Annexin A11 is targeted by IgG4 and IgG1 autoantibodies in IgG4-related disease

Gut Microbiota Involved in the Immunopathogenesis of Autoimmune Pancreatitis

Autoimmune pancreatitis (AIP), which is considered the pancreatic expression of a systemic immunoglobulin G4-related disease, is characterized by excessive infiltration of plasmacytes bearing immunoglobulin G4 and a unique form of fibrosis in multiple organs. This relatively new disease entity has garnered great attention from clinicians, but its pathophysiology remains poorly understood. Recent discoveries indicate that plasmacytoid dendritic cell activation followed by robust production of type I interferon and interleukin-33 plays a key role in driving chronic fibro-inflammatory responses in both murine and human AIP. Furthermore, the compositional alterations in the gut microbiota, known as intestinal dysbiosis, triggered plasmacytoid dendritic cell-driven pathogenic type I interferon responses. Intestinal dysbiosis is associated with a breakdown in intestinal barrier function; thus, we examined whether the latter condition affects the development of experimental AIP. Our recent research has revealed that intestinal barrier disruption worsens experimental AIP by facilitating the translocation of pathogenic bacteria, such as Staphylococcus sciuri, to the pancreas from the gut. These results indicate the "gut-pancreas axis" underlies the immunopathogenesis of AIP, and the maintenance of intestinal barrier integrity can prevent the worsening of AIP by inhibiting pancreatic colonization by harmful gut bacteria. In this mini review, the interactions between AIP development and gut microbiota are discussed with the aim of providing useful information not only for researchers but also for clinicians.

The immunological pathogenesis of IgG4-related disease categorized by clinical characteristics

IgG4-related disease (IgG4-RD) is an immune disorder characterized by organ enlargement and fibrosis leading to functional impairment. Key immune cell subsets contributing to the pathogenesis of IgG4-RD include T follicular helper 2 cells (Tfh2), Tfh1, CX3CR1 + cytotoxic T cells (CX3CR1 + CTLs), Tregs and IgG4 + B cells. Tfh2 and Tregs are commonly involved in inducing IgG4 class-switching in this disease. Importantly, IgG4-RD can be classified into four clinical phenotypes based on the distribution of affected organs, with each phenotype showing different dominant immune cell subsets involved in its pathogenesis. Specifically, the clinical phenotype of retroperitoneal fibrosis/aortitis is characterized by CX3CR1 + CTLs as the dominant key immune cell subset, while Mikulicz disease with systemic involvement is dominated by Tfh2. In addition to classification based on organ distribution, IgG4-RD can also be categorized into phenotypes associated with malignancy or allergy. The malignancy phenotype is characterized by an increase in CXCR5 + CD2-double negative T cells compared to the allergy phenotype, along with a decrease in naive CD8 + T cells. Moreover, several autoantigens have been identified, and the presence of autoimmune phenotype has been revealed. Due to the pathogenicity of IgG1-type autoantibodies, Tfh1 may be important inducing IgG1 class-switching by IFNγ in autoimmune phenotype. In IgG4-RD with hypocomplementemia, activation of the complement pathway is thought to be induced by IgG1 or IgG2 antibodies, suggesting the involvement of Tfh1 in the disease pathogenesis. Therefore, elucidating the immunological features specific to each clinical characteristic is believed to lead to a deeper understanding of the pathogenesis of IgG4-RD and the discovery of novel therapeutic targets. This review provides an overview of the immunological mechanisms common to IgG4-RD as well as those specific to each clinical characteristic.

Sequential activation of conventional and plasmacytoid dendritic cells in autoimmune pancreatitis and systemic lupus erythematosus: similarities and dissimilarities

Type 1 autoimmune pancreatitis (AIP) and systemic lupus erythematosus (SLE) are caused by type I IFNs secreted by plasmacytoid dendritic cells (pDCs). Our understanding of the immune consequences before and after pDC activation in SLE is expanding, whereas knowledge on those in AIP are insufficient. In this article, we summarize the similarities and dissimilarities in pDC activation between AIP and SLE. In SLE, neutrophil extracellular traps containing self-DNA, anti-microbial peptides, and endogenous alarmins form anti-DNA antibody complexes, promoting type I IFN production by pDCs. Type I IFNs produced by pDCs function as initiators rather than effectors in SLE, as evidenced by the fact that these cytokines induce the maturation of conventional DCs (cDCs) leading to the expansion of autoreactive T cells and B cells. Notably, type I IFNs produced by pDCs were observed at the maturation phase but not at the induction phase in experimental AIP. Mechanistically, cDCs producing type I IFNs, C-X-C motif chemokine ligand 9 (CXCL9), and CXCL10 are initiator cells of AIP, and C-X-C chemokine receptor 3 (CXCR3)+T helper type 1(Th1) cells migrate to the pancreas in response to CXCL9 and CXCL10. CXCR3+Th1 cells produce C-C chemokine ligand 25 (CCL25) to attract C-C chemokine receptor 9 (CCR9)+pDCs to the pancreas. Pancreatic pDCs producing type I IFNs, CXCL9, CXCL10, and CXCR3+Th1 cells producing CCL25 form a positive feedback loop in which the sensing of intestinal dysbiosis induces large amounts of type I IFNs by pDCs.

IgG4-related Disease: Recent Topics on Immunological Aspects of This Disorder and Their Application in New Treatment Strategies

IgG4-related disease (IgG4-RD) is a systemic and chronic inflammatory disorder that can affect every part of the body. The formation of tertiary lymphoid tissues (TLT) in the affected organs may be a key phenomenon in understanding the pathogenesis of this disease because T follicular helper (Tfh) 2 cells play an important role in IgG4 class switching within TLT in the affected organs or tissues. TLT formation leads to the formation of masses or swelling of the affected organs. Interleukin (IL)-4 and IL-10 are critical cytokines for IgG4-class switching and are produced in TLT. Other factors, such as CD4-positive (CD4+) cytotoxic T cells, M2 macrophages, and LAG3+ Tfh cells, have been identified as disease-specific contributors to lesion formation. In this review, I describe the current knowledge necessary to understand the pathogenesis of this disease and recent developments in treatment strategies beyond B-cell depletion therapy.

Journey to diagnosis: An unfinished exploration of IgG4-related sclerosing cholangitis

IgG4-related sclerosing cholangitis (IgG4-SC) is an inflammatory disease that leads to bile duct stricture, characterized by the infiltration of IgG4-positive plasma cells into the bile duct wall, thickening of the bile duct wall, and narrowing of the lumen. The differential diagnosis of IgG4-SC mainly includes primary sclerosing cholangitis, cholangiocarcinoma, and pancreatic cancer. IgG4-SC is often associated with autoimmune pancreatitis and can be accurately diagnosed based on clinical diagnostic criteria. However, isolated IgG4-SC is difficult to distinguish from biliary tumors. Given the significant differences in biological behavior, treatment, and prognosis between these diseases, accurately identifying isolated IgG4-SC has very important clinical significance.

Omics in IgG4-related disease

ABSTRACT

Research on IgG4-related disease (IgG4-RD), an autoimmune condition recognized to be a unique disease entity only two decades ago, has processed from describing patients' symptoms and signs to summarizing its critical pathological features, and further to investigating key pathogenic mechanisms. Challenges in gaining a better understanding of the disease, however, stem from its relative rarity-potentially attributed to underrecognition - and the absence of ideal experimental animal models. Recently, with the development of various high-throughput techniques, "omics" studies at different levels (particularly the single-cell omics) have shown promise in providing detailed molecular features of IgG4-RD. While, the application of omics approaches in IgG4-RD is still at an early stage. In this paper, we review the current progress of omics research in IgG4-RD and discuss the value of machine learning methods in analyzing the data with high dimensionality.

IgG4 autoantibodies and autoantigens in the context of IgG4-autoimmune disease and IgG4-related disease

Immunoglobulins are an essential part of the humoral immune response. IgG4 antibodies are the least prevalent subclass and have unique structural and functional properties. In this review, we discuss IgG4 class switch and B cell production. We review the importance of IgG4 antibodies in the context of allergic responses, helminth infections and malignancy. We discuss their anti-inflammatory and tolerogenic effects in allergen-specific immunotherapy, and ability to evade the immune system in parasitic infection and tumour cells. We then focus on the role of IgG4 autoantibodies and autoantigens in IgG4-autoimmune diseases and IgG4-related disease, highlighting important parallels and differences between them. In IgG4-autoimmune diseases, pathogenesis is based on a direct role of IgG4 antibodies binding to self-antigens and disturbing homeostasis. In IgG4-related disease, where affected organs are infiltrated with IgG4-expressing plasma cells, IgG4 antibodies may also directly target a number of self-antigens or be overexpressed as an epiphenomenon of the disease. These antigen-driven processes require critical T and B cell interaction. Lastly, we explore the current gaps in our knowledge and how these may be addressed.

