Pathogenicity of IgG in patients with IgG4-related disease

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.

Clinical Perspectives on IgG4-Related Disease and Its Classification

Immunoglobulin G4-related disease (IgG4-RD) is a systemic immune-mediated fibroinflammatory disease. Since its discovery nearly two decades ago, our understanding of its pathophysiology and clinical manifestations has grown substantially. Early diagnosis and treatment of this elusive disease can prevent substantial organ damage from end-stage fibrosis, emphasizing the need for prompt recognition and accurate characterization of IgG4-RD. The classification criteria endorsed by the American College of Rheumatology and the European Alliance of Associations for Rheumatology in 2019 provide a framework for establishing the diagnosis in the clinical setting. This process involves recognizing the typical manifestations of the disease and incorporating clinical, radiological, serological, and histopathological information as well as excluding disease mimickers. Glucocorticoids and rituximab are effective at inducing remission in IgG4-RD in most patients, but the optimal approach to long-term management of IgG4-RD remains an area of active clinical research. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

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-related disease and idiopathic multicentric Castleman's disease: confusable immune-mediated disorders

IgG4-related disease (IgG4-RD) and idiopathic multicentric Castleman's disease (iMCD) are both rare systemic immune-mediated disorders. However, pathogenesis differs markedly between the two diseases, and differing therapeutic strategies are adopted: IgG4-RD is treated using a moderate dose of glucocorticoids or rituximab, while iMCD therapy involves an interleukin (IL)-6 targeted approach. Nonetheless, some clinical features of IgG4-RD and iMCD overlap, so differential diagnosis is sometimes difficult, even though the classification and diagnostic criteria of the diseases require careful exclusion of the other. The key findings in IgG4-RD are high IgG4/IgG ratio, allergic features, and germinal centre expansion involving T follicular helper cells, while iMCD involves polyclonal antibody production (high IgA and IgM levels), sheet-like mature plasma cell proliferation, and inflammatory features driven by IL-6. The distribution of organ involvement also provides important clues in both diseases. Particular attention should be given to differential diagnosis using combined clinical and/or pathological findings, because single features cannot distinguish IgG4-RD from iMCD. In the present review, we discuss the similarities and differences between IgG4-RD and iMCD, as well as how to distinguish the two diseases.

Immunoglobulin G4 (IgG4)-related autoimmune hepatitis and IgG4-hepatopathy: A histopathological and clinical perspective

Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a chronic inflammatory disease that simultaneously or consecutively involves multiple organs of the body. It is characterized by elevated serum IgG4 levels and massive infiltration of IgG4⁺ plasma cells in the damaged tissues. IgG4-related autoimmune hepatitis (IgG4-AIH) and IgG4-hepatopathy are relatively new entities that have been proposed as a phenotype of IgG4-RD in the liver. Immunoglobulin G4-AIH is defined as a disorder with serological, histopathological, and clinical features of both IgG4-RD and AIH, simultaneously satisfying the diagnostic criteria of both classical AIH and IgG4-RD. Although there are several case reports and studies of IgG4-AIH among the published works, no consensus regarding the histopathological characteristics of IgG4-AIH has been established, and its clinical implications remain obscure. Immunoglobulin G4-hepatopathy is defined as a comorbidity of IgG4-RD in the liver, and patients not meeting the diagnostic criteria of classical AIH could be diagnosed with IgG4-hepatopathy. Numerous issues regarding these diseases, especially their epidemiology, histopathological and clinical characteristics, and treatment response to corticosteroids, remain unsolved, and need to be determined to establish the disease concepts of IgG4-AIH and IgG4-hepathopathy.

Allergic Aspects of IgG4-Related Disease: Implications for Pathogenesis and Therapy

IgG4-related disease (IgG4-RD) is a rare systemic fibroinflammatory disease frequently associated with allergy. The pathogenesis of IgG4-RD is poorly understood, and effective therapies are limited. However, IgG4-RD appears to involve some of the same pathogenic mechanisms observed in allergic disease, such as T helper 2 (Th2) and regulatory T cell (Treg) activation, IgG4 and IgE hypersecretion, and blood/tissue eosinophilia. In addition, IgG4-RD tissue fibrosis appears to involve activation of basophils and mast cells and their release of alarmins and cytokines. In this article, we review allergy-like features of IgG4-RD and highlight targeted therapies for allergy that have potential in treating patients with IgG4-RD.

[Recent Updates of Immunoglobulin G4-related Pancreatobiliary Disease]

