Arthritogenic T cell epitope in glucose-6-phosphate isomerase-induced arthritis. Arthritis Res Ther. 2008;10:R130. [PMID: 18992137 PMCID: PMC2656230 DOI: 10.1186/ar2545]

A subset of type-II collagen-binding antibodies prevents experimental arthritis by inhibiting FCGR3 signaling in neutrophils

Rheumatoid arthritis (RA) involves several classes of pathogenic autoantibodies, some of which react with type-II collagen (COL2) in articular cartilage. We previously described a subset of COL2 antibodies targeting the F4 epitope (ERGLKGHRGFT) that could be regulatory. Here, using phage display, we developed recombinant antibodies against this epitope and examined the underlying mechanism of action. One of these antibodies, R69-4, protected against cartilage antibody- and collagen-induced arthritis in mice, but not autoimmune disease models independent of arthritogenic autoantibodies. R69-4 was further shown to cross-react with a large range of proteins within the inflamed synovial fluid, such as the complement protein C1q. Complexed R69-4 inhibited neutrophil FCGR3 signaling, thereby impairing downstream IL-1β secretion and neutrophil self-orchestrated recruitment. Likewise, human isotypes of R69-4 protected against arthritis with comparable efficiency. We conclude that R69-4 abrogates autoantibody-mediated arthritis mainly by hindering FCGR3 signaling, highlighting its potential clinical utility in acute RA.

A subset of antibodies targeting citrullinated proteins confers protection from rheumatoid arthritis

Although elevated levels of anti-citrullinated protein antibodies (ACPAs) are a hallmark of rheumatoid arthritis (RA), the in vivo functions of these antibodies remain unclear. Here, we have expressed monoclonal ACPAs derived from patients with RA, and analyzed their functions in mice, as well as their specificities. None of the ACPAs showed arthritogenicity nor induced pain-associated behavior in mice. However, one of the antibodies, clone E4, protected mice from antibody-induced arthritis. E4 showed a binding pattern restricted to skin, macrophages and dendritic cells in lymphoid tissue, and cartilage derived from mouse and human arthritic joints. Proteomic analysis confirmed that E4 strongly binds to macrophages and certain RA synovial fluid proteins such as α-enolase. The protective effect of E4 was epitope-specific and dependent on the interaction between E4-citrullinated α-enolase immune complexes with FCGR2B on macrophages, resulting in increased IL-10 secretion and reduced osteoclastogenesis. These findings suggest that a subset of ACPAs have therapeutic potential in RA.

Pertussis toxin-induced inhibition of Wnt/β-catenin signaling in dendritic cells promotes an autoimmune response in experimental autoimmune uveitis

BACKGROUND

Previous reports have indicated that disrupting the Wnt/β-catenin pathway in dendritic cells (DCs) may affect the progression of autoimmune inflammation; however, the factors and timing that regulate Wnt/β-catenin signaling have not been clearly understood.

METHODS

Experimental autoimmune uveitis (EAU) mice and Vogt-Koyanagi-Harada disease (VKH) patient samples were used to detect the expression of Wnt/β-catenin pathway genes. Western blot, real-time PCR, flow cytometry, and ELISA were performed to examine the expression of components of the Wnt/β-catenin pathway and inflammatory factors. DC-specific β-catenin knockout mice and 6-bromoindirubin-3'-oxime (BIO) administered mice were used to observe the effect of disrupting the Wnt pathway on EAU pathogenesis.

RESULTS

Wnt/β-catenin signaling was inhibited in DCs during the induction phase of EAU. The inhibition was mediated by pertussis toxin (PTX), which promoted DC maturation, in turn promoting pathogenic T cell proliferation and differentiation. In vivo experiments confirmed that deleting β-catenin in DCs enhanced EAU severity, and pre-injection of PTX advanced EAU onset. Administration of a Wnt activator (BIO) limited the effects of PTX, in turn ameliorating EAU.

CONCLUSIONS

Our results demonstrate that PTX plays a key role as a virulence factor in initiating autoimmune inflammation via DCs by inhibiting Wnt/β-catenin signaling in EAU, and highlight the potential mechanism by which infection can trigger apparent autoimmunity.

