Vol.3, No.5, 304-311 (2011)
doi:10.4236/health.2011.35053
C
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Health
Endogenous prostaglandin D2 synthesis inhibits
e-selectin generation in human umbilical vein
endothelial cells
Hideyuki Negoro1*, Hiroyuki Kobayashi2, Yoshio Uehara3
1Harvard Medical School, Internal Medicine, Boston, USA; *Corresponding Author:
2 Department of Hospital Administration, Graduate School of Medicine, Juntendo University, Tokyo, Japan;
3University of Tokyo Internal Medicine, Tokyo, Japan.
Received 14 March 2011; revised 25 April 2011; accepted 29 April 2011.
ABSTRACT
We examined the role of prostaglandin D2 (PGD2)
in the formation of E-selectin following inter-
leukin-1 (IL-1) stimulation in human umbilical
vein endothelial cells (HUVEC) transfected with
lipocaline-type PGD2 synthase (L-PGDS) genes.
HUVEC were isolated from human umbilical
vein and incubated with 20 U/mL IL-1 and vari-
ous concentrations of authentic PGD2. The iso-
lated HUVEC were also transfected with L-PGDS
genes by electroporation. The L-PGDS-trans-
fected HUVEC were used to investigate the role
of endogenou s PGD2 in IL-1-stimulated E-selectin
biosynthesis. We also used an anti-PGD2 anti-
body to examine whether an intracrine mecha-
nism was involved in E-selectin production.
PGD2 and E-selectin levels were determined by
radio-immunoassay and enzyme-immunoassay,
respectively. E-selectin mRNA was assessed by
real-time RT-PCR. IL-1-stimulated E-selectin
production by HUVEC was dose-dependently
inhibited by authentic PGD2 at concentrations
greater than 10−6 mol/L. L-PGDS gene-trans-
fected HUVEC produced more PGD2 than HU-
VEC transfected with the reporter gene alone.
IL-1 induced increases in E-selectin production
in HUVEC transfected with the reporter genes
alone. However, this effect was significantly
attenuated in the case of IL-1 stimulation of
HUVEC transfected with L-PGDS genes, and
accompanied by an apparent suppression of
E-selectin mRNA expression. Neutralization of
extracellular PGD2 by anti-PGD 2- sp ecifi c antibody
influenced neither E-selectin mRNA expression
nor E-selectin biosynthesis. HUVEC transfected
with L-PGDS genes showed increased PGD2
synthesis. This increase was associated with
attenuation of both E-selectin generation and
E-selectin mRNA expression. The results sug-
gest that endogenous PGD2 decreases E-se-
lectin synthesis and E-selectin mRNA expres-
sion, probably through an intracrine mecha-
nism.
Keywords: Prostaglandin; E-Selectin; P GDS;
Endothelial Cell
1. INTRODUCTION
Adhesion molecules play an important role in the de-
velopment and progression of atherosclerosis. The hy-
pothesis proposed by Ross and its modifications have
been generally accepted as a mechanism of atherosclero-
sis where adhesion of circulating monocytes and lym-
phocytes to vascular endothelium presumably initiates a
series of events toward atherosclerosis [1]. Cellular ad-
hesion molecules mediate the adhesion, margination, and
transendothelial migration of circulating mononuclear
cells from the blood stream to the extravascular com-
partment to have an important part in the progression of
atherosclerotic plaque [2]. Recent studies have eluci-
dated further that to anchor leukocytes onto the endothe-
lial cells, the adhesion molecules expressed on the sur-
face of endothelial cells necessitated to bind to their
ligands expressed on leukocytes. Endothelial cells are
stimulated by inflammatory agents to express selectins,
such as endothelial-leukocyte adhesion molecule-1
(E-selectin), which interact with carbohydrate ligands on
leukocytes, and to express immunoglobulin superfamily
proteins, such as vascular cell adhesion molecule-1
(VCAM-1). The adhesion molecules expressed on the
endothelial cells include VCAM-1, intracellular adhe-
sion molecule (ICAM)-1, P-selectin and E-selectin [3].
Selectins, including E-selectin and P-selectin, are in-

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305305
volved in the first step of leukocyte adhesion at sites of
inflammation or injury. Selectins are characterized by
rolling and tethering of leukocytes to the endothelial
surface, to platelets or to other leukocytes [4]. In fact,
E-selectin is demonstrated to occur in atherosclerotic
lesions in the coronary artery of humans [5]. Therefore,
E-selectin is believed to be a key factor for the develop-
ment of immune-mediated cardiovascular injury.
