Role of Grail in intestinal inflammation

Intestinal homeostasis depends on interaction between the microbiota and host immune system, and disruption of this balance results in predominance of inflammatory responses leading to inflammatory bowel disease. However, to date, precise cell-intrinsic regulatory mechanisms that controls intestinal inflammation are poorly understood. Here we show that expression of the E3 ubiquitin ligase Grail is diminished in colon tissues of mice with colitis and Grail deficiency leads to increased susceptibility to colitis. Importantly, Grail deficiency disrupted pro-/anti-inflammatory balance towards inflammatory immune responses at the steady state and during colitis. Mechanistically, loss of Grail intrinsically diminished the expression of IL-10 and IL-10 receptor (IL-10R) by adaptive and innate immune cells in colonic mucosa. Besides the intestinal immunity, Grail deficiency leads to a decrease in microbial diversity and an enrichment of pro-inflammatory microbiota. Thus, Grail plays a protective role during intestinal inflammation by supporting regulatory immune responses and shaping the microbiota.

Abstract 503: Multiparameter Mass Cytometry Reveals The Unique Response Of NaïVe B Cell Cd27 - Subset With The Increase Of T-bet And Cd38 Expression After Radiation Therapy In Thoracic Cancer Patients

Cancer Radiation therapy (RT) induces cardiovascular disease (CVD) even when the heart is shealed or not irradiated, but there is a paucity of available preventive measures for RT-induced CVD. Ionizing radiation (IR) induces senescence, which was originally discovered to suppress tumorigenesis by inducing cell cycle blockade and necrosis, and positioned IR as pro-senescence cancer therapy. IR-induced senescence cells secrete cytokines, growth factors, and reactive oxygen species (ROS), becoming so called senescence associated secretory phenotype (SASP), and we hypothesize that SASP induction in immune cells cause CVD after RT. Although the involvement of DNA damage response (DDR), efferocytosis, and clonal hematopoiesis drivers (CHD) to SASP induction has been suggested, the exact mechanisms through which RT induces SASP in a specific cell type remains unclear. We characterize most of the major human immune cell lineages in a single assay using mass cytometery (CyTOF). We generated a CyTOF panel which includes antibodies against various senescence phenotype, DDR, efferocytosis, and CHD. We isolated peripheral blood mononuclear cells (PBMCs) before and 3 month after RT from 16 thoracic cancer patients. First, we found the frequency of only B cell subtype was decreased after RT. Second, we obtained 138 functional profiling subsets by unsupervised clustering with our antibody set, and found that T-bet expression was increased in the largest B cell subset of naïve B Cell (CD27 - ) Ki67 lo CD38 lo DNMT3a hi after RT, which showed the good correlation with p-p90RSK expression in the samples from pre-RT and post-RT. Lastly, the significant increase of CD38 expression in the subsets of naïve B cell (CD27 - ) and CD8 + T cell (EMRA) was detected. These data suggest the unique response of naïve B cell (CD27-) to RT with the increase of CD38 expression, and T-bet in the subset of B Cell (CD27 - ) Ki67 lo CD38 lo DNMT3a hi , and also the potential role of p90RSK activation in IR-induced T-bet expression. T-bet plays a role in developing the age-associated B cell (ABC), and the increase of CD38 expression promotes aging-related events. Therefore, the induction of T-bet and CD38 in naïve B (CD27 - ) cell after RT supports the novel role of naïve B cell in IR-induced SASP and subsequent CVD.

Therapeutic potential of follicular helper T cells for melanoma treatment

Clinical relapse and metastases are the major causes of death in melanoma. Currently, adoptive T cell therapy using tumor-infiltrating lymphocytes rich in cytotoxic CD8+ T cells (CTLs) is one of the promising approaches that helps overcome this major challenge in melanoma; however, CTL cell transfer alone does not improve clinical response, suggesting a supportive role of helper CD4+ T cells. There is increasing evidence on the potential contribution of tumor-infiltrated CD4+ T follicular helper (Tfh) cells and intratumoral lymphoid structure formation in tumor eradication; however to date, the role of Tfh cells in anti-tumor immunity has not been clearly elucidated. Remarkably, using a murine melanoma model, we found that the percentage of intratumoral Tfh cells negatively correlates with melanoma growth. In addition, we observed enhanced tumor growth in Bcl6 T-cell conditional knockout mice, which lack Tfh cells as compared to wild-type mice, suggesting that Tfh cells might play a protective role in tumor growth and could serve as a marker for tumor regression. Importantly, in support of mouse studies, in melanoma patients the number of Tfh cells correlate with the rate of patient survival. Importantly, adoptive transfer of antigen specific Tfh cells into tumor bearing mice results in increased number of intratumoral CTLs, as well as in an efficient tumor eradication, indicating the essential role of Tfh cells in promoting CTL expansion and anti-tumor reactivity. Our results thus, for the first time, indicate the therapeutic potential of Tfh cells in promoting CTL-mediated anti-tumor immunity against melanoma and provide the basis for potential usage of these cells to improve current immunotherapy approaches.

Function of T follicular helper cells in anti-tumor immunity

Clinical relapse and metastases are the major causes of death in melanoma. Currently, adoptive T cell therapy using tumor-infiltrating lymphocytes rich in cytotoxic CD8+ T cells (CTLs) is one of the promising approaches that helps overcome this major challenge in melanoma; however CTL cell transfer alone does not improve clinical response suggesting a role of helper CD4+ T cells. Recently, it has been noted that infiltration of a CD4+ T helper subset, named as T follicular helper (Tfh) cells into tumor sites correlates with increased survival of cancer patients; however their role in tumor immunity has not been clearly elucidated till date. In our hands, both pre-clinical murine tumor studies and patient studies show correlation between increased number of intratumoral Tfh cells and reduced melanoma tumor growth and improved survival, suggesting the novel function of Tfh cells in promoting anti-tumor immunity against melanoma. Remarkably, transfer of tumor antigen-specific Tfh cells in melanoma tumor-bearing mice results in increased intratumoral CTL number and function, as well as in more efficient tumor eradication, indicating the role of Tfh cells in antitumor immunity by promoting CTL expansion and/or activity. Moreover, we determined that Tfh derived cytokine interleukin (IL)-21 contributes to intratumoral CTL activity. Our results thus for first time indicate the therapeutic potential of Tfh cells in promoting anti-tumor immunity against melanoma and provide the basis for potential usage of these cells to improve current immunotherapy approaches.

