Induction of interleukin 4 (IL-4) expression in T helper (Th) cells is not dependent on IL-4 from non-Th cells

From bite to brain: Neuro-immune interactions in food allergy

Immunoglobulin E (IgE)-mediated food allergies are reported to affect around 3.5% of children and 2.4% of adults, with symptoms varying in range and severity. While being the gold standard for diagnosis, oral food challenges are burdensome, and diagnostic tools based on specific IgE can be flawed. Furthering our understanding of the mechanisms behind food allergy onset, severity and persistence could help reveal immune profiles associated with the disease, to ultimately aid in diagnosis. Alterations to cytokine levels and immune cell ratios have been identified, though further research is needed to fully capture the heterogenous nature of food allergy. Moreover, the existence of such immune alterations also raises the question of potential wider systemic effects. For example, recent research has emphasised the existence and impact of neuro-immune interactions and implicated behavioural and neurological changes associated with food allergy. This review will provide an overview of such food allergy-driven neuro-immune interactions, with the aim of emphasising the importance of furthering our understanding of the immune mechanisms underlying IgE-mediated food allergy.

Analyzing some concepts of immune regulation of the last three decades: Fostering greater research resilience despite the information overload. A personal view

There is considerable interest in whether increased investment in science, made by society, pays dividends. Some plausibly argue the increased rate of production of information results in an ossification of the canon. Reports, challenging the canon, fall by the wayside. The field thus becomes increasingly complex, reflecting not so much the reality of nature but how we investigate the subject. I suggest that focusing on and resolving the paradoxes evident within a canon will free the logjam, resulting in more resilient research. Immunology is among the fastest growing of biological sciences and is, I suggest, an appropriate case study. I examine the commonly accepted frameworks employed over the last three decades to address two major, related immunological questions: what determines whether antigen activates or inactivates CD4 T cells, and so whether immune responses are initiated or this potential ablated; secondly, what determines the Th subset to which the activated Th cells belong, thus determining the class of immunity generated. I show there are major paradoxes within these frameworks, neglected for decades. I propose how research focused on resolving paradoxes can be better fostered, and so support the evolution of the canon. This perspective is pertinent in facing critical issues on how immune responses are regulated, and to more general issues of both the philosophy of science and of science policy.The last section is in response to questions and comments of the reviewers. It brings together several considerations to express my view: the same frameworks, formulated in response to the two questions, are useful in understanding the regulation of the immune response against model antigens, against self and foreign antigens, those of tumors and of pathogens.

The role of cytokines in determining the Th1/Th2 phenotype of an immune response: Coherence of the T cell response and the Cytokine Implementation Hypothesis

The widely accepted Cytokine Milieu Hypothesis proposes that the cytokine milieu, in which antigen activates CD4 T cells, from a non‐T cell source, primarily determines the Th subset to which the ensuing effector Th cells belong. We focus on the generation of Th1 and Th2 cells. We briefly restate the grounds for the Threshold Hypothesis we favour for how the Th1/Th2 phenotype of a response is primarily determined: tentative and robust thresholds of antigen‐mediated CD4 T cell interactions lead to the generation of Th1 and Th2 cells. The component antigens of pathogens are present in different amounts. It is expected, within the context of the threshold mechanism that, although there is often an initial predominance of Th1 or Th2 cells, some Th cells of the opposing type are initially generated. An initially somewhat heterogeneous Th response is known to become with time more ‘coherent’ in its Th1/Th2 phenotype. I propose The Cytokine Implementation Hypothesis as a mechanism for how coherence is achieved. Most cytokines made by Th cells of one subset tend to facilitate the further generation of Th cells of this subset and/or inhibit the generation of Th cells of opposing subsets, accounting for how coherence may be achieved. Many observations on which The Cytokine Milieu Hypothesis is based are accounted for by this alternative hypothesis. We outline predictions of the new hypothesis and discuss the importance of coherence of immune responses for their efficacy in protecting against foreign invaders.

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.

Mast cells have no impact on cutaneous leishmaniasis severity and related Th2 differentiation in resistant and susceptible mice

The genus leishmania comprises different protozoan parasites which are causative agents of muco-cutaneous and systemic, potentially lethal diseases. After infection with the species Leishmania major, resistant mice expand Th1 cells which stimulate macrophages for Leishmania destruction. In contrast, susceptible mice generate Th2 cells which deactivate macrophages, leading to systemic spread of the pathogens. Th-cell differentiation is determined within the first days, and Th2 cell differentiation requires IL-4, whereby the initial IL-4 source is often unknown. Mast cells are potential sources of IL-4, and hence their role in murine leishmaniasis has previously been studied in mast cell-deficient Kit mutant mice, although these mice display immunological phenotypes beyond mast cell deficiency. We therefore readdressed this question by infecting Kit-independent mast cell-deficient mice that are Th1 (C57BL/6 Cpa(Cre) ) or Th2 (BALB/c Cpa(Cre) ) prone with L. major. Using different parasite doses and intra- or subcutaneous infection routes, the results demonstrate no role of mast cells on lesion size development, parasite load, immune cell phenotypes expanding in draining lymph nodes, and cytokine production during murine cutaneous leishmaniasis. Thus, other cell types such as ILCs or T cells have to be considered as primary source of Th2-driving IL-4.

Interleukin-25 initiates Th2 differentiation of human CD4(+) T cells and influences expression of its own receptor

Human CRTh2⁺ Th2 cells express IL‐25 receptor (IL‐25R) and IL‐25 has been shown to potentiate production of Th2 cytokines. However, regulation of IL‐25R and whether it participates in Th2 differentiation of human cells have not been examined. We sought to characterize IL‐25R expression on CD4⁺ T cells and determine whether IL‐25 plays a role in Th2 differentiation. Naïve human CD4⁺ T cells were activated in the presence of IL‐25, IL‐4 (Th2 conditions) or both cytokines to assess their relative influence on Th2 differentiation. For experiments with differentiated Th2 cells, CRTh2‐expressing cells were isolated from differentiating cultures. IL‐25R, GATA3, CRTh2 and Th2 cytokine expression were assessed by flow cytometry, qRT‐PCR and ELISA. Expression of surface IL‐25R was induced early during Th2 differentiation (2 days). Addition of IL‐25 to naïve CD4⁺ T cells revealed that it induces expression of its own receptor, more strongly than IL‐4. IL‐25 also increased the proportions of IL‐4‐, GATA3‐ and CRTh2‐expressing cells and expression of IL‐5 and IL‐13. Activation of differentiated CRTh2⁺ Th2 cells through the TCR or by CRTh2 agonist increased surface expression of IL‐25R, though re‐expression of CRTh2 following TCR downregulation was impeded by IL‐25. These data suggest that IL‐25 may play various roles in Th2 mediated immunity. We establish here it regulates expression of its own receptor and can initiate Th2 differentiation, though not as strongly as IL‐4.

