Interferon‐γ regulates susceptibility to collagen‐induced arthritis through suppression of interleukin‐17

Objective

The enhanced expression of experimental arthritis in the absence of interferon‐γ (IFNγ) suggests that IFNγ suppresses arthritis. Interleukin‐17 (IL‐17) is a pivotal T cell cytokine in arthritis, and in vitro studies have indicated that IFNγ suppresses IL‐17 production. We undertook this study to test the hypothesis that resistance to collagen‐induced arthritis (CIA) in C57BL/6 (B6) mice is regulated by IFNγ‐mediated suppression of IL‐17.

Methods

Wild‐type (WT) B6 mice, IFNγ‐knockout (KO) B6 mice, and DBA/1 mice were immunized with type II collagen (CII) in Freund's complete adjuvant (CFA). Lymphocytes from immunized mice were analyzed for cytokine production ex vivo by intracellular staining or restimulation with CII and enzyme‐linked immunosorbent assays. In vivo blockade of IL‐17 was achieved with an anti–IL‐17 monoclonal antibody (mAb).

Results

CII restimulation of T cells from CII/CFA‐immunized mice resulted in an ∼5‐fold increase in IL‐17 production in IFNγ‐KO B6 mice compared with WT B6 mice. Neutralization of IFNγ increased IL‐17 production in WT B6 mice, and neutralization of IL‐4 had a synergistic effect. Interestingly, the prototypical CIA‐susceptible strain DBA/1 also demonstrated a high IL‐17 and a low IFNγ cytokine profile compared with WT B6 mice. Administration of the anti–IL‐17 mAb attenuated arthritis in DBA/1 mice and almost completely prevented expression of arthritis in IFNγ‐KO B6 mice.

Conclusion

These results indicate that sensitivity of IFNγ‐deficient B6 mice to CIA is associated with high IL‐17 production and that this cytokine is required for expression of arthritis in this strain.

     

Role of interleukin‐18 in experimental group B streptococcal arthritis

Objective

To assess the role of interleukin‐18 (IL‐18) in the evolution of septic arthritis induced by group B streptococci (GBS) in mice.

Methods

CD1 mice were inoculated intravenously with 8 × 10⁶ colony‐forming units (CFU) of type IV GBS (strain 1/82), and administered intraperitoneally 1 hour before infection with anti–IL‐18 monoclonal antibodies (0.25 mg/mouse). In a subsequent set of experiments, mice infected with a suboptimal arthritogenic dose of GBS (4 × 10⁶ CFU/mouse) were administered different doses of recombinant IL‐18 for 4 days, starting 1 hour after infection. Mortality, evolution of arthritis, bacterial clearance, joint histopathology, and cytokine production were examined in infected mice that did or did not receive treatment with anti–IL‐18 antibodies or IL‐18.

Results

IL‐18 was produced during GBS infection. Neutralization of IL‐18 resulted in a decrease in mortality rates, and in the incidence and severity of arthritis. Amelioration of arthritis was accompanied by a dramatic reduction in local IL‐1β, IL‐6, macrophage inflammatory protein 1α (MIP‐1α) and MIP‐2 production, and reduced bacterial burden. Administration of exogenous IL‐18 resulted in increased mortality rates and increased incidence and severity of GBS arthritis, concomitant with a higher number of GBS and increased levels of IL‐6, IL‐1β, MIP‐1β, and MIP‐2 production in the joints.

Conclusion

The present study indicated some involvement of IL‐18 in the pathogenesis of GBS‐induced arthritis. The role of IL‐18 in joint pathology is shown by a regulatory effect on inflammatory mediator levels and local cell influx. Thus, IL‐18 should be regarded as a potential therapeutic target in GBS infection and arthritis.

     

Acute CD4+ T lymphocyte–dependent interleukin‐1–driven arthritis selectively requires interleukin‐2 and interleukin‐4, joint macrophages,granulocyte–macrophage colony‐stimulating factor,interleukin‐6, and leukemia inhibitory factor

Objective

To further investigate the effects of interleukin‐1 (IL‐1) in immune‐mediated joint inflammation, we examined the role of IL‐2, Th1 interferon‐γ (IFNγ), and Th2 (IL‐4) cytokines, joint macrophages, and macrophage‐derived cytokines (IL‐12 p40, IL‐6, leukemia inhibitory factor [LIF], oncostatin M [OSM], and granulocyte–macrophage colony‐stimulating factor [GM‐CSF]) in a CD4+ T lymphocyte–dependent model of acute arthritis.

