The interleukin-4 enhancer CNS-2 is regulated by Notch signals and controls initial expression in NKT cells and memory-type CD4 T cells

The role of dendritic cells in the instruction of helper T cells in the allergic march

Allergy is a complex array of diseases influenced by innate and adaptive immunity, genetic polymorphisms, and environmental triggers. Atopic dermatitis is a chronic inflammatory skin disease characterized by barrier defects and immune dysregulation, sometimes leading to asthma and food allergies because of the atopic march. During atopic skin inflammation, Langerhans cells and dendritic cells (DCs) in the skin capture and deliver allergen information to local lymph nodes. DCs are essential immune sensors coordinating immune reactions by capturing and presenting antigens to T cells. In the context of allergic responses, DCs play a crucial role in instructing two types of helper T cells-type 2 helper T (Th2) cells and follicular helper T (TFH) cells-in allergic responses and IgE antibody responses. In skin sensitization, the differentiation and function of Th2 cells and TFH cells are influenced by skin-derived factors, including epithelial cytokines, chemokines, and signalling pathways to modify the function of migratory DCs and conventional DCs. In this review, we aim to understand the specific mechanisms involving DCs in allergic responses to provide insights into the pathogenesis of allergic diseases and potential therapeutic strategies.

The sEVs miR-487a/Notch2/GATA3 axis promotes osteosarcoma lung metastasis by inducing macrophage polarization toward the M2-subtype

Small extracellular vesicles (sEVs) are important mediators of intercellular communication between tumor cells and their surrounding environment. Furthermore, the mechanisms by which miRNAs carried in tumor sEVs regulate macrophage polarization remain largely unknown. To concentrate sEVs, we used the traditional ultracentrifugation method. Western blot, NanoSight, and transmission electron microscopy were used to identify sEVs. To determine the function of sEVs-miR-487a, we conducted in vivo and in vitro investigations. The intercellular communication mechanism between osteosarcoma cells and M2 macrophages, mediated by sEVs carrying miR-487a, was validated using luciferase reporter assays, transwell assays, and Western blot analysis. In vitro, sEVs enriched in miR-487a and delivered miR-487a to macrophages, promoting macrophage polarization toward an M2-like type, which promotes proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) of osteosarcoma cells. In vivo, sEVs enriched in miR-487a facilitate lung metastasis of osteosarcoma. Moreover, plasma miR-487a in sEVs was shown to be a potential biomarker applicable for osteosarcoma diagnosis. In summary, miR-487a derived from osteosarcoma cells can be transferred to macrophages via sEVs, then promote macrophage polarization towards an M2-like type by targeting Notch2 and activating the GATA3 pathway. In a feedback loop, the activation of macrophages accelerates epithelial-mesenchymal transition (EMT), which in turn promotes the migration, invasion, and lung metastasis of osteosarcoma cells. This reciprocal interaction between activated macrophages and osteosarcoma cells contributes to the progression of the disease. Our data demonstrate a new mechanism that osteosarcoma tumor cells derived exosomal-miR-487a which is involved in osteosarcoma development by regulating macrophage polarization in tumor microenvironment (TME).

Regulation of T helper cell differentiation by the interplay between histone modification and chromatin interaction

The development and function of the immune system are controlled by temporospatial gene expression programs, which are regulated by cis-regulatory elements, chromatin structure, and trans-acting factors. In this study, we cataloged the dynamic histone modifications and chromatin interactions at regulatory regions during T helper (Th) cell differentiation. Our data revealed that the H3K4me1 landscape established by MLL4 in naive CD4+ T cells is critical for restructuring the regulatory interaction network and orchestrating gene expression during the early phase of Th differentiation. GATA3 plays a crucial role in further configuring H3K4me1 modification and the chromatin interaction network during Th2 differentiation. Furthermore, we demonstrated that HSS3-anchored chromatin loops function to restrict the activity of the Th2 locus control region (LCR), thus coordinating the expression of Th2 cytokines. Our results provide insights into the mechanisms of how the interplay between histone modifications, chromatin looping, and trans-acting factors contributes to the differentiation of Th cells.

A bifurcated role for c-Maf in Th2 and Tfh2 cells during helminth infection

Differences in transcriptomes, transcription factor usage, and function have identified T follicular helper 2 (Tfh2) cells and T helper 2 (Th2) cells as distinct clusters of differentiation 4+",(CD4) T-cell subsets in settings of type-2 inflammation. Although the transcriptional programs driving Th2 cell differentiation and cytokine production are well defined, dependence on these classical Th2 programs by Tfh2 cells is less clear. Using cytokine reporter mice in combination with transcription factor inference analysis, the b-Zip transcription factor c-Maf and its targets were identified as an important regulon in both Th2 and Tfh2 cells. Conditional deletion of c-Maf in T cells confirmed its importance in type-2 cytokine expression by Th2 and Tfh2 cells. However, while c-Maf was not required for Th2-driven helminth clearance or lung eosinophilia, it was required for Tfh2-driven Immunoglobulin E production and germinal center formation. This differential regulation of cell-mediated and humoral immunity by c-Maf was a result of redundant pathways in Th2 cells that were absent in Tfh2 cells, and c-Maf-specific mechanisms in Tfh2 cells that were absent in Th2 cells. Thus, despite shared expression by Tfh2 and Th2 cells, c-Maf serves as a unique regulator of Tfh2-driven humoral hallmarks during type-2 immunity.

Role of CNSs Conserved Distal Cis-Regulatory Elements in CD4 + T Cell Development and Differentiation

Naïve CD4⁺ T cells differentiate into diverse subsets of effector cells and perform various homeostatic and immune functions. The differentiation and maintenance of these different subsets are controlled through the upregulation and silencing of master genes. Mechanistic studies of the regulation of these master genes identified conserved and distal intronic regulatory elements, which are accessible subsets of conserved non-coding sequences (CNSs), acting as cis-regulatory elements in a lineage-specific manner that controls the function of CD4⁺ T cells. Abnormal CNS activity is associated with incorrect expression of master genes and development of autoimmune diseases or immune suppression. Here, we describe the function of several conserved, distal cis-regulatory elements at the Foxp3, Rorc, Il-4, Il-10 and Il-17 gene locus were shown to play important roles in CD4⁺ T cells differentiation. Together, this review briefly outlines currently known CNSs, with a focus on their regulations and functions in complexes modulating the differentiation and maintenance of various CD4⁺ T cells subsets, in health and disease contexts, as well as during the conversion of T regulatory cells to T helper 17 cells. This article will provide a comprehensive view of CNSs conserved distal cis-regulatory elements at a few loci that control aspects of CD4⁺ T cells function.

