Immune mechanisms of fibrosis and inflammation in IgG4-related disease

Management of ureteral IgG4-Related Disease: The great masquerader

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory condition that can mimic malignancies, including ureteric urothelial carcinoma (UCC). This case report describes a 65-year-old female presenting with obstructive uropathy due to IgG4-related ureteritis. Initial imaging suggested UCC, however ureteric biopsy was negative. Elevated serum IgG4 levels (3.77 g/L) supported the diagnosis of IgG4-related ureteritis. Treatment with methotrexate, prednisolone, and rituximab led to significant improvement, with subsequent imaging showing resolution of obstructive uropathy. This case highlights the importance of considering IgG4-RD in the differential diagnosis of ureteric malignancies to prevent unnecessary invasive procedures and optimize patient outcomes through appropriate immunosuppressive therapy.

IgG4-related disease for the hematologist

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated disease with many important manifestations in hematopoietic and lymphoid tissue. IgG4 is the least naturally abundant IgG subclass, and the hallmark feature of IgG4-RD is markedly increased IgG4-positive plasma cells (with an IgG4 to IgG ratio >40%) in affected tissue, along with elevated polyclonal serum IgG and IgG4 in most patients. Histological diagnosis is essential, and other key features include storiform fibrosis, lymphoplasmacytic infiltrate, tissue eosinophilia, and obliterative phlebitis. The disease can present with predominantly proliferative features, such as swollen lacrimal and salivary glands, orbital pseudotumor, autoimmune pancreatitis, polyclonal hypergammaglobulinemia (PHGG), eosinophilia, and tubulointerstitial nephritis of the kidneys, or predominantly fibrotic disease, including mediastinal and retroperitoneal fibrosis, sclerosing mesenteritis, and hypertrophic pachymeningitis. This review focuses on 4 key hematological manifestations: PHGG, IgG4-positive plasma cell enriched lymphadenopathy (LAD), eosinophilia, and retroperitoneal fibrosis (RPF). These features are found in 70%, 60%, 40%, and 25% of IgG4-RD patients, respectively, but can also represent key hematological "mimickers" of IgG4-RD, including Castleman disease (PHGG, LAD), eosinophilic vasculitis (eosinophilia, PHGG, LAD), hypereosinophilic syndromes (eosinophilia, LAD, PHGG), and histiocyte disorders (PHGG, LAD, RPF). An organized approach to these 4 manifestations, and how to distinguish IgG4-RD from its mimickers, is explained. Proliferative manifestations typically respond very well to treatment corticosteroids, rituximab, and other immunosuppressives, whereas chronic fibrotic disease may not be reversible with current treatment modalities.

IgG4-related disease mimicking a liver abscess

IgG4-related disease (IGRD) is a complex medical condition affecting multiple organs, including the liver. The condition is characterized by excessive production of IgG4 antibodies, leading to chronic inflammation and tissue damage. We present a case of a 37-year-old man with a history of chronic pancreatitis was diagnosed with a liver mass. Initial treatment included piperacillin and tazobactam, but the patient's condition worsened. An ultrasound-guided biopsy revealed increased IgG4 positive cells, leading to the diagnosis of an inflammatory pseudotumor associated with IGRD. The patient was treated with prednisone taper therapy, and the liver mass resolved after six months of corticoid treatment.

IgG4-related disease with nasopharyngeal malignancy-like manifestations

Background

IgG4-related disease (IgG4-RD) was characterized by single or multiple masses in organs, which may mimic various inflammatory and malignant diseases. Here, we summarize 4 patients with aggressive manifestations of IgG4-RD that mimic nasopharynx cancer to provide some new sights for the diagnosis of IgG4-RD.

Case summary

Four patients were included in our series. The age ranged from 53 to 64 years old, and the duration of the disease ranged from 4 to 6 months. The chief complaints included headache, rhinorrhea, or diplopia. All patients had more than 10 IgG4+ plasma cells/HPF in immunohistochemistry with plasma lgG4 levels ranging from 218 mg/dL to 765 mg/dL. All of them met the diagnostic criteria of lgG4-RD.