Methods

Methylated bovine serum albumin (mBSA)/IL‐1–induced arthritis was elicited in wild‐type, gene‐knockout, and monoclonal antibody–treated mice. Synovial lining macrophages were selectively depleted by intraarticular injection of clodronate liposomes prior to disease induction. The severity of arthritis was assessed histologically.

Results

Mice deficient in IL‐2 were almost completely protected from arthritis, and neutralization of IL‐4 reduced the severity of disease. In contrast, arthritis severity and resolution appeared to be independent of IFNγ. Synovial lining macrophage depletion markedly reduced arthritis severity. IL‐6 or LIF deficiency was only modestly protective, although as previously reported, GM‐CSF deficiency conferred profound disease resistance. IL‐12 p40–deficient mice (which lack IL‐12 and IL‐23) and OSM receptor–deficient mice were susceptible to mBSA/IL‐1–induced arthritis.

Conclusion

Acute mBSA/IL‐1–induced arthritis is dependent on IL‐2 and IL‐4, but not IFNγ. In vivo, the Th1/Th2 paradigm may be distorted by the presence of macrophage‐derived cytokines such as IL‐1. Synovial lining macrophages are essential in mBSA/IL‐1–induced arthritis. However, the requirement for macrophage‐derived cytokines is selective; that is, IL‐6, LIF, and especially GM‐CSF are necessary, but IL‐12, IL‐23, and OSM are dispensable. IL‐1 may therefore influence both adaptive and innate immune mechanisms in acute inflammatory arthritis.

     

Blockade of the interleukin‐21/interleukin‐21 receptor pathway ameliorates disease in animal models of rheumatoid arthritis

Objective

Interleukin‐21 (IL‐21) is a T cell–derived cytokine that modulates T cell, B cell, and natural killer cell responses. In this study, the effects of blocking IL‐21 were examined in 2 rodent models of rheumatoid arthritis (RA) to determine whether IL‐21 contributes to their pathologic processes.

Methods

DBA/1 mice were immunized with bovine type II collagen and then treated with murine IL‐21 receptor Fc fusion protein (IL‐21R.Fc), which was initiated after the onset of arthritis symptoms in 10% of the cohort. The mice were assessed 3 times per week for signs of disease, including histologic features as well as serum cytokine, Ig, and cytokine messenger RNA (mRNA) levels in the paws. In a separate experiment, Lewis rats were immunized with Freund's complete adjuvant followed by administration of IL‐21R.Fc at the peak of inflammation in the joints. Rats were assessed daily for histologic features and for scoring of arthritis severity. In addition, the effects of IL‐21R.Fc on the production of interferon‐γ (IFNγ) by T cells were examined.

Results

Treatment of DBA/1 mice with IL‐21R.Fc reduced the clinical and histologic signs of collagen‐induced arthritis. Nonspecific IgG1 levels were decreased in response to treatment. The levels of IL‐6 mRNA in the paws and the serum IL‐6 levels were decreased after treatment with IL‐21R.Fc. IFNγ mRNA levels were increased in the paws, and the addition of IL‐21R.Fc to collagen‐activated lymph node cultures enhanced the levels of IFNγ. Collagen‐specific spleen cell responses in IL‐21R.Fc–treated mice were observed as reduced levels of IFNγ and increased levels of IL‐6. Treatment of Lewis rats with IL‐21R.Fc after induction of adjuvant‐induced arthritis resulted in reversal of disease signs and improvements in histologic parameters.

Conclusion

These findings demonstrate a pathogenic role for IL‐21 in animal models of RA, and support consideration of IL‐21 as a therapeutic target in human 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.

     

Interleukin‐17 as a molecular target in immune‐mediated arthritis: Immunoregulatory properties of genetically modified murine dendritic cells that secrete interleukin‐4

Objective

Our previous studies have shown that murine dendritic cells (DCs) genetically modified to express interleukin‐4 (IL‐4) reduce the incidence and severity of murine collagen‐induced arthritis. The present studies were performed to assess the immunoregulatory mechanisms underlying this response, by assessing the effects of IL‐4 DCs on cytokine production by subsets of T helper cells.