Therapeutic strategy for rheumatoid arthritis by induction of myeloid-derived suppressor cells with high suppressive potential

Combination treatment using fingolimod (FTY720), an immunomodulator, and a pathogenic antigen prevents the progression of glucose-6-phosphate isomerase (GPI)_325-339-induced arthritis. In this study, we focused on myeloid-derived suppressor cells (MDSCs; CD11b⁺Gr-1⁺ cells) and investigated the effects of the combination treatment on these cells. DBA/1J mice with GPI_325-339-induced arthritis were treated using FTY720 and/or GPI_325-339 for five days. The expanded CD11b⁺Gr-1⁺ cell population and its inhibitory potential were examined. The percentage of CD369⁺CD11b⁺Gr-1⁺ cells effectively increased in the combination-treated mice. The inhibitory potential of CD369⁺CD11b⁺Gr-1⁺ cells was higher than that of cells not expressing CD369. Among bone marrow cells, the expression of CD369 in CD11b⁺Gr-1⁺ cells increased following stimulation with granulocyte-macrophage colony-stimulating factor, and the expression of CD11c increased accordingly. The increased CD11c expression indicated a decrease in the potential to suppress T cell proliferation based on the results of the suppression assay. The percentage of CD11c^-CD369⁺ cells in CD11b⁺Gr-1⁺ cells that were induced by the combination treatment also increased, and these cells tended to have a higher capacity to inhibit T cell proliferation. In conclusion, the combination treatment using FTY720 and the pathogenic antigen effectively induces MDSC, which demonstrates a high potential for suppressing T cell proliferation in the lymph nodes, thereby establishing an immune-tolerant state.

PD-1 agonism by anti-CD80 inhibits T cell activation and alleviates autoimmunity

Targeted blockade of the checkpoint molecule programmed cell death 1 (PD-1) can activate tumor-specific T cells to destroy tumors, whereas targeted potentiation of PD-1 is expected to suppress autoreactive T cells and alleviate autoimmune diseases. However, the development of methods to potentiate PD-1 remains challenging. Here we succeeded in eliciting PD-1 function by targeting the cis-PD-L1-CD80 duplex, formed by binding of CD80 to the PD-1 ligand PD-L1, that attenuates PD-L1-PD-1 binding and abrogates PD-1 function. By generating anti-CD80 antibodies that detach CD80 from the cis-PD-L1-CD80 duplex and enable PD-L1 to engage PD-1 in the presence of CD80, we demonstrate that the targeted dissociation of cis-PD-L1-CD80 duplex elicits PD-1 function in the condition where PD-1 function is otherwise restricted. We demonstrate using murine models that the removal of PD-1 restriction is effective in alleviating autoimmune disease symptoms. Our findings establish a method to potentiate PD-1 function and propose the removal of restraining mechanisms as an efficient strategy to potentiate the function of inhibitory molecules.

Specific Increase in Joint Neutrophil Extracellular Traps and Its Relation to Interleukin 6 in Autoimmune Arthritis

Neutrophils and their extracellular traps have been shown to play an important role in the pathogenesis of rheumatoid arthritis (RA), but the detailed mechanisms in joints are still unclear, and their regulation remains to be solved. Here, we explored neutrophil extracellular trap (NET)osis in experimental models of arthritis and further investigated the effects of interleukin-6 (IL-6) inhibition in neutrophils and NETosis. In skins of peptide GPI-induced arthritis (pGIA), citrullinated protein was detected as well as citrullinated histone expression in immunized skin but this was not specific to pGIA. Citrullinated histone expression in pGIA joints was specific to pGIA and was merged with neutrophil elastase, suggesting NETosis. Neutrophils in joints tend to upregulate IL-6 receptors when compared with bone marrow neutrophils. Administration of mouse anti-IL-6 receptor antibodies in pGIA suppressed arthritis in association with a decrease in neutrophil infiltration and NETosis in joints. In the plasma of RA patients, citrullinated protein was significantly reduced after tocilizumab treatment. Our results suggest that IL-6 enhances neutrophil chemotaxis and NETosis in inflammatory joints and could be the source of citrullinated proteins.

Defining Target Engagement Required for Efficacy In Vivo at the Retinoic Acid Receptor-Related Orphan Receptor C2 (RORγt)

The Th17 pathway has been implicated in autoimmune diseases. The retinoic acid receptor-related orphan receptor C2 (RORγt) is a master regulator of Th17 cells and controls the expression of IL-17A. RORγt is expressed primarily in IL-17A-producing lymphoid cells. Here we describe a virtual screen of the ligand-binding pocket and subsequent screen in a binding assay that identified the 1-benzyl-4',5'-dihydrospiro[piperidine-4,7'-thieno[2,3-c]pyran]-2'-carboxamide scaffold as a starting point for optimization of binding affinity and functional activity guided by structure-based design. Compound 12 demonstrated activity in a mouse PK/PD model and efficacy in an inflammatory arthritis mouse model that were used to define the level and duration of target engagement required for efficacy in vivo. Further optimization to improve ADME and physicochemical properties with guidance from simulations and modeling provided compound 22, which is projected to achieve the level and duration of target engagement required for efficacy in the clinic.

