Glucocorticoids in the treatment of IgG4-related disease-Prospects for new international treatment guidelines.

Immunoglobulin G4-related disease (IgG4-RD) is a chronic fibro-inflammatory disease that may cause dysfunction in various organs. Worldwide multidisciplinary experts attending the Fourth International Symposium on IgG4-Related Disease in Japan in 2021 discussed treatments for IgG4-RD, especially glucocorticoid (GC) therapy. This review describes the efficacy, safety, and cost of treatments for IgG4-RD based on findings presented at the international symposium. A medium dose of GC was considered appropriate for the initial treatment of IgG4-RD. A randomized controlled trial and an open-label prospective study have shown that long-term maintenance GC therapy (prednisolone ≥ 5 mg/day) could prevent disease relapse. In addition, two open-label randomized controlled trials reported the effects of combinational use of GC and synthetic immunosuppressive agents, mycophenolate mofetil and leflunomide, on relapse prevention. Moreover, an open-label single-arm study showed an excellent rate of clinical response to rituximab. Many observational studies have shown the efficacy of an appropriate GC regimen in patients with IgG4-RD. Synthetic immunosuppressive agents and a molecular-targeted agent can be potent alternatives to GCs, but additional studies are required comparing their efficacy, risk of infection, and costs.

Long-term evaluation of E6011, an anti-fractalkine monoclonal antibody, in patients with rheumatoid arthritis inadequately responding to biological disease-modifying antirheumatic drugs.

OBJECTIVES: The objective of the study is to evaluate the long-term safety and efficacy of E6011, a humanized anti-fractalkine monoclonal antibody, in patients with rheumatoid arthritis with an inadequate response to biological disease-modifying antirheumatic drugs. METHODS: In the double-blind treatment phase (24 weeks), placebo or E6011 400 mg was administered until Week 10. Thereafter, E6011 200 mg or 400 mg was administered to Week 22. Subjects who completed the evaluation at Week 24 of the treatment phase were rolled over into the extension phase. The extension phase lasted until Week 104, and all subjects received E6011 400 mg or 200 mg every 2 weeks in an open-label manner until Week 102. RESULTS: A total of 47 subjects completed the double-blind treatment phase and were rolled over into the extension phase. In total, 46 (97.9%) subjects experienced any adverse events, and the incidence of treatment-related adverse events was 57.4%. No clear efficacy trend in the American College of Rheumatology 20% response rates was observed. CONCLUSIONS: E6011 was well tolerated in active rheumatoid arthritis patients who had shown an inadequate response to biologic disease-modifying antirheumatic drugs, but no clear benefit in the American College of Rheumatology 20% response rates was observed. Further studies are needed to clarify the clinical benefit of E6011.

Long-term safety and efficacy of E6011, an anti-fractalkine monoclonal antibody, in patients with rheumatoid arthritis inadequately responding to methotrexate.

OBJECTIVES: To evaluate the long-term safety and efficacy of E6011, a humanized anti-fractalkine monoclonal antibody, in patients with rheumatoid arthritis (RA) with an inadequate response to methotrexate (MTX). METHODS: Active RA patients with an inadequate response to MTX were randomly assigned to the E6011 or placebo group and received the study drug subcutaneously every 2 weeks during a 24-week double-blind study period. Subjects who completed evaluations at Week 24 were rolled over into the extension phase and received open-label E6011 (200 or 400 mg) every 2 weeks until Week 102. The safety analysis was conducted up to Week 104, and the efficacy analysis was conducted up to Week 84. RESULTS: A total of 169 subjects completed the double-blind treatment phase and were rolled over into the extension phase. In total, 167 (98.8%) subjects experienced any adverse events, and the incidence of treatment-related adverse events was 56.2%. The American College of Rheumatology 20 response rates were observed between 40 and 70% during the extension phase. CONCLUSIONS: E6011 was safe and well tolerated with no notable safety concerns up to 102 weeks in RA patients with an inadequate response to MTX.

The 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD.

