Published online before print October 3, 2008
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Institute of Experimental and Clinical Pharmacology, Medical University Graz, Graz, Austria
1 Correspondence: Institute of Experimental and Clinical Pharmacology, Medical University of Graz, Universitaetsplatz 4. A-8010 Graz, Austria. E-mail: akos.heinemann{at}meduni-graz.at
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Key Words: allergy • D-type prostanoid • HEK293 • D-type prostanoid receptor • platelet aggregation • degranulation
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Two G-protein-coupled receptors for PGD2 have been described to date: chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2) and D-type prostanoid receptor (DP). CRTH2 was discovered as a seven transmembrane-spanning protein expressed by Th2 cells, eosinophils, and basophils [9
]. In fact, PGD2 is chemotactic for Th2 cells, eosinophils, and basophils. However, CRTH2 has been shown to have a broader spectrum of ligands, as it is also activated by several PGD2 metabolites, including 13,14-dihydro-15-keto-PGD2, PGJ2, 15-deoxy-
12,14-PGJ2, 12-PGJ2 [10
, 11
], as well as 9
,11β-PGF2 and its stereoisomer PGF2 [12
] and a thromboxane (TX) metabolite, 11-dehydro-TXB2 [13
].
CRTH2 activation can lead to a plethora of biological effects that include the induction of the chemotaxis of eosinophils, basophils, and Th2 cells [9 , 14 ], the respiratory burst of eosinophils [11 , 15 ], and enhancement of histamine release from basophils [16 ]. Interestingly, osteoblasts and osteoclasts express CRTH2, which modulates their migration and activity [8 , 17 ]. Moreover, we have shown that CRTH2 agonists prime eosinophils for chemotaxis toward other chemoattractants [11 , 18 ] and are capable of mediating the rapid mobilization of eosinophils from the isolated hind limb of guinea pigs [11 ]. In rats, CRTH2 mediates eosinophil infiltration into the lungs and skin [19 , 20 ], and studies in murine models of allergic disease revealed that the PGD2-CRTH2 system plays a significant role in chronic allergic skin inflammation [21 22 23 ], pollen-induced rhinitis [24 ], and allergic airway inflammation [21 , 25 , 26 ].
The alternate PGD2 receptor DP is expressed more widely, including platelets, several types of leukocytes, osteoblasts, the vasculature, the CNS, retina, nasal mucosa, lungs, and intestine [8 , 9 , 27 28 29 30 ]. Functionally, DP-mediated responses include inhibition of platelet aggregation, induction of vasorelaxation, mucin secretion, and lowering intraocular pressure [30 31 32 ]. DP agonists have been suggested to inhibit neutrophil, basophil, and dendritic cell function [33 34 35 36 ]. Eosinophils also express the DP receptor [37 , 38 ] and show delayed apoptosis after treatment with a selective DP agonist [37 ]. Recently, we described that the DP receptor plays an important modulator role in the trafficking of eosinophils [38 ]. In vivo, DP has been shown to mediate antigen-induced rhinitis, conjunctivitis, and pulmonary inflammation in the guinea pig [39 ], and DP-deficient mice exhibit reduced pulmonary inflammation in response to allergen [40 ].
The accumulating body of data suggesting a pathogenic role of PGD2 in allergic disease has prompted the interest in CRTH2 and DP as potentially useful therapeutic targets. Accordingly, synthesis of several CRTH2 and DP antagonists has been reported in the meanwhile [15 , 39 , 41 42 43 44 45 46 47 48 49 ]. In addition, the selective inhibition of PGD2 biosynthesis by means of PGDS inhibitors is being considered [22 , 50 51 52 ]. In this case, PGH2 would not be isomerized to PGD2 but be metabolized by an alternate PG synthase present in the cell or released unmodified from the cell. In fact, release of PGH2 from cells under normal and/or inflammatory conditions has been reported [53 , 54 ]. PGH2 has been shown to be a highly potent agonist on the TX receptor, TP [55 ], but its effect on PGD2 receptors has not been investigated. Here, we describe that PGH2 mimics the effect of PGD2 on CRTH2 and DP receptors and may, therefore, play a role in allergic inflammation, even in the absence of functional PGDS.