Conclusion

The described case is highly similar to the clinical manifestations of nasopharyngeal carcinoma. Although pathology is the gold standard, there are still limitations. Serological IgG4 can help confirm the diagnosis. Timely diagnosis of IgG4-RD is of great significance in preventing secondary organ damage in patients with active diseases.

Exploring the depths of IgG4: insights into autoimmunity and novel treatments

IgG4 subclass antibodies represent the rarest subclass of IgG antibodies, comprising only 3-5% of antibodies circulating in the bloodstream. These antibodies possess unique structural features, notably their ability to undergo a process known as fragment-antigen binding (Fab)-arm exchange, wherein they exchange half-molecules with other IgG4 antibodies. Functionally, IgG4 antibodies primarily block and exert immunomodulatory effects, particularly in the context of IgE isotype-mediated hypersensitivity reactions. In the context of disease, IgG4 antibodies are prominently observed in various autoimmune diseases combined under the term IgG4 autoimmune diseases (IgG4-AID). These diseases include myasthenia gravis (MG) with autoantibodies against muscle-specific tyrosine kinase (MuSK), nodo-paranodopathies with autoantibodies against paranodal and nodal proteins, pemphigus vulgaris and foliaceus with antibodies against desmoglein and encephalitis with antibodies against LGI1/CASPR2. Additionally, IgG4 antibodies are a prominent feature in the rare entity of IgG4 related disease (IgG4-RD). Intriguingly, both IgG4-AID and IgG4-RD demonstrate a remarkable responsiveness to anti-CD20-mediated B cell depletion therapy (BCDT), suggesting shared underlying immunopathologies. This review aims to provide a comprehensive exploration of B cells, antibody subclasses, and their general properties before examining the distinctive characteristics of IgG4 subclass antibodies in the context of health, IgG4-AID and IgG4-RD. Furthermore, we will examine potential therapeutic strategies for these conditions, with a special focus on leveraging insights gained from anti-CD20-mediated BCDT. Through this analysis, we aim to enhance our understanding of the pathogenesis of IgG4-mediated diseases and identify promising possibilities for targeted therapeutic intervention.

Granzyme K- and amphiregulin-expressing cytotoxic T cells and activated extrafollicular B cells are potential drivers of IgG4-related disease

BACKGROUND

IgG4-related disease (IgG4-RD), an example of a type I immune disease, is an immune-mediated fibrotic disorder characterized by dysregulated resolution of severe inflammation and wound healing. However, truly dominant or pathognomonic autoantibodies related to IgG4-RD are not identified.

OBJECTIVE

We sought to perform single-cell RNA sequencing and T-cell receptor and B-cell receptor sequencing to obtain a comprehensive, unbiased view of tissue-infiltrating T and B cells.

METHODS

We performed unbiased single-cell RNA-sequencing analysis for the transcriptome and T-cell receptor sequencing and B-cell receptor sequencing on sorted CD3+ T or CD19+ B cells from affected tissues of patients with IgG4-RD. We also conducted quantitative analyses of CD3+ T-cell and CD19+ B-cell subsets in 68 patients with IgG4-RD and 30 patients with Sjögren syndrome.

RESULTS

Almost all clonally expanded T cells in these lesions were either Granzyme K (GZMK)-expressing CD4+ cytotoxic T cells or GZMK+CD8+ T cells. These GZMK-expressing cytotoxic T cells also expressed amphiregulin and TGF-β but did not express immune checkpoints, and the tissue-infiltrating CD8+ T cells were phenotypically heterogeneous. MKI67+ B cells and IgD-CD27-CD11c-CXCR5- double-negative 3 B cells were clonally expanded and infiltrated affected tissue lesions. GZMK+CD4+ cytotoxic T cells colocalized with MKI67+ B cells in the extrafollicular area from affected tissue sites.

CONCLUSIONS

The above-mentioned cells likely participate in T-B collaborative events, suggesting possible avenues for targeted therapies. Our findings were validated using orthogonal approaches, including multicolor immunofluorescence and the use of comparator disease groups, to support the central role of cytotoxic CD4+ and CD8+ T cells expressing GZMK, amphiregulin, and TGF-β in the pathogenesis of inflammatory fibrotic disorders.