The role of IL-4 derived from T follicular helper cells and TH2 cells

IL-4 is known to be the quintessential regulatory cytokine, playing a role in a vast number of immune and non-immune functions. This cytokine is commonly secreted by TH2 cells and follicular helper T (TFH) cells after antigenic sensitization. TH2 cells have been classically thought to be the major contributor to B cell help as a source of IL-4 responsible for class-switch recombination to Immunoglobulin G1 (IgG1) in mice (IgG4 in humans) and to IgE in mice and humans. Recent in vivo observations have shown that IgE and IgG1 antibody responses are mainly controlled by IL-4-secreting TFH cells but not by classical TH2 cells. IL-4 is distinctively regulated in these two T cell subsets by the GATA-3-mediated HS2 enhancer in TH2 cells and the Notch-mediated CNS-2 enhancer in TFH cells. Moreover, the IL-4 derived from TFH cells has an essential role in germinal center (GC) formation in the secondary lymphoid organs during humoral immune responses.

Therapeutic Targeting of Notch Signaling: From Cancer to Inflammatory Disorders

Over the past two decades, the Notch signaling pathway has been investigated as a therapeutic target for the treatment of cancers, and more recently in the context of immune and inflammatory disorders. Notch is an evolutionary conserved pathway found in all metazoans that is critical for proper embryonic development and for the postnatal maintenance of selected tissues. Through cell-to-cell contacts, Notch orchestrates cell fate decisions and differentiation in non-hematopoietic and hematopoietic cell types, regulates immune cell development, and is integral to shaping the amplitude as well as the quality of different types of immune responses. Depriving some cancer types of Notch signals has been shown in preclinical studies to stunt tumor growth, consistent with an oncogenic function of Notch signaling. In addition, therapeutically antagonizing Notch signals showed preclinical potential to prevent or reverse inflammatory disorders, including autoimmune diseases, allergic inflammation and immune complications of life-saving procedures such allogeneic bone marrow and solid organ transplantation (graft-versus-host disease and graft rejection). In this review, we discuss some of these unique approaches, along with the successes and challenges encountered so far to target Notch signaling in preclinical and early clinical studies. Our goal is to emphasize lessons learned to provide guidance about emerging strategies of Notch-based therapeutics that could be deployed safely and efficiently in patients with immune and inflammatory disorders.

Notch signaling licenses allergic airway inflammation by promoting Th2 cell lymph node egress

Allergic asthma is mediated by Th2 responses to inhaled allergens. Although previous experiments indicated that Notch signaling activates expression of the key Th2 transcription factor Gata3, it remains controversial how Notch promotes allergic airway inflammation. Here we show that T cell-specific Notch deficiency in mice prevented house dust mite-driven eosinophilic airway inflammation and significantly reduced Th2 cytokine production, serum IgE levels, and airway hyperreactivity. However, transgenic Gata3 overexpression in Notch-deficient T cells only partially rescued this phenotype. We found that Notch signaling was not required for T cell proliferation or Th2 polarization. Instead, Notch-deficient in vitro-polarized Th2 cells showed reduced accumulation in the lungs upon in vivo transfer and allergen challenge, as Notch-deficient Th2 cells were retained in the lung-draining lymph nodes. Transcriptome analyses and sequential adoptive transfer experiments revealed that while Notch-deficient lymph node Th2 cells established competence for lung migration, they failed to upregulate sphingosine-1-phosphate receptor 1 (S1PR1) and its critical upstream transcriptional activator Krüppel-like factor 2 (KLF2). As this KLF2/S1PR1 axis represents the essential cell-intrinsic regulator of T cell lymph node egress, we conclude that the druggable Notch signaling pathway licenses the Th2 response in allergic airway inflammation via promoting lymph node egress.

Human Lymphoid Stromal Cells Contribute to Polarization of Follicular T Cells Into IL-4 Secreting Cells

Fibroblastic reticular cells (FRCs) are the specialized lymphoid stromal cells initially identified as triggering T-cell recruitment and dynamic motion in secondary lymphoid organs. Interestingly, FRCs also display antigen presentation capacities and support lymphocyte survival. CXCR5⁺CD4⁺ follicular T cells are important players of B-cell maturation and antibody response. Our study reported that in vitro-differentiated FRC-like cells enhanced the growth of the whole CXCR5⁺CD4⁺ T-cell compartment, while enhancing IL-4 secretion specifically by the PD1^dimCXCR5⁺CD4⁺ cell subset, in a Notch- and ICAM1/LFA1-dependent manner. In addition, we revealed that in follicular lymphoma (FL) tissues, previously identified as enriched for PD1^hiCXCR5^hiCD4⁺ mature follicular helper T cells, PD1^dimCXCR5⁺CD4⁺ T cells displayed an enrichment for Notch and integrin gene signatures, and a Notch and ICAM-1-dependent overexpression of IL-4 compared to their non-malignant counterparts. These findings suggest that the crosstalk between FRCs and CXCR5⁺PD1^dimCD4⁺ T cells may contribute to the FL IL-4 rich environment, thus providing new insights in FL lymphomagenesis.

Allergin-1 Immunoreceptor Suppresses House Dust Mite-Induced Allergic Airway Inflammation

House dust mite (HDM) allergens are leading causes of allergic asthma characterized by Th2 responses. The lung-resident CD11b⁺ dendritic cells (DCs) play a key role in Th2 cell development in HDM-induced allergic asthma. However, the regulatory mechanism of HDM-induced CD11b⁺ DC activation remains incompletely understood. In this study, we demonstrate that mice deficient in an inhibitory immunoreceptor, Allergin-1, showed exacerbated HDM-induced airway eosinophilia and serum IgE elevation. By using bone marrow-chimeric mice that were sensitized with adoptively transferred HDM-stimulated wild-type or Allergin-1-deficient CD11b⁺ bone marrow-derived cultured DCs (BMDCs), followed by challenge with HDM, we show that Allergin-1 on the BMDCs suppressed HDM-induced allergic airway inflammation. We also show that Allergin-1 suppressed HDM-induced PGE₂ production from CD11b⁺ BMDCs by inhibiting Syk tyrosine kinase activation through recruitment of SHP-1, subsequently leading to negative regulation of Th2 responses. These results suggest that Allergin-1 plays an important role in regulation of HDM-induced allergic airway inflammation.

Notch Signaling Orchestrates Helminth-Induced Type 2 Inflammation

Infection with helminth parasites poses a significant challenge to the mammalian immune system. The type 2 immune response to helminth infection is critical in limiting worm-induced tissue damage and expelling parasites. Conversely, aberrant type 2 inflammation can cause debilitating allergic disease. Recent studies have revealed that key type 2 inflammation-associated immune and epithelial cell types respond to Notch signaling, broadly regulating gene expression programs in cell development and function. Here, we discuss new advances demonstrating that Notch is active in the development, recruitment, localization, and cytokine production of immune and epithelial effector cells during type 2 inflammation. Understanding how Notch signaling controls type 2 inflammatory processes could inform the development of Notch pathway modulators to treat helminth infections and allergies.

