Immune-Mediated Non-Infectious Periaortitis After Aortic Graft Replacement Surgery: A Case Report Highlighting the Need for Immunosuppressive Therapy.

BACKGROUND A non-infectious inflammatory reaction against replaced aortic graft for aortic dissection often manifests as fever, malaise, and peri-graft effusion. It usually lasts less than 1 month and subsides spontaneously without immunosuppressive treatment. CASE REPORT A 49-year-old man underwent ascending aorta and total arch replacement for acute thoracic aortic dissection. He had fever, malaise, nausea, and elevated serum C-reactive protein for 1 month postoperatively. Pathological examination of the aorta revealed no aortitis, and repeated blood cultures were negative. We also noted periaortic graft fluid collection, and a small amount of pleural and pericardial effusions. We suspected post-pericardiotomy syndrome. Colchicine and prednisolone were administered, with an excellent clinical response. Three weeks after discontinuation of a 7-week prednisolone treatment, the same symptoms recurred and gradually worsened. Prednisolone was restarted 6 months after the first surgery, with good clinical response. Thereafter, he developed left-sided weakness and dysarthria, being diagnosed as ischemic stroke. Contrast-enhanced computed tomography revealed fluid collection with contrast leak around the aortic grafts, suggesting peel dehiscence, and thrombus formation in anastomotic pseudoaneurysm. He underwent surgical repair. He was diagnosed with non-infectious periaortitis, likely due to an immune reaction to the grafts, based on an excellent clinical response to immunosuppressive therapy. CONCLUSIONS We report a case of non-infectious periaortitis around a thoracic aortic graft, probably with an immune-mediated mechanism, requiring immunosuppressive treatment. When fever persists after aortic graft replacement surgery, non-infectious periaortitis should be considered and immunosuppressive treatment should be considered to prevent critical complications of anastomotic pseudoaneurysm and graft dehiscence.

Six-transmembrane epithelial antigen of prostate4 (STEAP4) is a tumor necrosis factor alpha-induced protein that regulates IL-6, IL-8, and cell proliferation in synovium from patients with rheumatoid arthritis.

Human six-transmembrane epithelial antigen of prostate4 (STEAP4), an ortholog of mouse tumor necrosis factor-α-induced adipose-related protein (TIARP), plays a role in tumor necrosis factor (TNF)-dependent arthritis models. However, its role in rheumatoid arthritis (RA) is still obscure. This study explored such a role for STEAP4. The expressions of STEAP4, TNFα, and IL-6 were compared in synovia of RA and osteoarthritis patients. STEAP4 induction was examined in TNFα-stimulated fibroblast-like synoviocytes (FLS) in vitro. FLS (with/without TNFα stimulation) were also analyzed for IL-6 expression after STEAP4 knockdown, using siRNA or transfection with STEAP4-plasmid DNA. IL-8, cell proliferation, and apoptosis were also evaluated in STEAP4-overexpressing FLS. The expression of STEAP4 in joints correlated with TNFα expression, specifically in RA synovium. In the cultured FLS, STEAP4 protein expression was augmented by TNFα activation, and localized in endosomal/lysosomal compartments. STEAP4 downregulation by siRNA enhanced the expression of IL-6 mRNA, while STEAP4 overexpression suppressed IL-6 and IL-8 expression, inhibited cell proliferation, and induced apoptosis via caspase-3. The results indicated that human STEAP4 is regulated by TNFα in synovium, where it controls IL-6 secretion and proliferation of FLS, suggesting that STEAP4 might potentially suppress the pathogenesis of TNFα-induced arthritis such as RA.

Disseminated tuberculosis following invasive procedures for peripancreatic lymph node tuberculosis with portal vein obstruction: a case report.

Peripancreatic tuberculous lymphadenopathy can mimic pancreatic cancer on imaging. There have only a few reports on varices from portal vein obstruction due to abdominal tuberculous lymphadenopathy. Iatrogenic disseminated tuberculosis is also rare. Herein, we present a rare case of peripancreatic tuberculous lymphadenopathy with ruptured duodenal varices due to portal vein obstruction. The patient presented to our hospital with hematemesis. Computed tomography revealed a peripancreatic mass. Duodenal varices rupture from portal vein obstruction due to pancreatic cancer were initially suspected. The patient underwent portal vein stenting for portal vein obstruction and endoscopic ultrasound-guided fine-needle aspiration for diagnosis, which revealed granulomas indicative of tuberculosis. The patient was discharged once because fine-needle aspiration did not lead to a definitive diagnosis of tuberculosis. Subsequently, he developed disseminated tuberculosis. Peripancreatic tuberculous lymphadenopathy can cause ectopic varices with portal vein obstruction. Tuberculosis should also be included in the differential diagnosis in the case of portal vein obstruction, to facilitate early treatment and avoid unnecessary surgery. Furthermore, fine-needle aspiration or portal vein stenting for tuberculous lesions can cause disseminated tuberculosis. Since a diagnosis might not be made until after several fine-needle aspirations have been conducted, careful follow-up is necessary after the procedure for such lesions.

