类风湿关节炎滑膜细胞向破骨细胞分化实验研究

目的观察类风湿关节炎(RA)滑膜组织中破骨细胞来源以及核因子κB受体活化子配体(RANKL)在诱导破骨细胞分化过程中的作用。方法取6例RA和6名正常关节的滑膜组织,用胶原酶消化法获得滑膜细胞,通过免疫磁珠法分选获得CD68+/-滑膜细胞。用外源性RANKL16μg/L、巨细胞集落刺激因子(M-CSF)25μg/L及地塞米松醋酸酯1×10-8mol/L诱导各组滑膜细胞分化。通过抗酒石酸酸性磷酸酶(TRAP)染色、降钙素受体(CTR)免疫荧光检测、骨吸收陷窝形成方法鉴定破骨细胞。并在RA滑膜CD68+细胞中加入0~8ng/ml梯度浓度的RANKL,观察不同浓度RANKL对RA滑膜CD68+细胞分化的影响。结果RA滑膜CD68+细胞在RANKL诱导14d后,RA滑膜CD68+细胞组出现CTR阳性、TRAP染色阳性细胞并有骨吸收陷窝形成。RA滑膜CD68+细胞在体外经RANKL诱导后分化形成的破骨细胞功能与RANKL剂量有关。结论RA滑膜组织中前体破骨细胞来源于滑膜CD68+细胞,在体外RANKL诱导下可以分化为成熟破骨细胞。RANKL体外诱导剂量影响RA滑膜CD68+细胞分化功能。     

RANKL诱导破骨细胞前体细胞分化成熟

目的 用核因子-κB受体活化因子配体(RANKL)诱导破骨细胞前体细胞分化成熟,建立获取成熟破骨细胞的方法.方法 用破骨细胞前体细胞RAW264.7细胞为模型,RANKL诱导培养4～9 d,抗酒石酸酸性磷酸酶(TRAP)染色观察TRAP阳性多核细胞形成,罗丹明-鬼笔环肽荧光染色观察纤维性肌动蛋白(F-actin)环,DAPI染色观察细胞核,甲苯胺蓝染色观察牛骨片表面的吸收陷窝情况.结果 RANKL可诱导RAW264.7细胞形成TRAP染色阳性的多核细胞,形成F-actin环,骨片吸收陷窝明显.结论 RANKL可诱导RAW264.7细胞向成熟破骨细胞分化,该诱导模型可用于破骨细胞分化研究.     

Kruppel样因子4抑制巨噬细胞向破骨细胞分化介导平滑肌细胞钙化

目的探讨Kruppel样因子4(KLF4)在巨噬细胞向破骨细胞分化中的作用及相关机制。方法提取雄性C57BL/6J小鼠腹腔原代巨噬细胞并鉴定,将其分为对照组,NF-κB受体激动剂配体(RANKL)组,共刺激组(KLF4抗体和RANKL共刺激4 d),用抗酒石酸酸性磷酸酶(TRAP)染色检测破骨细胞分化情况,用鬼笔环肽染色检测破骨细胞成熟程度;通过骨吸收陷窝实验测破骨细胞骨吸收能力;通过qRT-PCR检测破骨细胞分化相关基因表达,用钙盐染色检测血管平滑肌细胞钙化情况。结果 TRAP染色显示,TRAP阳性细胞直径约100μm,细胞核3个。共刺激组破骨细胞数量较RANKL组明显增多(P0.05)。与RANKL组比较,共刺激组破骨细胞成熟程度进一步升高、陷窝面积及数量升高(P0.05)。RANKL组较对照组相关破骨基因表达明显升高(P0.05);共刺激组较RANKL组相关破骨基因表达明显升高(P0.05),而血管平滑肌细胞钙化明显降低(P0.05)。结论KLF4抗体可促进巨噬细胞向破骨细胞转分化,进而抑制平滑肌细胞钙化。     

