IL-4 gene therapy for collagen arthritis suppresses synovial IL-17 and osteoprotegerin ligand and prevents bone erosion

Influence of heme oxygenase 1 modulation on the progression of murine collagen-induced arthritis

OBJECTIVE

Heme oxygenase 1 (HO-1) can be induced by inflammatory mediators as an adaptive response. The objective of the present study was to determine the consequences of HO-1 modulation in the murine collagen-induced arthritis (CIA) model.

METHODS

DBA/1J mice were treated with an inhibitor of HO-1, tin protoporphyrin IX (SnPP), or with an inducer of HO-1, cobalt protoporphyrin IX (CoPP), from day 22 to day 29 after CIA induction. The clinical evolution of disease was monitored visually. At the end of the experiment, joints were examined for histopathologic changes. Cytokine levels in paws were measured by enzyme-linked immunosorbent assay. Levels of HO-1, cyclooxygenase 2 (COX-2), and prostaglandin E2 (PGE2) were determined. Effects of treatments on the early phase of disease and after prophylactic administration were also assessed.

RESULTS

CoPP strongly induced HO-1, resulting in the inhibition of cartilage erosion accompanied by extensive fibrosis in the joint. Levels of tumor necrosis factor alpha (TNFalpha), interleukin-2 (IL-2), and IL-10 were inhibited by CoPP, whereas levels of vascular endothelial growth factor were increased. Treatment with SnPP significantly reduced the severity of CIA, with inhibition of joint inflammation and cartilage destruction. The levels of PGE2, IL-1beta, and TNFalpha were also significantly reduced by SnPP treatment, which did not modify COX-2 protein expression. SnPP was more effective than CoPP in preventing the development of CIA (prophylactic administration).

CONCLUSION

HO-1 is induced during CIA. Although overexpression of this protein causes some beneficial effects, strategies aimed at HO-1 overexpression cannot slow the progression of the chronic inflammatory disease, whereas treatment with SnPP, which inhibits HO-1, exerts prophylactic and therapeutic effects.

Analysis of the kinetics of osteoclastogenesis in arthritic rats

OBJECTIVE

To analyze the kinetics of osteoclastogenesis in 2 models of chronic immune-mediated arthritis and 1 model of acute arthritis.

METHODS

Adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) in Lewis rats were used as models of chronic arthritis. Acute arthritis was induced in Lewis rats by injecting carrageenan into the hind paw. Osteoclasts were identified by cathepsin K immunohistochemistry at various time points after the onset of arthritis. The location, size, and nucleation of osteoclasts were also analyzed.

RESULTS

In both AIA and CIA, multinucleated and cathepsin K-positive osteoclasts first were observed on the day of disease onset. Initially, osteoclasts were localized at the periosteum next to the synovial membrane and in subchondral bone channels. The number, size, and nucleation of osteoclasts rapidly increased, leading to severe bone loss within days after disease onset. In addition, numerous mononucleated cathepsin K-positive osteoclast precursor cells emerged in the synovial membrane. All osteoclasts (cathepsin K-positive, multinucleated, attached to bone) and osteoclast precursors (cathepsin K-positive, mononucleated or multinucleated, within synovial tissue) were also positive for a macrophage-specific marker. Upon induction of acute arthritis with carrageenan, osteoclasts formed transiently in subchondral bone, but regressed 7 days after disease onset.

CONCLUSION

Functional osteoclasts are generated at the earliest stage of arthritis, and new precursors are continuously formed in the synovial membrane to replenish the osteoclast pool. These data indicate that anti-resorptive therapies may provide the most effective bone protection, when treatment is started soon after the onset of arthritis.

The role of T-cell interleukin-17 in conducting destructive arthritis: lessons from animal models

Interleukin-17 (IL-17) is a T cell cytokine spontaneously produced by cultures of rheumatoid arthritis (RA) synovial membranes. High levels have been detected in the synovial fluid of patients with RA. The trigger for IL-17 is not fully identified; however, IL-23 promotes the production of IL-17 and a strong correlation between IL-15 and IL-17 levels in synovial fluid has been observed. IL-17 is a potent inducer of various cytokines such as tumor necrosis factor (TNF)-alpha, IL-1, and receptor activator of NF-kappaB ligand (RANKL). Additive or even synergistic effects with IL-1 and TNF-alpha in inducing cytokine expression and joint damage have been shown in vitro and in vivo. This review describes the role of IL-17 in the pathogenesis of destructive arthritis with a major focus on studies in vivo in arthritis models. From these studies in vivo it can be concluded that IL-17 becomes significant when T cells are a major element of the arthritis process. Moreover, IL-17 has the capacity to induce joint destruction in an IL-1-independent manner and can bypass TNF-dependent arthritis. Anti-IL-17 cytokine therapy is of interest as an additional new anti-rheumatic strategy for RA, in particular in situations in which elevated IL-17 might attenuate the response to anti-TNF/anti-IL-1 therapy.

Individual differences in behavior of inbred Lewis rats are associated with severity of joint destruction in adjuvant-induced arthritis

The aim of our study was to test the hypothesis that differences in behavioral characteristics are linked to severity of arthritis in association with neuro-endocrine and immune reactivity in an inbred strain of rats. Lewis rats were selected as high-active (HA) and low-active (LA) animals based on their exploratory activity in the open field. Subsequently, adjuvant-arthritis (AA) was induced in both groups. We observed no differences in the severity of inflammation as determined by paw swelling and redness. However, LA and HA animals differed in the severity of bone destruction as determined on radiographs taken on day 30 after induction of AA. LA rats had more osteoporosis, periostal new bone formation, and bone destruction than HA rats. There were no differences between HA and LA rats in corticosterone response after acute or chronic immune challenge. Splenocytes of LA rats had a lower mitogen-induced IL-10 and IFNgamma production during AA. Histological examination revealed more intense factor VIII staining in arthritic joints of LA animals, indicating more pronounced synovial angiogenesis. In addition, LA rats had higher plasma VEGF, an important angiogenic factor. Expression of RANKL, a crucial factor promoting bone resorption, was also higher in joints of LA animals. Our data demonstrate that activity in the open field, a behavioral trait, is associated with the severity of bone destruction in AA. Lower production of bone-protective cytokines and a higher rate of angiogenesis leading to more synovial proliferation may be responsible for the more severe joint destruction in LA animals.

