ABSTRACT: Using a Teflon culture system we analyzed different aspects of cell maturation and phagocytic activities in neonatal monocyte-derived macrophages. Morphological and cytochemical characteristics as well as the protein composition of neonatal macrophages were identical with those of adult controls; actin binding protein (265,000 Da), myosin (210,000), α-actinin (102,000) and actin (42,000) could be identified in cells from either source. All phagocytic functions were shown to be perfectly normal in neonatal macrophages when compared with adult cells: random migration, chemotactic response to zymosan-activated serum and formyl-methionyl-leucyl-phenylal-anin, ingestion, and killing of Staphylococcus aureus, phagocytosis-associated chemiluminescence, production of oxygen intermediates (superoxide anion, O-2; hydrogen-peroxide, H2O2). Phorbol myristate acetate-stimulated O-2 -generation by 1 X 105 macrophages was 11.8 ± 4.7 nmol/h for neonates, and 10.2 ± 3.9 for controls; production of H2O2 was 7.6 ± 3.5 nmol/h in neonatal macrophages and 6.4 ± 2.8 in adult controls. It is unlikely, then, that the increased susceptibility of human neonates to systemic bacterial infections can be related to an abnormality in the essential phagocyte functions of macrophages.
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