Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Adora2b Adenosine Receptor Engagement Enhances Regulatory T Cell Abundance during Endotoxin-Induced Pulmonary Inflammation

Adora2b Adenosine Receptor Engagement Enhances Regulatory T Cell Abundance during Endotoxin-Induced Pulmonary Inflammation

  • Heidi Ehrentraut, 
  • Joseph A. Westrich, 
  • Holger K. Eltzschig, 
  • Eric T. Clambey
PLOS
x

Abstract

Anti-inflammatory signals play an essential role in constraining the magnitude of an inflammatory response. Extracellular adenosine is a critical tissue-protective factor, limiting the extent of inflammation. Given the potent anti-inflammatory effects of extracellular adenosine, we sought to investigate how extracellular adenosine regulates T cell activation and differentiation. Adenosine receptor activation by a pan adenosine-receptor agonist enhanced the abundance of murine regulatory T cells (Tregs), a cell type critical in constraining inflammation. Gene expression studies in both naïve CD4 T cells and Tregs revealed that these cells expressed multiple adenosine receptors. Based on recent studies implicating the Adora2b in endogenous anti-inflammatory responses during acute inflammation, we used a pharmacologic approach to specifically activate Adora2b. Indeed, these studies revealed robust enhancement of Treg differentiation in wild-type mice, but not in Adora2b−/− T cells. Finally, when we subjected Adora2b-deficient mice to endotoxin-induced pulmonary inflammation, we found that these mice experienced more severe inflammation, characterized by increased cell recruitment and increased fluid leakage into the airways. Notably, Adora2b-deficient mice failed to induce Tregs after endotoxin-induced inflammation and instead had an enhanced recruitment of pro-inflammatory effector T cells. In total, these data indicate that the Adora2b adenosine receptor serves a potent anti-inflammatory role, functioning at least in part through the enhancement of Tregs, to limit inflammation.

Introduction

Inflammation in response to tissue injury is a carefully orchestrated process, and insufficient or overexuberant inflammation can have catastrophic effects. One major pathway by which inflammation and tissue homeostasis is regulated is through the generation of extracellular adenosine, which can serve as a highly effective “safety” signal [1]. In healthy individuals, extracellular adenosine levels are low. During tissue injury and inflammation, however, extracellular adenosine levels significantly increase due to: 1) ATP release from activated and dead/dying cells, followed by 2) generation of adenosine from ATP, ADP, and AMP, a process critically dependent on the enzyme CD73 [2], [3]. The appropriate generation and clearance of extracellular adenosine are critical in limiting tissue pathology, with mice genetically deficient either in the generation (CD73-deficient mice) or clearance (adenosine deaminase, ADA-deficient mice) of extracellular adenosine displaying profound pathologies due to inappropriate control of inflammation [3], [4], [5], [6].

Extracellular adenosine mediates its biological effects through four adenosine receptors (Adora) (Adora1, Adora2a, Adora2b, Adora3), each with distinct expression patterns and different genetic roles in regulating physiology and inflammation [7]. Based on genetic studies, adenosine-dependent signaling can play a critical role in limiting tissue damage [8], [9], [10], [11]. Significantly, the anti-inflammatory adenosine pathway is coordinately induced following injury/inflammation, with both CD73 (the extracellular adenosine-generating enzyme) and adenosine receptors (Adora2a, Adora2b) simultaneously induced [12]. Furthermore, by screening for the relative activities of multiple Adoras, studies have revealed that Adora2b (also known as the A2B receptor) is a potent anti-inflammatory receptor [9], [10], [11], [13], [14].

T cells are a major cell type of the adaptive immune system that orchestrate the immune response. Within the T cell compartment, regulatory T cells (Tregs) serve a critical function in restraining inappropriate immune responses and inhibiting inflammation. Tregs mediate these inhibitory effects by multiple mechanisms depending on the tissue and nature of injury/inflammation (e.g. production of the anti-inflammatory cytokines interleukin (IL)-10, IL-35 and transforming growth factor (TGF)-β, generation of extracellular adenosine, and cell-contact dependent mechanisms) [15], [16], [17]. Notably, Tregs can limit immune responses to a specific infection or insult (this specificity resulting from the unique T cell receptor expressed by the Tregs in question) or Tregs can have a more general, nonspecific inhibitory effect [18], [19]. While Tregs can achieve their fate either during development (natural Tregs, nTregs) or they can differentiate from a naïve T cell into an induced Treg (iTreg) [20], both cells express the transcription factor FoxP3, a critical molecular determinant essential for Treg function [21]. Recent studies have shown that extracellular adenosine is one factor that can enhance the differentiation and function of Tregs, potentially through signaling through Adora2a [22], [23], [24], [25].

While many studies have focused on the role of Adora2a in regulating T cell function, much less is known about the contribution of Adora2b and its effects on T cell differentiation. In this study, we directly investigated the Adora2b receptor as a regulator of Treg differentiation. These studies reveal a previously unappreciated role for Adora2b in promoting Tregs both in vitro and in vivo, and identify a previously unappreciated mechanism by which Adora2b might limit inflammation.

Results

A pan-adenosine receptor agonist enhances the abundance of Tregs following in vitro stimulation of primary mouse T cells

Given the potent anti-inflammatory effects mediated by extracellular adenosine, we tested the effect of a general adenosine receptor agonist (NECA) on the relative abundance of Tregs, an anti-inflammatory subset of T cells, after in vitro stimulation of primary murine T cells. Consistent with previous reports [24], NECA stimulation enhanced the relative abundance of FoxP3 expressing Tregs in stimulated splenocyte cultures (Fig. 1A–B).

thumbnail
Figure 1. Adenosine receptor activation enhances the abundance of Tregs following in vitro stimulation of primary mouse T cells.

(A) Adenosine receptor activation enhances the abundance of Tregs following antibody-mediated stimulation of T cells (using anti-CD3 antibody, 1 µg/mL combined with 10 ng/mL of IL-2, in the absence of TGF-β). Samples were either untreated (+Vehicle) or treated with 10 µM of NECA (+NECA), a potent adenosine receptor agonist, analyzed three days post-stimulation for the relative abundance of FoxP3-expressing Tregs. The numbers present in the upper left-hand corner of each flow cytometry plot indicate the percentage of cells that are FoxP3+ as defined by the square gate. Background staining with an isotype control antibody is indicated in the leftmost panel. (B) Quantitation of FoxP3-expressing cells following either control (vehicle treated, white bars) or NECA treated (black bars), with data indicating mean +/− SEM of triplicate cultures done in two separate experiments. (C) Adenosine receptor activation enhances the abundance of Tregs following antibody-mediated stimulation of T cells in the presence of TGF-β, a known inducer of Tregs (using anti-CD3 antibody, 1 µg/mL combined with 10 ng/mL of IL-2, combined with 0.75 ng/mL TGF-β), showing flow cytometric analysis (C) and quantitation (D). The numbers present in the upper left-hand corner of each flow cytometry plot indicate the percentage of cells that are FoxP3+ as defined by the square gate. Relative abundance of Tregs within cultures were defined by flow cytometry, with Tregs defined as live, MHC class II negative, CD8−, CD4+ cells that express the transcription factor FoxP3. Data indicate mean +/− SEM of triplicate cultures, representative of two independent experiments. (E) Tregs generated by TGF-β with NECA (solid black line) relative to Tregs generated by TGF-β treatment alone (indicated in gray) have a comparable cell surface expression of CD25, CD39 and CD73. Results representative of results from three independent cultures, done in two independent experiments. Statistical analysis was performed using unpaired t test, with statistically significant differences as indicated.

https://doi.org/10.1371/journal.pone.0032416.g001

TGF-β is a potent inducer of FoxP3 expression and an inducer of Tregs. Adenosine receptor stimulation further enhanced Tregs differentiation in the presence of TGF-β (Fig. 1C–D). Tregs present following adenosine receptor stimulation had comparable expression relative to normal Tregs based on their cell surface expression of three proteins expressed on Tregs, CD25, CD39 and CD73 (Fig. 1E), indicating that adenosine receptor stimulation did not perturb the general phenotype of Tregs after in vitro culture.

