Number of Circulating Follicular Helper 2 T Cells Correlates With IgG4 and Interleukin-4 Levels and Plasmablast Numbers in IgG4-Related Disease

Biomarkers in autoimmune pancreatitis and immunoglobulin G4-related disease

Solitary organ autoimmune disorders, formerly known as autoimmune pancreatitis (AIP), autoimmune sialadenitis, and autoimmune sclerosing cholangitis, are now considered organ-specific manifestations of systemic immunoglobulin G4-related disease (IgG4-RD). AIP and IgG4-RD are characterized by elevated serum concentration of IgG4 antibody (Ab), accumulation of IgG4-expressing plasmacytes in the affected organs, and involvement of multiple organs. It is well established that enhanced IgG4 Ab responses are a hallmark of AIP and IgG4-RD for diagnosis and monitoring disease activity. However, a significant fraction of patients with AIP and IgG4-RD who develop chronic fibroinflammatory responses have normal serum concentrations of this IgG subtype. In addition, disease flare-up is sometimes seen even in the presence of normalized serum concentrations of IgG4 Ab after successful induction of remission by prednisolone. Therefore, it is necessary to identify new biomarkers based on the understanding of the pathophysiology of AIP and IgG4-RD. Recently, we found that activation of plasmacytoid dendritic cells producing both interferon-α (IFN-α) and interleukin-33 (IL-33) mediate murine AIP and human IgG4-RD. More importantly, we provided evidence that serum concentrations of IFN-α and IL-33 could be useful biomarkers for the diagnosis and monitoring of AIP and IgG4-RD activity after induction of remission in these autoimmune disorders. In this Frontier article, we have summarized and discussed biomarkers of AIP and IgG4-RD, including Igs, autoAbs, and cytokines to provide useful information not only for clinicians but also for researchers.

Specific Follicular Helper T Cell Signature in Takayasu Arteritis

OBJECTIVE

Our aim was to compare transcriptome and phenotype profiles of CD4+ T cells and CD19+ B cells in patients with Takayasu arteritis (TAK), patients with giant cell arteritis (GCA), and healthy donors.

METHODS

Gene expression analyses, flow cytometry immunophenotyping, T cell receptor (TCR) gene sequencing, and functional assessments of cells from peripheral blood and arterial lesions from TAK patients, GCA patients, and healthy donors were performed.

RESULTS

Among the most significantly dysregulated genes in CD4+ T cells of TAK patients compared to GCA patients (n = 720 genes) and in CD4+ T cells of TAK patients compared to healthy donors (n = 1,447 genes), we identified a follicular helper T (Tfh) cell signature, which included CXCR5, CCR6, and CCL20 genes, that was transcriptionally up-regulated in TAK patients. Phenotypically, there was an increase in CD4+CXCR5+CCR6+CXCR3- Tfh17 cells in TAK patients that was associated with a significant enrichment of CD19+ B cell activation. Functionally, Tfh cells helped B cells to proliferate, differentiate into memory cells, and secrete IgG antibodies. Maturation of B cells was inhibited by JAK inhibitors. Locally, in areas of arterial inflammation, we found a higher proportion of tertiary lymphoid structures comprised CD4+, CXCR5+, programmed death 1+, and CD20+ cells in TAK patients compared to GCA patients. CD4+CXCR5+ T cells in the aortas of TAK patients had an oligoclonal α/β TCR repertoire.

CONCLUSION

We established the presence of a specific Tfh cell signature in both circulating and aorta-infiltrating CD4+ T cells from TAK patients. The cooperation of Tfh cells and B cells might be critical in the occurrence of vascular inflammation in patients with TAK.

The Role of B Cells and B Cell Therapies in Immune-Mediated Liver Diseases

B cells form a branch of the adaptive immune system, essential for the body’s immune defense against pathogens. B cell dysfunction has been implicated in the pathogenesis of immune mediated liver diseases including autoimmune hepatitis, IgG4-related hepatobiliary disease, primary biliary cholangitis and primary sclerosing cholangitis. B cells may initiate and maintain immune related liver diseases in several ways including the production of autoantibodies and the activation of T cells via antigen presentation or cytokine production. Here we comprehensively review current knowledge on B cell mechanisms in immune mediated liver diseases, exploring disease pathogenesis, B cell therapies, and novel treatment targets. We identify key areas where future research should focus to enable the development of targeted B cell therapies.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Human PD-1hiCD8+ T Cells Are a Cellular Source of IL-21 in Rheumatoid Arthritis

Background

Rheumatoid arthritis (RA) is a prototypical autoantibody-driven autoimmune disease in which T-B interactions play a critical role. Recent comprehensive analysis suggests that PD-1⁺CD8⁺ T cells as well as two distinct IL-21-producing PD-1⁺CD4⁺ T cell subsets, follicular helper T (Tfh) and peripheral helper T (Tph) cells, are involved in the pathogenesis of RA. Herein, we aimed to clarify a generation mechanism of IL-21-producing CD8⁺ T cells in humans, and to characterize this novel subset in patients with RA.

Methods

CD8⁺ T cells in the peripheral blood (PB) and synovial fluid (SF) of healthy control (HC) and patients with RA were subject to the analysis of IL-21 mRNA and protein. We evaluated the surface marker, cytokine and transcription profiles of IL-21-producing CD8⁺ T cells in HCPB, RAPB and RASF.

