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48
VOLUME 115 | NUMBER 1 | January 2007
•
Environmental Health Perspectives
Research
The prevalence and morbidity of asthma and
other allergic diseases have increased dramati-
cally during the last 30 years, particularly in
industrial countries (Burr et al. 2006). The
onset of asthma most commonly occurs in
early childhood (Yunginger et al. 1992).
Asthma is more common in males during
infancy, childhood, and preadolescence
(Yunginger et al. 1992). However, from late
adolescence to middle age, females have a
higher prevalence and morbidity from asthma
(De Marco et al. 2002; Yunginger et al.
1992). Although the increase in overall preva-
lence and the cause of these pattern differ-
ences between the sexes are not well
understood, we questioned whether female
gonadal hormones and their mimetics might
be involved.
We recently found that physiologic con-
centrations of estradiol (E
2
) rapidly stimulate
murine and human mast cell lines (RBL-2H3
and HMC-1) and primary cultures of bone
marrow–derived mast cells (BMMC) to release
β-hexosaminadase (β-hex), a marker for the
granules that contain preformed allergic medi-
ators (Zaitsu et al. 2006). These low doses of
E
2
also enhanced the synthesis and release of
leukotriene C
4
(LTC
4
) by RBL-2H3 cells. In
addition to these direct effects, E
2
potentiated
IgE-dependent synthesis and release of β-hex,
and particularly LTC
4
. The finding that the
estrogen receptor (ER) antagonists tamoxifen
and ICI 182,780 inhibited these effects sug-
gested that these estrogenic effects were medi-
ated through specific ERs (ER-α or ER-β).
This proposition was substantiated by demon-
strating that BMMCs derived from ER-α
knockout (KO) mice did not degranulate in
response to E
2
. We also analyzed the expres-
sion of ER-α and ER-β by reverse transcrip-
tase-polymerase chain reaction and could
detect only ER-α on RBL-2H3, HMC-1,
and BMMCs (Zaitsu et al. 2006). Another
recent study provided evidence for estrogen
effects on allergic sensitization/reactions by
showing a relationship between an ER-α gene
(ESR1) polymorphism and airway hypersensi-
tivity, and an age-related decline in lung
function in females with asthma (Dijkstra
et al. 2006).
Estrogens and other steroid hormones use
two different major cellular pathways to exert
their regulatory effects. One pathway is via
genomic receptors acting as transcription fac-
tors on gene expression. However, an alterna-
tive pathway acting via plasma membrane
receptors is more often involved in the rapid
effects of steroids occurring within seconds to
minutes (Watson et al. 1999; Watson and
Gametchu 2003). This nongenomic pathway
is involved in secretory responses to both
physiologic and nonphysiologic estrogens
(Bulayeva et al. 2005).
Many environmental pollutants have
estrogen-like activities and thus are termed
environmental estrogens or xenoestrogens
(Newbold et al. 2006; Wozniak et al. 2005).
These components can be involved in both
genomic and nongenomic pathways of estro-
gen action, but have recently been shown to
be very potent when acting via the non-
genomic pathway (Wozniak et al. 2005),
although they are very weak activators of the
genomic pathway. If environmental estrogens
act at such low levels, then the widespread
presence of these compounds in our environ-
ment are of concern as causes for the increas-
ing prevalence of diseases such as asthma.
Examples of environmental estrogens
include the dioxins, dichlorodiphenyl-
trichloroethane (DDT) and its metabolite
dichlorodiphenylethylene (DDE), hexachloro-
cyclohexane, polychlorinated biphenyls
(PCBs), and alkylphenols and their derivatives
(nonylphenol, octylphenol, bisphenol A). The
most common source of these pollutants is
through contaminated water and foods
(Aravindakshan et al. 2004; Falconer et al.
2006). We therefore questioned whether envi-
ronmental estrogens could have effects on
allergic sensitization and clinically relevant
reactions, such as for asthma. The goal of the
present study was to identify possible mecha-
nisms by which environmental estrogens,
alone or in combination with endogenous
Address correspondence to T. Midoro-Horiuti, Child
Health Research Center, University of Texas Medical
Branch, 2.300 Children’s Hospital, 301 University
Blvd., Galveston, TX 77555-0366 USA. Telephone:
(409) 772-3832. Fax: (409) 772-1761. E-mail:
tmidoro@utmb.edu
This work was a pilot project supported by the
NIEHS (National Institute of Environmental Health
Sciences) Center for Environmental Science at the
University of Texas Medical Branch (pilot project
grant P30 E06676 to T.M.H.) and by grants R01
AI052428 (R.M.G.) and K08 AI055792 (T.M.H.)
from the National Institute of Allergy and Infectious
Diseases.