Regulation of Tfh cell development through STAT1 signaling

T follicular helper (Tfh) cells play a key role in providing help to B cells during germinal center (GC) reactions. The generation and function of Tfh cells is regulated by multiple checkpoints including their early priming stage in T zones and throughout the effector stage of differentiation in GCs. Signaling pathways activated downstream of cytokine and costimulatory receptors as well as consequent activation of subset-specific transcriptional factors are essential steps for Tfh cell generation. While to date early signaling events for fate committed differentiation of Tfh cells are sufficiently studied, mechanisms allowing Tfh cells to maintain their commitment/programming are still unclear. Here we report that signal transducer and activator of transcription 1 (STAT1) deficiency in CD4+ T cells leads to a diminished number of Tfh cells at day 7 and 14 days after antigen immunization, while at day 3–4, number of Tfh cells was comparable between STAT1-sufficient and STAT1 deficient mice, suggesting the role of STAT1 in Tfh lineage maintenance rather than in Tfh cell priming. In fact, in both mouse and human Tfh cells interleukin (IL)-21 mRNA and protein expression is dependent on the presence of STAT1. Functionally, STAT1 in cooperation with STAT3, Batf, and IRF4 triggers IL-21 production in Tfh cells by directly binding to and activation of the IL-21 gene locus. Moreover, utilizing gene knockout approach, we have determined that Batf is a crucial connector to form STAT1/STAT3/Batf/IRF4 active complex for triggering IL-21 transcription. Our results thus indicate functional contribution of STAT1 towards regulation of IL-21 expression and Tfh lineage maturation/maintenance.

Role of E3 ubiquitin ligase GRAIL in B cell activation and tolerance

To date, B cells are believed to play a central role in pathogenesis of various autoimmune diseases as loss of B-cell tolerance with emergence of autoreactive B cells and pathogenic autoantibodies are the hallmark features of autoimmune disorders; however the intrinsic mechanisms that underlie initial breaks in B cell tolerance have not been completely defined. GRAIL, gene related to anergy in lymphocytes (encoded by Rnf128) is an E3 ubiquitin ligase associated with CD4+ and CD8+ T cell tolerance. Our data for first time show GRAIL expression in both mouse and human B cells, with higher expression in anergic B cells and that GRAIL deficiency in B cells leads to impaired B cell peripheral tolerance induction and greater susceptibility to autoimmune diseases. GRAIL deficient B cells exhibited hyperresponsivness in terms of proliferation and antibody production upon antigen stimulation in vitro and in vivo. Concomitantly, GRAIL-deficient B cells were less efficient in downregulation of IgM after B cell receptor (BCR) crosslinking and exhibited increased CD79a expression and activation leading to elevated activation of proximal BCR-signaling components and Ca2+mobilization; GRAIL expression promoted CD79a ubiquitination and degradation. Interestingly, GRAIL expression is also essential to control antigen-presenting property of B cells towards T helper 1 (Th1), Th2, Th17 and follicular helper T (Tfh) cells; since GRAIL deficiency in B cells leads to augmented development and function of Th1, Th2, Th17 and Tfh cells in vitro and in vivo. Thus, our results indicate that GRAIL is a crucial intrinsic factor controlling B cell activation and tolerance by targeting of BCR component CD79a for degradation.

STAT1 is required for Tfh lineage maintenance through regulation of IL-21 expression

T follicular helper (Tfh) cells are a specialized subset of T helper 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 to date early signaling events for fate committed differentiation of Tfh cells are sufficiently studied, mechanisms allowing Tfh cells to maintain their commitment/programming are still unclear. Here we report that STAT1 deficiency in CD4+ T cells leads to diminished number of Tfh cells at day 7 and 14 days after antigen immunization, while at day 3–4, number of Tfh cell were comparable between STAT1-sufficient and STAT1-deficient mice, suggesting the role of STAT1 in Tfh lineage maintenance rather than in Tfh cell priming. Interestingly STAT 1 deficiency in both mouse and human Tfh cells leads to significant drop in IL-21 expression, while the expression of Tfh-specific genes such as Bcl6, CXCR5 and c-Maf was not affected. Functionally, STAT1 in cooperation with STAT3 triggers IL-21 production in Tfh cells by directly binding to and activation of the IL-21 gene locus. In addition, STAT1/STAT3 cooperation influences the expression of transcriptional factor Batf as well as determines Batf-driven IL-21 expression in Tfh cells. Our results thus indicate STAT1 dependent mechanism for IL-21 expression and Tfh lineage maturation and maintenance.