Results

IL-21-producing CD8⁺ T cells were enriched in the CD45RA^-(memory) PD-1⁺, especially PD-1^hi subpopulation, and IL-12 and IL-21 synergistically induced IL-21 production by naïve CD8⁺ T cells. Memory PD-1^hiCD8⁺ T cells in HCPB facilitated plasmablast differentiation and IgG production in an IL-21-dependent manner. In addition, PD-1^hiCD8⁺ T cells in RASF and RAPB produced large amounts of IL-21 and were characterized by high levels of CD28, ICOS, CD69, HLA-DR, and CCR2 but not CXCR5. Furthermore, PD-1^hiCD8⁺ T cells expressed high levels of transcripts of MAF and PRDM1, a feature observed in Tph cells.

Conclusions

Identification of IL-21-producing PD-1^hiCD8⁺ T cells expands our knowledge of T cell subsets with B helper functions in RA. Selective targeting of these subsets could pave an avenue for the development of novel treatment strategies for this disease.

B cell targeted therapy for immunoglobulin G4-related disease

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

A disease-associated mutation that weakens ZAP70 autoinhibition enhances responses to weak and self-ligands

The cytoplasmic kinase ZAP70 is critical for T cell antigen receptor (TCR) signaling. The R360P mutation in ZAP70 is responsible for an early-onset familial autoimmune syndrome. The structural location and biochemical signaling effects of the R360P mutation are consistent with weakening of the autoinhibitory conformation of ZAP70. Mice with a ZAP70 R360P mutation and polyclonal TCR repertoires exhibited relatively normal T cell development but showed evidence of increased signaling. In addition, the R360P mutation resulted in enhanced follicular helper T cell expansion after LCMV infection. To eliminate the possibility of a TCR repertoire shift, the OTI transgenic TCR was introduced into R360P mice, which resulted in enhanced T cell responses to weaker stimuli, including weak agonists and a self-peptide. These observations suggest that disruption of ZAP70 autoinhibition by the R360P mutation enables increased mature T cell sensitivity to self-antigens that would normally be ignored by wild-type T cells, a mechanism that may contribute to the break of tolerance in human patients with R360P mutation.

Roles of follicular helper and regulatory T cells in allergic diseases and allergen immunotherapy

Allergic diseases are characterized by overactive type 2 immune responses to allergens and immunoglobulin E (IgE)-mediated hypersensitivity. Emerging evidence suggests that follicular helper T (T_FH ) cells, rather than type 2 T-helper (T_H 2) cells, play a crucial role in controlling IgE production. However, follicular regulatory T (T_FR ) cells, a specialized subset of regulatory T (T_REG ) cells resident in B-cell follicles, restricts T_FH cell-mediated help in extrafollicular antibody production, germinal center (GC) formation, immunoglobulin affinity maturation, and long-lived, high-affinity plasma and memory B-cell differentiation. In mouse models of allergic asthma and food allergy, CXCR5⁺ T_FH cells, not CXCR5^- conventional T_H 2 cells, are needed to support IgE production, otherwise exacerbated by CXCR5⁺ T_FR cell deletion. Upregulation of T_FH cell activities, including a skewing toward type 2 T_FH (T_FH 2) and IL-13 producing T_FH (T_FH 13) phenotypes, and defects in T_FR cells have been identified in patients with allergic diseases. Allergen immunotherapy (AIT) reinstates the balance between T_FH and T_FR cells in patients with allergic diseases, resulting in clinical benefits. Collectively, further understanding of T_FH and T_FR cells and their role in the immunopathogenesis of allergic diseases creates opportunities to develop novel therapeutic approaches.

Identification of Markers Predicting Clinical Course in Patients with IgG4-Related Ophthalmic Disease by Unbiased Clustering Analysis

Purpose: To describe the clinical features of patients with immunoglobulin G4 (IgG4)-related ophthalmic disease (IgG4-ROD) grouped by unbiased cluster analysis using peripheral blood test data and to find novel biomarkers for predicting clinical features. Methods: One hundred and seven patients diagnosed with IgG4-ROD were divided into four groups by unsupervised hierarchical cluster analysis using peripheral blood test data. The clinical features of the four groups were compared and novel markers for prediction of clinical course were explored. Results: Unbiased cluster analysis divided patients into four groups. Group B had a significantly higher frequency of extraocular muscle enlargement (p < 0.001). The frequency of patients with decreased best corrected visual acuity (BCVA) was significantly higher in group D (p = 0.002). Receiver operating characteristic (ROC) curves for the prediction of extraocular muscle enlargement and worsened BCVA using a panel consisting of important blood test data identified by machine learning yielded areas under the curve of 0.78 and 0.86, respectively. Clinical features were compared between patients divided into two groups by the cutoff serum IgE or IgG4 level obtained from ROC curves. Patients with serum IgE above 425 IU/mL had a higher frequency of extraocular muscle enlargement (25% versus 6%, p = 0.004). Patients with serum IgG4 above 712 mg/dL had a higher frequency of decreased BCVA (37% versus 5%, p ≤ 0.001). Conclusion: Unsupervised hierarchical clustering analysis using routine blood test data differentiates four distinct clinical phenotypes of IgG4-ROD, which suggest differences in pathophysiologic mechanisms. High serum IgG4 is a potential predictor of worsened BCVA, and high serum IgE is a potential predictor of extraocular muscle enlargement in IgG4-ROD patients.

Increased Circulating Th1 and Tfh1 Cell Numbers Are Associated with Disease Activity in Glucocorticoid-Treated Patients with IgG4-Related Disease

Background

This study is aimed at exploring the changes and significance of circulating Th and Tfh cell subsets in glucocorticoid-treated IgG4-RD patients.

