Leukocyte recruitment in preterm and term infants

Impaired cellular innate immune defense accounts for susceptibility to sepsis and its high morbidity and mortality in preterm infants. Leukocyte recruitment is an integral part of the cellular immune response and follows a well-defined cascade of events from rolling of leukocytes along the endothelium to firm adhesion and finally transmigration which is concerted by a variety of adhesion molecules. Recent analytical advances such as fetal intravital microscopy have granted new insights into ontogenetic regulation and maturation of fetal immune cell recruitment. Understanding the fetal innate immune system is essential for targeted prevention and therapy of premature infants with severe infections or disorders of the immune system. This review gives an overview of the basic principles of leukocyte recruitment, particularly neutrophil trafficking, and its development during early life and highlights technical limitations to our current knowledge.