Absence of Grail in CD8+ T cells confers spontaneous tumor regression

T cell tolerance is the main obstacle to successful cancer immunotherapy; thus, it is of high priority to develop strategies to break immune tolerance to malignancy. Here we report that expression of the E3 ubiquitin ligase Grail is significantly upregulated in CD8+T cells infiltrated into lymphoma tumors and Grail-deficiency confers tumor rejection. Importantly, therapeutic transfer of Grail-deficient CD8+ T cells was sufficient to reject established tumors. Mechanistically, loss of Grail enhanced anti-tumor reactivity and survival of CD8+ T cells. Unexpectedly, Grail ablation was associated with ability of CD8+ T cells to evade regulatory T cell-mediated suppression. In addition, Grail deficient CD8+ T cells exhibited increased IL-21R expression and subsequently are hyper-responsive to IL-21 treatment. Finally, CD8+ T cells isolated from human lymphoma patients expressed high levels of Grail and lower levels of IL-21R compared with normal donors. Altogether, our data demonstrate that Grail is a crucial factor that controls CD8+ T cell anti-tumor activity.

Interleukin (IL)-21 promotes intestinal IgA response to microbiota

Commensal microbiota-specific T helper type 17 (Th17) cells are enriched in the intestines, which can convert into T follicular helper (Tfh) in Peyer's patches, and are crucial for production of intestinal immunoglobulin A (IgA) against microbiota; however, the role of Th17 and Tfh cytokines in regulating the mucosal IgA response to enteric microbiota is still not completely known. In this study, we found that intestinal IgA was impaired in mice deficient in interleukin (IL)-17 or IL-21 signaling. IL-21, but not IL-17, is able to augment B-cell differentiation to IgA(+) cells as mediated by transforming growth factor β1 (TGFβ1) and accelerate IgA class switch recombination (CSR). IL-21 and retinoic acid (RA) induce IgA(+) B-cell development and IgA production and drives autocrine TGFβ1 production to initiate IgA CSR. Repletion of T-cell-deficient TCRβxδ(-/-) mice with Th17 cells specific for commensal bacterial antigen increased the levels of IgA(+) B cells and IgA production in the intestine, which was blocked by neutralizing IL-21. Thus IL-21 functions to strongly augment IgA production under intestinal environment. Furthermore, IL-21 promotes intestinal B-cell homing through α4β7 expression, alone or with TGFβ and RA. Together, IL-21 from microbiota-specific Th17 and/or Tfh cells contributes to robust intestinal IgA levels by enhancing IgA(+) CSR, IgA production and B-cell trafficking into the intestine.

CCAAT/enhancer-binding protein α negatively regulates IFN-γ expression in T cells

Humoral immunity, including Ab switching and somatic hypermutation, is critically regulated by CD4(+) T cells. T follicular helper (Tfh) cells have been recently shown to be a distinct T cell subset important in germinal center reactions. The transcriptional regulation of Tfh cell development and function has not been well understood. In this study, we report that C/EBPα, a basic region/leucine zipper transcription factor, is highly expressed in Tfh cells. Cebpa-deficient CD4(+) T cells exhibit enhanced IFN-γ expression in vitro and in vivo. T cell-specific Cebpa knockout mice, although not defective in Tfh cell generation, produce significantly increased levels of IgG2a/b and IgG3 following immunization with a protein Ag. Moreover, C/EBPα binds to the Ifng gene and inhibits T-bet-driven Ifng transcription in a DNA binding-dependent manner. Our study thus demonstrates that C/EBPα restricts IFN-γ expression in T cells to allow proper class switching by B cells.

Activation of the transcription factor c-Maf in T cells is dependent on the CARMA1-IKKβ signaling cascade

The proto-oncogene c-Maf is a transcription factor that plays a critical role in the differentiation of various T helper (T(H)) cell subsets. The amount of c-Maf increases after stimulation of the T cell receptor (TCR), which results in the production of multiple cytokines. We showed that two essential regulators of the transcription factor nuclear factor κB (NF-κB), the scaffold protein CARMA1 and the kinase IKKβ [inhibitor of NF-κB (IκB) kinase β], are also critical for the activation of c-Maf. Although CARMA1 deficiency did not affect the TCR-dependent increase in c-Maf abundance in T cells, CARMA1-dependent activation of the IKK complex was required for the nuclear translocation of c-Maf and its binding to the promoters of its target genes. Consistent with a role for c-Maf in the development of T follicular helper (T(FH)) cells, which provide help to B cells in the germinal centers of the spleen, CARMA1- or IKKβ-deficient mice immunized with peptide antigen had defects in the generation of T(FH) cells, formation of germinal centers, and production of antigen-specific antibodies. Together, these data suggest a mechanism by which c-Maf is regulated during T cell activation and differentiation.

Transcriptional regulation of follicular T-helper (Tfh) cells

T-follicular helper (Tfh) cells are a new subset of effector CD4(+) T cells that are specialized in helping B cells in the germinal center reaction. Tfh cells are distinct from other established CD4(+) T-cell lineages, Th1, Th2, Th17, and T-regulatory cells, in their gene expression profiles. Tfh cell differentiation results from a network of transcriptional regulation by a master transcriptional factor Bcl6 as well as IRF4, c-Maf, Batf, and STAT3/5. During Tfh cell ontogeny, increased CXCR5 expression directs activated T-cell migration to the follicles, and their interaction with B cells leads to Bcl6 upregulation, which helps establish effector and memory Tfh cell program. This review summarizes the recent progress in molecular mechanisms underlying Tfh differentiation and discusses the future perspectives for this important area of research.

Bcl6 expression specifies the T follicular helper cell program in vivo

A novel Bcl6 reporter mouse is used to dissect the developmental requirements, plasticity, and genetic profile of Tfh cells.

T follicular helper cells (Tfh cells) play a pivotal role in germinal center reactions, which require B cell lymphoma 6 (Bcl6) transcription factor. To analyze their relationships with other effector T cell lineages and their stability in vivo, we developed and analyzed a new Bcl6 reporter mouse alone or together with other lineage reporter systems. Assisted with genome-wide transcriptome analysis, we show substantial plasticity of T cell differentiation in the early phase of immune response. At this stage, CXCR5 appears to be expressed in a Bcl6-independent manner. Once Bcl6 is highly expressed, Tfh cells can persist in vivo and some of them develop into memory cells. Together, our results indicate Bcl6 as a bona fide marker for Tfh polarized program.

