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Many patients with systemic lupus erythematosus also have osteoporosis, according to a study of 30 women with lupus. More than one-third had osteoporosis. This was due in part to decreased bone formation.

Immunmediierte inflammatorische Erkrankungen (IMID) sind eine klinisch heterogene Gruppe von Erkrankungen, die genetische, ätiologische und auch klinische Überschneidungen aufweisen. Nach dem heutigen Stand der Forschung liegen den sog. primären IMID gemeinsame pathogene Mechanismen und zytokinassoziierte Signaltransduktionswege zugrunde. Zu den primären IMID zählen unter anderem chronisch-entzündliche Darm‑, Haut- und Augenerkrankungen sowie rheumatische Erkrankungen. Patienten, die an einer primären IMID erkrankt sind, weisen ein erhöhtes Risiko für die Entwicklung einer sekundären IMID auf. Die vorliegende Arbeit skizziert die Abgrenzung zwischen primären und sekundären IMID unter Berücksichtigung von Komplikationen und Komorbiditäten. Ausgehend von den Fächern Gastroenterologie, Dermatologie, Rheumatologie und Ophthalmologie wird ein möglicher optimaler interdisziplinärer Umgang mit IMID-Patienten diskutiert. Im speziellen werden Leitsymptome, die auf eine IMID hinweisen, und diagnostische Maßnahmen beschrieben, die vor Überweisung eines Patienten zum entsprechenden Spezialisten durchgeführt werden sollten. Da einzelne Patienten, die unter mehreren IMID leiden, eine therapeutische Herausforderung darstellen, können hierfür interdisziplinäre Sprechstunden bzw. sog. Immunoboards in der klinischen Praxis hilfreich sein.

Evidence for non-pharmacological interventions in hand osteoarthritis is promising but still scarce. Combined interventions are most likely to best cover the clinical needs of patients with hand osteoarthritis (OA). The aim of this study was to evaluate the effect of a combined, interdisciplinary intervention feasible in both primary and specialist care compared to routine care plus placebo in patients with hand OA. This was a randomised, controlled 2-month trial with a blinded assessor. In the combined-intervention group, rheumatology-trained health professionals from different disciplines delivered a one-session individual intervention with detailed information on functioning, activities of daily living, physical activity, nutrition, assistive devices, instructions on pain management and exercises. Telephone follow up was performed after 4 weeks. The primary outcome was grip strength after 8 weeks. Secondary outcomes were self-reported pain, satisfaction with treatment, health status, two of the Jebsen-Taylor Hand Function subtests and the total score of the Australian/Canadian Hand Osteoarthritis Index (AUSCAN). Statistical significance was calculated by Student’s ttest or the Mann-Whitney U test depending on data distribution. Binominal logistic regression models were fitted, with the primary outcome being the dependent and the group allocation being the independent variable. There were 151 participating patients (74 in the combined-intervention and 77 in the routine-care-plus-placebo group) with 2-month follow-up attendance of 84% (n= 128). Grip strength significantly increased in the combined-intervention group and decreased in the routine-care group (dominant hand, mean 0.03 bar (SD 0.11) versus − 0.03 (SD 0.13), pvalue = 0.001, baseline corrected values) after 8 weeks. The combined one-session individual intervention significantly improved grip strength and self-reported satisfaction with treatment in patients with hand OA. It can be delivered by different rheumatology-trained health professionals and is thus also feasible in primary care. ISRCTN registry, ISRCTN62513257. Registered on 17 May 2012.

