Lineage specification and heterogeneity of T follicular helper cells. Curr Opin Immunol. 2009;21:619-625. [PMID: 19896816 DOI: 10.1016/j.coi.2009.09.013]

The regulation of Tfh cell differentiation by β-hydroxybutyrylation modification of transcription factor Bcl6

Transcriptional repressor B cell lymphoma 6 (Bcl6) is a major transcription factor involved in Tfh cell differentiation and germinal center response, which is regulated by a variety of biological processes. However, the functional impact of post-translational modifications, particularly lysine β-hydroxybutyrylation (Kbhb), on Bcl6 remains elusive. In this study, we revealed that Bcl6 is modified by Kbhb to affect Tfh cell differentiation, resulting in the decrease of cell population and cytokine IL-21. Furthermore, the modification sites are identified from enzymatic reactions to be lysine residues at positions 376, 377, and 379 by mass spectrometry, which is confirmed by site-directed mutagenesis and functional analyses. Collectively, our present study provides evidence on the Kbhb modification of Bcl6 and also generates new insights into the regulation of Tfh cell differentiation, which is a starting point for a thorough understanding of the functional involvement of Kbhb modification in the differentiations of Tfh and other T cells.

Germinal center B cell initiation, GC maturation, and the coevolution of its stromal cell niches

Throughout the developing GC response, B cell survival and fate choices made at the single cell level are dependent on signals received largely through interactions with other cells, often with cognate T cells. The type of signals that a given B cell can encounter is dictated by its location within tissue microarchitecture. The focus of this review is on the initiation and evolution of the GC response at the earliest time points. Here, we review the key factors influencing the progression of GC B cell differentiation that are both stage and context dependent. Finally, we describe the coevolution of niches within and surrounding the GC that influence the outcome of the GC response.

The E3 ubiquitin ligase Itch restricts antigen-driven B cell responses

The E3 ubiquitin ligase Itch regulates antibody levels and prevents autoimmune disease in humans and mice, yet how Itch regulates B cell fate or function is unknown. We now show that Itch directly limits B cell activity. While Itch-deficient mice displayed normal numbers of preimmune B cell populations, they showed elevated numbers of antigen-experienced B cells. Mixed bone marrow chimeras revealed that Itch acts within B cells to limit naive and, to a greater extent, germinal center (GC) B cell numbers. B cells lacking Itch exhibited increased proliferation, glycolytic capacity, and mTORC1 activation. Moreover, stimulation of these cells in vivo by WT T cells resulted in elevated numbers of GC B cells, PCs, and serum IgG. These results support a novel role for Itch in limiting B cell metabolism and proliferation to suppress antigen-driven B cell responses.

Regulation of T Follicular Helper Cells in Islet Autoimmunity

T follicular helper (TFH) cells are an integral part of humoral immunity by providing help to B cells to produce high-affinity antibodies. The TFH precursor compartment circulates in the blood and TFH cell dysregulation is implied in various autoimmune diseases including type 1 diabetes (T1D). Symptomatic T1D is preceded by a preclinical phase (indicated by the presence of islet autoantibodies) with a highly variable progression time to the symptomatic disease. This heterogeneity points toward differences in immune activation in children with a fast versus slow progressor phenotype. In the context of T1D, previous studies on TFH cells have mainly focused on the clinically active state of the disease. In this review article, we aim to specifically discuss recent insights on TFH cells in human islet autoimmunity before the onset of symptomatic T1D. Furthermore, we will highlight advances in the field of TFH differentiation and function during human islet autoimmunity. Specifically, we will focus on the regulation of TFH cells by microRNAs (miRNAs), as well as on the potential use of miRNAs as biomarkers to predict disease progression time and as future drug targets to interfere with autoimmune activation.

MyD88 Signaling in T Cells Is Critical for Effector CD4 T Cell Differentiation following a Transitional T Follicular Helper Cell Stage

Activation of CD4 T cells by dendritic cells leads to their differentiation into various effector lineages. The nature of the effector lineage is determined by the innate cues provided by dendritic cells to newly primed T cells. Although the cytokines necessary for several effector lineages have been identified, the innate cues that drive T follicular helper (Tfh) lineage cell development remain unclear. Here we found that following priming, CD4 T cells undergoing clonal expansion acquire a transient Tfh-like phenotype before differentiating into other effector lineages. In addition, we found that T cell-intrinsic myeloid differentiation antigen 88 (MyD88) signaling, which occurs downstream of interleukin-1 (IL-1) and IL-18 receptors, is critical for the primed CD4 T cells to transition out of the temporary Tfh lineage. Mice with T cell-specific deletion of MyD88 have a higher proportion of Tfh cells and germinal center (GC) B cells. These exaggerated Tfh cell and GC B cell responses, however, do not lead to protective immunity against infections. We demonstrate that T cell-intrinsic MyD88 is critical for effector lineage differentiation as well as production of the cytokines that are necessary for class switching. Overall, our study establishes that following priming and clonal expansion, CD4 T cells undergo a transitional Tfh-like phase and that further differentiation into effector lineages is dictated by T cell-intrinsic MyD88-dependent cues.

Human Vγ9Vδ2-T Cells Synergize CD4+ T Follicular Helper Cells to Produce Influenza Virus-Specific Antibody

Human Vγ9Vδ2-T cells recognize nonpeptidic antigens and exert effector functions against microorganisms and tumors, but little is known about their roles in humoral immune response against influenza virus infection. Herein, in the coculture of autologous human B cells, dendritic cells and/or naïve CD4 T cells, and Vγ9Vδ2-T cells, we demonstrated that Vγ9Vδ2-T cells could facilitate H9N2 influenza virus-specific IgG and IgM productions in a CD4 T cell-dependent manner. Vγ9Vδ2-T cells promoted the differentiation of CXCR5⁺PD1⁺CD4⁺ T follicular helper (Tfh) cells, CD19⁺IgD⁻CD38⁺⁺ plasma cells (PCs), and drove B cell proliferation as well as immunoglobulin class switching. Interestingly, Vγ9Vδ2-T cells acquired Tfh-associated molecules such as CXCR5, PD1, CD40L, and ICOS during influenza virus stimulation, especially in the presence of CD4 T cells. Moreover, Vγ9Vδ2-T cells promoted CD4 T cells to secrete IL-13 and IL-21, and neutralizing IL-13 and IL-21 significantly reduced the number of CD19⁺IgD⁻CD38⁺⁺ PCs. Using humanized mice, we further demonstrated that Vγ9Vδ2-T cells could synergize CD4 T cells to produce influenza virus-specific antibody. Our findings provide a greater scope for Vγ9Vδ2-T cells in adaptive immunity, especially for the Tfh development and humoral immune responses against influenza virus infection.

