Lipopolysaccharide binding protein ( LBP ) is a glycoprotein that is synthesized principally by hepatocytes. LBP is a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides ( LPSs ). LBP binds directly to the outer membrane of Gram-negative bacteria and to purified aggregates of extracted endotoxin, and catalyses the delivery of endotoxin to membrane ( mCD14,GPI-Linked ) and soluble ( sCD14 ) forms of CD14, thereby markedly increasing host cell sensitivity to endotoxin. LBP efficiently catalyses the transfer of individual molecules of endotoxin to (s)CD14 only when LBP–endotoxin aggregates are formed in the presence of albumin. In the presence of EDTA, LBP binding promotes further disaggregation of endotoxin. LBP binding does not have such drastic effects under more physiological conditions, but may still induce more subtle topological rearrangements of endotoxin.