A regulatory effect of IL-21 on T follicular helper-like cell and B cell in rheumatoid arthritis

Influence of environmental exposures on T follicular helper cell function and implications on immunity: a comparison of Bangladeshi and American children

T follicular helper (Tfh) cells are crucial for B cell activation and subsequent antibody production. This functionality is influenced by surface markers such as CD40L, a costimulatory factor which promotes B cell activation, and CD57, which is a well-known marker of senescence. This study examined age-specific differences in Tfh cell function in Bangladeshi and American children. At age two, Bangladeshi children displayed impaired CD40L upregulation and significant CD57 downregulation upon stimulation. These patterns, not observed in American children of the same age, suggested an exhaustion-like phenotype potentially driven by environmental factors. Random forest and generalized estimating equations (GEE) modeling was used to analyze predictors of Tfh cell response to stimulation. Days since the last antibiotic treatment, total antibiotic treatments, diarrheal episodes, and malnutrition were identified as variables that significantly impacted the Tfh response to stimuli. To assess Tfh cell ability to promote antibody responses, we correlated Tfh functionality with antibody concentration post-vaccination and in response to infection with Cryptosporidium, an endemic apicomplexan parasite. Increased CD40L expression upon stimulation correlated positively with anti-Poliovirus type 2/3 neutralizing antibody and anti-Cp17 (a Cryptosporidium sporozoite antigen) IgA concentrations. In contrast, increased CD57 expression was significantly correlated with decreased anti-Cp17 IgA. This indicates that an activation-supportive phenotype (CD40L+) may be more effective in promoting immunity than a senescent phenotype (CD57+). Together, these findings suggest that early-life environmental exposures may program Tfh cell functionality, impacting immune response potential in settings with high pathogen exposure.

IMPORTANCE

T follicular helper (Tfh) cells are upstream mediators that shape the humoral immune response to specific antigens. The generation of an effective memory response to infection is vital to prevent subsequent reinfections. However, in areas with high burdens of exposure to infections, such as the urban community from Bangladesh studied here, children are consistently exposed to inflammatory pathogens. Specific environmental exposures significantly influenced Tfh cell activation and senescence phenotypes. Additionally, Tfh cell responses correlated with antibody concentrations following vaccination or infection, indicating that environmental factors may play a critical role in shaping effective immunity in early childhood.

Polarization of circulating follicular helper T cells correlates with bullous pemphigoid severity

BACKGROUND

Follicular helper T (Tfh) cells form a distinct population of T-helper cells with different polarizations (type 1, type 2 and type 17) that regulates humoral responses and may participate in the pathophysiology of B-cell-mediated autoimmune diseases such as bullous pemphigoid (BP), a dermatosis mediated by autoantibodies specific for hemi-desmosomal proteins.

OBJECTIVES

To evaluate the impact on circulating Tfh cells of super potent topical corticosteroid (TCS) treatment, which is more effective and safer than high doses of oral corticosteroids, and is the recommended first-line treatment of BP.

METHODS

Using flow cytometry, we compared the frequency, polarization and activation of Tfh cells in the blood of patients with BP with age- and sex-matched control participants without BP at baseline and longitudinally, after the initiation of TCS treatment.

RESULTS

We found that, at baseline, circulating Tfh cells were more frequent in patients with BP than in participants without BP and exhibited an activated phenotype. We further showed a decrease in type 1 and an increase in type 17 Tfh cells in the blood of patients with BP, which resulted in a higher type 2 + type 17 to type 1 Tfh cell ratio. This ratio correlated positively with disease severity, as measured by the Bullous Pemphigoid Disease Area Index. Remarkably, with TCS treatment, although the frequency of Tfh cells in patients with BP returned to a level similar to that of control participants, the activated phenotype persisted. Interestingly, serum interleukin-21 levels and the Tfh cell subset ratio, similarly to disease activity and serum anti-BP180 and anti-BP230 autoantibodies, decreased with TCS treatment.

CONCLUSIONS

Overall, our findings suggest the involvement Tfh cell polarization in the pathophysiology of BP and open the door to modulation of Tfh cell activity for treatment purposes.

The PPAR-α selective agonist WY14643 improves lupus nephritis via the downregulation of the RORγT/STAT3 signaling pathway in MRL/lpr mice

Systemic lupus erythematosus (SLE) is a classic autoimmune disorder that mostly affects young women and involves various organs, such as the skin, joints, central nervous system, and kidneys. WY14643, a selective agonist of peroxisome proliferator-activated receptor-α, has previously shown anti-inflammatory effects in various disease models. However, its effects on lupus nephritis are yet to be explored. Therefore, the efficacy of WY14643 on renal biomarkers and lupus nephritis was assessed in MRL/lpr mice. Flow cytometry was used to examinethe effects of WY14643 on the expression of IL-17A, STAT3, RORγT, IL-21, IL-21R, IL-22, and TNF-α in splenic CD4+ T cells. We further investigated the impact of WY14643 on the mRNA expression of IL-17A, STAT3, RORγT, IL-21, IL-21R, IL-22, and TNF-α in kidney tissue via RT-PCR analysis. The administration of WY14643 effectively improved the symptoms of lupus nephritis in MRL/lpr mice. The administration of WY14643 decreased serum albumin, urine protein, serum creatinine, and blood urea nitrogen levels in MRL/lpr mice. WY14643 reduced the levels of inflammatory markers, including CD4+IL-17A+, CD4+STAT3+, CD4+RORγT+, CD4+IL-21+, CD4+IL-21R+, CD4+IL-22+, and CD4+TNF-α+, in the spleen cells of MRL/lpr mice. Additionally, we discovered that the administration of WY14643 resulted in the suppression of mRNA levels of IL-17A, STAT3, RORγT, IL-21, IL-22, and TNF-α. The current work shows that the suppression of inflammatory cells by WY14643 may effectively reduce autoimmune characteristics, such as renal inflammation, in lupus-prone MRL/lpr mice. Therefore, WY14643, being a specific PPAR-α agonist, shows significant potential as a novel therapeutic option for treatingnephritis associated with SLE, offering hope for future treatments in this challenging field.

Helper T Cells are Hyperactive and Contribute to the Dysregulation of Antibody Production in Patients with Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease, mediated by a complex interaction between B cells and various subsets of T cells. Dysfunction of helper T (Th) and regulatory T (Treg) cells may contribute to the breakdown of self-tolerance and the progression of autoimmune disease. In this study, we investigated the activity of Th and Treg cells on the differentiation of autologous B cells in vitro using cell cultures from the peripheral blood of healthy controls (HCs) and RA patients. The expressions of programmed death 1 (PD-1) and IL-21 were monitored as activation markers for Th cells. Unstimulated Th cells from RA patients showed remarkably higher PD-1 expression than HC samples. Stimulation of Th cells from RA patients with Staphylococcus enterotoxin B (SEB) in the presence of B cells significantly induced their PD-1 and IL-21 expression at a considerably higher level in RA compared to HCs, and Treg cells did not affect IL-21 production. When monitoring B-cell differentiation, a significantly higher frequency of plasma cells was observed, even in unstimulated samples of RA patients compared to HCs. In the SEB-stimulated co-cultures of the RA samples, plasma cell frequency and IgG production were considerably higher than in HCs and were not significantly affected by Tregs. These findings demonstrate that Th cells are constitutively active in RA, and their hyperactivity upon interaction with diseased B cells may lead to uncontrolled antibody production.