Methods

39 glucocorticoid-treated IgG4-RD patients and 22 healthy controls (HC) were enrolled. Peripheral blood mononuclear cells were separated, and circulating Th and Tfh cell subsets were examined by flow cytometry according to the surface and intranuclear markers. Disease activity was accessed by the IgG4-RD responder index (RI) score. Correlation analyses were conducted between Th/Tfh subset numbers and clinical indicators. The receiver operating characteristic (ROC) curve was used to evaluate the efficacy of Th and Tfh subsets to distinguish active IgG4-RD patients from remission IgG4-RD patients.

Results

Circulating Th1, Th17, Tfh1, and Tfh17 cells were significantly increased in active IgG4-RD patients compared with HC. Th1 and Tfh1 numbers were positively correlated with serum IgG4 levels in patients with IgG4-RD. Meanwhile, the absolute numbers of circulating Th1 and Tfh1 cells were positively correlated with IgG4-RD RI scores. The areas under the curve (AUC) were 0.8276 for Th1 and 0.7310 for Tfh1, 0.5862 for Tfh2, and 0.6810 for Tfh17.

Conclusion

Increased circulating Th1 and Tfh1 subsets are related to elevated serum IgG4 levels in active IgG4-RD patients during glucocorticoid treatment, which may play an important role in the course of IgG4-RD disease, and could be potential biomarkers for monitoring disease activity of IgG4-RD.

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

Objective

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

Methods

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

Results

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

Conclusion

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

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

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

Overexpression of FcγRIIB regulates downstream protein phosphorylation and suppresses B cell activation to ameliorate systemic lupus erythematosus

The present study aimed to examine the effects of FcγRIIB on systemic lupus erythematosus (SLE) and to investigate the underlying mechanisms. For this purpose, lentiviral vector carrying the membrane-bound type FcγRIIB gene (mFcγRIIB lentivirus) and soluble FcγRIIB (sFcγRIIB) protein were used to treat B cells from patients with SLE. The B cells were treated with calf thymus DNA (ctDNA) and anti-calf thymus DNA-immune complexes (anti-ctDNA-IC). mFcγRIIB lentivirus and sFcγRIIB protein were also injected into MRL/lpr SLE mice. The results revealed that anti-ctDNA-IC treatment significantly downregulated the IgG antibody secretion of B cells treated with mFcγRIIB lentivirus. mFcγRIIB and sFcγRIIB decreased the phosphorylation level of Bruton's tyrosine kinase (BTK) in B cells, and increased the phosphorylation level of Lyn proto-oncogene (Lyn), docking protein 1 (DOK1) and inositol polyphosphate-5-phospha-tase D (SHIP). mFcγRIIB promoted the apoptosis of B cells. Following the treatment of MRL/lpr SLE mice with mFcγRIIB lentivirus, the levels of urinary protein, serum anti-nuclear and anti-dsDNA antibodies were decreased, while the levels of mFcγRIIB in B cells were increased. mFcγRIIB ameliorated the pathologies of the kidneys, liver and lymph node tissues of the MRL/lpr SLE mice. Following treatment of the MRL/lpr SLE mice with sFcγRIIB, the levels of urinary protein, serum anti-dsDNA antibody and BTK and SHIP phosphorylation levels in B cells were decreased, while the serum sFcγRIIB and sFcγRIIB-IgG levels were increased. On the whole, the findings of the present study demonstrate that recombinant FcγRIIB inhibits the secretion of IgG antibody by B cells from patients with SLE, ameliorates the symptoms of SLE in mice, and alters the phosphorylation levels of downstream proteins of the FcγRIIB signaling pathway in B cells. These results suggest that FcγRIIB may play preventive and therapeutic roles in SLE by inhibiting B cell activation via the FcγRIIB signaling pathway, which provides a novel theory and strategy for the prevention and treatment of SLE.

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.

Shared and distinct roles of T peripheral helper and T follicular helper cells in human diseases

The interactions of CD4⁺ T cells and B cells are fundamental for the generation of protective antibody responses, as well as for the development of harmful autoimmune diseases. Recent studies of human tissues and blood samples have established a new subset of CD4⁺ B helper T cells named peripheral helper T (Tph) cells. Unlike T follicular helper (Tfh) cells, which interact with B cells within lymphoid organs, Tph cells provide help to B cells within inflamed tissues. Tph cells share many B helper-associated functions with Tfh cells and induce B cell differentiation toward antibody-producing cells. The differentiation mechanism is also partly shared between Tph and Tfh cells in humans, and both Tfh and Tph cells can be found within the same tissues, including cancer tissues. However, Tph cells display features distinct from those of Tfh cells, such as the expression of chemokine receptors associated with Tph cell localization within inflamed tissues and a low Bcl-6/Blimp1 ratio. Unlike that of Tfh cells, current evidence shows that the target of Tph cells is limited to memory B cells. In this review, we first summarize recent findings on human Tph cells and discuss how Tph and Tfh cells play shared and distinct roles in human diseases.

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.

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.

European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations

The overall objective of these guidelines is to provide evidence-based recommendations for the diagnosis and management of immunoglobulin G4 (IgG4)-related digestive disease in adults and children. IgG4-related digestive disease can be diagnosed only with a comprehensive work-up that includes histology, organ morphology at imaging, serology, search for other organ involvement, and response to glucocorticoid treatment. Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis. Treatment with glucocorticoids should be weight-based and initiated at a dose of 0.6-0.8 mg/kg body weight/day orally (typical starting dose 30-40 mg/day prednisone equivalent) for 1 month to induce remission and then be tapered within two additional months. Response to initial treatment should be assessed at week 2-4 with clinical, biochemical and morphological markers. Maintenance treatment with glucocorticoids should be considered in multi-organ disease or history of relapse. If there is no change in disease activity and burden within 3 months, the diagnosis should be reconsidered. If the disease relapsed during the 3 months of treatment, immunosuppressive drugs should be added.

