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

Low-grade chronic inflammation in regions of the normal mouse arterial intima predisposed to atherosclerosis

Atherosclerotic lesions develop in regions of arterial curvature and branch points, which are exposed to disturbed blood flow and have unique gene expression patterns. The cellular and molecular basis for atherosclerosis susceptibility in these regions is not completely understood. In the intima of atherosclerosis-predisposed regions of the wild-type C57BL/6 mouse aorta, we quantified increased expression of several proinflammatory genes that have been implicated in atherogenesis, including vascular cell adhesion molecule–1 (VCAM-1) and a relative abundance of dendritic cells, but only occasional T cells. In contrast, very few intimal leukocytes were detected in regions resistant to atherosclerosis; however, abundant macrophages, including T cells, were found throughout the adventitia (Adv). Considerably lower numbers of intimal CD68⁺ leukocytes were found in inbred atherosclerosis-resistant C3H and BALB/c mouse strains relative to C57BL/6 and 129; however, leukocyte distribution throughout the Adv of all strains was similar. The predominant mechanism for the accumulation of intimal CD68⁺ cells was continued recruitment of bone marrow–derived blood monocytes, suggestive of low-grade chronic inflammation. Local proliferation of intimal leukocytes was low. Intimal CD68⁺ leukocytes were reduced in VCAM-1–deficient mice, suggesting that mechanisms of leukocyte accumulation in the intima of normal aorta are analogous to those in atherosclerosis.

Transgenic expression of a CD83-immunoglobulin fusion protein impairs the development of immune-competent CD4-positive T cells

The murine transmembrane glycoprotein CD83 is an important regulator for both thymic T cell maturation and peripheral T cell response. CD83 deficiency leads to a block in the thymic maturation of CD4-positive T cells, and interference with peripheral CD83/CD83 ligand interaction by addition of soluble CD83 suppresses immune responses in vivo and in vitro. Here we report the generation of a mouse transgenic for a fusion protein consisting of the extracellular domain of murine CD83 fused to the constant part of human IgG1 heavy chain. Thymic selection of CD4-positive T cells was unchanged in CD83Ig transgenic and in CD83Ig/OT-2 double-transgenic mice. However, thymic and peripheral CD4-positive T cells derived from CD83Ig/OT-2 transgenic mice displayed a reduced cytokine response to antigenic stimulation in vitro, whereas CD83Ig/OT-1-derived CD8-positive T cells showed normal cytokine secretion. The T cell defect was relevant in vivo, since a sub-lethal infection with Trypanosoma cruzi led to an increased parasitemia and reduced survival rate of CD83Ig transgenic mice compared to wild-type C57BL/6 mice. In contrast, in vivo application of recombinant CD83Ig did not result in an increase in parasitemia. Taken together our data suggest that thymic selection in the presence of CD83Ig leads to an intrinsic T cell defect of CD4-positive T cells resembling the phenotype described for CD4-positive T cells derived from CD83-deficient mouse strains.

Determination of the inhibitory activity and biological half-live of soluble CD83: comparison of wild type and mutant isoforms

A soluble form of CD83 ("sCD83") has been shown to block DC-mediated T cell stimulation in vitro and an immunosuppressive role has also been shown in vivo using an experimental-autoimmune-encephalomyelits (EAE) model. Using recombinant mutational analyses, recently, we could show that sCD83 forms a homo-dimer, whereby four cysteines are involved in the intra-molecular disulfide bonds and the fifth cysteine is responsible for the inter-molecular bridging of the two molecules. Further studies revealed that the two CD83-isoforms, i.e. the dimer and the monomer, have a similar inhibitory capacity when tested in vitro. Here we show that the biological (in vivo) half-life of the two sCD83 isoforms is comparable and was between 2 and 3h. In addition, using the EAE-model, we were able to show that a monomeric-mutant isoform of soluble CD83 has a similar inhibitory activity in vivo when compared with a dimeric-wildtype isoform.