IgG4-related disease (IgG4-RD) is a fascinating clinical entity first reported in this century in Japan, and includes a wide variety of diseases, such as formerly named Mikulicz's disease (MD), autoimmune pancreatitis (AIP), interstitial nephritis, prostatitis and retroperitoneal fibrosis. The Japanese IgG4 team organized by the Ministry of Health, Labor and Welfare (MHLW) of Japan has published the first criteria, comprehensive diagnostic (CD) criteria for IgG-RD 2011. Thereafter, IgG4-RD has been accepted widely and many cases have been reported from all over the world. Several problems have arisen in clinical practice, however, including the difficulty obtaining biopsy samples, and the sensitivity and specificity in cut off level of serum IgG4 and impaired immunostaining of IgG4. Given these situations, the Japanese IgG4 team has updated the 2011 comprehensive diagnostic criteria for IgG4-RD and propose the 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD, which consists of 3 domains; 1) Clinical and radiological features, 2) Serological diagnosis and 3) Pathological diagnosis. In addition, the new pathological diagnosis is composed by three sub-items including storiform fibrosis and obliterative phlebitis.

A phase 2 study of E6011, an anti-Fractalkine monoclonal antibody, in patients with rheumatoid arthritis inadequately responding to biological disease-modifying antirheumatic drugs.

OBJECTIVES: To evaluate the safety and efficacy of E6011, a novel humanized anti-fractalkine monoclonal antibody, in patients with active rheumatoid arthritis (RA) with an inadequate response to biological disease-modifying antirheumatic drugs (DMARDs). METHODS: Active RA patients inadequately responding to biological DMARDs were randomly assigned to placebo or E6011 400-mg group at a 1:1 ratio, and administered E6011 at weeks 0, 1, 2, and subsequently every 2 weeks. Primary endpoint was American College of Rheumatology (ACR)20 response at week 12. RESULTS: Of 64, 33 received placebo, 31 received E6011 400-mg. The ACR20 response rate at week 12 (non-responder imputation) was 27.3% and 22.6% in the placebo and E6011 groups, respectively. ACR50, ACR70 response rates at week 12 were 3.0%, 0% in the placebo and 9.7%, 3.2% in the E6011 group. Exploratory PK exposure analysis revealed that the effect of E6011 tended to be clearer in patients with higher serum trough E6011 concentration. E6011 was well tolerated with no notable safety concerns. CONCLUSIONS: E6011 400-mg was well tolerated but had no clear efficacy at week 12 in RA patients with inadequate response to biologics. Further investigations are warranted to determine the optimal clinical dose and evaluation period for E6011.

The 2019 American College of Rheumatology/European League Against Rheumatism classification criteria for IgG4-related disease.

IgG4-related disease (IgG4-RD) can cause fibroinflammatory lesions in nearly any organ. Correlation among clinical, serological, radiological and pathological data is required for diagnosis. This work was undertaken to develop and validate an international set of classification criteria for IgG4-RD. An international multispecialty group of 86 physicians was assembled by the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR). Investigators used consensus exercises; existing literature; derivation and validation cohorts of 1879 subjects (1086 cases, 793 mimickers); and multicriterion decision analysis to identify, weight and test potential classification criteria. Two independent validation cohorts were included. A three-step classification process was developed. First, it must be demonstrated that a potential IgG4-RD case has involvement of at least one of 11 possible organs in a manner consistent with IgG4-RD. Second, exclusion criteria consisting of a total of 32 clinical, serological, radiological and pathological items must be applied; the presence of any of these criteria eliminates the patient from IgG4-RD classification. Third, eight weighted inclusion criteria domains, addressing clinical findings, serological results, radiological assessments and pathological interpretations, are applied. In the first validation cohort, a threshold of 20 points had a specificity of 99.2% (95% CI 97.2% to 99.8%) and a sensitivity of 85.5% (95% CI 81.9% to 88.5%). In the second, the specificity was 97.8% (95% CI 93.7% to 99.2%) and the sensitivity was 82.0% (95% CI 77.0% to 86.1%). The criteria were shown to have robust test characteristics over a wide range of thresholds. ACR/EULAR classification criteria for IgG4-RD have been developed and validated in a large cohort of patients. These criteria demonstrate excellent test performance and should contribute substantially to future clinical, epidemiological and basic science investigations.

Impaired expression of innate immunity-related genes in IgG4-related disease: A possible mechanism in the pathogenesis of IgG4-RD.

