Neutrophil Function in Preterm and Term Infants

Abstract

After completing this article, readers should be able to: 1. List the primary cell functions of circulating neutrophils in response to microbial invasion and inflammation. 2. Describe the interaction between neutrophils and endothelial cells and how these interactions differ between neonatal and adult cells. 3. Describe differences in adhesion of phagocytes between neonatal and adult neutrophils. 4. Describe the phagocytosis-associated respiratory burst and deficiencies seen in neonatal neutrophils. Polymorphonuclear neutrophils (PMN) constitute the primary line of defense in the cellular immune system. Inborn defects in the generation of neutrophils or in neutrophil function are predisposing risk factors for life-threatening infections in infants and children. In general, newborns have an increased risk for systemic infections, and very immature preterm infants are especially prone to developing nosocomial bloodstream infections that clearly have been associated with increased morbidity and mortality. In this review, we attempt to identify possible quantitative and qualitative deficiencies observed in neonatal neutrophils and try to define, whenever possible, the underlying mechanisms of neutrophil dysfunctions in term and preterm infants. (1) ### Bone Marrow Storage Pool and Circulating Pool Neutrophils and cells of the mononuclear-phagocyte system originate in the bone marrow as a common committed progenitor cell for the granulocyte and the monocyte-macrophage pathways: the colony-forming unit-granulocyte monocyte (CFU-GM). Glycoprotein hormones termed colony-stimulating factors (G-CSF/GM-CSF) induce proliferation, maturation, and differentiation into neutrophils and monocytes. (1) The sequential development of neutrophilic granulocytes proceeds from pluripotent progenitor cell to committed stem cell to myeloblast to promyelocyte to myelocyte to metamyelocyte to band to segmented neutrophil. This sequence occurs within the bone marrow and possibly is regulated by the interaction of the hematopoietic inductive environment, CSF, and specific inhibitors of granulopoiesis. (2) Myeloblasts, promyelocytes, myelocytes, and other cells of the CFU-GM possess the possibility of cell division and form, by definition, the proliferative pool. Rodent studies have shown clearly that the total …