Breast- and bottle-fed monkeys develop distinct immune systems and communities of gut microbes.

Populations of gut flora vary among adult primates, but little is known about what drives these differences. Dennis Hartigan-O'Connor of the University of California, Davis, and his colleagues found that breast-fed rhesus macaques (Macaca mulatta) reared by their mothers had different gut flora from bottle-fed macaques raised in a nursery.

Breast-fed infants also developed a larger population of immune-system cells called TH17 cells, which are important mediators of anti-pathogen responses. These differences persisted for six months after the infants began receiving identical diets.

Some metabolites, including arachidonic acid, in the macaques' stool correlated with these differences, suggesting that these compounds could be mediating the effects on gut flora and the immune system.

Sci. Transl. Med. 6, 252ra120 (2014)