Infectious diseases are the leading cause of childhood mortality in the world.
According to an article published by Johns Hopkins Public Health School, they cause about two-thirds of pediatric deaths. This is in part because newborns are introduced to a host of microbes — bacteria, protists and viruses — that the still developing immune system is not equipped to defend against.
In the past, it was proposed that most changes to the immune system occurred after birth in response to a baby’s environment; however, Gomez de Aguero et al. now suggest that maternal microbiota — the community of microorganisms that reside in the body during pregnancy — affects postnatal immune system of a woman’s offspring. Many of us inherit a number of things from our mothers, from our hair color to height. Gomez de Aguero and his colleagues are the first to consider the possibility that a mother’s microbiota could affect her children.
The recent study performed by Gomez de Aguero and colleagues looked specifically at the maternal gut microbiota — microbes living in the intestine — and how it affects the immune system of her offspring. Gut microbiota was evaluated because it plays an integral part in the body’s immune system throughout life. A person’s gut microbiota interacts with his or her immune system by sending signals that promote immune cell maturation, thus impacting the cellular composition of the entire system.
Because the human genome is quite similar to that of other mammals, the authors conducted their study in mice, which are a well-understood genetic model of diseases. The team injected pregnant mice with genetically engineered E.coli designed to diminish with time, such that the mice could be germ-free by the time of birth and give birth to germ-free offspring. These infected mice were compared to a control group of mice that were kept germ-free throughout the study.
The researchers observed that colonization of mothers’ intestinal tracts by the bacteria during gestation affected the immune composition of her offspring’s intestine. The variation between the control and the colonized mice was marked by an increase in the number of cells that prepare the immune system for defense against infectious diseases. The increase in these cell types was observed already at 14 days after birth and continued to increase for another week after that.
To confirm that the increase in these immune cells could not be attributed to the immune system’s natural adaptation to its environment, the authors conducted an additional study to identify whether the “molecular signature” for mature immune cells was present in young offspring. This work confirmed the presence of immune cells only in the offspring from pre-infected mothers, providing evidence that maternal microbiota can shape postnatal immunity independent of other environmental factors.
Importantly, this study also suggests that a child’s immunity to specific microbes is reinforced during breastfeeding by his or her mother. To arrive at this conclusion, the authors performed an additional experiment in which they exchanged the nursing offspring of females that had been infected with E.coli during pregnancy with those of the control mothers that were germ-free. Analysis of the immune system composition in each set of offspring demonstrated a lack of any difference between the two sets of young animals.
For there to be a significant increase in the immune cells, the offspring from infected females had to be nursed by their mother, who continued to produce antibodies to the E.coli even after her initial infection during pregnancy had cleared. This finding is consistent with other research, which indicates that maternal antibodies to indwelling pathogens are transferred through the placenta and from the maternal milk.
We share our environment with a host of other organisms, many of which are virtually invisible to us. The biological “tug-of-war” that our immune system plays with these organisms helps establish resistance to infection on a daily basis, apparently even before we are born. From the womb to breastfeeding, a mother is influencing the immune system of her child. The unique combination of her own gut microbiota and breast milk antibodies contributes to the immune health of her offspring, priming them for exposure to the immunologically “dangerous” world into which they emerge at birth. You can add this to the list of things to thank your mom for!
Sources
Eric W. Rogier, Aubrey L. Frantz, Maria E. C. Bruno, Leia Wedlund, Donald A. Cohen, Arnold J. Stromberg, and Charlotte S. Kaetzela. “Secretory antibodies in breast milk promote long-term intestinal homeostasis by regulating the gut microbiota and host gene expression.” Proceedings of the National Academy of Sciences of the United States of America (PNAS) (2014): 3074-3079. Web.
“John Hopkins.” 11 May 2010. John Hopkins Bloomberg School of Public Health. Web. April 2016. <http://www.jhsph.edu/news/news-releases/2010/black-mortality-causes.html>.
