Neutralizing and cross-reactive antibodies against enterobacterial lipopolysaccharide

Lipopolysaccharide (LPS, endotoxin) elicits an immune reaction which is responsible for many of the harmful effects seen in septic shock patients. The eradication of bacteria by antibiotics is insufficient to resolve the pathology due to the lack of LPS neutralization. LPS-neutralizing antibodies have been described; however, these were specific for the serotype of the infecting bacteria and thus not useful for the treatment of septic shock patients. Structural analyses revealed that the LPS structures of Escherichia coli and Salmonella are structurally conserved in the inner core region. Using whole LPS and a panel of neoglycoconjugates containing purified LPS oligosaccharides, which we have obtained from all E. coli core types (K-12, R1, R2, R3 and R4), Salmonella enterica, and the mutant strain E. coli J-5, we have identified an epitope which is bound with high affinity by the monoclonal antibody WN1 222-5, which has been shown previously shown to be cross-reactive against a large collection of blood, fecal, and urinary isolates of E. coli, S. enterica, some Citrobacter, independently of the serotype [Di Padova, F.E., Brade, H., Barclay, G.R., Poxton, I.R., Liehl, E., Schuetze, E., Kocher, H.P., Ramsay, G., Schreier, M.H., McClelland, D.B., Rietschel, E.T., 1993. A broadly cross-protective monoclonal antibody binding to Escherichia coli and Salmonella lipopolysaccharides. Infect. Immun. 61, 3863–3872]. Importantly, WN1 222-5 was protective in various models of endotoxic shock. The minimal structural element necessary for high-affinity binding consists of R1-α-d-Glcp-(1→3)-[l-α-d-Hepp-(1→7)]-l-α-d-Hepp 4P-(1→3)-R2 (R1, R2=additional sugars of LPS) in which the side-chain heptose and the 4-phosphate on the branched heptose are the main determinants of the epitope. Additional sugars of the outer core (R1) enhance the affinity, whereas loss of an intact Kdo region and/or lipid A (R2) prevent binding. The identification of the epitope provides the structural basis for the rational development of a potential vaccine against E. coli LPS.