Intrestngly, we have recently reported that PGD2 at-
tenuates inducible nitric oxide generation in vascular
smooth muscle cells [6]. Endogenous prostaglandin D2
synthesis reduces plasminogen activator inhibitor-1 gen-
eration following cytokines stimulation in bovine endo-
thelial cells [7]. Especially, PGD2 is synthesized in vas-
cular components of atheromatous lesions including
endothelial cells, macrophages, platelets, and mast cells
[8] and lipocalin-type PGD2 synthase (L-PGDS) is
demonstrated to occur in atheromatous lesions in the
cardiovascular system [9]. These data strongly suggest
that L-PGDS/PGD2 is upregulated in response to im-
mune-related vascular lesions and in turn, the increase of
L-PGDS/PGD2 is exerted to attenuate the progression of
the arterial remodeling.
Taken together, we proposed the hypothesis that PGD2
regulates E-selectin expression in endothelial cells,
thereby contributing to leukocyte adhesion, an integral
component of the development of vascular injury. How-
ever, there had been few data investigating the crosstalk
between endogenous L-PGDS/PGD2 system and the
adhesion molecule expression by cytokines. In the pre-
sent study, in order to test our hypothesis that L-PGDS/
PGD2 protects the vascular wall against immune-related
vascular injury, we examined the relationship between
endogenous PGD2 and E-selectin expression by endo-
thelial cells and attempted to reveal its intracellular
mechanism mediated by PGD2 using L-PGDS gene-
transfected endothelial cells in culture. We also exam-
ined whether the increases in intracellular PGD2 synthesis
influenced E-selectin mRNA expression and E-selectin
biosynthesis observed following interleukin-1b (IL-1)
stimulation.
2. MATERIALS AND METHODS
2.1. Materials
Eicosanoids and related compounds were purchased
from Funakoshi chemicals (Tokyo, Japan). Arachidonic
acid was purchased from Sigma (St. Louis, MO, USA).
Recombinant murine IL-1 was purchased from R&D
Systems (Minneapolis, MN, USA). Radioactively la-
beled materials were purchased from Amersham (Tokyo,
Japan). A 3-kb gene for rat brain PGDS [(5Z, 13E)-
(15S)-9a, 11a -epidoxy-15-hydroxyprosta-5,13-dienoate
D-isomerase, EC 5.3.99.2] was isolated from a rat ge-
nomic DNA library by plaque hybridization with cDNA
for the PGDS enzyme, as described in our previous
studies [10]. A 3-kb BamHI fragment of rat PGDS,
which belongs to the lipocalin family, was inserted into a
pcD2 plasmid containing the SV40 promoter, along with
a polyA signal at the XhoI site (Invitrogen, Carlsbad, CA,
USA) [11]. The b-galactosidase gene with a cytomega-
lovirus (CMV) promoter at an XbaI site was inserted
into the pBluescript 2 KS+ plasmid (Stratagene, La Jolla,
CA, USA).
2.2. Cell Culture
Human umbilical vein endothelial cells (HUVEC)
were harvested enzymatically as described previously
[12]. They were maintained in medium 199 (GIBCO
BRL, Gaithersburg, MD), containing Hepes, heparin
(1%), endothelial cell growth factor (50 mg/ml),
L-glutamin (1%), antibiotics, and 5% fetal bovine serum
(FBS). When the cells reached confluence, they were
replanted onto low pyrogen fibronectin at 20,000 cells/
cm2. HUVEC which were isolated from a confluent
monolayer of polygonal cells. The cells expressed von
Willbrand factor as determined by their content of spe-
cific mRNA and immunoreactive protein. Cellular vi-
ability was assessed by Trypan blue exclusion.
2.3. Effect of Exogenous PGD2 on
E-Selectin Expression in Endothelial
Cells
Cultures of HUVEC were treated with 20 U/ml IL-1,
according to the previous study, in the presence of vari-
ous concentrations of PGD2 to be incubated for 18 h.
Thereafter, the HUVEC were washed three times with
FBS-free Dulbecco’s phosphate-buffered saline (D-PBS;
Gibco) and the cells were re-incubated in 1 ml of fresh
D-PBS for 2 h. Subsequently, the cells and culture su-
pernatants were used in various assays.
