Thymic stromal lymphopoietin as a key initiator of allergic airway inflammation in mice

Genomic profiling of high-risk acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a heterogeneous disease comprising multiple subtypes with different genetic alterations and responses to therapy. Recent genome-wide profiling studies of ALL have identified a number of novel genetic alterations that target key cellular pathways in lymphoid growth and differentiation and are associated with treatment outcome. Notably, genetic alteration of the lymphoid transcription factor gene IKZF1 is a hallmark of multiple subtypes of ALL with poor prognosis, including BCR-ABL1-positive lymphoid leukemia and a subset of 'BCR-ABL1-like' ALL cases that, in addition to IKZF1 alteration, harbor genetic mutations resulting in aberrant lymphoid cytokine receptor signaling, including activating mutations of Janus kinases and rearrangement of cytokine receptor-like factor 2 (CRLF2). Recent insights from genome-wide profiling studies of B-progenitor ALL and the potential for new therapeutic approaches in high-risk disease are discussed.

Modeling asthma in mice: what have we learned about the airway epithelium?

Clinical reports of areas of damaged airway epithelium associated with shed epithelial cells in bronchoalveolar lavage fluid, aberrant epithelial repair processes, and altered cytokine and growth factor release have highlighted some fundamental differences between the airway epithelium in individuals with and without asthma. However, the consequences of these epithelial changes are not clearly defined, and may be difficult to assess in the clinic. In this Review, we answer the two questions. (1) What in vivo models and methods have been used to inform us about airway epithelium damage, repair, and immune responses? Our response focuses on genetic influences as well as allergen exposure, environmental/chemical, and mechanical models. (2) How can we improve on existing mouse models to understand changes in airway epithelium biology in asthma? In answering the second question, we include exciting recent studies that have combined multiple exposure methods and/or epithelium-centric outcome measurements. By addressing these two questions, we propose that future interrogation of epithelial responses of both existing and nascent mouse models may provide greater understanding of the mechanisms underlying airway inflammation and remodeling in asthma with hope of generating novel therapeutic targets.

Vitamin D3 attenuates Th2 responses to Aspergillus fumigatus mounted by CD4+ T cells from cystic fibrosis patients with allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is caused by a dominant Th2 immune response to antigens derived from the opportunistic mold Aspergillus, most commonly Aspergillus fumigatus. It occurs in 4%-15% of patients with cystic fibrosis (CF); however, not all patients with CF infected with A. fumigatus develop ABPA. Therefore, we compared cohorts of A. fumigatus-colonized CF patients with and without ABPA to identify factors mediating tolerance versus sensitization. We found that the costimulatory molecule OX40 ligand (OX40L) was critical in driving Th2 responses to A. fumigatus in peripheral CD4+ T cells isolated from patients with ABPA. In contrast, CD4+ T cells from the non-ABPA cohort did not mount enhanced Th2 responses in vitro and contained a higher frequency of TGF-beta-expressing regulatory T cells. Heightened Th2 reactivity in the ABPA cohort correlated with lower mean serum vitamin D levels. Further, in vitro addition of 1,25 OH-vitamin D3 substantially reduced DC expression of OX40L and increased DC expression of TGF-beta. This in vitro treatment also resulted in increased Treg TGF-beta expression and reduced Th2 responses by CD4+ T cells from patients with ABPA. These data provide rationale for a therapeutic trial of vitamin D to prevent or treat ABPA in patients with CF.

Programming dendritic cells to induce T(H)2 and tolerogenic responses

A fundamental puzzle in immunology is how the immune system decides what types of immune responses to launch against different stimuli. Although much is known about control of T helper type 1 (T(H)1) and T(H)17 responses, the mechanisms that initiate T(H)2 and T regulatory (T(reg)) responses remain obscure. Emerging studies suggest a fundamental role for the innate immune system, particularly dendritic cells (DCs), in this process. We review these studies, and suggest that the innate control of T(H)2 and T(reg) responses can be viewed as different hierarchies of organization, in which DCs, their innate receptors and signaling networks, and their interactions with other cells and local microenvironments represent different levels of the hierarchy.

Thymic stromal lymphopoietin-activated invariant natural killer T cells trigger an innate allergic immune response in atopic dermatitis

BACKGROUND

Although invariant natural killer T (iNKT) cells have been shown to play a critical role in the pathogenesis of asthma, the role of iNKT cells in atopic dermatitis (AD) has not been well evaluated.

OBJECTIVE

We investigated whether iNKT cells in patients with AD increased and whether iNKT cells were activated by thymic stromal lymphopoietin (TSLP), which is highly expressed in keratinocytes of AD.

METHODS

We assessed the population of iNKT cells in PBMCs of patients with AD and healthy controls (HCs) using flow cytometry. Immunohistochemistry was used to evaluate iNKT cells and TSLP expression in AD and HC skin. We also evaluated whether iNKT cells expressed the TSLP receptor, the effects of TSLP on iNKT cells, and iNKT cell-dendritic cell interactions in a TSLP-rich environment.

RESULTS

There were more iNKT cells among PBMCs of patients with moderate to severe AD than mild AD (P < .05) and HC (P < .001). The number of iNKT cells was significantly larger in severe AD skin lesions than in mild (P < .001) or moderate AD skin lesions (P < .05). TSLP expression increased in lesional skin (P < .001) but not in the sera of patients with AD (P = .729) compared with HC. iNKT cells expressed TSLP receptor protein and mRNA. TSLP directly activated iNKT cells to secrete IL-4 and IL-13, and the concurrent addition of dendritic cells further activated IFN-gamma expression.

CONCLUSION

Increased iNKT cells activated by TSLP, especially in patients with severe AD, might play an essential role in the innate allergic immune response in AD.

The many paths to asthma: phenotype shaped by innate and adaptive immunity

Asthma is a very complex and heterogeneous disease that is characterized by airway inflammation and airway hyper-reactivity (AHR). The pathogenesis of asthma is associated with environmental factors, many cell types, and several molecular and cellular pathways. These include allergic, non-allergic and intrinsic pathways, which involve many cell types and cytokines. Animal models of asthma have helped to clarify some of the underlying mechanisms of asthma, demonstrating the importance of T helper type 2 (T(H)2)-driven allergic responses, as well as of the non-allergic and intrinsic pathways, and contributing to understanding of the heterogeneity of asthma. Further study of these many pathways to asthma will greatly increase understanding of the distinct asthma phenotypes, and such studies may lead to new therapies for this important public health problem.

