosylated when expressed in eukaryotic cells, existing naturally in two forms: membrance-bound CD83 (mCD83) and soluble CD83 (sCD83), the latter was identified to be generated mainly from mCD83 by proteolytic shedding. The pCD83 was a dimmer mediated by intermolecular disulfide bond formed by the fifth cysteine in the exrtracellular domain. Functionally, the recombinant porcine sCD83 was preliminarily tested to have the ability to inhibit DC-mediated T cell activition. This study provided necessary fundation for further investigation on pCD83 functions.

The Analysis of CD83 Expression on Human Immune Cells Identifies a Unique CD83+-Activated T Cell Population

CD83 is a member of the Ig gene superfamily, first identified in activated lymphocytes. Since then, CD83 has become an important marker for defining activated human dendritic cells (DC). Several potential CD83 mRNA isoforms have been described, including a soluble form detected in human serum, which may have an immunosuppressive function. To further understand the biology of CD83, we examined its expression in different human immune cell types before and after activation using a panel of mouse and human anti-human CD83 mAb. The mouse anti-human CD83 mAbs, HB15a and HB15e, and the human anti-human CD83 mAb, 3C12C, were selected to examine cytoplasmic and surface CD83 expression, based on their different binding characteristics. Glycosylation of CD83, the CD83 mRNA isoforms, and soluble CD83 released differed among blood DC, monocytes, and monocyte-derived DC, and other immune cell types. A small T cell population expressing surface CD83 was identified upon T cell stimulation and during allogeneic MLR. This subpopulation appeared specifically during viral Ag challenge. We did not observe human CD83 on unstimulated human natural regulatory T cells (Treg), in contrast to reports describing expression of CD83 on mouse Treg. CD83 expression was increased on CD4+, CD8+ T, and Treg cells in association with clinical acute graft-versus-host disease in allogeneic hematopoietic cell transplant recipients. The differential expression and function of CD83 on human immune cells reveal potential new roles for this molecule as a target of therapeutic manipulation in transplantation, inflammation, and autoimmune diseases.

Distinct immune tones are established by Lactococcus lactis BFE920 and Lactobacillus plantarum FGL0001 in the gut of olive flounder (Paralichthys olivaceus)

The immune tone is defined as an immunological state during which the readiness for immune response is potentiated. The establishment of immune tone in the gut of olive flounder (Paralichthys olivaceus) was investigated by feeding Lactococcus lactis BFE920 (LL) or Lactobacillus plantarum FGL0001 (LP). LL-fed flounder showed significantly increased levels of regulatory genes (FOXP3, IL-10, and TGF-β1), CD18, and CD83 in the gut. In contrast, LP feeding drastically increased proinflammatory genes (T-bet, IL-1β, and IFN-γ) and CD18. This indicates that LL and LP establish different types of local immune tones in the gut through differential activation of innate immune cells: LL activates both macrophages and dendritic cells while LP activates macrophages only. Both of the immune tones required at least a total of 6 probiotic feeds during 72 h for a stable establishment. Once established, the type of immune tone remained steady even up to 30 days (a total of 60 feeds) probiotics feeding. The LL-induced regulatory immune tone enhanced the level of occludin, a tight junction molecule, significantly more than that observed with the proinflammatory immune tone established by LP feeding. Consequently, LL-fed fish showed considerably lower gut permeability than that of the LP-fed group. Furthermore, when orally challenged by Edwardsiella tarda, LL-fed flounder survived at a significantly higher rate than LP-fed fish. The data clearly demonstrate that individual probiotics establish distinct types of immune tone in the fish gut, which in turn influences the immunological status as well as the physiology of the gut. Selection of proper probiotics may be essential for optimal effects in aquaculture farming.

Establishing Porcine Monocyte-Derived Macrophage and Dendritic Cell Systems for Studying the Interaction with PRRSV-1

Monocyte-derived macrophages (MoMØ) and monocyte-derived dendritic cells (MoDC) are two model systems well established in human and rodent systems that can be used to study the interaction of pathogens with host cells. Porcine reproductive and respiratory syndrome virus (PRRSV) is known to infect myeloid cells, such as macrophages (MØ) and dendritic cells (DC). Therefore, this study aimed to establish systems for the differentiation and characterization of MoMØ and MoDC for subsequent infection with PRRSV-1. M-CSF differentiated MoMØ were stimulated with activators for classical (M1) or alternative (M2) activation. GM-CSF and IL-4 generated MoDC were activated with the well established maturation cocktail containing PAMPs and cytokines. In addition, MoMØ and MoDC were treated with dexamethasone and IL-10, which are known immuno-suppressive reagents. Cells were characterized by morphology, phenotype, and function and porcine MØ subsets highlighted some divergence from described human counterparts, while MoDC, appeared more similar to mouse and human DCs. The infection with PRRSV-1 strain Lena demonstrated different replication kinetics between MoMØ and MoDC and within subsets of each cell type. While MoMØ susceptibility was significantly increased by dexamethasone and IL-10 with an accompanying increase in CD163/CD169 expression, MoDC supported only a minimal replication of PRRSV These findings underline the high variability in the susceptibility of porcine myeloid cells toward PRRSV-1 infection.

CD83 Modulates B Cell Activation and Germinal Center Responses

CD83 is a maturation marker for dendritic cells. In the B cell lineage, CD83 is expressed especially on activated B cells and on light zone B cells during the germinal center (GC) reaction. The function of CD83 during GC responses is unclear. CD83(-/-) mice have a strong reduction of CD4(+) T cells, which makes it difficult to analyze a functional role of CD83 on B cells during GC responses. Therefore, in the present study we generated a B cell-specific CD83 conditional knockout (CD83 B-cKO) model. CD83 B-cKO B cells show defective upregulation of MHC class II and CD86 expression and impaired proliferation after different stimuli. Analyses of GC responses after immunization with various Ags revealed a characteristic shift in dark zone and light zone B cell numbers, with an increase of B cells in the dark zone of CD83 B-cKO mice. This effect was not accompanied by alterations in the level of IgG immune responses or by major differences in affinity maturation. However, an enhanced IgE response was observed in CD83 B-cKO mice. Additionally, we observed a strong competitive disadvantage of CD83-cKO B cells in GC responses in mixed bone marrow chimeras. Furthermore, infection of mice with Borrelia burgdorferi revealed a defect in bacterial clearance of CD83 B-cKO mice with a shift toward a Th2 response, indicated by a strong increase in IgE titers. Taken together, our results show that CD83 is important for B cell activation and modulates GC composition and IgE Ab responses in vivo.

