A prime time for trained immunity: innate immune memory in newborns and infants.

The newborn and infant periods of early life are associated with heightened vulnerability to infection. Limited antigen exposure and distinct adaptive immune function compared to the adult places a greater burden on innate immunity for host defense to microbial challenge during this time. Trained immunity describes the phenomenon of augmented innate immune function following a stimulus that is not specific to the original stimulus. We review the concept of trained immunity in the context of the newborn's unique innate immune system function, the preclinical and clinical evidence that supports the tenet of innate immune memory in early life, and potential consequences of altered innate immune host responses.