Extrafollicular IgD-CD27-CXCR5-CD11c- DN3 B cells infiltrate inflamed tissues in autoimmune fibrosis and in severe COVID-19

IgG4-related disease and other fibro-inflammatory conditions

IgG4-related disease (IgG4-RD) is a fibro-inflammatory disorder usually characterized by multi-organ involvement. Its pathogenesis is complex and involves genetic and environmental factors, while immune responses usually mediate organ damage and promote fibrosis, which is a key feature of the disease. IgG4 responses, however, are not exclusive to IgG4-RD and can be encountered in other diseases with phenotypes that partially overlap that of IgG4-RD. Although IgG4-RD has clinical and histological hallmarks, the lack of validated diagnostic criteria often makes the diagnosis challenging, requiring a multi-dimensional approach that integrates clinical, radiological and serological data. The present Review covers recent advances in the understanding of disease drivers and its clinical phenotypes, mainly focusing on the differential diagnosis with potential IgG4-RD mimickers, namely histiocytoses, lymphoproliferative disorders, systemic vasculitides and other immune-mediated conditions. The Review also provides a schematic approach to IgG4-RD treatment, including a brief overview of glucocorticoid-sparing agents and emerging therapies, from B cell-depleting monoclonal antibodies to cytokine-targeting drugs, the majority of which are currently under investigation in randomized clinical trials.

The regulatory functions of G protein-coupled receptors signaling pathways in B cell differentiation and development contributing to autoimmune diseases

Autoimmune diseases are characterized by a dysfunction of the immune system. Disruptions in the balance of B-cell dynamics and the increase in auto-antibody levels are pivotal in the triggering of several autoimmune disorders. All of this is inextricably linked to the differentiation, development, migration, and functional regulation of B cells in the human immune response. G protein-coupled receptors (GPCR) are recognized as crucial targets in drug development and play pivotal roles in both B cell differentiation and the underlying mechanisms of autoimmune diseases. However, there has been an inadequate comprehension of how GPCR intricately modulate B cell development and impact the pathogenesis of autoimmune diseases. Ligands and functions of GPCR-chemokine receptors including CXCR3, CXCR4, CXCR5 and CCR7, lipid receptors including S1PR1-5, cannabinoid receptor CB2 as well as orphan GPCR including GPR132, GPR183, GPR174, and P2RY8 in B cell differentiation and development, will be elaborated in this review. The roles these GPCR play in mediating B cells in several autoimmune diseases will also be discussed. The elucidation of the multifaceted mechanisms controlled by GPCR not only enriches our comprehension of immune responses but also provides a promising avenue for therapeutic interventions in the domain of autoimmune disorders.

The role of double-negative B cells in the pathogenesis of systemic lupus erythematosus

B cells are essential to the pathophysiology of systemic lupus erythematosus (SLE), a chronic autoimmune illness. IgD-CD27-double negative B cells (DNB cells) are one of the aberrant B cell subsets linked to SLE that have attracted much scientific interest. There is growing evidence that DNB cells play a significant role in the development of the disease and are strongly linked to the activity of lupus. These cells play a pivotal role in the pathogenesis of SLE by producing a diverse array of autoantibodies, which form immune complexes that drive target organ damage. A comprehensive understanding of SLE pathophysiology necessitates in-depth investigation into DNB cells, not only to elucidate their mechanistic contributions but also to uncover novel therapeutic strategies. According to available data, treatments that target B cells have proven effective in managing SLE; nevertheless, a significant breakthrough in precision medicine for SLE may come from targeting DNB cells specifically. Despite growing interest in DNB cells, their precise characteristics, developmental trajectories, and regulatory mechanisms remain incompletely defined, posing significant challenges to the field. A comprehensive investigation of the regulatory mechanisms governing DNB cell differentiation and expansion in SLE may facilitate novel therapeutic discoveries. This review aims to provide an updated synthesis of current research on DNB cells, with a focus on their origins, developmental trajectories in SLE, and potential as precision therapeutic targets.

