Single-cell transcriptome analysis and protein profiling reveal broad immune system activation in IgG4-related disease

Submandibular gland tissue RNAseq and spatial transcriptome analyses in IgG4-related disease

OBJECTIVE

To identify genes that could provide clues leading to the discovery of drugs to treat IgG4-related disease (IgG4-RD).

METHODS

Submandibular gland tissue bulk RNAseq analysis of 45 cases with a definite diagnosis of IgG4-RD was integrated with Visium spatial transcriptome analysis of two cases to identify pathogenic genes expressed in tertiary lymphoid tissues.

RESULTS

Bulk RNAseq and pathway analyses showed upregulation of cell cycle and T cell-related signals in IgG4-RD. Spatial transcriptome analysis identified the cluster corresponding to germinal centres and the top 38 common genes that showed significant variations in expression compared with other clusters. The top 20 genes were extracted by comparing the bulk RNAseq data. Network analysis identified CDK1 as the gene most strongly associated of the top 20 genes.

CONCLUSION

The CDK1 gene may be a regulator of the pathogenesis of IgG4-RD and provide clues for drug discovery.

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

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

Successful rituximab treatment in IgG4-related coronary periarteritis: a case-based review

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated disorder characterized by elevated serum IgG4 levels and the enlargement and fibrosis of organs. As a rare manifestation, coronary arteries can be affected by IgG4-RD as coronary periarteritis, leading to serious complications such as stenosis or aneurysm. Although coronary periarteritis poses a life-threatening condition, optimal treatment strategies remain unclear due to its extreme rarity. While glucocorticoids have shown efficacy in several reported cases of IgG4-related coronary periarteritis, many cases experience relapse during glucocorticoid tapering. Furthermore, long-term use of glucocorticoids promotes atherosclerosis and increases the risk of major adverse cardiovascular events. Given that rituximab has been reported to be effective in treating IgG4-RD, it may be a potential treatment option for this condition. We present a case of IgG4-related coronary periarteritis, in which the patient achieved and maintained remission with rituximab. Furthermore, our review of the literature identified 17 cases of IgG4-related coronary periarteritis, all of which were successfully treated with rituximab. These findings suggest that rituximab serves as a viable option for both induction and maintenance therapy in IgG4-related coronary periarteritis.

Omics in IgG4-related disease

ABSTRACT

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

Pathogenic roles of follicular helper T cells in IgG4-related disease and implications for potential therapy

IgG4-related disease (IgG4-RD) is a recently described autoimmune disorder characterized by elevated serum IgG4 levels and tissue infiltration of IgG4+ plasma cells in multiple organ systems. Recent advancements have significantly enhanced our understanding of the pathological mechanism underlying this immune-mediated disease. T cell immunity plays a crucial role in the pathogenesis of IgG4-RD, and follicular helper T cells (Tfh) are particularly important in germinal center (GC) formation, plasmablast differentiation, and IgG4 class-switching. Apart from serum IgG4 concentrations, the expansion of circulating Tfh2 cells and plasmablasts may also serve as novel biomarkers for disease diagnosis and activity monitoring in IgG4-RD. Further exploration into the pathogenic roles of Tfh in IgG4-RD could potentially lead to identifying new therapeutic targets that offer more effective alternatives for treating this condition. In this review, we will focus on the current knowledge regarding the pathogenic roles Tfh cells play in IgG4-RD and outline potential therapeutic targets for future clinical intervention.

Remodeling of T-cell mitochondrial metabolism to treat autoimmune diseases

T cells are key drivers of the pathogenesis of autoimmune diseases by producing cytokines, stimulating the generation of autoantibodies, and mediating tissue and cell damage. Distinct mitochondrial metabolic pathways govern the direction of T-cell differentiation and function and rely on specific nutrients and metabolic enzymes. Metabolic substrate uptake and mitochondrial metabolism form the foundational elements for T-cell activation, proliferation, differentiation, and effector function, contributing to the dynamic interplay between immunological signals and mitochondrial metabolism in coordinating adaptive immunity. Perturbations in substrate availability and enzyme activity may impair T-cell immunosuppressive function, fostering autoreactive responses and disrupting immune homeostasis, ultimately contributing to autoimmune disease pathogenesis. A growing body of studies has explored how metabolic processes regulate the function of diverse T-cell subsets in autoimmune diseases such as systemic lupus erythematosus (SLE), multiple sclerosis (MS), autoimmune hepatitis (AIH), inflammatory bowel disease (IBD), and psoriasis. This review describes the coordination of T-cell biology by mitochondrial metabolism, including the electron transport chain (ETC), oxidative phosphorylation, amino acid metabolism, fatty acid metabolism, and one‑carbon metabolism. This study elucidated the intricate crosstalk between mitochondrial metabolic programs, signal transduction pathways, and transcription factors. This review summarizes potential therapeutic targets for T-cell mitochondrial metabolism and signaling in autoimmune diseases, providing insights for future studies.

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.