GATA-3 function in innate and adaptive immunity

The zinc-finger transcription factor GATA-3 has received much attention as a master regulator of T helper 2 (Th2) cell differentiation, during which it controls interleukin-4 (IL-4), IL-5, and IL-13 expression. More recently, GATA-3 was shown to contribute to type 2 immunity through regulation of group 2 innate lymphoid cell (ILC2) development and function. Furthermore, during thymopoiesis, GATA-3 represses B cell potential in early T cell precursors, activates TCR signaling in pre-T cells, and promotes the CD4(+) T cell lineage after positive selection. GATA-3 also functions outside the thymus in hematopoietic stem cells, regulatory T cells, CD8(+) T cells, thymic natural killer cells, and ILC precursors. Here we discuss the varied functions of GATA-3 in innate and adaptive immune cells, with emphasis on its activity in T cells and ILCs, and examine the mechanistic basis for the dose-dependent, developmental-stage- and cell-lineage-specific activity of this transcription factor.

Group 2 innate lymphoid cells in lung inflammation

Although allergic asthma is a heterogeneous disease, allergen-specific T helper 2 (Th2) cells producing the key cytokines involved in type 2 inflammation, interleukin-4 (IL-4), IL-5 and IL-13, are thought to play a major role in asthma pathogenesis. This model is challenged by the recent discovery of group 2 innate lymphoid cells (ILC2) that represent a critical innate source of type 2 cytokines. These ILC2 are activated by epithelial cell-derived cytokines, including IL-25 and IL-33, which have been implicated in the initiation of asthma. In this review, we will discuss recent studies supporting a significant role for ILC2 in lung inflammation, with special attention to allergen-induced asthma.

Stochastic cytokine expression induces mixed T helper cell States

During early differentiation of T helper cells, stochastic cytokine expression triggers the co-expression of antagonistic transcription factors at high levels, buffered by the interplay between extracellular and intracellular signaling components.

During eukaryotic development, the induction of a lineage-specific transcription factor typically drives differentiation of multipotent progenitor cells, while repressing that of alternative lineages. This process is often mediated by some extracellular signaling molecules, such as cytokines that can bind to cell surface receptors, leading to activation and/or repression of transcription factors. We explored the early differentiation of naive CD4 T helper (Th) cells into Th1 versus Th2 states by counting single transcripts and quantifying immunofluorescence in individual cells. Contrary to mutually exclusive expression of antagonistic transcription factors, we observed their ubiquitous co-expression in individual cells at high levels that are distinct from basal-level co-expression during lineage priming. We observed that cytokines are expressed only in a small subpopulation of cells, independent from the expression of transcription factors in these single cells. This cell-to-cell variation in the cytokine expression during the early phase of T helper cell differentiation is significantly larger than in the fully differentiated state. Upon inhibition of cytokine signaling, we observed the classic mutual exclusion of antagonistic transcription factors, thus revealing a weak intracellular network otherwise overruled by the strong signals that emanate from extracellular cytokines. These results suggest that during the early differentiation process CD4 T cells acquire a mixed Th1/Th2 state, instructed by extracellular cytokines. The interplay between extracellular and intracellular signaling components unveiled in Th1/Th2 differentiation may be a common strategy for mammalian cells to buffer against noisy cytokine expression.

During the development of a multicellular organism, the progenitor cells, which have the potential to become any of several different cell lineages with specialized functions, commit and differentiate into one particular lineage. This differentiation of progenitors is driven by the induction of lineage-specific transcription factors, molecules that regulate gene expression. This process is often mediated by extracellular signaling molecules, including a class of molecules called cytokines that can bind to cell surface receptors, activating and/or repressing transcription factors. Here we explored the early differentiation of naive T helper (Th) cells, an important class of T lymphocytes that help effector immune cells to defend the body against various pathogens. We measured both mRNA and protein levels of cytokines and transcription factors in individual cells. In particular, mRNA levels were measured with single-molecule resolution. Contrary to the expression of only one set of lineage-specific transcription factors, we observed ubiquitous high-level co-expression of antagonistic transcription factors in individual cells. We found that cytokines are expressed only in a small subpopulation of cells, independent from the expression of transcription factors in individual cells. When cytokine signaling is inhibited, each cell expressed only one of the antagonistic transcription factors at high levels. This reveals a weak intracellular network that is otherwise overruled by the strong signals that emanate from extracellular cytokines. These results suggest that during the early differentiation process T helper cells acquire a mixed Th1/Th2 state, instructed by extracellular cytokines. The interplay between extracellular and intracellular signaling components unveiled in Th1/Th2 differentiation may be a common strategy for mammalian cells to buffer against noisy cytokine expression.

Role of the Transcriptional Repressor BCL6 in Allergic Response and Inflammation

Various molecules participate in different phases of allergic reactions. This means that many genes are encoding molecules related to allergic reactions, such as cytokines, chemokines, and their receptors as effect or molecules. The transcriptional repressor BCL6 has emerged as a multifunctional regulator of lymphocyte differentiation and immune responses. BCL6-deficient (BCL6) mice display T helper type 2 (Th2)-type inflammation, which is caused by abnormality of both lymphoid cells and nonlymphoid cells. Thus, BCL6 apparently contributes to negative regulation of various central molecules such as cytokines, in particular Th2 cytokines, CC chemokines, and immunoglobulin E in allergic diseases. Therefore, BCL6 may be a molecular target for Th2-type allergic diseases.

Th2 cells and cytokine networks in allergic inflammation of the lung

The cytokines released from Th2 and Th2-like cells are likely to be central to the pathophysiolgy of asthma and allergy, contributing to aberrant IgE production, eosinophilia and, perhaps, mucosal susceptibility to viral infection. IL-4 has emerged as a central target, not only for B cell IgE production, but also in the commitment of both CD4+ and CD8+ T cells to cells with Th2 effector function capable of secreting IL-5 resultlng in eosinophilic inflammation. In view of the central role of this cytokine and the evidence that glucocorticoids are unable to modify many IL-4 dependent effects, Th2 inhibitors may prove to be novel therapies for the treatment of bronchial asthma.

A novel mechanism for ERK-dependent regulation of IL4 transcription during human Th2-cell differentiation

We demonstrate that the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)-1 and ERK-2 have a central role in mediating T-cell receptor-dependent induction of IL4 expression in human CD4⁺ T cells. Significantly, this involved a novel mechanism wherein receptor cross-linking induced activated ERK to physically associate with a promoter element on the IL4 gene. The proximally localized ERK then facilitated recruitment of the key transcription factors necessary for initiating IL4 gene transcription. Although both ERK-1 and ERK-2 bound to the promoter, recruitment of either one alone was found to be sufficient. We thus identify a novel mode of function for ERK wherein its physical association with the promoter serves as a prerequisite for enhanceosome assembly. This unusual pathway is also indispensable for human Th2-cell differentiation.

