Narita, S, RM Goldblum, CS Watson, EG Brooks, DM Estes, EM Curran and T Midoro-Horiuti. 2007. Environmental Estrogens Induce Mast Cell Degranulation and Enhance IgE-mediated Release of Allergic Mediators. Environmental Health Perspectives 115:48–52.

Scientists report in a new study that six environmental contaminants which act like the hormone estrogen increase the speed and intensity of immune reactions in human and mouse cells. The affected cells, called mast cells, play a key role in allergic reactions, including asthma. The doses used were selected to be well within the range of human exposures. The results suggest that these contaminants may be contributing to the epidemic of asthma.

The results also coincide with what is known about how estradiol affects mast cell degranulation. Mainly it is fast, incomplete, two phased and additive under certain conditions. Like estradiol, EE can activate mast cells and start the degranulation that leads to allergic reaction. 

EE are found in pesticides, plastics, and polychlorinated biphenyls (PCBs).  They can bind with estrogen receptors to produce estrogen-like responses that are usually weaker than the natural estrogen estradiol. Widespread exposure to these vastly different kinds of compounds occurs through air, food, water, and consumer products.

What did they do?

Narita et al. exposed mast cells obtained from people and mice to environmental estrogens (EE) alone, in combination with the hormone estradiol, or in combination with dust mite allergen. Then, they measured an allergy-related enzyme released from the cells to determine speed and intensity of the allergic reactions.

The authors wanted to see the extent female hormones and their synthetic counterparts interact with allergens to produce allergic responses.

In the study, a series of four laboratory experiments tested the effects of six environmental estrogens on human mast cells (HMC-1) and bone marrow derived mast cells (BMMC) from either wild type mice or from genetically engineered mice that do not express a functional estrogen receptor-alpha (ER-alpha). The cells were grown in cell culture for the experiment.

The environmental estrogens included: the organochloride pesticides endosulfan, dieldrin and DDE; plastics by-product nonylphenol; and polychlorinated biphenyls Arochlor 1242 and Aroclor 1254. The concentrations used were within the ranges found commonly in people.

In all parts of the study, cultures were incubated for 30 minutes followed by measurement of cellular release of beta-hexosaminadase (B-hex), an enzyme associated with mast cell degranulation. Degranulation is when allergens trigger immune cells to release histamine and other products that cause allergy symptoms.

Exp. 1. Estradiol and EE alone. Five concentrations of estradiol and each EE were added individually to human mast cell cultures. Results determined each EEs allergic response.

Exp. 2. Estradiol and EE alone and combined. Additive effects were investigated by adding estradiol alone, or in combination with each EE to human mast cell cultures.

Exp. 3. EE and dust allergen.  In an effort to assess how EE influence the allergic response in patients with known allergic sensitivity to dust mites, mast cells were obtained from these patients and degranulation was measured when EE and dust mites were added to the cells in combination.

Exp. 4. EE and mice mast cells. In order to determine what contribution the estrogen receptor played in mediating the degranulation response to EE, various concentrations of EE were added to mast cells obtained from wild type mice, or mast cells from mice without an ER.

What did they find?

The six EE caused rapid immune responses in human and mice mast cells. When combined with estradiol or dust mite allergen, most of the estrogenic compounds significantly increased cell degranulation in both cell types. The only one that showed no statistically-significant effect was a PCB, Aroclor 1254.

These results are shown to below. The research team measured the percent of a protein called ß-hexosaminidase present in mast cells that was released by exposure to the chemical agent. This is a standard test for degranulation in studies of allergic reactions. Higher percent releases mean greater degranulation and would lead to a stronger allergic reaction.

They tested concentrations ranging from a part per trillion (10 to the minus twelfth) to 10 parts per billion (10 to the minus eighth). The researchers found that human immune cells exposed to estradiol and each EE alone caused degranulation, although EE affected the cells at a wider range of concentrations than the natural estrogen. In three of the five concentrations tested (10-11 to 10-8 M), each EE, with the exception of Arochlor 1254, released significant amounts of B-hex. Remarkably, up to half of each cell’s available B-hex was dumped within 30 minutes of treatment. The "inverted-U" dose response (also known as a "non-monotonic dose response curve") in Figure 1, which is typical for sex steroid hormones, shows the strongest effect at an intermediate dose (in this case, one tenth of a part per billion). The highest concentration tested, equivalent to 10 parts per billion, had no effect, nor did the lowest, equivalent to 1 part per trillion.