Biology of recently discovered cytokines: interleukin-17--a unique inflammatory cytokine with roles in bone biology and arthritis

IL-17 and its receptor are founding members of an emerging family of cytokines and receptors with many unique characteristics. IL-17 is produced primarily by T cells, particularly those of the memory compartment. In contrast, IL-17 receptor is ubiquitously expressed, making nearly all cells potential targets of IL-17. Although it has only limited homology to other cytokines, IL-17 exhibits proinflammatory properties similar to those of tumor necrosis factor-alpha, particularly with respect to induction of other inflammatory effectors. In addition, IL-17 synergizes potently with other cytokines, placing it in the center of the inflammatory network. Strikingly, IL-17 has been associated with several bone pathologies, most notably rheumatoid arthritis.

Gene therapy for autoimmune diseases: quo vadis?

Biological therapies using antibodies and cytokines are becoming widespread for the treatment of chronic inflammatory autoimmune diseases. However, these treatments have several limitations - such as expense, the need for repeated injections and unwanted side-effects - that can be overcome by genetic delivery. This review summarizes the ingenuity, sophistication and variety of gene-therapy approaches that have been taken in the design of therapeutic molecules and vectors, the engineering of cells and the regulation of gene expression for the targeting of disease outcome. We focus our attention on multiple sclerosis, type 1 diabetes and rheumatoid arthritis.

Protection against collagen-induced arthritis by electrotransfer of an expression plasmid for the interleukin-4

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease, leading to cartilage and bone destruction. We investigated whether the electrotransfer of IL-4 DNA could regulate the disease progress of murine collagen-induced arthritis (CIA). The maximum serum level of mIL-4 was measured by 340 pg/ml on day 1 following DNA transfer. The onset of severe CIA and the degree of synovitis and cartilage erosion were significantly reduced in mice treated with IL-4 DNA (P<0.05). The beneficial effect of IL-4 gene transfer lasted for at least 17 days subsequent to treatment. The expression of IL-1beta was considerably decreased in the paws by IL-4 DNA transfer (P<0.01). On the contrary, the ratio of TIMP2 to MMP2 significantly increased in the IL-4 DNA-treated group (P<0.01). These data demonstrated that electroporation-mediated gene transfer could provide a new approach as an IL-4 therapy for autoimmune arthritis.

Zoledronic acid protects against local and systemic bone loss in tumor necrosis factor-mediated arthritis

OBJECTIVE

Increased osteoclast activity is a key factor in bone loss in rheumatoid arthritis (RA). This suggests that osteoclast-targeted therapies could effectively prevent skeletal damage in patients with RA. Zoledronic acid (ZA) is one of the most potent agents for blocking osteoclast function. We therefore investigated whether ZA can inhibit the bone loss associated with chronic inflammatory conditions.

METHODS

Human tumor necrosis factor (TNF)-transgenic (hTNFtg) mice, which develop severe destructive arthritis as well as osteoporosis, were treated with phosphate buffered saline, single or repeated doses of ZA, calcitonin, or anti-TNF, at the onset of arthritis.

RESULTS

Synovial inflammation was not affected by ZA. In contrast, bone erosion was retarded by a single dose of ZA (-60%) and was almost completely blocked by repeated administration of ZA (-95%). Cartilage damage was partly inhibited, and synovial osteoclast counts were significantly reduced with ZA treatment. Systemic bone mass dramatically increased in hTNFtg mice after administration of ZA, which was attributable to an increase in trabecular number and connectivity. In addition, bone resorption parameters were significantly lowered after administration of ZA. Calcitonin had no effect on synovial inflammation, bone erosion, cartilage damage, or systemic bone mass. Anti-TNF entirely blocked synovial inflammation, bone erosion, synovial osteoclast formation, and cartilage damage but had only minor effects on systemic bone mass.

CONCLUSION

ZA appears to be an effective tool for protecting bone from arthritic damage. In addition to their role in antiinflammatory drug therapy, modern bisphosphonates are promising candidates for maintaining joint integrity and reversing systemic bone loss in patients with arthritis.

Role for osteoprotegerin in rheumatoid inflammation

Osteoprotegerin (OPG), a member of the TNF-receptor family expressed by osteoblasts, has documented effects on the regulation of bone metabolism. OPG inhibits bone resorption and binds with strong affinity to its ligand RANKL, thereby preventing RANKL from binding to its receptor RANK. This system is regulated by calcium-modifying hormones. OPG may also be pivotal in modulating the immune system. RANKL-deficient mice exhibit both severe immunological abnormalities and osteopetrosis, and activated T cells express RANKL mRNA. RANKL secretion by activated T cells may induce osteoclastogenesis via a mechanism enhanced by several cytokines (TNF-alpha, IL-1, and IL-17) that promote both inflammation and bone resorption. Conversely, this mechanism is inhibited by OPG, IL-4, and IL-10, which have antiinflammatory effects and inhibit osteoclast formation. Activated T cells in the rheumatoid synovium express RANKL. Synoviocytes can differentiate to osteoclast-like cells under specific conditions, particularly when they are cultured with M-CSF and RANKL. Thus, the bony erosions seen in RA may result from RANKL/RANK system activation by activated T cells. This raises the possibility that OPG therapy to block this mechanism might prove beneficial in patients with RA.

Plasmid encoding interleukin-4 in the amelioration of murine collagen-induced arthritis

OBJECTIVE

To evaluate the therapeutic effect of the administration of plasmid encoding interleukin-4 (IL-4) via gene-gun delivery and via intradermal injection on collagen-induced arthritis (CIA).

METHODS

IL-4 plasmid was administered by gene-gun delivery and intradermal injection to DBA/1 mice immunized with type II collagen (CII). The therapeutic effect on the development of CIA was evaluated clinically with a visual scoring method for arthritis and serologically by enzyme-linked immunosorbent assays and polymerase chain reaction.

RESULTS

Treatment with IL-4-expressing plasmid significantly reduced the incidence and severity of CIA, including a reduction in the anti-CII antibody level. In particular, gene-gun delivery had a higher immunosuppressive effect on CIA compared with intradermal injection. As shown by in vitro stimulation assay, the spleen cells from mice immunized with CII and treated with IL-4 plasmid via gene gun exhibited higher Th2 cytokine responses compared with cells treated with control plasmid after in vitro stimulation with CII.

CONCLUSION

The results of this study suggest that treatment with IL-4 plasmid may constitute a new clinical use of cytokine gene therapy for rheumatoid arthritis.