Chylous Ascites Due to Hyperthyroidism and Heart Failure.

Chylous ascites (CA) is the accumulation of fluid with a high triglyceride content in the peritoneal cavity. Only two cases in the literature have reported CA with hyperthyroidism. A 28-year-old previously healthy woman presented with gradual-onset abdominal swelling, exertional dyspnea, and diarrhea. Hyperthyroidism and heart failure were diagnosed using laboratory investigation and echocardiography. Ultrasonography revealed a large amount of ascites. The ascitic fluid was milky with elevated triglyceride levels. Treatment with anti-thyroid therapy and diuretics improved all symptoms, and the free triiodothyronine (T3) level normalized after five days. Hyperthyroidism and heart failure should be considered as reversible causes of CA.

Spontaneous Recovery of Hemophagocytic Lymphohistiocytosis Due to Primary Epstein-Barr Virus Infection in an Adult Patient.

BACKGROUND Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening systemic hyperinflammatory condition. Most adult HLH cases are secondary to infection, malignancy, and rheumatic diseases. Epstein-Barr virus (EBV) infection is the most frequent cause of infection-induced HLH. Early treatment with dexamethasone, etoposide, and cyclosporine is generally recommended for adult patients with HLH. However, this treatment regimen was established based on pediatric clinical trial data; thus, its efficacy and validity in adults remain unclear. Because little is known about the disease course of untreated adult EBV-associated HLH (EBV-HLH), we report a case of an adult patient who recovered from EBV-HLH spontaneously without specific treatment and discuss potential treatment strategies. CASE REPORT A 34-year-old man presented to the emergency department with a 7-day history of fever, headache, and sore throat. The main laboratory test abnormalities were elevated liver enzymes, hyperbilirubinemia, hypertriglyceridemia, and hyperferritinemia. Serologic tests confirmed acute primary EBV infection. He was diagnosed with EBV-HLH based on the HLH-2004 diagnostic criteria and the HLH probability calculator (HScore). Because he was clinically stable, we did not initiate immunosuppressive/cytotoxic treatment targeting HLH. High-grade fever persisted, but the abnormalities in his laboratory data improved spontaneously, and he did not develop major organ failure. His fever resolved on day 29 without HLH-specific treatment. CONCLUSIONS In clinically stable adult patients with EBV-HLH without major organ failure, it might be an acceptable alternative to observe the patient for several weeks before initiating HLH-specific treatment. Further research is required to better predict the subset of patients who can be safely observed without treatment.

A case of hereditary angioedema due to C1-inhibitor deficiency with recurrent abdominal pain diagnosed 40 years after the occurrence of the initial symptom.

Hereditary angioedema due to C1-inhibitor deficiency (HAE-C1-INH) is a rare disease, which induces an acute attack of angioedema mediated by bradykinin. HAE-C1-INH can cause serious abdominal pain when severe edema develops in the gastrointestinal tract. However, because it takes a long time, 13.8 years on average in Japan, from the occurrence of the initial symptom to the diagnosis due to low awareness of the disease, undiagnosed HAE-C1-INH patients sometimes undergo unnecessary surgical procedures for severe abdominal pain. We herein present a 56-year-old patient with HAE-C1-INH, who underwent numerous abdominal operations. He frequently needed hospitalization with the administration of opioid due to severe abdominal pain. However, after he was accurately diagnosed with HAE-C1-INH at 55 years of age, he could start self-administration for an acute attack with icatibant, a selective bradykinin B2 receptor antagonist. Consequently, he did not need hospitalizing for ten months after the beginning of the treatment. A series of an accurate diagnosis and appropriate treatment for HAE-C1-INH improved his quality of life. Thus, HAE-C1-INH should be considered, when we meet patients with unidentified recurrent abdominal pain. This case highlights significance of an early diagnosis and appropriate treatment for HAE-C1-INH.

Recurrent Acute Abdomen as the Main Manifestation of Hereditary Angioedema.

