A new study has found that mothers can pass allergies to their offspring while they are developing in the womb, according to researchers from the Agency for Science, Technology and Research (A*STAR), KK Women's and Children's Hospital (KKH), and Duke-NUS Medical School in Singapore.

The study used an animal model that was conducted according to the National Advisory Committee for Laboratory Animal Research (NACLAR) guidelines. They found that the key antibody responsible for triggering allergic reactions, immunoglobin E (IgE), can cross the placenta and enter the fetus. While inside the fetus, the antibody binds to fetal mast cells, which are a type of immune cell that releases chemicals that trigger allergic reactions, according to the study.

After birth, newborn mice developed allergic reactions to the same type of allergen as their mothers at the time of first exposure, unlike adult mice, which require 2 exposures. Additionally, studies in the laboratory showed that maternal IgE can bind to human fetal mast cells, indicating they might cross the placenta in humans in a similar way, according to the researchers.

"There is currently a significant lack of knowledge on mast cells that are present early on in the developing fetus. Here, we discovered that fetal mast cells phenotypically mature through the course of pregnancy, and can be sensitized by IgE of maternal origin that cross the placental barrier,” said senior principal investigator at A*STAR, Florent Ginhoux, MD, in a press release. “The study suggests that a highly allergic pregnant mother may potentially transfer her IgE to her baby that consequently develop allergic reactions when exposed to the first time to the allergen."

Following NACLAR guidelines, the researchers exposed mice to ragweed pollen prior to pregnancy. The mice that developed a sensitivity to the pollen had offspring that also showed an allergic reaction to ragweed. Since the sensitivity is allergen-specific, the offspring did not react to dust mites, according to the study.

Further, the transfer of sensitivity appears to fade with time, with the newborn mice having allergic reactions when tested at 4 weeks, but less or none at 6 weeks.

Using cellular tests and imaging, the researchers were able to analyze maternal IgE bound to fetal mast cells, triggering the mast cells to release chemicals in reaction to an allergen, or degranulation.

The study also found that the IgE transfer across the placenta requires the help of another protein, FcRN, which helped knock out the lacked maternal IgE attached to their mast cells and did not develop allergies after birth.

The findings potentially open new intervention strategies to limit such transfer to minimize the occurrence of neonatal allergies, according to the researchers. The study authors next hope to better understand the mechanism of IgE transfer through the placenta, how IgE binding to mast cells in fetal skin modulate their functions, and how it could affect skin physiology after birth.

REFERENCE
Mothers pass on allergies to offspring. ScienceDaily. https://www.sciencedaily.com/releases/2020/10/201030111832.htm. Published October 30, 2020. Accessed October 30, 2020.