Autoimmunity and mast cell-related diseases

Allergy and autoimmunity are complex inflammatory processes caused by dysregulation of the immune system. There are select situations in which allergy and autoimmunity coexist pathologically. Traditionally considered unrelated, recent evidence suggests unexpected roles for allergic mediators in several autoimmune diseases. This review presents updated evidence for allergic mediators in several autoimmune diseases, as well as autoimmune phenomena in mast cell-related conditions. We will describe the concomitant manifestation of these conditions in patients and in animal models. The involvement of the main effectors of the immune system - mast cells, T lymphocytes, antibodies and cytokines - in both conditions is also discussed.

Signal transduction by the atopy-associated human thymic stromal lymphopoietin (TSLP) receptor depends on Janus kinase function

Thymic stromal lymphopoietin (TSLP) is an interleukin-(IL)-7-like cytokine with emerging pathological importance for the development of atopic diseases such as allergic asthma bronchiale. The TSLP receptor (TSLPR), a heterodimeric type I cytokine receptor, shares the IL-7R alpha-subunit with the IL-7 receptor system. The specific TSLPR alpha-chain shows similarities with the gammac receptor chain, but has some unusual features within the receptor family in both its ligand-binding and cytoplasmic domain. The murine TSLPR signals via the signal transducers and activators of transcription STAT5 and STAT3, but is unique among cytokine receptors in that it activates STATs without the involvement of Janus (JAK) tyrosine kinases, but instead utilizes the Src type kinase Tec. Here, we show by Western blotting and reporter gene experiments in combination with the application of a specific JAK inhibitor that the human TSLP receptor, in contrast, requires the function of JAK1 and JAK2 for STAT activation. Moreover, we demonstrate that the human TSLPR mediates gene regulation not only through STAT5 and STAT3 but has also the potential to mediate transcription via STAT1. Our work should help to understand more thoroughly how TSLP triggers inflammatory responses in the course of atopic diseases.

Alarming dendritic cells for allergic sensitization

Allergic patients mount a Th2 response to common allergens, like house dust mite (HDM), pollens, molds and animal dander. Most inhaled antigens are immunologically inert, however if these antigens are accompanied by microbial or endogenous danger patterns (alarmins), they can be recognized by inflammatory cells. Dendritic cells are the most potent antigen presenting cells, which express a wide variety of receptors on their cell surface, recognizing these microbial patterns, damage induced molecules and cytokines. Dendritic cells become reporters of the microenvironment if exposed to the allergen, subsequently migrating to the draining lymph nodes where they activate naïve T lymphocytes. Dendritic cells could also be indirectly activated by epithelial cells, which express various receptors and secrete a variety of cytokines early after allergen exposure. Upon HDM exposure these cells secrete chemokines to attract monocytes and immature dendritic cells, and GM-CSF, TSLP and IL-33 to activate dendritic cells, mast cells and basophils. Danger signals which alert dendritic cells and epithelial cells comprise many proteins and molecules, contributing to an enhanced immune response to inhaled allergens. This review focuses on the role of dendritic cells and alarmins in the sensitization to inhaled allergens in allergic asthma.

Thymic stromal lymphopoietin receptor-mediated IL-6 and CC/CXC chemokines expression in human airway smooth muscle cells: role of MAPKs (ERK1/2, p38, and JNK) and STAT3 pathways

Thymic stromal lymphopoietin (TSLP) plays a pivotal role in allergic diseases such as asthma, chronic obstructive pulmonary disease, and atopic dermatitis. Enhanced TSLP expression has been detected in asthmatic airways that correlated with both the expression of Th2-attracting chemokines and with disease severity. Although cumulative evidence suggests that human airway smooth muscle (HASM) cells can initiate or perpetuate the airway inflammation by secreting a variety of inflammatory cell products such as cytokines and chemokines, the role of TSLP in this pathway is not known. In the current study, we sought to investigate whether HASM cells express the TSLP receptor (TSLPR) and whether it is functional. We first demonstrated that primary HASM cells express the transcript and protein of both TSLPR subunits (TSLPR and IL-7Ralpha). Functionally, TSLPR-mediated HASM activation induced a significant increase in CXC (IL-8/CXCL8), CC (eotaxin-1/CCL11) chemokines, and proinflammatory cytokine IL-6 expression. Furthermore, using biochemical and genetic approaches, we found that TSLP-induced proinflammatory gene expression in HASM involved the transcriptional mechanisms, MAPKs (ERK1/2, p38, and JNK), and STAT3 activation. Finally, TSLPR immunoreactivity in bronchial sections from mild allergic asthmatics suggested the potential in vivo TSLP targeting of HASM. Altogether, our data suggest that the TSLPR-mediated HASM activation induces proinflammatory cytokine and chemokines release that may facilitate inflammatory immune cells recruitment in airways. In addition, it may be inferred that TSLPR is involved in the pathogenesis of allergic asthma through the activation of HASM cells by TSLP.

Sensing the outside world: TSLP regulates barrier immunity

Thymic stromal lymphopoietin (TSLP) is an interleukin 7 (IL-7)-like cytokine originally characterized by its ability to promote the activation of B cells and dendritic cells (DCs). Subsequent studies have shown that TSLP promotes T helper type 2 (TH2) cell responses associated with immunity to some helminth parasites and the pathogenesis of many inflammatory diseases, including atopic dermatitis and asthma. This review will focus on recent findings indicating that in addition to influencing B cell and DC function, TSLP can promote TH2 cytokine-associated inflammation by directly promoting the effector functions of CD4+ TH2 cells, basophils and other granulocyte populations while simultaneously limiting the expression of DC-derived proinflammatory cytokines and promoting regulatory T cell responses in peripheral tissues.

Interactions between innate and adaptive immunity in asthma pathogenesis: new perspectives from studies on acute exacerbations

Asthma is a complex multigenic disease. The most frequently encountered form is atopic asthma, which is at its highest prevalence during childhood/young adulthood, and this represents the main focus of this review. The primary risk factor for atopic asthma is sensitization to perennial aeroallergens resulting from a failure to generate protective immunologic tolerance. This tolerance process is orchestrated by airway mucosal dendritic cells and normally results in programming of regulatory T cells, which inhibit activation of the T(H)2 memory cells that, among other activities, drive IgE production and prime the effector populations responsible for IgE-mediated tissue damage. Emerging evidence highlights the complexity of this process, in particular the iterative nature of the underlying interactions between innate and adaptive immune mechanisms in which virtually every signal emanating from one cellular compartment provokes an answering response from the other. To further complicate this picture, the local mesenchyme can also interpose signals to fine tune immune responses to optimally meet local microenvironmental needs. Perturbation of the balance between these interlinked innate and adaptive immune pathways is increasingly believed to be the basis for disease expression, and in the specific case of atopic asthma, the prototypic example of this (discussed below) is acute exacerbations triggered by viral infections.

