Dendritic cells and the pathogenesis of rheumatoid arthritis

Exploring the therapeutic potential of regulatory T cell in rheumatoid arthritis: Insights into subsets, markers, and signaling pathways

Rheumatoid arthritis (RA) is a complex autoimmune inflammatory rheumatic disease characterized by an imbalance between immunological reactivity and immune tolerance. Regulatory T cells (Tregs), which play a crucial role in controlling ongoing autoimmunity and maintaining peripheral tolerance, have shown great potential for the treatment of autoimmune inflammatory rheumatic diseases such as RA. This review aims to provide an updated summary of the latest insights into Treg-targeting techniques in RA. We focus on current therapeutic strategies for targeting Tregs based on discussing their subsets, surface markers, suppressive function, and signaling pathways in RA.

Role of miRNAs in Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease characterized by autoimmunity, synovial inflammation and joint destruction. Pannus formation in the synovial cavity can cause irreversible damage to the joint and cartilage and eventually permanent disability. Current conventional treatments for RA have limitations regarding efficacy, safety and cost. microRNA (miRNA) is a type of non-coding RNA (ncRNA) that regulates gene expression at the post-transcriptional level. The dysregulation of miRNA has been observed in RA patients and implicated in the pathogenesis of RA. miRNAs have emerged as potential biomarkers or therapeutic agents. In this review, we explore the role of miRNAs in various aspects of RA pathophysiology, including immune cell imbalance, the proliferation and invasion of fibroblast-like synovial (FLS) cell, the dysregulation of inflammatory signaling and disturbance in angiogenesis. We delve into the regulatory effects of miRNAs on Treg/Th17 and M1/M2 polarization, the activation of the NF-κB/NLRP3 signaling pathway, neovascular formation, energy metabolism induced by FLS-cell-induced energy metabolism, apoptosis, osteogenesis and mobility. These findings shed light on the potential applications of miRNAs as diagnostic or therapeutic biomarkers for RA management. Furthermore, there are some strategies to regulate miRNA expression levels by utilizing miRNA mimics or exosomes and to hinder miRNA activity via competitive endogenous RNA (ceRNA) network-based antagonists. We conclude that miRNAs offer a promising avenue for RA therapy with unlimited potential.

Immunology of osteoporosis: relevance of inflammatory targets for the development of novel interventions

Osteoporosis is recognized as low bone mass and deteriorated bone microarchitecture. It is the leading cause of fractures and consequent morbidity globally. The established pathophysiological evidence favors the endocrine factors for osteoporosis and the role of the immune system on the skeletal system has been recently identified. Due to the common developmental niche bone and immune system interactions have led to the emergence of osteoimmunology. Immune dysregulation can initiate inflammatory conditions that adversely affect bone integrity. The role of immune cells, such as T-lymphocytes subsets (Th17), cannot be neglected in the pathogenesis of osteoporosis. Local inflammation within the bone from any cause attracts immune cells that participate in the activation of osteoclasts. This work summarizes the present knowledge of osteoimmunology in reference to osteoporosis and identifies novel targets for immunotherapy of osteoporosis.

Suppression of Dendritic Cell Maturation by Kefir Peptides Alleviates Collagen-Induced Arthritis in Mice

Arthritis is a disorder that is characterized by joint inflammation and other symptoms. Rheumatoid arthritis (RA), an autoimmune disease, is one of the most common arthritis in worldwide. Inflammation of the synovium is the main factor that triggers bone erosion in the joints in RA, but the pathogenesis of RA is not clearly understood. Kefir grain-fermented products have been demonstrated to enhance immune function and exhibit immune-modulating bioactivities. This study aims to explore the role of kefir peptides (KPs) on the regulation of dendritic cell, which are found in RA synovial fluid, and the protection effects of KPs on mice with collagen-induced arthritis (CIA). Immature mouse bone marrow-derived dendritic cells (BMDCs) were treated with KPs (2.2 and 4.4 mg/ml) and then exposed to lipopolysaccharide (LPS) to study the immune regulation function of KPs in dendritic cells. Mice with CIA (n = 5 per group) were orally administrated KPs (3.75 and 7.5 mg/day/kg) for 21 days and therapeutic effect of KPs on mice with arthritis were assessed. In this study, we found that KPs could inhibit surface molecule expression, reduce inflammatory cytokine release, and repress NF-κB and MAPK signaling in LPS-stimulated mouse BMDCs. In addition, a high dose of KPs (7.5 mg/kg) significantly alleviated arthritis symptoms, decreased inflammatory cytokine expression, suppressed splenic DC maturation and decrease the percentage of Th1 and Th17 in the spleens on mice with CIA. Our findings demonstrated that KPs ameliorate CIA in mice through the mechanism of suppressing DC maturation and inflammatory cytokine releases.

A novel CD209 polymorphism is associated with rheumatoid arthritis patients in Taiwan

Single nucleotide polymorphisms (SNPs) in the promoter region of CD209 (cluster of differentiation 209) may influence expression levels, and higher expression of CD209 on immune cells correlate with severity of cartilage destruction in patients with rheumatoid arthritis (RA). Due to the lack of a comprehensive study, this study aimed to investigate the CD209 promoter variants and haplotypes in a Taiwanese population and the association with RA development. Deoxyribonucleic acid (DNA) of peripheral blood mononuclear cells from 126 RA patients and 124 healthy controls was purified, and the CD209 gene promoter was amplified by polymerase chain reaction and analyzed by Sanger sequencing. Results showed that a novel variant −96C>A polymorphism in CD209 promoter was identified in the Taiwanese population, and the frequency was significantly higher in RA patients than in controls (11.51% vs. 2.42%, P < .0001). The odds ratio (OR) for the development of RA was 5.88 (95% CI 2.35–14.74, P < .0001). Other known variants were also evaluated; for instance, −1180 T/T (rs7359874) was increased in RA patients, and the OR for the development of RA was 3.26, 95% CI 0.85–12.52, P = .07). Besides, the haplotype frequencies were calculated; −1180A‐939C‐871 T‐336 T‐139 T‐96A and −1180 T‐939 T‐871C‐336 T‐139C‐96A were increased in RA patients (P = .004 and 0.05, respectively). In summary, CD209‐96A variant could be an important factor for the development of RA in the Taiwanese population.

Potential efficacy of dendritic cell immunomodulation in the treatment of osteoarthritis

Dendritic cells (DCs) are a cluster of heterogeneous antigen-presenting cells that play a pivotal role in both innate and adaptive immune responses. Rare reports have discussed their role in OA immunopathogenesis. Recently, DCs derived from the synovial fluid of OA mice were shown to have increased expression of toll-like receptors. Moreover, from in vitro studies it was concluded that DCs derived from OA patients had secreted high levels of inflammatory cytokines. Likewise, a significant increase in CD123+BDCA-2 plasmacytoid DCs has been observed in the synovial fluid of OA patients. Furthermore, DCs have a peripheral tolerance potential and can become regulatory under specific circumstances. This could be exploited as a promising tool to eliminate immunoinflammatory manifestations in OA disease. In this review, the potential roles DCs could play in OA pathogenesis have been described. In addition, suggestions for the development of new immunotherapeutic strategies involving intra-articular injections of tolerogenic plasmacytoid DCs for treating OA inflammations have been made.

