How Do Infant Immune Systems Learn to Tolerate Gut Bacteria? | The Scientist
Scientists are beginning to unravel the ways in which we develop a healthy relationship with the bugs in our bodies.
Our relationship with microbes begins early in life. As an infant passes from the womb to the world through her mother’s birth canal, she is exposed to a multitude of bacteria and fungi. Although a handful of studies now suggest that the womb may not be sterile as many once believed, microbes are much more abundant in the outside world.
How our bodies learn to peacefully coexist with cells that are not our own is still unclear. Afterall, we spend most of our lives fighting off microbial invaders. “Once you’re born, you’re assaulted by billions of bacteria, so if the babies’ [immune systems] responded in the appropriate adult manner, they would just be auto-inflammatory bundles,” says Grace Aldrovandi, a professor of pediatrics at the University of California, Los Angeles. “The [question] then is: How does the immune system learn when to relax and when to respond?”
Over the last few years, researchers have started to uncover how the immune system dampens its response to friendly microbes. For example, one 2013 study, published in Nature, revealed that a specific population of red blood cells possessing the CD71 protein—which is only plentiful during the first week or so of life—helped suppress the immune response in baby mice. In humans, these CD71+ cells, which the team found were abundant in the blood of umbilical cords (but scarce in adult blood), also appeared to have immunosuppressive properties.
“When I went to medical school, I learned that babies had immature, wimpy immune systems,” Aldrovandi says. “We now realize that in fact they have very sophisticated immune systems, they’re just programmed in a different way.”
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