Fas-activated serine/threonine phosphoprotein promotes immune-mediated pulmonary inflammation

We generated Fas-activated serine threonine phosphoprotein (FAST)-deficient mice (FAST(-/-)) to study the in vivo role of FAST in immune system function. In a model of house dust mite-induced allergic pulmonary inflammation, wild type mice develop a mixed cellular infiltrate composed of eosinophils, lymphocytes, and neutrophils. FAST(-/-) mice develop airway inflammation that is distinguished by the near absence of neutrophils. Similarly, LPS-induced alveolar neutrophil recruitment is markedly reduced in FAST(-/-) mice compared with wild type controls. This is accompanied by reduced concentrations of cytokines (TNF-alpha and IL-6 and -23) and chemoattractants (MIP-2 and keratinocyte chemoattractant) in bronchoalveolar lavage fluids. Because FAST(-/-) neutrophils exhibit normal chemotaxis and survival, impaired neutrophil recruitment is likely to be due to reduced production of chemoattractants within the pulmonary parenchyma. Studies using bone marrow chimeras implicate lung resident hematopoietic cells (e.g., pulmonary dendritic cells and/or alveolar macrophages) in this process. In conclusion, our results introduce FAST as a proinflammatory factor that modulates the function of lung resident hematopoietic cells to promote neutrophil recruitment and pulmonary inflammation.

How are T(H)2-type immune responses initiated and amplified?

CD4(+) T helper (T(H)) cells have crucial roles in orchestrating adaptive immune responses. T(H)2 cells control immunity to extracellular parasites and all forms of allergic inflammatory responses. Although we understand the initiation of the T(H)2-type response in tissue culture in great detail, much less is known about T(H)2 cell induction in vivo. Here we discuss the involvement of allergen- and parasite product-mediated activation of epithelial cells, basophils and dendritic cells and the functions of the cytokines interleukin-4 (IL-4), IL-25, IL-33 and thymic stromal lymphopoietin in the initiation and amplification of T(H)2-type immune responses in vivo.

Effects of diisononyl phthalate on atopic dermatitis in vivo and immunologic responses in vitro

BACKGROUND

Diisononyl phthalate (DINP), a principal plasticizer in many polyvinyl chloride products, has been shown to have an adjuvant effect on immunoglobulin (Ig) production in mice. However, the effects of DINP on allergic diseases have not been fully elucidated.

OBJECTIVES

In the present study we investigated the effects of DINP on atopic dermatitis (AD)-like skin lesions induced by Dermatophagoides pteronyssinus (Dp) in atopic-prone NC/Nga mice.

METHODS

Mice were injected intradermally with Dp on their ears and were exposed to DINP (0, 0.15, 1.5, 15, or 150 mg/kg/day) intraperitoneally. We evaluated clinical scores, ear thickening, histologic findings, protein expression of cytokines/chemokines in the ear, and serum levels of Ig and histamine. Furthermore, we investigated the effects of DINP on bone-marrow-derived dendritic cells (BMDCs) or splenocytes in vitro. After exposure to DINP (0-100 microM), cells were evaluated for phenotype and function.

RESULTS

DINP aggravated AD-like skin lesions related to Dp. The aggravation was consistent with eosinophilic inflammation, mast cell degranulation, and thymic stromal lymphopoietin (TSLP) expression in the ear. DINP enhanced the expression of cell surface activation markers on BMDCs and their production of TARC/CCL17 (thymus- and activation-regulated chemokine) and MDC/CCL22 (macrophage-derived chemokine), as well as their capacity to stimulate Dp-specific T-cell proliferation. DINP also enhanced interleukin-4 production and Dp-stimulated proliferation of splenocytes.

CONCLUSIONS

DINP can aggravate AD-like skin lesions related to Dp. The mechanisms of the aggravation might be mediated, at least partly, through the TSLP-related activation of dendritic cells and by direct or indirect activation of the immune cells.

Molecular cloning and characterization of equine thymic stromal lymphopoietin

Thymic stromal lymphopoietin (TSLP) is a novel cytokine that plays a central role in T helper 2 (Th2) cell differentiation and allergic inflammation. It is predominantly expressed by epithelial cells, and its expression is increased in patients with atopic dermatitis and asthma. Mice overexpressing TSLP in the skin develop allergic dermatitis and mice overexpressing TSLP in lungs develop asthma-like disease. However, it is not known whether TSLP plays an important role in equine allergies. Therefore, we cloned and sequenced the complete translated region of equine TSLP gene and measured its expression in various tissues. The equine TSLP gene is organized in 4 exons and encodes a protein of 143 amino acids, which has 62% amino acid identity with human TSLP.

Increased muscarinic receptor activity of airway smooth muscle isolated from a mouse model of allergic asthma

The mechanisms leading to airway hyper-responsiveness (AHR) in asthma are still not fully understood. AHR could be produced by hypersensitivity of the airway smooth muscle or hyperreactivity of the airways. This study was conducted to ascertain whether AHR in a murine model of asthma is produced by changes at the level of the airway smooth muscle. Airway smooth muscle responses were characterised in vitro in isolated trachea spirals from naive mice and from an acute ovalbumin (OVA) challenge model of allergic asthma. AHR was investigated in vivo in conscious, freely moving mice. Inflammatory cell influx into the lungs and antibody responses to the antigen were also measured. In vitro study of tracheal airway smooth muscle from naïve mice demonstrated concentration-related contractions to methacholine and 5-HT, but no responses to histamine or adenosine or its stable analogue, 5'-N-ethyl-carboxamidoadenosine. The contractions to 5-HT were inhibited by ketanserin and alosetron indicating involvement of 5-HT(2A) and 5-HT(3) receptors, respectively. In an acute model of allergic asthma, OVA-treated mice were shown to be atopic by inflammatory cell influx to the lungs after OVA challenge, increases in total IgE and OVA-specific IgG levels and contractions to OVA in isolated trachea. In the asthmatic model, AHR to methacholine was demonstrated in conscious, freely moving mice in vivo and in isolated trachea in vitro 24 and 72h after OVA challenge. No AHR in vitro was seen for 5-HT, histamine or adenosine. These results suggest that, in our mouse model of asthma, changes occur at the level of the muscarinic receptor transduction pathway of coupling to airway smooth muscle contraction. These changes are maintained when tissues are removed from the inflammatory environment and for at least 3 days.

