One of the most fascinating mysteries of our time is the low rate of mother-to-infant transmission of HIV via the milk of an infected mother. In the absence of antiretroviral drug therapy (ART), 10-15% of babies born to infected mothers acquire the virus from breastmilk; when both mother and infant are treated with ART, this incidence can be reduced to 2% or less.
Several components of human milk have been shown to offer protection to those more than 85% of babies who don’t get HIV after repeated exposures. Immunoglobulins, like IgA, IgG, and IgM provide specific immune response to certain pathogens; lactoferrin accomplishes various tasks, to include killing bacteria and preventing surviving bacteria from multiplying. In a study released earlier this year, researchers at Duke University in North Carolina reported that HIV-specific B-cells found in the colostrum of infected mothers actually neutralize the virus. An international team of researchers based in California, New York, Boston, and Zambia, in a study released on August 15 by the American Journal of Clinical Nutrition (Bode, et al., 2012) identifies yet another protective component: human milk oligosaccharides.
Oligosaccharides are plentiful in breastmilk, and there are over 130 of them (Smith, 2008). They are made from chains of simple sugars, and they do a few things that make them superheroes in the fight against pathogens – any invading virus or bacteria. Oligosaccharides are PREbiotics, which act like food for good bacteria in the baby’s gut. Prebiotics feed and promote the proliferation of PRObiotics, which crowd out pathogens. Another important, protective function of oligosaccharides is that they prevent pathogens from attaching to the gut lining. They do this either by attaching to the part of the bacteria or virus that would attach to the baby’s gut, or by themselves attaching to the gut epithelium and, in essence, occupying all of the “docks” where pathogens might seek to put down a mooring. Oligosaccharides are most plentiful in the earliest days, weeks, and months of breastfeeding, decreasing in number and volume as the baby gets older. Oligosaccharides are undigestible, which allows them to populate the baby’s intestine; the large volume of oligosaccharides is part of what causes a newborn to stool often, perhaps every time he breastfeeds.
This mechanism is also protective against HIV and other viruses, because the frequency of the bowel being emptied doesn’t give pathogens time to “set up shop” and get down to the business of infecting the baby. This is one possible explanation for why the protective effect of breastfeeding against HIV may wane as the baby gets older. Of the 12.1% of infants who acquired HIV through their mother’s breastmilk, 68.2% of those transmissions occurred after 6 months (Iliff et al., 2005). The addition of complementary foods may also cause or allow for breaches in the infant’s gut integrity; it is through these breaches that HIV can be acquired. The findings reported by Bode, et al. are exciting. We already knew that oligosaccharides play a significant role in keeping babies healthy and free from infection, but recognizing that, in high enough concentrations, they actually protect infants from a pathogen that is present in the milk is remarkable. In nations where the risk of infant death from gastrointestinal or respiratory infections is higher than the risk of transmission of HIV from an infected mother to her baby, understanding why and how a mother’s own milk gives her infant his best chance for survival can provide important teaching points for public health workers, especially when cautioning against mixed feeding of these vulnerable infants. Additionally, these innate protective factors in human milk offer insight into how a vaccine against HIV might be developed for use in adults at risk of acquiring the virus.
References:
Smith, L. (2008). Biochemistry of human milk. In R. Mannel, P. J. Martens, & M. Walker (Eds.), Core Curriculum for Lactation Consultant Practice (pp. 269-284). Sudbury, MA: Jones & Bartlett.
Diana Cassar-Uhl, IBCLC and La Leche League Leader, enjoys writing to share breastfeeding information with mothers and those who support them. In addition to her frequent contributions to La Leche League International’s publication Breastfeeding Today, Diana blogs about normalizing breastfeeding in American culture at http://DianaIBCLC.com and has been a guest blogger at Best for Babes and The Leaky Boob. Diana can be found lecturing at breastfeeding education events around the United States. She is pursuing a Master of Public Health, and upon graduation hopes to work in public service as an advisor to policymakers in maternal/child health and nutrition. Mother to three breastfed children, Diana recently retired after serving as a clarinetist on active military (Army) duty in the West Point Band since 1995.