Enhanced Anti-Tumor Efficacy through a Combination of Integrin αvβ6-Targeted Photodynamic Therapy and Immune Checkpoint Inhibition

“Training” the host immune system to recognize and systemically eliminate residual tumor lesions and micrometastases is a promising strategy for cancer therapy. In this study, we investigated whether integrin αvβ6-targeted photodynamic therapy (PDT) of tumors using a phthalocyanine dye-labeled probe (termed DSAB-HK) could trigger the host immune response, and whether PDT in combination with anti-PD-1 immune checkpoint inhibition could be used for the effective therapy of primary tumors and metastases. By near-infrared fluorescence imaging, DSAB-HK was demonstrated to specifically target either subcutaneous tumors in a 4T1 mouse breast cancer model or firefly luciferase stably transfected 4T1 (4T1-fLuc) lung metastatic tumors. Upon light irradiation, PDT by DSAB-HK significantly inhibited the growth of subcutaneous 4T1 tumors, and in addition promoted the maturation of dendritic cells and their production of cytokines, which subsequently stimulated the tumor recruitment of CD8⁺ cytotoxic T lymphocytes. Furthermore, DSAB-HK PDT of the first tumor followed by PD-1 blockade markedly suppressed the growth of a second subcutaneous tumor, and also slowed the growth of 4T1-fLuc lung metastasis as demonstrated by serial bioluminescence imaging. Together, our results demonstrated the synergistic effect of tumor-targeted PDT and immune checkpoint inhibition for improving anti-tumor immunity and suppressing tumor growth/metastasis.

Improved antitumor activity of immunotherapy with BRAF and MEK inhibitors in BRAF(V600E) melanoma

Combining immunotherapy and BRAF targeted therapy may result in improved antitumor activity with the high response rates of targeted therapy and the durability of responses with immunotherapy. However, the first clinical trial testing the combination of the BRAF inhibitor vemurafenib and the CTLA4 antibody ipilimumab was terminated early because of substantial liver toxicities. MEK [MAPK (mitogen-activated protein kinase) kinase] inhibitors can potentiate the MAPK inhibition in BRAF mutant cells while potentially alleviating the unwanted paradoxical MAPK activation in BRAF wild-type cells that lead to side effects when using BRAF inhibitors alone. However, there is the concern of MEK inhibitors being detrimental to T cell functionality. Using a mouse model of syngeneic BRAF(V600E)-driven melanoma, SM1, we tested whether addition of the MEK inhibitor trametinib would enhance the antitumor activity of combined immunotherapy with the BRAF inhibitor dabrafenib. Combination of dabrafenib and trametinib with pmel-1 adoptive cell transfer (ACT) showed complete tumor regression, increased T cell infiltration into tumors, and improved in vivo cytotoxicity. Single-agent dabrafenib increased tumor-associated macrophages and T regulatory cells (Tregs) in tumors, which decreased with the addition of trametinib. The triple combination therapy resulted in increased melanosomal antigen and major histocompatibility complex (MHC) expression and global immune-related gene up-regulation. Given the up-regulation of PD-L1 seen with dabrafenib and/or trametinib combined with antigen-specific ACT, we tested the combination of dabrafenib, trametinib, and anti-PD1 therapy in SM1 tumors, and observed superior antitumor effect. Our findings support the testing of triple combination therapy of BRAF and MEK inhibitors with immunotherapy in patients with BRAF(V600E) mutant metastatic melanoma.

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.

Anti-CD83 promotes IgG1 isotype switch in marginal zone B cells in response to TI-2 antigen

CD83 is a transmembrane glycoprotein that is rapidly up-regulated on activated B cells. Although CD83 itself is incapable to transduce intracellular signaling, it acts as a negative regulator of B cell function. We have recently described that a single application of anti-CD83 antibody results in dramatically enhanced production of antigen-specific IgG1 but not other isotypes upon immunization of mice with the TI-2 model antigen (Ag) NIP-Ficoll. This effect was mediated by the binding of anti-CD83 to CD83 on the surface of B cells themselves. In the current study we show that administration of anti-CD83 enhances IgG1-production independent of IL-4. Application of anti-CD83 does not alter the proliferation and general expansion of NIP-specific B cells. In the presence of anti-CD83, immunized mice develop normal frequencies of plasmablasts in response to NIP-Ficoll of which an increased number produces IgG1. These cells localize in extrafollicular foci in the spleen of immunized mice and originate from the marginal zone B cell pool. Taken together, our results indicate that CD83 engagement in vivo does not generally enhance B cell activation but selectively promotes IgG1 class switch in marginal zone B cells in response to TI-2 Ag.

Improved antitumor activity of immunotherapy with BRAF and MEK inhibitors in BRAF(V600E) melanoma