Two distinct durable human class-switched memory B cell populations are induced by vaccination and infection

Memory lymphocytes are durable cells that persist in the absence of antigen, but few human B cell subsets have been characterized in terms of durability. The relative durability of eight non-overlapping human B cell sub-populations covering 100% of all human class-switched B cells was interrogated. Only two long-lived B cell populations persisted in the relative absence of antigen. In addition to canonical germinal center-derived switched-memory B cells with an IgD-CD27+CXCR5+ phenotype, a second, non-canonical, but distinct memory population of IgD-CD27-CXCR5+ DN1 B cells was also durable, exhibited a unique TP63-linked transcriptional and anti-apoptotic signature, had low levels of somatic hypermutation, but was more clonally expanded than canonical switched-memory B cells. DN1 B cells likely evolved to preserve immunological breadth and may represent the human counterparts of rodent extrafollicular memory B cells that, unlike canonical memory B cells, can enter germinal centers and facilitate B cell and antibody evolution.

Dysfunctional CD11c-CD21- extrafollicular memory B cells are enriched in the periphery and tumors of patients with cancer

Many patients with recurrent and metastatic cancer fail to produce a durable response to immunotherapy, highlighting the need for additional therapeutic targets to improve the immune landscape in tumors. Recent studies have highlighted the importance of B cells in the antitumor response, with memory B cells (MBCs) being prognostic in a variety of solid tumors. MBCs are a heterogenous B cell subset and can be generated through both germinal center reactions and extrafollicular (EF) responses. EF-derived MBCs have been recently linked to poor prognosis and treatment resistance in solid tumors and thus may represent candidate biomarkers or immunotherapy targets. EF-derived MBCs, termed "double-negative" (DN) MBCs may be further classified on the basis of surface expression of CD11c and CD21 into DN1, DN2, and DN3 MBCs. CD11c-CD21+ DN1 MBCs and CD11c+CD21- DN2 MBCs have been well studied across inflammatory diseases; however, the biology and clinical relevance of CD11c-CD21- DN3 MBCs remain unknown. Here, we report an accumulation of DN3 MBCs in the blood and tumors of patients with head and neck squamous cell carcinoma (HNSCC) and an increase in DN3 MBCs in locally advanced HNSCC tumors. Circulating and intratumoral DN3 MBCs were hyporesponsive to antigen stimulation, had low antibody production, and failed to differentiate into antibody-secreting cells. Moreover, DN3 MBCs accumulated selectively outside of tertiary lymphoid structures. Last, circulating DN3 MBCs correlated with poor therapeutic response, advanced disease, and worse outcomes in patients with HNSCC and melanoma, supporting further assessment of EF-derived MBCs as potential biomarkers and therapeutic targets.

B cells in non-lymphoid tissues

B cells have long been understood to be drivers of both humoral and cellular immunity. Recent advances underscore this importance but also indicate that in infection, inflammatory disease and cancer, B cells function directly at sites of inflammation and form tissue-resident memory populations. The spatial organization and cellular niches of tissue B cells have profound effects on their function and on disease outcome, as well as on patient response to therapy. Here we review the role of B cells in peripheral tissues in homeostasis and disease, and discuss the newly identified cellular and molecular signals that are involved in regulating their activity. We integrate emerging data from multi-omic human studies with experimental models to propose a framework for B cell function in tissue inflammation and homeostasis.

Elucidating the causal associations and mechanisms between circulating immune cells and idiopathic pulmonary fibrosis: new insights from Mendelian randomization and transcriptomics

Background

Growing evidence indicates an association between circulating immune cell phenotypes and idiopathic pulmonary fibrosis (IPF). Although studies have attempted to elucidate the causal relationship between the two, further clarification of the specific mechanisms and causal linkages is warranted.

Objective

We aimed to conduct a two-sample Mendelian randomization (MR) analysis with transcriptomics data analysis to elucidate the causal relationship between circulating immune cells and IPF and to explore potential biomarkers.