Therapeutic blockade of CXCR2 rapidly clears inflammation in arthritis and atopic dermatitis models: demonstration with surrogate and humanized antibodies

Neutrophils are the most abundant effector cells of the innate immune system and represent the first line of defense against infection. However, in many common pathologies, including autoimmune diseases, excessive recruitment and activation of neutrophils can drive a chronic inflammatory response leading to unwanted tissue destruction. Several strategies have been investigated to tackle pathologic neutrophil biology, and thus provide a novel therapy for chronic inflammatory diseases. The chemokine receptor CXCR2 plays a crucial role in regulating neutrophil homeostasis and is a promising pharmaceutical target. In this study, we report the discovery and validation of a humanized anti-human CXCR2 monoclonal antibody. To enable in vivo studies, we developed a surrogate anti-mouse CXCR2 antibody, as well as a human knock-in CXCR2 mouse. When administered in models of atopic dermatitis (AD) and rheumatoid arthritis (RA), the antibodies rapidly clear inflammation. Our findings support further developments of anti-CXCR2 mAb approaches not only for RA and AD, but also for other neutrophil-mediated inflammatory conditions where neutrophils are pathogenic and medical needs are unmet.

Relevance of Nrf2 and heme oxygenase-1 in articular diseases

Joint conditions pose an important public health problem as they are a leading cause of pain, functional limitation and physical disability. Oxidative stress is related to the pathogenesis of many chronic diseases affecting the joints such as rheumatoid arthritis and osteoarthritis. Cells have developed adaptive protection mechanisms to maintain homeostasis such as nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) which regulates the transcription of many genes involved in redox balance, detoxification, metabolism and inflammation. Activation of Nrf2 results in the synthesis of heme oxygenase-1 (HO-1) leading to the formation of a number of bioactive metabolites, mainly CO, biliverdin and bilirubin. Ample evidence supports the notion that Nrf2 and HO-1 can confer protection against oxidative stress and inflammatory and immune responses in joint tissues. As a consequence, this pathway may control the activation and metabolism of articular cells to play a regulatory role in joint destruction thus offering new opportunities for better treatments. Further studies are necessary to identify improved strategies to regulate Nrf2 and HO-1 activation in order to enable the development of drugs with therapeutic applications in joint diseases.

Endothelial IL-8 induced by porcine circovirus type 2 affects dendritic cell maturation and antigen-presenting function

Background

Porcine circovirus (PCV) disease caused by PCV type 2 (PCV2) is mainly attributed to immunosuppression and immune damage. PCV2 can infect vascular endothelial cells and induce high expression of endothelial IL-8. Dendritic cells (DCs), as professional antigen-presenting cells, can not only present antigens but also activate naïve T-cells, causing an immune response.

Methods

To demonstrate whether endothelial IL-8 is the main factor inhibiting the maturation and related functions of dendritic cells during PCV2 infection, monocyte-derived DCs (MoDCs) and porcine iliac artery endothelial cells (PIECs) processed by different methods were co-cultured in two ways. Flow cytometry, molecular probe labeling, fluorescence quantitative PCR, and the MTS assay were used to detect the changes in related functions and molecules of MoDCs.

Results

Compared to those in the PIEC-DC group, the endothelial IL-8 upregulation co-culture group showed significantly lower double-positive rates for CD80/86 and MHC-II of MoDCs and significantly increased endocytosis of MoDCs. Meanwhile, the adhesion rate and average fluorescence intensity of MoDCs were significantly downregulated in migration and adhesion experiments. Furthermore, the MHC-I and LAMP7 mRNA levels in MoDCs and the proliferation of MoDC-stimulated T-cells were markedly reduced. However, the changes in MoDCs of the endothelial IL-8 downregulation co-culture group were the opposite.

Conclusions

PCV2-induced endothelial IL-8 reduces the adhesion and migration ability of MoDCs, resulting in a decreased maturation rate of MoDCs, and further inhibits antigen presentation by DCs. These results may explain the immunosuppressive mechanism of PCV2 from the perspective of the interaction between endothelial cells and DCs in vitro.

Dendritic cells, T cells and their interaction in rheumatoid arthritis

Dendritic cells (DCs) are the key professional antigen-presenting cells which bridge innate and adaptive immune responses, inducing the priming and differentiation of naive to effector CD4+ T cells, the cross-priming of CD8+ T cells and the promotion of B cell antibody responses. DCs also play a critical role in the maintenance of immune homeostasis and tolerance. DC-T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). Here we describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self-peptide by DCs that triggers differentiation and activation of autoreactive T cells. Finally, we discuss the emerging field of targeting the DC-T cell interaction for antigen-specific immunotherapy of RA.

Regulatory effects of paeoniflorin-6'-O-benzene sulfonate (CP-25) on dendritic cells maturation and activation via PGE2-EP4 signaling in adjuvant-induced arthritic rats

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease. Dendritic cells (DCs) are one of the most powerful antigen-presenting cells, and they play an important role in RA pathogenesis. Prostaglandin E2 (PGE2) is a potent lipid mediator that can regulate the maturation and activation of DCs, but the molecular mechanisms have not been elucidated. In this study, both in vitro and in an RA rat model, we investigated the mechanisms involved by focusing on PGE2-mediated signaling and using a novel anti-inflammatory compound, paeoniflorin-6'-O-benzene sulfonate (CP-25). PGE2 combined with tumor necrosis factor-α promoted DC maturation and activation through EP4-cAMP signaling. Treatment with CP-25 increased the endocytic capacity of DCs induced by PGE2. CP-25 inhibited the potency of DCs induced by the EP4 receptor agonist, CAY10598, to stimulate allogeneic T cells. Consistent with these findings, the CAY10598-induced upregulation of DC surface activation markers and production of IL-23 was significantly inhibited by CP-25 in a concentration-dependent manner. In vivo administration of CP-25 alleviated adjuvant arthritis (AA) in rats through inhibition of DC maturation and activation. Our results indicate that PGE2-EP4-cAMP signal hyperfunction can lead to abnormal activation of DC functions, which correlates with the course of disease in AA rats and provides a possible treatment target. The inhibition of DC maturation and activation by CP-25 interference of the PGE2-EP4 pathway may significantly contribute to the immunoregulatory profile of CP-25 when used to treat RA and other immune cell-mediated disorders.

Updates on Osteoimmunology: What's New on the Cross-Talk Between Bone and Immune System

The term osteoimmunology was coined many years ago to describe the research field that deals with the cross-regulation between bone cells and the immune system. As a matter of fact, many factors that are classically considered immune-related, such as InterLeukins (i.e., IL-6, -11, -17, and -23), Tumor Necrosis Factor (TNF)-α, Receptor-Activator of Nuclear factor Kappa B (RANK), and its Ligand (RANKL), Nuclear Factor of Activated T-cell, cytoplasmatic-1 (NFATc1), and others have all been found to be crucial in osteoclast and osteoblast biology. Conversely, bone cells, which we used to think would only regulate each other and take care of remodeling bone, actually regulate immune cells, by creating the so-called "endosteal niche." Both osteoblasts and osteoclasts participate to this niche, either by favoring engraftment, or mobilization of Hematopoietic Stem Cells (HSCs). In this review, we will describe the main milestones at the base of the osteoimmunology and present the key cellular players of the bone-immune system cross-talk, including HSCs, osteoblasts, osteoclasts, bone marrow macrophages, osteomacs, T- and B-lymphocytes, dendritic cells, and neutrophils. We will also briefly describe some pathological conditions in which the bone-immune system cross-talk plays a crucial role, with the final aim to portray the state of the art in the mechanisms regulating the bone-immune system interplay, and some of the latest molecular players in the field. This is important to encourage investigation in this field, to identify new targets in the treatment of bone and immune diseases.