Unmet needs in biomarkers for autoimmune pancreatitis diagnosis

Autoimmune pancreatitis (AIP) is a rare chronic autoimmune disorder. The diagnosis of AIP mainly depends on histopathology, imaging and response to treatment. Serum immunoglobulin 4 (IgG4) is used only as collateral evidence in diagnostic criteria for AIP because of its moderate sensitivity. Serum IgG4 levels are normal in 15%-37% of type 1 AIP and most of type 2 AIP patients. In these patients, the indeterminate imaging and histopathology may lead to the difficulty in definitive diagnosis of AIP. Therefore, discovery of new biomarkers is important for AIP diagnosis. Here, we provide some views on the progression and challenges in identifying novel serological biomarkers in AIP diagnosis.

Galectin-3 and prohibitin 1 are autoantigens in IgG4-related cholangitis without clear-cut protective effects against toxic bile acids

Background and aims

IgG4-related cholangitis (IRC) is the hepatobiliary manifestation of IgG4-related disease, a systemic B cell-driven fibro-inflammatory disorder. Four autoantigens have recently been described in IgG4-RD: annexin A11, galectin-3, laminin 511-E8, and prohibitin 1. We have previously reported a protective role of annexin A11 and laminin 511-E8 in human cholangiocytes against toxic bile acids. Here, we explored the potentially protective role of the carbohydrate-binding lectin galectin-3 and the scaffold proteins prohibitins 1 and 2.

Methods

Anti-galectin-3, anti-prohibitin 1 and 2 autoantibody positivity in IRC and healthy and disease (primary sclerosing cholangitis (PSC)) control sera was assessed by ELISA/liquid chromatography-tandem mass spectrometry (LC-MS/MS). Human H69 cholangiocytes were subjected to short hairpin RNA (shRNA) knockdown targeting galectin-3 (LGALS3), prohibitin 1 (PHB1), and prohibitin 2 (PHB2). H69 cholangiocytes were also exposed to recombinant galectin-3, the inhibitor GB1107, recombinant prohibitin 1, and the pan-prohibitin inhibitor rocaglamide. Protection against bile acid toxicity was assessed by intracellular pH (pHi) measurements using BCECF-AM, 22,23-3H-glycochenodeoxycholic acid (3H-GCDC) influx, and GCDC-induced apoptosis using Caspase-3/7 assays.

Results

Anti-galectin-3 autoantibodies were detected in 13.5% of individuals with IRC but not in PSC. Knockdown of LGALS3 and galectin-3 inhibition with GB1107 did not affect pHi, whereas recombinant galectin-3 incubation lowered pHi. LGALS3 knockdown increased GCDC-influx but not GCDC-induced apoptosis. GB1107 reduced GCDC-influx and GCDC-induced apoptosis. Recombinant galectin-3 tended to decrease GCDC-influx and GCDC-induced apoptosis. Anti-prohibitin 1 autoantibodies were detected in 61.5% and 35.7% of individuals with IRC and PSC, respectively. Knockdown of PHB1, combined PHB1/2 KD, treatment with rocaglamide, and recombinant prohibitin 1 all lowered pHi. Knockdown of PHB1, PHB2, or combined PHB1/2 did not alter GCDC-influx, yet knockdown of PHB1 increased GCDC-induced apoptosis. Conversely, rocaglamide reduced GCDC-influx but did not attenuate GCDC-induced apoptosis. Recombinant prohibitin 1 did not affect GCDC-influx or GCDC-induced apoptosis. Finally, anti-galectin-3 and anti-prohibitin 1 autoantibody pretreatment did not lead to increased GCDC-influx.

Conclusions

A subset of individuals with IRC have autoantibodies against galectin-3 and prohibitin 1. Gene-specific knockdown, pharmacological inhibition, and recombinant protein substitution did not clearly disclose a protective role of these autoantigens in human cholangiocytes against toxic bile acids. The involvement of these autoantibodies in processes surpassing epithelial secretion remains to be elucidated.

IgG4-related retroperitoneal fibrosis: A case report of a challenging disease

Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a multi-organ immune-mediated fibroinflammatory disorder that may imitate malignancy, infectious or any other inflammatory disorder. IgG4-related retroperitoneal fibrosis (IgG4-RPF) is a rare form of IgG4-RD, diagnosis of which is often relied on radiological technology. Herein, we describe a case of 60 year old male, presenting with low back pain and weight loss for a period of 2 months and 15 days. Imaging studies showed a retroperitoneal tumorous mass along with bilateral hydroureteronephrosis, which was later confirmed to be IgG4-related retroperitoneal fibrosis on the basis of extensive histopathological analysis. Immunosuppressive therapy resulted in a decrease in fibrosis and restoration of renal function.

A Case of Immunoglobulin G4-Related Disease Presenting as a Parapharyngeal Mass

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells. The presentation of IgG4-RD is heterogenous, making it difficult to diagnose. IgG4-RD presenting as a parapharyngeal mass is extremely rare. This report discusses the case of a 69-year-old African American female presenting with intermittent bilateral frontal headaches. Initial imaging revealed an ill-defined parapharyngeal mass encasing the left internal carotid artery and left internal jugular vein. Subsequent biopsy and immunohistochemistry showed a high concentration of IgG4-positive plasma cells with storiform fibrosis, despite normal serum IgG4 levels. The patient opted for conservative management. The localized parapharyngeal mass has remained stable over two years on annual imaging. This case report highlights that IgG4-RD can have varied and nonspecific presentations requiring high clinical suspicion to diagnose. Histopathology and IgG4 staining are vital to confirm the diagnosis of IgG4-RD, particularly in atypical cases not meeting the standard inclusion criteria.

Development of targeted therapies in IgG4-related disease

IgG4-related disease (IgG4-RD) is a systemic disease characterized by high serum IgG4 levels, infiltration of lymphocytes and IgG4-positive plasma cells into affected tissues, and subsequent fibrosis, forming mass, nodular, and thickened lesions in organs. Although glucocorticoids (GCs) are the first-line treatment for IgG4-RD, the disease often relapses during dose reduction or after discontinuation of GC. Long-term treatment with GC is associated with adverse effects such as infection, osteoporosis, and atherosclerosis. Therefore, there is an urgent need to develop a treatment strategy that specifically addresses the pathogenesis of IgG4-RD. As immunocompetent cells and immune-related molecules involved in the pathogenesis of IgG4-RD are increasingly being identified, there is a growing demand for new molecular-targeted drugs that target them. In particular, favourable results have been reported for drugs that target B cells, such as anti-cluster of differentiation (CD)20 and anti-CD19 antibodies. In addition, clinical trials are underway for new therapeutic agents, such as anti-signalling lymphocytic activation molecule family 7 antibodies that target T cells and other cells.

Roles of IgG4 and IgG4/IgG ratio to IgG4-related disease in patients with elevated serum IgG4 level

OBJECTIVE

To evaluate the performance of elevated serum IgG4 and IgG4/IgG in IgG4-related disease (IgG4-RD) and other diseases.

METHODS

Seven hundred seventy-three patients with elevated serum IgG4 level (> 2.01 g/L) were reviewed in Zhongda Hospital of Southeast University from 1 July 2016 to 31 December 2021. Demographic, disease distribution and the role of elevated serum IgG4 and IgG4/IgG in IgG4-RD and other diseases were analysed. The alteration of IgG4 and IgG4/IgG in pre-therapy and post-treatment were also assessed in IgG4-RD.

RESULTS

Patients with elevated serum IgG4 were principally observed in older males. Chronic diseases of various organs (21.7%), rheumatic immune diseases (19.4%), bacterial infection disease (11.5%) and malignant tumor (5.2%) were the common diseases with elevated serum IgG4, but only 3.2% was IgG4-RD. The level of IgG4 and IgG4/IgG in IgG4-RD was significantly higher than that in various diseases except for eosinophilia group. Serum IgG4 and IgG4/IgG manifested a similar diagnostic capacity for IgG4-RD among this study cohort and the optimal cut-off values were 3.345 g/L and 0.295 respectively. The sensitivity and specificity were 96% and 71% for the optimal cut-off value of IgG4, and 80% and 88.8% for the optimal cut-off value of IgG4/IgG4. IgG4 and IgG4/IgG both were remarkably reduced in IgG4-RD after therapy compared with prior treatment (P < 0.05).

CONCLUSIONS

Elevated serum IgG4 was found in a variety of diseases, especially in chronic diseases of various organs. IgG4 and IgG4/IgG manifest a great value for IgG4-RD diagnosis, and are available for the treatment evaluation of IgG4-RD. Key Points • Elevated serum IgG4 level was not a specific marker to IgG4-related disease and can be observed in various diseases. • Patients with IgG4-related disease or eosinophilia manifest a higher level of serum IgG4 and IgG4/IgG. • Both of IgG4 and IgG4/IgG are available for the diagnosis and the clinical treatment evaluation of IgG4-related disease.

[Autoimmune diagnostics in gastroenterology and hepatology]

Autoimmune diseases may affect all parts of the gastrointestinal system and the liver. Autoantibodies can be very helpful in the diagnosis of these diseases. For detection, two main diagnostic techniques are available: indirect immunofluorescence technique (IFT) as well as solid phase assays as e. g. ELISA or immunoblot. Depending on symptoms and differential diagnosis, IFT may serve as screening assay and solid phase assays may serve as confirmatory assays. The esophagus can sometimes be affected by systemic autoimmune diseases; diagnosis is often facilitated by the proof of circulating autoantibodies. Atrophic gastritis is the most prominent autoimmune disease of the stomach also displaying circulating autoantibodies. Antibody diagnosis for celiac disease has been implemented in all common guidelines. For liver and pancreatic autoimmune diseases, there is a solid history for the significance of the detection of circulating autoantibodies. Knowledge of available tests and accurate implementation accelerates correct diagnosis in many cases.