Combining immunotherapy and BRAF targeted therapy may result in improved antitumor activity with the high response rates of targeted therapy and the durability of responses with immunotherapy. However, the first clinical trial testing the combination of the BRAF inhibitor vemurafenib and the CTLA4 antibody ipilimumab was terminated early because of substantial liver toxicities. MEK [MAPK (mitogen-activated protein kinase) kinase] inhibitors can potentiate the MAPK inhibition in BRAF mutant cells while potentially alleviating the unwanted paradoxical MAPK activation in BRAF wild-type cells that lead to side effects when using BRAF inhibitors alone. However, there is the concern of MEK inhibitors being detrimental to T cell functionality. Using a mouse model of syngeneic BRAF(V600E)-driven melanoma, SM1, we tested whether addition of the MEK inhibitor trametinib would enhance the antitumor activity of combined immunotherapy with the BRAF inhibitor dabrafenib. Combination of dabrafenib and trametinib with pmel-1 adoptive cell transfer (ACT) showed complete tumor regression, increased T cell infiltration into tumors, and improved in vivo cytotoxicity. Single-agent dabrafenib increased tumor-associated macrophages and T regulatory cells (Tregs) in tumors, which decreased with the addition of trametinib. The triple combination therapy resulted in increased melanosomal antigen and major histocompatibility complex (MHC) expression and global immune-related gene up-regulation. Given the up-regulation of PD-L1 seen with dabrafenib and/or trametinib combined with antigen-specific ACT, we tested the combination of dabrafenib, trametinib, and anti-PD1 therapy in SM1 tumors, and observed superior antitumor effect. Our findings support the testing of triple combination therapy of BRAF and MEK inhibitors with immunotherapy in patients with BRAF(V600E) mutant metastatic melanoma.

Soluble CD83 inhibits human monocyte differentiation into dendritic cells in vitro

Human CD83 is type I transmembrane glycoprotein, mainly expressed on mature dendritic cells (DCs), so it was first described as a molecular marker for mature DC. However, increasing evidence has demonstrated that CD83 is also an immunomodulatory molecule either its membrane-bound CD83 (mCD83) or soluble CD83 (sCD83) released from DCs. Intriguingly, the mCD83 possesses stimulatory effects on immune response, on the contrary, the sCD83 has inhibitory effects. Whether the sCD83 has the inhibitory effects on human monocyte differentiation into DCs is unknown. To this end, we prepared the recombinant human sCD83 in HEK293T cells and treated human monocytes being differentiated into DCs in vitro with the sCD83, and evaluate sCD83 inhibitory effects on immune response by analyzing the surface marker pattern of the cells. The results showed that the sCD83, especially glycosylated sCD83 could bind the monocytes and significantly inhibited the depression of CD14 expressions (P<0.01) and reduced CD1a, CD80, CD86 and MHC II expressions (P<0.01 or P<0.05) during the differentiation, indicating that the sCD83 can inhibit monocyte differentiation into DCs, and suggesting that a negative feedback regulation may exist in monocyte differentiation into DCs based on sCD83 released from the mature DCs.

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.

Identification of dendritic cells, B cell and T cell subsets in Tasmanian devil lymphoid tissue; evidence for poor immune cell infiltration into devil facial tumors

The Tasmanian devil is under threat of extinction due to the transmissible devil facial tumor disease (DFTD). This fatal tumor is an allograft that does not induce an immune response, raising questions about the activity of Tasmanian devil immune cells. T and B cell analysis has been limited by a lack of antibodies, hence the need to produce such reagents. Amino acid sequence analysis revealed that CD4, CD8, IgM, and IgG were closely related to other marsupials. Monoclonal antibodies were produced against CD4, CD8, IgM, and IgG by generating bacterial fusion proteins. These, and commercial antibodies against CD1a and CD83, identified T cells, B cells and dendritic cells by immunohistochemistry. CD4⁺ and CD8⁺ T cells were identified in pouch young thymus, adult lymph nodes, spleen, bronchus‐ and gut‐associated lymphoid tissue. Their anatomical distribution was characteristic of mammalian lymphoid tissues with more CD4⁺ than CD8⁺ cells in lymph nodes and splenic white pulp. IgM⁺ and IgG⁺ B cells were identified in adult lymph nodes, spleen, bronchus‐associated lymphoid tissue and gut‐associated lymphoid tissue, with more IgM⁺ than IgG⁺ cells. Dendritic cells were identified in lymph node, spleen and skin. This distribution is consistent with eutherian mammals and other marsupials, indicating they have the immune cell subsets for an anti‐tumor immunity. Devil facial tumor disease tumors contained more CD8⁺ than CD4⁺ cells, but in low numbers. There were also low numbers of CD1a⁺ and MHC class II⁺ cells, but no CD83⁺ IgM⁺ or IgG⁺ B cells, consistent with poor immune cell infiltration. Anat Rec, 297:925–938, 2014. © 2014 The Authors. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology Published by Wiley Periodicals, Inc.

Isolation and characterization of equine nasal mucosal CD172a + cells

The nasal mucosa surface is continuously confronted with a broad variety of environmental antigens, ranging from harmless agents to potentially harmful pathogens. This area is under rigorous control of professional antigen presenting cells (APCs), such as dendritic cells (DCs) and macrophages. Mucosal APCs play a crucial role in inducing primary immune responses and the establishment of an immunological memory. In the present study, a detailed characterization of CD172a(+) cells, containing the APCs residing in the equine nasal mucosa was performed for the first time. CD172a(+) cells were isolated from collagenase-treated equine nasal mucosa fragments by MACS. Expression of surface markers was determined by flow cytometry and functional analysis was done by measuring the uptake of FITC conjugated ovalbumin (FITC-OVA). Cell surface phenotype of the isolated cells was as follows: 90% CD172a(+), 30% CD1c(+), 46% CD83(+), 42% CD206(+) and 28% MHC II(+). This clearly differs from the phenotype of blood-derived monocytes: 96% CD172a(+), 4% CD1c(+), 11% CD83(+), 9% CD206(+), 72% MHC II(+) and blood monocyte derived DCs: 99% CD172a(+), 13% CD1c(+), 30% CD83(+), 51% CD206(+) and 93% MHC II(+). The CD172a(+) nasal mucosal cells were functionally able to endocytose FITC-OVA but to a lesser degree than monocyte-derived DCs. Together, these results demonstrate that the isolated CD172a(+) nasal mucosal cells resemble immature DCs in the nasal area.