Notch Signaling Regulates Immune Responses in Atherosclerosis

Atherosclerosis is a chronic autoimmune inflammatory disease that can cause coronary artery disease, stroke, peripheral artery disease, depending on which arteries are affected. At the beginning of atherosclerosis plasma lipoproteins accumulate in the sub-endothelial space. In response, monocytes migrate from the circulation through the endothelium into the intima where they differentiate into macrophages. These early events trigger a complex immune response that eventually involves many cellular subtypes of both innate and adaptive immunity. The Notch signaling pathway is an evolutionary conserved cell signaling system that mediates cell-to-cell communication. Recent studies have revealed that Notch modulate atherosclerosis by controlling macrophages polarization into M1 or M2 subtypes. Furthermore, it is known that Notch signaling controls differentiation and activity of T-helper and cytotoxic T-cells in inflammatory diseases. In this review, we will discuss the role of Notch in modulating immunity in the context of atherosclerosis and whether targeting Notch may represent a therapeutic strategy.

A conserved enhancer regulates Il9 expression in multiple lineages

Cytokine genes are regulated by multiple regulatory elements that confer tissue-specific and activation-dependent expression. The cis-regulatory elements of the gene encoding IL-9, a cytokine that promotes allergy, autoimmune inflammation and tumor immunity, have not been defined. Here we identify an enhancer (CNS-25) upstream of the Il9 gene that binds most transcription factors (TFs) that promote Il9 gene expression. Deletion of the enhancer in the mouse germline alters transcription factor binding to the remaining Il9 regulatory elements, and results in diminished IL-9 production in multiple cell types including Th9 cells, and attenuates IL-9-dependent immune responses. Moreover, deletion of the homologous enhancer (CNS-18) in primary human Th9 cultures results in significant decrease of IL-9 production. Thus, Il9 CNS-25/IL9 CNS-18 is a critical and conserved regulatory element for IL-9 production.

Interleukin-9 (IL-9) is important for allergy, autoimmunity and tumor immunity, but how its expression is regulated is unclear. Here the authors show the essential function of an enhancer, CNS-25 in mouse and CNS-18 in human, for IL-9 expression, with the deletion of this enhancer severely hampering IL-9 production in mice or human cells.

Cancer Cells Exploit Notch Signaling to Redefine a Supportive Cytokine Milieu

Notch signaling is a well-known key player in the communication between adjacent cells during organ development, when it controls several processes involved in cell differentiation. Notch-mediated communication may occur through the interaction of Notch receptors with ligands on adjacent cells or by a paracrine/endocrine fashion, through soluble molecules that can mediate the communication between cells at distant sites. Dysregulation of Notch pathway causes a number of disorders, including cancer. Notch hyperactivation may be caused by mutations of Notch-related genes, dysregulated upstream pathways, or microenvironment signals. Cancer cells may exploit this aberrant signaling to "educate" the surrounding microenvironment cells toward a pro-tumoral behavior. This may occur because of key cytokines secreted by tumor cells or it may involve the microenvironment through the activation of Notch signaling in stromal cells, an event mediated by a direct cell-to-cell contact and resulting in the increased secretion of several pro-tumorigenic cytokines. Up to now, review articles were mainly focused on Notch contribution in a specific tumor context or immune cell populations. Here, we provide a comprehensive overview on the outcomes of Notch-mediated pathological interactions in different tumor settings and on the molecular and cellular mediators involved in this process. We describe how Notch dysregulation in cancer may alter the cytokine network and its outcomes on tumor progression and antitumor immune response.

Notch Signaling as a Regulator of the Tumor Immune Response: To Target or Not To Target?

The Notch signaling pathway regulates important cellular processes involved in stem cell maintenance, proliferation, development, survival, and inflammation. These responses to Notch signaling involving both canonical and non-canonical pathways can be spatially and temporally variable and are highly cell-type dependent. Notch signaling can elicit opposite effects in regulating tumorigenicity (tumor-promoting versus tumor-suppressing function) as well as controlling immune cell responses. In various cancer types, Notch signaling elicits a "cancer stem cell (CSC)" phenotype that results in decreased proliferation, but resistance to various therapies, hence potentially contributing to cell dormancy and relapse. CSCs can reshape their niche by releasing paracrine factors and inflammatory cytokines, and the niche in return can support their quiescence and resistance to therapies as well as the immune response. Moreover, Notch signaling is one of the key regulators of hematopoiesis, immune cell differentiation, and inflammation and is implicated in various autoimmune diseases, carcinogenesis (leukemia), and tumor-induced immunosuppression. Notch can control the fate of various T cell types, including Th1, Th2, and the regulatory T cells (Tregs), and myeloid cells including macrophages, dendritic cells, and myeloid-derived suppressor cells (MDSCs). Both MDSCs and Tregs play an important role in supporting tumor cells (and CSCs) and in evading the immune response. In this review, we will discuss how Notch signaling regulates multiple aspects of the tumor-promoting environment by elucidating its role in CSCs, hematopoiesis, normal immune cell differentiation, and subsequently in tumor-supporting immunogenicity.

Notch signaling represents an important checkpoint between follicular T-helper and canonical T-helper 2 cell fate

Type-2 immunity is regulated by two distinct CD4+ T-cell subsets. T follicular helper (Tfh) cells are required for humoral hallmarks of type-2 inflammation. T-helper type-2 (Th2) cells orchestrate type-2 inflammation in peripheral tissues, such as the lung and intestine. Given the importance of Notch signaling in the establishment of other CD4+ T-helper cell subsets, we investigated whether canonical Notch activation could differentially impact Tfh and Th2 cell fate during the induction of type-2 immunity. These studies show that Tfh cell, but not Th2 cell, generation and function is reliant on Notch signaling. While early Tfh cell specification is influenced by functional Notch ligands on classical dendritic cells, functional Notch ligands on cells other than dendritic cells, T cells, B cells, and follicular dendritic cells are sufficient to achieve full Tfh cell commitment. These findings identify Notch signaling as an early lineage-determining factor between Tfh and Th2 cell fate.

A Review of Notch Processing With New Insights Into Ligand-Independent Notch Signaling in T-Cells

The Notch receptor is an evolutionarily highly conserved transmembrane protein essential to a wide spectrum of cellular systems, and its deregulation has been linked to a vast number of developmental disorders and malignancies. Regulated Notch function is critical for the generation of T-cells, in which abnormal Notch signaling results in leukemia. Notch activation through trans-activation of the receptor by one of its ligands expressed on adjacent cells has been well defined. In this canonical ligand-dependent pathway, Notch receptor undergoes conformational changes upon ligand engagement, stimulated by a pulling-force on the extracellular fragment of Notch that results from endocytosis of the receptor-bound ligand into the ligand-expressing cell. These conformational changes in the receptor allow for two consecutive proteolytic cleavage events to occur, which release the intracellular region of the receptor into the cytoplasm. It can then travel to the nucleus, where it induces gene transcription. However, there is accumulating evidence that other pathways may induce Notch signaling. A ligand-independent mechanism of Notch activation has been described in which receptor processing is initiated via cell-internal signals. These signals result in the internalization of Notch into endosomal compartments, where chemical changes existing in this microenvironment result in the conformational modifications required for receptor processing. This review will present mechanisms underlying both canonical ligand-dependent and non-canonical ligand-independent Notch activation pathways and discuss the latter in the context of Notch signaling in T-cells.