T follicular helper cell subsets: a potential key player in autoimmunity

Follicular helper T (Tfh) cells are one of CD4+ helper T subsets which promote B cell maturation, activation and antigen-specific antibody production. Autoantibodies are hallmarks of autoimmune diseases, and crucial contributions of Tfh cells in development of these diseases are now evident. Deregulation of Tfh activities can contribute to a pathogenic autoantibody production and can play an important role in the promotion of autoimmune diseases. These days multiple researchers reported three subpopulations which has distinct effector functions in Tfh cells: Tfh1, Tfh2 and Tfh17 cells. In this review, we summarize the observed alterations in whole Tfh cells and subset distribution during autoimmune diseases.

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.

Association of circulating SLAMF7+Tfh1 cells with IgG4 levels in patients with IgG4-related disease

BACKGROUND

Follicular helper CD4+ T (Tfh) cells have a critical role in IgG4 production by B cells in IgG4-related disease (IgG4-RD). Recent studies including ours showed that SLAMF7+CD4+ T cells are an important pathological driver of IgG4-RD. In this study, we have sought to elucidate a relationship between helper CD4+ T (Th), particularly Tfh, cells and SLAMF7+ CD4+ T cells in IgG4-RD.

RESULTS

The patients with IgG4-RD enrolled in this study were aged 66 ± 12 years and their titers of serum IgG4 were 372 ± 336 mg/dl. Th1 cells, activated circulating Tfh1 (cTfh1), and activated cTfh2 cells increased in IgG4-RD. SLAMF7 was mainly expressed on Th1 and cTfh1, but not cTfh2, cells in the patients. SLAMF7+ cTfh1 cells were PD-1/CD28 double-positive, whereas SLAMF7+ Th1 cells were CD28 negative. Positive correlations were noted between serum IgG4 levels and the number of activated cTfh2 cells and SLAMF7+ cTfh1 cells, but not SLAMF7+ Th1 cells. Intriguingly, among cTfh1 cells, activated SLAMF7+ cTfh1 cells were high producers of IL-10 along with IL-21. Blimp-1, but not Bcl-6, mRNA was expressed at high levels in activated SLAMF7+ cTfh1 cells. In addition to CD4+ T cells, the frequency of SLAMF7+ fraction was higher in memory B cells than naïve B cells in patients with IgG4RD. Finally, upon stimulation via B-cell receptor and CD40, Tfh1-associated cytokines, IL-21 and IFN-γ, most significantly induced SLAMF7 expression in memory B cells.

CONCLUSIONS

Together, these results suggest that circulating SLAMF7+ Tfh1 cells, along with Tfh2 cells, play a pathologic role in IgG4 production in IgG4-RD.

Divergent chemokine receptor expression and the consequence for human IgG4 B cell responses

IgG4 antibodies are unique to humans. IgG4 is associated with tolerance during immunotherapy in allergy, but also with pathology, as in pemphigus vulgaris and IgG4-related disease. Its induction is largely restricted to nonmicrobial antigens, and requires repeated or prolonged antigenic stimulation, for reasons poorly understood. An important aspect in generating high-affinity IgG antibodies is chemokine receptor-mediated migration of B cells into appropriate niches, such as germinal centers. Here, we show that compared to IgG1 B cells, circulating IgG4 B cells express lower levels of CXCR3, CXCR4, CXCR5, CCR6, and CCR7, chemokine receptors involved in GC reactions and generation of long-lived plasma cells. This phenotype was recapitulated by in vitro priming of naive B cells with an IgG4-inducing combination of T_FH /T_H2 cytokines. Consistent with these observations, we found a low abundance of IgG4 B cells in secondary lymphoid tissues in vivo, and the IgG4 antibody response is substantially more short-lived compared to other IgG subclasses in patient groups undergoing CD20⁺ B cell depletion therapy with rituximab. These results prompt the hypothesis that factors needed to form IgG4 B cells restrain at the same time the induction of a robust migratory phenotype that could support a long-lived IgG4 antibody response.

Intestinal dysbiosis mediates experimental autoimmune pancreatitis via activation of plasmacytoid dendritic cells

Autoimmune pancreatitis (AIP) is a pancreatic manifestation of a newly proposed disease entity, IgG4-related disease (IgG4-RD), characterized by enhanced IgG4 antibody responses and involvement of multiple organs. We have previously reported that innate immune activation contributes to the development of AIP and IgG4-RD, as these diseases are characterized by the production of IFN-α and IL-33 by plasmacytoid dendritic cells (pDCs) that mediate chronic fibroinflammatory responses. In this study, we investigated the roles played by innate immunity against intestinal microflora in experimental AIP induced in MRL/MpJ mice by repeated administrations of 100 µg of polyinosinic-polycytidylic acid [poly (I:C)]. Bowel sterilization with a broad spectrum of antibiotics inhibited pancreatic accumulation of pDCs producing IFN-α and IL-33, and thereby suppressed the development of AIP. Mice treated with 10 µg of poly (I:C) developed severe AIP equivalent to that induced by 100 µg of poly (I:C) upon co-housing with mice treated with 100 µg of poly (I:C). Fecal microbiota transplantation (FMT) from donor mice treated with 100 µg of poly (I:C) led to the development of severe AIP in the recipient mice upon injection with 10 µg of poly (I:C). Induction of severe AIP in mice with 10 µg of poly (I:C) was associated with pancreatic accumulation of pDCs producing IFN-α and IL-33 in the co-housing and FMT experiments. These data collectively suggest that innate immune responses against intestinal microflora are involved in the development of experimental AIP, and that intestinal dysbiosis increases sensitivity to experimental AIP via activation of pDCs.