Deoxyhypusine synthase promotes differentiation and proliferation of T helper type 1 (Th1) cells in autoimmune diabetes

In type 1 diabetes, cytokines arising from immune cells cause islet β cell dysfunction even before overt hyperglycemia. Deoxyhypusine synthase catalyzes the crucial hypusine modification of the factor eIF5A, which promotes the translation of a subset of mRNAs involved in cytokine responses. Here, we tested the hypothesis that deoxyhypusine synthase and, secondarily, hypusinated eIF5A contribute to the pathogenesis of type 1 diabetes using the non-obese diabetic (NOD) mouse model. Pre-diabetic NOD mice that received injections of the deoxyhypusine inhibitor N1-guanyl-1,7-diaminoheptane (GC7) demonstrated significantly improved glucose tolerance, more robust insulin secretion, and reduced insulitis compared with control animals. Analysis of tissues from treated mice revealed selective reductions in diabetogenic T helper type 1 (Th1) cells in the pancreatic lymph nodes, a primary site of antigen presentation. Isolated mouse CD90.2(+) splenocytes stimulated in vitro with anti-CD3/anti-CD28 and IL-2 to mimic autoimmune T cell activation exhibited proliferation and differentiation of CD4(+) T cell subsets (Th1, Th17, and Treg), but those treated with the deoxyhypusine synthase inhibitor GC7 showed a dose-dependent block in T cell proliferation with selective reduction in Th1 cells, similar to that observed in NOD mice. Inhibition of deoxyhypusine synthase blocked post-transcriptional expression of CD25, the high affinity IL-2 receptor α chain. Our results suggest a previously unrecognized role for deoxyhypusine synthase in promoting T cell proliferation and differentiation via regulation of CD25. Inhibition of deoxyhypusine synthase may provide a strategy for reducing diabetogenic Th1 cells and preserving β cell function in type 1 diabetes.

Topical application of soluble CD83 induces IDO-mediated immune modulation, increases Foxp3+ T cells, and prolongs allogeneic corneal graft survival

Modulation of immune responses is one of the main research aims in transplant immunology. In this study, we investigate the local immunomodulatory properties of soluble CD83 (sCD83) at the graft-host interface using the high-risk corneal transplantation model. In this model, which mimics the inflammatory status and the preexisting vascularization of high-risk patients undergoing corneal transplantation, allogeneic donor corneas are transplanted onto sCD83-treated recipient animals. This model allows the direct and precise application of the immune modulator at the transplantation side. Interestingly, sCD83 was able to prolong graft survival after systemic application as well as after topical application, which is therapeutically more relevant. The therapeutic effect was accompanied by an increase in the frequency of regulatory T cells and was mediated by the immune-regulatory enzyme IDO and TGF-β. In vitro, sCD83 induced long-term IDO expression in both conventional and plasmacytoid dendritic cells via autocrine or paracrine production of TGF-β, a cytokine previously shown to be an essential mediator of IDO-dependent, long-term tolerance. These findings open new treatment avenues for local immune modulation after organ and tissue transplantation.

Differentiation and activation of equine monocyte-derived dendritic cells are not correlated with CD206 or CD83 expression

Dendritic cells (DC) are the main immune mediators inducing primary immune responses. DC generated from monocytes (MoDC) are a model system to study the biology of DC in vitro, as they represent inflammatory DC in vivo. Previous studies on the generation of MoDC in horses indicated that there was no distinct difference between immature and mature DC and that the expression profile was distinctly different from humans, where CD206 is expressed on immature MoDC whereas CD83 is expressed on mature MoDC. Here we describe the kinetics of equine MoDC differentiation and activation, analysing both phenotypic and functional characteristics. Blood monocytes were first differentiated with equine granulocyte-macrophage colony-stimulating factor and interleukin-4 generating immature DC (iMoDC). These cells were further activated with a cocktail of cytokines including interferon-γ) but not CD40 ligand to obtain mature DC (mMoDC). To determine the expression of a broad range of markers for which no monoclonal antibodies were available to analyse the protein expression, microarray and quantitative PCR analysis were performed to carry out gene expression analysis. This study demonstrates that equine iMoDC and mMoDC can be distinguished both phenotypically and functionally but the expression pattern of some markers including CD206 and CD83 is dissimilar to the human system.

A new monoclonal anti-human CD83 antibody for flow cytometry, western blot analysis, and ELISA

CD83 is expressed on mature dendritic cells (DCs) and many immune cells, including B and T lymphocytes upon activation. CD83 is essential for the development of CD4 single positive T cells and involved in the regulation of peripheral T and B cell responses. Here we generated a new monoclonal antibody against human CD83, which we named ELBE-1. ELBE-1 recognizes a linear epitope and cannot only be applied for Western blot analysis and flow cytometry, but also detects soluble CD83 (sCD83) by ELISA. As with other anti-CD83 antibodies described thus far, ELBE-1 does not influence T cell activation. Nevertheless, it represents a useful new tool for the detection and functional characterization of CD83.

Immunological effects of Oenothein B, an ellagitannin dimer, on dendritic cells

Oenothein B is a unique macrocyclic ellagitannin dimer that has been found in various medicinal plants belonging to Onagraceae, Lythraceae, and Myrtaceae, with diverse biological activities. The immunological effects of tannins in terms of cytokine-release from macrophages and monocytes have been discussed, while the effects on other immunocompetent cells have been the subject of minimal investigation. We evaluated the immunomodulatory effects induced by tannin treatment in human dendritic cells (DCs), which play a critical role in the initial immune response, by measuring the changes in cytokine production, cell differentiation, and cell viability. Oenothein B showed significant down-regulation of the expression of cell surface molecules, CD1a and CD83, suggesting the inhibition of DC differentiation and/or maturation. The suppressive effect on DCs was associated with the induction of apoptosis without the activation of caspase-3/7, 8, and 9, and this was supported by the morphological features indicating significant nuclear condensation. Oenothein B also markedly suppressed the production of inflammatory cytokines, such as IL-1β and IL-6, in a dose-dependent manner. These data may, in part, be able to explain the traditional use of tannin-containing medicinal plants for the treatment of a variety of inflammatory diseases, including inflammatory bowel disease, celiac disease, and rheumatoid arthritis.