Type 1 autoimmune pancreatitis and IgG4-related sclerosing cholangitis (IgG4-SC) are the pancreatobiliary manifestations of IgG4-related disease. IgG4-related disease is a newly named fibroinflammatory condition that is characterized by tumefactive lesions that contain dense lymphoplasmacytic infiltrates rich in IgG4-positive cells and often by elevated serum IgG4 concentrations. IgG4-related pancreatobiliary disease is often disguised as pancreatobiliary malignancies owing to its tumefactive nature and clinical presentations, such as obstructive jaundice. The differentiation of IgG4-SC from primary sclerosing cholangitis is also essential because of the significant differences in treatment responses and prognosis. A timely diagnosis of IgG4-related pancreatobiliary disease can lead clinicians to prescribe adequate glucocorticoid treatment that can reverse the pancreatobiliary duct strictures and obstructive jaundice. On the other hand, the diagnosis of IgG4-related pancreatobiliary disease is sometimes challenging because there is no single diagnostic clinical test. The diagnosis of IgG4-related pancreatobiliary disease rests on fulfilling the diagnostic criteria, including imaging, serology, other organ involvement, histology, and response to steroids. Approximately 50% of patients with IgG4-related pancreatobiliary disease experience relapse, despite IgG4-related pancreatobiliary disease showings a favorable short-term prognosis after glucocorticoid therapy. To reduce the relapse, long maintenance treatment for 3 years may be necessary. The purposes of this review were to emphasize the clinical problem of diagnosing IgG4-related pancreatobiliary disease as well as to highlight the use of the published guidelines for the diagnosis and management of IgG4-related pancreatobiliary disease.

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.

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.

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.

Emerging therapy options for IgG4-related disease

INTRODUCTION

Awareness of IgG4-related disease (IgG4-RD) is increasing worldwide and specialists are now familiar with most of its clinical manifestations and mimickers. IgG4-RD promptly responds to glucocorticoids and repeated courses are typically used to induce and maintain remission because the disease relapses in most patients. If left untreated, it can lead to organ dysfunction, organ failure and death. Advancement in our understanding of IgG4-RD pathogenesis is leading to the identification of novel therapeutic targets and emerging treatments are now setting the stage for personalized therapies for the future.

AREAS COVERED

This review focuses on emerging treatment options for IgG4-RD based on our advancing understanding of disease pathophysiology. Research was performed in the English literature on Pubmed and clinicaltrials.gov databases.

EXPERT OPINION

Glucocorticoids remain the first-line induction treatment for the multi-organ manifestations of IgG4-RD. Alternative immunosuppressive agents for maintaining remission are warranted in order to avoid long-term steroid toxicity, and to offer a more mechanistic and personalized therapeutic strategy. Targeting B and T-lymphocyte activation represents the most promising approach, but randomized controlled trials are eagerly awaited to confirm positive preliminary experiences reported in case series and small cohort studies.

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.

B cell targeted therapy for immunoglobulin G4-related disease

Glucocorticoids are the first-line drug for the remission induction therapy of immunoglobulin (Ig) G4-related disease. Achieving drug-free remission using glucocorticoids alone is difficult, however, and many patients require maintenance therapy with glucocorticoids and immunosuppressants. Studies have recently found that the number of peripheral memory B cells and plasmablasts is increased in IgG4-related disease and have indicated the efficacy of rituximab, which, in remission induction therapy, rapidly reduces serum IgG4 levels and has the tapering effect of glucocorticoids. Rituximab has been shown to reduce the risk of relapse more than oral immunosuppressants such as azathioprine. However, maintaining drug-free remission is difficult with a single course of rituximab alone, and many cases require maintenance therapy with rituximab. This article outlines the potential of B-cell targeted therapy, focusing on the efficacy, and safety of rituximab for IgG4-related disease.

Acquired Hemophilia A in IgG4-Related Disease: Case Report, Immunopathogenic Study, and Review of the Literature

We report the observation of a 75-year-old patient referred for cervical lymphadenopathies. A pre-lymphadenectomy blood work revealed an asymptomatic elevation of aPTT with low factor VIII (FVIII) levels and high anti-FVIII antibodies titers, consistent with acquired hemophilia A (AHA). Histological work-up of a cervical lymphadenopathy revealed benign follicular hyperplasia with IgG4⁺ lymphoplasmacytic infiltration; and serum IgG4 levels were markedly elevated, compatible with IgG4-related disease (IgG4-RD). He was successfully treated with a 9-month course of prednisone, secondarily associated with rituximab when an AHA relapse occurred. As this patient presented with an unusual association of rare diseases, we wondered whether there was a link between the two conditions. Our first hypothesis was that the anti-FVIII autoantibodies could be directly produced by the proliferating IgG4⁺ plasma cells as a result of broken tolerance to autologous FVIII. To test this assumption, we determined the anti-FVIII IgG subclasses in our patient and in a control group of 11 AHA patients without IgG4-RD. The FVIII inhibitor was mostly IgG4, with an anti-FVIII IgG4/IgG1 ratio of 42 at diagnosis and 268 at relapse in our patient; similar values were observed in non-IgG4-RD AHA patients. As a second hypothesis, we considered whether the anti-FVIII activity could be the result of a non-specific autoantibody production due to polyclonal IgG4⁺ plasma cell proliferation. To test this hypothesis, we measured the anti-FVIII IgG4/total IgG4 ratio in our patient, as well as in several control groups: 11 AHA patients without IgG4-RD, 8 IgG4-RD patients without AHA, and 11 healthy controls. We found that the median [min-max] ratio was higher in AHA-only controls (2.4 10^-2 [5.7 10^-4-1.79 10^-1]), an oligoclonal setting in which only anti-FVIII plasma cells proliferate, than in IgG4-RD-only controls (3.0 10^-5 [2.0 10^-5-6.0 10^-5]), a polyclonal setting in which all IgG4⁺ plasma cells proliferate equally. Our patient had intermediate ratio values (2.7 10^-3 at diagnosis and 1.0 10^-3 at relapse), which could plead for a combination of both mechanisms. Although no definitive conclusion can be drawn, we hypothesized that the anti-FVIII autoantibody production in our IgG4-RD AHA patient could be the result of both broken tolerance to FVIII and bystander polyclonal IgG4⁺ plasma cell proliferation.