Characterization of an Expanded IL-10-Producing-Suppressive T Cell Population Associated with Immune Tolerance

An increase in the number of glucocorticoid-induced tumor necrosis factor receptor-family related gene/protein (GITR)⁺CD25^- (or fork-head box protein 3: Foxp3^-) CD4⁺ T cells, after treating a mouse model of arthritis with fingolimod (FTY720), and a pathogenic antigen may play a key role in the establishment of immune tolerance. In this study, we characterized a specific expanded T cell subset in this population. Mice with glucose-6-phosphate isomerase peptide (GPI_325-339)-induced arthritis were treated with FTY720 (1 mg/kg, per os) and GPI_325-339 (10 µg/mouse, intravenously) for five days, starting from the onset of symptoms. The expanded GITR⁺CD25^- (or Foxp3^-) CD4⁺ T cell population and its cytokine production were examined using flow cytometry. Furthermore, time-dependent changes in T-bet and/or early growth response gene 2 (Egr-2) expression in this T cell subset were examined. The density of T cell immunoreceptors with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibition motif domains (TIGIT)⁺CD39⁺ cell subset in the GITR⁺Foxp3^-CD4⁺ T cell population was significantly increased only in the combined treatment group, compared to that in the untreated and single-treatment groups. In the TIGIT⁺CD39⁺GITR⁺Foxp3^-CD4⁺ T cell population, T-bet⁺Egr-2⁺/T-bet⁺Egr-2^- cell ratio increased in the latter stage of the treatment. Furthermore, this T cell subset, which corresponded to a T helper 1 (Th1) response, produced high levels of both interleukin (IL)-10 and interferon (IFN)-γ. In conclusion, expanded TIGIT⁺CD39⁺GITR⁺Foxp3^-CD4⁺ T cells shifted from an effector Th1 to IL-10-producing-suppressor T cell phenotype, which may promote an immune-tolerant state.

Citrullinated inter-alpha-trypsin inhibitor heavy chain 4 in arthritic joints and its potential effect in the neutrophil migration

The citrullinated inter-alpha-trypsin inhibitor heavy chain 4 (cit-ITIH4) was identified as its blood level was associated with the arthritis score in peptide glucose-6-phosphate-isomerase-induced arthritis (pGIA) mice and the disease activity in patients with rheumatoid arthritis (RA). This study aimed to clarify its citrullination pathway and function as related to neutrophils. In pGIA-afflicted joints, ITIH4 and cit-ITIH4 levels were examined by immunohistochemistry (IHC), immunoprecipitation (IP) and Western blotting (WB), while peptidylarginine deiminase (PAD) expression was measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), IHC and immunofluorescent methods. The pGIA mice received anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibodies to deplete neutrophils and the expression of cit-ITIH4 was investigated by WB. The amounts of ITIH4 and cit-ITIH4 in synovial fluid (SF) from RA and osteoarthritis (OA) patients were examined by I.P. and W.B. Recombinant ITIH4 and cit-ITIH4 were incubated with sera from healthy volunteers before its chemotactic ability and C5a level were evaluated using Boyden's chamber assay and enzyme-linked immunosorbent assay (ELISA). During peak arthritic phase, ITIH4 and cit-ITIH4 were increased in joints while PAD4 was over-expressed, especially in the infiltrating neutrophils of pGIA mice. Levels of cit-ITIH4 in plasma and joints significantly decreased upon neutrophil depletion. ITIH4 was specifically citrullinated in SF from RA patients compared with OA patients. Native ITIH4 inhibited neutrophilic migration and decreased C5a levels, while cit-ITIH4 increased its migration and C5a levels significantly. Cit-ITIH4 is generated mainly in inflamed joints by neutrophils via PAD4. Citrullination of ITIH4 may change its function to up-regulate neutrophilic migration by activating the complement cascade, exacerbating arthritis.

Lactate Buildup at the Site of Chronic Inflammation Promotes Disease by Inducing CD4+ T Cell Metabolic Rewiring

Accumulation of lactate in the tissue microenvironment is a feature of both inflammatory disease and cancer. Here, we assess the response of immune cells to lactate in the context of chronic inflammation. We report that lactate accumulation in the inflamed tissue contributes to the upregulation of the lactate transporter SLC5A12 by human CD4+ T cells. SLC5A12-mediated lactate uptake into CD4+ T cells induces a reshaping of their effector phenotype, resulting in increased IL17 production via nuclear PKM2/STAT3 and enhanced fatty acid synthesis. It also leads to CD4+ T cell retention in the inflamed tissue as a consequence of reduced glycolysis and enhanced fatty acid synthesis. Furthermore, antibody-mediated blockade of SLC5A12 ameliorates the disease severity in a murine model of arthritis. Finally, we propose that lactate/SLC5A12-induced metabolic reprogramming is a distinctive feature of lymphoid synovitis in rheumatoid arthritis patients and a potential therapeutic target in chronic inflammatory disorders.

