Dendritic cells: the driving force behind autoimmunity in rheumatoid arthritis?

Monocyte Expressed Macromolecular C1 and C1q Receptors as Molecular Sensors of Danger: Implications in SLE

The ability of circulating blood monocytes to express C1q receptors (cC1qR and gC1qR) as well as to synthesize and secrete the classical pathway proteins C1q, C1r, and C1s and their regulator, C1-INH is very well established. What is intriguing, however, is that, in addition to secretion of the individual C1 proteins monocytes are also able to display macromolecular C1 on their surface in a manner that is stable and functional. The cell surface C1 complex is presumably formed by a Ca²⁺-dependent association of the C1r₂⋅C1s₂ tetramer to C1q, which in turn is anchored via a membrane-binding domain located in the N-terminus of its A-chain as shown previously. Monocytes, which circulate in the blood for 1–3 days before they move into tissues throughout the body, not only serve as precursors of macrophages and dendritic cells (DCs), but also fulfill three main functions in the immune system: phagocytosis, antigen presentation, and cytokine production. Since the globular heads of C1q within the membrane associated C1 are displayed outwardly, we hypothesize that their main function – especially in circulating monocytes – is to recognize and capture circulating immune complexes or pathogen-associated molecular patterns in the blood. This in turn may give crucial signal, which drives the monocytes to migrate into tissues, differentiate into macrophages or DCs, and initiate the process of antigen elimination. Unoccupied C1q on the other hand may serve to keep monocytes in a pre-dendritic phenotype by silencing key molecular players thus ensuring that unwarranted DC-driven immune response does not occur. In this paper, we will discuss the role of monocyte/DC-associated C1q receptors, macromolecular C1 as well as secreted C1q in both innate and acquired immune responses.

Evidence for active antigen presentation by monocyte/macrophages in response to stimulation with particles: the expression of NFκB transcription factors and costimulatory molecules

BACKGROUND

The macrophage and lymphocyte response to wear debris contributes to the failure of some joint replacements. Costimulatory molecule expression by particle-containing macrophages is an evidence for antigen presentation. The NFκB transcription factors are regulators of costimulatory molecules and are present in tissue near failed joint prostheses. The tissue localisation of NFκB and the expression of these factors and costimulatory molecules by U937 cells stimulated with nano- and microparticles are reported, together with the effects of an NFκB inhibitor (sc514).

MATERIALS AND METHODS

The tissue localisation of RelA, RelB, c-rel, p50, p52 and NF-IL6 was examined by immunohistochemistry in samples from 15 patients with failure of metal against polyethylene total hip replacements. The expression of these NFκB factors by U937 cells stimulated with microparticles (CoCr, diamond) and nanoparticles (diamond) was examined by quantified RT-PCR. Lipopolysaccharide provided positive controls while negative controls had no additions to culture. Inhibition of NFκB activity by sc-514 was studied. The expression of costimulatory molecules (CD80, CD86 and HLA-DR) was evaluated in parallel cell culture studies by tricolour flow cytometry.

RESULTS AND DISCUSSION

Immunohistochemistry of tissue showed the highest expression for NF-IL6 (32.56 ± 11.61 per cent), RelA (33.66 ± 9.98 per cent) and p52 (32.07 ± 12.90 per cent), then RelB (22.63 ± 7.49 per cent), c-rel (14.07 ± 6.72 per cent) and p50 (13.07 ± 5.99 per cent). NF-IL6 was localised to macrophages, RelB to RFD1+ dendritic cells. U937 cells showed an increased expression of all NFκB factors (p < 0.01) in response to CoCr and diamond microparticles. Only RelA and c-rel (p < 0.01) were increased by one diamond nanoparticle and p52 and c-rel (p < 0.01) by another nanoparticulate diamond. Inhibition by sc-514 of RelA, c-rel and p50 expression occurred with all four particles, p52 was decreased for all diamond particles (but not CoCr) and RelB was not inhibited with any of the particles. CD86 and HLA-DR expression were upregulated by microparticles (CoCr, diamond) (p ≪ 0.01) with lower levels (significant) of these molecules found with diamond nanoparticles. CD80 expression was much less than CD86 and HLA-DR. Costimulatory molecule expression in the bone-implant interface indicates antigen presentation by macrophages. Functional studies with U937 monocytes show the same molecules expressed on exposure to micro- and nanoparticles. Highest values occur with CoCr while the smallest diamond nanoparticles are the least stimulatory. NFκB expression gives an insight into the immunogenic potential of the different particles.

Synovium CD20 expression is a potential new predictor of bone erosion progression in very-early arthritis treated by sequential DMARDs monotherapy -- a pilot study from the VErA cohort

OBJECTIVE

Because available biomarkers (rheumatoid factors [RF], anti-cyclic citrullinated autoantibodies [anti-CCP2], erythrocyte sedimentation rate at 1st hour [ESR]/C-reactive peptide [CRP] and bone erosions) are insufficient to predict rheumatoid arthritis (RA) structural damage, to determine whether synovium expression of greater or equal to 1 markers could constitute new prognostic factor(s).

METHOD

The study was conducted on 18 prospectively enrolled disease-modifying anti-rheumatic drug (DMARD)- and glucocorticoid-naïve, VErA cohort patients with very-early arthritis (median duration: 4months). Recorded at baseline were: clinical and biological (serum ESR, CRP, RF-isotypes, anti-CCP2, osteoprotegerin, receptor activator of nuclear κB-ligand [RANK-L] and cartilage oligomeric matrix protein [COMP] levels) data; synovium expression (HLA-DR, CD163, CD3, CD20, VEGF, osteoprotegerin, RANK-L, Bcl2 and global inflammation index) for a metacarpophalangeal joint-synovium biopsy. Baseline and 3-year hand-and-foot X-rays were graded with the van der Heijde-modified-Sharp score; the judgment criterion was its progression during follow-up. Pearson's product moment correlation statistics were used to test for association between paired samples.

RESULTS

A baseline, a significant relationship was found between erosive damage and markers of B-cell activation, notably the synovium CD20 expression (r=0.68; P=0.0001). Quantified by the modified-Sharp erosion score variation, the 3-year structural damage progression was significantly correlated with: serum levels of RF-IgG (r=0.75; P=0.0003), -IgM (r=0.69; P=0.001), anti-CCP2 (r=0.53; P=0.02) and RANK-L (r=0.61; P=0.007); synovium CD20 expression (r=0.70; P=0.001).