Role of gene therapy in tissue engineering procedures in rheumatology: the use of animal models

Tissue engineering is not only the application of cells and scaffolds to generate a new tissue but should also bring into play biological principles to guide cellular behavior. A way to modify cellular behavior is genetic modification of the cells used for tissue engineering (gene therapy). In the field of rheumatic diseases, cellular modification by overexpressing anabolic factors, such as insulin-like growth factor-I or transforming growth factor beta, or inhibitors of catabolic cytokines or proteolytic enzymes can protect tissues form further destruction and stimulate tissue repair. To test the effect of transgenes on tissue engineering adequate test systems have to be available. Initial testing can be done in simple in vitro systems. However, animal models are unavoidable to study the interaction between the environment and tissue engineering. Optimal models to study gene therapy in combination with tissue engineering in the field of rheumatology are not available at this moment. Arthritis models are mainly developed in small animals while high-quality tissue engineering experiments ask for a large animal model. Development of animal models that can be used for tissue engineering experiments and mimic end stage arthritic diseases is needed.

Treatment with a neutralizing anti-murine interleukin-17 antibody after the onset of collagen-induced arthritis reduces joint inflammation, cartilage destruction, and bone erosion

OBJECTIVE

Interleukin-17 (IL-17) is a proinflammatory cytokine that is expressed in the synovium of rheumatoid arthritis (RA) patients. This T cell cytokine is implicated in the initiation phase of arthritis. However, the role of IL-17 during the effector phase of arthritis has still not been identified; this was the objective of the present study.

METHODS

Mice with collagen-induced arthritis (CIA) were treated with polyclonal rabbit anti-murine IL-17 (anti-IL-17) antibody-positive serum or normal rabbit serum after the first signs of arthritis. In addition, during a later stage of CIA mice were selected and treated with anti-IL-17 antibody or control serum. Arthritis was monitored visually, and joint pathology was examined radiologically and histologically. Systemic IL-6 levels were measured by enzyme-linked immunosorbent assay, and local synovial IL-1 and receptor activator of NF-kappaB ligand (RANKL) expression was analyzed using specific immunohistochemistry.

RESULTS

Treatment with a neutralizing anti-IL-17 antibody after the onset of CIA significantly reduced the severity of CIA. Radiographic analysis revealed marked suppression of joint damage in the knee and ankle joints. Histologic analysis confirmed the suppression of joint inflammation and showed prevention of cartilage and bone destruction after anti-IL-17 antibody therapy. Systemic IL-6 levels were significantly reduced after anti-IL-17 antibody treatment. Moreover, fewer IL-1beta-positive and RANKL-positive cells were detected in the synovium after treatment with neutralizing IL-17. Interestingly, initiation of anti-IL-17 antibody therapy during a later stage of CIA, using mice with higher clinical arthritis scores, still significantly slowed the progression of the disease.

CONCLUSION

IL-17 plays a role in early stages of arthritis, but also later during disease progression. Systemic IL-6 was reduced and fewer synovial IL-1-positive and RANKL-positive cells were detected after neutralizing endogenous IL-17 treatment, suggesting both IL-1-dependent and IL-1-independent mechanisms of action. Our data strongly indicate that IL-17 neutralization could provide an additional therapeutic strategy for RA, particularly in situations in which elevated IL-17 may attenuate the response to anti-tumor necrosis factor/anti-IL-1 therapy.

Protective effects of IL-1Ra or vIL-10 gene transfer on a murine model of wear debris-induced osteolysis

The current study evaluated the protective effects of anti-inflammatory cytokine gene transfer on osteolysis provoked by orthopedic biomaterial particles using a murine model of inflammatory bone loss. A section of bone was surgically implanted into an air pouch established on a syngeneic recipient mouse. Inflammation was provoked by introduction of ultra-high-molecular-weight polyethylene (UHMWPE) particles into the pouch, and retroviruses encoding for interleukin-1 receptor antagonist (hIL-1Ra), viral interleukin-10 (vIL-10), or LacZ genes were injected. Pouch fluid and tissue were harvested 7 days later for histological and molecular analyses. The results indicated that IL-1Ra or vIL-10 gene transfer significantly inhibited IL-1beta and tumor necrosis factor (TNF) expression at both mRNA and protein levels. There were significantly lower mRNA expressions of calcitonin receptor and cathepsin K in RNA isolated from hIL-1Ra- or vIL-10-transduced pouches than LacZ-transduced and virus-free controls. Both anti-inflammatory cytokine gene transfers significantly reduced the mRNA expression of M-CSF (70-90%) and RANK (>65%) in comparison with LacZ- and virus-free controls. Histological examination showed that hIL-1Ra or vIL-10 gene transfer dramatically abolished UHMWPE-induced inflammatory cellular infiltration and bone pit erosion compared to LacZ-transduced and virus-free controls. Histochemical staining revealed significantly fewer osteoclast-like cells in samples treated with IL-1Ra or vIL-10 gene transfer. In addition, bone collagen content was markedly preserved in the groups with anti-inflammatory cytokine gene transfers compared with the other two groups. Overall, retrovirus-mediated hIL-1Ra or vIL-10 gene transfer effectively protected against UHMWPE-particle-induced bone resorption, probably due to the inhibition of IL-1/TNF-induced M-CSF production and the consequent osteoclast recruitment and maturation.

Suppression of collagen-induced arthritis by natural killer T cell activation with OCH, a sphingosine-truncated analog of ?-galactosylceramide

OBJECTIVE

OCH, a synthetic analog of alpha-galactosylceramide with a truncated sphingosine chain, stimulates natural killer T (NKT) cells to produce predominantly Th2 cytokines. Thus, OCH may be a potential agent for the treatment of Th1-mediated autoimmune diseases. This study was designed to evaluate the protective effects of OCH on collagen-induced arthritis (CIA) in mice.

METHODS

Mice were immunized with type II collagen (CII) and injected intraperitoneally twice per week with OCH, before or after the onset of CIA. They were monitored to assess the effect of OCH treatment on the severity of disease. Anti-CII antibodies and cytokine production were measured by enzyme-linked immunosorbent assay. Expression of cytokine genes was determined by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

OCH inhibited CIA in wild-type C57BL/6 (B6) mice but not in NKT-deficient mice. OCH suppressed CIA in SJL mice, which are prone to autoimmune diseases and have a deficiency in the number and function of NKT cells which is similar to that in patients with autoimmune diseases, even after disease has already developed. Disease protection conferred by OCH correlated with its ability to selectively induce Th2 cytokine production mediated by NKT cells and to promote collagen-specific Th2 responses. Neutralization of interleukin-4 (IL-4) or IL-10 with monoclonal antibodies abolished disease protection by OCH, indicating a critical role for these cytokines.

CONCLUSION

Taken together, our findings suggest that OCH holds possibilities as a therapeutic agent for autoimmune diseases such as rheumatoid arthritis.

