Expansion of circulating T cells resembling follicular helper T cells is a fixed phenotype that identifies a subset of severe systemic lupus erythematosus

Circulating TFH subset distribution is strongly affected in lupus patients with an active disease

Follicular helper T cells (T_FH) represent a distinct subset of CD4⁺ T cells specialized in providing help to B lymphocytes, which may play a central role in autoimmune diseases having a major B cell component such as systemic lupus erythematosus. Recently, T_FH subsets that share common phenotypic and functional characteristics with T_FH cells from germinal centers, have been described in the peripheral blood from healthy individuals. The aim of this study was to analyze the distribution of such populations in lupus patients. Circulating T_FH cell subsets were defined by multicolor flow cytometry as T_FH17 (CXCR3^-CCR6⁺), T_FH1 (CXCR3 ⁺ CCR6^-) or T_FH2 (CXCR3^-CCR6^-) cells among CXCR5 ⁺ CD45RA^-CD4⁺ T cells in the peripheral blood of 23 SLE patients and 23 sex and age-matched healthy controls. IL-21 receptor expression by B cells was analyzed by flow cytometry and the serum levels of IL-21 and Igs were determined by ELISA tests. We found that the T_FH2 cell subset frequency is strongly and significantly increased in lupus patients with an active disease (SLEDAI score>8), while the T_FH1 cell subset percentage is greatly decreased. The T_FH2 and T_FH1 cell subset frequency alteration is associated with the presence of high Ig levels and autoantibodies in patient’s sera. Moreover, the T_FH2 cell subset enhancement correlates with an increased frequency of double negative memory B cells (CD27^-IgD^-CD19⁺ cells) expressing the IL-21R. Finally, we found that IgE levels in lupus patients’ sera correlate with disease activity and seem to be associated with high T_FH2 cell subset frequency. In conclusion, our study describes for the first time the distribution of circulating T_FH cell subsets in lupus patients. Interestingly, we found an increased frequency of T_FH2 cells, which correlates with disease activity. Our results suggest that this subset might play a key role in lupus pathogenesis.

The adaptor molecule signaling lymphocytic activation molecule (SLAM)-associated protein (SAP) is essential in mechanisms involving the Fyn tyrosine kinase for induction and progression of collagen-induced arthritis

Signaling lymphocytic activation molecule-associated protein (SAP) is an Src homology 2 domain-only adaptor involved in multiple immune cell functions. It has also been linked to immunodeficiencies and autoimmune diseases, such as systemic lupus erythematosus. Here, we examined the role and mechanism of action of SAP in autoimmunity using a mouse model of autoimmune arthritis, collagen-induced arthritis (CIA). We found that SAP was essential for development of CIA in response to collagen immunization. It was also required for production of collagen-specific antibodies, which play a key role in disease pathogenesis. These effects required SAP expression in T cells, not in B cells. In mice immunized with a high dose of collagen, the activity of SAP was nearly independent of its ability to bind the protein tyrosine kinase Fyn and correlated with the capacity of SAP to promote full differentiation of follicular T helper (TFH) cells. However, with a lower dose of collagen, the role of SAP was more dependent on Fyn binding, suggesting that additional mechanisms other than TFH cell differentiation were involved. Further studies suggested that this might be due to a role of the SAP-Fyn interaction in natural killer T cell development through the ability of SAP-Fyn to promote Vav-1 activation. We also found that removal of SAP expression during progression of CIA attenuated disease severity. However, it had no effect on disease when CIA was clinically established. Together, these results indicate that SAP plays an essential role in CIA because of Fyn-independent and Fyn-dependent effects on TFH cells and, possibly, other T cell types.

Human circulating PD-1+CXCR3-CXCR5+ memory Tfh cells are highly functional and correlate with broadly neutralizing HIV antibody responses

The vast majority of currently licensed human vaccines work on the basis of long-term protective antibody responses. It is now conceivable that an antibody-dependent HIV vaccine might be possible, given the discovery of HIV broadly neutralizing antibodies (bnAbs) in some HIV-infected individuals. However, these antibodies are difficult to develop and have characteristics indicative of a high degree of affinity maturation in germinal centers (GCs). CD4⁺ T follicular helper (Tfh) cells are specialized for B cell help and necessary for GCs. Therefore, the development of HIV bnAbs might depend on Tfh cells. Here, we identified in normal individuals a subpopulation of circulating memory PD-1⁺CXCR5⁺CD4⁺ T cells that are resting memory cells most related to bona fide GC Tfh cells by gene expression profile, cytokine profile, and functional properties. Importantly, the frequency of these cells correlated with the development of bnAbs against HIV in a large cohort of HIV⁺ individuals.

Induction of ICOS+CXCR3+CXCR5+ TH cells correlates with antibody responses to influenza vaccination

Seasonal influenza vaccine protects 60 to 90% of healthy young adults from influenza infection. The immunological events that lead to the induction of protective antibody responses remain poorly understood in humans. We identified the type of CD4+ T cells associated with protective antibody responses after seasonal influenza vaccinations. The administration of trivalent split-virus influenza vaccines induced a temporary increase of CD4+ T cells expressing ICOS, which peaked at day 7, as did plasmablasts. The induction of ICOS was largely restricted to CD4+ T cells coexpressing the chemokine receptors CXCR3 and CXCR5, a subpopulation of circulating memory T follicular helper cells. Up to 60% of these ICOS+CXCR3+CXCR5+CD4+ T cells were specific for influenza antigens and expressed interleukin-2 (IL-2), IL-10, IL-21, and interferon-γ upon antigen stimulation. The increase of ICOS+CXCR3+CXCR5+CD4+ T cells in blood correlated with the increase of preexisting antibody titers, but not with the induction of primary antibody responses. Consistently, purified ICOS+CXCR3+CXCR5+CD4+ T cells efficiently induced memory B cells, but not naïve B cells, to differentiate into plasma cells that produce influenza-specific antibodies ex vivo. Thus, the emergence of blood ICOS+CXCR3+CXCR5+CD4+ T cells correlates with the development of protective antibody responses generated by memory B cells upon seasonal influenza vaccination.