Background: IgG4-related disease (IgG4-RD) is characterized by elevated serum IgG4 and tissue infiltration by IgG4-positive plasma cells. The pathogenesis of this disease is not clear. Transcriptome analysis was performed to identify genes over- and under-expressed in patients with IgG4-RD.Method: DNA microarray analysis was performed using RNA from peripheral blood mononuclear cells of two patients with IgG4-RD and four healthy individuals. Genes showing a greater than threefold change in expression in IgG4-RD patients following steroid therapy were identified. Four genes related to innate immunity such as transcobalamin I (TCN1), secretory leukocyte peptidase inhibitor (SLPI), bactericidal/permeability-increasing protein (BPI) and lactotransferrin (LTF) were assessed by real-time PCR in 15 IgG4-RD patients and 13 healthy individuals.Result: DNA microarray analysis identified 30 genes showing a greater than threefold change in expression in IgG4-RD patients following steroid therapy. Real-time RT-PCR showed that the levels of mRNAs encoding TCNI and SLPI, except for BPI and LTF, were significantly lower in patients with IgG4-RD than in healthy people. The levels of all four mRNAs in patients with IgG4-RD were significantly increased after steroid treatment.Conclusion: These results indicate that reduction in expression of innate immunity-related genes may participate in the pathogenesis of IgG4-RD that steroid treatment may rectify impaired innate immunity as well as acquired immunity.

The front line of research into immunoglobin G4-related disease - Do autoantibodies cause immunoglobin G4-related disease?

IgG4-related disease (IgG4-RD) is a novel clinical disease entity characterized by elevated serum IgG4 concentration and tumefaction or tissue infiltration by IgG4-positive plasma cells. Although IgG4-RD is attracting strong attention as a new clinical entity, the pathogenesis of IgG4-RD and the roles of IgG4 are still unknown. Recently, self-antigens including Laminin 511 E8, Galectin-3 and Annexin A11, have been reported from one to the next as autoantigens which may be involved in the pathogenesis of IgG4-RD. In this review, we describe up-to-date information on the research of this emerging disease entity. Moreover, we discuss the pathogenesis of IgG4-RD by focusing on recent reports concerning autoantibodies.

Splicing variant of WDFY4 augments MDA5 signalling and the risk of clinically amyopathic dermatomyositis.

OBJECTIVES: Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of rare autoimmune diseases in which both genetic and environmental factors play important roles. To identify genetic factors of IIM including polymyositis, dermatomyositis (DM) and clinically amyopathic DM (CADM), we performed the first genome-wide association study for IIM in an Asian population. METHODS: We genotyped and tested 496 819 single nucleotide polymorphism for association using 576 patients with IIM and 6270 control subjects. We also examined the causal mechanism of disease-associated variants by in silico analyses using publicly available data sets as well as by in in vitro analyses using reporter assays and apoptosis assays. RESULTS: We identified a variant in WDFY4 that was significantly associated with CADM (rs7919656; OR=3.87; P=1.5×10-8). This variant had a cis-splicing quantitative trait locus (QTL) effect for a truncated WDFY4isoform (tr-WDFY4), with higher expression in the risk allele. Transexpression QTL analysis of this variant showed a positive correlation with the expression of NF-κB associated genes. Furthermore, we demonstrated that both WDFY4 and tr-WDFY4 interacted with pattern recognition receptors such as TLR3, TLR4, TLR9 and MDA5 and augmented the NF-κB activation by these receptors. WDFY4 isoforms also enhanced MDA5-induced apoptosis to a greater extent in the tr-WDFY4-transfected cells. CONCLUSIONS: As CADM is characterised by the appearance of anti-MDA5 autoantibodies and severe lung inflammation, the WDFY4 variant may play a critical role in the pathogenesis of CADM.

Current Concept of IgG4-Related Disease.

IgG4-related disease (IgG4-RD) is a fibroinflammatory disease of unknown etiology, which is characterized by a tendency to form tumefactive lesions, increased serum levels of IgG4, and massive infiltration of IgG4-positive plasma cells with storiform fibrosis and/or obliterative phlebitis. Patients with IgG4-RD have frequently multiorgan involvements such as the pancreas, biliary tree, salivary glands, periorbital tissues, kidneys, lungs, lymph nodes, and retroperitoneum. IgG4-RD mainly affects middle-aged to elderly men except for involvement in lachrymal and salivary glands, so-called Mikulicz's disease. The clinical manifestations of IgG4-RD depend on individually involved organs and respond well to steroid, but the prognosis still remains unclear. Some patients develop serious complications such as obstructive jaundice due to hepatic, gallbladder, or pancreatic lesions; hydronephrosis due to retroperitoneal fibrosis; or respiratory symptoms due to pulmonary lesions. Nomenclatures of individual organ manifestation of IgG4-RD have been internationally consented.