Subtoxic concentrations of allergenic haptens induce LC migration and maturation in a human organotypic skin explant culture model: a novel method for identifying potential contact allergens

The accelerated migration of Langerhans cells (LCs) out of the epidermis and up-regulation of maturation markers, upon treatment with subtoxic concentrations of chemicals, were used as the criteria to determine the potential of allergenic chemicals capable of inducing a hapten-specific delayed-type hypersensitivity reaction. Here we report the findings of a study in which seven chemicals, coded and tested in a blind fashion, were classified as contact allergens or non-allergens using the human organotypic skin explant culture (hOSEC) model. All chemicals that were identified as a contact sensitizer on decoding induced a definite decrease in the number of CD1a and HLA-DR-positive epidermal LCs in the epidermis of the skin explants, as determined by both semiquantitative immunohistochemistry and quantitative flow cytometric analysis. A significant increase in the number of CD83(+) cells was accompanied by up-regulation of activation molecules in the epidermis of hOSEC exposed specifically to contact allergens. In contrast, there were only minor alterations in epidermal LC numbers, expression of CD83 and other activation markers by LCs when the biopsies were treated with non-toxic concentrations of non-allergenic irritants and vehicles. The data suggest that an increased epidermal LC migration and maturation accompanied by increased expression of activation markers could be used as end-point determinants to screen allergens in a non-animal alternative hOSEC model.

Dendritic cells interacting mainly with B cells in the lymphoepithelial symbiosis of the human palatine tonsil

The lymphoepithelial symbiosis (LES) of the human palatine tonsil is composed of spindle- or star-shaped epithelial cells forming a loose meshwork, containing numerous lymphocytes and dendritic cells (DCs). In the present study, we immunohistochemically characterized DCs in the LES (LES-DCs). LES-DCs were phenotypically immature DCs that were S100beta+, fascin-, HLA-DR+, CD1a-, CD80-, CD83-, CD86-, and CD123-. The most characteristic feature of LES-DCs was that they contacted many B cells, which were mostly IgM+ IgD+ resting naive B cells. Langerhans cells (LCs) located in the nonsymbiotic squamous epithelium were immature DCs that were S100beta+, fascin-, and CD1a+ and did not contact lymphocytes. In contrast to LES-DCs, interdigitating dendritic cells (IDCs) in the T zone were mature DCs that were HLA-DR+, CD1a-, fascin+, CD80+, CD83+, and CD86+ and contacted numerous CD4+ T cells. Two subsets of IDC, S100beta+ fascin+ IDC (IDC-1) and S100beta- fascin+ IDC (IDC-2), were identified, and the majority of IDCs are IDC-2. In contrast to IDCs, which were distributed in the T-cell area in groups, LES-DCs were distributed along the crypt as if forming a barrier. These findings suggest that LES-DCs are a novel type of DC playing an important role in the induction of humoral immune response against incoming air- or food-borne pathogenic antigens.

Characterization of human peritoneal dendritic cell precursors and their involvement in peritonitis

Scattered evidence suggests that the human peritoneal cavity contains cells of the dendritic cell (DC) lineage but their characterization is missing. Here, we report that the peritoneal cavity of normal subjects and of stable patients on peritoneal dialysis (PD) contains a population of CD14(+) cells that can differentiate into DCs or macrophages. Within this pool, we characterized a CD14(+)CD4(+) cell subset (2.2% of the peritoneal cells) fulfilling the definition of myeloid DC precursors or pre-DC1 cells. These cells expressed high levels of HLA-DR, CD13, CD33, and CD86, and low levels of CD40, CD80, CD83, CD123, CD209, TLR-2 and TLR-4. These cells retained CD14 expression until late stages of differentiation, despite concomitant up-regulation of DC-SIGN (CD209), CD1a, CD80 and CD40. Peritoneal pre-DC1 cells had endocytic capacity that was down-regulated upon LPS/IFN-gamma stimulation, were more potent allo-stimulators than peritoneal CD14(+)CD4(-/lo) cells and monocyte-derived macrophages, and induced Th1 cytokine responses. More importantly, the number of peritoneal pre-DC1 cells increased during PD-associated peritonitis, with a different profile for Gram positive and Gram negative peritonitis, suggesting that these cells participate in the induction of peritoneal adaptive immune responses, and may be responsible for the bias towards Th1 responses during peritonitis.