Suppressive Effect of Kanzo-bushi-to, a Kampo Medicine, on Collagen-Induced Arthritis

Kanzo-bushi-to (KBT) is a traditional Japanese herbal medicine (Kampo medicine), which is used in Japan to treat rheumatoid arthritis. In the present study, we investigated the suppressive effect of KBT on collagen-induced arthritis (CIA) and further studied the underlying mechanism. CIA was induced in male DBA/1J mice by immunization with bovine type II collagen, followed by a booster injection 21 d later. KBT was given at a dose of 430 mg/kg/d from three days before the first immunization to the end of the experiment. KBT suppressed CIA development effectively and further protected focal bone erosion and bone destruction as evidenced by the reduced histological score. Histochemical examination revealed that KBT decreased TRAP-positive cells at the synovium-bone interface and at the sites of focal bone erosion, coincident with the findings that RANKL/OPG mRNA ratio was significantly reduced by KBT treatment. KBT also decreased mRNA levels of M-CSF and iNOS in joints and of iNOS in peritoneal macrophages. In conclusion, KBT prevented osteoclast generation by decreasing RANKL/OPG ratio and M-CSF mRNA levels, resulting in reduction in bone erosion and destruction. In addition, KBT has anti-inflammatory effect such as the suppression of iNOS expression in peritoneal macrophages and joints of CIA mice. These finding suggests that KBT is a potential new therapeutic agent for the treatment of RA.

Interleukin-4 directly inhibits tumor necrosis factor-alpha-mediated osteoclast formation in mouse bone marrow macrophages

Recently it has been found that osteoclast differentiation is induced by tumor necrosis factor (TNF)-alpha. Interleukin (IL)-4 was reported to suppress osteoclast differentiation and bone resorption. However, no study has investigated the effect of IL-4 on TNF-alpha-induced osteoclast formation. In this study, we investigated whether IL-4 inhibits TNF-alpha-mediated osteoclast formation in mouse bone marrow derived macrophages (BMM). First, IL-4 suppresses RANKL-induced osteoclast formation and bone resorption. Next, when BMM were cultured with TNF-alpha, osteoclast-like cells were formed. When they were cultured with both TNF-alpha and IL-4, osteoclast formation and bone resorption was suppressed by IL-4 in a dose-dependent manner. It has been recently found that TNF-alpha and RANKL synergistically promote osteoclastogenesis. Finally, we investigated whether IL-4 had the ability to inhibit synergistic TNF-alpha and RANKL-induced osteoclastogenesis, with the result that it effectively inhibited the synergistic osteoclast formation in a dose-dependent manner. We conclude that IL-4 can strongly inhibit osteoclast formation that is related to both physiological bone resorption induced by RANKL and pathological bone resorption induced by TNF-alpha.

Osteoprotegerin protects against generalized bone loss in tumor necrosis factor-transgenic mice

OBJECTIVE

To investigate the role of tumor necrosis factor (TNF) in systemic bone loss of chronic inflammatory conditions, such as rheumatoid arthritis (RA), and to address the therapeutic potential of osteoclast blockade.

METHODS

We investigated systemic bone changes in human TNF transgenic (hTNFtg) mice, which spontaneously developed severe inflammatory arthritis.

RESULTS

Osteodensitometry revealed a significant decrease in trabecular bone mineral density (BMD) (-37%) in hTNFtg mice, and histomorphometry revealed a dramatic loss of bone volume (-85%) compared with wild-type controls. Osteoclast-covered bone surface and serum levels of deoxypyridinoline crosslinks were significantly elevated, suggesting increased osteoclast-mediated bone resorption in hTNFtg mice. Osteoprotegerin (OPG) completely blocked TNF-mediated bone loss by increasing BMD (+89%) and bone volume (+647%). Most strikingly, formation of primary spongiosa was dramatically increased (+563%) in hTNFtg mice after OPG treatment. Osteoclast-covered bone surface and serum levels of deoxypyridinoline crosslinks were significantly decreased by OPG, suggesting effective blockade of osteoclast-mediated bone resorption. OPG did not influence levels of hTNF, TNF receptor I (TNFRI), interleukin-1beta (IL-1beta), and IL-6. However, OPG decreased bone formation parameters (osteoblast-covered bone surface and serum osteocalcin levels), which were elevated in hTNFtg mice. In contrast to OPG, bisphosphonates and anti-TNF treatment did not affect generalized bone loss in hTNFtg mice. Anti-TNF, however, did not affect levels of TNF and TNFRI at the concentrations tested. These data indicate that generalized bone loss due to increased TNF can be blocked by OPG.

CONCLUSION

OPG may represent a potent tool for preventing generalized loss of bone mass in chronic inflammatory disorders, especially RA.

T-cells mediate an inhibitory effect of interleukin-4 on osteoclastogenesis

IL-4 is an important cytokine that can influence bone. We identified two distinct actions of IL-4 to inhibit osteoclast formation: one direct on osteoclast progenitors and the second through the production of a novel T-cell surface-associated molecule(s). These data show a new link between the immune system and bone. The Th2 cytokine interleukin (IL)-4 inhibits osteoclast formation in vitro but also acts on other cell types found in bone, including T-cells and macrophages. Because some osteoclastogenesis inhibitors (e.g., IL-12) act indirectly through T-cells, we investigated IL-4 action on osteoclastogenesis in the presence of T-cells. Osteoclast formation from murine spleen cells treated with RANKL and macrophage colony-stimulating factor (M-CSF) was blocked by IL-4 even when spleen cells were depleted of T-cells (Thy 1.2+) and/or B-cells (B220+). Also, IL-4 inhibited osteoclastogenesis in RANKL/M-CSF-stimulated adherent spleen cells, Rag1 -/- (lymphocyte-deficient) spleen cells, and bone marrow macrophages, indicating an action on myelomonocytic cells to block osteoclastogenesis. In contrast, IL-4 did not inhibit osteoclastogenesis in cells from IL-4 receptor null mice (IL-4R -/-). However, when wildtype T-cells were added to IL-4R -/- spleen cell cultures, IL-4 inhibited osteoclast formation, indicating a T-cell-dependent action. Osteoclast formation in RANKL-stimulated RAW 264.7 cells was not inhibited by IL-4 unless T-cells were added to the culture. Separation of RAW 264.7 cells and T-cells by semipermeable membrane ablated this action of IL-4, suggesting the induction of a membrane-associated osteoclastogenesis inhibitor. However, membrane-bound inhibitors thymic shared antigen-1 (TSA-1) and osteoclast inhibitory lectin (OCIL) were not regulated by IL-4. In summary, at least two mechanisms of IL-4 -mediated osteoclastogenesis inhibition exist, including a direct action on myelomonocytic progenitors (from which osteoclasts derive) and an indirect action through T-cells that may involve novel anti-osteoclastic factors.