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

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

Performance of the 2019 ACR/EULAR Classification Criteria for IgG4-Related Disease in a Large Chinese Cohort

OBJECTIVE

The purpose of this research was to ascertain the effectiveness of the newly established criteria for classifying IgG4-related disease (IgG4-RD), as applied to a large Chinese cohort in real-world clinical settings.

METHODS

Patient data were procured from the digital health records of 4 prominent academic hospitals. The criterion standard for identifying IgG4-RD patients was from a seasoned rheumatologist. The control group consisted of individuals with other ailments such as cancer, other forms of pancreatitis, infectious diseases, and illnesses that mimic IgG4-RD.

RESULTS

A total of 605 IgG4-RD patients and 760 mimickers were available for analysis. The 2019 EULAR/ACR criteria have a sensitivity of 69.1% and a specificity of 90.9% in this large Chinese cohort. IgG4-RD had a greater proportion of males (55.89% vs 36.25%, p < 0.001), an older average age at diagnosis (54.91 ± 13.44 vs 48.91 ± 15.71, p < 0.001), more pancreatic (29.59% vs 6.12%, p < 0.001) and salivary gland (63.30% vs 27.50%, p < 0.001) involvement, and a larger number of organ involvement (3.431 ± 2.054 vs 2.062 ± 1.748, p < 0.001) compared with mimickers.

CONCLUSIONS

The 2019 EULAR/ACR criteria are effective in classifying IgG4-RD in Chinese patients, demonstrating high specificity and moderate sensitivity.

Enfermedad relacionada con inmunoglobulina G4, un diagnóstico a tener en cuenta: a propósito de un caso

La enfermedad relacionada con inmunoglobulina G4 (ER-IgG4) es una condición inmunomediada y multisistémica asociada al desarrollo de lesiones fibroinflamatorias en cualquier órgano. El diagnóstico se realiza bajo la suma de criterios clínicos, serológicos, radiológicos e histopatológicos; sin embargo, este suele ser difícil debido a su similitud con neoplasias, infecciones u otras enfermedades inmunomediadas. El tratamiento se basa en corticosteroides, en una posible combinación con inmunomoduladores. El presente caso trata de un varón de 59 años con historia de síndrome ictérico y baja de peso, admitido por sospecha de neoplasia maligna de la vía biliar. Las imágenes revelaron estenosis con dilatación de las vías biliares intrahepáticas, páncreas prominente, estenosis del conducto pancreático y lesiones nodulares renales. Debido al antecedente de submandibulectomía izquierda 2 años antes de la enfermedad actual e histología compatible con tumor de Küttner, más los valores elevados de IgG4 sérico, se estableció el diagnóstico de ER-IgG4. Inició tratamiento con corticosteroides y cursó asintomático durante el seguimiento.

Immune dysregulation in immunoglobulin G4-related disease

(IgG4-RD) is an immune-mediated fibrotic disorder characterized by severe resolution of inflammation and dysregulation of wound healing. IgG4-RD has been considered a unique disease since 2003, and significant progress has been achieved in the understanding of its essential features. The central role of B cells in IgG4-RD has been demonstrated by the robust clinical responsiveness of IgG4-RD to B cell depletion and the identification of multiple self-antigens that promote B cell expansion. Studies have increasingly revealed critical roles of these B cells and T cells in the pathogenesis of IgG4-RD, and we and other authors further identified CD4⁺ cytotoxic T lymphocytes as the main tissue-infiltrating CD4⁺ T cell subset in IgG4-RD tissues. Additionally, T follicular helper cell subsets that play a role in IgG4 isotype switching have been identified. In this review, we discuss research on IgG4-RD and the roles of B cell and T cell subsets, as well as the functions of CD4⁺ cytotoxic T cells in IgG4-RD pathogenesis. We highlight our findings from ongoing research using single-cell analysis of infiltrating CD4⁺ cytotoxic T cells, CD4⁺ follicular helper T cells, and infiltrating B cells in IgG4-RD and propose a model for the pathogenesis of IgG4-RD.

