Peripheral imbalanced TFH/TFR ratio correlates with intrathecal IgG synthesis in multiple sclerosis at clinical onset

CXCL13/CXCR5 axis facilitates TFH expansion and correlates with disease severity in adults with immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder defined by a diminished platelet count. ITP pathogenesis involves intricate changes to both cellular and humoral immunity. The pivotal roles of follicular helper T (TFH) cells in the maturations of B cells and the production of antibodies are well-established. However, the specific role of TFH to the immunopathogenesis of ITP remain incompletely understood. This study aimed to clarify the association of CXCL13/CXCR5 axis with TFH in adults with ITP.

METHODS

A total of 97 ITP patients and 41 healthy controls were enrolled. CD4+CXCR5+ TFH, CD4+CXCR5+PD-1+ TFH, CD4+CXCR5+Foxp3+ follicular regulatory T cells (TFR), and desialylated platelets in peripheral blood were measured by flow cytometry. Plasma cytokines were assessed by enzyme-linked immunosorbent assay. CD4+ T cells cocultured with chemokine CXCL13 in vitro was performed for the measurement of TFH proliferation. Intracellular production of reactive oxygen species (ROS) was examined by dichlorodihydrofluorescein diacetate (DCFH-DA) probe staining.

RESULTS

We observed a significant increase in circulating TFH and a marked decrease in circulating TFR in the entire ITP cohort. The ratio of TFH/TFR was elevated, accompanied by heightened levels of platelet desialylation, cytokines BAFF, HMGB1, and IL-21, while levels of IL-10 were downregulated in adults with ITP. Notably, patients with ITP exhibiting platelet count below 50 × 109/L had dramatically elevated levels in both chemokine CXCL13 and its receptor CXCR5+ TFH compared to those with platelet count above 100 × 109/L. High frequencies of TFH correlated with poor therapeutic response. Furthermore, in vitro CD4+ T cell proliferation assay demonstrated a CXCL13 dose-dependent increase in the frequencies in both CD4+CXCR5+ TFH and CD4+CXCR5+PD-1+ TFH from ITP patients. Intriguingly, DCFH-DA assay illustrated a significant enhancement in intracellular ROS generation in CXCR5+ T cell subsets, especially in CD4+CXCR5+PD-1+ TFH from 4 patients with ITP.

CONCLUSIONS

These results underscore the pivotal role of CXCL13/CXCR5 axis-drived TFH expansion in the pathogenesis of ITP, providing a potential disease severity biomarker.

Association between peripheral blood immunological status and intrathecal inflammatory markers differentiate multiple sclerosis clinical phenotypes

BACKGROUND

The difference in the clinical course, response to therapy, and distribution of CNS inflammation in primary-progressive (PPMS) and relapsing-remitting multiple sclerosis (RRMS) suggests differences in the underlying immunological characteristics of the disease. We aimed to investigate differences in immunological profiles in relation to intrathecal inflammation in different MS forms.

METHODS

The peripheral blood (PB) proportions of CD4 + and CD8 + T-cells and CD19 + B-cells were retrospectively compared with the markers of intrathecal immunoglobulin G (IgG) synthesis at diagnosis: IgG index, percentage of intrathecal IgG synthesis (IF IgG), the number of oligoclonal bands (OCB), depending on the blood-brain barrier (BBB) function, and antibody specific index to neurotrophic viruses (MRZH reaction).

RESULTS

Thirty-six controls, 71 RRMS and 25 PPMS were enrolled. PPMS had higher percentage of CD4 + T-cells compared to RRMS (P = 0.043) and controls (P = 0.003). The percentage of CD8 + T-cells and CD19 + B-cells, and respective absolute cell counts did not differ according to the MS phenotype. In RRMS with the dysfunctional BBB, the IgG index (r = 0.642, P = 0.012) correlated significantly with the CD19 + B-cells while the CD4 + T-cells inversely correlated with IF IgG (r=-0.574, P = 0.039). Interestingly, in PPMS the number of OCB was positively associated with CD4+ (r = 0.603, P = 0.015) and negatively associated with CD8 + T-cells (r=-0.554, P = 0.033), while IF IgG negatively correlated with CD8 + T-cells (r=-0.689, P = 0.003), but only in the preserved BBB function.