Increased frequency of bone marrow T follicular helper cells in patients with immune-related pancytopenia

Immune-related pancytopenia (IRP) is one kind of bone marrow failure diseases which is related to autoantibodies. Autoantibodies have been detected on the membrane of various bone marrow (BM) hemopoietic cells by BM mononuclear-cell-Coombs test or flow cytometric analysis. There are autoantibodies in the BM supernatant of IRP patients, which can target several antigens on hematopoietic cells membranes by western blot. T follicular helper (Tfh) cells are the true helper cells for Ab responses, which represent one of the most numerous and important subsets of effector T cells. Dysregulation of Tfh cell function or expression of Tfh cell-associated molecules could contribute to the pathogenesis of autoimmune diseases. Currently, there are no studies regarding the role of Tfh cells in IRP patients. The percentages of Tfh cells, Tfh-related molecules ICOS, CD40L, IL-21, and Bcl-6 in BM were investigated in 90 patients with IRP, and 25 healthy controls. We observed that there exist increased quantity and hyperfunction of Tfh cells in IRP, and the results were correlated with patient characteristics. It was indicated that dysregulated Tfh cells might be involved in the pathogenesis of IRP and that inhibition of Tfh cells effector molecules might provide opportunities for new therapeutic approaches to IRP and even other human autoimmune diseases.

IL-17RA is essential for optimal localization of follicular Th cells in the germinal center light zone to promote autoantibody-producing B cells

Germinal centers (GCs) provide a microenvironment that promotes and regulates the interactions of B cells with follicular Th (TFH) cells. In this study, we show that there are significantly higher frequencies of CXCR5(+)ICOS(+) TFH cells in autoimmune BXD2 mice, and these cells express both IL-21R and IL-17RA. Although IL-17 and IL-21 are both important for the formation of spontaneous GCs and development of pathogenic autoantibodies, IL-21, but not IL-17, is required for the proper development of TFH cells in BXD2 mice. The total numbers of TFH cells and their ability to induce B cell responses in vitro were not affected by a deficiency of IL-17RA in BXD2-Il17ra(-/-) mice, the majority of CXCR5(+) TFH cells from BXD2-Il17ra(-/-) mice were, however, not localized in the GC light zone (LZ). Interruption of IL-17 signaling, either acutely by AdIL-17R:Fc or chronically by Il17ra(-/-), disrupted TFH-B interactions and abrogated the generation of autoantibody-forming B cells in BXD2 mice. IL-17 upregulated the expression of regulator of G-protein signaling 16 (RGS16) to promote the ability of TFH to form conjugates with B cells, which was abolished in TFH cells from BXD2-Rgs16(-/-) mice. The results suggests that IL-17 is an extrinsic stop signal that it acts on postdifferentiated IL-17RA(+) TFH to enable its interaction with responder B cells in the LZ niche. These data suggest a novel concept that TFH differentiation and its stabilization in the LZ are two separate checkpoints and that IL-21 and IL-17 act at each checkpoint to enable pathogenic GC development.

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.

Modulation of B-cell tolerance by murine gammaherpesvirus 68 infection: requirement for Orf73 viral gene expression and follicular helper T cells

Viruses such as Epstein-Barr virus (EBV) have been linked to mechanisms that support autoantibody production in diseases such as systemic lupus erythematosus. However, the mechanisms by which viruses contribute to autoantibody production remain poorly defined. This stems in part, from the high level of seropositivity for EBV (> 95%) and the exquisite species specificity of EBV. In this study we overcame these problems by using murine gammaherpesvirus 68 (MHV68), a virus genetically and biologically related to EBV. We first showed that MHV68 drives autoantibody production by promoting a loss of B-cell anergy. We next showed that MHV68 infection resulted in the expansion of follicular helper T (Tfh) cells in vivo, and that these Tfh cells supported autoantibody production and a loss of B-cell anergy. Finally, we showed that the expansion of Tfh cells and autoantibody production was dependent on the establishment of viral latency and expression of a functional viral gene called Orf73. Collectively, our studies highlighted an unexpected role for viral latency in the development of autoantibodies following MHV68 infection and suggest that virus-induced expansion of Tfh cells probably plays a key role in the loss of B-cell anergy.

MicroRNAs of the miR-17∼92 family are critical regulators of T(FH) differentiation

T follicular helper (T_FH) cells provide critical help to B cells during humoral immune responses. Here we report that mice with T cell-specific deletion of miR-17~92 family miRNAs (tKO mice) exhibited severely compromised T_FH differentiation, germinal center formation, antibody responses, and failed to control chronic virus infection. Conversely, T cell-specific miR-17~92 transgenic mice spontaneously accumulated T_FH cells and developed fatal immunopathology. Mechanistically, miR-17~92 family miRNAs control CD4⁺ T cell migration into B cell follicles by regulating ICOS-PI3K signaling intensity through suppressing the expression of the Akt phosphatase Phlpp2. These findings demonstrate that miR-17~92 family microRNAs play an essential role in T_FH differentiation and establish Phlpp2 as an important mediator of their function in this process.

