Human T follicular helper cells and their impact on IgE and IgG4 production across allergy, malignancy, and IgG4-related disease

Human T follicular helper (Tfh) cells play a crucial role in orchestrating B cell differentiation, maturation, and immunoglobulin class switching. Recent studies have underscored the presence of Bcl-6 + Tfh cells not only in secondary lymphoid organs but also within tertiary lymphoid structures at inflammatory sites, emphasizing their pivotal role in disease pathogenesis. Furthermore, Tfh cells have been found to transit between lesion sites, lymph nodes, and peripheral blood, as revealed by T cell receptor repertoire analysis. Among Tfh subsets, Tfh2 cells have emerged as central orchestrators in driving the production of IgE and IgG4 from B cells. Their critical role in diseases such as allergy, malignancy, and IgG4-related disease highlights their profound impact on balancing inflammation and immune tolerance. Our current review provides the molecular characteristics of human Tfh cells, the differentiation pathways of Tfh subsets, mechanisms by which Tfh subsets induce IgE and IgG4 production, and their clinical implications in allergy, malignancy, and IgG4-related disease.

Delayed Induction of Noninflammatory SARS-CoV-2 Spike-Specific IgG4 Antibodies Detected 1 Year After BNT162b2 Vaccination in Children

Humoral immune responses after BNT162b2 vaccination are predominantly composed of immunoglobulin (Ig) G1 and IgG3 subclass antibodies. As previously described in adults, S1-specific and receptor-binding domain-specific IgG4 levels increase significantly 1 year after the second BNT162b2 vaccination in children 5-11 years of age. Understanding mRNA vaccine-specific IgG4 responses in all age groups is crucial as more mRNA vaccines will reach licensure in the coming years.

Tubulointerstitial nephritis with storiform fibrosis in a patient with angioimmunoblastic T-cell lymphoma

We present a case of an angioimmunoblastic T-cell lymphoma (AITL) and tubulointerstitial nephritis with storiform fibrosis in a 76-year-old man. The patient exhibited lymphadenopathy, polyclonal hypergammaglobulinemia, and renal dysfunction and was diagnosed with AITL on the basis of lymph node biopsy findings. The serum IgG4 level was highly elevated. Renal biopsy revealed IgG4-positive plasma cells and storiform fibrosis without infiltration of AITL, and the findings indicated IgG4-related kidney disease (IgG4-RKD). Following THPCOP therapy for AITL, the renal function improved. While diagnosing IgG4-RKD in a patient with AITL poses challenges, follicular helper T cell involvement appeared crucial in AITL and renal tubulointerstitial lesions in this case.

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

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

Pediatric IgG4-related disease: a descriptive review

INTRODUCTION

IgG4-related disease (IgG4-RD) is an immune-mediated systemic fibroinflammatory condition characterized by serum IgG4 elevation and IgG4-positive plasma cell infiltration into various organs. It generally occurs in elderly males. Pediatric cases have been reported, albeit rarely, accordingly lack of recognition of such cases could delay therapeutic intervention leading to poorer outcomes.

AREAS COVERED

The present review is a descriptive review of all published case reports, cohort studies, and reviews of pediatric IgG4-RD listed in PubMed. Characteristics of pediatric IgG4-RD were clarified, including sex, organ involvement, serological and histological findings, and treatment. We assessed how many published cases met current classification and comprehensive diagnostic criteria.

EXPERT OPINION

The characteristics of pediatricIgG4-RD differed from adult IgG4-RD in terms of sex and involved organs. There was no clear male dominance in numbers of cases, and surface organ involvement such as ophthalmic diseases were more common in the pediatric IgG4-RD. Organ involvement tended to be indolent and unilateral, causing difficulty in definitively diagnosing pediatric IgG4-RD. Only about 20% of published cases met IgG4-RD classification or comprehensive diagnostic criteria. Physicians should be careful in diagnosing pediatric IgG4-RD after excluding mimickers. International collaboration toward high-quality evidence to support diagnosis and treatment of pediatric IgG4-RD is advised.

Disordered Balance of T-Cell Subsets in Arterial Tertiary Lymphoid Organs in Immunoglobulin G4-Related Vascular Disease

BACKGROUND

Arterial/aortic tertiary lymphoid organs (ATLOs), characterized by germinal centers, control local arterial immune responses. T follicular helper cells (Tfh), resident in germinal centers, regulate immunoglobulin production and germinal center development. They consist of Tfh1, Tfh2, and Tfh17 subsets. T follicular regulatory (Tfr) cells possess suppressive functions as regulatory T cells and migrate into germinal centers. Immunoglobulin G4 (IgG4)-related diseases manifest in vascular lesions as frequently formed inflammatory aneurysms (IgG4-related abdominal aortic aneurysm [IgG4-AAAs]). IgG4-AAAs contain several ATLOs.

METHODS AND RESULTS

We performed whole-slide immunohistochemical image analysis in surgical specimens of IgG4-AAAs (n=21), non-IgG4-related inflammatory AAAs (n=17), atherosclerotic AAAs (n=10), and Takayasu arteritis (n=5). IgG4-AAA was characterized by numerous, large, irregular-shaped ATLOs, and higher numbers of Tfr and Tfh2 cells than Tfh1 cells were present compared with others. The morphologic abnormalities (in number, area, and form) of ATLOs in IgG4-AAAs and the increased number of Tfr cells are closely related to the activity of IgG4-related diseases. All T-cell subsets were more enriched within ATLOs than outside ATLOs. In particular, an increase in Tfr cells in IgG4-AAAs was associated with ATLO formation. Increased Tfh17 cells were found in Takayasu arteritis, and atherosclerotic AAA and non-IgG4-related inflammatory AAAs were characterized by increased Tfh1 cells.

CONCLUSIONS

In the classification of vascular lesions, considering the imbalance in T-cell subsets, IgG4-AAA should be positioned as adventitial vasculitis with predominant Tfr and Tfh2 cells, accompanied by the abnormal appearance of ATLOs.

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.