Thymic stromal lymphopoietin-induced human asthmatic airway epithelial cell proliferation through an IL-13-dependent pathway

BACKGROUND

Thymic stromal lymphopoietin (TSLP) plays a pivotal role in the initiation of allergic airway inflammation. This cytokine is produced by several cell types, including human epithelial cells.

OBJECTIVE

We sought to determine the effect of TSLP on proliferation and repair of epithelial cells isolated from asthmatic patients and healthy subjects.

METHODS

Expression of TSLP receptor (TSLPR) and its response to inhaled corticosteroids was evaluated on bronchial biopsy specimens of healthy control subjects and asthmatic patients by means of immunohistochemistry. TSLPR, TSLP, and IL-13 mRNA expression was determined by means of quantitative PCR, and protein expression was measured by means of ELISA and Western blotting in epithelial cells isolated from asthmatic subjects compared with those isolated from healthy control subjects. The effect of TSLP on cell proliferation and wound healing was performed.

RESULTS

TSLPR is expressed by bronchial epithelial cells in bronchial biopsy specimens and in cultured cells, with no difference between asthmatic patients and healthy control subjects. Inhaled corticosteroids did not affect this expression. TSLP mRNA and protein levels were significantly higher in epithelial cells isolated from asthmatic patients compared with those from healthy control subjects. TSLP stimulated IL-13 production by bronchial epithelial cells. TSLP induced airway epithelial cell proliferation and enhanced epithelial injury repair. This effect was abrogated with IL-13 neutralization.

CONCLUSIONS

Our data indicate that epithelial cells express TSLPR and that TSLP induces bronchial epithelial cell proliferation and increases injury repair through IL-13 production. This suggests that TSLP and IL-13 loops play a homeostatic role on epithelial cell proliferation and repair.

TSLP directly impairs pulmonary Treg function: association with aberrant tolerogenic immunity in asthmatic airway

Background

Even though thymic stromal lymphopoietin (TSLP) has been implicated in the development of allergic inflammation, its influence on immune tolerance mediated by regulatory T cells (Treg) have not been explored. We aimed to dissect the influence of TSLP on immunosuppressive activities of Treg and its potential consequences in human allergic asthma.

Methods

In vitro culture system was utilized to study the effects of TSLP on human Treg. The functional competency of pulmonary Treg from a cohort of 15 allergic asthmatic, 15 healthy control, and 15 non-allergic asthmatic subjects was also evaluated by suppression assays and flow cytometric analysis.

Results

Activated pulmonary Treg expressed TSLP-R and responded to TSLP-mediated activation of STAT5. TSLP directly and selectively impaired IL-10 production of Treg and inhibited their suppressive activity. In human allergic asthma, pulmonary Treg exhibited a significant decrease in suppressive activity and IL-10 production compared to healthy control and non-allergic asthmatic counterparts. These functional alterations were associated with elevated TSLP expression in bronchoaveolar lavage fluid (BAL) of allergic asthmatic subjects. Furthermore, allergic asthmatic BAL could suppress IL-10 production by healthy control pulmonary Treg in a TSLP-dependent manner.

Conclusions

These results provide the first evidences for a direct role of TSLP in the regulation of suppressive activities of Treg. TSLP mediated inhibition of Treg function might present a novel pathologic mechanism to dampen tolerogenic immune responses in inflamed asthmatic airway.

Thymic stromal lymphopoietin

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine expressed in skin, gut, lungs, and thymus. TSLP signals via a TSLP receptor (TSLPR), a heterodimer of the IL-7 receptor alpha chain and the TSLPR chain. The TSLPR chain is closely related to the common receptor gamma chain that is expressed on a wide range of cell types in the adaptive and innate immune system. TSLP exerts a profound influence on the polarization of dendritic cells to drive T helper (Th) 2 cytokine production. TSLP also directly promotes T-cell proliferation in response to T-cell receptor activation and Th2 cytokine production and supports B-cell expansion and differentiation. TSLP further amplifies Th2 cytokine production by mast cells and natural killer T cells. These properties confer on TSLP a critical role in driving Th2-mediated inflammation. This role is supported by the finding that TSLP expression is upregulated in keratinocytes of atopic dermatitis skin lesions and in bronchial epithelial cells in asthma.

TLR4 signaling in stromal cells is critical for the initiation of allergic Th2 responses to inhaled antigen

Allergic asthma is an inflammatory lung disease driven by Th2. We have shown that both Th1 and Th2 sensitization to inhaled OVA depend on the presence and concentration of LPS, where high concentrations (LPS(hi)) induce Th1 and low concentrations (LPS(lo)), Th2. Stromal cells (SCs), such as airway SCs, exacerbate established airway disease; however, little is known about their role early during sensitization. In this study, using bone marrow chimeric mice to restrict TLR4 signaling to either the SC compartment (SC(+)HPC(-)) or the hematopoietic cell (HPC) compartment (SC(-)HPC(+)), we report that HPC TLR4 is necessary and sufficient for Th1 sensitization to OVA-LPS(hi), whereas TLR4 in both compartments is required for Th2 sensitization to OVA-LPS(lo). Surprisingly, although SC(+)HPC(-) mice were unable to generate a Th1 response to OVA-LPS(hi), they instead mounted a robust Th2 response, indicating that in the presence of higher concentrations of LPS, SC TLR4 is sufficient for Th2 sensitization. We show that the SC TLR4 response to LPS leads to induction of Th2-inducing dendritic cells that upregulate Notch ligand Jagged-1 but not Delta-4. Furthermore, airway SCs upregulate thymic stromal lymphopoietin in response to exposure to both OVA-LPS(lo) and OVA-LPS(hi). These studies demonstrate that SC TLR4 signaling is critically involved in Th2 but not Th1 sensitization to inhaled Ag.

The influence of TSLP on the allergic response

Exposure to allergens first occurs at body surfaces in direct contact with the environment such as the skin, airways, and gastrointestinal tract, and compelling evidence suggests that allergic inflammatory responses are profoundly influenced by the products of epithelial cells located at these sites. One such product is thymic stromal lymphopoietin (TSLP), which is capable of affecting multiple cell lineages involved in allergic reactions. In this review we discuss recent work that has provided insight into the role TSLP plays in both aberrant and protective allergic inflammatory responses, as well as regulation, associations with disease, sources, and functions of this important cytokine.