Human T follicular helper cells: development and subsets

Antibody response constitutes one of the key immune protection mechanisms. T follicular helper (Tfh) cells represent the major CD4⁺ T cell subset that provides help to B cells to induce antibody response. How Tfh cells develop and how Tfh cells or their associated subsets regulate antibody response in humans remains largely unknown. In this review, we will summarize the recent discoveries on the biology of Tfh cells, with a particular focus on human Tfh cells.

Baicalin inhibits IL-17-mediated joint inflammation in murine adjuvant-induced arthritis

T-helper-17 (Th17) cells are implicated in a number of inflammatory disorders including rheumatoid arthritis. Antagonism of Th17 cells is a treatment option for arthritis. Here, we report that Baicalin, a compound isolated from the Chinese herb Huangqin (Scutellaria baicalensis Georgi), relieved ankle swelling and protected the joint against inflammatory destruction in a murine adjuvant-induced arthritis model. Baicalin inhibited splenic Th17 cell population expansion in vivo. Baicalin prevented interleukin- (IL-) 17-mediated lymphocyte adhesion to cultured synoviocytes. Baicalin also blocked IL-17-induced intercellular adhesion molecule 1, vascular cell adhesion molecule 1, IL-6, and tumor necrosis factor-alpha mRNA expression in cultured synoviocytes. Collectively, these findings suggest that Baicalin downregulates the joint inflammation caused by IL-17, which is likely produced by an expanded population of splenic Th17 cells in experimental arthritis. Baicalin might be a promising novel therapeutic agent for treating rheumatoid arthritis in humans.

The role of T cell immunity in HIV-1 infection

The interplay between the T cell immune response and human immunodeficiency virus (HIV)-1 largely determines the outcome of infection. Typically, the virus overcomes the immune defences leading to a gradual decline in function that permits the development of disease. In recent years, a concerted effort in comparing T cell responses between 'controllers' and 'progressors' is beginning to identify the T cell subsets and factors that affect disease progression related to the effector functions of both CD4 and CD8 T cells. These efforts are providing opportunities for development of novel therapies and vaccines.

Follicular helper T cells may play an important role in the severity of primary Sjögren's syndrome

The aim of this study was to investigate the possible role of follicular helper T (TFH) cells in the pathogenesis of primary Sjögren's syndrome (pSS) by analyzing immune-competent cells and serological markers with special emphasis on clinical symptoms. We enrolled 50 pSS patients and 16 healthy individuals in the study. Patients had elevated ratio of peripheral TFH cells, however, when dividing patients into two groups defined by the presence of extraglandular manifestations (EGMs), only patients with EGMs differed from controls significantly. Moreover, TFH cell percentages correlated positively with both activated T cell and Tr1 cell values. On the contrary, TFH cell percentages showed negative correlation with both IgM and IgG memory B cell proportions. Elevated TFH percent\ages were observed in the anti-SSA/SSB positive patients, and also in patients with higher IL-12, IL-21 levels and focus score values. Increased TFH cell proportions seem to have an important role in disease development.

T follicular helper cells mediate expansion of regulatory B cells via IL-21 in Lupus-prone MRL/lpr mice

T follicular helper (Tfh) cells can mediate humoral immune responses and augment autoimmunity, whereas the role of Tfh cells on regulatory B (B10) cells in autoimmunity diseases is not clear. Here, we investigated the percentages of Tfh cells and B10 cells in lupus-prone MRL/Mp-lpr/lpr (MRL/lpr) mice and examined the effects and mechanism of Tfh cell-derived interleukin-21 (IL-21) on IL-10 production during the differentiation of B10 cells. Both Tfh cells and B10 cells were expanded in spleens of MRL/lpr mice. In addition, a positive correlation between the proportions of Tfh cells and B10 cells was observed. Tfh cell-derived IL-21 from MRL/lpr mice could promote IL-10 production during the differentiation of B10 cells. Importantly, neutralization of IL-21 inhibited IL-10 production and expansion of B10 cells both in vitro and in vivo. IL-21 induced IL-10 production via activation of phosphorylated signal transduction and activator of transcription 3 (p-STAT3). Inhibition of p-STAT3 effectively blocked IL-10 production during the differentiation of B10 cells. Moreover, IL-21-induced IL-10 exerted a regulatory function by inhibiting the proliferation of T cells. These data suggest that Tfh cells not only mediate humoral immune responses and augment autoimmunity but also play a broader role in immune regulatory actions via the induction of IL-10 production.

Harnessing CD4⁺ T cell responses in HIV vaccine development

CD4(+) T cells can perform a panoply of tasks to shape an effective response against a pathogen. Limited attention has been paid to the potential importance of functional CD4(+) T cell responses in the context of the development of next-generation vaccines, including HIV vaccines. Many CD4(+) T cell functions are newly appreciated and only partially understood. A workshop was held as a forum to bring together a small group of experts to exchange ideas on the role of CD4(+) T cells in developing durable functional antibody responses, via follicular helper T cells, as well as on the roles of CD4(+) T cells in other aspects of protective immunity. Here we discuss whether CD4(+) T cell responses may represent a beneficial component of an efficacious HIV vaccine.

Expansion of circulating counterparts of follicular helper T cells in patients with myasthenia gravis

Growing evidence has demonstrated that dysfunction of follicular helper T (TFH) cells results in an abnormal positive selection of autoreactive B cells, which contributes to the development of autoimmune diseases. This study reveals that the frequency of circulating counterparts of TFH cells in myasthenia gravis (MG) patients is significantly higher compared to healthy controls. Interestingly, the frequencies of circulating TFH cells were positively correlated with the levels of serum anti-AChR Ab in MG patients. Our data suggest the presence of overactivation and expansion of circulating counterparts of TFH cells in MG patients, which may contribute to the immunopathogenesis of MG.