Immunometabolic Activation of Invariant Natural Killer T Cells

Invariant natural killer T (iNKT) cells are lipid-reactive T cells with profound immunomodulatory potential. They are unique in their restriction to lipid antigens presented in CD1d molecules, which underlies their role in lipid-driven disorders such as obesity and atherosclerosis. In this review, we discuss the contribution of iNKT cell activation to immunometabolic disease, metabolic programming of lipid antigen presentation, and immunometabolic activation of iNKT cells. First, we outline the role of iNKT cells in immunometabolic disease. Second, we discuss the effects of cellular metabolism on lipid antigen processing and presentation to iNKT cells. The synthesis and processing of glycolipids and other potential endogenous lipid antigens depends on metabolic demand and may steer iNKT cells toward adopting a Th1 or Th2 signature. Third, external signals such as toll-like receptor ligands, adipokines, and cytokines modulate antigen presentation and subsequent iNKT cell responses. Finally, we will discuss the relevance of metabolic programming of iNKT cells in human disease, focusing on their role in disorders such as obesity and atherosclerosis. The critical response to metabolic changes places iNKT cells at the helm of immunometabolic disease.

Allergic TH2 Response Governed by B-Cell Lymphoma 6 Function in Naturally Occurring Memory Phenotype CD4+ T Cells

Transcriptional repressor B-cell lymphoma 6 (Bcl6) appears to regulate T_H2 immune responses in allergies, but its precise role is unclear. We previously reported that Bcl6 suppressed IL-4 production in naïve CD4⁺ T cell-derived memory T_H2 cells. To investigate Bcl6 function in allergic responses in naturally occurring memory phenotype CD4⁺ T (MPT) cells and their derived T_H2 (MPT_H2) cells, Bcl6-manipulated mice, highly conserved intron enhancer (hcIE)-deficient mice, and reporter mice for conserved noncoding sequence 2 (CNS2) 3′ distal enhancer region were used to elucidate Bcl6 function in MPT cells. The molecular mechanisms of Bcl6-mediated T_H2 cytokine gene regulation were elucidated using cellular and molecular approaches. Bcl6 function in MPT cells was determined using adoptive transfer to naïve mice, which were assessed for allergic airway inflammation. Bcl6 suppressed IL-4 production in MPT and MPT_H2 cells by suppressing CNS2 enhancer activity. Bcl6 downregulated Il4 expression in MPT_H2 cells, but not MPT cells, by suppressing hcIE activity. The inhibitory functions of Bcl6 in MPT and MPT_H2 cells attenuated allergic responses. Bcl6 is a critical regulator of IL-4 production by MPT and MPT_H2 cells in T_H2 immune responses related to the pathogenesis of allergies.

Innate and adaptive type 2 immunity in lung allergic inflammation

Allergic inflammation is a type 2 immune disorder classically characterized by high levels of immunoglobulin E (IgE) and the development of Th2 cells. Asthma is a pulmonary allergic inflammatory disease resulting in bronchial hyper-reactivity. Atopic asthma is defined by IgE antibody-mediated mast cell degranulation, while in non-atopic asthma there is no allergen-specific IgE and more involvement of innate immune cells, such as basophils, group 2 innate lymphoid cells (ILC2), and eosinophils. Recently, protease allergens were shown to cause asthmatic responses in the absence of Th2 cells, suggesting that an innate cell network (IL-33/TSLP-basophil-ILC2-IL-5/IL-13 axis) can facilitate the sensitization phase of type 2 inflammatory responses. Recent evidence also indicates that in the chronic phase, these innate immune cells directly or indirectly contribute to the adaptive Th2 cell responses. In this review, we discuss the role of Th2 cytokines (IL-4 and IL-13) and innate immune cells (mast cells, basophils, ILC2s, and dendritic cells) in the cross-talk between innate and adaptive inflammatory responses.

Novel TCR-Mediated Mechanisms of Notch Activation and Signaling

The Notch receptor is an evolutionarily highly conserved transmembrane protein that is essential to a wide spectrum of cellular systems. Notch signaling is especially important to T cell development, and its deregulation leads to leukemia. Although not well characterized, it continues to play an integral role in peripheral T cells, in which a unique mode of Notch activation can occur. In contrast to canonical Notch activation initiated by adjacent ligand-expressing cells, TCR stimulation is sufficient to induce Notch signaling. However, the interactions between these two pathways have not been defined. In this article, we show that Notch activation occurs in peripheral T cells within a few hours post-TCR stimulation and is required for optimal T cell activation. Using a panel of inhibitors against components of the TCR signaling cascade, we demonstrate that Notch activation is facilitated through initiation of protein kinase C-induced ADAM activity. Moreover, our data suggest that internalization of Notch via endocytosis plays a role in this process. Although ligand-mediated Notch stimulation relies on mechanical pulling forces that disrupt the autoinhibitory domain of Notch, we hypothesized that, in T cells in the absence of ligands, these conformational changes are induced through chemical adjustments in the endosome, causing alleviation of autoinhibition and receptor activation. Thus, T cells may have evolved a unique method of Notch receptor activation, which is described for the first time, to our knowledge, in this article.

Notch and T Cell Function - A Complex Tale

Notch drives critical decisions in a multitude of developmental decisions in many invertebrate and vertebrate organisms including flies, worms, fish, mice and humans. Therefore, it is not surprising that Notch family members also play a key role in cell fate choices in the vertebrate immune system. This review highlights the critical function of Notch in the development of mature T lymphocytes from hematopoietic precursors and describes the role of Notch in mature T cell activation, proliferation and differentiation.

Natural Killer T Cells: An Ecological Evolutionary Developmental Biology Perspective

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

The Notch pathway inhibitor stapled α-helical peptide derived from mastermind-like 1 (SAHM1) abrogates the hallmarks of allergic asthma

BACKGROUND

The Notch signaling pathway has been implicated in the pathogenesis of allergic airway inflammation. Targeting the active Notch transactivation complex by using the cell-permeable, hydrocarbon-stapled synthetic peptide stapled α-helical peptide derived from mastermind-like 1 (SAHM1) resulted in genome-wide suppression of Notch-activated genes in leukemic cells and other models. However, the efficacy of SAHM1 in allergic asthma models has remained unexplored.

OBJECTIVE

We aimed to investigate the therapeutic efficacy of SAHM1 in a house dust mite (HDM)-driven asthma model.

