Neonatal immunity.

TL;DR: Neonatal immunity relies on maternal antibodies to modify and control the severity of neonatal diseases.

Abstract: The immune system of neonates is relatively under-developed and relies on maternal antibodies transmitted in utero to modify and control the severity of neonatal diseases. These antibodies are of the class IgG, which can be transported across the placenta. This is an active, selective process that involves intracellular pathways and is specifically mediated by the neonatal Fc receptor FcRn. Fc receptors are expressed by the trophoblastic cell layer which surrounds the developing foetus. Once the receptor has bound IgG it is transported to the foetal circulation.