Role of T follicular helper cells in autoimmune rheumatic Diseases: A systematic review on immunopathogenesis and response to treatment

BACKGROUND

T follicular helper (Tfh) cells are a subdivision of T helper cells involved in antigen-specific B cell immunity. Tfh cells play an essential role in the interaction of T cells/B cells in the germinal centers (GC), and dysregulation of Tfh actions can offer pathogenic autoantibody formation and lead to the development of autoimmune diseases. This study seeks to evaluate changes in Tfh frequency and its related cytokines in autoimmune disease, its association with disease phase, severity, prognosis, and the effect of immunosuppressive treatment on the Tfh population.

METHOD

The study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 Statement. Electronic databases, including PubMed, Scopus, Web of Science, and Embase, were systematically searched for potentially eligible studies up to January 1, 2024.

RESULTS

We identified 4998 articles in the initial search, from which 1686 similar titles were removed. A total of 3312 articles were initially screened, and 3051 articles were excluded by title/abstract screening. A total of 261 studies were considered for full-text assessment, and 205 articles were excluded by reason. Finally, a total of 56 studies were included in our review.

CONCLUSION

The population of Tfh cells is generally higher in autoimmune diseases versus Health control. Moreover, the number of Tfh cells is associated with the disease severity and can be considered for determining the prognosis of studies. Also, peripheral blood circulating Tfh (cTfh) cells are an available sample that can be used as an indicator for diagnosing diseases.

Exploring the Role of PD-1 in the Autoimmune Response: Insights into Its Implication in Systemic Lupus Erythematosus

Despite advances in understanding systemic lupus erythematosus (SLE), many challenges remain in unraveling the precise mechanisms behind the disease's development and progression. Recent evidence has questioned the role of programmed cell death protein 1 (PD-1) in suppressing autoreactive CD4+ T cells during autoimmune responses. Research has investigated the potential impacts of PD-1 on various CD4+ T-cell subpopulations, including T follicular helper (Tfh) cells, circulating Tfh (cTfh) cells, and T peripheral helper (Tph) cells, all of which exhibit substantial PD-1 expression and are closely related to several autoimmune disorders, including SLE. This review highlights the complex role of PD-1 in autoimmunity and emphasizes the imperative for further research to elucidate its functions during autoreactive T-cell responses. Additionally, we address the potential of PD-1 and its ligands as possible therapeutic targets in SLE.

The role of Interleukin-21 (IL-21) in allergic disorders: Biological insights and regulatory mechanisms

In recent decades, allergic diseases subsequent from an IgE-mediated response to specific allergens have become a progressively public chronic disease worldwide. They have shaped an important medical and socio-economic burden. A significant proportion of allergic disorders are branded via a form 2 immune response relating Th2 cells, type 2 natural lymphoid cells, mast cells and eosinophils. Interleukin-21 (IL-21) is a participant of the type-I cytokine family manufactured through numerous subsets of stimulated CD4+ T cells and uses controlling properties on a diversity of immune cells. Increasingly, experimental sign suggests a character for IL-21 in the pathogenesis of numerous allergic disorders. The purpose of this review is to discuss the biological properties of IL-21 and to summaries current developments in its role in the regulation of allergic disorders.

The changes of intestinal flora and its relevance with memory Tfh and B cells in rheumatoid arthritis patients treated with csDMARDs and csDMARDs + bDMARDs

BACKGROUND

A growing body of experimental and clinical evidence has implicated gut microbiota in the onset and course of rheumatoid arthritis (RA). The imbalance of intestinal flora in RA patients may lead to abnormal expression of immune cells and related cytokines.

PURPOSE

Conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) and conventional synthetic disease-modifying antirheumatic drugs combined with biological disease-modifying antirheumatic drugs (csDMARDs + bDMARDs) are widely used to treat RA, but the characteristics of gut microbiota before and after treatment and their relationship with memory Tfh/B cells and cytokines remain unclear.

METHODS

Stool samples were collected from 50 RA patients and 25 healthy controls (HCs) for 16SrRNA gene sequencing. We examined the proportion of lymphocyte subsets in healthy controls and RA patients. Enzyme linked immunosorbent assay (ELISA) was used to detect the levels of related cytokines in serum. The α and β diversity of intestinal flora, and the correlation between intestinal flora and clinical indicators, lymphocyte subsets, cytokines were analyzed.

RESULT

At the genus level, Ruminococcaceae_Ruminococcus was decreased in the csDMARDs and csDMARDs + bDMARDs treatment group, whereas Faecalibacterium was reduced in the csDMARDs treatment group, compared to untreated group. CD4+CD45RO+CCR7+CXCR5+central memory Tfh cells and CD4+CD45RO+CCR7-CXCR5+effector memory Tfh cells were significantly lower in the csDMARDs + bDMARDs treatment group than in untreated group. CD19+CD27+IgD+pre-switched memory B cells were higher in the csDMARDs and csDMARDs + bDMARDs treatment groups, whereas CD19+CD27+IgD-switched memory B cells were significantly lower than in untreated group. Ruminococcaceae_Ruminococcus was negatively correlated with CD19+CD27+IgD+ pre-switched memory B cells but positively correlated with CD4+CD45RO+CCR7-CXCR5+effector memory Tfh and CD19+CD27+IgD-switched memory B cells in patients with RA treated with DMARDs.

CONCLUSION

The gut microbiota, memory Tfh cells, memory B cells, and cytokines of patients with RA changed significantly under different treatment regimens and had certain correlations with the clinical indicators of RA.

T-cell help in the germinal center: homing in on the role of IL-21

Interleukin 21 (IL-21) is a pleiotropic cytokine that is overproduced in multiple autoimmune settings. Provision of IL-21 from follicular helper T cells is an important component of T-cell help within germinal centers (GC), and the last few years have seen a resurgence of interest in IL-21 biology in the context of the GC environment. While it has been more than a decade since T cell-derived IL-21 was found to upregulate B-cell expression of the GC master transcription factor B-cell lymphoma 6 (Bcl-6) and to promote GC expansion, several recent studies have collectively delivered significant new insights into how this cytokine shapes GC B-cell selection, proliferation, and fate choice. It is now clear that IL-21 plays an important role in GC zonal polarization by contributing to light zone GC B-cell positive selection for dark zone entry as well as by promoting cyclin D3-dependent dark zone inertial cycling. While it has been established that IL-21 can contribute to the modulation of GC output by aiding the generation of antibody-secreting cells (ASC), recent studies have now revealed how IL-21 signal strength shapes the fate choice between GC cycle re-entry and ASC differentiation in vivo. Both provision of IL-21 and sensitivity to this cytokine are finely tuned within the GC environment, and dysregulation of this pathway in autoimmune settings could alter the threshold for germinal center B-cell selection and differentiation, potentially promoting autoreactive B-cell responses.

T cell help shapes B cell tolerance

T cell help is a crucial component of the normal humoral immune response, yet whether it promotes or restrains autoreactive B cell responses remains unclear. Here, we observe that autoreactive germinal centers require T cell help for their formation and persistence. Using retrogenic chimeras transduced with candidate TCRs, we demonstrate that a follicular T cell repertoire restricted to a single autoreactive TCR, but not a foreign antigen-specific TCR, is sufficient to initiate autoreactive germinal centers. Follicular T cell specificity influences the breadth of epitope spreading by regulating wild-type B cell entry into autoreactive germinal centers. These results demonstrate that TCR-dependent T cell help can promote loss of B cell tolerance and that epitope spreading is determined by TCR specificity.