CONCLUSION

This analysis of the prognostic value of a large panel of synovium markers in a limited sample of prospectively followed, well-documented patients suggested that both synovial CD20 and serum RANK-L levels might be new predictors of structural damage progression in very-early RA.

Berberine induces dendritic cell apoptosis and has therapeutic potential for rheumatoid arthritis

OBJECTIVE

To investigate the effects of berberine on dendritic cell (DC) apoptosis and its potential as a therapeutic agent in rheumatoid arthritis (RA).

METHODS

Bone marrow (BM)-derived myeloid DCs (MDCs) and plasmacytoid DCs (PDCs) were generated by culturing BM cells with granulocyte-macrophage colony-stimulating factor/interleukin-4 or flt3L, respectively. Splenic DCs, T cells, and B cells were purified using a magnetic-activated cell sorting system. In vitro apoptosis was assessed by annexin V/propidium iodide or Hoechst 33258 staining. The in vivo effects of berberine were examined in mice with collagen-induced arthritis (CIA). Immune responses against type II collagen (CII) were determined by assaying serum antibody levels, lymphocyte proliferation, and cytokine production. The proportions of DCs and apoptosis of different immune cell subsets in spleens and lymph nodes were analyzed by flow cytometry and immunohistochemistry after subset-specific surface marker labeling and TUNEL staining.

RESULTS

Exposure of MDCs to berberine during BM cell differentiation reduced cell recovery by inducing apoptosis. Sensitivity to berberine-induced apoptosis was acquired starting on day 3 of DC differentiation, and mature DCs were more sensitive to berberine than immature DCs. Murine peritoneal macrophages, RAW 264.7 cells, and Jurkat cells were insensitive to berberine-induced apoptosis. Splenic DCs were more sensitive to berberine than T and B cells. Susceptibility of PDCs to berberine-induced apoptosis was similar to that of MDCs. In mice with CIA, berberine treatment ameliorated arthritis, suppressed CII-specific immune responses, and selectively increased the incidence of apoptosis in DCs within spleens and lymph nodes.

CONCLUSION

These findings show that berberine selectively induces apoptosis in DCs. Berberine may thus represent a novel therapeutic agent for RA.

The type I IFN system in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder characterized by joint inflammation, immune cell infiltration of the synovia, and cartilage/bone destruction. Despite noteworthy progress in the treatment of RA in recent years, many patients remain refractory to current therapeutic strategies that target either the adaptive immune system or mediators of the innate system. Type I interferons (IFNs) play a significant role in regulation of the innate immune system, originally being discovered as part of intracellular immune defence against viral infection. IFNs are pleiotropic cytokines, mediating both immunostimulatory and immunosuppressive effects. IFN-alpha and beta have been detected in RA synovial fluid and tissue and subsequent therapeutic approaches using type I IFN in murine models of arthritis and in human RA have produced different and controversial results. Great interest has been directed toward principally plasmacytoid dendritic cells (pDCs), although also toward myeloid dendritic cells, as sources of type I IFN. Furthermore, manipulation of DC populations in murine RA models demonstrated that pDCs could suppress the development of arthritis and autoimmunity and may offer an attractive therapy for T-cell-mediated autoimmune diseases. Finally, dendritic cells (DCs) are vehicles for the delivery of therapeutic vaccines, and clinical trials are ongoing in RA with "tolerogenic" DC populations. Further, studies on animal models of RA will elucidate how IFN and DCs contribute to the establishment of autoimmune arthritis and the potential for manipulation of these cell populations and products to re-establish the immune tolerance.

Subcutaneous allergen immunotherapy restores human dendritic cell innate immune function

BACKGROUND

We recently reported that human blood dendritic cells from allergic subjects have impaired IFN-alpha production following toll-like receptor 9 (TLR9)-dependent innate immune stimulation. It is not known how subcutaneous allergen immunotherapy (SCIT) affects dendritic cell immune responses.

OBJECTIVE

The aim of this study is to determine how SCIT affects human dendritic cell function.

METHODS

Peripheral blood mononuclear cell (PBMC) and plasmacytoid dendritic cells (pDCs) were isolated from the blood of seven dust mite allergic subjects at baseline and upon reaching a standard SCIT maintenance dose that included dust mite and other aeroallergens. Cells were stimulated with various adaptive and innate immune receptor stimuli, or media alone for 20 h with secreted cytokine levels determined by ELISA. A portion of the cells were used to measure intracellular signalling proteins by flow cytometry. Humoral immune responses were measured from plasma.

RESULTS

SCIT resulted in a threefold increase in PBMC production of IFN-alpha in response to CpG at 100 nM (P=0.015) and at 500 nM (P=0.015), n=7. The predominant cell type known to produce IFN-alpha in response to CpG (CpG ODN-2216) and other TLR9 agonists is the pDC. As expected, a robust innate immune response from isolated pDCs was re-established among allergic subjects undergoing SCIT resulting in a fivefold increase in IFN-alpha production in response to CpG at 500 nM (P=0.046), n=7. In contrast, IL-6 production was unaffected by SCIT (P=0.468). Consistent with published reports, IgG4 blocking antibody increased 10-fold with SCIT (P=0.031), n=7. There was no significant increase in the frequency of pDCs or the expression of TLR9 that would account for the rise in IFN-alpha production.

CONCLUSIONS

Allergen immunotherapy increases dendritic cell TLR9-mediated innate immune function, which has previously been shown to be impaired at baseline in allergic subjects.

Therapeutic agents for patients with rheumatoid arthritis and an inadequate response to tumour necrosis factor-alpha antagonists

BACKGROUND

Rheumatoid arthritis (RA) is a disabling autoimmune disease; unless adequately controlled, patients have a poor long-term prognosis. Tumour necrosis factor (TNF)-alpha antagonists have provided relief for many RA patients; however, despite their efficacy, some patients do not respond or fail to maintain initial response. In the UK, patients with an inadequate response to TNF-alpha antagonists have limited options, as the National Institute of Clinical Excellence (NICE) currently only recommend switching to an alternative TNF-alpha antagonists if discontinuation occurs due to safety during the first 6 months of treatment. The EU has approved three biological agents, rituximab, abatacept, and tocilizumab, for patients with RA with an inadequate response to TNF-alpha antagonists.

