Involvement of activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors in enhanced IgG4 responses in autoimmune pancreatitis

IgG4-related disease: an update on pathology and diagnostic criteria with a focus on salivary gland manifestations

Immunoglobulin G4-related disease (IgG4-RD) is a multi-organ disorder characterized by a highly variable clinical presentation depending on the affected organ/s, extent of tumefactive fibroinflammatory lesions, and associated functional impairment. The disease pursues a chronic, relapsing, often asymptomatic course and hence may pose a significant diagnostic challenge. Diagnostic delay can lead to progressive fibrosis and irreversible organ damage resulting into significant morbidity and even mortality. Given its broad clinical spectrum, physicians of all specialties may be the first clinicians facing this diagnostic challenge. Outside the pancreatobiliary system, the head and neck represents the major site of IgG4-RD with variable organ-specific diffuse or mass-forming lesions. In up to 75% of cases, elevated serum IgG4 levels are observed, but this figure possibly underestimates the fraction of seronegative cases, as the disease manifestations may present metachronously with significant intervals. Together with negative serology, this can lead to misdiagnosis of seronegative cases. A standardized nomenclature and diagnostic criteria for IgG4-RD were established in 2012 and revised in 2020 facilitating scientific research and expanding the range of diseases associated with IgG4 abnormalities. In addition to orbital pseudotumor, dacryoadenitis, Riedel thyroiditis, sinonasal manifestations, and rare miscellaneous conditions, IgG4-related sialadenitis is one of the most frequent presentations in the head and neck region. However, controversy still exists regarding the relationship between sialadenitis and IgG4-RD. This review focuses on the clinicopathological features of IgG4-related sialadenitis and its contemporary diagnostic criteria.

IgG4-related cholangitis - a mimicker of fibrosing and malignant cholangiopathies

IgG4-related cholangitis (IRC) is the major hepatobiliary manifestation of IgG4-related disease (IgG4-RD), a systemic fibroinflammatory disorder. The pathogenesis of IgG4-RD and IRC is currently viewed as multifactorial, as there is evidence of a genetic predisposition while environmental factors, such as blue-collar work, are major risk factors. Various autoantigens have been described in IgG4-RD, including annexin A11 and laminin 511-E8, proteins which may exert a partially protective function in cholangiocytes by enhancing secretion and barrier function, respectively. For the other recently described autoantigens, galectin-3 and prohibitin 1, a distinct role in cholangiocytes appears less apparent. In relation to these autoantigens, oligoclonal expansions of IgG4+ plasmablasts are present in patients with IRC and disappear upon successful treatment. More recently, specific T-cell subtypes including regulatory T cells, follicular T helper 2 cells, peripheral T helper cells and cytotoxic CD8+ and CD4+ SLAMF7+ T cells have been implicated in the pathogenesis of IgG4-RD. The clinical presentation of IRC often mimics other biliary diseases such as primary sclerosing cholangitis or cholangiocarcinoma, which may lead to inappropriate medical and potentially invalidating surgical interventions. As specific biomarkers are lacking, diagnosis is made according to the HISORt criteria comprising histopathology, imaging, serology, other organ manifestations and response to therapy. Treatment of IRC aims to prevent or alleviate organ damage and to improve symptoms and consists of (i) remission induction, (ii) remission maintenance and (iii) long-term management. Glucocorticosteroids are highly effective for remission induction, after which immunomodulators can be introduced for maintenance of remission as glucocorticosteroid-sparing alternatives. Increased insight into the pathogenesis of IRC will lead to improved diagnosis and novel therapeutic strategies in the future.

Basophils beyond allergic and parasitic diseases

Basophils bind IgE via FcεRI-αβγ2, which they uniquely share only with mast cells. In doing so, they can rapidly release mediators that are hallmark of allergic disease. This fundamental similarity, along with some morphological features shared by the two cell types, has long brought into question the biological significance that basophils mediate beyond that of mast cells. Unlike mast cells, which mature and reside in tissues, basophils are released into circulation from the bone marrow (constituting 1% of leukocytes), only to infiltrate tissues under specific inflammatory conditions. Evidence is emerging that basophils mediate non-redundant roles in allergic disease and, unsuspectingly, are implicated in a variety of other pathologies [e.g., myocardial infarction, autoimmunity, chronic obstructive pulmonary disease, fibrosis, cancer, etc.]. Recent findings strengthen the notion that these cells mediate protection from parasitic infections, whereas related studies implicate basophils promoting wound healing. Central to these functions is the substantial evidence that human and mouse basophils are increasingly implicated as important sources of IL-4 and IL-13. Nonetheless, much remains unclear regarding the role of basophils in pathology vs. homeostasis. In this review, we discuss the dichotomous (protective and/or harmful) roles of basophils in a wide spectrum of non-allergic disorders.

Case report: Clinical highlights and radiological classification of IgG4-related spinal pachymeningitis: A rare case series and updated review of the literature

Purpose

Hypertrophic pachymeningitis associated with immunoglobulin G4-related disease (IgG4-RD) has been rarely reported, and there is little information and no clear consensus on the management of IgG4-related spinal pachymeningitis (IgG4-RSP). The present study described its possible clinical features, including the symptoms, imaging, treatment and prognosis of patients with IgG4-RSP.

Methods

We report three patients who presented with progressive neurological dysfunction due to spinal cord compression. Relevant articles were searched from the PubMed, Web of Science, and Embase databases, and the resulting literature was reviewed.

Results

The literature review provided a summary of 45 available cases, which included three cases from our center. Progressive worsening of neurological impairment was observed in 22 patients (48.9%). The lesions involved the thoracic spine (n=28, 62.2%), cervical spine (n=26, 57.8%), lumbar spine (n=9, 20.0%), and sacral spine (n=1, 2.2%). Furthermore, the lesions were located in the dura mater (n=18, 40.0%), epidural space (n=17, 37.8%), intradural-extramedullary space (n=9, 20.0%), and intramedullary space (n=1, 2.2%). On magnetic resonance imaging (MRI), the lesions generally appeared as striated, fusiform, or less often lobulated oval changes, with homogeneous (n=17,44.7%) and dorsal (n=15,39.5%) patterns being the most common. Thirty-five patients had homogeneous T1 gadolinium enhancement. Early surgical decompression, corticosteroid treatment, and steroid-sparing agents offered significant therapeutic advantages. A good therapeutic response to disease recurrence was observed with the medication.

Conclusion

The number of reported cases of IgG4-RSP remains limited, and patients often have progressive worsening of their neurological symptoms. The features of masses identified on the MRI should be considered. The prognosis was better with decompression surgery combined with immunosuppressive therapy. Long-term corticosteroid treatment and steroid-sparing agent maintenance therapy should be ensured. A systemic examination is recommended to identify the presence of other pathologies.