Serum biomarkers for the differentiation of autoimmune pancreatitis from pancreatic ductal adenocarcinoma

Autoimmune pancreatitis (AIP), a chronic inflammation caused by the immune system attacking the pancreas, usually presents imaging and clinical features that overlap with those of pancreatic ductal adenocarcinoma (PDAC). Serum biomarkers, substances that quantitatively change in sera during disease development, are a promising non-invasive tool with high utility for differentiating between these diseases. In this way, the presence of AIP is currently suspected when serum concentrations of immunoglobulin G4 (IgG4) antibody are elevated. However, this approach has some drawbacks. Notably, IgG4 antibody concentrations are also elevated in sera from some patients with PDAC. This review focuses on the most recent and relevant serum biomarkers proposed to differentiate between AIP and PDAC, evaluating the usefulness of immunoglobulins, autoantibodies, chemokines, and cytokines. The proposed serum biomarkers have proven useful, although most studies had a small sample size, did not examine their presence in patients with PDAC, or did not test them in humans. In addition, current evidence suggests that a single serum biomarker is unlikely to accurately differentiate these diseases and that a set of biomarkers will be needed to achieve adequate specificity and sensitivity, either alone or in combination with clinical data and/or radiological images.

Current status of type 1 (IgG4-related) autoimmune pancreatitis

In 1995, Yoshida et al. proposed first the concept of "autoimmune pancreatitis" (AIP). Since then, AIP has been accepted as a new pancreatic inflammatory disease and is now divided two subtypes. Type 1 AIP affected immunoglobulin G4 (IgG4) and implicates the pancreatic manifestation of IgG4-related disease, while type 2 is characterized by neutrophil infiltration and granulocytic epithelial lesions (GEL). Recent research has clarified the clinical and pathophysiological aspects of type 1 AIP, which is more than type 2 among the Japanese population. However, many details remain unclear about the pathogenesis and progression of this disease. In this review, we discuss the current knowledge and recent advances relating to type 1 AIP.

A Case Report of a Prevertebral Mass in an Elderly Male Post Hodgkin's Lymphoma

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory autoimmune disease characterized by tissue infiltration by dense lymphoplasmacytic infiltrate composed of T cells, activated B-cells, and plasma cells expressing IgG4 and has varied presentations with similar histopathology. It can involve visceral organs, glands, aorta, lymph nodes, and retroperitoneal tissue. In our case, a 68-year-old male with a past history of Hodgkin's lymphoma and in remission presented for investigation of polyclonal gammopathy. Serum electrophoresis showed increased free kappa light chains, free lambda light chains, and kappa lambda ratio; immunoglobulin G (IgG) levels were also increased. A positron emission tomography (PET) scan and magnetic resonance imaging (MRI) thoracic spine suggested a hypermetabolic prevertebral soft tissue density. Biopsy of the mass suggested IgG4-related disease (IgG4-RD). He also had a compression fracture of the T7 vertebra. He was started on intravenous methylprednisolone and rituximab, following which he had a significant decrease in the size of the mass along with a decline in the levels of IgG, kappa, and lambda chains.

[Immunoglobulin-G4-related disease]

After years of confusion about apparently distinct clinical disease symptoms, the term IgG4-related disease (IgG4-RD) has been coined in 2001, uniting these fibroinflammatory clinical entities with a tendency for tumorous enlargement and tissue fibrosis. Over the past two decades, experimental and clinical studies could make astounding progress in the understanding of this elusive disease. By now, we have a reasonable idea of the pathophysiological mechanisms, which opens up new avenues for therapeutic approaches. It seems like a dense lymphoplasmacytic cell infiltrate, consisting of B‑cells, IgG4⁺ plasma cells, follicular T‑helper cells, CD4⁺ cytotoxic T‑cells and M2 macrophages induces a smoldering inflammatory reaction with a fibrogenic cytokine milieu. This stimulates fibroblasts to secrete extracellular matrix components, leading to the histopathologically characteristic storiform fibrosis and obliterative phlebitis. Macroscopically, this reaction results in diffuse organ swelling and tumorous lesions. The macroscopic and histological differentiation from conditions mimicking IgG4-RD can be challenging. This is especially true for granulomatous diseases, such as antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The situation is further complicated by the fact that ANCAs can be positive in IgG4-RD and, vice versa IgG4 antibodies can be elevated in numerous differential diagnoses, such as infections, AAV, sarcoidosis, and malignancies. This article provides an overview of the multifaceted clinical condition of IgG4-RD with respect to the pathophysiology, diagnostic steps and treatment. Furthermore, an overview of the differential diagnoses is discussed especially with respect to granulomatous diseases.

The Clinical Utility of Soluble Serum Biomarkers in Autoimmune Pancreatitis: A Systematic Review

Autoimmune pancreatitis (AIP) is a rare etiological type of chronic pancreatitis. The clinical and radiological presentation of AIP often resembles that of pancreatic cancer. Identifying non-invasive markers for their early distinction is of utmost importance to avoid unnecessary surgery or a delay in steroid therapy. Thus, this systematic review was conducted to revisit all current evidence on the clinical utility of different serum biomarkers in diagnosing AIP, distinguishing AIP from pancreatic cancer, and predicting disease course, steroid therapy response, and relapse. A systematic review was performed for articles published up to August 2021 by searching electronic databases such as MEDLINE, Web of Science, and EMBASE. Among 5123 identified records, 92 studies were included in the qualitative synthesis. Apart from immunoglobulin (Ig) G4, which was by far the most studied biomarker, we identified autoantibodies against the following: lactoferrin, carboanhydrase II, plasminogen-binding protein, amylase-α2A, cationic (PRSS1) and anionic (PRSS2) trypsinogens, pancreatic secretory trypsin inhibitor (PSTI/SPINK1), and type IV collagen. The identified novel autoantigens were laminin 511, annexin A11, HSP-10, and prohibitin. Other biomarkers included cytokines, decreased complement levels, circulating immune complexes, N-glycan profile changes, aberrant miRNAs expression, decreased IgA and IgM levels, increased IgE levels and/or peripheral eosinophil count, and changes in apolipoprotein isoforms levels. To our knowledge, this is the first systematic review that addresses biomarkers in AIP. Evolving research has recognized numerous biomarkers that could help elucidate the pathophysiological mechanisms of AIP, bringing us closer to AIP diagnosis and its preoperative distinction from pancreatic cancer.

Colchicine as an Alternative First-Line Treatment of Sclerosing Mesenteritis: A Retrospective Study

BACKGROUND

Sclerosing mesenteritis is a rare condition characterized by chronic inflammation and fibrotic changes of the mesentery.

AIMS

To determine the long-term management and outcomes of patients with sclerosing mesenteritis.

METHODS

Patients with biopsy-proven sclerosing mesenteritis at the Mayo Clinic between January 2006 and December 2016 were identified. Clinical data were collected retrospectively.

RESULTS

One hundred and three patients were identified, median age 68.0 years (range 35.0-85.3). Most patients were symptomatic (87.4%) at presentation. Patients received no treatment (52.4%), medical therapy (42.7%) or surgery (4.9%) on initial diagnosis. The most common initial regimens were prednisone plus tamoxifen (41.9%), prednisone alone (23.3%), and prednisone plus colchicine (11.6%) with 55.6%, 57.2%, and 60% of patients improving, respectively, p = 0.85 for a difference in response rates. At least half of the patients responded to prednisone plus tamoxifen, prednisone plus colchicine, or prednisone alone at 6.0, 7.2, and 8.4 months, respectively. At a median follow-up of 45.6 months (95% CI 24.1-69.7), 65.4% of patients were receiving medical therapy. Of those receiving tamoxifen-based, steroid-based, or steroid-sparing regimens, 100%, 87.5%, and 77.8% had improved by their last follow-up appointment respectively, p = 0.15.

CONCLUSION

Prednisone plus colchicine has a similar efficacy to prednisone plus tamoxifen for the initial and long-term treatment of sclerosing mesenteritis. The majority of patients were initiated on medical therapy over the long term with most reporting symptomatic improvement within a year. Death from SM was rare.

Orchestration of Immune Cells Contributes to Fibrosis in IgG4-Related Disease

This review summarizes recent progress in understanding the pathogenesis of IgG4-related disease (IgG4-RD), with a focus on fibrosis. Several studies reported that CD4+ T cells with cytotoxic activity promoted by the secretion of granzyme and perforin, cytotoxic CD4+ T cells (CD4+CTLs), and disease-specific activated B cells, infiltrated inflamed tissues and cooperated to induce tissue fibrosis in autoimmune fibrotic diseases such as IgG4-RD, systemic sclerosis, and fibrosing mediastinitis. An accumulation of cells undergoing apoptotic cell death induced by CD4+CTLs and CD8+CTLs followed by macrophage-mediated clearing and finally tissue remodeling driven by cytokines released by CD4+CTLs, activated B cells, and M2 macrophages may contribute to the activation of fibroblasts and collagen production. In IgG4-RD, this process likely involves the apoptosis of non-immune, non-endothelial cells of mesenchymal origin and subsequent tissue remodeling. In summary, CD4+CTLs infiltrate affected tissues where they may cooperate with activated B cells, CD8+CTLs, and M2 macrophages, to induce apoptosis by secreting cytotoxic cytokines. These immune cells also drive fibrosis by secreting pro-fibrotic molecules in IgG4-RD.

