Mother’s gut microbiota strengthens newborn's immunity

Babies are born with immature immune systems. Up until now, scientists have assumed that newborns start after birth to adapt to the host of microorganisms that compose their own intestinal microbiome. In experiments with mice, scientists from Bern University Hospital, the University of Bern, the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) and ETH Zurich have now discovered that the mother's gut microbiota prepares the baby already in the womb for the process of microbial colonization that takes place after birth. The gut research group at the University Hospital of Bern (Inselspital) has been pursuing basic and clinical research in this field for many years and ranges among the world's most renowned research teams. Mathias Heikenwälder from the DKFZ and his group supported their Swiss colleagues by conducting an analysis of the immune system, particularly of the secondary lymphatic organs, during this phase in immune development.

Microbial invasion after birth

When a baby is born, it leaves the sterile, sheltered environment of the uterus and enters a world that teems with microbes. After birth, microorganisms quickly colonize all surfaces of the body. Within a few days, the intestine is inhabited by ten times more microbes than there are cells in the baby's whole body.

Newborns normally survive this sudden invasion of bacteria without problems. However, more than six million infants under the age of five still die worldwide each year, most of them as a result of intestinal infections or malnutrition. The critical challenge after birth is that trillions of microbes must colonize the intestine without infecting the newborn, provoking a strong immune response or impeding the gut's capacity to absorb nutrients.

Harmless molecules from the gut

In their current article, the researchers report that molecules of microbes living in the maternal intestine can enter the mother's body and then get transmitted to the baby via the placenta or, after birth, during breast feeding via antibodies that are contained in the mother's milk. These microbial fragments are harmless and do not cause any infection. Instead, they stimulate cells in the baby's body to prepare its immune system and gut for the time after birth when the newborn has to cope with the microorganisms living in its own intestine.

“For this work, we studied bacteria that do not cause disease,” says Heikenwälder. “But our results most likely also hold true for dangerous pathogens, against which the newborn can produce a better defense thanks to this preparation of the immune system.” Andrew Macpherson, Research Director at Bern University Hospital, added: “We have always known that we may be grateful to our mothers for their love and protection, now we know that we should also be grateful to them for their gut microbiota.”

Mercedes Gomez de Agüero, Stephanie C. Ganal-Vonarburg, Tobias Fuhrer, Sandra Rupp, Yasuhiro Uchimura, Hai Li, Anna Steinert, Mathias Heikenwälder, Siegfried Hapfelmeier, Uwe Sauer, Kathy D. McCoy, Andrew J. Macpherson: The maternal microbiota drives early postnatal innate immune development: Science 2016, DOI: 10.1126/science.aad2571