CONCLUSIONS

The PB CD4 + T-cells and B-cells were associated with the intrathecal inflammation in RRMS with BBB dysfunction while CD8 + T-cells were involved in PPMS with CNS-compartmentalized inflammation.

Changes of B cell subsets in different types of diabetes and its effect on the progression of latent autoimmune diabetes in adults

PURPOSE

Developmental abnormalities in B cells is one of the key players in autoimmune diabetes, but little is known about its role in latent autoimmune diabetes in adults (LADA). This study aimed to investigate the distribution of B cell subsets in different types of diabetes and to analyze their correlations with other biochemical parameters.

METHODS

A total of 140 participants were prospectively enrolled from January 2021 to December 2022. Diabetes-related autoantibodies and laboratory indicators were tested. Flow cytometry was used to analyze the percentage of circulating B cell subsets and T follicular cells. The correlation of B cell subsets with different indicators was assessed by Spearman's correlation method.

RESULTS

We observed that the Naïve phenotype cells tended to be less frequent in patients with diabetes than in healthy controls. The frequency of plasmablasts (PB) and Breg cell-related phenotype (B10) were significantly higher in LADA. Notably, the percentage of PB was positively associated with levels of islet cell antibody (ICA) and insulin autoantibody (IAA), but inversely associated with fasting C-peptide (FCP), further indicating that PB may promote the destruction of β-cell in patients with diabetes.

CONCLUSIONS

This study showed that patients with LADA had significantly altered frequencies of B cell subsets, particularly in the naïve to memory B cell ratio. Our study provided valuable information on the distribution characteristics of B cell subsets in LADA and suggested the feasibility of B-cell targeted therapy in LADA patients.

Sustained effects on immune cell subsets and autoreactivity in multiple sclerosis patients treated with oral cladribine

Introduction

Cladribine tablet therapy is an efficacious treatment for multiple sclerosis (MS). Recently, we showed that one year after the initiation of cladribine treatment, T and B cell crosstalk was impaired, reducing potentially pathogenic effector functions along with a specific reduction of autoreactivity to RAS guanyl releasing protein 2 (RASGRP2). In the present study we conducted a longitudinal analysis of the effect of cladribine treatment in patients with RRMS, focusing on the extent to which the effects observed on T and B cell subsets and autoreactivity after one year of treatment are maintained, modulated, or amplified during the second year of treatment.

Methods

In this case-control exploratory study, frequencies and absolute counts of peripheral T and B cell subsets and B cell cytokine production from untreated patients with relapsing-remitting MS (RRMS) and patients treated with cladribine for 52 (W52), 60 (W60), 72 (W72) and 96 (W96) weeks, were measured using flow cytometry. Autoreactivity was assessed using a FluoroSpot assay.

Results

We found a substantial reduction in circulating memory B cells and proinflammatory B cell responses. Furthermore, we observed reduced T cell responses to autoantigens possibly presented by B cells (RASGRP2 and a-B crystallin (CRYAB)) at W52 and W96 and a further reduction in responses to the myelin antigens myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) after 96 weeks.

Conclusion

We conclude that the effects of cladribine observed after year one are maintained and, for some effects, even increased two years after the initiation of a full course of treatment with cladribine tablets.

Pathogenic Role of Fibrinogen in the Neuropathology of Multiple Sclerosis: A Tale of Sorrows and Fears

