Phagocytic dysfunction in monocytes of normal newborn infants.

The kinetics of phagocytosis by monocytes isolated from cord blood and from the blood of adult volunteers was studied. Monocytes attached to glass coverslips were incubated with polystyrene spheres (1.1 mu diameter) for up to 120 minutes. In this system, the rate of phagocytosis was considerably slower in newborn monocytes than in those from adults. By the time phagocytosis had occurred in virtually all of the adult cells, only 38% of the neonatal monocytes had engulfed particles. However, this defect was not absolute, since ultimately all of the newborn cells contained engulfed spheres. Levamisole had no effect on normal adult monocytes but accelerated phagocytosis of newborn cells to a rate identical with that of adult cells. These data demonstrate that newborn monocytes are less efficient in the early stages of phagocytosis than are comparable cells from adults, raising the question of the impact of phagocytic kinetics in the development of neonatal sepsis. The correction of this defect by levamisole suggests that the differences in neonatal and adult monocytes may be evaluated more thoroughly by similar pharmacologic probes.