The authors declare they have no competing
financial interests.
Received 25 May 2006; accepted 3 October 2006.
Environmental Estrogens Induce Mast Cell Degranulation and Enhance
IgE-Mediated Release of Allergic Mediators
Shin-ichiro Narita,
1
Randall M. Goldblum,
1
Cheryl S. Watson,
2
Edward G. Brooks,
1
D. Mark Estes,
1
Edward M. Curran,
1
and Terumi Midoro-Horiuti
1
1
Department of Pediatrics, Child Health Research Center; and
2
Department of Biochemistry and Molecular Biology, University of Texas
Medical Branch, Galveston, Texas, USA
BACKGROUND: Prevalence and morbidity of allergic diseases have increased over the last decades.
Based on the recently recognized differences in asthma prevalence between the sexes, we have exam-
ined the effect of endogenous estrogens on a key element of the allergic response. Some lipophilic
pollutants have estrogen-like activities and are termed environmental estrogens. These pollutants
tend to degrade slowly in the environment and to bioaccumulate and bioconcentrate in the food
chain; they also have long biological half-lives.
O
BJECTIVES: Our goal in this study was to identify possible pathogenic roles for environmental
estrogens in the development of allergic diseases.
M
ETHODS: We screened a number of environmental estrogens for their ability to modulate the
release of allergic mediators from mast cells. We incubated a human mast cell line and primary
mast cell cultures derived from bone marrow of wild type and estrogen receptor α (ER-α)–deficient
mice with environmental estrogens with and without estradiol or IgE and allergens. We assessed
degranulation of mast cells by quantifying the release of β-hexosaminidase.
R
ESULTS: All of the environmental estrogens tested caused rapid, dose-related release of
β-hexosaminidase from mast cells and enhanced IgE-mediated release. The combination of physi-
ologic concentrations of 17β-estradiol and several concentrations of environmental estrogens had
additive effects on mast cell degranulation. Comparison of bone marrow mast cells from ER-α–
sufficient and ER-α–deficient mice indicated that much of the effect of environmental estrogens
was mediated by ER-α.
C
ONCLUSIONS: Our findings suggest that estrogenic environmental pollutants might promote
allergic diseases by inducing and enhancing mast cell degranulation by physiologic estrogens and
exposure to allergens.
K
EY WORDS: allergy, asthma, β-hexosaminidase, environmental estrogen, estradiol, estrogen
receptor α, IgE, mast cells. Environ Health Perspect 115:48–52 (2007). doi:10.1289/ehp.9378 avail-
able via http://dx.doi.org/ [Online 3 October 2006]
estrogens, might promote the development of
allergic diseases.
Materials and Methods
Cells and cell culture. We obtained the
HMC-1 human mast cell line from J.H.
Butterfield (Mayo Clinic, Rochester, MN)
(Butterfield et al. 1988). Cells were cultured
in Iscove's modified Dulbecco's medium
(IMDM; Cellgro, Kansas City, MO) with
10% iron-supplemented calf serum (Hyclone,
South Logan, UT). To avoid exposure to
estrogens during culture, we used steroid-
stripped fetal calf serum (FCS) and phenol
red–free media throughout this study, as
described previously (Lambert et al. 2005).
We developed primary cultures of bone
marrow-derived mast cells (BMMC) from the
marrow of the femurs of C57B6 mice, as
described by Odom et al. (2004). We
obtained wild type (WT) C57B6 mice from
the Jackson Laboratory (Houston, TX) and
produced ER-α KO mice by back-cross of the
previously generated heterozygous ER-α KO
mice (Lambert et al. 2005). BMMC cultures
contained > 98% pure mast cells after
4 weeks, as assessed by toluidine blue staining.
For the last 48 hr before harvesting, we cul-
tured these BMMCs in medium with estro-
gen-stripped FCS (Invitrogen, Carlsbad,
CA). We used BMMCs to confirm that the
effects of E
2
were through ER-α, by compar-
ing the cells from WT and ER-α KO mice.
All animal experimental protocols were
approved by the University of Texas Medical
Branch Institutional Animal Care and Use
Committee. The animals were treated
humanely and with regard for alleviation of
suffering.
