Understanding the development and function of T follicular helper cells

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.

Distinct Transcriptional and Alternative Splicing Signatures of Decidual CD4+ T Cells in Early Human Pregnancy

Decidual CD4⁺ T (dCD4 T) cells are crucial for the maternal-fetal immune tolerance required for a healthy pregnancy outcome. However, their molecular and functional characteristics are not well elucidated. In this study, we performed the first analysis of transcriptional and alternative splicing (AS) landscapes for paired decidual and peripheral blood CD4⁺ T (pCD4 T) cells in human early pregnancy using high throughput mRNA sequencing. Our data showed that dCD4 T cells are endowed with a unique transcriptional signature when compared to pCD4 T cells: dCD4 T cells upregulate 1,695 genes enriched in immune system process whereas downregulate 1,011 genes mainly related to mRNA catabolic process and the ribosome. Moreover, dCD4 T cells were observed to be at M phase, and show increased activation, proliferation, and cytokine production, as well as display an effector-memory phenotype and a heterogenous nature containing Th1, Th17, and Treg cell subsets. However, dCD4 T cells undergo a comparable number of upregulated and downregulated AS events, both of which are enriched in the genes related to cellular metabolic process. And the changes at the AS event level do not reflect measurable differences at the gene expression level in dCD4 T cells. Collectively, our findings provide a comprehensive portrait of the unique transcriptional signature and AS profile of CD4⁺ T cells in human decidua and help us gain more understanding of the functional characteristic of these cells during early pregnancy.

T cells targeting neuromyelitis optica autoantigen aquaporin-4 cause paralysis and visual system injury

Aquaporin-4 (AQP4)-specific antibodies are instrumental in promoting central nervous system (CNS) tissue injury in neuromyelitis optica (NMO), yet evidence indicates that AQP4-specific T cells also have a pivotal role in NMO pathogenesis. Although considerable effort has been devoted to creation of animal models to study how AQP4-specific T cells and antibodies may cooperate in development of both clinical and histologic opticospinal inflammatory disease, the initial attempts were unsuccessful. Recently, it was discovered that T cells from AQP4-deficient (AQP4^-/-) mice recognize distinct AQP4 epitopes that were not identified previously in wild-type (WT) mice, and that donor Th17 cells from AQP4^-/- mice that target those novel epitopes could cause paralysis and visual system injury associated with opticospinal inflammation in WT recipient mice. These observations indicate that the pathogenic AQP4-specific T cell repertoire is normally controlled by negative selection. Here, we describe the advances leading to development of an animal model for aquaporin-targeted CNS autoimmunity (ATCA). This new model provides a foundation to investigate immune mechanisms that may participate in NMO pathogenesis. It should also permit preclinical testing of agents considered for treatment of NMO.

The role of follicular T helper cells in patients with malignant lymphoid disease

OBJECTIVES

To investigate the dynamic change of follicular T helper cells (T_FH) in patients with malignant lymphoid disease (MLD) and to explore its clinical significance.

METHODS

The dynamic change of T_FH cells, ICOS⁺- and PD-1⁺ T_FH cells at pretreatment and different treatment periods was determined by flow cytometry in 85 MLD patients. Concentration of interleukin 21 (IL-21) was evaluated by ELISA, and the correlation between clinical prognosis and the ratio of T_FH cells was analyzed.

RESULTS

Significantly increased ICOS⁺- and PD-1⁺ T_FH cells were found in MLD patients at pretreatment compared to healthy controls. Decreased or even close to normal levels of ICOS⁺- and PD-1⁺ T_FH cells were found at the end of treatment. However, in the patients with progressive disease, high levels of ICOS⁺- and PD-1⁺ T_FH cells were found. Moreover, a significantly increased plasma IL-21 level was found in MLD patients. Negative correlation was found between the level of ICOS⁺-, PD-1⁺ T_FH cells, as well as IL-21 and the prognosis of MLD.

CONCLUSIONS

Significantly increased T_FH cell ratios were found in patients with MLD, and decreased T_FH cells ratios could be expected in those treatment-effective patients, which could be used as the therapeutic efficacy index.

