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and IL-10 Regulate Lipopolysaccharide-Stimulated Human Choriodecidual Cytokine and Prostaglandin E2 Production1
Liggins Institute and Division of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
| Abstract |
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production, peaking at
4 h. In contrast, IL-10, IL-1
, and PGE2 production
rates peaked 8, 12, and 24 h, respectively, after LPS stimulation.
Immunoneutralization studies indicated that TNF-
was a primary
regulator of IL-1
, IL-10, and PGE2 production, while
IL-1
stimulated only PGE2 production. Neutralization of
endogenous IL-10 resulted in increased TNF-
and PGE2
production. IL-10 treatment markedly decreased TNF-
and IL-1
production, but had no effect on PGE2 production. Taken
together, these results demonstrate that the effects of LPS on
choriodecidual cytokine and PG production are modulated by both
positive and negative feedback loops. In the setting of an infection of
the intrauterine, TNF-
may be a potential target for treatment
intervention; IL-10 could be one such therapeutic. | Introduction |
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510% of all pregnancies
(1). Despite advances in the understanding of the
mechanisms that result in preterm birth, this rate has remained
relatively constant for decades. Between 30 and 70% of very preterm
births are associated with an ascending intrauterine infection in which
microorganisms, originating from the vagina, rise through the
choriodecidua and subsequently colonize the chorion, amnion, amniotic
fluid, and ultimately the fetus (2). In response to the
infective pathogen, the maternal immune system initiates an
inflammatory response that frequently results in the onset of preterm
labor. The choriodecidua is a tissue composed of interdigitating fetal and maternal cells. In an ascending intrauterine infection it is the first tissue colonized by the microbial pathogen and is the main barrier to progression of the infection into the amniotic cavity. The response of the choriodecidua to the presence of the microorganism is likely an integral part in determining the severity, extent, and consequences of the infection.
Human gestational membranes produce a number of proinflammatory
cytokines (e.g., IL-1
, TNF-
, IL-6, and IL-8) and PGs, both
constitutively and in response to inflammatory stimuli and bacterial
cell wall products such as LPS (3, 4, 5, 6). At parturition,
both at term as well as preterm, there is an increase in the production
of these proinflammatory mediators within the uterus, but in
the case of intrauterine infection, this response is significantly
increased (4, 7, 8). Previous studies have shown that LPS
treatment of pregnant mice leads to an increase in IL-1
and
PGE2 production by decidual caps in vitro
(9, 10) and preterm delivery (3). Mice
treated with LPS also have elevated circulating levels of both TNF-
and IL-10 (11). These findings indicate that cytokines and
PGs produced by gestational tissues as a result of LPS treatment might
play an important role in the initiation of preterm labor leading to
delivery.
In addition to proinflammatory cytokines, gestational tissues can also
produce anti-inflammatory cytokines such as IL-10 (12, 13). IL-10 is a potent inhibitor of the production of IL-1
,
IL-6, IL-8, and TNF-
by human monocytes and macrophages
(11). It is produced by chorion, decidual, and placental
tissues (14, 15, 16, 17, 18, 19, 20) and has been detected in the amniotic
fluid of women during late gestation (21, 22, 23). IL-10
production by decidual cells in vitro has been reported to increase
upon treatment with IL-1
and bacterial cell wall products
(14, 15, 16, 17). IL-10 inhibits cytokine and PG production by
human chorion, decidual, and placental cells in vitro
(24, 25, 26, 27, 28, 29), although the effects of endogenous IL-10 on the
local inflammatory response have not been determined. However, it has
been reported that treatment with IL-10 prevented LPS-induced preterm
delivery in mice (30) as well as rats (31).
IL-10 thus has therapeutic potential for the treatment of intrauterine
infection-associated preterm labor.