Microbiota in the Natural History of Pancreatic Cancer: From Predisposition to Therapy

Early microbiome insights came from gut microbes and their role among intestinal and extraintestinal disease. The latest evidence suggests that the microbiota is a true organ, capable of several interactions throughout the digestive system, attracting specific interest in the biliopancreatic district. Despite advances in diagnostics over the last few decades and improvements in the management of this disease, pancreatic cancer is still a common cause of cancer death. Microbiota can influence the development of precancerous disease predisposing to pancreatic cancer (PC). At the same time, neoplastic tissue shows specific characteristics in terms of diversity and phenotype, determining the short- and long-term prognosis. Considering the above information, a role for microbiota has also been hypothesized in the different phases of the PC approach, providing future revolutionary therapeutic insights. Microbiota-modulating therapies could open new issues in the therapeutic landscape. The aim of this narrative review is to assess the most updated evidence on microbiome in all the steps regarding pancreatic adenocarcinoma, from early development to response to antineoplastic therapy and long-term prognosis.

Autoimmune Pancreatitis: From Pathogenesis to Treatment

Autoimmune pancreatitis (AIP) is a rare disease. The diagnosis of AIP is difficult and should be made by a comprehensive evaluation of clinical, radiological, serological, and pathological findings. Two different types of AIP have been identified: autoimmune pancreatitis type 1 (AIP-1), which is considered a pancreatic manifestation of multiorgan disease related to IgG4, and autoimmune pancreatitis type 2 (AIP-2), which is considered a pancreas-specific disease not related to IgG4. Although the pathophysiological conditions seem to differ between type 1 and type 2 pancreatitis, both respond well to steroid medications. In this review, we focused on the pathogenesis of the disease to develop a tool that could facilitate diagnosis and lead to the discovery of new therapeutic strategies to combat autoimmune pancreatitis and its relapses. The standard therapy for AIP is oral administration of corticosteroids. Rituximab (RTX) has also been proposed for induction of remission and maintenance therapy in relapsing AIP-1. In selected patients, immunomodulators such as azathioprine are used to maintain remission. The strength of this review, compared with previous studies, is that it focuses on the clear difference between the two types of autoimmune pancreatitis with a clearly delineated and separate pathogenesis. In addition, the review also considers various therapeutic options, including biologic drugs, such as anti-tumor necrosis factor (TNF) therapy, a well-tolerated and effective second-line therapy for AIP type 2 relapses or steroid dependence. Other biologic therapies are also being explored that could provide a useful therapeutic alternative to corticosteroids and immunosuppressants, which are poorly tolerated due to significant side effects.

Potential roles of non-lymphocytic cells in the pathogenesis of IgG4-related disease

Studies have confirmed the involvement of a variety of lymphocyte subsets, including type 2 helper T lymphocytes (Th2) and IgG4⁺ B lymphocytes, in the pathogenesis of IgG4-related disease (IgG4-RD). Those lymphocytes contribute to the major pathogenetic features of IgG4-RD. However, they are not the only cellular components in the immunoinflammatory environment of this mysterious disease entity. Recent studies have suggested that various non-lymphocytic components, including macrophages and fibroblasts, may also play an important role in the pathogenetic process of IgG4-RD in terms of contributing to the chronic and complex progress of the disease. Therefore, the potential role of non-lymphocyte in the pathogenesis of IgG4-RD is worth discussing.

Single-Cell Sequencing of Immune Cell Heterogeneity in IgG4-Related Disease

Background

The IgG4-related disease (IgG4-RD) is an immune-mediated disorder with fibrotic manifestations. However, the transcriptional profiles of immune cell subsets at single-cell level are unknown. Herein, single-cell sequencing was used to assess the specific cell subpopulations and pathways in peripheral blood mononuclear cells (PBMCs) of IgG4-RD.

Methods

Single-cell sequencing was performed using the PBMCs from four patients with IgG4-RD and three healthy controls (HCs). Functional enrichment and cell analysis were performed through re-clustering of PBMCs to assess functional pathways and intercellular communication networks in IgG4-RD. Western blot and flow cytometry were used to verify sequencing and functional enrichment results.

Results

Four major cell types and 21 subtypes were identified. Further subclustering demonstrated that plasma B-cell proportions increased with increasing glycolysis/gluconeogenesis activity in IgG4-RD. Re-clustering of myeloid cells showed that EGR1 and CD36 expressions were significantly increased in CD14⁺ monocytes of IgG4-RD, as validated by Western blot analysis. Moreover, tumor necrosis factor (TNF) production pathways were positively regulated in CD14⁺ monocytes of IgG4-RD. In vitro stimulation showed that CD14⁺ monocytes of IgG4-RD could secrete higher levels of TNF-α . Notably, the proportions of CD8 central memory T (TCM) and TIGIT⁺ CD8 cytotoxic T (CTL) increased in patients with IgG4-RD compared with HCs. Further interaction analysis showed that B cell activation factor (BAFF) signaling pathways were enriched from myeloid cells subsets to B cells.

Conclusion

This study enhances the understanding of the cellular heterogeneity and transcriptional features involved in the pathogenesis of IgG4-RD, providing key clinical implications.

IgG4-related diseases of the digestive tract

IgG4-related conditions affecting the digestive tract are part of a multi-organ fibro-inflammatory disorder termed IgG4-related disease (IgG4-RD), with autoimmune pancreatitis and IgG4-related cholangitis being the most prominent manifestations. Gastrointestinal symptoms include jaundice, weight loss, abdominal pain, biliary strictures, and pancreatic and hepatic masses that mimic malignant diseases. IgG4-RD manifestations occur less frequently elsewhere in the digestive tract, namely in the oesophagus, retroperitoneum or intestine. Evidence-based European guidelines frame the current state-of-the-art in the diagnosis and management of IgG4-related digestive tract disease. Diagnosis is based on histology (if available), imaging, serology, other organ involvement and response to therapy (HISORt criteria). Few biomarkers beyond serum IgG4 concentrations are reliable. The first-line therapy (glucocorticoids) is swiftly effective but disease flares are common at low doses or after tapering. Second-line therapy might consist of other immunosuppressive drugs such as thiopurines or rituximab. Further trials, for example, of anti-CD19 drugs, are ongoing. Although an association between IgG4-RD and the development of malignancies has been postulated, the true nature of this relationship remains uncertain at this time.

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.

