T-cells in the pathogenesis of rheumatoid arthritis villains or accomplices?

Structure of PD1 and its mechanism in the treatment of autoimmune diseases

PD-1 and CTLA-4 can play an important role in addressing the issue of autoimmune diseases. PD-1 is a transmembrane glycoprotein expressed on T, B, and Dentric cells. This molecule functions as a checkpoint in T cell proliferation. Ligation of PD-1 with its ligands inhibits the production of IL-2, IL-7, IL-10, and IL-12 as well as other cytokines by macrophages, natural killer (NK) cells, and T cells, which can suppress cell proliferation and inflammation. Today, scientists attempt to protect against autoimmune diseases by PD-1 inhibitory signals. In this review, we discuss the structure, expression, and signaling pathway of PD-1. In addition, we discuss the importance of PD-1 in regulating several autoimmune diseases, reflecting how manipulating this molecule can be an effective method in the immunotherapy of some autoimmune diseases.

Changes in the pattern of cytokine production from peripheral blood mononuclear cells in patients with rheumatoid arthritis treated with infliximab and their relation to plasma arginase activity

AIM

The aim of this study was to quantify the production of T-cell cytokines from the peripheral blood mononuclear cells (PBMCs) of RA patients before and after treatment with anti-tumor necrosis factor (TNF)-α infliximab (IFX).

METHOD

We stimulated the PBMCs of RA patients (n = 24) in vitro and quantified the cytokines in the culture supernatant using enzyme-linked immunosorbent assay.

RESULTS

Unexpectedly, the cytokines tested, interferon (IFN)-γ, interleukin (IL)-4 and IL-17, were all found to have increased, rather than decreased, after the treatment. When the patients were divided into two groups according to the plasma activity of arginase, which is implicated in the immune-suppressive function of myeloid-derived suppressor cells, the substantial increase in the cytokine production ex vivo was only detected in the group in which the arginase activity was decreased after the treatment with IFX. In fact, although the ex vivo production of IL-21 increased along with the other cytokines, the plasma concentration of IL-21 decreased significantly after IFX treatment.

CONCLUSION

It is important to exercise caution in interpreting ex vivo cytokine production data, in that they can be negatively influenced by the immune-suppressive mechanisms that prevent excessive inflammation. Thus, to analyze the T-cell response accurately, T-cell markers that are detectable in the serum or plasma need to be discovered. The concentrations of IFN-γ, IL-4 and IL-17 were all below detection limits, but that of IL-21 was detectable in the plasma and inversely correlated with the production of IL-21 ex vivo. This may indicate the involvement of Th17 response in the pathogenesis of RA.

Mechanisms of tissue damage in arthritis

The destruction of articular structures in the course of inflammatory arthritides such as rheumatoid arthritis (RA) or seronegative spondyloarthropathies is the most serious direct consequence of these diseases. Indeed, joint damage constitutes the "organ damage" of RA and-just like in all other diseases with organ involvement-such damage will usually be irreversible, cause permanent loss of function and subsequent disability. Research has identified a number of mechanisms and mediators of damage to articular structures such as bone and cartilage, ranging from proinflammatory cytokines, signal transduction pathways and cells types, which will be discussed in this review.

(Auto)immunity to cartilage matrix proteins - a time bomb?

Geng and colleagues consolidate and detail the role of cartilage oligomeric matrix protein (COMP) as a (potential) autoantigen in experimental and human arthritis, a finding also supported by the detection of COMP fragments and anti-COMP antibodies in rheumatoid arthritis serum and/or synovial fluid and by synovial B-cell responses against COMP. The reactivity to COMP is yet another example of how, in addition to collagen II and the large aggregating proteoglycan, cartilage-specific proteins can induce arthritis and contribute to autoimmunity. Progression of cartilage damage and degradation in disease is believed to promote the autoimmune reaction to cartilage components. However, Geng and colleagues show that anti-COMP mAbs bind in vivo to undamaged cartilage, as previously also observed for anti-collagen II antibodies. Whether this autoimmunity also involves modifications of cartilage matrix proteins, such as citrullination, remains to be further investigated. Latent, subpathogenic (auto)immune reactions directed against cartilage matrix proteins may thus eventually contribute to the outbreak of human arthritis.

Aberrant integrin activation induces p38 MAPK phosphorylation resulting in suppressed Fas-mediated apoptosis in T cells: implications for rheumatoid arthritis

Delayed Fas-mediated apoptosis in T cells is associated with inflammatory diseases including rheumatoid arthritis (RA). CD3(+) T cells in RA synovia expressed high amounts of phospho-p38 MAPK. Exposure to RA synovial fluid or soluble collagen, a degradation product of extracellular matrix abundant in RA synovium, induced the phosphorylation of p38 MAPK in Jurkat T cells accompanied by resistance against Fas-mediated apoptosis. Blocking beta1 integrin by antibody diminished this effect. In addition, ectopic expression of auto-activated beta1 integrin variant in T cells profoundly induced the phosphorylation of p38 MAPK. Suppression of p38 MAPK sensitized T cells to Fas-mediated apoptosis and increased caspase-8 and caspase-3 cleavage. A physical interaction of p38 MAPK and caspase-8 was demonstrated by using confocal microscopic imaging and co-immunoprecipitation assay. RA synovial fluid markedly increased the formation of phospho-p38 MAPK/caspase-8 complex in Jurkat T cells. In conclusion, abnormal activation of p38 MAPK to prevent Fas-mediated apoptosis may represent a common survival mechanism of RA synovial T cells contributing to the persistent inflammation of affected synovium.

Interactions of T helper cells with fibroblast-like synoviocytes: up-regulation of matrix metalloproteinases by macrophage migration inhibitory factor from both Th1 and Th2 cells

OBJECTIVE

Interactions of immune cells, such as activated T helper cells, with fibroblast-like synoviocytes (FLS) play a crucial role in the joint destruction during human rheumatoid arthritis (RA). This study was undertaken to investigate the expression of the proinflammatory cytokine macrophage migration inhibitory factor (MIF) by T helper cells, and to assess the role of MIF in overexpression of matrix metalloproteinases (MMPs) in cocultures of FLS from arthritic mice with either Th1 or Th2 cells.

METHODS

MIF expression by in vitro-polarized murine Th1 and Th2 cells was determined using 2 different generation protocols. FLS were isolated from the inflamed joints of mice with antigen-induced arthritis. MMP expression was analyzed in cocultures of the FLS with T helper cell subsets. Effects of MIF were blocked by a neutralizing anti-MIF antibody. In addition, analyses were performed on cocultures of either Th1 or Th2 cells with FLS from MIF-deficient mice.