Tolerance checkpoint bypass permits emergence of pathogenic T cells to neuromyelitis optica autoantigen aquaporin-4

Aquaporin-4 (AQP4)-specific T cells are expanded in neuromyelitis optica (NMO) patients and exhibit Th17 polarization. However, their pathogenic role in CNS autoimmune inflammatory disease is unclear. Although multiple AQP4 T-cell epitopes have been identified in WT C57BL/6 mice, we observed that neither immunization with those determinants nor transfer of donor T cells targeting them caused CNS autoimmune disease in recipient mice. In contrast, robust proliferation was observed following immunization of AQP4-deficient (AQP4^-/-) mice with AQP4 peptide (p) 135-153 or p201-220, peptides predicted to contain I-A^b-restricted T-cell epitopes but not identified in WT mice. In comparison with WT mice, AQP4^-/- mice used unique T-cell receptor repertoires for recognition of these two AQP4 epitopes. Donor T cells specific for either determinant from AQP4^-/-, but not WT, mice induced paralysis in recipient WT and B-cell-deficient mice. AQP4-specific Th17-polarized cells induced more severe disease than Th1-polarized cells. Clinical signs were associated with opticospinal infiltrates of T cells and monocytes. Fluorescent-labeled donor T cells were detected in CNS lesions. Visual system involvement was evident by changes in optical coherence tomography. Fine mapping of AQP4 p201-220 and p135-153 epitopes identified peptides within p201-220 but not p135-153, which induced clinical disease in 40% of WT mice by direct immunization. Our results provide a foundation to evaluate how AQP4-specific T cells contribute to AQP4-targeted CNS autoimmunity (ATCA) and suggest that pathogenic AQP4-specific T-cell responses are normally restrained by central tolerance, which may be relevant to understanding development of AQP4-reactive T cells in NMO.

Characterization of T follicular helper cells in allogeneic normal pregnancy and PDL1 blockage-induced abortion

A deeper understanding of the immunological events during pregnancy will provide novel insights into the pathogenesis of pregnancy complications. The fundamental function of T follicular helper (Tfh) cells is to provide cognate help to B cells. Dysregulations of Tfh-cell function and/or development can result in various immunological diseases. However, the role and characteristics of Tfh cells during pregnancy remain unknown. Herein, an allogeneic-normal-pregnant mouse model was used, and we found that the CD4⁺ T cells residing at the uterus and placenta (UP) displayed a Tfh-like phenotype; and the UP-derived CD4⁺CXCR5^hiPD-1^hi and CD4⁺CXCR5^hiICOS^hi Tfh cells, which showed a memory/activation phenotype, reached their peak at mid-pregnancy. These Tfh cells were located abundantly in the uterus at mid-pregnancy, but greatly increased in the placenta at late-pregnancy. Furthermore, increased foetal resorption by PDL1 blockade correlated with enhanced accumulation of Tfh cells and upregulated expressions of ICOS and PD-1 on these cells. Collectively, our findings are the first to indicate that an adequate and balanced accumulation of Tfh cells during gestation is likely to help maintaining a successful pregnancy, whereas an excessively high level of these cells could lead to abortion.

Insights into the development and regulation of T follicular helper cells

T follicular helper (Tfh) cells are specialized subset of T helper (Th) cells necessary for germinal center reaction, affinity maturation and the differentiation of germinal center B cells to antibody-producing plasma B cells and memory B cells. The differentiation of Tfh cells is a multistage, multifactorial process involving a variety of cytokines, surface molecules and transcription factors. While Tfh cells are critical components of protective immune responses against pathogens, regulation of these cells is crucial to prevent autoimmunity and airway inflammation. Recently, it has been noted that Tfh cells could be potentially implicated either in cancer progression or prevention. Thus, the elucidation of the mechanisms that regulate Tfh cell differentiation, function and fate should highlight potential targets for novel therapeutic approaches. In this review, we summarize the latest advances in our understanding of the regulation of Tfh cell differentiation and their role in health and disease.

Blockade of STAT3 in T Cells Inhibits Germinal Center Reactions against Intranasal Allergens

Understanding the developmental mechanisms of humoral immunity against intranasal antigens is essential for the development of therapeutic approaches against air-borne pathogens as well as allergen-induced pulmonary inflammation. Follicular helper T (Tfh) cells expressing CXCR5 are required for humoral immunity by providing IL-21 and ICOS costimulation to activated B cells. However, the regulation of Tfh cell responses against intranasal antigens remains unclear. Here, we found that the generation of Tfh cells and germinal center B cells in the bronchial lymph node against intranasal proteinase antigens was independent of TGF-β. In contrast, administration of STAT3 inhibitor STA-21 suppressed the generation of Tfh cells and germinal center B cells. Compared with wild-type OT-II T cells, STAT3-deficient OT-II T cells transferred into recipients lacking T cells not only showed significantly reduced frequency Tfh cells, but also induced diminished IgG as well as IgE specific for the intranasal antigens. Cotransfer study of wild-type OT-II and STAT3-deficient OT-II T cells revealed that the latter failed to differentiate into Tfh cells. These findings demonstrate that T cell-intrinsic STAT3 is required for the generation of Tfh cells to intranasal antigens and that targeting STAT3 might be an effective approach to ameliorate antibody-mediated pathology in the lung.