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.

Research progress on the clinical application and mechanism of iguratimod in the treatment of autoimmune diseases and rheumatic diseases

Autoimmune diseases are affected by complex pathophysiology involving multiple cell types, cytokines, antibodies and mimicking factors. Different drugs are used to improve these autoimmune responses, including nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, antibodies, and small molecule drugs (DMARDs), which are prevalent clinically in the treatment of rheumatoid arthritis (RA), etc. However, low cost-effectiveness, reduced efficacy, adverse effects, and patient non-response are unattractive factors driving the development of new drugs such as iguratimod. As a new disease-modifying antirheumatic drug, iguratimod has pharmacological activities such as regulating autoimmune disorders, inflammatory cytokines, regulating immune cell activation, differentiation and proliferation, improving bone metabolism, and inhibiting fibrosis. In recent years, clinical studies have found that iguratimod is effective in the treatment of RA, SLE, IGG4-RD, Sjogren 's syndrome, ankylosing spondylitis, interstitial lung disease, and other autoimmune diseases and rheumatic diseases. The amount of basic and clinical research on other autoimmune diseases is also increasing. Therefore, this review systematically reviews the latest relevant literature in recent years, reviews the research results in recent years, and summarizes the research progress of iguratimod in the treatment of related diseases. This review highlights the role of iguratimod in the protection of autoimmune and rheumatic bone and related immune diseases. It is believed that iguratimod's unique mode of action and its favorable patient response compared to other DMARDs make it a suitable antirheumatic and bone protective agent in the future.

Is it bad, is it good, or is IgG4 just misunderstood?

Repeated doses of mRNA vaccines for COVID-19 result in increased proportions of anti-spike antibodies of the IgG4 subclass, which are known to neutralize well and to form mixed immune complexes with IgG1 but, in a pure form, might be less effective than IgG1 or IgG3 antibodies in facilitating opsonization by phagocytes, complement fixation, and NK cell-dependent elimination of infected cells (see related Research Article by Irrgang et al.).

Perspectives on current and emerging therapies for immunoglobulin G4-related disease

Understanding of the pathophysiology of immunoglobulin G4-related disease (IgG4-RD) over the last dozen years has opened the door to a variety of targeted treatment approaches. Glucocorticoids are an effective treatment for IgG4-RD if used at a sufficiently high dose, but disease flares are common during or after glucocorticoid tapers and these medications seldom lead to long-term, treatment-free remissions. Moreover, their long-term use in a disease that frequently affects middle-aged to elderly individuals and often causes major pancreatic damage leads to a narrow therapeutic index. Biological therapies offer the possibility of effective disease control with fewer treatment-associated side effects. Promising avenues of investigation include B-cell depletion, immunomodulation of B-cell subsets, interference with co-stimulation, Bruton's tyrosine kinase inhibition, and Signaling lymphocytic activation molecule F7-directed treatment.

Lymph Nodes With Increased IgG4-positive Plasma Cells and Patterns Suspicious for IgG4-related Disease: Can Lymph Nodes Be the Only Site of Disease?

