Many components of complement are decreased in newborns compared to adults (Holladay and Smialowicz 2000; Vetro and Bellanti 1989). In one study, the lytic activity associated with the classical pathway matured between 1-3 months and then exceeded that of adults between 7 and 24 months (Ferriani et al. 1990). The lytic activity associated with the alternative pathway reaches adult levels around the 13th month (Ferriani et al. 1990). A subsequent study by the same researchers demonstrated age-dependent variations in C3 and factor B concentrations, but not in C4, in the sera of healthy children 3 to 14 years old. The highest values occurred in 5-6 year old children (Ferriani et al. 1999).
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