Breast milk is a complex, living fluid that provides comprehensive nutrition and immune protection for the infant. Pumped milk does contain antibodies; the act of expression does not destroy these protective components. Antibody concentration changes throughout lactation, with colostrum having a significantly higher concentration of immunoglobulins compared to mature milk. A mother’s immune system constantly adapts to her and the baby’s shared environment, producing targeted antibodies that are then transferred into the milk. This dynamic biological process ensures the infant receives protection tailored to the pathogens they are currently exposed to.
Defining Immune Components in Breast Milk
The immune defense system in breast milk extends beyond simple antibodies. The most abundant antibody is Secretory Immunoglobulin A (sIgA), making up 80 to 90% of all immunoglobulins. This specialized antibody resists breakdown by the infant’s digestive enzymes and stomach acid. Its primary function is to coat the lining of the infant’s respiratory and gastrointestinal tracts, acting like a protective paint that prevents pathogens from attaching to the cell surfaces and causing infection.
Breast milk also contains powerful non-antibody immune factors. Lactoferrin is a protein that binds to iron, starving harmful bacteria of a necessary resource, which gives it antibacterial and anti-inflammatory properties. Another enzyme, Lysozyme, is present at levels much higher than in infant formula, actively breaking down the cell walls of certain bacteria.
Antibody Retention During Pumping and Storage
The method used to handle and store expressed milk primarily determines how well the immune components are preserved. Pumping itself does not significantly degrade the antibodies, but storage conditions influence their stability.
Temperature Effects on Antibodies
Refrigeration, typically at 4°C (39°F), is very effective for short-term storage, keeping sIgA and lysozyme activity stable for several days. Freezing milk, often at -20°C (-4°F), is the best method for long-term preservation of antibody content, though some minimal loss of activity can occur over time. Conversely, the use of high heat, such as pasteurization, can cause destruction of delicate antibodies and living cells. Pasteurization, a process used for donor milk, has been shown to reduce antibody levels.
Minimizing Contamination
To maximize the retention of protective factors, avoid contamination during pumping and storage. Use clean, sterilized pump parts and airtight, food-grade containers to maintain milk quality. Storing milk in the main body of the refrigerator or freezer, rather than the door, minimizes temperature fluctuations that compromise stability.
How Breast Milk Immunity Protects the Infant
The bioactive components in pumped milk provide the infant with passive immunity localized to their mucosal surfaces. Since the infant’s own immune system is still developing, maternal sIgA acts as an important first line of defense against environmental pathogens. This protection is especially important in the gastrointestinal and respiratory tracts, where most infections begin.
The presence of these antibodies is associated with a lower incidence of common infant illnesses, including respiratory infections, ear infections, and diarrhea. For premature infants, the immune factors in human milk are highly important, reducing the risk of a severe intestinal disease called necrotizing enterocolitis (NEC). The antibodies also help establish a healthy gut microbiome by neutralizing harmful bacteria and guiding the growth of beneficial ones.