RESULTS

Both Th1 and Th2 cells expressed high quantities of MIF. MMPs were overexpressed by FLS after coculture with both Th1 and Th2 cells. Activated T helper cells were more effective than resting cells. Neutralization of MIF by an anti-MIF antibody led to a marked reduction in MMP expression in Th1- and Th2-stimulated FLS. T helper cells generated from MIF-deficient mice exhibited a T helper cell-specific cytokine profile comparable with that in wild-type cells, except in the expression of MIF, but showed an impaired ability to stimulate MMP expression in FLS.

CONCLUSION

MIF is an important Th1 and Th2 cell-derived proinflammatory cytokine that stimulates MMP expression in FLS from arthritic mice, and therefore inhibition of MIF might be a promising target for novel therapeutic strategies in human RA.

The role of collagen antibodies in mediating arthritis

This review examines evidence that rheumatoid arthritis (RA) depends on autoimmunity to articular collagen, and mechanisms whereby autoantibodies to type II collagen contribute to disease development. Three major autoantigenic reactants have been identified in RA; the corresponding autoantibodies are rheumatoid factor (RF), antibodies to citrullinated peptide antigens (ACPA), citrullinated peptides (anti-CCP), and anti-type II collagen (anti-CII). Both RF and ACPA are well-validated and predictive markers of severe erosive RA, but cannot be linked to pathogenesis. By contrast, in various animal species immunized with CII there occurs an erosive inflammatory arthritis resembling that seen in human RA, together with antibodies to CII with an epitope specificity similar to that in RA. We discuss the well-known role of immune complexes in the induction of inflammation within the joint, and present recent data showing, additionally, that antibodies to CII cause direct damage to cartilage in vitro. The close resemblances between human RA and collagen-induced arthritis in animals suggest that autoimmunity, and particularly autoantibodies to CII, are important for both the initiation and perpetuation of RA in a dual manner: as contributors to the inflammation associated with immune complex deposition, and as agents with direct degradative effects on cartilage integrity and its repair.

Osteoimmunological insight into bone damage in rheumatoid arthritis

Research into the bone destruction associated with rheumatoid arthritis has highlighted the importance of the interplay of the immune and skeletal systems. Arthritic bone destruction is attributable to the defective control of osteoclastogenesis by T cells. We revealed that excessive expression of receptor activator of NF-kappaB ligand (RANKL) and a paucity of interferon-gamma underlie the enhanced osteoclastogenesis in arthritis. The interdisciplinary research field called osteoimmunology has attracted further attention after identification of a number of unexpected bone phenotypes in mice lacking immunomodulatory molecules. Accumulating evidence suggests that the immune and skeletal systems share not only cytokines but also various signaling molecules, transcription factors, and membrane receptors. Thus, bone turns out to be a dynamic tissue that is constantly renewed, where the immune system participates to a hitherto unexpected extent. This emerging field will be of great importance for a better understanding and treatment of rheumatic diseases.

Osteoimmunology

Osteoimmunology is an interdisciplinary research field combining the exciting fields of osteology and immunology. An observation that contributed enormously to the emergence of osteoimmunology was the accelerated bone loss caused by inflammatory diseases such as rheumatoid arthritis. Receptor activator of nuclear factor kappaB ligand (RANKL), which is the main regulator of osteoclastogenesis, was found to be the primary culprit responsible for the enhanced activation of osteoclasts: activated T cells directly and indirectly increased the expression of RANKL, and thereby promoted osteoclastic activity. Excessive bone loss is not only present in inflammatory diseases but also in autoimmune diseases and cancer. Furthermore, there is accumulating evidence that the very prevalent skeletal disorder osteoporosis is associated with alterations in the immune system. Meanwhile, numerous connections have been discovered in osteoimmunology beyond merely the actions of RANKL. These include the importance of osteoblasts in the maintenance of the hematopoietic stem cell niche and in lymphocyte development as well as the functions of immune cells participating in osteoblast and osteoclast development. Furthermore, research is being done investigating cytokines, chemokines, transcription factors and co-stimulatory molecules which are shared by both systems. Research in osteoimmunology promises the discovery of new strategies and the development of innovative therapeutics to cure or alleviate bone loss in inflammatory and autoimmune diseases as well as in osteoporosis. This review gives an introduction to bone remodeling and the cells governing that process and summarizes the most recent discoveries in the interdisciplinary field of osteoimmunology. Furthermore, an alternative large animal model will be discussed and the pathophysiological alterations of the immune system in osteoporosis will be highlighted.

Osteoclasts, rheumatoid arthritis, and osteoimmunology

PURPOSE OF REVIEW

Osteoclasts are terminally differentiated cells of the monocyte/macrophage lineage that resorb bone matrix. Bone destruction in rheumatoid arthritis is mainly attributable to the abnormal activation of osteoclasts, and studies on activation of osteoclasts by the immune system have led to the new research field called osteoimmunology. This interdisciplinary field is very important to biologic research and to the treatment of diseases associated with the bone and immune systems.

RECENT FINDINGS

The T-cell-mediated regulation of osteoclast differentiation is dependent on cytokines and membrane-bound factors expressed by T cells. The cross-talk between receptor activator of nuclear factor-kappaB ligand and interferon-gamma has been shown to be crucial for the regulation of osteoclast formation in arthritic joints. Recent studies indicate that an increasing number of immunomodulatory factors are associated with the regulation of bone metabolism: nuclear factor of activated T cells c1 has been shown to be the key transcription factor for osteoclastogenesis, the activation of which requires calcium signaling induced by the immunoglobulin-like receptors.

SUMMARY

New findings in osteoimmunology will be instrumental in the development of strategies for research into the treatment of various diseases afflicting the skeletal and immune systems.

Th17 functions as an osteoclastogenic helper T cell subset that links T cell activation and bone destruction

In autoimmune arthritis, traditionally classified as a T helper (Th) type 1 disease, the activation of T cells results in bone destruction mediated by osteoclasts, but how T cells enhance osteoclastogenesis despite the anti-osteoclastogenic effect of interferon (IFN)-γ remains to be elucidated. Here, we examine the effect of various Th cell subsets on osteoclastogenesis and identify Th17, a specialized inflammatory subset, as an osteoclastogenic Th cell subset that links T cell activation and bone resorption. The interleukin (IL)-23–IL-17 axis, rather than the IL-12–IFN-γ axis, is critical not only for the onset phase, but also for the bone destruction phase of autoimmune arthritis. Thus, Th17 is a powerful therapeutic target for the bone destruction associated with T cell activation.

