Comparison of the endotoxin-binding capacity of human transferrin and a human applicable immunoglobulin preparation

Data obtained by in vitro experiments concerning the binding kinetics of the transferrin-endotoxin interactions are provided. The separation of protein-bound and free tritiated endotoxin of E. coli O 111:B4 is achieved by a simple precipitation method using ethanol. The main features of this reaction are the velocity of the saturation--saturation is reached after 2-3 min--and the requirement of divalent cations. EDTA (ethylenediaminetetraacetic acid) strongly inhibits the binding reaction of endotoxin to transferrin. The specificity of this interaction as well as the physiological importance can be demonstrated by the replacement of the radioactively labelled lipopolysaccharide preparation of E. coli 0 111:B4, by non-radioactive preparations of Salmonella minnesota, Serratia marcescens, E. coli 0 55:B5 and E. coli 0 111:B4. The described ethanol precipitation procedure for separating protein-bound and free endotoxin was applied to a commercially available immunoglobulin preparation. Although this preparation is known to exhibit high antibody titers against the lipid A moiety of lipopolysaccharides, no specific binding with the intact lipopolysaccharide can be found.