Synergistic effect of IgG4 antibody and CTLs causes tissue inflammation in IgG4-related disease

IgG4-related disease (IgG4-RD) is characterized by multi-organ irreversible damage resulting from tissue-specific infiltration of IgG4+ plasma cells and cytotoxic T lymphocytes (CTLs). However, whether IgG4 antibody contributes to the inflammation remains unclear. In this study, we established a mouse model that enabled us to evaluate the pathogenic function of IgG4 antibodies in response to a tissue-specific autoantigen using recombinant ovalbumin (OVA)-specific human IgG4 monoclonal antibody (rOVA-hIgG4 mAb) and the mice expressing OVA of the pancreatic islets (RIP-mOVA mice). We found no inflammatory effect of rOVA-hIgG4 mAb transfer alone; however, co-transfer with OVA-specific CD8 CTLs (OT-I T cells) induced tissue damage with dense lymphocytic inflammation in the pancreas of RIP-mOVA mice. rOVA-hIgG4 mAb caused accumulation of conventional DC1 cells (cDC1s) in the lymphoid tissues, and the dendritic cells (DCs) activated the OT-I T cells via cross-presentation. We also revealed that the synergistic effects of CTLs and antibodies were observed in the other subclasses including endogenous antibodies if they recognized the same antigen. The transfer of OVA-specific CD4 helper T cells (OT-II T cells) into RIP-mOVA mice induced the production of anti-OVA antibody, which had a synergistic effect, through acquisition of a T follicular helper (TFH) phenotype. Moreover, using OT-II T cells deficient in Bcl6 caused lower anti-OVA antibody production and inflammation with OT-I T cells. Our results indicated that autoreactive IgG4 antibodies play an important role of the tissue-specific CTL response in IgG4-RD.

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.

Immune mechanisms of fibrosis and inflammation in IgG4-related disease

PURPOSE OF REVIEW

To summarize recent advances in the understanding of the pathogenesis of IgG4-related disease.

RECENT FINDINGS

Limited data exist to explain genetic susceptibility to IgG4-related disease and the underlying triggers for this disease have not yet been identified. Cytotoxic CD4 T cells and activated B cells infiltrate affected organs and express proinflammatory and profibrotic molecules. Antigen presented by activated B cells likely reactivates cytotoxic CD4 T cells in disease tissues and these T cells in turn induce the targeted apoptotic death of host cells in certain organs - which presumably present the same antigenic peptide on human leukocyte antigen class II molecules of relevance that was also presented on B cells during reactivation. A subsequent exaggerated tissue remodeling process is orchestrated by cytokines, chemokines, and enzymes secreted by both activated B cells and CD4CTLs. These molecules induce an overexuberant repair process resulting in fibrosis and loss of target organ function.

SUMMARY

In IgG4-related disease, presumably self-reactive cytotoxic CD4 T cells infiltrate tissues, are reactivated by T cells and induce apoptotic death. Molecules secreted by activated B cells and by CD4CTLs drive an exaggerated wound healing response resulting in fibrosis and compromised tissue function.

Multiple Processes May Involve in the IgG4-RD Pathogenesis: An Integrative Study via Proteomic and Transcriptomic Analysis

Immunoglobulin G4-related disease (IgG4-RD) is a newly defined disease entity, while the exact pathogenesis is still not clear. Identifying the characters of IgG4-RD in proteomic and transcriptomic aspects will be critical to investigate the potential pathogenic mechanisms of IgG4-RD. We performed proteomic analysis realized with iTRAQ technique for serum samples from eight treatment-naive IgG4-RD patients and eight healthy volunteers, and tissue samples from two IgG4-RD patients and two non-IgG4-RD patients. Transcriptomic data (GSE40568 and GSE66465) was obtained from the GEO Dataset for validation. The weighted correlation network analysis (WGCNA) was applied to detect the gene modules correlated with IgG4-RD. KEGG pathway analysis was used to investigate pathways enriched in IgG4-RD samples. As a result, a total of 980 differentially expressed proteins (DEPs) in tissue and 94 DEPs in serum were identified between IgG4-RD and control groups. Three hundred fifty-four and two hundred forty-seven genes that most correlated with IgG4-RD were detected by WGCNA analysis in tissue and PBMC, respectively. We also found that DEPs in IgG4-RD samples were enriched in several immune-related activities including bacterial/viral infections and platelet activation as well as some immune related signaling pathways. In conclusion, we identified multiple processes/factors and several signaling pathways that may involve in the IgG4-RD pathogenesis, and found out some potential therapeutic targets for IgG4-RD.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Clinicopathological Features of Autoimmune Hepatitis with IgG4-Positive Plasma Cell Infiltration

BACKGROUND

We aimed to elucidate the characteristics and prognosis of autoimmune hepatitis (AIH) patients with immunoglobulin (Ig) G4-positive plasma cell infiltration.

