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.
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Laboratory of Developmental and Molecular Immunity, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
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Stone
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Robbins
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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