LLLI Center for Breastfeeding Information

Journal Abstract of the Month for February 2007

“Why We Develop Food Allergies”

Author: Per Brandtzaeg

American Scientist 2007 Jan/Feb 95: 28-35

This month’s journal article is a bit of a departure from most other JAOMs in that it comes not from a medical journal, but instead from American Scientist, the official magazine of science and technology published by Sigma Xi, the Scientific Research Society. It is a review article rather than a research article. It was selected because not only does it provide excellent information on breastfeeding’s role in the development of a baby’s immune system, but also because it is a pleasant surprise to find such a topic for an article intended for a more general population than the medical journals.

Highlights

The human immune system and the gut mature together.
Challenges to the immune system (such as various microbes) appear to help in the maturation process.
Maternal antibodies, especially Secretory Immunoglobin A (SIgA), help protect the infant until his system matures.
Human milk is the only significant source of SIgA for the first weeks and months of a newborn’s life.
Allergies are the result of a number of factors including genetics, the barrier function of the gut lining, and the timing and dose of challenges to the system.

Abstract:

In this article, Per Brandtzaeg states, “A human being is born with an immature immune system and an immature gut, and they grow up together.” He describes the mechanisms involved in this maturation and discusses how this process may go awry in the development of food allergies. He reviews the evidence suggesting that human milk is important for the normal development of the immature gut, and in the prevention of food allergies.

The human immune response is essentially a cellular sentry of sorts, with two critical determinations to be made any time the body comes in contact with a foreign substance. The first determination is “me” vs “not me.” The “not me” substances are then subjected to another critical determination: “safe” vs “not safe.” Generally, the body recognizes itself as “safe,” and it must learn what constitutes “not safe.” This requires establishing equilibrium between tolerating what is safe and aggressively attacking the rest. An allergic response happens when the immune system is intolerant, and fails to suppress that aggression.

The fetal environment is safe, warm, free from germs, and has little need for its own immune system. He is protected by his mother’s immune system. Until, that is, the newborn finds itself on the outside of the womb and thus surrounded by all manner of microorganisms and other foreign substances called antigens. The presence of these antigens helps stimulate the newborn’s immune system, primarily through mucosal surfaces such as the gut and respiratory structures.

The first line of defense in a newborn’s gut is the system of immune exclusion, which uses exported antibodies to bind germs and potentially harmful compounds on the mucosal surface. Antibodies coat the pathogens to prevent them from invading the gut wall.

This immune exclusion is largely handled by a class of antibodies called secretory immunoglobin A (SIgA). Newborns produce little or no SIgA of their own. Guess what is the only significant source of SIgA during the first weeks and months of a child’s life? Human milk. The simple act of breastfeeding helps the infant protect himself until his immune system is mature enough to do this on its own.

SIgA antibodies also help the infant’s gut to develop by strengthening the gut lining to act as a barrier. In some children, this barrier is inadequate for longer than for others, and a lack of SIgA seems to make the difference. At this level, the role of breastfeeding again seems relevant. Babies who are not getting their mothers’ milk—and therefore her stores of SIgA—may see a delay in the maturation of this barrier function. Brandtzaeg states that “. . . babies who breastfeed exclusively for at least the first four months appear to have fewer allergies.”

A baby’s chances of having allergic reactions to food appear to be affected by both genetics and circumstance. Indeed, the microbes that an infant encounters during a vaginal delivery may be important for initiating the proper development of the immune systems. Citing a 2003 study by Eggesbo et al, Brandtzaeg suggests that children whose mothers suffer from various allergic reactions are “at least eight times as likely to develop food allergy when delivered by caesarean section,” although caesarean delivery of maternal allergy alone do not significantly increase risk.

Human milk also appears to help the infant’s gut to tolerate food antigens as he begins to consume other-than-human milk. To the immature immune system, food particles are just as foreign as are bacteria and other microbes. Importantly, human milk contains antibodies to food antigens which may help with gut tolerance. Brandtzaeg suggests that a gradual, rather than sudden, weaning “may promote greater tolerance to food proteins in general.”

Interestingly enough, where a child lives can help determine how quickly the maturation happens. In developed countries, it may take one to ten years. In developing countries where morbidity and mortality rates are typically much higher, this maturation often happens much earlier. The difference? Quite possibly a greater exposure to germs that help stimulate the system. Obviously, there must be a balance between good hygiene and the need for immune system maturation.

Brandtzaeg also discusses whether the use of probiotic preparations, “which deliver to the gut new colonists—either commensal bacteria or intestinal parasites from other species,” might be useful in counteracting the “too-hygienic lifestyle in industrialized countries” that may be slowing the maturation rates of the mucosal immune system:

In a double-blind study of infants with a family history of atopy, babies who received a daily dose of a probiotic (Lactobacillus GG strain) for the first six months of life had 50 percent less atopic dermatitis at age two than did babies who received a placebo. Allergy prevalence still differed between study groups four years later.

He encourages further research in this area.

Much of the article details the very specific responses to foreign antigens by the immune system. Brandtzaeg ends the article by pointing out that:

. . . the current epidemic of allergy in industrialized countries is a small price to pay for the remarkable reduction of infant mortality provided by the elimination of pathogens through improved hygiene. Having too few microbes in our immediate environment seems to be problematic, but having many pathogens is far, far worse. Nevertheless, the pace of research raises hope that future therapies will compensate for the missing good microbes needed to develop homeostasis of mucosal immunity.

Reference:

Eggesbo, M., G. Botten, H. Stigum, P. Nafstad and P. Magnus. 2003. Is delivery by cesarean section a risk factor for food allergy? Journal of Allergy and Clinical Immunobiology 112:420-426.

Keywords:

Allergy
Immune System
Breastfeeding

The full text of this article is available for free at:
http://www.americanscientist.org/template/AssetDetail/a ssetid/54436

For more information on allergies, see the collection of FAQs, New Beginnings, and Leaven articles at
http://www.llli.org/NB/NBallergies.html

abstract by Melissa Clark Vickers, Huntingdon, TN USA

Past Journal Abstracts of the Month