Mixtures increased the responses. In human mast cells, 10 parts per trillion (10 to the minus 11th) estradiol in combination with sub-optimal concentrations of each individual EE produced greater effects together than by themselves. Total degranulation occurred within a half an hour and effects were additive.

Effects were even more striking with a dust mite allergen. When they exposed IgE sensitized mast cells from humans and mice to EEs (10-13 to 10-9 M) and a mite allergen, they found that, in almost all cases, significantly more B-Hex was released from the combined exposure than was released in cells exposed to just the allergen. The only exception was nonylphenol, which did not significantly increase degranulation in the wild type mice culture.

In this case, the greatest additive IgE-regulated effects occurred at the lowest concentrations. A further look at one compound, Arochlor 1242, showed significant responses at middle-range concentrations between 10-14 and 10-12 M.

Finally, Narita et al. compared degranulation in mast cells from mice with and without receptors for estrogen, called the estrogen receptor, or ER. Previous experiments have shown that cells lacking the estrogen receptor do not degranulate when exposed to estradiol. In contrast, while degranulation caused by EEs was reduced at some concentrations of exposure, at others it did not. In fact, for several EEs at some concentrations, degranulation was greater in cells lacking ER than in cells with ER.

What does it mean?

This study supports prior findings that estradiol influences immune cell responses and goes further by providing solid evidence that environmental estrogens cause similar immune responses as the natural hormone estradiol, in both human and mouse cells. In addition, most of the environmental estrogens when mixed with either dust allergen or estradiol increased allergic releases in an additive way when compared to EEs, estradiol or dust allergen alone.

Rising asthma rates during the last decade cannot be fully attributed to dirtier air or more allergen exposure. These results, then, provide another explanation for why more people are affected from this respiratory illness today than in the past. According to Narita et al. “effects of EEs on mast cell degranulation may help explain the increasing prevalence of asthma and other allergic diseases in recent decades.”

The first signs of asthma are typically seen in childhood but severity of the condition changes with age and gender. Males are more likely to suffer during childhood and adolescence while females experience the highest rates and most severe symptoms as adults. Estrogens most likely play a role in these sex differences. Prior studies show estrogens can directly or indirectly activate mast cells to release proteins and other cell products responsible for asthma and allergy symptoms.

Another important finding is that both estrogens and the EEs tested had their greatest effects at mid ranges although the EE affected cells at broader concentrations. This non-monotonic response (an inverted-U shaped curve), where the lowest and highest amounts tested produced weaker effects than the middle concentrations, will not be detected by traditional toxicity tests, which are the basis for setting public health standards. These results strongly suggest that immune system dangers posed by environmental estrogens will have been missed by those approaches.

The paper also provides more evidence that estradiol and EEs may act through more than one type of ER. Receptors in the cell’s surface are known to control chemical reactions that lead to rapid results rather than the slower route of gene expression mediated by ER-alpha. The very fast responses and activity seen in cells lacking ER-alpha observed by Narita et al. suggest the environmental estrogens could be causing this immune system impact through such a membrane estrogen receptor. Prior work has shown that responses mediated by this receptor are much more sensitive to environmental estrogens than are events mediated by the nuclear hormone receptor.

Environmental compounds with broad human exposure have the ability to initiate and increase intensity of allergic reactions in both human and mouse immune cells. Some of these long-lived, fat-loving environmental estrogens may be passed from mother to baby during development or breast milk. Breastfeeding, the authors point out, may expose babies to these pollutants “which might enhance their risk of developing asthma or other allergic diseases.”

Overall, the results of this cell study suggest we must “consider the possible impact of environmental estrogens on normal immune function and on the development and morbidity of immunologic diseases such as asthma.”