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.
Fetal dendritic cells suppress pro-inflammatory T cell activity.
Ashley Moffett describes a 1995 paper by Colonna and Samaridis that provided the stimulus to understanding the link between NK cells and pre-eclampsia.
Although healthy pregnancies were traditionally considered to require an anti-inflammatory state, emerging evidence suggests that inflammation is important for a healthy pregnancy. Here, the authors discuss how the immune response varies throughout the main stages of pregnancy, and they consider how bacterial and viral infections can affect immune responses at the maternal–fetal interface.
This Review discusses how genetically discordant microchimeric cells transferred between a mother and her offspring during pregnancy have important implications for definitions of immunological identity and tolerance.
Why are newborns more vulnerable to infection? Here, the authors explain that it is not the immaturity of the immune system per se, but the unique regulation of immune responses in early life that limits immunity to infection yet allows safe developmentin uteroand the accommodation of microbial colonization at birth.
This Review discusses the importance of the maternal microbiota in shaping the development of the fetus, with a focus on the developing immune system.
Accumulating evidence suggests that environmental experiences during childhood can result in the development of allergies that persist into adulthood. In this Review, the authors present the evidence for specific early life exposures that may tip the balance between tolerance and allergic sensitization.