Our aim was to investigate the role of nicotinic acetylcholine receptors (nAChRs) in in-vitro osteoclastogenesis and in in-vivo bone homeostasis. The presence of nAChR subunits as well as the in-vitro effects of nAChR agonists were investigated by ex vivo osteoclastogenesis assays, real-time polymerase chain reaction, Western blot and flow cytometry in murine bone marrow-derived macrophages differentiated in the presence of recombinant receptor activator of nuclear factor kappa B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). The bone phenotype of mice lacking various nAChR subunits was investigated by peripheral quantitative computed tomography and histomorphometric analysis. Oscillations in the intracellular calcium concentration were detected by measuring the Fura-2 fluorescence intensity. We could demonstrate the presence of several nAChR subunits in bone marrow-derived macrophages stimulated with RANKL and M-CSF, and showed that they are capable of producing acetylcholine. nAChR ligands reduced the number of osteoclasts as well as the number of tartrate-resistant acidic phosphatase-positive mononuclear cells in a dose-dependent manner. In vitro RANKL-mediated osteoclastogenesis was reduced in mice lacking α7 homomeric nAChR or β2-containing heteromeric nAChRs, while bone histomorphometry revealed increased bone volume as well as impaired osteoclastogenesis in male mice lacking the α7 nAChR. nAChR ligands inhibited RANKL-induced calcium oscillation, a well-established phenomenon of osteoclastogenesis. This inhibitory effect on Ca2+oscillation subsequently led to the inhibition of RANKL-induced NFATc1 and c-fos expression after long-term treatment with nicotine. We have shown that the activity of nAChRs conveys a marked effect on osteoclastogenesis in mice. Agonists of these receptors inhibited calcium oscillations in osteoclasts and blocked the RANKL-induced activation of c-fos and NFATc1. RANKL-mediated in-vitro osteoclastogenesis was reduced in α7 knockout mice, which was paralleled by increased tibial bone volume in male mice in vivo.

Chronic inflammation of articular joints causing bone and cartilage destruction consequently leads to functional impairment or loss of mobility in affected joints from individuals affected by rheumatoid arthritis (RA). Even successful treatment with complete resolution of synovial inflammatory processes does not lead to full reversal of joint functionality, pointing to the crucial contribution of irreversibly damaged structural components, such as bone and cartilage, to restricted joint mobility. In this context, we investigated the impact of the distinct components, including synovial inflammation, bone erosion or cartilage damage, as well as the effect of blocking tumor necrosis factor (TNF) on functional impairment in human-TNF transgenic (hTNFtg) mice, a chronic inflammatory erosive animal model of RA. We determined CatWalk-assisted gait profiles as objective quantitative measurements of functional impairment. We first determined body-weight-independent gait parameters, including maximum intensity, print length, print width and print area in wild-type mice. We observed early changes in those gait parameters in hTNFtg mice at week 5 – the first clinical signs of arthritis. Moreover, we found further gait changes during chronic disease development, indicating progressive functional impairment in hTNFtg mice. By investigating the association of gait parameters with inflammation-mediated joint pathologies at different time points of the disease course, we found a relationship between gait parameters and the extent of cartilage damage and bone erosions, but not with the extent of synovitis in this chronic model. Next, we observed a significant improvement of functional impairment upon blocking TNF, even at progressed stages of disease. However, blocking TNF did not restore full functionality owing to remaining subclinical inflammation and structural microdamage. In conclusion, CatWalk gait analysis provides a useful tool for quantitative assessment of functional impairment in inflammatory destructive arthritis. Our findings indicate that cartilage damage and bone erosion, but not synovial inflammation, are the most important determinants for progressive functional impairment in this chronic erosive arthritis model.