Blocking Matrix Metalloproteinase-9 Abrogates Collagen-Induced Arthritis via Inhibiting Dendritic Cell Migration

Trafficking of dendritic cells (DCs) to lymph nodes (LNs) to present Ags is a crucial step in the pathogenesis of rheumatoid arthritis (RA). Matrix metalloproteinase-9 (MMP-9) is the key molecule for DC migration. Thus, blocking MMP-9 to inhibit DC migration may be a novel strategy to treat RA. In this study, we used anti-MMP-9 Ab to treat collagen-induced arthritis (CIA) in DBA/1J mice and demonstrated that anti-MMP-9 Ab treatment significantly suppressed the development of CIA via the modulation of DC trafficking. In anti-MMP-9 Ab-treated CIA mice, the number of DCs in draining LNs was obviously decreased. In vitro, anti-MMP-9 Ab and MMP-9 inhibitor restrained the migration of mature bone marrow-derived DCs in Matrigel in response to CCR7 ligand CCL21. In addition, blocking MMP-9 decreased T and B cell numbers in LNs of CIA mice but had no direct influence on the T cell response to collagen II by CD4⁺ T cells purified from LNs or spleen. Besides, anti-MMP-9 Ab did not impact on the expression of MHC class II, CD40, CD80, CD86, and chemokine receptors (CCR5 and CCR7) of DCs both in vivo and in vitro. Furthermore, we discovered the number of MMP-9^-/- DCs trafficking from footpads to popliteal LNs was dramatically reduced as compared with wild type DCs in both MMP-9^-/- mice and wild type mice. Taken together, these results indicated that DC-derived MMP-9 is the crucial factor for DC migration, and blocking MMP-9 to inhibit DC migration may constitute a novel strategy of future therapy for RA and other similar autoimmune diseases.

Monocytes in rheumatoid arthritis: Circulating precursors of macrophages and osteoclasts and, their heterogeneity and plasticity role in RA pathogenesis

Rheumatoid arthritis (RA) is a chronic systemic, autoimmune and inflammatory disease represented as synovitis, pannus formation, adjacent bone erosions, and joint destruction. The major cells involved in the perpetuation of RA pathogenesis are CD4⁺ T-cells (mainly Th1 cells and Th17 cells), fibroblasts like synoviocytes (FLS), macrophages and B cells. Other autoimmune cells such as dendritic cells, neutrophils, mast cells, and monocytes also contribute to RA pathogenesis. Monocytes are mainly bone marrow (BM) derived cells in the circulation. The chemokine receptors CCR2 and CX3CR1 expressed by monocytes interact with chemokine ligands CCL2 (MCP-1) and CX3CL1 (fractalkine) respectively produced by FLS and this interaction promotes their migration and recruitment into RA synovium. Activated monocytes on their surface exhibit upregulated antigenic expressions such as CD14, CD16, HLA-DR, toll-like receptors (TLRs), and adhesion molecules B1 and B2 integrins. RA monocytes interconnect with other cells in a positive loop manner in the propagation of the rheumatoid process. They skew towards mainly intermediate monocyte subsets (CD14⁺⁺ CD16⁺) which produce proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. Moreover, the predominant intermediate monocytes in RA differentiate into M1-macrophages which play a major role in synovial inflammation. Demonstrations suggest monocytes with CD14⁺ and CD16^- expression (classical monocytes?) differentiate to osteoclasts which are the cells responsible for bone erosion in RA synovial joints. Th17 cells induce the production of RANKL by FLS which promotes osteoclastogenesis. Cytokines mainly TNF-α, IL-1β, and IL-6 amplify osteoclastogenesis. Hence, monocytes are the circulating precursors of macrophages and osteoclasts in RA. AIM OF THE REVIEW: To enlighten the identity of monocytes, the antigenic expression on monocyte surface and their cytokines role in RA. We also emphasize about the chemokine receptors expressed by monocytes subsets and chemotaxis of circulating monocytes into RA synovium. Additionally, we review monocytes as the circulating precursors of macrophages and osteoclasts in RA joints and their heterogeneity and plasticity role in RA.

Granulocyte-macrophage colony-stimulating factor-dependent CD11c-positive cells differentiate into active osteoclasts

Levels of circulating cytokines are elevated in inflammatory diseases. Previously, it was shown that interleukin (IL-)17A, in synergism with 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] and tumor necrosis factor α (TNFα), induces the release of granulocyte-macrophage colony-stimulating factor (GM-CSF) by murine osteoblasts in vitro. In this study, we further analyzed the effects of GM-CSF on osteoclast development in vitro. The effects of IL-17A, TNFα, and 1,25(OH)₂D₃ on the regulation of osteoclast development were investigated in cocultures of bone marrow-derived osteoclast progenitor cells (OPC) and mouse calvarial osteoblasts. Additionally, OPC were grown for 3days in media containing macrophage colony-stimulating factor (M-CSF), GM-CSF, or M-CSF/GM-CSF. Subsequently, the osteoclastogenic potential and the capacity to dissolve amorphous calcium phosphate were assessed in each of the three populations of OPC. IL-17A, in synergism with TNFα and 1,25(OH)₂D₃, inhibited the development of osteoclasts in cocultures by stimulating the osteoblast lineage cells to release GM-CSF. GM-CSF-treated OPC expressed traits characteristic of dendritic cells. Upon removal of GM-CSF and supplementation of the culture media with M-CSF/RANKL, the cells lost their dendritic cell characteristics and differentiated into osteoclasts. OPC pretreated with GM-CSF and M-CSF/GM-CSF exhibited delayed development to osteoclasts and an extended proliferation phase. Elevated levels of GM-CSF in systemic inflammatory diseases may cause an expansion of the OPC pools in the bone, bone marrow, and blood. Upon homing to the bone, this may lead to an increase in the number of osteoclasts and in bone resorption.

Collagen induces maturation of human monocyte-derived dendritic cells by signaling through osteoclast-associated receptor

Osteoclast-associated receptor (OSCAR) is widely expressed on human myeloid cells. Collagen types (Col)I, II, and III have been described as OSCAR ligands, and ColII peptides can induce costimulatory signaling in receptor activator for NF-κB-dependent osteoclastogenesis. In this study, we isolated collagen as an OSCAR-interacting protein from the membranes of murine osteoblasts. We have investigated a functional outcome of the OSCAR-collagen interaction in human monocyte-derived dendritic cells (DCs). OSCAR engagement by ColI/II-induced activation/maturation of DCs is characterized by upregulation of cell surface markers and secretion of cytokines. These collagen-matured DCs (Col-DCs) were efficient drivers of allogeneic and autologous naive T cell proliferation. The T cells expanded by Col-DCs secreted cytokines with no clear T cell polarization pattern. Global RNA profiling revealed that multiple proinflammatory mediators, including cytokines and cytokine receptors, components of the stable immune synapse (namely CD40, CD86, CD80, and ICAM-1), as well as components of TNF and TLR signaling, are transcriptional targets of OSCAR in DCs. Our findings indicate the existence of a novel pathway by which extracellular matrix proteins locally drive maturation of DCs during inflammatory conditions, for example, within synovial tissue of rheumatoid arthritis patients, where collagens become exposed during tissue remodeling and are thus accessible for interaction with infiltrating precursors of DCs.

