Understanding the pathogenic significance of altered calcium-calmodulin signaling in T cells in autoimmune diseases.

Calcium/calmodulin-dependent protein kinase IV (CaMK4) serves as a pivotal mediator in the regulation of gene expression, influencing the activity of transcription factors within a variety of immune cells, including T cells. Altered CaMK4 signaling is implicated in autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and psoriasis, which are characterized by dysregulated immune responses and clinical complexity. These conditions share common disturbances in immune cell functionality, cytokine production, and autoantibody generation, all of which are associated with disrupted calcium-calmodulin signaling. This review underscores the consequences of dysregulated CaMK4 signaling across these diseases, with an emphasis on its impact on Th17 differentiation and T cell metabolism-processes central to maintaining immune homeostasis. A comprehensive understanding of roles of CaMK4 in gene regulation across various autoimmune disorders holds promise for the development of targeted therapies, particularly for diseases driven by Th17 cell dysregulation.

Influences of advanced age in rheumatoid arthritis: A multicentre ultrasonography cohort study.

OBJECTIVES: We aimed to evaluate the effects of age on clinical characteristics and outcomes in biologic or targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD)-naïve patients with rheumatoid arthritis (RA). METHODS: We analysed the cases of 234 Japanese b/tsDMARD-naïve RA patients who underwent b/tsDMARD treatment in a multicentre ultrasound prospective observational cohort. We compared the clinical characteristics at baseline and outcomes at 12 months between those aged ≥60 years and those <60 years. RESULTS: Compared to the <60-year-old group (n = 78), the ≥60-year-old group (n = 156) had higher inflammatory marker values and ultrasound combined scores, especially wrist joints, at baseline. Age at baseline positively correlated significantly with the ultrasound scores at baseline; however, age was not a significant variable by the multiple regression analysis. The patients treated with different MOAs in the ≥60-year-old group had comparable outcomes and multiple regression analysis revealed that mechanism of action (MOA) was not a significant contributor to the Clinical Disease Activity Index at 12 months. CONCLUSIONS: RA patients with advanced age demonstrated distinctive clinical characteristics. The MOAs were not associated with clinical outcomes and ultrasound outcomes in RA patients with advanced age.

Increase in the number of new cases of ANCA-associated vasculitis in the COVID-19 vaccine era.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune vasculitis characterized by the production of antibodies against ANCA, with unclear pathogenesis. With the ongoing COVID-19 pandemic, COVID-19 mRNA vaccination has been available in Japan since February 2021. Although autoimmune symptoms have been reported after COVID-19 vaccinations, there have been no clinical investigations regarding the relationship between COVID-19 mRNA vaccines and the pathogenesis of AAV. Thus, the present study aimed to investigate whether the administration of COVID-19 mRNA vaccines affects the development of AAV. The study identified patients with new-onset AAV who were MPO-ANCA or PR3-ANCA positive and met the entry criteria of the AAV EMA classification algorithm. The study compared the number of new AAV cases per year before and after the start of the COVID-19 mRNA vaccine program in Japan. The study found that the annual number of new cases of AAV in Japan's Nagasaki Prefecture increased by approximately 1.5-fold since the COVID-19 vaccine program was initiated, suggesting a possible link between the COVID-19 mRNA vaccines and the development of AAV. Although the study provides insight into the clinical evaluation and management of autoimmune symptoms following COVID-19 vaccination, further investigation of the possible association between COVID-19 mRNA vaccines and the pathogenesis of AAV is required.

Efficacy and safety of 5-aminolevulinic acid in adult-onset Still's disease: A preclinical study in mice and a pilot study in humans.

The study aimed to investigate the therapeutic effects of 5-aminolevulinic acid/sodium ferrous citrate (5-ALA/SFC) on adult-onset Still's disease (AOSD), specifically focusing on arthritis and macrophage activation syndrome (MAS). We used mouse models to assess the impact of 5-ALA/SFC on collagen-induced arthritis (CIA) and MAS induced by synthetic oligonucleotides containing CpG motifs (CpG-S-ODN). Additionally, we conducted a pilot study with AOSD patients receiving prednisolone (PSL) treatment and 5-ALA/SFC administration to evaluate its efficacy and safety. The 5-ALA/SFC group exhibited significantly lower joint scores in CIA mice. In CpG-S-ODN-treated mice, 5-ALA/SFC administration led to reduced hemophagocytosis and splenomegaly. The anti-inflammatory properties of 5-ALA/SFC were attributed to the suppression of CCL4 and CXCL10 production in monocytes and the induction of M2 macrophages. AOSD patients treated with 5-ALA/SFC demonstrated successful PSL tapering without adverse events. Collectively, the administration of 5-ALA/SFC showed promising potential in ameliorating arthritis and MAS in AOSD patients.