Autoreactive T cells are a central element in many systemic autoimmune diseases. The generation of these pathogenic T cells is instructed by antigen-presenting cells (APCs). However, signaling pathways in APCs that drive autoimmune diseases, such as rheumatoid arthritis, are not understood. We measured phenotypic maturation, cytokine production and induction of T cell proliferation of APCs derived from wt mice and mice with a myeloid-specific deletion of PTEN (myeloid PTEN-/-) in vitro and in vivo. We induced collagen-induced arthritis (CIA) and K/BxN serum transfer arthritis in wt and myeloid-specific PTEN-/-mice. We measured the cellular composition of lymph nodes by flow cytometry and cytokines in serum and after ex vivo stimulation of T cells. We show that myeloid-specific PTEN-/-mice are almost protected from CIA. Myeloid-specific deletion of PTEN leads to a significant reduction of cytokine expression pivotal for the induction of systemic autoimmunity such as interleukin (IL)-23 and IL-6, leading to a significant reduction of a Th17 type of immune response characterized by reduced production of IL-17 and IL-22. In contrast, myeloid-specific PTEN deficiency did not affect K/BxN serum transfer arthritis, which is independent of the adaptive immune system and solely depends on innate effector functions. These data demonstrate that the presence of PTEN in myeloid cells is required for the development of CIA. Deletion of PTEN in myeloid cells inhibits the development of autoimmune arthritis by preventing the generation of a pathogenic Th17 type of immune response.

Despite their different targets, biologic agents used for blockade of TNF and IL-6, inhibition of T-cell co-stimulation and B-cell depletion all have similar beneficial effects on the outcome of rheumatoid arthritis (RA). This observation raises questions as to whether the targets of these therapies might all be involved in a common pathogenetic pathway. However, blockade of TNF and IL-6 has a similar inhibitory effect on joint damage progression in patients with either early or late disease. In comparison, B-cell depletion and inhibition of T-cell co-stimulation seem to have a somewhat delayed effect on joint damage (compared with cytokine inhibition), which suggests that these approaches affect upstream pathogenetic events. This article discusses these disparities and presents hypotheses as to whether clinical trial data can be used to determine at which point a biologic agent might interfere with the pathogenetic cascade in RA.

Rheumatoid arthritis is a heterogeneous disease with respect to clinical manifestations, serologic abnormalities, joint damage and functional impairment. Predicting outcome in a reliable way to allow for strategic therapeutic decision-making as well as for prediction of the response to the various therapeutic modalities available today, especially biological agents, would provide means for optimization of care. In the present article, the current information on biological and clinical markers related to disease activity and joint damage as well as for predictive purposes is reviewed. It will be shown that the relationship of many biomarkers with disease characteristics is confounded by factors unrelated to the disease, and that only few biomarkers exist with some predictive value. Moreover, clinical markers appear of equal value as biomarkers for this purpose, although they likewise have limited capacity in these regards. The analysis suggests the search for better markers to predict outcomes and therapeutic responsiveness in rheumatoid arthritis needs to be intensified.

Activator protein 1 (AP-1) (Fos/Jun) is a transcriptional regulator composed of members of the Fos and Jun families of DNA binding proteins. The functions of AP-1 were initially studied in mouse development as well as in the whole organism through conventional transgenic approaches, but also by gene targeting using knockout strategies. The importance of AP-1 proteins in disease pathways including the inflammatory response became fully apparent through conditional mutagenesis in mice, in particular when employing gene inactivation in a tissue-specific and inducible fashion. Besides the well-documented roles of Fos and Jun proteins in oncogenesis, where these genes can function both as tumor promoters or tumor suppressors, AP-1 proteins are being recognized as regulators of bone and immune cells, a research area termed osteoimmunology. In the present article, we review recent data regarding the functions of AP-1 as a regulator of cytokine expression and an important modulator in inflammatory diseases such as rheumatoid arthritis, psoriasis and psoriatic arthritis. These new data provide a better molecular understanding of disease pathways and should pave the road for the discovery of new targets for therapeutic applications.

In rheumatoid arthritis (RA), the chronically inflamed joint undergoes profound phenotypical changes. Aside synovial inflammation and cartilage degeneration, subchondral bone erosions emerge early in the course of disease and are associated with functional impairment in RA patients. Chronic joint inflammation injures the bone as consequence of two key pathophysiological mechanisms: On the one hand, the proliferative synovial tissue (“pannus”) attracts monocytes/macrophages to migrate into the joint and provides specific signals for these cells to differentiate into bone-resorbing osteoclasts. These cells are activated by pro-inflammatory cytokines and resorb mineralized tissue. Second, the injured bone attempts to counteract bone resorption by attracting osteoblasts at the site of erosion. However, the inflammatory local environment prevents significant repair by overproduction of osteoblast-inhibitory mediators and facilitation of osteoblast apoptosis. Until now, osteoimmunology research in arthritis primarily focused on the mechanism of joint destruction and the effects of inhibiting osteoclasts. However, recent experimental studies imply that fostering bone formation in chronic erosive arthritis could potentially reverse joint destruction with induction of repair phenomena. This review discusses the pathomechanisms leading to impaired bone turnover and potential mediators that could be targeted to reverse bone loss in RA.