A diagnosis of hereditary angioedema is usually made with recurrent episodes of swelling of the subcutaneous tissue with a family history. We herein report a case in which recurrent acute abdomen was the main manifestation of hereditary angioedema. A 45-year-old womon presented with a 10-year history of recurrent severe abdominal pain. Abdominal computed tomography revealed remarkable submucosal edema of the ileum. A blood examination revealed grossly reduced complement C4 and CH50 with deficiency of C1-inhibitor. Genetic testing revealed a heterozygous nonsense mutation of the SERPING1 gene, and a diagnosis of hereditary angioedema was made. Hereditary angioedema should be listed as a differential diagnosis of recurrent acute abdomen.

IgG4-related Pericarditis in which Oral Corticosteroid Therapy Was Effective.

IgG4-related diseases (IgG4-RDs) have recently been reported in many organs other than the salivary, pancreatic and hepatobiliary systems. A 64-year-old woman was referred to our department for her abdominal fullness and cardiomegaly on chest X-ray. After draining the pericardial fluid, her symptom promptly diminished, and pericardial friction rubbing became clearly audible. Elevated serum levels of IgG and IgG4 and ureteral wall thickening on computed tomography suggested IgG4-RD. After the initiation of oral corticosteroid therapy, the pericardial effusion was resolved, and she has been in a steady-state condition for the past two years.

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.

[Autoimmunity to glycolytic enzyme in rheumatoid arthritis].

Prognosis of rheumatoid arthritis (RA) patients has significantly improved with the recent use of biologics targeting TNFα, IL-6, and co-stimulatory molecule. In US and Europe, clear therapeutic benefit of anti-CD20 antibodies is also confirmed. As a disease specific marker, rheumatoid factor and anti-citrullinated protein antibody are crucial in RA, although the pathology of them is not defined. Here we focus on glycolytic enzyme such as glucose-6-phospate isomerase, that is confirmed as arthritogenic in two different mouse models, and discuss about pathogenic relevance to RA.

[The role of TNFalpha-induced adipose-related protein (TIARP) in TNFalpha dependent arthritic model--GPI-induced arthritis].

Rheumatoid arthritis (RA) is a chronic inflammatory disease with a variable disease outcome, and is characterized with synovitis, erosive changes of the joints, pain and functional deficit. Etiology is unknown. In the pathogenesis of rheumatoid arthritis the key role have proinflammatory cytokines, particularly, tumour necrosis factor (TNFalpha). The prognosis of RA patients has improved significantly during recent years, after the introduction of TNFalpha-based therapy. Despite the wide use of these biologics, their precise mechanisms of action in RA remain unclear. In the K/BxN mice, glucose-6-phosphate isomerase (GPI) is an autoantigen recognized by T and B cells. Recombinant GPI immunization to DBA/1 mice also induced acute severe arthritis. This arthritis was clearly controlled by anti-TNFalpha Abs, suggesting similar etiology to RA. In this study, to understand the mechanisms of arthritis that was regulated by TNFalpha, we focused on TNFalpha-induced adipose-related protein (TIARP) in the generation of GPI-induced arthritis.

Tumor necrosis factor alpha-induced adipose-related protein expression in experimental arthritis and in rheumatoid arthritis.

INTRODUCTION: Tumor necrosis factor-alpha (TNFalpha) plays a pivotal role in rheumatoid arthritis (RA); however, the mechanism of action of TNFalpha antagonists in RA is poorly defined. Immunization of DBA/1 mice with glucose-6-phosphate isomerase (GPI) induces severe acute arthritis. This arthritis can be controlled by TNFalpha antagonists, suggesting similar etiology to RA. In this study, we explored TNFalpha-related mechanisms of arthritis. METHODS: First, we performed GeneChip analysis using splenocytes of mice with GPI-induced arthritis. Expression of TNFalpha-induced adipose-related protein (TIARP) mRNA and protein in spleens, joints and lymph nodes was evaluated, and fluctuation of TIARP mRNA was analyzed after administration of anti-TNFalpha monoclonal antibody (mAb). Localization of TIARP in spleen and joints was also explored. Six-transmembrane epithelial antigen of the prostate (STEAP) families of proteins, the human ortholog of TIARP gene, were also evaluated in human peripheral blood mononucleocytes and synovium. RESULTS: Among the arrayed TNFalpha-related genes, the expression of TIARP mRNA was the highest (more than 20 times the control). TIARP mRNA was detected specifically in joints and spleens of arthritic mice, and their levels in the synovia correlated with severity of joint swelling. Treatment with anti-TNF mAb significantly reduced TIARP mRNA expression in splenocytes. Among the splenocytes, CD11b+ cells were the main source of TIARP mRNA. Immunohistochemistry showed that TIARP protein was mainly localized in hyperplastic synovium. Among the STEAP family of proteins, STEAP4 was highly upregulated in joints of patients with RA and especially co-localized with CD68+ macrophages. CONCLUSIONS: The results shed light on the new mechanism of action of TNFalpha antagonists in autoimmune arthritis, suggesting that TIARP plays an important role in inflammatory arthritis, through the regulation of inflammatory cytokines.