To define potential mechanisms by which adenosine receptor engagement might enhance Treg abundance, we measured relative expression levels of the four adenosine receptors in both naïve CD4 T cells and Tregs. This analysis identified that both T cell subsets expressed all four of the adenosine receptors, with mRNA expression of Adora2a and FoxP3 upregulated in Tregs relative to naïve CD4 T cells (Fig. 2).

thumbnail
Figure 2. Relative expression levels of adenosine receptor genes in T cell subsets.

Real-time PCR analysis of mRNA for the four adenosine receptor genes in FACS purified CD4 T cell subsets of naïve CD4 T cells or Tregs, with Tregs isolated from FoxP3GFP or DEREG mice. Values were standardized to bulk spleen mRNA, with each value showing expression relative to actin. High level expression of FoxP3 mRNA is consistent with a highly purified population of Tregs. Data representative of two to three independent experiments, analyzing at least three independently isolated populations for both naïve CD4 T cells and Tregs. Data depict mean ± SEM for each transcript. Statistically significant differences were calculated by unpaired t test comparing expression in naïve CD4 T cells relative to Tregs, as indicated.

https://doi.org/10.1371/journal.pone.0032416.g002

An Adora2b-specific agonist enhances Treg abundance in vitro following activation of murine T cells

Previous studies have implicated the Adora2a adenosine receptor in promoting Treg abundance [24]. Given the expression of the Adora2b receptor in both naïve T cells and Tregs, and the accumulated evidence of an anti-inflammatory effect for Adora2b in vivo, we directly tested the consequence of an Adora2b-specific agonist (Bay60-6583) [13] on in vitro cultures of activated primary murine T cells. While Bay60-6583 treatment of control Adora2b+/+ splenocytes resulted in an increased frequency of Tregs after three days of culture, this compound had no effect on Treg abundance in Adora2b−/− cultures (Fig. 3). These data identify that an Adora2b-specific agonist is capable of enhancing Tregs in vitro.

thumbnail
Figure 3. An Adora2b-specific agonist enhances Treg abundance in vitro following activation of murine T cells.

Bulk splenocytes from either Adora2b+/+ (C57BL/6J) or Adora2b−/− mice were cultured with soluble anti-CD3 for three days with or without the Bay60-6583 compound, at which time the relative abundance of Tregs was assessed. (A) Fold change in Treg abundance relative to Adora2b+/+ cultures without the Bay compound control, where Tregs were defined as viable, CD4+ FoxP3+ cells by flow cytometry. (B) Flow cytometry plots shown from Adora2b+/+ cultured splenocytes. Bay60-6583, an Adora2b-specific agonist was added to a final concentration of 4 nM. Data from two independent experiments, each containing 1–3 independent replicates. The numbers present on each flow cytometry plot indicate the percentage of cells that are FoxP3+ as defined by the square gate, with FoxP3 expressing cells defined relative to isotype control-stained samples (not shown). Statistically significant differences are indicated and were calculated by one-way ANOVA followed by Bonferroni's post-test correction. ns indicates a comparison that is not statistically significantly different.

https://doi.org/10.1371/journal.pone.0032416.g003

Adora2b-deficient mice fail to increase Tregs after endotoxin-induced pulmonary inflammation

We next sought to investigate the in vivo consequence of Adora2b deficiency on T cell populations during pulmonary inflammation. Previous studies have revealed that Adora2b-deficient mice have enhanced pulmonary inflammation, marked by increased neutrophil infiltration, elevated levels of pro-inflammatory cytokines (e.g. IL-6, TNF-α), and decreased levels of the anti-inflammatory cytokine IL-10 [26]. Consistent with these earlier studies, we found that lipopolysaccharide (LPS) exposed Adora2b−/− mice had increased cellularity in the airways after LPS exposure and increased protein leakage into the airways relative to wild-type controls (Fig. 4A–B), with pronounced neutrophil infiltration (Fig. 4C). Given the ability of an Adora2b agonist to enhance Tregs, we tested the relative change in Treg abundance in Adora2b−/− mice following LPS exposure. Notably, Adora2b−/− mice failed to induce an increase in Tregs in the lung or the airway after LPS exposure (Fig. 4D, E). Conversely, Adora2b−/− mice had an increased infiltration of CD4 effector T cells, such that the relative ratio of CD4 effector T cells to Tregs in Adora2b−/− was elevated relative to Adora2b+/+ controls (Fig. 4F). The failure to increase Treg abundance, coupled with an enhanced recruitment of CD4 effector T cells identifies Adora2b as a critical regulator which influences the relative contribution of anti-inflammatory Tregs to pro-inflammatory effector T cells during inflammation.

thumbnail
Figure 4. Adora2b-deficient mice have increased inflammation with impaired induction of Tregs after LPS-induced lung injury.

LPS-induced inflammation was initiated in 9–12 wk-old male Adora2b+/+ (C57BL/6J) or age and weight matched Adora2b−/− mice by intratracheal instillation of LPS or saline. Bronchoalveolar lavage (BAL) fluids were collected 1 d post treatment. A) Leukocyte cell counts of BAL fluid were determined utilizing a cellometer (mean ± SEM, n = 2–4). B) Protein content of BAL fluid was determined with BCA assay. Fold increase of protein concentration in LPS treated BAL samples over respective saline BAL samples is displayed (mean ± SEM, n = 3–10). C) Analysis of cell infiltration into the lung airspace (BAL) of mice exposed to inhaled LPS. Mice (Adora2b+/+ or Adora2b−/−) were exposed to nebulized saline or lipopolysaccharide (LPS); 24 hours post-exposure, mice were euthanized, and BAL was harvested. Cells were then subjected to flow cytometric analysis to identify neutrophils (highly granular, Gr1+ cells). D) Analysis of FoxP3 gene expression in lungs of mice exposed to inhaled LPS. Mice (Adora2b+/+ or −/−) were exposed to nebulized saline or lipopolysaccharide (LPS); 24 hours post-exposure, mice were euthanized, and perfused lungs were harvested. Total RNA was harvested from lungs, cDNA prepared and analyzed by real-time PCR. Data depict mean (± SEM) fold changes in indicated genes. Fold change was calculated based on primer efficiencies, standardized to changes in actin, with Adora2b+/+ Saline mean value defined as 1. E) Fold change in cell number of either regulatory T cells (lymphocyte size, CD3+ CD4+ FoxP3+) in the lung airspace (BAL) of mice exposed to inhaled saline or LPS as above. Data are from 2–6 mice; 2 independent experiments. F) Relative abundance of CD4 effector T cells (Teffs, defined as lymphocyte size, CD3+ CD4+ CD44high cells) to Tregs based on cell counts from either Adora2b+/+ or Adora2b−/− mice, with pie charts depicting mean cell count for the indicated cell populations from 2–6 mice; 2 independent expts. Analysis of total cellular infiltration into airways and protein leakage (panels A–B) was done in animals treated with intratracheal LPS. Analysis of neutrophil infiltration and Tregs (panels C–F) was done in animals treated with inhaled LPS. Statistically significant differences are indicated and were calculated either by one-way ANOVA (A) or by unpaired t test (B–E) with a focus on whether Adora2b−/− LPS treated animals were statistically different from either saline treated or Adora2b+/+ LPS treated mice.