Chronic inflammation and bone loss are closely linked pathophysiologic events. The most typical example of inflammatory bone loss is seen in patients with rheumatoid arthritis who develop systemic osteopenia as well as local breakdown of bone in the direct vicinity of inflamed joints. Understanding the mechanisms of arthritic bone degradation is crucial for designing therapies that can specifically protect joints from structural damage. Since osteoclast differentiation and activity are key events in arthritic bone damage, the signals that trigger osteoclastogenesis are potential therapeutic targets. Receptor activator of nuclear factor-?B (RANK) is activated by its ligand, RANKL, an essential molecule for osteoclast development: in the absence of RANKL or RANK, osteoclast differentiation from monocyte precursors does not occur. RANKL is expressed on T cells and fibroblasts within the synovial inflammatory tissue of patients with RA and its expression is regulated by proinflammatory cytokines. In animal models of arthritis, blockade of RANKL–RANK interactions, or a genetic absence of RANKL or RANK, protects against joint damage despite the presence of joint inflammation. Therefore, inhibition of RANKL is regarded as a promising future strategy for inhibiting inflammatory bone loss in patients with chronic inflammatory arthritis.

Tumour necrosis factor (TNF) signalling molecules are considered as promising therapeutic targets of antirheumatic therapy. Among them, mitogen-activated protein kinases are thought to be of central importance. Herein, we investigate the role in vivo of TNF-α signalling through c-Jun N-terminal kinase (JNK)1 in destructive arthritis. Human TNF transgenic (hTNFtg) mice, which develop inflammatory arthritis, were intercrossed with JNK1-deficient (JNK1-/-) mice. Animals (n = 35) of all four genotypes (wild-type, JNK1-/-, hTNFtg, JNK1-/-hTNFtg) were assessed for clinical and histological signs of arthritis. Clinical features of arthritis (swelling and decreased grip strength) developed equally in hTNFtg and JNK1-/-hTNFtg mice. Histological analyses revealed no differences in the quantity of synovial inflammation and bone erosions or in the cellular composition of the synovial infiltrate. Bone destruction and osteoclast formation were observed to a similar degree in hTNFtg and JNK1-/-hTNFtg animals. Moreover, cartilage damage, as indicated by proteoglycan loss in the articular cartilage, was comparable in the two strains. Intact phosphorylation of JNK and c-Jun as well as expression of JNK2 in the synovial tissue of JNK1-/-hTNFtg mice suggests that signalling through JNK2 may compensate for the deficiency in JNK1. Thus, JNK1 activation does not seem to be essential for TNF-mediated arthritis.

