How nutrition and the maternal microbiota shape the neonatal immune system

Key Points The maternal microbiota itself affects the development of the fetus and the neonate. Metabolic exposure of the fetus in utero depends on maternal nutrition and xenobiotic exposure, both of which are modulated by microbial metabolism. Molecules that originate from the intestinal microorganisms of a mother reach her offspring via the placenta during fetal development, and through maternal milk during the postnatal period. Maternal antibodies amplify microbial molecular transfer, both in utero and during lactation. Signalling from maternal microbial molecules shapes the development and function of the immune system in early life. This Review discusses the importance of the maternal microbiota in shaping the development of the fetus, with a focus on the developing immune system. The mucosal surfaces of mammals are densely colonized with microorganisms that are commonly referred to as the commensal microbiota. It is believed that the fetus in utero is sterile and that colonization with microorganisms starts only after birth. Nevertheless, the unborn fetus is exposed to a multitude of metabolites that originate from the commensal microbiota of the mother that reach systemic sites of the maternal body. The intestinal microbiota is strongly personalized and influenced by environmental factors, including nutrition. Members of the maternal microbiota can metabolize dietary components, pharmaceuticals and toxins, which can subsequently be passed to the developing fetus or the breast-feeding neonate. In this Review, we discuss the complex interplay between nutrition, the maternal microbiota and ingested chemicals, and summarize their effects on immunity in the offspring.