Safety, pharmacokinetics, and efficacy of E6011, an antifractalkine monoclonal antibody, in a first-in-patient phase 1/2 study on rheumatoid arthritis.

OBJECTIVE: Fractalkine (CX3CL1/FKN) is a chemokine that regulates chemotaxis and adhesion of CX3C chemokine receptor 1 (CX3CR1)-expressing inflammatory cells. We conducted the first phase 1/2, open-label, multiple ascending dose study of E6011, a humanized anti-FKN monoclonal antibody, in Japanese rheumatoid arthritis (RA) patients (clinicaltrial.gov identifier: NCT02196558). METHODS: Active RA patients with an inadequate response or intolerance to methotrexate or tumor necrosis factor (TNF) inhibitor received E6011 at week 0, 1, 2, and thereafter every 2 weeks for 12 weeks. RESULTS: Twelve, 15, and 10 subjects were enrolled in the 100, 200, and 400 mg cohorts, respectively. No severe adverse events (AEs) or deaths occurred, and no major differences were observed in the incidence or severity of AEs across the cohorts. Serum E6011 concentrations increased dose dependently. American College of Rheumatology (ACR) 20, 50, and 70 responses at week 12 were 75.0%, 33.3%, and 8.3% in the 100 mg cohort; 66.7%, 20.0%, and 13.3% in the 200 mg cohort; and 60.0%, 30.0%, and 20.0% in the 400 mg cohort, respectively. CONCLUSIONS: E6011 appeared to be safe and well tolerated in RA patients during this 12-week treatment period, suggesting that E6011 has an effective clinical response in active RA patients.

Comparison of performance of the 2016 ACR-EULAR classification criteria for primary Sjögren's syndrome with other sets of criteria in Japanese patients.

OBJECTIVES: To compare the performance of the new 2016 American College of Rheumatology (ACR)-European League Against Rheumatism (EULAR) classification criteria for primary Sjögren's syndrome (SS) with 1999 revised Japanese Ministry of Health criteria for diagnosis of SS (JPN), 2002 American-European Consensus Group classification criteria for SS (AECG) and 2012 ACR classification criteria for SS (ACR) in Japanese patients. METHODS: The study subjects were 499 patients with primary SS (pSS) or suspected pSS who were followed up in June 2012 at 10 hospitals in Japan. All patients had been assessed for all four criteria of JPN (pathology, oral, ocular, anti-SS-A/SS-B antibodies). The clinical diagnosis by the physician in charge was set as the 'gold standard'. RESULTS: pSS was diagnosed in 302 patients and ruled out in 197 patients by the physician in charge. The sensitivity of the ACR-EULAR criteria in the diagnosis of pSS (95.4%) was higher than those of the JPN, AECG and ACR (82.1%, 89.4% and 79.1%, respectively), while the specificity of the ACR-EULAR (72.1%) was lower than those of the three sets (90.9%, 84.3% and 84.8%, respectively). The differences of sensitivities and specificities between the ACR-EULAR and other three sets of criteria were statistically significant (p<0.001). Eight out of 302 patients with pSS and 11 cases out of 197 non-pSS cases satisfied only the ACR-EULAR criteria, compared with none of the other three sets. CONCLUSIONS: The ACR-EULAR criteria had significantly higher sensitivity and lower specificity in diagnosis of pSS, compared with the currently available three sets of criteria.

Current approach to the diagnosis of IgG4-related disease - Combination of comprehensive diagnostic and organ-specific criteria.

IgG4-related disease (IgG4-RD) is a fascinating clinical entity proposed by Japanese investigators, and includes a wide variety of diseases, formerly diagnosed as Mikulicz's disease (MD), autoimmune pancreatitis (AIP), interstitial nephritis, prostatitis, retroperitoneal fibrosis, etc. Although all clinicians in every field of medicine may encounter this new disease, a unifying diagnostic criterion has not been established. In 2011, the Japanese IgG4 team, organized by the Ministry of Health, Labor and Welfare (MHLW) of Japan, published comprehensive diagnostic criteria for IgG4-RD. Several problems with these criteria have arisen in clinical practice, however, including the difficulty obtaining biopsy samples from some patients, and the sensitivity and the specificity of techniques used to measure serum IgG4 concentrations. Although serum IgG4 concentration is an important clinical marker for IgG4-RD, its diagnostic utility in differentiating IgG4-RD from other diseases, called IgG4-RD mimickers, remains unclear. This review describes the current optimal approach for the diagnosis of IgG4-RD, based on both comprehensive and organ-specific diagnostic criteria, in patients with diseases such as IgG4-related pancreatitis (AIP), sclerosing cholangitis, and renal, lung and orbital diseases.