Evolving concepts of rheumatoid arthritis

Rheumatoid arthritis is the most common inflammatory arthritis and is a major cause of disability. It existed in early Native American populations several thousand years ago but might not have appeared in Europe until the 17th century. Early theories on the pathogenesis of rheumatoid arthritis focused on autoantibodies and immune complexes. T-cell-mediated antigen-specific responses, T-cell-independent cytokine networks, and aggressive tumour-like behaviour of rheumatoid synovium have also been implicated. More recently, the contribution of autoantibodies has returned to the forefront. Based on the pathogenic mechanisms, specific therapeutic interventions can be designed to suppress synovial inflammation and joint destruction in rheumatoid arthritis.

Gene therapy for arthritis

Rheumatoid arthritis is an autoimmune disease with intra-articular inflammation and synovial hyperplasia that results in progressive degradation of cartilage and bone, in severe cases it causes systemic complications. Recently, biological agents that suppress the activities of proinflammatory cytokines have shown efficacy as antiarthritic drugs, but require frequent administration. Thus, gene transfer approaches are being developed as an alternative approach for targeted, more efficient and sustained delivery of inhibitors of inflammatory cytokines as well as other therapeutic agents. Indeed, the efficacy of gene transfer for the treatment of arthritis has been demonstrated in mouse, rat, rabbit, and horse models of disease whereas the feasibility of the approach has been demonstrated in Phase I clinical trials. In this review, the current status of both preclinical and clinical arthritis gene therapy is presented. In addition, the advantages and disadvantages of different types of vectors, target cells and therapeutic genes being developed for the treatment of arthritis are summarized. Finally, the future directions of the rapidly developed field of arthritis gene therapy are outlined.

[Pathogenesis of osteoporosis in rheumatoid arthritis]

Osteoporosis is a major clinical problem in rheumatoid arthritis. Patients with rheumatoid arthritis frequently not only present with juxta articular osteopenia and bone erosions but also with generalized axial and appendicular osteoporosis at sites distant from inflamed joints. The pathogenesis of bone loss in rheumatoid arthritis is multifactorial; disease activity certainly is a major determinant of bone mass. Further pathogenetic factors include effects of anti-inflammatory therapies (in particular glucocorticoids), reduced mobility, estrogen and/or androgen deficiency. Recently, receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG), a decoy receptor for receptor activator of nuclear factor kappa B ligand, were identified as central regulators of osteoclast recruitment and activation. Osteoprotegerin and receptor activator of nuclear factor kappa B ligand production is modulated by several cytokines, growth factors and hormones. In rheumatoid synovium both fibroblasts and activated T cells express receptor activator of nuclear factor kappa B ligand and thereby promote osteoclast recruitment and activation. Thus, osteoprotegerin and receptor activator of nuclear factor kappa B ligand appear to represent important molecular links between the immune system and bone metabolism in rheumatoid arthritis.

Interleukin-17 family and IL-17 receptors

Interleukin-17 (IL-17) is a pro-inflammatory cytokine secreted by activated T-cells. Recently discovered related molecules are forming a family of cytokines, the IL-17 family. The prototype member of the family has been designated IL-17A. Due to recent advances in the human genome sequencing and proteomics five additional members have been identified and cloned: IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. The cognate receptors for the IL-17 family identified thus far are: IL-17R, IL-17RH1, IL-17RL (receptor like), IL-17RD and IL-17RE. However, the ligand specificities of many of these receptors have not been established. The IL-17 signaling system is operative in disparate tissues such as articular cartilage, bone, meniscus, brain, hematopoietic tissue, kidney, lung, skin and intestine. Thus, the evolving IL-17 family of ligands and receptors may play an important role in the homeostasis of tissues in health and disease beyond the immune system. This survey reviews the biological actions of IL-17 signaling in cancers, musculoskeletal tissues, the immune system and other tissues.

IL-17 promotes bone erosion in murine collagen-induced arthritis through loss of the receptor activator of NF-kappa B ligand/osteoprotegerin balance

IL-17 is a T cell-derived proinflammatory cytokine in experimental arthritis and is a stimulator of osteoclastogenesis in vitro. In this study, we report the effects of IL-17 overexpression (AdIL-17) in the knee joint of type II collagen-immunized mice on bone erosion and synovial receptor activator of NF-kappa B ligand (RANKL)/receptor activator of NF-kappa B/osteoprotegerin (OPG) expression. Local IL-17 promoted osteoclastic bone destruction, which was accompanied with marked tartrate-resistant acid phosphatase activity at sites of bone erosion in cortical, subchondral, and trabecular bone. Accelerated expression of RANKL and its receptor, receptor activator of NF-kappa B, was found in the synovial infiltrate and at sites of focal bone erosion, using specific immunohistochemistry. Interestingly, AdIL-17 not only enhanced RANKL expression but also strongly up-regulated the RANKL/OPG ratio in the synovium. Comparison of arthritic mice from the AdIL-17 collagen-induced arthritis group with full-blown collagen-arthritic mice having similar clinical scores for joint inflammation revealed lower RANKL/OPG ratio and tartrate-resistant acid phosphatase activity in the latter group. Interestingly, systemic OPG treatment prevented joint damage induced by local AdIL-17 gene transfer in type II collagen-immunized mice. These findings suggest T cell IL-17 to be an important inducer of RANKL expression leading to loss of the RANKL/OPG balance, stimulating osteoclastogenesis and bone erosion in arthritis.

Antigen inhibition of collagen-induced arthritis is associated with up-regulation of IL-4 mRNA and induction of Ox40 on T cells in draining lymph nodes

The addition of a foreign antigen to an inoculum completely inhibits the development of collagen-induced arthritis (CIA). However, the mechanism of this phenomenon, antigen -inhibition, is incompletely understood. Previous studies have demonstrated that the inhibition of arthritis is not mediated through suppression of the antibody response to cartilage antigens. In this paper we investigated cytokine mRNA levels in lymph nodes cells recovered 3, 7 or 16 days from animals immunized with either collagen II in IFA or OVA + collagen II in IFA. At day 7, but not at other time-points, IL-4 mRNA was up-regulated in the lymph nodes of OVA-inhibited non-arthritic animals compared to control animals which all developed arthritis. No significant differences between the two groups could be detected when expression of IFN-gamma, IL-2, TNF-alpha, IL-1beta or IL-10 mRNA was analysed. Flow cytometry analysis of draining lymph node cells demonstrated that the T cell marker Ox40 was up-regulated in the OVA-inhibited group. Our results indicate that the complete inhibition of CIA caused by addition of OVA to the collagen II inoculum is due to the presence of a TH2 environment resulting from an increased production of IL-4 mRNA and a parallel increase in Ox40+ T cells.

