An Explanation of The Enteromammary Secretory Host Immune System: How A Mother’s Immune System is Shared Through Breast Milk

As people who work in the lactation field, we are sometimes presented with a situation that requires us to review the collective knowledge available on how the immune system works. A question about the protection breast milk offers may lead to a complicated query into how a mother’s body is able to share the antibodies it makes. A mother might ask, “Is it okay to nurse while I’m feeling ill?” A mother might wonder whether or not her baby will get sick through her milk due to the interconnectedness of the mother-child relationship. Depending on how thorough your answer is, the amount of information can get overwhelming very quickly.

At its best, the explanation of the shared immune system can be simple and direct. Current studies supply evidence that the active components of breastmilk support normal development of the human infant and offer continuous immune system support for many years. Greater detail about the immune system has been discovered and provides deeper understanding of the protection is offered through mothers’ milk. Combined with continued study of the human immune system, a great deal of focus has been placed on studying the Enteromammary Pathway. We now understand precisely how milk is manufactured in the body and how the immune system is shared between mother and child.

Why Is the Maternal Immune System Shared?
Why is the shared immune system necessary in the first place? Goldman (2007) discusses the topic of delayed maturity of the newborn infant’s immune system: “further analysis suggested that such developmental delays allowed considerable energy and nutrients to be diverted to the growth and development of other systems such as the central nervous system, skeleton, and skeletal muscles as long as the mother was providing the necessary defense agents through her milk.” Augmenting the newborn’s immune system allows the infant to prioritize growth and divert energy to areas that are critical to survival. Rapid skeletal and neurological growth cannot happen safely while the baby is in the womb and must continue postnatally. The mother supports her newborn baby during these phases of accelerated growth by sharing her immune system through her breast milk. In the Journal of Nutrition, an example of how important breast milk is in relation to the baby’s immune system is offered: “The unfavorable effects of neonatal immunodeficiency are limited by some naturally occurring compensatory mechanisms, such as the introduction of protective and immunological components of human milk.” (Chirico, Marzolo, Cortinovis & Fonte 2008).

How is the Immune System Shared?

When speaking with a mother about how the Enteromammary Secretory Host Immune System works, you could consider beginning the conversation with a description of how the maternal immune system protects the mother from “germs” in her own environment. By starting your discussion with an explanation of the mother’s own immune system, you are opening with an simple overview of the system that donates immune factors and modulators to human milk.

A pathogen is “a specific causative agent (as a bacterium or virus) of a disease.” (Merriam-Webster 2003). Pathogens are responsible for illness and disease, and they are present everywhere. When pathogens are able to find a vulnerable breech through the barrier of a mother’s skin or another route into the her body, they make their way into the general circulation. Her immune response begins an elaborate dance of protection that starts producing and releasing specific antibodies.  These different antibodies exit the lymph nodules, transit through the lymph into the thoracic duct, and then enter into the blood itself. The antibodies travel to distant sites all over the body by coursing through the blood and protecting the body from further infection. Some of the mother’s blood travels into the breast, and the antibodies within are attracted to the exchange layers in the breast tissue (basolateral membranes of the mammary epithelium). The system is still more complicated; some specific cells originating from the Peyer’s Patches in the digestive tract turn into plasma-making cells which stay in the breast and produce their own specific type of antibody to donate to the breast milk.

What If There is Exposure to Grave Illness?

If a mother is exposed in an ongoing situation to a particularly virulent pathogen/disease, her baby will also have a measure of exposure. Disease travels in predictable ways: we contract them from the environment, through inanimate vectors or other infected people. Then, we may share them ourselves through our saliva, mucous, coughing, feces, or vomit. Less common venues for communication of disease are through blood or breast milk: in some special situations, pathogens can be shed through breast milk. By the time a mother with a normal immune system is infectious with a virus such as Cytomegalovirus (CMV), she has already donated copious amounts of antibodies (as the titers of antibodies within her blood increase drastically). Uninterrupted breastfeeding is recommended during most illnesses, and only in isolated and uncommon cases should a mother avoid nursing while she is sick. At this time, these instances might include infection with Human Immunodeficiency Virus (HIV), active Tuberculosis, or Human T-cell Leukemia Virus type 1 (HTLV-1). In some areas of the world, a mother is encouraged to breastfeed even after having a positive test for HIV, due to geographically-intensified childhood mortality risks. Some research has suggested that instead of total weaning during infection with N. gonorrheae, H. influenzae, group B streptococci and staphylococci, a brief break from nursing would suffice (Chirico, et al., 2008). Chirico’s particular study was supported indirectly by Danone Research, which is in the business of making artificial baby milk. It would make sense to observe these sorts of scholarly suggestions with a critical eye due to the potential conflict of interest and ask whether even temporary weaning is the best answer for mothers and their babies. A degree in science does not necessarily equate to a deep understanding of the psychophysiological breastfeeding relationship. In rare cases, weaning for the suggested time seems reasonable, but what we see in practice is that interruption of nursing rarely turns out well. Other references cite that human milk components are, in vitro, able to degrade many pathogens including but not limited to N. gonorrheae, H. influenzae, V. cholera, H. pylori, S. flexneri, and B. pertussis. The question we ask ourselves should be, “What is the best choice for mother and infant?” As Lactation Consultants, we must also remain aware that the infant’s exposure to the mother’s shared environment will likely mean exposure to illness as well. Through continued study, breastmilk has been shown repeatedly to have a wide array of effectiveness against disease-causing agents and lead to an overall positive immunological effect on the health and well being of the infant and mother.

What Area In the Body Does the Information About Infection Come From?

