Newborn Baby's Susceptibility to Infection Explained by Gut Bacteria

Does it ever feel like your child is constantly sick? There may be a reason behind a newborn infant's susceptibility to infection. It turns out that cells that allow helpful bacteria to safely colonize intestines of newborns also suppress their immune systems to make them more vulnerable to infections because their immune system cells are immature or underdeveloped.

"The first few days after birth represent a critical developmental period when a baby's immune system must adapt to many new stimulants," said Sing Sing Way, one of the researchers, in a news release. "This includes environmental microbes that are not present in the womb, but immediately colonize tissues such as the intestine and skin. Our findings fundamentally change how we look at neonatal susceptibility to infection by suggesting it is caused by active immune suppression during this developmental period, as opposed to the immaturity of immune cells."

Named CD71+, these suppressive cells are precursors of mature red blood cells. In order to learn a bit more about these cells, the scientists conducted a series of tests in human blood cells and mouse models. They found that a temporary immune suppression in newborns extends beyond the intestines to also affect other parts of the body.

The researchers also found that CD71+ cells are enriched in newborn mice and in human umbilical cord blood to prevent an over reactive immune response as newborns adapt to their new microbe-filled world.  CD71+ cells express an enzyme that is essential to suppress cells. This process plays a vital role in infants' developing intestines by preventing an onslaught of inflammation in response to colonizing bacteria.

The findings reveal the benefits of CD71+ immune suppression to allow a healthy bacterial colonization of intestines. This, in turn, outweighs the threat of systemic infant infections. That said, follow up studies are necessary to develop new strategies for protecting newborns against systemic infections.

The findings are published in the journal Nature.