Osteopontin and allergic disease: pathophysiology and implications for diagnostics and therapy

Osteopontin (OPN) is a phosphoglycoprotein that is expressed by various immune cells in a secreted and intracellular form. It has cytokine, chemotactic and cell signaling functions enhancing Th1 and Th17 immunity and protects against apoptosis. Recent studies found OPN to be modulatory in cell-mediated and immediate-type allergic diseases. In allergic asthma, OPN enhances sensitization but downmodulates Th2-driven IL-4-dominated inflammation. The finding that OPN expression is augmented during specific immunotherapy supports a Th2 suppressive effect of OPN. In Th1-driven delayed-type allergy, such as allergic contact dermatitis, OPN supports dendritic cell migration and IL-12 expression and is secreted by T effector cells and keratinocytes, augmenting Th1-mediated allergy and supporting disease chronification. There are numerous missing links as to how OPN variants modulate allergic inflammation through different OPN receptors. OPN research in allergy is an interesting, rapidly expanding field that has high potential for translational research.

TCF1 and beta-catenin regulate T cell development and function

T cell factor-1 (TCF1) critically regulates T cell development. However, signals that control TCF1 function in developing and mature T cells remain unknown. TCF1 along with beta-catenin activates gene transcription and in cooperation with Groucho family of proteins mediates gene repression. It has been established that the beta-catenin-dependent gene expression is often downstream of the canonical Wnt signaling pathway. We have genetically manipulated the beta-catenin gene and generated mutant mice that have shown an essential role for beta-catenin and TCF1 during pre-T cell receptor (TCR) and TCR-dependent stages of T cell development. We have also demonstrated a function for TCF1 and beta-catenin downstream of TCR signaling in the differentiation of mature CD4 T cells into T helper lineages.

Mechanisms of tolerance and allergic sensitization in the airways and the lungs

The respiratory mucosa is constantly exposed to non-infectious substances that have the potential of triggering inflammation. While many particles are excluded, soluble molecules can reach the epithelium surface, where they can be uptaken by dendritic cells and stimulate an adaptive immune response. Most mucosal responses result in tolerance to subsequent antigen encounters, which is mediated by Foxp3(+) regulatory T cells. Genetic and environmental factors, added to the ability of certain allergens to induce innate responses, can predispose to allergic sensitization. In this review we discuss recent advances in the understanding of the mechanisms of tolerance and allergic sensitization to airborne allergens.

T cell factor 1 initiates the T helper type 2 fate by inducing the transcription factor GATA-3 and repressing interferon-gamma

The differentiation of activated CD4(+) T cells into the T helper type 1 (T(H)1) or T(H)2 fate is regulated by cytokines and the transcription factors T-bet and GATA-3. Whereas interleukin 12 (IL-12) produced by antigen-presenting cells initiates the T(H)1 fate, signals that initiate the T(H)2 fate are not completely characterized. Here we show that early GATA-3 expression, required for T(H)2 differentiation, was induced by T cell factor 1 (TCF-1) and its cofactor beta-catenin, mainly from the proximal Gata3 promoter upstream of exon 1b. This activity was induced after T cell antigen receptor (TCR) stimulation and was independent of IL-4 receptor signaling through the transcription factor STAT6. Furthermore, TCF-1 blocked T(H)1 fate by negatively regulating interferon-gamma (IFN-gamma) expression independently of beta-catenin. Thus, TCF-1 initiates T(H)2 differentiation of activated CD4(+) T cells by promoting GATA-3 expression and suppressing IFN-gamma expression.

At the crossroads of T helper lineage commitment-Epigenetics points the way

The immune system has the capacity to respond to various types of pathogens including bacteria, viruses, tumors and parasites. This requires a flexible immune system, which in part depends on the development of alternative effector T helper cells, with different cytokine repertoires that direct the overall immune response. The reciprocal effects of the T helper subtypes Th1 and Th2 are well documented, but the mechanisms involved in alternative cytokine expression and silencing are less well defined. Introduction of advances within the field of chromatin folding and epigenetic regulation of transcription has begun to explain some of the fundamental principles of T helper cell development. In addition, epigenetic regulation has proven essential also for the more recently discovered T helper cell subtypes; regulatory T cells and the Th17 lineage. As the importance of proper epigenetic regulation becomes evident, attention is also focused on the potential harmfulness of epigenetic dysregulation. Autoimmunity and allergy are two clinical situations that have been implicated as results of imperfect cytokine silencing. This review will address recent advances in the field of epigenetic regulation of T lymphocytes and their maturation from naive cells into different effector T cell lineages. In particular, epigenetic involvement in regulation of key effector cytokines and specific transcription factors determining the CD4(+) T lymphocyte lineage commitment will be discussed.

Interferon regulatory factor 4 differentially regulates the production of Th2 cytokines in naive vs. effector/memory CD4+ T cells

Interferon regulatory factor (IRF) 4 is a member of the IRF family of transcription factors and plays critical roles in the development of CD4(+) T cells into Th2 and Th17 cells. Using the infection model of Nippostrongyrus brasiliensis, we have confirmed the critical roles of IRF-4 in Th2 development in vivo by using IRF-4(-/-) BALB/c mice. However, naïve IRF-4(-/-)CD4(+) T cells produced Th2 cytokines, including IL-4, IL-5, and IL-10, but not IL-2 or IFN-gamma, at levels higher than wild-type BALB/c CD4(+) T cells in response to T cell receptor stimulation. In contrast, effector/memory IRF-4(-/-)CD4(+) T cells did not exhibit increased production of Th2 cytokines. Knockdown of IRF-4 expression by using small interfering RNA promoted IL-4 production in naïve CD4(+) T cells but inhibited it in effector/memory CD4(+) T cells. These results indicate that IRF-4 plays differential roles in the regulation of Th2 cytokine production in naïve CD4(+) T cells and effector/memory CD4(+) T cells. IRF-4 inhibits Th2 cytokine production in naïve CD4(+) T cells, whereas it promotes Th2 cytokine production in effector/memory CD4(+) T cells.

An insight into molecular mechanisms of human T helper cell differentiation

Selective activation of T helper (Th) cell subsets plays an important role in immune response to pathogens as well as in the pathogenesis of human allergy and inflammatory diseases. Th1 cells along with the recently discovered Th17 cells play a role in the pathogenesis of autoimmune diseases. Th2 cytokines lead to series of inflammatory processes characteristic for asthma and other atopic diseases. To understand the pathogenesis of immune-mediated diseases it is crucial to dissect pathways and regulatory networks leading to the development of distinct Th subsets. Such knowledge may lead to better strategies for developing diagnostics and therapies for these diseases. The differentiation of Th1, Th2, and Th17 effector cells is driven by signals originating from T cell and costimulatory receptors as well as cytokines in the surroundings of activated naive T helper cells. There are several proteins involved in the regulation of this differentiation process. Most of the data on T helper cell differentiation have been acquired using mouse. In this review, we have summarized what is known about human T helper differentiation. In addition, selected differences between human and mouse will be discussed.