Revisit of autoimmunity to glucose-6-phosphate isomerase in experimental and rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory disorder characterized by synovial inflammation in multiple joints. Autoantibodies (Abs) are the hallmark of RA, and as disease-specific and diagnostic markers, rheumatoid factor and anti-citrullinated protein antibody (ACPA) are produced pre-clinically, but their pathogenic roles in RA remain elusive. In this review, we focus on one of the candidate autoantigens in RA; glucose-6-phosphate isomerase (GPI). The arthritogenic role of GPI has been confirmed in two different mouse models: the K/BxN- and GPI-induced arthritis models. Both anti-GPI Abs and citrullinated-GPI peptide Abs have been detected in human RA. Studies conducted in these rodent models have confirmed that the pathogenesis of arthritis involves the localization of autoantigens not only in the joints but also in the circulation. In this review, we revisit and summarize the arthritogenic relevance of GPI in animal RA models and in human RA, and extend the discussion to joint-specific inflammation.

Identification of novel biomarker as citrullinated inter-alpha-trypsin inhibitor heavy chain 4, specifically increased in sera with experimental and rheumatoid arthritis

Background

Anticitrullinated protein antibodies (ACPA) and citrullinated proteins play key roles in the pathogenesis of rheumatoid arthritis (RA). Many candidate citrullinated antigens have been identified in joints, but citrullinated proteins in sera are mostly uncertain in patients with RA. We explored the expression of citrullinated proteins in joints and sera of experimental arthritis, and we further investigated their specific expression correlated with the disease activity in patients with RA.

Methods

Citrullinated protein expression in tissues was examined by IHC in peptide glucose-6-phosphate isomerase-induced arthritis (pGIA). Serum citrullinated proteins from pGIA were examined by Western blotting, and the sequence was identified by MS. With the same methods, serum citrullinated proteins were analyzed in patients with RA, primary Sjögren’s syndrome, systemic lupus erythematosus, and osteoarthritis as well as in healthy subjects, by Western blotting and MS. In patients with RA, the relationship between the expression of the identified protein (inter-alpha-trypsin inhibitor heavy chain 4 [ITIH4]) and clinical features was evaluated, and the levels of citrullinated ITIH4 were compared before and after biological treatment. The antibody response against citrullinated ITIH4 peptide was measured by enzyme-linked immunosorbent assay.

Results

Citrullinated proteins were detected specifically in arthritic joints and sera from pGIA relative to controls. In sera, a common band of citrullinated protein at 120 kDa was revealed, and it fluctuated in parallel with arthritis score of pGIA by Western blotting. Interestingly, in 82% of RA patient sera, similar bands of citrullinated protein were specifically detected. These proteins were identified as citrullinated ITIH4, and especially the R438 site was commonly citrullinated between mice and humans. Citrullinated ITIH4 levels were associated with clinical parameters such as C-reactive protein (CRP), rheumatoid factor, and Disease Activity Score in 28 joints as measured by CRP in patients with RA. Its levels were decreased in correlation with the reduction of disease activity score after effective treatment in patients with RA. Moreover, antibody response to citrullinated epitope in ITIH4 was specifically observed in patients with RA.

Conclusions

Our results suggest that serum citrullinated ITIH4 was specifically increased in patients with RA and could be a novel biomarker for assessing disease activity in patients with RA.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1562-7) contains supplementary material, which is available to authorized users.

Targeting IgG in Arthritis: Disease Pathways and Therapeutic Avenues

Rheumatoid arthritis (RA) is a polygenic and multifactorial syndrome. Many complex immunological and genetic interactions are involved in the final outcome of the clinical disease. Autoantibodies (rheumatoid factors, anti-citrullinated peptide/protein antibodies) are present in RA patients' sera for a long time before the onset of clinical disease. Prior to arthritis onset, in the autoantibody response, epitope spreading, avidity maturation, and changes towards a pro-inflammatory Fc glycosylation phenotype occurs. Genetic association of epitope specific autoantibody responses and the induction of inflammation dependent and independent changes in the cartilage by pathogenic autoantibodies emphasize the crucial contribution of antibody-initiated inflammation in RA development. Targeting IgG by glyco-engineering, bacterial enzymes to specifically cleave IgG/alter N-linked Fc-glycans at Asn 297 or blocking the downstream effector pathways offers new avenues to develop novel therapeutics for arthritis treatment.