METHODS

We enrolled 84 AIH patients. The number of IgG- and IgG4-positive plasma cells was immunohistochemically counted per high-power field in the portal area. Patients with 3 or more IgG4-positive plasma cells on average and a ratio of IgG4 to IgG-positive plasma cells ≥5% were defined as IgG4-associated AIH (IgG4-AIH), and their clinicopathological characteristics and prognosis were compared to those of the remaining classical-AIH patients.

RESULTS

Ten (11.9%) and 74 patients (88.1%) were categorized as IgG4-AIH and classical-AIH patients, respectively. The median age of the IgG4-AIH patients was 67 years, the majority was female (80.0%), and the distribution was similar to that of the classical-AIH patients. The IgG4-AIH patients exhibited significantly more severe phenotypes in portal inflammation, interface hepatitis, fibrosis, and rosette formation. All clinical laboratory data were similar except for serum IgG4 levels, which were higher in IgG4-AIH patients (168.5 vs. 22.9 mg/dL, p = 0.014). During a median follow-up period of 139 months, the relapse rate was significantly lower in the IgG4-AIH group than in the classical-AIH group (11.1 vs. 49.2%; p = 0.048). Twelve (16.2%) and 6 (8.1%) classical-AIH patients underwent liver-related events and liver-related deaths, respectively. In contrast, none of the IgG4-AIH patients progressed to severe liver disease.

CONCLUSIONS

The IgG4-AIH patients had more severe inflammation and advanced fibrosis in the liver. However, their prognosis was not poor compared to that of classical-AIH patients. IgG4-AIH may have a phenotype distinct from classical-AIH.

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.

Immunological Role of IgG Subclasses

The loss of tolerance to self-antigens is the unequivocal "red line" of autoimmunity: both development of autoreactive T and B cells and production of polyclonal autoantibodies represent seminal keys to the pathogenesis of protean autoimmune diseases. Most of these autoantibodies are immunoglobulins G (IgG), functionally distinguished in four subclasses named IgG1, IgG2, IgG3, and IgG4, due to structural differences in the hinge and heavy chain constant regions. Different studies analyzed serum levels of IgG subclasses in the course of different disorders, showing that they might have a pathogenic role by regulating interactions among immunoglobulins, Fc-gamma receptors, and complement. To date, the mechanisms promoting different IgG subclasses distribution during the natural history of most autoimmune diseases remain somewhat unclear. Evidence from the medical literature shows that the serum IgG profile is peculiar for many autoimmune diseases, suggesting that different subclasses could be specific for the underlying driving autoantigens. A better knowledge of IgG subsets may probably help to elucidate their pathological task, but also to define their relevance for diagnostic purposes, patients' personalized management, and prognosis assessment.

[IgG4-related disease: what do we know after 20 years]

IgG4-related disease is immunomediated fibroinflammatory condition, characterized by tumefective lesions in different organs with distinctive pathomorphological features and IgG4 hypersecretion in serum and tissues in the majority of patients. IgG4-RD has been established as a separate clinical in the early 2000s. In the review we focus on the evolution of views on ethiopathogenesis of the disease, therapeutic and diagnostic options and classification of the disease.

Pleural effusion related to IgG4

Purpose of review

The causes of exudative pleural effusions are diverse and frequently remain unclear despite exhaustive examinations. Recently recognized IgG4-related disease (IgG4-RD) is a fibroinflammatory disorder that can affect nearly any organ including the lungs. This review will focus on the involvement of IgG4 in exudative pleural effusion of unknown cause.

Recent findings

IgG4 is found to be involved in a proportion of patients with undiagnosed pleural effusions. Pleural involvement in IgG4-RD can be seen in isolation or association with other organ disease. Pleural thickening and/or effusion are common clinical features of IgG4-related pleural lesions, and this condition is histologically characterized by a lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cells in the pleura. Although the pathogenesis of IgG4-RD is poorly understood, there is a growing body of evidence that indicates an antigen-driven process requiring T-cell and B-cell interaction in which autoantibodies, plasmablasts, follicular helper T cells and CD4+ cytotoxic T lymphocytes participate.

Summary

The possibility of IgG4-related pleural lesion should be considered in patients with pleural effusion of unexplained cause when lymphoplasmacytic infiltration is seen in a pleural biopsy specimen. This condition is responsive to systemic steroid therapy.

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.

Abundant a proliferation-inducing ligand (APRIL)-producing macrophages contribute to plasma cell accumulation in immunoglobulin G4-related disease

Background

This study aimed to investigate the contribution of a proliferation-inducing ligand (APRIL), a member of the tumor necrosis factor (TNF) superfamily implicated in plasma cell survival, to the development of plasma cell–rich lesions in immunoglobulin G4–related disease (IgG4-RD).

Methods

We performed immunohistochemical staining for APRIL with Stalk-1 and Aprily-8 antibodies specifically recognizing APRIL-producing cells and secreted APRIL, respectively, in renal and submandibular lesions of IgG4-RD in comparison with those of Sjögren’s syndrome and sialolithiasis.

Results

Numerous Stalk-1-positive APRIL-producing cells were detectable in lesions of IgG4-RD. These cells, identified as CD163-positive M2 macrophages, secreted APRIL that distributed close to and even on infiltrating plasma cells. In contrast, APRIL-producing cells and the secreted form of APRIL were rarely detectable in lesions of Sjögren’s syndrome or sialolithiasis. Notably, APRIL expression decreased concomitantly with the level of plasma cell infiltration after successful glucocorticoid treatment.