RHOA G17V Induces T Follicular Helper Cell Specification and Promotes Lymphomagenesis

Angioimmunoblastic T cell lymphoma (AITL) is an aggressive tumor derived from malignant transformation of T follicular helper (Tfh) cells. AITL is characterized by loss-of-function mutations in Ten-Eleven Translocation 2 (TET2) epigenetic tumor suppressor and a highly recurrent mutation (p.Gly17Val) in the RHOA small GTPase. Yet, the specific role of RHOA G17V in AITL remains unknown. Expression of Rhoa G17V in CD4⁺ T cells induces Tfh cell specification; increased proliferation associated with inducible co-stimulator (ICOS) upregulation and increased phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase signaling. Moreover, RHOA G17V expression together with Tet2 loss resulted in development of AITL in mice. Importantly, Tet2^-/-RHOA G17V tumor proliferation in vivo can be inhibited by ICOS/PI3K-specific blockade, supporting a driving role for ICOS signaling in Tfh cell transformation.

The curious origins of angioimmunoblastic T-cell lymphoma

PURPOSE OF REVIEW

Once an obscure disease, recent studies have transformed our understanding of angioimmunoblastic T-cell lymphoma (AITL). In this review, we summarize new major advances in the genetics and biology of AITL.

RECENT FINDINGS

Genome wide sequencing studies have dissected the repertoire of the genetic alterations driving AITL uncovering a highly recurrent Gly17Val somatic mutation in the small GTPase RHOA and major role for mutations in epigenetic regulators, such as TET2, DNMT3A and IDH2, and signaling factors (e.g., FYN and CD28). These findings support a multistep model of follicular T helper cell transformation in AITL and pinpoint novel candidates for the development of targeted therapies in this disease.

SUMMARY

AITL originates from follicular T helper cells and is characterized by the presence of RHOA G17V mutation together with genetic alterations in TET2, DNMT3A, and IDH2. Research efforts now focus on the elucidation of the specific roles and interplay of these genetic alterations in the pathogenesis of AITL.

T follicular helper cells regulate the activation of B lymphocytes and antibody production during Plasmodium vivax infection

Although the importance of humoral immunity to malaria has been established, factors that control antibody production are poorly understood. Follicular helper T cells (Tfh cells) are pivotal for generating high-affinity, long-lived antibody responses. While it has been proposed that expansion of antigen-specific Tfh cells, interleukin (IL) 21 production and robust germinal center formation are associated with protection against malaria in mice, whether Tfh cells are found during Plasmodium vivax (P. vivax) infection and if they play a role during disease remains unknown. Our goal was to define the role of Tfh cells during P. vivax malaria. We demonstrate that P. vivax infection triggers IL-21 production and an increase in Tfh cells (PD-1+ICOS+CXCR5+CD45RO+CD4+CD3+). As expected, FACS-sorted Tfh cells, the primary source of IL-21, induced immunoglobulin production by purified naïve B cells. Furthermore, we found that P. vivax infection alters the B cell compartment and these alterations were dependent on the number of previous infections. First exposure leads to increased proportions of activated and atypical memory B cells and decreased frequencies of classical memory B cells, whereas patients that experienced multiple episodes displayed lower proportions of atypical B cells and higher frequencies of classical memory B cells. Despite the limited sample size, but consistent with the latter finding, the data suggest that patients who had more than five infections harbored more Tfh cells and produce more specific antibodies. P. vivax infection triggers IL-21 production by Tfh that impact B cell responses in humans.

Plasmodium vivax is the most widely spread malaria parasite species and represents a significant impediment to social and economic development in endemic countries. Our goal was to assess the importance of T follicular helper cells in the development of the immune response during malaria. We found that P. vivax infection promotes expansion of circulating Tfh cells that secrete IL-21 to boost immunoglobulin production by B-cells. Accordingly, malaria infection led to marked changes in B cell subpopulations, including expansion of plasma cells and increased production of antigen-specific IgG1 and IgG3. Re-exposure to P. vivax led to amplified Tfh cells cell responses that were concomitantly associated with increased frequencies of classical memory B cells. Thus, Tfh cells that are induced during P. vivax infection could impact the efficiency of humoral immune responses that underlie protective immunity.

Effect of follicular helper T cells on the pathogenesis of asthma

Follicular helper T (TFH) cells are considered to be a separate T helper cell subset, specifically to help memory B cell participate in humoral immunity. It has been reported that there is an association between the imbalance of TFH function and certain autoimmune diseases. However, to the best of our knowledge, the effect of TFH cells on the process of bronchial asthma has not been investigated. The aim of the present study was to investigate the associated markers of TFH cells in bronchial asthma-induced mice. In the current study, sensitized and long-term challenges induced a mouse asthmatic model and were used to investigate the associated markers of TFH cells in the pathogenesis of asthma. The results demonstrated that B cell lymphoma 6, inducible T-cell costimulator (ICOS), ICOS ligand, C-X-C chemokine receptor type 5 (CXCR5) and interleukin (IL)-21 protein and mRNA expression levels were higher in the asthma group, as compared with the control group. Furthermore, the ratio of cluster of differentiation (CD) 4⁺CXCR5⁺/CD4⁺ and CD4⁺CXCR5⁺ICOS⁺/CD4⁺CXCR5⁺ was significantly increased in the asthma group. The results of the current study suggest that TFH cells and associated markers may have a role in the pathogenesis of chronic bronchial asthma.