The present studies were conducted to characterize auto regulatory interactions between pro- and anti-inflammatory cytokines in choriodecidual explants upon stimulation with LPS. Although it has been established that LPS elicits an inflammatory response within gestational tissues, the significance and role of local mediators in the elaboration of the response is not clear. Potential targets for intervention could potentially be identified if they werefound to be key mediators in the response. Explants were chosen as the model of study to ensure that the structural and cellular architecture of the choriodecidual membrane was maintained.
| Materials and Methods |
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DMEM-199 culture was obtained from Irvine Scientific
(Santa Ana, CA). FCS and streptavidin-alkaline phosphatase were
purchased from Invitrogen (Auckland, New Zealand). Bovine
-globulin and LPS (serotype 055:B5) were purchased from
Sigma-Aldrich (St. Louis, MO). Human IL-1
was a generous gift of
Immunex (Seattle, WA). IL-1R antagonist
(IL-1Ra)3 was a gift
from Synergen (Boulder, CO). For experimental studies, the human
rTNF-
was provided by Dr. J. Fraser (Department of Molecular
Medicine, University of Auckland, Auckland, New Zealand). Recombinant
IL-1
and anti-IL-1
antiserum were purchased from R&D Systems
(Minneapolis, MN). Abs to IL-10 and TNF-
were purchased from BD
PharMingen (San Diego, CA). Tritiated PGE2 was
purchased from Amersham Pharmacia Biotech (Aylesbury, U.K.).
Recombinant IL-10 and TNF-
used to calibrate the ELISAs were
purchased from R&D Systems.
Explant culture
All procedures involving human placentas were approved by the
Auckland Ethics Committee. Placentas were obtained with informed
consent from women undergoing elective Cesarean section at term before
the onset of labor. After manually removing the amnion, choriodecidual
membranes were washed carefully in medium to remove residual RBCs
without causing damage to the integrity of the membrane. Tissue
explants (6-mm disks) were excised with a cork borer as described
previously (32). Explants were pooled and randomly
distributed into six-well plates (six explants per well, three wells
per treatment) containing medium supplemented with 10% FCS and
antibiotics (33). The explants were allowed to equilibrate
overnight at 37°C in a humidified atmosphere of 5%
CO2/95% air. The following day, media were
replaced with serum-free media containing 0.1% bovine
-globulin and
antibiotics. Explants were then treated with the various test
substances or the appropriate vehicle control. At the indicated time
points, the media were collected. Production rates were normalized to
the wet weight of the explants in the individual wells.
Immunoneutralization experiments
Commercially available neutralizing Abs were used to neutralize
the effects of the LPS-stimulated TNF-
and IL-10. The Ab at various
concentrations was added concurrently with the LPS and supernatants
were harvested 24 h later. The explants were pretreated with the
IL-1Ra for 1 h before the addition of LPS and supernatants were
harvested 24 h later. The concentrations selected were chosen
according to manufacturers specifications for neutralizing the
cytokines (34, 35).
Immunoassays
IL-1
, IL-10, and TNF-
were measured by ELISA as
previously described. (32, 33). PGE2
production was determined by RIA as described previously using an
antiserum generated in our laboratory (36).
Data presentation and statistics
Cytokine and PG production rates, calculated as picograms per milligram of wet weight/24 h, are represented as a percent of control for each experiment (mean ± SEM). Results are presented as pooled data from multiple experiments performed in triplicate. Statistical significance was determined by ANOVA followed by Dunnetts test. A value of p < 0.05 was considered to be significant.
| Results |
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Results presented in Fig. 1
show the
time course of choriodecidual IL-1
(Fig. 1
a), IL-10 (Fig. 1
b), TNF-
(Fig. 1
c), and
PGE2 (Fig. 1
d) production at 2, 8, 12,
and 24 h after stimulation with LPS (5 µg/ml). The production of
IL-1
was significantly elevated compared with control at the 8
h time point, reaching maximum levels at 12 h post-LPS.
PGE2 production followed a similar time course to
that of IL-1
. IL-10 production was significantly elevated 4 h
after LPS stimulation and maximal production rates were observed 8
h after stimulation. TNF-
production was maximal 4 h after LPS
stimulation and subsequently decreased by approximately one-third over
424 h; production of TNF-
at 24 h post-LPS stimulation was
similar to that observed at the 2-h time point. The basal production of
TNF-
leveled off after 8 h and remained constant for the
subsequent time points studied. The basal production of the other
cytokines as well as PGE2 also showed similar
patterns. This pattern of TNF-
production remained evident when the
data were expressed as picograms per milligram of tissue rather than
normalized to control (Fig. 2
).
