Human complement: onset and site of synthesis during fetal life. 
The site and onset of synthesis of the various components of complement (C), in man and other mammals, has been studied by incubating fetal tissues in media containing labelled amino acid, and by the analysis of the culture fluids for the presence of newly synthesised proteins.  Another useful approach has been that of detecting genetic variants of single components in pairs of maternal and fetal samples.  These investigations have shown that all components of human C are produced at an early stage of fetal development and that, in cord blood, the mean level of most components is about half the value detected in samples from normal adults.  In agreement with the results observed in man, the maturation of C occurs at an early stage of life in many other mammals.