Methods

Male DBA mice ages 6–8 weeks old were immunized with type II collagen. Splenic T cells obtained during the initiation phase and the end stage of arthritis were cultured with IL‐4 DCs or untransduced DCs in the presence of collagen rechallenge. Interferon‐γ (IFNγ) and IL‐17 responses were measured. Antibodies to IL‐4, IL‐12, and IL‐23, and recombinant IL‐4, IL‐12, and IL‐23 were used to further study the regulation of T cell cytokine production by IL‐4 DCs.

Results

Splenic T cells obtained during the initiation phase of arthritis produced less IL‐17 when cultured in the presence of IL‐4 DCs, despite their production of increased quantities of other proinflammatory cytokines (IFNγ and tumor necrosis factor). T cell IL‐17 production after collagen rechallenge was not inhibited by a lack of IL‐23, since IL‐4–mediated suppression of IL‐17 was not reconstituted by IL‐23, an otherwise potent inducer of IL‐17 production by T cells. Although IL‐4 DCs can produce increased quantities of IL‐12 and IFNγ, suppression of IL‐17 production by IL‐4 DCs was independent of both. While IL‐17 production by T cells obtained during the initiation phase of arthritis was regulated by IL‐4 DCs, IL‐17 production by T cells obtained during end‐stage arthritis was not altered.

Conclusion

Our data suggest that IL‐4 DCs exert a therapeutic effect on collagen‐induced arthritis by targeting IL‐17. IL‐17 suppression by IL‐4 DCs is robust and is not reversed by IL‐23. Timing might be important in IL‐17–targeted therapy, since IL‐17 production by T cells obtained during end‐stage arthritis did not respond to suppression by IL‐4 DCs.

     

Dysregulation of interleukin‐10–dependent gene expression in rheumatoid arthritis synovial macrophages

Objective

The inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin‐1 (IL‐1) are produced by activated macrophages, are key mediators of pathogenesis, and are validated therapeutic targets in rheumatoid arthritis (RA) and seronegative spondylarthritis (SpA). IL‐10 is a potent antiinflammatory cytokine that suppresses macrophage TNFα and IL‐1 production, yet is not effective in suppressing inflammatory arthritis. To gain insight into IL‐10 responses in inflammatory arthritis, we used microarray analysis to determine the patterns of IL‐10–inducible gene expression in freshly isolated RA and seronegative SpA synovial macrophages.

Methods

Macrophages from the synovial fluid of 5 patients with RA and 3 with seronegative SpA (2 with psoriatic arthritis and 1 with ankylosing spondylitis) were isolated by positive selection and stimulated ex vivo with IL‐10 or interferon‐γ (IFNγ). Gene expression was analyzed using Affymetrix microarrays and protocols. Real‐time polymerase chain reaction was used to confirm changes in gene expression.

Results

The number of genes induced by IL‐10 in arthritic macrophages was markedly smaller than that induced in control macrophages, and the strength of induction was lower in arthritic macrophages for most genes. The residual response of arthritic macrophages to IL‐10 stimulation was qualitatively altered, such that IL‐10 preferentially increased expression of IFNγ‐inducible genes. In contrast, arthritic macrophages expressed many IFNγ‐inducible genes prior to stimulation, and their response to IFNγ remained mostly intact.

Conclusion

These results demonstrate that IL‐10 responses are dysregulated in RA synovial macrophages. An altered biologic response to IL‐10, with attenuation of its antiinflammatory function and a concomitant retention of IFNγ‐like activating functions, provides a basis for the lack of efficacy of IL‐10 in suppressing inflammatory arthritis.

     

Important role of interleukin‐3 in the early phase of collagen‐induced arthritis

Objective

Activation of basophils contributes to memory immune responses and results in exacerbation of collagen‐induced arthritis (CIA). We undertook the present study to analyze the production and biologic effects of interleukin‐3 (IL‐3), a strong activator of basophils, in CIA.

Methods

Arthritis was induced by immunization with type II collagen. Mice were treated with blocking monoclonal antibodies against IL‐3 or with recombinant IL‐3. Clinical scoring, histologic analysis, fluorescence‐activated cell sorter analysis, enzyme‐linked immunosorbent assay, and cell culturing were performed to assess disease activity and IL‐3 production.