Multiple sclerosis (MS) is an autoimmune demyelinating neurodegenerative disease of the central nervous system (CNS) due to injury of the myelin sheath by immune cells. The clotting factor fibrinogen is involved in the pathogenesis of MS by triggering microglia and the progress of neuroinflammation. Fibrinogen level is correlated with MS severity; consequently, inhibition of the fibrinogen cascade may reduce MS neuropathology. Thus, this review aimed to clarify the potential role of fibrinogen in the pathogenesis of MS and how targeting of fibrinogen affects MS neuropathology. Accumulation of fibrinogen in the CNS may occur independently or due to disruption of blood-brain barrier (BBB) integrity in MS. Fibrinogen acts as transduction and increases microglia activation which induces the progression of inflammation, oxidative stress, and neuronal injury. Besides, brain fibrinogen impairs the remyelination process by inhibiting the differentiation of oligodendrocyte precursor cells. These findings proposed that fibrinogen is associated with MS neuropathology through interruption of BBB integrity, induction of neuroinflammation, and demyelination with inhibition of the remyelination process by suppressing oligodendrocytes. Therefore, targeting of fibrinogen and/or CD11b/CD18 receptors by metformin and statins might decrease MS neuropathology. In conclusion, inhibiting the expression of CD11b/CD18 receptors by metformin and statins may decrease the pro-inflammatory effect of fibrinogen on microglia which is involved in the progression of MS.

Cladribine Effects on T and B Cells and T Cell Reactivity in Multiple Sclerosis

OBJECTIVE

Cladribine tablet therapy is an efficacious treatment for multiple sclerosis (MS), however, its mechanism of action on T and B cell subsets remains unclear. The purpose of this study was to investigate the treatment effects of cladribine on the peripheral pool of T and B cells subsets and reactivity toward central nervous system (CNS) antigens.

METHODS

In this cross-sectional exploratory study, frequencies and absolute counts of peripheral T and B cell subsets and B cell cytokine production from untreated patients with relapsing-remitting MS (RRMS) and patients treated with cladribine for 1 year were measured using flow cytometry. Autoreactivity was assessed using a FluoroSpot assay.

RESULTS

We found that 1 year after initiation of cladribine treatment, a lower number of CD4+ T cells was persisting whereas CD19+ B cell counts were normalized compared to untreated patients with RRMS. Follicular helper T cells and their effecter subsets producing cytokines exerting distinct B cell helper activity were lower and, additionally, the peripheral B cell pool was skewed toward a naïve and anti-inflammatory phenotype. Finally, reactivity to the recently identified CNS-enriched autoantigen RAS guanyl-releasing protein 2 (RASGRP2), but not to myelin basic protein and myelin oligodendrocyte glycoprotein, was lower in cladribine-treated patients.

INTERPRETATION

Together, these investigations on T and B cell subsets suggest that cladribine treatment impairs the B-T cell crosstalk and reduces their ability to mediate pathogenic effector functions. This may result in specific reduction of autoreactivity to RASGRP2 which is expressed in B cells and brain tissue. ANN NEUROL 2023;94:518-530.

Diagnostic significance of IgG and albumin indices versus oligoclonal band types in demyelinating disorders

AIMS

The laboratory diagnosis of demyelinating inflammatory disorders (DIDs) relies on both intrathecal oligoclonal band (OCB) positivity and IgG index. Although OCB typing remains the gold-standard test for DIDs, it can be laborious and ambiguous, complicating diagnostics, and unduly increasing diagnostic time. We examined whether serum or cerebrospinal fluid (CSF) parameters can classify OCB types and, thus, be used as a replacement test to standard OCB typing.

METHODS

We retrospectively analysed >1000 prospectively collected samples of patients with DIDs and quantified albumin and IgG levels in the CSF and serum. We determined OCB types by isoelectric focusing combined with immunofixation and evaluated the diagnostic accuracies of IgG and albumin indices in discriminating OCB types by receiver operating characteristic curves and multinomial regression.

RESULTS

An IgG index cut-off of 0.589 differentiated types 2/3 from types 1/4 (area under the curve 0.780, 95% CI 0.761 to 0.812, p<0.001; specificity: 71.10%, sensitivity: 73.45%). Albumin quotient cut-off values of 6.625 and of 6.707 discriminated type 1 from type 4 and type 2 from type 3, respectively (specificity: <55%, sensitivity: <75%). Female sex, age, IgG index, CSF IgG and serum albumin were associated with different OCB types.

CONCLUSIONS

Our study reveals that IgG and albumin index can differentiate OCB types with adequate accuracy, especially if refined by age and gender.

