Mother’s milk protects offspring from allergies

Mice exposed to allergens pass on protective proteins to offspring through breastfeeding

Food allergies affect around 2% of adults and 8% of children in the UK, and these numbers seem to be rising. Having a food allergy means that your body’s immune system treats that food as if it were a virus or bacterium. When that food is encountered, the immune system overreacts, producing an allergic reaction.

Scientists don’t fully understand why people become allergic to certain foods, but many believe that a pregnant mother’s diet could be partly to blame, although this viewpoint is controversial. Eating more "allergenic" foods, like milk, eggs, peanuts and so on, might, some say, make her child more likely to become allergic to those foods later.  Then again, other studies suggest the opposite: that eating allergenic foods while pregnant may actually help prevent the child from becoming allergic to those foodstuffs.

Now, a new study has shown that pregnant mice exposed to allergenic foods produce specific kinds of proteins in their breast milk. These proteins, called antibodies, help prevent the offspring from developing allergies to the foods in the mother's diet. The study was performed by Harvard scientist Michiko Oyoshi and her colleagues, and was published this week in the Journal of Experimental Medicine.

The researchers took pregnant mice and regularly exposed their skin to the protein "ovalbumin" from egg whites (a common allergen). After birth, the offspring also had their skin exposed to ovalbumin before being fed the protein. Mice whose mothers had been exposed to the protein did not show any allergic response, whereas mice whose mothers had not been exposed did show allergic responses. The researchers repeated the experiments with peanut butter instead of ovalbumin, and found the same results.

In order to understand what was happening, the team then examined the mothers’ breast milk, which the offspring were feeding on. They found that the breast milk contained antibodies which would specifically bind to the allergen, preventing the immune system from overreacting to it. These antibodies also stimulated the offspring to produce specific immune cells, so that even after being weaned off the milk, the offspring would still be able to tolerate the allergen and not have an allergic reaction. 

The next step was to test if human breast milk is also able to prevent food allergies from developing in offspring. For this, they used genetically modified mice which make human immune proteins instead of mouse immune proteins. Offspring of these mice were fed human breast milk containing antibodies specific to egg white protein, and were later fed egg white protein. These mice were able to tolerate the egg white. On the other hand, mice fed with human breast milk which did not contain the antibodies were not able to tolerate egg white, and produced allergic responses.

These findings suggest that human breast milk may also help prevent babies from developing food allergies, if the mother has been exposed to allergens during pregnancy. However, this is not conclusive. Oyoshi and her team hope to perform a new study with human mothers, in order to test this idea. Hopefully, this future research will provide clear information to advise pregnant mothers on this controversial issue.