Many believe that the first exposure and subsequent sensitization to foods occurs in maternal milk or formula ingested by the infant after birth. However, research has shown that this may transpire in the uterus during pregnancy. In fact, allergen-induced responses have been detected as early as 22 weeks of gestation .
Allergen Proteins in Amniotic Fluid
To dive further into this topic, one lab collected amniotic fluid from 20 women, 8 after delivery and 12 during amniocentesis between weeks 15-20 of gestation. Researchers were able to detect stable food allergens in all 20 samples, with overall concentrations being higher in the amniocentesis group. These food allergen proteins included dairy, wheat, egg, and more .
Allergen proteins can enter amniotic fluid when allergens from the mother’s diet pass from her bloodstream through the placenta and into the amniotic fluid. Amniotic fluid is continuously cycled through the fetal respiratory and gastrointestinal tract until birth .
IgE in Amniotic Fluid
Immunoglobulin E (IgE) is an antibody which is vital for immunity against parasites as well as in response to various allergic diseases. The immune system makes IgE antibodies which react to a certain food or foods. IgE mediated allergic reactions can involve the lungs, eyes, mouth, intestines, brain, heart, or skin and range from mild to life-threatening. The most common allergens in infants are milk, soy, eggs, peanuts, tree nuts, and wheat.
In another study, researchers collected amniotic fluid and maternal blood from 23 women at 16 weeks and then later at term. Interestingly, all the analyzed samples contained detectable levels of IgE at both timepoints which correlated with the amount found in the maternal blood samples . Scientists predict that the IgE in amniotic fluid comes predominately from the mother’s blood stream and directly crosses fetal membranes. It is believed that this mechanism was developed over time to protect the fetus from parasites ingested by the mother during pregnancy. Additionally, the fetus can begin synthesizing its own IgE as early as 11 weeks of gestation .
Putting it together
Studies such as these have bridged a gap in describing how infants are born with food sensitivities. While the fetus is inhaling and ingesting the amniotic fluid, it is taking in allergen proteins as well as IgE antibodies. This could allow for IgE “focusing” to occur, which essentially means that the antibodies are forming a response mechanism against certain proteins.
This is supported by many follow-up articles. In 2010, the Sampson lab discovered that maternal consumption of peanuts during pregnancy was significantly associated with peanut allergies in the infant after birth . This has since been reinforced by additional research on the topic.
The existence of both allergen proteins and IgE antibodies in amniotic fluid may shed a light on how children are born with food sensitivities before they are orally exposed to any outside substances. Of course, there are millions of people born each day without any food sensitivities which leads to the question of why this occurs for some fetuses and not others. More research is needed to establish exactly how and when IgE focusing occurs in amniotic fluid. Once that is determined, scientists can concentrate on therapeutic targets which could block this response from happening.
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