The Role of IgG4 in Autoimmunity and Rheumatic Diseases

The distinguishing of the IgG4-related disease (IgG4-RD) from among other rheumatic diseases has brought attention to the IgG4 subclass of immunoglobulins. It is the least numerous subclass among immunoglobulins G. In general, IgG4 is considered to be non-inflammatory and tolerance inducing, due to its unique structure. However, in IgG4-RD this antibody plays a pathogenic role in activation of the fibrinogenesis and of the inflammatory process; there are also suggestions that it may be a marker of an abnormal inflammatory response. The importance of IgG4 for the pathogenesis of allergic diseases, with a vital role of its ratio to immunoglobulin E (IgE/IgG4 ratio), has been known for years. The role of IgG4 in the course and pathogenesis of rheumatic diseases is still being researched and is not yet fully understood. Increased IgG4 levels have been revealed in rheumatoid arthritis, although no clear link between this phenomenon and disease activity has been demonstrated. There are articles on the potential importance of IgG4 concentration (of both elevated and decreased serum levels) in Sjogren’s syndrome. Additionally, anti-nuclear IgG4 antibody significant titers have been detected in SLE patients, and it has been suggested that the effect of these antibodies on complement consumption and the production of proinflammatory cytokines may play a role in inhibiting the progression of SLE. IgG4 plays a role in autoimmune diseases other than rheumatic diseases, such as pemphigus, bullous pemphigoid, idiopathic membranous glomerulonephritis, or myasthenia gravis, but also in helmints infections. Research shows the importance of IgG4 in malignancy of neoplasms. Melanoma cells are known to stimulate IgG4 production through a modified Th2-based inflammatory response. The role of this immunoglobulin in cholangiocarcinoma is also considered as possible. The aim of this review article is to discuss the current knowledge of IgG4 not only from the perspective of the IgG4-RD but also from a point of view of other autoimmune diseases with particular emphasis on rheumatic diseases.

Anti-Neuronal IgG4 Autoimmune Diseases and IgG4-Related Diseases May Not Be Part of the Same Spectrum: A Comparative Study

Background

IgG4 is associated with two emerging groups of rare diseases: 1) IgG4 autoimmune diseases (IgG4-AID) and 2) IgG4-related diseases (IgG4-RLD). Anti-neuronal IgG4-AID include MuSK myasthenia gravis, LGI1- and Caspr2-encephalitis and autoimmune nodo-/paranodopathies (CNTN1/Caspr1 or NF155 antibodies). IgG4-RLD is a multiorgan disease hallmarked by tissue-destructive fibrotic lesions with lymphocyte and IgG4 plasma cell infiltrates and increased serum IgG4 concentrations. It is unclear whether IgG4-AID and IgG4-RLD share relevant clinical and immunopathological features.

Methods

We collected and analyzed clinical, serological, and histopathological data in 50 patients with anti-neuronal IgG4-AID and 19 patients with IgG4-RLD.

Results

A significantly higher proportion of IgG4-RLD patients had serum IgG4 elevation when compared to IgG4-AID patients (52.63% vs. 16%, p = .004). Moreover, those IgG4-AID patients with elevated IgG4 did not meet the diagnostic criteria of IgG4-RLD, and their autoantibody titers did not correlate with their serum IgG4 concentrations. In addition, patients with IgG4-RLD were negative for anti-neuronal/neuromuscular autoantibodies and among these patients, men showed a significantly higher propensity for IgG4 elevation, when compared to women (p = .005). Last, a kidney biopsy from a patient with autoimmune paranodopathy due to CNTN1/Caspr1-complex IgG4 autoantibodies and concomitant nephrotic syndrome did not show fibrosis or IgG4+ plasma cells, which are diagnostic hallmarks of IgG4-RLD.

Conclusion

Our observations suggest that anti-neuronal IgG4-AID and IgG4-RLD are most likely distinct disease entities.

Amendment of the Japanese consensus guidelines for autoimmune pancreatitis, 2020

In response to the latest knowledge and the amendment of the Japanese diagnostic criteria for autoimmune pancreatitis (AIP) in 2018, the Japanese consensus guidelines for managing AIP in 2013 were required to be revised. Three committees [the professional committee for developing clinical questions (CQs) and statements by Japanese specialists; the expert panelist committee for rating statements by the modified Delphi method; and the evaluating committee of moderators] were organized. Twenty specialists in AIP extracted the specific clinical statements from a total of 5218 articles (1963-2019) from a search in PubMed and the Cochrane Library. The professional committee made 14, 9, 5, and 11 CQs and statements for the current concept and diagnosis, extra-pancreatic lesions, differential diagnosis, and treatment, respectively. The expert panelists regarded the statements as valid after a two-round modified Delphi approach with individually rating these clinical statements, in which a clinical statement receiving a median score greater than 7 on a 9-point scale from the panel was regarded as valid. After evaluation by the moderators, the amendment of the Japanese consensus guidelines for AIP has been proposed in 2020.

IgG4-Related Sclerosing Cholangitis: Rarely Diagnosed, but not a Rare Disease

IgG4-related sclerosing cholangitis, a biliary manifestation of an IgG4-related disease, belongs to the spectrum of sclerosing cholangiopathies which result in biliary stenosis. It presents with signs of cholestasis and during differential diagnosis it should be distinguished from cholangiocarcinoma or from other forms of sclerosing cholangitis (primary and secondary sclerosing cholangitis). Despite increasing information and recently established diagnostic criteria, IgG4-related sclerosing cholangitis remains underdiagnosed in routine clinical practice. The diagnosis is based on a combination of the clinical picture, laboratory parameters, histological findings, and a cholangiogram. Increased serum IgG4 levels are nonspecific but are indeed a part of the diagnostic criteria proposed by the Japan Biliary Association and the HISORt criteria for IgG4-SC. High serum IgG4 retains clinical utility depending on the magnitude of elevation. Approximately 90% of patients have concomitant autoimmune pancreatitis, while 10% present with isolated biliary involvement only. About 26% of patients have other organ involvement, such as IgG4-related dacryoadenitis/sialadenitis, IgG4-related retroperitoneal fibrosis, or IgG4-related renal lesions. A full-blown histological finding characterized by IgG4-enriched lymphoplasmacytic infiltrates, obliterative phlebitis, and storiform fibrosis is difficult to capture in practice because of its subepithelial localization. However, the histological yield is increased by immunohistochemistry, with evidence of IgG4-positive plasma cells. Based on a cholangiogram, IgG-4 related sclerosing cholangitis is classified into four subtypes according to the localization of stenoses. The first-line treatment is corticosteroids. The aim of the initial treatment is to induce clinical and laboratory remission and cholangiogram normalization. Even though 30% of patients have a recurrent course, in the literature data, there is no consensus on chronic immunosuppressive maintenance therapy. The disease has a good prognosis when diagnosed early.

Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas

BACKGROUND & AIMS

Immunoglobulin G4-related disease (IgG4-RD) of the biliary tract and pancreas is a fibroinflammatory disease of unknown origin with striking male predominance. We aimed to investigate whether blue-collar work and occupational contaminant exposure are risk factors for IgG4-RD of the biliary tract and pancreas.

METHOD

We performed an age-/sex-matched case-control study in the largest academic medical centers of the Netherlands. Occupational history was surveyed by questionnaires. The International Standard Classification of Occupations (ISCO88) was used to classify jobs. Job exposure matrices ALOHA and DOM were utilized to assess the years individuals were exposed to compounds. The disease control cohort consisted of patients from 6 equally sized groups. Conditional logistic regression was used to assess effects of blue-collar work and exposure to occupational contaminants on developing IgG4-RD of the biliary tract and pancreas.

RESULTS

Overall, 101 patients with IgG4-RD of the biliary tract and pancreas were matched 1:3 to 303 controls. Patients with IgG4-RD had a lower level of education (p = 0.001). Individuals who at least once performed blue-collar work (>1 year), had higher odds of developing IgG4-RD than individuals that only performed white-collar work (odds ratio [OR] 3.66; CI 2.18-6.13; p <0.0001). Being ever exposed (>1 year) to industrial ALOHA (e.g. mineral dust; vapors-dust-gases-fumes) and DOM compounds (e.g. asbestos) resulted in higher odds of IgG4-RD (OR 2.14; 95% CI 1.26-3.16; p <0.001 and OR 2.95; 95% CI 1.78-4.90; p <0.001, respectively).

CONCLUSION

Blue-collar work is a risk factor for developing IgG4-RD of the biliary tract and pancreas putatively driven by exposure to selected industrial compounds; this may explain the striking male predominance among patients.