Conclusions

Abundant infiltration into tissue lesions of APRIL-producing M2 macrophages and retention of secreted APRIL in plasma–cell–rich areas support a role for APRIL in the pathogenesis of plasma cell–rich lesions in IgG4-RD.

Pathophysiology of IgG4-related disease: A T follicular helper cells disease?

IgG4-related disease is a chronic inflammatory disease characterized by clinical, biological and pathological unifying findings. Because these criteria are not always all together available in patients and because biological and pathological markers are not totally specific, the diagnosis should be retained after exclusion of mimickers. Since the individualization of IgG4-RD, several studies have allowed to better characterize immunological abnormalities associated with this particular condition. B and T cell oligoclonal activation is associated with T helper 2 cytokine production leading to IgG4 production and profibrotic cytokine release. A central role for T follicular helper 2 cells is suggested from recent findings. We summarize here recent advances in understanding of immune abnormalities in IgG4-related disease.

Immunoglobulin G4-related Disease

Immunoglobulin G4 (IgG4)-Related Disease (IgG4-RD) can cause fibroinflammatory lesions in nearly any organ and lead to organ dysfunction and irreversible damage. In addition to frequent involvement of the salivary glands, lacrimal glands, and/or pancreas, IgG4-RD often affects the chest. Thoracic manifestations include lung nodules and consolidations, pleural thickening, aortitis, and lymphadenopathy. The diagnosis is made after careful clinicopathologic correlation because there is no single diagnostic test with excellent sensitivity or specificity. Biopsy of pulmonary lesions can be useful for distinguishing IgG4-RD from common mimickers. Immunosuppressive regimens, such as glucocorticoids and/or glucocorticoid-sparing agents, form the cornerstone of treatment.

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.

Disease Severity Linked to Increase in Autoantibody Diversity in IgG4-Related Disease

OBJECTIVE

Four autoantigens have been described recently in IgG4-related disease (IgG4-RD): prohibitin, annexin A11, laminin 511-E8, and galectin-3. However, no external validation has been performed, and the possibility that some individuals break tolerance to more than 1 autoantigen has not been explored. We undertook this study to evaluate the relative frequencies of antibody responses against these autoantigens in order to explore the role of adaptive immune response in IgG4-RD.

METHODS

Autoantibody responses against prohibitin, annexin A11, and laminin 511-E8 were measured among a clinically diverse cohort of IgG4-RD patients (n = 100) using enzyme-linked immunosorbent assays. Autoantibody responses were correlated with disease severity and organ distribution.

RESULTS

The frequencies of IgG4 autoantibody responses against prohibitin (10%), annexin A11 (12%), and laminin 511-E8 (7%) were not significantly different from those of controls. A portion of the cohort (n = 86) had been analyzed previously at our center for anti-galectin-3 antibody responses, with 25 patients (29%) having IgG4 anti-galectin-3 antibodies. Of these 86 patients, 32 (37%) had IgG4 antibodies to ≥1 of the 4 autoantigens and 12 (14%) showed reactivity with ≥2 of the tested antigens. The subset of patients with ≥2 autoantibodies had higher total levels of IgG1, IgG2, IgG4, and C-reactive protein, were more commonly hypocomplementemic, and were more likely to have visceral organ involvement.

CONCLUSION

Antibodies against prohibitin, annexin A11, and laminin 511-E8 were found in only a small portion of patients with IgG4-RD. A subset of IgG4-RD patients, however, had IgG4 antibodies against ≥2 autoantigens. These patients presented with robust IgG subclass elevations, complement consumption, and visceral organ involvement. This broader break in immunologic tolerance in IgG4-RD was associated with more severe disease.

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.

Hypocomplementemia is related to elevated serum levels of IgG subclasses other than IgG4 in IgG4-related kidney disease

OBJECTIVES

This study investigated the clinical features of IgG4-RKD patients with hypocomplementemia compared with those without it, so as to clarify the factors related to hypocomplementemia.

METHODS

In this single-center retrospective study, we analyzed the clinical features of 25 patients with IgG4-RKD according to the presence/absence of hypocomplementemia. Additionally, we validated the results of a single-center study in a separate large multicenter cohort of 328 patients with IgG4-RD, and searched for factors related to hypocomplementemia.

RESULTS

Serum IgG levels (p < .001), non-IgG4 IgG levels, calculated as the total IgG minus IgG4 (p < .001), serum IgG1 levels (p = .017), and the number of involved organs (p = .018) were significantly higher in the hypocomplementemia group. At relapse of renal lesions in four patients, all had serum IgG4 re-elevation, with the three with hypocomplementemia presenting worsening of hypocomplementemia and re-elevation of non-IgG4 IgG levels. In a validation cohort of 328 patients with IgG4-RD, multivariate logistic regression analysis indicated elevation of non-IgG4 IgG levels to be an independent factor related to hypocomplementemia in the patients with IgG4-RKD.

CONCLUSION

The present study suggests that hypocomplementemia is associated with elevation of IgG subclasses other than IgG4 including IgG1 in IgG4-RKD.

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.