T follicular helper cells in autoimmune diseases

T follicular helper (Tfh) cells with the phenotype of mainly expressing surface molecules C-X-C motif chemokine receptor type 5 (CXCR5), inducible co-stimulator (ICOS), secreting cytokine interleukin-21 (IL-21) and requiring the transcription factor B cell lymphoma 6 (BCL-6) have been recently defined as a new subset of CD4⁺ T cells. They exist in germinal centers (GCs) of lymphoid organs and in peripheral blood. With the ability to promote B cell development, GC formation and antibody production, Tfh cells play critical roles in the pathogenesis of many autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), primary Sjögren's syndrome (pSS), etc. The aberrant proliferation and function of Tfh cells will cause the pathological process like autoantibody production and tissue injury. In this paper, we review the recent advances in Tfh cell biology and their roles in autoimmune diseases, with a mention of their use as therapeutic targets, which will shed more light on the pathogenesis and treatment of certain autoimmune diseases.

T follicular helper cells and T follicular regulatory cells in autoimmune diseases

T follicular helper (Tfh) cells are heterogeneous and mainly characterized by expressing surface markers CXCR5, ICOS, and PD-1; cytokine IL-21; and transcription factor Bcl6. They are crucial for B-cell differentiation into long-lived plasma cells and high-affinity antibody production. T follicular regulatory (Tfr) cells were described to express markers of conventional T regulatory (Treg) cells and Tfh cells and were able to suppress Tfh-cell and B-cell responses. Evidence has revealed that the dysregulation of Tfh and Tfr cells is positively associated with the pathogenic processes of autoimmune diseases. Herein, we briefly introduce the phenotype, differentiation, and function of Tfh and Tfr cells, and review their potential roles in autoimmune diseases. In addition, we discuss perspectives to develop novel therapies targeting Tfh/Tfr balance.

Increased Intrathecal Activity of Follicular Helper T Cells in Patients With Relapsing-Remitting Multiple Sclerosis

BACKGROUND AND OBJECTIVES

Follicular helper T (Tfh) cells play a critical role in protective immunity helping B cells produce antibodies against foreign pathogens and are likely implicated in the pathogenesis of various autoimmune diseases. The purpose of this study was to investigate the role of Tfh cells in the pathogenesis of multiple sclerosis (MS).

METHODS

Using flow cytometry, we investigated phenotype, prevalence, and function of Tfh cells in blood and CSF from controls and patients with relapsing-remitting MS (RRMS) and primary progressive MS (PPMS). In addition, an in vitro blood-brain barrier coculture assay of primary human astrocytes and brain microvascular endothelial cells grown in a Boyden chamber was used to assess the migratory capacity of peripheral Tfh cells.

RESULTS

This study identified 2 phenotypically and functionally distinct Tfh cell populations: CD25^- Tfh cells (Tfh1-like) and CD25^int Tfh cells (Tfh17-like). Whereas minor differences in Tfh cell populations were found in blood between patients with MS and controls, we observed an increased frequency of CD25^- Tfh cells in CSF of patients with RRMS and PPMS and CD25^int Tfh cells in patients with RRMS, compared with controls. Increasing frequencies of CSF CD25^- Tfh cells and the CD25^- Tfh/Tfr ratio scaled with increasing IgG index in patients with RRMS. Despite an increased prevalence of intrathecal Tfh cells in patients with MS, no difference in the migratory capacity of circulating Tfh cells was observed between controls and patients with MS. Instead, CSF concentrations of CXCL13 scaled with total counts of Tfh and Tfr cell subsets in the CSF.

DISCUSSION

Our study indicates substantial changes in intrathecal Tfh dynamics, particularly in patients with RRMS, and suggests that the intrathecal inflammatory environment in patients with RRMS promotes recruitment of peripheral Tfh cells rather than the Tfh cells having an increased capacity to migrate to CNS.

Ofatumumab Modulates Inflammatory T Cell Responses and Migratory Potential in Patients With Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The anti-CD20 antibody ofatumumab is an efficacious therapy for multiple sclerosis (MS) through depletion of B cells. The purpose of this study was to examine the derivative effects of B cell depletion on the peripheral immune system and a direct treatment effect on T cells expressing CD20.