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

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

Immunological mechanism of IgG4-related disease

IgG4-related disease (IgG4-RD) is an immune-mediated inflammatory disorder in multiple organs, characterized by abundant infiltration of IgG4-positive plasmacytes and fibrosis in the involved organs. The precise pathogenic mechanism of IgG4-RD still remains unclear. Aberrant innate and adaptive immunity are considered as the main pathogenesis of IgG4-RD. Recent studies have shown that abnormal adaptive immune responses mediated by T helper type 2 ​cells, regulatory T lymphocytes, CD4+ cytotoxic T lymphocytes, T follicular helper cells, T follicular regulatory cells, PD-1hiCXCR5-peripheral T helper cells and B cell subsets are involved in IgG4-RD. In addition to adaptive immune responses, innate immune responses play pathogenic roles in IgG4-RD. Macrophages, mast cells, basophils, complement, and plasmacytoid dendritic cells are activated to produce various kinds of cytokines in IgG4-RD. This review aims to summarize the most recent knowledge in the pathogenesis of IgG4-RD.

Review of a novel disease entity, immunoglobulin G4-related disease

Immunoglobulin G4 (IgG4)-related dacryoadenitis and sialoadenitis (IgG4-DS) are part of a multiorgan fibroinflammatory condition of unknown etiology termed IgG4-related disease (IgG4-RD), which has been recognized as a single diagnostic entity for less than 15 years. Histopathologic examination is critical for diagnosis of IgG4-RD. CD4+ T and B cells, including IgG4-expressing plasma cells, constitute the major inflammatory cell populations in IgG4-RD and are thought to cause organ damage and tissue fibrosis. Patients with IgG4-RD who have active, untreated disease exhibit significant increase of IgG4-secreting plasmablasts in the blood. Considerable insight into the immunologic mechanisms of IgG4-RD has been achieved in the last decade using novel molecular biology approaches, including next-generation and single-cell RNA sequencing. Exploring the interactions between CD4+ T cells and B lineage cells is critical for understanding the pathophysiology of IgG4-RD. Establishment of pathogenic T cell clones and identification of antigens specific to these clones constitutes the first steps in determining the pathogenesis of the disease. Herein, the clinical features and mechanistic insights regarding pathogenesis of IgG4-RD were reviewed.

Imbalance in B cell and T Follicular Helper Cell Subsets in Pulmonary Sarcoidosis

Sarcoidosis is a systemic granulomatous disease that develops due to the Th1, Th17 and Treg lymphocytes disturbance. There is an assumption, that B cells and follicular T-helper (Tfh) cells may play an important role in this disorder, as well as in several other autoimmune diseases. The aim of this study was to determine CD19+ B cells subset distribution in the peripheral blood and to define disturbance in the circulating Tfh cells subsets in patients with sarcoidosis. The prospective comparative study was performed in 2016-2018, where peripheral blood B cell subsets and circulating Tfh cell subsets were analyzed in 37 patients with primarily diagnosed sarcoidosis and 35 healthy donors using multicolor flow cytometry. In the results of our study we found the altered distribution of peripheral B cell subsets with a predominance of "naïve" (IgD + CD27-) and activated B cell (Bm2 and Bm2') subsets and a decreased frequency of memory cell (IgD+ CD27+ and IgD- CD27+) in peripheral blood of sarcoidosis patients was demonstrated. Moreover, we found that in sarcoidosis patients there are increased levels of B cell subsets, which were previously shown to display regulatory capacities (CD24+++ CD38+++ and CD5 + CD27-). Next, a significantly higher proportion of CXCR5-expressing CD45RA - CCR7+ Th cells in patients with sarcoidosis in comparison to the healthy controls was revealed, that represents the expansion of this memory Th cell subset in the disease. This is the first study to demonstrate the association between the development of sarcoidosis and imbalance of circulating Tfh cells, especially CCR4- and CXCR3-expressing Tfh subsets. Finally, based on our data we can assume that B cells and Tfh2- and Tfh17-like cells - most effective cell type in supporting B-cell activity, particularly in antibody production - may be involved in the occurrence and development of sarcoidosis and in several other autoimmune conditions. Therefore, we can consider these results as a new evidence of the autoimmune mechanisms in the sarcoidosis development.

Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling

Objective

IgG4‐related disease (IgG4‐RD) is a unique inflammatory disorder in which Th2 cytokines promote IgG4 production. In addition, recent studies have implicated the Toll‐like receptor (TLR) pathway. This study was undertaken to examine the expression of TLRs in salivary glands (SGs) from patients with IgG4‐RD.

Methods

SGs from 15 patients with IgG4‐RD, 15 patients with Sjögren's syndrome (SS), 10 patients with chronic sialadenitis, and 10 healthy controls were examined histologically. TLR family gene expression (TLR‐1 through TLR‐10) was analyzed by DNA microarray in the submandibular glands (SMGs). Up‐regulation of TLRs was confirmed in SGs from patients with IgG4‐RD. Finally, the phenotype of human TLR‐7 (huTLR‐7)–transgenic C57BL/6 mice was assessed before and after stimulation with TLR agonist.