T helper 2 and T follicular helper cells: Regulation and function of interleukin-4

Type 2 immunity is characterized by expression of the cytokines interleukin (IL)-4, IL-5, IL-9 and IL-13, which can function in mediating protective immunity in the host or possess a pathogenic role. T helper (Th) 2 cells have emerged to play a beneficial role in mediating anti-parasitic immunity and are also known to be key players in mediating allergic diseases. In addition to the Th2 cells, recent studies have identified T follicular helper (Tfh) cells as an alternative source of IL-4 to regulate type 2 humoral immune responses, indicating that Th2 and Tfh cells exhibit overlapping phenotypical and functional characteristics. Th2 and Tfh cells appear to utilize distinct mechanisms for regulation of IL-4 expression; however unlike Th2 cells, the regulation and function of Tfh-derived IL-4 is not yet fully understood. Understanding of the molecular mechanisms for IL-4 expression and function in both cell subsets will be beneficial for the development of future therapeutic interventions.

Loss of miR-182 affects B-cell extrafollicular antibody response

MicroRNAs have been shown to play a role in B-cell differentiation and activation. Here, we found miR-182 to be highly induced in activated B cells. However, mice lacking miR-182 have normal B-cell and T-cell development. Interestingly, mutant mice exhibited a defective antibody response at early time-points in the immunization regimen when challenged with a T-cell-dependent antigen. Germinal centres were formed but the generation of extrafollicular plasma cells was defective in the spleens of immunized miR-182-deficient mice. Mutant mice were also not able to respond to a T-cell-independent type 2 antigen, which typically elicited an extrafollicular B-cell response. Taken together, the data indicated that miR-182 plays a critical role in driving extrafollicular B-cell antibody responses.

Mycobacterium tuberculosis-Specific IL-21+IFN-γ+CD4+ T Cells Are Regulated by IL-12

In the current study of Mycobacterium tuberculosis (MTB)-specific T and B cells, we found that MTB-specific peptides from early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) induced the expression of IL-21 predominantly in CD4⁺ T cells. A fraction of IL-21-expressing CD4⁺ T cells simultaneously expressed Th1 cytokines but did not secrete Th2 or Th17 cytokines, suggesting that MTB-specific IL-21-expressing CD4⁺ T cells were different from Th1, Th2 and Th17 subpopulations. The majority of MTB-specific IL-21-expressing CD4⁺ T cells co-expressed IFN-γ and IL-21⁺IFN-γ⁺CD4⁺ T cells exhibited obviously polyfunctionality. In addition, MTB-specific IL-21-expressing CD4⁺ T cells displayed a CD45RO⁺CD62L^lowCCR7^lowCD40L^highICOS^high phenotype. Bcl-6-expression was significantly higher in IL-21-expressing CD4⁺ T cells than IL-21^-CD4⁺ T cells. Moreover, IL-12 could up-regulate MTB-specific IL-21 expression, especially the frequency of IL-21⁺IFN-γ⁺CD4⁺ T cells. Taken together, our results demonstrated that MTB-specific IL-21⁺IFN-γ⁺CD4⁺ T cells from local sites of tuberculosis (TB) infection could be enhanced by IL-12, which have the features of both Tfh and Th1 cells and may have an important role in local immune responses against TB infection.

Modulation of Dendritic Cell Activation and Subsequent Th1 Cell Polarization by Lidocaine

Dendritic cells play an essential role in bridging innate and adaptive immunity by recognizing cellular stress including pathogen- and damage-associated molecular patterns and by shaping the types of antigen-specific T cell immunity. Although lidocaine is widely used in clinical settings that trigger cellular stress, it remains unclear whether such treatment impacts the activation of innate immune cells and subsequent differentiation of T cells. Here we showed that lidocaine inhibited the production of IL–6, TNFα and IL–12 from dendritic cells in response to toll-like receptor ligands including lipopolysaccharide, poly(I:C) and R837 in a dose-dependent manner. Notably, the differentiation of Th1 cells was significantly suppressed by the addition of lidocaine while the same treatment had little effect on the differentiation of Th17, Th2 and regulatory T cells in vitro. Moreover, lidocaine suppressed the ovalbumin-specific Th1 cell responses in vivo induced by the adoptive transfer of ovalbumin-pulsed dendritic cells. These results demonstrate that lidocaine inhibits the activation of dendritic cells in response to toll-like receptor signals and subsequently suppresses the differentiation of Th1 cell responses.