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.

Arthritogenic T cell epitope in glucose-6-phosphate isomerase-induced arthritis.

INTRODUCTION: Arthritis induced by immunisation with glucose-6-phosphate isomerase (GPI) in DBA/1 mice was proven to be T helper (Th) 17 dependent. We undertook this study to identify GPI-specific T cell epitopes in DBA/1 mice (H-2q) and investigate the mechanisms of arthritis generation. METHODS: For epitope mapping, the binding motif of the major histocompatibility complex (MHC) class II (I-Aq) from DBA/1 mice was identified from the amino acid sequence of T cell epitopes and candidate peptides of T cell epitopes in GPI-induced arthritis were synthesised. Human GPI-primed CD4+ T cells and antigen-presenting cells (APCs) were co-cultured with each synthetic peptide and the cytokine production was measured by ELISA to identify the major epitopes. Synthetic peptides were immunised in DBA/1 mice to investigate whether arthritis could be induced by peptides. After immunisation with the major epitope, anti-interleukin (IL) 17 monoclonal antibody (mAb) was injected to monitor arthritis score. To investigate the mechanisms of arthritis induced by a major epitope, cross-reactivity to mouse GPI peptide was analysed by flow cytometry and anti-GPI antibodies were measured by ELISA. Deposition of anti-GPI antibodies on the cartilage surface was detected by immunohistology. RESULTS: We selected 32 types of peptides as core sequences from the human GPI 558 amino acid sequence, which binds the binding motif, and synthesised 25 kinds of 20-mer peptides for screening, each containing the core sequence at its centre. By epitope mapping, human GPI325-339 was found to induce interferon (IFN) gamma and IL-17 production most prominently. Immunisation with human GPI325-339 could induce polyarthritis similar to arthritis induced by human GPI protein, and administration of anti-IL-17 mAb significantly ameliorated arthritis (p < 0.01). Th17 cells primed with human GPI325-339 cross-reacted with mouse GPI325-339, and led B cells to produce anti-mouse GPI antibodies, which were deposited on cartilage surface. CONCLUSIONS: Human GPI325-339 was identified as a major epitope in GPI-induced arthritis, and proved to have the potential to induce polyarthritis. Understanding the pathological mechanism of arthritis induced by an immune reaction to a single short peptide could help elucidate the pathogenic mechanisms of autoimmune arthritis.

Therapeutic effects of antibodies to tumor necrosis factor-alpha, interleukin-6 and cytotoxic T-lymphocyte antigen 4 immunoglobulin in mice with glucose-6-phosphate isomerase induced arthritis.

INTRODUCTION: Immunization with glucose-6-phosphate isomerase (GPI) induces severe arthritis in DBA/1 mice. The present study was designed to identify the cytokines and co-stimulatory molecules involved in the development of GPI-induced arthritis. METHODS: Arthritis was induced in DBA/1 mice with 300 microg human recombinant GPI. CD4+ T cells and antigen-presenting cells from splenocytes of arthritic mice were cultured in the presence of GPI. Tumor necrosis factor (TNF)-alpha, IFN-gamma, IL-2, IL-4, IL-5, IL-6, IL-10, and IL-12 levels were assessed using cytometric bead array. Monoclonal antibodies to TNF-alpha, IFN-gamma, IL-12, CD40L, inducible co-stimulator (ICOS), and cytotoxic T-lymphocyte antigen 4 immunoglobulin (CTLA-4Ig) were used to block TNF-alpha and IFN-gamma production, examine clinical index in mice with GPI-induced arthritis, and determine anti-GPI antibody production. RESULTS: Large amounts of TNF-alpha and IFN-gamma and small amounts of IL-2 and IL-6 were produced by splenocytes from mice with GPI-induced arthritis. Anti-TNF-alpha mAbs and CTLA-4Ig suppressed TNF-alpha production, whereas anti-IFN-gamma mAbs, anti-IL-12 mAbs, and CTLA-4 Ig inhibited IFN-gamma production. A single injection of anti-TNF-alpha and anti-IL-6 mAbs and two injections of CTLA-4Ig reduced the severity of arthritis in mice, whereas injections of anti-IFN-gamma and anti-IL-12 mAbs tended to exacerbate arthritis. Therapeutic efficacy tended to correlate with reduction in anti-GPI antibodies. CONCLUSION: TNF-alpha and IL-6 play an important role in GPI-induced arthritis, whereas IFN-gamma appears to function as a regulator of arthritis. Because the therapeutic effects of the tested molecules used in this study are similar to those in patients with rheumatoid arthritis, GPI-induced arthritis appears to be a suitable tool with which to examine the effect of various therapies on rheumatoid arthritis.