Inhibition of aberrant circulating Tfh cell proportions by corticosteroids in patients with systemic lupus erythematosus

OBJECTIVE

To observe the proportion of peripheral T follicular helper (Tfh) cells in patients with systemic lupus erythematosus (SLE) and to assess the role of steroids on Tfh cells from SLE patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) from 42 SLE patients and 22 matched healthy subjects were collected to assess proportions of circulating CXCR5(+)PD1(+)/CD4(+) T cells (Tfh), CD4(+)CCR6(+) T cells (Th17-like) and CD19(+)CD138(+) plasma cells by flow cytometry. 8 of the patients had their blood redrawn within one week after receiving methylprednisolone pulse treatment. Disease activity was evaluated by SLE disease activity index. To test the effect of IL-21 and corticosteroids on Tfh cells in vitro, PBMCs harvested from another 15 SLE patients were cultured with medium, IL-21, or IL-21+ dexamethasone for 24 hours and 72 hours. PBMCs from an independent 23 SLE patients were cultured with different concentrations of dexamethasone for 24 hours.

RESULTS

Compared to normal controls, percentages of circulating Tfh cells, but not Th17 cells, were elevated in SLE patients and correlated with disease activity. Proportions of Tfh cells in SLE patients were positively correlated with those of plasma cells and serum levels of antinuclear antibodies. After methylprednisolone pulse treatment, both percentages and absolute numbers of circulating Tfh cells were significantly decreased. In vitro cultures showed an increase of Tfh cell proportion after IL-21 stimulation that was totally abolished by the addition of dexamethasone. Both 0.5 and 1 µM dexamethasone decreased Tfh cells dose dependently (overall p = 0.013).

CONCLUSIONS

We demonstrated that elevated circulating Tfh cell proportions in SLE patients correlated with their disease activities, and circulating levels of plasma cells and ANA. Corticosteroids treatment down-regulated aberrant circulating Tfh cell proportions both in vivo and in vitro, making Tfh cells a new treatment target for SLE patients.

The receptor PD-1 controls follicular regulatory T cells in the lymph nodes and blood

CD4(+)CXCR5(+)Foxp3(+) follicular regulatory T cells (T(FR) cells) inhibit humoral immunity mediated by CD4(+)CXCR5(+)Foxp3(-) follicular helper T cells (T(FH) cells). Although the inhibitory receptor PD-1 is expressed by both cell types, its role in the differentiation of T(FR) cells is unknown. Here we found that mice deficient in PD-1 and its ligand PD-L1 had a greater abundance of T(FR) cells in the lymph nodes and that those T(FR) cells had enhanced suppressive ability. We also found substantial populations of T(FR) cells in mouse blood and demonstrated that T(FR) cells in the blood homed to lymph nodes and potently inhibited T(FH) cells in vivo. T(FR) cells in the blood required signaling via the costimulatory receptors CD28 and ICOS but were inhibited by PD-1 and PD-L1. Our findings demonstrate mechanisms by which the PD-1 pathway regulates antibody production and help reconcile inconsistencies surrounding the role of this pathway in humoral immunity.

Interferon-γ excess leads to pathogenic accumulation of follicular helper T cells and germinal centers

Overactivity of the germinal center (GC) pathway resulting from accumulation of follicular helper T (Tfh) cells causes autoimmunity, underscoring the need to understand the factors that control Tfh cell homeostasis. Here we have identifed posttranscriptional repression of interferon-γ (Ifng) mRNA as a mechanism to limit Tfh cell formation. By using the sanroque lupus model, we have shown that decreased Ifng mRNA decay caused excessive IFN-γ signaling in T cells and led to accumulation of Tfh cells, spontaneous GC, autoantibody formation, and nephritis. Unlike ICOS and T-bet deficiency that failed to rescue several autoimmune manifestations, interferon-γ receptor (IFN-γR) deficiency prevented lupus development. IFN-γ blockade reduced Tfh cells and autoantibodies, demonstrating that IFN-γ overproduction was required to sustain lupus-associated pathology. Increased IFN-γR signaling caused Bcl-6 overexpression in Tfh cells and their precursors. This link between IFN-γ and aberrant Tfh cell formation provides a rationale for IFN-γ blockade in lupus patients with an overactive Tfh cell-associated pathway.

The pathogenesis of systemic lupus erythematosus-an update

Systemic lupus erythematosus (SLE, lupus) is characterized by a global loss of self-tolerance with activation of autoreactive T and B cells leading to production of pathogenic autoantibodies and tissue injury. Innate immune mechanisms are necessary for the aberrant adaptive immune responses in SLE. Recent advances in basic and clinical biology have shed new light on disease mechanisms in lupus, with this review discussing the recent studies that offer valuable insights into disease-specific therapeutic targets.

Developing connections amongst key cytokines and dysregulated germinal centers in autoimmunity

Systemic autoimmunity owing to overactivity of Tfh and dysregulated germinal centers has been described in mice and humans. Cytokines such as IL-21, IFN-γ, IL-6 and IL-17 are elevated in the plasma of mouse models of lupus, arthritis, and multiple sclerosis, and in subsets of patients with autoimmune disease. Monoclonal antibodies targeting these cytokines are entering clinical trials. While these cytokines exert pleiotropic effects on immune cells and organs, it is becoming clear that each and all of them can profoundly regulate Tfh numbers and/or function and induce or maintain the aberrant germinal center reactions that lead to pathogenic autoantibody formation. Here we review recent discoveries into the roles of IL-21, IFN-γ, IL-6, and IL-17 in germinal center responses and antibody-driven autoimmunity. These new insights used in conjunction with biomarkers of an overactive Tfh pathway may help stratify patients to rationalize the use of emerging monoclonal anti-cytokine antibody therapies.