Structure-Based Design of Human TLR8-Specific Agonists with Augmented Potency and Adjuvanticity

Human Toll-like receptor 8 (hTLR8) is expressed in myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells. Engagement by TLR8 agonists evokes a distinct cytokine profile which favors the development of type 1 helper T cells. Crystal structures of the ectodomain of hTLR8 cocrystallized with two regioisomers of a dual TLR7/8-agonistic N1-substituted imidazoquinolines showed subtle differences in their interactions in the binding site of hTLR8. We hypothesized that the potency of a previously reported best-in-class pure TLR8 agonist, 3-pentylquinoline-2-amine, could be further enhanced by “designing in” functional groups that would mimic key intermolecular interactions that we had observed in the crystal structures. We performed a focused exploration of decorating the quinoline core with alkylamino groups at all possible positions. These studies have led to the identification of a novel TLR8 agonist that was ∼20-fold more potent than the parent compound and displays prominent adjuvantic activity in a rabbit model of immunization.

Recent Breakthroughs in the Antioxidant and Anti-Inflammatory Effects of Morella and Myrica Species

Oxidative stress is one of the risk factors for the development of several chronic diseases, such as diabetes, cancer, cardiovascular and neurodegenerative diseases. Antioxidants are therefore highly sought and can be seen as a type of preventive medicine against several diseases. Myrica and Morella genus (Myricaceae) are taxonomically very close and their species are trees or shrubs with edible fruits that exhibit relevant uses in traditional medicine, for instance in Chinese or Japanese folk medicine they are used to treat diarrhea, digestive problems, headache, burns and skin diseases. Nearly 36 compounds were isolated from different morphological parts of Myrica and/or Morella species and their antioxidant and anti-inflammatory activities evaluated. Thirteen of these compounds exhibit greater effects than the positive controls used. Adenodimerin A was the most active compound reported (in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay EC50= 7.9 ± 0.3 µM). These results are just one aspect of the antioxidant and anti-inflammatory evaluations reported regarding Myrica and Morella species, so a comprehensive overview on the current status, highlighting the antioxidant health promoting effect of these species, their key antioxidant compounds as well as the compounds with protective effects against oxidative stress related diseases such as inflammation, is relevant.

Cytokines in Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a complication of allogeneic bone marrow transplantation whereby transplanted naive and marrow-derived T cells damage recipient tissue through similar mechanisms to those that allow destruction of malignant cells, the therapeutic intent of bone marrow transplantation. The manifestations and severity of GVHD are highly variable and are influenced by the proportions of naive cells maturing along regulatory T cell, Th1, Th2, or Th17 phenotypes. This maturation is largely influenced by local cytokines, which, in turn, activate transcription factors and drive development toward a dominant phenotype. In addition, proinflammatory cytokines exert direct effects on GVHD target tissues. Our knowledge of the role that cytokines play in orchestrating GVHD is expanding rapidly and parallels other infective and inflammatory conditions in which a predominant T cell signature is causative of pathology. Because a broad spectrum of cytokine therapies is now routinely used in clinical practice, they are increasingly relevant to transplant medicine.

Fusion with human lung cancer cells elongates the life span of human umbilical endothelial cells and enhances the anti-tumor immunity

PURPOSE

Human umbilical endothelial cells (HUVECs) have been proved as an effective whole-cell vaccine inhibiting tumor angiogenesis. However, HUVECs divide a very limited number of passages before entering replicative senescence, which limits its application for clinical situation. Here, we fused HUVECs with human pulmonary adenocarcinoma cell line A549s and investigated the anti-tumor immunity of the hybrids against mice Lewis lung cancer.

METHODS

HUVECs were fused with A549s using polyethylene glycol and were sorted by flow cytometry. The fusion cells (HUVEC-A549s) were confirmed by testing the expression of telomerase and VE-cadherin, the senescence-associated β-galactosidase activity, and tube formation ability. HUVEC-A549s were then irradiated and injected into the C57BL/6 mice of protective, therapeutic, and metastatic models. The mechanism of the anti-tumor immunity was explored by analyzing mice sera, spleen T lymphocytes, tumor microenvironment, and histological changes.

