SERUM COMPLEMENT LEVELS IN INFANCY - AGE-RELATED CHANGES

Levels of 8 complement [c] components and 2 control proteins were determined on cord serum from normal full term neonates and serum from healthy infants aged 1 and 6 mo. For all proteins, the levels were below the adult normal at birth and rose toward the adult range by age 6 mo. In a 2nd group of 271 patients, ages 1-36 mo., serum Clq [q fragment of Cl] and properdin levels were measured. For both proteins, the mean values in early infancy were more than 2 SD below the adult range and did not reach the adult range until 18-21 mo. of age. The Clq concentration was more variable than that for any other component studied. In infants from 11 mo.-3 yr of age, Clq levels correlated with serum Ig[immunoglobulin]G levels, but properdin levels did not. Low serum C levels in neonates may contribute to their increased susceptibility to infections. Correlations between synthetic rates of Clq and IgG is suggested as the mechanism responsible for the correlation in serum levels of these proteins after age 1 yr.