Regulation of T lymphocyte subsets

Patterns of cytokine secretion and functional differences distinguish T lymphocyte subsets. T lymphocyte subsets are also regulated differentially. Most established CD8+ lymphocyte clones secrete gamma-interferon (IFN-gamma) but not interleukin 2 (IL-2) or IL-4. Using murine T cells which express a transgenic, antigen-specific alpha/beta T cell receptor (TCR) specific for L(d) class I major histocompatibility complex antigen, we have found that CD8+ lymphocytes can be divided into functional subsets. Freshly isolated CD8+ T cells are not cytolytic, do not proliferate and do not proliferate and do not secrete cytokines. Stimulation of TCR alone does not induce cytokine secretion, but cells become responsive to exogenous IL-2 or IL-4. Stimulation of CD28 together with TCR induces secretion of IL-2 and IFN-gamma, and cells proliferate without exogenous cytokines. Proliferation is necessary for the development of cytolytic activity. If IL-4 is present during initial stimulation, IL-4 is secreted following restimulation. Upon stimulation, some IL-4-producing murine CD8+ T cell clones express CD40 ligand (CD40L), and they potentiate proliferation and immunoglobulin secretion by small resting B cells. Thus, the CD8+ T cell subsets T cytotoxic 1 (Tc1) and Tc2 are analogous to CD4+ T helper 1 (Th1) and Th2. IL-2 production by naive CD8+ cells requires co-stimulation. IL-4 production by CD8+ T cells requires the presence of IL-4 during initial stimulation. Some IL-4-producing CD8+ T cells express CD40L following TCR stimulation and provide help for B cells.

Dendritic cells: a conductor of T cell differentiation

Induction of different types of adaptive immune responses depending on the nature of antigens and the environmental context is crucial to cope with a variety of pathogens and concurrently to avoid pathological reaction to self antigens. Recent studies have been elucidating that the diversity of immune responses is critically controlled by dendritic cells (DCs). Two DC subsets have been identified in humans: myeloid DCs and plasmacytoid DCs. The DC subsets induce different types of adaptive immune responses depending on environmental factors. Interleukin (IL)-12 from myeloid DCs is a dominant factor for the induction of a Th1 response, whereas OX40 ligand on myeloid DCs is important for the induction of a Th2 response. Furthermore, inducible costimulator (ICOS) ligand on plasmacytoid DCs is critical for the induction of IL-10-producing regulatory T cells. Elucidating cellular and molecular mechanisms by which functions of the two DC subsets are modulated will lead to understanding the pathogenesis of various immune-related diseases and to developing novel immunological therapies.

Direct regulation of Gata3 expression determines the T helper differentiation potential of Notch

CD4(+) T helper cells differentiate into T helper 1 (Th1) or Th2 effector lineages, which orchestrate immunity to different types of microbes. Both Th1 and Th2 differentiation can be induced by Notch, but what dictates which of these programs is activated in response to Notch is not known. By using T cell-specific gene ablation of the Notch effector RBP-J or the Notch1 and 2 receptors, we showed here that Notch was required on CD4(+) T cells for physiological Th2 responses to parasite antigens. GATA-3 was necessary for Notch-induced Th2 differentiation, and we identified an upstream Gata3 promoter as a direct target for Notch signaling. Moreover, absence of GATA-3 turned Notch from a Th2 inducer into a powerful inducer of Th1 differentiation. Therefore, Gata3 is a critical element determining inductive Th2 differentiation and limiting Th1 differentiation by Notch.

Suppression of early IL-4 production underlies the failure of CD4 T cells activated by TLR-stimulated dendritic cells to differentiate into Th2 cells

Dendritic cells (DCs) activated through TLRs provide a potent negative signal for Th2 cell development that is independent of positive signals for Th1 cell development such as IL-12 and IFN-gamma. In this study we demonstrate that the ability of TLR-activated DCs to suppress Th2 cell development is Ag dose-independent and unique to DCs that have been activated through TLRs vs by cytokines. We show that TLR-activated DCs inhibit early IL-4 production by CD4 T cells and thus inhibit their ability to subsequently increase GATA-3 expression and commit to the Th2 lineage. This occurs independently of expression of the GATA-3 antagonist T-bet. Although CD4 T cells activated by TLR-activated DCs make IL-2, they are not capable of phosphorylating STAT5 in response to this cytokine. This inhibition of responsiveness to IL-2 appears to underlie the failure to make early IL-4. Our findings suggest that DCs provide instructional signals for T cell differentiation before cytokine-mediated Th cell selection and outgrowth.

Worms and allergy

Worms and asthma are associated with a type 2 immune response, but evidence has accumulated that helminth infection is negatively associated with atopy, prevalence of allergic diseases and severity of asthma. One important difference between these polarized type 2 responses is that in allergy modulation of the immunological response is not appropriate, whereas in infection with helminths, several host mechanisms down-regulate the host immune response. As a result, patients infected with worms have a decrease in both type 1 and type 2 responses. The main mechanism involved in this down-modulation is increased production of IL-10, but expansion of regulatory T cells and NKT cells may also participate. Regarding the interaction between worms and allergy, a few variables need to be taken in account: phase (acute or chronic) of helminth infection, parasite load and species of helminth. In animals and humans, acute helminth infection may increase manifestations of allergy, whereas chronic infection with parasites decreases atopy. The modulation of the immune response by helminths is dependent on having an adequate parasite load. Moreover, although several helminth species have been shown to modulate immune responses, most in vitro and in vivo studies have focused on the importance of Schistosoma mansoni in down-modulating allergic reactions.

Regulation of Th2 differentiation and Il4 locus accessibility

Helper T cells coordinate immune responses through the production of cytokines. Th2 cells express the closely linked Il4, Il13, and Il5 cytokine genes, whereas these same genes are silenced in the Th1 lineage. The Th1/Th2 lineage choice has become a textbook example for the regulation of cell differentiation, and recent discoveries have further refined and expanded our understanding of how Th2 differentiation is initiated and reinforced by signals from antigen-presenting cells and cytokine-driven feedback loops. Epigenetic changes that stabilize the active or silent state of the Il4 locus in differentiating helper T cells have been a major focus of recent research. Overall, the field is progressing toward an integrated model of the signaling and transcription factor networks, cis-regulatory elements, epigenetic modifications, and RNA interference mechanisms that converge to determine the lineage fate and gene expression patterns of differentiating helper T cells.