Functional identification of dendritic cells in the teleost model, rainbow trout (Oncorhynchus mykiss)

Dendritic cells are specialized antigen presenting cells that bridge innate and adaptive immunity in mammals. This link between the ancient innate immune system and the more evolutionarily recent adaptive immune system is of particular interest in fish, the oldest vertebrates to have both innate and adaptive immunity. It is unknown whether dendritic cells co-evolved with the adaptive response, or if the connection between innate and adaptive immunity relied on a fundamentally different cell type early in evolution. We approached this question using the teleost model organism, rainbow trout (Oncorhynchus mykiss), with the aim of identifying dendritic cells based on their ability to stimulate naïve T cells. Adapting mammalian protocols for the generation of dendritic cells, we established a method of culturing highly motile, non-adherent cells from trout hematopoietic tissue that had irregular membrane processes and expressed surface MHCII. When side-by-side mixed leukocyte reactions were performed, these cells stimulated greater proliferation than B cells or macrophages, demonstrating their specialized ability to present antigen and therefore their functional homology to mammalian dendritic cells. Trout dendritic cells were then further analyzed to determine if they exhibited other features of mammalian dendritic cells. Trout dendritic cells were found to have many of the hallmarks of mammalian DCs including tree-like morphology, the expression of dendritic cell markers, the ability to phagocytose small particles, activation by toll-like receptor-ligands, and the ability to migrate in vivo. As in mammals, trout dendritic cells could be isolated directly from the spleen, or larger numbers could be derived from hematopoietic tissue and peripheral blood mononuclear cells in vitro.

The adaptor protein Bam32 in human dendritic cells participates in the regulation of MHC class I-induced CD8+ T cell activation

The B lymphocyte adaptor molecule of 32 kDa (Bam32) is strongly induced during the maturation of dendritic cells (DC). Most known functions of Bam32 are related to the signaling of the B cell receptor for Ag. Because DC do not express receptors specific for Ags, we aim at characterizing the role of Bam32 in human monocyte-derived DC in this study. Our results show that binding of allogeneic T cells to mature DC causes accumulation of Bam32 on the contact sites and that this translocation is mimicked by Ab-mediated engagement of MHC class I. Silencing of Bam32 in mature monocyte-derived DC results in an enhanced proliferation of CD8(+) T cells in an Ag-specific T cell proliferation assay. Further studies identify galectin-1 as an intracellular binding partner of Bam32. Regulating immune responses via regulatory T cell (Treg) modulation is one of the many immunological activities attributed to galectin-1. Therefore, we assayed mixed leukocyte reactions for Treg expansion and found fewer Treg in reactions stimulated with DC silenced for Bam32 compared to reactions stimulated with DC treated with a nontarget control. Based on our findings, we propose a role for Bam32 in the signaling of MHC class I molecules in professional Ag-presenting DC for the regulation of CD8(+) T cell activation. It is distinct from that of MHC class I recognized by CD8(+) T cells leading to target [corrected] cell death. Thus, our data pinpoint a novel level of T cell regulation that may be of biological relevance.

Eukaryotic expression of functionally active recombinant soluble CD83 from HEK 293T cells

The cell surface protein CD83 belongs to the immunoglobulin super family and is highly expressed on mature dendritic cells (DCs). A membrane bound and a soluble form of CD83 (sCD83) have been described. Previously, the isolation of a purified recombinant sCD83 molecule from bacterial cultures using high pressure liquid chromatography was reported. This recombinant protein reduced DC-mediated T cell proliferation in vitro and displayed an inhibitory effect in the experimental autoimmune encephalomyelitis (EAE) model. When purifying sCD83 from bacteria, however, a lipopolysaccharide fraction is frequently co-isolated with the recombinant sCD83 protein. Moreover, the subsequent separation of sCD83 from contaminating LPS is usually accompanied by a considerable loss of soluble CD83. A further disadvantage of soluble CD83 expression in prokaryotic cells is the lack of functional glycosylation. To overcome these problems, we developed an alternative strategy to express sCD83 in eukaryotic human embryonic kidney (HEK) 293 T cells. Using this system, we showed that recombinant sCD83 was LPS-free and effectively glycosylated with all three asparagine residues at least partially involved. The functionality of the expressed sCD83 protein was examined using the mixed lymphocyte reaction (MLR) assay, demonstrating a reduced DC-mediated T cell proliferation as previously reported for the sCD83 protein purified from E. coli. Thus, a new protocol for efficient eukaryotic expression and purification of sCD83 was established, which might have several advantages compared to prokaryotic expression systems.

Engagement of CD83 on B cells modulates B cell function in vivo

The transmembrane glycoprotein CD83 is an important regulator of both thymic T cell maturation and peripheral T cell response. Recent studies suggested that CD83 is also involved in the regulation of B cell maturation, activation, and homeostasis. In this study, we show that in vivo overexpression of CD83 dose dependently interfered with the Ig response to thymus-dependent and thymus-independent model Ag immunization. CD83 deficiency, in contrast, which was restricted to B cells in mixed bone marrow chimeras, led to unchanged or even slightly increased Ig responses. Strikingly, the engagement of CD83 that is naturally up-regulated on wild-type B cells by injection of anti-CD83 mAb in vivo induced a 100-fold increase in the IgG1 response to immunization. Kinetic analysis revealed that CD83 had to be engaged simultaneously or shortly after the B cell activation through injection of Ag, to modulate the IgG1 secretion. Furthermore, using mixed bone marrow chimeras in which either selectively the B cells or the dendritic cells were CD83 deficient, we demonstrate that anti-CD83 mAb mediated its biologic effect by engaging CD83 on B cells and not on CD11c(+) dendritic cells. Taken together, we provide strong evidence that CD83 transduces regulatory signals into the very B cell on which it is expressed.