The phenotype of circulating follicular-helper T cells in patients with rheumatoid arthritis defines CD200 as a potential therapeutic target

Rheumatoid arthritis (RA) is a systemic autoimmune disease primarily affecting synovial joints in which the development of autoantibodies represents a failure of normal tolerance mechanisms, suggesting a role for follicular helper T cells (T_FH) in the genesis of autoimmunity. To determine whether quantitative or qualitative abnormalities in the circulating T_FH cell population exist, we analysed by flow cytometry the number and profile of these cells in 35 patients with RA and 15 matched controls. Results were correlated with patient characteristics, including the presence of autoantibodies, disease activity, and treatment with biologic agents. Circulating T_FH cells from patients with RA show significantly increased expression of the immunoglobulin superfamily receptor CD200, with highest levels seen in seropositive patients (P = 0.0045) and patients treated with anti-TNFα agents (P = 0.0008). This occurs in the absence of any change in T_FH numbers or overt bias towards Th1, Th2, or Th17 phenotypes. CD200 levels did not correlate with DAS28 scores (P = 0.887). Although the number of circulating T_FH cells is not altered in the blood of patients with RA, the T_FH cells have a distinct phenotype. These differences associate T_FH cells with the pathogenesis of RA and support the relevance of the CD200/CD200R signalling pathway as a potential therapeutic target.

The origins, function, and regulation of T follicular helper cells

The generation of high-affinity antibodies (Abs) plays a critical role in the neutralization and clearance of pathogens and subsequent host survival after natural infection with a variety of microorganisms. Most currently available vaccines rely on the induction of long-lived protective humoral immune responses by memory B cells and plasma cells, underscoring the importance of Abs in host protection. Ab responses against most antigens (Ags) require interactions between B cells and CD4(+) T helper cells, and it is now well recognized that T follicular helper cells (Tfh) specialize in providing cognate help to B cells and are fundamentally required for the generation of T cell-dependent B cell responses. Perturbations in the development and/or function of Tfh cells can manifest as immunopathologies, such as immunodeficiency, autoimmunity, and malignancy. Unraveling the cellular and molecular requirements underlying Tfh cell formation and maintenance will help to identify molecules that could be targeted for the treatment of immunological diseases that are characterized by insufficient or excessive Ab responses.

Selective localization of T helper subsets in labial salivary glands from primary Sjögren's syndrome patients

The aim of this study was to investigate the initiation and progression of autoimmune damage in the lesions of labial salivary glands (LSGs) from primary Sjögren's syndrome (SS) patients by examining the selective localization of T helper (Th) subsets such as Th1, Th2, Th17 regulatory T cells (T_regs) and follicular T helper cells (Tfh). The expression of cytokines and transcription factors associated with these Th subsets in the LSGs from 54 SS patients and 16 healthy controls was examined using real-time polymerase chain reaction (PCR) and immunostaining. Additionally, infiltrating lymphocytes without germinal centre (GC^-) and with GC (GC⁺) in the LSGs specimens from eight SS patients were extracted selectively by laser capture microdissection (LCM). The mRNA expression of these molecules was compared between the two sample groups of GC^- and GC⁺ by real-time PCR. The mRNA expression of cytokines and transcription factors of all T helper (Th) subsets in the LSGs from the SS patients was increased significantly in comparison with controls. In LSGs from the SS patients, Th2 and Tfh was associated closely with strong lymphocytic infiltration; however, Th1, Th17 and T_regs was not. In the selectively extracted lesions of LSGs, Th1 and Th17-related molecules were detected strongly in the GC^-, while Th2 and Tfh-related molecules were detected in the GC⁺. In contrast, no significant association with strong lymphocytic infiltration was observed in T_reg-related molecules. These results indicate that SS has selective localization of Th subsets such as Th1, Th2, Th17 and Tfh in the LSGs, which is associated closely with disease severity and/or status. SS might be initiated by Th1 and Th17 cells, and then progressed by Th2 and Tfh cells via GC formation.

The Therapeutic Potential for PI3K Inhibitors in Autoimmune Rheumatic Diseases

The class 1 PI3Ks are lipid kinases with key roles in cell surface receptor-triggered signal transduction pathways. Two isoforms of the catalytic subunits, p110γ and p110δ, are enriched in leucocytes in which they promote activation, cellular growth, proliferation, differentiation and survival through the generation of the second messenger PIP3. Genetic inactivation or pharmaceutical inhibition of these PI3K isoforms in mice result in impaired immune responses and reduced susceptibility to autoimmune and inflammatory conditions. We review the PI3K signal transduction pathways and the effects of inhibition of p110γ and/or p110δ on innate and adaptive immunity. Focusing on rheumatoid arthritis and systemic lupus erythematosus we discuss the preclinical evidence and prospects for small molecule inhibitors of p110γ and/or p110δ in autoimmune disease.

Patients with chronic hepatitis C express a high percentage of CD4(+)CXCR5(+) T follicular helper cells

BACKGROUND

T follicular helper (T(FH)) cells are a subpopulation of T-helper cells which regulate humoral immune responses. The role of T(FH) cells in viral infection is unclear. This study examined the possible involvement of CD4(+)CXCR5(+) T(FH) cells in chronic hepatitis C (HCV) infection.

METHODS

The percentages of peripheral blood CD4(+)CXCR5(+) T(FH) cells, inducible T-cell costimulator cells, and/or programmed death 1-positive CD4(+)CXCR5(+) T(FH) cells in 39 HCV-infected patients, 12 patients with spontaneously resolved HCV infection (SR-HCV), and 12 healthy controls were characterized by flow cytometry analysis. The subjects' serum HCV RNA loads and alanine aminotransferase and aspartate aminotransferase levels were measured. The potential association of the percentage of peripheral CD4(+)CXCR5(+) T(FH) cells with clinical data was analyzed.