Results

In patients with IgG4‐RD, TLR‐4, TLR‐7, TLR‐8, and TLR‐9 were overexpressed. Polymerase chain reaction validated the up‐regulation of TLR‐7 in IgG4‐RD compared with the other groups. Immunohistochemical analysis confirmed strong infiltration of TLR‐7–positive cells in the SGs of patients with IgG4‐RD. Double immunohistochemical staining showed that TLR‐7 expression colocalized with CD163+ M2 macrophages. After in vitro stimulation with a TLR‐7 agonist, CD163+ M2 macrophages produced higher levels of interleukin‐33 (IL‐33), which is a Th2‐activating cytokine. In huTLR‐7–transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild‐type mice (P < 0.05). Moreover, the concentration of serum IgG, IgG1, and IL‐33 in huTLR‐7–transgenic mice was distinctly increased upon stimulation with a TLR‐7 agonist (P < 0.05).

Conclusion

TLR‐7–expressing M2 macrophages may promote the activation of Th2 immune responses via IL‐33 secretion in IgG4‐RD.

The role of follicular T helper cells in the humoral alloimmune response after clinical organ transplantation

Over the past decade, antibody‐mediated or humoral rejection in combination with development of de novo donor‐specific antibodies (DSA) has been recognized as a distinct and common cause of transplant dysfunction and is responsible for one‐third of the failed allografts. Detailed knowledge of the mechanisms that initiate and maintain B‐cell driven antidonor reactivity is required to prevent and better treat this antidonor response in organ transplant patients. Over the past few years, it became evident that this response largely depends on the actions of both T follicular helper (Tfh) cells and the controlling counterparts, the T follicular regulatory (Tfr) cells. In this overview paper, we review the latest insights on the functions of circulating (c)Tfh cells, their subsets Tfh1, Tfh2 and Tfh17 cells, IL‐21 and Tfr cells in antibody mediated rejection (ABMR). This may offer new insights in the process to reduce de novo DSA secretion resulting in a decline in the incidence of ABMR. In addition, monitoring these cell populations could be helpful for the development of biomarkers identifying patients at risk for ABMR and provide novel therapeutic drug targets to treat ABMR.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Follicular Helper T Cell Derived Exosomes Promote B Cell Proliferation and Differentiation in Antibody-Mediated Rejection after Renal Transplantation

Follicular helper T cells (Tfh cells) are closely related to the occurrence and development of antibody-mediated rejection (AMR) after renal transplantation. Exosomes play a key role in the rejection after organ transplantation. However, whether Tfh-derived exosomes are involved in AMR has not been reported. We collected peripheral blood from 42 kidney transplant patients and found no significant differences in CD4+CXCR5+ and CD4+CXCR5+CXCR3+CCR6-exosomes between AMR and non-AMR groups, whereas the proportion of CD4+CXCR5+CXCR3-exosomes was significantly higher in AMR group than that in non-AMR group; CTLA-4 expression of CD4+CXCR5+exosomes was significantly lower in AMR group than that in non-AMR group. HLA-G expression was not significantly different between two groups. We further separated CD4+CXCR5+cells from patients by magnetic beads. Coculture experiments showed that Tfh cell-derived exosomes in AMR patients significantly promoted B cell proliferation and differentiation, compared with non-AMR group, the percentage of B cells and plasma cells increased by 87.52% and 110.2%, respectively. In conclusion, our study found that Tfh cell-derived exosomes could promote the proliferation and differentiation of B cells and they may play an important role in the development of AMR after renal transplantation.

Activated T-Follicular Helper 2 Cells Are Associated With Disease Activity in IgG4-Related Sclerosing Cholangitis and Pancreatitis

Immunoglobulin G4-related sclerosing cholangitis (IgG4-SC) and autoimmune pancreatitis (AIP) are characterized by an abundance of circulating and tissue IgG4-positive plasma cells. T-follicular helper (Tfh) cells are necessary for B-cell differentiation into plasma cells. We aimed at elucidating the presence and phenotype of Tfh cells and their relationship with disease activity in IgG4-SC/AIP.

Circulating CXCR3-CCR6-CXCR5+CD4+ T cells are associated with acute allograft rejection in liver transplantation

Circulating T follicular helper (cTFH) cells have been demonstrated to be involved in B-cell-mediated alloreactive responses in kidney and liver transplantation; however, whether these cells are involved in acute liver allograft rejection after liver transplantation, and which subsets are involved, remains to be clarified. The present study aimed to investigate the profiles of cTFH cells in acute liver allograft rejection, including the CXC motif receptor 3 (CXCR3)⁺ chemokine receptor 6 (CCR6)^- subset, the CXCR3^-CCR6^- subset, and the CXCR3^-CCR6⁺ subset. Twelve liver transplant patients with acute rejection (AR) and 20 with no acute rejection (NAR) were enrolled in the study. The results showed that the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was significantly increased and the proportion of CXCR3^-CCR6⁺CXCR5⁺CD4⁺ T cells was significantly decreased in patients with AR compared with patients with NAR. In addition, the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was positively correlated with the proportion of B cells in patients with AR. The level of serum interleukin (IL)-21 was higher in the AR group than in the NAR groups. Furthermore, the proportion of CXCR3-CCR6-CXCR5⁺CD4⁺ T cells was positively correlated with alanine amino transferase (ALT), whereas the proportion of CXCR3^-CCR6⁺ CXCR5⁺CD4⁺ T cells was negatively correlated with ALT. B cells and TFH cells were detected in follicular-like structures in liver allograft tissues from patients with AR. These results suggest that CXCR3-CCR6-CXCR5⁺CD4⁺ T cells may be involved in acute allograft rejection after liver transplantation.