2.4. Transfection of L-PGDS Genes into
HUVEC
HUVEC were transfected with L-PGDS genes using
the Shimadzu GTE-10 electroporation device (Gene
Transfer Equipment-10, Shimadzu Co., Ltd., Kyoto,
Japan). This equipment transiently increases the perme-
ability of plasma membranes of HUVEC, thereby facili-
tating translocation of genes into the cytoplasm. Briefly,
the cells were washed three times with FBS-free D-PBS
and 10 mg of pcD2-rat PGDS in 0.5 ml of fresh D-PBS
were added to each well [13]. A transient electrical cur-
rent was applied onto HUVEC growing in the culture
dishes, using a 35-mm round electrode (Model FTC-

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306
33D3, Shimadzu Co., Ltd., Kyoto, Japan), after which
the cells were incubated for 30 minutes.
Following transfection, 2 ml of DMEM containing
10% FBS was added to the HUVEC and the dishes were
incubated for an additional 24 hours. Endogenous PGD2
production was stimulated by adding 10–6 mol/l arachi-
donic acid for 24 hours. Fresh medium containing 10–6
mol/l arachidonic acid was then added and E-selectin
mRNA expression and E-selectin expression were
stimulated for 18 hours by the addition of 20 U/ml IL-1.
At the end of this incubation period, the HUVEC were
washed three times with FBS-free D-PBS and incubated
in 1 ml of fresh D-PBS for 2 hours. Finally, the cells and
culture supernatants were collected for analysis.
For comparison, HUVEC were transfected with b-
galactosidase genes (b-gal) by electroporation to deter-
mine the efficacy of gene transfection. Three days after
the transfection, HUVEC were stained with X-gal [14],
and b-galactasidase expression was measured. Transfec-
tion efficacy was estimated as the ratio of the X-gal
stained area to the sectional area of the HUVEC.
2.5. Neutralizing Extrinsic PGD2 Released
from HUVEC
We attempted to neutralize PGD2 using an anti-PGD2-
specific antibody in order to investigate the effects of
PGD2 released from L-PGDS-transfected HUVEC. We
estimated the amount of anti-PGD2 antibody required to
completely neutralize the secreted PGD2 using the
Scatchard analysis. The binding affinity was 0.0051
ml/pg, and the Bmax (maximal binding capacity) was 25
pg/l [15]. Therefore, 1 liter of antibody had the capacity
to bind 25 pg PGD2. Taking into account of these results,
we used 200 ml of the antibody to inhibit the receptor-
mediated actions of PGD2 in HUVEC under our culture
conditions. The anti-PGD2 antibody was raised in our
laboratories using PGD2-conjugated thyroglobulin and
Freund’s complete adjuvant. The antibody cross-reacted
0.003% with thromboxane B2, 0.01% with prostaglandin
E2 (PGE2), 0.009% with prostaglandin F2a (PGF2a),
0.008% with 6-keto-PGF1a and 0.01% with arachidonate
[16]. Antibody activity was confirmed by suppression of
intracellular cyclic AMP (cAMP) following PGD2
stimulation via PGD2 receptor, which acts as a second
messenger for PGD2 signal transduction [17].
2.6. Eicosanoid Radioimmunoassay
Eicosanoids were determined in culture media using
the direct radioimmunoassay method described previ-
ously [16]. Briefly, 0.1 ml of sample, 0.1 ml of [3H] ei-
cosanoid (5000 dpm) and 0.1 ml of the diluted antibody
were mixed and incubated at 4˚C for 24 hours. To sepa-
rate bound from free [3H] eicosanoid, 0.1 ml of dex-
tran-coated charcoal in a 50 mmol/l phosphate buffer at
pH 7.4 containing 0.1% gelatin and 100 mmol/l NaCl
was added to the ice-chilled assay mixture. The mixture
was vortexed and centrifuged at 3000 rpm for 5 min at
4˚C. The supernatant was assayed for [3H] eicosanoids
bound to the antibody. Radioactivity was determined
using an automatic liquid scintillation counter. The
properties of the anti-6keto-PGF1a antibody was de-
scribed previously [15,16]. The cross-reactivity and its
properties of the anti-PGD2 antibody was detailed above.
The low cross-reactivity of each antibody made it feasi-
ble to measure directly the eicosanoid in media.