https://doi.org/10.1371/journal.pone.0032416.g004

Discussion

During acute inflammatory responses, the generation of extracellular adenosine is an important feedback mechanism that limits inflammation [1], [8]. The stepwise generation of extracellular adenosine by CD39 and CD73 from ATP is thought to limit inflammation by at least two ways: i) through the enzymatic degradation of extracellular ATP, which can promote inflammation [27] and ii) by extracellular adenosine directly signaling through adenosine receptors [1]. Notably, signaling through adenosine receptors triggers multiple anti-inflammatory pathways including the induction of IL-10 [28], the impaired immunogenicity of dendritic cells [29], and the deneddylation of cullin-1 to limit NF-κB activation [30]. In this manuscript, we present data for a new anti-inflammatory mechanism downstream of Adora2b: Adora2b-dependent induction of regulatory T cells.

The potent anti-inflammatory effects of Adora2b during acute inflammation have been revealed in multiple studies of acute inflammatory insults including studies of localized or systemic microbial challenge [11], [14], [31], [32], [33]. Adora2b also has a pronounced anti-inflammatory role in the context of ischemic tissue injury (i.e. transient tissue hypoxia) such that Adora2b-deficient mice have more severe acute ischemic injury in studies of both renal and myocardial ischemia [9], [10]. Notably, hypoxia elicits multiple adaptive responses within cells to deal with limited oxygen availability, including induction of the extracellular adenosine sensing pathway [12], [34], [35], induction of toll-like receptors TLR2 and TLR6 [36], activation of the NF-κB machinery [37], and upregulation of integrins which modulate cell trafficking [38]. Given the integration of hypoxic sensing machinery with Adora2b, future studies will focus on how hypoxia and extracellular adenosine signaling intersect in regulating the generation of Tregs. This work is especially relevant given our recent studies demonstrating that hypoxia can enhance the generation of Tregs, thereby restricting hypoxia-associated inflammation (Clambey et al, submitted).

While Adora2b signaling can be tissue protective, Adora2b can also inappropriately restrict inflammation. This balance between tissue-protection versus host-defense has been nicely revealed by studies of cecal ligation and puncture, in which Adora2b-deficient mice were more resistant to sepsis and sepsis-associated mortality [33]. Furthermore, Belikoff et al found that an Adora2b antagonist was capable of increasing survival in septic mice, even those, that based on increased levels of IL-6 in the blood, were predicted to succumb to mortality [33].

In contrast to the potential beneficial effects of Adora2b in acute inflammatory contexts, this receptor can be detrimental in conditions of prolonged inflammation [39], [40], [41]. For example, in elegant studies from the Blackburn laboratory, the pulmonary inflammation and fibrosis observed in adenosine deaminase (ADA) deficient mice is significantly improved upon treatment of these mice with an Adora2b-specific antagonist [39]. Surprisingly, however, Adora2b genetic deficiency worsened ADA-deficient inflammation [42]. This apparent discrepancy in the role of Adora2b is likely due to the kinetics of Adora2b loss-of-function, where pharmacological studies focused on the effects of blocking Adora2b after the onset of inflammation [39] in contrast to genetic ablation of Adora2b that occurred prior to the induction of inflammation [42]. Consistent with this idea, direct comparison of acute and chronic models of bleomycin-induced lung injury demonstrated that while Adora2b served a potent anti-inflammatory role during acute lung injury, Adora2b had little effect on inflammation and was instead pro-fibrotic during chronic pulmonary fibrosis [43]. The pathogenic potential of Adora2b in chronic inflammation is not restricted to the lung. For example, Adora2b signaling was recently revealed to be detrimental in sickle cell anemia, a context in which elevated levels of extracellular adenosine-Adora2b signaling promotes red blood cell sickling, contributing to the pathogenesis of this disease [44].

Based on our current observations that Adora2b enhances Tregs, it is interesting to speculate that some of the detrimental effects of Adora2b in chronic pathologies may be due to excessive generation or function of Tregs. A detrimental role for an adenosine-driven Treg pathway may be particularly relevant in the context of elevated extracellular adenosine levels (e.g. in pulmonary fibrosis, sickle cell anemia, fibrosis or solid tumors [5], [44], [45], [46]). In fact, recent data indicate that Tregs may participate in the process of fibrosis [47], [48], with a pro-fibrotic outcome occurring through increased Treg production of TGF-β1 and subsequent collagen production following immune activation [49].

The divergent effects of Adora2b in acute and chronic inflammatory contexts indicate that Adora2b function is likely to be shaped by the cells and environments in which inflammation is occurring. Our data define a role for Adora2b in enhancing Tregs either in primary activated murine T cell cultures or after LPS exposure, a finding consistent with a recent report showing that antagonizing Adora2b signaling inhibits the generation of Tregs in vitro [50]. In contrast to our findings, however, a recent paper reported that Adora2b promoted the generation of pro-inflammatory Th17 cells [51]. While the explanation for this apparent discrepancy remains to be elucidated, it is notable that the Th17-promoting effects of Adora2b in these studies were isolated to effects of Adora2b specifically on dendritic cells, and not on macrophages [51]. This observation raises the possibility that the contribution of Adora2b to T cell differentiation depends on the type of antigen presenting cell (e.g. dendritic cell versus macrophage) and microenvironment. For example, while treatment of dendritic cells with NECA induces IL-6 expression in an Adora2b-dependent mechanism [51], Adora2b-deficient mice or macrophages had increased levels of IL-6 during acute inflammation, indicating that Adora2b can limit IL-6 in certain contexts [26], [33]. This cell-type specific regulation of IL-6 by Adora2b is particularly relevant to understanding how Adora2b could either induce anti-inflammatory Tregs, as we show here, or pro-inflammatory Th17 cells [51], given that Treg differentiation can be diverted to Th17 differentiation in the presence of IL-6 [52]. It will be important for future studies to elucidate the cell-type specific contributions of Adora2b in controlling both acute and chronic inflammatory responses.