Results

IL‐3 was produced in large quantities by collagen‐specific CD4+ T cells in the spleen and was present in the synovial tissue during onset of arthritis, but was down‐regulated in paws with severe inflammation. Blockade of IL‐3 during the time of arthritis onset resulted in profound improvement of the disease, with reductions in synovial leukocyte and cytokine levels, peripheral blood basophil levels, and anticollagen antibody titers. Blockade of IL‐3 during the late phase of arthritis had no beneficial effect. Administration of recombinant IL‐3 during onset of arthritis induced a marked exacerbation of the disease, with increased peripheral blood basophil and plasma IL‐6 levels and increased titers of anticollagen antibody. In studies of the regulation of IL‐3 expression in CD4+ T cells, IL‐6 and IL‐4 suppressed the release of IL‐3 by activated CD4+ T cells, whereas lipopolysaccharide and CpG DNA up‐regulated IL‐3 secretion in activated CD4+ T cells by acting on costimulatory cells.

Conclusion

Taken together, the present results demonstrate for the first time that IL‐3 has an important role in the early phase of CIA.

     

T cell dependence of chronic destructive murine arthritis induced by repeated local activation of toll‐like receptor–driven pathways: Crucial role of both interleukin‐1β and interleukin‐17

Objective

The pathogenesis of rheumatoid arthritis is often linked to bacterial infections. The present study was undertaken to develop a mouse model of chronic destructive arthritis induced by repeated intraarticular (IA) exposure to bacterial cell wall fragments and to investigate the cytokine dependence of this model.

Methods

Mice that were deficient in various cytokines were injected IA with cell wall fragments of Streptococcus pyogenes on days 0, 7, 14, and 21. The development of chronic destructive arthritis was compared between groups of mice lacking different cytokines, to assess which cytokines were crucial for development of chronic destructive arthritis.

Results

Repeated exposure of a joint to S pyogenes cell wall fragments resulted in the development of chronic destructive arthritis. In mice deficient in recombination‐activating gene 2, streptococcal cell wall (SCW)–directed T cell reactivity was found and chronic arthritis did not develop, implicating T cells in the generation of chronic SCW‐induced arthritis. Interleukin‐17 (IL‐17) receptor–deficient mice showed a reduction of joint destruction in the chronic stage, implicating a detrimental role of the recently discovered IL‐17–producing T helper cells (Th17 cells). IL‐23 expression was apparent during the late stages of arthritis. Joint swelling was no longer dependent on tumor necrosis factor α (TNFα) after the last flare, and pronounced cartilage damage was found after 28 days in TNFα‐deficient mice. In contrast, IL‐1β–deficient mice were fully protected against joint swelling and cartilage and bone destruction during the late stages of disease.

Conclusion

These findings indicate that the TNFα dependence of arthritis is lost during the erosive stage, when Th17 cells become crucial. IL‐1β dependence remains strong, consistent with its pivotal role in the generation of Th17 cells.

     

Endogenous interleukin‐6, but not tumor necrosis factor α, contributes to the development of toll‐like receptor 4/myeloid differentiation factor 88–mediated acute arthritis in mice

Objective

To generate a mouse model of reactive arthritis (ReA), an aseptic synovitis that develops in joints distant from the primary bacterial infection site, to examine roles for Toll‐like receptors (TLRs) that recognize bacterial components involved in the development of this arthritis, and to identify the cytokine(s) relevant to this arthritis.

Methods

Mice were treated with cell wall extract from Escherichia coli (ECW) gram‐negative bacterium by injection into the footpads. Seven days later, the mice were challenged with lipopolysaccharide (LPS), a TLR‐4 ligand, which was injected into the knee joint cavity. To investigate the cytokine(s) involved in this arthritis, mice deficient in various arthritogenic cytokines, such as interleukin‐6 (IL‐6), IL‐12, IL‐18, interferon‐γ, and tumor necrosis factor α (TNFα), were sequentially treated with ECW and LPS.

Results

ECW‐primed mice manifested acute severe arthritis after intraarticular challenge with ECW or LPS, while unprimed mice exhibited modest changes after these challenges. Mutant mice lacking functional TLR‐4 or myeloid differentiation factor 88 (MyD88), an adaptor molecule of TLR‐4 signaling, were resistant to this arthritis. Although both TNFα and IL‐6 were equally expressed in the joint after LPS challenge, Il6^−/− mice, but not Tnf^−/− mice, were resistant to ECW/LPS‐induced arthritis.