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

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

New insights into IgG4-related disease: emerging new CD4+ T-cell subsets

PURPOSE OF REVIEW

New insights into IgG4-related disease (IgG4-RD) have recently been obtained. A better understanding of the mechanisms underlying this disease is important for identification of therapeutic targets, which will lead to the development of specific strategies for treatment.

RECENT FINDINGS

Infiltration of activated T follicular helper (Tfh) cells is observed in affected tissues of IgG4-RD. Such Tfh cells have a greater capacity than tonsillar Tfh cells to help B cells produce IgG4. Circulating PD-1CXCR5 peripheral T helper (Tph)-like cells are also increased in patients with IgG4-RD. Because Tph-like cells express high levels of chemokine receptors and granzyme A, they have the capacity to infiltrate affected tissues and exert a cytotoxic function. Tph-like cells can also produce CXCL13, and CXCR5 Tfh cells and B cells are therefore preferentially recruited to form ectopic lymphoid structures in the sites. Tph cells may have a role to ignite inflammation and maintain persistent fibroinflammation in collaboration with Tfh cells in lesions of IgG4-RD.

SUMMARY

Recent advances in understanding the pathogenesis of IgG4-RD are remarkable. In this review, we summarize and discuss the possible pathologic role of CD4 T-cell subsets in IgG4-RD.

Constitutive Changes in Circulating Follicular Helper T Cells and Their Subsets in Patients with Graves' Disease

Background

Follicular helper T (Tfh) cells are critical for high-affinity antibody generation and B cell maturation and differentiation, which play important roles in autoimmune diseases. Graves' disease (GD) is one prototype of common organ-specific autoimmune thyroid diseases (AITD) characterized by autoreactive antibodies, suggesting a possible role for Tfh cells in the pathogenesis of GD. Our objective was to explore the role of circulating Tfh cell subsets and associated plasma cells (PCs) in patients with GD.

Methods

Thirty-six patients with GD and 20 healthy controls (HC) were enrolled in this study. The frequencies of circulating Tfh cell subsets and PCs were determined by flow cytometry, and plasma cytokines, including interleukin- (IL-) 21, IL-4, IL-17A, and interferon- (IFN-) γ, were measured using an enzyme-linked immunosorbent assay (ELISA). The mRNA expression of transcription factors (Bcl-6, T-bet, GATA-3, and RORγt) in peripheral blood mononuclear cells (PBMCs) was evaluated by real-time quantitative PCR. Results. Compared with HC, the frequencies of circulating CD4⁺CXCR5⁺CD45RA⁻Tfh (cTfh) cells with ICOS and PD-1 expression, the Tfh2 subset (CXCR3⁻CCR6⁻Tfh) cells, and PCs (CD19⁺CD27^highCD38^high) were significantly increased in the GD patients, but the frequencies of Tfh1 (CXCR3⁺CCR6⁻Tfh) and Tfh17 (CXCR3⁻CCR6⁺Tfh) subset cells among CD4⁺T cells were significantly decreased in GD patients. The plasma concentrations of IL-21, IL-4, and IL-17A were elevated in GD patients. Additionally, a positive correlation was found between the frequency of PD-1⁺Tfh cells (Tfh2 or PCs) and plasma IL-21 concentration (or serum TPO-Ab levels). The mRNA levels of transcription factors (GATA-3 and RORγt) were significantly increased, but T-bet and Bcl-6 mRNA expression was not obviously varied in PBMCs from GD patients. Interestingly, Tfh cell subsets and PCs from GD patients were partly normalized by treatment.

Conclusion

Circulating Tfh cell subsets and PCs might play an important role in the pathogenesis of GD, which are potential clues for GD patients' interventions.

New insights into the pathophysiology of IgG4-related disease and markers of disease activity

INTRODUCTION

Recently, IgG4-related disease (IgG4-RD) has become a well-recognized clinical entity, although its causes are still not well understood. The pathophysiology of IgG4-RD has been reported from a variety of aspects. Areas covered: In this review, we outline a number of recent advances in our understanding of the pathogenesis of IgG4-RD, divided according to acquired immunology and innate immunology and other topics. Furthermore, we also focus on some proposed markers of disease activity of IgG4-RD. Expert commentary: One striking advance made recently is the identification of novel autoantigens of IgG4-RD. At the onset of IgG4-RD, various T cell side factors such as Tfh, Th2 cells are at work, in addition to B cell side factors like plasmablasts and plasma cells, and innate immunology via TLR and M2 macrophages. The efficacy of B cell depletion therapy using rituximab has been reported, with the establishment of steroid-sparing therapies targeting other molecules also anticipated.

Association of serum levels of fibrosis-related biomarkers with disease activity in patients with IgG4-related disease

BACKGROUND

The aim of this study was to identify fibrosis-related serological surrogate outcome measures in patients with immunoglobulin G4-related disease (IgG4-RD).

METHODS

This was a clinical observational study of 72 patients with untreated IgG4-RD from four institutions in Japan. The serum concentrations of growth differentiation factor 15 (GDF-15), CCL2, hyaluronic acid (HA), amino-terminal propeptide of type III procollagen (PIIINP), and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by enzyme-linked immunosorbent assays. The enhanced liver fibrosis (ELF) score was calculated from the TIMP-1, PIIINP, and HA values. We evaluated associations between the values of these biomarkers and laboratory data, the IgG4-RD responder index (IgG4-RD RI) score, and organ involvements.