LAY SUMMARY

Immunoglobulin G4-related disease (IgG4-RD) causes tumor-like lesions and typically affects middle-aged to elderly men. The background and cause of this disease remain relatively unknown. In this study, we identified blue-collar work as a risk factor for developing IgG4-RD of the biliary tract and pancreas, which may explain the striking male predominance among patients. Furthermore, these results suggest that toxic exposure to occupational contaminants may drive autoimmunity in IgG4-RD of the biliary tract and pancreas.

Histological features of autoimmune pancreatitis and IgG4-related sclerosing cholangitis with a correlation with imaging findings

Autoimmune pancreatitis (AIP) is characterized by a tumefactive inflammatory lesion resembling pancreatic carcinoma. Type 1 AIP is a pancreatic manifestation of IgG4-related disease characterized by unique histological features that can be identified on imaging. The capsule-like rim, which is a collar of hypertrophic lesion surrounding the pancreas, consists of lymphoplasmacytic infiltration and fibrosis, and storiform fibrosis is often identified. Hypertrophic lesions of various microscopic architectures such as the ducts, veins (obliterative phlebitis), arteries (periarteritis), and nerves are observed without parenchymal damage. The pancreatic lobules keep their contours, but the acinar cells are diminished and replaced by numerous inflammatory cells. These features provide clues to arrive at a diagnosis of type 1 AIP and to distinguish it from pancreatic carcinoma on imaging. In contrast, type 2 AIP is an epithelium-centered inflammation involving the ducts and lobules. Neutrophilic infiltration in the epithelium and/or lumens (granulocytic epithelial lesion) is a characteristic finding. Lobular swelling due to inflammation is the cause of pancreatic enlargement. IgG4-related sclerosing cholangitis is histologically similar to the hypertrophic ductal lesion in type 1 AIP and characterized by wall thickening due to inflammation and luminal stenosis. The epithelium is intact, which is different from bile duct carcinomas and primary sclerosing cholangitis, the latter of which is characterized by inflammation targeting the epithelium. Although the histological features of type 1 AIP and IgG4-related sclerosing cholangitis are unique, the biopsy diagnosis of these diseases has limitations, which should be recognized by clinicians.

Clinicopathological Patterns and Predictors of the Functional Restoration of Immunoglobulin G4-Related Kidney Disease: A Chinese Single-Center Cohort Study

Background: Immunoglobulin G4-related disease (IgG4-RD) is a systemic immunoreactivity-based fibro-inflammatory disease. Immunoglobulin G4-related kidney disease (IgG4-RKD) is a frequently overlooked diagnosis. This study aimed to describe IgG4-RKD and examine the factors relevant to the renal outcomes of IgG4-RD. Methods: We studied a prospective IgG4-RKD cohort between January 2012 and December 2020 with close follow-up. Clinicopathologic data at kidney biopsy were collected and analyzed. We aimed to explore independent risk factors for long-term renal outcome and disease relapse. Patients with an eGFR<45 ml/min per 1.73m2 at 12 months were defined as having poor outcomes. Results: The included 42 patients with IgG4-RKD had a mean age of 58.5 ± 8.7 years (male-to-female ratio = 5:1). The IgG4-RD responder index (RI) was 12.2 ± 3.3. A total of 66.7% of the patients presented with acute on kidney disease or acute on chronic kidney disease. Eight patients (19.0%) showed nephrotic-range proteinuria, and nine (21.4%) had high-titer IgG4-autoantibodies, including antineutrophil cytoplasmic antibody and anti-phospholipase A2 receptor. A kidney biopsy was conducted in 40 patients. Thirty-seven (90.0%) patients were diagnosed with IgG4-related tubulointerstitial nephritis, and 19 (47.5%) of them had concurrent glomerular diseases (membranous nephropathy [MN], n = 3; crescentic glomerulonephritis [CrGN], n = 11; diabetic kidney disease, n = 3; and both MN and CrGN, n = 2). IgG4-RD RI had a close relationship with serum C3 (R = -0.509, P = 0.001), C4 (R = -0.314, P = 0.049) levels, and peripheral blood eosinophil count (PBEC; R = 0.377, P = 0.024), factors that were not included in RI scores. Correlation analysis disclosed that IgG4-RD RI (R = 0.422, P = 0.007), organs involved (R = 0.452, P = 0.003), and C3 (R = -0.487, R = 0.002) were correlated with the percentage decrease of serum creatinine at 1 month. However, multivariate regression analysis failed to identify any clinicopathological parameters that could predict short-term renal restoration and IgG4-RKD relapse. Ten out of 29 variables, of most importance, were identified by the least absolute shrinkage and selection operator (LASSO) regression analysis. By multivariate logistic regression a higher serum IgG4 (OR = 0.671, P = 0.010), IgG1 (OR = 1.396, P = 0.049), IgG3 (OR = 19.154, P = 0.039), and erythrocyte sedimentation rate (ESR; OR = 1.042, P = 0.032) were found to be independent factors for poor long-term outcome. Conventional immunosuppressive medications and/or rituximab were prescribed, and in 83.3% of the patients, the kidney function improved. Repeat kidney biopsies confirmed the remission of interstitial inflammation in two patients under immunosuppressive therapy. However, the disease relapse rate was as high as 31.0%. Conclusions: We strongly recommend a kidney biopsy in active IgG4-RD, especially when there is proteinuria and renal dysfunction, because concurrent glomerular involvement and active interstitial inflammation should be assessed. A higher serum IgG1, IgG3, and ESR were independent factors for the poor long-term renal outcome; however, elevated IgG4 predicted a good renal prognosis, and appropriate and timely immunosuppressive therapy can help achieve a better prognosis.

Interleukin-35 Promotes Th9 Cell Differentiation in IgG4-Related Disorders: Experimental Data and Review of the Literature

IgG4-related disease (IgG4-RD) is characterized by intense infiltration of IgG4-positive plasma cells in affected organs. However, the mechanisms acting in the immune responses in IgG4-RD are not fully understood. The aim of this study was to dissect the mechanism underlying the immunoglobulin class switch in IgG4-RD by addressing the crosstalk between IL-35-producing and Th9 cells. The expression level of IL-35 was examined in plasma samples from patients with hepatobiliary and/or pancreatic manifestations of IgG4-RD. Our data demonstrate that IgG4-RD patients exhibit significantly high-level productions of IL-35 as compared to disease and healthy controls. We detected the two subunits of IL-35, EBI3 and IL-12p35, in the two major affected organs, liver and pancreatic tissue, from IgG4-RD. The EBI3- and IL-12p35-positive cells were significantly higher in affected organs in IgG4-RD as compared to disease controls. The colocalization of EBI3 with CD19 and CD38, markers for B cells, suggest the presence of IL-35-producing B cells in affected organs in IgG4-RD. The effects of IL-35 in Th9 differentiation and IL-9 in production of immunoglobulin were then assessed. Surprisingly, IL-35 treatment promoted naïve CD4 T cell differentiating towards Th9 cells through IRF4 signaling. As a consequence, IL-9 secreted by Th9 cells promoted the differentiation of plasma cells and production of IgG1 and IgG4, predominantly IgG4. In conclusion, our data demonstrate that IL-35 actively participates in the process of inflammation and plays an important role in Th9 differentiation resulting in an immunoglobulin class switch towards IgG4.

Immune Dysregulation in IgG4-Related Disease

Immunoglobin G₄-related disease (IgG₄-RD) is one of the newly discovered autoimmune diseases characterized by elevated serum IgG₄ concentrations and multi-organ fibrosis. Despite considerable research and recent advances in the identification of underlying immunological processes, the etiology of this disease is still not clear. Adaptive immune cells, including different types of T and B cells, and cytokines secreted by these cells play a vital role in the pathogenesis of IgG₄-RD. Antigen-presenting cells are stimulated by pathogens and, thus, contribute to the activation of naïve T cells and differentiation of different T cell subtypes, including helper T cells (Th1 and Th2), regulatory T cells, and T follicular helper cells. B cells are activated and transformed to plasma cells by T cell-secreted cytokines. Moreover, macrophages, and some important factors (TGF-β, etc.) promote target organ fibrosis. Understanding the role of these cells and cytokines implicated in the pathogenesis of IgG₄-RD will aid in developing strategies for future disease treatment and drug development. Here, we review the most recent insights on IgG₄-RD, focusing on immune dysregulation involved in the pathogenesis of this autoimmune condition.

IgG4 as a Biomarker in Graves' Orbitopathy

Immunoglobulin G4-related disease (IgG4-RD) is a chronic inflammatory disorder associated with fibrosis and abundant tissue lymphoplasmacytic infiltrations. It typically affects the pancreas, the salivary glands, and the retroperitoneal space. However, it might also involve multiple other organs, including the orbit and the thyroid. Recent studies have suggested that IgG4 plays a role in the pathophysiology of autoimmune thyroid diseases. This ultimately led to the establishment of new clinical entities called IgG4-related thyroid disease and thyroid disease with an elevation of IgG4. The aim of this paper is to describe the pathophysiological, histopathological, and clinical features of Graves' Disease (GD) and Graves' Orbitopathy (GO) with elevated IgG4 levels. Multiple studies have demonstrated higher IgG4 serum concentrations in GD patients than in healthy euthyroid controls. Depending on the studied population, elevated serum IgG4 levels occur in 6.4-23% (average: 10.3%) of all patients with GD, 8.3-37.5% (average: 17.6%) of patients with GO, and 0-9.8% (average: 5.4%) of patients with GD without GO, while GO patients comprise 37.5-100% (average: 65.8%) of all GD patients with elevated IgG4 levels. Characteristic features of GD with elevated IgG4 levels include lower echogenicity of the thyroid gland on ultrasound examination, peripheral blood eosinophilia, higher prevalence of orbitopathy, and better response to antithyroid drugs with a tendency to develop hypothyroidism when compared to patients with GD and normal levels of IgG4. Typical signs of GO accompanied by increased concentration of IgG4 include younger age at diagnosis, and more severe course of the disease with a higher Clinical Activity Score (CAS).. We strongly recommend considering the diagnosis of GO with elevated IgG4 in patients with an established diagnosis of GD, elevated serum IgG4 levels, and clinical features of ophthalmic disease overlapping with those of IgG4-related orbital disease.