Lymphadenopathy with increased immunoglobulin (Ig) G4 + plasma cells can be a nonspecific finding or a manifestation of immunoglobulin G4-related disease (IgG4-RD). It remains unclear whether there are characteristic pathologic features of IgG4-RD involving lymph nodes, or if IgG4-RD lymphadenopathy can occur without other manifestations of IgG4-RD. In this study, we assessed 55 lymph node biopsy specimens (44 men and 11 women with a mean age of 55 y) with increased IgG4 + plasma cells that had 1 of the 6 well-described pathologic patterns. We also correlated these findings with IgG4 serum levels and followed these patients for 7 to 108 months (mean, 34.9 mo) for the occurrence of extranodal IgG4-RD. We further compared lymphadenopathy in patients who developed other manifestations of IgG4-RD (RD + , n=20, 36%) versus those who did not (RD - , n=35, 64%). We found that there were only minor significant differences between 2 groups, including frequency of receiving treatment (RD + , 90% vs. RD - , 60%, P =0.021) and higher serum levels of C-reactive protein (>8 mg/L, RD + , 53% vs. RD - , 13%, P =0.007). Other differences were either borderline or not significant, including mean age (RD + , 59.8 y vs. RD - , 51.9 y, P =0.097), male-to-female ratio (RD + , 16:4 vs. RD - , 28:7, P =1), constitutional symptoms (RD + , 25% vs. RD - , 9%, P =0.096), multiple enlarged lymph nodes (RD + , 45% vs. RD - , 26%, P =0.143), good response to therapy (RD + , 94% vs. RD - , 94%, P =1); higher serum IgG4 levels (>280 mg/dL, RD + , 75% vs. RD - , 51%, P =0.086), anemia (RD + , 45% vs. RD - , 43%, P =0.877), leukopenia (RD + , 0% vs. RD - , 3%, P =0.446), thrombocytopenia (RD + , 10% vs. RD - , 6%, P =0.556), positivity for antinuclear antibody (RD + , 24% vs. RD - , 29%, P =0.688), elevated serum levels of lactate dehydrogenase (>225 U/L, RD + , 0% vs. RD - , 20%, P =0.064), elevated serum IgE level (>100 IU/mL, RD + , 75% vs. RD - , 92%, P =0.238), and hypergammaglobulinemia (RD + , 90% vs. RD - , 86%, P =0.754). There were also no differences in morphologic patterns ( P =0.466), IgG4 + cell location ( P =0.104), eosinophil counts (RD + , 10.3±11.3 vs. RD - , 13.4±17.5, P =0.496), Epstein-Barr virus positivity (RD + , 35% vs. RD - , 60%, P =0.074), and Epstein-Barr virus-positive cell location ( P =0.351). Our findings suggest that there are minimal differences between stringently defined IgG4-RD lymphadenopathy with versus without other manifestations of IgG4-RD. These findings also suggest the existence of IgG4-RD lymphadenopathy as the sole presentation of IgG4-RD.

Clinical value of plasmablasts in predicting disease relapse in patients with IgG4-related disease

OBJECTIVES

To explore the value of plasmablasts in predicting disease relapse in IgG4-related diseases (IgG4-RD).

METHODS

Treatment-naïve IgG4-RD patients treated with glucocorticoid (GC) monotherapy or leflunomide (LEF) and GC combination therapy diagnosed at the Chinese PLA General Hospital during February 2017 and January 2018 were included in this study. The absolute plasmablast count was measured by using the absolute count tubes with flow cytometry. Patients were categorized into high and low plasmablast level groups by defining the median number of plasmablasts as the cut-off value. The characteristics of the clinical manifestations between the two groups were compared. In addition, the correlation of plasmablast count with other indicators and its clinical value in predicting disease relapse were evaluated.

RESULTS

Data of 37 treatment-naïve IgG4-RD patients were analyzed. The median (IQR) absolute count of plasmablasts was 4.0 (2.8-7.5)/μL, which was correlated with the lymphocyte percentage, serum IgG, IgG4, and IgG4/IgG. The baseline absolute count of plasmablasts was an independent risk factor for disease relapse in IgG4-RD patients (HR, 1.199; 95% CI, 1.030-1.396, P = 0.019), and the application of LEF was an independent protective factor (HR, 0.283; 95% CI, 0.106-0.759, p = 0.012).

CONCLUSIONS

The present study preliminarily indicated that baseline absolute plasmablast count may independently predict disease relapse in patients with IgG4-RD treated with GC monotherapy or LEF and GC combination therapy. More efforts are still needed to be performed in the future. Key Points • The absolute count of plasmablasts is correlated with the lymphocyte percentage, serum IgG, IgG4 and IgG4/IgG. • The baseline absolute plasmablast count may predict disease relapse in patients with IgG4-RD treated with GC monotherapy or LEF and GC combination therapy. • The application of LEF is an independent protective factor for disease relapse in IgG4-RD.

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

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

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

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

Curcumin deactivates M2 macrophages to alleviate lung fibrosis in IgG4-related disease through activating the toll-like receptor 9 pathway

OBJECTIVES

To explore the effects and mechanism of Curcumin on pulmonary fibrosis in IgG4-related disease (IgG4-RD).