Solution chemistry of 1,15-bis(N,N-dimethyl)-5,11-dioxo-8-(N-benzyl)-1,4,8,12,15-pentaazapentadecane with metal ions of biological interest-Insights toward active metal ion containing therapeutics and diagnostic agents

The equilibrium constants of Cu(II), Zn(II), Ca(II) and Gd(III) with 1,15-bis(N,N-dimethyl)-5,11-dioxo-8-(N-benzyl)-1,4,8,12,15-pentaazapentadecane (La) have been studied at 25 degrees C and an ionic strength of 0.15 mol dm-3. Copper forms more stable complexes with La than the other metal ions investigated. This is probably due to the ease with which Cu(II) deprotonates the nitrogen donor atoms of the amide groups. UV/Vis spectrophotometric data indicate tetradentate binding of the ligand towards copper in [CuLaH-1] and pentadentate binding in [CuLaH-2]. Octanol-water partition coefficients of Cu(II)-La complexes indicate that although these species are largely hydrophilic, approximately 5.62% of the [CuLaH-1] complex goes into the organic phase. This percentage may promote dermal absorption of copper with a calculated penetration rate of 3.75x10(-4) mm h-1. The [CuLaH-1] species which predominates at pH 7.4 is a poor mimic of native copper-zinc superoxide dismutase. Blood-plasma simulation studies predict that La is unable to increase the low molecular mass copper fraction in vivo. This has been confirmed by biodistribution patterns, which are similar to those of 64CuCl2.

T-bet negatively regulates autoimmune myocarditis by suppressing local production of interleukin 17

Experimental autoimmune myocarditis (EAM) appears after infectious heart disease, the most common cause of dilated cardiomyopathy in humans. Here we report that mice lacking T-bet, a T-box transcription factor required for T helper (Th)1 cell differentiation and interferon (IFN)-γ production, develop severe autoimmune heart disease compared to T-bet^−/− control mice. Experiments in T-bet^−/−IL-4^−/− and T-bet^−/− IL-4Rα^−/− mice, as well as transfer of heart-specific Th1 and Th2 cell lines, showed that autoimmune heart disease develops independently of Th1 or Th2 polarization. Analysis of T-bet^−/−IL-12Rβ1^−/− and T-bet^−/− IL-12p35^−/− mice then identified interleukin (IL)-23 as critical for EAM pathogenesis. In addition, T-bet^−/− mice showed a marked increase in production of the IL-23–dependent cytokine IL-17 by heart-infiltrating lymphocytes, and in vivo IL-17 depletion markedly reduced EAM severity in T-bet^−/− mice. Heart-infiltrating T-bet^−/− CD8⁺ but not CD8⁻ T cells secrete IFN-γ, which inhibits IL-17 production and protects against severe EAM. In contrast, T-bet^−/− CD8⁺ lymphocytes completely lost their capacity to release IFN-γ within the heart. Collectively, these data show that severe IL-17–mediated EAM can develop in the absence of T-bet, and that T-bet can regulate autoimmunity via the control of nonspecific CD8⁺ T cell bystander functions in the inflamed target organ.

Prevention of arthritic inflammation using an oriental herbal combination BDX-1 isolated from Achyranthes bidentata and Atractylodes japonica

An oriental herbal combination (BDX-1) was isolated from Achyranthes bidentata and Atractylodes japonica. We previously tested the clinical effectiveness of BDX-1 in rheumatoid arthritis (RA) patients and found that it has a beneficial therapeutic effect. Here, we provide experimental evidence for the effectiveness of BDX-1 on RA in murine models. The oral administration of BDX-1 was found to markedly inhibit collagen-induced arthritis, adjuvant-induced arthritis, and zymosan-induced inflammation. It also inhibited carrageenan-induced acute edema and acetic acid-induced writhing response. In addition, the biological activity of BDX-1 was found to be strongly increased by fermentation. Our results suggest that BDX-1 could be useful for the treatment of rheumatoid arthritis.

Interplay between interferon and other cytokine systems in bone metabolism

Interferons (IFNs) play crucial roles in the regulation of a wide variety of innate and adaptive immune responses. Type I interferons (IFN-alpha/beta) are central to the host defense against pathogens such as viruses, whereas type II interferon (IFN-gamma) mainly contributes to the T-cell-mediated regulation of the immune responses. Studies of bone destruction associated with rheumatoid arthritis have highlighted the importance of the interaction between the immune and skeletal systems. Recently, a new research area, termed osteoimmunology, has been spawned by a series of studies focusing on the signaling networks between IFN and other cytokines in bone metabolisms. It has been revealed that IFN-gamma interferes with the osteoclast differentiation induced by receptor activator of nuclear factor-kappaB ligand (RANKL), and this mechanism is critical for the suppression of pathological bone resorption associated with inflammation. In addition, RANKL induces the IFN-beta gene in osteoclast precursor cells, and this induction constitutes a critical aspect of the negative feedback regulation mechanisms of RANKL signaling to suppress excessive osteoclastogenesis. Furthermore, a novel function of signal transducer and activator of transcription 1 (Stat1), the essential transcription factor for both type I and type II IFN responses, was revealed in the regulation of osteoblast differentiation. Collectively, these studies unveil novel aspects of the IFN system and indicate the operation of the intricate signaling network among IFN and other cytokine systems in bone remodeling, which might offer a molecular basis for the treatment of bone diseases.

Site-specific intraoperative efficacy of arthroscopic knee joint synovectomy in rheumatoid arthritis

PURPOSE

To assess the intraoperative reduction of inflammatory infiltrates achieved by arthroscopic knee joint synovectomy in patients with rheumatoid arthritis (RA) with special regard to the removal site, using preoperative and postoperative synovial tissue (ST) samples.

TYPE OF STUDY

A histologic and immunohistochemical study.

METHODS

Eleven patients with treatment-refractory RA knee synovitis underwent arthroscopic synovectomy. In each patient, ST specimens were obtained immediately before and after synovectomy from 9 defined sites covering the whole joint. The samples were graded using an acute synovitis score (ASS; presence of polymorphonuclear neutrophilic leukocytes [PMN] and fibrin) and a chronic synovitis score (CSS; e.g., lining cell hyperplasia, presence of diffuse and lymphoid aggregates). Immunohistologic analyses were performed using 7 monoclonal antibodies directed against PMN, macrophages, and T-cell subsets (total of 1,584 preparations). Knee function was assessed after an average follow-up of 28 months by Lysholm score (modified by Klein and Jensen), Insall functional and knee scores, and Lequesne score.