Identification of an interleukin (IL)-25-dependent cell population that provides IL-4, IL-5, and IL-13 at the onset of helminth expulsion

Type 2 immunity, which involves coordinated regulation of innate and adaptive immune responses, can protect against helminth parasite infection, but may lead to allergy and asthma after inappropriate activation. We demonstrate that il25^−/− mice display inefficient Nippostrongylus brasiliensis expulsion and delayed cytokine production by T helper 2 cells. We further establish a key role for interleukin (IL)-25 in regulating a novel population of IL-4–, IL-5–, IL-13–producing non–B/non–T (NBNT), c-kit⁺, FcɛR1⁻ cells during helminth infection. A deficit in this population in il25^−/− mice correlates with inefficient N. brasiliensis expulsion. In contrast, administration of recombinant IL-25 in vivo induces the appearance of NBNT, c-kit⁺, FcɛR1⁻ cells and leads to rapid worm expulsion that is T and B cell independent, but type 2 cytokine dependent. We demonstrate that these IL-25–regulated cells appear rapidly in the draining lymph nodes, implicating them as a source of type 2 cytokines during initiation of worm expulsion.

Signals from OX40 regulate nuclear factor of activated T cells c1 and T cell helper 2 lineage commitment

T cell helper type 2 (Th2) differentiation is driven by a source of IL-4 receptor (IL-4R) that mobilizes IL-4R signaling pathways and the transcription factor GATA-3. Naïve CD4 cells can secrete IL-4 independently of IL-4R signals, but how this secretion is regulated is not understood. Here we demonstrate that costimulation through the tumor necrosis factor receptor family molecule OX40, in synergy with CD28, is essential for high levels of nuclear factor of activated T cells c1 to accumulate in the nucleus of a recently activated naïve T cell. This action is not dependent on either IL-4R or IL-2R signals and results in OX40 controlling initial naïve T cell IL-4 transcription. OX40 signals subsequently enhance nuclear GATA-3 accumulation through an IL-4R-dependent action, leading to Th2 differentiation. These data show that, in the absence of an exogenous source of IL-4, OX40 provides a critical synergistic and temporal signal with other noncytokine receptors to modulate nuclear factor of activated T cells c1 and to promote optimal Th2 generation.

T cells use two directionally distinct pathways for cytokine secretion

Activated T helper cells produce many cytokines, some of which are secreted through the immunological synapse toward the antigen-presenting cell. Here we have used immunocytochemistry, live-cell imaging and a surface-mediated secretion assay to show that there are two cytokine export pathways in T helper cells. Some cytokines, including interleukin 2 and interferon-gamma, were secreted into the synapse, whereas others, including tumor necrosis factor and the chemokine CCL3 (MIP-1alpha), were released multidirectionally. Each secretion pathway was associated with different trafficking proteins, indicating that they are molecularly distinct processes. These data suggest that T helper cells release some cytokines into the immunological synapse to impart specific communication and others multidirectionally to promote inflammation and to establish chemokine gradients.

Functional Diversity and Plasticity of Human Dendritic Cell Subsets

The induction of different types of innate and adaptive immune responses, depending on the nature of the antigens and the environmental context, is crucial to cope with a variety of pathogens and concurrently to avoid pathologic reaction to self antigens. Recent studies have elucidated that the diversity of immune responses is critically controlled by dendritic cells (DCs). Two DC subsets, myeloid DCs and plasmacytoid DCs, have been identified in humans. The DC subsets recognize different microbial pathogens by expressing distinct repertoires of Toll-like receptors and induce different types of innate and adaptive immune responses, depending on the environmental factors. In particular, plasmacytoid DC precursors produce vast amounts of type I interferons in response to viruses and thus play an important role in antiviral immunity. Elucidating the cellular and molecular mechanisms that modulate the functions of the 2 DC subsets will lead to an understanding of the pathogenesis of various immune-related diseases and to the development of novel immunologic therapies.

IL-2 and autocrine IL-4 drive the in vivo development of antigen-specific Th2 T cells elicited by nematode parasites

The intestinal nematode parasite, Nippostrongylus brasiliensis, triggers potent type 2 immunity. Using OVA peptide as a model Ag, we have examined the adjuvant effects of this parasite on the in vivo development of Ag-specific Th2 cells from naive DO11.10 T cells. Our findings show that Th2 cells can develop from transferred naive OVA-specific DO11.10 T cells in recipient IL-4-/- mice inoculated with N. brasiliensis plus OVA. However, autocrine IL-4 is required for in situ Th2 cell differentiation since transferred IL-4Ralpha-deficient DO11.10 T cells showed greatly reduced Th2 cell development in inoculated IL-4-/- recipient mice. Surprisingly, we also found that IL-2 blockade promoted B7-dependent T cell cycling, but inhibited the development of OVA-specific Th2 cells. Furthermore, the effects of IL-2 occurred independently of CD25+ T regulatory cells. These studies establish a previously unrecognized requirement for autocrine IL-4 and IL-2 in Th2 responses elicited by nematode parasites.

Bcl6 regulates Th2 type cytokine productions by mast cells activated by FcepsilonRI/IgE cross-linking

Bcl6-deficient (Bcl6-/-) mice displayed Th2 type inflammation, which caused by abnormality of non-lymphoid cells. However, initiators for the Th2 type inflammation were not clear. In order to elucidate the initiators, we investigated property and function of mast cells derived from Bcl6-/- mice. Mast cells were developed from bone marrow cells cultured with IL-3 (BMMCs). Although the development of BMMCs from Bcl6-/- mice was similar to that from wild-type mice, proliferation of Bcl6-/- BMMCs stimulated with IL-3 was slightly lower than that of wild-type BMMCs. When these BMMCs were stimulated by FcepsilonRI/IgE cross-linking, Bcl6-/- BMMCs produced Th2 cytokines more than wild-type BMMCs did. Thus, Bcl6-/- mast cells are one of the initiators for Th2 type inflammation in Bcl6-/- mice, and Bcl6 may be a molecular target for Th2 type allergic diseases.

IL-6 Plays a Unique Role in Initiating c-Maf Expression during Early Stage of CD4 T Cell Activation

The transcription factor c-Maf plays a critical and selective role in IL-4 gene transcription. Little is known about the mechanism that guides c-Maf regulation during early T cell activation. We report that IL-6 but not IL-4 or other cytokines, rapidly up-regulates c-Maf transcription, as early as 3 h after TCR activation in naive CD4(+) T cells. c-Maf induction requires both IL-6- and TCR-initiated signals, and is independent of IL-4/Stat6 signals. Cyclosporin A and FK506, which target calcineurin and thereby inhibit TCR-mediated Ca(2+) signal pathways, block IL-6-mediated c-Maf expression. We show that Stat3 binds the c-maf promoter in CD4 T cells after IL-6 stimulation, and also transactivates the c-maf promoter in reporter gene assays. IL-6 induces similar c-Maf expression in protein kinase Ctheta-deficient CD4(+) T cells. Furthermore, IL-6 enhances IL-4 gene expression very early after TCR activation in both wild-type and Stat6-deficient CD4(+) T cells. Our findings suggest that IL-6 plays a unique role in initiating c-Maf expression after TCR engagement, and may subsequently regulate early IL-4 production and Th2 commitment.