Arthritis can destroy the cortical bone barrier and expose bone marrow to synovial tissue. This study examines bone marrow changes in arthritis and its effects on cortical bone remodeling. Bone marrow next to arthritic lesions exhibits B‐lymphocyte‐rich infiltrates, which express BMPs and stimulate endosteal bone formation. Thus, bone marrow actively participates in the arthritic process.Introduction:Imaging studies have shown that bone marrow changes occur in patients with rheumatoid arthritis (RA). To examine whether bone marrow is affected during arthritis, human TNF transgenic (hTNFtg) mice, which constitute an established animal model of human RA, were examined for bone marrow changes.Materials and Methods:The hind paws (tarsal area) of 22 untreated hTNFtg mice, 5 hTNFtg mice treated with anti‐TNF (infliximab), and 5 wildtype (WT) mice were examined histologically, immunohistochemically, and by means of mRNA in situ hybridization.Results and Conclusions:All untreated hTNFtg mice with moderate (n= 10) and severe (n= 7) disease developed inflammatory bone marrow lesions during the course of disease, whereas no such lesions appeared in hTNFtg mice with mild disease (n= 5) and WT mice. Bone marrow infiltrates were almost exclusively composed of lymphocytes, and the overwhelming proportion (>80%) was B‐cells. Presence and extent of bone marrow infiltrates were closely linked to severity of arthritis. In addition, blockade of TNF effectively reduced bone marrow inflammation. Interestingly, osteoblast numbers were increased at the endosteal surface in the vicinity of these lesions. Moreover, osteoid deposition; expression of bone matrix proteins, such as osteocalcin and osteopontin; and mineralization were enhanced, suggesting that inflammatory bone marrow infiltrates induce bone formation. Indeed, B‐lymphocytes of these lesions expressed bone morphogenetic protein (BMP)‐6 and −7, which are important stimulators of new bone formation. Thus, we conclude that bone marrow actively participates in destructive arthritis by generating B‐lymphocyte‐rich bone marrow lesions and inducing endosteal bone formation.

Local bone erosion and systemic bone loss are hallmarks of rheumatoid arthritis and cause progressive disability. Tumor necrosis factor (TNF) is a key mediator of arthritis and acts catabolically on bone by stimulating bone resorption and inhibiting bone formation. We hypothesized that the concerted action of anti-TNF, which reduces inflammation and parathyroid hormone (PTH), which stimulates bone formation, or osteoprotegerin (OPG), which blocks bone resorption and could lead to repair of local bone erosions and reversal of systemic bone loss. To test this, human TNF-transgenic mice with established erosive arthritis and systemic bone loss were treated with PTH, OPG, and anti-TNF, alone or in combination. Local bone erosions almost fully regressed, on combined treatment with anti-TNF and PTH and/or OPG, suggesting repair of inflammatory skeletal lesions. In contrast, OPG and anti-TNF alone led to arrest of bone erosions but did not achieve repair. Treatment with PTH alone had no influence on the progression of bone erosions. Local bone erosions all showed signs of new bone formation such as the presence of osteoblasts, osteoid formation, and mineralization. Furthermore, systemic bone loss was completely reversed on combined treatment and this effect was mediated by osteoblast stimulation and osteoclast blockade. In summary, we conclude that local joint destruction and systemic inflammatory bone loss because of TNF can regress and that repair requires a combined approach by reducing inflammation, blocking bone resorption, or stimulating bone formation.

Bone erosion is a hallmark of rheumatoid arthritis. Recent evidence from experimental arthritis suggests that osteoclasts are essential for the formation of local bone erosions. Two essential regulators of osteoclastogenesis have recently been described: the receptor-activator of nuclear factor kappa B ligand, which promotes osteoclast maturation, and osteoprotegerin (OPG), which blocks osteoclastogenesis. The present review summarizes the current knowledge on the role of osteoclasts in local bone erosion. In addition, the role of OPG as a therapeutic tool to inhibit local bone erosion is addressed. Finally, evidence for OPG as an inhibitor of systemic inflammatory bone loss is discussed.

OBJECTIVE: To test if markers of bone metabolism are altered in patients with seronegative spondyloarthropathies (SSpA). METHODS: We studied biochemical markers of bone resorption and bone formation, osteoprotegerin (OPG), and bone mineral density (BMD) in patients with psoriatic arthritis (PsA), ankylosing spondylitis (AS), and reactive arthritis (ReA) and healthy volunteers. RESULTS: The bone resorption markers urinary deoxypyridinoline and crosslinked telopeptide of collagen-I were significantly increased in patients with AS, PsA, and ReA; in PsA they correlated with the acute phase response (C-reactive protein and erythrocyte sedimentation rate). The bone formation markers were divergent: bone-specific alkaline phosphatase was increased in PsA, but not in AS or ReA. Osteocalcin levels were only elevated in AS. Serum levels of OPG were significantly increased in both AS and PsA. Dual energy x-ray absorptiometry (DEXA) measurements of lumbar spine and femoral neck revealed osteopenia in patients with AS, whereas the DEXA distribution was within normal range in PsA. CONCLUSION: Our data indicate high and, particularly in AS, unbalanced bone turnover in SSpA, consistent with the decrease in BMD found in patients with AS.