Methods

We first explored the bidirectional causal association between IPF and immune cell phenotypes using two-sample MR analysis. Genome-wide association studies data for immune cell phenotype and IPF were obtained from publicly available databases. A standardized instrumental variable screening process was used to select single nucleotide polymorphisms (SNPs) for inclusion in the MR. Five methods represented by IVW were used to assess causal effects. Subsequently, SNP-nearest genes combined with the transcriptomics data of IPF were subjected to multiple bioinformatics analyses such as TIMER, WGCNA, functional enrichment analysis, protein-protein interaction analysis, and ROC to identify IPF biomarkers. Finally, the single-cell RNA sequencing (scRNA-seq) data was used to validate our findings by single-cell analysis.

Results

The MR study identified 27 immune cell phenotypes causally associated with IPF, of which 20 were associated with a decreased risk of developing IPF and 7 were associated with an increased risk. CTSB (AUC=0.98), IL10 (AUC=0.83), and AGER (AUC=0.87) were identified as promising biomarkers of IPF. Single cell analysis showed differences in CD14+ CD16+ monocytes, CD16+ monocytes and Granulocyte-monocyte progenito between the IPF group and the healthy control group. The three hub genes were highly expressed in three immune cell subsets of IPF patients. It underscores the potential feasibility of three genes as biomarkers.

Conclusions

Our study demonstrates the causal associations of specific immune cell phenotypes with IPF through genetic methods and identifies CTSB, IL10, and AGER as biomarkers of IPF through bioinformatics analysis. These findings provide guidance for future clinical and basic research.

Disease-associated B cells and immune endotypes shape adaptive immune responses to SARS-CoV-2 mRNA vaccination in human SLE

Severe acute respiratory syndrome coronavirus 2 mRNA vaccination has reduced effectiveness in certain immunocompromised individuals. However, the cellular mechanisms underlying these defects, as well as the contribution of disease-induced cellular abnormalities, remain largely unexplored. In this study, we conducted a comprehensive serological and cellular analysis of patients with autoimmune systemic lupus erythematosus (SLE) who received the Wuhan-Hu-1 monovalent mRNA coronavirus disease 2019 vaccine. Our findings revealed that patients with SLE exhibited reduced avidity of anti-receptor-binding domain antibodies, leading to decreased neutralization potency and breadth. We also observed a sustained anti-spike response in IgD-CD27- 'double-negative (DN)' DN2/DN3 B cell populations persisting during memory responses and with greater representation in the SLE cohort. Additionally, patients with SLE displayed compromised anti-spike T cell immunity. Notably, low vaccine efficacy strongly correlated with higher values of a newly developed extrafollicular B and T cell score, supporting the importance of distinct B cell endotypes. Finally, we found that anti-BAFF blockade through belimumab treatment was associated with poor vaccine immunogenicity due to inhibition of naive B cell priming and an unexpected impact on circulating T follicular helper cells.

Subset of DN Memory B Cells Expressing Low Levels of Inhibitory Receptor BTLA Is Enriched in SLE Patients

The dialogue between T and B cells can be regulated by different mechanisms, such as co-inhibitory receptors, which therefore play a crucial role in preventing autoimmune diseases such as systemic lupus erythematosus (SLE). B and T lymphocyte attenuator (BTLA) is a co-inhibitory receptor expressed on many myeloid and lymphoid cells. Although peripheral B cells express a very high amount of BTLA, previous works in the context of autoimmunity mainly focused on T cells, and whether BTLA expression on B cells plays a role in the lupus pathogenesis is still unclear. In the present study, we examine the expression of BTLA, as well as its ligand HVEM (Herpesvirus Entry Mediator), on various B cell subsets in lupus patients compared to healthy controls (HCs). We evidenced the existence of double-negative (DN; IgD-CD27-) memory B cells expressing very low levels of BTLA, which are enhanced in active lupus patients. An in-depth analysis revealed that these BTLAlow DN cells mainly correspond to the newly reported DN3 B cell subset, originally described in the context of SARS-CoV2 infection. These cells display an activated and antibody-secreting cell phenotype, and we propose that their low BTLA expression may favor their expansion and rapid differentiation into plasmablasts in lupus patients.