Requirements for the development of IL-4-producing T cells during intestinal nematode infections: what it takes to make a Th2 cell in vivo

Components of the type 2 immune response may mediate host protection against both helminthic parasites and harmful allergic responses. A central player in this response is the T-helper 2 (Th2) effector cell, which produces interleukin (IL)-4, IL-5, IL-13, and other Th2 cytokines during the primary and memory response. Specific aspects of the parasite that trigger Th2-cell differentiation are not yet defined. Furthermore, the cell types and cell surface and secreted molecules that provide the immune milieu required for the development of Th2 effector cells and also Th2 memory cells are not well understood. They will probably vary with the particular helminth or other antigen inducing the Th2 response. We have used third stage larvae of intestinal nematode parasites as adjuvants to promote naïve nonparasite antigen-specific T cells to differentiate into Th2 cells. This model system avoids possible parasite antigen-specific T-cell clones or cross-reactive memory T cells that may preferentially differentiate into Th2 effector cells during the course of infection and confound the stereotypical components of parasite-induced Th2 cell differentiation. We have found that these parasites have a potent adjuvant effect and have used our model system to begin to investigate the events that lead to the development of polarized Th2 cells in vivo.

TLR Ligands Can Activate Dendritic Cells to Provide a MyD88-Dependent Negative Signal for Th2 Cell Development

During infection, CD4(+) Th cell responses polarize to become primarily Th1 or Th2. Th1 cells, which make IFN-gamma, are crucial for immunity to many bacterial and protozoal infections, whereas Th2 cells, which make IL-4, IL-5, and IL-13, are important for resistance to helminth infections. Polarized Th1 responses are induced by dendritic cells (DCs), which respond to pathogen-derived TLR ligands to produce IL-12 and related cytokines that are instrumental in Th1 cell outgrowth, and coordinately process and present Ag in the context of MHC class II to activate naive Th cells. In this study we show that in addition to providing positive signals for Th1 cell development, mouse DCs activated by TLR engagement can also provide a potent negative signal that prevents the development of Th2 cells. Production of this signal, which is not IL-12, IL-18, IL-23, IL-27, or IFN-gamma and is not provided via Th1 cells, is dependent upon a MyD88-dependent, TNF receptor-associated factor-6-independent signaling pathway in DCs. The signal is released from DCs in response to activation via TLR ligands and exerts an effect directly on Th cells rather than through a third-party cell. Our findings indicate that DCs can provide potent negative as well as positive instruction for Th response polarization, and that these instructional signals are distinct and independent.

Th2 response polarization during infection with the helminth parasite Schistosoma mansoni

T-helper 2 (Th2) cell responses play a critical role in protection against helminth infections. In the case of Schistosoma mansoni, an important helminth parasite of man, data from a mouse model of human disease have shown that Th2 responses are essential to allow host survival. In this infection, parasite eggs are the primary stimulus for Th2 response development. Recent work has shown that egg molecules exert multiple levels of control over the development of host interferon-gamma-associated inflammatory responses. Soluble egg antigen inhibits the ability of dendritic cells to make interleukin-12 and induces Th2-polarized adaptive immune responses that in combination with regulatory T-cell responses effectively limit Th1 response development. In this article, we discuss the factors influencing Th2 response polarization during infection with S. mansoni.

Parasite-induced Th2 polarization is associated with down-regulated dendritic cell responsiveness to Th1 stimuli and a transient delay in T lymphocyte cycling

The nature of the signals that bias Th effector choice is still not completely understood. Using parasite extracts from pathogens known to induce polarized Th1 or Th2 responses and an in vitro experimental model for priming murine CD4(+) cells, we demonstrated that splenic dendritic cells (DC), but not B cells, promote Th1/Th2 differentiation of naive CD4(+) lymphocytes. Th polarization in this system was found not to depend on DC secretion of the polarizing cytokines IL-12/IL-4, but instead correlated with distinct states of DC activation induced by the different parasite preparations. As expected, conditioning of DC for Th1 development was associated with up-regulation of costimulatory molecules and enhanced chemokine production and required intact MyD88 signaling. In contrast, conditioning of DC for Th2 differentiation correlated with down-regulation of many of the same functions and was MyD88 independent. This dampened DC activation was accompanied in the cocultures by a reduction in the frequency of CD4(+) lymphocytes exiting the first division of the cell cycle. When the latter was mimicked by drug-induced arrest of peptide-primed CD4(+) cells after the S phase of the first cycle, a marked Th2 polarization was also observed. Together, these findings suggest that the emergence of IL-4-producing CD4(+) lymphocytes results from a suppression in DC function leading to a temporary delay in initial T cell cycling.

Instruction of distinct CD4 T helper cell fates by different notch ligands on antigen-presenting cells

Antigen-presenting cells (APC) tailor immune responses to microbial encounters by stimulating differentiation of CD4 T cells into the Th1 and Th2 lineages. We demonstrate that APC use the Notch pathway to instruct T cell differentiation. Strikingly, of the two Notch ligand families, Delta induces Th1, while Jagged induces the alternate Th2 fate. Expression of these different Notch ligands on APC is induced by Th1- or Th2-promoting stimuli. Th2 differentiation has been considered a default process as APC-derived instructive signals are unknown. We demonstrate that Jagged constitutes an instructive signal for Th2 differentiation, which is independent of IL4/STAT6. Th2 differentiation induced by APC is abrogated in T cells lacking the Notch effector RBPJkappa. Notch directs Th2 differentiation by inducing GATA3 and by directly regulating il4 gene transcription through RBPJkappa sites in a 3' enhancer.

Pinpointing IL-4-independent acquisition and IL-4-influenced maintenance of Th2 activity by CD4 T cells

Naive CD4 T cells develop Th2 activity early in primary responses to alum-precipitated proteins by producing IL-4 mRNA and inducing B cells to produce gamma1 and epsilon switch transcripts. Both IL-4-dependent and IL-4-independent pathways for IL-4 induction are recognized, but their relative contribution to the different phases of primary Th2 responses in vivo is uncertain. We show the primary induction of IL-4 synthesis in lymph nodes responding to alum-precipitated protein is overwhelmingly in antigen-specific CD4 T cells and is unimpaired in IL-4Ralpha(-/-) mice, which can produce but do not respond to IL-4 and IL-13. Ig class-switching in extra-follicular responses, reflecting Th2 activity, is also unimpaired in these mice. By contrast, 7 days after immunization--when T cells are selecting B cells in germinal centers and T cell priming has occurred--non-responsiveness to IL-4 is associated with smaller germinal centers, increased levels of T-bet and gamma2a switch transcripts and reduced gamma1 and epsilon transcripts. These data indicate that Th2 characteristics acquired during T cell priming and the initial CD4 T cell interaction with B cells are largely IL-4-independent, whereas IL-4 production induced during priming has a significant role in maintaining the Th2 phenotype as T cells select B cells in germinal centers.