RESULTS

Higher percentages of peripheral blood CD4(+)CXCR5(+) T(FH) cells were found in SR-HCV and HCV-infected patients as compared with healthy controls. Interestingly, a statistically significant negative correlation was found between the percentage of CD4(+)CXCR5(+) T(FH) cells and the HCV RNA load.

CONCLUSIONS

These data suggest that CD4(+)CXCR5(+) T(FH) cells may participate in HCV-related immune responses. Increased T(FH) cells in peripheral blood may help to control HCV infection.

Expansion of HIV-specific T follicular helper cells in chronic HIV infection

HIV targets CD4 T cells, which are required for the induction of high-affinity antibody responses and the formation of long-lived B cell memory. The depletion of antigen-specific CD4 T cells during HIV infection is therefore believed to impede the development of protective B cell immunity. Although several different HIV-related B cell dysfunctions have been described, the role of CD4 T follicular helper (TFH) cells in HIV infection remains unknown. Here, we assessed HIV-specific TFH responses in the lymph nodes of treatment-naive and antiretroviral-treated HIV-infected individuals. Strikingly, both the bulk TFH and HIV-specific TFH cell populations were significantly expanded in chronic HIV infection and were highly associated with viremia. In particular, GAG-specific TFH cells were detected at significantly higher levels in the lymph nodes compared with those of GP120-specific TFH cells and showed preferential secretion of the helper cytokine IL-21. In addition, TFH cell expansion was associated with an increase of germinal center B cells and plasma cells as well as IgG1 hypersecretion. Thus, our study suggests that high levels of HIV viremia drive the expansion of TFH cells, which in turn leads to perturbations of B cell differentiation, resulting in dysregulated antibody production.

The darker side of follicular helper T cells: from autoimmunity to immunodeficiency

Follicular helper T (T(FH)) cells represent a distinct subset of CD4⁺ helper T (T(H)) cells specialized in providing help to B cells. They are characterized by their unique transcriptional profile (Bcl6), surface marker expression (CXCR5, PD-1, ICOS and CD40L) and cytokine production pattern (IL-21 and IL-6). T(FH) cells provide help to B cells both to form germinal centers (GCs) and to differentiate into memory B cells and plasma cells for generation of humoral responses. However, there is emerging evidence that implicates T(FH) cells in the development of various human pathologies, such as autoimmune diseases, immunodeficiency and lymphoma. This review focuses on the current progress in this area including mouse and human studies. A clearer understanding of the mechanisms of T(FH) cell-mediated immunity and pathology may be exploited for rational development of therapeutic strategies.

T cells that promote B-Cell maturation in systemic autoimmunity

Follicular helper T (Tfh) cells play an essential role in helping B cells generate antibodies upon pathogen encounters. Such T-cell help classically occurs in germinal centers (GCs) located in B-cell follicles of secondary lymphoid organs, a site of immunoglobulin affinity maturation and isotype switching. B-cell maturation also occurs extrafollicularly, in the red pulp of the spleen and medullary cords in lymph nodes, with plasma cell formation and antibody production. Development of extrafollicular foci (EF) in T-cell-dependent (TD) immune responses is reliant upon CD4(+) T cells with characteristics of Tfh cells. Pathogenic autoantibodies, arising from self-reactive B cells having undergone somatic hypermutation with affinity selection and class switching within GCs and EF, are major contributors to the end-organ injury in systemic autoimmunity. B cells maturing to produce autoantibodies in systemic autoimmune diseases, like those in normal immune responses, largely require T-helper cells. This review highlights Tfh cell development as an introduction to a more in-depth discussion of human Tfh cells and blood borne cells with similar features and the role of these cells in promotion of systemic autoimmunity.

Expansion of follicular helper T cells in the absence of Treg cells: implications for loss of B-cell anergy

The maintenance of B-cell anergy is essential to prevent the production of autoantibodies and autoimmunity. However, B-cell extrinsic mechanisms that regulate B-cell anergy remain poorly understood. We previously demonstrated that regulatory T (Treg) cells are necessary for the maintenance of B-cell anergy. We now show that in Treg-cell-deficient mice, helper T cells are necessary and sufficient for loss of B-cell tolerance/anergy. In addition, we show that the absence of Treg cells is associated with an increase in the proportion of CD4(+) cells that express GL7 and correlated with an increase in germinal center follicular helper T (GC-T(FH) ) cells. These GC-T(FH) cells, but not those from Treg-cell-sufficient hosts, were sufficient to drive antibody production by anergic B cells. We propose that a function of Treg cells is to prevent the expansion of T(FH) cells, especially GC-T(FH) cells, which support autoantibody production.

Impaired peripheral blood T-follicular helper cell function in HIV-infected nonresponders to the 2009 H1N1/09 vaccine

The generation of Ab-secreting plasma cells depends critically on CD4 T-follicular helper (TFH) cells during the germinal center reaction. Germinal center TFH cells share functional properties with circulating CXCR5(+) CD4 T cells, referred to herein as peripheral TFH (pTFH) cells. Because deficient Ab production and CD4 T-cell loss are recognized features of HIV infection, in the present study, we investigated pTFH cells in 25 HIV-infected patients on antiretroviral therapy. pTFH frequency was equivalent in patients and healthy controls (HCs), and these cells displayed a central memory phenotype. Sixteen patients and 8 HCs in this group were given a single dose of H1N1/09 influenza vaccine during the 2009 H1N1 influenza outbreak. In the vaccine responders (n = 8) and HCs, pTFH cells underwent expansion with increased IL-21 and CXCL13 secretion in H1N1-stimulated PBMC culture supernatants at week 4 (T2). These changes were not seen in vaccine nonresponders (n = 8). In coculture experiments, sorted pTFH cells supported HIN1-stimulated IgG production by autologous B cells only in vaccine responders. At T2, frequencies of pTFH were correlated with memory B cells, serum H1N1 Ab titers, and Ag-induced IL-21 secretion. Characterization of pTFH cells may provide additional insight into cellular determinants of vaccine-induced Ab response, which may have relevance for vaccine design.