类风湿关节炎中白三烯B4间接分化破骨细胞的实验研究

目的探讨在类风湿关节炎（RA）中,白三烯B4（LTB4）能否通过促进核因子Kappa B受体激活剂配体（RANKL）的表达,起到间接分化破骨细胞的作用.方法利用RA滑膜成纤维细胞（RAFLs）和人外周血单核细胞的共培养体系,对照组2.5 ng/ml巨噬细胞集落刺激因子（M-CSF）刺激、实验a组2.5 ng/ml M-CSF＋10-8mol/L LTB4刺激、实验b组2.5 ng/ml M-CSF＋10-8 mol/L LTB4＋100 ng/ml骨保护素（OPG）刺激,培养3周后行抗酒石酸酸性磷酸酶（TRAP）细胞化学染色,通过计数多核性TRAP酶染色阳性的破骨细胞样细胞,比较各组的分化破骨细胞作用.结果对照组几乎没有破骨细胞样细胞,而实验a组则出现较多的破骨细胞样细胞,实验b组则与对照组相似,几乎没有破骨细胞样细胞.结论在RA中,LTB4能够通过促进RAFLs细胞RANKL的表达来间接分化破骨细胞.     

晚期氧化蛋白终产物对破骨细胞分化的影响

目的探讨晚期氧化蛋白终产物(AOPPs)对破骨细胞分化的影响。方法体外分离培养大鼠骨髓单核细胞,分为空白对照组、阴性对照组(RSA)、AOPPs组、阳性对照组(RANKL)、还原型烟酰胺腺嘌呤二核苷酸磷酸(NADPH)氧化酶抑制剂组(AOPPs+夹竹桃麻素),干预6 d后,通过抗酒石酸酸性磷酸酶(TRAP)染色观察TRAP阳性多核细胞,鬼笔环肽荧光染色观察F肌动蛋白(F-actin)环,甲苯胺蓝染色观察骨磨片的骨吸收陷窝。此外,AOPPs刺激2 h后,通过DCFH-DA荧光探针法检测细胞内活性氧(ROS)生成。结果 AOPPs及阳性对照组RANKL均可诱导TRAP阳性多核细胞、F-actin环及骨吸收陷窝形成,并且AOPPs刺激后细胞ROS生成明显增多。AOPPs所致以上效应均能被NADPH氧化酶抑制剂夹竹桃麻素阻断。结论 AOPPs可诱导大鼠骨髓单核细胞向破骨细胞分化。     

白细胞介素-23刺激的类风湿关节炎成纤维细胞对人破骨样细胞形成的研究

目的 探讨向细胞介素(IL)-23刺激的类风湿关节炎(RA)滑膜成纤维细胞(FLS)在人破骨样细胞形成中的作用.方法 用不同浓度(1、5和10 ng/ml)的IL-23刺激RA和骨关节炎(OA)患者滑膜FLS 72 h,实时荧光定量聚合酶链反应(real time-PCR)检测RA和OA滑膜FLS核因子κB受体激活剂配体(RANKL)mRNA表达.分离人外周血单核细胞(MN),与IL-23刺激的RA和OA滑膜FLS共培养,通过抗酒石酸酸性磷酸酶(TRAP)染色观察是否有破骨样细胞形成;同时,real time-PCR法检测破骨样细胞形成的分子标志.结果 不同浓度的IL-23均能上调RA滑膜FLS RANKL的表达;但几乎不诱导OA滑膜细胞RANKL的表达.在IL-23刺激的RA FLS和MN共培养体系中能观察到TRAP染色阳性的破骨样细胞形成;并且破骨样细胞形成的分子标志表达增高.而无IL-23刺激的RA FLS或IL-23刺激的OAFLS和MN共培养体系中未见TRAP染色阳性的破骨样细胞的形成.结论 IL-23通过诱导RA滑膜细胞RANKL的表达促进人MN分化衍生为破骨样细胞.     

降钙素对体外培养破骨细胞功能的影响

目的　观察降钙素对体外培养破骨细胞功能以及成骨细胞的骨保护素 (OPG)、细胞核因子 κB受体活化因子配基 (RANKL)的表达的影响。方法　分别用酶消化法和机械分离获得新生SD大鼠成骨细胞、破骨细胞 ,在培养液中分别加入不同浓度的降钙素 ,以抗酒石酸酸性磷酸酶 (TRAP)染色观察破骨细胞数目、形态 ,Image ProPlus图像软件分析骨片上骨吸收陷窝的数目和面积。用RT PCR方法观察成骨细胞OPG、RANKL的表达。结果　各组破骨细胞数目随着降钙素浓度增加而减少 (P <0 .0 5 )。骨片培养5天 ,吸收陷窝计数的结果显示 ,10 -14 mol/L以上浓度降钙素对破骨细胞吸收功能均有明显抑制作用 ,并呈剂量相关性。 10 -12 mol/L组陷窝面积为对照组的 49% (P <0 .0 1) ,10 -8mol/L组为对照组的 3 0 % (P <0 .0 1)。降钙素组破骨细胞OPGmRNA表达较对照组升高 ,RANKL降低 (均P <0 .0 5 )。结论　除了直接作用于破骨细胞外 ,降钙素还通过影响成骨细胞上OPG、RANKL的分泌间接调控破骨细胞功能 ,抑制骨吸收。     