Human Immunodeficiency Virus Playing Hide-and-Seek: Understanding the TFH Cell Reservoir and Proposing Strategies to Overcome the Follicle Sanctuary

Human immunodeficiency virus (HIV) infects millions of people worldwide, and new cases continue to emerge. Once infected, the virus cannot be cleared by the immune system and causes acquired immunodeficiency syndrome. Combination antiretroviral therapeutic regimen effectively suppresses viral replication and halts disease progression. The treatment, however, does not eliminate the virus-infected cells, and interruption of treatment inevitably leads to viral rebound. The rebound virus originates from a group of virus-infected cells referred to as the cellular reservoir of HIV. Identifying and eliminating the HIV reservoir will prevent viral rebound and cure HIV infection. In this review, we focus on a recently discovered HIV reservoir in a subset of CD4⁺ T cells called the follicular helper T (T_FH) cells. We describe the potential mechanisms for the emergence of reservoir in T_FH cells, and the strategies to target and eliminate this viral reservoir.

The Role of CD4+ T Follicular Helper Cells in HIV Infection: From the Germinal Center to the Periphery

T follicular helper cells (TFh) are key components of the adaptive immune system; they are primarily found in germinal centers (GCs) where their interaction with B cells supports humoral immune responses and efficient antibody production. They are defined by the expression of CXC receptor 5, program death-1, ICOS, and secretion of IL-21. Their differentiation is regulated by B-cell lymphoma 6. The relationship and function of circulating TFh to bona fide TFh resident in the GC is much debated. HIV infection impacts the TFh response with evidence of aberrant TFh function observed in acute and chronic infection. Effective TFh responses are associated with the development of broadly neutralizing antibody responses to HIV and may be important for viral control. In addition, TFh are preferentially infected and act as a key reservoir for latent HIV infection. This review explores recent developments in our understanding of TFh differentiation, regulation, function, and the relationship between cTFh and those in GCs, and the complex interaction between TFh and HIV infection.

Tfh cell-mediated humoral immune response and HBsAg level can predict HBeAg seroconversion in chronic hepatitis B patients receiving peginterferon-α therapy

Hepatitis B e antigen (HBeAg) seroconversion constitutes a significant milestone in the treatment of HBeAg-positive patients with chronic hepatitis B (CHB), but studies have yet to identify the specific humoral immune mechanisms behind the process or any accurate markers that can determine the virus-host immune status and, thereby, predict the degree of HBeAg seroconversion achievable. In the present longitudinal study, higher frequencies of circulating CXCR5(+)CD4(+) T cells and CD19(+)CD38(+) B cells were found in peginterferon-α treated HBeAg-positive CHB patients in whom HBeAg seroconversion had been achieved. What's more, both cell types peaked at 24 weeks for the HBeAg seroconversion group, while showing only a slight variation in the HBeAg non-seroconversion group. In addition, circulating CXCR5(+)CD4(+) T cells and hepatitis B surface antigens (HBsAg) were assessed at 24 weeks and 12 weeks, respectively, and the use of their ratio was explored in terms of its ability to predict HBeAg seroconversion.

CONCLUSION

Dysfunction of the humoral immune response mediated by CXCR5(+)CD4(+) T cells is associated with the failure of HBeAg seroconversion. The CXCR5(+)CD4(+) T cells/HBsAg ratio is an ideal marker for predicting HBeAg seroconversion in CHB patients.

T follicular helper expansion and humoral-mediated rejection are independent of the HVEM/BTLA pathway

The molecular pathways contributing to humoral-mediated allograft rejection are poorly defined. In this study, we assessed the role of the herpesvirus entry mediator/B- and T-lymphocyte attenuator (HVEM/BTLA) signalling pathway in the context of antibody-mediated allograft rejection. An experimental setting was designed to elucidate whether the blockade of HVEM/BTLA interactions could modulate de novo induction of host antidonor-specific antibodies during the course of graft rejection. To test this hypothesis, fully allogeneic major histocompatibility complex-mismatched skin grafts were transplanted onto the right flank of recipient mice that were treated with isotype control, anti-CD40L or modulatory antibodies of the HVEM/BTLA signalling pathway. The frequencies of CD4 T follicular helper (Tfh) cells (B220-, CD4+ CXCR5+ PD-1high), extrafollicular helper cells (B220-, CD4+ CXCR5- PD-1+ and PD-1-) and germinal centre (GC) B cells (B220+Fas+ GL7+) were analysed by flow cytometry in draining and non-draining lymph nodes at day 10 post transplantation during the acute phase of graft rejection. The host antidonor isotype-specific humoral immune response was also assessed. Whereas blockade of the CD40/CD40L pathway was highly effective in preventing the allogeneic humoral immune response, antibody-mediated blockade of the HVEM/BTLA-interacting pathway affected neither the expansion of Tfh cells nor the expansion of GC B cells. Consequently, the course of the host antidonor antibody-mediated response proceeded normally, without detectable evidence of impaired development. In summary, these data indicate that HVEM/BTLA interactions are dispensable for the formation of de novo host antidonor isotype-specific antibodies in transplantation.

Higher Frequency of CD4+CXCR5+ICOS+PD1+ T Follicular Helper Cells in Patients With Infectious Mononucleosis

Follicular helper T (Tfh) cells are recognized as a distinct CD4helper T cell subset, and mainly dysregulated in the autoimmune disease, whether it plays a role in the infectious mononucleosis (IM) diseases is unknown. In this study, we found that the CD4CXCR5 Tfh cells were not significantly changed, but the CD4CXCR5ICOS and CD4CXCR5ICOSPD1 Tfh subsets were significantly increased in the IM patients, and all these cells were significantly changed after antiviral therapy. Second, only the numbers of CD4CXCR5ICOSPD1 Tfh cells correlated with the Epstein-Barr virus (EBV) DNA load, negatively correlated with the numbers of naive B cells and amount of IL-21, and positively correlated with the numbers of plasma cells, memory B cells, and atypical lymphocytes. Third, the frequency of CD4CXCR5ICOSPD1 Tfh subset was significantly higher in lymphadenectasis or hepatosplenomegaly patients, and associated with the level of alanine aminotransferase (ALT). All together, our findings discovered this CD4CXCR5ICOSPD1 Tfh cell subset might play an important role in the pathogenesis of IM.