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,2(Z),3|,4]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazine]methyl]-7-oxabicylo[2.2.1] hept-2-yl]-5-heptenoic acid (SQ29548), and 3-[(2-cyclohexyl-2-hydroxyethyl)amino]-2,5-dioxo-1-(phenylmethyl)-4-imidazolidine-heptanoic acid (BWA868c) were purchased from Cayman (Ann Arbor, MI, USA). CellFix® and FACS-Flow® were from Becton Dickinson (Vienna, Austria). Fixative solution was prepared by adding 9 mL distilled water and 30 mL FACS-Flow® to 1 mL CellFix®. Collagen was obtained from Probe&Go (Endingen, Germany). Drugs were dissolved in ethanol or DMSO and diluted further in assay buffer to give a final concentration of the solvents <0.1%.
Cloning and expression of human CRTH2 and DP receptors
The DNA coding for the human DP receptor was cloned into a modified eukaryotic expression vector SSFLAG-pcDNA3.1(+) [56
] and verified by sequencing. Dr. Evi Kostenis (Institute of Pharmaceutical Biology, University of Bonn, Germany) provided the human CRTH2 receptor cloned into the eukaryotic expression vector pcDNA3.1 (+) and the constructs hemagglutinin (HA)-6-Gqi4-myr-pcDNA3.1 Zeo and HA-6-Gqs5-myr-pcDNAI.
Human embryonic kidney (HEK)293 cells (American Type Culture Collection, Manassas, VA, USA) were maintained in culture in DMEM (Invitrogen), supplemented with 10% FCS at 37°C in a 5% CO2-humidified atmosphere. Stable cell lines expressing recombinant receptors were generated by clonal selection in drug-containing media: HEK293 cells stably expressing DP or CRTH2 were cultured in DMEM containing 10% FCS and 0.1 mg/ml Zeocin (Invitrogen) or 0.2 mg/ml Geneticin 418 (Invitrogen), respectively. For transient coexpression of 6-Gqs5-myr and DP or 6-Gqi4-myr and CRTH2, 40,000 cells were transfected with 200 ng of the respective DNA by using Lipofectamin2000 (Invitrogen), according to the manufacturer’s instructions.
Leukocyte shape-change assay
The Ethics Committee of the Medical University of Graz (Austria) approved this study. Prior to blood sampling from healthy volunteers, all donors signed an informed consent form. Aliquots (90 µL) of citrated whole blood were stimulated with 10 µl agonists for 4 min at 37°C. The samples were then transferred to ice and fixed with 250 µl fixative solution followed by NH4Cl–induced lysis of RBC [57
]. Cells were then washed and resuspended in 250 µL fixative solution. To record shape-change responses in the absence of plasma, preparations of polymorphonuclear leukocytes (PMN; containing eosinophils and neutrophils) were obtained by dextran sedimentation of whole blood and centrifugation on Histopaque gradients as described [11
]. Samples were analyzed immediately on a FACSCalibur flow cytometer (Becton Dickinson, Mountain View, CA, USA). Eosinophils were distinguished from other cells according to their autofluorescence in the fluorescence 1 (FL-1) and FL-2 channels (see Fig. 1A
) [11
].
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Figure 1. PGH2 induces the shape change of eosinophils by activation of CRTH2. (A) Original flow cytometric plots of PGH2-induced eosinophil shape change. Eosinophils in whole blood were gated by autofluorescence in FL-1 and FL-2 and then plotted separately from other leukocytes. As compared with the vehicle-stimulated sample, the mean value (X) for the forward-scatter (FSC) increased markedly after stimulation with 75 nM PGH2. (B) Samples of whole blood were pretreated with vehicle or the hematopoietic PGDS inhibitor HQL79 (6.6 µM) and stimulated with vehicle or various concentrations of PGH2, PGD2, eotaxin, or arachidonic acid. (C) PMN in PBS without BSA or with 1% of BSA were pretreated with vehicle or the CRTH2 antagonist Cay10471 (100 nM) for 10 min and then stimulated with various concentrations of PGH2 or PGD2. Shape change was recorded as the flow cytometric increase in forward-scatter, and responses were expressed as percent of baseline. Data are the mean ± SEM of four to six experiments.