Transcriptional regulation of Th2 cell differentiation

CD4 T helper 2 (Th2) cells have critical functions in immune responses against extracellular parasites and are involved in asthma and other allergic diseases. The differentiation of naïve CD4 T cells into Th2 cells is initiated from T-cell receptor and cytokine-mediated signaling followed by upregulation of GATA3 and activation of signal transducer and activator of transcription 5 (STAT5), two indispensable events for this differentiation process. In this review, regulation of GATA3 expression and STAT5 activation and functions of these two transcription factors in inducing the expression of Th2 cytokines, cytokine receptors as well as epigenetic modification at Th2 cytokine locus are summarized. Furthermore, I present positive and negative regulatory networks important for Th2 cell commitment, selective growth of committed Th2 cells and suppression of alternative lineage fates. Finally, the difference between in vitro and in vivo Th2 differentiation is discussed.

Targeting allergen to FcgammaRI reveals a novel T(H)2 regulatory pathway linked to thymic stromal lymphopoietin receptor

BACKGROUND

The molecule H22-Fel d 1, which targets cat allergen to FcgammaRI on dendritic cells (DCs), has the potential to treat cat allergy because of its T-cell modulatory properties.

OBJECTIVE

We sought to investigate whether the T-cell response induced by H22-Fel d 1 is altered in the presence of the T(H)2-promoting cytokine thymic stromal lymphopoietin (TSLP).

METHODS

Studies were performed in subjects with cat allergy with and without atopic dermatitis. Monocyte-derived DCs were primed with H22-Fel d 1 in the presence or absence of TSLP, and the resulting T-cell cytokine repertoire was analyzed by flow cytometry. The capacity for H22-Fel d 1 to modulate TSLP receptor expression on DCs was examined by flow cytometry in the presence or absence of inhibitors of Fc receptor signaling molecules.

RESULTS

Surprisingly, TSLP alone was a weak inducer of T(H)2 responses irrespective of atopic status; however, DCs coprimed with TSLP and H22-Fel d 1 selectively and synergistically amplified T(H)2 responses in highly atopic subjects. This effect was OX40 ligand independent, pointing to an unconventional TSLP-mediated pathway. Expression of TSLP receptor was upregulated on atopic DCs primed with H22-Fel d 1 through a pathway regulated by FcgammaRI-associated signaling components, including src-related tyrosine kinases and Syk, as well as the downstream molecule phosphoinositide 3-kinase. Inhibition of TSLP receptor upregulation triggered by H22-Fel d 1 blocked TSLP-mediated T(H)2 responses.

CONCLUSION

Discovery of a novel T(H)2 regulatory pathway linking FcgammaRI signaling to TSLP receptor upregulation and consequent TSLP-mediated effects questions the validity of receptor-targeted allergen vaccines.

Dibutyl phthalate-induced thymic stromal lymphopoietin is required for Th2 contact hypersensitivity responses

Thymic stromal lymphopoietin (TSLP) is an IL-7-related cytokine, produced by epithelial cells, that has been linked to atopic dermatitis and asthma; however, it remains unclear how TSLP shapes the adaptive immune response that causes these allergic disorders. In this study, we demonstrate a role for TSLP in a Th2 model of contact hypersensitivity in mice. TSLP is required for the development of Th2-type contact hypersensitivity induced by the hapten FITC in combination with the sensitizing agent dibutyl phthalate. TSLPR-deficient mice exhibited a dramatically reduced response, including markedly reduced local infiltration by eosinophils, Th2 cytokine production, and serum IgE levels, following FITC sensitization and challenge. The reduced response by TSLPR-deficient mice is likely due to decreased frequency and reduced T cell stimulatory function of skin-derived Ag-bearing FITC(+)CD11c(+) dendritic cells in draining lymph nodes following FITC sensitization. These data suggest that skin-derived dendritic cells are direct or indirect targets of TSLP in the development of type 2 immune responses in the skin, where TSLP drives their maturation, accumulation in skin draining lymph nodes, and ability to induce proliferation of naive allergen-specific T cells.

Atopic dermatitis-like disease and associated lethal myeloproliferative disorder arise from loss of Notch signaling in the murine skin

Background

The Notch pathway is essential for proper epidermal differentiation during embryonic skin development. Moreover, skin specific loss of Notch signaling in the embryo results in skin barrier defects accompanied by a B-lymphoproliferative disease. However, much less is known about the consequences of loss of Notch signaling after birth.

Methodology and Principal Findings

To study the function of Notch signaling in the skin of adult mice, we made use of a series of conditional gene targeted mice that allow inactivation of several components of the Notch signaling pathway specifically in the skin. We demonstrate that skin-specific inactivation of Notch1 and Notch2 simultaneously, or RBP-J, induces the development of a severe form of atopic dermatitis (AD), characterized by acanthosis, spongiosis and hyperkeratosis, as well as a massive dermal infiltration of eosinophils and mast cells. Likewise, patients suffering from AD, but not psoriasis or lichen planus, have a marked reduction of Notch receptor expression in the skin. Loss of Notch in keratinocytes induces the production of thymic stromal lymphopoietin (TSLP), a cytokine deeply implicated in the pathogenesis of AD. The AD-like associated inflammation is accompanied by a myeloproliferative disorder (MPD) characterized by an increase in immature myeloid populations in the bone marrow and spleen. Transplantation studies revealed that the MPD is cell non-autonomous and caused by dramatic microenvironmental alterations. Genetic studies demontrated that G-CSF mediates the MPD as well as changes in the bone marrow microenvironment leading to osteopenia.

Significance

Our data demonstrate a critical role for Notch in repressing TSLP production in keratinocytes, thereby maintaining integrity of the skin and the hematopoietic system.

The role of thymic stromal lymphopoietin in allergic inflammation and chronic obstructive pulmonary disease

Thymic stromal lymphopoietin (TSLP) primes dendritic cells to promote a Th2 inflammatory response. Its action is mediated by a heterodimeric receptor which consists of the interleukin-7 receptor alpha chain and the TSLP receptor chain (TSLPR). TSLPR resembles the common gamma chain subunit utilized by many type 1 cytokine receptors. Normal epithelial cells, keratinocytes, and stromal cells constitutively express TSLP. Dendritic cells that are activated by TSLP promote the development of CD4(+) T cells into pro-inflammatory Th2 cells. TSLP thus plays a potentially important role in the pathogenesis of allergic inflammation in asthma and atopic dermatitis. TSLP also has direct effects on other types of cells in the bronchial mucosa. It is over-expressed in the bronchial mucosa in chronic obstructive pulmonary disease (COPD), which is traditionally described as a Th1-related disease, as well as severe asthma, which is traditionally described as a Th2-related disease. In this review we will discuss TSLP expression, function, and available and potential mechanisms in both allergic inflammation and COPD.