Systemic IgG4-Related Disease Masquerading as Cholangiocarcinoma: A Case Report Underscoring the Importance of Medical History

BACKGROUND Immunoglobulin (Ig) G4-related disease is a rare disease of unknown pathophysiology, which can affect multiple organs leading to tissue fibrosis and organ failure. The present case report describes a patient with systemic IgG4-related disease (IgG4-RD) that occurred over a 1-year period and affected multiple organs at different times. Imaging studies, interventional procedures, changes in laboratory parameters, and histopathology demonstrate the novel and known aspects of this disease before and during prednisolone monotherapy and in combination with azathioprine. CASE REPORT A 64-year-old man presented with weight loss and painless jaundice, which was highly suspicious for cholangiocarcinoma. A thorough medical history together with laboratory tests, imaging procedures, and endoscopic interventions confirmed that surgery was not needed and led to the final diagnosis of histologically-confirmed, IgG4-related sclerosing cholangitis and autoimmune pancreatitis type 1. Other typical organ manifestations of systemic IgG4-RD were diagnosed through a thorough medical review, which led to immunohistochemical reevaluation of past surgical specimens. Besides the IgG4-related organ manifestations, which can include periorbital xanthelasmas, our patient developed a pulmonary adenocarcinoma 6 years after the initial clinical onset of IgG4-RD. After immunosuppressive treatment with prednisolone alone and subsequently in combination with azathioprine, the patient's IgG4-RD resolved. CONCLUSIONS Interdisciplinary collaboration is required to diagnose IgG4-RD that involves multiple organs. Patient medical history remains crucial for diagnosis and attention should be paid to avoiding unnecessary surgery. Tumors (lung adenocarcinomas) and xanthelasmas can develop because of IgG4-RD. Glucocorticoids and additional azathioprine may be advisable for maintenance treatment.

Biomarkers in autoimmune pancreatitis and immunoglobulin G4-related disease

Solitary organ autoimmune disorders, formerly known as autoimmune pancreatitis (AIP), autoimmune sialadenitis, and autoimmune sclerosing cholangitis, are now considered organ-specific manifestations of systemic immunoglobulin G4-related disease (IgG4-RD). AIP and IgG4-RD are characterized by elevated serum concentration of IgG4 antibody (Ab), accumulation of IgG4-expressing plasmacytes in the affected organs, and involvement of multiple organs. It is well established that enhanced IgG4 Ab responses are a hallmark of AIP and IgG4-RD for diagnosis and monitoring disease activity. However, a significant fraction of patients with AIP and IgG4-RD who develop chronic fibroinflammatory responses have normal serum concentrations of this IgG subtype. In addition, disease flare-up is sometimes seen even in the presence of normalized serum concentrations of IgG4 Ab after successful induction of remission by prednisolone. Therefore, it is necessary to identify new biomarkers based on the understanding of the pathophysiology of AIP and IgG4-RD. Recently, we found that activation of plasmacytoid dendritic cells producing both interferon-α (IFN-α) and interleukin-33 (IL-33) mediate murine AIP and human IgG4-RD. More importantly, we provided evidence that serum concentrations of IFN-α and IL-33 could be useful biomarkers for the diagnosis and monitoring of AIP and IgG4-RD activity after induction of remission in these autoimmune disorders. In this Frontier article, we have summarized and discussed biomarkers of AIP and IgG4-RD, including Igs, autoAbs, and cytokines to provide useful information not only for clinicians but also for researchers.

Review of Diagnostic Biomarkers in Autoimmune Pancreatitis: Where Are We Now?

Autoimmune pancreatitis (AIP) is a pancreatic manifestation of an IgG4-related disease (IgG4-RD). AIP lacks disease-specific biomarkers, and therefore, it is difficult to distinguish AIP from malignancies, especially pancreatic cancer. In this review, we have summarized the latest findings on potential diagnostic biomarkers for AIP. Many investigations have been conducted, but no specific biomarkers for AIP are identified. Therefore, further studies are required to identify accurate diagnostic biomarkers for AIP.

Peripheral TIGIT+ T Follicular Helper Cells That Produce High Levels of Interleukin-21 via OX40 Represent Disease Activity in IgG4-Related Disease

Objectives

Multiple studies suggest that interleukin (IL)-21 plays a pivotal role in the differentiation of B cells and activation of cytotoxic T cells and is involved in the pathogenesis of IgG4-related disease (IgG4-RD). T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) is a new marker of T follicular helper (Tfh) cells, yet its significance remains unknown. The objective of this study was to investigate whether TIGIT expression could detect high IL-21-producing peripheral Tfh populations and their association with disease activity in IgG4-RD.

Methods

TIGIT expression in peripheral CD4+T cell subsets was comprehensively analyzed by multi-color flow cytometry. Single cell mapping was performed by t-SNE method, and IL-21 production was compared in TIGIT+ and TIGIT-T cells. The effect of OX40 signal on cytokine expression was analyzed by RNA-sequencing. Clinical significance of TIGIT+ and TIGIT- peripheral T cells was analyzed in active patients with IgG4-RD, both at baseline and after 12 weeks of glucocorticoid treatment.

Results

Unbiased single cell mapping revealed two high IL-21-producing peripheral T cell populations; TIGIT+ Tfh and TIGIT-T helper cells. OX40 signal was associated with high IL-21 production in TIGIT+ Tfh and TIGIT-T helper cells. IL-21 production in Tfh cells correlated with the proportion of TIGIT+ cells in Tfh cells, serum IgG4 level, and scores of disease activity. Furthermore, the skewing toward peripheral TIGIT+ Tfh cells, particularly TIGIT+Tfh2 subset correlated with disease activity and was corrected by glucocorticoid treatment in IgG4-RD.

Conclusions

OX40 is associated with high IL-21 production in peripheral TIGIT+ Tfh cells, and the increase in peripheral TIGIT+ Tfh cells reflects disease activity in IgG4-RD.

Clinical characteristics and outcome of IgG4-related disease with hypocomplementemia: a prospective cohort study

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) is a newly recognized systemic, immune-mediated, and fibro-inflammatory disease. Hypocomplementemia was found in part of IgG4-RD patients especially in the setting of active disease.

OBJECTIVES

This study aimed to clarify the clinical features, treatment efficacy, and outcome in IgG4-RD patients with hypocomplementemia.

METHODS

312 IgG4-RD patients were recruited in our prospective cohort conducted in Peking Union Medical College Hospital. Patients were divided into hypocomplementemia group and normal complement group according to serum C3 and C4 levels measured at baseline before treatment. Low serum C3 levels (< 0.73 g/L) and/or C4 levels (< 0.10 g/L) were defined as hypocomplementemia. Demographic data, clinical characteristics, laboratory parameters, treatment, and outcome of two groups were analyzed and compared.

RESULTS

Hypocomplementemia was identified in 65 (20.8%) cases of untreated IgG4-RD patients at baseline. The average age of hypocomplementemia group was 55.85 ± 10.89 years, with male predominance (72.3%). Compared with normal complement group, patients with hypocomplementemia were likely to have more involved organs, higher IgG4-RD responder index (IgG4-RD RI), and higher laboratory parameters such as counts of eosinophils, inflammatory markers, immunoglobulin G (IgG), IgG1, IgG3, IgG4, and IgE. In addition, lymph nodes, lacrimal gland, submandibular gland, parotid gland, paranasal sinus, bile ducts, and prostate gland were more commonly affected (p < 0.05). Serum C3 and C4 showed a significant positively correlation with each other. Both C3 and C4 were negatively correlated with the number of involved organs, IgG, IgG3, IgG4, and IgG4-RD RI, as well as positively correlated with IgA and hypersensitive C reactive protein (hsCRP). 64 (98.5%) patients responded quickly to initial therapy at a 3-month follow-up. Fifteen (23.1%) patients relapsed during follow-up with mean recurrence time of 14.2 ± 13.8 months. Compared with normal complement group, there was no significant difference of relapse rate in two groups (P = 0.401).

CONCLUSIONS

Clinical characteristics of IgG4-related disease with hypocomplementemia differ from normal complement group. Serum C3 and C4 at baseline before treatment could be biological markers for disease activity. IgG4-RD with hypocomplementemia responded well to treatment and had no significant difference of relapse rate in IgG4-RD with normal complement.