Cytokine-mediated bone destruction in rheumatoid arthritis

Bone homeostasis, which involves formation and resorption, is an important process for maintaining adequate bone mass in humans. Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammation and bone loss, leading to joint destruction and deformity, and is a representative disease of disrupted bone homeostasis. The bone loss and joint destruction are mediated by immunological insults by proinflammatory cytokines and various immune cells. The connection between bone and immunity has been intensely studied and comprises the emerging field of osteoimmunology. Osteoimmunology is an interdisciplinary science investigating the interplay between the skeletal and the immune systems. The main contributors in osteoimmunology are the bone effector cells, such as osteoclasts or osteoblasts, and the immune cells, particularly lymphocytes and monocytes. Physiologically, osteoclasts originate from immune cells, and immune cells regulate osteoblasts and vice versa. Pathological conditions such as RA might affect these interactions, thereby altering bone homeostasis, resulting in the unfavorable outcome of bone destruction. In this review, we describe the osteoclastogenic roles of the proinflammatory cytokines and immune cells that are important in the pathophysiology of RA.

Blood dendritic cells: "canary in the coal mine" to predict chronic inflammatory disease?

The majority of risk factors for chronic inflammatory diseases are unknown. This makes personalized medicine for assessment, prognosis, and choice of therapy very difficult. It is becoming increasingly clear, however, that low-grade subclinical infections may be an underlying cause of many chronic inflammatory diseases and thus may contribute to secondary outcomes (e.g., cancer). Many diseases are now categorized as inflammatory-mediated diseases that stem from a dysregulation in host immunity. There is a growing need to study the links between low-grade infections, the immune responses they elicit, and how this impacts overall health. One such link explored in detail here is the extreme sensitivity of myeloid dendritic cells (mDCs) in peripheral blood to chronic low-grade infections and the role that these mDCs play in arbitrating the resulting immune responses. We find that emerging evidence supports a role for pathogen-induced mDCs in chronic inflammation leading to increased risk of secondary clinical disease. The mDCs that are elevated in the blood as a result of low-grade bacteremia often do not trigger a productive immune response, but can disseminate the pathogen throughout the host. This aberrant trafficking of mDCs can accelerate systemic inflammatory disease progression. Conversely, restoration of dendritic cell homeostasis may aid in pathogen elimination and minimize dissemination. Thus it would seem prudent when assessing chronic inflammatory disease risk to consider blood mDC numbers, and the microbial content (microbiome) and activation state of these mDCs. These may provide important clues (“the canary in the coal mine”) of high inflammatory disease risk. This will facilitate development of novel immunotherapies to eliminate such smoldering infections in atherosclerosis, cancer, rheumatoid arthritis, and pre-eclampsia.

Intra-articular CD1c-expressing myeloid dendritic cells from rheumatoid arthritis patients express a unique set of T cell-attracting chemokines and spontaneously induce Th1, Th17 and Th2 cell activity

INTRODUCTION

Myeloid dendritic cells (mDCs) are potent T cell-activating antigen-presenting cells that have been suggested to play a crucial role in the regulation of immune responses in many disease states, including rheumatoid arthritis (RA). Despite this, studies that have reported on the capacity of naturally occurring circulating mDCs to regulate T cell activation in RA are still lacking. This study aimed to evaluate the phenotypic and functional properties of naturally occurring CD1c (BDCA-1)+ mDCs from synovial fluid (SF) compared to those from peripheral blood (PB) of RA patients.

METHODS

CD1c+ mDC numbers and expression of costimulatory molecules were assessed by fluorescence-activated cell sorting (FACS) analysis in SF and PB from RA patients. Ex vivo secretion of 45 inflammatory mediators by mDCs from SF and PB of RA patients was determined by multiplex immunoassay. The capacity of mDCs from SF to activate autologous CD4+ T cells was measured.

RESULTS

CD1c+ mDC numbers were significantly increased in SF versus PB of RA patients (mean 4.7% vs. 0.6%). mDCs from SF showed increased expression of antigen-presenting (human leukocyte antigen (HLA) class II, CD1c) and costimulatory molecules (CD80, CD86 and CD40). Numerous cytokines were equally abundantly produced by mDCs from both PB and SF (including IL-12, IL-23, IL-13, IL-21). SF mDCs secreted higher levels of interferon γ-inducible protein-10 (IP-10), monokine induced by interferon γ (MIG) and, thymus and activation-regulated chemokine (TARC), but lower macrophage-derived chemokine (MDC) levels compared to mDCs from PB. mDCs from SF displayed a strongly increased capacity to induce proliferation of CD4+ T cells associated with a strongly augmented IFNγ, IL-17, and IL-4 production.

CONCLUSIONS

This study suggests that increased numbers of CD1c+ mDCs in SF are involved in the inflammatory cascade intra-articularly by the secretion of specific T cell-attracting chemokines and the activation of self-reactive T cells.

The Interplay between the bone and the immune system

In the last two decades, numerous scientists have highlighted the interactions between bone and immune cells as well as their overlapping regulatory mechanisms. For example, osteoclasts, the bone-resorbing cells, are derived from the same myeloid precursor cells that give rise to macrophages and myeloid dendritic cells. On the other hand, osteoblasts, the bone-forming cells, regulate hematopoietic stem cell niches from which all blood and immune cells are derived. Furthermore, many of the soluble mediators of immune cells, including cytokines and growth factors, regulate the activities of osteoblasts and osteoclasts. This increased recognition of the complex interactions between the immune system and bone led to the development of the interdisciplinary osteoimmunology field. Research in this field has great potential to provide a better understanding of the pathogenesis of several diseases affecting both the bone and immune systems, thus providing the molecular basis for novel therapeutic strategies. In these review, we reported the latest findings about the reciprocal regulation of bone and immune cells.

Targeting BCL2 family in human myeloid dendritic cells: a challenge to cure diseases with chronic inflammations associated with bone loss

Rheumatoid arthritis (RA) and Langerhans cell histiocytosis (LCH) are common and rare diseases, respectively. They associate myeloid cell recruitment and survival in inflammatory conditions with tissue destruction and bone resorption. Manipulating dendritic cell (DC), and, especially, regulating their half-life and fusion, is a challenge. Indeed, these myeloid cells display pathogenic roles in both diseases and may be an important source of precursors for differentiation of osteoclasts, the bone-resorbing multinucleated giant cells. We have recently documented that the proinflammatory cytokine IL-17A regulates long-term survival of DC by inducing BCL2A1 expression, in addition to the constitutive MCL1 expression. We summarize bibliography of the BCL2 family members and their therapeutic targeting, with a special emphasis on MCL1 and BCL2A1, discussing their potential impact on RA and LCH. Our recent knowledge in the survival pathway, which is activated to perform DC fusion in the presence of IL-17A, suggests that targeting MCL1 and BCL2A1 in infiltrating DC may affect the clinical outcomes in RA and LCH. The development of new therapies, interfering with MCL1 and BCL2A1 expression, to target long-term surviving inflammatory DC should be translated into preclinical studies with the aim to increase the well-being of patients with RA and LCH.

Distribution of regulatory T cells and interaction with dendritic cells in the synovium of rheumatoid arthritis

OBJECTIVES

The aim of this study was to investigate the tissue distribution of regulatory T cells (Treg cells) and their interaction with dendritic cells (DCs) in synovium from patients with rheumatoid arthritis (RA) or osteoarthritis (OA).

METHODS

Immunohistochemical staining was used to investigate the distribution of Treg cells and the interaction between Treg cells and DCs in RA (n = 30) and OA synovium (n = 8). mRNA levels were measured by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Large numbers of Treg cells were observed in lymphoid aggregates and perivenular infiltration areas in the RA synovium. Specific cellular markers for Treg cells (Foxp3, CD39, LAG-3, and Nrp-1) were found in lymphoid aggregates, perivenular infiltration, and scattered in lining layer areas. As molecular markers for DCs, DC-LAMP, DEC-205, CD80/86, and CD83 were also detected in the lymphoid aggregates and perivenular infiltration areas in RA. Furthermore, the co-localization of Treg cells and DCs was confined mainly in the lymphoid aggregation areas. The number of DCs increased significantly more than the number of Treg cells with inflammatory progression in RA. mRNA expression of the cellular markers for Treg cells (Foxp3, LAG-3, and Nrp-1) and the molecular markers for DCs (DC-LAMP and DEC-205) was increased in RA compared with OA synovium.