The central role of Adora2b in determining the outcome of both acute and chronic pathologies identifies this molecule as a promising point of intervention. Since Adora2b serves as a receptor both for extracellular adenosine as well as for alternative ligands (e.g. Netrin-1, [53], [54], [55]), this receptor may function to integrate multiple extrinsic cues to promote Tregs to restrict the duration and magnitude of inflammation. Pharmacologic targeting of adenosine pathways such as Adora2b may also synergize with modalities that activate the hypoxic response and have been shown to be tissue-protective in models of colitis [56], [57]. Conversely, since both Adora2a and Adora2b signaling promote Tregs, transient depletion of extracellular adenosine through the administration of pegylated-ADA may be a potent method to transiently limit the generation or activity of Tregs. Based on the potential of Adora2b-targeted treatments to modulate regulatory T cells, future studies will interrogate the consequences and therapeutic benefits of manipulating the Adora2b-Treg axis in both acute and chronic states of inflammation.

Methods

Mice

Adora2b+/+ (C57BL/6J) and Adora2b−/− [13] mice were bred in house. B6.Cg-Foxp3tm2Tch/J (here referred to as FoxP3GFP [58]) were obtained from Jax and DEREG mice were kindly provided by Dr. Tim Sparwasser [59]. All mouse experiments were done using age- and sex-matched mice, with mice typically used between 8–12 weeks of age. The animal protocol was approved by the Institutional Animal Care and Use Committee of the University of Colorado Denver (under Animal Welfare Assurance Policy A3269-01, IACUC protocol B83708(07)1D) and is in accordance with the National Institutes of Health guidelines for use of live animals. The University of Colorado Denver, Anschutz Medical Campus is accredited by the American Association for Accreditation of Laboratory Animal Care (#00235).

Tissue harvest

At time of harvest, bronchoalveolar lavage (BAL) was harvested by performing three sequential lavages of the airways, using an ice-cold PBS solution containing 5 mM EDTA. Lungs were harvested from mice, following perfusion of the lungs using saline. For lungs subjected to flow cytometric analysis, lung tissue was mechanically disrupted by scissors, followed by a one-hour incubation of lung tissue with collagenase D at a final concentration of 1 mg/mL at 37 C. Following collagenase treatment, lung material was placed over a 100 micron mesh and cells were forced through using the plunger of a 3 mL syringe and multiple washes of disrupted material.

T cell purification

T cells were purified from the spleen of mice, mechanically disrupted over a 100 micron filter, subjected to magnetic bead enrichment for CD4 T cells using a CD4 T cell isolation kit (Miltenyi Biotec, Germany). Enriched CD4 T cells were then subjected to FACS purification on a FACSAria (BD), with naïve CD4 T cells purified based on the cell surface phenotype CD4+ CD62Lhigh CD44low. FoxP3-expressing Tregs were purified from two different genetically engineered mice which express GFP specifically in Tregs, the FoxP3GFP (B6.Cg-Foxp3tm2Tch/J from Jax [58], [60]) and DEREG mice (kindly provided by Dr. Tim Sparwasser [59]). In both strains of mice, GFP expression is directly linked to the regulatory sequences from the FoxP3 locus, either using an internal ribosome entry site at the end of the endogenous FoxP3 gene (in FoxP3GFP mice) or using a bacterial artificial chromosome-based transgenic in which GFP was placed downstream of the FoxP3 promoter (in DEREG mice). FoxP3 expressing cells were purified for subsequent qPCR analysis, with Tregs identified and isolated by sorting as CD4+ GFP+ [58], [60].

In vitro T cell cultures

Bulk splenocytes or purified CD4 T cells were cultured in Iscove's modified Dulbeco's medium (IMDM, Gibco) containing 5% FBS, L-glutamine, penicillin/streptomycin and β-mercaptoethanol (50 µM). All cultures were done using cells at a concentration of 1×106 cells/mL. For cultures subjected to T cell receptor stimulation, bulk splenocytes were stimulated with 1 µg/mL soluble anti-CD3ε (clone 145-2C11, eBioscience), supplemented with 10 ng/mL of recombinant mouse IL-2 (eBioscience). In vitro Treg differentiation assays were done for 3 days. In certain assays, exogenous TGF-β was added to the culture, using recombinant human TGF-β1 (eBioscience). For assays in which cells were stimulated with a pan receptor agonist, cultures were treated with 10 µM NECA (5′-N-Ethylcarboxamidoadenosine, Tocris Bioscience, MO, USA) for the duration of the culture. For cultures stimulated with the Adora2b-specific agonist Bay60-6583, cultures were treated with 4 nM Bay60-6583 (obtained from Bayer, Germany).

RNA isolation and Real-time PCR

Total RNA was extracted from cells or tissue by Trizol, followed by cDNA synthesis using iScript cDNA Synthesis Kit (Bio-Rad Laboratories, Inc, Munich, Germany) according to the manufacturer's instructions. Quantitative real-time reverse transcriptase PCR (qPCR) (iCycler; Bio-Rad Laboratories, Inc.) was performed to measure relative mRNA levels for various transcripts, with qPCR master mix contained 1 µM sense and 1 µM antisense primers with iQ™ SYBR® Green (Bio-Rad Laboratories, Inc.). For every assay, melt curve analysis was performed and samples with aberrant melt curves were discarded. All qPCR assays were standardized relative to β-actin levels.

Antibodies and Flow cytometric analysis

Antibodies were purchased from eBioscience unless otherwise noted. Anti-mouse antibodies included CD4 (GK1.5), CD25 (PC61.5), CD39 (24DMS1), CD73 (eBioTY/11.8 (TY/11.8)), FoxP3 (FJK-16s), Gr1 (RB6-8C5), and MHC class II (M5/114.15.2). Single cell suspensions of cultured cells or disrupted tissue were stained with a cocktail of antibodies for 30 minutes at room temperature in the dark, in staining buffer containing an anti-Fc receptor antibody (2.4G2). When cells were stained for FoxP3, staining was done using FoxP3 staining buffer according to manufacturer's instructions (eBioscience). Unless stated otherwise, all stains included a viability dye to identify viable cells (LIVE/DEAD® Fixable Aqua Dead Cell Stain Kit, Invitrogen), with Tregs routinely identified as lymphocytes (based on forward and side scatter profiles) that were viable, MHC class II negative cells, which expressed CD4 and FoxP3. FoxP3-expressing Tregs were identified by comparing fluorescent signal between samples stained with an isotype control antibody (background staining), relative to samples stained with a FoxP3-specific antibody. Isotype stained controls routinely had less than 0.5% positive events within the FoxP3+ gate. All flow cytometry was done on an LSRII (BD), with compensation done using FACSDiva software. All flow cytometry data is show on a log10 scale.

Primers for qPCR analysis

All primers used for qPCR are indicated below, with a 5′ to 3′ orientation, and m referring to mouse. mbeta-actin: Fwd-CTAGGCACCAGGGTGTGAT, Rev-TGCCAGATCTTCTCCATGTC; mFoxP3: Fwd-TCTCCAGGTTGCTCAAAGTC, Rev-GCAGAAGTTGCTGCTTTAGG; mAdora1: Fwd-AGAACCACCTCCACCCTTCT, Rev-TACTCTGGGTGGTGGTCACA; mAdora2a: Fwd-GAAGCAGATGGAGAGCCAAC, Rev-GAGAGGATGATGGCCAGGTA; mAdora2b: Fwd-TGCATGCCATCAACTGTATC, Rev-TGGAAACTGTAGCGGAAGTC; mAdora3: Fwd-TCCCTGATTACCACGGACTC, Rev-CAATTCGCTCCTTCTGTTCC.