Taming lupus-a new understanding of pathogenesis is leading to clinical advances

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by the loss of tolerance to nuclear self antigens, the production of pathogenic autoantibodies and damage to multiple organ systems. Over the years, patients with SLE have been managed largely with empiric immunosuppressive therapies, which are associated with substantial toxicities and do not always provide adequate control of the disease. The development of targeted therapies that specifically address disease pathogenesis or progression has lagged, largely because of the complex and heterogeneous nature of the disease, as well as difficulties in designing uniform outcome measures for clinical trials. Recent advances that could improve the treatment of SLE include the identification of genetic variations that influence the risk of developing the disease, an enhanced understanding of innate and adaptive immune activation and regulation of tolerance, dissection of immune cell activation and inflammatory pathways and elucidation of mechanisms and markers of tissue damage. These discoveries, together with improvements in clinical trial design, form a platform from which to launch the development of a new generation of lupus therapies.

The development and function of follicular helper T cells in immune responses

Follicular helper T cells (Tfh) have been referred as a lineage that provides a help for B cells to proliferate and undergo antibody affinity maturation in the germinal center. Evidence has supported that Tfh subset development, like other lineages, is dependent on microenvironment where a particular transcriptional program is initiated. It has been shown that Bcl-6 and IL-21 act as master regulators for the development and function of Tfh cells. Tfh dysregulation is involved in the development of autoimmune pathologies, such as systemic lupus erythematosus, rheumatoid arthritis and other autoimmune diseases. The present review highlights the recent advances in the field of Tfh cells and focus on their development and function.

Granulomatosis with polyangiitis involves sustained mucosal inflammation that is rich in B-cell survival factors and autoantigen

OBJECTIVE

Granulomatosis with polyangiitis (GPA) is a rare chronic autoimmune disease that may be triggered by upper airway infection. ANCAs specific for PR3 that is expressed by activated neutrophils and macrophages are associated with GPA. Our aim was to investigate regional immune mechanisms that might induce or support the autoimmune response in GPA.

METHODS

Biopsy samples from 77 patients including 8 with GPA were studied by immunohistochemistry. B-cell homing subsets in blood samples from 16 patients with GPA and 11 healthy controls were studied by FACS. The distribution of B-cell clones was searched in paired biopsies and blood samples from one patient by analysing immunoglobulin heavy chain gene (IGH) junctional sequences.

RESULTS

Activated B cells were located alongside PR3-expressing cells and B-cell survival factors BAFF and APRIL in mucosa from patients with GPA. We detected APRIL production by the granulomas and giant cells. B cells were proliferating in all cases and persistent for 5 years in biopsies obtained from one patient. However, there was no evidence of B-cell clones from the mucosal biopsies circulating in peripheral blood in GPA or any numerical or proportional change in B-cell subsets expressing markers of regional homing in blood in GPA.

CONCLUSIONS

Our study illustrates chronically activated B cells alongside autoantigens and B-cell survival factors in the mucosa in GPA.

Increased frequency of circulating follicular helper T cells in patients with rheumatoid arthritis

Follicular helper T (Tfh) cells are recognized as a distinct CD4⁺ helper T-cell subset, which provides for B-cell activation and production of specific antibody responses, and play a critical role in the development of autoimmune disease. So far, only one study investigated the circulating Tfh cells increased in a subset of SLE patients. Since relatively little is known about the Tfh cells in rheumatoid arthritis (RA) patients, in this study, Tfh-cell frequency, related cytokine IL-21, and transcription factor Bcl-6 were investigated in 53 patients with RA and 31 health controls. Firstly, we found that the frequency of CD4⁺CXCR5⁺ICOS^high Tfh cells was increased significantly in the peripheral blood of RA patients, compared with that in healthy controls. It is known that Tfh cells are critical for directing the development of an antibody response by germinal centers B cells; secondly, we observed that the Tfh-cell frequency is accompanied by the level of anti-CCP antibody in RA patients. Furthermore, expression of Bcl-6 mRNA and plasma IL-21 concentrations in RA patients was increased. Taken together, these findings have shown that the increased frequency of circulating Tfh cells is correlated with elevated levels of anti-CCP antibody, indicating the possible involvement of Tfh cells in the disease progression of RA.

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.

Follicular helper T cells in immunity and systemic autoimmunity

Follicular helper T (T(FH)) cells are essential for B-cell maturation and immunoglobulin production after immunization with thymus-dependent antigens. Nevertheless, the development and function of T(FH) cells have been less clearly defined than classic CD4(+) effector T-cell subsets, including T-helper-1 (T(H)1), T(H)2 and T(H)17 cells. As such, our understanding of the genesis of T(FH) cells in humans and their role in the development of autoimmunity remains incomplete. However, evidence from animal models of systemic lupus erythematosus (SLE) and patients with systemic autoimmune diseases suggests that these cells are necessary for pathogenic autoantibody production, in a manner analogous to their role in promotion of B-cell maturation during normal immune responses. In this Review, I discuss the findings that have increased our knowledge of T(FH)-cell development and function in normal and aberrant immune responses. Such information might improve our understanding of autoimmune diseases, such as SLE, and highlights the potential of T(FH) cells as therapeutic targets in these diseases.