Differentiation of naive CD4+ T cells towards T helper 2 cells is not impaired in rheumatoid arthritis patients

An impaired differentiation of naive CD4+ T cells towards Th2 cells may contribute to the chronic tissue-destructive T-cell activity in rheumatoid arthritis (RA). The differentiation of naive CD4+ T cells into memory Th2 cells by IL-7 in comparison with that by IL-4 was studied in RA patients and in healthy controls. Naive CD4+ T cells from peripheral blood were differentiated by CD3/CD28 costimulation in the absence of or in the presence of IL-7 and/or IL-4. The production of IFN-gamma and IL-4 was measured by ELISA and by single-cell FACS analysis to indicate Th1 and Th2 cell activity. CD3/CD28 costimulation and IL-7 were early inducers of IL-4 production, but primarily stimulated IFN-gamma production. In contrast, in short-term cultures exogenously added IL-4 did not prime for IL-4 production but suppressed IL-7-induced IFN-gamma production. Upon long-term stimulation of naive CD4+ T cells, IFN-gamma production was differentially regulated by IL-7 and IL-4, but IL-4 production was increased by both IL-7 and IL-4. IL-7 and IL-4 additively induced polarization towards a Th2 phenotype. This susceptibility of naive CD4+ T cells to become Th2 cells upon culture with IL-7 and IL-4 was increased in RA patients compared with that in healthy controls. These findings demonstrate that, in RA patients, differentiation of naive CD4+ T cells towards a Th2 phenotype by CD3/CD28 costimulation, IL-7 and IL-4 is not impaired. The perpetuation of arthritogenic T-cell activity in RA therefore seems not to be the result of intrinsic defects of naive CD4+ T cells to develop towards suppressive memory Th2 cells.

The role of transcription factors in allergic inflammation

The induction of allergic inflammation and the expression of allergic disorders are dependent on the coordinated regulation of numerous genes. The products of these genes determine lymphocyte phenotype, immunologic responsiveness, eosinophil and mast cell development, activation, migration and life span, adhesion molecule expression, cytokine synthesis, cell-surface receptor display, and processes governing fibrosis and tissue repair. Although the expression of gene products involved in these processes is regulated at multiple levels (eg, transcription, mRNA processing, translation, phosphorylation, and degradation), transcription represents an essential and often the most important determinant of their contribution to cellular function. Signal-dependent and cell type-specific regulation of gene expression is generally achieved by means of combinatorial interactions between sequence-specific transcription factors that recruit chromatin remodeling machinery and general transcription factors to promoter and enhancer regions of RNA polymerase II-dependent genes. As targets of signal-transduction pathways, transcription factors integrate the response of the cell to the myriad of inputs it receives. This integration can be accomplished by the effect of signaling cascades on the activation status or subcellular locus of transcription factors or by transcription factor dimerization induced by means of ligand binding. This review will identify the major families of transcription factors important in allergic mechanisms and discuss their interactions, their mechanisms of action, and their interrelated and competitive actions, as well as implications for therapy of allergic disorders.

Preparations of heterospirostanols and their pharmacological activities

(3beta,20S,22S,25R)-22-Thiospirosol-5-en-3-ol (9) and (3beta,20S,22S,25R)-22-seleno-spirosol-5-en-3-ol (11) were prepared from diosgenin (3) via 26-iodopseudodiosgenin (6) as a key intermediate. Diosgenone (15), solasodinone (16), (20S,22S,25R)-22-thio-spirosol-4-en-3-one (17), (20S,22S,25R)-22-selenospirosol-4-en-3-one (18) and (20R,22S,25R)-spirosol-4-en-3-one (19) were prepared by Oppenauer oxidation of 3, solasodine 4, 9, 11 and (3beta,20R,22R,25R)-spirosol-5-en-3-ol 14, respectively. Oxidations of 15 and 16 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) provided corresponding dienone products, (20S,22S,25R)-spirosol-1,4-dien-3-one (20) and (20S,22S,25R)-22-thiospirosol-1,4-dien-3-one (21), respectively, while oxidation of 19 (C-20 diastereoisomer of 15) gave no dienone product but 21-exo vinyl product 22. 26-Thioacetylpseudodiosgenone (24) and 26-cyanoselenopseudodiosgenone (25) were prepared by treatment of 26-iodopseudodiosgenose (23), which was obtained by Oppenauer oxidation of 6, with potassium thioacetate and potassium selenocyanate, respectively. Compounds 15 and 19 exhibited more than 80% inhibitions in INF-gamma productions at 10.0 microM. Compounds 4 and 25 showed cytotoxic activities (IC(50) = 6 and 5 microM, respectively) against cancerous HCT 116 cell lines. Compounds 12 and 25 had antiurease activities (IC(50) = 12.4 and 11.4 microM, respectively), in which only the latter showed an inhibition zone (mean zone diameter = 12.2 mm) formed by Bacillus subtilis 168 trp.

Cytokines and chemoattractants in allergic inflammation

It is now generally accepted type 2 T helper (Th2) cytokines and some chemoattractants play an essential role in the pathogenesis of the allergic inflammation. The effects of Th2 cytokines, such as interleukin (IL)-4, IL-5, IL-9, and IL-13, account for virtually all the pathophysiological manifestations of allergy and asthma. Moreover, both Th2 cells and the effector cells usually present in the areas of allergic inflammation (basophils, mast cells, and eosinophils) express chemoattractant receptors, such as CCR3, CCR4, CCR8 and CRTH2. Therefore, interactions of eotaxin(s), eotaxin/CCL11, RANTES/CCL5, and MCP-1/CCL2, MCP-2/CCL8, MCP-3/CCL7, MCP-4/CCL13 with CCR3 are responsible for the recruitment of basophils, eosinophils and mast cells, whereas interactions of CCR4 with MDC/CCL22 or TARC/CCL17, CCR8 with I-309/CCL1, and CRTH2 with prostaglandin D(2) play a critical role in the allergen-induced recruitment of Th2 cells in the target tissues of allergic inflammation. The demonstration that Th2-polarized responses against allergens represent the triggering event for the development of allergic diseases, together with the recognition that some chemoattractants are responsible for the recruitment of both Th2 cells and other effector cells of allergic inflammation, can provide the conceptual basis for the development of new therapeutic strategies in allergic conditions.