TFH cells accumulate in mucosal tissues of humanized-DRAG mice and are highly permissive to HIV-1

CD4⁺ T follicular helper cells (T_FH) in germinal centers are required for maturation of B-cells. While the role of T_FH-cells has been studied in blood and lymph nodes of HIV-1 infected individuals, its role in the mucosal tissues has not been investigated. We show that the gut and female reproductive tract (FRT) of humanized DRAG mice have a high level of human lymphocytes and a high frequency of T_FH (CXCR5⁺PD-1⁺⁺) and precursor-T_FH (CXCR5⁺PD-1⁺) cells. The majority of T_FH-cells expressed CCR5 and CXCR3 and are the most permissive to HIV-1 infection. A single low-dose intravaginal HIV-1 challenge of humanized DRAG mice results in 100% infectivity with accumulation of T_FH-cells mainly in the Peyer’s patches and FRT. The novel finding of T_FH-cells in the FRT may contribute to the high susceptibility of DRAG mice to HIV-1 infection. This mouse model thus provides new opportunities to study T_FH-cells and to evaluate HIV-1 vaccines.

Cross-regulation between cytokine and microRNA pathways in T cells

microRNA (miRNA) mediated regulation of protein expression has emerged as an important mechanism in T-cell physiology, from development and survival to activation, proliferation, and differentiation. One of the major classes of proteins involved in these processes are cytokines, which are both key input signals and major products of T-cell function. Here, we summarize the current data on the molecular cross-talk between cytokines and miRNAs: how cytokines regulate miRNA expression, and how specific miRNAs control cytokine production in T cells. We also describe the inflammatory consequences of deregulating the miRNA/cytokine axis in mice and humans. We believe this topical area will have key implications for immune modulation and treatment of autoimmune pathology.

CD4 T Cells Mediate Both Positive and Negative Regulation of the Immune Response to HIV Infection: Complex Role of T Follicular Helper Cells and Regulatory T Cells in Pathogenesis

HIV-1 infection results in chronic activation of cells in lymphoid tissue, including T cells, B-cells, and myeloid lineage cells. The resulting characteristic hyperplasia is an amalgam of proliferating host immune cells in the adaptive response, increased concentrations of innate response mediators due to viral and bacterial products, and homeostatic responses to inflammation. While it is generally thought that CD4 T cells are greatly depleted, in fact, two types of CD4 T cells appear to be increased, namely, regulatory T cells (Tregs) and T follicular helper cells (Tfh). These cells have opposing roles, but may both be important in the pathogenic process. Whether Tregs are failing in their role to limit lymphocyte activation is unclear, but there is no doubt now that Tfh are associated with B-cell hyperplasia and increased germinal center activity. Antiretroviral therapy may reduce the lymphocyte activation, but not completely, and therefore, there is a need for interventions that selectively enhance normal CD4 function without exacerbating Tfh, B-cell, or Treg dysfunction.

Interleukin‑21 promotes the development of ulcerative colitis and regulates the proliferation and secretion of follicular T helper cells in the colitides microenvironment

Patients with ulcerative colitis (UC) are at increased risk of developing colitis‑associated colon cancer. Previous studies have indicated that interleukin (IL)‑21, which is predominantly secreted by follicular T helper (Tfh) cells, is overproduced in inflammatory bowel diseases. In order to investigate the role of IL‑21 in UC and the association between IL‑21 and Tfh cells, the number of Tfh cells and the level of IL‑21 were investigated in colonic tissues from UC patients and wild‑type (WT) mice, which were induced by dextran sulphate sodium (DSS). High Tfh cell counts and levels of IL‑21 were observed in UC patients and WT mice with DSS‑induced colitis. Subsequent comparison of the mucosal damage and expression of Tfh‑associated cytokines in the WT mice and IL‑21 knockout (IL‑21KO) mice following DSS administration, revealed that IL‑21KO mice were largely protected against colitis and exhibited reduced infiltration of Tfh cells, as well as decreased production of Tfh‑associated cytokines. The present study also found that IL‑21 was necessary for the proliferation and secretion of Tfh cells in vitro. In addition, neutralization of IL‑21 in DSS‑administered WT mice using anti‑IL‑21 reduced the number of Tfh cells and the level of mucosal damage. Administration of a neutralizing IL‑21 antibody decreased the colonic infiltration of Tfh cells and reduced damage to the mucosa. These results indicated that Tfh cells are important in UC and that its effector molecule, IL‑21, is not only a critical regulator of inflammation, but also regulates the proliferation and response of Tfh cells in the colitis microenvironment.

Characterisation of tissue transglutaminase-reactive T cells from patients with coeliac disease and healthy controls

Previous studies have shown evidence for T lymphocytes specific for tissue transglutaminase (tTG) in the periphery of coeliac disease (CD) patients. These cells could play a role in disease pathogenesis and may be involved in providing help for the production of anti-tTG autoantibodies. The objective of this study was to further investigate the presence of tTG-specific T cells in patients with treated and untreated CD, and normal controls. Positive proliferative responses to three different commercial tTG antigens were detected in all groups tested, occurring more frequently and at higher levels in untreated CD patients. The addition of antibodies to HLA-DQ and HLA-DR caused a significant reduction in the proliferative response to tTG. T cell lines specific for tTG and composed predominantly of CD4-positive T cells were generated from responsive CD and control individuals, and were found to produce large amounts of interferon-γ, as well as interleukins 10, 17A, and 21.

A preliminary study on the characterization of follicular helper T (Tfh) cells in rheumatoid arthritis synovium

Rheumatoid arthritis (RA) is a chronic and systematic autoimmune inflammatory disease. Recently, a novel T cell subset, follicular helper CD4 T cell (Tfh cells) was found in relation to the pathogenesis and progression of RA, and increased numbers of circulating Tfh cells were found in RA patients. However, there is little evidence regarding the localization of Tfh cells in synovium tissues from RA patients, owing to the lack of an available method to characterize their localization in tissue. The aim of our present study was to characterize the Tfh cells in rheumatoid synovium tissues from RA patients by using immunohistochemistry and triple-fluorescence immunostaining methods. Our results showed that specific staining of CD4, CXCR5 and ICOS could be found on infiltrating immune cells in rheumatoid synovium tissues. The use of triple-fluorescence immunostaining and confocal laser scanning showed immunolocalization of CD4(+)CXCR5(+)ICOS(+)T cells (Tfh cells) in the rheumatoid synovium tissues, whereas these signals were absent in osteoarthritis (OA) synovium and in normal synovium tissues. Thus the data from our present preliminary study support the notion that CD4(+)CXCR5(+)ICOS(+)Tfh cells could be found in rheumatoid synovium tissues from RA patients, indicating the possibility that this T cell subset in synovium tissues may have important roles in the pathogenesis and progression of RA.

