• Molecules and Cells
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• v.38 no.3
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• pp.195-201
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• 2015

Antibodies are powerful defense tools against pathogens but may cause autoimmune diseases when erroneously directed toward self-antigens. Thus, antibody producing cells are carefully selected, refined, and expanded in a highly regulated microenvironment (germinal center) in the peripheral lymphoid organs. A subset of T cells termed T follicular helper cells (Tfh) play a central role in instructing B cells to form a repertoire of antibody producing cells that provide life-long supply of high affinity, pathogenspecific antibodies. Therefore, understanding how Tfh cells arise and how they facilitate B cell selection and differentiation during germinal center reaction is critical to improve vaccines and better treat autoimmune diseases. In this review, I will summarise recent findings on molecular and cellular mechanisms underlying Tfh generation and function with an emphasis on T cell costimulation.

• Hanyang Medical Reviews
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• v.33 no.1
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• pp.10-16
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• 2013

Follicular helper T cells (Tfh) play a significant role in providing T cell help to B cells during the germinal center reaction, where somatic hypermutation, affinity maturation, isotype class switching, and the differentiation of memory B cells and long-lived plasma cells occur. Antigen-specific T cells with IL-6 and IL-21 upregulate CXCR5, which is required for the migration of T cells into B cell follicles, where these T cells mature into Tfh. The surface markers including PD-1, ICOS, and CD40L play a significant role in providing T cell help to B cells. The upregulation of transcription factor Bcl-6 induces the expression of CXCR5, which is an important factor for Tfh differentiation, by inhibiting the expression of other lineage-specific transcription factors such as T-bet, GATA3, and RORγt. Surprisingly, recent evidence suggests that CD4 T cells already committed to Th1, Th2, and Th17 cells obtain flexibility in their differentiation programs by downregulating T-bet, GATA3, and RORγt, upregulating Bcl-6 and thus convert into Tfh. Limiting the numbers of Tfh within germinal centers is important in the regulation of the autoantibody production that is central to autoimmune diseases. Recently, it was revealed that the germinal center reaction and the size of the Tfh population are also regulated by thymus-derived follicular regulatory T cells (Tfr) expressing CXCR5 and Foxp3. Dysregulation of Tfh appears to be a pathogenic cause of autoimmune disease suggesting that tight regulation of Tfh and germinal center reaction by Tfr is essential for maintaining immune tolerance. Therefore, the balance between Tfh and Tfr appears to be a critical peripheral tolerance mechanism that can inhibit autoimmune disorders.

• IMMUNE NETWORK
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• v.14 no.1
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• pp.21-29
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• 2014

Follicular helper T ($T_{FH}$) cells are recently highlighted as their crucial role for humoral immunity to infection as well as their abnormal control to induce autoimmune disease. During an infection, na$\ddot{i}$ve T cells are differentiating into $T_{FH}$ cells which mediate memory B cells and long-lived plasma cells in germinal center (GC). $T_{FH}$ cells are characterized by their expression of master regulator, Bcl-6, and chemokine receptor, CXCR5, which are essential for the migration of T cells into the B cell follicle. Within the follicle, crosstalk occurs between B cells and $T_{FH}$ cells, leading to class switch recombination and affinity maturation. Various signaling molecules, including cytokines, surface molecules, and transcription factors are involved in $T_{FH}$ cell differentiation. IL-6 and IL-21 cytokine-mediated STAT signaling pathways, including STAT1 and STAT3, are crucial for inducing Bcl-6 expression and $T_{FH}$ cell differentiation. $T_{FH}$ cells express important surface molecules such as ICOS, PD-1, IL-21, BTLA, SAP and CD40L for mediating the interaction between T and B cells. Recently, two types of microRNA (miRNA) were found to be involved in the regulation of $T_{FH}$ cells. The miR-17-92 cluster induces Bcl-6 and $T_{FH}$ cell differentiation, whereas miR-10a negatively regulates Bcl-6 expression in T cells. In addition, follicular regulatory T ($T_{FR}$) cells are studied as thymus-derived $CXCR5^+PD-1^+Foxp3^+\;T_{reg}$ cells that play a significant role in limiting the GC response. Regulation of $T_{FH}$ cell differentiation and the GC reaction via miRNA and $T_{FR}$ cells could be important regulatory mechanisms for maintaining immune tolerance and preventing autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Here, we review recent studies on the various factors that affect $T_{FH}$ cell differentiation, and the role of $T_{FH}$ cells in autoimmune diseases.

• IMMUNE NETWORK
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• v.24 no.1
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• pp.8.1-8.17
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• 2024

Follicular helper T cells (Tfh) play a crucial role in generating high-affinity antibodies (Abs) and establishing immunological memory. Cytokines, among other functional molecules produced by Tfh, are central to germinal center (GC) reactions. This review focuses on the role of cytokines, including IL-21 and IL-4, in regulating B cell responses within the GC, such as differentiation, affinity maturation, and plasma cell development. Additionally, this review explores the impact of other cytokines like CXCL13, IL-10, IL-9, and IL-2 on GC responses and their potential involvement in autoimmune diseases, allergies, and cancer. This review highlights contributions of Tfh-derived cytokines to both protective immunity and immunopathology across a spectrum of diseases. A deeper understanding of Tfh cytokine biology holds promise for insights into biomedical conditions.