Exposure to receptor-activator of NFkappaB ligand renders pre-osteoclasts resistant to IFN-gamma by inducing terminal differentiation

While it has been established that IFN-gamma is a strong activator of macrophages and a potent inhibitor of osteoclastogenesis in vitro, it is also known that this cytokine is produced in particular settings of inflammatory bone loss, such as infection and psoriatic arthritis. Because of the different kinetics between rapid IFN-gamma macrophage activation (<24 hours) and the slower receptor-activator of NFkappaB ligand (RANKL) osteoclast differentiation (7 days), we postulated that IFN-gamma would have different effects on early-stage and late-stage osteoclast precursors. In RAW264.7 cells and primary splenocyte cultures, pretreatment with RANKL rendered these cells resistant to maximally anti-osteoclastogenic doses of IFN-gamma. These cells were also resistant to IFN-gamma-induced nitric oxide production, morphological change, and surface upregulation of CD11b and receptor-activator of NFkappaB, suggesting that early exposure of osteoclast precursors to RANKL induces a broad resistance to the cellular effects of IFN-gamma. Changes in STAT1 activation did not correlate with this resistance, as IFN-gamma activated STAT1 equally in both early-stage and late-stage pre-osteoclasts. Furthermore, we failed to observe changes in TRAF6 expression following IFN-gamma treatment in pre-osteoclasts. Together these data support a model of inflammatory bone loss in which early exposure to RANKL can prime osteoclast precursors to form in the presence of high levels of IFN-gamma using mechanisms independent of the signal molecules STAT1 and TRAF6.

The role of osteoprotegerin in arthritis

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.

Retroviral gene therapy of collagen-induced arthritis by local delivery of IL-4

Rheumatoid arthritis (RA) is an autoimmune arthritis, for which treatment options remain limited. This study investigated the potential role of adoptive cellular gene therapy as a novel means for treating the RA animal model collagen-induced arthritis (CIA). Adoptive transfer of antigen-specific T-cell hybridomas retrovirally transduced to express IL-4 1 day before booster immunization significantly reduced the number of inflamed joints. Cell transfer after clinical onset of disease had no therapeutic effect. Bioluminescence imaging showed that the hybridomas migrated to the inflamed joints, thus delivering the regulatory protein locally at the site of inflammation. The homing was, at least in part, due to chemotaxis in response to proinflammatory chemokines that are expressed in inflamed joints. There were no significant changes in the cytokine milieu of the draining lymph nodes, nor in the systemic levels of anti-collagen antibodies in treated mice. We conclude that the beneficial clinical effects observed in our model were most likely based on the local action(s) of IL-4 in the inflamed joints and that the local delivery (and effects) of regulatory cytokines, like IL-4, constitutes a novel and effective method of preventing organ-specific autoimmune disease and of minimizing systemic adverse effects.

Interleukin 17: an example for gene therapy as a tool to study cytokine mediated regulation of hematopoiesis

Interleukin 17 (IL-17) is an essential proinflammatory T-cell derived cytokine with various biological actions. IL-17 was found to have a pivotal role in microbial host defense by interconnecting lymphoid and myeloid host defense. It also acts as a stimulatory hematopoietic cytokine by expanding myeloid progenitors and initiating proliferation of mature neutrophils. This article summarizes results to date on IL-17 research and discusses gene therapy based strategies that were employed to determine its biological functions and significance. A comprehensive working model for IL-17 is introduced.

Increase in expression of receptor activator of nuclear factor kappaB at sites of bone erosion correlates with progression of inflammation in evolving collagen-induced arthritis

OBJECTIVE

The receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL) pathway is critical in osteoclastogenesis and bone resorption and has been implicated in the process of focal bone erosion in arthritis. This study was undertaken to identify in vivo the hitherto-unknown origin and localization of RANK-expressing osteoclast precursor cells at sites of bone erosion in arthritis.

METHODS

DBA-1 mice were immunized with bovine type II collagen/Freund's complete adjuvant and were given an intraperitoneal booster injection of type II collagen on day 21. Arthritis was monitored visually, and joint pathology was examined histologically. RANK and RANKL expression were analyzed using specific immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining was performed. In addition, TRAP and cathepsin K messenger RNA expression were analyzed by in situ hybridization.

RESULTS

A marked increase in the number of cells expressing RANK correlated with the progression of synovial inflammation and clinical disease severity in evolving collagen-induced arthritis (CIA). Interestingly, RANK expression demonstrated a gradient pattern with increased numbers of RANK-positive cells within the synovial infiltrate in areas closer to periosteum and cortical bone. Cells expressing RANK included cells in synovial tissue, bone lining cells on the surface of trabecular bone at sites of erosion, and cells in periosteal areas adjacent to synovial inflammation. In areas where RANK-positive cells were abundant, TRAP-positive, multinucleated osteoclast-like cells were also present at sites of focal bone erosion, suggesting differentiation of synovially derived RANK-positive osteoclast precursor cells into osteoclasts. In addition, TRAP- and cathepsin K-double-positive osteoclast-like cells were detected on the synovial side of cortical bone at sites of early and advanced cortical bone erosion. Sites of RANK expression also correlated well with sites of RANKL expression, and there was a close correlation of the temporal expression of the receptor-ligand pair.

CONCLUSION

Cells expressing RANK increased in abundance with the progression of arthritis in evolving CIA, and sites of RANK-expressing cells correlated with sites of TRAP-positive, multinucleated osteoclast-like cells as well as with sites of RANKL expression. These data support the hypothesis that the RANK/RANKL pathway plays an important role in the process of bone erosion in CIA.

Gene therapy for rheumatoid arthritis

Rheumatoid arthritis (RA) is a severe autoimmune systemic disease. Chronic synovial inflammation results in destruction of the joints. No conventional treatment is efficient in RA. Gene therapy of RA targets mainly the players of inflammation or articular destruction: TNF-alpha or IL-1 blocking agents (such as anti-TNF-alpha monoclonal antibodies, soluble TNF-alpha receptor, type II soluble receptor of IL-1, IL-1 receptor antagonist), antiinflammatory cytokines (such as IL-4, IL-10, IL-1), and growth factors. In this polyarticular disease, the vector expressing the therapeutic protein can be administered as a local (intra-articular injection) or a systemic treatment (extra-articular injection). All the main vectors have been used in experimental models, including the more recent lentivirus and adeno-associated virus. Ex vivo gene transfer was performed with synovial cells, fibroblasts, T cells, dendritic cells, and different cells from xenogeneic origin. In vivo gene therapy is simpler, although a less controlled method. Clinical trials in human RA have started with ex vivo retrovirus-expressing IL-1 receptor antagonists and have demonstrated the feasibility of the strategy of gene therapy. The best target remains to be determined and extensive research has to be conducted in preclinical studies.