RESULTS

HUVEC-A549s coexpressed tumor and endothelial markers and maintained the vascular function of tube forming at passage 30 without showing signs of senescence. HUVEC-A549s could induce protective and therapeutic anti-tumor activity for LL(2) model and presented stronger activity against metastasis than HUVECs. Both humoral and cellular immunity were participated in the anti-angiogenic activity, as HUVECs-neutralizing IgG and HUVECs-toxic lymphocytes were increased. Angiogenic mediators (VEGF and TGF-β) and tumor microenvironment cells MDSCs and Tregs were also diminished.

CONCLUSIONS

Our findings might provide a novel strategy for HUVECs-related immunotherapy, and this vaccine requires lower culture condition than primary HUVECs while enhancing the anti-tumor immunity.

Cohabitation with a sick partner increases allergic lung inflammatory response in mice

The bidirectional relationship between the nervous system and the immune system is relevant for homeostatic organism maintenance. Studies from our laboratory showed that 14days of cohabitation with a sick partner (injected with Ehrlich tumor cells-TAE) produced behavioral, neurochemical, endocrinological and immunological changes. This study analyzes the effects of cohabitation with an Ehrlich tumor-bearing animal on ovalbumin (OVA)-induced lung inflammatory response in mice. Pairs of male mice were divided into three groups: naïve, control and experimental. Animals of the naïve group were kept undisturbed being used for the assessment of basal parameters. One animal of each experimental and control pair of mice was immunized with OVA. On ED(0), these OVA-immunized animals received an OVA booster. At this day (D(0)) the experimental mice that were kept undisturbed were inoculated with 5×10(6) Ehrlich tumor cells; their immunized cage-mates were then referred as to CSP ("companion of sick partner"). The undisturbed mice of each control pair were i.p. treated on D(0) with 0.9% NaCl; their sensitized cage-mates were subsequently referred as CHP ("companion of health partner"). The OVA challenge was performed on CSP and CHP mice on ED(12) and ED(13); blood and tissue collection were performed on ED(14). Fourteen days after cohabitation, in comparison to the CHP mice, the CSP mice displayed the following: (1) an increased number of eosinophils and neutrophils in the BAL, (2) a decreased bone marrow cell count, (3) increased levels of IL-4 and IL-5 and decreased levels of IL-10 and IFN-γ in the BAL supernatant, (5) increased levels of IgG1-OVA, decreased levels of IgG2a-OVA and no changes in OVA-specific IgE in the peripheral blood, (6) increased expression of L-selectin in the BAL granulocytes, (7) decreased tracheal reactivity to methacholine measured in vitro, (8) no changes in plasma corticosterone levels and (9) increased levels of plasmatic noradrenaline. These results suggest that allergic lung inflammatory response exacerbation in CSP mice is a consequence of the psychological stress induced by forced cohabitation with the sick partner. Strong involvement of the sympathetic nervous system (SNS) through adrenaline and noradrenaline release and a shift of the Th1/Th2 cytokine profile toward a Th2 response were considered to be the mechanisms underlying the cell recruitment to the animal's airways.

Identification of early interactions between Francisella and the host

The adaptive immune response to Francisella tularensis is dependent on the route of inoculation. Intradermal inoculation with the F. tularensis live vaccine strain (LVS) results in a robust Th1 response in the lungs, whereas intranasal inoculation produces fewer Th1 cells and instead many Th17 cells. Interestingly, bacterial loads in the lungs are similar early after inoculation by these two routes. We hypothesize that the adaptive immune response is influenced by local events in the lungs, such as the type of cells that are first infected with Francisella. Using fluorescence-activated cell sorting, we identified alveolar macrophages as the first cell type infected in the lungs of mice intranasally inoculated with F. novicida U112, LVS, or F. tularensis Schu S4. Following bacterial dissemination from the skin to the lung, interstitial macrophages or neutrophils are infected. Overall, we identified the early interactions between Francisella and the host following two different routes of inoculation.

PD-1(HIGH) Follicular CD4 T Helper Cell Subsets Residing in Lymph Node Germinal Centers Correlate with B Cell Maturation and IgG Production in Rhesus Macaques

CD4+ T follicular helper (TFH) cells guide development and maturation of B cells and are crucial for effective antibody responses. Here we found rhesus macaque TFH cells, defined as CXCR5+CD4 T cells, contain two major populations: PD-1^INT and PD-1^HIGH cells. Of these, PD-1^HIGHCD4+ T cells highly co-express ICOS but little CCR7, and reside in lymph node germinal centers (GCs), but not in blood. These cells secrete IL-21 and express transcriptional factor Bcl-6 at higher levels than CXCR5+PD-1^INTCD4+ T cells. In addition, the frequency of PD-1^HIGHCD4+ T cells is low in lymph nodes of newborns, but increases with age. Levels of PD-1^HIGHCD4+ T cells correlate with mature B cells in lymph nodes, and PD-1 blockade in PD-1^HIGHCD4+ T and B cell co-cultures significantly inhibits IgG production. In summary, PD-1^HIGHCD4+ T cells residing in GC represent a specific TFH subset that contributes to maturation of B cells and IgG production.