Selective blockade of IL-21 by myricetin impedes T follicular helper cell differentiation by negatively regulating the JAK/STAT/Bcl-6 pathway in a rheumatoid arthritis animal model

Interleukin (IL)-21 is a major lineage-defining factor that promotes Tfh cell differentiation. The current study investigated the molecular basis of myricetin, a flavonoid that impedes IL-21-mediated differentiation of Tfh cells in RA. Through high-throughput virtual screening of natural compounds that inhibit IL-21, we found that myricetin binds to IL-21 and hampers its interaction with IL-21 receptor (IL-21R). Our in vivo studies demonstrated that myricetin treatment ameliorated the clinical manifestations in adjuvant-induced arthritis (AIA) mice by reducing paw thickness and cellular infiltration. In addition, myricetin inhibited splenic Tfh cell differentiation and IL-21 production in AIA mice. Myricetin negatively regulates JAK/STAT signaling and the downstream Bcl-6 transcription factor at the molecular level, which arrests Tfh cell differentiation. Our current research proposal to target IL-21 with myricetin inevitably represents a new molecular approach that expedites new alternative drugs for rheumatoid arthritis therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03880-w.

IL-21 shapes germinal center polarization via light zone B cell selection and cyclin D3 upregulation

Germinal center (GC) dysregulation has been widely reported in the context of autoimmunity. Here, we show that interleukin 21 (IL-21), the archetypal follicular helper T cell (Tfh) cytokine, shapes the scale and polarization of spontaneous chronic autoimmune as well as transient immunization-induced GC. We find that IL-21 receptor deficiency results in smaller GC that are profoundly skewed toward a light zone GC B cell phenotype and that IL-21 plays a key role in selection of light zone GC B cells for entry to the dark zone. Light zone skewing has been previously reported in mice lacking the cell cycle regulator cyclin D3. We demonstrate that IL-21 triggers cyclin D3 upregulation in GC B cells, thereby tuning dark zone inertial cell cycling. Lastly, we identify Foxo1 regulation as a link between IL-21 signaling and GC dark zone formation. These findings reveal new biological roles for IL-21 within GC and have implications for autoimmune settings where IL-21 is overproduced.

Anti-human-TIGIT agonistic antibody ameliorates autoimmune diseases by inhibiting Tfh and Tph cells and enhancing Treg cells

T cells play important roles in autoimmune diseases, but it remains unclear how to optimally manipulate them. We focused on the T cell immunoreceptor with Ig and ITIM domains (TIGIT), a coinhibitory molecule that regulates and is expressed in T cells. In autoimmune diseases, the association between TIGIT-expressing cells and pathogenesis and the function of human-TIGIT (hu-TIGIT) signalling modification have not been fully elucidated. Here we generated anti-hu-TIGIT agonistic monoclonal antibodies (mAbs) and generated hu-TIGIT knock-in mice to accurately evaluate the efficacy of mAb function. Our mAb suppressed the activation of CD4⁺ T cells, especially follicular helper T and peripheral helper T cells that highly expressed TIGIT, and enhanced the suppressive function of naïve regulatory T cells. These results indicate that our mAb has advantages in restoring the imbalance of T cells that are activated in autoimmune diseases and suggest potential clinical applications for anti-hu-TIGIT agonistic mAbs as therapeutic agents.

CXCR3 antagonist NBI-74330 mitigates joint inflammation in Collagen-Induced arthritis model in DBA/1J mice

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by uncontrolled synovial proliferation, pannus formation, cartilage injury, and bone destruction. We used the CXCR3-specific antagonist NBI-74330 to block T-cell-mediated signaling in a DBA/1J mouse model of collagen-induced arthritis (CIA). After CIA induction, DBA/1J mice were treated with NBI-74330 (100 mg/kg) daily from day 21 until day 34 and evaluated for arthritic score and histopathological changes. Furthermore, using flow cytometry, we investigated the effects of NBI-74330 on Th1 (IFN-γ, TNF-α, T-bet, STAT4, Notch-3, and RANKL), Th17 (IL-21, IL-17A, STAT3, and RORγt), and Th22 (IL-22) cells in splenic CD4⁺ and CXCR3⁺T-cells. We also used RT-PCR to assess the effect of mRNA levels of IFN-γ, TNF-α, T-bet, RANKL, IL-17A, RORγt, and IL-22 in knee tissues. The IFN-γ, TNF-α, and IL-17A serum protein levels were measured using ELISA. Compared to vehicle-treated CIA mice, the severity of arthritic scores and histological severity of inflammation decreased significantly in NBI-74330-treated CIA mice. Moreover, compared to vehicle-treated CIA mice, the percentages of CD4⁺IFN-γ⁺, CD4⁺TNF-α⁺, CD4⁺T-bet⁺, CD4⁺STAT4⁺, CD4⁺Notch-3⁺, CXCR3⁺IFN-γ⁺, CXCR3⁺TNF-α⁺, CXCR3⁺T-bet⁺, CXCR3⁺STAT4⁺, CXCR3⁺Notch-3⁺, CD4⁺RANKL⁺, CD4⁺IL-21⁺, CD4⁺IL-17A⁺, CD4⁺STAT3⁺, CD4⁺RORγt⁺, and CD4⁺IL-22⁺ cells decreased in NBI-74330-treated CIA mice. Furthermore, NBI-74330-treatment downregulated IFN-γ, TNF-α, T-bet, RANKL, STAT3, IL-17A, RORγt, and IL-22 mRNA levels. Serum IFN-γ, TNF-α, and IL-17A levels were significantly lower in NBI-74330-treated CIA mice than in vehicle-treated CIA mice. This study demonstrates the antiarthritic effects of NBI-74330 in CIA mice. Therefore, these data suggest that NBI-74330 could be considered a potential RA treatment.

The endogenous repertoire harbors self-reactive CD4+ T cell clones that adopt a follicular helper T cell-like phenotype at steady state

The T cell repertoire of healthy mice and humans harbors self-reactive CD4+ conventional T (Tconv) cells capable of inducing autoimmunity. Using T cell receptor profiling paired with in vivo clonal analysis of T cell differentiation, we identified Tconv cell clones that are recurrently enriched in non-lymphoid organs following ablation of Foxp3+ regulatory T (Treg) cells. A subset of these clones was highly proliferative in the lymphoid organs at steady state and exhibited overt reactivity to self-ligands displayed by dendritic cells, yet were not purged by clonal deletion. These clones spontaneously adopted numerous hallmarks of follicular helper T (TFH) cells, including expression of Bcl6 and PD-1, exhibited an elevated propensity to localize within B cell follicles at steady state, and produced interferon-γ in non-lymphoid organs following sustained Treg cell depletion. Our work identifies a naturally occurring population of self-reactive TFH-like cells and delineates a previously unappreciated fate for self-specific Tconv cells.