CONCLUSIONS

Our results indicate that DCs play a dominant role in regulating the activation and progression of immune responses in RA, even though the number of Treg cells was upregulated at the same time. This suggests that Treg cells do not function normally to suppress the maturation of DCs in the RA synovium.

SB1578, a novel inhibitor of JAK2, FLT3, and c-Fms for the treatment of rheumatoid arthritis

SB1578 is a novel, orally bioavailable JAK2 inhibitor with specificity for JAK2 within the JAK family and also potent activity against FLT3 and c-Fms. These three tyrosine kinases play a pivotal role in activation of pathways that underlie the pathogenesis of rheumatoid arthritis. SB1578 blocks the activation of these kinases and their downstream signaling in pertinent cells, leading to inhibition of pathological cellular responses. The biochemical and cellular activities of SB1578 translate into its high efficacy in two rodent models of arthritis. SB1578 not only prevents the onset of arthritis but is also potent in treating established disease in collagen-induced arthritis mice with beneficial effects on histopathological parameters of bone resorption and cartilage damage. SB1578 abrogates the inflammatory response and prevents the infiltration of macrophages and neutrophils into affected joints. It also leads to inhibition of Ag-presenting dendritic cells and inhibits the autoimmune component of the disease. In summary, SB1578 has a unique kinase spectrum, and its pharmacological profile provides a strong rationale for the ongoing clinical development in autoimmune diseases.

[Regulation of inflammation through JAK3-Stat6 pathway in dendritic cells]

Dendritic cells (DCs) is the cell that act as source of the immune response by exquisitely presenting antigens to acquired immunity such as the T cells. Janus kinase (JAK) is a tyrosine kinase that is activated immediately after the cytokine binds to its unique receptor expressed on the cell surface. Among the JAKs, expression of JAK3 is limited on haematopoietic cells and is indispensable for lymphocyte development and proliferation. We have demonstrated that JAK3-deficient DCs normally develop, uptake antigens, produce inflammatory cytokines and function as an antigen-presenting cell, although they over-produce IL-10. Among the transcription factors that are known to be activated by JAK3, we explored the phenotype of Stat6-deficient DCs which is a transcription factor specifically activated by JAK3. Interestingly, development, function and inflammatory cytokine production was normal with over-production of IL-10 which was in line with the JAK3-deficient DCs. IL-4 is well known to activate JAK3-Stat6 in the cytoplasm and has been reported to be produced in the synovial fluid of rheumatoid arthritis patients. Hence the suppression of IL-10 production by IL-4 can be considered as one of the inflammatory process of arthritis. Moreover, induction of IL-10 production by DCs can be one mechanism of action of the JAK inhibitor (tofacitinib) which have shown high efficiency on active rheumatoid arthritis in clinical trials.

Dendritic cells in the pathogenesis and treatment of human diseases: a Janus Bifrons?

Dendritic cells (DCs) represent the bridging cell compartment between a variety of nonself antigens (i.e., microbial, cancer and vaccine antigens) and adaptive immunity, orchestrating the quality and potency of downstream immune responses. Because of the central role of DCs in the generation and regulation of immunity, the modulation of DC function in order to shape immune responses is gaining momentum. In this respect, recent advances in understanding DC biology, as well as the required molecular signals for induction of T-cell immunity, have spurred many experimental strategies to use DCs for therapeutic immunological approaches for infections and cancer. However, when DCs lose control over such 'protective' responses - by alterations in their number, phenotype and/or function - undesired effects leading to allergy and autoimmune clinical manifestations may occur. Novel therapeutic approaches have been designed and currently evaluated in order to address DCs and silence these immunopathological processes. In this article we present recent concepts of DC biology and some medical implications in view of therapeutic opportunities.

Histone deacetylase inhibition alters dendritic cells to assume a tolerogenic phenotype and ameliorates arthritis in SKG mice

INTRODUCTION

The purpose of this study was to elucidate the effects of histone deacetylase inhibition on the phenotype and function of dendritic cells and on arthritis in SKG mice.

METHODS

Arthritis was induced in SKG mice by zymosan A injection. Trichostatin A, a histone deacetylase inhibitor, was administered and its effects on arthritis were evaluated by joint swelling and histological evaluation. Interleukin-17 production in lymph node cells was determined by an enzyme-linked immunosorbent assay (ELISA). Foxp3 expression in lymph node cells and the phenotypes of splenic dendritic cells were examined by fluorescence-activated cell sorting (FACS). Bone marrow-derived dendritic cells (BM-DC) were generated with granulocyte macrophage colony-stimulating factor. The effects of trichostatin A on cell surface molecules, cytokine production, indoleamine 2,3-dioxygenase (IDO) expression and T cell stimulatory capacity were examined by FACS, ELISA, quantitative real-time polymerase chain reaction and Western blot, and the allo-mixed lymphocyte reaction, respectively.

RESULTS

Trichostatin A, when administered before the onset of arthritis, prevented SKG mice from getting arthritis. Trichostatin A treatment also showed therapeutic effects on arthritis in SKG mice, when it was administered after the onset of arthritis. Trichostatin A treatment reduced Th17 cells and induced regulatory T cells in lymph node, and also decreased co-stimulatory molecule expression on splenic dendritic cells in vivo. In vitro, trichostatin A markedly suppressed zymosan A-induced interleukin-12 and interleukin-6 production by BM-DC and up-regulated IDO expression at mRNA and protein levels. Trichostatin A-treated BM-DC also showed less T cell stimulatory capacity.

CONCLUSIONS

Histone deacetylase inhibition changes dendritic cells to a tolerogenic phenotype and ameliorates arthritis in SKG mice.

Dendritic cell responses to surface properties of clinical titanium surfaces

Dendritic cells (DCs) play pivotal roles in responding to foreign entities during the innate immune response and in initiating effective adaptive immunity as well as maintaining immune tolerance. The sensitivity of DCs to foreign stimuli also makes them useful cells to assess the inflammatory response to biomaterials. Elucidating material property-DC phenotype relationships using a well-defined biomaterial system is expected to provide criteria for immunomodulatory biomaterial design. Clinical titanium (Ti) substrates, including pretreatment (PT), sand blasted and acid etched (SLA), and modified SLA (modSLA), with different roughnesses and surface energies were used to treat DCs and resulted in differential DC responses. PT and SLA induced a mature DC (mDC) phenotype, while modSLA promoted a non-inflammatory environment by supporting an immature DC (iDC) phenotype, based on surface marker expression, cytokine production profiles and cell morphology. Principal component analysis (PCA) confirmed these experimental results, and also indicated that the non-stimulating property of modSLA covaried with certain surface properties, such as high surface hydrophilicity, percent oxygen and percent Ti of the substrates. In addition to previous research that demonstrated superior osteogenic properties of modSLA compared with PT and SLA, the results reported herein indicates that modSLA may further benefit implant osteointegration by reducing local inflammation and its associated osteoclastogenesis.