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Calcium ion (Ca2+) flux
Intracellular Ca2+ levels in eosinophils were analyzed by flow cytometry as described [10
, 11
, 59
]. PMN (107 cells/ml) were treated with 2 µM of the acetoxymethyl ester of Fluo-3 in the presence of 0.02% pluronic F-127 for 60 min at room temperature and washed in PBS without Ca2+/Mg2+. The leukocytes were then labeled with anti-CD16 (PE) for 6 min at room temperature, washed, and resuspended in assay buffer without Ca2+/Mg2+ to give a concentration of 3 x 106 leukocytes/ml. Aliquots (950 µl) of the leukocyte suspension were removed and treated with 50 µl PBS containing Ca2+ (36 mM) and Mg2+ (20 mM) for 5 min. Changes in intracellular-free Ca2+ levels were detected at room temperature by flow cytometry as increases in fluorescence intensity of the Ca2+-sensitive dye Fluo-3 in the FL-1 channel. In some experiments, a first agonist was added to the cell sample followed by a second agonist 6 min later. Maximal Ca2+ responses were determined by the addition of the Ca2+ ionophore A23187 (10 µM) at the end of each experiment.
In addition, agonist-induced Ca2+ signaling was measured in HEK293 cells coexpressing 6-Gqs5-myr and DP or 6-Gqi4-myr and CRTH2, respectively. Twenty-four hours post-transfection, cells were loaded for 60 min with a Ca2+ fluorophore (FLIPR® Calcium 4 Assay Kit, Molecular Devices, Sunnyvale, CA, USA). Intracellular Ca2+ mobilization was measured immediately after agonist application and recorded for 2 min in a FlexStationTM II system (Molecular Devices). EC50 values were determined by nonlinear regression analysis using the GraphPad Prism 4.0 software.
Eosinophil degranulation
To determine the release of eosinophil peroxidase (EPO) and myeloperoxidase (MPO) from activated granulocytes, purified human eosinophils or neutrophils were resuspended in assay buffer at 1 x 106 cells/ml, mixed with cytochalasin B (10 µg/ml), and 50 µl aliquots were loaded into the wells of a 96-well microplate. Cells were stimulated with 20 µl of various concentrations of C5a for 20 min at 37°C. Thereafter, 60 µl H2O2 (1 mM) was added to each well to start the peroxidase reaction. To detect the reaction, 70 µl 2.8 mM tetramethylbenzidine was added. Following incubation for 1 min at room temperature, the peroxidase reaction and the color development were terminated with 4 M acetic acid [60
]. Microplates were analyzed on a bench reader at a wavelength of 630 nm. Data were expressed as percent of the maximal control response (C5a at 300 nM).
Platelet aggregation
Human platelet-rich plasma and platelet-poor plasma were prepared from citrated whole blood by centrifugation. Platelet aggregation was recorded at 37°C with constant stirring (1000 rpm) in a four-channel Aggrecorder II aggregometer (KDK Corp., Kyoto, Japan) as described [13
, 61
]. Platelet aggregation was measured as the increase in light transmission for 5 min, starting with the addition of collagen (1.25–10 µg/ml) as a proaggregatory stimulus. CaCl2 at a final concentration of 1 mM was added 2 min before collagen. To record inhibition of collagen-induced aggregation, PGD2 or PGH2 was added 2 min before collagen. The antagonists or their vehicle were added 10 min before PGD2. Data were expressed as percent of maximum light transmission, and nonstimulated, platelet-rich plasma was 0% and platelet-poor plasma, 100%.
Statistical analyses
Data are shown as mean ± SEM for n observations. Comparisons of groups were performed using two-way ANOVA for repeated measurements, and probability values of P < 0.05 were considered as statistically significant.
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To test the involvement of CRTH2 in the eosinophil shape-change responses to PGH2, cells were pretreated with the CRTH2 antagonist Cay10471 (100 nM) or vehicle for 10 min at 37°C. In fact, Cay10471 abolished the shape-change responses of eosinophils to PGH2 and PGD2 (Fig. 1C) but had no effect on eosinophil responses to eotaxin (data not shown, n=4). The conjecture of PGH2 acting through the same receptor as PGD2 was also confirmed in Ca2+ flux assays: PGH2 elicited effective Ca2+ responses in eosinophils in a concentration-dependent manner (Fig. 2A ) and completely desensitized eosinophils to a subsequent challenge with PGD2 but not eotaxin (Fig. 2B) . PGH2 exhibited similar efficacy as PGD2 but was 30-fold less potent at inducing Ca2+ flux in eosinophils (Fig. 2A) . None of these chemoattractants induced Ca2+ flux in neutrophils (data not shown, n=4).
