[The importance of serum components, particularly complement factors, properdin and transferrin, in inhibition of bacterial growth by human serum (author's transl)].

In this study human serum was broken down of column chromatography into its protein components, which were than examined singly and in comnination for antibacterial activity. The bactericidal effect of serum was retained to an apperciable extent in only one of six fractions. Antibacterial inhibitory activity could be restored fully by combining the fractions however. There was no correlation with the specific antibody titers. Complement had an essential part in this unspecific defence. In the absence of C'9 all other combinations of the remanining complement components exhibited no appreciable inhibitory effect. Not all complement componets are required, however, for unspcific bacterial growth inhibition. In contrast to this all complement components are necessary in the antigen-antibody reaction. Futhermore, properdin displays bactericidal activity which is related to the presence of complements. A great deal of the antibacterial activity of human serum thus arises only from the combined action of several components. These do not include proteins with a molecular weight between 100,000 and 70,000, whereby transferrin plays a part.