Cross-reactivity between six Enterobacteriaceae complete lipopolysaccharide core chemotypes.

To gain insight into the value of lipopolysaccharide (LPS) core determinants for cross-protective immunisation the serological relationships between six complete (LPS) core types from Enterobacteriaceae were investigated. Hyperimmune sera were raised in mice by repeated immunisation with heat-killed strains of Salmonella choleraesuis (Ra core type) or Escherichia coli (core types R1, R2, R3, R4 and K12) and characterised for reactivity with complete and incomplete core chemotypes by ELISA and immunoblotting. Three sera (anti-Ra, anti-R2 and anti-R3) reacted strongly with 3-5 different complete core types whereas the other three (anti-R1, anti-R4 and anti-K12) reacted strongly only with their homologous core types in these assays.

All accessible epitopes in the Salmonella lipopolysaccharide core are associated with branch residues.

Antisera generated against each of the nine known chemotypes of Salmonella lipopolysaccharide (LPS) core were characterized in order to delineate cross-reactive epitopes and define the bases for their accessibility. Strongly cross-reactive epitopes were associated with three chemotypes: Ra and Rb4, which recognized alpha-GlcNAc-1-->2-alpha-Glc, and Rd1, which recognized L-alpha-D-heptose-1-->7-L-alpha-D-heptose. Both these disaccharides and the more weakly cross-reactive alpha-Gal-1-->6-alpha-Glc terminal in Rb3 LPS represent branch points along the core oligosaccharide.

alpha-GlcNAc-1-->2-alpha-glc, the Salmonella homologue of a conserved lipopolysaccharide motif in the Enterobacteriaceae, elicits broadly cross-reactive antibodies.

To define cross-reactive epitopes in Salmonella lipopolysaccharide (LPS), antisera designated anti-S, anti-Ra, and anti-Re were generated against smooth (S), complete-core (Ra), and deep-core mutant (Re) strains, respectively, and characterized immunochemically. The reactivities of anti-Ra and anti-S with rough LPS (rLPS) chemotypes in enzyme-linked immunosorbent assays (ELISA) decreased progressively with increasing truncation of the complete-core oligosaccharide (e.g.

O-antigenic determinants in Salmonella species of serogroup C1 are expressed in distinct immunochemical populations of chains.

The O-antigenic specificities found among Salmonellae of serogroup C1 are O:6(1),7, O:6(2),7, O:6(1),6(2),7 and O:6,7,14, as defined by classical serology. Factor O:7 is the group-wide determinant while factors O:6(1), O:6(2) and O:14 are found in some strains but not others. Strains of the O:6(2),7 specificity are subject to lysogenic conversion by phages 6(1) and 14 to the O:6(1),7 and O:6,7,14 specificities, respectively.

Cross-reactivity between the mannan of Candida species, Klebsiella K24 polysaccharide and Salmonella C1 and E O-antigens is mediated by a terminal non-reducing beta-mannosyl residue.

Rat monoclonal antibody MASC1-MR9 (MR9) binds to a mannan of Candida species and the O-antigenic polysaccharides of Salmonella bacteria of serogroups C1 (CO) and E (EO). Mannan and glycoconjugates comprising BSA and O-antigen polysaccharides, decasaccharide-BSA (CO-BSA) or trisaccharide-BSA (EO-BSA), inhibited each other's reactivity with MR9. The saccharides beta-D-Manp-(1-->6)-alpha-D-Manp-1-OMe, beta-D-Manp(1-->3)-alpha-D-Manp-1-OMe, beta-D-Manp(1-->2)-alpha-D-Manp-1-OMe (corresponds to the terminal non-reducing end of Salmonella serogroup C1 O-antigen) and beta-D-Manp(1-->4)-alpha-L-Rhap(1-->3)-alpha-D-Galp-1-O-p-++ +trifluoroacetamido aniline (corresponds to the backbone of Salmonella serogroup E O-antigen) inhibited the binding of MR9 to these antigens whereas alpha-D-Manp(1-->3)-alpha-D-Manp-1-OMe and alpha-D-Manp(1-->4)-alpha-L- Rhap-1-O-p-nitrophenyl did not.