Immunoglobulin G4-related Disease: A New Systemic Disease Emerging in Japan

Immunoglobulin G4-related disease (IgG4-RD) is a fibro-inflammatory disease characterized by organ enlargement and elevated serum IgG4 levels. In 2003, IgG4-RD was proposed as a distinct form of IgG4-related systemic disease based on a histopathological study involving patients with autoimmune pancreatitis. IgG4-RD occurs mainly in older men and can affect almost any organ simultaneously or metachronously. Pathophysiologically, IgG4-RD occurs when an autoantigen triggers an immune response characterized by Th2 predominance with increased production of cytokines, such as interleukin 4 (IL-4), IL-5, IL-10, IL-13, and tumor growth factor-β (TGF-β), in the affected organ. IL-10 and TGF-β produced by the increased number of regulatory T cells induce a switch from B cells to IgG4-producing plasma cells and fibrosis, respectively. The characteristic histological features consist of dense infiltration of lymphocytes and IgG4-positive plasma cells, storiform fibrosis, and obliterative phlebitis. IgG4-RD is diagnosed based on a combination of clinical, serological, radiological, and histopathological findings. Differentiating IgG4-RD from malignant tumors or similar inflammatory diseases in the affected organs is important. The 2019 America College of Rheumatology/European League against Rheumatism classification criteria for IgG4-RD have high diagnostic sensitivity and specificity. IgG4-RD generally responds well to treatment with steroids, and a swift response is reassuring and provides further diagnostic confirmation. However, relapses are common during tapering or after cessation of steroids. In Japan, low-dose steroid maintenance therapy is usually given to prevent a relapse. B-cell depletion with rituximab is effective in patients resistant to or dependent on steroids. Most patients with IgG4-RD who receive steroid therapy show good short-term clinical, morphological, and functional outcomes. However, long-term outcomes, such as relapse, fibrosis development, and associated malignancies, have not been clearly defined. Therefore, novel treatment strategies, including rituximab, need to be tested in international randomized controlled clinical trials.

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.

CD163+ M2 macrophages promote fibrosis in IgG4-related disease via TLR7/IRAK4/NF-κB signaling

Objective

IgG4‐related disease (IgG4‐RD) is a fibro‐inflammatory condition that can affect multiple organs. We previously demonstrated that TLR7‐transgenic C57BL/6 mice showed elevated serum IgG1 levels and inflammation with fibrosis in the salivary glands (SGs), lungs, and pancreas. Moreover, we observed extensive Toll‐like receptor 7 (TLR‐7)–positive CD163+ M2 macrophage infiltration in SGs from IgG4‐RD patients. We undertook this study to examine the fibrotic mechanism via the TLR‐7 pathway.

Methods

Gene expression in SGs from human TLR7‐transgenic mice and IgG4‐RD patients was analyzed using DNA microarrays. We extracted the common up‐regulated TLR‐7–related genes in SGs from TLR7‐transgenic mice and IgG4‐RD patients. Finally, we investigated the interaction between CD163+ M2 macrophages and fibroblasts before and after stimulation with the TLR‐7 agonist loxoribine.

Results

In TLR7‐transgenic mice and IgG4‐RD patients, IRAK3 and IRAK4 were significantly overexpressed. Real‐time polymerase chain reaction validated the up‐regulation of only IRAK4 in IgG4‐RD patients compared with the other groups (P < 0.05). Interleukin‐1 receptor–associated kinase 4 (IRAK4) was strongly detected in and around germinal centers in SGs from patients with IgG4‐related dacryoadenitis and sialadenitis alone. Double immunofluorescence staining showed that IRAK4‐positive cells were mainly colocalized with CD163+ M2 macrophages in SGs (P < 0.05). After stimulation with loxoribine, CD163+ M2 macrophages exhibited significantly enhanced expression of IRAK4 and NF‐κB and increased supernatant concentrations of fibrotic cytokines. Finally, we confirmed that the number of fibroblasts was increased by culture with the supernatant of CD163+ M2 macrophages following stimulation with loxoribine (P < 0.05).

Conclusion

CD163+ M2 macrophages promote fibrosis in IgG4‐RD by increasing the production of fibrotic cytokines via TLR‐7/IRAK4/NF‐κB signaling.

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.

Is simultaneous presence of IgG4-positive plasma cells and giant-cell hepatitis a coincidence in autoimmune hepatitis? A case report

BACKGROUND

The immune-mediated invasion of IgG4-positive plasma cells in the liver is found in some autoimmune hepatitis. Giant-cell hepatitis (GCH) is a very rare pathological feature in adults, and the clinical characteristics of the simultaneous appearance of the two pathological phenomena are not clear.

CASE SUMMARY

A 68-year-old woman was hospitalized with fatigue, poor appetite, and yellow urine for 20 d. Liver function tests and immunological indexes were significantly abnormal and accompanied by elevated serum IgG4 levels. Liver pathology revealed severe inflammation of the interface between the portal tract and hepatocytes, portal area inflammation, plasma cell infiltration, formation of rosette cells, IgG4-positive plasma cells > 10/high-power field, IgG4/IgG > 40%, and multinucleated liver cell swelling. IgG4-related autoimmune hepatitis (AIH) combined with GCH was diagnosed, and methylprednisolone was administered at 40 mg/day. Two weeks later, the clinical symptoms disappeared, and the liver function and immunological indicators were significantly improved. Methylprednisolone was reduced at a rate of 4–8 mg per week to 8 mg/day for maintenance. A second liver biopsy 48 wk later indicated that liver inflammation and fibrosis were significantly improved. IgG4-positive plasma cells and GCH were not detected. A literature search was conducted to analyze articles reporting similar pathological phenomena.

CONCLUSION

AIH with simultaneous IgG4-positive plasma cell infiltration and GCH, liver inflammation, and fibrosis is possibly more severe than typical AIH but sensitive to corticosteroids.

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.

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.

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.

Mer tyrosine kinase (MerTK) as a possible link between resolution of inflammation and tissue fibrosis in IgG4-related disease

OBJECTIVES

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory disorder characterized by a dysregulated resolution of inflammation and wound healing response that might develop after an apoptotic insult induced by cytotoxic T lymphocytes (CTLs). Mer receptor tyrosine kinase (MerTK) and its ligand Protein S (ProS1) have a pivotal role in the resolution of inflammation, being implicated in the clearance of apoptotic cells, quenching of the immune response and development of tissue fibrosis. In the present work we aimed to investigate a possible involvement of the MerTK signalling pathway in the pathogenesis of IgG4-RD and development of tissue fibrosis.

METHODS

MerTK and ProS1 expression patterns in IgG4-RD lesions were evaluated by immunohistochemistry and immunofluorescence studies. Circulating MerTK+ monocytes, soluble Mer and MerTK ligands were measured in the peripheral blood of IgG4-RD patients and healthy controls by flow cytometry and ELISA, respectively.

