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., Ra > Rb1 >.Re), while that of anti-Re increased (Ra < Rb1 <.Re). Anti-Ra was relatively more reactive with nonhomologous smooth LPS (sLPS) than anti-S, which in turn was more reactive than anti-Re. This order reflected the relative reactivities of these sera with outer-core rLPS but not those with inner-core rLPS, which suggests that the cross-reactivities of all three sera with sLPS were mediated by antibodies which bind outer-core determinants. Anti-Ra, but not anti-S or anti-Re, reacted with molecules substituted by O chains in immunoblots and revealed ladder-like patterns in sLPSs of various serospecificities. Anti-Ra, however, did not react with O-antigen-specific neoglycoconjugates in ELISA, thus demonstrating specificity for core epitopes. Ra and Rb1 but not other Salmonella core chemotypes inhibited the reactivity of anti-Ra with sLPS in ELISA, which showed that the terminal outer-core disaccharide, alpha-GlcNAc-1-->2-alpha-Glc (GlcNAc-->Glc), was the major epitope of cross-reactive antibodies in the serum. GlcNAc-->Glc represents the conserved motif alpha-hexose-1-->2-alpha-hexose in cores of the Enterobacteriaceae, other homologues of which should likewise be cross-reactive. These results demonstrate that S or Re strains do not elicit cross-reactive antibodies and indicate that immunization with Ra strains may represent a general strategy for eliciting cross-reactive antibodies against LPSs from enteric bacteria.
Department of Medical Microbiology, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates. nnnalue@kumc.edu
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D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology*; D001666:Binding Sites, Antibody; D002240:Carbohydrate Sequence; D017124:Conserved Sequence; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D004755:Enterobacteriaceae / Q000276:immunology*; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D006001:Glycoconjugates; D015151:Immunoblotting; D008070:Lipopolysaccharides / Q000737:chemistry / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D011817:Rabbits; D012475:Salmonella / Q000276:immunology*
D000907:Antibodies, Bacterial; D018985:Epitopes, B-Lymphocyte; D006001:Glycoconjugates; D008070:Lipopolysaccharides