RESULTS

Arthroscopic synovectomy led to an overall significant (P between .005 and .05) reduction of the acute inflammatory infiltrates (ASS) by 82.1%, but to a significant reduction of chronic inflammatory infiltrates (CSS) by only 62.5%. Accordingly, the density of PMN was reduced by 81.8%, whereas that of macrophages and different T-cell subsets was only decreased by < or = 61.6%. With respect to the anatomic regions, a significantly (P < or = .05) less marked reduction of inflammatory infiltrates was observed in the upper lateral and central recess, at the medial and lateral capsule, as well as at the femoral insertion of the anterior cruciate ligament. All knee joint scores showed a significant (P < or = .01) improvement over preoperative values at follow-up.

CONCLUSIONS

Arthroscopic synovectomy effectively reduces acute and chronic inflammatory infiltrates in patients with RA who have refractory synovitis of the knee joint (immediately after synovectomy) and improves knee function (28-month follow-up). However, the reduction of inflammatory infiltrates appears to depend on the anatomic region of the joint.

LEVEL OF EVIDENCE

Level III.

Inflammatory bone destruction and osteoimmunology

OBJECTIVES

The metabolism of hard tissue is influenced by the immune system. Research into the bone destruction associated with inflammatory diseases such as periodontal disease and rheumatoid arthritis has highlighted the importance of the interplay of the immune and skeletal systems. This interdisciplinary research field, called 'osteoimmunology', has become increasingly important for each system by itself as well as the biology linking them. The history and recent progress of this field are reviewed.

MATERIAL AND METHODS

'Osteoimmunology' was coined to describe the pioneering work on the T-cell regulation of osteoclastogenesis by the receptor activator of nuclear factor-kappaB ligand (RANKL) and interferon (IFN)-gamma. Accumulating evidence suggests that the immune and skeletal systems share not only cytokines but also various signaling molecules, transcription factors and membrane receptors. The contribution of T cells to the pathogenesis of inflammatory bone destruction is discussed, and our recent findings are summarized to illustrate how the osteoimmunological network functions.

RESULTS

RANKL is an osteoclastogenic cytokine that links bone and the immune system. Immunomodulatory cytokines such as IFNs also participate in the regulation of RANKL signaling and inflammatory bone loss. The transcription factor nuclear factor of activated T cells c1 (NFATc1) has been identified as a master switch regulator of osteoclastogenesis. In addition, immunoglobulin-like receptors are critically involved in bone homeostasis.

CONCLUSION

Bone turns out to be a dynamic tissue that is constantly renewed, where the immune system participates to a hitherto unexpected extent. This emerging field will be of great importance to a better understanding and treatment of diseases of the skeletal and immune systems, as well as to the fundamental biology underpinning both.

Expression of cytokine mRNA and protein in joints and lymphoid organs during the course of rat antigen-induced arthritis

Cytokine expression was assessed during antigen-induced arthritis (AIA) in synovial membrane (SM), inguinal lymph node (LN), and spleen using competitive RT-PCR and sandwich ELISA. In the SM, early elevations of IL-1β and IL-6 mRNA (by 6 hours; 450- and 200-fold, respectively) correlated with the joint swelling; a 6-fold increase in tumor necrosis factor α (TNFα) was not significant. Not only IL-2 and IFN-γ (which increased 10,000-fold and 200-fold, respectively), but also IL-5 and IL-10, increased acutely (6 hours – day 1; 3-fold and 35-fold, respectively) in the SM. In general, the protein levels in the SM for IL-1β, IL-6, TNFα, IFN-γ, IL-4, and IL-10 (increase from 4-fold to 15-fold) matched the course of mRNA expression. In the inguinal LN, there were early mRNA elevations of IL-6 (a 2.5-fold increase by 6 hours, which correlated positively with the joint swelling) and IL-2 (4-fold by 6 hours), as well as later rises of IL-4 and IL-5 (2.5- and 4-fold, respectively, by day 3). No significant elevations of the corresponding proteins in this tissue were observed, except for IL-1β (by day 6) and IL-10 (by day 1). In the spleen, there were significant mRNA elevations at 6 hours of IL-1β (1.5-fold), IL-6 (4-fold; positively correlated with the joint swelling), IFN-γ (3-fold), and IL-2 (7- to 10-fold). IL-5 and IL-10 (2- and 3-fold, respectively) peaked from 6 hours to day 3 in the spleen. Increases of the corresponding proteins were significant in comparison with day 0 only in the case of IL-2 (day 6). By day 6 (transition to the chronic phase), the mRNA for cytokines declined to or below prearthritis levels in all the tissues studied except for IL-1β in the SM and IL-6 in the spleen. AIA is thus characterized by four phenomena: early synovial activation of macrophages, T helper (Th)1-like, and Th2-like cells; late, well-segregated Th2-like responses in the inguinal LN; late, overlapping Th1-like/Th2-like peaks in the spleen; and chronic elevation of synovial IL-1β mRNA and spleen IL-6 mRNA.

The role of regulatory T cells in antigen-induced arthritis: aggravation of arthritis after depletion and amelioration after transfer of CD4+CD25+ T cells

It is now generally accepted that CD4⁺CD25⁺ T_reg cells play a major role in the prevention of autoimmunity and pathological immune responses. Their involvement in the pathogenesis of chronic arthritis is controversial, however, and so we examined their role in experimental antigen-induced arthritis in mice. Depletion of CD25-expressing cells in immunized animals before arthritis induction led to increased cellular and humoral immune responses to the inducing antigen (methylated bovine serum albumin; mBSA) and autoantigens, and to an exacerbation of arthritis, as indicated by clinical (knee joint swelling) and histological scores. Transfer of CD4⁺CD25⁺ cells into immunized mice at the time of induction of antigen-induced arthritis decreased the severity of disease but was not able to cure established arthritis. No significant changes in mBSA-specific immune responses were detected. In vivo migration studies showed a preferential accumulation of CD4⁺CD25⁺ cells in the inflamed joint as compared with CD4⁺CD25^- cells. These data imply a significant role for CD4⁺CD25⁺ T_reg cells in the control of chronic arthritis. However, transferred T_reg cells appear to be unable to counteract established acute or chronic inflammation. This is of considerable importance for the timing of T_reg cell transfer in potential therapeutic applications.

