Immunoprotective murine monoclonal antibodies specific for the outer-core polysaccharide and for the O-antigen of Escherichia coli 0111:B4 lipopolysaccharide (LPS).

The antigen specificity of two immunoprotective monoclonal antibodies derived from mice immunized with Escherichia coli 0111:B4 bacteria and boosted with purified lipopolysaccharide (LPS) were investigated. One of the antibodies, B7, was shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunostaining to bind to the O-antigen containing LPS species, whereas the other antibody, 5B10, reacted with both O-antigen containing homologs and the O-antigen-deficient LPS. 5B10 did not bind to LPS from E. coli J5, an Rc mutant of E. coli 0111:B4 that lacks both the O-antigen and outer core sugars. 5B10 did not cross-react with LPS from several other E. coli strains. Thus 5B10 appeared to recognize a type-specific epitope in the outer core of LPS exclusive of Rc determinants. The monoclonal antibody specific for the polymeric O-antigen is of the IgG3 subclass, and the monoclonal antibody 5B10 specific for the outer core of LPS is an IgG2a. Although B7 and 5B10 were equally able to protect mice from a lethal challenge of E. coli 0111:B4 organisms, the outer core-specific IgG2a antibody was much more efficient at mediating the binding of human complement C3 than the O-antigen-specific IgG3 monoclonal antibody.