Dynamics of circulating follicular helper T cell subsets and follicular regulatory T cells in rheumatoid arthritis patients according to HLA-DRB1 locus

B cells, follicular helper T (Tfh) cells and follicular regulatory T (Tfr) cells are part of a circuit that may play a role in the development or progression of rheumatoid arthritis (RA). With the aim of providing further insight into this topic, here we evaluated the frequency of different subsets of Tfh and Tfr in untreated and long-term treated RA patients from a cohort of Argentina, and their potential association with particular human leukocyte antigen (HLA) class-II variants and disease activity. We observed that the frequency of total Tfh cells as well as of particular Tfh subsets and Tfr cells were increased in seropositive untreated RA patients. Interestingly, when analyzing paired samples, the frequency of Tfh cells was reduced in synovial fluid compared to peripheral blood, while Tfr cells levels were similar in both biological fluids. After treatment, a decrease in the CCR7^loPD1^hi Tfh subset and an increase in the frequency of Tfr cells was observed in blood. In comparison to healthy donors, seropositive patients with moderate and high disease activity exhibited higher frequency of Tfh cells while seropositive patients with low disease activity presented higher Tfr cell frequency. Finally, we observed that HLA-DRB1*09 presence correlated with higher frequency of Tfh and Tfr cells, while HLA-DRB1*04 was associated with increased Tfr cell frequency. Together, our results increase our knowledge about the dynamics of Tfh and Tfr cell subsets in RA, showing that this is altered after treatment.

Olfactory Ecto-mesenchymal Stem Cell-derived Exosomes Ameliorate Murine Sjögren's Syndrome via Suppressing Tfh Cell Response

Objectives

To investigate the effect of olfactory ecto-mesenchymal stem cell-derived exosomes (OE-MSC-Exos) on T follicular helper (Tfh) cell response and their implication in treating experimental Sjögrens syndrome (ESS).

Methods

C57BL/6 mice were immunized with salivary glands (SG) proteins to induce ESS mouse model. OE-MSC-Exos were added to the Tfh cell polarization condition, and the proportion of Tfh cells was detected by FCM. The PD-L1 of OE-MSCs was silenced with small interfering RNA to extract siPD-L1-OE-MSC-Exos.

Results

We found that transfer of OE-MSC-Exos markedly attenuated disease progression and reduced Tfh cell response in mice with ESS. In culture, OE-MSC-Exos potently inhibited the differentiation of Tfh cells from naïve T cells. Moreover, OE-MSC-Exos expressed high level of the ligand for the programmed cell death protein 1 (PD-L1), knocking down PD-L1 expression in OE-MSC-Exos significantly decreased their capacity to suppress Tfh cell differentiation in vitro. Consistently, transfer of OE-MSC-Exos with PD-L1 knockdown exhibited profoundly diminished therapeutic effect in ESS mice, accompanied with sustained Tfh cell response and high levels of autoantibody production.

Conclusion

Our results suggest that OE-MSC-Exos may exert their therapeutic effect in ameliorating ESS progression via suppressing Tfh cell response in a PD-L1-dependent manner.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

Abnormal Function of Circulating Follicular Helper T Cells Leads to Different Manifestations of B Cell Maturation and Differentiation in Patients with Osteosarcoma

Objective

The objective of this study is to investigate the effect of dysfunctional circulating follicular helper T cells (Tfh) on B cell maturation and differentiation in patients with osteosarcoma (OS).

Method

Data from 30 OS patients who underwent diagnosis and treatment in our hospital, as well as those of 30 healthy subjects (HC), were collected at the same time. Flow cytometry was employed to identify proportions of CD4+CXCR5+Tfh cells and Tfh cell subtypes Tfh17, Tfh1, and Tfh2 in the patient's peripheral blood. CD40 L and IFNγ levels were detected after stimulating Tfh cells with an influenza antigen; the positive rates of CD27 and CD38 in B cells were detected before and after coculture with Tfh cells. qRT-PCR was carried out for Blimp-1 expression in B cells, and ELISA was employed to identify the levels of IgM, IgG, and IgA in B cells and IL-2, IL-10, and IL-4 in Tfh cells before and after coculture.

Results

The percentage of CD4+CXCR5+Tfh cells in OS patients' peripheral blood increased significantly. The Tfh cell ratio increased along with the TNM stage, and the Tfh cell ratio in OS metastasis patients is greater than that in nonmetastatic patients. In addition, Tfh2 and Tfh17 cells increased drastically in OS patients, and no meaningful change was seen in Tfh1 cells. CD40 L levels of Tfh cells in OS patients were less than those of the HC group, and IFNγ was substantially increased. After coculturing the OS group's B cells with Tfh cells, the CD27+ and CD38+ cells of B cells were drastically greater, and Blimp-1 expression was also significantly increased. In addition, the levels of IL-21, IL-4, and IL-10 of Tfh cells in the OS group and the levels of IgA, IgG, and IgM in B cells were significantly reduced after coculture.

Conclusion

Dysfunctional Tfh in OS patients can severely inhibit B cell development, maturation, and differentiation.

Increased Frequency of CD4+ Follicular Helper T and CD8+ Follicular T Cells in Human Lymph Node Biopsies during the Earliest Stages of Rheumatoid Arthritis

Follicular T helper cells (Tfh cells) provide key B-cell help and are essential in germinal center formation and (auto) antibody generation. To gain more insight into their role during the earliest phase of rheumatoid arthritis (RA), we analyzed their frequencies, phenotypes, and cytokine profiles in peripheral blood and lymph node biopsies of healthy controls (HCs), autoantibody-positive individuals at risk for developing RA (RA-risk individuals), and early RA patients. Subsequently, we confirmed their presence in lymph nodes and synovial tissue of RA patients using immunofluorescence microscopy. In the blood, the frequency of Tfh cells did not differ between study groups. In lymphoid and synovial tissues, Tfh cells were localized in B-cell areas, and their frequency correlated with the frequency of CD19⁺ B cells. Compared to lymphoid tissues of healthy controls, those of RA patients and RA-risk individuals showed more CD19⁺ B cells, CD4⁺CXCR5⁺ follicular helper T cells, and CD8⁺CXCR5⁺ follicular T cells. These Tfh cells produced less IL-21 upon ex vivo stimulation. These findings suggest that Tfh cells may present a novel rationale for therapeutic targeting during the preclinical stage of RA to prevent further disease progression.

Role of the CXCL13/CXCR5 Axis in Autoimmune Diseases

CXCL13 is a B-cell chemokine produced mainly by mesenchymal lymphoid tissue organizer cells, follicular dendritic cells, and human T follicular helper cells. By binding to its receptor, CXCR5, CXCL13 plays an important role in lymphoid neogenesis, lymphoid organization, and immune responses. Recent studies have found that CXCL13 and its receptor CXCR5 are implicated in the pathogenesis of several autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, systemic lupus erythematosus, primary Sjögren’s syndrome, myasthenia gravis, and inflammatory bowel disease. In this review, we discuss the biological features of CXCL13 and CXCR5 and the recent findings on the pathogenic roles of the CXCL13/CXCR5 axis in autoimmune diseases. Furthermore, we discuss the potential role of CXCL13 as a disease biomarker and therapeutic target in autoimmune diseases.

A review of signaling and transcriptional control in T follicular helper cell differentiation

T follicular helper (Tfh) cells are a critical component of adaptive immunity and assist in optimal Ab-mediated defense. Multiple effector functions of Tfh support germinal center B cell survival, Ab class switching, and plasma cell maturation. In the past 2 decades, the phenotype and functional characteristics of GC Tfh have been clarified allowing for robust studies of the Th subset including activation signals and environmental cues controlling Tfh differentiation and migration during an immune response. A unique, 2-step differentiation process of Tfh has been proposed but the mechanisms underlying transition between unstable Tfh precursors and functional mature Tfh remain elusive. Likewise, newly identified transcriptional regulators of Tfh development have not yet been incorporated into our understanding of how these cells might function in disease. Here, we review the signals and downstream transcription factors that shape Tfh differentiation including what is known about the epigenetic processes that maintain Tfh identity. It is proposed that further evaluation of the stepwise differentiation pattern of Tfh will yield greater insights into how these cells become dysregulated in autoimmunity.

