Anti-endotoxin antibodies: A cross-reactive and cross-protective monoclonal antibody against a conserved epitope of Escherichia coil and Salmonella enterica

Lipopolysaccharide (LPS, endotoxin) is a potent inducer of the innate immune response and thus of the production of a large number of proinflammatory cytokines. An uncontrolled immune reaction elicited by LPS is responsible for many of the harmful effects seen in septic shock patients. A successful treatment strategy must thus aim at the neutralization of LPS, in addition to the eradication of bacteria by antibiotics. Antibodies neutralizing LPS 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. We have obtained a monoclonal antibody (mAb WN1 222-5) which bound strongly to all blood, faecal, and urinary isolates of a large collection of E. coli, S. enterica, some Citrobacter, and weakly with some Enterobacter and Klebsiella strains in ELISA, independently of the serotype. Apart from binding to bacteria WN1 222-5 bound to isolated LPS, LPS complexed to HDL and also to deacylated LPS. Furthermore, mAb WN1 222-5 was able to neutralize the effects of LPS during experimental bacteremia and endotoxemia in several in vivo assays in a dose dependent manner and to protect mice from death. The protective effects were correlated with a reduction of TNF-a serum levels. In vitro mAb WN1 222-5 inhibited the release of TNF-a and IL-6 from peritoneal cells. Using whole LPS and a panel of neoglycoconjugates containing purified LPS oligosaccharides obtained from E. coli core-types R1, R2, R3 and R4, S. enterica, and the mutant strain E. coli J-5 we showed that mAb WN1 222-5 binds with high affinity to the structural element R 1 -a-D-Glcp-(1→3)-[L-a-D-Hepp-( 1 → 7)]-L-a-D-Hepp 4P-(1→3)-R 2 (R 1 , R 2 = additional sugars of LPS) which is common to LPS from all E. coli, Salmonella, Shigella and Citrobacter. The side-chain heptose and the 4-phosphate on the branched heptose are main determinants of the epitope. Additional sugars of the outer core (R 1 ) enhance the affinity, whereas loss of an intact Kdo-region and/or lipid A (R 2 ) prevent binding.