Cutting Edge: Processing of Oxidized Peptides in Macrophages Regulates T Cell Activation and Development of Autoimmune Arthritis

APCs are known to produce NADPH oxidase (NOX) 2-derived reactive oxygen species; however, whether and how NOX2-mediated oxidation affects redox-sensitive immunogenic peptides remains elusive. In this study, we investigated a major immunogenic peptide in glucose-6-phosphate isomerase (G6PI), a potential autoantigen in rheumatoid arthritis, which can form internal disulfide bonds. Ag presentation assays showed that presentation of this G6PI peptide was more efficient in NOX2-deficient (Ncf1^m1J/m1J mutant) mice, compared with wild-type controls. IFN-γ-inducible lysosomal thiol reductase (GILT), which facilitates disulfide bond-containing Ag processing, was found to be upregulated in macrophages from Ncf1 mutant mice. Ncf1 mutant mice exhibited more severe G6PI peptide-induced arthritis, which was accompanied by the increased GILT expression in macrophages and enhanced Ag-specific T cell responses. Our results show that NOX2-dependent processing of the redox-sensitive autoantigens by APCs modify T cell activity and development of autoimmune arthritis.

Combination treatment with fingolimod and a pathogenic antigen prevents relapse of glucose-6-phosphate isomerase peptide-induced arthritis

INTRODUCTION

Combination treatment with fingolimod (FTY720) plus pathogenic antigen is thought to prevent glucose-6-phosphate isomerase (GPI)325-339-induced arthritis progression by effective induction of immune tolerance. Here, we examined the efficacy of this combination treatment on remission maintenance.

METHODS

GPI325-339-induced arthritis mice were treated for 5 days with FTY720 (1.0 mg/kg, p.o.) alone, GPI325-339 (10 μg/mouse, i.v.) alone, or with the FTY720 plus GPI325-339 combination. In some experiments, mice were resensitized with GPI325-339.

RESULTS

Following resensitization with GPI325-339, combination-treated mice exhibited neither severe relapse nor elevated lymphocyte infiltration in joints. Neither anti-human nor mouse GPI325-339 antibody levels were correlated with clinical symptoms. This suggests that combination treatment prevents relapse following resensitization via regulation of pathogenic antigen-specific T cells. The proportion of regulatory T (Treg) cells in inguinal lymph nodes was increased post treatment in the FTY720 alone and FTY720 plus GPI325-339 groups. In contrast, the proportion of glucocorticoid-induced tumor necrosis factor receptor-family-related gene/protein (GITR)(+) non-Treg cells was increased only in combination-treated mice. Furthermore, GITR(+) non-Treg cells, which were induced by the combination treatment in vivo, possess suppressive activity and high ability to produce interleukin (IL)-10.

CONCLUSION

GITR(+) non-Treg cells might play a key role in relapse prevention following resensitization. Thus, this combination treatment might establish immune tolerance by induction of GITR(+) non-Treg cells.

Experimental priming of encephalitogenic Th1/Th17 cells requires pertussis toxin-driven IL-1β production by myeloid cells

CD4⁺ Th17 are heterogeneous in terms of cytokine production and capacity to initiate autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE). Here we demonstrate that experimental priming of encephalitogenic Th cells expressing RORγt and T-bet and producing IL-17A, IFN-γ and GM-CSF but not IL-10 (Th1/Th17), is dependent on the presence of pertussis toxin (PTX) at the time of immunization. PTX induces early production of IL-1β by CD11b⁺CCR2⁺Gr1⁺ myeloid cells, which are rapidly recruited to antigen-draining lymph nodes. PTX-induced generation of Th1/Th17 cells is impaired in IL-1β- and ASC-deficient mice and in mice in which myeloid cells are depleted or fail to migrate to lymph nodes and requires expression of IL-1R1 and MyD88 on both T cells and non-T cells. Collectively, these data shed light on the enigmatic function of PTX in EAE induction and suggest that inflammatory monocytes and microbial infection can influence differentiation of pathogenic Th1/Th17 cells in autoimmune diseases through production of IL-1β.

Pertussis toxin enhances the induction of autoreactive T cells in mouse models of autoimmunity. Here the authors show that stimulation of IL-1β production in myeloid cells by pertussis toxin is necessary to prime pathogenic Th1/Th17 cells in experimental autoimmune encephalopathy.