CD83 is a dimer: Comparative analysis of monomeric and dimeric isoforms

Recently, we reported that soluble CD83 has a strong immunosuppressive activity in vitro as well as in vivo. Sequence alignment of CD83 between different species revealed the presence of five cysteines in the extracellular Ig-domain of the protein. This opens up the possibility that four cysteines are involved in the formation of two intramolecular disulfide bonds and a possible involvement of the remaining fifth cysteine in the formation of an intermolecular covalent disulfide bond, leading to the dimerization of the extracellular protein domains. Using recombinant mutational analyses, where the fifth cytosine at amino acid position 129 was mutated to a serine, we could prove that the fifth cysteine residue was indeed necessary for the dimerization. Functional analyses revealed that the mutant protein inhibited almost completely the upregulation of CD83-expression during DC maturation. Furthermore, the functional activity of the mutant protein was investigated using MLR assays and we could show that the mutant soluble CD83 protein inhibited DC-mediated allogeneic T-cell stimulation in vitro.

Oligoclonal T cells in histiocytic necrotizing lymphadenopathy are associated with TLR9+ plasmacytoid dendritic cells

Histiocytic necrotizing lymphadenopathy (HNL), a disease of unknown cause, is characterized pathologically by the presence of plasmacytoid dendritic cells (pDCs), which are frequently mixed with oligoclonal T cells (OTCs) and myeloid cells. Toll-like receptors (TLRs 1-10) are a family of pattern recognition receptors of DCs. To investigate the interactions between pDCs and T cells, and to look for an etiology of HNL, we studied 24 HNLs for the profile of TLRs. Transcripts of TLR7, a receptor on pDCs for single-stranded RNA, were found in every case, confirming the universal presence of pDCs. Transcripts of TLR9, another receptor on pDCs for microbial unmethylated CpG-rich DNA, were correlated with OTCs, implying T-cell expansion stimulated by TLR9+ pDCs in response to a microbe. Because PCRs for bacterial 16S rDNAs were negative in the lymph nodes, a bacterial origin seems unlikely, but a virus remains a possible candidate. The pDCs lacked the maturation marker CD83, which suggested ineffective stimulation of T cells and might account for the usually benign course of HNL. Taken together, these data illustrate a novel approach, based upon TLR transcript analysis, for the integration of pathology, immunology, and clinical findings of HNL.

Dendritic cells activate autologous T cells and induce IL-4 and IL-10 production in myasthenia gravis

Dendritic cells (DC), as initiators and orchestrators of immune responses, control both naive and primed T cell responses. Depending on their maturation stage, DC promote immunity or tolerance. Here we investigated (1) the phenotype and cytokine secretion patterns of IL-10-modulated immature DC (IL-10-DC) and lipopolysaccharide (LPS)-driven mature DC (LPS-DC) in comparison with unmodulated immature DC (imDC) and (2) the effects of IL-10-DC, and of LPS-DC, vs. imDC on autologous T cell responses in patients with myasthenia gravis (MG) compared with healthy controls (HC). All three types of DC derived from MG significantly increased the levels of CD4+CD25+ T cells and of their subfraction expressing CD69, when compared to DC derived from HC. IL-10-DC induced production of IL-10 and IL-4 by T cells from MG patients, but only IL-10 production from HC. LPS-DC activated autologous T cells as reflected by augmented CD25, CD69 and CTLA-4 expression on CD4+ T cells, without differences between MG and HC. This was associated with increased production of both Th1 (IFN-gamma) and Th2 (IL-10 and IL-4) cytokines by T cells. These results indicate that DC-induced activation of autologous T cells is more pronounced in MG than in HC. In addition, DC-induced T cell responses in MG vs. HC are more Th2-prone.

Prevention and treatment of experimental autoimmune encephalomyelitis by soluble CD83

CD83 is up-regulated on the surface of dendritic cells (DCs) during maturation and has been widely used as a marker for mature DCs. Recently, we reported the recombinant expression of the extracellular immunoglobulin domain of human CD83 (hCD83ext). Using this soluble form of CD83, allogeneic as well as specific cytotoxic T lymphocyte proliferation could be blocked in vitro. Here we report the functional analysis of soluble CD83 in vivo, using murine experimental autoimmune encephalomyelitis (EAE) as a model. Strikingly, only three injections of soluble CD83 prevented the paralysis associated with EAE almost completely. In addition, even when the EAE was induced a second time, CD83-treated mice were protected, indicating a long-lasting suppressive effect. Furthermore, soluble CD83 strongly reduced the paralysis in different therapeutic settings. Most important, even when the treatment was delayed until the disease symptoms were fully established, soluble CD83 clearly reduced the paralyses. In addition, also when EAE was induced a second time, soluble CD83-treated animals showed reduced disease symptoms. Finally, hCD83ext treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In summary, this work strongly supports an immunosuppressive role of soluble CD83, thereby indicating its therapeutic potential in the regulation of immune disorders in vivo.