Conclusion

Our present results clearly indicate the importance of priming with ECW and the requirement of TLR‐4/MyD88–mediated IL‐6, but not TNFα, for the development of ECW/LPS‐induced arthritis. LPS‐induced IL‐6, in the absence of TNFα, mediates LPS‐induced arthritis. These results suggest that IL‐6 is a rational target for therapeutic regimens for inflammatory arthritis, including ReA and rheumatoid arthritis.

     

Induction of cartilage damage by overexpression of T cell interleukin‐17A in experimental arthritis in mice deficient in interleukin‐1

Objective

To examine the capacity of T cell interleukin‐17A (IL‐17A; referred to hereinafter as IL‐17) to induce cartilage damage during experimental arthritis in the absence of IL‐1.

Methods

Local IL‐17 gene transfer was performed in the knee joint of IL‐1–deficient mice and wild‐type controls during streptococcal cell wall (SCW)–induced arthritis. Knee joints were isolated at various time points for histologic analysis of cartilage proteoglycan (PG) depletion. Expression of messenger RNA for inducible nitric oxide synthase, matrix metalloproteinases (MMPs) 3, 9, and 13, and ADAMTS‐4 was determined by quantitative polymerase chain reaction analysis. VDIPEN staining was analyzed to study MMP‐mediated cartilage damage. In addition, systemic anti–IL‐1α/β antibody treatment was performed in mice immunized with type II collagen and injected locally with an adenoviral vector expressing IL‐17 or with control adenovirus. Knee joints were isolated and analyzed for cartilage PG depletion, chondrocyte death, and cartilage surface erosion.

Results

During SCW‐induced arthritis, local T cell IL‐17 gene transfer turned this acute, macrophage‐driven joint inflammation into a severe, chronic arthritis accompanied by aggravated cartilage damage. Of high interest, the IL‐1 dependency of cartilage PG depletion was fully abrogated when IL‐17 was locally overexpressed in the joint. Moreover, local IL‐17 gene transfer increased MMP expression without the need for IL‐1, although IL‐1 remained essential for part of the cartilage VDIPEN expression. Furthermore, when IL‐17 was overexpressed in the knee joints of mice with collagen‐induced arthritis, anti–IL‐1 treatment did not reduce the degree of chondrocyte death or cartilage surface erosion.

Conclusion

These data show the capacity of IL‐17 to replace the catabolic function of IL‐1 in cartilage damage during experimental arthritis.

     

Immunoregulatory effects of allogeneic mixed chimerism induced by nonmyeloablative bone marrow transplantation on chronic inflammatory arthritis and autoimmunity in interleukin‐1 receptor antagonist–deficient mice

Objective

To investigate the immunoregulatory effects of allogeneic mixed chimerism induced by T cell–depleted, nonmyeloablative bone marrow transplantation (BMT) on chronic inflammatory arthritis and autoimmunity in mice deficient in interleukin‐1 receptor antagonist (IL‐1Ra).

Methods

IL‐1Ra^−/− mice (H‐2K^d) were treated with antibody to asialoganglioside G_M1 (anti–natural killer cell), total body irradiation (500 cGy), and T cell–depleted, nonmyeloablative BMT derived from C57BL/6 mice (H‐2K^b). Engraftment and chimerism were evaluated in peripheral blood, lymph nodes, and spleen by multicolor flow cytometry. The severity of arthritis was evaluated by clinical scoring and histopathologic assessment. Levels of IgG1 and IgG2a subtypes of anti–type II collagen (anti‐CII) antibodies were measured in serum samples. After T cells were stimulated with CII, ovalbumin, and phytohemagglutinin, T cell proliferative responses and levels of cytokine production (interferon‐γ [IFNγ], tumor necrosis factor α [TNFα], interleukin‐10 [IL‐10], and IL‐17) were assayed in culture supernatants.

Results

All IL‐1Ra^−/− mice receiving BMT showed marked improvement in arthritis within 3 weeks, as well as successful induction of mixed chimerism. These mice showed higher levels of IgG1, and lower levels of IgG2a anti‐CII antibodies and weaker T cell proliferative responses than did mice in the control groups (either no treatment or conditioning alone without bone marrow rescue). In mixed chimeras, the levels of IFNγ, TNFα, and IL‐17 produced from CII‐stimulated T cells were significantly suppressed and IL‐10 production was significantly higher as compared with controls.