Osteoclastogenesis and arthritis

There is emerging interest for osteoclasts as key players in the erosive and inflammatory events leading to joint destruction in chronic arthritis. In fact, chronic inflammatory joint diseases such as psoriatic arthritis and rheumatoid arthritis are often characterized by destruction of juxta-articular bone and erosions due to the elevated activity of osteoclasts, which are involved in bone resorption. The main step in inflammatory bone erosion is an imbalance between bone resorption and bone formation: osteoclast formation is enhanced by proinflammatory cytokines such as TNF-α, IL-1β, and IL-17 and is not balanced by increased activity of bone-forming osteoblasts. T-cells, stromal cells, and synoviocytes enhance osteoclast formation via expression of RANKL and, under pathologic conditions, of proinflammatory cytokines. In rheumatoid arthritis, accumulation of osteoclasts in synovial tissues and their activation associated with osteoclastogenic cytokines and chemokines at cartilage erosion sites suggest that they could be usefully selected as therapeutic target. In particular, in consideration of the primary role of RANKL and TNF-α in osteoclastogenesis, the control of the production of RANKL and the inhibition of TNF-α represent important strategies for reducing bone damage in this disease.

Genome-wide expression analyses establish dendritic cells as a new osteoclast precursor able to generate bone-resorbing cells more efficiently than monocytes

Dendritic cells (DCs), mononuclear cells that initiate immune responses, and osteoclasts (OCs), multinucleated bone-resorbing cells, are hematopoietic cells derived from monocytic precursor cells. Using in vitro generated dendritic cells, we previously showed that human and murine DCs could transdifferentiate into resorbing osteoclasts in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kappaB ligand (RANKL). In this study we globally compared by transcriptomic profiling this new osteoclast differentiation pathway from DCs with the canonical differentiation pathway from monocytes. DNA chip data revealed that starting from two very distinct cell types, treatment with M-CSF and RANKL generated two highly similar types of osteoclast. In particular, DC-derived osteoclasts expressed all the characteristic marker genes of monocyte-derived osteoclasts. Two major molecular events could be observed during osteoclastogenesis: downregulation of a large set of monocyte or DC specific markers, together with upregulation of characteristic osteoclast marker genes. Most interestingly, our transcriptomic data showed a closer molecular profile between DCs and OCs than between monocytes and OCs. Our data establish DCs as a new osteoclast precursor able to generate OCs more efficiently than monocytes.

Dendritic cells as targets for therapy in rheumatoid arthritis

Dendritic cells (DCs) are central in inducing immunity and in mediating immune tolerance in their role as professional antigen-presenting cells. In the absence of DCs, a fatal autoimmunity develops in animal models. Although the role of DCs has been investigated extensively in the pathogenesis of rheumatoid arthritis (RA), it remains unclear whether DCs initiate autoimmunity in this disease. Nevertheless, evidence points towards a significant role for DCs in disease maintenance and progression. Current biologic therapies target cytokine products of antigen-presenting cells, such as tumor necrosis factor, interleukin-1 and interleukin-6. Emerging therapies for RA exploit the tolerogenic capacity of DCs. 'Tolerogenic' DCs can be generated from myeloid precursors ex vivo, loaded with antigen, and manipulated to suppress autoimmune responses in vivo, through the induction of activation-induced cell death, anergy, and/or regulatory T cells. Cells that are primed by DCs, such as B cells, type 1 and type 17 T helper cells, and that have been implicated in certain models of autoimmunity, are also being considered as additional targets for immune-based therapy. Studies to validate these approaches to ameliorate autoimmunity will be necessary before their application in the clinic.

A novel paradigm for dendritic cells as effectors of cartilage destruction

OBJECTIVE

Dendritic cells (DCs) are enriched in RA synovium and have been implicated in the pathogenesis of RA primarily through their ability to present autoantigen and activate T cells. However, whether DCs play an effector role in cartilage destruction is unknown. The aim of this study was to investigate whether DCs can induce collagen release from cartilage and the mechanism involved.

METHODS

Human monocyte-derived DCs (mDCs) were activated with CD40 ligand (CD40L) to mimic DC-T-cell interaction, and supernatants were incubated with cartilage explants. Hydroxyproline was assessed as a measure of collagen release and collagenolytic activity was measured by a bioassay using tritiated collagen. TNF-alpha in DC supernatants was measured by specific ELISA.

RESULTS

Supernatants from CD40L-activated mDCs, but not unstimulated mDCs, strongly induced the destruction of cartilage collagen. mDC supernatants did not contain collagenases but did induce collagenolytic activity in cartilage explants. Neutralization of TNF-alpha in mDC supernatants completely abolished collagenolysis.

CONCLUSIONS

This study shows that mDCs, upon CD40-ligation, induce cartilage collagen degradation through an indirect mechanism via the production of TNF-alpha. Our data suggest a potential important role for mDC-derived TNF-alpha in RA, which is in line with the previously reported observations that DCs are a major source of TNF-alpha in early autoimmune lesions and that anti-TNF-alpha therapeutics effectively suppress joint damage in RA patients. We propose that DCs can act as effectors in cartilage destruction, adding a new aspect to the functional role of DCs in RA pathogenesis.

Endogenous galectin-3 is localized in membrane lipid rafts and regulates migration of dendritic cells

This study reveals a function of endogenous galectin-3, an animal lectin recognizing beta-galactosides, in regulating dendritic cell motility both in vitro and in vivo, which to our knowledge is unreported. First, galectin-3-deficient (gal3(-/-)) bone marrow-derived dendritic cells exhibited defective chemotaxis compared to gal3(+/+) cells. Second, cutaneous dendritic cells in gal3(-/-) mice displayed reduced migration to draining lymph nodes upon hapten stimulation compared to gal3(+/+) mice. Moreover, gal3(-/-) mice were impaired in the development of contact hypersensitivity relative to gal3(+/+) mice in response to a hapten, a process in which dendritic cell trafficking to lymph nodes is critical. In addition, defective signaling was detected in gal3(-/-) cells upon chemokine receptor activation. By immunofluorescence microscopy, we observed that galectin-3 is localized in membrane ruffles and lamellipodia in stimulated dendritic cells and macrophages. Furthermore, galectin-3 was enriched in lipid raft domains under these conditions. Finally, we determined that ruffles on gal3(-/-) cells contained structures with lower complexity compared to gal3(+/+) cells. In view of the participation of membrane ruffles in signal transduction and cell motility, we conclude that galectin-3 regulates cell migration by functioning at these structures.

Transcriptional outcome of Wnt-Frizzled signal transduction in inflammation: evolving concepts

Wnt-Frizzled signaling was first identified as a key event in Drosophila development. Over the years, ample evidence has accumulated regarding the multiple roles of Wnt-Frizzled signaling in mammalian cell differentiation and tissue/organ morphogenesis. It is thus not surprising that variations in the regulatory network of the Wnt signaling scheme would lead to alterations in cellular organization and cell activation and to the development of pathogenic conditions. Several reports have accordingly implied the involvement of Wnt-Frizzled signaling in the activation of proinflammatory mediators in inflammatory disorders. We will discuss how Wnt-Frizzled signaling may initiate/augment inflammation, focusing on its transcriptional outcome.

Cells of the synovium in rheumatoid arthritis. Dendritic cells

Dendritic cells are the major antigen-presenting and antigen-priming cells of the immune system. We review the antigen-presenting and proinflammatory roles played by dendritic cells in the initiation of rheumatoid arthritis (RA) and atherosclerosis, which complicates RA. Various signals that promote the activation of NF-κB and the secretion of TNF and IL-1 drive the maturation of dendritic cells to prime self-specific responses, and drive the perpetuation of synovial inflammation. These signals may include genetic factors, infection, cigarette smoking, immunostimulatory DNA and oxidized low-density lipoprotein, with major involvement of autoantibodies. We propose that the pathogenesis of RA and atherosclerosis is intimately linked, with the vascular disease of RA driven by similar and simultaneous triggers to NF-κB.