Interleukin-10-modulated immature dendritic cells control the proinflammatory environment in multiple sclerosis

Multiple sclerosis (MS) is a disabling, inflammatory, demyelinating disease of the central nervous system considered to be mediated by autoreactive T cells. Dendritic cells (DC), being professional antigen-presenting cells, play a pivotal role in the decision between T-cell activation and anergy. It has been suggested that mature DC (mDC) induce immunity, whereas immature DC (imDC) have the potential to induce tolerance. In this study, we investigated the effects of autologous imDC versus autologous mDC on lymphocytes with respect to the expression of functionally important cell-surface molecules and production of cytokines. Our aims were to investigate whether the maturation status of DC differs between MS and healthy controls (HC) and to explore whether the effects of DC on T-cell responses differ between MS and HC. DC were generated from adherent blood mononuclear cells from patients with MS and HC. imDC were obtained by culture with either granulocyte-macrophage colony-stimulating factor (GM-CSF) + interleukin-4 (IL-4) or GM-CSF + IL-4 + IL-10. mDC were obtained by adding lipopolysaccharide to DC cultures. Upon coculture with autologous lymphocytes, mDC activated the autologous T cells as reflected by increased CD25 and cytotoxic T-lymphocyte antigen-4 expression on CD4(+) T cells together with the increased production of both T helper 1 (Th1) (IL-2 and interferon-gamma) and Th2 (IL-10 and IL-4) cytokines. Unmodulated naïve imDC induced the production of only IL-4. An exposure of imDC to IL-10 induced the production of IL-4 as well as IL-10 by autologous lymphocytes. We hypothesize that such imDC are important in controlling the proinflammatory environment in vivo in patients with MS.

Dichotomy between CD1a+ and CD83+ dendritic cells in lymph nodes during SIV infection of macaques

The prevalence and differentiation of dendritic cells (DC) in lymphoid tissue of simian immunodeficiency virus (SIV)-infected cynomolgus monkeys was studied during disease progression. Lymph node biopsies were consecutively obtained from clinical rapid and slow progressors until the development of disease consistent with simian acquired immunodeficiency syndrome (sAIDS) occurred. Quantitative evaluation of CD1a+ DC and the expression of DC antigens related to maturation (CD83, DC-LAMP and S100b) were performed at the single cell level by in situ image analysis. Despite a persistent prevalence of CD1a+ DC in lymphoid tissue during disease progression, there was a subsequent drop of mature CD83+, DC-LAMP+ and S100b+ DC, correlating with the decline of CD4+ T cells in blood. Thus, disease progression to sAIDS was associated with impaired maturation of DC, and lack of CD83, DC-LAMP and S100b expression.

The soluble form of CD83 dramatically changes the cytoskeleton of dendritic cells

CD83 is the best-known surface marker for mature dendritic cells (DC) and recently we could show that a soluble form of CD83 inhibits DC maturation. In addition, this soluble form inhibits DC-mediated T cell proliferation in vitro and in vivo. Furthermore, several viruses induce CD83 degradation or shedding in infected DC. A soluble form of CD83 was also found in plasma and serum of healthy individuals and interestingly at highly elevated levels in a number of haematological malignancies. Thus, CD83 also has functional implications for the immune response. However, the molecular mechanism is not well defined. Here we describe for the first time that soluble CD83 completely changed the cytoskeleton (analysed using phalloidin-, tubulin- and fascin-specific antibodies) when administered at a concentration of 10 microg/ml to mature DC. The cells rounded off and had only short, truncated, or no veils at all. Furthermore, soluble CD83-treated cells were completely inhibited in their ability to form clusters with T cells, an absolute prerequisite in order to stimulate T cells.