Exploring the role of insulin-like growth factor binding protein-1 in identifying idiopathic multicentric Castleman's disease types: Implications for the mTOR signaling pathway.

OBJECTIVE: To determine the molecular differences between iMCD-thrombocytopenia, anasarca, fevers, reticulin myelofibrosis, organomegaly (TAFRO), and iMCD-not otherwise specified (NOS). METHODS: CD4-positive T cells were isolated from two iMCD-TAFRO and two iMCD-NOS patients for RNA sequencing comparison. Serum proteins of two iMCD-TAFRO and four iMCD-NOS patients were comprehensively analyzed to identify pathogenesis-associated proteins. IGFBP-1 protein, extracted from serum analysis, was compared to healthy controls, iMCD, systemic lupus erythematosus, and rheumatoid arthritis patients. RESULTS: RNA sequencing of CD4-positive T cells revealed enhanced mTOR-related signaling in iMCD-TAFRO compared to iMCD-NOS. Comprehensive serum analysis found IGFBP-1 linked to iMCD pathogenesis, significantly higher in iMCD-TAFRO. This protein may be elevated in patients with iMCD caused by an enhanced mTOR pathway. CONCLUSION: The mTOR pathway is suggested to be activated in iMCD-TAFRO compared to iMCD-NOS, which may elevate the protein IGFBP-1. This protein may be a biomarker to distinguish iMCD-TAFRO from iMCD-NOS.

Inhibition of calcium/calmodulin-dependent protein kinase IV in arthritis: dual effect on Th17 cell activation and osteoclastogenesis.

OBJECTIVE: To investigate the role of calcium/calmodulin-dependent protein kinase IV (CaMK4) in the development of joint injury in a mouse model of arthritis and patients with RA. METHODS: Camk4-deficient, Camk4flox/floxLck-Cre, and mice treated with CaMK4 inhibitor KN-93 or KN-93 encapsulated in nanoparticles tagged with CD4 or CD8 antibodies were subjected to collagen-induced arthritis (CIA). Inflammatory cytokine levels, humoral immune response, synovitis, and T-cell activation were recorded. CAMK4 gene expression was measured in CD4+ T cells from healthy participants and patients with active RA. Micro-CT and histology were used to assess joint pathology. CD4+ and CD14+ cells in patients with RA were subjected to Th17 or osteoclast differentiation, respectively. RESULTS: CaMK4-deficient mice subjected to CIA displayed improved clinical scores and decreased numbers of Th17 cells. KN-93 treatment significantly reduced joint destruction by decreasing the production of inflammatory cytokines. Furthermore, Camk4flox/floxLck-Cre mice and mice treated with KN93-loaded CD4 antibody-tagged nanoparticles developed fewer Th17 cells and less severe arthritis. CaMK4 inhibition mitigated IL-17 production by CD4+ cells in patients with RA. The number of in vitro differentiated osteoclasts from CD14+ cells in patients with RA was significantly decreased with CaMK4 inhibitors. CONCLUSION: Using global and CD4-cell-targeted pharmacologic approaches and conditionally deficient mice, we demonstrate that CaMK4 is important in the development of arthritis. Using ex vivo cell cultures from patients with RA, CaMK4 is important for both Th17 generation and osteoclastogenesis. We propose that CaMK4 inhibition represents a new approach to control the development of arthritis.

Efficient detection of somatic UBA1 variants and clinical scoring system predicting patients with variants in VEXAS syndrome.

OBJECTIVES: To efficiently detect somatic UBA1 variants and establish a clinical scoring system predicting patients with pathogenic variants in VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. METHODS: Eighty-nine Japanese patients with clinically suspected VEXAS syndrome were recruited [81 males and 8 females; median onset age (IQR) 69.3 years (62.1-77.6)]. Peptide nucleic acid-clamping PCR (PNA-PCR), regular PCR targeting exon 3 clustering UBA1 variants, and subsequent Sanger sequencing were conducted for variant screening. Partitioning digital PCR (pdPCR) or targeted amplicon deep sequencing (TAS) was also performed to evaluate the variant allele frequency (VAF). We developed our clinical scoring system to predict UBA1 variant-positive and ­negative patients and assessed the diagnostic value of our system using receiver operating characteristic (ROC) curve analysis. RESULTS: Forty patients with reported pathogenic UBA1 variants (40/89, 44.9%) were identified, including a case having a variant with VAF of 1.7%, using a highly sensitive method. Our clinical scoring system considering >50 years of age, cutaneous lesions, lung involvement, chondritis, and macrocytic anaemia efficiently predicted patients with UBA1 variants (the area under the curve for the scoring total was 0.908). CONCLUSIONS: Genetic screening with the combination of regular PCR and PNA-PCR detected somatic UBA1 variants with high sensitivity and specificity. Our scoring system could efficiently predict patients with UBA1 variants.