To study the effects of osteoclast-targeted therapies, such as osteoprotegerin (OPG) and pamidronate, on joint inflammation and bone destruction using a tumor necrosis factor α (TNFα)-transgenic mouse model. Mice were placed into 5 groups that received either OPG, pamidronate, a combination of both agents, infliximab as a positive control, or phosphate buffered saline as a negative control. Treatment was initiated at the onset of arthritis, continued over 6 weeks, and thereafter, the clinical, radiologic, and histologic outcomes were assessed. A significant improvement in clinical symptoms, as assessed by the reduction of paw swelling, was only found in the infliximab group, whereas all other treatment groups failed to show significant improvement. However, when assessing structural damage with radiographic analysis, a significant retardation of joint damage was evident in animals treated with OPG (55% reduction of erosions), pamidronate (50% reduction of erosions) the combination therapy of OPG and pamidronate (64% reduction of erosions), and with infliximab (66% reduction of erosions). Confirming these data, quantitative histologic analysis revealed a significant reduction in the size of bone erosions in all treatment groups (OPG 56%, pamidronate 53%, OPG and pamidronate 81%, and infliximab 46%) compared with the control group. Furthermore, a significant reduction of osteoclast numbers was seen in animals treated with OPG alone or in combination with pamidronate as well as in animals treated with infliximab. These data suggest that OPG alone or in combination with bisphosphonates is an effective therapeutic tool for the prevention of TNFα-mediated destruction of bone by reducing the number of bone-resorbing cells in the inflammatory tissue.

To determine the effect of joint protection and home exercises on hand function of patients with hand osteoarthritis (OA). Randomized, controlled, 3-month trial with a blinded assessor. Primary outcome parameter was grip strength; secondary parameters were Health Assessment Questionnaire and visual analog scales (VAS) for pain and global hand function. Forty patients with hand OA were randomly assigned to 2 groups: One group received instruction for joint protection and home hand exercises (JPE group), the control group received an information session about hand OA. Grip strength improved by 25% in the JPE group (right hand, P < 0.0001; left hand, P = 0.0005), but not in the control group. Global hand function (by VAS) improved in a larger proportion (65%) of patients in the JPE group (P < 0.05). Joint protection and hand home exercises, easily administered and readily acceptable interventions, were found to increase grip strength and global hand function.

To investigate the expression of the transcription factor Ets‐1 in synovial tissue and cultured synovial fibroblasts from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and to study the regulation of Ets‐1 expression and activation in synovial fibroblasts by proinflammatory cytokines.In situ expression of Ets‐1 in synovial tissue from RA and OA patients was examined by double immunohistochemistry. The effects of interleukin‐1 (IL‐1) or tumor necrosis factor α (TNFα) on Ets‐1 expression and activation (DNA binding) in cultured synovial fibroblasts were analyzed by Western blotting and DNA gel shift assay, respectively. In addition, the intracellular location of Ets‐1 in synovial fibroblasts was determined by immunofluorescence.Pronounced expression of Ets‐1 was detected in synovial tissues from all RA patients evaluated, particularly in the synovial lining layer and the sublining areas. Ets‐1 was expressed by both fibroblasts and macrophages as well as by endothelial cells, while only a few T cells stained positive for Ets‐1. In synovial specimens from OA patients, Ets‐1 expression was much less frequently observed and was largely restricted to vascular cells. Ets‐1 was expressed to a similar degree in cultured synovial fibroblasts from RA and OA patients, as demonstrated by reverse transcriptase–polymerase chain reaction and Western blotting. Both IL‐1 and TNFα induced pronounced up‐regulation of Ets‐1 in synovial fibroblasts. Moreover, binding of Ets‐1 to its specific DNA binding site was induced by both cytokines, although with different time courses. Immunofluorescence staining revealed a dominant nuclear localization of Ets‐1 in IL‐1– or TNFα‐stimulated synovial fibroblasts.The overexpression of Ets‐1 observed in RA synovial tissue appears to be caused by TNFα and IL‐1, suggesting that Ets‐1 may be an important factor in the cytokine‐mediated inflammatory and destructive cascade characteristic of RA.