OBJECTIVE

This review examines the clinical experience with two therapies targeting key immune cells involved in RA -- rituximab (lyses B-cells), and abatacept (T-cell co-stimulation modulator) -- specifically focusing on patients with an inadequate response to TNF-alpha blockade.

METHODS

Phase II/III clinical trials and original studies were identified using Medline and Pubmed; articles assessing the efficacy and/or safety of rituximab or abatacept in patients with RA refractory to TNF-alpha blockade were reviewed.

CONCLUSIONS

Clinical data for rituximab and abatacept demonstrate that both reduce disease activity in TNF-alpha antagonist inadequate responders, suggesting that agents with alternative mechanisms of action, such as those targeting key immune cells, may be useful in this patient population.

Photodynamic therapy in immune (non-oncological) disorders: focus on benzoporphyrin derivatives

This review examines the efficacy of photodynamic therapy in the treatment of immunological disorders. Photodynamic therapy (PDT) is a 2-step procedure. Firstly, a photosensitiser is introduced into the body, where it accumulates selectively in cells with elevated metabolism, such as cancer cells or activated cells of the immune system. Second, light is applied at a wavelength that excites the photosensitiser, producing a variety of short-lived oxygen-derived species. The effect is dependent on the doses of both photosensitiser and activating light. The mechanisms of action of PDT are multifactorial. Induction of high levels of oxidative stress results in necrotic cell death, while lower intensity oxidative stress initiates apoptosis. Sublethal doses may result in the modification of cell surface receptor expression levels and cytokine release and consequently influence cell behaviour. Immunomodulatory PDT (IPDT) utilises mainly apoptotic and sublethal doses. The studies reported here utilise verteporfin, a benzoporphyrin-derived chlorin-like photosensitiser. Veteporfin is a second generation photosensitiser, displaying rapid clearance and consequently a reduced period of skin photosensitivity compared with the first generation photosensitiser, porfimer sodium. In vivo studies showed that IPDT was effective in alleviating immunopathology in murine models of arthritis, contact hypersensitivity, experimental allergic encephalomyelitis and retention of allogeneic skin grafts. Based on these findings, early stage clinical trials with IPDT were initiated recently for the treatment of psoriasis, psoriatic arthritis and rheumatoid arthritis. While verteporfin has been the photosensitiser which pioneered IPDT, a new benzoporphyrin derivative photosensitiser, QLT0074, is under development. This has demonstrated an enhanced avidity for target cells as well as improved clearance characteristics.

Cysteine cathepsin S as an immunomodulatory target: present and future trends

OBJECTIVE

Antigen presentation is the key to immune response. Cathepsin S plays a major role in the degradation of the invariant peptide chain associated with the major histocompatibility complex and thus affects antigen presentation. This review will focus on the recent developments made in field of cysteine cathepsins especially cathepsin S and their future prospects as a therapeutic target.

METHODS

Selective cathepsin inhibitors for targeting autoimmune disorders, atherosclerosis, osteoporosis, osteoarthritis and cancer are being pursued by many pharmaceutical companies. Recent publications in this field have been used as references to evaluate the current and future trends in cathepsin S inhibitors as an immunomodulatory target.

CONCLUSIONS

The temporal and spatial position occupied by cathepsin S in immune presentation, gives rise to the hope that an inhibitor would impart selectivity with a lesser propensity for side effects than other immunosuppressive agents.

Recruitment of dendritic cells and macrophages during T cell-mediated synovial inflammation

Adoptive transfer of adjuvant-induced arthritis was used in this study to examine local macrophages and dendritic cells (DCs) during T cell-mediated synovial inflammation. We studied the influx of CD11b⁺CD11c⁺ putative myeloid DCs and other non-lymphoid CD45⁺ cells into synovium-rich tissues (SRTs) of the affected hind paws in response to a pulse of autoreactive thoracic duct cells. Cells were prepared from the SRTs using a collagenase perfusion-digestion technique, thus allowing enumeration and phenotypic analysis by flow cytometry. Numbers of CD45⁺ cells increased during the first 6 days, with increases in CD45⁺MHC (major histocompatibility complex) II⁺ monocyte-like cells from as early as day 3 after transfer. In contrast, typical MHC II^- monocytes, mainly of the CD4^- subset, did not increase until 12 to 14 days after cell transfer, coinciding with the main influx of polymorphonuclear cells. By day 14, CD45⁺MHC II^hi cells constituted approximately half of all CD45⁺ cells in SRT. Most of the MHC II^hi cells expressed CD11c and CD11b and represented putative myeloid DCs, whereas only approximately 20% were CD163⁺ macrophages. Less than 5% of the MHC II^hi cells in inflamed SRT were CD11b^-, setting a maximum for any influx of plasmacytoid DCs. Of the putative myeloid DCs, a third expressed CD4 and both the CD4⁺ and the CD4^- subsets expressed the co-stimulatory molecule CD172a. Early accumulation of MHC II^hiCD11c⁺ monocyte-like cells during the early phase of T cell-mediated inflammation, relative to typical MHC II^- blood monocytes, suggests that recruited monocytes differentiate rapidly toward the DC lineage at this stage in the disease process. However, it is possible also that the MHC II^hiCD11c⁺ cells originate from a specific subset of DC-like circulating mononuclear cells.

Destructive periodontitis lesions are determined by the nature of the lymphocytic response

It is now 35 years since Brandtzaeg and Kraus (1965) published their seminal work entitled "Autoimmunity and periodontal disease". Initially, this work led to the concept that destructive periodontitis was a localized hypersensitivity reaction involving immune complex formation within the tissues. In 1970, Ivanyi and Lehner highlighted a possible role for cell-mediated immunity, which stimulated a flurry of activity centered on the role of lymphokines such as osteoclast-activating factor (OAF), macrophage-activating factor (MAF), macrophage migration inhibition factor (MIF), and myriad others. In the late 1970s and early 1980s, attention focused on the role of polymorphonuclear neutrophils, and it was thought that periodontal destruction occurred as a series of acute exacerbations. As well, at this stage doubt was being cast on the concept that there was a neutrophil chemotactic defect in periodontitis patients. Once it was realized that neutrophils were primarily protective and that severe periodontal destruction occurred in the absence of these cells, attention swung back to the role of lymphocytes and in particular the regulatory role of T-cells. By this time in the early 1990s, while the roles of interleukin (IL)-1, prostaglandin (PG) E(2), and metalloproteinases as the destructive mediators in periodontal disease were largely understood, the control and regulation of these cytokines remained controversial. With the widespread acceptance of the Th1/Th2 paradigm, the regulatory role of T-cells became the main focus of attention. Two apparently conflicting theories have emerged. One is based on direct observations of human lesions, while the other is based on animal model experiments and the inability to demonstrate IL-4 mRNA in gingival extracts. As part of the "Controversy" series, this review is intended to stimulate debate and hence may appear in some places provocative. In this context, this review will present the case that destructive periodontitis is due to the nature of the lymphocytic infiltrate and is not due to periodic acute exacerbations, nor is it due to the so-called virulence factors of putative periodontal pathogens.