Extrafollicular CD19lowCXCR5-CD11c- double negative 3 (DN3) B cells are significantly associated with disease activity in females with systemic lupus erythematosus

Objective

B cells play a major role in the development and maintenance of systemic lupus erythematosus (SLE). Double negative (DN) B cells defined by the lack of surface expression of IgD and CD27 have attracted recent interest for their sensitivity to Toll-like receptor 7 (TLR7) ligands and their potential role in the production of autoantibodies. Here we aimed at investigating the possible association of DN B cells and their subsets with SLE disease activity specifically in female patients, in which TLR7 gene has been reported to escape X chromosome inactivation.

Methods

Peripheral blood mononuclear cells were purified from woman participating to the clinically well-characterized Swiss SLE Cohort Study (SSCS). PBMC from age-matched healthy females were used as controls. PBMC were stained for cell surface markers, intracellular Tbet and analyzed by multicolor cytofluorimetry. Single nucleotide TLR7 polymorphisms were assessed by polymerase chain reaction.

Results

The median SLE disease activity index of the 86 females was 2, IQR [0-6], all but 8 were under chronic SLE treatment. B cells co-expressing CD11c and Tbet were increased, the mean fluorescence intensity (MFI) of CD19 was considerably reduced and we observed a large increase in CD11c + CXCR5-and CD11c-CXCR5-concomitantly with a reduction of CD11c-CXCR5+ B cells in SLE compared to 40 healthy donors (HD). When focusing on the DN B cell subset, we found a reduction of DN1 (CD11c-CXCR5+) and an increase of DN2 (CD11c + CXCR5-) and most impressively of DN3 (CD11c-CXCR5-) cells. The DN subset, particularly DN3, showed the lowest level of CD19 expression. Both DN1 and DN3 percentages as well as the CD19 MFI of DN cells were associated with SLE disease activity. The use of glucocorticoids, immunosuppressants, and antimalarials impacted differentially on the frequencies of DN B cell subsets. CD19 MFI in B cells and the percentage of DN3 were the strongest biomarkers of disease activity. The TLR7 snp3858384 G allele was associated with increased percentages of B cells and CD19+CD11c-CXCR5+ and decreased CD19+CD11c-CXCR5-.

Conclusions

DN3 B cells are strongly associated with SLE clinical activity pointing to their potential involvement in disease pathogenesis, and CD19 expression level performs accurately as disease activity biomarker.

Possible involvement of Toll-like receptor 8-positive monocytes/macrophages in the pathogenesis of Sjögren's disease

Background

Sjögren's disease (SjD) is an autoimmune disease marked by lymphocytic infiltration of salivary and lacrimal glands, leading to glandular dysfunction, where CD4-positive helper T (Th) cells and their cytokines are crucial in the pathogenesis. Recent studies have demonstrated that Toll-like receptors (TLRs), particularly those recognizing immune complexes containing DNA and RNA, contribute to Th cell activation in various autoimmune diseases. This study explores the expression and function of these TLRs in SjD.

Methods

DNA microarray analysis of salivary gland tissue from six SjD patients and real-time PCR (n = 32) was used to identify overexpressed TLRs. Single-cell RNA sequencing (scRNA-seq) was performed using tissue lesions and integrated with published scRNA-seq data from tissues and peripheral blood mononuclear cells to examine gene expression in macrophages and monocytes. Finally, multi-color immunofluorescence staining was conducted to confirm TLR8 expression and function in SjD lesions (n = 19).

Results

DNA microarray analysis revealed the up-regulation of TLR8, along with other TLRs and innate immune response genes in SjD. Real-time PCR showed significant up-regulation of TLR7 and TLR8. TLR8 up-regulated in both analyses. In scRNA-seq analysis, the TLR8-expressing cluster comprised macrophages and monocytes, which also produced T cell activation genes like CD86. TLR8-positive macrophages infiltrated inflammatory sites and frequently expressed CD86 in quantitative imaging approaches.

Conclusions

These results suggest that infiltrating monocytes and macrophages may produce cytokines and chemokines through TLR8 stimulation, potentially enhancing B7 molecule expression, promoting the adaptive immune response, and contributing to SjD pathogenesis.