Cutting edge: polarized Th cell response induction by transferred antigen-pulsed dendritic cells is dependent on IL-4 or IL-12 production by recipient cells

To assess the influence of dendritic cell (DC) production of polarizing cytokines on Th2 and Th1 development we transferred Ag-pulsed DC generated from wild-type, IL-4(-/-), or IL-12(-/-) mice into wild-type, IL-4(-/-), or IL-12(-/-) recipients. We found that DC IL-4 was not necessary for Th2 induction and that, surprisingly, DC IL-12 was not an absolute requirement for Th1 development. However, DC IL-12 production facilitated optimal Th1 response development. Critically, recipient ability to produce IL-4 or IL-12 was essential for either Th2 or Th1 development. These data help delineate the source and importance of IL-4 and IL-12 in the process of induction of polarized T cell responses by DC.

Indirect IL-4 pathway in type 1 immunity

Recall Ag-specific IL-4 was detected in the spleen and in the blood, but not in lymph nodes of mice in which polarized type 1 immunity was induced. This IL-4 was not produced by T cells, but soluble factors secreted by the recall Ag-activated T cells, including IL-3, triggered cells of the innate immune system, primarily mast cells, to secrete IL-4. This notion has profound implications for immunodiagnostics: the detection of apparently recall Ag-specific IL-4 does not necessarily reflect the presence of Th2 or Th0 memory T cells with long-term cytokine commitment as is of interest for assessing adoptive immunity. We found that in vivo the indirect IL-4 pathway did not suffice to trigger IgE isotype switching, but promoted IgG1 production and inhibited type 1 T cell differentiation. Therefore, the indirect IL-4 pathway can explain partial type 2 immune response phenotypes in vivo in face of unipolar Th1 T cell immunity. The representation of mast cells in different tissues may explain why immune responses in certain organs are more type 2 biased. Therefore, the indirect pathway of IL-4 production represents a novel type of interaction between the innate and the adoptive immune system that can contribute to the outcome of host defense and immune pathology.

Histamine regulates cytokine production in maturing dendritic cells, resulting in altered T cell polarization

Atopic diseases such as allergy and asthma are characterized by increases in Th2 cells and serum IgE antibodies. The binding of allergens to IgE on mast cells triggers the release of several mediators, of which histamine is the most prevalent. Here we show that histamine, together with a maturation signal, acts directly upon immature dendritic cells (iDCs), profoundly altering their T cell polarizing capacity. We demonstrate that iDCs express two active histamine receptors, H1 and H2. Histamine did not significantly affect the LPS-driven maturation of iDCs with regard to phenotypic changes or capacity to prime naive T cells, but it dramatically altered the repertoire of cytokines and chemokines secreted by mature DCs. In particular, histamine, acting upon the H2 receptor for a short period of time, increased IL-10 production and reduced IL-12 secretion. As a result, histamine-matured DCs polarized naive CD4(+) T cells toward a Th2 phenotype, as compared with DCs that had matured in the absence of histamine. We propose that the Th2 cells favor IgE production, leading to increased histamine secretion by mast cells, thus creating a positive feedback loop that could contribute to the severity of atopic diseases.

The roles of interleukin-1 and interleukin-1 receptor antagonist in antigen-specific immune responses

Despite evidence that interleukin (IL)-1 promotes the proliferation of some T helper 2 (Th2) cell clones in vitro, the physiological role of IL-1 in the regulation of antigen-specific immune responses remains undefined. Using a liposome-DNA delivery system, we transiently expressed IL-1 receptor antagonist (IL-1Ra) to suppress IL-1 functions at the site of the antigen-specific primary immune response. Our data indicate, for the first time, that IL-1Ra downregulates antigen-specific IL-4 and IgE responses, with concomitant enhancement of interferon-gamma and IgG2a responses in vivo. In addition, IL-1 can promote Th2 development in an IL-4-independent manner in vitro. Thus, the balance between endogenous IL-1 and IL-1Ra during the primary immune response can be an important factor in determining the antigen-specific effector function of T cells.

T(H)1 and T(H)2 cells: a historical perspective

Demonstration of the existence and functions of T helper (T(H))1 and T(H)2 cells has had an enormous impact on basic and applied immunology. T(H)1 and T(H)2 cells have a crucial role in balancing the immune response. In this article, I attempt to trace the historical events contributing to the development of the T(H)1/T(H)2 concept, the current state of play, and briefly discuss the future prospects for the field.

The IL-4 production capability of different strains of naive CD4(+) T cells controls the direction of the T(h) cell response

The qualitative nature of an immune response raised against infectious pathogens depends upon the phenotypes of T(h) cell subsets, which secrete distinct types of cytokines. Genetic background is known to greatly influence the nature of the T(h) cell response. However, the precise nature of this influence still remains unclear. In the present study, we demonstrate that CD62L(+), CD44(low) and CD4(+) naive T cells from BALB/c mice are capable of producing significant amounts of IL-4, while naive T cells from B10.D2 mice exhibit no IL-4 production. The addition of exogenous IL-4 into the B10.D2 induction culture recovered T(h)2 development, thereby indicating that the potential of naive T cells to secrete IL-4 at primary activation is likely to substantially influence development of T(h)2. Regulation of the IL-4 gene in naive T cells differs from that in cells committed towards becoming T(h)2 cells, based on the observation that naive T cells from STAT6-deficient mice having a BALB/c background produce detectable amounts of IL-4. The IL-4 promoter region was found to be equally histone acetylated in both BALB/c and B10.D2 naive T cells by primary TCR activation. Interestingly, the expression levels of transcription factors NF-AT and GATA-3, which regulate promoter activity, differ between BALB/c and B10.D2 cells. These results suggest that the differences in expression level between the two transcriptional factors may affect the potential of naive T cells to secrete IL-4, which may subsequently influence the development of T(h) cell phenotypes.

Histamine regulates cytokine production in maturing dendritic cells, resulting in altered T cell polarization

Atopic diseases such as allergy and asthma are characterized by increases in Th2 cells and serum IgE antibodies. The binding of allergens to IgE on mast cells triggers the release of several mediators, of which histamine is the most prevalent. Here we show that histamine, together with a maturation signal, acts directly upon immature dendritic cells (iDCs), profoundly altering their T cell polarizing capacity. We demonstrate that iDCs express two active histamine receptors, H1 and H2. Histamine did not significantly affect the LPS-driven maturation of iDCs with regard to phenotypic changes or capacity to prime naive T cells, but it dramatically altered the repertoire of cytokines and chemokines secreted by mature DCs. In particular, histamine, acting upon the H2 receptor for a short period of time, increased IL-10 production and reduced IL-12 secretion. As a result, histamine-matured DCs polarized naive CD4(+) T cells toward a Th2 phenotype, as compared with DCs that had matured in the absence of histamine. We propose that the Th2 cells favor IgE production, leading to increased histamine secretion by mast cells, thus creating a positive feedback loop that could contribute to the severity of atopic diseases.