MLN51 and GM-CSF involvement in the proliferation of fibroblast-like synoviocytes in the pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease of unclear etiology. This study was conducted to identify critical factors involved in the synovial hyperplasia in RA pathology. We applied cDNA microarray analysis to profile the gene expressions of RA fibroblast-like synoviocytes (FLSs) from patients with RA. We found that the MLN51 (metastatic lymph node 51) gene, identified in breast cancer, is remarkably upregulated in the hyperactive RA FLSs. However, growth-retarded RA FLSs passaged in vitro expressed small quantities of MLN51. MLN51 expression was significantly enhanced in the FLSs when the growth-retarded FLSs were treated with granulocyte – macrophage colony-stimulating factor (GM-CSF) or synovial fluid (SF). Anti-GM-CSF neutralizing antibody blocked the MLN51 expression even though the FLSs were cultured in the presence of SF. In contrast, GM-CSF in SFs existed at a significant level in the patients with RA (n = 6), in comparison with the other inflammatory cytokines, IL-1β and TNF-α. Most RA FLSs at passage 10 or more recovered from their growth retardation when cultured in the presence of SF. The SF-mediated growth recovery was markedly impaired by anti-GM-CSF antibody. Growth-retarded RA FLSs recovered their proliferative capacity after treatment with GM-CSF in a dose-dependent manner. However, MLN51 knock-down by siRNA completely blocked the GM-CSF/SF-mediated proliferation of RA FLSs. Taken together, our results imply that MLN51, induced by GM-CSF, is important in the proliferation of RA FLSs in the pathogenesis of RA.

Inhibition of macropinocytosis blocks antigen presentation of type II collagen in vitro and in vivo in HLA-DR1 transgenic mice

Professional antigen-presenting cells, such as dendritic cells, macrophages and B cells have been implicated in the pathogenesis of rheumatoid arthritis, constituting a possible target for antigen-specific immunotherapy. We addressed the possibility of blocking antigen presentation of the type II collagen (CII)-derived immunodominant arthritogenic epitope CII_259–273 to specific CD4 T cells by inhibition of antigen uptake in HLA-DR1-transgenic mice in vitro and in vivo. Electron microscopy, confocal microscopy, subcellular fractionation and antigen presentation assays were used to establish the mechanisms of uptake, intracellular localization and antigen presentation of CII by dendritic cells and macrophages. We show that CII accumulated in membrane fractions of intermediate density corresponding to late endosomes. Treatment of dendritic cells and macrophages with cytochalasin D or amiloride prevented the intracellular appearance of CII and blocked antigen presentation of CII_259–273 to HLA-DR1-restricted T cell hybridomas. The data suggest that CII was taken up by dendritic cells and macrophages predominantly via macropinocytosis. Administration of amiloride in vivo prevented activation of CII-specific polyclonal T cells in the draining popliteal lymph nodes. This study suggests that selective targeting of CII internalization in professional antigen-presenting cells prevents activation of autoimmune T cells, constituting a novel therapeutic strategy for the immunotherapy of rheumatoid arthritis.

Enumeration and phenotypical analysis of distinct dendritic cell subsets in psoriatic arthritis and rheumatoid arthritis

Dendritic cells (DCs) comprise heterogeneous subsets of professional antigen-presenting cells, linking innate and adaptive immunity. Analysis of DC subsets has been hampered by a lack of specific DC markers and reliable quantitation assays. We characterised the immunophenotype and functional characteristics of psoriatic arthritis (PsA)-derived and rheumatoid arthritis (RA)-derived myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) to evaluate their potential role in arthritis. Circulating peripheral blood (PB) pDC numbers were significantly reduced in PsA patients (P = 0.0098) and RA patients (P = 0.0194), and mDCs were significantly reduced in RA patients (P = 0.0086) compared with healthy controls. The number of circulating mDCs in RA PB was significantly inversely correlated to C-reactive protein (P = 0.021). The phenotype of both DC subsets in PsA PB and RA PB was immature as compared with healthy controls. Moreover, CD62L expression was significantly decreased on both mDCs (PsA, P = 0.0122; RA, P = 0.0371) and pDCs (PsA, P = 0.0373; RA, P = 0.0367) in PB. Both mDCs and pDCs were present in PsA synovial fluid (SF) and RA SF, with the mDC:pDC ratio significantly exceeding that in matched PB (PsA SF, P = 0.0453; RA SF, P = 0.0082). pDCs isolated from RA SF and PsA SF displayed an immature phenotype comparable with PB pDCs. RA and PsA SF mDCs, however, displayed a more mature phenotype (increased expression of CD80, CD83 and CD86) compared with PB mDCs. Functional analysis revealed that both SF DC subsets matured following toll-like receptor stimulation. pDCs from PB and SF produced interferon alpha and tumour necrosis factor alpha on TLR9 stimulation, but only SF pDCs produced IL-10. Similarly, mDCs from PB and SF produced similar tumour necrosis factor alpha levels to TLR2 agonism, whereas SF mDCs produced more IL-10 than PB controls. Circulating DC subset numbers are reduced in RA PB and PsA PB with reduced CD62L expression. Maturation is incomplete in the inflamed synovial compartment. Immature DCs in SF may contribute to the perpetuation of inflammation via sampling of the inflamed synovial environment, and in situ presentation of arthritogenic antigen.