RESULTS

MerTK was highly expressed by macrophages infiltrating IgG4-RD lesions. MerTK+ macrophages were more abundant in IgG4-RD than in Sjögren syndrome and interacted with apoptotic cells and ProS1 expressing T and B lymphocytes. Moreover, they expressed the pro-fibrotic cytokine TGF-β and their numbers declined following rituximab induced disease remission. Circulating MerTK+ monocytes, soluble Mer and MerTK ligands were not increased in the peripheral blood of patients with IgG4-RD.

CONCLUSIONS

The MerTK-ProS1 axis is activated in IgG4-RD lesions, possibly leading to persistent stimulation of processes involved in the resolution of inflammation and tissue fibrosis.

IgG4-related disease: Changing epidemiology and new thoughts on a multisystem disease

IgG4-related disease (IgG4-RD) represents an immune-mediated fibroinflammatory condition with peculiar histopathologic changes that can affect various organs. In 2012 its unified nomenclature was published, which allows to abandon other synonymous names. Up to now, only little is known about its epidemiology around the world. However, although it is generally considered a rare condition, the number of patients with IgG4-RD is increasing enormously. Likewise, the annual number of publications on this subject has increased progressively. The spectrum of clinical manifestations in IgG4-RD is highly variable, depending on the severity of the disease as well as the presence of organ(s) involvement. This review gives an overview on changing epidemiology of IgG4-RD focusing the attention on the large cohorts of patients published in the literature.

Pathology of IgG4-related sclerosing mastitis

Immunoglobulin G4-related sclerosing mastitis (IgG4-RM) is a recently recognised member of the IgG4-related disease (IgG4-RD) family, a multisystem fibroinflammatory condition that can affect any organ system. IgG4-RM is rare and predominantly occurs in middle-aged women. It may present with painless palpable mass and/or lymphadenopathy thereby mimicking breast cancer. Although there is an abundance of literature describing the clinicopathological characteristics of IgG4-RD in a variety of organs, data on IgG4-RM are limited due to its rarity. This review describes the manifestation of the disease in the breast based on reported cases, emphasising the clinicopathological features, pathophysiology, differential diagnosis, treatment and prognosis.

Pancreatic Diseases and Microbiota: A Literature Review and Future Perspectives

Gut microbiota represent an interesting worldwide research area. Several studies confirm that microbiota has a key role in human diseases, both intestinal (such as inflammatory bowel disease, celiac disease, intestinal infectious diseases, irritable bowel syndrome) and extra intestinal disorders (such as autism, multiple sclerosis, rheumatologic diseases). Nowadays, it is possible to manipulate microbiota by administering prebiotics, probiotics or synbiotics, through fecal microbiota transplantation in selected cases. In this scenario, pancreatic disorders might be influenced by gut microbiota and this relationship could be an innovative and inspiring field of research. However, data are still scarce and controversial. Microbiota manipulation could represent an important therapeutic strategy in the pancreatic diseases, in addition to standard therapies. In this review, we analyze current knowledge about correlation between gut microbiota and pancreatic diseases, by discussing on the one hand existing data and on the other hand future possible perspectives.

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.

Alcohol and Smoking Mediated Modulations in Adaptive Immunity in Pancreatitis

Pancreatitis is a condition of pancreatic inflammation driven by injury to the pancreatic parenchyma. The extent of acinar insult, intensity, and type of immune response determines the severity of the disease. Smoking, alcohol and autoimmune pancreatitis are some of the predominant risk factors that increase the risk of pancreatitis by differentially influencing the adaptive immune system. The overall decrease in peripheral lymphocyte (T-, B- and (natural killer T-) NKT-cell) count and increased infiltration into the damaged pancreatic tissue highlight the contribution of adaptive immunity in the disease pathology. Smoking and alcohol modulate the responsiveness and apoptosis of T- and B-cells during pancreatic insult. Acute pancreatitis worsens with smoking and alcohol, leading to the development of systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome, suggesting the critical role of adaptive immunity in fatal outcomes such as multiple organ dysfunction. The presence of CD4⁺ and CD8⁺ T-lymphocytes and perforin-expressing cells in the fibrotic tissue in chronic pancreatitis modulate the severity of the disease. Due to their important role in altering the severity of the disease, attempts to target adaptive immune mediators will be critical for the development of novel therapeutic interventions.

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.

Intestinal dysbiosis mediates experimental autoimmune pancreatitis via activation of plasmacytoid dendritic cells

Autoimmune pancreatitis (AIP) is a pancreatic manifestation of a newly proposed disease entity, IgG4-related disease (IgG4-RD), characterized by enhanced IgG4 antibody responses and involvement of multiple organs. We have previously reported that innate immune activation contributes to the development of AIP and IgG4-RD, as these diseases are characterized by the production of IFN-α and IL-33 by plasmacytoid dendritic cells (pDCs) that mediate chronic fibroinflammatory responses. In this study, we investigated the roles played by innate immunity against intestinal microflora in experimental AIP induced in MRL/MpJ mice by repeated administrations of 100 µg of polyinosinic-polycytidylic acid [poly (I:C)]. Bowel sterilization with a broad spectrum of antibiotics inhibited pancreatic accumulation of pDCs producing IFN-α and IL-33, and thereby suppressed the development of AIP. Mice treated with 10 µg of poly (I:C) developed severe AIP equivalent to that induced by 100 µg of poly (I:C) upon co-housing with mice treated with 100 µg of poly (I:C). Fecal microbiota transplantation (FMT) from donor mice treated with 100 µg of poly (I:C) led to the development of severe AIP in the recipient mice upon injection with 10 µg of poly (I:C). Induction of severe AIP in mice with 10 µg of poly (I:C) was associated with pancreatic accumulation of pDCs producing IFN-α and IL-33 in the co-housing and FMT experiments. These data collectively suggest that innate immune responses against intestinal microflora are involved in the development of experimental AIP, and that intestinal dysbiosis increases sensitivity to experimental AIP via activation of pDCs.

Extracellular vesicles microRNA analysis in type 1 autoimmune pancreatitis: Increased expression of microRNA-21

BACKGROUND

The molecular basis of type 1 autoimmune pancreatitis (AIP) remains unclear. Recent attention on the role of extracellular vesicles microRNA (EV miRNA) in immune homeostasis has prompted us to perform an extensive miRNA screening of serum-derived EV in AIP.

METHODS

EV miRNA expression was analyzed using microarrays in AIP, chronic pancreatitis (CP), and healthy adult (HC) samples (n = 10 from each group). Differences in signals, > 3 or <1/3 times, represented significant differences in expression. Another cohort of AIP (n = 14), CP (n = 10), and HC (n = 10) samples of EV miRNA was analyzed using reverse-transcription polymerase chain reaction (RT-PCR). miRNA expression in pancreatic tissues was evaluated using in situ hybridization (ISH) in three additional subjects from each group.