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.

Transcription of Il17 and Il17f is controlled by conserved noncoding sequence 2

T helper 17 (Th17) cells specifically transcribe the Il17 and Il17f genes, which are localized in the same chromosome region, but the underlying mechanism is unclear. Here, we report a cis element that we previously named conserved noncoding sequence 2 (CNS2) physically interacted with both Il17 and Il17f gene promoters and was sufficient for regulating their selective transcription in Th17 cells. Targeted deletion of CNS2 resulted in impaired retinoic acid-related orphan receptor gammat (RORγt)-driven IL-17 expression in vitro. CNS2-deficient T cells also produced substantially decreased amounts of IL-17F. These cytokine defects were associated with defective chromatin remodeling in the Il17-Il17f gene locus, possibly because of effects on CNS2-mediated recruitment of histone-modifying enzymes p300 and JmjC domain-containing protein 3 (JMJD3). CNS2-deficient animals were also shown to be resistant to experimental autoimmune encephalomyelitis (EAE). Our results thus suggest that CNS2 is sufficient and necessary for Il17 and optimal Il17f gene transcription in Th17 cells.

Molecular mechanisms of T-cell tolerance

CD4(+) T cells are the master regulators of adaptive immune responses, and many autoimmune diseases arise due to a breakdown of self-tolerance in CD4(+) T cells. Activation of CD4(+) T cells is regulated by not only the binding of peptide-major histocompatibility complexes to T-cell receptor but also costimulatory signals from antigen-presenting cells. Recently, there has been progress in understanding the extracellular and intracellular mechanisms that are required for implementation and maintenance of T-cell tolerance. Understanding of the molecular mechanisms underlying T-cell tolerance will lead to development of pharmacological approaches either to promote the tolerance state in terms of autoimmunity or to break tolerance in cancer.

Follicular regulatory T cells expressing Foxp3 and Bcl-6 suppress germinal center reactions

Foxp3(+) regulatory T (T(reg)) cells suppress different types of immune responses to help maintain homeostasis in the body. How T(reg) cells regulate humoral immunity, including germinal center reactions, is unclear. Here we identify a subset of T(reg) cells expressing CXCR5 and Bcl-6 that localize to the germinal centers in mice and humans. The expression of CXCR5 on T(reg) cells depends on Bcl-6. These CXCR5(+)Bcl-6(+) T(reg) cells are absent in the thymus but can be generated de novo from CXCR5(-)Foxp3(+) natural T(reg) precursors. A lack of CXCR5(+) T(reg) cells leads to greater germinal center reactions including germinal center B cells, affinity maturation of antibodies and the differentiation of plasma cells. These results unveil a Bcl-6-CXCR5 axis in T(reg) cells that drives the development of follicular regulatory T (T(FR)) cells that function to inhibit the germinal center reactions.

Ursolic acid suppresses interleukin-17 (IL-17) production by selectively antagonizing the function of RORgamma t protein

Th17 cells have recently emerged as a major player in inflammatory and autoimmune diseases via the production of pro-inflammatory cytokines IL-17, IL-17F, and IL-22. The differentiation of Th17 cells and the associated cytokine production is directly controlled by RORγt. Here we show that ursolic acid (UA), a small molecule present in herbal medicine, selectively and effectively inhibits the function of RORγt, resulting in greatly decreased IL-17 expression in both developing and differentiated Th17 cells. In addition, treatment with UA ameliorated experimental autoimmune encephalomyelitis. The results thus suggest UA as a valuable drug candidate or leading compound for developing treatments of Th17-mediated inflammatory diseases and cancer.

The E3 ubiquitin ligase GRAIL regulates T cell tolerance and regulatory T cell function by mediating T cell receptor-CD3 degradation

T cell activation is tightly regulated to avoid autoimmunity. Gene related to anergy in lymphocytes (GRAIL, encoded by Rnf128) is an E3 ubiquitin ligase associated with T cell tolerance. Here, we generated and analyzed GRAIL-deficient mice and found they were resistant to immune tolerance induction and exhibited greater susceptibility to autoimmune diseases than wild-type mice. GRAIL-deficient naive T cells, after activation, exhibited increased proliferation and cytokine expression than controls and did not depend on costimulation for effector generation. Moreover, GRAIL-deficient regulatory T (Treg) cells displayed reduced suppressive function, associated with increased Th17 cell-related gene expression. GRAIL-deficient naive and Treg cells were less efficient in downregulating T cell receptor (TCR)-CD3 expression after activation and exhibited increased NFATc1 transcription factor expression; GRAIL expression promoted CD3 ubiquitinylation. Our results indicate that GRAIL, by mediating TCR-CD3 degradation, regulates naive T cell tolerance induction and Treg cell function.

Understanding the development and function of T follicular helper cells

A fundamental function of T helper (Th) cells is to regulate B-cell proliferation and immunoglobulin class switching, especially in the germinal centers. Th1 and Th2 lineages of CD4(+) T cells have long been considered to play an essential role in helping B cells by promoting the production immunoglobulin G2a (IgG2a) and IgG1/IgE, respectively. Recently, it has become clear that a subset CD4(+) T cells, named T follicular helper (Tfh) cells, is critical to B-cell response induction. In this review, we summarize the latest advances in our understanding of the regulation of Tfh cell differentiation, the relationship of Tfh cells to other CD4(+) T-cell lineages, and the role of Tfh cells in health and disease.