Different clinical patterns of IgG4-RD patients with and without eosinophilia

It has been reported that patients with IgG4-related disease (IgG4-RD) showed an elevated incidence of eosinophilia. We aim to explore the clinical patterns of IgG4-RD patients with and without eosinophilia. Four hundred and twenty-five IgG4-RD patients referred to Peking Union Medical College Hospital were enrolled. Blood eosinophil count higher than 0.5 × 10⁹/L was defined as eosinophilia. Clinical features of all the participants were collected and analyzed statistically. Eighty-seven patients (20%) with eosinophilia were found. As compared to those with a normal range of blood eosinophil count, male predominance, longer disease duration, increased prevalence of dacryoadenitis, sialadenitis, lymphadenopathy, and skin rash, higher IgG4-RD responder index, more organ involvement and higher levels of serum IgG4 (17.0 g/L vs 6.5 g/L, P < 0.001) was found in patients with eosinophilia. There was no significant difference in the incidence of allergic disease between the two groups. Peripheral eosinophil counts were positively correlated with disease duration, the number of involved organs, IgG4-RD responder index, and serum IgG4. Higher recurrence rate during follow-up period was found in patients with eosinophilia [28.6% (20/70) vs 17.1% (42/245), P = 0.034]. IgG4-RD patients with eosinophilia exhibited different clinical patterns from patients without. Eosinophilia appeared independent of allergies in IgG4-RD.

Tumefactive Inflammatory Diseases of the Pancreas

Advances in the past two decades have resulted in the recognition of several tumefactive pancreatic lesions that, on histologic evaluation, show a varying combination of inflammation and fibrosis. Autoimmune pancreatitis, the prototypic tumefactive pancreatic fibroinflammatory lesion, is composed of two distinct diseases, type 1 autoimmune pancreatitis and the less common type 2 autoimmune pancreatitis. Although designated as autoimmune pancreatitis, the two diseases show little morphologic or pathogenic overlap. In type 1 disease, subsets of T lymphocytes (type 2 helper T cells, regulatory T cells, and T follicular helper 2 cells) are hypothesized to drive the inflammatory reaction. The B-cell response is characterized by an oligoclonal expansion of plasmablasts, with dominant clones that vary among patients and distinct clones that emerge at the time of relapse. Although the precise role of IgG4 in this condition remains uncertain, recent studies suggest that other IgG subclasses (eg, IgG1) may mediate the immune reactions, whereas IgG4 represents a response to dampen excessive inflammation. A recent study of type 2 autoimmune pancreatitis highlights the role of CXCL8 (alias IL-8), with duct epithelium and infiltrating T lymphocytes expressing this chemokine; the latter may contribute to the distinct form of neutrophilic inflammation in this disease. The review also highlights other forms of mass-forming chronic pancreatitis: follicular pancreatitis, groove pancreatitis, and those associated with rheumatologic diseases.

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.

Unique patterns of glycosylation in immunoglobulin subclass G4-related disease and primary sclerosing cholangitis

BACKGROUND AND AIM

Immunoglobulin subclass G4-related disease (IgG4-RD) is characterized by an abundance of IgG4 antibodies in the serum and tissue. Glycosylation status of antibodies can impact on immune effector functions and disease pathophysiology. We sought to establish glycosylation patterns in a prospective cohort of patients with IgG4-RD and the relationship with disease activity and response to treatment.

METHODS

We assessed IgG Fc-tail and Fab-arm glycosylation status in patients with IgG4-RD (n = 22), disease controls with primary sclerosing cholangitis (PSC) (n = 22), and healthy controls (n = 22). Serum IgG and subclasses were quantified using ELISA. Fc and Fab glycosylation were analyzed by mass spectrometry and lectin affinity chromatography, respectively. Disease activity, organ damage, and response to treatment were assessed using the IgG4 Responder Index.

RESULTS

Immunoglobulin G Fab sialylation was increased in IgG4-RD compared with PSC and healthy control (P = 0.01), with a preferential increase in IgG4-specific Fab sialylation, which was independent of IgG4 Fab-arm exchange. There was a reduction in IgG1-specific Fc bisection and hybrid structures in IgG4-RD (P < 0.01), which recovered upon steroid treatment and correlated with disease activity. Overall, IgG Fc galactosylation was reduced in both IgG4-RD and PSC (P < 0.01), with a preferential reduction in IgG1-specific sialylation and enhancement of IgG4-specific bisection in PSC. IgG4 fucosylation and IgG1/2/3 hybrid structures negatively correlated with complement C3 and C4 levels in IgG4-RD (P < 0.01), but not PSC.

CONCLUSION

We report the first study showing unique antibody glycosylation status in a prospective cohort of IgG4-RD and PSC patients, which may determine modulation of the immune system and contribute to disease pathophysiology.

IgG4-related disease in the Japanese population: a genome-wide association study

BACKGROUND

IgG4-related disease is a newly recognised immunopathological entity that includes autoimmune pancreatitis, IgG4-related sialadenitis, and IgG4-related kidney disease. To understand the genetic landscape of IgG4-related disease, we did a genome-wide association study.