2.7. E-Secletin and E-Secletin mRNA
Measurements
We measured E-selectin expression by commercially
available cell surface enzyme immunoassay as described
previously (R&D Systems, Inc., USA).
Cultured E-selectin transcripts were detected using the
real-time reverse transcription-polymerase chain reaction
(real-time RT-PCR) method using real-time RT-PCR
machine as described previously [18].
2.8. Statistical Analysis
All values are expressed as the mean ± SE. The dif-
ferences between values were assessed by an one-way
ANOVA and Duncan’s multiple range test using the
STATISTICA program (StatSoft, Tulsa, OK, USA) on a
Gateway G6-400 computer system (Gateway Inc., N
Sioux City, SD, USA) running the Windows 98 operat-
ing system. P values less than 0.05 were considered sta-
tistically significant.
3. RESULTS
3.1. Effect of Exogenous PGD2 on
E-Selectin Expression in Endothelial
Cells
Stimulation of endothelial cells with IL-1 significantly
increased E-selectin expression. The increase was re-
duced in a dose-dependent manner by the addition of
PGD2 at concentrations ranging from 10–7 to 10–4 mol/l
(Figure 1).
3.2. Gene Transfection and Eicosanoid
Generation in HUVEC
We transfected HUVEC with L-PGDS genes in order
to increase endogenous PGD2 formation. PGD2 was as-
sayed using radioimmunoassay. The basal levels of PGD2
in reporter-gene-transfected HUVEC maintained in

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307307
Figure 1. Effect of exogenous PGD2 on E-selectin generation in
endothelial cells. Stimulation of endothelial cells with IL-1 sig-
nificantly increased E-selectin generation (left two columns).
The increase was reduced in a dose-dependent manner by the
addition of PGD2 at concentrations ranging from 10–7 to 10–4
mol/l. All experiments were performed three different times with
at least six replicates. Statistical differences were analyzed by
one-way ANOVA and Duncan’s multiple range tests. *P < 0.01
vs the value at 0 mol/L PGD2.
arachidonate-free media were as low as 51.5 ± 2.2
pg/106 cells/2 hours, and the addition of 10–6 mol/l ara-
chidonate had no effect on PGD2 synthesis. In contrast,
L-PGDS gene-transfected HUVEC showed an increase
(178.0%) in PGD2 generation even in arachidonate-free
media, as compared with control HUVEC carrying re-
porter genes alone. Furthermore, 10–6 mol/l arachidonate
markedly stimulated PGD2 biosynthesis by 640.7%, as
compared with control HUVEC carrying vector genes
alone (Figure 2(a)). Thereafter, PGI2 was assayed as
6-keto-PGF1a using radioimmunoassay. Basal levels of
prostacyclin (PGI2), the major eicosanoid synthesized in
HUVEC, were 1488 ± 66 pg/106 cells/2 hours in cells
having reporter genes alone under arachidonate-free
conditions. The PGI2 generation was a markedly in-
creased by 327% when the cells were stimulated with
10–6 mol/l arachidonate (Figure 2(b)). L-PGDS gene
transfection did not influence PGI2 synthesis in HUVEC
maintained under either arachidonate-free or arachido-
nate-stimulated conditions, as compared to HUVEC
transfected with reporter genes. These data clearly sug-
gest that the L-PGDS genes alter the phenotype of HU-
VEC so that the recombinant cells acquire the capacity
to produce PGD2 in response to arachidonate stimula-
tion.
3.3. Effect of L-PGDS Gene Transfection on
E-Selectin Expression in HUVEC
Using the HUVEC having L-PGDS genes, we invest-
(a)
(b)
Figure 2. PGD2 and PGI2 generation in endothelial cells. PGD2
was assayed using radioimmunoassay. 10–6 mol/l arachidonate
did not stimulate PGD2 generation in cells having reporter
genes alone (two columns to the left in Graph a). However,
cells carrying the L-PGDS genes acquired the ability to
produce PGD2 with or without arachidonate stimulation (two
columns to the right in Graph a). (Graph a). PGI2 was assayed
as 6-keto-PGF1a using radioimmunoassay. The addition of 10–6
mol/L arachidonate to the cultures increased PGI2 generation;
however, there were no differences in PGI2 production between
PGDS(–), AA(+) and PGDS(+), AA(+) lines. (Graph b). Statis-
tical differences were assessed by Student’s t-test (n = 6). *P <
0.01. N.S. represents not statistically significant.
tigated the effects of endogenous PGD2 on the expres-
sion of E-selectin with or without IL-1 stimulation. The
E-selectin expression was significantly increased upon
IL-1 stimulation in endothelial cells transfected with
transporter genes. This increase in E-selectin with or
without IL-1 stimulation was significantly blunted in
HUVEC transfected with L-PGDS genes that produced
indeed endogenous PGD2 in response to arachidonate
stimulation (Figure 3).