Toll-like receptor 2 signaling in CD4(+) T lymphocytes promotes T helper 17 responses and regulates the pathogenesis of autoimmune disease

Toll-like receptors (TLRs) have previously been shown to play critical roles in the activation of innate immunity. Here, we describe that T cell expression of TLR2 regulates T helper 17 (Th17) cell responses. Stimulation with TLR2 agonists promoted Th17 differentiation in vitro and led to more robust proliferation and Th17 cytokine production. Using the experimental autoimmune encephalomyelitis (EAE) model, we found that TLR2 regulated Th17 cell-mediated autoimmunity in vivo and that loss of TLR2 in CD4(+) T cells dramatically ameliorated EAE. This study thus reveals a critical role of a TLR in the direct regulation of adaptive immune response and pathogenesis of autoimmune diseases.

MKP-1 is necessary for T cell activation and function

MAPKs are evolutionarily conserved immune regulators. MAPK phosphatases (MKPs) that negatively regulate MAPK activities have recently emerged as critical players in both innate and adaptive immune responses. MKP-1, also known as DUSP1, was previously shown to negatively regulate innate immunity by inhibiting pro-inflammatory cytokine production. Here, we found that MKP-1 is necessary in T cell activation and function. MKP-1 deficiency in T cells impaired the activation, proliferation, and function of T cells in vitro, associated with enhanced activation of JNK and reduced NFATc1 translocation into the nucleus. Consistently, MKP-1(-/-) mice were defective in anti-influenza immunity in vivo and resistant to experimental autoimmune encephalomyelitis. Our results thus demonstrate that MKP-1 is a critical positive regulator of T cell activation and function and may be targeted in treatment of autoimmune diseases.

Bcl6 mediates the development of T follicular helper cells

A fundamental function of CD4+ helper T (T(H)) cells is the regulation of B cell-mediated humoral immunity. Development of T follicular helper (T(FH)) cells that provide help to B cells is mediated by the cytokines interleukin-6 and interleukin-21 but is independent of TH1, TH2, and TH17 effector cell lineages. Here, we characterize the function of Bcl6, a transcription factor selectively expressed in T(FH) cells. Bcl6 expression is regulated by interleukin-6 and interleukin-21. Bcl6 overexpression induced T(FH)-related gene expression and inhibited other T(H) lineage cell differentiation in a DNA binding-dependent manner. Moreover, Bcl6 deficiency in T cells resulted in impaired T(FH) cell development and germinal center reactions, and altered production of other effector T cell subsets. Our data thus illustrate that Bcl6 is required for programming of T(FH) cell generation.

Yin-Yang of costimulation: crucial controls of immune tolerance and function

SUMMARY

In addition to signals from the T-cell receptor complex, it has been recognized for many years that a 'second' signal, most notably from CD28, is also important in T-cell activation. In the recent years, many new members of CD28 family as well as the molecules that share structural homology to CD28 ligands CD80 and CD86 have been discovered. Interestingly, some of these proteins function to dampen T-cell activation and regulate the induction of T-cell tolerance. Therefore, positive and negative costimulation are the two sides of the coin to fine tune T-cell receptor signaling to determine the outcome of T-cell receptor engagement-tolerance versus function.

Cutting edge: A critical role of B and T lymphocyte attenuator in peripheral T cell tolerance induction

T cell activation and tolerance are delicately regulated by costimulatory molecules. Although B and T lymphocyte attenuator (BTLA) has been shown as a negative regulator for T cell activation, its role in peripheral T cell tolerance induction in vivo has not been addressed. In this study, we generated a novel strain of BTLA-deficient mice and used three different models to characterize the function of BTLA in controlling T cell tolerance. In an oral tolerance model, BTLA-deficient mice were found resistant to the induction of T cell tolerance to an oral Ag. Moreover, compared with wild-type OT-II cells, BTLA(-/-) OT-II cells were less susceptible to tolerance induction by a high-dose OVA peptide administered i.v. Finally, BTLA(-/-) OT-I cells caused autoimmune diabetes in RIP-mOVA recipient mice. Our results thus demonstrate an important role for BTLA in the induction of peripheral tolerance of both CD4(+) and CD8(+) T cells in vivo.

Keeping autoimmunity in check: how to control a Th17 cell controller

The transcription factor IRF-4 is necessary for Th17 cell differentiation. In this issue of Immunity, Chen et al. (2008) show that IRF-4-binding protein is a critical negative regulator of IRF-4 function, regulating production of the cytokines IL-21 and IL-17.

Regulation and function of proinflammatory TH17 cells

Naïve CD4(+) helper T (TH) cells, upon activation by antigen-presenting cells (APC), differentiate into different types of effector cells that are characterized by their distinct cytokine production profiles and immune regulatory functions. In addition to TH1 and TH2 cells, a third subset of effector TH cells has recently been described and termed TH17. Since their identification, TH17 cells have emerged as crucial players in infectious, inflammatory, and autoimmune diseases, and cancer. In this review, we summarize the latest discoveries on the cytokine-mediated regulation and transcriptional programming of TH17 cells and their roles in different immune responses and diseases.

A costimulation-initiated signaling pathway regulates NFATc1 transcription in T lymphocytes

T cell activation and differentiation is accompanied and mediated by transcriptional reprogramming. The NFATc1 transcription factor is strongly induced upon T cell activation and controls numerous genes involved in the T cell effector function. However, its regulation by physiological stimuli in primary T cells has not been well understood. We previously found that ICOS synergizes with TCR and CD28 to greatly enhance NFATc1 expression in primary T cells. In this study, we have examined the signaling mechanisms whereby costimulation regulates NFATc1 expression. We found that CD28 and ICOS regulate sustained PI3K activity in primary T cells, which is required for NFATc1 up-regulation. CD28 and ICOS costimulation, possibly through Itk, a Tec kinase downstream of the PI3K, enhanced phosphorylation of phospholipase C gamma1 and increased and sustained Ca(2+) flux in T cells. Costimulation of T cells potentiated transcription of the Nfatc1 gene P1 promoter in a PI3K-dependent manner. This work demonstrates an important role for costimulatory receptors in sustaining T cell activation programs leading to Nfatc1 gene transcription and has implications in our understanding of the immune response and tolerance.

