Concentrations of C1q, Factor B, Factor D and Properdin in Healthy Children, and the Age‐Related Presence of Circulating C1r‐C1s Complexes

The concentrations of C1q, factor B, factor D and properdin were determined in healthy children belonging to various age groups of one through five years of age. All concentrations were found to be age-dependent, though they varied from one component to another with regard to ontogenetic pattern. Thus, the concentrations of factor B were high, and those of factor D low throughout the age range studied. C1q and properdin levels were lowest in the younger children, who also showed a fairly high incidence of C1r-C1s complexes in excess of C1q. Since the concentrations of C1q are influenced by those of IgG, the presence of C1r-C1s complexes might partly have reflected maturation of immunoglobulin synthesis during ontogeny.