Estrogens. We obtained 17β-estradiol from
Sigma-Aldrich Corporation (St. Louis, MO).
We used the following environmental estro-
gens in our studies: organochloride pesticides
or their metabolites (endosulfan, dieldrin, and
DDE); a by-product of plastics manufacturing
(nonylphenol); and the PCBs Aroclor 1242
and Aroclor 1254. We obtained DDE and
endosulfan from Ultra Scientific (North
Kingstown, RI) and nonylphenol, dieldrin,
Aroclor 1242, and Aroclor 1254 from Sigma.
Patient serum samples. We obtained sam-
ples of sera from patients who had a history of
asthma and had a positive skin prick test to
house dust mites (DM). We complied with
all applicable U.S. requirements and/or inter-
national regulations (including institutional
review board approval), and human partici-
pants gave written informed consent prior to
the study.
Mast cell activation experiments. We har-
vested cells by trypsinization, cultured them
on 96-well plates for 2 days to allow mem-
brane receptors to be resynthesized, and then
stimulated cells with various concentrations of
E
2
and environmental estrogens for 30 min.
To examine the interaction between exposure
to environmental estrogens and allergens in
the release of allergic mediators, we sensitized
BMMC for 1 hr with 100 ng/mL mouse
anti-dinitrophenyl (DNP) IgE antibody
(Sigma-Aldrich) and HMC-1 cells for 90 min
with a 1:5 dilution of patient serum. After
washing away unbound IgE, we stimulated
cells with DNP-bovine serum albumin (BSA)
complexes (10 haptenes per carrier molecule
used at 10 ng/mL; Biosearch Technologies,
Inc., Novato CA) or 0.75 AU/mL of dust
mite allergen extract (Dermatophagoides fari-
nae; Hollister-Stier, Spokane, WA) for 30 min
in the presence or absence of E
2
or environ-
mental estrogens. We performed all mediator
measurements in duplicate.
Assessment of degranulation by release of
the granular protein β-hex. Enzymatic assays
for β-hex have been used extensively to assess
the extracellular release of mast cell and
basophil granule contents (Dastych et al.
1999). We stimulated cells (2 × 10
4
) in
Tyrode’s buffer (Dastych et al. 1999) contain-
ing various concentrations of E
2
. We meas-
ured β-hex release as previously described
(Dastych et al. 1999), using p-nitrophenyl-N-
acetyl-β-
D
-glucopyranoside (8 mM; Sigma-
Aldrich) as the substrate. We expressed the
amount of β-hex release into media as the per-
centage of the total amount of β-hex originally
in the cells [% release = 100 × (experimental
β-hex release – spontaneous β-hex release)
÷ total cellular β-hex].
Statistical analyses. Data were expressed as
the mean ± SE. Statistical analysis was per-
formed by one-way analysis of variance.
Where differences between groups were pre-
sent, they were further analyzed by the multi-
ple comparisons (Bonferroni) for Figure 1 and
Student t-test for Figures 2–5. A p-value of
< 0.05 was defined as statistically significant.
Results
Environmental estrogens induce degranulation
of HMC-1 cells. We performed a series of
experiments to screen for the effects of various
concentrations (1 × 10
–12
–10
–8
M) of E
2
and
six different environmental estrogens on mast
Environmental estrogens enhance mast cell degranulation
Environmental Health Perspectives
•
VOLUME 115 | NUMBER 1 | January 2007
49
20
15
10
5
0
EE [log(M)]
β-hex (% release)
10
–12
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
E
2
Dieldrin
Endosulfan
DDE
Nonylphenol
Aroclor 1254
Aroclor 1242
10
–11
10
–10
10
–9
10
–8
Figure 1. Release of β-hex from HMC-1 after incu-
bation with six different environmental estrogens
(EEs): E
2
, dieldrin, endosulfan, DDE, nonylphenol,
Aroclor 1254, and Aroclor 1242. Experiments were
conducted in triplicate and expressed as mean ± SE.
*
p
< 0.05 vs. phosphate buffered saline control.
20
15
10
5
0
E
2
alone
β-hex (% release)
Dieldrin
Endosulfan
DDE
Nonylphenol
Aroclor 1254
Aroclor 1242
*
*
10
–11
E
2
EE
EE + E
2
Figure 2. Additive effects of environmental estro-
gens (EEs) and E
2
on β-hex release from HMC-1
cells incubated with 10
–11
M E
2
, dieldrin, endosulfan,
DDE, nonylphenol, Aroclor 1254, or Aroclor 1242
alone; or each EE plus E
2
. Experiments were con-
ducted in triplicate and expressed as mean ± SE.
