Pregnancy-associated microbiota modules newborn's group 3 innate lymphoid cells (ILC3)

It is common believe that newborns are born sterile and their immune system undergoes changes at post-natal period in response to their own microbial exposure.

However, new study in Science challenges this concept by showing that mother's microbiota during pregnancy has permanent impact on offspring's postnatal innate immune system. 

To distinguish effects of maternal vs. neonatal microbiota on neonate's immune system, the authors used a "system in which pregnant dams are transiently colonized with genetically engineered Escherichia coli HA107", a E. coli strain that does not persist in the host and "pregnant dams become germ-free again before term and naturally deliver germ-free pups". Compared to control, microbiota-nil pregnant females, offsprings derived from temporally colonized pregnant females contained more IL-22 producing intestinal ILC3 (there was no effect on T or B cell numbers).

Maternal microbiota effect on newborn's ILC3 numbers could be reproduced by injecting germ-free pregnant females with serum (IgG) derived from HA107 colonized females (though it is not clear whether microbiota-specific IgG or any random IgG could produce the same effect).

Similarly, maternal microbiota effect on newborn's ILC3 numbers was lost in pregnant females lacking B cells (Ig_H^-/-).

In summary, this study suggests that pregnancy-associated microbiota does have an independent effect on maturation of newborn's innate immune system, at least via maternally-derived antibodies.

David Usharauli