氨基多糖对RANKL诱导的RAW264.7向破骨细胞样细胞分化的抑制作用观察

目的 探讨氨基多糖(GAGs)对核因子KB受体活化因子配体(RANKL)诱导的RAW264.7向破骨细胞分化的影响.方法 采用RANKL单独诱导RAW264.7细胞(对照组),分别采用不同浓度肝素、高分子量透明质酸(HA)、硫酸软骨素(CS)C联合RANKL诱导RAW264.7分化(分别为肝素组、HA组、CSC组).细胞培养第3、5、7、8天采用抗酒石酸酸性磷酸酶染色法(TRAP)检测破骨细胞样细胞并计数;ELISA法检测第8天各组培养液上清中抗酒石酸酸性磷酸酶5b(TRAP5b)含量.结果 与对照组比较,诱导第3、5、7、8天,破骨样细胞数均明显减少(P＜0.05);其中肝素组随浓度的增大而减少(P＜0.05).第8天培养液中TRAP5b含量与细胞计数结果相符.结论 氨基多糖对RANKL诱导下RAW264.7向破骨细胞样细胞的分化具有抑制作用;肝素的作用具有剂量依赖性.     

白三烯B4对人破骨细胞直接分化和激活功能的实验研究

目的探讨白三烯(LT)B4能否不依赖细胞核因子资B受体激活剂配体(RANKL)直接促进人破骨细胞的分化和激活。方法阳性对照组用25ng/ml巨噬细胞集落刺激因子(M-CSF)和30ng/mlsRANKL来诱导人外周血单核细胞的培养,实验组用25ng/mlM-CSF和10-9、10-8、10-7mol/LLTB4来诱导。通过抗酒石酸磷酸酶(TRAP)染色及10mm×10mm玻片上多核性TRAP染色(+)的破骨细胞样细胞计数,来确定LTB4的直接分化作用,并与RANKL的作用比较。通过甲苯胺蓝染色10mm×10mm牛皮质骨片上的骨质吸收陷窝并计数,来确定LTB4直接功能激活作用,并与RANKL的作用比较。结果当M-CSF存在时,LTB4能够直接分化人外周血单核细胞为破骨细胞样细胞,并能激活其骨质吸收功能。且随LTB4浓度的增加而增强,但要弱于RANKL。结论LTB4对人破骨细胞有不依赖RANKL的直接分化和激活作用。     

两种大鼠骨髓源破骨样细胞诱导方法的比较

目的 比较两种不同的大鼠骨髓源破骨样细胞(Osteoclast-like cells,OLC)体外分离培养的方法.方法 收集5周龄SD大鼠骨髓细胞悬液,加入M-CSF(10 ng/ml)培养24 h后置入不同的诱导培养体系中,即A组:巨噬细胞集落刺激因子(M-CSF)+破骨细胞分化因子(RANKL),B组:M-CSF+1,25二羟基维生素D3[1,25(OH)2D3]+地塞米松(Dexamethasone),分别于培养3、5、7、9、12 d利用抗酒石酸碱性磷酸酶(TRAP)染色、骨吸收陷窝检测等对获得的OLC进行形态学和功能观察,并进行计数比较.结果 两种方法 均可诱导出TRAP染色阳性的多核细胞.两组细胞数量均于第7天达到最高峰,B组于7、9、12 d获得的细胞数量较A组多(P<0.05);B组骨吸收陷窝数于9、12 d时多于A组(P<0.05).结论 两种方法 均诱导出破骨样细胞,B组诱导OLC的细胞活性和细胞数量高于A组.     