A proinflammatory role for Fas in joints of mice with collagen-induced arthritis

Collagen-induced arthritis (CIA) is a chronic inflammatory disease bearing all the hallmarks of rheumatoid arthritis, e.g. polyarthritis, synovitis, and subsequent cartilage/bone erosions. One feature of the disease contributing to joint damage is synovial hyperplasia. The factors responsible for the hyperplasia are unknown; however, an imbalance between rates of cell proliferation and cell death (apoptosis) has been suggested. To evaluate the role of a major pathway of cell death – Fas (CD95)/FasL – in the pathogenesis of CIA, DBA/1J mice with a mutation of the Fas gene (lpr) were generated. The susceptibility of the mutant DBA-lpr/lpr mice to arthritis induced by collagen type II was evaluated. Contrary to expectations, the DBA-lpr/lpr mice developed significantly milder disease than the control littermates. The incidence of disease was also significantly lower in the lpr/lpr mice than in the controls (40% versus 81%; P < 0.05). However DBA-lpr/lpr mice mounted a robust immune response to collagen, and the expression of local proinflammatory cytokines such as, e.g., tumor necrosis factor α (TNF-α) and IL-6 were increased at the onset of disease. Since the contribution of synovial fibroblasts to inflammation and joint destruction is crucial, the potential activating effect of Fas on mouse fibroblast cell line NIH3T3 was investigated. On treatment with anti-Fas in vitro, the cell death of NIH3T3 fibroblasts was reduced and the expression of proinflammatory cytokines TNF-α and IL-6 was increased. These findings suggest that impairment of immune tolerance by increased T-cell reactivity does not lead to enhanced susceptibility to CIA and point to a role of Fas in joint destruction.

Anti-CD4 monoclonal antibody treatment in acute and early chronic antigen-induced arthritis: influence on T helper cell activation

To examine the effects of anti-CD4 mAb treatment in acute and chronic antigen-induced arthritis (AIA), C57BL/6 mice were treated intraperitoneally either with the depleting anti-CD4 mAb GK1.5 or with rat-IgG (control) on Days -1, 0, 1, 3, 5, and 7. Arthritis was monitored by assessment of joint swelling and histological evaluation in the acute (Day 3) and the chronic phase (Day 21) of AIA. To determine the effects on cellular immune responses, in vivo T-cell reactivity (delayed type hypersensitivity; DTH) was measured, as well as protein levels of TH1- (IL-2, IFN-gamma) and TH2-cytokines (IL-4, IL-10) in joint extracts and supernatants of ex vivo stimulated spleen and lymph node cells. The humoral immune response was analysed by measuring serum antibodies against methylated bovine serum albumine (mBSA) and extracellular matrix proteins. Treatment with GK1.5 reduced swelling, inflammation, and destruction of the arthritic joint. Unexpectedly, the effects were even more pronounced in the acute than in the chronic phase. The anti-inflammatory effect was accompanied by a diminished DTH against the arthritogen mBSA and a decrease of TH1-cytokine production in spleen and pooled body lymph nodes, whereas the TH2-cytokine production in these organs was unchanged and the humoral immune response was only moderately reduced. There was a failure of depleting CD4+ T-cells in the joint, reflected also by unchanged local cytokine levels. Therefore, systemic rather than local effects on the TH1/TH2 balance appear to underlie the therapeutic efficacy of anti-CD4 treatment in AIA.

Suppression of osteoclastogenesis in rheumatoid arthritis by induction of apoptosis in activated CD4+ T cells

OBJECTIVE

To examine the suppressive effect of anti-human Fas monoclonal antibody (mAb) on osteoclastogenesis in rheumatoid arthritis (RA) both in vitro and in vivo.

METHODS

For in vitro analysis, activated CD4+ T cells derived from peripheral blood mononuclear cells were left untreated or were treated with humanized anti-human Fas mAb (R-125224) and cocultured with human monocytes. On day 12, the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells was counted. For in vivo analysis, tissue derived from human RA pannus was implanted with a slice of dentin subcutaneously in the backs of SCID mice (SCID-HuRAg-pit model). R-125224 was administered intravenously once a week for 3 weeks. The implanted tissue and dentin slice were removed, and the pits formed on the dentin slice were analyzed.

RESULTS

In vitro, coculture of activated CD4+ T cells and peripheral monocytes induced osteoclastogenesis. The number of TRAP-positive multinucleated cells was reduced when activated CD4+ T cells were treated with R-125224. We established a new animal model for monitoring osteoclastogenesis, SCID-HuRAg-pit. We found that with R-125224 treatment, the number of pits formed on the implanted dentin slices was significantly reduced and the number of lymphocytes in the implanted RA synovial tissue was dramatically reduced in this model.

CONCLUSION

This is the first study to demonstrate the suppressive effect of anti-human Fas mAb on osteoclastogenesis in RA synovial tissues through the induction of T cell apoptosis. Induction of apoptosis of infiltrated lymphocytes could be a useful therapeutic strategy for RA, in terms of suppressing both inflammation and bone destruction.

In vitro and in vivo stability investigations of Cu(ii), Zn(ii), Ca(ii) and Gd(iii) complexes with N,N′-bis(2-hydroxyiminopropionyl) propane-1,3-diamine

Formation constants of copper(II), zinc(II), calcium(II) and gadolinium(III) with N,N'-bis(2-hydroxyiminopropionyl) propane-1,3-diamine (L2) have been studied at 25 degrees C and an ionic strength of 0.15 mol dm(-3). The reasonably high formation constants of the copper with this ligand are due to the ease with which the metal ion deprotonates the amide moieties. The square-planar coordination of L2 towards copper as predicted from UV-visible data may also account for the high selectivity of L2 towards the metal ion. Octanol/water partition coefficients of Cu(II)-L2 complexes indicate that although these complexes are largely hydrophilic, approximately 1.86% of the [CuL2H(-1)] species goes into the octanol layer and hence may promote dermal absorption of copper with a calculated penetration rate of 1.24 x 10(-5) cm h(-1). The [CuL2H(-1)] complex which predominates at pH 7.4 is a poor mimic of native copper-zinc superoxide dismutase. Blood-plasma simulation studies predict that, despite the high concentration of zinc and calcium in vivo, L2 is able to increase the low-molecular-mass fraction of copper. Biodistribution experiments using 64Cu-labelled [CuL2H(-1)] indicate an initial high uptake of this species in the liver, but it is predominantly excreted through the renal system.

