Mothers can pass on allergies to offspring while they are developing in the womb and that is one reason why babies exhibit allergies early in life, according to a Singapore preclinical study.
Findings from the research published 30 October in Science show that the key antibody, immunoglobulin E (IgE), responsible for triggering allergic reactions, can enter the fetus from the mother's body through the placenta. Once inside the fetus, it binds with fetal mast cells which are immune cells responsible for causing allergic reactions, such as runny noses and asthma.
Globally, 10—30 per cent of the population is affected by allergies and this number continues to increase. The sensitization rates for allergies in school children are close to 40—50 per cent, according to the World Allergy Organization White Book on Allergy 2013 update.
This is a previously unappreciated way that the mother's immune system can influence the offspring during development and after birth and it could possibly explain why some offspring develop an immune response the very first time they encounter an allergen, even when they have never been exposed before."
Ashley St. John, study co-author and immunologist at Duke-NUS Medical School
Researchers exposed mice to ragweed pollen, a common allergen, before pregnancy. Mice that developed sensitivity to the pollen had offspring that also exhibited allergic reactions to ragweed. However, the sensitivity was allergen-specific and the offspring did not show any reaction to dust mites or other common allergens.
Researchers noted that the allergen-specific sensitivity faded with time. The new-born mice had allergic reactions when tested at four weeks, but less or none at six weeks.
"Antibodies have a half-life, which means that the antibodies that transfer from the mother to the foetus will slowly break down over time. Therefore, they only confer allergic responses for a period of time and then slowly decline in concentration and influence. We don't yet know if they promote the offspring to develop its own allergies to those allergens and this is something we will be studying in the future," St. John tells SciDev.Net.
The study, a collaboration 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), further showed that for IgE to transfer across the placenta, it required the help of another protein called the neonatal Fc receptor (FcRN).
"FcRN is a protein that is expressed at the interface between the mother and developing fetus. It binds specifically to antibodies and acts as a shuttle, carrying them across this placental barrier that is usually quite tight and does not allow the flow of antibodies without active transport. Mast cells can bind to IgE, but there is no source in the fetus, so FcRN acts, in combination with other molecules, to deliver IgE to mast cells," St. John explains.
Currently, there is a significant lack of knowledge on mast cells that are present early on in the developing fetus, notes Florent Ginhoux, study co-author and senior principal investigator at A*STAR's Singapore Immunology Network.
The research, in laboratory studies, also demonstrated that maternal IgE can bind to human fetal mast cells, suggesting that a similar crossover takes place in humans.
The findings open up the possibility of new intervention strategies to prevent allergies being passed from mother to child. "We could identify highly allergic mothers and try to reduce their IgE levels during pregnancy by removing them from blood circulation," Ginhoux tells SciDev.Net.
"From a clinical point of view, developing a further understanding in placental transfer of IgE, and the mechanism of foetal mast cell activation would be key to developing strategies to reduce the chance of eczema or other allergies from being transferred from mother to baby," Jerry Chan, senior consultant, department of reproductive medicine at KKH, said in a statement.
"This study is important for the Asia Pacific region, which is well known to have diverse food patterns with numerous vegetables, legumes and fruits. During pregnancy, women take many food items mainly offered to them by their extended family," says Ajith Amarasinghe, pediatric allergy specialist at Lanka Hospitals in Colombo (Sri Lanka) and member of the European Academy of Allergy, Asthma and Clinical Immunology.
"As to how this type of diverse food patterns would affect the antigen FcRN and mast cells is an important observation to make," says Amarasinghe. "This research should lead to further studies on causation of specific allergic symptoms and diseases based on the fact that maternal allergen exposure would prime the mast cells and would cause the foetus and the neonatal to produce allergens."
According to a 2019 study, in Asia, some unique food allergies arise in part from the distinctive cultural food practices of the region and environmental exposure. Cow's milk and egg are two of the most common food allergens in young children. Wheat is emerging as an important allergen in some developing parts of Asia.