Serum hemolytic and bactericidal activity in breast and formula-fed infants.

Whether formula or breast feeding influences the functional activity of the complement system from birth to three months of age has been studied. The classical pathway was evaluated by assessing hemolytic activity, based on the capacity of the intact complement system to lyse sheep erythrocytes when coated with specific antibodies. The bactericidal activity of the serum against Staphylococcus aureus and Escherichia coli was used to evaluate the alternative complement pathway. Sera were obtained from neonates (40 +/- 2 weeks of gestation), and one-month or three-month old infants, fed either breast or formula. Control serum was obtained from healthy adults between 22 and 30 years of age. The hemolytic capacity of serum from breast-fed infants of one month and three months of age was significantly greater than that of the serum from infants which had been fed formula milk.