IL-21 impairs pro-inflammatory activity of M1-like macrophages exerting anti-inflammatory effects on rheumatoid arthritis

Objective：Macrophages are the main source of inflammatory mediators and play important roles in the pathogenesis of rheumatoid arthritis (RA). Interleukin-21 (IL-21) regulates both innate and adaptive immune responses and exerts major effects on inflammatory responses that promote the development of RA. However, its effect on macrophage polarisation remains unclear.Methods：CD14⁺ monocytes of the peripheral blood of Human healthy donors (HD) and RA, and macrophages of RA synovial fluid (RA-SF MΦs) were isolated. IL-21 receptor (IL-21R) was detected by flow cytometry. Cytokine production by MΦs from different sources pre-treated with IL-21 and/or LPS was measured by real-time polymerase chain reaction (RT-PCR) and ELISA. CD14⁺ monocytes were differentiated into M1-like and M2-like macrophages via stimulation with GM-CSF, interferon-γ (IFN-γ), and LPS or M-CSF, IL-4, and IL-13, respectively. To determine the effect of IL-21 on macrophage polarisation, macrophage phenotypes, gene expression, and cytokine secretion were detected by flow cytometry, RT-PCR, and ELISA. TLR4 and ERK1/2 were determined by western blotting.Results：IL-21 exerted different effects on LPS-mediated inflammatory responses in various derived MΦs, and inhibited macrophages polarisation to M1-like macrophages and promote their polarisation to M2-like macrophages in HD and RA. Moreover, IL-21 inhibited LPS-mediated secretion of inflammatory cytokines, probably by downregulating the ERK1/2, in RA-SF MΦs.Conclusion：For the first time, we indicated that IL-21 inhibits LPS-mediated cytokine production in RA-SF MΦs, and impairs pro-inflammatory activity of M1-like macrophages, hereby exerting anti-inflammatory effects on RA. Thus, IL-21 might not be an appropriate therapeutic target for RA.

Follicular T cells are clonally and transcriptionally distinct in B cell-driven mouse autoimmune disease

Pathogenic autoantibodies contribute to tissue damage and clinical decline in autoimmune disease. Follicular T cells are central regulators of germinal centers, although their contribution to autoantibody-mediated disease remains unclear. Here we perform single cell RNA and T cell receptor (TCR) sequencing of follicular T cells in a mouse model of autoantibody-mediated disease, allowing for analyses of paired transcriptomes and unbiased TCRαβ repertoires at single cell resolution. A minority of clonotypes are preferentially shared amongst autoimmune follicular T cells and clonotypic expansion is associated with differential gene signatures in autoimmune disease. Antigen prediction using algorithmic and machine learning approaches indicates convergence towards shared specificities between non-autoimmune and autoimmune follicular T cells. However, differential autoimmune transcriptional signatures are preserved even amongst follicular T cells with shared predicted specificities. These results demonstrate that follicular T cells are phenotypically distinct in B cell-driven autoimmune disease, providing potential therapeutic targets to modulate autoantibody development.

B Cells in Rheumatoid Arthritis：Pathogenic Mechanisms and Treatment Prospects

Rheumatoid arthritis (RA) is a common, chronic, systemic autoimmune disease, and its clinical features are the proliferation of joint synovial tissue, the formation of pannus and the destruction of cartilage. The global incidence of RA is about 1%, and it is more common in women. The basic feature of RA is the body’s immune system disorders, in which autoreactive CD4⁺T cells, pathogenic B cells, M1 macrophages, inflammatory cytokines, chemokines and autoantibodies abnormally increase in the body of RA patients B cell depletion therapy has well proved the important role of B cells in the pathogenesis of RA, and the treatment of RA with B cells as a target has also been paid more and more attention. Although the inflammatory indicators in RA patients receiving B-cell depletion therapy have been significantly improved, the risk of infection and cancer has also increased, which suggests that we need to deplete pathogenic B cells instead of all B cells. However, at present we cannot distinguish between pathogenic B cells and protective B cells in RA patients. In this review, we explore fresh perspectives upon the roles of B cells in the occurrence, development and treatment of RA.

AIRE-overexpressing BMDCs suppress TFH cells through ICOSL to prevent and attenuate autoimmune diabetes in NOD mice

The strong genetic association between autoimmune regulator (AIRE) and autoimmune diseases indicates its critical role in immune tolerance. AIRE deficiency is thought to promote the development of follicular helper T (TFH) cells, which are considered to be essential in B cell proliferation. Excessive TFH cell generation is a key step towards the development of autoimmune diseases, including type 1 diabetes. However, the potential mechanism by which AIRE contributes to the generation and function of the TFH cell population has remained elusive. We show that AIRE reduced TFH cell generation by inhibiting the expression of inducible costimulatory ligand (ICOSL), interleukin (IL)-6 and IL-27 in dendritic cells (DCs). To understand the precise impact of AIRE-overexpressing bone marrow-derived DCs (AIRE-BMDCs) on type 1 diabetes progression and the associated molecular mechanisms, we transferred AIRE-BMDCs to recipient NOD mice and found that transplantation of AIRE-BMDCs can prevent or delay the onset of diabetes, attenuate diabetes after the establishment of overt hyperglycaemia, and lead to the inhibition of autoreactive pathological TFH cells and germinal centre (GC) B cells. To further determine the potential mechanism underlying this TFH cell depletion, BMDCs were cotransferred with recombinant mouse ICOSL (ICOSLG protein). We demonstrated that NOD mice were more susceptible to diabetes when they received AIRE-BMDCs and ICOSLG than when they received only mock-vehicle BMDCs (GFP-BMDCs). In addition, we did not observe the reversal of diabetes in any mice subjected to this cotransfer system. A single cycle of ICOSLG treatment temporarily promoted TFH cell proliferation and GC development. Our results reveal a mechanistic role of AIRE-BMDCs in the initiation of TFH cell differentiation, and the AIRE-mediated decrease in ICOSL expression in BMDCs plays a critical role. The effect of decreased ICOSL expression in type 1 diabetes will guide the design and evaluation of parallel studies in patients.

Altered distributions in circulating follicular helper and follicular regulatory T cells accountable for imbalanced cytokine production in multiple sclerosis

Follicular T helper (Tfh) and regulatory (Tfr) cells are distinct subsets of CD4+ T lymphocytes, regulating humoral immune responses in the germinal center. It is widely accepted that dysregulated Tfh and Tfr cells are associated with autoimmunity. In this study, we evaluated the frequencies of circulating chemokine receptor (CXCR)5+ programmed cell death 1 (PD-1+ ) Tfh (cTfh) and CXCR5+ PD-1+ forkhead box protein 3 (FoxP3+ ) CD25+ Tfr (cTfr) cells, and their corresponding cytokines from the peripheral blood mononuclear cells of 28 patients with relapsing-remitting multiple sclerosis (MS) and 16 age- and sex-matched healthy controls (HC). Subsets of cTfh cells by Th1- and Th17-related surface markers (CXCR3 and CCR6) were also evaluated. We found that the frequency of cTfh cells was significantly higher in MS patients compared to that of HC. Conversely, the frequency of cTfr cells was lower in MS patients than that of HC. Interleukin (IL)-21-producing cTfh cells were significantly increased in MS patients, while IL-10-secreting cTfr cells were lower in MS patients compared to levels in HC. Among cTfh cells, cTfh17.1 cells were the major subtypes that were significantly increased in MS patients compared to HC, with the frequency of IL-21-secreting cells being the highest. These results suggest that an imbalanced distribution of cTfh and cTfr exist in MS patients, which contributes to the reciprocally altered IL-21 and IL-10 production.