Use of laser microdissection in the analysis of renal-infiltrating T cells in MRL/lpr mice.

To clarify the role of T cells in the kidneys of MRL/MpJ-lpr (MRL/lpr) mice, cytokine mRNA expression was analyzed, and tissue localization of T cells was examined by immunohistochemistry. Cells infiltrating the glomeruli, glomerular circumference, and perivascular areas in ten female MRL/lpr mice were captured by laser microdissection (LMD). Nested reverse transcription polymerase chain reaction (RT-PCR) of samples was performed with primers specific for beta-actin, T-cell receptor beta chain (TCR-Cbeta), Thy-1, B220, CD4, CD8, interleukin (IL)-2, IL-4, IL-10, IL-13, IL-17, and interferon (IFN)-gamma. Frozen sections of lesions were also stained immunohistochemically. B220, MAC-1, Thy-1, CD4, and CD8 staining was observed in glomeruli and perivascular areas, especially in glomerular circumference areas. T cells infiltrating the glomeruli, glomerular circumference areas, and perivascular areas produce INF-gamma, IL-13, and IL-17 predominately. IL-10 positivity was identified in 60% of perivascular T cells but not in a substantial number of glomerular or periglomerular T cells. The results of our study suggest that the pathogenesis of renal lesions in MRL/lpr mice is complex and not due simply to the Th1 and Th2 balance. These findings also support the concept of different molecular mechanisms for glomerulonephritis and vasculitis in these mice.

Crucial role of the interleukin-6/interleukin-17 cytokine axis in the induction of arthritis by glucose-6-phosphate isomerase.

OBJECTIVE: To clarify the glucose-6-phosphate isomerase (GPI)-specific CD4+ T cell lineage involved in GPI-induced arthritis and to investigate their pathologic and regulatory roles in the induction of the disease. METHODS: DBA/1 mice were immunized with GPI to induce arthritis. CD4+ T cells and antigen-presenting cells were cocultured with GPI, and cytokines in the supernatant were analyzed by enzyme-linked immunosorbent assay. Anti-interferon-gamma (anti-IFNgamma) monoclonal antibody (mAb), anti-interleukin-17 (anti-IL-17) mAb, or the murine IL-6 receptor (IL-6R) mAb MR16-1 was injected at different time points, and arthritis development was monitored visually. After MR16-1 was injected, percentages of Th1, Th2, Th17, and Treg cells were analyzed by flow cytometry, and CD4+ T cell proliferation was analyzed using carboxyfluorescein diacetate succinimidyl ester. RESULTS: GPI-specific CD4+ T cells were found to be differentiated to Th1 and Th17 cells, but not Th2 cells. Administration of anti-IL-17 mAb on day 7 significantly ameliorated arthritis (P < 0.01), whereas administration of anti-IFNgamma mAb exacerbated arthritis. Neither anti-IL-17 mAb nor anti-IFNgamma mAb administration on day 14 ameliorated arthritis. Administration of MR16-1 on day 0 or day 3 protected against arthritis induction, and MR16-1 administration on day 8 significantly ameliorated existing arthritis (P < 0.05). After administration of MR16-1, there was marked suppression of Th17 differentiation, without an increase in Th1, Th2, or Treg cells, and CD4+ T cell proliferation was also suppressed. CONCLUSION: IL-6 and Th17 play an essential role in GPI-induced arthritis. Since it has previously been shown that treatment with a humanized anti-IL-6R mAb has excellent effects in patients with rheumatoid arthritis (RA), we propose that the IL-6/IL-17 axis might also be involved in the generation of RA, especially in the early effector phase.