Drug delivery strategies for cathepsin inhibitors in joint diseases

Cathepsins play important roles in the development of joint and bone diseases such as osteoporosis, rheumatoid arthritis (RA) and osteoarthritis (OA). Cathepsin inhibitors are presently in development and clinical testing for use as novel disease-modifying drugs for the improved treatment of osteoporosis. They may also be applicable for the treatment of joint diseases. However, some barriers still hamper their clinical applications in these indications. Based on pathophysiological features of RA and OA, the authors discuss six potential drug delivery strategies for the effective delivery of cathepsin inhibitors or other antiarthritic drugs to the arthritic joint tissue. Successful application of these strategies may significantly contribute to a more effective and safe treatment of RA and OA.

MHC II+ CD45+ cells from synovium-rich tissues of normal rats: phenotype, comparison with macrophage and dendritic cell lineages and differentiation into mature dendritic cells in vitro

Synovial tissues are frequent sites of inflammatory disorders in which dendritic cells (DCs) may play an important role. This study examines potential antigen-presenting cells obtained from synovium-rich tissues (SRTs) by vascular perfusion of rat hind limbs with collagenase and further enzymatic digestion of the disarticulated hind paws in vitro. The three sub-populations of interest were: CD45+MHC IIhi, mainly CD11c+ and CD163-; CD45+MHC IIlo, mainly CD11c- and CD163+ and CD45+MHC II-, mainly CD11c- and CD163+. Expression of CD11c and CD163 correlated with ruffled cell-surface (CD11c+CD163-) and highly vacuolated cytoplasm (CD11c-CD163+), respectively. Culture of the CD45+CD163- sub-population in granulocyte macrophage colony-stimulating factor (GM-CSF) yielded CD45+MHC IIhi CD11c+CD163- cells with veiled morphology, while the large vacuolated cells that expressed CD163 resembled type A synoviocytes in both surface antigen phenotype and morphology. These results demonstrate that SRTs contain indeterminate cells that can differentiate into mature DCs in vitro in response to GM-CSF, plus mature synovial lining macrophages.

MHC class II compartment, endocytosis and phagocytic activity of macrophages and putative dendritic cells isolated from normal tissues rich in synovium

The endocytic and phagocytic activities of a population of MHC IIhi CD11c+ dendritic cell (DC)-like cells in synovium-rich tissues (SRTs) of normal rat paws were compared with CD163+ cells (putative macrophages) from the same tissues and pseudo-afferent lymph DCs, peritoneal macrophages and blood monocytes. Fifty percent of CD11c+ cells and 75% of CD163+ cells isolated from SRT internalized fluorescein-conjugated dextran (FITC-DX). Of these endocytic cells, half of those expressing CD11c, but only 30% of those expressing CD163, were surface MHC class II+ (sMHC II+). CD11c+ cells were more endocytic than monocytes or pseudo-afferent lymph DC, but some CD163+ cells (type A synoviocytes) were found to be highly endocytic. CD163+ cells from SRT were more phagocytic (25%) than the general MHC class II+ population (16%). Of phagocytic cells, 40% of CD163+ cells were sMHC II(variable) and they constituted 60% of all MHC class II+ phagocytic cells. Only 18% of phagocytic MHC II+ cells expressed CD11c and the most of these were MHC IIhi. In comparison, 60% of CD163+ peritoneal macrophages were phagocytic, while blood monocytes were poorly phagocytic. Intracellular MHC class II-rich compartments (MIIC) were prominent in sMHC IIhi cells in SRT but rare in CD163+ cells. Most MHC IIhi CD11c+ cells did not have a detectable MIIC.

The active metabolite of leflunomide, A77 1726, interferes with dendritic cell function

Leflunomide, a potent disease-modifying antirheumatic drug used in the treatment of rheumatoid arthritis (RA), exhibits anti-inflammatory, antiproliferative and immunosuppressive effects. Although most of the beneficial effects of leflunomide have been attributed to its antimetabolite activity, mainly in T cells, other targets accounting for its potency might still exist. Because of mounting evidence for a prominent role of dendritic cells (DCs) in the initiation and maintenance of the immune response in RA, we analyzed the effect of the active metabolite of leflunomide (A77 1726; LEF-M) on phenotype and function of human myleloid DCs at several stages in their life cycle. Importantly, DCs differentiated in the presence of LEF-M exhibited an altered phenotype, with largely reduced surface expression of the critical co-stimulatory molecules CD40 and CD80. Furthermore, treatment of DCs during the differentiation or maturation phase with LEF-M aborted successful DC maturation. Exogenous addition of uridine revealed that DC modulation by LEF-M was independent of its proposed ability as an antimetabolite. In addition, the ability of DCs to initiate T-cell proliferation and to produce the proinflammatory cytokines IL-12 and tumour necrosis factor-α was markedly impaired by LEF-M treatment. As a molecular mechanism, transactivation of nuclear factor-κB, an transcription factor essential for proper DC function, was completely suppressed in DCs treated with LEF-M. These data indicate that interference with several aspects of DC function could significantly contribute to the beneficial effects of leflunomide in inflammatory diseases, including RA.

Involvement of CC chemokine ligand 18 (CCL18) in normal and pathological processes

CC chemokine ligand 18 (CCL18) was originally discovered as pulmonary and activation-regulated chemokine (PARC), dendritic cell (DC)-chemokine 1 (DC-CK1), alternative macrophage activation-associated CC chemokine-1 (AMAC-1), and macrophage inflammatory protein-4 (MIP-4). CCL18 primarily targets lymphocytes and immature DC, although its agonistic receptor remains unknown so far. CCL18 is mainly expressed by a broad range of monocytes/macrophages and DC. A more profound understanding of the various activation programs and functional phenotypes of these producer cells might give a better insight in the proinflammatory versus anti-inflammatory role of this CC chemokine. It is interesting that CCL18 is constitutively present at high levels in human plasma and likely contributes to the physiological homing of lymphocytes and DC and to the generation of primary immune responses. Furthermore, enhanced CCL18 production has been demonstrated in several diseases, including various malignancies and inflammatory joint, lung, and skin diseases. The lack of a rodent counterpart for human CCL18 sets all hope on primate animal models to further elucidate the importance of CCL18 in vivo. This review will address these different aspects in more detail.