METHODS

Topical therapeutic intervention with SAHM1 or a control peptide was performed during sensitization, challenge, or both with HDM in mice. Airway inflammation was assessed by using multicolor flow cytometry, and bronchial hyperreactivity was studied. Additionally, SAHM1 therapy was investigated in mice with established allergic airway inflammation and in a model in which we neutralized IFN-γ during HDM challenge to support the T_H2 response and exacerbate asthma.

RESULTS

SAHM1 treatment during the challenge phase led to a marked reduction of eosinophil and T cell numbers in bronchoalveolar lavage fluid compared with those in diluent-treated or control peptide-treated mice. Likewise, T-cell cytokine content and bronchial hyperreactivity were reduced. SAHM1 treatment dampened T_H2 inflammation during ongoing HDM challenge and enhanced recovery after established asthma. Additionally, in the presence of anti-IFN-γ antibodies, SAHM1 downregulated expression of the key T_H2 transcription factor GATA3 and intracellular IL-4 in bronchoalveolar lavage fluid T cells, but expression of the T_H17 transcription factor retinoic acid-related orphan receptor γt or intracellular IL-17 was not affected. SAHM1 therapy also reduced serum IgE levels.

CONCLUSIONS

Therapeutic intervention of Notch signaling by SAHM1 inhibits allergic airway inflammation in mice and is therefore an interesting new topical treatment opportunity in asthmatic patients.

Protective role of NKT cells and macrophage M2-driven phenotype in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is a result of an abnormal wound healing in lung tissue triggered by an excessive accumulation of extracellular matrix proteins, loss of tissue elasticity, and debit of ventilatory function. NKT cells are a major source of Th1 and Th2 cytokines and may be crucial in the polarization of M1/M2 macrophages in pulmonary fibrogenesis. Although there appears to be constant scientific progress in that field, pulmonary fibrosis still exhibits no current cure. From these facts, we hypothesized that NKT cells could influence the development of pulmonary fibrosis via modulation of macrophage activation. Wild type (WT) and NKT type I cell-deficient mice (Jα18^-/-) were subjected to the protocol of bleomycin-induced pulmonary fibrosis with or without treatment with NKT cell agonists α-galactosylceramide and sulfatide. The participation of different cell populations, collagen deposition, and protein levels of different cytokines involved in inflammation and fibrosis was evaluated. The results indicate a benign role of NKT cells in Jα18^-/- mice and in wild-type α-galactosylceramide-sulfatide-treated groups. These animals presented lower levels of collagen deposition, fibrogenic molecules such as TGF-β and vimentin and improved survival rates. In contrast, WT mice developed a Th2-driven response augmenting IL-4, 5, and 13 protein synthesis and increased collagen deposition. Furthermore, the arginase-1 metabolic pathway was downregulated in wild-type NKT-activated and knockout mice indicating lower activity of M2 macrophages in lung tissue. Hence, our data suggest that NKT cells play a protective role in this experimental model by down modulating the Th2 milieu, inhibiting M2 polarization and finally preventing fibrosis.

T follicular helper and TH2 cells in allergic responses

IL-4 is a cytokine commonly secreted by T_H2 and follicular helper T (T_FH) cells after antigenic sensitization. T_H2 cells have been thought to be the major contributor of B cell help as a source of IL-4 responsible for class switch recombination to Immunoglobulin G1 (IgG1) and Immunoglobulin E (IgE). Importantly, there are some differences in transcriptional regulation between these two T cell subsets. The IL-4 production by T_H2 and T_FH cells is distinctively regulated by two pathways, GATA-3-mediated Il4-HS2 enhancer and Notch mediated Il4-CNS-2 enhancer. IgE and IgG1 antibody responses are mainly controlled by IL-4-secreting T_FH cells, but not by T_H2 cells. In this review, we discuss the role of T_H2 and T_FH cells in IgE production and allergic responses.

Notch Signaling in T Helper Cell Subsets: Instructor or Unbiased Amplifier?

For protection against pathogens, it is essential that naïve CD4⁺ T cells differentiate into specific effector T helper (Th) cell subsets following activation by antigen presented by dendritic cells (DCs). Next to T cell receptor and cytokine signals, membrane-bound Notch ligands have an important role in orchestrating Th cell differentiation. Several studies provided evidence that DC activation is accompanied by surface expression of Notch ligands. Intriguingly, DCs that express the delta-like or Jagged Notch ligands gain the capacity to instruct Th1 or Th2 cell polarization, respectively. However, in contrast to this model it has also been hypothesized that Notch signaling acts as a general amplifier of Th cell responses rather than an instructive director of specific T cell fates. In this alternative model, Notch enhances proliferation, cytokine production, and anti-apoptotic signals or promotes co-stimulatory signals in T cells. An instructive role for Notch ligand expressing DCs in the induction of Th cell differentiation is further challenged by evidence for the involvement of Notch signaling in differentiation of Th9, Th17, regulatory T cells, and follicular Th cells. In this review, we will discuss the two opposing models, referred to as the “instructive” and the “unbiased amplifier” model. We highlight both the function of different Notch receptors on CD4⁺ T cells and the impact of Notch ligands on antigen-presenting cells.

Notch Signaling and Immune Regulation in Alloimmunity

Notch signaling plays a pivotal role in the differentiation and fate determination of T cells, B cells, dendritic cells (DCs) and innate lymphoid cells (ILCs). Recent gene-targeting and antibody approaches advanced our knowledge of the importance of Notch signaling in fine-tuning the peripheral immune response. Here we review current knowledge of the Notch pathway, focusing on solid organ transplant and graft-versus-host disease preclinical models, and discuss the potential of targeting Notch to suppress the immune response and improve transplant outcomes.

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.

BATF Modulates the Th2 Locus Control Region and Regulates CD4+ T Cell Fate during Antihelminth Immunity

The AP-1 factor basic leucine zipper transcription factor, ATF-like (BATF) is important for CD4⁺ Th17, Th9, and follicular Th cell development. However, its precise role in Th2 differentiation and function remains unclear, and the requirement for BATF in nonallergic settings of type-2 immunity has not been explored. In this article, we show that, in response to parasitic helminths, Batf^-/- mice are unable to generate follicular Th and Th2 cells. As a consequence, they fail to establish productive type-2 immunity during primary and secondary infection. Batf^-/- CD4⁺ T cells do not achieve type-2 cytokine competency, which implies that BATF plays a key role in the regulation of IL-4 and IL-13. In contrast to Th17 and Th9 cell subsets in which BATF binds directly to promoter and enhancer regions to regulate cytokine expression, our results show that BATF is significantly enriched at Rad50 hypersensitivity site (RHS)6 and RHS7 of the locus control region relative to AP-1 sites surrounding type-2 cytokine loci in Th2 cells. Indeed, Batf^-/- CD4⁺ T cells do not obtain permissive epigenetic modifications within the Th2 locus, which were linked to RHS6 and RHS7 function. In sum, these findings reveal BATF as a central modulator of peripheral and humoral hallmarks of type-2 immunity and begin to elucidate a novel mechanism by which it regulates type-2 cytokine production through its modification of the Th2 locus control region.