T follicular helper cells and T peripheral helper cells in rheumatic and musculoskeletal diseases

Recent technological progress has greatly advanced our understanding of human immunology. In particular, the discovery of human T follicular helper (Tfh) and T peripheral helper (Tph) cells has significantly advanced our understanding of human adaptive immune system. Tfh and Tph cells share similar molecular characteristics and both play critical roles in B cell differentiation and maturation. However, they differ in their functional properties, such as chemokine receptor expression and cytokine production. As a result, Tfh cells are mainly involved in B cell differentiation and maturation in germinal centres of secondary lymphoid tissues, while Tph cells are involved in B cell differentiation and tissue damage in peripheral inflammatory lesions. Importantly, the involvement of Tfh and Tph cells in the pathogenesis of rheumatic and musculoskeletal diseases has become clear. In rheumatoid arthritis and systemic lupus erythematosus, Tph cell infiltration is predominant in peripheral inflammatory lesions, whereas Tfh cell infiltration is predominant in the affected lesions of IgG4-related disease. Therefore, the contribution of Tfh and Tph cells to the development of rheumatic and musculoskeletal diseases varies depending on each disease. In this review, we provide an overview of human Tfh and Tph cells and summarise the latest findings on these novel T cell subsets in various rheumatic and musculoskeletal diseases.

Single-Cell RNA-Sequencing Reveals Peripheral T Helper Cells Promoting the Development of IgG4-Related Disease by Enhancing B Cell Activation and Differentiation

Abnormal B cell differentiation plays a critical role in IgG4-related disease (IgG4-RD), but the underlying mechanism remains largely unknown. We investigated the cell landscape from three IgG4-RD retroperitoneal tissues and three control tissues using single-cell RNA-sequencing. Critical cell type or markers were further validated in the peripheral blood from the patients with IgG4-RD and healthy controls via flow cytometry as well as in the IgG4-RD and control tissue via immunofluorescence staining. The increases in B cells, plasma cells, and CD4+ T cells were found in IgG4-RD retroperitoneal tissue. Importantly, among CD4+ T cells, an increase in CD4+CXCR5-PD1hi peripheral T helper (Tph) cells with a high expression of IL-21 and TIGIT was discovered in IgG4-RD tissue, which was further validated in peripheral blood of the patients with IgG4-RD. The Tph cell and TIGIT+ Tph cell proportion were remarkably higher in active IgG4-RD patients and correlated with disease activity. Moreover, TIGIT+CD4+ cells were able to promote B cell differentiation via IL-21. Our study revealed that Tph cells are increased in IgG4-RD and probably play critical roles in B cell differentiation through TIGIT-IL-21 axis. Peripheral Tph cell and TIGIT+Tph cell are potential markers for IgG4-RD disease activity.

Orbital inflammatory pseudotumor revealing multi-organ immunoglobulin G4-related disease

Relatively recently, the concept that immunoglobulin G4 (IgG4)-related disease is a distinct chronic inflammatory disorder rather than a subset of Sjögren's syndrome has been accepted. IgG4-related disease (IgG4-RD) is a fibro-inflammatory systemic immune-mediated condition that can affect the pancreas, salivary glands, and lymph nodes. Almost every organ may be impacted synchronously or metachronously by this illness, which causes the development of sclerotic masses of varying sizes. Numerous other rheumatic diseases can present with characteristics of IgG4-RD, making it difficult to distinguish between them. However, cases of IgG4-RD involving the bilateral orbits, and pancreas with biological abnormalities are rare. We present a case of an 18-year-old female with vitiligo since the age of 3 years who presented with acute pancreatitis and acalculous cholecystitis, bilateral orbital masses, palpebral edema, and eosinophilia. The patient was diagnosed with IgG4-RD in keeping with clinical presentation and the elevated serum IgG4 level and after elimination of other differential diagnoses. The patient's symptoms gradually relieved after glucocorticoid therapy. This case presents an uncommon combination of clinical features infrequently reported in the literature. Multi-organ IgG4-RD is a multisystemic mass, commonly creating diagnostic challenges for clinicians. Furthermore, and more importantly, it highlights the need to keep a differential of IgG4-RD in mind, to aid in the early and correct treatment of the disease.

Immunoglobulin G4-Related Disease, Lymphadenopathy, and Lymphoma

Lymphadenopathy occurring in patients with immunoglobulin G4 (IgG4)-related disease, termed IgG4-related lymphadenopathy, shows morphologic heterogeneity and overlap with other nonspecific causes of lymphadenopathy including infections, immune-related disorders, and neoplasms. This review describes the characteristic histopathologic features and diagnostic approach to IgG4-related disease and IgG4-related lymphadenopathy, with comparison to nonspecific causes of increased IgG4-positive plasma cells in lymph nodes, and with emphasis on distinction from IgG4-expressing lymphoproliferative disorders.

Multidisciplinary diagnosis and management of inflammatory aortic aneurysms

BACKGROUND

Inflammatory abdominal aortic aneurysms (IAAAs) are a variant involving a distinct immunoinflammatory process, with nearly one half believed to be associated with IgG4-related disease (IgG4-RD).

METHODS

MEDLINE and Google Scholar searches were conducted for English-language publications relevant to inflammatory aortic aneurysms from January 1970 onward. The search terms included inflammatory aortic aneurysms, aortitis, periaortitis, IgG4-related disease, and retroperitoneal fibrosis. Relevant studies were selected for review based on their relevance.

RESULTS

Morphologically, IAAAs are characterized by a thickened aneurysm wall often displaying contrast enhancement and elevated metabolic activity on fluorine-18 fluorodeoxyglucose-positron emission tomography imaging. A strong association exists with perianeurysmal and retroperitoneal fibrosis. Although the rupture risk appears lower with IAAAs than with noninflammatory abdominal aortic aneurysms (AAAs), the currently recommended diameter threshold for operative management is the same. Open repair has been associated with increased morbidity compared with noninflammatory AAAs, and a retroperitoneal approach or minimal dissection transperitoneal approach has been recommended to avoid duodenal and retroperitoneal structural injuries. Endovascular aneurysm repair has been increasingly used, especially for patients unfit for open surgery. It is important to exclude an infectious etiology before the initiation of immunosuppressive therapy or operative repair. Multimodality imaging follow-up is critical to monitor disease activity and secondary involvement of retroperitoneal structures by the associated fibrotic process. Maintenance of immunosuppressive therapy will be needed postoperatively for most patients with active systemic disease, especially those with IgG4-RD and those with persistent symptoms. Additional interventions aimed at ureteral decompression could also be required, and lifelong follow-up is mandatory.

CONCLUSIONS

Preoperative multimodality imaging is a diagnostic cornerstone for assessment of the disease extent and activity. IgG4-RD is an increasingly recognized category of IAAAs, with implications for tailoring adjunctive medical therapy. Open surgical repair remains the procedure of choice, although endovascular aneurysm repair is increasingly being offered. Maintenance immunosuppressive therapy can be offered according to the disease activity as assessed by follow-up imaging studies.