RESULTS

Signals of eight miRNAs (miR-659-3p, -27a-3p, -99a-5p, -21-5p, -205-5p, -100-5p, -29c-3p, and -125b-1-3p) were significantly higher, while those of two miRNAs (miR-4252 and -5004-5p) were significantly lower in AIP than in HC. EV miR-21-5p was significantly up-regulated in AIP than in HC (P = 0.035) and CP (P = 0.048). The number of miR-21-5p positive inflammatory cells was significantly elevated in AIP than in CP (P = 0.014).

CONCLUSIONS

Circulating EVs exhibited altered miRNA expression patterns with elevated miR-21-5p in AIP when compared with those in HC and CP. miR-21-5p was highly expressed in pancreatic inflammatory cells in AIP. Our data suggests that miR-21-5p may be involved in the regulation of effector pathways in the pathophysiology of AIP, thus differentiating AIP from CP.

Immunological mechanism of IgG4-related disease

IgG4-related disease (IgG4-RD) is an immune-mediated inflammatory disorder in multiple organs, characterized by abundant infiltration of IgG4-positive plasmacytes and fibrosis in the involved organs. The precise pathogenic mechanism of IgG4-RD still remains unclear. Aberrant innate and adaptive immunity are considered as the main pathogenesis of IgG4-RD. Recent studies have shown that abnormal adaptive immune responses mediated by T helper type 2 ​cells, regulatory T lymphocytes, CD4+ cytotoxic T lymphocytes, T follicular helper cells, T follicular regulatory cells, PD-1hiCXCR5-peripheral T helper cells and B cell subsets are involved in IgG4-RD. In addition to adaptive immune responses, innate immune responses play pathogenic roles in IgG4-RD. Macrophages, mast cells, basophils, complement, and plasmacytoid dendritic cells are activated to produce various kinds of cytokines in IgG4-RD. This review aims to summarize the most recent knowledge in the pathogenesis of IgG4-RD.

Orbital inflammation and colitis in pediatric IgG4-related disease: A case report and review of the literature

IgG4-related disease (IgG4-RD) is an inflammatory disorder characterized by tumor-like swelling in one or more organs, elevated serum IgG4 levels, and histological alterations with infiltration of IgG4-positive plasma cells. IgG4-RD is rare and likely underdiagnosed in children. We report a case of a 16-year-old girl with IgG4-positive colitis that developed weeks after IgG4-related ophthalmic disease and discuss diagnosis and treatment in the context of the literature available. Since the pathophysiology of IgG4-RD is unknown, treatment options are empiric and, for the most part, untargeted. Systemic corticosteroid treatment is the basis of anti-inflammatory treatment in IgG4-RD and induced early remission in our patient. During corticosteroid taper, the patient developed weight loss and intestinal inflammation. Histopathological assessment of the intestinal walls confirmed IgG4-positive colitis. Immune-modulating treatment with non-biologic (e.g., methotrexate (MTX) and mycophenolate mofetil) or biologic (rituximab) disease-modifying antirheumatic drugs has been reported in treatment refractory or corticosteroid-dependent patients. The patient responded to treatment with anti-inflammatory therapy with food rich in TGF-β2 (modulen) and MTX. This is one of the first pediatric patients reported with IgG4-related colitis extending the phenotype of pediatric IgG4-RD. International collaboration to prospectively document clinical presentation and treatment responses may help to further establish the phenotype and treatment options and to raise awareness for IgG4-RD.

Review of a novel disease entity, immunoglobulin G4-related disease

Immunoglobulin G4 (IgG4)-related dacryoadenitis and sialoadenitis (IgG4-DS) are part of a multiorgan fibroinflammatory condition of unknown etiology termed IgG4-related disease (IgG4-RD), which has been recognized as a single diagnostic entity for less than 15 years. Histopathologic examination is critical for diagnosis of IgG4-RD. CD4+ T and B cells, including IgG4-expressing plasma cells, constitute the major inflammatory cell populations in IgG4-RD and are thought to cause organ damage and tissue fibrosis. Patients with IgG4-RD who have active, untreated disease exhibit significant increase of IgG4-secreting plasmablasts in the blood. Considerable insight into the immunologic mechanisms of IgG4-RD has been achieved in the last decade using novel molecular biology approaches, including next-generation and single-cell RNA sequencing. Exploring the interactions between CD4+ T cells and B lineage cells is critical for understanding the pathophysiology of IgG4-RD. Establishment of pathogenic T cell clones and identification of antigens specific to these clones constitutes the first steps in determining the pathogenesis of the disease. Herein, the clinical features and mechanistic insights regarding pathogenesis of IgG4-RD were reviewed.

IgG4-related disease: How to place it in the spectrum of immune-mediated and rheumatologic disorders?

IgG4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory disorder that results from massive expansion of polyclonal IgG4-switched B and/or plasma cells. It can virtually affect all organs and its diagnosis relies on clinical, serological and histopathological criteria. The role of autoimmunity and adaptive immune system in IgG4-RD is reflected in plasmablast differentiation, germinal center formation and IgG4 production induced by CD4+ cells expressing CD40 ligand. IgG4-RD has been considered to be a Th2/Treg-driven disorder, but follicular helper T cells are important in driving the IgG subclass switch. Prompt clinical responses to rituximab, human leukocyte antigen (HLA) associations and the presence of autoantibodies also point to the importance of adaptive immune system. However, innate immunity may induce storiform fibrosis through T-cell independent responses as a consequence of toll-like receptors activation by microbe-and damage-associated molecular patterns, while macrophages and basophils also appear to have a significant role in IgG4-RD pathogenesis. Allergic mechanisms may drive IgG4-RD, but only a subgroup has elevated IgE serum levels and peripheral eosinophilia. Finally, the 2012 revised Chapel Hill Consensus Conference nomenclature pointed IgG4-RD as a cause of large-vessel vasculitis. This review aims to discuss how to place IgG4-RD in the spectrum of immune-mediated and rheumatologic disorders.

Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling

Objective

IgG4‐related disease (IgG4‐RD) is a unique inflammatory disorder in which Th2 cytokines promote IgG4 production. In addition, recent studies have implicated the Toll‐like receptor (TLR) pathway. This study was undertaken to examine the expression of TLRs in salivary glands (SGs) from patients with IgG4‐RD.

Methods

SGs from 15 patients with IgG4‐RD, 15 patients with Sjögren's syndrome (SS), 10 patients with chronic sialadenitis, and 10 healthy controls were examined histologically. TLR family gene expression (TLR‐1 through TLR‐10) was analyzed by DNA microarray in the submandibular glands (SMGs). Up‐regulation of TLRs was confirmed in SGs from patients with IgG4‐RD. Finally, the phenotype of human TLR‐7 (huTLR‐7)–transgenic C57BL/6 mice was assessed before and after stimulation with TLR agonist.