Fc gamma R expression on NK cells influences disease severity in rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with autoantibodies, the best known of which is rheumatoid factor (RF). RF/IgG complexes interact with FcgammaR on the surface of neutrophils, NK cells and monocyte/macrophages. We have analyzed the expression pattern and allelic polymorphisms of three FcgammaR genes (FcgammaRIIA, FcgammaRIIC and FcgammaRIIIA) in a large sample of RA patients and normal donors. We have found that the level of FcgammaR (CD16 and CD32) expression on NK cells is lower in RA patients than in normal individuals. Genotypic analysis demonstrated that the CD32 isoform expressed by the majority of RA patients was not the activating FcgammaRIIc1 isoform, commonly seen in normal individuals, but rather the inhibitory FcgammaRIIb isoform. The combination of the FcgammaRIIIA-176F allele with a lack of CD32 expression in NK cells appeared to be characteristic of RA subjects with aggressive disease. Since FcgammaRII and FcgammaRIIIA are predominantly expressed by NK cells, these data further suggest that FcgammaR-mediated activation of NK cells could be a disease-determining factor in RA patients.

Dendritic cells in the cerebrospinal fluid and peripheral nerves in Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy

The role of antigen-presenting cells (APC) involved in induction of T and B cell mediated autoaggressive immunity in Guillain-Barre syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is poorly understood. We studied the numbers and phenotype of dendritic cells (DC) in blood and cerebrospinal fluid (CSF) over the course of GBS and CIDP before and after immunomodulatory treatment. Four out of seven GBS patients examined prior to treatment with high-dose intravenous immunoglobulins (IvIg) had elevated numbers of CD123(+) plasmacytoid DC in the CSF, while both GBS and CIDP patients examined prior to treatment had elevated numbers of CD11c(+) myeloid DC in the CSF, as compared to patients with noninflammatory neurological diseases (OND). The percentages of blood DC expressing the cell surface marker CD1a, co-stimulatory molecules CD80 and CD86, adhesion molecule CD54, and chemokine receptors CCR1, CCR2, CCR5, and CXCR4 were not affected in GBS or CIDP. The immunohistochemistry of sural nerve biopsies revealed CD11c(+)CD83(-)CD14(-)CD16(-) immature myeloid DC at low numbers, mostly in the perineurium, without difference between CIDP patients and controls. In contrast, the numbers of CD11c(+)CD14(+)/CD16(+) macrophages were higher within the endoneurium in CIDP patients compared with the controls. The recruitment of DC to CSF in GBS and CIDP may be important in capturing antigens released from inflamed spinal nerve roots into CSF and in transferring these antigens from CSF to local lymph nodes, where naive T and B cells may be activated.

Increased expression of CCL18, CCL19, and CCL17 by dendritic cells from patients with rheumatoid arthritis, and regulation by Fc gamma receptors

BACKGROUND

Dendritic cells (DC) have a role in the regulation of immunity and tolerance, attracting inflammatory cells by the production of various chemokines (CK). Fc gamma receptors (Fc gamma R) may be involved in regulation of the DC function.

OBJECTIVE

To assess the expression of CK by immature (iDC) and mature DC (mDC) and its regulation by Fc gamma R in patients with RA and healthy donors (HC).

METHODS

Expression of CK by DC from patients with RA and from HC was determined by real time quantitative PCR and ELISA. DC were derived from monocytes following standardised protocols. To study the potential regulation by Fc gamma R, iDC were stimulated with immune complexes (IC) during lipopolysaccharide (LPS) induced maturation. The presence of CK was studied in synovial tissue from patients with RA, osteoarthritis, and healthy subjects by RT-PCR and immunohistochemistry.

RESULTS

iDC from patients with RA had markedly increased mRNA levels of the CK CCL18 and CXCL8. Upon maturation with LPS, expression of CCL18, CCL19, CXCL8, CCL3, and CCL17 increased dramatically, reaching significantly higher levels in patients with RA. Monocytes failed to express these CK, except for CXCL8 and CCL3. IC-mediated triggering of the Fc gamma R on DC from patients with highly active RA down regulated all CK, whereas the reverse was seen when DC from patients with low disease activity and healthy donors were stimulated. CCL18 was significantly increased in RA synovial tissue.

CONCLUSION

Increased CK expression by DC was found in patients with RA. This expression is partly regulated by Fc gamma R triggering and results in an inhibitory DC subtype in RA upon Fc gamma R-mediated triggering.

Dendritic cells, T cell tolerance and therapy of adverse immune reactions

Dendritic cells (DC) are uniquely able to either induce immune responses or to maintain the state of self tolerance. Recent evidence has shown that the ability of DC to induce tolerance in the steady state is critical to the prevention of the autoimmune response. Likewise, DC have been shown to induce several type of regulatory T cells including Th2, Tr1, Ts and NKT cells, depending on the maturation state of the DC and the local microenvironment. DC have been shown to have therapeutic value in models of allograft rejection and autoimmunity, although no success has been reported in allergy. Several strategies, including the use of specific DC subsets, genetic modification of DC and the use of DC at various maturation stages for the treatment of allograft rejection and autoimmune disease are discussed. The challenge for the future use of DC therapy in human disease is to identify the appropriate DC for the proposed therapy; a task made more daunting by the extreme plasticity of DC that has recently been demonstrated. However, the progress achieved to date suggests that these are not insurmountable obstacles and that DC may become a useful therapeutic tool in transplantation and autoimmune disease.

The power of the third dimension: tissue architecture and autoimmunity in rheumatoid arthritis

Lymphoid organs are the anatomic solution to the challenge of responding to minute amounts of antigen with powerful effector mechanisms. By arranging interacting cells in complex three-dimensional topographies lymphoid organs provide an optimal match between form and function. This principle is exploited in ectopic lymphoid structures that characteristically appear in rheumatoid synovitis. Synovial tissue T cells and B cells cooperate in different types of lymphoid organizations. Dendritic cell networks in the inflamed synovial membrane optimize antigen collection, storage, processing, and presentation. Synovial tissue cells participate in lymphocyte recruitment and the formation of tissue architectures that amplify immune responses. Recent data support the concept that the tissue organization in the rheumatoid joint fosters a breakdown in self-tolerance by promoting a phase transition from self-limited immune responses to self-perpetuating autoimmune responses.