Contributions of neutrophils to the adaptive immune response in autoimmune disease

Neutrophils are granulocytic cytotoxic leukocytes of the innate immune system that activate during acute inflammation. Neutrophils can also persist beyond the acute phase of inflammation to impact the adaptive immune response during chronic inflammation. In the context of the autoimmune disease, neutrophils modulating T and B cell functions by producing cytokines and chemokines, forming neutrophil extracellular traps, and acting as or priming antigen presentation cells. Thus, neutrophils are actively involved in chronic inflammation and tissue damage in autoimmune disease. Using rheumatoid arthritis as an example, this review focuses on functions of neutrophils in adaptive immunity and the therapeutic potential of these cells in the treatment of autoimmune disease and chronic inflammation.

Functional Mechanism(s) of the Inhibition of Disease Progression by Combination Treatment with Fingolimod Plus Pathogenic Antigen in a Glucose-6-phosphate Isomerase Peptide-Induced Arthritis Mouse Model

We previously reported that combination treatment with fingolimod (FTY720) plus antigenic peptide of glucose-6-phosphate isomerase (residues 325-339) (GPI325-339) from the onset of symptoms significantly inhibited disease progression in a mouse model of GPI325-339-induced arthritis. In this study, we investigated the mechanism(s) involved. The model mice were treated from arthritis onset with FTY720 alone, GPI325-339 alone, or the combination of FTY720 plus GPI325-339. At the end of treatment, inguinal lymph nodes (LNs) were excised and examined histologically and in flow cytometry. Levels of apoptotic cells, programmed death-1-expressing CD4(+)forkhead box P3(-) nonregulatory T cells (non-Tregs), and cytotoxic T-lymphocyte antigen 4-expressing non-Tregs in inguinal LNs were markedly increased in the combination treatment group mice. Regulatory T cells (Tregs) were also increased. These results indicate that combination treatment with FTY720 plus GPI325-339 inhibits the progression of arthritis by inducing clonal deletion and anergy of pathogenic T cells and also by immune suppression via Tregs.

Collagenase-3 (MMP-13) deficiency protects C57BL/6 mice from antibody-induced arthritis

Introduction

Matrix metalloproteinases (MMPs) are important in tissue remodelling. Here we investigate the role of collagenase-3 (MMP-13) in antibody-induced arthritis.

Methods

For this study we employed the K/BxN serum-induced arthritis model. Arthritis was induced in C57BL/6 wild type (WT) and MMP-13-deficient (MMP-13^–/–) mice by intraperitoneal injection of 200 μl of K/BxN serum. Arthritis was assessed by measuring the ankle swelling. During the course of the experiments, mice were sacrificed every second day for histological examination of the ankle joints. Ankle sections were evaluated histologically for infiltration of inflammatory cells, pannus tissue formation and bone/cartilage destruction. Semi-quantitative PCR was used to determine MMP-13 expression levels in ankle joints of untreated and K/BxN serum-injected mice.

Results

This study shows that MMP-13 is a regulator of inflammation. We observed increased expression of MMP-13 in ankle joints of WT mice during K/BxN serum-induced arthritis and both K/BxN serum-treated WT and MMP-13^–/– mice developed progressive arthritis with a similar onset. However, MMP-13^–/– mice showed significantly reduced disease over the whole arthritic period. Ankle joints of WT mice showed severe joint destruction with extensive inflammation and erosion of cartilage and bone. In contrast, MMP-13^–/– mice displayed significantly decreased severity of arthritis (50% to 60%) as analyzed by clinical and histological scoring methods.

Conclusions

MMP-13 deficiency acts to suppress the local inflammatory responses. Therefore, MMP-13 has a role in the pathogenesis of arthritis, suggesting MMP-13 is a potential therapeutic target.

Activation of Invariant NKT cells with glycolipid ligand α-galactosylceramide ameliorates glucose-6-phosphate isomerase peptide-induced arthritis

Objective

Invariant natural killer T (iNKT) cells regulate collagen-induced arthritis (CIA) when activated by their potent glycolipid ligand, alpha-galactosylceramide (α-GalCer). Glucose-6-phosphate isomerase (GPI)-induced arthritis is a closer model of human rheumatoid arthritis based on its association with CD4+ T cells and cytokines such as TNF-α and IL-6 than CIA. Dominant T cell epitope peptide of GPI (GPI325-339) can induce arthritis similar to GPI-induced arthritis. In this study, we investigated the roles of activation of iNKT cells by α-GalCer in GPI peptide-induced arthritis.

