Neutrophil production: Using soluble Fc receptor III (sFcR III) as a surrogate marker for estimation of total neutrophil mass, it has been shown that newborn infants born before 32 weeks of gestation have 20% of the adult neutrophil mass. Normal levels of neutrophil mass are attained at 4 weeks of age in premature neonates. However, full-term neonates have neutrophil stores within the normal adult range.
Neutrophil Function in the Newborn
• Chemotaxis: Decreased in newborn infants. Normal chemotactic ability is attained at 2 weeks of age in term and preterm neonates.
• Vascular rolling of neutrophils: Also decreased due to decreased expression of L-selectin on the neutrophil cell membrane.
• Vascular endothelial adhesion: Also decreased due to decreased expression of P2-integrin Mac-1 on the neutrophil cell membrane in neonates.
• Dynamics of change of shape: Newborn neutrophils are rigid because of impaired ability to form polymers of actin (P-actin) and reduced formation of micro-tubules.
• Phagocytosis: Neutrophils of term neonates have a normal ability for phagocytosis of gram-positive and gram-negative bacteria. However, their ability for phagocytosis of candida is abnormal up to 2 weeks of age. Preterm neonates have abnormal bacterial phagocytosis. However, when treated with therapeutic doses of intravenous gamma globulin G (IV IG) the neutrophils are able to ingest bacteria normally.
• Respiratory burst: Respiratory burst in term neonates is normal under normal conditions. In contrast, it is less active under the conditions of stress and sepsis. For this reason, neonates are more susceptible to overwhelming infections with group B streptococci, Staphylococcus epidermis, S. aureus, and E. coli. Respiratory burst performance of neutrophils in preterm neonates remains abnormal for more than 2 months of age. In term neonates, the generation of superoxide and hydrogen peroxide is increased, but because the levels of lactoferrin and myeloperoxidase are low, there is truncation of the later respiratory burst activity, resulting in abnormal bacterial killing.
G-CSF or GM-CSF may be helpful in term and preterm neonates during sepsis. The prophylactic use of G-CSF is more effective in preterm infants. The use of IVIgG to improve opsonization and phagocytosis has been disappointing.
Neonatal preeclampsia-associated neutropenia occurs in low-birth-weight neonates with a maternal history of pregnancy-induced hypertension. Treatment includes the prophylactic use of G-CSF.
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