Inflammatory T cells rapidly induce differentiation of human bone marrow stromal cells into mature osteoblasts

Activated T cells secrete multiple osteoclastogenic cytokines which play a major role in the bone destruction associated with rheumatoid arthritis. While the role of T cells in osteoclastogenesis has received much attention recently, the effect of T cells on osteoblast formation and activity is poorly defined. In this study, we investigated the hypothesis that in chronic inflammation activated T cells contribute to enhanced bone turnover by promoting osteoblastic differentiation. We show that T cells produce soluble factors that induce alkaline phosphatase activity in bone marrow stromal cells and elevated expression of mRNA for Runx2 and osteocalcin. This data indicate that T cell derived factors have the capacity to stimulate the differentiation of bone marrow stromal cells into the osteoblast phenotype. RANKL mRNA was undetectable under any conditions in highly purified bone marrow stromal cells. In contrast, RANKL was constitutively expressed in primary osteoblasts and only moderately up-regulated by activated T cell conditioned medium. Interestingly, both bone marrow stromal cells and osteoblasts expressed mRNA for RANK, which was strongly up-regulated in both cell types by activated T cell conditioned medium. Although, mRNA for the RANKL decoy receptor, osteoprotegerin, was also up-regulated by activated T cell conditioned medium, it's inhibitory effects may be mitigated by a simultaneous rise in the osteoprotegerin competitor TNF-related apoptosis-inducing ligand. Based on our data we propose that during chronic inflammation, T cells regulate bone loss by a dual mechanism involving both direct stimulation of osteoclastogenesis, by production of osteoclastogenic cytokines, and indirectly by induction of osteoblast differentiation and up-regulation of bone turnover via coupling.

Differential clinical efficacy of anti-CD4 monoclonal antibodies in rat adjuvant arthritis is paralleled by differential influence on NF-kappaB binding activity and TNF-alpha secretion of T cells

The aim of this study was to analyze the differential effects of three anti-CD4 monoclonal antibodies (mAbs) (with distinct epitope specifities) in the treatment of rat adjuvant arthritis (AA) and on T-cell function and signal transduction. Rat AA was preventively treated by intraperitoneal injection of the anti-CD4 mAbs W3/25, OX35, and RIB5/2 (on days -1, 0, 3, and 6, i.e. 1 day before AA induction, on the day of induction [day 0], and thereafter). The effects on T-cell reactivity in vivo (delayed-type hypersensitivity), ex vivo (ConA-induced proliferation), and in vitro (mixed lymphocyte culture) were assessed. The in vitro effects of anti-CD4 preincubation on T-cell receptor (TCR)/CD3-induced cytokine production and signal transduction were also analyzed. While preventive treatment with OX35 and W3/25 significantly ameliorated AA from the onset, treatment with RIB5/2 even accelerated the onset of AA by approximately 2 days (day 10), and ameliorated the arthritis only in the late phase (day 27). Differential clinical effects at the onset of AA were paralleled by a differential influence of the mAbs on T-cell functions, i.e. in comparison with OX35 and W3/25, the 'accelerating' mAb RIB5/2 failed to increase the delayed-type hypersentivity (DTH) to Mycobacterium tuberculosis, increased the in vitro tumor necrosis factor (TNF)-alpha secretion, and more strongly induced NF-kappaB binding activity after anti-CD4 preincubation and subsequent TCR/CD3-stimulation. Depending on their epitope specificity, different anti-CD4 mAbs differentially influence individual proinflammatory functions of T cells. This fine regulation may explain the differential efficacy in the treatment of AA and may contribute to the understanding of such treatments in other immunopathologies.

Signaling crosstalk between RANKL and interferons in osteoclast differentiation

Regulation of osteoclast differentiation is an aspect central to the understanding of the pathogenesis and the treatment of bone diseases such as autoimmune arthritis and osteoporosis. In fact, excessive signaling by RANKL (receptor activator of nuclear factor kappaB ligand), a member of the tumor necrosis factor (TNF) family essential for osteoclastogenesis, may contribute to such pathological conditions. Here we summarize our current work on the negative regulation of osteoclastogenesis by unique signaling crosstalk between RANKL and interferons (IFNs). First, activated T cells maintain bone homeostasis by counterbalancing the action of RANKL through production of IFN-gamma. This cytokine induces rapid degradation of the RANK (receptor activator of nuclear factor kappaB) adapter protein TRAF6 (TNF-receptor-associated factor 6), resulting in strong inhibition of the RANKL-induced activation of NF-kappaB and JNK (c-Jun N-terminal kinase). Second, RANKL induces the IFN-beta gene but not IFN-alpha genes, in osteoclast precursor cells, and that IFN-beta strongly inhibits the osteoclast differentiation by interfering with the RANKL-induced expression of c-Fos. The series of in vivo experiments revealed that these two distinct IFN-mediated regulatory mechanisms are both important to maintain homeostasis of bone resorption. Collectively, these studies revealed novel aspects of the two types of IFN, beyond their original roles in the immune response, and may offer a molecular basis for the treatment of bone diseases.

The autoimmune pathogenesis of rheumatoid arthritis: role of autoreactive T cells and new immunotherapies

OBJECTIVES

To review the role of T lymphocytes in the pathogenesis of rheumatoid arthritis (RA) and discuss the relevance of the components of the trimolecular complex (synovial T cells, autoantigens, and antigen presenting cells) in the pathogenic autoimmune response in RA.

METHODS

Currently available experimental data are combined into a hypothetical pathway that may explain some of the events in the RA process. The literature regarding the potential therapeutic strategies that interfere with specific components of the trimolecular complex and other mediators are discussed briefly.

RESULTS

T cells are activated in the peripheral blood, cross the endothelial cell wall, and migrate into the joints. Once in the synovial joints, T cells are reactivated by cross-reactive antigens and clonally expand. Clonally expanded T cells accumulate in the diseased joint and secrete proinflammatory cytokines that attract and activate other cells, such as monocytes and macrophages. Treatment with anti-CD4 monoclonal antibodies or anticytokine agents that prevents antigen presentation and/or T-cell activation were effective in RA. Other therapies, such as T-cell vaccination and T-cell receptor peptide vaccination targeting autoreactive T cells, showed clinical improvement, suggesting a pathogenic role of these lymphocytes in disease progression.

CONCLUSION

T cells appear to be actively involved in the pathogenesis of RA, but several parts of the pathway are hypothetical and further research is needed.