Transmission of survival signals through Delta-like 1 on activated CD4+ T cells

Notch expressed on CD4⁺ T cells transduces signals that mediate their effector functions and survival. Although Notch signaling is known to be cis-inhibited by Notch ligands expressed on the same cells, the role of Notch ligands on T cells remains unclear. In this report we demonstrate that the CD4⁺ T cell Notch ligand Dll1 transduces signals required for their survival. Co-transfer of CD4⁺ T cells from Dll1^−/− and control mice into recipient mice followed by immunization revealed a rapid decline of CD4⁺ T cells from Dll1^−/− mice compared with control cells. Dll1^−/− mice exhibited lower clinical scores of experimental autoimmune encephalitis than control mice. The expression of Notch target genes in CD4⁺ T cells from Dll1^−/− mice was not affected, suggesting that Dll1 deficiency in T cells does not affect cis Notch signaling. Overexpression of the intracellular domain of Dll1 in Dll1-deficient CD4⁺ T cells partially rescued impaired survival. Our data demonstrate that Dll1 is an independent regulator of Notch-signaling important for the survival of activated CD4⁺ T cells, and provide new insight into the physiological roles of Notch ligands as well as a regulatory mechanism important for maintaining adaptive immune responses.

Notch Signaling Regulates the Homeostasis of Tissue-Restricted Innate-like T Cells

Although Notch signaling plays important roles in lineage commitment and differentiation of multiple cell types including conventional T cells, nothing is currently known concerning Notch function in innate-like T cells. We have found that the homeostasis of several well-characterized populations of innate-like T cells including invariant NKT cells (iNKT), CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells is controlled by Notch. Notch selectively regulates hepatic iNKT cell survival via tissue-restricted control of B cell lymphoma 2 and IL-7Rα expression. More generally, Notch regulation of innate-like T cell homeostasis involves both cell-intrinsic and -extrinsic mechanisms and relies upon context-dependent interactions with Notch ligand-expressing fibroblastic stromal cells. Collectively, using conditional ablation of Notch receptors on peripheral T cells or Notch ligands on putative fibroblastic stromal cells, we show that Notch signaling is indispensable for the homeostasis of three tissue-restricted populations of innate-like T cells: hepatic iNKT, CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells, thus supporting a generalized role for Notch in innate T cell homeostasis.

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.

Structural similarities of human and mammalian lipocalins, and their function in innate immunity and allergy

Owners and their domestic animals via skin shedding and secretions, mutually exchange microbiomes, potential pathogens and innate immune molecules. Among the latter especially lipocalins are multifaceted: they may have an immunomodulatory function and, furthermore, they represent one of the most important animal allergen families. The amino acid identities, as well as their structures by superposition modeling were compared among human lipocalins, hLCN1 and hLCN2, and most important animal lipocalin allergens, such as Can f 1, Can f 2 and Can f 4 from dog, Fel d 4 from cats, Bos d 5 from cow's milk, Equ c 1 from horses, and Mus m 1 from mice, all of them representing major allergens. The β-barrel fold with a central molecular pocket is similar among human and animal lipocalins. Thereby, lipocalins are able to transport a variety of biological ligands in their highly conserved calyx-like cavity, among them siderophores with the strongest known capability to complex iron (Fe(3+) ). Levels of human lipocalins are elevated in nonallergic inflammation and cancer, associated with innate immunoregulatory functions that critically depend on ligand load. Accordingly, deficient loading of lipocalin allergens establishes their capacity to induce Th2 hypersensitivity. Our similarity analysis of human and mammalian lipocalins highlights their function in innate immunity and allergy.

Regulation of IL-4 Expression in Immunity and Diseases

IL-4 was first identified as a T cell-derived growth factor for B cells. Studies over the past several decades have markedly expanded our understanding of its cellular sources and function. In addition to T cells, IL-4 is produced by innate lymphocytes, such as NTK cells, and myeloid cells, such as basophils and mast cells. It is a signature cytokine of type 2 immune response but also has a nonimmune function. Its expression is tightly regulated at several levels, including signaling pathways, transcription factors, epigenetic modifications, microRNA, and long noncoding RNA. This chapter will review in detail the molecular mechanism regulating the cell type-specific expression of IL-4 in physiological and pathological type 2 immune responses.

Notch in T Cell Differentiation: All Things Considered

Differentiation of naïve T cells into effector cells is required for optimal protection against different classes of microbial pathogen and for the development of immune memory. Recent findings have revealed important roles for the Notch signaling pathway in T cell differentiation into all known effector subsets, raising the question of how this pathway controls such diverse differentiation programs. Studies in preclinical models support the therapeutic potential of manipulating the Notch pathway to alleviate immune pathology, highlighting the importance of understanding the mechanisms through which Notch regulates T cell differentiation and function. We review these findings here, and outline both unifying principles involved in Notch-mediated T cell fate decisions and cell type- and context-specific differences that may present the most suitable points for therapeutic intervention.

Bortezomib enhances expression of effector molecules in anti-tumor CD8+ T lymphocytes by promoting Notch-nuclear factor-κB crosstalk

The immunosuppressive tumor microenvironment usurps host antitumor immunity by multiple mechanisms including interference with the Notch system, which is important for various metazoan cell fate decisions and hematopoietic cell differentiation and function. We observed that treatment with the proteasome inhibitor bortezomib in mice bearing various solid tumors resulted in an upregulated expression of various Notch signaling components in lymphoid tissues, thereby increasing CD8+T-lymphocyte IFNγ secretion and expression of effector molecules, perforin and granzyme B, as well as the T-box transcription factor eomesodermin. Bortezomib also neutralized TGFβ-mediated suppression of IFNγ and granzyme B expression in activated CD8+T-cells. Of note, bortezomib reversed tumor-induced downregulation of Notch receptors, Notch1 and Notch2, as well as increased the levels of cleaved Notch intracellular domain (NICD) and downstream targets Hes1 and Hey1 in tumor-draining CD8+T-cells. Moreover, bortezomib promoted CD8+T-cell nuclear factor-κB (NFκB) activity by increasing the total and phosphorylated levels of the IκB kinase and IκBα as well as the cytoplasmic and nuclear levels of phosphorylated p65. Even when we blocked NFκB activity by Bay-11-7082, or NICD cleavage by γ-secretase inhibitor, bortezomib significantly increased expression of Notch Hes1 and Hey1 genes as well as perforin, granzyme B and eomesodermin in activated CD8+T-cells. Data suggest that bortezomib can rescue tumor-induced dysfunction of CD8+T-cells by its intrinsic stimulatory effects promoting NICD-NFκB crosstalk. These findings provide novel insights on using bortezomib not only as an agent to sensitize tumors to cell death but also to provide lymphocyte-stimulatory effects, thereby overcoming immunosuppressive actions of tumor on anti-tumor T-cell functions.

