Cells that allow
helpful bacteria to safely colonize the intestines of newborn infants also
suppress their immune systems thus making them more vulnerable to infections,
according to new research led by a team of scientists at Cincinnati Children’s.
These findings, published online Nov. 6, 2013 in Nature, could prompt a major shift in
how medicine views the threat of neonatal infections – and how researchers go
about looking for new strategies to stop it.
During the first
few days after birth, a baby’s immune system must adapt to many new stimulants.
This includes environmental microbes that are not present in the womb, but
immediately colonize tissues such as the intestine and skin. Leading up to this
study, the prevailing view has been that newborn infants are susceptible to
infection because their immune system cells are immature or underdeveloped.
“Our findings suggest that neonatal
susceptibility to infection is caused by active immune suppression during this
developmental period, as opposed to the immaturity of immune cells,” says Sing Sing Way, MD, senior
investigator and a physician in the Division of Infectious Diseases at Cincinnati Children’s.
cells in this case are CD71+ precursors of mature red blood cells. The
researchers found CD71+ precursor cells are enriched in newborn mice (and in
human umbilical cord blood) to prevent an over-reactive immune response as
infants adapt to their new microbe-filled world. CD71+ cells express an enzyme
called arginase-2 that is essential to suppressing immune cells. This process
plays a vital role in developing intestines by preventing an onslaught of
inflammation in response to colonizing bacteria that help digestion and related
In general, the
benefits of healthy bacterial colonization of intestines outweigh the threat of
other infections, Way says. But it may be possible to modulate the process to
improve protection from infection while still allowing CD71+ cells to do their
job. However, much more follow-up research is needed before these findings
could be applied to human infants, Way says.