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Relation between structure and immunologic properties of the Vi capsular polysaccharide.
1Laboratory of Developmental and Molecular Immunity, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Infection and Immunity
|December 1, 1991
Summary
The O-acetylation of Salmonella typhi Vi capsular polysaccharide is crucial for its immunogenicity. Modifications like O-deacetylation significantly impact antibody response and antigenicity, highlighting the structural basis of typhoid fever immunity.
Area of Science:
- Immunology
- Microbial Pathogenesis
- Structural Biology
Background:
- The Vi capsular polysaccharide (Vi) of Salmonella typhi is a key antigen for protective immunity against typhoid fever.
- Understanding the structure-function relationship of Vi is essential for vaccine development.
Purpose of the Study:
- To investigate the relationship between the structural modifications of the Vi antigen and its immunologic properties.
- To elucidate the role of O-acetylation and carboxyl groups in Vi antigenicity and immunogenicity.
Main Methods:
- Chemical modifications of Vi: carboxyl reduction, O-deacetylation, and acid hydrolysis.
- Assessment of immunogenicity and antigenicity of modified Vi.
- Molecular modeling using Courtauld-Koltun space-filling models.
Main Results:
- Immunogenicity of Vi is highly dependent on its degree of O-acetylation; complete deacetylation abolishes immunogenicity.
- O-deacetylated Vi retains reactivity with specific antisera, indicating partial antigenicity.
- Carboxyl reduction has a minor effect on both immunogenicity and antigenicity.
- Molecular modeling reveals O-acetyl groups dominate the Vi surface, explaining their critical role.
Conclusions:
- The O-acetyl groups on the Vi polysaccharide are the primary determinants of its immunogenicity.
- Structural integrity, particularly O-acetylation, is vital for effective antibody recognition and protective immunity against Salmonella typhi.