Tumour immunity: effector response to tumour and role of the microenvironment

Substantial evidence shows that inflammation promotes oncogenesis and, occasionally, participates in cancer rejection. This paradox can be accounted for by a dynamic switch from chronic smouldering inflammation promoting cancer-cell survival to florid, tissue-disruptive inflammatory reactions that trigger cancer-cell destruction. Clinical and experimental observations suggest that the mechanism of this switch recapitulates the events associated with pathogen infection, which stimulate immune cells to recognise danger signals and activate immune effector functions. Generally, cancers do not have danger signals and, therefore, they cannot elicit strong immune reactions. Synthetic molecules have been developed that mimic pathogen invasion at the tumour site. These compounds activate dendritic cells to produce proinflammatory cytokines, which in turn trigger cytotoxic mechanisms leading to cancer death. Simultaneously, dendritic cells capture antigen shed by dying cancer cells, undergo activation, and stimulate antigen-specific T and B cells. This process results in massive amplification of the antineoplastic inflammatory process. Thus, although anti-inflammatory drugs can prevent onset of some malignant diseases, induction of T cells specific for tumour antigen by active immunisation, combined with powerful activation signals within the cancer microenvironment, might yield the best strategy for treatment of established cancers.

Blood dendritic cell levels and phenotypic characteristics in relation to etiology of end-stage heart failure: implications for dilated cardiomyopathy

BACKGROUND

Dysregulation of dendritic cell (DC) mediated immune responses towards auto-antigens, is considered an important feature in the maintenance of experimentally induced heart failure (HF). In order to evaluate the role of blood DCs in cardiomyopathies of different origins, we examined myeloid (mDC) and plasmacytoid (pDC) subset levels and maturation characteristics, according to HF severity and etiology in humans.

METHODS

Absolute numbers of mDCs and pDCs in 12 New York Heart Association (NYHA) class-II, 28 NYHA class III-IV HF patients and 18 healthy controls, were studied by 4-colour whole blood flow cytometry.

RESULTS

End-stage (NYHA III-IV) HF patients had comparable circulating DC subset levels to NYHA-II patients and controls. However, within the NYHA III-IV group total DC levels in patients with non-ischemic dilated cardiomyopathy (DCM) were higher (P<0.001) than in patients with coronary artery disease (CAD), hypertrophic cardiomyopathy (HCM) or other HF etiology. This was due to a significant increase of primarily mDCs (P<0.0001) and to a lesser extent of pDCs (P<0.05) in idiopathic DCM patients, independent of systolic or diastolic cardiac dysfunction. Maturation marker CD83 and lymphoid homing chemokine receptor CCR7 surface expression was enhanced only on mDCs, but not pDCs from DCM patients (P<0.05), compared to patients with CAD, HCM or other underlying cardiac pathophysiology.

CONCLUSIONS

Total blood DC levels in end-stage HF are elevated in patients with DCM. Whole blood DC characterisation may lead to new insights into the pathophysiology of idiopathic DCM in humans.

Involvement of dendritic cells in autoimmune diseases in children

Dendritic cells (DCs) are professional antigen-presenting cells that are specialized in the uptake of antigens and their transport from peripheral tissues to the lymphoid organs. Over the last decades, the properties of DCs have been intensely studied and much knowledge has been gained about the role of DCs in various diseases and health conditions where the immune system is involved, particularly in cancer and autoimmune disorders. Emerging clues in autoimmune diseases, suggest that dendritic cell dysregulation might be involved in the development of various autoimmune disorders in both adults and children. However, studies investigating a possible contribution of DCs in autoimmune diseases in the pediatric population alone are scanty. The purpose of this review is to give a general overview of the current literature on the relevance of dendritic cells in the most common autoimmune conditions of childhood.

Dendritic cells at the osteo-immune interface: implications for inflammation-induced bone loss

Within the past decade, the critical roles of T cells and T cell-mediated immunity in inflammation-induced osteoclastogenesis and subsequent bone loss have been extensively studied, thereby establishing the new paradigm of osteoimmunology. Therefore, dendritic cells (DCs), the most potent antigen-presenting cells, responsible for activation of naïve T cells and orchestration of the immune response, became critically situated at the osteo-immune interface. Today, emerging new evidence suggests that DC may be directly involved in inflammation-induced osteoclastogenesis and bone loss, by acting as osteoclast (OC) precursors that can further develop into DC-derived OCs (DDOC) under inflammatory conditions. These findings have tremendous implications, because in addition to DC's important roles in regulating innate and adaptive immunity, a direct contribution by these cells to inflammation-induced bone loss may provide a promising therapeutic target not only for controlling inflammation but also for modulating bone destruction.

The Influence of MHC Class II Molecules Containing the Rheumatoid Arthritis Shared Epitope on the Immune Response to Aggrecan G1 and Its Peptides

Aggrecan has been implied as an autoantigen in rheumatoid arthritis (RA). Immunization with aggrecan induces arthritis in BALB/c (H-2(d)) mice but not in other strains of mice [e.g. C57BL/6 (H-2(b))]. In humans, the strongest genetic association with RA is to the shared epitope (SE), and aggrecan peptides are predicted to bind to the SE. Therefore, we hypothesized that C57BL/6 mice transgenic (tg) for the RA SE (DR4 tg mice) may be susceptible to aggrecan-induced arthritis. C57BL/6 and DR4 tg mice were immunized with a mixture of SE-binding aggrecan peptides and tested for immune responses to the corresponding peptides as well as aggrecan. Sustained T- and B-cell immune responses to aggrecan and several of its peptides were detected in DR4 tg mice. C57BL/6 mice showed only transient T-cell responses to different immunizing peptides and little B-cell response. Therefore, an immune response to peptides of aggrecan can be induced experimentally in DR4 tg mice as anticipated from the predicted and actual binding affinities of these peptides for the RA SE. Failure to induce arthritis in these DR4 tg mice may be due to a lack of appropriate non-MHC genes.

Breast cancer instructs dendritic cells to prime interleukin 13-secreting CD4+ T cells that facilitate tumor development

We previously reported (Bell, D., P. Chomarat, D. Broyles, G. Netto, G.M. Harb, S. Lebecque, J. Valladeau, J. Davoust, K.A. Palucka, and J. Banchereau. 1999. J. Exp. Med. 190: 1417–1426) that breast cancer tumors are infiltrated with mature dendritic cells (DCs), which cluster with CD4⁺ T cells. We now show that CD4⁺ T cells infiltrating breast cancer tumors secrete type 1 (interferon γ) as well as high levels of type 2 (interleukin [IL] 4 and IL-13) cytokines. Immunofluorescence staining of tissue sections revealed intense IL-13 staining on breast cancer cells. The expression of phosphorylated signal transducer and activator of transcription 6 in breast cancer cells suggests that IL-13 actually delivers signals to cancer cells. To determine the link between breast cancer, DCs, and CD4⁺ T cells, we implanted human breast cancer cell lines in nonobese diabetic/LtSz-scid/scid β2 microglobulin–deficient mice engrafted with human CD34⁺ hematopoietic progenitor cells and autologous T cells. There, CD4⁺ T cells promote early tumor development. This is dependent on DCs and can be partially prevented by administration of IL-13 antagonists. Thus, breast cancer targets DCs to facilitate its development.