The disturbance of the distribution of T helper cell subsets in the mantle area surrounding germinal centers in immunoglobulin G4-related sclerosing sialadenitis

The function of germinal centers (GCs) is an important factor in the pathogenesis of immunoglobulin G4 (IgG4)-related disease, in which inflammatory and fibrotic processes are controlled by type 2 helper T (Th) cells and regulatory T cells. T follicular helper cells (Tfh), which are present in GCs, regulate GC development, and they consist of Tfh1, Tfh2, and Tfh17 subsets. This study examined the association of Th cell subsets in IgG4-RD and pathogenesis of the disease using whole-slide image analysis for immunohistochemistry. IgG4-related sclerosing sialadenitis (IgG4-SS, n = 19) was characterized by higher numbers of Tfh2 and Tfh17 cells than Tfh1 cells compared to the findings in patients with chronic sialadenitis (n = 18) or Sjögren syndrome (n = 17). The number of Tfh2 cells was significantly associated with all parameters of GC structures and the number of IgG4 + plasmacytes, whereas the number of Tfh1 cells was inversely associated with the aforementioned parameters. Concerning extrafollicular helper T (Teh) cells, among three groups, the Tfh2/Teh2 ratio was highest and the Tfh1/Teh1 ratio was lowest in the IgG4-SS group, which exhibited a characteristically regional distribution of Tfh and Teh subsets, especially higher numbers of Teh2 cells and lower numbers of Teh1 cells in the mantle areas surrounding GCs. Mantle Teh2 cells and central Tfh17 cells were significantly correlated with morphological abnormalities of GCs. Our results indicated that the peculiar regional distribution and altered balance of Tfh and Teh subsets are novel hallmarks of IgG4-SS that are associated with GC formation in IgG4-SS.

Case Report: A Programmed Cell Death-1 Inhibitor-Related Abdominal Fibroinflammatory Reaction Affecting Multiple Organs in A Non-Small-Cell Lung Cancer Patient

Immunotherapy utilizing programmed cell death-1 (PD-1)/PD-L1 inhibitors has been regarded as a rising hope for tumor patients, and their effects have been demonstrated in many clinical trials. However, immune-related adverse events also occur in patients and can sometimes have severe consequences. Pembrolizumab (Keytruda) is a humanized monoclonal anti-PD-1 antibody that has been approved by the US Food and Drug Administration for non-small-cell lung cancer. Here, we report a rare case of an abdominal fibroinflammatory reaction that affected multiple organs during anti-PD-1 immunotherapy using pembrolizumab in a non-small-cell lung cancer patient. The patient’s case demonstrates that immunotherapy-related abdominal fibroinflammatory reactions need to be considered, especially for patients with a history of pre-existing conditions in the abdomen. Glucocorticoids may be useful as a treatment when a diagnosis is confirmed.

T Cell Roles and Activity in Chronic Sclerosing Sialadenitis as IgG4-Related Disease: Current Concepts in Immunopathogenesis

IgG4-related disease is a multiorgan immunological fibroinflammatory disorder characterized by lymphoplasmacytic infiltration and fibrosis in multiple organs accompanied by high serum IgG4 levels. The salivary glands are the most common organs involved in this disease. Recently, chronic sclerosing sialadenitis affecting salivary glands, formerly known as Küttner's tumor, and Mikulicz's disease have been classified as a class of IgG4-related diseases. The etiopathobiology of IgG4-related disease is not fully understood. It has recently been hypothesized that the inflammatory and fibrotic process and the increased serum IgG4⁺ levels in IgG4-related disease are the result of an interaction between B cells and T helper cells, suggesting that T cells may play a key role in the pathogenesis of this disease. The aim of this review is to discuss the proposed roles of different T cell subsets in the pathogenesis of IgG4-related disease focusing on their roles in immunopathogenesis of IgG4-related sialadenitis.

Dawn of Precision Medicine in Psoriatic Arthritis

The establishment of precision medicine is considered particularly important in heterogeneous autoimmune diseases (e.g., psoriatic arthritis, systemic lupus erythematosus), which reveal clinical and molecular heterogeneity. The selection of optimal treatment strategies for individual patients may be more important and complex in autoimmune diseases than in other diseases. Two factors are important in precision medicine: patient stratification and use of targeted. When both factors work, patients are likely to have good outcomes. However, research into precision medicine and its practice in systemic autoimmune diseases is lacking. In contrast, the usefulness of peripheral immune cell phenotyping in the evaluation of immunological characteristics and stratification into subgroups of individual patients with systemic autoimmune diseases such as immunoglobulin 4-related disease, systemic lupus erythematosus, and anti-neutrophil cytoplasmic antibody-related vasculitis was reported. Furthermore, the potential of precision medicine using biological disease-modifying antirheumatic drugs based on peripheral immune cell phenotyping was recently demonstrated for psoriatic arthritis in the clinical setting. Precision medicine has not yet been sufficiently investigated in real world clinical settings. However, a dawn of precision medicine has emerged. We should shed further light on precision medicine in PsA and other autoimmune diseases. Here, we first review the usefulness of peripheral immune cell phenotyping in systemic autoimmune diseases and the potential of precision medicine in PsA based on this method.

The Possible Pathogenic Role of IgG4-Producing Plasmablasts in Stricturing Crohn's Disease

BACKGROUND

Crohn's disease (CD) is a condition on the spectrum of inflammatory bowel disease that affects up to 20 people per 100,000 in the US annually, and with incidence increasing. One of the most significant sources of morbidity in CD is the formation of strictures, with resultant intestinal blockage a common indication for hospitalization and surgical intervention in these patients. The pathophysiology of stricture formation is not fully understood. However, the fibroplasia that leads to fibrostenotic stricture formation may have shared pathophysiology with IgG4-related fibrosis.

SUMMARY

Initial intestinal inflammation recruits innate immune cells, such as neutrophils, that secrete IL-1β and IL-23, which induces a type 17 CD4+ T-helper T-cell (Th17)-mediated adaptive immune response. These CD4+ Th17 T cells also contribute to inflammation by secreting proinflammatory cytokines such as IL-17 and IL-21. IL-21 recruits and stimulates CD4+ T follicular helper (Tfh) cells, which secrete more IL-21. This causes ectopic germinal center formation, recruiting and stimulating naïve B cells. The IL-17 and IL-21 produced by Th17 cells and Tfh cells also induce IgG4 plasmablast differentiation. Finally, these IgG4-producing plasmablasts secrete platelet-derived growth factor (PDGF), which activates local PDGF-receptor expressing fibroblasts and myofibroblasts, resulting in uncontrolled fibroplasia.