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.

Fibrotic phenotype of IgG4-related disease

A prompt response to glucocorticoids is a clinical hallmark of IgG4-related disease. However, manifestations characterised by prominent tissue fibrosis on histological examination can be less responsive to glucocorticoid therapy than other types of IgG4-related disease. These manifestations include retroperitoneal fibrosis, fibrosing mediastinitis, Riedel thyroiditis, orbital pseudotumor, and hypertrophic pachymeningitis, among others. To explain this discrepancy, a preliminary distinction into proliferative and fibrotic phenotypes of IgG4-related disease has been proposed on the basis of clinical presentation, pathological features, and response to immunosuppressive therapy. Implications of this classification for patient management remain an important area of investigation. In this Series paper, we aim to dissect the pathophysiology of tissue fibrosis in IgG4-related disease and discuss how clinicians should approach the management of fibrotic manifestations of IgG4-related disease based on the most recent diagnostic and therapeutic developments.

Sex as a predictor of clinical phenotype and determinant of immune response in IgG4-related disease: a retrospective study of patients fulfilling the American College of Rheumatology-European League Against Rheumatism classification criteria

BACKGROUND

IgG4-related disease is a multiorgan fibroinflammatory disease considered to have an autoimmune origin. Case series describing individual organ involvement have suggested differences in phenotypic expression between males and females. We aimed to characterise differences in IgG4-related disease manifestations between male and female patients in a large single-centre cohort.

METHODS

In this retrospective, single-centre cohort study, patients were recruited from the Massachusetts General Hospital Rheumatology Clinic (Boston, MA, USA) and classified according to the American College of Rheumatology-European Alliance of Associations for Rheumatology (ACR-EULAR) classification criteria. Only patients satisfying the ACR-EULAR classification criteria were included in the study. Data on age at diagnosis, organ involvement at baseline, treatment status, and pre-treatment laboratory values were collected. Circulating plasmablasts and B-cell subsets were quantitated by flow cytometry. Active disease was defined by an IgG4-related disease Responder Index score of more than 0. Laboratory values were analysed for patients who were untreated at baseline and had active IgG4-related disease. The main outcomes were assessed in all participants with available data.

FINDINGS

Of the 564 participants enrolled in the Massachusetts General Hospital Rheumatology Clinic IgG4-related disease Registry, 328 fulfilled ACR-EULAR classification criteria and were included between January, 2008, and May, 2023. There was a strong male predominance (male:female ratio 2·2:1) with 226 (69%) males and 102 (31%) females, which contrasted markedly with our general rheumatology clinic population (0·4:1; p<0·001). The male predominance increased with each decade of life starting at age 40 years. On average, male patients were 5·5 years older at diagnosis than female patients (63·7 years vs 58·2 years; p=0·0031). We observed male patients to have higher ACR-EULAR classification criteria scores at baseline with a median score of 35·0 (IQR 28·0-46·0), compared with 29·5 (25·0-39·0) for females (p=0·0010). The proportion of male patients with pancreatic and renal involvement was almost double the proportion observed in female patients (50% of the male patients had pancreatic involvement, compared with about 26% of the female patients; p<0·0001). Male patients were more likely to have serological abnormalities at baseline. The distribution of IgG4 values differed significantly between male an female sexes, favouring higher values in males. We found that male patients with IgG4-related disease were more likely to have active B-cell responses in the blood as defined by plasmablast expansions.

INTERPRETATION

IgG4-related disease is unusual among autoimmune diseases in that it is more likely to affect males than females and to present with a striking sex-dependent organ distribution and degree of B-cell response. These findings highlight important variation between IgG4-related disease and other conditions generally believed to have an autoimmune basis. Most autoimmune diseases, by contrast to IgG4-related disease, demonstrate pronounced predilections for affecting females more frequently than males. Hypotheses surrounding the cause and pathophysiology of this condition need to consider this unusual sex distribution among patients with IgG4-related disease.