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Figure 3. Effect of PGD2 synthase gene transfection on
E-selectin expression in endothelial cells. Under normal (un-
stimulated) conditions, endothelial ells bearing L-PGDS genes
(IL-1(–), PGDS(+)) expressed less E-selectin than those bear-
ing reporter genes alone (IL-1(–), PGDS(–)). E-selectin ex-
pression increases observed following IL-1 stimulation were
significantly attenuated in cells carrying L-PGDS genes in
response to arachidonic acid stimulation (IL-1(+), PGDS(+),
AA(+)), though there was no attenuation of E-selectin expres-
sion in cells carrying L-PGDS genes but not stimulated by
arachidonic acid (IL-1(+), PGDS(+), AA(–)), compared to
endothelial cells having only reporter genes (IL-1(+), PGDS
(–)). The experiment was carried out in the presence of 10–6
mol/l arachidonate. Statistical differences were assessed by
Student’s t-test (n = 6). *P < 0.01.
3.4. Intracellular Effects of PGD2 on
E-Selectin Expression
In order to assess the role of PGD2 receptor-mediated
signal transduction in E-selectin expression, we studied
changes in cAMP, a second messenger of PGD2 signal
transduction in HUVEC transfected with transporter
gene alone. Intracellular cAMP was unaffected by
L-PGDS transfection per se. However, intracellular cAMP
was increased by exogenous PGD2 stimulation [19]. This
response was completely abrogated by addition of
anti-PGD2 antibody to the media, the amount of which
was more than the concentrations sufficient to neutralize
PGD2 in the media (Figure 4(a)). Using such a dose of
anti-PGD2 antibody enough to inhibit the receptor-me-
diated cyclic AMP rising, we investigated contribution
of PGD2 receptor-mediated signal transduction to the
PGD2-mediated E-selectin expression, and determined
E-selectin expression in the supernatants following neu-
tralization with an anti-PGD2-specific antibody. The ad-
dition of anti-PGD2 antibody to the media did not influ-
ence E-selectin expression following IL-1 stimulation in
the endothelial cells transfected with L-PGDS genes
(Figure 4(b)).
(a)
(b)
Figure 4. Effect of endogenous PGD2 on E-selectin expression
in endothelial cells. cAMP levels were measured to assess the
antibody inhibition of PGD2 receptor-mediated signal trans-
duction in the cells with transporter gene alone (Graph a). 10-5
mol/l PGD2 greatly increased cAMP formation in the cells in
the absence of anti-PGD2 antibody (anti-PGD2(–)). This in-
crease was completely abolished to the basal levels by the ad-
dition of anti-PGD2 antibody in the media. Using such a dose
of anti-PGD2 antibody, we examined the effects of neutraliza-
tion of PGD2 in media on E-selectin expression (Graph b).
E-selectin expression following IL-1 stimulation was signify-
cantly reduced in endothelial cells having L-PGDS genes and
without anti-PGD2 antibody (PGDS(+), anti-PGD2(–)), com-
pared to endothelial cells with reporter genes alone (PGDS(–),
anti-PGD2(–)). The reduction in E-selectin expression was
unaffected when PGD2 in the culture was neutralized with an
anti-PGD2-specific antibody (PGDS(+), anti-PGD2(+)). These
studies were carried out in the presence of 10–6 mol/l arachi-
donate. Statistical differences were assessed by Student’s t-test.
*P < 0.01. N.S. represents not statistically significant.
These results clearly indicated that anti-PGD2-specific
antibody inhibited the PGD2 receptor-mediated signal
transduction and that PGD2-mediated reduction in

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309309
E-selectin expression was not due to the PGD2 receptor-
mediated events.
3.5. L-PGDS Genes and Expression of
E-Selectin mRNA
We demonstrated that L-PGDS gene transfection onto
HUVEC brought about increases in PGD2 formation and
decreases in E-selectin expression using real-time
RT-PCR (Figure 5). The expression of E-selectin mRNA
following IL-1 stimulation was significantly less in the
HUVEC carrying L-PGDS genes. Expression was nor-
malized to β-actin. Values are expressed as fold change
compared to untreated controls.