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Figure 2. PGH2 induces Ca2+ flux in eosinophils and desensitizes eosinophils selectively against PGD2. Ca2+ flux was assayed in PMN preparations loaded with Fluo-3 and labeled with CD16 antibodies by flow cytometry. Fluorescence changes in response to agonists were recorded in CD16-negative eosinophils in the FL-1 fluorescence channel. (A) Responses to increasing concentrations of PGH2 and PGD2 and 1 nM eotaxin (Eotax) were recorded. Data are the mean ± SEM of 10 experiments. (B) Cells were stimulated with a first agonist and 5 min later, by a second agonist. The graph shows a typical tracing out of five experiments.
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Figure 3. PGH2 induces eosinophil migration. Purified eosinophils were applied to the top wells of microBoyden chambers and were allowed to migrate toward PGH2 or PGD2 diluted in PBS with and without 1% of plasma. Cells that had migrated to the bottom wells were enumerated by flow cytometry. Data are the mean ± SEM of seven experiments performed in duplicate.
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Figure 4. PGH2 inhibits eosinophil degranulation by activation of CRTH2 receptors. (A) Purified eosinophils or neutrophils were mixed with vehicle or PGH2 at the concentrations indicated and then stimulated with C5a, and EPO or MPO activity was measured by photometry. (B) Purified eosinophils were pretreated with vehicle or the CRTH2 antagonist Cay10471 (100 nM) and mixed with vehicle or PGH2 at the concentrations indicated. Cells were then stimulated with C5a, and EPO or MPO activity was measured by photometry. Data are mean ± SEM of three to nine independent experiments performed in duplicate. *, P < 0.05, versus the control concentration response curve to C5a.
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1 µM) were able to induce platelet aggregation of a moderate extent, and as expected, this effect was abolished after pretreatment for 10 min with 100 nM of the TP receptor antagonist SQ29548 (Fig. 6A
). However, the efficacy of PGH2 to induce platelet aggregation was increased markedly after pretreatment of platelets with the DP antagonist BWA868c (100 nM) for 10 min (Fig. 6A)
. Similarly, the potency of PGH2 to induce platelet aggregation was tenfold and its efficacy twofold, increased in the absence of plasma, i.e., in washed platelet preparations, as compared with platelet-rich plasma (Fig. 6B)
. This was not a result of nonspecific enhancement of the sensitivity of the platelets, as the aggregatory effect of collagen was similar in washed platelet preparations and platelet-rich plasma (Fig. 6C)
.
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Figure 5. PGH2 inhibits collagen-induced platelet aggregation by activation of DP receptors. Platelet-rich plasma was pretreated with vehicle, the hematopoietic PGDS inhibitor HQL79 (6.6 µM), or the DP receptor antagonist BWA868c (100 nM). Samples were then incubated with various concentrations of PGH2 (A) or PGD2 (B), and finally, platelet aggregation in response to collagen was recorded. Data are the mean ± SEM of four to six experiments. *, P < 0.05, versus pretreatment with vehicle.
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Figure 6. Blockade of DP receptors enhances the stimulatory effect of high concentrations of PGH2 on the aggregation of platelets. (A) Platelet-rich plasma was pretreated with vehicle, the DP receptor antagonist BWA868c or BWA868c plus the TP receptor antagonist SQ29548 at the concentration of 100 nM each, and then platelet aggregation in response to various PGH2 was recorded. (B and C) Platelet-rich plasma or washed platelets were stimulated with PGH2 or collagen, and platelet aggregation was recorded. Data are the mean ± SEM of four to six experiments. *, P < 0.05, versus the control concentration response curve to PGH2.
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6Gqs5myr, which is capable of transforming the activation Gs-coupled receptors into Gq-induced Ca2+ signals [63
]. For the same reason, CRTH2-expressing cells were cotransfected with the chimeric G protein G6Gqi4myr. Untransfected HEK293 cells did not respond with Ca2+ flux to PGH2 or PGD2 (data not shown, n=3). In contrast, cells transfected with human DP and G6Gqs5myr were highly sensitive to PGD2 and responded to PGH2 (Fig. 7A
). The EC50 values for PGD2 and PGH2 for the induction of Ca2+ flux in DP-expressing cells were 0.0002 ± 0.21 and 0.04 ± 0.21 nM, respectively. Similarly, PGH2 and PGD2 potently elicited Ca2+ flux in HEK293 transfected with human CRTH2 and G6Gqi4myr (Fig. 7B)
. In this case, the EC50 values for PGD2 and PGH2 were 0.24 ± 0.20 and 6.24 ± 0.16 nM, respectively. The DP antagonist BWA868c and the CRTH2 antagonist Cay10471 (1 µM each) largely abolished the Ca2+ responses to PGH2 in DP- and CRTH2-expressing cells, respectively (Fig. 7 C and D)
. In contrast, the TP antagonist SQ29548 had no effect, demonstrating that TP receptors endogenously expressed by HEK293 cells are not involved in the response to PGH2 (Fig. 7D)
.