Recent Advances in Understanding the Role of TIGIT+ Follicular Helper T Cells in IgG4-Related Disease

IgG4-related disease (IgG4-RD) is a fibro-inflammatory disease characterized by elevated serum IgG4 levels and massive infiltration of IgG4+plasma cells. Although storiform fibrosis, obliterative phlebitis and IgG4+plasma cell infiltration are well described pathological features in this disease, the excessive formation of tertiary lymphoid organs (TLOs), particularly in the early phase of the disease lesions, has gained much attention. TLOs of IgG4-RD are orchestrated by specific immune cell subsets including follicular helper T cells (Tfh), CD20+ B cells, and CD21+ follicular dendritic cells (FDCs). Tfh is the key player of this disease because recent studies have suggested the pathological role of this immune cell subset in formation of TLOs, helping IgG4+plasma cell differentiation, inducing storiform fibrosis by secreting interleukin-4, and activating cytotoxic T cells by secreting interleukin-21. We have recently identified a new Tfh subset which expresses T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT). TIGIT+Tfh efficiently produces interleukin-21 through OX40 signal, and the increase in peripheral TIGIT+Tfh cells reflects disease activity in IgG4-RD. TIGIT is important to mediate the retention and positioning of TIGIT+Tfh within TLOs through interaction with CD155 expressed on CD21+ FDCs. In this review, we summarize and discuss recent progress in understanding the pathogenesis of IgG4-RD, focusing on TIGIT+Tfh.

Increased Circulating CD4+CXCR5+ Cells and IgG4 Levels in Patients with Myelodysplastic Syndrome with Autoimmune Diseases

Objectives

Immune abnormalities play an important role in the pathogenesis and progression of myelodysplastic syndrome (MDS). Some patients with MDS have autoimmune diseases (AI). Follicular helper T (Tfh) cells help B cells produce antibodies. The role of Tfh in MDS with AI has not been studied.

Methods

We enrolled 21 patients with MDS with AI and 21 patients with MDS without AI. The proportion of peripheral blood CD4⁺CXCR5⁺ cells and the PD1 expression on CD4⁺CXCR5⁺ cells were detected by flow cytometry. Serum levels of immunoglobulin G (IgG) and IgG4 were measured. The survival and progression of MDS to acute myeloid leukemia (AML) in MDS patients with or without AI were compared.

Results

MDS with AI accounted for 19.6% of all MDS cases in our study. The overall response rate was 81% (17/21) in MDS patients with AI for the first-line treatment. The proportion of circulating CD4⁺CXCR5⁺ cells was increased, but the expression of PD1 was decreased in MDS patients with AI. Serum IgG4 levels were also increased in MDS patients with AI. The proportion of peripheral blood CD4⁺CXCR5⁺ cells and the level of serum IgG4 decreased after therapy, but the expression of PD1 increased. There were no differences in overall survival and progress to acute myeloid leukemia between MDS with AI and without AI groups.

Conclusion

CD4⁺CXCR5⁺ cells and IgG4 levels increased in patients with MDS and AI.

Regional disturbance of the distribution of T regulatory cells and T helper cells associated with irregular-shaped germinal centers in immunoglobulin G4-related sialadenitis

Although many germinal centers (GCs) have been reported in immunoglobulin (Ig) G4-related disease, the significance of GCs in IgG4-related disease has not received attention. Both T follicular regulatory cells (Tfr), which are regulatory T cells (Treg) in GCs, and T follicular helper cells (Tfh) produce the cytokine interleukin (IL)-10 and regulate GC development. In whole-slide image analysis in surgical specimens using immunohistochemistry, IgG4-related sclerosing sialadenitis (IgG4-SS, n = 17) was characterized by markedly numerous, large, and irregular-shaped GCs with increased IL-10 + cells and Tfr and Tfh in the total area of the salivary gland compared with controls, including patients with chronic sialadenitis (n = 17) and Sjögren syndrome (n = 15). In particular, the central area of GC in IgG4-SS showed a higher Tfr number and Tfr/Tfh ratio than controls. The number of Tfr in the central area was significantly correlated with the number of IgG4 + plasmacytes and the number, size, and irregularity of GCs. In the mantle area, which surrounds GCs, IgG4-SS showed a higher Treg number and Treg/T helper cells (Th) ratio than controls. In IgG4-SS, the Treg/Th ratio was highest in the mantle area outside GCs and the Tfr/Tfh ratio was highest in the central area inside GCs. However, in controls, the Treg/Th ratio gradually decreased from outside to inside GCs. Our findings reveal that the morphological abnormality of GCs and the characteristic localization and altered balance of Treg and Th in the different compartments of inside and outside GCs would be the novel hallmarks of IgG4-SS.

Co-occurrence of IgA nephropathy and IgG4-Tubulointersitial nephritis effectively treated with tacrolimus: a case report

BACKGROUND

Cases of concurrent immunoglobulin A nephropathy (IgAN) and IgG4-related tubulointerstitial nephritis (IgG4-TIN) are rare and previous case reports have lacked important data. KDIGO suggests a treatment with systemic glucocorticoids in IgAN patients. Glucocorticoids are recommended as the first-line therapy for IgG4-TIN. The use of tacrolimus as a long-term maintenance treatment has not been described. We report the case of a man who developed IgAN and IgG4-TIN without abnormalities in extra-renal tissue, without renal function abnormalities or impairment as well, and was treated by tacrolimus as a long-term maintenance during 45 months follow-up.

CASE PRESENTATION

A 56-year-old Chinese man first presented to our hospital with the chief complaint of foamy urine for 1 year and hematuria for 3 months, with a medical history of hypertension. Testing revealed a notable increase in serum IgG4 level without abnormalities in renal function or imaging, or in dysfunction other organs. Renal biopsy showed mesangial extracellular matrix proliferation, increased mesangial cell numbers and infiltration of plasma cells. Immunofluorescence showed mesangial positivity for IgA and C3. Immunohistochemistry staining showed widespread IgG4 and increased CD38 and CD138 expression. Electron microscopy showed immune complexes located on the tubular basement membrane. He was diagnosed with IgAN and IgG4-TIN. He received glucocorticoids, leflunomide and tacrolimus to induce remission. He was given tacrolimus as long-term maintenance treatment. When tacrolimus was temporarily withdrawn, proteinuria recurred. After resuming tacrolimus therapy, he again entered complete remission. After 45 months of therapy, he remains in complete remission and the serum IgG4 level is normal.

