Human neonatal monocyte-derived macrophages and neutrophils exhibit normal nonopsonic and opsonic receptor-mediated phagocytosis and superoxide anion production.

Human neonates are at risk for invasive infections with fungi and gram-negative bacteria, microorganisms which are often susceptible to phagocytosis in either the presence or the absence of opsonins. Although opsonic phagocytosis has been investigated, to date there have been no systematic studies of nonopsonic phagocytosis in neonates. We investigated receptor-mediated phagocytosis by neonatal neutrophils and monocyte-derived macrophages in order to determine if a functional defect exists in any of the classes of nonopsonic or opsonic receptors. Ingestion or binding by mannosyl/fucosyl, Fc and complement receptors and the receptor(s) for unopsonized Pseudomonas aeruginosa were normal in neutrophils and macrophages from the cord blood of 26 healthy full-term neonates as compared to simultaneous normal adult controls. Superoxide anion production by neonatal neutrophils in response to both soluble and particulate stimuli was also normal. We conclude that neonatal nonopsonic and opsonic receptor-mediated phagocytosis are normal.