Murine LPS exposure models

Male Adora2b+/+ (C57BL/6J mice, The Jackson Laboratory, ME) and Adora2b−/− on a C57BL/6J background were randomly assigned to saline or LPS treatment groups at age 9–12 wk. LPS from Escherichia coli 0111:B4 (L4391, Sigma-Aldrich) was dissolved in 0.9% saline (2 mg/mL). Animals were anesthetized with pentobarbital (70 mg/kg i.p.). A volume of either 50 µL LPS (100 µg/animal) or saline was instilled intratracheally via a 22-gauge canule, followed by 0.1 mL of air. Animals were harvested 24 hours after instillation. For studies in which mice were exposed to aerosolized LPS, mice were exposed to aerosolized LPS in a cylindrical chamber connected to an air nebulizer (MicroAir; Omron Healthcare, Mannheim, Germany) as published previously [26].

Measurement of BAL fluid protein content

After collection samples were centrifuged for 1 min at 3,000× g, and supernatant was stored at −80°C. Colorimetric Pierce bicinchoninic acid (BCA) protein assay (Thermo Scientific) was performed according to the manufacturer's protocol to determine protein content of BAL supernatant.

Leukocyte counts of BAL fluid

BAL samples were mixed gently prior to diluting 50 µL of BAL fluid with 50 µl of Trypan blue (1∶5 in 1× PBS) for viable cell counts. 20 µl of diluted cell sample were pipetted on a cellometer cell counting chamber. Leukocytes were automatically counted using a Cellometer Auto T4 (Nexcelom Bioscience, Lawrence, MA, USA).

Software & statistical analysis

Data analysis and plotting were done using Prism 4.0c (GraphPad Software, Inc, San Diego, CA). Flow cytometric data were analyzed using FlowJo (TreeStar, Inc, Ashland, OR), with data displayed as high-resolution zebra plots showing outliers, using log10 scales. Statistical analyses were performed using Prism 4.0c, with unpaired t-tests or one-way ANOVA and Bonferroni's multiple comparison post-test correction for all other analyses.

Acknowledgments

The authors thank Elizabeth Kelly-McKnight for technical assistance with flow cytometry, Kristann Magee for expert technical assistance with mice, Dr. Tim Sparwasser for permission to use the DEREG mice, Dr. Ross Kedl for access to DEREG mice, Dr. Edwin de Zoeten for the FoxP3GFP mice, and Dr. Linda van Dyk for critical discussion.

Author Contributions

Conceived and designed the experiments: HKE ETC. Performed the experiments: HE JAW ETC. Analyzed the data: HE JAW ETC. Wrote the paper: HKE ETC.

