Innate immune cell recruitment in the fetus and neonate

Recruitment of innate immune cells from the vasculature into infected tissue is a key event in primary host defense against invading pathogens. This highly regulated process requires a functional interplay of specialized adhesion molecules and involves a series of steps leading from rolling of leukocytes along the endothelium to firm adhesion and finally transmigration. In the developing fetus, innate immune functions are ontogenetically regulated and show increasing maturation throughout gestation. Developmental differences in the innate immune response leave the neonate and especially the premature newborn at high risk of severe infections. Understanding the ontogeny of immune functions in the fetus and newborn is therefore essential for the prevention and treatment of neonatal infections. In this review, an overview will be given of the developmental aspects of innate immune cell recruitment including a discussion of controversial findings and open questions.