Role of regulatory T cells in pathogenesis and biological therapy of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease in which the myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms. It is caused by an autoimmune response to self-antigens in a genetically susceptible individual induced by unknown environmental factors. Principal cells of the immune system that drive the immunopathological processes are T cells, especially of T_H1 and T_H17 subsets. However, in recent years, it was disclosed that regulatory T cells took part in, too. Subsequently, there was endeavour to develop ways how to re-establish their physiological functions. In this review, we describe known mechanisms of action, efficacy, and side-effects of contemporary and emerging MS immunotherapeutical agents on Treg cells and other cells of the immune system involved in the immunopathogenesis of the disease. Furthermore, we discuss how laboratory immunology can offer physicians its help in the diagnosis process and decisions what kind of biological therapy should be used.

IL-21 regulates the differentiation of a human γδ T cell subset equipped with B cell helper activity

Vγ9Vδ2 T lymphocytes recognize nonpeptidic antigens without presentation by MHC molecules and display pleiotropic features. Here we report that coculture of Vγ9Vδ2 cells with phosphoantigen and IL-21 leads to selective expression of the transcription repressor Bcl-6 and polarization toward a lymphocyte subset displaying features of follicular B-helper T (T_FH) cells. T_FH-like Vγ9Vδ2 cells have a predominant central memory (CD27⁺CD45RA⁻) phenotype and express ICOS, CD40L and CXCR5. Upon antigen activation, they secrete IL-4, IL-10 and CXCL13, and provide B-cell help for antibody production in vitro. Our findings delineate a subset of human Vγ9Vδ2 lymphocytes, which, upon interaction with IL-21-producing CD4 T_FH cells and B cells in secondary lymphoid organs, is implicated in the production of high affinity antibodies against microbial pathogens.

Aquaporin 4-specific T cells in neuromyelitis optica exhibit a Th17 bias and recognize Clostridium ABC transporter

OBJECTIVE

Aquaporin 4 (AQP4)-specific autoantibodies in neuromyelitis optica (NMO) are immunoglobulin (Ig)G1, a T cell-dependent Ig subclass, indicating that AQP4-specific T cells participate in NMO pathogenesis. Our goal was to identify and characterize AQP4-specific T cells in NMO patients and healthy controls (HC).

METHODS

Peripheral blood T cells from NMO patients and HC were examined for recognition of AQP4 and production of proinflammatory cytokines. Monocytes were evaluated for production of T cell-polarizing cytokines and expression of costimulatory molecules.

RESULTS

T cells from NMO patients and HC proliferated to intact AQP4 or AQP4 peptides (p11-30, p21-40, p61-80, p131-150, p156-170, p211-230, and p261-280). T cells from NMO patients demonstrated greater proliferation to AQP4 than those from HC, and responded most vigorously to p61-80, a naturally processed immunodominant determinant of intact AQP4. T cells were CD4(+), and corresponding to association of NMO with human leukocyte antigen (HLA)-DRB1*0301 and DRB3, AQP4 p61-80-specific T cells were HLA-DR restricted. The T-cell epitope within AQP4 p61-80 was mapped to 63-76, which contains 10 residues with 90% homology to a sequence within Clostridium perfringens adenosine triphosphate-binding cassette (ABC) transporter permease. T cells from NMO patients proliferated to this homologous bacterial sequence, and cross-reactivity between it and self-AQP4 was observed, supporting molecular mimicry. In NMO, AQP4 p61-80-specific T cells exhibited Th17 polarization, and furthermore, monocytes produced more interleukin 6, a Th17-polarizing cytokine, and expressed elevated CD40 and CD80 costimulatory molecules, suggesting innate immunologic dysfunction.

INTERPRETATION

AQP4-specific T-cell responses are amplified in NMO, exhibit a Th17 bias, and display cross-reactivity to a protein of an indigenous intestinal bacterium, providing new perspectives for investigating NMO pathogenesis.