Methods

Arthritis was induced in susceptible DBA1 mice with GPI peptide and its severity was assessed clinically. The arthritic mice were treated with either the vehicle (DMSO) or α-GalCer. iNKT cells were detected in draining lymph nodes (dLNs) by flow cytometry, while serum anti-GPI antibody levels were measured by enzyme-linked immunosorbent assay. To evaluate GPI peptide-specific cytokine production from CD4+ T cells, immunized mice were euthanized and dLN CD4+ cells were re-stimulated by GPI-peptide in the presence of antigen-presenting cells.

Results

α-GalCer induced iNKT cell expansion in dLNs and significantly decreased the severity of GPI peptide-induced arthritis. In α-GalCer-treated mice, anti-GPI antibody production (total IgG, IgG1, IgG2b) and IL-17, IFN-γ, IL-2, and TNF-α produced by GPI peptide-specific T cells were significantly suppressed at day 10. Moreover, GPI-reactive T cells from mice immunized with GPI and α-GalCer did not generate any cytokines even when these cells were co-cultured with APC from mice immunized with GPI alone. In vitro depletion of iNKT cells did not alter the suppressive effect of α-GalCer on CD4+ T cells.

Conclusion

α-GalCer significantly suppressed GPI peptide-induced arthritis through the suppression of GPI-specific CD4+ T cells.

Infection and autoimmunity: Lessons of animal models

While the key initiating processes that trigger human autoimmune diseases remain enigmatic, increasing evidences support the concept that microbial stimuli are among major environmental factors eliciting autoimmune diseases in genetically susceptible individuals. Here, we present an overview of evidences obtained through various experimental models of autoimmunity for the role of microbial stimuli in disease development. Disease onset and severity have been compared in numerous models under conventional, specific-pathogen-free and germ-free conditions. The results of these experiments suggest that there is no uniform scheme that could describe the role played by infectious agents in the experimental models of autoimmunity. While some models are dependent, others prove to be completely independent of microbial stimuli. In line with the threshold hypothesis of autoimmune diseases, highly relevant genetic factors or microbial stimuli induce autoimmunity on their own, without requiring further factors. Importantly, recent evidences show that colonization of germ-free animals with certain members of the commensal flora [such as segmented filamentous bacteria (SFB)] may lead to autoimmunity. These data drive attention to the importance of the complex composition of gut flora in maintaining immune homeostasis. The intriguing observation obtained in autoimmune animal models that parasites often confer protection against autoimmune disease development may suggest new therapeutic perspectives of infectious agents in autoimmunity.

Ameliorated course of glucose-6-phosphate isomerase (G6PI)-induced arthritis in IFN-γ receptor knockout mice exposes an arthritis-promoting role of IFN-γ

The absence of IFN-γ signaling leads to an increased inflammatory response in many murine models of autoimmune diseases induced by a CFA-assisted immunization schedule. We investigated the role of endogenous IFN-γ in arthritis induced by immunization with glucose-6-phosphate isomerase (G6PI) in CFA in DBA/1 mice. Surprisingly, and in contrast to our previous findings in collagen-induced arthritis (CIA), G6PI-induced arthritis was found to be reduced in IFN-γ receptor-deficient (IFN-γR KO) mice, demonstrating a proinflammatory role for IFN-γ in this model. Milder disease in IFN-γR KO mice was associated with less vigorous innate and adaptive immune responses early (day 9) after immunization: less proliferation of myeloid cells in the spleen, less osteoclast formation, less G6PI-reactive Th cells (as measured by ex vivo stimulation and flow cytometry and by in vivo skin reactivity to G6PI) and lower G6PI-specific immunoglobulin serum levels. Surprisingly, on day 21, despite continued milder disease in IFN-γR KO mice, their Th cell responses were no longer diminished but augmented as compared to wild-type mice, and their numbers of immature myeloid splenocytes were also more increased. These data reveal that IFN-γ signaling is critical for the induction of the early immune responses which trigger G6PI-induced arthritis. The strikingly different clinical consequences of absent IFN-γ signaling in G6PI-induced arthritis compared with the very similarly induced CIA emphasize that the role of a single cytokine in experimentally induced arthritis depends critically on the very nature of the inciting (auto)antigen and in particular on the kinetics of the disease manifestation elicited by the antigen.

In vivo molecular imaging of experimental joint inflammation by combined (18)F-FDG positron emission tomography and computed tomography

Introduction

The purpose of this work was to establish and validate combined small animal positron emission tomography - computed tomography (PET/CT) as a new in vivo imaging method for visualisation and quantification of joint inflammation.

