Breastmilk “teaches” immune system to ward off allergens in mice.

Apr 05, 2010

Verhasselt, V. 2010. Neonatal tolerance under breastfeeding influence: The presence of allergen and transforming growth factor-ß in breast milk protects the progeny from allergic asthma. The Journal of Pediatrics 156(2) Suppl. 1: S16-S20.

Synopsis by Thea M. Edwards and Wendy Hessler

A new study in mice shows that exposure to an allergen through breast milk can actively program a pup's immune system to prevent asthma later in life. Exposure to both the allergen and a specific immune factor passed on through the milk by the mother was necessary for protection. This study suggests that a mom's exposure to allergens during breastfeeding can help protect her baby from reacting to those allergens later in life.


Allergies occur when the immune system overreacts to what should be a harmless substance, such as pollen or dust. Asthma is a specific type of allergic disease of the lungs.

Allergies and asthma are the most common chronic childhood diseases in the U.S. According to the American Academy of Pediatrics (AAP), almost five million American children have asthma and 50 million have allergies.

Asthma develops when an initial exposure sensitizes a person to an allergen found in the air. Further exposures then produce the classic asthma allergic symptoms – such as wheezing and shortness of breath. The frequency and severity of asthmatic attacks can be reduced by avoiding the airborne allergens that trigger an attack.

The likelihood of becoming sensitized to a particular allergen varies from person to person. The cause is not well understood but the answer might lie in exposures that occur – or do not occur – during development, both in the womb and during the first year or two of life. This idea is known as fetal programming or fetal origins of disease.

Many components of breast milk – including cholesterol, specific sugars and enzymes – contribute to a baby’s growth and development. Also important to health is the mother-to-baby transfer of antibodies, growth factors and other immune-related items that boost immune system function and protect against infections.

According to the U.S. Center for Disease Control and Prevention, for U.S. babies born in 2006, 43.4 percent were breastfeeding at 6 months and 22.7 percent were still breastfed at 12 months.

Recent studies suggest that breastfeeding for at least three months can reduce a child’s risk of developing asthma (Gdalevich et al. 2001, Greer et al. 2008). However, other research shows either no effect or the opposite – an increased risk of asthma – with breastfeeding. Due to these conflicting results, AAP currently considers the relationship between breastfeeding and asthma prevention as inconclusive because no clear pattern of effect has been found (Greer et al. 2008).

Mice were exposed to an allergen, first as babies through breast milk, and again as adults to determine if early life exposure would protect against developing asthma later in life.

The mother mice were exposed through air to an allergen – ovalbumin – for 20 minutes every other day during lactation. This continued until the baby mice were weaned between six and eight weeks old. Ovalbumin is used to induce asthma in research animals. Control mothers were not exposed.

Researchers analyzed breast milk samples for ovalbumin and maternal immune factors to determine if the mother mice were passing these on to their babies through nursing.

As adults, the offspring were injected twice – one week apart – with ovalbumin to sensitize them to the allergen. Ten days after the second injection, the mice were exposed to airborne ovalbumin once a day for five days to initiate asthma symptoms.

The researchers analyzed the lungs and airways for signs of asthma. They examined blood samples for antibodies against ovalbumin and other asthma-specific immune factors, including transforming growth factor beta (TGF-beta).

All the signs of asthma were reduced by more than 50 percent in mice whose mothers were exposed to ovalbumin while they were breastfeeding. The mice whose mothers had not been exposed to ovalbumin had greater allergic reactions to the allergen as adults.

Exposed mother mice passed ovalbumin and the immune factor TGF-beta through their milk to their babies.

The key to asthma prevention in this study is the combination of allergen and immune factors from the mom’s mature immune system, which are found together in breast milk.

This study shows that when mother mice are exposed to an allergen during lactation, their babies are less likely to develop asthma when exposed to the same allergen as adults.

The breast milk taken from the exposed mothers contained both the allergen ovalbumin and the immune factor TGF-beta. This combination was necessary to prevent the offspring from becoming sensitive to ovalbumin.

The results of this study are important because they explain how breast milk can help a baby’s immature immune system develop in a way that prevents allergies – like asthma – later in life. This brings researchers closer to understanding if and how breastfeeding can prevent allergies.

Although this study looked at a specific allergen, breastfeeding for longer periods may be more protective. It allows for the mother to be exposed to many of the allergens her baby might encounter in adulthood. For example, a full year of breastfeeding would expose the mother to the different pollens, dusts and other airborne pollutants that come with each season.

In this study, the researchers found that the combination of TGF-beta and ovalbumin in breast milk was necessary to protect offspring from ovalbumin-initiated asthma. Given the complexity of breast milk, it is possible there are other immune factors that are also important in conferring allergen tolerance.

The results of this animal study set the stage for targeted human studies to determine if mothers exposed to specific allergens during nursing can protect their children from reacting to those allergens later.  It appears that the baby must receive the allergen in combination with maternal immune factors to develop protection from asthma and potentially other allergies.  Additionally, babies only develop tolerance to allergens they received during nursing.  There is no protection from new allergens encountered after the baby has weaned.


Allergy. MedlinePlus. National Institutes of Health.

Gdalevich, M, D Mimouni and M Mimouni. 2001. Breast-feeding and the risk of bronchial asthma in childhood: a systematic review with meta-analysis of prospective studies. Journal of Pediatrics 139: 261–266.

Greer, FR, SH Sicherer, AW Burks and the Committee on Nutrition and Section on Allergy and Immunology. 2008. Effects of early nutritional interventions on the development of atopic disease in infants and children: The role of maternal dietary restriction, breastfeeding, timing of introduction of complementary foods and hydrolyzed formulas. Pediatrics 121: 183-191.

National breastfeeding statistics. U.S. Center for Disease Control and Prevention.



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