RESULTS

Compared with the 44 healthy controls, the patients with IgG4-RD showed significantly elevated serum concentrations of GDF-15, MCP-1, HA, PIIINP, and TIMP-1 and ELF scores. The patients' serum concentrations of GDF-15, CCL2, HA, and TIMP-1 (but not PIIINP) were positively correlated with each other. Among them, serum GDF-15 most efficiently distinguished patients with IgG4-RD from healthy controls. Serum GDF-15 was not associated with the IgG4-RD RI score or the number of organ involvements but was independently associated with the presence of retroperitoneal fibrosis and with parotid gland involvement.

CONCLUSIONS

We observed increased serological surrogate outcome measures of fibrosis in IgG4-RD. GDF-15 may precisely reflect the fibrotic degree in patients with IgG4-RD.

Cytokines produced by innate immune cells in IgG4-related disease

IgG4-related disease (IgG4-RD) is a newly defined multi-organ disease proposed by Japanese physicians. IgG4-RD is characterized by elevated serum levels of IgG4 and massive infiltration of IgG4-expressing plasma cells in the affected organs. Recent studies have shown that abnormal adaptive immune responses mediated by T helper type 2 cells, regulatory T cells, follicular helper T cells, cytotoxic CD4⁺ T cells, and plasmablasts are involved in IgG4-RD immunopathogenesis. In addition to adaptive immune responses, innate immune responses play pathogenic roles in IgG4-RD. Plasmacytoid dendritic cells (pDCs), M2 macrophages, and basophils are activated to produce various kinds of cytokines in IgG4-RD. Recent studies highlight the importance of type I IFN and IL-33 produced by pDCs in IgG4-RD immunopathogenesis.

New insights into immune cells cross-talk during IgG4-related disease

Immunoglobulin G4-related disease (IgG4-RD) is a newly acknowledged entity, characterized by an immune-mediated fibro-inflammatory process affecting virtually all organs, with infiltration of IgG4⁺ bearing plasma cells. Until today the pathogenesis of IgG4-RD remains unknown. Treatment with anti-CD20 monoclonal antibodies efficiently induced remission and attenuated the secretory phenotype of myofibroblasts responsible of uncontrolled collagen deposition. This supports the pathogenic role of the adaptive immunity, particularly B cell compartment and B cell/T cell interaction. Latest studies have also highlighted the importance of innate immune system that has been underestimated before and the key role of a specific T cell subset, T follicular helper cells that are involved in IgG4-class-switching and plasmablast differentiation. In this review, we aim to review the most recent knowledge of innate immunity, T and B cells involvement in IgG4-RD, and introduce tertiary lymphoid organs (TLO) as a potential marker of relapse in this condition.

The Immunobiology of Receptor Activator for Nuclear Factor Kappa B Ligand and Myeloid-Derived Suppressor Cell Activation in Immunoglobulin G4-Related Sclerosing Cholangitis

The primary function of myeloid-derived suppressor cells (MDSCs) is reflected in their immune modulatory role in several immune-mediated diseases. In immunoglobulin G4 (IgG4)-related disease (IgG4-RD), it has been hypothesized that there are selective regulatory defects that lead to a T helper 2 (Th2) bias immune response. Herein we have taken advantage of a large cohort of patients with IgG4-related sclerosing cholangitis (IgG4-SC), the most common extrapancreatic involvement of IgG4-RD, as well as controls consisting of primary sclerosing cholangitis, autoimmune hepatitis, and healthy volunteers, to study MDSCs. We report dramatically increased levels of receptor activator for nuclear factor kappa B ligand (RANKL) expression in serum and liver from patients with IgG4-SC compared to both liver-disease and healthy controls. Moreover, in IgG4-SC liver, RANKL-secreting cells specifically colocalized with cluster of differentiation 38-positive plasma cells and MDSCs, particularly monocytic MDSCs, and express the RANKL receptor in liver. Similarly, the frequency and number of peripheral blood MDSCs were significantly increased. Importantly, serum expression levels of RANKL were inversely correlated with the serum level of gamma-glutamyltransferase but significantly positively correlated with the frequency of MDSCs. Moreover, we confirmed that RANKL induced the expansion and activation of MDSCs through the RANKL/RANK/nuclear factor kappa B signal pathway. Of note, RANKL-treated MDSCs suppressed T-cell proliferation and induced Th2 differentiation. Conclusion: Our data suggest that plasma cell-derived RANKL induces the expansion and activation of MDSCs, which suppress T-cell proliferation and contribute to the Th2-type response characteristic of IgG4-SC.

Mechanistic Insights into Autoimmune Pancreatitis and IgG4-Related Disease

Autoimmune pancreatitis (AIP) is a pancreatic manifestation of a recently defined disease form known as IgG4-related disease (AIP/IgG4-RD). AIP/IgG4-RD is characterized by elevated systemic IgG4 antibody concentrations and lesional tissues infiltrated by IgG4-expressing plasmacytes. In addition, recent studies have revealed that, in common with other autoimmune diseases, such as systemic lupus erythematosus (SLE) and psoriasis, AIP/IgG4-RD is associated with increased type I IFN (IFN-I) production by plasmacytoid dendritic cells (pDCs). However, unlike SLE, AIP/IgG4-RD is characterized by elevated IFN-I-dependent IL-33 production, the latter emerging as an important contributor to inflammation and fibrotic responses characterizing this disease. On this basis, we propose that blockade of the IFN-I/IL-33 axis might constitute a successful approach to treating this unique type of autoimmunity.