Cut-off values of serum IgG4 among three reagents, including a novel IgG4 reagent: a multicenter study

Elevated serum IgG4 is a useful marker of IgG4-related disease (IgG4-RD) activity. However, there is no uniformity in the cut-off values of IgG4 among the various reagents. The aim of this study was to compare the measured and cut-off values of IgG4 assessed using three different reagents. This study enrolled 466 IgG4-RD and non-IgG4-RD patients who required measurement of serum IgG4 levels to diagnose or treat IgG4-RD. Serum IgG4 was measured using three reagents: N-assay LA IgG4 Nittobo (Nittobo), BS-NIA IgG4 (TBS), and N Latex IgG4 (Siemens). The values obtained using the three reagents were compared, and cut-off values were calculated for each. Although there was good correlation among the results with the three reagents, the measured and cut-off values were all different. The Nittobo values were 1.4 times the TBS values and the TBS values were almost half those of the Siemens values. ROC curve analysis showed cut-off values for the Nittobo, TBS, and Siemens reagents of 1.42, 1.31, and 2.38 g/L, respectively. The measured and cut-off values of serum IgG4 vary depending on the reagents used for the assay, although there is good correlation among the values measured by the three reagents.

Clinical features and relapse risks of IgG4-related ophthalmic disease: a single-center experience in China

Background

IgG4-related ophthalmic disease (IgG4-ROD) is one of the phenotypes of IgG4-related disease (IgG4-RD), and its lesions are mainly located in the ocular. Currently, there are few studies on IgG4-ROD and no study has compared the phenotypic differences between IgG4-ROD and non IgG4-ROD (nIgG4-ROD). Thus, it is difficult to establish the optimal treatment strategy for IgG4-ROD. The aim of this study was to identify the disparities between the two groups and to clarify the risk factors for IgG4-ROD relapse.

Methods

434 IgG4-RD patients met comprehensive diagnostic criteria and diagnosed at Peking University People’s Hospital between January 2009 and January 2020 were recruited in this study. Patients were divided into IgG4-ROD and nIgG4-ROD group according to the ophthalmic involvement. Demographic, clinical, and laboratory data of two groups were collected and compared. Cox regression analysis was used to identify the independent risk factors for IgG4-ROD relapse.

Results

255 IgG4-ROD patients were identified in this study. IgG4-ROD group had almost equal sex ratio, younger age of disease onset and diagnosis comparing with nIgG4-ROD patients. As compared to nIgG4-ROD group, higher percentage of IgG4-ROD patients met the 2019 American College of Rheumatology/European League Against Rheumatism classification criteria (AECC) for IgG4-RD; moreover, IgG4-ROD patients had higher AECC scores and IgG4-RD responder index (RI). Allergic diseases and multiorgan involvement were more common in IgG4-ROD group. IgG4-ROD was frequently associated with salivary gland, paranasal sinus, lung, and lymph node involvement, while retroperitoneal fibrosis and biliary system lesions were more common in nIgG4-ROD. IgG4-ROD patients had higher serum IgG4 levels, IgG4/IgG ratio, IgE levels, and lower CRP levels. The initial glucocorticoid plus immunosuppressant was a protective factor for IgG4-ROD relapse. IgG4-ROD patients treated with initial glucocorticoid plus immunosuppressant had longer relapse-free survival time than patients treated with initial glucocorticoid monotherapy.

Conclusions

IgG4-ROD patients had distinctive clinical features compared with nIgG4-ROD patients. The initial glucocorticoid plus immunosuppressant was a protective factor for IgG4-ROD relapse, which could prolong the relapse-free survival time of IgG4-ROD patients. These findings may have important implications for understanding and management of IgG4-ROD.

Intestinal Dysbiosis and Autoimmune Pancreatitis

Autoimmune pancreatitis (AIP) is a chronic fibro-inflammatory disorder of the pancreas. Recent clinicopathological analysis revealed that most cases of AIP are pancreatic manifestations of systemic IgG4-related disease (IgG4-RD), a newly established disease characterized by enhanced IgG4 antibody responses and the involvement of multiple organs. Although the immuno-pathogenesis of AIP and IgG4-RD has been poorly defined, we recently showed that activation of plasmacytoid dendritic cells (pDCs) with the ability to produce large amounts of IFN-α and IL-33 mediates chronic fibro-inflammatory responses in experimental and human AIP. Moreover, M2 macrophages producing a large amount of IL-33 play pathogenic roles in the development of human IgG4-RD. Interestingly, recent studies including ours provide evidence that compositional alterations of gut microbiota are associated with the development of human AIP and IgG4-RD. In addition, intestinal dysbiosis plays pathological roles in the development of chronic pancreatic inflammation as dysbiosis mediates the activation of pDCs producing IFN-α and IL-33, thereby causing experimental AIP. In this Mini Review, we focus on compositional alterations of gut microbiota in AIP and IgG4-RD to clarify the mechanisms by which intestinal dysbiosis contributes to the development of these disorders.

Congruent microbiome signatures in fibrosis-prone autoimmune diseases: IgG4-related disease and systemic sclerosis

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) and systemic sclerosis (SSc) are rare autoimmune diseases characterized by the presence of CD4+ cytotoxic T cells in the blood as well as inflammation and fibrosis in various organs, but they have no established etiologies. Similar to other autoimmune diseases, the gut microbiome might encode disease-triggering or disease-sustaining factors.

METHODS

The gut microbiomes from IgG4-RD and SSc patients as well as healthy individuals with no recent antibiotic treatment were studied by metagenomic sequencing of stool DNA. De novo assembly-based taxonomic and functional characterization, followed by association and accessory gene set enrichment analysis, were applied to describe microbiome changes associated with both diseases.

RESULTS

Microbiomes of IgG4-RD and SSc patients distinctly separated from those of healthy controls: numerous opportunistic pathogenic Clostridium and typically oral Streptococcus species were significantly overabundant, while Alistipes, Bacteroides, and butyrate-producing species were depleted in the two diseases compared to healthy controls. Accessory gene content analysis in these species revealed an enrichment of Th17-activating Eggerthella lenta strains in IgG4-RD and SSc and a preferential colonization of a homocysteine-producing strain of Clostridium bolteae in SSc. Overabundance of the classical mevalonate pathway, hydroxyproline dehydratase, and fibronectin-binding protein in disease microbiomes reflects potential functional differences in host immune recognition and extracellular matrix utilization associated with fibrosis. Strikingly, the majority of species that were differentially abundant in IgG4-RD and SSc compared to controls showed the same directionality in both diseases. Compared with multiple sclerosis and rheumatoid arthritis, the gut microbiomes of IgG4-RD and SSc showed similar signatures; in contrast, the most differentially abundant taxa were not the facultative anaerobes consistently identified in inflammatory bowel diseases, suggesting the microbial signatures of IgG4-RD and SSc do not result from mucosal inflammation and decreased anaerobism.

CONCLUSIONS

These results provide an initial characterization of gut microbiome ecology in fibrosis-prone IgG4-RD and SSc and reveal microbial functions that offer insights into the pathophysiology of these rare diseases.

[Immunoglobulin G4-related disease in gastroenterology]

IgG4-related disease is a recently defined clinical entity that can manifest itself in any organ. The most common gastrointestinal manifestations are diseases of the pancreas (autoimmune pancreatitis type 1) and biliary tree (IgG4-associated cholangitis); involvement of liver parenchyma is uncommon and the affection of tubular organs is very rare. IgG4-related pancreatitis and cholangitis can mimic malignancies in their clinical presentation. Diagnosis is often difficult and requires careful evaluation of the combination of symptoms, serology and imaging findings, while adhering to the established diagnostic criteria. The first line of treatment is the administration of corticoids and the remission is achieved in the vast majority of patients. In case of contraindication, intolerance or failure of corticotherapy, patients should receive B cell depletion therapy (rituximab). Based on the available knowledge, monotherapy with other immunosuppressants is not considered to be sufficiently effective. Some patients may benefit from maintenance treatment to prevent relapse, which is otherwise common in both IgG4-related pancreatitis and cholangitis. Recognized IgG4-related disease has a good prognosis, but some patients develop irreversible fibrotic changes in the affected organ with consequent dysfunction; the possible association of the disease with a higher risk of malignancy has not yet been reliably elucidated.

CD4+CTLs in Fibrosing Mediastinitis Linked to Histoplasma capsulatum

Although fibrotic disorders are frequently assumed to be linked to T_H2 cells, quantitative tissue interrogation studies have rarely been performed to establish this link and certainly many fibrotic diseases do not fall within the type 2/allergic disease spectrum. We have previously linked two human autoimmune fibrotic diseases, IgG4-related disease and systemic sclerosis, to the clonal expansion and lesional accumulation of CD4⁺CTLs. In both these diseases T_H2 cell accumulation was found to be sparse. Fibrosing mediastinitis linked to Histoplasma capsulatum infection histologically resembles IgG4-related disease in terms of the inflammatory infiltrate and fibrosis, and it provides an example of a fibrotic disease of infectious origin in which the potentially profibrotic T cells may be induced and reactivated by fungal Ags. We show in this study that, in this human disease, CD4⁺CTLs accumulate in the blood, are clonally expanded, infiltrate into disease lesions, and can be reactivated in vitro by H. capsulatum Ags. T_H2 cells are relatively sparse at lesional sites. These studies support a general role for CD4⁺CTLs in inflammatory fibrosis and suggest that fibrosing mediastinitis is an Ag-driven disease that may provide important mechanistic insights into the pathogenesis of idiopathic fibrotic diseases.

