Immunity: babies handle new friendly bacteria (Introduction)

by David Turell , Saturday, January 13, 2018, 20:35 (2288 days ago) @ David Turell

Babies enter the world from a uterus that is not entirely clean, but the vagina has lots of bugs to encounter and bacteria have to colonize the baby's colon at the start. How it is handles is better understood:

https://www.the-scientist.com/?articles.view/articleNo/51317/title/How-Do-Infant-Immune...

"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.”

"Recent rodent studies have revealed that, in the adult mouse colon, bacterial metabolites such as butyrate, a product of fermentation, can accelerate the differentiation of progenitor cells into regulatory T cells, which help keep the immune system in check.

"While these studies indicate that products of some bacterial species may help induce tolerance in the adult immune system, Rodney Newberry, a professor of gastroenterology at Washington University School of Medicine, says that “the role for these tolerance-inducing species is not straightforward,” since your ability to become tolerant is better early in life when, paradoxically, these species are less abundant than in later childhood and adulthood.

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"Newberry and his colleagues recently examined the early interactions between the immune system and certain harmless gut bacteria, such as Lachnospiraceae, in newborn mice. Their results, which they reported last month (December 17) in Science Immunology, revealed a time window during early life when the animals developed antigen-specific regulatory T cells specific to those microbes.

"This critical phase, which occurred between 10 and 20 days of life, was initiated by a drop in levels of epidermal growth factor (EGF), a protein abundant in breast milk during the pre-weaning period, in the GI tract of mice. During the first week or so, high concentrations of gut EGF in the mouse pups blocked the formation of goblet cell-associated antigen passages (GAPs)—channels that allow antigens from the gut lumen to enter the lamina propria, where the immune cells lie—preventing the development of regulatory T cells.

"Essentially, what appears to be happening is that the reduction of EGF during this time period allows bacterial antigens to pass through pups’ guts, enabling the immune system to learn to not to initiate an inflammatory response.

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"The most surprising result in this paper, according to Gérard Eberl, an immunologist at the Instutit Pasteur in Paris who did not take part in this work, was that EGF levels determined when the animal needed to be exposed to microbes. Although levels of this protein in mothers’ milk were not directly examined in this study, Newberry says that his team is currently performing additional experiments to confirm that this process is under maternal control. If deemed true, this finding could be relevant to people as well, given that researchers have found that human breast milk is rich in EGF and tapers over time.

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"The idea that there may be a window of optimal bacterial colonization supports the work of those who promote “vaginal seeding,” a procedure in which a newborn born via C-section is swabbed with a sterile gauze that was incubated in the mother’s vagina shortly before birth, to restore microbial communities to levels found in vaginally born babies. Last year, a group of researchers published a small pilot trial—with four mothers who volunteered to undergo the procedure—that reported promising results.

"Studies have found that exposure to the microbes in a mother’s vagina at birth might contribute to their infants’ health later in life."

Comment: Since these immune systems to protect the newborn are also active in the mother it raises the issue of how a chance Darwin style evolution can develop such systems in two separate individuals. It is a mechanism that must be developed intact in both to go with live birth, or babies would not have developed enough immunity to survive. It had to develop in the earliest placental animals. God at work!?