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LPS induced a significant increase in IL-1
, IL-10, and
PGE2 production. Immunoneutralization of TNF-
bioactivity resulted in a significant reduction in LPS-stimulated
production of IL-1
(Fig. 3
a), IL-10 (Fig. 3
b), and PGE2 (Fig. 3
c)
over a 24-h incubation period. A significant reduction of IL-1
production was observed with the TNF-
neutralizing Ab at a
concentration of 3 µg/ml, while LPS-stimulated production rates of
IL-10 and PGE2 were significantly reduced at 13
µg/ml anti-TNF-
Ab.
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production over the 24-h culture
period (Fig. 4
(Fig. 4
, neutralization of IL-10 resulted in a
4-fold increase in the production of TNF-
after 24 h
stimulation with LPS. The addition of exogenous IL-10 (25100 ng/ml)
resulted in a decrease in IL-1
production (Fig. 5
production were more pronounced (Fig. 5
production. The effect was concentration-dependent,
with the higher concentrations of IL-10 exerting the greatest degree of
inhibition. Addition of IL-10 had no effect on
PGE2 production by LPS-stimulated choriodecidual
explants (Fig. 5
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(Fig. 6
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| Discussion |
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We have previously reported that the exogenous treatment of
choriodecidual explants with TNF-
and IL-1
results in increased
production of both PGE2 and IL-10 after 24 h
(32, 41). These results confirmed the immunomodulatory
role of TNF-
and IL-1
in the regulation of anti-inflammatory
cytokines as well as PGs. Results reported in this study demonstrated
that the TNF-
produced by choriodecidual explants in response to LPS
exposure is a crucial modulator of further cytokine and PG production.
TNF-
is a potent proinflammatory mediator and has been implicated as
the primary cause of many immunopathologies ranging from arthritis
(42, 43, 44) to septic shock (45, 46), in
addition to preterm labor (47). Mice treated with Abs or
antagonists to TNF-
are subsequently protected from LPS-induced
death (45, 48, 49). Our data would suggest that, in the
choriodecidua, the inflammatory response elicited by bacteria might be
mediated and modulated to a large extent by the actions of endogenous
cytokines. TNF-
is the critical stimulating factor in regulating
choriodecidual IL-1
, IL-10, and PGE2
production, although it should be noted that neutralization of TNF-
did not result in a complete inhibition of LPS-stimulated cytokine and
PG production. The concentrations of the Abs used were chosen based on
the manufacturers recommendations (34, 35) and confirmed
by removal of immunodetectable TNF-
in preliminary experiments.
However, the lack of complete inhibition could reflect inadequate
penetration of the neutralizing Abs as they were added concurrently
with the LPS treatment. Additionally, cytokine measurements reflect the
concentrations present in the media, whereas the localized
concentrations of the cytokines within the tissues may be significantly
higher. Alternatively, the LPS treatment could have resulted in the
production of other as yet unidentified factors that may also exert
proinflammatory actions. IL-1
may be a candidate factor because it
is a potent proinflammatory cytokine that has been shown to be released
by decidual cells and to increase PG production by gestational tissues
through increased expression of PGH synthase (PGHS)-II
(50). Results presented in this study demonstrated that
IL-1
production was significantly increased 8 h after LPS
stimulation, while PGE2 production did not reach
a maximum until 1224 h after LPS stimulation. Therefore, the IL-1
produced may contribute to PGE2 production as it
is present in significantly increased levels 16 h before the
medium was harvested. Antagonism of IL-1 activity by IL-1Ra resulted in
a decrease in PGE2 production, supporting this
conclusion. Immunoneutralization of IL-10 resulted in an increase in
PGE2 production. However, addition of exogenous
IL-10 failed to exert any effects on PGE2
production despite a reduction in IL-1
and TNF-
production. These
apparently conflicting data may be explained by the possibility that
IL-10 may not be having a direct effect itself on
PGE2 production, but that an additional factor(s)
may be produced upon LPS treatment of the choriodecidual explants.
These data are not consistent with those of others showing inhibition
of PG production by IL-10 in gestational membranes (51, 52).