Isolation of vascular smooth muscle antigen-reactive CD4(+)αßTh1 clones that induce pulmonary vasculitis in MRL/Mp-Fas(+/+) mice.

Here, we established CD4(+)αßTh1 clones specific for rat vascular smooth muscle antigen (VSMAg) that induced vasculitis lesions in the lungs of MRL/Mp-Fas(+/+) mice following adoptive transfer. Six different T cell clones, MV1b1 (Vß1), MV1b4 (Vß4), MV1b8.3 (Vß8.3), MV1b61 (Vß6), MV1b62 (Vß6), and MV1b63 (Vß6), were isolated from the MV1 T cell line from the regional lymph nodes of immunized MRL/Mp-Fas(+/+) mice; the three (Vß6) clones had unique CDR3 amino acid sequences. Following stimulation with VSMAg-pulsed antigen presenting cells, MV1b61 and MV1b62 failed to secrete interferon-γ and tumor necrosis factor-α, although the other four clones secreted high levels of both cytokines. In adoptive transfer experiments, MV1b61 and MV1b62 did not induce organ involvement including pulmonary vasculitis. In contrast, MV1b1, MV1b4, MV1b8.3, and MV1b63 induced perivascular mononuclear cell infiltration in pulmonary small arteries. These clones may provide useful tools for investigating the underlying mechanisms of vasculitis syndromes and for developing therapeutic strategies.

Deficient leptin signaling ameliorates systemic lupus erythematosus lesions in MRL/Mp-Fas lpr mice.

Leptin is secreted by adipocytes, the placenta, and the stomach. It not only controls appetite through leptin receptors in the hypothalamus, it also regulates immunity. In the current study, we produced leptin-deficient MRL/Mp-Fas(lpr) mice to investigate the potential role of leptin in autoimmunity. C57BL/6J-ob/ob mice were backcrossed with MRL/Mp-Fas(lpr) mice, which develop human systemic lupus erythematosus (SLE)-like lesions. The effects of leptin deficiency on various SLE-like manifestations were investigated in MRL/Mp-Fas(lpr) mice. The regulatory T cell population in the spleen was analyzed by flow cytometry, and the effects of leptin on regulatory T cells and Th17 cells were evaluated in vitro. Compared with leptin-producing MRL/Mp-Fas(lpr) mice, leptin-deficient MRL/Mp-Fas(lpr) mice showed less marked splenomegaly and a particularly low population of CD3(+)CD4(-)CD8(-)B220(+) T cells (lpr cells). Their serum concentrations of Abs to dsDNA were lower, and renal histological changes at age 20 wk were ameliorated. Regulatory T cells were increased in the spleens of leptin-deficient MRL/Mp-Fas(lpr) mice. Leptin suppressed regulatory T cells and enhanced Th17 cells in vitro. In conclusion, blockade of leptin signaling may be of therapeutic benefit in patients with SLE and other autoimmune diseases.

The SSB-positive/SSA-negative antibody profile is not associated with key phenotypic features of Sjögren's syndrome.

OBJECTIVE: To determine whether the Sjögren's syndrome B (SSB)-positive/Sjögren's syndrome A (SSA)-negative antibody profile is associated with key phenotypic features of SS. METHODS: Among registrants in the Sjögren's International Collaborative Clinical Alliance (SICCA) with possible or established SS, we compared anti-SSA/anti-SSB reactivity profiles against concurrent phenotypic features. We fitted logistic regression models to explore the association between anti-SSA/anti-SSB reactivity profile and each key SS phenotypic feature, controlling for potential confounders. RESULTS: Among 3297 participants, 2061 (63%) had negative anti-SSA/anti-SSB, 1162 (35%) had anti-SSA with or without anti-SSB, and 74 (2%) anti-SSB alone. Key SS phenotypic features were more prevalent and had measures indicative of greater disease activity in those participants with anti-SSA, either alone or with anti-SSB, than in those with anti-SSB alone or negative SSA/SSB serology. These between-group differences were highly significant and not explained by confounding by age, race/ethnicity or gender. Participants with anti-SSB alone were comparable to those with negative SSA/SSB serology in their association with these key phenotypic features. Among SICCA participants classified with SS on the basis of the American-European Consensus Group or American College of Rheumatology criteria, only 2% required the anti-SSB-alone test result to meet these criteria. CONCLUSIONS: The presence of anti-SSB, without anti-SSA antibodies, had no significant association with SS phenotypic features, relative to seronegative participants. The solitary presence of anti-SSB antibodies does not provide any more support than negative serology for the diagnosis of SS. This serological profile should thus be interpreted cautiously in clinical practice and potentially eliminated from future classification criteria.