Modulatory effects of bortezomib on host immune cell functions

Bortezomib is an inhibitor of the ubiquitin-proteasome proteolytic pathway responsible for intracellular protein turnover. Cellular proteins controlled by this pathway represent a diverse group of potential therapeutic targets, particularly in cancer cells, which exploit this proteasomal pathway to promote their growth and diminish apoptosis. Along with inhibiting the proteasome and thus sensitizing tumor cells to apoptosis, bortezomib may also have multiple effects on the host immune responses. This review summarizes the effects that bortezomib may play on immune cell subsets in various disease states in modifying lymphocyte receptors, ligands, the expression of various cytokines and chemokines and their downstream signaling. We also propose steps that can be taken to refine combinatorial strategies that include bortezomib to improve current immunotherapeutic approaches.

The differential expression of IL-4 and IL-13 and its impact on type-2 immunity

Allergic disease represents a significant global health burden, and disease incidence continues to rise in urban areas of the world. As such, a better understanding of the basic immune mechanisms underlying disease pathology are key to developing therapeutic interventions to both prevent disease onset as well as to ameliorate disease morbidity in those individuals already suffering from a disorder linked to type-2 inflammation. Two factors central to type-2 immunity are interleukin (IL)-4 and IL-13, which have been linked to virtually all major hallmarks associated with type-2 inflammation. Therefore, IL-4 and IL-13 and their regulatory pathways represent ideal targets to suppress disease. Despite sharing many common regulatory pathways and receptors, these cytokines perform very distinct functions during a type-2 immune response. This review summarizes the literature surrounding the function and expression of IL-4 and IL-13 in CD4+ T cells and innate immune cells. It highlights recent findings in vivo regarding the differential expression and non-canonical regulation of IL-4 and IL-13 in various immune cells, which likely play important and underappreciated roles in type-2 immunity.

Risk factors for visible lesions or positive laboratory tests in bovine tuberculosis reactor cattle in Northern Ireland

An observational case-control study was conducted to investigate risk factors for confirmed bovine tuberculosis (bTB) infection in cattle reacting positively to the single intradermal comparative cervical test (SICCT) in Northern Ireland in the years 1998, 2002 and 2006. Macroscopic lesions were detected at slaughter (positive visible lesion (VL) status) in 43.0% of reactor cattle, whilst 45.3% of those sampled were confirmed as bTB positive due to the presence of lesions or positive histopathology/mycobacterial culture (positive bTB status). In 97.5% of the reactors, the VL status and bTB status were either both negative or both positive. Generalized linear mixed model analyses were conducted on data of 24,923 reactor cattle with the variables herd identifier, local veterinary office (DVO) and abattoir being used as random effects within all the models generated at univariable and multivariable level. The other variables within the dataset were used as fixed effects. Significant risk factors associated with VL status and bTB status at multivariable level (p<0.05) included age at death, breed, sex, test year, net increase in skin thickness at bovine tuberculin injection site, epidemiological status of skin test, total number of reactors at the disclosure test, mean herd size and prior response to the skin test. These risk factors are likely related to the time since infection, the strength of the challenge of infection and the susceptibility of the animal. These findings are important as the detection of visible lesions and the confirmation of bTB are an integral part of the overall bTB control programme in Northern Ireland and the veterinary meat inspection and hygiene programme. The visible lesion status and bTB status of an animal can affect the way in which bTB breakdowns are managed, since failure to detect visible lesions and recovery of Mycobacterium bovis can lead to a less stringent follow-up after other risk factors have been taken into account.

Notch signaling enhances FcεRI-mediated cytokine production by mast cells through direct and indirect mechanisms

Th2-type cytokines and TNF-α secreted by activated mast cells upon cross-linking of FcεRI contribute to the development and maintenance of Th2 immunity to parasites and allergens. We have previously shown that cytokine secretion by mouse mast cells is enhanced by signaling through Notch receptors. In this study, we investigated the molecular mechanisms by which Notch signaling enhances mast cell cytokine production induced by FcεRI cross-linking. FcεRI-mediated production of cytokines, particularly IL-4, was significantly enhanced in mouse bone marrow-derived mast cells by priming with Notch ligands. Western blot analysis showed that Notch signaling augmented and prolonged FcεRI-mediated phosphorylation of MAPKs, mainly JNK and p38 MAPK, through suppression of the expression of SHIP-1, a master negative regulator of FcεRI signaling, resulting in the enhanced production of multiple cytokines. The enhancing effect of Notch ligand priming on multiple cytokine production was abolished by knockdown of Notch2, but not Notch1, and FcεRI-mediated production of multiple cytokines was enhanced by retroviral transduction with the intracellular domain of Notch2. However, only IL-4 production was enhanced by both Notch1 and Notch2. The enhancing effect of Notch signaling on IL-4 production was lost in bone marrow-derived mast cells from mice lacking conserved noncoding sequence 2, which is located at the distal 3' element of the Il4 gene locus and contains Notch effector RBP-J binding sites. These results indicate that Notch2 signaling indirectly enhances the FcεRI-mediated production of multiple cytokines, and both Notch1 and Notch2 signaling directly enhances IL-4 production through the noncoding sequence 2 enhancer of the Il4 gene.

Notch controls the survival of memory CD4+ T cells by regulating glucose uptake

CD4+ T cells differentiate into memory T cells that protect the host from subsequent infection. In contrast, autoreactive memory CD4+ T cells harm the body by persisting in the tissues. The underlying pathways controlling the maintenance of memory CD4+ T cells remain undefined. We show here that memory CD4+ T cell survival is impaired in the absence of the Notch signaling protein known as recombination signal binding protein for immunoglobulin κ J region (Rbpj). Treatment of mice with a Notch inhibitor reduced memory CD4+ T cell numbers and prevented the recurrent induction of experimental autoimmune encephalomyelitis. Rbpj-deficient CD4+ memory T cells exhibit reduced glucose uptake due to impaired AKT phosphorylation, resulting in low Glut1 expression. Treating mice with pyruvic acid, which bypasses glucose uptake and supplies the metabolite downstream of glucose uptake, inhibited the decrease of autoimmune memory CD4+ T cells in the absence of Notch signaling, suggesting memory CD4+ T cell survival relies on glucose metabolism. Together, these data define a central role for Notch signaling in maintaining memory CD4+ T cells through the regulation of glucose uptake.