METHODS

Frequency and absolute numbers of peripheral leukocytes of treatment-naive patients with relapsing-remitting MS (RRMS) and patients treated with ofatumumab for a mean of 482 days were assessed in this observational study by flow cytometry. In addition, effector function and CNS migration of T cells using a human in vitro blood-brain barrier (BBB) assay were analyzed.

RESULTS

This study showed that ofatumumab treatment of patients with RRMS increased the control of effector T cells and decreased T cell autoreactivity. It also showed that ofatumumab reduced the level of peripheral CD20⁺ T cells and that the observed decrease in CNS-migratory capacity of T cells was caused by the depletion of CD20⁺ T cells. Finally, our study pointed out a bias in the measurement of CD20⁺ cells due to a steric hindrance between the treatment antibody and the flow cytometry antibody.

DISCUSSION

The substantial ofatumumab-induced alteration in the T cell compartment including a severely decreased CNS-migratory capacity of T cells could partly be attributed to the depletion of CD20⁺ T cells. Therefore, we propose that depletion of CD20⁺ T cells contributes to the positive treatment effect of ofatumumab and suggests that ofatumumab therapy should be considered a B cell and CD20⁺ T cell depletion therapy.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that compared with treatment-naive patients, ofatumumab treatment of patients with RRMS decreases peripheral CD20⁺ T cells, increases effector T cell control, and decreases T cell autoreactivity.

Follicular Helper CD4+ T Cells, Follicular Regulatory CD4+ T Cells, and Inducible Costimulator and Their Roles in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Follicular helper CD4+ T (TFH) cells are a specialized subset of effector T cells that play a central role in orchestrating adaptive immunity. TFH cells mainly promote germinal center (GC) formation, provide help to B cells for immunoglobulin affinity maturation and class-switch recombination of B cells, and facilitate production of long-lived plasma cells and memory B cells. TFH cells express the nuclear transcriptional repressor B cell lymphoma 6 (Bcl-6), the chemokine (C-X-C motif) receptor 5 (CXCR5), the CD28 family members programmed cell death protein-1 (PD-1) and inducible costimulator (ICOS) and are also responsible for the secretion of interleukin-21 (IL-21) and IL-4. Follicular regulatory CD4+ T (TFR) cells, as a regulatory counterpart of TFH cells, participate in the regulation of GC reactions. TFR cells not only express markers of TFH cells but also express markers of regulatory T (Treg) cells containing FOXP3, glucocorticoid-induced tumor necrosis factor receptor (GITR), cytotoxic T lymphocyte antigen 4 (CTLA-4), and IL-10, hence owing to the dual characteristic of TFH cells and Treg cells. ICOS, expressed on activated CD4+ effector T cells, participates in T cell activation, differentiation, and effector process. The expression of ICOS is highest on TFH and TFR cells, indicating it as a key regulator of humoral immunity. Multiple sclerosis (MS) is a severe autoimmune disease that affects the central nervous system and results in disability, mediated by autoreactive T cells with evolving evidence of a remarkable contribution from humoral responses. This review summarizes recent advances regarding TFH cells, TFR cells, and ICOS, as well as their functional characteristics in relation to MS.

The OX40/OX40L Axis Regulates T Follicular Helper Cell Differentiation: Implications for Autoimmune Diseases

T Follicular helper (Tfh) cells, a unique subset of CD4+ T cells, play an essential role in B cell development and the formation of germinal centers (GCs). Tfh differentiation depends on various factors including cytokines, transcription factors and multiple costimulatory molecules. Given that OX40 signaling is critical for costimulating T cell activation and function, its roles in regulating Tfh cells have attracted widespread attention. Recent data have shown that OX40/OX40L signaling can not only promote Tfh cell differentiation and maintain cell survival, but also enhance the helper function of Tfh for B cells. Moreover, upregulated OX40 signaling is related to abnormal Tfh activity that causes autoimmune diseases. This review describes the roles of OX40/OX40L in Tfh biology, including the mechanisms by which OX40 signaling regulates Tfh cell differentiation and functions, and their close relationship with autoimmune diseases.