To investigate whether stress- and mitogen-activated protein kinases (SAPK/MAPK), such as extracellular signal–regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, are significantly activated in rheumatoid arthritis (RA) synovial tissue compared with their activation in degenerative joint disease; to assess the localization of SAPK/MAPK activation in rheumatoid synovial tissue; and to search for the factors leading to stress kinase activation in human synovial cells. Immunoblotting and immunohistology by antibodies specific for the activated forms of SAPK/MAPK were performed on synovial tissue samples from patients with RA and osteoarthritis (OA). In addition, untreated and cytokine-treated human synovial cells were assessed for SAPK/MAPK activation and downstream signaling by various techniques. ERK, JNK, and p38 MAPK activation were almost exclusively found in synovial tissue from RA, but not OA, patients. ERK activation was localized around synovial microvessels, JNK activation was localized around and within mononuclear cell infiltrates, and p38 MAPK activation was observed in the synovial lining layer and in synovial endothelial cells. Tumor necrosis factor α, interleukin-1 (IL-1), and IL-6 were the major inducers of ERK, JNK, and p38 MAPK activation in cultured human synovial cells. Signaling through SAPK/MAPK pathways is a typical feature of chronic synovitis in RA, but not in degenerative joint disease. SAPK/MAPK signaling is found at distinct sites in the synovial tissue, is induced by proinflammatory cytokines, and could lead to the design of highly targeted therapies.

To investigate the expression of the stroma cell product stem cell factor (SCF) in synovial fibroblasts (SFB) in patients with rheumatoid arthritis (RA) and osteoarthritis (OA), and to analyze the capacity of SFB to induce mast cell (MC) chemotaxis. Synovial tissue was obtained from 29 patients with RA and 25 patients with OA. Tissue was dispersed by enzymatic digestion using collagenase. SFB were grown in serial passage and exposed to tumor necrosis factor α (TNFα) or control medium. Expression of SCF in cultured SFB was analyzed by reverse transcription–polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and immunostaining. The ability of SFB (supernatants) to induce MC migration was analyzed using a double-chamber chemotaxis assay and the human mast cell line HMC-1. In situ expression of SCF in synovial tissue from patients with RA (n = 6) and OA (n = 6) was examined by double immunohistochemistry using antibodies against SCF and the fibroblast-specific antibody ASO2. In both RA and OA, cultured SFB were found to express SCF messenger RNA, as assessed by RT-PCR. In addition, the SCF protein was detectable in cell lysates and supernatants of SFB by ELISA. Incubation of SFB with TNFα resulted in an increased expression and release of SCF. Recombinant human SCF (rHuSCF) and SFB supernatants induced significant migration of HMC-1 cells above control levels. In addition, exposure of SFB to TNFα led to an increased migration of HMC-1, and a blocking anti-SCF antibody inhibited the rHuSCF- and SFB-induced migration of HMC-1. In situ double immunostaining revealed expression of SCF in ASO2-positive SFB in the synovium of patients with RA. Our results show that SFB (in RA and OA) express SCF and induce MC chemotaxis. Furthermore, TNFα was found to augment SCF expression in SFB. It is hypothesized that these cellular interactions play an important role in MC accumulation and related events in RA.