Bactericidal capacity of monocytes of newborn infants.

The peripheral leukocytes of newborn infants and of adult volunteers were studied after separation of polymorphonuclear and mononuclear cells. Monocytes were identified and quantitated with the aid of histochemical staining. The in vitro killing capacity of PMN and of monocytes was assayed against Staphylococcus aureus and Escherichia coli. The monocytes of both infants and adults were significantly less active than were their PMN, but the bactericidal capacity did not differ appreciably between newborn and adult cells of either type.