O-antigenic chains of lipopolysaccharide prevent binding of antibody molecules to an outer membrane pore protein in Enterobacteriaceae

The accessibility of outer membrane pore protein PhoE to antibody molecules at the cell surface of intact cells of various Enterobacteriaceae was investigated. Significant antibody binding was observed for only two of the nine strains tested. Analysis of the lipopolysaccharide by sodium dodecyl sulphate gel electrophoresis revealed a clear correlation between the presence of an O-antigenic side chain and the inability to bind PhoE protein-specific antibodies. As mutants that lack the O-antigen chain appeared to have acquired the ability to bind antibody, it must be concluded that the presence of O-antigenic chains of lipopolysaccharide prevents binding of antibodies to PhoE protein at the surface of intact cells. The relevance of this conclusion for the potential use of enterobacterial outer membrane pore proteins as vaccine components is discussed.