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.

[IgG4-related disease and renal and urological involvement]

Hyper-IgG4 syndrome, or IgG4-related disease, is an emerging disorder, involving one or more organ(s), and characterized by "storiform" fibrosis and inflammatory lesions with a predominance of IgG4+ plasma cells and increased IgG4 serum levels. Since the first report of auto-immune pancreatitis, numerous organ lesions have been reported and have been found to occur in a same patient including: sialadenitis, dacryoadenitis, lymphadenopathy, liver and biliary tract involvement, and renal and retroperitoneal lesions. Renal involvement was first described in 2004 and usually presents as functional and/or morphological abnormalities. In most cases, renal pathological analysis reveals tubulointerstitial nephritis that is rarely associated with glomerular lesions. Retroperitoneal fibrosis is also a typical feature that may be associated with periaortitis or inflammatory abdominal aortic aneurysm. First line treatment is based on corticosteroid therapy. Short-term outcome is usually favorable. However, patients should be carefully monitored for relapses and long-term complications. Although the multiple organ lesions share common clinical, biological, radiological and pathological features, no consensus diagnostic criteria have yet been validated for IgG4-related disease. Ruling out differential diagnoses is thus mandatory. Our literature review provides nephrologists, urologists and pathologists with key elements that will help in the early diagnosis and proper management of this new and emerging disorder.

Increased frequency of follicular helper T cells in patients with autoimmune thyroid disease

CONTEXT

Follicular helper T (Tfh) cells exert an important role in the autoimmune diseases.

AIM

Our study aimed to explore the role of Tfh cells in patients with autoimmune thyroid disease (AITD).

DESIGN

Tfh cell is a new subset regulating the antibody production of B cell. Previous studies implicated CD4+CXCR5+ICOShigh or CD4+CXCR5+PD-1high as the markers of circulating Tfh cells. Sixty-five patients with AITD and 30 healthy controls were enrolled in the current study. The percentages of circulating Tfh cells were assessed by flow cytometry. The correlation between the percentages of CD4+CXCR5+ICOShigh T cells and the levels of autoantibodies or hormones was also analyzed. Additionally, polyphasic methods were applied to investigate the status of Tfh cells in thyroid glands of Hashimoto's thyroiditis patients.

RESULTS

Increased percentages of circulating Tfh cells in AITD patients were detected, and a positive correlation between the percentages of circulating Tfh cells and the serum concentrations of anti-TSH receptor-Ab/thyroperoxidase-Ab/thyroglobulin-Ab was confirmed. A positive or modest relationship between the percentages of circulating Tfh cells and serum free T3 or free T4 was revealed in Graves' disease patients. Additionally, follow-up analysis indicated that in some Graves' disease patients the percentage of circulating Tfh cells decreased after treatment. Furthermore, a certain number of CD4+CXCR5+ICOShigh T cells together with enhanced expression of IL-21 and Bcl-6 mRNA were detected in thyroid tissues from Hashimoto's thyroiditis patients.

CONCLUSION

The current study discovered an increased frequency of Tfh cells in AITD patients, which implies that this cell subset might play an important role in the pathogenesis of AITD.

Evidence for gene-gene epistatic interactions among susceptibility loci for systemic lupus erythematosus

OBJECTIVE

Several confirmed genetic susceptibility loci for lupus have been described. To date, no clear evidence for genetic epistasis in lupus has been established. The aim of this study was to test for gene-gene interactions in a number of known lupus susceptibility loci.

METHODS

Eighteen single-nucleotide polymorphisms tagging independent and confirmed lupus susceptibility loci were genotyped in a set of 4,248 patients with lupus and 3,818 normal healthy control subjects of European descent. Epistasis was tested by a 2-step approach using both parametric and nonparametric methods. The false discovery rate (FDR) method was used to correct for multiple testing.

RESULTS

We detected and confirmed gene-gene interactions between the HLA region and CTLA4, IRF5, and ITGAM and between PDCD1 and IL21 in patients with lupus. The most significant interaction detected by parametric analysis was between rs3131379 in the HLA region and rs231775 in CTLA4 (interaction odds ratio 1.19, Z = 3.95, P = 7.8 × 10(-5) [FDR ≤0.05], P for multifactor dimensionality reduction = 5.9 × 10(-45)). Importantly, our data suggest that in patients with lupus, the presence of the HLA lupus risk alleles in rs1270942 and rs3131379 increases the odds of also carrying the lupus risk allele in IRF5 (rs2070197) by 17% and 16%, respectively (P = 0.0028 and P = 0.0047, respectively).

CONCLUSION

We provide evidence for gene-gene epistasis in systemic lupus erythematosus. These findings support a role for genetic interaction contributing to the complexity of lupus heritability.

The regulation and role of T follicular helper cells in immunity

It is well established that the generation of a high-affinity long-lived antibody response requires the presence of T cells, specifically CD4+ T cells. These CD4+ T cells support the generation of a germinal centre (GC) response where somatic hypermutation and affinity maturation take place leading to the generation of memory B cells and plasma cells, which provide long-lasting protection. Greater insight into the nature of the CD4+ T cells involved in this process was provided by two studies in 2000 that described CD4+ T cells residing in the B cell follicle that expressed CXCR5. As a result these cells were named follicular B helper T cells, now more commonly known as T follicular helper (Tfh) cells. Since then there has been enormous growth in our understanding of these cells, now considered a distinct T helper (Th) cell lineage that can arise from naive CD4+ T cells following activation. This review summarizes some of the most recent work that has characterized Tfh cells and the pathways that lead to their generation.