Distinct signal codes generate dendritic cell functional plasticity

Our adaptive immune system induces distinct responses to different pathogens because of the functional plasticity of dendritic cells (DCs); however, how DCs program unique responses remains unclear. Here, we found that the cytokine thymic stromal lymphopoietin (TSLP) potently transduced a unique T helper type 2 (T(H)2)-inducing compound signal in DCs. Whereas activation of nuclear factor kappaB (predominantly p50) drove DCs to produce OX40L to induce T(H)2 differentiation, the activation of signal transducer and activator of transcription 6 (STAT6) triggered DCs to secrete chemokines necessary for the recruitment of T(H)2 cells. In addition, TSLP signaling limited the activation of STAT4 and interferon regulatory factor 8 (IRF-8), which are essential factors for the production of the T(H)1-polarizing cytokine interleukin-12 (IL-12). By contrast, Toll-like receptor ligands and CD40 ligand did not activate STAT6 in myeloid DCs, but instead increased the abundance of STAT4 and IRF-8 to induce T(H)1 responses through the production of IL-12. Therefore, we propose that the functional plasticity of DCs relies on elaborate signal codes that are generated by different stimuli.

Epithelium: the interplay between innate and Th2 immunity

Mucosal epithelium functions not only as a physical barrier, but also as a regulator of innate and adaptive immune responses against foreign substances and microorganisms. In particular, epithelial cells have been directly implicated in Th2 responses, serving as a critical interface between innate immune responses and Th2 immunity. Emerging studies have revealed the cellular and molecular mechanisms by which the epithelium modulates Th2 responses through the production of a group of epithelial-derived Th2-driving cytokines, including interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin. These epithelial-derived Th2-driving cytokines execute a regulatory function of the epithelium on mucosal immunity by promoting Th2 responses and maintaining the balance of host immune homeostasis and defense against various pathogens. Dysregulation of these Th2-driving cytokines can lead to detrimental Th2-dependent inflammatory responses, often manifested in various forms of allergic and inflammatory diseases.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.

Intestinal bacteria and the regulation of immune cell homeostasis

The human intestine is colonized by an estimated 100 trillion bacteria. Some of these bacteria are essential for normal physiology, whereas others have been implicated in the pathogenesis of multiple inflammatory diseases including IBD and asthma. This review examines the influence of signals from intestinal bacteria on the homeostasis of the mammalian immune system in the context of health and disease. We review the bacterial composition of the mammalian intestine, known bacterial-derived immunoregulatory molecules, and the mammalian innate immune receptors that recognize them. We discuss the influence of bacterial-derived signals on immune cell function and the mechanisms by which these signals modulate the development and progression of inflammatory disease. We conclude with an examination of successes and future challenges in using bacterial communities or their products in the prevention or treatment of human disease.

Pathogenic mechanisms of allergic inflammation: atopic asthma as a paradigm

Prospective studies tracking birth cohorts over periods of years indicate that the seeds for atopic asthma in adulthood are sewn during early life. The key events involve programming of functional phenotypes within the immune and respiratory systems which determine long-term responsiveness to ubiquitous environmental stimuli, particularly respiratory viruses and aeroallergens. A crucial component of asthma pathogenesis is early sensitization to aeroallergens stemming from a failure of mucosal tolerance mechanisms during the preschool years, which is associated with delayed postnatal maturation of a range of adaptive and innate immune functions. These maturational defects also increase risk for severe respiratory infections, and the combination of sensitization and infections maximizes risk for early development of the persistent asthma phenotype. Interactions between immunoinflammatory pathways stimulated by these agents also sustain the disease in later life as major triggers of asthma exacerbations. Recent studies on the nature of these interactions suggest the operation of an infection-associated lung:bone marrow axis involving upregulation of FcERlalpha on myeloid precursor populations prior to their migration to the airways, thus amplifying local inflammation via IgE-mediated recruitment of bystander atopic effector mechanisms. The key participants in the disease process are airway mucosal dendritic cells and adjacent epithelial cells, and transiting CD4(+) effector and regulatory T-cell populations, and increasingly detailed characterization of their roles at different stages of pathogenesis is opening up novel possibilities for therapeutic control of asthma. Of particular interest is the application of genomics-based approaches to drug target identification in cell populations of interest, exemplified by recent findings discussed below relating to the gene network(s) triggered by activation of Th2-memory cells from atopics.

Immunologic messenger molecules: cytokines, interferons, and chemokines

Cytokines and chemokines are secreted proteins involved in numerous aspects of cell growth, differentiation, and activation. A prominent feature of these molecules is their effect on the immune system with regard to cell trafficking and development of immune tissue and organs. The nature of an immune response determines which cytokines are produced and ultimately whether the response is cytotoxic, humoral, cell mediated, or allergic. For this chapter, cytokines are grouped according to those that are predominantly antigen-presenting cell or T lymphocyte derived; that mediate cytotoxic, humoral, cell mediated, and allergic immunity; or that are immunosuppressive. A discussion of chemokine function and their role in cell trafficking and disease follows.

Rearrangement of CRLF2 in B-progenitor- and Down syndrome-associated acute lymphoblastic leukemia

Aneuploidy and translocations are hallmarks of B-progenitor acute lymphoblastic leukemia (ALL), but many individuals with this cancer lack recurring chromosomal alterations. Here we report a recurring interstitial deletion of the pseudoautosomal region 1 of chromosomes X and Y in B-progenitor ALL that juxtaposes the first, noncoding exon of P2RY8 with the coding region of CRLF2. We identified the P2RY8-CRLF2 fusion in 7% of individuals with B-progenitor ALL and 53% of individuals with ALL associated with Down syndrome. CRLF2 alteration was associated with activating JAK mutations, and expression of human P2RY8-CRLF2 together with mutated mouse Jak2 resulted in constitutive Jak-Stat activation and cytokine-independent growth of Ba/F3 cells overexpressing interleukin-7 receptor alpha. Our findings indicate that these two genetic lesions together contribute to leukemogenesis in B-progenitor ALL.

Intestinal effector T cells in health and disease

Crohn's disease and ulcerative colitis are the two major forms of chronic relapsing inflammatory disorders of the human intestines collectively referred to as inflammatory bowel disease (IBD). Though a complex set of autoinflammatory disorders that can be precipitated by diverse genetic and environmental factors, a feature that appears common to IBD pathogenesis is a dysregulated effector T cell response to the commensal microbiota. Due to the heightened effector T cell activity in IBD, developmental and functional pathways that give rise to these cells are potential targets for therapeutic intervention. In this review, we highlight recent advances in our understanding of effector T cell biology in the context of intestinal immune regulation and speculate on their potential clinical significance.