IgG4-related disease: a contemporary review

Background/aim

Immunoglobulin G4-related disease (IgG4-RD), is an immune-mediated fibroinflammatory condition, which may involve multiple organs and mostly presents with high serum IgG4 levels and specific histopathological characteristics. As IgG4-RD is a relatively new entity the etiology, prevalence and epidemiologic knowledge is quite limited. Although involvement of almost all anatomical regions has been reported, the most commonly affected regions are pancreas, lacrimal glands, salivary glands, retroperitoneum, orbita, lymph nodes, kidney and lungs. Diagnosis is made with combined evaluation of clinical, radiological and histopathological findings. Typical histopathological features include storiform fibrosis, dense lymphoplasmacytic infiltrates and obliterative phlebitis. Its course is typically marked by remission and relapsing attacks and it may lead to fibrosis, destructive lesions in tissues and organ failure unless promptly treated. In the treatment of IgG4-RD, many approaches including surgical resection of tissues, systemic glucocorticoids, steroid-sparing immunosuppressive drugs, and biological agents are employed. Although association is not clear, malignancies are frequently reported in IgG4-RD patients. Therefore, it is prudent to monitor patients for the symptoms of malignant diseases.

Conclusion

In this review, recent advances in clinico-pathological characteristics, diagnosis, and treatment of IgG4–RD are discussed.

IgG4 thyroiditis in the Asian population

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated fibro-inflammatory condition that often causes the formation of tumefactive lesions. The discovery of IgG4-RD linked many well-known isolated conditions as a distinct multi-organ disease, and started an era of promoting investigation and treatment in relevant fields. In the thyroid gland, a subcategory of Hashimoto thyroiditis (HT) with IgG4-rich inflammation was first discovered and named IgG4 thyroiditis by our group. This subtype of HT presents with rapidly progressive clinical manifestations and destructive histopathological features underlying thyroid dysfunction, which are significantly different from the common type of HT. Moreover, other IgG4-rich thyroid conditions in patients with Graves' disease and systemic IgG4-RD have been described. These observations are most frequently reported in the Asian population for unknown reasons. Although recent studies demonstrated that IgG4 thyroiditis is a specific entity independent from IgG4-RD, recognition of this unique subset of thyroid disease has yielded important insights into understanding its pathogenesis and the development of novel therapeutic approaches.

Gut microbiome alterations in type 1 autoimmune pancreatitis after induction of remission by prednisolone

Although increasing evidence demonstrates the association between intestinal dysbiosis and pancreatic diseases such as chronic pancreatitis and pancreatic cancer, it remains largely unknown whether intestinal dysbiosis is involved in the immunopathogenesis of autoimmune pancreatitis (AIP). Recently, we found that intestinal dysbiosis mediates experimental AIP via the activation of plasmacytoid dendritic cells (pDCs), which can produce interferon (IFN)-α and interleukin (IL)-33. However, candidate intestinal bacteria, which promote the development of AIP, have not been identified. Fecal samples were obtained from type 1 AIP patients before and after prednisolone (PSL) treatment and subjected to 16S ribosomal RNA sequencing to evaluate the composition of intestinal bacteria. Induction of remission by PSL was associated with the complete disappearance of Klebsiella species from feces in two of the three analyzed patients with type 1 AIP. To assess the pathogenicity of Klebsiella species, mild experimental AIP was induced in MRL/MpJ mice by repeated injections of 10 μg of polyinosinic-polycytidylic acid [poly(I:C)], in combination with oral administration of heat-killed Klebsiella pneumoniae. The AIP pathology score was significantly higher in MRL/MpJ mice that received both oral administration of heat-killed K. pneumoniae and intraperitoneal injections of poly(I:C) than in those administered either agent alone. Pancreatic accumulation of pDCs capable of producing large amounts of IFN-α and IL-33 was also significantly higher in mice that received both treatments. These data suggest that intestinal colonization by K. pneumoniae may play an intensifying role in the development of type 1 AIP.

Identification of serum IFN-α and IL-33 as novel biomarkers for type 1 autoimmune pancreatitis and IgG4-related disease

IgG4-related disease (IgG4-RD) is a multi-organ autoimmune disease characterized by elevated serum IgG4 concentration. Although serum IgG4 concentration is widely used as a biomarker for IgG4-RD and type 1 autoimmune pancreatitis (AIP), a pancreatic manifestation of IgG4-RD, a significant number of patients have normal serum IgG4 levels, even in the active phase of the disease. Recently, we reported that the development of experimental AIP and human type 1 AIP is associated with increased expression of IFN-α and IL-33 in the pancreas. In this study, we assessed the utility of serum IFN-α and IL-33 levels as biomarkers for type 1 AIP and IgG4-RD. Serum IFN-α and IL-33 concentrations in patients who met the diagnostic criteria for definite type 1 AIP and/or IgG4-RD were significantly higher than in those with chronic pancreatitis or in healthy controls. Strong correlations between serum IFN-α, IL-33, and IgG4 concentrations were observed. Diagnostic performance of serum IFN-α and IL-33 concentrations as markers of type 1 AIP and/or IgG4-RD was comparable to that of serum IgG4 concentration, as calculated by the receiver operating characteristic curve analysis. Induction of remission by prednisolone treatment markedly decreased the serum concentration of these cytokines. We conclude that serum IFN-α and IL-33 concentrations can be useful as biomarkers for type 1 AIP and IgG4-RD.

IgG4-related disease: an update on pathophysiology and implications for clinical care

IgG4-related disease (IgG4-RD) has only existed as a unique disease entity since 2003, yet remarkable progress has already been achieved in describing the essential features of the disease. A framework for systematic clinical studies has been created by the development of a quantitative disease activity tool (the IgG4-RD Responder Index) and the validation of classification criteria, both of which were the products of international, multi-centre investigations. In addition, substantial strides have been made in understanding the pathophysiology of IgG4-RD. In particular, the central role of B cells in the disease has been demonstrated by both the robust clinical responsiveness of IgG4-RD to B cell depletion and by the identification of multiple self-antigens that promote B cell expansion. CD4⁺ T cells have also been investigated in detail; CD4⁺ cytotoxic T lymphocytes (suspected of promoting disease) and a specific T follicular helper cell subset that contributes to IgG4 isotype switching have both been defined by multiple groups. The mechanisms by which these immune cells converge on target tissues, interact with fibroblasts and promote tissue remodelling are beginning to be understood and will be an important research focus in the coming years.

The Cellular and Molecular Bases of Allergy, Inflammation and Tissue Fibrosis in Patients with IgG4-related Disease

IgG4-related disease (IgG4-RD) is a spectrum of complex fibroinflammatory disorder with protean manifestations mimicking malignant neoplasms, infectious or non-infectious inflammatory process. The histopathologic features of IgG4-RD include lymphoplasmacytic infiltration, storiform fibrosis and obliterative phlebitis together with increased in situ infiltration of IgG4 bearing-plasma cells which account for more than 40% of all IgG-producing B cells. IgG4-RD can also be diagnosed based on an elevated serum IgG4 level of more than 110 mg/dL (normal < 86.5 mg/mL in adult) in conjunction with protean clinical manifestations in various organs such as pancreato–hepatobiliary inflammation with/without salivary/lacrimal gland enlargement. In the present review, we briefly discuss the role of genetic predisposition, environmental factors and candidate autoantibodies in the pathogenesis of IgG4-RD. Then, we discuss in detail the immunological paradox of IgG4 antibody, the mechanism of modified Th2 response for IgG4 rather than IgE antibody production and the controversial issues in the allergic reactions of IgG4-RD. Finally, we extensively review the implications of different immune-related cells, cytokines/chemokines/growth factors and Toll-like as well as NOD-like receptors in the pathogenesis of tissue fibro-inflammatory reactions. Our proposals for the future investigations and prospective therapeutic strategies for IgG4-RD are shown in the last part.

Advances in the diagnosis and management of IgG4 related disease

IgG4 related disease was recognized as a unified disease entity only 15 years ago. Awareness of IgG4 related disease has increased worldwide since then, and specialists are now familiar with most of its clinical manifestations. Involvement of the pancreato-biliary tract, retroperitoneum/aorta, head and neck, and salivary glands are the most frequently observed disease phenotypes, differing in epidemiological features, serological findings, and prognostic outcomes. In view of this multifaceted presentation, IgG4 related disease represents a great mimicker of many neoplastic, inflammatory, and infectious conditions. Histopathology remains key to diagnosis because reliable biomarkers are lacking. Recently released classification criteria will be invaluable in improving early recognition of the disease. IgG4 related disease is highly treatable and responds promptly to glucocorticoids, but it can lead to end stage organ failure and even death if unrecognized. Prolonged courses of corticosteroids are often needed to maintain remission because the disease relapses in most patients. Rapid advancement in our understanding of the pathophysiology of IgG4 related disease is leading to the identification of novel therapeutic targets and possible personalized approaches to treatment.