METHODS

The expression of fibrosis factors, inflammatory factors and markers of M1/M2 macrophages in lung tissue of IgG4-RD patients was detected by RT-qPCR or Western blotting. The macrophages of IgG4-RD patients were isolated and treated with different concentrations of Curcumin, and the markers of M1/M2 macrophages were detected by RT-qPCR, Western blotting or ELISA. Next, the pulmonary fibroblasts of IgG4-RD patients were isolated and cultured with the supernatant of macrophages treated with Curcumin. Cell proliferation and migration were detected by CCK-8 and Transwell assay, respectively. SOD activity and ROS content were detected by the xanthine oxidase method and flow cytometry, respectively. Then the expression of Toll-like Receptor 9 (TLR9) and its downstream proteins were detected by Western blotting. After treating the cells with TLR9 antagonist IRS869, the changes in the above indicators were further detected.

RESULTS

The collagen deposition, inflammatory factors secretion and M2 polarization of macrophages were increased in lung tissue of IgG4-RD patients. Curcumin decreased the macrophage M2 polarization and inhibited the proliferation and migration of fibroblasts, reduced the level of oxidative stress, and suppressed the occurrence of fibrosis. The TLR9 pathway was inhibited in IgG4-RD lung tissues, and Curcumin activated this pathway and reduced macrophage M2 polarization. And the inhibitory effect of Curcumin on pulmonary fibrosis could be reversed by IRS869.

CONCLUSIONS

Curcumin inhibited the occurrence of pulmonary fibrosis in IgG4-RD by inhibiting the TLR9 signaling pathway-mediated macrophage M2 polarization.

Peripheral B-Cell Immunophenotyping Identifies Heterogeneity in IgG4-Related Disease

Objectives

To elucidate heterogeneity of IgG4-related disease (IgG4-RD) based on B cell immunophenotyping.

Methods

Immunophenotyping of 4 B-cell subsets in peripheral blood from patients with active IgG4-RD (aIgG4-RD, n=105) was performed using flow cytometry to get preliminary B-cell heterogeneity spectrum. Then 10 B-cell subsets were characterized in aIgG4-RD (n = 49), remissive IgG4-RD (rIgG4-RD, n = 49), and healthy controls (HCs, n = 47), followed by principal components analysis (PCA) and cluster analysis to distinguish B-cell immunophenotypes and classify IgG4-RD patients into subgroups.

Results

Cluster analysis identified two endotypes in 105 aIgG4-RD patients based on 4 B-cell subsets: Group1 with higher Breg and naive B cells (n = 48), and Group2 with higher plasmablasts and memory B cells (MBCs) (n = 57). PCA indicated that aIgG4-RD consisted of plasmablast-naive B cell and MBCs-Breg axes abnormalities. There was a negative relationship between naive B cells and disease activity. Both plasmablasts and MBCs were positively associated with serological biomarkers. Cluster analysis stratified aIgG4-RD patients into 3 subgroups based on 10 B-cell subsets: subgroup1 with low MBCs and normal Breg, subgroup2 with high MBCs and low Breg, and subgroup3 with high plasmablasts and low naive B cells. Patients in subroup2 and subgroup3 were more likely to be resistant to treatment.

Conclusion

Patients with aIgG4-RD can be divided into 3 subgroups based on B cell heterogeneity. The B cell immunophenotyping could help elucidate the pathogenesis of IgG4-RD, identify patients with potential refractory IgG4-RD, and provide important information for the development of new therapies.

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.

Differential Tissue Metabolic Signatures in IgG4-Related Ophthalmic Disease and Orbital Mucosa-Associated Lymphoid Tissue Lymphoma

Purpose

To identify tissue metabolomic profiles in biopsy specimens with IgG4-related ophthalmic disease (IgG4-ROD) and mucosa-associated lymphoid tissue (MALT) lymphoma and investigate their potential implication in the disease pathogenesis and biomarkers.