The CD83 reporter mouse elucidates the activity of the CD83 promoter in B, T, and dendritic cell populations in vivo

CD83 is the major surface marker identifying mature dendritic cells (DCs). In this study, we report the generation of reporter mice expressing EGFP under the control of the CD83 promoter. We have used these mice to characterize CD83 expression by various immune system cell types both in vivo and ex vivo and under steady-state conditions and in response to stimulation with a Toll-like receptor (TLR) ligand. With those mice we could prove in vivo that the CD83 promoter is highly active in all DCs and B cells in lymphoid organs. Interestingly, this promoter activity in B cells mainly depended on the stage of development, is up-regulated in the late pre-B cell stage, and was maintained on a high level in all peripheral B cells. We also confirmed that CD83 in those cells is mainly intracellular but is up-regulated after TLR stimulation. Otherwise, CD83 promoter activity in T cells seemed to depend on stimulation and could be found mainly in CD4(+)CD25(+) and CD8(+)CD25(+) T cells and in CD4(+) and CD8(+) memory cells. In addition, we identified the murine homologues of the human CD83 splice variants. In contrast to those in human, those extremely rare short transcripts were never found without the expression of the highly dominant full-length form. So, the murine CD83 surface expression is mainly regulated posttranslationally in vivo. Our CD83 reporter mice represent a useful mouse model for monitoring the activation status and migration of DCs and lymphocytes under various conditions, and our results provide much needed clarification of the true nature of CD83 promoter activity.

CD83 regulates splenic B cell maturation and peripheral B cell homeostasis

The central function of murine CD83 that is expressed on thymic epithelial cells is to induce the progression of double-positive thymocytes to single CD4-positive T cells. Several lines of evidence suggest an additional role for CD83 in the regulation of peripheral T and B cell responses. Here we show that CD83 is expressed by immature B cells and regulates their further maturation and survival in the periphery. Employing mixed bone marrow chimeras, we compare wild-type, CD83 over-expressing and CD83-deficient B cells within the same host. CD83 over-expression on the immature B cells themselves led to an accumulation of transitional B cells and a reciprocally reduced maturation of follicular B cells that was strictly correlated to the intensity of CD83 over-expression. The absence of CD83 on B cells resulted in a decreased maturation of marginal zone B cells and conferred a mild selection advantage for B cell survival in the periphery. Consenting with these findings, the over-expression of CD83 specifically and dose dependently interfered with homeostasis of B cells while T cell survival was not affected by CD83 over-expression over a period of 30 weeks. Taken together, our data suggest that CD83 negatively regulates B cell maturation and survival.

Tissue-specific reduction in DC-SIGN expression correlates with progression of pathogenic simian immunodeficiency virus infection

Studies were undertaken to determine whether previously described reductions in splenic DC-SIGN expression in simian acquired immune deficiency syndrome (AIDS) are limited to pathogenic simian immunodeficiency virus (SIV) infection. DC-SIGN expression was evaluated by immunohistochemistry in lymphoid tissues from AIDS-susceptible Asian macaque monkeys as compared with AIDS-resistant sooty mangabey monkeys in the presence and absence of SIV infection. The phenotype of DC-SIGN+ cells in susceptible and resistant species was identical and most consistent with macrophage identity. Significantly lower levels of DC-SIGN expression were identified in spleen, mesenteric lymph node, and bone marrow of macaques with AIDS (P<0.05). Reduced levels of splenic DC-SIGN correlated significantly with CD4T cell depletion in long-term pathogenic infection of macaques (P<0.01), whereas SIV-infected mangabeys retained high levels of DC-SIGN expression in spleen despite persistent infection. Reduced expression of DC-SIGN in spleen specifically characterizes pathogenic forms of SIV infection, correlates with disease progression, and may contribute to SIV pathogenesis.

CD83 expression in CD4+ T cells modulates inflammation and autoimmunity

The transmembrane protein CD83 has been initially described as a maturation marker for dendritic cells. Moreover, there is increasing evidence that CD83 also regulates B cell function, thymic T cell maturation, and peripheral T cell activation. Herein, we show that CD83 expression confers immunosuppressive function to CD4(+) T cells. CD83 mRNA is differentially expressed in naturally occurring CD4(+)CD25(+) regulatory T cells, and upon activation these cells rapidly express large amounts of surface CD83. Transduction of naive CD4(+)CD25(-) T cells with CD83 encoding retroviruses induces a regulatory phenotype in vitro, which is accompanied by the induction of Foxp3. Functional analysis of CD83-transduced T cells in vivo demonstrates that these CD83(+)Foxp3(+) T cells are able to interfere with the effector phase of severe contact hypersensitivity reaction of the skin. Moreover, adoptive transfer of these cells prevents the paralysis associated with experimental autoimmune encephalomyelitis, suppresses proinflammatory cytokines IFN-gamma and IL-17, and increases antiinflammatory IL-10 in recipient mice. Taken together, our data provide the first evidence that CD83 expression can contribute to the immunosuppressive function of CD4(+) T cells in vivo.

CD83 regulates lymphocyte maturation, activation and homeostasis

The transmembrane CD83 molecule, a conserved member of the immunoglobulin superfamily, is known as one of the most characteristic cell surface markers for fully matured dendritic cells (DCs) in the peripheral circulation. An essential role for CD83 on murine DCs has not been found; however, evidence shows that its function primarily lies in the regulation of T- and B-lymphocyte maturation and in the regulation of their peripheral responses. Here, we review evidence for a role of CD83 in central lymphocyte maturation and novel, sometimes contradictory findings, regarding the function of CD83 in peripheral immune responses.

Trauma-hemorrhage inhibits splenic dendritic cell proinflammatory cytokine production via a mitogen-activated protein kinase process

Although splenic dendritic cell (DC) functions are markedly altered following trauma-hemorrhage, the mechanism(s) responsible for the altered DC functions remains unknown. We hypothesized that trauma-hemorrhage inhibits DC function via suppressing toll-like receptor 4 (TLR4) expression and mitogen-activated protein kinases (MAPKs). To examine this, male C3H/HeN (6–8 wk) mice were randomly assigned to sham operation or trauma-hemorrhage. Trauma-hemorrhage was induced by midline laparotomy and ∼90 min of hypotension [blood pressure (BP) 35 mmHg], followed by fluid resuscitation (4× the shed blood volume in the form of Ringer lactate). Two hours later, mice were euthanized, splenic DCs were isolated, and the changes in their MAPK activation, TLR4-MD-2 expression, and ability to produce cytokines were measured. The results indicate that trauma-hemorrhage downregulated the lipopolysaccharide (LPS)-induced MAPK activation in splenic DCs. In addition to the decrease in MAPK activation, surface expression of TLR4-MD-2 was suppressed following trauma-hemorrhage. Furthermore, LPS-induced cytokine production from splenic DCs was also suppressed following trauma-hemorrhage. These findings thus suggest that the decrease in TLR4-MD-2 and MAPK activation may contribute to the LPS hyporesponsiveness of splenic DCs following trauma-hemorrhage. Hyporesponsiveness of splenic DCs was also found after stimulation with the TLR2 agonist zymosan. Our results may thus explain the profound immunosuppression that is known to occur under those conditions.

