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Newborns’ weak immunity may allow helpful bacteria to gain a foothold

Though infant immune systems raise risk of infection, they also allow good microbes into the body

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1:02pm, November 6, 2013

GROWING GOOD BACTERIA  An immature form of red blood cell helps suppress the immune system of newborns, experiments with mice suggest. Immune suppression leaves infant mice and humans susceptible to infection but may allow good bacteria to settle in the gut.

The seeming failure of newborns to muster a robust defense against infections is a trade-off that delivers long-term benefits, a new study suggests. In infants, the body’s immune army stands down for a month or two and then gears up. While this gap leaves babies at risk of infection, it also may allow beneficial bacteria to populate an infant’s intestines, a development that carries lifelong advantages, researchers working with mice report November 6 in Nature.

The findings suggest that the lackluster response of the neonatal immune system “is a normal developmental feature,” says biochemist Sidney Morris Jr. of the University of Pittsburgh School of Medicine, who wasn’t involved in the study. The immune suppression shows up “during the transition from the sterile in utero setting to a decidedly nonsterile external environment,” he says.

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