Opposing effects of ICOS on graft-versus-host disease mediated by CD4 and CD8 T cells

ICOS, a CD28 family member expressed on activated CD4(+) and CD8(+) T cells, plays important roles in T cell activation and effector function. Here we studied the role of ICOS in graft-vs-host disease (GVHD) mediated by CD4(+) or CD8(+) T cells in allogeneic bone marrow transplantation. In comparison of wild-type and ICOS-deficient T cells, we found that recipients of ICOS(-/-) CD4(+) T cells exhibited significantly less GVHD morbidity and delayed mortality. ICOS(-/-) CD4(+) T cells had no defect in expansion, but expressed significantly less Fas ligand and produced significantly lower levels of IFN-gamma and TNF-alpha. Thus, ICOS(-/-) CD4(+) T cells were impaired in effector functions that lead to GVHD. In contrast, recipients of ICOS(-/-) CD8(+) T cells exhibited significantly enhanced GVHD morbidity and accelerated mortality. In the absence of ICOS signaling, either using ICOS-deficient donors or ICOS ligand-deficient recipients, the levels of expansion and Tc1 cytokine production of CD8(+) T cells were significantly increased. The level of expansion was inversely correlated with the level of apoptosis, suggesting that increased ability of ICOS(-/-) CD8(+) T cells to induce GVHD resulted from the enhanced survival and expansion of those cells. Our findings indicate that ICOS has paradoxical effects on the regulation of alloreactive CD4(+) and CD8(+) T cells in GVHD.

Regulation of immune and autoimmune responses by ICOS-B7h interaction

Proper T cell activation and function are regulated by the innate immune system, importantly through positive and negative costimulatory molecules of the B7 superfamily. Inducible costimulator (ICOS) is expressed on T cells after T cell activation. A ligand for ICOS, B7h (also known as B7RP-1), is expressed on B cells and induced in nonlymphoid tissues by TNF-alpha. The wide distribution of B7h may play essential roles in different phases and types of immune function. In this review, we summarize the latest data about inducible costimulator and its receptor and their roles in regulation of immune and autoimmune responses.

Immune regulation by novel costimulatory molecules

CD4 helper T (Th)-cells and the cytokines that they produce play essential regulatory roles in immune and autoimmune responses. Th activation and differentiation is regulated by costimulatory receptors. CD28 and CTLA-4 are important in maintaining the threshold of T-cell activation. ICOS and PD-1 are novel costimulatory receptors expressed on activated T-cells. B7-H3 recognizes a putative costimulatory receptor on activated T-cells. Here we summarize the latest developments in the novel costimulatory molecules and their roles in regulating Th activation, differentiation, and function.

B7h is required for T cell activation, differentiation, and effector function

T helper (Th) cell activation, differentiation, and immune function are regulated by costimulatory molecules. Inducible costimulator (ICOS) is a recently identified costimulatory receptor expressed on activated T cells. A ligand for ICOS, B7h, is expressed on B cells and other types of antigen-presenting cells (APC). Although ICOS has been shown to be essential in T cell activation and differentiation, the regulatory roles of B7h at different stages of T cell immune responses have not been examined genetically. In this study, we generated and analyzed B7h-deficient mice. We present evidence that B7h is the only ligand for ICOS, and ICOS, its only corresponding receptor. Th cells, when activated with B7h-deficient APC, exhibited reduced proliferation and IL-2 production. In addition, Th cells produced significantly reduced amounts of IL-4 and -13 after differentiation at the presence of B7h-/- APC. This cytokine defect was associated with a deficiency in c-Maf expression and could be rescued completely by c-Maf overexpression in T cells. Furthermore, we showed that effector T cells, when restimulated in the presence of B7h-deficient APC, exhibited reduced Th2 cytokine production. Therefore, B7h is required for proper Th cell activation, differentiation, and effector cytokine expression.

Regulation of immune and autoimmune responses by ICOS

Proper T cell activation and function are regulated by the innate immune system, importantly through positive and negative costimulatory molecules in the B7 superfamily. Inducible costimulator (ICOS), the receptor for B7h (also known as B7RP-1), is expressed on T cells after T cell activation. Recently, using ICOS-deficient mice, we have examined the roles of ICOS in immune responses. ICOS is required for humoral immunity. In organ-specific autoimmune responses, however, ICOS has contrast roles in different disease models. On the one hand, ICOS-/- mice exhibited extreme sensitivity to experimental autoimmune encephalomyelitis (EAE); on the other, ICOS gene deletion led to complete resistance to collagen-induced arthritis (CIA) in mice. Our work not only illustrates the complexity of immune regulation by costimulatory molecules, but also suggests novel therapeutic strategies for various autoimmune diseases.

Transcriptional regulation of th2 differentiation by inducible costimulator

Helper T (Th) cell differentiation is accompanied by complex transcriptional changes. Although costimulatory receptors are important in Th differentiation, the underlying mechanisms are poorly understood. Here we examine the transcriptional mechanisms by which ICOS regulates Th2 differentiation and selective IL-4 expression by effector T cells. We found impaired expression of c-Maf transcription factor functionally associated with the IL-4 defect in ICOS(-/-) cells. c-Maf expression in effector cells was regulated by IL-4 levels during Th differentiation. ICOS costimulation potentiated the T cell receptor (TcR)-mediated initial IL-4 production, possibly through the enhancement of NFATc1 expression. These data indicate that ICOS, by enhancing TcR signals at an early stage of T cell activation, regulates IL-4 transcription and T cell function in effector cells.