METHODS

We did a genome-wide association study of Japanese individuals, initially screening 857 patients with IgG4-related disease at 50 Japanese research institutions and DNA samples from 2082 healthy control participants from the Nagahama Prospective Genome Cohort for the Comprehensive Human Bioscience. From Oct 27, 2008, to July 22, 2014, we enrolled 835 patients and used data from 1789 healthy participants. Only patients with confirmed diagnosis of IgG4-related disease according to the international diagnostic criteria were included. Genotyping was done with the Infinium HumanOmni5Exome, HumanOmni2.5Exome, or HumanOmni2.5 Illumina arrays, and genomic distributions were compared between case and control samples for 958 440 single nucleotide polymorphisms. The HLA region was extensively analysed using imputation of HLA alleles and aminoacid residues. Fine mapping of the FCGR2B region was also done. Associations between clinical manifestations of disease and the genetic variations identified in these two genes were examined.

FINDINGS

We identified the HLA-DRB1 (p=1·1×10-11) and FCGR2B (p=2·0×10-8) regions as susceptibility loci for IgG4-related disease. We also identified crucial aminoacid residues in the β domain of the peptide-binding groove of HLA-DRB1, in which the seventh aminoacid residue showed the strongest association signal with IgG4-related disease (p=1·7×10-14), as has been reported with other autoimmune diseases. rs1340976 in FCGR2B showed an association with increased FCGR2B expression (p=2·7×10-10) and was in weak linkage disequilibrium with rs1050501, a missense variant of FCGR2B previously associated with systemic lupus erythematosus. Furthermore, rs1340976 was associated with the number of swollen organs at diagnosis (p=0·011) and IgG4 concentration at diagnosis (p=0·035).

INTERPRETATION

Two susceptibility loci for IgG4-related disease were identified. Both FCGR2B and HLA loci might have important roles in IgG4-related disease development. Common molecular mechanisms might underlie IgG4-related disease and other immune-related disorders FUNDING: The Japanese Ministry of Health, Labour, and Welfare, the Japanese Agency of Medical Research and Development, and Kyoto University Grant for Top Global University Japan Project.

Immunoglobulin G4-related sclerosing cholangitis

Immunoglobulin (Ig)G4-related sclerosing cholangitis (IgG4-SC) is a biliary tract manifestation of IgG4-related diseases (IgG4-RD); a subgroup of SC defined as a condition with progressive stenosis and destruction of the bile ducts due to diffuse inflammation and fibrosis. IgG4-SC is clinically characterized by the (a) chronic elevation of cholestatic enzyme levels, (b) significant elevation of serum IgG4 levels, (c) diffuse or segmental narrowing of intra and/or extra hepatic bile ducts with thickening of the bile duct wall in imaging studies, (d) marked lymphoplasmacytic and IgG4-positive plasma cell infiltration and fibrosis in histology, (e) presence of IgG4-RD in other organs, mainly involving autoimmune pancreatitis, and (f) excellent response to corticosteroids. The diagnosis of IgG4-SC is based on a combination of these findings. Although the IgG4-SC diagnosis is different from that of primary sclerosing cholangitis (PSC) or biliary and pancreatic malignancies, it is extremely important to diagnose or suspect IgG4-SC appropriately; as the incorrect diagnosis of PSC or malignant diseases may lead to the progression of fibrosis in patients due to untreated chronic cholestasis, or to unnecessary major surgical resections. Although its etiology remains unclear, recent studies of IgG4-SC have attempted to clarify the roles of the IgG4 molecule and novel autoantibodies detected in patients with IgG4-SC.

Advances in IgG4-related pancreatobiliary diseases

Autoimmune pancreatitis is an unusual form of pancreatitis that is histologically characterised by a massive infiltration of lymphocytes and IgG4-positive plasma cells and storiform fibrosis. The disease is recognised as a pancreatic manifestation of IgG4-related disease. IgG4-related sclerosing cholangitis is a biliary counterpart that is typically associated with autoimmune pancreatitis. Two parallel immunological responses are thought to underlie the pathophysiology of these diseases: a pro-inflammatory, tissue-destructive process and an anti-inflammatory feedback response, which probably relates to IgG4 production. These diseases should be differentiated from conditions with a similar presentation (eg, pancreatobiliary malignancy, primary sclerosing cholangitis) by comparison of serum IgG4 concentration, imaging features, other organ involvement, histology, and steroid responsiveness. Corticosteroids are first-line drugs, although rituximab has been shown to effectively deplete B cells in IgG4-related disease. Although the risk of relapse is high, no standardised treatment protocol exists for relapsed cases.