Osteoprotegerin reduces osteoclast numbers and prevents bone erosion in collagen-induced arthritis

Rheumatoid arthritis is characterized by progressive synovial inflammation and joint destruction. While matrix metalloproteinases (MMPs) are implicated in the erosion of unmineralized cartilage, bone destruction involves osteoclasts, the specialized cells that resorb calcified bone matrix. RANK ligand (RANKL) expressed by stromal cells and T cells, and its cognate receptor, RANK, were identified as a critical ligand-receptor pair for osteoclast differentiation and survival. A decoy receptor for RANKL, osteoprotegerin, (OPG) impinges on this system and regulates osteoclast numbers and activity. RANKL is also expressed in collagen-induced arthritis (CIA) in which focal collections of osteoclasts are prominent at sites of bone destruction. To determine the role of RANK signaling events in the effector phase of CIA, we investigated effects of Fc-osteoprotegerin fusion protein (Fc-OPG) in CIA. After induction of CIA in Dark Agouti rats, test animals were treated with or without Fc-OPG (3 mg/kg/day) subcutaneously for 5 days, beginning at the onset of disease. Paraffin-embedded joints were then analyzed histologically and the adjacent bone assessed by histomorphometry. Osteoclasts were identified using TRAP staining and expression of the mRNA for OPG and RANKL was identified by in situ hybridization. The results indicated that short-term Fc-OPG effectively prevented joint destruction, even though it had no impact on the inflammatory aspects of CIA. In arthritic joints, Fc-OPG depleted osteoclast numbers by over 75% and diminished bone erosion scores by over 60%. Although cartilage loss was also reduced by Fc-OPG, the effects on cartilage were less striking than those on bone. In arthritic joints OPG mRNA was highly expressed and co-localized with RANK ligand, and treatment with Fc-OPG did not affect the expression of endogenous RANKL or OPG mRNA. These data demonstrate that short term Fc-OPG treatment has powerful anti-erosive effects, principally on bone, even though synovitis is not affected. These findings indicate the potential utility of disrupting RANK signaling to preserve skeletal integrity in inflammatory arthritis.

C3-Tat/HIV-regulated intraarticular human interleukin-1 receptor antagonist gene therapy results in efficient inhibition of collagen-induced arthritis superior to cytomegalovirus-regulated expression of the same transgene

OBJECTIVE

To achieve disease-inducible expression of recombinant antiinflammatory proteins in order to allow autoregulation of drug dose by natural homeostatic mechanisms.

METHODS

We compared the inducible 2-component expression system (C3-human immunodeficiency virus/transactivator of transcription [C3-Tat/HIV]) with the constitutive cytomegalovirus (CMV) promoter in the polyarticular collagen-induced arthritis (CIA) model in mice. DBA/1 mice were immunized with bovine type II collagen and were given boosters on day 21. On day 22, mice were injected intraarticularly with the adenoviral vectors AdCMVLuc, AdCMVhIL-1Ra, AdC3-Tat/HIV-Luc, or AdC3-Tat/HIV-hIL-1Ra. The injected knee joints and hind paws were then scored for signs of arthritis, and knee joint histology was compared.

RESULTS

The CMV-driven interleukin-1 receptor antagonist (IL-1Ra) expression resulted in a high constitutive expression and amelioration of CIA. C3-Tat/HIV-driven IL-1Ra expression could be detected only on days 24, 29, and 35. Fourteen days after injection of the vectors, CIA was significantly better inhibited by the C3-Tat/HIV-driven IL-1Ra expression compared with the CMV-driven IL-1Ra expression. Moreover, prevention of CIA in the knee joints also prevented CIA in the untreated hind paws.

CONCLUSION

Our data demonstrate for the first time the feasibility of an inducible expression system for local production of IL-1Ra for treatment of arthritis in the CIA model.

Lessons from animal models of arthritis

There is increasing thought that autoantibodies to systemic self-antigens may provide a principal effector mechanism for the initiation and propagation of joint inflammation. The recent identification of arthritis transfer with antibodies to the self-antigen glucose-6-phosphate isomerase has boosted this interest. Fc receptor involvement in arthritis has been evaluated, identifying pro-inflammatory and inhibitory Fc gamma receptor subtypes, and demonstrating a link between Fc gamma receptor expression, cytokine production, cartilage destruction, and mouse strain susceptibility to immune complex arthritis. Further proof of a key role of interleukin (IL)-1 in arthritis was provided by the occurrence of spontaneous arthritis in IL-1 receptor antagonist knockout mice and elicitation of full-blown arthritis in tumor necrosis factor (TNF)-deficient mice. IL-18 (part of the IL-1 family) is a crucial upstream cytokine that, with IL-12, induces IL-1 and TNF and promotes arthritis and T-cell differentiation. IL-18 neutralization improved arthritis outcome, but its central role in host defense against bacterial infections may complicate therapeutic IL-18 targeting. T helper 1 (Th1) cells may aggravate arthritis and joint destruction through the production of IL-17, which shows joint destructive potential independent of IL-1. Studies have also focused on the control of receptor activator of nuclear factor kappaB ligand, modulation with IL-4, and regulation of downstream mediators in tissue destruction. Gene therapeutic approaches proved efficacious and will provide future ways to control arthritis.

Adenoviral transfer of murine oncostatin M elicits periosteal bone apposition in knee joints of mice, despite synovial inflammation and up-regulated expression of interleukin-6 and receptor activator of nuclear factor-kappa B ligand

Oncostatin M (OSM) has been described as a bone-remodeling factor either stimulating osteoblast activity or osteoclast formation in vitro. To elucidate the in vivo effect of OSM on bone remodeling, we injected an adenoviral vector encoding murine OSM in knee joints of mice. OSM strongly induced interleukin (IL)-6 gene expression, a known mediator of osteoclast development. We investigated the OSM effect in wild-type and IL-6-deficient mice and found a similar degree of OSM-induced joint inflammation. Within the first week of inflammation, the periosteum along the femur and tibia increased in cell number and stained positive for the osteoblast marker alkaline phosphatase. At these sites bone apposition occurred in both strains as demonstrated by Goldner and Von Kossa staining. In vitro OSM enhanced the effect of bone morphogenetic protein-2 on osteoblast differentiation. Immunohistochemistry demonstrated expression of receptor activator of nuclear factor-kappa B ligand (RANKL) and its receptor, receptor activator of nuclear factor-kappa B (RANK), in the periosteum but osteoclasts were not detected at sites of bone apposition. Induced mRNA expression for the receptor activator of nuclear factor-kappa B ligand inhibitor osteoprotegerin probably controlled osteoclast development during OSM overexpression. Our results show that OSM favors bone apposition at periosteal sites instead of resorption in vivo. This effect was not dependent on or inhibited by IL-6.