*
p
< 0.05 compared with EE alone.
Figure 3. Effects of environmental estrogens (EEs) on IgE-dependent degranulation from HMC-1 cells and
BMMC. (
A
) Release of β-hex from HMC-1 cells by 0.75 AU/mL DM alone; 10 pM of dieldrin, endosulfan, DDE,
nonylphenol, Aroclor 1254, or Aroclor 1242 alone; or each EE plus DM. (
B
) Release of β-hex from BMMC by
anti-DNP IgE/DNP-BSA alone; 10
–13
M dieldrin, 10
–12
M endosulfan, 10
–11
M DDE, 10
–11
M nonylphenol,
10
–9
M Aroclor 1254, or 10
–12
M Aroclor1242 alone; or each EE plus anti-DNP IgE/DNP-BSA. Experiments
were conducted in triplicate and expressed as mean ± SE.
*
p
< 0.05 compared with EE alone.
12
10
8
6
4
2
0
DM alone
β-hex (% release)
Dieldrin
Endosulfan
DDE
Nonylphenol
Aroclor 1254
Aroclor 1242
*
*
*
*
*
A
DM
EE
EE + DM
DNP alone
Dieldrin
Endosulfan
DDE
Nonylphenol
Aroclor 1254
Aroclor 1242
15
10
5
0
*
*
*
*
*
B
β-hex (% release)
DNP-BSA
EE
EE + DNP-BSA
cell degranulation, using release of β-hex from
HMC-1 cells as a marker for degranulation
and release of allergic mediators. Figure 1
shows that all of the environmental estrogens
tested except Aroclor 1254 caused the release
of a significant portion of intracellular β-hex at
concentrations ranging from 10
–11
to 10
–8
M
after 30 min of stimulation. For comparison, a
Ca
2+
ionophore induced approximately 30%
release of intracellular β-hex (data not shown),
presumably because not all β-hex resides in
releasable granules. Therefore the environmen-
tal estrogens alone released up to 50% of the
releasable granular contents.
Combined effects of E
2
and environmen-
tal estrogens on degranulation of HMC-1
cells. To analyze the effect of combinations of
endogenous estrogen with environmental
estrogens, we incubated HMC-1 cells with
combinations of suboptimal concentrations of
E
2
(1 × 10
–11
M) and varying concentrations
of all six estrogenic compounds. We used
suboptimal concentrations to test for additive
effects, because the release of β-hex from cells
incubated with an optimal dose of the estro-
genic compounds was not significantly
increased by other estrogens (data not shown).
Figure 2 shows that these combinations of
estrogenic compounds induced degranulation
more effectively than either of the compounds
alone at these concentrations. The resulting
stimulations were approximately additive and
again were fairly rapid (< 30 min).
Environmental estrogens enhance IgE-
mediated degranulation of HMC-1 cells and
BMMC. We then evaluated the effect of envi-
ronmental estrogens on IgE-dependent
degranulation using our responsive cell sys-
tems, which were sensitized with IgE anti-
bodies from the appropriate species. When
HMC-1 cells sensitized with human IgE were
subsequently exposed to combination of DM
allergen and 10
–13
–10
–9
M environmental
estrogens, the release of β-hex was signifi-
cantly enhanced compared to cells exposed to
the same concentration of DM allergen alone
(Figure 3A). This was the case for all of the
environmental estrogens tested.
We also tested the effects of environmental
estrogens on IgE-induced degranulation of pri-
mary cultures of BMMCs. We sensitized
BMMCs with monoclonal IgE anti-DNP anti-
bodies and stimulated them with DNP-BSA in
the presence of 10
–13
–10
–9
M concentrations
of our six test environmental estrogens. Each
of these environmental estrogens, except
nonylphenol, significantly enhanced the β-hex
release induced by DM (Figure 3B). We
assessed the dose–response relationship
for one of these environmental estrogens
(Aroclor 1242) to define the concentrations
that had the strongest additive effects on IgE-
mediated degranulation and the shape of the
dose–response curve. Concentrations of
Aroclor 1242 of 10
–14
–10
–12
M significantly
enhanced the effect of IgE cross-linking,
whereas higher concentrations of Aroclor 1242
also appeared to increase the response, but not
to significant levels (Figure 4).