Methods

We conducted a comprehensive analysis of the metabolomes and lipidomes of biopsy-proven IgG4-ROD (n = 22) and orbital MALT lymphoma (n = 21) specimens and matched adjacent microscopically normal adipose tissues using liquid chromatography time-of-flight mass spectrometry. The altered metabolomic profiles were visualized by heat map and principal component analysis. Metabolic pathway analysis was performed by Metabo Analyst 4.0 using differentially expressed metabolites. The diagnostic performance of the metabolic markers was evaluated using receiver operating characteristic curves. Machine learning algorithms were implemented by random forest using the R environment. Finally, an independent set of 18 IgG4-ROD and 17 orbital MALT lymphoma specimens were used to validate the identified biomarkers.

Results

The principal component analysis showed a significant difference of both IgG4-ROD and orbital MALT lymphoma for biopsy specimens and controls. Interestingly, lesions in IgG4-ROD were uniquely enriched in arachidonic metabolism, whereas those in orbital MALT lymphoma were enriched in tricarboxylic acid cycle metabolism. We identified spermine as the best discriminator between IgG4-ROD and orbital MALT lymphoma, and the area under the receiver operating characteristic curve of the spermine to discriminate between the two diseases was 0.89 (95% confidence interval, 0.803–0.984). A random forest model incorporating a panel of five metabolites showed a high area under the receiver operating characteristic curve value of 0.983 (95% confidence interval, 0.981–0.984). The results of validation revealed that four tissue metabolites: N¹,N¹²-diacetylspermine, spermine, malate, and glycolate, had statistically significant differences between IgG4-ROD and orbital MALT lymphoma with receiver operating characteristic values from 0.708 to 0.863.

Conclusions

These data revealed the characteristic differences in metabolomic profiles between IgG4-ROD and orbital MALT lymphoma, which may be useful for developing new diagnostic biomarkers and elucidating the pathogenic mechanisms of these common orbital lymphoproliferative disorders.

IgG4-Related Disease and the Salivary Glands: A Review of Pathophysiology, Diagnosis, and Management

IgG4-related disease is a rare, immune-mediated, systemic disease that is characterized by soft tissue lymphocyte infiltration and resultant fibrosis. The salivary glands are among the most commonly affected organs. Patients present with subacute submandibular and/or parotid swelling and sialadenitis. Diagnosis incorporates clinical, serologic, radiologic, and pathologic findings. Most cases respond quickly to systemic glucocorticoids. IgG4-related disease mimics many infectious, inflammatory, and neoplastic diseases. Therefore, IgG4-related disease is frequently misdiagnosed. A knowledge of the pathophysiology, diagnosis, and management of IgG4-related disease is important for providers who treat salivary gland diseases.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Imaging of IgG4-related disease in the extracranial head and neck

PURPOSE

Immunoglobulin G4-related disease (IgG4-RD) is a newly defined fibro-inflammatory multisystemic condition defined by a triad of diagnostic criteria based on clinical presentation, biochemical and histopathological findings. Whereas some subsites of this disease have been well described in the literature so far (e.g. pancreas, kidneys, retroperitoneum, salivary glands), more recently identified anatomical sites of involvement in the head and neck are less well understood (e.g. nose, paranasal sinuses).

METHOD

This pictorial review details the imaging appearances of extracranial IgG4-RD in the Head & Neck. Multimodality imaging appearance and features are presented, with reference to the published literature to date.

RESULTS

Following a subsite-based approach, we present both the most common and the more rarely encountered imaging patterns of IgG4-RD in the extracranial head and neck, along with the relevant differential diagnoses to consider. Our institutional experience not only cements what is already known in the existing literature on this topic, but also reveals new imaging features of IgG4-RD, notably in the sinonasal tract.

CONCLUSIONS

This pictorial review of extracranial head & neck IgG4-RD will enable radiologists to recognise the features of this condition and propose it as a differential diagnosis to include alongside other probable entities. It establishes the place of the radiologist in the diagnosis and management of IgG4-RD.