Prediction of radiographic progression during a treat-to-target strategy by the sequential application of MRI-proven bone marrow oedema and power-Doppler grade ≥2 articular synovitis in rheumatoid arthritis: Retrospective observational study.

OBJECTIVES: To investigate the appropriate timing, useful findings and combination of magnetic resonance imaging (MRI) and ultrasound (US) for predicting the radiographic progression in early rheumatoid arthritis (RA). METHODS: Forty-four active RA patients, who examined by both of MRI and US in the symptomatic wrist and finger joints, were recruited in Nagasaki University Hospital from 2010 to 2017 and treated by the treat-to-target therapeutic strategy for 1 year. MRI was evaluated by RA MRI scoring and US by Outcomes Measures in Rheumatology Clinical Trial, respectively. Plain radiographs were assessed by the Genant-modified Sharp score for the symptomatic side in the same manner as MRI and US. Radiographic progression was defined as an annual increase ≥0.75 at 1 year. Factors associated with radiographic progression were analysed. Also, the optimal combination of MRI and US at each timepoint was considered. RESULTS: Logistic regression model revealed that MRI-proven bone marrow oedema at baseline and 6 months and joint counts of power-Doppler grade ≥2 articular synovitis at 3 or 6 months were significantly associated with radiographic progression at 1 year. CONCLUSION: This study may suggest the favourable timing and combination of MRI and US at each point to predict radiographic progression in patients with early-stage RA.

Tissue resident cell processes determine organ damage in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects almost any organ. Multiple immunological abnormalities involving every domain of the immune system contribute to the expression of the disease. It is now recognized that elements of the immune system instigate processes in tissue resident cells which execute organ damage. Although correction of ongoing immune aberrations is important in the control of disease activity, targeting tissue specific injurious processes may prove desirable in limiting organ damage.

Generation of antagonistic monoclonal antibodies against the neoepitope of active mouse interleukin (IL)-18 cleaved by inflammatory caspases.

Interleukin 18 (IL-18) is a member of the IL-1 family and plays an important role in both the innate and acquired immune systems. It is constitutively expressed as an inactive precursor (24 kDa) in various cell types, and the mature IL-18 (18 kDa) cleaved by inflammatory caspase-1/4 binds to the interleukin-18 receptor, thereby activating downstream signaling pathways. We previously generated anti-human IL-18 antibodies that specifically recognize the human IL-18 neoepitope cleaved by inflammatory caspase-1/4. Because the N-terminal amino acid sequences of the neoepitopes are different between human IL-18 and mouse IL-18, the anti-human IL-18 neoepitope antibodies do not recognize mouse mature IL-18. We have now generated novel anti-mouse IL-18 neoepitope antibodies. We also confirmed CXCL2 secretion from P-815 mouse cells by mouse IL-18 stimulation, and established a simple assay to evaluate the activity of mouse IL-18. Using this evaluation system, we confirmed that the anti-mouse IL-18 neoepitope antibodies could inhibit mouse IL-18. By demonstrating the therapeutic efficacy of the anti-mouse IL-18 neoepitope and function-blocking mAbs established in the present study in mouse models, corresponding to human inflammatory diseases in which IL-18 may be involved, such as inflammatory bowel diseases, we can provide the proof-of-concept that the previously established anti-human IL-18 neoepitope and function-blocking mAbs work in human inflammatory disorders corresponding to mouse models.

A randomised, double-blind, placebo-controlled phase III trial on the efficacy and safety of tocilizumab in patients with familial Mediterranean fever.

