Relation between structure and immunologic properties of the Vi capsular polysaccharide.
The Vi capsular polysaccharide of Salmonella typhi is a linear homopolymer of poly-alpha(1----4)GalNAcp variably O acetylated at the C-3 position. Serum antibodies elicited by this antigen confer protective immunity against typhoid fever. The relation between the immunologic properties and structure of Vi was investigated by carboxyl reduction, O deacetylation, and acid hydrolysis. The immunogenicity of Vi was closely related to its degree of O acetylation. Partial O deacetylation slightly increased immunogenicity; complete O deacetylation eliminated the immunogenicity of Vi. O-deacetylated Vi, however, still reacted with antisera prepared by injection of whole bacteria. Carboxyl reduction, in contrast, had a comparatively slight effect upon both the immunogenicity and antigenicity of Vi. Retention levels of antigenicity after acid treatment were greater for both the native and carboxyl-reduced Vi than for the O-deacetylated product. The Courtauld-Koltun space-filling model of a pentamer of Vi demonstrated that the bulky nonpolar O-acetyls, which protrude in rows on both sides, make up most of the surface. The carboxyls are less exposed and are partially shielded by the O-acetyls. The molecular model thus provides an explantation for the dominant role of the O-acetyls, as well as the lesser effect of carboxyl reduction, upon the immunologic properties of Vi.
Laboratory of Developmental and Molecular Immunity, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
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D000107:Acetylation; D000818:Animals; D000942:Antigens, Bacterial / Q000737:chemistry / Q000276:immunology*; D005260:Female; D051379:Mice; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*; D013329:Structure-Activity Relationship
D000942:Antigens, Bacterial; D011135:Polysaccharides, Bacterial