The benefits of breast milk are many and varied, and one of the things that is always included is the presence of antibodies that help protect the baby from pathogens until it is able to develop its own immune system. This concept is not completely true, since it depends on the type of antibody we are talking about and if we find it in high or low levels.
What antibodies are found in breast milk?
Antibodies are the agents of the immune system that patrol our interior in search of molecules that may seem dangerous to the body. Five types of antibodies are known based on their structure and function: IgA, IgD, IgE, IgG and IgM . Each type can be found in breast milk at different concentrations, but the amount is not the only factor to consider. Another very important aspect is whether these antibodies have specificity, that is, whether they are capable of recognizing a specific molecule.
Of all the types of antibodies, the IgA group is known to be the most relevant in mucosal immunity. This refers to the protection mechanism against external agents that is present on specific surfaces such as the respiratory tract or the intestine. In our body, the levels of IgA in the blood are quite low, in breast milk they are found in high concentrations .
IgD-type antibodies are still a great unknown today, since some of their possible functions are unknown. However, already in a 1985 study he was able to detect IgD antibodies in the blood and colostrum of 14 lactating mothers. Colostrum is the name given to the first milk produced by the mother and is often said to contain high levels of nutrients. The results showed that, although in lower amounts than in the mothers’ blood, IgD antibodies could be detected in the colostrum .
In previous articles we have explained that IgE-type antibodies are responsible for triggering allergic reactions when they come into contact with allergens (pollen, food, mites, etc.). IgE levels in the blood are used to diagnose and assess the risk of reactions. So, can a nursing mother transfer these IgE antibodies to her baby and put her at risk for allergies? The answer is no . Milk is perfectly healthy for the baby, as it does not contain IgE antibodies at very low levels, even if the mother has a severe allergy. Even though they can be detected in the milk, it does not transfer the sensitivity or risk to the baby.
Finally, we have the IgG and IgM type antibodies. Both types have low levels in milk, and the newborn must create its own IgG/IgM antibodies during the development of its own immune system . Now that we know what types of antibodies are found in breast milk, what are they for? Do they play any role in the immune defense of the newborn?
What function do these antibodies have?
Since the antibodies that are in higher concentration in breast milk are the IgA type, it is these that will play a more relevant role. However, another very important process now comes into action. If the newborn is fed breast milk that contains high levels of antibodies, but his body is not able to assimilate them, the benefit would be lost . One of the characteristic functions of IgA antibodies is that they can be absorbed by the baby’s intestine and will serve as a protective barrier against infections and clearly harmful pathogens. IgAs work as broad-spectrum antibiotics , which prevent the most basic and common dangers to which the baby may be exposed. This has been verified in several studies using mouse models and in human observations with newborns receiving breast milk or formula milk.
However, antibody levels do not remain constant throughout lactation. One study looked at antibody levels in the breast milk of 116 lactating mothers throughout the time of lactation, from the start to 48 months later. The results demonstrated that the levels vary over time, where IgA and IgG antibodies are present at low levels in the first year and reach maximum levels at the end of lactation . However, these changes were affected by the number of takes you took.
Breastfeeding is recommended to the extent that circumstances allow it and there are no contraindications because the benefits are widely evaluated and confirmed. The presence of antibodies and, specifically of the IgA type, is one of the reasons. Despite the studies, in some cases it may be advisable to opt for alternative options to breastfeeding. As always, in case of doubt, it is best to consult a specialist who will resolve them and help find the best option .
Keller et al. 1985. IgD in Human Colostrum. Pediatric Reserach. doi: 10.1203/00006450-198501000-00032Duchén et al. 1996. Total IgE levels in human colostrum. Pediatr Allergy Immunol. doi: 10.1111/j.1399-3038.1996.tb00104.xCzosnykowska-Łukacka et al. 2020. Changes in Human Milk Immunoglobulin Profile During Prolonged Lactation. Front Pediatr. doi: 10.3389/fped.2020.00428Rogier et al. 2014. Secretory antibodies in breast milk promote long-term intestinal homeostasis by regulating the gut microbiota and host gene expression. Proc Natl Acad Sci. doi: 10.1073/pnas.1315792111