Inducible costimulator is essential for collagen-induced arthritis

CD4(+) helper Th cells play a major role in the pathogenesis of rheumatoid arthritis. Th cell activation, differentiation, and immune function are regulated by costimulatory molecules. Inducible costimulator (ICOS) is a novel costimulatory receptor expressed on activated T cells. We, as well as others, recently demonstrated its importance in Th2 cytokine expression and Ab class switching by B cells. In this study, we examined the role of ICOS in rheumatoid arthritis using a collagen-induced arthritis model. We found that ICOS knockout mice on the DBA/1 background were completely resistant to collagen-induced arthritis and exhibited absence of joint tissue inflammation. These mice, when immunized with collagen, exhibited reduced anti-collagen IgM Ab's in the initial stage and IgG2a Ab's at the effector phase of collagen-induced arthritis. Furthermore, ICOS regulates the in vitro and in vivo expression of IL-17, a proinflammatory cytokine implicated in rheumatoid arthritis. These data indicate that ICOS is essential for collagen-induced arthritis and may suggest novel means for treating patients with rheumatoid arthritis.

Influence of synthetic peptide corresponding to the ACTH-like sequence of human immunoglobulin G1 on activity of murine thymocytes and peritoneal macrophages

The purpose of the present study was to investigate properties and mechanism of action of the synthetic adrenocorticotropin (ACTH)-like peptide VKKPGSSVKV, corresponding to the sequence 11-20 of the variable part of human immunoglobulin G1 (IgG1) heavy chain. The ACTH-like peptide was shown to act as an immunosuppressive agent in vitro: it inhibits the blast transformation of mouse thymocytes and reduces the spontaneous motility of mouse peritoneal macrophages as well as their bactericidal activity against Salmonella typhimurium 415 virulent strain bacteria. High affinity receptors for the ACTH-like peptide were found on thymocytes and macrophages and shown to be at the same time the receptors for ACTH. The kinetic characteristics of the ACTH-like peptide and 125I-labeled ACTH (13-24) (ACTH 'address segment') specific binding to the receptors were determined. It was found that the ACTH-like peptide binding to the receptors on target cells is accompanied by an increase in both adenylate cyclase activity and intracellular cAMP content.

Influence of synthetic peptide corresponding to the ACTH-like sequence of human immunoglobulin G1 on proliferation of lymphoblastoid cells

Influence of the ACTH-like peptide H-Val-Lys-Lys-Pro-Gly-Ser-Ser-Val-Lys-Val-OH corresponding to the sequence 11-20 of the variable part of human immunoglobulin G1 (IgG1) heavy chain on growth of MT-4 human T-lymphoblastoid cell line was investigated. It was found that the ACTH-like peptide at concentration range 10(-11) -10(-7) M inhibits the proliferation of MT-4 cells. Labeled ACTH 'address segment' [(125)I]ACTH (13-24) was used to establish that MT-4 cells express specific receptors for ACTH (K(d) = 97 pM). The ACTH-like peptide and human ACTH (but not IgG1 heavy chain) were shown to compete with [(125)I]ACTH (13-24) for binding to these receptors (K(i1) = 0.38 nM and K(i2) = 0.34 nM).

[Hormone-like activity of a synthetic decapeptide with the adrenocorticotropin-like sequence of human immunoglobulin G1]

The antiproliferative and immunosuppressive in vitro effects of immunocortin, a synthetic adrenocorticotropin-like (ACTH-like) decapeptide H-Val-Lys-Lys-Pro-Gly-Ser-Ser-Val-Lys-Val-OH, whose sequence corresponds to segment 11-20 of the variable part of the human IgG1 heavy chain, were studied. At concentrations of 10(-11)-10(-7) M, immunocortin was found to inhibit the growth of the human MT-4 T-lymphoblastoid cell line, to suppress the blast transformation of thymocytes, and to decrease the spontaneous mobility of peritoneal macrophages and their bactericidal action toward the virulent strain Salmonella typhimurium 415. By using a 125I-labeled "addressing" fragment of ACTH ¿[125I]ACTH-(13-24)¿, we showed that MT-4 cells express specific receptors for ACTH (Kd 97 pM). Immunocortin and human ACTH (but not the heavy chain of IgG1) competitively inhibited the binding of [125I]ACTH-(13-24) to these receptors with Ki1 of 0.38 and Ki2 of 0.34 nM, respectively. Specific receptors for ACTH (Kd 5.8 nM) on mouse thymocytes were detected and characterized. The unlabeled immunocortin was shown to complete with labeled ACTH-(13-24) for binding to these receptors (Ki = 1.8 nM) and this binding of immunocortin to receptors on thymocytes activates adenylate cyclase from these cells and increases the intracellular concentration of cAMP.

[L-glutamic acid--a modulator of the physiological status of myeloid series blood cells]

The effects of L-glutamic acid on the differentiation of HL-60 and K-562 cell lines and on the expression level of mRNAs encoding IL-1 beta, IL-6, and TNF alpha were studied. It was shown that TNF alpha actively induces the differentiation of these cell lines, whereas L-glutamic acid enhances its effect. Our results indicated that L-glutamic acid modulates the physiological state of the myeloid cell line in blood, in particular, by affecting both the reception and expression of cytokines functionally important for these cells.