TCR peptide therapy in human autoimmune diseases

Inflammatory Th1 cells reacting to tissue/myelin derived antigens likely contribute to the pathogenesis of diseases such as multiple sclerosis (MS), rheumatoid arthritis (RA), and psoriasis. One regulatory mechanism that may be useful for treating autoimmune diseases involves an innate second set of Th2 cells specific for portions of the T cell receptor of clonally expanded pathogenic Th1 cells. These Th2 cells are programmed to respond to internally modified V region peptides from the T cell receptor (TCR) that are expressed on the Th1 cell surface in association with major histocompatibility molecules. Once the regulatory Th2 cells are specifically activated, they may inhibit inflammatory Th1 cells through a non-specific bystander mechanism. A variety of strategies have been used by us to identify candidate disease-associated TCR V genes present on pathogenic Th1 cells, including BV5S2, BV6S5, and BV13SI in MS, BV3, BV14, and BV17 in RA, and BV3 and BV13S1 in psoriasis. TCR peptides corresponding to the mid region of these BV genes were found to be consistently immunogenic in vivo when administered either i.d. in saline or i.m. in incomplete Freund's adjuvant (IFA). In MS patients, repeated injection of low doses of peptides (100-300 microg) significantly boosted the number of TCR-reactive Th2 cells. These activated cells secreted cytokines, including IL-10, that are known to inhibit inflammatory Th1 cells. Cytokine release could also be induced in TCR-reactive Th2 cells by direct cell-cell contact with Th1 cells expressing the target V gene. These findings indicate the potential of regulatory Th2 cells to inhibit not only the target Th1 cells, but also bystander Th1 cells expressing different V genes specific for other autoantigens. TCR peptide vaccines have been used in our studies to treat a total of 171 MS patients (6 trials), 484 RA patients (7 trials), and 177 psoriasis patients (2 trials). Based on this experience in 824 patients with autoimmune diseases, TCR peptide vaccination is safe and well tolerated, and can produce significant clinical improvement in a subset of patients that respond to immunization. TCR peptide vaccination represents a promising approach that is well-suited for treating complex autoimmune diseases.

In Vitro andIn Vivo induction of bone formation using a recombinant adenoviral vector carrying the human BMP-2 gene

It has been well established that bone morphogenetic protein-2 (BMP-2) can induce bone formation bothin vivo andin vitro, although high concentrations (up to milligrams) of BMP-2 have been required to achieve this effectin vivo. Further, clinical applications are usually limited to a single dose at the time of implantation. In an attempt to prolong the transforming effect of BMP-2 we used a recombinant adenoviral vector carrying the human BMP-2 gene (Adv-BMP2) to transduce marrow-derived mesenchymal stem cells (MSC) of skeletally mature male New Zealand white rabbits. The pluripotential MSC were incubated with Adv-BMP2 overnight followed by culture in growth medium for 1 week. Assays on tissue cultures demonstrated that these Adv-BMP2 transduced MSC produced BMP-2 protein, differentiated into an osteoprogenitor line, and induced bone formationin vitro. These MSC had increased alkaline phosphatase activity, increased expression of type I collagen, osteopontin, and osteocalcin mRNA, and induced matrix mineralization compared with both nontransduced cells and cells transduced with a control adenoviral construct. To analyze the osteogenic potentialin vivo, Adv-BMP2-transduced MSC were autologously implanted into the intertransverse process space between L5 and L6 of the donor rabbits. The production of new bone was demonstrated by radiographic examination 4 weeks later in areas implanted with cells transduced with Adv-BMP2, whereas no bone was evident at sites implanted with cells transduced with the control adenoviral construct. Histological examination further confirmed the presence of new bone formation. These accumulated data indicate that it is possible to successfully transduce mesenchymal stem cells with a recombinant adenoviral vector carrying the gene for BMP-2 such that these cells will produce BMP-2, differentiate into an osteoprogenitor line, and induce bone formation bothin vitro andin vivo. Moreover, incubation of the Adv-BMP2-transduced cells for an additional 7 days in culture before transplantation enhances the success rate in bone formation (three out of three) as compared with our previous report (one out of five, Calcif Tissue Int 63:357-360, 1998).

T-cell-mediated regulation of osteoclastogenesis by signalling cross-talk between RANKL and IFN-gamma

Bone resorption is regulated by the immune system, where T-cell expression of RANKL (receptor activator of nuclear factor (NF)-kappaB ligand), a member of the tumour-necrosis factor family that is essential for osteoclastogenesis, may contribute to pathological conditions, such as autoimmune arthritis. However, whether activated T cells maintain bone homeostasis by counterbalancing the action of RANKL remains unknown. Here we show that T-cell production of interferon (IFN)-gamma strongly suppresses osteoclastogenesis by interfering with the RANKL-RANK signalling pathway. IFN-gamma induces rapid degradation of the RANK adapter protein, TRAF6 (tumour necrosis factor receptor-associated factor 6), which results in strong inhibition of the RANKL-induced activation of the transcription factor NF-kappaB and JNK. This inhibition of osteoclastogenesis is rescued by overexpressing TRAF6 in precursor cells, which indicates that TRAF6 is the target critical for the IFN-gamma action. Furthermore, we provide evidence that the accelerated degradation of TRAF6 requires both its ubiquitination, which is initiated by RANKL, and IFN-gamma-induced activation of the ubiquitin-proteasome system. Our study shows that there is cross-talk between the tumour necrosis factor and IFN families of cytokines, through which IFN-gamma provides a negative link between T-cell activation and bone resorption. Our results may offer a therapeutic approach to treat the inflammation-induced tissue breakdown.

Skewed T-cell receptor variable gene usage in the synovium of early and chronic rheumatoid arthritis patients and persistence of clonally expanded T cells in a chronic patient

OBJECTIVE

Autoreactive T cells may contribute to the pathogenesis of rheumatoid arthritis (RA). We studied the T-cell receptor (TCR) V-gene repertoire in the blood and synovium of early and chronic RA patients using polymerase chain reaction-enzyme-linked immunosorbent assay to evaluate possible differences between these patient groups.

RESULTS

Over-represented TCR V genes were observed in the synovium, but not in the blood of all RA patients (n = 38). The number of over-represented V genes was higher in the synovium of chronic RA patients (n = 31) than in that of early RA patients (n = 7). The V-gene profile was different among patients, and similar in the two knees for patients with bilateral synovitis (n = 5). The clonal composition of over-represented TCR BV genes in a patient with early RA and a patient with chronic RA was further studied by CDR3 region sequence analysis. A high level of clonal diversity was found in the joints and the blood of the early RA patient, suggesting a polyclonal T-cell expansion. In the chronic RA patient, predominant clonal expansions were observed in the blood and synovium, and some expanded clones were still present 2 yr later.