Dendritic cells in hyperplastic thymuses from patients with myasthenia gravis

To investigate the role of dendritic cells (DCs) in the hyperplastic myasthenia gravis (MG) thymus, we studied the frequency and distribution of three mature DC phenotypes (CD83(+)CD11c(+), CD86(+)CD11c(+), and HLA-DR(+)CD11c(+)) in samples from patients with MG whose symptoms dramatically improved following thymectomy and in non-MG control thymuses. In hyperplastic MG thymuses, mature DCs were much more numerous in nonmedullary areas, such as the subcapsular/outer cortex; around the germinal centers; and in extralobular connective tissue, particularly around blood vessels. Mature DCs strongly coexpressed CD44 and appeared to be components of a CD44-highly positive (CD44(high)) cell population migrating from the vascular system. Furthermore, in the hyperplastic MG thymus, the expression of secondary lymphoid-tissue chemokine (SLC) markedly increased especially around extralobular blood vessels, where the CD44(high) cell population accumulated. These findings suggest that DCs may migrate into the hyperplastic thymus from the vascular system via mechanisms that involve CD44 and SLC. DCs may present self-antigens, thereby promoting the priming and/or boosting of potentially autoreactive T cells against the acetylcholine receptor.

A novel dendritic cell-induced model of erosive inflammatory arthritis: distinct roles for dendritic cells in T cell activation and induction of local inflammation

Transferring collagen-pulsed, bone marrow-derived dendritic cells (DCs) into congenic DBA/1 recipient mice produced arthritis in joints adjacent to the site of DC transfer and could be inhibited by treatment with TNF antagonists. Disease was Ag specific, as transfer of control, unpulsed DCs, or DCs pulsed with OVA did not produce arthritis. In contrast to other experimental arthritis models, DC-induced arthritis localized to the site of injection and did not spontaneously generalize to uninvolved joints, despite the demonstration of circulating collagen-reactive T cells. Similarly, transfer of T cells primed by collagen/DCs was not sufficient to produce arthritis in recipient mice. In collagen/DC-primed mice however, disease could be induced in uninvolved joints by local administration of noncollagen-pulsed DCs and this could be reduced through TNF inhibition. Similarly, injection of collagen/DC-primed mice with low-dose TNF also resulted in local induction of arthritis, as did administration of TNF to mice receiving T cells from collagen/DC but not OVA/DC-primed mice. Thus, we have demonstrated for the first time that administration of collagen-pulsed mature DCs is sufficient for the induction of arthritis. Furthermore, this disease process is mediated through both adaptive and innate effects of DCs; first, priming of autoreactive T cells and, second, induction of local inflammation via mediators such as TNF.

Antigen-presenting cells in human periodontal disease tissues

T cells are present in the inflammatory infiltrates of periodontal disease lesions and require antigen presentation by antigen-presenting cells (APCs). While it is still not known whether Th1 or Th2 cells predominate in these lesions, it has been reported that different APCs may induce activation of different T-cell subsets. An immunoperoxidase technique was used to investigate the presence of CD1a+, CMRF-44+, CMRF-58+ and CD83+ dendritic cells, CD14+ macrophages or dendritic cell precursors and CD19+ B cells in gingival biopsies from 21 healthy or gingivitis and 25 periodontitis subjects. The samples were divided into three groups according to the size of infiltrate (group 1, small infiltrates; group 2, medium infiltrates; group 3, extensive infiltrates). The presence of numerous CD1a+ Langerhans cells was noted in the epithelium with no differences between the healthy/gingivitis and periodontitis groups. The percentage of CD83+ dendritic cells in the infiltrates was higher than the percentage of CD1a+, CMRF-44+ or CMRF-58+ dendritic cells. Endothelial cells positive for CD83 were found predominantly in areas adjacent to infiltrating cells, CD83+ dendritic cells being noted in the region of CD83+ endothelium. The percentage of CD14+ cells in the inflammatory infiltrates was similar to that of CD83+ dendritic cells. B cells were the predominant APC in group 2 and 3 tissues. The percentage of B cells in group 3 periodontitis lesions was increased in comparison with group 1 periodontitis tissues and also in comparison with group 3 healthy/gingivitis sections. Functional studies are required to determine the roles of different APC subpopulations in periodontal disease.

Co-stimulatory and adhesion molecules of dendritic cells in rheumatoid arthritis

Dendritic cells (DCs) in the rheumatoid arthritis (RA) joint mediate the immunopathological process and act as a potent antigen presenting cell. We compared the expression of co-stimulatory and adhesion molecules on DCs in RA patients versus controls with traumatic joint lesions and evaluated the correlation between the immunophenotypical presentation of DCs and the clinical status of the disease. Samples of peripheral venous blood, synovial fluid (SF) and synovial tissue (ST) were obtained from 10 patients with RA at the time of hip or knee replacement and from 9 control patients with knee arthroscopy for traumatic lesions. Clinical status was appreciated using the DAS28 score. Blood, SF and dissociated ST cell populations were separated by centrifugation and analyzed by flow cytometry. Cells phenotypes were identified using three-color flow cytometry analysis for the following receptors HLA-DR, CD80, CD83, CD86, CD11c, CD18, CD54, CD58, CD3, CD4, CD8, CD19, CD20, CD14, CD16, CD56. HLA-DR molecules, co-stimulatory receptors CD80, CD86, CD83 and adhesion molecules CD18, CD11c, CD54, CD58, were analyzed by two-color immunofluorescence microscopy on ST serial sections. In patients with active RA (DAS28>5.1) we found a highly differentiated subpopulation of DCs in the ST and SF that expressed an activated phenotype (HLA-DR, CD86+, CD80+, CD83+, CD11c+, CD54+, CD58+). No differences were found between circulating DCs from RA patients and control patients. Our data suggest an interrelationship between clinical outcome and the immunophenotypical presentation of DCs. Clinical active RA (DAS28>5.1) is associated with high incidence of activated DCs population in the ST and SF as demonstrated by expression of adhesion and co-stimulatory molecules.

Elevated expression of CCR5 by myeloid (CD11c+) blood dendritic cells in multiple sclerosis and acute optic neuritis

Myeloid and plasmacytoid dendritic cells (DC) are present in cerebrospinal fluid (CSF) in non-inflammatory neurological diseases (NIND) and elevated in clinically definite multiple sclerosis (MS) and in early MS - acute monosymptomatic optic neuritis (ON). Here, we show that expression of CCR5, a chemokine receptor for regulated on activation, normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein (MIP)-1alpha/beta, is elevated on blood myeloid (CD11c+) DC in MS and ON compared to non-inflammatory controls. In contrast, expression of CXCR4, a receptor for stromal cell-derived factor (SDF)-1alpha, is similar in all groups. Blood myeloid DC from MS patients respond chemotactically to RANTES and MIP-1beta, which are expessed in MS lesions. In active MS and ON, expression of CCR5 by myeloid DC in blood correlates with numbers of these cells in CSF. Thus, elevation of CCR5 may contribute to recruitment of myeloid DC to CSF in MS and ON. Recruitment of plasmacytoid DC to CSF appears to be CCR5-independent.