Differentiation, functions, and roles of T follicular regulatory cells in autoimmune diseases

T follicular helper cells participate in stimulating germinal center (GC) formation and supporting B cell differentiation and autoantibody production. However, T follicular regulatory (Tfr) cells suppress B cell activation. Since changes in the number and functions of Tfr cells lead to dysregulated GC reaction and autoantibody response, targeting Tfr cells may benefit the treatment of autoimmune diseases. Differentiation of Tfr cells is a multistage and multifactorial process with various positive and negative regulators. Therefore, understanding the signals regulating Tfr cell generation is crucial for the development of targeted therapies. In this review, we discuss recent studies that have elucidated the roles of Tfr cells in autoimmune diseases and investigated the modulators of Tfr cell differentiation. Additionally, potential immunotherapies targeting Tfr cells are highlighted.

Frontiers of Autoantibodies in Autoimmune Disorders: Crosstalk Between Tfh/Tfr and Regulatory B Cells

Balance of Tfh/Tfr cell is critically important for the maintenance of immune tolerance, as evidenced by the fact that T follicular helper (Tfh) cells are central to the autoantibodies generation through providing necessary help for germinal center (GC) B cells, whereas T follicular regulatory (Tfr) cells significantly inhibit autoimmune inflammation process through restraining Tfh cell responses. However, signals underlying the regulation of Tfh and Tfr cells are largely undefined. Regulatory B cells (Bregs) is a heterogeneous subpopulation of B cells with immunosuppressive function. Considerable advances have been made in their functions to produce anti‐inflammatory cytokines and to regulate Th17, Th1, and Treg cells in autoimmune diseases. The recent identification of their correlations with dysregulated Tfr/Tfh cells and autoantibody production makes Bregs an important checkpoint in GC response. Bregs exert profound impacts on the differentiation, function, and distribution of Tfh and Tfr cells in the immune microenvironment. Thus, unraveling mechanistic information on Tfh-Breg and Tfr-Breg interactions will inspire novel implications for the establishment of homeostasis and prevention of autoantibodies in diverse diseases. This review summarizes the dysregulation of Tfh/Tfr cells in autoimmune diseases with a focus on the emerging role of Bregs in regulating the balance between Tfh and Tfr cells. The previously unsuspected crosstalk between Bregs and Tfh/Tfr cells will be beneficial to understand the cellular mechanisms of autoantibody production and evoke a revolution in immunotherapy for autoimmune diseases.

Ectopic Lymphoid Follicles in Multiple Sclerosis: Centers for Disease Control?

While the contribution of autoreactive CD4⁺ T cells to the pathogenesis of Multiple Sclerosis (MS) is widely accepted, the advent of B cell-depleting monoclonal antibody (mAb) therapies has shed new light on the complex cellular mechanisms underlying MS pathogenesis. Evidence supports the involvement of B cells in both antibody-dependent and -independent capacities. T cell-dependent B cell responses originate and take shape in germinal centers (GCs), specialized microenvironments that regulate B cell activation and subsequent differentiation into antibody-secreting cells (ASCs) or memory B cells, a process for which CD4⁺ T cells, namely follicular T helper (T_FH) cells, are indispensable. ASCs carry out their effector function primarily via secreted Ig but also through the secretion of both pro- and anti-inflammatory cytokines. Memory B cells, in addition to being capable of rapidly differentiating into ASCs, can function as potent antigen-presenting cells (APCs) to cognate memory CD4⁺ T cells. Aberrant B cell responses are prevented, at least in part, by follicular regulatory T (T_FR) cells, which are key suppressors of GC-derived autoreactive B cell responses through the expression of inhibitory receptors and cytokines, such as CTLA4 and IL-10, respectively. Therefore, GCs represent a critical site of peripheral B cell tolerance, and their dysregulation has been implicated in the pathogenesis of several autoimmune diseases. In MS patients, the presence of GC-like leptomeningeal ectopic lymphoid follicles (eLFs) has prompted their investigation as potential sources of pathogenic B and T cell responses. This hypothesis is supported by elevated levels of CXCL13 and circulating T_FH cells in the cerebrospinal fluid (CSF) of MS patients, both of which are required to initiate and maintain GC reactions. Additionally, eLFs in post-mortem MS patient samples are notably devoid of T_FR cells. The ability of GCs to generate and perpetuate, but also regulate autoreactive B and T cell responses driving MS pathology makes them an attractive target for therapeutic intervention. In this review, we will summarize the evidence from both humans and animal models supporting B cells as drivers of MS, the role of GC-like eLFs in the pathogenesis of MS, and mechanisms controlling GC-derived autoreactive B cell responses in MS.

