Setting the table for immune tolerance.

From birth, newborn babies become colonized with trillions of microbes, creating the daunting challenge of rapidly and accurately discerning which ones are beneficial or harmful for human health. Neonates must develop tolerance to beneficial or commensal microbiota while mounting effective immune responses against pathogens. Maternal antibodies transferred in utero and through breast milk have roles in protecting newborns from pathogenic microbes, yet whether they shape other immunological responses has been unclear. On page 703 of this issue, Shenoy et al. (1) report that during the first week of life, immunoglobulin G (IgG) antibodies in maternal milk of mice interact with nonpathogenic members of the mouse microbiota to regulate immune responses in pups to microbial and dietary antigens in the gut encountered later during the weaning transition to solid food. Providing microbiota-reactive maternal antibodies could potentially prevent human infants from developing colitis, as well as dangerous allergic responses to food antigens. [ABSTRACT FROM AUTHOR]