AsianScientist (Nov. 17, 2020) – Using animal models, scientists in Singapore have shown that expectant mothers can pass allergies onto babies developing in their wombs. Their findings were reported in Science.
Whether it’s a reaction to shellfish, soy, dust or dairy, allergies result from an overly enthusiastic immune response. Whenever we encounter an allergen, our immune system kicks into overdrive, producing immunoglobulin E (IgE) antibodies that trigger a cascade of chemical reactions. Eventually, this cascade leads to the classic symptoms we associate with allergies: sneezing, runny noses, rashes and even swollen lips, among many others.
With 10 to 30 percent of the world’s population affected by allergies, researchers are searching for novel ways to lower these numbers over time. This led a team from the Agency for Science, Technology and Research (A*STAR), KK Women and Children’s Hospital (KKH) and Duke-NUS Medical School to retrace the origins of these allergies.
“Allergies begin very early in life,” said study co-author Associate Professor Ashley St. John from Duke-NUS Medical School. “Infants experience allergic responses closely linked with the mother’s allergic response in ways that cannot only be explained by genetics.”
To investigate allergies’ maternal link, St. John and her team exposed mice to ragweed pollen, a common allergen, before inducing pregnancy. Mice that developed a sensitivity to ragweed had offspring that immediately had the same reaction to the allergen. In comparison, adult mice typically need to be exposed twice to an allergen before developing sensitivity.
Dust mites, another common allergen, had no effect on the offspring. This means that the transfer of sensitivity is allergen-specific. Notably, the transfer of sensitivity appears to fade with time. While the newborn mice had allergic reactions when tested at four weeks, there was less or no reaction at all at six weeks.
Through cellular tests and imaging, the authors then showed that maternal IgE travelled across the placenta to bind to mast cells found in the fetus’ immune system. Once bound, these mast cells release chemicals that trigger the symptoms of allergic reactions—explaining the transfer of sensitivity.
It turns out that another protein, called the neonatal FC receptor (FcRN), facilitates the transport of IgE across the placenta. Notably, knocking out FcRN in pregnant mice resulted in offspring with no maternal IgE attached to their mast cells and no allergies after birth. Further studies showed that maternal IgE can also bind to human fetal mast cells, suggesting that they might cross the placenta in humans in a similar way.
Moving forward, the authors hope to dive deeper into the mechanism of IgE transfer through the placenta as well as the effects of IgE binding to mast cells found in fetal skin.
“Our research has exciting findings that may explain the high incidence of early onset atopic dermatitis (eczema) in children of mothers with clinically proven eczema,” said study-co-author Professor Jerry Chan from KKH. “[This study is] key to developing strategies to reduce the chance of eczema or other allergies from being transferred from mother to baby.”
The article can be found at: Msallam et al. (2020) Fetal Mast Cells Mediate Postnatal Allergic Responses Dependent on Maternal IgE.
Source: Duke-NUS Medical School; Photo: Hu Chen/Unsplash.
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