OBJECTIVES: To evaluate the efficacy and safety of tocilizumab (TCZ), an interleukin 6 receptor monoclonal antibody, in a subset of Japanese patients with familial Mediterranean fever (FMF). METHODS: We performed a double-blind, randomised, parallel-group trial, followed by an open-label extension trial, in patients with colchicine-resistant or -intolerant FMF (crFMF) (UMIN000028010). Patients were randomly assigned (1:1) to receive TCZ (162 mg every week) or placebo, administered subcutaneously, for 24 weeks. Rescue treatment was allowed if the rescue criteria were met. The primary endpoint was the number of fever attacks over the 24 weeks of treatment. Secondary endpoints included the frequency of accompanying symptoms during attacks, serum CRP and SAA values, and adverse events (AEs). The open-label extension study evaluated the long-term safety and efficacy of TCZ in patients who had completed the preceding study (UMIN000032557). RESULTS: We randomly assigned 23 patients to either TCZ (n=1) or placebo (n=12). The TCZ-placebo rate ratios were 0.691 (95% confidence intervals (CI), 0.189-2.531; p=0.577) for the fever attacks, based on the group rates per week. The recurrence of attacks was significantly lower in the TCZ group (hazard ratio = 0.457; 95% CI, 0.240-0.869). Fever attacks, accompanying symptoms, serum CRP and SAA values were controlled in most of the patients who received long-term TCZ. In these trials, the numbers and severity of AEs did not differ between groups. CONCLUSIONS: Although a primary endpoint was not met in the preceding trial, long-term administration of TCZ showed stable efficacy and safety for patients with crFMF.

Efficacy and safety of canakinumab for colchicine-resistant or colchicine-intolerant familial Mediterranean fever: A single-centre observational study.

OBJECTIVES: To evaluate the efficacy and safety of canakinumab in Japanese patients with colchicine-resistant or colchicine-intolerant familial Mediterranean fever (FMF) in a real-world clinical setting. METHODS: We reviewed 13 Japanese FMF patients to whom canakinumab was introduced during the period of October 2017 to December 2020. All patients were diagnosed as FMF according to Tel-Hashomer criteria. We performed genetic analyses for Mediterranean fever or MEFV by targeted next-generation sequencing. Efficacy was assessed by attack frequency and the percentage of patients who achieved attack improvement at 24 weeks. Safety was assessed by adverse events observed during canakinumab treatment. RESULTS: The median duration and follow-up of canakinumab treatment were 13 and 16 months, respectively. The median attack frequency was 0.50 [0.30-1.00] at 24 weeks, which was a significant decrease from 2.00 [0.85-2.88] at the time of induction (p = .019). There were three patients (23%) with complete resolution of attacks at 24 weeks. No serious adverse events were observed. However, one patient had small intestinal ulceration which led to the discontinuation of canakinumab. CONCLUSIONS: Although the number of cases is small, this study suggests that canakinumab is efficacious and safe for use in Japanese patients with colchicine-resistant or colchicine-intolerant FMF in a real-world clinical setting in Japan.

Current insights and future prospects for the pathogenesis and treatment for rheumatoid arthritis.

Genetic, environmental, and epigenetic factors simultaneously or serially contribute to immune cells and resident joint tissue cell abnormalities, invariably leading to joint destruction. Understanding the immune cell dysfunction in earlier years has brought forward life-changing therapeutics to patients with rheumatoid arthritis (RA). Further advances in the understanding of the immune and joint tissue-resident cell signaling and metabolic defects should produce additional tools to treat people with RA and foretell those who will respond to each biological or small drug. This review presents the latest evidence on RA pathogenesis and outlines the prospects for achieving precision medicine.

Systemic lupus erythematosus overlapping dermatomyositis owing to a heterozygous TREX1 Asp130Asn missense mutation.

The 3' repair exonuclease 1 (TREX1) gene encodes a nuclear protein with 3' exonuclease activity, and the mutations have been associated with autoimmune diseases. Herein, we performed genetic analysis for the TREX1 gene in 55 patients with systemic lupus erythematosus (SLE). We identified one SLE patient with overlapping dermatomyositis having a heterozygous p.Asp130Asn mutation in the TREX1 gene. The patient had a high level of serum interferon (IFN)-α compared with that in healthy controls and other patients with SLE. In addition, the patient expressed elevated IFN signature genes compared with healthy controls. Our molecular dynamics simulation of the TREX1 protein in a complex with double-stranded DNA revealed that the D130N mutant causes significant changes in the active site's interaction network. One of our cases exhibited a heterozygous TREX1 p.Asp130Asn mutation that contributed to the type I IFN pathway, which may lead to the development of a severe SLE phenotype.