CONCLUSIONS

The observation of similar T-cell populations in both joints in patients with bilateral synovitis and the persistence of clonally expanded T cells for more than 2 yr in the joints of a chronic RA patient may indicate a pathogenic role for these cells in the disease process.

Carrageenan-induced arthritis in the rat

This study documents a model of carrageenan-induced chronic inflammatory arthritis in the rat, using quantitative histomorphometric assessment. Ten Sprague-Dawley female rats were randomly assigned to one of two groups. Arthritis was induced in the right tibiofemoral joint by 7 intra-articular injections of 0.02 mL of 1% carrageenan in the arthritic group over 24 days. The control (normal) group was injected with 0.02 mL of saline in the right tibiofemoral joint. Sagittal sections of the right knee joint (distal femur and proximal tibia) were assessed by histomorphometry using the LECO 2001 image analysis system. Articular cartilage thickness, epiphyseal plate thickness, subchondral bone plate thickness, trabecular bone volume and thickness of the synovial lining cell layer were measured. Differences between normal and arthritic groups were statistically significant for articular cartilage thickness of the femur, epiphyseal plate thickness of both the femur and tibia, subchondral bone plate thickness of the tibia and the thickness of the synovial lining cell layer. These findings demonstrate that carrageenan-induced arthritic changes are similar to other, established models of arthritis in the rat.

Blood levels of CD11b+ memory T lymphocytes are selectively upregulated in patients with active rheumatoid arthritis

The adhesion molecules CD11b (a beta2-integrin component) and CD54 (ICAM-1) on blood leukocytes were studied by flow cytometry in patients with rheumatoid arthritis (RA). The fractions of CD4+ cells co-expressing CD11b were elevated in 16 patients with active RA compared with those in 16 RA patients who improved during therapy and 8 healthy controls: 0.8+/-0.12% (mean+/-SEM) versus 0.3+/-0.06% (p<0.002) and 0.3+/-0.06% (p<0.005), respectively. Increased levels of CD11b+CD45R0+ cells were observed in patients with active RA compared to those with improved RA and controls: 12.6+/-3.9% versus 4.8+/-2.7% (p<0.002) and 6.1+/-1.2% (p<0.003), respectively. Disease activity, determined by C-reactive protein, correlated with the numbers of CD11b+CD45R0+ cells: r=0.62 (p<0.001). Seven patients were followed during induction of remission with methotrexate and glucocorticoids. The numbers of CD11b+CD4+ and CD11b+CD45R0+ cells fell significantly after clinical improvement. The levels of CD11b+CD14+ cells (monocytes) did not differ between the groups. The number of CD11b+CD15+ cells (neutrophils) was elevated in patients with RA irrespective of disease activity. The levels of CD54+ cells were not different between the RA and control groups. We conclude that the increased numbers of CD11b+ memory T cells may arise from exposure to stimuli outside the synovial compartment.

Cytokine gene activation in synovial membrane, regional lymph nodes, and spleen during the course of rat adjuvant arthritis

Cytokine gene activation was assessed during rat adjuvant arthritis (AA) in synovial membrane (SM), popliteal lymph node (popl-LN), and spleen, using semiquantitative, competitive RT-PCR. Changes in the popl-LN were considerably higher than in spleen or SM. In the preclinical phase (day 6), cytokine mRNA elevations occurred exclusively in the popl-LN and included IFN-gamma, IL-1beta, IL-5, IL-6, and IL-10. In the acute phase (days 13-16) all three organs became involved: (i) in the SM, significant elevations were limited to IL-1beta and IL-6, which, notably, correlated positively with the degree of arthritis; (ii) in the popl-LN, IFN-gamma, IL-1beta, IL-6, and IL-10 (but not IL-5) were still elevated, while IL-2 rose significantly; (iii) in the spleen, TNF-alpha peaked simultaneously with the arthritis score (day 16) and dramatically dropped thereafter. Upon transition into the chronic phase (day 20) the following phenomena were observed: (i) IL-1beta and IL-6 were still significantly increased in the SM; (ii) IFN-gamma, IL-1beta, IL-2, IL-6, and IL-10 were still elevated in the popl-LN; and (iii) there was a progressive rise of IL-5 mRNA in the spleen, positively correlated with the arthritis score. In conclusion, cytokines with pro- and anti-inflammatory functions overlap throughout disease, but in different organ-related patterns. Local (SM) and regional (popl-LN) IL-1beta and IL-6, elevated throughout the entire course of AA, may directly contribute to disease severity. While in AA spleen TNF-alpha appears to be a systemic marker of acute disease, spleen IL-5 may be involved in disease resolution.

A novel T cell cytokine stimulates interleukin-6 in human osteoblastic cells

Rheumatoid arthritis (RA) is an autoimmune disease characterized by a heavy lymphocytic infiltration into the synovial cavity, resulting in the secretion of a variety of cytokines which ultimately leads to destruction of joint tissue. Among the infiltrating cells are activated T cells which produce specific cytokines capable of osteoclast progenitor cell expansion, fusion, and activation. Cultures of activated human T cells and human osteoblasts (hOBs) were used to study the possibility that lymphokines may act on osteoblasts to produce the osteoclastogenic factor interleukin-6 (IL-6). Purified T cells were activated with a combination of anti-CD3 and anti-CD28 antibodies, cocultured with hOBs in direct physical contact or separated by a transwell system, and conditioned media (CM) were assayed for IL-6 production. After a 72 h incubation period, activated T cell-hOB interaction resulted in a 100-fold increase of IL-6 production over basal levels. The immunosuppressant cyclosporine A (CsA) inhibited T cell tumor necrosis factor alpha and IL-6 production but did not inhibit the T cell induction of IL-6 from hOB. Assay of activated T-cell CM on hOB revealed that a soluble factor, not cell-cell contact, was the major inducer of IL-6. The induction of IL-6 mRNA by both activated T cell CM and CsA-treated activated T cell CM was confirmed by Northern blot analysis. Neutralizing antibodies to IL-13 and IL-17 did not affect IL-6 production. These findings suggest that activated T cells produce a novel, potent, IL-6 inducing factor that may be responsible for the bone loss observed in RA patients.