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Figure 7. PGH2 induces Ca2+ flux in HEK293 cells expressing human DP or CRTH2 receptors. HEK293 cells were transfected with CRTH2 and G6Gqi4myr or DP and G6Gqs5myr proteins. Cells were loaded with a Ca2+ fluorophore, and agonist-induced changes in intracellular Ca2+ levels were measured with a fluorescence plate reader for 2 min after application of PGH2, PGD2, or their vehicle. (B and C) Cells were pretreated with the CRTH2 antagonist Cay10471, the DP antagonist BWA868c, the TP antagonist SQ29548 (1 µM each), or their vehicle and were then stimulated with PGH2. Data are the mean ± SEM of three to five independent experiments performed in duplicate. *, P < 0.05, versus the control concentration response curve to PGH2.
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In detail, in agreement with previous studies, we observed that PGH2 was able to induce platelet aggregation [55 ], and this was prevented by the TP receptor antagonist SQ29548. However, under physiological conditions (i.e., in the presence of plasma), its proaggregatory potency and efficacy were low (EC50=1–3 µM; maximal efficacy, 42% aggregation). At considerably lower concentrations (IC50=100 nM), however, PGH2 exhibited potent inhibitory action against collagen-induced platelet aggregation. This antiaggregatory effect was mediated by DP receptors, as inferred from BWA868c preventing it. These observations, therefore, suggest that PGH2 activates DP and TP receptors in platelets, but under physiological conditions, DP receptor activation and ensuing inhibition of platelet aggregation are predominant.
The effect of PGH2 on CRTH2 was tested in eosinophils. We have shown previously that CRTH2 activation in these cells causes flow cytometric shape change that is mediated by Gq proteins, phospholipase C, and actin rearrangement [58
]. In fact, PGH2 induced the shape change of human peripheral blood eosinophils in a CRTH2-dependent manner, but in the absence of plasma, the potency of PGH2 was low, i.e., 100-fold lower than that of PGD2. In whole blood, however, PGH2 was highly potent and effective, almost as potent as the CCR3 ligand eotaxin, which is among the most potent eosinophil chemoattractants known to date. Similar results were obtained with basophils, where PGH2 induced shape change with a similar potency as in eosinophils. Consistent with its effect to cause eosinophil shape change, PGH2 also induced the elevation of intracellular-free Ca2+ in eosinophils to similar levels as PGD2 and eotaxin. The involvement of CRTH2 in this mechanism was demonstrated by homologous receptor desensitization, as PGD2 and PGH2 mutually desensitized eosinophils to each other but not to eotaxin, suggesting that the two PGs were acting via the same receptor.
The primary role of PGD2 and CRTH2 in eosinophil function is the regulation of eosinophil trafficking, as activation of CRTH2 results in eosinophil mobilization from bone marrow, direct stimulation of chemotaxis, and priming of eosinophils for migration toward other chemoattractants [9 , 11 , 18 , 41 ]. Accumulation of eosinophils at sites of allergic reactions, such as eczema or asthma, is a hallmark of tissue injury and lung dysfunction [70 ]. Asthmatic patients that receive treatment based on eosinophil counts in sputum have significantly fewer severe asthma exacerbations than patients treated according to standard management therapy [71 ]. Moreover, genetically modified mice lacking eosinophils are protected against allergen-induced lung injury and asthma [72 , 73 ]. In keeping with the ability of PGH2 to activate CRTH2, eosinophils migrated toward PGH2 in chemotaxis assays. As also observed for inhibition of platelet aggregation, the addition of plasma (1%) to the assay buffer markedly enhanced the chemotactic efficacy of the prostanoid. This observation and the fact that the PGH2-induced shape change of eosinophils and inhibition of platelet aggregation were substantially more prominent in whole blood and plasma, respectively, prompt the question of whether PGH2 is being transformed to active metabolites, such as PGD2, in the presence of plasma proteins. On the other hand, the fact that PGH2 was also chemotactic in protein-free assay buffer is remarkable and suggests that short-term exposure of eosinophils to a CRTH2 ligand for a few minutes is sufficient to initiate and maintain directed movement of the cells.