A case of tocilizumab-refractory idiopathic multicentric Castleman's disease successfully treated with sirolimus.

mTOR signaling may be a new therapeutic target for IL-6 inhibitor refractory iMCD-NOS.

Mediterranean fever gene variants modify clinical phenotypes of idiopathic multi-centric Castleman disease.

Four cases of idiopathic multi-centric Castleman disease (iMCD) reportedly have variants in hereditary autoinflammatory disease-related genes; however, the frequency and role of these variants in iMCD is still unknown. We therefore investigated such gene variants among patients with iMCD and aimed to reveal the relationship between iMCD and autoinflammatory disease-related genes. We reviewed 14 Japanese iMCD patients who were recruited between January 2015 and September 2019. All patients met both the Japanese tentative diagnostic criteria for Castleman disease and the international consensus diagnostic criteria for iMCD. We performed genetic analyses for 31 autoinflammatory disease-related genes by targeted next-generation sequencing. The MEFV gene variants were observed in 10 of 14 patients with iMCD. Although iMCD had a high percentage of exons 2 or 3 variants of MEFV, comparison of data from healthy Japanese subjects indicated that there was no significant difference in the percentage between healthy Japanese subjects and patients with iMCD. Variants of uncertain significance (VUS) in the TNFRSF1A and CECR1 genes were observed in two of the patients, respectively. We divided patients into two groups-those with MEFV variants (excluding E148Q variants) and those without MEFV variants-and compared the clinical characteristics between these two groups. Patients with MEFV variants, excluding E148Q variants, exhibited a significantly higher likelihood of fever and significantly lower levels of hemoglobin than those lacking MEFV variants. Our results indicated that patients with iMCD tended to have a high frequency of MEFV gene variants and the presence of such variants can affect iMCD clinical phenotypes.

Idiopathic multicentric Castleman disease with novel heterozygous Ile729Met mutation in exon 10 of familial Mediterranean fever gene.

OBJECTIVE: While the aetiology of idiopathic multicentric Castleman disease (iMCD) remains unclear, the involvement of autoinflammatory mechanisms has been suggested. Herein we report a Japanese patient with iMCD with a novel heterozygous Ile729Met mutation in exon 10 of the Mediterranean fever (MEFV) gene. METHODS: We performed genetic analysis via targeted next-generation sequencing analysis and Sanger sequencing and conducted molecular dynamics simulations to investigate the hydrophobic interactions around the 729th amino acid in human pyrin. RESULTS: In February 2011, a 59-year-old man was diagnosed with IgG4-related disease at our department based on the findings of cervical and hilar lymphadenopathies, typical lung lesions and cervical lymph node biopsy. The patient was followed up without treatment, as he was asymptomatic. However, he had been experiencing prolonged fatigue and fever with high levels of CRP since June 2017. Axillary lymph node biopsy findings led to the diagnosis of iMCD. He was successfully treated with an IL-6 inhibitor and has been in remission for 12 months. Genetic analyses for hereditary autoinflammatory disease-related genes were performed, revealing a novel heterozygous Ile729Met mutation in exon 10 of the MEFV gene. We identified that this novel mutation significantly altered the local interaction of the human pyrin B30.2 domain by molecular dynamics simulation analysis and experimentally had the potential for inflammasome activation with increased inflammatory cytokines. CONCLUSION: The abnormal function of pyrin due to a mutation in the MEFV gene in this patient may have contributed to the development of MCD by inducing IL-6 production via inflammasome signalling.

Life prognosis and renal relapse after induction therapy in Japanese patients with proliferative and pure membranous lupus nephritis.

OBJECTIVE: We aimed to compare life prognosis and renal relapse after induction therapy in proliferative (PLN) and pure membranous LN (MLN). METHODS: We retrospectively analysed the cases of 140 of 172 patients with LN who underwent a renal biopsy at our hospital or community hospitals from 1993 to 2016. We determined the complete response (CR) rate at 12 months after the patients had started induction therapy, and we evaluated the predictive factors for CR, life prognosis and renal relapse in PLN and pure MLN. We defined PLN as International Society of Neurology and the Renal Pathology Society (ISN/RPS) Class III or IV and MLN as ISN/RPS Class V. RESULTS: The renal pathology of 99 (70.7%) patients was classified as PLN, and that of the other 41 (29.3%) patients as MLN. Fifty patients (50.5%) with PLN and 22 patients (53.7%) with MLN achieved a CR at 12 months. A multivariate analysis showed that a lower index of chronicity in PLN and a higher total haemolytic complement (CH50) level in MLN were predictive factors for achieving a CR at 12 months. A Kaplan-Meier analysis showed that the life prognosis (P = 0.93) and renal relapse (P = 0.52) were not significantly different between PLN and MLN. CONCLUSIONS: The predictive factors for a CR at 12 months post-induction therapy were index of chronicity in PLN and CH50 level in MLN. There were no significant differences in life prognosis or renal relapse between PLN and MLN in the achievement of a CR at 12 months post-induction therapy.