Expansion of circulating TFH cells and their associated molecules: involvement in the immune landscape in patients with chronic HBV infection

Background

Blood CXCR5+CD4+ T cells are defined as circulating T follicular helper (TFH) cells, which is required for effective humoral immunity. This study aimed to investigate the role of circulating TFH cells in patients with chronic hepatitis B virus (CHB) infection.

Methods

The frequency and phenotype of circulating TFH cells were monitored by flow cytometry in CHB patients and in healthy controls (HC). The expression of BCL-6, IL-21, IL-4, CXCR5, and IL-6R mRNA was analyzed using real-time PCR. Serum HBsAg, HBeAg, HBeAb, HBV DNA loads, ALT and AST were determined. The potential association of the frequency of TFH cells and their surface markers with clinical parameters was assessed.

Results

The frequency of CXCR5+CD4+ T cells was increased in CHB patients and positively correlated with ALT and AST but not with HBV DNA loads. Moreover, an expansion of ICOS-, PD-1-, CD40L-, and IL-21R-expressing TFH cells occurred in CHB patients, but failed to correlate with ALT, AST and HBV DNA loads. Interestingly, the frequency of CXCR5+CD4+ T cells and ICOS+CXCR5+CD4+ T cells was significantly higher in HBeAg positive CHB patients than in HC. Additionally, the percentages of CXCR5+CD4+ T cells were positively correlated with AST, and ICOS-expressing CXCR5+CD4+ T cells were negatively correlated with HBV DNA loads. No significant differences in the frequency of CXCR5+CD4+ T cells were observed between inactive carrier (IC) patients and healthy controls. However, ICOS-, PD-1-, CD40L-expressing TFH cells were increased in IC patients and positively correlated with AST. Furthermore, the expression of BCL-6, IL-21, IL-4, CXCR5, and IL-6R mRNA in TFH cells was higher in CHB patients than in HC.

Conclusions

These data demonstrate that circulating TFH cells may participate in HBV-related immune responses. In addition to the frequency of TFH cells, the phenotype of these cells plays an important role in CHB patients.

Circulating precursor CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells indicate Tfh cell activity and promote antibody responses upon antigen reexposure

Follicular B helper T (Tfh) cells support high affinity and long-term antibody responses. Here we found that within circulating CXCR5⁺ CD4⁺ T cells in humans and mice, the CCR7(lo)PD-1(hi) subset has a partial Tfh effector phenotype, whereas CCR7(hi)PD-1(lo) cells have a resting phenotype. The circulating CCR7(lo)PD-1(hi) subset was indicative of active Tfh differentiation in lymphoid organs and correlated with clinical indices in autoimmune diseases. Thus the CCR7(lo)PD-1(hi) subset provides a biomarker to monitor protective antibody responses during infection or vaccination and pathogenic antibody responses in autoimmune diseases. Differentiation of both CCR7(hi)PD-1(lo) and CCR7(lo)PD-1(hi) subsets required ICOS and BCL6, but not SAP, suggesting that circulating CXCR5⁺ helper T cells are primarily generated before germinal centers. Upon antigen reencounter, CCR7(lo)PD-1(hi) CXCR5⁺ precursors rapidly differentiate into mature Tfh cells to promote antibody responses. Therefore, circulating CCR7(lo)PD-1(hi) CXCR5⁺ CD4⁺ T cells are generated during active Tfh differentiation and represent a new mechanism of immunological early memory.

T cell vaccination inhibits Th1/Th17/Tfh frequencies and production of autoantibodies in collagen-induced arthritis

The aim of this study is to determine whether the regulatory role of T cell vaccination (TCV) is through inhibition of Th1/Th17/Tfh and production of autoantibodies on collagen-induced arthritis (CIA). First, CIA mice were treated with TCV. After disease onset, the incidence and severity of change in joint histopathology were evaluated. Mice in the TCV-treated group showed less disease severity and less infiltration of inflammatory cells in the joint sections. TCV decreased the frequencies of Th1/Th17/Tfh cells and related cytokines. Reduction of IL-21 may be associated with both Tfh and Th17, which further influence B cell and T cell responses. In addition, inhibition of Th1/Th17/Tfh frequencies led to the reduced expression of T-bet, RORα, RORγt, and Bcl6. Lastly, the proliferation of type-II-collagen-(CII-) specific T cells and the production of anti-CII antibodies were inhibited in the TCV-treated group. The results provide novel evidence that the therapeutic effects of TCV on CIA are associated with the inhibition of Th1/Th17/Tfh frequencies and autoantibodies production.

MicroRNA regulation of T-cell development

MicroRNAs are short, 19-24 nucleotide long, RNA molecules capable of regulating the longevity and, to a lesser extent, translation of messenger RNA (mRNA) species. The function of the microRNA network, and indeed, even that of individual microRNA species, can have profoundly different roles in even a single cell type as the microRNA/mRNA composition evolves. As the role of microRNA within T cells has come under increasing scrutiny, several distinct checkpoints have been demonstrated to have a particular reliance on microRNA regulation. MicroRNAs are arguably most important in T cells during the earliest and last stages in T-cell biology. The first stages of early thymic differentiation have a crucial reliance on the microRNA network, while later stages and peripheral homeostasis are largely, although not completely, microRNA-independent. The most profound effects on T cells are in the activation of effector and regulatory functions of conventional and regulatory T cells, where microRNA deficiency results in a near-complete loss of function. In this review, we focus on integrating the research on individual microRNA into a more global understanding of the function of the microRNA regulatory network in T cells.