The anti-inflammatory effects of IL-10 have been well-documented
(12). Previous studies have demonstrated that IL-10 can
decrease TNF-
production in human macrophages and monocytes
(53). Cassatella et al. (13) demonstrated
that IL-10 diminished the levels of TNF, IL-1-
, and IL-8 mRNA late
after the onset of stimulation of polymorphonuclear leukocytes with
LPS. Previous studies in gestational tissues indicated that IL-10
inhibits basal- as well as LPS-stimulated PGE2
production by intact fetal membranes (52). In the present
study, we observed that IL-10 was produced at the time when TNF-
levels were beginning to decrease, and one interpretation of these data
is that the effects of IL-10 on PGE2 production
are mediated by its inhibition of TNF-
production. It has been
reported that the inhibitory effects of IL-10 on TNF-
production are
independent of its ability to suppress the effects of NF-
B
activation (54, 55). Studies conducted on human monocytes
demonstrated that IL-10 can down-regulate surface expression of the TNF
receptor while increasing production of the soluble TNF-
receptor,
in addition to inhibiting the release of TNF-
itself (56, 57). The effects of IL-10 on TNF-
receptor expression in
human gestational tissues are unknown at this time. It is possible that
IL-10 could suppress TNF-
receptor expression in addition to
decreasing TNF-
production, thus exerting a more complete antagonism
of TNF-
effects. IL-10 has also been reported to increase IL-1Ra
production from LPS-stimulated human polymorphonuclear leukocytes
(58) as well as the decidua (59), offering
the possibility of an additional route of action of IL-10 in the
gestational membranes.
IL-10 has been shown to inhibit PGHS-II mRNA expression in human
monocytes (60) and neutrophils (61), and also
in IL-1
- and TNF-
-stimulated trophoblast cells (51).
However, PG activity can also be regulated by catabolism.
15-Hydroxyprostaglandin dehydrogenase (PGDH) is an NAD-dependent
cytoplasmic enzyme that reduces the biological activity of PGs by
catalyzing the first reaction in the catabolic pathway for PG
degradation and inactivation. PGDH is expressed and functions in human
placenta and fetal membranes (62, 63). A reduction of
chorion PGDH activity and expression has been demonstrated in
association with preterm birth, particularly in pregnancies with
intrauterine infection (64). In villous and chorionic
trophoblasts, IL-1
increases levels of PGHS-II mRNA and decreases
PGDH mRNA in villous trophoblasts; both of these effects can be
reversed by IL-10 (51). Hence, in addition to its effects
mediated by TNF-
inhibition, IL-10 could also both decrease the
synthesis and increase catabolism of PGs in these tissues.
The results of the present studies are summarized in the schematic
pathway presented in Fig. 7
. Upon LPS
exposure, the human choriodecidua membranes initially produce TNF-
,
which in turn induces the production of IL-1
,
PGE2, and IL-10. Endogenous IL-1
potentiates
the production of PGE2 while IL-10 inhibits the
production of TNF-
and PGE2. The choriodecidua
is composed of cells of both fetal and maternal origin. Previous
studies have characterized cytokine production by chorion and decidual
cells and also identified the localization of cytokine receptors
present (7, 47, 50, 59). Apart from resident cells of
these tissues, other potential sources of cytokine production are the
lymphocytes that infiltrate as the onset of labor approaches
(65, 66, 67). All the placentas used in this study were from
patients undergoing elective Cesarean sections at term. However, it is
feasible that decidual lymphocytes may have contributed to cytokine and
PG production and interacted with the resident cells of the
choriodecidua to modulate the responses.
|
appears to be pivotal in the elaboration of the
inflammatory response to LPS. These studies suggest that
pharmacological agents that inhibit TNF-
synthesis or actions might
be an effective therapeutic intervention aimed at preventing or
delaying infection-associated preterm delivery. IL-10 may be such an
agent as results presented in this study demonstrated that
itcan inhibit TNF-
and IL-1
production by LPS-stimulated
choriodecidual membranes and is also involved in the
suppression of PG production.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Timothy A. Sato, Liggins Institute, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail address: t.sato{at}auckland.ac.nz ![]()
3 Abbreviations used in this paper: IL-1Ra, IL-1R antagonist; PGHS, PGH synthase; PGDH, 15-hydroxyprostaglandin dehydrogenase. ![]()
Received for publication August 5, 2002. Accepted for publication October 22, 2002.
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