CONCLUSIONS

The finding of concurrent IgAN and IgG4-TIN without abnormalities in renal function, imaging or extra-renal tissue is rare and their coexistence may be coincidental. Long-term treatment with tacrolimus proved effective and he has remained in remission during 45 months follow-up.

Intrathecal activation of CD8+ memory T cells in IgG4-related disease of the brain parenchyma

IgG4-related disease (IgG4-RD) is a fibroinflammatory disorder signified by aberrant infiltration of IgG4-restricted plasma cells into a variety of organs. Clinical presentation is heterogeneous, and pathophysiological mechanisms of IgG4-RD remain elusive. There are very few cases of IgG4-RD with isolated central nervous system manifestation. By leveraging single-cell sequencing of the cerebrospinal fluid (CSF) of a patient with an inflammatory intracranial pseudotumor, we provide novel insights into the immunopathophysiology of IgG4-RD. Our data illustrate an IgG4-RD-associated polyclonal T-cell response in the CSF and an oligoclonal T-cell response in the parenchymal lesions, the latter being the result of a multifaceted cell-cell interaction between immune cell subsets and pathogenic B cells. We demonstrate that CD8⁺ T effector memory cells might drive and sustain autoimmunity via macrophage migration inhibitory factor (MIF)-CD74 signaling to immature B cells and CC-chemokine ligand 5 (CCL5)-mediated recruitment of cytotoxic CD4⁺ T cells. These findings highlight the central role of T cells in sustaining IgG4-RD and open novel avenues for targeted therapies.

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.

Upregulated Expression of Activation-Induced Cytidine Deaminase in Ocular Adnexal Marginal Zone Lymphoma with IgG4-Positive Cells

Immunoglobulin G4-related disease (IgG4-RD) is a systemic disorder characterized by tissue fibrosis and intense lymphoplasmacytic infiltration, causing progressive organ dysfunction. Activation-induced cytidine deaminase (AID), a deaminase normally expressed in activated B-cells in germinal centers, edits ribonucleotides to induce somatic hypermutation and class switching of immunoglobulin. While AID expression is strictly controlled under physiological conditions, chronic inflammation has been noted to induce its upregulation to propel oncogenesis. We examined AID expression in IgG4-related ophthalmic disease (IgG4-ROD; n = 16), marginal zone lymphoma with IgG4-positive cells (IgG4+ MZL; n = 11), and marginal zone lymphoma without IgG4-positive cells (IgG4- MZL; n = 12) of ocular adnexa using immunohistochemical staining. Immunohistochemistry revealed significantly higher AID-intensity index in IgG4-ROD and IgG4+ MZL than IgG4- MZL (p < 0.001 and = 0.001, respectively). The present results suggest that IgG4-RD has several specific causes of AID up-regulation in addition to inflammation, and AID may be a driver of oncogenesis in IgG4-ROD to IgG4+ MZL.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Challenges in Medicine: The Odyssey of a Patient with Isolated IgG4-Related Eosinophilic Angiocentric Fibrosis Presenting as a Locally Destructive Sinonasal Mass

Eosinophilic angiocentric fibrosis (EAF) is an exceeding rare clinical entity and is considered a part of the spectrum of IgG4-related disease (IgG4RD). We hereby present such an unusual case of a 60-year-old female who presented to us with recurrent sinonasal mass, after a decade long haul of multiple clinical evaluations, biopsies, and debulking surgery without a definitive diagnosis. Over this period, the mass eroded through the ethmoid cells along with nasal septal destruction leading to saddle nose deformity, extended superiorly through the cribriform plates to right frontal lobe, and compressed the optic nerve leading to visual loss. Although initial biopsy was negative, repeat biopsy was performed owing to high clinical suspicion due to all the classic histopathological findings compatible with the diagnosis of eosinophilic angiocentric fibrosis IgG4-related disease (EAF-IgG4RD). Steroids are the recommended first-line therapy; however, our case was resistant to steroids needing rituximab to halt the disease progression. Our case interestingly also had T-cell clonality and isolated isocitrate dehydrogenase 2 enzyme mutation on next-generation sequencing, suggesting a possible role of novel molecular-targeted therapies in this rare disease. This case highlights the clinical challenges physicians face towards diagnosing and treating EAF-IgG4RD, emphasizing the need for high clinical suspicion and the possible role of targeted therapies for this rare disease.

Tertiary lymphoid tissue in early-stage IgG4-related tubulointerstitial nephritis incidentally detected with a tumor lesion of the ureteropelvic junction: a case report

Background

IgG4-related kidney disease causes renal impairment of unknown pathogenesis that may progress to kidney failure. Although ectopic germinal centers contribute to the pathogenesis of the head and neck lesions of IgG4-related disease, the presence of tertiary lymphoid tissue (TLT) containing germinal centers in IgG4-RKD has rarely been reported.

Case presentation

We report a 72-year-old Japanese man who had IgG4-related tubulointerstitial nephritis (TIN) with TLT formation incidentally detected in a resected kidney with mass lesion of IgG4-related ureteritis in the ureteropelvic junction. During follow-up for past surgical resection of a bladder tumor, renal dysfunction developed and a ureter mass was found in the right ureteropelvic junction, which was treated by nephroureterectomy after chemotherapy. Pathology revealed no malignancy but abundant IgG4-positive cell infiltration, obliterative phlebitis and storiform fibrosis, confirming the diagnosis of IgG4-related ureteritis. In the resected right kidney, lymphoplasmacytes infiltrated the interstitium with focal distribution in the renal subcapsule and around medium vessels without storiform fibrosis, suggesting the very early stage of IgG4-TIN. Lymphocyte aggregates were also detected at these sites and consisted of B, T, and follicular dendritic cells, indicating TLT formation. IgG4-positive cells infiltrated around TLTs.

Conclusions

Our case suggests that TLT formation is related with the development of IgG4-TIN and our analysis of distribution of TLT have possibility to elucidate IgG4-TIN pathophysiology.

Lymphadenopathy in IgG4-related disease: a phenotype of severe activity and poor prognosis, with eotaxin-3 as a new biomarker

Objective

To clarify relevant proteins and clinical characteristics of a phenotype of IgG4-related disease (IgG4-RD) with lymphadenopathy.

Methods

We enrolled patients newly diagnosed with IgG4-RD in our department between January 2000 and June 2018 and performed proteomic analysis to measure serum concentrations of 1305 proteins. We extracted proteins overexpressed in patients with IgG4-RD with lymphadenopathy by comparing between those with lymphadenopathy, those without lymphadenopathy and healthy controls. We further reviewed all the patients with IgG4-RD in our institution and investigated the characteristics and prognosis of the patients with IgG4-RD with lymphadenopathy.