References

  1. 1. Grenz A, Homann D, Eltzschig HK (2011) Extracellular Adenosine: A Safety Signal That Dampens Hypoxia-Induced Inflammation During Ischemia. Antioxid Redox Signal 15: 2221–2234.A. GrenzD. HomannHK Eltzschig2011Extracellular Adenosine: A Safety Signal That Dampens Hypoxia-Induced Inflammation During Ischemia.Antioxid Redox Signal1522212234
  2. 2. Linden J (2001) Molecular approach to adenosine receptors: receptor-mediated mechanisms of tissue protection. Annu Rev Pharmacol Toxicol 41: 775–787.J. Linden2001Molecular approach to adenosine receptors: receptor-mediated mechanisms of tissue protection.Annu Rev Pharmacol Toxicol41775787
  3. 3. Colgan SP, Eltzschig HK, Eckle T, Thompson LF (2006) Physiological roles for ecto-5′-nucleotidase (CD73). Purinergic Signal 2: 351–360.SP ColganHK EltzschigT. EckleLF Thompson2006Physiological roles for ecto-5′-nucleotidase (CD73).Purinergic Signal2351360
  4. 4. Thompson LF, Eltzschig HK, Ibla JC, Van De Wiele CJ, Resta R, et al. (2004) Crucial role for ecto-5′-nucleotidase (CD73) in vascular leakage during hypoxia. J Exp Med 200: 1395–1405.LF ThompsonHK EltzschigJC IblaCJ Van De WieleR. Resta2004Crucial role for ecto-5′-nucleotidase (CD73) in vascular leakage during hypoxia.J Exp Med20013951405
  5. 5. Blackburn MR, Volmer JB, Thrasher JL, Zhong H, Crosby JR, et al. (2000) Metabolic consequences of adenosine deaminase deficiency in mice are associated with defects in alveogenesis, pulmonary inflammation, and airway obstruction. J Exp Med 192: 159–170.MR BlackburnJB VolmerJL ThrasherH. ZhongJR Crosby2000Metabolic consequences of adenosine deaminase deficiency in mice are associated with defects in alveogenesis, pulmonary inflammation, and airway obstruction.J Exp Med192159170
  6. 6. Blackburn MR, Kellems RE (2005) Adenosine deaminase deficiency: metabolic basis of immune deficiency and pulmonary inflammation. Adv Immunol 86: 1–41.MR BlackburnRE Kellems2005Adenosine deaminase deficiency: metabolic basis of immune deficiency and pulmonary inflammation.Adv Immunol86141
  7. 7. Blackburn MR, Vance CO, Morschl E, Wilson CN (2009) Adenosine receptors and inflammation. Handb Exp Pharmacol 215–269.MR BlackburnCO VanceE. MorschlCN Wilson2009Adenosine receptors and inflammation.Handb Exp Pharmacol215269
  8. 8. Sitkovsky MV, Lukashev D, Apasov S, Kojima H, Koshiba M, et al. (2004) Physiological control of immune response and inflammatory tissue damage by hypoxia-inducible factors and adenosine A2A receptors. Annu Rev Immunol 22: 657–682.MV SitkovskyD. LukashevS. ApasovH. KojimaM. Koshiba2004Physiological control of immune response and inflammatory tissue damage by hypoxia-inducible factors and adenosine A2A receptors.Annu Rev Immunol22657682
  9. 9. Eckle T, Grenz A, Laucher S, Eltzschig HK (2008) A2B adenosine receptor signaling attenuates acute lung injury by enhancing alveolar fluid clearance in mice. J Clin Invest 118: 3301–3315.T. EckleA. GrenzS. LaucherHK Eltzschig2008A2B adenosine receptor signaling attenuates acute lung injury by enhancing alveolar fluid clearance in mice.J Clin Invest11833013315
  10. 10. Grenz A, Osswald H, Eckle T, Yang D, Zhang H, et al. (2008) The reno-vascular A2B adenosine receptor protects the kidney from ischemia. PLoS Med 5: e137.A. GrenzH. OsswaldT. EckleD. YangH. Zhang2008The reno-vascular A2B adenosine receptor protects the kidney from ischemia.PLoS Med5e137
  11. 11. Hart ML, Jacobi B, Schittenhelm J, Henn M, Eltzschig HK (2009) Cutting Edge: A2B Adenosine receptor signaling provides potent protection during intestinal ischemia/reperfusion injury. J Immunol 182: 3965–3968.ML HartB. JacobiJ. SchittenhelmM. HennHK Eltzschig2009Cutting Edge: A2B Adenosine receptor signaling provides potent protection during intestinal ischemia/reperfusion injury.J Immunol18239653968
  12. 12. Eltzschig HK, Ibla JC, Furuta GT, Leonard MO, Jacobson KA, et al. (2003) Coordinated adenine nucleotide phosphohydrolysis and nucleoside signaling in posthypoxic endothelium: role of ectonucleotidases and adenosine A2B receptors. J Exp Med 198: 783–796.HK EltzschigJC IblaGT FurutaMO LeonardKA Jacobson2003Coordinated adenine nucleotide phosphohydrolysis and nucleoside signaling in posthypoxic endothelium: role of ectonucleotidases and adenosine A2B receptors.J Exp Med198783796
  13. 13. Eckle T, Krahn T, Grenz A, Kohler D, Mittelbronn M, et al. (2007) Cardioprotection by ecto-5′-nucleotidase (CD73) and A2B adenosine receptors. Circulation 115: 1581–1590.T. EckleT. KrahnA. GrenzD. KohlerM. Mittelbronn2007Cardioprotection by ecto-5′-nucleotidase (CD73) and A2B adenosine receptors.Circulation11515811590
  14. 14. Frick JS, MacManus CF, Scully M, Glover LE, Eltzschig HK, et al. (2009) Contribution of adenosine A2B receptors to inflammatory parameters of experimental colitis. J Immunol 182: 4957–4964.JS FrickCF MacManusM. ScullyLE GloverHK Eltzschig2009Contribution of adenosine A2B receptors to inflammatory parameters of experimental colitis.J Immunol18249574964
  15. 15. Rubtsov YP, Rasmussen JP, Chi EY, Fontenot J, Castelli L, et al. (2008) Regulatory T cell-derived interleukin-10 limits inflammation at environmental interfaces. Immunity 28: 546–558.YP RubtsovJP RasmussenEY ChiJ. FontenotL. Castelli2008Regulatory T cell-derived interleukin-10 limits inflammation at environmental interfaces.Immunity28546558
  16. 16. Zheng Y, Chaudhry A, Kas A, deRoos P, Kim JM, et al. (2009) Regulatory T-cell suppressor program co-opts transcription factor IRF4 to control T(H)2 responses. Nature 458: 351–356.Y. ZhengA. ChaudhryA. KasP. deRoosJM Kim2009Regulatory T-cell suppressor program co-opts transcription factor IRF4 to control T(H)2 responses.Nature458351356
  17. 17. Vignali DA, Collison LW, Workman CJ (2008) How regulatory T cells work. Nat Rev Immunol 8: 523–532.DA VignaliLW CollisonCJ Workman2008How regulatory T cells work.Nat Rev Immunol8523532
  18. 18. Joetham A, Takeda K, Okamoto M, Taube C, Matsuda H, et al. (2009) Antigen specificity is not required for modulation of lung allergic responses by naturally occurring regulatory T cells. J Immunol 183: 1821–1827.A. JoethamK. TakedaM. OkamotoC. TaubeH. Matsuda2009Antigen specificity is not required for modulation of lung allergic responses by naturally occurring regulatory T cells.J Immunol18318211827
  19. 19. Szymczak-Workman AL, Workman CJ, Vignali DA (2009) Cutting edge: regulatory T cells do not require stimulation through their TCR to suppress. J Immunol 182: 5188–5192.AL Szymczak-WorkmanCJ WorkmanDA Vignali2009Cutting edge: regulatory T cells do not require stimulation through their TCR to suppress.J Immunol18251885192
  20. 20. Feuerer M, Hill JA, Mathis D, Benoist C (2009) Foxp3+ regulatory T cells: differentiation, specification, subphenotypes. Nat Immunol 10: 689–695.M. FeuererJA HillD. MathisC. Benoist2009Foxp3+ regulatory T cells: differentiation, specification, subphenotypes.Nat Immunol10689695
  21. 21. Zheng Y, Rudensky AY (2007) Foxp3 in control of the regulatory T cell lineage. Nat Immunol 8: 457–462.Y. ZhengAY Rudensky2007Foxp3 in control of the regulatory T cell lineage.Nat Immunol8457462