Expression of CD83 in the murine immune system

CD83 is used as a marker for mature dendritic cells (DC) in man. We have developed a new monoclonal antibody (mAb), Michel-17, that specifically recognizes mouse CD83. We show that murine CD83 is expressed mainly on mature DC and on activated T cells. Histological analysis of serial spleen sections revealed a CD83 expression pattern resembling that of MIDC-8, a known murine DC marker molecule. In contrast to other costimulatory receptors, cross-linking of CD83 with the mAb Michel-17 on DC or T cells does not induce any activation signals. Our data describe for the first time the expression pattern of murine CD83, which is comparable to that of human CD83. The unique mAb Michel-17 will help to elucidate the biological functions of the CD83 molecule in more detail.

Enhanced activation of CD83-positive T cells

CD83 is a marker molecule for mature dendritic cells (DCs) but is also substantially expressed on activated T cells in humans and mice. Its function is unknown, but CD83 knockout mice show an impaired thymic maturation of CD4-positive cells and soluble CD83 inhibits partially antigen-specific responses in vitro pointing to a role of CD83 in the immune system. Here we show that CD83-positive T cells produce strongly increased amounts of interferon-gamma and interleukin-2. In contrast, constitutive expression of CD83 on DCs alters neither the activation of DCs following addition of lipopolysaccharide nor the ability to present antigenic peptides. Thus, the expression of CD83 on T cells has direct functional consequences for tuning the activation threshold.

Role of CD83 in the immunomodulation of dendritic cells

Glycoprotein CD83 is one of the best-known maturation markers for human dendritic cells (DCs). The fact that CD83 is strongly upregulated together with co-stimulatory molecules such as CD80 and CD86 during DC maturation suggests it plays an important role in the induction of immune responses. Infection studies with herpes simplex virus type 1 (HSV-1) and the inhibition of the CD83 mRNA specific transport from the nucleus to the cytoplasm suggested a possible functional role for CD83. The first clear proof that CD83 is indeed important for DC biology came from recently performed studies using a soluble form of the extracellular CD83 domain. DC-mediated T cell proliferation could be completely inhibited using this recombinant molecule. Additional studies elucidated immunostimulatory as well as regulatory effects of the CD83 molecule. Furthermore, CD83-/- knockout mice revealed a block in CD4+ T cell generation, a new possible immunomodulatory function of CD83.

CD83 on dendritic cells: more than just a marker for maturation

CD83 has been known for a long time to be one of the best markers for mature dendritic cells (DCs). Studies with herpes simplex virus type 1 (HSV-1)-infected DCs, whereby the viral infection leads to the degradation of CD83, as well as investigations inhibiting CD83 mRNA transport, have provided evidence that CD83 might also be important for DC biology. Recently, we have shown that the soluble extracellular CD83 domain inhibits DC-mediated T-cell proliferation, representing the first report describing a functional role for CD83.

Overexpression, purification, and biochemical characterization of the extracellular human CD83 domain and generation of monoclonal antibodies

CD83 is a 45-kDa glycoprotein and member of the immunoglobulin (Ig) superfamily. It is the best known marker for mature dendritic cells. Although the precise function of CD83 is not known, its selective expression and upregulation together with the costimulators CD80 and CD86 suggests an important role of CD83 in the induction of immune responses. To perform functional studies and to elucidate its mode of action it is vital to obtain recombinant expressed and highly purified CD83 molecules. Therefore, the external Ig domain of human CD83 (hCD83ext) was expressed as a GST fusion protein (GST-hCD83ext) and the soluble protein was purified under native conditions. The fusion protein was purified using GSTrap columns followed by anion-exchange chromatography. GST-hCD83ext was then cleaved using thrombin and soluble hCD83ext was further purified using GSTrap columns and finally by a preparative gel filtration as a polishing step and used for further characterization. The purified GST-hCD83 fusion protein was also used to generate monoclonal anti-CD83 antibodies in a rat system. Two different monoclonal antibodies were generated. Using these antibodies, CD83 was specifically recognized in FACS and Western blot analyses. Furthermore, we showed that native CD83 is glycosylated and that this glycosylation influences the binding of the antibodies in Western blot analyses. Finally, the purified hCD83ext protein was analyzed by one-dimensional NMR and these analyses strongly indicate that hCD83ext is folded and could therefore be used for further structural and functional studies.