Results

Eighty-five patients with IgG4-RD were enrolled, of which, 55% had lymphadenopathy. Proteomic analysis in 31 patients with IgG4-RD and 6 healthy controls revealed that eotaxin-3 was a potential serum biomarker in the patients with lymphadenopathy versus those without lymphadenopathy and healthy controls. A cohort of 85 patients with IgG4-RD demonstrated that patients with lymphadenopathy showed a significantly higher serum IgG4, IgG4:IgG ratio, IgG4-RD responder index and eosinophilia (P &lt; 0.001 for all), irrelevant of the extent to which organ involvement developed. Patients with lymphadenopathy treated with glucocorticoid alone relapsed with significantly higher rates than those without lymphadenopathy (P = 0.03).

Conclusion

Lymphadenopathy in IgG4-RD represents a phenotype associated with high disease activities, eosinophilia and relapsing disease. Eotaxin-3 is a novel biomarker related to IgG4-RD with lymphadenopathy.

Evidence of potent humoral immune activity in COVID-19-infected kidney transplant recipients

Whether kidney transplant recipients are capable of mounting an effective anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) adaptive immune response despite chronic immunosuppression is unknown and has important implications for therapy. Herein, we analyzed peripheral blood cell surface and intracellular cytokine phenotyping by flow cytometry along with serum antibody testing in 18 kidney transplant recipients with active coronavirus disease 2019 (COVID-19) infection and 36 matched, transplanted controls without COVID-19. We observed significantly fewer total lymphocytes and fewer circulating memory CD4⁺ and CD8⁺ T cells in the COVID-19 subjects. We also showed fewer anergic and senescent CD8⁺ T cells in COVID-19 individuals, but no differences in exhausted CD8⁺ T cells, nor in any of these CD4⁺ T cell subsets between groups. We also observed greater frequencies of activated B cells in the COVID-19 patients. Sixteen of 18 COVID-19 subjects tested for anti-SARS-CoV-2 serum antibodies showed positive immunoglobulin M or immunoglobulin G titers. Additional analyses showed no significant correlation among immune phenotypes and degrees of COVID-19 disease severity. Our findings indicate that immunosuppressed kidney transplant recipients admitted to the hospital with acute COVID-19 infection can mount SARS-CoV-2-reactive adaptive immune responses. The findings raise the possibility that empiric reductions in immunosuppressive therapy for all kidney transplant recipients with active COVID-19 may not be required.

Characteristics and prognosis of ANCA-positive retroperitoneal fibrosis: A systematic literature review

OBJECTIVE

Anti-neutrophil cytoplasmic autoantibody (ANCA)-positive retroperitoneal fibrosis (RPF) is extremely rare. This study aimed to clarify the clinical characteristics and prognosis of patients with ANCA-positive RPF.

METHODS

We conducted a systematic literature review of articles reporting on ANCA-positive RPF from the database inception dates until March 8, 2020.

RESULTS

We identified 19 patients with ANCA-positive RPF with a mean age of 62 years; a male dominance (68.4%) was noted. Most patients presented with systemic symptoms and/or lower back or abdominal pain. Proteinase 3 (PR3) -ANCA positivity was predominant compared with myeloperoxidase (MPO)-ANCA (63.2% vs. 36.8%, respectively), and all patients showed elevated serum C-reactive protein levels. Of note, 26.7% of patients had isolated RPF without any other ANCA-associated systemic organ involvement. Regarding typical manifestations of ANCA- associated vasculitis, ear, nose, and throat involvement occurred in 26.3%, lung involvement in 36.8%, and kidney involvement (rapidly progressive glomerulonephritis) in 31.6% of patients. Necrosis and granulomatous inflammation, vasculitis, and multinucleated giant cells were pathologically observed in tissue sections of RPF, whereas tertiary lymphoid organ formation was not identified. Glucocorticoids with or without other immunosuppressive treatments were effective in most patients, but 4 patients experienced disease relapse during the clinical course. All relapsed patients were positive for PR3-ANCA.

CONCLUSION

Clinical features of ANCA-positive RPF are associated with systemic inflammatory components such as fever and elevated serum C-reactive protein levels. ANCA-. positive RPF presents as an "isolated" involved organ in one-third of patients. Immunosuppressive treatments are effective, but the disease can recur, particularly in PR3-ANCA-positive patients.

Adventitial matrix metalloproteinase production and distribution of immunoglobulin G4-related abdominal aortic aneurysms

Objective

IgG4-related diseases are systemic inflammatory fibrous lesions characterized by elevated serum IgG4 and infiltration of IgG4-positive plasmacytes. They can manifest in vascular lesions as frequently formed aneurysms with prominent thickening of the adventitia (IgG4-related abdominal aortic aneurysm; IgG4-AAA). Matrix metalloproteinases (MMPs) degrade the extracellular matrix, mainly in the tunica media, resulting in destruction of aortic structures to cause enlargement of the aneurysm. However, the expression of adventitial MMPs in IgG4-AAAs is poorly understood.

Methods

MMPs and MMPs-presenting cells in the adventitia of IgG4-AAAs (n = 19) of human surgical specimens were evaluated by immunohistochemistry and dual messenger RNA in situ hybridization. The results were compared with those from control groups of non-IgG4-related inflammatory AAA (n = 18), atherosclerotic AAA (aAAA; n = 11), and autopsy cases (n = 11). Preoperative serum MMPs levels of these groups were compared with the histologic data.

Results

Expression of MMP-9, MMP-2, and MMP-14 at the protein and messenger RNA levels in the adventitia was significantly higher in IgG4-AAAs than in controls. Other MMPs were scarce. The total number of MMP-9-positive cells was positively correlated with the diameter of the aneurysm (R = 0.461; P = .031), the adventitial thickness (R = 0.688; P < .001), and the number of IgG4-positive cells (R = 0.764; P < .001). Within lymphoid follicles, MMP-9-presenting cells were predominantly detected in large follicular dendritic cells, followed by histiocytes, fibroblasts, and plasmacytic dendritic cells. Outside lymphoid follicles, fibroblasts, and histiocytes mainly expressed MMP-9, and tissue dendritic cells also produced MMP-9. The levels of MMP-9 derived from follicular dendritic cells and histiocytes and plasmacytic dendritic cells outside lymphoid follicles were significantly higher in IgG4-AAA group than in other groups. Expression of adventitial MMP-2 and MMP-14 by histiocytes and fibroblasts was predominantly detected outside lymphoid follicles. Serum MMP-9 levels were significantly higher in IgG4-AAAs (835 ng/mL) than in controls, and correlated with serum IgG4 levels and the total numbers of adventitial MMP-9-positive cells, whereas serum MMP-2 levels did not differ among the three aneurysmal groups.