Study of immunosuppressive activity of a synthetic decapeptide corresponding to an ACTH-like sequence of human immunoglobulin G1

The synthetic ACTH-like decapeptide H-Val-Lys-Lys-Pro-Gly- Ser-Ser-Val-Lys-Val-OH, corresponding to amino acid residues 11-20 of the variable part of the human IgG1 heavy chain (referred to as immunocortin) was found to have an immunosuppressive effect on cells in vitro: it inhibits blast transformation of mouse thymocytes and reduces spontaneous motility of mouse peritoneal macrophages as well as their bactericidal activity against the virulent bacterial strain Salmonella typhimurium 415. Tritium-labeled immunocortin binds with high affinity to ACTH receptors on thymocytes and macrophages (Kd 2. 1 and 2.5 nM, respectively) and activates adenylate cyclase in these cells. Thus, the interaction of immunocortin with the target cell includes the following main steps: binding to the receptor, activation of adenylate cyclase, and elevation of the intracellular content of cAMP.

[Appearance of glutamate receptors on the surface of HL-60 cells upon differentiation]

A specific interaction of L-glutamic acid with promyelocytic leukemia HL-60 cells completely differentiated by all-E-retinoic acid (Kd = 0.5 microM) and by plasma membrane fraction from the same cells (Kd = 1 microM) was detected through radioligand analysis and characterized. Quisqualate, a nonlabeled structural analogue of glutamic acid, was found to inhibit competitively the specific binding of L-[3H]glutamic acid to the membranes (Ki = 0.24 microM). The stereospecificity of the binding was demonstrated. These data suggest that specific glutamate receptors appear on the surface of HL-60 cells during their differentiation.

Influence of L-glutamic acid on binding of interleukin-1beta, tumour necrosis factor-alpha and interleukin-6 to HL-60 cells

To elucidate the mechanism of differentiating activity on L-Glu to HL-60 cells, its influence on binding of human recombinant interleukine-1beta (rHuIL-1beta), tumour necrosis factor-alpha (rHuTNF-alpha) and interleukine-6 (IL-6) by HL-60 cells was studied. It was established, that L-Glu converted the high affinity binding of [125I]rHuIL-1beta (Kd = 0.32 nM) and [125I]rHuIL-6 (Kd = 0.075 nM) to HL-60 cells into low affinity (corresponding Kd values -13.3 and 2.1 nM) at concentration 0.1 microM. The preincubation for an hour of HL-60 cells with 0.1 microM L-Glu was shown to result in an increase of affinity and number of [125I]rHuTNF-alpha binding sites. Thus, L-Glu decreases the sensitivity of the HL-60 cells to IL-1beta and IL-6 and increases TNF-alpha binding at concentration 0.1 microM.

[Effect of L-glutamic acid on the reception of cytokines by HL-60 cells]

L-Glutamic acid at a concentration of 0.1 microM was found to induce differentiation of the cell line of HL-60 promyelocytic leukemia into granulocytes or neutrophils. The HL-60 cells have no specific glutamate-binding sites, but L-glutamic acid influences the reception of several cytokines by these cells. At a concentration of 0.1 microM, L-glutamic acid completely inhibits the high-affinity binding of 125I-labeled human recombinant interleukin-1 beta (Kd = 0.32 nM) to the HL-60 cells, but does not affect their low-affinity binding (Kd = 13.3 nM) and does not change the total number of the IL-1 beta-binding sites. Preincubation of the HL-60 cells with 0.1 microM of L-glutamic acid increases 2.5 times the number of receptors for 125I-labeled human recombinant tumor necrosis factor beta. These results suggest that L-glutamic acid plays an important role in the differentiation of the blood myeloid cells.

[Interaction of L-glutamic acid with human T-lymphocytes]

A specific interaction of [3H]Glu with T lymphocytes from the blood of healthy donors (Kd = 0.236 microM) was revealed and described. It was found that unlabeled quisqualate, a structural analogue of L-glutamic acid, and unlabeled dipeptides Ala-Glu, Glu-Ala, and Glu-Glu competitively inhibit the specific binding of [3H]Glu to T lymphocytes (with Ki 0.19, 2.4, 3.4, and 1.2 microM, respectively). Binding experiments with conjugates of labeled and unlabeled glutamic acid with dextran showed that the receptors of [3H]Glu are localized on the outer surface of the plasma membrane of T lymphocytes.

Study of interaction between L-glutamate and human blood lymphocytes

The presence of specific glutamate receptors on T lymphocytes separated from normal human blood was investigated. Upon study of T lymphocytes interaction with [3H]glutamate the last one was found to bind specifically to these cells, Kd = 2.36 x 10(-7) M. Thirteen unlabelled compounds were tested as potential glutamate competitors. It was shown that only quisqualate (a structural analogue of glutamate) and dipeptides Ala-Glu, Glu-Ala, Glu-Glu competed with [3H]glutamate in binding to a common binding site. The experiments on binding of labelled and unlabelled glutamate bulky conjugates with dextran have demonstrated that both conjugated and free glutamate interacted with the common binding sites on the outer cell membrane. By this means it was shown that T lymphocytes exposed quisqualate-sensitive glutamate receptors on the outer surface of the plasma membrane.

The effect of total saponins from Panax Ginseng C.A. Meyer on the intracellular signalling system in Ehrlich ascites tumor cells

The mechanisms of action of total saponins from Panax Ginseng C.A. Meyer on the elements of intracellular signalling system in Ehrlich ascites tumor cells were studied. The action of total saponins was compared with the effect of ATP, a classical activator of these cells. Saponins at concentrations of 10(-6)-10(-3)% increased [Ca2+]i, mobilized Ca2+ ions from the endoplasmic reticulum (ER) and activated the influx of Ca2+ to cells. Like ATP, saponins activated the Na+/H+ exchange and Ca(2+)-dependent K+ channels. Of all the parameters, only the activation of Ca2+ influx in cell is directly affected by saponins. The changes in other parameters are connected with nonspecific activation of purinoreceptors. The analysis of the kinetic data suggests that, as distinct from ATP-dependent activation of purinoreceptor, saponins first activate the Ca2+ influx to cells and only then induce the mobilization of Ca2+ from ER.