Local interleukin-12 gene transfer promotes conversion of an acute arthritis to a chronic destructive arthritis

OBJECTIVE

To determine whether local overexpression of interleukin-12 (IL-12), a pleiotropic cytokine that promotes the development of naive T cells into Th1 cells, could aggravate murine streptococcal cell wall (SCW)-induced arthritis, a model of acute arthritis.

METHODS

C57BL/6 mice were injected intraarticularly with saline or with 10(7) plaque-forming units of control vector (Ad5del70-3) or IL-12 vector (AdmIL-12.1) into the right knee joint 1 day before intraarticular injection of 25 microg of SCW fragments. The development of joint swelling, changes in chondrocyte proteoglycan (PG) synthesis, and joint destruction were examined thereafter.

RESULTS

In normal joints, high levels of IL-12 (20 ng/ml on day 1) could be detected after application of the AdmIL-12.1 vector. After 14 days, expression of IL-12 was still found locally, but IL-12 alone did not induce protracted inflammation. Local expression of IL-12, in combination with SCW, markedly aggravated SCW-induced arthritis, as determined by enhanced joint swelling and prolonged inhibition of chondrocyte PG synthesis. Histologic examination on day 21 showed a chronic inflammatory process, with persistent cartilage PG depletion, cartilage erosion, and VDIPEN neoepitope expression (indicative of metalloproteinase activation). The mixture of IL-12 with SCW fragments did not lead to a chronic destructive process in mice deficient for recombination-activating gene 2, indicating the involvement of lymphocytes. In addition, systemic flare of smoldering SCW arthritis, produced by intravenous injection of SCW fragments, was only seen in the AdmIL-12/SCW group.

CONCLUSION

These results indicate that local overexpression of IL-12 promotes conversion of an acute arthritis to a chronic destructive immune-mediated process, which is more susceptible to flares.

Association between IL-4 genotype and IL-4 production in the Japanese population

We have identified that there are only two IL-4 gene haplotypes (I and II) in the Japanese population. There are significant differences among three genotypes (I/I, I/II and II/II) in the IL-4 producing proportion of peripheral Th cells using intracellular cytokine detection assay. These results make it likely that IL-4 genotype could influence the type of immune response.

Involvement of receptor activator of NFkappaB ligand and tumor necrosis factor-alpha in bone destruction in rheumatoid arthritis

Bone loss represents a major unsolved problem in rheumatoid arthritis (RA). The skeletal complications of RA consist of focal bone erosions and periarticular osteoporosis at sites of active inflammation, and generalized bone loss with reduced bone mass. New evidence indicates that osteoclasts are key mediators of all forms of bone loss in RA. TNF-alpha is one of the most potent osteoclastogenic cytokines produced in inflammation and is pivotal in the pathogenesis of RA. Production of tumor necrosis factor-alpha (TNF-alpha) and other proinflammatory cytokines in RA is largely CD4(+) T-cell dependent and mostly a result of interferon-gamma (IFN-gamma) secretion. Synovial T cells contribute to synovitis by secreting IFN-gamma and interleukin (IL)-17 as well as directly interacting with macrophages and fibroblasts through cell-to-cell contact mechanisms. Activated synovial T cells express both membrane-bound and soluble forms of receptor activator of NF-kappaB ligand (RANKL). In rheumatoid synovium, fibroblasts also provide an abundant source of RANKL. Furthermore, TNF-alpha and IL-1 target stromal-osteoblastic cells to increase IL-6, IL-11, and parathyroid hormone-related protein (PTHrP) production as well as expression of RANKL. In the presence of permissive levels of RANKL, TNF-alpha acts directly to stimulate osteoclast differentiation of macrophages and myeloid progenitor cells. In addition, TNF-alpha induces IL-1 release by synovial fibroblasts and macrophages, and IL-1, together with RANKL, is a major survival and activation signal for nascent osteoclasts. Consequently, TNF-alpha and IL-1, acting in concert with RANKL, can powerfully promote osteoclast recruitment, activation, and osteolysis in RA. The most convincing support for this hypothesis has come from in vivo studies of animal models. Protection of bone in the presence of continued inflammation in arthritic rats treated with osteoprotegerin (OPG) supports the concept that osteoclasts mediate bone loss, providing further evidence that OPG protects bone integrity by downregulating osteoclastogenesis and promoting osteoclast apoptosis. Modulation of the RANKL/OPG equilibrium in arthritis may provide additional skeletal benefits, such as chondroprotection. The nexus between T-cell activation, TNF-alpha overproduction, and the RANKL/OPG/RANK ligand-receptor system points to a unifying paradigm for the entire spectrum of skeletal pathology in RA. Strategies that address osteoclastic bone resorption will represent an important new facet of therapy for RA.

Suppressive effects of interleukin-4 and interleukin-10 on the production of proinflammatory cytokines induced by titanium-alloy particles

We investigated the effects of two anti-inflammatory cytokines, interleukin (IL)-4 and IL-10, on the production of two proinflammatory cytokines, tumor necrosis factor (TNF)-alpha and IL-6, induced by titanium-alloy (Ti6Al4V) particles. Human monocytes isolated from the peripheral blood of six healthy donors were cultured and exposed to retrieved titanium-alloy particles, together with IL-4 or IL-10. Enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction showed that both IL-4 and IL-10 significantly reduced the production of TNF-alpha and IL-6. The level of TNF-alpha decreased by 74% with IL-4 and 56% with IL-10. The level of IL-6 decreased by 55% with IL-4 and by 66% with IL-10. IL-4 had more consistent suppressive effect on TNF-alpha production. The results from this study provide in vitro evidence of the possible utility of IL-4 and IL-10 in suppression of particle-induced activation of macrophages.

The molecular mechanism of osteoclastogenesis in rheumatoid arthritis

Bone-resorbing osteoclasts are formed from hemopoietic cells of the monocyte-macrophage lineage under the control of bone-forming osteoblasts. We have cloned an osteoblast-derived factor essential for osteoclastogenesis, the receptor activator of NF-kappaB ligand (RANKL). Synovial fibroblasts and activated T lymphocytes from patients with rheumatoid arthritis also express RANKL, which appears to trigger bone destruction in rheumatoid arthritis as well. Recent studies have shown that T lymphocytes produce cytokines other than RANKL such as IL-17, granulocyte-macrophage colony-stimulating factor and IFN-gamma, which have powerful regulatory effects on osteoclastogenesis. The possible roles of RANKL and other cytokines produced by T lymphocytes in bone destruction are described.