FUNDING

National Institutes of Health, National Institute of Allergy and Infectious Diseases, Rheumatology Research Foundation, and the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

Proliferative features of IgG4-related disease

IgG4-related disease is an immune-mediated disease that can lead to substantial morbidity and organ damage. Capable of affecting nearly any organ system or anatomic site, and showing considerable overlap in clinical presentation with various other diseases, IgG4-related disease often poses a diagnostic challenge for clinicians. Furthermore, there are no diagnostic biomarkers with high specificity for IgG4-related disease, and histopathological examination is nuanced and requires clinical correlation for accurate diagnosis. Therefore, it is crucial for clinicians to recognise the clinical phenotypes of IgG4-related disease. The disease is generally considered to have predominantly fibrotic and proliferative (or inflammatory) manifestations, with distinct clinical, serological and histopathological findings associated with each manifestation. However, the fibrotic and proliferative manifestations of this disease frequently occur together, thereby blurring this dichotomous distinction. In this Series paper, we provide a detailed overview of the clinical manifestations typical of the proliferative features of IgG4-related disease, with an emphasis on the diagnostic evaluation and differential diagnosis of each proliferative disease manifestation. In addition, we summarise the immune mechanisms underlying IgG4-related disease, suggest a framework for how to approach management and monitoring after the diagnosis is established, and highlight current unmet needs for patient care surrounding this disease.

Expansion of HLA-DR Positive Peripheral Helper T and Naive B Cells in Anticitrullinated Protein Antibody-Positive Individuals At Risk for Rheumatoid Arthritis

OBJECTIVE

To investigate immune dysregulation in the peripheral blood that contributes to the pre-rheumatoid arthritis (RA) stage of RA development in anticitrullinated protein antibody (ACPA)+ individuals.

METHODS

Using 37 markers by mass cytometry, we investigated peripheral blood mononuclear cells (PBMCs) from ACPA+ at-risk individuals, ACPA+ early untreated patients with RA, and ACPA- controls in the Tokyo Women's Medical University cohort (n = 17 in each group). Computational algorithms, FlowSOM and Optimized t-Distributed Stochastic Neighbor Embedding, were employed to explore specific immunologic differences between study groups. These findings were further evaluated, and longitudinal changes were explored, using flow cytometry and PBMCs from the US-based Targeting Immune Responses for Prevention of RA cohort that included 11 ACPA+ individuals who later developed RA (pre-RA), of which 9 had post-RA diagnosis PBMCs (post-RA), and 11 ACPA- controls.

RESULTS

HLA-DR+ peripheral helper T (Tph) cells, activated regulatory T cells, PD-1hi CD8+ T cells, and CXCR5-CD11c-CD38+ naive B cells were significantly expanded in PBMCs from at-risk individuals and patients with early RA from the Tokyo Women's Medical University cohort. Expansion of HLA-DR+ Tph cells and CXCR5-CD11c-CD38+ naive B cells was likewise found in both pre-RA and post-RA time points in the Targeting Immune Responses for Prevention of RA cohort.

CONCLUSION

The expansion of HLA-DR+ Tph cells and CXCR5-CD11c-CD38+ naive B cells in ACPA+ individuals, including those who developed inflammatory arthritis and classified RA, supports a key role of these cells in transition from pre-RA to classified RA. These findings may identify a new mechanistic target for treatment and prevention in RA.

Novel B-cell subsets as potential biomarkers in idiopathic inflammatory myopathies: insights into disease pathogenesis and disease activity

Idiopathic inflammatory myopathies are a heterogeneous group of rare autoimmune disorders characterized by progressive muscle weakness and the histopathologic findings of inflammatory infiltrates in muscle tissue. Although their pathogenesis remains indefinite, the association of autoantibodies with clinical manifestations and the evidence of high effectiveness of depleting therapies suggest that B cells could be implicated. Therefore, we explored the landscape of peripheral B cells in this disease by multiparametric flow cytometry, finding significant numerical decreases in memory and double-negative subsets, as well as an expansion of the naive compartment relative to healthy controls, that contribute to defining disease-associated B-cell subset signatures and correlating with different clinical features of patients. Additionally, we determined the potential value of these subsets as diagnostic biomarkers, thus positioning B cells as neglected key elements possibly participating in idiopathic inflammatory myopathy onset or development.