Methods

Signalling of radioisotope ¹⁸F labelled Fluorodeoxyglucose (¹⁸F-FDG) injected in mice with glucose-6-phosphate isomerase (G6PI)-induced arthritis was analysed by PET/CT. Accumulation of ¹⁸F-FDG in tissue was quantified by PET measurement, whereas high definition CT delivered anatomical information. The fusion of both images revealed in detail spatial and temporal distribution and metabolism of ¹⁸F-FDG.

Results

A distinct ¹⁸F-FDG signal could be measured by PET in carpal and tarsal joints, from mice with early or established arthritis. In contrast, no accumulation of ¹⁸F-FDG was detectable before arthritis onset. Comparison of ¹⁸F-FDG joint uptake with histopathological evaluation revealed a significant correlation of both methods.

Conclusions

Small animal PET/CT using ¹⁸F-FDG is a feasible method for monitoring and, more importantly, quantitative assessment of inflammation in G6PI-arthritis. Since it is possible to perform repeated non-invasive measurements in vivo, not only numbers of animals in preclinical studies can markedly be reduced by this method, but also longitudinal studies come into reach, e. g. for individual flare-up reactions or monitoring therapy response in progressive arthritis.

Altered peptide ligands inhibit arthritis induced by glucose-6-phosphate isomerase peptide

INTRODUCTION

Immunosuppressants, including anti-TNFalpha antibodies, have remarkable effects in rheumatoid arthritis; however, they increase infectious events. The present study was designed to examine the effects and immunological change of action of altered peptide ligands (APLs) on glucose-6-phosphate isomerase (GPI) peptide-induced arthritis.

METHODS

DBA/1 mice were immunized with hGPI325-339, and cells of draining lymph node (DLN) were stimulated with hGPI325-339 to investigate the T-cell receptor (TCR) repertoire of antigen-specific CD4+ T cells by flow cytometry. Twenty types of APLs with one amino acid substitution at a TCR contact site of hGPI325-339 were synthesized. CD4+ T cells primed with human GPI and antigen-presenting cells were co-cultured with each APL and cytokine production was measured by ELISA to identify antagonistic APLs. Antagonistic APLs were co-immunized with hGPI325-339 to investigate whether arthritis could be antigen-specifically inhibited by APL. After co-immunization, DLN cells were stimulated with hGPI325-339 or APL to investigate Th17 and regulatory T-cell population by flow cytometry, and anti-mouse GPI antibodies were measured by ELISA.

RESULTS

Human GPI325-339-specific Th17 cells showed predominant usage of TCRVbeta8.1 8.2. Among the 20 synthesized APLs, four (APL 6; N329S, APL 7; N329T, APL 12; G332A, APL 13; G332V) significantly reduced IL-17 production by CD4+ T cells in the presence of hGPI325-339. Co-immunization with each antagonistic APL markedly prevented the development of arthritis, especially APL 13 (G332V). Although co-immunization with APL did not affect the population of Th17 and regulatory T cells, the titers of anti-mouse GPI antibodies in mice co-immunized with APL were significantly lower than in those without APL.

CONCLUSIONS

We prepared antagonistic APLs that antigen-specifically inhibited the development of experimental arthritis. Understanding the inhibitory mechanisms of APLs may pave the way for the development of novel therapies for arthritis induced by autoimmune responses to ubiquitous antigens.

Immunization with an immunodominant self-peptide derived from glucose-6-phosphate isomerase induces arthritis in DBA/1 mice

Introduction

T-helper (Th) lymphocytes are critically required for the pathogenesis of glucose-6-phosphate isomerase (G6PI)-induced arthritis, but neither the G6PI epitopes recognized by arthritogenic T cells nor their pathogenic effector functions have been fully elucidated to date. We aimed at identifying arthritogenic G6PI peptides.

Methods

We used a library of overlapping peptides spanning the entire G6PI sequence to identify the epitopes recognized by G6PI-specific Th cells. Immunodominant peptides were then used to immunize mice. Arthritis development was evaluated clinically and histologically. The humoral and cellular immune responses upon peptide immunization were analyzed by ELISA and multiparameter flow cytometry, respectively.

Results

We identified six immunodominant T-cell epitopes in DBA/1 mice, of which three are arthritogenic. One of these peptides (G6PI_469–483) is identical in man and mice. Immunization with this peptide induces arthritis, which is less severe and of shorter duration than arthritis induced by immunization with full-length G6PI. Upon immunization with either G6PI or peptide, the antigen-specific Th cells produce IL-17, RANKL, IFNγ and TNFα.

Conclusions

We identified immunodominant and arthritogenic epitopes of G6PI. Not all immunodominant peptides are arthritogenic. This is the first description of arthritis induced by immunization with a self-peptide in mice.