CD83 expression influences CD4+ T cell development in the thymus

T lymphocyte selection and lineage commitment in the thymus requires multiple signals. Herein, CD4+ T cell generation required engagement of CD83, a surface molecule expressed by thymic epithelial and dendritic cells. CD83-deficient (CD83-/-) mice had a specific block in CD4+ single-positive thymocyte development without increased CD4+CD8+ double- or CD8+ single-positive thymocytes. This resulted in a selective 75%-90% reduction in peripheral CD4+ T cells, predominantly within the naive subset. Wild-type thymocytes and bone marrow stem cells failed to differentiate into mature CD4+ T cells when transferred into CD83-/- mice, while CD83-/- thymocytes and stem cells developed normally in wild-type mice. Thereby, CD83 expression represents an additional regulatory component for CD4+ T cell development in the thymus.

The extracellular domain of CD83 inhibits dendritic cell-mediated T cell stimulation and binds to a ligand on dendritic cells

CD83 is an immunoglobulin (Ig) superfamily member that is upregulated during the maturation of dendritic cells (DCs). It has been widely used as a marker for mature DCs, but its function is still unknown. To approach its potential functional role, we have expressed the extracellular Ig domain of human CD83 (hCD83ext) as a soluble protein. Using this tool we could show that immature as well as mature DCs bind to CD83. Since CD83 binds a ligand also expressed on immature DCs, which do not express CD83, indicates that binding is not a homophilic interaction. In addition we demonstrate that hCD83ext interferes with DC maturation downmodulating the expression of CD80 and CD83, while no phenotypical effects were observed on T cells. Finally, we show that hCD83ext inhibits DC-dependent allogeneic and peptide-specific T cell proliferation in a concentration dependent manner in vitro. This is the first report regarding functional aspects of CD83 and the binding of CD83 to DCs.

Signaling lymphocytic activation molecule is expressed on mature CD83+ dendritic cells and is up-regulated by IL-1 beta

Signaling lymphocyte activation molecule (SLAM), a 70-kDa costimulatory molecule that mediates CD28-independent proliferation of T cells and IFN-gamma production, has been identified on human T cells, immature thymocytes, and a subset of B cells. We have found that SLAM is expressed on mature but not immature dendritic cells (DC). However, the SLAM-associated protein, is missing in DC. SLAM surface expression is strongly up-regulated by IL-1beta. Addition of IL-1beta to the DC maturation mixture also increases the stimulatory properties of DC. These findings provide a new marker for DC maturation and help to explain two areas of DC biology. First, SLAM is a receptor for the measles virus, previously shown to infect DC. Second, SLAM could possibly contribute to the enhanced immunostimulatory functions of DC that are observed following the addition of IL-1.

A soluble form of CD83 is released from activated dendritic cells and B lymphocytes, and is detectable in normal human sera

CD83 is an inducible glycoprotein expressed predominantly by dendritic cells (DC) and B lymphocytes. Expression of membrane CD83 (mCD83) is widely used as a marker of differentiated/activated DC but its function and ligand(s) are presently unknown. We report the existence of a soluble form of CD83 (sCD83). Using both a sCD83-specific ELISA and Western blotting, we could demonstrate the release of sCD83 by mCD83(+) B cell and Hodgkin's disease-derived cell lines, but not mCD83(-) cells. Inhibition of de novo protein synthesis did not affect the release of sCD83 during short-term (2 h) culture of cell lines although mCD83 expression was significantly reduced, suggesting sCD83 is generated by the release of mCD83. Isolated tonsillar B lymphocytes and monocyte-derived DC, which are mCD83(low), released only low levels of sCD83 during culture. However, the differentiation/activation of these populations both up-regulated mCD83 and increased sCD83 release significantly. Analysis of sera from normal donors demonstrated the presence of low levels (121 +/- 3.6 pg/ml) of circulating sCD83. Further studies utilizing purified sCD83 and the analysis of sCD83 levels in disease may provide clues to the function and ligand(s) of CD83.