  22. 22. Naganuma M, Wiznerowicz EB, Lappas CM, Linden J, Worthington MT, et al. (2006) Cutting edge: Critical role for A2A adenosine receptors in the T cell-mediated regulation of colitis. J Immunol 177: 2765–2769.M. NaganumaEB WiznerowiczCM LappasJ. LindenMT Worthington2006Cutting edge: Critical role for A2A adenosine receptors in the T cell-mediated regulation of colitis.J Immunol17727652769
  23. 23. Deaglio S, Dwyer KM, Gao W, Friedman D, Usheva A, et al. (2007) Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression. J Exp Med 204: 1257–1265.S. DeaglioKM DwyerW. GaoD. FriedmanA. Usheva2007Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression.J Exp Med20412571265
  24. 24. Zarek PE, Huang CT, Lutz ER, Kowalski J, Horton MR, et al. (2008) A2A receptor signaling promotes peripheral tolerance by inducing T-cell anergy and the generation of adaptive regulatory T cells. Blood 111: 251–259.PE ZarekCT HuangER LutzJ. KowalskiMR Horton2008A2A receptor signaling promotes peripheral tolerance by inducing T-cell anergy and the generation of adaptive regulatory T cells.Blood111251259
  25. 25. Ernst PB, Garrison JC, Thompson LF (2010) Much Ado about Adenosine: Adenosine Synthesis and Function in Regulatory T Cell Biology. J Immunol 185: 1993–1998.PB ErnstJC GarrisonLF Thompson2010Much Ado about Adenosine: Adenosine Synthesis and Function in Regulatory T Cell Biology.J Immunol18519931998
  26. 26. Schingnitz U, Hartmann K, Macmanus CF, Eckle T, Zug S, et al. (2010) Signaling through the A2B adenosine receptor dampens endotoxin-induced acute lung injury. J Immunol 184: 5271–5279.U. SchingnitzK. HartmannCF MacmanusT. EckleS. Zug2010Signaling through the A2B adenosine receptor dampens endotoxin-induced acute lung injury.J Immunol18452715279
  27. 27. Idzko M, Hammad H, van Nimwegen M, Kool M, Willart MA, et al. (2007) Extracellular ATP triggers and maintains asthmatic airway inflammation by activating dendritic cells. Nat Med 13: 913–919.M. IdzkoH. HammadM. van NimwegenM. KoolMA Willart2007Extracellular ATP triggers and maintains asthmatic airway inflammation by activating dendritic cells.Nat Med13913919
  28. 28. Nemeth ZH, Lutz CS, Csoka B, Deitch EA, Leibovich SJ, et al. (2005) Adenosine augments IL-10 production by macrophages through an A2B receptor-mediated posttranscriptional mechanism. J Immunol 175: 8260–8270.ZH NemethCS LutzB. CsokaEA DeitchSJ Leibovich2005Adenosine augments IL-10 production by macrophages through an A2B receptor-mediated posttranscriptional mechanism.J Immunol17582608270
  29. 29. Wilson JM, Ross WG, Agbai ON, Frazier R, Figler RA, et al. (2009) The A2B adenosine receptor impairs the maturation and immunogenicity of dendritic cells. J Immunol 182: 4616–4623.JM WilsonWG RossON AgbaiR. FrazierRA Figler2009The A2B adenosine receptor impairs the maturation and immunogenicity of dendritic cells.J Immunol18246164623
  30. 30. Khoury J, Ibla JC, Neish AS, Colgan SP (2007) Antiinflammatory adaptation to hypoxia through adenosine-mediated cullin-1 deneddylation. J Clin Invest 117: 703–711.J. KhouryJC IblaAS NeishSP Colgan2007Antiinflammatory adaptation to hypoxia through adenosine-mediated cullin-1 deneddylation.J Clin Invest117703711
  31. 31. Yang D, Zhang Y, Nguyen HG, Koupenova M, Chauhan AK, et al. (2006) The A2B adenosine receptor protects against inflammation and excessive vascular adhesion. J Clin Invest 116: 1913–1923.D. YangY. ZhangHG NguyenM. KoupenovaAK Chauhan2006The A2B adenosine receptor protects against inflammation and excessive vascular adhesion.J Clin Invest11619131923
  32. 32. Csoka B, Nemeth ZH, Rosenberger P, Eltzschig HK, Spolarics Z, et al. (2010) A2B adenosine receptors protect against sepsis-induced mortality by dampening excessive inflammation. J Immunol 185: 542–550.B. CsokaZH NemethP. RosenbergerHK EltzschigZ. Spolarics2010A2B adenosine receptors protect against sepsis-induced mortality by dampening excessive inflammation.J Immunol185542550
  33. 33. Belikoff BG, Hatfield S, Georgiev P, Ohta A, Lukashev D, et al. (2011) A2B adenosine receptor blockade enhances macrophage-mediated bacterial phagocytosis and improves polymicrobial sepsis survival in mice. J Immunol 186: 2444–2453.BG BelikoffS. HatfieldP. GeorgievA. OhtaD. Lukashev2011A2B adenosine receptor blockade enhances macrophage-mediated bacterial phagocytosis and improves polymicrobial sepsis survival in mice.J Immunol18624442453
  34. 34. Eltzschig HK, Abdulla P, Hoffman E, Hamilton KE, Daniels D, et al. (2005) HIF-1-dependent repression of equilibrative nucleoside transporter (ENT) in hypoxia. J Exp Med 202: 1493–1505.HK EltzschigP. AbdullaE. HoffmanKE HamiltonD. Daniels2005HIF-1-dependent repression of equilibrative nucleoside transporter (ENT) in hypoxia.J Exp Med20214931505
  35. 35. Kong T, Westerman KA, Faigle M, Eltzschig HK, Colgan SP (2006) HIF-dependent induction of adenosine A2B receptor in hypoxia. Faseb J 20: 2242–2250.T. KongKA WestermanM. FaigleHK EltzschigSP Colgan2006HIF-dependent induction of adenosine A2B receptor in hypoxia.Faseb J2022422250
  36. 36. Kuhlicke J, Frick JS, Morote-Garcia JC, Rosenberger P, Eltzschig HK (2007) Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia. PLoS One 2: e1364.J. KuhlickeJS FrickJC Morote-GarciaP. RosenbergerHK Eltzschig2007Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia.PLoS One2e1364
  37. 37. Cummins EP, Berra E, Comerford KM, Ginouves A, Fitzgerald KT, et al. (2006) Prolyl hydroxylase-1 negatively regulates IkappaB kinase-beta, giving insight into hypoxia-induced NFkappaB activity. Proc Natl Acad Sci U S A 103: 18154–18159.EP CumminsE. BerraKM ComerfordA. GinouvesKT Fitzgerald2006Prolyl hydroxylase-1 negatively regulates IkappaB kinase-beta, giving insight into hypoxia-induced NFkappaB activity.Proc Natl Acad Sci U S A1031815418159
  38. 38. Keely S, Glover LE, MacManus CF, Campbell EL, Scully MM, et al. (2009) Selective induction of integrin beta1 by hypoxia-inducible factor: implications for wound healing. Faseb J 23: 1338–1346.S. KeelyLE GloverCF MacManusEL CampbellMM Scully2009Selective induction of integrin beta1 by hypoxia-inducible factor: implications for wound healing.Faseb J2313381346
  39. 39. Sun CX, Zhong H, Mohsenin A, Morschl E, Chunn JL, et al. (2006) Role of A2B adenosine receptor signaling in adenosine-dependent pulmonary inflammation and injury. J Clin Invest 116: 2173–2182.CX SunH. ZhongA. MohseninE. MorschlJL Chunn2006Role of A2B adenosine receptor signaling in adenosine-dependent pulmonary inflammation and injury.J Clin Invest11621732182
  40. 40. Mustafa SJ, Nadeem A, Fan M, Zhong H, Belardinelli L, et al. (2007) Effect of a specific and selective A(2B) adenosine receptor antagonist on adenosine agonist AMP and allergen-induced airway responsiveness and cellular influx in a mouse model of asthma. J Pharmacol Exp Ther 320: 1246–1251.SJ MustafaA. NadeemM. FanH. ZhongL. Belardinelli2007Effect of a specific and selective A(2B) adenosine receptor antagonist on adenosine agonist AMP and allergen-induced airway responsiveness and cellular influx in a mouse model of asthma.J Pharmacol Exp Ther32012461251