Biology of lung dendritic cells at the origin of asthma

Dendritic cells (DCs) initiate and maintain adaptive T helper 2 (Th2) cell responses to inhaled allergens in asthma. Various functions like antigen uptake, migration to the draining LNs, and induction of tolerance and adaptive immunity are not equally shared by all subsets of DCs, adding considerable complexity to understanding the immunology of allergic sensitization. Whereas the epithelium was initially considered solely as a physical barrier, it is now seen as a central player in controlling the function of lung DCs through release of Th2 cell-promoting cytokines. Although DCs are sufficient and necessary for induction of Th2 cell responses to many antigens, some allergens might require antigen presentation by basophils. Clinically relevant allergens, as well as environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells, basophils, and DCs. This review summarizes the recent progress on our understanding how DCs control Th2 cell immunity in the lung.

Innate cells and T helper 2 cell immunity in airway inflammation

Activated mast cells, eosinophils, and basophils infiltrate the airways of asthmatics as a result of an overexuberant T helper 2 (Th2) cell immune response that drives the production of IgE, primes mast cells and basophils, and promotes tissue eosinophilia and mast cell hyperplasia. Recent evidence demonstrates that these innate effectors can be activated outside of this classical Th2 cell paradigm and that they have additional roles in promoting the development of innate and adaptive pulmonary inflammation. There is also an appreciation for the role of airway epithelial cells in orchestrating allergic pulmonary inflammation. Emerging data from basic research highlight the involvement of many unique pathways in the inflammation triggered by complex native allergens and microbes at the airway mucosal surface. Here, we review the role of effector cells and airway epithelial cells in augmenting and, at times, bypassing traditional Th2 cell-mediated allergic inflammation.

Influence of the tissue microenvironment on Toll-like receptor expression by CD11c+ antigen-presenting cells isolated from mucosal tissues

It is recognized that functional activities of antigen-presenting cells (APCs) in mucosal tissue sites differ from those of systemic APCs; however, it is unknown whether there are further differences between APC populations residing in different mucosal sites. In this study, we directly compared murine CD11c+ APCs isolated from colon, lung, and spleen and found that APCs isolated from these tissues differ considerably in Toll-like receptor (TLR) expression and responses to in vitro TLR ligand stimulation. We also provide evidence that tissue microenvironments dictate distinct patterns of TLR expression by CD11c+ APCs in different mucosal tissues. Moreover, CD11c+ cells isolated from different tissues have varied capacities to induce the development of T helper 1 (Th1), Th2, or regulatory CD4+ T cells. Thus, unique tissue microenvironments have a significant influence on determining TLR expression by CD11c+ cells that migrate to and reside in each mucosal tissue and are likely to modulate their functional activities.

TSLP and IL-7 use two different mechanisms to regulate human CD4+ T cell homeostasis

Whether thymic stromal lymphopoietin (TSLP) directly induces potent human CD4⁺ T cell proliferation and Th2 differentiation is unknown. We report that resting and activated CD4⁺ T cells expressed high levels of IL-7 receptor a chain but very low levels of TSLP receptor (TSLPR) when compared with levels expressed in myeloid dendritic cells (mDCs). This was confirmed by immunohistology and flow cytometry analyses showing that only a subset of mDCs, with more activated phenotypes, expressed TSLPR in human tonsils in vivo. IL-7 induced strong STAT1, -3, and -5 activation and promoted the proliferation of naive CD4⁺ T cells in the presence of anti-CD3 and anti-CD28 monoclonal antibodies, whereas TSLP induced weak STAT5 activation, associated with marginally improved cell survival and proliferation, but failed to induce cell expansion and Th2 differentiation. The effect of TSLP on enhancing strong human T cell proliferation was observed only when sorted naive CD4⁺ T cells were cultured with mDCs at levels as low as 0.5%. TSLP could only induce naive CD4⁺ T cells to differentiate into Th2 cells in the presence of allogeneic mDCs. These results demonstrate that IL-7 and TSLP use different mechanisms to regulate human CD4⁺ T cell homeostasis.

The role of dendritic cells and regulatory T cells in the regulation of allergic asthma

Airways hyperresponsiveness (AHR) is one of the major clinical features of allergic airways disease including allergic asthma, however the immunological mechanisms leading to the induction and regulation of this disorder are not fully understood. In this review we will summarise the evidence of a number of studies, principally in murine models of AHR, suggesting a central role for respiratory tract dendritic cells (RTDC) in the induction of AHR through the generation of lung-homing, allergen-specific effector T cells. We will also summarise the evidence supporting a role for regulatory T cells in the attenuation of AHR and will propose that, as a counterpoint to their capacity to induce AHR, RTDC may also play a role in the attenuation of AHR through the generation of regulatory T cells (T(reg)). A better understanding of the relationship between the physiological and immunological responses to allergen-induced AHR attenuation, and particularly the role of RTDC and T(reg) in this process, will be essential for the development of new treatments and therapies.

Helminth products bypass the need for TSLP in Th2 immune responses by directly modulating dendritic cell function

Thymic stromal lymphopoietin (TSLP) is an interleukin (IL)-7-like cytokine, mainly expressed by epithelial cells, and key to the development of allergic responses. The well-documented involvement of TSLP in allergy has led to the conviction that TSLP promotes the development of inflammatory Th2 cell responses. However, we now report that the interaction of TSLP with its receptor (TSLPR) has no functional impact on the development of protective Th2 immune responses after infection with 2 helminth pathogens, Heligmosomoides polygyrus and Nippostrongylus brasiliensis. Mice deficient in the TSLP binding chain of the TSLPR (TSLPR(-/-)) exhibited normal Th2 cell differentiation, protective immunity and memory responses against these two distinct rodent helminths. In contrast TSLP was found to be necessary for the development of protective Th2 responses upon infection with the helminth Trichuris muris (T. muris). TSLP inhibited IL-12p40 production in response to T. muris infection, and treatment of TSLPR(-/-) animals with neutralizing anti-IL-12p40 monoclonal antibody (mAb) was able to reverse susceptibility and attenuate IFN-gamma production. We additionally demonstrated that excretory-secretory (ES) products from H. polygyrus and N. brasiliensis, but not T. muris, were capable of directly suppressing dendritic cell (DC) production of IL-12p40, thus bypassing the need for TSLP. Taken together, our data show that the primary function of TSLP is to directly suppress IL-12 secretion, thus supporting Th2 immune responses.

