Infant rhesus monkeys receiving different diets early in life develop distinct immune systems that persist months after weaning, a study has shown. While the researchers expected different diets would promote different intestinal bacteria (microbiota), they were surprised at how dramatically these microbes shaped immunologic development. Specifically, breast-fed macaques had more “memory” T cells and T helper 17 (TH17) cells, which are known to fight Salmonella and other pathogens.