Results

In patients with IgG4‐RD, TLR‐4, TLR‐7, TLR‐8, and TLR‐9 were overexpressed. Polymerase chain reaction validated the up‐regulation of TLR‐7 in IgG4‐RD compared with the other groups. Immunohistochemical analysis confirmed strong infiltration of TLR‐7–positive cells in the SGs of patients with IgG4‐RD. Double immunohistochemical staining showed that TLR‐7 expression colocalized with CD163+ M2 macrophages. After in vitro stimulation with a TLR‐7 agonist, CD163+ M2 macrophages produced higher levels of interleukin‐33 (IL‐33), which is a Th2‐activating cytokine. In huTLR‐7–transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild‐type mice (P < 0.05). Moreover, the concentration of serum IgG, IgG1, and IL‐33 in huTLR‐7–transgenic mice was distinctly increased upon stimulation with a TLR‐7 agonist (P < 0.05).

Conclusion

TLR‐7–expressing M2 macrophages may promote the activation of Th2 immune responses via IL‐33 secretion in IgG4‐RD.

Laminin 511 is a target antigen in autoimmune pancreatitis

Autoimmune pancreatitis (AIP), a major manifestation of immunoglobulin G4-related disease (IgG4-RD), is an immune-mediated disorder, but the target autoantigens are still unknown. We previously reported that IgG in patients with AIP induces pancreatic injuries in mice by binding the extracellular matrix (ECM). In the current study, we identified an autoantibody against laminin 511-E8, a truncated laminin 511, one of the ECM proteins, in patients with AIP. Anti-laminin 511-E8 IgG was present in 26 of 51 AIP patients (51.0%), but only in 2 of 122 controls (1.6%), by enzyme-linked immunosorbent assay. Because truncated forms of other laminin family members in other organs have been reported, we confirmed that truncated forms of laminin 511 also exist in human and mouse pancreas. Histologic studies with patient pancreatic tissues showed colocalization of patient IgG and laminin 511. Immunization of mice with human laminin 511-E8 induced antibodies and pancreatic injury, fulfilling the pathologic criteria for human AIP. Four of 25 AIP patients without laminin 511-E8 antibodies had antibodies against integrin α6β1, a laminin 511 ligand. AIP patients with laminin 511-E8 antibodies exhibited distinctive clinical features, as the frequencies of malignancies or allergic diseases were significantly lower in patients with laminin 511-E8 antibodies than in those without. The discovery of these autoantibodies should aid in the understanding of AIP pathophysiology and possibly improve the diagnosis of AIP.

Pathogenesis of IgG4-related disease. Comparison with Sjögren's syndrome

IgG4-related disease (IgG4-RD) is characterized by lympho-plasmacytic infiltration and fibrosis in multiple organs, accompanied by high serum IgG4 levels. Although both IgG4-RD and Sjögren's syndrome (SS) frequently affect salivary and lacrimal glands, the clinical and pathological features of these two conditions are different. In an attempt to delineate the pathomechanisms of IgG4-RD, we compared the gene expression patterns of various molecules in labial salivary glands (LSGs) between IgG4-RD and SS. First, using quantitative PCR, we demonstrated significantly higher mRNA expression levels of activation-induced cytidine deaminase (AID), IL-10, and TGFβ in LSGs of IgG4-RD than SS and healthy controls (HCs). We propose that the combination of AID and IL-10 contributes to IgG4-specific immunoglobulin class switch recombination, and that TGFβ induces LSGs fibrosis in IgG4-RD. Second, DNA microarray identified 2641 differentially expressed genes (DEGs) in LSGs; with 1321 up-regulated and 1320 down-regulated genes in IgG4-RD, relative to SS. Among the up-regulated DEGs in IgG4-RD, quantitative PCR confirmed significantly higher expression levels of chemokine (C-C motif) ligand 18 (CCL18) and lactotransferrin in LSGs of IgG4-RD than SS and HCs. The former has chemotactic activity on various types of lymphocytes and enhances collagen production from fibroblasts, while lactotransferrin is an iron-binding protein abundantly present in milk and has a wide range of functions, including fibroblast proliferation and maturation of dendritic cells (DCs). Third, immunofluorescence staining confirmed specific upregulation of CCL18 in macrophages, CD11c + and B cells, and plasmacytes of LSGs-IgG4-RD. These pathological findings could help in the identification of disease-specific biomarkers as well as development of novel therapeutic strategies.

B lymphocytes directly contribute to tissue fibrosis in patients with IgG4-related disease

BACKGROUND

IgG₄-related disease (IgG₄-RD) is a fibroinflammatory condition marked by rapid clinical improvement after selective depletion of B lymphocytes with rituximab. This feature suggests that B cells might participate in fibrogenesis and wound healing.

OBJECTIVE

In the present work we aimed to demonstrate that B lymphocytes contribute directly to tissue fibrosis in patients with IgG₄-RD.

METHODS

Total circulating CD19⁺ B lymphocytes, naive B cells, memory B cells, or plasmablasts from patients with IgG₄-RD were cultivated with human fibroblasts. Profibrotic soluble factors and collagen production in cocultures were assessed by using ELISAs and Luminex assays. RNA sequencing and quantitative RT-PCR were used to assess fibroblast activation in the presence of B cells, as well as induction of profibrotic pathways in B-cell subsets. Relevant profibrotic and inflammatory molecules were confirmed in vitro by using functional experiments and on IgG₄-RD tissue sections by using multicolor immunofluorescence studies.

RESULTS

B cells from patients with IgG₄-RD (1) produced the profibrotic molecule platelet-derived growth factor B and stimulated collagen production by fibroblasts; (2) expressed enzymes implicated in extracellular matrix remodeling, such as lysyl oxidase homolog 2; (3) produced the chemotactic factors CCL4, CCL5, and CCL11; and (4) induced production of these same chemokines by activated fibroblasts. Plasmablasts expressed sets of genes implicated in fibroblast activation and proliferation and therefore represent cells with intrinsic profibrotic properties.

CONCLUSION

We have demonstrated that B cells contribute directly to tissue fibrosis in patients with IgG₄-RD. These unanticipated profibrotic properties of B lymphocytes, particularly plasmablasts, might be relevant for fibrogenesis in patients with other fibroinflammatory disorders and for wound-healing processes in physiologic conditions.