Dendritic cell CD83: a therapeutic target or innocent bystander?

CD83 represents an intriguing target for immunotherapy due to its preferential expression on mature DCs, the most efficient of antigen presenting cells. Based on its restricted expression pattern, structure, and the paucity of CD4+ T cells in CD83-deficient mice, multiple immunologically important functions for CD83 during immune responses have been proposed. Indeed, several studies have reported that CD83 blockade using soluble receptor constructs inhibits T cell responses in vitro and in vivo, can affect autoimmune disease development and progression, and can inhibit transplant rejection. However, others have not been able to reproduce some of these findings, and antigen presenting cells deficient in CD83 expression or expressing a mutated form of CD83 induce normal T cell responses in vitro. This review examines the controversy surrounding CD83 function, alleged CD83 ligands, the potential therapeutic utility of recombinant proteins targeting CD83 function, and the importance of soluble serum CD83. While the validity of multiple previous studies needs to be confirmed, CD83 remains a fascinating cell surface molecule with a unique pattern of expression that has multiple confirmed functions in regulating immune system development and function.

MCS-18, a novel natural product isolated from Helleborus purpurascens, inhibits dendritic cell activation and prevents autoimmunity as shown in vivo using the EAE model

Here we report for the first time that MCS-18, a novel natural product isolated from Helleborus purpurascens, is able to inhibit the expression of typical molecules of mature dendritic cells (DC) such as CD80, CD86, and especially of CD83 subsequently leading to a clear and dose-dependent inhibition of the DC-mediated T-cell stimulation. Furthermore, MCS-18 impeded the formation of the typical DC/T-cell clusters, which are essential to induce potent immune responses. Interestingly, MCS-18 also inhibited CCR7 expression on DC which subsequently lead to a dose-dependent block of the CCL19-mediated DC migration. MCS-18 not only inhibited the DC-mediated T-cell stimulation but also the anti-CD3/anti-CD28-mediated T-cell stimulation. Strikingly, MCS-18 also strongly reduced the paralysis associated with the experimental autoimmune encephalomyelitis (EAE), which is a murine model for human multiple sclerosis, in a prophylactic as well as in a "real" therapeutic setting. Even when the EAE was induced for a second time, the MCS-18-treated animals were still protected, suggesting that MCS-18 induces a long-lasting suppressive effect. In addition, and very important for the potential practical application in humans, MCS-18 was also active when administered orally. MCS-18 treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In conclusion, using in vitro as well in vivo assays we were able to show that MCS-18 exerts a strong immunosuppressive activity with remarkable potential for the therapy of diseases characterized by a pathologically over-activated immune system.

CD83 expression is a sensitive marker of activation required for B cell and CD4+ T cell longevity in vivo

CD83 is a surface marker that differentiates immature and mature human dendritic cell populations. Thymic epithelial cell expression of CD83 is also necessary for efficient CD4+ T cell development in mice. The altered phenotypes of peripheral B and CD4+ T cells, and the reduction of peripheral CD4+ T cells in CD83-/- mice, suggest additional functions for CD83. To assess this, a panel of mAbs was generated to characterize mouse CD83 expression by peripheral leukocytes. As in humans, activation of conventional and plasmacytoid murine dendritic cell subsets led to rapid up-regulation of CD83 surface expression in mice. In primary and secondary lymphoid compartments, a subset of B cells expressed low-level CD83, while CD83 was not detected on resting T cells. However, CD83 was prominently up-regulated on the majority of spleen B and T cells within hours of activation in vitro. In vivo, a low dose of hen egg lysozyme (1 microg) induced significant CD83 but not CD69 expression by Ag-specific B cells within 4 h of Ag challenge. Although B cell development appeared normal in CD83-/- mice, B and CD4+ T cell expression of CD83 was required for lymphocyte longevity in adoptive transfer experiments. Thus, the restricted expression pattern of CD83, its rapid induction following B cell and T cell activation, and its requirement for B cell and CD4+ T cell longevity demonstrate that CD83 is a functionally significant and sensitive marker of early lymphocyte activation in vivo.

CD83 expression in sea bream macrophages is a marker for the LPS-induced inflammatory response

CD83, a cell surface membrane glycoprotein member of the Ig superfamily which is commonly used as standard surface marker for dendritic cells, was cloned from gilthead sea bream macrophages using degenerate primers against conserved motifs of known CD83 sequences. The obtained cDNA contains an open reading frame of 669 nucleotides that translate into a 222 amino acid putative peptide. The deduced protein sequence shows conservation of features shared by vertebrate CD83 and multiple alignment with fish CD83 sequences reveals high homology. In cultured sea bream macrophages CD83 mRNA expression was significantly enhanced in a dose- and time-dependent fashion after stimulation with Escherichia coli LPS. These results indicate that in fish, macrophages express high levels of CD83 mRNA after LPS exposure and CD83 is therefore a good marker for activated mature myeloid cells in fish.