The multifaceted functions of follicular regulatory T cells

The immune system is capable of generating robust antibody responses to foreign antigens during infection and vaccination, while simultaneously limiting antibodies to self-antigens. T follicular regulatory (Tfr) cells are a subset of follicular T cell with specialized roles in regulating humoral immunity. Although Tfr cells have been studied for the past 10 years, their roles have remained elusive. In this review we discuss the current understanding of Tfr cell functions in autoimmunity and how Tfr cells simultaneously control foreign and autoantigen specific antibody responses. We highlight new tools that enable in-depth study of Tfr cells in vivo and recent data suggesting an important role for Tfr cells in limiting participation of autoreactive B cells in germinal centers.

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.

Immune and Inflammatory Determinants Underlying Alzheimer's Disease Pathology

This study examines the link between peripheral immune changes in perpetuation of the Alzheimer's disease (AD) neuropathology and cognitive deficits. Our research design using human AD patients and rodent model is supported by past evidence from genomic studies. We observed an active immune response against Aβ as indicated by the increased Aβ specific IgG antibody in the serum of AD and patients with mild cognitive impairments as compared to healthy controls. A similar increase in IgG and decrease in IgM antibody against Aβ was also confirmed in the 5xFAD mouse model of AD. More importantly, we observed a negative correlation between reduced IgM levels and cognitive dysfunction that manifested as impaired memory consolidation. Strong peripheral immune activation was supported by increased activation of microglia in the brain and macrophages in the spleen of AD mice compared to wild type control littermates. Furthermore, inflammatory cytokine IL-21 that is involved in antibody class switching was elevated in the plasma of AD patients and correlated positively with the IgG antibody levels. Concurrently, an increase in IL-21 and IL-17 was observed in spleen cells from AD mice. Further investigation revealed that proportions of T follicular helper (Tfh) cells that secrete IL-21 are increased in the spleen of AD mice. In contrast to Tfh, the frequency of B1 cells that produce IgM antibodies was reduced in AD mice. Altogether, these data indicate that in AD the immune tolerance to Aβ is compromised leading to chronic immune/inflammatory responses against Aβ that are detrimental and cause neuropathology. Graphical Abstract Healthy subjects are tolerant to Aβ and usually react weakly to it resulting the in the production of IgM class of antibodies that are efficient at clearing up self-antigens such as Aβ without causing inflammation. In contrast, Alzheimer's disease patients mount a strong immune response against Aβ probably in an effort to clear up excessive Aβ. There is enhanced production of inflammatory cytokines such as IL-21 as well as an increase in Tfh cells that cause antibody class switching form IgM to IgG. The strong immune response is inefficient at clearing up Aβ and instead exacerbates inflammation that causes AD neuropathology and cognitive dysfunction.

Follicular regulatory T cells: a novel target for immunotherapy?

High‐affinity antibodies are produced during multiple processes in germinal centres (GCs), where follicular helper T (Tfh) cells interact closely with B cells to support B‐cell survival, differentiation and proliferation. Recent studies have revealed that a specialised subset of regulatory T cells, follicular regulatory T (Tfr) cells, especially fine‐tune Tfh cells and GC B cells, ultimately regulating GC reactions. Alterations in frequencies or function of Tfr cells may result in multiple autoantibody‐mediated or autoantibody‐associated diseases. This review discusses recent insights into the physiology and pathology of Tfr cells, with a special emphasis on their potential roles in human diseases. Discrepancies are common among studies, reflecting the limited understanding of Tfr cells. Further exploration of the mechanisms of Tfr cells in these diseases and thus targeting Tfr cells may help reinstate immune homeostasis and provide novel immunotherapy.

