These studies have considered the separate functions of polymorphonuclear leukocytes (PMN's) and plasma in phagocytosis of yeast particles and compared the activity of each in the newborn infant (2 to 4 days of age) with that in normal adults. Conditions of phagocytosis were rigidly controlled. A fixed ratio of yeast: PMN (100:1) was employed and phagocytosis was carried out at 37°C. for 1/2 hour with constant rotation to favor randon PMN-yeast interaction. Results were highly reproducible. Plasma from newborn infants had considerably less opsonizing activity toward yeast than that from adults; following absorption of both groups of plasma with yeast, this difference was no longer found. In the presence of pooled plasma, PMN's from normal newborn infants took up a significantly lower average number of yeast particles; this difference was most apparent when plasma concentration in the system was 2 1/2 per cent or less. © 1969 The C. V. Mosby Company.