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.

COVID-19 in Systemic Lupus Erythematosus patients treated with belimumab: a retrospective clinical study

BACKGROUND

Routine use of immunosuppressive agents in systemic lupus erythematosus (SLE) patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) potentially increases the risk of adverse outcomes. belimumab, a monoclonal antibody for the treatment of SLE, remains untested for its specific impact on coronavirus disease 2019 (COVID-19) symptoms in these patients. Here, this research investigated the effect of belimumab on COVID-19 symptoms in SLE patients infected with SARS-CoV-2.

METHODS

This study enrolled SLE patients who underwent treatment with belimumab. After thorough screening based on the inclusion and exclusion criteria, data pertaining to COVID-19 for both the participants and their cohabitants were obtained through telephone follow-up. The potential impact of belimumab on COVID-19 was evaluated by comparing COVID-19 symptoms and medication use across various groups to investigate the association between belimumab treatment and COVID-19 in SLE.

RESULTS

This study involved 123 SLE patients, of whom 89.4% tested positive for SARS-CoV-2. Among cohabitants of SLE patients, the SARS-CoV-2 positive rate was 87.2% (p = 0.543). Patients treated with belimumab exhibited a lower incidence of multiple COVID-19 symptoms than their cohabitating counterparts (p < 0.001). This protective effect was found to be partially related to the time of last belimumab administration. Among those with COVID-19, 30 patients opted to discontinue their anti-SLE drugs, and among them, 53% chose to discontinue belimumab. Discontinuing drugs did not increase the risk of hospitalization due to SARS-CoV-2 infection.

CONCLUSION

This study concluded that treatment with belimumab did not increase susceptibility to COVID-19 and beneficially alleviated the symptoms of COVID-19.

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.

Systems biology of B cells in COVID-19

The integration of multi-'omic datasets into complex systems-wide assessments has become a mainstay in immunologic investigation. This focus on high-dimensional data collection and analysis was on full display in the investigation of COVID-19, the respiratory illness resulting from infection by the novel coronavirus SARS-CoV-2. Particularly in the area of B cell biology, tremendous efforts in both cellular and serologic investigation have resulted in an increasingly detailed mapping of the coordinated effector, memory, and antibody secreting cell responses that underpin the development of humoral immunity in response to primary viral infection. Further, the rapid development and deployment of effective vaccines has allowed for the assessment of developing memory responses across a wide variety of immune contexts, including in patients with compromised immune function. The result has been a period of rapid gains in the understanding of B cell biology unrestricted to the study of COVID-19. Here, we outline the systems-level technologies that have been routinely implemented in these investigations throughout the pandemic, and discuss how their use has led to clear and applicable gains in pursuance of the amelioration of human infectious disease and beyond.

Single-cell RNA sequencing of submandibular gland reveals collagen type XV-positive fibroblasts as a disease-characterizing cell population of IgG4-related disease

OBJECTIVES

IgG4-related disease (IgG4-RD) is a systemic autoimmune disease with an unknown etiology, affecting single/multiple organ(s). Pathological findings include the infiltration of IgG4-producing plasma cells, obliterative phlebitis, and storiform fibrosis. Although immunological studies have shed light on the dysregulation of lymphocytes in IgG4-RD pathogenesis, the role of non-immune cells remains unclear. This study aimed to investigate the demographics and characteristics of non-immune cells in IgG4-RD and explore potential biomarkers derived from non-immune cells in the sera.

METHODS

We conducted single-cell RNA sequence (scRNA-seq) on non-immune cells isolated from submandibular glands of IgG4-RD patients. We focused on fibroblasts expressing collagen type XV and confirmed the presence of those fibroblasts using immunohistochemistry. Additionally, we measured the levels of collagen type XV in the sera of IgG4-RD patients.