Conclusions

MMP-9 production in adventitial immune cells concerning lymphoid follicles was characteristic of IgG4-AAAs and might work in its activity with aneurysmal dilatation and adventitial thickening. Expressions of adventitial MMP-2 and MMP-14 were detected in histiocytes and fibroblasts outside lymphoid follicles, and were less concerned with the activity of IgG4-AAAs.

This retrospective multicenter study analyzed adventitial matrix metalloproteinases (MMPs) production in 19 patients with IgG4-related abdominal aortic aneurysms (AAAs) and 40 control cases. Adventitial MMP-9 production by various kinds of immune cells was increased in patients with IgG4-related AAAs and concerned with IgG4-AAA activity to cause aneurysmal progression and adventitial fibrosis, compared with aAAA. Serum MMP-9 levels reflected histologic MMP-9. Adventitial MMP-2 and MMP-14 were less concerned with IgG4-AAA activity. Thus, for IgG4-AAA patients, monitoring serum MMP-9 level might be the exacerbating factors related to adverse events during the treatment course.

In vitro IL-6/IL-6R Trans-Signaling in Fibroblasts Releases Cytokines That May Be Linked to the Pathogenesis of IgG4-Related Disease

Background: The remarkable mechanisms of storiform fibrosis and the formation of high levels of IgG4 with a pathogenic germinal center (GC) in the inflammatory tissue of IgG4-RD remains unknown and may be responsible for the unsatisfactory therapeutic effect on IgG4-related diseases when using conventional therapy.

Objectives: To investigate the mechanisms of interleukin 6 (IL-6) inducing fibroblasts to produce cytokines for pathogenic GC formation in the development of IgG4-related disease (IgG4-RD).

Methods: The clinical data and laboratory examinations of 56 patients with IgG4-RD were collected. IL-6 and IL-6R expression in the serum and tissues of patients with IgG4-RD and healthy controls were detected by ELISA, immunohistochemistry, and immunofluorescence. Human aorta adventitial fibroblasts (AAFs) were cultured and stimulated with IL-6/IL-6 receptor (IL-6R). The effect of IL-6/IL-6R on AAFs was determined by Luminex assays.

Results: The serum IL-6 and IL-6R levels were elevated in active IgG4-RD patients and IL-6 was positively correlated with the disease activity (e.g., erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], and IgG4-RD responder index). IL-6 and IL-6R expression in the tissue lesions of IgG4-related retroperitoneal fibrosis and IgG4-related sialadenitis patients were also significantly higher than that in the normal tissues. In addition, there is a relative abundance of myofibroblasts as well as IgG4⁺ plasma cells in the tissues of IgG4-related retroperitoneal fibrosis. α-SMA and B cell differentiation cytokines (i.e., B cell activating factor), and α-SMA and T follicular helper (Tfh) cell differentiation cytokines (e.g., IL-7, IL-12, and IL-23) were co-expressed in the local lesions. In vitro, IL-6/IL-6R significantly promoted the production of B cell activating factor, IL-7, IL-12, and IL-23 in AAFs in a dose-dependent manner. This effect was partially blocked by JAK1, JAK2, STAT3, and Akt inhibitors, respectively.

Conclusions:In vitro IL-6/IL-6R trans-signaling in fibroblasts releases Tfh and B cell differentiation factors partially via the JAK2/STAT3, JAK1/STAT3, and JAK2/Akt pathways, which may be linked to the pathogenesis of IgG4-RD. This indicated that IL-6 and fibroblasts may be responsible for GC formation and fibrosis in the development of IgG4-RD. Blocking IL-6 with JAK1/2 inhibitors or inhibiting fibroblast proliferation might be beneficial for IgG4-RD treatment.

Analysis of Innate and Adaptive Immunological Characteristics in Patients with IgG4-Related Disease

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) is a systemic immunological disorder characterized by fibro-inflammatory conditions; however, the pathobiology of IgG4-RD has not been fully identified.

OBJECTIVE

This study aimed to analyze systemic differences of innate and adaptive immune cells from healthy controls and patients with IgG4-RD.

METHODS

Healthy controls (n = 9) and IgG4-RD patients (n = 7) were recruited with informed consent. Peripheral blood was collected from healthy controls and IgG4-RD patients, and three blood samples from IgG4-RD patients were re-collected two months after the last rituximab (RTX) treatment. The various immune cells and cytokine productions were measured by flow cytometry.

RESULTS

Blood CD14+ monocytes and steady-state follicular helper T cells were increased in patients with IgG4-RD. However, there were no changes in other immune cell populations, including B cells, CD4 T cells, CD8 T cells, and innate lymphoid cells. Also, the TGF-β-producing CD14+ monocytes were significantly augmented in patients with IgG4-RD. Two months after RTX treatment, total B cells (CD19+) were depleted; however, the expressions of TGF-β from CD14+ monocytes remained unchanged.

CONCLUSION

These findings showed that IgG4-RD is related to the increment of CD14+ monocytes. Besides, controlling increased TGF-β-producing CD14+ monocytes with RTX treatment might be a conducive way to regulate IgG4-RD.

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.

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.

High-throughput sequencing of CD4+ T cell repertoire reveals disease-specific signatures in IgG4-related disease

Background

CD4⁺ T cells play critical roles in the pathogenesis of IgG4-related disease (IgG4-RD). The aim of this study was to investigate the TCR repertoire of peripheral blood CD4⁺ T cells in IgG4-RD.

Methods

The peripheral blood was collected from six healthy controls and eight IgG4-RD patients. TCR β-chain libraries of CD4⁺ T cells were constructed by 5′-rapid amplification of cDNA ends (5′-RACE) and sequenced by Illumina Miseq platform. The relative similarity of TCR repertoires between samples was evaluated according to the total frequencies of shared clonotypes (metric F), correlation of frequencies of shared clonotypes (metric R), and total number of shared clonotypes (metric D).