Previous studies showed that the isomerization of PGH2 into PGD2 can be catalyzed by serum albumin [74 ] and that lipocalin-type PGDS is present in plasma [75 , 76 ]. This would support the possibility that rapid conversion of PGH2 to PGD2 in plasma accounts for the CRTH2- and DP-stimulating activity of PGH2. To test the hypothesis that PGH2 directly binds to CRTH2 and DP and to minimize the possibility of PGH2 being transformed to PGD2, we used HEK293 cells transfected with CRTH2 or DP and recorded agonist-induced Ca2+ flux as an indirect but immediate (within less than 3 s) measure of receptor binding in protein-free assay buffer. This approach was preferred over conventional binding studies, which imply incubation times of at least 1 h, hence, allowing decomposition of labile ligands. The fact that HEK293 cells transfected with CRTH2 or DP responded with Ca2+ flux within 3 s following PGH2 stimulation argues for a direct binding of PGH2 to these prostanoid receptors. In contrast, the half-life of PGH2 in aqueous media has been described to be 4–5 min [77 ]. Moreover, in the absence of proteins, PGH2 isomerizes almost exclusively to PGE2 [74 , 77 ], which in turn lacks any agonistic activity on DP or CRTH2. The effects of PGH2 on platelet aggregation, however, probably involve conversion of PGH2 to PGD2, as the DP-dependent activity of PGH2 could only be observed in the presence of plasma, and the TP-mediated stimulation of platelet aggregation was obliterated by plasma. Similarly, eosinophil chemotaxis toward PGH2 was enhanced in the presence of plasma, which suggests the generation of the more potent CRTH2 ligand, PGD2.
The binding of chemoattractants to plasma proteins and also cellular components can fundamentally alter their potency. With respect to the current data, it might be of importance that eotaxin binds to the Duffy antigen of erythrocytes, which reduces its potency more than tenfold [78 ]. Similarly, the potency of another eosinophil chemoattractant, 5-oxo-6,8,11,14-eicosatetraenoic acid, is reduced by plasma proteins 30-fold [18 ]. The same does not hold true for PGD2, as responses of eosinophils to PGD2 were not different in whole blood versus PBS [18 ]. However, we also observed that there is a time-dependent metabolism of PGD2 in plasma with an estimated half-life of 35 min for PGD2 [61 ]. These observations show that the dynamics and kinetics of chemoattractants are altered by blood components.
Finally, we tested the effect of PGH2 on eosinophil degranulation, i.e., the release of EPO activity into the supernatants of eosinophils. As we have shown previously for PGD2 [41 ], PGH2 did not stimulate EPO release by itself but effectively inhibited the C5a-induced EPO release from eosinophils. PGH2 mimicked the inhibitory effect of PGD2 on eosinophil degranulation in two ways: First, this effect was selective for eosinophils, as neutrophil degranulation was left largely unaltered by PGH2, and second, the inhibitory effect of PGH2 was reversed by the CRTH2 antagonist Cay10471. This observation further supports the role of CRTH2 ligands as initial chemoattractants in the hierarchy of chemoattractants, governing the evasion of eosinophils from the vascular space but restraining their degranulator activity. This stands in contrast to endpoint chemoattractants, such as eotaxin or C5a, which are effective degranulators of eosinophils [18 ].
In summary, we have demonstrated that PGH2 is a potent agonist on the PGD2 receptors CRTH2 and DP. Given that PGH2 is released in substantial amounts from activated endothelial cells and lung tissue, our data suggest that PGH2 might be involved in the recruitment of CRTH2-expressing inflammatory cells, such as eosinophils, basophils, and Th2 cells, to sites of allergic reactions. The interaction of PGH2 with CRTH2 and DP appears to take place directly and by means of PGH2 isomerization to PGD2 in plasma.
Received June 25, 2008; revised August 22, 2008; accepted September 11, 2008.
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12,14-prostaglandins D2 and J2 are potent activators of human eosinophils J. Immunol. 168,3563-356912-Prostaglandin J2, a plasma metabolite of prostaglandin D2, causes eosinophil mobilization from the bone marrow and primes eosinophils for chemotaxis J. Immunol. 170,4752-4758,11β-PGF2 and its stereoisomer PGF2 are novel agonists of the chemoattractant receptor, CRTH2 FEBS Lett. 580,373-379[CrossRef][Medline]12,14-prostaglandin J2, and selective DP1 and DP2 receptor agonists on pulmonary infiltration of eosinophils in Brown Norway rats J. Pharmacol. Exp. Ther. 313,64-69
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