Follicular helper T Cells (Tfh) and IL-21 involvement in the pathogenesis of bullous pemphigoid

The pathogenesis of bullous pemphigoid (BP) is characterized by the T cell-dependent production of autoantibodies. Recent studies have indicated that follicular T helper cells (Tfh), the key modulator of B cell activation and autoantibody production, are critical in the development of several autoimmune diseases. Tfh cells perform their functions via IL-21, their hallmark cytokine. In the present study, the frequencies of Tfh cells were investigated in the peripheral blood samples of BP patients to evaluate whether Tfh cells involve in this clinical entity. Significantly higher Tfh cell counts were observed in the peripheral blood of BP patients than those in healthy controls (median: 11.25% vs. 4.95%, respectively; P<0.001). Additionally, the serum IL-21 levels in BP patients were higher than those of the healthy controls (median: 103.98 pg/mL vs 46.77 pg/mL, respectively; P<0.001). The frequencies of Tfh cells and IL-21 levels were both positively correlated with anti-BP180-NC16A autoantibody titers (R = 0.712, P<0.01 and R = 0.578, P = 0.030, respectively). After effective therapy, the frequencies of Tfh cells as well as the serum IL-21 levels in BP patients decreased along with clinical improvement. Most importantly, Tfh depleted CD4(+) T cells and anti-IL-21 neutralization antibody could inhibit the T cell-induced B cell activation and secretion of BP autoantibody in vitro. Those results suggest that Tfh cells play an important role in autoantibody production and are involved in the pathogenesis of BP.

Simian immunodeficiency virus infects follicular helper CD4 T cells in lymphoid tissues during pathogenic infection of pigtail macaques

T follicular helper (Tfh) cells are a specialized subset of memory CD4(+) T cells that are found exclusively within the germinal centers of secondary lymphoid tissues and are important for adaptive antibody responses and B cell memory. Tfh cells do not express CCR5, the primary entry coreceptor for both human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), and therefore, we hypothesized that these cells would avoid infection. We studied lymph nodes and spleens from pigtail macaques infected with pathogenic strain SIVmac239 or SIVmac251, to investigate the susceptibility of Tfh cells to SIV infection. Pigtail macaque PD-1(high) CD127(low) memory CD4(+) T cells have a phenotype comparable to that of human Tfh cells, expressing high levels of CXCR5, interleukin-21 (IL-21), Bcl-6, and inducible T cell costimulator (ICOS). As judged by either proviral DNA or cell-associated viral RNA measurements, macaque Tfh cells were infected with SIV at levels comparable to those in other CD4(+) memory T cells. Infection of macaque Tfh cells was evident within weeks of inoculation, yet we confirmed that Tfh cells do not express CCR5 or either of the well-known alternative SIV coreceptors, CXCR6 and GPR15. Mutations in the SIV envelope gp120 region occurred in chronically infected macaques but were uniform across each T cell subset investigated, indicating that the viruses used the same coreceptors to enter different cell subsets. Early infection of Tfh cells represents an unexpected focus of viral infection. Infection of Tfh cells does not interrupt antibody production but may be a factor that limits the quality of antibody responses and has implications for assessing the size of the viral reservoir.

Follicular T-cell lymphoma: a member of an emerging family of follicular helper T-cell derived T-cell lymphomas

Unlike B-cell lymphomas, where knowledge of normal B-cell origin and differentiation has greatly contributed to their classification, the current classification of peripheral T-cell lymphomas is limited by a lack of understanding of their cellular origin. In the current World Health Organization classification of lymphomas, follicular T-cell lymphoma was formally recognized as a morphologic variant of peripheral T-cell lymphoma, not otherwise specified. There is growing evidence, however, that follicular T-cell lymphoma may be a unique clinicopathologic entity based on its morphologic features and derivation from follicular helper T-cells. In addition, there are abundant recent data supporting the concept that follicular helper T-cells can give rise to other types of T-cell lymphoma, including angioimmunoblastic T-cell lymphoma, primary cutaneous CD4+ small/medium T-cell lymphoma, and a subset of neoplasms, in addition to follicular T-cell lymphoma, currently classified as peripheral T-cell lymphoma, not otherwise specified. In this review, we focus primarily on the clinicopathologic, immunophenotypic, and molecular features of follicular T-cell lymphoma and discuss its potential relationship with other types of T-cell lymphoma thought to be derived from follicular helper T-cells.

Correlation between percentages of peripheral blood CD4+CXCR5+Tfh cells and those of FoxP3+Treg cells in patients with chronic hepatitis B virus infection

AIM: To investigate the correlation between the percentages of blood CD4⁺CXCR5⁺Tfh cells and those of CD4⁺CD25⁺FoxP3⁺Treg cells in patients with chronic hepatitis B virus (HBV) infection.

METHODS: Fresh peripheral blood samples were collected from 15 chronic asymptomatic HBV carriers (AsC), 42 chronic hepatitis B (CHB) patients, of whom 25 were seropositive and 17 seronegative for HBeAg, 11 inactive HBsAg carriers (InC), and 15 healthy controls. The percentages of CD4⁺CXCR5⁺Tfh cells and CD4⁺CD25⁺FoxP3⁺Treg cells were measured by flow cytometry.

RESULTS: The percentages of CD4⁺CXCR5⁺Tfh cells in total CD4⁺T cells isolated from AsC, HBeAg(+)CHB and HBeAg(-)CHB patients were significantly higher than that from healthy controls [17.66 (15.34%-20.56%), 21.95 (19.60%-26.32%), 22.33 (17.58%-24.85%) vs 13.67 (9.80%-15.32%), all P < 0.001]. The percentages of CD4⁺CXCR5⁺Tfh cells in HBeAg(+)CHB or HBeAg(-)CHB patients were elevated significantly compared to those in AsC or InC patients, 16.11 (12.33%-19.73%), P < 0.05. The percentage of CD4⁺CD25⁺FoxP3⁺Treg cells in AsC patients was significantly higher than that in healthy controls, 7.70 (6.35%-9.13%) vs 6.53 (5.54%-7.35%), P < 0.05. Meanwhile, there was a decreasing tendency of the percentages of CD4⁺CD25⁺FoxP3⁺Treg cells in HBeAg(+)CHB patients, 7.52 (6.09%-8.49%) compared to AsC patients. A negative correlation was found between the percentages of circulating CD4+CXCR5+Tfh cells and the HBV DNA load (r = -0.275, P < 0.05), while no significant correlation was found between the percentages of circulating CD4⁺CXCR5⁺Tfh cells and ALT or HBsAg levels.