• IMMUNE NETWORK
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• v.16 no.4
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• pp.219-232
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• 2016

Production of high affinity antibodies for antigens is a critical component for the immune system to fight off infectious pathogens. However, it could be detrimental to our body when the antigens that B cells recognize are of self-origin. Follicular helper T, or Tfh, cells are required for the generation of germinal center reactions, where high affinity antibody-producing B cells and memory B cells predominantly develop. As such, Tfh cells are considered as targets to prevent B cells from producing high affinity antibodies against self-antigens, when high affinity autoantibodies are responsible for immunopathologies in autoimmune disorders. This review article provides an overview of current understanding of Tfh cells and discusses it in the context of animal models of autoimmune diseases and allograft rejections for generation of novel therapeutic interventions.

• IMMUNE NETWORK
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• v.14 no.5
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• pp.227-236
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• 2014

Understanding germinal center reactions is crucial not only for the design of effective vaccines against infectious agents and malignant cells but also for the development of therapeutic intervention for the treatment of antibody-mediated immune disorders. Recent advances in this field have revealed specialized subsets of T cells necessary for the control of B cell responses in the follicle. These cells include follicular regulatory T cells and Qa-1-restricted cluster of differentiation $(CD)8^+$ regulatory T cells. In this review, we discuss the current knowledge related to the role of regulatory T cells in the B cell follicle.

• Biomolecules & Therapeutics
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• v.25 no.2
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• pp.130-139
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• 2017

$CXCR5^+$ T follicular helper (Tfh) cells are associated with aberrant autoantibody production in patients with antibody-mediated autoimmune diseases including lupus. Follicular regulatory T (Tfr) cells expressing CXCR5 and Bcl6 have been recently identified as a specialized subset of $Foxp3^+$ regulatory T (Treg) cells that control germinal center reactions. In this study, we show that retroviral transduction of CXCR5 gene in $Foxp3^+$ Treg cells induced a stable expression of functional CXCR5 on their surface. The Cxcr5-transduced Treg cells maintained the expression of Treg cell signature genes and the suppressive activity. The expression of CXCR5 as well as Foxp3 in the transduced Treg cells appeared to be stable in vivo in an adoptive transfer experiment. Moreover, Cxcr5-transduced Treg cells preferentially migrated toward the CXCL13 gradient, leading to an effective suppression of antibody production from B cells stimulated with Tfh cells. Therefore, our results demonstrate that enforced expression of CXCR5 onto Treg cells efficiently induces Tfr cell-like properties, which might be a promising cellular therapeutic approach for the treatment of antibody-mediated autoimmune diseases.

• IMMUNE NETWORK
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• v.19 no.1
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• pp.7.1-7.11
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• 2019

Sjögren's syndrome (SS) is a chronic inflammatory autoimmune disorder that affects mainly salivary and lacrimal glands, but its cause remains largely unknown. Clinical data indicating that SS occurs in a substantial proportion of patients with lupus points to common pathogenic mechanisms underlying the two diseases. To address this idea, we asked whether SS develops in the lupus-prone mouse strain sanroque (SAN). Owing to hyper-activation of follicular helper T (Tfh) cells, female SAN mice developed lupus-like symptoms at approximately 20 wk of age but there were no signs of SS at that time. However, symptoms typical of SS were evident at approximately 40 wk of age, as judged by reduced saliva flow rate, sialadenitis, and IgG deposits in the salivary glands. Increases in serum titers of SS-related autoantibodies and numbers of autoantibody-secreting cells in cervical lymph nodes (LNs) preceded the pathologic manifestations of SS and were accompanied by expansion of Tfh cells and their downstream effector cells. Thus, our results suggest that chronic dysregulation of Tfh cells in salivary gland-draining LNs is sufficient to drive the development of SS in lupus-prone mice.

• Molecules and Cells
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• v.42 no.11
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• pp.747-754
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• 2019

The incidence of atherosclerosis is higher among patients with several autoimmune diseases such as psoriasis, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). It is well documented that innate immune cells including macrophages and dendritic cells sense lipid species such as saturated fatty acids and oxidized low-density lipoprotein and produce pro-inflammatory cytokines and chemokines. However, whether a hyperlipidemic environment also impacts autoimmune T cell responses has been unclear. Among $CD4^+$ T cells, Th17 and follicular helper T (Tfh) cells are known to play pathogenic roles in the development of hyperlipidemia-associated autoimmune diseases. This review gives an overview of the cellular and molecular mechanisms by which dysregulated lipid metabolism impacts the pathogenesis of autoimmune diseases, with specific emphasis on Th17 and Tfh cells.

• Korean Journal of Clinical Laboratory Science
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• v.54 no.1
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• pp.68-72
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• 2022

Angioimmunoblastic T-cell lymphoma (AITL) is a lymphoproliferative disorder of mature T follicular helper cells. Atypical lymphoid cells were observed in the bone marrow of an 80-year-old woman, and the flow cytometric determined immunophenotypes of B-cells were unusual, that is, CD19+, CD20-, and CD22- with lambda light chain restriction. Initially, we suspected BM involvement of B-cell lymphoma based on the presence of abnormal B-cells. However, the patient was diagnosed with AITL involving BM. A re-analysis of flow cytometric immunophenotyping revealed a minor, aberrant T-cell population, and the lambda light chain restriction observed by surface staining was considered non-specific binding. This case demonstrates B-cells in patients with EBV-positive T-cell lymphoma may exhibit immunophenotypes resembling those of plasma cells, and that proliferation of abnormal B-cells or plasma cells could also potentially mask underlying T-cell lymphoma. A more integrated approach is required for accurate diagnosis.