Synovial fibroblasts promote osteoclast formation by RANKL in a novel model of spontaneous erosive arthritis

OBJECTIVE: Erosion of cartilage and bone is a hallmark of rheumatoid arthritis (RA). This study was undertaken to explore the roles of hyperproliferating synovial fibroblasts and macrophages in abnormal osteoclast formation, using the recently described BXD2 mouse model of RA. METHODS: Cell distribution in the joints was analyzed by immunohistochemistry, using tartrate-resistant acid phosphatase (TRAP) staining to identify osteoclasts. To identify the defective cells in BXD2 mice, mouse synovial fibroblasts (MSFs) were cultured with bone marrow-derived macrophages. Osteoclast formation was assayed by TRAP staining and bone resorption pit assay, and the cytokine profiles of the MSFs and macrophages were determined by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. RESULTS: In BXD2 mice, TRAP-positive osteoclasts were found at sites of active bone erosion, in close proximity to hyperproliferating synovial fibroblasts. On coculture, MSFs from BXD2 mice, but not C57BL/6 mice, produced high levels of RANKL messenger RNA, induced macrophages to form osteoclasts, and actively eroded bone slices, through a mechanism(s) that could be blocked by pretreatment with osteoprotegerin. Although macrophages from BXD2 mice expressed higher basal levels of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-6 than those from C57BL/6 mice, abnormal osteoclast formation was not due to enhanced sensitivity of the BXD2 mouse macrophages to RANKL. TNFalpha, produced by both BXD2 MSFs and BXD2 mouse macrophages, had a strong stimulatory effect on RANKL expression. CONCLUSION: BXD2 MSFs produce RANKL and induce the development of osteoclasts from macrophages. The enhanced production of RANKL is possibly due to autocrine stimulation, together with paracrine stimulation by factors produced by macrophages.     

Synovial macrophage-osteoclast differentiation in inflammatory arthritis

BACKGROUND: Pathological bone resorption (marginal erosions and juxta-articular osteoporosis) by osteoclasts commonly occurs in rheumatoid arthritis (RA). OBJECTIVES: To define the nature of the mononuclear precursor cells from which osteoclasts are formed in inflamed synovial tissues and to determine the cellular and humoral factors which influence osteoclast differentiation. METHOD: Macrophage (CD14+), non-macrophage (CD14-), and unsorted (CD14+/CD14-) synovial cell populations from RA and inflammatory/non-inflammatory osteoarthritis (OA) synovium were cultured in the presence of receptor activator for nuclear factor kappaB ligand (RANKL) and monocyte-colony stimulating factor (M-CSF; in the presence/absence of prostaglandin E(2) (PGE(2)), interleukin 1beta (IL1beta), tumour necrosis factor alpha (TNFalpha), and IL6). Osteoclast differentiation was assessed by expression of tartrate resistant acid phosphatase (TRAP), vitronectin receptor (VNR), and lacunar resorption. RESULTS: TRAP+ and VNR+ multinucleated cells capable of lacunar resorption were only formed in cultures of CD14+-containing synovial cell populations (that is, CD14+ and CD14+/CD14- cells). No difference in the extent of osteoclast formation was noted in cultures of CD14+ cells isolated from RA, inflammatory OA, and non-inflammatory OA synovium. However, more TRAP+/VNR+ cells and more lacunar resorption was noted in CD14+/CD14- cells from RA and inflammatory OA synovial tissues. The addition of PGE(2), IL1beta, TNFalpha, and IL6 did not increase RANKL/M-CSF-induced osteoclast formation and lacunar resorption of both CD14+/CD14- and CD14+ synovial cell populations. CONCLUSIONS: Osteoclast precursors in synovial tissues are CD14+ monocyte/macrophages. The increase in osteoclast formation in cultures of CD14+/CD14- compared with CD14+ synovial cells in RA and inflammatory OA points to a role for CD14- cells in promoting osteoclast differentiation and bone resorption in inflamed synovial tissues by a mechanism which does not involve a direct effect of proinflammatory cytokines/prostaglandins on RANKL-induced macrophage-osteoclast differentiation.     

