Complement activating and opsonic capacity of monoclonal antibodies raised against Escherichia coli O111 and its rough mutant J5.

Six monoclonal antibodies raised against Escherichia coli O111 and against its rough mutant J5 (chemotype Rc) were studied. One IgG2A, one IgM anti-J5, and one IgG2A anti-O111 monoclonal antibody did not bind to lipopolysaccharides of the homologous strain, but cross-reacted with heterologous gram-negative rods in an enzyme-linked immunosorbent assay. These three monoclonal antibodies activated complement when incubated with homologous or heterologous strains, but were opsonic neither in the presence nor in the absence of complement. The other three monoclonal antibodies were directed against lipopolysaccharide of the homologous strain, but showed no cross-reactivity. The IgG3 and one IgM anti-J5 monoclonal antibodies activated complement and were opsonic only in the presence of complement. The IgM anti-O111 monoclonal antibody activated complement and was opsonic both in the presence and absence of complement. Thus, the outcome of the interaction between bacteria, antibodies, and complement is influenced primarily by whether antibodies are directed against lipopolysaccharides or against other cell wall components.