B cell: T cell interactions occur within hepatic granulomas during experimental visceral leishmaniasis

Hepatic resistance to Leishmania donovani infection in mice is associated with the development of granulomas, in which a variety of lymphoid and non-lymphoid populations accumulate. Although previous studies have identified B cells in hepatic granulomas and functional studies in B cell-deficient mice have suggested a role for B cells in the control of experimental visceral leishmaniasis, little is known about the behaviour of B cells in the granuloma microenvironment. Here, we first compared the hepatic B cell population in infected mice, where ≈60% of B cells are located within granulomas, with that of naïve mice. In infected mice, there was a small increase in mIgM(lo)mIgD(+) mature B2 cells, but no enrichment of B cells with regulatory phenotype or function compared to the naïve hepatic B cell population, as assessed by CD1d and CD5 expression and by IL-10 production. Using 2-photon microscopy to quantify the entire intra-granuloma B cell population, in conjunction with the adoptive transfer of polyclonal and HEL-specific BCR-transgenic B cells isolated from L. donovani-infected mice, we demonstrated that B cells accumulate in granulomas over time in an antigen-independent manner. Intra-vital dynamic imaging was used to demonstrate that within the polyclonal B cell population obtained from L. donovani-infected mice, the frequency of B cells that made multiple long contacts with endogenous T cells was greater than that observed using HEL-specific B cells obtained from the same inflammatory environment. These data indicate, therefore, that a subset of this polyclonal B cell population is capable of making cognate interactions with T cells within this unique environment, and provide the first insights into the dynamics of B cells within an inflammatory site.

STAT5 protein negatively regulates T follicular helper (Tfh) cell generation and function

Recent work has identified a new subset of CD4(+) T cells named as Tfh cells that are localized in germinal centers and critical in germinal center formation. Tfh cell differentiation is regulated by IL-6 and IL-21, possibly via STAT3 factor, and B cell lymphoma 6 (Bcl6) is specifically expressed in Tfh cells and required for their lineage specification. In the current study, we characterized the role of STAT5 in Tfh cell development. We found that a constitutively active form of STAT5 effectively inhibited Tfh differentiation by suppressing the expression of Tfh-associated factors (CXC motif) receptor 5 (CXCR5), musculoaponeurotic fibrosarcoma (c-Maf), Bcl6, basic leucine zipper transcription factor ATF-like (Batf), and IL-21, and STAT5 deficiency greatly enhanced Tfh gene expression. Importantly, STAT5 regulated the expression of Tfh cell suppressor factor B lymphocyte-induced maturation protein 1 (Blimp-1); STAT5 deficiency impaired Blimp-1 expression and resulted in elevated expression of Tfh-specific genes. Similarly, inhibition of IL-2 potentiated Tfh generation, associated with dampened Blimp-1 expression; Blimp-1 overexpression inhibited Tfh gene expression in Stat5-deficient T cells, suggesting that the IL-2/STAT5 axis functions to regulate Blimp-1 expression. In vivo, deletion of STAT5 in CD4(+) T cells resulted in enhanced development of Tfh cells and germinal center B cells and led to an impairment of B cell tolerance in a well defined mouse tolerance model. Taken together, this study demonstrates that STAT5 controls Tfh differentiation.

Early Th1 cell differentiation is marked by a Tfh cell-like transition

Follicular helper T (Tfh) cells comprise an important subset of helper T cells; however, their relationship with other helper lineages is incompletely understood. Herein, we showed interleukin-12 acting via the transcription factor STAT4 induced both Il21 and Bcl6 genes, generating cells with features of both Tfh and Th1 cells. However, STAT4 also induced the transcription factor T-bet. With ChIP-seq, we defined the genome-wide targets of T-bet and found that it repressed Bcl6 and other markers of Tfh cells, thereby attenuating the nascent Tfh cell-like phenotype in the late phase of Th1 cell specification. Tfh-like cells were rapidly generated after Toxoplasma gondii infection in mice, but T-bet constrained Tfh cell expansion and consequent germinal center formation and antibody production. Our data argue that Tfh and Th1 cells share a transitional stage through the signal mediated by STAT4, which promotes both phenotypes. However, T-bet represses Tfh cell functionalities, promoting full Th1 cell differentiation.