Immunoglobulin G4-related Disease: An Overview

Immunoglobulin G4-related disease (IgG4-RD) is a recently established systemic disease that is characteristically associated with elevated serum immunoglobulin G4 (IgG4) levels and believed to be caused by autoimmune mechanisms. The clinical features of IgG4-RD include (i) systemic distribution, (ii) imaging findings of swelling, nodules, and/or wall thickening, (iii) high serum IgG4 levels, (iv) abundant IgG4-bearing plasma cell infiltration and fibrosis in affected organs, (v) a favorable response to corticosteroid therapy, and (vi) coexistence with other IgG4-RD manifestations simultaneously or in a metachronous fashion. The concept of IgG4-RD was established based on the culmination of specific discoveries. Specifically, a close association between autoimmune pancreatitis (AIP) and high serum IgG4 levels, massive IgG4-bearing plasma cell infiltration in pancreatic tissues affected by AIP, and systemic other organ involvements in AIP with similar IgG4-bearing plasma cell features opened the gateway from AIP to IgG4-RD. The systemic distribution of IgG4-RD seems to be capable of affecting every organ, causing well-established members including AIP, lacrimal and salivary gland lesions such as Mikulicz’s disease, respiratory diseases, sclerosing cholangitis, kidney diseases, and retroperitoneal fibrosis. IgG4-RD has been diagnosed worldwide, and international collaboration efforts on the disease have led to consensus publications on its nomenclature, pathology findings, and management approach. The algorithms developed for the comprehensive diagnostic criteria for IgG4-RD have remarkably increased detection sensitivity. Oral glucocorticoids are the first-line agents for remission induction, and certain patients with high disease activity may benefit from maintenance therapy afterwards. Originally, IgG4-RD had been considered reversible and to have a good prognosis; however, long-term afflictions sometimes result in transition to advanced-stage conditions with dysfunction and/or complicating malignancy. The immunological abnormalities in IgG4-RD have been reported in both innate and adaptive immune systems; however, it remains unclear whether IgG4 has a pathogenic role or a protective one in disease onset and progression.

Clinical features and mechanistic insights regarding IgG4-related dacryoadenitis and sialoadenitis: a review

Immunoglobulin G4-related disease (IgG4-RD), recognized only recently as a single diagnostic entity, is a chronic inflammatory condition of unknown etiology. The diagnosis of IgG4-RD relies heavily on histopathological analysis and the correlation of histology findings with clinical, serological, and radiological data. CD4⁺ T and B cells, including IgG4-expressing plasmablasts, constitute the major inflammatory cell populations in IgG4-RD and are believed to cause organ damage and tissue fibrosis. Patients with IgG4-RD, who have active, untreated disease, exhibit marked expansion of IgG4-secreting plasmablasts in the blood. Important mechanistic insights correlated with the pathogenesis of IgG4-RD have been disclosed in recent years through the application of novel molecular biology approaches, including next-generation and single-cell RNA sequencing. Exploration of the interactions between these CD4⁺ T cells and cells of the B lymphocyte lineage is critical to understanding the pathophysiology of IgG4-RD. The establishment of pathogenic T cell clones and the identification of antigens specific to these clones constitute the first steps in determining the pathogenesis of this disease. This review focuses on clinical features and mechanistic insights regarding IgG4-related dacryoadenitis and sialoadenitis, from a perspective suitable for oral and maxillofacial surgeons.

Clinical practice guidelines for IgG4-related sclerosing cholangitis

IgG4‐related sclerosing cholangitis (IgG4‐SC) is a distinct type of cholangitis frequently associated with autoimmune pancreatitis and currently recognized as a biliary manifestation of IgG4‐related disease. Although clinical diagnostic criteria of IgG4‐SC were established in 2012, differential diagnosis from primary sclerosing cholangitis and cholangiocarcinoma is sometimes difficult. Furthermore, no practical guidelines for IgG4‐SC are available. Because the evidence level of most articles retrieved through searching the PubMed, Cochrane Library, and Igaku Chuo Zasshi databases was below C based on the systematic review evaluation system of clinical practice guidelines MINDS 2014, we developed consensus guidelines using the modified Delphi approach. Three committees (a guideline creating committee, an expert panelist committee for rating statements according to the modified Delphi method, and an evaluating committee) were organized. Eighteen clinical questions (CQs) with clinical statements were developed regarding diagnosis (14 CQs) and treatment (4 CQs). Recommendation levels for clinical statements were set using the modified Delphi approach. The guidelines explain methods for accurate diagnosis, and safe and appropriate treatment of IgG4‐SC.

High accuracy differentiating autoimmune pancreatitis from pancreatic ductal adenocarcinoma by immunoglobulin G glycosylation

Background

Misdiagnosis of autoimmune pancreatitis (AIP) as pancreatic cancer (PDAC) or vice versa can cause dismal patents’ outcomes. Changes in IgG glycosylation are associated with cancers and autoimmune diseases. This study investigated the IgG glycosylation profiles as diagnostic and prognostic biomarkers in PDAC and AIP.

Methods

Serum IgG-glycosylation profiles from 86 AIP patients, 115 PDAC patients, and 57 controls were analyzed using liquid chromatography–electrospray ionization mass spectrometry. Classification and regression tree (CART) analysis was applied to build a decision tree for discriminating PDAC from AIP. The result was validated in an independent cohort.

Results

Compared with AIP patients and controls, PDAC patients had significantly higher agalactosylation, lower fucosylation, and sialylation of IgG1, a higher agalactosylation ratio of IgG1 and a higher agalactosylation ratio of IgG2. AIP patients had significantly higher fucosylation of IgG1 and a higher sialylation ratio of IgG subclasses 1, 2 and 4. Using the CART analysis of agalactosylation and sialylation ratios in the IgG to discriminate AIP from PDAC, the diagnostic accuracy of the glycan markers was 93.8% with 94.6% sensitivity and 92.9% specificity. There were no statistically significant difference of IgG-glycosylation profiles between diffuse type and focal type AIP.

Conclusions

AIP and PDAC patients have distinct IgG-glycosylation profilings. IgG-glycosylation could different PDAC from AIP with high accuracy.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9221-1) contains supplementary material, which is available to authorized users.