ER-α is required for β-hex release induced
by some concentrations of environmental estro-
gens. To determine which types of ERs were
involved in the degranulation of mast cells by
environmental estrogens, we performed a
dose–response analysis on BMMCs derived
from WT versus ER-α KO mice. Figure 5
indicates that some concentrations of environ-
mental estrogens induce significantly more
degranulation of mast cells from the WT com-
pared with the ER-α KO mice (Figure 5).
However, the degranulation response to some
concentrations of environmental estrogens was
not significantly reduced by the absence of
ER-α expression. In fact, many of the concen-
trations of environmental estrogens alone cause
significant degranulation of ER-α–deficient
mast cells. This is in contrast to the effects of
E
2
, which seems to require ER-α, because E
2
did not induce significant degranulation from
BMMC derived from ER-α KO mice (Zaitsu
et al. 2006).
Discussion
In this study, we examined the effects of envi-
ronmental estrogens—alone and in combina-
tion with physiologic concentrations of
E
2
—on the activation of a human mast cell
line and primary cultures of murine mast cells.
We found that, like E
2
, low concentrations of
environmental estrogens caused a rapid, partial
Narita et al.
50
VOLUME 115 | NUMBER 1 | January 2007
•
Environmental Health Perspectives
20
15
10
5
0
β-hex (% release)
10
0
10
–14
10
–13
10
–12
10
–11
10
–10
*
*
*
Aroclor 1242 [log (M)]
DNP-BSA
Aroclor 1242
Aroclor 1242 + DNP-BSA
Figure 4. Dose–response effects of DNP-BSA,
Aroclor 1242, and Aroclor 1242 plus DNP-BSA on
IgE-mediated degranulation of BMMCs from WT
mice. Experiments were conducted in triplicate
and expressed as mean ± SE.
*p
< 0.05 compared with Aroclor 1242 alone.
Figure 5. Requirement for ER-α expression for degranulation of BMMCs from WT and ER-α KO mice shown by the release of β-hex by various concentrations of
endosulfan (
A
), DDE (
B
), dieldrin (
C
), nonylphenol (
D
), Aroclor 1254 (
E
), and Aroclor 1242 (
F
). Experiments were conducted in triplicate and expressed as mean ± SE.
*p
< 0.05 WT compared with KO.
6
5
4
3
2
1
0
β-hex (% release)
A
10
–12
10
–11
10
–10
*
10
–9
10
–8
Endosulfan [log (M)]
WT
ER-α KO
6
5
4
3
2
1
0
*
*
Nonylphenol [log (M)]
D
B
6
5
4
3
2
1
0
*
*
*
DDE [log (M)]
*
6
5
4
3
2
1
0
Aroclor 1254 [log (M)]
E
6
5
4
3
2
1
0
Aroclor 1242 [log (M)]
F
6
5
4
3
2
1
0
C
*
*
*
*
Dieldrin [log (M)]
β-hex (% release)
β-hex (% release)
β-hex (% release)
β-hex (% release)
β-hex (% release)
10
–12
10
–11
10
–10
10
–9
10
–8
10
–12
10
–11
10
–10
10
–9
10
–8
10
–13
10
–12
10
–11
10
–10
10
–9
10
–8
10
–11
10
–10
10
–9
10
–8
10
–7
10
–12
10
–11
10
–10
10
–9
10
–8
Environmental estrogens enhance mast cell degranulation
Environmental Health Perspectives
•
VOLUME 115 | NUMBER 1 | January 2007
51
degranulation of mast cells. The range of envi-
ronmental estrogen concentrations that
induced β-hex release was somewhat broader
for environmental estrogens (10
–8
–10
–12
) com-
pared to that of E
2
[10
–9
–10
–11
(Zaitsu et al.
2006)]. However, the dose–response curves for
the environmental estrogens were similar to
that for E
2
, in that they are biphasic (inverted
U-shaped) curves. This type of response is also
typical for other steroid-induced responses
(Watson et al. 1999; Welshons et al. 2003).