4. DISCUSSION
Both PGD2 and adhesion molecules play a very im-
portant part in the process of atherosclerosis. In the pre-
sent study, we demonstrated that PGD2 regulates E-se-
lectin generation in HUVEC following IL-1stimulation.
More interestingly, we demonstrated that endogenous
PGD2 production in HUVEC transfected with L-PGDS
genes brought about a decrease of E-selectin expression.
This effect was observed even if the PGD2-mediated
cAMP increase was reversed to basal levels using
anti-PGD2-specific antibody. These findings strongly
suggest that PGD2 exerts inhibitory effects on E-selectin
expression via an intracellular mechanism as well as the
well-known receptor-mediated mechanism [20].
In this context, recent studies have demonstrated that
the orphan nuclear receptor of peroxysome proliferator-
activated receptor (PPAR)-g, a member of the nuclear
receptor superfamily of ligand-dependent transcription
factors, binds to PGD2 metabolites and thereby regulates
adipocyte differentiation and glucose homeostasis [21,
22].
PGD2 is converted quickly to PGJ2, delta 12-PGJ2,
and 15-deoxy-delta12,14 PGJ2 in plasma [23]. 15-deoxy-
delta12,14 PGJ2 inhibits inhibitor of kB kinase that
phosphorylates another inhibitor of kB after activation
with cytokines and also affects the DNA-binding do-
mains of nuclear factor-kB (NF-kB) subunits [24]. Be-
cause the genes involved in E-selectin expression in-
clude the NF-kB binding site in its promoter regions [25],
it is presumable that PGD2 and its metabolites inhibit
cytokine induced E-selectin expression, at least in part,
through inhibition of NF-kB translocation.
It is reported that E-selectin mRNA and E-selectin are
much expressed in vascular lesions such as atherosclero-
sis [5]. Different cell lines like macrophages, platelets or
lymphocytes work together to secrete cytokines in re-
sponse to the inflammatory events, and in turn, the se-
creted cytokines stimulate the endothelial cells, thereby
Figure 5. Effect of PGD2 synthase gene transfection on
E-selectin mRNA. Changes in E-selectin mRNA levels were
investigated using real-time RT-PCR. The expression of
E-selectin mRNA following IL-1 stimulation was significantly
less in the HUVEC carrying L-PGDS genes. Expression was
normalized to β-actin. Values are expressed as fold change
compared to untreated controls. Statistical differences were
assessed by Student’s t-test. *P < 0.01.
increasing E-selectin mRNA and E-selectin expression
in the atherosclerotic lesions. In fact, it is well postulated
that L-PGDS is highly expressed in the stenotic lesions
and in the lipid core of advanced atherosclerotic plaques
in patients with stable angina [9]. Moreover, PGD2 re-
duces inducible nitric oxide synthase formation. These
actions of PGD2 and metabolites on vasoactive sub-
stances regulated by cytokines are in favor of vascular
protection against vascular injury [6].
The endothelial cells exhibited a striking increase in
PGI2 generation, but not PGD2, following arachidonate
stimulation, suggesting that these cells have a large ca-
pacity to synthesize PGI2, but not PGD2. In spite of this,
L-PGDS gene transfection greatly enhanced PGD2 syn-
thesis in EC. This was particularly apparent when eico-
sanoid expression was stimulated with its precursor,
arachidonate. The alteration of phenotype of these cells
reduced E-selectin mRNA expression and consequently
E-selectin expression. This genetic procedure would
provide a new strategy against vascular lesions. These
activities have relevance to the in vivo situation, and
remain to be clarified.
In conclusion, the introduction of PGD2 synthase
genes into endothelial cells increased endogenous PGD2
generation. This brought about a reduction in E-selectin
expression and a decrease in E-selectin mRNA expres-
sion following IL-1 stimulation. The inhibitory effects of
PGD2 on E-selectin expression were due to an intracrine
mechanism rather than to any receptor-mediated events.
Since suppression of the E-selectin system is postulated

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310
to be protective, an increase in endogenous PGD2 syn-
thesis might represent a novel strategy to prevent car-
diovascular injury in humans.
5. ACKNOWLEDGEMENTS
The authors acknowledge Yukari Kawabata and Chieko Henmi for
technical assistance.
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