CONCLUSION: CD4⁺CXCR5⁺Tfh cells may participate in chronic HBV-related immune response, and the relative bias between CD4⁺CD25⁺FoxP3⁺Treg cells and CD4⁺CXCR5⁺Tfh cells may correlate with disease activity.

Role of the frequency of blood CD4(+) CXCR5(+) CCR6(+) T cells in autoimmunity in patients with Sjögren's syndrome

The blood CD4(+) CXCR5(+) T cells, known as "circulating" Tfh, have been shown to efficiently induce naïve B cells to produce immunoglobulin. They play an important role in certain autoimmune diseases. In the present study, we show for the first time that the frequency of CD4(+) CXCR5(+) T cells is increased in pSS patients and positively correlated with autoantibodies in the blood. The concentration of Th17-like subsets (CD4(+) CXCR5(+) CCR6(+)) in pSS patients was found to be significantly higher than in healthy controls. Functional assays showed that activated Th17-like subtypes in the blood display the key features of Tfh cells, including invariably coexpressed PD-1, ICOS, CD40L and IL-21. Th17 subsets were found to highly express Bcl-6 protein and Th1 and Th2 were not. Bcl-6 is believed to be a master transforming factor for Tfh cell differentiation and facilitate B cell proliferation and somatic hypermutation within the germinal center. These data indicate that Th17 subsets of CD4(+) CXCR5(+) T cells in the blood may participate in the antibody-related immune responses and that high frequency of CD4(+) CXCR5(+) CCR6(+) Tfh cells in blood may be suitable biomarkers for the evaluation of the active immune stage of pSS patients. It might provide insights into the pathogenesis and perhaps help researchers identify novel therapeutic targets for pSS.

Germinal center B cell and T follicular helper cell development initiates in the interfollicular zone

We identify the interfollicular (IF) zone as the site where germinal center B cell and T follicular helper (Tfh) cell differentiation initiates. For the first 2 days postimmunization, antigen-specific T and B cells remained confined within the IF zone, formed long-lived interactions, and upregulated the transcriptional repressor Bcl6. T cells also acquired the Tfh cell markers CXCR5, PD-1, and GL7. Responding B and T cells migrated to the follicle interior directly from the IF zone, T cell immigration preceding B cells by 1 day. Notably, in the absence of cognate B cells, Tfh cells still formed and migrated to the follicle. However, without such B cells, PD-1, ICOS, and GL7 were no longer expressed on follicular Bcl6(hi) T cells that nevertheless persisted in the follicle. Thus, Ag-specific B cells are required for the maintenance of the PD-1(hi)ICOS(hi)GL7(hi) Tfh cell phenotype within the follicle, but not for their initial differentiation in the IF zone.

SLAM family receptors and SAP adaptors in immunity

The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia. SAP consists almost entirely of a single SH2 protein domain that interacts with the cytoplasmic tail of SLAM and related receptors, including 2B4, Ly108, CD84, Ly9, and potentially CRACC. SLAM family members are now recognized as important immunomodulatory receptors with roles in cytotoxicity, humoral immunity, autoimmunity, cell survival, lymphocyte development, and cell adhesion. In this review, we cover recent findings on the roles of SLAM family receptors and the SAP family of adaptors, with a focus on their regulation of the pathways involved in the pathogenesis of XLP and other immune disorders.

CXCR5 expressing human central memory CD4 T cells and their relevance for humoral immune responses

High expression of CXCR5 is one of the defining hallmarks of T follicular helper cells (T(FH)), a CD4 Th cell subset that promotes germinal center reactions and the selection and affinity maturation of B cells. CXCR5 is also expressed on 20-25% of peripheral blood human central memory CD4 T cells (T(CM)), although the definitive function of these cells is not fully understood. The constitutive expression of CXCR5 on T(FH) cells and a fraction of circulating T(CM) suggests that CXCR5(+) T(CM) may represent a specialized subset of memory-type T(FH) cells programmed for homing to follicles and providing B cell help. To verify this assumption, we analyzed this cell population and show its specialized function in supporting humoral immune responses. Compared with their CXCR5(-) T(CM) counterparts, CXCR5(+) T(CM) expressed high levels of the chemokine CXCL13 and efficiently induced plasma cell differentiation and Ig secretion. We found that the distinct B cell helper qualities of CXCR5(+) T(CM) were mainly due to high ICOS expression and pronounced responsiveness to ICOS ligand costimulation together with large IL-10 secretion. Furthermore, B cell helper attributes of CXCR5(+) T(CM) were almost exclusively acquired on cognate interaction with B cells, but not with dendritic cells. This implies that a preferential recruitment of circulating CXCR5(+) T(CM) to CXCL13-rich B cell follicles is required for the promotion of a quick and efficient protective secondary humoral immune response. Taken together, we propose that CXCR5(+) T(CM) represent a distinct memory cell subset specialized in supporting Ab-mediated immune responses.

Dysregulated generation of follicular helper T cells in the spleen triggers fatal autoimmune hepatitis in mice

BACKGROUND & AIMS

To clarify mechanisms involved in the development of autoimmune hepatitis (AIH), we recently developed a mouse model of spontaneous AIH by inducing a concurrent loss of Foxp3(+) regulatory T cells and programmed cell death 1 (PD-1)-mediated signaling. Fatal AIH in these mice was characterized by severe T-cell infiltration and huge production of antinuclear antibodies (Abs). This study aims to identify induction sites, responsible T-cell subsets, and key molecules for induction of AIH.

METHODS

To develop the mouse model of AIH, neonatal thymectomy (NTx) was performed on PD-1-deficient (PD-1(-/-)) mice. We then conducted neonatal splenectomy or in vivo administration of Abs to cytokines, chemokines, or cell-surface molecules.