New insights into the regulation of T cells by gamma(c) family cytokines

Common cytokine receptor gamma-chain (gamma(c)) family cytokines have crucial roles in the development, proliferation, survival and differentiation of multiple cell lineages of both the innate and adaptive immune systems. In this Review, we focus on our current understanding of the distinct and overlapping effects of interleukin-2 (IL-2), IL-7, IL-9, IL-15 and IL-21, as well as the IL-7-related cytokine thymic stromal lymphopoietin (TSLP), on the survival and proliferation of conventional alphabeta T cells, gammadelta T cells and regulatory T cells. This knowledge potentially allows for the therapeutic manipulation of immune responses for the treatment of cancer, autoimmunity, allergic diseases and immunodeficiency, as well as for vaccine development.

Inflammatory signals in dendritic cell activation and the induction of adaptive immunity

Pathogen invasion induces a rapid inflammatory response initiated through the recognition of pathogen-derived molecules by pattern recognition receptors (PRRs) expressed on both immune and non-immune cells. The initial wave of pro-inflammatory cytokines and chemokines limits pathogen spread and recruits and activates immune cells to eradicate the invaders. Dendritic cells (DCs) are responsible for initiating a subsequent phase of immunity, dominated by the action of pathogen-specific T and B cells. As for the early pro-inflammatory response, DC activation is triggered by PRR signals. These signals convert resting DCs into potent antigen-presenting cells capable of promoting the expansion and effector differentiation of naive pathogen-specific T cells. However, it has been argued that signals from PRRs are not a prerequisite for DC activation and that pro-inflammatory cytokines have the same effect. Although this may appear like an efficient way to expand the number of DCs that initiate adaptive immunity, evidence is accumulating that DCs activated indirectly by inflammatory cytokines are unable to induce functional T-cell responses. Here, we review the differences between PRR-triggered and cytokine-induced DC activation and speculate on a potential role for DCs activated by inflammatory signals in tolerance induction rather than immunity.

Early production of thymic stromal lymphopoietin precedes infiltration of dendritic cells expressing its receptor in allergen-induced late phase cutaneous responses in atopic subjects

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is an interleukin (IL)-7-like cytokine that triggers dendritic cell-mediated T helper (Th)2 inflammatory responses through a receptor consisting of a heterodimer of the IL-7 receptor alpha (IL-7Ralpha) chain and the TSLP receptor (TSLPR), which resembles the cytokine receptor common gamma chain. Dendritic cells activated by TSLP prime development of CD4(+) T cells into Th2 cells contributing to the pathogenesis of allergic inflammation. We hypothesized that allergen exposure induces expression of TSLP and results in recruitment of TSLPR bearing cells in the cutaneous allergen-induced late-phase reaction (LPR) in atopic subjects.

METHODS

Skin biopsies were obtained from atopic subjects (n = 9) at various times after cutaneous allergen challenge. In situ hybridization and immunohistochemistry were used to determine TSLP mRNA expression and to measure infiltration of TSLPR(+) DC in skin LPR. RT-PCR and flow cytometry were employed to analyse TSLPR expression on isolated blood DC.

RESULTS

Allergen-induced skin TSLP expression occurred as early as 1 h after allergen challenge, whereas TSLPR(+) and CD11c(+) cells infiltrated relatively late (24-48 h). The majority of TSLPR(+) cells were DC co-expressing blood DC antigen-1 (BDCA-1) or BDCA-2. Freshly isolated blood DC expressed both TSLPR and IL-7Ralpha chains. Maturation and stimulation with TSLP or polyriboinosinic-polyribocytidylic acid in vitro upregulated the expression of both TSLPR and IL-7Ralpha chains in DC but not in chemoattractant receptor-homologous molecule expressed on Th2 cells(+) CD4(+) T cells.

CONCLUSION

The data suggest that TSLP plays a role in augmenting, through DC recruitment and activation, the development of Th2-type T cells in allergic inflammation.

Effect of TLR3 and TLR7 activation in uterine NK cells from non-obese diabetic (NOD) mice

Toll-like receptor (TLR)-TLR cross talk is thought to be important in TLR signaling. Herein, we investigated the effect of specific TLR3 and TLR7 agonists, poly (I:C) and R837, individually and in combination, on uterine immune cell function and their subsequent effects on pregnancy outcome. Allogeneic pregnancies in the non-obese diabetic (NOD) mousexC57BL/6 and wild-type BALB/cxC57BL/6 model were used. An additive increase in embryo resorption was observed after induction with both poly (I:C) and R837, and was associated with elevated numbers of both TNF-alpha- and IFN-gamma-producing CD45(+) cells in the uterus. Further examination showed that while cytokine expression was detected in both CD3(+) cells and CD49b(+) cells in BALB/c mice, NOD mouse cells behaved differently. In NOD mice, elevated cytokine expression was attributed to CD3(+) T cells, with no response detected in the CD49b(+) NK cells. The additive effect of combined agonists was partially inhibited by the Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) inhibitor SP600125 and almost completely abrogated by the extracellular signal-regulated kinase (ERK) MAPK inhibitor PD98059. These results suggest that increased TLR3 and TLR7 signals are transmitted via Th1-type T cells, rather than NK cells, in NOD mice. Furthermore, the ERK MAPK pathway may be critical in TLR3 and TLR7 signaling.

Proteases induce production of thymic stromal lymphopoietin by airway epithelial cells through protease-activated receptor-2

Thymic stromal lymphopoietin (TSLP) is produced by epithelial cells and triggers dendritic cell-mediated Th2-type inflammation. Although TSLP is up-regulated in epithelium of patients with asthma, the factors that control TSLP production have not been studied extensively. Because mouse models suggest roles for protease(s) in Th2-type immune responses, we hypothesized that proteases from airborne allergens may induce TSLP production in a human airway epithelial cell line, BEAS-2B. TSLP mRNA and protein were induced when BEAS-2B cells were exposed to prototypic proteases, namely, trypsin and papain. TSLP induction by trypsin required intact protease activity and also a protease-sensing G protein-coupled receptor, protease-activated receptor (PAR)-2; TSLP induction by papain was partially dependent on PAR-2. In humans, exposure to ubiquitous airborne fungi, such as Alternaria, is implicated in the development and exacerbation of asthma. When BEAS-2B cells or normal human bronchial epithelial cells were exposed to Alternaria extract, TSLP was potently induced. The TSLP-inducing activity of Alternaria was partially blocked by treating the extract with a cysteine protease inhibitor, E-64, or by infecting BEAS-2B cells with small interfering RNA for PAR-2. Protease-induced TSLP production by BEAS-2B cells was enhanced synergistically by IL-4 and abolished by IFN-gamma. These findings demonstrate that TSLP expression is induced in airway epithelial cells by exposure to allergen-derived proteases and that PAR-2 is involved in the process. By promoting TSLP production in the airways, proteases associated with airborne allergens may facilitate the development and/or exacerbation of Th2-type airway inflammation, particularly in allergic individuals.