Are allergies acquired in the womb?

Around 10% to 30% of the global population is affected by allergies, and this number continues to increase. The sensitization rates for allergies in school children are even higher, at 40% to 50%. These numbers are based on the World Allergy Organization White Book on Allergy 2013.

But where do we acquire allergies? Can allergies be acquired while the fetus is still developing in the womb?

Just recently, a team of researchers embarked on a study to find the link between a mother’s immune system and the developing fetus in utero. This link could possibly explain why some infants develop an immune response the first time they encounter an allergen even when they have never been exposed to it before.

According to a Singapore study, it is possible for mothers to pass on allergies to an offspring still developing in the womb. Researchers believe this is one of the reasons why some babies exhibit symptoms of allergy early in life.

The research, published in October, led to findings showing that the key antibody called immunoglobulin E (IgE), which is responsible for triggering allergic reactions, can enter the fetus through the placenta. When it enters the fetus, the antibody binds with mast cells, which are immune cells responsible for causing allergic reactions including asthma and a runny nose.

The researchers exposed mice to a common allergen, ragweed pollen, before pregnancy. Mice that had sensitivity to the allergen gave birth to offspring that were also allergic or sensitive to ragweed. Interestingly, the mice only showed allergic reactions to this specific allergen and did not show any reaction to other common allergens.

Another thing that the researchers found out was that the newborn mice’s allergen-specific sensitivity faded over time. While they had allergic reactions at four weeks, they had less or none at six weeks.

According to Ashley St. John, co-author of the study and immunologist at Duke-NUS Medical School, antibodies have a half-life, so the antibodies that are transferred from the mother to the offspring will gradually break down over time. This explains why the allergic responses are only exhibited within a period of time and then slowly decline.

St. John adds that we don’t yet know if they have an impact on the offspring developing its own allergies.

The team, which is made up of scientists and clinicians from Singapore’s Duke-NUS, Agency for Science, Technology and research (A*STAR), and KK Women’s and Children’s Hospital (KKH), also found out that for IgE to be transferred across the placenta, it needs the presence of another protein: the neonatal Fc receptor (FcRN).

St. John explains that FcRN is a protein that specifically binds to antibodies and carries them across the placental barrier. Without the presence of FcRN, antibodies cannot flow through it.

Florent Ginhoux, co-author of the study and senior principal investigator at A*STAR’s Singapore Immunology Network, notes that there is still a significant lack of knowledge on mast cells that are present in the early stages of a fetus’ development.

The same study also explored the possibility of having new intervention strategies that could prevent a mother from passing on allergies to the child. Ginhoux says that one strategy could include identifying highly allergic mothers and reducing their levels of IgE during pregnancy.