IgG4-related disease and its pathogenesis-cross-talk between innate and acquired immunity.

IgG4-related disease (IgG4-RD) is a novel clinical entity proposed in Japan in the 21th century and is attracting strong attention over the world. The characteristic manifestations of IgG4-RD are increased serum IgG4 concentration and tumefaction by IgG4(+) plasma cells. Although the clinical manifestations in various organs have been established, the pathogenesis of IgG4-RD is still unknown. Recently, many reports of aberrant acquired immunity such as Th2-diminated immune responses have been published. However, many questions still remain, including questions about the pathogenesis of IgG4-RD and the roles of IgG4. In this review, we discuss the pathogenesis of IgG4-RD by focusing on the cross-talk between innate and acquired immunity.

Primary and secondary surveys on epidemiology of Sjögren's syndrome in Japan.

OBJECTIVE: To characterize the epidemiology of Sjögren's syndrome (SS), including prevalence, disease type, extra-glandular involvement, satisfaction of diagnostic criteria sets, and treatment used in Japan. METHODS: The Research Team for Autoimmune Diseases, the Research Program for Intractable Disease by the Ministry of Health, Labor and Welfare conducted primary and secondary surveys on epidemiology of SS in 2011. The primary survey covered 4,729 out of 14,095 Japan-wide Hospital Departments to investigate the prevalence of SS. The secondary survey encompassed 214 Hospital Departments that agreed to the survey, to characterize disease type, extra-glandular involvement, satisfaction of diagnostic criteria sets, and treatments. RESULTS: The number of patients with SS in Japan estimated by the primary survey was 68,483. The secondary survey involving data collected from 2,195 SS patients from 98 Hospital Departments showed that the mean age of patients was 60.8 ± 15.2 years, male/female ratio was 1/17.4, primary/secondary SS was about 60%/40% and glandular/extra-glandular form in primary SS was about 70%/25%. The satisfaction rate was 53.8% for the 1999 revised Japanese Ministry of Health criteria for the diagnosis of SS, 47.7% for the 2002 American-European Consensus Group classification criteria for SS and 49.6% for 2012 American College of Rheumatology classification criteria for SS. Corticosteroids were used by 752 of 2,195 patients (34%), immunosuppressants by 358 patients (16%), biologics by 68 patients (3%) and secretagogues by 695 patients (32%). CONCLUSION: The surveys provided valuable information on the epidemiology of SS including prevalence, disease type, extra-glandular involvement, satisfaction of diagnostic criteria sets and treatments used today in Japan.

Expression of USP25 associates with fibrosis, inflammation and metabolism changes in IgG4-related disease.

IgG4-related disease (IgG4-RD) has complex clinical manifestations ranging from fibrosis and inflammation to deregulated metabolism. The molecular mechanisms underpinning these phenotypes are unclear. In this study, by using IgG4-RD patient peripheral blood mononuclear cells (PBMCs), IgG4-RD cell lines and Usp25 knockout mice, we show that ubiquitin-specific protease 25 (USP25) engages in multiple pathways to regulate fibrotic and inflammatory pathways that are characteristic to IgG4-RD. Reduced USP25 expression in IgG4-RD leads to increased SMAD3 activation, which contributes to fibrosis and induces inflammation through the IL-1ß inflammatory axis. Mechanistically, USP25 prevents ubiquitination of RAC1, thus, downregulation of USP25 leads to ubiquitination and degradation of RAC1. Decreased RAC1 levels result in reduced aldolase A release from the actin cytoskeleton, which then lowers glycolysis. The expression of LYN, a component of the B cell receptor signalosome is also reduced in USP25-deficient B cells, which might result in B cell activation deficiency. Altogether, our results indicate a potential anti-inflammatory and anti-fibrotic role for USP25 and make USP25 a promising diagnostic marker and potential therapeutic target in IgG4-RD.