A large amount of the information that our bodies collects about pathogens (organisms that cause illness) comes from the following areas:
· Gut-associated Lymphatic Tissue (GALT)
· Bronchio-associated Lymph Tissue (BALT)
· Mucosa-associated Lymphatic Tissue (MALT)

MALT includes the more diffuse mucosal lymphoid tissue known as the gut, lungs, mammary glands, salivary and lacrimal glands, and the genital tract. “The parts of the body that harbor the largest and most diverse populations of microorganisms are the respiratory and gastrointestinal tracts. The most heavily infected site is the oral cavity. The extensive mucosal surfaces of these tissues make them particularly vulnerable to infection and they are therefore heavily invested with secondary lymphoid tissue.” (Parham 2005).  Mucosal tissue traps pathogens with the help of M cells, and the presence of these pathogens then activates a specialized cell called a lymphocyte which transfers the pathogen into the lymph node where it is broken down into harmless particles.

Why Are GALT, BALT and MALT So Important?

Lymph areas are important because they are intimately connected to the common pathogens that can impair a newborn’s ability to survive, particularly in regions of the world where adequate drinking water is not readily available, and health care is in short supply. Diseases like Rotavirus can cause critical cases of diarrhea and death in infants, and Respiratory Syncytial Virus (RSV) can cause major bronchial congestion and in many cases results in bacterial bronchiolitis and pneumonia. In the United States, cases of RSV are treated with hospital care, and they effect a population mostly under six months of age. It is easy to see that the primary areas of maternal antibody-sharing work to protect the baby from the most hazardous of diseases.

The Communication of Information Between the Mother and Child

Normal human bodies have the ability to protect and defend against intruders by manufacturing immunoglobulins, particulary secretory IgA. A study by Kleinman and Walker discussed the conclusion that IgA was the main immunoglobulin in “external secretions.” (Breast milk is a secretion.) The study went on to say, “[T]here is a continuous traffic of plasma cells between the gut-associated lymphatic tissue into the systemic circulation.” (Kleinman & Walker 1979, abstract). This observation shows that there is communication between lymphatic areas; because we also know that the mammary gland is part of the system, we have reproducible evidence that a mother’s milk receives new antibodies as they appear. The presence of the active lymph system in the breast implies that any pathogen that might enter the mammary gland from the baby’s mouth or body would be ensnared in the secondary lymphoid tissues in the breast (axillary lymph nodules). Following that circular pathway, the antibodies to the pathogen would be secreted back into the milk as part of the Enteromammary Secretory Host Immune System, as was researched by Cantani (2008). In terms of physiology, a mother’s breast milk is both suited to all her baby’s nutritional needs and also specifically made to protect the infant from the pathogens in the mother’s environment.  This phenomenon is best described by Cantani: “The Enteromammary Axis is the system that shares the information it has about past and current infections, and passes it through the lymph nodes, then the thoracic duct and into the blood where it transfers ultimately into human milk.” (Cantani 2008).

Bibliography

Avery, Gordon B., Mhairi G. MacDonald, Mary M. K. Seshia, Martha D. Mullett (2005) Avery’s Neonatology: Pathophysiology & Management of the Newborn. Philadelphia, Penn.: Lippincott Williams & Wilkins.

Bagge, Linda, Line W. Hollesen, and Anders Dalsgaard (2003) Occurrence and Survival of Viruses in Composted Human Feaces, Sustainable Urban Renewal and Wastewater Treatment, no. 32.

Block, Seymour (2001) Disenfection, Sterilization, and Preservation, fifth edition. Philadelphia, Penn.: Lippincott Williams & Wilkins.

Cantini, Arnaldo (2008) Pediatric Allergy, Asthma, and Immunology. Heidelburg, N.Y.: Springer.

Chirico, G., R. Marzolo, S. Cortinovis, and C. Fonte (2008, September) Supplement: Influence of Diet on Infection and Allergy in Infants, Antiinfective Properties of Human Milk. Journal of Nutrition 138:9, pp. 1801S–1806S.

Encyclopedia Britannica Company (2003) Merriam-Webster’s Collegiate Dictionary, eleventh edition. Springfield, Mass.

Goldman, Armond S., M.D. (2007) The Immune System in Human Milk and the Developing Infant, Breastfeeding Medicine 2:4.

Hanson, L. A. (2007) Feeding and Infant Development Breastfeeding and Immune Function. Proceedings of the Nutrition Society 66:3, pp. 384–96.

Kleinman, Ronald E., and W. Allan Walker (1979, November)  The Enteromammary Immune System: An Important New Concept in Breast Milk Host Defense,  Digestive Diseases and Sciences 24:11.

May, John T., comp. (2011, August) Molecular Virology: Tables of Antimicrobial Factors and Microbial Contaminants in Human Milk Table 1: Antibacterial Factors Found in Human Milk.  La Trobe University: Molecular Biology Dept. La Trobe U.

Mohrbacher, Nancy, and Julie Stock. (2003) Breastfeeding Answer Book, third edition. Schaumburg, Illinois: La Leche League International.

Newburg, David S. “Neonatal Protection by an Innate Immune System of Human Milk Consisting of Oligosaccharides and Glycans.” Journal of Animal Science (November 21, 2008), Division of Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital for Children and Harvard Medical School, Boston.

Parham, Peter. (2005) The Immune System. New York: Garland Science Publishing.

Wilson, Eric, Ph.D. (2008, October) Brigham Young University. “How Breastfeeding Transfers Immunity to Babies.” Science Daily.

( c ) Serena Meyer, IBCLC 2012–2013 All Rights Reserved.

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