IL-21 enhances the potential of human γδ T cells to provide B-cell help

Vγ9/Vδ2 T cells are a minor subset of T cells in human blood and differ from all other lymphocytes by their specific responsiveness to (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), a metabolite produced by a large range of microbial pathogens. Vγ9/Vδ2 T cells can be skewed towards distinct effector functions, in analogy to, and beyond, the emerging plasticity of CD4(+) T cells. As such, depending on the microenvironment, Vγ9/Vδ2 T cells can assume features reminiscent of Th1, Th2, Th17 and Treg cells as well as professional APCs. We here demonstrate that Vγ9/Vδ2 T cells express markers associated with follicular B helper T (T(FH) ) cells when stimulated with HMB-PP in the presence of IL-21. HMB-PP induces upregulation of IL-21R on Vγ9/Vδ2 T cells. In return, IL-21 plays a co-stimulatory role in the expression of the B-cell-attracting chemokine CXCL13, the CXCL13 receptor CXCR5 and the inducible co-stimulator by activated Vγ9/Vδ2 T cells, and enhances their potential to support antibody production by B cells. The interaction between HMB-PP-responsive Vγ9/Vδ2 T cells, IL-21-producing T(FH) cells and B cells in secondary lymphoid tissues is likely to impact on the generation of high affinity, class-switched antibodies in microbial infections.

Transferrin conjugation confers mucosal molecular targeting to a model HIV-1 trimeric gp140 vaccine antigen

The generation of effective immune responses by mucosal vaccination without the use of inflammatory adjuvants, that compromise the epithelial barrier and recruit new cellular targets, is a key goal of vaccines designed to protect against sexually acquired pathogens. In the present study we use a model HIV antigen (CN54gp140) conjugated to transferrin (Tf) and evaluate the ability of the natural transferrin receptor CD71 to modulate immunity. We show that the conjugated transferrin retained high affinity for its receptor and that the conjugate was specifically transported across an epithelial barrier, co-localizing with MHC Class II⁺ cells in the sub-mucosal stroma. Vaccination studies in mice revealed that the Tf-gp140 conjugate elicited high titres of CN54gp140-specific serum antibodies, equivalent to a systemic vaccination, when conjugate was applied topically to the nasal mucosae whereas gp140 alone was poorly immunogenic. Moreover, the Tf-gp140 conjugate elicited both IgG and IgA responses and significantly higher gp140-specific IgA titre in the female genital tract than unconjugated antigen. These responses were achieved after mucosal application of the conjugated protein alone, in the absence of any pro-inflammatory adjuvant and suggest a potentially useful and novel molecular targeting approach, delivering a vaccine cargo to directly elicit or enhance pathogen-specific mucosal immunity.

CD4+ T Lymphocytes with follicular helper phenotype (T(FH)) in patients with SH2D1A deficiency (XLP)

Peripheral blood mononuclear cells with T(FH) phenotype from two asymptomatic XLP patients were studied. Normal/high numbers of CXCR5+, CD4+ T cells coexpressing PD-1 were demonstrated. Peripheral blood mononuclear cells (PBMC) from these patients responded to sub-optimal PHA/IL-2 stimulation upregulating ICOS and CD40L and increasing intracellular expression of IL-10, IL-21 and IL-4 by CD4+ T(FH) cells. However when compared to N, the time profile of activation and cytokine synthesis was different in XLP and N. While ICOS and CD40L expression in N decreased after 6-8 days, it continued to increase or was maintained in XLP cultures. Intracellular IL-10, IL-21 and IL-4 reached higher values in XLP than N after 8 days. Rather than the absence of T(FH) cells or their intrinsic inability to respond to stimuli, differences in the time profile of their response could contribute to impair their role as helpers of B lymphocytes.

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.

Vibrio cholerae O1 infection induces proinflammatory CD4+ T-cell responses in blood and intestinal mucosa of infected humans

Vibrio cholerae O1 is a noninvasive enteric pathogen and serves as a model for studies of mucosal immunity. Although symptomatic V. cholerae infection induces durable protection against subsequent disease, vaccination with oral killed whole-cell V. cholerae stimulates less long-lasting protection against cholera. In this study, we demonstrated that cholera induces an early proinflammatory cellular immune response that results in priming of Th1- and Th17-type cytokine responses to ex vivo antigenic stimulation and an increase in the ratio of Th1 to Th2 CD4(+) T-cell responses. Comparable priming of Th1 and Th17 responses, with an increased ratio of Th1 to Th2 CD4(+) T-cell responses, was not observed in subjects who received two doses of the oral cholera vaccine Dukoral (a whole-cell cholera toxin B subunit containing [WC-CTB] vaccine). These findings suggest that natural V. cholerae infection induces an early, proinflammatory cellular immune response, despite the apparent lack of clinical signs of inflammation. The failure of the WC-CTB vaccine to activate equivalent, CD4(+) T-cell responses is a potential explanation for the shorter duration of protection following immunization with this vaccine. Additional studies are needed to determine whether these early T-cell-mediated events predict the subsequent duration of immunologic memory.