Exposing HMC-1 cells to a combination of
suboptimal concentrations of E
2
and an envi-
ronmental estrogen had an additive effect on
degranulation. Environmental estrogens also
enhanced the release of β-hex induced by aller-
gen cross-linking of IgE on the surface of these
cells. However, when these mast cells were
incubated with an optimal dose of environ-
mental estrogens, the addition of E
2
did not
enhance the effects of the environmental estro-
gen alone (data not shown). Finally, BMMCs
deficient in ER-α expression had significantly
reduced responses to some concentrations of
environmental estrogens, suggesting that at
least part of the degranulating activity of envi-
ronmental estrogens on mast cells is mediated
through ER-α.
These findings taken together suggest that
the mechanisms of activation of mast cells by
environmental estrogens are similar to those
of the endogenous estrogen E
2
. Key charac-
teristics of that response are high sensitivity
and rapid onset (minutes), partial degranula-
tion, biphasic dose response, requirements for
ER-α and extracellular Ca
2+
, and additivity or
synergy with IgE cross-linking (Zaitsu et al.
2006). Many of these characteristics are also
consistent with those described for activation
of the nongenomic (membrane) form of
ER-α (Watson et al. 1999; Watson and
Gametchu 2003). However, some of the envi-
ronmental estrogens had residual activity at
some concentrations in ER-α KO mast cells.
These might be due to compound-specific
binding to truncated ER-α in the KO cells
(Kos et al. 2002) or to nonclassical ERs, such
as the newly described estrogen-binding pro-
tein GPR30 (Bologa et al. 2006; Thomas
et al. 2005), or other unrecognized receptors.
For instance, we previously described low-
dose and rapid effects of environmental estro-
gens via a membrane-resident ER-α in
pituitary tumor cells (Bulayeva and Watson
2004; Wozniak et al. 2005). In that model,
environmental estrogens in nanomolar (parts
per billion) to picomolar (parts per trillion)
concentrations induced extracellular-regulated
kinase-1 (ERK-1) and ERK-2 activation via
ER-α and Ca
2+
elevations, leading to rapid
prolactin secretion. We have not studied the
effects of environmental estrogens on these
specific signaling pathways of mast cells, but
our recent data suggests that intracellular
Ca
2+
levels rise within 1 min of exposure to
E
2
(Zaitsu et al. 2006).
In the present study, we chose endogenous
and environmental estrogen concentrations
that would mimic tissue levels that occur in
individuals after typical environmental expo-
sures (Ayotte et al. 2003; Ibarluzea et al. 2004;
Metcalfe et al. 2001; Solomon and Weiss
2002; Vartiainen et al. 1997; Wang et al.
2004). However, an additional concern is that
most environmental estrogens are present in
the environment and in tissues and fat stores in
combinations, because of their long half-lives
and co-prevalence in the environment. Our
demonstrations of additive effects between
environmental and endogenous estrogens are
the first steps toward understanding exposure
to complex mixtures of estrogenic compounds.
The results of these experiments are consistent
with the hypothesis that the effects of both
xenoestrogens and physiologic estrogens
together will determine the estrogenic impact
on an individual. This estrogenic impact is
likely to be important both for rapid disease-
promoting responses, such as mast cell activa-
tion, and for more long-term pathogenesis,
such as estrogen-induced cancers.
Some chemicals that accumulate in
women’s tissues are also transferred to their
infants during breast-feeding. This is espe-
cially true for environmental lipid-soluble
pollutants such as polyhalogenated com-
pounds, because these chemicals tend to
degrade slowly in the environment, to bio-
accumulate and bioconcentrate in the food
chain, and to have long half-lives in humans.
Although the World Health Organization
(WHO) strongly supports breast-feeding,
breast milk–monitoring studies suggest that
environmental chemicals that may affect chil-
dren’s health are transmitted through breast-
feeding (Solomon and Weiss 2002; Wang
et al. 2004). Because the fat content of breast
milk is relatively high, the concentration of
some of these pollutants is 100 times higher
in milk than in plasma (Dewailly et al. 1993).
As the final consumers in the food chain,
human infants may consume the highest con-
centrations of lipid-soluble environmental
pollutants, which might enhance their risk of
developing asthma or other allergic diseases.
Our findings on the effects of environ-
mental estrogens on mast cell degranulation
may help explain the increasing prevalence of
asthma and other allergic diseases in recent
decades. A number of sex-steroid effects on
immune system functions have been described
(Watson and Gametchu 2001), yet relatively
few have been explored mechanistically. The
results described here indicate that we must
also consider the possible impact of environ-
mental estrogens on normal immune function
and on the development and morbidity of
immunologic diseases such as asthma.
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