Conventional type 2 lung dendritic cells are potent inducers of follicular helper T cells in the asthmatic lung

BACKGROUND

Follicular helper T (Tfh) cells represent a unique subset of helper CD4⁺ T cells in lymphoid follicles. Recently, Tfh cells were shown to play an important role in asthma through B cell differentiation. Conventional lung DCs are classified into two major subsets: conventional type 1 (cDC1) and type 2 (cDC2). Although the two subsets are different in driving particular T cell responses, the subset that induces Tfh cells in the asthmatic lung primarily has yet to be fully elucidated.

METHODS

We evaluated Tfh cells, defined by the expression of CD4 and CXCR5, in HDM-challenged mice. Next, we characterized cDC1 and cDC2 purified from antigen-primed lung and examined their Tfh cell-inducing capacity. Additionally, the ability of lung DC-induced Tfh cells to cause germinal center B (GCB) cells to produce antigen-specific IgE was assessed.

RESULTS

In HDM-challenged mice, Bcl-6-expressing Tfh cells were significantly increased in the mediastinal lymph nodes. Lung cDC2, but not lung cDC1, increased after HDM priming, and cDC2 secreted larger amounts of IL-6 with higher ICOS-L expression than cDC1. In the co-cultures with OVA-specific naïve CD4⁺ T cells, cDC2 from OVA-primed lung induced Bcl-6-expressing Tfh cells more efficiently, together with larger amounts of IL-6 and IL-21, than cDC1. Blockage of IL-6 or ICOS-L significantly reduced Tfh cell induction. Finally, cDC2-induced Tfh cells enabled GCB cells to produce OVA-specific IgE.

CONCLUSIONS

In asthmatic lung, cDC2 is the primary DC subset responsible for Tfh cell differentiation and plays an important role in humoral immunity in asthma by inducing Tfh cells.

Follicular helper T cells: potential therapeutic targets in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease with joint and systemic inflammation that is accompanied by the production of autoantibodies, such as rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies. Follicular helper T (Tfh) cells, which are a subset of CD4+ T cells, facilitate germinal center (GC) reactions by providing signals required for high-affinity antibody production and the generation of long-lived antibody-secreting plasma cells. Uncontrolled expansion of Tfh cells is observed in various systemic autoimmune diseases. Particularly, the frequencies of circulating Tfh-like (cTfh-like) cells, their subtypes and synovial-infiltrated T helper cells correlate with disease activity in RA patients. Therefore, reducing autoantibody production and restricting excessive Tfh cell responses are ideal ways to control RA pathogenesis. The present review summarizes current knowledge of the involvement of Tfh cells in RA pathogenesis and highlights the potential of these cells as therapeutic targets.

Helper T Cells in Idiopathic Membranous Nephropathy

Idiopathic membranous nephropathy (IMN) is an autoimmune disease in which the immune system produces an antibody response to its own antigens due to impaired immune tolerance. Although antibodies are derived from plasma cells differentiated by B cells, the T-B cells also contribute a lot to the immune system. In particular, the subsets of helper T (Th) cells, including the dominant subsets such as Th2, Th17, and follicular helper T (Tfh) cells and the inferior subsets such as regulatory T (Treg) cells, shape the immune imbalance of IMN and promote the incidence and development of autoimmune responses. After reviewing the physiological knowledge of various subpopulations of Th cells and combining the existing studies on Th cells in IMN, the role model of Th cells in IMN was explained in this review. Finally, the existing clinical treatment regimens for IMN were reviewed, and the importance of the therapy for Th cells was highlighted.

Objective and noninvasive biochemical markers in rheumatoid arthritis: where are we and where are we going?

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects approximately 1% of the adult population. RA is multi-factorial, and as such our understanding of the molecular pathways involved in the disease is currently limited. An increasing number of studies have suggested that several molecular phenotypes (i.e. endotypes) of RA exist, and that different endotypes respond differently to various treatments. Biochemical markers may be an attractive means for achieving precision medicine, as they are objective and easily obtainable.

AREAS COVERED

We searched recent publications on biochemical markers in RA as either diagnostic or prognostic markers, or as markers of disease activity. Here, we provide a narrative overview of different classes of markers, such as autoantibodies, citrulline products, markers of tissue turnover and cytokines, that have been tested in clinical cohorts or trials including RA patients.

EXPERT OPINION

Although many biochemical markers have been identified and tested, few are currently being used in clinical practice. As more treatment options are becoming available, the need for precision medicine tools that can aid physicians and patients in choosing the right treatment is growing.

Alcohol Consumption in Rheumatoid Arthritis: A Path through the Immune System

Benefits and harms of different components of human diet have been known for hundreds of years. Alcohol is one the highest consumed, abused, and addictive substances worldwide. Consequences of alcohol abuse are increased risks for diseases of the cardiovascular system, liver, and nervous system, as well as reduced immune system function. Paradoxically, alcohol has also been a consistent protective factor against the development of autoimmune diseases such as type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis (RA). Here, we focused on summarizing current findings on the effects of alcohol, as well as of its metabolites, acetaldehyde and acetate, on the immune system and RA. Heavy or moderate alcohol consumption can affect intestinal barrier integrity, as well as the microbiome, possibly contributing to RA. Additionally, systemic increase in acetate negatively affects humoral immune response, diminishing TFH cell as well as professional antigen-presenting cell (APC) function. Hence, alcohol consumption has profound effects on the efficacy of vaccinations, but also elicits protection against autoimmune diseases. The mechanism of alcohol's negative effects on the immune system is multivariate. Future studies addressing alcohol and its metabolite acetate's effect on individual components of the immune system remains crucial for our understanding and development of novel therapeutic pathways.

Proportion of T follicular helper cells in peripheral blood of rheumatoid arthritis patients: a systematic review and meta-analysis

Introduction:Alterations in the levels and activity of Tfh may lead to impaired immune tolerance and autoimmune diseases. The aim of this study was to investigate the proportion and types of Tfh cells in the peripheral blood (PB) of RA patients.Areas covered:Comprehensive databases were searched for studies evaluating the proportion of Tfh cells in the PB of patients with RA compared to healthy control (HCs).The proportion of Tfh cells in RA patients was significantly higher than in HCs (SMD 0.699, [0.513, 0.884], p < 0.0001). Furthermore, Tfh cells proportion in untreated-RA and early-RA patients was markedly greater than HCs, when comparisons done without considering the definition markers, and also when Tfh cells were defined by the specified definition markers. While the proportion of Tfh cells by all definitions was higher in active-RA compared to HCs, analysis of two definitions, CD4⁺CXCR5⁺ and CD4⁺CXCR5⁺ICOS⁺, didn't show significant differences. Furthermore, higher proportion of Tfh cells defined by all definitions and a specified definition (CD4⁺CXCR5⁺PD-1^high) was observed when S⁺RA compared to S^-RA patients.Expert opinion:The results demonstrate that circulating Tfh are highly elevated in RA patients highlights its potential use as a biomarker and a target for RA therapy.