New insights into the pathophysiology of IgG4-related disease and markers of disease activity

INTRODUCTION

Recently, IgG4-related disease (IgG4-RD) has become a well-recognized clinical entity, although its causes are still not well understood. The pathophysiology of IgG4-RD has been reported from a variety of aspects. Areas covered: In this review, we outline a number of recent advances in our understanding of the pathogenesis of IgG4-RD, divided according to acquired immunology and innate immunology and other topics. Furthermore, we also focus on some proposed markers of disease activity of IgG4-RD. Expert commentary: One striking advance made recently is the identification of novel autoantigens of IgG4-RD. At the onset of IgG4-RD, various T cell side factors such as Tfh, Th2 cells are at work, in addition to B cell side factors like plasmablasts and plasma cells, and innate immunology via TLR and M2 macrophages. The efficacy of B cell depletion therapy using rituximab has been reported, with the establishment of steroid-sparing therapies targeting other molecules also anticipated.

Cytokines produced by innate immune cells in IgG4-related disease

IgG4-related disease (IgG4-RD) is a newly defined multi-organ disease proposed by Japanese physicians. IgG4-RD is characterized by elevated serum levels of IgG4 and massive infiltration of IgG4-expressing plasma cells in the affected organs. Recent studies have shown that abnormal adaptive immune responses mediated by T helper type 2 cells, regulatory T cells, follicular helper T cells, cytotoxic CD4⁺ T cells, and plasmablasts are involved in IgG4-RD immunopathogenesis. In addition to adaptive immune responses, innate immune responses play pathogenic roles in IgG4-RD. Plasmacytoid dendritic cells (pDCs), M2 macrophages, and basophils are activated to produce various kinds of cytokines in IgG4-RD. Recent studies highlight the importance of type I IFN and IL-33 produced by pDCs in IgG4-RD immunopathogenesis.

New insights into immune cells cross-talk during IgG4-related disease

Immunoglobulin G4-related disease (IgG4-RD) is a newly acknowledged entity, characterized by an immune-mediated fibro-inflammatory process affecting virtually all organs, with infiltration of IgG4⁺ bearing plasma cells. Until today the pathogenesis of IgG4-RD remains unknown. Treatment with anti-CD20 monoclonal antibodies efficiently induced remission and attenuated the secretory phenotype of myofibroblasts responsible of uncontrolled collagen deposition. This supports the pathogenic role of the adaptive immunity, particularly B cell compartment and B cell/T cell interaction. Latest studies have also highlighted the importance of innate immune system that has been underestimated before and the key role of a specific T cell subset, T follicular helper cells that are involved in IgG4-class-switching and plasmablast differentiation. In this review, we aim to review the most recent knowledge of innate immunity, T and B cells involvement in IgG4-RD, and introduce tertiary lymphoid organs (TLO) as a potential marker of relapse in this condition.

Mechanistic Insights into Autoimmune Pancreatitis and IgG4-Related Disease

Autoimmune pancreatitis (AIP) is a pancreatic manifestation of a recently defined disease form known as IgG4-related disease (AIP/IgG4-RD). AIP/IgG4-RD is characterized by elevated systemic IgG4 antibody concentrations and lesional tissues infiltrated by IgG4-expressing plasmacytes. In addition, recent studies have revealed that, in common with other autoimmune diseases, such as systemic lupus erythematosus (SLE) and psoriasis, AIP/IgG4-RD is associated with increased type I IFN (IFN-I) production by plasmacytoid dendritic cells (pDCs). However, unlike SLE, AIP/IgG4-RD is characterized by elevated IFN-I-dependent IL-33 production, the latter emerging as an important contributor to inflammation and fibrotic responses characterizing this disease. On this basis, we propose that blockade of the IFN-I/IL-33 axis might constitute a successful approach to treating this unique type of autoimmunity.

IgG4-related retroperitoneal fibrosis overlapping with primary biliary cirrhosis and primary Sjögren's syndrome: A case report

RATIONALE

IgG4-related disease (IgG4-RD) is a chronic fibro-inflammatory disorder which is characterized by elevated levels of serum IgG4 and infiltration of IgG4-bearing plasma cells in the involved organs. Primary biliary cirrhosis (PBC) and Primary Sjögren's syndrome (pSS) are both distinct from IgG4-related disease. We herein describe a Chinese patient with IgG4-related RPF overlapping with PBC and pSS.

PATIENT CONCERNS

We report a case of 69-year-old male with recurrent lower abdominal pain for 10 months. Laboratory data showed elevated erythrocyte sedimentation rate and hepatobiliary enzymes, renal dysfunction, high titers of antinuclear antibody, anti-SS-A antibody and anti-mitochondrial type 2, high immunoglobulin (Ig) G levels and elevated serum IgG4 (9 g/L). Contrast-enhanced computed tomography and magnetic resonance imaging were suggestive of retroperitoneal fibrosis and unilateral ureteral occlusion. Immunohistochemical staining for IgG4 did not demonstrate infiltration of IgG4-positive plasma cells in the retroperitoneal mass, but revealed significant infiltration of lymphocytoplasma cells as well as fibrosis and fibrin accumulation.

DIAGNOSES

The patient was diagnosed with IgG4-related retroperitoneal fibrosis based on the International Consensus Diagnostic Criteria. He was also diagnosed with primary biliary cirrhosis and primary Sjögren's syndrome.

INTERVENTIONS

250 mg ursodeoxycholic acid was administered twice daily, and prednisolone was initiated at a dose of 40 mg/day and then tapered to 25 mg after 45 days.

OUTCOMES

The size of the retroperitoneal soft tissue mass gradually reduced and the abnormal laboratory parameters were restored to normal.

LESSONS

This rare clinical condition has seldom been reported in the literature, which suggests that common immunogenetic factors may be involved in the development of IgG-related RPF, PBC and pSS.

Gut Microbiota-Immune System Crosstalk and Pancreatic Disorders

Gut microbiota is key to the development and modulation of the mucosal immune system. It plays a central role in several physiological functions, in the modulation of inflammatory signaling and in the protection against infections. In healthy states, there is a perfect balance between commensal and pathogens, and microbiota and the immune system interact to maintain gut homeostasis. The alteration of such balance, called dysbiosis, determines an intestinal bacterial overgrowth which leads to the disruption of the intestinal barrier with systemic translocation of pathogens. The pancreas does not possess its own microbiota, and it is believed that inflammatory and neoplastic processes affecting the gland may be linked to intestinal dysbiosis. Increasing research evidence testifies a correlation between intestinal dysbiosis and various pancreatic disorders, but it remains unclear whether dysbiosis is the cause or an effect. The analysis of specific alterations in the microbiome profile may permit to develop novel tools for the early detection of several pancreatic disorders, utilizing samples, such as blood, saliva, and stools. Future studies will have to elucidate the mechanisms by which gut microbiota is modulated and how it tunes the immune system, in order to be able to develop innovative treatment strategies for pancreatic disorders.

