Early life immunology

Pregnancy and birth present unique challenges to the immune systems of both the mother and the child. For example, how does the maternal immune system tolerate the paternal antigens of the fetus and how does the neonatal immune system adapt to exposure to the marked increase in environmental antigens in early life? New research contests long-held beliefs that the maternal immune system is suppressed and the neonatal immune system is immature. It is now appreciated that unique pathways of immune regulation in early life ensure the appropriate level of responsiveness. Moreover, it is now clear that experiences in early life — in the womb and in infancy — have lasting effects on the developing immune system, determining how it responds to harmful as well as harmless agents.

In this Focus issue, five Review articles discuss how factors such as maternal nutrition, microbial colonization, infection and pregnancy-associated microchimerism shape the developing immune system, modulating its response to infection or vaccination, the risk of allergic and immune-mediated diseases, and the likelihood of successful reproduction.

The Focus also features a Comment article, in which Martin Blaser proposes that the extinction of certain commensal microorganisms, owing to modern changes in early life events, explains the increase in numerous immune-mediated diseases, from allergy to autism, in industrialized countries.