Plasma interleukin-21 levels and genetic variants are associated with susceptibility to rheumatoid arthritis

Background

Rheumatoid Arthritis (RA) is a chronic inflammatory condition characterized by autoantibodies development and an elevated spectrum of pro-inflammatory cytokines. Previous reports highlighted a relationship between IL-21and the pathogenesis of RA. Although elevated IL-21 levels have been reported in RA patients, the association of common IL-21 genetic variants with a predisposition to RA development in the Chinese population lacks.

Materials and methods

Five hundred and fourteen Chinese subjects (healthy controls: 303 and rheumatoid arthritis patients: 211) were enrolled in the study. Clinical data of patients were collected from medical records, and patients were treated as per the guidelines. Common single nucleotide polymorphisms in the IL-21 gene (rs907715, rs2221903, rs2055979 and rs6822844) were genotyped by TaqMan SNPs genotyping method. IL-21 level in plasma of RA patients and healthy subjects was measured by ELISA.

Results

The plasma level of IL-21 was significantly higher in subjects with rheumatoid arthritis relative to healthy controls (p < 0.0001). A positive correlation was observed between IL-21 level and DAS28 score, indicating the association of the cytokine with the worsening of the disease (Spearman r = 0.61, p < 0.0001). The prevalence of AA genotype (rs2055979) was significantly higher in RA subjects than in the controls (p < 0.0001, χ2 = 34.73, OR = 4.34, 95% CI = 2.623 to 7.219). Furthermore, elevated plasma IL-21 was observed in the rs2055979-AA genotype compared to CC type (p < 0.0001).

Conclusion

IL-21 plays a crucial function in rheumatoid arthritis pathogenesis. IL-21 rs2055979 polymorphism is associated with IL-21 plasma levels and is predisposed to RA development in the Chinese population.

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.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Functional differentiation and regulation of follicular T helper cells in inflammation and autoimmunity

Follicular T helper (T_FH ) cells are specialized T cells that support B cells, which are essential for humoral immunity. T_FH cells express the transcription factor B-cell lymphoma 6 (Bcl-6), chemokine (C-X-C motif) receptor (CXCR) 5, the surface receptors programmed cell death protein 1 (PD-1) and inducible T-cell costimulator (ICOS), the cytokine IL-21 and other molecules. The activation, proliferation and differentiation of T_FH cells are closely related to dynamic changes in cellular metabolism. In this review, we summarize the progress made in understanding the development and functional differentiation of T_FH cells. Specifically, we focus on the regulatory mechanisms of T_FH cell functional differentiation, including regulatory signalling pathways and the metabolic regulatory mechanisms of T_FH cells. In addition, T_FH cells are closely related to immune-associated diseases, including infections, autoimmune diseases and cancers.

Role of Adiponectin in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic chronic inflammatory autoimmune joint disease, characterized by progressive articular damage and joint dysfunction. One of the symptoms of this disease is persistent inflammatory infiltration of the synovial membrane, the principle site of inflammation in RA. In the affected conditions, the cells of the synovial membrane, fibroblast-like synoviocytes and macrophage-like synovial cells, produce enzymes degrading cartilage and underlining bone tissue, as well as cytokines increasing the infiltration of immune cells. In patients with RA, higher levels of adiponectin are measured in the serum and synovial fluid. Adiponectin, a secretory product that is mainly white adipose tissue, is a multifunctional protein with dual anti-inflammatory and pro-inflammatory properties. Several studies underline the fact that adiponectin can play an important pro-inflammatory role in the pathophysiology of RA via stimulating the secretion of inflammatory mediators. This narrative review is devoted to the presentation of recent knowledge on the role played by one of the adipokines produced by adipose tissue—adiponectin—in the pathogenesis of rheumatoid arthritis.

Genome-wide association study in a Korean population identifies six novel susceptibility loci for rheumatoid arthritis

OBJECTIVE

Genome-wide association studies (GWAS) in rheumatoid arthritis (RA) have discovered over 100 RA loci, explaining patient-relevant RA pathogenesis but showing a large fraction of missing heritability. As a continuous effort, we conducted GWAS in a large Korean RA case-control population.

METHODS

We newly generated genome-wide variant data in two independent Korean cohorts comprising 4068 RA cases and 36 487 controls, followed by a whole-genome imputation and a meta-analysis of the disease association results in the two cohorts. By integrating publicly available omics data with the GWAS results, a series of bioinformatic analyses were conducted to prioritise the RA-risk genes in RA loci and to dissect biological mechanisms underlying disease associations.

RESULTS

We identified six new RA-risk loci (SLAMF6, CXCL13, SWAP70, NFKBIA, ZFP36L1 and LINC00158) with pmeta<5×10-8 and consistent disease effect sizes in the two cohorts. A total of 122 genes were prioritised from the 6 novel and 13 replicated RA loci based on physical distance, regulatory variants and chromatin interaction. Bioinformatics analyses highlighted potentially RA-relevant tissues (including immune tissues, lung and small intestine) with tissue-specific expression of RA-associated genes and suggested the immune-related gene sets (such as CD40 pathway, IL-21-mediated pathway and citrullination) and the risk-allele sharing with other diseases.

CONCLUSION

This study identified six new RA-associated loci that contributed to better understanding of the genetic aetiology and biology in RA.

Immunomodulatory Effects of Mesenchymal Stem Cells and Mesenchymal Stem Cell-Derived Extracellular Vesicles in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects the joints and other organs for which there is currently no effective treatment. Mesenchymal stem cells (MSCs) have therapeutic potential due to their immunomodulatory and differentiation effects. While extensive experimental studies and clinical trials have demonstrated the effects of MSCs in various diseases, MSCs have been found to cause abnormal differentiation and tumor formation. Therefore, extracellular vesicles derived from MSCs (MSC-EVs) are more effective, less toxic, and more stable than the parental cells. MSC-EVs transfer various nucleic acids, proteins, and lipids from parent cells to recipient cells, and thus participate in chronic inflammatory and immune processes. In this review, we summarize the properties and biological functions of MSCs and MSC-EVs in RA. Improvement in our understanding of the mechanisms underlying MSC and MSC-EVs in RA provides an insight into potential biomarkers and therapeutic strategies for RA.

B cell helper T cells and type 1 diabetes

Type 1 diabetes is an autoimmune disease typically starting in childhood that culminates in the destruction of insulin‐producing beta cells in the pancreas. Although type 1 diabetes is considered to be a primarily T cell–mediated disease, B cells clearly participate in the autoimmune process, as autoantibodies recognizing pancreatic islet antigen commonly appear in circulation before the onset of the disease. T cells providing helper functions to B cells have recently been shown to be involved in the pathogenesis of a wide range of antibody‐associated immune disorders. These T cells include CXCR5‐positive follicular T helper (Tfh) cells, and a recently described closely related CXCR5‐negative subset coined peripheral T helper (Tph) cells. Here, we review the current state of knowledge on different B cell helper T cell subsets, focusing on their potential involvement in the development of type 1 diabetes.