CD83 modulates B cell function in vitro: increased IL-10 and reduced Ig secretion by CD83Tg B cells

The murine transmembrane glycoprotein CD83 is an important regulator for both thymic T cell maturation and peripheral T cell responses. Recently, we reported that CD83 also has a function on B cells: Ubiquitous transgenic (Tg) expression of CD83 interfered with the immunoglobulin (Ig) response to infectious agents and to T cell dependent as well as T cell independent model antigen immunization. Here we compare the function of CD83Tg B cells that overexpress CD83 and CD83 mutant (CD83mu) B cells that display a drastically reduced CD83 expression. Correlating with CD83 expression, the basic as well as the lipopolysaccharide (LPS) induced expression of the activation markers CD86 and MHC-II are significantly increased in CD83Tg B cells and reciprocally decreased in CD83mu B cells. Wild-type B cells rapidly upregulate CD83 within three hours post BCR or TLR engagement by de novo protein synthesis. The forced premature overexpression of CD83 on the CD83Tg B cells results in reduced calcium signaling, reduced Ig secretion and a reciprocally increased IL-10 production upon in vitro activation. This altered phenotype is mediated by CD83 expressed on the B cells themselves, since it is observed in the absence of accessory cells. In line with this finding, purified CD83mu B cells displayed a reduced IL-10 production and slightly increased Ig secretion upon LPS stimulation in vitro. Taken together, our data strongly suggest that CD83 is expressed by B cells upon activation and contributes to the regulation of B cell function.

CD83: an update on functions and prospects of the maturation marker of dendritic cells

CD83 is one of the most characteristic cell surface markers for fully matured dendritic cells (DCs). In their function as antigen presenting cells they induce T-cell mediated immune responses. In this review we provide an overview on well described and proposed functions of this molecule as well as on very recent insights and new hypothesis. Already the CD83 messenger RNA processing differs remarkably from the processing of other cellular mRNAs: instead of the usual TAP mRNA export pathway, the CD83 mRNA is exported by the specific CRM1-mediated pathway, utilized only by a minority of cellular mRNAs. On the protein level, two different isoforms of CD83 exist: a membrane-bound and a soluble form. The isoforms are generated by different subsets of cells, including DCs, T-cells and B-cells, and also differ in their biological function. While the membrane-bound CD83 is of immune stimulatory capacity, activates T-cells and is important for the generation of thymocytes, the soluble CD83 has the opposite effect and has an immune inhibitory capacity. Due to its immune inhibitory function, CD83 has great potential for treatment of autoimmune diseases, for organ transplantations, and for immunotherapy, just to name a few examples. Moreover, some viruses prevent recognition by the host's immune system by specifically targeting CD83 surface expression.

A limited course of soluble CD83 delays acute cellular rejection of MHC-mismatched mouse skin allografts

CD83 is a surface marker expressed on matured dendritic cells (DCs). It plays a pivotal role in the mediation of DC/T cell interaction and induction of T-cell activation. Previous studies have suggested that a soluble form of CD83 could suppress DC maturation and inhibit T-cell activation and, as a result, it can prevent paralysis associated with experimental autoimmune encephalomyelitis. Here, we explored its potential effect on allograft rejection in a fully major histocompatibility complex-mismatched murine skin transplantation model. A form of mouse soluble CD83 (CD83-Ig) fused the extracellular domain of murine CD83 with human IgG1alpha Fc tail was purified from transfected COS-7 cell. It was found that the treatment of recipient mice with CD83-Ig significantly delayed allograft rejection. Especially, when T cells originated from recipients treated with CD83-Ig re-stimulated with donor-specific splenocytes, they showed a significant reduced responding capability as compared with that of originated from control recipients. In line with these results, a reduction for serum IFN-gamma and IL-2 and a decreased mRNA expression of IFN-gamma and IL-2 in allograft infiltrated immune cells were also observed. Our results suggest that CD83-Ig could be useful for the treatment of allograft rejection in combination with other therapeutic strategies.

CD83 is a regulator of murine B cell function in vivo

The transmembrane glycoprotein CD83 has been described as a specific maturation marker for dendritic cells and several lines of evidence suggest that CD83 regulates thymic T cell maturation as well as peripheral T cell activation. Here we show for the first time that CD83 is involved also in the regulation of B cell function. CD83 is up-regulated on activated B cells in vivo, specifically in the draining lymph nodes of Leishmania major-infected mice. The ubiquitous transgenic (Tg) expression of CD83 interferes with Leishmania-specific T cell-dependent and with T cell-independent antibody production. This defect is restricted to the B cell population since the antigen-specific T cell response of CD83Tg mice to L. major infection is unchanged. The defective immunoglobulin (Ig) response is due to Tg expression of CD83 on the B cells because wild-type B cells display normal antigen-specific responses in CD83Tg hosts and CD83Tg B cells do not respond to immunization in a mixed wild-type/CD83Tg bone marrow chimera. Finally, the treatment of non-Tg C57BL/6 mice with anti-CD83 mAb induces a dramatic increase in the antigen-specific IgG response to immunization, thus demonstrating a regulatory role for naturally induced CD83 on wild-type B cells.

Trauma-Hemorrhage Induces Depressed Splenic Dendritic Cell Functions in Mice

Although Kupffer cell, splenic, and peritoneal macrophage functions are markedly altered following trauma-hemorrhage (T-H), it remains unclear whether T-H also affects splenic dendritic cell (sDC) functions. We hypothesized that sDC functions will also be compromised following T-H. Male C3H/HeN (6- to 8-wk) mice were randomly assigned to sham operation or T-H. T-H was induced by midline laparotomy and approximately 90 min of hemorrhagic shock (blood pressure 35 mmHg), followed by fluid resuscitation (four times the shed blood volume in the form of Ringer's lactate). Two hours later, the mice were sacrificed; sDC were isolated; and the changes in their apoptosis, MHC class II expression, and ability to produce costimulatory cytokines and Ag presentation were measured. The results indicate that sDC Ag presentation capacity was significantly decreased and MHC class II expression was also significantly decreased following T-H. Moreover, LPS-induced IL-12 production and LPS- or IL-12-induced IFN-gamma production following T-H were significantly decreased. Thus, the markedly decreased MHC class II expression and cytokine (IL-12, IFN-gamma) production following T-H may be the cause for the depressed sDC Ag presentation under those conditions. This depression in Ag presentation could contribute to the host's enhanced susceptibility to sepsis following T-H.