CD4+CTLs in Fibrosing Mediastinitis Linked to Histoplasma capsulatum

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

Long-term effects of intensive B cell depletion therapy in severe cases of IgG4-related disease with renal involvement

IgG4-related disease (IgG4-RD) is an immune-mediated disorder often showing elevated serum IgG4 concentrations, dense T and B lymphocyte infiltration, and IgG4-positive plasma cells and storiform fibrosis. We prospectively evaluated for 4 years 5 patients with histologically proven IgG4-RD of whom 3 had tubulointerstitial nephritis (TIN) and 2 had retroperitoneal fibrosis (RPF). They received an intensive B depletion therapy with rituximab. The estimated glomerular filtration rate of TIN patients after 1 year increased from 9 to 24 ml/min per 1.73 m2. IgG/IgG4 dropped from 3236/665 to 706/51 mg/dl, C3/C4 went up from 49/6 to 99/27 mg/dl, and the IgG4-RD responder index fell from 10 to 1. CD20+ B cells decreased from 8.7 to 0.5%. A striking drop in interstitial plasma cell infiltrate as well as normalization of IgG4/IgG-positive plasma cells was observed at repeat biopsy. Both clinical and immunological improvement persisted over a 4-year follow-up. Treating these patients who were affected by aggressive IgG4-RD with renal involvement in an effort to induce a prolonged B cells depletion with IgG4 and cytokine production decrease resulted in a considerable rise in eGFR, with IgG4-RD RI normalization and a noteworthy improvement in clinical and histological features. Furthermore, the TIN subgroup was shown not to need for any maintenance therapy.

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.

Distinctive Tissue and Serum MicroRNA Profile of IgG4-Related Ophthalmic Disease and MALT Lymphoma

The molecular pathogenesis of orbital lymphoproliferative disorders, such as immunoglobulin G4-related ophthalmic disease (IgG4-ROD) and orbital mucosa-associated lymphoid tissue (MALT) lymphoma, remains essentially unknown. Differentiation between the two disorders, which is important since the work-up and treatment can vary greatly, is often challenging due to the lack of specific biomarkers. Although miRNAs play an important role in the regulation of carcinogenesis and inflammation, the relationship between miRNA and orbital lymphoproliferative diseases remains unknown. We performed a comprehensive analysis of 2565 miRNAs from biopsy and serum specimens of 17 cases with IgG4-ROD, where 21 cases with orbital MALT lymphoma were performed. We identified specific miRNA signatures and their miRNA target pathways, as well as the network analysis for IgG4-ROD and orbital MALT lymphoma. Machine-learning analysis identified miR-202-3p and miR-7112-3p as the best discriminators of IgG4-ROD and orbital MALT lymphoma, respectively. Enrichment analyses of biological pathways showed that the longevity-regulating pathway in IgG4-ROD and the mitogen-activated protein kinase (MAPK) signaling pathway in orbital MALT lymphoma was most enriched by target genes of downregulated miRNAs. This is the first evidence of miRNA profiles of biopsy and serum specimens of patients with IgG4-ROD and orbital MALT lymphoma. These data will be useful for developing diagnostic and therapeutic interventions, as well as elucidating the pathogenesis of these disorders.

[IgG4-related disease: Diagnostic criteria evolution toward the 2019 ACR/EULAR classification criteria]

The concept of IgG4-related disease (IgG4-RD) has recently been individualized in the early 2000s, but most of the organ involvements are known since more than 100 years. IgG4-RD is a non-malignant fibroinflammatory disorder, characterized by peculiar immunological and pathological abnormalities, which can affect virtually all organs or tissues. Diagnostic criteria have been proposed and have evolved rapidly, with general or organ specific criteria. An international and multidisciplinary group assembled by the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) has recently developed and validated a set of classification criteria called 2019 ACR/EULAR classification criteria for IgG4-related disease. The objective of this review is to discuss the evolution from organ specific and general diagnostic criteria toward the 2019 ACR/EULAR classification criteria, as well as respective benefits and limits of these criteria. The use of the 2019 ACR/EULAR classification criteria will help to better define homogeneous group of IgG4-RD patients in future clinical, epidemiological and basic science research studies on the disease.

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.

Advances in the diagnosis and management of IgG4 related disease

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

[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.