Regulation of the germinal center and humoral immunity by interleukin-21

Here we review the critical and non-redundant functions of IL-21 in regulating humoral immune responses. We particularly focus on studies in natura—from individuals from inborn errors of immunity that impact on IL-21 production and/or function.

Cytokines play critical roles in regulating the development, survival, differentiation, and function of immune cells. Cytokines exert their function by binding specific receptor complexes on the surface of immune cells and activating intracellular signaling pathways, thereby resulting in induction of specific transcription factors and regulated expression of target genes. While the function of cytokines is often fundamental for the generation of robust and effective immunity following infection or vaccination, aberrant production or function of cytokines can underpin immunopathology. IL-21 is a pleiotropic cytokine produced predominantly by CD4⁺ T cells. Gene-targeting studies in mice, in vitro analyses of human and murine lymphocytes, and the recent discoveries and analyses of humans with germline loss-of-function mutations in IL21 or IL21R have revealed diverse roles of IL-21 in immune regulation and effector function. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in T cell–dependent B cell activation, germinal center reactions, and humoral immunity and how impaired responses to, or production of, IL-21 can lead to immune dysregulation.

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.

Ethanol consumption inhibits TFH cell responses and the development of autoimmune arthritis

Alcohol consumption is a consistent protective factor for the development of autoimmune diseases such as rheumatoid arthritis (RA). The underlying mechanism for this tolerance-inducing effect of alcohol, however, is unknown. Here we show that alcohol and its metabolite acetate alter the functional state of T follicular helper (T_FH) cells in vitro and in vivo, thereby exerting immune regulatory and tolerance-inducing properties. Alcohol-exposed mice have reduced Bcl6 and PD-1 expression as well as IL-21 production by T_FH cells, preventing proper spatial organization of T_FH cells to form T_FH:B cell conjugates in germinal centers. This effect is associated with impaired autoantibody formation, and mitigates experimental autoimmune arthritis. By contrast, T cell independent immune responses and passive models of arthritis are not affected by alcohol exposure. These data clarify the immune regulatory and tolerance-inducing effect of alcohol consumption.

Moderate consumption of alcohol is associated with protection from some autoimmune diseases. Here the authors show that ethanol and its metabolite acetate can protect mice from collagen-induced arthritis and provide evidence that the mechanism of this effect might be via inhibition of the effector function of T follicular helper cells.

Targeting inducible costimulator expressed on CXCR5+PD-1+ TH cells suppresses the progression of pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune bullous disease mediated by autoantibodies against desmoglein 3 (DSG3). Inducible costimulator (ICOS) is a costimulatory receptor expressed on T cells and influences the activity of T follicular helper (T_FH) cells in various autoimmune diseases, but the roles of ICOS and T_FH cells in PV remain unclear.

OBJECTIVE

We examined the immunological characteristics, antigen specificity, and pathogenicity of CD4⁺ T-cell subpopulations, as well as the therapeutic effect of anti-ICOS blocking antibodies in PV.

METHODS

A mouse model of PV was established by adoptive transfer of immune cells from the skin-draining lymph nodes or spleens of DSG3-expressing skin-grafted Dsg3^-/- mice into Rag1^-/- mice. The T_FH cells and CD4⁺ T cells in PBMCs from PV patients were examined by flow cytometry.

RESULTS

Among CD4⁺ T cells from the mouse model, ICOS-positive T_FH cells were associated with B-cell differentiation and were required for disease induction. Using an MHC class II tetramer, DSG3-specific ICOS⁺ T_FH cells were found to be associated with anti-DSG3 antibody production and expanded in the absence of B cells. In human PV, the frequency of ICOS⁺CXCR5⁺PD-1⁺ memory CD4⁺ T cells correlated with the autoantibody level. Treatment with anti-ICOS blocking antibodies targeting ICOS⁺ T_FH cells decreased the anti-DSG3 antibody level and delayed disease progression in vivo.

CONCLUSIONS

Mouse Dsg3-specific ICOS⁺ T_FH cells and human ICOS⁺CXCR5⁺PD-1⁺ T_H cells are associated with the anti-DSG3 antibody response in PV. ICOS expressed on CXCR5⁺PD-1⁺ T_H cells may be a therapeutic target for PV.

Antagonizing miR-7 suppresses B cell hyperresponsiveness and inhibits lupus development

OBJECTIVES

The objective of this study was to address the biological function of miR-7 in an animal model of systemic lupus erythematosus.

METHODS

MRL^lpr/lpr lupus mice were administrated antagomiR-7 or a scramble control by tail vein for 5weeks. Three groups of animals' tissues were assessed for lupus manifestations by immunofluorescence and immunohistochemistry, and serum was examined for levels of autoantibodies and inflammatory cytokines. Splenic B cell subsets were assessed for intracellular expression of PI3K signaling by FACS. Finally, the ability of the miR-7 antagomir to regulate the expansion of T follicular helper (Tfh) cells and B cell hyperresponsiveness was further explored.

RESULTS

We found that miR-7 was up-regulated in MRL^lpr/lpr lupus mice and directly targeted PTEN mRNA in B cells. Up-regulated miR-7 in MRL^lpr/lpr lupus B cells was negatively correlated with PTEN expression. Notably, miR-7 antagomir treatment reduced lupus manifestations in MRL^lpr/lpr lupus mice. miR-7-mediated down-regulation of PTEN/AKT signaling promoted B cell differentiation into plasmablasts/plasma cells and spontaneous germinal center (GC) formation, whereas miR-7 antagomir normalized splenic B cell subtypes. Besides suppressing the activation of B cells, miR-7 antagomir intervention also down-regulated STAT3 phosphorylation and production of IL-21 and reduced Tfh expansion.

CONCLUSION

The above data have demonstrated the critical roles of miR-7 not only in regulating PTEN expression and also B cell and Tfh cell function in lupus-prone MRL^lpr/lpr lupus mice. Furthermore, the disease manifestations in MRL^lpr/lpr lupus mice are efficiently improved by miR-7 antagomir, indicating miR-7 as a potential treatment strategy in SLE.

Sex differences in Tfh cell help to B cells contribute to sexual dimorphism in severity of rat collagen-induced arthritis

The study examined germinal centre (GC) reaction in lymph nodes draining inflamed joints and adjacent tissues (dLNs) in male and female Dark Agouti rat collagen type II (CII)-induced arthritis (CIA) model of rheumatoid arthritis. Female rats exhibiting the greater susceptibility to CIA mounted stronger serum CII-specific IgG response than their male counterparts. This correlated with the higher frequency of GC B cells in female compared with male dLNs. Consistently, the frequency of activated/proliferating Ki-67+ cells among dLN B cells was higher in females than in males. This correlated with the shift in dLN T follicular regulatory (Tfr)/T follicular helper (Tfh) cell ratio towards Tfh cells in females, and greater densities of CD40L and CD40 on their dLN T and B cells, respectively. The higher Tfh cell frequency in females was consistent with the greater dLN expression of mRNA for IL-21/27, the key cytokines involved in Tfh cell generation and their help to B cells. Additionally, in CII-stimulated female rat dLN cell cultures IFN-γ/IL-4 production ratio was shifted towards IFN-γ. Consistently, the serum IgG2a(b)/IgG1 CII-specific antibody ratio was shifted towards an IgG2a(b) response in females. Thus, targeting T-/B-cell interactions should be considered in putative further sex-based translational pharmacology research.