Comparison of the quantitative measurement of 18F-FDG PET/CT and histopathological findings in IgG4-related disease.

OBJECTIVES: To investigate the utility of 18F-FDG PET/CT in the diagnostic procedure of IgG4-related disease (IgG4-RD), we analysed the association between quantitative method of 18F-FDG PET/CT and histological findings. METHODS: Twenty-one patients with IgG4-RD in whom 18F-FDG PET/CT was performed at the time of diagnosis were enrolled. Tissue biopsy was performed at 24 sites in 21 patients. To perform quantitative analysis of 18F-FDG PET/CT imaging, the highest standardised uptake value (SUV) of the pixels (SUVmax) and the average SUV (SUVmean) within the biopsied lesion were measured. The SUVmean of the liver was also measured as a reference. RESULTS: The mean age at diagnosis was 64.6±11.9 years, and the median serum IgG4 level was 650 mg/dl. Histological findings were consistent with IgG4-RD (histopathology-positive) at 19 out of 24 sites. Although there was no significant difference in the values of SUVmax between histopathology-positive and histopathology-negative tissues, the values of SUVmean were significantly higher in the histopathology-positive tissue (4.98 and 3.54, respectively p<0.05). The values of SUVmean/liver were also higher in the histopathology-positive tissue (2.17 and 1.52, respectively p<0.05). To establish a cut-off value of SUVmean to determine which of multiple lesions should be biopsied, a ROC curve was constructed. ROC curve analysis indicated SUVmean=4.07 or SUVmean/liver=1.66 as a cut-off value. CONCLUSIONS: Our present study suggested that quantitative analysis of 18F-FDG-PET/CT imaging might be useful for selecting the biopsy site in IgG4-RD. The calculation of SUVmean, not of SUVmax, is important for evaluating IgG4-RD-related lesions in 18F-FDG PET/CT imaging.

Association between serum bone biomarker levels and therapeutic response to abatacept in patients with rheumatoid arthritis (RA): a multicenter, prospective, and observational RA ultrasound cohort study in Japan.

BACKGROUND: To evaluate the effect of treatment on serum bone biomarkers and explore whether serum bone biomarkers are associated with therapeutic response in rheumatoid arthritis (RA) patients treated with abatacept. METHODS: We enrolled 59 RA patients treated with abatacept from a multicenter, exploratory, short-term, prospective and observational ultrasound cohort study of patients who received biologic or targeted synthetic disease-modifying antirheumatic drug (DMARD) therapy. We evaluated the patients' clinical disease activity and musculoskeletal ultrasound (MSUS) scores. The serum concentrations of five bone biomarkers were evaluated (dickkopf-1 [Dkk-1], sclerostin [SOST], osteocalcin [OC], osteopontin [OPN], and osteoprotegerin [OPG]) by multiplex bead assays at baseline, 3, and 6 months: the change over 6 months was defined as the Δ value. 'Power Doppler (PD) responder' was defined as a patient whose Δtotal PD score over 6 months was greater than the median change. RESULTS: Abatacept significantly improved the clinical disease activity and MSUS score over 6 months. Serum OPG was significantly elevated at 6 months after the abatacept introduction (p = 0.016). The ΔSOST and ΔOPG were significantly greater in the PD responders versus the non-PD responders (p = 0.0041 and 0.0073, respectively). The serum Dkk-1 at baseline was significantly lower in the PD responders (n = 30) vs. the non-PD responders (n = 29) (p = 0.026). A multivariate logistic regression analysis showed that the serum Dkk-1 at baseline (odds ratio 0.50, 95% confidence interval [CI] 0.23-0.91, p = 0.043) was an independent predictor of PD responder status. CONCLUSION: Serum levels of bone biomarkers may be useful for predicting RA patients' therapeutic responses to abatacept. TRIAL REGISTRATION: Name of the registry: Assessment of therapeutic responsiveness by imaging of the joints in patients with rheumatoid arthritis; A observational cohort study Trial registration number: UMIN000012524 Date of registration: 12/9/2013 URL of trial registry record: https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000014657.