Dendritic cells in rheumatoid synovial membrane after total removal of the hyaline articular cartilage

OBJECTIVE

To investigate the effect of total removal of the hyaline articular cartilage on dendritic cells in synovial membrane in rheumatoid arthritis (RA) or ankylosing spondylitis (AS).

PATIENTS AND METHODS

Immunohistochemical staining for two dendritic cell markers, CD35 and RFD1, was carried out on synovial membrane specimens from arthritis patients undergoing primary (n=10) or revision (n=8) total hip replacement (THR). The results are expressed as the number (mean+/-standard deviation) of positive cells per 1000 total cells.

RESULTS

CD35-(112+/-9) and RFD1-(27+/-5) positive cells were found in all primary RA synovial membrane, while only two out of eight synovial membrane samples from revision THR contained CD35-positive follicular dendritic cells (nine and 12 cells), and no revision samples contained any RFD1-positive interdigitating dendritic cells.

CONCLUSION

Removal of the hyaline articular cartilage reduces the infiltration and functional differentiation of dendritic cells in synovial membrane. Our findings suggest that the antigen driving chronic arthritis/synovitis is contained in the hyaline articular cartilage.

Recruitment of dendritic cells to the cerebrospinal fluid in bacterial neuroinfections

Dendritic cells (DC) accumulate in the CNS during inflammation and may contribute to local immune responses. Two DC subsets present in human cerebrospinal fluid (CSF) are probably recruited from myeloid (CD11c(+)CD123(dim)) and plasmacytoid (CD11c(-)CD123(high)) blood DC. In bacterial meningitis and especially in Lyme meningoencephalitis, numbers of myeloid and plasmacytoid DC in CSF were increased, compared to non-inflammatory neurological diseases, and correlated with chemotactic activity of CSF for immature monocyte-derived DC (moDC). Multiple DC chemoattractants, including macrophage inflammatory protein (MIP)-1beta, monocyte chemotactic protein (MCP)-1, MCP-3, RANTES and stromal cell-derived factor (SDF)-1alpha were elevated in CSF in these two neuroinfections. Chemotaxis of immature moDC induced by these CSFs could be partially inhibited by mAbs against CXCR4, the receptor for SDF-1alpha, and CD88, the receptor for C5a. SDF-1alpha present in CSF also chemoattracted mature moDC, which in vivo could correspond to a diminished migration of antigen-bearing DC from the CSF to secondary lymphoid organs. Regulation of DC trafficking to and from the CSF may represent a mechanism of controlling the CNS inflammation.

Association of clinical, radiological and synovial immunopathological responses to anti-rheumatic treatment in rheumatoid arthritis

OBJECTIVES

To compare immunohistochemical scoring with clinical scoring and radiology for the assessment of rheumatoid arthritis (RA) disease activity, synovial tissue (ST) biopsied arthroscopically was assessed from 18 patients before and after commencement of disease-modifying anti-rheumatic drug (DMARD) therapy.

METHODS

Lymphocytes, macrophages, differentiated dendritic cells (DC), vascularity, tumour necrosis factor (TNF) alpha and interleukin-1beta levels were scored. Clinical status was scored using the American College of Rheumatology (ACR) core set and serial radiographs were scored using the Larsen and Sharp methods. Histopathological evidence of activity included infiltration by lymphocytes, DC, macrophages, tissue vascularity, and expression of lining and sublining TNFalpha. These indices co-varied across the set of ST biopsies and were combined as a synovial activity score for each biopsy.

RESULTS

The change in synovial activity with treatment correlated with the ACR clinical response and with decreased radiological progression by the Larsen score. The ACR response to DMARD therapy, the change in synovial activity score and the slowing of radiological progression were each greatest in patients with high initial synovial vascularity.

CONCLUSIONS

The data demonstrate an association between clinical, radiological and synovial immunopathological responses to anti-rheumatic treatment in RA. High ST vascularity may predict favourable clinical and radiological responses to treatment.

The impact of recent advances in immunology and cancer therapy on nuclear medicine

The explosive expansion of knowledge in immunology in recent decades has already affected the research and practice of nuclear medicine in several ways. New hematopoietic cells have been isolated and their functions discovered, including hematopoietic stem cells and dendritic cells (DCs). Many new humeral factors have been found that have potent effects on cells, including cytokines, growth factors, and specialized proteins. Radiolabeled compounds are needed to follow the pharmacodynamics of the humeral factors and to follow the migration of mobile cells in animals and humans. In this article, only DCs, cytokines, and growth factors used clinically are discussed. DCs are essential for defense against infectious diseases. Autologous DCs cultured for a week and pulsed with tumor antigens have already proved highly immunogenic compared with other methods for activating cytotoxic T cells, and preliminary studies suggest that DCs are more potent for tumor cell killing than monoclonal antibodies. DCs, unfortunately, also play an important role in causing certain human diseases. In allograft transplants, residual donor DCs are responsible for the cellular rejection; if they could be eliminated, rejection could be prevented. These cells are also detrimental in rheumatoid arthritis, other autoimmune diseases, asthma, and chronic obstructive pulmonary disease. Cytokines such as interleukin-2 and such growth factors as granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor, administered to patients with malignancies to alleviate the leukopenia of chemotherapy agents, frequently alter the tissue distribution of radiopharmaceuticals; these alterations may be confused with disease.

Macrophages in rheumatoid arthritis

The abundance and activation of macrophages in the inflamed synovial membrane/pannus significantly correlates with the severity of rheumatoid arthritis (RA). Although unlikely to be the 'initiators' of RA (if not as antigen-presenting cells in early disease), macrophages possess widespread pro-inflammatory, destructive, and remodeling capabilities that can critically contribute to acute and chronic disease. Also, activation of the monocytic lineage is not locally restricted, but extends to systemic parts of the mononuclear phagocyte system. Thus, selective counteraction of macrophage activation remains an efficacious approach to diminish local and systemic inflammation, as well as to prevent irreversible joint damage.