RESULTS

In NTx-PD-1(-/-) mice, either neonatal splenectomy or in vivo CD4(+) T-cell depletion suppressed CD4(+) and CD8(+) T-cell infiltration in the liver. In the induction phase of AIH, splenic CD4(+) T cells were localized in B-cell follicles with huge germinal centers and showed the Bcl6(+) inducible costimulator (ICOS)(+) interleukin (IL)-21(+) IL-21 receptor (IL-21R)(+) follicular helper T (T(FH)) cell phenotype. Blocking Abs to ICOS or IL-21 suppressed T(FH)-cell generation and induction of AIH. In addition, IL-21 produced by T(FH) cells drove CD8(+) T-cell activation. Splenic T(FH) cells and CD8(+) T cells expressed CCR6, and CCL20 expression was elevated in the liver. Administration of anti-CCL20 suppressed migration of these T cells to the liver and induction of AIH.

CONCLUSIONS

Dysregulated T(FH) cells in the spleen are responsible for the induction of fatal AIH, and CCR6-CCL20 axis-dependent migration of splenic T cells is crucial to induce AIH in NTx-PD-1(-/-) mice.

Genomic views of STAT function in CD4+ T helper cell differentiation

Signal transducer and activator of transcription (STAT) proteins are well known for their essential roles in transmitting cytokine-mediated signals and specifying T helper (T(H)) cell differentiation. Recent technological advances have revealed that STAT proteins have broad and complex roles in gene regulation and epigenetic control, including important roles as functional repressors. However, the challenge of how to link signal transduction, nucleosome biology and gene regulation remains. The relevance of tackling this problem is highlighted by genome-wide association studies that link cytokine signalling and STATs to various autoimmune or immune deficiency disorders. Defining exactly how extrinsic signals control the specification and plasticity of T(H) cells will provide important insights and perhaps therapeutic opportunities in these diseases.

IL-27 supports germinal center function by enhancing IL-21 production and the function of T follicular helper cells

IL-27 signaling directly into T cells is needed for follicular T helper cell survival, germinal center formation, and the production of T cell–dependent high-affinity antibodies in mice.

Maturation and selection of high-affinity B cell clones in the germinal center (GC) relies on support from T follicular helper (T_FH) cells. T_FH cells are characterized by their localization to the B cell follicle and their high expression of the costimulatory molecules ICOS and PD1 and the cytokine IL-21, which promotes immunoglobulin (Ig) class switching and production by B cells. We show that the heterodimeric cytokine IL-27 is critical for the function of T_FH cells and for normal and pathogenic GC responses. IL-27 signaling to T cells results in the production of IL-21, a known autocrine factor for the maintenance of T_FH cells, in a STAT3-dependent manner. IL-27 also enhances the survival of activated CD4⁺ T cells and the expression of T_FH cell phenotypic markers. In vivo, expression of the IL-27Rα chain is required to support IL-21 production and T_FH cell survival in a T cell–intrinsic manner. The production of high-affinity antibodies is reduced, and pristane-elicited autoantibodies and glomerulonephritis are significantly diminished, in Il27ra^−/− mice. Together, our data show a nonredundant role for IL-27 in the development of T cell–dependent antibody responses.

Mucosal adjuvants and long-term memory development with special focus on CTA1-DD and other ADP-ribosylating toxins

The ultimate goal for vaccination is to stimulate protective immunological memory. Protection against infectious diseases not only relies on the magnitude of the humoral immune response, but more importantly on the quality and longevity of it. Adjuvants are critical components of most non-living vaccines. Although little attention has been given to qualitative aspects of the choice of vaccine adjuvant, emerging data demonstrate that this function may be central to vaccine efficacy. In this review we describe efforts to understand more about how adjuvants influence qualitative aspects of memory development. We describe recent advances in understanding how vaccines induce long-lived plasma and memory B cells, and focus our presentation on the germinal center reaction. As mucosal vaccination requires powerful adjuvants, we have devoted much attention to the adenosine diphosphate (ADP)-ribosylating cholera toxin and the CTA1-DD adjuvants as examples of how mucosal adjuvants can influence induction of long-term memory.

Follicular helper T cell differentiation requires continuous antigen presentation that is independent of unique B cell signaling

Effective humoral immunity depends on the support of B cell responses by T follicular helper (Tfh) cells. Although it has been proposed that Tfh cell differentiation requires T-B interactions, the relative contribution of specific populations of Ag-presenting cells remains unknown. We employed three independent strategies that compromised interactions between CD4(+) T cells and activated B cells in vivo. Whereas the expansion of CD4(+) T cells was relatively unaffected, Tfh cell differentiation was completely blocked in all scenarios. Surprisingly, augmenting antigen presentation by non-B cells rescued Tfh cell differentiation, as determined by surface phenotype, gene expression, and germinal center localization. We conclude that although Ag presentation by responding B cells is typically required for the generation of Tfh cells, this does not result from the provision of a unique B cell-derived signal, but rather because responding B cells rapidly become the primary source of antigen.

Cellular choreography in the germinal center: new visions from in vivo imaging

Germinal centers (GC) are large aggregates of proliferating B lymphocytes within follicles of lymphoid tissue that form during adaptive immune responses. GCs are the source of long-lived B cells that form the basis for pathogen-specific lifelong B cell immunity. The complex architecture of these structures includes subdomains that differ significantly in their stromal cell and T lymphocyte subset composition. In part due to their structural complexity and potential to generate some lymphomas, much interest and many theories about GC dynamics have emerged. Here, we review recent research employing in vivo imaging that has begun to untangle some of the mysteries.

Multiple checkpoints keep follicular helper T cells under control to prevent autoimmunity

Follicular helper T (Tfh) cells select mutated B cells in germinal centres, which can then differentiate into long-lived high affinity memory B cells and plasma cells. Tfh cells are regulated by a unique molecular programme orchestrated by the transcriptional repressor Bcl6. This transcription factor turns down expression of multiple genes, including transcriptional regulators of other T helper lineages and a vast amount of microRNAs. This enables Tfh cells to express a suite of chemokine receptors, stimulatory ligands and cytokines that enable migration into B-cell follicles, and provision of effective help to B cells. Not surprisingly, dysregulation of this powerful helper subset can lead to a range of autoantibody-mediated diseases; indeed, aberrant accumulation of Tfh cells has been linked with systemic lupus erythematosus, Sjogren's disease and autoimmune arthritis. Here we dissect multiple checkpoints that operate throughout Tfh cell development and maturation to maintain immunological tolerance while mounting robust and long-lasting antibody responses.