LIGHT (TNFSF14), a novel mediator of bone resorption, is elevated in rheumatoid arthritis

OBJECTIVE: Human osteoclast formation from mononuclear phagocyte precursors involves interactions between tumor necrosis factor (TNF) ligand superfamily members and their receptors. LIGHT is a transmembrane protein expressed and shed from the surface of activated T cells. Since activated T cells have been implicated in osteoclastogenesis in rheumatoid arthritis (RA), this study sought to determine whether LIGHT can regulate RANKL/cytokine-induced osteoclast formation, to identify the mechanism by which LIGHT influences osteoclastogenesis, and to investigate the presence of LIGHT in the serum of RA patients. METHODS: The effect of LIGHT on human and murine osteoclast formation was assessed in the presence and absence of neutralizing reagents to known osteoclastogenic factors. Serum levels of LIGHT in RA patients were measured by enzyme-linked immunosorbent assay. RESULTS: In the presence and absence of RANKL, LIGHT induced osteoclast formation from both human peripheral blood mononuclear cells and murine macrophage precursors, in a dose-dependent manner, whereas no inhibition was observed by adding osteoprotegerin, RANK:Fc, TNFalpha, or interleukin-8 or by blocking the LIGHT receptors herpesvirus entry mediator or lymphotoxin beta receptor. However, formation of osteoclasts was significantly decreased by the soluble decoy receptor for LIGHT, DcR3, and by blocking antibodies to the p75 component of the TNF receptor. A significant increase in LIGHT levels in the serum of RA patients compared with normal controls was also noted. CONCLUSION: Our results indicate that LIGHT promotes RANKL-mediated osteoclastogenesis and that it can induce osteoclast formation by a mechanism independent of RANKL. The increased concentration of LIGHT in patients with RA raises the possibility that LIGHT may play a role in immunopathogenic conditions that are associated with localized or systemic bone loss.     

Interleukin (IL) 18 stimulates osteoclast formation through synovial T cells in rheumatoid arthritis: comparison with IL1 beta and tumour necrosis factor alpha

OBJECTIVE: To determine whether IL18 has any indirect effects on osteoclastogenesis mediated by T cells in RA synovium, and compare its effects with those of IL1 beta and TNF alpha. METHODS: Resting T cells were isolated from peripheral blood of healthy donors, and stimulated with 2 microg/ml phytohaemagglutinin (PHA) and 0.5 ng/ml IL2 for 24 hours. Synovial T cells were isolated from RA synovial tissue. The levels of soluble receptor activator of the NF-kappa B ligand (RANKL), osteoprotegerin (OPG), IFN gamma, M-CSF, and GM-CSF were determined by ELISA. Membrane bound RANKL expression was analysed by flow cytometry. Commercially available human osteoclast precursors were cocultured with T cells to induce osteoclast formation, which was determined with tartrate resistant acid phosphatase staining and pit formation assay. RESULTS: In PHA prestimulated T cells or RA synovial T cells, IL18, IL1 beta, or TNFalpha increased soluble RANKL production and membrane bound RANKL expression in a dose dependent manner. IL18, IL1 beta, and TNF alpha did not induce M-CSF, GM-CSF, IFN gamma, or OPG production in PHA prestimulated T cells or RA synovial T cells. IL18 increased the number of osteoclasts and bone resorption area on dentine slices in the coculture of human osteoclast precursors with PHA prestimulated T cells or RA synovial T cells; its ability was equivalent to that of IL1 beta, but less potent than that of TNF alpha. In the coculture system, OPG completely blocked osteoclast induction by IL18 or IL1 beta, and greatly inhibited induction by TNF alpha. CONCLUSION: IL18, IL1 beta, or TNF alpha can indirectly stimulate osteoclast formation through up regulation of RANKL production from T cells in RA synovitis; IL18 is as effective as IL1 beta, but less potent than TNF alpha.     

Osteoclast differentiation factor induces synovial macrophage–osteoclast differentiation in rheumatoid arthritis