Conclusion

The introduction of allogeneic mixed chimerism showed a strong immunoregulatory potential to correct established chronic inflammatory arthritis and autoimmunity originating from a dysregulated proinflammatory cytokine network.

     

Expression of Toll‐like receptors 2 and 4 in rheumatoid synovial tissue and regulation by proinflammatory cytokines interleukin‐12 and interleukin‐18 via interferon‐γ

Objective

To study the expression of Toll‐like receptor 2 (TLR‐2) and TLR‐4 and its association with proinflammatory cytokines in synovial tissue from patients with rheumatoid arthritis (RA), osteoarthritis (OA), and healthy individuals.

Methods

Synovial tissue specimens from 29 RA patients were stained for TLR‐2, TLR‐4, and proinflammatory cytokines (interleukin‐1β [IL‐1β], IL‐12, IL‐17, IL‐18, and tumor necrosis factor α [TNFα]). The expression of TLR‐2, TLR‐4, and cytokines as well as the degree of inflammation in synovial tissue were compared between patients with RA, patients with OA (n = 5), and healthy individuals (n = 3). Peripheral blood mononuclear cells (PBMCs) were incubated with IL‐12 and IL‐18, and TLR expression was assessed using fluorescence‐activated cell sorter analysis. Production of TNFα and IL‐6 was measured using Luminex bead array technology.

Results

In RA synovial tissue, the expression of TLR‐2 was slightly higher than that of TLR‐4. Interestingly, both TLR‐2 and TLR‐4 were expressed at higher levels in moderately inflamed synovium, as compared with synovial tissue with no or severe inflammation. TLR expression in both the lining and the sublining was associated with the presence of IL‐12 and IL‐18, but no other cytokines, in the lining. The expression of both TLRs was low in synovial tissue from OA patients and healthy donors. Stimulation of PBMCs with IL‐12 and IL‐18 resulted in increased expression of both TLR‐2 and TLR‐4; this could be blocked with anti–interferon‐γ (anti‐IFNγ) antibodies, suggesting a role for IFNγ. Lipopolysaccharide‐ or lipoteichoic acid–mediated triggering of PBMCs incubated with IL‐12/IL‐18 or IFNγ led to an increased production of both TNFα and IL‐6, indicating the functionality of TLR‐2 and TLR‐4.

Conclusion

TLR‐2 and TLR‐4 are expressed in synovial tissue of patients with clinically active disease and are associated with the levels of both IL‐12 and IL‐18. The synergistic effect of IL‐12 and IL‐18 on T cell IFNγ production seems to regulate expression of TLR‐2 and TLR‐4 in the synovial tissue of RA patients.

     

Interferon‐γ protects against the development of structural damage in experimental arthritis by regulating polymorphonuclear neutrophil influx into diseased joints

Objective

Local interaction between soluble mediators within the inflamed synovium is a key factor that governs the pathologic outcome of inflammatory arthritides. Our aim was to investigate the interplay between the Th1 lymphokine interferon‐γ (IFNγ) and pivotal cytokines that drive rheumatoid arthritis (RA) pathology (interleukin‐1β [IL‐1β] and tumor necrosis factor α [TNFα]) in modulating inflammation and arthritis in vitro and in vivo.

Methods

Monarticular antigen‐induced arthritis (AIA) was initiated in IFNγ‐deficient (IFNγ^−/−) mice and age‐matched wild‐type (IFNγ^+/+) mice. Joint swelling was measured and histologic analysis was performed in order to assess changes in both inflammatory and degenerative parameters in vivo. In vitro, the influence of IFNγ in regulating IL‐1β– and TNFα‐driven CXCL8 and CCL2 production was quantified by enzyme‐linked immunosorbent assay.

Results

In murine AIA, both inflammatory and degenerative arthritis parameters were significantly exacerbated in the absence of IFNγ. IFNγ appeared to be a crucial factor in regulating CXCR2+ neutrophil influx in the joint. In in vitro studies using RA fibroblast‐like synoviocytes, IFNγ modulated both IL‐1β– and TNFα‐driven chemokine synthesis, resulting in the down‐regulation of CXCL8 production.

Conclusion

IFNγ exerts antiinflammatory, chondroprotective, and antiosteoclastogenic effects in murine AIA through a mechanism that involves the regulation of chemokine synthesis and local neutrophil recruitment. These studies suggest a potential therapeutic role of modulating IFNγ signaling in the treatment of inflammatory arthritides.