For a newborn, nothing comes close in nutrient density which is so perfectly customized for an infant as it grows. Breastfed infants gain incredible protection from antibodies, proteins and immune cells in breastmilk.
The molecules in breastmilk cells help to prevent microorganisms from penetrating the body’s tissues. Some of the molecules bind to microbes in the hollow space (lumen) of the gastrointestinal tract. In this way, they block microbes from attaching to and crossing through the mucosa-the layer of cells, also known as the epithelium, that lines the digestive tract and other body cavities.
Other molecules lessen the supply of particular minerals and vitamins that harmful bacteria need to survive in the digestive tract. Certain immune cells in human milk are phagocytes that attack microbes directly. Another set produces chemicals that invigorate the infant’s own immune response.
Naturally-occurring sugars found in breastmilk provide protection against life-threatening bacterium by acting as a food source for ‘friendly bacteria’ in a baby’s intestine.
Researchers have identified a specific sugar – lacto-n-difucohexaose I —in breastmilk that proved better at killing the bacterium Streptococcus agalacticae than breastmilk without this sugar.
Antibodies, which are also called immunoglobulins, take five basic forms, denoted as IgG, IgA, IgM, IgD, and IgE. All have been found in human milk, but by far the most abundant type is IgA, specifically the form known as secretory IgA, which is found in great amounts throughout the gut and respiratory system of adults.
These antibodies consist of two joined IgA molecules and a so-called secretory component that seems to shield the antibody molecules from being degraded by the gastric acid and digestive enzymes in the stomach and intestines. Infants who are bottle-fed have few means for battling ingested pathogens until they begin making secretory IgA on their own, often several weeks or even months after birth.
The secretory IgA molecules passed to the suckling child are helpful in ways that go beyond their ability to bind to microorganisms and keep them away from the body’s tissues. First, the collection of antibodies transmitted to an infant is highly targeted against pathogens in that child’s immediate surroundings. The mother synthesizes antibodies when she ingests, inhales or otherwise comes in contact with a disease-causing agent.
Each antibody she makes is specific to that agent; that is, it binds to a single protein, or antigen, on the agent and will not waste time attacking irrelevant substances. Because the mother makes antibodies only to pathogens in her environment, the baby receives the protection it most needs-against the infectious agents it is most likely to encounter in the first weeks of life.
Second, the antibodies delivered to the infant ignore useful bacteria normally found in the gut. This flora serves to crowd out the growth of harmful organisms, thus providing another measure of resistance. Researchers do not yet know how the mother’s immune system knows to make antibodies against only pathogenic and not normal bacteria, but whatever the process may be, it favors the establishment of “good bacteria” in a baby’s gut.
Secretory IgA molecules further keep an infant from harm in that, unlike most other antibodies, they ward off disease without causing inflammation – a process in which various chemicals destroy microbes but potentially hurt healthy tissue. In an infant’s developing gut, the mucosal membrane is extremely delicate, and an excess of these chemicals can do considerable damage.
Interestingly, secretory IgA can probably protect mucosal surfaces other than those in the gut. In many countries, particularly in the Middle East, western South America and northern Africa, women put milk in their infants’ eyes to treat infections there. I do not know if this remedy has ever been tested scientifically, but there are theoretical reasons to believe it would work. It probably does work at least some of the time, or the practice would have died out.
The findings on breastmilk antibodies serve to reinforce the superior nutritional value of breastmilk for newborns, which offers the baby long-term benefits that infant formula has been unable to match.
“Furthermore, the quantity of sugars produced by the mother changes as the baby ages so that a newborn baby will receive a higher amount of sugars in the breastmilk compared to a six-month-old.”
The presence of these sugars allows ‘friendly’ bacteria to flourish and out-compete any harmful bacteria that may be in the baby’s gut, such as Group B streptococcus.
Since protection by breastmilk occurs primarily at the mucosal surface from factors including secretory IgA (sigA) and human milk oligosaccharides (HMOs) such as lacto-N-difucohexaose I, it becomes more resilient to protein breakdown and so is able to exert its function in the gastrointestinal tract.
The pathogens attach onto the sugar, which is subsequently excreted by the body’s immune system.
Research from the University of North Carolina School of Medicine explored this paradox demonstrating that breast milk has a strong virus killing effect and protects against oral transmission of HIV.
“What happens at an early age is that natural killer cells, like many other immune cells, do not complete their functional maturation until adulthood,” says study senior author Yasmina Laouar, Ph.D., assistant professor in the U-M Department of Microbiology and Immunology.
“During this time we are left with an immature immune system that cannot protect us against infections, the reason why newborns and infants are more prone to infection,” she says.
There is a large gap in understanding infant immunity, specifically why the natural killer cell responses are deficient. The study by immunologists at the U-M demonstrates the role of a cell called transforming growth factor beta that can explain why most vaccine scientists mistakenly believe that suppression of the body’s natural signaling mechanisms benefits immunity when it actively suppresses it.
As is true of defensive molecules, immune cells are abundant in human milk. They consist of white blood cells, or leukocytes, that fight infection themselves and activate other defense mechanisms.
The most impressive amount is found in colostrum. Most of the cells are neutrophils, a type of phagocyte that normally circulates in the bloodstream. Some evidence suggests that neutrophils continue to act as phagocytes in the infant’s gut. Yet they are less aggressive than blood neutrophils and virtually disappear from breast milk six weeks after birth.
Milk lymphocytes manufacture several chemicals-including gamma-interferon, migration inhibition factor and monocyte chemotactic factor-that can strengthen an infant’s own immune response.
Infants aren’t allergic to human milk protein – and mothers naturally provide antibodies to their babies in breast milk, as breast milk is rich in living white blood cells, millions per feeding and rich in immunoglobulins which benefit the immature immune system.