NF-kappa B as a therapeutic target in autoimmune disease

NF-kappaB transmits signals from the cell surface to the nucleus. Signaling through cell surface receptors to activate NF-kappaB and mitogen-activated protein kinases through adaptor molecules is of critical importance to survival and activation of all cells in the body, including those regulating innate and adaptive immunity. As such, NF-kappaB is a key signaling component in autoimmunity and an attractive target for autoimmune disease therapy. However, given its global importance, targeting NF-kappaB tends to be immunosuppressive. In this review, the authors discuss the roles played by NF-kappaB in autoimmunity, drugs which target it, and complexities which need to be addressed to improve the use of NF-kappaB as a target. Finally, the authors highlight some novel approaches that are likely to be important in the next generation of NF-kappaB therapies.

Immune interactions with CD4+ T cells promote the development of functional osteoclasts from murine CD11c+ dendritic cells

Dendritic cells (DC) are innate immune effectors and are critically involved in regulating T cell immunity. Osteoclasts (OC) are bone-resorbing cells derived from the monocyte/macrophage lineage in response to receptor activator of NF-kappaB ligand (RANKL). DC and T cells form aggregates in the inflammatory infiltrates at active disease sites in human and in experimental rheumatoid arthritis and periodontitis. We investigated whether DC interactions with T cells in the bone environment can support the development of functional OC. In the present study, we demonstrate that upon proper activation by microbial or protein Ags (namely Actinobacillus actinomycetemcomitans, bovine insulin, and outer membrane protein-1) and during immune interactions with CD4+ T cells in vitro, murine BM-derived and splenic CD11c+ DC (CD11b- F4/80- Ly-6C- CD31-) develop into TRAP+ CT-R+ cathepsin-k+ functional OC in a RANKL/RANK-dependent manner. Rescue and blocking experiments using CD11c+ DC derived from Csf-1(-/-) op/op mice show that M-CSF is required "before" developing such osteoclastogenic potential upstream of RANKL/RANK signaling, suggesting that immature CD11c+ DC can indeed act like OC precursors. In addition, these CD11c+ DC-derived OC are capable of inducing bone loss after adoptive transfer in vivo. These data suggest a direct contribution of DC during immune interactions with CD4+ T cells to inflammation-induced osteoclastogenesis. Therefore, our findings not only provide further evidence for DC plasticity, but also extend the current paradigm of osteoimmunology.

Novel insights in the regulation of CCL18 secretion by monocytes and dendritic cells via cytokines, toll-like receptors and rheumatoid synovial fluid

BACKGROUND

The T cell attracting chemokine CCL18 is produced by antigen presenting cells and a role for CCL18 has been suggested in the pathogenesis of a variety of diseases. Rheumatoid arthritis (RA) is one of these conditions, in which abundant CCL18 production is present. Although Th2 cytokines and IL-10 are known to have an effect on CCL18 production, there are several gaps in our knowledge regarding the exact regulation of CCL18 secretion, both in general and in RA. In this study we provide new insights in the regulation of CCL18 secretion by monocytes and dendritic cells.

RESULTS

In contrast to a large panel of pro-inflammatory stimuli (IL-1beta, TNF-alpha, IL-10, IL-13, IL-15, IL-17, IL-18, IFN-gamma), T cell mimicking molecules (RANKL, CD40L) or TLR driven maturation, the anti-inflammatory IL-10 strongly stimulated DC to secrete CCL18. On freshly isolated monocytes, CCL18 secretion was induced by IL-4 and IL-13, in strong synergy with IL-10. This synergistic effect could already be observed after only 24 hours, indicating that not only macrophages and dendritic cells, but also monocytes secrete CCL18 under these stimulatory conditions. A high CCL18 expression was detected in RA synovial tissue and incubation of monocytes with synovial fluid from RA patients clearly enhanced the effects of IL-4, IL-13 and IL-10. Surprisingly, the effect of synovial fluid was not driven by IL-10 of IL-13, suggesting the presence of another CCL18 inducing factor in synovial fluid.

CONCLUSION

In summary, IL-10 synergistically induces CCL18 secretion in combination with IL-4 of IL-13 on monocytes and monocyte derived cells. The effects of IL-14, IL-13 and IL-10 are strongly enhanced by synovial fluid. This synergy may contribute to the high CCL18 expression in RA.

Cancer immunotherapy using dendritic/tumour-fusion vaccine induces elevation of serum anti-nuclear antibody with better clinical responses

Dendritic cell (DC) vaccines might induce both anti-tumour immunity and autoimmunity. In this report, we demonstrate elevated levels of anti-nuclear antibody (ANA) in the sera of patients with cancer who had received immunotherapy with a dendritic/tumour-fusion vaccine. Twenty-two patients were treated with DC vaccine of fusion cells composed of autologous DCs and tumour cells (DC/tumour-fusion vaccine), which was generated by treating each cell type with polyethylene glycol. Nine of the 22 patients were treated with both the DC/tumour-fusion vaccine and systemic administration of recombinant human interleukin (rhIL)-12. Serum levels of ANA were examined with an enzyme-linked immunosorbent assay kit. One patient with gastric carcinoma (patient 1, DC/tumour-fusion vaccine alone), one patient with breast cancer (patient 2, DC/tumour-fusion vaccine alone) and one patient with ovarian cancer (patient 3, DC/tumour-fusion vaccine + rhIL-12) showed significant elevations of serum ANA levels during treatment. In patient 1 malignant ascitic effusion resolved and serum levels of tumour markers decreased. Patients 2 and 3 remained in good physical condition during treatment for 24 and 9 months, respectively. Immunoblot analysis indicated antibody responses to autologous tumour cells after vaccination in patient 2. None of the treated patients showed clinical symptoms suggesting autoimmune disease. Patients with elevated serum levels of ANA had significantly longer treatment periods than those without it. Elevated serum levels of ANA after DC/tumour-fusion cell vaccine might be associated with anti-tumour immune response induced by the vaccination.

IL-32, a proinflammatory cytokine in rheumatoid arthritis

IL-32 is a recently discovered cytokine that induces TNFalpha, IL-1beta, IL-6, and chemokines. We investigated whether IL-32 is expressed in the synovia of patients with rheumatoid arthritis (RA) and studied associations with disease severity and the presence of other cytokines. Immunohistochemistry revealed that IL-32 is highly expressed in RA synovial tissue biopsies, whereas IL-32 was not observed in synovial tissues from patients with osteoarthritis. Moreover, in synovial biopsies from 29 RA patients with active disease, the level of IL-32 staining correlated with erythrocyte sedimentation rate, a marker of systemic inflammation (R = 0.63 and P < 0.0003). Synovial staining of IL-32 also correlated with indices of synovial inflammation (R = 0.80 and P < 0.0001) as well as synovial presence of TNFalpha (R = 0.68 and P < 0.004), IL-1beta (R = 0.79 and P < 0.0001), and IL-18 (R = 0.82 and P < 0.001). IL-32 was a potent inducer of prostaglandin E(2) release in mouse macrophages and human blood monocytes, an important property for inflammation. After the injection of human IL-32gamma into the knee joints of naïve mice, joint swelling, with pronounced influx of inflammatory cells and cartilage damage, was observed. In TNFalpha-deficient mice, IL-32-driven joint swelling was absent and cell influx was markedly reduced, but loss of proteoglycan was unaffected, suggesting that IL-32 activity is, in part, TNFalpha-dependent. IL-32, strongly associated with TNFalpha, IL-1beta, and IL-18, appears to play a role in human RA and may be a novel target in autoimmune diseases.