Results

The clonal expansion and diversity of CD4⁺ T cell repertoire were comparable between healthy controls and IgG4-RD patients, while the proportion of expanded and coding degenerated clones, as an indicator of antigen-driven clonal expansion, was significantly higher in IgG4-RD patients. There was no significant difference in TRBV and TRBJ gene usage between healthy controls and IgG4-RD patients. The complementarity determining region 3 (CDR3) length distribution was skewed towards longer fragments in IgG4-RD. Visualization of relative similarity of TCR repertoires by multi-dimensional scaling analysis showed that TCR repertoires of IgG4-RD patients were separated from that of healthy controls in F and D metrics. We identified 11 IgG4-RD-specific CDR3 amino acid sequences that were expanded in at least 2 IgG4-RD patients, while not detected in healthy controls. According to TCR clonotype networks constructed by connecting all the CDR3 sequences with a Levenshtein distance of 1, 3 IgG4-RD-specific clusters were identified. We annotated the TCR sequences with known antigen specificity according to McPAS-TCR database and found that the frequencies of TCR sequences associated with each disease or immune function were comparable between healthy controls and IgG4-RD patients.

Conclusion

According to our study of CD4⁺ T cells from eight IgG4-RD patients, TCR repertoires of IgG4-RD patients were different from that of healthy controls in the proportion of expanded and coding degenerated clones and CDR3 length distribution. In addition, IgG4-RD-specific TCR sequences and clusters were identified in our study.

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.

Management of IgG4-related disease

IgG4-related disease was unrecognised as a unified disease entity until this century, yet in a short period of time the disease has been appreciated to have a worldwide distribution, and its clinical, pathological, and radiological features have been described in considerable detail. The disease has strong organ predilections, and many of the clinical presentations of disease are increasingly familiar to both generalists and specialists. Early recognition of IgG4-related disease is crucial because although the disease is highly treatable, it can lead to serious organ damage and even death if undiagnosed until advanced stages. Its indolent nature often makes diagnosis challenging, and IgG4-related disease is one of the great mimickers of other diseases in the current era. Glucocorticoids are an effective treatment for IgG4-related disease, but their long-term use is problematic in a disease that frequently affects middle-aged to elderly individuals and often leads to pancreatic dysfunction. Our understanding of the pathophysiology of the disease is surprisingly advanced given the relatively recent recognition of this condition. Insights into disease pathophysiology offer the possibility of a variety of targeted treatment approaches. Looking ahead, biological therapies could profoundly alter the way in which IgG4-related disease is managed, permitting the use of specific therapies that are tailored to patients' clinical phenotypes.

The potential role of follicular helper T cells in idiopathic multicentric Castleman disease with and without TAFRO syndrome

Idiopathic multicentric Castleman disease (iMCD) is a systemic inflammatory disease of unknown etiology caused by hypercytokinemia. Recently, TAFRO (thrombocytopenia, anasarca, fever, renal failure or reticulin fibrosis, and organomegaly) syndrome has been reported, which shows similar histopathological findings to iMCD and factors associated with a poor prognosis. iMCD shows no plasma cell infiltration in the germinal center (GC), but CD38-positive (CD38⁺)-plasma cells are observed in the interfollicular area. Our previous report revealed that atrophic change of GC, glomeruloid vascular proliferation, and abnormal proliferation of follicular dendritic cells are more prominent in iMCD with TAFRO (TAFRO⁺) in comparison to iMCD without TAFRO (TAFRO^-). In addition, the numbers of CD38⁺ and immunoglobulin G4-positive (IgG4⁺) plasma cells were decreased in the interfollicular area. The roles of T follicular helper cells (Tfh) are well-known to assist B-cell proliferation, maturation, and differentiation．It maintains the formation of GC and is also related in the class switching of IgG isotypes, including IgG4. Thus, we immunohistochemically examined the number of Tfh in GCs in both TAFRO^- and TAFRO⁺ iMCD. The number of Tfh was significantly decreased in TAFRO^- iMCD (n = 9) and was further decreased in TAFRO⁺ iMCD (n = 18) in comparison to non-specific lymphadenopathy (n = 6) and IgG4-related disease (n = 4). These results suggest that decreased Tfh may be one etiology of iMCD.

Characteristics and prognosis of IgG4-related periaortitis/periarteritis: A systematic literature review

OBJECTIVE

Immunoglobulin G4 (IgG4)-related disease is a systemic chronic fibroinflammatory disease that can affect almost every organ of the body. IgG4-related periaortitis/periarteritis is a newly recognized subset of IgG4-related disease, and its characteristics and prognosis remain unclear. We investigated the clinical characteristics and prognosis of IgG4-related periaortitis/periarteritis.

METHODS

We performed a systematic literature review of IgG4-related periaortitis/periarteritis. Additionally, we have summarized the characteristics and prognosis of IgG4-related coronary arteritis.

RESULTS

We investigated 248 patients with IgG4-related periaortitis/periarteritis. All studies reported the condition in elderly patients, and male predominance was observed. The infra-renal abdominal aorta and iliac arteries were the most commonly affected sites. Most reports showed the serum C-reactive protein elevation in this disease entity, in contrast to non-vascular IgG4-related disease. Based on radiological findings observed in 27 patients with IgG4-related coronary arteritis, vasculitic lesions were classified into 3 types: stenotic (67% of patients), aneurysmal (42%), and diffuse wall thickening type (92%). Serum IgG4 level, but not C-reactive protein level, was associated with the number of affected organs in IgG4-related coronary arteritis. Corticosteroid treatment with or without cardiac surgery or percutaneous coronary intervention was effective in most patients with IgG4-related coronary arteritis; however, 33% of patients showed an unfavorable clinical course including disease progression, relapse, or death. Pre-treatment stenosis and/or aneurysms were associated with progression of stenosis or aneurysm after corticosteroid treatment.

CONCLUSION

Most clinical characteristics were similar between the IgG4-related periaortitis/periarteritis and the non-vascular IgG4-related disease groups; however, serum C-reactive protein level elevation was observed only in the former. Although corticosteroid treatment was effective, this disease can be life-threatening secondary to myocardial infarction, aortic dissection, and aneurysmal rupture. Pre-treatment evaluation of stenosis or aneurysms is important for predicting progression of stenosis or aneurysm after corticosteroid treatment.

IgG4-Related Disease with Emphasis on Its Gastrointestinal Manifestation

IgG4-related disease is an immune-mediated fibroinflammatory condition with a diverse spectrum of organ involvement, commonly in the pancreas and bile ducts among other organs such as salivary and lacrimal glands. Classic histopathologic findings are the gold standard for confirmation of diagnosis, although diagnosis remains challenging, as biomarkers to date are neither sufficient nor necessary. Glucocorticoids are the most effective initial treatment, generally having a dramatic response, although limited clinical evidence exists regarding effective maintenance therapy. This review summarizes key GI manifestations of this condition for the practicing gastroenterologist and addresses the pathology, disease mechanism, and current therapeutic recommendations.