Abrogation of Rbpj attenuates experimental autoimmune uveoretinitis by inhibiting IL-22-producing CD4+ T cells

Experimental autoimmune uveoretinitis (EAU) is an organ-specific T cell-mediated disease induced by immunizing mice with interphotoreceptor retinoid binding protein (IRBP). Autoaggressive CD4(+) T cells are the major pathogenic population for EAU. We investigated the contribution of Notch signaling in T cells to EAU pathogenesis because Notch signaling regulates various aspects of CD4(+) T cell functions. Rbpj is required for Notch signaling, and Rbpj deficiency in T cells inhibited EAU disease severity. The amelioration of EAU in T cell-specific Rbpj-deficient mice correlated with low levels of IL-22 production from CD4(+) T cells, although IRBP-specific CD4(+) T cell proliferation and Th17 differentiation were unaffected. Administration of recombinant IL-22 during the late phase, but not the early phase, of EAU increased EAU clinical scores in T cell-specific Rbpj-deficient mice. Notch inhibition in mice immunized with IRBP with a γ-secretase inhibitor (GSI) suppressed EAU progression, even when GSI was administered as late as 13 days after IRBP immunization. Our data demonstrate that Rbpj/Notch-mediated IL-22 production in T cells has a key pathological role in the late phase of EAU, and suggest that Notch blockade might be a useful therapeutic approach for treating EAU.

STAT5-induced lunatic fringe during Th2 development alters delta-like 4-mediated Th2 cytokine production in respiratory syncytial virus-exacerbated airway allergic disease

Notch activation plays an important role in T cell development and mature T cell differentiation. In this study, we investigated the role of Notch activation in a mouse model of respiratory syncytial virus (RSV)-exacerbated allergic airway disease. During RSV exacerbation, in vivo neutralization of a specific Notch ligand, Delta-like ligand (Dll)-4, significantly decreased airway hyperreactivity, mucus production, and Th2 cytokines. Lunatic Fringe (Lfng), a glycosyltransferase that enhances Notch activation by Dll4, was increased during RSV exacerbation. Lfng loss of function in Th2-skewed cells inhibited Dll4-Notch activation and subsequent IL-4 production. Further knockdown of Lfng in T cells in CD4Cre(+)Lfng(fl/fl) mice showed reduced Th2 response and disease pathology during RSV exacerbation. Finally, we identified STAT5-binding cis-acting regulatory element activation as a critical driver of Lfng transcriptional activation. These data demonstrate that STAT5-dependent amplification of Notch-modifying Lfng augments Th2 response via Dll4 and is critical for amplifying viral exacerbation during allergic airway disease.

Reversible expression of CD138 on mature follicular B cells is downregulated by IL-4

CD138, known as a marker of plasma cells, was reported to be expressed to an intermediate level in the murine bone marrow precursor B cells. Here an intermediate level of CD138 expression was also noted in a subpopulation of splenic follicular B cells, which were distinguishable from CD138(high) plasma cells, whereas the majority of transitional or marginal zone B cells did not express CD138. These CD138(int) B cells were IgM(low)IgD(high) mature B cells, located within follicular B cell zone, and expressed a lower level of CD21 than CD138(-) follicular B cells. During in vitro culture of splenic cells, the proportion of CD138(int) B cells increased, which was noticeably reversed by the addition of IL-4 to the culture. The experiments with sorted CD138(int) cells showed that IL-4-mediated regulation of the CD138 expression was B cell-intrinsic and independent of in vitro B cell death. Our results demonstrate that mouse CD138(int) B cells characterize a subpopulation of IgM(low)IgD(high) mature follicular B cells. The CD138 expression on follicular B cells may represent a reversible status, reflecting a dynamic state probably influenced by IL-4.

Epigenetic control of cytokine gene expression: regulation of the TNF/LT locus and T helper cell differentiation

Epigenetics encompasses transient and heritable modifications to DNA and nucleosomes in the native chromatin context. For example, enzymatic addition of chemical moieties to the N-terminal "tails" of histones, particularly acetylation and methylation of lysine residues in the histone tails of H3 and H4, plays a key role in regulation of gene transcription. The modified histones, which are physically associated with gene regulatory regions that typically occur within conserved noncoding sequences, play a functional role in active, poised, or repressed gene transcription. The "histone code" defined by these modifications, along with the chromatin-binding acetylases, deacetylases, methylases, demethylases, and other enzymes that direct modifications resulting in specific patterns of histone modification, shows considerable evolutionary conservation from yeast to humans. Direct modifications at the DNA level, such as cytosine methylation at CpG motifs that represses promoter activity, are another highly conserved epigenetic mechanism of gene regulation. Furthermore, epigenetic modifications at the nucleosome or DNA level can also be coupled with higher-order intra- or interchromosomal interactions that influence the location of regulatory elements and that can place them in an environment of specific nucleoprotein complexes associated with transcription. In the mammalian immune system, epigenetic gene regulation is a crucial mechanism for a range of physiological processes, including the innate host immune response to pathogens and T cell differentiation driven by specific patterns of cytokine gene expression. Here, we will review current findings regarding epigenetic regulation of cytokine genes important in innate and/or adaptive immune responses, with a special focus upon the tumor necrosis factor/lymphotoxin locus and cytokine-driven CD4+ T cell differentiation into the Th1, Th2, and Th17 lineages.

Regulation of innate and adaptive immunity by Notch

Coordinated function of the innate and adaptive arms of the immune system in vertebrates is essential to promote protective immunity and to avoid immunopathology. The Notch signalling pathway, which was originally identified as a pleiotropic mediator of cell fate in invertebrates, has recently emerged as an important regulator of immune cell development and function. Notch was initially shown to be a key determinant of cell-lineage commitment in developing lymphocytes, but it is now known to control the homeostasis of several innate cell populations. Moreover, the roles of Notch in adaptive immunity have expanded to include the regulation of T cell differentiation and function. The aim of this Review is to summarize the current status of immune regulation by Notch. A better understanding of Notch function in both innate and adaptive immunity will hopefully provide multiple avenues for therapeutic intervention in disease.

Jagged2-signaling promotes IL-6-dependent transplant rejection

The Notch pathway is an important intercellular signaling pathway that plays a major role in controlling cell fate. Accumulating evidence indicates that Notch and its ligands present on antigen-presenting cells might be important mediators of T helper cell differentiation. In this study, we investigated the role of Jagged2 in murine cardiac transplantation by using a signaling Jagged2 mAb (Jag2) that activates recombinant signal-binding protein-Jκ. While administration of Jag2 mAb had little effect on graft survival in the fully allogeneic mismatched model BALB/c→B6, it hastened rejection in CD28-deficient recipients. Similarly, Jag2 precipitated rejection in the bm12→B6 model. In this MHC class II-mismatched model, allografts spontaneously survive for >56 days due to the emergence of Treg cells that inhibit the expansion of alloreactive T cells. The accelerated rejection was associated with upregulation of Th2 cytokines and proinflammatory cytokine IL-6, despite expansion of Treg cells. Incubation of Treg cells with recombinant IL-6 abrogated their inhibitory effects in vitro. Furthermore, neutralization of IL-6 in vivo protected Jag2-treated recipients from rejection and Jagged2 signaling was unable to further accelerate rejection in the absence of Treg cells. Our findings therefore suggest that Jagged2 signaling can affect graft acceptance by upregulation of IL-6 and consequent resistance to Treg-cell suppression.