Abstract

The aim of this study was to clarify the role of osteoclast differentiation factor (ODF) and osteoprotegerin (OPG) in synovial macrophage–osteoclast differentiation. Synovial macrophages were cultured in the presence of macrophage-colony-stimulating factor (M-CSF) and/or ODF. OPG was added to cocultures of synovial macrophages and UMR106. The cultures on glass coverslips were stained with osteoclast-associated markers, tartrate-resistant acid phosphatase (TRAP), and vitronectin receptor (VNR), as well as macrophage-associated markers CD11b and CD14. Functional evidence of osteoclast formation was determined by a resorption pit assay. To investigate whether rheumatoid arthritis (RA) synovial cells expressed messenger RNA (mRNA) for ODF, OPG, and the receptor activator of NF-κB (RANK), we performed a polymerase chain reaction (PCR) analysis. The addition of M-CSF or ODF alone induced TRAP-positive multinucleated cell formation. Resorption pits were rarely detected with M-CSF alone. ODF was capable of inducing bone resorption and enhancing osteoclastogenesis, as well as bone resorption in the presence of M-CSF. In the coculture system, both osteoclast formation and bone resorption were inhibited by OPG in a dose-dependent manner. In all experiments, synovial cells, including macrophages and fibroblasts, expressed the mRNA for RANK, ODF, and OPG. Our findings suggest that ODF plays a role in regulating RA synovial macrophage–osteoclast differentiation, and that synovial cells might have the ability to produce ODF. OPG might be further developed as a new strategy for treating bone destruction in RA joints.     

Osteoclast differentiation factor induces synovial macrophage–osteoclast differentiation in rheumatoid arthritis

The aim of this study was to clarify the role of osteoclast differentiation factor (ODF) and osteoprotegerin (OPG) in synovial macrophage–osteoclast differentiation. Synovial macrophages were cultured in the presence of macrophage-colony-stimulating factor (M-CSF) and/or ODF. OPG was added to cocultures of synovial macrophages and UMR106. The cultures on glass coverslips were stained with osteoclast-associated markers, tartrate-resistant acid phosphatase (TRAP), and vitronectin receptor (VNR), as well as macrophage-associated markers CD11b and CD14. Functional evidence of osteoclast formation was determined by a resorption pit assay. To investigate whether rheumatoid arthritis (RA) synovial cells expressed messenger RNA (mRNA) for ODF, OPG, and the receptor activator of NF-κB (RANK), we performed a polymerase chain reaction (PCR) analysis. The addition of M-CSF or ODF alone induced TRAP-positive multinucleated cell formation. Resorption pits were rarely detected with M-CSF alone. ODF was capable of inducing bone resorption and enhancing osteoclastogenesis, as well as bone resorption in the presence of M-CSF. In the coculture system, both osteoclast formation and bone resorption were inhibited by OPG in a dose-dependent manner. In all experiments, synovial cells, including macrophages and fibroblasts, expressed the mRNA for RANK, ODF, and OPG. Our findings suggest that ODF plays a role in regulating RA synovial macrophage–osteoclast differentiation, and that synovial cells might have the ability to produce ODF. OPG might be further developed as a new strategy for treating bone destruction in RA joints. Received: January 30, 2001 / Accepted: May 18, 2001     

Osteoclast formation and activity in the pathogenesis of osteoporosis in rheumatoid arthritis

OBJECTIVE: Rheumatoid arthritis (RA) is often complicated by generalized osteopenia due to increased bone resorption by osteoclasts. We analysed a number of cellular and humoral factors that influence osteoclast formation from circulating precursors in RA patients. METHODS: Monocytes isolated from RA patients and normal controls were cultured with macrophage colony-stimulating factor (M-CSF) and nuclear factor-kappaB ligand (RANKL), or with RANKL-expressing UMR106 cells and 1,25 dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. Osteoclast differentiation was assessed by expression of tartrate-resistant acid phosphatase (TRAP) and vitronectin receptors (VNR) and lacunar resorption. RESULTS: Osteoclasts formed from RA patients exhibited increased resorptive activity but there was no difference in the relative proportion of circulating osteoclast precursors between RA patients and normal controls. Osteoclast precursors in RA patients were not more sensitive to the osteoclastogenic effects of 1,25(OH)(2)D(3), M-CSF or RANKL. Dexamethasone, but not interleukin (IL) 1beta, tumour necrosis factor alpha and IL-6, increased osteoclast formation and lacunar resorption. CONCLUSION: There is an increase in the extent of lacunar resorption carried out by osteoclasts formed from circulating precursors in RA patients. This is not due to an increase in the number of circulating precursors or increased sensitivity to the osteoclastogenic effects of 1,25(OH)(2)D(3), M-CSF, RANKL or inflammatory cytokines. Our findings suggest that increased osteoclast functional activity rather than osteoclast formation is more likely to play a role in the generalized bone loss that occurs in RA, and that corticosteroids stimulate osteoclast formation and resorption.