  41. 41. Zaynagetdinov R, Ryzhov S, Goldstein AE, Yin H, Novitskiy SV, et al. (2010) Attenuation of chronic pulmonary inflammation in A2B adenosine receptor knockout mice. Am J Respir Cell Mol Biol 42: 564–571.R. ZaynagetdinovS. RyzhovAE GoldsteinH. YinSV Novitskiy2010Attenuation of chronic pulmonary inflammation in A2B adenosine receptor knockout mice.Am J Respir Cell Mol Biol42564571
  42. 42. Zhou Y, Mohsenin A, Morschl E, Young HW, Molina JG, et al. (2009) Enhanced airway inflammation and remodeling in adenosine deaminase-deficient mice lacking the A2B adenosine receptor. J Immunol 182: 8037–8046.Y. ZhouA. MohseninE. MorschlHW YoungJG Molina2009Enhanced airway inflammation and remodeling in adenosine deaminase-deficient mice lacking the A2B adenosine receptor.J Immunol18280378046
  43. 43. Zhou Y, Schneider DJ, Morschl E, Song L, Pedroza M, et al. (2011) Distinct Roles for the A2B Adenosine Receptor in Acute and Chronic Stages of Bleomycin-Induced Lung Injury. J Immunol 186: 1097–1106.Y. ZhouDJ SchneiderE. MorschlL. SongM. Pedroza2011Distinct Roles for the A2B Adenosine Receptor in Acute and Chronic Stages of Bleomycin-Induced Lung Injury.J Immunol18610971106
  44. 44. Zhang Y, Dai Y, Wen J, Zhang W, Grenz A, et al. (2011) Detrimental effects of adenosine signaling in sickle cell disease. Nat Med 17: 79–86.Y. ZhangY. DaiJ. WenW. ZhangA. Grenz2011Detrimental effects of adenosine signaling in sickle cell disease.Nat Med177986
  45. 45. Dai Y, Zhang W, Wen J, Zhang Y, Kellems RE, et al. (2011) A2B adenosine receptor-mediated induction of IL-6 promotes CKD. J Am Soc Nephrol 22: 890–901.Y. DaiW. ZhangJ. WenY. ZhangRE Kellems2011A2B adenosine receptor-mediated induction of IL-6 promotes CKD.J Am Soc Nephrol22890901
  46. 46. Sitkovsky MV, Kjaergaard J, Lukashev D, Ohta A (2008) Hypoxia-adenosinergic immunosuppression: tumor protection by T regulatory cells and cancerous tissue hypoxia. Clin Cancer Res 14: 5947–5952.MV SitkovskyJ. KjaergaardD. LukashevA. Ohta2008Hypoxia-adenosinergic immunosuppression: tumor protection by T regulatory cells and cancerous tissue hypoxia.Clin Cancer Res1459475952
  47. 47. Du G, Jin L, Han X, Song Z, Zhang H, et al. (2009) Naringenin: a potential immunomodulator for inhibiting lung fibrosis and metastasis. Cancer Res 69: 3205–3212.G. DuL. JinX. HanZ. SongH. Zhang2009Naringenin: a potential immunomodulator for inhibiting lung fibrosis and metastasis.Cancer Res6932053212
  48. 48. Liu F, Liu J, Weng D, Chen Y, Song L, et al. (2010) CD4+CD25+Foxp3+ regulatory T cells depletion may attenuate the development of silica-induced lung fibrosis in mice. PLoS One 5: e15404.F. LiuJ. LiuD. WengY. ChenL. Song2010CD4+CD25+Foxp3+ regulatory T cells depletion may attenuate the development of silica-induced lung fibrosis in mice.PLoS One5e15404
  49. 49. Zeng M, Smith AJ, Wietgrefe SW, Southern PJ, Schacker TW, et al. (2011) Cumulative mechanisms of lymphoid tissue fibrosis and T cell depletion in HIV-1 and SIV infections. J Clin Invest 121: 998–1008.M. ZengAJ SmithSW WietgrefePJ SouthernTW Schacker2011Cumulative mechanisms of lymphoid tissue fibrosis and T cell depletion in HIV-1 and SIV infections.J Clin Invest1219981008
  50. 50. Nakatsukasa H, Tsukimoto M, Harada H, Kojima S (2011) Adenosine A2B receptor antagonist suppresses differentiation to regulatory T cells without suppressing activation of T cells. Biochem Biophys Res Commun 409: 114–119.H. NakatsukasaM. TsukimotoH. HaradaS. Kojima2011Adenosine A2B receptor antagonist suppresses differentiation to regulatory T cells without suppressing activation of T cells.Biochem Biophys Res Commun409114119
  51. 51. Wilson JM, Kurtz CC, Black SG, Ross WG, Alam MS, et al. (2011) The A2B adenosine receptor promotes Th17 differentiation via stimulation of dendritic cell IL-6. J Immunol 186: 6746–6752.JM WilsonCC KurtzSG BlackWG RossMS Alam2011The A2B adenosine receptor promotes Th17 differentiation via stimulation of dendritic cell IL-6.J Immunol18667466752
  52. 52. Kimura A, Kishimoto T (2010) IL-6: regulator of Treg/Th17 balance. Eur J Immunol 40: 1830–1835.A. KimuraT. Kishimoto2010IL-6: regulator of Treg/Th17 balance.Eur J Immunol4018301835
  53. 53. Rosenberger P, Schwab JM, Mirakaj V, Masekowsky E, Mager A, et al. (2009) Hypoxia-inducible factor-dependent induction of netrin-1 dampens inflammation caused by hypoxia. Nat Immunol 10: 195–202.P. RosenbergerJM SchwabV. MirakajE. MasekowskyA. Mager2009Hypoxia-inducible factor-dependent induction of netrin-1 dampens inflammation caused by hypoxia.Nat Immunol10195202
  54. 54. Aherne CM, Collins CB, Masterson JC, Tizzano M, Boyle TA, et al. (2011) Neuronal guidance molecule netrin-1 attenuates inflammatory cell trafficking during acute experimental colitis. Gut. CM AherneCB CollinsJC MastersonM. TizzanoTA Boyle2011Neuronal guidance molecule netrin-1 attenuates inflammatory cell trafficking during acute experimental colitis.GutAug 3 [Epub ahead of print]. Aug 3 [Epub ahead of print].
  55. 55. Mirakaj V, Thix CA, Laucher S, Mielke C, Morote-Garcia JC, et al. (2010) Netrin-1 dampens pulmonary inflammation during acute lung injury. Am J Respir Crit Care Med 181: 815–824.V. MirakajCA ThixS. LaucherC. MielkeJC Morote-Garcia2010Netrin-1 dampens pulmonary inflammation during acute lung injury.Am J Respir Crit Care Med181815824
  56. 56. Robinson A, Keely S, Karhausen J, Gerich ME, Furuta GT, et al. (2008) Mucosal protection by hypoxia-inducible factor prolyl hydroxylase inhibition. Gastroenterology 134: 145–155.A. RobinsonS. KeelyJ. KarhausenME GerichGT Furuta2008Mucosal protection by hypoxia-inducible factor prolyl hydroxylase inhibition.Gastroenterology134145155
  57. 57. Cummins EP, Seeballuck F, Keely SJ, Mangan NE, Callanan JJ, et al. (2008) The hydroxylase inhibitor dimethyloxalylglycine is protective in a murine model of colitis. Gastroenterology 134: 156–165.EP CumminsF. SeeballuckSJ KeelyNE ManganJJ Callanan2008The hydroxylase inhibitor dimethyloxalylglycine is protective in a murine model of colitis.Gastroenterology134156165
  58. 58. Lin W, Haribhai D, Relland LM, Truong N, Carlson MR, et al. (2007) Regulatory T cell development in the absence of functional Foxp3. Nat Immunol 8: 359–368.W. LinD. HaribhaiLM RellandN. TruongMR Carlson2007Regulatory T cell development in the absence of functional Foxp3.Nat Immunol8359368
  59. 59. Lahl K, Loddenkemper C, Drouin C, Freyer J, Arnason J, et al. (2007) Selective depletion of Foxp3+ regulatory T cells induces a scurfy-like disease. J Exp Med 204: 57–63.K. LahlC. LoddenkemperC. DrouinJ. FreyerJ. Arnason2007Selective depletion of Foxp3+ regulatory T cells induces a scurfy-like disease.J Exp Med2045763
  60. 60. Haribhai D, Lin W, Relland LM, Truong N, Williams CB, et al. (2007) Regulatory T cells dynamically control the primary immune response to foreign antigen. J Immunol 178: 2961–2972.D. HaribhaiW. LinLM RellandN. TruongCB Williams2007Regulatory T cells dynamically control the primary immune response to foreign antigen.J Immunol17829612972