RESULTS

The scRNA-seq analysis revealed several distinct clusters consisting of fibroblasts, endothelial cells, ductal cells, and muscle cells. Differential gene expression analysis showed upregulation of COL15A1 in IgG4-RD fibroblasts compared to control subjects. Notably, COL15A1-positive fibroblasts exhibited a distinct transcriptome compared to COL15A1-negative counterparts. Immunohistochemical analysis confirmed a significant presence of collagen type XV-positive fibroblasts in IgG4-RD patients. Furthermore, immune-suppressive therapy in active IgG4-RD patients resulted in decreased serum levels of collagen type XV.

CONCLUSIONS

Our findings suggest that collagen type XV-producing fibroblasts may represent a disease-characterizing non-immune cell population in IgG4-RD and hold potential as a disease-monitoring marker.

Sarcoidosis-related autoimmune inflammation in COVID-19 convalescent patients

Currently, there are a large number of reports about the development of autoimmune conditions after COVID-19. Also, there have been cases of sarcoid-like granulomas in convalescents as a part of the post-COVID-19 syndrome. Since one of the etiological theories of sarcoidosis considers it to be an autoimmune disease, we decided to study changes in the adaptive humoral immune response in sarcoidosis and SARS-CoV-2 infection and to find out whether COVID-19 can provoke the development of sarcoidosis. This review discusses histological changes in lymphoid organs in sarcoidosis and COVID-19, changes in B cell subpopulations, T-follicular helper cells (Tfh), and T-follicular regulatory cells (Tfr), and analyzes various autoantibodies detected in these pathologies. Based on the data studied, we concluded that SARS-CoV-2 infection may cause the development of autoimmune pathologies, in particular contributing to the onset of sarcoidosis in convalescents.

Expansion of CD4+ cytotoxic T lymphocytes with specific gene expression patterns may contribute to suppression of tumor immunity in oral squamous cell carcinoma: single-cell analysis and in vitro experiments

Background

Cancer immunotherapy targeting CD8+ T cells has made remarkable progress, even for oral squamous cell carcinoma (OSCC), a heterogeneous epithelial tumor without a substantial increase in the overall survival rate over the past decade. However, the therapeutic effects remain limited due to therapy resistance. Thus, a more comprehensive understanding of the roles of CD4+ T cells and B cells is crucial for more robust development of cancer immunotherapy.

Methods

In this study, we examined immune responses and effector functions of CD4+ T cells, CD8+ T cells and B cells infiltrating in OSCC lesions using single-cell RNA sequencing analysis, T cell receptor (TCR) and B cell receptor (BCR) repertoire sequencing analysis, and multi-color immunofluorescence staining. Finally, two Kaplan-Meier curves and several Cox proportional hazards models were constructed for the survival analysis.

Results

We observed expansion of CD4+ cytotoxic T lymphocytes (CTLs) expressing granzymes, which are reported to induce cell apoptosis, with a unique gene expression patterns. CD4+ CTLs also expressed CXCL13, which is a B cell chemoattractant. Cell-cell communication analysis and multi-color immunofluorescence staining demonstrated potential interactions between CD4+ CTLs and B cells, particularly IgD- CD27- double negative (DN) B cells. Expansion of CD4+ CTLs, DN B cells, and their contacts has been reported in T and B cell-activated diseases, including IgG4-related disease and COVID-19. Notably, we observed upregulation of several inhibitory receptor genes including CTLA-4 in CD4+ CTLs, which possibly dampened T and B cell activity. We next demonstrated comprehensive delineation of the potential for CD8+ T cell differentiation towards dysfunctional states. Furthermore, prognostic analysis revealed unfavorable outcomes of patients with a high proportion of CD4+ CTLs in OSCC lesions.

Conclusion

Our study provides a dynamic landscape of lymphocytes and demonstrates a systemic investigation of CD4+ CTL effects infiltrating into OSCC lesions, which may share some pathogenesis reported in severe T and B cell-activated diseases such as autoimmune and infectious diseases.

A twist in the tail: Of T cell subsets and disease

In this issue of JEM, the work of Joachim et al. (2023. J. Exp. Med.https://doi.org/10.1084/jem.20231028) on knockin mice with a specific tail mutation in LAT provides valuable insights about cytotoxic CD4+ T cells and human inflammatory diseases.