Immunoglobulin G4-related kidney diseases: An updated review

This review will encompass definition, pathogenesis, renal clinical manifestations and treatment of immunoglobulin G4-related diseases (IgG4-RDs). IgG4-RD is a recently recognized clinical entity that often involves multiple organs and is characterized by high levels of serum immunoglobulins G4, dense infiltration of IgG4⁺ cells and storiform fibrosis. Cellular immunity, particularly T-cell mediated immunity, has been implicated in the pathogenesis of IgG4-RDs. The most frequent renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis, membranous glomerulopathy and obstructive nephropathy secondary to urinary tract obstruction due to IgG4-related retroperitoneal fibrosis. IgG4-RD diagnosis should be based on specific histopathological findings, confirmed by tissue immunostaining, typical radiological findings and an appropriate clinical context. The first line treatment is the steroids with two warnings: Steroid resistance and relapse after discontinuation. In the case of steroid resistance, B cell depleting agents as rituximab represent the second-line treatment. In the case of relapse after discontinuation, steroid treatment may be associated with steroid sparing agents. Since the disease has been only recently identified, more prospective, long-term studies are needed to an improved understanding and a more correct and safe treatment.

Current perspectives on autoimmune pancreatitis and IgG4-related disease

IgG4-related disease (IgG4-RD) is a fibroinflammatory disorder recognized as a novel clinical entity with either synchronous or metachronous multi-organ involvement. Patients with IgG4-RD show diffuse or focal organ enlargement and mass-forming or nodular/thickened lesions with abundant infiltration of IgG4-positive plasmacytes and fibrosis, and such patients respond well to steroid treatment. It should be differentiated from mimics by a combination of serum IgG4 level, imaging features, and histopathological findings. The current first-line drug is corticosteroids, or rituximab in high-risk patients for steroid intolerance. Although relapse rates are high, standardized protocols for relapsed cases have not been approved yet. Based on genetic factors, disease-specific or -related antigens, abnormal innate and adaptive immunity may be involved, although the precise pathogenic mechanism and long-term outcome still remain unclear.

Clinical and pathophysiological aspects of type 1 autoimmune pancreatitis

In 1995, Yoshida and colleagues proposed the concept of "autoimmune pancreatitis" (AIP), which has recently been recognized as a new pancreatic inflammatory disease. Recent studies have suggested the existence of two subtypes of AIP: type 1, which involves immunoglobulin G4 (IgG4) and is the pancreatic manifestation of IgG4-related disease (IgG4-RD); and type 2, which is characterized by granulocytic epithelial lesions. Type 2 AIP is thought to be rare in Japan. Type 1 AIP is characterized by increased serum IgG4 concentrations, lymphoplasmacytic infiltrations, storiform fibrosis, and obliterative phlebitis. However, although type 1 AIP has become increasingly recognized, many clinical and basic issues remain to be solved. This review provides an overview of the recent clinical and basic knowledge of type 1 AIP.

Th1/Th2 Immune Balance and Other T Helper Subsets in IgG4-Related Disease

IgG4-related disease (IgG4-RD) is a systemic disease characterized by elevated serum IgG4 levels and a strong infiltration of IgG4-positive plasma cells in various organs. IgG4-RD patients also frequently suffer from allergic diseases, including asthma and atopic dermatitis. It is well known that T helper type 2 (Th2) cells have an important role in the initiation of allergic diseases, and Th2 cytokines such as interleukin (IL)-4 and IL-13 promote class switching to IgG4. Therefore, IgG4-RD is considered to be a Th2-predominant disease. However, other Th subsets, including regulatory T cells and T follicular helper cells, have recently received increasing attention with regard to the pathogenesis of IgG4-RD. Exploring the interconnected network of Th subsets in IgG4-RD is a highly promising field of investigation. In this review, we focus on the localization and functions of individual Th subsets to clarify the involvement of these cells in the pathogenesis of IgG4-RD.

Immunoglobulin G4-related kidney disease: Pathogenesis, diagnosis, and treatment

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized clinical entity that often involves multiple organs; it is characterized by high levels of serum immunoglobulin G4 (IgG4), dense infiltration of IgG4+ cells, and storiform fibrosis. Cellular immunity, particularly T cell-mediated immunity, has been implicated in the pathogenesis of IgG4-RD. The most frequent renal manifestations of IgG4-RD are IgG4-related tubulointerstitial nephritis, membranous glomerulonephropathy (MGN), and obstructive nephropathy secondary to urinary tract obstruction due to IgG4-related retroperitoneal fibrosis, prostatitis, or ureter inflammation. Kidney function impairment can be acute or chronic. In IgG4-MGN, proteinuria can be in the nephrotic range. The diagnosis of IgG4-related kidney disease should not be based solely on serum IgG4 levels or the number of tissue-infiltrating IgG4+ plasma cells. Diagnosis should be based on specific histopathological findings, confirmed by tissue immunostaining and an appropriate clinical context. Steroid treatment is the first-line therapy. For relapsing or refractory cases, immunosuppressants could be combined with steroids. In hydronephrosis patients, appropriate immunosuppressive therapy could preclude the implantation of a double J ureteral catheter.

Chronic Fibro-Inflammatory Responses in Autoimmune Pancreatitis Depend on IFN-α and IL-33 Produced by Plasmacytoid Dendritic Cells

In previous studies, we found that human IgG4-related autoimmune pancreatitis (AIP) and murine AIP are driven by activation of plasmacytoid dendritic cells (pDCs) producing IFN-α. In the present studies we examined additional roles of pDC-related mechanisms in AIP pathogenesis, particularly those responsible for induction of fibrosis. We found that in murine AIP (MRL/Mp mice treated with polyinosinic-polycytidylic acid) not only the pancreatic infiltration of immune cells but also the development of fibrosis were markedly reduced by the depletion of pDCs or blockade of type I IFN signaling; moreover, such treatment was accompanied by a marked reduction of pancreatic expression of IL-33. Conversely, polyinosinic-polycytidylic acid-induced inflamed pancreatic tissue in murine AIP exhibited increased expression of type I IFNs and IL-33 (and downstream IL-33 cytokines such as IL-13 and TGF-β1). pDCs stimulated by type I IFN were the source of the IL-33 because purified populations of these cells isolated from the inflamed pancreas produced a large amount of IL-33 upon activation by TLR9 ligands, and such production was abrogated by the neutralization of type I IFN. The role of IL-33 in murine AIP pathogenesis was surprisingly important because blockade of IL-33 signaling by anti-ST2 Ab attenuated both pancreatic inflammation and accompanying fibrosis. Finally, whereas patients with both conventional pancreatitis and IgG4-related AIP exhibited increased numbers of acinar cells expressing IL-33, only the latter also exhibited pDCs producing this cytokine. These data thus suggest that pDCs producing IFN-α and IL-33 play a pivotal role in the chronic fibro-inflammatory responses underlying murine AIP and human IgG4-related AIP.