Lymphoid Aggregates in the CNS of Progressive Multiple Sclerosis Patients Lack Regulatory T Cells

In gray matter pathology of multiple sclerosis, neurodegeneration associates with a high degree of meningeal inflammatory activity. Importantly, ectopic lymphoid follicles (eLFs) were identified at the inflamed meninges of patients with progressive multiple sclerosis. Besides T lymphocytes, they comprise B cells and might elicit germinal center (GC)-like reactions. GC reactions are controlled by FOXP3⁺ T-follicular regulatory cells (T_FR), but it is unknown if they participate in autoantibody production in eLFs. Receiving human post-mortem material, gathered from autopsies of progressive multiple sclerosis patients, indeed, distinct inflammatory infiltrates enriched with B cells could be detected in perivascular areas and deep sulci. CD35⁺ cells, parafollicular CD138⁺ plasma cells, and abundant expression of the homing receptor for GCs, CXCR5, on lymphocytes defined some of them as eLFs. However, they resembled GCs only in varying extent, as T cells did not express PD-1, only few cells were positive for the key transcriptional regulator BCL-6 and ongoing proliferation, whereas a substantial number of T cells expressed high NFATc1 like GC-follicular T cells. Then again, predominant cytoplasmic NFATc1 and an enrichment with CD3⁺CD27⁺ memory and CD4⁺CD69⁺ tissue-resident cells implied a chronic state, very much in line with PD-1 and BCL-6 downregulation. Intriguingly, FOXP3⁺ cells were almost absent in the whole brain sections and CD3⁺FOXP3⁺ T_FRs were never found in the lymphoid aggregates. This also points to less controlled humoral immune responses in those lymphoid aggregates possibly enabling the occurrence of CNS-specific autoantibodies in multiple sclerosis patients.

Imbalance of Circulatory T Follicular Helper and T Follicular Regulatory Cells in Patients with ANCA-Associated Vasculitis

Antineutrophil cytoplasmic antibody- (ANCA-) associated vasculitis (AAV) is characterized by small-vessel inflammation in association with autoantibodies. Balance between T follicular helper (Tfh) cells and T follicular regulatory (Tfr) cells is critical for humoral immune responses. Accumulating evidence supports that Tfh and Tfr are involved in autoimmune diseases; however, their roles in AAV are unclear. In this study, we tested the changes of circulatory Tfh and Tfr in patients with AAV. Twenty patients with AAV and twenty healthy controls were enrolled. Sixteen AAV patients had kidney involvement. We found that the AAV patients had increased circulating Tfh cells (CD4⁺CXCR5⁺CD25^-CD127^interm-hi), decreased Tfr cells (CD4⁺CXCR5⁺CD25⁺CD127^lo-interm), and elevated Tfh/Tfr ratios compared with healthy controls (P < 0.01). The Tfh percentage and Tfh/Tfr ratio, but not Tfr percentage, were positively correlated to proteinuria levels and BVAS scores in patients with AAV (P < 0.01). In addition, AAV patients had decreased circulating Tfh1 (CCR6^-CXCR3⁺), but increased Tfh2 cells (CCR6^-CXCR3^-), compared with healthy controls (P < 0.01), indicating a Tfh1-to-Tfh2 shift. Furthermore, remission achieved by immunosuppressive treatment markedly attenuated the increase of total Tfh (P < 0.01) and Tfh2 cells (P < 0.05), promoted the Tfh1 response (P < 0.05), and recovered the balance between Tfh/Tfr cells (P < 0.05) and between Tfh1/Tfh2 cells (P < 0.05) in patients with AAV. Plasma levels of IL-21, a cytokine secreted by Tfh cells, were elevated in AAV patients compared with healthy controls (P < 0.01), which was attenuated by immunosuppressive treatment (P < 0.05). Taken together, our findings indicate that circulatory Tfh/Tfr ratios, Tfh2/Tfh1 shift, and plasma IL-21 levels are associated with AAV and disease activity.